Research On Electrothermal Reliability Of High Power SiC Rectifier

Silicon carbide(SiC)material,representative of the third-generation wide bandgap semiconductor,has higher thermal conductivity,higher critical breakdown electric field,and higher electron saturation drift speed than the typical of first-generation semiconductor silicon(Si)material.SiC material and device shows great advantages and broad application prospects in extreme applications such as high power,high temperature,high voltage,and are particularly suitable for use in power electronic power circuits.And in the global market in recent years,the commercialization of SiC power devices has become increasingly mature.4H-SiC SBD/JBS power diode has been commercialized.However,as the forward current of the 4H-SiC JBS power diode increases,due to the different heat dissipation conditions of the JBS chip after packaging,the temperature of the JBS chip will be unbalanced.On the other hand,in order to reduce costs,SiC power diode with higher withstand voltage can be obtained by means of internal series.The problem of uneven temperature may affect the reliability of the device.In this paper,theoretical research and experimental research are carried out to solve the electrothermal reliability problem of 4H-SiC JBS high power diodes.The following is the main research work of this article:(1)An electrothermal simulation mode of the 4H-SiC JBS rectifier diode based on TCAD,MATLAB and ANSYS software is established.It can truly and efficiently reflect the problem of electrothermal coupling of the 4H-SiC JBS rectifier diode.Based on the TCAD software SiC JBS diode electrical model and thermal model,an accurate analytical model of device on-resistance is obtained,and then the device temperature-varying power model is obtained.Finally,the power model is imported into ANSYS for electrothermal simulation of the device,which solves the difficulty of TCAD software to simulate the self-heating effect of large size devices.(2)The temperature distribution of 40 A 4H-SiC JBS diode is studied.First,based on the aforementioned method,the temperature distribution of the 40 A 4H-SiC JBS diode is performed,and the temperature unevenness of the chip center temperature is 9.62 K higher than the chip edge.Then,the infrared temperature experiment is performed on the metalencapsulated and plastic-encapsulated 4H-SiCJBS diodes under the condition of 10 A,and the spraying method is used to solve the test problems caused by the different thermal emissivity of the material.(3)In order to solve the problem of temperature unevenness of large-area devices,a design idea of Schottky contact uneven distribution is proposed.By reducing the Schottky contact area of the chip center and increasing the Schottky contact area of the chip edge,the temperature difference between the chip center and the edge is reduced.Finally,under the premise of ensuring that the blocking characteristics do not deteriorate,the temperature difference is reduced from 9.62 K to 1.87 K,and the effective resistance is reduced by 5.38%.(4)The theoretical analysis of the electrothermal characteristics of the 9000 V 4H-SiC internal series diode is studied.First,a model of 3000 V 4H-SiC JBS diode turn-on voltage with temperature is established.Next,the reverse recovery characteristics of 4H-SiC JBS diodes are studied and a reverse recovery model under a simple circuit is established.The internal series reverse recovery model is obtained.The reverse recovery characteristics of the internal series diodes are better than those of the same withstand voltage in conclusion.Finally,the temperature distribution simulation of the ceramic-packaged 4H-SiC internal series diode is performed.The simulation really finds that JBS chips in different cavities will have a temperature difference of about 2K.The calculated resistance difference from this temperature is only 0.055?.For SiC 9000 V internal series diode Reliability has no effect.(5)The experimental analysis of the electrothermal characteristics of a 9000 V 4H-SiC internal series diode is studied.Basic 9000 V 4H-SiC internal diode series forward and reverse tests and forward temperature change experiments are performed to verify the correctness of the 4H-SiC JBS turn-on voltage with temperature change model.Next,the reverse temperature change experiments of the 4H-SiC internal series diode find that a spark phenomenon occurred after the temperature is higher than 175 ° C.After repeated experiments and field observation and analysis,the breakdown occurres due to air breakdown between the package metal cover and the electrodes,and the chip inside the device is not damaged.