Study On The Thermal Characteristics Of GaN HEMT Under Small Size

In recent years,AlGaN/GaN HEMT have been widely developed in the fields of high frequency and high power due to their excellent performance.However,with the progress of the device technology,the feature size of the HEMT are becoming smaller and smaller,causing the problems such as rising temperature,degradation of electrical properties and increasing thermal efficiency.The study shows that nearly 55%of electronic device failure is related to temperature,and 50%of IC failure is related to thermal stress.Therefore,the research of temperature rise of HEMT has important reference value for thermal evaluation and design of HEMT.Although there has been considerable research on the steady-state heat source temperature of GaN HEMT,the study on the mechanism of thermal resistance and transient thermal characteristics is not deep enough.In this context,the change mechanism of thermal resistance and transient thermal characteristics of HEMT are studied by means of experiment and simulation.The main works are as follows:1)This paper will introduce the commonly used methods of temperature measurement infrared thermometry,electric thermometry and Raman thermometry and the heat propagation equation used for the theoretical analysis of the junction temperature.The physical model used for modeling HEMT in sentaurus TCAD simulation tool is explicated.2)The CREE company produces the AlGaN/GaN HEMT as the main research object,using the infrared thermal imager with spatial resolution of 7 um to measure the steady state temperature of HEMT work in V_ds=28 v,I_ds=500 mA bias conditions,platform temperature is 60??70??75??80??90??100?respectively.Then the simulation model of Sentaurus TCAD was optimized by the infrared experiment results.3)Base on the optimized simulation model,the thermal distribution of HEMT with different gate length?gate width?substrate thickness working in V_ds=28 V,I_ds=500mA,as well as the HEMT working in different source leakage voltages and source leakage flows is simulated.By heat conduction equation,the thermal propagation model of GaN HEMT is established,and the thermal resistance formula of the device is derived.This article analyzes the influence mechanism of gate length,gate width,substrate thickness and power on the thermal resistance of HEMT,and propose the effective measures to improve the thermal characteristics of the HEMT.4)When GaN HEMT work under the condition of the pulse,heat source temperature increasing--lowering–increasing process is analogous to charging–discharging-charging process of capacitance.The heat source temperature varies with the size of the HEMT parameters and the working conditions relationship is derived.Using the optimized simulation model,simulation of HEMT under the different condition such as in different gate length,power,frequency and duty ratio of the change of the heat source temperature,compared with theoretical analysis.Analysis of these factors on the GaN HEMT devices the effects of transient heat transfer characteristics of the mechanism.Finally,based on the above analysis,the GaN HEMT safety work scope optimization measures are put forward.