Design and Fabrication of Piezoelectric MEMS Generator Based on Stainless Steel Substrates
Date Issued
2012
Date
2012
Author(s)
Shih, Ya-Shan
Abstract
Of late years, the growing interest in the field of power harvesting technologies has been brought to researchers’ attentions. With the increasing interests in biomedical monitoring and sensor network applications, supplying power to the implanted biochips and wireless sensor devices have become an important issue[1]. Also, due to the miniaturization of electronics devices, the power consuming scale has been lowered to the micro-watts level. Summing up the above reasons, MEMS power harvesting device seems to be an optimistic solution, avoiding power source replacement, which may be impractical in some cases.
In this thesis, miniaturized power harvesting devices based on stainless steels in the form of cantilever beam is presented. Utilizing the lead zirconate titanate (PZT) as the piezoelectric transforming material, the fabricated devices own the ability to scavenge energy from ambient mechanical vibrations. To increase the voltage output, a home-made PZT deposition chamber which could deposit thin films having the thickness as thick as 10μm was used to deposit the PZT layer of the structures. Different harvesting modes of d31, d33, dual layer d33, and a dual oscillator structure are simulated and afterwards discussed. Subsequently, experimental results of the three similar structures are compared.
Experimental results confirm that the stainless steel substrates have superior robustness, allowing the MEMS device to withstand harsher environments comparing to previous researches. The experimental results show that the d31 device is able to provide the output power of 10.533 μW under the resonance frequency of 213.9 Hz; the d33 device is able to give the output power of 0.214 μW, under 136.2 Hz; the dual d33 device can output four folds the output of single d33, which is 0.927 μW, under 127.9 Hz. The fabricated devices are able to generate power output in scales of micro-watts and the voltage outputs have overcome the threshold voltage of a rectifying bridge, enabling the storage of harvested energy. A newly designed structure of dual oscillator is also presented. With the structure of dual oscillator, the device has lowered the resonance frequency to 27 Hz and 66.4 Hz for different thicknesses of substrate, 30 and 50 μm. This structure also enables the up-conversion of the device. The up-conversion effect not only causes multi-peak frequencies, it also broadens the bandwidth of low vibrating frequencies. It is predicted that the device can be able to operate in circumstances under frequencies lower than 10 Hz.
Subjects
aerosol PZT deposition
MEMS generator
cantilever beam
power harvesting
piezoelectric generator
stainless steel substrate
Type
thesis
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