JPH0792457A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To obtain a liquid crystal display element which is low in driving voltage, bright, high in contrast ratio, and superior in gradation, and has wide visual dependency by specifying the pretilt angle and tilt direction of the molecular array of a liquid crystal layer. CONSTITUTION:The liquid crystal layer 20 formed of a nematic liquid crystal composition is inserted and held between two substrates 11 and 12 which have electrodes 13 and 14, which are composed of conductor parts 13a and 14a and nonconductor parts 13b and 14b as units of fine areas of <=3mum in the narrowest width, pixel by pixel; and at least parts of the conductor parts 13a (14a) of the electrodes 13 (14) and the nonconductor parts 14b (13b) of the electrodes 14 (130 are arranged opposite each other between both the substrates 11 and 12. The pretilt angles alpha0 of the molecule array of the liquid crystal layer 20 on the surfaces of both the substrates 11 and 12 are >=45 deg. and the tilt directions on both the substrates match each other. When the liquid crystal is put in a bend array, variation in the direction of liquid crystal molecules based upon whether or not there is an applied voltage having a lateral electric field component is utilized.

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.

[0002]

2. Description of the Related Art Generally, when a liquid crystal display element (hereinafter abbreviated as LCD) is classified from the viewpoint of light control, a combination of a polarization effect of liquid crystal molecules and a polarizer and a phase transition of liquid crystal are used. However, it is classified into those generated by light scattering and transmission, and those generated by adding a dye to control the visible light absorption amount of the dye and changing the shade of the color.

L, which is a combination of the former polarization effect and a polarizer
CD is, for example, a twisted nematic (TN) type liquid crystal having a 90 ° twisted molecular arrangement. In principle, a thin liquid crystal layer and polarization control can be performed at a low voltage, so that a high response speed, low power consumption, and high contrast are achieved. The ratio is used for a clock, a calculator, a simple matrix drive, an active matrix drive provided with a switching element for each pixel, and in combination with a color filter, it is applied to a full color display liquid crystal TV or the like.

However, an LCD combining these polarization effects and a polarizer has a remarkably low transmissivity of the element since it uses a polarizing plate in principle, and the display color and the contrast ratio depend on the viewing angle / direction depending on the orientation of the molecular arrangement. Cold-cathode ray tube (CRT) that has a viewing angle dependency such as a large change in
The display performance of is completely exceeded.

On the other hand, the latter one utilizing the phase transition of liquid crystal and the LCD in which the visible light absorption amount of the dye is controlled, for example, from a cholesteric phase having a molecular structure of helical structure to a nematic phase of homeotropic molecular alignment. A PC-type liquid crystal which causes a phase transition by applying an electric field and a white Taylor type GH liquid crystal obtained by adding a dye to the PC-type liquid crystal, which does not use a polarizer and theoretically does not use a polarization effect.
It is bright and has a wide viewing angle, and is used in automobile equipment and projection displays.

However, in order to obtain sufficient light scattering, it is necessary to make the liquid crystal phase thick enough or to increase the helical strength that causes the scattering, which requires a high driving voltage and an extremely slow response speed. Therefore, it has been difficult to apply it to a display element having a large display amount (number of pixels). In addition, it has been considered difficult to provide gradation because the transmittance changes abruptly as the applied voltage increases.
Further, the applied voltage-transmittance characteristic has a hysteresis, and there is a practical problem that it is difficult to perform multiplex driving.

To further explain, when the polarization effect and the polarizer are used, the transmittance is lowered in principle, and the viewing angle dependency is caused. That is, since at least one polarizing plate is used, the amount of transmitted light is at least 50% or less, and a pretilt angle is provided for manufacturing and stabilization of orientation, which affects the viewing angle characteristics. Especially in principle, the transmittance is low,
Using this method is an unavoidable problem.

When the phase transition of the liquid crystal is used, these problems such as low transmittance and viewing angle dependence do not occur, but in order to sufficiently scatter light, the liquid crystal layer thickness should be sufficiently thick as described above. , It is necessary to increase the helical strength. This is because the scattering of light is due to various liquid crystal molecule arrangements. In other words, in order to scatter light sufficiently,
For example, in the case of a cholesteric phase having a helical molecular arrangement, it becomes necessary to have a helical axis in every direction with respect to the incident light direction. As described above, in order to have the helical axes in many directions, the liquid crystal phase thickness must be increased. In addition, a means (generally called the DS effect) for obtaining a scattering property by applying a high voltage at a low frequency using Nn liquid crystal in which a conductive substance such as an organic electrolyte is dissolved has been proposed. In order to obtain the property, it is necessary to have the above problems. Of course, the same applies when the phase transition is caused by the thermo-optic effect.

Further, in the methods utilizing these various phase transitions, the molecular alignment of the liquid crystal is remarkably different between the light scattering state and the light transmitting state. Therefore, the mutual change between the above two states can be achieved by electric field control. In that case, hysteresis will occur in the electro-optical characteristics. The cause of this hysteresis has not been clarified due to various theories, but it occurs when the molecular arrangement is significantly different, and it also occurs in the light-scattering state (the molecular arrangement of liquid crystals is a collection of fine domains) when no electric field is applied. It is known that this is more likely to occur when the body is in a state).

Further, as shown in FIG.
A large number of capsules are formed in the polymer 3 held between them, and the liquid crystal 4 is enclosed in the capsule-shaped structure, and the liquid crystal 6 is sandwiched between the fibrous polymers 5 as shown in FIG.
A polymer-dispersed LCD that uses a fibrous polymer structure in which is dispersed to enhance scattering properties has been proposed, but it has not yet achieved the required properties such as high scattering properties, a sufficiently low driving voltage, and a response speed. This is because, due to the manufacturing method and the principle of the shape of the polymer, there is a restriction on the mixing ratio of the polymer and the liquid crystal layer, and again, when trying to satisfy the required driving characteristics, sufficient scattering cannot be obtained. Is.

Also in these systems, since the molecular alignment of the liquid crystal is significantly different between the light scattering state and the light transmitting state,
As described above, hysteresis occurs in electro-optical characteristics. On the other hand, the liquid crystal molecular alignment in the scattering state is controlled to some extent (for example, a polymer is mixed with a hydrophobic substance to control the liquid crystal molecular alignment on the inner surface of the capsule).
However, it is possible to reduce the hysteresis, but this also weakens the light scattering and is not practical.

Capsule-like polymer dispersion type NCAP type L
The CD is a scattering mode liquid crystal display element, and since it does not have a polarizing plate, it is bright and has a wide viewing angle, and is applied to automobile equipment, projection type displays and the like. However, the voltage applied from the outside is divided between the organic polymer and the liquid crystal, and only a part of the applied voltage is applied to the liquid crystal, which causes a problem that the operating voltage is practically increased. Further, in order to obtain sufficient light scattering, it is necessary to make the liquid crystal thickness sufficiently thick, and there is a problem that the response speed is extremely slow, so that it is difficult to apply it to a display element with a large display amount (number of pixels). Was there. Further, the applied voltage-transmittance characteristic has a hysteresis, and there is a practical problem that it is difficult to perform multiplex driving. The polymer-dispersed LCD in which liquid crystal is held in a network organic polymer of fibrous polymer, which operates on the same operation principle, has the same problem.

Further, as a method of scattering light, an alignment treatment is performed for each fine region so that liquid crystal molecules are arranged in various directions on the surfaces of two electrode-attached substrates, and these are treated as inner surfaces to form a gap facing each other. It is conceivable to sandwich the liquid crystal, but this is not a means for solving the above-mentioned problem of hysteresis, and a means for realizing such a structure has not been found, which is a practical method. Not not. The reason why such a configuration cannot be realized is that it is difficult to make the orientation processing direction (for example, the rubbing direction) different for each fine region.

[0014]

As described above, the conventional liquid crystal display device has a low transmittance and a viewing angle dependency.
There was a problem that a high drive voltage was required and the response speed was slow.

Therefore, as means for scattering light,
Does not require any medium other than liquid crystal to obtain the light scattering state,
Moreover, the above-mentioned problems do not occur as long as the molecular arrangement of the liquid crystal is not significantly different from that in the light-transmitting state and a good light-scattering state is obtained, and there is no restriction in the manufacturing method.

The present invention provides a novel structure satisfying this condition.

[0017]

As a means for solving the problem, the present invention sandwiches a liquid crystal layer made of a nematic liquid crystal composition between two substrates each having electrodes facing each other to form a plurality of pixels, The electrodes of the both substrates are composed of a conductor portion and a non-conductor portion in units of a fine region having a narrowest width of 3 μm or less for each pixel. In a liquid crystal display device characterized in that at least a part of non-conductor parts of electrodes are arranged so as to face each other, the pretilt angle α0 on the surfaces of both substrates is larger than 45 °. And a tilt direction is the same in both substrates.

Furthermore, the present invention provides a liquid crystal display device characterized in that the difference in pretilt angle between the liquid crystals on both substrates is 0.5 ° or less.

[0019]

The structure of the liquid crystal display element of the present invention is the same as the prior application No.
The function similar to that of the molecular arrangement structure and the electrode structure proposed in No. 184273 is used. This Japanese Patent Application 5
The molecular arrangement structure proposed in No. 184273 is a so-called splay arrangement and a molecular arrangement obtained by adding a twist thereto, and is characterized in that liquid crystal molecule pretilt angles on the upper and lower substrate surfaces are substantially equal in the vertical direction. In such a molecular arrangement, the tilt directions of the molecules are two directions depending on how the electric field is applied. This is because the liquid crystal molecule alignment in the state where no voltage is applied has a symmetrical shape in the upper half and the lower half of the liquid crystal layer. That is, the tilt direction of the liquid crystal molecules has two or more degrees of freedom. Therefore, only when a voltage is applied, a disclination line can be generated at the boundary portion in the tilt direction of the molecule, and a function of scattering incident light can be obtained. The present invention thus provides one configuration in which the tilt direction of liquid crystal molecules has two or more degrees of freedom.

In the present invention, when it is desired to arrange the liquid crystal in a bend alignment (a molecular alignment having a pretilt angle in the same direction), the direction of the liquid crystal molecules changes depending on the presence or absence of an applied voltage having a transverse electric field component. It is designed to enhance the effect by forming a conductor part and a non-conductor part in a small area of the electrode, and between the substrates, the conductor part of one electrode and the other part of the other electrode which face each other with the liquid crystal layer interposed therebetween. The non-conducting part of is faced.

FIG. 1 shows the structure of an embodiment of the present invention.

FIG. 1A shows an example of the electrode structure of the upper and lower substrates and an example of the rubbing direction for realizing the structure of the liquid crystal display device of the present invention (in this example, the liquid crystal layer is arranged so as not to have twist). 1B is a cross-sectional view illustrating a nematic liquid crystal having a negative dielectric anisotropy in which a chiral agent is not mixed as a liquid crystal composition, and FIG. FIG. 3 is a diagram conceptually illustrating a direction in which an electric field is applied (indicated by a dotted line) and a direction in which liquid crystal molecules fall when a voltage is applied to the electrodes. FIG. 1C is a diagram showing the molecular arrangement of this constitution. In the molecular arrangement shown in FIG. 1C, the molecular arrangement F of the upper substrate and the molecular arrangement R of the lower substrate are in the same direction, and the molecular arrangement is such that the pretilt angle α0 of liquid crystal molecules is 4
The angle is larger than 5 ° and gradually increases from the pretilt angle α0 of the upper substrate 11 to the substrate 1 at the midpoint d / 2 of the liquid crystal layer thickness d.
After being almost perpendicular to 1, the pretilt angle α of the lower substrate 12
It is designed to incline in the opposite angle to 0. Such a sequence is called a bend sequence.

Therefore, as shown in FIG. 1 (b) showing the present embodiment, the upper electrode 13 has an electrode pattern in which a plurality of stripe-shaped conductor portions 13a are arranged at equal intervals through the non-conductor portion 13b, and The lower electrode 14 has a pattern in which a plurality of stripe-shaped conductor portions 14a are arranged at equal intervals through the non-conductor portion 14b, and when these electrodes are opposed to each other, the conductor portion 13a or 14a of one electrode is formed. Overlap so as to form a gap between the substrates so as to face the non-conductor portion 14b or 13b of the other electrode. In this case, rubbing treatment is performed so that the liquid crystal alignment directions of the upper and lower substrates are the same. As a result, when no voltage is applied, the liquid crystal maintains the bend alignment state in an orderly manner, but when a voltage is applied, the conductor parts are displaced between the upper and lower electrodes, so an oblique electric field having a transverse electric field component is generated between the electrodes. , The electric force lines e whose inclination directions are alternately changed are formed as shown in the drawing. Since the liquid crystal molecules M are arranged in a tilted manner along the lines of electric force, the liquid crystal alignment becomes discontinuous at the boundary between the obliquely upward electric field rising to the right and the oblique electric field rising left to generate a disclination line DL. Since the disclination line DL is an array discontinuity point caused by a slight liquid crystal alignment change, in order to distinguish it from the phenomenon of appearance of disclination upon application of an electric field having a strong memory property, the wall will be referred to as a wall in the present invention. Called.

If a large number of conductive parts and non-conductive parts of electrodes are formed in one pixel, the direction in which the liquid crystal molecules fall is minutely divided, so that many walls can be generated in one pixel. Then, light scattering can be caused in this portion.

The light-scattering region has a width of 3 to 50 around the boundary.
Since it is μm, if the size of a fine area is matched within this value range (the narrowest width can be 3 μm or less), or if it is divided into smaller values, the light will be distributed over the entire surface of one pixel. Can be scattered, and in the state where no voltage is applied, the liquid crystal molecules are continuously arranged over the entire surface, so that a light transmitting state can be obtained. Therefore, according to the present invention, it is possible to perform electric field control to obtain a light transmission state when no voltage is applied and a light scattering state when a voltage is applied.

Since the liquid crystal display device of the present invention controls the tilting direction of the liquid crystal molecules according to the direction of the applied electric field, it is desirable that the pretilt angles of the upper and lower substrates are equal to each other, and a difference is practically applied. It is desirable that the angle be 0.5 ° or less. However, even if the pretilt angles are different, some effects are exhibited.

Microscopically, the change in the molecular sequence in each region is equal to the change in the molecular sequence, and the response speed takes a value in accordance with this, so that the response speed is the same as that of the conventional uniform twisted array TN-LCD or It is known to be even faster than STN-LCD and homogeneous array LCD,
Therefore, the liquid crystal display device of the present invention can also obtain an extremely fast response speed (Japanese Patent Application No. 3-344592 of the prior application).
See Japanese Patent Application No. 3-34493).

Further, the liquid crystal display device of the present invention obtains two states, a light transmission state and a light scattering state, by a slight change in the alignment of liquid crystal molecules, so that hysteresis does not occur in electro-optical characteristics.

Further, depending on the difference in the pretilt angle α 0 of the liquid crystal, various ones such as one having a steep electro-optical characteristic and one having a gentle slope can be realized.

Further, in the liquid crystal display device of the present invention, since the light scattering state of the liquid crystal layer can be realized by a slight change in the alignment of the liquid crystal molecules, the applied voltage becomes a very small value.
Therefore, an advantage that low voltage driving is possible can be obtained.

[0031]

EXAMPLES Examples of the liquid crystal display device of the present invention will be described below.

(Embodiment 1) FIG. 1 shows this embodiment.
FIG. 1A is a perspective view showing patterns of upper and lower electrodes, FIG.
Is a schematic sectional view of a liquid crystal cell in which electrodes are opposed to each other, FIG.
3 is a schematic view showing a bend alignment state of liquid crystal molecule alignment when no voltage is applied.

An ITO transparent common electrode 13 is formed on the entire surface of one surface of an upper substrate 11 made of glass, and an upper alignment film (AL-3046, made by Japan Synthetic Rubber) 15 of polyimide is laminated on the surface. . The lower electrode 12 made of the other glass is provided on one surface thereof with pixel electrodes 14 of 300 μm × 300 μm, which are made of ITO and are arranged in a mosaic in pixel units, and a polyimide lower alignment film (AL-3046,
16 made of Japanese synthetic rubber are laminated. A silane-based alcohol treatment liquid (trade name OSD) that is a vertical alignment treatment agent for each substrate
-E, manufactured by Chisso), ultrasonic waves are applied for 3 minutes and then dried, and rubbing treatment is performed in the directions F and R shown in the figure to set the final pretilt angle to 89 °.

The upper electrode 13 has a width of 2.5 μm for each pixel p.
A plurality of slits, that is, non-conductive portions 13b and conductive portions 13a having a width of 2.5 μm are arranged in a stripe pattern at a pitch of 5 μm, and a large number of conductive portions 13a are formed in one pixel 300 μm width. ing.

The lower electrodes 14 facing each other also have a pattern in which conductive portions 14a having a width of 2.5 μm and non-conductive portions 14b having a width of 2.5 μm are arranged at equal intervals, and a large number of conductive portions 14a are arranged within a width of 300 μm. Is forming.

The conductive portions of these electrodes are offset from each other by 2.5 μm with the upper and lower substrates facing each other, and the conductive portion 13a or 14a of one electrode is the non-conductive portion 14 of the other electrode.
face b or 13b.

The lower electrode 14 is a TFT switching element 17
And is connected to the gate line 18 and the signal line 19.

As shown in the figure, the orientation directions F and R of the upper and lower substrates are perpendicular to the conductive portions of the electrodes and in the same direction, and the gap between the upper and lower substrates is 10 μm to form a cell. Nematic liquid crystal with negative dielectric anisotropy (ZLI-
4850, manufactured by Merck Japan) to fill the liquid crystal layer 20. This liquid crystal has a large Δn of 0.2080, and the liquid crystal layer was selected to be as thick as 10 μm in order to enhance the light scattering property in the light scattering state.

A voltage was applied from the power source 21 to the liquid crystal display element of the present invention thus obtained through the TFT 17, and the electro-optical characteristics (transmittance-applied voltage curve) were measured. When a voltage is applied, an electric field having a lateral electric field component is generated between the electrodes, and the direction of the lateral electric field component changes in a minute range of one pixel. Therefore, the liquid crystal molecules M of the liquid crystal layer 20 change their arrangement according to the electric field. . Therefore, a large number of walls D are formed at the boundary of the liquid crystal alignment.
L is generated to create a light scattering state.

In order to obtain a transmittance-applied voltage curve, a He-Ne laser beam was made incident on the liquid crystal display element, and the transmittance was measured. The spot diameter of the light was 2 mm, and the transmitted laser light was detected by a photodiode located at a distance of 20 cm from the liquid crystal display element. FIG. 2 shows a transmittance-applied voltage curve when the applied voltage is gradually increased from 0V to 5V and gradually decreased from 5V to 0V. The transmittance is about 80 when no voltage is applied (0 V is applied).
% (Transmittance of two glass substrates) is shown. Further, when the applied voltage was 3.7 V, the minimum transmittance was 0.4%, and a good scattering state was obtained. Further, as is clear from the figure, there was no hysteresis in the electro-optical characteristics. The applied voltage is 3.7V
When the response speed was measured at 0 and 0V, it started up 6
A very fast value was obtained with msec and a fall of 21 msec.

[0041]

According to the present invention, a liquid crystal display element having a high scattering characteristic, a low driving voltage, a bright and high contrast ratio and an excellent gradation property, and a viewing angle at which the display is inverted even when gradation display is performed are eliminated. A liquid crystal display device having an extremely wide viewing angle dependency can be obtained.

[Brief description of drawings]

1A and 1B are diagrams illustrating an embodiment of a liquid crystal display device of the present invention, in which FIG. 1A is a perspective view of an electrode, FIG. 1B is a sectional view for explaining an operation, and FIG. .

FIG. 2 is a transmittance-applied voltage curve diagram of the device of Example 1 of the present invention.

3A and 3B are schematic cross-sectional views of a capsule-like structure and FIG. 3B is a schematic cross-sectional view of a fibrous polymer structure for explaining a conventional device.

[Explanation of symbols]

 11 ... Upper substrate 12 ... Lower substrate 13 ... Upper electrode 13a ... Conductor part 13b ... Non-conductor part 14 ... Lower electrode 14a ... Conductor part 14b ... Non-conductor part 15, 16 ... Alignment film 20 ... Liquid crystal layer

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Hitoshi Hato 8 Shinsita-cho, Isogo-ku, Yokohama-shi, Kanagawa Incorporated company Toshiba Yokohama Office

Claims (2)

[Claims] 1. A liquid crystal layer made of a nematic liquid crystal composition is sandwiched between two substrates each having electrodes which face each other and form a plurality of pixels, and the electrodes of both substrates are provided for each pixel.
At least a part of the conductor part of one electrode and the non-conductor part of the other electrode between the two substrates, which is made up of a conductor part and a non-conductor part with the smallest width being 3 μm or less as a unit. In the liquid crystal display element, the liquid crystal layer has a molecular arrangement in which the pretilt angle α 0 on the surfaces of both substrates is larger than 45 ° and the tilt directions are the same for both substrates. A liquid crystal display element characterized by being directional. 2. The difference between the pretilt angles of the liquid crystals of both substrates is 0.
The liquid crystal display element according to claim 1, wherein the liquid crystal display element has an angle of 5 ° or less.