Accurate evaluation of fast threshold voltage shift for SiC MOS devices under various gate bias stress conditions

We investigated methods of measuring the threshold voltage (Vth) shift of 4H-silicon carbide (SiC) metal–oxide–semiconductor field-effect transistors (MOSFETs) under positive DC, negative DC, and AC gate bias stresses. A fast measurement method for Vth shift under both positive and negative DC stresses revealed the existence of an extremely large Vth shift in the short-stress-time region. We then examined the effect of fast Vth shifts on drain current (Id) changes within a pulse under AC operation. The fast Vth shifts were suppressed by nitridation. However, the Id change within one pulse occurred even in commercially available SiC MOSFETs. The correlation between Id changes within one pulse and Vth shifts measured by a conventional method is weak. Thus, a fast and in situ measurement method is indispensable for the accurate evaluation of Id changes under AC operation.