Fabrication Technology For Monolithic GaAs VFETs*

Monolithic gallium arsenide vertical FETs have been fabricated with a suspended gate, 0.7 /spl mu/m long, and a drain on top of a vertical pillar 4 /spl mu/m high and 0.3 /spl mu/m thick with a doping concentration of 2 x 10 /sup 17/ cm/sup -3/. VFET channels were combined with air bridges attached to bond pads situated on a semi-insulating substrate. A computer-generated VFET equivalent circuit based on s-parameters indicated a source-drain feedback capacitance of 0.008 pF at 240 /spl mu/m, which is an order of magnitude lower than has been observed in planar MESFETs, with an associated VFET output impedance of 1230 ohm at 240 /spl mu/m. Under RF test, VFETs yielded 11.3 dB maximum stable gain at 18 GHz with an F/sub t/ of 13 GHz and an extrapolated F /sub max/of 67 GHz.