An investigation of avalanche ruggedness and failure mechanisms of 4H SiC trench MOSFETs in unclamped inductive switching by varying load inductances over a wide range

Abstract

The avalanche ruggedness of unclamped inductive switching of 1.2 kV SiC trench MOSFETs was investigated with load inductances ranging from 1 μH to 5 mH. The SiC trench MOSFETs showed an extremely high avalanche current of more than 6000 A cm−2 at 1 μH, which was 3.3 times higher than state-of-the-art 1.2 kV Si IGBTs. This indicates that modules of SiC trench MOSFETs could show higher ruggedness for parallel connections. In addition, SiC trench diodes in which only the n+ source regions were eliminated from the MOSFETs were fabricated to verify the failure mechanism by the activation of parasitic bipolar transistors. In medium-load inductances from 10 μH to 100 μH, the MOSFETs showed lower avalanche ruggedness than the diodes, and failures were caused by the activation of the parasitic bipolar transistors. For inductances outside that range, the MOSFETs showed identical ruggedness to the diodes, and the failures were caused by the source metals melting.