JP3222533B2 - Liquid crystal display device - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention improves the viewing angle characteristics,
The present invention relates to a liquid crystal display device capable of viewing a good image from a wide angle with respect to a screen.

[0002]

2. Description of the Related Art Liquid crystal display devices are used as OA devices such as word processors and personal computers, and image display devices such as portable televisions and information processing devices, taking advantage of their features such as thinness, light weight and low power consumption. . In addition, it has attracted attention as a next-generation image display device that replaces the cathode ray tube in televisions and various information devices, and has realized a multi-pixel screen and higher definition to realize high-quality image display over a larger area. Research and development on the driving method in that case is being advanced.

[0003] However, the liquid crystal display element has a disadvantage that the viewing angle characteristics are inferior to CRTs and the like. An active matrix type liquid crystal display element using a TFT switching element is effective as a liquid crystal display element for realizing the multi-pixel and high definition of the screen as described above. As a liquid crystal, a TN (twisted nematic) liquid crystal is usually used. Used. Especially this T
N-type liquid crystals have a narrow viewing angle range. For this reason, the active matrix type liquid crystal display device using the NT liquid crystal has a problem that the viewing angle characteristics are inferior and that an image is difficult to see from an oblique direction.

As means for solving such a problem,
As disclosed in JP-A-61-67021, JP-A-61-198211, JP-A-61-245186, etc., the surface of a glass substrate or an insulating film underlayer thereon is 1 to 100%. Form a wavy structure in the order of μm, or form a wavy structure with the surface grain system such as an insulating film underlayer of about 0.1 to 1 μm. There is known a technique for improving the viewing angle characteristics by shaking the display.

However, it is difficult to form the surface of the glass substrate or the underlayer of the insulating film thereon on the order of 1 to 100 μm in a wave-like structure in the actual manufacturing process, and there is a problem that the transmission Since the light is scattered by the wavy structure, there is a problem that a displayed image is entirely dark and display quality is deteriorated.

Also, Kalluri R. Sarma et al., “A Wide
-Viewing-Angle 5-in.-Diagonal AMLCD Using Halftone
Grayscale ”, SID 1991 Digest, Paper No.27.7 p555〜
557 discloses a technique in which an insulating film having an outer dimension slightly smaller than the pixel electrode is provided on the pixel electrode to improve the viewing angle characteristics.

FIG. 4 is a plan view of such a liquid crystal display device according to the prior art, and FIG. 5 is a sectional view taken along line A ₁ -A ₂ .

A TFT 4 formed on a TFT substrate 401
03 denotes a gate electrode 407 integral with the scanning line 405, a drain electrode 411 integral with the signal line 409, and a display pixel electrode 4
13 connected to the source electrode 415 and the semiconductor layer 41
7 is a general one whose main part is constituted. On the display pixel electrode 413, an insulating film 419, which is a feature of the liquid crystal display device according to this technique, is formed. The insulating film 419 is provided as one substantially rectangular large pattern in which the display pixel electrode 413 is slightly smaller so as to cover the center of the display pixel electrode 413 except for the peripheral portion. An alignment film 423 is formed on a surface in contact with the liquid crystal 421. On the other hand, the opposite substrate 4
A common electrode 425 and an alignment film 427 are formed on 30. The display pixel electrode 413 and the common electrode 425
The TFT substrate 401 and the opposing substrate 430 are combined so that they face each other, and the liquid crystal 421 is held between the two substrates.

In the liquid crystal display device having such a structure, when a video signal voltage is applied to the display pixel electrode 413, the portion where the insulating film 419 is not disposed on the display pixel electrode 413, that is, the portion of the display pixel electrode 413 The superposed voltage of the video signal voltage and the common electrode application voltage is applied to the liquid crystal 421 in contact with the peripheral portion, and the portion where the insulating film is provided on the display pixel electrode 413, that is, the display pixel electrode 413
Is applied to a portion of the liquid crystal 421 that is in contact with the center of the liquid crystal 421 through a series capacitance of the capacitance of the liquid crystal 421 and the capacitance of the insulating film 419. As described above, the voltage applied to the liquid crystal 421 differs in one pixel.
As a result, two regions with different light transmittance of the liquid crystal are formed within one pixel,
The viewing angle characteristic is improved by making the brightness of the screen when viewed from the front direction and the brightness when viewed from the oblique direction as a whole uniform.

However, in the case where the insulating film 419 is provided on the display pixel electrode 413 as described above, the light transmittance of the liquid crystal greatly changes stepwise within one pixel.
Since there are two areas, the image displayed as one pixel looks like a rough image quality, looks like periodic noise, or suppresses the average brightness of the entire screen There has been a problem that the display quality of the image is deteriorated, for example, the screen appears dark.

[0011]

As described above, the conventional liquid crystal display devices, particularly those using TN type liquid crystal, have a problem that the viewing angle range is narrow and the screen is hard to see. And in the technology devised to solve this problem,
The surface of the glass substrate or the insulating film
In the case of forming a wavy structure on the order of 0 μm, the displayed image is difficult due to the difficulty of forming the wavy structure in the actual manufacturing process and the transmitted light is scattered by the wavy structure. However, there is a problem that the overall image becomes darker and the display quality deteriorates.In addition, when an insulating film is provided on the display pixel electrode, the displayed image looks rough or has a periodic noise. There is a problem that the display quality of an image is deteriorated, for example, the image is seen or the screen appears dark.

The present invention has been made to solve such a problem, and an object of the present invention is to improve the display quality of an image such that the displayed image looks rough or the screen appears dark. It is an object of the present invention to provide a liquid crystal display device having a wide viewing angle and good quality of displayed images by improving the viewing angle characteristics without causing a decrease.

[0013]

Means for Solving the Problems A liquid crystal display device of the present invention includes two substrates having <br/> display pixels electrodes and the common counter electrode are opposed, liquid crystal sandwiched in a gap between the substrate has the door, the arranged opposite the display pixel electrodes, the common counter
In the liquid crystal display device in which a plurality of pixels by the liquid crystal and Contact electrodes are formed, the on the display pixel electrodes of each pixel, the transparent formed in a plurality of islands or stripes each having a tapered side surface insulating Turkey be provided with a film
With the above, regions having different light transmittances are dispersed in each pixel.
It is characterized by being arranged .

[0014] Incidentally, the transparent insulating film, as a specific material, material whose light transmittance and excellent high and insulation, for example _{SiN, Si 3 N 4, Si} x O y , etc. is used. In addition, the dimensions and form are actually set in consideration of the dimensions of the display pixel electrodes, but generally one side is 5 to 10 μm.
A square or rectangular shape of about m, a stripe pattern (or comb shape), or the like is preferable. The film thickness is also set in consideration of the cell gap d and the like so that the viewing angle characteristics can be more effectively improved, but it is generally preferable that the film thickness be about 1 μm or less.

It is preferable to dispose about 20 to 30 such transparent insulating films on one display pixel electrode in consideration of light transmittance and viewing angle characteristics. At this time, it is preferable to set the interval between adjacent pixels to be about the length of one side of one transparent insulating film. Also, the angle of the taper of the side surface is about 30 degrees or more and about 80 degrees or less with respect to the glass substrate surface,
At this time, the area of the tapered surface is 20 to
It is desirable to set it to about 50%.

As the liquid crystal display element, specifically, a TFT active matrix type liquid crystal display element is suitable.

[0017]

In a liquid crystal display element having a display pixel electrode disposed to face and a liquid crystal composition sandwiched between the gaps,
There is a viewing angle dependency of light transmittance caused by light passing through liquid crystals that are relatively different in arrangement depending on the viewing angle of the screen, and the screen is dark and hard to see particularly in an oblique direction. Therefore, a transparent insulating film is partially formed on the display pixel electrode, and 1
A region having two different light transmittances is formed in a pixel to reduce and improve the variation in the apparent brightness of the screen due to the viewing angle characteristics. However, at this time, if the region having the different light transmittance is divided into two large regions within one pixel, the displayed image looks rough or has a periodic noise. Or the average brightness of the entire screen is suppressed, so that the screen looks dark, and the display quality of the image is degraded. Therefore, the regions having different light transmittances are appropriately dispersed and arranged in one pixel. That is, by forming and disposing the transparent insulating film on the display pixel electrode in a plurality of islands or stripes (or a comb shape or the like), the rate of suppressing the light transmittance is adjusted and the light transmittance is increased. By avoiding a step change from a portion, it is possible to avoid a decrease in display quality due to a displayed image appearing rough or periodic noise being seen.

Further, the transparent insulating film has a tapered side surface of about 30 degrees, at which light is appropriately scattered to further improve the viewing angle characteristics.

The effect of the light scattering on the tapered surface and the effect of reducing the apparent brightness of the screen by forming two regions having different light transmittances in one pixel as described above. In combination, the transparent insulating film of the liquid crystal display device according to the present invention can more effectively improve the viewing angle characteristics.

[0020]

Embodiments of the present invention will be described below in detail with reference to the drawings.

FIG. 1 is a plan view showing a TFT substrate of a liquid crystal display device of the present invention, and FIG. 2 is a sectional view showing a structure of the liquid crystal display device of the present invention.

The liquid crystal display device of the present invention has a TFT substrate 20
A counter substrate 30 having a common counter electrode 31 disposed opposite to the TFT substrate 20;
The liquid crystal 21 sandwiched therebetween constitutes the main part. The TFT substrate 20 is provided with a TFT 3 in the vicinity of the intersection between the scanning line 1 and the signal line 2.

The TFT 3 includes a gate electrode 4 formed integrally with the scanning line 1, a drain electrode 5 formed integrally with the signal line 2, a source electrode 6 connected to the display pixel electrode 7, and a semiconductor layer 8. Unit is configured.

On the display pixel electrode 7, a plurality of transparent insulating films 19 having a rectangular pattern are arranged in a diagonal arrangement as shown in FIG.

As described above, by dividing the transparent insulating film 19 into a plurality of parts and distributing them at a plurality of positions, the distance between the alignment surface 12 of the TFT substrate 20 and the alignment surface 13 of the opposing substrate 30 ( Regions having different optical rotation rates and light transmittances due to different cell gaps) are dispersedly arranged at a plurality of positions. This reduces the variation in the apparent brightness of the screen and improves the viewing angle characteristics.

Here, the region a is a region where the transparent insulating film 19 is not formed on the display pixel electrode 7, and the region a is applied to the display pixel electrode 7 via the signal line 2 and the TFT 3. The voltage is applied to the liquid crystal 21 as it is. Further, the region b has a transparent insulating film 1 on the display pixel electrode 7.
In this region b, a voltage that has been divided by a capacitance through a series capacitance of the capacitance of the liquid crystal 21 and the capacitance of the insulating film 19 is applied to the liquid crystal 21. You. As a result, the arrangement state of the liquid crystal 21 corresponding to the region b is different from that of the region a.

As described above, by forming two regions having different voltages applied to the liquid crystal 21 in one pixel in a dispersed manner, the ratio of suppressing the light transmittance is adjusted to reduce the light transmittance more than necessary. Display quality, such as darkening the screen, appearing rough or periodic noise, etc. While avoiding
It is possible to improve the viewing angle characteristics.

Further, the regions c and d are so-called tapered portions on the side surfaces of the transparent insulating film 19, and the regions c and d
In this case, a voltage about the middle of the area a and the area b is applied to the liquid crystal 21, and the arrangement state also becomes a state about the middle between the areas a and b. Becomes And this taper part
It is not formed over the entire surface of the pixel electrode 7, but has an area of about 20% to 50% of the area of the display pixel electrode 7, that is, the area for improving the viewing angle characteristics without deteriorating the quality of the display image. Is set.

Therefore, the areas c and d are the area a and the area b
, The light transmittance does not change stepwise (steeply) between the region a and the region b, but slowly and gradually through the regions c and d in the intermediate state. As a result, it is possible to improve the viewing angle characteristics while more effectively avoiding the deterioration of the display quality due to the appearance of the displayed image appearing rough or periodic noise. ing.

Further, the regions c and d are positioned with respect to the substrate surface.
Since it has an angle of 30 degrees or more, it has an effect of appropriately scattering incident light according to the angle, and has an effect of further widening the viewing angle range. In addition, since the area is set to about 20 to 50% of the area of the display pixel electrode 7 as described above, the viewing angle characteristics can be improved without deteriorating the quality of the displayed image.

The regions c and d have the effect of suppressing the difference in viewing angle characteristics between different video signal voltages.

As described above, the regions c and d correspond to the regions a and
The viewing angle characteristics can be further improved in combination with the effect of b.

The transparent insulating film 19 is made of a material having a high light transmittance and an excellent insulating property, for example, SiN,
_{Si 3 N 4, Si x O} y , etc. is used. In particular, in the case of a TFT active matrix type liquid crystal display device as in this embodiment, a passivation film such as SiO _{2 provided} on the TFT and its wiring may be used as the transparent insulating film 19, and when the passivation film is etched. Since the transparent insulating film 19 may be formed by changing the etching pattern, it is not necessary to add a complicated process for forming the transparent insulating film 19 at the time of manufacturing, and the manufacturing is simple and preferable.

The dimensions and form are set in consideration of the dimensions of the display pixel electrode 7 and the like, and are set to a square or a rectangle having a side of about 5 to 10 μm for patterning.
In addition, the film thickness is set to 1 μm in order to more effectively improve the viewing angle characteristics in consideration of the cell gap d and the like.
m or less. About 20 to 30 such transparent insulating films 19 are arranged on one display pixel electrode 7. At this time,
The interval between adjacent pixels is set to be about the length of one side of the transparent insulating film 19. The number and interval are
It is set appropriately in consideration of light transmittance and viewing angle characteristics.

The angle of the taper of the side surface is about 30 ° to 80 ° with respect to the surface of the glass substrate. At this time, the area of the tapered surface is set to about 20 to 50% of the area of the display pixel electrode 7. desirable.

FIG. 3 is a plan view showing a TFT substrate 20 of a liquid crystal display device according to a second embodiment of the present invention.

The second embodiment is characterized in that the transparent insulating film 29 indicated by oblique lines in the figure is formed in a substantially striped pattern having a plurality of slits. The area ratios and dimensions of the regions a, b, c and d are the same as those of the transparent insulating film 19 of the above-described first embodiment, and substantially the same effects as those of the first embodiment are realized. it can.

The pattern of the transparent insulating film is not limited to the above. In addition, for example, a circular or hexagonal pattern may be used.

[0039]

As described in the detailed description above, the liquid crystal display device of the present invention reduces the display quality of an image such that the displayed image looks rough or the screen appears dark. This is a liquid crystal display device having a wide viewing angle and good display image quality by improving the viewing angle characteristics without causing a problem.

The present invention is particularly suitable for an active matrix type liquid crystal display device using the TN type liquid crystal 21.

[Brief description of the drawings]

FIG. 1 is a plan view showing a TFT substrate of a liquid crystal display device of the present invention.

FIG. 2 is a cross-sectional view illustrating a structure of a liquid crystal display element of the present invention.

FIG. 3 shows T of the liquid crystal display device according to the second embodiment of the present invention.
FIG. 2 is a plan view showing the FT substrate 20.

FIG. 4 is a plan view of a liquid crystal display device according to the related art.

FIG. 5 is a cross-sectional view of a liquid crystal display device according to the related art.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Scan line 2 ... Signal line 3 ... TFT 4 ... Gate electrode 5 ... Drain electrode 6 ... Source electrode 7 ... Display pixel electrode 8 ... Semiconductor layer 12 ... Alignment film on TFT substrate side 13 ... Alignment film on counter substrate side 19 ... Transparent insulating layer 20: TFT substrate 21: liquid crystal 30: counter substrate 31: common counter electrode

Claims (1)

(57) [Claims] 1. A display disposed opposite the pixel electrodes and the common
A display pixel electrode having two substrates each having a counter electrode and a liquid crystal interposed between the substrates;
Electrode, formed in the liquid crystal display device in which a plurality of pixels are formed by the liquid crystal and Contact common counter electrode, wherein on the display pixel electrodes of each pixel, a plurality of islands or stripes each having a tapered side surface in Rukoto be equipped with the transparent insulation film, different light transmissive
A liquid crystal display device, wherein regions having a ratio are dispersedly arranged in each of the pixels .