In this work, dielectric ultracapacitors were designed and fabricated using the combination of the phase boundary and nanograin strategies. Such ultracapacitors are based on submicron-thick Ba(Zr_0.2Ti_0.8)O₃ ferroelectric films sputter-deposited on Si at 500 ℃. With a composition near a PPB, a compressive strain and a high nucleation rate due to the lowered deposition temperature, these films exhibit a columnar nanograined microstructure with gradient phases along the growth direction. Such a micro-structure presents three-dimensional polarization inhomogeneities on a nanoscale, thereby significantly delays the saturation of the overall electric polarization. Consequently, a pseudo-linear, ultra-slim polarization-electric field hysteresis loop was obtained, featuring a high maximum applicable electric field (~5.7 MV/cm), a low remnant polarization (~5.2 μC/cm²) and a high maximum polarization (~92.1 μC/cm²). Such a P-E loop corresponds to a high recyclable energy density (W_rec~208 J/cm³) and charge-discharge efficiency (~88%). An in-depth electron microscopy study revealed that the gradient ferroelectric phases consist of tetragonal (T) and rhombohedral (R) polymorphs along the growth direction of the film. The T-rich phase is abundant near the bottom of the film and gradually transformed into the R-rich one near the surface. These films also exhibited a high Curie temperature of ~460 ℃ and a stable capacitive energy storage up to 200 ℃. These results suggest a feasible pathway for design and fabrication of high-performance dielectric film capacitors.

The aerosol deposition (AD) method utilizes high kinetic-energy submicron powders to impact and form a film on a substrate. It is a highly efficient deposition method, capable of producing films or coatings with a strong interfacial bonding and a dense nano-grain structure without thermal assistance. In this work, PbZr_0.53Ti_0.47O₃ (PZT53/47) films (~1.2 μm thick) were deposited on Pt/Ti/Si(100) substrates via the AD method. After a conventional annealing process (700 °C for 1 h), these PZT53/47 films displayed a dense, crack-free, nano-grained morphology, corresponding to an optimal electrical performance. A large maximum polarization (P_max = 70 μC/cm²) and a small coercive field (E_c = 104 kV/cm) were achieved under the maximum applicable electric field of 1.6 MV/cm. The PZT53/47 films also exhibited a large small-field dielectric constant of ~984, a high tunability of 72%, and a low leakage current of ~3.1 × 10⁻⁵ A/cm² @ 40 V. Moreover, the transverse piezoelectric coefficient (e_31.f) of these AD-processed films was as high as −4.6 C/m², comparable to those of sputter-deposited PZT53/47 films. These high-quality PZT53/47 thick films have broad applications in piezoelectric micro-electromechanical systems.

BaTiO₃-based lead-free ferroelectric films with a large recoverable energy density (W_rec) and a high energy efficiency (η) are crucial components for next-generation dielectric capacitors, which are used in energy conditioning and storage applications in integrated circuits. In this study, grain-engineered (Ba_0.95,Sr_0.05)(Zr_0.2,Ti_0.8)O₃ (BSZT) ferroelectric thick films (~500 nm) were prepared on Si substrates. These films were deposited at 350 °C, 100 °C lower than the temperature at which the LaNiO₃ buffer layer was deposited on Pt/Ti. This method reduced the (001) grain population due to a weakened interface growth mode, while promoting volume growth modes that produced (110) and (111) grains with a high polarizability. As a result, these films exhibited a maximum polarization of ~88.0 μC/cm², a large W_rec of ~203.7 J/cm³, and a high energy efficiency η of 81.2% (@ 6.4 MV/cm). The small-field dielectric constant nearly tripled as compared with that of the same BSZT/LaNiO₃ heterostructure deposited at the same temperature (350 °C or 450 °C). The enhanced linear dielectric response, delayed ferroelectric polarization saturation, and increased dielectric strength due to the nano-grain size, collectively contributed to the improved energy storage performance. This work provides a novel approach for fabricating high-performance dielectric capacitors for energy storage applications.

In our previous work, epitaxial Ba(Zr_0.2Ti_0.8)O₃ thick films (~1–2 μm) showed an excellent energy storage performance with a large recyclable energy density (~58 J/cc) and a high energy efficiency (~92%), which was attributed to a nanoscale entangled heterophase polydomain structure. Here, we propose a detailed analysis of the structure–property relationship in these film materials, using an annealing process to illustrate the effect of nanodomain entanglement on the energy storage performance. It is revealed that an annealing-induced stress relaxation led to the segregation of the nanodomains (via detailed XRD analyses), and a degraded energy storage performance (via polarization-electric field analysis). These results confirm that a nanophase entanglement is an origin of the high-energy storage performance in the Ba(Zr_0.2Ti_0.8)O₃ thick films.

Integration of lead zirconate titanate (PZT) films on metallic substrates is important for flexible piezoelectric devices, but achieving highly textured crystallinity without detrimental interfacial diffusion or oxidation remains challenging. In this work, PZT thick films (~1.3 μm) were deposited on titanium substrates using radio-frequency magnetron sputtering at 400 °C followed by rapid thermal processing at 640 °C for 2.5 min. A conductive LaNiO₃ buffer layer was introduced to promote the nucleation of the perovskite phase and suppress interfacial degradation. The resulting PZT films on the LNO/Pt/Ti substrates exhibit a strong (001) preferred orientation and a dense microstructure. The films show a large remnant polarization P_r of ~61 μC cm⁻² and a low coercive field E_c of ~56 kV cm⁻¹ at 60 V, together with a dielectric constant ε_r of ~1350–1612 and a dielectric loss tanδ ≤ 0.06 in the frequency range of 1 kHz to 1 MHz. Patterned Pt/PZT/LNO/Pt/Ti cantilevers yield a transverse piezoelectric coefficient e_31,f of ~−6.7 C/m², significantly outperforming reported piezoelectric films deposited on Ti. These results demonstrate that controlled nucleation and rapid thermal crystallization enable highly textured PZT films on reactive metallic substrates, providing a viable route for flexible piezoelectric MEMS devices.

Integration of lead zirconate titanate (PZT) films on metallic substrates is important for flexible piezoelectric devices, but achieving highly textured crystallinity without detrimental interfacial diffusion or oxidation remains challenging. In this work, PZT thick films (~1.3 μm) were deposited on titanium substrates using radio-frequency magnetron sputtering at 400 °C followed by rapid thermal processing at 640 °C for 2.5 min. A conductive LaNiO₃ buffer layer was introduced to promote nucleation of the perovskite phase and suppress interfacial degradation. The resulting PZT films on LNO/Pt/Ti substrates exhibit a strong (001) preferred orientation and dense micro-structure. The films show a large remnant polarization Pr of ~61 μC cm^-2 and a low coercive field E_c of ~56 kV cm⁻¹ at 60 V, together with dielectric constants ε_r of ~1350–1612 and dielectric loss tanδ ≤ 0.06 in the frequency range of 1 kHz–1 MHz. Patterned Pt/PZT/LNO/Pt/Ti cantilevers yield a transverse piezoelectric coefficient e_31,f of ~ –6.7 C m^-2, significantly outperforming reported piezoelectric films deposited on Ti. These results demonstrate that controlled nucleation and rapid thermal crystallization enable highly textured PZT films on reactive metallic substrates, providing a viable route for flexible piezoelectric MEMS devices.