JP3095005B2 - Reflective liquid crystal display - Google Patents

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 device, and more particularly, to an arrangement of an optical axis of a polarizing plate, a half-wave retardation film and a quarter-wave retardation film in which a viewing angle of a liquid crystal layer changes. The change in retardation due to the change in retardation due to the change in viewing angle of each retardation film,
The present invention relates to a reflection type liquid crystal display device arranged so as to totally cancel each other.

[0002]

2. Description of the Related Art Recently, a reflection type liquid crystal display (LCD) is used.
Is widely used in battery-powered portable devices, which do not require a backlight and have low power consumption. Among the operation methods of the reflection type liquid crystal display device, the method most commonly used at present is a twisted nematic (hereinafter, referred to as TN) method. Less than,
A conventional reflection type liquid crystal display device will be described with reference to the drawings.

FIG. 9 is a side sectional view showing the structure of a first conventional TN type reflection type liquid crystal display device. As shown in FIG. 9, a conventional first reflective liquid crystal display device 100 includes an upper substrate 101 and a lower substrate 102, which are a pair of transparent substrates that are overlapped at a distance of about 5 μm, and both substrates. In the meantime, the liquid crystal layer 10 is oriented so as to be twisted by about 90 degrees.
3 is sandwiched.

[0004] Polarizing plates 15 and 16 are attached to outer surfaces of the pair of transparent substrates which are not in contact with the liquid crystal layer, respectively.
Further, on the lower substrate 102, a reflector 108 is formed outside the polarizer 107. Further, transparent electrodes 104 made of a transparent conductive material such as indium tin oxide (ITO) are formed on inner surfaces of the upper substrate 101 and the lower substrate 102 which are in contact with the liquid crystal layer. On the transparent electrode 104, an alignment film 105 is formed. Then, by applying an electric field to the liquid crystal layer 103 via the transparent electrode 104, the alignment state of the liquid crystal changes. When the alignment state of the liquid crystal changes, the incident light that enters is reflected by the reflection plate 10.
The display can be performed by changing the intensity of the light reflected by the light 8 and reaching the user.

However, the first reflection type liquid crystal display device 100 of the conventional TN system has the following problems. The incident light is transmitted twice one way, that is, four times back and forth, and the two polarizing plates 10 are used.
After passing through 6, 107, it is emitted. Two polarizing plates 10
6 and 107 slightly absorb not only the polarized light in the direction of the absorption axis but also the polarized light in the direction of the transmission axis perpendicular to the direction of the absorption axis. Occurs. Due to this loss, the brightness is insufficient, and it is difficult to obtain a bright display in the first reflective liquid crystal display device 100 using the two polarizing plates 106 and 107.

Further, a lower substrate 102 which is a transparent substrate having a thickness of about 1 mm exists between the liquid crystal layer 103 and the reflection plate 108. For this reason, when viewed obliquely, the display looks double due to parallax. Conventionally, a reflection type liquid crystal display device of a super twisted nematic (hereinafter, referred to as STN) system in which the twist angle of the liquid crystal layer 103 is increased to about 200 degrees is also used. The use of the polarizing plate is not preferable from the viewpoint of insufficient brightness and parallax as in the case of the TN method.

As a solution to these problems, Proceedings of the SI
D) Vol. 21, No. 2, pp. 63-65 (1980); R. A report by AR Kmetz describes a configuration of a reflection type liquid crystal display device using only one polarizing plate. According to this document, the reflection type liquid crystal display device can be configured so that the number of times that the incident light passes through the polarizing plate is only two times. Light loss can be suppressed. In addition, since it is not necessary to dispose a polarizing plate on the back side of the liquid crystal layer, the electrode of the substrate on the side opposite to the incident side can be formed using a metal or the like and used as a reflective electrode, thereby reducing parallax. The difficulties are also eliminated.

Japanese Patent Laid-Open Publication No. Hei 4-116515 discloses a configuration of a reflection type liquid crystal display device using only one polarizing plate as described above. Also, optimization of three parameters of a twist angle of the liquid crystal layer, a product (hereinafter, Δnd) of a refractive index anisotropy of the liquid crystal layer and a layer thickness (hereinafter, referred to as a cell gap), and a polarizing plate angle. It has been disclosed. Here, the polarizing plate angle is an angle between the transmission axis or the absorption axis of the polarizing plate and the liquid crystal orientation azimuth on the incident side. FIG.
Is the second disclosed in Japanese Patent Application Laid-Open No. 4-116515.
FIG. 2 is a side sectional view showing a configuration of a reflection type liquid crystal display device. As shown in FIG. 10, an upper substrate 101 on which a transparent electrode 104 and an alignment film 105 are sequentially formed and a lower substrate 102 on which a reflection electrode 109 and an alignment film 105 are sequentially formed face each other so as to sandwich the liquid crystal layer 103. It is piled up together. A polarizing plate 106 is attached to the incident side of the upper substrate 101, that is, the surface on the side facing the transparent electrode 104.

Next, an example of an optimized design parameter disclosed in Japanese Patent Laid-Open Publication No. 4-116515 will be described.
The optimized design parameters are such that the twist angle of the liquid crystal layer 103 is 63 degrees and the Δnd of the liquid crystal layer 103 is 0.2 μm.
m, the angle of the polarizing plate 106 is 0 degree.

In the second reflective liquid crystal display device 100 designed and manufactured with the above-described design parameters, the linearly polarized light incident on the liquid crystal layer 103 becomes substantially circularly polarized light on the reflection surface after passing through the liquid crystal layer 103. After being reflected and transmitted through the liquid crystal layer 103, the light becomes linearly polarized light whose polarization plane is rotated by approximately 90 degrees with respect to the incident light. Therefore, the polarization conversion by the liquid crystal layer 103 is performed with extremely high efficiency.

Further, the 1997 SIDD International Symposium Digest of Technical Papers (1997 SID International Sympos
iumDigestof Technical Papers) Volume 28 643-646
Page (1997). -T. Wu (S.-TW
In the report of u) and the like, as shown in the conventional second liquid crystal display device 100, optimized design parameters in a reflection type liquid crystal display device using only one polarizing plate are described. The design parameters of an example (Example 1) of the reflection type liquid crystal display device disclosed in this document are shown below. The design parameters are as follows: the twist angle of the liquid crystal layer is 90 degrees, the Δnd of the liquid crystal layer is 0.25 μm, and the polarizing plate angle is 20 degrees. The design parameter of another example (Example 2) of the reflection type liquid crystal display device disclosed in this document is that the twist angle of the liquid crystal layer is 7 °.
0 degree, the liquid crystal layer Δnd is 0.28 μm, and the polarizing plate angle is 20.
Degrees.

Using the above design parameters, FIG.
When a device having the structure shown in FIG. 1 is designed and manufactured, it operates as a normally black device. That is, a dark state can be displayed when no voltage is applied, and a bright state can be displayed when a voltage is applied.

FIG. 11 is a side sectional view showing a third conventional reflection type liquid crystal display device. As shown in FIG. 11, the conventional third reflective liquid crystal display device 100 is different from the conventional second reflective liquid crystal display device 100 in that the polarizing plate of the second conventional reflective liquid crystal display device 100 is used. A quarter-wave plate (λ / 4 plate) 110 is additionally provided between 106 and the upper substrate 101, and the other configuration is the same as that of the second conventional reflection type liquid crystal display device 100. Configuration. With this configuration, a normally white element can be manufactured.

The quarter-wave plate 110 is a birefringent plate whose thickness is determined so as to generate a quarter-wavelength optical path difference between linearly polarized lights vibrating in directions perpendicular to each other. . Since the linearly polarized light is converted into clockwise or counterclockwise circularly polarized light by the quarter-wave plate 110, according to the configuration of the third reflective liquid crystal display device 100, the bright state and the voltage applied state when no voltage is applied are provided. Can display the respective dark states. Further, as shown in FIG. 11, a device having a normally white configuration has a high reflectance when displaying a dark state.
Since the dependence on the cell gap and the wavelength is small, the second reflective liquid crystal display device 100 as shown in FIG. 10 is more preferable than the normally black element.

Furthermore, Japanese Patent Application Laid-Open No. 10-232390 discloses that the liquid crystal layer has only one polarizing plate and has a twist angle of one.
STN set to 80 degrees or more, preferably set to 240 degrees
A configuration of a reflective liquid crystal display device using a liquid crystal layer is disclosed. In this configuration, there is disclosed a technique for optimizing design parameters of a liquid crystal layer, a retardation film, and a polarizing plate to achieve achromatic display and high contrast.

[0016]

However, in the reflection type liquid crystal display device 100 using only one polarizing plate, the substantial retardation value of the liquid crystal layer or the retardation film changes due to the change of the viewing angle direction. However, there is a problem that the display looks yellowish depending on the direction in which the display is viewed, which gives the user discomfort.

In the technique disclosed in Japanese Patent Application Laid-Open No. Hei 10-232390, in the frontal observation,
Achromatic display can be performed, but when the viewing angle is tilted, the display is colored, which causes a problem of giving the user discomfort.

The present invention has been made in view of the above problems, and is intended to comprehensively cancel a change in retardation due to a change in viewing angle of a liquid crystal layer and a change in retardation due to a change in viewing angle of a retardation film. An object of the present invention is to provide a liquid crystal display device that can eliminate display coloring due to a change in a user's viewing direction by disposing a retardation film.

[0019]

In a reflection type liquid crystal display device according to the present invention, an upper substrate, a lower substrate facing the upper substrate, and a liquid crystal layer sandwiched between the upper substrate and the lower substrate. A transparent electrode and an alignment film are formed on the upper substrate on the side in contact with the liquid crystal layer, and a reflective electrode and an alignment film are formed on the lower substrate on the side in contact with the liquid crystal layer, A laminated type 1 having a 位相 retardation film and a 位相 retardation film on a side of the upper substrate opposite to the liquid crystal layer.
A quarter-wave plate and a polarizing plate are formed, and the twist direction of the liquid crystal when the liquid crystal layer is traced from the upper substrate side to the lower substrate side is positive with reference to the upper substrate side alignment direction of the liquid crystal layer. When the arrangement angle α of the polarization absorption axis of the polarizing plate is 5 degrees to 35 degrees, the arrangement angle β of the optical axis of the 位相 retardation film is −15 degrees to 15 degrees, and the 1/4 position The arrangement angle γ of the optical axis of the phase difference film is from −75 degrees to −45 degrees.

In the present invention, the twist angle of the liquid crystal layer is 66 to 74 degrees, and the product of the refractive index anisotropy of the liquid crystal layer and the thickness of the liquid crystal layer is 0.21 μm to 0.3.
It is preferably 1 μm.

In the present invention, the laminated type 1 /
The four-wavelength plate is preferably made of a plurality of retardation films for providing a retardation.

Further, in the present invention, it is preferable that the retardation film, the 及 び retardation film and the 位相 retardation film are made of a polycarbonate polymer or a polysulfone polymer. In addition, it is preferable that the reflection electrode has a surface having irregularities.

Still further, the liquid crystal layer is a twisted liquid crystal layer.
It is preferably a nematic liquid crystal.

In the present invention, the polarizing plate and the laminated type 1 /
A four-wavelength plate is provided, and a polarizing plate, a 1/2 retardation film and 1
By regulating the arrangement angle of the optical axis of the / 4 retardation film, a change in retardation due to a change in the viewing angle of the liquid crystal layer and a change in retardation due to a change in the viewing angle of the retardation film can be totally cancelled. The saturation when no voltage is applied can be prevented from exceeding 20 in a viewing angle range within ± 60 degrees from the front in all directions.

[0025]

BEST MODE FOR CARRYING OUT THE INVENTION Hereinafter, embodiments of the present invention will be described.
This will be described in detail with reference to the accompanying drawings. FIG. 1 is a side sectional view showing a reflective liquid crystal display device according to a first embodiment of the present invention. FIG. 2 is a schematic diagram showing the alignment state of the liquid crystal and the arrangement angles of the polarizing plate, the half-wave retardation film, and the quarter-wave retardation film in the reflective liquid crystal display device according to the first embodiment of the present invention. .

In the reflection type liquid crystal display device 1 according to the first embodiment of the present invention, the upper substrate 2 on which the transparent electrode 5 and the alignment film 6 are sequentially formed, and the reflection electrode 7 and the alignment film 6 are sequentially formed. The lower substrate 3 is facing the alignment film 6. In the meantime, the liquid crystal layer 4 having the TN liquid crystal is sandwiched.

On the outer side of the upper substrate 2b which is not in contact with the liquid crystal layer 4, a laminated quarter-wave plate 10 and a polarizing plate 11 are sequentially formed. The laminated 波長 wavelength plate 10 is a stretched film that gives a phase difference of 波長 wavelength to monochromatic light.
It is composed of a combination of a two-wavelength retardation film 9 and a quarter-wave retardation film 8 which is also a stretched film that gives a quarter-wave retardation.

The reflection type liquid crystal display device 1 of this embodiment is a normally white element which shows a bright state when no voltage is applied, and the incident light is reflected by the polarizing plate 11 and the multilayer type 1.
By sequentially passing through the quarter-wave plate 10, the light is converted into circularly polarized light or light in a polarization state close to circularly polarized light, and enters the liquid crystal layer 4. By applying an electric field to the liquid crystal layer 4 via the transparent electrode 5, the orientation of the liquid crystal is changed, so that the incident light is reflected by the reflective electrode 7 and the intensity of the light reaching the user is changed. it can.

In this embodiment, as shown in FIG.
Although the configuration in which the half-wave retardation film 9 and the quarter-wave retardation film 8 are laminated one by one is shown, the present invention is not particularly limited to this, and three or more Lamination using a stretched film can also be adopted. Further, as a material for forming these stretched films, for example, a polycarbonate-based polymer or a polysulfone-based polymer can be used.

As shown in FIG. 2, the alignment state of the liquid crystal in the liquid crystal layer 4 is determined by the alignment direction of the upper substrate 2 and the lower substrate 3 with respect to the alignment film 6, and is directed from the upper substrate 2 interface to the lower substrate 3 interface. Oriented so as to be continuously twisted. The polarization absorption axis A of the polarizing plate 11, the optical axis B of the half-wave retardation film 8, and the optical axis C of the quarter-wave retardation film 9 are based on the upper substrate side alignment direction D of the liquid crystal layer 4 (angle Reference) and the lower substrate side alignment direction E of the liquid crystal layer 4 and the upper substrate 2
The liquid crystal is arranged so as to have the arrangement angles α, β, and γ, respectively, where the twist direction of the liquid crystal when traced from the side to the lower substrate 3 side is positive.

In this embodiment, after the incident light sequentially passes through the polarizing plate 11, the half-wave retardation film 9 and the quarter-wave retardation film 8, the polarization state is changed to the circularly polarized light or the circularly polarized light. In order to obtain the above arrangement angles α, β,
In general, it is necessary to configure the relationship between γ such that the relationship shown in the following Expression 1 is established.

[0032]

## EQU1 ## γ−α = 2 (β−α) ± 45 degrees

However, according to the study of the present inventors, circularly polarized light is incident on the liquid crystal layer 4 with respect to incident light from the front by using a combination of (α, β, γ) satisfying the above equation (1). Even with such a configuration, since the apparent retardation of the liquid crystal layer 4, the half-wave retardation film 9 and the quarter-wave retardation film 8 is changed by tilting the viewing angle, depending on the viewing direction, the original display may be different. May look yellow or bluish. In particular, when the display looks yellowish due to a change in the viewing angle, a strong discomfort is given to the user. Among the innumerable combinations that satisfy Equation 1, the condition for circularly polarized light over almost the entire visible wavelength range is that the half-wave retardation films 9 and 1 /
It depends on the material used for the four-wavelength retardation film 8. That is, it depends on the wavelength dependence (wavelength dispersion characteristics) of the refractive index anisotropy of the material used for the half-wave retardation film 9 and the quarter-wave retardation film 8. in this way,
Even when the reflection type liquid crystal display device 1 is configured to have excellent broadband characteristics, when the viewing angle is inclined, the color of the display changes.

For each of the above arrangement angles α, β, γ,
By optimizing with further detailed examination, the change in retardation due to the change in the viewing angle of the liquid crystal layer 4 and the change in the retardation due to the change in the viewing angle of the half-wave retardation film 9 and the quarter-wave retardation film 8 are substantially the same. By setting so as to cancel each other, the saturation when no voltage is applied (L ^* a ^* b
^* Value of C ^{* in} the color system) does not exceed 20 in a viewing angle range within ± 60 degrees of the polar angle in all directions. With such a configuration, the coloring of the display due to the change in the viewing direction, which is a problem in the conventional technology, can be eliminated.

By setting the twist angle of the liquid crystal layer 4 to about 70 degrees and the value of Δnd of the liquid crystal layer 4 to about 0.27 μm, the reflection type liquid crystal display device 1 with little display coloration can be obtained.
Can be realized. There is an allowable range of about ± 4 degrees for the twist angle and about ± 0.4 μm for the value of Δnd. That is, the twist angle of the liquid crystal layer 4 can be 66 degrees to 74 degrees, and the value of Δnd of the liquid crystal layer 4 is
It can be 0.21 μm to 0.31 μm.

Further, the arrangement angle α is 5 to 35 degrees, the arrangement angle β is -15 degrees to 15 degrees, and the arrangement angle γ is -75 degrees to-
By setting the angle to 45 degrees, the saturation of the display color in the viewing angle range within the omnidirectional polar angle of 60 degrees does not exceed 20. That is, the coloring of the display due to the change in the viewing direction, which is a problem in the related art, can be eliminated.

In this embodiment, the reflection type liquid crystal display device 1
Can be segmented, simple matrix or active matrix. Alternatively, a monochrome type or a color type using a color filter may be used.

In this embodiment, the reflective electrode 7 can be formed so that its surface has minute irregularities. The minute unevenness causes a local cell gap distribution. This distribution can be eliminated by forming the average value of the minute unevenness to a desired cell gap value. These minute irregularities provide an appropriate scattering property and enable display without a metallic feeling. When the surface of the reflective electrode 7 has a flat shape, for example, a display without a metallic feeling is provided by disposing a diffusion film between the upper substrate 2 and the laminated 波長 wavelength plate 10. be able to.

Next, a first analysis calculation example in this embodiment will be described. In this analysis calculation example, in the reflection type liquid crystal display device 1 of the present embodiment, the twist angle of the liquid crystal layer 4 was set to about 70 degrees, and the liquid crystal layer 4 was twisted.
This is an example of an analysis calculation showing that the reflection type liquid crystal display device 1 with less display coloration is realized by setting the value of Δnd of about 0.27 μm. FIG. 3 shows the reflectance on the vertical axis,
Taking Δnd on the abscissa and calculating the twist angle of the liquid crystal layer as a parameter without applying a voltage, the Δnd of the liquid crystal layer is calculated.
FIG. 7 is a graph showing the dependence of Δnd of the liquid crystal layer on the reflectance, in which the result of determining the dependence of reflectance on the liquid crystal layer is represented by a curve.

As shown in FIG. 3, comparing the maximum points of the curves of the twist angles of the liquid crystal layer 4, a high reflectance can be obtained when the twist angle of the liquid crystal layer 4 is set to about 80 degrees or less. It can be seen that at a twist angle of 60 degrees, the reflectance is maximized for two values of Δnd. Even at a twist angle of 70 degrees, there are two local maxima, but the depression in the curve showing the decrease in reflectance between them is small and the curve is flat. Accordingly, the twist angle is set to about 70 degrees, and the cell gap design value is set to a value corresponding to the flat portion of the dependency curve. That is,
If Δnd is set to be about 0.27 μm, the dependence of the reflectance on Δnd of the liquid crystal layer 4 is minimized. In addition, since the dependency on Δnd has a correlation with the wavelength dependency, the wavelength dependency can be greatly improved. That is, a display with little coloring can be obtained. Therefore, according to this analysis calculation example, in this embodiment, a display with little coloring can be obtained by setting the twist angle of the liquid crystal layer 4 to about 70 degrees and the value of Δnd of the liquid crystal layer 4 to about 0.27 μm. it can. As is apparent from FIG. 3, even when the value of Δnd of the liquid crystal layer 4 is in the range of 0.21 to 0.31 μm, a high reflectance can be obtained and the value of Δnd of the liquid crystal layer 4 having the reflectance can be obtained. Dependence is small.

Next, a second analysis calculation example in this embodiment will be described. In this analysis calculation example, in the reflection type liquid crystal display device 1 of the first embodiment shown in FIG. 1, the arrangement angle α of the polarizing plate 11 and the arrangement angles β and 1 of the half-wave retardation film 9 are different.
By changing the arrangement angle γ of the 波長 wavelength retardation film 8 as a parameter, the saturation (C ^* ) of the display color when no voltage is applied is calculated by simulation. The twist angle of the liquid crystal layer 4 is 7
Assuming 0 degree, Δnd of the liquid crystal layer 4 is 0.27 μm (the cell gap is 4.0 μm).

The half-wave retardation film 9 includes:
For a stretched film made of a polycarbonate polymer, a half wavelength (approximately 27
Assuming that a retardation of about 5 nm is given, the quarter-wave retardation film 8 is a stretched film of a polycarbonate-based polymer and has a wavelength of about 1/4 wavelength (about 138 nm) with respect to monochromatic light having a wavelength of about 550 nm. Assume one that gives a phase difference.

As described above, when the polycarbonate-based polymer is used as the material of the half-wave retardation film 9 and the quarter-wave retardation film 8, the following equations 2 to 5 are generally satisfied. Must be configured.

[0044]

## EQU2 ## β = α-17.5 degrees, γ = α-80 degrees

[0045]

## EQU3 ## β = α + 17.5 degrees, γ = α + 80 degrees

[0046]

## EQU4 ## β = α + 72.5 degrees, γ = α + 10 degrees

[0047]

## EQU5 ## β = α−72.5 degrees, γ = α−10 degrees

When the above equations (1) to (5) are satisfied, the incident light is reflected by the polarizing plate 11, the half-wave retardation films 9 and 1, and
After sequentially passing through the 位相 wavelength retardation film 8, the light becomes circularly polarized over almost the entire visible wavelength range.

FIG. 4 shows the maximum value C ^* max of the color saturation of the display color in the viewing angle range within 60 degrees of the omnidirectional polar angle on the vertical axis, and the value of the arrangement angle α on the horizontal axis. FIG. 9 is a graph showing a result of performing a simulation calculation for a combination of arrangement angles α, β, and γ that satisfy the relationship of FIG. In FIG. 4, a solid line, a dotted line, a broken line, and a dashed line
Equations 2, 3, 4 and 5 respectively correspond. In the reflection of incident light on the reflection electrode 7, the reflectance is 100.
% Specular reflection, and the light source is assumed to be a D65 light source specified in JIS Z8720. In the simulation calculation, reflection on the surface of the reflective liquid crystal display device 1 was ignored.

According to this analysis calculation example, the arrangement angle α is set to be approximately 5 to 35 degrees under the condition of Expression 2, that is, the arrangement angle α is 5 to 35 degrees and the arrangement angle β is −1.
By setting the arrangement angle 5 to 15 degrees and the arrangement angle γ from -75 degrees to -45 degrees, the saturation of the display color in the viewing angle range within the omnidirectional polar angle of 60 degrees does not exceed 20. That is, the coloring of the display due to the change in the viewing direction, which is a problem in the related art, can be eliminated. Therefore, according to this analysis calculation example, in this embodiment, the twist angle of the liquid crystal layer 4 is about 70 degrees, and the value of Δnd of the liquid crystal layer 4 is about 0.27 μm.
m, the arrangement angle α is 5 to 35 degrees, and the arrangement angle β is −15.
When the arrangement angle γ is between −75 degrees and −45 degrees, a display with less coloring can be obtained.

Next, a second embodiment of the present invention will be described with reference to FIG.
It will be described based on. The same components as those of the first embodiment shown in FIG. 1 are denoted by the same reference numerals, and detailed description thereof will be omitted. FIG. 5 is a partial cross-sectional perspective view showing a configuration of a reflective liquid crystal display device according to a second embodiment of the present invention. FIG. 6 is a side sectional view showing a configuration of a TFT and a pixel electrode of an active matrix substrate of a reflection type liquid crystal display device according to a second embodiment of the present invention.

This embodiment is different from the first embodiment in the point that 6.
An active matrix type reflective liquid crystal display device 1 (reflective color LCD) of 1 type having 640 × 480 pixels and capable of displaying an active matrix color has an active matrix substrate 14 and a color filter substrate 12 facing each other. The difference is that the liquid crystal layer 4 is interposed between them, and the other configuration is the same as that of the first embodiment.

As shown in FIGS. 5 and 6, on the active matrix substrate 14, the reflective electrodes 7 are formed in a matrix of vertical and horizontal directions. A gate electrode 19 made of, for example, chromium is formed on the substrate 18. An insulating film 20 is formed on the gate electrode 19 and the substrate 18. A source 21 and a drain 22 are formed on the insulating film 20, and an island-like channel layer 23 made of, for example, amorphous silicon is formed between the source 21 and the drain 22. On this insulating film 20, a resin layer 24 is formed. On this resin layer 24, a reflection electrode 7 made of, for example, aluminum is formed. A contact portion 25 reaching the drain 22 is formed on the reflective electrode 7.
The reflection electrode 7 is insulated from the lower structure by the resin layer 24 except for the contact part 25.

A drain 22 of a thin film transistor (hereinafter, referred to as TFT) 17 is connected to each of the reflection electrodes 7. The gate electrode 19 of the TFT 17 is connected to the gate bus line 16, and the source 21 is connected to the signal bus line 15.
Connected to each other. On the surface of the reflective electrode 7, minute irregularities for diffusing and reflecting the incident light are formed.

On the other hand, the color filter substrate 12 has red,
Green and blue color layers 13 are formed in stripes so as to correspond to the reflection electrodes 7 on the active matrix substrate 14 side. For example, on the inner surfaces of the color filter substrate 12 and the active matrix substrate 14 that are in contact with the liquid crystal layer 4, for example,
An alignment film (not shown) made of a polyimide resin is formed, and a rubbing process is performed to bring the liquid crystal layer 4 into a predetermined alignment state.

On the other side of the color filter substrate 12 on which the alignment film is formed, a laminated quarter-wave plate 1 is provided.
0 and the polarizing plate 11 are attached in this order. The laminated quarter-wave plate 10 is a half-wave retardation film 9
(Not shown) and a quarter-wave retardation film 8 (not shown) are laminated one by one in this order from the side close to the polarizing plate 11.

In manufacturing the reflection type liquid crystal display device 1 of this embodiment, the twist angle of the liquid crystal layer 4 and the Δn of the liquid crystal layer
d, polarizing plate arrangement angle α, 位相 retardation film arrangement angle β,
Optical design parameters such as the １ ／ phase difference and the film arrangement angle γ are the same as the values shown in the first embodiment.

As described above, by adopting the structure of the present embodiment, the display is excellent in that it is bright, has a high contrast ratio, has no unevenness, and is not colored yellowish even when the viewing angle is changed during bright display. It is possible to obtain the liquid crystal display device 1 capable of displaying a full color image.

[0059]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the embodiment of the present invention will be described in detail by making a reflection type liquid crystal display device having the structure of the first embodiment shown in FIG. 1 and comparing it with a comparative example outside the scope of the claims. explain. FIG. 7 shows the chromaticity of blue to yellow (b ^* ) on the vertical axis and the chromaticity of green to red (a ^* ) on the horizontal axis. FIG. 7 is a graph showing the locus of changes in chromaticity, that is, the values of a ^* and b ^* in the L ^* a ^* b ^* color system when the observation azimuth angle is changed in the range of 0 to 360 degrees. In FIG. 7, the distance from the center corresponds to the saturation C ^* .

First, a first embodiment will be described. Example 1 had the same configuration as the reflective liquid crystal display device 1 shown in FIG. As shown in FIG. 2, the alignment state of the liquid crystal layer 4 is twisted counterclockwise from the upper substrate 2 toward the lower substrate 3, and the alignment direction of the liquid crystal near the middle of the liquid crystal layer 4 is different from that of the reflective liquid crystal display device 1. It was made to be parallel to the vertical direction.

The half-wave retardation film 9 is made of a stretched film made of a polycarbonate-based polymer, and has a half wavelength (about 275 nm) for monochromatic light having a wavelength of about 550 nm.
m) is used, and the quarter-wave retardation film 8 is a stretched film made of a polycarbonate-based polymer material and has a wavelength of about 550 nm for monochromatic light.
The one giving a phase difference of wavelength (about 138 nm) was used.

The twist angle of the liquid crystal layer 4 in the first embodiment,
The Δnd and the arrangement angles α, β, and γ are such that the twist angle of the liquid crystal layer 4 is 70 degrees (counterclockwise) and the Δnd of the liquid crystal layer 4 is 0.27.
μm (the cell gap is 4.0 μm), the arrangement angle α
Is 26 degrees, the arrangement angle β is 8 degrees, and the arrangement angle γ is −55 degrees.

For the reflection type liquid crystal display device 1 of Example 1, the voltage reflectance characteristics were measured. The measurement result is
The reflectivity was 40% when no voltage was applied, and the contrast ratio was 40 when 5 V was applied.

As shown in FIG. 7, the coloration of the display due to the change in the viewing direction could be eliminated without exceeding 20 in the viewing angle range within the omnidirectional polar angle of 60 degrees.

Next, a second embodiment will be described. In the present embodiment, a reflective liquid crystal display device 1 similar to the first embodiment is used.
The design parameters are such that the twist angle of the liquid crystal layer 4 is 70 degrees (counterclockwise), the Δnd of the liquid crystal layer 4 is 0.27 μm (cell gap 4.0 μm), the arrangement angle α is 17 degrees, and the arrangement angle β is −2 degrees. And the arrangement angle γ was −62 degrees.

With respect to the reflective liquid crystal display device 1 of Example 2, the voltage reflectance characteristics were measured. As a result, the reflectivity was 40% when no voltage was applied, and the contrast ratio was 40 when 5 V was applied. Also in the configuration of this example, it was confirmed that there was no coloring of the display when the viewing angle was inclined.

Next, Comparative Example 3 will be described. FIG. 8 shows the chromaticity of blue to yellow (b ^* ) on the vertical axis and the chromaticity of green to red (a ^* ) on the horizontal axis. FIG. 10 is a graph showing a locus of change in chromaticity when the observation azimuth is changed in a range of 0 to 360 degrees. In FIG. 8, the distance from the center corresponds to the saturation C ^* .

In Comparative Example 3, the same reflection type liquid crystal display device 1 as in Example 1 was used except that the design parameters were such that the twist angle of the liquid crystal layer 4 was 70 degrees (counterclockwise) and the Δnd of the liquid crystal layer 4 was 0.2.
7 μm (the cell gap is 4.0 μm), the arrangement angle α is 20 degrees, the arrangement angle β is 37.5 degrees, and the arrangement angle γ is 1
Created as 00 degrees.

The configuration of Comparative Example 3 is similar to that of S. −
T. Based on the report of S.-T. Wu et al.
Is set as the optimum angle in the configuration of the normally black of the prior art, and the half retardation films 9 and 1/4
The retardation film 8 is inserted based on Equation 3 to form a normally white element.

With respect to the reflective liquid crystal display device 1 of Comparative Example 3, the voltage reflectance characteristics were measured. The measurement result is
The reflectivity was 40% when no voltage was applied, and the contrast ratio was 40 when 5 V was applied. As shown in FIG. 8, it was confirmed that the tint of the display significantly changed due to the change in the viewing angle azimuth. In particular, when the viewing angle was inclined in the left-right direction (left-right direction in FIG. 2) of the reflective liquid crystal display device 1, the display was colored yellow.

[0071]

As described in detail above, in the present invention,
By arranging the change of the retardation due to the change of the viewing angle of the liquid crystal layer and the change of the retardation due to the change of the viewing angle of the retardation film so as to totally cancel each other,
The saturation when no voltage is applied can be set to 20 or less in a viewing angle range within ± 60 degrees of a polar angle in all directions. Therefore, it is possible to obtain a reflection type liquid crystal display device which can eliminate coloring of the display due to a change in the viewing direction.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a reflective liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a schematic diagram showing an alignment state of liquid crystal and arrangement angles of a polarizing plate, a half-wave retardation film, and a quarter-wave retardation film in the reflective liquid crystal display device according to the first embodiment of the present invention. is there.

FIG. 3 is a graph showing the result of determining the dependency of the reflectance on Δnd of the liquid crystal layer by a curve.

FIG. 4 is a graph showing a result of performing a simulation calculation for a combination of arrangement angles α, β, and γ.

FIG. 5 is an exploded perspective view illustrating a configuration of a reflective liquid crystal display device according to a second embodiment of the present invention.

FIG. 6 is a side sectional view showing a configuration of a TFT and a pixel electrode of an active matrix substrate of a reflective liquid crystal display device according to a second embodiment of the present invention.

FIG. 7 is a graph showing a locus of change in chromaticity when the observation azimuth is changed in a range of 0 to 360 degrees at a polar angle of 60 degrees.

FIG. 8 is a graph showing a locus of a change in chromaticity when the observation azimuth is changed in a range of 0 to 360 degrees at a polar angle of 60 degrees.

FIG. 9 is a side sectional view showing a configuration of a first TN type first reflection type liquid crystal display device.

FIG. 10 is a side sectional view showing a configuration of a second reflective liquid crystal display device.

FIG. 11 is a side sectional view showing a third conventional reflective liquid crystal display device.

[Explanation of symbols]

 1, 100; reflective liquid crystal display device 2, 101; upper substrate 3, 102; lower substrate 4, 103; liquid crystal layer 5, 104; transparent electrode 6, 105; alignment film 7, 109; reflective electrode 8; Retardation film 9; 1/2 retardation film 10; laminated quarter-wave plate 11, 106, 107; polarizing plate 12; color filter substrate 13; color layer 14; active matrix substrate 15; signal bus line 16; Bus line 17; TFT 18; Substrate 19; Gate electrode 20; Insulating film 21; Source 22; Drain 23; Channel layer 24; Resin layer 25; Contact portion A; Polarization absorption axis B, C; Optical axis D; Alignment direction (Angle origin) E; Lower substrate side orientation direction α, β, γ; Arrangement angle 108; Reflector 110; 1/4 wavelength plate

Claims (6)

(57) [Claims] An upper substrate; a lower substrate facing the upper substrate; and a liquid crystal layer sandwiched between the upper substrate and the lower substrate. The upper substrate is in contact with the liquid crystal layer. A transparent electrode and an alignment film are formed on the lower substrate, a reflective electrode and an alignment film are formed on the lower substrate in contact with the liquid crystal layer, and a half of the upper substrate is opposite to the liquid crystal layer. Laminated type 1 / having a retardation film and a 1/4 retardation film
A four-wavelength plate and a polarizing plate are formed, and the twist direction of the liquid crystal when the liquid crystal layer is traced from the upper substrate side to the lower substrate side is defined as positive with reference to the upper substrate side alignment direction of the liquid crystal layer. In this case, the arrangement angle α of the polarization absorption axis of the polarizing plate is 5 ° to 35 °, the arrangement angle β of the optical axis of the フ ィ ル ム retardation film is −15 ° to 15 °, and the ４ retardation A reflection type liquid crystal display device, wherein an arrangement angle γ of an optical axis of the film is −75 degrees to −45 degrees. 2. The liquid crystal layer has a twist angle of 66 to 7 degrees.
2. The reflection type liquid crystal display device according to claim 1, wherein the angle is 4 degrees, and the product of the refractive index anisotropy of the liquid crystal layer and the thickness of the liquid crystal layer is 0.21 μm to 0.31 μm. . 3. The reflection type liquid crystal display device according to claim 1, wherein the laminated quarter-wave plate is composed of a plurality of retardation films for giving a retardation. 4. The film according to claim 1, wherein the retardation film, the 位相 retardation film, and the 位相 retardation film are made of a polycarbonate-based polymer or a polysulfone-based polymer. 2. The reflection type liquid crystal display device according to claim 1. 5. The reflection type liquid crystal display device according to claim 1, wherein the reflection electrode has an uneven surface. 6. The reflection type liquid crystal display device according to claim 1, wherein the liquid crystal layer is a twisted nematic liquid crystal.