In-Situ Growth Of High Temperature Superconducting Films By High Pressure Reactive Evaporation

We have developed a high pressure reactive evaporation (HPRE) process that has proven successful for the in-situ formation of the superconducting phase of YBa2Cu307 thin films at relatively low temperatures, T = 625 C. The process involves the evaporation of the three metallic components in a relatively high pressure oxygen atmosphere, P = 0.65 mTorr. When the deposition is followed by a cool-down anneal in a high pressure oxygen ambient, P~20 Torr, the result is a film with a relatively sharp superconducting transition. The best films, which have been obtained on yttria-stabilized zirconia substrates, have a zero resistance Tc of 86 K. The HPRE process generally results in a highly oriented growth habit, usually with the c-axis of the film being predominantly normal to the substrate plane. This result has been obtained both for (100) zirconia and (100) MgO substrates. Measurements of critical current densities on 20 gm constrictions have yielded values greater than 105 A/cm2 at 77 K and greater than 106 A/cm2 at 4.2 K on zirconia substrates. The constrictions were formed by photolithography and ion beam etching.