Transient Junction Temperature Measurement Error of SiC MOSFETs in Power Cycling – A Parameter Study

Abstract:
It has been demonstrated that transient effects may occur in SiC MOSFETs, when the virtual junction temperature (Tvj) is measured by the body-diode VSD(T)-method. This has the potential to result in an erroneous estimation of Tvj in power cycling tests (PCT) and overestimation of the device’s lifetime. This work focuses on the influence on the off gate voltage and temperature on the transient effect through a comprehensive parameter study involving 2880 test runs with twelve SiC MOSFETs from three manufacturers. The results demonstrate that the transient effect is strongly dependent on the manufacturer therefore presumably respectively on the device design and processes. It can be significantly reduced by applying a negative gate voltage (VGS,off) during the cooling phase. While manufacturers A and B can achieve complete compensation, the effect persists for manufacturer C. The study recommends extending the allowable datasheet values for VGS,off in PCTs to ensure more accurate temperature measurements. Future investigations are planned to analyse the effects at cryogenic temperatures.