JPH05196963A - Liquid crystal element - Google Patents

Abstract

PURPOSE:To conceal the orientation abnormality and orientation defect of the liquid crystals in the outside edges of picture element electrodes to be the cause for light leakage of the liquid crystal element by providing light shielding parts with high registration accuracy without more than needed narrowing of the apertures of the picture elements. CONSTITUTION:This liquid crystal element is constituted by providing light shieldable accumulative capacity electrodes 102 in the lower parts of the outside edges of the picture element electrodes 108. Since the ends of the light shieldable accumulative capacity electrodes 102 exist under the picture element electrodes, the generation of the electric field in the cross direction affecting the liquid crystal layer is limited to the outer edges of the picture element electrodes and the liquid crystal orientation abnormality is concealed from the apertures of the picture elements by the light shieldable accumulative capacity electrodes 102. Since the light shieldable accumulative capacity electrodes 102 are formed by a picture element electrode forming process, the high registration accuracy with the picture element electrodes 108 is attained and the need for narrowing the apertures by taking the mis-registration at the time of sticking substrates is eliminated.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display element and a light modulation element using liquid crystal.

[0002]

2. Description of the Related Art A liquid crystal element has been actively researched and developed as a display element or a light modulation element, and a direct-view type display device using the liquid crystal element is currently widely used, and also applied to a projection type display device. Has been done.

A liquid crystal element generally has two electrode plates facing each other and a liquid crystal material sandwiched between the electrode plates as basic constituent elements.
In the case of a liquid crystal element having a plurality of pixels, the sizes of both electrodes are often different. Especially TFT (thin film transistor)
In a liquid crystal element having an active element such as, an active element and a pixel electrode connected thereto are provided on one substrate (main substrate), and a common electrode on one surface is provided on the other substrate (counter substrate).

FIG. 15 shows a pixel portion of a general liquid crystal display device using a TN (twisted nematic) liquid crystal and a TFT, and FIG. 16 shows a cross section taken along the line AA 'in FIG. It is a thing. A transparent pixel electrode 1108 and a counter electrode 1110 are formed on a main substrate 1101 and a counter substrate 1109, respectively, and an alignment film 1118 is applied thereon, and a TN liquid crystal material 1119 is sandwiched therebetween. In such an element, since a voltage cannot be applied to the liquid crystal material in the gap (boundary portion 1121) between the pixel electrodes, the transmitted light in this portion cannot be controlled. Further, also on the pixel electrode, an abnormal alignment (disclination or the like) occurs in the liquid crystal layer 1119 in the outer edge portion where the direction of the electric field is not perpendicular to the electrode, and the transmitted light cannot be controlled again. That is, in such an element, even if a sufficient voltage is applied, the boundary portion 11
Since the transmitted light of 21 and its vicinity cannot be controlled sufficiently, the display ratio such as a reduction in the light-dark ratio of the pixel, image burn-in, and an afterimage will occur as it is. Therefore, in a liquid crystal element in which such a problem usually occurs, some kind of light shielding portion is provided at the pixel boundary portion. For example, the opposite-side light shielding unit 111 in FIG.
1. A light-shielding portion is provided so as to largely cover the outer edge portion of the pixel electrode as shown in FIG. 1, and the area is enlarged particularly in a portion where an abnormal alignment is likely to appear, and the boundary portion 1121 where transmitted light cannot be controlled and its vicinity are hidden from the pixel opening portion. (Japanese Patent Laid-Open No. 1-266512). 15 and 16, 1103 is a gate electrode, 1104 is a gate insulating film, 1105 is a semiconductor layer, 1106 is a drain electrode, 1
107 is a source electrode.

Further, as the size and density of the element become higher, securing the aperture ratio becomes a problem, but the factors that limit the aperture ratio are the opening area of the light shielding portion 1111 and the storage capacitance provided below the pixel electrode 1108. The area of the light shielding portion of the electrode 1102.
Of these, the light shielding portion 1111 provided on the counter electrode 1110 needs to have a projecting portion corresponding to the viewing angle with respect to the pixel electrode 1108. In addition, the opening must be narrowed in advance in consideration of the positional deviation with respect to the pixel electrode, but the positional accuracy of the light shielding part on the counter substrate with respect to the pixel part on the main substrate is
It depends on the precision of the alignment in the substrate bonding process, which is difficult to improve the precision as compared with the photolithography used when forming the sapphire, and causes the reduction of the aperture ratio. Therefore, for example, as shown in FIGS. 17 and 18, a method of improving the aperture ratio by providing a conductive light shielding portion 1117 insulated from other electrodes at the pixel boundary portion on the same substrate as the pixel electrode by using photolithography is devised. Has been done (Science Technical Report V
ol. 90 No. 431 P.M. 59-63). In addition,
FIG. 18 shows a cross section taken along the line AA ′ in FIG.

[0006]

As described above, the conventional device cannot sufficiently control the transmitted light in the vicinity of the pixel boundary portion.
If the pixel is left as it is, the brightness of the pixel is deteriorated and a display defect occurs. Therefore, as shown in FIG. 15, a light shielding portion is provided on the counter substrate. If a high aperture ratio is to be achieved in order to improve the light utilization efficiency of the device, a high positioning accuracy is required in the substrate bonding process, which makes manufacturing difficult. Therefore, there is a demand for a means capable of ensuring the aperture ratio without deteriorating the display quality even if the substrate bonding accuracy is not extremely increased.

In the case of a liquid crystal element having an active element, providing an extra conductive layer on the main substrate affects the electrical characteristics of the active element and the electric field applied to the liquid crystal material, and also restricts the manufacturing process and lowers the yield. Therefore, it is not always preferable. In addition, the storage capacitor electrode is a means for improving display performance in a liquid crystal element having an active element, but at the same time, it is a cause for lowering the aperture ratio.

The present invention solves the above-mentioned problems and prevents the leakage of light at the pixel boundary portion and at the same time conceals the liquid crystal misalignment (disclination) generated at the outer edge portion of the pixel electrode. It is an object of the present invention to improve the display performance of a liquid crystal display device by realizing the liquid crystal display device without narrowing it more than necessary or without requiring high alignment accuracy in the substrate bonding process.

[0009]

The present invention provides a liquid crystal element in which a liquid crystal material is sandwiched in a gap between a main substrate having a pixel electrode and active elements and wirings connected to the pixel electrode and a counter substrate having a counter electrode, The light-shielding storage capacitor electrode is arranged below the outer edge portion of the pixel electrode on the main substrate.

[0010]

By adopting the structure of the present invention, it is possible to hide the alignment abnormality generated at the outer edge portion of the pixel electrode of the liquid crystal display element from the pixel opening portion, and at the same time improve the pixel opening ratio. The abnormal alignment of the liquid crystal on the pixel electrode is caused by the lateral electric field generated at the outer edge of the pixel electrode and occurs in the vicinity thereof. 1 is a plan view showing the basic structure of the present invention, and FIG. 2 is a cross-sectional view taken along the line AA ′ in FIG. 1. The light-shielding storage capacitor electrode 102 is formed below the outer edge of the pixel electrode 108. If such an arrangement is provided, a problematic alignment abnormality will occur on the light-shielding storage capacitor electrode 102, and the desired light-shielding effect can be obtained. 1 and 2, the light-shielding storage capacitor electrode 102 is connected to the wiring of the active element (gate electrode 10
3, the drain electrode 106) is provided independently, but other shapes such as a so-called gate storage type in which a part of the adjacent scanning electrodes are used as a light-shielding storage capacitor electrode are also conceivable. The light-shielding storage capacitor electrode 102 is
For that purpose, it is necessary to overlap the pixel electrode 108 through the insulating layer 113 for a certain area, but the area of the overlapping portion is an area where light cannot be shielded regardless of where it is arranged in the pixel electrode. .. When such a light-shielding storage electrode is arranged in the central portion of the pixel, the aperture ratio is lowered, but when it is arranged in a portion where the transmitted light cannot be sufficiently controlled as a pixel, the pixel opening portion can be effectively used. Become.

The pixel electrode 10 of the light-shielding storage capacitor electrode 102
Since the relative position with respect to 8 is determined by the pixel electrode forming process, it is easy to realize high precision during panel manufacturing. Further, since the light-shielding layer is provided below the pixel electrode 108, the function can be sufficiently fulfilled if there is an area capable of concealing the alignment abnormality. For this reason, the area of the light-shielding portion can be suppressed to a necessary minimum, which leads to improvement of the aperture ratio.

In a liquid crystal element having an active element on the main substrate, it may not be desirable or impossible to bring another conductive layer close to the active element, wiring, etc. Providing a section is not appropriate. In such an element, as shown in FIG. 2, the light-shielding storage capacitor electrode 102 is arranged below the pixel electrode 108 on the main substrate, and the opposite-side light-shielding portion 111 is provided so as to overlap with the pixel electrode 108, thereby preventing the abnormal alignment of the outer edge portion of the pixel electrode. It can be hidden from the pixel opening. The opposite-side light-shielding portion 111 can prevent the active element from being exposed to light and can close a gap that cannot be closed by the structure on the main substrate 101. The opening portion at this time does not depend on the opposite side light shielding portion 111 and can be determined by the light shielding storage capacitor electrode 102 on the main substrate. Therefore, it is not necessary to narrow the opening portion of the opposite side light shielding layer as in the conventional method. In addition, it is not necessary to increase the positioning accuracy when the substrates are bonded together.

[0013]

EXAMPLE 1 FIG. 3 is a plan view showing an example of a liquid crystal element to which the present invention is applied, and FIG. 4 is a sectional view taken along the line AA ′ in FIG. .. A glass substrate 201 serving as a main substrate has a light-shielding storage capacitor electrode 202 made of chromium,
Gate electrode 203, drain electrode 206, source electrode 2
07, a gate insulating film 204 made of silicon nitride, a semiconductor layer 205 made of amorphous silicon, and a transparent ITO (I
A pixel electrode 208 made of ndium tin oxide (indium tin oxide) was formed, and a counter electrode 210 made of ITO and a light-shielding portion 211 made of chromium on the opposite side were formed on a glass substrate 209 serving as a counter substrate. Here, the light-shielding storage capacitor electrode 202 has a width of about 6 μm, and has a width of about 6 μm.
The outer edge of No. 8 has an overlap with a width of about 5 μm. The opposite-side light-shielding portion 211 is provided so that its opening end portion is located substantially in the middle between the outer periphery and the inner periphery of the light-shielding storage capacitor electrode 202 when the substrates are combined, and ± 3 μ when the substrates are laminated.
Even if a deviation of m occurs, it does not affect the aperture ratio. A polyimide alignment film 218 is applied to both surfaces of the substrates, baked, and subjected to an alignment treatment such that the alignment directions on the surfaces of the substrates are approximately 90 ° when the substrates are bonded together, and then the substrates are made to have a gap of about 5 μm. Were bonded together, and the TN liquid crystal material 219 was injected and sealed to obtain a liquid crystal surface element.

When a drive voltage is applied to each electrode in such an element and display is performed in a normally white mode, it is easy to obtain a clear image with a pixel ratio of 60 μm and an aperture ratio of 35% or more and a light-dark ratio of 200: 1 or more. Could be realized. For comparison, when a liquid crystal display device having a conventional structure was manufactured and confirmed, the light-dark ratio was 10: 1 or less when the aperture ratio was 35%, and the aperture ratio was 10 to obtain a light-dark ratio of 200: 1.
I had to drop it to below%.

In the embodiments of FIGS. 3 and 4, the light-shielding storage capacitor electrode 202 is arranged so that the outer edge portion of the pixel electrode 208 is evenly and entirely overlapped, but as shown in FIG. Even if the invention is applied, the same function is achieved in the relevant part. Further, as shown in FIG. 6, the location where the alignment abnormality occurs depends on the rubbing direction, and when the rubbing is performed at 45 ° with respect to the side of the pixel, it almost always occurs at the pixel electrode corner 220 on the rubbing start side. The effect can be further enhanced by providing the light-shielding portion 202 having a wider width at that portion.

In the above example, the outer periphery of the pixel electrode is shown inside the outer periphery of the light-shielding storage capacitor electrode, but the invention is not necessarily limited to this, and an overlap is provided on the outer edge of the pixel electrode. For example, the outer circumference of the light-shielding storage capacitor electrode may be located at any position with respect to the outer circumference of the pixel electrode.

In this example, chromium was used as the electrode material for the gate, source, drain, and storage capacitors, but the suitable material is not limited to this, and any light-shielding conductive pair such as aluminum or molybdenum may be used. The material of the pixel electrode and the counter electrode is not limited to ITO as long as it is a light transmissive conductive material.

(Embodiment 2) FIG. 7 is a plan view showing an embodiment of a liquid crystal element to which the present invention is applied, and FIG. 8 is a sectional view taken along the line AA 'in FIG. The glass substrate 501 serving as the main substrate has a gate electrode 5 made of chromium.
03, a drain electrode 506, a source electrode 507, a gate insulating film 504 made of silicon nitride, a semiconductor layer 505 made of amorphous silicon, and a pixel electrode 508 made of ITO.
And ITO is formed on the glass substrate 509 serving as a counter substrate.
A counter electrode 510 made of and a counter-side light shielding portion 511 made of chromium were formed. Here, the gate electrode 50 of the adjacent pixel
Part of 3 has a so-called gate storage structure that acts as a storage capacitor electrode, and this storage capacitor portion overlaps the outer edge portion of the pixel electrode 508 with a width of about 5 μm. The opposite-side light-shielding portion 511 is provided so that the end portion of the opening thereof is located substantially in the middle between the outer end and the inner end of the light-shielding storage capacitor portion when the substrates are combined. After the polyimide alignment film 518 is applied to both substrate surfaces, baked, and subjected to alignment treatment, approximately 5
Substrates were bonded together with a gap of μm, TN liquid crystal material 519 was injected and sealed, and a liquid crystal display element was obtained.

When a driving voltage is applied to each electrode in such an element and display is performed in a normally white mode, it is possible to easily obtain a clear pixel with an aperture ratio of 37% or more and a light / dark ratio of 200: 1 or more in a pixel of 60 μm pitch. Could be realized.

In this example, the light-shielding storage capacitor portion of the gate electrode 503 is arranged so as to overlap a part of the outer edge portion of the pixel electrode 508, but it may be provided so as to overlap over the entire circumference as in the first embodiment. Further, as shown in FIG. 9, it is more preferable to partially change the overlapping width according to the liquid crystal disclination generation position 520. If the outer edge of the pixel electrode is overlapped, the outer edge of the light-shielding storage capacitor portion of the gate electrode has the same function regardless of the position of the outer edge of the pixel electrode.

(Embodiment 3) FIG. 10 is a plan view showing an embodiment of a liquid crystal element to which the present invention is applied, and FIG. 11 is shown in FIG.
FIG. 6 is a cross-sectional view taken along the line AA ′ in FIG. A glass substrate 701 serving as a main substrate has a light-shielding storage capacitor electrode 702, a gate electrode 703, and a drain electrode 7 made of chromium.
06, a source electrode 707, an insulating layer 713 made of silicon oxide, a gate insulating film 704 made of silicon nitride, a semiconductor layer 705 made of amorphous silicon, and a pixel electrode 708 made of ITO are formed.
A counter electrode 710 made of TO and a counter side light shield 711 made of chromium were formed. Here, the light-shielding storage capacitor electrode 70
2 overlaps the outer edge of the pixel electrode 708 with a width of about 5 μm and overlaps with the gate wiring and the drain wiring by about 2 μm. The opposite-side light-shielding portion 711 is provided so as to protrude from the channel portion 715 by approximately 10 μm so as to shield the TFT channel portion 715 from light. Approximately 5μ after polyimide alignment film 718 is applied to both substrate surfaces, baked, and subjected to alignment treatment.
TN liquid crystal material 7
19 was injected and sealed to obtain a liquid crystal display element.

When a drive voltage was applied to each electrode in such an element to display in a normally white mode, it was possible to easily obtain a clear image with an aperture ratio of 36% or more and a light / dark ratio of 200: 1 or more in a pixel of 60 μm pitch. Could be realized.

In this example as well, it is more desirable to partially change the overlapping width according to the position where liquid crystal disclination occurs, as in the first and second embodiments. Further, the light-shielding storage capacitor electrode 702 may be partially or wholly connected under the gate wiring or the drain wiring. 12
As described above, it is possible to adopt a structure in which the light-shielding storage capacitor electrode 702 does not overlap the gate wiring or the drain wiring, and the opposite-side light-shielding portion 711 corresponding to the gap is provided. When the storage capacitance is insufficient only in the area where the light-shielding electrode and the outer edge of the pixel electrode overlap easily in the orientation, the area of the storage capacitance electrode 712 is increased by a transparent electrode material such as ITO as shown in FIG. Can supplement the storage capacity.

In FIG. 14, a light shielding layer 716 made of aluminum is provided in the channel portion 715 of the TFT via an insulating layer 714 of silicon nitride instead of providing the light shielding portion 711 on the opposite side to the liquid crystal element shown in FIG. Is. This device does not require alignment at the time of laminating the substrates, which makes it easier to fabricate the device,
As a result of 12, the abnormal alignment of the liquid crystal was hidden from the pixel opening, and as a result, a clear image with a light / dark ratio of 150: 1 or more was obtained.

Although the above example relates to a TN liquid crystal element using an amorphous silicon TFT, the present invention is not limited to this, and can be applied to liquid crystal elements using active elements in general, It is also applicable to other liquid crystal display modes such as the super homeotropic mode.

[0026]

As described above, according to the present invention, in a liquid crystal element having an active element, light leakage at a pixel boundary portion is prevented, and liquid crystal alignment abnormality (disclination) generated at an outer edge portion of a pixel electrode is prevented. ) Liquid crystal defects) can be concealed with high alignment accuracy without unnecessarily narrowing the pixel opening. As a result, high-quality display can be realized without lowering the light utilization efficiency of the element, which is a great advantage especially when the liquid crystal display element is downsized and the density is increased.

[Brief description of drawings]

FIG. 1 is a plan view showing a basic configuration of a liquid crystal element 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 liquid crystal element that is an embodiment of the present invention.

FIG. 4 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 5 is a plan view showing a modified example of the liquid crystal element of FIG.

6 is a plan view showing a modified example of the liquid crystal element of FIG.

FIG. 7 is a plan view of a liquid crystal element that is an embodiment of the present invention.

8 is a cross-sectional view taken along the line AA ′ of FIG.

9 is a plan view showing a modified example of the liquid crystal element of FIG.

FIG. 10 is a plan view of a liquid crystal element that is an embodiment of the present invention.

11 is a cross-sectional view taken along the line AA ′ of FIG.

12 is a plan view showing a modified example of the liquid crystal element of FIG.

13 is a plan view showing a modified example of the liquid crystal element of FIG.

14 is a plan view showing a modified example of the liquid crystal element of FIG.

FIG. 15 is a plan view of a conventional liquid crystal element.

16 is a cross-sectional view taken along the line AA ′ of FIG.

FIG. 17 is a plan view of a conventional liquid crystal element.

18 is a cross-sectional view taken along the line AA ′ of FIG.

[Explanation of symbols]

101, 201, 501, 701, 1001, 1101
Main glass substrate 102, 202, 302, 702, 1002, 1102
Light-shielding storage capacitor electrodes 103, 203, 503, 603, 703, 1003
1103 gate electrode 204, 504, 704, 1104 gate insulating film 205, 505, 705, 1105 semiconductor layer 106, 206, 506, 706, 1106 drain electrode 207, 507, 707, 1107 source electrode 108, 208, 508, 708, 1008,1108
Pixel electrodes 109, 209, 509, 709, 1009, 1109
Opposing glass substrate 110, 210, 510, 710, 1010, 1110
Opposing electrodes 211, 511, 1111 Opposite-side light-shielding portion 712 Light-transmissive storage capacitor electrode 113, 713, 1013, 1014 Insulating film 715, 1015 Channel 1016 Channel light-shielding portion 1217 Light-shielding layer 118, 218, 518, 718, 1018, 1118
Alignment film 119, 219, 519, 719, 1019, 1119
Liquid crystal layer 220,520 Disclination generation part 1121 Pixel electrode boundary part 122 TFT

Claims (1)

[Claims] 1. A liquid crystal element in which a liquid crystal material is sandwiched in a gap between a main substrate having a pixel electrode, an active element and a wiring connected to the pixel electrode, and a counter substrate having a counter electrode. A liquid crystal element, which is arranged below an outer edge portion of a pixel electrode on a substrate.