Broadband and High-Gain 400-GHz InGaAs mHEMT Medium-Power Amplifier S-MMIC

In this paper, the design and performance of a medium-power amplifier (MPA) submillimeter-wave monolithic integrated circuit (S-MMIC) is presented. The MPA demonstrates a flat small-signal gain of approximately 20 dB, measured over a frequency span from 290 to 410 GHz, and a respective 3-dB bandwidth from 280 to 430 GHz. The measured output power ranges from 1.5 to 3.3 dBm, over a large-signal drive from 355 to 395 GHz — limited by the measurement set-up — at a peak input power of -13 dBm. The power-added efficiency varies from 1 to 1.5%. The amplifier utilizes four cascode stages, each realized via two 8-µm finger-width InAlAs/InGaAs metamorphic high-electron-mobility transistors in parallel for the common-source part and respectively two devices for the common-gate part of the cascode. Each transistor consists of two gate fingers. The total gate width (TGW) of the output stage is 32 µm. The total chip size, without RF- and DC-pads, is 200 × 800 µm². The respective matching networks are implemented via miniaturized thin-film microstrip lines in tandem with metal-insulator-metal capacitors. A maximum output power per TGW of 66.2mW/mm is achieved with a transducer gain of 16 dB, representing a state-of-the-art performance for MMIC-based amplifiers between 355 and 395 GHz.