Thermal Characteristics Simulation And Structure Optimization Of AlGaN/GaN Hemt Device

Al Ga N/Ga N heterojunction has a strong spontaneous and piezoelectric polarization effect.Even without any doping,only polarization stress can generate a high-density two-dimensional electron gas in the quantum well at the Al Ga N/Ga N heterogeneous interface.Al Ga N/Ga N HEMTs have great potential to be used in high power and high frequency electronics devices.However,in high power device application,the continuous rising of the junction temperature of the Al Ga N/Ga N HEMTs has limited its further development severely.Al Ga N/Ga N HEMTs on conventional substrates usually have a significant self-heating effect,and we need to take the thermal factor into consideration.Diamond material has high thermal conductivity.The introduction of diamond layer provides us an effective thermal management method on Ga N HEMTs.In this dissertation,the simulation research and structural optimization of Al Ga N/Ga N HEMT device characteristics are carried out.The effects of temperature,gate length and diamond material on the channel temperature,DC and AC characteristics of the device under the self-heating effect are analyzed.It provides an effective way to improve the heat dissipation of the device.It also provides theoretical guidance for the application and development of diamond on Ga N devices.The specific research content and results are as follows:Firstly,the influence of self-heating effect on device characteristics is analyzed.In order to consider the self-heating effect of the device,the self-heating model is introduced in the simulation.The basic characteristics of the device are obtained and the simulation model is verified by comparison with experimental data,which provides a basis for the subsequent thermal simulation of the device.And based on the simulation under the self-heating model,the influence of temperature and gate length on the output characteristics of Ga N HEMT is studied.The simulation shows that as the temperature increases,the output drain current of the device decreases;as the gate length decreases,the output drain current of the device increases,but the self-heating effect of the device is more significant.This shows that in order to improve the reliability of Ga N HEMTs operating at high temperatures and high currents,it is necessary to suppress the self-heating effect of the device.Secondly,the diamond substrate and the diamond passivation layer are used to optimize the device structure to improve the heat dissipation problem of the device.For the diamond substrate structure,the lattice temperature distribution of the device on the diamond substrate and the sapphire substrate and the lateral temperature distribution curve at the channel are obtained by simulation.The simulation results show that when the drain voltage is 20 V and the gate voltage is 0V,the maximum crystal lattice temperature of the device based on the diamond substrate is 265 K lower than that of the device based on the sapphire substrate,and the diamond substrate can effectively reduce the channel temperature of the device.At the same time,when the applied bias voltage is larger,the effect of the diamond substrate on the crystal lattice temperature of the device is more obvious.For the structure of the diamond passivation layer,the lattice temperature distribution of the device under different thickness of the diamond passivation layer is simulated.The research results show that as the thickness of the passivation layer increases,the lattice temperature of the device is lower.Therefore,the application of diamond materials can enable devices to obtain better heat dissipation capabilities and promote the development of Ga N devices in the high-power field.Thirdly,in terms of DC and AC characteristics,the influence of diamond substrate on the DC and AC characteristics of the Ga N device and the back barrier structure device is simulated.The results show that the output drain current density of Ga N HEMT devices on diamond substrate and Ga N HEMT devices with back barrier structure are increased from0.61A/mm to 0.92A/mm,0.4A/mm to 0.58A/mm respectively.In terms of AC characteristics,the optimization of the diamond substrate structure on the device has increased the cut-off frequency and the highest oscillation frequency of the basic Ga N HEMT device by 23% and 54%,respectively.The cutoff frequency and the maximum oscillation frequency of Ga N HEMT devices with the back barrier structure are also increased from 28.6GHz to 32.9GHz and 81.7GHz to 101.6GHz,respectively.Therefore,it can be concluded that Ga N-on-diamond devices have broad prospects in RF and microwave applications.Finally,through the above simulation research,the channel temperature,DC and AC characteristics of the device under the self-heating effect,and the optimization results of the diamond material on the device structure are obtained.