JPS63279228A - Liquid crystal display device - Google Patents

Abstract

PURPOSE:To prevent the generation of a domain phenomenon by forming an insulating plate having a flat surface on a picture element electrode base and forming picture element electrodes to be connected to a switching element through a contact hole on the surface of the insulating layer. CONSTITUTION:The insulating layer 57 for flatting a step difference due to the switching element 15 or the like is formed and the picture electrodes 51a, 51b are formed on the surface of the layer 57. Consequently, the generation of a domain phenomenon can be prevented. In addition, the electrodes 51 can be formed up to the upper area of source and gate electrodes 11, 13 by covering the element 15 and the source and gate electrodes 11, 13 with the layer 57. Thereby, an electric separation area is formed between picture element electrodes in which the domain phenomenon may be easily generated and to interrupt the domain phenomenon generated by the curve of lines of electric force by means of the electrode 11. Consequently, the domain phenomenon is not easily generated, and even if it is generated, its generation is not easily observed to improve contrast characteristics and visual field angle characteristics.

Description

Detailed Description of the Invention (Field of Industrial Application) The present invention relates to a liquid crystal display device, and particularly relates to a liquid crystal display device capable of preventing deterioration in display quality caused by poor alignment of liquid crystals. It is something.

(Prior Art) Liquid crystal display devices are expected to be used as a flat panel display to replace CRTs. Furthermore, since liquid crystal display devices consume extremely less power than other LI* display devices that use light emission, they are suitable for small battery-powered display devices such as ultra-compact televisions, and are therefore popular in this field. There is also a lot of research going on. Furthermore, since vivid color display is possible by combining a liquid crystal panel and a color filter, research has been conducted into color display, and some of them have been put into practical use.

Although various methods can be considered for driving such a liquid crystal display bag M, the method that has been mainly used in recent years is the active matrix driving method.

Such an active matrix! ! l! Although liquid crystal display devices of a type suitable for the dynamic method are well known, the general structure of a conventional liquid crystal display device of this type will be briefly explained below with reference to FIGS. 3 to 5. .

FIG. 3 is a partial diagram mainly showing the W distribution relationship of each component on the substrate (sometimes referred to as a pixel electrode substrate) on which switching elements are provided in a conventional active matrix liquid crystal display device. FIG. In this case, an example is shown in which the switching element Im film transistor (TPT) is used.

In FIG. 3, reference numeral 11 indicates a source electrode as a data electrode, and reference numeral 13 indicates a gate electrode as a scanning electrode. These electrodes are preferably made of, for example, a glass substrate.

are formed in a matrix on a substrate. Further, a TPTI 5 is formed in a region where these two electrodes intersect, and the one indicated by 17 in the figure becomes a train electrode of this TPTI 5. A pixel electrode 19 (shown with diagonal lines in the figure) is connected to the train electrode 17.

4 is a schematic cross-sectional view of the pixel electrode substrate shown in FIG. 3 taken along the line II shown in FIG. 3. FIG. Note that, in order to avoid complicating the drawings, some hatchings indicating the cross section are omitted from the illustration.

In FIG. 4, 21 indicates a glass substrate as a substrate, 23 indicates a gate insulating film, and 25 indicates an amorphous S.
27 represents a protective film.

Further, FIG. 5 is constructed using the pixel electrode substrate explained using FIGS. 3 and 4 and another separately prepared substrate having a common electrode (sometimes referred to as a common electrode substrate). 1 is a cross-sectional view schematically showing a conventional liquid crystal display device.

The liquid crystal display device shown in FIG. 5 is an example of a color display device.

Also, in order to avoid complicating the drawing, hatching indicating the cross section is partially omitted from this figure.

In FIG. 5, 31 indicates the second substrate. This board 3
On top of 1 is a color filter 33 for color display from the board side.
and a common electrode 35 are sequentially provided. Moreover, what is indicated by 37 in the figure is 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 these substrates 21 and 31.

In the conventional liquid crystal display device, the region in which the TPTI 5, the scanning electrode (gate electrode) 13, and the data electrode (source electrode) 15 are formed protrudes from the substrate surface, resulting in the formation of a convex portion 41, and also monochrome display. This is not a problem with the common electrode of a liquid crystal display device, but when the color filter 33 is used on the liquid crystal injection side of the common electrode substrate as shown in FIG. As described above, in conventional liquid crystal display devices, steps of about 1 to 2 μm exist continuously and periodically on the surface of one or both of the open substrates facing each other on the liquid crystal filling region side. was.

Also, as is clear from FIG. 3, in the conventional liquid crystal display device, the pixel electrode 19 is
It was necessary to space the pixel electrodes from these electrodes so as not to short-circuit them.

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

One of the causes of such a domain phenomenon is the above-mentioned level difference existing on the substrate. For example, T
It is assumed that the PT portion protrudes from the substrate surface by about 2 um to form a step. Although it varies depending on the type of liquid crystal display device, the distance between opposing substrates is only about 510 μm at the widest, so if there is a step on the substrate of about <2 μm as described above, there will be a difference between the part with the step and the part without the step. As a result, the dimensions of the cavity for filling the liquid crystal will be different.
It is thought that the orientation of the liquid crystal molecules in each of these two sections will be different from each other, and this will cause a domain phenomenon.

Another possible cause of the domain phenomenon is the bending of electric lines of force. This will be explained with reference to FIG.

In an active matrix type liquid crystal display device, a large number of gate electrodes are sequentially selected, and a data signal is applied to each source electrode of a large number of pixels belonging to the selected gate electrode. Now, consider a case where a large number of pixels T belonging to a certain gate electrode are turned on every other time and the remaining pixels are turned off. FIG. 6 is a diagram schematically showing the state of electric lines of force when a conventional liquid crystal display device is driven in this manner. The case where a voltage is applied to 19 is shown. Originally, electric lines of force from the pixel electrode 19 to the common electrode 37 should occur between the pixel electrode of the driven TPT and the common electrode, but between the driven TPT and the undriven TPT. It is thought that unnecessary lines of electric force (curved lines of electric force indicated by 41 in FIG. 6) are also generated between the pixel electrode and the pixel electrode. The alignment direction of liquid crystal molecules in the area where these unnecessary electric lines of force occur is different from the alignment direction in the area where normal electric lines of force occur, so this is also likely to cause the domain phenomenon. Seem. Such unnecessary electric lines of force also occur in the end regions of off-state pixel electrodes that line up along data electrodes to which on-signals are applied.

This domain phenomenon should be viewed as a problem and solved (
An example of a document in which research has been conducted and the results thereof are presented is Japanese Patent Application Laid-Open No. 60-243633.

According to this publication, in order to quickly eliminate the domain phenomenon after it occurs, the gap between the source electrode of the TFT and the side of the pixel electrode is made as straight as possible. Roughly speaking, in the case of a liquid crystal display device for color display, the gap created between adjacent color filters is replaced by the gap between the above-mentioned source electrode and the pixel electrode on the side that is not driven by this source electrode, which is close to this source electrode. They are aligned so that they face each other.

(Problems to be Solved by the Invention) However, as described above, making the gap between the source electrode and the pixel electrode as straight as possible impairs the degree of freedom in pixel arrangement of the liquid crystal display device. . Further, alignment so that the gaps accurately face each other requires more accurate alignment, which is not preferable in terms of the manufacturing process.

In addition, no countermeasures will be taken against the domain phenomenon at the bent part of the electric fiber (the part indicated by 41 in Figure 6), and the display quality will deteriorate due to defects in the alignment of liquid crystal molecules in this part. It will be damaged.

The present invention has been made in view of the above-mentioned points, and an object of the present invention is to provide a liquid crystal display Mf! in which the domain phenomenon is less likely to occur, and even if the domain phenomenon occurs, it is less visible. It is about providing.

(Means for Solving the Problems) In order to achieve this object, according to the present invention, an active matrix drive type liquid crystal display device includes a pixel electrode substrate provided with a switching element and a common electrode substrate. An insulating layer having a flat surface is provided on the above-mentioned pixel electrode substrate surface, and an insulating layer is formed on the above-mentioned flat surface of this insulating layer (to be connected to the above-mentioned switching element through a contact hole provided in this insulating layer). It is characterized in that a pixel electrode is provided at.

In carrying out the present invention, it is preferable to provide the electrical isolation region of the pixel electrode in a region above the data electrode of the switching element.

Note that if the liquid crystal display device is capable of color display and has a color filter on the common electrode substrate, there is a layer on the color filter of the common electrode substrate between the color filter and the substrate surface. It is preferable to provide an insulating layer for flattening the concave and convex structure, and to provide a common electrode on this insulating layer.

(Function) According to such a configuration, the irregularities mainly formed by the switching element, the scanning electrode of the switching element, the data electrode of this switching element, and the pixel electrode substrate surface are covered with an insulating layer having a flat surface. I can do it. Therefore, the gap for liquid crystal filling between the pixel electrode substrate and the common electrode substrate has a substantially uniform size in any part of the open substrate surface, so that the various conditions for aligning the liquid crystal molecules can also be made uniform. Therefore, it is possible to prevent the domain phenomenon caused by the step from occurring.

Furthermore, since the switching element and its scanning and data electrodes are covered with an insulating layer, it is possible to form the pixel electrode on this insulating layer up to the area above where the switching element and both electrodes are formed. become able to do. Therefore, an isolation region for electrically isolating the pixel electrodes in contact with IIa can be provided in the region above the scanning electrode and the region above the data electrode.

In a preferred embodiment of the invention, between adjacent pixel electrodes,
An electrically isolated region in a direction parallel to the stripe direction of the data electrode of the switching element is provided in a region above the insulating layer portion above the data electrode. The data electrodes and scanning electrodes are generally formed of a light-shielding metal thin film. In this way, the electrically isolated region between the data electrode and the parallel pixel electrode, where domain phenomena caused by bending of electric lines of force are likely to occur, can be covered with these light-shielding metals, thereby preventing this domain phenomenon. will no longer be recognized by those looking at display bag M.

(Example) The active matrix type liquid crystal display bag of the present invention will be described below with reference to FIGS. 1 and 2. An example will be explained below. It should be noted that the drawings used in the following explanation are only schematic illustrations to facilitate understanding of the present invention, and therefore, it should be understood that the present invention is not limited only to these illustrated examples.

Further, in each figure, common constituent components are indicated by the same reference numerals. Furthermore, constituent components similar to those of the prior art are denoted by the same reference numerals as those of the prior art.

8.6 Figure 1 (A) mainly shows the M distribution relationship of each component on the substrate (pixel electrode substrate) on the side where the switch jig element is provided in the active matrix type liquid crystal display device of the present invention. FIG.

In this case, the switching element is a thin film transistor (
This will be explained using an example of TPT).

In FIG. 1(A), 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. . In addition, a TFT 15 is formed in the area where these two electrodes intersect, and is indicated by 1 in the figure.
The part indicated by 7 becomes the train electrode of this TF''N5.

Although not shown in FIG. 1(A) (described later with reference to FIG. 1(B)), the liquid crystal display device of the present invention includes a source electrode 11, a source electrode 11, An insulating layer with a flat surface is provided to cover the irregularities mainly formed by the gate electrode 13, TPT+5 and the substrate surface, and a pixel electrode 51 (indicated by diagonal lines in FIG. 1(A)) is provided under this insulating layer. (shown). This pixel electrode 51 is connected to the train electrode 17 under this insulating layer through a contact hole 53 provided in the insulating layer. Further, by utilizing the presence of such an insulating layer, the pixel electrode 51 in this embodiment is formed as follows.

An electrically isolated region 551Fr above the source electrode 11 in a direction parallel to the stripe direction of the source electrode between m-contact pixel electrodes 51 among the pixel electrodes 51 linearly arranged along the stripe direction of the gate electrode 13 The source electrode is formed in the region so as to fit within the region where the source electrode is formed. Therefore, the pixel electrode in this case also exists above the region where the TFT 15 is formed.

FIG. 1(B) is a schematic cross-sectional view of the pixel electrode substrate shown in FIG. 1(A) taken along the line ■--■ shown in FIG. 1(A). Note that, in order to avoid complicating the drawings, hatching indicating a cross section is partially omitted from the illustration.

In FIG. 1(B), 21 indicates a glass substrate as a substrate, 23 indicates a gate insulating film, 25 indicates an amorphous film, and 57 indicates the source electrode 11, the gate electrode 13, the TPTI 5, and the substrate surface. The above-mentioned insulating layer 57 is shown for flattening the unevenness mainly composed of the insulating layer 57, and a contact hole 53 is formed in a region of the insulating layer 57 corresponding to the train electrode 17.

As can be understood from FIG. 1 CB), since the insulating layer 57 is provided, the electrical reduction region M 55 between the pixel electrodes can be formed above the source electrode.

For this reason, the display data of one data electrode among the many source electrodes (data electrodes) into which display data is always written becomes a signal that continuously shows a high level, and this data electrode and this data electrode are Even if a domain phenomenon occurs for a long time between the pixel electrode and the pixel electrode in the off-state, this domain phenomenon can be shielded by the source electrode and not be noticed by the person viewing the liquid crystal display device.

If a liquid crystal display device is constructed using such a pixel electrode substrate of the present invention and a conventional common electrode substrate, the domain phenomenon caused by steps will be completely eliminated if the liquid crystal display device is a monochrome display device. It will no longer occur. In general, regardless of color display or monochrome display, the domain phenomenon caused by the bending of electric lines of force is blocked by the gate electrode. There will be no more recognition.

Further, in the case where the liquid crystal display device is a color display device, a device using a conventional common electrode substrate provided with a color filter and the pixel electrode substrate of the present invention as shown in FIG. Since there is no difference in level on the pixel electrode substrate side, the display quality is superior to that of conventional ones.In addition, with a color display liquid crystal display device having such a configuration, it is difficult to obtain an excellent display. In this case, it is preferable that the common electrode substrate has a structure as shown in the cross-sectional view in FIG.

In FIG. 2, numeral 31 indicates a glass substrate, and a color filter 33 is provided on this glass substrate 31. Further, in the common electrode substrate according to the present invention, the color filter 33 is placed on the glass substrate 31 including the color filter 33.
In order to flatten the step mainly formed on the surface of the substrate 31, an insulating layer 61 covering the step and having a flat surface is provided, and a common electrode 37 is provided on the insulating layer 61.

The color display liquid crystal of the present invention is formed by sealing liquid crystal between a pixel electrode substrate as shown in FIGS. 1(A) and (8) and a common electrode substrate as shown in FIG. In the display device, the domain phenomenon caused by the step 1 does not occur at all, but the domain phenomenon occurs due to the step in the contact hole 53 portion and the bending of the lines of electric force in the electrical isolation region 55 between the pixel electrodes. However, since this domain phenomenon is blocked by the source and train electrodes, a person viewing the liquid crystal display device from the pixel electrode substrate side will not notice this domain phenomenon.

2 Crystal 6 4 Glue 1 Method Next, in order to deepen the understanding of the liquid crystal display device of the present invention, an example of a method for 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. I will explain about it. It should be noted that the materials, forming methods, numerical conditions, etc. described below are merely examples, and it should be understood that the present invention is not limited to these materials, forming methods, and numerical conditions.

Using an ordinary thin film forming technique, a TF 15 as a switching element, its scanning electrode 13 and data electrode 11 are formed on a glass substrate 21. In this step, a conventional method for manufacturing an active matrix type liquid crystal display device can be used.

Next, T P T +5 and both electrodes +3. In the case of this example, in which an insulating layer 57 having a flat surface was formed on the glass substrate 21 on which I+ was formed, the insulating layer 57 was formed as follows.

On the glass substrate 21 on which the TPT 15 and both electrodes 13 and 11 are formed, polyimide varnish (using something called Sunever 120 manufactured by Hittame Chemical Co., Ltd.) is applied by a spin coating method, and then heated at about 170°C. at a temperature of about 1
Let dry for an hour. The spin coating conditions were set so that the thickness of the polyimide varnish on the flat part of the glass substrate 21 was 4 um. When polyimide varnish was applied under the film formation conditions described above on the step caused by TPTI5 that protruded about 2 um from the substrate surface, the step was 0°3 um on the polyimide varnish surface.
As a result, the protrusion became smoother.

The conditions for forming the polyimide varnish mentioned above should be determined by taking into consideration the shape of the TPT, etc., the viscosity of the varnish used, etc., and are not limited to the conditions of this example.
In general, the material constituting 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 this embodiment includes forming a contact hole 53 in a region corresponding to the train electrode of the TPTI 5, and a separately prepared drive element. such as exposing portions of the scan and data electrodes from the insulating layer 57 to connect them to the insulating layer 57. These processes were carried out by forming a resist mask using a conventional photoetch jig technique, and removing unnecessary portions of the insulating layer 57 using an etching liquid and a rinsing liquid exclusive to Sunever manufactured by Yasan Kagaku Co., Ltd.

Next, the ITOIii! This ITO film is then processed into a predetermined shape (see 9 in FIG. 1(A)) using a photoetching technique to form a pixel electrode 51. and (B) of the present invention (a pixel electrode substrate according to this invention was obtained).

On the other hand, the common electrode substrate already explained using FIG. 2 was formed as follows.

A color filter 3 is formed on a glass substrate 31 by a conventionally known method.
form 3. In this case as well, planarization was performed using SunEver 120 under the same film forming conditions as when forming the 0 pixel electrode substrate with a step difference of approximately 2 um between the color filter 33 surface and the substrate surface. , Sunever 12
Remove unnecessary parts of 0 in the same way as when forming the pixel electrode substrate,
An insulating layer 69 was formed. A common electrode 37 was formed on this insulating layer 69 by a conventionally known method.

The pixel electrode substrate and the common electrode substrate formed as described above are subjected to alignment treatment, and then these substrates are bonded together with a spacer interposed therebetween. After filling the gap between the substrates with liquid crystal, the filling port was sealed to obtain a liquid crystal display device M according to the present invention.

Note that this invention is not limited to the embodiments described above.

In the above-described embodiment, the region that electrically isolates the pixel electrodes 51 in the direction perpendicular to the stripe direction of the data (source) electrode is not particularly formed above the scanning (gate) electrode. We are continuing as usual.

This is because, unlike the data electrodes, the scan electrodes are driven one by one line-by-line at a fairly high speed from the perspective of the person viewing the liquid crystal display M, so the person viewing the liquid crystal display N is on the side of the scan electrodes. This is because it is hardly conceivable to admit domain phenomena. However, it is also possible, of course, to provide this isolation region above the scanning (gate) electrode in a direction perpendicular to the stripe direction of the data electrode, so that the domain phenomenon occurring in this region is covered by the gate electrode.

Further, in the above embodiment, the switching element is TP
This is explained using an example of T. However, if the switching element is a diode or M I M (Metal Insul
It is clear that the present invention can also be applied to liquid crystal display devices configured with other nonlinear switching elements such as ator 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 that flattens the level difference caused by switching elements, etc. For this reason, the domain phenomenon is less likely to occur, and bubbles are less likely to be generated when liquid crystal is sealed. Since the source of the problem can be prevented, the degree of freedom in pixel arrangement is not impaired.

Furthermore, since the insulating layer can be provided to cover the switching elements and the source and gate electrodes, the pixel electrode can be formed even in the upper region where the source and gate electrodes are formed. Therefore, by forming an electrically isolated region between the pixel electrodes, which is a region where the domain phenomenon is likely to occur, for example above the source electrode, the domain phenomenon caused by the bending of the lines of electric force can be shielded by the source electrode.

Therefore, it is possible to provide a liquid crystal display bag Ml in which the domain phenomenon is less likely to occur, and even if the domain phenomenon occurs, it is less visible.Therefore, the liquid crystal display device of the present invention has better contrast characteristics and viewing angle than the conventional one. Improve characteristics.

[Brief explanation of the drawing]

1(A) and 1(B) are a plan view and a cross-sectional view of essential parts for explaining the liquid crystal display device of the present invention, and are a plan view and a cross-sectional view showing a part of a pixel electrode substrate; FIG. 3 is a cross-sectional view of a main part of a liquid crystal display device of the present invention, showing a part of a common electrode substrate. FIGS. 3 to 5 are views of a conventional liquid crystal display device. 3 and 4 are a plan view and a sectional view showing a part of a pixel electrode substrate, FIG. 5 is a sectional view showing a part of a liquid crystal display device, and FIG. 6 is an explanation of the conventional method and the present invention. FIG. 11...Data electrode (source electrode) 13...Scanning electrode (gate electrode) 15...Switching element 17...Train electrode 23...Gate insulating film 25...Amorphous S1.51.51a , 51b・
...Pixel electrode 53...Contact hole 55...Electrical isolation region 57,61 between pixel electrodes...
・An insulating layer with a flat surface. Patent Applicant: Oki Electric Industry Co., Ltd. 61: Insulating layer with flat surface Cross-sectional view showing a part of the liquid crystal display device of this invention FIG. 2 FIG. 3 If D 17 FIG. 4 Provides explanation of a conventional liquid crystal display device Figure 5 for whistling Figure 6 for explaining the conventional and present invention

Claims (2)

[Claims] (1) A pixel electrode substrate provided with a switching element,
In an active matrix drive type liquid crystal display device comprising a common electrode substrate, an insulating layer having a flat surface is provided on the surface of the pixel electrode substrate, and a contact provided on the insulating layer is provided on the flat surface of the insulating layer. A liquid crystal display device comprising a pixel electrode connected to the switching element via a hole. (2) A liquid crystal display device according to claim 1, characterized in that an electrical isolation region of the pixel electrode is provided in a region above the data electrode of the switching element.