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

Abstract

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 (E_T) 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, E_T 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.