Design Of Test Circuit And Analysis Of Degradation For Dynamic-resistance In GaN HEMT Devices

Gallium Nitride?GaN?High Electron Mobility Transistor?HEMT?suffers from the current collapse when working under high voltage conditions,which leads to an increase in dynamic on-state resistance R_dyon macroscopically.To evaluate the current collapse effect,the degradation of device can be quantified by measuring the value of R_dyon.If R_dyony_on is directly extracted from the conventional switching circuit,the range of oscilloscope probe should be set large enough to detect the leakage voltage,which changes between hundreds of volts in the off-state and hundreds of mill-volts in the on-state.At this time,the accuracy of the oscilloscope is insufficient,and the value of on-voltage-drop cannot be read accurately,which resulting in an error in the extraction of the dynamic resistance.Therefore,it is important to study the accurate test method for R_dyon in GaN HEMT devices.The test circuit for R_dyon of GaN HEMT devices in this thesis is based on the the traditional switching test circuit and adds a voltage clamping module in it to improve the accuracy of the oscilloscope by clamping the off-state drain voltage to a small value.The thesis elaborates on the functional design of the gate drive module,the functional design of the voltage clamping module and the optimized design of the test circuit.Functional design of the gate drive module includes power isolation,signal source isolation,digital-to-analog isolation,voltage regulation,and any gate-voltage drive.The functional design of the voltage clamping module includes the determination of voltage clamping scheme and RC filtering scheme.The optimized design of the test circuit includes circuit parameter deviation based on simulation software and parasitic parameter optimization of board level circuit.Based on the test circuit of this thesis,the accurate value of R_dyon can be extracted within 180 ns after the DUT turnning on.Based on the test circuit,the thesis also deeply studies the mechanism for the degradation of R_dyon under different stress conditions.The research indicates that the degeneration of R_dyon is proportional to the magnitude of the blocking-voltage,blocking-voltage application time and temperature.The effect of blocking-voltage and blocking-voltage application time on the degradation of R_dyon under the high gate voltage is about twice as fast as that under the low gate voltage.The research of the thesis provides important guiding significance for the design to suppress current collapse in GaN HEMT devices.