T-gate, Γ-gate, and air-bridge fabrication for monolithic microwave integrated circuits by mixed ion-beam, high-voltage electron-beam, and optical lithography

Abstract

Mixed lithography combining a 140 keV Be++ focused ion beam and a 60 keV electron beam has been applied to fabricate T-section and Γ-section structures for gate electrodes in GaAs metal–semiconductor field effect transistors for monolithic microwave integrated circuits. The gates are formed by lift-off metallization, following successive electron and ion beam exposures of a single resist layer and a single stage of development. Gates with lengths down to 170 nm have been fabricated. Gate resistance parameters given by reverse modeling with data from microwave measurements are consistent with direct measurements on test structures. Forward modeling shows the benefits of the Γ-gate structure for well-balanced device design. High-voltage lithography has been applied also to a novel procedure for generating air-bridges for monolithic microwave integrated circuits.