Low Thermal Resistance X-band AlGaN/GaN/AlN-on-SiC RF Power HEMTs with Record P out = 41 W/mm and f T ×BV = 31 THz•V

The maximum output power density (Pout) in GaN RF power devices at X-band has remained around 30-33 W/mm for nearly two decades, mainly constrained by the device’s high thermal resistance (RT). This work demonstrates a new record Pout of 41 W/mm at 10 GHz in an AlGaN/GaN/ AlN-on-SiC RF power HEMT. This breakthrough is enabled by deploying an ultra-wide-bandgap (UWBG) AlN buffer and reducing the combined channel and buffer thickness to just 400 nm. By optimizing the V:III ratio and growth rate during AlN epitaxy, we suppress conventional island-like nucleation, achieving rapid film coalescence, low dislocation density, and reduced thickness. Thermoreflectance (TR) measurements reveal a low device RT of 2.1 K•mm/W, which is less than 1/3 of conventional device with μm-thick GaN buffer and island-nucleated AlN layer. Meanwhile, the use of UWBG AlN buffer and thin GaN channel boost device breakdown voltage (BV) and carrier confinement. As a result, the fabricated RF HEMTs achieve a Pout of 41 W/mm at 10 GHz with an associated power-added efficiency (PAE) of 51% and a record high fT×BV figure-of-merit (FOM) of 31 THz•V. These results mark a new milestone for X-band GaN RF performance and suggest the promise of the AlGaN/GaN/AlN material platform for high-power and high-efficiency RF applications.