JP2000193964A - Reflective liquid crystal display - Google Patents

Abstract

(57) Abstract: Provided is a reflection type liquid crystal display device using a polarizing plate, which suppresses coloring caused by a transparent electrode and a polarizing plate and is capable of good color display without black and white. SOLUTION: A reflection layer 2 (which also functions as an electrode in this case) provided on a reflection substrate 1 and a transparent electrode 4 provided on a counter substrate 3 are arranged so as to face each other. In a reflection type liquid crystal display device in which a liquid crystal layer 5 is interposed in a gap and a polarizing plate 7 is disposed on a surface of the opposite substrate 3 opposite to a surface on which the transparent electrode 4 is formed, color characteristics of the transparent electrode 4 formed on the opposite substrate 3 Is formed to have a bluish color. Therefore, since the transparent electrode 4 formed on the counter substrate 3 has a bluish color, a yellowish color produced by the polarizing plate 7 can be suppressed, and a reflective liquid crystal display device having good white display characteristics can be provided. .

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflection type liquid crystal display, and more particularly to a reflection type liquid crystal display using a polarizing plate.

[0002]

2. Description of the Related Art A reflection type liquid crystal display device having features of light weight, thinness, and ultra-low power consumption has been conventionally developed. This is a reflection type liquid crystal display device capable of displaying.

In order to perform color display by installing a color filter (CF), it is necessary to establish a technology for ensuring brightness and a technology for neutral black-and-white display without coloring more than before. Since the brightness depends on the light transmittance of each member constituting the liquid crystal display device, the light transmittance of the members constituting the liquid crystal display device (for example, a substrate, a polarizing plate, a transparent electrode, an alignment film, etc.) is increased. Was designed to be.

[0004]

Therefore, the transparent electrode and the alignment film developed in the transmission type liquid crystal display device include the spectral transmittance characteristics of the broken transparent electrode shown in FIGS. 3 and 7, and the alignment film shown in FIG. As shown in the spectral transmittance characteristics of the material PI1, the brightness was improved by setting the transmittance near 540 nm, which has visibility, to be high. This has resulted in transmittance characteristics having an absorption region on the short wavelength side at the same time.

On the other hand, as shown in FIG. 9, the polarizing plate has a transmittance characteristic such that the polarizing plate has an absorption region on the short wavelength side due to the influence of the dye and pigment constituting the polarizing plate.

When a reflective liquid crystal display device is manufactured using a polarizing plate and a substrate provided with a transparent electrode and an alignment film having such characteristics, the wavelength characteristics of the two interact to produce a yellowish display. Would.

Here, in the case of a transmission type liquid crystal display device, since a backlight is used, it is possible to improve the color characteristics by adjusting the wavelength characteristics of the backlight by coloring the transparent electrode and the polarizing plate. Therefore, it was not a big issue.

However, in the case of the reflection type liquid crystal display device, since the display is performed using external light, the display of the liquid crystal panel is reflected as it is, and the display becomes yellowish. was there.

The present invention has been made in order to solve the above-mentioned problems, and provides a reflection-type liquid crystal display device capable of suppressing coloration caused by a transparent electrode and a polarizing plate and exhibiting good color without black and white. Is what you do.

[0010]

According to a first aspect of the present invention, there is provided a reflective liquid crystal display device including a reflective layer side substrate provided with a reflective layer and a counter substrate provided with a transparent electrode, which are opposed to each other. In a reflective liquid crystal display device in which a liquid crystal layer is interposed between the two substrates and a polarizing plate is disposed on the opposite substrate, a transmittance obtained by combining components provided between the polarizing plate and the reflective layer. The characteristic shows that the transmittance at a wavelength of 500 nm
It is characterized by a high transmittance at 50 nm.

According to a second aspect of the present invention, there is provided the reflective liquid crystal display device according to the first aspect, wherein a transmittance characteristic of the transparent electrode and the alignment film is 500 nm. Is characterized in that the transmittance at a wavelength of 450 nm is higher than that of.

According to a third aspect of the present invention, there is provided the reflective liquid crystal display device according to the first or second aspect, wherein the transmittance characteristics of the transparent electrode are higher than the transmittance at a wavelength of 500 nm. It is characterized by high transmittance at a wavelength of 450 nm.

According to a fourth aspect of the present invention, there is provided the reflective liquid crystal display device according to any one of the first to third aspects, wherein the transmittance characteristics of the transparent electrode are such that the average transmission at a wavelength of 520 nm to 640 nm. It is characterized in that the average transmittance at wavelengths from 400 nm to 520 nm is higher than the transmittance.

According to a fifth aspect of the present invention, there is provided a reflective liquid crystal display device according to any one of the first to fourth aspects, wherein the transparent electrode formed on the opposite substrate is formed of indium tin oxide (ITO). ), Wherein the film thickness is not less than 200 angstroms and not more than 1300 angstroms.

According to a sixth aspect of the present invention, there is provided a reflective liquid crystal display device according to the fifth aspect, wherein the transparent electrode formed on the opposite substrate is ITO.
The film thickness is not less than 600 Å and not more than 1200 Å.

Hereinafter, the operation of the above configuration will be described.

In a reflection type liquid crystal display device in which a polarizing plate is disposed on a counter substrate, the transmittance characteristic of the combined components provided between the polarizing plate and the reflecting layer has a wavelength characteristic as shown by a solid line in FIG. Wavelength 4 from transmission at 500 nm (about 88%)
Since the transmittance at 50 nm (about 92%) is high, even if a reflection type liquid crystal display device in which a polarizing plate is arranged is manufactured, coloring is performed by reducing the absorption phenomenon existing on the short wavelength side. And a reflection type liquid crystal display device capable of excellent black and white display can be provided.

That is, the yellow tint which is the cause of the coloring phenomenon is related to the magnitude relationship between the transmittance at a wavelength of 500 nm and the transmittance at a wavelength of 450 nm, and as shown by the broken line in FIG. The rate (about 97%) is 45
When combined with a polarizing plate in a state where the transmittance at 0 nm (about 93%) is larger, a coloring phenomenon occurs.

Therefore, by combining the transmittance characteristics of the polarizing plate having the opposite relationship between the transmittance at the wavelength of 500 nm and the transmittance at the wavelength of 450 nm and the transmittance characteristics of the other components, the mutual relationship is obtained. Since the transmittance characteristics are compensated, the coloring phenomenon can be reduced.

Here, as a component provided between the polarizing plate and the reflecting plate, a color filter, a retardation plate, a glass substrate, a transparent electrode, an alignment film and the like can be considered. Among these, when a general-purpose material is used, the components that affect the transmittance characteristics and facilitate the adjustment of the transmittance characteristics are the transparent electrode and the alignment film. Therefore, a reflective liquid crystal display device in which a polarizing plate is disposed on a counter substrate has a transmittance characteristic of the polarizing plate and a transparent electrode and an alignment film in which the magnitude relationship between the transmittance at a wavelength of 500 nm and the transmittance at a wavelength of 450 nm is opposite. By combining the transmittance characteristics with the above, the transmittance characteristics of each other are compensated, and the coloring phenomenon can be reduced.

Further, the transmittance characteristic of the transparent electrode is set to be higher at a wavelength of 450 nm than at a wavelength of 500 nm, whereby the coloring phenomenon can be easily reduced. In general, since the alignment film is formed of a resin, the transmittance characteristic often depends on the material,
As shown in I1 and PI2, the contribution of the improvement of the transmittance characteristics is small (see Table 1).

[0022]

[Table 1]

On the other hand, since the transparent electrode is formed of ITO, the transmittance characteristics can be easily and effectively adjusted by adjusting the conditions at the time of manufacturing the thin film. For example, as shown by a solid line in FIG. As described above, it is possible to realize a transmittance characteristic in which the transmittance at a wavelength of 450 nm (about 93%) is higher than the transmittance at a wavelength of 500 nm (about 89%).

Furthermore, the transmittance characteristic of the transparent electrode can be further reduced by increasing the average transmittance at a wavelength of 400 nm to 520 nm from the average transmittance at a wavelength of 520 nm to 640 nm. .

The transparent electrode formed on the opposing substrate is made of ITO, and the film thickness is preferably set in the range of 200 to 1300 angstroms, more preferably in the range of 600 to 1200 angstroms. The reason will be described below.

The transparent electrode is made of ITO and has a thickness of 130
If the thickness is larger than 0 Å, the peak of the spectral transmittance is on the longer wavelength side than 520 nm. That is,
The average transmittance from a wavelength of 520 nm to 640 nm is higher than the average transmittance from a wavelength of 400 nm to 520 nm. Then, the reflective liquid crystal display device made of the transparent electrode and the polarizing plate that absorbs light in a short wavelength range has a yellow tint. Therefore, the thickness of the transparent electrode is preferably set to 1300 angstroms or less. Further, by setting the thickness of the transparent electrode to 1200 angstroms or less,
Since coloring is further reduced, the color balance of red, green, and blue in color display is also improved.

On the other hand, the thinner the thickness of the transparent electrode, the more preferable it is to secure high transmittance. However, if the thickness is too small, there arises a problem (cutting) that the surface resistance becomes large and the transparent electrode is easily cut in the middle. For example, the color layer of CF has a step because the film thickness is different for each color.
When a transparent electrode is formed on the colored layer of F, disconnection is particularly likely to occur. Therefore, the transparent electrode preferably has a thickness of 200 Å or more in order to prevent disconnection.

Further, since it functions as an electrode, it is necessary to consider the surface resistance. If the surface resistance exceeds 100Ω / □, the distortion generated in the drive voltage waveform differs from place to place, causing display failure. Therefore, by setting the thickness of the transparent electrode to 600 Å or more,
The surface resistance becomes 100Ω / □ or less, and the state of the drive voltage waveform becomes almost uniform, so that a uniform display is possible.

[0029]

Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 1 is a structural view of a reflection type liquid crystal display device according to an embodiment of the present invention.

First, a reflective layer 2 made of a metal having high reflectivity such as aluminum (Al) or silver (Ag) is formed on an insulating reflective substrate 1 made of glass or the like. Here, the electrode disposed on the reflection substrate 1 may be a reflection layer 2 made of a metal such as Al, or a transparent electrode such as ITO may be formed on the reflection layer 2 and the electrode may be used. It may be patterned. In the case of a simple matrix liquid crystal display device, the electrodes are patterned into a stripe shape by a photolithography method.

Next, I is placed on a counter substrate 3 made of glass or the like.
A transparent electrode 4 made of TO is formed. Thereafter, the reflective substrate 1 and the opposing substrate 3 are bonded together such that the reflective layer 2 and the transparent electrode 4 face each other, and a liquid crystal layer 5 is disposed between the two substrates to form a panel. Here, it is desirable to form an alignment layer 6 made of a polyimide film (PI) or the like between the reflection substrate 1 and the liquid crystal layer 5 and between the counter substrate 3 and the liquid crystal layer 5 in order to control the alignment of the liquid crystal.

Further, a polarizing plate 7 and a scattering plate 8 are adhered to the surface of the opposing substrate 3 of the panel having such a configuration, so that a reflection type liquid crystal display device can be provided.

Here, the transparent electrode 4 according to the present invention will be described in detail.

The transparent electrode shown in this embodiment is formed with a thickness of 200 Å to 1300 Å by a sputtering apparatus or the like using ITO. Further, preferably, the thickness of the transparent electrode is formed in a range from 600 Å to 1200 Å. In the present embodiment, the thickness is set to 1200 Å.

The transmittance characteristics of the transparent electrode 4 thus formed were measured. FIG. 2 shows the transmittance characteristics of the transparent electrode 4 of the present embodiment.

The transmittance characteristics of the transparent electrode are determined by MICRO COLORANALYZER manufactured by Tokyo Denshoku Co., Ltd.
Using a TC-1800M measuring instrument, the visible light range (from 400 nm to 700
nm) was measured. The thickness of the transparent electrode is
TENCOR INSTRUMENTS TENC
It measured and evaluated using ORP-1.

The measured transmittance characteristics were in the blue band (400 n
m-520 nm) and the green band (530n).
(m to 640 nm) and evaluated. The average transmittance was calculated by an average value in each of the wavelength ranges of the blue band and the green band, by determining the transmittance at a wavelength of 10 nm.

As shown in FIG. 2, the transparent electrode 4 of this embodiment has a transmittance peak near a wavelength of 450 nm.
The transmittance characteristics are such that the average transmittance (about 87%) at a wavelength of 520 nm to 640 nm is about 400 nm to 520 nm.
Has a high average transmittance (about 92%). Therefore, a transparent electrode having such a spectral transmittance and a wavelength of 500
The reflective liquid crystal display device using a polarizing plate having absorption in a short wavelength region of not more than nm could realize good white display without coloring.

On the other hand, as shown in FIG. 3, the conventional transparent electrode has a transmittance peak near the wavelength of 550 nm, and the transmittance characteristic is different from the average transmittance (about 84%) in the wavelength range of 400 to 520 nm. The average transmittance from 520 nm to 640 nm (about 91%) is high. Therefore, a transparent electrode having such a spectral transmittance and a wavelength of 500
A reflective liquid crystal display device using a polarizing plate having absorption in a short wavelength range of not more than nm attains a yellowish display.

(Embodiment 2) Next, an embodiment in which a thin film transistor (TFT), which is one of the active elements, is formed on a reflective substrate as shown in FIG. 4 will be described.

FIG. 4 is a configuration diagram of a reflection type liquid crystal display device according to another embodiment of the present invention.

A plurality of gate bus lines (not shown) made of a metal having a relatively low resistance such as chromium (Cr), tantalum (Ta), or Al are formed on an insulating reflective substrate 11 made of glass or the like in parallel with each other. It is provided in. Further, the gate electrode 12 is formed of the same metal from the gate bus line.
Has branched. Note that this gate bus wiring functions as a scanning line.

Tantalum oxide (Ta) covers the entire surface of the substrate covering these gate bus lines and gate electrode 12.
₂ O ₅ ), silicon nitride (SiNx), silicon oxide (S
A gate insulating film 13 made of iOx) or the like is formed.

Further, a semiconductor layer 14 made of amorphous silicon (a-Si), polycrystalline silicon (p-Si) or the like is formed on the gate insulating film 13 formed on the gate electrode 12.

A source electrode 15 and a drain electrode 16 are formed at both ends of the semiconductor layer 14. Here, as the source electrode 15, titanium (Ti), molybdenum (M
o), Al or the like, and as the drain electrode 16, a metal such as Ti, Mo, Al or the like, or a transparent electrode such as ITO can be used as the source electrode 15. The source electrode 15 has
The source bus wiring 17 crossing the gate bus wiring with the gate insulating film 13 interposed therebetween is connected. The source bus wiring 17 functions as a signal line. The source bus line 17 is formed of the same metal as the source electrode 15.

The gate electrode 12 and the gate insulating film 1
3, semiconductor layer 14, source electrode 15 and drain electrode 1
Reference numeral 6 denotes a TFT, which functions as a switching element of each pixel.

On the substrate on which the TFT is formed, an insulating film 18 made of an organic substance such as an acrylic resin is formed.
The contact hole 1 for partially connecting the pixel electrode and the drain electrode 16 is formed in the insulating film 18 made of an organic material.
After that, a reflective electrode 20 made of a material having a high reflectance in the visible light region such as Al or Ag is formed. Further, an alignment film 21 is formed on the reflection electrode 20.
Note that the reflection electrode 20 functions as a pixel electrode.

Thus, an active substrate is formed.

On the other hand, the CF 23 is formed on the counter substrate 22. In the CF 23, red (R), green (G), and blue (B) color filters are formed at positions facing the reflective electrode 20 on the active substrate, and a black mask is formed on other portions of the display screen. (BM) 24 is formed.

Further, a transparent electrode 25 made of ITO and having a thickness of 1000 angstroms is formed on the CF 23 as a counter electrode, and the alignment film 2 is further formed thereon.
1 is formed.

The active substrate and the opposing substrate described above are positioned such that the reflective electrode 20 and each color filter match.
In addition, a panel is formed by opposing and bonding together so that the gap between the two substrates for each pixel is uniform. In this gap, a liquid crystal layer 26 is arranged by injection, and the periphery of the panel is sealed with a sealing material (not shown).

A polarizing plate 27 and, if necessary, a scattering plate 28 are adhered to the surface of the counter substrate of the panel having the above-mentioned structure, thereby providing a reflection type liquid crystal display device.

The color characteristics of the reflection type liquid crystal display devices of Embodiments 1 and 2 manufactured as described above will be described below.

[0055]

[Table 2]

FIG. 5 shows xy chromaticity coordinates.
b, c, and d correspond to reference signs a, b, c, and d in Table 2, respectively. Symbols b and c denote Embodiments 1 and 2 of the present invention,
Symbol a indicates a conventional example. The symbol d indicates the chromaticity of the standard light source. As shown in FIG. 5, it can be seen that the chromaticity of the first and second embodiments (reference numerals b and c) is closer to the standard light source (reference numeral d) than the chromaticity of the conventional example (reference numeral a). . Therefore, it was found that the reflection-type liquid crystal display devices manufactured in the first and second embodiments can realize good white display.

Here, the reflection type liquid crystal display devices are roughly divided into those using an internal scattering plate having a scattering function inside the panel (in the space between both substrates), and those outside the panel (substrate surface). Some observers use an external scattering plate having a scattering function. When an internal scattering plate is used, the shape of the insulating film 18 is made to have desired irregularities. On the other hand, when an external scattering plate is used or when the liquid crystal layer has a scattering function, the insulating film 18 is made flat.

In this embodiment (FIG. 4), the case where the external scattering plate 28 is used simply is shown, but the same effect can be obtained when the internal scattering plate is used.

Further, the component that transmits light disposed between the polarizing plate and the reflective layer has a spectral transmittance characteristic that can reduce the coloring phenomenon by compensating the spectral transmittance characteristic of the polarizing plate. For example, the same effect can be obtained by using a material other than the transparent electrode and the alignment film (for example, a color filter and a phase difference plate).

[0060]

As described above, according to the present invention,
The transmittance characteristic of the combined components provided between the polarizing plate and the reflective layer is smaller than the transmittance at a wavelength of 500 nm by 45 nm.
Since the transmittance at 0 nm is high, even in a reflection type liquid crystal display device provided with a polarizing plate, good white display can be realized without coloring the optical characteristics.

The transmittance characteristics of the transparent electrode and the alignment film together are different from the transmittance at a wavelength of 500 nm by a wavelength of 450 nm.
, The optical characteristics are not colored and a good white display can be realized even in a reflective liquid crystal display device provided with a polarizing plate.

The transmittance characteristic of the transparent electrode is 500 nm
Since the transmittance at a wavelength of 450 nm is higher than the transmittance at,
By adjusting the conditions during thin film production, the transmittance characteristics can be easily and effectively adjusted, and even in a reflective liquid crystal display device equipped with a polarizing plate, good white display is realized without coloring the optical characteristics. it can.

The transmittance characteristic of the transparent electrode is 520 nm.
Is set so that the average transmittance at a wavelength of 400 nm to 520 nm is higher than the average transmittance at a wavelength of 640 nm to 640 nm. White display can be realized.

The transparent electrode is made of ITO and has a thickness of 200
Since the film is formed to have a thickness of not less than 1 Å and not more than 1300 Å, an appropriate distribution of spectral transmittance can be obtained. Optical properties can be achieved without coloring, and a good white display can be realized.
The transparent electrode is not cut off.

Further, since the transparent electrode is made of ITO and has a film thickness of not less than 600 Å and not more than 1200 Å, the optical characteristics of the reflection type liquid crystal display device are further reduced in coloring, so that color display is performed. In this case, the color balance of red, green, and blue becomes good, and the surface resistance becomes 100 Ω / □ or less. When the electrode functions as an electrode, the state of the voltage waveform applied in the display region becomes almost uniform. In addition, uniform display can be performed as a liquid crystal display device.

[Brief description of the drawings]

FIG. 1 is a structural diagram of a reflective liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is an example of a spectral transmittance characteristic of a transparent electrode of the present embodiment.

FIG. 3 shows a spectral transmittance characteristic of a conventional transparent electrode.

FIG. 4 is a configuration diagram of a reflective liquid crystal display device according to another embodiment of the present invention.

FIG. 5 is an explanatory diagram showing color characteristics of the reflection type liquid crystal display device of the present invention by chromaticity.

FIG. 6 shows a spectral transmittance characteristic of an alignment film.

FIG. 7 shows a spectral transmittance characteristic of a transparent electrode.

FIG. 8 shows spectral transmittance characteristics when components provided between a polarizing plate and a reflective layer are combined.

FIG. 9 shows spectral transmittance characteristics of a polarizing plate.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Reflective substrate 2 Reflective layer 3 Counter substrate 4 Transparent electrode 5 Liquid crystal layer 6 Alignment layer 7 Polarizer 8 Scattering plate 11 Reflective substrate 12 Gate electrode 13 Gate insulating film 14 Semiconductor layer 15 Source electrode 16 Drain electrode 17 Source bus wiring 18 Insulating film DESCRIPTION OF SYMBOLS 19 Contact hole 20 Reflecting electrode 21 Alignment film 22 Counter substrate 23 Color filter (CF) 24 Black mask (BM) 25 Transparent electrode 26 Liquid crystal layer 27 Polarizing plate 28 Scattering plate

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Sayuri Fujiwara 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation (72) Inventor Iwao Iwao 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka Inside the corporation

Claims (6)

[Claims] 1. A reflection-layer-side substrate provided with a reflection layer and a counter substrate provided with a transparent electrode are disposed to face each other, a liquid crystal layer is sandwiched between the two substrates, and a polarizing plate is provided on the counter substrate. In the reflection type liquid crystal display device, the transmittance characteristics of the combined components provided between the polarizing plate and the reflection layer are higher in the transmittance at the wavelength of 450 nm than at the wavelength of 500 nm. A reflective liquid crystal display device characterized by the above-mentioned. 2. The transmittance characteristic of the transparent electrode and the alignment film together is smaller than the transmittance at a wavelength of 500 nm by a wavelength of 45 nm.
2. The reflective liquid crystal display device according to claim 1, wherein the transmissivity at 0 nm is high. 3. The transmittance characteristic of the transparent electrode is 50 wavelengths.
3. The reflective liquid crystal display device according to claim 1, wherein the transmittance at a wavelength of 450 nm is higher than the transmittance at 0 nm. 4. The transmittance characteristic of the transparent electrode is set to a wavelength of 52
For an average transmission from 0 nm to 640 nm, a wavelength of 40
4. The reflective liquid crystal display device according to claim 1, wherein an average transmittance from 0 nm to 520 nm is high. 5. The transparent electrode formed on the counter substrate is made of indium tin oxide (ITO) and has a thickness of 200.
5. The reflection type liquid crystal display device according to claim 1, wherein said reflection type liquid crystal display device has a thickness of not less than 1 Å and not more than 1300 Å. 6. The reflection type liquid crystal display device according to claim 5, wherein said transparent electrode formed on said counter substrate is made of ITO and has a film thickness of not less than 600 Å and not more than 1200 Å.