(A) transmission electron microscopy study on the crystallization of amorphous $SrBi_2Ta_2O_9$ thin films deposited by metalorganic decomposition

Abstract

The use of ferroelectric thin films such as $SrBi_2Ta_2O_9$ (SBT) and $YMnO_3$ is of great importance in the application to non-volatile ferroelectric random access memory (NV-FRAM) devices. Particularly, it is very attractive to use them as gate materials in the MEFSFET and MEFISFET devices. In these points, both the fundamental study and applied study have been performed in this thesis. A transmission electron microscopy study of the solid phase crystallization of amorphous SBT thin films, deposited by metal-organic decomposition and annealed at 800℃ in a dry $O_2$ ambient, was carried out, in order to investigate the grain formation and origins of grain growth. The grains grew preferentially to the ＜110＞ direction resulting in elliptical grains. Because the highest ionic packing planes are the (001) planes with heights of 0.9217 and 0.5783, which planes are very the planes including $TaO_6$ octahedra in SBT crystal structure, and the nearest bonding direction of these planes is the ＜110＞ direction, the grains grew to ＜110＞ direction preferentially. As the annealing time was increased, elliptical grains maintained the preferential growth of the ＜110＞ direction. High-resolution (HR) TEM and HR image computer simulation studies of the solid-phase crystallization of amorphous SBT thin films, prepared by metal-organic decomposition, were carried out, in order to investigate defect structure and its effect on the grain growth of the SBT films on an atomic level. In most of the grains, there were antiphase boundaries of which lattice on the one side is displaced by $d_(005)$ toward the ＜001＞ direction compared with the lattice on the other side. The formation of a stacking fault induces the antiphase boundary at the amorphous/crystalline interface. A corner of the antiphase boundary at the interface acts as preferable nucleation sites for an atomic step of the {001} planes, and nuclei of {001} planes are formed easily in the corner. Thus, the antiphase boundary en...