Revisiting the effectiveness of diamond heat spreaders on multi-finger gate GaN HEMT using chip-to-package-level thermal simulation

The study of chip-level and package-level heat transfer in a GaN high electron mobility transistor (HEMT) is often disconnected due to limited resources and tools. In this work, device simulation from Silvaco Victory Device is carried forward to the chip-to-package-level simulation using Icepak to provide a complete picture of the proposed thermal management strategies using polycrystalline diamond (PCD) heat spreaders. The max junction temperature, T_j = 105.8 °C and the relative magnitude of max temperature on the GaN surface, ΔT_j = 18 % are recorded for the original Si-GaN-Si₃N₄ chip inside TO-220 at 6.0 Wmm⁻¹. Replacing the Si₃N₄ with PCD (thermal conductivity of 500 Wm⁻¹ K⁻¹) results in T_j = 98.2 °C and ΔT_j = 8 %, while replacing the Si results in T_j = 97.0 °C and ΔT_j = 11 %. The top layer PCD spreads the heat from hotspot regions to the surrounding epoxy, while the bottom layer PCD improves the heat path from the hotspots to the base plate. Therefore, the reduction in T_j by the bottom layer PCD is more important than the reduction in ΔT_j by the top layer PCD. Implementing both the top and bottom layers of PCD results in the best offers of T_j = 92.9 °C and ΔT_j = 6 %. The performance of PCD as heat spreaders in multi-finger gate GaN HEMT suggested by these chip-to-package-level simulations are more reliable than device simulation alone since they cover the complete heat path from generation, conduction within the package, and convection to the ambient air.