Fabrication of Three-Dimensional Nanobridge Junction Arrays for SQIFs

Superconducting quantum interference filters (SQIFs) are arrays of superconducting quantum interference devices with various loop areas. In contrast to the SQIFs of conventional Josephson junctions, we propose a way for creating highly integrated SQIFs using 50 × 50 nm
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three-dimensional (3-D) nanobridge junctions. Here, we report the fabrication of arrays composed of a hundred 3-D nanobridge junctions. Current-voltage curves of single, 10, and 100 junctions in series were measured and analyzed. Measurements of single junctions revealed an average critical current of 104 μA with a standard deviation of 24 μA. Furthermore, the 10 junctions in series had randomly distributed switching events. The normal resistance as the function of the number of junctions in series showed a good linearity, indicating a good uniformity of the junctions. Therefore, we propose that the local differences in the thermal-dissipation conditions and random trapped vortices were likely responsible for the random switching of the nanobridge junctions in series.