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.