Electrowetting displays (EWDs) have attracted increasing attention recently due to the rapid growth of portable applications such as electronic paper (E-paper). Compared with other display technologies, EWDs have shown their obvious advantages for reflective displays. In this dissertation, novel EWD materials and architectures for flexible and tunable color surfaces were explored.
First, EWDs on flexible substrate were reported. A scalable fabrication process using self-assembly oil dosing method was introduced. The process is capable of producing pixels which are switched at <15V and which have individual sub-pixel areas of < 50x150 µm2. Spinodal dewetting of oil film during operation was observed and its implication on display optical performance was studied. With decreasing wavelength, the increased number of dewetted droplets inside pixel will decrease the display maximum reflection or transmission.
Next, novel electrowetting microwells were presented. Colored oils and aqueous solutions were electromechanically pumped in and out of arrayed microwells. The arrayed microwells were fabricated by etching pyramidal pits in (100) Si substrates. When colored oil was placed behind the substrate, surface tension forces caused the oil to completely fill the microwells and provide brilliant red coloration to the array. With application of 30~50 V, electrowetting drove the colored oil behind the substrate and the reflection was made dominantly white.
Finally, a new technology, referred to as an “Electrofluidic Chromatophore”, was developed for novel colored-water electrowetting designs. With 30~50V applied, electrowetting force/pressure pulls the colored water out of a small-area reservoir, makes it spread over the whole pixel, and Young-Laplace pressure pushes the spread color water back to the reservoir when voltage is removed. The display demonstrated excellent color saturation, high contrast ratio, fast switching speed, and shows the promise to be successful for display applications.