Bias temperature instability and condition monitoring in SiC power MOSFETs

Threshold voltage shift due to bias temperature instability (BTI) is a major concern in SiC power MOSFETs. The SiC/SiO2 gate dielectric interface is typically characterized by a higher density of interface traps compared to the conventional Si/SiO2 interface. The threshold voltage shift that arises from BTI has significant implications on the reliability of SiC power MOSFETs, hence, techniques for detecting the change in electrical parameters due to gate oxide degradation are desirable. Using accelerated high temperature gate bias stress tests on SiC MOSFETs, it has been shown that the output and transfer characteristics are affected by BTI. This paper presents the impact BTI induced threshold voltage shift on the forward voltage of the SiC MOSFET body diode during third quadrant operation. Using the forward voltage of the body diode during reverse conduction of low currents, threshold voltage shift can be detected, hence, the impact of BTI can be evaluated. The implications of the body diode forward voltage shift on junction temperature measurements are also studied in the context of TSEPs. The findings in this paper are important for engineers seeking to implement condition and health monitoring techniques on SiC power devices.