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

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 −16.8μm. Time-domain thermoreflectance measurements reveal an effective GaN thermal conductivity (κ_eff-GaN) of 65.7±9.2Wm⁻¹K⁻¹ and an effective GaN/Si thermal-boundary conductance of 0.17±0.02GWm⁻²K⁻¹, compared with 110.8±7.0Wm⁻¹K⁻¹ and 0.012±0.006GWm⁻²K⁻¹ for the conventional multilayer buffer, respectively. The thermal resistance (R _th) 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 (P _out) 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.