This article discusses and experimentally verifies how to lower the operating voltage that drives liquid droplets by the principle of electrowetting on dielectric (EWOD). A significant contact angle change (120°→80°) is desired to reliably pump the droplet in microchannels for applications such as lab-on-a-chip or micrototal analysis systems. Typically, much higher voltages (>100 V) are used to change the wettability of an electrolyte droplet on a dielectric layer compared with a conductive layer. The required voltage can be reduced by increasing the dielectric constant and decreasing the thickness of the dielectric layer, thus increasing the capacitance of the insulating layer. This dependence of applied voltage on dielectric thickness is confirmed through EWOD experiments for three different dielectric materials of varying thickness: Amorphous fluoropolymer (Teflon® AF, Dupont), silicon dioxide and parylene. The dependence on the dielectric constant is confirmed with two different dielectric materials of similar thickness: and barium strontium titanate. In all cases, the surface is coated with a very thin (200 Å) layer of amorphous fluoropolymer to provide initial hydrophobicity. Limiting factors such as the dielectric breakdown and electrolysis are also discussed. By using very thin (700 Å) and high dielectric constant (∼180) materials, a significant contact angle change (120°→80°) has been achieved with voltages as low as 15 V. Based on these results, a microfluidic device has been fabricated and tested, demonstrating successful transporting (pumping) of a 460 nL water droplet with only 15 V.
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1 October 2002
Research Article|
October 01 2002
Low voltage electrowetting-on-dielectric
Hyejin Moon;
Hyejin Moon
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles (UCLA), Los Angeles, California 90095-1597
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Sung Kwon Cho;
Sung Kwon Cho
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles (UCLA), Los Angeles, California 90095-1597
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Robin L. Garrell;
Robin L. Garrell
Department of Chemistry and Biochemistry, University of California, Los Angeles (UCLA), Los Angeles, California 90095-1597
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Chang-Jin “CJ” Kim
Chang-Jin “CJ” Kim
Department of Mechanical and Aerospace Engineering, University of California, Los Angeles (UCLA), Los Angeles, California 90095-1597
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J. Appl. Phys. 92, 4080–4087 (2002)
Article history
Received:
May 15 2002
Accepted:
July 09 2002
Citation
Hyejin Moon, Sung Kwon Cho, Robin L. Garrell, Chang-Jin “CJ” Kim; Low voltage electrowetting-on-dielectric. J. Appl. Phys. 1 October 2002; 92 (7): 4080–4087. https://doi.org/10.1063/1.1504171
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