Computer graphics processing and selective visual display system – Plural physical display element control system – Display elements arranged in matrix
Reexamination Certificate
1999-11-03
2002-11-26
Saras, Steven (Department: 2675)
Computer graphics processing and selective visual display system
Plural physical display element control system
Display elements arranged in matrix
C345S084000, C359S296000
Reexamination Certificate
active
06486866
ABSTRACT:
BACKGROUND OF THE INVENTION
The present invention relates to a display device and a method of driving the display device, and particularly to a display device including small-sized two-color ball type electrophoretic particles each of which is composed of hemispherical portions different in color from each other for performing various kinds of display by making use of the electrophoretic particles, and a method of driving the display device.
In recent years, CRTs and liquid crystal displays have been mainly used as display devices. However, light emission type displays such as CRTs are not suitable for reading of documents, etc., because they cause fatigue of eyes of a viewer. Meanwhile, as for liquid crystal displays, a type adopting a backlight tends to cause fatigue of eyes like CRTs, and a type not adopting a backlight is disadvantageous in that the contrast is poor, which also tends to cause strong fatigue to eyes of a viewer if the viewer has a look at the screen for a long period of time. Also, these displays generally have no memory capabilities, to give rise to a disadvantage that an image disappears when a power supply is cut off.
In view of the foregoing, displays used for portable information equipment expected to be widespread for the future, for example, PDAs, note type personal computers and electronic book players, are required to be reduced in power consumption and to have a memory capability of images.
As the display capable of satisfying the above-described requirements to some extent, there have been known an electrophoretic display device and a two-color ball display device.
The electrophoretic display device is configured to make use of a principle in which electrophoretic particles composed of charged fine particles migrate toward an electrode having a polarity reversed to that of electric charges of the electrophoretic particles due to the effect of an electric field.
The electrophoretic display device has a configuration, for example, shown in
FIG. 18
, in which a transparent substrate
102
provided with transparent electrodes
101
made from ITO or the like is opposed to a substrate
104
provided with electrodes
103
not requiring transparency with a specific gap kept therebetween, and the gap formed between the transparent substrate
102
and the substrate
104
is filled with an electrophoretic particles
105
composed of, for example, white charged particles, and a dispersion medium
106
in which the electrophoretic particles
105
are dispersed. The electrophoretic particles
105
are made from, for example, a white pigment, and the dispersion medium
106
is colored into, for example, black.
In the above electrophoretic display device, as shown by a portion A in
FIG. 18
, if the electrophoretic particles
105
are negatively charged, when a plus voltage is applied to the transparent electrode
101
and a minus voltage is applied to the other electrode
103
, the electrophoretic particles
105
migrate to the plus side electrode, that is, to the transparent electrode
101
by coulomb forces and adhere on the transparent electrode
101
. When a viewer turns his eyes upon the portion A of electrophoretic display device from an eye position E shown in
FIG. 18
, he perceives through the transparent electrode
101
and the transparent substrate
102
that the portion, on which the white charged particles (electrophoretic particles
105
) adhere, of the transparent electrode
101
is white-colored.
When the polarity of the applied voltage is reversed, as shown by a portion B in
FIG. 18
, the white charged particles (electrophoretic particles
105
) migrate to the back side electrode, that is, to the electrode
103
and adhere thereon, and accordingly, they are hidden by the black dispersion medium
106
. When a viewer turns his eyes upon the portion B from the eye position E in
FIG. 18
, he perceives that the portion B is black-colored. In addition, according to this electrophoretic display device, if the white charged particles (electrophoretic particles
105
) adhere on the electrode
101
(or
103
), they stand still for a short while after cutoff of the applied voltage.
In the above-described electrophoretic display device, either the color of the electrophoretic particles
105
or the color of the dispersion medium
106
is displayed. If the color of the electrophoretic particles
105
is white and the color of the dispersion medium
106
is black as described above, since the black dispersion medium
106
remains in gaps among the white particles
105
collected by migration, the display of clear white cannot be realized. If the color of the electrophoretic particles
105
is black and the color of the dispersion medium
106
is white, it is possible to realize the display of clear white by increasing the density of the white color of the dispersion medium
106
;, however, in this case, upon black display, a dense white dispersion medium
106
remains in gaps among the black particles
105
, so that the display of true black cannot be realized. As a result, it is difficult to obtain a high contrast ratio.
The two-color ball display device includes a plurality of two-color balls each typically having a white hemispherical portion and a colored half, for example blackened hemispherical portion, which are different from each other in terms of zeta-potential. Such a display device is operated on the basis of a principle in which a large number of the above two-color balls are rotated by the effect of an electric field.
The two-color display device has a configuration, for example, shown in
FIG. 19
in which a transparent substrate
111
provided with transparent electrodes
110
made from ITO or the like is opposed to a substrate
113
provided with electrodes
112
not requiring transparency with a specific gap kept therebetween, and the above gap is filled with a large number of two-color balls
114
and a liquid
115
rotatably surrounding the two-color balls
114
. In the example show n in
FIG. 19
, white hemispherical portions
114
a
of the two-color balls
114
are positively charged, and colored, for example, blackened hemispherical portions
114
b
thereof are negatively charged.
In this two-color ball display device , when a voltage (electric field) is applied between the electrodes
110
and
112
provided on the inner surfaces of the substrates
111
and
113
holding the two-color balls
114
as display media and the liquid
115
therebetween, each two-color ball
114
rotates on the basis of a relationship between the polarity thereof and correspons to the polarity of the voltage applied to the transparent electrode
110
or electrode
112
in such a manner that the colored hemispherical portion
114
b
is directed to the transparent substrate
111
side as shown by a portion A in
FIG. 19
or directed to the substrate
113
side as shown by a portion B in FIG.
19
. Accordingly, the white or black display can be realized by adjusting the rotation of the two-color balls
114
. In the two-color ball display device, even if the supply of the voltage is cut off, the display state remains for a short while.
Even in the two-color ball display device shown in
FIG. 19
, however, it is difficult to obtain a high contrast ratio. This is because, the contrast between the colors of the two hemispherical portions of the two-color ball is high;, however, since a gap required for the liquid to enter between the two-color balls must be provided for rotating the two-color balls, the two-color balls cannot be closely packed.
To solve the above disadvantage, there has been proposed a display device shown in
FIG. 20
in which two-color balls are arranged in multiple levels (multiple layers) for covering gaps among the two-color balls in the first layer with the two-color balls in the second layer. In such a display device, however, the white color in the second layer, which is affected by the black color in the first layer, becomes darker than the white layer in the first layer. As a result, according to this display device, it fails to obtai
Kuwahara Soichi
Matsui Eriko
Matsute Masataka
Bell Paul A.
Saras Steven
Sonnenschein Nath & Rosenthal
Sony Corporation
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