Improving energy density of crystalline–amorphous multilayer films deposited on Ti foils by structural modulation

Abstract Dielectric capacitors are one of the most important energy‐storage components specifically used for various high‐power pulse applications. However, the low energy‐storage density ( U _e ) of dielectrics used today limits their application. In this study, crystalline–amorphous multilayer films of crystalline Sr _0.85 Bi _0.1 TiO ₃ (SBT)/amorphous SBT/amorphous Al ₂ O ₃ (S _c –(8−n)S _a –nA _a ) were fabricated on flexible Ti foils using the sol–gel method. An enhancement in energy density was achieved by adjusting the thicknesses of the amorphous SBT and Al ₂ O ₃ (AO) layers. The crystalline SBT layer contributes to an increase in the dielectric constant and the amorphous AO layer to an increase in the breakdown strength. Moreover, the AO layers that are inserted are capable of suppressing the leakage current by eliminating the space charge limited conductance mechanism and thereby effectively decreasing the probability of breakdown of the SBT layers. A lower leakage current and higher breakdown strength can be further achieved using an Al electrode instead of the Au electrode. A large energy density of 27.2 J cm ⁻³ can be realized via the crystalline–amorphous multilayer films with the Al electrode, which represents an enhancement of ~234% over that of the amorphous SBT film (8.14 J cm ⁻³ ). In addition to the high energy‐storage enhancement, this study also presents a promising method that can be used to fabricate flexible multilayer films for lightweight and high energy density applications and for devices used to service high‐temperature conditions.