Research On SiC MOSFET Gate Oxide Condition Monitoring And Junction Temperature Estimation

Power devices are key components of power electronic systems,and are widely used in aerospace,medical,power grid,electric vehicles and other industries.With the rapid development of power electronics technology,some application scenarios have more and more requirements for power devices.Silicon Carbide(SiC)Metal-Oxide-Semiconductor Field-Effect Transistor(MOSFET)is a new type of wide bandgap semiconductor device,which has the advantages of large bandgap,high breakdown electric field,fast switching speed,etc..It is considered to be a new generation of power electronic equipment that can replace traditional silicon power devices,and has broad application prospects.However,high voltage field strength and high switching frequency will degrade the gate oxide of SiC MOSFET.When the degradation accumulates to a certain extent,it will affect the operating characteristics of the device,such as turn-on and turn-off characteristics,making the device unable to operate stably,and even causing the breakdown of the gate oxide,leading to device failure.SiC MOSFET working at high temperature is an important factor to aggravate gate-oxide degradation,and junction temperature is an important basis for condition monitoring and reliability evaluation of power devices.Therefore,it is of great significance to study the gate oxide condition monitoring method and junction temperature estimation method of SiC MOSFET.In this paper,SiC MOSFET is taken as the research object,the device structure and operating characteristics are analyzed in detail,and the gate oxide condition monitoring method and junction temperature estimation method are proposed.The specific research contents are as follows:(1)The physical structure,package structure and switching characteristics of SiC MOSFET are introduced.The mechanism of gate-oxide degradation,the causes and characteristics of each type of charge trap are explained from the perspective of device internal structure.The changes of carrier mobility and threshold voltage after gate oxide degradation are analyzed.(2)A condition monitoring method of SiC MOSFET gate oxide based on differential mode electromagnetic interference(DM EMI)signal is proposed.Taking the buck converter composed of SiC MOSFET as the research object.The equivalent model of the converter is established,and the conduction paths of common mode electromagnetic interference(CM EMI)signals and DM EMI signals are analyzed.On this basis,the influence mechanism of gate-oxide degradation on differential mode interference signal in the circuit is described.The relationship between DM EMI signal and gate-oxide degradation is established.The DM EMI signal spectrum in the circuit is measured by voltage method and current method.The condition of SiC MOSFET gate oxide is monitored by the peak value of DM EMI signal in the low frequency band.The applicability of this method in different operating frequencies and voltages is verified.(3)A method of SiC MOSFET junction temperature estimation based on Miller platform voltage is proposed.This paper analyzes the reason of the Miller platform generated in the device conduction process.The effects of load current,driving resistance and inductance on the turn-on Miller platform voltage are studied,and several calibration experiments are carried out under different operating conditions.A junction temperature estimation model considering the changes of load current and driving parameters is established.