Small-signal analysis of high maximum frequency of oscillation 0.1-μm off-set gamma-shaped gate InGaAs/InAlAs/GaAs metamorphic high-electron-mobility transistors

We examined the effects of gate recess process conditions on the electrical characteristics of 0.1-mum-gate-length metamorphic high-electron-mobility transistors (MHEMTs) by the comparative analysis of small-signal parameters. When the wide-gate-recess method is adopted, significant reductions in gate-to-drain conductance and gate-to-drain capacitance were obtained compared with those obtained by the of narrow-gate-recess method. These differences in small-signal parameters are due to the removal of the entire n+ cap layer and corresponding dissimilarity in gate structure when the wide-gate-recess method is used. The wide-gate-recess method produced similar to1/2 drain-source saturation Current and extrinsic transconductance compared with the narrow-gate-recess method. In contract to the DC performances, a markedly enhanced S-21 gain of 3.5 dB and an f(max) of 447 GHz were obtained from the MHEMTs processed by the wide-gate-recess method. This high f(max) is responsible for the proper selection of the gate recess method for what and is one of the best data thus far reported for 0.1-mum-gate-length MHEMTs.