HOMOGENEOUS HIGH-QUALITY YBA(2)CU(3)O7 FILMS ON 3'' AND 4'' SUBSTRATES

The fabrication of homogeneous high quality YBa2Cu3O7 films on large a rea substrates is the first essential step on the way to commercial hi gh temperature superconductor devices. We have succeeded in growing YB a2Cu3O7 films with excellent electronic properties and outstanding hom ogeneity in thickness and composition up to 4'' diameter. This was pos sible by employing reactive co-evaporation in combination with a speci al substrate heater design: a rotating disk holder separates oxidation and deposition enabling a reactive high oxygen pressure zone in a sur rounding high vacuum background. Epitaxial YBa2Cu3O7 films were grown either directly on MgO (30 x 30 mm(2)) and LaAlO3 (3'') or with interm ediate buffer layers on sapphire (4''), silicon (4'') and GaAs (3''). For GaAs substrates we developed a chemical encapsulation to avoid con tamination by volatile arsenic. On all of these substrates we obtained zero resistance temperatures around 86 K and critical current densiti es j(c)(77 K) greater than or equal to 2 x 10(6) A/cm(2).