In a typical liquid crystal (LC) display the three color cells: Red, Green and Blue (RGB) are placed side by side with respect to each other and are covered by a polarizer. The RGB color filter in LC displays use almost one third (⅓) of the incident light. To achieve high brightness and resolution the LC display requires back lighting. The back lighting consumes a considerable amount of energy and rapidly drains the battery of a portable device. The reflected ambient light display with individual color cells stacked on top of each other is capable of much higher pixel density per square inch than a conventional LC display. Thus, in principle, the pixel density per unit area could be much higher than what it is for the LC horizontally placed color cell pixel display and the energy and cost of operating such a display would be much smaller.
Many attempts were made to build a three level, three color reflective display. In such a display the pixels have to be placed (stacked) on top of each other rather than side by side as is the case in a typical LC display. In U.S. Pat. No. 5,796,447 which issued Aug. 18, 1998 to Okumura et al., a liquid crystal display is described having each pixel formed by a plurality of liquid crystal layers and a plurality of transparent electrodes which are alternately stacked on a first electode functioning as a reflecting plate to display a plurality of different colors.
The most difficult part in building such a vertically stacked color cell reflective display is providing the vertical electrical connections between the electrodes at individual levels in each pixel and the respective TFT on the substrate below.