Study and Preparation of High-T_c Superconducting (HTSC) Thin Films for Electronic Applications

High-quality superconducting YBa₂Cu₃O_7−x thin films are reproducibty prepared through thermal co-evaporation of BaF₂, Y, and Cu. Uniformity in thickness and composition of the deposited films can be achieved for a 2.5-in-diameter area on the substrate holder. Four-probe resistivity, critical current measurements, and X-ray diffractions were used to characterize these films after a post-deposition annealing in mixture of O₂ and H₂O. Highly “c”-oriented films with total transition temperature above 90 K were reproducibly made on (001)SrTiO₃ with critical current above 10⁵ A/cm² at 77 K. The total transition temperatures (T_c at R =0) of YBa₂Cu₃O_7−x films on ZrO₂, (001) YAG, (001) MgO, and (001) MgAl₂O₄ are 87, 74, 63, and 57 K, respectively. The effect of the post-deposition processing ambient on the preparation of YBa₂Cu₃O_7−x thin films was studied. The role of H₂O vapor and the role of an HF getter (e.g., SiO₂) during the high-temperature anneal is understood through a thermodynamic analysis of the fluorine removal reaction. Photolithography and argon ion milling have been employed to produce YBa₂Cu₃O_7−x wires from several micrometers to submicrometer in size. The resulting wires behaved as scaled down bulk superconducting films not weak links. Modification of superconducting thin films induced by laser irradiation (beam diameter 5 µm, λ = 515 nm) in a controlled ambient was studied. The two types of films (pure YBa₂Cu₃O_7−x films and mixture of YBa₂Cu₃O_7−x and Y₂Ba₄Cu₈O_x films) exhibit different transport behavior after modification. The mixture films show characteristic second transition at 76 K independent of the increase of room temperature resistance, while the pure YBa₂Cu₃O_7−x film exhibits decreasing second transition temperature with increasing room temperature resistance. The properties of the modified region can be recovered by plasma oxidation at room temperature. This technique may prove to be a viable way for fabricating novel structures for scientific studies and device applications.