JP2000131700A - Liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To widen a manufacturing margin of alignment processing even in the case of an active matrix type using a lateral electric field system having a wide view angle characteristic and suited to a large-sized display. SOLUTION: This device is constituted of providing a pair of substrates 1, 1', a liquid crystal layer 32 arranged between a pair of substrates 1, 1', an electrode structure formed on one side substrate of a pair of substrates 1, 1' and for applying an electric field predominantly parallel to at least one side substrate surface between a pair of substrates 1, 1' to the liquid crystal layer 32 and alignment control layers 8, 8' formed between the electrode structure and the liquid crystal 32. In such a case, a step of film thickness or above of the thinnest part of at least the alignment control layers 8, 8' is given onto the alignment control layers 8, 8' of the liquid crystal display device of the lateral electric field system, and a forward tapered slope of 8.5 degree or below in an angle or 0.15 or below in an aspect (longitudinal/lateral) ratio is formed on the end parts of the step.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an active matrix type liquid display device, and more particularly to an electrode structure (electrode group) formed on the same substrate to apply an electric field to a liquid crystal layer in a direction substantially parallel to the substrate. The present invention relates to a so-called in-plane switching mode liquid crystal display device which is operated by applying a voltage.

[0002]

2. Description of the Related Art In a conventional liquid crystal display device, electrodes for driving a liquid crystal layer are formed on two substrates, respectively.
Opposing transparent electrodes were used. This is due to the adoption of a display system typified by a twisted nematic display system, which operates by making the direction of the electric field applied to the liquid crystal substantially perpendicular to the substrate surface.

On the other hand, as a method of making the direction of an electric field applied to the liquid crystal substantially parallel to the substrate surface, a comb-shaped electrode (Inter digita) is used.
l electrode) is used, for example, in Japanese Patent Publication No. 63-21907.
No., USP4345249, WO91 / 10936, JP-A-6-
22397 and JP-A-6-16078. In this case, the electrode does not need to be transparent, and a highly conductive and opaque metal electrode is used.

The present invention relates to a display system in which the direction of an electric field applied to a liquid crystal is set to a direction substantially parallel to the surface of a substrate (hereinafter, referred to as an in-plane switching (IPS) system). No mention is made of a method for imparting uniform orientation to a target liquid crystal display device having a stepped structure.

[0005]

In these known in-plane switching type liquid crystal display devices, it is difficult to perform alignment processing. The margin is remarkably narrower than the conventional TN (Twisted Nematic) system, especially the currently mainstream normally open TN system (bright display at low voltage and dark display at high voltage).
The reasons for the narrow margin are the following three points (1) to (3).

(1) Step Structure In a horizontal electric field type liquid crystal display device, an elongated electrode (inter digital electrode) having a width of about several μm in principle is used.
ctrode) (sometimes called ctrode). Therefore, a fine step structure is formed. The size of the step is determined by the thickness of the electrode and the shape of various films formed thereon, but is usually 0.1 μm or more. A polymer film such as polyimide is formed as an alignment control film (also referred to as an alignment film) on the uppermost layer of these films. In a conventional mass production technique, a rubbing treatment is performed on the alignment control film to impart liquid crystal alignment ability.

On the other hand, the cloth used for the rubbing treatment is composed of long and thin fibers having a thickness of about 10 to 30 μm, and each of the fibers substantially causes friction with a local portion on the surface of the alignment film. By applying a shear force in a certain direction while generating heat, liquid crystal alignment ability is provided. Several μm as fiber
Although some ultrafine fibers are present, they have not been put into practical use for rubbing because they require a stiffness for imparting a certain frictional force.

Since the distance between the electrodes in the horizontal electric field method is about 10 to 30 μm, which is almost the same as the diameter of the fiber, the rubbing orientation treatment near the step is not sufficiently performed, and the orientation tends to be disordered.
For example, the step end acts as a guide for the fiber of the rubbing cloth, and the fiber is drawn in the direction in which the step is extended,
The fiber does not reach the corner of the step, and the orientation treatment cannot be performed, and poor orientation occurs.

As a method for solving this problem, a method for flattening the surface of the alignment film has been proposed. However, complete flattening makes it easy for a spacer for controlling a constant liquid crystal layer thickness to move. This is not practical. The movement of the spacer causes the spacer distribution to become non-uniform and the liquid crystal layer thickness to become non-uniform, thereby causing luminance unevenness.
In addition, when the spacer moves, the surface of the alignment film is damaged, causing light leakage. From this point, it is understood that a certain level difference is necessary.

(2) Orientation Angle In principle, the initial orientation direction needs to be set at a certain angle or more from the direction in which the signal wiring electrode extends or the direction perpendicular thereto. In order to define the initial alignment direction by rubbing, it is necessary to rub the fiber with a fiber of about 10 to 30 μm in a predetermined angle direction as described above. However, in a horizontal electric field type liquid crystal display device, a signal wiring electrode, a common electrode and a pixel are used. There are many linear electrodes such as electrodes, and due to the wiring extending in a certain direction and the step at the end, the fiber is dragged in the direction of the step from the design angle, and it is shifted from the normal orientation direction of the flat area, or it is completely oriented This causes a problem that an unprocessed area is left behind.

(3) Sinking of Dark Level One of the features of the liquid crystal display device of the horizontal electric field system is that the sinking of the dark level (black display) is good.
Therefore, the disorder of the orientation is more conspicuous than in other systems.

In the conventional normally open TN system, a dark level can be obtained with a high voltage applied. in this case,
At a high voltage, most of the liquid crystal molecules are aligned in the direction of the electric field, which is one direction perpendicular to the substrate surface, and a dark level is obtained in relation to the arrangement of the liquid crystal molecules and the arrangement of the polarizing plate. Therefore,
The uniformity of the dark level does not largely depend on the initial alignment state at low voltage in principle. Further, human eyes recognize luminance unevenness as a relative ratio of luminance, and respond to an almost logarithmic scale. From this point of view, the conventional normally open TN mode in which liquid crystal molecules are forcibly aligned in one direction at a high voltage is insensitive to the initial alignment state, which is advantageous. On the other hand, in the horizontal electric field method, a dark level is displayed at a low voltage or zero voltage, and therefore, it is sensitive to disturbance in the initial alignment state. In particular, the liquid crystal molecules are arranged in a homogeneous arrangement in which the orientation directions of the liquid crystal molecules are parallel to each other on the upper and lower substrates, and the light transmission axis of one polarizing plate is parallel to the orientation direction of the liquid crystal molecules and the other polarizing plate is orthogonal (birefringence mode). ), The polarized light incident on the liquid crystal layer propagates the linearly polarized light with little disturbance. This works effectively to lower dark levels.

In general, the transmittance T of the birefringent mode can be expressed by the following equation (1).

T = T ₀ · sin ² ｛2θ (E)｝ · sin ² ｛(π · deff · Δn) / λ｝ (1) where T ₀ is a coefficient and is mainly used for a liquid crystal panel. The value determined by the transmittance of the polarizing plate, θ (E) is the angle between the effective optical axis of the liquid crystal layer and the polarization transmission axis, E is the applied electric field strength,
deff is the effective thickness of the liquid crystal layer, Δn is the refractive index anisotropy of the liquid crystal, and λ is the wavelength of light. Further, here, the product of the effective thickness deff of the liquid crystal layer and the refractive index anisotropy Δn of the liquid crystal, that is, deff · Δn is called retardation. The thickness deff of the liquid crystal layer here does not correspond to the thickness of the entire liquid crystal layer but to the effective thickness of the liquid crystal layer that actually changes the alignment direction when a voltage is applied. This is because the liquid crystal molecules in the vicinity of the interface of the liquid crystal layer do not change their orientation direction even when a voltage is applied due to the effect of anchoring at the interface. Therefore, assuming that the thickness of the entire liquid crystal layer sandwiched by the substrates is d _LC , there is always a relationship of d eff <d _LC between the thicknesses d _LC and deff, and the difference is the liquid crystal material used for the liquid crystal panel. And it depends on the interface in contact with the liquid crystal layer, for example, the type of alignment film material, but can be estimated to be approximately 20 to 40 nm.

As is apparent from the above equation (1), the term sin ² {2θ (E)} depends on the electric field intensity, and the angle θ
Is changed according to the electric field strength E, the luminance can be adjusted.
In order to obtain a normally closed type, the polarizing plate is set so that θ = 0 ° when no voltage is applied, so that the polarizing plate acts so as to be sensitive to disturbance in the initial alignment direction.

As described above, the liquid crystal display device of the in-plane switching mode has many linear electrodes in the display portion, and the use of the birefringence mode makes the device more susceptible to non-uniform alignment processing. Had occurred.

An object of the present invention is to provide a liquid crystal display device having high quality image quality in which the occurrence of display defects due to fluctuations in the initial alignment direction is reduced by making the alignment control ability on the film surface of the alignment control film uniform. To provide.

[0018]

SUMMARY OF THE INVENTION An object of the present invention is to provide an active matrix type horizontal electric field liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of transparent substrates, at least one of which is in contact with at least one of the liquid crystal layers. On the surface of the surface, the average inclination angle of the end (1/2 of the sum of the maximum inclination and the minimum inclination)
To form an orientation control film having a step of 8.5 degrees or less or a step having a forward taper slope of 0.15 or less in aspect (length / width) ratio. By providing the alignment control film with such a step having the characteristics of the end portion, the liquid crystal alignment ability can be provided to the vicinity of the step.

As described above, one pixel (in other words, 1
The uniform initial alignment within one scanning wiring and one signal wiring (the smallest unit capable of controlling the display) makes the alignment direction of the alignment control film of all the pixels uniform, and the uniformity over the entire display screen. It is possible to provide a liquid crystal display device capable of displaying.

The effect of the step structure having such a forward tapered slope is effective even on the substrate side having an electrode structure that generates an electric field predominantly parallel to the substrate. May be a substrate opposed to a substrate having.

In particular, when such an orientation control film is formed on a substrate having an electrode structure, since the lateral electric field method is used, the electrode structure is linear, and the step is extremely large. The effect of defining the inclination angle is remarkable. The forward tapered inclined structure may be formed of an insulating film or an electrode structure material interposed between the orientation control film and the substrate.

Further, when the black matrix formed at the boundary of the color filter is made of a resin material and a black pigment, the black matrix must be made thicker than the light-transmitting pixel, so that a step is formed. It is easy to occur and the present invention works more effectively. Conversely, when a black matrix is formed of a metal thin film material such as chromium, the black matrix portion may be relatively thin. The present invention is also effective in this case. Also, in the transverse electric field liquid crystal, as is apparent from the equation (1), since the liquid crystal layer thickness deff giving the maximum transmittance is different for each light wavelength λ, even when the liquid crystal layer thickness deff is changed for each color of the color filter. Since the step occurs, the present invention is effective.

In addition, when the dielectric anisotropy of the liquid crystal is positive and the angle between the alignment direction and the electric field direction when no electric field is applied on the alignment control film is 45 to 88 degrees, When the rate anisotropy is negative and the angle between the orientation direction and the electric field direction when no electric field is applied on the orientation control film is 2 to 45 degrees,
That is, it is more effective to combine the present invention with a display mode using birefringence.

It is also effective when spacers are formed with regularity in opaque portions of pixels instead of dispersed spacers. Further, when the shape of the spacer is a conical shape, an n-pyramidal shape (n is a natural number of 3 or more), a polygonal pyramid shape, a cylindrical shape having a forward taper or an n-shaped prism (n is a natural number of 3 or more), more effect is obtained. It is a target. In particular, the taper inclination angles of these spacers are preferably 8.5 degrees or less. This regular spacer can be formed by, for example, a photolithography process.

On the other hand, as an alignment treatment method other than the rubbing method, there is known an optical alignment method in which the alignment function of an alignment control film is controlled by irradiating linearly polarized light from a certain direction.
However, in the horizontal electric field method, since a large number of elongated electrodes made of metal are provided, the orientation may be disturbed due to light reflection or interference on the surface of the metal electrode.

By setting the average inclination ((maximum inclination angle + minimum inclination angle) / 2) of the steps of the orientation control film within a predetermined range as in the present invention, uniform light in a certain direction can be formed even in a fine portion. Irradiation can be performed, good orientation ability can be provided, and display unevenness can be prevented. Further, when a plurality of steps are provided, it is more effective if the average inclination of each of the steps is set within an error of about 10%.

In the photo-alignment method, when an azobenzene group, a stilbene group, or the like is introduced and a photoisomerization reaction is used, problems of adhesion and coloring between the alignment film material and the substrate arise. This problem can be solved by interposing a transparent organic polymer layer thicker than the alignment control film between the alignment control film and the substrate. Since this organic polymer layer has a certain thickness, it acts to reduce distortion caused by a temperature change or the like.

More preferably, if both the orientation control film and the transparent organic polymer layer are polyimide, the adhesion is further enhanced because they are of the same type.

As another means, the thickness of the orientation control film is formed to be 0.04 to 0.3 μm. Such an orientation control film can more effectively realize the above-described forward tapered inclined structure.

As another means, a soluble polyimide or polyamic acid having a concentration of 1 to 15% is used as a material for the alignment control film. The forward tapered structure described above can be realized by applying these soluble polyimides or polyamic acids and heating them at least to a temperature at which the solvent evaporates. In the case of a polyamic acid, a more preferable orientation control film can be realized by raising the temperature to a temperature at which imidization proceeds.

According to the present invention, a liquid crystal display device having a uniform alignment control film and having no display unevenness can be realized.

[0032]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The specific structure of the embodiment will be described below.

Embodiment 1 FIG. 2 is a schematic sectional view of a cell of a liquid crystal display device according to an embodiment of the present invention. Liquid crystal layer 3 composed of a plurality of compounds between a pair of transparent substrates 1 and 1 '
2 are pinched. FIG. 2 schematically shows rod-like liquid crystal molecules 6. Polarizing plates 9, 9 'are arranged on both outer sides of the pair of substrates 1, 1'. Stripe-shaped electrodes 2 and 3 are formed on the inner surface of the cell of one substrate 1, an insulating layer 4 is formed thereon, and an alignment control film 8 is further formed thereon.
Are formed. The electrode 2 is a common electrode for applying a voltage having a fixed waveform independent of the image signal, and the electrode 3 is a pixel electrode whose waveform changes according to the image signal. The video signal electrode 10 is arranged at the same height as the pixel electrode 3. Each of the pixel electrode 3 and the video signal electrode 10 has a thickness of 0.2 μm. The insulating layer 4 has two layers, both of which are made of a silicon nitride film, and each has a thickness of 0.4 μm. On the other opposing substrate, a color filter 5 for performing color display is formed.

FIG. 1 is a schematic diagram showing the film structure around the electrode group of FIG. 2 in more detail. Insulating layer 4 covering electrodes 3 and 10
An alignment control film 8 is formed thereon by coating. The thickness of the orientation control film was 0.12 μm. However, the film thickness of the orientation control film on the upper part of the wiring electrode was slightly reduced to about 0.08 μm due to the flow during application of the varnish for the orientation control film.

An 8% solution of polyamic acid as a precursor of the orientation control film 8 was applied. Then, at 200 ° C,
Firing and imidization were performed for 30 minutes. The orientation control film 8
Is a polyamic acid which is a polyimide precursor, and as a monomer component, as a diamine compound, 4,
It was synthesized as polyamic acid using 4'-diaminodiphenylmethane and pyromellitic dianhydride and 1,2,3,4-cyclobutanetetracarboxylic dianhydride.

A buff cloth made of rayon fiber having a thickness of about 18 μm is placed on the alignment control film 8 so that the major axis direction of the liquid crystal molecules to be aligned is at an angle Φ _LC = 75 degrees defined in FIG. A rubbing treatment was performed.

Thereafter, polymer spacer beads having a particle size of 4.2 μm dispersed in methanol were dispersed in a solution state. Since the dispersion medium was alcohol, it evaporated within 1 minute, leaving only the spacer beads. The dispersion density was about 100 per 1 mm ² .

Thereafter, the upper and lower substrates were overlapped, and assembled into an empty cell state using a sealing agent at the peripheral portion. Thereafter, the liquid crystal composition was sealed at room temperature, and thereafter, annealing was performed at 100 ° C. for 10 minutes to obtain a favorable liquid crystal alignment. Thus, a liquid crystal display having a liquid crystal layer thickness d of 4.0 μm was obtained. A nematic liquid crystal having a positive dielectric anisotropy was used as the liquid crystal composition. The value of the dielectric anisotropy Δε is 10.2, and the refractive index anisotropy Δn is 0.073.

FIG. 4 shows the switching principle of the liquid crystal molecules in the panel thus obtained. In this embodiment, the liquid crystal molecules 6 are set so that Φ _LC = 75 degrees with respect to a direction perpendicular to the longitudinal direction of the stripe-shaped electrode when no electric field is applied, but the dielectric anisotropy of the liquid crystal is positive. some cases, 45 degrees ≦ | Φ _LC | <should be such that 90 degrees. The liquid crystal composition in FIG. 4 may have a negative dielectric anisotropy. In that case, the initial alignment state is 0 degree ≦ | Φ _LC from the vertical direction of the stripe electrode.
It is preferable to make the orientation of | <45 degrees. In FIG. 4, the orientation direction 11
Is indicated by an arrow. Next, as shown in FIGS. 4B and 4D, when an electric field 13 is applied between the electrodes 2 and 3, the electric field 13
The direction of the liquid crystal molecules 6 is changed so that the long axis of the molecules is parallel to the direction. At this time, θ in Expression (1) changes according to the electric field intensity E, and the transmittance changes.

In this embodiment, a liquid crystal is sandwiched between orthogonal polarizing plates because a display system of a birefringence mode is employed. Further, in order to obtain a normally closed characteristic in which a dark display is obtained at a low voltage, the polarization transmission axis of one of the polarizing plates is perpendicular to the initial alignment direction. The observed transmitted light intensity is determined by equation (1).

FIG. 5 shows the arrangement of the electrode group, the insulating film, and the alignment control film in the unit pixel portion in this embodiment. FIG. 5A is a front view seen from a direction perpendicular to the panel surface, and FIG.
(c) is a diagram showing a side cross section. The pixel is a video signal electrode 10
Are divided into four parts by a common electrode 2 and a pixel electrode 3 which are parallel to.

FIG. 6 shows a circuit system configuration in the liquid crystal display device of this embodiment. It comprises a vertical scanning signal circuit 17, a video signal circuit 18, a common electrode driving circuit 19, a power supply circuit and a controller 20, but the present invention is not limited to this configuration.

FIG. 7 shows the configuration of an optical system in the liquid crystal display device of this embodiment. On the back surface of the liquid crystal panel 27, a backlight unit 26 including a light source 21, a light cover 22, a light guide 23, and a diffusion plate 24 is provided. Here, the light-collecting sheet 25 for increasing the front luminance is provided, but there is no problem if it is not provided. Rather, it is better not to reduce the viewing angle dependency of luminance.

In this embodiment, as shown in FIG. 1, the step having the forward taper slope on the alignment control film 8 is larger than the thinnest 0.08 μm of the alignment control film 8 above the electrode wiring, and is approximately 0 μm. The taper inclination angle was 8.5 degrees or less, and the aspect ratio (vertical / horizontal) was 0.15 or less.

Incidentally, the state of the taper inclination at the end of the step can be obtained by measuring the cross-sectional profile of the substrate using a scanning electron microscope (cross-sectional SEM), a scanning atomic force microscope (AFM), or the like. This makes it possible to perform a rubbing alignment treatment near the step, to obtain a good dark level sinking as a liquid crystal display device, and to obtain a high contrast ratio.

Here, in the same manner as described above, the thickness and shape of the electrode wiring and the insulating film, and the concentration and viscosity of the alignment control film varnish are changed to provide a liquid crystal display device having several steps and taper inclination angles. It was fabricated, and the uniformity of the liquid crystal alignment due to the rubbing near the step, that is, the degree of sinking of the dark level was evaluated as the contrast ratio. As can be seen from the evaluation results shown in FIG. 8, the size of the step is 0.1 μm.
Even if it changes from m to 0.5 μm, a good dark level sinking is obtained when the taper inclination angle at the step end is 10 degrees or less and the aspect ratio (vertical / horizontal) is 0.176 or less,
As a result, it was confirmed that the contrast ratio could be improved. In particular, when the taper inclination angle is 8.5 or less and the aspect ratio is 0.15 or less, even better contrast can be obtained. The lower limit value should be larger than 0 °, but is desirably a step end having a taper inclination angle of 5 ° or more.

This is because the forward taper inclination at the step end is 10 degrees.
゜ or less, desirably at an angle of 8.5 ° or less, each hair tip of the fiber used in the rubbing treatment reaches the tapered portion at the step end sufficiently, and has sufficient frictional heat to the orientation control film and desired It is considered that it became possible to apply a shear force in a certain direction.

Also, the case where the step taper evaluated here is larger than the thickness of the alignment control film is shown, but when the size of the step is smaller than the film thickness of the alignment control film, the alignment control is performed. The film is considerably flattened by the coating process, and no remarkable difference is observed.

However, when the step is larger than the thickness of the orientation control film, the above-mentioned remarkable effect was obtained.

With the above configuration, the diagonal is 13.3 inches,
A trial production of an in-plane switching mode liquid crystal display device having 1024 × RGB × 768 pixels resulted in a liquid crystal display device having a contrast ratio of over 250 over the entire surface and excellent display uniformity.

(Embodiment 2) The following points are different from Embodiment 1.

A step structure was provided on the other substrate facing the substrate having the electrode group. A color filter is formed on the counter substrate, and a black matrix made of a mixture of a resin material and a black pigment is provided on the boundary between red (R), green (G), and blue (B), which are the three primary colors. Formed.
FIG. 9 shows the configuration.

The thickness of the black matrix is larger than any of the three primary color filter portions. On the black matrix and the color filters of the three primary colors, a protective film of a color filter composed of a transparent organic polymer layer 7 and an orientation control film 8 are applied. Since the thickness of the liquid crystal layer giving the maximum transmittance differs for each color as described in the equation (1), in this embodiment, the liquid crystal layer of the blue pixel using light of shorter wavelength is thinned. The thickness of the color filter was increased by about 0.2 μm. In this case, the step on the surface of the orientation control film 8 is at most 0.5 μm. Further, this step portion has a taper inclination angle of 8 as in the case of the electrode side substrate of the first embodiment.
A forward taper inclination of about 0.14 in degree and aspect ratio is formed.

As described above, display unevenness could be eliminated by forming the alignment control film having the above-mentioned steps between the liquid crystal layer and the substrate on which the color filter and the black matrix were formed.

When a liquid crystal display device of a lateral electric field type having a diagonal of 13.3 inches and a number of pixels of 1024 × RGB × 768 was prototyped with such a configuration, the contrast ratio exceeded 250 over the entire surface and the display was completed. A liquid crystal display having good uniformity was obtained.

(Embodiment 3) In Embodiments 1 and 2, polymer beads were used as spacers in a dispersed manner. In this embodiment, a columnar spacer 31 having regularity was formed on a black matrix by a photolithography process. Formed. Its configuration is, as shown in FIG.
Example 1 is exactly the same as Example 1 except that No.1 is used.
Since the columnar spacer had a forward tapered slope at the base thereof, the liquid crystal alignment by the rubbing alignment treatment near the periphery was also good.

The diagonal formed by setting the thickness of the liquid crystal layer to 3.7 μm is 13.3 inches, and the number of pixels is 1024 × RGB × 768.
As a result, a liquid crystal display device having a contrast ratio exceeding 300 over the entire surface and having good display uniformity was obtained. In this liquid crystal display device, since the polymer beads used in Examples 1 and 2 are not present in the display pixel region, it is possible to prevent the alignment disorder due to the movement of the beads and the display unevenness due to the change in the gap of the liquid crystal layer. The contrast could be improved.

(Example 4) In the same manner as in Example 3 except for the shape of the spacer used, a quadrangular pyramid spacer 31 is formed on a black matrix by photolithography with regularity, as shown in FIG. Such a configuration was adopted.

The thickness of the liquid crystal layer was 4.2 μm, and the diagonal was 1
When a liquid crystal display device of 3.3 inches and 1024 × RGB × 768 pixels was manufactured, a contrast ratio exceeded 300 over the entire surface and a liquid crystal display device having good display uniformity was obtained. . In this liquid crystal display device, as in the case of the third embodiment, polymer beads randomly dispersed in the display pixel region do not exist, so that higher contrast can be achieved.

Example 5 A diazobenzene group was contained as a diamine compound in the same manner as in Example 1 except for the alignment control film used.

[0061]

Embedded image

Using a mixture of 4,4'-diaminodiphenylmethane (the above structural formula) in an equimolar ratio, pyromellitic dianhydride and 1,2,3,4-cyclobutanetetracarboxylic dianhydride are used. Synthesized as a polyamic acid using an acid anhydride, applied to the substrate surface,
Calcination and imidation.

In this case, a forward taper having a taper inclination angle of about 6 degrees near the step of the electrode group and an aspect ratio of about 0.11 was formed. Thereafter, polymer spacer beads having a particle diameter of 4.2 μm dispersed in methanol were dispersed in a solution state.

After the dispersion solvent was dried, the upper and lower substrates were overlapped, and the sealant previously applied to the periphery was cured to form an empty cell. After that, polarized light irradiation was performed through a polarizing plate using a high-pressure mercury lamp having a wavelength of 436 nm as a light source. The irradiation light amount is about ² J / cm ² . Thereafter, the nematic liquid crystal composition was sealed in the same manner as in Example 1,
Annealing was performed at 10 ° C. for 10 minutes to obtain a liquid crystal alignment uniformly aligned in a direction substantially perpendicular to the above-mentioned polarized light direction. Thus, a liquid crystal display having a liquid crystal layer thickness of 4.0 μm was obtained.

With the above configuration, the diagonal is 13.3 inches,
A trial production of an in-plane switching mode liquid crystal display device having 1024 × RGB × 768 pixels resulted in a liquid crystal display device having a contrast ratio of over 250 over the entire surface and excellent display uniformity.

[0066]

According to the present invention, the problem that the manufacturing margin of the alignment process is narrow, which is an inherent problem of the in-plane switching method, in which an electric field is applied to the liquid crystal layer in a direction substantially parallel to the substrate. Resolve. At the same time, it is possible to provide a liquid crystal display device having high quality image quality in which the occurrence of display defects due to the fluctuation of the initial alignment direction is reduced.

[Brief description of the drawings]

FIG. 1 is an enlarged view of a part of the schematic cross-sectional view of FIG. 2 showing a step on an orientation control layer surface and a tapered shape thereof.

FIG. 2 is a schematic sectional view of a cell of the liquid crystal display device of the present invention.

FIG. 3 is a diagram showing angles formed by a liquid crystal molecule long axis alignment direction with respect to an electric field direction and a polarization transmission axis of a polarizing plate.

FIG. 4 is a schematic view showing the operation principle of liquid crystal in a liquid crystal display device of a horizontal electric field system.

FIG. 5 is a schematic diagram showing a plane and a cross section showing an arrangement of an electrode group, an insulating film, and an alignment control film of a unit pixel portion in the first embodiment.

FIG. 6 is a diagram showing an example of a circuit system configuration in a liquid crystal display device of the present invention.

FIG. 7 is a diagram showing an example of an optical system configuration in a liquid crystal display device of the present invention.

FIG. 8 is a diagram illustrating a relationship between a step taper inclination angle and a contrast ratio according to the first embodiment of the present invention.

FIG. 9 is a diagram showing an example of a configuration having a step structure on the color filter side of the present invention.

FIG. 10 is a diagram showing an example of the present invention having a configuration having a spacer formed with regularity in an opaque portion of a pixel.

FIG. 11 is a diagram showing another example of the present invention having a configuration having a spacer formed in an opaque portion of a pixel with regularity.

[Explanation of symbols]

1, 1 '... substrate, 2 ... common electrode, 3 ... pixel electrode, 4,
4 ': insulating layer, 5: color filter, 6: liquid crystal molecule,
7, 7 ': transparent organic polymer layer; 8, 8': alignment control film; 9, 9 ': polarizing plate; 10: video signal electrode; 11: rubbing direction; 12: polarizing plate transmission axis direction; Electric field direction, 14: scanning electrode (gate wiring electrode), 15: TFT
Element, 16 ... Amorphous silicon (a-Si), 17
... vertical scanning signal circuit, 18 ... video signal circuit, 19 ... common electrode driving circuit, 20 ... power supply circuit and controller,
21 light source, 22 light cover, 23 light guide, 24
... Diffusion plate, 25 ... Condenser sheet, 26 ... Backlight unit, 27 ... Liquid crystal panel, 28 ... Black matrix,
29 ... electrode group, 30 ... dispersed spacer beads, 31
... regularly arranged spacers, 32 ... liquid crystal layer.

 ──────────────────────────────────────────────────続 き Continuing on the front page (72) Inventor, Kazukazu Aratani 7-1-1, Omika-cho, Hitachi City, Ibaraki Prefecture Inside Hitachi Research Laboratory, Hitachi, Ltd. (72) Inventor Kenji Okidai 7, Omika-cho, Hitachi City, Ibaraki Prefecture No. 1 F term in Hitachi Research Laboratory, Hitachi Ltd. (Reference) 2H092 GA14 PA01 PA02 PA03 PA08 PA09 PA11 QA06 5C094 AA02 AA43 BA03 BA43 CA19 CA20 DA13 EA04 EA07 EC03 ED14 ED20 FA03 FB01 FB16 GB10 JA08 JA09

Claims (11)

[Claims] 1. A pair of substrates, a liquid crystal layer disposed between the pair of substrates, and formed on one of the pair of substrates and dominant over at least one substrate surface of the pair of substrates. A liquid crystal display device having an electrode structure for applying an electric field parallel to the liquid crystal layer and an alignment control film formed between the electrode structure and the liquid crystal layer, wherein the alignment control film has a step. The inclination of the step is a forward taper having an average angle of 0 degree or more and 8.5 degrees or less, or an aspect (vertical / horizontal) ratio of 0 or more and 0.15 or less. . 2. A plurality of spacers according to claim 1, wherein a plurality of spacers are formed on one of said pair of substrates, and said plurality of spacers have one of a conical shape, a polygonal pyramid shape, a columnar polygonal columnar shape, and the like. A liquid crystal display device characterized by having two shapes. 3. The liquid crystal display device according to claim 1, wherein said alignment control film has a thickness of 0.04 to 0.3 μm. 4. A pair of substrates, a liquid crystal layer disposed between the pair of substrates, and formed on one of the pair of substrates and dominant over at least one substrate surface of the pair of substrates. A liquid crystal display device having an electrode structure for applying an electric field parallel to the liquid crystal layer, wherein an alignment control film formed between any one of the pair of substrates and the liquid crystal layer; A liquid crystal display device comprising a soluble polyimide or polyamic acid having a concentration of 1 to 15%. 5. The liquid crystal display device according to claim 1, wherein said alignment control film is made of a material having a photoreactive structure. 6. The liquid crystal display device according to claim 5, wherein the material having the photoreactive structure controls the alignment direction of the liquid crystal layer by irradiating polarized light. 7. A liquid crystal according to claim 6, wherein said material having a photoreactive structure is an organic polymer containing at least one polymer or oligomer containing a diazobenzene group or a derivative thereof. Display device. 8. A liquid crystal display according to claim 6, wherein said material having a photoreactive structure is an organic polymer containing a polymer or oligomer containing at least one or more stilbene groups or derivatives thereof. apparatus. 9. The organic polymer according to claim 6, wherein the material having a photoreactive structure is a polymer precursor or a polymer which is cured by irradiation treatment of at least one of heat, light, and radiation. A liquid crystal display device, characterized in that: 10. A liquid crystal display device according to claim 9, wherein said polymer precursor or polymer has an ethylene group, an acetylene group, a diacetylene group, or a maleimide group. 11. The liquid crystal display device according to claim 10, wherein both the alignment control film and the transparent organic polymer layer are made of polyimide.