JP3819104B2 - Liquid crystal display - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a liquid crystal display device, and more particularly to an active matrix liquid crystal display device.
[0002]
[Prior art]
In recent years, large-sized, high-definition active matrix liquid crystal display devices have been developed in the field of information equipment centered on computers and the field of video equipment centered on televisions.
[0003]
An example of a FT (thin film transistor) array substrate, which is a first substrate constituting an active matrix liquid crystal display device, is shown in FIG. In the TFT array substrate, a plurality of scanning lines 1 and a plurality of signal lines 2 intersect with each other on an insulating substrate, and each pixel section formed in a matrix by intersecting these lines has a pixel. An electrode 3 is provided, and a TFT 4 is formed for each pixel electrode 3. A storage capacitor electrode (auxiliary capacitor electrode) 5 for forming a storage capacitor added to the pixel extends to the pixel section and is formed integrally with the scanning line 1. The gate electrode 6 of the TFT 4 is formed integrally with the scanning line 1, and the drain electrode 7 is formed extending from the signal line 2. The source electrode 8 is connected to the pixel electrode 3. Further, an insulating protective film (not shown) is formed on these.
[0004]
In the active matrix liquid crystal display device, such a TFT array substrate and a second substrate (counter substrate) having a counter electrode and a color filter are placed opposite to each other while maintaining a certain gap with a gap material (spacer), A liquid crystal layer is sandwiched between substrates, but in recent years, columnar spacers are being used as spacers instead of plastic beads. In other words, in order to eliminate cell gap unevenness due to light leakage and scattering unevenness around the plastic beads, a plurality of columnar bodies are formed by laminating a plurality of colored layers on the counter substrate side, and this columnar body forms a space between the substrates. It has been practiced to keep the gap between these constant.
[0005]
[Problems to be solved by the invention]
However, in such a conventional active matrix type liquid crystal display device, there is a problem that the aperture ratio is lowered due to the installation of the storage capacitor electrode 5 or the wiring for forming the storage capacitor. A display device with a large screen and high definition that is required to eliminate cell gap unevenness due to installation has increased the power consumption due to an increase in the size of the backlight, and a decrease in the aperture ratio has become a serious problem.
[0006]
Furthermore, the fluorescent tube normally used for the backlight of the liquid crystal display device is a three-wavelength tube that emits three colors of blue, green, and red, and the distribution of the phosphors that emit each color is, for example, blue phosphor: green. Phosphor: red phosphor and 5: 2: 3. That is, by increasing the proportion of phosphors having a blue emission color with low visibility characteristics, the white light is balanced, but on the other hand, this causes the power consumption to increase.
[0007]
The present invention has been made to solve these problems. The display has a high aperture ratio, can reduce the power consumption of the backlight, has no cell gap unevenness, is uniform in quality, and has a high contrast ratio. An object of the present invention is to provide a liquid crystal display device capable of obtaining the above.
[0008]
[Means for Solving the Problems]
The liquid crystal display device of the present invention includes a plurality of scanning lines and signal lines formed on an insulating substrate, pixel electrodes formed in matrix-like sections formed by the scanning lines and signal lines, and these A first substrate having a switching element provided for each pixel electrode; a columnar spacer formed by stacking a plurality of colored layers to maintain a gap between the first substrate; and a counter electrode. In the liquid crystal display device comprising: a second substrate disposed opposite to the first substrate; and a liquid crystal layer sandwiched between the first substrate and the second substrate, the columnar spacer The counter electrode is formed to extend in a portion of the first substrate in contact with the first substrate, and the extension portion of the counter electrode is interposed between the pixel electrode of the first substrate and at least one insulating layer. Abutting and forming storage capacity To.
[0009]
In the liquid crystal display device of the present invention, the storage capacitor electrode is formed on the first substrate, the first storage capacitor is formed between the electrode and the pixel electrode, and the first storage capacitor on the storage capacitor electrode is formed. A columnar spacer formed on the second substrate is disposed in the formation region of the second substrate, and the second storage capacitor is formed by the extension portion of the counter electrode on the columnar spacer and the pixel electrode of the first substrate. it can.
[0010]
Further, the sum of the first storage capacitor and the second storage capacitor is set to a substantially constant value in all the pixels, and the extension of the counter electrode that forms the second storage capacitor in the specific pixel is performed. By making the area of the portion larger than the area of the other pixels, the area of the storage capacitor electrode forming the first storage capacitor can be made smaller than that of the other pixels, and thereby the aperture ratio in a specific pixel Can be further improved. Note that the specific pixel is desirably a pixel corresponding to the blue colored layer of the color filter formed on the second substrate.
[0011]
In the liquid crystal display device of the present invention, the counter electrode is formed on the columnar spacer of the second substrate so as to cover the portion in contact with the first substrate. The pixel electrode of the substrate is in contact with at least one insulating layer interposed therebetween, and a storage capacitor is formed between the extension portion of the counter electrode to the columnar spacer and the pixel electrode. Therefore, the storage capacitor electrode or the storage capacitor wiring can be omitted, and the aperture ratio can be improved.
[0012]
In particular, in the case where the first substrate has a storage capacitor electrode, and a storage capacitor (first storage capacitor) is formed between the storage capacitor electrode and the pixel electrode, the columnar spacer is formed with a non-opening portion. By installing it in a region where a certain storage capacitor electrode is formed, it is possible to efficiently form a storage capacitor (second storage capacitor) without reducing the aperture ratio. At this time, since the second storage capacitor formed by the extension portion of the counter electrode is added to the first storage capacitor, the first storage capacitor can be reduced as compared with the conventional one. That is, the area of the storage capacitor electrode can be reduced or the storage capacitor wiring can be made thinner, and the aperture ratio can be increased.
[0013]
Furthermore, the columnar spacers need only be installed at a density that can maintain a predetermined cell gap, and the total cross-sectional area of the columnar spacers installed need not be the same in all pixels. Therefore, in a specific pixel, the cross-sectional area of the columnar spacers to be installed is changed to change the area of the extension portion of the counter electrode that forms the second storage capacitor, and the first storage capacitor is correspondingly changed. By changing the area of the storage capacitor electrode that forms the electrode, a design in which the aperture ratio of only a specific pixel is changed is possible.
[0014]
In particular, it is possible to increase the aperture ratio of a specific pixel as a blue pixel corresponding to the blue colored layer of the color filter. And, by improving the aperture ratio of such blue pixels, it is possible to reduce the proportion of blue phosphor in the backlight fluorescent tube, thereby reducing power consumption and reducing power consumption. By directing the reduced amount to red and green light emission, higher brightness display is possible.
[0015]
Further, in the case where it is not always necessary to install columnar spacers in all the pixels in the display area, columnar spacers may be installed only in the pixels whose aperture ratio is desired to be improved. Then, in a specific pixel provided with a columnar spacer, the area of the storage capacitor electrode forming the first storage capacitor is much smaller than that of the other pixels, and a structure with an extremely high aperture ratio can be obtained.
[0016]
DETAILED DESCRIPTION OF THE INVENTION
Embodiments of the present invention will be described below with reference to the drawings.
[0017]
FIG. 1 is a plan view of a liquid crystal cell obtained by combining a TFT array substrate and a counter substrate in a first embodiment of the liquid crystal display device of the present invention, as seen through from the counter substrate side. 2 shows a cross-sectional view taken along the line AA of the TFT portion in FIG. 1, and FIG. 3 shows the first storage capacitor portion, that is, the columnar spacer installation portion in FIG. FIG.
[0018]
In the liquid crystal display device of the embodiment, as shown in these drawings, in the TFT array substrate, a plurality of metals made of metal such as Al, Mo, W, Ta, Ti, etc. are formed on a transparent insulating substrate 9 such as a glass substrate. The scanning lines 10 and the signal lines 11 are formed so as to intersect with each other, and a TFT 12 is formed for each pixel section arranged in a matrix. In each pixel, the storage capacitor electrode 13 extends from the scanning line 10 and is integrally formed. The TFT 12 includes a gate electrode 14 integrated with the scanning line 10, a gate insulating film 15 such as silicon oxide (SiO _x ) formed on the gate electrode 14, and a stacked on the gate insulating film 15 in order. A semiconductor layer 16 such as -Si (amorphous silicon), a low resistance semiconductor layer (contact layer) 17, an etching protection film 18 such as silicon nitride, and the low resistance semiconductor layer 17 are formed to extend from the signal line 11. The drain electrode 19 and the island-like source electrode 20 formed in the same layer as the drain electrode 19 are configured. A pixel electrode 21 made of a transparent material such as indium tin oxide (ITO) is provided on the insulating substrate 9 in the pixel portion via the gate insulating film 15, and the scanning line 10 in the previous stage (n−1 stage). A storage capacitor (first storage capacitor) is formed between the storage capacitor electrode 13 and the storage capacitor electrode 13 formed integrally therewith. In addition, the pixel electrode 21 is electrically connected to the source electrode 20 of the FT 12 formed on the n-th scanning line 10. Further, an insulating protective film 22 made of, for example, silicon nitride (SiN _x ) having a thickness of 200 nm is formed on the entire surface by a plasma CVD method or the like. The entire display area excluding the area is coated with an alignment film 23 made of low-temperature cure type polyimide or the like and subjected to an alignment process by rubbing.
[0019]
On the other hand, in the counter substrate, a light shielding layer (black matrix) 24 is formed of a light shielding material on a transparent insulating substrate 9 such as a glass substrate, and blue, green, and red colored layers are formed in stripes. Thus, a color filter (not shown) is formed. In forming the color filter, the columnar spacer 25 is formed by sequentially laminating the blue colored layer B, the green colored layer G, and the red colored layer R at predetermined positions on the light shielding layer 24. . A counter electrode 26 made of ITO is formed on the color filter, and the counter electrode 26 is formed so as to cover the entire outer peripheral surface of the columnar spacer 25. Further, an alignment film 23 made of a low-temperature cure type polyimide or the like is applied to the entire display area excluding the outer peripheral surface of the columnar spacer 25 and subjected to an alignment process by rubbing.
[0020]
The counter substrate and the TFT array substrate described above each have a columnar spacer 25 formed so that the surface on which the alignment film 23 is formed is inward and projecting toward the counter substrate side. The counter electrode 26 disposed opposite to the first storage capacitor forming portion on the electrode 13 and formed on the columnar spacer 25 is part of the pixel electrode 21 in which the first storage capacitor is formed. The contact is made through the insulating protective film 22. A liquid crystal composition 27 such as TN liquid crystal is sandwiched between these substrates.
[0021]
In this liquid crystal display device, the counter electrode is formed by forming the alignment film 23 except for the outer peripheral surface of the columnar spacer 25 on the counter substrate side and the portion where the columnar spacer 25 abuts on the TFT array substrate side. Only the insulating protective film 22 is interposed between the pixel electrode 21 and the pixel electrode 21. However, when a soluble polyimide film as a dielectric is used as the alignment film 23, the second alignment film having a thickness of, for example, 20 nm is left. Alternatively, the storage capacitor may be formed.
[0022]
FIG. 4 shows an equivalent circuit diagram of a portion corresponding to one pixel in the TFT array substrate of the liquid crystal display device configured as described above. As is apparent from the figure, the liquid crystal display device of the embodiment has a function of compensating for the liquid crystal capacitance CLC formed between the pixel electrode 21 connected to the source electrode 20 of the TFT 12 and the counter electrode 26 of the counter substrate. As the storage capacitor, in addition to the first storage capacitor Cs1 formed between the pixel electrode 21 and the storage capacitor electrode 13 of the n-1 stage scanning line 10, the pixel electrode 21 and the counter electrode 26 on the columnar spacer 25 are provided. The second storage capacitor Cs2 formed between the two is added.
[0023]
Therefore, the area of the storage capacitor electrode 13 formed integrally with the scanning line 10 can be reduced while ensuring sufficient storage as a whole, and the aperture ratio is improved. That is, conventionally, since the storage capacitor for the pixel is formed only by Cs1, it is necessary to take a sufficiently large area of the storage capacitor electrode 13 for forming Cs1, but since Cs2 is added, the entire storage capacitor (Cs1 and The area of the storage capacitor electrode 13 can be reduced and the aperture ratio can be increased while keeping the sum of Cs2) as usual.
[0024]
In addition, the gate insulating film 15 that forms Cs1 interposed between the storage capacitor electrode 13 and the pixel electrode 21 is made of silicon oxide (SiO _x ) having a dielectric constant of 4.8, whereas the pixel. Since the insulating protective film 22 that forms Cs2 interposed between the electrode 21 and the counter electrode 26 is made of silicon nitride (SiN _x ) having a dielectric constant of 6.2, a large capacity can be efficiently used as Cs2. The area of the storage capacitor electrode 13 that forms Cs1 can be effectively reduced.
[0025]
Therefore, in the liquid crystal display device of the embodiment, the aperture ratio of the pixels is high, the cell gap is kept uniform by the columnar spacer, and the second storage capacitor formed in the installation portion of the columnar spacer is effective. Since it functions, a high-brightness and good display image can be obtained.
[0026]
Next, a second embodiment of the liquid crystal display device of the present invention will be described with reference to FIG.
[0027]
In the liquid crystal display device of the second embodiment, in each pixel of the TFT array substrate, the sum of the first storage capacitor Cs1 and the second storage capacitor Cs2 is substantially constant, but the respective values (Cs1 and Cs2) are Each pixel differs, and in particular, a pixel corresponding to the blue colored layer (represented by B) of the color filter is more columnar than a pixel corresponding to the red and green colored layers (represented by R and G). The area of the extended portion of the counter electrode 26 corresponding to the cross-sectional area of the spacer 25 is large, and the value of the second storage capacitor Cs2 is large. Therefore, the storage that overlaps the pixel electrode 21 and forms the first storage capacitor Cs1. The area of the capacitive electrode 13 is small. Since other configurations are the same as those in the first embodiment, the same portions are denoted by the same reference numerals and description thereof is omitted.
[0028]
In the liquid crystal display device of the second embodiment configured as described above, the cell gap is kept uniform by the columnar spacers 25 as in the first embodiment, so that a good display without unevenness can be obtained. In addition, the aperture ratio of the pixel corresponding to the blue filter position is higher than that of the pixel corresponding to the red or green filter position. Therefore, in the fluorescent tube of the backlight, the ratio of the blue phosphor can be reduced, and thus the power consumption can be reduced while balancing the intensity of transmitted light of each color.
[0029]
Furthermore, a third embodiment of the liquid crystal display device of the present invention will be described with reference to FIG. In the liquid crystal display device of this embodiment, in the TFT array substrate, the columnar spacer 25 is provided only in the pixel corresponding to the blue colored layer of the color filter, the second storage capacitor Cs2 is formed, and the first storage is performed. The area of the overlapping portion of the storage capacitor electrode 13 and the pixel electrode 21 forming the capacitor Cs1 is much smaller than that of the pixels corresponding to the filter positions of other colors. Since other configurations are the same as those in the first embodiment, the same portions are denoted by the same reference numerals and description thereof is omitted.
[0030]
In the liquid crystal display device of the third embodiment configured as described above, the aperture ratio of the pixel corresponding to the blue filter position can be further increased as compared with the second embodiment, thereby further reducing the power consumption. Can be reduced. Also, in this embodiment, the installation density of the columnar spacers 25 for maintaining the cell gap is smaller than in the first and second embodiments, but a sufficiently uniform cell gap is maintained even at this density. Good display without unevenness can be obtained.
[0031]
In the above embodiment, the first storage capacitor Cs1 is formed between the storage capacitor electrode 13 and the pixel electrode 21 integrated with the (n-1) th scanning line 10, but is independent of the pixel electrode 21. It is also possible to adopt a configuration in which Cs1 is formed between the storage capacitor wirings.
[0032]
In each pixel, the first storage capacitor Cs1 and the second storage capacitor Cs2 are used together, but it is needless to say that only Cs2 may be used. Further, the gate electrode 14 of the TFT 12 is provided on the scanning line 10. However, the present invention is not limited to the TFT 12 having such a structure, and the TFT 12 provided with the gate electrode 14 in a shape branched from the scanning line 10 is further provided. The present invention can also be applied to a TFT using polycrystalline silicon as a semiconductor.
[0033]
In the second and third embodiments, the specific pixel on which the columnar spacer 25 having a larger cross-sectional area is installed is a pixel corresponding to the blue filter position, but depending on the use and environment of the liquid crystal display device, In some cases, display in which other colors are emphasized is required, and in that case, columnar spacers 25 may be provided in pixels corresponding to filter positions of other colors.
[0034]
【The invention's effect】
As is clear from the above description, according to the liquid crystal display device of the present invention, the aperture ratio is improved by forming a storage capacitor between the counter electrode and the pixel electrode formed at the contact portion of the columnar spacer. Can be made. Therefore, it is possible to obtain an active matrix liquid crystal display device with a high aperture ratio while maintaining a good display quality with a uniform cell gap and high contrast ratio, which is also effective in reducing power consumption.
[Brief description of the drawings]
FIG. 1 is a plan view of a liquid crystal cell seen through from a counter substrate side in a first embodiment of a liquid crystal display device of the present invention.
2 is a cross-sectional view taken along line AA of the TFT portion in FIG.
3 is a cross-sectional view taken along the line BB of the first storage capacitor portion, that is, the columnar spacer installation portion in FIG. 1. FIG.
FIG. 4 is an equivalent circuit diagram of a portion corresponding to one pixel of the liquid crystal display device of the first embodiment.
FIG. 5 is a plan view of a liquid crystal cell seen through from a counter substrate side in a second embodiment of the liquid crystal display device of the present invention.
FIG. 6 is a plan view of a liquid crystal cell seen through from a counter substrate side in a third embodiment of the liquid crystal display device of the present invention.
FIG. 7 is a plan view corresponding to one pixel of an array substrate used in a conventional liquid crystal display device.
[Explanation of symbols]
9 ......... Insulating substrate 10 ......... Scanning line 11 ......... Signal line 12 ......... TFΤ
13 ... Storage capacitor electrode 14 ... Gate electrode 15 ... Gate insulating film 16 ... Semiconductor layer 17 ... Low resistance semiconductor layer 18 ... Etch protection film 19 ... Drain electrode 20 ... ... Source electrode 21 ......... Pixel electrode 22 ......... Insulating protective film 24 ......... Light shielding layer 25 ......... Columnar spacer 26 ......... Counter electrode 27 ......... Liquid crystal composition

Claims (4)

A plurality of scanning lines and signal lines formed on an insulating substrate, pixel electrodes formed in matrix sections formed by the scanning lines and signal lines, and switching provided for each of these pixel electrodes A first substrate having an element; a columnar spacer formed by stacking a plurality of colored layers to maintain a gap between the first substrate; and a counter electrode; In a liquid crystal display device comprising: a second substrate arranged as described above; and a liquid crystal layer sandwiched between the first substrate and the second substrate.
The counter electrode is formed to extend at a portion of the columnar spacer that contacts the first substrate, and the extension portion of the counter electrode is at least one insulating layer with the pixel electrode of the first substrate. The liquid crystal display device is characterized in that a storage capacitor is formed through contact with each other. The first substrate includes a storage capacitor electrode that forms a storage capacitor with the pixel electrode, and the columnar spacer is disposed in a region where the first storage capacitor is formed by the storage capacitor electrode. 2. The liquid crystal display device according to claim 1, wherein a second storage capacitor is formed between the extended portion of the electrode and the pixel electrode. The sum of the first storage capacitor and the second storage capacitor is made substantially constant for all the pixels, and the area of the extension portion of the counter electrode that forms the second storage capacitor is determined in a predetermined pixel. 3. The liquid crystal display device according to claim 2, wherein the area of the storage capacitor electrode forming the first storage capacitor is reduced while increasing. 4. The liquid crystal display device according to claim 3, wherein the predetermined pixel is a pixel corresponding to a blue colored layer of a color filter formed on the second substrate.

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