JP2582479B2 - Liquid crystal display - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a matrix type liquid crystal display device which performs display with a large number of picture element electrodes arranged in a matrix.

[0002]

2. Description of the Related Art In an active matrix type liquid crystal display device, a liquid crystal display cell is formed by sandwiching a liquid crystal layer between a picture element electrode substrate and a counter electrode substrate. The pixel electrode substrate has a large number of pixel electrodes arranged in a matrix on an insulating transparent substrate. A functional element for applying a predetermined voltage is connected to each picture element electrode. As the functional element connected to the picture element electrode, a TFT (thin film transistor), an MIM (metal-insulating layer-metal) element, a transistor, a diode, a varistor, and the like are used.

[0003] In such a pixel electrode substrate, in order to prevent mechanical or chemical damage to each of the pixel electrodes and each of the functional elements, and to prevent electrical leakage between the respective pixel electrodes, an external device is provided. An insulating protective film is formed on the entire surface of the pixel electrode substrate except for a portion for connecting to a terminal or the like. The insulating protective film is S
It is made of an inorganic nitride such as iN _x or SiO ₂ , an inorganic oxide or the like. An alignment film for aligning liquid crystal molecules of the liquid crystal layer is laminated on the insulating protective film. The alignment film is formed, for example, by rubbing a polyimide resin film.

A counter electrode is provided on a counter electrode substrate opposed to a picture element electrode substrate with a liquid crystal layer interposed therebetween. Further, an alignment film is formed on the entire surface on the counter electrode. This alignment film is formed in the same manner as the alignment film on the pixel electrode substrate. By the alignment film on the pixel electrode substrate and the alignment film on the counter electrode substrate,
Twist alignment of liquid crystal molecules becomes possible.

As described above, in a liquid crystal display device using a polyimide resin as an alignment film, it has been clarified that internal polarization easily occurs between the alignment film and a pixel electrode (see Japanese Patent Application Laid-Open No. HEI 9-163572). No. 2-171721). The detailed mechanism of the occurrence of internal polarization has not been clarified, and there are various theories. The present inventors believe that the cause is an electric double layer formed between the pixel electrodes due to the specific adsorption of polar molecules and ions to the polyimide film inside or on the surface. This internal polarization adversely affects the voltage applied to the liquid crystal layer. That is,
Due to this internal polarization, a DC offset voltage is superimposed on an AC voltage applied between the picture element electrode and the counter electrode to change the orientation of the liquid crystal molecules, and the AC voltage is in a non-equilibrium state. As described above, when the DC component is superimposed on the AC voltage applied to the liquid crystal layer to be in an offset state, flicker occurs on the display screen, and the contrast is reduced. Furthermore, the unevenness of the DC component to be superimposed causes unevenness of the contrast, thereby significantly deteriorating the display quality.

When a TFT is used as a functional element connected to each pixel electrode, the gate voltage due to the capacitance formed between the gate electrode and the drain electrode is coupled to the drain voltage, and the DC component is superimposed. You. This DC component is compensated to some extent by applying a DC component to the counter electrode. However, the DC component superimposed on the drain electrode greatly varies depending on the source electrode voltage level, and cannot be completely compensated. Therefore, the DC component that cannot be completely compensated is applied to the polyimide-based resin alignment film, and further increases the internal polarization described above. The increased internal polarization is one cause of an afterimage.

In order to solve the above problems, for example, the insulating protective film on each pixel electrode is partially removed, and an alignment film of a polyimide resin is directly laminated so as to be in contact with a part of the pixel electrode. Configurations are possible. According to this configuration,
Functional elements and the like in portions other than the pixel electrodes are protected by the insulating protective film, and the internal polarization generated on each pixel electrode can be suppressed.

However, in such a structure, conductive foreign matter is mixed in the liquid crystal layer, and the alignment film on the region of the pixel electrode where the insulating protective film is not formed and the alignment film on the counter electrode are in contact with each other. Then, a leak current is generated between these electrodes. When such a leak current is generated, a voltage is not sufficiently applied to the liquid crystal layer in a portion where the current is generated, which causes a pixel defect. The occurrence of picture element defects causes a decrease in display quality of the liquid crystal display device, and lowers the yield of the display device.

In order to solve the problem of the occurrence of picture element defects due to the incorporation of foreign matter into the liquid crystal layer, as disclosed in Japanese Patent Application Laid-Open No. H2-219028, the region from which the insulating protective film has been removed is divided into a large number. It is conceivable to reduce the area of the divided part. In the picture element electrode substrate described in this publication,
On a pixel electrode formed in a rectangular area defined by the gate bus wiring and the source bus wiring, an insulating protective film is formed in an area excluding a large number of small rectangular areas. If the region where the insulating protective film is removed is divided into a number of small portions in this way, even if foreign matter enters the liquid crystal layer,
Generation of a leak current can be suppressed.

[0010]

However, if there is a region where the insulating protective film is formed on the picture element electrode and a region where the insulating protective film is not formed, the alignment film formed thereon may have irregularities. become. When the rubbing treatment is performed on the alignment film having such irregularities, there are portions where the rubbing treatment cannot be sufficiently performed. In a portion where the rubbing treatment of the alignment film is insufficient, the alignment of the liquid crystal layer is disturbed, and the display quality of the liquid crystal display device is reduced.

To solve such a problem, FIG.
(Japanese Patent Application No. 1-27) has been proposed.
No. 6332). In the substrate of FIG. 6, the region from which the insulating protective film has been removed is defined as a vertically long region 25, and the longitudinal direction of the vertically long region 25 matches the rubbing direction 26. Depending on the shape and direction of such a vertically long region 25, the pixel electrode 12
There is almost no rubbed portion on the top.

However, even if the region where the insulating protective film is not formed is formed in such a shape, a portion that is not subjected to the rubbing treatment may remain. FIG. 7 is a sectional view of the picture element electrode substrate taken along the line CC in FIG. As shown in FIG. 6, the substrate 10 has a gate bus line 1 on an insulating substrate 11.
4 are formed, and the source bus wiring 13 is provided on the gate insulating film 15b covering the gate bus wiring 14. The picture element electrode 12 is formed on the gate insulating film 15b. As shown in FIGS. 6 and 7, an insulating protective film 16 is formed in a region other than the vertically long region 25 on the picture element electrode 12. The alignment film 17 is formed on the entire surface of the insulating protection film 16 and the vertically long region 25 of the pixel electrode 12.

As shown in FIG. 7, on the picture element electrode 12, a step is formed at the end of the vertical region 25 by the insulating protective film 16, so that the alignment film 17 near the end of the vertical region 25 is subjected to the rubbing treatment. Some parts may not be created. If the rubbing treatment is insufficient, the orientation of the liquid crystal molecules in the liquid crystal layer will be insufficient, and this will appear as display unevenness on the display screen. Such display unevenness degrades image quality.

An object of the present invention is to solve the above-mentioned problems, and an object of the present invention is to suppress the influence of the internal polarization phenomenon when using a polyimide resin as an alignment film, It is an object of the present invention to provide a liquid crystal display device capable of suppressing the generation of picture element defects due to leakage between the liquid crystal display and the counter electrode, and capable of uniformly performing a rubbing treatment on the picture element electrodes.

[0015]

According to the present invention, there is provided a liquid crystal display device comprising: a pair of insulating substrates; a large number of picture element electrodes arranged in a matrix on an inner surface of one of the pair of substrates; A liquid crystal layer sealed between the pair of substrates, an insulating protective film formed of any of an inorganic nitride and an inorganic oxide formed in a region excluding a vertically long region on the picture element electrode; A film and an alignment film formed of a rubbed polyimide resin formed on the entire surface of the vertical region, wherein an end of the vertical region is located outside the pixel electrode, and The longitudinal direction substantially coincides with the direction of the rubbing treatment of the alignment film, whereby the object is achieved.

[0016]

The magnitude of the internal polarization can be determined by measuring the offset DC voltage of the counter electrode required to eliminate flicker on the display screen. In this measurement, it is necessary to fix the gate voltage to the ON voltage in order to remove the coupling of the gate voltage waveform. It is also possible to make a simple liquid crystal cell without a functional element such as a TFT and evaluate by applying a simulated waveform from the outside between electrodes sandwiching the liquid crystal layer.

FIG. 4 shows the difference in the magnitude of the internal polarization depending on the presence or absence of the insulating protective film. FIG. 4 shows the magnitude of the internal polarization after applying the DC voltage shown on the horizontal axis to the display device for 30 minutes. The value of internal polarization was determined by measuring the voltage required to eliminate flicker as described above. FIG. 4 shows the internal polarization of a display device having a pixel electrode substrate in which an insulating protective film is formed on the entire surface of the pixel electrode substrate, and a polyimide resin alignment film is further formed thereon. FIG. 4 shows the internal polarization of the display device in which the insulating protective film only on the pixel electrodes of the pixel electrode substrate has been removed. As is clear from the comparison of and in FIG.
The internal polarization of the display device in which the insulating protective film on the pixel electrode is removed is smaller than that of the display device in which the insulating protective film is formed on the entire surface of the pixel electrode substrate. The size of the area from which the insulating protective film has been removed is about 1 of the pixel electrode area.
It has been confirmed that an effect of suppressing internal polarization is obtained when the ratio is / 100 or more.

FIG. 5 (a) is a schematic diagram for explaining how the occurrence of leakage current is suppressed by the vertically long region where the insulating protective film of the present invention is not formed. For comparison, FIG. 5B is a schematic diagram illustrating a case where the region where the insulating protective film is not formed forms one large region.
In FIG. 5A, a pixel electrode 41 is placed on an insulating substrate 40.
And a functional element 48 are provided.
6 have been deposited. The insulating protective film 46 is formed of the pixel electrode 41.
It is deposited in a region excluding the upper vertical region 50. An alignment film 43 is deposited on the entire surface of the insulating protection film 46 to form a pixel electrode substrate 52. In the counter electrode substrate 53 facing the pixel electrode substrate 52, the color filter 47 is formed on the insulating substrate 45, and the counter electrode 42 is formed on the entire surface of the color filter 47. Further, the counter electrode 42
An alignment film 44 is formed on the entire upper surface. Liquid crystal 55 is sealed between the pixel electrode substrate 52 and the counter electrode substrate 53.

In such a liquid crystal display device, when conductive foreign matter 49 is mixed in the liquid crystal layer, the foreign matter 49 is electrically connected to the counter electrode 42 on the counter electrode substrate 45 via the alignment film 44. It will be in the connected state. However, since the vertically long region 50 where the alignment film 43 is in contact with the pixel electrode substrate 52 is narrow, the foreign matter 49 and the pixel electrode 41 are not electrically connected. That is, the state between the pixel electrode 41 and the counter electrode 42 is kept electrically insulated. Therefore, no leak current due to the foreign matter 49 occurs.

On the other hand, as shown in FIG. 5B, a large area 51 on the picture element electrode 41 where the insulating protective film 46 is not formed.
, The conductive foreign matter 49 is electrically connected to the pixel electrode 41 on the pixel electrode substrate 52 via the alignment film. Therefore, the pixel electrode 41 and the counter electrode 4
2 are electrically connected to each other, and a leak current is generated between these electrodes.

In the present invention, since the longitudinal direction of the vertically long region where the insulating protective film is not formed substantially coincides with the direction of the rubbing treatment of the alignment film, the rubbing treatment can be performed uniformly. In addition, since the end of the vertical region is not on the pixel electrode, even if a region that is not subjected to the rubbing process is generated at the end of the vertical region, the unprocessed region does not occur on the pixel electrode. Therefore, deterioration of image quality due to poor alignment of liquid crystal molecules does not occur.

[0022]

Embodiments of the present invention will be described below. FIG. 1 is a plan view of a picture element electrode substrate used in one embodiment of the liquid crystal display device of the present invention. A large number of gate bus lines 14 are formed in parallel on an insulating substrate,
A large number of source bus lines 13 are formed orthogonally to. The pixel electrodes 12 are arranged in a large number of rectangular regions in a matrix defined by the gate bus lines 14 and the source bus lines 13. On the gate bus wiring 14 near the intersection of the gate bus wiring 14 and the source bus wiring 13, a TFT 15 is provided as a functional element. The picture element electrode 12 is connected to the gate bus wiring 14 via the TFT 15.
And the source bus line 13.

FIG. 1 shows a display device using the substrate 10 of FIG.
FIG. 2 is a sectional view taken along the line AA in FIG. Also,
FIG. 3 is a cross-sectional view taken along the line BB of FIG. This embodiment will be described according to the manufacturing process. On an insulating substrate 11 such as a glass substrate, a Ta metal
deposited to a thickness of nm. This Ta metal layer is patterned by photolithography and etching,
Gate bus wiring 14 was formed. Part of the gate bus wiring 14 functions as a gate electrode. Next, a 200 nm-thick Ta ₂ O _{5 is formed} on the gate bus line 14 by anodic oxidation.
An anodic oxide film 15a made of was formed. Anodized film 15
a 200 nm thick by plasma CVD
A gate insulating film 15b made of SiN _x was deposited. Intrinsic semiconductor amorphous silicon (a-Si (i)) to be a semiconductor layer 15c later on the entire surface on the gate insulating film 15b.
The layer was continuously deposited to a thickness of 30 nm, and a SiN _x layer, which later became the insulating layer 15d, was deposited to a thickness of 200 nm. The SiN _x layer was patterned into a predetermined shape, and an insulating layer 15 d was formed except for a portion of the gate bus line 14 that functions as a gate electrode.

An a-Si (n ⁺ ) layer which will later become a contact layer 15 e is formed on the entire surface covering the insulating layer 15 d by plasma C
It was deposited to a thickness of 40 nm by the VD method. Next, this a
The -Si (n ⁺ ) layer and the a-Si (i) layer were patterned into a predetermined shape to form a semiconductor layer 15c and a contact layer 15e. The contact layer 15e is provided for ohmic contact between the semiconductor layer 15c and the source electrode 15f and the drain electrode 15g. At this point, the contact layer 15e is connected on the insulating layer 15d.

A metal layer made of Ti metal or Mo metal is formed on the entire surface of the substrate by sputtering to a thickness of 300 nm.
This metal layer is patterned by etching to form a source electrode 15f and a drain electrode 15g.
Was formed. At this time, the contact layer 15e is also etched away on the insulating layer 15d, and the source electrode 15f is removed.
And a portion below the drain electrode 15g. The TFT 15 is manufactured as described above. Further, the source bus wiring 13 is formed simultaneously with the source electrode 15f and the drain electrode 15g. Therefore, the source bus wiring 13 is formed by the gate insulating film 15b and the anodic oxide film 1
It intersects with the gate bus line 14 via 5a.

Next, an ITO film was deposited to a thickness of 100 nm on the entire surface of the substrate 11 by a sputtering method. This ITO film is patterned into a predetermined shape, and the picture element electrode 1 is formed.
2 was formed. Next, the entire surface of the pixel electrode 12 is covered with SiN.
_An insulating protective film 16 made of _x was deposited to a thickness of 500 nm. The insulating protective film 16 was removed by photolithography and etching to form a vertically long region 25 having the shape shown in FIG. The material of the insulating protective film 16 is not limited to inorganic nitrides such as SiN _x , but may be SiO ₂ , Ta ₂ O ₅ , Al
Inorganic oxides such as ₂ O ₃ , Y ₂ O ₃ and TiO ₂ can also be used. The vertically long regions 25 are provided at three places per one pixel electrode 12 and are formed substantially in the diagonal direction of the pixel electrode 12. The longitudinal direction of the vertically long region 25 coincides with the rubbing direction of the alignment film 17 made of a polyimide resin to be formed later. 3 vertical areas 2
5, the vertically long region 25 located at the center is longer than the other two vertically long regions. As shown in FIGS. 1 and 3, neither end of the vertically long region 25 exists on the pixel electrode 12, but between the pixel electrode 12 and the gate bus line 14 and between the pixel electrode 12 and the source. It is located between the bus wiring 13.

Further, an alignment film 17 made of a polyimide resin was formed on the entire surface of the insulating protective film 16. The alignment film 17
After offset printing of a polyimide resin (trade name Optmer AL, manufactured by Nippon Synthetic Rubber Co., Ltd.) to a thickness of 60 nm, 20
It is formed by performing a heat treatment at 0 ° C. for one hour.
The alignment film 17 is rubbed using a nylon woven fabric in a direction indicated by an arrow 26 in FIG. As described above, in the present embodiment, the longitudinal direction of the vertically elongated region 25 is made to coincide with the direction of the rubbing treatment of the alignment film 17. As described above, the picture element electrode substrate 10 is completed.

Next, the counter electrode substrate 20 will be described. First, a color filter 22 was formed on a glass substrate 21 by a gelatin staining method. The colors of the color filter 22 are three colors of red, green, and blue. A counter electrode 23 made of ITO was deposited on the entire surface of the color filter 22. Further, an alignment film 24 was formed on the counter electrode 23. Alignment film 2
4 is formed in the same manner as the alignment film 17 described above.

A plastic bead of 5 μm is interposed between the pixel electrode substrate 10 and the counter electrode substrate 20 as a spacer, and these substrates 10 and 2 are separated by using an epoxy adhesive.
0 were pasted together. Further, a liquid crystal (phenylcyclohexane-based liquid crystal, manufactured by Merck) was sealed between the substrates 10 and 20 to complete a liquid crystal display device.

In this embodiment, since the region where the insulating protective film 16 is not formed is provided, internal polarization hardly occurs. Therefore, generation of flicker and reduction in contrast are prevented. In this embodiment, the insulating protective film 16 is used.
Vertically long area 2 in which the area where no is formed has a long shape
5, conductive foreign matter is removed from the liquid crystal layer 30.
, Almost no leakage current occurs between the pixel electrode 12 and the counter electrode 23. Furthermore, since the longitudinal direction of the vertically long region 25 and the direction of the rubbing process of the alignment film 17 are coincident, the rubbing process of the alignment film 17 is performed uniformly. In addition, since the end of the vertically elongated region 25 is not on the pixel electrode 12, even if a portion of the alignment film 17 that has not been subjected to the rubbing process occurs, the unprocessed portion does not exist on the pixel electrode 12. .

[0031]

In the liquid crystal display device of the present invention, the picture element electrode has a region from which the insulating protective film has been removed.
The occurrence of flicker and a decrease in contrast are prevented, and the image quality is improved. In addition, the functional element can be protected. Further, the removal region is a vertically long region, and a leak current between electrodes due to conductive foreign matter is prevented, so that the yield of the liquid crystal display device is improved. Further, in the liquid crystal display device of the present invention, the rubbing treatment of the alignment film can be performed uniformly by the shape of the vertically long region, and thus the image quality is also improved. Even if a portion that is not subjected to the rubbing process occurs, the end of the vertically long region does not exist on the picture element electrode, so that the image quality is not deteriorated due to the disorder of the alignment of the liquid crystal molecules.

[Brief description of the drawings]

FIG. 1 is a plan view of a picture element electrode substrate constituting one embodiment of a liquid crystal display device of the present invention.

FIG. 2 is a cross-sectional view taken along line AA of the liquid crystal display device of the present invention using the picture element electrode substrate of FIG.

FIG. 3 is a sectional view taken along line BB of FIG. 1;

FIG. 4 is a diagram showing a difference in internal polarization depending on the presence or absence of an insulating protective film.

FIGS. 5A and 5B are diagrams showing whether or not a leak current due to foreign matter mixing occurs due to a difference in shape of a region where an insulating protective film is not formed.

FIG. 6 is a diagram showing an improved example of a pixel electrode substrate.

FIG. 7 is a sectional view taken along the line CC of FIG. 6;

[Explanation of symbols]

 Reference Signs List 10 picture element electrode substrate 11, 21 insulating substrate 12 picture element electrode 13 source bus wiring 14 gate bus wiring 15 TFT 15a anodized film 15b gate insulating film 16 insulating protective film 17, 24 alignment film 20 counter electrode substrate 22 color filter 23 Counter electrode 25 Vertical region 26 Arrow indicating rubbing direction

Claims (1)

(57) [Claims] 1. A pair of insulating substrates, a large number of picture element electrodes arranged in a matrix on the inner surface of one of the pair of substrates, and a liquid crystal layer sealed between the pair of substrates. An insulating protection film formed of any of an inorganic nitride and an inorganic oxide formed in a region excluding the vertical region on the picture element electrode, and formed on the entire surface of the insulating protection film and the vertical region. An alignment film made of a rubbed polyimide resin, and the end of the elongated region is located outside the picture element electrode, and the longitudinal direction of the elongated region and the rubbing direction of the alignment film. The liquid crystal display device which approximately matches.