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BRUNO MORTEN

DOCENTE A CONTRATTO presso: Dipartimento di Scienze Fisiche, Informatiche e Matematiche sede ex-Fisica


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Pubblicazioni

- TRASDUTTORE PIEZOELETTRICO TORSIONALE [Brevetto]
DE CICCO, Giorgio; Morten, Bruno
abstract

Ogetto dell'invenzione è un trasduttore piezoelettrico torsionale utilizzabile sia come attuatore che come sensore. Lo scopo dell'invenzione è la realizzazione semplice ed economica di tale trasduttore. Esso consiste di una struttura laminare che funge da substrato che in prossimità di un suo estremo supporta almeno uno strato di materiale piezoelettrico. Ad esso è associato internamente allo strato, almeno un sistema elettrodico interdigitato costituito da una pluralità di elementi orientato secondo una direzione inclinata rispetto all'asse longitudinale del substrato. L'ecitazione piezoelettrica dello strato induce in torsione la struttura laminare su cui esso è collocato.


2015 - Suono: cibo dell'anima [Esposizione]
Brunetti, Rossella; Jacoboni, Carlo; Morten, Bruno
abstract

Tra tanto parlar di cibo, proviamo a parlare anche di cibo dell’anima, cioè di musica e dei suoni di cui la musica si compone. Dai tempi più antichi delle comunità umane non c’è cultura che non abbia sviluppato la propria musica e i propri strumenti per produrla, non c’è festa o banchetto, lieto o triste evento che non sia accompagnato da musica. La musica è così “innata” nell’uomo che qualcuno sostiene che forse si è cominciato a cantare prima che a parlare….Comunque sia andata il cibo dell’anima è sempre esistito per tutti, nobili, colti, ricchi, semplici o poveri. L’esplorazione della natura fisica del suono e delle possibilità di produzione ed elaborazione dei suoni hanno accompagnato lo sviluppo della scienza dalle epoche più antiche fino alla nostra era digitale. Le possibilità aperte all’impiego tecnologico e artistico dei suoni sono aumentate di pari passo con la conoscenza fisica e la capacità manipolativa del mondo sonoro. Questa eredità preziosa, che ha attraversato e coinvolto tutte le civiltà, è, come poche altre, un patrimonio planetario comune di Scienza, Tecnologia e Arte. Il progetto 2015 del ciclo La Curiosità fa lo Scienziato propone una esplorazione della natura fisica del suono, con alcuni approfondimenti tematici sulle possibilità offerte dagli strumenti musicali tradizionali e dalla voce umana e anche sulla manipolazione digitale del suono. L’ illustrazione dei contenuti scientifici e tecnologici relativi al mondo dei fenomeni sonori mostrerà come un sapere scientifico molto antico si è tramandato attraverso i secoli e si è progressivamente arricchito attraverso l’avanzamento delle Scienze e della Tecnologia, mantenendo ancora sorprendentemente “giovani” e attuali i contenuti delle antiche teorie e pratiche. Gli incontri previsti all’interno del Progetto e dedicati a platee di età diverse includono conversazioni a tema arricchite da esperimenti ed esecuzioni di brani musicali.


2012 - Dynamic torsion of laminar beams as a working principle for sensors [Articolo su rivista]
DE CICCO, Giorgio; Morten, Bruno
abstract

ABSTRACT: A method is presented in order to put planar structures in a pure torsion, bydirectly acting from their surfaces where a stress state is induced, taking advantage ofpiezoelectric layers that are integral with them. An experimental investigation was carriedout on alumina beams which, in a portion of their faces, support two ferroelectric layers ofPZT created using conventional thick-film technology processes. A suitable system ofcoplanar electrodes, embedded in the layers, promotes piezoelectric deformations parallel tothe substrate, induced by a voltage across them. At the layer-substrate interfaces,completely in-plane stresses are created and when they are conveniently oriented, the beamis prompted into pure torsion which takes on the characteristics of a vibration following theapplication of alternated voltage.Besides describing the design and realization of the sample beams, this work reports ontheir dynamic behaviour in torsion, the experimental set-ups and the procedures for itscharacterization. The results are discussed and highlighted in order to outline the potentialof the method with regard to using the realized beams as primary sensors for physicalquantities. To this end, proposals for possible


2009 - Thick-film piezoelectric actuator for micripositioning [Articolo su rivista]
Giorgio De, Cicco; Morten, Bruno
abstract

Driven by the versatility of conventional thick-film technology , this work was aimed at investigating the application chances of the electric field induced strains in ferroelectric (thick-film) material layers. To this end an experimental investigation is described, which concerns the piezoelectric potenstial of PZT thick-films, screen printed and fired on ceramic substrates, for applications in actuator development. It was carried out on a structure consisting of an alumina plate, clamped as a cantilever beam, the faces of which were supporting two symmetrically placed ferroelectric layers. An interdigital electrode system, created inside them, enabled a polarization parallel to the substrate, hence bending occured in the regions of the beam that were coverted by the film when opposite driving voltages were applied. The deflection measurements and their voltage dependence are shown, together with: strcture design and realization, an analysis and the performance highlighted as a micro-displacement actuator.


2008 - Method for specific heat measurement of thick film layers [Articolo su rivista]
G., DE CICCO; Morten, Bruno
abstract

A method of simple implementation is presented for the measurement of the specific heat of thick-film layers. It has to do with a system, operating at room temperature in accordance with a dynamic non-adiabatic technique, whose function regards the transient phase of a heating process between two steady states. It consists of a compact ensemble of three elements: a small plate thermistor serving as a heater, an alumina disk as a sample support and a tiny calibrated thermistor as a temperature sensor. The voltage across the heater and temperature from the sensor are monitored. An accurate evaluation of the dissipated energy allows the absorbed energy, responsible for the temperature variation, to be brought out. That makes possible the determination of thermal capacity of a small mass material deposited on a substrate. The achievement of the result simply involves the recording of a voltage and temperature during the transient phase, a fitting procedure with given analytical functions and a mathematical elaboration.The measuring system, its calibration procedure together with the transient operation are described. An application is presented concerning screen-printed ferroelectric thick films on alumina substrate and the results discussed.


2008 - New approach to the excitation of plate waves for piezoelectric thick-films devices [Articolo su rivista]
DE CICCO, G; Morten, Bruno
abstract

A method is presented for exciting the propagation of plate waves in elastic guides. It is implemented in a device whose minimum working structure consists of a non-piezoelectric plane guide and two piezoelectric transducers operating as a generator and detector. The device is entirely in accordance with thick-film technology standard procedures. Both transducers are composed of a PZT ferroelectric layer deposited on a ceramic substrate and a suitable system of three coplanar metal electrodes placed inside the same layer. Beside setting the wavelength of propagation, the electrode system promotes piezoelectric deformations parallel to the substrate simultaneously contracting and extending contiguous active regions in the layer. Pure shear stresses are then induced on the involved guide surface, alternately distributed, with the spatial periodicity of the wave that will propagate in the guide. The propagation of several kinds of guided waves is possible so the selection of the one that meets a specific device design best is allowed. This work describes the design, realization and operation of a prototype structure consisting of an alumina plate guide and two pairs of piezoelectric thick-film transducers realized on it. The results related to the propagation of symmetric and asymmetric Lamb modes are reported. Moreover, the potential of the method is highlighted, emphasizing its effectiveness, easy implementation and application in the development of devices for the sensing and non-destructive testing areas.


2007 - Environment friendly perovskite ruthenate based thick film resistors [Articolo su rivista]
S., Rane; Prudenziati, Maria; Morten, Bruno
abstract

It is well known that the dielectric matrix of air-fireable thick film resistors (TFRs) presently used in hybrid microelectronics and passive components invariably consists of a high-lead silicate glass. However, the current trend in the electronic industry is to restrict and eliminate the hazardous elements viz. lead, cadmium etc. from electronic components. An attempt to develop suitable RuO2-based or pyrochlore ruthenate based Pb-Cd free TFRs has been only partially successful till now. We report here the preliminary results of a study aimed to investigate the feasibility of CaRuO3 perovskite-based lead-free TFRs. Our results showed that sheet resistances higher than 1 k Omega/sq. can be easily achieved in a controlled way, with hot and cold temperature coefficients of resistance (TCR) in the range of 325-580 ppm/degrees C and 180-500 ppm/degrees C, respectively. Similarly, the compositions also exhibit negligible piezoresistive effects with gauge factor, GF < 1. Additionally, the resistors do not exhibit negative structural features, like bleeding or devitrification of glass, observed in previous attempts to develop reliable lead-free TFRs. (c) 2006 Elsevier B.V. All rights reserved.


2005 - Structural and electrical properties of perovskite ruthenate-based lead-free thick film resistors on alumina and LTCC [Articolo su rivista]
S., Rane; Prudenziati, Maria; Morten, Bruno; L., Golonka; A., Dziedzic
abstract

CaRuO3 perovskite-based lead-free thick-film resistors (TFRs) were prepared on 96%-alumina and Low Temperature Co-fired Ceramic (LTCC) substrates. The microstructure evolution, possible interactions, and electrical properties of resistors were investigated. The hot and cold TCR values of all the resistors were measured in the temperature range (+20 to +120 ° C) and (+20 to -120 ° C), respectively. TFRs with 25% by vol. of CaRuO3 on alumina exhibit a sheet resistance R-s = 5 k Ohm/sq. with hot and cold TCR of 225 and 470 ppm/° C respectively, whereas the same composition gives 1.2 k Ohm/sq., 16.5 k Ohm/sq. and 0.7 k Ohm/sq. for co-fired, post-fired resistors on LTCC and buried resistors, respectively. The hot (HTCR) and cold (CTCR) values were evaluated; HTCR = 190 ppm/° C and CTCR = 314 ppm/°C were found for co-fired structures; HTCR = 216 ppm/degrees C and CTCR = 205 ppm/°C for post-fired samples and HTCR = 520 ppm/°C and CTCR = 350 ppm/° C for buried in LTCC structures.


2004 - Dissolution kinetics and diffusivity of silver in glassy layers for hybrid microelectronics [Articolo su rivista]
Prudenziati, Maria; Morten, Bruno; Gualtieri, Alessandro; M., Leoni
abstract

Silver and palladium/silver compositions are widely used in hybrid microelectronics, as electrodes for dielectric layers and multilayers, terminations of thick film resistors and interconnections. Interactions between Ag and the adjacent films are known to affect the microcircuit performances. The present study is aimed at collecting data on the behavior of Ag-based films in contact with glassy layers. Most experiments were performed with a glass with composition 68.2 PbO:30.5 SiO2:1.3 Al2O3 wt%. Two different systems were analyzed. The first system consists of thick films prepared from a paste containing glass and either 3 or 15 wt% silver particles; both fine (spherical grains, 0.5-1 mum diameter) and coarse (flakes, 2-5 mum, &lt; 1 μm thick) Ag powders were used for these pastes. The distribution of Ag in the film was studied with X-ray diffraction, scanning electron microscopy and fluorescence analysis. The results show that Ag floats on the glassy layer. Diffraction of X-rays generated by a synchrotron radiation source allowed us to study the kinetics of silver dissolution in the glass; this phenomenon is consistent with the Avrami theory, with an apparent activation energy E-dis = 0.69 +/- 0.04 eV. The second system analyzed, Ag-based terminations of glass layers fired at various peak temperatures, enabled us to obtain quantitative values for both Ag solid solubility (about 2.5 wt%) and Ag diffusion coefficients D-Ag(T). Typical values of D-Ag(850°C) are 30.3 +/- 11.9 10(-8) cm(2)/S; an apparent activation energy of the diffusion process is E-a = 0.6 +/- 0.1 eV.


2004 - Microstructure and elelectrical propperties of perovskite ruthenate-based lead free thick-film resistors on alumina and LTCC. [Relazione in Atti di Convegno]
S., Rane; Prudenziati, Maria; Morten, Bruno; L., Golonka; A., Dziedzic
abstract

CaRuO3, perovskite-based lead-free thick-film resstors were processed on 96%-alumina and Low Temperature Co-fired Ceramic (LTCC) substrates. The microstructure evolution, possible interaction and electrical properties of resistors were ivestigated. TFR with 25% by vol. of ruthenate on alumina exhibit a sheet resistance Rs=5 KOhm/sqwith hot and cold TCR of 225 and 470 ppm/degree C respectively, whereas the same composition gives 1.2 KOhm/sq and 16.5 KOhm/sq. for cofired and postfired samples, respectively, on LTCC, wuth hot and cold TCR of 190 and 314 ppm/degreeC for co-fired structures, and 216 and 250-ppm/degreeC for post-fired LTCC structires.


2004 - Perovskite ruthenate-based lead free thick film resistores [Relazione in Atti di Convegno]
Prudenziati, Maria; Morten, Bruno; S., Rane
abstract

As well Know, the dielectric matrix of air-fireable thick-film resistors(TFRs) presently used in hybrid microelectronics and passive components invariably consists in hifh-lead silicate glass. However the actual trend is to restrict and possibly eleiminate Pb from electronic components. Attempts to develop suita. RuO2-based or pyrochlore ruthenate-based Pb-Cd free TFRs has been only partiallt successful till now. We report here the preliminary results of a study aimed to investigate the flexibility of CaRuO3 perovskite-based lead-free TFRs. The results show that sheet resistances larger than 1 KOhm/square cab be easily achieved in a controlled way, with hot temperature coefficient of resistance in the the range of a few hundreds ppm/deg.C. In addition, the resistors do not exhibit negative structural features, like bleeding or devitrification, observed in previous attempts to develop reliable lead-free TFRs.


2004 - “Microstructure and electrical properties of perovskite Ruthenate-based Lead Free Thick-Film Resistors on alumina and LTCC” [Relazione in Atti di Convegno]
S., Rane; Prudenziati, Maria; Morten, Bruno; L. J. GOLONKA AND A., Dziedzic
abstract

CaRuO3 perovskite-based lead-free thick-film resistors (TFRs) were prepared on 96%-alumina and Low Temperature Co-fired Ceramic (LTCC) substrates. The microstructure evolution, possible interactions, and electrical properties of resistors were studied. The hot and cold TCR values of all the resistors were measured in the temperature range (+20 to +120°) and (+20 to -120°), respectively. TFRs with 25% by volume of CaRuO3 on alumina exhibit a sheet resistance Rs = 5kohm/sq. with hot and cold TCR of 225 and 470 ppm/ C, respectively, whereas the same composition gives 1.2 kohm/sq., 16.5 kohm/sq. and 0.7 kohm/sq. for co-fired, post-fired resistors on LTCC and buried resistors, respectively. The hot (HTCR) and cold (CTCR) values were evaluated; HTCR = 190 ppm/ °C and CTCR = 314 ppm/ °C were found for co-fired structures; HTCR = 216 ppm/ °C and CTCR = 205 ppm/ °C for post-fired samples and HTCR = 520 ppm/ °C and CTCR = 350 ppm/ °C for buried in LTCC structures.


2003 - Reduction process of RuO2 powder and kinetics of their re-oxidation [Articolo su rivista]
Prudenziati, Maria; Morten, Bruno; E., Travan
abstract

With the aim of improving knowledge of the phenomena occurring during the development of thick-film resistors (TFRs), redox reactions were studied in fine powders of Ru and RuO2 by means of thermogravimetric analyses and x-ray diffraction as well as observations in scanning electron microscope and x-ray fluorescence. Reduction of RuO2 powders by forming gas (10% H2 in N2) occurs in a few minutes, after an induction period, at temperatures as low as approximately 100°C, at a rate essentially independent of temperature (50-150°) and grain size. The oxidation process is well described by the Avrami model, according to a diffusion limited reaction with an apparent activation energy of 1.5 +- 0.1 eV and it requires long times for completion even at relative high temperatures (700-850°C). The order of magnitude for the diffusivity of the mobile species was derived. In addition, the reduction and further re-oxidation of RuO2 powders blended with Et cellulose were studied. Possible implications of the results on the properties of RuO2-based TFRs are discussed.


2002 - Electric force microscopy investigation of the microstructure of thick film resistors [Articolo su rivista]
Alessandrini, Andrea; G., Valdre'; Morten, Bruno; Prudenziati, Maria
abstract

Maps of the electric field distribution on the surface of thick film resistors (TFRs) have been acquired by using electric force microscopy (EFM). TFRs based on various types of conducting phases (Bi-ruthenate, Pb-ruthenate, or RuO2) and with different volume fractions in the glassy matrix have been examined. Scanning electron microscopy, x-ray energy dispersive spectroscopy and x-ray diffraction have been used to correlate the EFM results to the morphological, microchemical, and structural characteristics of the samples. The evolution of the TFRs microstructure and the segregation characteristic with the firing conditions have been investigated. The results showed that the concentration of the electric field around the conductive grains is a general feature of all the films, independently of the resistor composition, and a meander-like path of charge carriers on a microscopic scale has been assessed. The observations also indicated that at high firing temperatures the segregated structure did not disappear, but on the contrary was enhanced. All the results are critically discussed in relation to the electrical and piezoresistive properties of the TFRs and suggestions for new models to correlate the microstructure and the electric properties are presented.


2002 - IrO2-based thick-film resistors [Articolo su rivista]
S., Tankiewicz; Morten, Bruno; Prudenziati, Maria; L., Golonka
abstract

IrO2-based thick-film resistors were prepared and their microstructure/electrical property relationship was studied as a function of the firing temperature T-f and composition. The resistor microstructure exhibits a notable change, from a strongly segregated structure for T-f=750 degreesC, to a quasihomogeneous one when the firing temperature increases to T-f=850 degreesC. Likewise, a substantial change is observed in the sheet resistance (R-s) dependence on the volume fraction (v) of the conductive phase. For resistors prepared at T-f=750 degreesC the percolation power law R(s)approximate to(v-v(c))(-t) (where v(c) and t are the critical volume fraction and exponent, respectively) is observed, while samples fired at T(f)greater than or equal to850 degreesC follow the relation ln R(s)approximate toa(v-v(0)) where a and v(0) are proper constants. In addition, the slope of plot a is affected by the firing temperature T-f as well as by the measuring temperature at T<50 K. Very high temperature coefficients of resistance are measured at cryogenic temperatures. The longitudinal gauge factor values are in the range from 3 to 12.4 according to the resistor composition and firing temperature, with the highest values in samples fired at 950 degreesC with sheet resistance in the range from 10(4) to 10(7) Omega/square.


2002 - Lead-free thick film resistors: an explorative investigation [Articolo su rivista]
Prudenziati, Maria; F., Zanardi; Morten, Bruno; Gualtieri, Alessandro
abstract

Pastes prepared with seven lead-free glass particles were screen-printed and fired on 96\%-Al2O3 substrates. The fired films were studied in terms of sintering, devitrification, crack propagation and bleeding. The most promising glass compositions were selected for the preparation of RuO2-based thick film resistors (TFRs), on pre-fired PtAu- or PdAg-based terminations; electrical properties of the resistors (sheet resistance vs. RuO2 volume fraction, temperature coefficient of resistance and size effects) were investigated. The study evidenced a myriad of complex phenomena, including devitrification, relevant bleeding of the glass on alumina substrates, anomalous distribution of conductive grains in the glassy matrix, phase separations. Contrarily to what happens in traditional systems, it is difficult to get a wide resistance range simply by changing the fraction of the conductive phase. These results emphasize the criticality in the choice of the glass composition for the preparation of lead-free thick film resistors.


2001 - Devitrification kinetics of high lead glass for hybrid microelectronics [Articolo su rivista]
Prudenziati, Maria; Morten, Bruno; B., Forti; Gualtieri, Alessandro; G., MIHAI DILLIWAY
abstract

In order to elucidate crystallization phenomena in high lead glasses for hybrid microelectronics, we studied the devitrification in screen printed and annealed films made with borosilicate glass particles with the composition PbO-SiO2-B(2)iO(3) = 65:25:10 % wt. Formation of SiO2 polymorphs, beta -cristobalite and quartz, was observed in films printed on alumina (Al2O3) or beryllia (BeO) and fired in the temperature range from 700 to 1000 degreesC. X-ray diffraction of samples annealed in isothermal conditions enabled the collection of data for studying the kinetics of formation and dissolution of the crystalline phases. The crystallization of beta -cristobalite on both substrates is governed by an Avrami model. At lower temperatures, the reaction order coefficient indicates an interface controlled reaction with an instantaneous or deceleratory nucleation rate and 3D growth. The apparent activation energy of the crystallization process is independent of the substrate being 15(1) kcal/mol and 14.7(9) kcal/mol for samples on Al2O3 and BeO substrates, respectively, whereas the decomposition reaction is favored on alumina, with E-d = 30(2) kcal/mol in this case, but 55(3) kcal/mol for beryllia substrates. (C) 2001 Elsevier Science Ltd. All rights reserved.


2001 - New thick-film material for piezoresistive sensors [Articolo su rivista]
S., Tankiewicz; Morten, Bruno; Prudenziati, Maria; L., Golonka
abstract

IrO2-based resistors were prepared with the standard methods of thick-film technology and their electrical properties were studied in order to identify the best composition for piezoresistors suitable for sensors to be operated continuously at temperatures exceeding 150 degreesC. The obvious criterion was to minimise the temperature coefficient of resistance (TCR) and the temperature coefficient of the gauge factor (TCGF), with minimum shift of the resistance in long term high temperature operation, without sacrificing the gauge factor (GF). The results achieved include resistors with sheet resistance lower than 100 k Omega/square; TCR values lower than 250 ppm/degreesC over the temperature range from -40 to 200 degreesC and lower than 100 ppm/degreesC from 25 to 200 degreesC; GF approximate to 7-10; TCGF approximate to -130 ppm/degreesC; relative change of resistance DeltaR/R < 0.1% after ageing at 150 degreesC for 1000 h. Performance characteristics, studied in the temperature range of 25-175 degreesC, of a gauge pressure sensor exploiting IrO2 piezoresistors are reported. (C) 2001 Elsevier Science B.V. All rights reserved.


2000 - Lead free glasses for new generation of thick-film resistors: an explorative investigation [Abstract in Atti di Convegno]
Prudenziati, Maria; Zanardi, F.; Morten, Bruno; Gualtieri, A. F.
abstract

Pastes prepared with seven lead-free glass particles were screen-printed and fired on 96%-Al2O3 substrates. The fired films were studied in terms of sintering, devitrification, crack propagation and bleeding. The most promising glass compositions were selected for the preparation of RuO2-based tghick-film resistors (TFRs), on pre-fired PtAu - or PdAg based terminations; electrical properties of resistors (Rsvs:RuO2 volume fraction, temperature coefficient of resistanceand size effects) were investigated. The study eviced a myriad of complex phenomena occuring in the films, and emphasized the criticality in the choice of glass composition.


2000 - Microstructural analysis of RuO2-basede thick-film resistors [Abstract in Atti di Convegno]
R., Benedetti; C., Meneghini; Morten, Bruno; Prudenziati, Maria
abstract

This paper presents results of a microstructural analysis on RuO2-based Thick Film Resistors performed by X.ray diffraction and absorption spectroscopy. The study concerns four different types of RuO2-based TFRS, prepared changing the substrate, the glass of matrix and the vehicle but keeping the RUO2 powder fixed. In addition each type has been fired at different temperatures, ranging from 450 deg. C up to 1000 deg. C . The collected data clearly indicated that changes in resistivity are directly related to structural modification of the glass matrix and a consistent interaction with the alumina substrate exists. On the contrary firing temperature and substrates have minor effects on RuO2 conductive phase.


2000 - Microstructure and surface composition of ferromagnetic thick films prepared with NiCo Polyol derived powders [Articolo su rivista]
A., Bianco; G., Gusmano; G., Montesperelli; Morten, Bruno; Prudenziati, Maria; G., Righini; R., Zanoni
abstract

Interest in ferromagnetic thick films stems from their magnetoresistive properties which open new opportunities for achieving reliable and cheap contactless physical sensors. In previous work we have studied the properties of different classes of ferromagnetic metal-based thick films, either prepared from commercial Ni-based pastes, or from prototype NiCo-based pastes, including those prepared with NiCo powders obtained with a polyol process. The latter has been found to give comparatively better magnetoresistive and magnetic responses; nevertheless the information on the real microstructure of the films was incomplete, especially with regard to the surface composition and contamination. In this paper results of an investigation aimed at clarifying these features and their evolution with the firing conditions are reported. The study included analyses of powders and films with scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS). Results show the evolution of sintering and grain growth with the peak firing temperature and give evidence of residual contamination of carbonaceous residues on the films together with an extensive surface oxidation, although the firing process was carried out in nitrogen flow. Moreover the film surfaces are Co rich. These results can guide in the choice of composition and processing conditions for further improvement of the magnetic and magnetoresistive properties of the films.


2000 - The women scientists of Bologna [Articolo su rivista]
Cieslak Golonka, M; Morten, Bruno
abstract

Short biographies of four scientists women operating in Bologna (Italy) in eighteen century are reported. They refer to Laura Bassi (electricity and hydrodinamics topics), Anna Morandi Manzolini (reproduction of anatomical body organs), Maria Gaetana Agnesi (linguist and mathematician) and Maria Dalle Donne ((midwifery and newborn care).


1999 - Correlation between electric force microscopy and scanning electron microscopy for the characterization of percolative conduction in electronic devices [Articolo su rivista]
Alessandrini, Andrea; G., Valdre'; Morten, Bruno; S., Piccinini; Prudenziati, Maria
abstract

The correlation betweem electric force microscopy (EFM) and scanning electron microscopy (SEM)techniques provide interpretation of the contrast features of electric force images and gave an insight into the two-dimensional (2D) electrical transport properties of RuO2-based thick film resisitors (TFRs). From the comparison between EFM. tapping mode-atomic force microscopy, SEM (secondary electrons, specimen current and X-ray energy-dispersive spectroscopy) of TFRs on the same specimen area, it turned out that the conduction mechanism was related to the grain size and to how RuO2 crystals were distributed in the glassy matrix. Dark area in EFM images corresponded to conductive-insulating interfaces. In SEM the same areas were the interfaces between the Ru=2 crystals and the insulating matrix. The 2D percolative path of the electrical current near the surface was observed in connection with the net of RuO2 grains not homogeneously dispersed in the insulating matrix.


1999 - Correlation between electric force spectroscopy and scanning electron microscopy for the characterization of percolative conduction in electronic devices [Articolo su rivista]
Alessandrini, Andrea; G., Valdre'; Morten, Bruno; S., Piccinini; Prudenziati, Maria
abstract

The correlation between electron force microscopy (EFM) and SEM techniques provided interpretation of the contrast features of electron force images and gave an insight into the two-dimensional (2D) electron transport properties of RuO2-based thick film resistors (TFRs). From the comparison between EFM, tapping-mode atomic force microscopy, SEM (secondary electrons, specimen current and x-ray energy-dispersive spectroscopy) of TFRs on the same specimen area, the conduction mechanism was related to the grain size and to how RuO2 crystals were distributed in the glassy matrix. Dark areas in EFM images corresponded to conductive-insulating interfaces. In SEM the same areas were the interfaces between the RuO2 crystals and the insulating matrix. The 2-dimensional percolative path of the electron current near the surface was observed in connection with the net of RuO2 grains not homogeneously dispersed in the insulating matrix.


1999 - IrO2-based thick-film piezoresistors for pressure sensors [Abstract in Atti di Convegno]
S., Tankiewicz; L., Golonka; H., Toszczak; Morten, Bruno; Prudenziati, Maria; G., DE CICCO
abstract

The subject concerns thick-film resistors whose conductive component is based on IRO2 grains. TCR and Gauge factor values are reported together with a resistors application as sensing elements for pressure sensors.


1999 - MICROSTRUCTURE AND SURFACE COMPOSITION OF FERROMAGNETIC THICK-FILM PREPARED WITH NiCo POLYOL DERIVED POWDERS [Articolo su rivista]
A., Bianco; G., Gusmano; G., Montesperelli; Morten, Bruno; Prudenziati, Maria; G., Righini; R., Zanoni
abstract

Interest in ferromagnetic thick films stems from their magnetoresistive properties which open new opportunities for achieving reliable and cheap contactless physical sensors. In previous work we have studied the properties of different classes of ferromagnetic metal-based thick films, either prepared from commercial Ni-based pastes, or from prototype NiCo-based pastes, including those prepared with NiCo powders obtained with a polyol process. The latter has been found to give comparatively better magnetoresistive and magnetic responses; nevertheless the information on the real microstructure of the films was incomplete, especially with regard to the surface composition and contamination. In this paper results of an investigation aimed at clarifying these features and their evolution with the firing conditions are reported. The study included analyses of powders and films with scanning electron microscopy (SEM) and X-ray photoemission spectroscopy (XPS). Results show the evolution of sintering and grain growth with the peak firing temperature and give evidence of residual contamination of carbonaceous residues on the films together with an extensive surface oxidation, although the firing process was carried out in nitrogen flow. Moreover the film surfaces are Co rich. These results can guide in the choice of composition and processing conditions for further improvement of the magnetic and magnetoresistive properties of the films.


1999 - Magnetic properties of Ni-Co thick-film magnetoresistors [Articolo su rivista]
A., Masoero; Morten, Bruno; Gl, Olcese; Prudenziati, Maria; F., Tango; F., Vinai
abstract

Magnetic susceptibility from 300 to 900 K, room temperature hysteresis cycles and saturation magnetization were investigated in screen printed and fired NiCo-based layers prepared at various peak temperatures. A bulk NiCo metal sheet of comparable composition was also studied. Values of the magnetic polarization J of 0.28 and 0.435 T were obtained (at 200 kA/m) for films prepared at 750 and 950 degrees C, respectively, in contrast with J = 0.98 T for the bulk alloy. In addition, the magnetoresistive responses of the layers and the sheet were plotted. These data suggest that strains, pores and lack of composition homogeneity in the films concur in affecting their magnetic properties, and are responsible for their reduced magnetoresistance anisotropy (e.g. ca. 4% for films as compared to ca. 8% for the bulk alloy at H = 80 kA/m). (C) 1999 Elsevier Science S.A. All rights reserved.


1999 - Pyroelectricity in PZT-based thick-films [Articolo su rivista]
G., De Cicco; Morten, Bruno; D., Dalmonego; Prudenziati, Maria
abstract

We studied the pyroelectric properties of lead titanate-zirconate (PZT)-based layers prepared with standard procedures of thick film technology (950 degrees C peak temperature) on alumina substrate and with buried interdigital electrodes. The investigation was aimed at setting adequate procedures, and at identifying sample configurations, for measuring the relevant pyroelectric quantities rather than to optimize the material pyroelectric performances. The results show that the pyroelectric coefficient of our porous layers (similar to 1.2 +/- 0.1 x 10(-4) C/m(2) K) is lower than that of ceramic (similar to 3.8 x 10(-4) C/m(2) K) and dense thick-films (similar to 2 x 10(-4) C/m(2) K) of comparable composition, but the thermal properties of our samples (low heat capacity and thermal conductivity) as well as the low relative dielectric constant result in figures of merit better than the corresponding values either for ceramic PZT or other pyroelectric materials (including TGS and LiTaO3). Hence, porous ferroelectric thick-films are good candidate for new pyroelectric devices. (C) 1999 Elsevier Science S.A. All rights reserved.


1999 - RuO2-based thick film resistors studied by extended x-ray absorption spectroscopy [Articolo su rivista]
C., Meneghini; S., Mobilio; F., Pivetti; I., Selmi; Prudenziati, Maria; Morten, Bruno
abstract

RuO2-based thick film resistors were studied by extended x-ray absorption fine structure. A bimodal distribution of RuO2 particle size has been determined by comparing the obtained results with x-ray diffraction data. The partial dissolution of RuO2 particles into the glassy matrix is suggested to be one of the principal mechanisms responsible for the electrical conduction in these materials. (C) 1999 American Institute of Physics. [S0021-8979(99)07217-5].


1998 - Interactions between bismuth oxide and ceramic substrates for thick film technology [Articolo su rivista]
Immovilli, S; Morten, Bruno; Prudenziati, Maria; Gualtieri, Alessandro; Bersani, M.
abstract

We investigated the interactions between screen printed and fired layers of Bi2O3 and ceramic substrates of alumina and beryllia. It was found that the reaction products are invariably crystalline in nature. Several transitions of Bi2O3 in its polymorphic phases were found to occur on BeO substrates, while newly formed compounds have been observed to grow on alumina substrates, i.e., Al4Bi2O9 on 99.9% Al2O3 and Bi12SiO20 On 96% Al2O3 Bismuth deeply penetrates in the ceramic interstices in all the cases. Until Bi2O3 is not completely reacted, this penetration is diffusion limited (penetration depth w approximate to t(d)(1/2), where t(d) is the reaction time) with values of the activation energy ranging from 3.7 +/- 0.6 eV (BeO substrate) to 1.4 +/- 0.06 eV (96% Al2O3 substrate). It is shown that these processes are notably different to those occurring in PbO/ceramic systems; moreover, they imply different adhesion phenomena of thick films on different substrates.


1998 - Magnetoresistance of RuO2-based thick film resistors [Articolo su rivista]
Affronte, Marco; Campani, M; Morten, Bruno; Prudenziati, Maria; Laborde, O.
abstract

In a series of samples whose composition was systematically changed, we have studied the magnetoresistance (Delta R/R = [R(B)-R]/R) of RuO2-based thick film resistors (TFR's) in magnetic fields (B) up to 20 Tesla and in a temperature range (1.2K<T<40K) in which their resistance exhibits insulating behavior at the boundary between rite strong and the weak localization. At the higher temperatures, Delta R/R exhibits a positive bump, that does not depend on the RuO2 concentration but it changes with the concentration of magnetic Mn impurities diluted in the glassy matrix. For T less than or equal to 20 K magnetoresistance is entirely negative and it has a quadratic magnetic field dependence at low field. We use the weak localization theory to relate these features of the high temperature magnetoresistance to the composition of TFR's. At low temperature (T<4.2K) the negative magnetoresistance shows some peculiarities. The quadratic term shrinks, within a vanishing magnetic field range and the magnetoresistance linearly increases in a wide range of B. Ar the strongest fields and the lowest temperature Delta R/R shows a tendency to saturation. Although these results do not enable to discriminate among different mechanisms, we note that the low temperature (T<4.2 K) behavior is essentially consistent,with recent theory of Nguen et al.


1997 - A new ultrasonic composite transducer implemented with thick film technology [Articolo su rivista]
Decicco, G; Morten, Bruno; Prudenziati, Maria
abstract

A new ultrasonic transducer operating in air and fabricated by thick film technology is presented. It consists of a composite mechanical structure in which three active elements, made with planar alumina substrates supporting PZT-based piezoelectric films, behave as elastic guides. The active elements have a constant rectangular cross-section and are radially placed, 120 degrees apart. They are mounted between a rigid base (operating as the acoustic backing) and an alumina disk. On both sides of each substrate a piezoelectric layer las interdigital thick-film electrodes embedded in layer itself, so that it can be polarized parallel to the long side of the active element; consequently, it allows the creation of periodic surface stresses responsible for symmetric extensional strains in the alumina plates. The elements, synchronously driven in phase, form, with the disk, a vibrating resonant structure, which radiates acoustic energy perpendicular to the disk surface. The assembly of active elements, acoustic backing and radiating disk forms a composite ultrasonic transducer operating in air without the need of any acoustic matching layer. Among the prominent features offered by the transducer design are: a transduction efficiency of 25% at an exiting voltage of 100 V-p and a high directivity of the emitted beam.


1997 - Interactions between lead oxide and ceramic substrates for thick film technology [Articolo su rivista]
Bersani, M; Morten, Bruno; Prudenziati, Maria; Gualtieri, Alessandro
abstract

This paper deals with the mechanisms and kinetics of interactions between screen printed and fired PbO layers and ceramic substrates: alumina and beryllia. The interaction with alumina occurs via two main processes: (i) a reaction between PbO and Al2O3 grains, which induces the formation of a crystalline phase, Pb2Al2O5; and (ii) an interdiffusion process involving Pb and the intergranular amorphous phase in the ceramic substrate. This latter process results in a compositional change of the intergranular phase at considerable depths inside the ceramic substrate, as well as in the formation of a high lead glass layer on the substrate surface, Since PbO is not completely reacted, the Pb penetration in the ceramic is diffusion limited (penetration depth w approximate to t(d)(1/2) where t(d) is the reaction time) with an activation energy of 1.20 +/- 0.05 eV. The ceramic microstructure significantly affects the interaction processes.


1997 - Low temperature electronic transport in RuO2 based cermet resistors [Articolo su rivista]
Affronte, Marco; Campani, M; Piccinini, S; Tamborin, M; Morten, Bruno; Prudenziati, Maria; Laborde, O.
abstract

We have studied the temperature (T) dependence of resistance (R) of RuO2-based thick films down to 1.2 K. Samples were prepared from inks containing conductive RuO2 powders (less than or equal to 10% wt.), high lead-silicate glass particles and Mn (less than or equal to 1.4% wt.). We found that the resistance fits the exponential law R=R(0)exp(T-0/T)(x) with x=1/4 and the most resistive samples show a crossover to the x=1/2 regime as the temperature decreases. Both the fitting parameters R-0 and T-0 scale down as the RuO2 fraction increases and they are affected in a similar way by a change of the Mn content. The presence of the two regimes is similar way by a chang of the Mn content. The presence of the two regimes is similar to that observed in n-type GaAs [Phys. Rev. B 39, 8059 (1989)] and n-type CdSe [Phys. Rev. Lett. 64, 2687 (1990)] whilst it disagrees with the behaviour predicted for grain to grain hopping [Phys. Rev. B 27, 2583 (1983)] and with that expected for resonant tunneling between metallic particles [J. Appl. Phys. 48, 5152 (1977)]. We conclude that in our systems the driving charge transport mechanism is electron hopping within the glassy matrix. Since in our case the hopping length is of the same order of the localization length, the puzzling questions arising from our experiments are whether and how the variable range hopping model can be extended beyond its conventional limits.


1997 - Magnetic properties of Ni-Co-based thick films investigated with magnetic force microscopy [Articolo su rivista]
Bernardi, G; Morten, Bruno; Pergolini, S; Prudenziati, Maria; Valdre, G.
abstract

Preliminary results are presented of a magnetic force microscopy (MFM) investigation to characterize Ni-Co-based screen-printed and fired films magnetically. These systems are of interest not only for contactless magnetoresistive sensors of mechanical quantities but also because they are made of micrometre sized grains sintered (and, in the case of Ni plus Co grains, alloyed) during the thermal process. Hence, a detailed study of their magnetic properties has been undertaken. Typical domain structures and zones have been observed by MFM at resolutions of about 0.2 mu m (static mode) and 50 nm (dynamic mode). Changes in the domain structure and deflection forces acting on the magnetic force microscope tips have been observed in samples prepared at various peak firing temperatures, and in samples of different compositions.


1997 - Piezoresistive properties of RuO2-based thick-film resistors: The effect of RuO2 grain size [Articolo su rivista]
Tamborin, M; Piccinini, S; Prudenziati, Maria; Morten, Bruno
abstract

The piezoresistive properties of thick-film resistors are well documented and widely used in sensors of strain-related quantities. However, the origin of the effect is not well established, and correlations between resistor composition and relevant properties (such as strain sensitivity, temperature coefficient of resistance (TCR) and excess noise) have been not worked out yet. This paper reports a systematic study of these correlations in RuO2-based model resistors prepared with the same glass frit and RuO2 powders covering a range of particle sizes from a few nanometres to micrometres. Gauge factors (GFs) from 2 to 30 have been observed in resistors of sheet resistance R-square in the range 1 k Ohm/square to 3 M Ohm/square. At a selected R-square value, the GF increases linearly with the logarithm of RuO2 grain size, while the TCR and excess noise do not significantly depend on the RuO2 powder size.


1997 - Thick film resistors as cryogenic thermometers [Relazione in Atti di Convegno]
Affronte, Marco; M., Campani; Morten, Bruno; S., Piccinini; M., Prudenziati; M., Tamborin; O., Laborde
abstract

The work was aimed at assessing relatioships betwwen composition and performanceThe temperature dependence of resistance in RuO2-based TFRs was studied in the range 1.2 K to 300 K. The resistance fits the exponential relationship R=R0exp(T/T0)x with x=1/4 at higher temperatures with a transition to the x=1/2 regime on the same sample at lower temperatures (<20 K). The transition temperature Tc between these regimeshas a well defined dependence on the sample resitance Rs. Both the R0 ant T0 values scale down as the RuO2 fraction and show similar dependences on the Mn content. The magnetoresistve responses were measured in same temperature range in magnetic field H uo to 20 Tesla. The measured relative change of resistance never exceedes 0.02 up to 8 Tesla. In summary the developed resistors exhibit superior performances in comparison with the prently used thermometers. In addition they they show predictable properties at changing temperature and magnetic field strength, making easier their calibration.


1997 - Thick-film magnetoresistors and related sensors [Articolo su rivista]
Morten, Bruno; Prudenziati, Maria; Decicco, G; Bianco, A; Montesperelli, G; Gusmano, G.
abstract

This paper deals with ferromagnetic thick-film materials and with sensors relying on the resistance change due to an external magnetic field, usually in the range from 10(4) A m(-1) to 10(5) A m(-1). The research for the development of thick-film magnetoresistors (TF-MRs) is briefly summarized from Ni-based air-fireable pastes to NixCoy-based films fireable in N-2 atmosphere. The different materials are compared, regarding their magnetoresistive performances (mainly in terms of magnetoresistive anisotropy and temperature sensitivity). Some applications are described, covering the area of position sensing (displacement, proximity switch, angle) and the measurement of dynamic quantities (angular rotation) either for digital or analogue control systems.


1996 - Advanced thick film sensors [Relazione in Atti di Convegno]
G., De Cicco; Morten, Bruno; M., Prudenziati
abstract

Since many years we have devoted our activities to the study of new material prepared with the screen printing technology as well as the design and performance' evaluatuin of new thick film sensors and actuators. The contribution elucidates the reasons of this choice and provides a brief summary of the most recent activities and results, including the development of new thick-film materials for magnetoresistive contactless sensors and the development of new PZT-based thick film piezoelectric materials for several piezoelectric sensors and actuators. example of these devices will be mentioned and finally a composite ultrasonic transducer will be described.


1996 - Elastic surface wave devices based on piezoelectric thick-films [Articolo su rivista]
Decicco, G; Morten, Bruno; Prudenziati, Maria
abstract

A study has been performed for the development of elastic-waves structures, involving screen printed and fired piezoelectric layers on nonpiezoelectric substrates, intended for new families of thick film sensors. This study approached the electroacoustic effects, i.e., the coupling between electromechanical. parameters of the layers and elastic properties of the substrate, related to the wave propagation. In this work, particular attention is devoted to devices implemented on alumina substrates where SAW as well as (symmetric and antisymmetric) Lamb's waves are generated. The realization processes and the performance characteristics of these structures are presented.


1996 - Preparation and properties of new thick-film magnetoresistive materials [Articolo su rivista]
Bianco, A; Montesperelli, G; Gusmano, G; Morten, Bruno; Decicco, G; Masoero, A; Tombesi, P; Prudenziati, Maria
abstract

NixCoy-based thick-film magnetoresistors (TF-MRs) have been prepared with two different approaches: either the in situ alloy formation (and sintering) from fine powders of Ni and Co or the sintering of a Ni70Co30 powder obtained by co-reduction of Ni(II) and Co(II) acetates in diethyleneglycol. The pastes, printed on properly glazed alumina substrates in meander configuration, have been fired in N-2. The microstructure, electrical and magnetoresistive properties of these films have been studied. Both materials appear of interest for the implementation of contactless sensors.


1996 - Thick films of MgFe2O4 for humidity sensors [Articolo su rivista]
Gusmano, G; Montesperelli, G; Morten, Bruno; Prudenziati, Maria; Pumo, A; Traversa, E.
abstract

In this paper the humidity-sensitive electrical properties of MgFe2O4 thick-films are studied. Thick films were prepared by screen printing on alumina substrates and subsequent firing. Pastes for screen printing were obtained by adding an organic vehicle and Bi2O3, as a sintering aid, to MgFe2O4 powders. The microstructure of the films was varied using MgFe2O4 powders with different grain sizes and by changing the firing temperatures. The microstructure of the films was studied by scanning electron microscopy (SEM), energy dispersion spectroscopy (EDS), and Hg porosimetry. The humidity-sensitive electrical properties of thick films were tested by electrochemical impedance spectroscopy (EIS). D.C. measurements were made to test reproducibility and time response, and to study the conduction mechanism. The electrical response of the films was correlated with their microstructure and the distribution of Bi2O3 in the films.


1995 - MAGNETORESISTIVE THICK-FILM SENSOR FOR LINEAR DISPLACEMENTS [Articolo su rivista]
Morten, Bruno; Decicco, G; Prudenziati, Maria; Masoero, A; Mihai, G.
abstract

A new thick film material has been developed starting from Ni and Co powders in the ratio Ni:Co=3:1. The thermal treatment (in N,, up to 950 degrees C) of the metal films deposited on glazed alumina enables the in situ formation of the NiCo alloy. The films as created exhibit a high longitudinal (current I parallel to the field B) magnetoresistive response with Delta R/R approximate to 4% at 1.2 kGauss, and a negligible transverse one. The temperature coefficient of resistance (TCR) is approximate to 2700 ppm degrees C-1. These properties make the new material superior, from the point of view of magnetoresistive applications, to the Ni-based currently available thick film conductors. Contactless sensors for linear displacements have been created with the sensor's structure enclosing either Ni-based and Ni/Co-based meanders, having two magnetoresistive elements on each side of the substrate. This paper compares the magnetoresistive and thermoresistive properties of Ni and Ni/Co-based layers as well as the performances of the sensors in the range -20 to 120 degrees C.


1995 - Piezoelectric thick-film materials and sensors [Articolo su rivista]
Prudenziati, Maria; Morten, Bruno; G., De Cicco
abstract

The preparation, poling methods, and characteristics of PZT-based thick films obtained with standard hybrid microelectronics methods are summarized. The microstructure of the films is characterized by substantial porosity which, in turn, is responsible for the particular piezoelectric properties of the films, including low permittivity, high piezoelectric coefficients, and nonlinear behavior over wide pressure ranges. The flexibility in designing piezoelectric sensors for mechanical quantities (pressure, acceleration, torque) and chemical quantities (humidity) is emphasized, with examples given of the prototypes developed. Furthermore, these films offer the possibility of launching elastic waves in nonpiezoelectric substrates; the structures achieved can be used for the implementation of new classes of sensors and biosensors. The advantages of thick films in comparison with ceramic materials, in terms of low-voltage operation and easy change of shape, size, and operating mode, are demonstrated.


1995 - Thick film composite ultrasonic transducers operating in air [Relazione in Atti di Convegno]
G., De Cicco; Morten, Bruno; M., Prudenziati
abstract

A new ultrasonic transducer operating in air and fabricated by thick film technology is presented. It consists of a composite mechanical structure in which three active elements, made with planar alumina substrates supporting PZT-based piezoelectric films, behave as elastic guides. The active elements have a constant rectangular cross-section and are radially placed, 120 degrees apart. They are mounted between a rigid base (operating as the acoustic backing) and an alumina disk. On both sides of each substrate a piezoelectric layer las interdigital thick-film electrodes embedded in layer itself, so that it can be polarized parallel to the long side of the active element; consequently, it allows the creation of periodic surface stresses responsible for symmetric extensional strains in the alumina plates. The elements, synchronously driven in phase, form, with the disk, a vibrating resonant structure, which radiates acoustic energy perpendicular to the disk surface.


1995 - Thick film gas sensors [Relazione in Atti di Convegno]
Prudenziati, Maria; Morten, Bruno; G., De Cicco
abstract

A review, with 30 references, is given. The potential use of thick film technology for mass production of gas sensors is outlined, with particular attention to devices of interest in domestic applications. Achievements and trends are presented, and areas where further efforts for enabling a wide penetration of thick film gas sensors in current and predictable market are emphasized.


1994 - A NOVEL TORQUE SENSOR-BASED ON ELASTIC-WAVES GENERATED AND DETECTED BY PIEZOELECTRIC THICK-FILMS [Articolo su rivista]
Morten, Bruno; Decicco, G; Prudenziati, Maria
abstract

Screen-printed and fired PZT-based films have been used as the source and detectors of elastic waves near the surface of a torsional shaft. The change in wave propagation velocity due to applied torques has been taken as the operating principle of a torque sensor. The new opportunities opened by piezoelectric thick-film materials in the implementation of this novel sensor are demonstrated.


1994 - Evolution of ruthenate-based thick-film cermet resistors [Articolo su rivista]
Morten, Bruno; Masoero, A.; Prudenziati, Maria; Manfredini, Tiziano
abstract

An experimental investigation has been carried out to study variations of microstructure, composition., and electrical properties (sheet resistance and its temp. coefficient) occurring in thick-film (cermet) resistors during the annealing process which transforms the initial ink into a resistive layer. Resistors based on Bi2Ru2O7 and a lead silica glass have been studied. Analyses have been performed on the inks using thermogravimetric measurements, and on annealed (fired) layers by means of x-ray diffraction, atomic absorption, electron microscopy, microprobe analysis, and other complementary techniques. The results point out the role of exchange reactions and redox reactions inside the resistor body and emphasize the complexity of the phenomena which concur to define the final elecrical properties of these resistive systems. Interrelations between microstructure, composition , and elecrical properties have been found and tentative explanations proposed.


1994 - Influence of the preparing coditions on the Physicochemical chaarcteristics of glasses for thick film hybrid microelectronics [Articolo su rivista]
Prudenziati, Maria; Morten, Bruno; Savigni, P; Guizzetti, G.
abstract

Seven batches of a high-lead glass were used for the preparation of RuO2-based thick film resistors. Investigation of their electrical properties showed a lack of reproducibility of results whose origin was related to changes of the physicochemical properties of the glassy matrix. A systematic investigation of the glass batches, both in form of frit powders and screen printed and fired layers, was carried out with several spectroscopies to detect changes in composition and structure. The spectroscopic methods included x-ray Energy Dispersive Fluorescence (EDS), Scanning Electron Microscopy (SEM), Atomic Absorption (AA), diffuse optical reflection of the powders and specular reflection of the layers, optical transmission, and other complementary methods. The dissolution of Al, due to interaction between the glasses and the alumina substrate, as well as the diffusivity and solubility of Ag due to interaction with the Ag-bearing terminations were measured. The results demonstrated that, apart from small compositional differences, the various batches were characterized by differences in residual stresses, redox reactions, and ''microstructure.'' The latter was responsible for very notable differences in the optical properties of the glasses, which in turn are closely related with the difference in atomic solubility and diffusivity. Optical spectroscopies have been found to be a suitable means for testing reproducible preparation methods of glass frits for thick-film hybrid microelectronics.


1994 - Magnetoresitive thick film sensors [Capitolo/Saggio]
Morten, Bruno; Prudenziati, Maria; G., De Cicco
abstract

Research of the development of thick film magnetoresistive sensors is only just ininiated; Ni-based air-fireable pastes developed for non.sensing applications have been studied for the characterization of magnetoresistive responses and new systems are under development aimed at improving the magnetoresitive performance of these materials particularly in terms of magnetoresistive anysotropy and temperature sensitivity. The very promising results of these investigations are reviewed, basic and technological features of thick-film and thin-film ferromagnetic materials are compared and emerging applications of thick film magnetoresistors are delineated.


1994 - Piezoelectric thick-film sensors [Capitolo/Saggio]
G., De Cicco; Morten, Bruno; Prudenziati, Maria
abstract

Piezoelectric thick-film sensors may be considered an excellent example of the new opportunities offered for sensors (as well as for actuators) by the successful implementation of new sensor-oriented thick-film materials. Research has demonstrated that proper piezoelectric effects can be incorporated in thick films with adequate choice of active grains, bonding agent and processing conditions.Various properties are sharing by piezoelectric thick-film with ceramic materials already extensively used in the current technology of sensors and actuators. In fact both classes of materials are polycrystalline bodies, sintered in appropriate thermal processes and polarised in order to make the piezoelectrically active. However thick film exhibit distinct characteristics of physical behaviour and of technological interest which enable the dvelopment of really new sensors and actuators.


1994 - Piezoresistive thick.film sensors [Capitolo/Saggio]
Morten, Bruno; Prudenziati, Maria
abstract

Sensors of strain-related mechanical quantities relying on the piezoresistive properties of thick-film resistors are being increasingly employed in various measuring and control systems; the purpose of this section is to explain how and why thick-film strain gauges differ from metal and semiconductor strain gauges widely employed in similar devices, and to remark the specific methods and materials enabling the design of variety of new classes of sensors for pressure, force weight and acceleration. The potentials of this technology are are illustred by many examples. It is clear that this class of sensors has not reached yet his full potentials; on one side performance of piezoresistors might be improved with satisfactory models of the physical behaviour of thick film resistors, on the other hand we see a continuous search of new materials and structure for increangly integrated and small sensors. However piezoresistive sensors are the field where the possibility of a dynamic evolution of thick film technology as an advanced sensor technology has been demonstrated by a variety of new sensors developed in a short lapse of time.


1993 - A THICK-FILM RESONANT SENSOR FOR HUMIDITY MEASUREMENTS [Articolo su rivista]
Morten, Bruno; Decicco, G; Prudenziati, Maria
abstract

The paper describes the implementation and performance of a resonant humidity sensor relying on the piezoelectric properties of PZT-based thick films on an alumina diaphragm and the reversible hygroscopic behaviour of a cellulose acetate coating on the substrate. A shift of about 100 Hz of the resonance frequency f0 = 56.675 Hz (22-degrees-C, 35% RH) is obtained by changing the relative humidity from 10 to 95%, with a linear response over the whole range. In a time of 0.5 min the sensor changes its output when the relative humidity is varied from 10 to 40%. The dynamics of interaction between the water molecules and the organic film are discussed and related to the prompt response of the sensor to changes of environmental conditions. It is suggested that the joint exploitation of resonant techniques and thick-film technology can be a powerful strategy for manufacturing other inherently digital sensors of chemical species and biosensors.


1992 - HYBRID THICK-FILM MAGNETORESISTIVE SENSORS [Articolo su rivista]
Cirri, Gf; Matucci, A; Minucci, M; Decicco, G; Morten, Bruno; Prudenziati, Maria
abstract

This paper describes a first prototype of a thick-film sensor using Ni-based pastes, whose resistance changes with the applied magnetic field. The magnetoresistive properties of thick films (Ital. Patent No. 9477/A86 (1986)) have been exploited for the development of hybrid sensors for proximity detection and rotational speed. The conditioning electronic circuits are specifically designed to compensate the relevant temperature effects, which otherwise would overwhelm the weak magnetoresistive effects. The electronic solution, though simple, proves to be very effective. On this basis integrated magnetoresistive sensors, with standard trimmable hybrid circuits and Ni-based films on the same substrate, have been developed in the framework of a collaboration aimed at looking for reliable integrated sensors for various applications. The design and operation of a prototype are described. Some areas of application of hybrid magnetoresistive sensors will be analysed.


1992 - Interactions between beryllia and high-lead glasses [Articolo su rivista]
Moro, L; Lazzeri, P; Prudenziati, Maria; Morten, Bruno; Savigni, P.
abstract

Interactions between BeO substrates and high-lead glasses of typical composition for hybrid thick films have been studied by means of secondary neutral mass spectrometry. The Be atomic concentration on top of glass layers, 2-40 mum thick, prepared at various temperatures T(f), ranging from 750 to 1000-degrees-C have been measured. The results give insight of Be solubility values from 0.5 to about 6 at. %, according to the glass type and firing temperature, and diffusion coefficients higher than 10(-10) cm2/S. Moreover, the diffusion mechanism appears quite different from that involved in interactions between the same glasses and alumina substrates, since no correlated diffusion process has been observed in the present case.


1992 - PZT-based thick films and the development of a piezoelectric pressure sensor [Articolo su rivista]
Morten, Bruno; G., De Cicco; A., Gandolfi; C., Tonelli
abstract

A study was carried out on the relationship between the composition, poling condition and piezoelectric properties of thick-film layers. Pastes based on lead-titatnate zirconate (PZT) powders, with either Pbo or a lead-alumina -silicate glass frit as binder, were prepared . Microstructure, electrical and mechanical properties were analysed. processing and polig conditions modify these properties; then a wide latitude of opportunities is offered in the choice of ferroelectric/piezoelectric characteristics of the layers used as sensing elements for sensors. A pressure sensor was realised where a circular diaphragm of alumina supports two piezoelectric layers obtained by screen printing and firing a PZT/PbO-based ferroelectric paste. The design and performance characteristics are described.


1992 - RESONANT PRESSURE SENSOR BASED ON PIEZOELECTRIC PROPERTIES OF FERROELECTRIC THICK-FILMS [Articolo su rivista]
Morten, Bruno; Decicco, G; Prudenziati, Maria
abstract

The paper describes the design, implementation and performance of a resonant sensor for gas-pressure measurement realized with screen-printed and fired PZT-based layers on an alumina diaphragm. The piezoelectric properties of these layers have been exploited to excite (with low voltage signals) and detect oscillations of the diaphragm. The layer configurations and associated vibrational modes of the diaphragm have been designed and a phase-locked loop (PLL) technique implemented in electronic circuits able to keep the resonant condition, despite the change of resonance frequency due to variation of the applied differential pressure. It is shown that for an adequate choice of operating frequency (i.e. of the vibrational mode) a good sensitivity and thermal stability of the sensor can be obtained; in this device, operating at frequency around 57.8 kHz, corresponding to the third-mode frequency f0.3, a shift DELTA-f0.3 = 650 Hz is found by changing the pressure from 0 to 900 mmHg. We found also that f0.3 changes less than 6 x 10(-3) by changing the temperature from 23 to 100-degrees-C. Moreover the sensor allows long-term measurements of static pressures without significant hysteresis effects.


1992 - The state of the art in thick-film sensors [Articolo su rivista]
M., Prudenziati; Morten, Bruno
abstract

The speed of evolution of thick-film tchnology as an advanced technique for silid state sensors is illustrated. Recent innovations are mentioned with regard to modern techniques for the design, realization and test of hybrid circuits for signal processing, use of new materials both for substrates and transducing elements, new concept designs and processing techniques. Current research activies and programmes, which promise new interesting materials for, and emerging applications of, thick-film sensors, are described. However, several problems remain unsolved; some topics which should improve our understanting and performance of thick-film sensors are mentioned.


1991 - LEAD-FREE RUTHENIUM-BASED THICK-FILM RESISTORS - A STUDY OF MODEL SYSTEMS [Articolo su rivista]
Morten, Bruno; Ruffi, G; Sirotti, F; Tombesi, A; Moro, L; Akomolafe, T.
abstract

A model system of thick-film resistor (TFR) was prepared starting from RuO2 powders and a lead-free glass. The microstructural development was investigated by scanning and transmission electron microscopies, energy dispersive X-ray fluorescence, X-ray diffraction, thermogravimetry and other complementary techniques. The electrical properties of the resistors were analysed with particular attention to sheet resistance, temperature coefficient of resistance, size effects and piezoresistive properties. It was found that these simple systems are interesting with respect to their stability in ageing tests at relatively high temperatures but they are not promising for high-temperature piezoresistive gauges because of low strain sensitivity. Some samples were also prepared with a Bi2Ru2O7; a notable exchange reaction occurs between the conductive grains and the glass matrix which prevents the formation of pyrochlore-type based resistors with this glassy matrix.


1991 - Manganese in ruthenium dioxide-based thick film resistors. [Articolo su rivista]
Morandi, M.; Morten, Bruno; Prudenziati, Maria; Argentino, E.; Ruffi, G.
abstract

The effects of Mn as additive on the microstructure, composition, and electrical properties of RuO2-based thick-film resistors were examined. Samples were prepared with pastes containing either MnO2 or Mn octoate in small amounts. Resistors were screen-printed and fired on 96% alumina and 99.5% beryllia. Dissolution of Mn in glass and phase transformation of oxides were studied, as well as the effect of Mn on interdiffusion phenomena in the resistors. The electrical properties of resistors with and without Mn were measured and compared. Mn is a very effective negative temperature coefficient of resistance driver; moreover, this additive brings a further beneficial effect on the performance properties of the resistors by preventing large inverse size effects in resistors with Ag-bearing terminations. It is shown that organometallic compounds are more suitable than oxides as a Mn source.


1991 - Size effects in ruthenium-based thick-film resistors: rutile vs. pyrochlore-based resistors [Articolo su rivista]
M., Prudenziati; F., Sirotti; M., Sacchi; Morten, Bruno; A., Tombesi; T., Akomolafe
abstract

The size effect, namely the change of sheet resistance, R, as a function of resistor length, has been investigated in layers whose conductive phase evoves from Pb-rich (Ru-deficient pyrochlores) to Pb2Ru2O6.5 and finally to RuO2 by increasing the firing temperature. It is found that Bi diffusion from the terminations is responsible for lower sheet resistance values in shorter resistors whatever the conductive phase is. On the contrary, Ag diffusion is responsible for lower sheet resistance values in shorte resistors only in the case of ruthenate conductive grains while the reverse is observed in RuO2-based layers. Size effect can be suppressed with Pt/Au-based terminations provided that Bi is contained and with Au-metallorganic-based contact provided that the peak firing temperature is not too high.


1991 - Superconducting thick-films from a Y-Ba-Cu-O precursor [Articolo su rivista]
M., Sacchi; F., Sirotti; Morten, Bruno; M., Prudenziati
abstract

We have prepared scree-printed films of the Y-Ba-Cu-O composuperconductiund starting from a spray-pyrolysis precursor powder. BeO ceramic substrates are confirmed to be inert with respect to the film up to about 100 C. Electrical properties of oxigen annealed films are investigated,evidencing excellent superconducting behaviour,both in terms of Tc (=91K) and Jc (&gt;100 Asquarecm at 77K).


1990 - MAGNETORESISTIVE PROPERTIES OF NI-BASED THICK-FILMS [Articolo su rivista]
Morten, Bruno; Prudenziati, Maria; Sirotti, F; Decicco, G; ALBERIGI QUARANTA, A; Olumekor, L.
abstract

Investigations have been carried out on the electrical properties of nickel-based films prepared from air fireable pates on alumina substrates. In particular, magnetoresistive effects have been studied as a function of temperature, strength and direction of the magnetic field. These properties were detwrmined in films at different stages of formation, i.e. prepared at various peak firing temperatures and dwell times, and compared with those displayed by nickel folis. These results provide the basis for the development of magnetoresistive thick-film sensors.


1990 - PERFORMANCE OF THICK-FILM STRAIN-GAUGES AT CRYOGENIC TEMPERATURES [Articolo su rivista]
Ferrero, C; Marinari, C; Masoero, A; Morten, Bruno; Prudenziati, Maria
abstract

Thick-film resistors have been prepared on enamelled steel substrates and their extensometric properties have been investigated at 300, 77 and 4.2 K. The measurements made included the longitudinal and transverse gauge factors, the temperature coefficients of resistance and of the gauge factor, and current noise.Repeatability and apparent strain have also been evaluated. The characteristics of strain gauges prepared from two different resistive systems, based on RuO2 and ruthenate particles, respectively, have been compared. The results show that thick film resistors on enamelled steel are adequate for the development of sensors and transducers of strain strain-related physical quantities in cryogenic environments.


1989 - Ag-based thick-film front metallization of silicon solar cells [Articolo su rivista]
M., Prudenziati; L., Moro; Morten, Bruno; F., Sirotti; L., Sardi
abstract

The evolution of microstructure and electrical properties of silver-based thick-film metallizations of silicon solar cells prepared by infrared firing processes has been ivestigated. The performance of the cells are shown to be dependent on several dynamical and diffusive phenomena. In particular, the sintering of silver grains, silver diffusion in the glassand the flow of gas at the metal/silicon interface strongly affect important characteristics of the cells such as sheet and contatct resistivities and the adhesion of fingers and bus bars. The existance of an optimum value of the peak firing temperature is observed and explained in terms of competitive phenomena occuring at the metal/silicon interface. Moreover it is shown that IR firing treatments require aa careful consideration of the sequence of printing anf firing steps. The features of heat treatments performed in conveyor belt furnaces using Joule and infrared sources are compared.


1989 - Interactions between alumina and high lead glasses for hybrid components [Articolo su rivista]
Prudenziati, Maria; Morten, Bruno; F., Cilloni; G., Ruffi; M., Sacchi
abstract

Kinetics of dissolution of alumina substrates in 7 compositions of high lead glasses have been studied. The dissolution process is controlled by the correlated diffusion of Al and Pb (and/or B), with interdiffusion coefficients D, at 850°C, 10 min, in the range from 10-10 to 10-6 cm s-1, according to the different compositions Al solubility ranges from about 10 to 20%. The diffusivity and solubility increase by increasing the content of B and Pb. The reactivity of alumina substrates with the glassy component of thick-film resistors greatly affects their microstructure and electrical properties. Some consequences of these interactions have been evidenced: change in electrical resistivity and its dependence on the resistor thickness, changes in the sintering process and grain growth of RuO2 grains, and a catalytic effect on phase transformations of pyrochlore ruthenates in rutile RuO2 in the glassy matrix of resistors. Al dissolution moreover gives rise to a recession of the buried glass /substrate interface, which can easily be measured. When alumina is concerned, this measurement gives insight into the sum of twoprocesses: Al dissolution in the glass layer and grain-boundary diffusion of glass into the substrate itself.


1989 - Very high strain sensitivity in thick-film resistors: real and false super gauge factors. [Articolo su rivista]
Prudenziati, Maria; Morten, Bruno; Cilloni, F.; Ruffi, G.
abstract

An investigation was carried out on the correlations between composition/morphology of RuO2-based thick-film resistors and their strain sensitivity. Very high gauge factors (GFs), as well as satisfactory performance in terms of TCR (temperature coefficient of resistance), excess noise and reliability, are obtained with an appropriate choice of glassy matrix, RuO2 grain size and concentrations. Resistive systems modified with metal and metal oxide additions were analyzed. In some cases, notable changes of electrical properties are observed , related to defective structures. Methods for a simple and accurate diagnosis of reliable or fictitious performance of thick-film strain gauges are identified


1989 - Window size effect on lateral growth of nickel silicide. [Articolo su rivista]
Singh, Awatar; Khokle, W. S.; Prudenziati, Maria; Majni, G.; Morten, Bruno
abstract

Window size effect on lateral growth of nickel silicide in contact windows cut into oxide grown on Si (100) is studied. The growth rate is found to be independent of window size and follows the diffusion-limited process with activation energy of 1.5 eV. The Si erosions are observed to grow due to predominant Si diffusion for vacuum anneal above 600. This phenomenon becomes greatly pronounced with fine windows of 2 m in diameter. This phenomena can be attributed to (i) an enhanced stress level in fine windows causing reduction in the growth temperature of epitaxial NiSi2 in the windows and (ii) difference in surface energies of epitaxial NiSi2 formed and the Si substrate resulting in the shrinkage of the epitaxial NiSi2 dimension in the window. No such behavior is observed under identical conditions when Si(111) is used. This is due to the fact that the lateral growth of nickel silicide in this case is about a quarter of that for Ni-Si (100) lateral samples.


1988 - High Tc superconductivity in Y-ba-Cu-O screen printed films [Articolo su rivista]
M., Sacchi; F., Sirotti; Morten, Bruno; M., Prudenziati
abstract

We have prepared screen-printed films of the Y-Ba-Cu-O compound on BeO and Al2O3 ceramic substrates. Transition to full superconductive state was obtained for all samples. The related parmeters (Tonset, Tc, deltaT) and some structural properties are reported.


1988 - Phase transitions in Ru-based thick-film (cermet) resistors [Articolo su rivista]
Morten, Bruno; M., Sacchi; F., Sirotti; Prudenziati, Maria
abstract

Thick-film resistive inks have been prepared starting from powders obtained by precipitation of RuCl3 on two different lead-containing glasses. The structural and electrical properties of the films have been investigated after heat treatment at various temperatures. The evolution of microstructure involves phase transformations from Pb-rich (Ru-deficient) pyrochlores to Ru pyrochlores and finally to RuO2. Together with these crustallographic features, the atomic absorption spectroscopy shows a gradual decrease of the Ru dissolved in the glass when the firing temperature increases. The conductivity of the samples decreases according to the transition from pyrochlore to dioxide. These results empasize the role played by exchange reactions in the control of transport mechanisms in thick-film cermet resistors.


1988 - Photoconductivity of thick-film resistors [Articolo su rivista]
G. B., Parravicini; G., Samoggia; Morten, Bruno; M., Prudenziati
abstract

A weak change of resistivity caused by visible radiation both for commercial and for model thick-film (cermet) resistors (TFRs) has been observed and studied in the temperature range 10-380 K. A possible origin of this photoelectric effect in terms of photoexcited electrons emitted from the metallic grain surface into glassy region is discussed.


1986 - Interactions between thick-film resistors and terminations: the role of bismuth [Articolo su rivista]
M., Prudenziati; Morten, Bruno; L., Moro; L., Olumekor; A., Tombesi
abstract

The interactions of thick-film (cermet) resstors with terminations of various metals prepared on alumina substrates has been investigated. The resistivity was studied as a function of resistor length and temperature. The point-to-point voltage drop was measured over the entire length of the resistors. SEM and EDAX were used to investigate the termination material, the termination-resistor interface and the resistor, both lengthwise over the specimen and vertically downward into the substrate. The results show that bismuth, a common component of these termination materials, is primarily responsible of these interactions because bismuth has high diffusivity and high solubility in the matrix of the resistor. Moreover, a strong interaction of bismuth with the alumina substrate was observed.


1986 - Sensori e trasduttori a film spesso [Articolo su rivista]
M., Prudenziati; Morten, Bruno
abstract

E' riportata una rassegna riguardante sensori a film spesso e tecnologia a film spesso. Essa intende illustrare conoscenze e processi sviluppati in attività che coprono un arco di tempo poco più che decennale ma in rapida, crescente espansione.


1986 - Thick-film sensors: an overview [Articolo su rivista]
M., Prudenziati; Morten, Bruno
abstract

Sensors form a vital part of any measurement and control system,. Demand for sensors generally are increasing, but particularly for rugged, reliable, integrated sensors for computer control systems.Among the various sensor technologies, thick-film technology (TFT) does not really offer conceptually new sophisticated solutions, but does offer several appreciale capabilities, e. g., flexibility in chice of materials and design, easy integration with electronic circuits and packaging.This paer illustrates some specific features of TFT for sensor manufacture and overviews most of the types of devices used or developed at present. Moreover, some new sensors, which might be conceived and developed in the near future, are suggested.


1985 - Evolution of microstructure and performance of Pd/Ag-based thick-film conductors [Articolo su rivista]
M., Prudenziati; Morten, Bruno; M. F., Brigatti
abstract

Pd/Ag based inks are probably the most commonly used conductors in thick-film hybrid technology. The evolution of microsctructure of these films was studied on samples fired with isochronal cycles at a peak temperature in the range from 300 C to 850 C. The samples were investigated by means of X-ray diffraction, SEM amd EDAX analysis techiques; the results of these analises as well as those of thermogravimetry (TG, DTG) and differential thermal analysis (DTA), enable one to obtain a clear picture of the complex evolution of microstructure of these conductors, which correlates quite strictly with the performance of the films in terms of the resistivity and adhesion. The relevance and limitations of each analytical technique for the examination of thick-film conductors are emphasized.


1985 - Reverse photolitographic technique for thicl-film circuits [Articolo su rivista]
A., Singh; M., Prudenziati; Morten, Bruno
abstract

The paper deals with reverse photolitographic technique, applied for the first time for the processing of thick-film components on alumina substrates. The SEm phographs of the delineated patterns have revealed excellent edge line definition which is always saw-tooth shaped in the conventional process. various VLSI applicationpotentials have also been pointed out.


1985 - SEM-EDAX analysis of interaction of photoresist with thick-films [Articolo su rivista]
A., Singh; M., Prudenziati; Morten, Bruno
abstract

The SEM-EDAX anslysis of the interaction of shypley's positive photoresist AZ-1350J with thick-film pastes DP9596 and DP1441 is reported. The interaction is found to make the resistor surface smoother and conductor surface denser than those of processed conventionally. The golf from DP 9596 (pt-Au) paste is also observed to pass through the photoresist during firing and settle underneath on alumina substrate in tje form of 0.5 mircometers sizd grains. The interaction is found useful for fabricating microlines and cantilevered structures for sensor developmet.


1985 - Screen printed thick-film nickel-silicon interaction [Articolo su rivista]
A., Singh; M., Prudenziati; Morten, Bruno; M., Bosi
abstract

This paper reports the interaction of scrren printed thick film nickel with N-Si (100), 3-6 ohmcm resistivity both unoxidised and oxidised with windows defifined into it, The nickel film after printing was air dried at 150 C for 10 min and finally air fired at 550 C, 750 C and 850 C in a conveyor furnace with 60 min cycle. The high temperature firing yielded the minimum sheet resistance of 55 mohm/square. The barrier heights and the ideality factors were 0.74, 1.5 ; 0.70, 1.0; 0.69, 1.0; and 0.73, 2.8 at the above temperatures. The contact resistance was found to be lowest, i. e90 ohm squarecm at the firing temperature of 850 C respectively. The SEm combined with EDS of the topo surface and the cross sections of the interface revealed (1) the lead from the printed line flows by 40 micrometers and 100 micrometers at firing temperatures of 750 C and 850 C respectively, (2) the interface reaction zone consisting of Ni2Si is uniform and is 1 micrometer thick. However at 850 C a few V-groves 5 micrometer X 5 micrometer filled with lead and nickel are generated. The possible applications of interactions are suggested.


1985 - Technique for lifting off thick film printed on alumina [Articolo su rivista]
A., Singh; M., Prudenziati; Morten, Bruno
abstract

A technique for lifting off thick film DP 9596 print fired on alumina substrate is reported. The positive phoresist is used as a relif mask. Various applications of the technique are also pointed out.


1983 - Excess noise and its temperature dependence in thick-film (cermet) resistors [Articolo su rivista]
A., Masoero; A. M., Rietto; Morten, Bruno; M., Prudenziati
abstract

Measurements have been made of the current noise in thick-film resistors (TFR) based on Ru-pyrochlore conductive grains, with sheet resistivities covering a range of four decades. The temperature dependence of the exponent (alfa) in 1/f noise spectra and the relative integral noise was investigated in the temperature range from 77 to 650 K. It shown that the presence of a minimum in the realtive voltage noise fluctuations os a general phenomenon, as is the increase in (alfa) with increasing temperature. Tevetheless these two effects seem not be mutually correlated. The possibility of developing interpretative model for noise phenomenon in TFR is discussed.


1983 - Thick-film technology and sensors [Articolo su rivista]
Morten, Bruno; Prudenziati, Maria; Taroni, Andrea
abstract

The advantages of thick-film technology for the manufacture of sensors are emphasized and exemplified by pressure capsules for automotive applications and a force-control device for tractors. The preliminary results of the characterization of thick-film thermistors are presented in terms of tolerance, sensitivity and stability for the aging process and are related to an analysis of the film composition.


1982 - A temperature Compensated Ultrasonic Sensor Operating in Air for Distance and Proximity Measurements [Articolo su rivista]
Canali, Claudio; G., De Cicco; Morten, Bruno; Prudenziati, Maria; Taroni, Andrea
abstract

An ultrasonic sensor operating in air was developed to measure distance (up to 100 cm) or to operate as a proximity sensor in a presettable distance range. The error in the measured distance is about ± 1 mm while the accuracy is maintained within ±1% of the reading in the whole temperature range from -20 °C to +110 °C, being the temperature dependence of the sound velocity electronically compensated. As a proximity sensor it can overcome most of the drawbacks and limitations of inductive, capacitive, optical, and Hall-effect commercial proximity sensors.


1981 - An ultrasonic proximity sensor operating in air [Articolo su rivista]
C., Canali; G., De Cicco; Morten, Bruno; A., Taroni
abstract

The project and performances of an ultrasonic sensor in air is described which, for a number of characteristics, can replace conventional proximity sensors. The possibility of detecting the target presence is treated. Characteristics as high response speed, high ratio between maximum operating distance , immunity from dust, dirt, mechanical vibrations and not dependence of sensitivity from target are included.


1981 - Characterization of thick-film resistor strain gauges on enamel steel [Articolo su rivista]
M., Prudenziati; Morten, Bruno; A., Taroni
abstract

Recently it has been shown that thick-film resistor starin gauges on ceramic sub strates exhibit noticeable piezoresistive effects, which allow one to develop highly-resistive, low-cost mechanical transducers. In this paper piezoresistive effects in thick-film resistive systems for enameled steel are analyzed and it is shown that they are as interesting for such applications thancks to they high strain sensitivity, low temperature coefficient of resistance and of gauge factors, low excess noise and high stability. Moreover the elastic properties of the substrate enable one to strain the resistors at more than 1000 microstrain with linear and reproducible characteristics.


1981 - Excess noise and refiring processes in thick-film resistors [Articolo su rivista]
Prudenziati, Maria; Morten, Bruno; Masoero, Aldo
abstract

Excess noise in thick-film resistors fired 1 to10 times under the same firing profile was examined Changes in structure and composition, which are responsible for variations in sheet resistivity and temperature coefficient of resistance, also affect the noise index in thick-film resistors. Changes in the noise index depend on resistor composition and nature of the substrate. The excess noise correlates with physico-chemical phenomena induced by refiring in the bulk of the resistors.


1980 - Influence of the Substrate on the Electrical Properties of Thick-Film Resistors [Articolo su rivista]
A., Cattaneo; L., Pirozzi; Morten, Bruno; Prudenziati, Maria
abstract

Studies of the linear expansion coefficients and temperature coefficients of resistance of Ru-based thick-film resistors on ZrO2, BeO, Al2O3, and steatite substrates showed that the substrate effect plays an important role in Ru-based resistors, so that, to understand the thick-film conduction mechanisms, it is necessary to take the substrate-resistor system into consideration. The minimun in the resistance-temperature curve varies for different substrates, even with resistor films of the same composition and sheet resistance. An equation is proposed which correlates the resistor gage factor with the thermal expansion coefficients of the ceramic substrate.


1980 - Piezoresistive effects in thick-film resistors [Articolo su rivista]
Canali, Claudio; D., Malavasi; Morten, Bruno; Prudenziati, Maria; Taroni, Andrea
abstract

Piezoresistive properties of thick-film resistors obtained with ink series supplied by different manufacturers were investigated as a function of composition, structure, sheet resistivity, and applied strain between 0 and ±1000 m strain. The strain sensitivity of thick-film resistors appears to be a strong function of the nature of the conductive grains and of the sheet resistivity of the paste; the results obtained suggest a dominant role of the tunneling effect in the conduction mechanism and in the strain sensitivity.


1980 - Strain Sensitivity in Thick-Film Resistors [Articolo su rivista]
Canali, Claudio; D., Malvasi; Morten, Bruno; Prudenziati, Maria; Taroni, Andrea
abstract

Piezoresistive properties of Du Pont 1400 series thick-film resistors were investigated by measuring longitudinal and transverse gauge factors as a function of applied strain between 0 and ± 1000 µstrain from -70 to + 140°C. The relative change in resistance of thick-film resistors is linear, reproducible, and hysteresis free for the full range of applied strain. They appear more sensitive than metal resistors and have a low temperature coefficient of both resistance (TCR) and of gauge factor.


1979 - Piezoresistive effects in MOS-FET useful for pressure transducers [Articolo su rivista]
C., Canali; G., Ferla; Morten, Bruno; A., Taroni
abstract

The piezoresistivity coefficients in p- and n- channel MOS transitors manufactured on silicon wafers cut parallel to the (111) and (100) planes as a function of VD and VG and of the temperature, between-20 and 120 C, have been measured with the particular aim of investigating the possible application of MOS transistors for strain measurements, by comparing the advantages and the diadvantages with bulk and diffused resistors. The characteristics of the MOS devices can be consistently better than the corresonding ones of bulk semiconductor strain gauges, partucularly as regards the temperature stability of resistivity and the electrical charactristics.


1979 - Strain sensitivity in film and cermet resistors: measured and physical quantities [Articolo su rivista]
Morten, Bruno; M., Prudenziati; A., Taroni
abstract

The strain coefficient of resistivity of resistors deposited on a substrate is analysed, and an expression for its correlation to the measurable longitudinal and transverse gauge factors is given for isotropic (metal, amorphous semiconductor and cermet) resistors. The use of this expression for the evaluation of other physical quantities is exemplified by the calculation of the temperature coefficients of resistivity for resistors on substrates of different thermal expansivity.


1978 - Sensori termoresistivi:un po' di fisica e tanta fantasia [Articolo su rivista]
Morten, Bruno; M., Prudenziati; A., Taroni
abstract

Viene descritto l'effetto termoresistivo e considerato il suo impiego nell'area dei sensori. Sono descritti inoltre i materiali e le tecniche di realizzazione di realizzaione di sensori insieme con esempi di dispositivi per la misura di temperatura, flusso e controllo di grandezze elettriche e fisiche.


1978 - Trasduttori di pressione ad effetto piezoresistivo: vent'anni di ricerca verso l'applicazione industriale [Articolo su rivista]
Morten, Bruno; M., Prudenziati; A., Taroni
abstract

Viene descritto l'effetto di piezoresistenza in metalli e semiconduttori. E' presentata la struttutura di un sensore di pressione e descritti l'elemento sensibile e di trasduzione. Oltre alla tecnologia costruttiva è presentata il principio operativo per sensori basati elementi sensibili metallici e a semiconduttore. E' infine presentata l'evoluzione di tecnologie realizzative dei sensori di pressione verso l'applicazione industriale.


1977 - Interazioni silicio-film metallici nella tecnologia dei dispositivi elettronici [Articolo su rivista]
C., Canali; G., Majni; Morten, Bruno; G., Ottaviani
abstract

In questi ultimi anni si è assistito ad un crescente interesse per lo studio e la conoscenza delle interazioni che avvengono a basse temperature ed in fase solida fra silicio ed i film sottili usati nelle metallizzazioni in quanto fortemente correlate con le prestazioni, l'affidabilità e la stabilità dei dispositivi.Queste interazioni possono essere suddivise in due categorie: quelle che danno luogo a soluzioni solide dei due elementi e quelle che portano alla formazione di composti. Entrambe le categorie includono metalli di vasto impiego nella tecnologia dei dispositivi quali ad esempio l'Al e l'Au, con cui il silicio forma soluzioni solide, ed il Pt e Pd con cui il silicio forma composti, i siliciuri, attualmente usati per le metallizzazioni dei dispositivi ad alta affidabilità e stabilità.L'articolo si propone di fornire una rassegna dei dati ottenuti nello studio delle interazioni in fase solida silicio-film metallici sottili allo scopo di mostrare quale rilevanza essi possono avere nella progettazione e nella tecnologia dei dispositivi al silicio.


1977 - Low cost frequency conversion of signal sullied by physical quantity sensors [Articolo su rivista]
M., Dondi; Morten, Bruno; M., Prudenziati; A., Taroni
abstract

The use of a general purpose sweeplable function generator as a frequency converter is examined and its performance is compared with that of several voltage to frequency converters. As an example of application of the converter in connection with physical quantity sensors, a one-trhermistor linear temperature transducer is presented.


1977 - Misuratori di velocità di fluidi a termistore: comportamento dinamico [Articolo su rivista]
Morten, Bruno; M., Prudenziati; A., Taroni; G., Zanarini
abstract

Questo lavoro illustra i risultati di uno studio dell'influenza degli effetti non lineari sul comportamento dinamico di flussimetri a termistore. Viene risolta con metodi numerici l'equazione non lineare che descrive il bilancio termico del dispositivo e vengono confrontate le previsioni teoriche coi risultati sperimentali. I risultati sottolineano che la descrizione del comportamento dinamico di flussimetri a termistore per mezzo di una sola costante di tempo è isoddisfacente. Si èpossono infatti variare sia la sensibilità che la velocità di risposta del flussimetro variando le condizioni di polarizzazione del termistore autoriscaldato. Viene mostrato un criterio per la scelta delle condizioni di lavoro più opportune per massimizzare la velocità di risposta e la sensibilità del sistema. Sono inoltre analizzati i vantaggi conseguibili sia mediante il funzionamento adel termistore a temperatura costante sia con l'uso di un circuito elettronico per la elaborazione del segnale. Infine sono discusse le possibilità di ottenere flussometri a termistore ad ampia banda passante.


1977 - On the piezoresistance coefficients of holes in Ge [Articolo su rivista]
Morten, Bruno; L., Reggiani
abstract

The aim of this letter is to include the contribution of the optical phonon scattering mechanism in theory of piezoresitive effect for the case of holes in covalent semiconductors. In this way a more complete study of the dependence with temperature of the piezoresistance coefficients is made possible and a comparison between theory and experiment is carried out.


1977 - Preparazione e proprietà di termistori pirolitici al boro [Articolo su rivista]
G. F., Cirri; G., Fidanzati; F., Forlani; Morten, Bruno; M., Prudenziati; A., Taroni
abstract

Nel presente lavoro è illustrata una nuova tenica di preparazione di termistori basata sulla deposizione chimica da fase vapore di boro su fili di molibdeno incriciati. Sono descritte le condizioni di deposizione e sono mostrati i vantaggi della struttura a fili incrociati. Tale struttura consente infatti di ottenere con una sola operazione il termistore completo di adduttori e consente inoltre il controllo diretto, durante il processo di deposizione, del valore della resistenza del dispositivo.Sono inoltre presentate le caratteristiche dei termistori realizzate e confrontate con quelle dei termistori ad ossidi.Sono infine riportati risultati realtivi alla linearizzazione delle caratteristiche resistenza- temperatura dei termistori al boro a confronto con quelli ottenibili, con l'impiego delle stesse tecniche, con tradizionali termistori ad ossidi.


1976 - Experimental resuts on dynamic behaviour of thermistor flowmeters [Articolo su rivista]
Morten, Bruno; M., Prudenziati; A., Taroni; G., Zanarini
abstract

The influence of non linear effects on dynamic behaviour of self-heated thermistor flowmeters is studied. The non linear equation which describes the device thermal balance is solved by numerical methods and the theorical prevision are compared with the results of experimental measurements. The results emphasizes that a description of dynamic behavior of thermistor flowmeters by means one time constant is very unsotisfacoty. Either response time ore sensitivity can be change appreciably by changing the bias conditions of the self-heated thermistor and a criterion is suggested for the choice of bias conditions which provide the best response speed and sensitivity of the system.


1976 - Speed-up of flow measurements with thermistors [Articolo su rivista]
Morten, Bruno; M., Prudenziati; A., Taroni; G., Zanarini
abstract

In this work we present an application of an electronic prediction circuit for speed-up of flow measurement with thermistors. The matching betwee the circuit and thermistors is studied and some considerations are presented on the enhancement of bandwidth of thermistor anemometer. Operating conditions are suggested in order to optimize the dynamic behaviour of the system.


1975 - Some uniaxial piezoresistive effects in p-type silicon [Articolo su rivista]
Morten, Bruno; A., Taroni
abstract

Some experimental results obtained at 300 K and 77 are presented regardind the silicon crystal doped with boron.


1973 - Piezoresistive effect in silicon diffused layers [Articolo su rivista]
F., Conti; Morten, Bruno; C., Nobili; A., Taroni
abstract

In this work results are presented regarding measurements on silicon diaphragms with piezoresitive diffused layers subjected to a differential pressure. The geometric feature allows the simultaneous calculation of the fundamental piezoresivity coefficients,


1973 - Piezoresistive effects in sicon epitaxial layers [Articolo su rivista]
F., Conti; Morten, Bruno; C., Nobili; A., Taroni
abstract

This note are presented some experimental results on piezoresistive properties of p-type-boron doped silicon epitazial layers grown on single-crystal n-type silicon substrates.