Fabrication and Characterization of Electrowetting on the flexible substrate
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1004-P08-09
Fabrication and Characterization of Electrowetting on the flexible substrate JinYoung Kim1, JungHo Seo1, JungHwan Lee2, KyuChae Kim1, HyunWoo Lim2, JinGoo Park1, SungChae Jeon3, SeoungOh Jin3, and Young Huh3 1 Materials and Chemical Engineering, Hanyang University, Ansan, 426-791, Korea, Republic of 2 MicroBiochipCenter, Hanyang University, Ansan, 426-901, Korea, Republic of 3 Korea Electrotechnology Research Institute, Ansan, 426-801, Korea, Republic of ABSTRACT This paper reports the fabrication of and characterization on EWOD (electrowetting-ondielectric) devices on flexible substrates of interest to the flexible displays research field. The EWOD devices were fabricated on PET (poly ethylene terephthalate) and PMMA (polymethylmethacrylate) substrates. Au and ITO (indium tin oxide) were used as electrode materials. The wet etching process was developed to not attack plastic flexible substrates. The photo resist was used as an insulator material in EWOD devices due to the deformation of the substrate when the oxide layer was deposited on the plastic substrate. As a hydrophobic layer, cytop was spin-coated on the photo resist. Wetting tests were done with DI water in air environment. In sessile droplet test, the contact angle of droplet changed from 116◦ to 80◦ under DC power. Threshold voltage was 20 Vdc. The droplet was oscillated under AC power because of the frequency. The contact angle of droplet began to change at 30Vac and decreased with the increase in AC power. In droplet transporting test, a droplet (0.2 ㎕) began to be transported at 20Vac and the moving speed increased with the increase of AC power. Droplet transporting did not occur under DC power because of the slower contact angle recovery rate under DC power. INTRODUCTION Electrowetting (EW) is an electrostatically induced reduction in the contact angle of an electrically conductive liquid droplet on a surface [1,2]. Since a liquid droplet can be controlled by the electrical potential, EW has become one of the most widely studied tools for manipulating tiny amounts of liquids on surface. In addition, EW can be used as a liquid transport mechanism in a micro-fluidic system without the need of any mechanical component. The digital fluidic system using electrowetting can be used for biotechnology applications such as lab-on-a-chip or μTAS (micro total analysis system). EW also can be applied for flexible display [3- 6]. In recent years, the electrowetting added dielectric layer has been studied. This device, which is named as an electrowetting-on-dielectric device (EWOD), has the concept that the liquid separates from the metallic electrode to eliminate the problem of electrolysis. The sessile droplet test [5,7,8,9] and the performance of droplet [3,6,10,11,12] for EWOD have been studied by numerous researchers. The Lippmann-Young equation (1) is the most suitable equation to explain electrowetting phenomenon. Equation (1) describes the change of contact angle by the electric potential [1,2,8,10,11].
(1) where
is the contact angle when a
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