Towards Understanding the Physics of Gate Switching Instability in Silicon Carbide MOSFETs

Bias temperature instability (BTI) is a well-investigated degradation mechanism in technologies based on silicon, gallium nitride, or silicon carbide (SiC). Essentially, it leads to a drift in the threshold voltage and to a reduction in mobility after application of a gate bias, and becomes worse at elevated temperatures. However, as discovered recently, the threshold voltage drift of SiC metal-oxide-semiconductor field-effect transistors (MOSFETs) has different properties than those known from BTI when the gate terminal of the device is switched in a bipolar mode. This new degradation mechanism has recently been termed gate switching instability (GSI). To further understand this degradation mechanism and the underlying physics, we have used pre- and post-stress impedance characterization and in-situ ultra-fast threshold voltage measurements. Most importantly, we show that the gate switching leads to the creation of fast, acceptor-like interface defects that lead to a shift in threshold voltage, and hence appear to be responsible for GSI.