Evaluation of Bipolar Degradation in SiC MOSFETs for Converter Design

Bipolar degradation in 4H-SiC Power MOSFETs has a significant influence on the device performance. It originates from body diode operation and Shockley Stacking Faults (SSF) development in the basal plane. In this study, we have investigated the transients of initial SSF development of 1.7kV SiC MOSFETs by conducting stress current through body diode. The variation of forward voltage drop in discrete steps is shown, which explains SSF expansion exhibits a non-simultaneous occurrence across all defects. A test method has been proposed to ensure the full degradation to determine the device performance for converter design. Additionally, parallel-connected SiC MOSFETs have been tested to study impact of bipolar degradation on the early stages of converter operation.