Homogeneous high quality YBa₂Cu₃O₇ films on 3″ and 4″ substrates

The fabrication of homogeneous high quality YBa₂Cu₃O₇ films on large area substrates is the first essential step on the way to commercial high temperature superconductor devices. We have succeeded in growing YBa₂Cu₃O₇ films with excellent electronic properties and outstanding homogeneity in thickness and composition up to 4″ diameter. This was possible by employing reactive co-evaporation in combination with a special substrate heater design: a rotating disk holder separates oxidation and deposition enabling a reactive high oxygen pressure zone in a surrounding high vacuum background. Epitaxial YBa₂Cu₃O₇ films were grown either directly on MgO (30 × 30 mm²) and LaAlO₃ (3″) or with intermediate buffer layers on sapphire (4″), silicon (4″) and GaAs (3″). For GaAs substrates we developed a chemical encapsulation to avoid contamination by volatile arsenic. On all of these substrates we obtained zero resistance temperatures around 86 K and critical current densities j_c (77 K) ≥ 2 × 10⁶ A/cm².