Determination of equivalent network parameters of short-gate-length modulation-doped field-effect transistors

The small-signal intrinsic Y-parameters of millimeter-wave MODFETs are examined. These parameters were extracted from S-parameter data after removal of parasitics through a method of successive Z-to-Y and Y-to-Z transformations. This approach has yielded accurate values of all the parameters of an equivalent network model for the MODFETs tested, with the exception of some uncertainties in the determination of the intrinsic Y₂₁ phase-delay time constant. It is shown that accurate determination of the intrinsic carrier transit time (τ) is possible through the unity extrapolation of the intrinsic current gain ||h₂₁||, and this yields the related carrier average velocity (ν_av). Results obtained from three 0.25-μm-gate-length MODFETs, based on different heterostructures, and results obtained from a 0.15-μm-gate-length lattice-matched structure are presented