Research On New Structure And Reverse Recovery Characteristics Of 4H-SiC MOSFET

With the increasing requirements of power electronic system for blocking voltage and current capability,the third generation semiconductor,represented by Silicon Carbide,is receiving more and more attention.SiC MOSFET has been widely used for its excellent electrical performance.Compared with Silicon devices with the same voltage level,SiC MOSFETs have higher operating frequencies,lower on-state resistance,and higher extreme operating temperatures.Owning to the application of SiC MOSFETs in power management systems such as bridge circuits and inverters,the reverse recovery performance has been paid more and more attention.In order to avoid the effect on the electrical characteristics caused by the inherent bipolar degradation effect,and improve the reverse recovery performance,a Schottky barrier diode is usually anti-paralleled with the SiC MOSFET.The integration of Schottky barrier diode inside the cell of SiC MOSFET can further solve the problems of parasitic inductance and packaging cost.In this paper,two kinds of SiC MOSFET with integrated Schottky barrier diode are proposed.Their working mechanism and electrical characteristics are studied by simulation.1.A novel SiC trench MOSFET with integrated Schottky barrier diode?Trench MOSFET with SBD,S-TMOS?is proposed.The structure is characterized by a P-type shielding layer on the sidewall of the gate trench and a Schottky contact on the surface of the cell.In the blocking state,the P+shielding region and the N-type epitaxial layer deplete each other,which can effectively protect the Schottky junction from the high electric field and shield the coupling effect of the gate and the drain.In the freewheeling state,the intergrated SBD is preferentially turned on,so that the reverse conduction voltage drop?V_F?of the S-TMOS is smaller than that of a conventional SiC MOSFET,which reduces losses during freewheeling.At the same time,the integration of the SBD significantly reduces the number of the carriers stored in the drift region of the S-TMOS during freewheeling.The less carriers can be extracted more quickly during reverse recovery.Therefore,S-TMOS can achieve better reverse recovery characteristics.Compared with the conventional SiC MOSFET,the V_F of S-TMOS is reduced from2.7V to 1.6V,the reverse recovery time(t_rr)is shortened,the reverse recovery charge(Q_rr)is reduced by 82%,and the peak current is also reduced from 138 A/cm² to31A/cm².2.A novel SiC double trench MOSFET with integrated Schottky barrier diode and split-gate?Split-Gate and Double Trench MOSFET with SBD,SSGDT-MOS?is proposed.The shielding gate connected to the source contact shields the coupling effect between gate and drain,thereby effectively reducing the gate-drain capacitance(C_GD)and the gate-drain charge(Q_GD),and greatly improving the switching characteristics of the device.At the same time,the integrated SBD significantly improve the reverse recovery performance and the source trench protects the Schottky contact and gate oxide effectively.The simulation results show that the C_GD and Q_GD of the SSGDT-MOS are reduced by 97%and 96%,respectively compared with the conventional structure,and the turn-off loss is also reduced from 4.91mJ/cm² to0.27mJ/cm².In terms of reverse recovery characteristics,the t_rr of the SSGDT-MOS is shortened from 51ns to 26ns,the Q_rr is reduced by 68%,and the peak current during reverse recovery is decreased from 127A/cm² to 65A/cm².