(A) transmission electron microscopy study on the crystallization of amorphous $SrBi_2Nb_2O_9$ thin films dposited by metalorganic decomposition

Abstract

The promising potential of the ferroelectric thin films such as $SrBi_{2}Nb_{2}O_{9}$ and $YMnO_{3}$ is expected to lead an epoch of non-volatile ferroelectric random access memory devices. Especially, as the viewpoint of the gate materials, they are very attractive. In these points, both fundamental study and applied study have been performed in this thesis. The crystallization processes of the SBN thin films deposited by a MOD method were investigated by an in-situ TEM experiments for the first time. From the in-situ TEM results, the SBN thin film was crystallized to the large Bi-layered perovskite phase (0.2 - 0.3 ㎛) via the round nano-sized fluorite-like phase grains (10 - 20 nm), which was also confirmed by the ex-situ TEM experiments. It is expected that the crystallization processes of the SBN thin film had three stages; a grain shapes change, a formation of nano-crystalline grains, a large grain growth, in order. Therefore, the crystallization of the Bi-layered perovskite SBN phase is very closely related to the intermediate fluorite-like SBN phase. To understand the crystallization mechanism of the SBN thin films, it should be preceded to investigate the crystallographic relationships between the fluorite-like phase and the Bi-layered perovskite phase of the SBN films. The crystallization mechanism and crystallographic relationships between the fluorite phase and the Bi-layered perovskite phase have been investigated by high-resolution TEM and SAED experiments. The SBN thin films were post-annealed from 600 ℃ to 700 ℃ at interval 20 degrees in order to investigate the detail phase-transition processes. Using the SAED and HRTEM experiments, the fluorite-like phases were analyzed to the FCC cubic structure and lattice constant is 5.44 Å. Moreover, it was found that the (0 0 8) inter-planar distance of the Bi-layered perovskite SBN phase was the same as the (1 1 1) inter-planar distance of the fluorite-like SBN phase. Moreover, through a high-resolut...