Low-Temperature Bonded GaN-on-Diamond HEMTs With 11 W/mm Output Power at 10 GHz

We report recent progress on GaN-on-diamond high electron mobility transistors (HEMTs) fabricated using a low-temperature device-transfer process. The devices were first fabricated on a GaN-on-SiC epitaxial wafer and were subsequently separated from the SiC and bonded onto a high-thermal-conductivity diamond substrate at low temperature. The resulting $12 \times 50~\mu \text{m}$ GaN-on-diamond HEMTs demonstrated the state-of-the-art electrical characteristics, including a maximum drain current density of 1.2 A/mm and a peak transconductance of 390 mS/mm. CW load-pull measurements at 10 GHz yielded an RF output power density of 11 W/mm with 51% associated power-added efficiency. Device measurements show that the GaN-on-diamond devices maintained slightly lower channel temperatures than their GaN-on-SiC counterparts while delivering 3.6 times higher RF power within the same active area. These results demonstrate that the GaN device-transfer process is capable of preserving intrinsic GaN-on-SiC transistor electrical performance while taking advantage of the excellent thermal properties of diamond substrates.