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 recordfTcharacteristics and well-balancedfTandfmaxvalues. This result was obtained by improving short-channel effects through widening of the side-recess spacing (Lside) to 150 nm, as well as reducing parasitic source and drain resistances. To compensate for an increase inRsandRddue toLsidewidening, we optimized the ohmic contact process so as to decrease the specific ohmic contact resistance (Rc) to the InGaAs cap to 0.01 Ω·mm. A 30-nm InAs PHEMT withtins= 4 nm exhibits excellentgm,max of 1.9 S/mm,fTof 644 GHz, andfmaxof 681 GHz atVDS= 0.5 V simultaneously. To the knowledge of the authors, the obtainedfTin this work is the highest ever reported in any FET on any material system. This is also the first demonstration of simultaneousfTandfmaxhigher than 640 GHz in any transistor technology.