Impact of Layout Parameter Mismatches on Short Circuit Reliability of Parallel-Connected Planar, Trench, and Double-Trench SiC MOSFETs

Uneven electro-thermal conditions between parallel-connected devices can reduce the overall reliability of the power electronics systems, particularly during extreme cases such as short circuit. The current distribution between parallel devices is dynamically regulated during the transient and the degradation of devices is intertwined in the long run. To better understand the evolving patterns in the parallel configuration and to compare differences among various device structures, repetitive short circuit tests were conducted on planar, symmetrical double-trench, and asymmetrical trench SiC MOSFETs. Technology computer-aided design (TCAD) models were employed to analyze the evolution of current density and temperature profile between parallel devices. Test results indicate that the switching speed difference caused by gate resistance (Rg) mismatch leads to the asynchronous degradation of asymmetrical trench devices. The decreased threshold voltage (Vth) induce higher short circuit energy (Esc), forming a positive feedback for degradation. Besides, even if the current is dynamically shared between parallel SiC MOSFETs under different case temperature (Tcase), the initial temperature has a key impact on short-circuit reliability over Esc.