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Title: Microfluidic pumps employing surface acoustic waves generated in ZnO thin films

Abstract

ZnO thin film based surface acoustic wave (SAW) devices have been utilized to fabricate microfluidic pumps. The SAW devices were fabricated on nanocrystalline ZnO piezoelectric thin films deposited on Si substrates using rf magnetron sputtering and use a Sezawa wave mode for effective droplet motion. The as-deposited ZnO surface is hydrophilic, with a water contact angle of {approx}75 deg., which prevents droplet pumping. Therefore, the ZnO surface was coated using a self-assembled monolayer of octadecyltrichlorosilane which forms a hydrophobic surface with a water contact angle of {approx}110 deg. Liquid droplets between 0.5 and 1 {mu}l in volume were successfully pumped on the hydrophobic ZnO surface at velocities up to 1 cm s{sup -1}. Under acoustic pressure, the water droplet on an hydrophilic surface becomes deformed, and the asymmetry in the contact angle at the trailing and leading edges allow the force acting upon the droplet to be calculated. These forces, which increase with input voltage above a threshold level, are found to be in the range of {approx}100 {mu}N. A pulsed rf signal has also been used to demonstrate precision manipulation of the liquid droplets. Furthermore, a SAW device structure is demonstrated in which the ZnO piezoelectric only exists undermore » the input and output transducers. This structure still permits pumping, while avoiding direct contact between the piezoelectric material and the fluid. This is of particular importance for biological laboratory-on-a-chip applications.« less

Authors:
; ;  [1];  [1];  [2];  [1];  [2]
  1. Electrical Engineering Division, Department of Engineering, University of Cambridge, JJ Thomson Ave., Cambridge CB3 0FA (United Kingdom)
  2. (United Kingdom)
Publication Date:
OSTI Identifier:
21185989
Resource Type:
Journal Article
Resource Relation:
Journal Name: Journal of Applied Physics; Journal Volume: 105; Journal Issue: 2; Other Information: DOI: 10.1063/1.3068326; (c) 2009 American Institute of Physics; Country of input: International Atomic Energy Agency (IAEA)
Country of Publication:
United States
Language:
English
Subject:
36 MATERIALS SCIENCE; ASYMMETRY; CRYSTAL GROWTH; CRYSTALS; DEPOSITION; DROPLETS; ELECTRIC POTENTIAL; NANOSTRUCTURES; PIEZOELECTRICITY; SEMICONDUCTOR MATERIALS; SOUND WAVES; SPUTTERING; SUBSTRATES; THIN FILMS; TRANSDUCERS; WATER; ZINC OXIDES

Citation Formats

Du, X. Y., Flewitt, A. J., Milne, W. I., Fu, Y. Q., Department of Mechanical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, Luo, J. K., and Centre for Material Research and Innovation, University of Bolton, Deane Road, Bolton BL3 5AB. Microfluidic pumps employing surface acoustic waves generated in ZnO thin films. United States: N. p., 2009. Web. doi:10.1063/1.3068326.
Du, X. Y., Flewitt, A. J., Milne, W. I., Fu, Y. Q., Department of Mechanical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, Luo, J. K., & Centre for Material Research and Innovation, University of Bolton, Deane Road, Bolton BL3 5AB. Microfluidic pumps employing surface acoustic waves generated in ZnO thin films. United States. doi:10.1063/1.3068326.
Du, X. Y., Flewitt, A. J., Milne, W. I., Fu, Y. Q., Department of Mechanical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS, Luo, J. K., and Centre for Material Research and Innovation, University of Bolton, Deane Road, Bolton BL3 5AB. 2009. "Microfluidic pumps employing surface acoustic waves generated in ZnO thin films". United States. doi:10.1063/1.3068326.
@article{osti_21185989,
title = {Microfluidic pumps employing surface acoustic waves generated in ZnO thin films},
author = {Du, X. Y. and Flewitt, A. J. and Milne, W. I. and Fu, Y. Q. and Department of Mechanical Engineering, School of Engineering and Physical Sciences, Heriot-Watt University, Edinburgh EH14 4AS and Luo, J. K. and Centre for Material Research and Innovation, University of Bolton, Deane Road, Bolton BL3 5AB},
abstractNote = {ZnO thin film based surface acoustic wave (SAW) devices have been utilized to fabricate microfluidic pumps. The SAW devices were fabricated on nanocrystalline ZnO piezoelectric thin films deposited on Si substrates using rf magnetron sputtering and use a Sezawa wave mode for effective droplet motion. The as-deposited ZnO surface is hydrophilic, with a water contact angle of {approx}75 deg., which prevents droplet pumping. Therefore, the ZnO surface was coated using a self-assembled monolayer of octadecyltrichlorosilane which forms a hydrophobic surface with a water contact angle of {approx}110 deg. Liquid droplets between 0.5 and 1 {mu}l in volume were successfully pumped on the hydrophobic ZnO surface at velocities up to 1 cm s{sup -1}. Under acoustic pressure, the water droplet on an hydrophilic surface becomes deformed, and the asymmetry in the contact angle at the trailing and leading edges allow the force acting upon the droplet to be calculated. These forces, which increase with input voltage above a threshold level, are found to be in the range of {approx}100 {mu}N. A pulsed rf signal has also been used to demonstrate precision manipulation of the liquid droplets. Furthermore, a SAW device structure is demonstrated in which the ZnO piezoelectric only exists under the input and output transducers. This structure still permits pumping, while avoiding direct contact between the piezoelectric material and the fluid. This is of particular importance for biological laboratory-on-a-chip applications.},
doi = {10.1063/1.3068326},
journal = {Journal of Applied Physics},
number = 2,
volume = 105,
place = {United States},
year = 2009,
month = 1
}
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