Display device

A display device includes a first electrode layer, a color switching layer which is disposed on the first electrode layer, a second electrode layer which is disposed on the color switching layer and a color filter layer which is disposed on the second electrode layer. The color switching layer includes a first color cell, which transmits incident light or changes incident light to a first color light, a second color cell, which transmits incident light or changes incident light to a second color light and a third color cell, which transmits incident light or changes incident light to a third color light. The color filter layer includes a first filter which transmits a cyan light, a second filter which transmits a magenta light and a third filter which transmits a yellow light.

CROSS-REFERENCE TO RELATED APPLICATIONS

This application claims priority to Korean Patent Application No. 10-2010-0039168, filed on Apr. 27, 2010, and all the benefits accruing therefrom under 35 U.S.C. §119, the disclosure of which is incorporated herein in its entirety by reference.

BACKGROUND

Provided are display devices for displaying color images by using cyan, magenta, and yellow color filters.

2. Description of the Related Art

Devices using reflective display devices, such as electronic reading devices (e.g., e-book), are being actively developed and commercialized. Although products commercialized hitherto employ a black and white displaying method, most products to be further commercialized employ color displaying method. Color reflective display devices generally uses red (“R”), green (“G”), and blue (“B”) color filters. However, when RGB color filters are used, only a portion of white light contributes to formation of images, and thus, light efficiency is relatively low.

Research has been conducted to form a color image by using an electrochromic device which may switch a white color to a red, green, or blue color without using a color filter. However, in this case, although white color reflectivity is relatively high, it is difficult to form a black color and only colors in a relatively narrow range may be formed.

SUMMARY

Provided are display devices for displaying color images by using cyan, magenta, and yellow color filters.

Provided is a display device which includes a first electrode layer, a reflective layer which is disposed on the first electrode layer, a color switching layer which is disposed on the reflective layer and includes a first color cell which transmits incident light or changes incident light to a first color light, a second color cell which transmits incident light or changes incident light to a second color light and a third color cell which transmits incident light or changes incident light to a third color light, a second electrode layer which is disposed on the color switching layer, and a color filter layer which is disposed on the second electrode layer and includes a first filter which transmits a cyan light, a second filter which transmits a magenta light, and a third filter which transmits a yellow light.

In an embodiment, the first color light may have a color complementary with respect to the cyan light, the second color light may have a color complementary with respect to the magenta light, and the third color light may have a color complementary with respect to the yellow light.

In an embodiment, the first color light may include a red light, the second color light may include a green light, and the third color light may include a blue light.

In an embodiment, at least one of the first electrode layer and the second electrode layer may include a transparent conductive material.

In an embodiment, the color switching layer may include an electrochromic layer.

In an embodiment, the color switching layer may include a polymer dispersed liquid crystal (“PDLC”) layer mixed with a dichroic dye.

In an embodiment, the color switching layer may include red, green, and blue cholesteric liquid crystal layers.

In an embodiment, the color switching layer may include an electronic ink (e.g., e-ink) layer having red, green, blue, and white color balls.

In an embodiment, the first color cell and the first filter may be arranged to face each other, the second color cell and the second filter may be arranged to face each other, and the third color cell and the third filter may be arranged to face each other.

In an embodiment, the color filter layer may further include a fourth filter, which transmits incident light.

In an embodiment, the color switching layer may further include a fourth color cell which may be arranged to face the fourth filter.

In an embodiment, the fourth color cell may transmit incident light or may change incident light to a black light.

In an embodiment, the color switching layer transmits incident light or changes colors of incident light at each of color cells according to voltage application to the color cells.

Provided is a display device includes a first electrode layer, a color switching layer which may be disposed on the first electrode layer and may include a first color cell which transmits incident light or changes incident light to a first color light, a second color cell which transmits incident light or changes incident light to a second color light, and a third color cell, which transmits incident light or changes incident light to a third color light, a second electrode layer which may be disposed on the color switching layer and a color filter layer which may be disposed on the second electrode layer and may include a first filter which transmits a cyan light, a second filter which transmits a magenta light, and a third filter which transmits a yellow light.

DETAILED DESCRIPTION

Reference will now be made in detail to embodiments, examples of which are illustrated in the accompanying drawings, wherein like reference numerals refer to the like elements throughout and the size and relative sizes of layers and regions may be exaggerated for clarity. In this regard, the embodiments may have different forms and should not be construed as being limited to the descriptions set forth herein. Accordingly, the embodiments are merely described below, by referring to the figures, to explain the present invention.

FIG. 1is a diagram of an embodiment of a display device, according to the present invention. In the display device, a plurality of a pixel may be arranged in a matrix shape. For convenience of explanation,FIG. 1shows only one pixel1of the display device. The pixel1may include a plurality of a sub-pixel, and a color image of the display device may include color lights from each of the sub-pixels which are mixed together. Each of the sub-pixels may emit a different color light. However, the sub-pixels are not limited thereto, and the pixel1may include a plurality of a sub-pixel, which emits the same color light, in consideration of brightness or efficiency of each color light. In one embodiment, for example, the pixel1may include a first sub-pixel1a, a second sub-pixel1b, and a third sub-pixel1c.

The display device shown inFIG. 1may include a first electrode layer10, a color switching layer25disposed on the first electrode layer10, a second electrode layer30disposed on the color switching layer25, and a color filter layer35disposed on the second electrode layer30. The color switching layer25is interposed between the first electrode layer10and the second electrode layer30, and may switch the color of incident light as a voltage is applied thereto.

The first electrode layer10and the second electrode layer30may be arranged in a passive matrix (“PM”) arrangement or an active matrix (“AM”) arrangement. In a case of the PM arrangement, each of the first electrode layer10and the second electrode layer30may be arranged in stripes to cross each other, in a plan view of the display device. In a case of the AM arrangement, the first electrode layer10may be a common electrode, whereas the second electrode layer30may be a pixel electrode arranged in correspondence to the sub-pixels1a,1b, and1c. Alternatively, the first electrode layer10may be a pixel electrode, whereas the second electrode layer30may be a common electrode.

At least one of the first electrode layer10and the second electrode layer30may include a transparent conductive material, such as indium tin oxide (“ITO”). InFIG. 1, the second electrode layer30via which light is incident, may include a transparent material. However, the present invention is not limited thereto, and both the first electrode layer10and the second electrode layer30may include a transparent material.

A partition22may be interposed between each pair of adjacent sub-pixels of the color switching layer25, to reduce or effectively prevent mixtures of colors within the sub-pixels. Furthermore, a reflective layer15may be interposed between the color switching layer25and the first electrode layer10. The reflective layer15reflects light incident from an outside of the display device back toward the outside.

The color filter layer35may include a plurality of a filter which transmits predetermined color lights. In one embodiment, for example, the color filter layer35may include a first filter35awhich transmits cyan light, a second filter35bwhich transmits magenta light, and a third filter35cwhich transmits yellow light. The color filter layer35including a cyan filter, a magenta filter, and a yellow filter has high light transmittance, and thus colors with high reflectivity may be formed. Furthermore, black, white, and various other colors may be formed through color combinations using the color filter layer35and the color switching layer25.

The color switching layer25may operate in a transmittance mode for transmitting incident light, and a color changing mode for changing incident light to a predetermined color light. Each color cell of the color switching layer25may be switched between the transmittance mode and the color changing mode by applying a voltage thereto. The color switching layer25forms colors in cooperation with the color filter layer35, and may include a first color cell25a, a second color cell25b, and a third color cell25c. The first color cell25amay transmit incident light or change incident light to a first color light. The second color cell25bmay transmit incident light or change incident light to a second color light. The third color cell25cmay transmit incident light or change incident light to a third color light. The first color light may have a color complementary with respect to the cyan light, the second color light may have a color complementary with respect to the magenta light, and the third color light may have a color complementary with respect to the yellow light. In one embodiment, for example, the first color light may be a red light, the second color light may be a green light, and the third color light may be a blue light.

In an embodiment of the present invention, the color switching layer25may include an electrochromic device, for example. An electrochromic device displays images through absorption of natural light, and thus, has advantages such as low eye fatigue, low viewing angle dependency, memory characteristics, and small power consumption.

The color of the electrochromic device may be reversibly changed through electrochemical changes of an electrochromic material according to the direction of an electric field when a voltage is applied thereto. In one embodiment, for example, an electrochromic material may contain a cathodic coloration material which has a certain color in a reduction state, and is transparent in an oxidation state. The electrochromic material may be an organic material or an inorganic material. The cathodic coloration material may contain an inorganic material, such as WO3, MoO3, TiO3, or the like, for example. Alternatively, the cathodic coloration material may include organic materials, such as phthalate-based compound, such as viologen or isophthalate, a pyridine-based compound, an anthraquinone-based compound, an aminoquinone-based compound, a rare-earth-based organic metal compound, phthalocyanine, a ruthenium-based organic metal compound, a leuco dye-based compound, and a polymer-based electrochromic material.

Alternatively, an electrochromic material may contain an anodic coloration material which is transparent in a reduction state, and has a certain color in an oxidation state. The anodic coloration material may contain V2O5, IrO2, Nb2O5, or NiO, for example. Alternatively, the anodic coloration material may include organic compounds, such as phenothiazine or a polymer-based electrochromic material. From among the electrochromic materials, electrochromic materials which may be changed from a transparent state to a red color, green color, or blue color are used.

Furthermore, an electrochromic layer may contain an electrochromic material doped with nanoparticles. The nanoparticles may include a semiconductor material. Alternatively, the nanoparticles may include TiO2, ZnO2, WO3, or the like. Furthermore, the nanoparticles may have various shapes including a sphere, a tetrahedron, a cylinder, a triangle, a disc, a tripod, a tetrapod, a cube, a box, a star, a tube, etc. The size of a nanoparticle may be from about 1 nanometer (nm) to about 100 nanometers (nm). If nanoparticles are used in the electrochromic layer, the surface area of the electrochromic layer increases, and thus more electrochromic material may be applied. Therefore, the electrochromic device may be operated with improved efficiency.

Furthermore, the electrochromic layer may be a layer in which a polymer compound and an electrochromic material are mixed without being doped with nanoparticles. The electrochromic layer may contain a mixture, which contains from about 1 weight % to about 50 weight % of a polymer compound, such as polyvinylpyrrolidone, polyvinyl butyral, polyvinyl alcohol, or the like, and from about 50 weight % to about 99 weight % of an electrochromic material.

The color switching layer25may include a polymer dispersed liquid crystal (“PDLC”) layer mixed with a dichroic dye. The PDLC layer may include a polymer and liquid crystals dispersed in the polymer. The PDLC layer may form an image via anisotropy of liquid crystals. Liquid crystals are anisotropic, which also applies to an ordinary refractive index and extraordinary refractive index, whereas a polymer is isotropic. If no electric field is applied to the color switching layer25, dispersed liquid crystals are not oriented in a constant direction, and thus the refractive index of the polymer and the refractive index of the liquid crystals differ from each other. Therefore, diffusion occurs between the polymer and the liquid crystals, and thus the PDLC layer becomes opaque. A color is formed based on a dye contained in the PDLC layer.

If an electric field is applied to the color switching layer25, the liquid crystals are oriented in a direction parallel to the direction of the electric field, and the refractive index of the polymer and the ordinary refractive index of the liquid crystals become equal to each other, and thus the PDLC layer becomes transparent. Each sub-pixel of the PDLC layer may include a dye of a predetermined color. In one embodiment, for example, a first color cell of the PDLC layer may include a red dye, a second color cell of the PDLC layer may include a green dye, and a third color cell of the PDLC layer may include a blue dye. The dyes may be included in either of the polymer or the liquid crystals or in both of the polymer and the liquid crystals.

Alternatively, the color switching layer25may include red, green, and blue cholesteric liquid crystal layers or an electronic ink (e.g., e-ink) layer having red, green, blue, and white color balls, for example.

FIG. 1shows an embodiment using an electrochromic device as the color switching layer25, where an electrolyte layer20may be interposed between the reflective layer15and the color switching layer25, so that ions may move through the electrolyte layer20when electrochromism occurs.

FIGS. 2 through 4are diagrams for describing embodiments of a method of operating the display device shown inFIG. 1.

Referring toFIG. 2, a first voltage V1is applied to each of the first color cell25a, the second color cell25b, and the third color cell25c. In one embodiment, for example, the first color cell25amay form a red color when a voltage is applied thereto, the second color cell25bmay form a green color when a voltage is applied thereto, and the third color cell25cmay form a blue color when a voltage is applied thereto. Furthermore, the first filter35atransmits a cyan light, the second filter35btransmits a magenta light, and the third filter35ctransmits a yellow light.

When a white light is incident from the outside initially through the color filter layer35as shown by the first portion of the arrow inFIG. 2, a cyan light is transmitted through the first filter35aand towards the first color cell25a, the cyan light is mixed with red color at the first color cell25a, and thus black (“BL”) color is formed within the first sub-pixel1a. Furthermore, from the white light, a magenta light is transmitted through the second filter35band towards the second color cell25b, the magenta light is mixed with green color at the second color cell25b, and thus BL color is formed within the second sub-pixel1b. Furthermore, from the white light, a yellow light is transmitted through the third filter35cand towards the third color cell25c, is mixed with blue color at the third color cell25c, and thus BL color is formed within the third sub-pixel1c. As a result, the BL color light from each of the first to third sub-pixels1a,1band1care effectively mixed, and thus black color BLACK is formed by the pixel1.

Referring toFIG. 3, the first voltage V1is applied to the first color cell25aonly, and either no voltage or an inverse voltage is applied to the second color cell25band the third color cell25c. As a result, the first color cell25aforms a red color, and the second color cell25band the third color cell25cbecome transparent. Therefore, a cyan light is transmitted through the first filter35afrom a white light and towards the first color cell25a, the cyan light is mixed with the red color at the first color cell25a, and thus BL color is formed in the first sub-pixel1a. A magenta light M is transmitted through the second filter35bfrom a white light and towards the second color cell25b, the magenta light M is transmitted through the transparent second color cell25band is reflected outward by the reflective layer15, and thus the magenta light M travels to the outside of the second sub-pixel1bthrough the second color cell25band the second filter35b. A yellow light Y is transmitted through the third filter35cfrom a white light and towards the third color cell25c, the yellow light Y is transmitted through the transparent third color cell25cand is reflected outward by the reflective layer15, and thus yellow light Y travels to the outside of the third sub-pixel1cthrough the third color cell25cand the third filter35c. As a result, the magenta light M from the second sub-pixel1band the yellow light Y from the third sub-pixel1care mixed, and thus red color RED is formed by the pixel1.

In an alternative embodiment ofFIG. 3, in a case of applying the first voltage V1to the second color cell25bonly, and applying either no voltage or an inverse voltage to the first color cell25aand the third color cell25c, cyan color may be formed through the combination of the first filter35aand the first color cell25ain the first sub-pixel1a, BL color may be formed through the combination of the second filter35band the second color cell25bin the second sub-pixel1b, and yellow color may be formed through the combination of the third filter35cand the third color cell25cin the third sub-pixel. As a result, the cyan color from the first sub-pixel1aand the yellow color Y from the third sub-pixel1care mixed, and thus green color is formed by the pixel1.

Furthermore, in a case of applying the first voltage V1to the third color cell25conly, and applying either no voltage or an inverse voltage to the first color cell25aand the second color cell25b, cyan color may be formed through the combination of the first filter35aand the first color cell25ain the first sub-pixel1a, magenta color M may be formed through the combination of the second filter35band the second color cell25bin the second sub-pixel1b, and BL color may be formed through the combination of the third filter35cand the third color cell25cin the third sub-pixel1c. As a result, the cyan color from the first sub-pixel1aand the magenta color M from the second sub-pixel1bare mixed, and thus blue color is formed by the pixel1.

Furthermore, in a case of applying the first voltage V1to the first color cell25aand the second color cell25band applying either no voltage or an inverse voltage to the third color cell25c, BL color may be formed through the combination of the first filter35aand the first color cell25ain the first sub-pixel1a, BL color may be formed through the combination of the second filter35band the second color cell25bin the second sub-pixel1b, and yellow color Y may be formed through the combination of the third filter35cand the third color cell25cin the third sub-pixel1c. As a result, the yellow color Y is formed by the pixel1. In alternative embodiments, cyan color or magenta color may also be formed by the above method, where two of three sub-pixels are applied with the first voltage V1.

Referring toFIG. 4, either no voltage or an inverse voltage is applied to the first color cell25a, the second color cell25b, and the third color cell25c. As a result, all of the first color cell25a, the second color cell25b, and the third color cell25cbecome transparent. A cyan light C is transmitted through the first filter35afrom a white light and towards the first color cell25a, the cyan light C is transmitted through the transparent first color cell25aand is reflected outward by the reflective layer15, and thus the cyan light C travels to the outside of the first sub-pixel1a. Furthermore, a magenta light M is transmitted through the second filter35bfrom a white light and towards the second color cell25b, the magenta light M is transmitted through the transparent second color cell25band is reflected outward by the reflective layer15, and thus the magenta light M travels to the outside of the second sub-pixel1b. Furthermore, a yellow light Y is transmitted through the third filter35cfrom a white light and towards the third color cell25c, the yellow light Y is transmitted through the transparent third color cell25cand is reflected outward by the reflective layer15, and thus the yellow light Y travels to the outside of the third sub-pixel1c. As a result, the cyan light C from the first sub-pixel1a, the magenta light M from the second sub-pixel1b, and the yellow light Y from the third sub-pixel1care mixed, and thus white color WHITE is formed by the pixel1.

As described above, when all of the color cells of the color switching layer25are transparent, a cyan light C, a magenta light M, and a yellow light Y, which are lights of natural colors of the first, second and third color filters35a,35band35c, may be reflected within the first, second and third sub-pixels1a,1band1cto form a white color WHITE of the pixel1. Here, light transmitted through the color filter layer35may form a black color based on subtractive color mixture when the color switching layer25is in the color changing mode, whereas light transmitted through the color filter layer35may form a white color based on additive color mixture when the color switching layer25is in the transmittance mode.

FIG. 5is a diagram showing embodiments of light intensities according to wavelengths of light transmitted through a red filter, and light intensities according to wavelengths of light transmitted through a magenta filter, for example. Only a red light L1is transmitted through the red filter, whereas a blue light L2and a red light L3are transmitted through the magenta filter. Therefore, an amount of light transmitted through the magenta filter is greater than an amount of light transmitted through the red filter. As described above, amounts of lights transmitted through cyan, magenta, and yellow filters are greater than amounts of lights transmitted through red, green, and blue filters, and thus lights transmitted through cyan, magenta, and yellow filters form a white color with relatively high brightness. Therefore, a higher black and white contrast ratio may be obtained by using cyan, magenta, and yellow filters as compared to the case of using red, green, and blue filters. Furthermore, according to the illustrated embodiments, white color, black color, and various other colors may be formed through color combinations using cyan, magenta, and yellow color filters, and red, green, and blue color switching layers.

FIG. 6is a diagram of another embodiment of a display device, according to the present invention. In the display device shown inFIG. 6, a plurality of a pixel may be arranged in a matrix shape. For convenience of explanation,FIG. 6shows only one pixel200of the display device. The pixel200may include a plurality of a sub-pixel, and a color image of the display device may include color lights from each of the sub-pixels which are mixed together. Each of the sub-pixels may emit different color lights. However, the present invention is not limited thereto, and the pixel200may include a plurality of a sub-pixel, which emits the same color light, in consideration of brightness or efficiency of each color light. In one embodiment, for example, the pixel200may include a first sub-pixel200a, a second sub-pixel200b, a third sub-pixel200c, and a fourth sub-pixel200d.

The display device shown inFIG. 6may include a first electrode layer210, a color switching layer225which is disposed on the first electrode layer210, a second electrode layer230which is disposed on the color switching layer225, and a color filter layer235which is disposed on the second electrode layer230. The color switching layer225is interposed between the first electrode layer210and the second electrode layer230, and may switch the color of incident light as a voltage is applied to the color switching layer225.

The first electrode layer210and the second electrode layer230may be arranged in a PM arrangement or an AM arrangement. In a case of the PM arrangement, each of the first electrode layer210and the second electrode layer230may be arranged in stripes to cross each other, in a plan view of the display device. In a case of the AM arrangement, the first electrode layer210may be a common electrode, whereas the second electrode layer230may be a pixel electrode arranged in correspondence to the sub-pixels200a,200b,200c, and200d. Alternatively, the first electrode layer210may be a pixel electrode, whereas the second electrode layer230may be a common electrode. At least one of the first electrode layer210and the second electrode layer230may include a transparent conductive material, such as ITO.

A partition222may be interposed between each pair of adjacent sub-pixels of the color switching layer225, to reduce or effectively prevent mixtures of colors within the sub-pixels. Furthermore, a reflective layer215may be interposed between the color switching layer225and the first electrode layer210. The reflective layer215reflects externally incident light toward the outside. The reference numeral220indicates an electrolyte layer.

The color filter layer235may include a plurality of a filter which transmits predetermined color lights. In one embodiment, for example, the color filter layer235may include a first filter235awhich transmits cyan light, a second filter235bwhich transmits magenta light, a third filter235cwhich transmits yellow light, and a fourth filter235d, which transmits white light. In one embodiment, for example, the fourth filter235dmay be formed as a transparent layer.

The color switching layer225may operate in a transmittance mode for transmitting incident light, and a color changing mode for changing incident light to predetermined color light. The color switching layer225forms colors in cooperation with the color filter layer235, and may include a first color cell225a, a second color cell225b, a third color cell225c, and a fourth color cell225d. The first color cell225amay transmit incident light or change incident light to a first color light. The second color cell225bmay transmit incident light or change incident light to a second color light. The third color cell225cmay transmit incident light or change incident light to a third color light. The fourth color cell225dmay transmit incident light or change incident light to a fourth color light. The first color light may have a color complementary with respect to the cyan light, the second color light may have a color complementary with respect to the magenta light, and the third color light may have a color complementary with respect to the yellow light. In one embodiment, for example, the first color light may be a red light, the second color light may be a green light, and the third color light may be a blue light. Furthermore, the fourth color light may be a black light.

In an embodiment of the present invention, the color switching layer225may include an electrochromic device, for example. The color switching layer225may include a PDLC layer mixed with a dichroic dye. Alternatively, the color switching layer225may include red, green, and blue cholesteric liquid crystal layers or an e-ink layer having red, green, blue, and white color balls, for example. Since the mechanism of the color switching layer225has been described above, a detailed description thereof will be omitted here.

FIGS. 7 through 9are diagrams for describing embodiments of a method of operating the display device shown inFIG. 6.

Referring toFIG. 7, a second voltage V2is applied to each of the first color cell225a, the second color cell225b, the third color cell225c, and the fourth color cell225d. In one embodiment, for example, the first color cell225amay form a red color when a voltage is applied thereto, the second color cell225bmay form a green color when a voltage is applied thereto, the third color cell225cmay form a blue color when a voltage is applied thereto, and the fourth color cell225dmay form a black color when a voltage is applied thereto. Furthermore, the first filter235amay transmit a cyan light, the second filter235bmay transmit a magenta light, the third filter235cmay transmit a yellow light, and the fourth filter235dmay transmit a white light.

When a white light incident from the outside initially through the color filter layer235as shown by the first portion of the arrow inFIG. 7, a cyan light is transmitted through the first filter235aand towards the first color cell225a, the cyan light is mixed with red color at the first color cell225a, and thus a BL color is formed within the first sub-pixel200a. Furthermore, from the white light, a magenta light is transmitted through the second filter235band towards the second color cell225b, is mixed with green color at the second color cell225b, and thus a BL color is formed within the second sub-pixel200b. Furthermore, from the white light, a yellow light is transmitted through the third filter235cand towards the third color cell225c, is mixed with blue color at the third color cell225c, and thus a BL color is formed within the third sub-pixel200c. Furthermore, the white light is transmitted through the fourth filter235dtowards the fourth color cell225d, the white light is mixed with BL color at the fourth color cell225d, and thus a BL color is formed within the fourth sub-pixel200d. As a result, the BL color light from each of the first to fourth sub-pixels200a,200b,200cand200dare effectively mixed, and thus black color BLACK may be formed in a corresponding pixel200.

Referring toFIG. 8, the second voltage V2is applied to the first color cell225aonly, and either no voltage or an inverse voltage is applied to the second color cell225b, the third color cell225c, and the fourth color cell225d. As a result, the first color cell225aforms a red color, and the second color cell225b, the third color cell225c, and the fourth color cell225dbecome transparent. Therefore, a cyan light is transmitted through the first filter235afrom a white light and towards the first color cell225a, the cyan light is mixed with the red color at the first color cell225a, and thus a BL color is formed in the first sub-pixel200a. A magenta light M is transmitted through the second filter235bfrom a white light and towards the second color cell225b, the magenta light M is transmitted through the transparent second color cell225band is reflected outward by the reflective layer215, and thus the magenta light M travels to the outside of the second sub-pixel200bthrough the second color cell225band the second filter235b. A yellow light Y is transmitted through the third filter235cfrom a white light and towards the third color cell225c, the yellow light Y is transmitted through the transparent third color cell225cand is reflected outward by the reflective layer215, and thus the yellow light Y travels to the outside of the third sub-pixel200cthrough the third color cell225cand the third filter235c. Furthermore, the white light W is transmitted through the fourth filter235d, the white light W is transmitted through the transparent fourth color cell225dand is reflected outward by the reflective layer215, and thus the white light W travels to the outside of the fourth sub-pixel200d. As a result, the magenta light M from the second sub-pixel200b, the yellow light Y from the third sub-pixel200c, and the white light W from the fourth sub-pixel200dare mixed, and thus a red color RED1may be formed by the pixel200. The red color RED1may be formed as a brighter red color as compared to the red color RED described above with reference toFIG. 3.

In an alternative embodiment ofFIG. 7, in a case of applying the second voltage V2to the second color cell225bonly, and applying either no voltage or an inverse voltage to the first color cell225a, the third color cell225c, and the fourth color cell225d, a cyan color may be formed through the combination of the first filter235aand the first color cell225ain the first sub-pixel200a, a BL color may be formed through the combination of the second filter235band the second color cell225bin the second sub-pixel200b, a yellow color Y may be formed through the combination of the third filter235cand the third color cell225cin the third sub-pixel200c, and a white color may be formed through the combination of the fourth filter235dand the fourth color cell225din the fourth sub-pixel200d. As a result, the cyan color from the first sub-pixel200a, the yellow color Y from the third sub-pixel200c, and the white color W from the fourth sub-pixel200dare mixed, and thus a bright green color may be formed by the pixel200. Furthermore, in a case of applying the second voltage V2to the third color cell225conly, and applying either no voltage or an inverse voltage to the first color cell225a, the second color cell225b, and the fourth color cell225d, a cyan color may be formed through the combination of the first filter235aand the first color cell225ain the first sub-pixel200a, a magenta color M may be formed through the combination of the second filter235band the second color cell225bin the second sub-pixel200b, a BL color may be formed through the combination of the third filter235cand the third color cell225cin the third sub-pixel200c, and a white color W may be formed through the combination of the fourth filter235dand the fourth color cell225din the fourth sub-pixel200d. As a result, the cyan color from the first sub-pixel200a, the magenta color M from the second sub-pixel200b, and the white color W from the fourth sub-pixel200dare mixed, and thus a bright blue color may be formed by the pixel200.

Furthermore, in a case of applying the second voltage V2to the first color cell225aand the second color cell225b, and applying either no voltage or an inverse voltage to the third color cell225cand the fourth color cell225d, a BL color may be formed through the combination of the first filter235aand the first color cell225ain the first sub-pixel200a, a BL color may be formed through the combination of the second filter235band the second color cell225bin the second sub-pixel200b, a yellow color Y may be formed through the combination of the third filter235cand the third color cell225cin the third sub-pixel200c, and a white color W may be formed through the combination of the fourth filter235dand the fourth color cell225dfourth sub-pixel200d. As a result, a bright yellow color may be formed by the pixel200. In alternative embodiments, a bright cyan color or bright magenta color may be formed by the above method, where two of four sub-pixels are applied with the second voltage V2.

Referring toFIG. 9, either no voltage or an inverse voltage is applied to the first color cell225a, the second color cell225b, the third color cell225c, and the fourth color cell225d. As a result, all of the first color cell225a, the second color cell225b, the third color cell225c, and the fourth color cell225dbecome transparent. A cyan light C is transmitted through the first filter235afrom a white light and towards the first color cell225a, the cyan light C is transmitted through the transparent first color cell225aand is reflected outward by the reflective layer215, and thus the cyan light C travels to the outside of the first sub-pixel200a. Furthermore, a magenta light M is transmitted through the second filter235bfrom a white light and towards the second color cell225b, the magenta light M is transmitted through the transparent second color cell225band is reflected outward by the reflective layer215, and thus the magenta light M travels to the outside of the second sub-pixel200b. Furthermore, a yellow light Y is transmitted through the third filter235cfrom a white light and towards the third color cell225c, the yellow light Y is transmitted through the transparent third color cell225cand is reflected outward by the reflective layer215, and thus the yellow light Y travels to the outside of the third sub-pixel200c. Furthermore, a white light W is transmitted through the fourth filter235dtowards the fourth color cell225d, the white light W is transmitted through the transparent fourth color cell225dand is reflected outward by the reflective layer215, and thus the white light W travels to the outside of the fourth sub-pixel200d. As a result, the cyan light C from the first sub-pixel200a, the magenta light M from the second sub-pixel200b, the yellow light Y from the third sub-pixel200c, and the white light W from the fourth sub-pixel200dare mixed, and thus a bright white color WHITE1is formed by pixel200.

As described above, when all of the color cells of the color switching layer225become transparent, a cyan light C, a magenta light M, a yellow light Y, and a white light W, which are lights of natural colors of the first, second, third and fourth color filters235a,235b,235cand235d, may be reflected within the first, second, third and fourth sub-pixels200a,200b,200cand200dto form a bright white color of the pixel200. Here, a light transmitted through the color filter layer235may form a black color based on subtractive color mixture when the color switching layer225is in the color changing mode, whereas a light transmitted through the color filter layer235may form a white color based on additive color mixture when the color switching layer225is in the transmittance mode.

As described above, the present invention provides sub-pixels capable of forming a black color or white color by which contrast and color reproduction characteristic of a display device may be improved. Furthermore, white light efficiency and grayscale characteristic may also be improved. Although examples in which a pixel includes sub-pixels forming different colors from each others are described above, the present invention is not limited thereto, and a pixel may include sub-pixels with any color combinations. In one embodiment, for example, a color filter layer may include a first cyan filter, a second cyan filter, a magenta filter, and a yellow filter.

AlthoughFIGS. 1 and 6show reflective display devices including reflective layers, a display device may be configured without a reflective layer.

Another embodiment of display device which is shown inFIG. 10may include a first electrode layer310, a color switching layer325, which is disposed on the first electrode layer310, a second electrode layer330, which is disposed on the color switching layer325, and a color filter layer335, which is disposed on the second electrode layer330. The color switching layer325is interposed between the first electrode layer310and the second electrode layer330and may operate in a transmittance mode for transmitting incident light and a color changing mode for changing incident light to predetermined color light, where the color switching layer325may be switched between the transmittance mode and the color changing mode by applying a voltage thereto.

The color switching layer325may include a first color cell325awhich may transmit incident light or change incident light to a first color light, a second color cell325bwhich may transmit incident light or change incident light to a second color light, and a third color cell325cwhich may transmit incident light or change incident light to a third color light. Furthermore, the color filter layer335may include a first filter335awhich transmits a cyan light, a second filter335bwhich transmits a magenta light, and a third filter335cwhich transmits a yellow light. The first color cell325aand the first filter335aare arranged to face each other, the second color cell325band the second filter335bare arranged to face each other, and the third color cell325cand the third filter335care arranged to face each other, and a black color, white color, and various other colors may be formed through combinations of corresponding color cells and light transmitted through each of the filters335a,335b, and335c. Since the method of forming colors is identical to the method described above with reference toFIGS. 1 and 6, detailed descriptions thereof will be omitted here.

In the display device shown inFIG. 10, a plurality of a pixel may be arranged in a matrix shape. For convenience of explanation,FIG. 10shows only one pixel300of the display device. The pixel300may include a plurality of a sub-pixel, and a color image of the display device may include color lights from each of the sub-pixels which are mixed together. Each of the sub-pixels may emit different color lights. However, the present invention is not limited thereto, and the pixel300may include a plurality of a sub-pixel, which emits the same color light, in consideration of brightness or efficiency of each color light. In one embodiment, for example, the pixel300may include a first sub-pixel300a, a second sub-pixel300b, and a third sub-pixel300c.

A partition322may be interposed between each pair of adjacent sub-pixels of the color switching layer325, to reduce or effectively prevent mixtures of colors within the sub-pixels. The reference numeral320indicates an electrolyte layer. In contrast to the display devices inFIGS. 1 and 6, the display device shown inFIG. 10does not include a reflective layer.

The display device shown inFIG. 10may be used as a transparent display device. In other words, a color image is formed as an external light is transmitted through the color filter layer335and the color switching layer325, and the color image is viewed by a user. In this case, the image may be displayed on two opposite surfaces of the display device.

Display devices according to embodiments of the present invention may be applied to electronic reading devices (e.g., e-book), for example, where the same effect as forming colors on paper may be acquired. Furthermore, display devices according to embodiments of the present invention may be applied to a reflective display device, which forms a color image by using an external light and displays the color image by reflecting external light by a reflective layer.

Display devices according to embodiments of the present invention do not require a color filter layer stacking process or a color switching layer stacking process, either of which is complex and expensive. Furthermore, by operating each of sub-pixels and combining colors of the same, a black color, white color, and various other colors may be formed by a pixel, and improved contrast ratio and wider range of color formation may be acquired. Therefore, display devices according to embodiments of the present invention may improve display performance of reflective display devices, such as an e-book device.