In-situ growth of Y1Ba2Cu3O7-x films by molecular beam epitaxy with an activated oxygen source

doi:10.1016/0921-4534(89)91178-7

Physica C: Superconductivity and its Applications

Volumes 162–164, Part 1, December 1989, Pages 623-624

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Abstract

Epitaxial, (001) oriented Y₁Ba₂Cu₃O_7-x thin films were grown on MgO(100) by molecular beam epitaxy at 650°C. The activated oxygen species were produced by a remote microwave-excited discharge in a flow tube. Remarkable improvements of superconducting properties were demonstrated due to enhancements of the flow speed of O₂ stream. The as-prepared films 500Å thick show reproducibly R=0 transitions at 89K, and a ϱ(100K) of 70 μΩ-cm. Ultrathin films 90Å thick still exhibit metallic-like resistivity, and a T_c(R=0) of 70K.

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High-quality YBa₂Cu₃O_7−δ thin films with optimized surface smoothens suitable for multilayer technology have been deposited by DC-magnetron sputtering. The films not only show high critical temperatures (T_c) up to 90 K and high critical current densities (j_c) up to 4.2×10⁶ A/cm² at 77 K, but also a smooth surface with only one outgrowth of a size of more than 200 nm within an area of 150×150 μm². The T_c and j_c values are slightly lower than our best values for rough films with optimized conditions for T_c and j_c, where we reach up to 6×10⁶ A/cm² at 77 K and a T_c offset up to 91.5 K on SrTiO₃ and La AlO₃. Additionally, the surface resistances (R_s) of our films were measured using coplanar resonators. We determined an R_s of 120 μΩ at 77 K and 60 μΩ at 9 K and at 6.2 GHz for our best film. The penetration depth was evaluated to be between 160 and 200 nm for this film. A dependence of R_s on the surface magnetic field showed a higher crystal quality of our films with increasing j_c measured with a remanent field technique.
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Thin film synthesis of the high temperature superconductors in Y₁Ba₂Cu₃O_−x perovskite has been successfully carried out by the advanced molecular beam epitaxy technique. The development of an efficient activated oxygen source led to in-situ growth of high quality films of Y₁Ba₂Cu₃O_77minus;x and Dy₁Ba₂Cu₃O_7−x without high temperature annealing. Excellent superconducting properties have been achieved: the T_c, δT_c, normal state resistivity p, and critical current density J_c equal to the best records r eported to date for Y₁Ba₂Cu₃O_7−x films. This paper reviews in-situ MBE growth, structural and superconducting characteristics of the films. The result of tunneling in planar junctions of Y₁Ba₂Cu₃O_7−x/native barrier/Pb are also presented in the context of quasiparticle tunneling and Josephson behavior.
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In-situ growth of Y1Ba2Cu3O7-x films by molecular beam epitaxy with an activated oxygen source

Abstract

Appl. Phys. Lett.

In-situ growth of Y₁Ba₂Cu₃O_7-x films by molecular beam epitaxy with an activated oxygen source