HOMOGENEOUS HIGH-QUALITY YBA(2)CU(3)O7 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 x 30 mm(2)) 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) greater than or equal to 2 x 10(6) A/cm(2).