JPH0764087A - Production of liquid crystal display device - Google Patents

Abstract

PURPOSE:To easily control the visual angle direction by a pretilt angle. CONSTITUTION:The pretilt angle is stably controlled by controlling the quantity of oxygen affecting the surface of an oriented film 31c covered with a light shielding part 11a. The following two methods are applicable to the control of the oxygen quantity. One thereof is a method of subjecting the oriented film 31c to photoirradiation in an atmosphere partly replaced with an inert gas. The photoirradiation may be executed in a 100% inert gas. The ratio of the inert gas in the ordinary atm. is 80%. A reaction speed does not lower so much with the photoirradiation in the atmosphere contg. 85% inert gas but there is some influence on the light shielding part 11a. The light shielding part is not affected at all by the photoirradiation in the 100% inert gas but the reaction speed is lower. Another one is a method for subjecting the oriented film 31c to photoirradiation under a reduced pressure. This photoirradiation may be executed in the perfect vacuum. The reaction speed is lower as the degree of the reduced pressure is higher in this case, too.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method of manufacturing a liquid crystal display device having a wide viewing angle.

[0002]

2. Description of the Related Art A liquid crystal display device is a display device which utilizes an optical refractive index difference between a major axis direction and a minor axis direction of liquid crystal molecules in a liquid crystal layer provided between a pair of opposed substrates. An alignment film is provided on the liquid crystal layer side of the substrates sandwiching the liquid crystal layer. In this alignment film, the surface on the liquid crystal layer side is subjected to rubbing treatment so that liquid crystal molecules are aligned in a certain direction.

There are two types of alignment films, an inorganic alignment film made of oxides, organic silanes, metals, metal complexes, etc., and an organic alignment film represented by a polyimide resin. The rubbing treatment applied to such an alignment film is performed in a uniform direction in each part on the alignment film. Due to the existence of the alignment film subjected to the rubbing treatment, liquid crystal molecules are evenly distributed on the substrate. With a pre-tilt angle, a uniform viewing angle direction can be obtained within the display screen.

In a TFT liquid crystal display device having a thin film transistor (TFT) as a switching element, the liquid crystal molecules are twisted continuously while changing the direction at each position in the thickness direction of the liquid crystal layer, and 90 liquid crystal molecules are present in the vicinity of both substrates. Twisted (TN mode). The viewing angle direction of the liquid crystal display device is determined by the orientation of liquid crystal molecules in the liquid crystal layer, that is, the orientation with respect to the substrate and the twisting direction.

[0005]

In the TN type liquid crystal display device, the contrast changes depending on the viewing angle. In the normally white mode in which white is displayed when no voltage is applied, when viewed from the direction perpendicular to the substrate surface, L1 in FIG.
As described above, the light transmittance decreases as the applied voltage increases. On the other hand, when the viewing angle is tilted in the normal viewing angle direction, the transmittance drops once and then a small peak occurs (L2 in FIG. 3). Inversion of gradation occurs around this, and black and white of the image are inverted.

The reason why the transmittance characteristics differ depending on the viewing angle described above will be described with reference to FIGS. 4 and 5. FIG. 4 is a sectional view showing the liquid crystal display device. This liquid crystal display device
The structure has a pair of substrates 1 and 2 with a liquid crystal layer 3 in between. One substrate 1 is a glass substrate 1a, a transparent electrode 1
b and the alignment film 1c, the other substrate 2 is composed of a glass substrate 2a, a transparent electrode 2b and an alignment film 2c. The liquid crystal molecules 5 of the liquid crystal layer 3 are twisted 90 degrees between the substrates 1 and 2. The symbol δ indicates the pretilt angle, and the number 6 indicates the normal viewing angle direction.

In the liquid crystal display device having such a structure, as shown in FIG.
As shown in (a), when no voltage is applied or when a small voltage is applied, the observer 7 located in the normal viewing angle direction has the liquid crystal molecules 5 located in the central portion in the thickness direction of the liquid crystal layer 3.
Looks like an ellipse. Next, when a voltage is applied, the liquid crystal molecule 5 in the central portion changes its inclination in a direction parallel to the electric field direction, so that it looks like a perfect circle at some point (FIG. 5).
(B)). When the voltage is further increased, it looks like an ellipse again as shown in FIG. In the other viewing angle directions, the transmissivity characteristic is different from that in the vertical direction, and the inversion phenomenon does not occur, but the contrast ratio becomes lower as the viewing angle is tilted.

The following two methods have been proposed as a technique for improving the viewing angle characteristics peculiar to the TN mode (p591-p of JAPAN DISPLAY '92).
594 and p886). One of the methods is to rub the surface of the alignment film in a certain direction, then partially coat it with a resist and rub it in the opposite direction so that the coated region and the uncoated region have different rubbing directions, and the same liquid crystal This is a method of providing forward and reverse viewing angle directions in a layer. Another method is to form a plurality of pretilt angles by selectively forming a plurality of different alignment films, and in the combination of those with different pretilt angles, the viewing angle direction is controlled by the higher pretilt angle. Then, the same liquid crystal layer is provided with forward and reverse viewing angle directions.

According to these methods, since the viewing angle regions in the normal and reverse directions are formed in the same liquid crystal layer, the viewing angle characteristics in the two directions are seen by the observer as a mixture, and the inversion phenomenon in the normal viewing angle direction and A sharp decrease in contrast in the reverse viewing angle direction is alleviated and improved. However, since these methods include a photolithography process, the contamination of the alignment film becomes a problem.

Therefore, the applicant of the present application found that the pretilt angle was changed by irradiating the alignment film with light having high energy, thereby forming a plurality of liquid crystal layer regions having different pretilt angles, and the method disclosed in JAPAN DISPLAY. It was confirmed that a liquid crystal display device having a viewing angle direction of two or more directions can be manufactured without making the alignment film contaminated by making the same structure as the case of. It was also found that ultraviolet light of 400 nm or less is most effective for controlling the pretilt angle in this system. The change in pretilt angle due to the light irradiation is caused by the following two reactions. The first is the dissociation of the bond of the polymer of the alignment film or the generation of a new bond by applying high energy. The other is the generation of ozone / active oxygen by the absorption of short wavelength ultraviolet rays by oxygen in the air, and the modification of the surface of the alignment film.

When irradiating short wavelength ultraviolet rays in air, the latter reaction predominantly occurs, and ozone
Modification of the alignment film surface with active oxygen proceeds rapidly. However, in this reaction, the activated oxygen freely moves in the space, so that the reaction extends to the portion that is originally shielded from light and should be protected. When the light-shielding portion receives a reaction in this way, the pretilt angle of the liquid crystal molecules in contact with the light-shielding portion changes, so that it becomes difficult to control the viewing angle direction by the pretilt angle.
Further, also in the irradiation part, when the irradiation amount increases, the surface modification proceeds and the film loss occurs, and when the irradiation amount further increases, the film itself may disappear. In order to secure the difference in pretilt angle between the liquid crystal molecules in contact with the irradiation part and the liquid crystal molecules in contact with the light shielding part, it is necessary to strictly control the light irradiation conditions, for example, the light intensity and the irradiation amount.

The present invention has been made to solve the above problems of the prior art, and an object of the present invention is to provide a method of manufacturing a liquid crystal display device capable of easily controlling a viewing angle direction by a pretilt angle. And

[0013]

A method of manufacturing a liquid crystal display device according to the present invention comprises a pair of substrates each having an alignment film formed on the surface thereof.
In a method of manufacturing a liquid crystal display device, in which a pair of substrates are arranged so as to face each other with the alignment film inside, and a liquid crystal layer is sealed between both substrates to be bonded to each other, before bonding the both substrates, Since the alignment film formed on one of the pair of substrates is selectively irradiated with light in an atmosphere containing an inert gas, the above object is achieved thereby.

In this manufacturing method, the atmosphere preferably contains an inert gas in a volume ratio of 85% to 100%. The light may be ultraviolet light or ultraviolet laser light. Further, as the inert gas, nitrogen, helium, neon or argon can be used.

According to the method of manufacturing a liquid crystal display device of the present invention, a pair of substrates having an alignment film formed on the surface thereof are disposed so as to face each other with the alignment film inside, and a liquid crystal layer is provided between the substrates. In a method for manufacturing a liquid crystal display device in which both substrates are encapsulated and bonded together, in an atmosphere of reduced pressure or vacuum with respect to an alignment film formed on one of the pair of substrates, before the bonding of both substrates. Since the method includes the step of selectively irradiating light with the above method, the above object is achieved thereby.

In this manufacturing method, the atmosphere is preferably 0.5 atm or less and 0 atm or more. As the light, ultraviolet light, visible light, infrared light, or laser light in the same wavelength range as these can be used.

[0017]

According to the present invention, stable pretilt angle control can be performed by controlling the amount of oxygen that affects the alignment film surface of the light shielding portion. The following two methods can be applied to control the oxygen amount. One is a method of irradiating the alignment film with light in an atmosphere in which a part thereof is replaced with an inert gas. 100%
It may be in an inert gas. The proportion of inert gas in the normal atmosphere is 80%. Light irradiation in an atmosphere containing 85% of an inert gas does not significantly reduce the reaction speed, but has a slight effect on the light-shielding portion. Light irradiation in 100% inert gas does not affect the light-shielding portion at all, but the reaction speed becomes slow. The optimum mixing ratio is determined by the magnitude of the initial pretilt angle. The other is a method of irradiating the alignment film with light under reduced pressure. It may be in full vacuum. Also in this case, the reaction speed becomes slower as the degree of pressure reduction becomes higher.

By controlling the amount of oxygen by these methods, pretilt angle control in which the mechanism of dissociation / generation of polymer bonds by light is predominant is realized, and the pretilt of the light shielding portion is controlled regardless of the light irradiation conditions. Angular change is suppressed. This enables stable tilt angle control,
A wide viewing angle liquid crystal display device can be stably obtained with a high yield.

When light irradiation is carried out under reduced pressure or in vacuum, visible light or infrared light can be used in addition to ultraviolet light. When the pretilt angle control by light irradiation is performed with visible light or infrared light, ozone and active oxygen are not generated, but when irradiation is performed in the air, light is attenuated by absorption and scattering in the air layer. Is. According to the present invention, since light irradiation is performed under reduced pressure or in vacuum, the amount of light reaching the surface of the alignment film is increased and the irradiation efficiency is improved even when visible light or infrared light is used.

[0020]

Embodiments of the present invention will be specifically described below with reference to the drawings.

(Embodiment 1) FIG.
A sectional view of an active matrix type liquid crystal display device in which IM, TFT, etc. are added as switching elements is shown. This liquid crystal display device includes a pair of substrates 31 with a liquid crystal layer 33 interposed therebetween.
32 are arranged to face each other. One (lower) substrate 31
The electrode wiring 31b is formed on the base substrate 31a made of glass, a silicon wafer, or the like, and the alignment film 31c that defines the alignment of the liquid crystal is formed in the portion in contact with the liquid crystal layer 33. The electrode wiring 31b provided on the substrate 31 is
A plurality of strips are arranged side by side.

On the other (upper) substrate 32, electrode wiring 32b is formed on a base substrate 32a made of glass, silicon wafer, or the like, and an alignment film 32c for defining the alignment of liquid crystal is provided in a portion in contact with the liquid crystal layer 33. Has been formed. The electrode wiring 32b provided on the substrate 32 is formed by arranging a plurality of strip-shaped ones in parallel while intersecting the electrode wiring 31b provided on the substrate 31.
A picture element is formed at the intersection of b and 32b.

In the liquid crystal layer 33, regions X and Y having different alignment states are formed in one picture element. The region X has a 6 o'clock viewing angle, and the region Y has a 12 o'clock viewing angle. In FIG. 2, a short straight line in contact with the substrates 31 and 32 indicates the magnitude of the pretilt angle of the liquid crystal in contact with the alignment films 31c and 32c, and the inclination of the liquid crystal molecules 33a near the center of the liquid crystal layer 33 in the thickness direction is average. Shows the pretilt direction of the liquid crystal.

The end portions of these substrates 31 and 32 are sealed with resin or the like, and at least one of the substrates 31 and 32 is provided with a peripheral circuit such as a drive circuit around the outside of the display portion for displaying. It is implemented.

A method of manufacturing the liquid crystal display device having such a structure will be described below.

First, the electrode wirings 31b and 32b are formed on the base substrates 31a and 32a by a known method, and the alignment films 31c and 32c are further formed thereon. Then, the alignment films 31c and 32c are rubbed in a predetermined direction with a polishing cloth, for example.

Next, one of the two substrates 31, 32, for example, the substrate 31, is placed in an unillustrated chamber to form an alignment film 31c.
And the mask 11 having the light shielding part 11a and the light transmitting part 11b on the alignment film 31c as shown in FIG.
To place. The mask 11 has a structure in which light-transmitting portions 11b are provided in a matrix or stripe shape on a light-shielding portion 11a formed on almost the entire surface.
It is arranged such that a is located on a region corresponding to the region X of the electrode wiring 31b constituting one picture element.

Next, a gas containing 85% by volume of nitrogen as an inert gas is introduced into the chamber, and the atmosphere in the chamber is replaced with the gas. Then, the mask 11
The light 15 is applied to the alignment film 31c from above. Ultraviolet light can be used as the light 15. By such light irradiation, the light irradiation portion of the alignment film 31c has a surface state that reduces the pretilt angle of the liquid crystal.

Therefore, in the alignment film 31c thus irradiated with light, the pre-tilt angle is small in the light-irradiated portion, that is, the portion corresponding to the region Y, and the pre-tilt angle is in the non-light-irradiated portion, that is, the portion corresponding to the region X. Grows larger.

Next, the other substrate 32 is set in the chamber, and light irradiation is performed in the same manner as before. As a result, in the alignment film 32c, the pre-tilt angle is small in the light irradiation portion, that is, the portion corresponding to the region X, and
That is, the pretilt angle becomes large in the portion corresponding to the region Y. The step of irradiating the substrate 32 with light may be performed before the step of irradiating the substrate 31 with light.

Next, the substrates 31 and 32 are aligned with the alignment films 31c and 31c.
The 32c side is faced to the inside so that they face each other and are bonded together. At this time, the ends of the substrates 31 and 32 are sealed. Subsequently, a liquid crystal is injected between the substrates 31 and 32 to form a liquid crystal layer 33.
To get

Finally, peripheral circuits such as a drive circuit are mounted around the outside of the display section for displaying. As a result, the liquid crystal display device of this embodiment is completed.

Therefore, in this embodiment, the alignment film is irradiated with light in an atmosphere containing 85% by volume of nitrogen. Therefore, the volume ratio of oxygen in the atmosphere, which is usually 20%, can be reduced to 15%, and the influence on the light shielding portion can be suppressed. At this time, there was almost no decrease in reaction speed, and the amount of ultraviolet light irradiation required to set the initial pretilt angle of 5 degrees to 0 degrees was about 10 J / cm ² .

The present invention can be carried out even when the mixing ratio of the inert gas is 100%. In this case, there was no effect on the light-shielding portion, the reaction speed became about 1/5 times, and the irradiation amount of ultraviolet light was required to be 50 J / cm ² or more.

Although nitrogen is used as the inert gas in the above embodiment, the present invention is not limited to this, and helium, neon, argon or the like can be used. Even in that case, the compounding ratio may be the same as in the case of nitrogen.

Although ultraviolet light is used as the light for irradiating the alignment film in the above embodiment, it is possible to use laser light of ultraviolet light. Note that ultraviolet light having a wavelength of 400 nm or less is preferable as light from which high energy can be easily obtained. Light having such a wavelength can be obtained by a high pressure mercury lamp, a low pressure mercury lamp, a mercury xenon lamp or the like.

(Example 2) In Example 2, the amount of oxygen is reduced as in Example 1 by reducing the pressure around the surface of the alignment film during light irradiation.

Also in this embodiment, the substrate structure and the like are the same as those in the first embodiment. In particular,
One of the substrates 31 and 32 is set and a mask is placed in a chamber whose internal pressure is adjusted to 0.5 atm.
In that state, a predetermined portion of the alignment film was irradiated with ultraviolet light. Note that laser light in the same wavelength range as ultraviolet light can be used instead of ultraviolet light.

In the case of this embodiment, the influence on the light-shielding portion is almost the same as in the case of the volume ratio of the inert gas being 85% in the first embodiment, the reaction speed is slightly faster, and the initial pretilt angle is obtained. The irradiation dose of ultraviolet light required to set 5 degrees to 0 degrees was about 9 J / cm ² . Further, in the case of the present embodiment, by reducing or irradiating the irradiation environment, the light absorbed and scattered in the gas reaches the alignment film surface, so that the irradiation efficiency is improved and the throughput is shortened. be able to.

In the second embodiment, the pressure inside the chamber may be vacuum. In this case, there was no effect on the light-shielding portion, the reaction speed was slightly faster than that of the 100% inert gas of Example 1, and the ultraviolet light irradiation amount was 45 J / cm.
^{About 2} was needed. The difference in reaction speed depends on the presence or absence of light scattering by the gas.

Further, as described above, in the case of the present embodiment, since the pressure is reduced or the vacuum is applied at the time of light irradiation, it is possible to suppress the absorption and scattering by the gas in the atmosphere and reduce the degree of light attenuation. Therefore, according to the present embodiment, visible light, infrared light, or laser light in the same wavelength range as these can be used in addition to ultraviolet light and laser light in the same wavelength range as ultraviolet light.

As the alignment film that can be used in each of the first and second embodiments described above, a polyimide film or an alignment film made of another material may be used. An inorganic alignment film containing silicon nitride, silicon oxide, magnesium fluoride, gold or the like as a main component may be used, but in this case, irradiation with high energy light such as an ultraviolet laser is required.

The present invention is not limited to the active matrix type liquid crystal display device described above, but can be applied to a simple matrix type liquid crystal display device.

The light irradiation step in the present invention can be carried out at any time after the alignment film is formed. Specifically, it may be any time after application of the alignment film, after provisional firing, after main firing, after rubbing, and after washing after rubbing.

As the mask usable in the present invention, a mask pattern is formed by directly forming a mask pattern on the alignment film using a photolithography technique, irradiating with light, and then peeling off the mask. Good. Further, the condensed light may be applied to a desired region without using the mask.

[0046]

According to the present invention, it is possible to suppress the influence on the light shielding portion at the time of light irradiation, so that the margin of irradiation conditions is widened,
Pretilt angle control can be stably performed. According to the present invention, light irradiation can be efficiently performed even when light other than ultraviolet light is used, and a wide viewing angle liquid crystal display device can be obtained more easily.

[Brief description of drawings]

FIG. 1 is a cross-sectional view schematically showing a light irradiation step in a method for manufacturing a liquid crystal display device according to the present invention.

FIG. 2 is a sectional view showing an active matrix type liquid crystal display device to which the present invention is applied.

FIG. 3 is a graph showing applied voltage-transmittance characteristics in a conventional liquid crystal display device.

FIG. 4 is a diagram illustrating a reversal phenomenon in a conventional liquid crystal display device.

FIG. 5 is a cross-sectional view illustrating viewing angle characteristics of a conventional liquid crystal display device.

[Explanation of symbols]

 1, 2 substrate 1a, 2a glass substrate 1b, 2b transparent electrode 1c, 2c alignment film 3 liquid crystal layer 5 liquid crystal molecule 6 normal viewing angle direction 7 observer 11 mask 11a light shielding portion 11b light transmitting portion 15 light 31, 32 substrate 31a, 32a Base substrate 31b, 32b Electrode wiring 31c, 32c Alignment film

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Shigemitsu Mizushima 22-22 Nagaike-cho, Abeno-ku, Osaka-shi, Osaka Inside Sharp Corporation

Claims (7)

[Claims] 1. A pair of substrates each having an alignment film on the surface thereof, the pair of substrates being opposed to each other with the alignment film inside, and a liquid crystal layer sealed between the substrates to bond the substrates together. In the method for manufacturing a liquid crystal display device to be manufactured, before the two substrates are bonded together, the alignment film formed on one of the pair of substrates is selectively irradiated with light under an atmosphere containing an inert gas. A method of manufacturing a liquid crystal display device, including the steps of :. 2. The atmosphere is an inert gas in a volume ratio of 8
The method for manufacturing a liquid crystal display device according to claim 1, wherein the liquid crystal display device contains 5% to 100%. 3. The method of manufacturing a liquid crystal display device according to claim 1, wherein ultraviolet light or laser light of ultraviolet light is used as the light. 4. The method for manufacturing a liquid crystal display device according to claim 1, wherein nitrogen, helium, neon or argon is used as the inert gas. 5. A pair of substrates provided with an alignment film on the surface thereof, the pair of substrates facing each other with the alignment film inside, and a liquid crystal layer sealed between the substrates to bond the two substrates together. In the method of manufacturing a liquid crystal display device to be manufactured, a step of selectively irradiating the alignment film formed on one of the pair of substrates with light under a reduced pressure or vacuum atmosphere before the substrates are bonded to each other. A method for manufacturing a liquid crystal display device including the following. 6. The method for manufacturing a liquid crystal display device according to claim 5, wherein the atmosphere is 0.5 atm or less and 0 atm or more. 7. The method of manufacturing a liquid crystal display device according to claim 5, wherein ultraviolet light, visible light, infrared light, or laser light having the same wavelength range as these is used as the light.