HIGH-T-C DIRECT-CURRENT SQUIDS ON SILICON BICRYSTAL SUBSTRATES OPERATING AT 77 K

We investigated Josephson junctions and dc superconducting quantum int erference devices (SQUIDs) on silicon bicrystal substrates with epitax ially grown 24 degrees Y1Ba2Cu3O7-x, (YBCO) grain boundaries. Buffer l ayers and passivation/contact layers were prepared for the YBCO thin f ilms by laser deposition techniques. The observed current-voltage char acteristics of ion-beam etched, as well as direct laser patterned junc tions with products of the critical current and the normal resistance up to 150 mu V at 77 K, can be described within the resistively shunte d :unction model. The inductance of de SQUIDs was varied by additional laser patterning. In this way, de SQUIDs with transfer functions up t o 30 mu V/Phi(0) and a white noise level of 30 mu Phi(0)/root Hz at 77 K were reached. (C) 1998 American Institute of Physics.