加载功率与壳温对AlGaN/GaN高速电子迁移率晶体管器件热阻的影响

结温是制约器件性能和可靠性的关键因素, 通常利用热阻计算器件的工作结温. 然而, 器件的热阻并不是固定值, 它随器件的施加功率、温度环境等工作条件的改变而变化. 针对该问题, 本文以CREE公司生产的高速电子迁移率晶体管(HEMT)器件为研究对象, 利用红外热像测温法与Sentaurus TCAD模拟法相结合, 测量研究了AlGaN/GaN HEMT器件在不同加载功率以及管壳温度下热阻的变化规律. 研究发现: 当器件壳温由80 ℃升高至130 ℃时, 其热阻由5.9 ℃/W变化为6.8 ℃/W, 增大15%, 其热阻与结温呈正反馈效应; 当器件的加载功率从2.8 W增加至14 W时, 其热阻从5.3 ℃/W变化为6.5 ℃/W, 增大22%. 对其热阻变化机理的研究发现: 在不同的管壳温度以及不同的加载功率条件下, 由于材料导热系数的变化导致其热阻随温度与加载功率的变化而变化.

Influence of power dissipation and case temperature on thermal resistance of AlGaN/GaN high-speed electron mobility transistor

The junction temperature is a main factor affecting the device performance and reliability. The thermal resistance is usually used to calculate the junction temperature. However, the thermal resistance is not constant under different operating conditions. In this work, we examine the high-speed electron mobility transistor (HEMT) from the CREE Company to investigate its thermal resistances under different case temperatures and dissipation powers. To avoid the self-oscillating phenomenon of the HEMT device, a circuit is designed to prevent the self-oscillating in experiment. First, the temperatures of the active region of the GaN HEMT device are measured by the infrared image method under different dissipation powers (including 2.8, 5.6, 8.4, 11.2, and 14 W) and different case temperatures, respectively. Then according to the result of infrared image method, the simulation model is set up by using the Sentaurus TCAD. From the final optimized model, we extract the device junction temperature and calculate the thermal resistance. It is expected to ascertain the characteristic of the thermal resistance and compare it with the result from the infrared image method. It is found that as the device case temperature increases from 80 ℃ to 130 ℃, the thermal resistance changes from 5.9 ℃/W to 6.8 ℃/W, i.e., it is increased by 15%. When the power increases from 2.8 W to 14 W, the thermal resistance changes from 5.3 ℃/W to 6.5 ℃/W, i.e., it is increased by 22%. This phenomenon is mainly attributed to the changes of the thermal conductivity of device materials. According to the formula for the coefficient of the thermal conductivity of nonmetallic material SiC, the phonon scattering rate becomes larger with the increase of temperature. Thus, the phonon mean free path can decrease by reducing the average freedom time. Finally, the coefficient of thermal conductivity becomes smaller. It was reported by Kotchetkov et al. (Kotchetkov D, Zou J, Balandin A A, Florescu D I 2001 Appl. Phys. Lett. 79 4316) that the coefficient of thermal conductivity of GaN becomes smaller under high temperature. All of these have an effect on the heat dissipation of the device, which will cause the thermal resistance to increase. Based on the result from the infrared image method and TCAD simulation, the changing characteristic of the thermal resistance is obtained, thereby reducing the errors in the calculation of the junction temperature.