Research On SiC MOSFETs' Surge Reliability

Due to its wide band gap,high breakdown electric field,high thermal conductivity and high electron saturation speed,SiC semiconductor material is gradually emerging in the field of power electronic devices.The advantage of SiC devices lies in the superior performance at high temperature,high voltage and high frequency appications,which can effectively reduce the power loss of power electronic system.However,the cost of SiC devices is too high.The reliability of currently available commercial SiC devices is relatively poor.These issues still need to be addressed to further broaden the market of SiC devices.Surge performance is an important index to measure the reliability of devices.At present,the research on the surge reliability of SiC devices is mainly focused on the surge performance of SiC Schottky diodes.Furthermore,few research on the surge performance of SiC MOSFETs has been focused on the maximum surge currents that SiC MOSFETs can withstand,lacking in-depth analysis of the failure mechanisms.In this work,the surge reliability of 1200 V SiC metal-oxide-semiconductor field-effect transistors(MOSFETs)from various manufactures has been investigated in the reverse conduction mode.The surge current tests have been carried out in the channel conduction and non-conduction modes.The experimental results show that the maximum surge currents that the devices can withstand are similar for both cases.It is found that short circuits occurred between the gate and the source in the failed devices.The characteristics of the body diode have also changed after the tests.By measuring the device characteristics after each surge current is applied,it can be concluded that the damages to the gate oxide layer and the body diode occurred only when the maximum surge current is applied.By decapping the failed devices and observing the cross section of the damaged cell,it is found that high temperature caused by excessive current flow through the devices during the surge tests is the main reason for the device failure.Next,the TCAD simulation of the devices has been carried out to bring insight into the operation of the devices during the surge events.By observing the variation of the internal temperature and current density during the surge tests,it is found that when the surge current reaches a large value,the current mainly flows through the body diode.Therefore,whether the channel conducts or not has limited effect on the surge capability.This conclusion is consistent with the experimental results.Finally,some suggestions are put forward to improve the surge performance of SiC MOSFETs from two aspects: reducing the highest junction temperature inside the SiC MOSFET and improving the devices' capability to withstand high temperature.