Research On Reliability And Condition Monitoring Technology Of SiC MOSFET

Silicon Carbide(SiC)Metal-Oxide-Semiconductor Field-Effect Transistor(MOSFET),as the third generation of wide bandgap semiconductor device,is extensively utilized in aerospace,rail transit,electric vehicles and new energy power generation by virtue of its advantages of fast switching speed,high power density and high withstand voltage rating.Power devices undertake important tasks of power conversion and control in power electronic devices,so their high reliability is a prerequisite for ensuring the efficient and safe operation of power electronic devices.However,the characteristics of SiC MOSFET will change significantly under severe operating conditions.The accurate estimation of the junction temperature(T_j)of the SiC MOSFET is an important basis for realizing its reliability evaluation and life prediction.The threshold voltage(V_th)shift induced by Bias Temperature Instability(BTI)in SiC MOSFET is a key factor restricting its performance improvement.The drop across body diode voltage(V_SD)of SiC MOSFET can be employed to achieve accurate extraction of the threshold voltage.The occurrence of SiC MOSFE aging faults will dramatically reduce the reliable operation of power electronic devices.The bond wire aging of SiC MOSFET can be diagnosed by monitoring the change of the drop across on-state drain-source voltage(V_DS).In this paper,SiC MOSFET is taken as the research object,and its operating characteristics are analyzed in detail.Based on this,a series of models are established,and the junction temperature estimation method and condition monitoring method are proposed.The specific research contents are as follows:(1)A method for estimating junction temperature of SiC MOSFET is proposed.Firstly,starting with the physical properties of wide bandgap semiconductor materials,the turn-on behavior of SiC MOSFET and the rule of drain current changing with temperature are studied.Besides,the influence of temperature dependence of threshold voltage and carrier mobility on drain current is analyzed,and it is proved that the drain current has positive temperature coefficient in the rising stage during turn-on process.Finally,the junction temperature of SiC MOSFET is estimated by the drain current in the rising phase during turn-on process.(2)A method for monitoring threshold voltage of SiC MOSFET is proposed.Firstly,the body effect of SiC MOSFET and its influence mechanism on body diode voltage are analyzed.Besides,the influence mechanism of BTI on body diode voltage in SiC MOSFET is studied and high-temperature gate bias experiment is carried out on SiC MOSFET.Finally,the threshold voltage is monitored online using body diode voltage under body effect at small injecting current.(3)A method for monitoring bond wire aging of SiC MOSFET is proposed.Firstly,the temperature dependence of the on-state drain-source resistance of SiC MOSET is analyzed.Besides,the on-state drain-source voltage is divided into package voltage and chip on-state drain-source voltage,the package resistance in the package circuit is extracted and the analytical model of junction temperature estimation of SiC MOSFET is obtained.Finally,the drop across package voltage is adopted to monitor bond wire aging degree of SiC MOSFET and the flow chart of monitoring bond wire aging state is developed.