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Introduction 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.
Description 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.
