Observation and optical implications of oil dewetting patterns in electrowetting displays

Abstract

Growth of surface instabilities leading to periodic oil patterns in electrowetting display pixels has been experimentally observed. In the electrowetting display pixels, an electrical potential ranging between 0 V and 80 V is applied among a water electrode, dielectric layers consisting of an oil film, fluoropolymer, Parylene C and a lower electrode. As predicted by spinodal dewetting theory, application of electromechanical pressure to the oil film causes the film to dewet into a periodic arrangement of oil droplets. The separation distance, or wavelength, for the dewetted oil droplets decreases with increasing voltage or with decreasing oil film thickness. Various test voltages of 20-80 V and oil thicknesses values of 3.3-8.9 µm were shown to experimentally generate dewetting wavelengths ranging from 10's to 100's of µm. An increased number of oil droplets inside the display pixel decreases the maximum display transmission or reflection proportional to the cube root of the number of droplets. This work therefore provides a means to further understand oil film dewetting in electrowetting display pixels and explains the implications of the dewetting pattern on display optical performance. M This article features online multimedia enhancements

A numerical technique to simulate display pixels based on electrowetting

“…They appear in the present experiments (see Figs. 13,14,15), and they were observed before (Murade et al 2011;Staicu and Mugele 2006;Sun and Heikenfeld 2008). Using stability analysis in lubrication approximation of thin oil films between an electrode and a water film, it is possible to show that The dynamic response of the simulated oil is compared to the experimental results.…”

“…The electric fields lead to a Maxwell stress pulling on the liquid-liquid interface. In recent years, electrowetting (Mugele and Baret 2005) has evolved into the arguably most popular technique for electrical manipulation of liquids in microfluidics with a wide range of applications including lab-on-a-chip systems (Fair 2007), optofluidics (Berge and Perseux 2000;Kuiper and Hendriks 2004;Krupenkin et al 2003;Murade et al 2011Murade et al , 2012, energy harvesting (Krupenkin and Taylor 2011) and display technology (Hayes and Feenstra 2003;Sun and Heikenfeld 2008). Electrowetting on dielectric (EWOD) involves a specific geometry with a thin dielectric coating separating an electrode from the conductive liquid sitting on top of it ( Fig.…”

51.4: Development of Flexible Electrowetting Displays for Stacked Color

“…Processing variability also affects the oil droplet behavior among cells. For rectangular cell geometries it has been observed that upon actuation the oil-dye phase will split evenly between the two short walls, or move the oil-dye phase to only one side (12).…”

Electrowetting-actuated optical switch based on total internal reflection

“…Liquid optical switches have been intensively studied in recent years owing to the wide applications in spatial light modulators, microscopies, telecommunications, variable optical attenuators, and electronic displays [1][2][3][4]. According to the driving mechanisms, they can be roughly divided into mechanical driving, such as using an external mechanical motor, and nonmechanical driving [5][6][7], such as electric force or magnetic force.…”