Structural defects in Sr_0.7Bi_2.3Ta₂O₉ thin film for ferroelectric memory

Using transmission electron microscopy (TEM), we studied structural defects in a Sr_0.7Bi_2.3TA₂O₉ (SBT) thin film to be used for ferroelectric memory devices. We examined the effects of the substrate, crystal continuity, and dislocations in crystals as major causes of defects. For this study, we used an SBT thin film grown from an alkoxide solution. Since crystal growth was hardly influenced by the substrate, the substrate had little influence on the occurrence of defects resulted in misfit of lattice constant. Regions of partially low crystal continuity were observed in the SBT thin film. In these regions, the orientation was still uniform, but the continuity of the crystal grain was low because of the defects. In addition, variation in contrast was observed in the crystals, however, no obvious variation in chemical composition was found in this region of varying contrast. Therefore, the contrast variation is considered to be attributed to the dislocation. Such a dislocation was found to be occurred in the direction of the (2(MO) plane in many instances. The defects in the SBT film were also confirmed by the TEM observation.