Research On High Temperature Characteristics Of 1.2kV SiC VDMOS

Silicon carbide(SiC)semiconductor materials have the advantages of wide band-gap,great saturated carrier drift velocity,high critical breakdown electric field,high thermal conductivity and great potential in high power,high temperature and high speed switching applications.Compared to silcon(Si)vertical diffused metal oxide semiconductor transistor(VDMOS),SiC VDMOS has lower on-state resistance,higher breakdown voltage,and better thermal conductivity,which is widely used in aerospace,new energy vehicles,oil exploration and other fields.This thesis aims to study the high temperature characteristics of 1.2kV SiC VDMOS.According to the operational principle of SiC VDMOS,the high temperature test and simulation platforms for device electrical parameters are established.The static electrical parameters of SiC VDMOS at a wide temperature range from 25℃ to 325℃ are studied,revealing the intrinsic mechanism of the temperature characteristics of the static electrical parameters: the intrinsic carrier concentration and the mobility of carriers with temperature change determine the temperature characteristics of the static electrical parameters.The dynamic electrical parameters of SiC VDMOS at a wide temperature range from 25℃ to 325℃ are investigated,and the inherent mechanism of the temperature characteristics of dynamic electrical parameters is revealed: the decrease of the device threshold voltage leads to the decrease of the Miller platform voltage,so that the turn-on time decreases with temperature,and the turn-off time increase as the temperature increase.Then,the temperature characteristics of the short-circuit robustness of SiC VDMOS are studied.The results show that the gatesource leakage current of the device leads to the short-circuit failure.As the temperature increases,the gate leakage current increases and the short-circuit robustness of the device deteriorates.Finally,the temperature characteristics of an active boost PFC converter system using SiC VDMOS are studied.Based on the temperature characteristics of the device electrical parameters,the causes and mechanisms of the changes of the PFC converter system parameters at high temperatures are analyzed.As the temperature rises,the on-state resistance of the device increases and the output voltage of the system decreases.The feedback circuit keeps the output voltage constant by increasing the duty cycle,which ultimately leads to an increase in the input current and a decrease in system efficiency.