TCAD Analysis of SiC Trench MOSFET Structures with Improved Frequency Figure of Merit

In this paper, an optimized structure of 4H-SiC Trench MOSFET with an N+added layer completely enveloping a U-shaped P+shield layer is proposed. The structure mainly replaces the original single shaped P+shield region with a U-shaped P+shield region, which incompletely envelopes the bottom of the trench and completely envelopes the P+shield layer with the N+added layer, significantly improving the breakdown characteristics and switching characteristics of the device. Compared to the conventional trench structure, the U-shaped P+shield layer in the proposed structure reduces the gate-drain capacitance (CGD) and the gate-drain charge (QGD). And its HFFOM (CGD×Ron,sp) and HFOM (QGD×Ron,sp) are reduced by 92.1% and 62.2% respectively, and the switching loss is reduced by 31.5%. The addition of completely envelopes the P+shield layer with the N+added layer reduces the Electric field strength at the corner of the trench and increases the breakdown voltage (BV), which greatly ensure the reliability of the gate oxide layer. Also, the figure of merit (FOM=BV2/Ron,sp) is improved by 20.1%. In this paper, the dimensions of the N+added region and the P+shield region are discussed as well as the doping concentration to obtain the optimum performance.