Grain engineering of high energy density BaTiO₃ thick films integrated on Si

Abstract

Ferroelectric (FE) ceramics with a large relative dielectric permittivity and a high dielectric strength have the potential to store or supply electricity of very high energy and power densities, which is desirable in many modern electronic and electrical systems. For a given FE material, such as the commonly-used BaTiO₃, a close interplay between defect chemistry, misfit strain, and grain characteristics must be carefully manipulated for engineering its film capacitors. In this work, the effects of grain orientation and morphology on the energy storage properties of BaTiO₃ thick films were systematically investigated. These films were all deposited on Si at 500 °C in an oxygen-rich atmosphere, and their thicknesses varied between ~500 nm and ~2.6 μm. While a columnar nanograined BaTiO₃ film with a (001) texture showed a higher recyclable energy density W_rec (81.0 J/cm³ vs. 57.1 J/cm³ @3.2 MV/cm, ~40% increase) than that of a randomly-oriented BaTiO₃ film of about the same thickness (~500 nm), the latter showed an improved energy density at a reduced electric field with an increasing film thickness. Specifically, for the 1.3 μm and 2.6 μm thick polycrystalline films, their energy storage densities W_rec reached 46.6 J/cm³ and 48.8 J/cm³ at an applied electric field of 2.31 MV/cm (300 V on 1.3 μm film) and 1.77 MV/cm (460 V on 2.6 μm film), respectively. This ramp-up in energy density can be attributed to increased polarizability with a growing grain size in thicker polycrystalline films and is desirable in high pulse power applications.

Keywords

Energy storage / ferroelectric / grain engineering / BaTiO₃ / film capacitors / Si

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