Crosstalk in SiC Power MOSFETs for Evaluation of Threshold Voltage Shift Caused by Bias Temperature Instability

Abstract

Threshold voltage drift from Bias Temperature Instability is known to be a reliability concern for SiC MOSFETs. Negative bias temperature instability (NBTI) results from positive charge trapping at the gate dielectric interface and is more problematic in SiC due to the higher interface trap density. Turning SiC MOSFETs OFF with negative voltages to avoid Miller coupling induced cross-talk can cause $V_{TH}$ shifts in periods with long standby duration and high temperatures. This paper proposes a novel test method for BTI characterization that relies on measuring the shoot-through current and charge during switching transients. The method exploits the Miller coupling between 2 devices in the same phase and uses the shoot-through current from parasitic turn-ON to monitor $V_{TH}$. Standard techniques require the use of static measurements (typically from a parameter analyzer or a curve tracer) to determine the threshold voltage shift. These conventional methods can underestimate the $V_{TH}$ shift since the recovery from charge de-trapping can mask the true extent of the problem. The proposed methodology uses the actual converter environment to investigate the $V_{TH}$ shift and should therefore be of more interest to applications engineers as opposed to device physicists. Furthermore, it avoids the problem of $V_{TH}$ recovery and is therefore more accurate in $V_{TH}$ shift characterization.