Sputtered YBCO Films on Metal Substrates

Magnetron sputtering was used to deposit superconducting YBCO thin films on four polycrystalline metal substrates. Yttrium-stabilized zirconia (YSZ) and silver were used as buffer layers. The thermal expansion coefficient of the substrate was apparently correlated to the properties of the superconductor. Auger depth profiles showed that the YSZ buffer blocked diffusion of most metal elements from the substrate. Nevertheless, contamination of the films depressed T_c to 81 K on Hastelloy × from 87 K on single-crystal strontium titanate. The films on metal substrates were c-axis oriented, but with random rotation in the a-b plane and smaller grain size than epitaxial films on single crystals. The weak links from these factors restrict J_c to 10⁴ A/cm² at 40 K.