Edge-geometry YBa2Cu3O7-x/Au/Nb SNS devices

The fabrication and electrical properties of edge-geometry YBaCuO/Au/Nb weak links are described. Superconductor/normal-metal/superconductor (SNS) devices of this type serve as sensitive probes of the electrical quality of the YBaCuO/Au interface. For device applications, the edge geometry has the advantage of placing the critical N/S device interface on the longer coherence length a-b surface, and it simplifies the fabrication of weak links with submicron dimensions. These structures are fabricated using laser-ablated, in situ, c-axis-oriented YBaCuO thin films, with both oxygen-annealed and unannealed YBaCuO/Au interfaces. The YBaCuO film edges are patterned using ion milling, followed by a low-energy-ion cleaning step and in situ deposition of Au and Nb. Devices with areas in the 10^-7-10^-8-cm² range have been fabricated with R_nA products lower than 10 ^-8 Ω-cm² and critical current densities up to 3 kA/cm². Josephson coupling is verified by the observation of microwave steps under 10-GHz microwave irradiation. The best results have been obtained with annealed YBaCuO/Au interfaces