Significant improvements in the surface smoothness ofYBa2Cu3O7-δ films on high-temperature annealed CeO2-buffered r-cut sapphire

Abstract

YBa2Cu3O7-δ (YBCO) films were grownon CeO2-buffered r-cut sapphire (CbS) substrates using an off-axisdc magnetron sputtering method. Both as-grown and post-annealed CbSsubstrates were used for this purpose, with the post-annealed CbS preparedby annealing the as-grown CbS at 1000 °C for 1 h. The YBCO films onpost-annealed CbS showed significantly improved surface morphology andstructures than those on the as-grown CbS, with a peak-to-valley roughnessof 3.2 nm and a full-width at half-maximum of (005) YBCO rocking curve of0.47° for a 300 nm thick YBCO. The surface resistance of the 300 nmthick YBCO film on post-annealed CbS appeared as small as about110 µΩ at 60 K and about 230 µΩ at 77 K at about8.6 GHz.