JP2965829B2 - 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 having a controlled tilt angle and a method of manufacturing the same. In particular, the present invention relates to a liquid crystal display device having a novel structure having different viewing angle characteristics by forming alignment states having different tilt angles, and a method of manufacturing the same.

[0002]

2. Description of the Related Art In a liquid crystal display (LCD), a voltage is applied to a liquid crystal layer provided between a pair of opposing substrates to change the orientation of liquid crystal molecules, thereby causing a change in the optical refractive index of the liquid crystal layer. This is a device for displaying images by using a device. Therefore, it is important that the liquid crystal molecules in the liquid crystal layer are arranged as regularly as possible in the initial state before the voltage is applied. In order to arrange the liquid crystal molecules regularly in this manner, the surface state of the substrate sandwiching the liquid crystal layer regulates the interaction of the liquid crystal molecules.

By the way, as a method of aligning liquid crystal molecules in a fixed direction in an initial state, an alignment film material is applied to a liquid crystal layer side surface of a pair of substrates, and the applied material is dried and cured to form an alignment film. After that, a method of rubbing the surface of the alignment film is currently most widely used.

[0004] There are two types of the above-mentioned alignment films, an inorganic alignment film and an organic alignment film. Examples of the material of the inorganic alignment film include oxides, inorganic silanes, metals, and metal complexes. One of the materials for the organic alignment film is polyimide, and a typical example is 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. You. The reason why a polyimide resin is widely used as a liquid crystal alignment film material is as follows. That is, because the solubility in the state of the polyamic acid is good, it is easy to adjust the concentration and mucous membrane, etc., good applicability, easy to control the film thickness, and the like, In addition, 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 formed on the substrate as described above 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 the liquid crystal layer where the liquid crystal molecules are in contact with the alignment film, that is, the pretilt angles are all uniform. Therefore, the pretilt angles are substantially the same in each picture element constituting the unit dot of the matrix display pattern.

Meanwhile, in a liquid crystal display device, an active matrix type liquid crystal display device (TFT-LCD) using a thin film transistor as a switching element connected to each picture element electrode serving as a picture element to be displayed is a twisted nematic. A Mattic (TN) type configuration is employed. In the liquid crystal display device having this configuration, the liquid crystal molecules have different twisting directions at respective positions in the thickness direction of the liquid crystal layer, and are oriented so as to be twisted by 90 ° in the vicinity of both substrates. 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 of liquid crystal molecules of the liquid crystal layer, that is, the orientation direction that changes in the thickness direction of the liquid crystal layer and the tilt angle that is the inclination with respect to the substrate.

[0007]

In a TN type liquid crystal display device, since the liquid crystal molecules have anisotropy in refractive index (birefringence), the contrast depends on the angle at which a human (observer) views the liquid crystal display device. The phenomenon of changing occurs.

For example, in the case of a normally white mode in which light is transmitted when no voltage is applied and white display is performed, a voltage is applied between driving electrodes formed on both substrates, and the substrate surface is When the liquid crystal display device is viewed from the vertical direction, as shown by a solid line L1 in FIG. 3, the light transmittance decreases as the applied voltage value increases. When the value is saturated, the transmittance becomes substantially zero, and the transmittance remains substantially zero even when the applied voltage is further increased. However, the applied voltage-transmittance characteristic indicated by the solid line L1 in FIG. 3 changes due to a change in the viewing angle direction for observing the liquid crystal display screen. FIG.
This will be described with reference to FIG.

FIG. 4 is a perspective view showing a liquid crystal layer portion sandwiched between a pair of substrates 31 and 32, and FIG. 5 is a sectional view showing a liquid crystal layer portion sandwiched between a pair of substrates 31 and 32. In these figures, one (upper) substrate 31 has a glass substrate 31a, a transparent electrode 31b, and an alignment film 31c, and the other (lower) substrate 32 has a glass substrate 32 likewise.
a, a transparent electrode 32b and an alignment film 32c.
The liquid crystal molecules 35 in the liquid crystal cell are 9 between the substrates 31 and 32.
It is twisted by 0 °. In the figure, the symbol δ indicates the pretilt angle, and the number 36 indicates the normal viewing angle direction.

When a voltage is applied to the liquid crystal display device having such a configuration, the viewing angle is inclined in the normal viewing direction 36 from a direction perpendicular to the substrate surface, and 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 tilted with a tilt angle, and the refractive index is inverted 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. 6. As shown in FIG. 6 (a), when the applied voltage is zero or a relatively low voltage, an observer 37 located in the normal viewing direction is provided with a liquid crystal layer. The central molecule 35 in the middle looks elliptical, but when the applied voltage is gradually increased, the central molecule 35 moves so that its major axis direction is aligned in the direction of the electric field, that is, in the direction perpendicular to the substrate surface. For this reason, as shown in FIG.
7 has the 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 the central molecule 35 looks elliptical again to the observer 37 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 is increased by increasing the viewing angle. It has a viewing angle characteristic of being lowered.

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

As a technique for improving the reversal phenomenon, there is a technique disclosed in Japanese Patent Laid-Open No. 2-12. This technology divides a display electrode constituting one picture element into an inner electrode and an outer electrode in an active matrix type liquid crystal display device, and is applied to liquid crystal molecules corresponding to the inner electrode and liquid crystal molecules corresponding to the outer electrode. The viewing angle characteristic is improved by changing the electric field conditions. However, in the case of using this technique, it is necessary to change the shape pattern of the display electrode itself, so that the manufacturing process becomes complicated,
Further, there is a disadvantage that the driving method becomes complicated. Also,
It is hard to say that the effect of improving the viewing angle characteristics is also sufficient.

As another technique for improving the reversal phenomenon, the following two methods have been proposed (JAPAN).
P591-p594 and p of DISPLAY '92
886). As one proposed method, after rubbing the surface of the alignment film in one direction, a part of the surface is covered with a resist, and rubbing is performed in a direction opposite to the rubbing direction previously performed. This is a method in which the pre-tilt angle is made different by removing and giving the alignment film the alignment characteristics based on the difference in the rubbing direction between the surface of the alignment film coated with the resist and the surface of the alignment film not coated with the resist. . Another method is a method in which a plurality of pretilt angles corresponding to each material are formed on the surface of the alignment film by rubbing polyimide alignment films of different materials in parallel. However, in the case of the former proposed method, when the resist is coated on the surface of the alignment film, the alignment regulating force on the surface of the alignment film is significantly deteriorated. In the case of the latter proposed method, patterning of the alignment film is complicated. These methods are not practical because they are steps.

SUMMARY OF THE INVENTION The present invention has been made to solve the problems of the prior art, and a liquid crystal display device having a wide viewing angle with improved viewing angle characteristics and improved display quality, and a method of manufacturing the same. The purpose is to provide.

[0017]

[0018]

[0019]

Means for Solving the Problems] The liquid crystal display device of the present invention, the liquid crystal layer is sandwiched a pair of substrates, the interface made of an organic polymer for regulating the alignment of liquid crystal between the substrates and the liquid crystal layer In a liquid crystal display device in which an alignment film is formed, the liquid crystal layer has two or more liquid crystal layer regions having different alignment directions, and the alignment film formed on at least one of the substrates has a liquid crystal having different alignment directions. Since the surface corresponding to each layer region has a different oxygen atom concentration, the above object is achieved.

In this liquid crystal display, a plurality of regions having different oxygen atom concentrations of the alignment film may be formed in respective picture elements arranged in a matrix. In addition, a region where the oxygen atom concentration of the alignment film is high has a small pretilt angle of the liquid crystal, and a region where the oxygen atom concentration is low has a large pretilt angle of the liquid crystal. Further, the oxygen atom concentration is
The high region and the low oxygen atom concentration region correspond to the alignment film.
Are arranged alternately in both of the alignment films,
One of the regions where the oxygen atom concentration is high is the other of the alignment film.
Of the oxygen atom concentration is low.
be able to.

In the liquid crystal display device of the present invention, a liquid crystal layer is sandwiched between a pair of substrates, and an alignment film made of an organic polymer for regulating alignment of liquid crystal is formed at an interface between each substrate and the liquid crystal layer. In the liquid crystal display device, the liquid crystal layer has two or more liquid crystal layer regions having different alignment directions, and the alignment film formed on at least one substrate is provided for each of the liquid crystal layer regions having different alignment directions. Since the corresponding surfaces have different carbonyl group concentrations, the above object is achieved.

In this liquid crystal display device, each of the plurality of regions of the alignment film having different carbonyl group concentrations is
It is possible to adopt a configuration formed in each picture element arranged in a matrix. In addition, a region where the carbonyl group concentration is high in the alignment film has a small pretilt angle of the liquid crystal, and a region where the carbonyl group concentration is low has a large pretilt angle of the liquid crystal. In addition, the
The region where the concentration of carbonyl group is high and the concentration of carbonyl group are low
Regions are alternately arranged on both of the alignment films.
The carbonyl group concentration of one of the alignment films is high.
The region where the carbonyl group concentration of the other of the alignment films is low
A configuration facing the region can be adopted.

[0023]

[0024]

[0025]

[0026]

According to the liquid crystal display of the present invention, a plurality of regions having different pretilt angles can be formed in the liquid crystal layer.
Further, a plurality of regions having different pretilt angles can be formed in one picture element. For this reason, the pretilt direction (that is, the viewing angle direction) in the opposite direction can be formed in a plurality of picture element portions or in one picture element. As a result, a wide viewing angle liquid crystal display device with improved display quality can be provided.

[0027]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention will be specifically described below.

Embodiment 1 FIG. 1 is a sectional view showing a liquid crystal display device according to the present embodiment. This liquid crystal display device
It is an active matrix type, and has a pair of substrates 31 and 32 with a liquid crystal layer 35 interposed therebetween. On the other hand, the upper (upper) substrate 32 is provided with an opposing electrode 32b and an alignment film (not shown) on an insulating substrate 32a made of glass, a silicon wafer or the like.
Are formed in this order. This alignment film is formed of the liquid crystal layer 35.
Arranged on the side.

On the other (lower) substrate 31, a picture element electrode 31b and an alignment film (not shown) are formed in this order on an insulating substrate 31a made of glass, silicon wafer or the like. Although only one picture element electrode 31b is shown in the figure, a plurality of picture element electrodes 31b are provided in a matrix and are located on both sides of each picture element electrode 31b.
, A plurality of scanning lines (not shown) are arranged side by side, and intersect with the scanning lines and are positioned on both sides of each pixel electrode 31b. 31
A plurality of signal lines (not shown) are arranged side by side around b. Further, a thin film transistor (TFT) (not shown) as a switching element is provided near a portion where the signal line and the scanning line intersect with each other.
b, are electrically connected to the signal lines and the scanning lines. Further, an alignment film (not shown) is formed on the insulating substrate 31a in such a state. This alignment film is provided on the liquid crystal layer 35 side.

In the alignment film provided on the liquid crystal layer 35 side of the substrates 31 and 32, two regions having different pretilt angles 40 in different directions are set on the upper portions of the respective pixel electrodes 31b as shown in FIG. I have. Specifically, the alignment film formed on the substrate 31 has a pretilt angle of 4 on the upper portion of one pixel electrode 31b.
Area A with large 0 and area B with small pretilt angle 40
And On the other hand, the alignment film formed on the substrate 32 has a region C having a small pretilt angle 40 and a region D having a large pretilt angle 40 above one pixel electrode 31b.

The ends of the substrates 31 and 32 thus configured are sealed with a sealant made of resin or the like, and a peripheral circuit or the like is mounted outside.

In the liquid crystal display device of the present embodiment configured as described above, the alignment film was produced as follows. First, the substrate 31 and the substrate 32 are manufactured by a known method. Subsequently, the regions A, B, C, and D described above are provided for the outermost alignment film of each of the substrates 31 and 32. In the present embodiment, in an arbitrary step after the formation of the alignment film made of polyimide, a portion other than the region B of the alignment film formed on the substrate 31 is covered with a mask, and ultraviolet light is directed from above the mask toward the alignment film. Was irradiated. Before and after this, a portion other than the region C of the alignment film formed on the substrate 32 was covered with a mask, and ultraviolet light was irradiated from above the mask toward the alignment film.

By irradiating the surface of the alignment film with ultraviolet light, the surface tension of the surface of the alignment film at the irradiated portion increases, and the pretilt angle of the liquid crystal in contact with the alignment film decreases due to the increase in the surface tension. It will be. At this time, the pretilt angle 40 is made different between the opposing substrates 31 and 32, and the directions of the tilt are opposed to each other. As a result, as shown in FIG.
In the left half between 32, an area A having a large pretilt angle 40
And a region C having a small pretilt angle 40, and the directions in which the liquid crystal molecules 35a tilt are opposed to each other. In the right half, a region B having a small pretilt angle 40 and a region D having a large pretilt angle 40 exist.
The direction in which 5a is tilted faces each other.

In this case, the average pretilt angle of the liquid crystal molecules 35a located at the center in the thickness direction of the liquid crystal layer 35 is:
The larger the pretilt angle 40 on the substrate surface is, the more predominantly the pretilt angle 40 becomes, so that the left half of the liquid crystal molecules 35a has the normal viewing angle direction facing the near side, and the right half of the liquid crystal molecules 35a has the opposite normal viewing angle direction as shown in FIG. Is turned to the other side.

Therefore, in the liquid crystal display device of the present embodiment, even when a certain voltage is applied to the picture element electrode 31b, the display is performed in the left half and the right half with the viewing directions opposite to each other. For this reason,
It is not necessary to perform different driving for the right side and the left side as in the related art. Further, since the viewing angle direction is reversed, the viewing angle characteristics can be sufficiently improved.

The above-mentioned phenomenon that the surface tension of the surface of the alignment film at the irradiated portion increases can be confirmed by ordinary contact angle measurement using, for example, water or methylene iodide.

(Embodiment 2) This embodiment is a case where the surface of the alignment film is irradiated with ultraviolet light so as to increase the oxygen concentration on the surface of the alignment film at the irradiated portion.

In this case, the surface energy of the alignment film increases due to the increase in the oxygen concentration, and the pretilt angle of the liquid crystal in contact with the alignment film decreases.

Therefore, also in the second embodiment, an opposite pretilt direction (that is, a viewing angle direction) can be formed in one picture element as in the method described in the first embodiment.

The above-mentioned phenomenon that the oxygen concentration on the surface of the alignment film in the irradiated portion increases can be easily confirmed by surface elemental analysis such as XPS.

(Embodiment 3) In this embodiment, the surface of the alignment film is irradiated with ultraviolet light to increase the carbonyl group concentration on the surface of the alignment film at the irradiated portion.

In this case, the polarity of the surface of the alignment film changes due to the increase in the carbonyl group concentration, and the pre-silt angle of the liquid crystal in contact with the alignment film decreases.

Therefore, also in the third embodiment, the pretilt direction (that is, the viewing angle direction) in the opposite direction can be formed in one picture element as in the method described in the first embodiment.

The above-mentioned phenomenon that the concentration of carbonyl groups on the surface of the alignment film in the irradiated portion increases can be easily confirmed by surface infrared absorption such as FTIR.

FIG. 2 is a diagram showing the viewing angle characteristics in the case of the present invention, with the applied voltage on the horizontal axis and the transmittance on the vertical axis. As can be understood from this figure, in the case of the present invention, the inversion phenomenon does not occur, and good display can be performed.

In the above description, the pretilt angle 4
Although 0 is large and small in the right half and large and small in the left half, the present invention is not limited to this, and may be large and small in the right half, large and small in the left half, or small and large in the right half and large and small in the left half. In this case, when forming a region where the pretilt angle 40 is large and a region where the pretilt angle 40 is small in the opposing portion due to the surface tension difference, the surface tension difference is, for example, 2 dy.
It is good to be more than n / cm. Further, due to the difference in oxygen concentration, the pretilt angle 40
When forming a large region and a small region, the difference in oxygen concentration is set so that, for example, at a depth of about 100 Å from the surface, the at% of the low concentration region becomes 70% or less of the high concentration region. Is good. Further, when forming a region having a large pretilt angle 40 and a region having a small pretilt angle 40 in the opposing portion due to the difference in carbonyl group concentration,
The difference in the carbonyl group concentration is preferably such that it can be confirmed by the presence or absence of a new carbonyl group peak generated by light irradiation near 1700 cm ^-1 when measured by FTIR, for example.

Further, in the structure shown in FIG. 1 described above, regions having different pretilt angles are provided for both substrates. However, the present invention is not limited to this. Only one substrate has a plurality of pretilt angles. The other substrate may be formed to have an intermediate pretilt angle. In that case, the number of steps is reduced, so that it can be realized at low cost.

In the above description, a region having a different pretilt angle is provided for each pixel electrode, that is, for each pixel.
The present invention is not limited to this, and regions having different pretilt angles may be provided for every two or more picture elements or for a random number of picture elements.

In the above description, two types of regions having different pretilt angles are provided for each picture element. However, the present invention is not limited to this, and three or more types of regions having different pretilt angles are provided for each picture element. May be provided.

In the above description, the alignment film is irradiated with ultraviolet light. However, the present invention is not limited to this, and the present invention can be similarly implemented by irradiating light including an ultraviolet region.

In the above description, an alignment film made of polyimide is used as the alignment film material, but any material can be used as long as the material of the present invention can be obtained by light irradiation. At this time, an optimum irradiation wavelength or the like may be selected depending on the material. Further, the use of a laser enables more effective control.

Further, in the present invention, in addition to the method of partially irradiating light after forming the alignment film on the entire surface, the alignment film is partially formed by using photolithography or the like, and the alignment film portion is formed. , And then forming a remaining alignment film portion using photolithography or the like.

Further, the present invention can be applied not only to the active matrix type liquid crystal display device but also to a liquid crystal display device having any other structure.

The present invention is not limited to the TN type, but can be applied to a liquid crystal display of any mode.

[0055]

As described above, according to the present invention, the pretilt angle can be changed for each predetermined range to form different liquid crystal alignment states, so that the viewing angle characteristics can be sufficiently improved. The display quality can be improved and a wide viewing angle can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a viewing angle characteristic diagram of a liquid crystal display device to which the present invention is applied.

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

FIG. 4 is a perspective view for explaining viewing angle characteristics in a conventional liquid crystal display device.

FIG. 5 is a cross-sectional view for explaining viewing angle characteristics in a conventional liquid crystal display device.

FIGS. 6A, 6B, and 6C are diagrams for explaining an inversion phenomenon in a liquid crystal display device.

[Description of Signs] 31, 32 Substrate 31a, 32a Glass Substrate 31b Pixel Electrode 32b Counter Electrode 35 Liquid Crystal Layer 35a Liquid Crystal Molecule at Center (Representing Average Direction) 40 Pretilt Angle

──────────────────────────────────────────────────続 き Continued on the front page (58) Field surveyed (Int.Cl. ⁶ , DB name) G02F 1/1337 505 G02F 1/1337 520

Claims (8)

(57) [Claims] A liquid crystal layer is sandwiched between a pair of substrates.
Height to control the orientation of liquid crystal at the interface between the substrate and the liquid crystal layer
Liquid crystal display devices in which an alignment film made of molecules is formed
And the liquid crystal layer has two or more liquid crystal layer regions having different alignment directions.
The alignment film formed on at least one of the substrates is aligned.
The surface corresponding to each liquid crystal layer area with different direction is different
A liquid crystal display device having a configuration having a high oxygen atom concentration. 2. An alignment film having different oxygen atom concentrations.
Each of the multiple areas is arranged in a matrix
2. The liquid crystal display device according to claim 1, wherein the liquid crystal display device is formed in a device. 3. An alignment film according to claim 1, wherein said alignment film has a high oxygen atom concentration.
Region where the pretilt angle of the liquid crystal is small and the oxygen atom concentration is low
Wherein the pretilt angle of the liquid crystal is defined to be large.
Or the liquid crystal display device according to 2. 4. A liquid crystal layer sandwiched between a pair of substrates.
Height to control the orientation of liquid crystal at the interface between the substrate and the liquid crystal layer
Liquid crystal display devices in which an alignment film made of molecules is formed
And the liquid crystal layer has two or more liquid crystal layer regions having different alignment directions.
The alignment film formed on at least one of the substrates is aligned.
The surface corresponding to each liquid crystal layer area with different direction is different
Liquid crystal display with a carbonyl group concentration
Place. 5. A different carbonyl group concentration in the alignment film.
Each of a plurality of regions having is arranged in a matrix
5. The liquid crystal display device according to claim 4, wherein the liquid crystal display device is formed in each picture element.
Place. 6. A region in which the carbonyl group concentration of the alignment film is high.
The pretilt angle of the liquid crystal is small and the carbonyl group concentration is
The pretilt angle of the liquid crystal is largely specified in the low region.
The liquid crystal display device according to claim 4. 7. The oxygen-rich region and the oxygen
Regions with low atomic concentration alternate in both of the alignment films
And the oxygen atom of one of the alignment films
In the region where the concentration is high, the other oxygen atom concentration of the alignment film is higher.
2. The liquid crystal display device according to claim 1, which faces the low region.
Place. 8. The region having a high carbonyl group concentration and the region
A region having a low carbonyl group concentration is present on both of the alignment films.
And are alternately arranged, and the one of the alignment films is
The region where the carbonyl group concentration is high corresponds to the other region of the alignment film.
5. The method according to claim 4, which faces a region having a low concentration of rubonyl group.
Liquid crystal display device.