Investigation on Degradation of SiC MOSFET Under Accelerated Stress in a PFC Converter

摘要

The reliability concern of SiC MOSFETs has been extensively investigated with various accelerated stress tests. However, these conventional tests are predominantly performed in a simplified and controlled testing environment, which might or might not realistically simulate the actual device operation profiles in power converters. In this article, we report the longterm degradation phenomenon of several types of SiC MOSFETs in an actual 2-kW power factor correction (PFC) converter and provide an analysis of the degradation mechanisms. Compared to conventional dc power cycling tests, a large decrease in threshold voltage was observed due to gate oxide degradation of SiC MOSFET in a PFC converter. Online monitoring results show that the ON-state voltage drop of SiC MOSFET continuously rises with the increase of stress times. The increase in ON-state voltage is caused by the change of package resistance and channel resistance. Gate oxide degradation resulting in a large increase in drain-source leakage current and gate leakage current. Meanwhile, the variation of miller plateau voltage and threshold voltage results in a significant change of turn-on losses in SiC MOSFET. TCAD simulation, and C-V measurement indicate that the main degradation mechanism is hot holes accumulation within the gate oxide above the JFET region and channel region due to high electric field stress.