Femtosecond-Laser-Enabled Geometric Microengineering of PZT Films for Boosted Piezoelectric Response and Rainfall Monitoring Demonstration

Geometric microengineering of the active layer in a piezoelectric sensor has emerged as a hot topic to improve performance but meets challenges due to the brittle nature of piezoelectric ceramics. Here, we demonstrate that fs-laser-induced compressive stress leads to film bulging in the nanoscale and forms various shapes of nanostructures, including nanobumps, nanovolcanoes, and nanocaves on Pb_1.1Zr_0.52Ti_0.48O₃ (PZT) films, in a single-step, mask-free, large-scale, and rapid fashion. Highly reproducible 3D profiles of the nanostructures are finely controlled by carefully adjusting the laser energy density around the ablation threshold. Evaluation of piezoelectric response to external pressure pulses shows that the PZT films patterned with 450 nm high nanobumps exhibit a 30% increase in output voltage compared to flat PZT films. In a rainfall monitoring test, the PZT films patterned with 450 nm high nanobumps show a significantly enhanced response with varying rain droplet volumes and falling frequencies. Geometric microengineering of PZT films using a femtosecond laser direct writing route provides a guideline for material design in a wide range of microsensor applications.