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Research Papers

Fabrication and Energy Harvesting Measurements of Vibrating MEMS Piezoelectric Benders

[+] Author and Article Information
Changki Mo

School of Mechanical and Materials Engineering, Washington State University-Tri-Cities, Richland, WA 99354changki.mo@tricity.wsu.edu

Ryan R. Knight, Amanda A. Frederick, William W. Clark

School of Mechanical and Materials Engineering, Washington State University-Tri-Cities, Richland, WA 99354

J. Vib. Acoust 133(1), 011006 (Dec 17, 2010) (7 pages) doi:10.1115/1.4002784 History: Received January 14, 2010; Revised August 17, 2010; Published December 17, 2010; Online December 17, 2010

In this paper, a study is presented in which piezoelectric microbenders were fabricated and tested to demonstrate energy generating performance. Trapezoidal and diagonal (with respect to the substrate crystal directions) unimorph PZT cantilever benders with interdigitated electrode patterns were utilized. The interdigitated design is beneficial for microenergy harvesting devices because it utilizes the d33 mode, which can generate higher voltage than the d31 mode design. It can also eliminate the bottom electrode by only using an interdigitated top electrode, which facilitates fabrication, as opposed to the d31 mode design that requires both top and bottom electrodes. The micro-electromechanical system (MEMS) benders fabricated in this study consist of layers of SiO2/SiNx/ZrO2/PZT and Au/Cr interdigitated electrode on the top. The experimental results indicate that the fundamental frequencies of the microbenders are about 9.1 kHz for the trapezoidal bender and 18.48 kHz for the diagonal bender. The microtrapezoidal bender can generate power of approximately 1.4μW into a 680kΩ resistive load at the resonant frequency. The diagonal bender can generate power of about 18.2μW into a 100kΩ resistive load at the resonant frequency.

Copyright © 2011 by American Society of Mechanical Engineers
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References

Figures

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Figure 1

Rectangular array of MEMS beam designs

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Figure 2

Schematic of the fabrication process (note that the layer thicknesses are not drawn to scale)

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Figure 3

Electrode patterned on PZT surface

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Figure 4

Beam-patterned photoresist on electrode-patterned wafers

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Figure 5

SEM image of the released benders

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Figure 6

Photograph of a trapezoidal bender

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Figure 7

Photograph of a diagonal bender

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Figure 8

Photograph of the MEMS die and wire bonding chip package (wires from the die to the carrier chip are too small to be seen)

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Figure 9

Photograph of the vibration stage and PZT excitation source

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Figure 10

Schematic of the generated power measurement setup

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Figure 11

Photograph of the generated power measurement setup

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Figure 12

Measured frequency response of the trapezoidal bender

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Figure 13

Measured frequency response of the diagonal bender

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Figure 14

Generated power versus load resistance for the trapezoidal bender

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Figure 15

Generated power versus load resistance for the diagonal bender

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Figure 16

Magnified view of the piezoelectric layer of d33 bender with ideal poling

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Figure 17

Illustration of the nonuniform electric field that exists underneath the electrodes during poling

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