Oxygen Annealing of YBCO/Gold Thin-Film Contacts
The specific contact resistivity, defined as the product of the contact resistance and the contact area, of c-axis YBCO/Au thin-film contacts is measured as a function of oxygen annealing temperature to determine the optimum annealing conditions for this interface system. Square planar junctions with side widths of 2, 4, 8, and 16 μm were fabricated ex situ. Annealing was carried out at constant sample temperature for 10 minutes in atmospheric pressure of oxygen. The junction conductance characteristics were measured after each annealing and the process was repeated at progressively higher annealing temperatures, up to 650 °C. Before oxygen annealing, the junctions had contact resistivities of about 10−4 Ω•em2 or greater. The contact resistivity was unchanged for annealing temperatures below 300 °C. It decreased rapidly in an annealing temperature range from 300 °C to 450 °C. We found that 600 °C was a practical upper limit for annealing, at which temperature a contact resistivity in the 10−6 Ω•cm2 range may be achieved. We conclude that annealing-induced Au diffusion along grain-boundaries was responsible for the reduction in the contact resistivity.
KeywordsContact Resistance High Temperature Superconductor Rapid Thermal Annealing Contact Resistivity YBCO Film
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