Femtosecond-Laser-Enabled\nGeometric Microengineering\nof PZT Films for Boosted Piezoelectric Response and Rainfall Monitoring\nDemonstration

Geometric microengineering of the active layer in a piezoelectric\nsensor has emerged as a hot topic to improve performance but meets\nchallenges due to the brittle nature of piezoelectric ceramics. Here,\nwe demonstrate that fs-laser-induced compressive stress leads to film\nbulging in the nanoscale and forms various shapes of nanostructures,\nincluding nanobumps, nanovolcanoes, and nanocaves on Pb<sub>1.1</sub>Zr<sub>0.52</sub>Ti<sub>0.48</sub>O<sub>3</sub> (PZT) films, in a\nsingle-step, mask-free, large-scale, and rapid fashion. Highly reproducible\n3D profiles of the nanostructures are finely controlled by carefully\nadjusting the laser energy density around the ablation threshold.\nEvaluation of piezoelectric response to external pressure pulses shows\nthat the PZT films patterned with 450 nm high nanobumps exhibit a\n30% increase in output voltage compared to flat PZT films. In a rainfall\nmonitoring test, the PZT films patterned with 450 nm high nanobumps\nshow a significantly enhanced response with varying rain droplet volumes\nand falling frequencies. Geometric microengineering of PZT films using\na femtosecond laser direct writing route provides a guideline for\nmaterial design in a wide range of microsensor applications.