CRYSTALLIZATION PROCESS OF SR0.7BI2.3TA2O9 THIN-FILMS WITH DIFFERENT CRYSTAL ORIENTATION PREPARED BY CHEMICAL LIQUID DEPOSITION USING ALKOXIDE PRECURSOR

The crystallization process of Sr0.7Bi2.3Ta2O9 (SBT) ferroelectric thi n films with different crystal orientations formed by chemical liquid deposition using an alkoxide precursor was investigated. One film show ed strong c-axis orientation (a-type him), while another shows scarcel y any c-axis orientation (b-type film). We report that the crystalliza tion process was the same even when crystal orientation differed. Thin films first change from amorphous to fluorite fine grains; the fluori te grains then change to bismuth layer-structure grains. The different orientation of the SBT films is not caused by different crystallizati on process. Both SBT films with different crystal orientations consist of fine fluorite grains after 650 degrees C heat-treatment. Their lea kage current density characteristics differ, however. The leakage curr ent density of the a-type film was independent of the electric field, and showed a low value of 10(-8)/cm(2). The leakage current density of the b-type film, however, was dependent on the electric field, and in creased continuously with the increasing electric field. After 700 deg rees C heat-treatment, both films consist of large grains with bismuth layer-structure and fine fluorite grains. The matrix of both films co ntains large grains with bismuth layer-structure that determines the l eakage current density characteristics. Since the fluorite grain size after a 700 degrees C heat-treatment is the same as that after 650 deg rees C heat-treatment, nucleation is predominant at the structural pha se boundary from amorphous to fluorite. The bismuth layer-structure gr ains are large and single-crystal grains after both a 700 and 800 degr ees C heat-treatment. Increased grain size predominates at the structu ral phase boundary from fluorite to bismuth layer-structure grains. Cl early, Ferroelectric SBT films with bismuth layer-structure are crysta llized in two steps, each having a different predominant crystal growt h mechanism.