Enhancement of Hot Spot Cooling by Capped Diamond Layer Deposition for Multifinger AlGaN/GaN HEMTs

The impact of a capped diamond layer for enhanced cooling of multifinger AlGaN/GaN high-electron-mobility transistors (HEMTs) has been investigated under the steady-state operating condition. By depositing a capped diamond thin film onto the HEMTs, the temperature distribution around the hot spots tends to be more uniform and the junction temperature can be suppressed significantly. The capped diamond serves as a highly effective heat spreader, and its thermal spreading ability depends on the structural design patterns and working conditions. Some key parameters affecting the thermal performance of the capped diamond have been examined, including the heat dissipation power density, gate pitch distance, embedding depth of the heat source, thermal boundary resistance, substrate material, as well as the cap thickness. For the 12-finger model with 20-μm gate pitch distance and gate power density of 6 W/mm, a 20-μm layer of capped diamond could reduce the junction temperature by 12.1% for GaN-on-diamond HEMTs and by 25.3% for GaN-on-SiC HEMTs. Even with a 1-μm capped diamond layer, the reduction would be 7.6% and 9.9%, respectively. The temperature reduction for GaN-on-Si is more significant.