Growth and properties of MOCVD YBa2Cu3O7−x thin films

Epitaxial thin layers of YBa 2 Cu 3 O 7−x are synthesised by thermal decomposition (750 – 830 °C) of tetramethylheptanedionates of yttrium, barium and copper in the presence of oxygen. Argon is used as a carrier gas and the partial pressures of the different precursors are monitored via a careful control of the sources temperatures. The superconducting films with thicknesses ranging between 40 nm and 200 nm are grown on (100) SrTiO 3 , (012) LaA1O 3 or (100) MgO. The growth rate varies between 2.7 nm/min and 4 nm/min. The layers are analysed by scanning and transmission electron microscopy, x-ray diffraction and Rutherford backscattering spectrometry. The normal — superconductor transition is investigated via DC and AC resistance, magnetization and AC susceptibility measurements as a function of temperature. Magnetisation hysteresis loops recordings, I–V measurements on microbridges and non linear susceptibility analysis are used to explore the irreversible properties of the layers. Typical parameters for MOCVD films grown on LaA1O3 are as follows: T c = 90 K, Δ T c = 0.4 K and J c (77 K) = 2 10 6 A cm −2 .