Investigation on Single Pulse Avalanche Failure of 3.3kV planar-SiC power MOSFETs

In order to meet the requirement of improving conversion efficiency and power density for next generation rail traction converters, there is an urgent need to develop 3.3kV-rated SiC power MOSFETs and put them into field applications. However, the avalanche ruggedness of 3.3kV SiC power MOSFETs still remains one of the critical concerns before adopting them into practical traction converters. In this paper, single-pulse Unclamped Inductive Switching (UIS) tests on commercially available 3.3kV SiC power MOSFETs are performed with different inductive loads to evaluate their avalanche ruggedness as well as understand the possible failure mode. Experimental results show that the maximum avalanche energy of 3.3kV SiC power MOSFETs are 190.94mJ @ L
load
=6mH, 166.73 mJ @ L
load
=2.5mH, and 131.68 mJ @ L
load
=1.4mH. Compared with those reported UIS test results on SiC power MOSFETs with lower voltage ratings, it is interesting to observe that the maximum avalanche energy density of 3.3kV SiC power MOSFETs is significantly smaller. Conductive path among drain, gate and source electrodes are found after UIS tests, which means an electrode shorting failure mode for 3.3kV SiC power MOSFETs under UIS condition. Moreover, TCAD simulations reveal that the vertical electrical field in JFET region exceeds 5MV/cm when avalanche breakdown occurs, which causes strong impact ionization and may degrade gate oxide. All of these provide useful insight on R&D and application of 3.3kV SiC MOSFETs.