Research into developing reliable electronic paper has been going on for some time, but until now images - especially in colour – have been disappointingly dull. The response speed of the pixels in electrophoretic displays has also been slow, making video content and animations sluggish viewing.
Electrowetting, a process developed by Robert Hayes and Johan Feenstra of Philips Research Eindhoven, has now been enhanced to form a reflective display that is much faster than electrophoretic displays. The display has a coloured oil film next to a white substrate. The film is reversibly controlled via DC voltage control, and the colours achieved are four times brighter than reflective liquid crystal displays, and twice as bright as other emerging technologies.
The two-dimensional microfluidic motion uses a white reflector that is integrated into an optical stack. The reflector is formed as a white polymer foil with a thin electrode layer of indium tin oxide and a fluoropolymer insulator. The oil film is contained using a thin film fabrication procedure. ‘A black or transparent polymer sheet, typically 50µm thick, is laser cut to provide the required pixel sizes and patterns. It is then glued onto the insulator-covered substrate with a low viscosity two-part epoxy. Liquids are dosed and the test cells are sealed with an ITO-covered glass slide,’ says Hayes and Feenstra.