A Technique for Correction of Parasitic Capacitance on Microwave ftMeasurements of MESFET and HEMT Devices

The current gain cutoff frequency, ft, has become a critical figure-of-merit for evaluating performance of MESFET and HEMT devices. The ft is related to a capacitance parameter, Ctot, through the equation ft= Gm/(2πCtot). This capacitance, however, includes a parasitic component primarily due to contact pad and device geometry as well as a parasitic component due to Rd, Rs and Rds. This paper describes a technique which determines this parasitic capacitance for FET-type devices. Consistently accurate corrections can then be made to reported ft values. Ion implanted InGaAs MESFET’s with 0.25 µ gate lengths have achieved 120 GHz ft before correction and 151 GHz f, after correction.