Reliability of high voltage 4H-SiC MOSFET devices

The commercialization of 4H-SiC MOSFETs will greatly depend on the reliability of gate oxide. Long-term gate oxide reliability and device stability of 1200 V 4H-SiC MOSFETs are being studied, both under the on- and off-states. Device reliability is studied by stressing the device under three conditions: (a) Gate stress - a constant gate voltage of +15 V is applied to the gate at a temperature of 175 degrees C. The forward I-V characteristics and threshold voltage are monitored for device stability, (b) Forward current stress - devices are stressed under a constant drain current of I-d = 4 A and V-g = 20 V. The devices were allowed to self-heat to a temperature of T-sink = 125 degrees C and the I-V curves are monitored with time, and (c) High temperature reverse bias testing at 1200 V and 175 degrees C to study the reliability of the devices in the off-state. Our very first measurements on (a) and (b) show very little variation between the pre-stress and post-stress I-V characteristics and threshold voltage up to 1000 hrs of operation at 175 degrees C indicating excellent stability of the MOSFETs in the on-state. In addition, high temperature reverse bias stress test looks very promising with the devices showing very little variation in the reverse leakage current with time.