Study On 15kV 4H-SiC IGBT And Novel Structure

Compared with silicon(Si)material,silicon carbide(SiC)material has outstanding advantages in the band gap width,the critical electric field strength,the thermal conductivity and the electron saturation drift velocity,and so on.Therefore,silicon carbide insulated gate bipolar transistor(SiC IGBT)with conductance modulation effect can realize ultra-high blocking voltage while maintaining low on-resistance,which has important application potential in the field of ultra-high voltage power electronics.Combined with the structure and mechanism of traditional planar and trench devices,this thesis aims to improve the compromise relationship between the on-state voltage drop and the turn-off loss of the IGBT.Two new 15 kV 4H-SiC IGBT structures are proposed respectively,and the working principle,blocking characteristics,on-state characteristics and turn-off characteristics of the device are studied.The main contents are as follows:1.A novel hybrid-channel 4H-SiC IGBT(HC-IGBT)structure with enhanced conductance modulation is proposed.HC-IGBT devices benefit from the hybrid channel structure,which increases the electron density near the emitter,thus heightening the conductance modulation effect in the N-drift.Meanwhile,the hybrid channel provides more hole extraction paths when the device is turned off,significantly improving the equilibrium relation relationship between the on-state voltage drop and the turn-off loss,and improving the overall device performance.The breakdown voltage reaches 19 kV,and the electric field of gate oxide layer is kept below 3.0MV/cm,which ensures the blocking characteristics of the device and the reliability of gate oxide.The on-state voltage drop of HC-IGBT is reduced by 15% and 4%,respectively,compared with the conventional planar and channel structures.The corresponding differential specific ON-resistance is reduced by 52% and 18%,and the turn-off loss is reduced by 6% and18%,respectively.Therefore,the BFOM value of HC-IGBT is 63% and 15% higher than that of conventional planar and channel structures,while the IFOM value is 21%and 22% lower,respectively.2.A new structure of P-type potential Modulation 4H-SiC IGBT(P-type potential Modulation 4H-SiC IGBT,PM-IGBT)is put forward,which improves the contradiction between the blocking characteristics,on-state characteristics and turn-off characteristics of the device.PM-IGBT realizes the floating state of P-shield during on-state through the P-type potential modulation zone,so strengthens the conductance modulation effect of N-drift.The compromise between on-state voltage drop and turn-off loss of IGBT devices is further improved by the fact that the P-shield is grounded and the Miller capacitance of the device is reduced by reducing the gate area.The breakdown voltage of PM-IGBT is 20.8kV,which is the same as ground P-shield structure(GP-IGBT)and the gate oxide reliability better than floating P-shield structure(FP-IGBT).PM-IGBT on-state voltage drop is consistent with FP-IGBT,which is 17% lower than GP-IGBT,and the corresponding differential specific ON-resistance is 50% lower.Compared with GP-IGBT and FP-IGBT,the PM-IGBT turn-off loss is 27% and 77% lower,respectively.Therefore,the the IFOM optimal value decreased by 39% and 77% respectively,while the BFOM optimal value is 97% higher than that of GP-IGBT.