RF characteristics of 150‐nm AlGaN/GaN high electron mobility transistors fabricated using i‐line stepper lithography

Abstract This article reports radio frequency characteristics of 150‐nm gate aluminum gallium nitride (AlGaN)/gallium nitride (GaN) high electron mobility transistors (HEMTs) fabricated using i‐line stepper lithography and a thermal reflow technique. The authors have developed two different gate structures that were a field‐plated gate using the lift‐off process and a Y‐shaped gate using the ion‐milling process. Fabricated HEMTs using these different gate structures exhibited nearly equivalent DC characteristics. The field‐plated gate device showed a unity current gain cutoff frequency (fT) of 35 GHz and a maximum oscillation frequency (fmax) of 106 GHz, while the Y‐shaped gate device showed fT of 36 GHz and fmax of 115 GHz. The equivalent circuit analysis indicated a decrease in the gate‐drain capacitance and the drain conductance is responsible for the improved fmax in the Y‐shaped gate device