JP2000035570A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve coloring in a reflection mode of dark display by eliminating the variation of polarization in the light wavelength band, and approximately circular-polarizing the light in the reflection mode. SOLUTION: A λ/4-wave plate 7 is arranged on the opposite plane of the side where a counter electrode 4 of a substrate 2 is formed, and further, a λ/4-wave plate 10 is arranged on the opposite plane of the side where a reflecting electrode 3 and a transparent electrode 8 of a substrate 1 are formed, and the lagging axis, of the λ/4-wave plate 10 is set so as to be perpendicular to that of the λ/4-wave plate 7. A λ/2-wave plate 11 is arranged on the other side of the substrate 2 of the λ/4 board 7 and a λ/2-wave plate 12 is arranged on the other side of the substrate 1 of the λ/4-wave plate 10, respectively, and the lagging axis of the λ/2-wave plate 11 is set to be 60 degrees tilted against that of λ/4-wave plate 7; the lagging axis of the λ/2-wave plate 12 is set to be 60 degrees tilted against that of λ/4-wave plate 10; and the lagging axis of the λ/2-wave plate 12 is set to be perpendicular to that of the λ/2-wave plate 11.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a reflective type and a transmissive type used for OA equipment such as a word processor or a personal computer, portable information equipment such as an electronic organizer, or a camera-integrated VTR equipped with a liquid crystal monitor. The present invention relates to a liquid crystal display device having both of the above.

[0002]

2. Description of the Related Art Unlike CRTs (CRTs) and ELs (electroluminescence), liquid crystal displays do not emit light by themselves. Therefore, a transmissive liquid crystal display device in which a backlight is installed on the back of a liquid crystal display element to illuminate it is used. ing. However, backlights typically consume 50% or more of the total power consumption of liquid crystal displays. Therefore, in portable information devices that are often used outdoors or on a regular basis, a reflector is installed instead of the backlight and ambient light is used. A reflection type liquid crystal display device which performs display only by itself has been realized.

The display modes used in the reflection type liquid crystal display device include a type using a polarizing plate such as a TN (twisted nematic) mode and an STN (super twisted nematic) mode which are widely used in a transmission type, and a polarization mode. In recent years, a phase change type guest host mode capable of realizing a bright display because a plate is not used has been actively developed, and is disclosed in, for example, Japanese Patent Application Laid-Open No. 4-75022.

[0004]

However, in the phase transition type guest-host mode, a display is performed by using light absorption of a dye in a liquid crystal layer in which liquid crystal molecules and a dye are dispersed, so that sufficient contrast cannot be obtained. The display quality is remarkably deteriorated as compared with a liquid crystal display device using a polarizing plate, such as a nematic mode or an STN (super twisted nematic) mode.

In the case of a parallel or twisted liquid crystal display device, the liquid crystal molecules near the center of the liquid crystal layer are tilted in the direction perpendicular to the substrate surface when a voltage is applied, but the liquid crystal molecules near the alignment film surface are not tilted. The birefringence of the liquid crystal layer is far from 0 because it does not become perpendicular to the substrate even when voltage is applied. In the display mode in which black display is performed when voltage is applied, sufficient black is displayed due to the birefringence of the liquid crystal layer. No sufficient contrast can be obtained.

At present, it is difficult to say that TN mode and STN mode liquid crystal display devices have sufficient display quality in terms of brightness and contrast, and further improvement in display quality such as higher brightness and higher contrast is required. ing. Also,
Reflective liquid crystal display devices have the disadvantage that when ambient light is dark, the amount of reflected light used for display is reduced and visibility is extremely reduced. There was a problem that visibility under extremely bright sunny weather was reduced.

Accordingly, a display device combining transmission display and reflection display has been developed. However, in the case of black display, there is a problem that light leakage occurs and a sufficient black level cannot be obtained.

[0008]

According to a first aspect of the present invention, there is provided one substrate having a region having a reflective function and a region having a transmissive function, and another substrate having a counter electrode formed thereon. In a liquid crystal display device having a liquid crystal layer sandwiched between the one substrate and the other substrate, a first polarizing means provided on a surface of the other substrate opposite to the liquid crystal layer; A second polarizing means provided on a surface opposite to the layer, and a second polarizing means provided between the first polarizing means and the liquid crystal layer, wherein the linearly polarized light from the first polarizing means is circularly polarized. A first retardation plate, a second retardation plate provided between the second polarizing means and the liquid crystal layer, and configured to make linearly polarized light from the second polarizing means circularly polarized; Is provided between the polarizing means and the liquid crystal layer, and has a refractive index anisotropy of the first retardation plate. And having a third phase difference plate for compensating the length dependence.

According to a second aspect of the present invention, the third retardation plate disposed between the first polarization means and the first retardation plate is a λ / 2 plate, and the first polarization means is a λ / 2 plate. When the angle between the transmission axis of the third phase plate and the slow axis of the third retardation plate is α,
The angle between the transmission axis of the first polarizing means and the slow axis of the first retardation plate is 2α + 45 degrees.

The invention according to claim 3 is provided between the second polarizing means and the liquid crystal layer and compensates for the wavelength dependence of the refractive index anisotropy of the second retardation plate. 4 is provided.

In a preferred embodiment of the present invention, the fourth retardation plate disposed between the second polarizing plate and the second retardation plate is a λ / 2 plate, and the second polarizing means is provided. When the angle between the transmission axis of the second phase difference plate and the slow axis of the fourth phase difference plate is α, the angle between the transmission axis of the second polarizing means and the slow axis of the second phase difference plate is 2α + 45. Degree.

According to a fifth aspect of the present invention, the transmission axis of the first polarizing means and the transmission axis of the second polarizing means are orthogonal to each other, and the first retardation plate and the second phase difference The slow axis of the plate is orthogonal to the slow axis of the third retardation plate and the slow axis of the fourth retardation plate is orthogonal to the fourth retardation plate.

The invention according to claim 6 is characterized in that the liquid crystal layer is a vertically aligned liquid crystal material having a negative dielectric anisotropy. The invention according to claim 7 is characterized in that the liquid crystal display device is set to a normally black display mode.

The operation of the present invention will be described below. According to the liquid crystal display device of the first aspect of the present invention,
The first retardation plate can offset to some extent the wavelength dependence of the refractive index anisotropy generated when converting linearly polarized light to circularly polarized light. As a result, in the reflection mode, circular polarization can be achieved in a state where the dispersion of the polarization state is small in a wide wavelength band. For this reason, coloring in the reflection mode of dark display can be improved.

According to the liquid crystal display device of the second aspect of the present invention, the azimuth of the linearly polarized light that has passed through the polarizing plate is rotated by the third retardation plate, and then the first polarization plate is rotated by the first retardation plate. Since the light can be circularly polarized, the wavelength dependence of the refractive index anisotropy of the first retardation plate can be optimally compensated. As a result, in the reflection mode, the dispersion of the polarization state in a wide wavelength band is further reduced, and the light can be circularly polarized. For this reason, coloring in the reflection mode of dark display can be improved.

In particular, when the liquid crystal layer is in a vertical alignment mode or when the retardation remaining in the liquid crystal layer in a dark state can be ignored, the first retardation plate can be a λ / 4 plate.

In the dark state, when the retardation of γ remains in the liquid crystal layer in the reflection mode, the retardation of the first retardation plate is set to (λ / 4−γ) and shifted from the circularly polarized light. Light is incident on the liquid crystal layer. When the light reaches the reflector after passing through the liquid crystal layer, the polarization state does not vary in a wide wavelength band and the light becomes circularly polarized light, so that good black display is realized in the reflection mode.

According to the liquid crystal display device of the third aspect of the present invention, the wavelength dependence of the refractive index anisotropy generated when converting the linearly polarized light to the circularly polarized light is offset to some extent by the fourth retardation plate. can do. By this, by this,
In the transmission mode, it is possible to obtain circularly polarized light in which the dispersion of the polarization state is eliminated in a wide wavelength band. For this reason, in addition to the first aspect, coloring in the transmission mode of dark display can be improved, and excellent black display can be realized even when both the reflection mode and the transmission mode are used.

According to the liquid crystal display device of the fourth aspect of the present invention, the direction of the linearly polarized light that has passed through the polarizing plate is rotated by the fourth retardation plate, and then the second polarization plate is rotated by the second retardation plate. Since the light can be circularly polarized, the wavelength dependence of the refractive index anisotropy of the first retardation plate can be optimally compensated. Thereby, in the transmission mode, the dispersion of the polarization state is further reduced in a wide wavelength band, and circular polarization can be obtained.

In particular, when the liquid crystal layer is in a vertical alignment mode or when the retardation remaining in the liquid crystal layer in a dark state can be ignored, the second retardation plate can be a λ / 4 plate.

In the dark state, when a retardation of γ in the reflection mode and a retardation of Δ in the transmission mode remains in the liquid crystal layer, the retardation of the subsequent layers is ｛λ / 4.
− (Δ−γ)}, the light is shifted from the circularly polarized light and is incident on the liquid crystal layer. When the light passes through the liquid crystal layer, it is in the same polarization state in the wide wavelength band as the light emitted in the reflection mode. Therefore, when it passes through the third retardation plate, it is linearly polarized light orthogonal to the transmission axis of the first polarizing means. Thus, coloring in the transmission mode can be improved, and excellent black display can be realized even when both the transmission mode and the reflection mode are used.

According to the liquid crystal display device of the fifth aspect of the present invention, the wavelength dependence of the refractive index anisotropy of the phase difference plate is reduced by orthogonalizing the slow axis of the phase difference plate. The wavelength dependence of the anisotropy of the refractive index of the retardation plate can be offset, and the coloring of dark display can be improved.

According to the liquid crystal display device of the present invention, the retardation of the liquid crystal layer is substantially zero by using a vertically aligned liquid crystal material having a negative dielectric anisotropy for the liquid crystal layer. Since the state is realized, the dark state is darker, so that the contrast is high.

For example, when a parallel alignment liquid crystal is used for the liquid crystal layer, the residual retardation does not increase even if the voltage is applied to direct the long axis of the liquid crystal molecules in a direction perpendicular to the electrodes to make the retardation of the liquid crystal layer zero. Therefore, the retardation of the liquid crystal layer does not become zero. According to the liquid crystal display device of the present invention, normally black (NB)
), The change in the contrast ratio due to the change in the cell gap hardly occurs, and a certain margin for the cell gap control can be secured in terms of productivity.

In normally white (hereinafter referred to as NW), in which white display is performed when no voltage is applied to the liquid crystal layer and black display is performed when a voltage is applied, the voltage applied to the liquid crystal layer becomes black when the cell gap changes. On the other hand, in an NB that performs black display when no voltage is applied to the liquid crystal layer and white display when a voltage is applied, the voltage applied to the liquid crystal layer changes to white when the cell gap changes. Therefore, in the NW, since the contrast ratio changes significantly due to a change in the cell gap, high-precision cell gap control is required. In addition, since the point defect that was a bright point in the NW becomes a black point in the NB, an improvement in the non-defective product rate in manufacturing is expected, and a bright spot-free high-quality display panel can be realized. From these facts, NB is superior to NW as a display mode of a liquid crystal display device that can be used in any environment.

[0026]

(Embodiment 1) A liquid crystal display device of Embodiment 1 will be described with reference to FIG. A on substrate 1
Reflective electrode 3 formed of a material having a high reflectivity such as 1 or Ta
And transparent electrode 8 formed of a material having high transmittance such as ITO
And a counter electrode 4 is provided on the substrate 2, and a liquid crystal layer 5 made of a liquid crystal material having a negative dielectric anisotropy is sandwiched between the reflection electrode 3 and the transparent electrode 8 and the counter electrode 4. .

A vertical alignment film (not shown) is formed on each of the surfaces of the reflective electrode 3, the transparent electrode 8 and the counter electrode 4 which are in contact with the liquid crystal layer 5, and after the alignment film is applied, at least one of the alignment films is formed. The alignment film is subjected to an alignment treatment such as rubbing. In this case, without using rubbing, the orientation may be regulated by optical orientation, electrode shape, or the like. The liquid crystal molecules of the liquid crystal layer 5 have a tilt angle of about 0 degree or about 0.1 to 5 degrees with respect to the vertical direction of the substrate surface due to an alignment treatment such as rubbing of the vertical alignment film.

Here, the reflective electrode 3 is used as an electrode for applying a voltage to the liquid crystal layer. However, the reflective electrode is not used as an electrode but is used as a reflective plate, and the transparent electrode 8 is extended above the reflective plate to form a reflective area. May be used as an electrode for applying a voltage to the liquid crystal layer 5 at the time. Embodiment 1 As a liquid crystal material of the liquid crystal layer 5, Embodiment 1
A liquid crystal material having the same refractive index anisotropy as Ne = 1.5546 and No = 1.4773 was used.

A λ / 4 plate 7 is arranged on the surface of the substrate 2 opposite to the side on which the counter electrode 4 is formed.
And a λ / 4 plate 10 on the surface opposite to the side where the transparent electrode 8 is formed.
And the slow axis of the λ / 4 plate 10 is set to be orthogonal to the slow axis of the λ / 4 plate 7.

The λ / 4 plate 7 has λ /
The two plates 11 are provided with λ / 4 plates on the surface of the λ / 4 plate 10 opposite to the substrate 1.
The slow axis of the λ / 2 plate 11 is 60 degrees with respect to the slow axis of the λ / 4 plate 7, and the slow axis of the λ / 2 plate 12 is the λ / 4 plate. The slow axis of the λ / 2 plate 12 is tilted by 60 degrees with respect to the slow axis of the λ / 2 plate 11.
Are set so as to be orthogonal to the slow axis.

A polarizing plate 6 is provided on a surface of the λ / 2 plate 11 opposite to the substrate 2, and a polarizing plate 9 is provided on a surface of the λ / 2 plate 12 opposite to the substrate 1. The transmission axis of 6 is λ
75 degrees with respect to the slow axis of the λ / 2 plate 11 with respect to the slow axis of the / 4 plate 7, 15 degrees with respect to the slow axis of the λ / 2 plate 11,
The transmission axis of the polarizing plate 9 is λ / λ with respect to the slow axis of the λ / 4 plate 10.
The transmission axis of the polarizing plate 6 is inclined with respect to the transmission axis of the polarizing plate 9 so as to be inclined at 75 degrees in the direction sandwiching the slow axis of the two plates 12 and 15 degrees with respect to the slow axis of the λ / 2 plate 12. They are set to be orthogonal.

FIG. 2A is a schematic plan view of the active matrix substrate according to the first embodiment of the present invention, and FIG. 2B is a cross-sectional view taken along the line AA in FIG. The active matrix substrate includes a gate wiring 21, a data wiring 22, a driving element 23, a drain electrode 24, an auxiliary capacitance electrode 25, a gate insulating film 26, an insulating substrate 27, a contact hole 28, and an interlayer insulating film 29. Reflection picture element electrode 30 and transmission picture element electrode 3
1 is provided.

The auxiliary capacitance electrode 25 is electrically connected to the drain electrode 24 and overlaps with the gate wiring 21 via the gate insulating film 26 to form an auxiliary capacitance. The contact hole 28 is provided in the interlayer insulating film 29 to connect the transmission picture element electrode 31 and the auxiliary capacitance electrode 25.

This active matrix substrate is provided with a reflection picture element electrode 30 and a transmission picture element electrode 31 in one picture element, and a reflection picture element for reflecting external light in one picture element. The pixel electrode 30 and the transmissive picture element electrode 31 that transmits light of the backlight are formed. Here, FIG.
In (b), the surface shape of the reflective picture element electrode 30 is shown as a plane, but the surface shape may be made uneven to improve the reflection characteristics. Further, the pixel electrode is replaced with the reflective pixel electrode 3.
Although it is divided into 0 and the transmission picture element electrode 31, a semi-transmission electrode may be used without division.

The transmission state of light in the reflection mode and the transmission mode in the liquid crystal display device of the first embodiment will be described with reference to FIGS. FIG. 3A shows a case of a dark display in which no voltage is applied to the liquid crystal layer in the reflection mode, and FIG. 3B shows a case of a white display in which a voltage is applied to the liquid crystal layer in the reflection mode. . FIG. 4A shows a case of dark display in which no voltage is applied to the liquid crystal layer in the transmission mode, and FIG.
Indicates a white display in which a voltage is applied to the liquid crystal layer in the transmission mode.

The dark display in the reflection mode will be described with reference to FIG. The incident light entering from the surface of the polarizing plate 6 from above in FIG. 3A becomes linearly polarized light whose polarization axis coincides with the transmission axis of the polarizing plate after passing through the polarizing plate 6 and is incident on the λ / 2 plate 11. . The λ / 2 plate 11 is disposed so that the transmission axis direction of the polarizing plate 6 and the slow axis direction of the λ / 2 plate 11 are at 15 degrees. Becomes a linearly polarized light having a polarization direction of 30 degrees with respect to the slow axis direction of the λ / 2 plate 11 with respect to the transmission axis direction of the λ / 2 plate 11 and enters the λ / 4 plate 7.

The λ / 4 plate 7 is set so that the slow axis direction of the λ / 4 plate 7 is 75 degrees with respect to the transmission axis direction of the polarizing plate 6 with respect to the slow axis direction of the λ / 2 plate 11. Are located. That is, the slow axis direction of the λ / 4 plate 7 is arranged to be 45 degrees with respect to the polarization direction of the linearly polarized light that has passed through the λ / 2 plate 11, and the light that has passed through the λ / 4 plate 7 Becomes circularly polarized light.

When no electric field is applied to the liquid crystal layer 5,
In the liquid crystal layer 5 using a liquid crystal material exhibiting a negative dielectric anisotropy, liquid crystal molecules are oriented almost perpendicular to the substrate surface, and the liquid crystal layer 5 has a very small refractive index anisotropy with respect to incident light. The phase difference caused by the transmission of light through the liquid crystal layer 5 is almost zero. Therefore, the circularly-polarized light beam that has passed through the λ / 4 plate 7 passes through the liquid crystal layer 5 without substantially breaking the circularly-polarized light, and is reflected by the reflective electrode 3 on one substrate 1.

The reflected light becomes circularly polarized light whose rotation direction is reversed, passes through the λ / 4 plate 7, becomes linearly polarized light orthogonal to the time when the λ / 4 plate 7 is incident, and is incident on the λ / 2 plate 11. λ
The linearly polarized light that has passed through the / 2 plate 11 is linearly polarized light in a direction orthogonal to the transmission axis of the polarizing plate 6, and is absorbed by the polarizing plate 6 and is not transmitted. Thus, when no voltage is applied to the liquid crystal layer 5, a dark display is obtained.

Next, white display in the reflection mode will be described with reference to FIG. FIG. 3B shows a case in which a voltage is applied to the liquid crystal layer 5, and FIG.
And the description is omitted.

When a voltage is applied to the liquid crystal layer 5, the liquid crystal molecules oriented vertically from the substrate surface are slightly inclined in the horizontal direction with respect to the substrate surface, and the circularly polarized light from the λ / 4 plate 7 incident on the liquid crystal layer 5. Becomes elliptically polarized light due to the birefringence of the liquid crystal molecules. Thereafter, the light does not become linearly polarized light orthogonal to the transmission axis of the polarizing plate 6 but passes through the polarizing plate 6 to some extent. In this manner, by adjusting the voltage applied to the liquid crystal layer, the amount of light that can be transmitted through the polarizing plate 6 after being reflected can be adjusted, and gradation display can be performed.

When a voltage is applied from the reflective electrode 3 and the counter electrode 4 to the liquid crystal layer 5 to change the alignment state of the liquid crystal molecules so that the phase difference of the liquid crystal layer 5 becomes a 条件 wavelength condition, λ /
The circularly polarized light after passing through the four plates 7 becomes linearly polarized light orthogonal to the transmission axis of the polarizing plate 6 when passing through the liquid crystal layer 5 and reaching the reflective electrode 3, and passes through the liquid crystal layer 5 again and becomes circularly polarized light. After that, the light passes through the λ / 4 plate 7 and the λ / 2 plate 11, becomes linearly polarized light parallel to the transmission axis of the polarizing plate 6, and the reflected light passing through the polarizing plate 6 is maximized.

FIG. 3B shows the retardation condition of the liquid crystal layer 5 in which the light reflected by the reflective electrode 3 passes through the polarizer 6 most, and the transmission axis of the polarizer 6 on the reflective electrode 3. It is linearly polarized light in a direction orthogonal to.

Therefore, when no voltage is applied to the liquid crystal layer 5, a dark display is obtained with almost no birefringence in the liquid crystal layer 5, and when a voltage is applied to the liquid crystal layer 5, the light transmittance is reduced by the applied voltage. It changes and gray scale display becomes possible.

The dark display in the transmission mode will be described with reference to FIG. The light emitted from the lower side of FIG. 4A by a light source (not shown) passes through the polarizing plate 9 and becomes linearly polarized light that matches the transmission axis of the polarizing plate 9.

The λ / 2 plate 12 is oriented such that the transmission axis direction of the polarizing plate 9 and the slow axis direction of the λ / 2 plate 11 are at 15 degrees, and the λ / 2 plate 11 is The light passing through the λ / 2 plate 12 is disposed orthogonally to the transmission axis direction of the polarizing plate 9 with the slow axis direction of the λ / 2 plate 12 interposed therebetween.
The light becomes linearly polarized light having a polarization direction of 0 degrees and is incident on the λ / 4 plate 10.

The λ / 4 plate 10 is located between the λ / 2 plate 12 and the slow axis direction of the λ / 2 plate 12 with respect to the transmission axis direction of the polarizing plate 9.
Are arranged such that the slow axis direction is 75 degrees. That is, the slow axis direction of the λ / 4 plate 10 is arranged to be 45 degrees with respect to the polarization direction of the linearly polarized light that has passed through the λ / 2 plate 12, and the light that has passed through the λ / 4 plate 10 Becomes circularly polarized light.

When no electric field is generated in the liquid crystal layer 5,
In the liquid crystal layer 5 using a liquid crystal material exhibiting a negative dielectric anisotropy, liquid crystal molecules are oriented almost perpendicular to the substrate surface, and the liquid crystal layer 5 has a very small refractive index anisotropy with respect to incident light. The phase difference caused by the light passing through the liquid crystal layer 5 is almost zero. Therefore, the circularly polarized light emitted from the λ / 4 plate 10 passes through the liquid crystal layer 5 without breaking the circularly polarized light and enters the λ / 4 plate 7.

The slow axis direction of the λ / 4 plate 10 and the slow axis direction of the λ / 4 plate 7 are orthogonal to each other, and the circularly polarized light incident on the λ / 4 plate 7 The light becomes linearly polarized light in the orthogonal direction, and is incident on the λ / 2 plate 11. The linearly polarized light that has passed through the λ / 2 plate 11 is linearly polarized light in a direction orthogonal to the transmission axis of the polarizing plate 6, and is absorbed by the polarizing plate 6 and not transmitted. Thus, when no voltage is applied to the liquid crystal layer 5, a dark display is obtained.

Next, the bright display in the transmission mode will be described with reference to FIG. FIG. 4B shows a case where a voltage is applied to the liquid crystal layer, and FIG. 4A shows a state until light passes through the λ / 4 plate 10.
And the description is omitted.

When a voltage is applied to the liquid crystal layer 5, the liquid crystal molecules oriented vertically from the substrate surface are slightly inclined in the horizontal direction with respect to the substrate surface, and the circularly polarized light from the λ / 4 plate 10 incident on the liquid crystal layer 5. Becomes elliptically polarized light due to birefringence of liquid crystal molecules, and λ / 4
After passing through the plate 7 and the λ / 2 plate 11, the light does not become linearly polarized light orthogonal to the transmission axis of the polarizing plate 6 but passes through the polarizing plate 6 to some extent. In this manner, by adjusting the voltage applied to the liquid crystal layer, the amount of light that can be transmitted through the polarizing plate 6 after being reflected can be adjusted, and gradation display can be performed.

When a voltage is applied from the reflective electrode 3 and the counter electrode 4 to the liquid crystal layer 5 to change the alignment state of the liquid crystal molecules so that the phase difference of the liquid crystal layer 5 becomes a half wavelength condition, λ /
The circularly polarized light after passing through the four plates 7 becomes linearly polarized light at a half point of the cell thickness of the liquid crystal layer 5 and becomes circularly polarized light when passing through the remaining liquid crystal layer 5. The circularly polarized light emitted from the liquid crystal layer 5 is λ / 4
After passing through the plate 7 and the λ / 2 plate 11, the light becomes linearly polarized light parallel to the transmission axis of the polarizing plate 6, and the reflected light passing through the polarizing plate 6 becomes maximum.

FIG. 4B shows the retardation condition of the liquid crystal layer 5 in which the light passing through the polarizing plate 9 passes through the polarizing plate 6 the most. Therefore, when a voltage is not applied to the liquid crystal layer 5, the liquid crystal layer 5 has almost no birefringence and a dark display is obtained. Key display becomes possible.

Here, the phase difference of the liquid crystal layer 5 having the maximum reflectance in the bright state in the reflection mode is λ / 4, and the phase difference of the liquid crystal layer 5 having the maximum transmittance in the bright state of the transmission mode is λ / 4. λ /
2, when the thickness of the liquid crystal layer in the region used as the reflection mode is equal to the thickness of the liquid crystal layer in the region used as the transmission mode, the phase difference between the liquid crystal layer 5 in the region used as the reflection mode is λ / 4, The phase difference of the liquid crystal layer 5 in the region used as the above cannot satisfy the phase difference of λ / 2 at the same time.

That is, when gradation display is performed by changing the phase difference of the liquid crystal layer 5 in the region used as the reflection mode from 0 to λ / 4, the phase difference of the liquid crystal layer 5 in the region used as the transmission mode is also 0. Λ to λ / 4, the transmission mode cannot use light efficiently.

Therefore, the thickness of the liquid crystal layer in the region used as the reflection mode and the thickness of the liquid crystal layer in the region used as the transmission mode are changed, or the voltage applied to the liquid crystal layer in the region used as the reflection mode and the liquid crystal layer in the region used as the transmission mode are changed. By changing, the light can be efficiently used in both the reflection mode and the transmission mode. Here, when changing the thickness of the liquid crystal layer in the area used as the reflection mode and the thickness of the liquid crystal layer in the area used as the transmission mode, the thickness of the liquid crystal layer in the area used as the transmission mode is 2 times the thickness of the liquid crystal layer in the area used as the reflection mode. If it is doubled, the liquid crystal layer 5 in the region used as the reflection mode
Of the liquid crystal layer 5 in the region used as the transmission mode can be simultaneously satisfied with the phase difference of λ / 2, but the thickness of the liquid crystal layer in the region used as the transmission mode is used as the reflection mode. Even if the thickness of the liquid crystal layer in the region used as the transmission mode is not set to twice the thickness of the liquid crystal layer in the region, the thickness of the liquid crystal layer in the region used as the reflection mode is set to 2 times the thickness of the liquid crystal layer in the region used as the reflection mode.
By making the thickness of the liquid crystal layer in the region used as the transmission mode larger than the thickness of the liquid crystal layer in the region used as the reflection mode within a range not exceeding twice, light use efficiency is improved.

In the first embodiment, the slow axis of the λ / 4 plate 10 is λ
The slow axis of the λ / 2 plate 12 is orthogonal to the slow axis of the λ / 2 plate 11, and the transmission axis of the polarizing plate 6 is orthogonal to the slow axis of the λ / 2 plate 11. Is set so as to be orthogonal to the transmission axis, but linearly polarized light that has passed through the polarizing plate 9 in a state where there is no retardation in the liquid crystal layer in the transmission mode is
If linearly polarized light perpendicular to the transmission axis of the polarizing plate 6 is incident on the polarizing plate 6, dark display can be achieved.

That is, the angle between the transmission axis of the polarizing plate 6 and the slow axis of the λ / 4 plate 7 is equal to the transmission axis of the polarizing plate 6 and the λ / 2 plate 1.
Assuming that the angle between the first axis and the slow axis is α, approximately (2α +
45) At each angle, the angle between the transmission axis of the polarizing plate 9 and the slow axis of the λ / 4 plate 10 is α, and the angle between the transmission axis of the polarizing plate 9 and the slow axis of the λ / 2 plate 12 is α. If you do, approximately (2α + 45)
In this case, the linearly-polarized light that has been installed at an angle and that has passed through the polarizing plate 9 in a state where there is no retardation in the liquid crystal layer in the transmission mode enters the polarizing plate 6 as linearly-polarized light perpendicular to the transmission axis of the polarizing plate 6. For example, the slow axis of the λ / 4 plate 10 is λ /
Even if it is not orthogonal to the slow axis of the four plates 7, the slow axis of the λ / 2 plate 12 is not orthogonal to the slow axis of the λ / 2 plate 11, and the transmission axis of the polarizing plate 6 is Even if the liquid crystal layer 5 is not perpendicular to the transmission axis of the polarizing plate 9, when no voltage is applied to the liquid crystal layer 5, the liquid crystal layer 5 has almost no birefringence and a dark display is obtained.
When a voltage is applied to the device, the light transmittance changes according to the applied voltage, and a gray scale display is possible.

Here, the λ / 4 plates 7, 10 and the λ / 2 plate 1
Since the refractive indices of the birefringent materials 1 and 12 for both ordinary light and extraordinary light strongly depend on the wavelength, the phase delay accumulated in the wave plate having a specific thickness also depends on the wavelength. . In other words, providing a phase delay of λ / 4 to the linear polarization plane of the incident light can be completely achieved only when a single-wavelength light beam having a specified wavelength is incident. Therefore, due to the wavelength dependence of the refractive index anisotropy of the birefringent materials constituting the λ / 4 plates 7 and 10, the light is transmitted without being shielded by the polarizing plate 6 in a wavelength range where the phase delay of λ / 4 cannot be achieved. Although light is generated and coloring occurs in dark display, the λ / 4 plate 7, the λ / 2 plate 11,
By combining the / 4 plate 10 and the λ / 2 plate 12, λ /
The wavelength dependence of the refractive index anisotropy of the birefringent materials constituting the four plates 7 and 10 can be offset to some extent, and the λ / 4 condition can be satisfied in a relatively wide wavelength band.

Therefore, the coloring of the dark display in the reflection mode can be improved as compared with the first embodiment. Of course, the coloring of the dark display in the transmission mode is also performed such that the slow axis of the λ / 4 plate 10 is orthogonal to the slow axis of the λ / 4 plate 7 and the slow axis of the λ / 2 plate 12 is the λ / 2 plate. It is improved even if it is not orthogonal to the eleven slow axes. In the first embodiment, α = 15 degrees.
Can be changed by changing .alpha., .Alpha. May be changed according to the desired color. Further, the coloring of the dark display in the transmission mode is deteriorated, but λ / 2
It is also possible to omit the plate 12 to improve cost performance. However, in the transmission mode, the λ / 4 plate 1 is set so that the linearly polarized light that has passed through the polarizing plate 9 in a state where there is no retardation in the liquid crystal layer enters the polarizing plate 6 as linearly polarized light perpendicular to the transmission axis of the polarizing plate 6.
It is necessary to set a slow axis of 0 and a transmission axis of the polarizing plate 9.

Here, the slow axis of the λ / 2 plate 12 is set so that the slow axis of the λ / 4 plate 10 is orthogonal to the slow axis of the λ / 4 plate 7. And the polarizing plate 6
Is set so as to be orthogonal to the transmission axis of the polarizing plate 9, the wavelength dependence of the refractive index anisotropy of the λ / 4 plate 10 in the transmission mode is reduced. Can be offset by the wavelength dependency of the anisotropy, and the λ / 2 plate 1
2 can be offset by the wavelength dependence of the refractive index anisotropy of the λ / 2 plate 11, and the coloring of dark display can be further improved.

Further, in order to improve the viewing angle characteristics of the liquid crystal layer 5, another retardation plate is provided at least between the polarizing plate 6 and the liquid crystal layer 5 and between the polarizing plate 9 and the liquid crystal layer 5. Good display is realized in a wide viewing angle range. Further, in the first embodiment, the vertically aligned liquid crystal is used for the liquid crystal layer 5. However, when the orientation of the liquid crystal molecules near the substrate surface has a certain tilt angle with respect to the vertical direction of the substrate surface, the liquid crystal layer 5 may be used. When no voltage is applied to the polarizing plate, the retardation does not completely become 0, and when the retardation of γ remains in the reflection mode, the polarizing plate 6 is compensated for the retardation and approaches the zero.
A better dark display can be obtained by providing another retardation plate between at least one of between the liquid crystal layer 5 and at least one between the polarizing plate 9 and the liquid crystal layer 5.

When the retardation of γ remains in the reflection mode in the liquid crystal layer in which the liquid crystal molecules are oriented substantially in the direction perpendicular to the substrate surface, instead of the λ / 4 plate 7,
A retardation plate having a retardation of (λ / 4−γ) may be provided.

In the reflection mode, elliptically polarized light is incident on the liquid crystal layer, which is shifted from the circularly polarized light by the remaining retardation of the liquid crystal layer. The light passes through the liquid crystal layer and becomes circularly polarized light in a region having a reflection function, and is reflected and becomes circularly polarized light whose rotation direction is reversed. When the light passes through the liquid crystal layer and exits from the liquid crystal layer, the light becomes elliptically polarized light deviated from circularly polarized light. The elliptically polarized light at this time is
At the time of incidence, the phase is shifted by 90 degrees. After passing through the phase difference plate, the light becomes linearly polarized light orthogonal to the transmission axis of the polarizing plate 6.

When the reflection type display is mainly used, for example, when the reflection picture element electrode is larger than the transmission picture element electrode, the λ / 4 plate 10 used for transmission mode display may be left as it is. Therefore, even when the retardation remaining in the liquid crystal layer in a state where the liquid crystal molecules are oriented in the direction perpendicular to the substrate surface cannot be ignored, a display having a high contrast in the reflection mode can be obtained by arranging the retardation plate in consideration of the retardation. Can be realized.

Further, when the retardation of 液晶 remains in the liquid crystal layer in the reflection mode and △ in the transmission mode,
A phase difference plate having a retardation of (λ / 4−γ) in place of the / 4 plate 7 and (λ / 4− (△ −) in place of the λ / 4 plate 10
What is necessary is just to arrange | position the retardation film which has the retardation of (gamma))).

In the transmission mode in which the display is performed by the transmitted light in the region having the transmission function, in a state where the liquid crystal molecules are oriented in the direction perpendicular to the substrate surface, when the liquid crystal layer is emitted, the ellipse has the same state as the emitted light in the reflection mode when emitted from the liquid crystal layer. (Λ / 4-
A retardation plate having a retardation of (△ -γ)) is set, and the elliptically polarized light having the retardation is set to the above (λ / 4−).
γ) is incident on the retardation plate having the retardation, and when passing through the retardation plate having the retardation of (λ / 4−γ), the light becomes linearly polarized light orthogonal to the transmission axis of the polarizing plate 6 and light leakage occurs. And a dark display with less noise.

Therefore, even when the retardation remaining in the liquid crystal layer in a state where the liquid crystal molecules are oriented in the direction perpendicular to the substrate surface cannot be ignored, the contrast in the reflection mode can be obtained by arranging the retardation plate in consideration of the retardation. Display can be realized.

Further, in the first embodiment, the liquid crystal layer 5 is formed of a vertically oriented liquid crystal, but a display can be performed on the same principle by using a parallel oriented liquid crystal. However, when the parallel alignment liquid crystal is used, the retardation of the liquid crystal layer 5 decreases as the voltage is applied. However, even when the liquid crystal molecules other than the vicinity of the substrate are substantially oriented in the vertical direction of the substrate surface when the voltage is applied, the liquid crystal molecules near the substrate are not affected. Is hardly moved by an electric field, so that residual retardation occurs due to liquid crystal molecules near the substrate. Therefore, when the parallel alignment liquid crystal is used as compared with the case where the vertical alignment liquid crystal is used, the black level floats at the time of dark display due to the influence of the residual retardation, and the contrast is reduced.
Therefore, in order to display the same black level as vertical alignment liquid crystal using parallel alignment liquid crystal, liquid crystal molecules are placed on upper and lower substrates so as to cancel residual retardation due to liquid crystal molecules near each of the upper and lower substrates so as to compensate for residual retardation. Or a retardation plate needs to be added.

FIG. 5 shows the transmission region of this embodiment.
The slow axes of the λ / 4 plate 10 and the λ / 4 plate 7 are set to be parallel, and λ / 2
The case where the slow axes of the plate 11 and the λ / 2 plate 12 are parallel and the case where the slow axes of the λ / 4 plate 10 and the λ / 4 plate 7 are parallel and the λ / 2 plate is not provided as a comparative example. FIG. 6 is a diagram illustrating a relationship between the wavelength of light and the transmittance during black display. Therefore, as shown in FIG. 5, by providing the λ / 2 plate, it is possible to obtain a display with little light leakage in black display.

FIG. 6 shows the transmission region of this embodiment.
The slow axes of the λ / 4 plate 10 and the λ / 4 plate 7 are set to be parallel, and λ / 2
When the slow axes of the plate 11 and the λ / 2 plate 12 are parallel,
When the slow axes of the / 4 plate 10 and the λ / 4 plate 7 are orthogonal and the slow axes of the λ / 2 plate 11 and the λ / 2 plate 12 are orthogonal, the wavelength and transmission of light during black display It is a figure which shows the relationship of a rate. Therefore, as shown in FIG. 6, by arranging the λ / 4 plate and the λ / 2 plate at right angles, it is possible to obtain a display with little light leakage in black display.

[0072]

According to the liquid crystal display device of the first aspect of the present invention, in the reflection mode, there is no variation in the polarization state in a wide wavelength band, and almost circular polarization can be achieved.
For this reason, coloring in the reflection mode of dark display can be improved. According to the second aspect of the present invention, the wavelength dependence of the refractive index anisotropy of the first retardation plate can be optimally compensated.

According to the third aspect of the present invention, in the transmission mode, there is no variation in the polarization state in a wide wavelength band, and almost circular polarization can be achieved. For this reason, coloring can be improved not only in the reflection mode but also in the transmission mode of dark display, and a good black display is realized even when both the reflection mode and the transmission mode are used. According to the invention of claim 4, the wavelength dependence of the refractive index anisotropy of the second retardation plate can be optimally compensated.

According to the fifth aspect of the invention, by using a vertically aligned liquid crystal material having a negative dielectric anisotropy for the liquid crystal layer,
Since the state where the retardation of the liquid crystal layer is almost 0 is realized, the dark state becomes darker, and the contrast is increased. According to the invention of claim 6, in normally black (hereinafter referred to as NB), a change in the contrast ratio due to a change in the cell gap hardly occurs, and a certain margin for the cell gap control can be secured in terms of productivity.

[Brief description of the drawings]

FIG. 1 is a schematic cross-sectional view of a liquid crystal display device according to a first embodiment of the present invention.

FIG. 2 is a plan view of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 3 is a diagram illustrating a light transmission state in a reflection region of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 4 is a diagram illustrating a light transmission state in a transmission region of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 5 is a diagram showing the relationship between the wavelength of light and transmittance when black display is performed in a transmission region.

FIG. 6 is a diagram showing the relationship between the wavelength of light and transmittance when black display is performed in a transmission region.

[Explanation of symbols]

 1, 2 substrate 3 reflective electrode 4 counter electrode 5 liquid crystal layer 6, 9 polarizing plate 7, 10 λ / 4 plate 8 transparent electrode 11, 12 λ / 2 plate

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shogo Fujioka 22-22 Nagaikecho, Abeno-ku, Osaka-shi, Osaka F-term (in reference) 2H091 FA08X FA08Z FA11X FA11Z FA14Y FA15Y FD06 GA03 GA06 GA11 KA02 LA03 LA16 LA17

Claims (7)

[Claims] A first substrate on which a region having a reflection function and a region having a transmission function are formed; and a second substrate on which a counter electrode is formed, and a liquid crystal layer is interposed between the one substrate and the other substrate. In the sandwiched liquid crystal display device, a first polarizing unit provided on a surface of the other substrate opposite to the liquid crystal layer, and a second polarizing unit provided on a surface of the one substrate opposite to the liquid crystal layer. A polarizing means; a first retardation plate provided between the first polarizing means and the liquid crystal layer, for converting linearly polarized light from the first polarizing means to circularly polarized light; and the second polarizing means. And a second retardation plate provided between the first polarizing means and the liquid crystal layer, the second retardation plate being configured to make the linearly polarized light from the second polarizing means circularly polarized light, and provided between the first polarizing means and the liquid crystal layer. A third retardation plate for compensating for the wavelength dependence of the refractive index anisotropy of the first retardation plate; The liquid crystal display device characterized in that it comprises. 2. The third retardation plate disposed between the first polarizing means and the first retardation plate is a λ / 2 plate,
When the angle between the transmission axis of the first polarizing means and the slow axis of the third retardation plate is α, the transmission axis of the first polarizing means and the slow axis of the first retardation plate Angle with 2α + 4
The liquid crystal display device according to claim 1, wherein the angle is 5 degrees. 3. A fourth retardation plate provided between the second polarizing means and the liquid crystal layer, the fourth retardation plate compensating for the wavelength dependence of the refractive index anisotropy of the second retardation plate. The liquid crystal display device according to claim 1 or 2, wherein: 4. The fourth retardation plate disposed between the second polarizing plate and the second retardation plate is a λ / 2 plate, and the transmission axis of the second polarizing means and the fourth retardation plate are connected to each other. When the angle between the retardation plate and the slow axis of the second retardation plate is α, the angle between the transmission axis of the second polarizing means and the slow axis of the second retardation plate is 2α + 45.
The liquid crystal display device according to claim 1, wherein the liquid crystal display device has a degree. 5. The transmission axis of said first polarizing means and said second axis.
Are perpendicular to the transmission axis of the polarization means, the slow axes of the first and second retardation plates are perpendicular to each other, and the third and fourth retardation plates are orthogonal to each other. The liquid crystal display device according to claim 3, wherein the slow axis is orthogonal to the slow axis. 6. The liquid crystal display device according to claim 1, wherein the liquid crystal layer is a vertical alignment liquid crystal material having a negative dielectric anisotropy. 7. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is set to a normally black display mode.