Combination of solid state and electrochemical impedance spectroscopy to explore effects of porosity in sol-gel derived BaTiO3 thin films

BaTiO3 thin films were deposited onto polycrystalline Pt using a dip-coating technique, with annealing temperatures of 750 to 900 °C. To avoid film imperfections such as cracking or regions of zero BaTiO3 coverage (pinholes), key conditions, including aging periods, water content, and spin velocities, were refined to produce a pinhole free, uniform films with some porosity. Whilst those coated a single time short circuited during electrical characterization, this could be avoided in films produced by multiple coating cycles. The relative permittivity of a 600 nm BaTiO3 film was measured at 290 by fitting solid state impedance data in the frequency range 100 Hz to 1 MHz. Electrochemical impedance with an aqueous electrolyte allowed evaluation of the porosity, which remained fairly constant between one and five coating cycles. Using this method it was possible to estimate the relative permittivity of the BaTiO3 itself as 374 and hence to evaluate the increase in the relative permittivity that could be achievable by minimizing porosity