Nuova ricerca

MARCELLO CIONI

Home | Curriculum(pdf) |


Pubblicazioni

2023 - Gate-Bias Induced RON Instability in p-GaN Power HEMTs [Articolo su rivista]
Chini, Alessandro; Zagni, Nicolo'; Verzellesi, Giovanni; Cioni, Marcello; Giorgino, Giovanni; Nicotra, Maria Concetta; Castagna, Maria Eloisa; Iucolano, Ferdinando
abstract

In this letter, we investigate the on-resistance ( RON ) instability in p-GaN power HEMTs induced by a positive or negative gate bias ( VGB ), following the application of a quasi-static initialization voltage ( VGP ) of opposite sign. The transient behavior of this instability was characterized at different temperatures in the 90–135 °C range. By monitoring the resulting drain current transients, the activation energy as well as time constants of the processes are characterized. Not trivially, both RON increase/decrease were found to be thermally activated and with same activation energy. We attribute the thermal activation of both RON increase/decrease to the charging/discharging of hole traps present in the AlGaN barrier in the region below the gate.

2023 - Microwave and millimeter-wave GaN HEMTs: impact of epitaxial structure on short-channel effects, electron trapping and reliability [Abstract in Atti di Convegno]
Zanoni, Enrico; Gao, Zhan; Fornasier, Mirko; Saro, Marco; Rampazzo, Fabiana; De Santi, Carlo; Meneghesso, Gaudenzio; Meneghini, Matteo; Cioni, Marcello; Zagni, Nicolo'; Chini, Alessandro; Verzellesi, Giovanni
abstract

2023 - Unveiling the Role of Hole Barrier Traps on ON-Resistance Instability after Gate Bias Stress in p-GaN Power HEMTs [Relazione in Atti di Convegno]
Zagni, Nicolo'; Chini, Alessandro; Verzellesi, Giovanni; Cioni, Marcello; Giorgino, Giovanni; Nicotra, Maria Concetta; Eloisa Castagna, Maria; Iucolano, Ferdinando
abstract

Gate bias effects on p-GaN power HEMTs stability are primarily investigated in terms of threshold voltage (V T ) drifts. However, applying positive and negative gate bias for long time can also induce ON-resistance (R ON ) instability which is often overlooked in the literature. In this work, we characterize I D -V GS after applying a –6/+6 V gate initialization (VGP) bias for 3000 s at different temperatures and reproduce the same characteristics by means of numerical simulations. The comparison between measurements and simulations allowed attributing the observed R ON dispersion to barrier acceptor traps emitting/capturing holes (injected/removed by the Schottky contact on the p-GaN layer) after V GP = –6/+6 V, respectively. Characterization of I D /R ON transients at different temperatures obtained after initialization at +6 V while keeping a gate baseline bias V GB = –6 V allows extracting an activation energy E A ≈ 0.4 eV. This feature is also reproduced by the simulations, further indicating that the underlying mechanism of R ON increase is the charge of acceptor traps in the barrier mediated by hole removal through the Schottky gate contact on the p-GaN region.

2022 - A Novel Temperature Estimation Technique Exploiting Carrier Emission from Buffer Traps [Relazione in Atti di Convegno]
Cioni, Marcello; Zagni, Nicolo; Chini, Alessandro
abstract

We propose a novel technique for temperature estimation in electron devices based on the mutual correlation between emission time constant from traps ( τ ) and temperature ( T ). Arrhenius equation is employed as the physical model relating τ and T The reference system used to present the technique is AlGaN/GaN high electron mobility transistors (HEMTs) with Fe-doping in the buffer. Drain Current Transients (DCTs) are used for extracting the emission time constant ( τ ) from Fe traps and non-linear regression through Trust Region Reflective (TRR) optimization algorithm is used to learn the model parameters from data and infer device temperature. Electro-thermal device simulations are employed for validating the proposed technique, showing that this method is able to provide an improved accuracy with respect to conventional electrical techniques (e.g., McAlister method) promoting it as a valid alternative to state of-the-art optical techniques in GaN HEMTs.

2022 - Experimental and numerical investigation of Poole-Frenkel effect on dynamic RON transients in C-doped p-GaN HEMTs [Articolo su rivista]
Zagni, Nicolò; Cioni, Marcello; Iucolano, Ferdinando; Moschetti, Maurizio; Verzellesi, Giovanni; Chini, Alessandro
abstract

In this paper, we investigate the influence of Poole-Frenkel Effect (PFE) on the dynamic RON transients in C-doped p-GaN HEMTs. To this aim, we perform a characterization of the dynamic RON transients acquired during OFF-state stress (i.e., VGS,STR = 0 V < VT, VDS,STR = 25–125 V) and we interpret the results with the aid of numerical simulations. We find that dynamic RON transients at room temperature accelerate with VDS,STR1/2, which is signature of PFE, as further confirmed by the simultaneous decrease of the activation energy (EA) extracted from the Arrhenius plot of the dynamic RON transients at VDS,STR = 50 V and T = 30–110 °C. Results obtained by means of calibrated numerical simulations reproduce the exponential dependence of transients time constants (τ) on VDS,STR1/2 and consequent EA reduction only when including PFE enhancement of hole emission from dominant acceptor traps in the buffer related to C doping. This result is consistent with the model that considers hole emission from acceptor traps (rather than electron capture) as the mechanism underlying dynamic RON increase during OFF-state stress.

2022 - Fe-Traps Influence on Time-dependent Breakdown Voltage in 0.1-μm GaN HEMTs for 5G Applications [Relazione in Atti di Convegno]
Cioni, M.; Zagni, N.; Chini, A.
abstract

Scaled (LG = 0.1 μm) GaN HEMT technology is currently pursued for high-frequency applications (such as 5G), requiring high current/speed and blocking capability. However, traps introduced with intentional Fe doping yield time-dependent breakdown voltage (VBR), seriously affecting reliability. Here, we investigate the role of Fe traps by pulsed I-V characterization performed at different pulse durations (TOFF). A TOFF-dependent VBR is observed on tested devices and is ascribed to the time-dependent occupancy of deep acceptors in the buffer layer. More specifically, the decrease in VBR for short pulses is attributed to the increased leakage due to the reduced ionization of Fe-traps. This interpretation is supported by 2D numerical simulations.

2022 - Identification of Interface States responsible for VTHHysteresis in packaged SiC MOSFETs [Relazione in Atti di Convegno]
Cioni, M.; Fiorenza, P.; Roccaforte, F.; Saggio, M.; Cascino, S.; Messina, A.; Vinciguerra, V.; Calabretta, M.; Chini, A.
abstract

We investigate the mechanism governing threshold voltage (VTH) hysteresis in packaged SiC MOSFETs. A double-ramp measurement method was employed for this scope, being able to accurately evaluate the time-dependent recovery of the positive VTH shift induced by the sweep-up of the gate voltage. Particularly, we studied the effect of the (i) gate driving voltage (VGH), (ii) recovery time (TOFF) and (iii) temperature (T) on the VTH hysteresis. No appreciable differences were observed among data collected at different VGH, whereas a recovery speed-up was observed at higher T values. Temperature dependent measurement of VTH recovery yielded a 0.3 eV activation energy, that has been associated to SiC/SiO2 interface traps located ~0.3 eV below the SiC conduction band.

2022 - Role of carbon in dynamic effects and reliability of 0.15-um AlGaN/GaN HEMTs for RF power amplifiers [Relazione in Atti di Convegno]
De Santi, Carlo; Zanoni, Enrico; Meneghini, Matteo; Meneghesso, Gaudenzio; Rampazzo, Fabiana; Gao, Veronica Zhan; Sharma, Chandan; Chiocchetta, Francesca; Verzellesi, Giovanni; Chini, Alessandro; Cioni, Marcello; Zagni, Nicolò; Lanzieri, Claudio; Pantellini, Alessio; Peroni, Marco; Latessa, Luca
abstract

This paper presents results concerning the dynamic performance and reliability of Fe-doped and C-doped 0.15-m gate AlGaN/GaN HEMTs. Step-stress tests at increasing drain-source voltage and different gate-source voltages are specifically reported. Fe-doped HEMTs exhibit, under both off- and on-state conditions, excellent parametric stability up to breakdown. C-doped devices are instead affected by enhanced degradation effects during the step stress experiments compared to Fe-doped ones, consisting of RON increase during off-state stress and both threshold-voltage and RON increase under on-state conditions. 2D hydrodynamic device simulations are used to validate hypotheses on the physical mechanisms underlying the observed, distinctive degradation effects. The role of C doping in causing additional degradation compared to Fe-doped device is explained with the aid of device simulations as follows: 1) under off-state conditions, hole emission from the CN acceptor traps in the gate-drain region of the buffer leads to an RON increase which is not completely recovered during the typical recovery time interval following each stress phase and therefore accumulates during the step stress experiment; 2) under on-state conditions, channel hot electrons are injected (besides towards the surface) into the buffer where they can be captured by CN traps under the gate and in the gate-drain region, inducing semi-permanent threshold-voltage and RON increases.

2021 - Effect of Trap-Filling Bias on the Extraction of the Time Constant of Drain Current Transients in AlGaN/GaN HEMTs [Relazione in Atti di Convegno]
Zagni, Nicolo; Cioni, Marcello; Chini, Alessandro
abstract

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 - Evaluation of VTH and RON Drifts during Switch-Mode Operation in Packaged SiC MOSFETs [Articolo su rivista]
Cioni, Marcello; Bertacchini, Alessandro; Mucci, Alessandro; Zagni, Nicolò; Verzellesi, Giovanni; Pavan, Paolo; Chini, Alessandro
abstract

In this paper, we investigate the evolution of threshold voltage (VTH) and on-resistance (RON) drifts in the silicon carbide (SiC) power metal-oxide-semiconductor field-effect transistors (MOSFETs) during the switch-mode operation. A novel measurement setup for performing the required on-the-fly characterization is presented and the experimental results, obtained on commercially available TO-247 packaged SiC devices, are reported. Measurements were performed for 1000 s, during which negative VTH shifts (i.e., VTH decrease) and negative RON drifts (i.e., RON decrease) were observed. To better understand the origin of these parameter drifts and their possible correlation, measurements were performed for different (i) gate-driving voltage (VGH) and (ii) off-state drain voltage (VPH). We found that VTH reduction leads to a current increase, thus yielding RON to decrease. This correlation was explained by the RON dependence on the overdrive voltage (VGS–VTH). We also found that gate-related effects dominate the parameter drifts at low VPH with no observable recovery, due to the repeated switching of the gate signal required for the parameter monitoring. Conversely, the drain-induced instabilities caused by high VPH are completely recoverable within 1000 s from the VPH removal. These results show that the measurement setup is able to discern the gate/drain contributions, clarifying the origin of the observed VTH and RON drifts.

2021 - GaN-based power devices: Physics, reliability, and perspectives [Articolo su rivista]
Meneghini, Matteo; De Santi, Carlo; Abid, Idriss; Buffolo, Matteo; Cioni, Marcello; Khadar, Riyaz Abdul; Nela, Luca; Zagni, Nicolò; Chini, Alessandro; Medjdoub, Farid; Meneghesso, Gaudenzio; Verzellesi, Giovanni; Zanoni, Enrico; Matioli, Elison
abstract

Over the last decade, gallium nitride (GaN) has emerged as an excellent material for the fabrication of power devices. Among the semicon- ductors for which power devices are already available in the market, GaN has the widest energy gap, the largest critical field, and the highest saturation velocity, thus representing an excellent material for the fabrication of high-speed/high-voltage components. The presence of spon- taneous and piezoelectric polarization allows us to create a two-dimensional electron gas, with high mobility and large channel density, in the absence of any doping, thanks to the use of AlGaN/GaN heterostructures. This contributes to minimize resistive losses; at the same time, for GaN transistors, switching losses are very low, thanks to the small parasitic capacitances and switching charges. Device scaling and monolithic integration enable a high-frequency operation, with consequent advantages in terms of miniaturization. For high power/high- voltage operation, vertical device architectures are being proposed and investigated, and three-dimensional structures—fin-shaped, trench- structured, nanowire-based—are demonstrating great potential. Contrary to Si, GaN is a relatively young material: trapping and degradation processes must be understood and described in detail, with the aim of optimizing device stability and reliability. This Tutorial describes the physics, technology, and reliability of GaN-based power devices: in the first part of the article, starting from a discussion of the main proper- ties of the material, the characteristics of lateral and vertical GaN transistors are discussed in detail to provide guidance in this complex and interesting field. The second part of the paper focuses on trapping and reliability aspects: the physical origin of traps in GaN and the main degradation mechanisms are discussed in detail. The wide set of referenced papers and the insight into the most relevant aspects gives the reader a comprehensive overview on the present and next-generation GaN electronics.

2021 - Impact of Soft- and Hard-Switching transitions on VTH and RON Drifts in packaged SiC MOSFETs [Relazione in Atti di Convegno]
Cioni, M.; Chini, A.
abstract

2021 - Investigation on VTH and RON Slow/Fast Drifts in SiC MOSFETs [Relazione in Atti di Convegno]
Cioni, M.; Bertacchini, A.; Mucci, A.; Verzellesi, G.; Pavan, P.; Chini, A.
abstract

RON and VTH drifts in TO-247 SiC packaged MOSFETs are investigated in this paper. The use of a novel on-the-fly measurement setup able to capture their variation over a 100µs to 1000s time range revealed the presence of two separated fast and slow mechanisms affecting the VTH and RON stability. Particularly, fast drain-induced mechanisms were found to negatively shift VTH, whereas no appreciable fast drifts were observed on RON. Conversely, slow drifts were found on both parameters, yielding a decrease in VTH and an RON increase. To investigate their origin, measurements were carried out for either i) different Duty Cycles and ii) several on-state current levels, proving that device self-heating (i.e., temperature increase) is responsible for the observed slow instabilities.

2021 - Mechanisms Underlying the Bidirectional VT Shift After Negative-Bias Temperature Instability Stress in Carbon-Doped Fully Recessed AlGaN/GaN MIS-HEMTs [Articolo su rivista]
Zagni, Nicolo; Cioni, Marcello; Chini, Alessandro; Iucolano, Ferdinando; Puglisi, Francesco Maria; Pavan, Paolo; Verzellesi, Giovanni
abstract

In this brief, we investigate the bidirectional threshold voltage drift (VT) following negative-bias temperature instability (NBTI) stress in carbon-doped fully recessed AlGaN/GaN metal-insulator-semiconductor high-electron-mobility transistors (MIS-HEMTs). Several stress conditions were applied at different: 1) gate biases (VGS,STR); 2) stress times (tSTR); and 3) temperatures (T). Both negative and positive VT (thermally activated with different activation energies, EA) were observed depending on the magnitude of VGS,STR. In accordance with the literature, observed VT < 0 V (EA ≈ 0.5 eV) under moderate stress is attributed to the emission of electrons from oxide and interface traps. Instead, VT > 0 V (EA ≈ 0.9 eV) under high stress is attributed to the increased negatively ionized acceptor trap density in the buffer associated with carbon doping.

2021 - Partial Recovery of Dynamic RON Versus OFF-State Stress Voltage in p-GaN Gate AlGaN/GaN Power HEMTs [Articolo su rivista]
Cioni, Marcello; Zagni, Nicolo; Iucolano, Ferdinando; Moschetti, Maurizio; Verzellesi, Giovanni; Chini, Alessandro
abstract

Dynamic Ron dispersion due to buffer traps is a well-known issue of GaN power high electron mobility transistors (HEMTs), critically impacting their performance and stability. Several works show that the dynamic Ron reaches a maximum for some off-state drain-source voltage ( VDS,off ) value typically in the range of several hundred volts and then partially recovers to smaller values. In this work, we propose a quantitative explanation for this behavior, attributing it to the charging/discharging dynamics of carbon (C)-related buffer traps. We characterize the dynamic Ron in packaged p-GaN gate AlGaN/GaN HEMTs with a custom measurement setup. We find that in these devices, the relative Ron increase reaches a maximum of 60% for VDS,off≈100 -200 V, partially recovering to about 30% as VDS,off is raised to 500 V. We ascribe this behavior to the partial neutralization of C-related acceptor traps in the buffer due to trapping of holes produced by a high-field generation mechanism. This explanation is supported by calibrated 2-D numerical simulations, that successfully reproduce the experimentally observed Ron reduction only when including a hole generation mechanism.