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Non-Lead Based Piezoelectric Thin Films: Materials and Energy Harvesting Device
Keywords: Lead-free piezoelectric films, Sol-gel processing, Energy harvesting device
Piezoelectric materials are of importance due to their high energy-conversion efficiency, in particular from mechanical energy into electrical energy, and vice versa. In recent years, there has been a growing interest in microelectromechanical system (MEMS) piezoelectric vibration energy harvesting due to advances in low power digital signal processors. While many research groups have focused on the study of bulk prototypes of piezoelectric energy harvesting, only a few groups have demonstrated MEMS devices capable of generating useful power. Among many piezoelectrics, PZT films have been considered the most promising candidates for the piezoelectric MEMS energy harvesting devices since they can produce high mechanical strain under applied electric field and large output power. However, recently new piezoelectric materials are urgently required to replace PZT system, for which the toxicity of the lead component is a major concern. In this work, we propose to develop thin film-based piezoelectric materials from the promising sodium potassium niobate tantalate (K,Na)(Nb,Ta)O3–based system instead of conventional PZT system. We thoroughly investigated MEMS piezoelectric energy harvester both theoretically and experimentally using lead-free thin films. First, a macroscopically-verified modal model based on electromechanical coupling and beam dynamics is used to not only propose a power-optimized design of a microscale mechanical piezoelectric vibration energy harvester device, but also to simulate the device performances. Additionally, in order to obtain a high-quality piezoelectric thin-film, sol-gel processing conditions for lead-free piezoelectric thin films are considered through the analysis of material properties. Then, based upon the optimal parameters from modeling and material property analysis, a (K,Na)(Nb,Ta)O3–based piezoelectric cantilevered energy harvesting device with a proof mass is micromachined and the performance of the device is experimentally evaluated. Progress on fabrication and testing of a lead-free piezoelectric thin film MEMS harvester is also discussed along with device performance improvements.
Seung-Hyun Kim, Professor / Vice President
Brown University / INOSTEK Inc.
Providence, RI

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