Analysis Of Thermal Characteristics Of GaN HEMT On Diamond Substrate

GaN based high electron mobility transistor(HEMT)has been widely used in 5G technology,new energy vehicles,UAVs and other emerging industries in recent years due to its high power and high voltage resistance.However,because of the high power density of HEMT devices,the self thermal effect will cause the junction temperature of the devices to increase greatly,which seriously affects the performance,reliability and life of the devices.The combination of diamond materials with super high thermal conductivity and GaN materials will help to improve the thermal properties of GaN HEMT.In this paper,the thermal stress caused by the junction temperature and self thermal effect of GaN HEMT devices on diamond substrate is studied by using Sentaurus and COMSOL method.The thermal properties of GaN HEMT on diamond substrate are analyzed by taking into account the anisotropic thermal conductivity of diamond and replacing the concentrated heat source with distributed heat source.The main contents and results of this paper are as follows:1.The results of the electrical thermal simulation of traditional GaN HEMT show that the self thermal effect can reduce the output leakage current by 17%,and a peak temperature of 389K is formed near the drain side of the gate edge.The distributed heat sources along the channel of P=8W/mm single gate HEMT device are extracted,and the 3D thermal model of multi grid GaN HEMT on diamond substrate is established.The results show that the local thermal conductivity of the diamond substrate increases with the increase of the thickness of the substrate.2.Diamond as the substrate of HEMT device can effectively reduce the junction temperature of the device.The thermal properties of GaN HEMT on diamond substrate are studied.The results show that the thickness of the substrate is 100μm The peak temperature of GaN HEMT on diamond substrate is 382.69K,and the thermal stress and displacement deformation are mainly distributed at the diamond/GaN interface,with the maximum values of 178MPa and 2.32nm respectively.The thermal resistance of the diamond/GaN interface limits the heat dissipation capacity of HEMT devices.When the boundary thermal resistance of diamond/GaN interface increases from 0 to 80m2·K·G-1·W-1,the junction temperature increases 13%and the thermal stress increases 78%.The diamond substrate can still maintain a lower thermal resistance when the thickness of diamond substrate is from 50μm increases to 600μm.The junction temperature of the device only increased by 10.5K,which showed a huge heat dissipation advantage.3.The NCD heat sink is deposited on the top of GaN HEMT,which increases the transverse cooling channel,and greatly reduces the junction temperature of the device(37.53K).However,due to the thermal mismatch between diamond and Si3N4,there will be a large thermal stress(182MPa)and displacement deformation(6.3 1μm)on the top of the device.