High-Tc direct current SQUIDs on silicon bicrystal substrates operating at 77 K

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Abstract
We investigated Josephson junctions and dc superconducting quantum interference devices (SQUIDs) on silicon bicrystal substrates with epitaxially grown 24° Y1Ba2Cu3O7−x, (YBCO) grain boundaries. Buffer layers and passivation/contact layers were prepared for the YBCO thin films by laser deposition techniques. The observed current–voltage characteristics of ion-beam etched, as well as direct laser patterned junctions with products of the critical current and the normal resistance up to 150 μV at 77 K, can be described within the resistively shunted junction model. The inductance of dc SQUIDs was varied by additional laser patterning. In this way, dc SQUIDs with transfer functions up to 30 μV/Φ0 and a white noise level of 30 μΦ0/Hz at 77 K were reached.