Research On New SiC MOSFET Power Devices

Compared with Si material,SiC material has larger bandgap,larger critical electric field and larger thermal conductivity,so SiC is more suitable for high voltage and high power applications.SiC MOSFET power devices play a very important role in power devices because of their high input impedance and fast switching speed.Due to the low channel electron mobility of SiC MOSFET,this limits the reduction of channel resistance(R_channel),while there is still room to reduce the drift region resistance(R_drift).Therefore,improving the compromise relationship between the specific on-resistance(R_on,sp)and breakdown voltage（BV）of SiC MOSFET is the focus of current research.In this thesis,three new SiC MOSFET power devices are proposed,which effectively improve the compromise relationship between the R_on,sp and BV of SiC MOSFETs.The innovative content of this thesis is arranged as follows:1)A SiC LDMOSFET using double trench gate and VLD（Variation Lateral Doping）technology is proposed and compared with the conventional SiC LDMOSFET with field plate.The simulation results show that the R_on,sp of the proposed structure is 3.5 mΩ·cm²,and the BV is 1460V,while the R_on,sp of the conventional SiC LDMOSFET with field plate is 6.6 mΩ·cm²,and the BV is 1210 V.Compared with the conventional SiC LDMOSFET,the R_on,sp of the proposed structure is reduced by 46%,and the BV is also increased,which greatly improves the compromise relationship between the R_on,sp and BV.2)A high-k superjunction SiC MOSFET with integrated SBD（Schottky Barrier Diode）is proposed and compared with the conventional SiC MOSFET,conventional SiC superjunction MOSFET and conventional SiC high-k MOSFET.The simulation results show that the R_on,sp of the proposed structure is 0.67 mΩ·cm²,which is 72.4%,23%and5.6%lower than those of the conventional SiC MOSFET,SiC high-k MOSFET and SiC superjunction MOSFET,respectively.The reverse recovery time and reverse recovery charge of the proposed structure are 16 ns and 18 n C,respectively,which are 74%and94%lower than those of the other three structures.Therefore,proposed structure has a better compromise relationship between the R_on,sp and the BV,and a better reverse freewheeling ability.3)A quasi SiC MOSFET with low specific on-resistance is proposed and compared with the conventional SiC MOSFET.The proposed structure is controlled by MOSFET to turn the JFET on and off,so there is no issue of low channel mobility and gate oxide reliability.The simulation results show that the BV of the two devices is almost the same,and the R_on,sp of the proposed structure can be reduced by more than 25%.Compared with the conventional SiC MOSFET,the saturation current of the proposed structure is reduced,so the proposed structure has better safe operating area and better short-circuit characteristics.In summary,compared to conventional SiC MOSFET,the three new types of SiC MOSFET proposed in this thesis have better performance and better application prospects.