British Fabricate 120 nm GaAs Devices with
  f_T of 200 GHz

-- Semiconductor International, 11/1/1999

Researchers at the Nanoelectronics Laboratory of the University of Glasgow (Glasgow, Scotland) have constructed 0.12 µm (120 nm) devices with f_T values of 200 GHz. The group claims these devices, which are based on gallium arsenide, will be far easier to manufacture than those based on pure indium phosphide.

The Glasgow work employs indium phosphide-type layers grown on a gal lium arsenide substrate. In this way they obtain the advantage of the high electron velocity, mobility and low noise of indium phosphide without the difficulty of handling small wafers of this very brittle material. Transmission gates in the devices had a 120 nm channel length. The device characteristics were measured from 40 MHz to 110 GHz where the current gain roll-off was 20 dB per decade. The extrapolated transition frequency was 200 GHz, whereas pure gallium arsenide would have given a value of some 120-130 GHz.

The maximum stable gain was 4.7 dB at 94 GHz, but devices with a 25 µm channel width showed an improved gain of 9.0 dB at the same frequency, owing to the smaller gate resistance. Such devices could be used in broadband communication links in the frequency region of 60 GHz where there is a strong molecular resonance in the atmospheric oxygen. Thus radio signals are strongly attenuated in this band, so the same frequencies could be used in nearby locations without interference. Other applications anticipated are collision avoidance radar at 77 GHz and weather radar at more than 100 GHz.