Research On Characteristics And Failure Mechanism Of E-mode GaN HEMT Under UIS Stresses

GaN HEMT devices,which are widely used in the field of high voltage and high frequency power conversion,have the advantages of high breakdown voltage,high working temperature,low conduction loss and low switching loss.In practical applications,the unclamped inductive load switching process(UIS)is a typical reliability problem that power devices may face.In order to improve the reliability and robustness of E-mode GaN devices under UIS stresses,it is essential to make clear the UIS physical mechanism of E-mode GaN devices.While the structural mechanism of GaN HEMTs is different from that of Si-based devices,so it is impossible to directly learn from mature theory of Si-based devices for GaN HEMTs.Therefore,it is necessary to study the UIS physical mechanism of E-mode GaN devices.So as to reveal the UIS physical mechanism of E-mode GaN devices consisting of the UIS process mechanism and the UIS failure mechanism,the major works are as follows:1.The UIS process mechanism of E-mode GaN devices is described.By analyzing the single and multiple parallel UIS test results of three E-mode GaN devices with different structures,the UIS process of E-mode GaN devices can be divided into four stages.The E-mode GaN devices can withstand UIS surge energy though the energy transfer between the inductive load and the device capacitance.LRC charge-discharge model is proposed to explain the UIS oscillation behavior of E-mode GaN devices,the energy loss in the UIS process is also pointed out.3.An analytical model of energy loss in UIS process of E-mode GaN devices is proposed.Based on the circuit analysis and the equivalent circuit model of R_S and C_S in series for devices,the analytical model is developed to reveal the quantitative relationships among the E_loss,R_S,and the time shift?t between device current and voltage.The accuracy and feasibility of this analytical model are verified since the good fit between model and experiment.The origin and physical mechanism of E_loss are revealed with the help of TCAD simulation.The imbalance of the charges in devices due to the dynamic trapping and de-trapping of the acceptor traps is the origin of R_S and E_loss.The UIS energy loss model provides important references for alleviating the damage to performance and reliability of GaN devices from UIS stresses.4.The high E-field breakdown mechanism for UIS failure of E-mode GaN devices is proposed.The UIS failure phenomenon of the three different E-mode GaN devices at room temperature are discussed,the UIS failure voltages is proposed to represent the capability of E-mode GaN devices against UIS stresses.What's more,the UIS failure mechanism of high E-field breakdown under transient overvoltage is proposed,that is also verified through the high temperature UIS test experiment of E-mode GaN devices.The UIS failure positions of the three E-mode GaN devices are analyzed in detail with the help of TCAD simulation,electric-field breakdown of E-mode GaN devices under overvoltage easily occurs at the gate edge and drain edge.