JP2764770B2 - Liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a pixel structure of a liquid crystal display element in which a pixel is divided into a plurality of sub-pixels and capable of multi-gradation display, and more particularly to improving the multi-gradation display quality and aperture ratio. Things.

[0002]

2. Description of the Related Art Japanese Patent Laid-Open Publication No.
2 “Pixel of liquid crystal display device and image in liquid crystal display device
A method for realizing a plain gray scale "is known. Immediately
In other words, as shown in FIG.
A control capacitor electrode 2 is formed on the inner surface of a transparent substrate 1 such as
On the control capacitor electrode 2 and the control capacitor electrode.
An insulating film 3 is formed on the inner surface of the transparent substrate 1 where the pole 2 is not formed.
It is formed. A quadrangular sub-divided into four on the insulating film 3
Pixel electrode 4₁To 4_FourIs formed. These subpixels
Formed on the inner surface of a transparent substrate 5 such as glass
The common electrode 6 and the sub-pixel electrode 4_i
The liquid crystal 7 is sealed between (i = 1 to 4). Control con
Denser electrode 2, sub-pixel electrode 4_iAnd the common electrode 6 is made of ITO
It is a transparent electrode made of etc. One stroke in this way
The element is the sub-pixel electrode 4₁~ 4_FourCorresponding to the sub-pixel F₁~ F
_FourIs divided into four. Each sub-pixel electrode 4_iAnd control capacitor
Control capacitor using insulating film 3 as dielectric between electrode 2
C_CiAre formed, and the sub-pixel electrode 4_iAnd the common electrode 6
Liquid crystal capacitor C having liquid crystal 7 as a dielectric between_LCiFormed
Have been. FIG. 16 shows an electrical equivalent circuit of the pixel of FIG.
Show. Code C_CiAnd C _LCiIs used to express capacitance
Then C_C1> C_C2> C_C3> C_C4 (1) Each sub-pixel electrode 4 of the control capacitor electrode 2 is
_iHas been adjusted.

The control capacitor electrode 2 is connected to a drain electrode (D) of a thin film transistor (TFT) 8 (not shown) formed on the transparent substrate 1 adjacent to the pixel of FIG. Between the control capacitor electrode 2 and the common electrode 6 a predetermined voltage V _a is applied via the TFT 8.
When TFT8 is controlled to be on, the terminal voltage V _Ci of the supply voltage V _a control capacitor C _Ci in each subpixel F _i
To be divided terminal voltage V _LCi and half of the liquid crystal capacitor C _{LC i.} V _LCi

[0004]

(Equation 1) It is expressed as By setting the capacitance of each control capacitor C _Ci as in equation (1), each liquid crystal capacitor C Ci
_{The LCi} terminal voltage V _LCi is set to _satisfy V _LC1 > V _LC2 > V _LC3 > V _LC4 (3).

As shown in FIG. 17, the voltage V supplied to the pixel
the size of _a, (i) V _LCi = 0 If the (i = 1~4) (this time V _a
= 0). (B) V _LC1 = V _U, if the V _LC2 = V _L. The voltage at which the light transmission of the liquid crystal is saturated is V _U , and the threshold voltage is V _L. V _LC3 and V _LC4 are not more than _VL . It represents a supply voltage V _a when this V _a1. (C) V _LC2 = V _U, if the V _LC3 = V _L. It represents a supply voltage V _a when this V _a2. (D) When V _LC3 = V _U and V _LC4 = _VL . V at this time
the _a represented by V _a3. (E) When V _LC4 = V _U. Representing the V _a at this time in the V _a4.

Each case exists. Supply voltage V _ai is _{0 <V a1 <V a2 <} V a3 <V a4 (4). Variable to multi-grayscale display is performed the magnitude of the supply voltage V _a.

[0007]

In THE INVENTION Problem to be Solved] prior art, in the sub-pixel F _i, when the voltage V _a to be supplied to the pixels of the V _ai, the terminal voltage V _LCi of the liquid crystal capacitor C _LCi LCD light transmission is saturated It is set equal to the voltage V _U. That is,

[0008]

(Equation 2) The area of each control capacitor C _Ci that overlaps with the sub-pixel electrode 4 _i is set so that the capacitance satisfies the expression (5). While the dividing the pixel electrode to the sub-pixel electrode 4 _i is required a certain degree of gap between adjacent subpixel electrodes, the conventional control capacitor electrode 2, a shape that does not overlap the majority of these gaps Because there is a control capacitor electrode 2
The voltage cannot be applied to the liquid crystal layer facing the gap that does not overlap with the gap, so that the effective pixel area is reduced, and the aperture ratio of the pixel is reduced.

An object of the present invention is to solve the above-mentioned conventional disadvantages and to provide a liquid crystal display element in which an aperture ratio does not decrease due to a gap between adjacent sub-pixel electrodes.

[0010]

A plurality of sub-pixel electrodes constituting each pixel and separated by a gap are formed on an insulating substrate formed on a first substrate so as to face a common electrode on a second substrate with a liquid crystal interposed therebetween. A control capacitor electrode disposed on the film and facing at least a part of the at least one of the sub-pixel electrodes with the insulating film interposed therebetween;
Forming a control capacitor connected in series with a liquid crystal capacitor formed between the two sub-pixel electrodes and the common electrode;
In a liquid crystal display device having the pixel configured to be supplied with a drive voltage between the control capacitor electrode and the common electrode, in the present invention, the control capacitor electrode includes the plurality of pixels via the insulating film. It is formed so as to include a gap between the sub-pixel electrodes, a region overlapping substantially the entire length thereof, and a region which overlaps with each of the plurality of sub-pixel electrodes by a predetermined area.

[0011]

As described above, since the control capacitor electrode is formed so as to have a region overlapping substantially the entire length of the gap between the sub-pixel electrodes, a driving voltage is applied between the common electrode and the control capacitor electrode even in the gap, The liquid crystal can be driven. Therefore, the aperture ratio is substantially improved.

[0012]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Embodiments of the present invention are designated by the same reference numerals in FIGS. 1 and 2 as those in FIGS. 14 and 15, and redundant description is omitted. In the present invention additional capacitor electrode 12 through an insulating film 11 such as a sub-pixel electrode ₄₁ to ₄ on the silicon nitride (SiN _x) it is, in this example is formed in a U-shape. In this example, the control capacitor electrode 2 is formed in a cross shape so as to overlap the gap between the sub-pixel electrodes. Additional capacitor electrode 12 and sub-pixel electrode 4 _i (i = 1 to 4)
And an additional capacitor C _Si having the insulating film 11 as a dielectric.
Is formed.

An electrical equivalent circuit of the pixel shown in FIG. 1 is represented as shown in FIG. That is, the additional capacitor C _Si is electrically connected in parallel with the liquid crystal capacitor C _LCi . Driving voltage V _a applied between the control capacitor electrode 2 and the common electrode 6 is controlled capacitance C _Ci and the liquid crystal capacitance C _LCi and the additional capacitance C _Si composite capacitance C _LCi +
The voltage V _{LCi divided} by C _Si and applied to the liquid crystal capacitor C _LCi is

[0014]

(Equation 3) Is represented by In the prior art, the liquid crystal capacitor voltage V _LCi is set only by adjusting the control capacitor capacitance C _Ci , but in the present invention, the adjustment of the additional capacitance C _Si is also used. For example, when the terminal voltage V _{LC4 of the} capacitor is V _LC1 -V
When the smallest set in _LC4, C _S4 with the C _C4 is small is set larger, thereby (6) _{C C4 / (C LC4 + C} S4 + C C4) value i =. 1 to of 3 is set to be the smallest. When the additional capacitor C _Si is used together in this way, the control capacitor capacitance C _Ci is not made so small as in the conventional case, and the effect of the manufacturing variation is kept to a small extent. Additional capacitor electrode 12
It is preferable that even if the position shifts due to manufacturing variations, the area overlapping with each sub-pixel electrode 4 _i does not change so much that manufacturing variations in capacitance values are reduced.

Since the cross-shaped control capacitor electrode 2 overlaps with the gap between the sub-pixel electrodes, the voltage V _a applied between the control capacitor electrode 2 and the common electrode 6 is applied to the liquid crystal on these gaps. Is divided by the insulating films 3 and 11 and the liquid crystal, and the liquid crystal portion is controlled to be in a light transmitting or light blocking state depending on the magnitude of the voltage V ₄ , thereby contributing to multi-tone display similarly to the sub-pixel electrode. To do. Thereby, the aperture ratio of the pixel is improved.

[0016] Incidentally, the sub-pixel electrodes 4 ₁ and the control capacitor electrode 2 may also be electrically connected. (The embodiment described later corresponds to this case.) Design of Voltage-Transmittance Characteristics The voltage-transmittance characteristics of the sub-pixels F _{1 to} F ₄ are determined by the additional capacitor capacitance C _Si and the control capacitor capacitance C _Ci as described above. By controlling, the degree of freedom in designing the transmittance characteristics of the entire pixel is increased, and various preferable characteristics can be obtained. (A) By setting the characteristics of the sub-pixels F _{1 to} F ₄ at intervals in the direction of the voltage axis as shown in FIG. 4A, the overall characteristics of the pixel are stepped as shown in FIG. 4B. be able to. (B) the characteristics of the sub-pixel F ₁ to F ₄ as shown in A in FIG. 4, the applied voltage V _a when the light transmittance of the subpixel F _i becomes 90%
The subpixel F _{i + 1} of the light transmittance such that the applied voltage V _a at which the 10% is equal, by setting the characteristics of the sub-pixel F ₁ to F _4, overall characteristics of pixels 5 As shown in B, the inclination can be made gentler than the case where the inclination is not divided into sub-pixels. In this way, the deviation of the transmittance of each pixel F _i from the straight line in A of FIG. 5 results in a smaller compressed characteristic in the overall characteristic of FIG. 5B, and the linearity is improved. Also, the linear region of the overall characteristics of the pixel is wider than the individual characteristics in FIG. For this reason, when the liquid crystal display element is used as a video signal display, so-called γ (gamma) correction for adjusting the applied voltage value to correct the linearity becomes unnecessary.

Further, since the voltage-transmittance characteristic is moderate, a margin for an output deviation of a driving IC for supplying a signal to a source bus can be increased when performing video display or the like. When the voltage-transmittance characteristic is set as shown in FIG. 5, the voltage at which the transmittance of the pixel is saturated can be suppressed lower than in the case of FIG. 4, and lower voltage driving is possible. (C) The TN type liquid crystal display element for color display has a characteristic that a voltage versus transmittance characteristic of a pixel is different for each of R, G, and B colors as shown in FIG. However, according to the present invention, the degree of freedom in designing the voltage versus transmittance characteristics of the pixel is increased, so that it is easy to design a desired characteristic. As shown in FIG. Can be corrected to characteristics. This correction can be performed even when the pixel is not divided into sub-pixels, by the control capacitor capacitance C _C and the additional capacitance C _S , so that the liquid crystal capacitor voltage V _LC = V _a C _C /
Since (C _LC + C _S + C _C ) can be adjusted for each color, the same correction as described above is possible.

In the above description, the case where a pixel is divided into four sub-pixels has been described, but in general, n (an integer of 2 or more)
Obviously, it can be divided into pieces. Other Embodiments A plan view, an AA sectional view and a BB sectional view of another embodiment of the present invention are shown in FIGS. 7, 8 and 9, respectively, and the portions corresponding to FIG. Shown. A light shielding layer 13 is formed on the transparent substrate 1. The light shielding layer 13 prevents light from entering the TFT. An insulating film 14 such as silicon oxide (SiO ₂ ) is formed on the transparent substrate 1 and the light shielding layer 13.
Is formed, and a ring-shaped control capacitor electrode 2 is formed thereon.
Is formed by ITO or the like. Control capacitor electrode 2
An insulating film 15 such as silicon oxide is formed on the insulating film 14, and a source bus 21 made of ITO or the like is formed thereon.
A source electrode 21a, the drain electrode 22, the sub-pixel electrodes 4 _1, 4 ₂ are formed. Subpixel electrodes 4 ₁ in a contact hole formed in the insulating film 15 on the control capacitor electrode 2 is formed in close contact with the control capacitor electrode 2 is in a conductive state with each other. The sub-pixel electrode 4 ₁ is extended up to the drain electrode 22 are connected to each other. A semiconductor layer 23 such as amorphous silicon is formed over the source electrode 21a and the drain electrode 22. A gate insulating film 24 such as silicon nitride (SiN _x ) is formed over the semiconductor layer 23 and the sub-pixel electrodes 4 ₁ and 4 ₂ , and a gate bus 25, a gate electrode 25 a and an additional capacitor electrode 12 are formed thereon. You.

As described above, the TFT 8, the sub-pixel electrode 4 ₁ ,
4 ₂ such as a transparent substrate 1 formed is is arranged opposite to the transparent substrate 5 which common electrode 6 is formed on the inner surface, the liquid crystal 7 is sealed between the substrates. On the source bus 21, a semiconductor layer 23a and a gate insulating film 24 are sequentially stacked, and a gate bus 25 is formed on the source bus 21 so as to cross the source bus 21. The TFT 8 is formed near the intersection. In a region surrounded by the right and left source bus 21 and the upper and lower gate bus 25 and the sub-pixel electrodes 4 ₁ small-area subpixel electrodes 4 ₂ large area is formed. The control capacitor electrode 2 is formed in a loop shape overlaps with the peripheral portion surrounds the peripheral edge of the subpixel electrodes 4 _2. The sub-pixel electrodes 4 ₁ and the control capacitor electrode 2 are electrically connected to each other by a contact hole as already mentioned.

[0020] With this arrangement of subpixel electrodes 4 ₁ and the control capacitor electrode 2 connected thereto concentrically surrounding the subpixel electrode 4 _2, was placed subpixel electrodes as shown in FIG. 1 vertically, laterally It has been experimentally confirmed that the display quality is better than the case. The additional capacitor electrode 12 is a gate insulating film 2
4 through is formed on the subpixel electrodes 4 _2. Further, the control capacitor electrode 2 is disposed so as to overlap with the gap between the sub-pixel electrodes 4 ₁ and 4 ₂ .

[0021] While control capacitor C _C2 is formed between the control capacitor electrode 2 and the subpixel electrode 4 _2, since the control capacitor electrode 2 and the subpixel electrode 4 ₁ is electrically shorted, the control capacitor C _C1 is not formed. (Alternatively, it can be seen that C _C1 is formed but both ends are short-circuited.) Additional capacitor electrode 12 and sub-pixel electrode 4
₂ , an additional capacitance C _S2 is formed. In this example, direct additional capacitance C _S1 without formation, the control capacitor electrode 2 (connected with the sub-pixel electrode 4 ₁₎ instead and the additional capacitance electrode between the subpixel electrodes 4 ₁ and the additional capacitance electrode 12 12 is formed. The additional capacitor electrode 12 is provided on the source bus 21 with the semiconductor layer 23 b and the gate insulating film 2.
4 are sequentially crossed with the source bus 21. Liquid crystal capacitor C _LC1A between the subpixel electrodes 4 ₁ and the common electrode 6 is,
Liquid crystal capacitor C between the liquid crystal capacitor C _LC1b between the control capacitor electrode 2 and the common electrode 6 facing the gap between the sub-pixel electrodes, also a sub-pixel electrode 4 ₂ and the common electrode 6
_LC2 is formed respectively. Therefore, the electrical equivalent circuit of the pixel in the embodiment of FIGS. 7, 8 and 9 is as shown in FIG.

[0022] In the example of FIGS. 7, 8 and 9, a dimension control capacitor electrode 2 is overlapped with the peripheral edge portion of the subpixel electrode 4 ₂ 1
If the additional capacitance is not used as in the conventional example, the overlapped size is extremely small, for example, about 1.5 μm, so that a manufacturing margin for a pattern shift or the like cannot be obtained. As can be seen from FIG. 7, for the positional deviation of the vertical and lateral directions manufacture of additional capacitor electrode 12, the sub-pixel electrodes 4 ₂ and the overlap area and the control capacitor electrode 2 (connected to the subpixel electrode 4 ₁ ) And the overlapping area is devised so that it hardly changes. Therefore, the additional capacitor capacities C _S1 and C _S2 are kept substantially constant with respect to manufacturing variations due to pattern shifts and the like.

As is well known, this additional capacitor functions as a storage capacitor for holding signal charges, and contributes to improvement of display stability at high temperature operation. As shown in FIG. 11, omitted subpixel electrodes 4 ₁ 7, an enlarged view of the control capacitor electrode 2 sub-pixel electrode 4
Double as _1, it can be formed in the same layer as the control capacitor electrode 2 and the source electrode 21a and the drain electrode 22 of the TFT 8.

In the embodiments shown in FIGS. 7, 8 and 9, the sub-pixel electrode 4
_{Although the} additional capacitor electrode 12 is provided on the sub-pixel electrode 4, the additional capacitor electrode 12 may be provided on the same layer as the control capacitor electrode 2 below the sub-pixel electrodes 4 ₁ and 4 ₂ as shown in FIGS.

[0025]

[Effect of the Invention] This invention control capacitor electrode 2 is provided so as to overlap with the gap between the sub pixel electrodes 4 _i, the drive voltage to the liquid crystal facing the gap are applied by the control capacitor electrode 2. That is, since the control capacitor electrode 2 can function as one sub-pixel electrode, the aperture ratio of the pixel can be increased accordingly.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a principle configuration of a pixel in an embodiment of the present invention.

FIG. 2 is a diagram showing a capacitance formed between electrodes of FIG. 1;

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

FIG. 4 is a diagram illustrating an example of a voltage versus transmittance characteristic of the pixel and the sub-pixel in FIG.

5 is a diagram illustrating another example of the voltage versus transmittance characteristics of the pixel and the sub-pixel in FIG.

FIG. 6A shows R, 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, where B is R, G, and B in the liquid crystal display device of the present invention.
FIG. 4 is a diagram showing an example of a voltage versus transmittance characteristic of each pixel of FIG.

FIG. 7 is a plan view of another embodiment of the present invention.

FIG. 8 is a sectional view taken along line AA of FIG. 7;

FIG. 9 is a sectional view taken along line BB of FIG. 7;

FIG. 10 is a diagram showing an electrical equivalent circuit of the pixel in FIG. 7;

FIG. 11 is a sectional view showing a modification of the embodiment of FIG. 7;

FIG. 12 is a plan view of still another embodiment of the present invention.

13 is a sectional view taken along line AA of FIG.

FIG. 14 is a perspective view showing a principle configuration of a pixel in a conventional liquid crystal display element.

FIG. 15 is a diagram showing a capacitance formed between each electrode of FIG. 14;

16 is a diagram showing an electrical equivalent circuit of the pixel in FIG.

17 is a diagram showing an applied voltage V _a pair of liquid crystal capacitor voltage V _LCi characteristic in the sub-pixel F _{i (i} = 1~4) of FIG. 14.

────────────────────────────────────────────────── ─── Continuation of front page (56) References JP-A-63-170692 (JP, A) JP-A-2-12 (JP, A) JP-A-3-24635 (JP, U) (58) Survey Field (Int.Cl. ⁶ , DB name) G02F 1/1343

Claims (1)

(57) [Claims] 1. A plurality of sub-pixel electrodes constituting each pixel, which are separated from each other by a gap, are disposed on an insulating film formed on a first substrate to face a common electrode on a second substrate with a liquid crystal interposed therebetween. And a control capacitor electrode at least partially opposed to at least one of the sub-pixel electrodes via the insulating film, whereby the at least one sub-pixel electrode is provided between the at least one sub-pixel electrode and the common electrode. In a liquid crystal display element having a pixel configured to form a control capacitor connected in series to a liquid crystal capacitor to be formed and to be supplied with a drive voltage between the control capacitor electrode and the common electrode, The capacitor electrode includes a gap between the plurality of sub-pixel electrodes via the insulating film, a region overlapping substantially the entire length thereof, and a bulk having a predetermined area with each of the plurality of sub-pixel electrodes. A liquid crystal display device comprising: