In situ formation of YBa sub 2 Cu sub 3 O sub x thin films by physical sputtering.

We have found that in situ superconducting Y-Ba-Cu-O thin films can be produced by sputtering without the aid of any external O sub 2 source during deposition. The films were produced by RF magnetron sputtering from a composite target onto MgO (100) substrates heated at 650C. Films made in a pure Ar pressure of 24 mTorr and fast cooled in N sub 2 ambient contain the tetragonal YBa sub 2 Cu sub 3 O sub 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 sub c (R=0) at 71K with an onset at 85K. The T sub c (R=0) rises to 80K 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 YBa sub 2 Cu sub 3 O sub 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 O sub 2.