New Structure Design And Dynamic Characteristics Of 1200V SiC MOSFET

SiC has the outstanding material characteristics including wide band gap,high critical breakdown electric field,high saturated electron drift velocity and high thermal conductivity,which make it more effective in the fields of high temperature,high voltage and high frequency than Si material.Among them,SiC MOSFETs have a wider application than Si devices because of their characteristics of high breakingdown voltage and low on resistance.The application fields of SiC MOSFETs include smart grid,electric vehicle,rail transit,communication power supply,new energy grid connection and many other fields,covering products with several voltage levels.And SiC MOSFET is required to have strong current capability while maintaining high breakingdown voltage.At the same time,the application of SiC MOSFETs in bridge circuit,inverter and other modules makes people pay more attention to the reverse freewheeling ability of SiC MOSFETs.Although SiC MOSFETs have their inherent bulk PN junction diode,which can be used for reverse freewheeling,its reverse conduction voltage drop is usually high.Coupled with the influence of bipolar degradation effect,SiC MOSFETs'electrical characteristics are greatly affected.Aiming at this problem,taking the 1200V breakdown voltage level as an example,two new SiC MOSFET structures are proposed,and the author explores the working mechanism and electrical performance of the device through sentaurus TCAD simulation software,and optimizes the parameters.1.A Novel SBD-wall-integrated trench SiC MOSFET with a semi-superjunction and split trench gate(S~3-TMOS)is proposed.The integrated Schottky barrier diode(SBD)is adopted to realize low reverse turn on voltage;The double trench structure is adopted,and the side wall Schottky contact is formed in one trench,which can reduce the chip area and improve the ability of reverse conduction current;The split gate structure is introduced to reduce the gate drain capacitance(C_GD),improve the switching speed and reduce the switching loss.The simulation results show that compared with the conventional SiC trench MOSFET under the same parameters,the specific on resistance(R_on,sp)of the new structure is reduced by 60%,the breakdown voltage(BV)is increased by 16%,the reverse on voltage(V_F)is reduced by 42%,and the switching loss(E_switch)is reduced by 70%.2.A semi-superjunction SiC trench MOSFET with integrated heterojunction diode is proposed(SH-TMOS).The device integrates Si/SiC heterojunction diodes,which can turn on before the bulk diode of MOSFET do when the device is in reverse condution state,so as to reduce the reverse conduction voltage drop and avoid the bipolar degradation effect;The semi-superjunction structure optimizes the electric field distribution in the drift region when the device withstand high voltage,so as to realize the optimal compromise relationship between BV and R_on,sp.At the same time,P-type polysilicon can shield the coupling effect between gate electrode and drain electrode,reduce the gate drain capacitance and decrease the switching loss of the device.The simulation results show that,compared with the conventional SiC trench MOSFET under the same parameters,the R_on,sp of the new structure are reduced by 38%,BV is increased by 37%,V_F is reduced by 43%and E_switch is reduced by 70%.