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 interest. 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 is also incompatible with the integration process. In this study, we address this problem by creating a large field-induced polarization (~55.8 μC/cm²) in BaTiO₃ films sputter-deposited on Si at 200 °C via a buffer-layer technique. This large polarization led to a high energy density and efficiency (W_rec ≈ 94.7 J/cm³, η ≈ 78.2%@4 MV/cm). The thickness of LaNiO₃ buffer layer was revealed to be the key factor determining the electric polarization (remnant and field-induced ones). A 50 nm LaNiO₃ thickness, corresponding to the aforementioned polarization and energy storage performance, not only ensures proper crystallization in the BaTiO₃ film, but also leads to an optimal combination of polycrystalline grains with a high dielectric constant. The latter accounts for the majority of the field-induced polarization. Our results revealed the key role of a buffer layer in tuning the microstructure of a low-temperature deposited ferroelectric oxide film. Furthermore, the excellent charge/energy storage performance of these 200 °C-deposited BaTiO₃ films has provided many opportunities for this simple dielectric in microelectronics.