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Function-oriented Knowledge Base \ Electronic paper \ Decrease power consumtion of paper-like display

Monolayer gyricon display provides improved brightness/contrast performance

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Gyricon or twisting-ball displays are a type of flexible flat display. A conventional gyricon display contains several layers of bichromal balls. Bichromal balls are located inside spherical cavities formed by a dielectric fluid in an elastomer substrate. In the spherical cavities, the bichromal balls are free to rotate. The bichromal balls become electrically dipolar in the presence of the fluid, and can rotate in the electrical field of matrix-addressable electrodes. The electrode closest to the upper surface of the display is transparent. To an observer, the upper surface is an image formed by the black and white pattern of balls turned to the upper surface of the substrate with their black or white faces. Gyricon displays are more advantageous than conventional LC and CRT video displays. In particular, gyricon displays are suitable for viewing in ambient light, and retain an image indefinitely due to the absence of an applied electric field. Furthermore, gyricon displays can be light, flexible and foldable like conventional writing paper. Therefore, such a display is suitable for the conventional applications of a display, and for use as electric paper or interactive paper, in which gyricon displays act as an electrically addressable, replenishable, and environmentally friendly substitute for conventional paper. However, gyricon displays do not look like conventional paper. In particular, they do not have as high a reflectance as paper (the 85 percent diffuse reflectance of white paper). Also, they do not possess the high brightness and contrast characteristics of paper. In a multi-layer display, bichromal balls furthest from the viewing surface fill the gaps between the balls closest to the viewing surface. It is generally believed that because the two-dimensional projection of the balls that are turned with their white faces to the viewing surface substantially cover the viewing surface, a high-quality display will be produced. But in fact, due to the fact that the lighter upper surfaces of the lower layer balls reflect light onto the dark lower surfaces of the upper layer balls, the light is absorbed by these dark surfaces. As a result, the total reflection of the display does not exceed 20-40 percent. Correspondingly, the brightness/contrast performance is reduced. A method of providing improved brightness/contrast performance for a gyricon display is needed.
To provide improved brightness/contrast performance for a gyricon display, using one layer of closely packed bichromal rotating balls is proposed. In a display, light is reflected from one layer of closely packed bichromal balls with a uniform diameter so that lower bichromal balls are not needed. The balls in the monolayer are hexagonally packed. In the hexagonally closely packed monolayer, the amount of light reflected from the white hemisphere surfaces of the balls due to diffusion may be above 90 percent. Correspondingly, the display surface brightness rises, and so does the brightness difference between the darker portions of the image and the lighter ones. In other words, balls closely packed in a monolayer provide improved brightness/contrast performance of a gyricon display.
Additional information
To increase the reflectance, smaller bichromal balls fill the interstices of the array. To maximize the reflectance, the closely packed monolayer of gyricon balls can be placed in a fluid directly between transparent electrodes, without any cavity-containing elastomer. The diffuse reflectance may be more than 90 percent as a result. A monolayer display is thinner than a multilayer display. One layer of balls may in turn be set into motion by a lower applied voltage (bichromal balls with an average diameter of 80 microns, 50 volts). The lower applied voltage corresponds to the lower power consumption. Because the balls are closely packed and in a monolayer, control (narrowing) of the fringing fields improves. Good control of the fringing fields leads to better resolution. By selecting the particle material and size, it is possible to modulate infrared light or ultraviolet light.
US Patent 5825529; Link >>
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