JPH11258587A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display device permitting a bright color display using color filters of red, green, and blue. SOLUTION: In this device, a reflection electrode is formed on one of a pair of substrates opposing each other and holding a liquid crystal layer them, and a translucent counter electrode and a color filter is formed on the other substrate. Here, this color filter has a green color filter transmitting such light as chromaticity coordinates (x, y) in the chromaticity diagram in XYZ color system satisfy each of the formulae: 0.29<=x<=0.33 and 0.35<=y<=0.37 under the conditions of D65 light source and 2-degree filed of view, therefore, luminosity is high, and does not lose visibility of green which is hard to be contrasted against white and has no problem for displaying characters and graphics, and also permits a bright display.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective liquid crystal display device having a small size and low power consumption, and more particularly to a reflective liquid crystal display device capable of bright color display.

[0002]

2. Description of the Related Art Conventionally, a liquid crystal display device has been used as a display of information terminal equipment. This liquid crystal display device includes a transmission type in which a backlight system as a light source is mounted and enables bright display, and a reflection type in which display is performed by reflecting ambient light.

[0003] The above-mentioned transmission type liquid crystal display device has a problem that it can display brightly, but has a large weight and a large power consumption because it has a backlight. On the other hand, the reflection-type liquid crystal display device has the advantage of light weight and low power consumption because it is not necessary to use a backlight. Therefore, the reflection type liquid crystal display device is widely used especially for a display of a portable information terminal device.

By the way, as a reflection type liquid crystal display device,
Many monochrome display devices such as TN and STN modes have been put to practical use. Also, to realize colorization,
A reflective liquid crystal display device in which each pixel is provided with an RGB micro color filter is also under development.

As means for realizing colorization in a reflection type liquid crystal display device, a device utilizing light interference due to a birefringence effect of a liquid crystal without using a color filter or a device utilizing multiple interference by a multilayer film is used. However, in the former case, the hue itself may change because the retardation changes depending on the temperature and the viewing angle direction.
Even black and white display can be difficult. The latter case is disadvantageous in cost and production efficiency as compared with the case of using a color filter.

Generally, in a reflection type liquid crystal display device provided with a color filter, since ambient light passes through the color filter twice, if a color filter used in a transmission type liquid crystal display device is applied as it is, There is a problem that the light transmittance is extremely reduced and the display becomes dark. Therefore, it is necessary to use a color filter having a high light transmittance for a color filter used in a reflective liquid crystal display device.

[0007]

However, the higher the light transmittance of the color filter is, the lower the color purity is, and as a result, the display becomes faint as a whole, and the saturation is lowered. Therefore, the light transmittance of the color filter must be selected in consideration of the balance with the color purity.

By the way, for example, in a reflection type liquid crystal display device mainly for displaying characters and figures, such as a portable personal computer, a word processor, a game machine, etc., a natural image display is intended. In some cases, the brightness of the display is more important than that. In this case, the optimization of brightness and saturation (color purity) is different from that for the purpose of displaying a natural image, and a bright display is obtained even if the saturation is reduced to such an extent that each display color can be recognized. Is more desirable.

In view of the above, the present inventor, in displaying characters, figures, and the like, does not impair the visibility and lowers the saturation (color purity) to a level that does not cause a problem in display, thereby performing bright display. Optimization of color filters that can be performed.

The present invention has been made in view of the above problems, and has as its object to provide a reflection type liquid crystal display device which enables bright color display.

[0011]

According to a first aspect of the present invention, there is provided a reflective liquid crystal display device in which a reflective electrode is formed on one of a pair of substrates opposed to each other with a liquid crystal layer interposed therebetween, and a light-transmitting opposing substrate is formed on the other. In a reflective liquid crystal display device in which electrodes and three color filters of red, green, and blue are formed, a D ₆₅ light source and 2
The light whose chromaticity coordinates (x, y) in the XYZ color system chromaticity diagram satisfy the respective expressions of 0.29 ≦ x ≦ 0.33 and 0.35 ≦ y ≦ 0.37 under the condition of the visual field. A green color filter that transmits light.

In general, among red, green, and blue, green contains many wavelength regions with high visibility, so that when bright display is performed, the contrast between green and white is most difficult to obtain. Therefore, by designing the green color filter as described above, it is possible to perform display without any problem when performing characters and graphics.

Also, 0.34 ≦ x ≦ 0.37, and 0.3.
A red color filter that transmits light satisfying each of the following expressions: 28 ≦ y ≦ 0.32; 0.22 ≦ x ≦ 0.27; and x
+ 0.04 ≦ y ≦ x + 0.08, a blue color filter that transmits light that satisfies each of the following expressions, whereby yellow obtained by additive color mixing of green and red, and additive color mixing of green and blue Display can be performed without impairing the visibility of the obtained cyan.

Further, in the reflection type liquid crystal display device, chromaticity coordinates (x, x, y) in a white XYZ color system chromaticity diagram obtained by additive color mixing of the three color filters.
y) is 0.28 ≦ x ≦ 0.31, and 0.29 ≦ y ≦
If the red and blue color filters are set so as to satisfy each equation of 0.33, white without color can be reproduced.

[0015]

Embodiments of the present invention will be described with reference to the drawings.

FIG. 1 is a sectional view of a reflection type liquid crystal display device 30 according to one embodiment of the present invention. The TFT element 40 is formed on one substrate 31 using a known technique. Further, here, uneven interlayer insulating films 42 a and 42 b were formed, and the reflection electrode 38 was formed via the contact hole 43. Further, an alignment film 44 is formed thereon.

The structure of the opposite substrate, which is the other substrate, is as follows. A color filter 46 is provided on the substrate 45.
Are formed. The color filter 46 is provided on the substrate 31.
Any of red, green and blue color filters 46a is formed in a region corresponding to the reflective electrode 38, and a black filter 46b is formed in a region not corresponding to the reflective electrode 38. A protective film (not shown) is formed on the entire surface of the color filter 46, a transparent electrode 47 made of ITO or the like is formed thereon with a thickness of 150 nm, and an alignment film 48 is further formed thereon.

The substrate 45 and the substrate 31 having such a configuration are bonded to each other so that the position of one of the red, green, and blue filters and the reflective electrode 38 coincides with each other.

As the liquid crystal layer 49, for example, a guest-host liquid crystal mixed with a black dye (trade name: ZLI- manufactured by Merck Ltd.)
2327), an optically active substance (manufactured by Merck, trade name S8)
11) is used in which 4.5% is mixed. In the present embodiment, the liquid crystal layer 49 is formed using a liquid crystal having electro-optical characteristics as shown in FIG.

Ideally, the liquid crystal layer should have optical characteristics such that the reflectance in the dark state is lower and the reflectance in the bright state is higher. In particular, when the reflectance in the dark state is 15% or less, a color display with high contrast and high saturation can be realized. If the reflectance in the bright state is 40% or more, three color filters can be applied.

In this embodiment, the guest-host liquid crystal is used for the liquid crystal layer. However, if the reflectance in the dark state and the light state is at the above-mentioned level, another liquid crystal requiring a polarizing plate such as TN or STN may be used. You may use it.

Next, the configuration of the color filter 46 will be described. As described above, the color filter 46 includes red, green, and blue color filters 46a that form color pixels.
And a black filter 46b forming a light shielding portion.

Generally, the color reproduction range of a liquid crystal display device is determined mainly by the color purity of a color filter. The higher the color purity, the larger the color reproduction range. However, on the other hand, the light transmittance of the color filter is reduced, so that a bright display cannot be realized. Therefore, in the present embodiment, the color of the red, green, and blue color filters 46a is designed with priority given to the brightness at the time of display.

When the transmittance is increased while maintaining the saturation to some extent, when displaying colors such as green, yellow, and cyan, which include many wavelength regions with high visibility, the contrast with white becomes the lowest. Most difficult to recognize. For that purpose, it is necessary to design the color of the green color filter first, and to design the colors of the remaining red and blue color filters according to the green color filter.

Therefore, three color filters of Ag, Bg and Cg were prepared as green color filters having a high transmittance. Each chromaticity coordinate is expressed as Ag (0.309,
0.366), Bg (0.310, 0.354), Cg
(0.311, 0.341). Applying these color filters to a reflection type liquid crystal display device and performing green display, it was possible to perform display with practically no problem in the Ag and Bg color filters.
Cg color filters make it difficult to identify characters and figures, and are not suitable for use as a display device.

From the above, for the green color filter, the chromaticity coordinates (x,
In y), it can be seen that when the y coordinate is within 0.35 ≦ y ≦ 0.37, a bright display can be obtained without impairing the visibility of green. The y coordinate is 0.37
If it becomes larger, the brightness of the display is impaired. When the x coordinate of the green color filter is smaller than 0.29, the hue becomes bluish,
If the ratio is larger than 0.33, the hue becomes yellowish. Therefore, it is preferable that the ratio is in the range of 0.29 ≦ x ≦ 0.33.

FIG. 3 shows the range of chromaticity coordinates applicable to the green color filter and the chromaticity coordinates of the three color filters Ag, Bg, and Cg described above.

If the chromaticity coordinates of the green color filter are optimized as described above, the chromaticity coordinates of the red and blue color filters can be optimized accordingly.

It is desirable that the color design of the red color filter does not impair the visibility of yellow obtained by additive color mixing with green. FIG. 4 shows a range of chromaticity coordinates of a red color filter optimized according to the green color filter shown in FIG.

The color design of the blue color filter is as follows.
It is desirable not to impair the visibility of cyan obtained by additive color mixing with green. FIG. 5 shows the range of the chromaticity coordinates of the blue color filter optimized according to the green and red color filters shown in FIGS. 3 and 4.

When a display is performed by combining the above-described three color filters, it is preferable that the white color obtained by these additive color mixing be as pure white as possible without coloring. For this reason, the white color obtained by these additive color mixing is represented by chromaticity coordinates (x, y) in the XYZ color system.
Is the region shown in FIG. 6, ie, 0.28 ≦ x ≦ 0.31,
It is preferable to combine the above-mentioned three color filters so as to satisfy the following expressions: 0.29 ≦ y ≦ 0.33.

In general, the theoretical white point in the XYZ color system is (0.313, 0.329) under a D ₆₅ light source.
However, the color filter used in the liquid crystal display device needs to be laminated with a transparent conductive thin film such as ITO, a protective film, and the like. It has been known. Therefore, by subtracting the change in hue in advance and setting white in the shaded region in FIG. 6, it is possible to reproduce good white without color when used as a color filter.

Therefore, from the range of the chromaticity coordinates of the red and blue color filters shown in FIGS. 4 and 5, the red color filters Ar, Br, and the blue color filter are adapted to the above-mentioned green color filters Ag, Bg. Color filter A
b and Bb, a reflective liquid crystal display device using three color filters of Ar, Ag and Ab, and Br
When a reflective liquid crystal display device using three color filters consisting of Bg and Bb was prepared and characters and figures were displayed, white without any coloring was obtained, and practicality was observed in visibility. A bright display could be obtained without any problem.

The chromaticity coordinates of the red color filter Ar are (0.368, 0.306), and the chromaticity coordinates of Br are (0.344, 0.313). The chromaticity coordinates of the blue color filter Ab are (0.22
8, 0.284), and the chromaticity coordinates of Bb are (0.25
2,0.299). These chromaticity coordinates are shown in FIG. 4 and FIG.

In the present embodiment, the measurement of the chromaticity coordinates described above was performed under a D ₆₅ light source and a 2 ° visual field. D ₆₅
The light source is the same as the light illuminated by daylight and is used for measuring the color of an object, and has a wavelength component as shown in FIG. The D ₆₅ light source is CI
E, ISO reference light. In addition, the 2 ° field of view refers to FIG.
(A), it is a feeling when the human eye recognizes an object at a viewing angle of 1 ° to 4 °. As shown in FIG. 8B, the sensation of recognizing an object at a viewing angle larger than 4 ° is called a 10 ° viewing field. These sensations are all provided to standardize human color sensation.

By using a color filter designed as described above, the brightness of the display is prioritized over the saturation (color purity), for example, as in a portable personal computer, word processor, game machine, etc. To
In a reflective liquid crystal display device mainly for displaying characters, figures, and the like, a very bright display can be obtained.

[0037]

As described above, in the reflection type liquid crystal display device of the present invention, a reflection electrode is formed on one of a pair of substrates opposed to each other with a liquid crystal layer interposed therebetween, and a translucent counter electrode and a red electrode are formed on the other. , green, in the reflection type liquid crystal display device having a color filter formed consisting of three colors of blue, in the condition of illuminant D ₆₅ and 2 ° field of view, the chromaticity coordinates (x, y) in the XYZ color system chromaticity diagram , 0.29 ≦ x ≦ 0.33, and 0.35
Since it has a green color filter that transmits light that satisfies each formula of ≦ y ≦ 0.37, it includes many wavelength regions with high luminosity and reduces the visibility of green, which makes it difficult to obtain contrast with white. Therefore, there is an effect that display can be performed without any problem in displaying characters, figures, and the like.

Further, 0.34 ≦ x ≦ 0.37, and 0.3.
A red color filter that transmits light satisfying each of the following expressions: 28 ≦ y ≦ 0.32; 0.22 ≦ x ≦ 0.27; and x
+ 0.04 ≦ y ≦ x + 0.08, a blue color filter that transmits light that satisfies each of the following expressions, whereby yellow obtained by additive color mixing of green and red, and additive color mixing of green and blue There is an effect that display can be performed without impairing the visibility of the obtained cyan.

Further, in the reflection type liquid crystal display device, the chromaticity coordinates (x, x, y) in the XYZ color system chromaticity diagram of white obtained by the additive color mixture of the three color filters.
y) is 0.28 ≦ x ≦ 0.31, and 0.29 ≦ y ≦
If the red and blue color filters are set so as to satisfy each equation of 0.33, an effect of reproducing white without color can be obtained.

[Brief description of the drawings]

FIG. 1 is a sectional configuration view of a reflection type liquid crystal display device of the present invention.

FIG. 2 is a diagram showing electro-optical characteristics of a liquid crystal layer used in a reflection type liquid crystal display device of the present invention.

FIG. 3 is a diagram illustrating chromaticity coordinates of a green color filter according to the present invention.

FIG. 4 is a diagram showing chromaticity coordinates of a red color filter according to the present invention.

FIG. 5 is a diagram showing chromaticity coordinates of a blue color filter according to the present invention.

FIG. 6 is a diagram showing chromaticity coordinates of white obtained by additive color mixture using a single color filter according to the present invention.

7 is a spectral distribution diagram of illuminant D _65.

FIG. 8 is a diagram illustrating a 2 ° visual field and a 10 ° visual field.

[Explanation of symbols]

 Reference Signs List 30 reflective liquid crystal display device 31 substrate 38 reflective electrode 40 TFT 42 organic insulating film 43 contact hole 44 alignment film 45 counter substrate 46 color filter 49 liquid crystal layer

Claims (3)

[Claims] 1. A reflection panel in which a reflective electrode is formed on one of a pair of substrates opposed to each other with a liquid crystal layer interposed therebetween, and a transmissive counter electrode and a color filter of three colors of red, green and blue are formed on the other. in type liquid crystal display device, in the condition of the illuminant D ₆₅ and 2 ° field of view, the chromaticity coordinates (x, y) in the XYZ color system chromaticity diagram, 0.29 ≦ x ≦
A reflective liquid crystal display device comprising: a green color filter that transmits light satisfying each of 0.33 and 0.35 ≦ y ≦ 0.37. 2. Under the condition of D ₆₅ light source and 2 ° field of view,
The chromaticity coordinates (x, y) in the XYZ color system chromaticity diagram are
0.34 ≦ x ≦ 0.37 and 0.28 ≦ y ≦ 0.32
And a red color filter that transmits light satisfying the following expressions: 0.22 ≦ x ≦ 0.27, and x + 0.04 ≦ y ≦
2. The reflection type liquid crystal display device according to claim 1, further comprising: a blue color filter that transmits light satisfying each of x + 0.08. 3. Under the condition of D ₆₅ light source and 2 ° field of view,
Chromaticity coordinates (x, y) in the XYZ color system chromaticity diagram of white obtained by additive color mixing of the three color filters
Are 0.28 ≦ x ≦ 0.31 and 0.29 ≦ y ≦ 0.
33. The reflective liquid crystal display device according to claim 1, wherein each of the formulas (33) is satisfied.