Study On The Measurement Techniques Of Switching Characteristics Of E-mode GaN-based HEMTs

Gallium nitride(GaN)material has shown enormous advantages in the preparation of high-voltage,high-speed,and low-loss power switching devices by virtue of its superior characteristics such as wide band gap,high critical breakdown electric field,and high electron mobility.In the present circumstances,E-mode GaN-based high electron mobility transistor(HEMT)is the major power switching device.Different from Si-based MOSFET,GaN-based HEMTs has extremely fast switching speed and small switching loss.The dynamic switching characteristic parameters of devices mainly include dynamic capacitance,gate charge,and switching time.Further research of the switching characteristics can guide the rational design of driving circuits,reduce switching loss and prolong the service life of devices and circuits.Therefore,it is of great significance to study the accurate measurement technology of dynamic parameters to promote the practical application of devices.Firstly,this thesis introduces the advantages of GaN materials,and the excellent characteristics and application value of power devices based on GaN materials.The structure and working principle of two E-mode GaN-based HEMTs are introduced,and the basic electrical parameters are tested.Then,the PCB test board of dynamic capacitance and gate charge is designed,and two methods to test gate charge are proposed.Finally,the switching circuit with parasitic parameters is modeled,and the PCB test board of GaN-based HEMTs switching time is designed.The main research contents of this thesis are summarized as follows.1.An E-mode GaN-based HEMTs dynamic capacitance test circuit is designed and implemented.According to the principle of dynamic capacitance testing,input capacitance,output capacitance,and miller capacitance test boards are designed respectively.Due to the different packaging forms of the device and the test board,a DFN8*8 to TO220 Kelvin transfer plate is designed,and the test results are basically consistent with the specification.2.Two new techniques for measuring gate charge under high power conditions are proposed.One is the capacitance-current method,and the gate charge is calculated based on the measured dynamic capacitance and output characteristic curve,and another one is the two-step current method,based on the test results of high voltage and small current and low voltage and large current,the gate charge of high voltage large current test conditions is obtained.The results show that the two methods can obtain reliable results for the total gate charge,but the deviation between the latter and the datasheet is smaller,about 0.1 nC.The reason for the large deviation of the former may be that the capacitance is tested under off-state,ignoring the influence of high voltage and large current and parasitic parameters in the practical test.3.The test circuit of switching time is designed and implemented.Considering the actual test environment,the switching circuit with parasitic capacitance and inductance is modeled in stages according to the behavior of voltage and current in switching action,and the solution platform is built by MATLAB / Simulink simulation software.Then,based on 1EDF5673 GaN driver chip,the switching test board of E-mode GaN-based HEMTs is completed by combining standard gate driver with a passive RC circuit.The measured waveform oscillation is small and the delay time is only about 4 ns.Finally,the waveform of the model and the test board are compared and analyzed,and the results show that the model results match the actual waveform well.The oscillation frequency and voltage overshoot amplitude are basically consistent with the experiment,which has guiding significance for the circuit application of the device.