Optical: systems and elements – Optical modulator – Light wave temporal modulation
Reexamination Certificate
2002-08-20
2003-12-30
Sugarman, Scott J. (Department: 2873)
Optical: systems and elements
Optical modulator
Light wave temporal modulation
C430S035000
Reexamination Certificate
active
06671081
ABSTRACT:
BACKGROUND OF THE INVENTION
1. Technical Field of the Invention
The present invention relates to electrophoretic devices, and particularly relates to an electrophoretic device having opposing electrodes, members comprising an insulating material, and an electrophoretic dispersion liquid containing a liquid dispersion medium and electrophoretic particles, wherein the members and the dispersion liquid are placed between the opposing electrodes.
Furthermore, the present invention relates to various electronic devices including an electrophoretic display device having an electrophoretic device.
2. Description of the Related Art
Conventionally, among electrophoretic devices having a pair of electrodes between which an electrophoretic dispersion liquid containing a liquid dispersion medium and electrophoretic particles are located, the following device is known: an electrophoretic device utilizing a phenomenon wherein the distribution of the electrophoretic particles is changed by applying a voltage between a pair of the electrodes. FIG.
10
(
a
) is a general structural illustration showing an electrophoretic display device including the electrophoretic device.
The electrophoretic display device
20
includes a first substrate
1
having an electrode
3
, a second substrate
2
having a transparent electrode
4
, an electrophoretic dispersion liquid
10
packed into a space between the electrode
3
and the transparent electrode
4
, and a spacer
7
having a function of preventing the electrophoretic dispersion liquid
10
from leaking out. FIG.
10
(
a
) is a sectional view showing one pixel in a display.
The electrophoretic dispersion liquid
10
contains a liquid dispersion medium
6
and electrophoretic particles
5
dispersed in the liquid dispersion medium
6
. The liquid dispersion medium
6
has a color different from that of the electrophoretic particles
5
.
The electrophoretic display device
20
is connected to power supplies
9
a
and
9
b
for applying voltages in opposite directions through a selector switch
8
. That is, the electrode
3
is connected to one end of the power supplies
9
a
and
9
b
, and the electrode
4
is connected to the other end of the power supplies
9
a
and
9
b
through the selector switch
8
. In such a configuration, the direction of a voltage applied between the electrodes
3
and
4
can be changed by switching the selector switch
8
. Changing the direction of the applied voltage causes the electrophoretic particles to gather at a desired electrode, thereby performing desired display.
Referring to FIG.
10
(
b
), when the electrophoretic particles
5
are positively charged, applying a voltage from the power supply
9
a
causes the electrophoretic particles
5
to gather at the side of the transparent electrode
4
, which is close to the observer. In this situation, the observer sees the color of the electrophoretic particles
5
. In contrast, as shown in FIG.
10
(
c
), applying a voltage from the power supply
9
b
causes the electrophoretic particles
5
to gather at the side of the electrode
3
, which is away from the observer. In this situation, the observer sees the color of the liquid dispersion medium
6
. When the electrophoretic particles
5
are negatively charged, the particles migrate in the opposite direction to that in the above description.
As described above, when the configuration shown in FIG.
10
(
a
) is employed, two-color display is possible depending on the direction of an applied voltage. Therefore, electrophoretic displays for displaying desired images can be obtained by applying the configuration shown in the figure to all pixels.
Furthermore, other electrophoretic devices having electrodes covered with an insulating material are known. In the electrophoretic devices, an insulating layer is disposed on a surface of at least one of the mutually opposing electrodes and the maximum voltage applied to the insulating layer is designed to be smaller than the product of the dielectric breakdown strength and the thickness of the insulating layer. In such a configuration, the electrophoretic dispersion liquid can be prevented from deteriorating due to carrier transfer between the electrophoretic dispersion and the electrodes.
It is expected that electronic paper can be achieved by providing the above electrophoretic devices on a flexible substrate. In such electronic paper, it is necessary to hold the display content for a long time after the display content is written by applying a voltage.
In an electrophoretic device including electrodes provided with an insulating film thereon, when the time constant of the insulating film is adjusted to be larger than the time constant of the electrophoretic dispersion, holding the display content for a long time is impossible due to self-deletion.
When the time constant of the insulating film is reduced, self-deletion can be prevented. However, it is difficult to apply an electrical field having intensity sufficient to cause the electrophoretic particles to migrate in the electrophoretic dispersion liquid. Furthermore, there is a risk that the insulating performance of the insulating film will degrade, deteriorating the electrophoretic dispersion.
The present invention has been developed in order to solve the above disadvantages of conventional methods, and it is a first object of the present invention to provide an electrophoretic device in which the electrophoretic dispersion liquid is prevented from deteriorating and the image-retention characteristics are greatly improved to obtain, for example, electronic paper.
Furthermore, it is a second object to provide an electronic device including a display such as electronic paper, wherein the display is an electrophoretic display device and has greatly improved image-retention properties.
SUMMARY OF THE INVENTION
In order to solve the above problems and to achieve the first object, an electrophoretic device of the present invention includes a first substrate, a first electrode disposed on the first substrate, a second substrate, a second electrode disposed on the second substrate and facing the first electrode, an electro-optical layer having an electrophoretic dispersion liquid containing at least a dispersion medium and electrophoretic particles and located between the first and second electrodes, and an insulating member disposed between the first and second electrodes, wherein a voltage applied between the first and second electrodes has different values, and the time constant of the voltage is larger than the time constant of the insulating member when the voltage changes from one of the different values to another.
According to the above configuration, when the time constant of the insulating member is larger than that of the electrophoretic dispersion liquid, self-deletion can be prevented, thereby significantly improving the image-retention characteristics.
In the electrophoretic device of the present invention, the insulating member may be disposed at least either between the first electrode and the electro-optical layer or between the second electrode and the electro-optical layer. The first substrate and the first electrode may both have optical transparency, and the insulating member may be disposed between the first electrode and the electro-optical layer and may have optical transparency.
The following relationship is preferably satisfied:
R×C≧Rep×Cep
wherein R represents the electrical resistance of the insulating member, C represents the capacitance of the insulating member, Rep represents the electrical resistance of the electrophoretic dispersion liquid, and Cep represents the capacitance of the electrophoretic dispersion liquid.
According to this configuration, a high voltage can be applied to the electrophoretic dispersion liquid effectively.
The insulating member may include an insulating film disposed on at least one of the first substrate and the second substrate.
According to this configuration, the resistance and the capacitance can be adjusted by setting the type and the thickness of the
Hanig Richard
Harness & Dickey & Pierce P.L.C.
Seiko Epson Corporation
Sugarman Scott J.
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