JPH03239229A - Active matrix liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the degradation in an opening rate by forming electrodes for additive capacitors so as to cover the outer peripheral and peripheral edge parts of picture element electrodes. CONSTITUTION:The electrodes 5 for additive capacitors are formed to cover the outer periphery and peripheral edge parts of the picture element electrodes 4. The electrodes 5 for additive capacitors in common use as light shielding films are formed on the active matrix substrate provided with the picture element electrodes 4 and, therefore, the generation of the misregistration between the light shielding films (electrodes 5 for additive capacitors) and the picture element electrodes 4 which may arise at the time of sticking of the active matrix substrate and a counter substrate is obviated. The superposed parts between the light shielding films and the picture element electrodes 4 are diminished in this way and the lowering of the opening rate of the display device is lessened.

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to an active matrix display device having an electrode for additional capacitance.

(Prior Art) In an active matrix display device using a display medium such as a liquid crystal, picture element electrodes are arranged in a matrix, and each picture element electrode is provided with a switching element such as a thin film transistor (hereinafter referred to as rTFTJ). ing. Each picture element electrode is selected by a scanning line via a switching element,
A video signal is accumulated in the selected picture element electrode via a signal line.

The video signal accumulated in the picture element electrode is held for one frame until the next picture element electrode is selected.

In such an active matrix display device,
As display images are required to have higher definition, picture element electrodes are becoming smaller. As picture element electrodes become smaller, the capacitance formed between each picture element electrode and the counter electrode becomes smaller, making it difficult to hold the video signal accumulated in the picture element electrode for one frame. become unable. To compensate for this lack of capacity, additional capacitance electrodes are often provided.

The additional capacitance electrode is provided facing a part of the picture element electrode,
An insulating film is sandwiched between the additional capacitance electrode and the picture element electrode. The electrode for additional capacitance is generally formed of a metal film. An additional capacitance electrode provided opposite each picture element electrode is usually connected to an additional capacitance wiring. Additional capacitor electrodes facing the picture element electrodes arranged in a row in one direction are electrically connected to the additional capacitor wiring. Further, as described above, the additional capacitor wiring is not provided, and the additional capacitor electrode is connected to the scanning line connected to the next row of picture element electrodes.

Twisted nematic type liquid crystal display devices have a
There are two types: normally black method and normally white method. In the normally black method, the polarization directions of the two polarizers are set parallel to each other. With such a polarizer arrangement, light is transmitted when a voltage is applied to the liquid crystal layer between the picture element electrode and the counter electrode, and light is blocked when no voltage is applied to the liquid crystal layer. On the other hand, in the normally white method, the polarization directions of the two polarizers are set to be orthogonal to each other.

With such a polarizer arrangement, light is blocked when a voltage is applied to the liquid crystal layer, and light is transmitted when no voltage is applied to the liquid crystal layer.

(Problems to be Solved by the Invention) When these two methods are compared, the normally white method has the advantage of being able to obtain greater contrast. However, normally white liquid crystal display devices have a drawback in that light leaks from portions of the liquid crystal layer other than the liquid crystal layer located between the picture element electrode and the counter electrode. In order to prevent such light leakage, a light shielding film made of a metal film or the like is often provided on the counter substrate on which no picture element electrodes are provided. The light shielding film is formed to overlap the outer periphery of the picture element electrode.

However, since the light shielding film is provided on the counter substrate, when the active matrix substrate on which the picture element electrodes are provided and the counter substrate are bonded together, misalignment occurs between these substrates. In order to prevent light leakage due to such positional deviation, the light shielding film is formed so as to overlap not only the outer periphery of the picture element electrode but also the peripheral edge of the picture element electrode. If the light-shielding film is provided so as to overlap the peripheral edge of the picture element electrode, the area of the picture element electrode that can contribute to display will be reduced, and the aperture ratio of the active matrix display device will be significantly reduced.

In a normally black type liquid crystal display device, light does not pass through when no voltage is applied, so as in the above-mentioned normally white type liquid crystal display device, the portion other than the liquid crystal layer between the pixel electrode and the counter electrode There is no light leakage from the liquid crystal layer (there is no need to provide a light shielding film. However, when a voltage is applied to the picture element electrode, the tilt of the liquid crystal molecules on the picture element electrode changes, and the voltage is applied. Disclination occurs between the liquid crystal molecules in the area where the voltage is not applied.Due to this disclination, a defective area on the display is observed between the area where voltage is applied and the area where no voltage is applied.

The present invention is intended to solve the above-mentioned problems, and an object of the present invention is to provide a light-shielding film that does not have the problem of positional misalignment with the picture element electrode, and therefore can minimize the decrease in the aperture ratio. It is an object of the present invention to provide an active matrix liquid crystal display device.Another object of the present invention is to provide an active matrix liquid crystal display device that does not affect the display screen even if disclination occurs.

(Means for Solving the Problems) The active matrix liquid crystal display device of the present invention includes a pair of insulating substrates facing each other, and images arranged in a matrix on the inner surface of one of the pair of substrates. An active matrix liquid crystal display device comprising an element electrode and an additional capacitance electrode made of an opaque material and superimposed on a part of the picture element electrode with at least an insulating film in between, the additional capacitance electrode It is formed to cover the outer periphery and peripheral edge of the picture element electrode, thereby achieving the above object.

Further, the active matrix liquid crystal display device of the present invention includes:
a pair of insulating substrates facing each other, pixel electrodes arranged in a matrix on the inner surface of one of the pair of substrates;
an alignment film formed on the picture element electrode; a liquid crystal layer having liquid crystal molecules aligned at a predetermined pretilt angle with respect to the alignment film on the alignment film; (both are active matrix liquid crystal display devices equipped with additional capacitance electrodes made of an opaque material and overlapped with an insulating film in between, and directed from the alignment film to above the alignment film along the alignment direction of the liquid crystal molecules. The additional capacitance electrode is superimposed on a portion of the picture element electrode in a direction opposite to the direction of the projected vector with respect to the vector projected onto the alignment film, thereby achieving the above purpose. be done.

Further, in the configuration in which an additional capacitance electrode is superimposed on a portion of the picture element electrode in the opposite direction of the projection vector, a scanning line is provided on the one substrate, and the additional capacitance electrode is It may also be electrically connected to a line.

Furthermore, in any of the above, a switching element connected to each of the picture element electrodes is provided on the one substrate, and the switching element is provided on the other substrate -8= of the pair of substrates. It is also possible to adopt a configuration in which a light shielding film is formed overlapping the input terminal.

(Function) In the active matrix liquid crystal display device of the present invention, the additional capacitance electrode made of an opaque material and also serving as a light shielding film is formed on the active matrix substrate on which the picture element electrodes are provided. Misalignment between the light shielding film (electrode for additional capacitance) and the picture element electrode, which occurs when the substrate and the counter substrate are bonded together, does not occur. Therefore, the overlapping portion of the light-shielding film and the picture element electrode can be made smaller, and a reduction in the aperture ratio of the display device can be reduced. Furthermore, it is also possible to cover the portion where bright lines are generated due to disclination.

In a liquid crystal display device, the position where a bright line due to disclination is generated depends on the alignment direction of liquid crystal molecules. Each liquid crystal molecule on the alignment film formed on the picture element electrode is aligned at a predetermined pretilt angle with respect to the alignment film, and is aligned in a fixed direction when viewed from the top surface of the picture element electrode. Consider a vector projected onto the alignment film from a vector directed upward from the alignment film along the alignment direction of the liquid crystal molecules oriented in this manner. It has been found that the above-mentioned bright line is generated in a portion of the picture element electrode in the opposite direction of this projection vector. In the display device of the present invention, an additional capacitance electrode that also serves as a light-shielding film is formed on the picture element electrode, so even if the bright line is generated, it does not appear on the display screen. Moreover,
This additional capacitance electrode, which also serves as a light-shielding film, is formed on the active matrix substrate on which the pixel electrodes are formed, so the light-shielding film (additional capacitance electrode) that is formed when the active matrix substrate and the counter substrate are bonded together No misalignment occurs between the pixel electrode and the pixel electrode. Therefore, the overlapping portion of the picture element electrode and the additional capacitance electrode that also serves as a light shielding film can be made small, and the reduction in the aperture ratio of the display device can be made small.

(Example) The present invention will be described below with reference to an example. In the following examples, TPT is used as a switching element, but
Other methods such as MIM (metal-insulating layer-metal) can also be used.

FIG. 1 shows a plan view of an active matrix substrate used in the active matrix liquid crystal display device of the present invention. Gate bus lines 1 functioning as scanning lines are formed in parallel on an insulating substrate such as glass. A source bus line 2 that functions as a signal line is formed to intersect with the gate bus line l. A gate insulating film 8, which will be described later, is sandwiched between the gate bus line 1 and the source bus line 2. A gate electrode 1a branches from near the intersection of the gate bus line 1 and the source bus line 2. A TFT 3 is formed on the gate electrode la. A picture element electrode 5 is formed in each region defined by the gate bus wiring 1 and the source bus wiring 2. As will be described later, the source electrode 11 of the TFT 3 is electrically connected to the source bus wiring 2, and the drain electrode 12 is electrically connected to the picture element electrode 4.

Further, in this embodiment, the additional capacitance electrode 5 is formed so as to overlap the outer periphery and peripheral edge of the picture element electrode 4. As will be described later, the additional capacitance electrode 5 faces the peripheral edge of the picture element electrode 4 with the gate insulating film 8 in between. Since the additional capacitance electrode 5 is formed from an opaque metal layer, it can also function as a light shielding film. Adjacent additional capacitance electrodes 5 are electrically connected to each other.

FIG. 2 shows a sectional view taken along line nn in FIG. 1. Second
The active matrix liquid crystal display device of this embodiment will be explained according to the manufacturing process with reference to the drawings. Insulating substrate 20'' made of glass, quartz, etc. Second, Ta, AI, T1, MoS
A metal film such as Cu is formed, and gate bus wiring 1 and gate electrode 1 are formed by photolithography and etching.
a, and the additional capacitance electrode 5 were patterned. As shown in FIG. 1, the additional capacitance electrode 5 is formed so as to overlap the outer periphery and peripheral edge of the picture element electrode 4, which will be formed later. Next, a gate insulating film 8 was formed using an insulating material such as S+02 or SiNx. Next, a semiconductor layer 9 made of amorphous silicon was patterned. Furthermore, a contact layer 10.10 made of n" type amorphous silicon was patterned.

A source electrode 11 and a drain electrode 12 are patterned on the contact layers 10 and 10, respectively, and the source bus wiring 2 described above is also patterned at the same time.

Source bus wiring 2, v-sumi pole 11 and drain electrode 1
For 2, a conductive material such as Ta, AI, T1, Mo, Cu, ITO, etc. is used. Furthermore, a picture element electrode 4 made of ITO
is patterned. The picture element electrode 4 is the drain electrode 12
The pixel electrode 4 and the drain electrode 12 are electrically connected to each other. Further, the picture element electrode 5 is formed so as to partially overlap the additional capacitance electrode 5. Furthermore, an alignment film 13 is formed over the entire surface of the picture element electrode 4. The alignment film 13 is formed by applying polyimide, polyvinyl alcohol, etc., baking it, and performing a rubbing process.

A counter electrode, an alignment film, etc. are formed on a counter substrate that faces the active matrix substrate of FIG. The rubbing direction of the alignment film on the counter substrate is perpendicular to the rubbing direction of the alignment film 13 on the active matrix substrate. Next, plastic spacers were spread on either the active matrix substrate or the counter substrate shown in FIG. 1, and a liquid crystal layer was sealed between these substrates to obtain a liquid crystal cell. Furthermore, a polarizing plate was attached to the outside of each liquid crystal cell.

When the polarization directions of these polarizing plates are set to be perpendicular to each other, a normally white liquid crystal display device is obtained, and when they are set to be parallel to each other, a normally black liquid crystal display device is obtained. In this example, a normally white type was used. In the manner described above, a twisted nematic active matrix liquid crystal display device is obtained.

In the active matrix liquid crystal display device of this embodiment, the additional capacitance electrode 5 made of an opaque material and also serving as a light shielding film is formed on the active matrix substrate on which the picture element electrode 4 is provided. A light-shielding film (
No misalignment occurs between the additional capacitance electrode 5) and the picture element electrode 4.

Therefore, the weight of the light-shielding film and the picture element electrode can be reduced, and a liquid crystal display device with reduced reduction in aperture ratio can be obtained. Furthermore, it is also possible to cover the portion where bright lines are generated due to disclination.

FIG. 3 shows a plan view of an active matrix substrate used in another embodiment of the present invention. In the embodiment shown in FIG. 3, a gate bus wiring 1, a source bus wiring 2, a gate electrode 1a,
The TFT 3, picture element electrode 4, etc. are the same as those in the embodiment shown in FIG. 1 described above. The additional capacitance electrode 5 of this embodiment is the pixel electrode 4
It is provided so as to overlap the inner part of one side of the .

The position where the additional capacitance electrode 5 is formed is related to the alignment direction of the liquid crystal molecules.

As shown in FIG. 4, in this embodiment, the liquid crystal molecules 23 on the alignment film 13 are aligned at a predetermined pretilt angle θ with respect to the alignment film 13. Along the orientation direction of the liquid crystal molecules 23,
Consider a vector 22 directed upward from the alignment film. Seven vectors 21 are obtained by projecting this vector 22 onto the alignment film 13. The vector 21 has a direction diagonal to the picture element electrode 40, as shown in FIG. The additional capacitance electrode 5 of this embodiment is provided so as to overlap a portion of the picture element electrode 4 in the opposite direction to the direction of the vector 21.

In the substrate shown in FIG. 3, the additional capacitance electrode 5 also functions as a light shielding film, and the position where a bright line due to disclination is generated coincides with the position where the additional capacitance electrode 5 is formed. Therefore, when a display device is assembled using the active matrix substrate shown in FIG. 3, the bright lines become invisible on the display screen.

Furthermore, since the additional capacitance electrode 5 that also serves as a light-shielding film is formed on the active matrix substrate on which the picture element electrode 4 is formed, the light-shielding film (additional No misalignment occurs between the capacitor electrode 5) and the picture element electrode 4. Therefore, the decrease in the aperture ratio due to the provision of the additional capacitance electrode 5 which also serves as a light shielding film can be reduced.

FIG. 5 shows a plan view of an active matrix substrate used in another embodiment of the display device of the present invention.

In this embodiment, the additional capacitance electrode 5 has the same shape as the additional capacitance electrode 5 shown in FIG. In this embodiment, the wiring that electrically connects each additional capacitor electrode 5 is a gate bus connected to the pixel electrode 4 in the next row of the pixel electrode 4 facing the additional capacitor electrode 5. Wiring 1 also serves as this. That is, the gate bus wiring 1 and the additional capacitance electrode 5 are integrally formed. With such a configuration, there is no need for wiring to connect between the additional capacitance electrodes 5, so the area of the picture element electrodes 4 can be increased, and the aperture ratio of the display device can be increased.

In any of the above embodiments, the orientation of liquid crystal molecules located near the source electrode 11 may change depending on the video signal applied to the TFT 3, and light may leak. In such a case, a structure may be adopted in which a light shielding film covering the source electrode 11 is provided on the counter substrate. This light shielding film is formed to have the same shape as the source electrode 11 and to be the same or thicker than the source electrode 11. With this configuration, the above-mentioned leakage of light can be prevented without reducing the aperture ratio.

(Effects of the Invention) In the active matrix liquid crystal display device of the present invention, since the additional capacitance electrode that also functions as a light shielding film is formed on the active matrix substrate, it is possible to avoid misalignment when bonding the active matrix substrate and the counter substrate. There is no reduction in the aperture ratio due to this. Furthermore, since the additional capacitance electrode that also serves as a light-shielding film is superimposed on the portion where disclination occurs, bright lines caused by disclination do not appear on the display screen. Therefore, according to the present invention, an active matrix liquid crystal display device having a large aperture ratio and high image quality is provided.

[Brief explanation of drawings]

FIG. 1 is a plan view of an active matrix substrate constituting an embodiment of the active matrix liquid crystal display device of the present invention, FIG. 2 is a sectional view taken along the If-ff line in FIG. 1, and FIG.
The figure is a plan view of an active matrix substrate constituting another embodiment of the display device of the present invention, FIG. 4 is a diagram showing the alignment direction of liquid crystal molecules on the substrate of FIG. 3, and FIG. 5 is a display of the present invention. FIG. 7 is a plan view of an active matrix substrate constituting another embodiment of the device. 1... Gate bus wiring, la... Day +1 pole, 2...
...Source bus wiring, 3...TFT, 4...Picture element electrode, 5...Additional capacitance electrode, 8...Gate insulating film,
13... Alignment film, 23... Liquid crystal molecules. that's all

Claims (1)

[Claims] 1. A pair of insulating substrates facing each other, pixel electrodes arranged in a matrix on the inner surface of one of the pair of substrates, and at least a portion of the pixel electrodes having an insulating structure. An active matrix liquid crystal display device comprising additional capacitance electrodes made of an opaque material and overlapped with a film in between, the additional capacitance electrodes being formed to cover the outer periphery and peripheral edge of the picture element electrode. Active matrix liquid crystal display device. 2. A pair of opposing insulating substrates, picture element electrodes arranged in a matrix on the inner surface of one of the pair of substrates, an alignment film formed on the picture element electrode, and the alignment film. a liquid crystal layer having liquid crystal molecules oriented at a predetermined pretilt angle with respect to the alignment film thereon; and an additional capacitance electrode made of an opaque material and superimposed on a part of the picture element electrode with at least an insulating film in between. An active matrix liquid crystal display device comprising: a vector directed upward from the alignment film along the alignment direction of the liquid crystal molecules, with respect to a vector projected onto the alignment film; An active matrix liquid crystal display device in which the additional capacitance electrode is superimposed on a portion of the picture element electrode in the opposite direction. 3. The active matrix liquid crystal display device according to claim 2, further comprising a scanning line on the one substrate, and the electrode for additional capacitance is electrically connected to the scanning line. 4. A switching element connected to each of the picture element electrodes is provided on the one substrate, and a light shielding film is formed on the other substrate of the pair of substrates so as to overlap the input terminal of the switching element. 4. The active matrix liquid crystal display device according to claim 1, wherein the active matrix liquid crystal display device is