POLYCRYSTALLINE JOSEPHSON JUNCTION ELEMENT

PURPOSE:To obtain a polycrystalline Josephson junction element the superconducting thin film of which has a smooth surface except its junction section by minimizing the characteristic fluctuation by artificially controlling boundaries between crystal grains forming a Josephson junction. CONSTITUTION:After a ceramic superconducting thin film 2 of Y1Ba2Cu3Oy (hereinafter abbreviated to 'YBCO') is formed to a thickness of 50 to 100nm on a single-crystal MgO substrate 1 and a narrow bridge section 21 of 10mum in width is formed by cutting off rectangle pieces from parts of the film 2 on both sides, the section 21 is irradiated with an electron beam 3 in transversal direction. As a result, YBCO superconducting fine crystals 22 are precipitated in the film 2 by recrystallization caused by irradiation with the electron beam 3, with the a- or b-axes of the fine crystals being parallel with the a- or b-axis of the film 2 and c-axes of the crystals being parallel with the c-axis of the film 2. It can be recognized from characteristic-evaluated results that the Josephson junction thus obtained is less in fluctuation in critical current density and has excellent surface morphology.