Achieving a large field-induced polarization and energy density in BaTiO₃ films sputter-deposited on Si at 200 °C via a buffer-layer technique

Ferroelectric oxide films with a large field-induced polarization can be used in dielectric capacitors for charge or energy storage in microelectronic systems, and hence have attracted intense research interests. A high processing temperature is usually required to produce a well-crystallized polar phase and hence a large polarization in the film, corresponding to a high charge or energy density. However, high processing temperature not only reduces the charge-discharge efficiency by producing a sizable remnant polarization, but also is incompatible with the integration process. In this study, we address this problem by creating a large field-induced polarization (~55.8 mC/cm²) in BaTiO₃ films sputter-deposited on Si at 200 ^oC via a buffer-layer technique. Such a large polarization has led to a high energy density and efficiency (W_rec~94.7 J/cm³, h~78.2% @ 4 MV/cm). The thickness of the LaNiO₃ buffer layer was revealed to be the key factor determining the electric polarizations (remnant and field-induced ones). A 50 nm LaNiO₃ thickness, corresponding to the aforementioned polarization and energy storage performance, not only ensures a proper crystallization in the BaTiO₃ film, but also leads to an optimal combination of the polycrystalline grains with regard to a high dielectric constant. The latter accounts for the majority part of the field-induced polarization. Our results have revealed the key role played by a buffer layer on tuning the microstructure of a low-temperature deposited ferroelectric oxide film. Furthermore, the excellent charge/energy storage performances of these 200 ^oC-deposited BaTiO₃ films have opened up many opportunities for this simple dielectric in microelectronics.