High Tc YBa2Cu3O7−x superconducting thin films by rf magnetron sputtering

Thin films of YBa2 Cu 3O7−x were deposited by RF magnetron sputtering onto BaTiO3, Al2O3, MgO, and SrTiO3 substrates at ambient temperature to 500°C from a sintered powder target having the same nominal composition. Four point AC resistivity measurements indicate that these films (∼2μm thick) are superconducting after annealing in flowing oxygen at ∼900°C for several minutes. While the onset Tc remains fairly constant at ∼88–91 K, the ending T c depends strongly on the deposition and annealing conditions, and substrates used. The films deposited at 300°C and annealed at 900°C for 1min., for example, have an ending T c of 45–53, 70–83, and 80–86.5 K when deposited, respectively, on Al2O3, BaTiO3 and MgO, and SrTiO3. Electron microprobe analyses show that these films have a spatially homogeneous composition of typically ∼YBa2 Cu 3O8. X‐ray diffraction data also reveal that the annealed films have the characteristics orthorhombic structure with lattice constants practically identical to those of the bulk YBa2 Cu 3O7−x, although minor phases (e.g., BaCuO2) with concentration of up to 15% can also be detected. These effects of ion bombardment during deposition and of interdiffusion of film and substrate during annealing are also presented, with emphasis on the film composition and Tc, and stability in room ambient.