Energy storage performance of ferroelectric ZrO2 film capacitors: effect of HfO2:Al2O3 dielectric insert layer

Abstract

The present work reports for the first time, the employment of ferroelectric ZrO₂ films as energy storage capacitors utilized in pulsed power systems. Furthermore, the effect of insertion of a low permittivity dielectric HfO₂:Al₂O₃ (HAO) layer, with a thickness ranging from 2 to 8 nm, on the tunability of ferroelectric and energy storage characteristics of ZrO₂ films is assessed. The increase in thickness of the HAO layer gave rise to distorted ferroelectric loops with decreased polarization, coercive field, and hysteresis loss of the films. These results are correlated with the depolarization field induced by the insertion of the dielectric HAO layer. An optimum combination of high energy density of 54.3 J cm⁻³ and good storage efficiency of 51.3% are obtained for the ZrO₂ film capacitors with 2 nm-thick HAO insert layer. These values correspond to an increase of ∼55% and ∼92%, from the respective values of pure ZrO₂ film capacitors. In addition, the HAO/ZrO₂ films showed a good fatigue endurance of energy storage performance over 10⁹ electric field cycles. The energy storage density obtained from HAO(2 nm)/ZrO₂ film capacitor is found to be higher than that reported for several Pb-based as well as Pb-free ferroelectric ceramic films with complex compositions. The present study demonstrates that simple binary oxides such as ZrO₂ with ferroelectric behavior could be potential candidates for developing high performance energy storage capacitors.