JPH09176837A - Transparent conductive film - Google Patents

Abstract

(57) Abstract: The present invention relates to a transparent conductive film having a three-layer structure in which a silver-based thin film is sandwiched between transparent oxide thin films, and in particular, the thin film has high conductivity and visible light transmittance and is deteriorated with time. Another object of the present invention is to provide a transparent conductive film having no storage stability and excellent storage stability. In a transparent conductive film having a three-layer structure in which a silver-based thin film having a thickness of 5 to 20 nm is sandwiched between transparent oxide thin films, the transparent oxide thin film is a kind of a metal oxide that is easily solid-dissolved with silver. It is a mixed oxide of a first base material containing the above and a second base material containing one or more oxides of a metal that is hard to form a solid solution with silver, and the silver-based thin film is a silver alloy containing at least gold. A transparent conductive film characterized by the above.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a transparent conductive film used as a transparent electrode of a liquid crystal display, an input / output device, or a display device such as a plasma display. The present invention relates to improvement of a transparent conductive film which is high and has excellent storage stability.

[0002]

2. Description of the Related Art An electrode plate having a transparent conductive film in the form of an electrode for transmitting visible light on a substrate such as glass or plastic film is used as a display electrode for various display devices such as a liquid crystal display or a display for this display device. Widely used for input / output electrodes, etc. for direct input from the screen.

As this transparent conductive film, paying attention to its high conductivity, IT in which tin oxide is added to indium oxide is used.
O thin film is widely used, and its specific resistance is about 2.
4 × 10 ^-4 Ω · cm, usually applied as a transparent electrode 2
If the film thickness is 40 nm, the sheet resistance is about 10Ω / □
It is.

In addition to this, a tin oxide thin film, a thin film formed by adding antimony oxide to this tin oxide (nesa film), a thin film formed by adding aluminum oxide to zinc oxide, and the like are known. However, these are all the above IT
Its conductivity is inferior to that of the O thin film, and its chemical resistance to acids and alkalis, water resistance and the like are insufficient, so that it is not widely used.

On the other hand, in the 7th ICVM held in Japan in 1982, a transparent three-layer structure constituted by laminating an ITO thin film or an indium oxide thin film (IO thin film) on the front and back surfaces of a silver thin film as a heat ray reflecting film. Conductive films have been proposed. This transparent conductive film having a three-layer structure has a low sheet resistivity of about 5 Ω / □, and its high conductivity was expected to be applied to the transparent electrode.

[0006]

By the way, in the display device and the input / output device described above, it has been required in recent years to increase the pixel density to display a fine screen, and accordingly, the fineness of the transparent electrode pattern is required. It is required to form the terminal portions of the transparent electrodes at a pitch of, for example, about 100 μm. Further, in the method (COG) in which the liquid crystal driving IC is directly connected to the substrate in the liquid crystal display device, there is a portion where the wiring is a thin line with a width of 20 to 50 μm, and it has a high degree of suitability for etching, which is unprecedented. Conductivity (low resistivity) is required.

On the other hand, there is also a demand for a larger display screen. For such a large screen, a transparent electrode having a dense pattern as described above is formed so that a sufficient driving voltage can be applied to the liquid crystal. In order to do so, it is necessary to apply a transparent conductive film having a high conductivity of 5Ω / □ or less as the transparent electrode. In addition to this, S
In the case of performing multi-gradation display of 16 gradations or more in a simple matrix drive type liquid crystal display device using TN liquid crystal or the like, a lower sheet resistance of 3Ω / □ or less is required.

However, even in the transparent conductive film having the above-mentioned three-layer structure proposed in the 7th ICVM, at most 5
Only a sheet resistance of about Ω / □ is obtained, and there is a problem that sufficient conductivity cannot be secured. Although it is possible to reduce the sheet resistivity to about 3 Ω / □ by increasing the thickness of the silver thin film to about 16 to 18 nm, the visible light transmittance (especially for the long wavelength side of about 610 nm). The visible light transmittance) is lowered to about 75%, and the function as a transparent conductive film is impaired.

Further, in the transparent conductive film having the three-layer structure, the silver thin film is easily combined with moisture in the air invading from the laminated interface, etc., and oxides are formed on the surface to cause spot defects. For example, when applied to a transparent electrode of a liquid crystal display device, there is a problem that a display defect or the like is likely to occur on the display screen.

The present invention has been made by paying attention to such a problem. The problem is that the thin film has high conductivity and high visible light transmittance, and is excellent in storage stability without deterioration over time. It is to provide a transparent conductive film.

[0011]

Means for Solving the Problems The inventors of the present invention have made extensive studies in view of the above technical problems. As a result, in the transparent conductive film having the three-layer structure, oxidation is performed instead of the ITO thin film or the IO thin film. When a transparent oxide composed of a mixed oxide of indium and cerium oxide is used, its refractive index is increased, light reflectance is decreased, and visible light transmittance is increased. It was discovered that a transparent conductive film having a high visible light transmittance can be obtained by using a silver thin film, and that this transparent conductive film has extremely high moisture resistance.
The present invention has been made based on such technical findings.

The present inventors have made transparent a silver-based thin film containing 0.1 to 3 atomic percent (hereinafter simply referred to as “at%”) of copper as a structure having a low resistance of 5 Ω / □ or less and a high transmittance. A conductive film having a structure sandwiched between oxide thin films has also been proposed, but the moisture resistance of this structure was somewhat insufficient. For example, as an accelerated humidity resistance test, minute spots are generated in a conductive film pattern having a structure in which a silver-based thin film containing 1 at% copper is sandwiched under a high temperature and high humidity environment of 60 ° C. and 90% humidity. There were shortcomings and they were insufficient.

That is, the invention according to claim 1 has a thickness of 5
Sandwiching a silver-based thin film of ~ 20 nm between transparent oxide thin films 3
In the layer-structured transparent conductive film, the transparent oxide thin film,
It is a mixed oxide of a first base material containing one or more oxides of a metal that is likely to form a solid solution with silver and a second base material containing one or more oxides of a metal that is difficult to form a solid solution with silver. The transparent conductive film is characterized in that the system thin film is a silver alloy containing at least gold.

In the transparent conductive film according to the first aspect of the present invention, the transparent oxide thin film comprises a first base material made of indium oxide and titanium oxide, zirconium oxide, hafnium oxide, tantalum oxide or cerium oxide. It is a preferable example to be composed of a mixed oxide with one or more selected second base materials.

In the silver-based thin film, the silver-gold alloy containing a small amount of gold is a solid solution (peritectic) at all rates, and is completely solid-solved with each other.
Since there is no precipitation of copper in the silver alloy unlike the silver-copper alloy (eutectic), it has a fairly good transmittance in the visible range. When using a conductive film having a configuration in which a silver-based thin film is sandwiched in a simple matrix liquid crystal display device that requires a low resistance of 5Ω / □ or less, such as an STN liquid crystal display device, the addition amount of gold in a silver alloy is 4 at %, It is difficult to achieve both low resistance of 5Ω / □ or less and high transmittance. On the contrary, the contribution to the improvement of the moisture resistance of the conductive film constituted by sandwiching the silver-based thin film is 0.1
Effective from adding a small amount of at%. That is, the invention according to claim 2 is characterized in that the silver-based thin film is a silver alloy containing 0.1 to 4 at% (atomic percent) of gold.

Further, in the case where the transparent conductive film is patterned by using an etching solution, when the silver-based thin film containing more than 2.5 at% of gold is sandwiched, gold is mainly formed on the substrate surface after etching. Since the residue to be left easily remains,
More preferably, the amount of gold added should be 2.5 at% or less. That is, the invention according to claim 3 is characterized in that the silver-based thin film is a silver alloy containing 0.1 to 2.5 at% of gold.

In a structure in which a silver-based thin film is sandwiched, adding cerium oxide to indium oxide is effective in improving the moisture resistance of a transparent conductive film, and at the same time, a metal such as cerium oxide which is hard to form a solid solution with silver. Depending on the amount of oxide added,
It has the effect of improving the transmittance of the transparent conductive film. The transmittance of the transparent conductive film can be expected to improve by increasing the refractive index of the transparent oxide thin film when the thickness of the silver-based thin film is constant.
After examining various materials, the inventors of the present invention reduced the resistance,
A mixed oxide of indium oxide and cerium oxide was found as a transparent oxide thin film in consideration of high transmittance, moisture resistance and etching processability. That is, the invention according to claim 4 is characterized in that the first base material is indium oxide and the second base material is cerium oxide.

As a transparent oxide thin film, its refractive index is
It is desirable to be in the range of about 2.0 to 2.4. The higher the refractive index, the better, but if it exceeds 2.4, the reflection from the transparent oxide thin film itself becomes large, and it becomes difficult to maintain high transmittance and low reflectance as a transparent conductive film. Conversely 2.0
With the following refractive indexes, the reflection of light cannot be suppressed by the silver-based thin film inserted with a film thickness of 15 nm, for example, and high transmittance and low reflectance cannot be maintained. The addition amount of cerium oxide in a mixed oxide of indium oxide and cerium oxide is converted to a metal element (converted excluding oxygen element) 10 to 8
Assuming 0 at%, the refractive index is about 2.0 to 2.4.
Range. That is, in the invention according to claim 5, the transparent oxide thin film has a cerium oxide content of 10 to 10 in terms of metal element.
It is a mixed oxide with indium oxide containing 80 at%.

When pattern formation is premised, such as a transparent electrode for a simple matrix type liquid crystal display device, it is necessary to perform etching processing with a fine pattern. In the present invention, when the level of cerium oxide in the transparent oxide thin film exceeds 40 at%, pattern formation by wet etching becomes difficult. Desirably, the amount of cerium oxide added is 40 at% or less. That is, the invention according to claim 6 is characterized in that the transparent oxide thin film is a mixed oxide with indium oxide containing 10 to 40 at% of cerium oxide in terms of metal element. When a mixed oxide of cerium oxide and indium oxide is deposited by a sputtering method, a small amount of a different kind of oxide is added to form a target in order to improve the density, conductivity, and strength of the sputter target that is a raw material. It is possible to do so.

When the thickness of the silver-based thin film is less than 5 nm, the transparent conductive film has low conductivity, and the thickness is 20 nm.
If it exceeds, the light transmittance becomes low, and in any case, it becomes unsuitable for the transparent conductive film.

Both the transparent oxide thin film and the silver-based thin film can be patterned by an etching process using nitric acid as an etching solution. That is, three layers of a transparent oxide thin film, a silver-based thin film and a transparent oxide thin film are formed on a substrate to form a transparent conductive film according to the present invention, and then the transparent oxide thin film exposed on the surface is formed. After the resist film is formed in a pattern on the substrate, the portion exposed from the resist film is etched with a nitric acid-based etching solution, whereby the three thin films can be patterned into a pattern shape aligned with each other. As the etching solution, nitric acid, nitric acid-based mixed acid such as acid obtained by adding other kind of acid such as hydrochloric acid, sulfuric acid or acetic acid to nitric acid, or nitric acid to which a small amount of a surfactant is added can be used.

Further, both the silver-based thin film and the transparent oxide thin film can be formed by the above-mentioned sputtering method, or can be formed by a vacuum film-forming method such as a vacuum vapor deposition method or an ion plating method. However, the sputtering method is suitable from the viewpoint of productivity. Then, at the time of film formation, the oxygen content in the transparent oxide thin film can be adjusted by controlling the oxygen amount inside the film forming apparatus to control the refractive index thereof. Also, at this time,
In order to prevent the deterioration of the silver-based thin film, it is preferable that the water content inside the film forming apparatus is small, and in order to secure the etching suitability of the transparent oxide thin film, it is desirable to form the film at a substrate temperature of 180 ° C. or lower or room temperature. Then, after the entire silver-based thin film and the transparent oxide thin film are formed at a substrate temperature of 180 ° C. or lower or room temperature, the entire three-layer film is etched with a nitric acid-based etching solution, and then at a temperature of 200 ° C. or higher. By performing the annealing treatment, it is possible to increase the conductivity of the entire three-layer film.

Next, as the substrate for supporting the transparent conductive film according to the present invention, for example, glass, plastic board,
Plastic film etc. can be used. Further, the transparent conductive film according to the present invention can be applied as a transparent electrode of a liquid crystal display device with or without a color filter, and may be provided with a glass face plate of a CRT as a substrate on its display surface. The transparent conductive film according to the present invention can also be used as a transparent electrode arranged on the light incident side of a solar cell element.

A protective layer may be provided on the transparent conductive film according to the present invention. As such a protective layer, for example, a transparent synthetic resin or a transparent inorganic thin film such as SiO ₂ can be applied. Further, it is also possible to apply a resin layer having a low refractive index or a light scattering layer as the protective layer and use it as an AR (antireflection) or AG (anti-glare) film.

It may be laminated on the AG film as a low reflectance EMI (electromagnetic wave shield) film. Also, AR
From the viewpoint of the above, the reflectance and the transmittance may be optimized by laminating or inserting a transparent thin film having a different refractive index in an upper layer or a lower layer of the transparent conductive film according to the present invention.

According to the transparent conductive film of the first aspect of the present invention, since the silver-based thin film contains gold in silver or a silver alloy, the moisture resistance of the conductive film having a structure in which the silver-based thin film is sandwiched can be improved. Further, a conductive film having a better light transmittance can be obtained as compared with a conductive film having the same structure made of a silver alloy to which copper is added. According to the transparent conductive film of the second and third aspects of the present invention, since the amount of gold added to the silver-based thin film is 4 to 2.5 at% or less, the conductive film having low resistance and high transmittance can be etched. Can be provided as a transparent film. According to the transparent conductive film according to the inventions of claims 4 to 6, a transparent oxide thin film having a high refractive index can be used to provide a conductive film having high transmittance and low reflectance. In addition, by adding cerium oxide to indium oxide, a conductive film having high moisture resistance can be provided while maintaining etching property.

[0027]

BEST MODE FOR CARRYING OUT THE INVENTION Embodiments of the present invention will be described in detail below with reference to the drawings.

[0028]

【Example】

<Example 1> A transparent conductive film 1 according to this example includes a transparent oxide thin film 11 having a thickness of 33 nm sequentially laminated on a glass substrate 10 having a thickness of 0.7 mm as shown in FIG. 1
The silver-based thin film 12 having a thickness of 5 nm and the transparent oxide thin film 13 having a thickness of 34 nm form the main part. Each of the transparent oxide thin films 11 and 13 was a mixed oxide in which cerium oxide was added to the indium oxide thin film in an amount of 30 at% in terms of a metal element except oxygen. The silver-based thin film 12 is a silver alloy in which 1.0 at% of gold is added to silver.

The transparent conductive film 1 is formed by the following method. First, after cleaning the surface of the glass substrate 10 with an alkaline surfactant and water, the glass substrate 10 was housed in a vacuum chamber and subjected to a plasma treatment called reverse sputtering for further cleaning.

Next, without removing the glass substrate 10 from the vacuum chamber, the transparent oxide thin film 11, the silver thin film 12, and the transparent oxide thin film 13 are sequentially formed by the sputtering method while maintaining the glass substrate 10 at room temperature. A film was formed.

Next, an electrode-shaped resist film is formed on the transparent oxide thin film 13, and the portion exposed from the resist film is etched with a nitric acid-based etching solution to align the three thin films with each other. Then, the transparent conductive film 1 was formed by patterning into an electrode shape, followed by annealing at 220 ° C. for 1 hour. The sheet resistance of the transparent conductive film 1 thus obtained was about 2.9 Ω / □. The visible light transmittance is shown by a solid line in FIG. After the patterned transparent conductive film 1 was kept at 60 ° C. and a humidity of 95% for 500 hours, the surface was observed, but no change in appearance was observed. The refractive index of the transparent conductive film formed of this mixed oxide was 2.24.

Comparative Example Similar to Example 1, except that the silver-based thin film was a silver alloy in which copper was added to copper at 1.0 at%, and a transparent conductive film was formed with the same film thickness and manufacturing method. did. The visible light transmittance is also shown in FIG. The transmittance was slightly lower than that of Example 1. Furthermore, when the transparent conductive film of Comparative Example was stored at 60 ° C. and humidity of 95%, 1
After 90 hours, stains occurred and it became defective.

Example 2 The transparent conductive film 1 shown in FIG. 1 was formed on a glass substrate by the same structure and manufacturing method as in Example 1. However, although the thickness of the silver-based thin film 12 is the same as 15 nm, the area resistance value of each transparent conductive film in which the composition of the silver alloy of the silver-based thin film 12 is 0.1 to 4 at% is shown in Table 1. In addition,
The sheet resistance value is a value measured after annealing treatment at 220 ° C. for 1 hour.

[0034]

[Table 1]

As shown in Table 1, even a transparent conductive film made of a silver alloy containing 4 at% of gold has an extremely low sheet resistance value of 4.9 Ω / □. The light transmittance of each transparent conductive film after annealing at 220 ° C. for 1 hour is 5
All were 90% or more at a wavelength of 45 nm (green). At a wavelength of 610 nm (red), 4 at% of gold was added, and the light transmittance was slightly lowered to 89%. In terms of light transmittance, addition of gold in excess of 4 at% is not very preferable.

Further, each transparent conductive film is formed at 60 ° C. and a humidity of 95.
% Under high temperature and high humidity, and the appearance change after 200 hours was observed.
In addition, when the appearance of each transparent conductive film stored under the same conditions for 500 hours was examined, there was no change in the appearance in the case where 0.4 at% or more of gold was added. Microscopic stains were generated on 0.1 at% and 0.2 at%. All were better than the comparative example of the silver-copper alloy to which copper was added. In addition, the transparent conductive film made of pure silver to which neither gold nor copper is added has a temperature of 60 ° C. and a humidity of 9
Large stains occurred after 24 hours under the high temperature and high humidity condition of 5%.

[0037]

According to the transparent conductive film of the present invention, a conductive film having a structure in which a silver-based thin film is sandwiched between transparent oxide thin films,
Since the silver-based thin film contains gold in silver or silver alloy, it is possible to provide a transparent conductive film having sufficient moisture resistance, high light transmittance, and low resistance.

According to the transparent conductive film of the second and third aspects of the present invention, since the amount of gold added to the silver-based thin film is 4 to 2.5% or less, the conductive film having a low resistance and a high transmittance is obtained. There is an advantage that a fine pattern can be formed by wet etching. According to the transparent conductive film according to the invention described in claims 4 to 6, the transparent oxide thin film can be provided as a conductive film having a high refractive index and a low reflectance. In addition, by adding cerium oxide to indium oxide, a conductive film having high moisture resistance can be provided while maintaining etching property.

[0039]

[Brief description of the drawings]

FIG. 1 is a cross-sectional view showing an example of a transparent conductive film of the present invention.

FIG. 2 is a graph showing the spectral transmittance of the transparent conductive film of Example 1 of the present invention and the spectral transmittance of the conductive film of Comparative Example.

[Explanation of symbols]

 1 Transparent Conductive Film 10 Glass Substrate 11 Transparent Oxide Thin Film 12 Silver Thin Film 13 Transparent Oxide Thin Film

─────────────────────────────────────────────────── ─── Continuation of the front page (51) Int.Cl. ⁶ Identification number Office reference number FI Technical indication location H01J 11/02 H01J 11/02 B (72) Inventor Koji Imayoshi 1-5, Taito, Taito-ku, Tokyo No. 1 Toppan Printing Co., Ltd.

Claims (6)

[Claims] 1. A transparent conductive film having a three-layer structure in which a silver-based thin film having a thickness of 5 to 20 nm is sandwiched between transparent oxide thin films, wherein the transparent oxide thin film contains an oxide of a metal that is likely to form a solid solution with silver. It is a mixed oxide of a first base material containing at least one kind and a second base material containing at least one oxide of a metal that is hard to form a solid solution with silver, and the silver-based thin film is a silver alloy containing at least gold. There is a transparent conductive film. 2. The transparent conductive film according to claim 1, wherein the silver-based thin film is a silver alloy containing 0.1 to 4 at% (atomic percentage) of gold. 3. The transparent conductive film according to claim 1, wherein the silver-based thin film is a silver alloy containing 0.1 to 2.5 at% of gold. 4. The transparent conductive film according to claim 1, wherein the first base material is indium oxide and the second base material is cerium oxide. 5. The transparent conductive film according to claim 1, wherein the transparent oxide thin film is a mixed oxide of indium oxide containing 10 to 80 at% of cerium oxide in terms of metal element. 6. The transparent conductive film according to claim 1, wherein the transparent oxide thin film is a mixed oxide with indium oxide containing 10 to 40 at% of cerium oxide in terms of metal element.