| As a key technology in the power electronics industry,power semiconductors can provide efficient,reliable,and low-cost control and conversion capabilities.Among them,wide bandgap semiconductor Si C is leading the development of power semiconductors into the next generation of power conversion technology due to its excellent material advantages(high critical electric field,high saturation electromigration speed,hot topic conductivity,etc.).Nowadays,Si C power devices are gradually being used in a variety of power scenarios,such as white goods,new energy vehicles,industrial applications,etc.Due to advances in silicon carbide technology,Si C MOSFET devices are gradually starting to shine brightly in the field of power semiconductors.According to different application scenarios,currently commercial Si C MOSFETs mainly have 650 V,1200V,1700 V voltage level devices,of which 1200 V voltage level has a large market development demand.Although Si C MOSFETs have many advantages,there are still reliability issues that need to be addressed.This thesis first designs a 1200 V Si C MOSFET device via emulation,then conducts a series of reliability tests on the designed chip,analyzes the specific fault principle,and extracts temperature sensitive parameters under the ultimate stress state of the device for analysis and evaluation.The short circuit of the device and the UIS(Unclamped Stress Switching)capability can well reflect the reliability of the device.Short circuit is a measure of the device’s tolerance under high leakage pressure and large current,and UIS is a measure of the device’s tolerance under avalanche mode.After building the experimental platform,this thesis first tested the designed 1200 V Si C MOSFET for short circuits,combined with simulation verification analysis,and continuously increased the gate opening time until the device failed,and then analyzed the internal current before and after the short circuit time.The distribution and temperature field distribution of the device is concluded that the reason for the short circuit failure of the device is that the gate cannot be turned off normally due to the high junction temperature,which leads to a large tailing current.Then,the feasibility of extracting temperature sensitive parameters under extreme stress conditions of the device was evaluated to realize indirect measurement and monitoring of junction temperature,and the temperature sensitive characteristics of short-circuit current and the effect of temperature sensitive parameters under different bus voltages were evaluated.This thesis then performs a single UIS test and a repeat UIS test of the device.Through experiments and simulation analysis,it is concluded that the reason for the single UIS failure of the device is the opening of the parasitic transistor in the body caused by high temperature and large current,which triggers temperature feedback;the mechanism of repetitive UIS degradation of the device is due to the injection of hot holes in the JFET region of the device and the capture of gate oxygen.Then,the temperature sensitive parameters of the device in the UIS process are studied,and the avalanche breakdown voltage and shutdown delay time are extracted respectively.Analyze the junction temperature monitoring effect of the two as temperature sensitive parameters.In this thesis,starting from the short circuit of the device and the failure mechanism of UIS,it is concluded that the change of junction temperature is the key factor causing the failure,and a method for extracting relevant temperature sensitive parameters is designed to help monitor and improve the reliability of the device. |
