High-Gap Nb-AlN-NbN SIS Junctions for Frequency Band 790–950 GHz

We have designed, fabricated, and tested superconductor-insulator-superconductor (SIS) mixers based on Nb/AlN/NbN twin tunnel junctions for waveguide receivers operating in a frequency range of 790-950 GHz. Electromagnetic simulations and measurement results of the mixer performance are presented. The junctions have a high gap voltage of 3.15 mV and a high current density of about 30 kA/cm
²
, providing a wide receiver band, which was confirmed by Fourier transform spectrometer (FTS) and noise temperature measurements. The corrected receiver noise temperature varies from 240 K at low frequencies to 550 K at the high end of the band. The influence of the SIS junction heating on its characteristics has been studied and compared to another similar high current density technologies. The heating does not have a critical impact on the mixer performance.