Investigation on the Degradation Mechanism for SiC Power MOSFETs Under Repetitive Switching Stress

The degradation of electrical parameters for SiC power metal-oxide-semiconductor field-effect transistors (MOSFETs) under repetitive switching stress is investigated in detail. The dominant degradation mechanism is demonstrated to be the injection of negative charges into the gate oxide interface along the channel. It results in the increase in threshold voltage ( V_th) and the increase in ON-state resistance ( R_dson) under low gate bias condition. Furthermore, the influences of different stages during an entire switching process on the degradation trend of the device are verified. It is found that the charges are mainly injected into the gate oxide during the conduction stage. Even though the turn-on stage rarely results in the injection directly, it increases the junction temperature ( T_j), contributing to the injection of charges during the conduction stage. However, the turn-off stage barely degrades the performance of the device. The research also proves the robustness of SiC power MOSFETs under repetitive out-of-safe operating area (SOA) switching conditions. Moreover, the degradation of switching behaviors of the device is analyzed. The increased V_th increases the Miller plateau voltage ( V_gp), leading to the increase in turn-on time and the decrease in turn-off time. Hence, the turn-on dissipated energy ( E_on) increases, while the turn-off dissipated energy ( E_off) decreases after enduring the stress.