Lateral force microscopy investigations of the crystallization of SrBi₂Ta₂O₉ thin films

A lateral force microscope (LFM) was used for studying the surface morphologies of SrBi₂Ta₂O₉ thin films with varying post-annealing temperature. Specimens were prepared onto platinized silicon wafers by the sol-gel method and post-annealed at 600-800°C. Non-ferroelectric matrix phases were found for specimens annealed below 700°C, which were confirmed by the measurement of X-ray diffraction (XRD) patterns. The friction coefficients between the surface of ferroelectric grain and non-ferroelectric matrix, and the silicon nitride tip, were determined from the line profile of the LFM images. The measured coefficients of friction for a tip on grain and matrix are 0.19±0.08 and 0.28±0.08, respectively. In the LFM images, the matrix phases decreased with increasing post-anneal temperature and the surfaces of the specimens annealed above 700°C were filled with SBT grains which were consistent with the XRD results. Ferroelectricities of these specimens were confirmed by the measurement of polarization field hysteresis loops.