KR101201328B1 - Electrophoretic Display Device - Google Patents

Abstract

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophoretic display device having a front light source on a front surface where an image is displayed so that an image can be displayed even in a dark place where external light source is insufficient. A first substrate including a thin film transistor, a pixel electrode, and a storage capacitor in each defined pixel region, a second substrate opposed to and bonded to the first substrate, an electrophoretic film interposed between the first and second substrates, A lower portion provided between the third substrate facing the second substrate, the front light source partially provided between the second and third substrates, and the second substrate and the front light source to apply voltage to the front light source. And an upper electrode provided between the third substrate and the front light source to apply a voltage to the front light source. Characterized in that the configuration.

Electrophoretic Device, Front Light Source, Reflective Type

Description

Electrophoretic Display Device

1 is a schematic cross-sectional view of an electrophoretic display device according to the prior art.

2 is a cross-sectional view for explaining a method of driving a conventional electrophoretic display device.

3 is a cross-sectional view of an electrophoretic display device according to the present invention.

4 is a cross-sectional view for explaining a method of driving an electrophoretic display device according to the present invention;

5 is a plan view of a front light source driving electrode according to a first embodiment of the present invention;

6 is a plan view of a front light source driving electrode according to a second embodiment of the present invention;

7 and 8 are plan views illustrating a method of driving an electrode according to a second embodiment of the present invention.

* Explanation of symbols on the main parts of the drawings

104: microcapsules 105: electrophoretic membrane

111: first substrate 112a: gate electrode

113: gate insulating film 114: active layer

115a, 115b: source / drain electrodes 117: pixel electrodes

121: second substrate 124: common electrode

131: third substrate 132: capacitor lower electrode

135 capacitor upper electrode 150 front light source

161 and 162: upper and lower electrodes 165: light blocking layer

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an electrophoretic display device (EPD), and more particularly, to an electrophoretic display device intended to display by a front light source even in a dark place.

An electrophoretic display is an image display device using a phenomenon in which colloidal particles are moved to either polarity when a pair of electrodes applied with voltage is immersed in a colloidal solution. It is expected to be spotlighted as an electric paper because it has characteristics such as electric power.

Such an electrophoretic display device has a structure in which an electrophoretic film is interposed between two substrates. When the pixel electrode is formed on the lower substrate of the two substrates and a voltage is applied to the pixel electrode, the charged particles in the electrophoretic film move to the pixel electrode side or to the opposite side, whereby a viewing sheet is used. You can see the image.

In such an electrophoretic apparatus, at least one of the two substrates must be transparent to display an image in a reflective mode, which reflects and displays external light. Therefore, the display brightness and contrast ratio become very bad in a dark place, and cannot function as a display.

Hereinafter, an electrophoretic display device will be described in detail with reference to the accompanying drawings.

1 is a schematic cross-sectional view of an electrophoretic display device according to the prior art, and FIG. 2 is a cross-sectional view illustrating a method of driving the electrophoretic display device according to the prior art.

As shown in FIG. 1, an electrophoretic display device has a structure in which an upper substrate 1 and a lower substrate 2 on which a pixel electrode 12 are formed are disposed to face each other, and an electrophoretic film is interposed between the two substrates. .

At this time, the upper and lower substrates (1, 2) is formed of a thin, flexible film of a material, the pixel electrode 12 is a metal of high reflectivity, for example, aluminum, copper, or the like. However, the pixel electrode may be formed using a non-flexible substrate or a transparent conductive material such as ITO.

The electrophoretic film is composed of a solvent 4 including charged pigment particles 3 and is made into a microcapsule 5 by a coacervation method. (5) is mixed with a binder (6) to form a coating (coating) or laminating (base) on the base film.

At this time, the pigment particles (3) may be colored in different colors, by adding a pigment of B, W (Black, White) so that the image is represented. The solvent 4 and the binder 6 are formed of a transparent material to allow light to pass therethrough.

Since the electrophoretic film is surrounded by the microcapsule film, the pigment particles 3 can suppress the movement of the pigment particles in an undesired direction by a field of adjacent pixels, thereby realizing better image quality.

In such an electrophoretic display, when a voltage is applied to the pixel electrode 12, charged pigment particles 3 are moved to an electrode having a polarity opposite to that of the polarity. The predetermined image is displayed according to the reflection of light by the light. On the other hand, changing the polarity of the pigment particles (3) is moved to the electrode having the opposite polarity, and displays another image.

Referring to FIG. 2, a method of driving an electrophoretic display device according to on / off of a voltage will be described in detail. However, black particles are positively charged and white particles are negatively charged. Of course, negatively charged black particles and positively charged white particles may also be used.

FIG. 2A illustrates a distribution diagram of black particles (+) and white particles (−) when an intermediate voltage is applied to the pixel electrode 12. FIG. -) The distribution diagram of the black particles (+) and the white particles (-) when the voltage is applied is shown, and FIG. 2 (c) shows the black particles when the positive voltage is applied to the pixel electrode 12 ( The distribution of + and white particles (-) is shown.

As such, when a negative voltage is applied to the pixel electrode 12 as shown in FIG. 2 (b), the black particles (+) fall and the white particles (−) rise to form a white (on the upper substrate 1) side. When W) is observed and a positive voltage is applied to the pixel electrode 12 as shown in FIG. 2 (c), the white particles (-) fall and the black particles (+) rise to raise the upper substrate (1). Black B is observed from the side. When a predetermined voltage is applied to the pixel electrode 12 to properly adjust the distribution of the black particles and the white particles, the gray color G is observed on the upper substrate 1 side.

Based on this driving method, a negative voltage or a positive voltage is applied to each of the plurality of pixels according to the image data. In this case, a thin film transistor may be provided in each of the plurality of pixels to actively adjust a voltage value applied to the pixel electrode 12. Therefore, various images can be displayed by controlling the polarity of the applied voltage for each pixel.

However, the electrophoretic display device according to the prior art has the following problems.

That is, the conventional electrophoretic device is a reflective mode, and the image is displayed by the reflection of the pigment particles of the electrophoretic film, so that the brightness and contrast ratio worsens due to the lack of the external light source in a dark place without external light, thereby functioning as a display. There is a limit that can not be exercised.

Even if the pixel electrode is formed of a transparent conductive material and a backlight is used on the back of the electrophoretic device, the light is not absorbed by the pigment in the microcapsules without going out in front of the display by the electrophoretic film.

Accordingly, the present invention has been made to solve the above problems, an electrophoretic display device comprising a front light source in front of the image is displayed so that the image can be displayed in a dark place lacking external light source The purpose is to provide.

An electrophoretic display device of the present invention for achieving the above object is a first substrate having a thin film transistor, a pixel electrode and a storage capacitor in each pixel region defined by a gate wiring and a data wiring perpendicular to each other; A second substrate opposingly bonded to the first substrate, an electrophoretic film interposed between the first and second substrates, a third substrate opposingly bonded to the second substrate, and partially between the second and third substrates A front electrode provided between the second substrate and the front light source, a lower electrode configured to apply a voltage to the front light source, and an upper portion provided between the third substrate and the front light source to apply voltage to the front light source It is characterized by including an electrode.

That is, the present invention is characterized in that the front light source is further provided on the second substrate on which the image is displayed so that the image can be displayed even in the dark where the external light source is insufficient.

The front light source is disposed one for each of the plurality of pixel areas, and aligned with the gate line or data line as much as possible so as not to affect the displayed image.

In this case, the front light source includes an organic light emitting layer that emits visible light, and further includes a lower electrode between the second substrate and the front light source to apply a voltage to the front light source, and the third substrate and the front light source. The upper electrode is further provided therebetween. The upper and lower electrodes are provided in a lattice shape or in a cylindrical shape to apply a voltage to the front light source.

Hereinafter, an electrophoretic display device according to the present invention will be described with reference to the accompanying drawings.

3 is a cross-sectional view of an electrophoretic display device according to the present invention, FIG. 4 is a cross-sectional view illustrating a method of driving an electrophoretic display device according to the present invention, and FIG. 5 is a front light source according to the first embodiment of the present invention. Top view of the drive electrode.

6 is a plan view of a front light source driving electrode according to a second embodiment of the present invention, and FIGS. 7 and 8 are plan views illustrating a method of driving an electrode according to a second embodiment of the present invention.

In the electrophoretic display according to the present invention, as shown in FIG. 3, the second substrate 121 having the common electrode 124 formed thereon and the first substrate 111 having the pixel electrode 117 formed in a matrix arrangement. The opposingly disposed electrophoretic film 105 is microencapsulated with pigments having different colors and charged with different voltages between the two substrates, and a third substrate 131 on the second substrate 121. The front light source 150 is interposed between these opposing parts and a predetermined portion therebetween.

The image displayed in the dark can be seen by the light emitted by the front light source 150.

In this case, the first, second, and third substrates 111, 121, and 131 may be formed of a thin, flexible film with a material. The second, third, and third electrodes 121,131 and the common electrode 124 may be formed of light. The common electrode may be formed of a transparent material such as indium tin oxide (ITO). The common electrode 124 is formed on the front surface to flow the Vcom signal.

In addition, a gate wiring (not shown) for transmitting a scan signal and a data wiring (not shown) for transmitting an image data signal are provided on the first substrate 111 to actively drive a plurality of thin film transistors. The gate line and the data line cross each other to define a pixel area, and each pixel area includes a thin film transistor TFT and a storage capacitor Cst to control the polarity of the voltage applied to the electrode and to apply the voltage to the electrode. The electric field is applied to the electrophoretic film 105 by the pixel electrode 117 connected to the thin film transistor.

In this case, the thin film transistor (TFT) is formed at a point where a gate line and a data line defining each pixel cross each other, and are connected to the pixel electrode to apply a voltage having a corresponding polarity.

The thin film transistor TFT includes a gate electrode 112a branched from the gate wiring, a gate insulating layer 113 formed on the gate electrode 112a, and an active layer 114 formed on the gate electrode 112a. And source / drain electrodes 115a and 115b branched from the data line 115 and formed on the active layer 114, and the drain electrode 115b penetrates through the passivation layer 116. It is connected to the electrode 117.

The storage capacitor Cst includes a capacitor lower electrode 132 and a capacitor upper electrode 135 overlapping the capacitor lower electrode with the gate insulating layer 113 interposed therebetween. It maintains the voltage charged in the electrophoretic film in the turn-off period of to prevent the deterioration of image quality due to parasitic capacitance. In this case, the capacitor lower electrode extends outside the active region to receive a signal, and the capacitor upper electrode is connected to the pixel electrode or the drain electrode to receive a signal.

In addition, the pixel electrode 117 may be formed of a transparent conductive material or by depositing and patterning aluminum, an aluminum alloy, titanium, or the like as a high reflectance metal, for example, to reflect external natural light well.

On the other hand, the electrophoretic film 105 is composed of a base film, a microcapsule 104 and an adhesive film, it is laminated between the upper and lower substrates (121, 111). Of course, a polymer material composed of a microcapsule and a binder may be formed by applying and curing the first substrate. For reference, the base film of the electrophoretic film may also include a conductive film of ITO material. In this case, the common electrode may not be separately formed on the second substrate.

The microcapsules 104 are formed to a diameter of about 100㎛ or less, and the pigments charged with different voltages and different voltages are mixed therein. For example, the white particles 102 and the black particles 103 may be microencapsulated, whereby the white particles are positively charged and the black particles are negatively charged or the white particles are negatively charged. -) And black particles can be positively charged.

In addition, the front light source 150 is partially provided at a predetermined portion between the second substrate 121 and the third substrate 131, so that the front light source is provided at the edge of the pixel area so as not to affect the displayed image. do. One front light source is disposed for each of the plurality of pixel areas to provide light.

The front light source is to be turned on when the external light is dark, in order to selectively turn on the front light source, further comprising a lower electrode 162 on the second substrate 121 for applying a voltage to the front light source, An upper electrode 161 is further provided on the third substrate 131 to apply a voltage to the front light source.

Specifically, the front light source 150 may use WOLED (WHITE LIGHT EMITTING OLED), which is an organic light emitting device that emits white light, and typically, an electron injection layer 152, an electron transport layer (not shown), and organic light. A light emitting layer 151, a hole transport layer (not shown), and a hole injection layer 153 are laminated films.

Here, an electron injection layer, an electron transport layer, an organic light emitting layer, a hole transport layer and a hole injection layer may be sequentially stacked on the second substrate and patterned by photolithography, or may be formed in advance. Front light sources, such as these, may be provided by adhering to a 2nd board | substrate or a 3rd board | substrate with an adhesive agent.

In this case, when an electric field is applied to the upper and lower electrodes 161 and 162, electrons are injected from the lower electrode 162 through the electron injection layer 152 and the electron transport layer and injected into the organic light emitting layer 151, and the upper electrode 161. Holes are injected into the organic light emitting layer 151 through the hole injection layer 153 and the hole transport layer.

The electrons and holes injected into the organic light emitting layer 151 move to the organic light emitting layer under an electric field and combine with each other to form an exciton, and the electrons in the exciton excited state transition to the ground state to emit light in the visible region. By virtue of the visible light, an image of the electrophoretic device can be seen even in a dark place.

That is, as shown in FIG. 4, the pigments charged with different polarities are moved up and down by the voltages applied to the pixel electrodes 117 and the common electrode 124. The white particles 102 are microcapsules. If it is located above the white color appears on the side of the third substrate 131, when the black particles are located above the black color appears. However, this color is difficult to see in a dark place, and the front light source 150 emits light, thereby providing light to the image. On the white particle surface, light is reflected to make the white color (W) visible, and the black particle surface In light, light is absorbed and a black color (B) is seen.

On the other hand, since the image should be displayed only by the color reflected by the electrophoretic film, a light blocking layer 165 is further provided between the front light source 150 and the third substrate 131 to emit light directly to the front light source 150. Do not come out of the side of the third substrate.

In addition, in order to apply a voltage to the front light source 150, upper and lower electrodes 161 and 162 extending outside the active area are required. The light reflected from the electrophoretic film may be formed of a transparent conductive material such as ITO. Form.

In this case, as shown in FIG. 5, the upper and lower electrodes 161 and 162 may be integrally formed on the front surface of the substrate to form a cylindrical structure. In this case, the front light source may be simultaneously turned on for the front surface of the substrate. Or off.

Meanwhile, as shown in FIG. 6, the upper and lower electrodes 161 and 162 may be formed in a lattice structure. A plurality of upper electrodes 161 may be arranged in a line shape, and the lower electrodes 162 may be perpendicular to the upper electrode. Form to intersect. In this case, the upper and lower electrodes are formed to overlap the gate wiring or the data wiring so as not to affect the aperture ratio of the device, and the front light source 150 is disposed on the upper and lower electrodes. For example, the front light source may be disposed at the intersection of the upper electrode and the lower electrode.

In this case, the upper and lower electrodes 161 and 162 may be formed by depositing and patterning a metal material in addition to the transparent conductive material. In this case, since the front light source is covered by a metal material that shields light, the light blocking layer is formed between the front light source and the third substrate. It is not necessary to provide 165.

By applying voltage to the upper and lower electrodes of the lattice structure as a whole, the front light source disposed on the front surface of the substrate may be simultaneously turned on or off, or the light source may be partially turned on by applying a voltage to each electrode line like a passive matrix. You can also

That is, as shown in FIG. 7, one end of the upper electrode 161 formed in the plurality of line shapes is connected to the first drive IC 163, and one end of the lower electrode 162 is connected to the second drive. After connecting to the IC 164, the front light source is locally turned on by applying a voltage for each line.

For example, in FIG. 7, the front light source of region A is turned off and the front light source of region B is turned on by applying a voltage to the uppermost upper electrode 161 and applying a voltage to the lowermost lower electrode 162. Can be. As such, when the front light source is partially turned on, as shown in FIG. 8, the image of the upper left end of the front light source is not displayed, and in a dark environment, power consumption can be lowered by partially turning on the front light source. have.

The present invention described above is not limited to the above-described embodiment and the accompanying drawings, and it is common in the art that various substitutions, modifications, and changes can be made without departing from the technical spirit of the present invention. It will be evident to those who have knowledge of.

The electrophoretic display device according to the present invention as described above has the following effects.

First, when the front light source is provided in front of the image is displayed, the front light source can be turned on when the external light source is insufficient to view the image.

Therefore, it is possible to overcome the limitation as a reflective mode in which an image cannot be viewed in a dark place.

Second, the front light source can be partially turned on by arranging electrodes for applying a voltage to the front light source in a lattice shape and applying power to each electrode line like a passive matrix.

Therefore, local display is possible, and power consumption can be lowered by partially turning on the front light source in a non-dark environment.

Claims (19)

A first substrate having a thin film transistor, a pixel electrode, and a storage capacitor in each pixel region defined by gate lines and data lines perpendicular to each other; A second substrate opposed to the first substrate, An electrophoretic film interposed between the first and second substrates; A third substrate opposed to the second substrate, and And a front light source partially formed between the second and third substrates, The front light source includes a plurality of upper electrodes arranged in a line shape on the third substrate, a plurality of lower electrodes arranged in a line shape on the second substrate and vertically intersecting the upper electrode, and the upper and lower electrodes. WOLED (WHITE LIGHT EMITTING OLED) formed in, The upper and lower electrodes are formed to overlap the gate line or the data line. The method of claim 1, And the second substrate and the third substrate are transparent materials. The method of claim 1, The WOLED has an electrophoretic display device comprising a lamination film of an electron injection layer, an electron transport layer, an organic light emitting layer, a hole transport layer and a hole injection layer. delete The method of claim 1, And the front light source is adhered to the second substrate or the third substrate by an adhesive. The method of claim 1, The front light source is electrophoretic display device, characterized in that when the external light is dark. The method of claim 1, And the front light source is provided at an edge of the pixel region. The method of claim 1, And one front light source for each pixel area. delete delete delete delete The method of claim 1, And the upper and lower electrodes are formed of a transparent conductive material. The method of claim 13, An electrophoretic display device further comprising a light blocking layer between the third substrate and the front light source. The method of claim 1, And the upper electrode or the lower electrode is formed of a metal. 16. The method of claim 15, And wherein the light blocking layer is not provided between the third substrate and the front light source when the upper electrode is made of metal. delete delete The method of claim 1, Electrophoretic display device characterized in that only part of the front light source is turned on by applying a voltage to a portion of the upper and lower electrodes.

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