Test Analysis Of Threshold Voltage Drift Characteristics Of SiC MOSFET Devices

With the advantages of fast switching speed,low leakage current and high power density,SiC MOSFET devices are used in high temperature,high voltage and high power fields such as new energy vehicles and national defense industry.However,SiC MOSFET has complex drift characteristics under different bias temperature stress.The instability of V_thbecomes the key problem that hinders the widespread application of SiC MOSFET.The existing test techniques of V_thdrift are the longitudinal comparison of the methods themselves under different bias temperature stress conditions,and cannot be used as the standard test technology to evaluate the instability of V_th.This paper evaluates the instability of V_thby three testing techniques,which provides a new way to test the drift characteristics of V_thaccurately and construct the standard test technology to evaluate the instability of V_th.Based on the Si system and based on the limited reports,I discussed the internal physical mechanism of V_thdrift in this paper.Three threshold voltage drift testing techniques,namely the traditional voltage sweep method,the non-relaxation method and the fast pulse method,are implemented with respective measurement conditions.After analyzing the advantages and disadvantages,errors and applicability of the test technology,a V_thdrift evaluation system for SiC MOSFET devices is established.The experimental results show that:the traditional voltage sweeping method is simple to operate.However,this test method can only capture the influence of slow state trap,and the measured?V_this 0.01～0.03 V.The test error of this method is large,so it is suitable for testing non-commercial SiC MOSFETs with low accuracy requirements.The V_thdrift caused by the fast state trap and the slow state trap can be measured simultaneously by the non-relaxation method under the condition that the stress is not interrupted.Under the same bias temperature stress,the measured?V_this 1.5～6.5 V.However,the long-time stress makes the fast state trap unstable,which is caused by the tunneling behavior of carriers.With the increase of gate voltage duration,the?V_thdoes not increase but decreases,which lead to large errors.In addition,this method will cause irrecoverable damage to the device.Generally speaking,the non-relaxation method is more suitable for testing the long channel SiC MOSFETs with long service life.The fast pulse method uses the pulse edge test technology to avoid the influence of self-heating effect on the SiC MOSFETs,which shorten the test time to the millisecond level,and detect the influence of interface and near interface traps with the de-trapping rate below the millisecond level.Comparing to the other two methods,this method extracted more accuracy V_thdrift（0.3～1.8V）with smaller stress size and stress time,which can be used to accurately test the V_thinstability of commercial SiC MOSFET.The innovation of this work lies in the realization of the above three V_thdrift characteristics test methods at the same time,and the horizontal comparison is carried out.This provides a key test method for further research on SiC MOSFET V_thdrift suppression technology.