JP4709375B2 - Liquid crystal display element - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display element in which a liquid crystal layer is sandwiched as a cell of a liquid crystal composition between a pair of electrode substrates, and more particularly to a liquid crystal display element that secures a cell gap of the liquid crystal composition between these electrode substrates by columnar spacers.
[0002]
[Prior art]
In recent years, liquid crystal display elements (LCDs) have been widely used due to their advantages such as thinness, light weight, low power consumption, and low driving voltage. In particular, active matrix liquid crystal display elements have made remarkable development because they can display high-definition and high-quality images by adding thin film transistors (TFTs) as pixel switch elements. When a liquid crystal display element is used for a portable information device, it is desired to significantly reduce power consumption. In order to cope with this demand, development of a reflection type liquid crystal display element is currently in progress.
[0003]
In general, a reflective liquid crystal display element has a structure in which a liquid crystal layer is sandwiched between a pair of electrode substrates as a cell of a liquid crystal composition. For example, external light reflected by a reflector attached to the back of the liquid crystal display element is liquid crystal. The image is displayed by optical modulation with the layer. For this reason, an internal light source such as a backlight is not required. However, if this liquid crystal display element is a high-definition one using, for example, a thin film transistor, there is a problem that parallax due to the thickness of the substrate occurs when an image is observed from an oblique direction. In order to improve this problem, it is known that it is preferable to form a reflector with a plurality of pixel electrodes arranged on one electrode substrate. Further, the brightness of external light depends on the installation environment of the liquid crystal display element and is not as stable as the backlight. Therefore, it is important to display the bright image by making the area of the pixel electrode that determines the aperture ratio as large as possible and reflecting the external light with high efficiency.
[0004]
Recently, a plurality of columnar spacers are formed, for example, on one electrode substrate in order to ensure a cell gap of the liquid crystal composition between the pair of electrode substrates. When these columnar spacers overlap with a plurality of pixel electrodes arranged in a matrix on this electrode substrate, the liquid crystal alignment tends to be disturbed around each columnar spacer. For this reason, the plurality of pixel electrodes are formed so as not to overlap these columnar spacers. Here, since the pixel array on the electrode substrate is required to have high accuracy, the exposure process for forming the pixel electrode, the thin film transistor, and the like is generally performed while moving the mask pattern with an exposure machine called a stepper. Conventionally, all pixel electrodes have a common shape as shown in FIG. 4 based on a fixed idea that emphasizes ease of mask alignment and uniformity of aperture ratio.
[0005]
[Problems to be solved by the invention]
However, except for the case where a plurality of columnar spacers are formed for each pixel electrode, the common shape of the pixel electrodes shown in FIG.
[0006]
In view of the above-described problems, an object of the present invention is to provide a liquid crystal display element that can display a brighter image as a whole.
[0007]
[Means for Solving the Problems]
According to the present invention, the first and second electrode substrates, the liquid crystal layer sandwiched between the first and second electrode substrates as cells of the liquid crystal composition, and the liquid crystal composition formed on the first electrode substrate. A plurality of pixel electrodes for controlling the liquid crystal alignment, and a plurality of pixel electrodes formed on at least one of the first and second electrode substrates at a rate of one for every two or more pixel electrodes to ensure a cell gap of the liquid crystal composition. and a columnar spacer of the plurality of respective pixel electrodes is red, green, assigned to one of the blue color filter, defining a columnar spacer forming region number is limited in accordance with the number of the columnar spacers A plurality of notches, wherein the notches are provided in pixel electrodes other than the pixel electrode facing the green color filter having the highest transmittance among the red, green, and blue color filters, and the adjacent pixels On the electrode There are liquid crystal display elements arranged so as to face each other is provided.
[0008]
In this liquid crystal display element, the plurality of pixel electrodes include a plurality of notches that define a number of columnar spacer formation regions limited in correspondence with the number of columnar spacers. That is, since it is not necessary for all the pixel electrodes to have a notch, it is possible to prevent a useless decrease in the aperture ratio caused by the notch of the pixel electrode. Therefore, the utilization efficiency of the light source light is improved, and a brighter image as a whole can be displayed.
[0009]
DETAILED DESCRIPTION OF THE INVENTION
Hereinafter, a reflective liquid crystal display device according to an embodiment of the present invention will be described with reference to the accompanying drawings.
[0010]
FIG. 1 shows a cross-sectional structure in the vicinity of a pixel of the reflective liquid crystal display element, and FIG. 2 shows a planar arrangement and shape of pixel electrodes of the reflective liquid crystal display element. The liquid crystal display element includes an array substrate AR, a counter substrate CT, and a liquid crystal layer LQ sandwiched between the substrates AR and CT as cells of a liquid crystal composition such as nematic liquid crystal.
[0011]
The array substrate AR is an insulating substrate 10, a plurality of reflective pixel electrodes 11 arranged in a substantially matrix shape and controlling the liquid crystal arrangement of the liquid crystal composition, a plurality of signal lines 12 arranged along a row of these reflective pixel electrodes 11, A plurality of scanning lines 13 arranged along the row of the reflective pixel electrodes 11, a plurality of pixel thin film transistors (TFTs) 14, 2 arranged as switching elements near the intersections of the corresponding scanning lines 13 and the corresponding signal lines 12, 2 A plurality of columnar spacers SP that are formed at a ratio of one for each of the plurality of pixel electrodes 11 to secure a cell gap of the liquid crystal composition with respect to the counter substrate CT, and an alignment film 15 that covers the plurality of reflective pixel electrodes 11 are included. . The counter substrate CT is formed on the insulating substrate 20 as a blue, red, and green striped color filter arranged in the row direction in opposition to the light-transmissive insulating substrate 20 and the pixel electrodes 77 in the corresponding columns. It has a colored layer 21, a transparent counter electrode 22 that covers the colored layer 21, and an alignment film 23 that covers the counter electrode 22. The polarizing plate PL is attached to the transparent insulating substrate 20 on the side opposite to the colored layer 21. Here, the plurality of pixel electrodes 11 function as a reflecting plate that scatters light incident through the liquid crystal layer LQ from the counter substrate CT side with high reflectance, and are limited in number corresponding to the number of columnar spacers SP. It has a plurality of notches 11A that define the columnar spacer formation region SPR. These notches 11A are formed in a ratio of at most two for each of at least three pixel electrodes 11. At this time, the number of columnar spacer formation regions SPR is preferably equal to the number of columnar spacers SP. In FIG. 2, each columnar spacer formation region SPR is a pixel that is two of the three pixel electrodes 11 (B), 11 (R), and 11 (G) facing the blue, red, and green color filters. It is defined by a pair of notches 11A provided in the electrodes 11 (B) and 11 (R).
[0012]
In this reflective liquid crystal display element, the liquid crystal layer LQ is partitioned into a plurality of pixel regions PX corresponding to the plurality of reflective pixel electrodes 11, and each pixel region PX has two adjacent scanning lines 13 and two adjacent signals. It is arranged between the line 12. Each thin film transistor 14 becomes conductive in response to a scanning pulse supplied from the corresponding scanning line 13 and supplies the potential of the corresponding signal line 12 to the corresponding reflective pixel electrode 11. Each reflective pixel electrode 11 applies the potential of the corresponding signal line 12 as a pixel potential to the corresponding pixel region PX of the liquid crystal layer LQ, and changes the transmittance of the pixel region PX based on the potential difference between this pixel potential and the potential of the counter electrode 22. Control.
[0013]
In the array substrate AR, each TFT 14 includes an amorphous silicon or polysilicon semiconductor layer 16, a gate electrode 17 that is insulated above the semiconductor layer 16 and connected to the corresponding scanning line 13, and on both sides of the gate electrode 17. The semiconductor layer 16 has source and drain electrodes 18 and 19 that are in contact with the corresponding reflective pixel electrode 11 and the corresponding signal line 12 through contact holes 18H and 19H, respectively. The semiconductor layer 16 is formed on the insulating substrate 10 and is covered with the gate insulating film 30 together with the insulating substrate 10. The gate electrode 17 is insulated from the semiconductor layer 16 by the gate insulating film 30 and formed integrally with the corresponding scanning line 13 on the gate insulating film 30. The gate electrode 17 and the scanning line 13 are covered with an interlayer insulating film 31 together with the gate insulating film 30. The contact holes 18H and 19H are formed in the interlayer insulating film 31 and the gate insulating film 30 so as to expose the source and drain formed in the semiconductor layer 16 on both sides of the gate electrode 17. The source and drain electrodes 18 and 19 are formed on the interlayer insulating film 31 in contact with the source and drain of the semiconductor layer 16 in the contact holes 18H and 19H, respectively. The source electrode 19 is formed on the interlayer insulating film 31 so as to extend toward the pixel electrode 11, and the drain electrode 19 is formed integrally with the corresponding signal line 12 on the interlayer insulating film 31. The source electrode 18, the drain electrode 19, and the signal line 12 are covered with a protective insulating film 32 together with the interlayer insulating film 31. The protective insulating film 32 has a contact hole 32H that partially exposes the source electrode 18 and is covered with the organic insulating film 33. The organic insulating film 33 has a contact hole 33 </ b> H that partially exposes the source electrode 18 corresponding to the contact hole 32 </ b> H of the protective insulating film 32. The reflective pixel electrode 11 is formed on the organic insulating film 33 in contact with the source electrode 18 in the contact holes 32H and 33H. Further, the columnar spacer SP is also formed on the organic insulating film 33 at a position so as to overlap the corresponding signal line 12. Here, as shown in FIG. 2, the columnar spacer SP is adjacent to the two pixel electrodes 11 (B, R, G) adjacent to each other in the row direction and facing the blue, red, and green color filters ( B, R) is arranged in a columnar spacer formation region SPR defined by a notch 11A provided in B, R). The pixel electrode 11 and the columnar spacer 34 are covered with the alignment film 15. The plurality of reflective pixel electrodes 11 include a material such as silver, aluminum, or an alloy thereof, and are formed with a predetermined thickness with the undulation of the organic insulating film 33 as a base. Each pixel electrode 11 is composed of a plurality of hemispherical convex portions randomly arranged in the range of the corresponding pixel region PX and concave portions surrounding these convex portions.
[0014]
In the liquid crystal display element of the present embodiment, the plurality of pixel electrodes 11 are set in a shape cut out only in the vicinity of the plurality of columnar spacers SP. That is, a plurality of notches 11A are provided at a ratio of two for every three pixel electrodes 11, and the number of columnar spacer formation regions SPR equal to the number of columnar spacers SP is defined. Here, each columnar spacer formation region SPR is defined by a pair of notches 11A provided in two adjacent pixel electrodes 11. For this reason, the aperture ratio of the pixel region PX depending on the area of the pixel electrode 11 is not reduced unnecessarily, and the utilization efficiency of external light scattered by the pixel electrode 11 can be improved. Therefore, a brighter image as a whole can be displayed. If all the pixel electrodes 11 have the notches 11A as shown in FIG. 4, the aperture ratio of the pixel electrodes 11 is significantly lower than in the present embodiment.
[0015]
Further, in this embodiment, each notch 11A is not provided on the pixel electrode 11 (G) facing the green color filter having the highest transmittance among the blue, red, and green color filters, and blue and red. Are provided on the two pixel electrodes 11 (B) and 11 (R) facing the color filter. Thereby, the reflection efficiency as a whole is improved as compared with the case where the notch 11A is provided in one of the pixel electrodes 11 (B) and 11 (R) and the pixel electrode 11 (G), and the brightness of the display image is further increased. Can improve.
[0016]
In addition, this invention is not limited to the above-mentioned embodiment, It can deform | transform variously in the range which does not deviate from the summary.
[0017]
FIG. 3 shows a modification of the planar arrangement and shape of the pixel electrodes shown in FIG. In this modification, each notch 11A is provided only on the pixel electrode 11 (B) facing the blue color filter having the lowest transmittance among the blue, red, and green color filters, and the red and green colors. It is not provided on the two pixel electrodes 11 (R) and 11 (G) facing the filter. Even in this case, the reflection efficiency as a whole is improved, and the brightness of the display image can be further improved.
[0018]
【The invention's effect】
As described above, according to the present invention, it is possible to provide a liquid crystal display element capable of displaying a brighter image as a whole by preventing useless reduction of the aperture ratio and improving the utilization efficiency of light source light.
[Brief description of the drawings]
FIG. 1 is a diagram showing a cross-sectional structure near a pixel of a reflective liquid crystal display device according to an embodiment of the present invention.
2 is a diagram showing a planar arrangement and shape of pixel electrodes of the reflective liquid crystal display element shown in FIG. 1;
3 is a diagram showing a modification of the planar shape of the pixel electrode shown in FIG. 2. FIG.
FIG. 4 is a diagram showing a planar arrangement and shape of pixel electrodes of a conventional reflective liquid crystal display element.
[Explanation of symbols]
AR ... Array substrate CT ... Counter substrate LQ ... Liquid crystal layer SP ... Columnar spacer SPR ... Columnar spacer formation region PX ... Pixel region 11 ... Pixel electrode 11A ... Notch 21 ... Colored layer (color filter)

Claims (3)

First and second electrode substrates;
A liquid crystal layer sandwiched between the first and second electrode substrates as a liquid crystal composition cell;
A plurality of pixel electrodes formed on the first electrode substrate and controlling a liquid crystal alignment of the liquid crystal composition;
A plurality of columnar spacers formed on at least one of the first and second electrode substrates at a rate of one for every two or more pixel electrodes to ensure a cell gap of the liquid crystal composition;
Each of the plurality of pixel electrodes is assigned to one of red, green, and blue color filters, and includes a plurality of notches that define a number of columnar spacer forming regions limited in number corresponding to the number of columnar spacers, The notch is provided in a pixel electrode other than the pixel electrode facing the green color filter having the highest transmittance among the red, green, and blue color filters, and disposed so as to face each other in the adjacent pixel electrode. Liquid crystal display element.   2. The liquid crystal display element according to claim 1, wherein the plurality of notches are provided at a ratio of at most two for at least three of the pixel electrodes.   The liquid crystal display element according to claim 1, wherein the plurality of pixel electrodes constitute a reflection plate that scatters light incident through the second electrode substrate and the liquid crystal layer.

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