JP3850002B2 - Liquid crystal electro-optical device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To manufacture a liquid crystal electrooptical device which can enlarge viewing angle, improve display quality and improve contrast with an easy manufacturing process and a high yield. SOLUTION: A pair of substrates is provided with an interposed liquid crystal layer comprising a liquid crystal material exhibiting nematic phase at least within a specified temp. range and having negative dielectric anisotropy. A homeotropic alignment layer is located on the surface adjacent to the liquid crystal layer of each of the substrates 1, 2. Each of the alignment layers on the substrates 1, 2 is divided into two alignment regions with directions of pretilt different from each other by about 180 deg.. The two substrates 1, 2 are stuck with each other so as to make a boundary of the alignment regions on one substrate 1 and a boundary of the alignment regions on the other substrate 2 are at right angle with each other to form four alignment regions.

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention is mainly used as a display device and the like, and is preferably used for a flat display device such as a personal computer, a word processor, an amusement device, a television device, a display plate using a shutter effect, a window, a door, a wall, etc. The present invention relates to a liquid crystal electro-optical device that can perform the above.
[0002]
[Prior art]
Conventionally, in a liquid crystal electro-optical device, in particular, a liquid crystal display device, an attempt has been made to widen the viewing angle by so-called alignment division in which regions having different alignment directions of liquid crystal molecules are formed in a certain region. When this alignment division is performed, a twisted nematic mode (TN) is usually used as a display mode, and the alignment direction of liquid crystal molecules is different by performing mask rubbing of the alignment film, light irradiation, or the like. Was established.
[0003]
On the other hand, in recent years, development of a technique for aligning liquid crystal molecules perpendicularly to a substrate without applying an electric field to the liquid crystal layer has progressed from the viewpoint of widening the viewing angle, improving display quality, and improving contrast.
[0004]
Furthermore, an example in which this vertical alignment technique and the above-described alignment division technique are combined is also described in, for example, Japanese Patent Application Laid-Open No. 8-43285. Here, a vertical twisted nematic mode is realized by controlling the orientation direction or pretilt of liquid crystal molecules and adding a chiral dopant.
[0005]
[Problems to be solved by the invention]
As described above, the vertical alignment twisted nematic mode liquid crystal display device has advantages in that the viewing angle can be increased, the display quality can be improved, and the contrast can be improved as compared with the horizontal alignment twisted nematic mode.
[0006]
However, a liquid crystal display device combining a vertical alignment technique and an alignment division technique, particularly the liquid crystal display apparatus described in JP-A-8-43285 has the following problems.
[0007]
That is, in this liquid crystal display device, it is necessary to align the alignment division line between the array side substrate and the counter substrate. However, due to factors such as pattern accuracy, substrate shrinkage, and alignment device accuracy, the actual manufacturing process Then, a deviation of several μm occurs. This shift causes a region where the liquid crystal molecules cannot be well aligned, and the display quality may be remarkably lowered, and there is a concern that the yield rate and cost increase.
[0008]
Furthermore, in the conventional alignment dividing method, in order to realize a four-divided alignment state, it is necessary to form four different alignment states on both the upper and lower substrates, which complicates the manufacturing process. It was.
[0009]
The present invention has been made to solve the above-described problems of the prior art, and can facilitate the manufacturing process, improve the yield rate, and improve the viewing angle, display quality, and contrast. An object of the present invention is to provide a liquid crystal electro-optical device that can be used.
[0010]
[Means for Solving the Problems]
The liquid crystal electro-optical device of the present invention is provided with a pair of substrates sandwiching a liquid crystal layer made of a liquid crystal material exhibiting a nematic phase at least in a predetermined temperature range and having a negative dielectric anisotropy. In a liquid crystal electro-optical device having an alignment film for aligning liquid crystal molecules substantially perpendicularly to the surface of the substrate when no voltage is applied to the surface on the liquid crystal layer side, the alignment film on each substrate has the liquid crystal molecules on the substrate surface. Each of them is divided into two or more types of alignment regions having different pretilt directions that are slightly tilted from the perpendicular direction, and the boundary of the alignment region on one substrate intersects the boundary of the alignment region on the other substrate. The substrates are bonded together, thereby achieving the above object.
[0011]
Each of the alignment films on each substrate has two types of alignment regions whose pretilt directions of the liquid crystal molecules are different by about 180 °, and the boundary between the alignment regions on one substrate and the alignment region on the other substrate Both substrates may be bonded together so that is substantially orthogonal.
[0012]
In the alignment film on the one substrate and the alignment film on the other substrate, the pretilt directions of the liquid crystal molecules may be substantially orthogonal.
[0013]
The alignment film may be made of a material containing at least a part of at least one of polyimide, polyamide, and polysiloxane, or may be made of silicon oxide.
[0014]
The alignment film may be subjected to alignment treatment by a rubbing method, an ion beam irradiation method, a light irradiation method, a shape control method, or an oblique deposition method.
[0015]
The liquid crystal layer may be made of a liquid crystal material containing no chiral dopant.
[0016]
The operation of the present invention will be described below.
[0017]
In the present invention, the vertical alignment film on each substrate is divided into two or more alignment regions having different pretilt directions of liquid crystal molecules, and the two substrates are bonded so that the boundaries of the alignment regions on both substrates intersect. As a result, each region divided on one substrate is further divided on the boundary of the alignment region on the other substrate. Thereby, the alignment process performed on the alignment film on each substrate for alignment division can be reduced. For example, by dividing the alignment direction into two on each substrate, a four-division alignment state is obtained. It is done.
[0018]
Further, as disclosed in JP-A-8-43825, since it is not necessary to strictly align the boundary between the alignment regions of both substrates, a region where the liquid crystal cannot be well aligned does not occur, and a good display state can be obtained.
[0019]
The liquid crystal layer is made of a liquid crystal material that exhibits a nematic phase at least in a predetermined temperature range and has negative dielectric anisotropy. When no voltage is applied, liquid crystal molecules are aligned in a direction substantially perpendicular to the substrate, and voltage is applied. When applied, the liquid crystal molecules tilt in a direction perpendicular to the direction of the electric field according to the pretilt direction.
[0020]
Thus, by combining the vertical alignment and the alignment division, when used as a display device, it is possible to increase the viewing angle, improve the display quality, and improve the contrast.
[0021]
By the way, when the viewing angle is widened by the orientation division, the 90 ° twisted vertical orientation mode is usually used because a high contrast display can be obtained under a low driving voltage.
[0022]
Therefore, in the present invention, for example, as shown in FIGS. 1A and 1B, which will be described later, the alignment film on each substrate is aligned in two types of alignment regions in which the pretilt direction of the liquid crystal molecules differs by approximately 180 °. As shown in FIG. 2 to be described later, the two substrates are bonded so that the boundaries of the alignment regions on both substrates are substantially orthogonal, so that the pretilt directions of the liquid crystal molecules in the alignment films on both substrates are approximately orthogonal. May be. In this way, it is possible to realize a 90 ° twisted vertical alignment without the aid of a chiral dopant, and by dividing the alignment direction into two on each substrate, a quadrant as shown in FIG. A 90 ° twisted vertical alignment state is obtained.
[0023]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below.
[0024]
Here, an active matrix transmission type color liquid crystal display device having a structure in which a large number of pixel electrodes are provided on one substrate and a potential is selectively applied to each pixel electrode via a switching element composed of a low-temperature polysilicon thin film transistor. An example to which the present invention is applied will be described.
[0025]
This liquid crystal display device includes a thin film transistor having polysilicon formed as a semiconductor layer on a glass substrate at a low temperature of 600 ° C. or lower, an array side substrate on which pixel electrodes, bus lines, signal input terminals, and the like are formed, a color filter, and a light shielding A vertical alignment film is formed on both the opposite substrate on which the film and the like are formed.
[0026]
As shown in FIG. 1A, the vertical alignment film provided on one substrate (lower substrate) 1 initially slightly tilts liquid crystal molecules in contact with the vertical alignment film from a direction perpendicular to the substrate (pretilt). ) Is performed in two directions that are approximately 180 ° apart and is divided into two alignment regions. As shown in FIG. 1B, the vertical alignment film provided on the other substrate (upper substrate) 2 is subjected to alignment processes for pretilting the liquid crystal molecules in contact with the vertical alignment film in two directions that differ by approximately 180 °. It is divided into two alignment regions.
[0027]
As shown in FIG. 2, the two substrates 1 and 2 are bonded to each other so that the boundaries of the regions with different orientation directions on each substrate intersect (substantially orthogonal here). The pretilt direction of the alignment film is substantially orthogonal. In a state where the liquid crystal is sealed, four regions having different twist directions of liquid crystal molecules are formed, and four viewing angle directions are obtained.
[0028]
As the vertical alignment film, a material containing at least a part of at least one of polyimide, polyamide, and polysiloxane, for example, a polymer compound such as polyimide, polyamic acid, polyamide, polyamideimide, polysiloxane, or the like is used. For example, RN-783 (manufactured by Nissan Chemical Industries, Ltd.) can be used. Alternatively, an inorganic material such as silicon oxide may be used.
The vertical alignment film made of a polymer compound can be formed using, for example, a printing method, a spin coating method, a dipping method, or the like. On the other hand, the alignment film made of an inorganic material is generally formed by oblique deposition, and can also serve as an alignment treatment.
[0029]
The alignment treatment can be performed on an alignment film mainly composed of a polymer compound by using a rubbing method, an ion beam irradiation method, a light irradiation method, or the like.
[0030]
Here, since it is necessary to perform alignment processing in two directions on each substrate, a special alignment processing direction is required.
[0031]
For example, in the case of performing the rubbing method, first, rubbing is performed in one direction using a mask having an opening in a predetermined region, and then in the reverse direction using a mask having a complementary opening. There is a method of performing a rubbing process. However, in this method, due to the alignment accuracy of the mask, an area where alignment processing cannot be performed inevitably occurs. Therefore, it is desirable that the entire surface is once rubbed in a certain direction and then a necessary region is covered with a mask or a photoresist so that the rubbing treatment is performed in the reverse direction. As for the rubbing condition at this time, it is desirable to perform the second rubbing process stronger than the first.
[0032]
When the light irradiation method is used, a method of irradiating ultraviolet light from an oblique direction or a method of irradiating polarized ultraviolet light is generally used. However, since there is a problem similar to the rubbing method, it is desirable to perform alignment division by covering the necessary area with a photomask or the like and changing the light irradiation direction to each substrate and irradiating from two directions. Even in this case, it is possible to align the entire surface once in a certain direction and then perform the alignment processing in the reverse direction only in the necessary region. However, in the region subjected to the alignment processing twice, the alignment regulating force is slightly reduced. There is.
[0033]
Also in the ion beam irradiation method, alignment division can be performed by covering a necessary region with a metal mask or the like and irradiating each substrate from two directions while changing the irradiation direction. Also in this case, once the entire surface is aligned in a certain direction, it is possible to align only the necessary region in the reverse direction.
[0034]
In the case of the shape control method, as shown in FIG. 3, a shape for controlling the pretilt direction of the liquid crystal molecules is previously formed on the substrate 7 using a photoresist 8 or the like, and the vertical alignment is formed thereon. By forming a film, alignment division can be performed.
[0035]
In the case of the oblique deposition method, the necessary area is covered with a metal mask or the like, the deposition direction is changed with respect to each substrate, the deposition is performed twice, and further, the deposition is performed once for the vertical orientation, thereby dividing the orientation. It can be performed.
[0036]
In this way, the two substrates in which the regions of the orientation directions different from each other by 180 ° on the respective substrates are formed in a predetermined portion, as shown in FIG. Here, they are bonded together so as to face each other. Then, the periphery is sealed, and a liquid crystal panel having a negative dielectric anisotropy is injected into the gap between the two substrates to seal the injection port, thereby obtaining a liquid crystal panel. As the liquid crystal material at this time, for example, MLC-2012 (manufactured by Merck Japan Ltd.) can be used.
[0037]
A liquid crystal display device can be manufactured by attaching a polarizing plate to the liquid crystal panel in a predetermined direction, connecting to a driving circuit, and applying an appropriate signal.
[0038]
The liquid crystal display device thus manufactured can obtain a very wide viewing angle characteristic with a contrast angle of 5 or more and 70 ° or more each.
[0039]
Furthermore, since a four-division alignment state can be obtained simply by performing an alignment process in two directions on each substrate, the manufacturing process is much higher than in the prior art that requires an alignment process in four directions for each substrate. This is very advantageous in terms of both cost and yield rate.
[0040]
Although an active matrix type liquid crystal display device using a low-temperature polysilicon thin film transistor has been described here, a non-linear element array such as a thin film transistor or various diodes using amorphous silicon, polysilicon, single crystal silicon or the like is used as necessary. Can be provided. Alternatively, the present invention can also be applied to a liquid crystal electro-optical device having no configuration.
[0041]
In the case of a substrate provided with a nonlinear element array, it is common to divide the orientation direction into four for each pixel electrode. However, when displaying one dot with a plurality of pixel electrodes, The necessary number of orientation divisions may be performed.
[0042]
In FIGS. 1A and 1B, the pretilt direction is set substantially perpendicular to the boundary of the alignment region. However, the pretilt direction of the liquid crystal molecules on both the substrates is determined by crossing the boundary of the alignment region on both substrates. Other pretilt directions may be used as long as they can be twisted by 90 °. For example, a 90 ° twisted vertical alignment can be formed even if the pretilt direction is substantially parallel to the boundary of the alignment region, or even if it is oblique.
[0043]
It is also possible to divide the liquid crystal layer into regions having five or more alignment states by performing alignment treatment in one or more directions on one substrate or each substrate. However, since the light transmission characteristics in each alignment region are different, in the case of a liquid crystal display device, two regions having a pretilt direction different by 180 ° are formed on each substrate to form four alignment states. It is preferable to prepare a liquid crystal region. At this time, it is preferable that the areas of the portions to be subjected to the alignment treatment are made equal so that regions having different viewing angle directions appear at the same rate.
[0044]
The twist angle may be an angle other than 90 °, and the alignment division can be performed by setting the alignment processing direction and the crossing angle of the boundary of the alignment region according to the required characteristics.
[0045]
Furthermore, in order to increase the area of each alignment division region, as shown in FIG. 4, it is possible to make adjacent portions in the adjacent pixels have the same alignment direction, and such alignment division is performed on either one of the substrates. It is also possible to do only above. In FIG. 4, 5 indicates a pixel electrode.
[0046]
In this embodiment, the transmissive liquid crystal display device has been described. However, a reflective liquid crystal display device having a structure similar to that of the transmissive type and having a reflective plate disposed behind, or a reflective liquid crystal having an electrode on one substrate as a reflective electrode. The present invention can also be applied to a display device. In the case of performing transmissive display, a light-transmitting substrate may be used for both substrates, and in the case of performing reflective display, at least one of the substrates may be translucent. Alternatively, various configurations such as a combined liquid crystal display device combining a transmission type and a reflection type are possible, and the present invention can be applied not only to a direct view type but also to a projection type display device.
[0047]
The present invention is not limited to a liquid crystal display device, and can be applied to electro-optical devices other than display devices such as a display plate, a window, a door, a wall, and an information processing device using a shutter effect.
[0048]
【The invention's effect】
As described above in detail, according to the present invention, an excellent liquid crystal display device having a wide viewing angle, good display quality and contrast can be manufactured at a low cost by a simple method.
[0049]
The liquid crystal display device of the present invention having such excellent characteristics is suitably used for a flat display such as a personal computer, a word processor, an amusement device, a television device, a display plate using a shutter effect, a window, a door, a wall, etc. be able to.
[Brief description of the drawings]
1A and 1B are diagrams showing a liquid crystal display device according to an embodiment of the present invention, in which FIG. 1A shows the alignment direction of an alignment film provided on a lower substrate, and FIG. 1B is provided on an upper substrate; The alignment direction of the alignment film is shown.
FIG. 2 is a diagram showing a twist direction and a viewing angle direction of liquid crystal in a liquid crystal display device according to an embodiment of the present invention.
FIG. 3 is a diagram for explaining an example of an alignment treatment method for an alignment film;
FIG. 4 is a diagram for explaining how to perform alignment division in a liquid crystal display device according to another embodiment of the present invention.
[Explanation of symbols]
1 Lower substrate 2 Upper substrate 5 Pixel electrode 7 Substrate 8 Photoresist 9 Alignment film

Claims (5)

A pair of substrates is provided sandwiching a liquid crystal layer made of a liquid crystal material that exhibits a nematic phase at least in a predetermined temperature range and has negative dielectric anisotropy and does not contain a chiral dopant, and the liquid crystal layer of each of the substrates In the liquid crystal electro-optical device having an alignment film for aligning liquid crystal molecules substantially perpendicularly to the surface of each substrate when no voltage is applied to the side surface,
The alignment film on each substrate is divided into two or more alignment regions having different pretilt directions that slightly tilt the liquid crystal molecules from a direction perpendicular to the surface of each substrate. Each of the substrates is bonded so that the boundary and the boundary of the alignment region on the other substrate intersect,
The alignment film on the one substrate and the alignment film on the other substrate are arranged so that the boundary of the alignment region and the pretilt direction of the liquid crystal molecules are substantially parallel by oblique light irradiation from two directions. A liquid crystal electro-optical device in which each alignment region is formed .   Each of the alignment films on each substrate has two types of alignment regions in which the pretilt direction of the liquid crystal molecules differs by approximately 180 °, and a boundary between alignment regions on one substrate and a boundary between alignment regions on the other substrate The liquid crystal electro-optical device according to claim 1, wherein the substrates are bonded to each other so as to be substantially orthogonal to each other.   3. The liquid crystal electro-optical device according to claim 2, wherein the alignment film on the one substrate and the alignment film on the other substrate are substantially perpendicular to the pretilt direction of the liquid crystal molecules.   The liquid crystal electro-optic according to any one of claims 1 to 3, wherein the alignment film is made of a material containing at least a part of at least one of polyimide, polyamide, and polysiloxane, or made of silicon oxide. apparatus.   5. The liquid crystal electro-optical device according to claim 1, wherein the alignment film is subjected to alignment treatment by a rubbing method, an ion beam irradiation method, a light irradiation method, a shape control method, or an oblique deposition method.

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