Commercially available, 1200 V SiC power MOSFETs have been characterized under bias-temperature stress conditions. Two generations of devices from a single manufacturer were tested. For the first-generation MOSFETs, both plastic- and metal-packaged devices were evaluated, whereas for the second-generation MOSFETs, only plastic-packaged devices were tested. Threshold voltage was observed to decrease with increasing temperature in the absence of gate bias stress, as expected. Drain leakage current increased with increasing temperature above the rated temperature of 125°C for first-generation plastic-packaged parts, with the leakage ~10× higher for the plastic-packaged parts compared to the metal-packaged parts. A negative gate voltage was shown to reduce drain leakage current for the metal-packaged parts only, suggesting a parasitic leakage path associated with the plastic packaging. The threshold voltage shift ΔVT was minimal for T < 125°C. ΔVT increased with increasing temperature above 125°C, and was larger for negative gate voltage bias stress, suggesting that the oxide is more sensitive to trapping of holes than trapping of electrons. ΔVT was insensitive to the type of package. The second-generation SiC MOSFET showed significantly less susceptibility to bias temperature stress, especially for negative gate voltage, indicating improvement in device design and/or processing in the second-generation MOSFET. Switching gate stress showed complex behavior, with a rapid initial shift in VT followed by a much slower shift. Initial testing indicates a strong dependence on duty cycle and possible influence of self-heating. More detailed study of reliability under switching conditions is needed.
On the Lifetime Estimation of SiC Power MOSFETs for Motor Drive Applications