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

Abstract

Thin films of Y/sub 1/Ba/sub 2/Cu/sub 3/O/sub 7-x/ (YBCO) have been fabricated by sequential multilayer RF magnetron sputter-deposition from Y/sub 2/O/sub 3/, BaCo/sub 3/, 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 SrTiO/sub 3/, LaAlO/sub 3/, MgO and sapphire-are found to be c-axis oriented for film thicknesses between 300 AA and 10000 AA. Transport current densities in the range of 10/sup 6/ A/cm/sup 2/ are obtained on SrTiO/sub 3/ and LaAlO/sub 3/ substrates and in the range of 10/sup 5/ A/cm/sup 2/ on MgO and sapphire. Transition temperatures of 89 K (resistive) and 87 K (inductive) are obtained repeatably with LaAlO/sub 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 LaAlO/sub 3/ that is equal to the surface resistance of high-quality silver films. The fabrication and properties of these films are discussed.