JPH06324356A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display element realizing a wide and uniform visual field angle characteristic without generating inconvenient colorings being different from a color to be realized essentially in a picture. CONSTITUTION:A wide and uniform visual field angle characteristic is realized since orientation in which liquid crystal molecules rise up at the time of voltage impression is made random (to be not uniform) and T-V characteristic becomes almost the same in every orientation by forming the surfaces of oriented films 23, 25 on substrates so that liquid crystal molecules in a liquid crystal layer 19 are held almost in a horizontal posture with respect to the oriented films 23, 25 on the substrates 11, 17 and orientation of major axes of the liquid crystal molecules are not uniform in the of case where external is not applied applied. Further, the retardation value of the liquid crystal layer 19 is adjusted to be 440nm+ or -50nm and the twist angle of the liquid crystal molecules is adjusted in the range from 65 degrees to 115 degrees. Then, excellent picture displays are obtained since the inconvenient colorings in displaced pictures are eliminated.

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,
In particular, the present invention relates to a liquid crystal display device having improved viewing angle characteristics such as display contrast and display color of an image.

[0002]

2. Description of the Related Art Liquid crystal display elements are widely used in a wide variety of products such as wrist watches, calculators, Japanese word processors, and personal computers because they have the great features of thinness, light weight, and low power consumption. Most of these liquid crystal display devices are Twisted Nematic (hereinafter abbreviated as TN) type liquid crystal, or STN (Supe
r Twisted Nematic (hereinafter abbreviated as STN) type liquid crystal is used. For example, as a display used in a personal computer, a display having a large screen and a large display capacity is generally used, and the size of the display surface is A.
The so-called VGA display specifications with 4 or more sizes and 640 pixels in the horizontal and 480 pixels in the vertical have become the mainstream.

Liquid crystal display devices currently in the mainstream can be roughly classified into two types, an active matrix type and a simple matrix type. Both types of VG are as described above.
It is possible to realize the performance that almost satisfies the A display specifications. One of the main features of the simple matrix method is that it can be made inexpensive, and it is the two substrates with strip-shaped transparent electrodes arranged facing each other with a gap so that the transparent electrodes intersect in a matrix. This is due to the simple structure in which the liquid crystal layer is placed and sandwiched between the two. In order to realize the VGA display specifications by the simple matrix method having such a simple structure, the transmittance-applied voltage (TV) characteristic of the liquid crystal layer is required to have steepness. Here, the steepness refers to the degree of change in the transmitted light of the liquid crystal layer when the value of the voltage applied to the liquid crystal layer is changed. The TV characteristic can be made steep by increasing the total twist angle of the alignment of the liquid crystal layer (hereinafter referred to as the twist angle).

However, practically, the twist angle of a simple matrix type liquid crystal display element is required to be 180 degrees or more, and STN type liquid crystal is often used. When the twist angle becomes large like this, the display image is caused by optical rotation dispersion. However, there is a problem that it is colored in an inconvenient color different from the color of the image to be originally expressed.

On the other hand, in the active matrix system,
Thin film transistor for each pixel
Since a switching element such as r; hereinafter abbreviated as TFT) is arranged, the liquid crystal application voltage applied to the liquid crystal layer of each pixel can be set to an arbitrary voltage ratio regardless of the number of scanning lines. Therefore, the response speed is fast, and a sufficient response speed can be obtained even for a moving image of a television or a mouse used for CAD or the like. Control of voltage application to the liquid crystal layer is TF
Since a switching element such as T is used, it is not necessary to increase the steepness of the transmittance-applied voltage characteristic as in the simple matrix method, and it is not necessary to increase the twist angle. Therefore, a TN type liquid crystal having a twist angle of about 90 degrees is often used.

As described above, the steepness of the electro-optical characteristics of the TN type liquid crystal having a twist angle of 90 degrees is S with a larger twist angle.
Although inferior to the TN type liquid crystal, the twist angle is small, so the optical rotatory dispersion is small, and in the case of a polarizing plate arrangement (normally open) where a bright display can be obtained when no voltage is applied, the above-mentioned inconvenient coloring It is possible to obtain an image display that is almost inconspicuous. Therefore, by combining the active matrix system and the TN cell, it is possible to realize a liquid crystal display device having a large display capacity at a high speed. A full color image can be displayed by further combining this with a color filter.

[0007]

However, in the liquid crystal display elements according to these conventional techniques, there is a problem that the brightness and darkness of the display appear to be reversed depending on the direction and angle of viewing the screen, or the display image becomes dark and difficult to see. is there. Alternatively, there is a problem that the displayed image is colored inconveniently in addition to the original color of the image.

As a method of improving this problem, conventionally, a method of improving the viewing angle dependency by using a liquid crystal display element having two alignment regions in which the rising directions of liquid crystal molecules are different by about 180 degrees in one pixel ( Two Domain Twisted Nemati
c; hereinafter abbreviated as TDTN. This technique is disclosed, for example, in Japanese Patent Laid-Open No. 64-
88520), or a Domain Divided Twisted Nemat that uses a spray array to achieve the same effect as TDTN.
ic (hereinafter abbreviated as DDTN. This is, for example, Y. Koike, et.
al., 1992, SID, p798) method has been proposed. In general, in the electro-optical characteristics of a liquid crystal display element, the transmittance observed obliquely with respect to the rising direction of liquid crystal molecules is smaller than that from the front. In the case of the direction opposite to the rising direction, the transmittance observed obliquely becomes larger than that from the front. Therefore, in the above-mentioned DDTN method, one pixel is divided into two regions having different alignment directions, and the above-mentioned contradictory electro-optical characteristics observed obliquely in each region can be obtained by both alignment characteristics. The visual angle characteristics are combined and added together so as to complement each other so as to approach the electro-optical characteristics observed in the front direction.

However, in the case of manufacturing such a liquid crystal display device of the DDTN system, it is necessary to divide each pixel into regions having two different alignment directions, which makes the manufacturing process extremely complicated. There is a problem. As a result, the manufacturing yield will be significantly reduced.

As a technique similar to the above-mentioned DDTN, a technique called multi-domain has been reported in which a large number of alignment regions in which the orientations of liquid crystal molecules rising from the substrate surface are made ununiform are provided in one pixel ('93 Society for Information.
Display, Advance program, p.67). According to this multi-domain method, the azimuths in which the liquid crystal molecules are raised when a voltage is applied are almost random (unified). As a result, TV
The characteristics are almost the same in all directions, and wide and uniform viewing angle characteristics can be realized.

However, when a large number of alignment regions in which the rising directions of the liquid crystal molecules are made ununiform are provided in one pixel, the display image is colored. Therefore, in the case of performing full-color display in combination with a color filter, there is a problem that an inconvenient coloring different from the color originally intended to appear in the image occurs and the display quality is significantly deteriorated.

The present invention has been made to solve such a problem, and an object thereof is to provide a wide and uniform viewing angle characteristic without causing an inconvenient coloring different from the color originally desired to be expressed in an image. Another object of the present invention is to provide a liquid crystal display device capable of realizing the above.

[0013]

In order to solve the above problems, a liquid crystal display element of the present invention has an image display electrode, and a substrate surface is subjected to an alignment treatment for aligning the major axis directions of liquid crystal molecules in the same direction. The two substrates, which are formed so as to avoid being squeezed, are opposed to each other with a gap therebetween, and the long-axis direction of the liquid crystal molecules is held in a substantially horizontal posture with respect to the substrate surfaces when no voltage is applied. At the same time, the major axis direction of the liquid crystal molecules is oriented in a non-uniform azimuth direction on the substrate surface while maintaining the substantially horizontal posture, and the liquid crystal molecule is perpendicular to the substrate surface in a gap between the two substrates. And a liquid crystal layer sandwiched between the two substrates so that the liquid crystal molecules are twisted and aligned, and the retardation value of the liquid crystal layer is adjusted to a range of 440 nm ± 50 nm and the liquid crystal molecules of the liquid crystal layer are The twist angle is in the range of 65 to 115 degrees. It is characterized by being adjusted to.

The present invention also applies to a so-called simple matrix type liquid crystal display element in which strip-shaped transparent electrodes are arranged on the respective substrates as the image display electrodes.
Alternatively, it may be applied to a so-called active matrix type liquid crystal display element in which a counter (common) electrode is formed on one substrate as the image display electrode and a pixel electrode is arranged for each pixel on the other substrate. Not to mention coming.

Further, on the substrate surfaces of the above two substrates,
For example, it is possible to form a horizontal alignment film using polyimide as a material and use it without performing alignment treatment such as rubbing alignment, or use another alignment film material and perform the alignment treatment in the same manner as described above. It may be used without applying. In any case, while forming the substrate surface so that the long axis direction of the liquid crystal molecules can be held in a substantially horizontal posture, the long axis direction of the liquid crystal molecules can be held in a substantially horizontal posture,
The direction in which the long axis of the liquid crystal molecule faces the surface of the substrate may be made ununiform at each position in the pixel (for example, avoiding alignment treatment).

[0016]

[Function] As described above, the retardation value of the liquid crystal layer is set to 4
By adjusting to 40 nm ± 50 nm and adjusting the twist angle of the liquid crystal molecules in the liquid crystal layer from 65 degrees to 115 degrees, there is no inconvenient coloring different from the color originally intended for the image, and it is wide and uniform. It is possible to realize various viewing angle characteristics.

That is, the substrate surface is formed such that the liquid crystal molecules are kept substantially horizontal with respect to the substrate surface when no voltage is applied, and the major axis directions of the liquid crystal molecules are not aligned.
When the voltage is applied, the orientations of the liquid crystal molecules are raised (random). As a result, the TV characteristics are almost the same in any direction, and wide and uniform viewing angle characteristics can be realized.

At this time, however, the retardation value of the liquid crystal layer and the twist angle of the liquid crystal molecules are set to the conventional TN.
When manufactured under the same cell conditions as the liquid crystal cell, the display image is colored in an inconvenient color different from the desired color. This coloring is
It can be solved by setting the optimum retardation value and twist angle value of liquid crystal molecules so that the transmittance curves for the three primary colors of light, red, green and blue, are the closest to each other. . Therefore, as a result of obtaining the optimum retardation value and the twist angle value of the liquid crystal molecules by various experiments, the retardation value of the liquid crystal layer was determined to be 4
By adjusting to 40 nm ± 50 nm and adjusting the twist angle of the liquid crystal molecules of the liquid crystal layer within the range of 65 degrees to 115 degrees, it is possible to eliminate inconvenient coloring of the displayed image and obtain an extremely good image display. It turned out to be possible.

Further, according to the present invention, since complicated processing such as rubbing alignment processing for the alignment film can be omitted,
There is also an advantage that the manufacturing yield can be improved and the manufacturing process can be simplified.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the liquid crystal display device according to the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a diagram schematically showing the structure of a main part of a liquid crystal display element according to the present invention. Scan line 1 and signal line 3
Are arranged so as to be substantially orthogonal to each other, and are connected to the scanning line 1 and the signal line 3 at each intersection, and the pixel electrode 5
A TFT array substrate 11 in which an alignment film 9 which is not subjected to an alignment treatment is formed so that a TFT 7 as a switching element connected to the pixel electrode 5 for controlling the voltage application to the pixel electrode 5 is provided. , A counter electrode 13 arranged opposite to this is formed, and a counter substrate 17 on which an alignment film 15 which is not subjected to alignment treatment is formed so as to cover the counter electrode 13 is combined with a gap (cell gap). The liquid crystal layer 19 is sealed in the gap between the two substrates 11 and 17.
The liquid crystal cell 21 is sandwiched and formed. Then, the polarizing plates 23 and 25 are arranged so as to sandwich the liquid crystal cell 21 from above and below.
Is attached to the outer surface side of each of the glass substrates 27 and 29, and the main part of this liquid crystal display element is constituted.

In the liquid crystal cell 21, as described above, the alignment films 9 and 1 for performing horizontal alignment so as to cover almost the entire surface of the substrate.
No. 5 is formed, the surfaces of these alignment films 9 and 15 are not rubbed, and spacers (not shown) made by Sekisui Fine Chemical Co., Ltd. having a particle size of 5.0 μm are interposed as a gap material between both substrates. The cell gap is maintained at about 5.0 μm, and a sealing material (not shown) is applied to the periphery of the substrate to form both substrates 11 and 17 in combination.

As the liquid crystal layer 19, ZLI-4287 (E.
(Made by Merck), the twist pitch between the substrates of liquid crystal molecules is about
A liquid crystal composition was used in which a chiral agent S811 for left-handed twist (manufactured by E. Merck) was mixed at 90 degrees. This liquid crystal composition was injected into an empty cell in an isotropic phase state to form a liquid crystal layer 19
As a result, the substrates 11 and 17 were enclosed and sandwiched.

The retardation value Δnd of the liquid crystal display element thus formed was about 460 nm. The twist pitch is about 90 degrees as described above.

As the polarizing plates 23 and 25, crossed Nicols polarizing plates (G1220DU, manufactured by Nitto Denko) were used and were arranged so that their light absorption axes were orthogonal to each other.

Although not shown, the electrode lead-out portion of the liquid crystal cell 21 is supplied with a scanning signal voltage and a video signal voltage input from an external liquid crystal drive circuit, and drives the liquid crystal display element.

Here, there are roughly two types of arranging methods of the polarizing plates used in the TN cell, and a method of arranging the light absorption axes of the upper and lower polarizing plates in parallel with each other,
There is a method of arranging the light absorption axes of the upper and lower polarizing plates at right angles. In the former method, light is not transmitted when a voltage is not applied to the liquid crystal cell, and a light transmission state is obtained when a voltage is applied (normally closed). In the latter method, light is transmitted when a voltage is not applied to the liquid crystal cell, and light is blocked when a voltage is applied (normally open). FIG. 2 is a diagram showing the viewing angle dependence of the contrast ratio when the viewing angle is tilted to the left and right directions up to 60 degrees from the normal to the normally open and normally closed display surface of the conventional TN method. Comparing with, it can be seen that normally closed has less viewing angle dependence of contrast ratio than normally open. The contrast ratio is a value obtained by dividing the luminance in a state where light is transmitted (bright state) by the luminance in a state where light is blocked (dark state), and the contrast ratio greatly affects the luminance in a dark state. Then, when the viewing angle dependence of the brightness in the left-right direction in the dark state of both the normally open type and the normally closed type is measured, the characteristics as shown in FIG. 3 are obtained. As is clear from the figure, normally closed has a smaller viewing angle dependence in the dark state than normally open, and as a result, normally closed has a better viewing angle characteristic of contrast ratio than normally open. Considering the difference between the normally open and normally closed dark states, a voltage above the threshold is applied to the liquid crystal layer in the case of normally open, and a threshold voltage is applied to the liquid crystal layer in the case of normally closed. Only the following voltages are applied. When a voltage above the threshold value is applied to the liquid crystal layer, the liquid crystal molecules are aligned in the cell thickness direction and the twisted arrangement is released. In such an array state, the viewing angle change of the appearance of the array is large as compared with the array state in which the voltage is applied below the threshold value and the substrate is twisted substantially horizontally. Therefore, for the above reasons, it has been found that normally closed is better for widening the viewing angle.

On the other hand, as a technique for widening the viewing angle, there is a technique called a so-called multi-domain cell system in which a large number of alignment regions in which the rising directions of liquid crystal molecules are not uniform are provided in one pixel. This is because the long axes of the liquid crystal molecules maintain a substantially horizontal posture with respect to the substrate surface when no voltage is applied, and by avoiding alignment treatment, the long axes of the liquid crystal molecules are not aligned. The azimuths in which the liquid crystal molecules rise when voltage is applied become random, and as a result, the TV characteristics are almost the same in all azimuths. As an example thereof, FIGS. 4 and 5 show the TV characteristics in the up and down left azimuth directions at an incident angle of 60 degrees in the case of a conventional normally closed TN cell and the case of a multi-domain cell, respectively. It can be seen that in the multi-domain cell, the TV characteristic has almost no azimuth angle dependence. However, when the multi-domain cell is manufactured under the same cell conditions (retardation and the size of the twist angle) as the conventional TN cell, there is a problem that the display image is colored.

Here, a liquid crystal cell is disposed between the polarizing plates whose light absorption axes are orthogonal to each other, and the retardation Δnd of the liquid crystal cell is set.
FIGS. 6 and 7 show the results of plotting the change in transmittance when the difference between the refractive index difference Δn of the liquid crystal and the thickness d of the liquid crystal layer is plotted with respect to the dominant wavelengths of the three primary colors of red, green and blue. . The calculation of the above-mentioned transmittance was carried out based on the following formula. That is, when a liquid crystal cell having a liquid crystal layer having a twisted liquid crystal array is sandwiched between two polarizing plates, the transmittance is
E. P. It is guided by RAYNES as follows (Mol.Cryst.Liq.Letters Vol.4 (6), pp159-163) T = {cosβ · cos (θ−A + P) + sinβ · sin (θ−A + P) / ( 1 + α ² ) ^1/2 } ² + sin ² β · cos ² (θ−A−P) · α ² / (α ² +1) ... (1) where: T: Two polarizing plates are arranged in parallel. Of the transmittance when a liquid crystal cell with a twisted liquid crystal array is sandwiched between two polarizing plates with respect to the transmittance of θ: The twist angle of the liquid crystal (rad.) A: The absorption axis of the polarizing plate on the incident light side and the incidence Angle formed by the director of liquid crystal molecules on the light-side substrate surface (rad.) P: Angle formed by the absorption axis of the polarizing plate on the output light side and the director of liquid crystal molecules on the substrate surface of the incident light side (rad.) Α = Δndπ / (Λ · θ), π: circular constant, λ: incident light wavelength (nm) β = θ · (1 + α ² ) ^1/2 . In the above-mentioned '93 SID, Y. In the so-called multi-domain liquid crystal display element proposed by Toko et al., The director orientation of liquid crystal molecules on the incident light side substrate surface is random, and the value of A in the equation (1) is 0 to
It will take various values of 180 degrees. Therefore, the above
Y. 93 SID. To calculate the transmittance of the liquid crystal display device proposed by Toko et al., The equation (1) may be integrated from 0 to 180 degrees with respect to A and divided by 180 degrees. Therefore, if the angle formed by the main polarization axes of the two polarizing plates is 90 degrees (because they are arranged in the orthogonal Nicols as described above), the equation (1) can be converted as follows. That is, T = {cos β · cos (θ−π / 2) + sin β · sin (θ−π / 2) / (1 + α ² ) ^1/2 } ² + sin ² β · α ² / {2 · (α ² +1) } (2) By substituting the twist angle θ = 90 degrees into the equation (2), the transmittance can be obtained.

In the transmittance curves of FIGS. 6 and 7, red, green,
The display color is uncolored when the three blue curves match. FIG. 6 shows the case of a conventional 90 ° twist liquid crystal cell, and FIG. 7 shows the case of a 90 ° twist multi-domain liquid crystal cell. In the case of the conventional 90-degree twisted liquid crystal cell of FIG. 6, the range of retardation value (Δnd) at which the three curves of red, green and blue are almost the same is 550 nm ± 50n.
m, which is 440 nm ± 50 nm in the case of the 90 ° twist multi-domain liquid crystal cell in FIG. 7. As can be seen by comparing these results, the retardation value (Δnd) at which monochrome display is obtained in the multi-domain liquid crystal cell
Is different from the conventional TN cell, Δnd is 440nm ± 50n
It is concluded that this is the case for the range m. If the retardation value (Δnd) is adjusted within this range to produce a multi-domain liquid crystal cell, it is possible to obtain a black and white display with almost no coloring. As a result of similar examinations with respect to other twist angles, it was found that a good display image without coloring was obtained when the twist angle was in the range of 65 degrees to 115 degrees.

A TFT active matrix type liquid crystal display element having a screen size of 9.5 inches was manufactured by the above-mentioned structure of the main part, and was driven to display an image, and its image display quality was verified. It was confirmed that a liquid crystal display device with a black and white display and a wide viewing angle can be realized. Further, when the halftone display was performed, it was confirmed that a good display can be realized without causing the display image to be reversed in brightness regardless of the azimuth.

In the above embodiments, the case where the present invention is applied to the TFT active matrix type liquid crystal display element has been described, but the application of the present invention is such a T-type.
The invention is not limited to the FT active matrix type liquid crystal display element. Needless to say, the present invention can also be applied to an active matrix type liquid crystal display element using a two-terminal element such as an MIM element and a simple matrix type liquid crystal display element.

Needless to say, various changes can be made to the material for forming each part of the liquid crystal display device of the present invention without departing from the scope of the present invention.

(Comparative Example to the Above Example) In the above example, a liquid crystal display element was produced in which the liquid crystal cell 21 was replaced with a liquid crystal cell using a spacer having a diameter of 6 μm, and this was driven to display a display image. I observed. In this way, the diameter is 6μ
The cell gap of the liquid crystal cell is approx.
When m, the retardation Δnd is about 570 nm
Becomes In this case, the twist angle θ of the liquid crystal molecules of the liquid crystal layer was set to 90 degrees as in the above-mentioned embodiment, and the other settings were also set as in the above-mentioned embodiment.

When the liquid crystal display device of such a comparative example was driven under the same driving conditions as those of the above-mentioned embodiment to display an image of the same pattern as that of the above-mentioned embodiment, the image display was colored in light yellow, When full-color display is performed using a color filter or the like, an image is colored in an inconvenient color different from the color originally desired to be expressed, and the display quality is significantly deteriorated.

[0036]

As clearly described in the detailed description above, according to the present invention, a liquid crystal which realizes a wide and uniform viewing angle characteristic without causing inconvenient coloring different from the color originally desired to be expressed in an image. A display element can be provided.

[Brief description of drawings]

FIG. 1 is a diagram showing a configuration of a main part of a liquid crystal display element according to the present invention.

FIG. 2 is a diagram showing a viewing angle characteristic of a normally open and normally closed contrast ratio of a TN cell in the left-right direction.

FIG. 3 is a diagram showing viewing angle characteristics of luminance in a normally open and normally closed dark state of a TN cell in a dark state.

FIG. 4 is a diagram showing the transmittance-applied voltage characteristics of a normally closed TN cell at an incident angle of 60 degrees in the vertical and leftward directions.

FIG. 5 is a diagram showing the transmittance-applied voltage characteristics of a normally closed multi-domain cell at an incident angle of 60 degrees in the upper and lower left directions.

FIG. 6 is a diagram showing a relationship between a transmittance characteristic and a retardation value for each wavelength of red, blue, and green color light in a normally white 90 ° twist TN cell.

FIG. 7 is a diagram showing a relationship between a transmittance characteristic and a retardation value for each wavelength of red, blue, and green color light in a normally white 90 ° twist multi-domain cell.

[Explanation of symbols]

 1 ... Scanning line 3 ... Signal line 5 ... Pixel electrode 7 ... TFT 9, 15 ... Alignment film 11 ... TFT array substrate 13 ... Counter electrode 17 ... Counter substrate 19 ... Liquid crystal layer 21 ... Liquid crystal cell 23, 25 ... Polarizing plate 27, 29 ... Glass substrate

Claims (1)

[Claims] 1. An electrode for image display, which is formed so as not to be subjected to an alignment treatment for aligning the major axis directions of liquid crystal molecules in the same direction, and is arranged to face each other with a gap. The two substrates, the major axis direction of the liquid crystal molecules being held in a substantially horizontal position when no voltage is applied to the substrate surface, and the major axis direction of the liquid crystal molecules being held in the substantially horizontal position. The liquid crystal molecules are oriented in a substantially non-uniform orientation on the surface, and are sandwiched between the two substrates so that the liquid crystal molecules are twisted and aligned in the space between the two substrates in a direction perpendicular to the substrate surface. And a retardation value of the liquid crystal layer of 440 nm ± 50 nm.
And a twist angle of liquid crystal molecules of the liquid crystal layer in the range of 65 degrees to 115 degrees.