In situ Ag/YBa2Cu3O7 contacts for superconductor-normal-metal-superconductor devices.

Abstract

By use of a completely in situ process, we have investigated Ag metal contacts to thin films of ${\mathrm{YBa}}_{2}$${\mathrm{Cu}}_{3}$${\mathrm{O}}_{7}$ (YBCO), in order to study the properties of the Ag/YBCO interface as well as the Josephson effect in SNS bridges made with this technique. Measurements of the temperature dependence of the Josephson current in these devices have been made, and are compared to recent theoretical predictions. SNS devices which exhibited Josephson effects had the critical current--resistance (${\mathit{I}}_{\mathit{c}}$${\mathit{R}}_{\mathit{n}}$) products of the junctions limited by the high specific contact resistance of the SN interfaces. The lowest values of the specific contact resistance obtained were on the order of ${10}^{\mathrm{\ensuremath{-}}8}$ \ensuremath{\Omega} ${\mathrm{cm}}^{2}$ for contacts in the c-axis direction. The specific contact resistance was measured as a function of deposition conditions for the Ag as well as annealing temperature and time. The influence of the specific contact resistance on the magnitude of the Josephson current in SNS bridges is discussed, and a review of the contact literature for noble-metal/YBCO contacts is presented.