Natural-Superlattice-Structured Ferroelectric Bi4Ti3O12–SrBi4Ti4O15 Thin Films Prepared by Pulsed Laser Deposition

Abstract

C-axis-oriented natural-superlattice-structured Bi4Ti3O12–SrBi4Ti4O15 (BIT–SBTi) epitaxial ferroelectric thin films have been grown by a pulsed laser deposition (PLD) method on MgO (001) and SrTiO3 (001) substrates. The epitaxial growth of natural-superlattice-structured BIT-SBTi thin films was confirmed by X-ray diffraction (XRD) θ–2θ scans, pole figure plots, reciprocal-space mappings and transmission electron microscopy (TEM) images. The c-axis lattice constants (3.732 nm on MgO substrate and 3.715 nm on SrTiO3 substrate) of those BIT-SBTi thin films are very close to the average of those of the unit cells of Bi4Ti3O12 (3.296 nm) and SrBi4Ti4O15 (4.189 nm) films on MgO substrates. The annealed BIT–SBTi thin film on Pt/Ti/SiO2/Si substrate also has a superlattice structure and exhibits superior ferroelectricity with values of 2Pr and 2Ec that are 32.0 µC/cm2 and 190 kV/cm, respectively. The BIT-SBTi film on Pt/Ti/SiO2/Si substrate exhibits a degradation of switching charge after 1×1010 switching cycles that is 16.5%. This enhanced ferroelectric property is attributed to the structural stress induced through the Bi2O2 layer by the differences in lattice parameters and chemical characters of the pseudo-perovskite structures in the superlattice structure. The dielectric constant and dielectric loss were 433 and 0.037 measured at 1 MHz and room temperature, respectively.