Fabrication of YBCO superconducting tape by metal organic chemical vapor deposition method

YBCO films for coated conductors (CC) were fabricated by a metal organic chemical vapor deposition (MOCVD) system of hot-wall type using a single source. The deposition condition was optimized using (100) SrTiO₃ single crystal substrates in a steady state, and then the substrate was replaced by moving IBAD template (CeO₂/IBAD-YSZ/stainless steel) of 40 cm/hr. Two different types of IBAD templates with thin CeO₂ and thick CeO₂ layers were used. The mole ratio of MO source was Y(tmhd)₃:Ba(tmhd)₂:Cu(tmhd)₂=1:2.1:2.9, and the YBCO films were prepared at the deposition temperatures of 780∼890°C. The a-axis growth was observed together with the c-axis growth up to 830°C, while the c-axis growth became dominant above 830°C. The top surface of the c-axis film was fairly dense and crack-free. In case of the YBCO film with a 2.2 μm thickness deposited on the SrTiO₃ substrate at 860°C, the deposition rate was as high as 0.37 μm/min. The critical current and critical current density of the film was 104 A/cm-width and 0.47 MA/cm², respectively. The YBCO film deposited on the IBAD template with a thin CeO₂ layer showed a low critical current of 2.5 A/cm-width, while the YBCO film deposited on the IBAD template with a thick CeO₂ layer showed a higher critical current of 50 A/cm-width. It indicates that the stable buffer layer at high deposition temperature is needed for the MOCVD process.