Characterization of the IF Bandwidth of an All-NbN Superconductor-Insulator-Superconductor Mixer

Large intermediate-frequency (IF) bandwidth is of particular interest for heterodyne mixers, especially for those at THz frequencies. NbN superconductor-insulator-superconductor (SIS) junctions, with a gap frequency twice that of Nb, can be applied to mixers beyond 1 THz. The IF bandwidth of NbN SIS mixers, however, is yet to be fully understood. In this paper, we investigate the IF bandwidth of a 0.5 THz all-NbN SIS mixer. First, its IF bandwidth is numerically simulated in terms of the mixer conversion efficiency and time constant. Second, the mixer noise performance is experimentally characterized in the IF band of 0.5 ~ 12 GHz. Detailed theoretical simulation and experimental results will be presented.