JPH10239682A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain high contrast and to make a clear display of high quality by specifying the angle between the axes of polarization of a couple of polarizers. SOLUTION: A signal electrode and a scanning electrode are connected to driving circuits respectively, and those electrodes are applied with voltages selectively by the driving circuits. According to the voltages applied to those electrode, liquid crystal switch from one stable orientation state wherein it is orientated horizontally or nearly horizontally to a substrate to the other stable aligned state so that the optical axis is changed inward on the substrate surface. The axis B of polarization of one polarizing plate is arranged almost in parallel to the optical axis (alignment direction) P in one stable aligned state of the liquid crystal and at an angle α to the axis A of polarization of the other polarizing plate clockwise in the figure. Namely, the angle α between the axes A and B of polarization is set within a range of -45 deg.<=α<=+45 deg..

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly, to a liquid crystal display device using a liquid crystal such as a ferroelectric liquid crystal, an antiferroelectric liquid crystal or an in-plane switching type liquid crystal. The present invention relates to a liquid crystal display device that performs display by using a display.

[0002]

2. Description of the Related Art A liquid crystal display device has very advantageous characteristics for a flat display device such as a thin, lightweight, low power consumption, and low driving voltage. Therefore, a laptop personal computer, a word processor, a portable terminal, a portable television, and the like. Such displays are indispensable for these information devices. Currently, ST
A display mode using N (Super Twisted Nematic), a TFT (Thin Film Transistor) and a TN (Twisted Nematic).
Nematic) is actively used in two display modes, namely, a display mode combining the two display modes.

A liquid crystal display device is an EL (Electro Luminesc).
) and a self-luminous element such as a plasma display. Therefore, conventionally, the mere use of external light does not provide sufficient luminance as a display device. Therefore, a transmissive type using a backlight has been often used. However, a reflection type display that does not use a backlight is suitable for a demand for weight reduction and thickness reduction of a laptop personal computer or a word processor, or for display on a portable terminal.

FIGS. 2 and 3 both show an embodiment of the present invention, and show the structure of a transmissive liquid crystal display device using a backlight and a structure of a reflective liquid crystal display device without a backlight, respectively. , In a cross-sectional view. Also in the conventional liquid crystal display device, as shown in these figures, two glass substrates 1 and 2 are arranged so as to face each other, and the surface of one glass substrate 1 is indium tin oxide (hereinafter referred to as “ITO”). ) Are arranged in parallel with each other, and a transparent insulating film 4 made of SiO ₂ or the like is formed thereon.

[0005] On the surface of the other glass substrate 2 facing the signal electrode 3, a plurality of transparent scanning electrodes 5 made of ITO or the like are arranged parallel to each other in a direction orthogonal to the signal electrode 3. 5 is SiO ₂ formed thereon
And the like. On each of the insulating films 4 and 6, there are formed alignment films 7 and 8 that have been subjected to a uniaxial alignment process such as a rubbing process. Alignment film 7
8 is an organic polymer film such as a polyimide film, a nylon film or a polyvinyl alcohol film, or a SiO obliquely deposited film.

As described above, the two substrates 13 and 14 each having the electrodes 3 and 5 are bonded together with the sealing agent 10 except for a part of the injection port (not shown). 7
The liquid crystal 9 is sealed in the space sandwiched by 8.

When the display area is large, spacers (not shown) are arranged so that the two substrates 13 and 14 face each other in parallel with a constant cell thickness.

Further, these liquid crystal display devices are provided with a pair of polarizing plates 11 and 12 which are arranged so as to sandwich the two substrates 13 and 14. In a conventional configuration, these paired polarizing plates are usually provided. Are arranged such that their polarization axes are orthogonal to each other.

Further, as shown in FIG. 2, in a transmission type display device, a backlight 16
However, in the reflection type display device, as shown in FIG. 3, a reflection plate 15 is provided on the substrate 14 side, and there is no backlight 16 and an external light 18 is reflected by the reflection plate 15 for display. Is performed.

The polarizing plate 12 and the reflecting plate 15 are often formed as an integral member. The backlight 16 is
It is unitized as a part of the device, and a transmission type requires a power source for a backlight, while a reflection type uses an external light 18 and therefore does not require a power source for a light source.

The advantages of the reflective liquid crystal display device are not only lighter and thinner but also lower power consumption than the transmissive liquid crystal display device. The backlight 16 occupies a very high proportion of the power consumption of the entire liquid crystal display device, and a reflective display that does not require the backlight 16 is most suitable for a laptop machine or a portable terminal device that requires battery driving.

[0012]

The reflective display is very useful, but its use requires a further reduction in power consumption. For this purpose, it is effective to use a liquid crystal having a memory effect such as a ferroelectric liquid crystal. Ferroelectric liquid crystal (NA Clark and ST Lagerwall: Appl. Phy
Since s. Lett. 36 (1980) 899.) has a memory property, display information once written can be continuously displayed without consuming power until it is rewritten or erased next time. This memory effect is a characteristic not available in the conventional nematic liquid crystal, and can further reduce power consumption. In addition, it also has excellent features such as high-speed response and wide viewing angle, so that high-quality display can be obtained.

The ferroelectric liquid crystal will be described with reference to FIG. The ferroelectric liquid crystal switches between the two states shown in FIGS. 12A and 12B at an angle 2θ, which is twice the tilt angle θ, in parallel with the cell substrate plane by applying an electric field.
In addition, 19 is a liquid crystal molecule and 20 is a spontaneous polarization. On this occasion,
Each alignment state is stable even after the electric field is removed, whereby bistable optical switching (memory effect) can be obtained.

Normally, in a transmission type display, a liquid crystal cell is sandwiched between two orthogonally or substantially orthogonally polarizing plates 11 and 12 as shown in FIG. 12 in order to maximize the contrast. The polarization directions (polarization axes) of the respective polarizing plates 11 and 12 are indicated by arrows A and B.) At this time,
A dark state can be obtained by aligning one of the uniaxial orientation states with the incident polarization axis B or the transmission polarization axis A, and a bright state can be obtained by birefringence generated in the other orientation state.

[0015] The ferroelectric liquid crystal also has a feature that a viewing angle at which a display can be stably recognized is wide. For example,
FIG. 13 shows the display principle of the conventional TN type liquid crystal 21. Since the TN liquid crystal 21 switches between a horizontal alignment state and a vertical alignment state with respect to the substrate, it is turned on and off. Thus, the effective birefringence of the liquid crystal 21 for each viewing angle greatly differs. For this reason, there is a problem that the viewing angle becomes narrow. However, in the ferroelectric liquid crystal, switching is performed between two alignment states horizontal to the substrate as shown in FIG. The liquid crystal has substantially the same effective birefringence. Therefore, inversion of contrast and the like are unlikely to occur, and the viewing angle is wide.

The ferroelectric liquid crystal having the above-described excellent characteristics is used. However, when used in a reflection type, the brightness is high because only the reflection of external light is used without using a dedicated light source such as a backlight. There is a problem that there is a shortage. The main cause is light absorption by the polarizing plate, and it is necessary to set the polarizing plate to an optimum state.

As described above, the liquid crystal cell is usually sandwiched between two orthogonal or substantially orthogonal polarizing plates in order to maximize the contrast in the transmission type. In the TN liquid crystal 21, as shown in FIG. 13 (a), a bright state occurs due to optical rotation when no electric field is applied, and in the state where an electric field is applied, the liquid crystal is vertically aligned to polarize linearly polarized light that has passed through the incident polarizer. A good dark state is obtained by shielding the light from the orthogonally-polarized polarizing plates without performing the above operation. It is necessary to completely rotate the light when no electric field is applied in order to obtain a good bright state. If this state is achieved, the light reflected by the reflector even if it is of the reflection type is again 2. When the light passes through two polarizing plates, the light only passes along each polarization axis while being rotated, and is not largely absorbed by the polarizing plate in the reflected light path. For this purpose, it is an important technique to twist the liquid crystal molecules by the same angle with respect to the orthogonal state of the polarizing plate. This can be easily achieved by attaching the cells so that the uniaxial orientation directions of the substrates are orthogonal to each other, so that a relatively high contrast can be obtained even in the case of the reflection type.

There is another reason for using an orthogonal polarizer with a TN liquid crystal. The orthogonal polarizer of FIG. 13A is a so-called normally white, which is in a bright state when no electric field is applied and is in a dark state when an electric field is applied, but is dark when no electric field is applied when a parallel polarizer is used. It is a so-called normally black which becomes a bright state when an electric field is applied. This state is shown in FIG. Normally white display is preferable for a liquid crystal display in which information is drawn on so-called white paper in a relatively similar manner to paper. Since a normally white display cannot be obtained with a TN liquid crystal, a parallel polarizing plate is not often used.

FIG. 14 is a diagram showing the configuration in FIG. 12 showing the display principle of the ferroelectric liquid crystal as viewed from the front of the substrate. However, in the actual cell, the angle of the optical axis (memory angle) θ _m
Reduces to an angle slightly smaller than the tilt angle θ after removing the electric field. As in the case of the TN liquid crystal, a reflection type ferroelectric liquid crystal has conventionally used an orthogonal polarization plate or a substantially orthogonal polarization plate due to the superiority of the transmission type orthogonal polarization plate. Regarding the alignment state of the liquid crystal molecules, in one state shown in FIG. 14, since the optical axis P coincides with one of the orthogonal polarizing plates 12, the linearly polarized light passing through the incident polarizing plate 12 is polarized by the liquid crystal. The light is shielded by the output polarizing plate 11 and a good dark state can be obtained. On the other hand, in the other state, the optical axis Q is 2
θ _m , the incident polarizer 1
The linearly polarized light that has passed through 2 is elliptically polarized by the liquid crystal, and a part of the light passes through the output polarizing plate 11 to obtain a bright state. To obtain a good bright state, it is necessary to be close to the angle of 2 [Theta] _m is 45 °.

However, in the reflection type, the light reflected by the reflection plate becomes very dark in the reflection light path because the polarization by the liquid crystal and the elliptically polarized light by the polarization plate are absorbed similarly to the incident light path. For this reason, there is a problem that high contrast cannot be obtained and the display becomes unclear.

Although there is no memory effect, an antiferroelectric liquid crystal (ADL Chandani, E. Gorecka, Y. Ouchi,
H. Takezoe and A. Fukuda: Jap. J. Appl. Phys. 28
(1989) L1265.) And in-plane switching type liquid crystal (M. Oh-e, M. Ohta, S. Arataniand K. Kondo: Procee
ding of ASIA DISPLAY '95 (1995) 577.) is also attracting attention because of the wide viewing angle, but the same problem as described above occurs because the optical axis changes in the in-plane direction of the substrate like ferroelectric liquid crystals. is there.

The present invention has been made in view of the above-mentioned problems, and has as its object the in-plane direction of a substrate such as a ferroelectric liquid crystal, an antiferroelectric liquid crystal, or an in-plane switching liquid crystal. In a liquid crystal display device that performs display using a liquid crystal whose optical axis is changed, it is an object of the present invention to obtain a high contrast even in the case of a reflection type, thereby achieving a clear and high-quality display.

[0023]

According to a first aspect of the present invention, there is provided a liquid crystal display device comprising: a liquid crystal sealed between a pair of transparent substrates each having an electrode; A pair of polarizers arranged to sandwich the pair of translucent substrates, wherein the liquid crystal is horizontally or substantially horizontally with respect to the translucent substrate according to a voltage applied to the electrodes. Switching is performed so as to change the optical axis in the in-plane direction from the aligned state, and the polarization axis of one of the pair of polarizers is substantially parallel to the alignment direction of the stable alignment state of the liquid crystal. And the angle α between the polarization axes of the pair of polarizers is −45 ° ≦ α ≦ + 45 °
(However, α ≠ 0 °).

Further, the angle α is further -30 ° ≦ α ≦
It is preferable that the angle is in the range of + 30 °.

According to the above configuration, switching is performed so that liquid crystal molecules, such as a ferroelectric liquid crystal, an antiferroelectric liquid crystal, or an in-plane switching type liquid crystal, change the optical axis in the in-plane direction of the substrate. In a liquid crystal display device with a wide viewing angle, the conventional crossed Nicols display a bright display by reducing light absorption in the bright state, and conversely increase the light absorption in the dark state to provide a sufficiently dark display for practical use. High-contrast display that cannot be achieved with a polarizing plate can be performed. Hereinafter, this will be described with reference to FIGS.

FIG. 1 is a diagram showing a setting state of a pair of polarizing plates (polarizers) in a ferroelectric liquid crystal display device according to an embodiment of the present invention. It is contrasted. In the configuration shown in FIG. 1, one of the polarization axes A and B of the pair of polarizers coincides with one optical axis P of the liquid crystal, and the other polarization axis A is substantially parallel to the polarization axis B. It has become. Here, the polarization axes A and
When the angle formed by B is α, the transmitted light intensity when a uniaxial optically anisotropic medium such as a liquid crystal cell is provided between a pair of polarizing plates is expressed as follows.

I = I ₀ ｛cos ² α−sin2φ · sin2 (φ−α)
^{· Sin 2 (δ / 2)} } where, phi is the angle between the optical axis of the incident polarization axis and a medium, in FIG. 1 (and FIG. 14), corresponding to the 2 [Theta] _m. Δ is the phase difference of the medium and depends on the wavelength.
φ and δ are values determined by the liquid crystal cell. I ₀ is the incident light intensity. Assuming that the angle α between the polarizing plates is 90 ° or 0 °, the transmittance in crossed Nicols (orthogonal state: 90 °) and parallel Nicols (parallel state: 0 °) is calculated with respect to φ, as shown in FIG. Become. However, here, the influence sin ² (δ / 2) due to the phase difference δ of the liquid crystal cell is set to 1, which is the maximum.

From FIG. 4, it can be seen that the contrast can be obtained in principle even in the case of a parallel type Nicol which is not normally used because the contrast is low in the transmission type. The dark state is
In crossed Nicols, it can be obtained at φ = 0 °, ± 90 °, ± 180 °, while in Parallel Nicols, φ = ± 45 °,
Obtained at ± 135 °. However, in the dark state in crossed Nicols, the optical axis of the liquid crystal and the polarization axis are coincident, so no polarization occurs in the liquid crystal and the ideal dark state is independent of the wavelength. In the dark state, polarization occurs because the optical axis and the polarization axis of the liquid crystal have an angle, and an ideal dark state is obtained only at a wavelength that satisfies the condition sin ² (δ / 2) = 1 in the simulation in FIG. Becomes Actually, since the phase condition differs depending on the wavelength components constituting visible light, it is difficult to obtain an ideal dark state with parallel Nicols. In particular, since this point becomes a problem in the transmission type that gives strong incident light,
High contrast is difficult to obtain with parallel Nicols.

On the other hand, the reflection type uses only external light without using a backlight, so that the intensity of incident light is weak.
In display, it is more important to brighten a bright state than to darken a dark state. Although To brighten the bright state in crossed Nicols is required to be close to the angle of 45 ° of the 2 [Theta] _m, in the ferroelectric liquid crystal is a value around often 20 °, sufficient brightness can be obtained Not. On the other hand, in the bright state in the parallel Nicol, α = 0 in FIG.
In this case, linearly polarized light that has passed through the incident polarizer passes through the output polarizer without being polarized along the optical axis of the liquid crystal, and then reflects on the same reflected optical path while maintaining linear polarization. Will come. As a result, the polarized light is substantially absorbed by only one incident polarizer at the time of incidence, and the bright state in crossed Nicols is substantially equal to the absorption of polarized light by four polarizers in the incident optical path and the reflected optical path. , But very bright. The dark state in parallel Nicols is not ideal due to the problem of wavelength dependence, but since the incident light is weak and the polarized light is absorbed by four polarizing plates as in the bright state in cross Nicols, This problem is darkness that is hardly perceived by an observer and does not cause much problem in practical use.

As described above, the present invention exerts a great effect mainly on the reflection type display, but also has the following effects on the transmission type display. That is, in the reflection type with a long optical path,
Although a large effect can be obtained by suppressing the polarization absorption by the polarizing plate a plurality of times, the effect can be obtained by making the light amount of the backlight darker than usual in the transmission type.
In a transmissive display using a normal orthogonal polarizer, when the backlight is darkened, the bright state becomes dark, which hinders display. However, the present invention can brighten the bright state even with a dark backlight. The dark state is not ideal as described above, but the problem is reduced if the backlight is dark. Further, low power consumption, which is a direct merit of darkening the backlight, is achieved.

The operation of the present invention has been described with reference to ferroelectric liquid crystal as an example. However, switching is performed so that liquid crystal molecules such as antiferroelectric liquid crystal and in-plane switching type liquid crystal change the optical axis in the in-plane direction of the substrate. The same effect is obtained in a display device having a wide viewing angle for performing the above.

Therefore, a ferroelectric liquid crystal having a memory effect can display both normally white and normally black, but an antiferroelectric liquid crystal having no memory effect can be used.
Even in the case of an in-plane switching type liquid crystal,
Normally white display, which is brighter than a conventional orthogonal polarizer, can be performed. In a reflective display, which uses only a reflection of external light without using a backlight, a normally white display is suitable because it is necessary to improve the light use efficiency and to make the screen brighter and improve visibility. is there.

Incidentally, Japanese Patent Application Laid-Open No. 6-317792 discloses that
In a display device that performs color display using coloring by retardation Δn · d of a ferroelectric liquid crystal, a transmission axis of one polarizing plate is substantially parallel to one stable alignment direction of the ferroelectric liquid crystal, and a pair of polarizing plates is formed. Are arranged substantially in parallel with each other so as to perform bright color display.

On the other hand, in the configuration of the present invention, a practical display can be obtained when the angle α formed by the pair of polarizing plates is in the range of −45 ° ≦ α ≦ + 45 °. Hereinafter, differences between these two configurations will be described.

Usually, in a liquid crystal display device using a pair of polarizing plates, the angle between the polarizing plates has a great influence on the display.
However, this is a case of a transmissive display having a high light use efficiency, and when the light use efficiency is relatively low as in a reflective display, a slight displacement of the polarizing plate does not greatly affect the display contrast. Taking the case of ferroelectric liquid crystal as an example, in the case of the structure of Embodiment 1 described later, FIG.
The maximum contrast is obtained when the angle between the polarizers is ± 90 ° as shown in FIG. 6, while the angle between the polarizers is ± 45 ° in the reflective display device as shown in FIG. A relatively high contrast is obtained, and the characteristic has a so-called low angle dependency, in which the contrast is maximized particularly in the range of ± 30 °.

However, in the color display, not only the contrast but also the so-called tint such as the color tone and saturation of the display color are strongly affected by the angle of the polarizing plate. For this reason, Japanese Patent Application Laid-Open No. 6-317792 is limited to a case where the polarization axes of a pair of polarizing plates are substantially parallel.

Further, usually, the birefringence Δn of the liquid crystal is not limited to ferroelectric liquid crystal but is 0.15 to 0.2 at most.
As disclosed in Japanese Patent Application Laid-Open No. 6-317792, in the case of performing color display using coloring by greatly changing the retardation, it is necessary to change the cell thickness d. On the other hand, in the case of a ferroelectric liquid crystal, a cell thickness of 2 μm or less is generally used as described in a paper by Clark et al. This is because there is an advantage that the retardation becomes approximately 300 nm from 250 nm to obtain a good monochrome display and a good memory effect is obtained. The memory effect of the ferroelectric liquid crystal is due to the anchoring effect of liquid crystal molecules at the substrate interface, and the memory effect becomes unstable as the cell thickness increases.

However, according to the above premise,
In order to obtain the retardation disclosed in Japanese Patent No. 317992, the cell thickness needs to be 3 μm or more, and in that case, the memory effect becomes unstable. Usually 2 μm
The following cell thickness is used in the case of the antiferroelectric liquid crystal. In addition, the switching of liquid crystal molecules depends on the strength of the applied electric field regardless of whether the liquid crystal is a ferroelectric liquid crystal or an antiferroelectric liquid crystal having spontaneous polarization or a nematic liquid crystal performing switching based on dielectric anisotropy. Therefore, there is a problem that as the cell thickness increases, the driving voltage rises. The same applies to the in-plane switching type liquid crystal, because the liquid crystal molecules far from the electrode substrate are hardly switched when the cell thickness is large.

Therefore, in the liquid crystal display device of the present invention, it is effective and preferable to perform monochrome display.

As described above, according to the present invention, not only the configuration of the limited range in which the polarization axes of the pair of polarizing plates are arranged almost in parallel, but also the angle α formed by the polarizing axes of the pair of polarizing plates is −4.
In the configuration in which 5 ° ≦ α ≦ + 45 °, a practical display can be obtained, and the cell thickness can be reduced to less than 3 μm.

[0041]

BEST MODE FOR CARRYING OUT THE INVENTION

[Embodiment 1] An embodiment of the present invention will be described below with reference to FIGS.

The liquid crystal display device according to this embodiment is a ferroelectric liquid crystal display device, and two types of transmission type and reflection type ferroelectric liquid crystal display devices were manufactured as this embodiment. These transmissive and reflective configurations are shown in FIGS. 2 and 3, respectively. In any of the ferroelectric liquid crystal display devices, two glass substrates 1 and 2 are arranged to face each other, and a plurality of transparent signal electrodes 3 made of ITO or the like are provided on the surface of one glass substrate 1 in parallel with each other. A transparent insulating film 4 made of SiO ₂ is formed thereon.

On the surface of the other glass substrate 2 facing the signal electrode 3, a plurality of transparent scanning electrodes 5 made of ITO or the like are arranged in parallel with each other in a direction orthogonal to the signal electrodes 3. 5 is SiO ₂ formed thereon
And a transparent insulating film 6 made of On each of the insulating films 4 and 6, there are formed alignment films 7 and 8 that have been subjected to a uniaxial alignment process such as a rubbing process. Incidentally, the alignment film 7
-As for 8, PVA (polyvinyl alcohol) is used.

As described above, the two substrates (light-transmitting substrates) 13 and 14 each having the electrodes 3 and 5 are bonded together with the sealant 10 except for a part of the injection port (not shown). The liquid crystal 9 is sealed in a space sandwiched by the alignment films 7 and 8 from the injection port.

As the liquid crystal 9, a ferroelectric liquid crystal was used, and specifically, SCE8 manufactured by Merck was used. Further, at the time of bonding, the liquid crystal cell was manufactured such that the cell thickness was uniformly 1.5 μm. If the display area is large, 2
Spacers (not shown) are arranged so that the substrates 13 and 14 face each other in parallel with a constant cell thickness.

Further, these liquid crystal display devices are provided with a pair of polarizing plates (polarizers) 11 and 12 arranged so as to sandwich the two substrates 13 and 14. The polarization axes of 11 and 12 will be described later.

As shown in FIG. 2, in a transmission type display device, a backlight 16
However, in the reflection type display device, as shown in FIG. 3, a reflection plate 15 is provided on the substrate 14 side, and there is no backlight 16 and an external light 18 is reflected by the reflection plate 15 for display. Is performed.

Further, in the above configuration, the signal electrode 3 and the scanning electrode 5 are respectively connected to a drive circuit (not shown), and each of the electrodes 3 and 5 is selectively connected by the drive circuit. Is applied with a voltage. These electrodes 3 and 5
Of the liquid crystal 9 according to the voltage applied to the substrates 13 and 14
The switching is performed so that the optical axis is changed in the in-plane direction of the substrate from one stable alignment state horizontally or substantially horizontally to the other stable alignment state.

Further, as shown in FIG. 1, the polarization axis B of one polarizing plate 12 is arranged substantially parallel to the optical axis (orientation direction) P of one of the liquid crystal 9 in a stable alignment state, and The polarization axis A of the polarizing plate 11 is disposed so as to form an angle α with the clockwise direction in the drawing as the positive direction.

Regarding the angle α formed by the polarization axes A and B of the polarizing plates 11 and 12, an experiment was conducted to measure the contrast, which is the ratio of the brightness between the dark state and the bright state, while actually changing the angle α. went. The results are shown in FIGS.

In the transmission type display device, the maximum contrast is obtained when the angle α between the polarization axes A and B is ± 90 ° as shown in FIG. 5, whereas in the reflection type display device,
As shown in FIG. 6, the angle α between the polarization axes A and B is −45 °.
High contrast was obtained in the range of ≦ α ≦ + 45 °, and the contrast was maximized particularly when −30 ° ≦ α ≦ + 30 °.

Here, 0 ° and ± 180 ° are geometrically equivalent arrangements. Theoretically, the maximum brightness is obtained when the angle is 0 °. However, in actuality, the contrast of the reflection type is lower than that of the transmission type. The result is not sensitive to the angle α, but takes a high value in the range of −45 ° ≦ α ≦ + 45 ° around the parallel Nicols.

As described above, in the reflection type ferroelectric liquid crystal display device of this embodiment, the angle α formed by the polarization axes A and B is
By setting the range of −45 ° ≦ α ≦ + 45 °, a high-contrast display can be realized. Also, in the case of a transmissive display device, the light state can be made bright by this embodiment, so that the amount of light of the backlight 16 can be reduced without hindering practical use, and power consumption can be reduced. it can.

Embodiment 2 Another embodiment of the present invention will be described below with reference to FIGS. 7 and 8. For the sake of convenience, the same members as those shown in the drawings of the first embodiment are denoted by the same reference numerals, and description thereof will be omitted.

The liquid crystal display device according to the present embodiment is different from the liquid crystal display device of the first embodiment in that the liquid crystal 9 uses an antiferroelectric liquid crystal MHPOBC. Except for this, in the same manner as in Embodiment 1, two types of display devices of a transmission type and a reflection type were produced.

Accordingly, similarly to the configuration shown in FIG. 1, the polarization axis B of one of the polarizing plates 12 is arranged substantially parallel to the optical axis P of one of the liquid crystal 9 in the stable alignment state, and 1
It is arranged so as to form an angle α with one polarization axis A.

Then, the polarization axes A of the polarizing plates 11 and 12 are set.
With respect to the angle α formed by B, an experiment was conducted in which the contrast, which is the ratio of the luminance between the dark state and the bright state, was measured while actually changing the angle α. The results are shown in FIGS.

In the transmission type display device, the maximum contrast is obtained when the angle α between the polarization axes A and B is ± 90 ° as shown in FIG. 7, whereas in the reflection type display device,
As shown in FIG. 8, the angle α between the polarization axes A and B is −45 °.
High contrast was obtained in the range of ≦ α ≦ + 45 °, and the contrast was maximized particularly when −30 ° ≦ α ≦ + 30 °.

Here, 0 ° and ± 180 ° are geometrically equivalent arrangements. Theoretically, the maximum brightness is obtained when the angle is 0 °. However, in actuality, the contrast of the reflection type is lower than that of the transmission type. The result is not sensitive to the angle α, but takes a high value in the range of −45 ° ≦ α ≦ + 45 ° around the parallel Nicols.

As described above, also in the reflection type antiferroelectric liquid crystal display device of the present embodiment using the antiferroelectric liquid crystal as the liquid crystal 9, the angle α formed by the polarization axes A and B is −45 ° ≦ α. ≤ + 4
By setting the angle to 5 °, high-contrast display can be realized. Also, in the case of a transmissive display device, the light state can be made bright by this embodiment, so that the amount of light of the backlight 16 can be reduced without hindering practical use, and power consumption can be reduced. it can.

Embodiment 3 Another embodiment of the present invention will be described below with reference to FIGS. For convenience of description, the same members as those shown in the drawings of the first and second embodiments are denoted by the same reference numerals, and description thereof will be omitted.

The liquid crystal display device according to this embodiment is different from the liquid crystal display devices of the first and second embodiments in that an in-plane switching type liquid crystal is used for the liquid crystal 9. That is, as shown in FIG. 9, the electrode 5 has a comb-tooth structure, an in-plane switching type liquid crystal is used for the liquid crystal 9, and the other points are the same as in the first and second embodiments.
Two types of display devices, a transmission type and a reflection type, were produced. still,
As the in-plane switching type liquid crystal, ZLI-2806 manufactured by Merck, which is a nematic liquid crystal, was used.

Therefore, similarly to the configuration shown in FIG. 1, the polarization axis B of one polarizing plate 12 is arranged substantially parallel to the optical axis P of one of the liquid crystal 9 in a stable alignment state, and the other polarizing plate 12 1
It is arranged so as to form an angle α with one polarization axis A.

Then, the polarization axis A of the polarizing plates 11 and 12
With respect to the angle α formed by B, an experiment was conducted in which the contrast, which is the ratio of the luminance between the dark state and the bright state, was measured while actually changing the angle α. The results are shown in FIGS.

In the transmission type display device, the maximum contrast is obtained when the angle α between the polarization axes A and B is ± 90 ° as shown in FIG. 10, whereas in the reflection type display device, the maximum contrast is obtained in FIG. , The angle α between the polarization axes A and B is −
High contrast was obtained in the range of 45 ° ≦ α ≦ + 45 °, and particularly, the contrast became maximum when −30 ° ≦ α ≦ + 30 °.

Here, 0 ° and ± 180 ° are geometrically equivalent arrangements. Theoretically, the maximum brightness is obtained when the angle is 0 °. However, in actuality, the contrast of the reflection type is lower than that of the transmission type. The result is not sensitive to the angle α, but takes a high value in the range of −45 ° ≦ α ≦ + 45 ° around the parallel Nicols.

As described above, also in the reflection type liquid crystal display device of the present embodiment using the in-plane switching type liquid crystal as the liquid crystal 9, the angle α formed by the polarization axes A and B is -45 ° ≦
By setting α ≦ + 45 °, high-contrast display can be realized. Also, in the case of a transmissive display device, the light state can be made bright by this embodiment, so that the amount of light of the backlight 16 can be reduced without hindering practical use, and power consumption can be reduced. it can.

[0068]

According to the first aspect of the present invention, there is provided a liquid crystal display device.
As described above, a liquid crystal sealed between a pair of light-transmitting substrates each having an electrode, and a pair of polarizers arranged to sandwich the pair of light-transmitting substrates, wherein the liquid crystal is ,
In accordance with the voltage applied to the electrode, switching is performed so as to change the optical axis in the in-plane direction from a state in which the light-transmitting substrate is horizontally or substantially horizontally oriented,
The polarization axis of one of the pair of polarizers is disposed substantially parallel to the alignment direction of the liquid crystal in a stable alignment state, and the angle α formed by the polarization axes of the pair of polarizers is
The configuration is in the range of −45 ° ≦ α ≦ + 45 ° (here, α ≠ 0 °).

Therefore, in a liquid crystal display device that performs display using a liquid crystal whose optical axis changes in the in-plane direction of the substrate, such as a ferroelectric liquid crystal, an antiferroelectric liquid crystal, or an in-plane switching liquid crystal, Also in the case of a mold, it is possible to obtain a high contrast, thereby achieving an effect that a clear high-quality display can be achieved.

When the transmission type is used, the light amount of the backlight can be reduced, and the power consumption can be reduced.

As described above, in the liquid crystal display device according to the second aspect of the present invention, in the configuration of the first aspect, the angle α is
The configuration is in the range of −30 ° ≦ α ≦ + 30 °.

Therefore, good contrast can be obtained.

As described above, the liquid crystal display device according to the third aspect of the present invention has the configuration of the first or second aspect which is a reflection type having a reflection plate.

Therefore, in the case of the reflection type, a higher contrast can be obtained as compared with the related art, and a clear high-quality display can be achieved.

As described above, the liquid crystal display device according to the fourth aspect of the present invention is the liquid crystal display device according to any one of the first to third aspects,
The liquid crystal is a ferroelectric liquid crystal. Further, a liquid crystal display device according to a fifth aspect of the present invention is, as described above, in any one of the first to third aspects, wherein the liquid crystal is an antiferroelectric liquid crystal. Furthermore, a liquid crystal display device according to a sixth aspect of the present invention is, as described above, in any one of the first to third aspects, wherein the liquid crystal is an in-plane switching type liquid crystal.

Therefore, in a liquid crystal display device which performs display using a liquid crystal such as a ferroelectric liquid crystal, an anti-ferroelectric liquid crystal, or an in-plane switching type liquid crystal, whose optical axis is changed in the in-plane direction of the substrate, a high performance is achieved. Contrast can be obtained, and high-quality display can be realized.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram showing a positional relationship between liquid crystal molecules and polarization axes of a pair of polarizing plates and a positional relationship between polarization axes in a ferroelectric liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a cross-sectional view showing a transmission type configuration of the liquid crystal display device.

FIG. 3 is a cross-sectional view showing a reflection type configuration of the liquid crystal display device.

FIG. 4 is a graph showing a relationship between an angle between an incident polarization axis and an optical axis of a medium and transmittance in crossed Nicols and parallel Nicols.

FIG. 5 shows the transmission type ferroelectric liquid crystal display device.
6 is a graph showing a relationship between an angle between polarization axes of a polarizing plate and contrast.

FIG. 6 shows the reflection type ferroelectric liquid crystal display device.
6 is a graph showing a relationship between an angle between polarization axes of a polarizing plate and contrast.

FIG. 7 is a graph showing a relationship between an angle between polarization axes of polarizing plates and a contrast in a transmission type antiferroelectric liquid crystal display device according to another embodiment of the present invention.

FIG. 8 is a graph showing a relationship between an angle between polarization axes of polarizing plates and a contrast in a reflection type antiferroelectric liquid crystal display device according to another embodiment of the present invention.

FIG. 9 is a perspective view illustrating a schematic configuration of an in-plane switching type liquid crystal display device according to still another embodiment of the present invention.

FIG. 10 is a graph showing the relationship between the angle between the polarization axes of the polarizing plates and the contrast in the transmissive configuration of the in-plane switching type liquid crystal display device.

FIG. 11 is a graph showing the relationship between the angle between the polarization axes of the polarizing plates and the contrast in the reflective configuration of the in-plane switching type liquid crystal display device.

FIG. 12 is an explanatory diagram showing a display principle of a ferroelectric liquid crystal.

FIG. 13 is an explanatory diagram showing a display principle of a TN liquid crystal.

FIG. 14 is an explanatory diagram showing a positional relationship between liquid crystal molecules and the polarization axes of a pair of polarizing plates and a positional relationship between polarization axes in a conventional ferroelectric liquid crystal display device using a crossed Nicol polarizing plate.

[Explanation of symbols]

 1.2 Glass substrate 3 Signal electrode 5 Scan electrode 7.8 Alignment film 9 Liquid crystal 11/12 Polarizer (polarizer) 13.14 Substrate (light-transmitting substrate) 15 Reflector A / B Polarization axis PQ Liquid crystal Optical axis (orientation direction)

Claims (6)

[Claims] A liquid crystal sealed between a pair of light-transmitting substrates each having an electrode; and a pair of polarizers arranged so as to sandwich the pair of light-transmitting substrates. In accordance with a voltage applied to the electrode, switching is performed so as to change the optical axis in a direction in the plane of the substrate from a state of being oriented horizontally or substantially horizontally with respect to the translucent substrate, The polarization axis of one of the polarizers is disposed substantially parallel to the alignment direction of the liquid crystal in a stable alignment state, and the angle α formed by the polarization axes of the pair of polarizers is −45 ° ≦ α A liquid crystal display device characterized by being in the range of ≤ + 45 ° (α ≠ 0 °). 2. The liquid crystal display device according to claim 1, wherein said angle α is in a range of −30 ° ≦ α ≦ + 30 °. 3. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is a reflection type including a reflection plate. 4. The liquid crystal display device according to claim 1, wherein said liquid crystal is a ferroelectric liquid crystal. 5. The liquid crystal display device according to claim 1, wherein said liquid crystal is an antiferroelectric liquid crystal. 6. The liquid crystal display device according to claim 1, wherein said liquid crystal is an in-plane switching type liquid crystal.