JP2002229028A - Liquid crystal display - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a liquid crystal display having high transmittance, without display unevenness and with high quality. SOLUTION: In a multidomain VAN(vertically aligned nematic) mode, the liquid crystal display device is characterized by partly varying height and width of a furrow-shaped structural body (7), which is to become an element for domain division forming, by heightening the height and by locating the varied part in the vicinity of a pixel edge.

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 a high definition liquid crystal display having improved display characteristics.

[0002]

2. Description of the Related Art A liquid crystal display device using a liquid crystal element has features such as light weight, thin shape, and low power consumption, and is therefore applied to various fields such as OA equipment, information terminals, watches, and televisions. In particular, a liquid crystal display device using a TFT (Thin Film Transistor) element is used as a monitor for displaying data including a lot of information, such as a portable television and a computer, because of its good responsiveness.

In recent years, along with an increase in the amount of information, an improvement in the definition and display speed of an image of a liquid crystal display device has been required. In order to improve the definition, a TFT array structure is miniaturized. On the other hand, to improve the display speed, it is required that the response speed of the liquid crystal material be twice to several tens times faster than the current mode.

[0004] As a liquid crystal mode satisfying these requirements,
OCB method using nematic liquid crystal, VAN (Vartical
Aligned Necmatic), HAN (Hybrid Aligned Necmatic)
matic), π-array, interface-stable ferroelectric liquid crystal using smectic liquid crystal, and antiferroelectric liquid crystal.

[0005] Among them, in particular, the VAN type alignment mode can provide a faster response speed than the conventional twisted nematic type (TN) mode, and since it is a vertical alignment mode, the cause of defects such as electrostatic breakdown has conventionally occurred. This is a liquid crystal display mode that has attracted attention in recent years because there is no rubbing alignment treatment step that has been concerned. Further, as a VAN mode, a multi-domain VAN mode for realizing a wide viewing angle has attracted attention because a compensation design for a viewing angle is relatively easy.

[0006]

SUMMARY OF THE INVENTION Multi-domain VA
In the N mode, when an electrode pattern with a slit is selected as a means for forming the domain division, there is a problem that the resistance value of the electrode on the side opposite to the active element tends to increase. Further, when a method of partially providing a dielectric ridge structure or a depression structure above a pixel electrode as a means for forming a domain division is selected, the liquid crystal alignment is not uniform, and display unevenness is caused. And the transmittance becomes low.

Further, in a liquid crystal display device having a structure in which domain division is induced by providing a ridge-like structure or a depression structure above a pixel electrode, there is a problem of liquid crystal alignment in a domain and its uniformity. If a uniform liquid crystal arrangement can be realized, the transmittance of each domain and each pixel is kept constant, and a good display can be obtained.

FIG. 7 is a sectional view showing the structure of a conventional liquid crystal display device. In FIG. 7, on the active element substrate 11,
Pixel electrode 13 having slit 12 of predetermined pattern
Are formed. On the other hand, a color filter 15 is formed on a counter substrate 14 disposed opposite to the active element substrate 11, and a transparent electrode 16 is formed on the color filter 15.
Are formed on the transparent electrode 16, and a ridge-like structure 17 made of an insulator having a predetermined pattern is formed.

An orientation film (not shown) is formed on the opposing surfaces of the active element substrate 11 and the opposing substrate 14, and the active element substrate 11 and the opposing substrate 14 are bonded via a resin spacer 18. A liquid crystal material 19 is injected between them to form a liquid crystal display element.

FIG. 8 is a plan view showing the pattern shape and arrangement of the pixel electrode 13 and the ridge structure 17 of the liquid crystal display device having the structure shown in FIG.

When the ridge structure having the conventional pattern as shown in FIGS. 7 and 8 is used, disclination is performed in the vicinity of the ridge structure arranged linearly for domain division. Occurs, the liquid crystal alignment is not in the desired alignment, and a loss of transmittance occurs. Further, disclination is likely to occur near the same distance from the edge of the pixel on the ridge-shaped structure, but since the location is different for each pixel, display unevenness occurs. Further, since the location where the disclination occurs is not uniquely determined, the response time becomes longer.

Such a disclination is caused by distortion of an electric field formed by a ridge-shaped structure made of an insulator on the left side of the pixel and an ridge-shaped structure made of an insulator on the right side of the pixel. The electric field distortion causes the liquid crystal molecules to twist in the opposite direction, which causes the liquid crystal alignment induced near the left pixel edge and the liquid crystal alignment induced near the right pixel edge to collide at the pixel center. To happen. That is, since a single uniform insulator is formed from one pixel end to the opposite pixel end, liquid crystal arrays having opposite twist directions coexist in one domain.

[0013] The present invention solves these problems.
It is an object of the present invention to provide a high-quality liquid crystal display device having high transmittance and no display unevenness in a multi-domain VAN.

[0014]

Means for Solving the Problems The present inventor effectively solves the above-mentioned problems by changing the height and width of a ridge-like structure which is a forming element for dividing a domain in a multi-domain VAN. I found that I could. The present invention has been made based on such findings.

That is, in the first invention, a liquid crystal layer is sandwiched between a pair of substrates arranged opposite to each other, and a ridge-shaped structure for domain division is formed on one of the pair of substrates. In the liquid crystal display device described above, the ridge-like structure partially has a portion higher than other portions.

Here, the height of the ridge structure means a distance from a base (for example, an electrode) on which the ridge structure is formed to a top of the ridge structure. The first constructed in this way
According to the invention, since the height of the ridge-shaped structure is not made uniform and the height difference is partially provided, the disclination can be fixed, and the fluctuation of the transmittance for each pixel is suppressed.

According to a second aspect of the present invention, a liquid crystal layer is sandwiched between a pair of substrates arranged opposite to each other, and a ridge structure for domain division is formed on one of the pair of substrates. In the liquid crystal display device, there is provided a liquid crystal display device, wherein the ridge-shaped structure has a portion that is partially wider than other portions.

According to the second aspect of the present invention, since the ridge-like structure partially has a wider portion than other portions, the disclination can be fixed. In addition, the variation in transmittance for each pixel is suppressed.

As described above, according to the present invention, by changing the height and width of the ridge-like structure which is a forming element for dividing the domain in the multi-domain VAN, the disclination generated in the domain dividing portion is reduced. Since it can be fixed and small, a high-quality display device with high transmittance and no display unevenness can be obtained.

[0020]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Various embodiments of the present invention will be described below with reference to the drawings.

Embodiment 1 A manufacturing process of a liquid crystal display device having a ridge structure according to a first embodiment of the present invention will be described with reference to FIG. First, a TFT, a signal wiring, and an insulating film are respectively formed on the active element substrate 1, and then a pixel IT having a thickness of 100 nm is formed.
An O film is formed using a sputter deposition apparatus.
O film is patterned using a predetermined mask pattern,
A pixel electrode 3 having a slit portion 2 with a width of 5 μm where a part of the ITO electrode was missing was formed.

On the other hand, after a color filter 5 is formed on a counter substrate 4 which is disposed to face the active element substrate 1,
An ITO film 6 having a thickness of 100 nm was formed as a transparent electrode using a sputter deposition apparatus. Next, an acrylic photosensitive resin material having a thickness of 1.2 μm is formed on the ITO film 6, and the photosensitive resin film is patterned using a predetermined mask pattern to form a ridge-like structure 7 and a liquid crystal. An alignment mark (not shown) used for assembling the element was formed at the same time. After that, an acrylic photosensitive resin film is formed on a part of the ridge-shaped structure 7 so as to be overlapped with the ridge-shaped structure 7. 1.
It was set to 0 μm.

FIG. 2 shows a part of the cross section taken along line AA of FIG.
As shown in FIG. 2, the ridge structure 7 has a portion 7a having a height of 1.2 μm and a portion 7b having a height of 2.2 μm, which is higher by 1.0 μm.

Next, an alignment film material for vertically aligning liquid crystal molecules is formed on the surfaces of the active element substrate 1 and the counter substrate 4 to be opposed to each other so as to have a thickness of 70 nm. For 30 minutes to form alignment films (not shown).

Then, the active element substrate 1 and the opposing substrate 4 were arranged so that the respective alignment films faced each other, and were bonded together via a resin spacer 8, thereby forming an empty cell for a liquid crystal display element. At this time, the alignment mark formed on the opposing substrate 4 at the same time as the ridge-shaped structure 7 and the alignment mark formed in advance on the active element substrate 1 are aligned, and the active element substrate 1 and the opposing substrate 4 are bonded. Matched.

Thereafter, a liquid crystal material 9 having a negative dielectric anisotropy was injected between the active element substrate 1 and the opposing substrate 4 by a usual method to form a liquid crystal display element. Subsequently, a polarizing film (not shown) whose polarization axes are set to be orthogonal to each other is placed on each of the active element substrates 1.
Then, the liquid crystal display device was completed by sticking to the outer surface of the counter substrate 4.

FIG. 3 is a plan view showing an arrangement of pixels of the liquid crystal display device configured as described above. In FIG.
In the regions of the substrates 1 and 4, there are a seal portion 21 and an active area 22, in which a plurality of pixels 23 are arranged.

FIG. 4 is an enlarged plan view showing the pixel portion. In FIG. 4, lines m and n indicate the center lines of the pixel electrodes 3 in the vertical direction, and lines p indicate the center lines of the pixel electrodes 3 in the horizontal direction. That is, two pixels are shown in this figure. Reference numeral 25 denotes a vertical signal line, 26 denotes a horizontal signal line, and 26 denotes an active element.

The ridge structure 7 is arranged as shown in the figure, and the high portion 7b of the ridge structure 7 is provided near the pixel edge as shown in the figure.

In the liquid crystal display device configured as described above, by applying an electric field between the transparent electrode 6 of the counter substrate 4 and the pixel electrode 3 of the active element substrate 1, the liquid crystal molecules are parallel to the substrate surface. Transformed into an array. And the counter substrate 4
Due to the respective effects of the ridge-like structure 7 formed on the transparent electrode 6 and the pixel electrode 3 on the active element substrate 1, a domain in which the tilt direction of the liquid crystal molecules was controlled was formed.

When this liquid crystal display device was driven by a usual method and the light transmittance was measured, the total light transmittance was 6. when the liquid crystal display device had an aperture ratio of 60%.
5%, and no display unevenness was visually recognized.

Example 2 A photosensitive resin film is formed so as to overlap only near the pixel edge, and the height of the ridge structure 7 near the pixel edge is 2.2 μm.
A liquid crystal display device was manufactured in the same manner as in Example 1, except that the height difference from the other portions was 1.0 μm.

When this liquid crystal display device was driven by an ordinary method and the light transmittance was measured, the total light transmittance was 6. when the liquid crystal display device had an aperture ratio of 60%.
8%, and no display unevenness was visually recognized.

Embodiment 3 An acrylic photosensitive resin film is formed on a part of the ridge-shaped structure 7 so that the height of the ridge-shaped structure 7 is 2.4 μm.
m, and a height difference from other portions was 1.2 μm, thereby completing a liquid crystal display device in the same manner as in Example 1.

In the liquid crystal display device configured as described above, by applying an electric field between the transparent electrode 6 of the opposing substrate 4 and the pixel electrode 3 of the active element substrate 1, the liquid crystal molecules are parallel to the substrate surface. Transformed into an array. And the counter substrate 4
Due to the respective effects of the ridge-like structure 7 formed on the transparent electrode 6 and the pixel electrode 3 on the active element substrate 1, a domain in which the tilt direction of the liquid crystal molecules was controlled was formed.

When this liquid crystal display was driven by a normal method and the light transmittance was measured, the total light transmittance of the liquid crystal display having a structure having an aperture ratio of 60% was 6.
9%, and no display unevenness was visually recognized.

Embodiment 4 A photosensitive resin film is formed so as to overlap only near the pixel edge, and the height of the ridge structure 7 near the pixel edge is set to 2.4 μm.
A liquid crystal display device was manufactured in the same manner as in Example 1, except that the height difference from the other portions was 1.2 μm.

When this liquid crystal display device was driven by a usual method and the light transmittance was measured, the total light transmittance of the liquid crystal display device having the aperture ratio of 60% was 7.
2%, and display unevenness was not visually recognized.

Example 5 The ridge-shaped structure 7 was formed by using a predetermined mask pattern and having a constant height and a wide rectangular portion 10 as shown in FIG. A liquid crystal display device was manufactured in the same manner as described above.

When this liquid crystal display device was driven by a usual method and the light transmittance was measured, the total light transmittance was 6. when the liquid crystal display device had an aperture ratio of 60%.
4%, and no display unevenness was visually recognized.

Example 6 The ridge-shaped structure 7 was formed in the same manner as in Example 1 except that the ridge-shaped structure 7 was formed so as to have a constant height and the arrangement shown in FIG. 6 using a predetermined mask pattern. A liquid crystal display device was manufactured.

When this liquid crystal display was driven by a usual method and the light transmittance was measured, the total light transmittance was 6. when the liquid crystal display had a 60% aperture ratio.
5%, and no display unevenness was visually recognized.

Comparative Example 1 The ridge-shaped structure 7 was formed in the same manner as in Example 1 except that the ridge-shaped structure 7 was formed so as to have a constant height and the arrangement shown in FIG. 8 using a predetermined mask pattern. A liquid crystal display device was manufactured.

When this liquid crystal display was driven by a usual method and its light transmittance was measured, the total light transmittance of the liquid crystal display having a structure having an aperture ratio of 60% was 5.
4%, and display unevenness was visually recognized.

As described above, in the liquid crystal display devices according to Examples 1 to 6, the transmittance is improved and a high quality liquid crystal display device can be obtained, whereas the liquid crystal display device according to Comparative Example 1 can be obtained. For the device, a high-quality liquid crystal display device cannot be selected because the transmittance is low and display unevenness is visually recognized.

The height difference between the high part of the ridge structure and the other part is preferably 1 μm or more. Further, it is desirable that the ridge-like structure has a height of 0.5 μm or more even in a portion having a low height.

Also, the partially high portion of the ridge structure is
It is desirable that the liquid crystal layer has a height of at least half the thickness of the liquid crystal layer. As described above, since a part of the ridge-shaped structure has a height equal to or more than half of the thickness of the liquid crystal layer, the disclination can be fixed more reliably, and the transmittance variation for each pixel is suppressed. .

Here, the thickness of the liquid crystal layer means the distance from the electrode layer on the active element substrate side to the electrode layer on the counter substrate side. When the width of the ridge structure is partially widened, the shape of the wide portion can be, for example, a triangle, a semicircle, or a trapezoid when viewed from above. With such a ridge-shaped structure, the disclination can be effectively fixed.

In the above liquid crystal display device, it is preferable that a high portion or a wide portion of the ridge structure is located near the edge of the pixel. In particular, it is preferably located 5 to 10 μm from the pixel edge.

[0050]

As described above in detail, according to the liquid crystal display device of the present invention, in the multi-domain type liquid crystal display device, the ridge shape for domain division can be obtained without largely changing the conventional element form. A high-quality liquid crystal display device can be provided by changing the height or width of a part of the structure or by disposing the changed position of the ridge-shaped structure near a pixel edge.

[Brief description of the drawings]

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

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

FIG. 3 is a plan view showing an arrangement of pixels of the liquid crystal display device.

4 is an enlarged plan view showing a pixel portion of the liquid crystal display device shown in FIG.

FIG. 5 is a plan view showing the arrangement of pixel electrodes and ridge structures of a liquid crystal display device according to a fifth embodiment of the present invention.

FIG. 6 is a plan view showing the arrangement of pixel electrodes and ridge structures of a liquid crystal display device according to a sixth embodiment of the present invention.

FIG. 7 is a cross-sectional view illustrating a structure of a conventional liquid crystal display device.

FIG. 8 is a plan view showing an arrangement of pixel electrodes and a ridge structure of a conventional liquid crystal display device.

[Explanation of symbols]

 Reference numerals 1, 11 Active element substrate 2, 12 Slit part 3, 13 Pixel electrode 4, 14 Counter substrate 5, 15 Color filter 6, 16 Transparent electrode 7, 17 Layer ridge structure 8, 18 Resin spacers 9, 19: liquid crystal material 10: wide portion.

 ──────────────────────────────────────────────────続 き Continuation of the front page (72) Inventor Yasushi Kawada 1-9-9 Hara-cho, Fukaya-shi, Saitama Inside the Toshiba Fukaya Plant Co., Ltd. (72) Inventor Shoichi Kurauchi 1-9-9 Harara-cho, Fukaya-shi, Saitama No. 2 Inside Toshiba Fukaya Factory (72) Inventor Takeshi Yamaguchi 1-9-9 Hara-cho, Fukaya-shi, Saitama Prefecture No. 2 Inside Toshiba Fukaya Factory (72) Inventor Atsuyuki Manabe 1-Chamara-cho, Fukaya-shi, Saitama No. 9 No. 2 F-term in Toshiba Fukaya Plant (reference) 2H090 JA02 LA15 MA12 MA17

Claims (7)

[Claims] 1. A liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of substrates disposed opposite to each other, and a ridge structure for domain division is formed on one of the pair of substrates. The liquid crystal display device, wherein the ridge-like structure partially has a portion higher than other portions. 2. A partly high portion of the ridge structure is 1 μm or more higher than other portions.
3. The liquid crystal display device according to 1. 3. The liquid crystal display device according to claim 1, wherein the partially high portion of the ridge-shaped structure has a height that is at least half the thickness of the liquid crystal layer. 4. The liquid crystal display device according to claim 1, wherein the partially high portion of the ridge structure is located near an edge of a pixel. 5. A liquid crystal display device in which a liquid crystal layer is sandwiched between a pair of substrates arranged opposite to each other, and a ridge structure for domain division is formed on one of said pair of substrates. The liquid crystal display device, wherein the ridge-like structure partially has a portion wider than other portions. 6. The liquid crystal display device according to claim 5, wherein a partially wide portion of the ridge-like structure is located near an edge of a pixel. 7. The ridge-shaped structure is made of an insulator, and is formed on a transparent electrode formed on the other substrate, facing a pixel electrode formed on one of the pair of substrates. The liquid crystal display device according to claim 1, wherein: