Wideband and High Gain Cascode Amplifier using Metamorphic HEMT for Millimeter-wave Applications

In this paper, millimeter-wave coplanar high gain and wideband cascode amplifiers based on metamorphic high electron mobility transistor (MHEMT) were designed and fabricated. The fabricated 100 nm gate length MHEMT devices exhibit DC characteristics with a drain current density of 471 mA/mm and an extrinsic transconductance of 845 mS/mm. The current gain cutoff frequency (f_T) and the maximum oscillation frequency (f_max) are 193 GHz and 325 GHz, respectively. The matching circuit of cascode amplifier was designed for wideband characteristics using CPW (coplanar waveguide) transmission line. The one-stage amplifier showed a very wide 3 dB bandwidth of 37 GHz from 31.3 GHz to 68.3 GHz. The average S₂₁ gain was 9.7 dB in band, with the maximum gain of 11.3 dB at 40 GHz. The two-stage amplifier had a 3 dB bandwidth of 29.5 GHz from 32.5 GHz to 62.0 GHz. The two-stage amplifier showed an excellent gain characteristic with average S₂₁ gain of 20.4 dB in band and the maximum gain of 22.3 dB at 36.5 GHz. To our knowledge, these results have higher gain-per-stage with wider bandwidth than some other millimeter-wave amplifiers