MEMS Scale PVDF-TrFE-Based Piezoelectric Energy Harvesters

This paper presents the design, the fabrication, and the performance characterization of microelectromechanical systems (MEMS) scale cantilever-type piezoelectric energy harvesters (PEHs) that utilize the piezoelectric polymer polyvinylidene fluoride-trifluoroethylene (PVDF-TrFE). Ranges are determined for device dimensions according to the calculations based on mathematical models. Designed devices were fabricated using standard MEMS fabrication techniques. Electrodes were formed with sputtered Al and Ti/Al thin films, and a 1.3-μm-thick PVDF-TrFE film was deposited using spin coating. Cantilevers were suspended using a two-step process: backside DRIE to perform the bulk etch, followed by XeF₂ gaseous etch for the final release. Remnant polarization and coercive field of the fabricated devices were measured as 6.1 μC/cm² and 74.9 V/μm, respectively. Piezoelectric performances were evaluated by a press-and-release type of measurement. For these measurements, custom-made probe tips attached to micropositioners were used. Based on the experimental results, maximum power output was calculated as 35.1 pW for a peak tip displacement of 500 μm from a 1200 μm × 300 μm cantilever, which corresponds to a power output density of 97.5 pW/mm². The proposed method has the potential to create the PEHs that are monolithically integrated with complementary metal-oxide-semiconductor circuits and lead to self-sustained low power electronics.