Electron-beam fabrication of submicrometer gates for a GaAs MESFET logic

A direct electron-beam lithography is applied to the fabrication of a submicrometer gate for an enhancement-mode GaAs MESFET logic. Exposure doses to produce submicrometer stripes in the positive PMMA resist on a GaAs wafer are investigated for different beam scans of a 0.1-µm-diameter spot. The resist adhesion against a GaAs etchant under the gate recessing is tested to make a fine control of an epitaxial layer thickness with good results. A propagation delay of 64 ps with an associated power consumption of 0.4 mW is obtained with a 0.5 × 20-µm-gate GaAs MESFET, which demonstrates the fastest speed among the enhancement-mode logics.