Pulse Power Characteristics And Optimization Of Gate-Off Thyristor(GTO)

With the rapid expansion of pulse power technology applications,pulse power systems have put forward higher requirements for pulse switches.Silicon carbide gate turn-off thyristor(SiC GTO)because of its lower on-resistance and higher blocking voltage,it has a good application prospect in pulse switching,and compared with the traditional Si GTO thyristor,SiC GTO thyristor has a smaller volume under the same blocking voltage and can work at a higher temperature,which is very suitable for the field of pulse power.In practical applications,pulse switches will experience larger and faster pulse currents.However,in recent years,the research on the pulse reliability of SiC GTO thyristors has mostly focused on the failure mode of the device and the description of the degradation of the electrical characteristics of the device before the failure of the device.The failure mechanism of the device has not been studied too much.This article focuses on the above-mentioned problems and the main contents are as follows:1.The pulse discharge failure analysis of SiC GTO devices is carried out.The results of a single pulse current experiment conducted at room temperature show that the devices of the two structures of 4H-SiC GTO thyristors are damaged at pulse currents of 5 k A and 6k A,and the cathode-anode and gate-anode of the device are short-circuited.The cross-section results show that the devices all have severe thermal damage extending to the substrate under the anode.Numerical simulation results of the device show that the positive feedback of electric field concentration and thermal power concentration leads to thermal concentration under the anode(above the drift zone),which may induce device failure.However,the maximum internal junction temperature of the ideal device simulated based on actual test conditions is obviously not enough to cause such severe thermal damage to the SiC material.Therefore,further study the influence of non-ideal factors such as uneven gate trigger current,uneven doping concentration caused by process deviation,and the existence of defects on the pulse power characteristics of the device.The simulation results show that the uneven distribution of defects obviously aggravates the unevenness of the internal temperature distribution of the device,and causes the device to fail due to severe thermal damage during the pulse discharge process.2.Through the analysis of the pulse failure mechanism,the device structure is adjusted to effectively alleviate the uneven temperature distribution of the device.Through the simulation study of the temperature concentration phenomenon of 4H-SiC GTO devices during the pulse process,it is found that the main reason for the temperature concentration of the device is the uneven distribution of the lateral current density above the drift zone and the concentration of the electric field in the vertical direction of the drift zone.Therefore,two new structures of narrow gate lateral variable doping and multilayer in drift region are proposed.The narrow gate lateral variable doping structure can make the lateral current distribution above the drift region more uniform by changing the ratio of the gate and anode and the lateral variable doping.The maximum temperature inside the device is reduced from 1024 K to 964 K,and the temperature below the gate from 750 K to 865 K,the lateral temperature distribution inside the device is more uniform.The multilayer epitaxial structure of the drift region improves the concentration of the electric field inside the device by making the doping distribution inside the drift region of the device present a gradient distribution from high to low.The maximum-to-minimum ratio of the electric field inside the drift zone is reduced from 5:2to 2:1,and the maximum body temperature of the device during the pulse is also reduced from 1024 K to 865 K.In addition,because the built-in electric field formed by the concentration gradient makes the voltage rise rate of the device in the pulse circuit faster and reaches the highest The devices of the two structures have better pulse power characteristics than the devices of the original structure.