High-Performance AlN/GaN MISHEMTs on Si With In-Situ SiN Enhanced Ohmic Contacts for Mobile mm-Wave Front-End Applications

In this letter, we demonstrated an AlN/GaN metal-insulator-semiconductor high electron mobility transistor (MISHEMT) on a Si substrate with in-situ SiN as gate dielectric with excellent mm-wave performance at low supply voltages. Benefited from the thin in-situ SiN, a low ohmic contact resistance ${R} _{C}$ of $0.2 \sf {\Omega } \cdot \text {mm}$ was obtained. The device with a T-shape gate featuring 80 nm gate foot length ( ${L} _{G}$ ) and 620 nm total gate metal thickness shows a maximum drain current ( ${I} _{D}$ ) of 1.95 A/mm, a peak transconductance ( ${g} _{\text {mmax}}$ ) of 500 mS/mm, and a cut-off frequency/a maximum oscillation frequency ( ${f} _{T}/{f} _{\text {max}}$ ) of 165/255 GHz. To the best of our knowledge, the ${f} _{T}$ and ${f} _{\text {max}}$ are the highest among the reported AlN/GaN transistors on Si substrates. 28 GHz load-pull measurements at low drain voltages of 3.5/5/6 V show maximum output power densities ( ${P} _{\text {out},\text {max}}$ ) of 0.36/0.73/1.04 W/mm and peak power-added efficiencies (PAE) of 40%/42%/43%, respectively. These excellent results show that AlN/GaN HEMTs on Si have a great potential for power amplifiers (PAs) in mobile mm-wave front-end applications.