THZ SIS MIXERS WITH NORMAL-METAL AL TUNING CIRCUITS

Nb-based superconductor-insulator-superconductor (SIS) mixers with Nb tuning circuits have demonstrated good results up to the Nb gap freque ncy. Above the gap frequency the performance is expected to degrade qu ickly because RF loss in Nb becomes significant. In this paper we pres ent the results of an effort to extend Nb-based SIS mixers to THz freq uencies by employing lower-loss normal-metal Al wiring and tuning stru ctures. The SIS mixer has two Nb/Al-oxide/Nb junctions connected by an Al microstrip inductor. The direct detection response of the device w as measured by a Fourier transform spectrometer. A double-side-band re ceiver noise temperature of 840 K was obtained at 1042 GHz when the de vice was operated at 2.5 K.