Degradation of 900 V SiO2/4H-SiC MOSFETs Due to Negative Gate Voltage Stress

SiO₂/4H-SiC metal-oxide field-effect transistors (MOSFETs) have been attractive for next-generation power devices. We focused on negative bias temperature instability (NBTI) for the 900 V SiO₂/4H-SiC MOSFETs in this work. First, we measured gate leakage current in both positive and negative directions. From these measurements, we found that hole trapping was dominant during NBTI. We measured transfer characteristics before and after applying constant gate voltage stress. We also applied the stress at 150℃ for comparisons. We measured the threshold voltage in virgin state, stressed one, and after 24 hours of discharge, respectively. As a result, the threshold voltage was shifted negatively due to NBTI. This negative shift was attributed to a formation of positive charges. The NBTI induced oxide trap charging at room temperature and activated additional traps at 150oC. We also measured the change in gate leakage current, which did not change significantly.