Title :
Optimization of YBCO surfaces of tunnel junctions
Author :
Gavaler, J.R. ; Braginski, A.I. ; Forrester, M.G. ; Talvacchio, J. ; Greggi, J.
Author_Institution :
Westinghouse Res. & Dev. Center, Pittsburgh, PA, USA
fDate :
3/1/1989 12:00:00 AM
Abstract :
It is established that in YBa2Cu3O7 films prepared by annealing amorphous oxide deposits, Ba segregation in the amorphous phase and YBCO decomposition after recrystallization are the major causes of surface degradation. The authors have grown films by entirely in-situ processing in which these effects are minimized. The films were epitaxially grown on (100) SrTiO 3 substrates with the a-axis normal to the film plane. Both structural and chemical analyses indicated that they are homogeneous and have proper stoichiometry up to their surfaces. At 4.2 K, contact resistivities below 4×10-10 ohm-cm2 were obtained with gold overlayers. Junctions have been formed by depositing thin Au proximity layers over the YBCO films followed by MgO barriers and Nb counterelectrodes. In some of the junctions weak-link shorts were observed, providing unambiguous evidence that the growth procedures used can produce films that are superconducting up to their surfaces
Keywords :
annealing; barium compounds; high-temperature superconductors; superconducting epitaxial layers; superconducting junction devices; superconductive tunnelling; yttrium compounds; 4.2 K; Au proximity layers; Ba segregation; MgO barriers; SrTiO3; SrTiO3-YBa2Cu3O7 -Au-MgO-Nb; YBa2Cu3O7 films; amorphous phase; annealing amorphous oxide deposits; causes of surface degradation; chemical analyses; contact resistivities; decomposition after recrystallization; epitaxial layers; high temperature superconductor; in-situ processing; stoichiometry; structural analysis; surface optimisation; tunnel junctions; weak-link shorts; Amorphous materials; Annealing; Chemical analysis; Conductivity; Degradation; Gold; Niobium; Substrates; Superconducting films; Yttrium barium copper oxide;
Journal_Title :
Magnetics, IEEE Transactions on
