GaAs permeable base transistors fabricated with 240-mm-periodicity tungsten base gratings

The microwave performance of the first GaAs permeable base transistors (PBTs) fabricated with 240-nm-periodicity tungsten base gratings is described. These PBTs have demonstrated a maximum stable gain of 20.1 dB at 26.5 GHz, which is believed to be the largest small-signal power gain for any microwave transistor at this frequency. Extrapolation of this maximum stable gain using a 6 dB/octave rolloff yields a maximum frequency of oscillation (f_max) of 265 GHz. The breakdown voltage is approximately 20 V, which should make these devices excellent microwave power sources. Extrapolation microwave measurements on these devices from 3 GHz using a 6 dB/octave rolloff yields a unity-current-gain frequency (f_T) of 38 GHz, which matches the best prior result for a PBT. These 240-nm-periodicity PBTs that have given the best f_T have been depletion-mode devices, suggesting that 240-nm-periodicity depletion-mode PBTs should have f_T values above 38 GHz