Energy harvesters integrable on smart sensor systems have been strongly demanded. Horowitz et al. have recently reported on a MEMS acoustic energy harvester using a lead zirconate titanate (PZT) thin film as a diaphragm. Shinoda et al. also reported on similar acoustic energy harvesters with improved performances fabricated using sol/gel PZT thin film processes, and suggested that the PZT acoustic energy harvester may be suitable for use as a possible power source for silicon integrated circuits. This paper presents further improved power generation performances of PZT MEMS acoustic energy harvesters fabricated using improved PZT capacitor fabrication processes. The PZT acoustic energy harvester with the diaphragm diameter of 1.2 mm fabricated using a sol/gel process generated the highest energy density of 98 µW/m 2 under the sound pressure level of 100 dB (0.01 W/m 2 ) at 18.8 kHz.

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In this paper, we present the power generation performances of a lead–zirconate–titanate (PZT) microelectromechanical system (MEMS) acoustic energy harvester having dual top electrodes to utilize the different polarizations of charges on the surface of a vibrating PZT diaphragm at first resonance. The PZT acoustic energy harvester had a diaphragm with a diameter of 2 mm consisting of Al (0.1 µm)/PZT (1 µm)/Pt (0.1 µm)/Ti (0.1 µm)/SiO2 (1.5 µm), and the diaphragm vibrations were excited by sound pressure. The top Al electrodes independently cover the peripheral surface and the central surface of the PZT diaphragm. The peripheral energy harvester generated a power of 5.28×10-11 W, and the central energy harvester generated a power of 4.25×10-11 W at a sound pressure level of 100 dB (0.01 W/m2) at 4.92 kHz. Thus, nearly 80% of the total power of the energy harvesters can be increased by utilizing the polarization at the central part of the diaphragm, which was usually not considered when only the peripheral part of the diaphragm was utilized.

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