Thermal and microwave performance enhancement of AlGaN/GaN HEMT using an ultra-thin buffer on Si substrate for handset applications

Abstract

Gallium-nitride (GaN) high electron mobility transistors (HEMTs) are promising for handset applications. However, the self-heating effect significantly degrades the RF performance and reliability, making thermal management a critical bottleneck for device development. This challenge is further exacerbated on GaN-on-Si platforms, where thick buffer stacks are typically required to mitigate lattice and thermal mismatch. In this work, we propose an AlGaN/GaN HEMT using an ultra-thin buffer on high-resistivity Si substrate with a total thickness below 400 nm. Compared to a conventional thick-buffer reference, this simplified buffer design reduces buffer thickness by more than 70% while maintaining a wafer bow of −16.8 μm. Time-domain thermoreflectance measurements reveal an effective GaN thermal conductivity (κeff-GaN) of 65.7 ± 9.2 W m−1 K−1 and an effective GaN/Si thermal-boundary conductance of 0.17 ± 0.02 GW m−2 K−1, compared with 110.8 ± 7.0 W m−1 K−1 and 0.012 ± 0.006 GW m−2 K−1 for the conventional multilayer buffer, respectively. The thermal resistance (Rth) improvement of the ultra-thin buffer is further confirmed by the DC-pulsed I–V intersection method. Thanks to the improved thermal performance, along with the advantages in knee-walkout and current collapse, this device achieves an improvement of 22.5% in power density (Pout) and 2.6% in power-added efficiency. These results demonstrate that the ultra-thin buffer design not only improves thermal management but also enhances RF performance, offering a promising route for next-generation mobile RF front-end modules.