Reliability Investigation on SiC Trench MOSFET under Repetitive Surge Current Stress of Body Diode

Abstract

Although the body diode of SiC MOSFET has excellent surge capability, the reliability issues about commercial SiC MOSFET under repetitive surge current stress of body diode haven’t been studied thoroughly. In this work, repetitive surge current stress is applied to the body diode of commercial SiC trench MOSFET, and the surge tests are conducted under different gate biases and ambient temperatures. It is found that no bipolar degradation occurs in the body diode but degradation phenomena of gate oxide and package are observed in devices under tests (DUTs). At room temperature, the threshold voltage (VTH) related to gate oxide degradation degrades more seriously at a negative gate bias of -5V than at OV. At OV gate bias, gate oxide and package degenerate more severely at $125^{\circ}{C}$ than at $25^{\circ}{C}$. The evolution of on-state resistance $(R_{DSON})$ during the tests is influenced by the competitive mechanism between gate oxide degradation and package degradation. As a result, gate oxide degradation causes RDSON to reduce while package degradation makes RDSON rise. Meanwhile, the competitive mechanism is deeply influenced by the gate bias voltage and ambient temperature. The failure analysis shows that all DUTs fail with gate and source terminal shorted, which is mainly attributed to high junction temperature.