Electron-beam fabrication of GaAs low-noise MESFET's using a new trilayer resist technique

A LO/HI/LO resist system has been developed to produce sub-half-micrometer T-shaped cross section metal lines using e-beam lithography. The system provides T-shaped resist cavities with undercut profiles. T-shaped metal lines as narrow as 0.15 µm have been produced. GaAs MESFET's with 0.25-µm T-shaped Ti/Pt/Au gates have also been fabricated on MBE wafers using this resist technique. Measured end-to, end 0.25-µm gate resistance was 80 ω/mm, dc transconductance g
m
as high as 300 mS/mm was observed. At 18 GHz, a noise figure as low as 1.4 dB with an associated gain of 7.9 dB has also been measured. This is the lowest noise figure ever reported for conventional GaAs MESFET's at this frequency. These superior results are mainly attributed to the high-quality MBE material and the advanced T-gate fabrication technique employing e-beam lithography.