Orientation control of Sr_0.7Bi_2.3Ta₂O_9+α thin films by chemical liquid deposition

The orientation of Sr_0.7Bi_2.3Ta₂O_9+α (SBT) films, which are layer-type bismuth compounds, was controlled by varying the Sr-source. In this paper, the effect of crystal orientation on film characteristics is described. The crystal orientation of the SBT ferroelectric films did not affect the surface morphology, leakage current or fatigue characteristics, but it did affect the shape of the hysteresis loop (polarization) and the window value of the C-V characteristics when the films were connected to a metal-oxide-semiconductor (MOS) diode. Although a complete c-axis orientation film with a stoichiometry of SrBi₂Ta₂O₉ shows no spontaneous polarization in general, the highly c-axis orientated Sr_0.7Bi_2.3Ta₂O_9+α film in this study showed some spontaneous polarization. The polarization values are larger than the expected by considering orientation alone. A deviation from stoichiometry resulted in an increase made in the polarization along the c-axis. Therefore, control of the crystal orientation and composition of SBT films is quite an important factor in actual applications.