Novel Gate Fabrication Process Enhancing High-Frequency Operation in AlGaN/GaN HEMTs for Ka-Band Applications

In this study, AlGaN/GaN high-electron-mobility-transistor (HEMTs) with a small gate length were fabricated using a stepper. Additionally, a novel gate fabrication process was conducted to shrink the gate head, thus reducing the parasitic capacitance of the device to achieve high-power amplifier performance. The device performance in the research demonstrated a steady-state current density (Idss) of 975 mA/mm and a maximum transconductance (gm) of 369 mS/mm at a 20 V bias. Moreover, the cut-off frequency (fT) reached 50.6 GHz, and the maximum oscillation frequency (fmax) achieved 161 GHz as measured by S-parameter measurement. In the load-pull system, the frequency operation is under 28 GHz. For the $2\times 50~\mu $ m device at a drain bias of 20 V, it exhibits a maximum output power density (Pout) of 2.83 W/mm with a maximum 24.97% power-added efficiency (PAE). Additionally, for the $8\times 50~\mu $ m device at a drain bias of 32V, it achieves a $\mathrm { P_{out}}$ of 1.27 W (3.18 W/mm). This work demonstrates that the novel gate fabrication process of shrinking gate head by using $\mathrm { SiN_{x}}$ shield achieves high-frequency and high-output power characteristics for Ka-band application.