JP2010085550A - Liquid crystal display device and electronic equipment - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a liquid crystal display device reducing failures due to foreign material adhesion to an alignment layer, in a lateral electric field type that hardly cause display image sticking. <P>SOLUTION: The liquid crystal display device 100 has a first substrate 10 and a second substrate 20 and drives liquid crystal molecules by an electric field generated between a first electrode 11 and a second electrode 17, which are provided on the first substrate 10. A composite alignment layer 28 formed on the surface of a liquid crystal layer of the first substrate 10 is formed of a low-resistant component derived from polyamic acid and a liquid crystal alignment component derived from soluble polyimide. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a liquid crystal display device and an electronic apparatus.

2. Description of the Related Art Conventionally, a liquid crystal display device that displays an image by arranging a liquid crystal layer between opposed substrates and controlling the orientation of liquid crystal molecules contained in the liquid crystal layer is known.
In recent years, horizontal electric field type liquid crystal display devices have been put into practical use in order to obtain a wider viewing angle.
This is because a pixel electrode and a common electrode are formed on the same substrate as a pair of electrodes for driving the liquid crystal molecules of the liquid crystal layer, and a voltage is applied between the pixel electrode and the common electrode to thereby form a substrate surface. An electric field is generated in a direction substantially parallel to drive liquid crystal molecules in a plane substantially parallel to the substrate surface. In this lateral electric field method, an IPS (In Plane Switch) in which a pixel electrode and a common electrode are formed in the same layer.
hing) method, and FFS (Fringe Fie) in which a pixel electrode and a common electrode are stacked with an insulating film in between
ld Switching) method.

By the way, in a horizontal electric field type liquid crystal display device, the electric field applied to the liquid crystal layer is asymmetric between the two substrates due to its structure, so that the alignment balance of the liquid crystal molecules is likely to be lost, and the residual charges of the alignment film cause burn-in. Problems such as reduction in the contrast of the displayed image and inability to erase afterimages have become prominent.

Against this background, 2 having different characteristics as an alignment agent that is a material for forming an alignment film.
It has been proposed to form an alignment film from a composition containing a seed polyamic acid (for example,
Patent Document 1).
JP 11-193345 A

In Patent Document 1, as a material for forming an alignment film of a liquid crystal layer, a residual charge is small, and
There is disclosed a mixed solution in which a first polyamic acid constituting a polyimide having a large voltage holding ratio and a second polyamic acid constituting a polyimide having a large pretilt angle are mixed.
By using polyimide with a small residual charge and a large voltage holding ratio, once the voltage is applied and then cut off, the charge will not remain in the alignment film, preventing the image to be erased from remaining as an afterimage. it can. On the other hand, a wide viewing angle can be displayed by using polyimide having a large pretilt angle.

Further, Patent Document 1 discloses a method for producing a polyimide alignment film by applying a mixed solution of the two types of polyamic acids described above to a substrate and then heating to remove the solvent and simultaneously dehydrating and condensing the polyamic acid. It is disclosed.
However, in such a production method, it is difficult to make the imidation ratio of the polyamic acid in the mixed solution 100%, and the alignment film surface has adhesiveness due to the remaining polyamic acid, and during the production process There has been a problem that foreign matter adheres to the substrate surface.

The present invention has been made in view of such circumstances, and is a horizontal electric field type liquid crystal display device capable of solving the two problems of deterioration in display image quality due to burn-in and reduction in yield due to adhesion of foreign matter to the alignment film. The purpose is to provide.

In order to solve the above problems, a liquid crystal display device of the present invention includes a first substrate and a second substrate that sandwich a liquid crystal layer, and includes a first electrode and a second electrode provided on the first substrate. A liquid crystal display device for driving liquid crystal molecules constituting the liquid crystal layer by an electric field generated therebetween, wherein the liquid crystal alignment film formed on the liquid crystal layer side surface of the first substrate comprises a low resistance component derived from polyamic acid And a liquid crystal alignment component derived from a soluble polyimide.

According to the configuration of the liquid crystal display device of the present invention, the residual charge of the alignment film can be reduced by the low resistance component derived from polyamic acid, and image burn-in can be prevented. At the same time, a wide viewing angle can be displayed by using a liquid crystal alignment component derived from soluble polyimide. Thus, by using two kinds of aligning agent components, an alignment film having the characteristics of both components is obtained. Therefore, a liquid crystal display device having a wide viewing angle and no display image deterioration due to image sticking can be provided.
Moreover, according to such a structure, even if the imidation ratio of the polyamic acid in the heat treatment does not change, the concentration of the unreacted polyamic acid in the composite alignment film is reduced by using two alignment agents as the alignment agent. , The adhesion of the alignment film surface can be reduced. Therefore, defects due to foreign matters adhering to the alignment film surface can be reduced, and the yield can be improved.

In the liquid crystal display device of the present invention, the liquid crystal alignment film formed on the liquid crystal layer side surface of the second substrate comprises a low resistance component derived from polyamic acid and a liquid crystal alignment component derived from soluble polyimide. It may be a composite alignment film. Alternatively, the alignment film formed on the liquid crystal layer side surface of the second substrate may be made of a soluble polyimide involved in liquid crystal alignment.
According to the former configuration, the same alignment film material can be used for the first substrate and the second substrate,
A production line with good productivity can be constructed. On the other hand, according to the latter configuration, since the second substrate side that is far from the electric field and has little residual charge is only required to be one type of the alignment agent of soluble polyimide, there is an advantage that the alignment agent is easily available.

In the liquid crystal display device of the present invention, the composite alignment film of the first substrate is a first alignment film composed of a low resistance component derived from polyamic acid and a second alignment composed of a liquid crystal alignment component derived from soluble polyimide. It is preferable that a film is sequentially laminated on the surface of the first substrate liquid crystal layer.
According to this configuration, the second alignment film made of the liquid crystal alignment component derived from the soluble polyimide is the uppermost layer of the alignment film, and a liquid crystal display device capable of displaying an image with a wide viewing angle can be obtained. In addition, the adhesion of the alignment film surface due to the residual polyamic acid is eliminated, and foreign matter adhesion can be reduced as much as possible.

An electronic apparatus according to the present invention includes the above-described liquid crystal display device.
With this configuration, an electronic apparatus having a wide viewing angle and high display performance can be obtained.

Hereinafter, although one embodiment of the present invention is described, the following embodiment does not limit the invention according to the claims.
FIG. 1 is a plan view of the liquid crystal display device of the present embodiment as viewed from the counter substrate side together with each component.
FIG. 2 is a cross-sectional view taken along the line HH ′ of FIG. In each figure used for the following explanation,
In order to make each layer and each member large enough to be recognized on the drawing, the scale is different for each layer and each member. The liquid crystal layer side of each substrate of the liquid crystal display device is referred to as an inner surface side, and the opposite side is referred to as an outer surface side.

As shown in FIGS. 1 and 2, in the liquid crystal display device 100 of the present embodiment, the TFT array substrate 10 (first substrate) and the counter substrate 20 (second substrate) are bonded together by a sealing material 52,
A liquid crystal layer 50 is sealed in a region partitioned by the sealing material 52. Seal material 5
A light-shielding film (peripheral parting) 53 made of a light-shielding material is formed in a region inside the formation region 2. A data line driving circuit 201 and an input terminal 202 are formed along one side of the TFT array substrate 10 in the peripheral circuit region outside the sealing material 52, and the scanning line driving circuit is formed along two sides adjacent to the one side. 104 is formed. On the remaining side of the TFT array substrate 10, a plurality of wirings 105 are provided for connecting between the scanning line driving circuits 104 provided on both sides of the display area.

Next, the liquid crystal display device according to the present embodiment will be described with reference to FIGS. 3 is an enlarged plan view of each pixel of the liquid crystal display device, and FIG. 4 is a cross-sectional view of the liquid crystal display device taken along line AA ′ of FIG.

In the display area of the liquid crystal display device 100, a plurality of pixels G are arranged in a matrix. As shown in FIG. 3, the scanning line 1 extends in the horizontal direction (lateral direction in FIG. 3),
The data line 3 extends in the vertical direction (vertical direction in FIG. 3), and a region surrounded on all sides by the scanning line 1 and the data line 3 constitutes one pixel G. A semiconductor layer 4 made of a polycrystalline silicon film is formed in a substantially U shape near the intersection of the data line 3 and the scanning line 1. Contact holes 5 and 6 are formed at both ends of the semiconductor layer 4. One contact hole 5 is a source contact hole that electrically connects the data line 3 and the source region 4 s of the semiconductor layer 4. The contact hole 6 is a drain contact hole that electrically connects the drain region 4d of the semiconductor layer 4 and the drain electrode 7 (see FIG. 4). A pixel contact hole 12 for electrically connecting the drain electrode 7 and a pixel electrode 17 to be described later is formed on the side opposite to the side where the drain contact hole 6 is provided on the drain electrode 7. That is, the drain electrode 7 and the pixel contact hole 12 are provided for each pixel G.

In the TFT 13 in this embodiment, the substantially U-shaped semiconductor layer 4 intersects the scanning line 1.
Since the semiconductor layer 4 and the scanning line 1 intersect at two places, a TFT having two gates on one semiconductor layer, a so-called dual gate type TFT is formed.

The common electrode 11 constitutes a lower electrode, for example, ITO (Indium Tin Oxide, hereinafter referred to as ITO)
For example) and IZO (Indium Zinc Oxide, hereinafter abbreviated as IZO), and a plurality of pixels are formed over the entire display region arranged in a matrix. The pixel electrode 17 is also formed of a transparent electrode such as ITO, and a transparent electrode having fringe-like slits corresponding to one pixel region is patterned. Further, the pixel electrode 17 constitutes an upper electrode, has a slit-like opening 17a in an overlapping portion with the common electrode 11, and a band-like electrode part between the adjacent opening 17a and the opening 17a. 17b
Configure. Then, liquid crystal molecules are driven by an electric field applied between the common electrode 11 and the pixel electrode 17 through the opening 17a.

As shown in FIG. 4, the liquid crystal display device 100 includes a TFT array substrate 10 (lower substrate in FIG. 4) made of a transparent substrate 21 such as glass and quartz, and a counter substrate 20 made of a transparent substrate 22 such as glass and quartz. (The upper substrate in FIG. 4), and the liquid crystal layer 50 is sandwiched between the substrates. A semiconductor layer 4 made of polycrystalline silicon is provided on a transparent substrate 21 constituting the TFT array substrate 10, and a gate insulating film 23 made of a silicon oxide film or the like is formed so as to cover the semiconductor layer 4. The semiconductor layer 4 is a TF that controls switching of each pixel electrode 17.
T13 is configured, and the TFT 13 insulates the gate electrode composed of the scanning line 1 made of molybdenum or the like, the semiconductor layer 4 in which a channel is formed by an electric field from the gate electrode, and the gate electrode and the semiconductor layer 4. A gate insulating film 23, a source electrode constituted by a part of the data line 3, and a drain electrode 7 are provided.

On the TFT array substrate 10, a first interlayer insulating film 24 made of a silicon oxide film in which a source contact hole 5 leading to the source region 4 s in the semiconductor layer 4 and a drain contact hole 6 leading to the drain region 4 d are respectively formed. Is formed. That is, the data line 3 (source electrode) is electrically connected to the source region 4 s of the semiconductor layer 4 through the source contact hole 5 penetrating the first interlayer insulating film 24, and the drain electrode 7 is connected to the first interlayer insulating film 24. The drain region 4d of the semiconductor layer 4 through the drain contact hole 6 penetrating the insulating film 24.
Is electrically connected. The drain electrode 7 is made of the same material as the data line 3 and is formed on the first interlayer insulating film 24. Further, a second interlayer insulating film 25 in which a pixel contact hole 12 leading to the drain electrode 7 is formed is sequentially formed. The second interlayer insulating film 25 is made of an organic resin film such as acrylic.

A common electrode 11 made of a transparent conductive film such as ITO is formed on the second interlayer insulating film 25 so as to cover the entire surface in a substantially solid shape. A third interlayer insulating film 27 is provided on the common electrode 11. Then, the pixel electrode 17 is formed on the third interlayer insulating film 27 with fringe-shaped slits. With the above configuration, the pixel electrode 17 is connected to the pixel contact hole 12.
Thus, the drain electrode 7 is electrically connected to the drain region 4d of the semiconductor layer 4 using the relay electrode as a relay layer. A composite alignment film 28 is provided on the uppermost layer of the TFT array substrate 10 in contact with the liquid crystal layer 50.

The third interlayer insulating film 27 is made of a transparent insulating material such as a low-temperature SiN film. The liquid crystal display device 100 according to the present embodiment includes the common electrode 11 made of a transparent material (ITO) as described above.
The pixel electrode 17 and the third interlayer insulating film 27 sandwiched therebetween constitute a pixel capacitor. Thus, in the liquid crystal display device 100, since the pixel capacitance is made of a transparent material, the light shielding region can be reduced.

On the other hand, the counter substrate 20 has red (R), green (which constitutes a color filter on the transparent substrate 22).
A color material layer 31 of G) or blue (B) is formed for each pixel. Around each color material layer 31, a black matrix 43 (see FIG. 3) made of a light shielding material such as metallic chrome is formed in order to prevent light leakage around the pixels. A region covered with the black matrix 43 constitutes a light shielding region. Further, an overcoat layer 32 for protecting the color material layer 31 and flattening a step due to the color material layer 31 is formed, and an alignment film 33 is formed on the overcoat layer 32 and subjected to rubbing.

Polarizing plates 61 and 62 are disposed on the outer surface sides of the TFT array substrate 10 and the counter substrate 20. In addition, a backlight 90 including a light guide plate 91 and a reflection plate 92 is provided on the back side of the TFT array substrate 10 (the lower side in FIG. 4).

The composite alignment film 28 is formed of a low resistance component derived from polyamic acid and a liquid crystal alignment component derived from soluble polyimide. The “low resistance component” mentioned here is a polyimide resin obtained by subjecting a general polyamic acid (polyamic acid) as a material for forming a liquid crystal alignment film to a dehydration ring-closing reaction (imidation reaction) by heating. The specific resistance is low. Such a low-resistance component has a characteristic of approaching the optimum Vcom when the power supply is turned on again, although there is a fluctuation of the Vcom that has been adjusted initially when the power supply of the liquid crystal display device 100 is turned on and off. is doing. Therefore, it is disadvantageous for short-term image sticking for about 3 hours, but it is advantageous for long-term image burn of 1 day or longer.

The liquid crystal display device 100 of the present embodiment is for the purpose of compensating for the disadvantages of the low resistance component, that is, the weakness to short-term image sticking and the point that the surface has adhesiveness when the imidization rate is low. Soluble polyimide is mixed into the composite alignment film 28 as an alignment component.
Since soluble polyimide has a higher specific resistance than polyimide resin derived from polyamic acid, Vcom once adjusted is unlikely to fluctuate even when the power is turned on or off. On the other hand, when the power is turned on again, the adjusted optimum Vcom is shifted. Taking this into consideration, the optimum value of Vcom is preliminarily set and has a characteristic that the lifetime is shortened. Therefore, contrary to the low resistance component described above, it is advantageous for short-term seizure, but is disadvantageous for long-term seizure. is there.

In this way, by using together two components that have the properties of complementing each other against burn-in,
Each disadvantage can be solved, and an alignment film having excellent resistance to both short-term and long-term image sticking can be obtained. In addition, since the soluble polyamide is excellent in the liquid crystal alignment, the liquid crystal display device 100 having high image display characteristics can be provided by increasing the alignment of the liquid crystal molecules in the composite alignment film 28.

Since the low resistance component is derived from polyamic acid, the imidation rate is theoretically 10
Although 0% is required, in practice, it is inevitable that unreacted polyamic acid remains. For this reason, conventionally, there has been a defect that the surface exhibits adhesiveness and adheres foreign matter.
Also with respect to such a problem, by using soluble polyimide, the adhesiveness of the surface of the composite alignment film 28 can be reduced, and defects due to adhesion of foreign matter can be reduced.

The ratio of the low resistance component and the liquid crystal alignment component contained in the composite alignment film 28 is determined by the liquid crystal layer 50.
Depending on the type and desired characteristics, it can be appropriately selected.
The composite alignment film 28 may have a laminated structure in addition to a single layer structure. In the case of a single layer configuration, in addition to the configuration in which the two components are homogeneous in the composite alignment film 28, the concentration of the liquid crystal alignment component increases from the transparent substrate 21 side surface toward the liquid crystal layer 50 side surface. Good.

In the case of a laminated structure, it is necessary that the liquid crystal alignment component layer is stacked on the low resistance component layer, that is, the liquid crystal alignment component layer is the uppermost layer of the composite alignment film 28. With the liquid crystal alignment component layer as the uppermost layer, the alignment of the liquid crystal layer 50 is kept good, and the adhesive surface of the low resistance component layer is covered with the liquid crystal alignment component layer, so that foreign matters are present on the surface of the composite alignment film 28. It can prevent adhesion. In the case of the laminated structure, in addition to the two-layer laminated structure in which the boundary surface between the low-resistance component layer and the liquid crystal alignment component layer is clear, both components diffuse to each other at the boundary surface, and the composite layer 28
The structure may be a two-layer structure when the whole is viewed macroscopically. That is, there may be a mixed region composed of these two components between the low resistance component layer and the liquid crystal alignment component layer.

The composite alignment film 28 is prepared by preparing a mixed solution in which polyamic acid and soluble polyimide as raw materials are dissolved in an organic solvent, and applying this mixed solution, regardless of whether it is a single layer structure or a stacked structure. Then, it is obtained by drying and heating.
In addition to the flexographic printing method and the spin coating method, a droplet discharge method typified by an ink jet method can be used for applying the mixed solution. Also, the temperature and time of drying and heat treatment are
Although it can select suitably according to the kind of a solvent, a polyamic acid, and soluble polyimide, it shall be below the heat-resistant temperature of TFT structural members, such as the 3rd interlayer insulation layer 27 mentioned above.

The drying step is for vaporizing and removing the organic solvent of the mixed solution. During this step, the polyamic acid having a relatively high surface tension flows toward the transparent substrate (first substrate) 21 and the surface Soluble polyimide with low tension moves to the surface side and is fixed. Subsequently, the composite alignment film 28 having a structure in which the second alignment film derived from the soluble polyimide is laminated on the first alignment film derived from the polyamic acid by performing a heat treatment for dehydrating and ring-closing the polyamic acid to imidize.
Is obtained. As the polyamic acid and the soluble polyimide used here, general-purpose products for forming a liquid crystal alignment film can be used.

As described above, according to the present invention, even if unreacted polyamic acid remains in the composite alignment film 28, the outermost surface of the composite alignment film 28 becomes soluble polyimide, and thus exhibits adhesiveness. Therefore, it is possible to reduce the occurrence of defects due to foreign matter adhesion.

In the liquid crystal display device 100 of the present embodiment, the alignment film 33 on the counter substrate 20 (transparent substrate 22) side is a single component alignment film, but this is applied to the TFT array substrate 10 (transparent substrate 21).
It is also possible to use a composite alignment film 28 similar to
In addition, the liquid crystal device 100 of this embodiment is an FFS system in which the pixel electrode 17 and the common electrode 11 are stacked on the same substrate on the TFT array substrate 10 (transparent substrate 21). However, the present invention is not limited to this, and an IPS system in which the pixel electrode 17 and the common electrode 11 are formed in the same layer of the TFT array substrate 10 may be used.

(Electronics)
FIG. 5 is a perspective configuration diagram of a mobile phone which is an example of an electronic apparatus provided with a liquid crystal display device according to the present invention in a display unit. The mobile phone 1300 includes the liquid crystal display device of the present invention in a small size display unit. A plurality of operation buttons 1302, an earpiece 1303, and a transmission port 1304.
It is configured with.

The liquid crystal display device of the above embodiment is not limited to the above mobile phone, but an electronic book, a personal computer, a digital still camera, a liquid crystal television, a viewfinder type or a monitor direct view type video tape recorder, a car navigation device, a pager, an electronic notebook, It can be suitably used as an image display means for a calculator, a word processor, a workstation, a videophone, a POS terminal, a device equipped with a touch panel, etc. In any electronic device,
A liquid crystal display portion that is resistant to image sticking and has a wide viewing angle can be obtained.

It is a figure which shows the planar structure of a liquid crystal display device. It is a figure which shows the side cross-section structure by the HH 'arrow of FIG. It is an enlarged plan view of each pixel of a liquid crystal display device. It is a figure which shows the side cross-section structure by the AA 'line arrow of FIG. It is a perspective view of the mobile phone which is an example of an electronic device.

Explanation of symbols

10 ... TFT array substrate (first substrate), 11 ... Common electrode (first electrode), 17 ... Pixel electrode (
(Second electrode), 20 ... counter substrate (second substrate), 21 ... transparent substrate, 28 ... composite alignment film, 33 ...
Alignment film 50 ... Liquid crystal layer 100 ... Liquid crystal display device 1300 ... Mobile phone (electronic device)

Claims (5)

A first substrate and a second substrate sandwiching the liquid crystal layer are provided, and liquid crystal molecules constituting the liquid crystal layer are driven by an electric field generated between the first electrode and the second electrode provided on the first substrate. A liquid crystal display device,
The alignment film formed on the liquid crystal layer side surface of the first substrate is a composite alignment film comprising a low resistance component derived from polyamic acid and a liquid crystal alignment component derived from a soluble polyimide. apparatus. The alignment film formed on the liquid crystal layer side surface of the second substrate is a composite alignment film composed of a low resistance component derived from polyamic acid and a liquid crystal alignment component derived from soluble polyimide. 2. A liquid crystal display device according to 1. The liquid crystal display device according to claim 1, wherein the alignment film formed on the surface of the second substrate on the liquid crystal layer side is made of a soluble polyimide involved in liquid crystal alignment. The composite alignment film of the first substrate includes a first alignment film composed of a low-resistance component derived from polyamic acid and a second alignment film composed of a liquid crystal alignment component derived from soluble polyimide, on the first substrate liquid crystal layer side. The liquid crystal display device according to any one of claims 1 to 3, wherein the liquid crystal display device is sequentially laminated on a surface. An electronic apparatus comprising the liquid crystal display device according to any one of claims 1 to 4.

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