Leveraging the integration of perovskite BaTiO3 on ferroelectric fluorite HfO2 to enhance energy storage cyclability and efficiency

Perovskite relaxor ferroelectrics and antiferroelectrics have been the workhorse materials for energy storage electrostatic devices. Recently, there has been growing interest in ferroelectric HfO 2 , which is highly compatible with fabrication processes of the electronics industry and scalable down to the ultrathin limit. However, wake-up and fatigue phenomena in ferroelectric HfO 2 can limit the stability of energy storage capacity upon cycling. Interface engineering using simple A x O y (Ir, Ce, Ru, Al, La and Zr) binary oxides as capping layers is a promising strategy to mitigate these effects, but previous works have focused on optimizing high remanent polarization for memory applications. In contrast, for energy storage applications, the optimal parameters differ from those required for memory devices. Therefore, alternatives to A x O y capping layers must be investigated. Here, we demonstrate that the integration of the perovskite ferroelectric BaTiO 3 with the fluorite ferroelectric Hf 0.5 Zr 0.5 O 2 yields highly stable energy storage density and enhanced efficiency over cycling and at high temperatures. We study a set of samples combining epitaxial Hf 0.5 Zr 0.5 O 2 grown on Si(001) with polycrystalline BaTiO 3 of various thicknesses. The ferroelectricity of Hf 0.5 Zr 0.5 O 2 is preserved and the efficiency is enhanced without compromising the high breakdown voltage. The device performance is optimal for a BaTiO 3 thickness of 10 nm, exhibiting an energy storage density of 100 J/cm 3 , efficiency of 80% and breakdown field of 12 MV/cm. We attribute this remarkable performance to the distinct electrical properties of BaTiO 3 compared with previously investigated A x O y capping layers. The investigations are carried out on a system that combines memory and energy storage properties, enabling the design of prospective devices in which energy recovery and memory functionalities are integrated at the chip level. • BaTiO 3 has been successfully integrated on epitaxial BaTiO 3 grown on silicon. • Energy storage density 100 J/cm 3 , efficiency of 80% and breakdown field of 12 MV/cm are achieved. • A stable energy storage density of ≈25 J/cm 3 is maintained over 10 9 cycles. • Both the energy storage density and efficiency can be tuned by controlling the BaTiO₃ layer thickness.