JP3130682B2 - Liquid crystal display device - Google Patents

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 having a polarizer and a liquid crystal cell, and more particularly to a liquid crystal display device in which one pixel is divided in a plurality of directions.

[0002]

2. Description of the Related Art Liquid crystal display devices have been actively used as display devices for personal OA equipment such as word processors and desktop personal computers due to the advantages of thinness, light weight, and low power consumption. Liquid crystal display element (hereinafter L
Most of the CDs use nematic liquid crystals, and the display methods can be roughly classified into two types, a birefringence mode and an optical rotation mode.

A birefringent mode LCD using a twisted nematic liquid crystal has, for example, a molecular arrangement twisted by 90 ° or more and has a steep electro-optical characteristic (referred to as an ST mode). Even if there is no thin film transistor or diode, large capacity display can be easily obtained by time division driving.

On the other hand, the LCD in the optical rotation mode has a 90 ° twisted molecular arrangement (called a TN mode), and has a fast response speed (tens of milliseconds) and a high contrast ratio. An LCD (for example, a TFT-LCD) having a large display capacity, high contrast, and high display performance by providing an element for each pixel.
Can be realized.

In recent years, this TFT-LCD performs gradation display, and realizes other color display (for example, 512 gradations for 8 gradations) in combination with three color filters. These gradation displays are performed by changing the applied voltage. Here, an example of the applied voltage-transmittance characteristic of the TN method is shown in FIG. As is clear from the figure, the curve is a monotonically decreasing curve in the front, but the curve when viewed obliquely has an extreme value. Therefore, In its contact to the TN scheme <br/> applied voltage in the front - when determining the driving voltage to perform gradation display based on transmittance characteristics, collapse reversal or black display when viewed from an oblique, white A phenomenon such as omission occurs.

As a means for solving these problems, a method of improving the viewing angle dependency by using a liquid crystal display device having two regions in which the rising direction of liquid crystal molecules is different by 180 ° in one pixel (Two Domain TN: TDTN and Abbreviations, for example, JP-A-64-88520), and the same effect as TDTN can be obtained by using a spray arrangement.
(DDTN: Y.Koike, et.al., 1992, SID, p798)
And so on. These are applied voltage-
It is an object of the present invention to virtually eliminate the above-described extreme value by setting two regions having different viewing angle dependences of transmittance characteristics as one pixel.

However, in the TDTN, it is necessary to provide two or more orientation directions in each fine pixel, and it is difficult to realize the rubbing method which is practical for production. Also,
In the case of DDTN, it is necessary to provide two or more types of pretilt angles in each pixel. As a method for practically realizing the production, two or more types of alignment films are provided by using a patterning method or the like. Will be greatly increased. Furthermore, when an organic alignment film is used, it is difficult to form even two organic alignment films because the solvent used for forming the film has the ability to dissolve the other organic alignment film. When manufacturing a TFT-LCD, it is considered indispensable to use this organic alignment film from the viewpoint of charge retention, and it is practically difficult to provide two or more types of alignment films using a patterning method or the like. You can say that. In other words,
Providing two or more alignment states in one pixel has a practical problem.

[0008]

As described above, in the conventional LCD, when performing a gray scale display, the viewing angle dependence such as a display reversal phenomenon due to the presence of an extreme value in the applied voltage-transmittance characteristic. Had occurred. In order to solve these problems, it has been proposed that two or more directions in which liquid crystal molecules rise are provided in one pixel to eliminate a virtual extreme value. Since it is intended to be achieved by providing a state, it has been practically difficult to realize.

The present invention solves these inconveniences, and as described above, a liquid crystal molecule is provided in two or more directions in one pixel to eliminate a virtual extreme value by a novel cell configuration or the like. What you want to do.

In the conventional TN type liquid crystal, it is not preferable to set Δn · d to 0.4 μm or less from the viewpoint of optical rotation. For this reason, the viewing angle dependence of the contrast ratio has also been a problem.

[0011]

According to the present invention, as a means for solving the above-mentioned problems, a substrate having two electrodes and a liquid crystal layer of a nematic liquid crystal having a positive dielectric anisotropy sandwiched between the substrates are provided. And a pair of polarizers sandwiching the liquid crystal cell, the liquid crystal molecules of the liquid crystal molecules on the surfaces of the two substrates are arranged in the direction parallel to the substrate plane, and the refractive index of the liquid crystal is Anisotropy (Δ
n) and the thickness (d) of the liquid crystal layer (Δnd) is 0.25 ±
A means having a thickness of 0.05 μm and a non-electrode forming portion for partitioning this electrode are provided on one or both substrates forming one pixel, and when a voltage is applied to the liquid crystal layer, Means for causing the tilt direction to be two or more directions in one pixel by a lateral electric field.

The liquid crystal cell and the optically anisotropic element described above are sandwiched between orthogonal polarizers, and the sum of the refractive index anisotropy and the layer thickness of the liquid crystal cell and the optically anisotropic element is Δn · d = 0.
The selection is made to be 25 ± 0.05 μm.

Further, in the above-mentioned liquid crystal cell,
The tilt direction and the pretilt angle of the liquid crystal molecules on the surface of one substrate are equal or the pretilt angles are both 0.
°.

[0014]

The present invention attains the above object, and the principle and method of achieving the object will be described below with reference to the drawings.

First, the display principle of the display mode used in the present invention will be described.

The liquid crystal display element of the present invention uses a liquid crystal having a positive dielectric anisotropy, and the liquid crystal molecule arrangement when no voltage is applied is substantially a so-called homogeneous arrangement. The angle between the long axis direction of these molecules and the absorption axis of the polarizing plate is 45 °. Therefore, the transmittance when no voltage is applied can be expressed by the following equation.

T = T ₀ sin ² (Δn · dπ / λ) (1) T: transmittance T ₀ : transmittance of polarizing plates arranged in parallel Δn · d: effective a retardation value lambda: wavelength of incident light in addition, when a voltage is applied, the liquid crystal molecules are gradually tilted in the direction of the cell perpendicular to the plane in accordance with the applied voltage, the effective specific retardation of when observed from the front Becomes smaller (because Δn becomes smaller). Therefore,
From the equation (1), the transmittance when observed from the front also decreases as the voltage is applied. (When the liquid crystal molecules are almost vertical, the transmittance becomes almost zero.)
The liquid crystal display device of the present invention has a ΔΔ
The transmitted light based on the expression (1) is obtained by Δn equal to n, and when a voltage is applied, an effective Δn based on the applied voltage,
Then, the transmitted light based on the retardation value is obtained.

Here, the equation (1) is calculated based on the wavelengths of the three primary colors generally required for color display = 440 nm, 550 nm, and 620.
When calculated for nm, the relationship between Δn · d and T is as shown in FIG. As is apparent from this figure, Δn · d when no voltage is applied is 0.25 μm or ±
When the thickness is in the range of 0.05 μm, the difference in transmittance between the wavelengths becomes small, so that the transmitted light becomes almost white. Further, since Δn · d is reduced by applying a voltage, transmitted light is reduced at almost any wavelength.
In the liquid crystal display element of the present invention, when no voltage is applied: from white transmitted light, when voltage is applied: black transmitted light is controlled.

[0019]

Next, a liquid crystal display device according to an embodiment of the present invention will be described with reference to the drawings.

(Embodiment 1) FIGS. 1 to 10 show an embodiment of the present invention.

In FIG. 1, FIG. 3 and FIG. 4, a liquid crystal cell 13 is provided between a plate-like polarizer, ie, a pair of polarizers 11 and 12.
Is pinched. The absorption axis 11a of the upper polarizer 11 is disposed so as to be inclined 45 ° clockwise with respect to the display surface horizontal direction h, and the absorption axis 12a of the lower polarizer 12 is also counterclockwise with respect to the horizontal direction h. The polarizers are arranged at an angle of 45 °, and the crossing angle between the absorption axes of the polarizers is 90 °.

The liquid crystal cell 13 includes an upper substrate 15 made of glass having a transparent common electrode 14 and a lower substrate 17 having 640 × 400 matrix-arranged electrodes 16 defined for each pixel. A nematic liquid crystal having a positive dielectric anisotropy (ZLI-1165, manufactured by Merck Japan Ltd.) is sandwiched between them so as to form a liquid crystal layer 18.

The liquid crystal has a refractive index anisotropy Δn of 0.062.
5 , so Δn × d is 0.25 μm.

Alignment films 27 and 28 (FIG. 4) made of polyimide are formed on the electrode surface of each substrate, and both upper and lower substrates are tilted 90 ° with respect to the horizontal direction h in the vertical direction v in the display surface. Rubbing treatments 15a and 17a are performed. For this reason, the orientation of the liquid crystal is not twisted and is uniformly oriented in the v direction. This rubbing treatment may be performed once for each substrate. In this case, as shown in FIG. 6, the liquid crystal molecules 18a have a pretilt angle α on the upper substrate 15 and a pretilt angle α on the lower substrate 17 which is inclined in a direction opposite to the upper substrate.
, One end ma of the liquid crystal molecules is in close contact with each other, and the other end mb is in a mutually sparse molecular arrangement (spray arrangement). Here, the molecular position in the layer thickness direction parallel to the substrate surface is at d / 2, where d is the layer thickness at the center C position.

FIG. 2 shows one pixel electrode 16a in the electrodes 16 arranged in a matrix on the lower substrate 17. The electrode 16a is formed in a rectangular shape, and a slit, ie, a non-electrode forming portion 21, is formed at the center to divide the electrode into a region A and a region B, that is, a non-electrode forming portion 21.
23 has a configuration in which electrodes are connected. In this embodiment, the electrode size is 110 μm × 3300 μm, and the slit is 90 μm.
μm × 25 μm.

In one corner of the region A, a switching element 24 of a thin film transistor made of a-Si is arranged, connected to the electrodes, and connected to the signal line electrode 25 and the gate line electrode 26 arranged around the electrodes. I have. The pixel electrodes constitute one pixel of the display screen, and a large number of these pixel electrodes are arranged in a matrix to control liquid crystal display.

FIG. 4 shows an electric field generated when a drive voltage is applied from the drive power supply 30 to each electrode. In this case, due to the presence of the non-electrode forming portion 21 of the pixel electrode 16a,
Electric fields Ea and Eb having a horizontal electric field component are generated in the pixel electrode region between the upper electrode 15 and the counter electrode 14. This electric field divides the tilt alignment direction of the liquid crystal molecules into two.

That is, FIG. 5 shows the pixel electrode 1 by the same electric field.
6A shows the alignment state of the liquid crystal molecules on the regions A and B of FIG. 6A. In the region A, most of the liquid crystal molecules 18A in the layer thickness direction are arranged along the pretilt direction of the lower substrate 17; Almost all of the layers 18B in the thickness direction are arranged along the direction of the pretilt angle of the upper substrate 15. In other words, the position C where the liquid crystal molecules in the splay arrangement in FIG. 6 are parallel to both substrates is located on the upper substrate 15 side in the region A and on the lower substrate 17 side in the region B. For this reason, since the tilt directions of the liquid crystal molecules as a whole in the two regions are different, the viewing angle dependence is also different.

Here, the viewing angle dependency will be considered. When observing the liquid crystal display device of this embodiment obliquely,
There are two directions in which molecules tilt. Therefore, the applied voltage-transmittance curve does not have an extreme value, and the above-described inversion phenomenon can be reduced.

For example, when the observation from the L direction in FIG. 5 is considered, the apparent change in the retardation of the area A is as shown by the curve A in FIG. 7, and the applied voltage-transmittance curve is as shown by the curve A in FIG. Become like Further, in the region B, an apparent change in retardation is as shown by a curve B in FIG. 7, and an applied voltage-transmittance curve is as shown by a curve B in FIG. Therefore, the change in retardation as a whole is represented by the curve (A) in FIG.
+ B), and the applied voltage-transmittance curve is as shown by the curve (A + B) in FIG. Thereby, the viewing angle dependence of the applied voltage-transmittance characteristics in the two regions is reduced even when the liquid crystal display element of the present invention is observed obliquely.
The liquid crystal display element does not have an extreme value in the applied voltage-transmittance characteristic and has no practical inversion phenomenon.

Further, in order to obtain these effects, it is not necessary to make the alignment process different between the two regions unlike the prior art, so that the above-mentioned problem associated with the high definition of the element does not occur.

Further, Δn · d of the liquid crystal cell can be set to a minimum of 0.25 ± 0.05 μm in principle. In this case, the set value is smaller than that of the conventional TN-type liquid crystal display element, and so-called The viewing angle dependency of the contrast can be reduced.

In this embodiment, when the applied voltage-transmittance characteristic was measured while changing the viewing angle in the L direction, no extreme value was generated in the curve in any viewing angle direction as shown in FIG. When gradation display was performed using the liquid crystal display device of the present invention, good black-and-white display with no reversal phenomenon at any viewing angle was obtained. Further, when the isocontrast characteristics were measured, as shown in FIG. 10, an extremely wide viewing angle dependency was obtained.

(Example 2) In the same electrode structure as in Example 1, instead of the rubbed alignment film, a photosensitive alignment film Provimid having fine 2 μm pitch lines and spaces (Ciba Geigy Co., Ltd.) was used as an alignment film. ), The liquid crystal molecules were horizontally aligned with respect to the substrate plane in the same direction as in Example 1, and the pretilt angles of both the upper and lower substrates were 〜0 °. (This alignment treatment method is described in detail in p. 26 of the 17th Symposium on Liquid Crystal Symposium, 2F108 (1991), and is characterized in that the pretilt angle is 0 °.) Similar to the first embodiment, the viewing angle is reduced. When the applied voltage-transmittance characteristic was measured by shaking, the same effect as in Example 1 was obtained.

Comparative Example 1 The cell thickness of Example 1 was set to 6.0 μm.
When a cell was prepared in the same manner as in Example 1 except that the value was set to m, the transmitted light when no voltage was applied was colored yellow, and a monochrome display could not be realized. This means that the retardation of the cell is 0.
If the thickness is not set to 25 ± 0.05 μm, it means that transmitted light when no voltage is applied is colored.

(Comparative Example 2) In Example 1, a cell was prepared under the same conditions except that only the rubbing direction of one substrate was reversed. A voltage was applied to this cell, but the liquid crystal molecule alignment state did not become two types. From this,
As in the present invention, the direction in which the liquid crystal molecules are tilted is set to 2 using a lateral electric field.
If the orientation is greater than or equal to the
The tilt direction and the pretilt angle of the liquid crystal molecules on the surfaces of the substrates are equal, or both the pretilt angles are 0 °.
It means that it is necessary to be That is, it is necessary to make the directions in which the liquid crystal molecules can be tilted in two directions by setting the pretilt of the opposite polarity to the upper and lower sides or the pretilt to be both 0 °.

Example 3 A cell was prepared under the same conditions as in Example 1 except that Δn of the liquid crystal composition was set to 0.1 and the cell thickness was set to 3.5 μm, and the cell was rubbed. One R = 100 μm retardation film made of polycarbonate was stacked so that the optical axis came in the direction orthogonal to the direction, and sandwiched between orthogonal polarizers as in Example 1, to obtain a liquid crystal display device of the present invention.

When the applied voltage-transmittance characteristics were measured in the same manner as in Example 1, a contrast ratio similar to that of Example 1 could be obtained at a lower voltage than in Example 1 in the front.

Here, a change in molecular arrangement upon application of a voltage will be described. FIG. 12 shows the tilt angle of the liquid crystal molecules with respect to the cell thickness direction. As is clear from this figure, the tilt angle of the liquid crystal molecules on the substrate surface does not change much with the applied voltage. This means that the effective retardation value is 0
It means that it is difficult to become. Therefore, the transmittance is also 0.
It is hard to become. From this, in order to set the retardation value to 0, the remaining retardation value when a voltage is applied (the liquid crystal molecules whose tilt angle does not become 0 in FIG.
Optical anisotropic element having a retardation that cancels out the resulting retardation, 0.25 ± 0.0
What is necessary is just to make it 5 micrometers. In this embodiment, R =
For a 0.35 μm liquid crystal cell, a retardation film having a 0.1 μm retardation value having an optical axis in the direction orthogonal to the molecular alignment direction may be added. By doing so, the liquid crystal display device of the present invention can obtain a high contrast ratio at almost a desired drive voltage.

Further, by changing the retardation value of the above-described optically anisotropic element, the steepness of the applied voltage-transmittance characteristic can be freely controlled, so that a simple electrode structure without using a switching element can be used. Also, a large-capacity display is possible.

(Embodiment 4) In FIG.
a, 32a are arranged at right angles to a pair of polarizing plates 31, 32
Sandwiches a liquid crystal cell 33 having a simple matrix structure.
Further, a retardation film 39 is disposed between the upper polarizing plate 31 and the liquid crystal cell 33 as an optically anisotropic element. The liquid crystal cell 33 has a large number of striped electrodes 3 extending in the row direction.
4 and a lower substrate 37 having a large number of stripe-shaped electrodes 36 extending in the column direction are arranged at regular intervals (liquid crystal cell thickness) with the electrodes of each substrate facing each other. A liquid crystal layer (not shown) is sandwiched between the gaps.

As shown in FIG. 14, an area 40 where the electrode 34 of the upper substrate 35 and the substrate 36 of the lower substrate 37 intersect is defined as one pixel, and liquid crystal display is performed by applying voltages to these electrodes. In this embodiment, a slit-shaped non-electrode forming portion 41 is formed in the center of the lower substrate where the pixel region 40 of the electrode 36 is formed so as to divide the region into two. The non-electrode forming portion 41 generates an electric field having a horizontal electric field component (in the direction of the substrate surface) in the liquid crystal layer when a driving voltage is applied to both the electrodes 34 and 36. The transverse electric field of FIG. 4 and to <br/> the boundary of the non-electrode formation portion in the same manner in the region of two liquid crystal molecular orientation is formed in the same electrode area as well 5 since in the opposite direction . Therefore, the rubbing treatment of the orientation may be performed once for each substrate, and the manufacturing process is simplified.

In this embodiment, Δn of the liquid crystal of the liquid crystal cell 33
Was 0.2, the cell thickness was 5.0 μm, and a retardation film with R = 750 μm was used. When the applied voltage-transmittance characteristic was measured in the same manner as in Example 3, the curve became steeper than in Example 3. Using this liquid crystal display element, 1 /
When a multiplex drive of 400 duty was performed, a contrast ratio of 200: 1 was obtained in front of the display surface.
The viewing angle dependence of the contrast ratio also showed a symmetric azimuth.

[0044]

According to the present invention, in the same alignment treatment on the same substrate, the tilt direction of the liquid crystal molecules can be set to two or more directions. An extremely wide viewing angle liquid crystal display element that does not occur can be realized.

Although the description has been omitted in the embodiments, it goes without saying that the present invention can obtain the same effect even if a switching element made of MIM is used. it goes without saying that even if Na colorization obtain similar same effect.

In addition, the actual condition that occurs when obliquely observed
Needless to say, a wider viewing angle can be expected by adding an optically anisotropic element that can compensate for effective retardation.

[Brief description of the drawings]

FIG. 1 is an exploded perspective view showing an embodiment of the present invention.

FIG. 2 is a perspective view illustrating a main part of FIG. 1;

FIG. 3 is a schematic diagram showing a configuration of the embodiment of FIG. 1;

FIG. 4 is a cross-sectional view illustrating an example of how an electric field is applied when a voltage is applied to an electrode in one embodiment of the present invention.

5 is a cross-sectional view illustrating a liquid crystal molecule arrangement in a state where a voltage is applied in FIG.

FIG. 6 is a schematic diagram illustrating a splay arrangement of liquid crystal molecules.

FIG. 7 is a diagram illustrating a change in a retardation value with respect to an applied voltage according to one embodiment of the present invention.

FIG. 8 is a diagram showing an example of an applied voltage-transmittance characteristic according to one embodiment of the present invention.

FIG. 9 is a diagram showing an example of a measurement result of an applied voltage-transmittance characteristic of one example of the present invention.

FIG. 10 is a view showing an example of a measurement result of an equal contrast curve according to one embodiment of the present invention.

FIG. 11 is a diagram showing a calculation result of a relationship between transmitted light intensity and retardation value of the liquid crystal display element of the present invention.

FIG. 12 is a view for explaining the relationship between the liquid crystal molecule tilt angle and the liquid crystal layer thickness direction in another embodiment of the present invention.

FIG. 13 is an exploded perspective view illustrating the configuration of another embodiment of the present invention.

FIG. 14 is an enlarged partial perspective view showing a main part of FIG. 13;

FIG. 15 is a curve diagram showing an example of an applied voltage-transmittance characteristic of a conventional TN type liquid crystal display element.

[Explanation of symbols]

 11, 12: polarizing plate, 13: liquid crystal cell, 14, 16: electrode 15: upper substrate, 17: lower substrate, 18: liquid crystal layer 21: non-electrode formation part A, B: area within one pixel Ea, Eb ... Electric field with horizontal electric field component

──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor Tomiaki Yamamoto 8 Shinsugita-cho, Isogo-ku, Yokohama-shi, Kanagawa Prefecture Toshiba Corporation Yokohama Office (72) Inventor Hitoshi Hato 8 Shin-Sugita-cho, Isogo-ku, Yokohama-shi, Kanagawa (56) References JP-A-3-98018 (JP, A) JP-A-3-261914 (JP, A) JP-A-61-121087 (JP, A) JP-A-6-43461 (JP) , A) (58) Field surveyed (Int. Cl. ⁷ , DB name) G02F 1/1337 G02F 1/1343

Claims (3)

(57) [Claims] 1. A liquid crystal cell comprising two substrates with electrodes, a liquid crystal layer of nematic liquid crystal having a positive dielectric anisotropy sandwiched between these substrates, and a pair of polarizers sandwiching the liquid crystal cell. In the liquid crystal display device, the arrangement direction of the liquid crystal molecules of the liquid crystal on the surfaces of the two substrates is parallel to each other, and the product of the refractive index anisotropy (Δn) of the liquid crystal and the thickness (d) of the liquid crystal layer (Δn · d) is 0.25
A means for setting ± 0.05 μm, and a non-electrode forming portion for partitioning this electrode is provided on one or both substrates forming one pixel, and when a voltage is applied to the liquid crystal layer, the liquid crystal molecules are Means for making the tilt directions of two or more directions within one pixel by a lateral electric field. 2. A liquid crystal cell comprising two substrates with electrodes, a liquid crystal layer of a nematic liquid crystal having a positive dielectric anisotropy sandwiched between these substrates, and a pair of polarizers sandwiching the liquid crystal cell. In the liquid crystal display element, a non-electrode forming portion for partitioning the electrode is provided on the electrode of one or both substrates forming one pixel, and when a voltage is applied to the liquid crystal layer, the tilt direction of the liquid crystal molecules is changed. A liquid crystal cell having a means for causing two or more directions in one pixel by a lateral electric field; an optically anisotropic element having a retardation value of R disposed between at least one of the polarizers and the liquid crystal cell; The sum of the product Δn · d of the refractive index anisotropy Δn of the liquid crystal layer of the liquid crystal cell and the layer thickness d and the R of the optically anisotropic element is 0.25.
A liquid crystal display element comprising: means for adjusting the thickness to ± 0.05 μm. 3. The liquid crystal display element according to claim 1, wherein the tilt directions and the pretilt angles of the liquid crystal molecules on the surfaces of the two substrates are equal or both the pretilt angles are 0 °.