Defect visualization in large area YBCO thin films by magneto-optical scanning technique

Flux penetration in large area YBCO thin films has been studied by a magnet o-optical scanning technique. With a new apparatus HTS films as large as 20 cm x 20 cm can be investigated by scanning the films through an inhomogene ous magnetic field. The apparatus has been built to realize an effective ho mogeneity control of the electrical properties of large area HTS thin films used for device fabrication. Magnetic flux penetration into YBCO thin film s of different sizes and with intrinsic defects as well as artificial ones have been studied at 50 It. Magneto-optical measurements are compared with optical microscopy (OM) and inductive j(c)-characterizations. ii correlatio n between the kind of defect and its influence on the electrical properties has been studied with regard to device applications. YBCO films structured especially for high current applications were investigated magneto-optical ly. These results will be compared to optical photographs of the quenching process caused by currents I > I-c.