JP3410663B2 - Liquid crystal display - Google Patents

Description

Detailed Description of the Invention

[0001]

TECHNICAL FIELD OF THE INVENTION

[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. Also,
In the case of a liquid crystal display device with parallel alignment or twist alignment, 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 do not receive a voltage. Since the liquid crystal layer is not perpendicular to the substrate, the birefringence of the liquid crystal layer is far from 0, and in the display mode in which black display is performed when a voltage is applied, sufficient black cannot be displayed due to the birefringence of the liquid crystal layer. I can't get the contrast.

It is hard to say that the liquid crystal display devices of TN mode and STN mode have sufficient display quality in terms of brightness and contrast at present, and further improvement in display quality such as higher brightness and improvement in 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 in which transmissive display and reflective display are combined 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.

[0006]

According to the present invention, there is provided one substrate in which a region having a reflection function and a transmission function is formed and another substrate in which a counter electrode is formed, and between the one substrate and the other substrate. In a liquid crystal display device in which a liquid crystal layer is sandwiched between,
A first polarizing means provided on a surface of the one substrate opposite to the liquid crystal layer; a second polarizing means provided on a surface of the other substrate opposite to the liquid crystal layer; A first retardation plate provided between a polarizing means and the liquid crystal layer, and a second retardation plate provided between the second polarizing means and the liquid crystal layer.
And a transmission axis of the first polarizing means and a transmission axis of the second polarizing means are orthogonal to each other, and a slow axis of the first retardation plate and the second position The liquid crystal layer is perpendicular to the slow axis of the retardation plate and has a negative dielectric anisotropy.
It is characterized by being an oriented liquid crystal material .

The present invention is also 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. Position the refractive index for both ordinary light and extraordinary light of the birefringent material forming the retardation plate is strongly dependent on the wavelength of light, the accumulated phase delay in the phase difference plate of a particular thickness also Wavelength Depends on. That is, in order to give a phase delay of a certain special value (for example, λ / 4) to the plane of linear polarization of incident light,
It can be completely achieved only when a single wavelength light beam having a specified wavelength is incident. Therefore, in the wavelength range where the phase delay of λ / 4 cannot be achieved due to the wavelength dependence of the refractive index anisotropy of the birefringent material forming the retardation plate, the light transmitted without being blocked by the polarization means on the emission side. Occurs, and the dark display is colored.

In the present invention, by making the slow axes of the first retardation plate and the second retardation plate orthogonal to each other, the wavelength dependence of the refractive index anisotropy of the first retardation plate can be changed to the second one. This can be canceled by the wavelength dependence of the refractive index anisotropy of the phase difference plate, and a constant phase difference can be satisfied over the entire wavelength band of light. Therefore, coloring of 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, residual retardation occurs even if the retardation of the liquid crystal layer is set to 0 by applying a voltage to orient the long axis of the liquid crystal molecules in the direction perpendicular to the electrodes. The retardation of the liquid crystal layer does not become zero.

[0011] In addition, changes in the contrast ratio due to no (hereinafter referred to as NB) Mali black in the cell gap change hardly occurs, some margin can be taken 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 voltage applied 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.

[0013]

DESCRIPTION OF THE PREFERRED EMBODIMENTS (Embodiment 1) The structure of an active matrix substrate of Embodiment 1 will be described with reference to FIG. An insulating substrate 1 such as a glass substrate is provided with a reflective electrode 3 formed of a highly reflective material such as Al and Ta and a transparent electrode 8 formed of a highly transmissive material such as ITO. A counter electrode 4 formed of a material having a high transmittance such as ITO is provided on an insulating substrate 2 such as ITO, and exhibits negative dielectric anisotropy between the counter electrode 4 and the reflective electrode 3 and the transparent electrode 8. A liquid crystal layer 5 made of a liquid crystal material is sandwiched.

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. After the alignment film is applied, at least one of them is formed. The alignment film is subjected to an alignment treatment such as rubbing. Instead of alignment treatment by rubbing, alignment may be regulated by photo-alignment, electrode shape, or the like. The liquid crystal molecules of the liquid crystal layer 5 are aligned with a tilt angle of approximately 0 ° or approximately 0.1 ° to 5 ° with respect to the vertical direction of the substrate surface by an alignment treatment such as rubbing on a vertically aligned alignment film. To be done.

Here, the reflective electrode 3 is used as an electrode for applying a voltage to the liquid crystal layer, but the reflective electrode 3 may be used as a reflective plate without being used as an electrode. In that case, the transparent electrode 8 may be extended to the region of the reflection plate, and the transparent electrode 8 may be used as an electrode for applying a voltage to the liquid crystal layer 5 in the reflection region. As the liquid crystal material of the liquid crystal layer 5, Ne = 1.5546, No =
A liquid crystal material having a refractive index anisotropy of 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.

A polarizing plate 6 is provided on the surface of the λ / 4 plate 7 opposite to the substrate 2, and a polarizing plate 9 is provided on the surface of the λ / 4 plate 10 opposite to the substrate 1, respectively. The transmission axis of 6 is λ /
4 plate 7 has a slow axis of 45 degrees and polarizing plate 9 has a transmission axis of λ
The / 4 plate 10 is set to be inclined at 45 degrees with respect to the slow axis, and the transmission axis of the polarizing plate 6 is set to be orthogonal to the transmission axis of the polarizing plate 9. In this case, the transmission axis of the polarizing plate is λ
Although it is set to 45 degrees with respect to the slow axis of the / 4 plate, the direction of the angle may be either the + direction or the-direction.

FIG. 2A is a schematic plan view of the active matrix substrate of the liquid crystal display device according to the first embodiment.
2B is a sectional view taken along line AA of FIG. The active matrix substrate includes a gate wiring 21, a data wiring 22,
Drive element 23, drain electrode 24, auxiliary capacitance electrode 25,
A gate insulating film 26, an insulating substrate 27, a contact hole 28, an interlayer insulating film 29, a reflective pixel electrode 30 and a transparent pixel electrode 31 are provided.

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

This active matrix substrate is provided with a reflective picture element electrode 30 and a transmissive picture element electrode 31 in one picture element, and a reflective picture element for reflecting light from the outside 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, in FIG. 2B, the reflective picture element electrode 3 is used.
Although the surface shape of 0 is shown as a plane, the surface shape may be uneven in order to improve the reflection characteristics. Further, although the picture element electrode is divided into the reflection picture element electrode 30 and the transmission picture element electrode 31, a semi-transmission electrode may be used without dividing the picture element electrode.

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. 3A and 3B show a case where display is performed using a reflective electrode (reflection mode), and FIG. 3A shows a case of dark display in which no voltage is applied to the vertically aligned liquid crystal layer.
(B) shows a case of white display in which a voltage is applied to the vertically aligned liquid crystal layer. Further, FIG. 4 shows a case where display is performed using a transmission electrode (transmission mode), and FIG. 4 (a) shows a case of dark display in which no voltage is applied to the vertical alignment liquid crystal layer,
FIG. 4B shows a case of white display in which a voltage is applied to the vertically aligned liquid crystal layer.

Dark display in the reflection mode will be described with reference to FIG. Incident light entering 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 / 4 plate 7. .
The λ / 4 plate 7 is arranged so that the transmission axis direction of the polarizing plate 6 and the slow axis direction of the λ / 4 plate 7 are 45 °, and λ / 4
The light passing through the plate 7 becomes circularly polarized light.

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 becomes circularly polarized light whose rotation direction is reversed, passes through the λ / 4 plate 7 and becomes linearly polarized light orthogonal to the time of incidence, and enters the polarizing plate 6. The linearly polarized light that has passed through the λ / 4 plate 7 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 incident on the liquid crystal layer 5 is incident. Is elliptically polarized due to 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. After passing through the λ / 4 plate 7, the It does not become linearly polarized light orthogonal to the transmission axis, and passes through the polarizing plate 6 somewhat. 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 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 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 light transmittance changes due to the applied voltage, resulting in gradation display. Will be possible.

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 coincides with the transmission axis of the polarizing plate 9. The λ / 4 plate 10 has a λ / 4
The plate 10 and the polarizing plate 9 are arranged so that the slow axis direction of the plate 10 and the transmission axis direction of the polarizing plate 9 are 45 degrees, and the light passing through the λ / 4 plate 10 is circularly polarized.

When no electric field is applied to the liquid crystal layer 5, the liquid crystal layer 5 made of a liquid crystal material exhibiting negative dielectric anisotropy has liquid crystal molecules aligned substantially vertically from the substrate surface, and the liquid crystal for incident light is used. The refractive index anisotropy of the layer 5 is extremely small, and 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 is
It 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 in the transmission axis direction of the polarizing plate 9. It becomes a linearly polarized light in a direction orthogonal to each other and enters the polarizing plate 6. The linearly polarized light emitted from the λ / 4 plate 7 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 transmit light. 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 is the same as FIG. 3A until the light passes through the λ / 4 plate 10, and the description thereof will be omitted.

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 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, it 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 passes through the polarizing plate 6 after being reflected can be adjusted, and gradation display is possible.

Further, by applying a voltage to the liquid crystal layer 5, the liquid crystal layer 5
When the alignment state of the liquid crystal molecules is changed so that the phase difference of is equal to 1/2 wavelength condition, the circularly polarized light after passing through the λ / 4 plate 7 becomes linearly polarized light at a point half the cell thickness of the liquid crystal layer 5. Then, when it passes through the remaining liquid crystal layer 5, it becomes circularly polarized light. Circularly polarized light emitted from the liquid crystal layer 5 passes through the λ / 4 plate 7 and is then reflected by the polarizing plate 6
The linearly polarized light is parallel to the transmission axis of, 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 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.

FIG. 5 shows a case in which the slow axes of the λ / 4 plate 7 and the λ / 4 plate 10 of the structure of this embodiment are arranged orthogonally to each other, and as a comparative example, the λ / 4 plate 7 and the λ / 4 plate. It is a figure which shows the wavelength of the light at the time of a black display, and the relationship of a transmittance | permeability when 10 slow axes are arrange | positioned in parallel. In the present embodiment, by making the slow axis of the retardation plate orthogonal to each other, it is possible to cancel the wavelength dependence of the refractive index anisotropy of the retardation plate and satisfy a constant phase difference in the entire wavelength band of light. As a result, the coloring of the dark display can be improved.

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 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. 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 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
It is possible to simultaneously satisfy the retardation of λ / 4 and the retardation of the liquid crystal layer 5 in the region used as the transmission mode of λ / 2. Even if the thickness of the liquid crystal layer in the region used as the transmission mode is not twice the thickness of the liquid crystal layer in the region used as the reflection mode, the thickness of the liquid crystal layer in the region used as the transmission mode is 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 a range not exceeding twice the thickness.

Since the refractive index of the birefringent material forming the λ / 4 plates 7 and 10 for both ordinary light and extraordinary light strongly depends on the wavelength, it is accumulated in the wave plate having a specific thickness. The phase delay introduced is also wavelength dependent. That is, λ / 4
The phase delay of (1) can be completely achieved only when a single wavelength light beam with 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. Light is generated and dark display is colored, but λ /
By setting the slow axis of the four plate 10 to be orthogonal to the slow axis of the λ / 4 plate 7 and the transmission axis of the polarizing plate 6 to be orthogonal to the transmission axis of the polarizing plate 9, In mode,
The wavelength dependence of the refractive index anisotropy of the λ / 4 plate 10 can be canceled by the wavelength dependence of the refractive index anisotropy of the λ / 4 plate 7.
The λ / 4 condition is satisfied in the entire wavelength band. Therefore, coloring of dark display can be improved.

Further, in order to improve the viewing angle characteristics of the liquid crystal layer 5, another retardation plate is provided on at least one of 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 vertical alignment 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, Even when no voltage is applied to the liquid crystal layer 5, the retardation does not completely become 0. Therefore, if the retardation of the retardation plate is adjusted by replacing the λ / 4 plate 7 in order to compensate for that, a better dark display can be obtained. .

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

If the reflective pixel electrode is larger than the transmissive pixel electrode, such as when the reflective pixel electrode is mainly used, the λ / 4 plate 10 used for the transmissive mode display 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 α in the reflection mode and β in the transmission mode remains in the liquid crystal layer, λ
In place of the / 4 plate 7, a retardation plate having a retardation of (λ / 4-α), and in place of the λ / 4 plate 10 (λ / 4- (β-
A retardation plate having a retardation of α)) 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 in the same state as the emitted light in the reflective mode is emitted. The above (λ / 4-
A retardation plate having a retardation of (β−α) is set, and the elliptically polarized light having the retardation is (λ / 4−).
Since the light enters the retardation plate having the retardation of α), when it passes through the retardation plate having the retardation of (λ / 4-α), it becomes a linearly polarized light 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, light leakage occurs at the time of dark display due to the effect of residual retardation, the black level floats, 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.

[0050]

According to the present invention, the first retardation plate and the second retardation plate
The wavelength dependence of the refractive index anisotropy of the first retardation plate is offset by the wavelength dependence of the refractive index anisotropy of the second retardation plate by orthogonalizing the slow axes of the phase retardation plates. Therefore, the λ / 4 condition is satisfied in the entire wavelength band of light, and in the liquid crystal display device having the reflection function and the transmission function, the coloring of dark display can be improved even in the transmission mode.

[0051] 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.

[0052] In addition, changes in the contrast ratio due to no (hereinafter referred to as NB) Mali black in the cell gap change hardly occurs, some margin can be taken 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 and second embodiments 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.

[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

Front page continuation (72) Inventor Yoji Yoshimura 22-22 Nagaikecho, Naganocho, Abeno-ku, Osaka-shi, Osaka Prefecture Sharp Corporation (72) Inventor Mikio Katayama 22-22, Nagaike-cho, Abeno-ku, Osaka City, Osaka Prefecture (72) ) Inventor Hiroshi Ishii 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka (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 having one substrate in which a region having a reflection function and a transmission function is formed and another substrate in which a counter electrode is formed, and a liquid crystal layer sandwiched between the one substrate and the other substrate. In the display device, a first polarization unit provided on a surface of the one substrate opposite to the liquid crystal layer, and a second polarization unit provided on a surface of the other substrate opposite to the liquid crystal layer, A first retardation plate provided between the first polarizing means and the liquid crystal layer, and a second retardation plate provided between the second polarizing means and the liquid crystal layer.
The retardation plate of the first polarizing means and the transmission axis of the second polarizing means are orthogonal to each other, and the slow axis of the first retardation plate and the second position Vertically aligned liquid crystal material in which the slow axis of the phase difference plate is orthogonal to each other and 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.