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 εr = 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.