Abstract: We address the two critical challenges that currently limit the applicability of SiC MOSFETs in commercial power conversion systems: high-temperature gate oxide reliability and high total current rating. We demonstrate SiC MOSFETs with predicted gate oxide reliability of >106 hours (100 years) operating at a gate oxide electric field of 4 MV/cm at 250°C. To scale to high total currents, we develop the Power Overlay planar packaging technique to demonstrate SiC MOSFET power modules with total on-resistance as low as 7.5 m. We scale single die SiC MOSFETs to high currents, demonstrating a large area SiC MOSFET (4.5mm x 4.5 mm) with a total on-resistance of 30 m, specific on-resistance of 5 m-cm2 and blocking voltage of 1400V.
Abstract: We developed a JBS diode with characteristics of a low forward voltage and a low leakage current at 3kV. Further, we built a prototype of a 3kV/200A hybrid module, equipped with Si-IGBTs and SiC-JBS diodes. We attempted to decrease the recovery loss, and the decrease in the turn-on power loss, by using a hybrid module and a high-speed drive circuit. Moreover, we estimated that the total energy loss of the converter and the inverter were reduced to about 33%.
Abstract: This work demonstrates that a stable voltage reference with temperature, in the 25°C-300°C range is possible with SiC. This paper reports the simulated and experimental results as well and a practical and simplified vision on the principles of thermally compensated voltage reference circuits, usually named bandgap references. For our demonstration, we have used SiC Schottky diodes. The influence of the barrier height and the ideality factor on the voltage reference and a comparison between simulated and experimental results are also presented.
Abstract: The NASA Glenn Research Center has previously reported prolonged stable operation of simple prototype 6H-SiC JFET integrated circuits (logic gates and amplifier stages) for thousands of hours at +500 °C. This paper experimentally investigates the ability of these 6H-SiC JFET devices and integrated circuits to also function at cold temperatures expected to arise in some envisioned applications. Prototype logic gate ICs experimentally demonstrated good functionality down to -125 °C without changing circuit input voltages. Cascaded operation of gates at cold temperatures was verified by externally wiring gates together to form a 3-stage ring oscillator. While logic gate output voltages exhibited little change across the broad temperature range from -125 °C to +500 °C, the change in operating frequency and power consumption of these non-optimized logic gates as a function of temperature was much larger and tracked JFET channel conduction properties.
Abstract: It is strongly desired to operate SiC power devices at higher junction temperatures (Tj), but that often entails problems because they contain a variety of materials with thermal activity or weakness. An example of such troubles is the steep increase in resistance of the Al electrode in the source (or emitter) contact holes, caused by electromigration (EM). In this work, EM reliability of the contact hole in SiC power devices was evaluated for an improved Al electrode sandwiched between thin TaN layers. An estimated mean time to failure (MTTF) of approximately 3400 years was achieved under conditions of Tj = 300°C and J = 104 A/cm2.
Abstract: Normally-off 4H-SiC MOSFETs are used to build NMOS logic gates intended for high temperature operation. The logic gates are characterized between 25°C and 500°C. Stable gate operation for more than 200h at 400°C in air is demonstrated. The excellent MOS reliability is quantified using I-V curves to dielectric breakdown and constant voltage stress to breakdown at 400°C. Although the effective tunneling barrier height B for electrons lowers to 2eV at 400°C, the extrapolated lifetime from constant voltage stress to breakdown measurements is longer than 105h at 400°C for typical logic gate operating field strength of 2MV/cm.
Abstract: Bi-directional solid-state-circuit-breakers (SSCBs) are highly desirable in power-electronic fault-protection applications due to their high actuation speed and repeated fault isolation capability. Normally-on SiC vertical-channel JFETs (VJFETs) are excellent candidates for high power/temperature scalable SSCB applications as majority carrier devices with low conduction losses and stable +300°C thermal characteristics. 600-V / 2-A bi-directional power flow was demonstrated using two VJFETs connected back-to-back with their sources in common. The low VJFET pre-breakdown leakage currents and sharp onset of breakdown are critical in enabling bi-directional power flow. 0.1-cm2 low conduction-loss VJFETs were designed for efficient and reliable SSCB applications.
Abstract: The 50W Quasi-resonant mode SMPS which adopted a normally-on-type SiC JFET as a switch has been designed and characterized. A simple decision circuit and an auxiliary power supply was utilized to safely protect the JFET from an in-rush current at initial operation stage and to provide sufficient negative voltage for a complete JFET drive. Even without a refine engineering, the SMPS showed 96% efficiency at a full load state.
Abstract: Looking back to the development of inverters using SiC switches, it appears that SiC devices
do not behave like their silicon counterparts. Their ability to operate at high temperature makes
them attractive. Developing drivers suitable for 200 °C operation is not straightforward. In a perspective
of high integration and large power density, it is wise to consider a monolithic integration of the
driver parts for the sake of reliability. Silicon is not suitable for high ambient temperature; silicon-oninsulator
offers better performances and presents industrial perspectives.
The paper focuses on a SiC BJT driver: it processes logical orders from outside, drives adequately
the BJT to turn it either on or off, monitors the turn-off and turn-on state of the device, and acts accordingly
to prevent failure. SiC BJT imposes specific performances different from the well known
ones of SiC JFET or MOSFET. The paper addresses a preliminary analysis of a SOI driver, anticipating
the behavior of SiC-BJT and the change in behavior at high temperature. A discret driver has
been designed and fabricated. Elementary functional blocks have been validated, and a BJT converter
successfully operated at high temperature with high efficiency ( = 88%).
Abstract: Lateral normally-on dual gates MESFETs withstanding a drain/source voltage in excess of 200V have been fabricated on semi-insulating 4H-SiC substrate. This paper reports on the fabrication, DC characterization and in-circuit behavior of the MESFETs. Temperature dependent DC characterization has been carried out up to 473K. The performances of basic analog circuits such as an amplifier and a clock, using these MESFETs, are detailed and analyzed.