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LUCA SELMI

Professore Ordinario
Dipartimento di Ingegneria "Enzo Ferrari"

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Pubblicazioni

2024 - Characterization and Advanced Modeling of Dielectric Defects in Low-Thermal Budget RMG MOSFETs Using 1/f Noise Analysis [Articolo su rivista]
Asanovski, R.; Arimura, H.; de Marneffe, J. -F.; Palestri, P.; Horiguchi, N.; Kaczer, B.; Selmi, L.; Franco, J.
abstract

2024 - Characterization of DC performance and low-frequency noise of an array of nMOS Forksheets from 300 K to 4 K [Articolo su rivista]
Asanovski, R.; Grill, A.; Franco, J.; Palestri, P.; Mertens, H.; Ritzenthaler, R.; Horiguchi, N.; Kaczer, B.; Selmi, L.
abstract

2024 - Finite-element modeling of neuromodulation via controlled delivery of potassium ions using conductive polymer-coated microelectrodes [Articolo su rivista]
Verardo, Claudio; Mele, Leandro Julian; Selmi, Luca; Palestri, Pierpaolo
abstract

: Objective. The controlled delivery of potassium is an interesting neuromodulation modality, being potassium ions involved in shaping neuron excitability, synaptic transmission, network synchronization, and playing a key role in pathological conditions like epilepsy and spreading depression. Despite many successful examples of pre-clinical devices able to influence the extracellular potassium concentration, computational frameworks capturing the corresponding impact on neuronal activity are still missing.Approach. We present a finite-element model describing a PEDOT:PSS-coated microelectrode (herein, simplyionic actuator) able to release potassium and thus modulate the activity of a cortical neuron in anin-vitro-like setting. The dynamics of ions in the ionic actuator, the neural membrane, and the cellular fluids are solved self-consistently.Main results. We showcase the capability of the model to describe on a physical basis the modulation of the intrinsic excitability of the cell and of the synaptic transmission following the electro-ionic stimulation produced by the actuator. We consider three case studies for the ionic actuator with different levels of selectivity to potassium: ideal selectivity, no selectivity, and selectivity achieved by embedding ionophores in the polymer.Significance. This work is the first step toward a comprehensive computational framework aimed to investigate novel neuromodulation devices targeting specific ionic species, as well as to optimize their design and performance, in terms of the induced modulation of neural activity.

2024 - Machine learning and data augmentation methods for multispectral capacitance images of nanoparticles with nanoelectrodes array biosensors [Articolo su rivista]
Lombardo, F; Pittino, F; Goldoni, D; Selmi, L
abstract

A large number of technology applications still remain where Artificial Intelligence techniques, carefully tailored to the specific application needs, could provide performance benefits to hardware technologies. One such area is biosensing with innovative complementary-metal-oxide-semiconductor nanocapacitor arrays. These sensors operate as powerful imaging platforms but, despite the advancements in the field, the knowledge necessary for precise and robust interpretation of their response to analytes is still largely lacking.In this work, we leverage the ability of Machine Learning methods for computer vision to construct precise and robust models in different operation scenarios. By recognizing the similarity between multifrequency capacitance maps and multispectral images, we identified optimal Machine Learning algorithms to accurately estimate the size of analytes measured by the nanoelectrode array biosensor.As a relevant case study, we focus on measurements of the radius of dielectric spherical nano-particles dispersed in deionized water and phosphate buffer saline. The performance of large, established image-processing neural networks is compared to that of less complex, purposely developed ones. Sizable training data sets are generated by accurate finite element simulations of the sensor response combined with measured data. An excellent accuracy, comparable to traditional sizing technology, is achieved for the task of providing a quantitative measure of the nano-particle radius when the latter is comparable to the pitch of the pixels in the array. We report a size median error below 15% in all scenarios when a few percent of measured data samples is added to the simulation-based training data set.

2023 - Approaches for Nanoparticles Size Estimation with CMOS-based Nano-Capacitors Array Biosensor [Abstract in Atti di Convegno]
Goldoni, Daniele; Lombardo, Federico; Pittino, Federico; Rovati, Luigi; Selmi, Luca
abstract

2023 - Assessment of Advanced Nanoscale Bulk FinFET's Self-Heating accounting for degraded thermal conductivity at the nanoscale [Poster]
Tondelli, Lisa; Asanovski, Ruben; Selmi, Luca
abstract

We report self-consistent electrothermal simulations of large RF FinFET structures accounting for the multiscale effects of large BEOL metallizations and nanoscale device dimensions. A 6 fins x 4 fingers (24 channels) elementary cells is taken as a template reference device inspired by large RF transistors in 14-25 nm FinFET technology. Thermal resistances are extracted by means of the so-called AC small signal technique. The results highlight the sensitivity of the Rth to numerous geometrical and technological parameters, and the detrimental impact that reduced fin width and interfaces have on the thermal conductivity. The average temperature increase computed from the simulated thermal resistance provides useful guidelines for the design of RF FinFETs with lower maximum temperature, improved self-heating effects and reliability.

2023 - Estimation of Analyte's Vertical Positions above the Surface of Nanocapacitor Array Biosensors [Relazione in Atti di Convegno]
Goldoni, Daniele; Ongaro, Claudio; Orazi, Leonardo; Rovati, Luigi; Selmi, Luca
abstract

2023 - From Finite Element Simulations to Equivalent Circuit Models of Extracellular Neuronal Recording Systems based on Planar and Mushroom Electrodes [Articolo su rivista]
Leva, Federico; Verardo, Claudio; Palestri, Pierpaolo; Selmi, Luca
abstract

2023 - Identification of Axon Bendings in Neurons by Multiphysics FEM Simulations of High-Density MEA Extracellular Recordings [Relazione in Atti di Convegno]
Leva, Federico; Corna, Andrea; Werginz, Paul; Palestri, Pierpaolo; Zeck, Guenter; Selmi, Luca
abstract

2023 - Investigating the correlation between interface and dielectric trap densities in aged p-MOSFETs using current-voltage, charge pumping, and 1/f noise characterization techniques [Articolo su rivista]
Asanovski, Ruben; Franco, Jacopo; Palestri, Pierpaolo; Kaczer, Ben; Selmi, Luca
abstract

2023 - Mitigation of Electrical/Ionic Interference in Iontronic Neurostimulation/Neurosensing Platforms: A Simulation Study [Relazione in Atti di Convegno]
Nicolini, Jacopo; Leva, Federico; Palestri, Pierpaolo; Selmi, Luca
abstract

2023 - Towards Continuous Nano-Plastic Monitoring in Water by High Frequency Impedance Measurement with Nano-Electrode Arrays [Articolo su rivista]
Goldoni, D.; Rovati, L.; Selmi, L.
abstract

We explore the potentiality of high frequency impedance measurements with CMOS nano-electrode arrays for nano-plastic pollutant particles monitoring in water. This technology offers benefits as nano-scale resolution, high parallelization, scalability, label-free single particle detection, and automatic measurements without operator intervention. Simple models are proposed for size and concentration estimation. The former integrates measurements of adjacent electrodes and shows uncertainty comparable to the nominal one with mean prediction error lower than 45 % down to 50 nm radius. The latter accounts for noise in the definition of the sensing volume. We report a worst-case concentration error lower than a factor 1.7 under stationary and continuous flow, which demonstrates the potential of this technology for automated measurements.

2023 - Understanding the Excess 1/f Noise in MOSFETs at Cryogenic Temperatures [Articolo su rivista]
Asanovski, R; Grill, A; Franco, J; Palestri, P; Beckers, A; Kaczer, B; Selmi, L
abstract

Characterization, modeling, and development of cryo-temperature CMOS technologies (cryo-CMOS) have significantly progressed to help overcome the interconnection bottleneck between qubits and the readout interface in quantum computers. Nevertheless, available compact models still fail to predict the deviation of 1/f noise from the expected linear scaling with temperature ( $ extit{T}$ ), referred to as "excess 1/f noise ", observed at cryogenic temperatures. In addition, 1/f noise represents one of the main limiting factors for the decoherence time of qubits. In this article, we extensively characterize low-frequency noise on commercial 28-nm CMOS and on research-grade Ge-channel MOSFETs at temperatures ranging from 370 K down to 4 K. Our investigations exclude electron heating and bulk dielectric defects as possible causes of the excess 1/f noise at low temperatures. We show further evidence for a strong correlation between the excess 1/f noise and the saturation of the subthreshold swing (SS) observed at low temperatures. The most plausible cause of the excess noise is found in band tail states in the channel acting as additional capture/emission centers at cryogenic temperatures.

2022 - A simulation study of FET-based nanoelectrodes for active intracellular neural recordings [Relazione in Atti di Convegno]
Leva, Federico; Palestri, Pierpaolo; Selmi, Luca
abstract

2022 - Accurate Nonlocal Impact Ionization Models for Conventional and Staircase Avalanche Photodiodes derived by Full Band Monte Carlo Transport Simulations [Articolo su rivista]
Pilotto, A.; Esseni, D.; Selmi, L.; Palestri, P.
abstract

2022 - Importance of Charge Trapping/Detrapping Involving the Gate Electrode on the Noise Currents of Scaled MOSFETs [Articolo su rivista]
Asanovski, R.; Palestri, P.; Selmi, L.
abstract

Carrier trapping/detrapping from/to the gate into dielectric traps is often neglected when modeling noise in MOSFETs and, to the best of our knowledge, no systematic study of its impacts on scaled devices is available. In this article, we show that this trapping mechanism cannot be neglected in nowadays aggressively scaled gate dielectric thicknesses without causing errors up to several orders of magnitude in the estimation of the drain current noise. The noise generation mechanism is modeled analytically and then analyzed through the use of 2-D and 3-D TCAD simulations of scaled MOSFETs with different architectures and channel/gate-stack materials. The results provide new insights for technology and device designers, highlight the relevance of the choice of the gate metal work function (WF) and the role of valence band electron trapping at high gate voltages.

2022 - Modeling Approaches for Gain, Noise and Time Response of Avalanche Photodiodes for X-Rays Detection [Articolo su rivista]
Pilotto, A.; Antonelli, M.; Arfelli, F.; Biasiol, G.; Cautero, G.; Cautero, M.; Colja, M.; Driussi, F.; Esseni, D.; Menk, R. H.; Nichetti, C.; Rosset, F.; Selmi, L.; Steinhartova, T.; Palestri, P.
abstract

We report on a suite of modeling approaches for the optimization of Avalanche Photodiodes for X-rays detection. Gain and excess noise are computed efficiently using a non-local/history dependent model that has been validated against full-band Monte Carlo simulations. The (stochastic) response of the detector to photon pulses is computed using an improved Random-Path-Length algorithm. As case studies, we consider diodes consisting of AlGaAs/GaAs multi-layers with separated absorption and multiplication regions. A superlattice creating a staircase conduction band structure is employed in the multiplication region to keep the multiplication noise low. Gain and excess noise have been measured in devices fabricated with such structure and successfully compared with the developed models.

2022 - Modeling Non-Equilibrium Ion-Transport in Ion-Selective-Membrane/Electrolyte Interfaces for Electrochemical Potentiometric Sensors [Articolo su rivista]
Mele, L. J.; Palestri, P.; Selmi, L.; Alam, M. A.
abstract

We present an approach to simulate ion's drift and diffusion in chemical sensors based on ion-selective-membranes (ISMs) in either ion-selective electrode structures or coupled to field-effect transistors. The model is used to analyze the sensitivity, selectivity, and transient response of ISMs in non-equilibrium conditions upon real-time concentration changes. Our simple implementation combines advanced features from semiconductor theory and analytical electrochemistry, such as the Schafetter-Gummel discretization scheme and Chang-Jaffé boundary conditions for ions at the interfaces, thus allowing to perform simulations beyond sensing. The results are in agreement with experimental transient responses reported in the literature. As relevant case studies, we examine the ISM preconditioning in miniaturized sensors and the electrostatic interaction between the FET channel and ISMs. In the first case, simulations reveal that calibration curves performed on incomplete ISM conditioning can lead to hysteretical responses when the ion affinity in the electrolyte and ISM is similar (e.g., with organic ions). In the second case, we find that the gate oxide field in contact with the ISM affects the device characteristics such that the ion concentrations not only change the FET threshold voltage but also the slope of its IV curve. This effect can be minimized by working in the subthreshold regime or using extended gates.

2022 - Multiphysics Finite-Element Modeling of the Neuron/Electrode Electrodiffusive Interaction [Relazione in Atti di Convegno]
Leva, Federico; Verardo, Claudio; Mele, Leandro Julian; Palestri, Pierpaolo; Selmi, Luca
abstract

2022 - Multiscale simulation analysis of passive and active micro/nano-electrodes for CMOS-based in-vitro neural sensing devices [Articolo su rivista]
Leva, Federico; Selmi, Luca; Palestri, Pierpaolo
abstract

Neuron and neural network studies are remarkably fostered by novel stimulation and recording systems, which often make use of biochips fabricated with advanced electronic technologies and, notably, micro and nanoscale CMOS. Models of the transduction mechanisms involved in the sensor and recording of the neuron activity are useful to optimize the sensing device architecture and its coupling to the readout circuits, as well as to interpret the measured data. Starting with an overview of recently published integrated active and passive micro/nano-electrode sensing devices for in-vitro studies fabricated with modern (CMOS based) micro-nano technology, this paper presents a mixed-mode device-circuit numerical analytical multiscale and multiphysics simulation methodology to describe the neuron-sensor coupling, suitable to derive useful design guidelines. A few representative structures and coupling conditions are analyzed in more detail in terms of the most relevant electrical figures of merit including signal-to-noise ratio.

2022 - New insights on the excess 1/f noise at cryogenic temperatures in 28 nm CMOS and Ge MOSFETs for quantum computing applications [Relazione in Atti di Convegno]
Asanovski, R.; Grill, A.; Franco, J.; Palestri, P.; Beckers, A.; Kaczer, B.; Selmi, L.
abstract

2022 - On the accuracy of the formula used to extract trap density in MOSFETs from 1/f noise [Relazione in Atti di Convegno]
Asanovski, R.; Palestri, P.; Selmi, L.
abstract

Noise spectroscopy is a powerful non-destructive technique to characterize the quality of gate dielectrics in MOSFETs. Trap densities are routinely extracted by fitting the 1/f part of the drain current noise spectrum with a widely known analytical expression containing several approximations within. This paper compares this 1/f noise analytical expression with microscopic simulations, evaluates its accuracy under different scenarios, and highlights when the main assumptions fall short. It is found that the expression agrees well with non-radiative multi-phonon (NMP) models at room temperature for devices featuring a thick dielectric. However, the formula fails to correctly predict the noise of nowadays aggressively scaled devices, because it neglects trapping/de-trapping with the gate electrode and the electrostatic charge scaling of the traps due to their distance from the channel.

2022 - Selectivity, Sensitivity and Detection Range in Ion-Selective Membrane-based Electrochemical Potentiometric Sensors analyzed with Poisson-Boltzmann equilibrium model [Articolo su rivista]
Mele, L. J.; Palestri, P.; Alam, M. A.; Selmi, L.
abstract

We present and validate an equilibrium model based on the Poisson-Boltzmann equations that includes the main ingredients to simulate ion-sensitive membranes in the context of electrochemical potentiometric sensors with and without ionophores. With respect to phase boundary models, our model includes spatial resolution of the electrostatic potential and concentrations. The model enables the study of Nernstian and non-Nernstian equilibrium responses, helps improving the detection range and investigating selectivity and cross-sensitivity issues related to interferent ions in the sample solution. Therefore, the model is a useful support for the design of potentiometric microelectronic sensors and helps optimizing relevant membrane features such as ionic sites and ionophore concentration for best sensitivity and selectivity.

2021 - A Comprehensive Gate and Drain Trapping/Detrapping Noise Model and Its Implications for Thin-Dielectric MOSFETs [Articolo su rivista]
Asanovski, R.; Palestri, P.; Caruso, E.; Selmi, L.
abstract

We derive a complete set of expressions for the MOSFET gate and drain power spectral densities due to elastic and inelastic trapping/detrapping of channel carriers into the gate dielectric. Our calculations explain trapping/detrapping noise (TDN) in various FET operating regions and highlight trap's position-dependent terms, often neglected in the literature, which are instead important for devices with thin gate dielectrics. Furthermore, we show that TDN has a contribution to the gate current noise, correlated with the drain current fluctuations and we highlight the role of the transfer function between channel charge fluctuations and drain current on the noise characteristics. The model expressions are carefully validated by comparison with 2-D and 3-D TCAD simulations of scaled MOSFETs with different architectures (bulk, fully depleted-silicon-on-insulator (FD-SOI), FinFET), channel, and gate materials. Besides shedding new light on TDN, the results could enable trap density extraction from experimental samples with improved accuracy and pave the way to complete and accurate compact models for TDN in MOSFETs.

2021 - Device simulations of ion-sensitive FETs with arbitrary surface chemical reactions [Relazione in Atti di Convegno]
Mele, L. J.; Palestri, P.; Selmi, L.
abstract

In this work, we exploit the general-purpose solver COMSOL, equipped with electrolyte and semiconductor physics modules, to implement a versatile model of potentiometric chemical sensors including arbitrarily complex surface reactions at the oxide/electrolyte interface with examples on 2D devicelevel simulations of an ISFET. Firstly, Multiphysics simulations of VTH sensitivity to pH sensing are compared with analyses based on semiconductor TCAD. Then, more complex Na+ sensing experiments are examined and numerical simulations are compared against 1D electrochemical models.

2021 - Electric Field and Self-Heating Effects on the Emission Time of Iron Traps in GaN HEMTs [Articolo su rivista]
Cioni, Marcello; Zagni, Nicolo; Selmi, Luca; Meneghesso, Gaudenzio; Meneghini, Matteo; Zanoni, Enrico; Chini, Alessandro
abstract

In this paper we separately investigate the role of electric field and device self-heating (SHE) in enhancing the charge emission process from Fe-related buffer traps (0.52 eV from Ec) in AlGaN/GaN High Electron Mobility Transistors (HEMTs). The experimental analysis was performed by means of Drain Current Transient (DCT) measurements for either i) different dissipated power (PD,steady) at constant drain-to-source bias (VDS,steady) or ii) constant PD,steady at different VDS,steady. We found that i) an increase in PD,steady yields an acceleration in the thermally activated emission process, consistently with the temperature rise induced by SHE. On the other hand, ii) the field effect turned out to be negligible within the investigated voltage range, indicating the absence of Poole-Frenkel effect (PFE). A qualitative analysis based on the electric field values obtained by numerical simulations is then presented to support the interpretation and conclusions.

2021 - Electrochemical characterization of individual oil micro-droplets by high-frequency nanocapacitor array imaging [Articolo su rivista]
Renault, C.; Laborde, C.; Cossettini, A.; Selmi, L.; Widdershoven, F.; Lemay, S. G.
abstract

CMOS-based nanocapacitor arrays allow local probing of the impedance of an electrolyte in real time and with sub-micron spatial resolution. Here we report on the physico-chemical characterization of individual microdroplets of oil in a continuous water phase using this new tool. We monitor the sedimentation and wetting dynamics of individual droplets, estimate their volume and infer their composition based on their dielectric constant. From measurements before and after wetting of the surface, we also attempt to estimate the contact angle of individual micron-sized droplets. These measurements illustrate the capabilities and versatility of nanocapacitor array technology.

2021 - Modeling Nanoscale III–V Channel MOSFETs with the Self-Consistent Multi-Valley/Multi-Subband Monte Carlo Approach [Articolo su rivista]
Caruso, Enrico; Esseni, David; Gnani, Elena; Lizzit, Daniel; Palestri, Pierpaolo; Pin, Alessandro; Puglisi, Francesco Maria; Selmi, Luca; Zagni, Nicolò
abstract

We describe the multi-valley/multi-subband Monte Carlo (MV–MSMC) approach to model nanoscale MOSFETs featuring III–V semiconductors as channel material. This approach describes carrier quantization normal to the channel direction, solving the Schrödinger equation while off-equilibrium transport is captured by the multi-valley/multi-subband Boltzmann transport equation. In this paper, we outline a methodology to include quantum effects along the transport direction (namely, source-to-drain tunneling) and provide model verification by comparison with Non-Equilibrium Green’s Function results for nanoscale MOSFETs with InAs and InGaAs channels. It is then shown how to use the MV–MSMC to calibrate a Technology Computer Aided Design (TCAD) simulation deck based on the drift–diffusion model that allows much faster simulations and opens the doors to variability studies in III–V channel MOSFETs.

2021 - On the interpretation of MOS impedance data in both series and parallel circuit topologies [Articolo su rivista]
Caruso, E.; Lin, J.; Monaghan, S.; Cherkaoui, K.; Floyd, L.; Gity, F.; Palestri, P.; Esseni, D.; Selmi, L.; Hurley, P. K.
abstract

We investigate the interplay between the series (S) and parallel (P) equivalent circuit representations of the MOS system conductance (G) and capacitance (C) in inversion. Experimental and simulated data for Si and InGaAs MOSCAPs are firstly analyzed mathematically. It is found that by interpreting the measured data in both the series and parallel mode, five independent values are obtained for the magnitude and frequency of the maxima and minima points of the −ωdCS,P/dω and GS,P/ω functions versus angular frequency (ω). The significance and application of the approach is presented and discussed.

2021 - Sensitivity, noise and resolution in a beol-modified foundry-made isfet with miniaturized reference electrode for wearable point-of-care applications [Articolo su rivista]
Bellando, F.; Mele, L. J.; Palestri, P.; Zhang, J.; Ionescu, A. M.; Selmi, L.
abstract

Ion-sensitive field-effect transistors (ISFETs) form a high sensitivity and scalable class of sensors, compatible with advanced complementary metal-oxide semiconductor (CMOS) processes. Despite many previous demonstrations about their merits as low-power integrated sensors, very little is known about their noise characterization when being operated in a liquid gate configuration. The noise characteristics in various regimes of their operation are important to select the most suitable conditions for signal-to-noise ratio (SNR) and power consumption. This work reports systematic DC, transient, and noise characterizations and models of a back-end of line (BEOL)-modified foundry-made ISFET used as pH sensor. The aim is to determine the sensor sensitivity and resolution to pH changes and to calibrate numerical and lumped element models, capable of supporting the interpretation of the experimental findings. The experimental sensitivity is approximately 40 mV/pH with a normalized resolution of 5 mpH per µm2, in agreement with the literature state of the art. Differences in the drain current noise spectra between the ISFET and MOSFET configurations of the same device at low currents (weak inversion) suggest that the chemical noise produced by the random binding/unbinding of the H+ ions on the sensor surface is likely the dominant noise contribution in this regime. In contrast, at high currents (strong inversion), the two configurations provide similar drain noise levels suggesting that the noise originates in the underlying FET rather than in the sensing region.

2021 - Sensitivity, Selectivity and Chemical Noise Models for ion-sensitive FETs [Abstract in Atti di Convegno]
Mele, L. J.; Palestri, P.; Selmi, L.
abstract

2021 - Space and frequency dependence of nanocapacitor array sensors response to microparticles in electrolyte [Articolo su rivista]
Cossettini, A.; Laborde, C.; Brandalise, D.; Widdershoven, F.; Lemay, S. G.; Selmi, L.
abstract

We present new experimental evidence and extensive numerical simulations of a few distinct fingerprints generated by dielectric and conductive microparticles in electrolyte environment on the capacitance spectra of nanoelectrode array sensors. Finite element simulations in good agreement with measurements allow us to identify unambiguously the physical origin of these features, and to illustrate their dependence on the system's geometrical and physical properties. In particular, we show that conductive particles induce a response with complex space and frequency dependencies, caused by the formation of an AC electrical double layer at the particle surface, and its interaction with the working and counter electrodes in the array. Furthermore, we highlight features that could lead to false-negative detection events in sensing applications. The theoretical predictions are confirmed by experiments on a state of the art CMOS pixelated nanocapacitor biosensor platform.

2020 - A model for the jitter of avalanche photodiodes with separate absorption and multiplication regions [Articolo su rivista]
Rosset, F.; Pilotto, A.; Selmi, L.; Antonelli, M.; Arfelli, F.; Biasiol, G.; Cautero, G.; De Angelis, D.; Driussi, F.; Menk, R. H.; Nichetti, C.; Steinhartova, T.; Palestri, P.
abstract

An improved version of the Random Path Length algorithm is used to simulate the time response of Separate Absorption and Multiplication Avalanche PhotoDiodes (SAM-APDs) in the linear regime. The model takes into account both the diffusion and the drift of carriers in the absorption region as well as impact ionization scattering events in the multiplication region. An extended formulation of Ramo's theorem is used to determine the current waveforms. The new algorithm has been used to extract the jitter of the time response of avalanche photodiodes to photons, which is a relevant figure of merit for time of flight applications of SAM-APDs. It is found that an electric field in the absorption region small enough to avoid unwanted carrier multiplication or band-to-band tunneling, is beneficial to reduce the jitter. Furthermore, we have found that, in APDs working in the linear regime, the stochastic duration of the current pulse makes difficult the use of circuit techniques, such as crossover timing, with constant delay lines aimed at detecting the individual pulses. The problem is partly mitigated when SAM-APDs are used for the detection of high energy photons, such as X-rays.

2020 - Dependable contact related parameter extraction in graphene-metal junctions [Articolo su rivista]
Gahoi, Amit; Kataria, Satender; Driussi, Francesco; Venica, Stefano; Pandey, Himadri; Esseni, David; Selmi, Luca; Lemme, Max C.
abstract

The accurate extraction and the reliable, repeatable reduction of graphene - metal contact resistance (R$_{C}$) are still open issues in graphene technology. Here, we demonstrate the importance of following clear protocols when extracting R$_{C}$ using the transfer length method (TLM). We use the example of back-gated graphene TLM structures with nickel contacts, a complementary metal oxide semiconductor compatible metal. The accurate extraction of R$_{C}$ is significantly affected by generally observable Dirac voltage shifts with increasing channel lengths in ambient conditions. R$_{C}$ is generally a function of the carrier density in graphene. Hence, the position of the Fermi level and the gate voltage impact the extraction of R$_{C}$. Measurements in high vacuum, on the other hand, result in dependable extraction of R$_{C}$ as a function of gate voltage owing to minimal spread in Dirac voltages. We further assess the accurate measurement and extraction of important parameters like contact-end resistance, transfer length, sheet resistance of graphene under the metal contact and specific contact resistivity as a function of the back-gate voltage. The presented methodology has also been applied to devices with gold and copper contacts, with similar conclusions.

2020 - Effects of p doping on GaAs/AlGaAs SAM-APDs for X-rays detection [Articolo su rivista]
Nichetti, C.; Steinhartova, T.; Antonelli, M.; Biasiol, G.; Cautero, G.; De Angelis, D.; Pilotto, A.; Driussi, F.; Palestri, P.; Selmi, L.; Arfelli, F.; Danailov, M.; Menk, R. H.
abstract

This work focuses on avalanche photodiodes based on GaAs/AlGaAs with separated absorption and multiplication regions (SAM-APDs). The two regions are separated by a thin p-doped layer which, under the application of a reverse bias, is able to confine the potential drop only in the multiplication region. We realized such layer under the form of either a δ sheet of C atoms or a 50-nm-thick GaAs:C layer. Devices with these two structures will be discussed and compared in terms of capacitance and response to light.

2020 - Experimental and simulation analysis of carrier lifetimes in GaAs/AlGaAs Avalanche Photo-Diodes [Relazione in Atti di Convegno]
Driussi, F.; Pilotto, A.; De Belli, D.; Antonelli, M.; Arfelli, F.; Biasiol, G.; Cautero, G.; Menk, R. H.; Nichetti, C.; Selmi, L.; Steinhartova, T.; Palestri, P.
abstract

Extensive experimental characterization and TCAD simulation analysis have been used to study the dark current in Avalanche Photo-Diodes (APDs). The comparison between the temperature dependence of measurements and simulations points out that SRH generation/recombination is responsible for the observed dark current. After the extraction of the carrier lifetimes in the GaAs layers, they have been used to predict the APD collection efficiency of the photo-generated currents under realistic operation conditions and as a function of the photogeneration position inside the absorption layer.

2020 - Full-band monte carlo simulations of GaAs p-i-n avalanche PhotoDiodes: What are the limits of nonlocal impact ionization models? [Relazione in Atti di Convegno]
Pilotto, A.; Driussi, F.; Esseni, D.; Selmi, L.; Antonelli, M.; Arfelli, F.; Biasiol, G.; Carrato, S.; Cautero, G.; De Angelis, D.; Menk, R. H.; Nichetti, C.; Steinhartova, T.; Palestri, P.
abstract

We present a Full-Band Monte Carlo (FBMC) investigation of impact ionization in GaAs p-i-n Avalanche Photodiodes (APDs). FBMC simulations have been used to compute the gain and the excess noise factor and a new equation has been derived for the extraction of history-dependent impact ionization coefficients from FBMC simulations. Results from FBMC are then compared with the ones of nonlocal historydependent impact ionization models. We found that at high reverse bias voltages it is important to take into account the fact that secondary carriers are generated with nonzero kinetic energy. Finally, we propose an improved history-dependent model using an energy-dependent mean free path.

2020 - General Approach to Model the Surface Charge Induced by Multiple Surface Chemical Reactions in Potentiometric FET Sensors [Articolo su rivista]
Mele, L. J.; Palestri, P.; Selmi, L.
abstract

We propose a general methodology to calculate the individual sensitivity and the cross-sensitivities of potentiometric sensor devices (e.g., ion sensitive FETs (ISFETs), CHEMFETs) with an arbitrary number of non-interacting receptors binding to ionic species or analytes in the electrolyte. The surface charge generated at the (bare or functionalized) interface with the electrolyte is described by the Poisson equation coupled to a linear system of equations for each type of receptor, where the unknowns are the fractions of sites binding with a given ion/analyte. Our general model encompasses in a unique framework a few simple special cases so far separately reported in the literature and provides for them closed-form expressions of the average site occupation probability. Detailed procedural description of the usage and benefits of the model is shown for specific cases with concurring surface chemical reactions.

2020 - General model and equivalent circuit for the chemical noise spectrum associated to surface charge fluctuation in potentiometric sensors [Articolo su rivista]
Mele, L. J.; Palestri, P.; Selmi, L.
abstract

This paper firstly reports a general and powerful approach to evaluate the power spectral density (PSD) of the surface charge fluctuations, so-called “chemical noise”, from a generic set of reactions at the sensing surface of potentiometric sensors such as, for instance, Ion-Sensitive Field Effect Transistors (ISFETs). Starting from the master equation, the spectral noise signature of a reaction set is derived as a function of the reaction kinetic parameters and of the interface concentration of the ionic species. Secondly, we derive an equivalent surface admittance, whose thermal noise PSD produces a noise PSD equal to that of the surface charge fluctuations. We also show how to expand this surface admittance into stair-case RC networks, with a number of elementary cells equal to the number of surface reactions involved. This admittance can be included in circuit simulations coupled with a SPICE compact model of the underlying FET, to enable the physically based modelling of frequency dispersion and noise of the sensing layer when simulating the sensor and the read-out. Validation with existing models and literature results as well as new application examples are provided. The proposed methodology to compute the PSD from rate equations is amenable to use in different contexts where fluctuations are generated by random transitions between discrete states with given exchange rates.

2020 - Modeling Selectivity and Cross-sensitivity in membrane-based potentiometric sensors [Relazione in Atti di Convegno]
Mele, L. J.; Palestri, P.; Selmi, L.
abstract

We propose a steady state model for ion selective membranes (ISM) as selectivity element in potentiometric sensors. The model solves the Poisson-Boltzmann equation, coupled to distributed chemical reactions between ionophores and two types of competing ions. We show that a Donnan potential arises when ionic sites are present, while selectivity is achieved only if using ionophore-doped ISMs. The model allows to evaluate cross-sensitivities and can explain steady state non-Nernstian responses. We also provide an application example of sensor parameter design supported by the proposed model.

2020 - Modelling of vertical nano-needles as sensing devices for neuronal signal recordings [Relazione in Atti di Convegno]
Selmi, Luca; Palestri, Pierpaolo; Leva, Federico
abstract

This paper reports a design-oriented numerical study of vertical Si-nanowires to be used as sensing elements for the detection of the intracellular electrical activity of neurons. An equivalent lumped-element circuit model is derived and validated by comparison with physics-based numerical simulations. Most of the component values can be identified individually by geometrical and physical considerations. The transfer function and the SNR of the sensor in presence of thermal noise are derived, and the impact of the device geometry is shown.

2020 - Optimization of GaAs/AlGaAs staircase avalanche photodiodes accounting for both electron and hole impact ionization [Articolo su rivista]
Pilotto, A.; Nichetti, C.; Palestri, P.; Selmi, L.; Antonelli, M.; Arfelli, F.; Biasiol, G.; Cautero, G.; Driussi, F.; Esseni, D.; Menk, R. H.; Steinhartova, T.
abstract

A recently developed nonlocal history dependent model for electron and hole impact ionization is used to compute the gain and the excess noise factor in avalanche photodiodes featuring heterojunctions of III-V compound semiconductors while accounting for both carriers. The model has been calibrated with measurements by our group, as well as on noise versus gain data from the literature. We explore the avalanche photodiode design trade-offs related to the number of GaAs/AlGaAs conduction band steps for X-ray spectroscopy applications.

2020 - The Role of Oxide Traps Aligned With the Semiconductor Energy Gap in MOS Systems [Articolo su rivista]
Caruso, Enrico; Lin, Jun; Monaghan, Scott; Cherkaoui, Karim; Gity, Farzan; Palestri, Pierpaolo; Esseni, David; Selmi, Luca; Hurley, Paul K.
abstract

2020 - Ultra-High Frequency (500 MHz) Capacitance Spectroscopy for Nanobiosensing [Abstract in Atti di Convegno]
Cossettini, Andrea; Brandalise, Denis; Palestri, Pierpaolo; Bertacchini, Alessandro; Ramponi, Michele; Widdershoven, Frans; Benini, Luca; Selmi, Luca
abstract

Abstract—We report unprecedented ultra high frequency capacitance spectroscopy measurements up to 500 MHz on a nanoelectrode array for biosensing applications, which extends considerably the previous 70 MHz limit. To achieve this goal, a high-frequency adapter board and measurement system are designed to drive the sensing nanoelectrodes of an existing biochip with appropriate clocks generated by an advanced highspeed pulser. Experimental results in dry and in electrolyte conditions are reported. The extended frequency range enables to overcome the Debye screening cut-off frequency of electrolytes at physiological salt concentrations, thus disclosing new perspectives for single molecule detection.

2020 - 1/f noise model based on trap-assisted tunneling for ultra-thin oxides MOSFETs [Abstract in Atti di Convegno]
Caruso, Enrico; Palestri, Pierpaolo; Selmi, Luca; Asanovski, Ruben
abstract

We derive an analytical model for 1/f noise in MOSFETs, highlighting a term that is often neglected in literature but becomes important for ultra-thin oxides. Furthermore, we identify an interesting relationship between the thermal noise of the gate impedance and the gate noise due to trapping/detrapping between the free carriers in the channel and the oxide traps, as well as the 1/f noise cross-correlation between drain and gate, showing that a single voltage noise generator is not enough to describe completely the 1/f noise. TCAD simulations are used to verify the model predictive capabilities.

2019 - A model of the interface charge and chemical noise due to surface reactions in Ion Sensitive FETs [Relazione in Atti di Convegno]
Mele, Leandro Julian; Palestri, Pierpaolo; Selmi, Luca
abstract

We present a model of arbitrary chemical reactions at the interface between a solid and an electrolyte, aimed at computing the interface charge build-up and surface potential shift of ion-sensitive FETs in the presence of interfering ions. An expression for the rms value of the surface charge fluctuation and the resulting uncertainty in the ion concentration is derived as well. Application to nanoelectronic ISFET-based sensors for ions and proteins is demonstrated.

2019 - A new expression for the gain-noise relation of single-carrier avalanche photodiodes with arbitrary staircase multiplication regions [Articolo su rivista]
Pilotto, A.; Palestri, P.; Selmi, L.; Antonelli, M.; Arfelli, F.; Biasiol, G.; Cautero, G.; Driussi, F.; Menk, R. H.; Nichetti, C.; Steinhartova, T.
abstract

We propose a simple expression to relate the total excess noise factor of a single-carrier multiplication staircase avalanche photodiode (APD) to the excess noise factor and gain given by the individual conduction band discontinuities. The formula is valid when electron impact ionization dominates hole impact ionization; hence, it is especially suited for staircase APDs with In-rich multiplication regions, as opposed, for example, to GaAs/AlGaAs systems where hole ionization plays an important role. The formula has been verified by accurate means of numerical simulations based on a newly developed nonlocal history dependent impact ionization model.

2019 - Bayesian estimation of physical and geometrical parameters for nanocapacitor array biosensors [Articolo su rivista]
Stadlbauer, B.; Cossettini, A.; Morales, E. J. A.; Pasterk, D.; Scarbolo, P.; Taghizadeh, L.; Heitzinger, C.; Selmi, L.
abstract

Massively parallel nanosensor arrays fabricated with low-cost CMOS technology represent powerful platforms for biosensing in the Internet-of-Things (IoT) and Internet-of-Health (IoH) era. They can efficiently acquire "big data" sets of dependable calibrated measurements, representing a solid basis for statistical analysis and parameter estimation. In this paper we propose Bayesian estimation methods to extract physical parameters and interpret the statistical variability in the measured outputs of a dense nanocapacitor array biosensor. Firstly, the physical and mathematical models are presented. Then, a simple 1D-symmetry structure is used as a validation test case where the estimated parameters are also known a-priori. Finally, we apply the methodology to the simultaneous extraction of multiple physical and geometrical parameters from measurements on a CMOS pixelated nanocapacitor biosensor platform. (C) 2019 Elsevier Inc. All rights reserved.

2019 - Calibration of High-Frequency Impedance Spectroscopy Measurements with Nanocapacitor Arrays [Abstract in Atti di Convegno]
Cossettini, Andrea; Selmi, Luca
abstract

High frequency impedance spectroscopy (HFIS) biosensors based on nano-electrode arrays (NEA) demonstrated the capability to overcome the screening limits set by the Electrical Double Layer (EDL), thus enabling label-free detection and imaging of analytes far above the sensor surface [1,2]. In order to achieve quantitatively accurate results, a precise understanding and modeling of the signal transduction chain is necessary. With reference to the CMOS array platform in [1], capacitance is measured by CBCM. Hence, the nanoelectrodes are alternatively charged and discharged by two switch transistors (Fig.1, a), which are activated by non-overlapping clocks with typically 1 ns floating time between the two phases. The column readout circuits integrate and average over multiple cycles the charging current to obtain a capacitance information. The output signal is interpreted in terms of a switching capacitance (CSW), modeled by charge-pump analysis of an equivalent C-RC circuit excited by a square wave (EDL capacitance CS in series to a parallel RECE representing the bulk electrolyte [1]; CS, RE and CE are extracted with the biosensor simulator ENBIOS [3]), good agreement is obtained between experiments and simulations over a broad range of frequencies and electrolyte salt concentrations [1]. Residual discrepancies, however, require explanation and this is the main contribution of our abstract. To this end, we firstly, consider the role of leakage currents (ILEAK) in the sensor cell (due to subthreshold conduction of the inactive switch). The leakage current implies overestimating the column current IM (and hence the capacitance). Due to the large number of cells connected on each column, a value as large as 20pA is estimated for ILEAK, and measurements are corrected by compensating for it. Then, we consider the voltage waveforms at the nanoelectrode, as obtained by Spice simulations with Predictive Technology Models (PTM) of the sensor cell readout circuit (Fig.1 (b) for a 10mM electrolyte). Charge repartition between the nanoelectrode’s node and CGS/CGD capacitance of the switching transistors during the float time distorts the otherwise square-waveform. For electrolytes with high salt concentration this effect is mitigated (due to the larger load capacitance). To account for this effect, we extract the harmonic content of the waveform by Fourier expansion of the waveform (Fig.1, b). Then, ENBIOS simulations at all harmonic frequencies are used to reconstruct the capacitance response to the actual waveform (CF). Fig.1 (c) compares experiments (corrected for leakage) and simulations (CSW or CF). The impact of leakage is modest, whereas CF exhibits an improved agreement with experiments at high frequency, where waveform glitches are more relevant. These corrections highlight the importance of leakage and harmonic content of the input waveforms to achieve quantitatively accurate interpretation of NEA HFIS biosensor experiments. Further work is necessary to extend these results to electrolytes with physiological salinity.

2019 - Determination of Micro- and Nano-particle Properties by Multi-Frequency Bayesian Methods and Applications to Nanoelectrode Array Sensors [Relazione in Atti di Convegno]
Cossettini, A.; Stadlbauer, B.; Morales, J. A. E.; Taghizadeh, L.; Selmi, L.; Heitzinger, C.
abstract

We demonstrate a new and robust Bayesian estimation method to extract properties of micro- and nano-scale analytes from measurements on advanced high-frequency impedance spectroscopy nanoelectrode array sensors. Firstly, the method is validated on model systems of a-priori known properties using accurate analytical and numerical models in place of actual measurements. Then, applications to real measurements with an advanced CMOS sensor demonstrate the usefulness of the methodology for robust and fast estimation of multi-dimensional parameters and parameter uncertainty in the context of biosensing and possibly sensor-fusion problems.

2019 - Gain and noise in GaAs/AlGaAs avalanche photodiodes with thin multiplication regions [Articolo su rivista]
Nichetti, C.; Steinhartova, T.; Antonelli, M.; Cautero, G.; Menk, R. H.; Pilotto, A.; Driussi, F.; Palestri, P.; Selmi, L.; Arfelli, F.; Biasiol, G.
abstract

valanche photodiodes based on GaAs/AlGaAs with separated absorption and multiplication regions (SAM-APDs) will be discussed in terms of capacitance, response to light (gain and noise) and time response. The structures have been fabricated by molecular beam epitaxy introducing a δ p layer doped with carbon to separate the multiplication and the absorption regions. The thickness of the latter layer defines the detection efficiency and the time resolution of the structure, which in turn allows tailoring the device for specific scientific applications. Within the multiplication region a periodic modulation of the bandgap is obtained by growing alternating nanometric layers of AlGaAs and GaAs with increasing Al content; this staircase structure enables the tuning of the bandgap and subsequently provides a well-defined charge multiplication. The use of such staircase hetero-junctions enhances electron multiplication and conversely reduces—at least in principle—the impact of the noise associated to hole multiplication, which should result in a decreased overall noise, when compared to p-i-n diodes composed by a single material. The first part of this paper focuses on the electrical characteristics of the grown structure and on the comparison with the simulated behaviour of such devices. In addition, gain and noise measurements, which have been carried out on these devices by utilizing photons from visible light to hard X-rays, will be discussed and will be compared to the results of a nonlocal history-dependent model specifically developed for staircase APDs.

2019 - Investigation of the behaviour of GaAs/AlGaAs SAM-APDs for synchrotron radiation [Relazione in Atti di Convegno]
Nichetti, Camilla; Steinhartova, Tereza; Antonelli, Matias; Cautero, Giuseppe; Menk, Ralf Hendrik; Pilotto, Alessandro; Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca; Arfelli, Fulvia; Biasiol, Giorgio
abstract

This work reports on the fabrication and characterization of a novel high-speed, low-noise X-ray Avalanche Photodiode based on III-V compound semiconductors operating over an extended photon energy range. These materials were suggested as their higher atomic numbers allow for the absorption of higher photon energies; hence, shorter response times can be achieved by growing APDs with thinner active regions. In addition, the use of staircase hetero-junctions enhances electron multiplication and results in lower noise if compared with conventional p-i-n diodes. In this work, molecular beam epitaxy was used to produce GaAs/AlGaAs APDs with separated absorption and multiplication regions. The multiplication region, separated from the absorption region by a δ p-doped layer of carbon, contains a staircase structure composed of nanometric layers of AlGaAs and GaAs, which alternate periodically. The periodic modulation of the band gap enables a well-defined charge multiplication and results in low multiplication noise. Several devices were characterized in terms of dark current, photocurrents generated utilizing visible and hard X-ray sources as well as noise generated under laser light.

2019 - Optimizing the Number of Steps and the Noise in Staircase APDs with Ternary III - V Semiconductor Alloys [Relazione in Atti di Convegno]
Pilotto, A.; Nichetti, C.; Palestri, P.; Selmi, L.; Antonelli, M.; Arfelli, F.; Biasiol, G.; Cautero, G.; Driussi, F.; Esseni, D.; Menk, R. H.; Steinhartova, T.
abstract

2019 - Relationship between capacitance and conductance in MOS capacitors [Relazione in Atti di Convegno]
Caruso, E.; Lin, J.; Monaghan, S.; Cherkaoui, K.; Floyd, L.; Gity, F.; Palestri, P.; Esseni, D.; Selmi, L.; Hurley, P. K.
abstract

In this work, we describe how the frequency dependence of conductance (G) and capacitance (C) of a generic MOS capacitor results in peaks of the functions G/ω and - ωdC/dω. By means of TCAD simulations, we show that G/ω and -ωdC/dω peak at the same value and at the same frequency for every bias point from accumulation to inversion. We illustrate how the properties of the peaks change with the semiconductor doping (ND), oxide capacitance (COX), minority carrier lifetime (τg), interface defect parameters (NIT, σ) and majority carrier dielectric relaxation time (τr). Finally, we demonstrate how these insights on G/ω and -ωdC/dω can be used to extract COX, ND and τg from InGaAs MOSCAP measurements

2019 - Role of Different Receptor-Surface Binding Modes in the Morphological and Electrochemical Properties of Peptide-Nucleic-Acid-Based Sensing Platforms [Articolo su rivista]
Bartl, Johannes D.; Scarbolo, Paolo; Brandalise, Denis; Stutzmann, Martin; Tornow, Marc; Selmi, Luca; Cattani-Scholz, Anna
abstract

Label-free detection of charged biomolecules, such as DNA, has experienced an increase in research activity in recent years, mainly to obviate the need for elaborate and expensive pretreatments for labeling target biomolecules. A promising label-free approach is based on the detection of changes in the electrical surface potential on biofunctionalized silicon field-effect devices. These devices require a reliable and selective immobilization of charged biomolecules on the device surface. In this work, self-assembled monolayers of phosphonic acids are used to prepare organic interfaces with a high density of peptide nucleic acid (PNA) bioreceptors, which are a synthetic analogue to DNA, covalently bound either in a multidentate ( - PNA) or monodentate ( - PNA) fashion to the underlying silicon native oxide surface. The impact of the PNA bioreceptor orientation on the sensing platform's surface properties is characterized in detail by water contact angle measurements, atomic force microscopy, X-ray photoelectron spectroscopy, cyclic voltammetry, and electrochemical impedance spectroscopy. Our results suggest that the multidentate binding of the bioreceptor via attachment groups at the ?-points along the PNA backbone leads to the formation of an extended, protruding, and netlike three-dimensional metastructure. Typical "mesh" sizes are on the order of 8 ± 2.5 nm in diameter, with no preferential spatial orientation relative to the underlying surface. Contrarily, the monodentate binding provides a spatially more oriented metastructure comprising cylindrical features, of a typical size of 62 ± 23 × 12 ± 2 nm 2 . Additional cyclic voltammetry measurements in a redox buffer solution containing a small and highly mobile Ru-based complex reveal strikingly different insulating properties (ion diffusion kinetics) of these two PNA systems. Investigation by electrochemical impedance spectroscopy confirms that the binding mode has a significant impact on the electrochemical properties of the functional PNA layers represented by detectable changes of the conductance and capacitance of the underlying silicon substrate in the range of 30-50% depending on the surface organization of the bioreceptors in different bias potential regimes.

2019 - Semi-classical modeling of nanoscale nMOSFETs with III-V channel [Relazione in Atti di Convegno]
Palestri, P.; Caruso, E.; Badami, O.; Driussi, F.; Esseni, D.; Selmi, L.
abstract

We review recent results on the modeling of nanoscale nMOSFETs with III-V compounds channel material. The focus will be on semi-classical transport modeling in short channel devices; we will show that back-scattering in the channel still influences the device performance, and thus affects the choice of the channel material. The model ingredients necessary to describe III-V MOSFETs will be discussed, and major differences compared to silicon FETs will be highlighted.

2018 - A CMOS Pixelated Nanocapacitor Biosensor Platform for High-Frequency Impedance Spectroscopy and Imaging [Articolo su rivista]
Widdershoven, Frans; Cossettini, Andrea; Laborde, Cecilia; Bandiziol, Andrea; Paul van Swinderen, Peter; Lemay, Serge G.; Selmi, Luca
abstract

We describe the realization of a fully-electronic label-free temperature-controlled biosensing platform aimed to overcome the Debye screening limit over a wide range of electrolyte salt concentrations. It is based on an improved version of a 90 nm CMOS integrated circuit featuring a nanocapacitor array, readout and A/D conversion circuitry, and an FPGA-based interface board with NIOS II soft processor. We describe the chip's processing, the mounting, the microfluidics, the temperature control system, as well as the calibration and compensation procedures to reduce systematic errors, which altogether make up a complete quantitative sensor platform. Capacitance spectra recorded up to 50-70 MHz are shown and successfully compared to predictions by FEM numerical simulations in the Poisson-Drift-Diffusion formalism. They demonstrate the ability of the chip to reach high upper frequency of operation, thus overcoming the low-frequency Debye screening limit at nearly physiological salt concentrations in the electrolyte, and allowing for detection of events occurring beyond the extent of the electrical double layer. Furthermore, calibrated multi-frequency measurements enable quantitative recording of capacitance spectra, whose features can reveal new properties of the analytes. The scalability of the electrode dimensions, inter-electrode pitch and size of the array make this sensing approach of quite general applicability, even in a non-bio context (e.g. gas sensing).

2018 - An Improved Nonlocal History-Dependent Model for Gain and Noise in Avalanche Photodiodes Based on Energy Balance Equation [Articolo su rivista]
Nichetti, C.; Pilotto, A.; Palestri, P.; Selmi, L.; Antonelli, M.; Arfelli, F.; Biasiol, G.; Cautero, G.; Driussi, F.; Klein, N. Y.; Menk, R. H.; Steinhartova, T.
abstract

We present a non-local history-dependent model for impact ionization gain and noise in avalanche photodiodes (APDs) especially suited for staircase APDs. The model uses a simple energy balance equation to define effective electric fields valid also in the presence of band discontinuities which are then used to express the ionization coefficients. The model parameters have been calibrated against literature data for gain and noise in GaAs and AlxGa1-xAs (x = 0.2, 0.6, 0.8) p-i-n diodes. Application to experimental data for gain and noise in heterojunction and staircase SAM-APDs is reported to demonstrate the ability of the model in describing complex APD structures. It is found that, in spite of conduction band discontinuities being much larger than valence band ones, hole impact ionization contributes a significant degradation of the noise metrics in GaAs/AlGaAs staircase APDs. These non-trivial insights demonstrate the usefulness of the model to steer device design and optimization.

2018 - An Improved Random Path Length Algorithm for p-i-n and Staircase Avalanche Photodiodes [Relazione in Atti di Convegno]
Pilotto, Alessandro; Palestri, Pierpaolo; Selmi, Luca; Antonelli, Matias; Arfelli, Fulvia; Biasiol, Giorgio; Cautero, Giuseppe; Driussi, Francesco; Menk, Ralf H.; Nichetti, Camilla; Steinhartova, Tereza
abstract

We present an improved Random Path Length algorithm to accurately and efficiently estimate the design space of heterostructure avalanche photodiodes (APDs) in terms of gain, noise and bandwidth without any need of full Monte Carlo transport simulations. The underlying nonlocal model for impact ionization goes beyond the Dead Space concept and it is suited to handle staircase structures composed by a superlattice of III-V compounds as well as thick and thin p-i-n APDs. The model parameters have been calibrated on GaAs and AlxGa1−xAs p-i-n APDs in a previous work. In this work GaAs p-i-n APDs are compared to staircase structures in terms of noise and bandwidth.

2018 - Bayesian Estimation for Transport Equations for Nanocapacitors [Abstract in Atti di Convegno]
Stadlbauer, Benjamin; Taghizadeh, Leila; Morales Escalante, Jose A.; Heitzinger, Clemens; Cossettini, Andrea; Selmi, Luca
abstract

We use and evaluate different Bayesian estimation methods to quantify uncertainties in model parameters in nanocapacitors. Here, randomness arises due to process variations; also, parameters that cannot be measured directly are to be determined. The methods include the direct approach, the Markov-chain Monte-Carlo (MCMC) method, and an iterative version of the latter that we have developed, where we use the calculated posterior distribution as the prior distribution for a new MCMC analysis. We investigate the influence of the number of samples in each Markov chain and the number of iterations on the total computational work and the error achieved. In addition, we discuss the methods for estimating the posterior distribution based on samples provided by the MCMC analysis. We apply our algorithms to the Poisson-Boltzmann and Poisson-Nernst-Planck equations which arise from modeling nanoelectrode biosensors, which have recently been used to detect minute concentrations of target particles. This technology has many applications in precision medicine. Numerical examples show the estimation of parameters such as ionic concentration, size of Stern layer, and the sizes of multiple electrodes (multilevel Bayesian estimation) of sensors for which experimental data are available.

2018 - Calibration, Compensation, Parameter Estimation, and Uncertainty Quantification for Nanoelectrode Array Biosensors [Abstract in Atti di Convegno]
Cossettini, Andrea; Scarbolo, Paolo; Morales Escalante, Jose A.; Stadlbauer, Benjamin; Muhammad, Naseer; Taghizadeh, Leila; Heitzinger, Clemens; Selmi, Luca
abstract

This paper presents the use of a statistical approach to estimate physical/electrochemical parameters of impedance spectroscopy experiments performed with a realistic nanoelectrodes array biosensor platform. The Bayesian estimation methodology is based on the combination of nanobiosensor simulations, performed with the ENBIOS tool, with Markov-Chain Monte Carlo (MCMC) analyses. A simple 1D electrode-electrolyte geometry is first considered as a validation test case, allowing the accurate estimation of Stern layer permittivity and salt concentration, as set by a reference analytical model. Then, full 3D analyses of the nanoelectrodes’ array system are performed in order to estimate a number of relevant parameters for measurements in electrolyte. Furthermore, moving to more challenging test cases, size/permittivity of microparticles suspended in electrolyte will also be discussed. This methodology allows for the determination of impedance spectroscopy data parameters, and quantification of parameter uncertainties in these multi-variable detection problems. It is thus a very promising approach in order to improve the precision of biosensor measurement predictions, which are intrinsically affected by many parameters.

2018 - Digital and analog TFET circuits: Design and benchmark [Articolo su rivista]
Strangio, S.; Settino, F.; Palestri, P.; Lanuzza, M.; Crupi, F.; Essenia, D.; Selmi, L.
abstract

In this work, we investigate by means of simulations the performance of basic digital, analog, and mixed-signal circuits employing tunnel-FETs (TFETs). The analysis reviews and complements our previous papers on these topics. By considering the same devices for all the analysis, we are able to draw consistent conclusions for a wide variety of circuits. A virtual complementary TFET technology consisting of III-V heterojunction nanowires is considered. Technology Computer Aided Design (TCAD) models are calibrated against the results of advanced full-quantum simulation tools and then used to generate look-up-tables suited for circuit simulations. The virtual complementary TFET technology is benchmarked against predictive technology models (PTM) of complementary silicon FinFETs for the 10 nm node over a wide range of supply voltages (VDD) in the sub-threshold voltage domain considering the same footprint between the vertical TFETs and the lateral FinFETs and the same static power. In spite of the asymmetry between p- and n-type transistors, the results show clear advantages of TFET technology over FinFET for VDDlower than 0.4 V. Moreover, we highlight how differences in the I-V characteristics of FinFETs and TFETs suggest to adapt the circuit topologies used to implement basic digital and analog blocks with respect to the most common CMOS solutions.

2018 - General model for multiple surface reactions in ion-sensitive FETs [Abstract in Atti di Convegno]
Mele, LEANDRO JULIAN; Palestri, Pierpaolo; Cossettini, Andrea; Pittino, Federico; Selmi, Luca
abstract

The use of Field Effect Transistors as electrochemical sensor combined with integrated readouts in CMOS technology offers many potential advantages in terms of sensitivity, accuracy, repeatability, miniaturization, costs, parallelism, digitalization and communication. Modelling of the transduction mechanisms is necessary to enable quantitative understanding and prediction of the sensor signals, the selectivity and cross-sensitivities for optimized design. We propose a generalized model for the ISFET response to an arbitrary number of receptor types binding with different ionic species in the electrolyte suitable to assess cross-sensitivities in ISFET sensors. The model is implemented in the ENBIOS-1D platform [1], which solves the equilibrium Poisson- Boltzmann equation in the electrolyte coupled to the electrostatics in the FET channel. The interface charge generated at bare or functionalized surfaces by an arbitrary number of chemical reactions among surface binding sites and electrolyte ions is described by a linear system of equations for each type of receptor, whose unknowns are the fractions of sites binding with a given ion. Our approach generalizes the well-known Site Binding model of reactions between amphoteric sites at metal-oxide surfaces and H+ ions, which is commonly used to explain pH sensitivity in ISFETs [2]. It also includes the modified site binding model reported in [3], which considers specific absorption of ions (see Fig. 1). Competing reactions of multiple sites (bare surface plus ligand functionalization) can be described as well. In fact, the model matches the results in [4], where sensing of the FimH protein is demonstrated (Fig. 2).

2018 - Impact of different receptor binding modes on surface morphology and electrochemical properties of PNA-based sensing platforms. [Abstract in Atti di Convegno]
(5) Bartl, J. D.; Scarbolo, P.; Gremm, o. S.; Rziga, G.; Stutzmann, M.; Tornow, M.; Selmi, L.; Cattani-Scholz, A.
abstract

Silicon-based field-effect devices have been widely studied for label-free DNA detection in recent years. These devices rely on the detection of changes in the electrical surface potential during the DNA recognition event and thus require a reliable and selective immobilization of charged biomolecules on the device surface [1]. The preparation of self-assembled monolayers of phosphonic acids (SAMPs) on metal oxide surfaces is an efficient approach to generate well-defined organic interfaces with a high density of receptor binding sites close to the sensing surface [2,3]. In this work, we report the functionalization and characterization of silicon/silicon nitride surfaces with different types of peptide nucleic acid (PNA), a synthetic analogue to DNA [4]. Differently modified PNA molecules are covalently immobilized on the underlying SAMPs either in a multidentate or monodentate fashion to investigate the effect of different binding modes on receptor density and morphology important for PNA-DNA hybridization (Scheme 1). Multidentate immobilization of the bioreceptors via C6-SH attachment groups at the γ-points along the PNA backbone provides a rigid, lying configuration on the device surface (PNA 1), whereas a monodentate immobilization by Cys-capped PNA molecules (PNA 2) results in more flexible and more accessible receptor binding sites. Our results indicate that the presented functionalization scheme can be successfully applied to produce morphologically and electrochemically different PNA bioreceptor binding sites on silicon/silicon nitride surfaces. Consequently, a well-chosen modification of the PNA backbone is a valid approach to influence the sensing properties of surface-immobilized PNA bioreceptors, which might provide an additional parameter to further tune and tailor the sensing capabilities of PNA-based biosensing devices.

2018 - Morphological and electrochemical properties of different PNA-based sensing platforms – Impact of the receptor-surface binding modes [Poster]
Bartl, Johannes D.; Scarbolo, Paolo; Brandalise, Denis; Stutzmann, Martin; Tornow, Marc; Selmi, Luca; Cattani-Scholz, Anna
abstract

By using self-assembled monolayers of phosphonic acids (SAMPs) on silicon native oxide surfaces as anchor platforms, two distinct organic interfaces with a high density of PNA bioreceptors are prepared. The impact of the PNA-bioreceptor orientation on the surface properties of the sensing platform is characterized in detail by water contact angle (CA) measurements, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Our results suggest that multidentate binding of PNA bioreceptor via attachment groups at the γ-points along the PNA backbone produces an extended, protruding and netlike 3D-metastructure with no preferential spatial direction. Contrary, a spatially more localized and cylindrical metastructure is realized by the monodentate binding. Furthermore, cyclic voltammetry measurements performed in a redox buffer solution, which is containing a small and highly mobile Ru-based redox active complex, reveal strikingly different insulating properties (diffusion kinetics) of these two PNA layers. Finally, investigation by electrochemical impedance spectroscopy confirms that the binding mode has a significant impact on the electrochemical properties of the functional PNA sensing surface. Here, we could observe changes of the conductance and capacitance of the underlying silicon-based semiconducting substrate in the range of 30-50 % which are strongly depending on the surface organization of the bioreceptors at different bias potential regimes. Consequently, a well-chosen modification of the PNA backbone is a valid approach to influence the sensing properties of surface-immobilized PNA bioreceptors, which might provide an additional parameter to further tune and tailor the sensing capabilities of PNA-based biosensing devices.

2018 - Morphological and electrochemical properties of different PNA-based sensing platforms – Impact of the receptor-surface binding modes [Relazione in Atti di Convegno]
Bartl, Johannes D.; Scarbolo, Paolo; Brandalise, Denis; Stutzmann, Martin; Tornow, Marc; Selmi, Luca; Cattani-Scholz, Anna
abstract

By using self-assembled monolayers of phosphonic acids (SAMPs) on silicon native oxide surfaces as anchor platforms, two distinct organic interfaces with a high density of PNA bioreceptors are prepared. The impact of the PNA-bioreceptor orientation on the surface properties of the sensing platform is characterized in detail by water contact angle (CA) measurements, atomic force microscopy (AFM), X-ray photoelectron spectroscopy (XPS), cyclic voltammetry (CV) and electrochemical impedance spectroscopy (EIS). Our results suggest that multidentate binding of PNA bioreceptor via attachment groups at the γ-points along the PNA backbone produces an extended, protruding and netlike 3D-metastructure with no preferential spatial direction. Contrary, a spatially more localized and cylindrical metastructure is realized by the monodentate binding. Furthermore, cyclic voltammetry measurements performed in a redox buffer solution, which is containing a small and highly mobile Ru-based redox active complex, reveal strikingly different insulating properties (diffusion kinetics) of these two PNA layers. Finally, investigation by electrochemical impedance spectroscopy confirms that the binding mode has a significant impact on the electrochemical properties of the functional PNA sensing surface. Here, we could observe changes of the conductance and capacitance of the underlying silicon-based semiconducting substrate in the range of 30-50 % which are strongly depending on the surface organization of the bioreceptors at different bias potential regimes. Consequently, a well-chosen modification of the PNA backbone is a valid approach to influence the sensing properties of surface-immobilized PNA bioreceptors, which might provide an additional parameter to further tune and tailor the sensing capabilities of PNA-based biosensing devices.

2018 - New device concepts, transistor architectures and materials for high performance and energy efficient CMOS circuits in the forthcoming era of 3D integrated circuits [Relazione in Atti di Convegno]
Esseni, D.; Badami, O.; Driussi, F.; Lizzit, D.; Pala, M.; Palestri, P.; Rollo, T.; Selmi, L.; Venica, S.
abstract

This paper addresses selected topics about recent developments in CMOS technologies evolving towards 3D integrated circuits and incorporating innovative device concepts and ever new materials.

2018 - On the Adequacy of the Transmission Line Model to Describe the Graphene-Metal Contact Resistance [Articolo su rivista]
Venica, Stefano; Driussi, Francesco; Gahoi, Amit; Palestri, Pierpaolo; Lemme, Max C.; Selmi, Luca
abstract

The contact-end-resistance (CER) method is applied to transfer length method structures to characterize in-depth the graphene-metal contact and its dependence on the back-gate bias. Parameters describing the graphene-metal stack resistance are extracted through the widely used transmission line model. The results show inconsistencies which highlight application limits of the model underlying the extraction method. These limits are attributed to the additional resistance associated with the p-p+ junction located at the contact edge, that is not part of the conventional transmission line model. Useful guidelines for a correct application of the extraction technique are provided, identifying the bias range in which this additional resistance is negligible. Finally, the CER method and the transmission line model are exploited to characterize the graphene-metal contacts featuring different metals. © 2012 IEEE.

2018 - On the Response of Nanoelectrode Impedance Spectroscopy Measures to Plant, Animal, and Human Viruses [Articolo su rivista]
Cossettini, Andrea; Selmi, Luca
abstract

A simplified lumped geometrical and electrical model for the high-frequency impedance spectroscopy (HFIS) response of nanoelectrodes to T=3 capsids and full viruses is developed starting from atomistic descriptions, in order to test the theoretical response of a realistic HFIS CMOS biosensor platform to different viruses. Capacitance spectra are computed for plant (cowpea chlorotic mottle virus), animal (rabbit haemorrhagic disease virus), and human (hepatitis A virus) viruses. A few common features of the spectra are highlighted, and the role of virus charge, pH, and ionic strength on the expected signal is discussed. They suggest that the frequency of highest sensitivity at nearly physiological concentrations (100 mM) is within reach of existing HFIS platform designs.

2018 - Physics-based TCAD analysis of Border and Interface traps in Al2O3/InGaAs stacks using Multifrequency CV-curves [Relazione in Atti di Convegno]
Caruso, E.; Lin, J.; Burke, K. F.; Cherkaoui, K.; Esseni, D.; Gity, F.; Monaghan, S.; Palestri, P.; Hurley, P.; Selmi, L.
abstract

In this paper, we analyze the multi-frequency C-V curves of In0.53Ga0.47As MOSCAPs by employing physics-based TCAD simulations including both border and interface traps. The calculations reproduce the experimental inversion and accumulation capacitance, and the general trend of the depletion capacitance. A study of the influence of the quantization model on the extraction of the trap distribution is also carried out.

2018 - Profiling border-traps by TCAD analysis of multifrequency CV-curves in Al2O3/InGaAs stacks [Relazione in Atti di Convegno]
Caruso, E.; Lin, J.; Burke, K. F.; Cherkaoui, K.; Esseni, D.; Gity, F.; Monaghan, S.; Palestri, P.; Hurley, P.; Selmi, L.
abstract

2018 - Reliability analysis of the metal-graphene contact resistance extracted by the transfer length method [Relazione in Atti di Convegno]
Venica, Stefano; Driussi, Francesco; Gahoi, Amit; Kataria, Satender; Palestri, Pierpaolo; Lenirne, Max C.; Selmi, Luca
abstract

The transfer Length Method is a well-estab experimental technique to characterize the contact resista semiconductor devices. However, its dependability is ques for metal-graphene contacts. We investigate in-depth the si cal error of the extracted contact resistance values and we strategies to limit such error and to obtain reliable result method has been successfully applied to samples with dil contact metals.

2018 - Simulation and automated characterisation of optimal load for flexible composite generators based on piezoelectric ZnO nanowires [Relazione in Atti di Convegno]
Menin, D.; Parmar, M.; Tao, R.; Oliveira, P.; Mouis, M.; Selmi, L.; Ardila, G.
abstract

2017 - A scaled replacement metal gate InGaAs-on-Insulator n-FinFET on Si with record performance [Relazione in Atti di Convegno]
Hahn, H.; Deshpande, V.; Caruso, E.; Sant, S.; O'Connor, E.; Baumgartner, Y.; Sousa, M.; Caimi, D.; Olziersky, A.; Palestri, P.; Selmi, L.; Schenk, A.; Czornomaz, L.
abstract

2017 - Benchmarks of a III-V TFET technology platform against the 10-nm CMOS FinFET technology node considering basic arithmetic circuits [Articolo su rivista]
Strangio, Sebastiano; Palestri, Pierpaolo; Lanuzza, M.; Esseni, David; Crupi, F.; Selmi, Luca
abstract

In this work, a benchmark for low-power digital applications of a III-V TFET technology platform against a conventional CMOS FinFET technology node is proposed. The analysis focuses on full-adder circuits, which are commonly identified as representative of the digital logic environment. 28T and 24T topologies, implemented in complementary-logic and transmission-gate logic, respectively, are investigated. Transient simulations are performed with a purpose-built test-bench on each single-bit full adder solution. The extracted delays and energy characteristics are post-processed and translated into figures-of-merit for multi-bit ripple-carry-adders. Trends related to the different full-adder implementations (for the same device technology platform) and to the different technology platforms (for the same full-adder topology) are presented and discussed.

2017 - Detailed characterization and critical discussion of series resistance in graphene-metal contacts [Relazione in Atti di Convegno]
Venica, Stefano; Driussi, Francesco; Gahoi, Amit; Passi, Vikram; Palestri, Pierpaolo; Lemme, Max C.; Selmi, Luca
abstract

We apply the contact–end resistance method to TLM structures in order to characterize the graphene–metal contact resistance. A critical analysis of the experimental results shows that the commonly used transmission line model fails to accurately describe the graphene–metal contact under specific biasing conditions. The experiments suggest the presence of an additional resistance contribution associated to the p–p+ junction induced in the graphene in the proximity of the contact. This voltage dependent resistance limits the range of applicability of the extraction technique. However, for carefully chosen bias conditions that reduce this additional resistance to small values, the technique provides reliable results, useful to investigate the graphene–metal contact properties and their technology dependence.

2017 - Detecting microparticles and their charge-state by nanoribbon sensors and physical modeling [Relazione in Atti di Convegno]
Scarbolo, Paolo; Selmi, Luca
abstract

In the last decade, CMOS nano FETs have attracted increasing interest as sensing devices for impedance spectroscopy of biomolecules [1]. In this context, we present a quantitative numerical analysis of dielectric microbead detection and charge-state discrimination experiments with nanoribbon (NR) FETs operated in the frequency domain up to 1 MHz.

2017 - Graphene base transistors with bilayer tunnel barriers: Performance evaluation and design guidelines [Articolo su rivista]
Venica, Stefano; Driussi, Francesco; Vaziri, Sam; Palestri, Pierpaolo; Selmi, Luca
abstract

Graphene-based capacitors and Graphene base transistors (GBTs) featuring innovative engineered tunnel barriers are characterized in DC and the data are thoroughly analyzed by means of an electrical model and a Monte Carlo transport simulator. Following model calibration on experiments, we then propose strategies to improve the DC common-base current gain and the cutoff frequency of GBTs. The DC and RF performance of optimized GBT structures based on realistic technology data are analyzed in detail to highlight advantages and potential limits of this device concept.

2017 - Influence of δ p-doping on the behaviour of GaAs/AlGaAs SAM-APDs for synchrotron radiation [Articolo su rivista]
Steinhartova, T.; Nichetti, C.; Antonelli, M.; Cautero, G.; Menk, R. H.; Pilotto, A.; Driussi, F.; Palestri, P.; Selmi, L.; Koshmak, K.; Nannarone, S.; Arfelli, F.; Zilio, S. Dal; Biasiol, G.
abstract

Thiswork focuses on the development and the characterization of avalanche photodiodes with separated absorption and multiplication regions grown by molecular beam epitaxy. The i-GaAs absorption region is separated from the multiplication region by a δ p-doped layer of carbon atoms, which ensures that after applying a reverse bias, the vast majority of the potential drops in the multiplication region. Therein, thin layers of AlGaAs and GaAs alternate periodically in a socalled staircase structure to create a periodic modulation of the band gap, which under bias enables a well-defined charge multiplication and results in a low multiplication noise. The influence of the concentration of carbon atoms in the δ p-doped layer on the device characteristics was investigated and experimental data are presented together with simulation results.

2017 - Modeling and Simulation of Small CCMV Virus Detection by means of High Frequency Impedance Spectroscopy at Nanoelectrodes [Relazione in Atti di Convegno]
Cossettini, Andrea; Dalla Longa, Matteo; Scarbolo, Paolo; Selmi, Luca
abstract

We present an electrical model for the high frequency impedance spectroscopy (HFIS) response of nanoelectrodes to CCMV capsids and full virus biomolecules. The virus electrical and geometrical parameters are extracted from available atomistic descriptions. Simulations of the response at a realistic HFIS CMOS platform suggest that the frequency of optimum sensitivity is within reach of existing designs. Furthermore, they shed light on the role of virus charge and ionic strength on the expected signal. The detection of single viruses could be possible with decananometer scale electrodes operated in optimal conditions and low-noise readout circuitry. © 2017 IEEE.

2017 - Modeling charge collection in x-ray imagers [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Pinaroli, Giovanni; Pilotto, Alessandro; Selmi, Luca
abstract

2017 - Modelling nanoscale n-MOSFETs with III-V compound semiconductor channels: From advanced models for band structures, electrostatics and transport to TCAD [Relazione in Atti di Convegno]
Caruso, E.; Carapezzi, S.; Visciarelli, M.; Gnani, E.; Zagni, N.; Pavan, P.; Palestri, P.; Esseni, D.; Gnudi, A.; Reggiani, S.; Puglisi, F. M.; Verzellesi, G.; Selmi, L
abstract

We review a few state of the art solutions and recent developments to model short channel III-V compound semiconductor n-MOSFETs based on full quantum transport, semiclassical multi-valley / multi-subband transport and TCAD models. The pros and cons of each, and the insights they can deliver, are illustrated with examples from recent technology developments and literature. Areas where improvements and implementations at TCAD level are most necessary are highlighted as well.

2017 - On the electron velocity-field relation in ultra-thin films of III–V compound semiconductors for advanced CMOS technology nodes [Relazione in Atti di Convegno]
Caruso, Enrico; Pin, Alessandro; Palestri, Pierpaolo; Selmi, Luca
abstract

We report Multi-Valley-Multi-Subband Monte Carlo simulations of the velocity-field curves in bulk and thin film InAs, GaAs and In0.53Ga0.47As. Our model suggests that surface roughness scattering reduces the saturation velocity of nanometer- scale films significantly below the corresponding Silicon value. The injection velocity, instead, remains larger than for Silicon down to small film thickness. The results provide a useful reference for the calibration of TCAD compact models for thin films of InxGa(1-x) As compound semiconductors of interest for future CMOS technology nodes.

2017 - Performance comparison for FinFETs, nanowire and stacked nanowires FETs: Focus on the influence of surface roughness and thermal effects [Relazione in Atti di Convegno]
Badami, O.; Driussi, F.; Palestri, P.; Selmi, L.; Esseni, D.
abstract

We perform a comprehensive comparison of FinFETs, stacked nanowires (stacked NWs), circular and square gate-all-around (GAA) -FETs with same footprint, by using an in-house deterministic BTE solver accounting for quantum confinement, a wide set of scattering mechanisms and self-heating. We show that an increase in surface roughness (SR) can frustrate the improvement in on current, I, that for high-quality interfaces we observe in stacked NWs compared to FinFETs. Simulations suggest that SR also influences whether or not In0.53Ga0.47As can provide better I than strained silicon (sSi).

2017 - Performance Projection of III-V Ultra-Thin-Body, FinFET, and Nanowire MOSFETs for two Next-Generation Technology Nodes [Relazione in Atti di Convegno]
Rau, M.; Caruso, Enrico; Lizzit, D.; Palestri, Pierpaolo; Esseni, David; Schenk, A.; Selmi, Luca; Luisier, M.
abstract

Using state-of-the-art simulation tools ranging from semi-classical Monte-Carlo to full-quantum atomistic approaches, the competitiveness of III-V compounds for next-generation high-performance logic switches is confirmed. A planar double-gate ultra-thinbody (DG-UTB), a triple-gate FinFET, and a gate-allaround nanowire (NW) transistor have been designed according to the ITRS specifications for two technology nodes with physical gate lengths of LG=15 nm and 10.4nm. A thorough performance comparison of digital and analog figures of merit at these nodes reveals that for LG=15 nm, the performance of planar and 3-D architectures is comparable. At LG=10.4 nm, the III-V NW promises the highest performance, especially when lowering the supply voltage from 0.59 V to 0.50 V. It also significantly outperforms its strained silicon counterpart. Finally, the effects of series resistance combined with interface traps, surface roughness, alloy scattering, and electron-phonon interactions have been found to deteriorate the III-V ballistic ON-current by 50-60%.

2017 - Simulation Study of the Graphene Base Transistor [Relazione in Atti di Convegno]
Venica, Stefano; Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca
abstract

The Graphene Base Transistor (GBT) has been recently proposed to possibly overcome the THz limit for RF circuits. We developed a modelling framework to explore the GBT design space, the device optimization and the prediction of its RF performance. Via a proper scaling of the EBI and BCI thicknesses, the THz operation is achievable both in terms of fT and fmax. In this latter case, a very low RCONT value is required, thus it is necessary to improve the metal-graphene interface beyond state of the art graphene technology.

2017 - Understanding the Potential and Limitations of Tunnel FETs for Low-Voltage Analog/Mixed-Signal Circuits [Articolo su rivista]
Settino, Francesco; Lanuzza, Marco; Strangio, Sebastiano; Crupi, Felice; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

In this paper, the analog/mixed-signal performance is evaluated at device and circuit levels for a III-V nanowire tunnel field effect transistor (TFET) technology platform and compared against the predictive model for FinFETs at the 10-nm technology node. The advantages and limits of TFETs over their FinFET counterparts are discussed in detail, considering the main analog figures of merits, as well as the implementation of low-voltage track and-hold (T/H) and comparator circuits. It is found that the higher output resistance offered by TFET-based designs allows achieving significantly higher intrinsic voltage gain and higher maximum-oscillation frequency at low current levels. TFET-based T/H circuits have better accuracy and better hold performance by using the dummy switch solution for the mitigation of the charge injection. Among the comparator circuits, the TFET-based conventional dynamic architecture exhibits the best performance while keeping lower area occupation with respect to the more complex double-tail circuits. Moreover, it outperforms all the FinFET counterparts over a wide range of supply voltage when considering low values of the common-mode voltage.

2016 - An Improved Surface Roughness Scattering Model for Bulk, Thin-Body, and Quantum-Well MOSFETs [Articolo su rivista]
Badami, Oves Mohamed Hussein; Caruso, Enrico; Lizzit, Daniel; Osgnach, Patrik; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper reports about the implementation in a multisubband Monte Carlo device simulator of a comprehensive surface roughness scattering model, based on a nonlinear relation between the scattering matrix elements and the fluctuations Δ r) of the interface position. The model is first extended by including carrier screening effects and accounting for scattering at multiple interfaces, and it is then used for the analysis of relevant experimental data sets. We show that the new model can reproduce fairly well the silicon universal mobility curves as well as mobility data for ultrathin-body InGaAs MOSFETs using Δrms values consistent with atomic force microscopy (AFM) and TEM measurements. Our simulation results and some experimental data also indicate that mobility in InGaAs MOSFETs is reduced with decreasing well thickness, T W, with a weaker dependence compared with the TW 6 behavior observed in Si devices. © 1963-2012 IEEE.

2016 - Analysis of Dielectric Microbead Detection by Impedance Spectroscopy with Nanoribbons [Relazione in Atti di Convegno]
Scarbolo, Paolo; Accastelli, Enrico; Ernst, Thomas; Guiducci, Carlotta; Selmi, Luca
abstract

We present a quantitative numerical analysis of dielectric microbead detection experiments with nanoribbons operated in the AC small signal regime. To this purpose, a comprehensive model of nanoribbon operation in electrolyte environment and with DC/AC signals is extended to include the effect of site-binding charges in DC, transient and AC conditions. The model is calibrated against DC measurements and pH-transients data from the literature. The impact of the microfluidic chamber size, the interconnects and the site-binding charge is investigated. The calibrated model suggests that the impedance response to micron-sized beads cannot be explained without also taking into account the bead surface charge.

2016 - Assessment of InAs/AlGaSb Tunnel-FET Virtual Technology Platform for Low-Power Digital Circuits [Articolo su rivista]
Strangio, Sebastiano; Palestri, Pierpaolo; Lanuzza, Marco; Crupi, Felice; Esseni, David; Selmi, Luca
abstract

In this work, a complementary InAs/Al0.05Ga0.95Sb tunnel field-effect-transistor (TFET) virtual technology platform is benchmarked against the projection to the CMOS FinFET 10-nm node, by means of device and basic circuit simulations. The comparison is performed in the ultralow voltage regime (below 500 mV), where the proposed III–V TFETs feature ON-current levels comparable to scaled FinFETs, for the same low-operating-power OFF-current. Due to the asymmetrical n- and p-type I–Vs, trends of noise margins and performances are investigated for different Wp/Wn ratios. Implications of the device threshold voltage variability, which turned out to be dramatic for steep slope TFETs, are also addressed.

2016 - Benchmarks of a III-V TFET technology platform against the 10-nm CMOS technology node considering 28T Full-Adders [Relazione in Atti di Convegno]
Strangio, Sebastiano; Palestri, Pierpaolo; Lanuzza, M.; Esseni, David; Crupi, F.; Selmi, Luca
abstract

This paper presents a benchmark of a virtual III-V TFET nanowire technology platform against the predictive models of CMOS FinFETs for the 10-nm technology node. The standard 28T full adder and the 32-bits ripple carry adder are used as vehicle circuit/architecture for the comparison, respectively. Figures-ofmerit including delays, energy and energy-delay plots are discussed

2016 - Comprehensive comparison and experimental validation of band-structure calculation methods in III–V semiconductor quantum wells [Articolo su rivista]
Zerveas, George; Caruso, Enrico; Baccarani, Giorgio; Czornomaz, Lukas; Daix, Nicolas; Esseni, David; Gnani, Elena; Gnudi, Antonio; Grassi, Roberto; Luisier, Mathieu; Markussen, Troels; Osgnach, Patrik; Palestri, Pierpaolo; Schenk, Andreas; Selmi, Luca; Sousa, Marilyne; Stokbro, Kurt; Visciarelli, Michele
abstract

We present and thoroughly compare band-structures computed with density functional theory, tight-binding, k p and non-parabolic effective mass models. Parameter sets for the non-parabolic C, the L and X valleys and intervalley bandgaps are extracted for bulk InAs, GaAs and InGaAs. We then consider quantum-wells with thickness ranging from 3 nm to 10 nm and the bandgap dependence on film thickness is compared with experiments for In0:53Ga0:47As quantum-wells. The impact of the band-structure on the drain current of nanoscale MOSFETs is simulated with ballistic transport models, the results provide a rigorous assessment of III–V semiconductor band structure calculation methods and calibrated band parameters for device simulations.

2016 - ENBIOS-1D Lab [Software]
Pittino, Federico; Scarbolo, Paolo; Dalla Longa, Matteo; Cossettini, Andrea; Selmi, Luca
abstract

ENBIOS-1D Lab is a tool to illustrate and to study simple Electrolyte, Electrolyte/Insulator and /Electrolyte/Insulator/Semiconductor systems in one dimension. It is meant for use as a teaching tool in support of undergraduate or graduate courses on the basic physics of transduction in ion and particle sensors, and to assist early stage researchers getting familiar with some basic concepts in the field. At the present stage, ENBIOS-1D Lab supports simulation and visualization of impedance/admittance spectra as well as DC and AC potential/ion distributions in simple one-dimensional Electrolyte (E), Electrolyte/Insulator (EI) and Electrolyte/Insulator/Semiconductor (EIS) systems. A broader set of case studies will become available with future releases of the tool, possibly including Ion Sensitive Field Effect Transistor (ISFET) and Nanoelectrode array devices. The physical systems are modelled with the Poisson/Boltzmann (DC) and Poisson/Nernst/Planck - Poisson/Drift/Diffusion (AC small signal) equations. Dedicated models are implemented for the build up of site-binding charge at Electrolyte/Insulator interfaces and for the frequency and salinity dependence of the electrolyte electrical permittivity. ENBIOS-1D Lab is powered by ENBIOS, (Electronic Nano-BIOsensor Simulator), a general purpose three-dimensional Control Volume Finite Element Method (CVFEM) simulator developed in-house at the University of Udine - Italy. ENBIOS simulates in three dimensions (3D) the DC and AC small signal impedance response to ions and micro/nanoparticles of three-dimensional devices made of semiconductor, insulator and electrolyte materials.

2016 - ENBIOS-2D Lab [Software]
Hoxha, Aldi; Scarbolo, Paolo; Cossettini, Andrea; Pittino, Federico; Selmi, Luca
abstract

ENBIOS-2D Lab is a tool to illustrate and to study simple Ion Sensitive Field Effect Transistor structures in two dimensions. Together with its companion tool ENBIOS-1D Lab, it is meant for use as a teaching tool in support of undergraduate or graduate courses on the basic physics of transduction in ion and particle sensors, and to assist early stage researchers getting familiar with some basic concepts in the field. At the present stage, ENBIOS-2D Lab supports simulation and visualization of DC I-V characteristics, impedance/admittance spectra as well as DC and AC potential/carrier/ion distributions in simple two-dimensional ISFET structures. A broader set of case studies will become available with future releases of the tool. The companion ENBIOS-1D Lab tool offers the possibility to simulate simple Electrolyte/Insulator/Semiconductor systems in one-dimension. The physical system is modelled with the Poisson/Boltzmann (DC) and Poisson/Nernst/Planck - Poisson/Drift/Diffusion (AC small signal) equations coupled to the site-binding charge model equations at the Electrolyte/Insulator interfaces. Dedicated models are implemented for the frequency and salinity dependence of the electrolyte electrical permittivity and the temperature dependence of the ions' mobility (in water solvent). ENBIOS-2D Lab is powered by ENBIOS, (Electronic Nano-BIOsensor Simulator), a general purpose three-dimensional Control Volume Finite Element Method (CVFEM) simulator developed in-house at the University of Udine - Italy. ENBIOS simulates in three dimensions (3D) the DC and AC small signal impedance response to ions and micro/nanoparticles of three-dimensional devices made of semiconductor, insulator and electrolyte materials.

2016 - High-Frequency Nanocapacitor Arrays: Concept, Recent Developments, and Outlook [Articolo su rivista]
Lemay, Serge G.; Laborde, Cecilia; Renault, Christophe; Cossettini, Andrea; Selmi, Luca; Frans, Widdershoven
abstract

We have developed a measurement platform for performing high-frequency AC detection at nanoelectrodes. The system consists of 65 536 electrodes (diameter 180 nm) arranged in a sub-micrometer rectangular array. The electrodes are actuated at frequencies up to 50 MHz, and the resulting AC current response at each separately addressable electrode is measured in real time. These capabilities are made possible by fabricating the electrodes on a complementary metal–oxide–semiconductor (CMOS) chip together with the associated control and readout electronics, thus minimizing parasitic capacitance and maximizing the signal-to-noise ratio. This combination of features offers several advantages for a broad range of experiments. First, in contrast to alternative CMOS-based electrical systems based on field-effect detection, high-frequency operation is sensitive beyond the electrical double layer and can probe entities at a range of micrometers in electrolytes with high ionic strength such as water at physiological salt concentrations. Far from being limited to single- or few-channel recordings like conventional electrochemical impedance spectroscopy, the massively parallel design of the array permits electrically imaging micrometer-scale entities with each electrode serving as a separate pixel. This allows observation of complex kinetics in heterogeneous environments, for example, the motion of living cells on the surface of the array. This imaging aspect is further strengthened by the ability to distinguish between analyte species based on the sign and magnitude of their AC response. Finally, we show here that sensitivity down to the attofarad level combined with the small electrode size permits detection of individual 28 nm diameter particles as they land on the sensor surface. Interestingly, using finite-element methods, it is also possible to calculate accurately the full three-dimensional electric field and current distributions during operation at the level of the Poisson–Nernst–Planck formalism. This makes it possible to validate the interpretation of measurements and to optimize the design of future experiments. Indeed, the complex frequency and spatial dependence of the data suggests that experiments to date have only scratched the surface of the method’s capabilities. Future iterations of the hardware will take advantage of the higher frequencies, higher electrode packing densities and smaller electrode sizes made available by continuing advances in CMOS manufacturing. Combined with targeted immobilization of targets at the electrodes, we anticipate that it will soon be possible to realize complex biosensors based on spatial- and time-resolved nanoscale impedance detection

2016 - Impact of bias conditions on electrical stress and ionizing radiation effects in Si-based TFETs [Articolo su rivista]
Ding, Lili; Gnani, Elena; Gerardin, Simone; Bagatin, Marta; Driussi, Francesco; Selmi, Luca; Royer, Cyrille Le; Paccagnella, Alessandro
abstract

The interplay between electrical stress and ionizing radiation effects is experimentally investigated in Si-based Tunnel Field Effect Transistors (TFETs). In particular, the impact of bias conditions on the performance degradation is discussed. We found that the electrical stress effects in TFETs could not be ignored in radiation tests, since they can possibly overwhelm the radiation-induced degradation. Under this circumstance, the worst-case bias condition for studying radiation effects is not straightforward to be determined when there is an interplay between electrical stress and ionizing radiation effects.

2016 - Modeling electrostatic doping and series resistance in graphene-FETs [Relazione in Atti di Convegno]
Venica, Stefano; Zanato, Massimiliano; Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca
abstract

We model the source/drain series resistance and the electrostatic doping effects associated to the source and drain metals in graphene FETs using a Monte Carlo transport simulator. We compare the new model to simulations assuming chemical doping in the source/drain regions. A procedure to include the series resistance as part of the self–consistent Monte Carlo loop is proposed and verified against the widely employed method based on look–up tables.

2016 - Multi-Wire Tri-Gate Silicon Nanowires Reaching Milli-pH Unit Resolution in One Micron Square Footprint [Articolo su rivista]
Accastelli, Enrico; Scarbolo, Paolo; Ernst, Thomas; Palestri, Pierpaolo; Selmi, Luca; Guiducci, Carlotta
abstract

The signal-to-noise ratio of planar ISFET pH sensors deteriorates when reducing the area occupied by the device, thus hampering the scalability of on-chip analytical systems which detect the DNA polymerase through pH measurements. Top-down nano-sized tri-gate transistors, such as silicon nanowires, are designed for high performance solid-state circuits thanks to their superior properties of voltage-to-current transduction, which can be advantageously exploited for pH sensing. A systematic study is carried out on rectangular-shaped nanowires developed in a complementary metal-oxide-semiconductor (CMOS)-compatible technology, showing that reducing the width of the devices below a few hundreds of nanometers leads to higher charge sensitivity. Moreover, devices composed of several wires in parallel further increase the exposed surface per unit footprint area, thus maximizing the signal-to-noise ratio. This technology allows a sub milli-pH unit resolution with a sensor footprint of about 1 µm2, exceeding the performance of previously reported studies on silicon nanowires by two orders of magnitude.

2016 - Performance Study of Strained III-V Materials for Ultra-Thin Body Transistor Applications [Relazione in Atti di Convegno]
Rau, Martin; Markussen, Troels; Caruso, Enrico; Esseni, David; Gnani, Elena; Gnudi, Antonio; Khomyakov, Petr A.; Luisier, Mathieu; Osgnach, Patrik; Palestri, Pierpaolo; Reggiani, Susanna; Schenk, Andreas; Selmi, Luca; Stokbro, Kurt
abstract

A comprehensive description of band gap and effective masses of III-V semiconductor bulk and ultra-thin body (UTB) structures under realistic biaxial and uniaxial strain is given using numerical simulations from four different electronic structure codes. The consistency between the different tools is discussed in depth. The nearest neighbor sp3d5s* empirical tightbinding model is found to reproduce most trends obtained by ab initio Density Functional Theory calculations at much lower computational cost. This model is then used to investigate the impact of strain on the ON-state performance of realistic In0.53Ga0.47As UTB MOSFETs coupled with an efficient method based on the well-known top-of-the-barrier model. While the relative variation of effective masses between unstrained and strained cases seems promising at first, the calculations predict no more than 2% performance improvement on drive currents from any of the studied strain configurations.

2016 - Quasi-Ballistic Gamma - and L-Valleys Transport in Ultrathin Body Strained (111) GaAs nMOSFETs [Articolo su rivista]
Caruso, Enrico; Palestri, Pierpaolo; Lizzit, Daniel; Osgnach, Patrik; Esseni, David; Selmi, Luca
abstract

We carefully scrutinize the potential of ultrathin body strained (111) GaAs MOSFETs to achieve better performance than other GaAs-based channel FETs at scaled channel length and with relaxed thickness requirements, thanks to L-valleys enhanced density-of-states (DoS) and carrier transport. Calibrated multi-subband Monte Carlo simulations including scattering provide the modeling framework necessary for accurate simulations. The results show that L-valley-enhanced transport most likely will not yield the ION and switching time improvements observed in simple ballistic simulations, even if considering the ideal material properties and purely phonon scattering limited transport. In fact, the increased DoS and inversion charge at the virtual source provided by the L-valleys in the strained material is counterbalanced by an increased phonon scattering rate and reduced carrier velocity.

2015 - A TCAD-Based Methodology to Model the Site-Binding Charge at ISFET/Electrolyte Interfaces [Articolo su rivista]
Bandiziol, Andrea; Palestri, Pierpaolo; Pittino, Federico; Esseni, David; Selmi, Luca
abstract

We propose a new approach to describe in commercial TCAD the chemical reactions that occur at dielectric/electrolyte interface and make the ion sensitive FET (ISFET) sensitive to pH. The accuracy of the proposed method is successfully verified against the available experimental data. We demonstrate the usefulness of the method by performing, for the first time in a commercial TCAD environment, a full 2-D analysis of ISFET operation, and a comparison between threshold voltage and drain current differential sensitivities in the linear and saturation regimes. The method paves the way to accurate and efficient ISFET modeling with standard TCAD tools.

2015 - Backscattering and common-base current gain of the Graphene Base Transistor (GBT) [Articolo su rivista]
Venica, Stefano; Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca
abstract

In this paper, we investigate electron transport and electron scattering in the insulators of the Graphene Base Transistor (GBT) by means of a Monte Carlo transport model. We focus on electron backscattering in the base-collector insulator as the possible root cause of the large experimental base current and small measured common-base current gain (αF) of GBTs. Different GBT structures have been simulated and the impact of the scattering parameters on the base current is analyzed. Simulated backscattering-limited αF values are found to be much higher than available experimental data, suggesting that state-of-the-art technology is still far from being optimized. However, those simulated αF values can be low enough to limit the maximum achievable GBT performance.

2015 - Backscattering and common-base current gain of the Graphene Base Transistor (GBT) [Abstract in Atti di Convegno]
Venica, Stefano; Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca
abstract

In this paper, we investigate electron transport and backscattering in the EBI and BCI as possible root causes of the base current and of the common-base current gain degradation in GBTs by means of a Monte Carlo (MC) transport model. Backscattering limited αF values are found to be much higher than experiments in [1, 2], suggesting that state-of-the art technology is still far from being optimized, but they are low enough to limit the maximum achievable performance.

2015 - Characterization and modelling of differential sensitivity of nanoribbon-based pH-sensors [Relazione in Atti di Convegno]
Scarbolo, Paolo; Accastelli, E.; Pittino, Federico; Ernst, T.; Guiducci, C.; Selmi, Luca
abstract

We report accurate characterization, modelling and simulation of SOI nanoribbon-based pH sensors and we compare operation in air (dry) and electrolyte (wet) environments. We find remarkably different current density distributions and geometry scaling rules, but similar series resistances and active trap state densities in the two configurations. Calibrated TCAD based simulations implementing an original approach to model the site-binding harge, and in good agreement with experiments, provide the necessary insights to interpret the non trivial dependence of the threshold voltage and current sensitivity on pH.

2015 - Derivation and Numerical Verification of a Compact Analytical Model for the AC Admittance Response of Nanoelectrodes, Suitable for the Analysis and Optimization of Impedance Biosensors [Articolo su rivista]
Pittino, Federico; Scarbolo, Paolo; Widdershoven, Frans; Selmi, Luca
abstract

This paper presents a compact analytical model for the AC response of nanoelectrode-based impedimetric biosensors to dielectric nanoparticles suspended in the electrolyte. The model highlights the functional dependence of the impedance change on the nanoparticle and the system geometrical and physical parameters. The model is carefully verified by means of 2-D simulations carried out with an ad hoc numerical solver of the Poisson–Nernst–Planck (Poisson-Drift-Diffusion) equations. The results can be useful to determine optimum detection conditions for impedimetric nanobiosensors, and to interpret experimental results.

2015 - Design and implementation of switched coil LC-VCOs in the GHz range using the self-inductance technique [Articolo su rivista]
Cernoia, Federico; Ponton, Davide; Palestri, Pierpaolo; Thurner, Peter; Dalt, Nicola Da; Cecco, Giulio; Selmi, Luca
abstract

This paper presents the design and implementation of dual-band LC-VCOs in the GHz-range featuring a switched coil LC-tank. The proposed design exploits the self-inductance technique. The design of the coil starts from simple considerations and back-of-the-envelope calculations, then electromagnetic simulations are used to optimize the coil layout. The sizing of the switch and its impact on the VCO performance are addressed as well. The VCOs have been implemented in 65 nm CMOS technology. Good correlation between simulated and measured tuning range and phase noise is obtained for all designs, thus confirming the validity and robustness of the design methodology and coil models.

2015 - Design, characterization and signal integrity analysis of a 2.5 Gb/s high-speed serial interface for automotive applications overarching the chip/PCB wall [Relazione in Atti di Convegno]
Cossettini, Andrea; Cristofoli, A.; Grollitsch, W.; Alves, L.; Nonis, R.; Ricca, L. Della; Palestri, Pierpaolo; Selmi, Luca
abstract

A 2.5 Gb/s high-speed serial transmitter for automotive applications has been designed and a circuit/package/board integrated simulation procedure has been set up, enabling the co-design of High-Speed-Serial Interfaces. This simulation methodology employs transistor level models of the transmitter combined with physical-based models of the transmission channel, thus no simplified behavioral models are needed. Model/hardware correlation is reported, including eye closure and jitter effects. Good mutual agreement is found between experiments and simulations.

2015 - Effects of electrical stress and ionizing radiation on Si-based TFETs [Relazione in Atti di Convegno]
Ding, Lili; Gerardin, Simone; Paccagnella, Alessandro; Gnani, Elena; Bagatin, Marta; Driussi, Francesco; Selmi, Luca; Le Royer, Cyrille
abstract

The effects of electrical stress and ionizing radiation on the characteristics of Si-based TFETs were investigated experimentally. We found that the electrical stress effects in TFETs could not be ignored in radiation tests, since they can possibly overwhelm the radiation-induced degradation. Under this circumstance, a lower gate voltage under which the electrical stress effects were suppressed induced a stronger radiation induced degradation in threshold voltage shift and interface traps accumulation.

2015 - Experimental demonstration of improved analog device performance of nanowire-TFETs [Articolo su rivista]
Schulte Braucks, Christian; Richter, Simon; Knoll, Lars; Selmi, Luca; Zhao, Qing Tai; Mantl, Siegfried
abstract

We present experimental data on analog device performance of p-type planar- and gate all around (GAA) nanowire (NW) Tunnel-FETs (TFETs) as well as on n-type Tri-Gate-TFETs. A significant improvement of the analog performance by enhancing the electrostatics from planar TFETs to GAA-NW-TFETs with diameters of 20 nm and 10 nm is demonstrated. A maximum transconductance of 122 mu S/mu m and on-currents up to 23 mu A/mu m at a gate overdrive of V-gt = V-d = -1 V were achieved for the GAA NW-pTFETs. Furthermore, a good output current-saturation is observed leading to high intrinsic gain up to 217. The Tr-Gate nTFETs beat the fundamental MOSFET limit for the subthreshold slope of 60 mV/dec and by that also reach extremely high transconductance efficiencies up to 82 V-1.

2015 - Impact of TFET Unidirectionality and Ambipolarity on the Performance of 6T SRAM Cells [Articolo su rivista]
Strangio, Sebastiano; Palestri, Pierpaolo; Esseni, David; Selmi, Luca; Crupi, F.; Richter, S.; Zhao, Q.; Mantl, S.
abstract

We use mixed device-circuit simulations to predict the performance of 6T static RAM (SRAM) cells implemented with tunnel-FETs (TFETs). Idealized template devices are used to assess the impact of device unidirectionality, which is inherent to TFETs and identify the most promising configuration for the access transistors. The same template devices are used to investigate the VDD range, where TFETs may be advantageous compared to conventional CMOS. The impact of device ambipolarity on SRAM operation is also analyzed. Realistic device templates extracted from experimental data of fabricated state-of-the-art silicon pTFET are then used to estimate the performance gap between the simulation of idealized TFETs and the best experimental implementations.

2015 - Improved sensitivity of nanowire bio-FETs operated at high-frequency: a simulation study [Relazione in Atti di Convegno]
Pittino, Federico; Selmi, Luca
abstract

Silicon Nanowire (SiNW) Bio-FETs emerged as promising candidates for DNA and proteins detection, but static screening severely limits the response to analytes located beyond approximately one Debye length from the surface. In this paper we investigate for the first time the potential advantages of the small signal response of SiNW Bio-FETs in wet environment and up to frequency above the electrolyte’s dielectric relaxation cut-off frequency by means of three-dimensional simulations calibrated on experiments. We find that the static Debye screening limit is overcome at high frequency, where the change in capacitance due to the analyte binding is weakly sensitive on distance from electrode, salt concentration and hardly controllable surface charges.

2015 - Improved surface roughness modeling and mobility projections in thin film MOSFETs [Relazione in Atti di Convegno]
Badami, Oves Mohamed Hussein; Caruso, Enrico; Lizzit, Daniel; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

We report mobility simulations for long channel Si and InGaAs MOSFETs as a function of the semiconductor film thickness and inversion charge. Calculations account for numerous relevant scattering mechanisms and surface roughness is described by the recently developed non-linear model [1]. Reasonable agreement with available experiments is obtained employing the measured surface roughness r.m.s. value. The results reveal that the film thickness dependence of mobility in III-V MOSFETs is weaker than predicted by the T6w law typically observed in silicon devices.

2015 - Investigation of Hot Carrier Stress and Constant Voltage Stress in High-κ Si-Based TFETs [Articolo su rivista]
Ding, L.; Gnani, E.; Gerardin, S.; Bagatin, M.; Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca; Royer, C. Le; Paccagnella, A.
abstract

This paper reports the experimental investigation of hot carrier stress (HCS) and constant voltage stress (CVS) in high-κ Si-based tunnel FETs. For the devices in this paper, due to the large injection of cold carriers and to the presence of traps in the gate dielectric, the degradation of the transfer characteristics under CVS is much more severe than under HCS. The experimental results show that the sub-threshold swing remains stable under both HCS and CVS conditions, and it is not influenced by the stress-induced increase of the interface trap density.

2015 - Low-voltage high-performance III-V semiconductor MOSFETs for advanced CMOS nodes: impact of strain and interface traps [Relazione in Atti di Convegno]
Osgnach, Patrik; Caruso, Enrico; Lizzit, Daniel; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

2015 - Mixed device-circuit simulations of 6T/8T SRAM cells employing tunnel-FETs [Relazione in Atti di Convegno]
Strangio, Sebastiano; Palestri, Pierpaolo; Esseni, David; Selmi, Luca; Crupi, F.
abstract

2015 - Modeling approaches for band-structure calculation in III-V FET quantum wells [Relazione in Atti di Convegno]
Caruso, Enrico; Zerveas, G.; Baccarani, G.; Czornomaz, L.; Daix, N.; Esseni, David; Gnani, E.; Gnudi, A.; Grassi, R.; Luisier, M.; Markussen, T.; Palestri, Pierpaolo; Schenk, A.; Selmi, Luca; Sousa, M.; Stokbro, K.; Visciarelli, M.
abstract

We compare band-structure calculations obtained with modeling approaches hierarchically spanning from density functional theory to tight-binding, k⋅p and non-parabolic effective mass descriptions. We consider III-V quantum-wells with thickness ranging from 3nm to 10nm. Comparison with experiments for unstrained and strained InGaAs quantum-wells is also reported.

2015 - Real-time imaging of microparticles and living cells with CMOS nanocapacitor arrays [Articolo su rivista]
Laborde, C.; Pittino, Federico; Verhoeven, H. A.; Lemay, S. G.; Selmi, Luca; Jongsma, M. A.; Widdershoven, F. P.
abstract

Platforms that offer massively parallel, label-free biosensing can, in principle, be created by combining all-electrical detection with low-cost integrated circuits. Examples include fieldeffect transistor arrays, which are used for mapping neuronal signals1,2 and sequencing DNA3,4. Despite these successes, however, bioelectronics has so far failed to deliver a broadly applicable biosensing platform. This is due, in part, to the fact that d.c. or low-frequency signals cannot be used to probe beyond the electrical double layer formed by screening salt ions5–8, which means that under physiological conditions the sensing of a target analyte located even a short distance from the sensor (∼1 nm) is severely hampered. Here, we show that high-frequency impedance spectroscopy can be used to detect and image microparticles and living cells under physiological salt conditions. Our assay employs a large-scale, high-density array of nanoelectrodes integrated with CMOS electronics on a single chip and the sensor response depends on the electrical properties of the analyte, allowing impedance-based fingerprinting. With our platform, we image the dynamic attachment and micromotion of BEAS, THP1 and MCF7 cancer cell lines in real time at submicrometre resolution in growth medium, demonstrating the potential of the platform for label/tracer-free high-throughput screening of anti-tumour drug candidates.

2015 - Semi-analytic Modeling for Hot Carriers in Electron Devices [Capitolo/Saggio]
Alban, Zaka; Palestri, Pierpaolo; Quentin, Rafhay; Raphael, Clerc; Denis, Rideau; Selmi, Luca
abstract

The paradigm shift from a field- to an energy-based framework in the modeling of hot-carrier-induced degradation has triggered a detailed microscopic view on the degradation mechanisms in MOSFET devices (see also chapter “The Spherical Harmonics Expansion Method for Assessing Hot Carrier Degradation”). The knowledge of the carrier energy distribution inside the device is the main ingredient enabling the energy-dependent approaches. However, efficient and reliable hot-carrier modeling in electron devices is a challenging task. This chapter presents a novel semi-analytical approach to model hot-carrier transport in MOSFET devices. The new approach is inherently non-local and: (a) considers full-band aspects of the silicon band structure, (b) includes major inelastic scattering mechanisms such as optical phonons, impact ionization and carrier-carrier scattering. The model is extensively compared against reference full-band Monte Carlo simulations in terms of distribution functions as well as bulk and gate currents over a wide range of gate lengths and bias conditions. The obtained good agreement confirms the accuracy of the adopted approach that offers an efficient alternative to Monte Carlo and Spherical Harmonics Expansion for hot-carrier modeling.

2015 - Simulation analysis of III-V n-MOSFETs: channel materials, Fermi level pinning and biaxial strain [Relazione in Atti di Convegno]
Caruso, Enrico; Lizzit, Daniel; Osgnach, Patrik; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

In this work we employ a state-of-the-art Multi-Subband Monte Carlo simulator to investigate the performance of III-V n-MOSFETs with LG = 11.7nm. We analyze GaSb versus InGaAs strained and unstrained channel materials and the implications of Fermi level pinning on electrostatic and transport. We found that InGaAs MOSFETs can outperform strained silicon for low VDD applications. Advantages related to strained InGaAs are limited and mainly due to reduced Fermi Level Pinning.

2015 - State-of-the-art semi-classical Monte Carlo method for carrier transport in nanoscale transistors [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Caruso, Enrico; Driussi, Francesco; Esseni, David; Lizzit, Daniel; Osgnach, Patrik; Venica, Stefano; Selmi, Luca
abstract

We review the Monte Carlo method to model semi-classical carrier transport in advanced semiconductor devices. We report examples of the use of the Multi- Subband Monte Carlo method to simulate MOSFETs with III-V compound semiconductor channel. Monte Carlo transport modeling of graphene-based transistors is also addressed.

2015 - The impact of interface states on the mobility and drive current of In 0.53Ga 0.47As semiconductor n-MOSFETs [Articolo su rivista]
Osgnach, Patrik; Caruso, Enrico; Lizzit, Daniel; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

Accurate Schrödinger-Poisson and Multi-Subband Monte Carlo simulations are used to investigate the effect of interface states at the channel-insulator interface of In0:53Ga0:47As MOSFETs. Acceptor states with energy inside the conduction band of the semiconductor can explain the dramatic Fermi level pinning observed in the experiments. Our results show that these states significantly impact the electrical mobility measurements but they appear to have a limited influence on the static current drive of short channel devices.

2014 - A new formulation for surface roughness limited mobility in bulk and ultra-thin-body metal–oxide–semiconductor transistors [Articolo su rivista]
Lizzit, Daniel; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper presents a new model for the surface roughness (SR) limited mobility in MOS transistors. The model is suitable for bulk and thin body devices and explicitly takes into account the non linear relation between the displacement of the interface position and the SR scattering matrix elements, which is found to significantly influence the r.m.s value of the interface roughness that is necessary to reproduce SR-limited mobility measurements. In particular, comparison with experimental mobility for bulk Si MOSFETs shows that with the new SR scattering model a good agreement with measured mobility can be obtained with r.m.s. values of about 0.2 nm, which is in good agreement with several AFM and TEM measurements. For thin body III–V MOSFETs, the proposed model predicts a weaker mobility degradation at small well thicknesses (Tw), compared to the Tw^6 behavior observed in Si extremely thin body devices

2014 - A technique to model the AC response of diffuse layers at electrode/electrolyte interfaces and to efficiently simulate impedimetric biosensor arrays for many analyte configurations [Relazione in Atti di Convegno]
Pittino, Federico; Selmi, Luca
abstract

2014 - Analysis of TFET based 6T SRAM cells implemented with state of the art silicon nanowires [Relazione in Atti di Convegno]
S., Strangio; Palestri, Pierpaolo; Esseni, David; Selmi, Luca; F., Crupi
abstract

Tunnel-FETs are studied in a mixed device/circuit simulation environment. Model parameters calibrated on experimental DC as well as pulsed characterizations are then used for 6T SRAM cells investigation. Issues concerning fabricated devices, as the ambipolarity and the uni-directionality, are addressed at both device and circuit levels. Our results suggest that ambipolarity needs to be solved through device engineering and/or fabrication process improvements, while issues related to uni-directionality may be mitigated with a proper circuit design.

2014 - Challenges and opportunities in the design of Tunnel FETs: materials, device architectures, and defects [Relazione in Atti di Convegno]
Esseni, David; M. G., Pala; Revelant, Alberto; Palestri, Pierpaolo; Selmi, Luca; M., Li; G., Snider; D., Jena; H. G., Xing
abstract

Tunnel FETs are perceived as promising emerging devices to improve the energy efficiency of CMOS integrated circuits. This paper presents results and discussions about some selected topics concerning the working principles and design options of Tunnel FETs, which we believe will play an important role in the development and optimization of these transistors in the near term future.

2014 - Efficient Statistical Simulation of Intersymbol Interference and Jitter in High-Speed Serial Interfaces [Articolo su rivista]
Cristofoli, Andrea; Palestri, Pierpaolo; Nicola Da, Dalt; Selmi, Luca
abstract

We present and validate against experiments a modeling approach for high-speed serial links that combines the computational advantages of statistical techniques for intersymbol interference (ISI) (improved by employing the realistic pulse shape as from SPICE simulations) and a simple empirical methodology to account for the jitter of the transmitter. The proposed approach is validated by comparison with other modeling approaches such as full SPICE simulations (for ISI) and Simulink (for jitter) as well as against the experimental data for a 2.5 Gb/s CMOS differential transmitter driving different channels.

2014 - Experimental Demonstration of Improved Analog Device Performance in GAA-NW-TFETs [Relazione in Atti di Convegno]
C., Schulte Braucks; S., Richter; L., Knoll; Selmi, Luca; Q., Zao; S., Mantl
abstract

We present experimental data on analog device performance of p-type planar and gate all around (GAA) nanowire (NW) Tunnel-FETs (TFETs). 10nm diameter GAA-NW-TFETs reach a maximum transconductance efficiency of 12.7V −1 which is close to values obtained from simulations. A significant improvement of the analog performance by enhancing the electrostatics from planar TFETs to GAA-NW-TFETs with diameter of 20nm and 10nm is demonstrated. A maximum transconductance of 122 μS/μm and on-current up to 23 μA/μm at a gate overdrive of Vgt = Vd = −1V were achieved for the GAANW- TFETs. Furthermore a good output current-saturation is observed leading to high intrinsic gain up to 217 which is even higher than in 20nm FinFETs.

2014 - First Demonstration of Strained SiGe Nanowires TFETs with ION beyond 700μA/μm [Relazione in Atti di Convegno]
A., Villalon; C., Le Royer; P., Nguyen; S., Barraud; F., Glowacki; Revelant, Alberto; Selmi, Luca; S., Cristoloveanu; L., Tosti; C., Vizioz; J. M., Hartmann; N., Bernier; B., Prévitali; C., Tabone; F., Allain; S., Martinie; O., Rozeau; M., Vinet
abstract

We present for the first time high performance Nanowire (NW) Tunnel FETs (TFET) obtained with a CMOS-compatible process flow featuring compressively strained Si1-xGex (x=0, 0.2, 0.25) nanowires, Si0.7Ge0.3 Source and Drain and High-K/Metal gate. Nanowire architecture strongly improves electrostatics, while low bandgap channel (SiGe) provides increased band-to-band tunnel (BTBT) current to tackle low ON current challenges. We analyse the impact of these improvements on TFETs and compare them to MOSFET ones. Nanowire width scaling effects on TFET devices are also investigated, showing a W-3 dependence of ON current (ION) per wire. The fabricated devices exhibit higher ION than any previously reported TFET, with values up to 760μA/μm and average subthreshold slopes (SS) of less than 80mV/dec.

2014 - Graphene Base Transistors with optimized emitter and dielectrics [Relazione in Atti di Convegno]
Venica, S.; Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca
abstract

The Graphene Base Transistor (GBT) is a very promising device concept for analog applications. The device operates similar to the hot electron transistor and exploits the high carrier mobility of graphene to reduce the base resistance that limits the unity power gain frequency (fmax) and the noise figure (NF) of RF devices. Although the DC functionality of the GBT has been experimentally demonstrated, at present RF performance can be investigated by simulations only. In this paper, we predict the DC current and the cutoff frequency of different GBT designs (including dimensions and various materials), with the aim to optimize the GBT structure and to achieve THz operation. In particular, optimized emitter/dielectrics combinations are proposed to maximize RF figures of merit.

2014 - High Performance SiGe Nanowire Tunnel FETs: Low Temperature Characterization for Device Process Optimization [Relazione in Atti di Convegno]
A., Villalon; Revelant, Alberto; C., Le Royer; P., Nguyen; Selmi, Luca; S., Cristoloveanu
abstract

This paper presents SiGe nanowire tunneling field effect transistors (TFETs) cointegrated with MOSFETs. The process is detailed, and the differences between TFET injection (Band-to-Band Tunneling or BTBT) and MOSFET thermionic injection are outlined. The fabricated TFETs exhibit record ON-current performances at room temperature, three times higher than previous state of the art. Low-temperature measurements are conducted to clarify the device physics. It is shown that subthreshold slope degradation is a result of trap assisted tunneling; careful control of the defect-inducing process steps could lead to slopes lower than 60mV/dec at room temperature, without degradation of ON-state current.

2014 - Models for the use of commercial TCAD in the analysis of silicon-based integrated biosensors [Articolo su rivista]
Pittino, Federico; Palestri, Pierpaolo; Scarbolo, Paolo; Esseni, David; Selmi, Luca
abstract

We present a simple approach to describe electrolytes in TCAD simulators for the modeling of nano-biosensors. The method exploits the similarity between the transport equations for electrons and holes in semiconductors and the ones for charged ions in a solution. We describe a few workarounds to improve the model accuracy in spite of the limitations of commercial TCAD. Applications to the simulations of silicon nanowire and nanoelectrode biosensors are reported as relevant examples.

2014 - Numerical simulation of the position and orientation effects on the impedance response of nanoelectrode array biosensors to DNA and PNA strands [Articolo su rivista]
Pittino, Federico; F., Passerini; Selmi, Luca; F., Widdershoven
abstract

2014 - Performance analysis of different SRAM cell topologies employing tunnel-FETs [Relazione in Atti di Convegno]
Strangio, Sebastiano; Palestri, Pierpaolo; Esseni, David; Selmi, Luca; F., Crupi
abstract

2014 - Performance Benchmarking and Effective Channel Length for Nanoscale InAs, In0.53Ga0.47As, and sSi n-MOSFETs [Articolo su rivista]
Lizzit, Daniel; Esseni, David; Palestri, Pierpaolo; Osgnach, Patrik; Selmi, Luca
abstract

Thanks to the high electron velocities, III–V semiconductors have the potential to meet the challenging ITRS requirements for high performance for sub-22-nm technology nodes and at a supply voltage approaching 0.5 V. This paper presents a comparative simulation study of ultrathin-body InAs, In0.53Ga0.47As, and strained Si MOSFETs, by using a comprehensive semiclassical multisubband Monte Carlo (MSMC) transport model. Our results show that: 1) due to the finite screening length in the source-drain regions, III–V and Si nanoscale MOSFETs with a given gate length (LG) may have a quite different effective channel length (Leff); 2) the difference in Leff provides a useful insight to interpret the performance comparison of III–V and Si MOSFETs; and 3) the engineering of the source-drain regions has a remarkable influence on the overall performance of nanoscale III–V MOSFETs.

2014 - Sensitivity of Silicon Nanowire Biochemical Sensors [Capitolo/Saggio]
Palestri, Pierpaolo; M., Mouis; A., Afzalian; Selmi, Luca; Pittino, Federico; D., Flandre; G., Ghibaudo
abstract

2014 - Simulation of DC and RF Performance of the Graphene Base Transistor [Articolo su rivista]
Venica, Stefano; Driussi, Francesco; Palestri, Pierpaolo; Esseni, David; Sam, Vaziri; Selmi, Luca
abstract

We examined the DC and RF performance of the graphene base transistor (GBT) in the ideal limit of unity common base current gain. To this purpose, we developed a model to calculate the current–voltage characteristics of GBTs with semiconductor or metal emitter taking into account space charge effects in the emitter–base and base–collector dielectrics that distort the potential profile and limit the upper value of fT. Model predictions are compared with available experiments. We show that, in spite of space charge high current effects, optimized GBT designs still hold the promise to achieve intrinsic cutoff frequency in the terahertz region, provided that an appropriate set of dielectric and emitter materials is chosen.

2014 - Simulation of the Performance of Graphene FETs With a Semiclassical Model, Including Band-to-Band Tunneling [Articolo su rivista]
Alan, Paussa; Gianluca, Fiori; Palestri, Pierpaolo; Matteo, Geromel; Esseni, David; Giuseppe, Iannaccone; Selmi, Luca
abstract

We assess the analog/RF intrinsic performance of graphene FETs (GFETs) through a semiclassical transport model, including local and remote phonon scattering as well as band-to-band tunneling generation and recombination, validated by comparison with full quantum results over a wide range of bias voltages. We found that scaling is expected to improve the fT , and that scattering plays a role in reducing both the fT and the transconductance also in sub-100-nm GFETs. Moreover, we observed a strong degradation of the device performance due to the series resistances and source/drain to channel underlaps.

2014 - The impact of interface states on the mobility and the drive current of III-V MOSFETs [Relazione in Atti di Convegno]
Osgnach, Patrik; Caruso, Enrico; Lizzit, Daniel; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

We investigate the effect of interface states at the channel/insulator interface of III-V MOSFETs by means of accurate Schr¨odinger-Poisson and Multi-subband Monte Carlo simulations. Traps in the conduction band are found to be the main responsible of the Fermi level pinning observed in the experiments and impact the mobility measurements, but have a limited influence on the current drive of short channel devices.

2014 - Total Ionizing Dose Effects in Si-Based Tunnel FETs [Articolo su rivista]
Lili, Ding; Elena, Gnani; Simone, Gerardin; Marta, Bagatin; Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca; Cyrille Le, Royer; Alessandro, Paccagnella
abstract

Total ionizing dose (TID) effects in Si-based tunnel fi- nite element transfers (FETs) were investigated for the first time. Under 10-keV X-ray irradiation environment, along with the in- crease in total dose, a shift of the transfer characteristics and an increase in the interface trap density could be observed. After ir- radiation at 1 Mrad (SiO2) (and higher dose), the threshold voltage and the band-to-band tunneling conduction were only modestly affected, despite the thick buried oxide (140 nm). In contrast, under the same bias and irradiation environment, a FDSOI nMOSFET fabricated with a similar process presented a more severe degradation, suggesting the robustness of TFETs against TID effects. The underlying mechanism was explored through device simulation and ascribed to be due to the peculiarity of the doping structures of TFETs.

2014 - Use and comparative assessment of the CVFEM method for Poisson–Boltzmann and Poisson–Nernst–Planck three dimensional simulations of impedimetric nano-biosensors operated in the DC and AC small signal regimes [Articolo su rivista]
Pittino, Federico; Selmi, Luca
abstract

We specialize the Control Volume Finite Element Method (CVFEM) for the solution of the Poisson–Boltzmann and Poisson–Nernst–Planck (also known as Poisson–drift–diffusion) system of equations on unstructured 3D meshes describing nanoelectronic biosensors operated in the DC and AC small signal regimes. We provide the exact analytical expressions for volume and surface integrals derived by means of a linear coordinate transformation and show that they are both accurate and efficient, especially on coarse grids. Being of great importance for the chosen application, the conservation property is investigated and we show that, for the CVFEM to be conservative, the calculations on the boundary have to be performed with special care. CVFEM is carefully compared to the Galerkin Finite Element Method (GFEM) from the point of view of the underlying theory, implementation and solution calculation. The simulation tool is used to evaluate the response of a real nanoelectrode-based biosensor array to the introduction of small nanoparticles.

2014 - Welcome letter [Abstract in Atti di Convegno]
Selmi, L.; Klootwijk, J.; Meneghesso, G.; Toffoli, A.; Driussi, F.
abstract

2013 - An Improved Semi-Classical Model to Investigate Tunnel-FET performance [Relazione in Atti di Convegno]
Revelant, Alberto; Osgnach, Patrik; Palestri, Pierpaolo; Selmi, Luca
abstract

We present a model for Tunnel FETs (TFETs) capable to describe off equilibrium transport as well as Band to Band Tunneling (BtBT), that is implemented as an additional block into an existing Multi-Subband Monte Carlo (MSMC) transport simulator. To account for the quantum effect associated to the confinement of carriers in Ultra Thin Body SOI devices, a correction to the computation of the BtBT generation rate is proposed. The developed simulator is here applied to the study of III-V based TFETs.

2013 - An innovative band-to-band tunneling analytical model and implications in compact modeling of tunneling-based devices [Articolo su rivista]
DE MICHIELIS, Luca; N., Dağtekin; A., Biswas; L., Lattanzio; Selmi, Luca; M., Luisier; H., Riel; A. M., Ionescu
abstract

In this paper, an analytical band-to-band tunneling model is proposed, validated by means of drift-diffusion simulation and comparison with experimental data, implemented in Verilog-A, and finally proven with SPICE simulator through simulation of circuits featuring tunneling diodes. The p-n junction current calculation starts from a non-local Band-to-Band tunneling theory including the electron-phonon interaction and therefore it is particularly suited for indirect semiconductor materials such as silicon- or germanium-based interband tunneling devices.

2013 - Analysis of the Performance of n-Type FinFETs With Strained SiGe Channel [Articolo su rivista]
Lizzit, Daniel; Palestri, Pierpaolo; Esseni, David; Revelant, Alberto; Selmi, Luca
abstract

This paper reports a simulation study investigating the drive current of a prototypical SiGe n-type FinFET built on a relaxed SiGe substrate for different values of the Ge content x in the Si(1−x)Gex active layer. To this purpose, we performed strain simulations, band-structure calculations, and multisubband Monte Carlo transport simulations accounting for the effects of the Ge content on both the band-structure and the scattering rates in the transistor channel. Our results suggest that the largest on-current may be obtained with a simple Si active layer, because of the beneficial strain induced by the SiGe substrate. A SiGe channel instead is less performing because of strain relaxation and alloy scattering.

2013 - Calibrated multi-subband Monte Carlo modeling of tunnel-FETs in silicon and III–V channel materials [Articolo su rivista]
Revelant, Alberto; Palestri, Pierpaolo; Osgnach, Patrik; Selmi, Luca
abstract

We present a semiclassical model for Tunnel-FET (TFET) devices capable to describe band-to-band tunneling (BtBT) as well as far from equilibrium transport of the generated carriers. BtBT generation is implemented as an add-on into an existing multi-subband Monte Carlo (MSMC) transport simulator that accounts as well for the effects typical to alternative channel materials and high-j dielectrics. A simple but accurate correction for the calculation of the BtBT generation rate to account for carrier confinement in the subbands is proposed and verified by comparison with full 2D quantum calculation.

2013 - Demonstration of Improved Transient Response of Inverters with Steep Slope Strained Si NW TFETs by Reduction of TAT with Pulsed I-V and NW Scaling [Relazione in Atti di Convegno]
L., Knoll; Q. T., Zhao; A., Nichau; S., Richter; G. V., Luong; S., Trellenkamp; A., Schäfer; Selmi, Luca; K. K., Bourdelle; S., Mantl
abstract

We present gate all around strained Si (sSi) nanowire array TFETs with high ION (64μA/μm at VDD=1.0V). Pulsed I-V measurements provide small SS and record I60 of 1×10-2μA/μm at 300K due to the suppression of trap assisted tunneling (TAT). Scaling the nanowires to 10 nm diameter greatly suppresses the impact of TAT and improves SS and ION. Transient analysis of complementary TFET inverters demonstrates experimentally for the first time that device scaling and improved electrostatics yields to faster time response.

2013 - Experimental Verification of ISI and Jitter Modeling in High Speed Links [Relazione in Atti di Convegno]
Cristofoli, Andrea; Palestri, Pierpaolo; N., Da Dalt; Selmi, Luca
abstract

2013 - Impact of High-Mobility Materials on the Performance of Near- and Sub-Threshold CMOS Logic Circuits [Articolo su rivista]
Crupi, F; Albano, D; Alioto, M; Franco, J; Selmi, Luca; Mitard, J; Groeseneken, G.
abstract

This paper studies the impact of high-mobility materials on the performance and energy efficiency of near- and sub- threshold CMOS logic circuits by means of analytical equations and experimental data on SiGe pMOSFETs. The introduction of high-mobility materials is shown to improve the energy- performance trade-off in near-threshold circuits more than in above-threshold circuits, since the benefits of higher mobility are degraded at higher longitudinal and transversal electric fields. On the other hand, results show that high-mobility materials do not exhibit any advantage in terms of the energy-performance trade-off in sub-threshold logic circuits. This is explained by the fact that the benefits brought by the larger mobility of SiGe or other alternative materials can be obtained by tuning the threshold voltage of conventional Si devices.

2013 - Interpretation of graphene mobility data by means of a semiclassical Monte Carlo transport model [Articolo su rivista]
Bresciani, Marco; Palestri, Pierpaolo; Esseni, David; Selmi, Luca; B., Szafranek; D., Neumaier
abstract

In this paper we compare experimental data and simulations based on a semiclassical model in order to investigate the relative importance of a several scattering mechanisms on the mobility of graphene nano-ribbons. Furthermore, some new experimental results complementing the range of ribbon widths available in the literature are also reported. We show that scattering with remote phonons originating in the substrate insulator can appreciably reduce the mobility of graphene and it should not be neglected in the interpretation of graphene mobility data. In fact by accounting for remote phonon scattering we could reproduce fairly well the experimentally observed dependence of the mobility on the ribbon width, the temperature and the inversion density, whereas the agreement with experiments is much worse when remote phonons are not included in the calculations.

2013 - Inverters With Strained Si Nanowire Complementary Tunnel Field-Effect Transistors [Articolo su rivista]
Knoll, L; Zhao Q., J; Nichau, A; Trellenkamp, S; Richter, S; Schäfer, A; Esseni, David; Selmi, Luca; Bourdelle K., K; Mantl, S.
abstract

Inverters based on uniaxially tensile strained Si (sSi) nanowire (NW) tunneling field-effect transistors (TFETs) are fabricated. Tilted dopant implantation using the gate as a shadow mask allows self-aligned formation of p-i-n TFETs. The steep junctions formed by dopant segregation at low temperatures improve the band-to-band tunneling, resulting in higher oncurrents of n- and p-TFETs of >10 μA/μm at VDS = 0.5 V. The subthreshold slope for n-channel TFETs reaches a minimum value of 30 mV/dec, and is <60 mV/dec over one order of magnitude of drain current. The first sSi NW complementary TFET inverters show sharp transitions and fairly high static gain even at very low VDD = 0.2 V. The first transient response analysis of the inverters shows clear output voltage overshoots and a fall time of 2 ns at VDD = 1.0 V.

2013 - Modeling, simulation and design of the vertical Graphene Base Transistor [Articolo su rivista]
Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca
abstract

2013 - Modelling, simulation and design of the vertical Graphene Base Transistor [Abstract in Atti di Convegno]
Driussi, Francesco; Palestri, Pierpaolo; Selmi, Luca
abstract

2013 - Multi-scale strategy for high-k/metal-gate UTBB-FDSOI devices modeling with emphasis on back bias impact on mobility [Articolo su rivista]
Nier, Oliver; D., Rideau; Y. M., Niquet; F., Monsieur; V. H., Nguyen; F., Triozon; A., Cros; R., Clerc; J. C., Barbé; Palestri, Pierpaolo; Esseni, David; I., Duchemin; L., Smith; L., Silvestri; F., Nallet; C., Tavernier; H., Jaouen; Selmi, Luca
abstract

Mobility in high-k/metal-gate Ultra-Thin Body and Box Fully Depleted SOI devices has been extensively investigated by means of multi-scale simulations and experimental data. Split-CV mobility measurements have been performed for various Interfacial Layer Equivalent Oxide Thickness allowing an investigation of the physical mechanisms responsible for the mobility degradation at high-k/Interfacial layer interface. The impact of the back bias on transport properties is investigated and mobility enhancement in the reverse regime (back gate inversion) is studied. A multi-scale simulation strategy is ranging from quantum Non-equilibrium Green’s Functions to semi-classical Kubo Greenwood approach. These advanced solvers made possible a throughout calibration of empirical TCAD mobility models.

2013 - Numerical and analytical models to investigate the AC high-frequency response of nanoelectrode/SAM/electrolyte capacitive sensing elements [Articolo su rivista]
Pittino, Federico; Selmi, Luca; Widdershoven, F.
abstract

We develop theoretical models and numerical simulators to accurately describe the AC signal response of nanoelectrodes to the presence of biomolecules, in order to aid the design of capacitive biosensors. In particular, we first develop an analytical model for the electrolyte response to AC signal stimulation, showing that it is possible to define an AC screening length as in the standard Debye–Hückel theory. We then develop a full-custom numerical simulator for a simple nanoelectrode system, where the AC part is solved in the small-signal approximation, coupled to the DC solution. We validate the solver using the analytical model, and then use it to understand the effect of a dielectric biomolecule on the biosensor admittance.

2013 - On the Optimization of SiGe and III-V Compound Hetero-Junction Tunnel FET Devices [Relazione in Atti di Convegno]
Revelant, Alberto; Palestri, Pierpaolo; Osgnach, Patrik; Lizzit, Daniel; Selmi, Luca
abstract

We investigate the operation and performance of planar SiGe/Si and n0.53Ga0.47As/In0.7Ga0.3As/In0.53Ga0.47As hetero-junction Semiconductor on Insulator (ScOI) Tunnel FET (TFET) devices. The alignment between the hetero-junction, the gate edge and the source junction is systematically shifted to search for the highest ON-current and the lowest Subthreshold Swing (SS). A slight positive misalignment between the heterojunction and the metallurgical junction is beneficial to improve ION but for the considered devices the ON-current at VDD=0.5V and IOFF=1pA/m hardly exceeds 1A/m. Furthers reduction of the band gap by lattice strain appears mandatory to exceed this limit in the explored material systems.

2013 - On the response of nanoelectrode capacitive biosensors to DNA and PNA strands [Relazione in Atti di Convegno]
Pittino, Federico; Passerini, F; Palestri, Pierpaolo; Selmi, Luca; Widdershoven, F.
abstract

This paper investigates the response of a nanoelectrode based capacitive biosensor to the presence of single and double strands of DNA/PNA. The expected admittance spectrum for an idealized system with cylindrical symmetry, where the biomolecule is represented by a simple dielectric and charged rod, is calculated over a broad frequency range extending from below to above the electrolyte’s dielectric relaxation cut-off frequency. DNA and PNA hybridization is also considered. The results provide indications on optimum detection conditions for admittance based DNA biosensors.

2013 - Performance of III-V nanoscale MOSFETs: a simulation study [Relazione in Atti di Convegno]
Lizzit, Daniel; Osgnach, P; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

Channel materials alternative to silicon have been recently introduced as a new scaling scenario to operate at increasingly lower supply voltages and maintain high performance. Silicon-based devices might reach their scaling limit imposed by the fundamental physical properties of silicon in the next few years making it difficult to achieve the expected performance for the future CMOS [6]. While for pMOS transistors promising results have been obtained by using the Ge as channel material [7], the best candidates for nMOS transistors are III-V semiconductors.

2013 - Quantum Mechanical Study of the Germanium Electron-Hole Bilayer Tunnel FET [Articolo su rivista]
Cem, Alper; Livio, Lattanzio; Luca De, Michielis; Palestri, Pierpaolo; Selmi, Luca; Adrian Mihai, Ionescu
abstract

The electron-hole bilayer tunnel field-effect transistor (EHBTFET) is an electronic switch that uses 2-D-2-D sub-band-to-sub-band tunneling (BTBT) between electron and hole inversion layers and shows significant subthermal swing over several decades of current due to the step-like 2-D density of states behavior. In this paper, EHBTFET has been simulated using a quantum mechanical model. The model results are compared against transactions on computer-aided design simulations and remarkable differences show the importance of quantum effects and dimensionality in this device. Ge EHBTFET with channel thickness of 10 nm results as a promising device for low supply voltage, subthreshold logic applications, with a super steep switching behavior featuring SSavg ~ 40 mV/dec up to VDD. Furthermore, it has been demonstrated that high on current levels ( ~ 40 μA/μm) can be achieved due to the transition from phonon-assisted BTBT to direct BTBT at higher biases.

2013 - Simulation of low Schottky barrier MOSFETs using an improved Multi-subband Monte Carlo model [Articolo su rivista]
Gudmundsson, V; Palestri, Pierpaolo; Hellström P., E; Selmi, Luca; Östling, M.
abstract

We present a simple and efficient approach to implement Schottky barrier contacts in a Multi-subband Monte Carlo simulator by using the subband smoothening technique to mimic tunneling at the Schottky junction. In the absence of scattering, simulation results for Schottky barrier MOSFETs are in agreement with ballistic Non-Equilibrium Green’s Functions calculations. We then include the most relevant scattering mechanisms, and apply the model to the study of double gate Schottky barrier MOSFETs representative of the ITRS 2015 high performance device. Results show that a Schottky barrier height of less than approximately 0.15 eV is required to outperform the doped source/drain structure.

2013 - Simulation of nano-biosensors based on conventional TCAD [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Sette, R; Pittino, Federico; Saccon, F; Esseni, David; Selmi, Luca
abstract

We present a simple methodology to include the modeling of an electrolyte into a TCAD simulator exploiting the similarity between the transport equations for electrons and holes in semiconductors and the ones for charged ions in a solution. Applications to the simulation of pH-meters and biosensors are reported as examples.

2013 - Surface roughness limited mobility modeling in ultra-thin SOI and quantum well III-V MOSFETs [Relazione in Atti di Convegno]
Lizzit, Daniel; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper presents a new model for the surface roughness (SR) limited mobility (μSR). The model is suitable for bulk, for ultra thin body (UTB) and for Hetero-Structure Quantum Well (HS-QW) MOSFETs. Comparison with experimental mobility for Si bulk MOSFETs shows that a good agreement with measured mobility can be obtained with a r.m.s. value of the SR spectrum close to several AFM and TEM measurements. For III-V MOSFETs with small well thickness the proposed model shows a weaker mobility degradation with respect to the Tw6 behavior.

2013 - Technology Computer Aided Design [Capitolo/Saggio]
Esseni, David; Jungemann, C; Lorenz, J; Palestri, Pierpaolo; Sangiorgi, E; Selmi, Luca
abstract

2013 - Toward computationally efficient Multi-Subband Monte Carlo simulations of nanoscale MOSFETs [Relazione in Atti di Convegno]
Osgnach, Patrik; Revelant, Alberto; Lizzit, Daniel; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

We show how intense exploitation of multi-core architectures allowed us to cut by up to an order of magnitude the execution times of a Multi-Subband Monte Carlo (MSMC) simulator. The result brings simulations with the MSMC method out of the strictly academic domain and close to the execution time threshold for effective use in R&D departments of semiconductor research centres and industries.

2012 - A Multi-Subband Monte Carlo study of electron transport in strained SiGe n-type FinFETs [Relazione in Atti di Convegno]
Lizzit, Daniel; Palestri, Pierpaolo; Esseni, David; Conzatti, Francesco; Selmi, Luca
abstract

This paper reports a simulation study investigating the drive current in the prototypical SiGe n-type FinFET depicted in Fig.1 and for different values of the Ge content x in the Si(1−x)Gex active layer. To this purpose we performed strain simulations, band-structure calculations and Multi-Subband Monte Carlo transport simulations accounting for the effects of the Ge content on both the band-structure and scattering rates in the transistor channel. Our results suggest that the largest on-current may be obtained with a simple Si active layer.

2012 - An Efficient Nonlocal Hot Electron Model Accounting for Electron–Electron Scattering [Articolo su rivista]
Zaka, A; Palestri, Pierpaolo; Rafhay, Q; Clerc, R; Iellina, Matteo; Rideau, D; Tavernier, C; Pananakis, G; Herven, J; Selmi, Luca
abstract

This paper presents a nonlocal model for channel hot electron injection in MOSFETs and nonvolatile memories, which includes a full-band description of optical phonon scattering rates and carrier group velocity. By virtue of its efficient formalism, this model can also include carrier–carrier scattering, which has a marked impact on gate current at low gate voltages. The model is compared against full-band Monte Carlo simulations of typical NOR flash devices in terms of distribution functions, bulk current, gate current, and gate current density along the channel. A very good agreement is obtained for various drain and gate voltages and channel lengths.

2012 - An improved procedure to extract the limiting carrier velocity in ultra scaled CMOS devices [Relazione in Atti di Convegno]
Toniutti, Paolo; Clerc, R; Palestri, Pierpaolo; Diouf, C; Cros, A; Esseni, David; Boeuf, F; Ghibaudo, G; Selmi, Luca
abstract

The validity of a previously published extraction technique for the limiting carrier velocity responsible for current saturation in nano-MOSFETs is carefully re-examined by means of accurate Multi Subband Monte Carlo transport simulations. By comparing the extracted limiting velocity to the calculated injection velocity, we identify the main sources of error of the extraction method. Then, we propose a new extraction procedure and extensively validate it. Our simulations and experimental results reconcile the values and trends of the extracted limiting velocity with the expectations stemming from quasi ballistic transport theory.

2012 - An Improved Semi-classical Approach for Simulating Tunnel-FETs [Relazione in Atti di Convegno]
Revelant, Alberto; Osgnach, Patrik; Palestri, Pierpaolo; Selmi, Luca
abstract

2012 - Effect of the choice of the tunnelling path on semi-classical numerical simulations of TFET devices [Articolo su rivista]
DE MICHIELIS, Luca; Iellina, Matteo; Palestri, Pierpaolo; Ionescu, A; Selmi, Luca
abstract

In this work a non-local band-to-band tunnelling model has been successfully implemented into a fullband Monte Carlo simulator and applied to Tunnel-FET devices. No stability or statistical noise problems were encountered in spite of particle weights ranging over many orders of magnitude (due to vastly different generation rates at different positions inside the device and biases) so that Tunnel-FET I–V curves could be traced over the whole on–off range. Different approaches for the choice of the tunnelling path have been compared and relevant differences are observed in both the current levels and the spatial distribution of the generated carriers.

2012 - Efficient DC and AC simulation of nanoelectrode-nanoparticle interactions in capacitive biosensors [Relazione in Atti di Convegno]
Pittino, Federico; Widdershoven, F; Selmi, Luca
abstract

This paper presents a case study of the interaction between nanoelectrodes and dielectric nanoparticles possibly representative of biomolecules in a simple cylindrical capacitive biosensor. The small signal admittance change due to the insertion of the biomolecule in the biosensor electrolyte is studied as a function of the position, aspect ratio and charge of the biomolecule and of the signal frequency. Results suggest clear advantages in operating the biosensor beyond the electrolyte cutoff frequency.

2012 - Improved Modeling of Intersymbol Interference in High Speed Serial Links [Relazione in Atti di Convegno]
Cristofoli, Andrea; Palestri, Pierpaolo; Selmi, Luca; Da Dalt, N.
abstract

2012 - Improved modeling of Intersymbol Interference in high speed serial lynks [Relazione in Atti di Convegno]
Cristofoli, Andrea; Palestri, Pierpaolo; Da Dalt, N; Selmi, Luca
abstract

NA

2012 - Modeling of Field-Effect-Transistors with Strained and Alternative Channel Materials [Relazione in Atti di Convegno]
Conzatti, Francesco; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

In this paper we present a review of the modeling of strain effects in nano-scale transistors and we describe different approaches that can be followed in order to include the effect of strain in both conventional and innovative devices. We first describe the mathematical framework for the modeling of strain and then we present two important case-studies where we have successfully emploied advanced modeling techniques in order to investigate the effect of strain in germanium-based MOSFETs and in InAs Tunnel-FETs.

2012 - Multi-Subband Semi-classical Simulation of n-type Tunnel-FETs [Relazione in Atti di Convegno]
Revelant, Alberto; Palestri, Pierpaolo; Selmi, Luca
abstract

We present a newly developed model for Tunnel- FET (TFET) devices capable to describe band-toband tunneling (BtBT) as well as off-equilibrium transport of the generated carriers. BtBT generation is implemented as an add-on into an existing Multi-subband Monte Carlo (MSMC) transport simulator that accounts for the effects of alternative channel materials and high- dielectrics. A simple correction for the calculation of the BtBT generation rate is proposed to account for carrier confinement in the subbands.

2012 - On the origin of the mobility reduction in n- and p-metal-oxide-semiconductor field effect transistors with hafnium-based/metal gate stacks [Articolo su rivista]
Toniutti, Paolo; Palestri, Pierpaolo; Esseni, David; Driussi, Francesco; DE MICHIELIS, Marco; Selmi, Luca
abstract

We examine the mobility reduction measured in hafnium-based dielectrics in n- and p-MOSFETs by means of extensive comparison between accurate multi-subband Monte Carlo simulations and experimental data for reasonably mature process technologies. We have considered scattering with remote (soft-optical) phonons and remote Coulomb interaction with single layers and dipole charges. A careful examination of model assumptions and limitations leads us to the conclusion that soft optical phonon scattering cannot quantitatively explain by itself the experimental mobility reduction reported by several groups for neither the electron nor the hole inversion layers. Experimental data can be reproduced only assuming consistently large concentrations of Coulomb scattering centers in the gate stack. However, the corresponding charge or dipole density would result in a large threshold voltage shift not observed in the experiments. We thus conclude that the main mechanisms responsible for the mobility reduction in MOSFETs featuring Hafnium-based high-k dielectric have not been completely identified yet. Additional physical mechanisms that could reconcile simulations with experimental results are suggested and critically discussed.

2012 - Special Issue of IEEE Transactions on Semiconductor Manufacturing devoted to the 2011 International Conference on Microelectronic Test Structures [Curatela]
Selmi, Luca
abstract

2012 - Strain-Induced Performance Improvements in InAs Nanowire Tunnel FETs [Articolo su rivista]
Conzatti, Francesco; Pala, M; Esseni, David; Bano, E; Selmi, Luca
abstract

This paper investigates the electrical performance improvements induced by appropriate strain conditions in n-type InAs nanowire tunnel FETs in the context of a systematic comparison with strained silicon MOSFETs. To this purpose, we exploited a 3-D simulator based on an eight-band k · p Hamiltonian within the nonequilibrium Green function formalism. Our model accounts for arbitrary crystal orientations and describes the strain implicitly by a modification of the band structure. The effect of acoustic- and optical-phonon scattering is also accounted for in the self-consistent Born approximation. Our results show that appropriate strain conditions in n-type InAs tunnel FETs induce a remarkable enhancement of Ion with a small degradation of the subthreshold slope, as well as large improvements in the Ioff versus Ion tradeoff for low Ioff and VDD values. Hence, an important widening of the range of Ioff and VDD values where tunnel FETs can compete with strained silicon MOSFETs is obtained.

2011 - A simulation study of strain induced performance enhancements in InAs nanowire Tunnel-FETs [Relazione in Atti di Convegno]
Conzatti, Francesco; M. G., Pala; Esseni, David; E., Bano; Selmi, Luca
abstract

This work investigates the strain engineering in InAs nanowire Tunnel-FETs. To this purpose we developed a simulator based on the NEGF formalism and employing an 8×8 k·p Hamiltonian. The model accounts for arbitrary crystal orientations and describes the strain implicitly by a modification of the bandstructure. Elastic and inelastic phonon scattering is also accounted for in the self-consistent Born approximation. Our results show that appropriate strain conditions in InAs Tunnel- FETs enable: (a) a remarkable enhancement of the Ion with no significant degradation of the subthreshold slope (SS); (b) large improvements in the Ioff versus Ion tradeoff for low Ioff and VDD values; (c) significant widening of Ioff and VDD window where Tunnel-FETs can compete with silicon MOSFETs.

2011 - Corner Effect and Local Volume Inversion in SiNW FETs [Articolo su rivista]
DE MICHIELIS, Luca; Moselund, K. E.; Selmi, Luca; Ionescu, A. M.
abstract

In this paper, a quantitative study of the corner effect and of the local volume inversion on gate-all-around MOSFETs based on numerical simulations has been carried out; different angles and doping levels are compared, in order to understand the impact of the corner regions on the total current. A method for the extraction of the threshold voltage and of the subthreshold slope of the corner region has been proposed, and the resulting values have been analyzed in order to understand their effects on the device characteristics.

2011 - Device variability and correlation control by automated tuning of SPICE cards to PCM measurements [Relazione in Atti di Convegno]
Revelant, Alberto; Lucci, Luca; Selmi, Luca; Ankele, B.
abstract

We present an improved methodology to calibrate nominal SPICE models to individual or average PCM measurements at the die, wafer or lot level. The method overcomes previous difficulties in the structured handling of huge amounts of PCM data and it is validated in a state-of-the-art mixed-signal system-on-chip product development environment for the 65 nm CMOS technology node. The proposed approach is especially useful for real time process control to tackle model-hardware correlation problems in a multi-foundry design environment, to ease the burden of transferring designs to new production sites and to complement common tools available to the designers to cope with process variability such as worst-case corner models and Monte Carlo simulations.

2011 - Experimental Determination of the Impact Ionization Coefficients in Irradiated Silicon [Articolo su rivista]
Cristofoli, Andrea; Palestri, Pierpaolo; Giordani, Mario; Cindro, V.; DALLA BETTA, G. F; Selmi, Luca
abstract

We present new results on the influence of radiationinduced damage on the electron Impact Ionization (I.I.) coefficient , suggesting a small but distinct reduction of at high fluence with respect to unirradiated silicon. Experiments on thick (1.5 m) and thin (1 m) epitaxial silicon samples confirm that such a reduction of is expected even in cases where impact ionization is not simply a field driven process because of strongly non local transport conditions. A consistent increase on the breakdown voltage of a 3D radiation detector has been evaluated by means of TCAD simulations using the experimentally extracted I.I. coefficient for irradiated silicon. These results clarify the impact of radiation damage on some of the key model parameters for TCAD simulations and allow for improved accuracy toward predictive breakdown simulations of silicon particle detectors, e.g., for the ATLAS experiment.

2011 - Explanation of the Charge Trapping Properties of Silicon Nitride Storage Layers for NVMs - Part II: Atomistic and Electrical Modeling [Articolo su rivista]
Vianello, Elisa; Driussi, Francesco; Blaise, P.; Palestri, Pierpaolo; Esseni, David; Perniola, L.; Molas, G.; De Salvo, B.; Selmi, Luca
abstract

Based on the material analysis of the SiN layers presented in part I of this paper, we develop accurate atomistic and electrical models for the silicon nitride (SiN)-based nonvolatile memory devices, taking into account the candidate SiN defects responsible for the memory effect. Our analysis points out the role of the hydrogen atoms and Si dangling bonds in the trapping properties of SiN films with different stoichiometries. The atomistic models provide a comprehensive picture describing the energy level and the occupation number of the different defects in the SiN. The electrical model coupled with the atomistic results, for the first time, demonstrates the ability to describe the program/erase curves of charge-trap memory cells with SiN storage layers with diversified composition. Good agreement between simulations and experimental results coming from the material analysis and the electrical characterization of thin (type-B device) and thick (type-A device) tunnel oxide memory cells is shown.

2011 - Explanation of the Charge-Trapping Properties of Silicon Nitride Storage Layers for NVM Devices Part I: Experimental Evidences From Physical and Electrical Characterizations [Articolo su rivista]
Vianello, Elisa; Driussi, Francesco; Perniola, L; Molas, G; COLONNA J., P; DE SALVO, B; Selmi, Luca
abstract

In part I of this paper, we study the physicochemical structure and the electrical properties of low-pressure-chemical-vapor-deposited silicon nitride (SiN) aimed to serve as storage layers for nonvolatile memory applications. An in-depth material analysis has been carried out together with a comprehensive electrical characterization on two samples fabricated with recipes yielding rather standard SiN and Si-rich SiN. The investigation points out the impact of SiN stoichiometry and hydrogen content on the electrical characteristics of gate stacks designed in view of channel hot-electron/hole-injection program/erase (P/E) operation and tunnel P/E operation. The extensive and detailed characterization establishes a sound experimental basis for the development of the physics-based trap models proposed in the companion paper.

2011 - Impact of carrier heating on backscattering in inversion layers [Articolo su rivista]
R., Clerc; Palestri, Pierpaolo; Selmi, Luca; G., Ghibaudo
abstract

In this work, Monte Carlo simulations and analytical modeling are used to investigate quasi-ballistic transport in nanometric metal oxide semiconductor field effect transistors (MOSFETs). In particular, we examine how the thermal nature of the distribution functions, which is implicitly assumed in the most common expression for the backscattering coefficient, leads to an underestimation of the backscattering coefficient in high field conditions and erroneous velocity distribution along the channel. An improved analytical model is proposed, which better captures the nonequilibrium nature of the distribution function and its impact on backscattering and by allowing velocity profiles to exceed the thermal limit. The improved model provides additional insights on the impact of several assumptions on backscattering and could serve as the basis for the development of physically based compact models of quasi-ballistic MOSFETs.

2011 - Investigation of Strain Engineering in FinFETs Comprising Experimental Analysis and Numerical Simulations [Articolo su rivista]
Conzatti, Francesco; Serra, Nicola; Esseni, David; De Michielis, M.; Paussa, Alan; Palestri, Pierpaolo; Selmi, Luca; Thomas, S. M.; Whall, T. E.; Leadley, D.; Parker, E. H. C.; Witters, L.; Hytch, M. J.; Snoeck, E.; Wang, T. J.; Lee, W. C.; Doornbos, G.; Vellianitis, G.; van Dal, M. J. H.; Lander, R. J. P.
abstract

This study combines direct measurements of strain, electrical mobility measurements, and a rigorous modeling approach to provide insights about strain-induced mobility enhancement in FinFETs and guidelines for device optimization. Good agreement between simulated and measured mobility is obtained using strain components measured directly at device level by a novel holographic technique. A large vertical compressive strain is observed in metal gate FinFETs, and the simulations show that this helps recover the electron mobility disadvantage of the (110) FinFET lateral interfaces with respect to (100) interfaces, with no degradation of the hole mobility. The model is then used to systematically explore the impact of stress components in the fin width, height, and length directions on the mobility of both n- and p-type FinFETs and to identify optimal stress configurations. Finally, self-consistent Monte Carlo simulations are used to investigate how the most favorable stress configurations can improve the on current of nanoscale MOSFETs.

2011 - Nanoscale MOS Transistors: Semi-Classical Transport and Applications [Monografia/Trattato scientifico]
Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

Written from an engineering standpoint, this book provides the theoretical background and physical insight needed to understand new and future developments in the modeling and design of n- and p-MOS nanoscale transistors. A wealth of applications, illustrations and examples connect the methods described to all the latest issues in nanoscale MOSFET design. Key areas covered include: • Transport in arbitrary crystal orientations and strain conditions, and new channel and gate stack materials • All the relevant transport regimes, ranging from low field mobility to quasi-ballistic transport, described using a single modeling framework • Predictive capabilities of device models, discussed with systematic comparisons to experimental results.

2011 - On the Surface-Roughness Scattering in Biaxially Strained n- and p-MOS Transistors [Articolo su rivista]
DE MICHIELIS, Marco; Conzatti, Francesco; Esseni, David; Selmi, Luca
abstract

Electron- and hole-mobility enhancements in biaxially strained metal–oxide–semiconductor transistors are still a matter for active investigation, and this brief presents a critical examination of a recently proposed interpretation of the experimental data, according to which the strain significantly modifies not only the root-mean-square value but also the correlation length of the surface-roughness spectrum.We present a systematic comparison between comprehensive numerical simulations and experiments, which supports such an interpretation.

2011 - Phonon Limited Uniform Transport in Bilayer Graphene Transistors [Relazione in Atti di Convegno]
Paussa, Alan; Bresciani, Marco; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

We report modeling results for low-field mobility and velocity saturation in bilayer graphene based on a newly developed semiclassical transport Monte-Carlo simulator validated by comparison with momentum relaxation time (MRT) calculations. We show that remote phonons originating in the dielectric stack are expected to strongly affect the mobility, although assessing their actual influence at high inversion charge requires the development of an accurate model for dynamic screening. When the applied bias opens the energy gap, the mobility is significantly reduced. The saturation velocity is expected to be as high as 3×107 cm/s and less degraded than mobility by bandgap opening.

2011 - Simulation of graphene nanoscale RF transistors including scattering and generation/recombination mechanisms [Relazione in Atti di Convegno]
Paussa, A; Geromel, M; Palestri, Pierpaolo; Bresciani, M; Esseni, David; Selmi, Luca
abstract

We present a Monte Carlo simulator for RF graphene FETs including the dominant scattering mechanisms and a simple model for band-to-band tunneling. We found that in state-ofthe- art devices scattering is relevant and degrades the cut-off frequency compared to the predictions of ballistic models.

2011 - Simulations and Electrical Characterization of Double-side Double Type Column 3D Detectors [Relazione in Atti di Convegno]
Cristofoli, A.; DALLA COSTA, A.; Boscardin, M.; Cindro, V.; DALLA BETTA, G. F.; Driussi, Francesco; Giacomini, G.; Giordani, Mario; Palestri, Pierpaolo; Povoli, M.; Ronchin, S.; Vianello, E.; Selmi, Luca
abstract

2011 - Study of defects in Al2O3 blocking layers of TANOS memories by atomistic simulation, electrical characterization and physico-chemical material analyses [Relazione in Atti di Convegno]
Masoero, L.; Molas, G.; Blaise, P.; Colonna, J. P.; Vianello, Elisa; Selmi, Luca; Papon, A. M.; Lafond, D.; Martin, F.; Gely, M.; Licitra, C.; Barnes, J. P.; Ghibaudo, G.; DE SALVO, B.
abstract

In this work we investigate the correlation between hydrogen content and leakage current through the Al2O3 layers of TANOS memories. We put in evidence that retention of TANOS memories is improved with the decrease of H concentration in the Al2O3 layer. Using atomistic simulations consolidated by detailed Al2O3 physico-chemical analyses, we find that interstitial H produces a midgap trap likely to participate to trap assisted conduction.

2011 - Test beam results of 3D silicon pixel sensors for the ATLAS upgrade [Articolo su rivista]
Grenier, P; Alimonti, G; Barbero, M; Bates, R; Bolle, E; Borri, M; Boscardin, M; Buttar, C; Capua, M; CAVALLI-SFORZA, M; Cobal, M; Cristofoli, A; DALLA BETTA G., -F; Darbo, G; DA VIA, C; Devetak, Ce; Dewilde, B; DI GIROLAMO, B; Dobos, D; Einsweiler, K; Esseni, D; Fazio, S; Fleta, C; Freestone, J; Gallrapp, C; GARCIA-SCIVERES, M; Gariano, G; Gemme, C; GIORDANI M., -P; Gjersdal, H; Grinstein, S; Hansen, T; HANSEN T., -E; Hansson, P; Hasi, J; Helle, K; Hoeferkamp, M; Hagging, F; Jackson, P; Jakobs, K; Kalliopuska, J; Karagounis, M; Kenney, C; Kahler, M; Kocian, M; Kok, A; Kolya, S; Korokolov, I; Kostyukhin, V; Krager, H; LA ROSA, A; LAI C., H; Lietaer, N; Lozano, M; Mastroberardino, A; Micelli, A; Nellist, C; Oja, A; Oshea, V; Padilla, C; Palestri, P; Parker, S; Parzefall, U; Pater, J; Pellegrini, G; Pernegger, H; Piemonte, C; Pospisil, S; Povoli, M; Roe, S; Rohne, O; Ronchin, S; Rovani, A; Ruscino, E; Sandaker, H; Seidel, S; Selmi, L; Silverstein, D; Soabae, K; Slavicek, Kt; Stapnes, S; Stugu, B; Stupak, J; Su, D; Susinno, G; R., Thompson; TSUNG J., -W; Tsybychev, D; WATTS S., J; Wermes, N; Young, C; Zorzi, N
abstract

2011 - Thermal nonequilibrium and viscous dissipation in the thermal entrance region of a Darcy flow with streamwise periodic boundary conditions [Articolo su rivista]
Barletta, A.; Rossi Di Schio, E.; Selmi, L.
abstract

The thermal entrance region in a plane-parallel channel filled by a fluid saturated porous medium is investigated with reference to steady forced convection and to a thermal boundary condition given by a wall temperature longitudinally varying with a sinusoidal law. The effect of viscous dissipation in the fluid is taken into account, and a two-temperature model is employed in order to evaluate separately the local fluid and solid matrix temperatures. The asymptotic temperature distributions are determined analytically. The governing equations in the thermal entrance region are solved numerically by a finite element method and by the method of lines. © 2011 American Society of Mechanical Engineers.

2011 - Tunnel-FET architecture with improved performance due to enhanced gate modulation of the tunneling barrier [Relazione in Atti di Convegno]
DE MICHIELIS, Luca; Lattanzio, L; Palestri, Pierpaolo; Selmi, Luca; Ionescu, A. M.
abstract

The Tunnel-FET (TFET) device is a gated reverse biased p-i-n junction whose working principle is based on the quantum mechanical Band-to-Band Tunneling (B2BT) mechanism. The OFF-ON transition can be much more abrupt than for conventional MOSFETs, thus allowing a reduction of the supply voltage and power consumption in logic applications . Several TFETs with point Subthreshold Swing (SS) lower than 60mV/dec have been experimentally demonstrated with different architectures as conventional single gate Silicon-on-Insulator (SOI), Double Gate (DG) and Gate-All-Around (GAA). Unfortunately in all cases a relatively large average SS and a poor on-current have been observed. In conclusion with this work we have shown that although commonly fabricated TFETs feature source/channel interfaces normal to the transport direction, in a well-designed TFET the tunneling junction should have the same orientation of the component of the electric field modulated by the gate: only in this case the gate can effectively modulate the tunneling barrier, resulting in a steeper average SS and higher ION.

2011 - Tunneling path impact on semi-classical numerical simulations of TFET devices [Relazione in Atti di Convegno]
DE MICHIELIS, Luca; Iellina, Matteo; Palestri, Pierpaolo; Ionescu, A; Selmi, Luca
abstract

In this work a non-local band-to-band tunnelling model has been implemented into a full-band Monte Carlo simulator. Two different approaches for the choice of the tunnelling path have been implemented and their impact on the transfer characteristics of different Tunnel FET structures is investigated. In both the SOI and the DG TFET architectures we have simulated, up to 1 order of magnitude of underestimation in the current and up to 15% of difference in the value of the Subthreshold Slope can be found according to the choice of the tunnelling path.

2011 - 3D-FBK pixelsensors:Recent beam tests results with irradiated devices [Articolo su rivista]
Micelli, Andrea; K., Helle; H., Sandaker; B., Stugu; M., Barbero; F., Hugging; M., Karagounis; V., Kostyukhin; H., Kruger; J. W., Tsung; N., Wermes; M., Capua; S., Fazio; A., Mastroberardino; G., Susinno; C., Gallrapp; B., Digirolamo; D., Dobos; A., Larosa; H., Pernegger; S., Roe; T., Slavicek; S., Pospisil; K., Jakobs; M., Kohler; U., Parzefall; G., Darbo; G., Gariano; C., Gemmeg; A., Rovani; E., Ruscino; C., Butter; R., Bates; V., Oshea; S., Parker; M., Cavalli Sforza; S., Grinstein; I., Korokolov; C., Pradilla; K., Einsweiler; M., Garcia Sciveres; M., Borri; C., Davia; J., Freestone; S., Kolya; C. H., Lail; C., Nellist; J., Pater; R., Thompson; S. J., Watts; M., Hoeferkampm; S., Seidelm; E., Bolle; H., Gjersdal; K. N., Sjoebaek; S., Stapnes; O., Rohne; D., Suo; C., Young; P., Hansson; P., Grenier; J., Hasi; C., Kenney; M., Kocian; P., Jackson; D., Silverstein; H., Davetak; B., Dewilde; D., Tsybychev; G. F., Dallabetta; P., Gabos; M., Povoli; Cobal, Marina; Giordani, Mario; Selmi, Luca; Cristofoli, Andrea; Esseni, David; Palestri, Pierpaolo; C., Fleta; M., Lozano; G., Pellegrini; M., Boscardin; A., Bagolini; C., Piemonte; S., Ronchin; N., Zorzi; T. E., Hansen; T., Hansen; A., Kok; N., Lietaer; J., Kalliopuska; A., Oja
abstract

The Pixel Detector is the innermost part of the ATLAS experiment tracking device at the Large Hadron Collider, and plays a key role in the reconstruction of the primary vertices from the collisions and secondary vertices produced by short-lived particles. To cope with the high level of radiation produced during the collider operation, it is planned to add to the present three layers of silicon pixel sensors which constitute the Pixel Detector, an additional layer (Insertable B-Layer, or IBL) of sensors. 3D silicon sensors are one of the technologies which are under study for the IBL. 3D silicon technology is an innovative combination of very-large-scale integration and Micro-Electro-Mechanical-Systems where electrodes are fabricated inside the silicon bulk instead of being implanted on the wafer surfaces. 3D sensors, with electrodes fully or partially penetrating the silicon substrate, are currently fabricated at different processing facilities in Europe and USA. This paper reports on the 2010 June beam test results for irradiated 3D devices produced at FBK (Trento, Italy). The performance of these devices, all bump-bonded with the ATLAS pixel FE-I3 read-out chip, is compared to that observed before irradiation in a previous beam test.

2010 - A Consistent Explanation of the Role of the SiN Composition on the Program/Retention Characteristics of MANOS and NROM like Memories [Relazione in Atti di Convegno]
Vianello, Elisa; Nowak, E; Perniola, L; Driussi, Francesco; Blaise, P; Molas, G; DE SALVO, B; Selmi, Luca
abstract

In this work, we show that a detailed atomistic model of SiN defects provides a consistent explanation of the program/erase/retention characteristics of both NROM and MANOS charge-trap cells. Our analysis of devices with SiN layers of different stoichiometry is also consistent with original KFM measurements of trapped charge drift in SiN layers.

2010 - A numerical model for the oscillation frequency, the amplitude and the phase-noise of MOS-current-mode-logic ring oscillators [Articolo su rivista]
Nocente, M; Fontanelli, D; Palestri, P; Nonis, R; Esseni, D; Selmi, L
abstract

This paper presents a new model for the frequency of oscillation, the oscillation amplitude and the phase-noise of ring oscillators consisting of MOS-current-mode-logic delay cells. The numerical model has been validated through circuit simulations of oscillators designed with a typical 130 nm CMOS technology. A design flow based on the proposed model and on circuit simulations is presented and applied to cells with active loads. The choice of the cell parameters that minimize phase-noise and power consumption is addressed.

2010 - A quasi-analytical model for nanowire FETs with arbitrary polygonal cross section [Articolo su rivista]
DE MICHIELIS, Luca; Selmi, Luca; Ionescu, A. M.
abstract

In this work a quasi-analytical physical model has been developed for the prediction of the potential in SiNW devices with arbitrary polygonal cross section. The model is then extended to the transport direction; a method for the calculation of the natural channel length has been proposed and validated by means of 2D and 3D numerical device simulations. With the results based on the proposed model it is possible to compare nanowires with cross sections of different shape and predict the minimum technological gate length able to assure immunity to the SCEs.

2010 - A simulation study of the Punch-through Assisted Hot Holes Injection mechanism for non-volatile-memory cells [Articolo su rivista]
Iellina, Matteo; Palestri, Pierpaolo; Akil, N.; VAN DUUREN, M.; Driussi, Francesco; Esseni, David; Selmi, Luca
abstract

In this paper, we investigate the operating principle and the injection efficiency of the punch-through-assisted hot hole injection mechanism for programming nonvolatile memory cells by means of full-band Monte Carlo transport simulations of realistic device structures. The effects of terminal bias and cell scaling on the injection efficiency and the uniformity of charge injection along the channel are analyzed in detail.

2010 - An improved empirical approach to introduce quantization effects in the transport direction in multi-subband Monte Carlo simulations [Articolo su rivista]
Palestri, Pierpaolo; Lucci, Luca; DEI TOS, S; Esseni, David; Selmi, Luca
abstract

In this paper we propose and validate a simple approach to empirically account for quantum effects in the transport direction of MOS transistors (i.e. source and drain tunneling and delocalized nature of the carrier wavepacket) in multi-subband Monte Carlo simulators, that already account for quantization in the direction normal to the semiconductor-oxide interface by solving the 1D Schrödinger equation in each section of the device. The model has been validated and calibrated against ballistic non-equilibrium Green's function simulations over a wide range of gate lengths, voltage biases and temperatures. The proposed model has just one adjustable parameter and our results show that it can achieve a good agreement with the NEGF approach.

2010 - Comparison of Semiclassical Transport Formulations Including Quantum Corrections for Advanced Devices with High-K Gate Stacks [Relazione in Atti di Convegno]
BUFLER F., M; AUBRY FORTUNA, V; Bournel, A; Braccioli, M; Dollfus, P; Esseni, David; Fiegna, C; Gamizk, F; DE MICHIELIS, Marco; Palestri, Pierpaolo; SAINT MARTIN, J; Sampedrok, C; Sangiorgi, E; Selmi, Luca; Toniutti, Paolo
abstract

Long-channel effective mobilities as well as transfer characteristics of a 32 nm single-gate SOI and a 16 nm double-gate (DG) MOSFET have been simulated with live different Monte Carlo (MC) device simulators. The differences are mostly rather small for the SOI-FET with quantum effects having a minor effect on threshold voltage due to the lowly doped channel, while the two multi-subband MC simulators show some prominent deviations in the case of the DG-FET. High-K mobility degradation by remote phonon scattering (RPS) in free carrier MC approximation leads to smaller performance degradation compared to multi-subband MC with remote Coulomb scattering (RCS) and RPS, but requires further investigations.

2010 - Direct Probing of Trapped Charge Dynamics in SiN by Kelvin Force Microscopy [Relazione in Atti di Convegno]
Vianello, Elisa; Nowak, E; Mariolle, D; Chevalier, N; Perniola, L; Molas, G; Colonna, J; Driussi, Francesco; Selmi, Luca
abstract

In this work, we explore the potential of Kelvin Force Microscopy (KFM) measurements to investigate the lateral charge transport in SiN layers with two different compositions (standard, std, and Silicon rich, Si-rich). The dynamics of the lateral spread of the trapped charge is analyzed with the help of three dimensional numerical device simulations.

2010 - Drain Current Computation in Nanoscale nMOSFETs: Comparison of Transport Models [Relazione in Atti di Convegno]
Sangiorgi, E; Alexander, C; Asenov, A; AUBRY FORTUNA, V; Baccarani, G; Bournel, A; Braccioli, M; Cheng, B; Dollfus, P; Esposito, A; Esseni, David; FENOUILLET BERANGER, C; Fiegna, C; Fiori, G; Ghetti, A; Iannaccone, G; Martinez, A; Majkusiak, B; Monfray, S; Palestri, Pierpaolo; Peikert, V; Reggiani, S; Riddet, C; SAINT MARTIN, J; Schenk, A; Selmi, Luca; Silvestri, L; Walczak, J.
abstract

In this paper the modelling approaches for determination of the drain current in nanoscale MOSFETs pursued by various partners in the frame of the European Projects Pullnano and Nanosil are mutually compared in terms of drain current and internal quantities (average velocity and inversion charge). The comparison has been carried out by simulating template devices representative of 22 nm Double-Gate and 32 nm Single-Gate FD-SOI. A large variety of simulation models has been considered, ranging from drift-diffusion to direct solutions of the Boltzmann-Transport-Equation. The predictions of the different approaches for the 32 nm device are quite similar. Simulations of the 22 nm device instead, are much less consistent. Comparison with experimental data for a 32 nm device shows that the modeling approach used to explain the mobility reduction induced by the high-k dielectric is critical.

2010 - LC-Oscillator featuring independent Gate biasing implemented in 32 nm CMOS technology [Relazione in Atti di Convegno]
Ponton, Davide; Palestri, Pierpaolo; Knoblinger, G; Fulde, M; Selmi, Luca
abstract

This paper analyzes the potentials and the limitations of a novel LC-Oscillator topology featuring independent gate biasing. The topic is addressed from an experimental perspective. The novel topology has been implemented in a state-of-the-art 32 nm CMOS technology and used as a proof-of-concept. The performance of the oscillator has been evaluated in terms of power consumption and phase-noise. The independent gate biasing helps in relaxing the noise/power trade-off that limits the performance of conventional LC-Oscillators.

2010 - Leakage-Delay Tradeoff in finFET Logic Circuits: a Comparative Analysis with Bulk Technology [Articolo su rivista]
Agostinelli, M; Alioto, M; Esseni, D; Selmi, L
abstract

In this paper, we study the advantages offered by multi-gate fin FETs (FinFETs) over traditional bulk MOSFETs when low standby power circuit techniques are implemented. More precisely, we simulated various vehicle circuits, ranging from ring oscillators to mirror full adders, to investigate the effectiveness of back biasing and transistor-stacking in both FinFETs and bulk MOSFETs. The opportunity to separate the gates of FinFETs and to operate them independently has been systematically analyzed; mixed connected- and independent-gate circuits have also been evaluated. The study spans over the device, the layout, and the circuit level of abstraction and appropriate figures of merit are introduced to quantify the potential advantage of different schemes. Our results show that, thanks to a larger threshold voltage sensitivity to back biasing, the FinFET technology is able to offer a more favorable compromise between standby power consumption and dynamic performance and is well suited for implementing fast and energy-efficient adaptive back-biasing strategies.

2010 - Low-Field Mobility and High-Field Drift Velocity in Graphene Nanoribbons and Graphene Bilayers [Relazione in Atti di Convegno]
Bresciani, Marco; Paussa, Alan; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

In this paper we follow a semiclassical approach based on the Boltzmann Transport Equation (BTE) to simulate and compare with experiments the low-field mobility (μ) and the high-field drift velocity (vd) of graphene nano-ribbons (GNRs) and graphene bilayers (GbLs). It is found that remote phonons originating in the substrate have a large impact on the mobility, whereas their impact on the saturation velocity is smaller than predicted by recently proposed simplified model.

2010 - Modeling of End of the Roadmap nMOSFET with Alternative Channel Material [Capitolo/Saggio]
Rafhay, Q; Clerc, R; Ghibaudo, G; Palestri, Pierpaolo; Selmi, Luca
abstract

2010 - Multi-subband Monte Carlo simulation of fully-depleted silicon-on-insulator Schottky barrier MOSFETs [Relazione in Atti di Convegno]
V., Gudmundsson; Palestri, Pierpaolo; P. E., Hellstrom; Selmi, Luca; M., Ostling
abstract

We propose a new and simple way to account for tunneling in Schottky barrier (SB) contacts by using the effective potential approach. The method has been validated in 1D cases by comparison with the WK B method and then implemented in a Multi-Subband Monte Carlo simulator. Results for metallic Source/Drain (S/D) MOSFETs with Schottky barrier show that very low Schottky barrier heights (SBH) are needed to provide a current drive comparable to the one of doped-S/D devices. We also observe that SB-MOSFETs are working closer to the ballistic limit than their doped-S/D counterparts although the transport bottleneck is the SB contact.

2010 - Simple and efficient modeling of the E–k relationship and low-field mobility in Graphene Nano-Ribbons [Articolo su rivista]
Bresciani, Marco; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

This paper proposes a simple analytical formulation for the dispersion relationship of extended electronic states in Graphene Nano-Ribbons (GNRs). The model has been validated by comparison with Tight-Binding calculation of GNRs in the presence of edge disorder. The model is suited for inclusion in semiclassical models for GNRs featuring widths down to approximately 2 nm. Monte-Carlo simulations accounting for phonons and edge roughness scattering are then used to understand the ribbon width of the low-field mobility. The mechanisms responsible for the low mobility values measured in narrow ribbons compared to graphene sheets are the increased phonon scattering rate and mobility effective mass due to the strong band structure modification induced by the reduced lateral dimensions and the increased scattering with the edges. However, scattering with phonons and with edges is not sufficient to reproduce the experimental mobility on insulating substrates, suggesting that the effect of remote polar phonons originating in the substrate can be significant in graphene based devices.

2010 - Simulation study of the on-current improvements in Ge and sGe versus Si and sSi nano-MOSFETs [Relazione in Atti di Convegno]
Conzatti, Francesco; Toniutti, Paolo; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper employs a state-of-the-art semi-classical transport model for inversion layers to analyze the Ion in Si, sSi, Ge and sGe n- and p-MOSFETs by accounting for all the relevant scattering mechanisms (including the remote surface-optical phonons (SOph) and remote Coulomb scattering (remQ) related to high-κ dielectrics), in which strain is implicitly introduced by a modification of the band structure. Our models are first validated against experiments for both mobility and IDS in nanoscale transistors. Then the Ion in Ge and Si MOSFETs is compared for different crystal orientations and strain conditions.

2010 - Understanding the mobility reduction in MOSFETs featuring high-κ dielectrics [Relazione in Atti di Convegno]
Toniutti, Paolo; DE MICHIELIS, Marco; Palestri, Pierpaolo; Driussi, Francesco; Esseni, David; Selmi, Luca
abstract

In this paper we analyze by means of accurate Multi-Subband Monte Carlo simulations the mobility reduction associated to high-k dielectrics in a large number of n- and p-MOSFETs. We argue that soft optical phonon scattering can not explain the experimental mobility reduction for neither the electron nor the hole inversion layer. In order to reproduce the experimental data, a large amount of Coulomb centers in the gate stack is required, which would result in a huge threshold voltage shift not observed in the experiments. Even if we assume the remote charge to be in the form of dipoles, the associated theshold voltage shift is still large and not consistent with the experimental findings.

2010 - Understanding the mobility reduction in MOSFETs featuring high-&#954; dielectrics [Relazione in Atti di Convegno]
Toniutti, P; DE MICHIELIS, M; Palestri, P; Driussi, F; Esseni, D; Selmi, L
abstract

2009 - A better understanding of the low-field mobility in Graphene Nano-ribbons [Relazione in Atti di Convegno]
Bresciani, M; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

N/A

2009 - A comparison of advanced transport models for the computation of the drain current in nanoscale nMOSFETs [Articolo su rivista]
Palestri, Pierpaolo; C., Alexander; A., Asenov; V., Aubry Fortuna; G., Baccarani; A., Bournel; M., Braccioli; B., Cheng; P., Dollfus; A., Esposito; Esseni, David; C., Fenouillet Beranger; C., Fiegna; G., Fiori; A., Ghetti; G., Iannaccone; A., Martinez; B., Majkusiak; S., Monfray; V., Peikert; S., Reggiani; C., Riddet; J., Saint Martin; E., Sangiorgi; A., Schenk; Selmi, Luca; L., Silvestri; Toniutti, Paolo; J., Walczak
abstract

In this paper we compare advanced modeling approaches for the determination of the drain current in nanoscale MOSFETs. Transport models range from drift–diffusion to direct solutions of the Boltzmann-Transport-Equation with the Monte-Carlo method. Template devices representative of 22 nm Double-Gate and 32 nm Single-Gate Fully-Depleted Silicon-On-Insulator transistors were used as a common benchmark to highlight the differences between the quantitative predictions of different approaches. Using the standard scattering and mobility models for unstrained silicon channels and pure SiO2 dielectrics, the predictions of the different approaches for the 32 nm template are quite similar. Simulations of the 22 nm device instead, are much less consistent, particularly those achieved with MC simulators. Comparison with experimental data for a 32 nm device shows that the modeling approach used to explain the mobility reduction induced by the high-j dielectric is critical. In the absence of a clear understanding of the impact of high-j stack on transport, different models, all providing agreement with the experimental low-field mobility, predict quite different drain currents in saturation and in the sub-threshold region.

2009 - A model for robust electrostatic design of nanowire FETs with arbitrary polygonal cross sections [Relazione in Atti di Convegno]
DE MICHIELIS, Luca; Selmi, Luca; Ionescu, A. M.
abstract

In this work a quasi-analytical physical model for the accurate prediction of the potential of GAA nanowire transistors with an arbitrary regular polygon as a cross section is developed. Two case studies concerning triangular and square cross-sections are particularly investigated and analyzed. The model is then extended to the transport direction; general expressions for the natural length are derived and validated by means of two- and three-dimensional numerical device simulations. Basic design guidelines, using an original analytical expression of the natural length, for robust electrostatic design are proposed, to predict the minimum technological gate length able to assure immunity to the SCEs.

2009 - An in-depth investigation of physical mechanisms governing SANOS memories characteristics [Relazione in Atti di Convegno]
M., Bocquet; Vianello, Elisa; G., Molas; L., Perniola; H., Grampeix; F., Martin; J. P., Colonna; A. M., Papon; P., Brianceau; M., Gély; B., De Salvo; G., Pananakakis; G., Ghibaudo; Selmi, Luca
abstract

The goal of this work is to give a clear physical comprehension of the charge loss mechanisms of SANOS (Si/Al2O3/Si3N4/SiO2/Si) memories. Retention at room and high temperature is investigated on different samples through experiments and theoretical modeling. We argue that at room temperature, the charge loss essentially results from the tunneling of the electrons trapped at the nitride interface, and the retention life time increases with the nitride thickness. On the contrary, at high temperature, the trapped charges in the nitride volume quickly redistribute, thanks to the thermal emission process, and they migrate to the nitride interface. Indeed, this result suggests that thin-nitride thicknesses in SANOS devices allow keeping a fast program/erase speed without degrading the retention at high temperature.

2009 - Comparison of Advanced Transport Models for Nanoscale nMOSFETS [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Alexander, C; Asenov, A; Baccarani, G; Bournel, A; Braccioli, M; Cheng, B; Dollfus, P; Esposito, A; Esseni, David; Ghetti, A; Fiegna, C; Fiori, G; AUBRY FORTUNA, V; Iannaccone, G; Martinez, A; Majkusiak, B; Monfray, B; Reggiani, S; Riddet, C; SAINT MARTIN, J; Sangiorgi, E; Schenk, A; Selmi, Luca; Silvestri, L; Walczak, J.
abstract

In this paper we mutually compare advanced modeling approaches for the determination of the drain current in nanoscale MOSFETs. Transport models range from Drift-Diffusion to direct solution of the Boltzmann Transport equation with the Monte-Carlo methods. Template devices representative of 22 nm Double-Gate and 32 nm FDSOI transistors were used as a common benchmark to highlight the differences between the quantitative predictions of different approaches. Our results set a benchmark to assess modeling tools for nanometric MOSFETs.

2009 - Design and evaluation of mixed 3T-4T FinFET stacks for leakage reduction [Relazione in Atti di Convegno]
Agostinelli, M; Alioto, M; Esseni, David; Selmi, Luca
abstract

In this paper, FinFET stacks consisting of mixed three- (3T) and four-terminal (4T) devices are analyzed in terms of leakage. A novel figure of merit is introduced, and closed-form leakage models are derived. Analytical results are used to derive simple design criteria to minimize the leakage by properly mixing 3T and 4T devices in transistor stacks. The comparison with a bulk technology shows that properly designed FinFET circuits are able to reduce the leakage by one or two orders of magnitude.

2009 - Design of Ultra-Wideband Low-Noise Amplifiers in 45-nm CMOS Technology: Comparison Between Planar Bulk and SOI FinFET Devices [Articolo su rivista]
Ponton, Davide; Palestri, Pierpaolo; Esseni, David; Selmi, Luca; Tiebout, M; Parvais, B; Siprak, D; Knoblinger, G.
abstract

This paper deals with the design of single-stage differential low-noise amplifiers for ultra-wideband (UWB) applications, comparing state-of-the-art planar bulk and silicon-on-insulator (SOI) FinFET CMOS technologies featuring 45-nm gate length. To ensure a broadband input impedance matching, the g m-boosted topology has been chosen. Furthermore, the amplifiers have been designed to work over the whole UWB band (3.1-10.6 GHz), while driving a capacitive load, which is a realistic assumption for direct conversion receivers where the amplifier directly drives a mixer. The simulations (based on compact models obtained from preliminary measurements) highlight that, at the present stage of the technology development, the planar version of the circuit appears to outperform the FinFET one. The main reason is the superior cutoff frequency of planar devices in the inversion region, which allows the achievement of noise figure and voltage gain comparable to the FinFET counterpart, with a smaller power consumption.

2009 - Experimental and physics-based modeling assessment of strain induced mobility enhancement in FinFETs [Relazione in Atti di Convegno]
Serra, N; Conzatti, F; Esseni, David; DE MICHIELIS, M; Palestri, Pierpaolo; Selmi, Luca; Thomas, S; WHALL T., E; PARKER E. H., C; LEADLEY D., R; Witters, L; Hikavyy, A; HYTCH M., J; Houdellier, F; Snoeck, E; WANG T., J; LEE W., C; Vellianitis, G; VAN DAL M. J., H; Duriez, B; Doornbos, G; Lander, R. J. P.
abstract

This study combines direct measurements of channel strain, electrical mobility measurements and a rigorous modeling approach to provide insight about the strain induced mobility enhancement in FinFETs and guidelines for the device optimization. Good agreement between simulated and measured mobility is obtained using strain components measured directly at device level by a novel technique. A large vertical compressive strain is observed in FinFETs and the simulations show that this helps recover the electron mobility disadvantage of the (110) FinFETs lateral interfaces w.r.t. (100) interfaces, with no degradation of the hole mobility. The model is then used to systematically explore the impact of the fin-width, fin-height and fin-length stress components on n- and p-FinFETs mobility and to identify optimal stress configurations.

2009 - Experimental and Simulation Analysis of Program/Retention Transients in Silicon Nitride-Based NVM Cells [Articolo su rivista]
Vianello, Elisa; Driussi, Francesco; Arreghini, Antonio; Palestri, Pierpaolo; Esseni, David; Selmi, Luca; N., Akil; M. J., van Duuren; D. S., Golubovic
abstract

A new characterization technique and an improved model for charge injection and transport through ONO gate stacks are used to investigate the program/retention sequence of silicon nitride-based (SONOS/TANOS) nonvolatile memories. The model accounts for drift-diffusion transport in the conduction band of silicon nitride (SiN). A priori assumptions on the spatial distribution of the charge at the beginning of the program/retention operations are not needed. We show that the carrier transport in the SiN layer impacts the spatial distribution of the trapped charge and, consequently, several aspects of program and retention transients. A few model improvements allow us to reconcile the apparent discrepancy between the values of silicon nitride trap energies extracted from program and retention experiments, thus reducing the number of model parameters.

2009 - Foreword [Articolo su rivista]
Selmi, Luca; Esseni, David; Palestri, Pierpaolo
abstract

2009 - Mobility extraction in SOI MOSFETs with sub 1 nm body thickness [Articolo su rivista]
Schmidt, M; Lemme, Mc; Gottlob, Hdb; Driussi, Francesco; Selmi, Luca; Kurz, H.
abstract

In this work we discuss limitations of the split-CV method when it is used for extracting carrier mobilities in devices with thin silicon channels like FinFETs, ultra thin body silicon-on-insulator (UTB-SOI) transistors and nanowire MOSFETs. We show that the high series resistance may cause frequency dispersion during the split-CV measurements, which leads to underestimating the inversion charge density and hence overestimating mobility. We demonstrate this effect by comparing UTB-SOI transistors with both recessed-gate UTB-SOI devices and thicker conventional SOI MOSFETs. In addition, the intrinsic high series access resistance in UTB-SOI MOSFETs can potentially lead to an overestimation of the effective internal source/drain voltage, which in turn results in a severe underestimation of the carrier mobility. A specific MOSFET test structure that includes additional 4-point probe channel contacts is demonstrated to circumvent this problem, Finally, we accurately extract mobility in UTB-SOI transistors down to 0.9 nm silicon film thickness (four atomic layers) by utilizing the 4-point probe method and carefully choosing adequate frequencies for the split-CV measurements. It is found that in Such thin silicon film thicknesses quantum mechanical effects shift the threshold voltage and degrade mobility. (C) 2009 Elsevier Ltd. All rights reserved.

2009 - Mobility Extraction of UTB n-MOSFETs down to 0.9 nm SOI thickness [Relazione in Atti di Convegno]
Schmidt, M; LEMME M., C; GOTTLOB H. D., B; Kurz, H; Driussi, Francesco; Selmi, Luca
abstract

In this abstract, the impact of series resistance on mobility extraction in conventional and recessed-gate ultra thin body (UTB) n-MOSFETs is investigated. High series resistance leads to an overestimation of the internal source/drain voltage and influences the measurement of the gate to channel capacitance. A specific MOSFET design that includes additional channel contacts and recessed gate technology are used to successfully extract mobility down to 0.9 nm silicon film thickness (4 atomic layers). Quantum mechanical effects are found to shift the threshold voltage and degrade mobility at these extreme scaling limits.

2009 - Multi-Subband Monte Carlo simulations of ION degradation due to fin thickness fluctuations in FinFETs [Articolo su rivista]
Serra, N; Palestri, Pierpaolo; SMIT G. D., J; Selmi, Luca
abstract

The impact of fin thickness nonuniformities on carrier transport in n-type FinFETs is analyzed with a Multi-Subband Monte Carlo technique, which allows for an accurate description of the quasi-ballistic transport taking place in short channel devices and which comprises the dominant scattering mechanisms as well as a semi-empirical technique to handle quantization effects in the transport direction. We found that the impact of channel thickness discontinuity on the on-current is larger when the nonuniformities are located close to the Virtual Source of the device. Furthermore, the sensitivity of the on-current to thickness nonuniformity is essentially the same when considering devices with different crystal orientations. Comparison with drift-diffusion simulations reveals substantial differences in the predicted trends of the sensitivity of the drain current to thickness fluctuations in these nanoscale devices.

2009 - New insight on the charge trapping mechanisms of SiN--based memory by atomistic simulations and electrical modeling [Relazione in Atti di Convegno]
Vianello, Elisa; Perniola, L; Blaise, P; Molas, G; COLONNA J., P; Driussi, Francesco; Palestri, Pierpaolo; Esseni, David; Selmi, Luca; Rochat, N; Licitra, C; Lafond, D; Kies, R; Reimbold, G; DE SALVO, B; Boulanger, F.
abstract

In this paper, we have studied the charge trapping mechanisms of nitride-based non-volatile memories. The impact of different silicon-nitride (SiN) compositions (standard, std, and Si-rich) on the device characteristics has been investigated through material characterizations, electrical measurements, atomistic and electrical simulations. We found that the different physical nature of the dominant defects in the two SiN compositions is at the origin of the different device electrical behaviors. In particular, we argue that the different electron occupation number of the defect states of the two SiN materials explains the observed faster erasing speed and charge loss rate of Si-rich SiN devices, with respect to std SiN devices, in spite of comparable programming behavior. A simple trap model is proposed to improve state of the art simulators of SiN based memories.

2009 - On the Accuracy of Current TCAD Hot Carrier Injection Models for the Simulation of Degradation Phenomena in Nanoscale Devices [Relazione in Atti di Convegno]
A., Zaka; Q., Rafhay; Palestri, Pierpaolo; R., Clerc; D., Rideau; Selmi, Luca; C., Tavernier; H., Jaouen
abstract

The aim of this paper is to assess the capability of TCAD tools to accurately model hot electron injection in advanced device architecture versus state of the art full band Monte Carlo.

2009 - Optimization of the Channel Lateral Strain Profile for Improved Performance of Multi-Gate MOSFETs [Relazione in Atti di Convegno]
M., De Michielis; K., Boucart; K. E., Moselund; D., Bouvet; P., Dosbroz; S., Olsen; A., O’Neil; L., Lattanzio; Selmi, Luca; A. M., Ionescu
abstract

We report for the first time the optimization of the channel lateral strain profile as a new technological booster for improved performance of multi-gate n-channel MOSFET. We find that quasi-uniform or flat-Gaussian-close-to-the-drain profiles are optimum for the Ion boosting of sub-50 nm scaled MOSFETs, while the penalty on Ioff and subthreshold slope is minimum. The reported predictions use realistic lateral uniaxial strain profiles, with peaks up to few GPa's and average values of hundreds of MPa's.

2009 - Program efficiency and high temperature retention of SiN/high-K based memories [Articolo su rivista]
Vianello, Elena; M., Bocquet; Driussi, Francesco; L., Perniola; G., Molas; Selmi, Luca
abstract

This paper presents an experimental and simulation study of the program efficiency and retention of SANOS memory cells. We analyzed the experimental curves of the available cells by a physics based model that includes drift-diffusion transport of carriers in the nitride conduction band. We evidenced how the gate stack dimensions impact the program efficiency; in particular, thicker Si(3)N(4) layers allow for faster programming. However, the Si(3)N(4) thickness hardly influence the high temperature retention, since charge loss due to thermal emission dominates. Good agreement of the model with a wide set of experiments makes us confident on the validity of the interpretation of data which is suggested by the modeling results. (C) 2009 Elsevier B.V. All rights reserved.

2009 - Semiclassical Modeling of Quasi-Ballistic Hole Transport in Nanoscale pMOSFETs Based on a Multi-Subband Monte Carlo Approach [Articolo su rivista]
DE MICHIELIS, Marco; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper presents a new self-consistent multi-subband Monte Carlo (MSMC) simulator designed to investigate quasi-ballistic transport in nanoscale pMOSFETs. The simulator is 2-D in real space and k-space, and an accurate analytical model of the warped hole energy dispersion is adopted. The effects of the hole gas degeneracy are naturally included by accounting for the Pauli's exclusion principle. The simulator is implemented by resorting to original solutions for handling the hole-free flights consistently with the complicated energy dispersion. A detail description of the formulation of the scattering rates used in the simulator and a comparison to calculations based on a k middot p quantization model are given. Upon an appropriate calibration, the new MSMC tool can accurately reproduce the experimental data for low field mobility, and it can be used for the analysis of the semiballistic transport regime in nanoscale pMOSFETs. Preliminary results for the ballistic ratios BR in double-gate silicon-on-insulator pMOSFETs show that the BR in pMOS are not much worse than in nMOS transistors.

2009 - Semi-classical transport modelling of CMOS transistors with arbitrary crystal orientations and strain engineering [Articolo su rivista]
Esseni, David; F., Conzatti; M., De Michielis; N., Serra; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper reviews the basic methodologies and models used in the semi-classical modelling of CMOS transistors in the framework of the nowadays generalized scaling scenario. The capabilities to describe devices with arbitrary crystal orientations and strain configurations are discussed. Several simulation results are illustrated and compared to the experiments to assess the understanding of the underlying physics and the predictive capabilities of the models. A case study concerning the drain currents in nano-scale uniaxially strained MOSFETs is presented and it shows how the strain engineering may change the traditional on-current disadvantage of the p-MOS compared to the n-MOS transistors.

2009 - Special Issue of Solid State Electronics Devoted to the 2008 International Conference on Ultimate Integration on Silicon [Curatela]
Selmi, Luca; Esseni, David; Palestri, Pierpaolo
abstract

NA

2008 - A better understanding of the requirements for predictive modeling of strain engineering in nMOS transistors [Articolo su rivista]
Comparone, G; Palestri, Pierpaolo; Esseni, David; Lucci, L; Selmi, Luca
abstract

In this paper we use a Multi-Subband-Monte-Carlo model to study the transport in nMOSFETs featuring strained silicon channels. It is shown that state-of-the-art modeling of the mobility in n-type inversion layers cannot reproduce the mobility enhancements measured in Si devices with either uniaxial or biaxial strain. Possible reasons for this limitation are analyzed in detail.

2008 - A New Multi Subband Monte Carlo Simulator for Nano p-MOSFETs [Relazione in Atti di Convegno]
DE MICHIELIS, Marco; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper presents a new self-consistent Multi- Subband Monte Carlo (MSMC) simulator design to investigate quasi-ballistic transport in nano p-MOSFETs. The simulator adopts an accurate analytical description of the warped hole subbands. A first comparison between n− and p−MOSFET performance is reported.

2008 - Back-Scattering in Quasi Ballistic NanoMOSFETs: The Role of Non Thermal Carrier Distributions [Relazione in Atti di Convegno]
Clerc, R; Palestri, Pierpaolo; Selmi, Luca; Ghibaudo, G.
abstract

In this work, the kT layer theory for quasi ballistic transport in nanodevices has been reinvestigated, underlying the impact of carrier heating on backscattering. Assuming a constant mean free path, a differential equation for the currents fluxes has been derived, including both the impact of collision and field on backscattering. By making proper approximations on the impact of heating on carrier distribution functions, the backscattering coefficient and velocity profiles have been re-derived, and successfully compared to Monte Carlo simulations of template potential profiles. These results open new perspectives in the development of new physically based compact models for MOSFETs, better accounting for non equilibrium transport effects.

2008 - Comprehensive Behavioral modeling of conventional and Dual-Tuning PLLS [Articolo su rivista]
L., Bizjak; N., Da Dalt; P., Thurner; R., Nonis; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper presents a modular and comprehensive nonlinear time-domain behavioral model for phase-locked loops (PLLs) that are suitable for analyzing the impact on the output signal of the noise contribution and nonidealities of the constituent building blocks. The model building blocks are described by Simulink submodels and can be configured to implement different PLL topologies. Postprocessing of the PLL output provides the PLL phase noise and spur-to-carrier-ratio performances. The calculated phase-noise spectra are compared with those obtained with the well-known linear model and with measurements. To show the flexibility of this approach, many case studies are reported; among them, the analysis of the spurs due to charge pump mismatch and the transient phase noise, and spurs performances of a PLL featuring a dual control of the voltage-controlled oscillator.

2008 - Design of UWB LNA in 45nm CMOS Technology: Planar Bulk vs. FinFET [Relazione in Atti di Convegno]
D., Ponton; Palestri, Pierpaolo; Esseni, David; Selmi, Luca; M., Tiebout; B., Parvais; G., Knoblinger
abstract

This paper describes the design of a single-stage differential Low Noise Amplifier (LNA) for Ultra Wide Band(UWB) applications, implemented in state of the art Planar and FinFET 45nm CMOS technologies. A gm-boosted topology has been chosen and the LNA has been designed to work over the whole UWB band (3.1 – 10.6GHz), while driving a capacitive load. The simulations highlight that, at the present stage of the technology development, the Planar version of the LNA outperforms the FinFET one thanks to the superior cutoff frequency fT of Planar devices in the inversion region, achieving comparable Noise Figure and voltage gain, but consuming less power.

2008 - Impact of Device Layout and Annealing Process During the Passivation of Interface States in Presence of Silicon Nitride Layers [Articolo su rivista]
Driussi, Francesco; Selmi, Luca; N., Akil; M. J., van Duuren; R., van Schaijk
abstract

This paper reports the experimental evidence of anomalous electrical characteristics of large test structures for the characterization of both silicon-oxide-nitride-oxide-silicon (SONOS) and MOS gate stacks featuring nitride caps. The anomaly has been studied on devices featuring different layouts and it has been attributed to the property of silicon nitride layers to block the diffusion of hydrogen used for the passivation of the Si/SiO2 interface dangling bonds. Since the hydrogen passivation can occur only from the lateral sides of the device, our findings imply restrictions on the dimensions and on the layout of the test structures used to study the electrical properties of the gate stacks in SONOS or in large MOS devices featuring protective nitride caps.

2008 - Impact of the Charge Transport in the Conduction Band on the Retention of Si-Nitride Based Memories [Relazione in Atti di Convegno]
E., Vianello; Driussi, Francesco; Palestri, Pierpaolo; A., Arreghini; Esseni, David; Selmi, Luca; N., Akil; M., van Duuren; D. S., Golubović
abstract

An improved model for charge injection through ONO gate stacks, that comprises carrier transport in the conduction band of the silicon nitride (Si3N4), is used to investigate the program/retention sequence of Si3N4 based (SONOS/TANOS) non volatile memories without making assumptions on the initial distribution of the trapped charge at the beginning of retention. We show that carrier transport in the Si3N4 layer impacts the spatial charge distribution and consequently several other aspects of the retention transient. The interpretation of the Arrehnius plots of the high temperature retention data, typically used to infer the trap depth from the retention activation energy is discussed. The model provides a simple explanation of the small threshold voltage increase observed during retention experiments of thick tunnel oxide ONO stacks.

2008 - Investigation of the transport properties of silicon nanowires using deterministic and Monte Carlo approaches to the solution of the Boltzmann Transport Equation [Articolo su rivista]
Lenzi, M; Palestri, Pierpaolo; Gnani, E; Reggiani, S; Gnudi, A; Esseni, David; Selmi, Luca; Baccarani, G.
abstract

In this paper we investigate the transport properties of silicon nanowire FETs by using two different simulation approaches: the Monte Carlo method and a deterministic, numerical solution of the Boltzmann equation for the quasi-1D electron gas. In both cases we solve the coupled Schroedinger-Poisson equations to extract the profiles of the 1D subbands along the channel; next, the multi-subband Boltzmann equations are tackled with the two different procedures. A very good agreement is achieved between the two approaches to the transport problem in terms of mobility, drain current and internal physical quantities, such as carrier distribution functions and average velocities. Some peculiar features of the low-field mobility as a function of the wire diameter and gate bias are discussed and justified based on the subband energy and wave-function behavior within the cylindrical geometry of the nanowire, as well%

2008 - Long term charge retention dynamics of SONOS cells [Articolo su rivista]
Arreghini, A; Akil, N; Driussi, Francesco; Esseni, David; Selmi, Luca; VAN DUUREN, M. J.
abstract

We present a model for charge retention dynamics in SONOS non volatile memory cells which accounts for the space and energy distributions of the trapped charge in the silicon nitride, self consistently with the potential. Long term retention measurements (beyond 106 s) versus temperature allowed us to decouple two charge loss mechanisms, to calibrate the model parameters and then to reproduce a large set of measurements on devices featuring different gate stacks, initial threshold voltages (including negative ones) and operation temperatures. A detailed analysis has been also carried out to compare the retention dynamics of cells featuring thin or thick tunnel oxide barriers.

2008 - On the electron mobility enhancement in biaxially strained Si MOSFETs [Articolo su rivista]
Driussi, Francesco; Esseni, David; Selmi, Luca; P. E., Hellström; G., Malm; J., Hållstedt; M., Östling; T. J., Grasby; D. R., Leadley; X., Mescot
abstract

This paper reports a detailed experimental and simulation study of the electron mobility enhancement induced by the biaxial strain in (001) silicon MOSFETs. To this purpose, ad hoc test structures have been fabricated on strained Si films grown on different SiGe virtual substrates and the effective mobility of the electrons has been extracted. To interpret the experimental results, we performed simulations using numerical solutions of Schroedinger-Poisson equations to calculate the charge and the momentum relaxation time approximation to calculate the mobility. The mobility enhancement with respect to the unstrained Si device has been analyzed as a function of the Ge content of SiGe substrates and of the operation temperature. (c) 2007 Elsevier Ltd. All rights reserved.

2008 - Proceedings of the 2008 International Conference on Ultimate Integration of Silicon (ULIS) [Curatela]
Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

2008 - Programme and retention characteristics of SONOS memory arrays with layered tunnel barrier [Articolo su rivista]
D. S., Golubović; E., Vianello; A., Arreghini; Driussi, Francesco; M. J., van Duuren; N., Akil; Selmi, Luca; Esseni, David
abstract

Layered tunnel barriers (T-ONO) might help circumvent retention limitations of nitride charge trapping devices (SONOS) programmed/erased by direct tunnelling without invoking high-K dielectrics in the gate stack. In order to establish to what extent the properties of a T-ONO tunnel layer influence the performance of SONOS memories, NOR memory arrays containing a silicon oxide/silicon nitride/silicon oxide T-ONO layer, a silicon nitride charge trapping layer and a silicon oxide blocking layer were fabricated and investigated. The T-ONO layer was formed using wet reoxidation of the silicon nitride, as this process is known to generate a lot of traps at the interface between silicon nitride and silicon oxide, as well as in the reoxidized portion of the silicon nitride itself. Besides standard memory measurements like programme/erase behaviour, endurance and retention, charge centroid extraction measurements were carried out in order to explain the retention behaviour and associate it with the position of the charge. It has been demonstrated that the performance of SONOS memories with a T-ONO layer strongly depends on the technological properties/quality of the T-ONO barrier which, therefore, may not be a universal solution to retention problems in SONOS devices.

2008 - Revised analysis of the mobility and ION degradation in high-k gate stacks: surface optical phonons vs. remote Coulomb scattering [Relazione in Atti di Convegno]
Toniutti, P; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

We use Multi-Subband Monte Carlo simulations to understand which mechanism is mainly responsible for the mobility degradation observed in nMOSFETs featuring high-k dielectrics. Direct comparison with the experimental data of Cassé et al. points out that for realistic interfacial layer thicknesses the effect of surface optical phonons on the mobility is very modest, and that the measured mobility reduction can be attributed to remote Coulomb scattering of charge in the gate-stack with concentrations in the order of 10^14 cm-2. We found that the drain current reduction in short channel devices is, instead, not as strong as the mobility reduction.

2008 - The impact of longitudinal non-uniform Fin-thickness on quasi-ballistic transport in FinFETs [Relazione in Atti di Convegno]
Serra, N; Palestri, Pierpaolo; SMIT G. D., J; Selmi, Luca
abstract

The impact of fin-thickness nonuniformities on carrier transport in FinFETs is analyzed with a quasi-ballistic transport model based on the multisubband Monte Carlo technique. Silicon channels featuring thickness constrictions or enlargements show subband energy variations due to the changes in vertical quantization along the fin. We found that the impact on the on-current is larger when the nonuniformities are located close to the virtual source of the device. Furthermore, the sensitivity of on-current to thickness nonuniformity is essentially the same when considering different crystal orientations. Comparison with drift-diffusion simulations reveals quantitative and qualitative differences in the predicted drain current trends of these nanoscale, quasi-ballistic MOS devices.

2008 - The Monte Carlo approach to transport modeling in deca-nanometer MOSFETs [Articolo su rivista]
Sangiorgi, E; Palestri, P; Esseni, D; Fiegna, C; Selmi, L
abstract

2008 - ULIS 2008 - 9th International Conference on ULtimate Integration of Silicon: Foreword [Relazione in Atti di Convegno]
Selmi, L.; Esseni, D.; Palestri, P.; Driussi, F.
abstract

2007 - A design methodology for MOS Current-Mode Logic Frequency Dividers [Articolo su rivista]
Nonis, R; Palumbo, E; Palestri, Pierpaolo; Selmi, Luca
abstract

2007 - A new analytical model for the energy dispersion in two-dimensional hole inversion layers [Articolo su rivista]
DE MICHIELIS, Marco; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

2007 - A semi analytical description of the hole band structure in inversion layers for the physically based modelling of pMOS transistors [Articolo su rivista]
DE MICHIELIS, M; Esseni, D; TSANG Y., L; Palestri, P; Selmi, L; ONEILL A., G; Chattopadhyay, S
abstract

This paper presents a new semianalytical model for the energy dispersion of the holes in the inversion layer of pMOS transistors. The wave vector dependence of the energy inside the 2-D subbands is described with an analytical, nonparabolic, and anisotropic expression. The procedure to extract the parameters of the model is transparent and simple, and we have used the band structure obtained with the k·p method to calibrate the model for silicon MOSFETs with different crystal orientations. The model is validated by calculating several transport-related quantities in the inversion layer of a heavily doped pMOSFET and by systematically comparing the results to the corresponding k·p calculations. Finally, we have used the newly developed band-structure model to calculate the effective mobility of pMOS transistors and compare the results with the experimental data. The overall computational complexity of our model is dramatically smaller compared to a fully numerical treatment (such as the k·p method); hence, our approach opens new possibilities for the physically based modeling of pMOS transistors.

2007 - An efficient, mixed semiclassical/quantum mechanical model to simulate planar and wire nano-transistors [Relazione in Atti di Convegno]
Selmi, Luca; Palestri, Pierpaolo; Esseni, David; Lucci, Luca; DE MICHIELIS, Marco
abstract

2007 - Analysis of transport properties of nanoscale SOI devices: Full Quantum versus Semi Classical models [Relazione in Atti di Convegno]
Lucci, Luca; M., Bescond; R., Clerc; Palestri, Pierpaolo; Esseni, David; Selmi, Luca; S., Cristoloveanu
abstract

In this work recently developed 2D Multi-Subband Monte Carlo device simulator and a Non-Equilibrium Green's functions solver are compared focusing on the source-channel barrier height modeling in double gate SOI MOSFETs.

2007 - Characterization and Modeling of long term retention in SONOS Non Volatile Memories [Relazione in Atti di Convegno]
Arreghini, A; Akil, N; Driussi, Francesco; Esseni, David; Selmi, Luca; VAN DUUREN, M. J.
abstract

2007 - Comparison of modeling approaches for the capacitance-voltage and current voltage characteristics of advanced gate stacks [Articolo su rivista]
Palestri, Pierpaolo; N., Barin; D., Brunel; C., Busseret; A., Campera; P. A., Childs; Driussi, Francesco; C., Fiegna; G., Fiori; R., Gusmeroli; G., Iannaccone; M., Karner; H., Kosina; A. L., Lacaita; E., Langer; B., Majkusiak; C., Monzio Compagnoni; A., Poncet; E., Sangiorgi; Selmi, Luca; A. S., Spinelli; J., Walczak
abstract

In this paper, we compare the capacitance-voltage and current-voltage characteristics of gate stacks calculated with different simulation models developed by seven different research groups, including open and closed boundaries approaches to solve the Schrodinger equation inside the stack. The comparison has been carried out on template device structures, including pure SiO2 dielectrics and high-kappa, stacks, forcing the use of the same physical parameters in all models. Although the models are based on different modeling assumptions, the discrepancies among results in terms of capacitance and leakage current are small. These discrepancies have been carefully investigated by analyzing the individual modeling parameters and the internal quantities (e.g., tunneling probabilities and subband energies) contributing to current and capacitance.

2007 - Comparison of Monte Carlo Transport Models for Nanometer-Size MOSFETs [Relazione in Atti di Convegno]
Fiegna, C; Braccioli, M; BRUGGER S., C; BUFLER F., M; Dollfus, P; AUBRY FORTUNA, V; Jungemann, C; Meinerzhagen, B; Palestri, Pierpaolo; GALDIN RETAILLEAU, S; Sangiorgi, E; Schenk, A; Selmi, Luca
abstract

This paper presents the results of a comparison among five Monte Carlo device simulators for nano-scale MOSFETs. These models are applied to the simulation of the I-V characteristics of a 25 nm gate-length MOSFET representative of the high-performance transistor of the 65 nm technology node. Appreciable differences between the simulators are obtained in terms of simulated ION. These differences are mainly related to different treatments of the ionized impurity scattering (IIS) and pinpoint a limitation of the available models for screening effects at very large carrier concentrations.

2007 - Experimental and Simulation Study of the Biaxial Strain and Temperature dependence of the Electron Mobility Enhancement in Si MOSFETs [Relazione in Atti di Convegno]
Driussi, Francesco; Esseni, David; Selmi, Luca; P. E., Hellstrom; G., Malm; J., Hallstedt; M., Ostling; T. J., Grasby; D. R., Leadley; X., Mescot
abstract

2007 - Explanation of SILC probability density distributions with nonuniform generation of traps in the tunnel oxide of flash memory arrays [Articolo su rivista]
Vianello, Elisa; Driussi, Francesco; Esseni, David; Selmi, Luca; Widdershoven, F; VAN DUUREN, M. J.
abstract

In this paper, we develop a detailed physical model to interpret the dependence of the stress induced leakage current (SILC) distributions on the nature and position of the generated defects, and we exploit it to reconsider in detail previously published experimental data on the statistical distribution of the SILC in Flash arrays. We found that a unique symmetrical spatial distribution of traps, which is rapidly decreasing from the Si-SiO2 interfaces toward the center of the oxide, can explain the oxide-thickness and stress-level dependence of the measured SILC distributions. The generation of cooperating defects with increasing stress time is also analyzed and discussed.

2007 - Fabrication, Characterization and Modeling of Strained SOI MOSFETs with Very Large Effective Mobility [Relazione in Atti di Convegno]
Driussi, Francesco; Esseni, David; Selmi, Luca; M., Schmidt; M. C., Lemme; H., Kurz; D., Buca; S., Mantl; M., Luysberg; R., Loo; D., Nguyen; M., Reiche
abstract

Strained silicon on insulators (sSOI) wafers with a supercritical thickness of 58 nm were produced using thin strain relaxed SiGe buffer layers, wafer bonding, selective etch back and epitaxial overgrowth. Raman spectroscopy revealed an homogeneous strain of 0.63 plusmn 0.03 % in the strained Si layer. Long channel n-type SOI-MOSFETs showed very large electron mobilities up to 1200 cm2/Vs in the strained Si devices. These values are more than two times larger than those of reference SOI n-MOSFETs. Mobility simulations with state of the art scattering models are then used to interpret the experiments.

2007 - Mobility and Backscattering in Germanium n-type Inversion Layers [Relazione in Atti di Convegno]
Rafhay, Q; Palestri, Pierpaolo; Esseni, David; Clerc, R; Selmi, Luca
abstract

2007 - Monte Carlo modeling of nanometer scale MOSFETs [Relazione in Atti di Convegno]
Sangiorgi, E; Palestri, Pierpaolo; Esseni, David; Fiegna, C; Selmi, Luca
abstract

Recent developments in the Monte Carlo method for the simulation of semi-classical carrier transport in nano-MOSFETs include the treatment of quantum-mechanical effects in the simulation (using either the Multi-Subband approach or quantum corrections to the electrostatic potential). In this paper, after reviewing recent progress in this field, selected applications are presented, including the analysis of quasi-ballistic transport, the determination of the RF characteristics of deca-nanometric MOSFETs, and the study of non-conventional device structures and channel materials.

2007 - Monte-Carlo Simulation of Decananometric nMOSFETs: Multi-Subband vs. 3D-Electron Gas with Quantum Corrections [Articolo su rivista]
I., Riolino; M., Braccioli; Lucci, Luca; Palestri, Pierpaolo; Esseni, David; C., Fiegna; Selmi, Luca
abstract

In this paper two Monte-Carlo simulators implementing different models for the influence of carrier quantization on the electrostatics and transport are used to analyze sub-100 nm double-gate SOI devices. To this purpose a new stable and efficient scheme to implement the contacts in the simulation of double-gate SOI devices is introduced first. Then, results in terms of drain current and microscopic quantities are compared, providing new insight on the limitation of a well assessed semiclassical transport simulation approach and a more rigorous multi-subband model.

2007 - Multi-Subband Monte-Carlo study of Transport, Quantization and Electron Gas Degeneration in Ultra-Thin SOI n-MOSFETs [Articolo su rivista]
Lucci, L; Palestri, Pierpaolo; Esseni, David; Bergagnini, L; Selmi, Luca
abstract

2007 - On the Apparent Mobility in Nanometric n-MOSFETs [Articolo su rivista]
Zilli, M; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

This letter investigates the definition and determination of mobility in nanometric metal–oxide–semiconductor transistors by means of multisubband Monte Carlo simulations. Our results clearly show that the transport in nano-MOSFETs, even for very small VDS, is far from being uniform and local. Consequently, the apparent mobility extracted from the experiments is a channel-length-dependent quantity, which is only partly related to the uniform transport mobility. Our study comprises both the electrical and magnetoresistance mobility.

2007 - On the experimental determination of channel back-scattering in nanoMOSFETs [Relazione in Atti di Convegno]
Zilli, Massimiliano; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

By using accurate Multi-Subband-Monte-Carlo simulations of quasi-ballistic transport we carry out a detailed re-examination of the experimental extraction procedure for the ballistic-ratio BR=ID/IBAL in nanoMOSFETs proposed in [1]. It is found that the ballistic-ratio extracted applying this procedure to the simulated drain current severely underestimates the BR extracted by directly compare the simulated ID and IBAL. This is mainly due to inaccurate determination of the temperature dependence of the inversion charge. It is suggested that this limitation of the extraction procedure may explain the apparent lack of improvement in the ballisticity with the geometrical scaling.

2007 - Progress in Technology Oriented Analytical Models for Advanced MOSFET devices [Relazione in Atti di Convegno]
Clerc, R; Ferrier, M; Rafhay, Q; Ghibaudo, G; Palestri, Pierpaolo; Lucci, Luca; Selmi, Luca
abstract

2007 - Quasi Ballistic transport in advanced MOSFET devices [Relazione in Atti di Convegno]
R., Clerc; Palestri, Pierpaolo; Q., Rafhay; M., Ferrier; G., Pananakakis; G., Ghibaudo; Selmi, Luca
abstract

The Physics and understanding of ballistic and quasi ballistic transport in nanoMOSFET is reviewed, underlying main concepts, analytical models and open questions in this area.

2007 - Quasiballistic Transport in Nano-MOSFETs [Capitolo/Saggio]
Sangiorgi, E; Eminente, S; Fiegna, C; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

2007 - Technology Oriented Analytical Models of MOSFETs in the Quasi Ballistic Regime [Relazione in Atti di Convegno]
Clerc, R; Rafhay, Q; Ferrier, M; Palestri, Pierpaolo; Ghibaudo, G; Selmi, Luca
abstract

2007 - The Monte Carlo approach to transport modeling in deca-nanometer MOSFETs [Relazione in Atti di Convegno]
Sangiorgi, E.; Palestri, P.; Esseni, D.; Fiegna, C.; Selmi, L.
abstract

In this paper, we review recent developments of the Monte Carlo approach to the simulation of semi-classical carrier transport in nano-MOSFETs, with particular focus on the inclusion of quantum-mechanical effects in the simulation (using either the Multi-Subband approach or quantum corrections to the electrostatic potential) and on the numerical stability issues related to the coupling of the transport with the Poisson equation. Selected applications are presented, including the analysis of quasi-ballistic transport, the determination of the RF characteristics of deca-nanometric MOSFETs, and the study of non-conventional device structures and channel materials. © 2007 IEEE.

2007 - The Monte Carlo approach to transport modeling in decananometer MOSFETs [Relazione in Atti di Convegno]
Sangiorgi, E; Palestri, Pierpaolo; Esseni, David; Fiegna, C; Selmi, Luca
abstract

In this paper, we review recent developments of the Monte Carlo approach to the simulation of semi-classical carrier transport in nano-MOSFETs, with particular focus on the inclusion of quantum-mechanical effects in the simulation (using either the Multi-Subband approach or quantum corrections to the electrostatic potential) and on the numerical stability issues related to the coupling of the transport with the Poisson equation. Selected applications are presented, including the analysis of quasi-ballistic transport, the determination of the RF characteristics of deca-nanometric MOSFETs, and the study of nonconventional device structures and channel materials.

2007 - Trading off static power and dynamic performance in CMOS digital circuits: bulk versus double gate SOI MOSFETs [Relazione in Atti di Convegno]
Agostinelli, Matteo; Alioto, M.; Esseni, David; Selmi, Luca
abstract

This paper investigates with a mixed device/circuit simulation methodology the effectiveness of DG SOI MOSFETs compared to conventional bulkMOSFETs for the implementation of low standby power circuit techniques. Our results indicate that DG MOSFETs offer significant advantages essentially because of the larger VT sensitivity to back-biasing.

2007 - Validity of the parabolic effective mass approximation in silicon and germanium n-MOSFETs with different crystal orientations [Articolo su rivista]
J. L. P. J., van der Steen; Esseni, David; Palestri, Pierpaolo; Selmi, Luca; R. J. E., Hueting
abstract

2006 - A Model to Understand Current Consumption, Maximum Operating Frequency And Scaling Trends Of MCML Frequency Dividers [Relazione in Atti di Convegno]
Nonis, Roberto; Palumbo, Enzo; Palestri, Pierpaolo; Selmi, Luca
abstract

In this work, the effect of digital CMOS technology down scaling on the performances of MOS Current Mode Logic frequency dividers is addressed. A fast and effective methodology to design the dividers is presented. The insight given by the methodology is then exploited to study the down scaling of MCML dividers by considering two CMOS technologies representative of the 130nm and 90nm technology nodes. The model provides quantitatively accurate predictions of the advantages of scaling on current consumption and maximum frequency of operation.

2006 - Assessment of the Impact of Biaxial Strain on the Drain Current of Decanometric n-MOSFET [Relazione in Atti di Convegno]
Ponton, D; Lucci, L; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

2006 - Does Multi Trap Assisted Tunneling Explain the Oxide Thickness Dependence of the Statistics of SILC in FLASH Memory Arrays ? [Relazione in Atti di Convegno]
Vianello, E; Driussi, Francesco; Esseni, David; Selmi, Luca; VAN DUUREN, M; Widdershoven, F.
abstract

In this paper, we analyze the experimental SILC statistical data at low stress reported in [5]. To this purpose we developed an analytical physical model to study the statistical distribution of the TAT current due to single and multiple traps in the gate oxide of a Floating Gate memory cell. We modeled also the generation dynamics of conductive percolation paths due to more traps and we simulated the SILC statistical distribution in the memory cell. This study points out the differences in the statistical behavior of the TAT current due to defects formed by single and multiple traps.

2006 - Effect of the Gap Size on the Source-Side-Injection Efficiency of Split-gate Memory Cells [Articolo su rivista]
Palestri, Pierpaolo; Akil, N; Stefanutti, W; Slotboom, M; Selmi, Luca
abstract

2006 - Experimental Extraction of Charge Centroid and of Charge Type in the P/E operation of SONOS Memory Cells [Relazione in Atti di Convegno]
Arreghini, Antonio; Driussi, Francesco; Esseni, David; Selmi, Luca; VAN DUUREN, M. J.; VAN SCHAIJK, R.
abstract

2006 - Monte Carlo Simulation of Decananometric Double-Gate SOI devices: Multi-Subband vs. 3D-Electron Gas with Quantum Corrections [Relazione in Atti di Convegno]
Riolino, I; Braccioli, M; Lucci, L; Esseni, David; Fiegna, C; Palestri, Pierpaolo; Selmi, Luca
abstract

2006 - Monte Carlo Simulation of Substrate Enhanced Electron Injection in Split-gate Memory Cells [Articolo su rivista]
Stefanutti, W; Palestri, Pierpaolo; Akil, N; Selmi, Luca
abstract

In this paper, we use fullband Monte Carlo simulations and gate current measurements to investigate charge injection in split-gate memory cells under negative substrate bias. It is shown that, in the source-side-injection (SSI) regime, the enhancement of the programming efficiency due to the substrate bias is low, unless very low drain and floating-gate biases are considered. In particular, the enhancement of the efficiency is largely reduced if the drain current is kept constant when comparing different substrate biases. Furthermore, it is observed that the carrier injection profile under negative substrate bias is broader than in the SSI regime, and a substantial amount of charge is injected in the spacer region.

2006 - Multi-Subband-Monte-Carlo investigation of the mean free path and of the kT layer in degenerated quasi ballistic nanoMOSFETs [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Clerc, R; Esseni, David; Lucci, Luca; Selmi, Luca
abstract

This paper examines, by means of multi-subband-Monte-Carlo (MSMC) simulations, the prediction of the well known compact formula for back-scattering in nanoMOSFETs, analyzing the effect of carrier degeneracy and complex scattering mechanisms on the back-scattering. The paper also addresses the definition of an appropriate mean-free-path and its relationship to the low-field mobility

2006 - On the Passivation of Interface States in SONOS Test Structures: Impact of Device Layout and Annealing Process [Relazione in Atti di Convegno]
Driussi, Francesco; Selmi, Luca; Akil, N.; VAN DUUREN, M. J.; VAN SCHAIJK, R.
abstract

2006 - On the Physical Understanding of the kT-Layer Concept in Quasi-Ballistic Regime of Transport in Nanoscale Devices [Articolo su rivista]
Clerc, R.; Palestri, Pierpaolo; Selmi, Luca
abstract

2006 - Physical Description of the Mixed-Mode Degradation Mechanism for High Performance Bipolar Transistors [Relazione in Atti di Convegno]
Vanhoucke, T; HURKX G. A., M; Panko, D; Campos, R; Piontek, A; Palestri, Pierpaolo; Selmi, Luca
abstract

2006 - Quasi Ballistic transport in Fully Depleted SOI MOSFETs: the "kT layer concept revisited [Relazione in Atti di Convegno]
Clerc, R; Palestri, Pierpaolo; Selmi, Luca
abstract

2006 - Simulation of Double-Gate nano-MOSFETs with the Multi-subband Monte Carlo Method [Relazione in Atti di Convegno]
Lucci, Luca; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

A recently developed self-consistent Monte-Carlo (MC) simulator of confined electron's transport in the inversion layer of nano-MOSFETs is used to analyze three nano-scale ultra-thin body (UTB) SOI MOSFETs. The effect of the subband structure and carrier degeneracy as well as the relative importance of different scattering mechanisms is discussed.

2006 - Towards and Beyond 2015: technology, devices, circuits and systems [Monografia/Trattato scientifico]
Belleville, M; BOURGOIN J., P; Castello, R; DE MAN, H; Gessner, T; Schulz, S; Ionescu, A; Selmi, Luca; Semeria, M; Skotnicki, T; Tenhunen, H; Thewes, R; VAN ROSSUM, M; Veendrick, H; Widdershoven, F.
abstract

2006 - Transport in deca-nanometric MOSFETs: from bandstructure to on-currents [Relazione in Atti di Convegno]
Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

2006 - Validity of the effective mass approximation in silicon and germanium inversion layers [Relazione in Atti di Convegno]
VAN DER STEEN J., L; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

2005 - A Model to Understand Current Consumption, Maximum Operating Frequency And Scaling Trends Of MCML Frequency Dividers [Relazione in Atti di Convegno]
Nonis, Roberto; Palumbo, Enzo; Palestri, Pierpaolo; Selmi, Luca
abstract

In this work, the effect of digital CMOS technology down scaling on the performances of MOS Current Mode Logic frequency dividers is addressed. A fast and effective methodology to design the dividers is presented. The insight given by the methodology is then exploited to study the down scaling of MCML dividers by considering two CMOS technologies representative of the 130 nm and 90 nm technology nodes. The model provides quantitatively accurate predictions of the advantages of scaling on current consumption and maximum frequency of operation.

2005 - An Improved Semi-Classical Monte Carlo Approach for Nano-MOSFET Simulation [Articolo su rivista]
Palestri, Pierpaolo; Eminente, S; Esseni, David; Fiegna, C; Sangiorgi, E; Selmi, Luca
abstract

2005 - Ballistic Effects in Advanced MOSFETs along the Roadmap [Relazione in Atti di Convegno]
Sangiorgi, E; Palestri, Pierpaolo; Eminente, S; Esseni, David; Fiegna, C; Selmi, Luca
abstract

2005 - Experimental Characterization of Statistically Independent Defects in Gate Dielectrics - Part I: Description and Validation of the Model [Articolo su rivista]
Driussi, Francesco; F., Widdershoven; Esseni, David; Selmi, Luca; M., VAN DUUREN
abstract

A general statistical model to describe the generation of statistically independent defects in gate dielectrics is presented. In this first paper, the general model, suitable for different types of defects, is developed to describe the stress-induced oxide traps and the statistical properties of the trap-assisted tunneling current (TAT). With our model, it is possible to study the stress-induced leakage current statistics on large Flash memory arrays, to extract information about the number of generated defects, and to reconstruct the probability density distribution (PDD) of the gate current due to the single trap. We validated the statistical model by means of a Monte Carlo simulator developed to describe the oxide trap generation and the TAT statistics in large Flash memory arrays. In Part II, we applied the statistical model to experimental data measured on Flash memory arrays and we verified the possibility of studying, with our model, the trap generation dynamics and the PDD of the gate current produced by the single oxide defect.

2005 - Experimental Characterization of Statistically Independent Defects in Gate Dielectrics - Part II: Experimental Results on Flash Memory Arrays [Articolo su rivista]
Driussi, Francesco; F., Widdershoven; Esseni, David; Selmi, Luca; AND M., VAN DUUREN
abstract

In this paper we applied the statistical model for independent defects described in Part I, to experimental data measured on Flash memory arrays. The model, developed to describe the stress-induced leakage current (SILC) statistics, allowed us to study the oxide trap generation during program/erase (P/E) stress and to extract the discrete probability distribution (DPD) of the gate current increase due to the single oxide defect. For all the analyzed nonvolatile memory arrays and for all the P/E stresses, the experimental results are consistent with the simulations carried out in Part I, thus confirming the reliability of the statistical model and of its validation procedure. Measurements on Flash cell arrays with different oxide thickness show that the number of generated oxide traps increases linearly with the number of P/E cycles in the early stage of the stress. It is shown, for the first time, that the extracted DPD of the single-trap exhibits long tails with power law dependence on the trap current and with a slope of the tail that decreases with decreasing oxide thickness. These tails are responsible for the cells with the largest SILC values in the Flash memory arrays.

2005 - Gate Current in Stacked Dielectrics for Advanced FLASH EEPROM cells [Relazione in Atti di Convegno]
Driussi, Francesco; Marcuzzi, S; Palestri, Pierpaolo; Selmi, Luca
abstract

2005 - Mobility, Velocity and Average Energy in Ultra-Thin-Body SOI MOSFETs [Relazione in Atti di Convegno]
Lucci, Luca; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

2005 - Modeling, design and characterization of a new Low Jitter analog Dual Tuning LC-VCO PLL Architecture [Articolo su rivista]
Nonis, Roberto; DA DALT, N; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper describes the modeling, design, and characterization of a low-jitter 2.4-GHz LC-VCO PLL architecture realized in a standard 0.12-mu m CMOS technology. It features an analog dual control loop for fine and coarse VCO tuning that allows very low VCO gain (60 MHz/V) for noise rejection while maintaining a wide tuning range. The coarse input of the VCO is driven by an analog circuit that adjusts the VCO gain in a continuous manner. Measurements demonstrate an integrated jitter of 0.74 ps that is 43% lower compared to results from a standard PLL topology (STD PLL) with a single control loop. The PLLs have the same bandwidth and output frequency range and were built on the same wafer for comparison. The circuit area of the proposed LC-VCO PLL is 0.7 mm(2) and the power consumption is 32 mW. The area and power consumption of the proposed LC-VCO PLL are less than 1% larger compared to the STD PLL.

2005 - Modelling the Uniform Transport in Thin Film SOI MOSFETs with a Monte Carlo Simulator for the 2D Electron Gas [Articolo su rivista]
Lucci, L; Palestri, P; Esseni, D; Selmi, L
abstract

In this paper, we present simulations of some of the most relevant transport properties of the inversion layer of ultra-thin film SOI devices with a self-consistent Monte-Carlo transport code for a confined electron gas. We show that size induced quantization not only decreases the low-field mobility (as experimentally found in [Uchida K, Koga J, Ohba R, Numata T, Takagi S. Experimental eidences of quantum-mechanical effects on low-field mobility, gate-channel capacitance and threshold voltage of ultrathin body SOI MOSFETs, IEEE IEDM Tech Dig 2001;633–6; Esseni D, Mastrapasqua M, Celler GK, Fiegna C, Selmi L, Sangiorgi E. Low field electron and hole mobility of SOI transistors fabricated on ultra-thin silicon films for deep sub-micron technology application. IEEE Trans Electron Dev 2001;48(12):2842–50; Esseni D, Mastrapasqua M, Celler GK, Fiegna C, Selmi L, Sangiorgi E, An experimental study of mobility enhancement in ultra-thin SOI transistors operated in double-gate mode, IEEE Trans Electron Dev 2003;50(3):802–8. [1–3]]), but also the electron saturation velocity and the carrier heating depend on the subband structure, and thus on the silicon film thickness.

2005 - Monte-Carlo Analysis of Ballistic Transport in MOSFETs along the ITRS Roadmap [Relazione in Atti di Convegno]
Palestri, Pierpaolo; S., Eminente; Esseni, David; C., Fiegna; Selmi, Luca; E., Sangiorgi
abstract

Monte-Carlo simulations including quantum corrections to the potential are used to study electronic transport in Bulk and Double Gate (DG) SOI MOSFETs with LG down to 14 nm. The ON current (ION) and the ballistic current IBL of MOSFETs designed according to the 2003 Roadmap down to the 45 nm node are analyzed. Our results show that, for the explored LG values, scattering still controls ION; thanks to a lower transversal electric field, the DG SOI MOSFETs with low channel doping allow to get closer to the ballistic limit than bulk counterparts.

2005 - Multi-subband Monte Carlo modeling of nano-MOSFETs with strong vertical quantization and electron gas degeneration [Relazione in Atti di Convegno]
Lucci, Luca; Palestri, Pierpaolo; Esseni, David; Selmi, Luca
abstract

This paper presents a new self-consistent MC simulator for the 2D electron gas of nano-MOSFETs. The simulator is two-dimensional in real space and in k-space, and accounts for the electron gas degeneracy in the k-plane. Simulations of thin-film SOI MOSFETs show that the subband structure and the carrier degeneracy strongly affect the transport properties particularly the injection velocity. Our results also point-out the strong anisotropy of the occupation function, which seriously hampers the use of simulators based on the momentum of the BTE

2005 - New Charge Pumping model for the analysis of the spatial trap distribution in the nitride layer of SONOS devices [Articolo su rivista]
Arreghini, Antonio; Driussi, Francesco; Esseni, David; Selmi, Luca; M., VAN DUUREN; R., VAN SCHAIJK
abstract

This work presents a new analytical model for low frequency Charge Pumping measurements on SONOS memory cells. The charge per cycle that recombines into the nitride layer and its frequency dependence allow us to study the spatial distribution of nitride traps. Experimental results agree with reported nitride trap concentrations and show an interface between the nitride and the silicon substrate in good agreement with TEM pictures of the SONOS devices.

2005 - Understanding Quasi-Ballistic Transport in nano-MOSFETs. Part II: Technology Scaling along the ITRS [Articolo su rivista]
Eminente, S.; Esseni, David; Palestri, Pierpaolo; Fiegna, C; Selmi, Luca; Sangiorgi, E.
abstract

The on-current and its ballistic limit for MOSFETs designed according to the 2003 International Technology Roadmap for Semiconductors down to the 45-nm node, are evaluated by using the full-band, self-consistent Monte Carlo simulator with quantum–mechanical corrections described in Part I. Our results show that quasi-ballistic transport increases for G below approximately 50 nm and contributes most part of the ON improvements related to scaling. Thanks to a lower vertical electric field, double-gate silicon-on-insulator MOSFETs with ultrathin body and low channel doping achieve performance closer to the ballistic limit than the bulk counterparts.

2005 - Understanding Quasi-Ballistic Transport in nano-MOSFETs. Part I:Scattering in the Channel and in the Drain [Articolo su rivista]
Palestri, Pierpaolo; Esseni, David; S., Eminente; C., Fiegna; E., Sangiorgi; Selmi, Luca
abstract

In this paper, and in Part II, Monte Carlo (MC) simulations including quantum corrections to the potential and calibrated scattering models are used to study electronic transport in bulk and double-gate silicon-on-insulator MOSFETs with L-G down to 14-nm designed according to the 2003 International Technology Roadmap for Semiconductors. Simulations with and without scattering are used to assess the influence of quasi-ballistic transport on the MOSFET on-current. We analyze in detail the flux of back-scattered carriers. The role of scattering in different parts of the device is clarified and the MC results are compared to simple models for quasi-ballistic transport presented in the literature.

2004 - A Monte Carlo Study of the Role of Scattering in Deca-nanometer MOSFETs [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Esseni, David; S., Eminente; C., Fiegna; E., Sangiorgi; Selmi, Luca
abstract

In this paper, a Monte-Carlo simulator, including quantum corrections to the potential and an improved physically based model for surface roughness scattering is used to study the electronic transport in double gate (DG) SO1 MOSFETs with Lc down to 14nm. Our results demonstrate that, for the explored LG values, scattering still controls the ON current (IDS), which for Lc = 25nm is overestimated by about a factor of 2 by a ballistic model. By monitoring the electrons back-scattered at the source, we discuss the role of the scattering in different parts of the device.

2004 - An improved semiclassical Monte-Carlo approach for nano-scale MOSFET simulation [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Eminente, S; Esseni, David; Fiegna, C; Sangiorgi, E; Selmi, Luca
abstract

A conventional Monte-Carlo simulator has been extended to include electrostatic and transport effects that are most relevant for the analysis of nano-scale MOSFETs with either bulk or single and double gate SOI architecture and silicon film thickness down to approximately 10nm. Corrections to the self-consistent electrostatic potential and a new model for the surface roughness scattering have been included. The effectiveness of the approach has been tested simulating carrier transport in a 25nm double gate SOI MOSFET.

2004 - Comparative Analysis of Basic Transport Properties in the Inversion Layer of Bulk and SOI MOSFETs: a Monte-Carlo Study [Relazione in Atti di Convegno]
Lucci, Luca; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

2004 - Enhanced Ballisticity in nano-MOSFETs along the ITRS Roadmap: A Monte Carlo Study [Relazione in Atti di Convegno]
S., Eminente; Esseni, David; Palestri, Pierpaolo; C., Fiegna; Selmi, Luca; E., Sangiorgi
abstract

In this work we have simulated the ION and its ballistic limit I-BL of MOSFETs designed according to the 2003 Roadmap down to the 45 nm node, by using a Full-Band, self-consistent Monte Carlo simulator with quantum mechanical corrections. Our results show that scattering plays an important role by limiting the current for gate length down to at least 14 nm; the impact of quasi-ballistic transport increases for L-G below approximately 50 nm and contribute most part of the ION improvements related to scaling. Thanks to a lower transversal electric field, the DG SOI MOSFETs with low channel doping allow to get closer to the ballistic limit than bulk counterparts.

2004 - Experimental Evidence and Statistical Modeling of Cooperating Defects in Stressed Oxides [Relazione in Atti di Convegno]
Driussi, Francesco; Esseni, David; Selmi, Luca; VAN DUUREN, M. J.; Widdershoven, F.
abstract

2004 - Impact of band structure on charge trapping in thin SiO2/Al2O3/Poly-Si gate stacks [Articolo su rivista]
L., Pantisano; Lucci, Luca; E., Cartier; A., Kerber; G., Groeseneken; M., Green; Selmi, Luca
abstract

Electron and hole trapping were studied in sub-2-nm SiO2 Al2O3 poly-Si gate stacks. It was found that during substrate injection, electron trapping is the dominant mechanism. Conversely, during gate injection both hole and electron trapping can be observed, depending on the applied bias. These hot carrier effects are closely linked to the band structure of SiO2 Al2O3 poly-Si system.

2004 - Investigation of the Energy Distribution of Stress-Induced Oxide Traps by Numerical Analysis of the TAT of HEs [Articolo su rivista]
Driussi, Francesco; Iob, Romano; Esseni, David; Selmi, Luca; VAN SCHAIJK, R.; Widdershoven, F.
abstract

This paper investigates by numerical modeling the results of substrate hot electron (SHE) injection experiments in virgin and stressed devices and the corresponding increase of the contribution of HEs to the gate current due to the stress-induced oxide traps. Experimental evidence of HE trap-assisted tunneling (HE TAT) is found after Fowler-Nordheim (FN) stress and SHE stress. An accurate physically based model developed to interpret the experimental results allowed us to study the energy distribution of generated oxide traps in the two different stress regimes. It is found that degradation in HE stress conditions and FN stress conditions cannot be explained by the same trap distribution. For a given stress-induced low field leakage current, a larger concentration of traps in the top part of the oxide band gap is needed to explain HE TAT after SHE stress than after FN stress. The range of trap energy where each technique is sensitive is also identified.

2004 - Modeling, Design and Characterization of a new low Jitter Analog Dual Tuning LC-VCO PLL Architecture [Relazione in Atti di Convegno]
Nonis, Roberto; DA DALT, N; Palestri, Pierpaolo; Selmi, Luca
abstract

2004 - Nonvolatile memory cell with high programming efficiency [Brevetto]
Esseni, David; Selmi, Luca; Bez, R; Modelli, A.
abstract

2004 - On the extraction of the channel current in permeable gate oxide MOSFETs [Articolo su rivista]
Palestri, Pierpaolo; Esseni, David; Selmi, Luca; Guegan, G; Sangiorgi, E.
abstract

It is a common practice to extract the channel current in permeable gate MOSFETs as the average of the source and drain currents. This paper analyzes the extraction error associated to this procedure by means of theoretical calculations, measurements in a nMOS technology with 1.5 nm oxide thickness and a simple distributed model of the permeable gate MOSFET. The main dependencies of the extraction error on the bias conditions, the oxide thickness and the channel length are discussed in detail.

2004 - Performance, degradation monitors, and reliability of the CHISEL injection regime [Articolo su rivista]
Driussi, Francesco; Esseni, David; Selmi, Luca
abstract

2004 - Solid-State Electronics: Foreword [Articolo su rivista]
Selmi, L.
abstract

2003 - A Methodology to Extract the Channel Current of Permeable Gate Oxide MOSFETs [Articolo su rivista]
Palestri, P; Esseni, D.; Selmi, L.; Guegan, G.; Sangiorgi, E.
abstract

2003 - An Experimental Study of Mobility Enhacement in Ultra-Thin SOI Transistors Operated in Double-Gate Mode [Articolo su rivista]
Esseni, David; M., Mastrapasqua; G. K., Celler; C., Fiegna; Selmi, Luca; E., Sangiorgi
abstract

2003 - Carrier Quantization in SOI MOSFETs using an Effective Potential Based Monte-Carlo Tool [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Esseni, David; Abramo, Antonio; Clerc, R; Selmi, Luca
abstract

2003 - Device simulation for decananometer MOSFETs [Articolo su rivista]
Sangiorgi, Enrico; Palestri, Pierpaolo; Esseni, David; Fiegna, C.; Abramo, Antonio; Selmi, Luca
abstract

2003 - On the electrical monitor for device degradation in the CHISEL stress regime [Articolo su rivista]
Driussi, Francesco; Esseni, David; Selmi, Luca
abstract

2003 - Physically Based modeling of Low Field Electron Mobility in Ultrathin Single- and Double-Gate SOI n-MOSFETs [Articolo su rivista]
Esseni, David; Abramo, Antonio; Selmi, Luca; Sangiorgi, Enrico
abstract

2003 - Proceedings of the IEEE ULIS 2003 Conference [Curatela]
Selmi, Luca; Sangiorgi, E.
abstract

2003 - Quantitative Assesment of mobility degradation by Remote Coulomb Scattering in Ultra-thin oxide MOSFETs: measurement and simulations [Relazione in Atti di Convegno]
Lucci, Luca; Esseni, David; J., Loo; Y., Ponomarev; Selmi, Luca; Abramo, Antonio; Sangiorgi, Enrico
abstract

2003 - Quantitative assessment of mobility degradation by remote coulomb scattering in ultra-thin oxide MOSFETs: Measurements and simulations [Relazione in Atti di Convegno]
Lucci, L.; Esseni, D.; Loo, J.; Ponomarev, Y.; Selmi, L.; Abramo, A.; Sangiorgi, E.
abstract

In this paper we report measurements of electron effective mobility (μeff) in Ultra-Thin (UT) pure SiO2 bulk MOSFETs. A low substrate doping was intentionally used to better detect a possible μeff degradation at small Tox. New quantitative criteria were developed and used to obtain μeff measurements unaffected by either gate doping penetration or gate oxide leakage. Mobility simulations based on an improved and comprehensive Remote Coulomb Scattering (RCS) model exhibit a good agreement with the experimentally observed mobility reduction at small Tox. Our results indicate that the Polysilicon Screening is an essential ingredient to reconcile the RCS models with the experiments.

2003 - Special Issue of solid State Electronics devoted to the IEEE Ultimate Integration of Silicon (ULIS) 2003 Conference [Working paper]
Selmi, Luca; Guest, Editor
abstract

Special Issue of solid State Electronics devoted to the IEEE Ultimate Integratio

2003 - Towards Microscopic Understanding of MOSFET Reliability: the Role of Carrier Energy and Transport Simulations [Relazione in Atti di Convegno]
Selmi, Luca; Esseni, David; Palestri, Pierpaolo
abstract

2002 - A Comparative Analysis of Substrate Current Generation Mechanisms in Tunneling MOS Capacitors [Articolo su rivista]
Palestri, Pierpaolo; DALLA SERRA, Alberto; Selmi, Luca; M., Pavesi; Rigolli, P. L.; Abramo, Antonio; F., Widdershoven; Sangiorgi, Enrico
abstract

2002 - A New High Injection Efficiency Non Volatile Memory Cell: BipFlash [Articolo su rivista]
Esseni, David; Selmi, Luca; Roberto, Bez; Alberto, Modelli
abstract

2002 - Advanced Physically Based Device Modeling for Gate Current and Hot Carrier Phenomena in Scaled MOSFETs [Capitolo/Saggio]
Palestri, Pierpaolo; Selmi, Luca; DALLA SERRA, Alberto; Abramo, Antonio; Sangiorgi, Enrico; M., Pavesi; P., Rigolli; F., Widdershoven
abstract

2002 - Analytical and numerical study of the impact of HALOS on short channel and hot carrier effects in scaled MOSFETs [Articolo su rivista]
Abramo, Antonio; Selmi, Luca; Zanchetta, Sergio; Todon, A; Sangiorgi, Enrico
abstract

This paper investigates the relationship between various HALO parameters best suited to achieve short channel effect control in MOSFETs with channel lengths of ≃0.1 μm. New insights into the HALO control upon threshold voltage have been achieved by means of a simple analytical model. The analysis has been refined through extensive drift diffusion simulations based on a parametric representation of the HALO profile

2002 - Bipolar Flash Memory (BipFlash) - A new Architecture for a Non-Volatile Memory with a High Programming Efficiency [Brevetto]
Esseni, David; Selmi, Luca; R., Bez; A., Modelli
abstract

2002 - Can photon emission/absorption processes explain the substrate current of tunneling MOS capacitors ? [Articolo su rivista]
DALLA SERRA, Alberto; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper reports physically based numerical calculations on the relative importance of hot carrier induced photon emission and impact ionization in generating the substrate current of thin oxide MOS capacitors. In particular, we demonstrate that the generation efficiency of photons with energy above the band gap energy is at least 104 smaller than that of electron–hole pairs by impact ionization. Results provide a direct evidence that photon emission can not explain the substrate current which is measured during tunneling experiments from the gate, and set a lower limit to the probability of hole back-tunneling that could make anode hole injection the dominant substrate current generation mechanism in tunneling experiments from the inverted substrate.

2002 - Damage generation and location in n- and p-MOSFETs biased in the substrate-enhanced gate current regime [Articolo su rivista]
Driussi, Francesco; Esseni, David; Selmi, Luca; Fausto, Piazza
abstract

2002 - Erratum: A comparative analysis of substrate current generation mechanisms in tunneling MOS capacitors (IEEE Electron Devices (2002) 49 (1427-1435)) [Abstract in Rivista]
Palestri, P.; Serra, A. D.; Selmi, L.; Pavesi, M.; Rigolli, P. L.; Abramo, A.; Widdershoven, F.; Sangiorgi, E.
abstract

2002 - Monte Carlo simulation of program and erase charge distribution in NROM devices [Relazione in Atti di Convegno]
Ingrosso, G; Selmi, Luca; Sangiorgi, Enrico
abstract

2002 - On Interface and Oxide Degradation in VLSI MOSFETs - Part I: Deuterium Effect in CHE Stress Regime [Articolo su rivista]
Esseni, David; J. D., Bude; Selmi, Luca
abstract

This paper analyzes in detail the generation of interface states ( it) and stress-induced leakage current (SILC) during channel hot electron (CHE) stress experiments in the context of a possible hydrogen/deuterium (H/D) isotope effect. Our results show that it generation is related to the hydrogen release (HR) at the Si-SiO2 interface at relatively high where a large isotope effect is found. Instead, for gate voltages ( ) favorable for hot hole injection (HHI) the it creation becomes a unique function of hole fluence and the isotope effect disappears. In the studied stress conditions, we found no experimental evidence supporting a causal relation between SILC generation and HR because no isotope effect is observed even when the corresponding it measurements reveal a very different D/H release rate. Similar to it generation, we found that SILC becomes a unique function of hole fluence at low stress . Relevant implications and extensions of these results to the Fowler-Nordheim (FN) tunneling stress conditions are discussed in the companion paper.

2002 - On Interface and Oxide Degradation in VLSI MOSFETs, Part II: Fowler-Nordheim Stress Regime [Articolo su rivista]
Esseni, David; Bude, J.; Selmi, Luca
abstract

2002 - Phase Noise Modelling in Phase Locked Loop Frequency Synthesizer [Relazione in Atti di Convegno]
Nonis, Roberto; Palestri, Pierpaolo; DA DALT, N; Selmi, Luca
abstract

2002 - Polarity dependent charge Trapping in Thin SiO_2/Al_2O_3 Gate Stacks with Poly-Si Gate Electrodes: Influence of High Temperature Annealing [Relazione in Atti di Convegno]
Lucci, Luca; Pantisano, L.; Cartier, E.; Kerber, A.; Groeseneken, G.; Ho, M. Y.; Green, M.; Selmi, Luca
abstract

2002 - Spectroscopic Analysis of Trap Assisted Tunneling on This Oxides by Means of Substrate Hot Electron Injection Experiments [Relazione in Atti di Convegno]
Driussi, Francesco; Iob, R.; Esseni, David; Selmi, Luca; VAN SCHAIJK, R.; Widdershoven, F.
abstract

In this paper we present experimental evidence of the contribution of stress induced traps to Substrate Hot Electron (SHE) injection. We investigate the energy distribution of traps generated by Fowler Nordheim (FN) and Hot Electron (HE) stress with the aid of simulations and experiments. Results suggest that HE stress generates more oxide traps at high energy with respect to FN stress. The comparison between experiments and simulations also provides a new additional evidence of the inelastic nature of the trap assisted tunneling mechanism.

2002 - Spontaneous hot carrier photon emission rates in silicon: improved modeling and application to metal oxide semiconductor devices [Articolo su rivista]
Pavesi, M; Rigolli, Pl; Manfredi, M; Palestri, Pierpaolo; Selmi, Luca
abstract

The recent publication of controversial experimental evidence on the origin of hot-carrier currents in 4-10 nm tunnel metal oxide semiconductor capacitors renewed the interest in improving hot-carrier luminescence models for silicon devices. This work presents several such improvements, aimed at making possible a physically based analysis of the hot-carrier luminescence effects taking place during tunneling experiments in relatively thick SiO2 layers. To this purpose, silicon band structure and scattering rate calculations have been extended well above 10 eV by considering eight conduction bands, instead of the usual four, so as to allow for a detailed description of the high-energy carriers injected from silicon into silicon dioxide during tunneling experiments. The absolute contributions of the direct and phonon-assisted, interband and intraband transitions of electrons and holes to the total photon emission rate are analyzed, so the results can be directly compared with the experimental data. To the best of our knowledge, it is for the first time that results for valence-to-valence band transitions of holes are presented and compared with those of conduction-to-conduction band transitions of electrons. Results can be directly compared with experimental data. Template results obtained with a variety of carrier distributions (Maxwellian, Gaussian, and Dirac's delta-like) are shown and implications for device analysis are discussed.

2002 - Study of low field electron transport in ultra-thin single and double gate SOI MOSFETs [Relazione in Atti di Convegno]
Esseni, David; Abramo, Antonio; Selmi, Luca; Sangiorgi, Enrico
abstract

2002 - Ultra Thin SOI Transistors for Ultimate CMOS Technology: Fundamental Properties and Application Perspectives [Relazione in Atti di Convegno]
Esseni, David; Mastrapasqua, M; Fiegna, C; Celler, G; Selmi, Luca; Sangiorgi, E.
abstract

2001 - An Experimental Study of Low Field Electron Mobility in Double-Gate, Ultra-Thin SOI MOSFETs [Relazione in Atti di Convegno]
Esseni, David; M., Mastrapasqua; C., Fiegna; G. K., Celler; Selmi, Luca; Sangiorgi, Enrico
abstract

2001 - BipFLASH: a Novel Non-Volatile Memory Cell Concept for High Speed - Low Power Applications [Articolo su rivista]
Esseni, David; Selmi, Luca
abstract

We present a novel non-volatile memory cell architecture, which remarkably improves injection efficiency overconventional channel hot electron programming. We show how this superior performance can be traded to achieve either lowvoltage-low power or high-speed operation. The cell concept is validated by means of numerical device simulations. Criteriafor device optimization are also discussed.

2001 - Can Photon Emission / Absorption Processes Explain the Substrate Current of Tunneling MOS Capacitors? [Relazione in Atti di Convegno]
DALLA SERRA, A.; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper reports physically based numerical calculations on the relative importance of hot carrier induced photon emission and impact ionization in generating the substrate current of thin oxide MOS capacitors. In particular, we demonstrate that the generation efficiency of photons with energy above the band gap energy is at least 10-4 smaller than that of electron-hole pairs by impact ionization. Results provide a direct evidence that photon emission can not explain the substrate current which is measured during tunneling experiments from gate, and set a lower limit to the probability of hole back-tunneling that could make anode hole injection the dominant substrate current generation mechanism in tunneling experiments from the inverted substrate.

2001 - Closed- and Open- boundary Models for Gate-Current calculation in n-MOSFETs [Articolo su rivista]
DALLA SERRA, Alberto; Abramo, Antonio; Palestri, Pierpaolo; Selmi, Luca; Widdershoven, F.
abstract

2001 - Experimental Study of Low Voltage Anode Hole Injection in Thin Oxides [Relazione in Atti di Convegno]
Esseni, David; Bude, J; Selmi, Luca
abstract

2001 - Hot Hole Gate Current in Surface Channel p-MOSFETs [Articolo su rivista]
Driussi, Francesco; Esseni, David; Selmi, Luca; Piazza, F.
abstract

2001 - Low Field Electron and Hole Mobility of SOI Transistors Fabricated on Ultra-Thin Silicon Films for Deep Sub-Micron Technology Application [Articolo su rivista]
Esseni, David; Mastrapasqua, M.; Celler, G.; Fiegna, C.; Selmi, Luca
abstract

2001 - Measurements of Low Field Mobility in Ultra Thin SOI n- and p-MOSFETs [Articolo su rivista]
Mastrapasqua, M; Esseni, David; CELLER G., K; Fiegna, C; Selmi, Luca; Sangiorgi, Enrico
abstract

2001 - Measurements of Low field mobiliy in ultra-thin SOI n- and p-mosfets [Relazione in Atti di Convegno]
Mastrapasqua, M; Esseni, D; Celler, G; Baumann, F; Fiegna, C; Selmi, L; Sangiorgi, E
abstract

2001 - Microelectronic Engineering: Preface [Relazione in Atti di Convegno]
Sangiorgi, E.; Selmi, L.
abstract

2001 - Microelectronic Engineering Special Issue devoted to the 2001 Insulating Films on Semiconductors Conference, INFOS 2001 [Curatela]
Selmi, Luca; Sangiorgi, Enrico
abstract

2001 - Microscopic Analysis of the Impact of Substrate Bias on the Gate Current of pMOSFETs [Relazione in Atti di Convegno]
Zanchetta, Sergio; Esseni, David; Palestri, Pierpaolo; Selmi, Luca
abstract

This paper presents a detailed numerical investigation of the recently reported phenomenon of substrate enhanced hole gate current in deep submicron pMOS transistors [1]. To this purpose, full-band Monte Carlo simulations of carrier heating and injection in the gate oxide have been carried out at different substrate voltages. Results are in good qualitative agreement with previously reported measurements, and provide a clear microscopic picture to explain the experimentally observed features of electron and hole gate currents in pMOS devices.

2001 - Mobility in Single and Double Gate Ultra-Thin SOI MOSFETs [Relazione in Atti di Convegno]
Esseni, David; M., Mastrapasqua; C., Fiegna; G. K., Celler; Selmi, Luca; E., Sangiorgi
abstract

2001 - Non-local microscopic view of signal propagation times in BJTs biased up to high currents [Articolo su rivista]
Palestri, Pierpaolo; Selmi, Luca
abstract

This paper presents a microscopic analysis of signal propagation delay in bipolar transistors featuring relevant non-equilibrium transport effects. First, the physical mechanisms responsible of signal delay are reviewed. A novel technique to extract signal delays from self-consistent Monte Carlo device simulations is presented. These results are then used for a physically based comparison between compact quasi-static delay formulas and more accurate particle simulations carried out over a broad range of collector currents.

2001 - On the Extraction of Oxide Thickness and Sub-Band Energy Shift in Thin Oxide MOS Capacitors with Permeable Gates [Relazione in Atti di Convegno]
DALLA SERRA, Alberto; Palestri, Pierpaolo; Selmi, Luca; Widdershoven, F.
abstract

2000 - A better insight in the performance of silicon bjt's featuring highly non-uniform collector doping profiles [Articolo su rivista]
Palestri, Pierpaolo; Fiegna, C.; Selmi, Luca; Peter, M. S.; Hurkx, G. A. M.; Slotboom, J. W.; Sangiorgi, Enrico
abstract

This paper investigates the effects of highly nonuniform collector doping profiles on the speed and breakdown performance of silicon bipolar transistors. Monte Carlo and drift diffusion simulation results point out that a thin highly doped layer adjacent to the base collector junction can improve the device cut off frequency without deteriorating significantly the maximum oscillation frequency and the breakdown voltage, provided the voltage drop across this layer is lower than an effective threshold of approximately 1.2 V. Guidelines are given for choosing the doping, position, and thickness of this layer.

2000 - A comparison between semi-classical and quantum-mechanical escape-times for gate current calculations [Relazione in Atti di Convegno]
DALLA SERRA, Alberto; Abramo, Antonio; Palestri, Pierpaolo; Selmi, Luca
abstract

2000 - A Monte Carlo Technique to Investigate Signal Delays of Advanced Si BJT's up to High Currents [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Selmi, Luca; G. A. M., Hurkx; J. W., Slotboom
abstract

We present a new Monte Carlo technique to investigate the signal delay of advanced BJTs featuring relevant non-local effects. The method is suited to analyze base and collector signal delays in presence of significant nonequilibrium transport effects and up to high currents, and to verify the physical meaning and applicability of delay expressions for compact models.

2000 - Cathode Hot Electrons and Anode Hot Holes in Tunneling MOS Capacitors [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Selmi, Luca; Sangiorgi, Enrico; M., Pavesi; F., Widdershoven
abstract

2000 - Coupled Monte Carlo Simulation of Si and SiO2 Transport in MOS Capacitors [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Selmi, Luca; M., Pavesi; F., Widdershoven; Sangiorgi, Enrico
abstract

We present a Monte Carte (MC) model comprising SiO2 and Si transport, suitable to simulate carrier multiplication in MOS structures. The code extends full-band density of states (DoS) and scattering rate calculations in silicon up to high energy. Simulations of 5-15 nn oxides for Non Volatile Memory applications demonstrate the role of oxide transport on the distribution of the holes generated by impact ionization, which are often regarded as the origin of oxide degradation, SILC and breakdown.

2000 - Deuterium Effect on Interface States and SILC Generation in the CHE Stress Conditions: A Comparative Study [Relazione in Atti di Convegno]
Esseni, David; Bude, J.; Selmi, Luca
abstract

This paper investigates the generation of interface states (N/sub it/) and stress induced leakage current (SILC) in the stress regime of channel hot electrons (CHE) and the possible beneficial effect of deuterium annealing. Our results show that no isotope effect is observed on SILC even when a large isotope effect is simultaneously observed on N/sub it/. The generation of SILC seems to be always correlated to hot holes injection (HHI) whereas two different generation mechanisms for N/sub it/ can be identified.

2000 - European Patent application no.00830546.8, filing date july 31 2000 [Working paper]
Esseni, David; Selmi, Luca; Bez, R.; Modelli, A.
abstract

2000 - Hot carrier degradation and damage profiling of cmos devices with biased substrates [Relazione in Atti di Convegno]
Driussi, Francesco; Esseni, David; Piazza, F.; Selmi, Luca
abstract

2000 - Hot Carrier Effects in MOS capacitors: Improvements in Coupled Monte Carlo Simulations of Si and SiO2 Transport [Abstract in Atti di Convegno]
P., Rigolli; M., Manfredi; M., Pavesi; Palestri, Pierpaolo; Selmi, Luca
abstract

2000 - Impact Ionization and Photon Emission in MOS Capacitors and FETs [Relazione in Atti di Convegno]
Palestri, Pierpaolo; M., Pavesi; P., Rigolli; Selmi, Luca; DALLA SERRA, Alberto; Abramo, Antonio; F., Widdershoven; Sangiorgi, Enrico
abstract

2000 - Injection Efficiency of CHISEL Gate Currents in Short MOS Devices: Physical Mechanisms, Device Implications and Sensitivity to Technological Parameters", [Articolo su rivista]
Esseni, David; Selmi, Luca; A., Ghetti; Sangiorgi, Enrico
abstract

This paper analyzes MOSFET gate currents in the so-called channel initiated secondary electron injection regime (CHISEL). A Monte Carlo model of the phenomenon is validated and then extensively used to explore CHISEL scaling laws. Results indicate that, compared to conventional channel hot electron injection (CHE), CHISEL exhibits a weaker dependence on channel length and a larger sensitivity to short channel effects. These results are confirmed experimentally and exhaustively explained with the help of simulations; furthermore, some of their possible detrimental consequences on the programming efficiency of CHISEL based flash cells are analyzed. Finally, the impact of channel doping, oxide thickness, and junction depth on CHISEL efficiency has been explored, and guidelines to maintain high injection efficiency in short devices are derived.

2000 - Low Field Mobility of Ultra Thin SOI n- and p-MOSFETs: Measurement and Implications on the Performance of Ultra Short MOSFETs [Relazione in Atti di Convegno]
Esseni, D.; Mastrapasqua, M.; Celler, G. K.; Baumann, F. H.; Fiegna, C.; Selmi, L; Sangiorgi, E.
abstract

Electron and hole effective mobilities of ultra-thin SOI N- and P-MOSFETs have been measured at different temperatures using a special test structure able to circumvent parasitic resistance effects. At large inversion densities (N/sub inv/) ultra-thin SOI mobility can be higher than in heavily doped bulk MOS due a lower effective field and it is largely insensitive to silicon thickness (T/sub SI/). However, at small Ni/sub inv/ the mobility is clearly reduced for decreasing T/sub SI/. The effective mobility data are used to study the implications for ultra-short MOS transistor performance at device simulation level.

2000 - Monte Carlo Analysis of Signal Delays in BJTs [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Selmi, Luca; Sangiorgi, E.
abstract

NA

2000 - Non Local Electron and Hole Impact Ionization in Advanced Si BJTs [Working paper]
Palestri, Pierpaolo; Selmi, Luca; Hurkx, G. A. M.; Slotboom, J. W.; Terpstra, D; Peter, M; Woltjer, R; Sangiorgi, Enrico
abstract

This report describes a modeling and experimental study of electron and hole impact ionization in silicon bipolar transistors. A method is developed to extract simultaneously the effective field (carrier temperature) dependent electron and hole ionization coefficients from multiplication coefficient data. A simple non local impact ionization model for electrons and holes is developed and the model parameters are extracted by means of comparison with accurate Monte Carlo calculations. The model is used to predict the breakdown voltage of Zener diodes as well as collector-base and collector emitter breakdown voltages of a variety of silicon BJT's fabricated with the SUBILO and DOUBLE POLY processes. The operational validity limits of the model are also assessed by means of calculations on template rectangular and triangular field profiles of varying depletion-region-extension and peak-electricfield -value. The activities were carried out as part of Philips Nat. Labs. cooperation with DIEGM, University of Udine, Italy. Conclusions: In summary, our analysis of electron and hole impact ionization in advanced bipolar devices and Zener diodes concentrated on the following subjects: # Koninklijke Philips Electronics N.V. 2000 iii .

2000 - Observation of a new hole gate current component in p(+)-poly gate p-channel MOSFET's [Relazione in Atti di Convegno]
Driussi, Francesco; Esseni, David; Selmi, Luca; Piazza, F.
abstract

This paper reports experimental evidence of a new, substrate-enhanced component of the gate current of p+ -poly gate pMOS transistors. The phenomenon is characterized as a function of drain, gate and substrate bias on devices featuring three different drain engineering options. The new current component is ascribed to an impact ionization feedback mechanism similar to that responsible of CHISEL in nMOSFETs.

2000 - Short channel and hot carrier performance of ULSI MOSFETs with halo structures [Relazione in Atti di Convegno]
A., Todon; Selmi, Luca; Abramo, Antonio; Sangiorgi, Enrico
abstract

2000 - Substrate enhanced degradation of cmos devices [Relazione in Atti di Convegno]
Driussi, Francesco; Esseni, David; Selmi, Luca; F., Piazza
abstract

2000 - Substrate Enhanced Gate Currents in CMOS Devices [Relazione in Atti di Convegno]
Driussi, Francesco; Esseni, David; Selmi, Luca; F., Piazza; Sangiorgi, Enrico
abstract

2000 - Tunnelling Injection in Thin Oxide MOS Capacitors [Relazione in Atti di Convegno]
. DALLA SERRA, A.; Abramo, Antonio; Palestri, Pierpaolo; Selmi, Luca; Sangiorgi, E.
abstract

In this paper the semi-classical and quantum-mechanical definitions of escape-time from quasi-bound states have been compared in the frame of MOSFET gate leakage-current calculations. The theoretical background and the numerical issues involved in the implementation of these approaches inside device simulators have been compared. Results on many different thin gate-oxide capacitors, and on a special purpose test structure with mercury-probe contact, point out that the semi-classical approach is faster, less demanding from the numerical point of view, and surprisingly accurate compared to the fully quantum-mechanical treatment of more physically-sound models.

2000 - Two-dimensional quantum mechanical aspects in the charge distribution of ULSI silicon MOSFETs [Relazione in Atti di Convegno]
Abramo, Antonio; A., Cardin; Selmi, Luca; Sangiorgi, Enrico
abstract

2000 - Two-dimensional quantum mechanical simulation of charge distribution in silicon MOSFETs [Articolo su rivista]
Abramo, Antonio; Cardin, A.; Selmi, Luca; Sangiorgi, Enrico
abstract

2000 - Well-tempered MOSFETs: 1D versus 2D quantum analysis [Relazione in Atti di Convegno]
Abramo, Antonio; Selmi, Luca; Yu, Z; Dutton, R.
abstract

1999 - A Better Understanding of Substrate Enhanced Gate Current in VLSI MOSFET's and Flash Cells - Part I: Phenomenological Aspects [Articolo su rivista]
Esseni, David; Selmi, Luca
abstract

N/A

1999 - A Better Understanding of Substrate Enhanced Gate Current in VLSI MOSFET's and Flash Cells - Part II: Physical Analysis [Articolo su rivista]
Selmi, Luca; Esseni, David
abstract

In this work different physical mechanisms that could lead to the direct proportionality between la and IB highlighted in Part I as the signature of substrate enhanced electron injection (SEEI), are analyzed in detail. By means of experiments and simulations we substantiate the current interpretation of SEEI in terms of an impact ionization feedback process and attribute a quantitatively negligible role to both drain avalanche hot electron injection and substrate electrons generated by the photons emitted by channel hot electrons. These experiments reconcile the current explanation of SEEI with the well known phenomenon of photon assisted minority carrier injection in the substrate, whose presence is clearly detectable in our devices, but whose impact on the gate current is estimated to be orders of magnitude smaller than that of impact ionization feedback.

1999 - Analysis of highly non-uniform collector doping profiles for the optimization of the breakdown / speed trade off in advanced BJTs [Working paper]
Palestri, Pierpaolo; Fiegna, C; Selmi, Luca; PETER M., S; HURKX G. A., M; SLOTBOOM J., W; Sangiorgi, Enrico
abstract

Philips Research Nat. Laboratories Report 808/99

1999 - Evidence of Substrate Enhanced High Energy Tails in the Distribution Function of Deep Submicron MOSFETs by Light Emission Measurements [Articolo su rivista]
Pavesi, M; Selmi, Luca; Manfredi, M; Sangiorgi, Enrico; Mastrapasqua, M; Bude, J.
abstract

1999 - Low Voltage Hot Electrons and Soft-programming Lifetime Prediction in Non-Volatile Memory Cells [Articolo su rivista]
Ghetti, A; Selmi, Luca; Bez, R.
abstract

1999 - On the Optimization of HALOs for 0.1 micron MOSFETs and Below [Relazione in Atti di Convegno]
Todon, A; Selmi, Luca; Abramo, Antonio; Sangiorgi, Enrico
abstract

1999 - Physical Aspects of Cell Operation and Reliability [Capitolo/Saggio]
Selmi, Luca; Fiegna, C.
abstract

This chapter overviews the basic physical effects involved in programming and erasing of Flash memory cells, to provide the background for a deeper understanding of their operation and reliability. In particular, tunnelling and high field transport are treated and the associated phenomena in MOS-FETs and Flash cells are described by means of measurements and simulations. Device degradation induced by charge injection into thin silicon dioxide layers is also briefly discussed.

1999 - The scaling properties of CHISEL and CHE injection efficiency in MOSFETs and FLASH memory cells [Relazione in Atti di Convegno]
Esseni, David; Selmi, Luca; Ghetti, A; Sangiorgi, E.
abstract

1998 - Energy Dependent Electron and Hole Impact Ionization in Si Bipolar Transistors [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Selmi, Luca; Hurkx, F; Slotboom, J; Sangiorgi, Enrico
abstract

This paper describes a self-consistent procedure to extract energy dependent electron (/spl alpha/) and hole (/spl beta/) ionization coefficients directly from electrical measurements of multiplication factors (M/sub n/ and M/sub p/, respectively) carried out on a single reversed junction in a bipolar device. The extracted /spl alpha/ and /spl beta/ coefficients are used to accurately calculate breakdown voltages in a variety of bipolar devices. Results point out the role of holes and of non-local hole heating on the avalanche characteristics of modern bipolar devices.

1998 - Esercizi d’Esame di Elettronica Digitale [Monografia/Trattato scientifico]
FRANCHI SCARSELLI, E; Selmi, Luca
abstract

1998 - Experimental Signature and Physical Mechanisms of Substrate Enhanced Gate Current in MOS Devices [Relazione in Atti di Convegno]
Esseni, David; Selmi, Luca
abstract

This paper examines in detail the phenomenon of Substrate Enhanced Electron Injection (SEEI). By using floating gate devices less aggressively scaled than the MOSFETs of Bude (1995) we are able to: (1) develop criteria to separate SEEI from the coexisting channel hot electron (CHE) injection; (2) point out a direct proportionality between the gate (I/sub G/) and the substrate (I/sub B/) currents that provides a signature of SEEI; (3) reconcile SEEI with reported mechanisms of optical minority carrier generation in the substrate.

1998 - Monitoring Hot Carrier Degradation in SOI MOSFETs by Hot Carrier Luminescence Techniques [Articolo su rivista]
Selmi, Luca; Pavesi, M; WONG H., S; Acovic, A; Sangiorgi, Enrico
abstract

1998 - Optimization Guidelines for Epitaxial Collectors of Advanced BJT’s with Improved Breakdown Voltage and Speed [Relazione in Atti di Convegno]
Palestri, Pierpaolo; Fiegna, C; Selmi, Luca; Hurkx, F; Slotboom, J; Sangiorgi, Enrico
abstract

1998 - The Impact of Device Design on the Substrate Enhanced Gate Current of VLSI MOSFET's [Relazione in Atti di Convegno]
Esseni, David; Selmi, Luca; Bez, R.
abstract

1998 - Verification of Electron Distributions in Silicon by means of Hot-Carrier Luminescence Measurements [Articolo su rivista]
Selmi, Luca; Mastrapasqua, M; Boulin, D. M; Bude, J; Pavesi, M; Sangiorgi, E; Pinto, M. R.
abstract

1997 - Bias and Temperature Dependence of Homogeneous Hot-Electron Injection from Silicon into Silicon Dioxide at Low Voltages [Articolo su rivista]
Fischer, B; Ghetti, A; Selmi, Luca; Bez, R; Sangiorgi, Enrico
abstract

1997 - Trade-offs between tunneling and Hot-Carrier Injection in short channel Floating Gate MOSFETs [Articolo su rivista]
Selmi, Luca; Ghetti, A; Bez, R; Sangiorgi, E.
abstract

1996 - An Improved Test Structure to Characterize Ultra- Low Hot Carrier Injection in Homogeneous Conditions [Relazione in Atti di Convegno]
Selmi, Luca; Bez, R; Sangiorgi, Enrico
abstract

1996 - Characterization of the Transient Behavior of a GaAs MESFET Using Dynamic I-V and S-parameter Measurements [Articolo su rivista]
Begin, M; GHANNOUCHI F., M; Beauregards, F; Selmi, Luca; Ricco, B.
abstract

Dynamic I-V and S-parameter characterization of a medium-power MESFET is presented. In particular, this paper presents an innovative fully automated six-port network analyzer (SPNA) operated in pulse conditions. The results reveal the transient behavior of the GaAs MESFET under pulse conditions which may be attributed to self-heating and/or trap-related anomalies. Furthermore, using standard procedure, these S-parameters could readily be used to extract the dynamic electrical model elements (Cgs, Cgd, Gds, Gm , etc.) of the MESFET. This system is particularly suitable for studying trap-related phenomena and self-heating effects in GaAs devices and for large-signal/power characterization.

1996 - Electron Injection in the Gate Oxide of MOS Structures at Liquid Nitrogen Temperature: Measurement and Simulation [Articolo su rivista]
Fischer, B; Selmi, Luca; Ghetti, A; Sangiorgi, Enrico
abstract

1996 - Hot-carriers at low voltages: New experimental evidences and open issues [Relazione in Atti di Convegno]
Selmi, Luca; Fischer, B; Ghetti, A; Bez, R.
abstract

1996 - Monte Carlo Simulation of Low Voltage Hot Carrier Effects in Non Volatile Memory Cells [Relazione in Atti di Convegno]
Ghetti, A; Selmi, Luca; Bez, R; Sangiorgi, Enrico
abstract

1995 - A Comparative Study of Hot-Carrier Induced Light Emission and Degradation in Bulk and SOI MOSFETs [Relazione in Atti di Convegno]
Selmi, Luca; Pavesi, M; WONG H., S; Acovic, A; Sangiorgi, Enrico
abstract

1995 - Characterization and Modeling of Hot-Carrier Luminescence in Silicon n+/n/n+ Devices [Relazione in Atti di Convegno]
Selmi, Luca; Mastrapasqua, M; BOULIN D., M; Bude, J; Manfredi, M; Sangiorgi, Enrico; Pinto, M. R.
abstract

1995 - Frequency Resolved Measurements for the Characterization of MOSFET Parameters at Low Longitudinal Fields [Articolo su rivista]
Selmi, Luca; Ricco, B.
abstract

A new technique is presented to extract the main parameters required for transistor modeling at low longitudinal fields (parasitic resistance, intrinsic conductivity factor, threshold voltage, and body factor k) from a single MOSFET. The method makes use of easy-to-perform ac frequency-resolved measurements to overcome repeatability and accuracy problems encountered with de data. The technique has been satisfactorily validated on MOSFET's down to 0.8 mu m channel length.

1995 - Non-Local Effects in p-MOSFET Substrate Hot Hole Injection Experiments [Articolo su rivista]
Selmi, Luca; Sangiorgi, Enrico; Bez, R.
abstract

1995 - Silicon Luminescence Techniques for the Characterization of Hot-Carrier and Degradation Phenomena in MOS Devices [Articolo su rivista]
Selmi, Luca
abstract

1995 - Soft Programming in Scaled Flash EEPROM Cells [Relazione in Atti di Convegno]
Esseni, David; Selmi, Luca; Bez, R; L. RAVAZZI, L; Sangiorgi, E.
abstract

1995 - Temperature Dependence of Gate and Substrate Currents in the CHE Crossover Regime [Articolo su rivista]
Esseni, David; Selmi, Luca; Sangiorgi, E; Bez, R; Ricco, B.
abstract

1994 - A combined transport-injection model for hot-electron and hot-hole injection in the gate oxide of MOS structures [Relazione in Atti di Convegno]
A., Ghetti; Selmi, Luca; Sangiorgi, Enrico; Abramo, Antonio; F., Venturi
abstract

1994 - A Test Chip and an Accurate Measurement System to Characterize Hot Hole Injection in the Gate Oxide of p-MOSFET’s [Relazione in Atti di Convegno]
Selmi, Luca; Sangiorgi, Enrico; Bez, R; Ricco, B.
abstract

1994 - A Test Pattern to Investigate the Effect of Capping Layers on the Hot Carrier Induced Photon Spectra of MOSFET’s [Relazione in Atti di Convegno]
Lanzoni, M; Selmi, Luca; Bez, R; Manfredi, M.
abstract

1994 - AC Frequency Resolved Measurements for Direct Extraction of the Parasitic Resistance of Individual MOSFETs [Relazione in Atti di Convegno]
Selmi, Luca; Alfieri, A; Ricco, B.
abstract

1994 - Bias and Temperature Dependence of Gate and Substrate Currents in n-MOSFETs at Low Drain Voltage [Relazione in Atti di Convegno]
Esseni, David; Selmi, Luca; R., Bez; Sangiorgi, Enrico; B., Ricco
abstract

1994 - Characterization of Transient Effects in the S-Parameters of GaAs MESFETs by means of Pulsed Measurements [Relazione in Atti di Convegno]
Begin, M; GHANNOUCHI F., M; Beauregard, F; Selmi, Luca; Ricco, B; Borelli, V.
abstract

1994 - Comments on “Oxide-Field Dependence of Electron Injection from Silicon into Silicon Dioxide” [Articolo su rivista]
Fischetti, M. V.; Fiegna, C.; Sangiorgi, E.; Selmi, L.
abstract

In the study of electron injection from Si into S1O2 one would reach conclusions vastly different from those of the above paper when accounting for a realistic density-of-states in Si at high electron energy and employing a hetter approximation for the probability of transmission across the Si-SiO2 interface. © 1994, IEEE. All rights reserved.

1994 - Correlation between Substrate Hot Electron Energy and Homogeneous Degradation in n-MOSFETs [Articolo su rivista]
Selmi, Luca; Fiegna, C; Bez, R.
abstract

1994 - Experimental Analysis of Polarization in the Hot-Carrier Luminescence of Silicon Devices [Relazione in Atti di Convegno]
Selmi, Luca; Pieracci, A; Lanzoni, M; Pavesi, M; Bez, R; Sangiorgi, Enrico
abstract

1994 - Instanteneous S parameters measurements of MESFETs under burst bias conditions [Relazione in Atti di Convegno]
Begin, F; GHANNOUCHI F., M; Selmi, Luca; Ricco, B.
abstract

An innovative Six-Port Network Analyzer (SPNA) for characterizing GaAs MESFETs under pulsed bias and RF conditions is presented in this paper. This SPNA allows the measurements of instantaneous S parameters of microwave active devices. These S parameters may then be used to extract the electrical model elements (Cgs, Cgd, Gds, Gm, etc.) of the MESFET using standard procedures [1]. This system is particularly suitable for studying trapping and self-heating effects in GaAs devices.

1994 - Instanteneous S parameters measurements of MESFETs under burst bias conditions [Relazione in Atti di Convegno]
Begin, M.; Ghannouchi, F. M.; Selmi, L.; Ricco, B.
abstract

An innovative Six-Port Network Analyzer (SPNA) for characterizing GaAs MESFETs under pulsed bias and RF conditions is presented in this paper. This SPNA allows the measurements of instantaneous S parameters of microwave active devices. These S parameters may then be used to extract the electrical model elements (Cgs, Cgd, Gds, Gm, etc.) of the MESFET using standard procedures [1]. This system is particularly suitable for studying trapping and self-heating effects in GaAs devices.

1993 - A Study of Injection Conditions in the Substrate Hot Electron Induced Degradation of n-MOSFETs [Relazione in Atti di Convegno]
Selmi, Luca; Fiegna, C; Bez, R; Sangiorgi, Enrico; Ricco, B.
abstract

1993 - Design of an X-band, Transformer Coupled Amplifier with improved Stability and Layout [Articolo su rivista]
Selmi, Luca; B., Ricco'
abstract

1993 - Experimental Application of a Novel Technique to Extract Gate Bias Dependent Source and Drain Parasitic Resistances of GaAs MESFETs [Articolo su rivista]
Menozzi, R; Cova, P; Selmi, Luca
abstract

1993 - Investigation of Hot Electron Luminescence in Silicon by means of Dual Gate MOS Structures [Relazione in Atti di Convegno]
Selmi, Luca; WONG H., S; Sangiorgi, Enrico; Lanzoni, M; Manfredi, M.
abstract

1993 - Measurement of the Hot Hole Injection Probability from Si Into SiO2 in p-MOSFET’s [Relazione in Atti di Convegno]
Selmi, Luca; Sangiorgi, Enrico; Bez, R; Ricco, B.
abstract

1993 - Modelling temperature effects in the DC I-V characteristics of GaAs MESFETs [Articolo su rivista]
Selmi, Luca; Ricco, B.
abstract

This paper presents a simple model to account for the main temperature effects influencing the dc performance of GaAs MESFET's. The model is based on a consistent solution of heat flow and current equations, that accounts for nonuniform power dissipation within the device. The simulation results are satisfactorily compared with experimental data obtained with pulsed and dc measurements performed on conventional devices as well as on suitable test structures.

1993 - Oxide Field Dependence of Electron Injection From Silicon into Silicon Dioxide [Articolo su rivista]
Selmi, Luca; Sangiorgi, Enrico; Fiegna, C.
abstract

1993 - Photon emission from sub-micron p-channel mosfets biased at high fields [Relazione in Atti di Convegno]
Selmi, L.; Lanzoni, M.; Bigliardi, S.; Sangiorgi, E.
abstract

In this paper we report the first experimental data on hot carrier luminescence in silicon p-channel MOS transistors featuring sub-micron gate length. All the terminal currents of the devices (including the gate and substrate currents) were also measured, and their dependence on the applied bias is analyzed and compared to that of the emitted light intensity.

1992 - Analysis of Uniform Degradation in n-MOSFETs [Relazione in Atti di Convegno]
Selmi, Luca; Fiegna, C; Sangiorgi, Enrico; Bez, R; Ricco, B.
abstract

1992 - Hot-electron-induced photon energies in n-channel MOSFET's operating at 77 and 300 K [Articolo su rivista]
Lanzoni, Massimo; Manfredi, M.; Selmi, L.; Sangiorgi, Enrico; Capelletti, R.; Ricco, Bruno
abstract

A detailed experimental study of the spectral distribution of hot-electron-induced photon emission in n-channel MOSFETs is presented. The study significantly improves on previous work by considering energies up to 3.1 eV and different operating temperatures. It is shown that in contrast with previous results, the photon energy distribution is markedly non-Maxwellian, thus suggesting that the same is true for the energy distribution of the channel electrons.

1992 - Numerical Analysis of the Gate Voltage Dependence of the Series Resistances and Effective Channel Length in sub-micron GaAs MESFETs [Articolo su rivista]
Selmi, Luca; Menozzi, R; Gandolfi, P; Ricco, B.
abstract

1992 - Photon Emission from sub-micron p-channel MOSFETs Biased at High Fields [Relazione in Atti di Convegno]
Selmi, Luca; Lanzoni, M; Bigliardi, S; Sangiorgi, Enrico
abstract

1992 - Problematiche di affidabilità [Relazione in Atti di Convegno]
Selmi, Luca
abstract

Questo articolo descrive i principali fenomeni fisici in grado di degradare o danneggiare in modo permanente i circuiti integrati, limitandone l'affidabilità. In particolare verranno trattati quei problemi delle tecnologie MOS e BiCMOS che per il loro carattere fondamentale rimarranno di attualità anche nelle future versioni di queste tecnologie. Non verranno trattati, invece, i fenomeni responsabili di errori transitori (soft-errors), quali l'interazione tra dispositivi e radiazione ionizzante nella circuiteria e nelle celle delle memorie RAM dinamiche.

1992 - Small Signal MMIC Amplifiers with Bridged T-coil Matching Networks [Articolo su rivista]
Selmi, Luca; ESTREICH D., B; Ricco', B.
abstract

1991 - Adjacent structure interactions in latch-up dc triggering of CMOS twin-tub and epitaxial technologies [Relazione in Atti di Convegno]
Pavan, Paolo; Zanoni, E.; Menozzi, R.; Selmi, L.
abstract

In this paper a bulk twin-tub and an epitaxial CMOS technology are studied from the viewpoint of latch-up hardness reduction due to interaction between adjacent structures, by means of static triggering measurements performed on "ad hoc" test patterns. The experimental results indicate that such interactions can seriously increase the latch-up susceptibility of the devices under test in the case of the bulk twin-tub process, while the epitaxial one shows in general better stability of the latch-up behavior.

1991 - Adjacent structure interactions in the Latch-up triggering of CMOS twin-tub and epitaxial technologies [Relazione in Atti di Convegno]
Pavan, P; Zanoni, E; Menozzi, R; Selmi, Luca
abstract

1991 - Application of Bridged T-coils to the design of Multiplicative Gain MMIC Amplifiers [Relazione in Atti di Convegno]
Selmi, Luca; Estreich, D; Ricco, B.
abstract

1991 - Effects of the interaction of neighboring structures on the Latch-up behavior of C-MOS ICs [Articolo su rivista]
Menozzi, R; Selmi, Luca; Sangiorgi, Enrico; Ricco, B.
abstract

An experimental investigation on the interaction between different parasitic devices in CMOS ICs from the point of view of latchup triggering is outlined. The study, carried out by means of ad hoc test structures, shows that this interaction: (a) can lead to significant increase in latchup susceptibility; (b) can involve devices very distant from one another; and (c) is not always suppressed by guard ring protections. The main features of the experimental results are discussed and explained

1991 - Extraction of the Series Resistances and Effective Channel Length of GaAs MESFETs by means of Electrical Methods [Relazione in Atti di Convegno]
Menozzi, R; Selmi, Luca; Gandolfi, A; Ricco, B.
abstract

The authors present a numerical study on electrical methods to measure the source and drain resistances and the effective channel length of state-of-the-art gallium arsenide MESFETs. In particular, the effects of scaling on the physical meaning and gate voltage dependence of the extracted values are investigated. Fringing effects at the gate edges are found to be responsible for a substantial bias dependence of the series resistances, and hence for possible inaccuracies of extraction procedures that overlook such phenomena. A novel extraction technique is also proposed to overcome in part the limitations of conventional approaches.

1991 - Logiche di tipo BiCMOS [Articolo su rivista]
B., Riccò; M., Favalli; Selmi, Luca
abstract

Il lavoro presenta una panoramica dei principali aspetti relativi ai circuiti logici realizzati in tecnologia bipolare-CMOS (BiCMOS). In particolare, dopo una breve descrizione dei processi tecnologici, si discutono in qualche dettaglio i principali schemi elettrici utilizzati per la realizzazione dei gate. Inoltre, si introduce un modello analitico semplificato per il dimensionamento di massima dei circuiti, che è stato confrontato con i risultati di simulazioni circuitali.

1991 - Thermal Characterization of GaAs MESFETs by means of Pulsed Measurements [Relazione in Atti di Convegno]
Selmi, Luca; Ricco, B.
abstract

1990 - An accurate System for automated On-wafer Characterization of Three-port Devices [Relazione in Atti di Convegno]
Selmi, Luca; Estreich, D. B.
abstract

A general-purpose system for fast, automated acquisition of the S-parameters of three-port components is described, which is suitable for accurate device characterization as well as RF testing of three-port circuits in a production environment. Though based on conventional, nonrepeatable, electromechanical switches, the system achieves state of the art accuracy for on-wafer measurements by means of suitable hardware design and the application of time-domain gating. The system is applied to the characterization of MMIC (monolithic microwave IC) T-coils and single-pole double-throw (SPDT) switches. The bandwidth is now limited to 20 GHz but can be easily upgraded to 26.5 GHz by replacing one of the switches. Acquisition of the corrected S-parameters takes about 15 seconds (51 frequency points) with a HP 9000/330 controller.

1990 - An improved procedure to test CMOS ICs for Latch-up [Relazione in Atti di Convegno]
Menozzi, R; Lanzoni, M; Selmi, Luca; Ricco, B.
abstract

An improved, more complete strategy for latch-up testing of CMOS ICs is proposed in order to take into account important effects that have been neglected by standard procedures, but which are shown to reduce considerably the circuit resistance to latch-up. These phenomena include interactions among carriers injected by different p-n-p-n structures, voltage drops on power supply and ground lines caused by output pin load currents, and effects of power supply voltage and chip heating. All experiments with regard to this work have been performed by means of automatic test equipment, which provides the possibility of completely controlling the circuit state and operating conditions during testing

1990 - Effects of the interaction of neighboring structures on the Latch-up behavior of C-MOS ICs [Relazione in Atti di Convegno]
Menozzi, R; Selmi, Luca; Sangiorgi, Enrico; Ricco, B.
abstract

1990 - Latch-up in CMOS circuits: a review [Articolo su rivista]
Sangiorgi, Enrico; Fiegna, C; Menozzi, R; Selmi, Luca; Ricco, B.
abstract

In CMOS technologies, rapidly becoming the most important ones for VLSI microelectronics, the inherent phenomenon of latch-up, represents one of the most serious limitations for further dimension scaling in the deep sub-micron range. For this reason latch-up has attracted a lot of attention in the last decade and a deep understanding of its essential features has been achieved, although a few specific problems are still to be satisfactorily solved.

1989 - Hot-Electron induced Photon Energies in n-channel MOSFET’s operating at 77 and 300 K [Articolo su rivista]
Lanzoni, M; Manfredi, M; Selmi, Luca; Sangiorgi, Enrico; Cappelletti, R; Ricco, B.
abstract

A detailed experimental study of the spectral distribution of hot-electron-induced photon emission in n-channel MOSFETs is presented. The study significantly improves on previous work by considering energies up to 3.1 eV and different operating temperatures. It is shown that in contrast with previous results, the photon energy distribution is markedly non-Maxwellian, thus suggesting that the same is true for the energy distribution of the channel electrons.

1989 - Parameter extraction from I-V characteristics of single MOSFETs [Articolo su rivista]
Selmi, Luca; Sangiorgi, Enrico; Ricco, B.
abstract

A method is presented to extract the bias-dependent series resistances and intrinsic conductance factor of individual MOS transistors from measured I-V characteristics. If applied to groups of scaled channel length devices, it also allows determination of the effective channel length together with the transversal field dependence of the carrier mobility. The method is exactly derived from conventional MOS theory based on the gradual channel approximation, and the deviations from such an ideal case are studied by means of two-dimensional device simulations. Experimental results obtained with n- and p-channel transistors of conventional as well as LDD type are presented to show the correctness of the proposed extraction procedure

1989 - Three dimensional effects in dynamically triggered CMOS latch-up [Articolo su rivista]
Fiegna, C; Selmi, Luca; Sangiorgi, E; Ricco, B.
abstract

An analysis of three-dimensional (3-D) effects in CMOS latchup under dynamic conditions that expands on previous work limited to steady state is presented. Measurements of the minimum duration of voltage pulses and the ramp slew rate needed to induce latchup and have been performed on devices of different widths and layouts, and the latchup susceptibility to transient stimuli has been found to depend on the device dimensions and geometry. By means of simple analytical models it is shown that such a dependence originates from the nonideal scaling of the distributed resistances and capacitances due to the 3-D nature of the structure terminating regions

1988 - A novel method to determine the Source and Drain resistances of individual MOSFETs [Relazione in Atti di Convegno]
Ricco, B; Selmi, Luca; Sangiorgi, Enrico
abstract

A novel method is presented to determine the bias-dependent series resistances and intrinsic conductance factor of individual MOSFETs. The parameter-extraction procedure can also be applied to groups of scaled transistors to work out the device effective channel length. The method is derived analytically from the conventional theory of ideal MOSFETs, and the deviations of real devices from such a case are studied using two-dimensional device simulations. Experimental results with n- and p-channel conventional and LDD (lightly doped drain) MOSFETs are presented to demonstrate the correctness of the method

1988 - Hysteresis cycle in the Latch-up characteristic of wide CMOS structures [Articolo su rivista]
Selmi, Luca; Sangiorgi, Enrico; Crisenza, G; Re, D; Ricco, B.
abstract

Experimental results are interpreted in terms of a simple lumped-element model that is also used to reproduce the hysteresis phenomenon with discrete components. The hysteresis is related to a three-dimensional (3-D) nonuniformity in the current distribution. Such hysteresis can lead to an erroneous evaluation of latchup parameters, such as the holding current density.

1988 - Layout Dependence of CMOS Latchup [Articolo su rivista]
Menozzi, R; Selmi, Luca; Sangiorgi, Enrico; Crisenza, G; Cavioni, T; Ricco, B.
abstract

This paper presents a detailed analysis of CMOS latchup dependencies on layout and geometrical dimensions. To this purpose test structures have been fabricated featuring butted contacts and guard rings with different values of critical distances. The devices have been experimentally characterized in the triggering and sustaining regime, and numerical simulations have been extensively used to interpret the experimental data. It is shown that great care should be taken in designing protection structures since larger areas do not always lead to enhanced latchup immunity.

1987 - Three dimensional distribution of CMOS Latch-up current [Articolo su rivista]
Sangiorgi, E; Ricco, B; Selmi, Luca
abstract

This paper presents experimental evidence of relevant three-dimensional (3-D) effects in CMOS latch-up obtained by means of novel multicontact test structures. It is also shown that "quasi"-two-dimensional (2-D) experimental data in good agreement with numerical simulations can be achieved only by limiting the analysis to the central sections of wide experimental devices.

1987 - Three dimensional distribution of latch-up current in scaled CMOS structures [Relazione in Atti di Convegno]
Selmi, Luca; Venturi, F; Sangiorgi, Enrico; Ricco, B.
abstract

This paper presents a novel hysteresis phenomenon induced in the latch-up I-V characteristics of CMOS structures by three dimensional effects producing strongly bias dependent non-uniformities in the current lateral distribution. This behavior has been experimentally reproduced in a lumped element circuit, and a suitable model is presented.