Temperature Characteristic Research Of GaN HEMT Device

As the third generation semiconductor material,GaN takes advantages from the wide bandgap,high thermal conductivity and high electron mobility which are suitable for high-temperature power applications.In addition,AlGaN/GaN HEMTs have been investigated intensively,resulting from the promising potential for high-power,high-frequency and high-temperature applications.However,the thermal reliability issues are still unresolved.When the device temperature increase,the performance of AlGaN/GaN HEMTs?such as drain current,gain,output power and device life?get degraded,which may lead to system failure in severe cases.To solve this problem,many way of dissipating heat are employed to improve the performance.Benefiting from a high thermal conductivity,high resistivity,and high hardness,diamond material often provides an effective solution for thermal management in AlGaN/GaN HEMTs.In this dissertation,the study on the thermal performance of AlGaN/GaN HEMTs is conducted in details.Through this study,we hope to improve the operating temperature and the characteristics of high power GaN-based HEMTs.Three GaN-based HEMT structures are investigated:AlGaN/GaN HEMTs,AlGaN/GaN/AlGaN/GaN HEMTs,and AlGaN/GaN/AlGaN HEMTs.Firstly,high-temperature characteristics of GaN-based HEMTs including DC and C-V performances are studied in details from room temperature to 500K.The data show that the drain saturation current of GaN-based HEMTs get decreased when temperature increased from room temperature to 500K.The drain saturation current of AlGaN/GaN HEMTs declined to 0.70A/mm from 0.94A/mm which features a 25.5%drop,the drain saturation current of AlGaN/GaN/AlGaN/GaN HEMTs declined to 0.68A/mm from 0.86A/mm which features a 20.9%drop and the drain saturation current of AlGaN/GaN/AlGaN HEMTs declined to 0.61A/mm from 0.76A/mm which features a 19.7%drop.The results indicate that the performance of GaN-based HEMTs is degraded with the increasing temperature.Secondly,the influence of diamond layer on device's temperature are studied.In order to evaluate the influence of diamond layer on device operating temperature,the temperature distribution along the channel in AlGaN/GaN HEMT were simulated.When the drain bias V_DSS are set as 20V,the peak temperature is reduced from 523K to 488K with the aid of the diamond layer and the temperature shift reaches up to 35K.The results show that the diamond layer can moderate the peak temperature,indicating that the diamond layer has a significant effect on temperature moderation.The temperature distribution under different drain bias was simulated,the results show that the heat dissipation effect of the diamond layer is much higher under the high drain bias,indicating that introducing the diamond layer is a very effective technique for HEMTs in high-power applications.In addition,the peak temperature under different thickness diamond layer was considered.When the drain bias is as low as 5V,the peak temperature shift is negligible,and when the drain bias increases to 30V,the temperature shift reaches up to 52K.The results show that with the increasing thickness of the diamond layer,the peak temperature decreases.When the thickness is greater than 8?m,the effect of the heat spreader is getting weak.Finally,the influence of diamond layer on device performances under DC and AC are studied.The saturation drain currents of conventional AlGaN/GaN HEMT devices,AlGaN/GaN/AlGaN/GaN HEMT devices,and AlGaN/GaN/AlGaN HEMT devices are increased by 18.1%,18.6%,and 19.7%,respectively.The results show that the drain saturation current is increased,the gate leakage current is decreased,the transconductance is increased and the frequency is increased with the aid of diamond layer.These results indicate that the diamond layer plays a significant role in thermal performance enhancement of GaN-based HEMTs.