Structural and electrical properties of samarium-substituted bismuth titanate ferroelectric thin films on Pt/TiOx/SiO2/Si substrates

Polycrystalline samarium-substituted ferroelectric bismuth titanate films (Bi3.45Sm0.55Ti3O12) were prepared on Pt/TiOx/SiO2/Si substrates by chemical solution deposition (CSD) and were annealed at various temperatures. For comparison, films with similar composition were grown by pulsed laser deposition (PLD) and annealed at 700 °C. X-ray diffraction and Raman spectroscopy results showed similar crystallographic orientations and structures for the films fabricated using these different deposition methods. It was found that film crystallinity, structural, dielectric, ferroelectric and leakage current properties were strongly dependent upon the annealing temperature for CSD-derived films. Atomic force microscopy showed that film surface roughness values are comparable for both deposition methods following annealing at the same temperature, although PLD-grown films had a more uniform grain size. Cross-sectional images obtained by scanning electron microscopy revealed distinct grain shapes and structures: dense, columnar grains for PLD-grown films, spherical grains and a more porous structure for CSD-derived films. The remanent polarization of CSD-derived films increased with increasing annealing temperature. The PLD-grown films annealed at 700 °C showed higher remanent polarization (2Pr = 41.8 μC/cm2) and lower coercive field (Ec = 91 kV/cm), than CSD-derived films annealed at the same temperature (27.4 μC/cm2 and 121 kV/cm). The former also had a lower leakage current density (6.7 × 10−7 A/cm2) than the latter (4.6 × 10−6 A/cm2) at a dc electric field of 100 kV/cm (∼10 V), and both film types demonstrated fatigue-free behaviour up to 109 read/write switching cycles with 1 MHz bipolar pulses.