JP3410666B2 - 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 reflective type and a transmissive type used in office automation equipment such as word processors and personal computers, portable information equipment such as electronic notebooks, and camera integrated VTRs equipped with a liquid crystal monitor. And a liquid crystal display device having both.

[0002]

2. Description of the Related Art A liquid crystal display, unlike a CRT (CRT) or an EL (electroluminescence), does not emit light by itself. Therefore, a transmissive liquid crystal display device is used in which a backlight is installed on the back surface of a liquid crystal display element to illuminate it. ing. However, since the backlight usually consumes 50% or more of the total power consumption of a liquid crystal display, a reflector is installed in place of the backlight in portable information devices that are often used outdoors or always carried around, and ambient light is used. A reflective liquid crystal display device that displays only by itself has also been realized.

As a display mode used in the reflection type liquid crystal display device, a polarizing plate such as a TN (twisted nematic) mode or an STN (super twisted nematic) mode, which is widely used in the transmission type at present, is used. A phase transition type guest-host mode capable of realizing a bright display without using a plate has been actively developed in recent years, and is disclosed in, for example, Japanese Patent Laid-Open No. 4-75022.

[0004]

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

Further, in the case of a liquid crystal display device having parallel alignment or twist alignment, 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 liquid crystal molecules near the alignment film surface are The birefringence of the liquid crystal layer is far from 0 because it is not perpendicular to the substrate even when a voltage is applied. In the display mode in which black display is performed when a voltage is applied, sufficient black is displayed due to the birefringence of the liquid crystal layer. It is not possible to obtain sufficient contrast.

It is hard to say that TN mode and STN mode liquid crystal display devices have sufficient display quality in terms of brightness and contrast at present, and further improvement in display quality such as higher brightness and contrast is required. ing. Also,
The reflective liquid crystal display device has a drawback that the reflected light used for display is reduced and the visibility is extremely deteriorated when the ambient light is dark. There was a problem that the visibility was reduced in extremely bright sunny weather.

Therefore, although a display device combining the transmissive display and the reflective display has been developed, there is a problem in that in the case of black display, light leakage occurs and a sufficient black level cannot be obtained.

[0008]

SUMMARY OF THE INVENTION The present invention has one substrate having a region having a reflecting function and a region having a transmitting function, and the other substrate having a counter electrode formed thereon. In a liquid crystal display device in which a liquid crystal layer is sandwiched between the other substrate, the first polarizing means provided on the surface of the other substrate opposite to the liquid crystal layer and the liquid crystal layer of the one substrate are opposite to each other. A second polarizing means provided on the surface, and a first retardation plate provided between the first polarizing means and the liquid crystal layer, and linearly polarized from the first polarizing means into circularly polarized light. A second retardation plate which is provided between the second polarizing means and the liquid crystal layer, and which makes the linearly polarized light from the second polarizing means circularly polarized; the first polarizing means; It is provided between the liquid crystal layer and the wavelength difference of the refractive index anisotropy of the first retardation plate. Third have a retardation plate, wherein the
The liquid crystal layer is a vertically aligned liquid crystal material with negative dielectric anisotropy.
Characterized in that there.

[0009]

[0010]

[0011]

[0012]

Further, characterized in that the liquid crystal display device and a display mode of normally black.

The operation of the present invention will be described below. According to the present invention , the wavelength dependence of the refractive index anisotropy generated when converting linearly polarized light into circularly polarized light can be canceled to some extent by the first retardation plate. As a result, in the reflection mode, it is possible to make circularly polarized light in a state where the dispersion of the polarization state is small in a wide wavelength band. Therefore, coloring in the reflection mode of dark display can be improved.

Further, the linearly polarized light passed through the polarizing plate, the third
Since the azimuth of the first retardation plate can be rotated by the first retardation plate, the wavelength dependence of the refractive index anisotropy of the first retardation plate can be optimally compensated. be able to. As a result, in the reflection mode, the variation in the polarization state in the wide wavelength band is further reduced, and circularly polarized light can be obtained. Therefore, coloring in the reflection mode of dark display can be improved.

In particular, when the liquid crystal layer is in the vertical alignment mode, or when the retardation remaining in the liquid crystal layer in the 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 deviated from the circularly polarized light. It is incident on the liquid crystal layer. When the light passes through the liquid crystal layer and reaches the reflection plate, there is no variation in the polarization state in a wide wavelength band and the light is circularly polarized light, so that good black display is realized in the reflection mode.

Further, by the fourth retardation plate, the wavelength dependence of the refractive index anisotropy caused by transforming linearly polarized light into circularly polarized light can be canceled to some extent. As a result, in the transmissive mode, circularly polarized light with no variation in polarization state in a wide wavelength band can be obtained. Therefore , coloring in the transmissive mode of dark display can be improved, and excellent black display can be realized even when both the reflective mode and the transmissive mode are used.

Further, the linearly polarized light passing through the polarizing plate, the fourth
Since the azimuth of the first retardation plate can be rotated by the second retardation plate, the wavelength dependence of the refractive index anisotropy of the first retardation plate can be optimally compensated. be able to. As a result, in the transmission mode, the variation of the polarization state in the wide wavelength band is further reduced, and the circularly polarized light can be obtained.

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

In the dark state, when the retardation of γ in the reflective mode and Δ in the transmissive mode remains in the liquid crystal layer, the retardation of the layers thereafter is {λ / 4.
-([Delta]-[gamma])} and shift it from the circularly polarized light to make it enter the liquid crystal layer. When it passes through the liquid crystal layer, it is in the same polarization state as the outgoing light of the reflection mode in a wide wavelength band, so when it passes through the third retardation plate, it is a linearly polarized light that is orthogonal to the transmission axis of the first polarizing means. Therefore, coloring in the transmissive mode can be improved, and excellent black display can be realized even when both the transmissive mode and the reflective mode are used.

Further, by the orthogonal slow axis of the retardation plate, the wavelength dependence of the refractive index anisotropy of the retardation plate, offset by the wavelength dependence of the refractive index anisotropy of the other phase plate Therefore, the coloring of the dark display can be improved.

Further, by using a vertical alignment liquid crystal material having negative dielectric anisotropy liquid crystal layer, and the state Ritadeshon of the liquid crystal layer is substantially 0 is achieved, since the dark state becomes darker , The contrast becomes higher.

For example, when parallel-aligned liquid crystal is used for the liquid crystal layer, even if an attempt is made to make the retardation of the liquid crystal layer zero by applying a voltage to orient the long axes of the liquid crystal molecules in the direction perpendicular to the electrodes, the residual retardation is reduced. Since it occurs, the retardation of the liquid crystal layer does not become zero. Further , in normally black (hereinafter referred to as NB), the change in the contrast ratio due to the change in the cell gap hardly occurs, and a certain margin can be provided for the cell gap control 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 voltage is applied, the applied voltage to the liquid crystal layer changes to black when the cell gap changes. On the other hand, in the NB that displays black when no voltage is applied to the liquid crystal layer and white when no voltage is applied, the applied voltage to the liquid crystal layer changes to white in response to the change in cell gap. Therefore, in the NW, since the contrast ratio changes remarkably due to the change of the cell gap, it is necessary to control the cell gap with high accuracy. In addition, since the point defect which has been a bright spot in NW becomes a black spot in NB, it is expected that the yield rate of manufacturing will be improved, and a bright spot-free high-quality display panel can be realized. From these facts as well, NB is superior to NW as a display mode of a liquid crystal display device that can be used in any environment.

[0026]

BEST MODE FOR CARRYING OUT THE INVENTION (Embodiment 1) A liquid crystal display device of Embodiment 1 will be described with reference to FIG. A on board 1
Reflective electrode 3 formed of a material having a high reflectance such as 1, Ta
And a transparent electrode 8 made of a material having high transmittance such as ITO
Is provided, the counter electrode 4 is provided on the substrate 2, and the liquid crystal layer 5 made of a liquid crystal material having a negative dielectric anisotropy is sandwiched between the counter electrode 4 and the reflective electrode 3 and the transparent electrode 8. .

Alignment films (not shown) having vertical alignment properties are formed on 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, respectively. The alignment film is subjected to an alignment treatment such as rubbing. For this, the alignment may be regulated by photo-alignment, electrode shape, etc. without using rubbing. The liquid crystal molecules of the liquid crystal layer 5 have a tilt angle of approximately 0 degrees or approximately 0.1 degrees to 5 degrees with respect to the vertical direction of the substrate surface by an alignment treatment such as rubbing on a vertical alignment film.

Here, the reflection electrode 3 is used as an electrode for applying a voltage to the liquid crystal layer, but the reflection electrode is not used as an electrode but is used as a reflection plate, and the transparent electrode 8 is extended to above the reflection plate to form a reflection region. It may be an electrode for applying a voltage to the liquid crystal layer 5 in FIG. As the liquid crystal material of the liquid crystal layer 5, the first embodiment
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 the λ / 4 plate 10 on the surface opposite to the side where the transparent electrode 8 is formed.
Are arranged, 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.

On the surface of the λ / 4 plate 7 opposite to the substrate 2, λ /
2 plates 11 are provided on the surface of the λ / 4 plate 10 opposite to the substrate 1 by λ
/ 2 plates 12 are provided, 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 λ / 2 plate 12 has a λ / 2 plate 11 so that the λ / 2 plate 12 has a lagging angle of 60 ° with respect to the slow axis of 10
It is set to be orthogonal to the slow axis of.

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

FIG. 2A shows a schematic plan view of the active matrix substrate of Embodiment 1 of the present invention, and FIG. 2B shows a sectional view taken along the line AA of FIG. 2A. The active matrix substrate includes the gate wiring 21, the data wiring 22, the driving element 23, the drain electrode 24, the auxiliary capacitance electrode 25, the gate insulating film 26, the insulating substrate 27, the contact hole 28, and the interlayer insulating film 29. Reflecting pixel electrode 30 and transmitting pixel electrode 3
1 is provided.

The auxiliary capacitance electrode 25 is electrically connected to the drain electrode 24 and overlaps with the gate line 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 pixel electrode 31 and the auxiliary capacitance electrode 25.

This active matrix substrate has a reflective picture element electrode 30 and a transmissive picture element electrode 31 in one picture element, and a reflective picture element that reflects light from the outside is provided in one picture element. An elementary electrode 30 portion and a transmitting picture element electrode 31 portion that transmits the light of the backlight are formed. Here, FIG.
Although the surface shape of the reflective pixel electrode 30 is shown as a flat surface in (b), the surface shape may be uneven in order to improve the reflection characteristics. In addition, the pixel electrode is used as a 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. 3 and 4. FIG. 3A shows a case of dark display in which no voltage is applied to the reflection mode liquid crystal layer, and FIG. 3B shows a case of white display in which a voltage is applied to the reflection mode liquid crystal layer. . Further, 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.
Shows the case of white display in which a voltage is applied to the liquid crystal layer in the transmission mode.

Dark display in the reflection mode will be described with reference to FIG. Incident light entering from the surface of the polarizing plate 6 from the upper side of FIG. 3A becomes linearly polarized light whose polarization axis matches 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 arranged so that the transmission axis direction of the polarizing plate 6 and the slow axis direction of the λ / 2 plate 11 are 15 degrees, and the light passing through the λ / 2 plate 11 is polarized plate 6. The linearly polarized light having a polarization direction of 30 degrees is sandwiched in the slow axis direction of the λ / 2 plate 11 with respect to the transmission axis direction of and is incident on the λ / 4 plate 7.

The λ / 4 plate 7 is arranged 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 the slow axis direction of the λ / 2 plate 11 interposed therebetween. It is arranged. In other words, the slow axis direction of the λ / 4 plate 7 is arranged at 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 passing through the λ / 4 plate 7 is arranged. Becomes circularly polarized.

When no electric field is applied to the liquid crystal layer 5,
In the liquid crystal layer 5 made of a liquid crystal material exhibiting a negative dielectric anisotropy, liquid crystal molecules are aligned substantially vertically from the substrate surface, and the refractive index anisotropy of the liquid crystal layer 5 with respect to incident light is extremely small. The phase difference caused by the light passing through the liquid crystal layer 5 is almost zero. Therefore, the circularly polarized light beam that has passed through the λ / 4 plate 7 is transmitted through the liquid crystal layer 5 without substantially degrading the circularly polarized light, and is reflected by the reflective electrode 3 on one of the substrates 1.

The reflected light beam becomes circularly polarized light whose rotation direction is reversed, passes through the λ / 4 plate 7 and becomes linearly polarized light which is orthogonal to the incident time of the λ / 4 plate 7 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 does not pass therethrough. Thus, when no voltage is applied to the liquid crystal layer 5, dark display is provided.

Next, white display in the reflection mode will be described with reference to FIG. FIG. 3B shows a case where a voltage is applied to the liquid crystal layer 5, and FIG. 3A is shown until the voltage passes through the λ / 4 plate 7.
The description is omitted because it is the same.

When a voltage is applied to the liquid crystal layer 5, the liquid crystal molecules that are vertically aligned from the substrate surface are slightly tilted in the horizontal direction with respect to the substrate surface, and the circularly polarized light from the λ / 4 plate 7 that enters the liquid crystal layer 5 is incident. Is elliptically polarized by the birefringence of the liquid crystal molecules, is reflected by the reflective electrode 3, and is further affected by the birefringence of the liquid crystal molecules in the liquid crystal layer 5, and passes through the λ / 4 plate 7 and the λ / 2 plate 11. After that, the light does not become linearly polarized light orthogonal to the transmission axis of the polarizing plate 6, and passes through the polarizing plate 6 to some extent. Thus, 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.

Further, 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 quarter wavelength condition, λ /
The circularly polarized light that has passed through the four plates 7 becomes linearly polarized light that is orthogonal to the transmission axis of the polarizing plate 6 when passing through the liquid crystal layer 5 and reaches the reflective electrode 3, and then passes through the liquid crystal layer 5 again and becomes circularly polarized light. After that, the linearly polarized light passes through the λ / 4 plate 7 and the λ / 2 plate 11 and is parallel to the transmission axis of the polarizing plate 6, and the reflected light passing through the polarizing plate 6 becomes maximum.

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

Therefore, when no voltage is applied to the liquid crystal layer 5, there is almost no birefringence in the liquid crystal layer 5 and a dark display is obtained, and when a voltage is applied to the liquid crystal layer 5, the transmittance of light is increased by the applied voltage. It is possible to change the gradation display.

Dark display in the transmissive mode will be described with reference to FIG. Light emitted from a light source (not shown) from the lower side of FIG. 4A 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 arranged such that the transmission axis direction of the polarizing plate 9 and the slow axis direction of the λ / 2 plate 11 are 15 degrees, and the λ / 2 plate 11 is in the slow axis direction. The light passing through the λ / 2 plate 12 is arranged so as to be orthogonal to each other with the slow axis direction of the λ / 2 plate 12 sandwiched with respect to the transmission axis direction of the polarizing plate 9.
It becomes a linearly polarized light having a polarization direction of 0 degree and is incident on the λ / 4 plate 10.

The λ / 4 plate 10 sandwiches the slow axis direction of the λ / 2 plate 12 with respect to the transmission axis direction of the polarizing plate 9, and the λ / 4 plate 10
Are arranged so that the slow axis direction of is at 75 degrees. That is, the slow axis direction of the λ / 4 plate 10 is arranged at 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 passing through the λ / 4 plate 10 is arranged. Becomes circularly polarized.

When no electric field is generated in the liquid crystal layer 5,
In the liquid crystal layer 5 made of a liquid crystal material exhibiting a negative dielectric anisotropy, liquid crystal molecules are aligned substantially vertically from the substrate surface, and the refractive index anisotropy of the liquid crystal layer 5 with respect to incident light is extremely small. 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 is parallel to the transmission axis direction of the polarizing plate 9. It 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 does not pass therethrough. Thus, when no voltage is applied to the liquid crystal layer 5, dark display is provided.

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 case where light passes through the λ / 4 plate 10.
The description is omitted because it is the same.

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 circularly polarized light from the λ / 4 plate 10 incident on the liquid crystal layer 5 is incident. 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. Thus, 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.

Further, when a voltage is applied from the reflective electrode 3 and the counter electrode 4 to the liquid crystal layer 5 and the alignment state of the liquid crystal molecules is changed so that the phase difference of the liquid crystal layer 5 becomes a 1/2 wavelength condition, λ /
The circularly polarized light after passing through the four plates 7 becomes a linearly polarized light at a half point of the cell thickness of the liquid crystal layer 5, and becomes a 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, it becomes a 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 is most transmitted through the polarizing plate 6. Therefore, when no voltage is applied to the liquid crystal layer 5, there is almost no birefringence in the liquid crystal layer 5 and a dark display is obtained, and when a voltage is applied to the liquid crystal layer 5, the light transmittance changes due to the applied voltage. Key display becomes possible.

Here, the phase difference of the liquid crystal layer 5 having the maximum reflectance in the bright state of 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 /
Therefore, when 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 have the same thickness, the phase difference between the liquid crystal layer 5 in the region used as the reflection mode is λ / 4 and the transmission mode is The retardation of the liquid crystal layer 5 in the region used as can not simultaneously satisfy the retardation of λ / 2.

That is, when gradation display is performed by changing the phase difference of the liquid crystal layer 5 in the reflection mode region from 0 to λ / 4, the phase difference of the liquid crystal layer 5 in the transmission mode region is also 0. 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 liquid crystal layer in the region used as the transmission mode is 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 is changed. By changing it, 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 region used as the reflection mode and the thickness of the liquid crystal layer in the region used as the transmission mode, the thickness of the liquid crystal layer in the region used as the transmission mode is set to 2 of the thickness of the liquid crystal layer in the region used as the reflection mode. When doubled, the liquid crystal layer 5 in the region used as the reflection mode
Can simultaneously satisfy the phase difference of λ / 4 and the phase difference of the liquid crystal layer 5 in the region used as the transmission mode is 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 is not doubled, the thickness of the liquid crystal layer in the region used as the transmission mode is 2 times the thickness of the liquid crystal layer in the region used as the reflection mode.
The light utilization efficiency is improved 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 the range not exceeding twice.

In the first embodiment, the slow axis of the λ / 4 plate 10 is λ.
/ 4 plate 7, the λ / 2 plate 12 has a slow axis perpendicular to the λ / 2 plate 11, and the polarizing axis of the polarizing plate 6 has a transmission axis. Although it is set to be orthogonal to the transmission axis of, the linearly polarized light that has passed through the polarizing plate 9 in the transmission mode with no retardation in the liquid crystal layer 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 performed.

That is, the angle formed between the transmission axis of the polarizing plate 6 and the slow axis of the λ / 4 plate 7 is the transmission axis of the polarizing plate 6 and the λ / 2 plate 1.
If the angle made by the slow axis of 1 is α, then approximately (2α +
45 °, 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, about (2α + 45)
The linearly polarized light, which has been installed at a certain angle and has passed through the polarizing plate 9 in the transmission mode without retardation in the liquid crystal layer, is incident on 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 the slow axis of the λ / 2 plate 12 is not orthogonal to the slow axis of the 4 plate 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 it is not orthogonal to the transmission axis of the polarizing plate 9, when no voltage is applied to the liquid crystal layer 5, there is almost no birefringence in the liquid crystal layer 5 and a dark display is obtained.
When a voltage is applied to the display device, the transmittance of light is changed by the applied voltage, and gradation display is possible.

Here, the λ / 4 plates 7 and 10 and the λ / 2 plate 1
Since the refractive index of the birefringent materials constituting 1 and 12 for both ordinary light and extraordinary light strongly depends on the wavelength, the phase delay accumulated in the wave plate of a specific thickness also depends on the wavelength. . That is, a phase delay of λ / 4 can be completely achieved only when a light beam of a single wavelength having a specified wavelength is incident. Therefore, due to the wavelength dependence of the refractive index anisotropy of the birefringent material forming the λ / 4 plates 7 and 10, the light is transmitted without being shielded by the polarizing plate 6 in the wavelength region where the phase delay of λ / 4 cannot be achieved. Although light is generated and dark display is colored, the λ / 4 plate 7, the λ / 2 plate 11 and the λ / 4 plate 7
By combining the / 4 plate 10 and the λ / 2 plate 12, λ /
The wavelength dependence of the refractive index anisotropy of the birefringent material forming the four plates 7 and 10 can be canceled 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, even when the dark display in the transmission mode is colored, 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 slow axis of 11. In the first embodiment, α = 15 degrees, but α
Since it is possible to change the tint of the bright display by changing, the value α may be changed according to the desired tint. Moreover, although the coloration of the dark display in the transmissive mode becomes worse, λ / 2
It is also possible to omit the plate 12 and improve cost efficiency. 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 the state where the liquid crystal layer has no retardation is incident on the polarizing plate 6 as the linearly polarized light perpendicular to the transmission axis of the polarizing plate 6.
It is necessary to set the slow axis of 0 and the transmission axis of the polarizing plate 9.

Here, 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 slow axis of the λ / 2 plate 11. And the polarizing plate 6
Is set so as to be orthogonal to the transmission axis of the polarizing plate 9, so that the wavelength dependence of the refractive index anisotropy of the λ / 4 plate 10 in the transmission mode is It can be canceled out by the wavelength dependence of the refractive index anisotropy.
The wavelength dependence of the refractive index anisotropy of No. 2 can be canceled by the wavelength dependence of the refractive index anisotropy of the λ / 2 plate 11, and 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. In the first embodiment, the liquid crystal layer 5 is made of vertically aligned liquid crystal. However, when the alignment of 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 is formed. Even if no voltage is applied to the retardation plate, the retardation does not become 0 completely, and when the retardation of γ remains in the reflection mode, it is compensated for that amount and approaches 0.
By providing another retardation plate between at least one of the liquid crystal layer 5 and between the polarizing plate 9 and the liquid crystal layer 5, a better dark display can be obtained.

When the retardation of γ remains in the reflection mode in the liquid crystal layer in a state where 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 arranged.

In the reflection mode, elliptically polarized light, which is deviated from the circularly polarized light by the amount of the retardation remaining in the liquid crystal layer, is incident on 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 to become circularly polarized light with its rotation direction reversed. When the light passes through the liquid crystal layer and exits from the liquid crystal layer, it 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. When it passes through the retardation plate, it becomes linearly polarized light which is orthogonal to the transmission axis of the polarizing plate 6.

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

Furthermore, when the retardation of γ in the reflective mode and the retardation of Δ in the transmissive mode remain in the liquid crystal layer, λ
Instead of the / 4 plate 7, a retardation plate having a retardation of (λ / 4−γ), and instead of the λ / 4 plate 10 (λ / 4− (Δ−
A retardation plate having a retardation of γ)) may be arranged.

In the transmissive mode in which display is performed by the transmitted light in the region having the transmissive function, when the liquid crystal molecules are oriented in the direction perpendicular to the substrate surface, when the liquid crystal layer is emitted, an ellipse of the same state as the emitted light in the reflective mode is emitted. The above (λ / 4-
A retardation plate having a retardation of (Δ−γ)) is set, and the elliptically polarized light having the retardation is (λ / 4−).
Since it is incident on the retardation plate having the retardation of γ), when it passes through the retardation plate having the retardation of (λ / 4-γ), it becomes linearly polarized light which is orthogonal to the transmission axis of the polarizing plate 6 and leaks light. There is little dark display.

Therefore, even if the retardation remaining in the liquid crystal layer in the state where the liquid crystal molecules are oriented in the direction perpendicular to the substrate surface cannot be ignored, the retardation plate is arranged in consideration of the retardation to provide contrast in the reflection mode. High display can be realized.

Further, although the vertical alignment liquid crystal is used for the liquid crystal layer 5 in the first embodiment, it is possible to display on the same principle by using the parallel alignment liquid crystal. However, when the parallel alignment liquid crystal is used, the retardation of the liquid crystal layer 5 becomes smaller as the voltage is applied. However, even when the liquid crystal molecules other than the vicinity of the substrate are oriented substantially in the vertical direction of the substrate surface when the voltage is applied, the liquid crystal molecules near the substrate are Since it hardly moves due to an electric field, 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 effect of the residual retardation, and the contrast lowers.
Therefore, in order to display a black level similar to that of a vertically aligned liquid crystal using a parallel aligned liquid crystal, the liquid crystal molecules on the upper and lower substrates are set so as to cancel the residual retardation due to the liquid crystal molecules near the upper and lower substrates, respectively, so as to compensate the residual retardation. It is necessary to orient or to add a retardation plate.

FIG. 5 shows the transmission area of the present embodiment.
The slow axes of the λ / 4 plate 10 and the λ / 4 plate 7 are parallel, and λ / 2
In the case where the slow axes of the plate 11 and the λ / 2 plate 12 are parallel to each other, and as the comparative example, the slow axes of the λ / 4 plate 10 and the λ / 4 plate 7 are parallel to each other and the λ / 2 plate is not provided. It is a figure which shows the wavelength of light at the time of black display, and the relationship of transmittance. Therefore, as shown in FIG. 5, by providing the λ / 2 plate, it is possible to obtain a display with little light leakage during black display.

FIG. 6 shows the transmission area of the present embodiment.
The slow axes of the λ / 4 plate 10 and the λ / 4 plate 7 are 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 the transmission of light in black display are transmitted. 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 during black display.

[0072]

According to the present invention, in the reflective mode,
There is no variation in the polarization state in a wide wavelength band, and almost circularly polarized light can be obtained. Therefore, coloring in the reflection mode of dark display can be improved. Moreover , the wavelength dependence of the refractive index anisotropy of the first retardation plate can be optimally compensated.

[0073] Also, in the transmissive mode, there is no variation in the polarization state in a wide wavelength range, it can be substantially circularly polarized light. Therefore, not only in the reflective mode but also in the transmissive mode of dark display can be improved, and good black display can be realized even when both the reflective mode and the transmissive mode are used. Further , the wavelength dependence of the refractive index anisotropy of the second retardation plate can be optimally compensated.

[0074] Further, by using a vertical alignment liquid crystal material having negative dielectric anisotropy liquid crystal layer, and the state Ritadeshon of the liquid crystal layer is substantially 0 is achieved, since the dark state becomes darker , The contrast becomes higher. Further , in normally black (hereinafter referred to as NB), the change in the contrast ratio due to the change in the cell gap hardly occurs, and a certain margin can be provided for the cell gap control in terms of productivity.

[Brief description of drawings]

FIG. 1 is a schematic 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 showing a light transmission state in a reflective region of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 4 is a diagram showing 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 the transmittance when performing black display in the transmissive region.

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

[Explanation of symbols]

1, 2 substrate 3 Reflective electrode 4 Counter electrode 5 Liquid crystal layer 6, 9 Polarizer 7, 10 λ / 4 plate 8 transparent electrodes 11, 12 λ / 2 plate

Front page continuation (56) References International Publication 99/040480 (WO, A1) (58) Fields investigated (Int.Cl. ⁷ , DB name) G02F 1/1335

Claims (2)

(57) [Claims] 1. A liquid crystal layer is provided between one substrate and the other substrate, the substrate having one substrate on which a region having a reflection function and a region having a transmission function are formed and another substrate on which a counter electrode is formed. 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 which is provided between the first polarizing means and the liquid crystal layer, and which converts linearly polarized light from the first polarizing means into circularly polarized light, and the second polarizing means Is provided between the liquid crystal layer and the liquid crystal layer, and a second retardation plate that converts the linearly polarized light from the second polarizing means into circularly polarized light, and is provided between the first polarizing means and the liquid crystal layer. A third retardation plate for compensating the wavelength dependence of the refractive index anisotropy of the first retardation plate, Yes, and vertically aligned liquid crystal material wherein the liquid crystal layer has negative dielectric anisotropy
Liquid crystal display device characterized by being a fee . 2. A liquid crystal display device according to claim 1, characterized in that a display mode of a normally black liquid crystal display device.