Dielectric and ferroelectric response of sol-gel derived Pb_0.85La_0.15TiO₃ ferroelectric thin films on different bottom electrodes

Abstract

Sol-gel derived Pb_0.85La_0.15TiO₃ thin films were deposited on Pt, Pt/Si, RuO₂/Pt/Si and RuO₂/Si bottom electrodes. The structural and microstructural characteristics of the films were studied using X-ray diffraction and atomic force microscopy techniques. Dielectric, ferroelectric and leakage current characteristics were evaluated and depth profile Auger electron spectroscopy was used to obtain direct evidence for reactivity and compositional changes at the film/electrode interface and determine their effect on the ferroelectric and dielectric properties of films. Films deposited on Pt electrode showed a relatively higher dielectric constant of approximately 1300, while the films on RuO₂ exhibited lower dielectric constant of only 470. J-t characteristics with leakage current of approximately 10^-8 A/cm² under low biasing field (10 kV/cm) was observed for the films under study. The steady state field dependent dc conductivity was examined by the measurement of J-E characteristics. At very low fields (<30 kV/cm) films followed ohmic behavior and was fitted with a space-charge-limited conduction mechanism in the intermediate fields (30-60 kV/cm). The on-set voltage for the non-linearity was considered as V_TFL using which, the trap concentration estimated for films on RuO₂/Si electrode was 1.23× 10¹⁷ cm^-3. Observed current characteristics have been correlated with large interfacial resistance at the film-electrode boundary. In the case of RuO₂ bottom electrodes, the dielectric and ferroelectric properties are correlated with the electrode characteristics and Si diffusion at the film-electrode interface.