Co:BaTiO₃/Sn:BaTiO₃ Heterostructure Thin‐Film Capacitors with Ultrahigh Energy Density and Breakdown Strength

Abstract Ferroelectric (FE) capacitors exhibiting ultrahigh power densities are widely utilized as electrostatic energy storage devices in pulsed electronic devices. One approach to maximize the discharge energy density ( U d ) of capacitors is to increase the breakdown strength ( E b ) accompanied with high maximum polarization ( P m ) while suppressing the energy loss. However, the inverse relationship between E b and P m challenges the simultaneous enhancement of E b and U d . To overcome this limitation, FE/relaxor FE (RFE) heterostructure capacitors composed of Co‐doped BaTiO 3 (BTCO) and Sn‐doped BaTiO 3 (BTS) epitaxial thin film layers to decouple the E b and P m values are fabricated and the simultaneous enhancement of the E b and U d up to 7.9 MV cm −1 and 117 J cm −3 , respectively is achieved. The high E b and U d values can be attributed to the suppression of the leakage current at the BTCO/BTS interface, a narrower hysteresis loop contributed by the BTS, and high P m and E b from the BTCO layer. Additionally, the BTCO/BTS heterostructure capacitors exhibit excellent fatigue endurance of up to 10 8 cycles and are thermal stable even at 160 °C. Through properly designing the FE and RFE layers, thermally stable and reliable FE/RFE heterostructure capacitors exhibiting high U d and E b can be realized.