The Movement of Micro Droplet with the Effects of Dielectric Layer and Hydrophobic Surface Treatment with R.F. Atmospheric Plasma in EWOD Structure

Abstract

This study is about how to lower the driving voltage that enables to move the micro droplet by the EWOD (Electro Wetting On Dielectric) mechanism. EWOD is well known that it is used µ -TAS digital micro fluidics system. As voltages are applied to the device which is fabricated with dielectric layer between electrode and micro droplet, the hydrophobic surface is changed into the hydrophilic surface by its electrical property. EWOD induces the movement of micro droplet with reducing contact angle of micro droplet. Because the driving voltage depends on the dielectric constant of dielectric layer, it can be reduced by increase of dielectric constant. Typically, driving voltage of these devices was 30V∼100V and Teflon film was coated to provide hydrophobic surface. This high voltage induces many problems. In previous study, we used Ta2O5 as the dielectric layer and driving voltage was 23V that reduced 24 percent compared with SiO2. In this study, we used BZN (Bi2O3-ZnO-Nb2O5) layer which had high dielectric constant. It operated the just on 12V. And micro droplet was moved within 1s on 14V. It reduced the voltage until 35 percents compared with Ta2O5 and 50 percents compared with SiO2. The movement of micro droplet within 1s was achieved with BZN (ferroelectrics) just on 14V. Teflon film which is coated to provide hydrophobic surface is a very difficult to control accurate concentration, and unnecessary processes which uses metal as a protect layer in patterning should be added. So instead of Teflon coating, surface was treated to hydrophobic with R.F. atmospheric plasma.