High-gain submillimeter-wave mHEMT amplifier MMICs

A compact H-band (220–325 GHz) submillimeter-wave monolithic integrated circuit (S-MMIC) amplifier has been developed, based on a grounded coplanar waveguide (GCPW) technology utilizing 50 nm and 35 nm metamorphic high electron mobility transistors (mHEMTs). By applying the 35 nm gate-length process, a four-stage cascode amplifier circuit achieved a small-signal gain of 26 dB at 320 GHz and more than 20 dB in the bandwidth from 220 to 320 GHz. Based on the 50 nm mHEMT technology, the same amplifier design demonstrated a linear gain of 19.5 dB at 320 GHz and more than 15 dB between 240 and 320 GHz. Coplanar topology in combination with cascode transistors resulted in a very compact die size of only 0.6 mm2. For low-loss packaging of the circuit, a set of waveguide-to-microstrip transitions has been realized on 50 µm thick GaAs and quartz substrates demonstrating an insertion loss S21 of less than 2 dB and 1.25 dB at 320 GHz, respectively. Finally, successful mounting and packaging of the amplifier chip into an H-band waveguide module was accomplished with only minor reduction in performance.