Research On High Frequency,High Efficiency GaN DC-DC Buck Converter And GaN Devices Reliability

Compared with silicon-based power devices,Ga N HEMTs power devices can achieve smaller size,higher frequency and lower loss power conversion systems due to high concentration of 2-DEG,and low gate charge,zero reverse recovery charge and other excellent characteristics.Since p-Ga N HEMTs power devices have a good compromise between cost and performance,they have excellent application prospects in the field of power electronic conversion(such as consumer electronics,new energy vehicles,clean power supplies,data centers,etc.).Compared with silicon-based power devices,p-Ga N HEMTs have unique reliability problems such as current collapse and threshold voltage instability,which seriously limit the application of p-Ga N HEMTs in next-generation high-speed and high-efficiency switching power systems,and the excellent properties of Ga N material cannot be fully exerted.The threshold drift of p-Ga N HEMTs has always been the focus of international/domestic researchers,but few studies have discussed the threshold voltage drift characteristics from the system level.In this thesis,aiming at the application of p-Ga N HEMTs in high-speed and high-efficiency switching power supply systems,the performance stability of the device in the system,the physical mechanism affecting the performance stability and the impact on the system are discussed.The main research contents are as follows: The main research contents are as follows:(1)Low parasitic design of high-speed,high-efficiency DC-DC Buck Converter switching power supply reliability evaluation board(EV).This article designs a dedicated reliability EV that can directly characterize the device,with dead-time adjustment.The influence of the parasitic capacitance of the device on the switching characteristics of the system is discussed,and the variation of the electrical stress on the device during the switching process is discussed through simulation.The gate resistance design and the multi-layer printed circuit board layout design are optimized to minimize the parasitic inductance by analyzing the influence of gate loop and power loop parasitic parameters on switching characteristics and reliability evaluation.After optimization,the system can achieve the highest frequency greater than2 MHz,and the peak efficiency at 1 MHz is greater than 92%.(2)Device performance stability,physical mechanism and influence on the system in Buck Converter system.Firstly,the stability of the threshold voltage of the device in the system under longterm and different load system operating conditions is discussed.In the test,it is observed that the threshold voltage degradation of the device has saturation characteristics and spontaneous recovery characteristics.To further discuss the stability of system and device performance,the effects of high frequency switching and duty cycle on device threshold voltage stability were analyzed by operating the system at different frequencies and different duty cycles.it was observed that in high frequency test sthreshold voltage degradation is most severe,with an increase of 0.83 V,and the system power consumption increases by 1.94 times.In order to determine the physical mechanism of device performance change,the effects of different stress conditions in the system on the device threshold voltage stability were separated through hard switching tests.The results show that the hard-switching stress and the on-state stress have the greatest influence on the device performance degradation,which is 3.6 times and 2.83 times higher than the threshold voltage degradation of the off-state stress,respectively.Through the analysis of the established device physical model,it is believed that the threshold voltage degradation is affected by the hot electrons generated during the working process of the system.It is verified that the increase of the threshold voltage will mainly increase the power consumption of the turn-on process,and the turn-on process drives the increase of power consumption by establishing a hard switching model.In one cycle,the power consumption of the turn-on process increases by 180 m W from 124 m W when the threshold voltage changes by 1 V.