JP3448384B2 - 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 device in which an electric field in a cell is controlled to control the alignment of liquid crystals, and more particularly, a liquid crystal having a contrast ratio improved by shielding a defective alignment portion caused by the alignment control. The present invention solves the problems associated with display devices.

[0002]

2. Description of the Related Art Liquid crystal display devices have advantages such as small size, thin shape, and low power consumption, and are being put to practical use in fields such as OA equipment and AV equipment. In particular, a matrix type in which transparent electrodes for driving liquid crystal are crossed and voltage is applied while selecting display points in a matrix, and further, a display electrode for partitioning each pixel capacitance for driving liquid crystal is opposed to a common electrode. The active matrix type, in which a plurality of pixels are formed, and a switch element is connected to each display electrode to select a rewriting pixel in a line-sequential manner and always hold a signal voltage statically, has a high definition and a high contrast ratio. It has become possible to display moving images of, and has been put to practical use in personal computer displays, televisions, etc.

The transparent electrodes constituting the pixel capacitance are formed on a pair of electrode substrates, and these electrode substrates are bonded together with a narrow gap, and liquid crystal is sealed inside. The transparent electrodes form pixel capacitances at the portions facing each other with the liquid crystal interposed therebetween, and a desired voltage is applied to each pixel capacitance. The liquid crystal has anisotropy in dielectric constant and refractive index, and its alignment state changes according to an electric field formed in each pixel capacitance to modulate transmitted light. Since the transmittance is finely adjusted depending on the electric field strength, a desired display screen is created by controlling the applied voltage for each pixel capacitance.

FIG. 3 is a plan view of a pixel structure of a conventional liquid crystal display device, which the applicant of the present invention has already disclosed in Japanese Patent Application No. 5-84696.
Japanese Patent Application No. 5-153671, Japanese Patent Application No. 5-157120, Japanese Patent Application No. 5-169087, Japanese Patent Application No. 5-169088, Japanese Patent Application No. 5-216441, Japanese Patent Application No. 5-295731, Japanese Patent Application No. 6-21152, Japanese Patent Application No. Japanese Patent Application No. 6-92283, Japanese Patent Application No. 6-2
No. 07589, Japanese Patent Application No. 6-237482, the orientation control window and the orientation control electrode which have already been applied are used.
FIG. 4 is a sectional view corresponding to line BB in FIG. On a transparent substrate (100) such as glass, Cr, Mo, Ti
The alignment control electrode (101) made of, for example, is formed, and the display electrode (10) made of ITO is formed with the insulating layer (102) interposed therebetween.
There is a region in which the thin film transistor and its wiring (104) are formed between 3) and the display electrode (103). At positions facing each other with the liquid crystal layer (120) sandwiched between them, a light shielding film (111) made of an opaque metal such as Cr, Mo, or Ti, and a color filter layer such as R, G, or B on a substrate (110) such as glass. (112) and a common electrode (11) made of ITO
3) is formed to serve as a counter substrate. Common electrode (1
13) is formed over the entire surface and is divided by a portion facing the display electrode (103) to form a pixel capacitance. In this region, the alignment control window (11) formed by the absence of the electrode is formed.
4) is provided. The light-shielding film (111) serves as a black matrix outside the pixel capacitance region and is provided in the region corresponding to the alignment control window (114) to block unmodulated light and improve the contrast ratio. Further, although not shown, the outermost surface of both substrates (100, 110)
An alignment film made of a polymer film such as polyimide is formed,
A rubbing process is performed in a predetermined direction to control the initial alignment of the liquid crystal. Normally, in the TN (twisted nematic) mode, the rubbing direction is 90 between both substrates (100, 110).
They intersect at °. The orientation control window (114) is formed in a strip shape along the diagonal line of the pixel, and in particular, the substrate (1
It is formed along the diagonal line that intersects the rubbing direction on the side 10).

The action and effect of the orientation control window (114) will be briefly described below. For details, refer to the earlier application for the explanation. When a voltage is applied, the electric field (122) in the liquid crystal layer (120) is tilted obliquely at the portion corresponding to the edge of the display electrode (103), and accordingly, the liquid crystal director (121) changes to a stable alignment state with the minimum energy. To do. That is, the tilt direction of the liquid crystal director (121) is determined. This locally controlled orientation is
Due to the continuity of the liquid crystal, it spreads in the pixel capacitance region, but since the tilt direction of the liquid crystal director (121) is different on each side of the display electrode (103), in the pixel capacitance region they are aligned with each other. Boundaries of different areas arise. The liquid crystal has liquidity, and the liquid crystal director (12
Since the plane direction component of 1) changes relatively freely, the boundary region is also easy to move and may occur at different positions for each pixel. Such a boundary area is an area in which the transmittance cannot be controlled, and in the NW white mode, white is always displayed, which affects visual recognition. Further, if the boundary region is in an unstable state for each pixel, it is recognized as a rough feeling on the screen, which deteriorates the display quality.

The orientation control window (114) is provided to solve such a problem. That is, in the vicinity of the alignment control window (114) which is the electrode absent portion, the electric field (1
22) is absent or weak, and a layer is formed which is at least equal to or less than the threshold value for driving the liquid crystal, and the liquid crystal director (121) is fixed in the initial alignment state in this layer. Therefore, the boundary of each alignment state controlled from the edge of the display electrode (103) is the alignment control window (11
4), the alignment is stable over the entire area of the pixel capacitance and for all pixels due to the continuity of the liquid crystal, so that the roughness of the screen is prevented and the display quality is improved. The orientation control electrode (101) is the display electrode (10).
3) is provided so as to surround a peripheral portion of the display electrode (103) and a predetermined voltage can be applied. Due to a potential difference between the display electrode (103) and the display electrode (103), an oblique electric field (12
2) is positively generated, and in addition to the action of the alignment control window (114), the alignment state of the liquid crystal in the pixel capacitance is divided as predetermined to set the preferential viewing angle directions to a plurality of directions.
It widens the viewing angle. Further, by providing a light shielding film (111) at a portion corresponding to the alignment control window (111) to block light transmitted through the alignment control window (114), the contrast ratio is increased and the display quality is further improved.

[0007]

In the conventional structure, as shown in FIG.
Also, as shown in FIG. 4, the common electrode (113) is formed over the entire surface, and the light-shielding film (111) is conductive and is integrally formed outside the pixel capacitance region and in the alignment control window (114) region. Has been done. Therefore, outside the pixel capacity area,
A capacitance is formed between the light-shielding film (111) and the common electrode (113), and the light-shielding film (111) in the floating state is brought close to the potential of the common electrode (113) by the electric field effect.

The width of the strip area of the orientation control window (114) is
The distance between the light shielding film (111) and the common electrode (113) is about 1 μm, the pixel size is 100 to 200 μm, and the thickness of the liquid crystal layer (120) is about 5 to 10 μm. It is about 10 μm. Therefore, in practice, the light-shielding film (111) has the orientation control window (114).
In a portion corresponding to the alignment control window (114) by the light-shielding film (111) in a pseudo manner to the common electrode (11).
The same effect as 3) occurs, and the display electrode (103) at the facing position
An electric field is generated by the potential difference generated between and, and the liquid crystal is driven. Therefore, the effect of the alignment control window (114) of fixing the liquid crystal director (121) to the initial state and stabilizing the alignment due to the absence of the electrode is lost, and the problem such as the roughness of the screen occurs again.

[0009]

The present invention has been made in order to solve this problem. First, a display electrode supported on one substrate and a common electrode supported on the other substrate are provided. In the liquid crystal display device, the liquid crystal display device is arranged so as to face each other with a liquid crystal layer interposed therebetween, and an alignment control window is formed in the common electrode in a region facing the display electrode by the absence of electrodes. Is a structure in which a light shielding film electrically insulated from the display electrode is formed in a region corresponding to the alignment control window.

Secondly, an alignment control electrode having a voltage different from that of the display electrode is provided around the display electrode, and the light shielding film is made of the same material film as the alignment control electrode.

[0011]

In the first structure of the present invention, the orientation control window is used to
In a liquid crystal display device in which the orientation of liquid crystal is locally controlled to adjust the overall orientation, a light-shielding film electrically insulated from the display electrode is provided in a portion corresponding to the orientation control window on the substrate side where the display electrode is formed. Thereby, the light that is not modulated by the orientation control window is blocked, and the contrast ratio is improved. At this time,
Since the light-shielding film is not brought close to the common electrode, no capacitance is formed in the overlapping portion with the common electrode. As a result, the electric field of the common electrode is not generated in the region of the alignment control window and acts as a pseudo common electrode to drive the liquid crystal, and the effect of forming the alignment control window is lost due to the absence of the electrode. Is prevented.

Further, the overlapping portion of the display electrode and the light-shielding film is also used as an auxiliary capacitance for holding charges, and by overlapping the loss portion of the effective display area due to the auxiliary capacitance and the non-display area by the alignment control window, The reduction of the display area is suppressed to be small, and the aperture ratio is improved. In the second configuration of the present invention, the light-shielding film is formed of the same material film as the orientation control electrode, so that the number of manufacturing steps is reduced.

[0013]

EXAMPLES Next, examples of the present invention will be described in detail.
FIG. 1 is a plan view of a liquid crystal display device according to an embodiment of the present invention, and FIG. 2 is a sectional view taken along the line AA. An alignment control electrode (11) made of a light-shielding conductive material such as Cr and a first light-shielding film (11a) are formed on a transparent substrate (10) such as glass, and an insulation covering the entire surface is provided. On the layer (12), a display electrode (1
Between 3) and the display electrode (13), there is a region in which the thin film transistor and its wiring (14) are formed.

A second light-shielding film (21) made of a light-shielding metal such as Cr is formed on a substrate (20), which is opposed to the liquid crystal layer (30) as a counter substrate, and is displayed as a black matrix. It covers the area around the electrodes (13). On the second light-shielding film (21), R,
A color filter layer (22) for G, B, etc. is formed. The color filter is a dispersion method in which a photosensitive or non-photosensitive color resin in which a dye or a pigment is dispersed and colored is exposed, developed or subjected to patterning by photolithography, a patterning of a photosensitive dyed layer,
It is formed by a well-known method such as a dyeing method in which dyeing is repeated, or a printing method in which colored ink is transferred by letterpress or the like.

Further, after forming an overcoat layer if necessary, a common electrode (23) of ITO and an alignment control window (24) which is an electrode absent portion in the common electrode (23) are formed. The common electrode (23) and the orientation control window (2
In 4), the presence or absence of a predetermined electrode is formed by, for example, ITO sputtering and photoetching. In the TN method, the pattern of the alignment control window (24) is formed in a strip shape along the diagonal line of the pixel and along the diagonal line crossing the initial alignment direction.

Although not shown, both substrates (10, 2)
An alignment film made of polyimide or the like is formed on the contact interface with the liquid crystal layer (30) of (0), and the initial alignment is controlled by rubbing. The orientation control electrode (11) is a display electrode (13).
The pixel electrodes are arranged so as to surround the periphery of the display electrode (13) while being partially overlapped with each other, are connected between pixels, and the common electrode signal is applied from the end portion of the substrate. First light shielding film (11a)
Are arranged in the region corresponding to the orientation control window (24). The alignment control electrode (11) and the first light-shielding film (11a) are made of light-shielding metal and are formed by one photoetching.

As described above, according to the present invention, the light shielding film (11a) is formed on the substrate on which the thin film transistor is formed,
More generally, it is formed on the substrate opposite to the substrate on which the orientation control window (24) is formed. Usually, the alignment control window is formed in the common electrode, that is, in the larger one of the electrodes forming the pixel capacitance, in order to match the action of the oblique electric field generated at the edge portion of the pixel capacitance. For this reason,
When the light-shielding film is formed on the substrate on which the common electrode is formed, the voltage of the light-shielding film is brought close to the common electrode by the electric field effect of the common electrode in the overlapping portion of the light-shielding film and the common electrode outside the pixel capacitance region, and the alignment is performed. In the part corresponding to the control window, the light-shielding film drives the liquid crystal instead of the common electrode, and the effect of fixing the liquid crystal to the initial state by the alignment control window and stabilizing the overall alignment within the pixel capacitance is lost. Will end up. In the present invention, in order to solve this, the light shielding film (11
By forming a) on the side of the substrate on which the display electrodes (13) are formed, a non-electric field region is secured by the alignment control window (24), and the alignment of the liquid crystal is locally fixed to the initial state. The orientation of is stabilized.

Further, in the present invention, the oblique electric field at the pixel capacitance edge is strengthened to control the alignment of the liquid crystal, and in addition to the action of the alignment control window (24), the alignment control for dividing the liquid crystal alignment into pixels is performed. In the structure having the electrode (11), the light-shielding film (11a) is formed in the same step as the alignment control electrode (11), thereby avoiding an increase in the number of steps. Further, the light-shielding film (11a) is formed integrally with the alignment control electrode (11), a common electrode voltage is applied to the light-shielding film (11a), and an auxiliary capacitance for holding charges is formed in the overlapping portion with the display electrode (13). .
Therefore, the loss portion of the effective display area due to the alignment control window (24) is made common with the loss portion of the effective display area due to the auxiliary capacitance, thereby minimizing the reduction of the display area.

[0019]

As is apparent from the above description, in the present invention, in the region corresponding to the alignment control window for adjusting the alignment of the liquid crystal,
By forming a light-shielding film on the side of the substrate opposite to the substrate on which the alignment control window is formed, the light-shielding film is formed in the alignment control window portion by a voltage that is dielectrically induced from the overlapping portion with the electrode on which the alignment control window is formed. It is possible to prevent loss of the effect of the alignment control window of fixing the alignment of the liquid crystal in the initial state and stabilizing the overall alignment by acting as if the electrode exists and not having the electrode.

Further, such a light-shielding film is arranged in the peripheral region of the pixel capacitor to strengthen the oblique electric field in the peripheral portion, and at the same time as the alignment control electrode which functions as the alignment control window to divide the liquid crystal alignment into pixels. By forming, the man-hour is reduced and the cost is reduced. Further, by forming an auxiliary capacitance for holding charges in the overlapping portion of the light shielding film and the electrode on which the light shielding film is formed, the loss of the effective display area due to the alignment control window and the light shielding film is reduced by the effective display area due to the auxiliary capacitance. The loss of the display area is made common, the reduction of the display area is minimized, and the aperture ratio is improved.

[Brief description of drawings]

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

FIG. 2 is a sectional view taken along the line AA of FIG.

FIG. 3 is a plan view of a conventional liquid crystal display device.

FIG. 4 is a sectional view taken along line BB of FIG.

[Explanation of symbols]

10, 20 substrate 11 Orientation control electrode 11a First light-shielding film 12 Insulation layer 13 Display electrode 14 Thin film transistor and its wiring 21 Second light-shielding film 22 Color filter layer 23 Common electrode 24 Orientation control window 30 liquid crystal layer

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Claims (3)

(57) [Claims] 1. A plurality of display electrodes supported by a first substrate and a common electrode supported by a second substrate and facing the plurality of display electrodes are arranged to face each other with a liquid crystal layer interposed therebetween, In a liquid crystal display device provided with an alignment control window formed by the absence of electrodes in a region facing the display electrode in the common electrode, the first substrate in a region corresponding to the alignment control window, A liquid crystal display device, wherein a light shielding film electrically insulated from the display electrode is formed, and the light shielding film is arranged between the display electrode and the first substrate. 2. A first electrode supported on a first substrate,
In a liquid crystal display device in which second electrodes supported by a second substrate are arranged to face each other with a liquid crystal layer in between, and the first electrode is provided with an alignment control window formed by the absence of electrodes. A light-shielding film electrically insulated from an electrode on the second substrate is formed on the second substrate in a region corresponding to the alignment control window, and the light-shielding film is formed on the second electrode. A liquid crystal display device, wherein the liquid crystal display device is arranged between the second substrate and the second substrate. 3. The alignment control electrode having a voltage different from that of the display electrode is provided around the display electrode, and the light shielding film is made of the same material film as the alignment control electrode. 3. The liquid crystal display device according to any one of 2.