Enhanced electromechanical performance of Ag/HfO2/Ag multilayer thin film by surface patterning for lead free piezoelectric energy harvesting
Abstract
The development of lead-free piezoelectric energy harvesters for low-frequency vibration environments requires simultaneous selection of material, substrate, and structural characteristics. In this work, Ag/HfO2/Ag multilayer thin-film piezoelectric energy harvesters were fabricated on brass, aluminium, and copper substrates using electron-beam physical vapour deposition, with patterned and non-patterned configurations investigated to determine the influence of substrate selection and surface geometry. Structural morphology, wettability, and electrical characteristics were evaluated using x-ray diffraction, field-emission scanning electron microscopy, atomic force microscopy, contact-angle, I–V, and C–V measurements. Finite-element simulations were performed using COMSOL Multiphysics to investigate resonance characteristics, stress distribution, electric potential, electric-field intensity, and frequency-dependent response, followed by experimental vibration validation. At 1 g excitation, surface patterning increased the simulated voltage by 15.04%, 11.85%, and 42.57% for Brass, Al, and Cu, respectively. Patterning also reduced the simulated resonance frequency by 8.06%, 8.47%, and 14.08% for Brass, Al, and Cu, respectively. The patterned Ag/HfO2/Ag/Brass device exhibited the highest experimental voltage of 591.3 mV at 72 Hz, and the maximum simulated electric potential reached 576.8 mV at 74.1 Hz at 1 g excitation. The simulation–experiment resonance-frequency deviations remained below approximately 6.1%, while voltage deviations were within approximately 2.5%–10.9%. The substrate-dependent response is attributed to differences in substrate stiffness and density, which modify the effective mass–stiffness characteristics and strain transfer to the HfO2 layer, while surface patterning redistributes the mechanical stress and alters the effective structural stiffness, thereby enhancing the electromechanical response and shifting the resonance frequency.