Materials Science Forum Vols. 615-617

Abstract: Currently there are several silicon carbide (SiC) field effect or bipolar transistor types in development with normally-on and normally-off characteristics. It is not yet clear, which transistor type will prevail in the market and which will remain a niche product. This is not only determined by their electrical characteristics, but also by their acceptance by engineers. In this paper the implementation and the performance of 1200 V / 20 A / 100 m SiC-DMOSFETS and 1200 V / 12 A / 125 m normally-off SiC-JFETs in photovoltaic inverters (PV-inverters) is shown.

Abstract: The development of large area, up to 70m/1kV (0.45cm x 0.45cm) 4H-SiC vertical DMOSFETs is presented. DC and switching characteristics of high-current, 100Amp All-SiC power switching modules are demonstrated using 0.45cm x 0.225cm DMOSFET die and commercial Schottky diodes. The switching performance from room temperature up to T=200°C of the All-SiC modules is presented, with as much as ten times lower losses than co-fabricated Si-based modules using commercial IGBTs.

Abstract: For higher power application of SiC devices, we have designed and developed an inverter module with paralleled SiC-MOSFETs and SiC-SBDs.We have successfully completed the operation of the SiC inverter module at continuous rating of up to 11kW with carrier frequency of 20 kHz. The power loss during the operation was measured by calorimetric method and the results showed that the loss was considerably reduced by 30% of a similar rating commercialized IGBT power module at carrier frequency of 15 kHz.

Abstract: Because of the fixed chip size of available sample devices a comparison of SiC-JFET and silicon IGBT with another fixed chip size necessitates the regard to the active area of the chip. The paper presents measurement results considering the active area and shows a comparison of inverter losses depending on junction temperature and switching frequency.

Abstract: The expansion of the electrical communications and distribution networks strongly contribute to the increase in the risks of appearance of defaults, such as over-voltage and/or over-current. These developments promote the emergence of safety devices for serial protection commonly named Current Limiting Devices (CLD's). This work presents the design, manufacture and characterization of silicon carbide accuMOSFET of high power density ratings. Components able to limit the current up to 450A @ 350V were manufactured and characterized. Specific characterization test benches were developed, able to provide high energy pulses required for characterization. CLDs behavior subjected to short overloads has been measured experimentally and analyzed be means of simulations for long-time overloads. A maximum sustainable high energy of 35 Joules has been estimated. This achievement give opportunities to build new architectures of serial protection systems.

Abstract: The design of analog integrated circuits, for instance, the operational amplifiers, have been widely perfected with devices and processes available in silicon. However, analogous circuits have been the subject of research in Silicon Carbide (SiC). Among SiC devices, 4H-SiC Lateral-Trench JFET (LTJFET) transistor offers advantages and new opportunities to make affordable and reliable analog integrated circuits for harsh environment. In this paper: (1) SiC LTJFET is characterized for modeling and simulation, (2) effect of temperature variation on SiC LTJFET threshold voltage and small signal parameters are reported, (3) gain performance and small signal parameters of the basic analog circuit block, Common Source (CS) amplifier, based on the variation of the load transistors threshold voltage (Vth) are studied and analyzed, and (4) frequency and transient response of the cascoded CS amplifier (CS-Cas) are reported.

Abstract: Of all the wide bandgap semiconductors, SiC is currently the most attractive material for aerospace applications. It offers significant advantages at high temperatures and high voltage levels while benefiting from an excellent thermal conductivity, the resistance to a harsh radiation environment (in particular in medium low orbits (MEO) where the Van Allan belts show a high concentration of electron and proton radiation) and an advanced materials technology. Due to the significant progress in the last years in monocrystalline SiC material fabrication and process technology, the space industry is increasingly interested in exploiting the SiC characteristics for electronic application. Although the requirement for space components are highly demanding with space qualified technological processes required, it is expected that high quality commercial SiC components submitted to a stringent screening process will allow the realisation of highly reliable space components. Electronic applications of monocrystalline SiC for space mainly exploit the high breakdown electric field which allows for lower specific on-resistances due to high doping and thinner drift region layers in vertical SiC power device structures. Among all SiC power devices, high voltage rectifiers have reached the highest degree of maturity. EADS Astrium has started evaluation activities of commercially available 1200 V SiC diodes and also 4.5 kV diodes developed in the frame of the ESA CHPCA (components for high power conditioning application) project. One application is power supply of ion thrusters on satellites which require electric power in the range of 2 to 8 kW at voltages of 1 to 2 kV. Mechanical aerospace applications of polycrystalline SiC

Abstract: Silicon Carbide 300V-5A Ni and W Schottky diodes with high temperature operation capability (up to 300°C) have been fabricated. This paper reports on the stability tests (ESA space mission to Mercury, BepiColombo requirements) performed on these diodes. A DC current stress of 5A has been applied to these diodes at 270°C for 800 hours. These reliability tests revealed both, degradation at the Schottky interface (forward voltage drift) and at the diode top surface due to Aluminum diffusion (bond pull strength degradation). The use of W as Schottky metal allows eliminating the forward voltage drift producing stable metal–semiconductor interface properties. Nevertheless, SEM observations of the top metallization still reveal metal degradation after stress. The bond pull strength of the wire bond is also significantly reduced.

Abstract: This paper updates the long-term 500 °C electrical testing results from 6H-SiC junction field effect transistors (JFETs) and small integrated circuits that were introduced at ICSCRM-2007. Two packaged JFETs have now been operated in excess of 7000 hours at 500 °C with less than 10% degradation in linear I-V characteristics. Several simple digital and analog demonstration integrated circuits successfully operated for 2000-6500 hours at 500 °C before failure.

Abstract: GaN epitaxial layers were grown on sapphire substrate deposited an aluminum (Al) buffer layer using a hydride vapor phase epitaxy (HVPE) system with a two-zone resistance furnace. A 10nm-thick Al buffer layer was prepared by an e-beam evaporation in order to reduce the stress resulted from thermal mismatch between the GaN layer and the substrate. The growth temperature and growth rate for GaN epitaxial layer were 1050oC and 40 m/hr, respectively. GaN epitaxial layer grown on substrate with Al buffer layer exhibited uniform and smooth morphology on 2-inch whole substrate and a bow value of 33.5 m. The addition of Al-buffer layer apparently reduced the full width at half maximum (FWHM) value of GaN layer, which indicated the improvement of crystal quality.