BaTiO₃–Ni Flexible Thin-Film Capacitor via Photoassisted Chemical Solution Deposition Retaining Pristine Ni Foil Elasticity and Hardness

The direct deposition of piezoelectric ceramic thin films onto metal foils has become a significant challenge due to the increasing demand for embedded decoupling capacitors, nanogenerators, and flexible piezo-sensors. However, traditional thermal sintering (TS) methods present several issues for metal foils, including alterations in mechanical properties, the formation of wrinkles, and the need for precise control over the sintering atmosphere to prevent oxidation. In this study, we successfully crystallized BaTiO3 on a Ni foil under atmospheric conditions, mitigating thermal damage to the foil through a hybrid-solution-incorporated photoassisted chemical solution deposition (HS-PCSD) method. This technique combines a hybrid solution of metal-organic compounds and nanoparticles with ultraviolet pulse laser irradiation. We examined the influence of varying chemical solution mixing ratios on the morphology of the crystallized films and achieved a highly crystalline, dense BaTiO3 film exhibiting excellent dielectric properties with a capacitance >1.0 μC cm-2 and a loss <0.075. Unlike Ni used in conventional TS capacitors, the Ni in our HS-PCSD flexible capacitors maintains the mechanical properties of the pristine foil, including elasticity and hardness. The dielectric properties of the capacitor remained unchanged after up to 2500 cycles of dynamic bending and after storage for up to 144 h at 85 °C and 85% RH, demonstrating excellent long-term stability. Our results demonstrate the potential of HS-PCSD in the fabrication of flexible electronic devices.