Comparison of lead zirconate titanate (PZT) thin films for MEMS energy harvester with interdigitated and parallel plate electrodes

PZT thin films on insulator buffered silicon substrates with interdigitated electrodes (IDEs) have the potential to harvest more energy than parallel plate electrode (PPE) structures, because IDE structures exploit the longitudinal piezoelectric effect, which is about twice as high as the transverse piezoelectric effect exploited with PPE structures. There are only few studies on PZT IDE structures and their piezoelectric properties, and even no studies with a direct experimental comparison of the two options. The biggest challenge in using PZT with IDE structures are texture control on insulating buffer layers, and efficient poling at higher electrode gaps. Still, IDE structures are better suited for energy harvesting application as they can generate higher voltages with the same strain. We have proposed a figure of merit (FOM) for easy comparison with similar parallel plate electrode (PPE) structures. Our FOM corresponds to twice the energy density stored per unit strain deformation. For 1 μm random PZT on titania buffered silicon, a FOM of 1.26 × 10¹⁰ J/m³ and 12.9 mV/μ strain was achieved when compared to 1.03 × 10¹⁰ J/m³ and 1.14 mV/μ strain for highly oriented, well poled 1 μm PZT with PPE system.