547-GHz<tex>fₜ</tex>In<tex>₀.7</tex>Ga<tex>₀.3</tex>As–In<tex>₀.52</tex>Al<tex>₀.48</tex>As HEMTs With Reduced Source and Drain Resistance

We fabricated 30-nm gate pseudomorphic channel In/sub 0.7/Ga/sub 0.3/As-In/sub 0.52/Al/sub 0.48/As high electron mobility transistors (HEMTs) with reduced source and drain parasitic resistances. A multilayer cap structure consisting of Si highly doped n/sup +/-InGaAs and n/sup +/-InP layers was used to reduce these resistances while enabling reproducible 30-nm gate process. The HEMTs also had a laterally scaled gate-recess that effectively enhanced electron velocity, and an adequately long gate-channel distance of 12nm to suppress gate leakage current. The transconductance (g/sub m/) reached 1.5 S/mm, and the off-state breakdown voltage (BV/sub gd/) defined at a gate current of -1 mA/mm was -3.0 V. An extremely high current gain cutoff frequency (f/sub t/) of 547 GHz and a simultaneous maximum oscillation frequency (f/sub max/) of 400 GHz were achieved: the best performance yet reported for any transistor.