30-nm InAs PHEMTs With fT=644 GHz and fmax=681 GHz

We present 30-nm InAs pseudomorphic HEMTs (PHEMTs) on an InP substrate with record f(T) characteristics and well-balanced f(T) and f(max) values. This result was obtained by improving short-channel effects through widening of the side-recess spacing (L-side) to 150 nm, as well as reducing parasitic source and drain resistances. To compensate for an increase in R-s and R-d due to L-side widening, we optimized the ohmic contact process so as to decrease the specific ohmic contact resistance (R-c) to the InGaAs cap to 0.01 Omega . mm. A 30-nm InAs PHEMT with t(ins) = 4 nm exhibits excellent g(m,max) of 1.9 S/mm, f(T) of 644 GHz, and fmax of 681 GHz at V-DS = 0.5 V simultaneously. To the knowledge of the authors, the obtained f(T) in this work is the highest ever reported in any FET on any material system. This is also the first demonstration of simultaneous f(T) and f(max) higher than 640 GHz in any transistor technology.