Utilizing the Electroluminescence of SiC MOSFETs as Degradation Sensitive Optical Parameter

Bias Temperature Instability (BTI) is a major reliability challenge of SiC MOSFETs due to the high defect density of the gate oxide compared to Si MOSFETs. Charge trapping at these defects causes gradual threshold voltage drift and degradation of the on-state resistance, which leads to higher device losses and temperatures. To avoid critical failures, the health state of the gate oxide can be monitored by measuring the BTI-related degradation. This work demonstrates that the electroluminescence (EL) emitted by the body diode of SiC MOSFETs can be utilized as such an aging precursor. As trapped charges at the gate oxide influence the current proportions between the channel and the light-emitting body diode during third quadrant operation, the EL exhibits a sensitivity to BTI that can be sensed as part of online condition monitoring. This paper investigates the EL sensitivity to BTI by means of accelerated aging tests and EL measurements on an industry-standard SiC power MOSFET. The measurement results show a strong increase in the EL intensity for a positive threshold voltage drift, thereby validating the proposed sensing approach.