Research On Reliability Of P-GaN HEMTs Under Open-state Stress

The semiconductor power devices are the core components of power electronic systems.With the rapid development of power electronic technology,traditional Si-based power devices have been unable to meet the application requirements of high frequency,high speed,high efficiency and low consumption.Gallium nitride heterojunction high electron mobility transistor(Ga N HEMT,Ga N High Electron Mobility Transisitor)has the characteristics of high critical electric field strength,high electron saturation speed,and low on-resistance,which has broad application prospects.Ga N HEMTs(P-Ga N HEMTs,P-Ga N Gate E-Mode Al Ga N/Ga N HEMTs)which are using P-type gates are currently the mainstream alternatives for realizing enhancement-mode devices.With the development of P-Ga N HEMTs,the high power dissipation is brought about by high integration and the high power density,which inevitably makes the device face a higher operating junction temperature.And high temperature reliability has become a major challenge for device practicality.In the thesis,the performance degradation of P-Ga N HEMTs after self-thermal stress is taken as the research object,and the effects of electrical stress and thermal stress and their coupling effects on the gate carrier transport are studied.A physical model of trapping carriers by electric field and thermal field is presented.The main research contents of the thesis are as follows:(1)Design a self-thermal stress test scheme for P-Ga N HEMTs,and conduct a self-thermal stress test for schottky P-Ga N HEMT power devices in half-open state(V_GS=4V)and ful-open state(V_GS=6V).It is found that the threshold voltage drifts in a positive direction and the saturation drain current decreases after the semi-open state stress,while the threshold voltage drifts negatively and the saturation drain current decreases after the fully open state thermal stress,and the degradation of the saturation drain current is related to the maximum temperature which is reached during the device stress process.Based on the gate hole injection model of P-Ga N HEMTs,a new physical model is proposed that the gate electrical stress promotes hole injection due to thermal stress and the thermal stress stimulates the channel electron transition.(2)According to the actual device structure parameters,a P-Ga N HEMT power device model and the electro-thermal simulation experiments are completed with Sentaurus TCAD simulator.It is found that the peak junction of 408K and the peak electric field of 0.6m V/cm appeared in the channel region between the gate and the drain.The results show that the spatial distribution of channel junction temperature is consistent with the electric field distribution,which provides a mechanism explanation for the electro-thermal coupling effect of P-Ga N HEMT devices in the autothermal stress experiment.The 3-D model of P-Ga N HEMT wafer level device is established by ANSYS finite element simulator.The temperature uneven distribution in self-heating effect is studied by adding thermodynamic model to prove the seriousness of device heating in self-heating effect.