Effectiveness of the Thermal via in GaN HEMT Studied by a Co-Simulation Approach

Abstract

This article evaluates the effectiveness of polycrystalline diamond (PCD) thermal vias in mitigating self-heating issues in the two-dimensional electron gas (2DEG) layer of GaN high-electron mobility transistors (HEMTs). Thermal simulations conducted using Silvaco Victory Device identified and characterized hotspots within the 2DEG layer, which were further analyzed using Ansys Icepak. For GaN-on-sapphire HEMTs, the integration of PCD thermal vias resulted in a significant reduction of up to 23.5% in hotspot temperatures, with optimal performance observed when the thermal via protruded into the GaN layer. Even when the thermal via terminated at the GaN/sapphire interface, it still demonstrated substantial thermal management benefits. In contrast, for GaN-on-Si and GaN-on-SiC HEMTs, the effectiveness of PCD thermal vias was notably diminished. This is attributed to the higher thermal conductivities of Si (148 Wm⁻¹ K⁻¹) and SiC (490 Wm⁻¹ K⁻¹) compared to sapphire (23 Wm⁻¹ K⁻¹), limiting the potential for hotspot temperature reduction despite using high-quality PCD (1000 Wm⁻¹ K⁻¹). These results significantly extend existing thermal management studies by uniquely addressing the thermal challenges posed by GaN-on-sapphire substrates through the introduction of PCD thermal vias, a substrate-material combination that has not been comprehensively explored in prior research. The findings highlight that while PCD thermal vias offer substantial improvements in thermal management for GaN-on-sapphire HEMTs, their impact is less pronounced for GaN-on-Si and GaN-on-SiC HEMTs. A preliminary cost–benefit analysis suggests that while PCD thermal vias have a higher initial cost, their long-term reliability and reduction in thermal-induced failures make them a cost-effective solution. Future work will focus on experimental validation and exploring alternative thermal management strategies such as microchannel cooling and advanced thermal interface materials.