Research On SiC MOSFET Junction Temperature Estimation And Bias Temperature Instability

Silicon Carbide Based Metal-Oxide-Semiconductor Field-Effect Transistor(SiC MOSFET)is a new wide-bandgap power electronics device with technical advantages of large bandgap width,high breakdown electric field,high saturation drift speed,and thermal conductivity.It can operate with lower switching loss,faster switching frequency,and higher junction temperature,and has been widely used in industries such as aerospace,medical,new energy vehicles,etc.Power devices are the critical units of power electronics systems,and their safety and reliability determine whether the entire system can operate stably and efficiently.Junction temperature is one of the more critical operating parameters of SiC MOSFET.The accurate extraction and detection of SiC MOSFET junction temperature are essential for its loss calculation,life prediction,and reliability evaluation.Simultaneously,the threshold voltage drift caused by bias temperature instability(BTI)is also one of the most severe reliability problems of SiC MOSFETs.The drift of the threshold voltage(V_th)will affect the operating power consumption and switching characteristics of the device,which may cause the failure of the entire power system.Therefore,the ability to accurately detect and evaluate the BTI characteristics is critical in improving the device's reliability.Therefore,this thesis takes SiC MOSFET as the research object and researches two aspects:junction temperature prediction and BTI characteristic detection.The specific research content is as follows:1.The physical structure,working principle and characteristics of SiC MOSFET are summarized.The causes of BTI characteristics are analyzed in detail from the perspective of semiconductor physics.In-depth study of the mechanism of the influence of BTI characteristics on V_th.Furthermore,under the influence of BTI characteristics,the internal mechanism of SiC MOSFET on-resistance,switching time and other characteristic parameters changing accordingly,provides a theoretical basis for the following research.2.A method of junction temperature prediction based on thermal sensitive electrical parameters is proposed.First,the electrical behavior characteristics of the SiC MOSFET in the turn-off stage are studied,and the turn-off delay time(t_doff)interval is redefined.Secondly,the relationship between threshold voltage,Miller voltage,and temperature is analyzed,proving that this t_doffhas better temperature characteristics than t_doffunder the traditional definition.Finally,an online junction temperature estimation model based on the redefined t_doffis obtained.3.A method for measuring BTI characteristics is proposed.First,according to the physical structure and working principle of SiC MOSFET,an analytical model of source-drain voltage(V_sd)is established based on the reverse conduction resistance.Secondly,the model is used to study the influence mechanism of BTI characteristics on V_sd.Finally,a BTI characteristic measurement method based on V_sdis proposed,and a corresponding measurement platform is built.