INDUCTANCE MEASUREMENTS IN MULTILEVEL HIGH-T(C) STEP-EDGE GRAIN-BOUNDARY SQUIDS

Multilevel high T(c) SQUIDs, suitable for digital circuit applications, have been fabricated and tested. The devices employ a YBa2Cu3O7-delta (YBCO) ground plane, an epitaxial SrTiO3 insulator, and a YBCO microstrip layer. Junctions are formed by the step-edge grain boundary process, with a ground plane contact for the ''low'' side of each junction, using only isotropic sputtering and milling techniques. Control current is directly injected in a microstrip segment of the SQUID loop, allowing us to measure the microstrip inductance, and thus to infer the magnetic penetration depth of the YBCO. The SQUIDs are operational above 77 K, at which temperature we infer a penetration depth of 350 nm. The temperature dependence of the penetration depth is found to be in reasonable agreement with the Gorter-Casimir form close to T(c). (C) 1994 American Institute of Physics.