Characterization of the microstructural and piezoelectric properties of PbTiO₃ thin films synthesized by liquid-phase deposition

The microstructure and the ferroelectric properties of mirrorlike polycrystalline PbTiO₃ thin films were studied as a function of the film thickness. Highly uniform PbTiO₃ films were deposited onto LaNiO₃-buffered (100) Si substrates by liquid phase deposition at temperatures as low as 45 °C. The as-deposited films are amorphous and can be easily converted into single phase PbTiO₃ thin films upon a heat treatment at 750 °C in air for 6 h. X-ray diffraction patterns of the films have shown that they are chemically pure and adopt a tetragonal structure with the value of the lattice volume slightly smaller than that of the bulk material, indicating the presence of a compressive stress. This was furthermore confirmed by Raman spectroscopy by monitoring the variation of the positions of the soft optical phonon modes with the thickness of the films compared to that of those measured from a powdered sample. The E(1TO) and E(2TO) phonon modes undergo an upward shift and this shift decreases with increasing as the films get thicker indicating the presence of a compressive stress which decreases with increasing the film thickness. Piezoelectric force microscopy (PFM) and PFM bit-lithography experiments performed at room temperature allowed not only the visualization of the ferroelectric domain structure but also control the orientation of dipoles with an external electric field, thereby confirming the high quality of the films. The PbTiO₃ films are formed by 180° ferroelectric domains and the static value of the piezoelectric coefficient d₃₃ was found to increase with the film thickness, presumably as a result of the reduction of the stress and the substrate-induced clamping effect.