JPH11202338A - Liquid crystal display - Google Patents

Abstract

(57) [Summary] (with correction) [PROBLEMS] To provide a vertical alignment ECB liquid crystal display device having high contrast. The liquid crystal layer includes a pair of substrates, and a liquid crystal layer sandwiched between the pair of substrates. The pair of substrates includes a pair of electrode groups for applying an electric field to the liquid crystal layer. A liquid crystal display device having alignment films 3 and 6 for aligning liquid crystal molecules of the liquid crystal layer substantially perpendicular to the substrate surface between the pair of electrode groups and the liquid crystal layer; A light-shielding layer 13 that does not transmit light is formed, and the alignment film in a region shielded by the light-shielding layer can control its liquid crystal alignment ability by light irradiation, has photodissociation reactivity, and is shielded by the light-shielding layer of the alignment film. The region is an alignment film that has been subjected to a linearly polarized light irradiation process, and the light-shielded portion has a plurality of tilt angles.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to an ECB (Electrica
The present invention relates to a liquid crystal display device having a high contrast ratio of a liquid crystal display device using an lly controlled birefringence method.

[0002]

2. Description of the Related Art The display of a liquid crystal display device changes the orientation of the liquid crystal molecules by applying an electric field to the liquid crystal molecules of the liquid crystal layer sandwiched between the substrates. Done.

In a conventional liquid crystal display device, the alignment directions of the alignment films on the upper and lower substrates sandwiching the liquid crystal layer are made substantially orthogonal to each other so that the liquid crystal molecule arrangement is twisted by about 90 ° when no electric field is applied. Twisted nematic (T) that performs display using the change in the optical rotation of the liquid crystal layer by applying an electric field
N) Represented by a display system.

In the TN method, in order to set the liquid crystal alignment directions orthogonal to each other on the upper and lower substrates, a rubbing process is generally performed in which a surface of an alignment film made of a polymer film such as polyimide is rubbed in a specific direction with a nylon cloth or the like. A called process is used.

However, static electricity is generated by the rubbing process, and in an active matrix type liquid crystal display device using a thin film transistor or the like, for example, it causes a failure due to electrostatic breakdown of the transistor.

[0006] Further, scraping and chips of the alignment film and the rubbing cloth generated by mechanical stress during rubbing cause display defects and the like.

On the other hand, for example, a vertical alignment film in which liquid crystal molecules on the substrate surface are perpendicular to the substrate surface is used, and when the electric field is not applied with an electric field, the liquid crystal molecules are arranged almost vertically (homeotropic alignment) over the entire liquid crystal layer. A vertical alignment ECB display method in which display is performed by utilizing a change in birefringence of a liquid crystal layer due to the addition is known as another method.

FIGS. 1 and 2 show a conventional vertical alignment ECB.
FIG. 1 is a plan view, and FIG. 2 is a cross-sectional view taken along line AA ′ of FIG. 1.

As shown in FIG. 2, a TFT (Th
In Film Transistor, a substrate 2, a vertical alignment film 3, a liquid crystal layer 5 composed of a liquid crystal composition 4 having negative dielectric anisotropy 5, a vertical alignment film 6, a counter substrate 7, and a polarizing plate 8 are sequentially formed. .

The liquid crystal molecules 4 in the liquid crystal layer 5 are in a so-called homeotropic alignment state in which the alignment direction is substantially perpendicular to the substrate surface when no electric field is applied due to the vertical alignment films 3 and 6 of the upper and lower substrates.

The polarizing axes of the polarizing plates 1 and 7 are substantially orthogonal to each other, and are set in a so-called crossed Nicols state.

In the homeotropic state when no electric field is applied, the light that has passed through the polarizing plate on the incident side and becomes linearly polarized light is transmitted to the liquid crystal layer by the two polarizing plates set in crossed Nicols. Since the light is transmitted without substantially changing the polarization state, the light is cut by the polarizing plate on the emission side perpendicular to the polarization direction and is not transmitted.

On the TFT substrate 2, electrodes such as a transparent pixel electrode 9 made of an ITO film and a bus line electrode 10 are formed. On the other counter substrate 7, an ITO transparent counter (common) electrode 11 is also formed. Is formed.

When a voltage is applied between the pixel electrode 9 and the counter electrode 11 and an electric field in a substantially vertical direction is applied to the liquid crystal layer 5, the liquid crystal molecules having a negative dielectric anisotropy in the liquid crystal layer are turned on the substrate surface. Since the light transmitted through the liquid crystal layer undergoes birefringence and becomes elliptically polarized light, a component that is not orthogonal to the polarization axis on the emission side is generated, and light transmission occurs.

By appropriately setting the retardation of the liquid crystal layer, the above-mentioned light transmission can be used for display in a white state. Similarly, in a reflection type configuration in which a reflection plate is provided on one substrate, the same is true for the retardation. The display can be performed in the same manner as in the above-mentioned transmission type by appropriately setting the above and optionally adding optical means such as a phase plate.

In order to further improve the image quality such as contrast, there is no relation to display caused by a horizontal electric field between the pixel electrode and another pixel electrode adjacent to the pixel electrode and having a different potential state or the bus line electrode. A portion other than the normal effective display area 12 is covered with a light-shielding film 13 so that unnecessary light leakage is shielded and the spaces between pixels are always in a black state.

In the vertical alignment ECB method, since a vertical alignment film is used, a rubbing treatment is not necessary in principle, unlike the TN method. Therefore, there is no display defect caused by the above rubbing treatment, and display quality and mass productivity. This is a promising technology for realizing an excellent liquid crystal display device.

In particular, the above-mentioned reflection type ECB system is
Even when miniaturized and high-definition as a small high-definition liquid crystal light valve for liquid crystal projectors, the reduction in aperture ratio is significantly smaller than that of the transmissive type, and a small and high-definition liquid crystal without lowering the brightness. This is a promising technology as a method that can realize a projector.

[0019]

However, in the above-mentioned vertical alignment ECB method, in practice, the liquid crystal sealing condition in the liquid crystal panel, the non-uniformity of the surface state of the alignment film, etc. Due to the influence of the electrodes, a non-negligible transverse electric field component is generated in the electric field applied to the liquid crystal layer, so that domains having different alignment directions are generated. Further, the boundary between these domains is shown in FIG. A stripe called a disclination having a display luminance different from that of the surroundings also appears in the pixel, as shown at 14 in the example showing a state where a potential is applied).

The fringes due to the disclination decrease in brightness as black fringes during white display, leak light as white fringes during black display, cause a decrease in contrast, and further cause variations in liquid crystal panel production conditions. Since the occurrence location and the occurrence area are different, the display may be rough.

In order to avoid such problems due to disclination, a rubbing process for imparting a slight inclination (tilt) from the initial vertical alignment direction is performed on the entire surface of the substrate even in the vertical alignment ECB system in order to suppress the occurrence. Is needed.

In this case, since the tilt angle is uniformly provided in the substrate surface by the rubbing process, a slight light leak occurs due to the tilt angle in the pixel area at the time of the black display by the crossed Nicols, which causes a decrease in contrast. Become.

As described above, in the conventional vertical alignment ECB mode liquid crystal display device, when the rubbing process is not performed to improve the mass productivity, the display quality such as a decrease in contrast due to disclination is reduced. There is a problem that a decrease in the temperature occurs.

An object of the present invention is to provide a liquid crystal display device having a high contrast in a liquid crystal display device using a vertical alignment ECB system.

[0025]

The degradation of display quality due to the disclination occurring in the pixels of the vertical alignment ECB system is caused by the disclination of the parts other than the pixels.
For example, it is reduced by selectively generating light in a gap between pixel electrodes that are normally shielded by a light shielding layer. For this purpose, it is necessary to first perform some kind of processing for selectively setting the gap between the pixel electrodes, for example, to be in a state different from other portions.

In the liquid crystal display device using the vertical alignment ECB method of the present invention, first, at least one of the alignment films at the interface between the substrates is made of a material whose liquid crystal alignment ability, particularly its alignment direction can be controlled by irradiating linearly polarized light. The alignment film is selectively irradiated to a specific region other than the pixel region on the substrate surface, specifically, a region centered on a portion shielded by the light shielding layer other than the pixel region on the substrate surface. Have been.

In order to select a specific area in the irradiation process, for example, linearly polarized light irradiation may be performed using a mask pattern that transmits the linearly polarized light only in a portion to be selected.

Next, the area other than the pixel area selectively irradiated with the linearly polarized light must be a source of disclination.

In the liquid crystal display device of the present invention, the linearly polarized light irradiation treatment causes the vertical alignment film to be inclined from the initial alignment direction. The tilt angle from the normal direction is different depending on the position in the region selectively irradiated with the polarized light. In particular, when the light-shielding region has an opposite angle to the normal direction of the substrate, the manufacturing process can be facilitated.

Specifically, for example, an alignment film material having an alkyl chain which undergoes a photodissociation reaction is used as the alignment film material, and the inclination angle which varies depending on the location is, for example, in a region selectively irradiated with polarized light. For example, control the alignment direction by irradiating linearly polarized light using a mask pattern so that the alignment direction of the liquid crystal molecules on the alignment film is tilted to the right in the right half and to the left in the opposite direction in the left half. It is realized by.

The control of the tilt direction by the irradiation of the linearly polarized light (giving the tilt angle from the initial vertical alignment) is performed, for example, by Iimura et al., SDD Digest '97, 311.
As shown on the page, the irradiation can be performed by irradiating the linearly polarized light at an appropriate inclination to the substrate normal.

By giving the alignment film different inclination angles in the left and right directions to the alignment film in the gap portion selected as described above, the liquid crystal alignment in the vicinity of this portion of the liquid crystal panel after the liquid crystal is filled can be changed in the above-mentioned irradiation region. A state in which the inclination direction changes suddenly on the left and right with the center as a boundary can be set.

Disclination lines that cause display quality deterioration such as contrast deterioration occur at boundaries where the liquid crystal alignment direction changes discontinuously.
The portion where the inclination of the liquid crystal alignment provided by irradiating the linearly polarized light to the pixel electrode gap portion suddenly changes can be used as a seed for generating this disclination line.

In the liquid crystal display device of the vertical alignment ECB mode as in the present invention, the gap between the display electrodes where the disclination line hardly affects the display is generated by using the portion where the alignment control direction changes as a source when the device is driven. Since it occurs selectively in the portion, the occurrence in the pixel portion can be suppressed.

Further, in the method of selectively giving a tilt angle to a region other than the pixel region as in the present invention, unlike the ordinary rubbing method of giving a tilt to the entire substrate, light during black display due to the tilt angle of the pixel region is used. It is possible to prevent a decrease in contrast caused by leakage.

As described above, according to the present invention, the vertical alignment E
In the CB system, a liquid crystal display device which has almost no occurrence of disclination which causes a decrease in display quality in a pixel area, has high image quality with high display luminance and contrast, and has no problem of reduction in mass productivity due to a rubbing process. Can be obtained.

[0037]

Embodiments of the present invention will be specifically described below.

(Embodiment 1) The vertical alignment ECB mode liquid crystal display device of Embodiment 1 has a disk structure such that a portion centering on a light-shielding layer in the cross-sectional structure of the conventional example shown in FIG. The configuration is conceptually the same except that the region is selectively irradiated with linearly polarized light so as to be a point for fixing the ligation.

Hereinafter, a description will be given with reference to FIGS. 4 and 5 corresponding to FIGS.

As shown in FIG. 5, a TFT (Th
in Film Transistor: substrate 2, vertical alignment film 3, liquid crystal layer 5 composed of liquid crystal composition (liquid crystal molecules) 4 having negative dielectric anisotropy 5, vertical alignment film 6, facing (common)
A substrate 7 and a polarizing plate 8 are sequentially formed.

The above liquid crystal composition was manufactured by Merck MJ951152.
The value of the dielectric anisotropy Δε is −4.2, and the refractive index anisotropy Δ
n is 0.0827, and the thickness of the liquid crystal layer is set to 5.0 μm using spacer beads.

[0042]

Embedded image

The vertical alignment films 3 and 6 are made of JA Synthetic Rubber Co., Ltd., which is a polymer material mainly composed of a compound having a long-chain alkyl group as a side chain as shown in Chemical Formula 1 as an alignment film material.
The solution was applied by spin coating using LS-204, and then formed by heating and baking at 180 degrees for 1 hour.

The polarizing axes of the polarizing plates 1 and 8 are substantially orthogonal to each other, and are set in a so-called crossed Nicols state.

On the TFT substrate 2, a transparent pixel electrode 9 made of an ITO film, a bus line electrode 10, and a signal wiring (not shown) for driving the TFT and an electrical connection between the pixel electrode and the TFT are provided. A wiring layer composed of wirings and the like to be formed, and an insulating film made of silicon nitride as a protective film are formed thereon.
The O transparent counter electrode 11 and a color filter (not shown) are formed.

Further, a light-shielding film 13 is provided between pixels in order to improve image quality such as contrast.

The portion 15 centered on the portion where the light shielding film 13 is provided is selectively irradiated with linearly polarized light by an irradiation device using a mask pattern.

When no electric field is applied by the vertical alignment films 3 and 6 of the upper and lower substrates, the alignment direction of the liquid crystal molecules in the liquid crystal layer 5 is substantially the same as the alignment direction with respect to the substrate surface except for the portion where the polarized light is selectively irradiated. It is in a vertical, so-called homeotropic alignment state.

The irradiation of the selected region 15 with polarized light is performed by applying a high-pressure mercury lamp to the surface of the alignment film obtained as described above in the same manner as in Iimura et al., S.D.Digest '97, 311. Central wavelength 313nm as light source
UV light is passed through a polarizer using a multilayer dielectric film to irradiate linearly polarized light with an irradiation light amount of about 5 J / cm ² from an oblique direction of about 45 ° with respect to the substrate normal line, thereby irradiating linearly polarized light. As a result, a liquid crystal alignment inclined about 4 ° from the vertical direction with respect to the substrate was obtained by the selective photodissociation of the long-chain alkyl group.

At this time, using two mask patterns,
First, the right half of the selected area is shifted to the right 45
FIG. 5 shows that the polarized light irradiation is performed from an oblique direction at an angle of 45 °, and then the mask pattern is changed and the left half of the selected area is irradiated with the polarized light at an oblique direction of 45 ° to the left with respect to the substrate normal. As described above, the orientation control in which the inclination from the initial vertical orientation is reversed on the left and right of the selected region 15 is performed.

In this embodiment, the selective photodissociation reaction of a long-chain alkyl group by irradiation with polarized light is used as described above in order to impart and control the liquid crystal alignment inclined from the initial alignment direction of the alignment film. However, if similar effects can be obtained by other photoreactions such as a photoisomerization reaction using a material into which an azobenzene group or a stilbene group is introduced, or a photopolymerization reaction using a material into which a cinnamate group is introduced, it may be used. I can do it.

In this embodiment, materials having the same photoreactivity are used as the alignment film material for the upper and lower substrates. However, when light is irradiated only to the alignment film on the counter substrate side as in this embodiment. The alignment film material on the TFT substrate side may be a normal alignment film material having no photoreactivity.

Further, in this embodiment, the alignment film on the counter substrate side is irradiated with light as shown in FIG. 5, but the light irradiation is performed on the portion corresponding to the light shielding layer on the TFT substrate side as shown in FIG. The same effect can be obtained even if it is performed.

With the above configuration, a color liquid crystal panel having a diagonal of 10 inches and a number of pixels of 640 × 480 × 3 (three colors of RGB) was experimentally produced. A liquid crystal display device having no display and having a high contrast ratio of 260: 1 or more and a high luminance in a display image was obtained.

Further, the TF which does not operate due to electrostatic breakdown or the like
There was no T.

A reflection type liquid crystal light valve used in a projection type liquid crystal display is shown as a different structure of the present invention.
FIG. 7 shows the configuration.

The reflection type active matrix substrate 16 which is the first substrate is a MOS (M) which is an active element for driving a liquid crystal, which is independently disposed on a single crystal silicon substrate 17.
An etal oxide semiconductor (transistor) transistor 18 and a pixel electrode 19 also serving as an aluminum reflector are provided, on which an insulating film 20 is provided as a protective film, and a vertical alignment film 21 is formed on the re-surface thereof.

The above-mentioned vertical alignment control film was formed by applying a solution of a precursor of polyamic acid having a concentration of 5% by spin coating to form a polyimide precursor film, followed by imidization by heating and baking.

The polyamic acid of the present alignment control film precursor is:
As the monomer component, a mixture of 1,2-diamineoctadecane having a long-chain alkyl group as a diamine compound and p-phenylenediamine in a molar ratio of 1: 9 was used. It is synthesized as a polyamic acid from acid anhydrides of carboxylic dianhydride and 1,2,3,4-cyclobutanetetracarboxylic dianhydride.

The MOS transistor 18 was formed from a source diffusion layer, a source electrode, a drain diffusion layer, a drain electrode, a polysilicon gate and the like formed on a silicon substrate and a p-type well.

The electric signal controlled by the MOS transistor 18 is applied to the pixel electrode 19 through the through-hole contact 22, and a voltage is applied between the pixel electrode 19 and the opposing transparent electrode to drive the liquid crystal layer.

In addition, between the pixel electrode 19 and the layer on which the MOS transistor 18 is formed, a leak of accumulated charges due to photoconductivity in a MOS transistor diffusion layer or the like due to incident light from a gap between the pixel electrodes is generated. A light-shielding film 23 for prevention is formed. The opposing glass substrate 24, which is the second substrate, includes an opposing electrode 25 made of a transparent electrode formed on the glass substrate and a vertical alignment film 26. These two substrates are used to maintain a uniform cell gap. A liquid crystal display element is configured by sandwiching a liquid crystal layer 28 made of a liquid crystal composition 27 via the spacer.

The value of the dielectric anisotropy Δε of the liquid crystal composition 27 was -3.3, the refractive index anisotropy Δn was 0.0742, and the thickness of the liquid crystal layer was set at 4.0 μm by the spacer. I have.

A light-shielding film 29 is provided between the pixels.
A portion 30 centered on the portion where the light-shielding layer is provided is selectively tilted from the initial vertical orientation different in the irradiation region by an irradiation device using a plurality of mask patterns as in the first embodiment. It is irradiated with linearly polarized light so as to have an angle.

The above-mentioned irradiation of polarized light is performed by using a high-pressure mercury lamp having a peak at a wavelength of 436 nm as a light source and passing through a polarizer set at a Brewster angle to emit about 2 J / cm 2 of light.
^{In the same} manner as in Example 1, the linearly polarized light of No. ² was irradiated from an oblique direction of about 45 ° with respect to the normal to the substrate, and as a result, a liquid crystal alignment inclined by about 2 ° from the perpendicular direction to the substrate was obtained.

When a liquid crystal light valve having a diagonal of 1 inch and the number of pixels of 1024.times.768 was prototyped with the above configuration, a display image having almost no disclination and a contrast ratio of 300: 1 or more in a display image was obtained. The liquid crystal light valve of high display quality having the following was obtained without occurrence of defects in the MOS transistor.

[0067]

As described above, according to the present invention, the vertical alignment E
In the CB mode, a liquid crystal display device having high contrast can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view showing a configuration of a conventional vertical alignment ECB mode liquid crystal display device.

FIG. 2 is a cross-sectional view showing a configuration of a conventional vertical alignment ECB type liquid crystal display device.

FIG. 3 is a sectional view showing an example of occurrence of disclination.

FIG. 4 is a plan view showing a configuration of a vertical alignment ECB mode liquid crystal display device of the present invention.

FIG. 5 is a cross-sectional view illustrating a configuration of a vertical alignment ECB mode liquid crystal display device of the present invention.

FIG. 6 is a sectional view showing an alternative configuration of the vertical alignment ECB mode liquid crystal display device of the present invention.

FIG. 7 is a cross-sectional view showing a configuration of a vertical alignment ECB mode liquid crystal display device of the present invention.

[Explanation of symbols]

1, 8: polarizing plate, 2: TFT substrate, 3, 6, 21, 26
... vertical alignment film, 4,27 ... liquid crystal molecules in liquid crystal composition layer,
5, 28 liquid crystal layer, 7 counter substrate, 9 pixel electrode, 10
... bus line electrodes, 11, 25 ... opposed (common) electrodes, 1
2: Display area, 13, 23, 29 ... Light shielding film, 15, 30
... Linear polarized light irradiation area, 16 ... MOS transistor substrate, 17 ... Single crystal silicon substrate, 18 ... MOS transistor part, 19 ... Pixel electrode also serving as reflector, 20 ... Insulating film, 22 ... Through hole contact part, 24 ... Glass substrate.

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁶ Identification code FI G09F 9/35 303 G09F 9/35 303 308 308

Claims (4)

[Claims] A liquid crystal layer sandwiched between the pair of substrates; a pair of electrodes for applying an electric field to the liquid crystal layer on the pair of substrates; In a liquid crystal display device having an alignment film between the liquid crystal layer and the liquid crystal molecules of the liquid crystal layer to be substantially perpendicular to a substrate surface, a light blocking layer that does not transmit light is provided on one of the pair of substrates. The alignment film in a region formed and shielded by the light shielding layer is made of a material whose liquid crystal alignment ability can be controlled by light irradiation, and a portion of the alignment film shielded by the light shielding layer has a plurality of tilt angles. Characteristic liquid crystal display device. 2. The liquid crystal display device according to claim 1, wherein the alignment film is made of a material having photodissociation reactivity. 3. The liquid crystal display device according to claim 1, wherein the light-shielded region is an alignment film that has been subjected to a linearly polarized light irradiation process. 4. The liquid crystal display device according to claim 3, wherein the tilt angle has an angle relative to a normal direction of the substrate in the light-shielded region.