Characterization of the Ag/YBa₂Cu₃O_7-x contact in thin films

Silver (Ag) contacts to very thin superconducting YBa₂Cu ₃O_7-x films were prepared by thermal evaporation. The nature of the Ag/YBa₂Cu₃O_7-x contact during thermal treatment was in situ investigated by a combination of three- and four-terminal resistance measurements. The experimental results suggested that the interaction between Ag and the YBa₂Cu₃O_7-x film began at a temperature of around 370 °C. The contact resistance measurement for different films also demonstrated that the contact property was a strong function of the film quality and surface conditions. The lack of reproducibility in forming a low-resistance contact to very thin YBa ₂Cu₃O_7-x films and the high probability of degrading the film quality after thermal treatment of the contact might be due to the excess Ag doping in YBa₂Cu₃O_7-x. Ag island formation, as revealed by scanning electron microscopy after thermal treatment of the contact, is a limitation of Ag for use as a good contact electrode for very thin superconducting films.