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 receiver operating in frequency range of 790 - 950 GHz. The electromagnetic simulations and measurement results are presented. The junctions have high gap voltage of 3.2 mV and high current density of about 30 kA/cm2 providing wide receiver band confirmed by FTS and noise temperature measurements. The corrected receiver noise temperature is varying from 250 K at low frequencies to 500 K at the high end of the band. We observed the junction heating caused by the Andreev reflection and studied the influence of it on the SIS junction characteristics