HIGH-QUALITY YBA2CU3O7-X SUPERCONDUCTING THIN-FILMS GROWN BY MOCVD

YBCO thin films have been grown by Metal Organic Chemical Vapour Deposition in a cold wall type reactor. The beta-diketonates of yttrium, barium and copper are used as precursors. Films have been deposited on (001) MgO and (012) LaAlO3 single crystalline substrates. The morphology is very dependant on the gas phase composition. Different oxygen partial pressures have been investigated. An increasing oxygen partial pressure - at a fixed deposition temperature - is found to increase the growth rate and to promote the growth of a-axis grains (grains with the c axis parallel to the substrate's surface). In our standard deposition conditions, T-substrate (holder) = 875 degrees C, P-Total = 5 Torr, and PO2 = 2 Torr, high quality films are obtained, exhibiting T-c (similar to) 91 K (10%-90% of the resistive transition) and J(c) (77K) (similar to) 5.10(6) A/cm(2). A trilayer structure YBCO/Y2O3/YBCO (900 Angstrom/100 Angstrom/900 Angstrom) has been grown on LaAlO3 substrate, with the epitaxial relationship :<110> (001)(YBCO) // <100> or <010> (001)(Y2O3). No misorientations have been found in the (a,b) plane. The trilayer exhibits a sharp superconducting transition (Delta T-c = 0.4 K), with T-c = 82.5 K, and J(c)(77 K), (similar to) 10(6) A/cm(2).