COSS Measurements for Superjunction MOSFETs: Limitations and Opportunities

Small-signal measurements of output capacitance (COSS) are ubiquitous in power semiconductor datasheets and determine critical features of power converters. For silicon superjunction power MOSFETs (SJs), we report COSSmeasurements with two key anomalies: variation with ac perturbation frequency and hysteresis with dc sweep direction. Using mixed-mode simulations, we attribute the frequency shift to the fundamental SJ structure and find that dc hysteresis is caused by charge trapping from uneven depletion fronts. We show that COSSmeasurements on SJs do not accurately characterize large-signal operation, underestimating stored energy by up to four times and giving no indication of COSSlosses.