Epitaxial YBa₂Cu₃O_x thin films on sapphire with a PrBa2Cu3Ox buffer layer

Highly c‐axis‐oriented YBa2Cu3Ox thin films have been grown on (11̄02) sapphire substrates by a modified off‐axis magnetron rf‐sputtering technique. To prevent the interaction and to improve the lattice match between film and substrate a thin layer of 10–60 nm of PrBa2Cu3Ox was used as a buffer layer. The diffusion process was effectively blocked and the epitaxy was enhanced. The Jc (77 K) has been measured to be 4×105 A/cm2 which is significantly higher than the Jc of films directly grown on Al2O3 (∼8×104 A/cm2). The surface resistance of such films at 11 GHz and 4.2 K was measured to be 80 μΩ for 50‐nm thin films. These results are comparable to the best results reported so far on sapphire with other buffer layers.