This Small Business Innovation Research Phase I project will explore the failure mechanisms associated with hydrophobic dielectric coatings used in electronic paper (E paper) displays. Specifically, electrowetting (E paper) displays require such coatings in order to modulate the contact angle of colored fluids and produce visual images. In order to provide adequate electrical insulation, conventional dielectric coatings must be deposited at thicknesses that require high voltage operation. Conventional hydrophobic coatings deposited on top of these dielectrics are encumbered by electrolyte entrapment (which diminishes the electrowetting effect over time) and poor substrate conformality. We will design improved hydrophobic dielectrics that address the shortcomings of conventional offerings. Specifically, we will develop novel hydrophobic dielectric polymer coatings that exhibit the required combination of thinness, uniformity, and performance. The Phase I effort will identify promising coating recipes based on dielectric failure testing and electrowetting modulation testing. In Phase II, strategies will be developed for reducing dielectric coating defects to manufacturing levels, with an eye towards commercialization.
The broader impact/commercial potential of this project is embodied in the project's anticipated advance of the state-of-the-art in thin dielectric coatings, which are used in a wide range of applications. Applications in which these coatings are simultaneously exposed to ionic solutions and electrical potentials are particularly challenging. Such applications include E paper (electrowetting) displays, implanted medical devices (e.g. neuroprosthetics, cardiac pacemakers), and military electronics. The need to prevent ingress of water and ions is acute in these applications, avoiding the short circuiting and corrosion of encapsulated electronics. Thin dielectric coatings are increasingly being viewed as viable alternatives to bulkier, more expensive hermetic packaging. While thin inorganic coatings have often been employed in similar cases, the attendant high cost and high processing temperatures associated with these materials may be prohibitive. Organic polymer encapsulants are generally not considered to be hermetic, but the assumption that electronic device hermeticity is required is often erroneous. It is anticipated that this project will facilitate both a better match between coating performance and actual device needs, and the manufacturing of reliable, lower cost electronics.
GVD is developing novel coating technology to enable disruptive electronic paper displays. Electronic paper (e-Paper) displays based on electrowetting technology achieve the same high-resolution color video capability of liquid crystal displays (LCDs) with the power consumption and daylight visibility of E Ink electrophoretic displays (EPDs). This technology is further advantaged through a 90% overlap in manufacturing tooling with LCDs. Electrowetting displays (EWDs) are now being aggressively pursued for use in electronic-book readers and tablets, shelf-labels, indicators and outdoor signage. Electrowetting is a technique for manipulating small amounts of fluid on surfaces by applying electricity. In an electrowetting display, a simple optical switch is obtained by controlling the shape of a colored droplet over an underlying reflective surface. Rapid progress in electrowetting optoelectronics has been achieved in the past two decades due in large part to improvements in materials and processing. The electrowetting effect is now exploited commercially in switchable lens devices (Varioptic) and in lab-on-a-chip systems (Advanced Liquid Logic). Despite this progress, further material and process improvements are needed to afford electrowetting displays with reliable low-power operation, reduced manufacturing costs, and to enable high brightness, high resolution designs. GVD’s all-dry, low temperature polymer coating process addresses a critical need for advanced hydrophobic dielectric coatings and will enable reliable, high performance electrowetting displays at low manufacturing cost. Chemically pure fluoropolymer and polysiloxane coatings are grown directly on the device surface from the gas phase affording highly conformal and uniform films across the device. Coating thickness is precisely controlled to the nanoscale and post-process annealing is unnecessary. During Phase I, GVD polysiloxane dielectric coatings demonstrated superior dielectric stability compared with parylene-C coatings. GVD fluoropolymer hydrophobic coatings demonstrated low electrowetting hysteresis and high contact angle modulation required for high fidelity, fast switching speed performance. Successful device demonstrations were carried out with GVD coatings. GVD also developed additional fluoropolymer coating formulations offering very low water contact angle hysteresis. During Phase II, GVD will scale-up and further develop its coating technology to afford low-cost, high volume production of electrowetting displays. The tooling created will be compatible with existing LCD manufacturing lines, reducing barriers to market entry for first adopters and allowing them to more easily compete in the $30B/yr display market. By combining the advantages of e-Paper displays with the multi-function capabilities of tablets, the broader impact of this project will be the widespread replacement of paper-media with electronic paper, providing superior low power products to the burgeoning e-Paper market. Textbooks, magazines, newspapers could be replaced with a single lightweight color multimedia e-Paper tablet. Environmental benefits include significant reductions in paper usage saving millions of trees and reducing the landfill waste stream. Electrowetting technology is also well suited for low power electronic indoor/outdoor signage applications affording significant energy savings over signage using emissive and backlit displays. Further, advancements made in vapor deposited hydrophobic coatings developed during this SBIR project will open new market opportunities and increase scientific interest not only for other electrowetting devices, but also in applications ranging from anti-fouling surfaces, environmental protection, anti-stiction and more.
