Influence of Turn-Off Gate-Voltage Undershoots on the Turn-On Behavior of SiC MOSFETs

Abstract:
This paper discusses the influence of gate voltage undershoots occurring at turn-off on the turn-on switching characteristics. This influence can be traced back to the hysteresis effect that consists of fully recoverable transient shifts of the threshold voltage upon gate bias changes. Hysteresis is caused by short-term trapping and de-trapping of charges in defects on the semiconductor-insulator interface. Thereby, the switching properties of silicon carbide (SiC) MOSFETs can be affected. For our investigations, we used double-pulse measurements under application-relevant conditions. The results indicate that the turn-off gate voltage undershoot has the same effect on the threshold-voltage hysteresis as a constant turn-off gate voltage, and thereby on the turn-on switching characteristics. However, this effect seems to be relevant only if the boundary conditions for the minimum transient voltage defined within the datasheet is violated.