Fabrication and characterization of a 600-720 GHz resonant distributed SIS junction for fixed-tuned waveguide receiver

The non-linear quasiparticle tunnel current flowing in a distributed superconductor-insulator-superconductor (SIS) transmission line resonator has been exploited in a low-noise heterodyne fixed-tuned waveguide receiver in the 600-720 GHz band. The mixer employs two 1.4 μm wide half-wave or full-wave distributed SIS long junctions that are connected in series. These devices have been fabricated with optical lithography. Noise temperatures of 160-240 K have been measured at around 600 GHz. However, the achieved RF bandwidth is only about 5 % and the center frequency of the resonance is also shifted towards lower end of the target frequencies.