Design and Development of MEMS based Guided Beam Type Piezoelectric Energy Harvester by Shanky Saxena & Ritu Sharma & B. D. Pant

Author:Shanky Saxena & Ritu Sharma & B. D. Pant
Language: eng
Format: epub
ISBN: 9789811606069
Publisher: Springer Singapore

This pyramidal shape of the seismic mass is realized through wet bulk micromachining using Tetra Methyl Ammonium Hydroxide (TMAH) etching with suitable corner compensation structures. Dimensions for the seismic mass at the top are 3500 µm × 3500 µm (Fig. 4.1), and from the bottom is 3033 × 3033 µm and height is 330 µm as shown in Fig. 4.2.

Fig. 4.2Cross-sectional view of guided beam P-VEH

Figure 4.2 gives the cross-sectional view of the device giving the layer details. The base structure is of silicon giving beam thickness of 20 µm. Thermal oxide layer is grown for insulation between substrate and the bottom electrode. Gold (Au)/Aluminum (Al) metal is deposited and patterned over oxide layer to form the bottom electrodes. A piezoelectric layer of zinc oxide (ZnO) having c-axis orientation is deposited over bottom electrode. Gold (Au)/Aluminum (Al) metal is deposited over ZnO layer and patterned to form the bottom electrodes. Bottom and top electrodes (Au/Al) are sputtered over piezoelectric layer for charge collection. During device fabrication, a passivation layer of plasma enhanced chemical vapor deposition (PECVD) oxide of thickness 0.2 μm was deposited at the bottom and top surface of the ZnO layer to protect it from the environmental deterioration due to ambient oxygen and water vapor in the atmosphere.

A P-type silicon substrate (100) of 3 inches diameter having a thickness of 350 ± 25 µm is suitable for device fabrication. Zinc oxide material has been selected because of its compatibility with CMOS fabrication technology and higher piezoelectric coefficient. Ambient vibration displaces the guided beams which generate tensile and compressive stress in the beams resulting in the generation of charge along the piezoelectric layer due to piezoelectric effect.

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