Improvement of Switching Characteristics in 6.5-kV SiC IGBT with Novel Drift Layer Structure

6.5-kV SiC IGBT with novel drift layer structure is developed to eliminate collector voltage steepening during turn-off and thus to suppress a ringing noise. The proposed IGBT has a depletion-controlled structure (DCS) of a two-step drift layer to suppress the increase of a depletion layer during the turn-off. We fabricated n-channel SiC IGBTs with DCS designed for a blocking voltage of 6.5 kV. Also, we applied our original backside-grinding-last (BG-last) process that enables low switching loss. The DCS device successfully reduced a riging of the gate voltage and had a turn-off loss of 17.6 mJ with 3.6-kV and 32-A switching operation. Although this value is larger than that of the conventional devices (8.8 mJ) due to a tail current, it is still quite low compared with the reported switching loss of SiC IGBTs with the proper switching curves, which is estimated to be 46.1 mJ with the same rated voltage and current.