Experimental Investigations on Short-Circuit Capability of a New Structure Planar SiC MOSFETs

In this paper, a new structure named plasma spreading layer (PSL) is introduced into planar SiC MOSFETs to improve the short-circuit robustness. The short-circuit performance under 400V, 600V, and 800V bus voltage is tested. And two failure modes are discovered. The 3D TCAD simulations, Emission Microscope (EMMI), and Focused ion beam (FIB) are used to investigate the short-circuit failure mechanisms. Under 400V and 600V bus voltage, the interlayer dielectric between the source and the gate is damaged due to the high temperature generated in the short-circuit process, and the melted source metal Al is connected to the gate polysilicon, causing short circuit of the gate and source electrodes. Compared with commercial devices, the short-circuit capability of the device with PSL is improved by 3 to 7μs under 400V bus voltage. Under 800V bus voltage, the thermal power is almost twice that of 400V, which reduces the short circuit withstanding time (SCWT) of the device rapidly to just over 5µs. Due to such high instantaneous power, the device failure is characterized by the short circuit between the three electrodes, and thermal runaway is the cause of failure in this situation.