Enhancing Sensitivity of Flexible Piezoelectric Thin-Film Acoustic Sensors via Buffer Layer Engineering for Insulation Health Monitoring of Power Cables

Partial discharge (PD) detection is critical for evaluating insulation degradation in high-voltage power cables. Flexible piezoelectric acoustic sensors offer a compelling solution owing to their conformability to curved surfaces and strong immunity to electromagnetic interference. However, conventional piezoelectric thin films typically suffer from low sensitivity due to the intrinsic trade-off between piezoelectric coefficient (d₃₃) and dielectric constant (ε_r). In this work, a TiO₂ buffer layer is introduced to engineer Pb(Zr_0.52Ti_0.48)O₃ (PZT) thin films with significantly enhanced performance. The 266 nm TiO₂ buffer layer is prepared by the sol-gel method. The TiO₂ layer reduces ε_r from 650 to 150 at the frequency of ≈100 kHz, promotes refined grain, a self-poled state, and strong (100) texture, and increases d₃₃ from 45 to 160 pm V⁻¹, resulting in an estimated ultrahigh piezoelectric voltage constant g₃₃ of 124 mV·m·N⁻¹. The fabricated flexible sensor exhibits a wide frequency response up to 600 kHz with an average sensitivity of 65 dB and peak sensitivity exceeding 70 dB. It captures high-resolution acoustic signals of PD events in a 110 kV power cable, outperforming both unmodified PZT and commercial PVDF sensors. Long-term and thermal stability evaluations confirm excellent durability. This study presents a robust strategy for tuning piezoelectric thin-film properties via interface engineering and demonstrates the potential of TiO₂-buffered PZT sensors for advanced acoustic sensing in power equipment insulation health monitoring applications.