In this work, thick BiFeO₃ films (~1 μm) were prepared on LaNiO₃-buffered (111)Pt/Ti/SiO₂/(100)Si substrates via radio-frequency magnetron sputtering without post-growth annealing. Effects of the substrate temperature on the film’s crystalline quality, defect chemistry, as well as the associated electrical properties were investigated. In contrast to the poorly crystallized BiFeO₃ film deposited at 300 °C and the randomly-oriented & (111)-textured films deposited at 500 °C & 650 °C, respectively, a (001)-preferred orientation was achieved in the BiFeO₃ film deposited at 350 °C. Such a film not only showed a dense, fine-grained morphology, but also displayed enhanced electrical properties due to the (001) texture and an improved defect chemistry. These properties include a reduced leakage current (J ~ 2.4´10⁻⁵ A/cm² @ 200 kV/cm), a small dielectric constant (ε_r ~ 243-217) with a low loss (tand ≤ 0.086) measured from 100 Hz to 1 MHz, and an nearly-intrinsic remnant polarization P_r ~ 60 μC/cm². A detailed TEM analysis confirmed the R3c symmetry of the BFO films and hence ensured a good stability of their electrical properties. Particularly, single-beam cantilevers fabricated from the BiFeO₃/LaNiO₃/Pt/Ti/SiO₂/Si heterostructures showed an excellent electromechanical performance, including a large transverse piezoelectric coefficient e_31,f ~ ‒2.8 C/m², a high figure of merit parameter ~4.0 GPa, and a large signal-to-noise ratio ~1.5 C/m². An in-depth analysis revealed the intrinsic nature of the e_31,f piezoelectric coefficient, which is well fitted along a straight line of (e_31,f)_ratio = (P_r×e_r)_ratio with the representative results in the literature. These high-quality lead-free piezoelectric films processed with a reduced thermal budget can open up many possibilities for the integration of piezoelectricity into Si-based micro-electromechanical systems (MEMS).

Antiferroelectric PbZrO₃ (AFE PZO) films have great potential to be used as the energy storage dielectrics due to the unique electric field (E)-induced phase transition character. However, the phase transition process always accompanies a polarization (P) hysteresis effect that induces the large energy loss (W_loss) and lowers the breakdown strength (E_BDS), leading to the inferior energy storage density (W_rec) as well as low efficiency. In this work, the synergistic strategies by doping smaller ions of Li⁺–Al³⁺ to substitute Pb²⁺ and lowering the annealing temperature (T) from 700 to 550 ℃ are proposed to change the microstructures and tune the polarization characters of PZO films, except to dramatically improve the energy storage performances. The prepared Pb_(1−x)(Li_0.5Al_0.5)_xZrO₃ (P_(1−x)(L_0.5A_0.5)_xZO) films exhibit ferroelectric (FE)-like rather than AFE character once the doping content of Li⁺–Al³⁺ ions reaches 6 mol%, accompanying a significant improvement of W_rec of 49.09 J/cm³, but the energy storage efficiency (η) is only 47.94% due to the long-correlation of FE domains. Accordingly, the low-temperature annealing is carried out to reduce the crystalline degree and the P loss. P_0.94(L_0.5A_0.5)_0.06ZO films annealed at 550 ℃ deliver a linear-like polarization behavior rather than FE-like behavior annealed at 700 ℃, and the lowered remanent polarization (P_r) as well as improved E_BDS (4814 kV/cm) results in the superior W_rec of 58.7 J/cm³ and efficiency of 79.16%, simultaneously possessing excellent frequency and temperature stability and good electric fatigue tolerance.