I n s i t u formation of YBa2Cu3Ox thin films by physical sputtering

Abstract

We have found that in situ superconducting Y‐Ba‐Cu‐O thin films can be produced by sputtering without the aid of any external O₂ source during deposition. The films were produced by rf magnetron sputtering from a composite target onto MgO(100) substrates heated at 650 °C. Films made in a pure Ar pressure of 24 mTorr and fast cooled in N₂ ambient contain the tetragonal YBa₂Cu₃O_x phase with x estimated to be 6.1. Films made under the same sputtering conditions but cooled in 30 mTorr oxygen after deposition, show a superconducting transition T_c(R=0) at 71 K with an onset at 85 K. The T_c(R=0) rises to 80 K if 0.5 mTorr oxygen was added during sputtering. The experimental results provide conclusive evidence that sufficient oxygen can be incorporated into the films to form the tetragonal YBa₂Cu₃O_x phase simply by physical sputtering from an oxide target. The films absorb additional oxygen and transform into the orthogonal, superconducting phase when subsequently cooled in partial O₂.