Structural Defects in Sr_<0.7>Bi_<2.3>Ta_2O_9 Thin Film for Ferroelectric Memory(Special Issue on Advanced Memory Devices Using High-ε and Ferroelectric Films)

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Using transmission electron microscopy (TEM), we studied structural defects in a Sr_0.7Bi_2.3Ta_2O_9(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 (2010) plane in many instances.The defects in the SBT film were also confirmed by the TEM observation.
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1998-04-25