JPH11295720A - Reflection type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a reflection type liquid crystal display device capable of displaying in a high contrast ratio. SOLUTION: This normally white device 50 is composed by arranging, in the order from the incident side of the light, a polarizing plate 15, a quarter- wavelength plate 25, an upper transparent substrate 11, transparent electrodes 51, an alignment layer 21, and twisted nematic mode liquid crystal layer 20. In this case, an angle formed by the optical axis of the quarter-wave plate 25 with the polarizing plate 15 is regulated so as to be in a range from 43 deg. to 39 deg. or from 47 deg. to 51 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a reflection type liquid crystal display device, and more particularly, to a reflection type liquid crystal display device capable of displaying with a high contrast ratio.

[0002]

2. Description of the Related Art A reflection type liquid crystal display (LCD) does not require a backlight, consumes little power, and is frequently used in portable equipment driven by a battery. Among the operation methods of the reflection type liquid crystal display device, the method most commonly used at present is a twisted nematic (T).
N) method. Hereinafter, with reference to the drawings,
A conventional reflection type liquid crystal display device will be described with an example. FIG.
FIG. 1 is a side sectional view showing a configuration of a conventional TN type reflection type liquid crystal display device. Conventional reflective liquid crystal display device 10
As shown in FIG. 11, two transparent substrates, an upper substrate 11 and a lower substrate 12, which are superposed at a distance of about 5 μm, are aligned with each other so that the substrates are twisted by about 90 degrees. The liquid crystal layer 20 is provided, and polarizers 15 and 16 are respectively adhered to the outer surfaces (sides not in contact with the liquid crystal layer) of the two transparent substrates. In addition, the conventional reflection type liquid crystal display device 10 includes a transparent electrode 51 made of a transparent conductive material such as indium tin oxide (ITO) on the inner surfaces (the side in contact with the liquid crystal layer) of the upper substrate 11 and the lower substrate 12.
By applying an electric field to the liquid crystal layer 20 through the transparent electrodes 51 and 52, the alignment state of the liquid crystal layer 20 is changed, and the intensity of light reflected by the reflector 62 and reaching the user is changed. Can be displayed.

[0003] However, the conventional TN type reflection type liquid crystal display device 10 has the following difficulties. First, the incident light is emitted after passing through the polarizing plate twice one way, that is, four times reciprocally. Since the polarizing plates 15 and 16 have some absorption not only for polarized light in the direction of the absorption axis but also for polarized light in the direction of the transmission axis perpendicular thereto, light is lost every time the light passes through the polarizing plate. Therefore, in the reflective liquid crystal display device 10 using two polarizing plates, it is difficult to obtain a bright display (a disadvantage of insufficient brightness). The second difficulty is that since a transparent substrate having a thickness of about 1 mm exists between the liquid crystal layer and the reflector, the display appears double when viewed obliquely (parallax difficulty). . Conventionally, a super twisted liquid crystal layer in which the twist angle is increased to about 200 degrees.
A nematic (STN) type reflective liquid crystal display device is also used, but also in this case, since two polarizing plates are used, it is not preferable in terms of lack of brightness and parallax as in the TN type.

[0004] As a solution to these difficulties, Proceedings of the S.I.D.
the SID), 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 has a configuration in which the number of times that the incident light passes through the polarizing plate only needs to be twice, so that the loss of light can be suppressed as compared with the reflection type liquid crystal display device 10. it can. Further, since it is not necessary to dispose the 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, which causes a problem of parallax. Is also eliminated. Further, Japanese Patent Application Laid-Open No. 4-116515 discloses that in a reflection type liquid crystal display device having a configuration using only one polarizing plate as described above, the twist angle of the liquid crystal layer, the refractive index anisotropy and the layer thickness ( Cell gap) (Δnd),
Optimization of three parameters with the polarizer angle is described. Here, the polarizing plate angle is the angle between the transmission axis of the polarizing plate and the liquid crystal orientation on the incident side. FIG. 12 is a sectional view showing a configuration of a reflection type liquid crystal display device described in JP-A-4-116515. In FIG. 12, the transparent electrode 51
And an upper substrate 11 on which an alignment film 21 is sequentially formed, and a lower substrate 12 on which a reflective electrode 53 and an alignment film 22 are sequentially formed,
They are stacked facing each other so as to sandwich the liquid crystal layer 20,
A polarizing plate 15 is attached on the incident side of the upper substrate, that is, on the surface facing the transparent electrode. JP-A-4-11651
An example of the optimized design parameters disclosed in No. 5 is shown below. Twist angle of liquid crystal layer: 63 ° Δnd of liquid crystal layer: 0.2 μm Polarizer angle: 0 ° or 90 ° In a reflective liquid crystal display device designed and manufactured with the above design parameters, a straight line incident on the liquid crystal layer The polarized light becomes substantially circularly polarized light on the reflection surface after passing through the liquid crystal layer, and further becomes linearly polarized light whose polarization plane is rotated by approximately 90 degrees with respect to the incident light after being reflected and transmitted through the liquid crystal layer. Therefore, polarization conversion by the liquid crystal layer is performed with extremely high efficiency.

[0005] Also, the 1997 SID International Symposium Digest of Technical Papers (1997 SID International Sympos
iumDigest of Technical Papers) 28, 643-646
Page (1997). -T. Wu (S.-T.
Wu) et al. Reported that a polarizing plate as shown in FIG.
Optimized design parameters in the configuration of the reflection type liquid crystal display device using only one sheet 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. Twist angle of liquid crystal layer: 90 ° Δnd of liquid crystal layer: 0.25 μm Polarizer angle: 20 ° Further, design parameters of another example (Example 2) of the reflection type liquid crystal display device disclosed in this document are shown below. . Twist angle of liquid crystal layer: 70 ° Δnd of liquid crystal layer: 0.28 μm Polarizer angle: 20 ° Using the above design parameters, designing and manufacturing a device having the configuration shown in FIG. Works as That is, a dark state is displayed when no voltage is applied, and a bright state is displayed when a voltage is applied. Further, FIG.
As shown in 3, by additionally disposing a quarter-wave plate (λ / 4 plate) 25 between the polarizing plate 15 and the upper substrate 11, a normally white element can be manufactured. . The quarter-wave plate is a birefringent plate whose thickness is determined so as to generate a quarter-wavelength optical path difference between linearly polarized light beams vibrating in directions perpendicular to each other. Quarter wave plate 2
5 is arranged such that its optical axis forms an angle of 45 degrees with the polarization transmission axis of the polarizing plate 15. With this arrangement, linearly polarized light is converted to clockwise or counterclockwise circularly polarized light by a quarter-wave plate, so that a bright state is displayed when no voltage is applied and a dark state is displayed when voltage is applied. can do. The device having the normally white configuration as shown in FIG. 13 has a small dependence of the reflectance at the time of displaying a dark state on the cell gap and the wavelength, and therefore has the normally black configuration as shown in FIG. Preferred over elements.

[0006]

By the way, when the polarizing plate is 1
Reflection type liquid crystal display device (reflection type L
In CD), when a quarter-wave plate is combined with a polarizing plate to make a circularly polarized light incident on the liquid crystal layer and operate in a normally white mode, when a voltage is applied, the liquid crystal molecules move in the electric field direction (substrate normal). Direction), the effect of birefringence is lost, and as a result, a dark state is displayed. But,
Due to the liquid crystal molecules near the substrate interface which are relatively firmly fixed at the substrate interface, there is a problem that the effect of birefringence remains even when voltage is applied, and sufficient display contrast cannot be obtained. As a countermeasure, when the twist angle of the liquid crystal layer is 90 degrees as in Example 1, a relatively high contrast ratio can be obtained because the residual birefringence of the liquid crystal molecules at the interface between the upper and lower substrates compensates each other. However, as will be described later in detail, in terms of brightness when no voltage is applied and a cell gap margin, the twist angle is desirably 80 degrees or less, and preferably about 70 degrees. Therefore, it is difficult to achieve both brightness and contrast ratio. there were. In view of the circumstances as described above, an object of the present invention is to provide a reflective liquid crystal display device that can display a bright image with a high contrast ratio.

[0007]

The inventor of the present invention arranges a quarter-wave plate, which has been conventionally arranged at an angle of 45 degrees with respect to the polarization transmission axis of a polarizing plate, to be slightly shifted from 45 degrees. As a result, it has been found that the influence of birefringence remaining when a voltage is applied due to the liquid crystal at the substrate interface can be compensated, and a significant improvement in display contrast can be obtained, and the present invention has been completed. In order to achieve the above object, the reflective liquid crystal display device according to the present invention, when viewed from the light incident direction side,
In a normally white reflective liquid crystal display device in which a polarizing plate, a quarter-wave plate, a transparent substrate, a transparent electrode, an alignment film, and a twisted nematic liquid crystal layer are sequentially arranged, a quarter-wave plate is provided. The angle between the optical axis of (1) and the transmission axis of the polarizing plate is less than 65 ° and more than 45 °, or less than 45 ° and more than 25 °. Preferably, the angle between the optical axis of the quarter-wave plate and the transmission axis of the polarizing plate is 39 ° or more and 43 ° or less,
Alternatively, the angle is in the range of 47 ° or more and 51 ° or less. In the present specification, the twisted nematic liquid crystal layer is
Not only the liquid crystal layer having a twist angle of 90 ° but also a liquid crystal layer having a twist angle in a range from about 90 ° to about 50 ° is included. In this specification, “normally white” refers to a reflective liquid crystal display device configured to transmit light in the absence of an electric field, and the number of polarizing plates provided may be one.

If the quarter-wave plate is a broadband quarter-wave plate obtained by laminating uniaxial retardation plates, the effect of the present invention becomes more remarkable. Preferably, the twist angle of the liquid crystal layer is in the range of 60 ° or more and 85 ° or less. In this case, the angle is preferably in the range of 68 ° or more and 74 ° or less. The Δnd value, which is a product of the refractive index anisotropy Δn of the liquid crystal layer and the liquid crystal layer thickness d, which is the cell gap, is
When the value is in the range of 0.20 μm or more and 0.35 μm or less, preferably in the range of 0.24 μm or more and 0.31 μm or less, the reflective type is bright, has a high contrast ratio, and has small cell gap dependence and wavelength dependence. A liquid crystal display device is realized. In a preferred embodiment of the present invention, the liquid crystal layer has a twist angle of about 70 degrees and a Δnd value of about 0.27 μm.

[0009]

Embodiments of the present invention will be specifically and more specifically described below with reference to the accompanying drawings by way of example embodiments, analysis calculation examples, and examples. Embodiment Example The embodiment is an embodiment of the present invention. FIG.
FIG. 1 is a side sectional view showing a configuration of a reflection type liquid crystal display device according to an embodiment of the present invention. Reflective liquid crystal display device 5 of the present embodiment
0 is a polarizing plate 15, a quarter-wave plate 25, a transparent upper substrate 11, a transparent electrode 51,
This is a normally white reflective liquid crystal display device in which an alignment film 21, a twisted nematic liquid crystal layer 20, an alignment film 22, a reflective electrode 53, and a transparent lower substrate 12 are arranged. The quarter-wave plate 25 and the polarizing plate 15 are attached to the incident side of the upper substrate 11, that is, the side facing the alignment film 21. The liquid crystal layer 20 is a twisted nematic liquid crystal. In the present embodiment, the quarter-wave plate 25
A type called a broadband quarter-wave plate may be used. The broadband quarter-wave plate has a configuration in which a plurality of retardation films are stacked with their optic axis directions intersecting appropriately as described in JP-A-5-100114. By combining them so as to form a predetermined relative angle, linearly polarized light can be converted to circularly polarized light over a wide wavelength range.

FIG. 2 is a diagram for explaining the arrangement angles of the quarter-wave plate 25 and the polarizing plate 15. Quarter wave plate 25
2, and the polarization transmission axis of the polarizing plate 15 are arranged at angles α and β with respect to the upper substrate side liquid crystal alignment direction, respectively, as shown in FIG. In the present embodiment, the angle formed between the optical axis of the quarter-wave plate 25 and the polarization transmission axis of the polarizing plate 15, that is, the angle difference between α and β,
The angle is slightly shifted from the conventional angle of 45 °, and the relative angle between the quarter-wave plate and the polarizing plate is arranged to be different from the angle for converting linearly polarized light into circularly polarized light.

In the reflection type liquid crystal display device of this embodiment,
Conventionally, clockwise or counterclockwise circularly polarized light enters the liquid crystal layer, whereas imperfect circularly polarized light enters the liquid crystal layer. Therefore, the influence of birefringence due to the liquid crystal at the substrate interface can be compensated, the reflectance at the time of applying a voltage (dark state) is kept low, and the display contrast can be improved to achieve a remarkably high contrast. The reflection type liquid crystal display device 50 of the embodiment is a segment type, a simple matrix type,
Alternatively, an active matrix reflective liquid crystal display device can be used. Further, it may be a monochrome type or a color type using a color filter. The reflective electrode 52 may be formed so that its surface has minute irregularities, thereby providing an appropriate scattering property and enabling display without a metallic feeling. When the surface of the reflective electrode 52 has a flat shape, a display without a metallic feeling can be obtained by disposing a diffusion film between the upper substrate 11 and the quarter-wave plate 25, for example. it can.

Analysis Calculation Example 1 This analysis calculation example is the reflection type liquid crystal display device of the embodiment,
By setting the twist angle of the liquid crystal layer to about 70 degrees and the value of Δnd of the liquid crystal layer to about 0.27 μm, it is possible to realize a reflective liquid crystal display device that is bright, has small cell gap dependence and wavelength dependence. It is an analysis calculation example showing that this is the case. FIG.
FIG. 4 is a graph showing, as a curve, a result obtained by changing the twist angle of the liquid crystal layer as a parameter in a state where no voltage is applied and calculating the dependency of the reflectance on Δnd of the liquid crystal layer. When comparing the maximum points of each curve,
When the twist angle of the liquid crystal layer is set to about 80 degrees or less, a high reflectance is obtained, and when the twist angle is 60 degrees, the reflectance is maximized for two values of Δnd. Twist angle 70
Although the curve has two maxima at the same time, the depression (decrease in reflectance) of the curve therebetween is small and the curve is flat. That is, if 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 about 0.27 μm, the cell gap margin can be reduced. It turns out that it becomes the maximum.
In addition, since the cell gap dependency has a correlation with the wavelength dependency, the wavelength dependency can be improved. Conventionally, when the twist angle is about 70 degrees, the contrast ratio is reduced, and the practical characteristics are not good. According to this analysis calculation example, by shifting the relative arrangement of the quarter-wave plate and the polarizing plate, high contrast while maintaining advantages such as brightness and cell gap margin even at a twist angle of about 70 degrees is achieved. It has been found that this can be achieved.

Analysis Calculation Example 2 FIG. 3 shows the reflection type liquid crystal display device 50 of the embodiment shown in FIG. 1 based on Analysis Calculation Example 1, in which the twist angle of the liquid crystal layer is 70 degrees and Δnd of the liquid crystal layer is 0. FIG. 9 is a graph showing the results of simulation calculation of the contrast ratio when 5 V is applied, with the quarter-wave plate arrangement angle α and the polarization plate arrangement angle β being changed as parameters, with the cell gap being set to .27 μm (cell gap 4.0 μm). . In this simulation calculation, the refractive index anisotropy of the quarter-wave plate used was a value assuming a uniaxially stretched polycarbonate film in consideration of wavelength dependence. For the liquid crystal layer, the wavelength dependence of the refractive index anisotropy in a standard nematic liquid crystal was assumed. As can be seen from FIG. 3, it was confirmed that the contrast ratio was improved when the angle was shifted compared to the conventional reflective liquid crystal display device in which α = β + 45 degrees. The angle is 2 to 6 for the arrangement of α = β + 45 degrees.
It has been found that higher or lower angles, on the order of degrees, are preferred.

Analysis Calculation Example 3 This analysis calculation example is an example in which a laminated broadband quarter-wave plate is used as a quarter-wave plate to evaluate by simulation calculation. The conditions are the same as in the analysis calculation example 1. The wide-band quarter-wave plate assumed in the simulation calculation of this analysis calculation example is formed by laminating two uniaxially stretched polycarbonate layers, Nitto Denko Corporation.
"Broadband Wavelength Film". FIG. 4 is a graph showing the wavelength dependence of the phase difference obtained by the “broadband wavelength film” manufactured by Nitto Denko Corporation. As shown in FIG. 4, a phase difference of π / 2 is obtained over the entire visible light range, that is, linearly polarized light is converted into circularly polarized light. Since the broadband quarter-wave plate has a laminated structure, its optic axis cannot be defined in a strict sense.However, in this analysis calculation example, the arrangement is such that the incident linearly polarized light is converted to circularly polarized light. Here, the direction forming 45 degrees with the polarization direction of the incident linearly polarized light is defined as the optical axis 26 for convenience (FIG. 5). In the simulation calculation of this analysis calculation example, the analysis calculation example 2
Similarly, the twist angle of the liquid crystal layer is 70 degrees, and the Δnd of the liquid crystal layer is
Was set to 0.27 μm (cell gap: 4.0 μm), the quarter-wave plate arrangement angle α and the polarization plate arrangement angle β were changed, and the contrast ratio when 5 V was applied was calculated. FIG.
FIG. 9 is a graph showing a calculation result by a simulation calculation assuming a wide-band quarter-wave plate. In this simulation calculation, as in the case of the analysis calculation example 2, α =
It was confirmed that the contrast ratio was improved when the angle was shifted, as compared with the case of the conventional configuration in which the angle was β + 45 degrees (FIG. 6). It has been found that the angle is preferably shifted from the higher or lower one by about 2 to 6 degrees with respect to the arrangement of α = β + 45 degrees. Further, it was found that a higher contrast ratio was obtained by using the broadband quarter-wave plate, as compared with the calculation result in the case of using a normal quarter-wave plate (FIG. 3).

Analysis Calculation Example 4 In this analysis calculation example, first, in analysis calculation example 3, the twist angle of the liquid layer was set to 68 degrees, and the quarter-wave plate arrangement angle α and the polarization plate arrangement angle β were changed. Under the above conditions, the contrast ratio when 5 V was applied was calculated by simulation. The calculation conditions are
Except for the twist angle of the liquid crystal layer, it is the same as the analysis calculation example 3. FIG. 7 is a graph showing a result of the above-described simulation calculation. As can be seen from FIG.
Compared with the conventional reflective liquid crystal display device of +45 degrees,
It was confirmed that the contrast ratio was improved by displacing the angle. Further, the twist angle of the liquid layer is set to 7
The contrast ratio when 5 V was applied was calculated by changing the arrangement angle α of the quarter-wave plate and the arrangement angle β of the polarizing plate to 4 degrees. The calculation conditions are the same as in the analysis calculation example 3 except for the twist angle of the liquid crystal layer. FIG. 8 is a graph showing the results of the simulation. As can be seen from FIG. 8, it was confirmed that the contrast ratio was improved when the angle was shifted compared to the conventional reflective liquid crystal display device in which α = β + 45 degrees.

Hereinafter, based on analytical calculation examples 1 to 4, specific examples of the configuration of a reflection type liquid crystal display device to which the above-described embodiment of the present invention is actually applied will be described as examples. Example 1 In this example, the reflection type liquid crystal display device (reflection type LCD) shown in FIG. 1 was configured with the following design parameters. Twist angle of liquid crystal layer: 70 degrees Δnd of liquid crystal layer: 0.27 μm (cell gap 4.0 μm) Quarter wavelength plate arrangement angle α: 61 degrees Polarization plate arrangement angle β: 20 degrees (α = β + 41 degrees) Four As the half-wave plate, a two-layer laminated broadband quarter-wave plate manufactured by Nitto Denko Corporation was used. The voltage-reflectance characteristics of the reflective liquid crystal display device of this example were measured. When no voltage was applied, the reflectance was 40%.
When 5 V was applied, the contrast ratio was 40.

Comparative Example 1 of Example 1 The structure of the reflection type liquid crystal display device of this comparative example is the same as that of Example 1 , except that the arrangement angle α of the quarter-wave plate is 65 degrees (α = β + 45 degrees). This is the same as the reflective liquid crystal display device of Example 1. The voltage-reflectance characteristics of the reflective liquid crystal display device of this comparative example were measured.
%, Which is the same as Example 1, but the contrast ratio when 5 V is applied is 15, which is much lower than that of Example 1.

Comparative Example 2 of Example 1 In this comparative example, the configuration of the reflective LCD shown in FIG. 1 was determined based on the following design parameters. Twist angle of liquid crystal layer: 90 degrees Δnd of liquid crystal layer: 0.24 μm (cell gap 3.5 μm) Quarter wavelength plate arrangement angle α: 65 degrees Polarization plate arrangement angle β: 20 degrees (α = β + 45 degrees) The configuration of the reflective liquid crystal display device of this comparative example is the same as that of the first embodiment except for the above parameters. When the voltage reflectance characteristics of the reflective liquid crystal display device of this comparative example were measured, the reflectance was 32 when no voltage was applied.
%, The contrast ratio when 5 V is applied is 35,
Both were lower than in Example 1.

Embodiment 2 In this embodiment, the cell gap is set to 3.5 μm and 4.0 μm in the configuration of the reflection type liquid crystal display device of Embodiment 1.
m and 4.5 μm were manufactured. Δnd of the liquid crystal layer is 0.24 μm, 0.27 μm, and 0.2 μm, respectively, according to the value of each cell gap.
31 μm. The configuration of the reflection type liquid crystal display device of this embodiment is the same as that of Embodiment 1 except for these points. When the display from the bright state to the dark state was performed for each reflective liquid crystal display device of the present example, no difference due to the difference in the cell gap was visually observed by the inventors. According to the present embodiment, the cell gap accuracy in the recent mass production technology of the liquid crystal display device is within about ± 0.3 μm, which is narrower than the change range of the cell gap in the present embodiment. Therefore, according to this example, it was found that the liquid crystal display device having the design parameters shown in Example 1 had a sufficiently large cell gap margin.

Comparative Example of Example 1 and Example 2 In this comparative example, the twist angle of the liquid crystal layer was set to 63 based on the design parameters described in JP-A-4-116515.
Degrees, quarter-wave plate arrangement angle α is 45 degrees, polarizer arrangement angle β
Was set to 0 degree. The cell gap is 2.5 μm,
3.0 μm, 3.5 μm and three types of reflective LC
D was manufactured. Δnd of the liquid crystal layers are each 0.17 μm.
m, 0.20 μm, and 0.24 μm. The configuration of the reflection type liquid crystal display device of this comparative example is the same as that of the reflection type liquid crystal display device of Example 1 except for the above points. For each reflection type liquid crystal display device of this comparative example, when a display from a bright state to a dark state was performed, the difference in brightness and color due to the difference in cell gap was clearly observed by visual observation of the inventors. Was.

Embodiment 3 This embodiment is an example of a reflection type liquid crystal display device (reflection type color LCD) of 6.1-type 640 × 480 pixels capable of displaying an active matrix color. FIG. 9 is a developed view showing the configuration of the reflection type liquid crystal display device of the present embodiment. In the reflection type liquid crystal display device of this embodiment, the active matrix substrate 200 and the color filter
It is provided facing each other so as to sandwich 0. On the active matrix substrate 200, reflection electrodes are formed in a matrix of vertical and horizontal directions, and each reflection electrode is connected to a drain terminal of a thin film transistor (TFT). The gate terminal of the TFT is connected to the gate bus line 220,
The source terminals are connected to the signal bus lines 210, respectively. The surface of the pixel electrode 230 has a shape having minute irregularities that diffuse and reflect incident light. On the other hand, red, green, and blue color layers are formed in a stripe shape on the color filter substrate so as to correspond to the pixel electrodes on the active matrix substrate side. An alignment film (not shown) made of a polyimide resin is provided on the inner side surfaces (surfaces in contact with the liquid crystal layer) of the color filter substrate 100 and the active matrix substrate.
Is formed, and a rubbing process is performed to bring the liquid crystal layer into a predetermined alignment state. On the side of the color filter substrate 100 opposite to the side on which the alignment film is formed, a quarter-wave plate 300 and a polarizing plate 400 are attached in this order.

FIG. 10 shows the T of the active matrix substrate.
FIG. 3 is a side cross-sectional view illustrating a configuration of an FT and a pixel electrode. The active matrix substrate includes a gate terminal 242 formed of chromium formed on the substrate 201, an insulating layer 260 covering the gate terminal 242, an island-shaped channel layer 245 formed of amorphous silicon formed thereon, and chromium. And a source terminal 243 having a predetermined shape connected to the channel layer.
And a drain terminal 244, a resin layer 250 formed thereon, and a reflective electrode 230 thereon. The reflective electrode 230 is made of aluminum, and is insulated from the lower structure by the resin layer 250 except for the contact portion 231.
44. In manufacturing the reflection type liquid crystal display device of the present embodiment, the twist angle of the liquid crystal layer and Δn of the liquid crystal layer
The values shown in Example 1 were used for the optical design parameters such as d, the quarter-wave plate arrangement angle α, and the polarization plate arrangement angle β. The liquid crystal display device of the present example was able to display a full-color image that was bright, had a high contrast ratio, and had no unevenness.

[0023]

According to the present invention, the angle between the optical axis of the quarter-wave plate and the transmission axis of the polarizing plate is less than 65 ° and 45 °.
An angle greater than 25 ° or an angle less than 45 ° and greater than 25 °. This allows imperfect circularly polarized light to enter the liquid crystal layer and compensate for the effect of birefringence due to the liquid crystal at the substrate interface. Therefore, the reflectivity when a voltage is applied (in a dark state) is reduced, and the display contrast is reduced. Greatly improved and higher. Preferably, the Δnd value which is a product of the refractive index anisotropy of the liquid crystal layer and the thickness of the liquid crystal layer which is the cell gap is 0.24.
The value is in the range of not less than μm and not more than 0.31 μm. As a result, the contrast ratio can be significantly improved in a design in which the brightness and the cell gap margin are prioritized, so that it is possible to realize a reflection type liquid crystal display device excellent in all aspects of the brightness, the contrast ratio, and the cell gap margin. it can.

[Brief description of the drawings]

FIG. 1 is a side sectional view showing a configuration of a reflective liquid crystal display device according to an embodiment.

FIG. 2 is a schematic diagram illustrating an arrangement angle of a quarter-wave plate and a polarizing plate of the reflective liquid crystal display device of the embodiment.

FIG. 3 is a graph showing a result of a simulation calculation in Analysis Calculation Example 2.

FIG. 4 is a graph showing the wavelength dependence of the phase difference obtained by the broadband wavelength film used in Analysis Calculation Example 3.

FIG. 5 is a schematic diagram illustrating an optical axis of a broadband quarter-wave plate used in Analysis Calculation Example 3.

FIG. 6 is a graph showing a result of a simulation calculation in an analysis calculation example 3;

FIG. 7 is a graph showing a result of a simulation calculation in an analysis calculation example 4;

FIG. 8 is a graph showing a result of a simulation calculation in Analysis Calculation Example 4.

FIG. 9 is a development view illustrating a configuration of a reflective liquid crystal display device according to a third embodiment.

FIG. 10 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 third embodiment.

FIG. 11 is a side sectional view showing a configuration of an example of a conventional TN mode reflection type liquid crystal display device.

FIG. 12 is a side cross-sectional view showing a configuration of an example of a conventional TN type reflection type liquid crystal display device.

FIG. 13 is a side cross-sectional view showing a configuration of an example of a conventional TN type reflection type liquid crystal display device.

FIG. 14 is a graph showing a result of a simulation calculation in the first example of analysis calculation, and is a diagram for explaining the dependence of the reflectance on the twist angle and Δnd.

[Explanation of symbols]

 Reference Signs List 10 reflective liquid crystal display device 11 upper substrate 12 lower substrate 15, 16 polarizer 20 liquid crystal layer 21, 22 alignment film 25 quarter-wave plate 26 optical axis 50 reflective liquid crystal display device 51, 52 transparent electrode 53 reflective electrode 62 Reflecting plate 100 Color filter substrate 150 Color layer 200 Active matrix substrate 210 Signal bus line 220 Gate bus line 230 Reflecting electrode 231 Contact portion 240 TFT 242 Gate terminal 243 Source terminal 244 Drain terminal 245 Channel layer 250 Resin layer 260 Insulating layer 300 Quarter One-wavelength plate 400 Polarizing plate

Claims (7)

[Claims] 1. A normally white liquid crystal layer in which a polarizing plate, a quarter-wave plate, a transparent substrate, a transparent electrode, an alignment film, and a twisted nematic liquid crystal layer are sequentially arranged when viewed from a light incident direction side. The angle between the optical axis of the quarter-wave plate and the transmission axis of the polarizing plate is less than 65 ° and more than 45 °, or less than 45 ° and more than 25 °. A reflective liquid crystal display device, characterized in that: 2. An angle between an optical axis of a quarter-wave plate and a transmission axis of a polarizing plate is 39 ° or more and 43 ° or less, or 47 ° or less.
2. The reflection type liquid crystal display device according to claim 1, wherein the angle is in the range of not less than 50 degrees and not more than 51 degrees. 3. The reflection type liquid crystal display device according to claim 1, wherein the quarter-wave plate is a wide-band quarter-wave plate formed by laminating uniaxial retardation plates. . 4. The liquid crystal layer has a twist angle of 60 ° or more and 85 ° or more.
4. The reflective liquid crystal display device according to claim 1, wherein the angle is in a range of not more than °. 5. 5. The liquid crystal layer has a twist angle of 68 ° or more and 74 ° or more.
5. The reflection type liquid crystal display device according to claim 4, wherein the angle is in the range of not more than °. 6. A Δnd value which is a product of a refractive index anisotropy Δn of a liquid crystal layer and a liquid crystal layer thickness d which is a cell gap,
The reflective liquid crystal display device according to claim 1, wherein the value is in a range of 0.20 μm or more and 0.35 μm or less. 7. A Δnd value, which is a multiplication value of a refractive index anisotropy Δn of a liquid crystal layer and a liquid crystal layer thickness d which is a cell gap,
The reflective liquid crystal display device according to claim 6, wherein the value is in a range of 0.24 µm or more and 0.31 µm or less.