Papers by Author: Heather O'Brien

Abstract: High performance 15 kV n-GTOs were demonstrated for the first time in 4H-SiC. The device utilized a 140 μm thick, lightly doped n-type drift layer, with 1450°C lifetime enhancement oxidation, which resulted in a carrier lifetime of 17.5 μs. The p⁺ backside injector layer was thinned to minimize parasitic resistances. A room temperature forward voltage drop of 5.18 V was observed at a current density of 100A/cm². A 1 cm² device showed a leakage current of 0.17 μA at 15 kV. The 4H-SiC n-GTO showed latching characteristics, and showed a turn-off time of 170 ns in a resistive load switching setup, which represents about a factor of 45 improvement in turn-off speed over 4H-SiC p-GTOs with comparable voltage and current ratings.

Abstract: The Army Research Laboratory has collaborated with Cree, Inc. and Silicon Power Corp. to develop 9 kV-blocking, 1.0 cm² Super-GTOs. In this study, several 1.0 cm² GTOs were individually switched up to 6.0 kA in a low-inductance, high dI/dt (2.1 kA/µs) circuit to evaluate turn-on delay and optimize the gate control. Turn-on delay was evaluated relative to gate drive current, and the delay was reduced by 1.1 µs when gate amplitude was increased from 1 A to 8 A. Increasing gate current delivered to each GTO also successfully reduced variation in turn-on delay from device to device by at least 50%, and mitigated mismatch in turn-on between pairs of GTOs switched in parallel. As silicon carbide material processing and device development continue to evolve, the ultimate solution will be to reduce remaining material defects and to control minority carrier diffusion length through more uniform doping across the wafer. These steps will enable modules of parallel GTOs to perform at maximum capability.

Abstract: The development of new semiconductor designs requires that extensive testing be completed in order to fully understand the device’s characteristics and performance capabilities. This paper describes the evaluation of experimental Silicon Carbide high power Super Gate Turn Off Thyristors (SiC SGTOs) in a unique test bed that is capable of stressing the devices with very high energy/power levels while at the same time mimicking a realistic, real world application for such devices.

Abstract: In this paper, for the first time, we report 12 kV, 1 cm² SiC GTOs demonstrated with a novel negative bevel termination, which improves the breakdown voltage by >3.5 kV compared to the conventional multiple-zone Junction Termination Extension (JTE). The significant improvement in the blocking voltage was attributed to the elimination of the electrical field crowding in the periphery of the mesa with conventional JTE termination. This new termination has been used in both electrically and optically triggered SiC GTOs. An ultrafast turn-on speed of 70 ns has been measured on 12 kV, 1 cm² SiC light triggered GTOs.