Microstructure defects in YBCO thin films: A TEM study to discuss their influence on device properties

the microstructure of epitaxial c oriented YBa 2Cu 3O 7−δ films deposited and patterned by different routine methods typical of device layouts is studied by TEM. Film systems up to three layers were either deposited or sputtered onto SrTiO 3, LaAlO 3, MgO, and R-cut sapphire buffered by CeO 2 or YSZ. Specific grain boundaries of accidental grains either a-axis up oriented or in-plane rotated are discussed in terms of their growth, flux pinnig, and weak-link behavior. These properties should be affected by adhering Y 2O 3 inclusions which otherwise occur highly dispersed in the bulk, preferably of the sputtered films. Dislocations, probably attributed to twin boundaries and to faulty c-stacking, are considered in view of the film growth, mechanical relaxation, and flux pinning. Within a device pattern of YBCO/SrTiO 3/YBCO, thoroughly good epitaxial orientation is also found on top of crossing layer 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.