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AlGaN/GaN high-electron mobility transistors on (001)-oriented silicon substrates with a 0.1-mum gamma-shaped gate length are fabricated. The gate technology is based on a silicon nitride (SiN) thin film and uses a digital etching technique to perform the recess through the SiN mask. An output current density of 420 mA/mm and an extrinsic transconductance gm of 228 mS/mm are measured on 300-mum gate-periphery devices. An extrinsic cutoff frequency ft of 28 GHz and a maximum oscillation frequency fmax of 46 GHz are deduced from S-parameter measurements. At 2.15 GHz, an output power density of 1 W/mm that is associated to a power-added efficiency of 17% and a linear gain of 24 dB are achieved at VDS = 30 V and VGS = -1.2 V.