This study reports AlGaN/GaN high-electron-mobility transistors (HEMTs) fabricated by the Stepper Lithography on a 4-inch wafer for Ka-Band applications. Small gate length (L G ) of 100 nm was achieved through a 2-Step Photolithography Process and the gate region of the AlGaN/GaN HEMT was defined by using two lithography steps to form gamma-shaped gates. The 4-inch AlGaN/GaN HEMT wafer demonstrated high electrical performance uniformity with respect to the maximum drain-source current density (I DSS ), the peak extrinsic output transconductance (G m ), and the threshold voltage (V th ). At V DS = 20 V, the AlGaN/GaN HEMT exhibits an I DSS of 1004.2 mA/mm, a Gm value of 363.6 mS/mm, a maximum output power density (P OUT (MAX) ) of over 10 W/mm, and a power gain of 8.8 dB with a maximum 51.1% Power-added efficiency (PAE) at 28 GHz in Continuous Wave (CW) mode. The results show the potential of AlGaN/GaN HEMT fabrication with high yield and outstanding RF performance using Stepper Lithography for 5G applications.INDEX TERMS 5G, high uniformity, output power, stepper lithography, small gate length.

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