JP3164702B2 - 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 capable of improving viewing angle characteristics.

[0002]

2. Description of the Related Art In the above-mentioned liquid crystal display (LCD), a liquid crystal layer is sealed between a pair of substrates (liquid crystal cells), and the orientation of liquid crystal molecules contained in the liquid crystal layer is changed.
The display is obtained by changing the optical refractive index of the liquid crystal cell.

Conventionally, in order to control the orientation of the liquid crystal molecules, a twisted nematic (TN) type liquid crystal display device in which the liquid crystal molecules are oriented substantially parallel to the substrate and twisted by about 90 ° between a pair of substrates. Is mainly used. In a TN-type liquid crystal display device, electrode wiring is formed on a pair of substrates disposed opposite to each other, and an electric field is generated in a direction perpendicular to the substrates. When an electric field is applied to the liquid crystal layer, the liquid crystal molecules shift in the direction of the electric field due to the dielectric anisotropy of the liquid crystal, and the orientation state changes. This causes a change in the optical refractive index of the liquid crystal cell.

As an alignment method for twisting liquid crystal molecules by 90 ° as described above, a rubbing method in which an organic alignment film such as polyimide is formed on the electrode wiring and rubbed with a cloth such as nylon is widely used. ing.

FIG. 10 is a sectional view of a typical TN type liquid crystal display device, and FIG. 11 is a sectional view taken along line BB 'of FIG. One wiring substrate 131 has a glass substrate 111a, a transparent electrode 114, and an alignment film 116a. The other wiring substrate 132 has a glass substrate 111b, a transparent electrode 115, and an alignment film 116b. A liquid crystal layer 133 is provided between one wiring substrate 131 and the other wiring substrate 132 (in a liquid crystal cell). The liquid crystal molecules 133a in the liquid crystal cell are oriented so as to be twisted by about 90 ° between the substrates 131 and 132. Also, the substrate 131,
The liquid crystal molecules 133a have a pretilt angle of δ with respect to 132, and when a voltage is applied between the transparent electrodes 114 and 115, the liquid crystal molecules 133a rise uniformly in the direction of the pretilt angle. The ends of both substrates 131 and 132 are sealed with resin (not shown) or the like, and a peripheral circuit for driving liquid crystal layer 133 and the like are mounted. Electric signals of the scanning lines 112 and the signal lines 113 are supplied to the pixel electrodes 114 via the TFTs 120 to drive the liquid crystal layer. Although FIG. 10 shows an active matrix type liquid crystal display device, a liquid crystal display device other than the active matrix type can have the same structure except for the scanning lines, signal lines, TFTs, and the like.

In the TN type liquid crystal display device, the direction in which liquid crystal molecules rise when an electric field is applied is predetermined as a pretilt angle as shown in FIG. 11 in order to prevent the occurrence of discrimination due to multi-domain. ing.

However, since the direction in which the liquid crystal molecules rise when an electric field is applied is determined, a phenomenon occurs in which the contrast changes depending on the angle at which the observer views the liquid crystal display device.

As an example, FIG. 12 shows a voltage-transmittance (VT) characteristic in a normally white mode liquid crystal display device in which light is transmitted when no voltage is applied between the electrodes to obtain a white display. In the following description, with respect to the inclination of the liquid crystal molecules 133a shown in FIG. 11, the θ1 side is the normal viewing angle direction, and the θ2 side is the reverse viewing angle direction.

When viewed from directly above the liquid crystal display device (in a direction perpendicular to the substrate surface), V is as shown by a solid line L1 in FIG.
-T characteristic is obtained. That is, the transmittance of light decreases as the applied voltage value increases, the transmittance becomes almost zero at a certain applied voltage value, and the transmittance remains almost zero even when the applied voltage is further increased. .

However, in the normal viewing angle direction (θ in FIG. 11)
When the viewing angle is inclined toward (1 side), the VT characteristic becomes as shown by the solid line L2 in FIG. That is, as the applied voltage increases, the light transmittance decreases, and when a certain voltage value is reached, the light transmittance increases, and then gradually decreases again. Therefore, when the viewing angle is inclined in the normal viewing angle direction, an inversion phenomenon occurs in which the black and white of the image is inverted at a specific angle. That is, the inclination of the liquid crystal molecules becomes the same with respect to the incident angle (viewing angle) of light at a specific angle, and the anisotropy of the refractive index of the liquid crystal molecules is lost. As a result, the optical rotatory power is lost, and the above-mentioned reversal phenomenon occurs.

Also, in the reverse viewing angle direction (θ 2 in FIG. 11)
Side), the change in the refractive index of the liquid crystal molecules hardly occurs. For this reason, when the viewing angle is inclined in the reverse viewing angle direction, the VT characteristic as shown by the solid line L3 in FIG. 12 is obtained, and the change in light transmittance hardly occurs, so that the black and white contrast is significantly reduced.

The reversal phenomenon in the normal viewing angle direction and the decrease in contrast in the reverse viewing angle direction in the TN type liquid crystal display device are very obstructive to the observer, and the display characteristics of the liquid crystal display device are doubted. Become.

In order to improve the above phenomenon, both a normal viewing angle portion and a reverse viewing angle portion are formed in one picture element to compensate for a decrease in contrast in the reverse viewing angle direction and to increase the normal viewing angle. A method for suppressing the reversal phenomenon in the direction is being studied.

For example, when a rubbing process is performed on an organic alignment film to align liquid crystal molecules, a resist pattern or a mask formed by photolithography is used to move a plurality of regions in one pixel in different directions. Rubbing treatment. By making the rubbing directions different in this manner, both a portion having a normal viewing angle and a portion having a reverse viewing angle are formed in one picture element.

Also, by forming different organic alignment films in a plurality of regions within one picture element, portions having different pretilt angles are formed, and a pair of substrates are connected to each other by portions having different pretilt angles. There is also a method of combining them so as to face each other.

Further, when an inorganic alignment film for aligning liquid crystal molecules is formed, an inorganic alignment film is obliquely vapor-deposited in a plurality of directions in one picture element, so that a portion having a normal viewing angle is formed in one picture element. There is also a method of forming both the viewing angle portion.

[0017]

However, in the method of performing rubbing treatment in different directions and the method of forming a different organic alignment film as described above, the organic alignment film is in contact with a resist pattern or a mask. There is a problem that the display quality and reliability of the liquid crystal display device are deteriorated due to contamination.
Further, there is a problem that the production cost increases because the number of manufacturing steps of the liquid crystal display device increases.

In the method of obliquely depositing an inorganic alignment film in a plurality of directions, it is difficult to form an alignment film over a large area, and it has been difficult to produce a liquid crystal display device at low cost.

SUMMARY OF THE INVENTION The present invention has been made to solve the above-mentioned conventional problems, and an object of the present invention is to improve the viewing angle characteristics of a liquid crystal display device without lowering the display quality and reliability, and to produce the liquid crystal display device at low cost. It is an object of the present invention to provide a liquid crystal display device capable of performing the following.

[0020]

[0021]

[0022]

[0023]

The liquid crystal display device of the present invention According to an aspect of the pair of wiring substrate facing disposed in between the liquid crystal layer, each have a plurality of electrodes in the liquid crystal layer side, on both substrates In a liquid crystal display device in which a picture element is formed at a portion where the electrodes face each other, at least one linear low-dielectric-constant insulating film per picture element is provided on at least one electrode on one of the substrates in the long side direction. Are formed perpendicular to the average orientation direction of the liquid crystal molecules projected on the substrate, and the region constituting one pixel of the electrode on one substrate constitutes one pixel of the electrode on the other substrate The electrode is formed to have an arbitrary value larger in the direction parallel to the alignment direction than the region to be aligned, and the two opposing electrode portions are shifted in two directions parallel to the average alignment direction. This achieves the above object.

The linear low dielectric constant insulating film is formed between the electrodes on both the substrates and the liquid crystal layer, and the positions of the insulating film on one substrate and the insulating film on the other substrate are shifted. Along the direction parallel to the orientation direction, the openings may be formed alternately in a state where the openings of the other substrate are present in the other substrate portion facing between the adjacent openings on the one substrate. .

It is preferable that the width of the linear low dielectric constant insulating film is not less than the distance between the pair of wiring boards.

The linear low dielectric constant insulating film may have a tapered edge portion.

The liquid crystal molecules may have a Bretilt angle of 0 °.

[0028]

According to the present invention, one or more slit-shaped openings or linear low-dielectric insulating films for one picture element are provided on at least one of the pair of wiring substrates opposed to each other. Is formed. The long sides of the slit-shaped openings and the linear low-k insulating film are formed perpendicular to the average orientation direction of the liquid crystal molecules projected on the substrate, and the electrode on one of the substrates is formed. The area constituting one picture element is formed to have an arbitrary value larger in the direction parallel to the average orientation direction of the liquid crystal molecules projected on the substrate than the area constituting one picture element of the electrode on the other substrate. ing. As a result, the opposing electrode portions are displaced in two directions parallel to the average alignment direction of the liquid crystal molecules projected on the substrate, and an oblique electric field is generated therebetween. When the pretilt angle of the liquid crystal molecules is 0 °, the liquid crystal molecules rise in a direction parallel to the oblique electric field, so that the rise of the liquid crystal molecules can be easily controlled.

Since the regions where the rising directions of the liquid crystal molecules are different in one picture element can be formed due to the displacement of the opposing electrode portions, the viewing angle characteristics can be remarkably improved.

If the width of the slit-shaped opening and the linear low dielectric constant insulating film is too narrow, it is difficult to apply an oblique electric field component to the liquid crystal molecules.

The step of forming the slit-shaped opening and the step of forming the area of the electrode on one substrate larger than the area of the other electrode can be performed simultaneously with the conventional electrode patterning step. Further, the step of forming the linear low dielectric constant insulating film can be performed simultaneously with the step of forming the insulating protective film formed to prevent short circuit between the wiring boards. Subsequent formation and rubbing of the organic alignment film can be performed in a conventional process, so that the number of manufacturing steps is not increased, and the organic alignment film is not contaminated.

[0032]

Embodiments of the present invention will be described below with reference to the drawings. In the following embodiments, the present invention is applied to a TN type active matrix liquid crystal display device.

(Embodiment 1) FIG. 2 is a sectional view of a liquid crystal display device of Embodiment 1. In this liquid crystal display device, a wiring substrate 31 and a wiring substrate 32 on each of which a plurality of electrode wirings are formed are opposed to each other, and a liquid crystal layer 33 is sealed between them.

FIG. 1 is a plan view of the wiring board 31. In the wiring board 31, a scanning line 12 and a signal line 13 are provided on an insulating substrate 11a made of glass or the like so as to cross each other. A pixel electrode 14 is provided in a region surrounded by the scanning lines 12 and the signal lines 13. A switching element 20 is formed at a corner in each area, and is electrically connected to each pixel electrode 14 and one scanning line 12 and one signal line 13 adjacent to each pixel electrode 14. It is connected to the. The switching element 20 may have any structure. In this embodiment, an amorphous silicon thin film transistor (hereinafter, referred to as TFT) 20 is used.

On the other hand, on the wiring substrate 32, a light-shielding film (not shown) for shielding light other than the picture element portion and the counter electrode 15 are formed.

As shown by the broken line in FIG. 1, the counter electrode 15 has a slit-like opening 18 formed in a direction perpendicular to the average alignment direction of the liquid crystal molecules projected on the substrate. Here, the average alignment direction refers to the alignment direction of the liquid crystal molecules at the center of the liquid crystal layer 33. Also, one of the counter electrodes 15
As shown in FIG. 2, the rectangular region constituting the picture element is formed larger than the picture element electrode 14 in a direction parallel to the average orientation direction of the liquid crystal molecules projected on the substrate. In this embodiment, the width of the slit-like opening 18 is formed to be about 10 μm. If the width is too narrow, it is difficult to apply an oblique electric field component to the liquid crystal molecules.
Degree) or more is desirable. The slit-like opening 18 is formed simultaneously with the patterning of the counter electrode 15. The wiring substrates 31 and 32 are further provided with alignment films 16a and 16b made of an organic material for controlling the alignment state of the liquid crystal molecules, and are subjected to a rubbing process. The wiring substrates 31 and 32 are attached to each other, and liquid crystal is injected between the two substrates (liquid crystal cell) to form a liquid crystal layer 33. The pretilt angle of the liquid crystal molecules is 0 °. The ends (not shown) of the substrates 31 and 32 are sealed with a resin or the like, and peripheral circuits (not shown) are mounted thereon to form a liquid crystal display device.

In this liquid crystal display device, the counter electrode 1
5 is formed with a slit-shaped opening 18, so
As shown in (1), an oblique electric field is generated between the picture element electrode 14 and the counter electrode 15, and the rising direction of the liquid crystal molecules can be controlled as shown by the arrow. Since a region in which the rising directions of the liquid crystal molecules are opposite can be formed in one picture element, VT characteristics as shown in FIG. 9 can be obtained, and the viewing angle characteristics of the liquid crystal display device can be improved. .

In the first embodiment, the slit-like opening 18 is formed in the counter electrode 15. However, as shown in FIG. 3, the slit-like opening 18 of the picture element electrode 14 on the wiring board 31 (see FIG. Solid lines) and slit-shaped openings 18 (dashed lines in FIG. 3) of the counter electrode 15 on the wiring substrate 32 are alternately formed in a direction parallel to the average alignment direction of the liquid crystal molecules projected on the substrate. You may. Also, as shown in FIG. 4, the slit-shaped opening 18 (broken line in FIG. 4) formed in the counter electrode 15 is set to 1 / the end of the pixel electrode 14 on the wiring board 31.
It may be formed so as to face the second region. Further, when the slit-shaped opening 18 is formed in the pixel electrode 14, one short side of the slit-shaped opening 18 may be opened, and in this case, the pixel electrode 14 is comb-shaped or bellow-shaped. It becomes the shape of.

Since there is a possibility that a disclination line may be generated in the slit-shaped opening 18 due to the disorder of the alignment of the liquid crystal molecules, a light-shielding film may be formed on the portion to conceal the disclination line. In that case, it can be formed simultaneously with patterning of the light shielding film using a light shielding film material formed on the wiring board 32. Further, the switching element 20 formed on the wiring substrate 31 may be formed at the same time as patterning using an opaque film, for example, a film of titanium, tantalum, aluminum, or the like. Patterning can be performed simultaneously with the scanning line 12. Slit-shaped opening 1 as shown in FIG.
In the case where 8 is formed, the formation of a light-shielding film in the same manner as described above can be prevented for the discrimination line generated at the boundary between the regions where the rising directions of the liquid crystal molecules are different.

The slit-shaped openings 18 as shown in FIGS. 1, 3 and 4 can provide the same effect. The larger the number of divisions of a picture element, the more natural it can be seen by the observer's eyes, but the lower the aperture ratio of the liquid crystal display device. Therefore, it is desirable to set the most appropriate division number according to the size of the picture element. For example, the size of the picture element is about 70 μm × 230
In the case of μm, it is desirable to make it about 2 to 4 divisions.

In the above embodiment, in order to prevent a short circuit between the wiring board 31 and the wiring board 32, an insulating protective film (not shown) is formed on at least one of the picture element electrode 14 and the counter electrode 15. May be formed. It is preferable that at least a part of the insulating protective film has a window opening structure in order to prevent a DC component of an electric field from being applied to the liquid crystal molecules in the picture element portion. Further, a color display can be performed by further providing a color filter (not shown) on the wiring substrate 32.

(Embodiment 2) FIG. 5 is a sectional view of a liquid crystal display device of Embodiment 2. This liquid crystal display device has a counter electrode 15
As shown by a broken line in FIG. 1, a linear low dielectric constant insulating film 17 is formed in a direction perpendicular to the average alignment direction of liquid crystal molecules projected on the substrate, between arbitrary layers between the liquid crystal layer 33 and the liquid crystal layer 33. Have been. In addition, as shown in FIG. 5, the rectangular region forming one picture element of the counter electrode 15 is formed to be larger than the picture element electrode 14 in a direction parallel to the average alignment direction of the liquid crystal molecules projected on the substrate. Have been. If the width of the insulating film 17 is too small, it is difficult to apply an oblique electric field component to the liquid crystal molecules. The insulating film 17 is made of silicon oxide or silicon nitride or the like, and is formed simultaneously with an insulating protective film (not shown) formed to prevent a short circuit between the wiring board 31 and the wiring board 32. Other configurations can be the same as those in the first embodiment.

In this liquid crystal display device, the counter electrode 1
Since the linear low dielectric constant insulating film is formed between the liquid crystal layer 5 and the liquid crystal layer 33, the electric field applied to the liquid crystal layer 33 at that portion becomes low. Therefore, similarly to the first embodiment, an oblique electric field is generated during the period, and the rising direction of the liquid crystal molecules can be controlled as shown by the arrow. As in the first embodiment, the rising direction of the liquid crystal molecules can be reversed in one picture element, so that the viewing angle characteristics of the liquid crystal display device can be improved.

In the second embodiment, the low dielectric constant insulating film 17 is formed between the counter electrode 15 and the liquid crystal layer 33.
As shown in FIG. 3, the liquid crystal molecules projected onto the substrate are provided between the pixel electrode 14 and the liquid crystal layer 33 (solid line in FIG. 3) and between the counter electrode 15 and the liquid crystal layer 33 (dashed line in FIG. 3). May be alternately formed in a direction parallel to the average orientation direction. In addition, as shown in FIG.
The insulating film 17 (broken line in FIG. 4) formed between the pixel electrode 3 and the insulating film 17 may be formed so as to face a half area of the end of the pixel electrode 14 on the wiring board 31. Further, the insulating film 17
Instead of an independent island shape for each picture element, it may be formed in a structure continuous for two or more picture elements. In addition, as shown in FIG. 6, by using a structure in which the edge portion is tapered, the rising direction of the liquid crystal molecules can be further stabilized.

In the portion where the low dielectric constant insulating film 17 is formed, a light-shielding film may be formed in the same manner as in the first embodiment, in order to conceal discrimination lines caused by disordered alignment of liquid crystal molecules.

The low-dielectric-constant insulating film 17 as shown in FIGS. 1, 3 and 4 can provide the same effect. The larger the number of divisions of the picture element, the more natural the viewer sees it, but the lower the aperture ratio of the liquid crystal display device,
It is desirable to set the most appropriate division number according to the size of the picture element. For example, the size of the picture element is about 70 μm × 230 μm
In this case, it is preferable that the number of divisions is about two to four.

Further, a color filter (not shown) may be provided on the wiring substrate 32 to perform color display.

In the liquid crystal display device of the present invention, at least one of the electrodes on the substrate is provided with both the slit-shaped opening 18 shown in the first embodiment and the low dielectric constant insulating film 17 shown in the second embodiment. It can also be structured.

In the first and second embodiments, the present invention is applied to the liquid crystal display device of the active matrix drive system. However, the present invention can be applied to the liquid crystal display device of the duty drive system. In this case, as shown in FIGS. 7 and 8,
The slit-shaped opening 18a can be formed in the electrode 15a formed on one wiring board 32. Note that FIG.
And 8, the electrodes 1 formed on the wiring board 31
4a is indicated by a solid line, and the electrode 15 formed on the wiring board 32 is
a is shown by a broken line. In the liquid crystal display device shown in FIGS. 7 and 8, a low dielectric constant insulating film may be formed in a similar shape instead of the slit-shaped opening 18a.

[0050]

As is apparent from the above description, according to the present invention, the rising direction of the liquid crystal molecules can be easily controlled in a plurality of different directions, so that a plurality of viewing angle directions can be formed in one picture element. Can be. As a result, the viewing angle dependency of the liquid crystal display device can be suppressed.

The step of forming a slit-shaped opening in the electrode and the step of forming a low dielectric constant insulating film between the electrode and the liquid crystal layer should be performed simultaneously with the conventional electrode patterning step and the protective insulating film forming step. Therefore, a liquid crystal display device having good display quality and high reliability can be manufactured at low cost.

[Brief description of the drawings]

FIG. 1 is a plan view showing an active matrix type liquid crystal display device according to an embodiment of the present invention.

FIG. 2 is a sectional view taken along line A-A 'of FIG.

FIG. 3 is a plan view showing another embodiment of the liquid crystal display device of the present invention.

FIG. 4 is a plan view showing another embodiment of the liquid crystal display device of the present invention.

FIG. 5 is a sectional view showing another embodiment of the liquid crystal display device of the present invention.

FIG. 6 is a sectional view showing another embodiment of the liquid crystal display device of the present invention.

FIG. 7 is a sectional view showing another embodiment of the liquid crystal display device of the present invention.

FIG. 8 is a sectional view showing another embodiment of the liquid crystal display device of the present invention.

FIG. 9 is a graph showing an applied voltage-transmittance characteristic (VT characteristic) of the liquid crystal display device of the present invention.

FIG. 10 is a plan view illustrating an example of a conventional liquid crystal display device.

11 is a sectional view taken along line B-B 'of FIG.

FIG. 12 is a graph showing an applied voltage-transmittance characteristic (VT characteristic) of a conventional liquid crystal display device.

[Explanation of symbols]

 11a, 11b Transparent substrate 12 Scanning line 13 Signal line 14 Pixel electrode 15 Counter electrode 14a, 15a Electrode 16a, 16b Alignment film 17 Low dielectric constant insulating film 18, 18a Slit opening 20 TFT 31, 32 Wiring substrate 33 Liquid crystal layer

Continuation of the front page (56) References JP-A-6-194656 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) G02F 1/1337 G02F 1/1333 505

Claims (5)

(57) [Claims] 1. A pair of wiring boards, which are disposed to face each other with a liquid crystal layer interposed therebetween, each have a plurality of electrodes on the liquid crystal layer side, and a picture element is formed at a portion where the electrodes on both substrates face each other. In the liquid crystal display device, at least one linear low-dielectric-constant insulating film for one picture element is provided on at least one of the electrodes on the substrate, and the long side direction of the film is averaged of the liquid crystal molecules projected on the substrate. Are formed so as to be perpendicular to the orientation direction, and the region constituting one picture element of the electrode on one substrate is more parallel to the orientation direction than the region constituting one picture element of the electrode on the other substrate. A liquid crystal display device having a structure in which both opposing electrode portions are formed in two directions parallel to the average alignment direction. 2. The linear low dielectric constant insulating film is formed between an electrode on both substrates and a liquid crystal layer, and the positions of the insulating film on one substrate and the insulating film on the other substrate are shifted. Along the direction parallel to the orientation direction, the other substrate portion opposing between adjacent openings on one substrate is formed alternately in a state where openings of the other substrate are present. The liquid crystal display device according to claim 1 . Wherein the width of the linear low dielectric constant insulating film, a liquid crystal display device according to claim 1 or 2, wherein it is a pair of wiring substrate spacing above. Wherein said linear low dielectric constant insulating film, a liquid crystal display device according to claim 1, the shape of the edge portion has a taper. 5. A liquid crystal display device according to claim 1 Burechiruto angle of the liquid crystal molecules is 0 °.