JPH0720469A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To obtain excellent display characteristics which are free from a display irregularity even in an orientation treatment wherein no pretilt angle is generated by improving visual angle characteristics of the liquid, crystal display device. CONSTITUTION:Liquid crystal directors 10 are oriented in parallel to the surface of a counter display electrode 1 and an orientation control window 11 as a part where a specific part of the electrode is removed provided in a pixel of the counter display electrode 2. An orientation control electrode 6 is formed at the periphery of pixels of a display electrode 7. The orientation treatment is so performed that the liquid crystal directors 10 are changed corresponding to the colors of pixels. There are plural liquid crystal directors in a pixel. A light shield film is arranged at a place corresponding to the orientation control window 11.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device which achieves good viewing angle characteristics and high performance by controlling the tilt direction of a liquid crystal director by an electric field.

[0002]

2. Description of the Related Art In recent years, liquid crystal display devices have rapidly developed because of their thinness, light weight and low power consumption. The liquid crystal display device has a TN (Twisted Nematic)
Mode, STN (Super Twisted Nem)
atic) mode, homogenous type ECB (Elec)
tric controlled birefring
ence) mode, Heilmeier type GH (Gues
t-Host) mode and the like.

In each of these methods, a polymer film made of polyimide or the like formed above and below a liquid crystal layer is rubbed in a predetermined direction with a cotton cloth or the like (this treatment method is called rubbing treatment, and the rubbing direction is called rubbing direction). ), The step of aligning the alignment direction of the liquid crystal in the liquid crystal layer (this alignment direction is referred to as a director) is required. At this time, the rubbing direction coincides with the liquid crystal director in the plane parallel to the alignment film surface. Also, the rubbing process causes the liquid crystal director to have a certain angle with respect to the alignment film surface (this angle is called the pretilt angle),
Due to the occurrence of this pretilt angle, when a voltage is applied to the liquid crystal layer and the liquid crystal director stands upright with respect to the alignment film surface, the liquid crystal layer stands up in a certain direction, and the alignment due to the reverse tilt of the liquid crystal director occurs. It prevents irregularity (reverse tilt) from occurring irregularly.

However, in the above-described conventional liquid crystal display device, the performance of the liquid crystal display device and the yield are reduced due to the adhesion of foreign matter and the generation of static electricity due to the rubbing process. Further, when a voltage is applied to the liquid crystal layer, the liquid crystal director stands up in a fixed direction, which causes a problem that the viewing angle dependency is large.

FIG. 16 is a diagram showing the operation principle of a liquid crystal display device according to a conventional example. In the liquid crystal display device according to the conventional example,
A pretilt angle (36) is generated by rubbing, and the liquid crystal director (10) rises in the direction of the pretilt angle when a voltage higher than the threshold value of the liquid crystal is applied.

FIG. 17 is a top view showing a main portion of a conventional TN mode liquid crystal display device, and FIG. 18 is a sectional view taken along line d. The conventional TN mode liquid crystal display device includes a substrate (8), a display electrode (7) and a second polarizing plate (16) on a second polarizing plate (16).
Alignment film (5), liquid crystal layer (4), first alignment film (3),
The counter display electrode (2), the counter substrate (1), and the first polarizing plate (14) are sequentially formed. The first and second alignment films are subjected to rubbing treatments (37) and (38) so that the rubbing directions are 90 ° to each other. The liquid crystal layer (4) is composed of a chiral nematic liquid crystal to which a small amount of a left-handed chiral material is added in order to prevent occurrence of reverse twist failure (reverse twist).

The operation of the device is as follows.
Light is incident from the 6) side, and is incident on the liquid crystal layer (4) through the substrate (8). The counter substrate side liquid crystal director (21) and the substrate side liquid crystal director (2) in the liquid crystal layer (4)
3) forms an angle of 90 °, the pretilt angle is generated by rubbing, and the twist angle (22) of the liquid crystal layer is 90 ° due to the use of the left-handed chiral material. When the voltage is not applied to the liquid crystal layer (4), the light polarized by the second polarizing plate (16) is 9 at the liquid crystal layer (4).
It is twisted by 0 ° and passes through the first polarizing plate (14) to obtain a white display. When a voltage above the threshold value is applied to the liquid crystal layer (4), the liquid crystal director stands up against the alignment film surface, and when a sufficiently high voltage is applied, light passes through the first polarizing plate. A black display is obtained. Thus, in the TN mode liquid crystal display device according to the conventional example, an image can be displayed by turning on and off the voltage applied to the liquid crystal layer.

[0008]

However, the rubbing process is required in the above-mentioned conventional TN mode, and static electricity is generated by this process or foreign matter is attached to deteriorate the performance of the liquid crystal display device or to reduce the yield. Was lowered. Optical principle is different, but STN mode, ECB mode with homogeneous orientation, Heilmeier type GH
A rubbing process is also required in modes and the like, and problems such as static electricity generation and foreign matter adhesion occur as in the TN mode.

Further, in the above-mentioned conventional method, a pretilt angle is generated by a rubbing process in order to prevent irregular orientation disorder (reverse tilt) due to reverse tilt of the liquid crystal director. When an electric field is applied to the liquid crystal layer, the liquid crystal director stands up against the surface of the alignment film, but this pretilt angle makes the standing direction of the liquid crystal director a fixed direction, thereby preventing the occurrence of reverse tilt. However, this causes a problem of the viewing angle dependency that the display characteristics significantly change depending on the viewing angle, and deteriorates the display quality.

FIG. 16 shows a state in which the pretilt angle is generated by the rubbing process and the liquid crystal director stands in a certain direction when a voltage is applied to the liquid crystal layer. Definitions of parameters φ and θ representing the viewing angle direction are shown in FIG.
The conventional TN mode voltage transmittance characteristic and its viewing angle dependence are shown in FIG. Φ = 90,270 ° in the conventional TN method
Gradient reversal is large in each direction and display quality is poor.

[0011]

SUMMARY OF THE INVENTION The present invention is to solve the above-mentioned drawbacks of the prior art. A display electrode arranged on an insulating substrate and a counter substrate having at least a counter display electrode are attached with a liquid crystal layer interposed therebetween. In the liquid crystal display device that is combined,
The surface of at least one of the display electrode and the counter display electrode is oriented so that the liquid crystal director in the liquid crystal layer is parallel to the counter display electrode or the pretilt angle is 1 degree or less. It has been processed, and at least one of the display electrode and the counter display electrode is provided with an alignment control window which is a portion where a predetermined portion of the electrode is removed in the pixel, thereby improving the viewing angle characteristics, which is favorable. A liquid crystal display device capable of obtaining display characteristics. In the above liquid crystal display device, by forming an electrode for alignment control in a part or all of the periphery of at least one of the display electrode and the counter display electrode, the viewing angle characteristic is improved and good display characteristic is obtained. The present invention provides a liquid crystal display device capable of performing the above. In the above liquid crystal display device, a color filter including pixels of two or more colors is provided, and the alignment treatment is performed so that the liquid crystal director is changed according to the color of the pixel, whereby the viewing angle characteristics can be improved and good display characteristics can be obtained. A liquid crystal display device is provided. It is an object of the present invention to provide a liquid crystal display device capable of improving viewing angle characteristics and obtaining good display characteristics by aligning liquid crystal directors in a plurality of directions in a pixel in the liquid crystal display device. In the above liquid crystal display device, there is provided a liquid crystal display device in which a light-shielding film is arranged at a position corresponding to the alignment control window of at least one of the insulating substrate and the counter substrate, and good display characteristics can be obtained. It is a thing.

[0012]

According to the liquid crystal display device of the present invention, as shown in FIG. 2, when a voltage higher than the threshold value is applied to the liquid crystal layer to make the liquid crystal director stand up against the opposing display electrode surface,
Since the direction in which the liquid crystal director stands is controlled by the action of the electric field generated by the display electrode (7), the counter display electrode (2), and the alignment control window (11), the direction in which the liquid crystal director stands in a minute area is controlled. It is possible to make a plurality of them, so that the viewing angle dependence of the liquid crystal display device can be reduced. Further, it is possible to prevent irregular orientation (reverse tilt) from occurring due to the reverse tilt of the liquid crystal director.

In the liquid crystal display device of the present invention, a pretilt angle of 0 ° is preferable, and therefore, a method for forming an alignment film which does not require rubbing treatment, for example, an LB film, a SiO oblique vapor deposition film, a polyimide film having fine grooves formed by photolithography, etc. Since it can be used, it is possible to prevent adhesion of foreign matter, generation of static electricity, and the like, and it can be expected that the performance of the liquid crystal display device is improved and the yield is improved.

In the above liquid crystal display device, if the alignment control electrode (6) is provided as shown in FIG. 1, the electric field generated by the display electrode (7), the alignment control electrode (6) and the counter display electrode (2) is generated. The effect of controlling the liquid crystal director is increased by the action, and more favorable display characteristics can be obtained.

In the above liquid crystal display device, if a color filter including pixels of a plurality of colors is provided and the alignment process is performed so that the alignment direction of the liquid crystal molecules is changed according to the color of the pixel, TN is obtained.
It is possible to prevent coloring and deterioration of contrast due to mode wavelength dispersion or the like, and to realize good full-color display.

In the above liquid crystal display device, if the liquid crystal directors in the direction of the opposite display electrode surface are aligned in a plurality of directions within the pixel, a voltage higher than a threshold value is applied to the liquid crystal layer to act as a liquid crystal director. When the liquid crystal director rises with respect to the counter display electrode surface, the number of rising directions of the liquid crystal director in one pixel increases, so that a better viewing angle characteristic can be obtained.

In a system in which light may leak from the alignment control window, for example, a normally white system in the TN mode, a light-shielding film may be provided at the alignment control window to prevent deterioration of contrast. Excellent display characteristics can be obtained.

[0018]

EXAMPLE A liquid crystal display device according to the present invention will be described below with reference to FIGS. (1) First Example A first example of the liquid crystal display device according to the present invention will be described below. 3 is a top view of a main part of the liquid crystal display device according to the first embodiment of the present invention, FIG. 4 is a cross-sectional view of FIG. 4, and FIG. 5 is a view showing a longitudinal direction of a groove formed on the surface of an alignment film of a red pixel part. ,
FIG. 6 is a diagram showing the longitudinal direction of the grooves formed on the surface of the alignment film in the green pixel portion, and FIG. 7 is a diagram showing the longitudinal direction of the grooves formed on the surface of the alignment film in the blue pixel portion. As shown in FIGS. 3 and 4, the liquid crystal display device according to the first embodiment of the present invention includes a first polarizing plate (14), a counter substrate (1), a color filter layer (15), an alignment control window (12). ) Formed counter electrode (2), first alignment film (3), liquid crystal layer (4), second alignment film (5), display electrode (7), insulating substrate (8), second
Polarizing plate (16). First alignment film (3), second
On the surface of the alignment film (5), fine grooves having a pitch of 2 μm are formed on the polyimide film by a photolithography method in order to make the liquid crystal director constant. At this time, the use of photosensitive polyimide is advantageous because the steps of resist coating and resist stripping can be omitted. The light absorption axis (19) of the first polarizing plate and the light absorption axis (2) of the second polarizing plate
0) are arranged so as to be parallel to each other. The liquid crystal in the liquid crystal layer (4) is a chiral nematic liquid crystal in which a small amount of a left-handed chiral material is added to the nematic liquid crystal. Although not shown in the figure, the refractive index anisotropy Δn of the liquid crystal is 0.09.
0, the cell gap d is 5.0 μm. The color filter is composed of red, green and blue pixels. As shown in FIGS. 5 to 7, the longitudinal direction of the groove on the alignment film surface differs depending on the color of the pixel, and the liquid crystal director on the alignment film surface matches the longitudinal direction of the groove on the alignment film surface. The twist angle is also different. The twist angle of the liquid crystal layer is 70 ° for red pixels, 80 ° for green pixels, and 100 ° for blue pixels. FIG. 8 is a diagram showing the relationship between the twist angle of the liquid crystal layer and the wavelength dispersion of the transmittance. By combining the color of the color filter and the twist angle of the liquid crystal layer having the minimum transmittance for each color, the light leakage can be prevented. It can be seen that good display is possible. This combination is the relationship between the twist angle of the liquid crystal layer and the color of each pixel, and in the liquid crystal display device according to the first embodiment of the present invention, good black display without light leakage and good contrast can be obtained.

FIG. 9 is a diagram showing the definitions of the viewing angle directions θ and φ, and FIG. 10 is a diagram showing the viewing angle characteristics of the liquid crystal display device according to the first embodiment of the present invention. In this method, good viewing angle characteristics are obtained as compared with the conventional TN method.

(2) Second Embodiment A second embodiment of the liquid crystal display device according to the present invention will be described below. 11 is a top view showing a main part of a liquid crystal display device according to a second embodiment of the present invention, and FIG. 12 is a sectional view taken along line b. The liquid crystal display device according to the second embodiment of the present invention is an application of a positive stagger type TFT-LCD, in which a first polarizing plate (14), a counter substrate (1) and an alignment control window (11) are formed. The opposed display electrode (2), the first alignment film (3), the liquid crystal layer (4), the second alignment film (5), the alignment control electrode (28) also serving as the auxiliary capacitance electrode, and the display electrode (7) ), Drain line (26), gate line (27), TFT (29),
It comprises a substrate (8) and a second polarizing plate (16). Fine grooves having a pitch of 2 μm are formed on the surfaces of the first and second alignment films (3) and (5) by a photolithography method in order to make the liquid crystal director constant. The light absorption axis (19) of the first polarizing plate and the light absorption axis (2) of the second polarizing plate
0) are arranged so as to be orthogonal to each other. The liquid crystal in the liquid crystal layer (4) is a chiral nematic liquid crystal in which a small amount of a left-handed chiral material is added to the nematic liquid crystal. Although not shown in the figure, the refractive index anisotropy Δn of the liquid crystal is 0.09.
0, the cell gap is 5.0 μm. The groove longitudinal direction (17) on the surface of the first alignment film and the groove longitudinal direction (18) on the surface of the second alignment film are arranged so as to be orthogonal to each other, and the liquid crystal director is twisted by 90 ° in the liquid crystal layer. ing. Also the first,
Since the patterning is performed using the photolithography method so that the groove lengthwise direction (17) (18) on the surface of the second alignment film is in each of two directions within one pixel, the liquid crystal director on the substrate side when the liquid crystal is driven. There are four tilt directions in one pixel. Due to this effect, good viewing angle characteristics can be obtained. In order to prevent light leakage from the periphery of the orientation control window (11), the drain line (26) and the gate line (27), Cr is used.
The light-shielding layer (30) made of the above is provided on the counter substrate (1). In the liquid crystal display device according to the second embodiment of the present invention, this light shielding layer makes it possible to obtain good contrast without light leakage.

FIG. 13 is a diagram showing the viewing angle characteristics of the liquid crystal display device according to the second embodiment of the present invention. It can be seen that in the liquid crystal display device according to the second embodiment of the present invention, the front contrast is good, and good display characteristics with almost no inversion of gradation display in any viewing angle direction are obtained.

(3) Third Embodiment A third embodiment of the liquid crystal display device according to the present invention will be described below. FIG. 14 is a top view showing a main part of a liquid crystal display device according to a third embodiment of the present invention, and FIG. 15 is a sectional view taken on line C. The liquid crystal display device according to the third embodiment of the present invention is an application of the Heilmeier type guest-host mode.
Polarizing plate (14), counter substrate (1), alignment control window (1)
Counter display electrode (2) on which 1) is formed, first alignment film (3), liquid crystal layer (34) composed of guest-host liquid crystal in which a small amount of black guest dye is added to nematic liquid crystal, second alignment film ( 5), an insulating layer (35), an orientation control electrode (6), a display electrode (7) and a substrate (8). The first and second alignment films are polyimide LB films, and the directions of pulling up the counter substrate (1) and the edge substrate (8) from the polyimide LB film solution are the directions (32) and (33) in the figure, respectively. The counter substrate and the substrate-side liquid crystal directors (21) and (23) coincide with the direction in which the counter substrate and the substrate are pulled up from the LB film solution. When the polyimide LB film is used, the pretilt angle is almost 0 °.
Although the polyimide LB film is used here, an alignment film having grooves formed on the polyimide surface by photolithography or the like, or a SiO alignment film formed by oblique SiO vapor deposition may be used. Even with these alignment films, the pretilt angle of the liquid crystal can be about 0 °. First
The light absorption axis (19) of the polarizing plate is arranged so as to be orthogonal to the liquid crystal director. In the liquid crystal display device according to the third embodiment of the present invention, in addition to the guest-host effect, the rising directions of the substrate-side liquid crystal molecules are two directions within one pixel, so that good viewing angle characteristics can be obtained.

[0023]

As described above, according to the liquid crystal display device of the present invention, when a voltage higher than the threshold value is applied to the liquid crystal layer to make the liquid crystal director stand up against the alignment film surface,
It is possible to set a plurality of directions in which the liquid crystal director stands in a minute area, and thereby the viewing angle dependence of the liquid crystal display device can be reduced. Further, since a method for forming an alignment film having a pretilt angle of about 0 ° that does not require a rubbing treatment, such as a polyimide LB film, a SiO oblique deposition film, or a polyimide film having fine grooves formed by photolithography, can be used, it is possible to remove foreign matter. There is no concern about adhesion or generation of static electricity, and it can be expected that the performance and yield of the liquid crystal display device will be improved.

[Brief description of drawings]

FIG. 1 is a principle diagram of a liquid crystal display device according to the present invention.

FIG. 2 is a principle diagram of a liquid crystal display device according to the present invention.

FIG. 3 is a top view showing the configuration of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 4 is a side view showing the configuration of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 5 is a top view showing a longitudinal direction of a groove formed on an alignment film surface of a red pixel of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 6 is a top view showing a longitudinal direction of a groove formed on an alignment film surface of a green pixel of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 7 is a top view showing a longitudinal direction of a groove formed on an alignment film surface of a blue pixel of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 8 is a diagram showing a relationship between a twist angle of a liquid crystal layer and wavelength dispersion of transmittance.

FIG. 9 is a diagram showing a definition of a viewing angle.

FIG. 10 is a diagram showing viewing angle characteristics of the liquid crystal display device according to the first embodiment of the present invention.

FIG. 11 is a top view showing the configuration of the liquid crystal display device according to the second embodiment of the present invention.

FIG. 12 is a side view showing a configuration of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 13 is a diagram showing viewing angle characteristics of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 14 is a top view showing a configuration of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 15 is a side view showing a configuration of a liquid crystal display device according to a third embodiment of the present invention.

FIG. 16 is a principle diagram of a liquid crystal display device according to a conventional example.

FIG. 17 is a top view showing a configuration of a liquid crystal display device according to a conventional example.

FIG. 18 is a side view showing a configuration of a liquid crystal display device according to a conventional example.

FIG. 19 is a diagram showing viewing angle characteristics of a liquid crystal display device according to a conventional example.

[Explanation of symbols]

1 Counter Substrate 2 Counter Display Electrode 3 First Alignment Film 4 Liquid Crystal Layer 5 Second Alignment Film 6 Alignment Control Electrode 7 Display Electrode 8 Substrate 9 Electric Field 10 Liquid Crystal Director 11 Alignment Control Window 12 Counter Display Electrode Alignment Control Window 13 Display Electrode alignment control window 14 First polarizing plate 15 Color filter layer 16 Second polarizing plate 17 Groove longitudinal direction of first alignment film surface 18 Groove longitudinal direction of second alignment film surface 19 Light of first polarization plate Absorption axis 20 Light absorption axis of second polarizing plate 21 Opposite substrate side liquid crystal director 22 Liquid crystal layer twist angle 23 Substrate side liquid crystal director 24 First alignment film surface groove shape 25 Second alignment film surface groove shape 26 Drain line 27 Gate line 28 Alignment control electrode and auxiliary capacitance electrode 29 TFT 30 Light-shielding film (Cr) 31 Gate insulating film (SiNx) 32 Polyimide LB film solution? Pulling the substrate from the direction 33 polyimide LB film solution to raise the counter substrate direction 34 guest-host liquid crystal layer 35 insulating layer (SiNx) 36 pretilt angle 37 first alignment layer rubbing direction 38 second alignment layer rubbing direction

Claims (5)

[Claims] 1. A liquid crystal display device comprising a display electrode arranged on an insulating substrate and a counter substrate having at least a counter display electrode bonded to each other with a liquid crystal layer interposed therebetween. The director) is parallel to the display electrode surface and the counter display electrode surface, or at least one surface of the display electrode and the counter display electrode is oriented so that the pretilt angle is 1 degree or less. A liquid crystal which is processed and has an alignment control window which is a portion where a predetermined portion of the electrode is removed, in at least one pixel of the display electrode and the counter display electrode. Display device. 2. The liquid crystal display device according to claim 1, wherein an electrode for alignment control is formed in a part or all of the periphery of a pixel of at least one of the display electrode and the counter display electrode. Liquid crystal display device. 3. The liquid crystal display device according to claim 1, further comprising a color filter including pixels of two or more colors.
A liquid crystal display device characterized by being oriented so that the liquid crystal director is changed according to the color of a pixel. 4. A liquid crystal display device according to claim 1, 2 or 3, wherein the liquid crystal directors in the direction of the display electrode surface are aligned so as to have a plurality of directions within a pixel. 5. A liquid crystal display device, wherein a light-shielding film is arranged at a position corresponding to the alignment control window on at least one of the insulating substrate and the counter substrate.