Mushroom shaped gates defined by e-beam lithography down to 80 nm gate lengths and fabrication of pseudomorphic HEMTs with a dry-etched gate recess.

Sub 0.1 Mym mushroom shaped gates (T-gates) have been realized with a three layer resist technique using e- beam exposure. The exposure was carried out on a Philips EPBG-3 system operating at 50 kV. The resist system and writing strategy was investigated. Test exposures on SiN capped GaAs wafers with ohmic contacts having the same topography as active devices were carried out. Using this T-gate lithography pseudomorphic AlGaAs/InGaAs/GaAs HEMTs were fabricated. These devices have transit frequencies of 120 GHz.