Multilayer Josephson devices using high temperature superconducting bicrystal junctions

In this dissertation I report the fabrication and systematic study for the first time of multilayer bicrystal Josephson junctions made from YBa 2Cu3Ox/insulator/YBa2Cu3O x multilayer films grown on SrTiO3 bicrystal substrates. Josephson junctions are formed in each of the superconducting YBa2Cu 3Ox layers as a result of the vertical propagation of the grain boundary of the bicrystal substrate through the multilayers. This system shows behavior unique to the multilayer structure, such as resonances in the current-voltage (I-V) characteristics of the junctions in each layer. Strong interactions between the top and the bottom layer junctions in multilayer stacks in the forms of voltage locking and current locking were observed and discussed. We fabricated direct current superconducting quantum interference devices (dc SQUIDs) based on the stacked junctions. This type of SQUID has very low inductance that can meet the requirements of rapid single flux quantum (RSFQ) devices. We were able to use this type of SQUID to study penetration depth of the YBa2Cu3Ox films because it allows accurate measurement of the inductance of the films. All the studies of the multilayer devices were made possible because of the multilayer processes we developed, with which we fabricated crossovers and via connections, two basic building elements in any multilayer circuit, with highest critical current densities ever reported.