光/超伝導変換デバイスの感度向上を目的とした極薄高温超伝導膜の作製法の研究

概要

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We studied a method to obtain superconductivity even in very thin films of YBa2Cu3Oy (YBCO). These thinner YBCO films will be able to be applied to optics/superconductivity (opt/super) converters with high optical sensitivity. Opt/super converters composed of YBCO nano-bridges or nano-wires require a low critical current that is determined by the film thickness. According to X-ray diffraction, critical temperature (Tc) and residual resistivity ratio for the substrates of MgO (100), SrTiO3 (100) and NdGaO3 (110), superconducting features are influenced by the lattice mismatching layer in YBCO closing to a hetero-epitaxy interface between YBCO and single crystal substrate. YBCO films with different thicknesses varying from 80 to 10nm were prepared on SrTiO3, using a suitable temperature. The values of Tc slightly decreased when reducing YBCO thickness from 80 to 20 nm, and then declined sharply at less than 20nm. It is considered that a layer in the beginning of deposition less than 20nm causes stress in the crystal lattice. The Tc of 20 nm YBCO film on SrTiO3 was 80.8 K. It can work above liquid N2 temperature.