Patent Application
20090109172
This application claims priority from and the benefit of Korean Patent Application No. 10-2007-0108097, filed on Oct. 26, 2007, whose disclosure is hereby incorporated by reference for all purposes as if fully set forth herein.
1. Field of Disclosure
The present disclosure of invention relates to electrophoretic display devices, and more particularly to electrophoretic display devices structured to provide improved color gamut.
2. Technology Background
With rapid developments in the information age, information display devices have increasingly been used in a broad range of applications. Information display devices may include a liquid crystal display (“LCD”) devices, electrophoretic display (“EPD”) devices, plasma display panels, etc., which are connected to a digital computer or another source of image data.
In particular, the EPD device may be characterized as having high reflectivity and a high contrast ratio, and in distinction to conventional LCD devices, having no substantial limit as to user viewing angle. Accordingly, a user may experience the EPD device as displaying images as if it displays the images on paper. Unlike an LCD device, the EPD device does not require a polarizing plate, an alignment layer, liquid crystal, etc, where the latter result in increased costs and manufacturing complexities.
The conventional EPD device includes an electrophoretic layer containing microcapsules or barrier-type microcups in which white and black particles (or otherwise differently reflecting and absorbing particles) of respectively opposed electrical charge are formed. The charged particles move up and down so as to be more reflective on top (to display white) or to be more absorptive on top (to display a dark or black image are). Older EPD devices did not display various colors, just black and white areas. These older devices thus had difficulty in expressing much information with use of only black and white coloration. Although some newer EPD devices sport a structure in which plural color filters of different colorations are formed over the black-versus-white (absorptive versus reflective) electrophoretic layer regions, these devices suffer from lowered luminance because the amount of light (e.g., ambient light) that is reflected back to the user's eyes is substantially lowered due to all of the light passing through the color filters. Furthermore, an undesired color mixture effect may be generated due to misalignment of the color filters relative to a lower substrate that contains TFT-controlled pixel areas. The result is decreased luminance and reduced color gamut (ability of the display to display a full gamut of distinct colors).
The present disclosure of invention provides an EPD device in which structures of a color filter and the underlying pixel unit are changed to improve luminance, improve color gamut and/or reduce the possibility of undesired color mixture.
An electrophoretic display device in accordance with the disclosure comprises: a first substrate defining a plurality of sub-pixel areas; sub-pixel electrodes formed in the sub-pixel areas of the first substrate; and corresponding color filters formed in a second substrate facing a subset of the sub-pixel electrodes of the first substrate, where a combined area of the color filters is less than a total area of the sub-pixel electrodes in a given pixel area. In one class of embodiments, at least one of the sub-pixel electrodes does not have a color filter above it and therefore that at least one sub-pixel electrode controls reflection/nonreflection of incident light rather than reflection/nonreflection of light that passed through a color filter.
In one class of embodiments, the color filters in each pixel area comprise first to third primary color filters for displaying for example, red, green, and blue sub-pixels, respectively.
In one class of embodiments, the first substrate comprises first to fourth sub-pixel control areas for selectively controlling the display of first to third primary colors (e.g., red, green, and blue) and for selectively controlling the display of uncolored reflected light (e.g., white), respectively.
In one class of embodiments, the first to fourth sub-pixel electrodes are encompassed in first to fourth sub-pixel areas of a given pixel and have the same shape as underlying first to fourth sub-pixel electrodes, but smaller areas.
In one class of embodiments, the first to fourth sub-pixel areas each have a same size and shape.
The first to fourth sub-pixel areas may be formed in tetragonal shapes.
In one class of embodiments, the first to third sub-pixel areas have the same size and same shape as each other while the fourth sub-pixel has an area that is less than that of one of the first to third sub-pixel areas.
In one class of embodiments, the first to third sub-pixel areas surround the fourth sub-pixel area.
The first to third sub-pixel areas may be formed in as irregular pentagon shapes and the fourth sub-pixel electrode may be formed in a triangular shape.
The first to third sub-pixel areas may be formed in a structure in which two hexagons are adjacent to each other and the fourth sub-pixel electrode is formed in a hexagonal shape.
The first substrate may include first to fifth sub-pixel control areas in each pixel area for controllably displaying red, green, blue, and white from the pixel area.
Two sub-pixel areas of the first to fifth sub-pixel areas may display the same color.
First to fifth sub-pixel electrodes may be formed in the first to fifth sub-pixel areas and have the same shape as the first to fifth sub-pixel areas.
The first to fourth sub-pixel areas may have the same size and the same shape, and the fifth sub-pixel area may have a corresponding area that is less than the area of one of the first to third sub-pixel areas.
The first to third color filters may have the same shape as the first to fourth pixel areas and each of the first to third color filters may be of lesser area than each of the first to fourth sub-pixel electrodes.
The first to fourth sub-pixel areas may surround the fifth sub-pixel area. The first to fourth sub-pixel areas may be formed in a pentagonal shape and the fifth sub-pixel electrode may be formed in a tetragonal shape.
The combined areas of sub-pixel color filters of a given pixel may occupy about 50 to 65 percent of the entire area of the pixel.
It is to be understood that both the foregoing description and the following detailed description are exemplary and explanatory and are not intended to limit the teachings of the present disclosure.
The above features and aspects of the present disclosure will become apparent and more readily appreciated from the following description of the exemplary embodiments, taken in conjunction with the accompanying drawings, in which:
Referring to
The first substrate is organized to define respective primary color passing sub-pixels such as red (“R”), green (“G”), and blue (“B”), as well as a white (“W”) sub-pixel area where these areas are respectively denoted as 301, 302, 303, and 304 and disposed in spaced-apart adjacent relation to one another. Various permutations of how these R, G, B, W sub-pixel areas may be organized relative to one another are shown in the top plan views of
The lower substrate 101 may be formed of an electrically insulating material such as glass or plastic.
The TFTs 105 are formed in the R, G, B and W sub-pixel areas 301, 302, 303, and 304. Each of the TFTs 105 includes a gate electrode 111 formed on the lower substrate 101, a gate insulating layer 121, an active layer 131 (e.g., semiconductive layer), an ohmic contact layer 133, a source electrode 141, and a drain electrode 143.
The gate electrode 111 is connected to a gate line. The gate line is extendedly formed in one direction on the lower substrate 101. The gate insulating layer 121 is formed of an electrically insulating material on the gate electrode 111 and the gate line. For example, the gate insulating layer 121 is formed of a silicon nitride SiNx or a silicon oxide SiOx or a silicon oxynitride (SiOxNy) on essentially the whole surface of the lower substrate 101.
The active layer 131 formed on the gate insulating layer 121 overlaps the gate electrode 111. For example, the active layer 131 is formed of amorphous silicon (a-Si) on the gate insulating layer 121. Alternatively, the active layer 131 may be formed of polycrystalline silicon. In one embodiment, the ohmic contact layer 133 is formed of impurity-doped amorphous silicon on the active layer 131.
The source electrode 141 is connected to a data line on the gate insulating layer 121 and the ohmic contact layer 133 and overlaps the gate electrode 111. The drain electrode 143 overlaps the gate electrode 111 and faces the source electrode 141. The source electrode 141 and the drain electrode 143 are formed of the same material as that of the data line.
The protective layer (passivation layer) 150 is formed for insulation and passivation on the gate insulating layer 121, the active layer 131, the source electrode 141, and the drain electrode 143. The protective layer 150 is formed of at least one of an inorganic protective layer material and an organic protective layer material to improve the insulation and turn-off characteristics of the TFT 105. The protective layer 150 includes a contact hole 155 through which a portion of the drain electrode 143 is exposed.
Each sub-pixel electrode 160 is formed on the protective layer 150 and connected to the drain electrode 143 of the corresponding TFT 105 via the contact hole 155. In one embodiment, the sub-pixel electrode 160 is formed of a transparent conductive material, for example, indium tin oxide (ITO) or indium zinc oxide (IZO). Respective sub-pixel electrodes 160 are formed within the R, G, B, and W sub-pixel areas 301, 302, 303, and 304.
The electrophoretic layer 190 includes microcapsules 191 and an appropriate suspension solvent 195.
The microcapsules 191 include charged color particles, for example, black particles 192 charged with positive polarity and white particles 193 charged with negative polarity. When voltages are applied to an opposed pair of electrodes around the microcapsules (e.g., to a common electrode 210 and sub-pixel electrode 160) and an electric field is formed by the potential difference between the two electrodes, the black (light absorbing) particles 192 and the white (light reflecting) particles 193 respectively move towards the electrode of opposite polarity within each microcapsule. Then the charged light-reflecting/absorbing particles that preferentially move to the top (closer to the common electrode 210) reflect or absorb externally-provided incident light and the transparent microcapsules 191 consequently display images such as represented by black or white.
The capsule suspension solvent 195 surrounds the microcapsules 191 and is used to protect the microcapsules 191 from an external shock and it also fixes the microcapsules 191 one to the next so as to form the electrophoretic layer 190.
The electrophoretic layer 190 is attached to the first substrate 100 through an appropriate adhesive 170.
The second substrate 200 includes an upper substrate 201, a common electrode 210, a color filters layer 220, and an overcoat layer 230.
The upper substrate 201 is formed of an insulating material, such as glass or plastic, like the lower substrate 101. The upper substrate 201 may be formed of flexible plastic.
The common electrode 210 is formed of a transparent conductive material over the whole surface of the upper substrate 201. Like the pixel electrode 160, the common electrode 210 may be formed of ITO or IZO. The common electrode 210 forms an electric field together with the sub-pixel electrode 160 to control the movement of the black particles 192 and the white particles 193 of the electrophoretic layer 190.
The color filters layer 220 is disposed between the upper substrate 201 and the common electrode 210. The color filters layer 220 includes R, G, and B color filters for displaying primary colors such as R, G, and B colors, respectively.
Each color filter in layer 220 is formed to be smaller than the corresponding sub-pixel electrode 160 so as to prevent color mixture and color spreading caused by misalignment of the first substrate 100 and the second substrate 200 and by fringe electric fields between the sub-pixel electrodes 160 and the common electrode 210. “Color mixture” is an undesirable phenomenon that displays an unwanted color as well as a wanted specific color, caused by misalignment of the sub-pixel electrode 160 and the overlying color filters 220 upon bonding the first substrate 100 and the second substrate 200. “Color spreading” is an undesirable phenomenon that displays a color of reflective light throughout a wider range than an area of the color filter 220, and may be caused by an enlarged driving range of the electrophoretic layer 190. Such color spreading deteriorates color characteristics since the electrophoretic layer 190 negatively affects other pixels while a driving rage of the electrophoretic layer 190 is extended by fringe electric fields.
The color filter 220 is formed to correspond to a shape of the pixel electrode 160. The color filter 220 may be formed in the shape of a reduced version of the sub-pixel electrode 160.
Since the R, G, and B color filters 220 are formed separate from one another, this arrangement can prevent or reduce color mixture caused by reflective light being diffuse-reflected (or diffuse refracted) from the electrophoretic layer 190. In addition, the R, G, and B color filters 220 have spaces in preparation for alignment failure with the sub-pixel electrode 160 (to compensate for misalignment possibilities), thereby improving luminance and color gamut.
Referring to
In the embodiment of
The first to third sub-pixels 401, 402, and 403 include first to third sub-pixel electrodes 411, 412, and 413, respectively and also include first to third color filters 421, 422, and 423, respectively. The first to third sub-pixel electrodes 411, 412, and 413 and the first to third color filters 421, 422, and 423 are formed as concentric tetragonal shapes. The first to third color filters 421, 422, and 423 are smaller in area than the first to third sub-pixel electrodes 411, 412, and 413. The first to third color filters 421, 422, and 423 may be formed of materials that selectively pass through the R, G, and B light wavelengths, respectively.
The fourth sub-pixel 404 has a tetragonal shape and includes a fourth sub-pixel electrode 414. The fourth sub-pixel 404 does not include any color filter and thus it will reflect white light when its underlying electrophoretic particles are white. Presence of the fourth sub-pixel 404 helps to improve the luminance of an image displayed by the pixel 400.
Since the first to third color filters 421, 422, and 423 are smaller in size than the corresponding first to third sub-pixel electrodes 411, 412, and 413, the structure of the pixel 400 prevents color mixture from being caused by slight misalignments of the first and second substrates and/or by diffused light reflection or refraction from the electrophoretic layer.
In one class of embodiments, the combination of areas of the first to third color filters 421, 422, and 423 may be formed to be substantially less than about 75% of the area of the pixel 400 so as to thereby prevent color mixture being caused by misalignment with the first to third sub-pixel electrodes 411, 412, and 413. For example, in one embodiment, the combination of areas of the first to third color filters 421, 422, and 423 may occupy about 45% to about 55% of the area of the pixel 400 (e.g., 45%≦R+G+B≦55% of total pixel area), and nominally around 50% of the area of the pixel 400. It has been found that when the light controlling combined area of the first to third color filters 421, 422, and 423 is substantially less than 45% of the light passing area of the pixel 400, a color characteristic deteriorates. When the area of the first to third color filters 421, 422, and 423 is substantially greater than about 55% of the area of the pixel 400, a color mixture avoiding effect decreases. When the total area of the first to third color filters 421, 422, and 423 is in the nominal range centered at about 50% of the area of the pixel 400, the desired color mixture avoiding effect and color luminance characteristics are both obtainable.
The percentage of combined area of the first to third color filters 421, 422, and 423 (R+G+B) relative to the total area occupied by the pixel 400 is variable as a function of one or more of: (1) the spacing intervals provided between the first to fourth sub-pixels 401, 402, 403, and 404, and (2) the individual sizes of the first to third sub-pixel electrodes 411, 412, and 413. The area allotted to each of the first to third color filters 421, 422, and 423 may vary depending on the entire size of the EPD device.
The first to fourth sub-pixels 401, 402, 403, and 404 have been described thus far as including only the first to fourth sub-pixel electrodes 411, 412, 413, and 414 and the first to third color filters 421, 422, and 423. However, definition of the first to fourth sub-pixels 401, 402, 403, and 404 may further include corresponding portions of the first and second substrates, of the gate line, of the data line, of the associated TFT's, of the common electrode, etc.
Referring to
The first to fourth sub-pixels 401, 402, 403, and 404 of
In
As seen in
The pixel 400 of
An entire area of the first to third color filters 421, 422, and 423 combined may be about 60% to about 65% of an area of the pixel 400 in the embodiment of
In
Although the first to fifth sub-pixels 401, 402, 403, 404, and 405 of
Referring to
The first to third sub-pixels 401, 402, and 403 of
The fourth sub-pixel 405 of
The pixel 400 of
Since the pixel 400 is formed in a polygonal structure similar to a circle, the edges of the pixel 400 is prevented from looking crushed or flattened as they might be in a rectangular format.
Although the first to fourth sub-pixels 401, 402, 403, and 404 have been described as including the first to fourth sub-pixel electrodes 411, 412, 413, and 414 and the first to third color filters 421, 422, and 423, the sub-pixels 401, 402, 403, and 404 may include first and second substrates, a gate line, a data line, a TFT, a common electrode, etc.
Referring to
The first to third sub-pixels 401, 402, and 403 includes first to third sub-pixel electrode 411, 412, and 413, respectively and includes first to third color filters 421, 422, and 423, respectively. The first to third sub-pixel electrodes 411, 412, and 413 and the first to third color filters 421, 422, and 423 each have a structure in which two hexagons abutted to each other at one edge. The first to third color filters 421, 422, and 423 are smaller in area than their respective first to third sub-pixel electrodes 411, 412, and 413. The first to third color filters 421, 422, and 423 may be formed of materials for displaying primary colors such as R, G, and B, respectively. Then the first to third sub-pixels 401, 402, and 403 selectively display R, G, and B, respectively.
The fourth sub-pixel 404 is formed at the center of the pixel 400. The fourth sub-pixel 404 is surrounded with the first to third sub-pixels 401, 402, and 403. The area of the fourth sub-pixel 404 is smaller than the area of each of the first to third sub-pixels 401, 402, and 403. The fourth sub-pixel 404 includes a fourth sub-pixel electrode 414 and is formed in a hexagonal shape. The fourth sub-pixel 404 selectively displays the W color.
The pixel 400 of
Since the first to fourth sub-pixels 401, 402, 403, and 404 and the first to third color filters 421, 422, and 423 may be formed by using a hexagonal mask, a manufacturing process is reduced and costs can be saved.
Although the first to fourth sub-pixels 401, 402, 403, and 404 have been described as including the first to fourth sub-pixel electrodes 411, 412, 413, and 414 and the first to third color filters 421, 422, and 423, the sub-pixels 401, 402, 403, and 404 may include first and second substrates, a gate line, a data line, a TFT, a common electrode, etc.
Referring to
In step S11, a gate metal layer is deposited on a lower substrate by a deposition method such as sputtering. The gate metal layer is patterned by photolithography and etching processes to form a gate metal pattern group including a gate line and a gate electrode.
A gate electrode layer is formed on the lower substrate on which the gate metal pattern group is formed by plasma enhanced chemical vapor deposition (“PECVD”).
An amorphous silicon layer and an impurity-doped amorphous silicon layer are deposited on the gate insulating layer. The amorphous silicon layer and the impurity-doped amorphous silicon layer are patterned to form an active layer and an ohmic contact layer.
Next, a data metal layer is deposited on the gate insulating layer and the ohmic contact layer. The data metal layer is patterned to form a gate metal pattern group including a data line, a source electrode, and a drain electrode.
At least one of an inorganic insulating material and an organic insulating material is deposited on the gate insulating layer and the data metal pattern group by a deposition method such as PECVD, thereby forming a protective layer. A contact hole is formed by etching the protective layer to expose a part of the drain electrode.
A transparent conductive material (e.g., ITO) is deposited on the protective layer and the transparent conductive material is patterned to form sub-pixel electrodes in for example the shapes described to be according to any one of
In one embodiment, the sub-pixel electrode is formed to include a polygonal shape. For example, the polygonal portion of the sub-pixel electrode may be triangular, tetragonal, pentagonal, decagonal, etc., according to the desired shape of the sub-pixel.
In step S21, a pigment-colored filter for displaying a respective color such as one of R, G, and B is formed by coating a pigment-containing material (e.g., hardenable polymer) on an upper substrate and the so-deposited color filter pigment is patterned by a selective etching process so as to leave behind the desired pattern. Color filter pigments for displaying the other two colors are coated and patterned like the above described process, thereby forming R, G, and B color filters in the appropriate sub-pixel areas. In one embodiment, the R, G, and B color filters are formed in a polygonal shape like the pixel electrodes of sub-pixels. The R, G, and B color filters are formed to be smaller in area than the corresponding sub-pixel electrodes of respective sub-pixels and are spaced-apart from one another. For instance, the color filter may be formed as a scaled down replica (e.g., pentagon) of the underlying sub-pixel electrode.
In one embodiment, the R, G, and B color filters may be formed in an even-numbered polygonal shape such as tetragon, hexagon, octagon, etc. For example, the R, G, and B color filters may be formed in the shape of hexagonally-packable hexagons to thereby reduce the number of masks, leading to a reduction in a manufacturing process and costs. Namely, the number of processes, such as cleansing, photoresist deposition, development, exposure, baking, and ashing, is increased but the number of masks can be reduced.
A transparent organic or inorganic material is deposited on the upper substrate and the patterned color filters. A portion at which the R, G, and B color filters overlap the transparent organic or inorganic material is etched to form an overcoat layer. The overcoat layer has the same height (or a greater height) as that of the R, G, and B color filters and thus provides a substantially planar structure.
A transparent conductive material is deposited on the color filters and the overcoat layer to form a common electrode. For example, the common electrode is formed by depositing indium tin oxide (ITO) or indium zinc oxide (IZO) over the entire surface of the upper substrate.
In step S31, microcapsules and suspension solvent are mixed and then deposited on the second substrate. Next, an adhesive is applied on the microcapsules and suspension solvent. A release film is attached to the upper surface of the adhesive.
In step S41, the release film attached on the adhesive of the electrophoretic layer is removed. The first substrate, the second substrate, and the electrophoretic layer are attached to each other by a lamination method using a roller for example.
The EPD device according to the present disclosure forms color filters smaller in size than sub-pixels and has a separated distance between the color filters. Accordingly, the luminance of reflective light and color gamut may be prevented from being degraded, thereby improving display quality.
In addition, a W sub-pixel is formed to be smaller than each of R, G, and B sub-pixels and an area in which R, G, and B are displayed is enlarged, thereby improving color gamut.
Furthermore, since in some of the embodiments the each formed pixel (e.g., hexagon) is more similar to a circle than a square, the capability of expressing characters with slanted portions, diagonal lines, etc. with the more-circle like and efficiently packed pixels is improved and the edges of each pixel is prevented from looking like a crushed shape.
Although exemplary embodiments have been described in detail hereinabove, it should be clearly understood that many variations and/or modifications of the basic concepts taught herein will fall within the spirit and scope of the present disclosure of invention. Thus, it is intended that the present disclosure cover such various modifications and variations.
| Number | Date | Country | Kind |
|---|---|---|---|
| 10-2007-0108097 | Oct 2007 | KR | national |
