Applied Physics Letters

Sub-μm linewidth input coils for low Tc integrated thin-film dc superconducting quantum interference devices

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We have, for the first time, demonstrated integrated dc superconducting quantum interference devices (SQUIDs) with input coils of linewidth down to 0.5 μm. The SQUID inductance L consists of a single octagonal washer or two or four such washers configured in parallel. The input coil of inductance L i, which couples to L with a mutual inductance of Mi, consists of fine-line octagonal spiral(s) fabricated in close proximity to the washer(s). For a two-washer SQUID with twin 80-turn, 0.5 μm spirals, L i=2.5 μH, Mi=12.7 nH, L=109 pH, and the coupling constant k2=0.85. This entire device occupies an area of less than 0.2 mm2.