Analysis and Development of Submillimeter-Wave Stacked-FET Power Amplifier MMICs in 35-nm mHEMT Technology

This paper reports on the first stacked field-effect transistor (stacked-FET) submillimeter-wave monolithic integrated circuit (S-MMIC) power amplifier cell operating at 0.3 THz and the first stacked-FET medium power amplifier (MPA) at 240 GHz. Both circuits are fabricated using a 35-nm InGaAs-onGaAs metamorphic high electron mobility transistor (mHEMT) technology with grounded coplanar waveguide lines. In both cases, compactness and performance are enhanced thanks to the use of an in-house process, based on three-metallization layers, instead of the usual two-layer process. The single-stacked cell exhibits an ultrawide small-signal 3-dB relative bandwidth (RBW) of 47.3%, with output power levels higher than 4.3 dBm from 280 to 308 GHz (9.5%). The MPA MMIC combining four triple-stacked mHEMT cells in parallel achieves a small-signal 3-dB RBW of 24.2%, 10.8 dBm of output power, and a power-added efficiency of 5.02%. These values outperform the state-of-the-art results of MPAs published within a comparable technology.