Growth of ferroelectric oxide thin films by excimer laser ablation

Abstract

The pulsed ultraviolet excimer laser ablation technique was employed to deposit a variety of ferroelectric oxide thin film compositions, including lead zirconate titanate, Pb(Zr,Ti)O₃ (multiaxial), bismuth titanate, Bi₄Ti₃O₁₂ (biaxial), and lead germanate, Pb₅Ge₃O₁₁ (uniaxial), while maintaining the in situ stoichiometry of films close to that of targets. Growth process parameters such as deposition rates and the stoichiometry of the as-deposited films were examined and correlated with the ablation fluence, pressure, and substrate temperature. A threshold of ablation energy density has been identified for each type of ferroelectric composition. Evidence of intrinsic bombardment by energetic ablated species, during the thin film deposition, indicated an impact on the composition, structure, and the electrical properties as well. Electrical characterization of the ferroelectric films indicated a dielectric permittivity of 800-1000, a remanent polarization (Pr) of 32 μ C/cm², and a coercive field (Ec) of 100 kV/cm for polycrystalline PTZ films and corresponding properties of 150, 7 μ C/cm², and 20 kV/cm for in situ crystallized c-axis preferred oriented bismuth titanate thin films and a dielectric permittivity of 30, a Pr of 2.5 μ C/cm² and an Ec of 55 kV/cm for c-axis oriented lead germanate thin films. The polarization switching behavior in biaxial and uniaxial systems was strongly dependent on the orientation of the films while the multiaxial system was insensitive to film orientation.