Microstructural, transport, and RF properties of multilayer-deposited YBCO films

Thin films of Y₁Ba₂Cu₃O_7-x (YBCO) have been fabricated by sequential multilayer RF magnetron sputter-deposition from Y₂O₃, BaCo₃, and CuO targets and postannealing in oxygen. This approach readily allows precise control of the film stoichiometry and is promising for applications that require deposition over large areas. Films on different substrates-including SrTiO₃, LaAlO₃, MgO and sapphire-are found to be c-axis oriented for film thicknesses between 300 Å and 10000 Å. Transport current densities in the range of 10⁶ A/cm² are obtained on SrTiO₃ and LaAlO₃ substrates and in the range of 10⁵ A/cm² on MgO and sapphire. Transition temperatures of 89 K (resistive) and 87 K (inductive) are obtained repeatably with LaAlO ₃ substrates. Copper cavity end wall measurements at 77 K and 35.6 GHz set an upper limit for the surface resistance of the YBCO films on LaAlO₃ that is equal to the surface resistance of high-quality silver films. The fabrication and properties of these films are discussed