Study Of YBCO Superconducting Multilayer Film Fabricated By Photo-assisted MOCVD

High temperature superconductor YBCO, which can work in liquid nitrogen environment, has many advantages such as high current-carrying capability and low AC loss. It has great potential and commercial value in microwave and power application. How to improve the critical current density of YBCO superconducting films has became the research focus. According to the theory of flux pinning, it’s possible to improve the critical current density by introducing artificial pinning center in YBCO superconducting film. The defects in superconducting film can be improved by doping or the stress of lattice mismatch. These defects can work as effective pinning center and prevent the energy losses caused by vortices motion, so as to improve the current-carrying capability of the superconducting film.In this paper, photo-assisted metal organic chemical vapor deposition (MOCVD) epitaxial system was employed to fabricate YBCO multilayer film which was doped by buffer layer. The main contents are as follows:(1) The influence of barium source on crystalline quality, surface morphology was investigated. We found that the evaporation rate of barium source has a great influence on the crystalline quality and morphology of the film. Large amount of CuO particles was deposited in the surface of film because of the lack of barium. The surface impurity particles decreases gradually with the volatile rate of barium source increase. Films with excellent crystalline quality could obtained by choosing right heating temperature of barium source.(2)Y2O3nanodots was chosen as the buffer layer for the preparation of multilayer film. We have investigated the microstructure of Y2O3layer grown on YBCO by varying growth time(T). With elevating T, the nanostructures gradually grow larger and sparser due to the merger between dot and dot.(3) YBCO/ND-Y2O3/YBCO sandwich structure on LaAlO3(100) substrate were grown successfully by photo-assisted MOCVD. The influence of Y2O3layer on crystalline quality, surface morphology and critical current density was investigated. With elevating growth time, the nanostructures gradually grow larger. The lattice periodicity of YBCO was destroyed due to the large size of Y2O3nano-dots, which leads to the degradation of crystalline quality of the multilayer film. Self-field critical current density determined by AC magnetic induction method shows that sample with20seconds growth ND-Y2O3has the higher Jc of2.4MA/cm2, which is20%improved comparing with the samples without ND-Y2O3.