Investigations on degradation and optimization of 1.2kV 4H-SiC MOSFET under repetitive unclamped inductive switching stress

In this work, the degradation mechanism of 1.2kV 4H-SiC MOSFET under repetitive Unclamped Inductive Switching (UIS) stress has been investigated. The hot-holes injection and trapping into the gate oxide above the JFET region is observed, resulting in the increase of the off-state drain-source leakage current (I_DSS) and the decrease of the on-state resistance (R_dson). Moreover, an improved device with step gate oxide above the JFET region is proposed, which can effectively restrict the degradation under repetitive UIS stress, while the fresh breakdown voltage (BV) and R_dson are almost unaffected.