Investigation On High Frequency Dynamic On-resistance And Switching Power Loss Model Of AlGaN/GaN HEMT Power Devices

?-? groups based semiconductor materials are broadly developed in high electron mobility transistor(HEMT),etc.,benefiting by its wide bandgap,low permittivity,high critical breakdown electric field and high electron saturation velocity.The polarization effect and the discontinuity of the conduction band produce a high concentration of two-dimensional electron gas(2DEG)with a natural volume density of 1019,which makes the on-resistance(Rdson)of AlGaN/GaN HEMT devices very low.In addition,its input capacitance(Ciss),output capacitance(Coss)and feedback capacitance(Crss)are usually in the order of dozens of pF or several pF,thus this kind of device is outstanding in high frequency application.However,the intense strain which caused by the lattice mismatch is releeised in the form of crystal defects.Superior density defects lead to several reliability problems of AlGaN/GaN HEMT devices,such as current collapse,dynamic Rdson increase and gate delay,etc.These reliability problems are intensified in conditions of high voltage,high current and high frequency,and these problems significant effect on the power loss.Therefore,we need an effective test method and an analytical model to study the performances of HEMT devices in switching power supply application,as well as an analytical method for the design of back-end circuits.Therefore,it is essential to extract the dynamic Rdson of AlGaN/GaN HEMT device and to model its switching power loss.This paper systematically study the dynamic Rdson and power loss model of AlGaN/GaN HEMT device with three aspects of theories,simulations and experiments.The main research contents,methods and results are shown as follows:1.Through our novel double-diode-isolation(DDI)Tech.,the dynamic Rdson of AlGaN/GaN HEMT devices is successfully extracted,and the limitation of frequency response of this extraction circuit has been broke by studying the effect of the parasitic capacitance of various devices in this circuit.In addition,the forward voltage of the isolation diode can be measured in real time at a low voltage range,and the high dynamic performance constant current source with low current value can eliminate the influence of self-heating effect and improve the extraction accuracy.Finally,this method can be performed at high-frequency(up to 1 MHz)and high voltage(up to 600 V)with an extraction accuracy up to 97.8%.The relationship between the dynamic Rdson of AlGaN/GaN HEMT device and the off-state drain-source voltage(Yds off),the operating frequency(fs)and the operating duty ratio(Duty)is investigated systematically.The experimental results reveal that the dynamic Rdson of AlGaN/GaN HEMT device is several times than that of DC Rdson.The experimental results also confirm that the trapping effect is related to an electric field and switching time.2.Through a Floating buck-boost topology circuit in a continuous conduction mode(CCM)and a discontinuous conduction mode(DCM),the detailed high frequency switching processes of the AlGaN/GaN HEMT device are accurately measured,so as to obtain a nonlinear and piecewise model of the dynamic switching power loss for AlGaN/GaN HEMT devices.We divide a switching period into 12 small time intervals,then the drain voltage(Vds),drain current(Idrain),gate voltage(Vdrive)and time(t)at each time interval are accurately modeled.In this model,the exclusive problem of dynamic Rdson increase,the effect of drain current on switching time,and the discrepancy between drain current and real channel current are taken into account,making it conform to the actual working performances of AlGaN/GaN HEMT devices.The experimental results verify the correctness and accuracy of our model.Finally,a corresponding quasi-resonant mode(QRM)or critical conduction mode(BCM)is proposed to be the most suitable hard-switch operating mode.3.Through the extraction of dynamic Rdson and the relationship between the dynanic Rdson and the drain voltage,we find a new method and build a new model to characterize the average activation energy of device degradation of AlGaN/GaN HEMT devices by analyzing the dynamic Rdson of AlGaN/GaN HEMT devices.Thus,this new model can guide us that what kind of defects and which layers they are located will lead to the dynamic Rdson and current collapse(CC).This model follows the Arrheniuses law and the effect of the electric field is loaded.The temperature rise of devices is obtained through the calculation of the device losses,and then the relationship between the conduction loss caused by dynamic Rdson and the temperature rise is analyzed.Finally,the average activation energy of the device degradation is calculated by this model.The results explain why there is an inflection point in the relation curve of dynamic Rdson with the drain voltage around 200 V,and also analyze the location of the defect that dominates the influence at various voltages.4.Through the impact of parasitic drain-source capacitance(Cds)of AlGaN/GaN HEMT devices on channel current,the effect on dynamic Rdson and dynamic switching power loss is furtherly verified.We also consider the effect of the source inductor on switching time and dynamic switching loss.By assessing the impact of channel current and source inductance on the switching speed of the device,the correlation between dynamic Rdson and trapping effect is verified again,and then our dynamic switching loss model is modified.Finally,we use our model to estimate the dynamic switching power loss by an applieation and to compare the calculation results from the model with the experimental results.The comparison results show that the power loss calculated by this dynamic switching power loss model is in good agreement with the experimental test result.