S. Cassette

Ircom, Angers, Pays de la Loire, France

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Publications (37)33.61 Total impact

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    ABSTRACT: Channel temperature has a strong impact on the performance of a microwave power transistor. In particular, it has a strong influence on the power gain, energetic efficiency, and reliability of the device. The thermal optimization of device geometry is therefore a key issue, together with precise measurements of temperature within the channel area. In this paper, we have used scanning thermal microscopy to perform temperature mapping, at variable dc bias points, on an AlGaN/GaN high-electron mobility transistor made on epilayers grown on silicon carbide substrate. We have analyzed the variation of the thermal resistance values, which are deduced from these measurements, with bias conditions V<sub>GS</sub> and V<sub>DS</sub>. The observed nonlinear behavior is found to be in excellent agreement with physical simulations, strongly pointing out the large variability of the extension of the dissipation area with the dc bias conditions
    IEEE Transactions on Electron Devices 04/2007; · 2.06 Impact Factor
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    ABSTRACT: Within the european project Microtherm, we have developed a CCD-based thermoreflectance system which delivers thermal images of working integrated circuits with high spatial and thermal resolutions (down to 350 nm and 0.1 K respectively). We illustrate the performances of this set-up on several classes of semiconductor devices including high power transistors and transistor arrays in silicon, gallium arsenide and gallium nitride technologies.
    International Workshop on Thermal Investigation og ICs ans Systems, 27-30 Sep 2005, Belgirate Lake Maggiore, Italy, p224-228. 09/2005;
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    ABSTRACT: In this contribution we report on combined investigations of hot areas in a high power high electron mobility transistor (HEMT) using a scanning thermo-elastic microscope and finite element simulations of the problem. The sample was a AlGaN/GaN-HEMT grown on sapphire substrate, with a gold coating for improved thermal management. The FE simulations were performed based on the ANSYS program version 5.7. The thermo-elastic response was detected with an Explorer AFM-head of Topometrix. To allow simultaneous detection of the topology and of the thermo-elastic expansion images, the explorer had been modified for AFM measurements in the DC mode and at the double frequency of the thermal sinus in AFM contact mode. The thermo-elastic image of the hot area of the HEMT recorded at 2f shows a bright line as the hot area which is located along the gate, between gate and drain. The absolute value of the vertical expansion has been calibrated from the measured diode signal by use of the microscope’s force-distance calibration curve. In order to obtain a reliable estimate of the maximum temperature on the hot line, the temperature image obtained by FE simulation is calibrated using the thermal expansion of the gold film of known thermal expansion coefficient.
    Journal de Physique IV (Proceedings) 01/2005; · 0.29 Impact Factor
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    ABSTRACT: The temperature and thermo-elastic expansion of the heated area in a high power, high electron mobility transistor (HEMT) device have been investigated by means of finite element calculations and scanning thermal expansion microscopy. With both procedures a hot line is located near the gate line of the transistor. To determine the absolute temperature, the thermo-elastic response was calibrated on the basis of the force–distance curve of the AFM and the thermal expansion of the gold layer on top of the heated areas. The maximum temperatures deduced by the two procedures are in reasonable agreement whereas discrepancies are found for the temperature profile of the hot line, pointing towards a possible influence of the large aspect ratio of the device on the thermo-elastic measurement.
    Superlattices and Microstructures 03/2004; 35:477-484. · 1.56 Impact Factor
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    ABSTRACT: The burn-in effect in GaInP/GaAs HBTs has been associated to processes involving hydrogen contained in the GaAs carbon doped base region of this transistor. Looking for a better understanding of this effect we have realised a detailed study of the evolution of the charge transport properties during the burn-in effect and during the step by step thermal restoration to its initial condition. Our results indicate that hydrogen processes taking place in the emitter-base space charge region and in the neutral emitter region are the main mechanisms of the burn-in. Finally, solutions for reducing this burn-in effect are discussed.
    physica status solidi (c) 02/2003;
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    ABSTRACT: In this paper, we report on the properties of GaN films and AlGaN/GaN HEMT structures grown by molecular beam epitaxy on resistive Si(1 1 1) substrates. The properties of the GaN buffer layer and the AlGaN/GaN HEMTs are presented. Finally, both static and high-frequency performances of sub-micron gate length devices are analyzed demonstrating their RF power capability. (C) 2002 Elsevier Science B.V. All rights reserved.
    Journal of Crystal Growth 01/2003; · 1.55 Impact Factor
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    ABSTRACT: In this paper, we report on the properties of GaN films and AlGaN/GaN HEMT structures grown by molecular beam epitaxy on resistive Si(111) substrates. The properties of the GaN buffer layer and the AlGaN/GaN HEMTs are presented. Finally, both static and high frequency performances of submicron gate length devices are analysed demonstrating their RF power capability.
    physica status solidi (c) 01/2003;
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    ABSTRACT: Defects in the emitter region of Ga0.51In0.49P/GaAs heterojunction bipolar transistors (HBTs) were investigated by means of deep-level transient spectroscopy. Both annealed (635 °C, 5 min) and as grown metalorganic chemical vapor deposition epitaxial wafers were investigated in this study, with an electron trap observed in the HBT emitter space-charge region from both wafers. The deep-level activation energy was determined to be 0.87±0.05 eV below the conduction band, the capture cross section 3×10−14 cm2 and the defect density of the order of 1014 cm−3. This defect was also found to be localized at the emitter–base interface. © 2002 American Institute of Physics.
    Journal of Applied Physics 08/2002; 92(5):2803-2806. · 2.21 Impact Factor
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    ABSTRACT: Al<sub>0.3</sub>Ga<sub>0.7</sub>N/GaN high electron mobility transistor (HEMT) structures have been grown on resistive Si(111) substrate by molecular beam epitaxy (MBE) using ammonia (NH<sub>3</sub>). The use of an AlN/GaN intermediate layer allows a resistive buffer layer to be obtained. High sheet carrier density and high electron mobility arc obtained in the channel. A device with 0.5 μm gate length has been realised exhibiting a maximum extrinsic transconductance of 160 mS/mm and drain-source current exceeding 600 mA/mm. Small-signal measurements show f<sub>t</sub> of 17 GHz and f<sub>max</sub> of 40 GHz
    Electronics Letters 02/2002; · 1.04 Impact Factor
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    ABSTRACT: GaAs HBT (heterojunction bipolar transistor) technology has reached a certain degree of maturity in the last decade, although reliability problems are not completely solved. In consequence, a material system based on InGaP/GaAs is used, resulting in improved device reliability after the base-emitter interface and the metal contacts have been optimised. The increasing demand for security relevant applications and for the mass market requires not only highly reliable devices and their lifetime data, but also an increased physical understanding of degradation mechanisms and short times for reliability evaluation. In this paper, two approaches are presented for the excitement of the "hydrogen-effect", which has been reported in connection with InGaP HBTs.
    Physical and Failure Analysis of Integrated Circuits, 2002. IPFA 2002. Proceedings of the 9th International Symposium on the; 02/2002
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    ABSTRACT: For high-power and high-frequency electronic applications, the III-V nitride layers are usually grown on sapphire or silicon carbide substrates. However, the development of these applications on silicon substrates has obvious technological advantages (cost, integration). In the present work, AlGaN/GaN heterostructures are grown on a resistive [111] silicon substrate (4000-10000 Ω.cm) in a reactive molecular beam epitaxy system using ammonia (Riber Compact 21). The structural quality of the epilayers as well as electrical properties have been investigated. AlGaN/GaN HEMT devices with different gate lengths and source to drain spacings have been realized in order to investigate their static characteristics and RF power performances.
    Molecular Beam Epitaxy, 2002 International Conference on; 02/2002
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    ABSTRACT: An experimental characterization of GaN FETs is given in this paper. A pulsed I-V/pulsed S-parameters measurement set-up is used to investigate the trapping and thermal behavior of GaN MESFETs. It is shown that electrical performances are strongly affected by surface and substrate traps and that those effects are closely linked to the temperature of the device. RF measurements up to a drain voltage of 100 V and a temperature of 320°C are presented
    Microwave Symposium Digest, 2001 IEEE MTT-S International; 02/2001
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    ABSTRACT: This paper reports the present status of GaAs based-heterojunction bipolar transistor (HBT) under development at Thales. We have developed a complete GaInP/GaAs-based technological process from material studies to discrete devices and microwave monolithic integrated circuits (MMIC) realisations. This know-how has been transferred recently to Thales/United monolithic semi-conductors. Discrete devices with output power over 1 W and power added efficiency (PAE) over 50% have been obtained at 10 GHz in CW. 8 W MMIC amplifiers have been fabricated using the same unit cells. The first reliability results are promising: more than 6000 h without failure for devices stressed up to 210°C and 40 kA cm−2. However, it seems that these results can still be improved. Some physical properties of the GaInP/GaAs HBT structures are suspected to have a major impact on the device reliability. The role of key parameters such as hydrogen incorporation in the GaAs base layer or residual strain in the GaInP/GaAs HBT structure has been investigated and its effects on the device characteristics identified. However, the major reliability improvement came from a novel way to passivate the extrinsic base surface. A comparison of the obtained results (device performance and reliability) with some of the best reported values in the literature (HP, TI, Daimler-Benz, etc.) is presented.
    Materials Science in Semiconductor Processing 01/2001; · 1.34 Impact Factor
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    ABSTRACT: We report the result of investigation on hydrogen effects on GaInP/GaAs HBT structures originating from different MOCVD and CBE suppliers. It is demonstrated that hydrogen gives rise to initial unstable electrical behaviour by cross-examination of samples with and without hydrogen either intrinsically or by thermal-assisted removal. Annealing conditions to remove hydrogen have been optimized on the basis of SIMS analyses and Gummel plot characteristics to control eventual degradation of the junctions. It has been found that under particular doping and growth conditions, C2H complexes can be formed. These defects appear more stable than CH complexes which may explain the difficulty to remove hydrogen from some epitaxial layers.
    Materials Science and Engineering B 01/2001; 80(1):279-283. · 1.85 Impact Factor
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    ABSTRACT: This paper reports on the investigation of GaInP/GaAs HBT-advanced structures with well-controlled strained base layers based on GaAs : C/GaInAs : uid superlattice heterostructures. High-resolution X-ray diffraction (HRXRD) and TEM experiments performed on test GaAs : C/GaInAs : uid superlattice heterostructures reveal well defined and sharp GaInAs/GaAs well/barrier interfaces with a high structural quality. C- V measurements and SIMS analysis, indicate that a low base sheet resistance is achieved with less carbon concentration than needed in the commonly HBTs C-doped GaAs base layers, together with a large strain reduction as shown by X-ray. HBT test structures consisting of 8-11 (GaAs : C/GaInAs : uid) period superlattice base layers, with GaInAs thickness varying from 0.5 to 3.4 nm have been processed. It is demonstrated that the GaInAs layer thickness must be less than 1 nm to preserve the current gain β of the device.
    Journal of Crystal Growth 12/2000; 221(1):717-721. · 1.55 Impact Factor
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    ABSTRACT: A fast method for reliability evaluation and wafer level reliability measurements is presented. This method requires a physics-of-failure based approach. We propose pulsed electrical stress for reliability and thermal characterisation and present both experimental and theoretical results. An improved measurement set-up allows dynamic pulse-response measurement and direct parameter extraction. Dedicated analytical and numerical physical models have been developed. Step stress tests were carried out on HBT, Schottky diode and TLM structures. An extraction of electric field, internal temperature, carrier distribution and charge carrier temperature was performed, based on physical device models. Different device degradation mechanisms are analyzed and their relevance is discussed with respect to life-time calculation
    Integrated Reliability Workshop Final Report, 2000 IEEE International; 02/2000
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    ABSTRACT: The first fabrication and RF characterisation of an InGaP/GaAs single heterojunction bipolar transistor in collector-up topology with Schottky contact are reported. Boron implantation is employed to prevent current injection into the extrinsic base region. Realised devices exhibit F<sub>MAX</sub>=110 GHz and breakdown voltage BV<sub>CE0</sub>=16 V. The RF gain of these components appears to be less sensitive to HBT development than standard emitter-up HBTs
    Electronics Letters 05/1999; · 1.04 Impact Factor
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    ABSTRACT: The interface chemistry of WN/4H–SiC structures has been studied by means of X-ray photoelectron spectroscopy (XPS). XPS investigations have been performed on as deposited, 800°C and 1200°C annealed (4 min) samples. The as deposited and 800°C annealed samples are characterized by chemically inert interfaces. Complete nitrogen out-diffusion from the WN layer, significant carbon diffusion into the contact layer, tungsten carbide and tungsten silicide formation occur during the 1200°C annealing process. The 800°C annealed WN/4H–SiC contacts are found to be of a Schottky type with a barrier height of 0.91 eV. The Schottky barrier height and the ideality factor show no significant changes during 100 h storage at 500°C under nitrogen and during operation at increasing temperature up to 350°C in air.
    Applied Surface Science 01/1999; 151(3):225-232. · 2.54 Impact Factor
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    ABSTRACT: Annealed W (WN)/4H–SiC interfaces have been compared on the basis of X-ray photoelectron spectroscopy (XPS) studies. The 1200°C annealed W (WN)/4H–SiC structures are characterized by intense interface reactions leading to tungsten carbide and tungsten silicide formation in the contact layers. The 800°C annealed WN/4H–SiC structure exhibits a chemically inert interface, and the 800°C annealed WN/4H–SiC contact is found to be of a Schottky type with a barrier height of 0.94 eV and an ideality coefficient of 1.09.
    Thin Solid Films 01/1999; 337(1):180-183. · 1.87 Impact Factor
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    ABSTRACT: The interface chemistry of nickel and tungsten based contacts on SiC has been investigated by XPS on as-deposited samples and after contact formation. After annealing at 950 °C for 10 min, Ni/SiC and Ni/Si/SiC ohmic contacts are formed due to the chemical reactions, as a result of which Ni2Si appears. However, Ni/Si (instead of pure Ni) deposition on SiC leads to modification of the diffusion processes and formation of a contact layer free of carbon. After annealing at 1200 °C for 4 min, the WN (W)/SiC systems are characterized by strong interface reactions resulting in W5Si3 and W2C formation in the contact layer. The 800 °C annealed WN/SiC contact is characterized by a chemically inert interface, and is found to be of a Schottky type.
    Thin Solid Films 01/1999; 343:637-641. · 1.87 Impact Factor