JP2003195277A - Liquid crystal display device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device with excellent color reproducibility, especially the color reproducibility for white (W). <P>SOLUTION: The thickness of a common electrode 13 constituted of an indium tin oxide (ITO) is turned to be equal to or more than 80 nm and less than 100 nm. When an incident light is made incident on a liquid crystal layer 31 and when the incident light is reflected by a pixel electrode (reflection electrode) 23 and then emitted from an incident side substrate 11, transmissivity is high on the short wavelength side of 380 nm-480 nm as well in addition to the long wavelength side of a visible area. Thus, an observer can observe the white (W) as purer white (W) with the excellent color reproducibility. <P>COPYRIGHT: (C)2003,JPO

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention has a first substrate provided with an electrode made of indium tin oxide (ITO) and at least a part thereof having a function of reflecting incident light. The present invention relates to a liquid crystal display device in which a liquid crystal layer is held between the second substrate and a polarizing member provided on the side of the first substrate opposite to the side where the electrodes are provided, and particularly to a display for color display. The present invention relates to a liquid crystal display device suitable for use as a device.

[0002]

2. Description of the Related Art As a liquid crystal display device, for example, a light source (backlight) is provided on the back surface of a display cell, a transmissive device for displaying light from the light source and a reflecting member are provided, and There is a reflection type in which external light incident from the inside is reflected by a reflecting member to display reflected light.
Among them, the reflection type device can reduce the power consumption as compared with the transmission type device, and thus has attracted attention as a display device particularly used for portable electronic devices. In recent years,
With the diversification of information, the demand for color display capable of displaying images is increasing.

Conventionally, as a reflection type color liquid crystal display device, for example, an incident side substrate on which a color filter layer (coloring layer), a common electrode, an alignment film and the like are sequentially laminated, and a reflection electrode which also functions as a pixel electrode. And a thin film transistor (hereinafter, TFT (thin film transistor) for controlling each pixel electrode.
or)). ) Etc. are formed on the emission side substrate, and a liquid crystal layer is held between these substrates. This liquid crystal display device is also provided with a polarizing member on the side of the incident side substrate opposite to the liquid crystal layer, so as to transmit or block light according to an electric field. As the polarizing member, for example, a polarizing plate containing iodine and a stretched polymer film type retarder is used.

In this reflection type color liquid crystal display device, light from the outside passes through the polarizing member and is incident on the incident side substrate, and when it reaches the reflection electrode of the reflection side substrate, this light is reflected to pass through the color filter layer and the like. It passes through and is taken out from the incident side substrate. After that, the extracted reflected light passes through the polarizing plate according to the alignment state of the liquid crystal, and when it passes, it is perceived by the observer as a color image.

[0005]

However, in the reflective type color liquid crystal display device as described above, generally, in the polarizing member, the visible region is longer than the long wavelength side (hereinafter, also simply referred to as the long wavelength side) of the visible region. The short wavelength side (hereinafter, also simply referred to as the short wavelength side) absorbs a large amount of light, and when the reflected light reaches the polarizing member, the long wavelength side light of the reflected light has a high transmittance. Light on the wavelength side has a low transmittance. Therefore, for example, when reproducing white (W; specifically, for example, the standard light source D65 of JIS standard) realized by using all three primary colors of red, green, and blue, light on the short wavelength side is generated in the polarizing member. It was cut and had a yellow tint when observed by the observer. That is, the conventional reflective color liquid crystal display device has a problem that sufficient color reproducibility cannot be ensured. It is also possible to improve the transmittance of light on the short wavelength side of the reflected light by shifting the transmission wavelength of the color filter to the short wavelength (blue) side. However, depending on the color filter pigment currently used, There is a limit to shifting the transmission wavelength to the short wavelength side.
By the way, one of the reasons why the above-mentioned polarizing member has a large light absorption on the short wavelength side is that the liquid crystal material is deteriorated by ultraviolet rays, so that the polarizing member is designed to cut the light in the ultraviolet region, It is thought that this is because the short wavelength side in is also affected.

The present invention has been made in view of the above problems, and an object thereof is to provide a liquid crystal display device which is excellent in color reproducibility, particularly white (W) color reproducibility.

[0007]

A liquid crystal display device according to the present invention has one surface and the other surface facing each other, and an electrode made of indium tin oxide is in contact with one surface of the electrode, and is different from the electrode. A first substrate provided with a first layer having a refractive index and a second layer in contact with the other surface of the electrode and having a refractive index different from that of the electrode, and with respect to the first substrate Secondly arranged so as to face each other with a predetermined distance, and at least part of which has a function of reflecting incident light.
Substrate, a liquid crystal layer held between the first substrate and the second substrate, and a polarizing member provided on the side of the first substrate opposite to the side where the electrodes are provided. The liquid crystal display device is characterized in that the thickness of the electrode is 80 nm or more and less than 100 nm.

In the liquid crystal display device according to the present invention, since the first layer and the electrode and the second layer and the electrode have different refractive indexes, part of the incident light is transmitted through these interfaces. , Partly reflected. The reflected light is reflected again and travels in the same direction as the above-mentioned transmitted light, but at that time, there is an optical path difference between the transmitted light and the reflected light again, and according to this optical path difference, these two Lights strengthen and weaken each other. In order to increase the transmittance of light having a short wavelength of about 380 nm to 480 nm, it is sufficient to control the optical path difference so that the transmitted light and the light reflected again in this wavelength band are mutually strengthened. This is realized by setting the thickness of the film to be 80 nm or more and less than 100 nm. That is, the present inventors
The reason why the conventional liquid crystal display device is inferior in color reproducibility is that the film thickness of the electrode is 100 nm or more.
It has been found that by setting the thickness of the electrode to 80 nm or more and less than 100 nm, it is possible to compensate for the cut of light on the short wavelength side in the polarizing member.

The liquid crystal display device according to the present invention is
It is effective when the difference in refractive index between the electrode and each of the first layer and the second layer is 0.28 or less. This is because the refractive index of the layer differs depending on the wavelength of light, and therefore the difference in the refractive index of the two layers also differs, but the visible region (380 nm to 780 n
For the light of (m), the refractive index difference is larger than 0 and is 0.
This is because it is 28 or less. Further, it is particularly effective when it has a color display function.

[0010]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described in detail with reference to the drawings.

First, a schematic structure of a liquid crystal display device according to an embodiment of the present invention will be described.

FIG. 1 schematically shows a sectional structure of the liquid crystal display device according to the present embodiment. This liquid crystal display device has a liquid crystal cell 1. The liquid crystal cell 1 has an incident-side substrate 1 as a first substrate arranged on the incident side of external light.
1 and a reflection-side substrate 21 as a second substrate which is arranged to face the incidence-side substrate 11 with a predetermined gap, and between the incidence-side substrate 11 and the reflection-side substrate 21. A liquid crystal layer 31 is held in.

On the reflection-side substrate side of the incident-side substrate 11, for example, a color filter layer 12 as a first layer, a common electrode 13, and an alignment film 14 as a second layer are sequentially laminated. A polarizing member 41 is provided on the side of the incident side substrate 11 opposite to the side on which the common electrode 13 is provided.
On the other hand, on the incident-side substrate side of the reflective-side substrate 21, for example, a plurality of pixel electrodes 23 are formed in a matrix with the insulating layer 22 interposed therebetween, and the alignment film 2 covers the pixel electrodes 23.
4 are formed. The pixel electrode 23 is made of a material having a reflecting function, such as aluminum (Al), and also functions as a so-called reflecting electrode. A TFT 25 is provided inside the insulating layer 22 corresponding to each pixel electrode 23, and the pixel electrode 23 is electrically connected to, for example, a drain electrode of the TFT 25. In addition, each TFT 25
The gate electrode is electrically connected to the gate line, and the source electrode is electrically connected to the data line. By the way, TFT25
It is possible to use either a so-called top gate type or bottom gate type.

The incident side substrate 11 and the reflective side substrate 21 are made of, for example, glass and have a refractive index of about 1.5. In the color filter layer 12, for example, red (R), green (G), and blue (B) colored layers obtained by coloring a resin material with a dye or a pigment are arranged in a pattern corresponding to each pixel (pixel electrode 23). And its refractive index is the common electrode 1
3 is different from that of, for example, 1.46 to 1.70.
It is a degree.

The common electrode 13 is made of ITO,
Its refractive index is about 1.47 to 1.9. The common electrode 13 has a thickness of 80 nm or more and less than 100 nm, preferably 90 nm or more and less than 100 nm, and more preferably 100 nm. The reason for this will be described later. The refractive index of ITO can be appropriately adjusted depending on the film forming conditions at the time of manufacturing.

The alignment films 14 and 24 are made of, for example, polyimide and have a refractive index different from that of the common electrode 13, for example, 1.6 to 1.74. Liquid crystal layer 3
1 is composed of, for example, TN (Twisted Nematic) liquid crystal, and its refractive index is about 1.5.

The polarizing member 41 has, for example, a polarizing plate containing iodine and a polymer-stretched film type retardation plate. Specifically, for example, iodine formed on a polymer substrate is used. It is composed of the added polyvinyl alcohol (PVA) stretched film and a retardation plate using a norbornene-based material. The polarizing member 41 has a property that light on the long wavelength side is easily transmitted and light on the short wavelength side is difficult to transmit.

Next, the characteristic parts of the liquid crystal display device according to the present embodiment will be described in more detail.

As described above, the incident side substrate 1 of this device
The refractive index of 1 and each layer formed thereon are different, so that at the interface between two adjacent layers, part of the incident light is transmitted (hereinafter, this light is referred to as incident transmitted light),
Part of the light is reflected (hereinafter, this light is referred to as interface reflected light). Above all, the difference in refractive index between the color filter layer and the common electrode and between the common electrode and the alignment film is particularly large, and the interface between them has high reflectivity. For light in the visible region, the difference in refractive index is 0 to 0.28. Therefore, the present invention is considered to be effective when the difference in refractive index between adjacent two layers is 0.28 or less.

FIG. 2 schematically shows an example of incident transmitted light and interface reflected light at the interface. Incident light I transmitted through the incident side substrate 11 and the color filter layer 12
Enters the common electrode 13, and the common electrode 13 and the alignment film 14
Incident transmitted light T ₁ and interface reflected light R at the interface IF _{1 with}
And separated. Of these, the interface reflected light R is reflected again at the interface IF ₂ between the common electrode 13 and the color filter layer 12, passes through the common electrode 13 and the alignment film 14, and enters the liquid crystal layer 31 as incident transmitted light T _2. To do. As described above, the incident transmitted light T ₁ and the incident transmitted light T ₂ are incident on the liquid crystal layer 31.
However, the incident transmitted light T ₁ and the incident transmitted light T ₂ have an optical path difference corresponding to the optical path of the interface reflected light R. Therefore, depending on this optical path difference, the two incident transmitted lights T ₁ and T ₂ strengthen or weaken each other. Here, the optical path difference is, for example, the incident angle of light, the wavelength,
It is determined by the refractive index and the film thickness. Of these, the refractive index of light is unique and cannot be changed, and the incident angle of light is also usually not changeable.
Therefore, when considering transmitting light with a short wavelength of about 380 nm to 480 nm, the optical path difference can be controlled by changing the thickness of the common electrode 13.

The spectral transmission characteristics of external light when the thickness of the common electrode 13 is changed will be described below based on the results of a concrete simulation.

FIG. 3 shows the relationship between the wavelength and the transmittance when the thickness of the common electrode 13 of the liquid crystal display device according to the present embodiment is set to 80 nm (curve A) and 90 nm (curve B). It is a representation. In addition, as a comparative example with respect to the present embodiment, the results when the thickness of the common electrode 13 is set to 100 nm (curve C), 120 nm (curve D), 140 nm (curve E) are also shown. It should be noted that this measurement is performed on the light incident on the liquid crystal layer 31 as well as the light incident at an angle of about 0 ° with respect to the normal to the main surface of the polarizing member 41 (FIG. 1). . Here, the vertical axis represents the light transmittance, and the horizontal axis represents the wavelength (unit: nm) of the transmitted light.

As can be seen from FIG. 3, when the thickness of the common electrode 13 is 120 nm and 140 nm, it is 550 nm.
The transmittance in the yellow wavelength band of about 600 nm and on the longer wavelength side than that is higher, and when the thickness is 120 nm, the wavelength is about 380 nm to 430 nm and the thickness is 140 n.
In the case of m, the transmittances at wavelengths of about 380 nm to 470 nm are remarkably low. That is,
When the thickness of the common electrode 13 is 120 nm and 140 nm, the transmittance of light in the blue wavelength band is extremely low, and it is extremely difficult to obtain white (W). Therefore, the light reflected by the pixel electrode 23 and transmitted through the polarization member 41 (FIG. 1) will appear yellowish to the observer. On the other hand, the thickness is 80 nm, 90 nm, 10
In the case of 0 nm, the transmittance is high in the short wavelength range of 380 nm to 480 nm and the transmittance of light in the long wavelength range is also high. Therefore, in the liquid crystal cell 1 having the polarizing member 41,
The transmittance is well-balanced from the short-wavelength side to the long-wavelength side in a good balance, and the observer can observe white as pure white with excellent color reproducibility.

However, as described above, the results of FIG. 3 relate to the light incident at an angle of about 0 ° with respect to the normal to the main surface of the polarizing member 41, and the light is relative to the normal. For example, when incident at an angle of about 1 ° to 90 °, 0 °
The optical path in the common electrode 13 becomes longer than in the case of incidence at an angle of, and the apparent thickness of the common electrode 13 becomes 100 nm or more in consideration of the optical path difference. Therefore, when there is incident light I from all directions, it is optimal that the thickness is less than 100 nm.

Although not specifically described here,
When the thickness of the common electrode 13 is less than 80 nm, 1
Similar to the cases of 20 nm and 140 nm, the peak of transmittance appears on the long wavelength side, the transmittance of light on the short wavelength side is low, and it is extremely difficult to obtain white.

The liquid crystal display device having such a structure is
It works as follows.

In this liquid crystal display device, external light passes through the polarizing member 41, and the incident side substrate 11 and the color filter layer 1 are provided.
2, when passing through the common electrode 13, the alignment film 14, the liquid crystal layer 31, and the alignment film 24 in sequence and reaching the pixel electrode 23, this light is reflected and passes through each of the layers (films), and from the incident side substrate 11. Taken out. After that, for example, a black display state is obtained when a voltage is applied between the common electrode 13 and the pixel electrode 23 (on state), and a white display state is obtained when no voltage is applied (off state). Is obtained. Although the so-called normally white mode has been explained here,
Of course, the reverse, that is, a so-called normally black mode device can be used.

In the present embodiment, since the thickness of the common electrode 13 is 80 nm or more and less than 100 nm, when the incident light I enters the liquid crystal layer 31, and as will be described later, the incident light I is incident on the pixel electrode. When the light is emitted from the incident side substrate 11 after being reflected by the (reflection electrode) 23, the transmittance of light on the short wavelength side is high. Therefore, even if the transmittance of light on the short wavelength side of the polarizing member 41 is low, this is compensated for, and blue (B) or white (W) light that has passed through the polarizing member 41 after being emitted from the incident side substrate 11 is compensated. Are observed as pure blue and white with excellent color reproducibility.

In the above description, the operation when external light is incident on the pixel electrode 23 has been described with reference to FIG. 2, but the reflected light is incident on the incident side substrate 11 again.
The same thing happens when incident on.

As described above, according to the liquid crystal display device of the present embodiment, the common electrode 13 has a thickness of 80 nm or more and 100 nm or more.
Since it is set to be less than nm, in the liquid crystal cell 1,
In addition to the transmittance of light on the long wavelength side in the visible region, the transmittance of light on the short wavelength side can be increased. Therefore, the adjustable range of the color tone observed by the observer can be widened and the color reproducibility of the device can be improved.

Although the present invention has been described above with reference to the embodiments, the present invention is not limited to the above-mentioned embodiments and can be variously modified. For example, although the case where the common electrode 13 is directly provided on the color filter layer has been described in the above-described embodiment, protection and smoothing of the coloring material of the color filter layer 12 are provided between the color filter layer 12 and the common electrode 13. For example, an overcoat layer made of acrylic resin or epoxy resin (having a refractive index of about 1.4
6 to 1.7) may be provided. However, in the liquid crystal display device using the TFT as described above, the requirement for flattening is not so strict, and thus the overcoat layer is often omitted. Even when the overcoat layer is interposed, the overcoat layer is made of resin similarly to the base material of the color filter layer, and these can be regarded as equivalent materials. Therefore, it can be considered that these are integrated.

In the above embodiment, the case where the pixel electrode also functions as a reflection plate has been described, but the pixel electrode and the reflection plate may be provided separately. Furthermore,
In the above embodiment, the structure in which the polarization member 41 is provided on the incident side substrate 11 has been described. However, between the incident side substrate 11 and the polarization member 41, linearly polarized light is changed to circularly polarized light and circularly polarized light is changed to linearly polarized light. Needless to say, a λ / 4 plate for converting each may be provided.

Further, in the above embodiment, the active matrix liquid crystal display device using the TFT 25 as the switching element has been described.
(Metal oxide semiconductor-field effect transisto
Other switching elements such as r) may be used. Further, in the above embodiment, the so-called active matrix display device has been described, but the light reflector of the present invention is a so-called passive type which does not use a switching element.
It can also be applied to a matrix display device.

In addition, although a reflective liquid crystal display device has been described as a specific example of the liquid crystal display device in the above embodiment, the present invention has a structure in which a reflective type portion and a transmissive type portion are mixed. At least a part of the reflection side substrate side receives incident light, such as a liquid crystal display device or a liquid crystal display device in which the thickness of the pixel electrode 23 is thin so that light is partially reflected and partially transmitted. It can be widely applied to liquid crystal display devices having a reflecting function.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a structure of a liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a schematic diagram showing an optical path of incident light for explaining the operation of the liquid crystal display device shown in FIG.

FIG. 3 is a characteristic diagram showing a relationship between wavelength and transmittance of a liquid crystal display device according to an embodiment of the present invention and a comparative example.

[Explanation of symbols]

1 ... Liquid crystal cell 11 ... Incident side substrate 12 ... Color filter layer 13 ... Common electrodes 14, 24 ... Alignment layer 21 ... Reflection side substrate 22 ... Insulating layer 23 ... Pixel electrode 25 ... TFT 31 ... Liquid crystal layer 41 ... Polarizing member IF ₁ , IF ₂ ... Interface I ... Incident light T ₁ , T ₂ ... Incident transmitted light R ... Interface reflected light

─────────────────────────────────────────────────── ─── Continuation of front page (51) Int.Cl. ⁷ Identification code FI theme code (reference) G09F 9/30 338 G09F 9/30 338 9/35 9/35 (72) Inventor Miho Ii Kobe City, Hyogo Prefecture 4-3-1 Takatsukadai, Nishi-ku, Philips Mobile Display Systems Kobe Co., Ltd. (72) Inari, Yusei Ugawa 4-3-1 Takatsukadai, Nishi-ku, Kobe, Hyogo Prefecture F-Terms, Philips Mobile Display Systems Kobe, Ltd. (Reference) 2H048 BB02 BB14 BB42 2H049 BA02 BA06 BA27 BB43 BC22 2H091 FA02Y FA08X FA14Y FB02 FC08 FC23 FC29 FC30 FD07 FD14 FD23 FD24 GA13 LA03 LA11 LA12 LA13 LA14 LA15 LA20 5C094 AA08 BA03 CA19 CA24 CA24 CA14 CA14 CA24 CA19

Claims (3)

[Claims] 1. An electrode having one surface and another surface facing each other, an electrode made of indium tin oxide, and a surface having a refractive index different from that of the electrode, the first electrode being in contact with the one surface of the electrode.
And a second layer which is in contact with the other surface of the electrode and has a refractive index different from that of the electrode, and with a predetermined distance from the first substrate. A second substrate which is arranged to face each other and has a function of reflecting at least part of incident light; a liquid crystal layer held between the first substrate and the second substrate; And a polarizing member provided on the opposite side of the substrate from which the electrodes are provided, wherein the thickness of the electrodes is 80 nm or more and less than 100 nm. apparatus. 2. The liquid crystal display device according to claim 1, wherein the first layer or the second layer is a color filter layer. 3. The liquid crystal display device according to claim 1, wherein the polarizing member has a polarizing plate containing iodine and a polymer-stretched film type retardation plate.