Microwave performance of InP-based HEMTs for low voltage application fabricated by optical lithography

The low voltage high frequency performance of InP-based HEMTs is examined. All the devices are fabricated by simple optical lithography resulting in gate length ⩾0.5 μm. The RF results of the structures discussed show that uncompromised small RF performance of InP based FETs can be obtained in the low drain bias range below 2 V. Even for moderate gate lengths of 0.5 μm, operation down to Vd=1 V seems feasible. The highest cut-off frequencies extrapolated are f_t=60 GHz and f_max=160 GHz at Vd=1.6 V. This represents an ft*Lg-product of 39 GHzμm and a f_max/f_t of 2.6 at the identical gate and drain bias point. This indicates that high power gain is possible at high overshoot velocity. Three different material structures have been analysed. The drift-region analysis indicate that an optimum design is a structure with high open channel current density realised with high carrier concentration