EPITAXIAL-GROWTH OF YBCO/MGO/YBCO STRUCTURES

A Y1Ba2Cu3O7-y (YBCO) /MgO/Y1Ba2Cu3O7-y structure on a MgO(100) substrate was made and its crystallographic structure was investigated by cross-sectional transmission electron microscopy (TEM). A MgO ultra-thin film with (100) orientation as an intermediate layer was obtained on each of the (001) and (100) YBCO thin films at the substrate temperature of about 400-degrees-C. The crystallinity of the MgO layer as a function of the MgO thickness was investigated. The randomness of the crystallinity decreased with a decrease in the thickness. A (100) epitaxial MgO layer without other orientation was obtained at a thickness of 10nm. From the results of cross-sectional TEM observation of the YBCO/MgO/YBCO structure, it was found that the thickness of the MgO can be reduced to 5nm at a minimum. In the sample with a MgO thickness of 5nm, sharp interfaces were observed without any disrupted portion. When the thickness was reduced to 2nm, the interface between the top layer and the base layer was crushed.