High Energy-Storage Density in Ferroelectric La:HfO2-Based Thin-Film Capacitors

Abstract Ferroelectric and antiferroelectric hafnium and zirconium oxides have attracted considerable attention for the development of next-generation energy-storage capacitors owing to their high energy-storage density (ESD), high power density, moderately high efficiency (η), and scalability down to the ultrathin limit. Most research on dielectric energy-storage capacitors focuses on antiferroelectric hafnium oxide- and zirconium oxide-based capacitors, while ferroelectric hafnium oxide-based capacitors have been less extensively investigated. This work highlights the enhancement of the energy-storage characteristics of epitaxial ferroelectric orthorhombic lanthanum-doped hafnium oxide-based two-dimensional capacitors by introducing a thin dielectric amorphous alumina capping layer. It is revealed that the inclusion of a dielectric layer influences both the ESD and η of the fabricated capacitors due to the increased depolarization effect resulting from the presence of the alumina layer. The best balance between ESD and η is achieved through the insertion of a 2.3 nm-thick alumina layer, providing an ultra-high ESD of 142 J/cm3, with an η of 69% for an electric field of 7.7 MV/cm. Additionally, the capacitor displays an ESD greater than 120 J/cm3 after 106 cycles and a stable performance up to 120 °C. Therefore, this work foresees the potential of ferroelectric epitaxial hafnium oxide-based capacitors in energy-storage technologies.