JP2930228B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device in which the tilt angle of liquid crystal molecules is controlled. In particular, the present invention relates to a liquid crystal display device having an arbitrary viewing angle characteristic in which alignment states having different tilt angles are formed in the same liquid crystal cell, and regions having different viewing angle characteristics are formed at arbitrary positions.

[0002]

2. Description of the Related Art A liquid crystal display device (LCD) is a display device that changes the orientation of liquid crystal molecules in a liquid crystal cell between a pair of substrates, and uses the resulting change in the optical refractive index in the liquid crystal cell. Therefore, it is important that the liquid crystal molecules in the liquid crystal cell are initially arranged as regularly as possible. Thus, in order to arrange the liquid crystal molecules regularly, the surface state of the substrate sandwiching the liquid crystal cell regulates the interaction of the liquid crystal molecules.

The most widely used method for initially aligning liquid crystal molecules in a certain direction is to apply a liquid crystal alignment film material to opposing surfaces of a pair of substrates, and dry and cure the applied material. After the formation of the film, the surface of the alignment film is rubbed.

There are two types of alignment films for regulating the alignment of the liquid crystal: inorganic alignment films and organic alignment films. Examples of the material for the inorganic alignment film include an oxide, an inorganic silane, a metal, and a metal complex. Examples of the material for the organic alignment film include polyimide. A typical example of a liquid crystal alignment film material currently used is a polyimide resin. A polyimide resin is formed by applying a polyamic acid, which is a precursor of a wholly aromatic polyimide (a wholly aromatic PI), to a substrate and then causing a polyimide reaction by heating, thereby converting the polyamic acid into a polyimide resin. . The reason why polyimide resin is widely used as a liquid crystal alignment film material is that it has good solubility in the state of polyamic acid, so that concentration and mucous membrane can be easily prepared, coating properties are good, and film thickness is controlled. It is easy.
The produced polyimide resin is more energetically stable than polyamic acid, and does not cause a reversible reaction even when washed with water.

By subjecting the polyimide film thus formed on the substrate to a rubbing treatment with a polishing cloth or the like, the liquid crystal molecules can be oriented along the rubbing direction. Since the rubbing process is performed in a uniform direction on the substrate, the tilt angles of the liquid crystal molecules in contact with the alignment film, ie, the pretilt angles, are all uniform in the liquid crystal cell. Therefore, the pretilt angles are substantially the same in each picture element constituting the unit dot of the matrix display pattern.

An active matrix type liquid crystal display device (TFT) using a thin film transistor as a switching element connected to each picture element electrode serving as one picture element of a display pattern
-LCD) adopts a configuration of a twisted nematic (TN) type liquid crystal cell (TN mode liquid crystal display device). According to the configuration of the liquid crystal cell, the liquid crystal molecules move between the pair of substrates along the direction perpendicular to the substrate surface.
It is oriented to be twisted by 0 °. In the viewing angle characteristics of the liquid crystal display device, an optimum viewing angle azimuth and a viewing angle range are determined according to the orientation (alignment direction and tilt angle) of the liquid crystal molecules in the liquid crystal layer.

[0007]

In a twisted nematic type liquid crystal display device, since a liquid crystal molecule has anisotropic refractive index (birefringence), a human (observer) liquid crystal display device is viewed. The phenomenon that the contrast changes depending on the angle occurs. Generally, in a normally white mode liquid crystal display device in which light is transmitted when a voltage is not applied and a white display is performed, a voltage is applied between driving electrodes formed on both substrates of a liquid crystal cell, and a voltage is applied to a substrate surface. When the liquid crystal display device is viewed from a vertical direction, as shown by the solid line L1 in FIG. 9, the light transmittance decreases as the applied voltage value increases. When the value is saturated, the transmittance becomes almost zero,
Even if the applied voltage is further increased, the transmittance remains almost zero.

However, the applied voltage-transmittance characteristic indicated by a solid line L1 in FIG. 9 changes due to a change in the viewing angle direction for observing the liquid crystal display screen. This will be described with reference to FIGS.

FIGS. 10 and 11 are a perspective view and a sectional view of a liquid crystal cell sandwiched between a pair of substrates 31 and 32, respectively. In these figures, one substrate 31 has a glass substrate 31a, a transparent electrode 31b, and an alignment film 31c, and the other substrate 32 has a glass substrate 32a, a transparent electrode 32b, and an alignment film 32c. . The liquid crystal molecules 35 in the liquid crystal cell are twisted 90 ° between the substrates 31 and 32. 10 and 11, the symbol δ indicates the pretilt angle, and the number 36 indicates the normal viewing angle direction 36.
When the viewing angle is inclined in the normal viewing direction 36 from a direction perpendicular to the substrate surface while a voltage is applied to the liquid crystal cell, the applied voltage is reduced as shown by a solid line L2 in FIG.
The transmittance characteristics change. That is, a phenomenon occurs in which the transmittance decreases to some extent as the applied voltage increases, and then increases again when the voltage exceeds a specific voltage value, and thereafter gradually decreases again. Therefore, when the viewing angle is inclined in the normal viewing angle direction 36, a phenomenon occurs in which the black and white (negative or positive) of the image is inverted at a specific angle (this is called an inversion phenomenon). This is a phenomenon that occurs because the liquid crystal molecules in the liquid crystal layer are inclined with a tilt angle, and the refractive index changes depending on the viewing angle. This phenomenon is a major obstacle for the viewer of the image. This will be described with reference to FIG. 12. As shown in FIG. 12 (a), when the applied voltage is zero or a relatively low voltage, an observer 37 located in the normal viewing angle direction receives a central molecule in the liquid crystal layer. Although 35 looks elliptical, when the applied voltage is gradually increased, the central molecule 35 moves so that its major axis direction is arranged in the direction of the electric field, that is, in the direction perpendicular to the substrate surface. Therefore, as shown in FIG. 12B, the observer 37 has a moment when the central molecule 35 looks like a perfect circle.
When the voltage is further increased, the central molecule 35 becomes substantially parallel to the direction of the electric field, and as shown in FIG.

In a similar phenomenon, even in a viewing angle direction other than the normal viewing angle direction 36, even if the reversal phenomenon does not occur due to the difference in transmittance-voltage characteristics, the black-and-white contrast ratio increases as the viewing angle increases. It has a viewing angle characteristic of being lowered.

In a TN mode liquid crystal display device, the inversion phenomenon observed in the normal viewing angle direction is a great obstacle for a viewer, and results in deteriorating the display characteristics of the liquid crystal display device itself.

It is an object of the present invention to provide a low-cost wide-viewing-angle liquid crystal display device with improved display quality, in which the viewing angle characteristic, which is a major problem, is effectively controlled.

[0013]

According to a liquid crystal display device of the present invention, in a liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of substrates, an alignment film is formed on at least one of the pair of substrates. An unevenness for controlling a pretilt angle of liquid crystal molecules of the liquid crystal layer in contact with the surface of the alignment film is formed on the surface of the film, and the degree of the unevenness is different between a plurality of predetermined regions. Thus, the above object is achieved.

In one embodiment, the pretilt angle is set small in a region of the alignment film surface where the degree of the unevenness is large, and the pretilt angle is set large in a region of the alignment film surface where the degree of the unevenness is small.

In one embodiment, at least two or more of the plurality of regions having different degrees of unevenness have different viewing angle characteristics.

In one embodiment, a base film is formed between the alignment film and the substrate on which the alignment film is formed, and irregularities are formed on a surface of the base film in contact with the alignment film. The degree of the unevenness differs between the plurality of predetermined regions.

In one embodiment, the pretilt angle is set small in a region of the alignment film surface where the degree of the unevenness is large, and the pretilt angle is set large in a region of the alignment film surface where the degree of the unevenness is small.

In one embodiment, at least two or more of the plurality of regions having different degrees of unevenness have different viewing angle characteristics.

In one embodiment, the thickness of the alignment film formed so as to cover the base film varies depending on the location.

[0020]

In the liquid crystal display device of the present invention, the alignment characteristics of the alignment film formed on the substrate surface are different for each of a plurality of predetermined regions. This alignment characteristic is provided to the alignment film by the unevenness of the alignment film surface. The inclination of the liquid crystal molecules of the liquid crystal layer in contact with the alignment film surface, that is, the pretilt angle is determined according to the unevenness of the alignment film surface. Therefore, when the degree of the unevenness is changed for each predetermined region, the pretilt angle of the liquid crystal layer also changes for each predetermined region. In this case, as shown in FIG. 13A, when the degree of the unevenness is large, the difference in the pretilt angle between the liquid crystal molecules on the surface of the alignment film and the liquid crystal molecules located at a position distant from the surface of the alignment film is large, and the dynamic liquid crystal Can control molecules. FIG. 13B shows the transmission of the pretilt angle in the direction of the liquid crystal layer when the unevenness of the alignment film surface is small.

As described above, when a plurality of regions having different pretilt angles are formed in the same substrate and a region having a large pretilt angle and a region having a small pretilt angle are combined between a pair of substrates, the alignment state is regulated on the side having a large pretilt angle. You. By utilizing this phenomenon, it is possible to form an orientation in an arbitrary direction in an arbitrary region. As described above, by changing the alignment state of the liquid crystal in the same liquid crystal cell into at least two types, not only the change in the refractive index in the normal viewing angle direction is reduced and the viewing angle is widened, but also the opposite viewing angle characteristic is improved.

The present invention is also applicable to a scattering mode liquid crystal display device. Light incident on the liquid crystal display device according to the present invention in which a plurality of minute discontinuous alignment regions are formed in the same liquid crystal cell is scattered by a large number of minute regions having different alignment characteristics from each other. When no voltage is applied). However, when a predetermined voltage is applied between opposing substrates (in a liquid crystal cell), liquid crystal molecules can be uniformly aligned.

[0023]

Embodiments of the present invention will be described below.

(Embodiment 1) FIG. 1 schematically shows a substrate structure of a liquid crystal display device according to Embodiment 1. The picture element electrodes 1, 13 and 14 on an insulating substrate 16 such as glass
2 ', 13' and 14 'are formed. This picture element electrode 1
An alignment film 10 is formed on the entire surface of the substrate 16 so as to cover 2 ′, 13 ′, and 14 ′. As a specific substrate structure, a segment structure, a dot matrix structure, or the like can be applied. Further, the present invention is applicable to all substrate structures conventionally used in liquid crystal display devices. The substrate of such a liquid crystal display device is manufactured as follows.

First, the pixel electrodes 12 ', 13', and 14 'are formed on the surface of the substrate 16 by a known method.
Form 13 and 14.

Next, an alignment film 10 is formed on the entire surface of the substrate 16 so as to cover the picture element portions 12, 13, and 14. In Example 1, a polyimide (PI) film, which is one of organic polymer films, was used as the alignment film 10. Since the polyimide-based polymer has a polymer chain, and the long chain direction of the polymer chain on the surface of the polyimide film is oriented in the rubbing direction by the rubbing process, the liquid crystal molecules in contact with the alignment film 10 made of the polyimide film are It is considered to be oriented in the rubbing direction.

After forming the alignment film 10, light is applied to the alignment film 10.
Irradiation. Irradiation of light on the surface of the alignment film 10 forms irregularities on the surface of the alignment film 10. When the alignment film 10 is irradiated with light, the bonding chains of the polyimide molecules are cut and the portions are roughened to form irregularities. This has been experimentally confirmed. It has also been experimentally confirmed that the pretilt angle changes due to the change in the degree of unevenness on the surface of the alignment film 10. This is shown below.

As one method for indicating the state of unevenness on the surface of the film,
The average roughness shown in FIG. 2A is defined. The solid line curve shown in FIG. 2A is the actual surface of the alignment film, and the dashed line is the center plane of the irregularities on the actual surface. The center plane is defined as An (n is a natural number) and B is defined as the area of each projection on the real surface.
n is defined as a plane that satisfies the following equation and is parallel to a plane that minimizes the square of the difference from the real surface.

(A1 + A2 +... + An) = (B1 + B2 +... + Bn) The average roughness of the film surface is defined by the arithmetic average of the absolute value of the difference between the central plane and the real plane. FIG. 2B is a graph in which the average roughness is plotted on the horizontal axis and the pretilt angle is plotted on the vertical axis. In Example 1, a polyimide film was used as the material of the alignment film. However, as can be understood from the drawing, it can be seen that the pretilt angle decreases linearly as the average roughness of the surface of the alignment film increases. . Thus, by controlling the light irradiation amount, and thus controlling the unevenness of the alignment film surface, the pretilt angle of the liquid crystal can be arbitrarily controlled in the range of 0 ° to about 15 °. That is, various liquid crystal display devices having different pretilt angles can be manufactured. In this case, as described below, light irradiation can be selectively performed in place. As one method of selectively performing light irradiation, there is a method of irradiating light by disposing a mask.

FIG. 3 is a schematic diagram showing a case where the alignment film is selectively and selectively irradiated with light using a mask. When the light 15 is irradiated using the mask 11 as shown in FIG. 3, a portion 11a indicated by oblique lines is a light-shielding portion that does not substantially transmit the light 15. Portions 11b of the mask 11 that are not shaded are transmission portions that substantially transmit the light 15. As the mask 11, for example, a mask similar to a photomask usually used in photolithography technology can be used. Directly forming a mask pattern on the alignment film 10 using a photolithography technique,
After irradiation with light, the mask may be peeled off. However, when resist patterning is used, the degree of contamination of the alignment film 10 is large.

It is not necessary for the light shielding portion to completely block the light 15. It suffices if there is a difference in the degree of blocking between the light shielding part and the non-light shielding part. For example, a material having two or more types of regions having different light transmittances on the substrate 16 may be provided as the mask 11. In this case, two or more types of regions having different orientations can be formed in the same liquid crystal cell.

FIG. 4 shows that the pretilt angle of the liquid crystal in the region irradiated with light is different from the pretilt angle of the liquid crystal in the region not irradiated with light. The pretilt angle of the liquid crystal becomes α ゜ in the picture element portions 12 and 14 to which the light has not been irradiated, and the pretilt angle becomes β ゜ different from α ゜ in the picture element portion 13 to which the light has been irradiated.

FIG. 5 schematically shows a cross section of a main part of a liquid crystal display device provided with a pair of substrates 17 and 18 to which the alignment control method of the first embodiment is applied. As shown in FIG. 5, the pretilt angle δ of the liquid crystal on the surface of the alignment film 10 is different in the regions A, A ′, B, and B ′ in the same liquid crystal cell.

As a method of selectively irradiating light with a place, there is a method of selectively irradiating light to a predetermined area using condensed light, in addition to the method using a mask as described above. . In addition, any of ultraviolet light, visible light, infrared light, or a combination thereof may be used as light for irradiating the alignment film 10 made of a polyimide film, but high energy for changing the alignment state is easily obtained. UV light having a wavelength of 400 nm or less is preferable. Irradiation of light of such a wavelength is easily performed by using, for example, a high-pressure mercury lamp. When irradiating with ultraviolet light (UV light), 1000 (mJ / cm ² ) to 10,000 (mJ /
Irradiation is preferably performed under the condition of cm ² ).

In addition to ultraviolet light, laser light having a wavelength of visible light, infrared light, or a combination thereof may be used. In this case, the efficiency is high because the energy of the laser is added in addition to the energy of the wavelength of light.

Instead of light irradiation, it is also possible to change the degree of unevenness on the surface of the alignment film 10 by irradiation with another energy beam. For example, the degree of unevenness on the surface of the alignment film 10 can be changed by irradiation with an electron beam, an ion beam, X-rays, or the like.

Since fine processing using a mask or condensed light can be performed down to several microns, fine regions having different degrees of unevenness are formed in the alignment film 10 in an arbitrary plane shape using such a method. can do. For example, the first embodiment
In FIG. 3, as shown in FIG. 3, light is selectively irradiated for each unit picture element by the mask 11, but a region to which the light 15 is not irradiated and a region to be irradiated may be formed in the unit picture element. Also,
Instead of making a difference only between light irradiation and non-light irradiation, the light intensity between irradiation parts may be made different. The orientation characteristics can be changed more precisely and locally by various light irradiation patterns.

The step of irradiating the light 15 may be performed at any time after the formation of the alignment film 10. Specifically, it may be at any time after application of the alignment film 10, after calcination, after rubbing, or after cleaning of the substrate 16 after rubbing. After the opposing substrate (not shown) is bonded to the substrate 16, the light may be irradiated through the opposing substrate. Must be used.

Although a polyimide film is used as the alignment film 10 in the first embodiment, an alignment film 10 made of another material may be used. An appropriate wavelength of light to be irradiated is selected according to the type of the material.

Further, an inorganic alignment film containing silicon nitride, silicon oxide, magnesium fluoride, gold or the like as a main component may be used. In this case, a high energy light such as an ultraviolet laser or an electron beam is used. Irradiation is required.

(Embodiment 2) The substrate structure of Embodiment 2 is the same as that of Embodiment 1. In Example 2, a substrate having unevenness on the alignment film surface is also used. However, as a method for forming unevenness, a solution is brought into contact with the alignment film surface instead of light irradiation, and the solution does not dissolve the alignment film. A method of forming irregularities of an arbitrary size on the surface of the alignment film using uniformity will be described. In Example 2, polyimide was used as the material of the alignment film, and the alignment film was formed by spin coating or printing. Other materials for this alignment film include polyamide,
An organic film such as polystyrene, polyamide imide, epoxy acrylate, spirane acrylate, or polyurethane can be used.

First, similarly to the first embodiment, a plurality of picture element electrodes are formed in a predetermined area on the substrate surface, and the orientation film is baked so as to cover the picture element electrodes.

Subsequently, the surface of the alignment film was rubbed with a polishing cloth.

Next, the surface of the alignment film was brought into contact with an alkaline solution, and irregularities were formed on the surface of the alignment film by utilizing the non-uniformity of the dissolving action of the solution on the alignment film as described above. As an alkaline solution, a 0.5% NaOH aqueous solution or 2.3%
An 8% TMAH aqueous solution or the like can be used.

As a fluid to be brought into contact with the alignment film in order to form irregularities on the surface, hydrofluoric acid, nitric acid, or an acid solution containing both as main components may be used. Ozone or ammonia gas, which is a reactive gas, may be used. A gas in a plasma state containing oxygen, argon, krypton, or the like as a main component may be used.

(Example 3) In Example 3, irregularities are formed in the transparent conductive film formed below the alignment film, and the irregularities are transmitted to the upper alignment film to form irregularities on the alignment film surface. Liquid crystal display device. In the third embodiment, as a method of selectively forming unevenness on the transparent conductive film, a resist using conventional photolithography is patterned on a part of the transparent conductive film, and light is irradiated in this state to irradiate light. A method of forming a change in locational unevenness depending on the presence or absence of irradiation is adopted. FIG. 6 schematically shows a process of forming irregularities on the surface of the alignment film of the liquid crystal display device according to the fourth embodiment.

First, as shown in FIG.
A transparent conductive film 20 is formed thereon. Next, as shown in FIG. 6B, a resist 21 is formed on a part of the transparent conductive film 20.
To form In this state, as shown in FIG. 6C, light 15 is irradiated perpendicularly to the substrate 16 from the side where the transparent conductive film 20 is formed. Since the portion of the transparent conductive film 20 covered with the resist 21 is not irradiated with light, the surface state does not change from that at the time of forming the transparent conductive film 20, as shown in FIG. On the other hand, in the portion that has been irradiated with light, the chemical structure of the surface changes and irregularities occur.

After the light irradiation, the resist 21 is removed as shown in FIG.

Finally, as shown in FIG. 6E, an alignment film 10 is formed on the surface of the substrate 16 after removing the resist 21 so as to cover the transparent conductive film 20. The surface state of the transparent conductive film 20 is also reflected on the surface state of the alignment film 10 formed thereover in a portion where the transparent conductive film 20 has been irradiated with light and a portion where the transparent conductive film 20 has not been irradiated with light. A portion that has been formed and a portion that has not been formed are formed.

Example 4 Also in Example 4, irregularities were formed in the transparent conductive film as the base film of the alignment film, and the irregularities were transmitted to the upper alignment film, and the unevenness was formed on the alignment film surface. Adopt a liquid crystal display device.

In the fourth embodiment, an insulating film is used instead of the resist of the third embodiment to form a part of the unevenness of the underlying film. FIG. 7 shows a schematic manufacturing process when an insulating film is used. This is the same as the case where the resist is used, except that the removing step in the case of the resist is eliminated. Since the alignment film 10 is formed by covering the insulating film 22 while leaving the insulating film 22 on the transparent conductive film 20, not only the difference between the surface states of the insulating film 22 and the transparent conductive film 20 but also the region where the insulating film 22 is formed. In addition, the height difference between the surface of the insulating film 22 and the surface of the transparent conductive film 20 is also considered as an element of the concavo-convex shape transmitted to the alignment film 10.

In the portion where the insulating film 22 is formed, the uneven shape becomes gentle. When the insulating film 22 is used, the removal step in the case of using a resist is eliminated, so that the process is simplified. In addition, the manufacturing process is simplified in terms of performing both the insulating treatment and the alignment control, and a liquid crystal display device having a wide viewing angle characteristic can be obtained at low cost.

In order to form irregularities on the transparent conductive film 20 other than the resist 21 and insulating film 22 forming regions, a method of contacting the transparent conductive film 20 with an acid or alkali solution or a reactive gas or a gas in a plasma state is used. May be used.

The regions where the resist 21 and the insulating film 22 are formed can be determined for each picture element as in the previous embodiment, or for each of a plurality of areas within one picture element, and the formation of unevenness in various patterns can be performed. It is possible.

(Example 5) In Example 5, as in Examples 3 and 4, irregularities were formed on the base film of the alignment film, and the irregularities were transmitted to the upper alignment film. A liquid crystal display device with irregularities is adopted, but the irregularities are formed by forming an insulating film on the transparent conductive film, and the shape of the irregularities on each surface varies depending on the material of the transparent conductive film and the insulating film. It has been passed down. Such a liquid crystal display device is manufactured as follows. First, a transparent conductive film 20 is formed on a substrate 16 as shown in FIG. Next, as shown in FIG.
An insulating film 22 is formed on a part of the surface of No. 0. As the insulating film 22, silicon nitride, silicon oxide, or the like can be used.

Finally, as shown in FIG. 8C, an alignment film 10 is formed on the surface of the substrate 16 so as to cover the transparent conductive film 20 and the insulating film 22.

In the region where the insulating film 22 is formed, the insulating film 2
2 and the transparent conductive film 20, as well as the height difference between the surface of the insulating film 22 and the surface of the transparent conductive film 20.
It is taken into account the uneven shape elements transmitted to Insulating film 22
In the portion where is formed, the uneven shape becomes gentle.

In the fifth embodiment, since light irradiation and other operations for forming irregularities are not performed before forming the insulating film 22 and the insulating process and the orientation control are performed, the manufacturing process is greatly simplified. A low-cost and highly reliable liquid crystal display device having a wide viewing angle characteristic can be provided.

(Embodiment 6) As in Embodiments 3, 4, and 5, as in Embodiments 3, 4, and 5, irregularities are formed on the base film of the alignment film, and the irregularities are transmitted to the upper alignment film to form a surface of the alignment film. Although a substrate structure in which unevenness is formed is adopted, the degree of unevenness formed in the base film is not limited to each region as in the previous embodiments, but is formed almost arbitrarily in place. I have. Finally, the formation of the difference in the degree of unevenness for controlling the pretilt angle of the liquid crystal molecules near the alignment film is controlled by the thickness of the alignment film. In other words, the substrate structure is such that the portion of the alignment film having a small thickness has a stronger transmission of the unevenness of the underlying film, and the degree of the unevenness is larger than that of the thicker portion.

As a method of controlling the film thickness, there is a method of irradiating the alignment film with light. When the alignment film is irradiated with light, the bond chains of the polyimide molecules in the light-irradiated portion are torn off, passing through the formation of the irregularities, and as if the light-irradiated portion was removed by etching. As a method of controlling the film thickness of the alignment film, it is possible to contact with a solution such as an acid or an alkali, contact with a reactive gas, or contact with plasma in addition to light irradiation.

As described above, in the liquid crystal display device according to the present invention described in each embodiment, regions having different alignment states and therefore different viewing angle characteristics are formed in the same liquid crystal cell. Due to the presence of a plurality of different viewing angle characteristics, T
The viewing angle in the N mode or the STN mode is improved. For example,
When a TN mode liquid crystal display device is disposed between a pair of polarizers, in order to improve the viewing angle characteristic of inversion of liquid crystal display, refraction of liquid crystal molecules in the vertical direction (perpendicular to the observer) is required. It is considered that the ratio should be constant regardless of the viewing angle. That is, when viewed from the normal viewing angle direction, the anisotropy (Δn) of the refractive index in the vertical direction increases as the viewing angle increases from directly above the liquid crystal display device (perpendicular to the substrate surface).
However, it is only necessary to suppress the change from “large” → “0” → “large (reverse direction)”. In the liquid crystal display device of the present invention, the change in Δn is reduced by suppressing the anisotropy of the refractive index of the liquid crystal molecules.

[0062]

As described above, in the liquid crystal display device according to the present invention, unevenness is formed on the surface of the alignment film, and the degree of the unevenness is different between a plurality of regions.
The pre-tilt angle of the liquid crystal molecules is controlled by the unevenness, and different alignment states are formed at predetermined positions.
The viewing angle of the N mode or STN mode liquid crystal display device can be improved. In this liquid crystal display element, the change in the refractive index of the liquid crystal, which occurs in the thickness direction of the liquid crystal cell, can be reduced.
As a result, the reversal phenomenon of the normal viewing angle direction (the phenomenon that the black and white (negative / positive) of the image is reversed at a specific viewing angle) can be improved.

The liquid crystal display device according to the present invention in which the tilt angle is controlled and the orientation is controlled is a display device capable of providing a high-contrast and high-quality display.

[Brief description of the drawings]

FIG. 1 is a schematic diagram of a substrate of a liquid crystal display device according to a first embodiment.

FIG. 2A is a diagram showing a definition of an average roughness (irregularity) of an alignment film surface. (B) is a diagram showing the dependence of the pretilt angle on the average roughness (irregularity) of the alignment film surface.

FIG. 3 is a schematic view of a light irradiation step for forming irregularities on the surface of the alignment film of the substrate of the liquid crystal display device according to the first embodiment.

FIG. 4 is a cross-sectional view showing a state where a pretilt angle is changed for each picture element portion by light irradiation.

FIG. 5 is a cross-sectional view schematically showing a liquid crystal layer between substrates of a liquid crystal display device according to the present invention in which a pretilt angle is controlled.

FIG. 6 is a diagram showing a third embodiment according to the present invention.

FIG. 7 is a diagram showing a fourth embodiment according to the present invention.

FIG. 8 is a diagram showing a fifth embodiment according to the present invention.

FIG. 9 is a graph showing an applied voltage-transmittance characteristic in a liquid crystal display device.

FIG. 10 is a perspective view for explaining viewing angle characteristics in a liquid crystal display device.

FIG. 11 is a sectional view for explaining viewing angle characteristics in a liquid crystal display device.

FIGS. 12A, 12B, and 12C are diagrams for explaining an inversion phenomenon in a liquid crystal display device.

FIG. 13 is a schematic diagram showing how a pretilt angle is transmitted to a liquid crystal layer depending on the degree of unevenness of the alignment film surface. (A) is a figure which shows the case where the degree of unevenness is severe. (B) is a diagram showing a case where the degree of unevenness is small.

[Explanation of symbols]

 10, 31c, 32c Alignment film 11 Mask 11a Shielding part 11b Transmission part 12, 13, 14 Picture element part 15 Light 16, 31, 32 Substrate 20 Transparent conductive film 22 Insulating film 21 Resist 31a, 32a Glass substrate 31b, 32b Transparent electrode 33, 34 Rubbing direction of liquid crystal display element 35 Central molecule 36 Viewing angle direction 37 Observer δ Pretilt angle

Claims (7)

(57) [Claims] In a liquid crystal display device having a liquid crystal layer sandwiched between a pair of substrates, an alignment film is formed on at least one of the pair of substrates, and a surface of the alignment film is in contact with a surface of the alignment film. A liquid crystal display device in which unevenness for controlling a pretilt angle of liquid crystal molecules of the liquid crystal layer is formed, and the degree of the unevenness is different between a plurality of predetermined regions. 2. The pretilt angle is set to be small in a region of the alignment film surface where the degree of the unevenness is large, and to be large in a region of the alignment film surface where the degree of the unevenness is small. Liquid crystal display. 3. The method according to claim 2, wherein the plurality of regions having different degrees of unevenness are:
3. The liquid crystal display device according to claim 1, wherein at least two or more regions have different viewing angle characteristics. 4. An underlayer is formed between the alignment film and the substrate on which the alignment film is formed, and irregularities are formed on a surface of the underlayer that is in contact with the alignment film. The liquid crystal display device according to claim 1, wherein the degree of the difference is different between the plurality of predetermined regions. 5. The pretilt angle is set to be small in a region of the alignment film surface where the degree of the unevenness is large, and is set to be large in a region of the alignment film surface where the degree of the unevenness is small. Liquid crystal display. 6. A method according to claim 1, wherein said plurality of regions having different degrees of unevenness are:
The liquid crystal display device according to claim 4, wherein at least two or more regions have different viewing angle characteristics. 7. The liquid crystal display device according to claim 4, wherein the thickness of the alignment film formed so as to cover the base film varies depending on a location.