Improvement of the properties of CSD-processed (Pb_0.76Ca_0.24)TiO₃ thin films by control of the solution chemistry

Abstract

Ferroelectric (Pb_0.76Ca_0.24)TiO₃ thin films were prepared on platinized Si substrates by chemical solution deposition (CSD). Two different synthetic strategies were adopted to optimize the functionality of the resulting perovskite films: (1) tailoring the schedule of the solution synthesis and (2) chemical selectivity of the calcium precursor. The choice of an appropriate synthetic procedure led to homogeneous sols constituted by a single distribution of particles, as revealed by dynamic light scattering (DLS). Stronger polymeric structures in the sol network are believed to prevent atomic diffusion of metal cations during crystallization at higher temperatures, and perovskite films with a uniform compositional profile and without any detrimental interface with the electrode were measured by Rutherford backscattering spectroscopy (RBS). On the other hand, phase formation and microstructure of crystalline films were strongly affected by the calcium compound used, i.e. calcium acetate or calcium acetylacetonate. The single decomposition mechanism of the last one, with absence of intermediate carbonates, resulted in the prompt crystallization of the perovskite phase (375°C) and an enhanced grain-growth mechanism that led to dense films formed by larger grains. Consequently, the optimized ferroelectric (Pb_0.76Ca_0.24)TiO₃ films showed superior electrical properties: maximum values of dielectric constant nearly doubled and a relative increase in the remanent polarization being ∼40% (P _r =23 µC/cm²). The potential application of these films in functional microelectronic devices is also demonstrated.