Conducting Metallic Oxide Contacts on Superconducting YBa2CusO7−x Thin Films

Low resistance contacts to superconducting YBa2 Cu3O7−x (YBCO) thin films have been prepared by using conducting metallic ruthenium oxide, RuO2, as contact electrodes. The surface specific contact resistivity of the best contacts made by dc magnetron sputtering of RuO₂ and a structure of Au/RuO2 or Ag/RuO2 on YBCO thin films has an upper limit value in the range of 5 × 10−8Ω cm2 but less than 5 × 10−6Ω cm2 at 77K for a single layer RuO2 on YBCO thin films. Auger depth profiling shows diffusion of Y, Ba, and Cu into RuO2 but no apparent diffusion of Ru into YBCO thin films after thermal treatment of the contact at 500°C. No degradation of zero resistance temperature was seen for the superconducting thin films after the formation of the low resistance contacts. No special pretreatment of the YBCO film 'surface was required prior to depositing the contact electrodes but a post-deposition anneal was necessary to obtain a good contact.