Thermal Management Of AlGaN/GaN HEMT Device

Due to a series of excellent characteristics such as wide band gap,high breakdown voltage and high electron saturation speed,gallium nitride(GaN),as a third-generation semiconductor material,has a wide range of applications in the fields of high temperature,high frequency and microwave power.However,as the power demand continues to increase and the device size shrinks,the thermal reliability of GaN-based high electron mobility transistors(HEMTs)has gradually become one of the important factors restricting their development.For conventional single-channel AlGaN/GaN HEMTs devices,the two-dimensional electron gas(2DEG)has poor confinement in high-temperature applications,and the electrical characteristics of the devices will be severely degraded.In order to meet the needs of high-temperature and high-power applications,dual-channel GaN-based HEMTSs devices have been proposed.Compared with single-channel devices,dual-channel devices are more suitable for working under high temperature conditions,but they will generate higher heat under the same bias voltage,and the device temperature is high,so it is necessary to optimize the design of its structure.In the past,the optimization of the material layer structure mainly focused on the thermal analysis of traditional single-channel devices,while the research on dual-channel devices was relatively lacking.Therefore,from the perspective of temperature-changing characteristics and thermal design of dual-channel AlGaN/GaN HEMTs devices,the characteristics degradation phenomenon and mechanism of the devices at high temperatures and the thermal coupling between the two channels are studied,and the dual-channel devices are developed thermal design optimization.1.The DC and capacitance-voltage characteristics of conventional single-channel AlGaN/GaN HEMTs and double-channel AlGaN/GaN HEMTs have been studied.The results show that at room temperature,the saturated drain current of the double-channel device is higher and the off-state leakage is lower than that of the single-channel device.With the increase of temperature,the maximum saturation current and peak transconductance of the two devices degenerate to different degrees.The drain saturation current and peak transconductance of single-channel devices are reduced by 35% and 31%,respectively,while those of double-channel devices are reduced by 20% and 26%,respectively.This indicates that the degradation of the double-channel device at high temperature is less than that of the single-channel device.The main reason is that the two-dimensional electron gas in the channel is effectively confined in two barrier layers because a back barrier is inserted under the channel,which enhances the carrier confinement.The C-V test results also show that the 2DEG surface density of the single-channel device decreases at high temperature,while that of the double-channel device has little change.2.An electrical measurement method based on the drain current difference between DC and double-pulse conditions was used to characterize the junction temperatures of single-channel and double-channel devices.The results show that the temperature of the double-channel device is higher at the same power dissipation.The three-dimensional finite element model of the device was established by ANSYS simulation software,and the relationship between the junction temperature of the single-channel device and the double-channel device with the dissipated power was obtained.The accuracy of the model is verified by comparing the simulation results with the test results.3.Based on the finite element simulation model,the thermal coupling between the two channels and the thermal regulation of the top diamond on the device were studied.The results show that the junction temperature of the device gradually increases with the increase of the power ratio of the first channel.The junction temperature of the device decreases with the increase of GaN thickness between the two channels.This is mainly because the greater the thickness between two channels,the smaller the thermal crosstalk between channels.The higher the power ratio of the second channel is,the more easily heat is transferred from the substrate with high thermal conductivity below,and the lower the junction temperature of the device is.With the increase of diamond thickness,the junction temperature of the device decreases gradually.Compared with the 4?m long diamond layer deposited between source and drain,the junction temperature of the device with the diamond layer covering the top layer is the lowest.The final optimization results are as follows: when the total applied power is 10 W/mm,the upper heat source power is 1W/mm,the thickness of the upper GaN layer is 100 nm,and the diamond layer with a thickness of 10 ?m is deposited on the top layer of the device,the channel temperature of the device is the lowest 152.02 ?.Compared with the device without structural optimization,the junction temperature decreased by 41.15?.