MICROSTRUCTURE DEFECTS IN YBCO THIN-FILMS - A TEM STUDY TO DISCUSS THEIR INFLUENCE ON DEVICE PROPERTIES

The microstructure of epitaxial c oriented YBa2Cu3O7-delta, films depo sited and patterned by different routine methods typical of device lay outs is studied by TEM. Film systems up to three layers were either la ser deposited or sputtered onto SrTiO3, LaAlO3, MgO, and R-cut sapphir e buffered by CeO2 or YSZ. Specific grain boundaries of accidental gra ins either a-axis up oriented or in-plane rotated are discussed in ter ms of their growth, flux pinning, and weak-link behavior. These proper ties should be affected by adhering Y2O3 inclusions which otherwise oc cur highly dispersed in the bulk, preferably of the sputtered films. D islocations, probably attributed to twin boundaries and to faulty c-st acking, are considered in view of the film growth, mechanical relaxati on, and flux pinning. Within a device pattern of YBCO/SrTiO3/YBCO, tho roughly good epitaxial orientation is also found on top of crossing la yer edges in agreement with the measured high j(c) at the crossovers. Particular reference is given to the literature on the origin and the effects of microstructure defects.