Interface electron polarization based high-k Al₂O₃/ZnO nanolaminates with excellent temperature stability and ultrahigh energy-storage density by atomic layer deposition

Recently, high dielectric constant (high-k) materials have attracted considerable attention owing to their much better energy storing and charge controlling capability than common dielectrics, and are considered necessary for achieving high energy-storage density (ESD) and further down-scaling of electronics and integrated-circuits. However, their high permittivity suffers from severe degradation with decreasing temperature due to the large activation energy (ET) for polarization processes (0.2–1 eV) over thermal energy (0.026 eV). This is especially serious at higher frequencies owing to the temperature–frequency “reciprocity” in dielectrics, which greatly restricts the working temperature/frequency range of high-k materials and the device reliability. In this work, high-k nanolaminates consisting of alternating Al₂O₃/ZnO sublayers (AZ-NLs) are obtained by artificially constructing an insulating-“boundaries”/semiconducting-“grains” microstructure as in CaCu₃Ti₄O₁₂-type dielectrics, in which free electrons are employed as the primary polarization charges, instead of ions or polarons. Benefitting from the small migration barrier of electrons, ET in AZ-NLs can be reduced to nearly zero (∼10⁻³ eV), leading to greatly superior temperature/frequency stability. Particularly, the optimized AZ-NLs demonstrate a high permittivity of ∼800 with maximal relative change < 12% in the temperature range 25 °C ± 80 °C for all the testing frequencies from 100 Hz to above 1 MHz. Furthermore, the AZ-NLs have a maximal ESD of 221.4 J cm⁻³ at 2.5 MV cm⁻¹ and can maintain an ESD of 141.7 J cm⁻³ at 2 MV cm⁻¹ without detectable degradation after 1 × 10⁶ charge–discharge cycles, in comparison with the typical value of 10–50 J cm⁻³ for ferroelectrics. The outstanding dielectric performances, combined with excellent scalability and facile synthesis, endow AZ-NLs with great application potential in widespread electronic and energy-storage devices.