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

Volume

25

Issue

2

fYear

1989

fDate

3/1/1989 12:00:00 AM

Firstpage

803

Lastpage

805

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;

fLanguage

English

Journal_Title

Magnetics, IEEE Transactions on

Publisher

ieee

ISSN

0018-9464

Type

jour

DOI

10.1109/20.92407

Filename

92407