Characteristics of Nano-Channel GaN-on-SiC HEMTs with Different T-Shaped Gate Structures at Ka-Band

Two different T-shaped gate structures of high electron mobility transistors (HEMTs) were fabricated by using aluminum gallium nitride/gallium nitride (AlGaN/GaN) grown on silicon carbide (SiC) substrates. The design of these structures was analyzed to evaluate their direct current (DC), small-signal, and large-signal characteristics, with the primary objective of application in high-power output amplifiers. The T-shaped gate with silicon nitride (SiN x ) exhibited larger parasitic capacitance, which hindered the effective enhancement of the cut-off frequency and maximum oscillation frequency. Conversely, the floating T-gate structure reduced parasitic capacitance, resulting in a significant increase in current density from 1169 to 1530 mA mm −1 . Additionally, the cut-off frequency (f T ) and maximum oscillation frequency (f max ) were improved to 87.2 GHz and 77.1 GHz, respectively while the power-added efficiency reached 35.1% at 3 GHz.