JPH07209638A - Display device - Google Patents

Abstract

PURPOSE:To provide a display device which has high light shieldability and has a good insulating characteristic even under photoirradiation. CONSTITUTION:Liquid crystals 23 are held between the substrates 21 and 22 by providing the display device with the display pixel electrode array substrate 21 and the counter electrode substrate 22 opposed in parallel with each other. This display pixel electrode array substrate 21 is disposed with display pixel electrode 33 and thin-film transistors 34 (TFTs) in a matrix form on a glass substrate 24. Black inorg. insulator films 35 are formed on the TFTs 34 not formed with the display pixel electrodes 33 and wirings. The non-modulating light of the parts where the liquid crystals 23 are not acted is prohibited and a contrast ratio is improved, by these inorg. insulator films 35. The optical density and insulation characteristic equal to or higher than the optical density and insulation characteristic obtd. in the case of dispersion of dyes and pigments into a polymer material are obtd. in a smaller film thickness than in such a case as the inorg. materials are used. The defects of image quality by light distribution defects generated by the inorg. insulator films 35 are eliminated and an opening ratio is improved. Leakage of leak currents is obviated by the photocurrents generated by the photoirradiation and, therefore, the high insulation characteristic is obtd. even under the photoirradiation.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a display device having a so-called active matrix type electrode structure in which thin film transistors are provided at intersections of matrix wirings and operating liquid crystals.

[0002]

2. Description of the Related Art As shown in FIG. 2, a plurality of parallel signal lines 1 and a plurality of parallel scanning lines 2 orthogonal to the signal lines 1 are provided, and the signal lines 1 and the scanning lines 2 are arranged in a matrix. A thin film transistor (TFT) 3 is disposed at the intersection, the drain of the thin film transistor 3 is connected to the signal line 1, and the gate is connected to the scanning line 2. A display pixel electrode 4 arranged in a matrix between the signal line 1 and the scanning line 2 is connected to the source of the thin film transistor 3.

Further, the liquid crystal display device having the electrical connection shown in FIG. 2 is constructed as shown in FIG.
That is, in the liquid crystal display device shown in FIG. 3, the matrix array substrate 6 and the counter substrate 7 are opposed to each other in parallel, and the matrix array substrate 6 and the counter substrate 7 are electrically connected to each other.
A liquid crystal 8 as a light modulation substance is sandwiched.

The matrix array substrate 6 has a glass substrate 11, and a plurality of parallel signal lines 1 and scanning lines 2 orthogonal to these signal lines 1 are arranged on one main surface side of the glass substrate 11. Display pixel electrodes 4 are arranged in a matrix between the signal lines 1 and the scanning lines 2. A polarizing plate 12 is provided on the other main surface side of the glass substrate 11.

On the other hand, the counter substrate 7 also has a glass substrate 14, and one main surface of the glass substrate 14 facing the matrix array substrate 6 has red (R) and green (G) for color display.
And a blue (B) color filter 15 are provided.
A counter electrode 16 is formed on the color filter 15, and a polarizing plate 17 is provided on the other main surface side of the glass substrate 14.

When operating as a transmission type,
Since the display pixel electrode 4 uses a transparent conductive film and the liquid crystal 8 operates due to the electrode difference from the counter electrode 16, it is limited to only the region where the display pixel electrode 4 and the counter electrode 16 face each other.
That is, the part of the liquid crystal 8 excluding the display pixel electrode 4 region does not operate at all. Further, on the matrix array substrate 6 provided with the matrix-shaped wiring of the signal lines 1 and the scanning lines 2, there are the signal lines 1, the scanning lines 2, the thin film transistors 3 and the like other than the area of the display pixel electrodes 4, and these are multi-layered. They are electrically insulated from each other by structural wiring or arrangement of wiring. Therefore, for example, even if an opaque material such as a metal thin film is used as the electrode material, a space between wirings is often present, and since the liquid crystal 8 does not operate in this area, so-called non-modulated light is transmitted. .

Furthermore, this non-modulated light means that light always leaks to the display device, which causes an increase in the background, that is, a marked decrease in contrast.
Then, in the case of so-called normally white in which the polarizing plates of the liquid crystal 8 are arranged at right angles, the angular deviation only causes a slight decrease in the transmittance, has little influence on the contrast, and is suitable for mass production. . At this time, only the liquid crystal 8 corresponding to the region of the display pixel electrode 4 to which the signal voltage is applied gives the light modulation, and the above-mentioned non-modulated light reduces the contrast.

As a method for preventing this decrease in contrast, for example, the structure described in Japanese Patent Laid-Open No. 63-64023 is known. In the structure disclosed in Japanese Patent Laid-Open No. 63-64023, for example, as shown in FIGS. 4 and 5, the insulating light-shielding film 18 is formed on the region except the display pixel electrodes 4 formed on the matrix array substrate 6. To eliminate the transmission of unmodulated light. Insulating light-shielding film
18 is a mixture of a polymer as a base material with a black dye or dyes of two kinds of colors having complementary colors.

However, the insulating light-shielding film 18 using a polymer as a base material and a dye or the like requires a film thickness of several μm in order to obtain an optical density of about 2 to 3, and such a thick film. In the insulating light-shielding film 18, the pixel defect called alignment defect appears in the step portion with the display pixel electrode 4. In order to hide such defects, there has been considered a method of widening the width of the signal line 1 or the scanning line 2 formed of, for example, metal to shield a part of the display pixel electrode 4 from light.
This leads to a decrease in aperture ratio.

When the insulating light-shielding film 18 is used as a resist, if the resist is made of a polymer material in which dyes and pigments are dispersed, the concentration is increased as much as possible to improve the light-shielding performance. The pattern accuracy is poor and the alignment accuracy is also low.

On the other hand, as shown in FIG. 6, an insulating layer 18a made of silicon of a silicon nitride (SiN _x ) film as a light shielding material and an aluminum nitride (Al) film formed on the insulating layer 18a.
A configuration using two or more light blocking layers 18b made of a low resistance material such as N) is considered. The insulating layer 18
The specific resistance of silicon of a is as high as 10 ¹¹ Ωcm, and unlike metal materials, problems such as electrical short-circuiting and interlayer short-circuiting can be solved. Further, the floating potential of the insulating layer 18a generated by the photoelectromotive force caused by using silicon (Si) escapes from the light blocking layer 18b formed on the insulating layer 18a. The light blocking layer 18b has a thickness of 0.1 μm and can achieve the required optical density in the entire visible light region.

However, the insulating layer 18a and the light blocking layer 18b
In the method of using a material composed of two or more layers for the insulating light-shielding film 18, for example, light is blocked by the upper light blocking layer 18b, and insulation is performed by the lower insulating layer 18a. Current leakage occurs due to the generated photocurrent.

That is, for example, as shown in FIG. 6, the specific resistance of the SiNx film used for passivation is usually not sufficiently high, and a current easily flows in the film thickness direction of the insulating layer 18a. Therefore, the light blocking layer 18 on the insulating layer 18a is
b must have sufficient insulation and its value is 5
The leak current needs to be 10 ⁻¹⁰ A or less for a V signal voltage. When the distance between the signal line 1 and the display pixel electrode 4 is 5 μm, the required specific resistance is 10 ⁸ Ωcm.
That is all. Further, when light is irradiated from the Si side of Si / AlN, which is the back side, it depends on the carrier concentration, the mobility, and the amount of light, but under normal conditions Si cannot satisfy this condition. That is, the insulation between the display pixel electrode 4 and the signal line 1 cannot be sufficiently maintained, which causes a problem of malfunction.

[0014]

As described above, the insulating light-shielding film 18 using a dye or the like as a base material of polymer has an optical density of about 2 to 3 and cannot sufficiently shield light.

Further, in the insulating layer 18a and the light blocking layer 18b,
When silicon (Si) is used for the insulating layer 18a, there is a problem that leakage current is generated by photocurrent when light is irradiated.

The present invention has been made in view of the above problems, and an object of the present invention is to provide a display device having a high light-shielding property and exhibiting a good insulating property even under irradiation with light.

[0017]

According to the present invention, there is provided a thin film transistor, display pixel electrodes connected to the thin film transistor and arranged in a matrix, a plurality of scanning lines to which the thin film transistors are connected in each row, and the thin film transistors in each column. A plurality of signal lines connected to the display pixel electrode array substrate formed on one main surface of the first insulating substrate;
A counter electrode substrate having a counter electrode formed on one main surface of a second insulating substrate and a gap obtained by combining the display pixel electrode array substrate and the one main surface side of the counter electrode substrate so as to face each other. A display device including a liquid crystal sandwiched between the display pixel electrode array substrate and the display pixel electrode array substrate, the black inorganic insulating film covering a region excluding the display pixel electrodes.

[0018]

According to the present invention, since the area excluding the display pixel electrodes of the display pixel electrode array substrate is covered with the black inorganic insulating film, it has a function of sufficiently blocking the so-called unmodulated light in the portion where the liquid crystal does not act. , The contrast ratio can be improved, and since the inorganic insulating film is made of an inorganic substance, it is thinner than the case of the light-shielding film in which a dye or a pigment is dispersed in a polymer material, and the optical density and insulating property equal to or higher than that can be obtained. Since there is no defect in image quality due to the light distribution defect caused by the above, the aperture ratio can be improved, and the leakage current does not occur due to the photocurrent due to the light irradiation, so that a high insulating property can be obtained even under the light irradiation.

[0019]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment of the display device of the present invention will be described below with reference to the drawings.

As shown in FIG. 1, a display pixel electrode array substrate 21 and a counter electrode substrate 22 are provided so as to face each other in parallel, and a liquid crystal 23 is provided between the display pixel electrode array substrate 21 and the counter electrode substrate 22. Are pinched.

Then, the display pixel electrode array substrate 21 is made of de-alkalized glass (Hoya) as a first insulating substrate.
Manufactured by: NA-40) on one main surface of the glass substrate 24,
A gate electrode 25 and a wiring 26 made of aluminum (Al) or the like connected to a scanning line (not shown) are formed, and a gate insulating layer 27 such as a silicon oxide film is formed on the glass substrate 24 including the gate electrode 25 and the wiring 26. Form.

An etching stopper layer 28 such as a silicon nitride film is formed on the gate electrode 25 via the gate insulating layer 27, and ohmic contacts are formed on one end side and the other end side of the upper surface of the etching stopper layer 28. Form layers 29, 30. Then, a source electrode 31 such as aluminum (Al) connected to the ohmic contact layer 29 and connected to a signal line (not shown) is formed on the ohmic contact layer 29, and an ohmic contact is formed on the ohmic contact layer 30. A drain electrode 32, such as aluminum, connected to layer 30, is also formed.

Then, an ITO (Indium Tin Oxid) layer is formed on the gate insulating layer 27 by electrically connecting to the drain electrode 32.
Display pixel electrodes 33 are formed by arranging them in a matrix with a transparent conductive film such as e).

A thin film transistor (TFT) 34 is formed by the gate electrode 25, the source electrode 31, and the drain electrode 32. The thin film transistor 34 is provided for each display pixel electrode 33 arranged in a matrix, and the gate electrode
25 is connected to a scanning line not shown in each row, and the drain electrode 32 is connected to a signal line not shown in each column.

Further, a black inorganic insulating film 35 is formed on the upper surface of the thin film transistor 34 excluding the display pixel electrode 33.

A liquid crystal orientation control film 36 made of polyimide, polyamide, polyvinyl alcohol or the like is formed on the one surface including the inorganic insulating film 35 by a rubbing process, and the other main surface side of the glass substrate 24 is polarized. Board
37 is formed, and the display pixel electrode array substrate 21 is completed.

Next, a method for forming the inorganic insulating film 35 will be described.

First, hydrogenated amorphous silicon nitride (a-S)
iN _x : H) is vapor-deposited by a high-frequency plasma CVD method, and a cermet made of bismuth (Bi) is vapor-deposited by an electric heating method.

When depositing amorphous silicon nitride by the high frequency plasma CVD method, the source gas is Si.
The gas flow rate ratio of H ₄ and NH ₃ is set to 1: 2. Then, the gate insulating layer is formed on the glass substrate 24 by a usual technique.
The deposit of 27 was used as an anode substrate and heated and held at 270 ° C, and the high frequency output of 13.56 MHz was 0.02 W / cm.
² and total output is 20W. Further, the pressure of the total gas is 0.5 Torr, and the film forming rate is 10 angstrom / sec.

On the other hand, for bismuth, pellets having a purity of 99.99% are placed on a tungsten (W) board, electrically heated and simultaneously vapor-deposited at a temperature of 400 ° C., and the deposition rate is 3 Å / sec. The film thickness is controlled to 3000 Å based on the calibration curve of the film thickness indicated by the crystal oscillator type film thickness monitor and the value obtained by the Taristep method after film formation. The nitrogen content in silicon nitride was examined by Auger electron spectroscopy, and x = 0.3-0.4.
As a result of measuring the optical transmission spectrum of the prepared film, it was 99 in the visible light region of wavelength 380 to 780 nm.
%, The specific resistance is as high as 10 ⁸ Ωcm or more. The deposited film is patterned by a wet etching technique to shield the region except the display pixel electrode 33 from light.

The counter electrode substrate 22 is also made of dealkalized glass (manufactured by Hoya: NA) as a second insulating substrate.
A counter electrode 42 made of ITO is formed in a stripe shape on one main surface of a glass substrate 41 made of −40), and red (R), green (G) and blue (B) of the counter electrode 42 are formed on the surface of the counter electrode 42. A color filter 43 is laminated, and a liquid crystal alignment control film 44 made of polyimide, polyamide, polyvinyl alcohol, or the like is similarly formed on the color filter 43 by a rubbing process, and the other main surface side of the glass substrate 41 is polarized. The plate 45 is formed to complete the counter electrode substrate 22.

Then, the liquid crystal 23 is sandwiched between the display pixel electrode array substrate 21 and the counter electrode substrate 22 to complete the display device.

The atomic concentration of the metal or semimetal contained in the inorganic insulator film 35 is preferably 60% or less, and the concentration of the metal or semimetal has a concentration gradient in the film thickness direction, and the glass substrate 24 side. It is desirable that the concentration increases toward.

In addition, the inorganic insulating film 35 has at least one of the substances belonging to the IA group, IIA group, IIIA group and IVA group and at least the VIB group, the VIIB group and the VIIIB group in the periodic table. It is preferable that the optical bandgap of the compound consisting of the combination with one substance is 3.8 eV or more.

Further, the inorganic insulating film 35 is made of silicon oxide (SiO ₂ ), calcium oxide (CaO), strontium oxide (SrO), barium oxide (BaO), aluminum oxide (Al ₂ O ₃ ), and gold sulfide (Au ₂ ). S ₃ ), gallium oxide (Ga ₂ O ₃ ), lithium fluoride (Li
F), sodium fluoride (NaF), lithium chloride (L
iCl), lithium bromide (LiBr), sodium chloride (NaCl), sodium bromide (NaBr), potassium bromide (KF), potassium chloride (KCl), potassium bromide (KBr), potassium iodide (KI), Rubidium fluoride (RbF), rubidium chloride (RbCl), rubidium bromide (RbBr), rubidium iodide (RbI), cesium fluoride (CsF), cesium chloride (CsCl),
Cesium bromide (CsBr), cesium iodide (Cs
I), magnesium fluoride (MgF ₂ ), magnesium oxide (MgO), aluminum nitride (AlN), silicon nitride (Si ₃ N ₄ ), calcium fluoride (Ca)
F ₂ ), barium fluoride (BaF ₂ ), barium chloride (BaCl), cadmium fluoride (CdF ₂ ), or barium titanate (BaTiO ₃ ) may be contained.

Furthermore, the particle diameter of the constituent metal or constituent semi-metal of the inorganic insulator film 35 is preferably 330 nm or less.

By appropriately designing the shape distribution of the metal particles, the statistical distribution of the size, the dispersion state of the particles, etc. of the inorganic insulator film 35, the resonance absorption of the particles allows the entire wavelength range of the visible region to be absorbed. The light absorption rate can be increased. Further, the size of the metal particles needs to be a surface electric field that appears by the electric field of light to be an electrostatic field, and the size of the metal particles needs to be smaller than the wavelength of light in order to satisfy this.

More specifically, the number of fine particles per unit volume of metal particles is N, the particle radius is r, the complex dielectric constant of fine particles ε = ε ¹ + i ε ² , and the refractive index of the medium is n ^0. The absorption coefficient γ can be increased by appropriately setting these values on the basis of

[0039]

[Formula 1] For example, gold (Au), copper (Cu) or silver (Ag)
Table 1 shows the relationship between the particle size and the wavelength of absorption in the case of precious metals such as.

[0040]

[Table 1] Further, it is possible to make the inorganic insulating film 35 black by appropriately controlling each parameter of the equation 1, but it is experimentally blackened without controlling each of these values. It is also possible easily. That is, IA genus in the periodic table,
At least one of IIA, IIIA, and IVA substances
On the other hand, there is a large difference in binding energy between a compound or a metal or a semimetal, which is composed of a combination of at least one substance of Group VIB, Group VIIB, and Group VIIIB, and when these are vapor-deposited at the same time, the metal aggregates. . The size of the agglomerated metal particles is most strongly related to the kinetic energy of the particles during vapor deposition, and can be controlled by the film forming means, the substrate temperature during film formation, or the heat treatment after film deposition. In any case, if the temperature of the particles is 1/3 or more of the absolute temperature of the melting point of the substance, the particles can be easily aggregated. Also, the particle size increases as the temperature increases.
Further, as the constituent cations of the inorganic insulator film 35 have a smaller ionic radius, the wettability with the metal becomes worse, so that it is preferable to select an insulator having a small cation ion range in which the metal tends to aggregate.

Further, the light reflectance of the inorganic insulating film 35 is preferably low, and in order to satisfy this, it is desirable to select one having a refractive index close to 1.0.

Further, the metal filling rate is not made constant in the depth direction of the film, but the concentration is lowered toward the side closer to the surface,
It is preferable because it can reduce the reflection of light. As a concrete means, for example, there is a method of lightly oxidizing the formed film to reduce the metal concentration on the surface.

Further, regarding the electric resistance, if the band gap of the inorganic insulating film 35 is 3.8 eV or more, there is basically no photoconduction due to band-to-band transition, and if the metal filling rate is suppressed to 60% or less. , Conduction due to the tunnel phenomenon between metal particles can be suppressed considerably. The resistance value is related to the ease of tunneling due to the thermal excitation of charges once accumulated in the metal particles. The lower the filling rate and dielectric constant of the metal particles, the more effective mass of the metal, the interface between the insulator and the metal. The larger the barrier created by, the larger the resistance. Note that the resistance basically does not depend on the side of the particles of the metal, and the interface potential barrier of the metal between the inorganic insulator film 35 and the gate electrode 25, the source electrode 31, the drain electrode 32, or the like is, for example, hydrogen. It can be increased by containing a large amount.

In addition, among the insulating compounds forming the inorganic insulating film 35, silicon oxide (Si
O ₂ ), aluminum oxide (Al ₂ O ₃ ), magnesium oxide (MgO), and aluminum nitride (AlN), which tends to be a p-type semiconductor, require attention to the metal to be combined therewith. That is, in the former case, selecting a metal having a valence smaller than the valence of the cation constituting the compound and in the latter selecting a metal having a valence larger than the valence of the cation keeps the resistance high. You can

As described above, when the liquid crystal display device (LCD) was processed by the usual method and the image quality was evaluated, not only alignment defects did not appear, but also the screen became bright due to the light shielding effect of the inorganic insulating film 35, The contrast is also improved.

Furthermore, since the inorganic insulating film 35 is based on an insulating material having a large band gap, it is possible to maintain a sufficiently high insulating property even under irradiation of light such as a backlight.

Furthermore, the inorganic insulating film 35 has a function of sufficiently blocking so-called non-modulated light from the region excluding the display pixel electrode 33, and can greatly contribute to the improvement of the contrast ratio, which is one of the display performances. .

Since the inorganic insulating film 35 is made of an inorganic substance, it has an optical density equal to or higher than that of a light-shielding film in which a dye or a pigment is dispersed in a polymer material and has a thickness of 1/5 to 1/10. Since the property is obtained, there is no image quality defect due to the light distribution defect caused by the inorganic insulating film 35, and the aperture ratio can be improved.

[0049]

According to the display device of the present invention, since the area of the display pixel electrode array substrate excluding the display pixel electrodes is covered with the black inorganic insulating film, so-called non-modulated light in a portion where the liquid crystal is not acted is applied. It has a sufficient blocking function, can improve the contrast ratio, and because it is made of an inorganic substance, it is thinner than the case of a light-shielding film in which a dye or pigment is dispersed in a polymer material. There is no defect in the image quality due to the light distribution defect caused by the body film, the aperture ratio can be improved, and the leakage current does not occur due to the photocurrent due to the light irradiation, so that the high insulating property can be obtained even under the light irradiation.

[Brief description of drawings]

FIG. 1 is a sectional view showing an embodiment of a display device of the present invention.

FIG. 2 is a wiring diagram showing a conventional display device.

FIG. 3 is a sectional view of the same.

FIG. 4 is a cross-sectional view showing another conventional example.

FIG. 5 is a plan view of the same.

FIG. 6 is a schematic diagram showing a current leakage problem in a conventional example.

[Explanation of symbols]

 21 display pixel electrode array substrate 22 counter electrode substrate 23 liquid crystal 24 glass substrate as first insulating substrate 33 display pixel electrode 34 thin film transistor 35 inorganic insulating film 41 glass substrate as second insulating substrate 42 counter electrode

Claims (1)

[Claims] 1. A thin film transistor, display pixel electrodes connected to the thin film transistor and arranged in a matrix, a plurality of scanning lines to which the thin film transistors are connected in each row, and a plurality of signal lines to which the thin film transistors are connected in each column. A display pixel electrode array substrate formed on one main surface of a first insulating substrate; a counter electrode substrate having a counter electrode formed on one main surface of a second insulating substrate; In a display device comprising an array substrate and a liquid crystal sandwiched in a gap obtained by facing and combining the one main surface side of the counter electrode substrate, a region excluding the display pixel electrode of the display pixel electrode array substrate. And a black inorganic insulating film for covering the display device.