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.
In this paper, we report on microelectromechanical system (MEMS) energy harvesters with a diaphragm consisting of a 1-mm-thick lead zirconate titanate (PZT) film formed by the sol-gel method. Electrical power can be generated using the piezoelectric effects of the PZT diaphragm that vibrates in acoustic fields. Harvesters with different diaphragm diameters of 1.5 and 2.0 mm were fabricated. The top electrode covered the entire PZT diaphragm. The measured first resonance frequencies of those diaphragms were 6.02 and 5.72 kHz, and the third resonance frequencies were 24.02 and 18.02 kHz, respectively. The measured frequency spectrum indicated that the induced voltages are larger and more widely distributed for the third resonance than for the first resonance. Those devices generated power of 1:1 Â 10 À11 and 5:1 Â 10 À12 W under the irradiation of 100 dB sound pressure at their third resonance frequencies. #
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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