JP2521752B2 - Liquid crystal display - Google Patents

Description

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a liquid crystal display device, and more particularly to a liquid crystal display device capable of preventing deterioration of display quality caused by a defect in alignment of liquid crystals. Is.

(Prior Art) A liquid crystal display device is expected as one of flat panel displays that replaces a CRT. In addition, since the liquid crystal display device consumes extremely less power than other types of display devices that utilize light emission, it is suitable for a battery-powered small display device such as an ultra-small television and the like. Is being actively researched. Also, with a liquid crystal panel,
Since it is possible to display vivid colors by combining with a color filter, research on color display has been made and some of them have been put to practical use.

Although various methods can be considered for driving such a liquid crystal display device, it can be said that the method mainly performed in recent years is an active matrix driving method.

Although a liquid crystal display device of a type suitable for such an active matrix driving method is well known, a general structure of a conventional liquid crystal display device of this type will be described below with reference to FIGS. 3 to 5. Briefly explained.

FIG. 3 is a partial plan view mainly showing an arrangement relationship of each constituent component on a substrate (also referred to as a pixel electrode substrate) on a side where a switching element is provided in a conventional active matrix type liquid crystal display device. It is a figure. In this case, an example in which the switching element is a thin film transistor (TFT) is shown.

In FIG. 3, 11 indicates a source electrode as a data electrode, and 13 indicates a gate electrode as a scanning electrode. These electrodes are formed in a matrix on a suitable substrate such as a glass substrate. Further, a TFT 15 is formed in a region where these two electrodes intersect, and the one shown by 17 in the drawing is the drain electrode of this TFT 15. This drain electrode 17
A pixel electrode 19 (indicated by hatching in the figure) is connected to.

4 is a sectional view schematically showing the pixel electrode substrate shown in FIG. 3 taken along the line I-I shown in FIG. In order to avoid complication of the drawing, hatching showing a cross section is partially omitted.

In FIG. 4, reference numeral 21 designates, for example, a glass substrate as a substrate. Reference numeral 23 is a gate insulating film, 25 is an amorphous Si film, and 27 is a protective film.

Further, FIG. 5 is configured using the pixel electrode substrate described with reference to FIGS. 3 and 4 and the other substrate (also referred to as a common electrode substrate) prepared separately having a common electrode. FIG. 11 is a sectional view schematically showing a conventional liquid crystal display device. The liquid crystal display device shown in FIG. 5 is an example for a color display. Also, in order to avoid complication of the drawing, hatching showing a cross section is partially omitted in this drawing.

In FIG. 5, 31 indicates a second substrate. This board 31
On the top, from the substrate side, a color filter 33 for color display,
The common electrode 35 is sequentially provided. In addition, reference numeral 37 in the drawing denotes an alignment film, which is formed on the mutually opposing surfaces of the pixel electrode substrate 21 and the common electrode substrate 31, respectively. A liquid crystal 39 is sealed between the substrates 21 and 31.

In the conventional liquid crystal display device, the area where the TFT 15, the scanning electrode (gate electrode) 13, and the data electrode (source electrode) 15 are formed protrudes from the surface of the substrate, so that the convex portion 41 is formed. Further, although there is no problem in the common electrode of the liquid crystal display device of the mono-color display, when the color filter 33 is used on the liquid crystal injection side of the common electrode substrate as shown in FIG. A recess 43 is formed in the. As described above, in the conventional liquid crystal display device, a level difference of about 1 to 2 μm is continuously and periodically present on the liquid crystal enclosing region side surface of either or both of the opposed substrates.

Further, as is clear from FIG. 3, in the conventional liquid crystal display device, it is necessary to separate the pixel electrode and these electrodes so that the pixel electrode 19 does not short-circuit with the source electrode 11 and the gate electrode 13.

By the way, in the conventional active matrix type liquid crystal display device as described above, some molecules of the liquid crystal molecules are oriented in a direction other than the desired orientation direction for the reason described below (hereinafter, this is referred to as a domain phenomenon). Therefore, the display quality is deteriorated.

It can be said that one of the causes of causing such a domain phenomenon is the above-described step existing on the substrate. For example,
It is assumed that the TFT portion projects from the substrate surface by about 2 μm to form a step. Although it varies depending on the type of liquid crystal display device, the distance between the opposing substrates is only about 10 μm at the widest. Therefore, if there is a step of about 2 μm on the substrate as described above, the liquid crystal in the part with the step and the part without the step The size of the encapsulating voids will eventually be different. It is considered that the liquid crystal molecules in the two portions have different alignments from each other, which causes a domain phenomenon.

Another cause of the domain phenomenon may be bending of lines of electric force. This will be described with reference to FIG.

In an active matrix type liquid crystal display device, a large number of gate electrodes are sequentially selected, and data signals are applied to the source electrodes of a large number of pixels belonging to the selected gate electrodes. Now, let us consider a case where every other many pixels belonging to a certain gate electrode are turned on and the remaining pixels are turned off. FIG. 6 is a diagram schematically showing a state of lines of electric force when the conventional liquid crystal display device is driven in this manner. This pixel electrode 19 is set to have a positive potential with respect to the common electrode 37. The case where a voltage is applied to 19 is shown. Originally, an electric force line from the pixel electrode 19 to the common electrode 37 should be generated between the pixel electrode of the TFT being driven and the common electrode, but the TFT being driven and the TFT not being driven. It is considered that an unnecessary electric force line (bending of the electric force line 41 in FIG. 6) is also generated between the pixel electrode and the pixel electrode. Since the orientation direction of the liquid crystal molecules in the region where the unnecessary electric force lines are generated is different from the orientation direction in the region where the normal electric force lines are generated, it is considered that the domain phenomenon is caused also by this. Seem. Such unnecessary electric force lines are also generated in the end regions of the pixel electrodes in the off state, which are arranged along the data electrodes to which the on signal is applied.

As a document showing such a result, the research is conducted to solve such a domain phenomenon as a problem, and there is, for example, JP-A-60-243633. According to this publication,
After the domain phenomenon occurs, it disappears quickly, so TF
The gap between the source electrode of T and the side of the pixel electrode is made as linear as possible. Further, in the case of a liquid crystal display device for color display, the gap formed between the adjacent color filters faces the gap between the above-mentioned source electrode and the pixel electrode on the side which is not driven by this source electrode and is adjacent to this source electrode. The position is adjusted so that

(Problems to be Solved by the Invention) However, as described above, making the gap between the source electrode and the pixel electrode as linear as possible impairs the degree of freedom in the pixel arrangement of the liquid crystal display device. . Moreover, more accurate alignment is required to align the gaps so that they are exactly opposite to each other, which is not preferable in the manufacturing process. In addition, the part where the lines of electric force are bent (Fig.
No measures will be taken against the domain phenomenon in the portion (1), and the display quality will be impaired by the defective alignment of the liquid crystal molecules in this portion.

The present invention has been made in view of the above points, and an object of the present invention is to provide a liquid crystal display device in which a domain phenomenon is unlikely to occur, and which is difficult to be visually recognized even if the domain phenomenon occurs. .

(Means for Solving the Problems) In order to achieve this object, according to the present invention, a plurality of stripe-shaped scanning electrodes arranged in parallel are arranged, and the scanning electrodes are arranged in parallel so as to intersect with each scanning electrode. A pixel electrode substrate having a plurality of stripe-shaped data electrodes, switching elements respectively provided at the intersections of the scanning electrodes and the data electrodes, and pixel electrodes connected to each switching element, In addition, in a liquid crystal display device including a common electrode substrate facing the pixel electrode substrate and having a common electrode on a facing surface, a step due to a switching element, a scanning electrode and a data electrode is formed on the pixel electrode substrate surface. An insulating layer having a flat surface that is flattened so as to be lost is provided, and a contact hole is provided on the flat surface of the insulating layer and in the insulating layer. The pixel electrode is provided so as to be connected to the switching element, and the data electrode is made of a light-shielding metal. In addition, electrical conductivity between adjacent pixel electrodes in a direction parallel to the stripe direction of the data electrode is also provided. The isolation region is a region above the data electrode.

In addition, the liquid crystal display device is capable of color display,
When the common electrode substrate has a color filter, the color filter of the common electrode substrate is provided with an insulating layer for flattening the unevenness formed between the color filter and the substrate surface. It is preferable to provide a common electrode on top.

(Function) According to such a configuration, the unevenness mainly formed by the switching element, the scanning electrode of the switching element, the data electrode of the switching element, and the surface of the pixel electrode substrate is covered with the insulating layer having the flat surface. You can Therefore, the space for liquid crystal encapsulation between the pixel electrode substrate and the common electrode substrate has a substantially uniform size in any portion between the both substrates, so that various conditions for aligning liquid crystal molecules are also uniform. . Therefore, it is possible to prevent the occurrence of the domain phenomenon due to the step.

Further, since the switching element and the scanning and data electrodes thereof are covered with the insulating layer, the pixel electrode provided on this insulating layer can be formed up to a region above the switching element and both electrodes. become able to do.
Therefore, a separation region for electrically separating adjacent pixel electrodes can be provided in a region above the scan electrodes or a region above the data electrodes.

And in this invention, between the adjacent pixel electrodes,
An electrical isolation region parallel to the stripe direction of the data electrode of the switching element is provided in the region above the data electrode on the insulating layer portion. The data electrodes and scan electrodes are generally formed of a light-shielding metal thin film. In the present invention, at least the data electrode is made of a light-shielding metal thin film. With this configuration, the light-shielding metal (data electrode) is positioned below the electrical isolation region between the pixel electrode and the data electrode, which is likely to cause the domain phenomenon due to the bending of the lines of electric force. , This domain phenomenon will not be recognized by those who look at the display device.

(Embodiment) An embodiment of the active matrix type liquid crystal display device of the present invention will be described below with reference to FIGS. 1 and 2. It should be understood that the drawings used in the following description are only schematically shown so that the present invention can be understood, and therefore the present invention is not limited to these illustrated examples. Further, in each of the drawings, common components are designated by the same reference numerals. Further, the same components as those of the related art are denoted by the same reference numerals.

Configuration of Liquid Crystal Display Device FIG. 1 (A) mainly shows an arrangement relationship of respective constituent components on a substrate (pixel electrode substrate) on a side where a switching element is provided in an active matrix type liquid crystal display device of the present invention. It is a partial top view. In this case, an example in which the switching element is a thin film transistor (TFT) will be described.

In FIG. 1A, 11 indicates a source electrode as a data electrode, and 13 indicates a gate electrode as a scanning electrode. These electrodes are formed in a matrix on a suitable substrate such as a glass substrate. Further, a TFT 15 is formed in a region where these two electrodes intersect, and the one shown by 17 in the drawing is the drain electrode of this TFT 15.

Although not shown in FIG. 1A (which will be described later with reference to FIG. 1B), the liquid crystal display device of the present invention has a source electrode 11 The gate electrode 13, the TFT 15 and the substrate surface are provided with an insulating layer which covers the irregularities mainly formed and has a flat surface, and the pixel electrode 51 (in FIG. 1 (A), hatched lines are provided on the insulating layer. (Shown). The pixel electrode 51 is connected to the drain electrode 17 under the insulating layer via a contact hole 53 provided in the insulating layer. Further, by utilizing the fact that such an insulating layer is provided, the pixel electrode 51 in this embodiment is formed as follows.

Between adjacent pixel electrodes 51 of the pixel electrodes 51 linearly arranged along the stripe direction of the gate electrode 13,
An electric isolation region 55 parallel to the stripe direction of the source electrode is formed in a region above the source electrode 11 so as to fit within the formation region of the source electrode. Therefore, the pixel electrode in this case also exists above the region where the TFT 15 is formed.

FIG. 1 (B) is a cross-sectional view schematically showing the pixel electrode substrate shown in FIG. 1 (A) by cutting along the line II-II shown in FIG. 1 (A). In order to avoid complication of the drawing, hatching showing a cross section is partially omitted.

In FIG. 1 (B), reference numeral 21 indicates, for example, a glass substrate as a substrate. 23 is a gate insulating film, 25 is amorphous
The respective Si films are shown. Reference numeral 57 denotes the insulating layer which has been already described for flattening the unevenness mainly composed of the source electrode 11, the gate electrode 13, the TFT 15 and the substrate surface.
A contact hole 53 is formed in a region corresponding to the drain electrode 17 of the.

As can be understood from FIG. 1B, since the insulating layer 57 is provided, the electric isolation region 55 between the pixel electrodes can be formed above the source electrode. For this reason, the display data of a certain data electrode among a large number of source electrodes (data electrodes) to which the display data is always written becomes a signal that continuously indicates a high level, and such a data electrode,
Even if a domain phenomenon occurs between the pixel electrode in the off state along the data electrode for a long time, the domain phenomenon is shielded by the source electrode and can be prevented from being recognized by a viewer of the liquid crystal display device.

When a liquid crystal display device is constructed using such a pixel electrode substrate of the present invention and a conventional common electrode substrate, if the liquid crystal display device is a mono-color display device, a domain phenomenon due to a step is completely eliminated. It will never happen. further,
Regardless of color display or mono-color display, the domain phenomenon caused by the bending of the lines of electric force is shielded by the data electrode (source electrode), so that the viewer of the liquid crystal display device does not recognize this domain phenomenon. .

Further, in the case where the liquid crystal display device is a color display device and the conventional common electrode substrate provided with a color filter as shown in FIG. 5 and the pixel electrode substrate of the present invention are used, Since there is no step on the substrate side, the display quality is superior to the conventional one. In order to obtain a more excellent display in the color display liquid crystal display device having such a configuration, it is preferable that the common electrode substrate has a structure shown in a sectional view in FIG. .

In FIG. 2, 31 indicates a glass substrate. A color filter 33 is provided on the glass substrate 31.
Also, the common electrode substrate according to the present invention is a color filter.
On the glass substrate 31 including 33, the color filter 33 and the substrate
31 includes an insulating layer 61 having a flat surface for covering the step, which is mainly formed on the surface, and a common electrode 37 provided on the insulating layer 61.

Liquid crystal for color display of the present invention formed by enclosing a liquid crystal between a pixel electrode substrate as shown in FIGS. 1A and 1B and a common electrode substrate as shown in FIG. In the display device, the domain phenomenon caused by the step does not occur at all, and even if the domain phenomenon occurs due to the step of the contact hole 53 portion or the bending of the electric force line in the electric isolation region 55 between the pixel electrodes. However, since this is shielded by the source and drain electrodes, a viewer of this liquid crystal display device does not recognize this domain phenomenon.

Method for manufacturing liquid crystal display device Next, in order to deepen the understanding of the liquid crystal display device of the present invention,
An example of a method of manufacturing a liquid crystal display device according to an embodiment of the present invention will be described with reference to FIGS. 1 (B) and 2. It should be understood that the materials, forming methods, numerical conditions, and the like described below are merely examples, and the present invention is not limited to these materials, forming methods, and numerical conditions.

A TFT 15 as a switching element, a scan electrode 13 and a data electrode 11 of the TFT 15 are formed on a glass substrate 21 by using a normal thin film forming technique. In this step, a conventional method of manufacturing an active matrix type liquid crystal display device can be used.

Next, the glass substrate on which the TFT 15 and both electrodes 13 and 11 are formed
An insulating layer 57 having a flat surface is formed on 21. In the case of this example, the insulating layer 57 was formed as follows.

On the glass substrate 21 on which the TFT 15 and both electrodes 13 and 11 are formed, a polyimide varnish (San Ever 120 manufactured by Nissan Chemical Co., Ltd.
Was used) and was dried at a temperature of about 170 ° C. for about 1 hour. In addition, the conditions for spin coating are that the film thickness after drying of the flat part of the glass substrate 21 of polyimide varnish is 4
It was set to be μm. When the polyimide varnish was applied under the above-mentioned film forming conditions on the step due to the TFT 15 protruding from the substrate surface by about 2 μm, this step was mitigated to 0.3 μm on the surface of the polyimide varnish and the protruding condition was also smooth. It became a thing. The film forming conditions for the above-mentioned polyimide varnish should be determined in consideration of the shape of the TFT and the viscosity of the varnish used, and are not limited to the conditions of this embodiment. Further, the material forming the insulating layer 57 is not limited to the polyimide varnish of the embodiment, and other suitable materials can be used.

Next, the insulating layer 57 formed as described above is processed. The processing in the case of this embodiment is to form a contact hole 53 in a region corresponding to the drain electrode of the TFT 15,
Also, in order to connect the scanning and data electrodes to a separately prepared driving element, a part of these electrodes is exposed from the insulating layer 57. For these processes, a resist mask is formed by using a normal photo-etching technique, and an insulating layer is prepared by using an etching solution and a rinsing solution for exclusive use of Nissan Chemical Co.
This was done by removing 57 unnecessary parts.

Next, an ITO film is formed on the insulating layer 57 by a suitable method such as RF sputtering to have a film thickness of about 1000 Å, and then this ITO film is formed into a predetermined shape by a photoetching technique (see FIG. (See A)) to form the pixel electrode 51 to obtain a pixel electrode substrate according to the present invention as shown in FIGS. 1 (A) and 1 (B).

On the other hand, the common electrode substrate already described with reference to FIG. 2 was formed as follows.

A color filter 33 is formed on the glass substrate 31 by a conventionally known method.
To form. Also in this case, a step of about 2 μm is formed between the surface of the color filter 33 and the surface of the substrate. As in the case of forming the pixel electrode substrate, flattening is performed under the same film forming conditions using the sun ever 120, and the unnecessary portion of the sun ever 120 is removed as in the case of forming the pixel electrode substrate, and the insulating layer 69 is formed.
Was formed. The common electrode 37 was formed on the insulating layer 69 by a conventionally known method.

The pixel electrode substrate formed as described above and the common electrode substrate are subjected to alignment treatment, and then these substrates are bonded together via a spacer. After the liquid crystal was sealed in the space between the substrates, the sealing port was sealed to obtain the liquid crystal display device according to the present invention.

The present invention is not limited to the above embodiment.

In the above-described embodiment, the region for electrically separating the pixel electrodes 51 in the direction orthogonal to the stripe direction of the data (source) electrode is not particularly formed above the scan (gate) electrode. , As before.
This is because, unlike the data electrodes, the scan electrodes are driven line-sequentially one by one at a very high speed from the viewpoint of the liquid crystal display device, so that the domain phenomenon that occurs on the scan electrode side by the viewer of the liquid crystal display device. This is because admitting is unlikely. However, it is of course possible to provide this separation region in the direction orthogonal to the stripe direction of the data electrode above the scanning (gate) electrode so that the domain phenomenon occurring at this portion is blocked by the gate electrode.

Also, in the above embodiment, the switching element is
This is explained using the example of T. However, it is obvious that the present invention can be applied to a liquid crystal display device in which the switching element is configured as a diode or another non-linear switching element such as MIM (Metal Insulator Metal).

(Effects of the Invention) As is clear from the above description, the liquid crystal display device of the present invention includes an insulating layer for flattening a step due to a switching element or the like, and a pixel electrode on the insulating layer. . Therefore, the domain phenomenon is unlikely to occur, and bubbles are less likely to occur when the liquid crystal is sealed. Furthermore, since the occurrence of the domain phenomenon can be prevented without linearly forming the gap between the pixel electrode and the source electrode, the degree of freedom of the pixel arrangement is not impaired.

In addition, the data electrodes are made of light-shielding metal,
An electrical isolation region between adjacent pixel electrodes in a direction parallel to the stripe direction of the data electrode is defined as a region above the data electrode. Therefore, the domain phenomenon that is likely to occur due to the bending of the lines of electric force can be shielded by the light-shielding metal forming the data electrodes.

For this reason, it is possible to provide a liquid crystal display device in which the domain phenomenon is unlikely to occur and which is difficult to be visually recognized even if the domain phenomenon occurs. Therefore, the liquid crystal display device of the present invention has contrast characteristics and visual field The characteristics are improved.

[Brief description of drawings]

1 (A) and 1 (B) are a plan view and a cross-sectional view of an essential part for explaining a liquid crystal display device of the present invention, showing a plan view and a cross-sectional view showing a part of a pixel electrode substrate, and FIG. FIG. 3 is a cross-sectional view of an essential part for explaining a liquid crystal display device of the present invention, showing a part of a common electrode substrate, and FIGS. 3 to 5 are views for explaining a conventional liquid crystal display device. FIG. 3 and FIG. 4 are plan views and sectional views showing a part of the pixel electrode substrate, FIG. 5 is a sectional view showing a part of the liquid crystal display device, and FIG. FIG. 11 …… Data electrode (source electrode) 13 …… Scan electrode (gate electrode) 15 …… Switching element 17 …… Drain electrode, 23 …… Gate insulating film 25 …… Amorphous Si, 51, 51a, 51b …… Pixel electrode 53 ... Contact hole 55 ... Electrical isolation region between pixel electrodes 57, 61 ... Insulating layer with flat surface.

Claims (1)

(57) [Claims] 1. A plurality of stripe-shaped scanning electrodes arranged side by side, a plurality of stripe-shaped data electrodes arranged side by side so as to intersect each of the scanning electrodes, and each of the scanning electrodes and each of the data electrodes. A pixel electrode substrate having a switching element provided at each intersection and a pixel electrode connected to each switching element, and a common electrode having a common electrode on the opposite surface facing the pixel electrode substrate. In a liquid crystal display device including an electrode substrate, an insulating layer having a flat surface that is flattened so as to eliminate steps caused by switching elements, scanning electrodes and data electrodes is provided on the pixel electrode substrate surface, and the insulating layer The pixel electrode is provided on the flat surface so as to be connected to the switching element through a contact hole provided in the insulating layer. The data electrode is made of a light-shielding metal, and the electrical isolation region between adjacent pixel electrodes in the direction parallel to the stripe direction of the data electrode is a region above the data electrode. Characteristic liquid crystal display device.