JPH04348324A - Liquid crystal display element - Google Patents

Abstract

PURPOSE:To improve the display performance by increasing the degree of freedom of the design of capacity division voltages applied to liquid crystal capacitors prescribed by plural subordinate picture element electrodes of respective picture elements. CONSTITUTION:The respective picture element electrodes of the liquid crystal display element are divided into the subordinate picture element electrodes 41, 42..., which are mutually separated by a gap Ga; and a control capacitor electrode 2 is provided at least partially opposite across the respective subordinate picture element electrodes and a 1st insulating film 3. A control capacitor electrode 2 form control capacitors in series with liquid crystal capacitors that the subordinate picture element electrodes 41, 42... form with a counter common electrode 6. An additional capacitor electrode 12 faces the subordinate picture element electrodes 41, 42... partially across a 2nd insulating film 11 is formed and then additional capacitors which are equivalently to the liquid crystal capacitors are connected.

Description

[Detailed description of the invention]

0001

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to the structure of a pixel of a liquid crystal display element in which a pixel is divided into a plurality of sub-pixels and is capable of displaying multiple gradations.

0002

[Prior Art] As a prior art of this type, US Patent No. 4
, No. 840460 (Japanese Unexamined Patent Publication No. 2-12 "Pixels of liquid crystal display device and method for realizing gray scale of pixels in liquid crystal display device") is known. That is, as shown in FIG. 1, where one pixel area of a liquid crystal display panel is cut out perpendicularly to the panel, a control capacitor electrode 2 is formed on the inner surface of a transparent substrate 1 such as glass, and a control capacitor electrode 2 is formed on the inner surface of a transparent substrate 1 such as glass. An insulating film 3 is formed over the entire surface of the transparent substrate 1. A rectangular sub-pixel electrode 4 divided into four equal parts on the insulating film 3
1 to 44 are formed. A transparent substrate 5 made of glass or the like is provided facing these sub-pixel electrodes at a distance.
A common electrode 6 is formed on the inner surface of the pixel, and a liquid crystal 7 is sealed between the common electrode 6 and the sub-pixel electrodes 4i (i=1 to 4). The control capacitor electrode 2, subpixel electrode 4i, and common electrode 6 are transparent electrodes made of ITO or the like. In this way, one pixel is divided into four sub-pixels F1 to F4 corresponding to the sub-pixel electrodes 41 to 44. As shown in FIG. 2, a control capacitor Cci using an insulating film 3 as a dielectric is formed between each sub-pixel electrode 4i and a control capacitor electrode 2, and a liquid crystal 7 is formed between each sub-pixel electrode 4i and a common electrode 6. A liquid crystal capacitor CLCi is formed using the dielectric material CLCi. FIG. 3 shows an electrical equivalent circuit of the pixel in FIG. 1. When the symbols Cci and CLCi are used to represent capacitance, CC1>CC2>CC3>CC4
The area of the control capacitor electrode 2 overlapping with each sub-pixel electrode 4i is adjusted so that (1) is obtained.

The control capacitor electrode 2 is a thin film transistor (thin film transistor) formed on the transparent substrate 1 adjacent to the pixel in FIG.
Connected to the drain electrode D of TFT) 8 (Figure 2)
. A predetermined voltage Va is supplied between the control capacitor electrode 2 and the common electrode 6 via the TFT 8. When the TFT 8 is turned on, the supply voltage Va in each sub-pixel Fi is divided into the voltage VCi across the control capacitor CCi and the voltage VLCi across the liquid crystal capacitor CLCi. VLCi is

0004

It is expressed as [Equation 1]. The capacity of each control capacitor CCi is (1)
By setting as shown in the formula, the voltage VLCi across each liquid crystal capacitor CLCi becomes VLC1 > VLC2 > VLC3 > VLC4
(3) is set.

[0005] The voltage at which the light transmission of the liquid crystal is saturated is VU.
Assuming that the threshold voltage is VL, as shown in FIG. 4, depending on the magnitude of the voltage Va supplied to the pixel, the voltage VLCi across the liquid crystal capacitor CLCi may be as follows. (a) When VLCi = 0 for all i = 1 to 4. At this time, Va=0. (b) When VLC1 = VU and VLC2 = VL. VLC3 and VLC4 are below VL. The supply voltage Va at this time is represented by Va1. (c) When VLC2 = VU and VLC3 = VL. The supply voltage Va at this time is represented by Va2. (d) When VLC3 = VU and VLC4 = VL. Va at this time is expressed as Va3. (e) When VLC4 = VU. Va at this time is expressed as Va4.

[0006] The supply voltage Vai is as follows: Va1>Va2>Va3>Va4>0
(4). Multi-gradation display is performed by changing the magnitude of the supply voltage Va.

[0007]

[Problems to be Solved by the Invention] In the conventional technology, in the sub-pixel Fi, the voltage Va supplied to the pixel is Vai
When , the voltage VLCi across the liquid crystal capacitor CLCi
is set to be equal to the voltage VU at which the light transmission of the liquid crystal is saturated. That is,

[0008]

##EQU00002## The area of each control capacitor CCi overlapping with the sub-pixel electrode 4i is set so that its capacitance satisfies equation (5). As can be seen from equation (5), in order to make the voltage applied to the liquid crystal capacitor VLCi of a certain subpixel 4i very small, the capacitance of the corresponding control capacitor CCi must be made small. That is, it is necessary to reduce the area of the control capacitor electrode 2 that overlaps with the sub-pixel electrode 4i. However, the smaller this overlapping area becomes (in the above example, the overlapping area of CC4 is the smallest)
, the error in the capacitance value CCi increases due to variations in the overlapping area of the sub-pixel electrodes 41 to 44 and the control capacitor electrode 2 due to pattern misalignment or the like. The liquid crystal capacitor voltage VLCi has a large deviation from the light transmission saturation voltage VU, which increases the error in multi-gradation display, resulting in a problem that the display quality is significantly degraded.

Furthermore, since the sub-pixel electrode 4i is formed by simply dividing the pixel electrode in the row and column directions, there are two conditions: when only one sub-pixel is on and when multiple sub-pixels are on. The center of the on-region was different in the state where the monitor was on, and the quality of the displayed image was poor. A first object of the present invention is to provide a liquid crystal display element in which multi-gradation display quality is less degraded due to manufacturing variations in control capacitor capacitance.

A second object of the present invention is to provide a liquid crystal display element whose center does not move even if the on-area of a pixel increases or decreases, and which has excellent image display quality.

[0011]

[Means for Solving the Problems] According to a first aspect of the present invention, a plurality of mutually separated sub-pixel electrodes constituting each pixel face a common electrode on a second substrate with a liquid crystal interposed therebetween. A control capacitor electrode is disposed on the first substrate, forming a liquid crystal capacitor therebetween, and facing at least one of the subpixel electrodes with a first insulating film interposed therebetween. The at least one sub-pixel electrode thereby forms a control capacitor connected in series with the liquid crystal capacitor formed between the at least one sub-pixel electrode and the common electrode, and a driving voltage is applied between the control capacitor electrode and the common electrode. In a liquid crystal display element having a pixel configured to be supplied with An additional capacitor is formed equivalently in parallel to the liquid crystal capacitor.

According to the second aspect of the present invention, a plurality of mutually separated sub-pixel electrodes constituting each pixel are arranged on the first substrate opposite to a common electrode on the second substrate with the liquid crystal interposed therebetween. A control capacitor electrode is provided between the first substrate and the sub-pixel electrode, forming a liquid crystal capacitor therebetween, and facing at least one of the sub-pixel electrodes with a first insulating film interposed therebetween. At least one sub-pixel electrode forms a control capacitor connected in series to a liquid crystal capacitor formed between the common electrode, and a driving voltage is supplied between the control capacitor electrode and the common electrode. In the liquid crystal display element having the configured pixels, in the present invention, the plurality of sub-pixel electrodes define a central sub-pixel region and at least one loop-shaped sub-pixel region substantially concentrically surrounding the central sub-pixel region. It is formed.

[0013]

[Operation] According to the first aspect of the present invention, since the additional capacitor is connected equivalently in parallel to the liquid crystal capacitor connected in series with the control capacitor, neither the control capacitor electrode nor the additional capacitor electrode Even if the area is changed, the capacitance division voltage applied to the liquid crystal constituting the liquid crystal capacitor can be controlled, which increases the degree of freedom in pixel design.

According to the second aspect of the present invention, since the sub-pixels constituting each pixel are arranged concentrically with each other, even if the display state of the sub-pixels is changed, the center of the on area remains approximately at the center of the pixel. is fixed to improve the quality of the displayed image.

[0015]

[Embodiment] An embodiment of the present invention is shown in FIG. 5 by cutting out one pixel area thereof, and parts corresponding to those in FIG. 1 are given the same reference numerals.
Omit duplicate explanations. In this embodiment, the control capacitor electrode 2 overlaps the entire length of the cross gap Ga between the sub-pixel electrodes, and is shaped like a thick cross by removing a predetermined amount from each of the four corners of a substantially rectangular pixel area in this example. Made of ITO. Therefore, in the gap between the sub-pixel electrodes, the liquid crystal is driven by the voltage applied to the control capacitor electrode 2. According to the first aspect of this invention,
Additional capacitor electrode 12 and sub-pixel electrode 4i (i=1~
4), an additional capacitor CSi using the insulating film 11 as a dielectric is formed as shown in FIG. That is, the sub-pixel electrodes 41 to 44 are separated from each other by a cross-shaped gap Ga.
An additional capacitor electrode 12 is formed thereon with an insulating film 11 made of silicon nitride (SiNx) or the like in a U-shape, made of aluminum in this example. The U-shaped additional capacitor electrode 12 is formed to pass over these sub-pixel electrodes 41 to 44 one after another. Furthermore, the additional capacitor electrodes 12 of each pixel in each row are sequentially connected by wiring (not shown), and a constant potential is applied during operation of the liquid crystal display element.

The electrical equivalent circuit of the pixel in FIG. 5 is shown in FIG. That is, since the additional capacitor CSi is held at a constant potential by wiring (not shown), it is equivalently connected in parallel with the liquid crystal capacitor CLCi. The driving voltage Va applied between the control capacitor electrode 2 and the common electrode 6 is determined by the control capacitor capacitance CCi, the liquid crystal capacitor capacitance CLCi, and the additional capacitor capacitance CS.
The voltage VLCi that is divided by the combined capacitance CLCi +CSi of i and is applied to the liquid crystal capacitor CLCi is

[0017]

It is expressed as [Equation 3]. In the conventional example, the liquid crystal capacitor voltage VLCi
was set by adjusting only the control capacitor capacitance CCi, but in the present invention, adjustment of the additional capacitance CSi is also used. For example, when the voltage VLC4 across the capacitor CLC4 is set to the smallest among VLC1 to VLC4, CC4 is made smaller and CS4 is set larger, so that CC4/(C
LC4+CS4+CC4) is set to the smallest value than when i=1 to 3. In this way, the additional capacitor C
When Si is used in combination, the control capacitor capacitance CCi is not made so small as in the conventional case, and the influence of manufacturing variations can be kept to a level where it does not become a problem. Additional capacitor electrode 12
Even if the position of the sub-pixel electrode 4i is shifted due to manufacturing variations, it is desirable that the area overlapping with each sub-pixel electrode 4i does not change much, so that manufacturing variations in capacitance values can be suppressed to a small level.

Since the thick cross-shaped control capacitor electrode 2 overlaps the gap between the sub-pixel electrodes, the control capacitor electrode 2 and the common electrode 6 are connected to the liquid crystal above these gaps.
The voltage Va applied between the insulating films 3 and 11 and the liquid crystal 7 is divided between the insulating films 3 and 11 and the liquid crystal 7, and depending on the magnitude of the voltage Va, this liquid crystal portion is controlled to transmit or block light, and is connected to the sub-pixel electrode. Similarly, it is made to contribute to multi-gradation display. This improves the aperture ratio of the pixel.

Note that among the control capacitors CC1 to CC4, the maximum voltage is applied to the liquid crystal in the region of the sub-pixel electrode 41 that forms the maximum capacitance. When the voltage Va supplied to the pixel is constant, in order to make this maximum voltage as large as possible, the control capacitor electrode 2 should be shaped so that it faces and overlaps the entire surface of the subpixel electrode 41. and the control capacitor electrode 2 can also be electrically connected. The examples described below correspond to this case,
This is equivalent to making the capacitance of the control capacitor CC1 infinite. In that case, control capacitor electrode 2 and subpixel electrode 4
The overlap with 1 may be arbitrary, and there may be no overlap. Design of voltage vs. transmittance characteristics The voltage vs. transmittance characteristics of subpixels F1 to F4 are determined by the additional capacitor capacitance CSi and the control capacitor capacitance CC as described above.
By controlling by i, the degree of freedom in designing the transmittance characteristics of the entire pixel increases, and various preferable characteristics can be obtained. (B) By setting the characteristics of the sub-pixels F1 to F4 at intervals in the voltage axis direction as shown in A of FIG. 8, the overall characteristics of the pixels can be made step-like as shown in B of FIG. can. (b) The characteristics of the sub-pixels F1 to F4 are as shown in A in FIG. 9, where the applied voltage Va is when the light transmittance of the sub-pixel Fi is 90% and when the light transmittance of the sub-pixel Fi+1 is 10%. subpixel F1 so that the applied voltage Va of
If the characteristics of ~F4 are set, the overall characteristics of the pixel are as shown in Figure 9.
As shown in B of FIG. 2, the pixel becomes a straight line, and its slope can be made gentler than when the pixel is not divided into subpixels. In this way, the deviation of the transmittance of each sub-pixel Fi from the straight line in A of FIG. 9 results in a smaller compressed characteristic in the overall characteristic of B in FIG. 9, and the linearity is improved. Furthermore, the linear region of the overall characteristic of the pixel is also wider than the individual characteristics in A of FIG. Therefore, when a liquid crystal display element is normally used as a video signal display, so-called γ (gamma) correction, which corrects linearity by adjusting the applied voltage value, is not necessary. In addition, since the voltage vs. transmittance characteristics are gentle,
When performing video display or the like, it is possible to increase the margin for output deviation of the drive IC that supplies signals to the source bus. When the voltage vs. transmittance characteristics of each sub-pixel are set as shown in A of FIG. 9, the voltage at which the pixel transmittance is saturated can be suppressed to a lower level than in the case of B of FIG. 8, as shown in B of FIG.
Lower voltage driving becomes possible. (c) As an essential characteristic of a TN type liquid crystal display element for color display, the voltage versus transmittance characteristics of the pixel differ for each color of R, G, and B based on optical rotation dispersion, as shown in A in Figure 10. However, according to this invention, the degree of freedom in designing the voltage vs. transmittance characteristics of the pixel has increased, making it easier to design the desired characteristics, and as shown in B in FIG. 10, each color is almost the same. Can be corrected according to characteristics. Note that this correction applies even if a pixel is not divided into subpixels, since the liquid crystal capacitor voltage VLC is adjusted by the control capacitor capacitance CC and additional capacitance CS.
Since =Va CC /(CLC+CS +CC) can be adjusted for each color, the same correction as above is possible.

Although the explanation so far has shown the case where a pixel is divided into four sub-pixels, it is clear that it can generally be divided into n (an integer of 2 or more). According to the second aspect of the invention, a plurality of subpixel regions obtained by dividing each pixel are arranged concentrically with each other. For example, as shown in FIG. 11 with the same reference numerals assigned to those corresponding to those in FIG. 5, an ITO pixel electrode is concentrically divided into two rectangular loop-shaped subpixel electrodes 41 and 42 by a rectangular loop gap Ga. ing. A rectangular window W is formed in the center of the subpixel electrode 41 . As shown in FIG. 12, the control capacitor electrode 2 is formed in a hole 2a so as not to overlap with approximately half of the sub-pixel electrode 41.
is formed, and sub-pixel electrodes 41 and 42 are formed in areas other than the hole 2a.
The pixel is formed of ITO over almost the entire area of the pixel so as to face the rectangular window W with the insulating film 3 interposed therebetween. In this example, the region of the control capacitor electrode 2 that is electrically exposed through the insulating film 3 at the central window W defines a sub-pixel region F1. Therefore, the control capacitor electrode 2 and the common electrode 6
When the driving voltage Va applied between the two subpixel electrodes 41 and 41 is increased, the subpixel region F1 of the center window W is first turned on, and then the subpixel region F2 defined by the subpixel electrode 41 is additionally turned on. Finally, the subpixel region F3 defined by the subpixel electrode 42 is additionally turned on. Even if the on-area increases or decreases in this way, the center position of the on-area is fixed at approximately the center of the pixel, so a liquid crystal display element in which each pixel is configured in this way can produce images that are easy to see for human eyes. Experiments have confirmed that the display quality of the image is better than that in the case where the pixel electrodes are divided into rows and columns as shown in FIG. Other Embodiments A plan view of an embodiment according to the combination of the first and second aspects of the present invention in which each pixel is configured with two sub-pixels and the first sub-pixel electrode is connected to a control capacitor electrode. A-
A cross-sectional view and B-B cross-sectional view are shown in Figures 13, 14, and 15.
In the figure, parts corresponding to those in FIGS. 5 and 6 are denoted by the same reference numerals. A light shielding layer 13 is formed in an island shape on the transparent substrate 1. The light shielding layer 13 prevents light from entering the TFT. Silicon oxide (SiO
An insulating film 14 as shown in 2) is formed, and a loop-shaped control capacitor electrode 2 is formed thereon using ITO or the like. An insulating film 15 such as silicon oxide is formed on the control capacitor electrode 2 and the insulating film 14, and a source bus 21, a source electrode 21a, a drain electrode 22, and subpixel electrodes 41 and 42 are formed thereon using ITO or the like. . The subpixel electrode 41 is the insulating film 15 on the control capacitor electrode 2.
The contact hole 15H formed in the contact hole 15H is formed in contact with the control capacitor electrode 2, and is electrically connected to the control capacitor electrode 2. Further, the subpixel electrode 41 is extended to the drain electrode 22 of the TFT 8 and connected to each other. Source electrode 21
A semiconductor layer 23 made of amorphous silicon or the like is formed spanning the electrode 22 and the drain electrode 22 . A gate insulating film 24 made of silicon nitride (SiNx) or the like is formed over the semiconductor layer 23 and the sub-pixel electrodes 41 and 42.
Thereon, a gate bus 25, a gate electrode 25a, and an additional capacitor electrode 12 are simultaneously formed of aluminum, for example.

As mentioned above, the TFT 8 and the sub-pixel electrode 41
, 42, etc., is disposed opposite to a transparent substrate 5 having a common electrode 6 formed on its inner surface, and a liquid crystal 7 is sealed between these substrates. At the intersection between the source bus 21 and the gate bus 25 and at the intersection between the source bus 21 and the additional capacitor electrode 12, there are island-shaped semiconductor layers 23a and 23.
b is formed in a stacked manner under the gate insulating film 24 to improve insulation. A TFT 8 is formed near the intersection of the gate bus 25 and the source bus 21 . Left and right source bus 2
A sub-pixel electrode 41 with a small area and a sub-pixel electrode 42 with a large area are formed in a region surrounded by the gate bus 1 and the upper and lower gate buses 25. The control capacitor electrode 2 is formed in a loop shape, surrounding the periphery of the sub-pixel electrode 42 and overlapping with the periphery. As already mentioned, the subpixel electrode 41 and the control capacitor electrode 2 are electrically connected to each other through the contact hole 15H.

Since the control capacitor electrode 2 connected to the sub-pixel electrode 41 is arranged concentrically surrounding the sub-pixel electrode 42, when a certain voltage Va is applied through the TFT 8 when driving the liquid crystal display element, the sub-pixel electrode 2 is first connected to the sub-pixel electrode 41. The region of the control capacitor electrode 2 surrounding the pixel 42 (including the sub-pixel 41 region) is turned on (light transmission), and when the voltage Va is increased by a predetermined value, the region of the sub-pixel 42 is also turned on. When the display area of the pixels is controlled concentrically as described above, the display quality is better than when the sub-pixels are arranged vertically and horizontally as shown in FIG.

[0023] The additional capacitor electrode 12 is connected to the gate insulating film 2.
4 on the sub-pixel electrode 42. The additional capacitor electrode 12 has an H-shape in this embodiment, and its horizontal portion 12C extends horizontally across approximately the center of the control capacitor electrode 2, and has vertical portions 1 at both ends thereof.
2A and 12B are provided. Vertical parts 12A, 12B
extends overlapping the side edges of the control capacitor electrode 2. Both ends of the horizontal portion 12C are extended and connected to the additional capacitor electrodes 12 of adjacent pixels in the extending direction of the gate bus 25. During operation of the liquid crystal display element, these additional capacitor electrodes 12 of all pixels are maintained at a predetermined constant potential by applying a constant DC voltage to the extended end of the horizontal portion 12C. The control capacitor electrode 2 is arranged so as to overlap the gap Ga between the sub-pixel electrodes 41 and 42.

Control capacitor electrode 2 and subpixel electrode 42
However, since the control capacitor electrode 2 and the sub-pixel electrode 41 are electrically short-circuited, the control capacitor CC1 is not formed (
Alternatively, it can be seen that CC1 is formed but both ends are short-circuited). An additional capacitor CS2 is formed between the additional capacitor electrode 12 and the sub-pixel electrode 42. In this example, a subpixel electrode 41 and an additional capacitor electrode 12
No additional capacitance CS1 is formed directly between the control capacitor electrode 2 (connected to the sub-pixel electrode 41) instead.
and the additional capacitor electrode 12. A liquid crystal capacitor CLC is connected between the sub-pixel electrode 41 and the common electrode 6.
1a is a liquid crystal capacitor C between the control capacitor electrode 2 and the common electrode 6 facing the gap Ga between the sub-pixel electrodes.
A liquid crystal capacitor CLC2 is formed between the sub-pixel electrode 42 and the common electrode 6. Therefore, the electrical equivalent circuit of the pixel in the embodiments shown in FIGS. 13, 14 and 15 is as shown in FIG.

In the example of FIG. 13, the dimension at which the control capacitor electrode 2 overlaps the peripheral edge of the sub-pixel electrode 42 is 12 μm.
However, if a configuration is adopted in which additional capacitance is not used as in the conventional example, the dimensions of this overlap would be, for example, 1.
It needs to be extremely small, about 5 .mu.m, and it is difficult to ensure a manufacturing margin against pattern misalignment. Figure 13
As can be seen, the vertical portion 12 of the additional capacitor electrode 12
Since A and 12B overlap both side edges of the control capacitor 2 at the middle in the width direction, the additional capacitor electrode 1
Regarding manufacturing positional deviations in the vertical and horizontal directions of 2.
Both the area overlapping with the sub-pixel electrode 42 and the area overlapping with the control capacitor electrode 2 (connected to the sub-pixel electrode 41) hardly change. Therefore, additional capacitor capacitance CS1,C
S2 is kept approximately constant. Note that this additional capacitor C
S1 and CS2 act as storage capacitors for holding signal charges, and contribute to improving display stability during high-temperature operation where leakage current increases.

In FIGS. 13, 14, and 15, the control capacitor electrode 2 is formed to surround the sub-pixel electrode 42, but as shown in FIG. 17, the control capacitor electrode 2 corresponding to FIG. A capacitor electrode 2 is arranged in the center in the form of an island, and a sub-pixel electrode 4 is arranged so as to overlap and surround the periphery of the capacitor electrode 2.
2 may be formed. In that case, as the applied voltage Va is increased, the central sub-pixel region is turned on, and then the sub-pixel regions on its outer periphery are also turned on.

Furthermore, as shown only in cross section in FIG. 18, the source electrode 21a and drain electrode 22 of the TFT 8 in the embodiments of FIGS. 13, 14, and 15 are formed in the same layer as the control capacitor electrode 2, and the subpixel It is also possible to form the electrode 41 and the control capacitor electrode 2 into a continuous integral structure. In the embodiments shown in FIGS. 13, 14, and 15, the additional capacitor electrode 12 is provided on the sub-pixel electrode 42, but in the embodiments shown in FIGS.
9 and 20, it may be provided on the same surface as the control capacitor electrode 2 under the sub-pixel electrodes 41 and 42. That is, in the embodiment shown in FIGS. 19 and 20, a passage 2A is formed by removing a part of the rectangular loop-shaped control capacitor electrode 2 in FIG. The vertical portions 12A and 12B of the H-shaped electrode 12 are arranged on the outside and inside of the square loop-shaped electrode 2, respectively. Further, in this embodiment, the sub-pixel electrode 41 is formed so that its both sides overlap with the side edges of the control capacitor electrode 2 and the additional capacitor electrode 12, and has a distance Ga from the long side of the substantially rectangular sub-pixel electrode 42. and extends parallel to each other along almost the entire length. Both ends of the vertical portion 12A of the H-shaped additional capacitor electrode 12 are extended and connected to the vertical portions 12A of the additional capacitor electrodes of the vertically adjacent pixels, and the additional capacitor electrode 12 is maintained at a constant potential during operation of the liquid crystal display element. be done. The connection equivalent circuit of each capacitor in this embodiment is also exactly the same as that shown in FIG.

In each of the above-mentioned embodiments, the case is shown in which additional capacitors CS1, CS2, . . . are provided for all the sub-pixel electrodes 41, 42, . There is no need to connect an additional capacitor. For example, FIGS. 13, 14 and 1
A simplified embodiment in which the additional capacitor CS1 is omitted from the embodiment shown in FIG. 5 is shown in FIGS. 21, 22, and 23. In this embodiment, the additional capacitor electrode 12 consists of one side edge of the substantially rectangular sub-pixel electrode 42 and the gate insulating film 2.
They are simultaneously formed of the same material (for example, aluminum) in parallel with the gate bus 25 so as to overlap with each other through the gate bus 25. The subpixel electrode 41 is formed in the contact hole 15H formed in the insulating film 15 as in the embodiments of FIGS. 13, 14, and 15.
It is connected to the control capacitor electrode 2 through. The control capacitor electrode 2 and the additional capacitor electrode 12 do not overlap each other, so that in this embodiment no additional capacitor is connected to the sub-pixel electrode 41. The electrical equivalent circuit of the pixel in this embodiment is the same as that in FIG. 16 with the additional capacitor CS1 removed.

Similarly, a simplified embodiment in which the additional capacitor CS1 is removed from the embodiment shown in FIGS. 19 and 20 is shown in FIGS. 24, 25, and 26. In this embodiment, the additional capacitor electrode 12 is formed of ITO on the same surface as the control capacitor electrode 2 and extends in the same direction as the source bus 21 so as to overlap with the sub-pixel electrode 42 . The subpixel electrode 41 is connected to the control capacitor electrode 2 through a contact hole 15H formed in the insulating film 15, but does not overlap with the additional capacitor electrode 12. Therefore, no additional capacitor is connected to the sub-pixel electrode 41, and the electrical equivalent circuit of the pixel is the same as that in FIG. 16 with the additional capacitor CS1 removed.

As described above, the effect of the additional capacitor according to the principle of the first aspect of the present invention is that it increases the degree of freedom in designing the control capacitor for the sub-pixel electrode to which the additional capacitor is connected. Therefore, FIGS. 21, 22 and 23
As is clear from the embodiment and the embodiments of FIGS. 24, 25, and 26, the principle of the present invention cannot be applied to subpixel electrodes in which control capacitors are not connected in series.
There is no need to provide an additional capacitor. However, by connecting an additional capacitor, the capacitance of the liquid crystal capacitor increases, and a correspondingly larger amount of charge can be stored.As is well known, this has the effect of slowing down the voltage drop in response to an increase in leakage current at high temperatures.

[0031]

As explained above, according to the first aspect of the present invention, in at least one subpixel Fi among a plurality of subpixels, the additional capacitor CSi is connected to the liquid crystal capacitor CLCi together with the conventional control capacitor CCi. This is used to determine the voltage VLCi across the subpixel, and the degree of freedom in designing the voltage versus transmittance characteristic of that subpixel increases accordingly. Therefore, it is no longer necessary to reduce the area of the control capacitor electrode 2 overlapping with the sub-pixel electrode 4i to such an extent that the influence of capacitance error due to pattern misalignment becomes a problem, and each liquid crystal capacitor voltage VLCi can be set more accurately than before. Therefore, multi-gradation display of pixels can be performed more accurately than before, and display quality can be improved. By using this additional capacitor together, the voltage vs. transmittance characteristics of each subpixel can be set with high precision, making it easy to improve the linearity of the overall voltage vs. transmittance characteristics of the pixel, and linearity correction. Therefore, the so-called γ correction that has been performed in the past becomes unnecessary. Further, for the same reason, deviations in voltage versus transmittance characteristics between pixels of different colors caused by optical rotation dispersion in a color TN type liquid crystal display element can be easily corrected.

According to the second aspect of the present invention, since each pixel is configured such that a plurality of sub-pixels are arranged concentrically, the display quality of the image can be improved.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing a pixel configuration in a conventional liquid crystal display element.

FIG. 2 is a diagram showing capacitance formed between each electrode in FIG. 1;

FIG. 3 is a diagram showing an electrical equivalent circuit of the pixel in FIG. 1;

4 is a diagram showing the applied voltage Va vs. liquid crystal capacitor voltage VLCi characteristic in the subpixel Fi (i=1 to 4) in FIG. 1; FIG.

FIG. 5 is a perspective view showing a pixel configuration in an embodiment based on the first aspect of the invention.

6 is a diagram showing capacitance formed between each electrode in FIG. 5. FIG.

FIG. 7 is a diagram showing an electrical equivalent circuit of the pixel in FIG. 5;

8A is a diagram showing an example of the voltage vs. transmittance characteristic of each subpixel in FIG. 5, and B is a diagram showing the overall voltage vs. transmittance characteristic of A. FIG.

9A is a diagram showing another example of the voltage vs. transmittance characteristic of each subpixel in FIG. 5, and B is a diagram showing the overall voltage vs. transmittance characteristic of A. FIG.

[Fig. 10] A is R in a TN type color liquid crystal display element,
FIG. 3 is a diagram showing general voltage versus transmittance characteristics of each pixel of G and B, and B is a diagram showing general voltage versus transmittance characteristics of each pixel of G and B;
FIG. 3 is a diagram showing an example of voltage versus transmittance characteristics of each pixel in FIG.

FIG. 11 is a perspective view showing an example of a pixel configuration based on a second aspect of the invention.

FIG. 12 is a plan view of the control capacitor electrode in FIG. 11;

FIG. 13 is a plan view showing essential parts of another embodiment of the invention.

FIG. 14 is a sectional view taken along line AA in FIG. 13;

FIG. 15 is a sectional view taken along line BB in FIG. 13;

16 is a diagram showing an electrical equivalent circuit of the pixels in FIGS. 13, 14, and 15. FIG.

17 is a simplified plan view of a modified embodiment corresponding to FIG. 13; FIG.

18 is a sectional view showing a modification of the embodiment of FIGS. 13, 14 and 15. FIG.

FIG. 19 is a plan view showing still another embodiment of the invention.

FIG. 20 is a sectional view taken along line AA in FIG. 19;

FIG. 21 is a plan view of still another embodiment.

FIG. 22 is a sectional view taken along line AA in FIG. 21;

FIG. 23 is a sectional view taken along line BB in FIG. 21;

FIG. 24 is a plan view of still another embodiment.

25 is a sectional view taken along line AA in FIG. 24. FIG.

26 is a sectional view taken along line BB in FIG. 24. FIG.

Claims (14)

[Claims] 1. At least one sub-pixel electrode occupying a part of the area of each pixel is disposed on a first insulating film formed on a first substrate, facing a common electrode on a second substrate with a liquid crystal interposed therebetween. A control capacitor electrode is provided which is arranged at least partially opposite to the at least one sub-pixel electrode with the first insulating film interposed therebetween, so that the at least one sub-pixel electrode is connected to the common electrode. A liquid crystal display element having the pixel configured to form a control capacitor connected in series to a liquid crystal capacitor formed between the pixel and the control capacitor, and a driving voltage being supplied between the control capacitor electrode and the common electrode. An additional capacitor electrode is formed to face the at least one sub-pixel electrode via a second insulating film, thereby forming an additional capacitor equivalently parallel to the liquid crystal capacitor. A liquid crystal display element. 2. At least one sub-pixel electrode occupying a part of the area of each pixel is arranged on an insulating film formed on the first substrate and facing a common electrode on the second substrate with the liquid crystal interposed therebetween. , a control capacitor electrode at least partially facing the at least one sub-pixel electrode with the insulating film interposed therebetween is provided, whereby the at least one sub-pixel electrode is formed between the at least one sub-pixel electrode and the common electrode. A liquid crystal display element having the pixel configured to form a control capacitor connected in series to a liquid crystal capacitor, and a driving voltage being supplied between the control capacitor electrode and the common electrode, the two sub-pixel electrodes and the control capacitor electrode are arranged concentrically so that one substantially surrounds the other and overlaps each other at least at the periphery with the insulating film interposed therebetween;
A liquid crystal display element characterized in that this defines an island-shaped first sub-pixel region and a loop-shaped second sub-pixel region that substantially surrounds the island-shaped first sub-pixel region. 3. The first sub-pixel region is part of a region of the control capacitor electrode defined inside the second sub-pixel region, and the sub-pixel electrode substantially surrounds the first sub-pixel region. 3. The liquid crystal display element according to claim 2, wherein the liquid crystal display element is formed in a loop shape. 4. The first sub-pixel region is the at least one sub-pixel electrode disposed inside the second sub-pixel region, and the control capacitor electrode is the at least one sub-pixel electrode disposed inside the second sub-pixel region.
3. The liquid crystal display element according to claim 2, further comprising a region substantially surrounding two sub-pixel electrodes, defining said second sub-pixel region. 5. Another sub-pixel electrode separated from the at least one sub-pixel electrode by a gap,
2. The liquid crystal display element according to claim 1, wherein said another sub-pixel electrode and said control capacitor electrode are electrically connected. 6. The liquid crystal display element according to claim 5, wherein the control capacitor electrode substantially surrounds and overlaps the peripheral edge of the at least one sub-pixel electrode. 7. The liquid crystal display element according to claim 5, wherein said at least one sub-pixel electrode is formed to substantially surround and overlap a peripheral edge of said control capacitor electrode. 8. The second insulating film is formed over substantially the entire surface of the first substrate from above the at least one sub-pixel electrode, and the additional capacitor electrode is formed thereon. 1. The liquid crystal display element according to 1. 9. The liquid crystal display element according to claim 5, wherein the other sub-pixel electrode is formed integrally with the control capacitor electrode on the same plane. 10. The second insulating film is also used by the first insulating film, and the control capacitor electrode and the additional capacitor electrode are formed on the same surface.
The liquid crystal display element described above. 11. The liquid crystal display element according to claim 5, wherein the other sub-pixel electrode and the control capacitor electrode are connected to each other through a contact hole formed in the first insulating film. 12. The other sub-pixel electrode is formed on the same plane as the at least one sub-pixel electrode and separated from each other by a gap, and the control capacitor electrode has a region that overlaps the gap over substantially the entire length thereof. 6. The liquid crystal display element according to claim 5. 13. The liquid crystal display according to claim 1, wherein said additional capacitor electrode has an extension portion connected to said additional capacitor electrode of said pixel adjacent to said pixel in one direction of said row arrangement or column arrangement. element. 14. A plurality of sub-pixel electrodes each occupying a part of the area of each pixel are arranged on an insulating film formed on the first substrate and facing a common electrode on the second substrate with the liquid crystal interposed therebetween. , a liquid crystal display including a control capacitor electrode at least partially facing each of the plurality of sub-pixel electrodes via the insulating film, whereby each of the plurality of sub-pixel electrodes is formed between the plurality of sub-pixel electrodes and the common electrode. In the liquid crystal display element having the pixel configured such that a control capacitor is connected in series with each capacitor and a driving voltage is supplied between the control capacitor electrode and the common electrode, The pixel electrodes are arranged concentrically so that at least one other island-shaped one substantially surrounds one in the center and overlaps each other at least at the periphery with the insulating film interposed therebetween;
A liquid crystal display element characterized in that a central island-shaped first sub-pixel region and a loop-shaped second sub-pixel region substantially surrounding the central island-shaped first sub-pixel region are defined.