Short circuits that occur in power converters put the power semiconductor devices under considerable electrothermal stress. The electrothermal stress causes a rise in junction temperature and ultimately device failure if the thermal limits of the device are exceeded. The device ruggedness under short circuit conditions is quantified by the short circuit withstand time (SCWT), which is the maximum duration the power device can dissipate the short circuit energy without failure. SiC MOSFETs are known to have reduced short circuit capability compared to comparatively rated silicon MOSFETs and IGBTs due to higher thermal impedance and reduced gate oxide robustness. In this paper, 650V rated SiC planar MOSFETs, Trench MOSFETs and Cascode JFETs have been subjected to short circuits with initial junction temperatures of 25°C, 75°C and 150°C. The results show the peak SC energy density (in mJ/mm 2 ) has a negative temperature coefficient for the Planar and Trench MOSFETs and is temperature independent for the Cascode JFET. The SCWT reduces with initial junction temperature for the SiC Planar and Trench MOSFET while showing less temperature dependency in the SiC Cascode JFET. The SiC Trench MOSFET demonstrates the highest SCWT although all devices show reduced SCWT compared to similarly rated silicon MOSFETs and IGBTs.

Gallium Nitride (GaN) and Silicon Carbide (SiC) power cascode devices both take advantage of a low-voltage enhancementmode Silicon power MOSFET coupled with a high-voltage depletion-mode GaN HEMT or SiC JFET to realize high switching frequencies with the intention of avoiding charge trapping and threshold voltage drift in the gate oxide traps of enhancementmode SiC MOSFETs. Nevertheless, in this paper it is shown that SiC and GaN Cascodes will also suffer from the gate threshold voltage drift when subjected to significant electrothermal stress. This is partly due to the natural drift of threshold voltage in the gate, and partly due to the impact of the leakage current by the high-voltage device. The threshold voltage drift can lead to permanent degradations and potential failures, and as such is the subject of this investigation.