A structural study of BiFeO3-PbTiO3 thin films deposited by pulsed laser deposition

摘要

In recent years ferroelectric thin films have received an enormous amount of attention due to their potential use in electronic device applications. Bismuth ferrite lead titanate (xBiFeO3 – (1-x)PbTiO3) thin films are of special interest due to their multiferroic nature, exceptionally high tetragonality and high switchable polarization close to the morphotropic phase boundary. This work encompasses an initial structural investigation into xBiFeO3 – (1-x)PbTiO3 thin films deposited onto Pt/TiOx/SiO2/Si substrates by pulsed laser deposition. The effect of substrate orientation, film composition and film thickness are described as well as the growth mechanisms and interactions at the substrate – film interface. The pulsed laser deposition conditions were optimized to produce crystalline stoichiometric films of tetragonal and mixed phase tetragonal –rhombohedral phases. The films structure and growth mechanisms were studied using x-ray diffraction, scanning electron microscopy and atomic force microscopy. It was found that the substrate orientation, film composition and film thickness determine the structural properties of the deposited film. A critical film thickness of 290 nm was identified as the minimum for a piezoelectric response to be observed. The piezoelectric nature of the films was confirmed by piezoforce microscopy. Transmission electron microscopy analysis revealed the occurrence of interdiffusion at the substrate – film interface between the platinum bottom electrode and bismuth from within the deposited film. A strontium ruthanate buffer layer was deposited by pulsed laser deposition which prevented the interdiffusion, however local diffusion with the xBiFeO3 – (1-x)PbTiO3 deposited film was still present.