JPH1063203A - Reflection type color display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance the luminance and also to secure practically sufficient color reproducibility by improving the color constitution of a color filter to be used in a reflection type color display device. SOLUTION: The reflection type color display device is assembled by using one pair of upper and lower substrates 1. 2. The substrate 1 of the upper side is positioned at an incident side and transparent electrodes 3 having a prescribed pattern are formed on the substrate. The substrate 2 of the lower side is positioned at an opposite side and reflection electrodes 4 having the prescribed pattern are formed on the substrate and is joined to the substrate 1 of the upper side with a gap to stipulates matrix shaped pixels 6 in between both substrates opposed each other. A guest liquid crystal 7 is held in between the both substrates 1,2 to control transmission states of passing lights every pixel 6. Color filters 8 are formed on the substrate 2 of one side to realize a color display by an additive color mixing of plural pixels colored in different color components by selectively filtering plural kinds of the passing lights in the pixel unit. The filters 8 are divided into a Y segment selecting an yellow component, a C segment selecting a Cyan component, an M segment selecting a Msgenta component and a (g) segment selecting a green component in the pixel unit.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reflection type color display device. More specifically, the present invention relates to a color configuration of a color filter incorporated in a display device.

[0002]

2. Description of the Related Art An example of a conventional color display device will be briefly described with reference to FIG. As shown in the figure, the color display device has a pair of glass substrates 71 and 72 disposed opposite to each other,
The liquid crystal 73 is sealed in the gap as an electro-optical material. On one glass substrate 71, a signal line 74 and a scanning line 75 arranged in a matrix and a thin film transistor 76 and a pixel electrode 77 arranged at the intersection thereof.
Are formed. The thin film transistor 76 is a scanning line 75
, And the image signal supplied from the signal line 74 is written to the corresponding pixel electrode 77. On the other hand, a counter electrode 78 and a color filter 79 are formed on the inner surface of the upper glass substrate 72. The color filter 79 is divided into red (R), green (G), and blue (B) segments corresponding to each pixel electrode 77. When the active matrix liquid crystal display device having such a configuration is sandwiched between two polarizing plates 80 and 81 and white light is incident thereon, a desired full-color image display can be obtained.

[0003]

The color filter 79 selectively filters a plurality of types of color components (RGB) contained in the transmitted light on a pixel basis. Color display is realized by additive color mixing of a plurality of pixels colored for each of RGB.
The R segment transmits only the R component and absorbs the G component and the B component. The G segment transmits only the G component and absorbs the R and B components. The B segment transmits only the B component and absorbs the R and G components. As described above, since the conventional color filter absorbs two-thirds of the incident light, there is a problem that the luminance of the screen is low. Generally, color display devices using liquid crystal or the like as an electro-optical material are classified into a transmission type and a reflection type. The transmission type uses a backlight to illuminate the back surface of the display device and observe an image from the front surface. Therefore, if the illumination light amount of the backlight is sufficiently secured, a relatively bright display screen can be obtained regardless of the absorption of the color filter. On the other hand, in the reflection type, light incident from one substrate is reflected by the other substrate, and a reflection image is observed from the one substrate side. The display screen is projected using only external light such as sunlight without using a backlight. Therefore, the amount of light incident on the display device is limited, and it is necessary to improve the utilization efficiency of the incident light in order to obtain a bright screen. Anyway,
A conventional RGB color filter absorbs two-thirds of the incident light for each pixel, so that a reflective display device cannot display a bright color image.

[0004]

The following means have been taken in order to solve the above-mentioned problems of the prior art. That is, the reflection type color display device according to the present invention includes a pair of substrates, an electro-optical material, and a color filter as a basic configuration. One of the substrates is located on the incident side and has an electrode of a predetermined pattern. The other substrate is located on the reflection side and has electrodes of a predetermined pattern formed thereon. The substrate is joined to the one substrate via a gap, and defines a matrix of pixels between the two substrates facing each other. The electro-optical material is made of a liquid crystal or the like, and is held in a gap between a pair of substrates to control a transmission state of transmitted light for each pixel. The color filter is formed on one of the substrates, selectively filters a plurality of types of color components included in the transmitted light on a pixel-by-pixel basis, and implements color display by additive color mixing of a plurality of pixels colored into different color components. As a feature, the color filter includes a segment for selecting a yellow (Y) color component, a segment for selecting a cyan (C) color component, a segment for selecting a magenta (M) color component, and a green (g). A) a segment for selecting a color component. Specifically, each segment is composed of a film in which a pigment of a corresponding color component is dispersed. In one embodiment, the electro-optical material is composed of a guest-host liquid crystal containing a dichroic dye, and a quarter-wave plate layer is interposed between the guest-host liquid crystal and the substrate on the reflection side. In one embodiment, a plurality of pixel electrodes patterned in a matrix and switching elements for individually driving the pixel electrodes are integrally formed on one substrate, and a solid pattern counter electrode is formed on the other substrate. Is formed,
An active matrix type pixel is defined between a pixel electrode and a counter electrode facing each other.

In the present invention, a color filter having one unit of the Y, C, M, and g segments is used. This realizes color display by performing color reproduction by additive color mixture of four color segments. By the way, C has a complementary color relationship with R, M has a complementary color relationship with G,
Y has a complementary color relationship with B. While the RGB color filters absorb approximately two-thirds of the incident light, the CMY color filters only absorb approximately one-third of the incident light. Therefore, it is possible to improve the luminance during white display by using the CMY color filters. However, in the CMY color system, the selection range of the pigment corresponding to each color is limited, and it is not always possible to select the most suitable CMY pigment. In particular, the reproducibility of green was insufficient in the CMY color system using conventional pigments. Therefore, in the present invention, a g-segment is added in addition to each of the CMY segments to ensure color reproducibility.

[0006]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of the present invention will be described below in detail with reference to the drawings. FIG. 1 is a schematic view showing one embodiment of a reflection type color display device according to the present invention.
(A) is a partial plan view, (B) is a partial sectional view, and (C) is an operation explanatory view. As shown in (A) and (B), the reflective color display device is assembled using a pair of upper and lower substrates 1 and 2. The upper substrate 1 is located on the incident side and has a transparent electrode 3 having a predetermined pattern. In this example, the transparent electrodes 3 are patterned in rows. The lower substrate 2 is located on the reflection side and has a predetermined pattern of the reflection electrode 4.
Are formed. In this example, the reflective electrodes 4 are patterned in a row. Note that a transparent conductive film such as ITO is used as a material of the transparent electrode 3, and a metal film such as aluminum is used as a material of the reflective electrode 4. The lower substrate 2 is joined to the upper substrate 1 via a predetermined gap by a spacer 5. A matrix of pixels 6 is defined between the two substrates 1 and 2 facing each other. Specifically, pixels 6 arranged in a matrix at the intersection of the row-shaped transparent electrodes 3 and the column-shaped reflective electrodes 4 are defined. Therefore, this embodiment is a so-called simple matrix type display device. However, it is needless to say that the present invention is not limited to this and can be applied to an active matrix type display device. In the present embodiment, a guest host liquid crystal 7 as an electro-optical material is held in a gap between a pair of upper and lower substrates 1 and 2, and controls the transmission state of transmitted light for each pixel 6. A color filter 8 is formed on the lower substrate 2. However, the present invention is not limited to this.
May be formed. In the present embodiment, the color filter 8
Are patterned in alignment with the reflective electrode 4. The color filter 8 selectively filters a plurality of types of color components included in the transmitted light on a pixel-by-pixel basis, and realizes a color display by additive color mixing of the plurality of pixels 6 colored with different color components. As a feature, the color filter 8 includes a C segment for selecting a cyan component, an M segment for selecting a magenta component, and a Y segment for selecting a yellow component.
It is divided into a segment and a g segment for selecting a green color component. That is, the present color filter 8 is
A four-primary-color pixel system is adopted, which is based on a Y-segment color system and adds a g-segment for color reproduction correction thereto. A full-color display can be realized by additive color mixing of these four primary color pixels.

As shown in FIG. 1C, the reflective color display device displays a color image by applying a voltage between the upper transparent electrode 3 and the lower reflective electrode 4 via a drive circuit 9. Do. For example, the first row of transparent electrodes 3 and the first row of reflective electrodes 4
When a voltage is applied between the two, the guest-host liquid crystal 7 belonging to the pixel located at the intersection of the two changes from the light blocking state to the light transmitting state. Accordingly, light incident from the upper substrate 1 is reflected by the lower substrate 2, and a reflected image from the upper substrate 1 can be observed. Since the C segment corresponds to the pixel in the first row and the first column, a pixel colored in cyan can be observed. By sequentially applying a desired voltage between the row of the transparent electrodes 3 and the column of the reflective electrodes 4, a color display including a halftone becomes possible.

FIG. 2A shows the transmittance characteristics of each of the CMY segments, and FIG. 2B shows the transmittance characteristics of each of the RGB segments. As is clear from the comparison between (A) and (B), the C segment has a complementary color relationship with the R segment. R segment is from 400nm to 7
Only one third of the visible light distributed between 00 nm is transmitted and the remaining two thirds are absorbed. On the other hand, the C segment transmits two-thirds of the wavelength component included in the visible light region and absorbs one-third. Therefore, the C segment is twice as bright as the R segment when viewed qualitatively. Similarly, the M segment has a complementary color relationship with the G segment, and Y segment
The segment has a complementary color relationship with the B segment. As described above, the transmittance of the incident light amount in the CMY color system is twice that of the RGB color system.

FIG. 3 shows the principle of additive color mixing in the CMY system. For example, when displaying green in the CMY color system, by selecting the C segment and the Y segment, green can be displayed by additive color mixing of the corresponding two pixels. In this case, the combined transmittance of the C segment and the Y segment is as shown in FIG.
As shown in (1), there is a peak substantially at the center of the visible light wavelength region, and a desired green color can be expressed. It should be noted that light is also transmitted through regions located on both sides of this peak. That is, as schematically shown in FIG. 3, when the C segment and the Y segment are additively mixed, the green component is superimposed on the white level represented by the transmittance W. That is, in the case of the additive color mixture using the CMY color system, green is projected on a white background, so that a brighter screen can be obtained as compared with the RGB color system.

[0010] Coloring materials for color filters currently used can be roughly classified into dyes and pigments. In consideration of reliability and the like, it is advantageous to use a pigment system having a more robust molecular structure. Therefore, in the present invention, each segment is composed of a film in which a pigment of a corresponding color component is dispersed. However, when a CMY color filter is formed using pigments, it is difficult to perform color display that can withstand a practical level due to the limitations of the pigments themselves, even if the most important color reproduction is selected. FIG. 5 shows CIE standard chromaticity coordinates of the CYM color filter. As is clear from the chromaticity coordinate diagram, when the CMY color filter is used, the range in which color reproduction is possible is narrower than that of the RGB filter. The CMY color filter can reproduce red and blue colors to some extent, but the green color reproduction is completely insufficient. Although the description has been made before and after, the chromaticity coordinates in FIG. 5 are approximately the standard chromaticity coordinates of the RGB color filters used in the transmission type display device. In addition, the chromaticity coordinates of the CMY color filters, in which the color reproduction is given the highest priority, are set using a currently selectable pigment-based resist film.
As is clear from the graph of FIG. 5, when the CMY color filters are used, green color can hardly be reproduced in comparison with the color reproducibility of blue and red. Therefore, in the present invention, C
In addition to the basic three-color segments of MY, a fourth g segment is additionally provided. Color reproduction is performed by four-color additive mixing of CMYg. As a result, it is possible to represent the color in the rectangle connecting the CMYg. In the case of the example shown in FIG. 5, when the g segment is added, the color tone can be reproduced about twice as compared with the case where the g segment of the fourth color is not used. FIG.
Is an example, and the present invention is not limited to this. It is possible to optimally set the coordinates of g by using CMY pigment materials, white balance, and the like.

Finally, a specific embodiment of the reflection type color display device according to the present invention will be briefly described with reference to FIG. As shown in the figure, the present reflection type color display device has a first substrate 11 disposed on the incident side and a substrate 1 with a predetermined gap therebetween.
1 and a second substrate 12 arranged on the reflection side. At least a guest-host liquid crystal layer 13, a quarter-wave plate layer 14, and a light reflection layer 15 are interposed in the gap between the substrates 11, 12. The guest host liquid crystal layer 13 is located on the incident side of the substrate 11 in the gap, and includes vertically aligned nematic liquid crystal molecules 16 and a black dichroic dye 17. The light reflection layer 15 is located on the reflection side of the substrate 12 in the gap. The quarter wave plate layer 14 is interposed between the guest host liquid crystal layer 13 and the light reflection layer 15. A counter electrode 18 is formed on the inner surface of the substrate 11 on the incident side, and a pixel electrode 19 is formed on the inner surface of the substrate 12 on the reflective side. Apply signal voltage in units. Also, a color filter 40 is formed on the inner surface of the substrate 11 on the incident side. The color filter 40 is divided into a C segment, an M segment, a Y segment, and a g segment corresponding to each pixel. The surfaces of the counter electrode 18 and the pixel electrode 19 are covered with alignment films 20 and 21, respectively, and vertically align the guest-host liquid crystal layer 13. When no voltage is applied, the guest-host liquid crystal layer 13 is in a transmissive state, and when a voltage is applied, the state changes to a cut-off state.

The reflection type color display device is of an active matrix type, and a thin film transistor 22 for driving switching of a pixel electrode 19 is integrally formed on a substrate 12 on the reflection side. The thin film transistor 22 is a bottom gate type, and a gate electrode 23, a gate insulating film 24,
The semiconductor thin film 25 and the stopper 26 are laminated.
The thin film transistor 22 is covered with an interlayer insulating film 27, on which a source electrode 28 and a drain electrode 29 are patterned and connected to the thin film transistor 22 via a contact hole. The light reflection layer 15 described above is also formed by patterning on the interlayer insulating film 27 and has the same potential as the drain electrode 29. Thin film transistor 2
2 and the light reflecting layer 15 having irregularities are covered with a flattening layer 30, on which the above-described quarter-wave plate layer 14 is formed via a base alignment layer 31. Further, the pixel electrode 19 patterned on the quarter-wave plate layer 14 is electrically connected to the drain electrode 29 through the contact hole 32 opened in the quarter-wave plate layer 14 and the planarization layer 30. doing. The opening process of the contact hole 32 is performed by, for example, photolithography and etching using a positive photoresist. The alignment film 21 is formed by applying an alignment solvent in which polyimide or the like is dissolved on the surfaces of the pixel electrode 19 and the quarter-wave plate layer 14.

When no voltage is applied, the liquid crystal molecules 16 are vertically oriented, and the dichroic dye 17 is similarly oriented. Upper substrate 1
The light incident from 1 passes through the guest-host liquid crystal layer 13 without being absorbed by the dichroic dye 17 after the desired color component is selected by the color filter 40, and is affected by the quarter-wave plate layer 14. The light is reflected by the light reflection layer 15 without receiving light. The reflected light passes through the quarter-wave plate layer 14 again and exits without being absorbed by the guest-host liquid crystal layer 13.
Accordingly, colored display of pixels corresponding to each color segment of the color filter 40 can be performed. In contrast, the liquid crystal molecules 16 are horizontally oriented when a voltage is applied, and the dichroic dye 17 is similarly oriented. When light incident from the upper substrate 11 enters the guest-host liquid crystal layer 13 via the color filter 40, a component of the incident light having a vibration plane parallel to the major axis direction of the molecules of the dichroic dye 17 becomes two colors. It is absorbed by the sex pigment 17. The component of the incident light having a vibration plane perpendicular to the major axis direction of the molecules of the dichroic dye 17 passes through the guest-host liquid crystal layer 13 and forms a quarter wavelength formed on the lower substrate 12. The light is circularly polarized by the plate layer 14 and is reflected by the light reflecting layer 15. At this time, the polarization direction of the reflected light is reversed, passes through the quarter wavelength plate layer 14 again, and becomes light having a vibration plane parallel to the major axis direction of the molecules of the dichroic dye 17. Since this light is absorbed by the dichroic dye 17, a complete black display is obtained.

[0014]

As described above, according to the present invention, the color filter incorporated in the reflection type color display device has a C segment for selecting a cyan component and an M segment for selecting a magenta component for each pixel. It is divided into a Y segment for selecting a yellow color component and a g segment for selecting a green color component. By using the CMY color system, the luminance of white display can be improved as compared with the RGB color system. Further, by introducing the fourth g segment in addition to the CMY segment, the color reproducibility of the CMY color filter is remarkably improved.

[Brief description of the drawings]

FIG. 1 is a schematic diagram illustrating an embodiment of a reflective color display device according to the present invention.

FIG. 2 is a graph showing transmittance characteristics of a color filter.

FIG. 3 is a graph showing transmittance characteristics of a color filter.

FIG. 4 is a schematic partial cross-sectional view showing a specific example of a reflective color display device according to the present invention.

FIG. 5 is a graph showing CIE standard chromaticity coordinates of a color filter.

FIG. 6 is a schematic perspective view showing an example of a conventional color display device.

[Explanation of symbols]

1 ... substrate, 2 ... substrate, 3 ... electrode, 4 ... electrode, 6 ... pixel,
7: Guest host liquid crystal (electro-optical material), 8: Color filter

Claims (4)

[Claims] An electrode having a predetermined pattern formed on an incident side and an electrode having a predetermined pattern formed on a reflection side, wherein the one substrate is connected to the one substrate via a gap; The other substrate that defines a matrix of pixels between the two substrates that are joined and facing each other, an electro-optical material that is held in the gap and controls the transmission state of the transmitted light for each pixel, and the transmitted light that is formed on one substrate And a color filter for selectively filtering a plurality of types of color components included in the pixel unit to realize a color display by an additive color mixture of a plurality of pixels colored to different color components, wherein the color filter is a pixel unit. The segment is divided into a segment for selecting a yellow component, a segment for selecting a cyan component, a segment for selecting a magenta component, and a segment for selecting a green component. Reflective color display device according to claim that that. 2. The reflection type color display device according to claim 1, wherein each segment comprises a film in which a pigment of a corresponding color component is dispersed. 3. The electro-optical material is composed of a guest-host liquid crystal containing a dichroic dye, and a quarter-wave plate layer is interposed between the guest-host liquid crystal and the substrate on the reflection side. 2. The reflection type color display device according to claim 1, wherein: 4. A plurality of pixel electrodes patterned in a matrix and switching elements for individually driving them are integrated on one substrate, and a solid pattern counter electrode is formed on the other substrate. 2. The reflection type color display device according to claim 1, wherein an active matrix type pixel is defined between the pixel electrode and the counter electrode facing each other.