JPH10274777A - Active matrix type liquid crystal display device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To reduce staining at the hard angle of visibility, to prevent the lowering of transmissivity and to eliminate afterimage feeling by alternately arraying two kinds of unit pixels whose electrode directions of a pixel electrode and a common electrode are different on a screen. SOLUTION: Two kinds of display pixels of one provided with the pixel electrode and the common electrode which are arranged by alternately arraying comb-line electrode patterns in a longitudinal direction and the other provided with the pixel electrode and the common electrode which are arranged by alternately arraying the comb-line electrode patterns in a lateral direction in terms of planar shape viewed from above are alternately arrayed in adjacent pixel units or red, green and blue units, and electric field is impressed so that a parallel electric field direction may be different by every pixel. In such a case, the relation of the electric field and the initial orientation angle of the liquid crystal is contrastive between the pixel A an the pixel B, so that both pixels are rotated in a different direction. On white display, a major axis and a minor axis are simultaneously viewed from any visual field, whereby the staining is not caused. Since the boundary of rotation in the different direction appears on a wiring, it does not appear the aperture part.

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, and more particularly to an active matrix type liquid crystal display capable of obtaining a wide viewing angle.

[0002]

2. Description of the Related Art In a liquid crystal display device, as one of methods for applying an electric field to a liquid crystal, there is a static drive method for constantly supplying a constant voltage signal to each electrode.
In the case of a large-capacity display, the number of signal lines becomes enormous. Therefore, a multiplex driving method for supplying a signal voltage in a time-division manner is used for displaying a large amount of information. Among the multiplex driving methods, an active matrix method in which electric charges given to electrodes are held until the next frame has high display quality.

The direction of the electric field applied to the liquid crystal is classified into a method in which the electric field is applied perpendicularly to a glass substrate sandwiching the liquid crystal and a method in which the electric field is applied in parallel. Are suitable.

FIG. 7 shows an electrode structure of each pixel in a system in which an electric field is applied in parallel to a glass substrate sandwiching a liquid crystal.
No. 21907). As described later, the present invention employs a method of applying an electric field in parallel to the glass substrate (In Plane Switching, "IPS
) Active matrix liquid crystal display device.

First, the structure of the prior art will be described.
FIG. 7 is a plan view of a unit pixel according to the related art, and FIG. 8 is a cross-sectional view taken along line aa 'in FIG. FIG. 9 shows an arrangement of unit pixels.

Referring to FIG. 8, a thin film transistor (Th)
The pixel electrode 104 and the common electrode 106 are alternately formed on the glass substrate 102 on the side of an in-film-transistor (“TFT”).
Formed through. These electrodes are covered on the top with a protective insulating film 110, and a liquid crystal 1 is placed on the protective insulating film 110.
The TFT-side alignment film 120 necessary for orienting the layer 07 is applied and rubbed. Thus, the TFT-side substrate 203 is formed.

On the opposing glass substrate 101, opposing light-shielding films 141 for light-shielding are provided in a matrix, and are provided thereon (on the opposing glass substrate 110 and the opposing-side light-shielding film 141).
A color layer 142, which is a pigment necessary for color display, is composed of three primary colors of red, green, and blue light, and a flattening layer, which is a resin layer necessary for flattening a film surface of the liquid crystal 107, is formed thereon. A film 144 is applied. On the flattening film 144, the liquid crystal 1
The opposite-side alignment film 122 required for orienting 07 is applied and rubbed. The rubbing direction is the same as the direction applied to the TFT-side substrate 203. Like this,
The opposite substrate 202 is created.

[0008] The liquid crystal 107 is sealed between the TFT-side substrate 203 and the opposite-side substrate 202.

Finally, a TFT-side polarizing plate 145 is attached to the surface of the TFT glass substrate 102 on which the electrode pattern is not formed so that the transmission axis coincides with the rubbing direction. On the side where is not present, the opposite-side polarizing plate 143 is attached so that the transmission axis is orthogonal to the transmission axis direction of the TFT-side polarizing plate 145.

Thus, the liquid crystal display panel 301 is completed.

Next, the operation of the conventional liquid crystal display panel 301 will be described.

Referring to FIG. 7, ON / O of scanning line 115 is performed.
The thin film transistor 117 including the semiconductor layer 116 is switched by the FF signal, and when the thin film transistor 117 is in an ON state, charge flows from the video signal line 103 to the pixel electrode 104, and after being turned off, holds the charge.
Maintain a certain potential.

A constant voltage is constantly applied to the common electrode 106, the liquid crystal 107 is rotated by a horizontal electric field between the pixel electrode 104 and the common electrode 106, and the retardation change causes an opening in which the opposing light-shielding film 141 does not exist. Part 119
Light is transmitted at a portion where the pixel electrode 104 and the common electrode 106 are not provided.

FIG. 10 shows the display principle. By rubbing, the initial alignment direction of the liquid crystal molecules 118 is
In this case, the liquid crystal display panel 301 displays black without transmitting light. When a horizontal electric field E generated between the pixel electrode 104 and the common electrode 106 is applied to the liquid crystal molecules 118, the liquid crystal molecules 118 rotate.

The angle Ψ between the liquid crystal molecules and the initial alignment direction Ψ
And the transmittance are represented as in the following equation (1). However, the maximum transmittance is standardized as 1.

[0016]

(Equation 1)

Here, Ψ is an angle formed with the initial alignment direction, Δn
Indicates the refractive index anisotropy of the liquid crystal, d indicates the cell gap, and λ indicates the wavelength of the transmitted light.

When the angle is 45 ° from the initial alignment direction, the transmittance of the liquid crystal display panel 301 becomes maximum and white is displayed.

The angle θ ₀ (45 ° ≦ θ ₀ ≦ 90 °) between the initial alignment direction of the liquid crystal and the lateral electric field is appropriately determined depending on the purpose. The threshold voltage of the liquid crystal decreases as θ ₀ approaches 45 °. It is also a key parameter that directly affects the response speed.

Here, the problematic phenomenon is coloring when viewed from a severe viewing angle.

Estimated angle θ = 50 °, azimuth angle 0 ° ≦ φ ≦ 3
FIG. 1 shows the result of measuring the chromaticity variation in white display at 60 °.
It is shown in FIG.

FIG. 13 schematically shows the definition of the prospective angle θ and the azimuth angle φ. The interior angle between the panel normal direction and the line-of-sight direction is assumed angle θ, and the projection angle of the line-of-sight direction (vector) onto the panel and the interior angle between the panel upward direction is an azimuth angle φ.

FIG. 13 shows the direction in which coloring is most noticeable.
That is, as shown in FIG. 13, the liquid crystal molecule 118 has the bluish color when viewed from the long axis direction, and has the most yellow color when viewed from the short axis direction.

Next, the mechanism by which this coloring occurs will be described.

As can be seen from the above equation (1), the term including the wavelength has the maximum transmittance when Δn · d / λ = 1/2 (2) is satisfied.

Normally, when viewed from the front, green (wavelength λ = 5)
The cell gap d is determined so that 50 nm is transmitted at the maximum. However, when the viewing angle is changed and the actual retardation Δn ′ · d ′ changes, the maximum transmission wavelength changes and the color changes.

In any direction, the relationship between the expected angle θ and the optical path length d ′ is as follows: d ′ = d / cos (θ) (3)

The substantial refractive index anisotropy Δn ′ of the liquid crystal is Δn ′ = Δn in the minor axis direction, but depends on the expected angle θ as shown in the following equation (4) in the major axis direction of the liquid crystal. I do.

[0029]

(Equation 2)

Here, _ne is the refractive index in the major axis direction of the liquid crystal,
n _o is the refractive index of the liquid crystal in the minor axis direction.

FIG. 14 shows a calculation result of each retardation change when viewed from the long axis direction and the short axis direction. FIG.
From the above equation (2), it can be explained that the liquid crystal molecules are colored blue from the major axis direction and yellow from the minor axis direction.

[0032]

As a prior art for solving this problem, for example, Japanese Patent Application Laid-Open No. Hei 7-134301 discloses that a horizontal electric field is applied in two or more directions in one pixel to rotate the liquid crystal in both directions. A scheme is disclosed.

However, in this method, since the liquid crystal cannot substantially rotate in the boundary region of the rotation in each direction, a black stripe runs, and since this exists in the opening, the brightness is reduced and the afterimage feeling is seen. become.

Accordingly, the present invention has been made to solve the above problems, and has as its object the purpose of
A liquid crystal display that reduces the coloring at the severe expected angle that occurred in the PS system, and suppresses the appearance of black streaks on the bidirectional rotating surface of the liquid crystal in the opening, thereby reducing the luminance decrease and the afterimage feeling. It is to provide a device.

[0035]

In order to achieve the above object, an active matrix type liquid crystal display device according to the present invention has a pixel electrode and a common electrode in which comb teeth are alternately arranged in a vertical direction in a planar shape viewed from above. And a pixel having a common electrode and a pixel electrode in which the comb-tooth portions are alternately arranged in the horizontal direction. The two types of pixels are arranged in adjacent pixel units, or in red, green, and blue. It is characterized by being alternately arranged in units.

Further, according to the present invention, a display pixel is formed on a glass substrate by a scanning signal line provided in the same layer, a video signal line formed in the same layer, a pixel electrode, and a thin film transistor via a common electrode and an insulating film. A liquid crystal layer is sandwiched between the two substrates, and the electrodes and the thin film transistor element are substantially positioned with respect to the liquid crystal layer. The respective electrodes and the thin film transistor element are connected to external control means capable of arbitrarily controlling an applied electric field according to a display pattern, and the liquid crystal layer Polarizing means for changing the optical characteristics according to the alignment state of the pixel is arranged, and the display pixels are arranged so that the parallel electric field direction can apply an electric field in a different direction for each pixel.

[0037]

Embodiments of the present invention will be described below. According to a preferred embodiment of the present invention, a display pixel including a pixel electrode and a common electrode in which comb-shaped electrode patterns are alternately arranged in a vertical direction in a planar shape viewed from above is provided (see FIG. 1). And a display pixel (see FIG. 2) having a pixel electrode and a common electrode in which comb-shaped electrode patterns are alternately arranged in the horizontal direction. They are arranged so that an electric field can be applied in a different direction for each pixel in a parallel electric field direction. That is, by adopting a configuration in which two types of unit pixels having different electrode directions of the pixel electrode and the common electrode are alternately arranged in the screen, coloring at a severe viewing angle is reduced, and the transmittance is not reduced. Thus, it is possible to obtain a good liquid crystal display device having no afterimage feeling.

[0038]

BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a block diagram showing an embodiment of the present invention;

[Embodiment 1] A first embodiment of the present invention will be described first with reference to its structure. In the first embodiment of the present invention, the display pixel is composed of two types of elements, pixel A and pixel B. FIG. 1 shows a plan view of the pixel A, and FIG. 2 shows a plan view of the pixel B.

Referring to FIG. 1, in pixel A, pixel electrode 1
04, the common electrode 106 is formed such that the generated horizontal electric field forms an angle θ with the initial alignment direction. Referring to FIG. 2, the pixel B is formed so as to be inclined at −θ. Here, θ is a key parameter appropriately determined from characteristics such as a threshold voltage and a response speed as in the above-described conventional technology.

FIG. 3 shows a pixel arrangement of the pixels A and B. As shown in FIG. 3, pixels A and B are combined in a checkered pattern.

That is, the pixel arrangement is as shown in FIG. 3B, which is as shown in Table 1 below.

[0043]

[Table 1]

The cross section of the pixel in this embodiment is basically the same as that of the prior art described with reference to FIG. 8, and a description thereof will be omitted.

Next, the operation and effect of this embodiment will be described.

In the embodiment of the present invention, the estimated angle θ = 5
FIG. 4 shows the results of measuring the chromaticity variation in white display at 0 ° and azimuth angles 0 ° ≦ φ ≦ 360 °. In the result of FIG. 4, the amount of fluctuation is smaller than that of FIG. That is, coloring due to the viewing angle is greatly reduced. Furthermore, no black streaks run in the device.

FIG. 5 schematically shows a mechanism by which this effect occurs.

In the pixels A and B, since the relationship between the electric field E and the initial alignment angle of the liquid crystal is symmetrical, the pixels rotate in different directions. No coloring occurs.

Further, since the boundaries of the rotations in different directions appear on the wiring (ie, the boundaries between the pixels A and B), they do not appear at the openings.

[Embodiment 2] Next, a second embodiment of the present invention will be described. FIG. 6 is a view for explaining the second embodiment of the present invention, and is a view showing an arrangement of pixels.

This embodiment is the same as the first embodiment except for the pixel arrangement.

In this pixel array, pixels A (see FIG. 1) and pixels B (see FIG. 2) are arranged in a checkered pattern in units of R, G, and B colors. That is, the pixel arrangement is as shown in FIG. 6B, which is as shown in Table 2 below.

[0053]

[Table 2]

In this method as well, the coloring with white viewing angle dependence can be reduced in the same manner as in the first embodiment. Further, the black stripes run, that is, the boundary surface between the A and B elements which are unstable in terms of free energy can be reduced. As compared with the first embodiment,
It is possible to provide a liquid crystal display device in which the orientation of liquid crystal is stable, and which is excellent in mass productivity and reliability.

[0055]

As described above, according to the present invention,
By alternately arranging two types of unit pixels having different electrode directions of the pixel electrode and the common electrode in the screen, coloring at a severe viewing angle is reduced, and the transmittance is not reduced, and there is no afterimage. An advantageous effect is obtained that a liquid crystal display device can be obtained.

[Brief description of the drawings]

FIG. 1 is a plan view of a unit pixel A according to a first embodiment of the present invention.

FIG. 2 is a plan view of a unit pixel B according to the first embodiment of the present invention.

FIG. 3 is a diagram showing an array of unit pixels according to the first embodiment of the present invention.

FIG. 4 is a diagram showing viewing angle dependence characteristics (experimental results) of chromaticity fluctuation in the first embodiment of the present invention.

FIG. 5 is a diagram schematically illustrating a mechanism for reducing chromaticity fluctuation in the first embodiment of the present invention.

FIG. 6 is a diagram showing an array of unit pixels according to a second embodiment of the present invention.

FIG. 7 is a plan view of a unit pixel in the related art.

FIG. 8 is a cross-sectional view of a unit pixel in the related art.

FIG. 9 is a diagram showing an arrangement of unit pixels according to the related art.

FIG. 10 is an explanatory diagram schematically showing a display principle of a liquid crystal display device.

FIG. 11 is a definition diagram of a prospective angle θ and an azimuth angle φ.

FIG. 12 is a view showing a viewing angle dependence characteristic (experimental result) of chromaticity fluctuation in the related art.

FIG. 13 is a diagram illustrating a direction in which coloring occurs.

FIG. 14 is a diagram illustrating a graph for explaining a mechanism that causes coloring.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 101 Opposing glass substrate 102 TFT side glass substrate 103 Video signal line 104 Pixel electrode 106 Common electrode 107 Liquid crystal 110 Protective insulating film 115 Scanning line 116 Semiconductor layer 117 Thin film transistor 118 Liquid crystal molecule 119 Opening 120 TFT side alignment film 122 Opposite side alignment film 123 opposing substrate 130 gate insulating film 141 opposing light shielding film 142 color layer 143 opposing polarizing plate 144 flattening film 145 TFT side polarizing plate 202 opposing substrate 203 TFT side substrate 301 liquid crystal display panel 502 scanning signal line 504 opposing polarizing Board

Claims (7)

[Claims] 1. A pixel having a pixel electrode and a common electrode in which comb teeth are alternately arranged in a vertical direction in a planar shape viewed from above, and a pixel in which comb teeth are alternately arranged in a horizontal direction. A pixel having an electrode and a common electrode.
An active matrix liquid crystal display device, characterized in that kinds of pixels are alternately arranged in adjacent pixel units or in red, green, and blue units. 2. A display pixel is formed on a glass substrate by a scanning signal line and a common electrode provided in the same layer, a video signal line and a pixel electrode provided in the same layer via an insulating film, and a thin film transistor element. And a liquid crystal layer is sandwiched between the two substrates, and a liquid crystal layer is sandwiched between the two substrates, and each of the electrodes and the thin film transistor element are arranged with respect to the liquid crystal layer. The electrodes and the thin film transistor element are connected to external control means capable of arbitrarily controlling an applied electric field in accordance with a display pattern; and Polarizing means for changing the optical characteristics according to the alignment state of the, the display pixels are arranged so that the parallel electric field direction can apply an electric field in a different direction for each pixel, Active matrix liquid crystal display device according to symptoms. 3. The active matrix type liquid crystal display device according to claim 2, wherein said pixels are arranged so that an electric field can be applied in different directions for each adjacent pixel. 4. The active matrix type liquid crystal display device according to claim 2, wherein the direction of the parallel horizontal electric field can be applied in different directions in units of three pixels of red, green and blue. 5. A display pixel in which a scanning signal line and a common electrode are provided on a glass substrate on a side on which a thin film transistor element is formed, and an image is provided on the glass substrate on the same layer via an insulating film. It comprises a signal line and a pixel electrode, further comprises a protective insulating film thereon, and an alignment film, and on the glass substrate side disposed to face the glass substrate, a color layer, and an alignment film,
A liquid crystal layer sandwiched between the two substrates; the electrodes and the thin film transistor element being configured to apply an electric field substantially parallel to the substrate surface to the liquid crystal layer; The thin film transistor element is connected to external control means that can arbitrarily control an applied electric field in accordance with a display pattern, and includes a polarizing means that changes optical characteristics according to an alignment state of the liquid crystal layer. An active matrix liquid crystal display device, wherein the display pixels are arranged so that electric fields can be applied in different directions. 6. A pixel having a pixel electrode and a common electrode in which comb-shaped electrode patterns are alternately arranged in a vertical direction in a planar shape viewed from above, and a comb-shaped electrode pattern is alternately arranged in a horizontal direction. And a pixel having a common electrode and a pixel electrode arranged side by side, wherein two types of pixels are alternately arranged in adjacent pixel units or in red, green, and blue units. Item 6. An active matrix type liquid crystal display device according to item 5. 7. The active matrix liquid crystal display device according to claim 6, wherein said pixel electrode and said common electrode are formed in different layers on said substrate.