Ferroelectric property of an epitaxial lead zirconate titanate thin film deposited by a hydrothermal method

Deposition of thin films via hydrothermal method has various advantages: low deposition temperature, high purity, deposition on a three-dimensional structure, and a large thickness. Although an epitaxial lead zirconate titanate (PZT) thin-film deposition has been reported, the ferroelectric measurement has not been conducted due to the peel-off morphology of the film. The current paper investigates the improvement of an epitaxial PZT thin film deposited via a hydrothermal method. By adjusting the position at which the substrate was suspended in the solution, smooth morphology surface was successfully obtained. As a bottom electrode, a 200-nm SrRuO₃ thin film was deposited on SrTiO₃ single crystals, and the PZT thin film was deposited on SrRuO₃. The remanent polarization 2Pr and coercive electric field for PZT on SrRuO₃/SrTiO₃ (001) were 17.1 μC/cm² and 36 kV/cm, respectively, and those of PZT on SrRuO₃/SrTiO₃ (111) were 32.7 μC/cm² and 59 kV/cm, respectively. The reason for large imprint electrical field, 91 kV/cm and 40 kV/cm for each film, was unclear at this stage, although it is associated with self-alignment poling direction. This self-alignment poling direction was confirmed via scanning nonlinear dielectric microscopy and is thought to have been related to the deposition mechanisms.