JP2965826B2 - Manufacturing method of 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 method for manufacturing a liquid crystal display device having a wide viewing angle characteristic and a good contrast without light leakage.

[0002]

2. Description of the Related Art In a liquid crystal display (LCD), a liquid crystal layer is sandwiched between a pair of opposing substrates, and the difference in optical refractive index between the major axis direction and the minor axis direction of liquid crystal molecules is utilized. It is a configuration to display. Therefore, it is important to arrange the liquid crystal molecules regularly in advance. For this reason, generally, an alignment film is provided on the surface of the substrate sandwiching the liquid crystal layer, and the surface of the alignment film is rubbed to align the liquid crystal molecules in a certain direction.

[0003] There are two types of alignment films, inorganic alignment films and organic alignment films. An oxide, an organic silane, a metal, a metal complex, or the like is used for the inorganic alignment film. On the other hand, there are many polymer materials for the organic alignment film, and a polyimide resin is a typical alignment film material currently used. For example, by rubbing a polyimide film formed on a substrate using this polyimide resin as an alignment film material, liquid crystal molecules can be aligned. Such an alignment is because the rubbing process is performed in a uniform direction on the substrate, so that a uniform viewing angle direction and a uniform pretilt angle can be obtained in the liquid crystal cell.

In a twisted nematic liquid crystal display device (TFT-LCD) having a thin film transistor as a switching element, liquid crystal molecules are oriented so as to be twisted by 90 ° between a pair of substrates, and the viewing angle direction is the liquid crystal. It follows the orientation of the liquid crystal molecules in the layer.

[0005]

In the above twisted nematic liquid crystal display device, a phenomenon occurs in which the contrast changes depending on the viewing angle. Generally, in a normally white mode in which white display is performed when no voltage is applied, when a voltage is applied and the liquid crystal cell is viewed from directly above (in a direction perpendicular to the substrate surface), as shown by a solid line LI in FIG. As the value increases, the light transmittance decreases, and when the value is saturated, the transmittance becomes almost zero.

When the viewing angle is tilted from right above to the normal viewing angle direction, that is, the direction in which the edge of the liquid crystal molecules is tilted toward the observation side, the applied voltage-transmittance characteristic is reduced as shown by a solid line L2 in FIG. Change. That is, the transmittance decreases to some extent as the applied voltage increases, then increases again beyond a specific voltage value, and then gradually decreases again. In such a changing state, a grayscale inversion occurs in the vicinity where the reduced transmittance becomes high again, and a phenomenon occurs in which the black and white of the image is inverted. This occurs because the liquid crystal molecules are tilted and the refractive index changes depending on the viewing angle.

The reason why the above-described reversal phenomenon occurs will be described below with reference to FIGS. FIG. 7 is a sectional view of the liquid crystal cell. This liquid crystal cell comprises
Between 1 and 32, a liquid crystal layer having liquid crystal molecules 35 is provided. The substrate 31 includes a glass substrate 31a, a transparent electrode 3
The substrate 32 includes a glass substrate 32a, a transparent electrode 32b, and an alignment film 32c.
The liquid crystal molecules 35 are twisted by 90 degrees between the substrates 31 and 32. The symbol δ in FIG. 7 indicates the pretilt angle, and the number 36 indicates the normal viewing angle direction.

In such a liquid crystal cell, FIG.
As shown in (2), when the voltage applied between the transparent electrodes 31b and 32b is set to zero or a relatively low voltage, the central molecule 35 looks elliptical to the observer 37 located in the normal viewing direction. When the applied voltage is gradually increased, as shown in FIG. 6B, the central molecule 35 moves in the direction of the electric field, and at a certain point, the central molecule 35 looks like a perfect circle. When the applied voltage is further increased, as shown in FIG. 6C, the central molecule 35 approaches parallel to the direction of the electric field, and the observer 37 again sees the central molecule 35 as an ellipse.

In the viewing angle direction other than the normal viewing angle direction 36, the transmittance-applied voltage characteristic similarly changes, but the inversion phenomenon does not occur. Also, the contrast ratio decreases as the viewing angle increases.

A technique for obtaining such a liquid crystal display device in which the viewing angle characteristic peculiar to the TN mode is improved is disclosed in JAPA.
P591-p594 and p of N DISPLAY '92
886. One of them is to rub the surface of the alignment film in one direction, cover a part of it with resist, rub it in the direction opposite to the rubbing direction that was done earlier, then remove the resist and coat it with resist Rubbing direction is made different between the region which has been covered and the region which has not been covered with the resist, so that the viewing angle direction is made different in the same cell (hereinafter referred to as a double rubbing method).
It is. The other is a method of forming a plurality of pretilt angles corresponding to each material on the surface of the alignment film by rubbing the polyimide alignment films of different materials in parallel (hereinafter, referred to as an alignment film patterning method). It is. According to these methods, a region in two directions of a normal viewing angle direction and a reverse viewing angle direction (a direction opposite to the normal viewing angle direction) is formed in the same cell. It looks mixed and the reversal phenomenon in the normal viewing direction and the sharp decrease in contrast in the reverse viewing direction are alleviated and improved.

By the way, two regions having different viewing angles may be provided in units of picture elements, but it is preferable to divide one picture element into a plurality in order to obtain more precise display. In this case, a disclination line is generated at the boundary between two regions having different viewing angles. This disclination line, Ru Oko Ri by the scattering of light <br/> the discontinuity surface of the liquid crystal. In particular, in a normally white mode in which black display is performed when a voltage is applied, the contrast decreases due to the disclination line. The present invention has been made to solve such a problem of the related art, and provides a method of manufacturing a liquid crystal display device capable of preventing the occurrence of disclination lines at boundaries between regions having different viewing angles. The purpose is to:

[0012]

[0013]

[0014]

[0015]

According to a method of manufacturing a liquid crystal display device of the present invention, a liquid crystal layer sandwiched between a pair of substrates has one liquid crystal layer.
In a picture element, a liquid crystal molecule is inclined with respect to a substrate and has two or more regions having different alignment states, and a vertical alignment region in which liquid crystal molecules are vertically aligned with respect to the substrate between regions having different alignment states. A method of manufacturing a liquid crystal display device, comprising selectively irradiating light to a portion corresponding to the vertical alignment region in at least one of the alignment films provided in a portion of the pair of substrates in contact with the liquid crystal layer. a step of forming a vertical alignment region and Nde containing the above objects attained by its
Is done.

In this manufacturing method, the light may be ultraviolet light, visible light, infrared light, or laser light having the same wavelength range as these.

[0017]

[0018]

[0019]

According to the present invention, when at least one of the alignment films provided on each of the pair of substrates is selectively irradiated with light, the liquid crystal layer portion in contact with the alignment film portion irradiated with the light is changed. A state having a vertical alignment region is obtained. Therefore, a liquid crystal layer structure in which liquid crystal molecules are tilted with respect to the substrate and a vertical alignment region exists between liquid crystal layer regions having different alignment states in one pixel.

In the liquid crystal display device of the present invention having such a structure, the occurrence of disclination lines is eliminated at the boundary between regions having different viewing angles.

The principle of giving different alignment characteristics to the alignment film by light irradiation and the principle of eliminating disclination lines (= light leakage) are as follows. When high energy is applied to the alignment film by light irradiation, a change occurs in the structure of the polymer forming the alignment film. That is, a bond in a portion having a low binding energy is broken or another bond is formed. Then, when a high energy is sufficiently applied, these reactions occur one after another, and the surface of the alignment film is gradually eroded and roughened. When the roughening proceeds sufficiently on the surface of the alignment film, the liquid crystal molecules in contact with the roughened alignment film portion are aligned perpendicular to the substrate. That is, a vertical alignment region is formed.

In such a state, as shown in FIG. 8, the orientation of the liquid crystal molecules changes almost continuously between the liquid crystal molecules that rise when voltage is applied and the liquid crystal molecules that are vertically aligned in the vertical alignment region. Therefore, there is no discontinuous surface, and no light leakage occurs.

The vertical alignment region can also be formed by selective surface treatment of the alignment film or by selective formation of the alignment film. The former forms a vertical alignment region by roughening the surface of the alignment film in the same manner as light irradiation, and the latter forms a vertical alignment film only in a necessary region, thereby forming a vertical alignment region.

The present invention is effective in any liquid crystal display device having two or more alignment states in one picture element.

[0025]

Embodiments of the present invention will be described below in detail.

Embodiment 1 FIG. 1 is a sectional view showing a liquid crystal display device according to the present embodiment. The liquid crystal molecules in this figure show the case where a voltage is applied. In this liquid crystal display device, a liquid crystal layer 3 is provided between a pair of substrates 1 and 2 facing each other. The liquid crystal layer 3 has a twisted nematic structure twisted by 90 degrees between the two substrates, and has a normally white mode in which white display is performed when no voltage is applied.

One of the pair of substrates 1 and 2 (upper side)
In the substrate 2, a counter electrode 8 and an alignment film 9 are formed on a base substrate 7 in this order and almost over the entire surface.

The other (lower) substrate 1 is a base substrate 4
Pixel electrodes 5 are formed in a matrix on the substrate, and an alignment film 6 is formed on almost the entire surface of the base substrate 4 so as to cover the pixel electrodes 5. In the illustrated example, each picture element electrode 5
Constitutes one picture element. When a black mask having an opening smaller than the pixel electrode 5 is provided,
The size of the opening is the size of the picture element.

The alignment film 6 includes three regions 6a, 6b and 6 having different alignment states along one direction in one picture element.
The structure has c. Further, in the liquid crystal layer 3, the tilt direction of the liquid crystal molecules is different between a liquid crystal layer region A contacting the region 6a, a liquid crystal layer region B contacting the region 6b, and a liquid crystal layer region C contacting the region 6c. More specifically, in the liquid crystal layer region A, the upper end of the liquid crystal molecule is inclined so as to be located at the upper left, and in the liquid crystal layer region B, the upper end of the liquid crystal molecule is located at the upper right, contrary to the case of the liquid crystal layer region A. It is inclined to be located at. In the liquid crystal layer region C sandwiched between the liquid crystal layer region A and the liquid crystal layer region B,
Both ends of the liquid crystal molecules are perpendicular to both substrates 1 and 2. That is, it is a vertical alignment region.

FIG. 2 schematically shows a light irradiation step in the method of manufacturing such a liquid crystal display device. First, a pixel electrode 5 is formed on the lower substrate 1 by a known manufacturing method, and an alignment film 6 is formed on the entire surface of the substrate 1 so as to cover the pixel electrode 5.
To form In this embodiment, a polyimide film, which is one of organic polymer films, is used as the alignment film 6. After forming the alignment film 6, the picture element is divided into a plurality of regions 6a, 6b,
6c, the regions 6a and 6b are subjected to an orientation process,
The orientation states of the regions 6a and 6b are made different. Due to this change in the alignment state, the viewing angle direction differs in each region. At this time, the alignment processing may be performed on the region 6c in the same manner as the alignment state of one of the regions 6a and 6b. Note that the step of dividing the picture element to have different alignment characteristics may be configured by any method including the above-described double rubbing method and the alignment film patterning method.

Next, the light shielding unit 1 is placed on the substrate 1 in this state.
A mask 11 provided with a light transmitting portion 11b in a part of 1a is set. At the time of this set, the light transmitting portion 11b is positioned above an area between two areas having different alignment states.

Next, the alignment film 6 is irradiated with light 15 from above the mask 11. The light used is ultraviolet light, visible light,
Although any of infrared light may be used, ultraviolet light having a wavelength of 400 nm or less is preferable as a light source that easily obtains high energy for changing the alignment state. Light of such a wavelength can be obtained with a high-pressure mercury lamp, a low-pressure mercury lamp, a mercury-xenon lamp, or the like. When irradiating with ultraviolet light, 30 J / cm ²
Irradiation is preferably performed under the above conditions. In addition to ultraviolet light, visible light, infrared light, or laser light in the same wavelength range as these may be used. Further, an electron beam, an ion beam, X-rays, or the like can be used.

As a result of the light irradiation, the region 6c in the alignment film 6 is brought into a different alignment state from the regions 6a and 6b by the light irradiation.

When the other substrate 2 prepared in advance is opposed to the substrate 1 having such an alignment film 6, and a liquid crystal is injected between them to form a liquid crystal layer 3, the liquid crystal layer 3
In the liquid crystal layer region A that is in contact with the region 6a of the alignment film 6, the liquid crystal molecules are in an inclined state such that the upper ends of the liquid crystal molecules are located at the upper left. In the liquid crystal layer region B that is in contact with the region 6b, the liquid crystal layer is in an inclined state such that the upper end of the liquid crystal molecule is located at the upper right, contrary to the liquid crystal layer region A. In the liquid crystal layer region C which is in contact with the region 6c sandwiched between the regions 6a and 6b, the liquid crystal molecules are in a vertical alignment state in which both ends of the liquid crystal molecules are perpendicular to the substrates 1 and 2. That is, it becomes a vertical alignment region.

Therefore, in the above-mentioned liquid crystal display device, the presence of the liquid crystal layer region C which is a vertical alignment region causes
The occurrence of a disclination line is prevented at the boundary between regions having different viewing angles.

The light irradiation step can be performed at any time after the formation of the alignment film. Specifically, it may be at any time after the application of the alignment film 6, after the preliminary baking, after the main baking, after the rubbing treatment, or after the substrate cleaning after the rubbing treatment. Further, it may be before or after the step of dividing the picture element to have different alignment characteristics.

As the mask 11 described above, for example, a mask similar to a commonly used photomask can be used. Alternatively, a mask pattern may be formed directly on the alignment film 6 using the photolithography technique, and the mask may be peeled off after irradiation with light. Also, by condensing the light to a size equal to or smaller than the width of the boundary region, it is possible to irradiate only the desired region with light. As the means, a lens may be used, or laser light may be used.

(Embodiment 2) In this embodiment 2, the surface of the alignment film is subjected to a surface treatment so that the liquid crystal layer region C vertically aligned with the boundary between the liquid crystal layer regions A and B, similarly to the light irradiation described above.
Is formed. The substrate structure and the like are the same as in the first embodiment.

The manufacturing in this case is performed as follows. First, a pixel electrode 5 is formed on the lower substrate 1 by a known manufacturing method in the same manner as in Example 1, and an alignment film 6 is formed on the entire surface of the substrate 1 so as to cover the pixel electrode 5. .

Subsequently, a picture element is divided into a plurality of areas 6 by an arbitrary method.
The regions 6a and 6b are divided into regions a, 6b, and 6c, and the regions 6a and 6b are subjected to an alignment process so that the regions 6a and 6b have different alignment states.

Next, as shown in FIG. 3, a resist 17 is formed on the alignment film 6 by using, for example, a photolithography technique.
To form a pattern. At this time, a region other than the vertical alignment region is covered with the resist 17.

Thereafter, the surface of the alignment film 6 is brought into contact with an alkaline solution, and only the contact surface of the alignment film 6 is subjected to a surface treatment to roughen the surface. As the alkaline solution, a 0.5% aqueous solution of NaOH or a 2.38% aqueous solution of TMAH can be used.
Acid solutions can also be used for surface treatment. An example is nitric acid. Further, ozone or ammonia gas which is a reactive gas may be used.

As a result of the above surface treatment, the region 6c of the alignment film 6
Are vertical alignment regions different from the regions 6a and 6b. As a result, the liquid crystal layer 3 is in an alignment state in which the liquid crystal molecules are inclined with respect to the substrate in the liquid crystal layer region in contact with the region 6a and the liquid crystal layer region in contact with the region 6b, and the liquid crystal layer in contact with the region 6c. In the region, the liquid crystal molecules are in a vertical alignment state oriented perpendicular to the substrate. That is, it becomes a vertical alignment region.

Therefore, also in the liquid crystal display device of this embodiment, the existence of the vertical alignment region prevents the generation of disclination lines at the boundary between the regions having different viewing angles.

(Embodiment 3) In this embodiment 3, a liquid crystal oriented perpendicular to the boundary between the liquid crystal layer regions A and B is formed by forming another alignment film in the boundary region, similarly to the light irradiation described above. This is a case where the layer region C is formed. Example 1 of substrate structure
Is the same as

The manufacturing in this case is performed as follows. First, a pixel electrode 5 is formed on the lower substrate 1 by a known manufacturing method in the same manner as in Example 1, and an alignment film 6 is formed on the entire surface of the substrate 1 so as to cover the pixel electrode 5. .

Subsequently, a picture element is divided into a plurality of areas 6 by an arbitrary method.
The regions 6a and 6b are divided into regions a, 6b, and 6c, and the regions 6a and 6b are subjected to an alignment process so that the regions 6a and 6b have different alignment states.

Next, as shown in FIG. 4A, a pattern of a resist 17 is formed on the alignment film 6 by using, for example, a photolithography technique. At this time, regions other than the vertical alignment region are covered with the resist 17.

Thereafter, as shown in FIG. 4B, the alignment film 6 in the vertical alignment region is removed, and then, as shown in FIG. An alignment film 18 having a property is applied.

Next, as shown in FIG. 4D, the resist 17 is removed.

As a result of the above processing, the region 6c of the alignment film 6 becomes a vertical alignment region different from the regions 6a and 6b. Thus, in the liquid crystal layer 3 in the liquid crystal layer region in contact with the region 6a of the alignment film 6, and in the liquid crystal layer region in contact with the region 6b, the liquid crystal molecules are in an inclined state with respect to the substrate.
In the liquid crystal layer region in contact with the liquid crystal layer, the liquid crystal molecules are in a vertical alignment state oriented perpendicular to the substrate. That is, it becomes a vertical alignment region.

Therefore, also in the liquid crystal display device of this embodiment, the presence of the vertical alignment region prevents the generation of disclination lines at the boundary between the regions having different viewing angles.

In each of Embodiments 1 to 3 described above, the liquid crystal molecules in the vertical alignment region are vertically aligned regardless of the presence or absence of an electric field. Therefore, even when no voltage is applied, the boundary region is displayed in black, and the opening correspondingly increases. However, if the boundary area to be irradiated with light is formed into a line having a minimum width, the decrease in the aperture ratio is suppressed to about 5%, which is a level that is almost no problem. In the first embodiment, a polyimide film is used as the alignment film 6, but another material, for example, an organic polymer mainly composed of polyamide, polystyrene, polyamideimide, epoxy acrylate, spiranaacrylate or polyurethane may be used. . In addition, an inorganic material containing silicon nitride, silicon oxide, magnesium fluoride, gold, or the like as a main component may be used. In this case, irradiation with high-energy light such as an ultraviolet laser or an electron beam is necessary. is there.

In each of Embodiments 1 to 3 described above, light irradiation, surface treatment, or film formation using a different material is performed on one of the pair of substrates in order to form a vertical alignment region in the liquid crystal layer. The present invention is not limited to this, and may be applied to both the pair of substrates. Further, in order to form the liquid crystal layer regions A and B having different alignment characteristics, the alignment film 9 may have different alignment characteristics. Further, one of the alignment films may be processed to form the liquid crystal layer regions A and B, and the other alignment film may be processed to form the vertical alignment region C.

In the above embodiment, the liquid crystal layer has a twisted nematic structure in which the liquid crystal layer is twisted by 90 degrees between the two substrates.
Although the present invention is applied to a liquid crystal display device of a normally white mode in which white display is performed when no voltage is applied, the present invention is not limited to this, and the same applies to a liquid crystal display device having a liquid crystal layer of another structure and mode. It is possible to apply.

Further, the present invention is not limited to a liquid crystal display device having two regions in each picture element where liquid crystal molecules are in an inclined state with respect to the substrate as described above. The present invention can also be applied to a liquid crystal display device in which three or more regions in an inclined state exist in one picture element. Even in this case, the boundary (between) of the regions having different orientation states
Needless to say, a configuration in which a vertical alignment region is present is provided.

[0057]

According to the present invention, since light leakage due to disclination lines is eliminated, display contrast is improved, and a liquid crystal display device having a high quality and a wide viewing angle can be obtained. In particular, if the light irradiation method is used,
Since the orientation of the boundary region can be changed only by irradiating light through the mask, the display quality of the liquid crystal display device having a wide viewing angle can be easily and inexpensively improved.

[Brief description of the drawings]

FIG. 1 is a sectional view showing a liquid crystal display device according to the present invention.

FIG. 2 is a cross-sectional view schematically showing a light irradiation step in the method for manufacturing the liquid crystal display device shown in FIG.

FIG. 3 is a schematic cross-sectional view of another embodiment used for manufacturing the liquid crystal display device shown in FIG.

FIG. 4 is a schematic sectional view of still another embodiment used for manufacturing the liquid crystal display device shown in FIG.

FIG. 5 is a graph showing an applied voltage-transmittance characteristic in a conventional liquid crystal display device.

FIG. 6 is a diagram for explaining an inversion phenomenon in a conventional liquid crystal display device.

FIG. 7 is a cross-sectional view for explaining viewing angle characteristics in a conventional liquid crystal display device.

FIG. 8 is a schematic sectional view of a boundary portion in the liquid crystal display device of the present invention.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1, 2 Substrate 3 Liquid crystal layer 4, 7 Base substrate 5 Pixel electrode 6 Alignment film 6a, 6b, 6c Area 8 Counter electrode 9 Alignment film 11 Mask 11a Shielding part 11b Light transmission part 15 Light 17 Resist 18 Vertical alignment film A Liquid crystal layer region B Liquid crystal layer region C Liquid crystal layer region (vertical alignment region)

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-5-173138 (JP, A) JP-A-6-214235 (JP, A) (58) Fields investigated (Int. Cl. ⁶ , DB name) G02F 1/1337 505

Claims (2)

(57) [Claims] 1. A liquid crystal layer sandwiched between a pair of substrates,
In one picture element, a liquid crystal molecule is inclined with respect to a substrate and has two or more regions having different alignment states, and a vertical alignment region in which the liquid crystal molecules are vertically aligned with respect to the substrate between the regions having different alignment states. A method for manufacturing a liquid crystal display device comprising: selectively irradiating light to a portion corresponding to the vertical alignment region in at least one of the alignment films provided in a portion of the pair of substrates in contact with the liquid crystal layer. A method for manufacturing a liquid crystal display device including a step of forming the vertical alignment region. To wherein said light, ultraviolet light, visible light, a method of manufacturing a liquid crystal display device according to claim 1, wherein the use of infrared light or laser light of the same wavelength region.