Uis Characteristics And Mechanism Of P-GaN Gate GaN HEMT

In recent years,with the extensive application of GaN power devices in the field of power electronics,the reliability of GaN devices in various practical application scenarios has been paid more and more attention.Because of its high frequency characteristics,600V and higher voltage GaN devices as power switching appear in various k Hz high frequency switching topologies and circuit systems.However,in Buck-Boost,PFC,LLC and other converters,GaN switching power devices will face Unclamped-Inductive-Switching（UIS）events due to the mutual coupling resonance between GaN device and inductance and the internal structure characteristics of the devices,as well as the false turn-on of switching devices,lightning strikes and so on.Furthermore,the extremely high-voltage and high-current bias during UIS stress is a great ordeal for the reliability of the device.Therefore,this thesis takes the 650 V P-GaN Gate GaN HEMT,which is widely used in commercial applications,as an example to design an experimental platform dedicated to studying the UIS ability of this device,explore the behavior characteristics and relevant mechanisms of the device under UIS stress,and further study the degradation and failure mechanism of the device after single and repetitive UIS stresses.The main research contents of thesis are as follows:（1）Single UIS stress reliability of P-GaN Gate GaN HEMT devices.It is found that whether the device fails in a single UIS event depends on the value of the transient peak overvoltage V_peak sustained by the drain,rather than the energy value E_AV,which measures the UIS capability of Si/Si C devices.Further failure analysis of the damaged device shows that the burn point is located near the drain electrode of the device.At the same time,the influence of the power supply voltage,inductance and ambient temperature on the device’s UIS capability in a single UIS event is explored.It is found that the increase of the power supply voltage and inductance under the condition of the same current I_peakwill make the transient peak overvoltage V_peak of the device in a single UIS event increase and approach the critical point of failure.In addition,when the device is faced with a single UIS event in a high temperature environment,the UIS capability increases in terms of E_AV and V_peak dimensions,which further indicates the superiority of GaN devices under a single UIS event at high temperature.（2）Study on Repeatable UIS Stress Reliability of P-GaN Gate GaN HEMT devices.It is found that the electrical characteristics of devices under repetitive UIS stress will decline to a certain extent--V_th first positive and then negative drift,R_ds,on first increase and then decrease.Based on the"back-to-back"diode model and trap theory in the P-gate,combined with the high voltage of kilovolts endured by the drain in the UIS event,a physical model of the degradation of the electrical characteristics of the device in the repetitive UIS event is proposed--the high electric field between the drain gate of the device causes the reverse breakdown of grid PIN diode.At the same time,new electron hole pairs are generated by collision ionization in the channel.P-GaN grid accumulates positive space charge due to the space charge region generated by the reverse breakdown of PIN diode.However,due to potential difference collision ionization,the newly generated holes move to the gate,and the electrons move to the drain,and the mobility of the holes is smaller than that of the electrons.