Achieving an ultra-high capacitive energy density in ferroelectric films consisting of superfine columnar nanograins

Well-crystallized perovskite ferroelectric films usually display a bulk-like polarization response (P) under an external electric field (E), i.e., a large P-E hysteresis loop featuring a sizable remnant polarization and an early polarization saturation. Such characteristics are undesirable for capacitive energy storage applications. In this work, we demonstrate an optimal P-E behavior, i.e., a small remnant polarization and a delayed polarization saturation, in perovskite BaTiO3 films consisting of superfine columnar nanograins. In a low-temperature, nucleation-dominated sputtering deposition, an in-situ grown conducive buffer layer promotes the formation of these nanograins, which display a controllable diameter down to similar to 10 nm and extend throughout the film thickness. The deterioration of the remnant polarization and its delayed saturation under an electric field, can be attributed to a strong polarization-constraining effect from the densely-packed, non-ferroelectric grain boundaries, which is supported by a phase field modeling simulation. The resulted BaTiO3 film capacitors integrated on Si at 350 degrees C display a high recyclable energy density (W-rec similar to 135 +/- 10 J/cm(3)) and efficiency (eta similar to 80%+/- 4%) which are thickness-scalable. An intrinsically high power density, a simple and stable chemical composition, and good thermal (-150 degrees C similar to 170 degrees C) and cycling stabilities (up to similar to 2 x 10(8) charge-discharge cycles) warrant a broad range of applications for these film capacitors.