JPH07178863A - Transparent conductive film and production thereof - Google Patents

Abstract

PURPOSE:To obtain a transparent conductive film low in resistance and improved in stability by providing a crystalline inorg. substance as the substrate membrane of a transparent conductive membrane. CONSTITUTION:An inorg. substance having crystallinity, for example, cerium oxide is provided as the substrate membrane of a transparent conductive membrane. The transparent conductive membrane has both of transparency and conductive characteristics and, for example, there is a membrane composed of indium oxide, indium oxide-tin oxide(ITO), tin oxide, tin oxide-antimony, zinc oxide or zinc oxide-alminum. This membrane is desirably produced by a dry process such as vacuum vapor deposition or sputtering. In the formation of the substrate membrane composed of the crystalline inorg. substance, for example, a cerium oxide membrane, a sputtering method is most desirable. Since the cerium membrane is good in the matching properties with the transparent conductive membrane, the structure of the transparent conductive membrane is not amorphous and becomes crystalline and a transparent conductive film low in resistance and excellent in stability can be produced.

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 having low resistance and high stability, and a method for producing the transparent conductive film.

[0002]

2. Description of the Related Art A transparent conductive film in which a transparent and low-resistance compound is adhered on a polymer film is used for applications utilizing its conductivity, for example, flat displays such as liquid crystal displays and EL displays, and transparent solar cells. It is widely used in the fields of electric and electronic fields such as transparent electrostatics of electrodes and cathode ray tubes, or electromagnetic shield plates and heating elements. In addition, among such transparent conductive thin films, those having selective transmission are those that use the infrared light reflection characteristics to collect collector windows for solar energy, heat ray reflective materials for buildings, automobiles, etc. It is also used as.

As these transparent conductive thin films, tin oxide (SnO ₂ ) and indium oxide (In ₂ O) are generally used.
₃ ), indium oxide / tin (ITO), or zinc oxide (ZnO) is a typical one, and it is known that it can be produced by a vacuum deposition method, a sputtering method, a CVD method, a spray method, or the like. There is. These compound films have practical properties (surface resistance of several Ω / □ to several MΩ / □, visible light transmittance of 70 to 95%) under appropriate preparation conditions.
It is known that a transparent conductive thin film having

[0004]

The conventional transparent conductive film as described above has the following problems. When a transparent conductive thin film such as indium oxide or tin oxide is formed on a plastic substrate, the plastic substrate is generally 200
Since it cannot withstand a high temperature of ℃ or more, it is necessary to form the transparent conductive film at a relatively low temperature, for example, 200 ℃ or less. Furthermore, since the interface between the plastic base material and the transparent conductive thin film is poorly matched, a transparent conductive thin film grown on the base material at a low temperature of 200 ° C. or lower is, for example, a film grown at a high temperature of 450 ° C. to 500 ° C. In comparison, there is a drawback that the specific resistance of the film is generally large. This is said to be because the structure of the transparent conductive thin film formed at low temperature is amorphous. Further, since this amorphous structure is in a metastable state, there is a problem that the resistance characteristic changes with time. In addition, there is also a problem that the adhesion of the thin film is small due to the poor matching of the interface with the plastic substrate.

On the other hand, in order to bring such a transparent conductive thin film into a stable and low resistance crystalline state, a method of raising the substrate temperature during film formation or performing heat treatment after film formation has been proposed. However, on a plastic substrate, there is a limit to raising the substrate temperature and the heat treatment temperature, and even if it is crystallized, the properties obtained are insufficient and not very excellent. Also,
As a method of forming a transparent conductive thin film having a low resistance and a strong adhesive force on a plastic substrate, a method of using a thin film of silicon, aluminum or a titanium compound as a base film has been proposed (Japanese Patent Laid-Open No. SHO 61-242).
58-172810) was still insufficient in terms of low resistance, and the stability of performance was not sufficient. The present invention has been earnestly studied for the purpose of improving such defects, and as a result, by interposing cerium oxide at the interface with the transparent conductive film as an underlying compound film having good compatibility with the transparent conductive thin film, the above-mentioned low-temperature forming film is formed. The inventors have found that the drawbacks are improved, and have come to propose the present invention.

[0006]

SUMMARY OF THE INVENTION The present invention is intended to provide a transparent conductive film having low resistance and excellent stability. That is, the present invention is characterized in that, in a transparent conductive film in which a transparent conductive thin film is provided on a plastic substrate, an inorganic substance having crystallinity, such as cerium gold, is provided as a base film of the transparent conductive thin film. It is a transparent conductive film and a method for producing the same.

The plastic substrate in the present invention means an organic polymer melt-extruded, and if necessary, in the longitudinal direction,
And, or, is a film stretched in the width direction, cooled, heat-fixed, as the organic polymer, polyethylene,
Polypropylene, polyethylene terephthalate, polyethylene-2,6-naphthalate, nylon 6, nylon 4, nylon 66, nylon 12, polyvinyl chloride,
Examples thereof include polyvinylidene chloride, polyvinyl alcohol, wholly aromatic polyamide, polyamideimide, polyimide, polyetherimide, polysulfone, polyphenylene sulfide, and polyphenylene oxide.
Further, these (organic polymer) organic polymers may be copolymerized or blended with a small amount of another organic polymer. Among these, polyethylene terephthalate and the like are most used in the present invention.

Further, known additives such as an ultraviolet absorber, an antistatic agent, a plasticizer, a lubricant and a coloring agent may be added to the organic polymer, and its transparency is not particularly limited. However, when used in applications where transparency is important, those having a transmittance of 50% or more are preferable. The plastic film of the present invention may be subjected to corona discharge treatment, glow discharge treatment, or other surface roughening treatment prior to laminating the thin film layers, as long as the object of the present invention is not impaired. Also, known anchor coat treatment, printing, and decoration may be applied. The thickness of the plastic film of the present invention is not particularly limited, but it is preferably in the range of 3 to 500 μm, and more preferably in the range of 8 to 300 μm.
The product of the present invention may be used as it is, but may be used by laminating or coating a film or a thin layer of another organic polymer.

The transparent conductive thin film in the present invention is not particularly limited as long as it is a material having both transparency and conductive characteristics. Typical examples are indium oxide and
There are indium oxide-tin oxide (ITO), tin oxide, tin oxide-antimony, zinc oxide, zinc oxide-aluminum thin film and the like. These compound thin films have both transparency and conductivity under appropriate production conditions (surface resistance: several Ω / □ to several MΩ / □, visible light transmittance: 60 to 95%).
It is known to be a transparent conductive thin film. The thickness of these transparent conductive thin films is preferably about 80 to 8000 Å (angstrom), more preferably 100 to 5000 Å. The method for producing the transparent conductive thin film in the present invention includes vacuum deposition, sputtering, and CV.
D, ion plating method, spray method and the like are known. In the present invention, the method for forming the transparent conductive thin film is not particularly limited, but since the base film is formed by a dry process, the transparent conductive thin film is preferably dry process such as vacuum deposition or sputtering. For example, in the case of the sputtering method, ordinary sputtering using a compound target or reactive sputtering using a metal target is used. At this time, oxygen, nitrogen, water vapor or the like may be introduced as a reactive gas, or means such as ozone addition or ion assist may be used in combination. Regarding the substrate temperature, in the present invention, a transparent conductive film having good crystalline characteristics can be obtained without particularly raising the temperature, but as long as the object of the present invention is not impaired, the substrate temperature is raised or lowered. May be changed. The same applies to other manufacturing methods such as vapor deposition and CVD.

In the present invention, as a method for producing a crystalline inorganic substance as a base film, for example, a cerium oxide thin film, a vacuum deposition method, a sputtering method, a PVD method such as ion plating, etc. is used.
A method (physical vapor deposition method), a CVD method (chemical vapor deposition method), or the like is used as appropriate, but the sputtering method is most preferable from the viewpoint of controlling the film thickness. The thickness of the base film is 5
It should be 0 Å or more, preferably 100 Å or more 500
It is less than 0Å. The cerium oxide may contain a small amount (about 3% of all components) of other components as long as the characteristics are not impaired. The underlying film of the present invention, for example, the cerium oxide thin film of an inorganic substance, may be in direct contact with the transparent conductive film, and there is no particular limitation as to what is further below the underlying film of the cerium oxide film. For example, a silicon oxide or aluminum oxide thin film may be provided as a barrier layer further below the cerium oxide film, or the cerium oxide film may be in direct contact with the plastic substrate without attaching anything. In the present invention, if the cerium oxide thin film that is the base film is in direct contact with the transparent conductive film, the structure of the transparent conductive film becomes crystalline rather than amorphous, and it is transparent with low resistance and excellent stability. A conductive film can be produced.

Next, examples will be described. (Example 1) PET film (Toyobo Co., Ltd. E510)
0: 100 μm thick) as a base film of the transparent conductive thin film,
A cerium oxide thin film (50-1500Å thickness) was applied. The manufacturing method is a high frequency magnetron sputtering method, and a cerium oxide sintered target (size
100 × 400 mm) was used. As for the preparation conditions, the vacuum pressure during sputtering was 3 mTorr with Ar gas introduced.
With a constant r, the sputtering power (400 to 1000 W) and the film feeding speed (0.5 to 2 m / min) were changed to obtain a predetermined film thickness. Next, on this, In-Sn
An ITO film was formed by a DC reactive sputtering method using a (5 wt%) metal target. The conditions are as follows: the vacuum pressure during sputtering is constant at 4 mTorr, the sputtering current (1 to 5 A) and the film feed rate (0.5 to 2 m / m).
in) was changed to a film thickness of 200 or 1000Å. Regarding the degree of oxidation, the oxidizing atmosphere was controlled by introducing a mixed gas of Ar and O ₂ . The substrate temperature was not raised. (Table 1: Examples 1-1 to 8)

(Measurement Method of Surface Resistance) A four-end needle method was used for measurement of resistance characteristics. As a measuring machine, Mitsubishi Petrochemical Co., Ltd.
(Lotest APMCP-T400) was used for measurement.

(Method of X-ray Diffraction) Crystallinity is measured by a high-intensity X-ray diffractometer, Rotaflex (R manufactured by Rigaku Corporation).
It measured using AD-RAC). As the X-ray generation conditions, a Cu tube was used, and the excitation voltage and current were 40 KV,
It was 140 mA. The specific resistance of the obtained sample is 8 ×
It was 10 ⁻⁴ Ωcm or less. Furthermore, when the crystallinity was checked by X-ray diffraction, it was found that crystalline peaks (222) and (440) of indium oxide were observed near 2θ = 30 ° and 50 °, and the crystals were crystalline. (Fig. 1)

(Comparative Example 1) As in (Example 1), PE
An ITO film was formed on the T film to form a transparent conductive film. At this time, the ITO film was directly attached on the PET film without forming the base film. The sputter conditions were the same as in (Example 1), and the thin film thickness was 200 and 1000Å. (Table 1: Comparative Examples 1-1 and 2)

(Comparative Example 2) Silicon oxide, aluminum oxide, and titanium oxide were applied as a base film of a transparent conductive film on a PET film by an EB vapor deposition method to a predetermined film thickness, and then I
The TO film was applied by the sputtering method as in Example 1. ITO
The film thickness was 480Å. (Table 1: Comparative examples 2-1 to 2-1)
3) The crystallinity of the transparent conductive films obtained in Comparative Examples 1 and 2 was examined by X-ray diffraction, but no crystal peak was observed and it was found to be amorphous. Further, it was found that the resistance characteristics of the samples of the examples were 8 × 10 ⁻⁴ Ωcm or less, whereas the resistance characteristics of the comparative examples were 15 × 10 ⁻⁴ Ωcm or more, which was inferior.

(Example 2) SnO ₂ (Sb: 5 wt%)
The 125 μm thick PET film (TOYOBO E510
A tin oxide-antimony-based transparent conductive film (200 or 1000 Å thickness) was formed on the surface (0). The manufacturing conditions are as follows: vacuum pressure during sputtering 4 mTorr, sputtering power (1 K
W) constant, film feed speed (0.4-2 m / m
in) was changed to obtain a predetermined film thickness. The degree of oxidation is A
The oxidizing atmosphere was controlled by introducing a mixed gas of r and O ₂ . The substrate temperature was not raised at this time. The specific resistance of the sample thus obtained was measured in the same manner as in Example 1. (Table 2: Examples 2-1 to 6) Further, when the crystallinity was also examined, a crystal peak was observed and it was found to be crystalline.

(Comparative Example 3) As in (Example 2), PE
A tin oxide-antimony-based transparent conductive film was formed on the T film to form a transparent conductive film. At this time, a sample (Comparative Examples 3-1 and 2) in which a transparent conductive film was directly attached on a PET film without a base film, and a silicon oxide, aluminum oxide, or titanium oxide thin film as a base film was attached to a predetermined film thickness,
Further, a sample provided with a transparent conductive film (Comparative Example 3-3 to
5) was produced. The specific resistance of the sample thus obtained was measured in the same manner as in Example 1. (Table 2) As a result, the resistance characteristics of the samples of Examples are 10 × 10 ^−4.
It was found that the resistance characteristic of the comparative example was 35 × 10 ⁻⁴ Ωcm or more, while it was less than Ωcm. Furthermore, the crystallinity was also examined, but no crystal peak was observed and it was found to be amorphous. Next, in order to examine the thermal stability, the samples of Example 1-3 and Comparative examples 1-2 and 2-1 were left in a constant temperature bath at 80 ° C. As a result, the samples of the examples are stable after being left for 1000 hours,
The sample of the comparative example gradually changed, and the resistance value increased more than double after 1000 hours. (Fig. 2) Next, for the same sample, a keystroke test (10000
It was found that the resistance characteristics of the sample of the example were stable, but the resistance value of the sample of the comparative example increased 1.5 to 2 times, and the stability was poor. (Figure 3)

[0018]

That is, the present invention provides a transparent conductive film in which a transparent conductive thin film is provided on a plastic substrate,
By providing cerium oxide as a base film of the transparent conductive thin film, a transparent conductive film having low resistance and excellent stability can be provided.

[0019]

[Table 1]

[0020]

[Table 2]

[Brief description of drawings]

FIG. 1 shows an example of crystallinity measurement of a transparent conductive film by X-ray diffraction.

FIG. 2 shows an example of a result of a standing test for checking thermal stability of resistance characteristics.

FIG. 3 shows an example of the result of a keystroke test for checking the practical stability of resistance characteristics.

Claims (3)

[Claims] 1. A transparent conductive film in which a transparent conductive thin film is provided on a plastic substrate, wherein a crystalline inorganic substance is provided as a base film of the transparent conductive thin film. 2. A transparent conductive film, wherein the base film according to claim 1 is cerium oxide. 3. A method for producing a transparent conductive film, comprising: a transparent conductive film having a transparent conductive thin film provided on a plastic substrate, wherein a crystalline inorganic substance is provided as a base film of the transparent conductive thin film.