High Energy Storage Performance of Nanometer-Thick Al-Doped ZrO₂ Films with Antiferroelectricity for Electrostatic Capacitors

Electrostatic capacitors (ESCs) have received considerable attention owing to their rapid charge–discharge rates and ultrahigh power density. However, because ESCs have a very low energy storage density (ESD) compared with electrochemical capacitors or batteries, it is necessary to enhance their energy storage density for practical utilization. To increase the energy storage density, it is critical to enable operation at high electric fields by suppressing the leakage current. Therefore, this study focuses on enhancing the energy storage performance by controlling the leakage current through Al doping of nanoscale ZrO2 films with antiferroelectricity. Incorporating Al into ZrO2 thin films suppressed the leakage current, allowing them to operate in a higher electric-field region. Consequently, the energy storage performance of the Al-doped ZrO2 thin films was significantly better than that of pure ZrO2. Especially, a 7 nm-thick Al-doped ZrO2 thin film exhibited an excellent efficiency of approximately 70% at ESD values of above 60 J/cm3, with a maximum of 110 J/cm3. Furthermore, although the ESD decreased slightly as the temperature increased, it was sustained for up to 109 cycles without a hard breakdown. Therefore, Al-doped ZrO2 thin films can be applied as materials for next-generation nanoscale energy-storage devices.