ALD preparation of high-k HfO₂ thin films with enhanced energy density and efficient electrostatic energy storage

High-k dielectric HfO₂ thin films with a predominant monoclinic phase were prepared by atomic layer deposition (ALD). The annealed HfO₂ films exhibited a large dielectric constant, of up to ε_r = 26 with a high breakdown field of over 4000 kV cm⁻¹. The best performance with a maximum recoverable energy density of 21.3 J cm⁻³ and energy efficiency of 75% was obtained with the 63 nm HfO₂ films. In addition, a well-defined temperature dependence of the energy storage properties from room temperature to 150 °C was demonstrated, indicating a stable energy density variation between 11.0 and 13.0 J cm⁻³ with a high energy efficiency of about 80%. These achievements provide a platform for synthesizing high-k dielectric thin films with enhanced energy densities and efficiencies.