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-delt a (YBCO) ground plane, an epitaxial SrTiO3 insulator, and a YBCO micro strip layer. Junctions are formed by the step-edge grain boundary proc ess, with a ground plane contact for the ''low'' side of each junction , using only isotropic sputtering and milling techniques. Control curr ent is directly injected in a microstrip segment of the SQUID loop, al lowing us to measure the microstrip inductance, and thus to infer the magnetic penetration depth of the YBCO. The SQUIDs are operational abo ve 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) 1 994 American Institute of Physics.