Abstract: A method is disclosed for fabricating grain boundary junction devices, which comprises preparing a crystalline substrate containing at least one grain boundary therein, epitaxially depositing a high Tc superconducting layer on the substrate, patterning the superconducting layer to leave at least two superconducting regions on either side of the grain boundary and making electrical contacts to the superconducting regions so that bias currents can be produced across the grain boundary.

Abstract: High T.sub.c superconducting devices are described in which controlled grain boundaries in a layer of the superconductors forms a weak link or barrier between superconducting grains of the layer. A method is described for reproducibly fabricating these devices, including first preparing a substrate to include at least one grain boundary therein. A high T.sub.c superconductor layer is then epitaxially deposited on the substrate in order to produce a corresponding grain boundary in the superconducting layer. This superconducting layer is then patterned to leave at least two regions on either side of the grain boundary, the two regions functioning as contact areas for a barrier device including the grain boundary as a current flow barrier. Electrical contacts can be made to the superconducting regions so that bias currents can be produced across the grain boundary which acts as a tunnel barrier or weak link connection.

Abstract: A high T.sub.c oxide superconductive switching device [10] formed on a substantially planar substrate [18] includes a base electrode [12] comprised of a layer or film of anisotropic superconducting material. The layer has a first crystalline axis [c] along which a magnitude of an energy gap of the material is less than an energy gap of the material along other crystalline axes. The superconductive switching device further includes at least one injector electrode [14] forming a planar [16] or an edge tunneling junction with the base electrode for injecting, under the influence of a bias potential eV, quasiparticles into the base electrode. The first crystalline axis is aligned in a predetermined manner with the tunneling junction for optimizing a quasiparticle injection efficiency of the tunneling junction.

Abstract: A superconducting circuit including at least two DC SQUID stages integrated on the same superconducting chip and coupled by a circuit providing efficient transfer of current from the first SQUID stage to the second SQUID stage with large bandwidth. Each SQUID stage is comprised of a superconducting loop having at least two Josephson devices therein, there being shunt resistors across the Josephson devices to render them nonhysteretic. The coupling means between stages is directly connected to the shunt resistors of the first stage and includes a transmission line and an impedance circuit for matching the impedance of the transmission line, where the impedance circuit provides a real impedance over a large frequency range up to approximately the frequency of Josephson oscillation of the Josephson devices in DC SQUID. Feedback from the second SQUID stage to the first SQUID stage improves the input dynamic range and linearity of the circuit.