3-inch GaN-on-Diamond HEMTs With Device-First Transfer Technology

Based on a device-first transfer process, a 3-inch polycrystalline diamond substrate is bonded within 1.5 μm of the junction in GaN high electron mobility transistors (HEMTs) to enhance heat removal of the high-power RF devices. Highly preserved electrical performance is demonstrated by comparison exactly on the same HEMT device prior and after substrate transfer. The residual compressive strain relaxation of the whole GaN epilayer does not reduce the 2-D electron gas sheet density. The dc characteristics show weakened self-heating in the GaN-on-diamond HEMT with maximum current density increasing from 968 to 1005 mA/mm. The power density increases from 4.8 to 5.5 W/mm with the PAE slightly reducing from 50.9% to 50.5%. On-wafer infrared measurement is performed on a 1.25-mm GaN HEMT at power dissipation of 10 W/mm, and the peak juncture temperature of the device decreases from 241 °C to 191 °C after transferring to the diamond substrate.