SNAP structures with Nb-AlO/sub x/-Nb junctions for MM-wave receivers

High-quality small-area Nb-AlO/sub x/-Nb junctions have been fabricated by the selective niobium anodization process (SNAP). The influence of the preparation conditions on the junction properties were investigated. Numerical calculations based on I-V (current-voltage) characteristics measured by a data acquisition system were used to simulate the mixer performance. It has been shown that the knee-shaped structure on the I-V curve of refractory material junctions significantly affects the signal properties of the mixer. The signal and noise properties for different types of integrated SIS (superconductor-insulator-superconductor) mixing elements have been investigated experimentally in the frequency range of 37-53 GHz; the mixer conversion loss was as low as 4 dB at 45 GHz. The mixing elements consist of an odd number of SIS junctions connected in series for RF and in parallel for DC biasing. The DC bias wiring and IF (intermediate frequency) filters of these structures were designed to provide tuning out of junction capacitance and thin-film-electrode inductance.< >