Crystallization Process of Sr_<0.7>Bi_<2.3>Ta_2O_9 Thin Films with Different Crystal Orientation Prepared by Chemical Liquid Deposition Using Alkoxide Precursor(Special Issue on Advanced Memory Devices Using High-ε and Ferroelectric Films)

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The crystallization process of Sr_0.7Bi_2.3Ta_2O_9 (SBT) ferroelectric thin films with different crystal orientations formed by chemical liquid deposition using an alkoxide precursor was investigated.One film showed strong c-axis orientation (a-type film), while another shows scarcely any c-axis orientation (b-type film).We report that the crystallization process was the same even when crystal orientation differed.Thin films first change from amorphous to fluorite fine grains;the fluorite grains then change to bismuth layer-structure grains.The different orientation of the SBT films is not caused by different crystalization process.Both SBT films with different crystal orientations consist of fine fluorite grains after 650℃ heat-treatment.Their leakage current density characteristics differ, however.The leakage current density of the a-type film was independent of the electric field, and showed a low value of 10^-8 A/cm^2.The leakage current density of the b-type film, however, was dependent on the electric field, and increased continuously with the increasing electric field.After 700℃ heat-treatment, both films consist of large grains with bismuth layer-structure and fine fluorite grains.The matrix of both films contains large grains with bismuth layer-structure that determines the leakage current density characteristics.Since the fluorite grain size after a 700℃ heat-treatment is the same as that after 650℃ heat-treatment, nucleation is predominant at the structural phase boundary from amorphous to fluorite.The bismuth layer-structure grains are large and single-crystal grains after both a 700 and 800℃ heat-treatment.Increased grain size predominates at the structural phase boundary from fluorite to bismuth layer-structure grains.Clearly, ferroelectric SBT films with bismuth layer-structure are crystallized in two steps, each having a different perdominant crystal growth mechanism.
社団法人電子情報通信学会の論文
1998-04-25

Crystallization Process of Sr_<0.7>Bi_<2.3>Ta_2O_9 Thin Films with Different Crystal Orientation Prepared by Chemical Liquid Deposition Using Alkoxide Precursor(Special Issue on Advanced Memory Devices Using High-ε and Ferroelectric Films)

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