JP2859093B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION The present invention relates to an ECB (Electrically
More particularly, the present invention relates to a liquid crystal display device that achieves good viewing angle characteristics and high display quality by controlling the alignment of liquid crystal molecules.

[0002]

2. Description of the Related Art Liquid crystal display devices have advantages such as small size, thinness, and low power consumption, and have been put to practical use in fields such as OA equipment and AV equipment. In particular, an active matrix type liquid crystal display device using a thin film transistor (hereinafter abbreviated as TFT) as a switching element is capable of displaying fine moving images and is used for a display or the like.

[0003] As shown in FIG.
TF in which a predetermined conductor pattern is provided on a transparent substrate
A T-substrate (2) and a counter substrate (4) are attached to each other with a liquid crystal layer (3) having a thickness of several μm sandwiched therebetween, and furthermore, two polarizing plates ( 1)
It is constituted by sandwiching in (5). In particular, by performing vertical alignment treatment on the surfaces of both substrates (2) and (4) and using a liquid crystal having a negative dielectric anisotropy as the liquid crystal layer (3), the initial alignment of the liquid crystal molecules with respect to the substrates. The one set vertically is DAP (Deformation of Vertically
Aligned Phases) type.

For example, white light incident from the TFT substrate (2) is changed to linearly polarized light by the first polarizing plate (1). When no voltage is applied, the incident linearly polarized light does not undergo birefringence in the liquid crystal layer (3), so that the second polarizing plate (5)
And the display becomes black (normally black mode). Then, by applying a predetermined voltage to the liquid crystal layer (3) to tilt the liquid crystal molecules, the incident linearly polarized light undergoes birefringence to become elliptically polarized light, and the light passes through the second polarizing plate (5). Become like

Since the intensity of the transmitted light depends on the applied voltage, gradation can be displayed by adjusting the applied voltage.
Therefore, a desired color display can be obtained by further providing a color filter inside the liquid crystal panel or at a predetermined position outside the liquid crystal panel. Next, a conventional example will be described with reference to FIGS. FIG. 9 is a top view, and FIG. 10 is a cross-sectional view taken along line CC ′ of FIG. However,
Illustration of the polarizing plates (1) and (5) is omitted. First, a gate electrode (11) and a gate electrode (11) are formed on a glass substrate (10).
Gate line (12) and auxiliary capacitance electrode (13) integrated with
And an auxiliary capacitance line (1) integrated with the auxiliary capacitance electrode (13).
4) is formed of, for example, Cr. Then, a gate insulating film (15) such as SiN _x is formed on the entire surface so as to cover them.
Is provided.

On the gate insulating film (15) corresponding to the gate electrode (11), an a-Si layer (16) of the TFT,
An N ⁺ a-Si layer (18) is provided on both ends of the a-Si layer (16).
d) (18s), a semiconductor protective film (17) is provided between the a-Si layer (16) and the N ⁺ a-Si layer (18d) (18s). Also, the gate insulating film (15) in the display area
A display electrode (19) of ITO is formed on the upper side.
Further, a drain line (21) intersecting with the gate line (12) and the N line are formed integrally with the drain line (21).
a drain electrode (20) coated on the ⁺ a-Si layer (18d), and a source electrode (22) connected to the display electrode (19) and coated on the N ⁺ a-Si layer (18s).
Is formed, for example, in a two-layer structure of Al / Mo. Then, a substrate protective film (23) such as SiN _X and a first vertical alignment film (24) are formed on the entire surface, and a TFT is formed.
A substrate (2) is configured.

On the other hand, on the opposite glass substrate (25), T
A light-shielding film (26) of Cr or the like is formed in a region corresponding to the non-display region of the FT substrate (2), and covers the light-shielding film (26). Is provided. Further, a second vertical alignment film (28) is formed on the entire surface, and becomes a counter substrate (4). Further, a polyimide film is used as the alignment films (24) and (28), and a rubbing process is performed on the polyimide film to form a structure having a pretilt angle of 10 degrees or less with respect to the direction in which the major axis of the liquid crystal molecules is perpendicular to the substrate. Become. In this structure, by applying a predetermined voltage, the liquid crystal molecules are inclined in the direction along the rubbing direction according to the surfaces of the alignment films (24) and (28).

[0008]

Next, problems of the conventional liquid crystal display device will be described with reference to FIG. Part of the light incident from the glass substrate (10) is blocked by the auxiliary capacitance electrode (13) and the light shielding film (26) on the counter glass substrate (25), and turns black as a light shielding region (103). The remaining portion is controlled in transmittance by the opening (102), and a desired display is performed. However, the opening (1
02) also in the disclination (101a)
There is a problem that a black area called (101b) occurs. Disclination is a region in which, when a plurality of regions having different alignment vectors of liquid crystal are present in a cell, the alignment direction of liquid crystal molecules is disturbed on the boundary line, and has a transmittance different from other regions. . As shown in FIG. 11, disclinations (101a) (10
If 1b) occurs frequently, there are problems that the screen becomes rough and an expected color display cannot be obtained.

As a cause of the non-uniform orientation vector,
It is conceivable that the alignment process is incomplete at this portion due to a step formed by the wiring and the TFT on the substrate (10), and abnormalities in the tilt direction exist over a certain region due to the continuity of the liquid crystal. It may also be caused by an electric field in the cell. When the drain line (21) and the display electrode (19) have the same polarity, the lines of electric force in the cell are as shown in FIG. In the case where the dielectric anisotropy is negative, the liquid crystal molecules have their molecular long axes inclined in a direction perpendicular to the lines of electric force as the applied voltage increases. Therefore, when a predetermined voltage is applied, the liquid crystal molecules are inclined rightward on the display electrode (19) in FIG. 12 and leftward on the drain line (21) on the display electrode (19). Similarly, the drain line (21)
When the display electrodes (19) have different polarities, the lines of electric force are as shown in FIG. The tilt direction of the liquid crystal molecules caused by the electric field between the drain line (21) and the display electrode (19) is as follows:
The opposite is true in the left and right regions of the display electrode (19) in FIG. Therefore, in the display area, a boundary line of an area having a different orientation vector appears, and the declination (101) is performed.
a).

[0010] The same can be caused by an electric field generated between the gate line (12) and the display electrode (19). Also in this case, the lines of electric force are changed as shown in FIG.
13, and the liquid crystal molecules are inclined toward the center of the display electrode (19) accordingly.
Therefore, the boundary between the upper and lower regions of the display electrode (19) in FIG. 9 becomes the disclination (101a).

Further, as described above, the boundary line between the regions having different orientation vectors exists in the region of the wiring or the TFT, but this portion on the substrate is a region where the orientation is easily disturbed by the step. . Therefore, the alignment abnormality of the liquid crystal molecules extends to the display region, and as shown in FIG.
b) results. In particular, due to the large negative potential of the gate line (12), declination (101b) is likely to occur in a portion along the gate line (12).

In the structure having a pretilt angle, the tilt direction of the liquid crystal molecules is tilted in the same direction according to the rubbed polyimide alignment films (24) and (28). Therefore, the occurrence of disclination (101a) at the pixel central portion is suppressed, but the disclination (101b) caused by the step of the substrate cannot be prevented. Furthermore, due to static electricity generated during rubbing, T
The characteristics of the FT may change and electrostatic breakdown may occur. Further, since the inclination directions of the liquid crystal molecules are uniformly equal, there is a problem that the viewing angle dependence of the contrast ratio is large.

[0013]

SUMMARY OF THE INVENTION The present invention has been made in view of the above-mentioned problems, and has a display electrode arranged in a matrix on a transparent insulating substrate; a thin film transistor for supplying a signal to the display electrode; A thin film transistor substrate having at least a display electrode and an auxiliary capacitance electrode forming an auxiliary capacitance, and a counter substrate having at least a counter display electrode, which is a liquid crystal display device in which a liquid crystal layer is sandwiched therebetween.
The auxiliary capacitance electrode has a different potential from the display electrode,
The display electrode is provided so as to overlap with the insulating substrate side and partly protrudes along two opposing sides of the display electrode, and the liquid crystal layer side along another two sides of the display electrode. A structure in which an orientation control electrode having a potential different from that of the display electrode is provided. In the structure, the opposite display electrode has an orientation in which a predetermined portion is removed in a region corresponding to the display electrode. The object is achieved by a structure provided with a control window or the above structure, wherein the alignment control electrode has the same potential as the auxiliary capacitance electrode.

[0014]

When a voltage having a polarity different from that of the display electrode (19) is applied to the alignment control electrode (6), the lines of electric force take on the shape as shown in FIG. Both sides of the electrode (19) are equally inclined toward the center. Similarly, electric lines of force as shown in FIG. 6 are generated between the auxiliary capacitance electrode (13) and the display electrode (19), and the liquid crystal molecules are tilted accordingly.
As a result, the orientation direction of the liquid crystal molecules is controlled for the four sides of the display electrode (19), and the occurrence of disclination (101b) as shown in FIG. Can be prevented.

Further, since the alignment control window (7) provided in the counter display electrode (27 ') is a portion from which ITO is removed, the alignment control window (7) is not provided in the liquid crystal layer (3) corresponding to the alignment control window (7). ,
There are no lines of electric force. Therefore, the liquid crystal molecules in this region do not tilt, and maintain the vertical alignment state when no voltage is applied. For this reason, due to the continuity of the liquid crystal, the disclination which has occurred irregularly in the past is fixed for all the pixels according to the position of the alignment control window (7). In particular, when the orientation control window (7) is formed in an X-shaped pattern as shown in FIG. 7, the disclination coincides with the orientation control window (7). When the functions of the alignment control electrode (6) and the auxiliary capacitance electrode (13) are added to this, the inclination directions of the liquid crystal molecules in one pixel become equal in four directions. Therefore, the viewing angle dependency of the transmittance is reduced, and good viewing angle characteristics are obtained.

[0016]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS A first embodiment of the present invention will be described below.
FIG. 1 is a top view, and FIG. 3 is a sectional view taken along line AA ′ in FIG. 9 and FIG. 1 of a conventional example.
The same sign as 0 is used. A gate electrode (11), a gate line (12), an auxiliary capacitance electrode (13) and a gate electrode (11) are formed by laminating, for example, Cr on a glass substrate (10) to a thickness of about 1500 ° by sputtering and performing predetermined patterning. An auxiliary capacitance line (14) is formed.
As shown in FIGS. 1 and 3, the auxiliary capacitance electrode (13) has an H-shape so that a part thereof protrudes along two sides of the display electrode (19) which will be formed later in the row direction. The storage capacitor lines (14) are formed and connected to each other for pixels in the same row by a storage capacitor line (14). Although not shown, the storage capacitor lines (14) are connected to each other at a terminal portion.

Next, SiN is used as the gate insulating film (15).
x is set in the range of 2000 to 4000 °, and then a-Si is set in the
A film of SiNx having a thickness of 2500 ° is continuously formed by CVD. Then, the semiconductor protective film (17) is formed by patterning the uppermost layer of SiNx and leaving it in a region corresponding to the gate electrode (11). Subsequently, a-Si doped with phosphorus (hereinafter abbreviated as N ⁺ a-Si) is formed to a thickness of 500 ° by CVD, and N ⁺
a-Si and a-Si are etched with the same mask pattern to remove portions other than the TFT portion, so that a-S
i layer (16) and N ⁺ a-Si layer (18d) (18s)
Is formed. Then, ITO was sputtered for about 1
The display electrode (19) is formed by stacking the layers to a thickness of 000 mm and leaving them in the display area by patterning. Next, as a wiring material, for example, a two-layer film of Al / Mo is laminated by sputtering to a thickness of about 7000/1000 °, and a drain electrode (18d) is coated on the N ⁺ a-Si layer (18d) by predetermined patterning. 20), a drain line (21) integral with the drain electrode (20), N ⁺
A source electrode (22) which covers the a-Si layer (18s) and is connected to the display electrode (19) is formed. And
Using the drain electrode (20) and the source electrode (22) as a mask, the center of the N ⁺ a-Si (18) layer is removed by etching. Further, the substrate protective film (2
4) is provided.

Subsequently, a conductive substance such as Cr, Al, Ta, ITO or the like is formed as a material for the orientation control electrode (6) to a thickness of about 1000 to 8000 ° by sputtering or the like. Then, patterning is performed, and the display electrode (1) is separated from the two sides on which the auxiliary capacitance electrode (13) is provided.
By leaving a line outside the two sides of 9), an alignment control electrode (6) is formed in parallel with the gate line (12) as shown in FIGS. Although illustration is omitted,
The orientation control electrodes (6) are connected to each other at a terminal portion.
It is connected to the auxiliary capacitance line (14).

Then, a first vertical alignment film (24) is formed on the entire surface.
Are provided to form a TFT substrate (2). On the other hand, a light-shielding film (26) is provided by stacking, for example, Cr on the opposing glass substrate (25) by sputtering, and etching away a region to be an opening (102). An opposing display electrode (27 ′) of ITO is formed on the entire surface by sputtering, covering the light shielding film (26). The opposite display electrode (27 ') has a TFT
It is connected to the orientation control electrode (6) and the auxiliary capacitance electrode (13) on the substrate (2) side. Further, a counter display electrode (27 ')
By etching away the portion corresponding to the diagonal line of the display electrode (19) on the TFT substrate (2) side, the X-shaped alignment control window (7) is cut out in the counter display electrode (27 '). Provided. Then, a second vertical alignment film (28) is provided on the entire surface to form a counter substrate (4). No rubbing treatment is performed on any of the alignment films (24) and (28).

The two substrates (2) and (4) having the structure described above are bonded together with a gap of 5 to 8 μm as shown in FIG. 8, and the gap has a negative dielectric anisotropy. A liquid crystal layer (3) of nematic liquid crystal is provided.
Further, these are sandwiched between two polarizing plates (1) and (5) having polarizing axes in directions orthogonal to each other, thereby forming a liquid crystal display device according to the first embodiment of the present invention.

Next, a second embodiment of the present invention will be described. The points overlapping with the first embodiment are omitted,
Only the differences will be described. FIG. 2 is a top view, FIG.
FIG. 3 is a sectional view taken along line AA ′ of FIG. 2 and is the same as in the first embodiment. FIG. 4 is a cross-sectional view along the line BB 'in FIG. In this embodiment, as shown in FIG. 2, the orientation control electrode (6) on the substrate protective film (24) is provided on the opposite side of the display electrode (19) on the side where the auxiliary capacitance electrode (13) does not overlap. It is formed independently for each pixel along the side. Then, as shown in FIG. 4, in the overlapping portion with the auxiliary capacitance electrode (13), through the contact hole provided in the gate insulating film (15) and the substrate protection film (24), the auxiliary capacitance electrode (13) is formed. Connected to. In this structure, since the alignment control electrode (6) and the drain line (21) do not intersect, a short circuit due to a film defect is eliminated.

In the first and second embodiments, in particular, by connecting the alignment control electrode (6) to the counter display electrode (27 ') and the auxiliary capacitance electrode (13), the alignment control electrode (6) is connected.
Drive circuit is not required. When the liquid crystal display device having this structure is driven, regardless of the reversal of the polarity, the alignment control electrode (6), the counter display electrode (27 '), and the auxiliary capacitance electrode (1).
3) has the same potential and has the opposite polarity to the display electrode (19). Therefore, the shape becomes constant as shown in FIGS. 5 and 6 only by changing the direction of the line of electric force with the reversal of the polarity.
FIG. 5 is a schematic diagram showing lines of electric force generated between the display electrode (19), the alignment control electrode (6), and the counter display electrode (27 '), and a state in which the liquid crystal molecules are tilted according to the lines. As is clear from the figure, at the end of the display electrode (19), the lines of electric force are moved from the display electrode (19) to the alignment control electrode (6) and the counter display electrode (2) due to the influence of the alignment control electrode (6).
7 '), it extends obliquely upward from inside the display area to outside the display area. Liquid crystal molecules having negative dielectric anisotropy
Although it is inclined at right angles to the lines of electric force, in this part, the angle between the long axis of the molecule and the lines of electric force is close to a right angle at the shortest, especially due to the elasticity caused by the continuity of the liquid crystal. In addition, by tilting toward the center of the display electrode (19), an energetically stable state is obtained. FIG.
FIG. 9 is a schematic diagram showing lines of electric force generated between a display electrode (19), an auxiliary capacitance electrode (13), and a counter display electrode (27 ′), and a state in which liquid crystal molecules are tilted according to the lines of electric force. Also in this case, the display electrode (1) is located at the end of the display electrode (19).
Due to the effect of the auxiliary capacitance electrode (13) provided below 9), in the liquid crystal layer, electric lines of force move upward from the display electrode (19) from the display area to the outside of the display area. It extends diagonally. Therefore, the liquid crystal molecules are inclined toward the center of the display electrode (19) as in FIG.
FIGS. 5 and 6 show that the opposing display electrode (27 ') has
An alignment control window (7), which is a portion where the electrode is cut out, is shown. In the liquid crystal layer corresponding to this portion, there are no lines of electric force, and the liquid crystal molecules change their vertical alignment state when no voltage is applied. I keep it.

As described above, the display electrode (19)
By controlling the alignment of the liquid crystal molecules in the peripheral portion of the pixel and the portion of the alignment control window (7), the liquid crystal molecules in the entire region of all pixels are controlled by the alignment control window (7) due to the continuity of the liquid crystal. In the display area, the display area is inclined perpendicularly to the substrate, and in the display area, as shown in FIG. Therefore, the disclination coincides with the portion of the X-shaped alignment control window (7) for all the pixels, and the liquid crystal molecules are uniformly distributed in each of the four display sections divided by the alignment control window (7). , The conditions when viewed from four directions are equal.

[0024]

As is apparent from the above description, the orientation control electrode (6) makes the tilt direction of the liquid crystal molecules constant with respect to each side of the pixel, and makes the boundaries of the regions having different tilt directions different. By fixing on the alignment control window (7), the appearance of non-uniform disclinations that differ from pixel to pixel is prevented. In particular, when the alignment control window (7) is formed in an X shape, the alignment control window (7) is formed. In the area other than 7), the disclination completely disappeared. Further, since the area of the region in which the tilt direction of the liquid crystal molecules is different per pixel is equal in four directions, the viewing angle dependency of the contrast ratio is reduced and the viewing angle characteristics are improved.

Further, since the rubbing treatment of the alignment films (24) and (28) is not required, the effects of reducing the number of manufacturing steps and preventing electrostatic breakdown can be obtained.

[Brief description of the drawings]

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

FIG. 2 is a top view of a liquid crystal display device according to a second embodiment of the present invention.

FIG. 3 is a cross-sectional view taken along line AA ′ of FIGS. 1 and 2.

FIG. 4 is a sectional view taken along the line B-B 'of FIG.

FIG. 5 is a diagram illustrating the operation and effect of the present invention.

FIG. 6 is a diagram illustrating the operation and effect of the present invention.

FIG. 7 is a diagram illustrating the operation and effect of the present invention.

FIG. 8 is a principle diagram of a DAP type liquid crystal display device.

FIG. 9 is a top view of a conventional liquid crystal display device.

FIG. 10 is a sectional view taken along the line C-C 'of FIG.

FIG. 11 is a diagram illustrating a problem of a conventional liquid crystal display device.

FIG. 12 is a diagram illustrating a problem of a conventional liquid crystal display device.

FIG. 13 is a diagram illustrating a problem of a conventional liquid crystal display device.

[Explanation of symbols]

REFERENCE SIGNS LIST 1 first polarizing plate 2 TFT substrate 3 liquid crystal layer 4 counter substrate 5 second polarizing plate 6 alignment control electrode 7 alignment control window 10 glass substrate 11 gate electrode 12 gate line 13 auxiliary capacitance electrode 14 auxiliary capacitance line 15 gate insulating film Reference Signs List 16 a-Si layer 17 semiconductor protective film 18 N ⁺ a-Si layer 19 display electrode 20 drain electrode 21 drain line 22 source electrode 23 substrate protective film 24 first vertical alignment film 25 facing glass substrate 26 light shielding film 27 facing display electrode 28 Second vertical alignment film

Claims (3)

(57) [Claims] 1. A thin film transistor substrate having display electrodes arranged in a matrix on a transparent insulating substrate, a thin film transistor for supplying a signal to the display electrode, and an auxiliary capacitance electrode forming an auxiliary capacitance with the display electrode. A liquid crystal display device in which a counter substrate having a counter display electrode is bonded with a liquid crystal layer interposed therebetween, wherein the auxiliary capacitance electrode has a different potential from the display electrode;
The display electrode is provided so as to overlap with the insulating substrate side, and partly protrudes along two opposing sides of the display electrode, and the liquid crystal layer side along another two sides of the display electrode. A liquid crystal display device provided with an alignment control electrode having a potential different from that of the display electrode. 2. The liquid crystal according to claim 1, wherein the opposed display electrode is provided with an alignment control window formed by removing a predetermined portion in a region corresponding to the display electrode. Display device. 3. The liquid crystal display device according to claim 1, wherein the alignment control electrode has the same potential as the auxiliary capacitance electrode.