JPH06235938A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To provide a liquid crystal display device allowing uniform display even when the auxiliary capacity differs. CONSTITUTION:Part or all of the relative position of an auxiliary capacity electrode 16 forming the auxiliary capacity and a variable auxiliary capacity electrode 31 is made equal to the relative position of a source electrode 9 against a gate electrode 3. The auxiliary capacity by the auxiliary capacity electrode 16 and the variable auxiliary capacity electrode 31 is made to correspond to the overlap quantity of the gate electrode 3 and the source electrode 9, and the magnitude of the auxiliary capacity is increased or decreased in response to the increase or decrease of the overlap quantity of the source electrode 9 and the gate electrode 3. The change of the parasitic capacity for each divided area can be offset, the change of the picture element potential can be kept constant even when the parasitic capacity of TFT11 differs, and no flicker or no display irregularity is observed.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device capable of uniform display.

[0002]

2. Description of the Related Art In recent years, as electronic devices have become smaller, lighter and consume less power, flat panel displays have been researched in the field of displays as an alternative to cathode ray tubes (CRTs). , Is being actively developed. And, of these flat panel displays, the liquid crystal display is capable of displaying a large area, and full-color display is relatively easy.
It is attracting attention because of its low current and low voltage operation.

Liquid crystal displays have various operation systems according to their purposes, and the active matrix system can display full-color moving images with high resolution. In this active matrix system, the intersections of electrodes arranged in a matrix form one pixel, and a switching element is provided for each pixel. In addition, this switching element allows nonlinear diode type and thin film transistor (Thin Film Transistor)
sistor: TFT), but especially TF
Research and development of T is actively carried out.

Next, a general structure of the liquid crystal display device is shown in FIG.
And it demonstrates with reference to FIG.

As shown in FIGS. 4 and 5, the array substrate 1 has a gate electrode 3 formed on a first transparent insulating substrate 2 such as glass, and the gate insulating film 4 and the semiconductor on the gate electrode 3. The films 5 are sequentially formed, and the drain electrode 7 is formed on the semiconductor film 5 via the low resistance semiconductor film 6 and the source electrode 9 is formed on the low resistance semiconductor film 8 to form the TFT 11. .

The gate electrode 3 is provided with a gate line 12, and the drain electrode 7 is provided with a drain line 13
It is installed in the direction intersecting with.

For the source electrode 9, for example, ITO is used.
A transparent pixel electrode 14 such as (Indium Tin Oxide) is connected thereto, and an auxiliary capacitance electrode 16 is provided on the pixel electrode 14 so as to face the gate line 12 substantially in parallel with the gate insulating film 4 interposed therebetween.

Further, an insulating protection film (not shown) for protecting the TFT 11 and the like is formed on the TFT 11.

On the other hand, as shown in FIG. 5, a counter substrate 21 is provided so as to face the array substrate 1 and substantially parallel to the array substrate 1.

This counter substrate 21 is a light-shielding layer called black matrisk on a second transparent insulating substrate 22 such as glass.
23 is formed, a colored layer 24 is formed as necessary so as to cover the window opened in the light shielding layer 23, and a smooth layer (not shown) is formed on the light shielding layer 23 and the colored layer 24 as necessary. ,
The counter electrode 25 is formed on this smooth layer.

Further, an alignment film (not shown) is applied to each of the array substrate 1 and the counter substrate 21 in order to align the liquid crystal, and the array substrate 1 is opposed to these alignment films.
Further, the counter substrate 21 is attached to the substrate 1, and the liquid crystal 26 is sealed between the array substrate 1 and the counter substrate 21. Further, a deflection plate (not shown) is attached to the outside of the array substrate 1 and the counter substrate 21.

[0012]

Here, as shown in FIGS. 4 and 5, the gate electrode 3 and the source electrode 9 of the TFT 11 have a region where they overlap with each other via the semiconductor film 5 and the low resistance semiconductor film 8. Therefore, the parasitic capacitance Cgs is formed, and assuming that the pixel capacitance of the pixel electrode 14 is C _LC and the auxiliary capacitance Cs of the auxiliary capacitance electrode 16, the equivalent circuit shown in FIG. 6 is formed.

Considering the case where a pulse voltage is applied to the gate electrode 3 in the equivalent circuit shown in FIG. 6, the gate potential is high within the selection time, and the resistance between the source electrode 9 and the drain electrode 7 decreases, The pixel capacitance C _LC is charged to the signal potential. At this time, the parasitic capacitance Cgs is also charged.

After that, the non-selection time comes, the gate potential decreases, the resistance of the TFT 11 increases, and the operation of holding the charge charged in the pixel capacitance C _LC is performed. Here, in general, the gate potential Vg at the time of selection is higher than the signal potential that is the pixel potential, and the gate potential at the time of non-selection is lower than the signal potential that becomes the pixel potential. Therefore, the gate of the parasitic capacitance Cgs is selected and selected. The potential relationship between the electrode 3 and the source electrode 9 is always reversed.

Therefore, at the moment when the state changes from the selected state to the non-selected state, the charges move from the pixel capacitance C _LC to the parasitic capacitance Cgs, and the pixel potential fluctuates. The potential fluctuation Vp is expressed by the equation (1).

Vp = (Vg · Cgs) / (C _LC + Cs + Cgs) (1) Further, the pixel capacitance C _LC depends on the relative permittivity of the liquid crystal 26. Since it changes with the array, it changes with the signal voltage. Therefore, the pixel electrode 14
The amount of fluctuation of the potential of V will depend on the signal voltage.

Further, when the area of the display screen is increased, a method of dividing the display screen to form a plurality of patterns is generally adopted. In this case, the overlapping amount of the gate electrode 3 and the source electrode 9 may be different for each divided region, and the parasitic capacitance Cgs may be different for each divided region. If the parasitic capacitance Cgs is different, the pixel electrode 14
The variation amount Vp of the electric potential of V is different, which may cause display unevenness in each divided area.

In order to reduce the fluctuation amount of the potential of the pixel electrode 14, the auxiliary capacitance Cs is generally increased.

However, by increasing the auxiliary capacitance Cs, a large TFT 11 is generally required, so that the variation amount of the potential of the pixel electrode 14 tends to increase. Furthermore, T
As the FT11 becomes larger, the width of the light-shielding layer 23 becomes wider and the aperture ratio lowers, which lowers the overall display quality and imposes a heavy burden on the lighting device. Is limited.

In particular, when it is attempted to absorb the change in the parasitic capacitance Cgs for each divided area only by the auxiliary capacitance Cs, the pixel electrode 14
It is necessary that the electric potential of is hardly changed, and a very large auxiliary capacitance Cs is required.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a liquid crystal display device capable of performing uniform display even when parasitic capacitances are different.

[0022]

According to the present invention, there are provided pixel electrodes arranged in a matrix, a transistor having a gate electrode, a drain electrode and a source electrode for switching the pixel electrode, and an auxiliary capacitor for forming an auxiliary capacitance. In a liquid crystal display device including an array substrate having a capacitive electrode, one set of the auxiliary capacitive electrodes is provided, and at least a part of the electrodes on one side of the one set of the auxiliary capacitive electrodes is positioned relative to the gate electrode as a source. The auxiliary capacitance is made equal to the relative position of the electrodes, and the auxiliary capacitance is made to correspond to the overlapping amount of the gate electrode and the source electrode.

[0023]

According to the present invention, the relative position of at least a part of the electrodes on one side of the set of auxiliary capacitance electrodes forming the auxiliary capacitance is made equal to the relative position of the source electrode to the gate electrode, and this auxiliary capacitance is Since it corresponds to the overlap amount of the source electrode, the size of the auxiliary capacitance increases or decreases according to the increase or decrease of the overlap amount of the source electrode and the gate electrode, so that the change in the parasitic capacitance for each divided region can be offset. Even when the parasitic capacitances of the transistors are different, the change in pixel potential can be kept constant, and flicker and display unevenness are not visually recognized.

[0024]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the liquid crystal display device of the present invention will be described below with reference to the drawings. The parts corresponding to the conventional example will be described with the same reference numerals.

As shown in FIGS. 1 and 4, the array substrate 1 is formed on a first transparent insulating substrate 2 made of glass or the like.
For example, tantalum (Ta) is deposited to a thickness of about 0.2 μm by a sputtering method or the like, and a gate electrode 3, a gate line 12, an auxiliary capacitance electrode 16 and a connection terminal to an external circuit (not shown) are formed by a photolithography method or the like. And configure. At this time, when performing photolithography,
A notch portion 16a is formed in the auxiliary capacitance electrode 16 in a direction orthogonal to the longitudinal direction of the auxiliary capacitance electrode 16, and a narrow portion 16b having a width narrower than other portions is formed.

Next, plasma CVD (Chemical Vapor Deposit) is formed on the gate electrode 3 and the first transparent insulating substrate 2.
ion) method or the like to form a gate insulating film 4 of, for example, silicon oxide having a thickness of 0.3 μm, a semiconductor film 5 of, for example, amorphous silicon having a thickness of about 0.3 μm, such as amorphous silicon having a low resistivity. The low resistance semiconductor films 6 and 8 having a thickness of about 0.05 μm are sequentially and continuously laminated. And
The semiconductor film 5 and the low resistance semiconductor films 6 and 8 are formed in an island shape on the gate electrode 3 by a photolithography method or the like.

On the gate insulating film 4, an ITO (Indium Tin) film having a thickness of 0.1 μm is formed by, for example, a sputtering method.
Oxide) is deposited and the pixel electrode 14 is formed by the photolithography method or the like. And the notch of the auxiliary capacitance electrode 16
A portion corresponding to the upper portion of 16a forms a cutout 14a in the pixel electrode 14.

Next, for example, by a sputtering method,
Molybdenum (Mo) is deposited to a thickness of about 0.05 μm and aluminum (Al) is deposited to a thickness of about 1.0 μm.
Source electrode 9 electrically connected to the pixel electrode 18, and a variable auxiliary capacitance electrode which is electrically connected to the pixel electrode 18 and which is located on the cutout portion 16a of the auxiliary capacitance electrode 16 and constitutes a part of the auxiliary capacitance.
31, a drain electrode 7, a drain wire 13 electrically connected to the drain electrode 7, and a connection terminal to an external circuit are formed. Then, the thin film transistor (T
FT) 11.

Here, for example, as shown in FIG. 1, the relative positions of the gate electrode 3 and the source electrode 9 and a part or all of the variable auxiliary capacitance electrode 31 and the auxiliary capacitance electrode 16 forming the auxiliary capacitance. Make sure that the relative positions match.
Then, as shown in FIGS. 2A, 2B and 2C, for example, when the lateral shift amount is Δd, the shift amount Δd of do + Δd at the overlapping portion of the gate electrode 3 and the source electrode 9 is variable. Overlapping portion L of auxiliary capacitance electrode 31 and auxiliary capacitance electrode 16
The shift amount Δd of o + Δd matches.

On the other hand, the potential variation Vp of the parasitic capacitance Cgs and the pixel electrode 14 shown in (1), is represented by Vp = (Vg · Cgs) / (C LC + Cs + gs), infestation by deviation amount Δd in the relative position When DerutaCgs the variation of the capacitance Cgs, the pixel potential when adding (Cgs + ΔCgs) / (CLC + Cs + ΔCs + ΔCgs + ΔCgs) = Cgs / (C LC + Cs + Cgs) ...... (2) is satisfied, the variation DerutaCs auxiliary capacitance Cs The fluctuation amount does not change. Then, from the equation (2), ΔCs = {(C _LC + Cs) · ΔCgs} / Cgs (3) is obtained. Therefore, if _{K = (C LS + Cs)} / Cgs ( constant), and ΔCs = K · ΔCgs ...... (4 ).

Further, as shown in FIG. 2, for example, in the case of lateral displacement, the variation amount ΔCs of the auxiliary capacitance Cs and the variation amount ΔCgs of the parasitic capacitance Cgs are both the displacement amount Δd between the gate electrode 3 and the source electrode 9. The proportional constant K may be set by the electrode width W, for example.

Next, the drain electrode 7 and the source electrode 9
Using the as a mask, the low resistance semiconductor films 6 and 8 exposed between the drain electrode 7 and the source electrode 9 are removed by etching or the like.

Finally, an insulating protection film (not shown) for protecting the TFT 11, the gate line 12 and the drain line 13 is formed on the entire surface and connected to the external circuit connecting portion and the counter electrode 25 of the counter substrate 21 by a photolithography method or the like. Remove parts.

On the other hand, as shown in FIG. 4, a counter substrate 21 is provided so as to face the array substrate 1 and substantially parallel to the array substrate 1.

The counter substrate 21 is a light-shielding layer called black matrisk on a second transparent insulating substrate 22 such as glass.
23 is formed, a colored layer 24 is formed as necessary so as to cover the window opened in the light shielding layer 23, and a smooth layer (not shown) is formed on the light shielding layer 23 and the colored layer 24 as necessary. ,
A counter electrode 25 such as ITO is formed on this smooth layer.

Further, an alignment film (not shown) for aligning the liquid crystal 26 such as polyimide is applied on each of the array substrate 1 and the counter substrate 21, and the alignment films are rubbed. Then, an adhesive such as an epoxy resin is applied to the outer peripheral portions of the array substrate 1 and the counter substrate 21 outside the display region, except for a region serving as an injection port (not shown) for injecting the liquid crystal 26, and these alignment films are formed. And the array substrate 1 and the counter substrate 21 are opposed to each other by several μm.
Hold the gap evenly and stick together. The light-shielding layer 23
Has the purpose of blocking the light radiated to the TFT 11 and the light leaking from the gap between the pixel electrode 14 and the drain electrode 7, so that there is a gap when the array substrate 1 and the counter substrate 21 are bonded together. Considering this, the pixel electrodes 14 are combined so as to overlap with each other.

Next, the liquid crystal 26 is injected through the injection port, and the injection port is sealed with, for example, an epoxy resin. Further, the polarization axes are aligned with a direction determined with respect to the rubbing direction, and polarizing plates (not shown) are arranged on the array substrate 1 and the counter substrate, respectively.
Paste it on 21.

Then, after connecting the driving IC to the external circuit connecting terminal (not shown) and further connecting the driving circuit,
Installed in a case to make a liquid crystal display.

The liquid crystal display device manufactured as described above is connected to a drive circuit and placed in a case to manufacture a liquid crystal display device.

When the proportional constant K is relatively large, the auxiliary capacitance electrode 16 has a notch 16a as shown in FIG.
It is also possible to effectively increase the variation amount ΔCs of the auxiliary capacitance Cs by three times as compared with the case shown in FIG. it can.

[0041]

According to the liquid crystal display device of the present invention, the relative position of at least a part of the electrodes on one side of the set of auxiliary capacitance electrodes forming the auxiliary capacitance is made equal to the relative position of the source electrode with respect to the gate electrode. , Since the auxiliary capacitance is made to correspond to the overlapping amount of the gate electrode and the source electrode, the auxiliary capacitance is increased or decreased in accordance with the increase or decrease of the overlapping amount of the source electrode and the gate electrode. The change can be canceled out, the change in pixel potential can be kept constant even when the parasitic capacitances of the transistors are different, and flicker and display unevenness are not visually recognized, and high display quality can be obtained.

[Brief description of drawings]

FIG. 1 is a plan view showing an embodiment of a liquid crystal display device of the present invention.

FIG. 2 is a diagram showing a liquid crystal display device of the above. (A) Plan view showing the vicinity of the gate electrode (b) Plan view showing the vicinity of the variable auxiliary capacitance electrode (c) Sectional view showing the vicinity of the variable auxiliary capacitance electrode

FIG. 3 is a plan view showing a variable auxiliary capacitance electrode of another embodiment of the same as above.

FIG. 4 is a cross-sectional view showing a liquid crystal display device of the present invention and a conventional example.

FIG. 5 is a plan view showing a conventional liquid crystal display device.

FIG. 6 is a circuit showing an equivalent circuit of a pixel portion.

[Explanation of symbols]

 1 array substrate 3 gate electrode 7 drain electrode 9 source electrode 11 thin film transistor (TFT) 14 pixel electrode 16 auxiliary capacitance electrode 31 variable auxiliary capacitance electrode

Claims (1)

[Claims] 1. Pixel electrodes arranged in a matrix,
In a liquid crystal display device including an array substrate including a transistor having a gate electrode, a drain electrode and a source electrode for switching the pixel electrode, and an auxiliary capacitance electrode forming an auxiliary capacitance, one set of the auxiliary capacitance electrode is provided. The relative position of at least a part of the electrodes on one side of the one set of auxiliary capacitance electrodes is made equal to the relative position of the source electrode with respect to the gate electrode,
A liquid crystal display device, wherein the auxiliary capacitance is made to correspond to the amount of overlap between the gate electrode and the source electrode.