Preparation of CeO2-buffer layers for large-area MOD-YBCO films (10×30 cm2) with high-Jc

Epitaxial cerium oxide (CeO₂; thickness: 40 nm) buffer layers were deposited on large area (maximum size 10×30 cm²) R-cut single-crystal sapphire (α-Al₂O₃) substrates by double electron-beam guns. Substrate heater-and-holder system was modified to maintain the substrate temperature uniform over the large area during deposition. Oxygen gas of a pressure 4×10^-2 Pa was introduced to keep radio frequency plasma. When the substrate temperature was controlled in the range 640°-700°C, the CeO₂ buffer showed a complete [001] orientation and very smooth surfaces by x-ray diffraction analysis and atomic force microscopic observations, respectively, in the whole area of the large size substrates. These buffer layers without post-deposition annealing were quite suitable for preparing YBa₂Cu₃O₇ (YBCO) films by a metal-organic deposition (MOD) using a metal acetylacetonate-based solution. The average critical current density of the 210-nm-thick MOD-YBCO film was in excess of 2.6 MA/cm² measured by an inductive method at 77.3 K.