| A Gallium Nitride(Ga N)based high electron mobility transistor with p-type gate cap(p-GaN HEMT)behaves high switching speed,high blocking capability,and low power loss,which meets the development tend of miniaturization and high efficiency of power electronic systems,so it can be widely used in the field of consumer electronics,automotive electronics,et.al.Hower,high temperature,high voltage,high current and other stresses bring critical reliability problems to the p-GaN HEMT,furthermore,leading to the instability problems of power systems.Compared with the Silicon based power devices,investigations on the reliability problems of p-GaN HEMT are not enough,which restrains the wide scale applications of p-GaN HEMT.Therefore,investigating the reliability problems of p-GaN HEMT under complex electric and heat stresses becomes meaningful.Firstly,the methods of damage characterization are investigated.Then the mehcanisms behind the failure and degradations of electrical parameters under high temperature and bias stresses,unclamped-inductive-switching(UIS)stress,and short-circuit stress are revealed,also,a model for the degradations of electrical parameters is estabilished.Finally,a highly reliable 650 V p-GaN HEMT is designed based on the above investigation results.During the researches,7 journal papers have been published and indexed by SCI,3 conference papers have been published,including 2 oral reports.Innovations among the above researches are as follows:1,According to the segmental shifts of output capacitance curve of p-GaN HEMT,an innovative method is proposed to extract the damage information in drift region,including the location and trap density.2,Under dynamic gate bias stresses,it is revealed that there is carrier injection and trapping effect in p-Ga N gate cap layer,meanwhile,high temperatures can lower the barrier height of the traps,then enhancing the trapping effect and degradations of on-state resistance;a trapping-effect-based model is proposed to predict the degradations,the RMSE is less then 0.3%.3,Under UIS stresses,it is revealed that drain over-voltage of p-GaN HEMT triggers inverse-pizoelectronic effect and then leading to the falure,meawhile,over-voltage enhances the trapping effect in gate region and drift region,finally,electrical parameters degrade;accordingly,a model is established to predict the degradations,the RMSE is less than 0.7%.4,Under short-circuit stresses,it is found that heat is accumulated in local drift region,bringing high lattice temperature and burnout,also,activing deep level traps in drift region,finally,leading to the degradations of electrical parameters;accordingly,a model is established to predict the degradations,the RMSE is less than 1.7%.5,According to the researches on the above reliability problems,a highly reliable 650 V p-GaN HEMT is designed,experimental results indicate that the threshold voltage is 1.2V,the on-state resistance is 240mΩ,the continuous working current is above 10 A,the turn-on delay time is 9.4ns,the failure voltage duiring UIS is 1500 V,and the short-circuit withstanding time reaches above 1.5ms. |
