High Quality YBa₂Cu₃O_7-x Superconducting Thin Films Grown by MOCVD

Abstract
YBCO thin films have been grown by Metal Organic Chemical Vapour Deposition in a cold wall type reactor. The [MATH]-diketonates of yttrium, barium and copper are used as precursors. Films have been deposited on (001) MgO and (012) La AlO₃ single crystalline substrates. The morphology is very dependant on the gas phase composition. Different 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 grouwth of a-axis grains (grains with the c axis parallel to the substrate's surface). In our standard deposition conditions, T_{substrate holder} = 875°C, P_Total = 5 Torr, and P_O2 = 2 Torr, high quality films are obtained, exhibiting [MATH] of the resistive transition) and [MATH] . A trilayer structure YBCO/Y₂O₃/YBCO (900 Å/100Å/900Å) has been grown on La AlO₃ 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 ([MATH]), with T_c = 82.5 K, and J_c(77 K) - 10⁶ A/cm².