Stepper-based Lg = 0.5 μm In0.52Al0.48As/In0.7Ga0.3As PHEMTs on a 3-inch InP substrate with record product of fT and Lg

We have fabricated and characterized Lg = 0.5 μm In0.52Al0.48As/In0.7Ga0.3As pseudomorphic high-electron-mobility-transistors (PHEMTs) on a 3-inch InP substrate. Stepper-based photo-lithography was used in all the process steps for device fabrication, aiming to miniaturize key device geometries, such as gate-to-source and gate-to-drain spacing. The fabricated device with Lg = 0.5 μm exhibits an excellent maximum transconductance (gm_max) of 1.9 S/mm at VDS = 1.5 V and an ON-resistance (RON) of below 0.4 Ω-mm. A high value of gm in our device leads to a fantastic combination of current-gain cut-off frequency (fT) of 120 GHz and maximum oscillation frequency (fmax) of 366 GHz at VDS = 0.8 V. These remarkable characteristics stem from the compact geometry design of the In0.52Al0.48As/In0.7Ga0.3As PHEMTs with LGS = LGD = 0.4 μm, coupled with an optimized gate recess process that yields tight control of side-recess spacing (Lside). More importantly, the product of fT and Lg in this work yields 60 GHz-μm which is the highest in any field-effect-transistor (FET) technology on any material system.