JP2002139749A - Electrophoretic display - Google Patents

Abstract

(57) [Problem] To provide an electrophoretic display device having high contrast and low crosstalk. SOLUTION: An electrophoretic space in which electrophoretic particles move is limited to a triangle by using a triangular projection structure of a mountain shape or a pyramid shape. Electrodes are arranged at the bottom and the top of the triangular migration space, and the electrophoretic particles are adsorbed and separated from the electrodes to display an image. The electrode arranged at the apex may be a line-shaped or dot-shaped electrode. When the electrophoretic particles come to the bottom of the triangle, they spread out in a plane and display the color of the electrophoretic particles. When the electrophoretic particles reach the apex of the triangle, they are confined in a narrow space, and the surrounding area displays the color of the bottom of the electrophoretic space. By limiting the migration space, the contrast can be increased, and an electrophoretic display device with less crosstalk can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophoretic display device, and more particularly to an electrophoretic display device having a novel structure which can provide a beautiful screen with a vivid contrast of a display screen and a small crosstalk.

[0002]

2. Description of the Related Art In recent years, the development of information devices has been remarkable, and the demand for thin display devices with high resolution, low power consumption and high power consumption has been increasing, and research and development have been continued. Among them, liquid crystal display devices are expected to be able to respond to the above needs by electrically controlling the arrangement of liquid crystal molecules and changing the optical characteristics of liquid crystal. Developing liquid crystal display devices with large screens Have been. However, these liquid crystal display devices have problems such as difficulty in viewing the screen due to the angle of viewing the screen and reflected light, flickering of the light source, and an increase in the load on the vision due to low brightness. Reflective display devices are expected from the viewpoints of low power consumption and reduction of visual load.Electrophoretic display devices, one of them, have beautiful display quality and memory characteristics, so they are particularly static. It has been attracting attention as an image display device.

FIG. 8 is a schematic configuration diagram showing a main part of an electrophoretic display device. As shown in FIG. 8, substrates 2 and 3 made of two pieces of glass or the like on which display electrodes 4 and 5 made of a transparent conductive film such as indium tin oxide (ITO) are formed on opposite surfaces are formed. The dispersion medium in which the electrophoretic particles 16 are dispersed in the liquid electrophoresis medium 17 is sealed with a sealing member 15 using spacers 18 so as to be opposed to each other and to maintain an appropriate interval. It is enclosed in an electrophoresis space 6 composed of a substrate. The electrophoretic display device having this structure applies a display driving voltage to the display electrodes 4 and 5,
An electric field is applied to the electrophoretic medium 17 so that the electrophoretic particles 16 are adsorbed and separated from the display electrodes 4 and 5, and the distribution state of the electrophoretic particles 16 is changed to thereby display characters, symbols, or figures as desired. Is performed.

[0004] In general, an electrophoretic display device uses electrophoretic particles to display an image, so that it is possible to obtain a sharp image that cannot be enjoyed by a liquid crystal display device. Although it takes a long time to move the electrophoretic particles, it has a memory property and cannot follow a moving image. However, a still image has attracted attention as a method for displaying a clear image using the memory property.

[0005]

In the conventional electrophoretic display device, the contrast is still insufficient, and there is a lot of crosstalk. As a result, the contrast and the viewing angle are inferior, and a sufficiently clear image is obtained. There was no problem. An object of the present invention is to provide a novel electrophoretic display device for obtaining a display screen with higher contrast and less cross stroke.

[0006]

In order to solve the above problems, in an electrophoretic display device according to the present invention, a first substrate on which a first electrode is formed and a first substrate disposed opposite to the first substrate are provided. A second substrate provided with two electrodes, wherein a cross section between the first substrate and the second substrate is formed in a triangular space, and the electrophoretic particles are contained in the space. An electrophoretic display device enclosing the dispersed electrophoresis medium was used. As described above, when the electrophoretic particles are adsorbed to one electrode, the electrophoretic particle migration space is restricted to be narrow near the apex of the triangle, thereby increasing the density of the electrophoretic particles and providing a higher contrast than before. A clear image can be obtained.

In the present invention, a space constituted by triangular prisms can be used as the triangular space. Further, the triangular space may be a space composed of a continuum of quadrangular pyramids. By confining the electrophoretic particles in a narrow space delimited by a triangle, the particles are concentrated, and a clear image with higher contrast than before can be obtained.

In the present invention, the shapes of the first electrode and the second electrode can be asymmetrically formed. In the present invention, the first electrode may have a planar shape, and the second electrode may have a linear shape or a dot shape. One electrode is formed in a planar shape to disperse and adsorb the electrophoretic particles on one surface of the pixel, and the other electrode is for collecting the electrophoretic particles at the top of the triangular space,
It suffices to have electrodes only at the vertices of the triangular space. Therefore, it may be formed in the shape of a line or a point at the apex of the triangle. In the present invention, it is preferable that the second electrode is an electrode of a light transmitting electrode. This is because the electrode on the viewing side is transparent so that the color at the bottom of the migration space can be seen.

In the present invention, a light recursive structure may be used as the triangular space. The use of such a structure has the advantage that incident light can be reflected and taken out to the incident side to obtain a bright image.

The driving method according to the present invention can use either a simple matrix system or an active matrix system. The simple matrix method simplifies the electrode structure, and is sufficient to exhibit its functions on a simple stationary display screen. In addition, if the active matrix method is used, although the structure is slightly complicated, control can be performed for each pixel, so that a more complicated display screen can be handled.

[0011]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS FIG. 1 is a schematic diagram illustrating an electrophoresis apparatus according to the present invention. The electrophoretic display device 1 shown in FIG. 1 includes a first substrate 2 on which a first electrode 4 is provided,
The second substrate 3 provided with the electrodes 5 is disposed to face each other, and an electrophoretic space 6 partitioned by a triangular projection structure 7 is formed between the two substrates 2 and 3. The triangular projection structure 7 has a triangular cross section as shown in the figure.
An electrophoresis space 6 also having a triangular cross section is formed between the triangular cross sections. The migration space 6 is filled with a liquid migration medium 17 in which electrophoretic particles 16 are dispersed. Since the electrophoresis space 6 is partitioned by the surrounding triangular projection structure 7,
The top 6a is narrower than the lower 6b. In addition, the first electrode 4 is formed in a planar shape along the triangular lower portion 6b of the migration space 6, while the opposing second electrode 5 is formed at the top of the migration space 6 in the example of FIG. A line or a dot is formed at the position 6a. The gap between each of the electrodes 4 and 5 is isolated by an insulating layer 9. Here, the area of the first electrode 4 formed in a planar shape along the bottom side of the triangle of the migration space 6 is an individual pixel 10.

FIG. 2 shows an example of the triangular projection structure 7 used here. FIG. 2A is a perspective view showing the appearance of a triangular prism 7 a constituting the triangular projection structure 7. This triangular prism 7a
Has a triangular shape as shown in FIG. When a large number of the triangular prisms 7a are arranged in parallel, an electrophoresis space 6 having a triangular cross section as shown in FIG. 1 is formed. The ridge 6a on the lower side of the triangular prism shown in FIG. 2A is the top 6a of the migration space 6 shown in FIG. FIG. 2B shows a triangular projection structure 7.
Is a perspective view showing the appearance of a continuous body 7b of quadrangular pyramids constituting the above. When a large number of the quadrangular pyramids 7b are arranged in parallel in the same manner as described above, an electrophoresis space 6 having a triangular cross section as shown in FIG. 1 is formed. Each vertex 6a of the bottom surface of the continuous body 7b of the quadrangular pyramid shown in FIG.
The top 6a.

Next, the screen display function of the electrophoretic display device of the present invention will be described with reference to FIG. FIG. 3 is a diagram showing a cross section when a voltage is applied to the electrodes of the electrophoretic display device of the present invention. In the electrophoretic spaces 6-1 to 6-4, for example, electrophoresis in which the zeta potential is positively (+) charged An electrophoresis medium 17 in which particles 16 are dispersed is filled. Now pixel 10
In -1 and 10-3, a positive (+) potential is applied to the first electrodes 4-1 and 4-3 from the reference potential, and
A negative (-) potential from the reference potential is applied to -1 and 5-3. On the other hand, in pixels 10-2 and 10-4, the first
To the electrodes 4-2 and 4-4 are minus (-) than the reference potential.
And a positive (+) potential is applied to the second electrodes 5-2 and 5-4 from the reference potential. Then, the electrophoretic particles 16 charged to plus (+) become minus (−).
As shown in FIG. 3A, the electrophoretic particles 16 gather at the top of the migration space 6 in the pixels 10-1 and 10-3 as shown in FIG. On the other hand, in the pixels 10-2 and 10-4, the electrophoretic particles 16 are attracted toward the positive (+) potential electrode at the bottom of the migration space 6, and
Spreads out at the bottom of the

FIG. 3B and FIG. 3C show this state as viewed from the display surface side of the electrophoretic display device. FIG.
2B shows an example of a screen display when the triangular prism 7a shown in FIG. 2A is used as the triangular projection structure 7, and FIG. 2
FIG. 9B shows an example of a screen display when the continuous body 7b of quadrangular pyramids shown in FIG. When the triangular prism 7a shown in FIG. 2A is used as the triangular projection structure 7, the second electrode on the viewing side has a negative (-) potential as shown in FIG. Applied pixels 10-1 and 1
In 0-3, a linear image showing the color of the electrophoretic particles 16 appears at the center of the pixel, and the color of the electrophoretic medium 17, the color of the electrode, or the color of the substrate 2 or the color plate below the transparent electrode appears on both sides of the pixel. become. On the other hand, in the pixels 10-2 and 10-4 in which the second electrode on the viewing side is applied with a positive (+) potential, the entire surface of the pixel is displayed in the color of the electrophoretic particles 16.

When the continuous body 7b of quadrangular pyramids shown in FIG. 2B is used as the triangular projection structure 7, a screen display is as follows.
As shown in FIG. 3C, in the pixels 10-1 and 10-3 in which the second electrode on the visual field side is applied with a negative (−) potential, a dot indicating the color of the electrophoretic particles 16 is displayed at the pixel center. And the peripheral portion of the pixel becomes the color of the electrophoretic medium 17, the color of the electrode 4, or the color of the substrate 2 or the colored plate below the transparent electrode. On the other hand, in the pixels 10-2 and 10-4 in which the second electrode on the viewing side is applied with a positive (+) potential, the entire surface of the pixel is displayed in the color of the electrophoretic particles 16.

As described above, according to the electrophoretic display device of the present invention, the color of the electrophoretic particles and the color of the electrophoretic medium, the colored electrode or the colored pixel bottom are used to obtain high contrast. A color display image can be obtained. By adjusting the applied voltage, it is also possible to adjust the dispersion / aggregation state of the electrophoretic particles and control the tint to an intermediate color. Since the display image of the electrophoretic display device of the present invention has a high contrast and is colorful, it is most suitable for a sign display or the like mainly composed of a still image.

The triangular projection structure 7 used in the present invention comprises:
Those made of transparent glass or synthetic resin such as acrylic resin can be used. A transparent material can be etched or press-molded to obtain a large number of triangular projection structures arranged in parallel.

The electrophoretic particles used in the present invention must be stably dispersed in a liquid, have a single polarity, and have a narrow particle size distribution, from the viewpoint of the lifetime, contrast, resolution, etc. of the display device. Is desirable. The particle size is 0.1 μm
To about 5 μm. With such a particle size, the light scattering efficiency does not decrease, and a sufficient response speed can be obtained when a voltage is applied. As a material of such electrophoretic particles, for example, titanium oxide, zinc oxide, zirconium oxide,
Inorganic pigment particles such as iron oxide, aluminum oxide, cadmium selenide, carbon black, barium sulfate chromate, zinc sulfide, cadmium sulfide, or phthalocyanine blue, phthalocyanine green, Hansa yellow, watching red, diary light yellow, etc. Organic pigment particles can be used. Each of these pigment particles has a unique color, and may be selected according to the image to be composed. Further, for example, particles colored by mixing carbon black with a resin such as polyethylene or polystyrene may be used. These particles usually have a positive (+) surface potential (zeta potential).

In the present invention, the electrophoretic medium for dispersing the above-mentioned electrophoretic particles may have a low dissolving power for the electrophoretic particles, stably disperse the electrophoretic particles, contain no ions, and apply ions by applying a voltage. Insulating liquid that does not cause turbidity is desirable. Further, a liquid having a low viscosity is preferably equal to the specific gravity of the electrophoretic particles, and from the viewpoint of easy movement of the electrophoretic particles when a voltage is applied.
Examples of the insulating fluid medium that can be used as such an electrophoretic medium include hexane, decane, hexadecane, kerosene, toluene, xylene, olive oil,
Trixylene phosphate, isopropanol, trichlorotrifluoroethane, dibromotetrafluoroethane, tetrachloroethylene, diiodomethane, chlornaphthalene, bromobenzene, tetrabromomethane, silicone oil and the like can be used. When adjusting the specific gravity with the electrophoretic particles in order to prevent the floating and sedimentation of the electrophoretic particles, a mixed fluid of the above fluids can be used. Further, the electrophoresis medium may be colorless and transparent, or may be colored. When the electrophoresis medium is colorless and transparent, the pixel in which the electrophoretic particles are gathered at the apex of the triangular projection structure has the color of the electrode or the substrate at the bottom of the triangular projection structure. When a colored electrophoretic medium is used, pixels in which the electrophoretic particles are gathered at the apexes of the triangular protrusion structure have the color of the electrophoretic medium.

In the present invention, the mixing ratio of the electrophoretic particles to the electrophoretic medium is, for example, from 1% by weight to 2% by weight.
0% by weight is preferred. There is no particular limitation as long as the electrophoresis of the electrophoretic particles is not inhibited. In the present invention, an additive such as a surfactant or a resin can be added to the electrophoretic medium as needed to increase the charge of the electrophoretic particles or to make the polarity uniform.

In the present invention, a suitable thickness of the migration space is:
It is not particularly limited as long as it is larger than the diameter of the electrophoretic particles and does not hinder the movement of the particles, but it is preferable that the moving distance of the electrophoretic particles does not become too long in order to obtain a fast response speed when applying a voltage. From such a viewpoint, the thickness of the migration space is preferably about 5 μm to 200 μm. In such an electrophoretic display device, the distance of the gap between the electrodes is larger than that of the liquid crystal display device, so that a crosstalk phenomenon in which a signal current leaks to an unselected electrode is less likely to occur, resulting in a contrast or a viewing angle. , And a clear image can be obtained.

The electrode materials used in the present invention include silver,
Highly conductive metal films such as aluminum, gold, copper, platinum and platinum black, or indium tin oxide (Indium Tin Ox
ide: ITO), a transparent conductive film such as tin oxide, indium oxide, and copper iodide can be used. In the case of the display system using reflected light, a transparent electrode can be used for the electrode on the viewing side, and an opaque metal electrode can be used for the electrode on the side opposite to the viewing side. It is also possible to use a transparent electrode for the electrode on the side opposite to the viewing side, and arrange a color panel below the transparent electrode, or use a colored substrate to select the color of the display screen. it can. On the other hand, in the case of a display system using transmitted light, it is necessary to use a transparent electrode also for the electrode on the visual field side and the electrode on the opposite side to the visual field.

These electrode materials are formed into a thin film on a substrate by means of vapor deposition, sputtering or the like, and then a predetermined electrode pattern is formed by using a usual method such as photolithography. At this time, the electrode at the bottom of the migration space 6 is formed in a planar shape. Depending on the type of display screen, one common electrode or a striped common electrode may be used.
Also, the migration space 6 formed by the triangular projection structure 7
May be formed in a stripe shape so as to penetrate each pixel, or may be formed in a matrix for each pixel. When a triangular prism-shaped projection structure is used, it can be formed in a thin line along the ridgeline of the apex of the triangular projection structure 7. When a triangular projection structure 7 composed of a continuous body of quadrangular pyramids is used, electrodes can be formed in a matrix only at the apexes of the migration space 6 formed by the triangular projection structure 7. . Each electrode is protected by an insulating layer.

The driving method of each pixel can be a simple matrix method or an active matrix method using a driving element depending on a display method and an electrode arranging method.
Since a still image is often used, the present invention can be applied to a segment system. The DC voltage applied between the two electrodes depends on the distance between the two electrodes and the type of the dispersion medium, but is preferably about 10 to 50 V.

In the electrophoretic display device of the present invention, by using the triangular projection structure as a light-returning structure, the incident light can be reflected as it is, and the displayed image can be viewed from the incident light side. . Reflected light recurrence structure, having the schematic structure shown in FIG. 7, the light L ₁ incident back twice total reflection to the original direction on the surface of the triangular protrusion structure 7 functions It is a structure. Such a light-returning structure can be obtained by forming a dielectric multilayer film on the surface of the triangular projection structure 7 previously shown in FIG. Further, it can also be achieved by selecting the refractive index of the triangular projection structure 7 as a low refractive index and selecting a migration medium having a high refractive index. If the photoregressive structure is used in the electrophoretic display device of the present invention, the pixel 10-1 in which the electrophoretic particles 16 are gathered at the vertex of the triangle at the bottom of the electrophoretic space 6 as shown in FIG.
The pixel 1 that has undergone total reflection and is recognized as a reflection image of natural light, and the electrophoretic particles 16 have been adsorbed to the plane portion of the migration space 6
In 0-3, the reflection image of the electrophoretic particles 16 is recognized.
If the electrophoretic particles 16 are formed in black, incident light is absorbed and recognized as a black image. By extracting reflected light in the direction of the incident light in this way, a bright and high-contrast screen display can be achieved.

(First Embodiment) A continuous body of quadrangular pyramids as shown in FIG.
An electrophoretic display device having a cross-sectional structure similar to the cross-sectional structure shown in FIG. As the first substrate 2, a black glass plate having a thickness of 1 mm and a black pigment dispersed therein is used. In addition, a transparent glass plate having a thickness of 1 mm is used for the second substrate 3. An indium tin oxide (ITO) thin film is formed on the surface of the first substrate 2 by vacuum evaporation to a thickness of about 0.5 μm, and then has a predetermined width along the bottom of each pixel using photolithography. To form a stripe-shaped transparent first electrode 4. On the other hand, an ITO thin film having a thickness of about 0.5 μm is formed on the surface of the second substrate 3 by vacuum deposition, and then a transparent 10 μm side having a side of about 10 μm is formed at the center of each pixel by using photolithography. The two electrodes 5 are formed in a matrix. The triangular projection structure 7 is formed by press-molding a transparent acrylic resin and has a base of about 140 μm.
The pyramid-shaped protrusions having a height of about 100 μm are formed continuously. The first substrate 2, the second substrate 3 and the triangular projection structure 7 prepared in this way are
As shown in FIG. 3, the apex of the triangular projection structure 7 is
, So that the first substrate 2 is in the first position.
The electrodes 4 are superimposed so as to be at the center of each pixel, and the periphery thereof is bonded using a sealing member (not shown).

A dispersion medium is prepared as follows.
You. As the electrophoretic particles 16, high-purity particles having an average particle size of 2 μm are used.
Degree white titanium oxide (TiO _Two ). Also electrophoresis
Silicone oil is used as the medium 17 and both are electrically
Mix so that the mixing ratio of the migrating particles 16 is 5% by weight.
You. Add a small amount of surfactant to further improve dispersion stability
To form a dispersion medium. In this case, the electrophoretic particles 16
The surface has a positive (plus) zeta potential. This
The dispersion medium adjusted as described above is used for the first substrate 2 and the second medium.
Formed by a triangular projection structure 7 between the substrate 3
In addition, the electrophoresis is performed by enclosing the electrophoresis space 6 having a triangular cross section.
A moving display device.

Hereinafter, the driving operation of the electrophoretic display device configured as described above will be described. First, connections are made so that a DC voltage can be applied to the first and second electrodes 4 and 5 by an electric circuit (not shown). At this time, for example, an electric circuit is set so that the stripe-shaped first electrode 4 can apply a reference potential to each stripe, and the matrix-shaped second electrode 5 is set to a reference potential for each electrode. Plus (+)
Alternatively, an electric circuit is set so that a negative (-) potential can be applied. With such connection, the electric circuit is controlled so that a plus (+) or minus (−) potential is applied to the reference potential for each pixel. Although the voltage depends on the distance between the two electrodes and the type of the dispersion medium, approximately 10 to 50 V is suitable.

The display of each pixel is as follows. In a pixel in which the first electrode 4 is applied with the reference potential and the second electrode 5 is applied with a minus (−) potential with respect to the reference potential,
Since the electrophoretic particles are positively (+) charged, the electrophoretic particles are adsorbed on the second electrode 5 side and concentrated on the vertex 6 a of the pyramid-shaped electrophoretic space 6. Therefore, as shown by the pixels 10-1 and 10-3 in FIG. 3C, a white image of a small square titanium oxide appears at the center of the pixel. Since the periphery of the pixel passes through the electrophoresis medium 17 and the first electrode 4 and sees the first substrate 2, the black color of the first substrate 2 is displayed. As a result, the pixels 10-1 and 10-3 become almost black images having a small white point at the center.

On the other hand, in a pixel in which the first electrode 4 is applied with the reference potential and the second electrode 5 is applied with a plus (+) potential with respect to the reference potential, the electrophoretic particles are positive (+).
Therefore, the electrophoretic particles are adsorbed on the first electrode 4 side and spread and gather at the bottom of the pyramid-shaped electrophoretic space 6. Therefore, as shown by the pixels 10-2 and 10-4 in FIG. 3C, the entire pixel becomes a white image of titanium oxide. By controlling the polarity applied to each pixel in this manner, a clear black-and-white image with high contrast can be obtained.

(Second Embodiment) As in the first embodiment, a triangular projection structure made of a transparent acrylic resin as shown in FIG. An electrophoretic display having a cross-sectional structure similar to the cross-sectional structure shown in FIG. 1 except that the first electrode was formed on the entire surface using a continuous body in which pyramid-shaped protrusions having a length of about 100 μm were continuous. Create a device. As the first substrate 2, a glass plate having a thickness of 1 mm is used. In addition, a transparent glass plate having a thickness of 1 mm is used for the second substrate 3. First
A platinum / platinum black thin film is vacuum-deposited to a thickness of about 1.0 μm on the entire surface of the substrate 2 to form a black first electrode 4. On the other hand, an ITO thin film having a thickness of about 0.5 μm is also formed on the surface of the second substrate 3 by vacuum deposition, and then a side of about 10 μm is formed at the center of each pixel by using photolithography.
m transparent second electrodes 5 were formed in a matrix. The first substrate 2 and the second substrate 3 and the triangular projection structure 7 prepared in this way are connected to the predetermined positions of the second substrate 3 with the vertices of the triangular projection structure 7 as shown in FIG. The first substrate 2 is overlapped so that the first electrode 4 is located at the center of each pixel, and the periphery thereof is bonded using a sealing member (not shown).

The dispersion medium was prepared as follows.
Was. As the electrophoretic particles 16, high-purity particles having an average particle size of 2 μm are used.
Degree white titanium oxide (TiO _Two )It was used. Also electrophoresis
Toluene is used as the medium 17 and both are electrophoretic particles.
Is blended so that the mixing ratio of is 5% by weight. More minutes
Add a small amount of surfactant to improve dispersion stability and disperse
System medium. In this case, the surface of the electrophoretic particles 16
The potential is positively (plus). Adjust like this
Between the first substrate 2 and the second substrate 3
The cross section formed by the triangular projection structure 7
The electrophoretic display device is enclosed in the electrophoretic space 6
You.

In the electrophoretic display device according to the present embodiment, a plurality of pixels 10 formed in a matrix forming an image display area are connected to a thin film transistor (Thin Film Transistor).
An active matrix display system controlled by (r: TFT) is adopted. In the electrophoretic display device according to the present embodiment, the reference potential is given by using the planar first electrode 4 as a common electrode, and the second electrodes 5 arranged in a matrix are TFT-controlled to provide a positive or negative potential. Is applied to display an image. FIG. 4 is a diagram showing an equivalent circuit of the TFT control drive circuit used in the present invention. In the figure, the scanning line 31 is a TFT
The data line 35 is a wiring for sending an image signal to the source electrode of the TFT 30. A TFT 30 for driving a pixel is connected between the scanning line 31 and the data line 35 for each pixel. The drain electrode of the TFT 30 is connected to the second electrode 5 of each pixel of the electrophoretic display device, and the operation of the TFT 30 causes each pixel to have a positive (+) potential with respect to the reference potential of the first electrode 4. Alternatively, a negative (-) potential is applied.
In addition, a storage capacitor 70 is connected to the drain electrode of the TFT 30 in parallel with the second electrode 5, and serves to prevent the stored image signal from leaking.

Hereinafter, the driving operation of the electrophoretic display device thus configured will be described. First, a reference potential is applied to the first electrode 4 by an electric circuit device (not shown),
The electrode 5 is connected so that a plus (+) or minus (-) voltage can be applied to the reference potential. By connecting in this manner, plus and minus for each pixel using TFT control.
A driving circuit is configured so that the voltage can be controlled to a negative desired potential, and a DC voltage is applied.

The display of each pixel is as follows. In a pixel in which a positive (+) potential is applied to the second electrode 5 with respect to the reference potential, the electrophoretic particles 16 are positively (+) charged. 6 gather at the bottom 6b. Therefore, the whole pixel becomes a white image of titanium oxide. On the other hand, in a pixel in which a negative (−) potential is applied to the second electrode 5 with respect to the reference potential, the electrophoretic particles 16 are charged to the positive (+). 5 and concentrates on the vertex 6a of the pyramidal migration space 6. Therefore, a small square white image of titanium oxide appears at the center of the pixel. Since the periphery of the pixel passes through the electrophoresis medium 17 and the first electrode 4 and sees the first electrode 4 on the first substrate 2, the black color of the first electrode 4 is displayed. As a result, an almost black image having a small white point at the pixel center is obtained. By controlling the polarity applied to each pixel in this manner, a clear black-and-white image with high contrast can be obtained.

(Embodiment 3) Using a triangular prism made of a transparent acrylic resin as shown in FIG. 2A as a triangular projection structure, an electric having a cross-sectional structure similar to the cross-sectional structure shown in FIG. Create a migration display device. The height of the triangular prism is about 100 μm. The first substrate 2 has a thickness of 1 m
A red glass plate in which m red pigment is dispersed is used.
In addition, a transparent glass plate having a thickness of 1 mm is used for the second substrate 3. An indium tin oxide (ITO) thin film is formed on the surface of the first substrate 2 by vacuum evaporation to a thickness of about 0.5 μm, and then has a predetermined width along the bottom of each pixel using photolithography. To form a stripe-shaped transparent first electrode 4. On the other hand, an ITO thin film having a thickness of about 0.5 μm is also formed on the surface of the second substrate 3 by vacuum deposition, and then the first thin film is formed using photolithography.
In the direction orthogonal to the electrode 4 of the electrophoresis space 6 at the center of each pixel.
A thin transparent second electrode 5 is formed along the vertex 6a in a stripe shape.

The first substrate 2, the second substrate 3 and the triangular projection structure 7 prepared as described above are combined with the apex of the triangular projection structure 7 as shown in FIG. The first substrate 2 is overlapped so as to be at a predetermined position such that the first electrode 4 is located at the center of each pixel, and the periphery thereof is bonded using a sealing member (not shown). FIG. 5 shows the electrode arrangement when this state is seen through from the visual field side. Also, the line AA ′ in FIG.
FIG. 6 shows a cross-sectional view taken along the line. As shown in FIG. 5, when viewed from the viewing side, the pixels 10 are arranged in a matrix, and the first electrodes 4 in the form of stripes are formed in the horizontal direction on the paper, and the second electrodes 4 in the vertical direction on the paper. An electrode 5 is formed. The pitch between the first electrode 4 and the second electrode 5 is equal to the pitch between the pixels 10.

A dispersion medium is prepared as follows. As the electrophoretic particles 16, those obtained by coating the surface of a polyethylene particle having an average particle diameter of 2 μm with a yellow pigment are used. In addition, silicone oil is used as the electrophoresis medium 17, and both are blended so that the mixing ratio of the electrophoretic particles becomes 5% by weight. Further, a slight amount of a surfactant is added to improve the dispersion stability to obtain a dispersion medium. In this case, the zeta potential on the surface of the electrophoretic particles 16 is positively (plus). The dispersion medium adjusted in this manner is supplied to the first substrate 2.
The cross section formed by the triangular projection structure 7 between the substrate and the second substrate 3 is enclosed in the triangular electrophoretic space 6 to obtain an electrophoretic display device.

Hereinafter, the driving operation of the electrophoretic display device configured as described above will be described. First, connections are made so that a DC voltage can be applied to the first and second electrodes 4 and 5 by an electric circuit (not shown). At this time, for example, an electric circuit is configured so that a reference potential can be applied to the stripe-shaped first electrode 4 for each stripe. Further, an electric circuit is configured so that a positive (+) potential with respect to the reference potential or a negative (-) potential with respect to the reference potential can be applied to the stripe-shaped second electrodes 5 for each stripe. In this manner, the electric circuit is connected to select a certain stripe-shaped first electrode 4, and at the same time, each stripe-shaped second electrode 5 has a positive (+) with respect to the reference potential or a positive (+) with respect to the reference potential. A control circuit is configured to apply a desired negative (-) potential, and a DC voltage is applied.

The display of each pixel is as follows. Generally, electrophoretic display devices do not have remarkable threshold characteristics,
A matrix display like a liquid crystal display device is impossible.
Therefore, by utilizing the fact that the electrophoretic particles are adsorbed on the electrodes and have a memory property, data is selectively sent for each line and displayed as an image. When changing the image, the selected line is released electrically and data is sent. That is, a reference potential is applied to a selected line of each first electrode 4, and a negative (−) potential is applied to a line of the second electrode 5 having a pixel to be displayed in red.
In the pixel to which the voltage is applied as described above, the electrophoretic particles are positively (+) charged.
, And is concentrated on the vertex 6 a of the triangular migration space 6. Therefore, a thin linear yellow image appears at the center of the pixel. Since the periphery of the pixel passes through the electrophoresis medium 17 and the first electrode 4 and sees the first substrate 2, the first substrate 2 is displayed in red. As a result, the pixel becomes an almost red image having a thin yellow line at the center.

On the other hand, the second electrode 5 of the pixel to be displayed in yellow
Is applied a positive (+) potential with respect to the reference potential. In the pixel to which the voltage is applied as described above, the electrophoretic particles are positively (+) charged. Therefore, the electrophoretic particles are attracted to the first electrode 4 side and spread to the bottom 6 b of the triangular prism migration space 6. Get together. Therefore, the entire pixel becomes a yellow image of the electrophoretic particles. A red or yellow image is displayed along the line of the first electrode 4 thus selected. If the lines of the first electrode 4 are sequentially scanned and selected, and the applied voltage is controlled as described above, a high contrast and clear red / yellow image is displayed as a whole.

(Fourth Embodiment) An electrophoretic display device having a cross-sectional structure shown in FIG. 7 is prepared by using a continuous body of quadrangular pyramids as shown in FIG. 2B as a triangular projection structure. The triangular projection structure 7 is formed by pressing a transparent acrylic resin and continuously forming pyramid-shaped projections having a bottom of about 140 μm and a height of about 100 μm. On a slope of the pyramid-shaped protrusion, a transparent fluororesin is formed as a dielectric layer by dip coating to form five layers each having a thickness of 0.5 μm.

As the first substrate 2, a glass plate having a thickness of 1 mm was used. In addition, a transparent glass plate having a thickness of 1 mm is used for the second substrate 3. An aluminum (Al) thin film is formed on the surface of the first substrate 2 by vacuum evaporation to a thickness of about 0.5 μm, and one side is located at the center of the pixel at the bottom of each pixel using photolithography. A transparent first electrode 4 of about 10 μm is formed in a matrix. On the other hand, an ITO thin film having a thickness of about 0.5 μm is formed on the surface of the second substrate 3 by vacuum evaporation, and then a second electrode 5 in a matrix is formed using photolithography in accordance with each pixel. I do. The first substrate 2 and the second substrate 3 and the triangular projection structure 7 prepared in this way are connected to a predetermined position of the first substrate 2 with the vertex of the triangular projection structure 7 as shown in FIG. , The second substrate 3 is overlapped so that the second electrode 5 is located at the center of each pixel, and the periphery thereof is bonded using a sealing member (not shown).

The dispersion medium is prepared as follows. As the electrophoretic particles 16, carbon black having an average particle size of 2 μm is used. In addition, silicone oil is used as the electrophoresis medium 17, and both are blended so that the mixing ratio of the electrophoretic particles becomes 5% by weight. Further, a slight amount of a surfactant is added to improve the dispersion stability to obtain a dispersion medium. In this case, the zeta potential on the surface of the electrophoretic particles 16 is positively (plus). The dispersion medium thus adjusted is enclosed in a migration space 6 having a triangular projection structure 7 between the first substrate 2 and the second substrate 3 and having a triangular cross section. Display device.

Hereinafter, the driving operation of the electrophoretic display device configured as described above will be described. First, connections are made so that a DC voltage can be applied to the first and second electrodes 4 and 5 by an electric circuit (not shown). At this time, for example, an electric circuit is set so that the polarity of each of the first and second electrodes 4 and 5 can be changed. A circuit is configured so as to be connected in this way so that the plus / minus polarity can be controlled to a desired polarity for each pixel, and a DC voltage is applied.

The display of each pixel is as follows. As shown in FIG. 7, the pixel 1 in which a negative (−) potential is applied to the first electrode 4 and a positive (+) is applied to the second electrode 5
In the case of 0-1, since the electrophoretic particles are positively (+) charged, the electrophoretic particles are adsorbed on the first electrode 4 side and gather at the bottom of the triangular electrophoretic space 6. Therefore, the upper part of the electrophoresis space 6 becomes almost the electrophoresis medium 17 and the incident plate light L ₁ from above.
It may undergo total reflection at the slopes of the triangular protrusion structure 7, coming reflected in the same direction as the incident light L _1. Therefore, pixel 10
-1 indicates the color of the triangular projection structure 7, which is almost transparent.

On the other hand, as shown in FIG. 7, in a pixel 10-3 in which a positive (+) potential is applied to the first electrode 4 and a negative (-) potential is applied to the second electrode 5, Is positively (+) charged, so that the electrophoretic particles 1
6 attracts to the second electrode 5 side and concentrates on the top surface of the triangular migration space 6. The incident light L ₂ from above is the electrophoretic particles 1
6, the pixel 10-3 becomes black.

By controlling the polarity applied to each pixel in this way, a clear black image with high contrast can be obtained.

[0049]

As described in detail above, in the electrophoretic display device of the present invention, not only the area of the electrophoretic particles is made variable by adsorbing the electrophoretic particles only on the electrodes, but also the electrophoretic space of the electrophoretic particles is limited. Thereby, there is an advantage that a clear display image with higher contrast is obtained. Furthermore, the gap between the substrates is larger than that of the liquid crystal display device, and the crosstalk due to the leakage current between the selected and non-selected electrodes is reduced,
There is an advantage that a beautiful display image can be obtained. Further, by configuring the electrodes as a black matrix, the contrast can be further enhanced.

[Brief description of the drawings]

FIG. 1 is a schematic configuration diagram showing a main part of an electrophoretic display device of the present invention.

FIG. 2 is an external perspective view showing a triangular projection structure used in the present invention.

FIG. 3 is a diagram illustrating the operation principle of the electrophoretic display device of the present invention.

FIG. 4 is an equivalent circuit diagram showing a pixel driving circuit used in the present invention.

FIG. 5 is a perspective view showing an example of an electrode arrangement of the electrophoretic display device of the present invention.

FIG. 6 is a cross-sectional view taken along line A-A ′ of FIG.

FIG. 7 is a diagram illustrating an operation principle of another electrophoretic display device of the present invention.

FIG. 8 is a schematic configuration diagram for explaining an operation principle of a conventional electrophoretic display device.

[Explanation of symbols]

1 ... electrophoretic display device, 2,3 ... substrate, 4,5 ...
... Electrodes, 6 migration space, 7 triangular projection structure, 8, 9 insulating layer, 10 pixels , 15 ...
··· Sealing member, ······························································
..TFT, 31... Scanning line, 35... Data line, 7
0: Storage capacity

Claims (10)

[Claims] A first substrate on which a first electrode is formed;
A second substrate provided with a second electrode opposed to the first electrode, wherein a space having a triangular cross section is formed between the first substrate and the second substrate. An electrophoretic display device, wherein a migration medium in which electrophoretic particles are dispersed is enclosed in the triangular space. 2. The electrophoretic display device according to claim 1, wherein the triangular space is constituted by a triangular prism. 3. The electrophoretic display device according to claim 1, wherein the triangular space is formed by a continuum of quadrangular pyramids. 4. The apparatus according to claim 1, wherein said first electrode and said second electrode are asymmetric in shape.
An electrophoretic display device according to any one of the above. 5. The electrophoretic display device according to claim 4, wherein the first electrode has a planar shape, and the second electrode has a linear shape. 6. The electrophoretic display device according to claim 4, wherein the first electrode has a planar shape, and the second electrode has a point shape. 7. The electrophoretic display device according to claim 1, wherein the second electrode is a light transmissive electrode. 8. The electrophoretic display device according to claim 1, wherein the triangular space is a light-returning structure. 9. The electrophoretic display device according to claim 1, wherein the driving method is a simple matrix method. 10. The electrophoretic display device according to claim 1, wherein the driving method is an active matrix method.