InAs/AlSb HFETs with f/sub τ/ and f/sub max/ above 150 GHz for low-power MMICs

Abstract
Very low-power InAs/AlSb HFETs with excellent RF performance are reported. These metamorphic HFETs on GaAs substrates combine high microwave g/sub m/ of at least 1.1 S/mm with low parasitic resistances to offer simultaneous measured f/sub /spl tau// and f/sub max/ values of 160 GHz for both figures of merit. This performance is obtained at a drain bias voltage of only 0.35 V for an HFET with a 0.25-/spl mu/m gate length. The high current gain (f/sub /spl tau//) is attributable to the improved charge control due to scaling of the barrier thickness to 180 /spl Aring/. The maximum power gain (f/sub max/) depends on both g/sub m/ and the HFET output conductance, which is fundamentally limited by the low breakdown voltage gap of the InAs channel (E/sub g/ = 0.36 eV).