The Research On SiC Power Thyristor Based On Pulse Application

At present,the power electronic equipment is developing in the direction of miniaturization and high power density.Pulsed power systems in power electronic equipment have been increasingly used in high-tech fields,which makes the pulse power system have higher requirements on the switching frequency and operating temperature of the semiconductor switch.Gate Turn-off Thyristor(GTO)that made of silicon carbide(SiC)material has the characteristics of high current density,high blocking voltage,high switching frequency and high heat resistance,which is very suitable for pulse switching applications.In pulsed power systems,the reliability of SiC GTO thyristors in different application scenarios remains to be studied.This paper mainly carried out a series of reliability experiments of SiC GTO thyristors,and analyzed the degradation and failure mechanism of the devices in those experiments.The experimental analysis results obtained could help to improve the stability of SiC GTO thyristors in pulse power applications.The main research contents of this article are as follows:(1)The structure characteristics and operating principle of SiC GTO thyristor are studied.A 5.0k V P-type SiC GTO thyristor was built on the ISE simulation software for device characteristics simulation research.The theoretical analysis and simulation verified the influence of the epitaxial layer parameters on the forward blocking characteristics,forward conduction characteristics and switching characteristics of the device.(2)The degradation failure mechanism of SiC GTO thyristors under high pulse current is studied.The failure analysis of the failed SiC GTO thyristor in the pulse experiment was carried out,the simulation results clarified the temperature change process of the device during the pulse discharge and the cause of the device failure.The effect of carrier lifetime on SiC GTO thyristors in power pulse systems is studied.The results show that the too short carrier lifetime in the P-drift region will cause the device to heat up rapidly during the pulse discharge process.According to the results of pulse experiment failure analysis,it was determined that the anode region to the gate region of the SiC GTO thyristor were weak regions during pulse discharge,therefore,the further experiments were conducted on the surge characteristics of the device gate-anode:As the applied surge current increased,the leakage current between the gates and anodes increases gradually,and the hysteresis of the transient transient I-V curve becomes more and more obvious.The device fails when the surge current reaches 51A.The result of opening the cover of the failed device and the internal temperature distribution obtained from the simulation show that the cause of the failure is mainly due to the high temperature generated by the large current between gates and anodes which causing the gate metal lead to melt.The effect of SiC GTO thyristor epitaxial layer structure parameters and oxide layer interface defects on the device's gate-anode anti-surge current capability was studied.The simulation results show that:to obtain a good gate-anode anti-surge current capability,the device's finger width should be small.The doping concentration of the N-drift region should be above 3.0×10¹⁷cm^-3.In addition,the SiC/Si O₂ interface defects that may exist in the device will cause the maximum junction temperature during the surge of the device to quickly rise to above1000K,which could resulting in thermal failure of the device or plastic package.(3)The reliability experiment of SiC GTO thyristor under high temperature,high pressure and humidity environment was carried out,and the reason for the degeneration of the electrical characteristics of the device was analyzed in combination with numerical simulation.The variable temperature experiment results show that:when the ambient temperature of the SiC GTO thyristor increases from room temperature to 150?,the leakage current will gradually increase,and the on-resistance will decrease;the high temperature storage experiment results show that:There is no obvious degradation phenomenon when the SiC GTO thyristor under long-term storage at 150?environment.However,the SiC GTO thyristor will degrade or even fail under long-term storage at higher temperatures.The electrical test results and the cover opening results show that the device failure is mainly due to the TO plastic packaging structure;In the hot experiment,water vapor will enter the device through the TO247 package,resulting in poor passivation between the gate and the anode,and non-permanent degradation of the conduction characteristics of the device;high temperature reverse bias test results show that:SiC GTO thyristor under long-term storage at 175?and 2000V bias will induce interface defects in the p-n junction between the N-drift region and the P-drift region,causing the device on-resistance to become larger and the forward conduction characteristics to degrade.