Fabrication and characterization of Ti-Ba-Ca-Cu-O superconducting films on LaAlO3 substrates

A multi-step process is used to fabricate Tl₂Ba₂Ca₁Cu₂O₈ films on (100) LaA10₃ substrates. Submicron thick precursor films of Ba-Ca-Cu-O are rf magnetron sputter deposited from a single target. Film stoichiometry is measured by ion beam backscattering spectroscopy. Deficiencies of the alkaline earths that are found in the precursor films are then compensated for by the addition of appropriate CaF₂ and/or BaF₂ films onto the surface of the precursor film. Post deposition annealing of the films is then done in an atmosphere of thallium oxide and oxygen in order to form the superconducting phases. The annealed films are examined using x-ray diffraction (XRD), an ac inductance technique, and critical current in an external magnetic field. XRD shows the c-axis length of the superconducting phase to increase as the overall film stoichiometry approaches 2212. The transition widths measured by inductive coupling weakly correlate with 77 K critical current measurements. Our best critical current results are 1.5*10⁶ amps/ cm² for a film measured at 4 K in an 8 T magnetic field (parallel to the films' c-axis).