Piezoelectrically actuated tunable capacitor |
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Authors: | Chuang-Yuan Lee Eun Sok Kim |
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Affiliation: | Dept. of Electr. Eng.-Electrophys., Univ. of Southern California, Los Angeles, CA, USA; |
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Abstract: | This paper describes the design, fabrication, and characterization of the first MEMS piezoelectric tunable capacitors employing zinc oxide (ZnO) actuation. Relatively simple design rules for the device-structure optimization for largest deflection are shown from simulation results based on theoretical equations. The ZnO-actuated tunable capacitors are accordingly designed and fabricated with both surface and bulk micromachining techniques. Through the surface micromachining process, sacrificial silicon is removed with XeF/sub 2/, and parylene is successfully used as a supporting layer for a piezoelectric unimorph cantilever. For comparison, other two different structures using plasma-enhanced chemical-vapor deposition (PECVD) SiN and SU-8 as supporting layers are also fabricated. Deflection analyses are performed for three specific structures, among which the parylene-supported one is demonstrated to have the largest displacement and most suitable for tunable capacitor application. For bulk-micromachined tunable capacitor, we have implemented a novel design of a large structure driven by a ZnO unimorph, and obtained a tuning ratio of more than 21:1 (0.46 pF-10.02 pF). This is the highest tuning ratio reported to date for parallel-plate tunable capacitors while requiring an applied voltage of only 35 V. |
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