JP3562873B2 - Active matrix type liquid crystal display - Google Patents

Description

[0001]
TECHNICAL FIELD OF THE INVENTION
The present invention relates to an active matrix type liquid crystal display device.
[0002]
[Prior art]
An active matrix type liquid crystal display device is generally configured by holding liquid crystal between an array substrate and a counter substrate via an alignment film, and a plurality of pixel electrodes are electrically connected to switching elements on the array substrate. Connected and arranged.
[0003]
For example, in a conventional active matrix type liquid crystal display device, as shown in FIG. 5, in an array substrate 100, a plurality of signal lines 101 and a plurality of scanning lines 102 are arranged in a matrix on a glass substrate. A pixel electrode 104 made of ITO (Indium Tin Oxide) is arranged via a thin film transistor (hereinafter, referred to as a TFT) 103 arranged as a switching element near each intersection of the signal line 101 and the scanning line 102. I have. Below the pixel electrode 104, an auxiliary capacitance line 105 is arranged substantially in parallel with the scanning line 102 via an insulating film, and an auxiliary capacitance is formed between the auxiliary capacitance line 105 and the pixel electrode 104. .
[0004]
In the array substrate 100, in each pixel electrode 104, the distances d0, d0 between the signal lines 101, 101 adjacent to the pixel electrode 104 and the pixel electrode 104 are equal on both sides of the pixel electrode 104. The electrodes 104 and the signal lines 101 are arranged at equal intervals. This is because the distance d0 between the pixel electrode 104 and the signal line 101 is reduced to the limit of the array design in order to increase the aperture ratio as much as possible. The aperture ratio is obtained by setting the distances d0 and d0 from the base 101 as design limit values (for example, 5 μm).
[0005]
[Problems to be solved by the invention]
By the way, a coupling capacitance C0 is generated between the pixel electrode 104 and the signal line 101 adjacent thereto. The coupling capacitance C0 is generated in an adjacent portion where the side of the pixel electrode 104 and the signal line 101 are adjacent to each other, and the magnitude differs depending on the length of the adjacent portion.
[0006]
Here, in the conventional liquid crystal display device, as shown in FIG. 5, on the left side of the pixel electrode 104, the drain electrode 106 is extended from the signal line 101. The extracted drain electrode 106 generates a coupling capacitance between the drain electrode 106 and the adjacent pixel electrode 104, similarly to the signal line 101. Therefore, on the left side of the pixel electrode 104, the length of the adjacent portion for generating the coupling capacitance C0 is longer than the right side by the length of the drain electrode 106. As a result, the coupling capacitance C0 generated on the left side of the pixel electrode 104 is larger than the coupling capacitance C0 generated on the right side.
[0007]
If the coupling capacitances C0 and C0 are different on both sides of the pixel electrode 104, there is a problem particularly in the case of the so-called V-line inversion drive in which the display signal applied to the liquid crystal is inverted for each adjacent signal line. . In the case of the V-line inversion drive, since the positive and negative voltages of the signal lines 101 and 101 adjacent to the both sides of the pixel electrode 104 are different, the potentials of the signal lines 101 and 101 on both sides of the pixel electrode 104 during the holding operation are changed. This is because the change cannot be canceled well and the potential fluctuation of the pixel electrode 104 increases. As a result, there is a problem that good display cannot be obtained due to crosstalk.
[0008]
In view of the above problems, it is an object of the present invention to provide an active matrix type liquid crystal display device which does not generate crosstalk even when the V-line inversion driving is performed and which can provide a good display.
[0009]
[Means for Solving the Problems]
Active matrix liquid crystal display device of the present invention, a plurality of scanning lines and signal lines disposed to cross over an insulating substrate, a switching element disposed for each intersection of the scanning lines and the signal lines, An array substrate including: a pixel electrode connected to the switching element; and an auxiliary capacitance line provided below the pixel electrode and parallel to the scanning line and forming an auxiliary capacitance between the pixel electrode and the array substrate. In an active matrix type liquid crystal display device including a counter substrate having a counter electrode disposed to face a substrate and liquid crystal held between the array substrate and the counter substrate, a first side of the pixel electrode A drain electrode of the switching element is formed from the signal line located on the side toward the pixel electrode, and a shield member that forms an auxiliary capacitance between the switching element and the pixel electrode is provided at the front. Extends integrally along both sides of the pixel electrode from the auxiliary capacitance line, and a distance between the signal line adjacent to the first side edge and the first side edge of the pixel electrode, the second of said pixel electrodes The distance between the side line and the other signal line adjacent to the second side line is equalized, and the coupling capacitance generated between the pixel electrode and the drain electrode and the first side line of the pixel electrode are A first coupling capacitance which is a sum of a coupling capacitance generated between the signal line adjacent to the first side and the second side adjacent to the pixel electrode; The length of the shield member on the first side of the pixel electrode and the length of the shield on the second side of the pixel electrode are set such that a second coupling capacitance generated between the signal line and the other signal line is equal. It is different from the length of the member.
[0012]
[Action]
In the active matrix type liquid crystal display device of the present invention, since the shield member provided so as to extend along both sides of the pixel electrode forms an auxiliary capacitance with the pixel electrode, the shield member on the side is disposed. In such a portion, the potential of the pixel electrode does not fluctuate due to the change in the potential of the signal line, so that the coupling capacitance between the pixel electrode and the signal line can be ignored. That is, since the size of the coupling capacitance generated between the signal line and the signal line can be adjusted by the length of the shield member, for example, the length of the shield member is made different between the left and right sides of the pixel electrode, The left and right coupling capacities are set to be equal . If the length of the shield member is equal on both sides of the pixel electrode, the left and right coupling capacitances will not be equal due to the influence of the switching element and the like. Therefore, the length of the shield member on one side of the left and right sides is made longer than the length of the other side to reduce the coupling capacity of the one side by the influence of the above. Equal .
[0013]
More specifically, for example, a switching element is formed from a signal line located on the left side of the pixel electrode, and the left and right couplings are considered in consideration of the coupling capacitance generated between the switching element and the pixel electrode. The lengths of the shield members on the left and right sides of the pixel electrode are different so that the capacitances are equal . Alternatively, for example, a switching element is formed from a signal line located on the right side of the pixel electrode, and the left and right coupling capacitances are equal in consideration of the coupling capacitance generated between the switching element and the pixel electrode. Thus, the lengths of the shield members on the left and right sides of the pixel electrode are different.
[0014]
As described above, in the active matrix type liquid crystal display device of the present invention, since the coupling capacitance generated between both sides of the pixel electrode and the signal lines respectively adjacent to the both sides is equal, the V line inversion driving is performed. Even when the polarity of the voltage applied to the two signal lines adjacent to both sides of one pixel electrode is different from the reference voltage, the change in the signal line potential during the holding operation of the pixel electrode is It is possible to favorably cancel each other on both sides, and to suppress pixel potential fluctuation due to the potential change .
[0015]
BEST MODE FOR CARRYING OUT THE INVENTION
First , an active matrix liquid crystal display device 10 according to a reference example will be described with reference to FIGS.
[0016]
The active matrix type liquid crystal display device 10 is a light transmission type liquid crystal display device of a normally white mode, and has a twisted nematic type between the array substrate 12 and the counter substrate 14 via the alignment films 13 and 15. It comprises a liquid crystal panel 18 holding a liquid crystal 16.
[0017]
The array substrate 12 is arranged on a glass substrate 20 such that 640 × 3 signal lines 22 and 480 scanning lines 24 are substantially orthogonal to each other. The scanning lines 24 are arranged directly on the glass substrate 20, while the signal lines 22 are arranged on an insulating film 30 formed on the glass substrate 20 and formed of a multilayer film of silicon oxide and silicon nitride. In the vicinity of the intersections where the signal lines 22 and the scanning lines 24 intersect, a pixel electrode 28 is arranged via a TFT 26 at each intersection.
[0018]
In the TFT 26, the scanning line 24 itself is used as a gate electrode, an insulating film 30 is provided thereon, an a-Si: H film is provided as a semiconductor film 32 on the insulating film 30, and further, on the semiconductor film 32. A channel protection film 34 made of silicon nitride is provided. The semiconductor film 32 is electrically connected to the pixel electrode 28 disposed on the insulating film 30 via a low-resistance semiconductor film 36 made of an n ⁺ -type a-Si: H film and a source electrode 38. The semiconductor film 32 is electrically connected to the signal line 22 via the low-resistance semiconductor film 36 and the drain electrode 40 extending from the signal line 22.
[0019]
Now, the configuration of the pixel electrode 28 will be described with reference to FIG. The pixel electrode 28 has a substantially rectangular shape, and is adjacent to the signal lines 22 and 22 on the long sides arranged on the left and right in the figure, and the scanning lines 24 and 24 on the short sides arranged on the top and bottom in the figure. , Four signal lines 22, 22 and two scanning lines 24, 24 surround four sides. The upper side is connected to the left signal line 22 via the TFT 26, and the lower side is provided with a notch 42 for extending the TFT 26 of the next pixel electrode 28 as the drain electrode 40. Is formed.
[0020]
The distance d1L between the left side of the pixel electrode 28 and the signal line 22 adjacent to the left side is determined by the coupling capacitances C1L and C1R generated between the pixel electrode 28 and the signal lines 22 and 22. The distance d1R between the right side of the pixel electrode 28 and the signal line 22 adjacent to the right side is set to be equal (C1L = C1R) (d1L> d1R). This is because, on the left side of the pixel electrode 28, the length of the portion that generates the coupling capacitance is longer than the right side due to the influence of the drain electrode 40 in the next stage. This is because the capacity becomes large. As described above, the distances d1L and d1R between the left and right sides of the pixel electrode 28 and the signal line 22 are set so that C1L = C1R, whereby one signal line 22 is adjacent to the left and right sides thereof. The coupling capacitance between the two pixel electrodes 28 is also equal.
[0021]
Below the pixel electrode 28, an auxiliary capacitance line 44 is disposed substantially in parallel to the scanning line 24 and substantially through the center of the pixel electrode 28. This auxiliary capacitance line 44 is formed directly on the glass substrate 20. The insulating film 30 is interposed between the auxiliary capacitance line 44 and the pixel electrode 28 to form an auxiliary capacitance Cs. As shown in FIG. 1, the auxiliary capacitance line 44 is formed thick in an area overlapping with the pixel electrode 28 and thin in an area intersecting with the signal line 22 in order to secure the auxiliary capacitance Cs and avoid a short circuit with the signal line 22. Have been.
[0022]
On the other hand, the opposing substrate 14 is provided between a light-shielding film 50 made of a chromium oxide film for shielding the gap between the TFTs 26 and the pixel electrodes 28 of the array substrate 12 on a transparent glass substrate 48. And a color portion 52 composed of three primary colors of red (R), green (G), and blue (B) for realizing the color display. Further, a counter electrode 56 made of ITO is arranged thereon as a smoothing layer via an organic protective film 54.
[0023]
Note that, on the front and back surfaces of the liquid crystal panel 18 configured as described above, polarizing plates 58 and 60 are disposed on the outer surfaces of the glass substrates 20 and 48, respectively. The signal line 22 and the scanning line 24 are respectively drawn out to one side of the wiring, and connected to a driving circuit board (not shown) for driving the liquid crystal panel 18 via a TAB (not shown). Is supplied.
[0024]
In the liquid crystal display device 10 described above, the coupling capacitances C1L and C1R between the pixel electrode 28 and the signal line 22 are equal on both the left and right sides of the pixel electrode 28. In addition, the potential change of the signal lines 22 and 22 on both sides of the pixel electrode 28 holding the electric charge is effectively canceled, and the potential change of the pixel electrode 28 due to the potential change can be suppressed. Therefore, a good display, that is, an image without crosstalk or burn-in can be obtained.
[0025]
In addition, since the coupling capacitances C1L and C1R are equal on both sides of the pixel electrode 28, no undesired DC component is applied to the liquid crystal 16, so that the durability is improved, and the image is deteriorated even when used for a long time. Hard to happen. This is not limited to the above-described V-line inversion drive. For example, a so-called H-line inversion drive in which a display signal applied to the liquid crystal 16 is inverted for each adjacent one scanning line or several scanning lines with respect to a reference potential. In this case, the effect is also obtained in the HV inversion drive in which the V line inversion drive and the H line inversion drive are combined.
[0026]
Next, an active matrix type liquid crystal display device 70 according to an embodiment of the present invention will be described with reference to FIGS.
[0027]
This liquid crystal display device 70 is different from the above-described liquid crystal display device 10 in the arrangement of the pixel electrodes 28 with respect to the signal lines 22 and the shape of the auxiliary capacitance line 44. Hereinafter, only this difference will be described.
[0028]
In the array substrate 12 of the device 70, in each pixel electrode 28, the distance d2L, d2R between the left and right sides 28a, 28b of the pixel electrode 28 and the signal lines 22, 22 adjacent to the both sides 28a, 28b, respectively, The pixel electrodes 28 and the signal lines 22 are arranged at equal intervals so that both sides of the pixel electrodes 28 are equal (d2L = d2R).
[0029]
The auxiliary capacitance line 44 is formed from a narrow strip-shaped wiring portion 72 disposed at substantially equal intervals between two adjacent scanning lines 24 and in parallel with the two scanning lines 24, and from the upper and lower sides of the wiring portion 72. A strip-shaped extension 74 extends perpendicular to the wiring 72, and a storage capacitor Cs is formed between the extension 74 and the pixel electrode 28. The extension 74 is formed along the left and right sides 28a, 28b of the pixel electrode 28, and shields the edge area of the pixel electrode 28 inside the sides 28a, 28b, and It has an appropriate width so as to partially shield an area between the signal line 22 and the pixel electrode 28 outside the side sides 28a and 28b. The extending portion 74 is set such that the extending portion 74a on the left side 28a of the pixel electrode 28 is longer than the extending portion 74b on the right side 28b by k on both the upper and lower sides of the wiring portion 72. . The length difference 2k is set so that the coupling capacitances C2L and C2R between the pixel electrode 28 and the signal line 22 on the right and left sides of the pixel electrode 28 are equal (C2L = C2R).
[0030]
In the case of the liquid crystal display device 70, the extension 74 of the auxiliary capacitance line 44 of a constant potential extends along both sides 28a and 28b of the pixel electrode 28 adjacent to the signal line 22. In such a portion, the potential change of the pixel electrode 28 due to the change in the potential of the signal line 22 can be eliminated, so that the coupling capacitance with the signal line 22 can be ignored. Therefore, the size of the coupling capacitance generated between the extension 74 and the signal line 22 can be adjusted by the length of the extension 74. In the present device 70, the increase in the coupling capacitance on the left side of the pixel electrode 28 due to the influence of the drain electrode 40 in the next stage is made 2 k longer in the left extension 74a than in the right extension 74b. The relationship of C2L = C2R is maintained.
[0031]
Further, in the present device 70, as described above, the extension 74 of the auxiliary capacitance line 44 shields the influence of the potential change of the signal line 22. , The absolute values of the coupling capacitances C2L and C2R can be reduced.
[0032]
As described above, the device 70 is excellent in the effect of suppressing the fluctuation in the potential of the pixel electrode 28 when the V-line inversion driving is performed, and therefore, it is possible to obtain a favorable display without crosstalk or burn-in. Further, in various driving methods such as H-line inversion driving, the durability of the liquid crystal is improved, and image deterioration due to long-time use can be prevented.
[0033]
Further, since the relationship C2L = C2R is provided by the extension 74 of the auxiliary capacitance line 44, the distances d2L and d2R between the pixel electrode 28 and the signal line 22 can be reduced to the design limit. Since the region where the extension portion 74 is disposed is a region where light is shielded by the light shielding film 50 of the counter substrate 14, a decrease in the aperture ratio due to the auxiliary capacitance line 44 can be reduced. Therefore, in the case of the present device 70, the aperture ratio is high.
[0034]
In this embodiment, it is preferable that the extension 74 of the auxiliary capacitance line 44 be extended as long as possible, since the absolute values of the coupling capacitances C2L and C2R can be further reduced. If the length is too long, the scanning line 24 is likely to be short-circuited and the yield is deteriorated. Therefore, it is necessary to set the length in consideration of this point.
[0035]
Further, in this embodiment, the distances d2L and d2R between the pixel electrode 28 and the signal line 22 are set to be equal, but the distances on both sides of the pixel electrode 28 may be different as in the previous embodiment. However, even in that case, it is necessary to set the left and right coupling capacitances C2L and C2R of the pixel electrode 28 to be substantially equal.
[0036]
In each of the above-described embodiments, the case where the pixel electrode 28 and the signal line 22 are arranged at a positive interval has been described, but this is the case where the pixel electrode 28 and the signal line 22 are arranged at a negative interval. It does not matter even if the positions are partially overlapping.
[0037]
【The invention's effect】
In the active matrix type liquid crystal display device of the present invention, the coupling capacitance generated between the pixel electrode and each of the adjacent signal lines is equal. In this case, it is possible to suppress the pixel potential fluctuation due to the change in the signal line potential, and to obtain a favorable display without crosstalk or burn-in.
[Brief description of the drawings]
FIG. 1 is a partial schematic plan view of an array substrate 12 of an active matrix liquid crystal display device 10 according to a reference example .
FIG. 2 is a cross-sectional view of the active matrix liquid crystal display device taken along the line AA in FIG.
FIG. 3 is a partial schematic plan view of an array substrate 12 of an active matrix liquid crystal display device 70 according to one embodiment of the present invention.
FIG. 4 is a cross-sectional view of a main part of the active matrix liquid crystal display device 70 cut along the line BB in FIG. 3;
FIG. 5
It is a partial schematic plan view of an array substrate 100 of a conventional active matrix type liquid crystal display device.
[Explanation of symbols]
70 liquid crystal display device 12 array substrate 14 counter substrate 22 signal line 24 scanning line 26 TFT
28 pixel electrodes 28a, 28b side 44 of pixel electrode 28 adjacent to signal line 22 auxiliary capacitance line 74 extending portion d1L, R, d2L, R of auxiliary capacitance line 44 pixel electrode C1L, R, C2L, R between gaps 28 and signal line 22... Coupling capacitance between pixel electrode 28 and signal line 22

Claims (1)

A plurality of scanning lines and signal lines arranged so as to intersect on an insulating substrate, switching elements arranged at intersections of these scanning lines and signal lines, pixel electrodes connected to the switching elements, An array substrate including an auxiliary capacitance line provided below the pixel electrode in parallel with the scanning line and forming an auxiliary capacitance with the pixel electrode;
A counter substrate including a counter electrode arranged to face the array substrate,
In an active matrix liquid crystal display device including a liquid crystal held between the array substrate and the counter substrate,
A drain electrode of the switching element is formed from the signal line located on the first side of the pixel electrode toward the pixel electrode;
A shield member that forms an auxiliary capacitance with the pixel electrode is integrally extended from the auxiliary capacitance line along both sides of the pixel electrode,
The distance between the first side of the pixel electrode and the signal line adjacent to the first side, and the distance between the second side of the pixel electrode and another signal line adjacent to the second side. And
It is the sum of a coupling capacitance generated between the pixel electrode and the drain electrode and a coupling capacitance generated between a first side of the pixel electrode and the signal line adjacent to the first side. In order that a certain first coupling capacitance and a second coupling capacitance generated between a second side of the pixel electrode and another signal line adjacent to the second side are equal. An active matrix liquid crystal display device, wherein a length of the shield member on a first side of the pixel electrode is different from a length of the shield member on a second side of the pixel electrode.

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