Study on formation mechanism of different differential resistance branches at avalanche breakdown curve of SGT-MOSFET

The robustness of power devices is limited by the different differential resistance branches on the avalanche breakdown curve. The negative differential resistance branch can cause the current aggregation inside the device to form a positive feedback, resulting in an increasing local current density, which is not conducive to the robustness of the device. The avalanche breakdown curve of SGT-MOSFET shows differential resistance branches different from that of diodes and IGBTs. In this paper, the formation mechanism of different differential resistance branches is firstly studied in detail. It is found that the formation of the first negative differential resistance branch is related to the triggering of the parasitic npn transistor, and which was verified by comparing the avalanche characteristic curves of the structural with or without n+ source region. Finally, A p+ buried layer is introduced in the p-body region of SGT-MOSFET, which can effectively suppress the triggering of parasitic npn transistor by optimizing the avalanche current path, reduce the negative differential resistance branch, and improve the robustness of SGT-MOSFET.