Research On Short Circuit Related Reliability Mechanism Of P-GaN HEMTs

In recent ten years,with the continuous development and precipitation of GaN HEMTs technology,GaN HEMTs power devices have been widely used in high-frequency and high-power circuit systems such as MHz boost or buck converters and high-voltage inverters above 600 V.Due to the occurrence of unexpected events such as load short circuit,faulty gate control signal,high side and low side power devices punch through,the device will be in a serious short circuit state,which will seriously restrict the performance of high-frequency circuit system and endanger the safety of circuit system.At present,to explore the short circuit characteristics and related mechanisms of GaN HEMTs devices,and to deeply study the physical mechanism and failure mechanism of device degradation after short circuit stress has become the focus and hotspot of research in the field.The main research contents of this thesis are as follows:（1）By introducing the single short circuit stress test,it is found that the gate source voltage V_GS and short circuit current I_DSC continue to decline during the short circuit process.Based on the simulation results of thermal network model and the variation characteristics of channel temperature T_j,combined with the gate energy band theory and gate carrier transport characteristics,the thermal auxiliary effect dependent on T_j and the hot electron effect dependent on high electric field are proposed,which lead to the electron dominated gate leakage behavior mechanism,and the physical mechanism of V_GS decline is revealed.Combined with V_GS decline and T_j dependent electron mobility model,the physical mechanism of I_DSC decline is revealed.The gate leakage mechanism and related mechanism are further verified by single short circuit test and control group.By introducing the repetitive short circuit stress test control group,it is found that the degradation of electrical characteristics of the device increases with the increase of short circuit times and stress.Based on the proposed gate leakage mechanism,combined with stress bias conditions,gate energy band model theory and trap effect,it is proposed that the degradation mechanism of threshold voltage V_TH and saturated drain current I_Dsat lies in the capture of electrons overflowing 2DEG channel by Al GaN barrier layer traps and p-GaN/Al GaN interface traps.（2）The influence of stress intensity on recovery characteristics and its related degradation mechanism are further studied by introducing repetitive short circuit stress test.By monitoring the electrical characteristics of the recovery stage,it is found that V_THand I_Dsat can completely recover after lenient short circuit stress,based on the proposed traps capture electron mechanism,combined with the trap energy level theory and baking experiment,the trap charge and discharge mechanism dominated by Al GaN barrier layer traps and p-GaN/Al GaN interface traps is proposed,which leads to the degradation of the recoverability of V_TH and I_Dsat.V_TH and I_Dsat cannot recover completely after severe short circuit stress,through the design of high-temperature short circuit test,combined with the hot electron theory and the gate"back-to-back"diode model,it is proposed that the hot electrons induced by the peak electric field near the gate edge（drain side）and the drain electrode lead to new defects at the p-GaN/Al GaN interface and permanent hot electron capture in the Si N passivation layer near the drain electrode,resulting in the irrecoverability of V_TH and I_Dsat.The distribution characteristics of peak electric field in the process of short circuit are analyzed by TCAD,which strengthens the unrecoverable degradation mechanism caused by hot electrons.This study is of great value to evaluate the safe working ability of mainstream p-GaN HEMTs devices and has guiding significance to further improve the reliability of devices.