Growth of Phase-Controlled Bi₂Sr₂Ca_n-1Cu_nO_yThin Films Prepared by Off-Axis Sputtering using He Gas

Abstract

We prepared Bi2Sr2Can-1CunOy (BSCCO) (n=2, 3) thin films by rf magnetron sputtering with a single target using a mixture gas of He+O2 and off-axis geometry. Since He gas can effectively produce active O2+ and O+ particles by the Penning ionization effect, we expected the film crystallinity to improve as a result. We investigated the changes in the crystallinity and the superconductivity of the films using the various compositions of the targets. The phase of the films depended on the composition of the targets. From the results, we found that the optimum target compositions for good crystallinity were the stoichiometric composition of Bi:Sr:Ca:Cu=2:2:1:2 for Bi-2212 films and the Bi-rich composition of Bi:Sr:Ca:Cu=3:2:2:3 for Bi-2223 films. Therefore, the sputtering gas of He+O2 and off-axis geometry are effective in obtaining the phase-controlled BSCCO thin films. In addition, we confirmed the effects of in situ and ex situ annealing for the crystallinity and the superconductivity of the films.