Gate Stress Polarity Dependence of AC Bias Temperature Instability in Silicon Carbide MOSFETs

As the silicon carbide (SiC) power metal-oxide-semiconductor field-effect transistor (MOSFET) develops, increasing efforts are placed on ac bias temperature instability (AC BTI). It was reported that AC BTI becomes significant when and only when the gate stress is bipolar. A detailed study is made in this article to reveal the underpinning mechanism. A physical model is proposed to explain on how and why the gate stress bipolar affects the threshold drift. It is found that the gate stress polarity has to be carefully defined. As the model shows, it is the bipolar electric field, rather than the gate voltage itself, that speeds up the threshold voltage drift. It is hoped that this study provides a stepping stone toward the eventual understanding and management of AC BTI.