Simultaneous double-sided deposition of long-length epitaxial CeO2 buffer layers for YBCO coated conductors

A reel-to-reel system which allows simultaneous deposition of both sided long length epitaxial CeO2 buffer layers on biaxially textured Ni-5at.%W tape with direct-current (d.c.) reactive magnetron sputtering method is described. Deposition is accomplished through two opposite holes in the cavity by inverted cylindrical magnetron (ICM) sputtering guns. The films were characterized by means of x-ray diffraction (XRD), and atomic force microscope (AFM). The samples exhibited good epitaixal growth with c-axis perpendicular to the substrate surface for both sides. FWHM values of out-of-plane and in-plane for both sides were 3.2 degrees and 3.1 degrees, 5.3 degrees and 5.1 degrees, respectively. AFM observations revealed a smooth, dense and crack-free surface morphology. Biaxially textured CeO2 buffer layers up to 100-m length could be fabricated with production speed of about 1.2m/h. A 1-m CeO2 film was obtained with uniform thickness of 50nm, and Delta w of 3-3.5 degrees and Delta Phi of 5-6 degrees. Subsequently YSZ barrier and CeO2 cap layers were deposited to complete the buffer layer structure via the same process. Epitaxial YBa2Cu3O7-delta (YBCO) films grown by d.c. sputtering technique on the short prototype CeO2/YSZ/CeO2/NiW conductors yielded self-field critical current densities (Jc) as high as 1.3MA/cm(2) at 77K. An Ic values of 1.3A/cm was obtained for double-sided YBCO coated conductors.