Simulation study of 1200V SiC-based trench-gate MOSFET with vertical field plate protection

In this paper, a new structure of SiC-base trench-gate MOSFET protected by vertical field plate is proposed. Compared with conventional trench gate MOSFET, a deep trench connected to the source is added. The source trench is filled with polysilicon and acts as a vertical field plate. Under blocking state, the depletion charge between trenches is coupled with the vertical field plate, which can modify the electric field distribution near the gate oxide corner. Lower field strength in gate-oxide is the guarantee for long-term reliable operation of the device. In order to investigate the effect of charge-coupling, double doped epitaxial drift region is selected. The doping concentration of first epi-layer is lower than that of second eip-layer. The bottom of the deep source trench, that is, the end of vertical field plate, falls at the junction for the two epitaxial layer. The static characteristics are simulated for both conventional trench gate and dual trench dual epitaxy new structures by using Sentaurus TCAD. Simulation results show that the new structure with double trenches and double epitaxy has higher Baliga's figures of merit (FOM) Also, under the blocking state, the maximum electric field in gate oxide can be lower than 5MV/cm. That is desirable for the long-term operation reliability of the gate.