JPH0756159A - Display device - Google Patents

Abstract

PURPOSE:To prevent the transmission of non-modulated light, to improve an opening rate and to prevent the generation of the orientation defect by insulatable light shielding films by coating the surfaces of regions exclusive of pixel electrodes with these insulatable light shielding films. CONSTITUTION:The other parts exclusive of the regions of the pixel electrodes 4 of a first substrate, i.e., the regions of matrix wirings and thin-film transistors 13, are coated with the insulatable light shielding films 11 consisting of insulatable high- resistance layers and light shieldable low-resistance layers in order to prohibit the light transmitted through these regions. The insulatable high-resistance layers consist of the oxide or nitride of fine crystalline or amorphous silicon and the light shieldable low-resistance layers consist of the nitride, carbide or silicide of metals. Since the insulatable light shielding films 11 are formed directly on the substrate having the matrix wirings, i.e., on the pixel electrode side, the problem of the angle matching accuracy of polarizing plates and the problem of opening rates do not arise. In addition, the insulatable light shielding films 11 are composed of the composite layers consisting of the insulatable high-resistance layers and the light shieldable low- resistance layers, unlike the mere metallic materials and, therefore, the problems of electrical shorting and interlayer shorting are prevented as well.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device,
In particular, it relates to an active matrix type display device in which a switching element is provided for each pixel.

[0002]

2. Description of the Related Art In a flat panel display device, row electrodes and column electrodes arranged at a predetermined pitch are arranged on a substrate so as to be orthogonal to each other, and a minimum partition surrounded by these row electrodes and column electrodes. Is generally used as a pixel, and a matrix type display device in which an electro-optical modulator is sandwiched between two substrates is general. Above all, a liquid crystal display device using a liquid crystal composition as an electro-optical modulator is widely used in combination with the feature of low power consumption.

Further, as a large-capacity, high-accuracy liquid crystal display device for a television image or a graphic display, an active matrix liquid crystal display device in which a switching element is arranged for each pixel to drive and control each pixel. Has also been put to practical use. As such a switching element, Japanese Patent Laid-Open Nos. 56-25714 and 56-2577 have been disclosed.
As disclosed in Japanese Patent Publication No. 7, etc., it is widely used for a three-terminal type thin film transistor using polycrystalline silicon or amorphous silicon as a semiconductor layer and a two-terminal type non-linear resistance element made of metal-insulator-metal. Be separated. Among them, the thin film transistor is suitable as a device capable of high-speed response and capable of high-contrast display without crosstalk.

A liquid crystal display device using a thin film transistor as such a switching element will be described with reference to FIGS. 3 and 4. Note that FIG. 4 shows a cross-sectional configuration along the line BB in FIG. That is, the matrix wiring including the scanning line group 12 and the signal line group 5 corresponding to the row electrodes and the column electrodes, and the pixel electrode 4 which is the smallest section thereof form the electrode group of the first substrate 1. A thin film transistor is arranged at each intersection of the matrix wirings, and one of the source electrode and the drain electrode thereof is connected to the pixel electrode.

The second substrate 2 is provided with red (R), green (G), and blue (B) color filters 6 and a counter electrode 7 for each pixel in order to enable color display. Thus, for example, a nematic liquid crystal composition 8 is sandwiched between the first substrate 1 and the second substrate 2 which are arranged to face each other. still,
In the figure, the alignment film on the electrodes of each substrate is not shown. A polarizing plate 3 is provided outside each substrate. Then, the illumination device is provided outside one of the substrates.

In such a liquid crystal display device, the orientation of the liquid crystal molecules is changed by turning on and off the voltage applied to the electrodes of both substrates, and in the case of the transmissive type, the light 14 from the illuminating device is pixel by pixel. Modulate. Therefore, strictly speaking, the light modulation operation of the liquid crystal is limited to the region corresponding to the pixel electrode 4 and the counter electrode 7. That is, the liquid crystal in the portion excluding the pixel electrode region does not operate at all.

By the way, the substrate 1 provided with matrix wiring
In addition to the pixel electrode area, the wiring electrode of the signal line 5 and the scanning line are provided above.
Twelve wiring electrodes and thin film transistors are arranged, and these are electrically insulated from each other by a multilayer wiring or a wiring arrangement. Therefore, for example, even if an opaque material is used as the electrode material, there is a wiring space such as between the pixel electrode 4 and the signal line 5, and unmodulated light 15 irrelevant to the light modulation action of the liquid crystal is transmitted through this area. It will be. Such non-modulated light 15 always leaks a certain amount of light as a display device, which causes an increase in background, that is, a marked reduction in contrast.

[0008]

As a method of reducing the non-modulated light, for example, the alignment films of both substrates are arranged so that the rubbing directions thereof are orthogonal to each other, and the polarizing plates 3 of both substrates are arranged.
It is also conceivable to arrange so that the polarization directions of are parallel to each other so that light is not transmitted when no voltage is applied to the liquid crystal.

In this case, since only the pixel electrode region is optically modulated by the signal voltage, unmodulated light is theoretically impossible. However, in consideration of the manufacturing process as a display device, it is necessary to accurately align the polarization directions of the two polarizing plates, and the background due to leaked light is determined by this alignment accuracy. Even if the misalignment angle is within 1 degree as a practical alignment accuracy, it is very difficult to manage this during mass production.

On the other hand, when the polarizing plates 3 of both substrates are arranged so as to be orthogonal to each other along the rubbing directions of the alignment films which are orthogonal to each other, the misalignment of the angles merely causes a slight decrease in the transmittance. This alone has little effect on contrast and is suitable for mass production from the viewpoint of manufacturing. in this case,
Only the liquid crystal corresponding to the pixel electrode region to which the signal voltage is applied gives the light modulation effect, and this modulated light determines the contrast. As a countermeasure against this, a light-shielding screen made of a metal thin film may be provided outside the pixel electrode region on the counter substrate side.

That is, as shown in FIG. 5, color filters 6 of, for example, R, G, and B are arranged only in a region corresponding to the pixel electrode 4 on the counter substrate 2, and the remaining region is shielded by a metal thin film. It is a structure covered with the screen 9. While this configuration certainly achieves the initial objectives, it introduces other additional problems.

First, both the matrix wiring substrate 1 and the counter substrate 2 provided with the light shielding screen 9 must be fixed in an accurate positional relationship. In such a liquid crystal display device, the pixel pitch is often designed to be several hundreds of μm. For example, when the pitch is 200 μm, the alignment accuracy of both substrates is required to be about several μm in order to obtain a predetermined aperture ratio. To be done.

Further, the light from the light source cannot be said to be perfectly parallel rays, and the non-modulated light component 15 obliquely incident on the substrate 15
Taking the above into consideration, if the width of the light-shielding screen 9 is widened and a margin is taken, the aperture ratio is further reduced accordingly. For example
In the case of a 200 μm pitch, the electrode width of the signal line 5 is 10 μm, and the effective pixel electrode size is approximately 50 to 60% when the effective pixel electrode size is expressed in consideration of the area of the thin film transistor. If the margin of the width of the light-shielding screen for the above-mentioned alignment accuracy and the countermeasure against the obliquely incident non-modulated light component is incorporated into this, the aperture ratio becomes about 40 to 50%, which is about 10% lower. This reduction in aperture ratio directly leads to a reduction in image quality of the display device.

Alternatively, as disclosed in Japanese Patent Application No. 61-209065, by disposing the light shielding screen on the side of the matrix wiring substrate on the light incident side, the margin of the width of the light shielding screen is small. I will end up. That is, the matrix wiring substrate is covered with an insulating light-shielding film on the region excluding the pixel electrodes to prevent transmission of non-modulated light.

However, this insulating light-shielding film uses a polymer as a base material in which a black dye or two kinds of dyes having complementary colors are mixed. To obtain an optical density of about 3.0 with the light-shielding film having such a structure, a film thickness of 1.5 to 2.0 μm is required. The light-shielding screen made of such a thick film often causes an image defect called an alignment defect at a step portion with the pixel electrode. Further, from the viewpoint of manufacturing, when the insulating light-shielding film is processed into a predetermined shape by a photolithography method, a resist made of a polymer material in which a dye or a pigment having a large optical density is dispersed in order to improve the light-shielding performance is There is also a problem of poor alignment accuracy.

As a measure against such a problem, the width of a signal line or a gate line, which is formed of, for example, a metal material, in a portion which appears in a specific relationship with the rubbing direction of the alignment film is widened to reduce the pixel electrode. It is also possible to shield the part.
However, these measures lead to a decrease in aperture ratio and are not preferable.

As described above, with respect to the problem of non-modulated light, which is one of the causes of the deterioration of the image quality of the liquid crystal display device, the liquid crystal operation state depending on the polarization direction of the polarizing plate, the arrangement of the light shielding screen on the counter substrate, and the matrix substrate. Various proposals have been made for the arrangement of the above-mentioned light-shielding screen, but they each cause different problems and are not sufficient.

The present invention has been made in view of the above problems, and covers the region excluding the pixel electrodes with an insulating light-shielding film to prevent transmission of non-modulated light and improve the aperture ratio. Prevents the occurrence of alignment defects due to this insulating light-shielding film,
Another object of the present invention is to provide a liquid crystal display device that is easy to manufacture.

[0019]

SUMMARY OF THE INVENTION According to the present invention, a large number of row electrodes are arranged extending in one direction at a predetermined pitch, and a plurality of row electrodes are arranged extending in one direction at a predetermined pitch. A plurality of column electrodes orthogonal to each other, a minimum section surrounded by the row electrodes and the column electrodes is a pixel, a first substrate having at least a switching element for each pixel, and a second substrate having at least a counter electrode. Substrate, the first substrate and the second substrate
In a display device arranged opposite to the substrate of (1) and having an electro-optical modulator substance sandwiched between the substrates, an insulating light-shielding film including an insulating high-resistance layer and a light-shielding low-resistance layer on the region excluding the pixel region. And the insulating high-resistance layer is made of microcrystalline or amorphous silicon oxide or nitride, and the light-shielding low-resistance layer is made of metal nitride, carbide, or silicide. It is a display device.

[0020]

According to the present invention, since the insulating light-shielding film is directly provided on the substrate having the matrix wiring, that is, on the pixel electrode portion side, there is no problem of the angle alignment accuracy of the polarizing plate or the problem of aperture ratio. Further, unlike the mere metallic material, the light-shielding film is composed of a composite layer including an insulating high-resistance layer and a light-shielding low-resistance layer, so that the problem of electrical short-circuiting or interlayer short-circuiting can be prevented.

Further, although microcrystalline or amorphous silicon oxide or nitride is used as the insulating high resistance layer, a floating potential may be generated in the silicon layer due to photovoltaic. However, even if this floating potential is generated, it can be released from the low resistance layer laminated on the silicon layer, so that there is no problem.

As for the light-shielding effect, the silicon layer alone has a problem that the light-shielding effect is small particularly on the long wavelength side. However, if a black light-shielding low-resistance layer made of metal nitride, carbide, or silicide is used as the low-resistance layer laminated on the silicon layer, for example, aluminum nitride (AlN) has a thickness of only 0.1 μm. It is possible to easily achieve the optical density considered necessary for the large-sized active matrix type liquid crystal display device for OA in the entire visible light region.

In this black light-shielding low-resistance layer, light from the opposite substrate side is incident on the insulating high-resistance layer made of microcrystal or amorphous silicon oxide or nitride, and its resistance value is changed. It can be prevented at the same time. On the other hand, among the light transmitted from the light source of the illumination device through the matrix substrate, the transmission of non-modulated light formed through the insulating layer on the matrix wiring portion excluding the pixel electrode and the switching element is effectively transmitted. . If necessary, if the peripheral portion is arranged inside the matrix wiring, it is hardly affected.

An insulating light-shielding film composed of a composite layer composed of an insulating high-resistance layer and a light-shielding low-resistance layer is disclosed in Japanese Patent Application No.
Compared with the case where a light-shielding film is formed by dispersing a dye or a pigment in the polymer material disclosed in -209065 specification, 1 /
An optical density equal to or higher than that of 5 to 1/10 can be obtained. Therefore, the step caused by the thickness of the insulating light-shielding film can be reduced accordingly. As a result, when rubbing the alignment film, it is not necessary to provide a light-shielding portion that seals a poorly aligned region due to the presence of this step portion, and the aperture ratio is improved.

Further, from the viewpoint of manufacturing the insulating light-shielding film, it can be easily processed and formed on the completed matrix substrate by using a normal photolithography method. The pattern accuracy and alignment accuracy of the insulating light-shielding film are determined by the accuracy of photolithography used. The resist made of the polymer material in which the dyes and pigments are dispersed needs to increase the optical density of the dyes and pigments as much as possible to improve the light-shielding performance, and there is a problem that the pattern accuracy deteriorates and the alignment accuracy also deteriorates. . However, in the present invention, since a normal resist can be used, it is possible to maintain high accuracy in both pattern accuracy and alignment accuracy. For example, even during mass production, it is easy to maintain the accuracy within 3 μm, and a higher aperture ratio can be obtained.

[0026]

EXAMPLES Examples of the present invention will be described in detail below. 1 is a schematic plan view showing an embodiment of a display device according to the present invention, and FIG. 2 is a schematic cross section taken along the line AA of FIG. 1 and 2, the same components corresponding to those in FIGS. 3 and 4 are designated by the same reference numerals. In this embodiment, a liquid crystal composition 8 which is an electro-optical modulator substance is sandwiched between a first substrate 1 using a thin film transistor 13 as a switching element and a second substrate 2 on which a color filter 6 is formed. This is an example applied to a color liquid crystal display device used in a transmissive TN mode.

That is, the thin film transistor is formed on the inner surface of the first transparent insulating substrate 1 made of glass which serves as a matrix substrate.
The scanning line 12 connected to the gate electrode of 13, the signal line 5 connected to the drain electrode or the source electrode, and the pixel electrode 4 connected to the drain electrode or the source electrode are respectively formed by the same method as in the related art. . An insulating light-shielding film 11 is provided in order to block light transmitted through other portions of the first substrate 1 excluding the region of the pixel electrode 4, that is, the regions of the matrix wiring and the thin film transistor.

The insulating light-shielding film 11 is formed by first forming a thin film transistor.
An insulating film made of silicon oxide or nitride is formed to a thickness of 0.2 μm to 0.4 μm on 13 and the wiring portion by the CVD method. A silicon film is formed on this insulating film by the CVD method.
The film is formed to a thickness of 2 μm to 0.4 μm. An insulating high resistance layer is formed by the insulating film and the silicon film. Further, on the silicon film, aluminum is formed by a sputtering method in an argon gas containing nitrogen to form a black aluminum nitride film serving as a light-shielding low resistance layer with a thickness of 0.05 μm to 0.1 μm. That is, the insulating light-shielding film 11 is formed by stacking the insulating high-resistance layer and the light-shielding low-resistance layer.

Here, the film thickness of the silicon film and the aluminum nitride film is about 0.4 μm, the transmittance in the visible light region is 0.1% or less in all regions of the insulating light-shielding film 11, and the optical density is maintained at 3 or less. it can. The resistance values of the silicon film and the aluminum nitride film are 10 ¹¹ Ωcm and 10 ⁶ Ωcm, respectively.
In addition to aluminum nitride, nitrides such as TiN and TaN, metal carbides, and silicides can also be used.

Next, a resist is applied on the insulating light-shielding film 11, the aluminum nitride film in the pixel portion is etched with hot phosphoric acid, and then etched in plasma using SF ₆ as a main gas to form the pixel electrode. The insulating high resistance layer and the light blocking low resistance layer in the region 4 are removed, and the insulating light blocking film 11 is processed and formed.

A liquid crystal orientation control film (not shown) made of, for example, polyimide, polyamide, polyvinyl alcohol or the like is deposited on the entire surface of the first substrate 1 including the insulating light-shielding film 11 thus formed, The first substrate 1 is completed by rubbing in one direction with a cotton cloth or the like for rubbing treatment.

On the other hand, on the inner surface of the second substrate 2, R, G, B color filters 6 are formed at positions corresponding to the pixel electrodes 4 of the first substrate 1, and further, for example, IT.
A counter electrode 7 made of O and a liquid crystal orientation control film (not shown) are deposited, and rubbed in one direction with a cotton cloth or the like to perform a rubbing treatment to complete the second substrate 2.

Then, the alignment films of the two substrates are arranged so as to face each other so that the rubbing directions thereof are orthogonal to each other, and the peripheral edges of the substrates are adhesively fixed at predetermined intervals leaving liquid crystal injection holes. Next, for example, a nematic liquid crystal composition 8 is injected through the liquid crystal injection hole, and finally the liquid crystal injection hole is sealed. Polarizing plates 3 are attached to the outer sides of both substrates, for example, so that the respective polarization directions are along the rubbing directions of the respective substrates. Further, an illumination light source is arranged outside the matrix substrate (not shown), and a drive circuit is connected to each electrode of both substrates (not shown).

The liquid crystal display device thus completed was driven and the image quality thereof was evaluated. As a result, it was confirmed that alignment defects did not occur, the screen was brightened by the effect of the insulating light-shielding film, and the contrast was also improved. Was done.

[0035]

As described above, according to the present invention, so-called non-modulated light which is transmitted from the region other than the pixel electrode can be sufficiently blocked, and the contrast ratio which is one of the display performances can be suppressed. It can greatly contribute to the improvement. In addition, by stacking an insulating high-resistance layer and a light-blocking low-resistance layer as an insulating light-shielding film, it is not necessary to consider structurally electrical shorts, interlayer leaks, etc. Can be easily applied to the display device. In particular, as compared with a conventional light shielding film in which dyes or pigments are dispersed in a polymer material, an optical density equal to or higher than that of 1/5 to 1/10 can be obtained, so that it is caused by a step due to the thickness of the light shielding film. The occurrence of image quality defects due to alignment defects is extremely reduced, and the aperture ratio can be improved.

[Brief description of drawings]

FIG. 1 is a schematic plan view showing an embodiment of a display device according to the present invention.

FIG. 2 is a schematic cross-sectional view showing a configuration of a cross section taken along the line AA of FIG.

FIG. 3 is a schematic plan view showing the configuration of a conventional display device.

FIG. 4 is a schematic cross-sectional view showing a configuration of a cross section taken along the line BB in FIG.

FIG. 5 is a schematic sectional view showing a structure of a conventional display device.

[Explanation of symbols]

 1 ... 1st substrate 2 ... 2nd substrate 3 ... Polarizing plate 4 ... Pixel electrode 5 ... Signal line 6 ... Color filter 7 ... Counter electrode 8 ... Liquid crystal 11 ... Insulating light-shielding film

Claims (2)

[Claims] 1. A large number of row electrodes extending in one direction at a predetermined pitch and arranged, and a plurality of column electrodes extending in one direction at a predetermined pitch and substantially orthogonal to the row electrodes. A pixel defined by a minimum section surrounded by the row electrodes and the column electrodes, a first substrate having at least a switching element for each pixel, a second substrate having at least a counter electrode, and the first substrate. In a display device in which a substrate and a second substrate are opposed to each other and an electro-optical modulator substance is sandwiched between the substrates, an insulating high resistance layer and a light shielding low resistance layer are formed on a region excluding the pixel region. A display device characterized by being covered with an insulating light-shielding film. 2. The display device according to claim 1, wherein the insulating high-resistance layer is made of microcrystalline or amorphous silicon oxide or nitride, and the light-shielding low-resistance layer is metal nitride or carbide. Alternatively, a display device comprising a silicide.