Stepper-based L_g = 0.5 μm In_0.52Al_0.48As/In_0.7Ga_0.3As PHEMTs on a 3-inch InP substrate with record product of f_T and L_g

We have fabricated and characterized L_g = 0.5 μm In_0.52Al_0.48As/In_0.7Ga_0.3As 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 L_g = 0.5 μm exhibits an excellent maximum transconductance (g_{m_max}) of 1.9 S/mm at V_DS = 1.5 V and an ON-resistance (R_ON) of below 0.4 Ω-mm. A high value of g_m in our device leads to a fantastic combination of current-gain cut-off frequency (f_T) of 120 GHz and maximum oscillation frequency (f_max) of 366 GHz at V_DS = 0.8 V. These remarkable characteristics stem from the compact geometry design of the In_0.52Al_0.48As/In_0.7Ga_0.3As PHEMTs with L_GS = L_GD = 0.4 μm, coupled with an optimized gate recess process that yields tight control of side-recess spacing (L_side). More importantly, the product of f_T and L_g in this work yields 60 GHz-μm which is the highest in any field-effect-transistor (FET) technology on any material system.