Influence of the Threshold-Voltage Hysteresis on the Switching Properties of SiC MOSFETs

Typically, the turn-on switching characteristics of SiC-MOSFETs are considered to be completely independent of the turn-off gate voltage. This assumption originates in the physical understanding of Si-based power devices, but neglects specific properties of power devices based on SiC. One of these specific properties is that gate oxides in SiC-based power devices are typically characterized by a relatively large number of interface states, resulting in the so-called threshold-voltage hysteresis. This paper analyzes the influence of the threshold-voltage shift caused by the hysteresis effect on the switching performance of SiC MOSFETs. For this purpose, a theoretical explanation of the threshold-voltage hysteresis and its impact on the relation between threshold voltage and turn-off gate-driver voltage will be provided. Based on this, the relevance of the described phenomena for switching performance will be demonstrated experimentally by switching measurements carried out with a standard double-pulse setup. Furthermore, a method will be shown to quantify the threshold-voltage shift resulting from the hysteresis effect, directly from double pulse measurements. Finally, this paper also discusses the influence of the turn-off gate voltage on the gate-charge characteristics.