JP2010021048A - Transparent conductive film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To solve the problem wherein durability of a zinc oxide transparent conductive film is low and resistance thereof is increased under an environment of high temperature and high humidity. <P>SOLUTION: This transparent conductive film excellent in conductivity and durability is manufactured by constituting a zinc oxide transparent conductive oxide layer 3 on a surface side separated from a transparent substrate 1, to contain silicon dioxide and to form amorphous structure, in the transparent conductive film composed of two or more of the zinc oxide transparent conductive oxide layers 2, 3. Further, the transparent conductive film excellent in conductivity and durability, and further excellent in transparency, is manufactured by forming a carbon layer 4 of low refractive index between the two layers of zinc oxide transparent conductive oxide layers 2, 3. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention mainly includes touch panels, PDPs, LCDs, electroluminescence (EL) display materials, transparent electrodes and back electrodes of solar cells, transparent intermediate layers of hybrid solar cells, low dielectric constant films used in compound semiconductor high-speed devices, and surface elasticity. Wave elements, window glass coatings for the purpose of cutting infrared rays, gas sensors, prism sheets utilizing nonlinear optics, transparent magnetic materials, optical recording elements, optical switches, optical waveguides, optical splitters, photoacoustic materials, high-temperature heater materials The present invention relates to a transparent conductive film capable of achieving high environmental variability.

  In transparent conductive films used for touch panels, display materials, solar cells, and the like, indium tin oxide (ITO), tin oxide, zinc oxide, and the like are widely used as the transparent conductive layer. Such a transparent conductive layer is formed by a physical vapor deposition method (PVD method) such as magnetron sputtering method or molecular beam epitaxy method or a chemical vapor deposition method (CVD method) such as thermal CVD or plasma CVD, A method formed by an electroless method is known. Among them, ITO is a very excellent material as a transparent conductive material, and is currently widely used for a transparent conductive layer.

  However, there is a possibility that indium as a raw material may be depleted, and there is an urgent need to search for a material that can replace ITO in terms of resources and cost. A representative example of a material replacing ITO is zinc oxide (ZnO). ZnO is known to be excellent in transparency as compared with ITO, but inferior in stability to moisture and heat (Non-Patent Document 1).

  In addition, a technique for improving the chemical stability of ZnO by adding chromium, cobalt, silicon, or the like to ZnO is also known (Patent Documents 1 and 2). Zn is doped with silicon at 4 to 6 atm. A method for improving the durability in a high-temperature and high-humidity environment is also known (Patent Document 3). However, all still have problems in terms of conductivity and durability.

As described above, ZnO as a substitute for ITO has been widely used for the transparent conductive layer, but a material superior to ITO, which is currently mainstream, has not been put into practical use.
Supervised by Yutaka Sawada, "Transparent conductive film", 1999, page 6 (CMC Publishing) JP 2002-75061 A JP 2002-75062 A JP-A-8-45352

  In order to solve the above-mentioned problems, the present inventors have conducted intensive studies, and as a result, a zinc oxide transparent conductive film structure having two or more zinc oxide transparent conductive oxide layers and formed far from the transparent substrate. It has been found that the resistance to environmental variability can be improved while maintaining conductivity by coating the transparent conductive oxide layer on the substrate side with a transparent conductive oxide layer having an amorphous structure.

  That is, the present invention has the following configuration.

  1). A transparent conductive film having a transparent conductive oxide layer composed mainly of zinc oxide composed of two or more layers on a transparent substrate, wherein the transparent conductive oxide layer formed far from the transparent substrate is amorphous. A transparent conductive film.

  2). 1. The transparent conductive film according to 1), wherein a carbon layer is formed on one side or both sides of the amorphous transparent conductive oxide layer.

  3). The amorphous transparent conductive oxide layer is composed of 7 wt. % Or more of the transparent conductive film according to 1) or 2).

  4). The transparent conductive film according to 2) or 3), wherein the carbon layer has a refractive index of 1.25 to 1.80.

  5). 1. The transparent conductive film according to any one of 1) to 4), wherein the ratio of surface resistance before and after standing for 10 days in an environment of 85 ° C./85% RH is 1.0 to 1.5.

  According to the present invention, it is possible to form a transparent conductive film exhibiting favorable characteristics in “conductivity” and “environmental variability” which are particularly important elements in a touch panel, an electroluminescence electrode substrate, a solar cell, and the like.

  The present invention relates to "a transparent conductive film having a transparent conductive oxide layer composed mainly of zinc oxide consisting of two or more layers on a transparent substrate, wherein the transparent conductive oxide layer formed far from the transparent substrate is amorphous. The present invention discloses a “transparent conductive film characterized by being”.

  Zinc oxide is a compound with strong ion binding properties, and thin film materials are weak against water and chemicals. In order to reinforce this weak point, a method of blocking moisture by first providing a clothing layer on the surface of the zinc oxide transparent thin film is considered. Such a moisture barrier material is generally a material such as a metal material or polyolefin, and is often not suitable for a transparent conductive film material such as an opaque material or an insulator. Second, it is conceivable to impart stability by doping zinc oxide, and Patent Documents 1 to 3 describe that the stability is improved by doping cobalt, chromium, or silicon.

  In these methods, a method of forming a film after mixing a metal oxide or metal chloride with zinc oxide, a method of co-sputtering zinc oxide and silicon dioxide, or the like is used. Japanese Patent Laid-Open No. 10-237630 describes a method of forming a transparent conductive layer by a reactive sputtering method using carbon dioxide as a carrier gas for a metal target.

  Hereinafter, typical embodiments of the transparent conductive film according to the present invention will be described. 1 to 4 are sectional views of a transparent conductive film according to the present invention. Zinc oxide transparent conductive oxide layers 2 and 3 are formed on the transparent substrate 1 (FIG. 1). 2 to 4, the carbon layer 4 is formed on one side or both sides of the zinc oxide transparent conductive oxide layer 3 on the front side.

  The transparent substrate 1 is not particularly limited as long as it is a substrate that is transparent at least in the visible light region. Specific examples include glass and synthetic resin. Examples of the glass include alkali glass, borosilicate glass, non-alkali glass, and sapphire glass.

  When glass is used as a substrate, the thickness can be arbitrarily selected depending on the purpose of use, but practically, the thickness is practically 0.5 mm to 4.5 mm in consideration of the balance between handling and weight. Can be illustrated. A glass substrate that is too thin is not easily strong enough to be broken by impact. In addition, a glass substrate that is too thick becomes heavy and affects the thickness of the device, making it difficult to use it for portable devices. In addition, a thick substrate is not preferable in terms of transparency and cost.

  On the other hand, examples of the synthetic resin that can be used include thermoplastic resins and thermosetting resins. Specific examples of the thermoplastic resin include acrylic resin, polyester, polycarbonate resin, and polyolefin resin, and specific examples of the thermosetting resin include polyurethane. These synthetic resin materials can be used as plates, sheets, and films. Among them, a flexible sheet or film is preferable. Further, a synthetic resin material plate is preferable because it is lighter than glass and has excellent flexibility.

  As the synthetic resin material, a thermoplastic resin is preferable, and a polyolefin resin is particularly preferable. Among the polyolefin resins, cycloolefin polymer (COP) is preferable from the viewpoint of optical isotropy and water vapor blocking property. Furthermore, a film mainly composed of COP can be used effectively.

  Examples of COP include norbornene polymers, copolymers of norbornene and olefins, and polymers of unsaturated alicyclic hydrocarbons such as cyclopentadiene. From the viewpoint of water vapor barrier properties, it is preferable that the main chain and side chain of the constituent molecules do not contain a functional group having a large polarity, such as a carbonyl group or a hydroxyl group.

  From the viewpoint of excellent heat resistance, polyethylene naphthalate (PEN) and polyethersulfone (PES) are preferable.

  When a synthetic resin is used as a substrate, the thickness can be arbitrarily selected depending on the purpose of use, but handling is easy if it is about 0.03 mm to 3.0 mm. If it is too thin, handling is difficult and the strength is insufficient. On the other hand, if it is too thick, there are problems in transparency and cost, and the thickness of the device increases. Among these, a film shape of 0.03 mm to 1.0 mm, more preferably 0.035 mm to 0.5 mm is preferable.

  When a film is used as the transparent substrate 1, the substrate film can be stretched to give a phase difference. By providing a phase difference, it is possible to produce a low reflection panel by combining with a polarizing plate, and it is expected that the visibility of an image is greatly improved.

  The phase difference can be imparted by using a known method. For example, it is possible by stretching or orientation treatment such as uniaxial stretching or biaxial stretching. At this time, the orientation of the polymer skeleton can be promoted by applying a temperature close to the glass transition temperature to the film. The preferable range of the retardation value varies depending on the intended function, but in the case of providing an antireflection function, it is preferable to select the retardation value within a range of 50 to 300 nm. Thus, the vicinity of 137 nm, which is 1/4, is more preferable.

  In the present invention, a transparent conductive oxide having transparent conductive oxide layers (transparent conductive oxide layers 2 and 3) mainly composed of two layers of zinc oxide on a transparent substrate and formed far from the transparent substrate. The transparent conductive film is characterized in that the physical layer (transparent conductive oxide layer 3) is amorphous.

  Among the transparent conductive oxides, zinc oxide is used for the transparent conductive oxide layer 2 in the present invention because of its high transparency and that no reduction reaction occurs with respect to hydrogen plasma generated during the formation of the carbon film. A doping agent can be added to the transparent conductive oxide for the purpose of resistance control and stability. Examples of the doping agent include compounds containing aluminum, gallium, indium, tin, and boron, and compounds containing phosphorus and nitrogen, but are not limited thereto.

  The method for forming the transparent conductive oxide layer 2 is not particularly limited as long as it is a means for forming a uniform thin film. For example, in addition to PVD methods such as sputtering and vapor deposition, and vapor phase deposition methods such as various CVD methods, a solution containing a raw material for the transparent conductive oxide layer is spin coated, roll coated, spray coated, dipped coated, etc. A method of forming a transparent conductive oxide layer by a heat treatment or the like after coating by the above is mentioned, but a vapor deposition method is preferable from the viewpoint of easily forming a nanometer level thin film.

  When the transparent conductive oxide layer 2 is formed by the vapor deposition method, the temperature of the substrate varies depending on the softening temperature of the substrate, but is preferably room temperature to the glass transition temperature of the substrate, more preferably room temperature to the glass transition of the substrate. A temperature 30 ° C. lower than the temperature is preferred. When the temperature of the substrate is too low, the crystallinity of the transparent conductive oxide is deteriorated, and there is a possibility that the purpose of transparency and conductivity cannot be achieved. If the temperature of the substrate is too high, the phase difference imparted to the substrate may be lost. For the formation of the transparent conductive oxide layer, plasma discharge can be used as necessary.

  Although there is no restriction | limiting in particular in the power of plasma, 10W-600W are preferable from a viewpoint of productivity or crystallinity. If it is too low, the film may not be formed. If it is too high, there is a concern about damage to the substrate and damage to the device. As a carrier gas used for forming the transparent conductive oxide layer, a gas used in a general vapor deposition method can be used. For example, argon, hydrogen, oxygen, or nitrogen gas can be used.

  The film thickness of the transparent conductive oxide layer 2 is preferably 200 mm or more. By making a transparent conductive oxide layer into this range, the electroconductivity of the transparent conductive film required for this invention can be produced. When used for touch panel applications, an appropriate conductive transparent conductive film can be produced by setting the film thickness to 500 to 1000 mm. For solar cells and EL devices, an effect can be obtained by forming a transparent conductive oxide layer having a thickness larger than that.

  The transparent conductive oxide layer 3 is an amorphous layer composed of an oxide containing zinc oxide as a main component, and the amorphous layer is an important technique in the present invention. The inclusion of silicon dioxide is preferable because the transparent conductive oxide layer 3 tends to be amorphous. Since the transparent conductive oxide layer 3 is an amorphous layer, the durability of the transparent conductive film in a high temperature and high humidity environment is improved as a result.

  The durability of the transparent conductive film in a high-temperature and high-humidity environment is as follows. The transparent conductive film after film formation is placed in a high-temperature and high-humidity device set to an environment of 85 ° C./85% RH and left for 10 days. The resistance can be measured and the ratio can be evaluated as the degree of change. The value of this ratio is preferably 1.0 to 1.5, more preferably 1.0 to 1.4, and particularly preferably 1.05 to 1.35.

  Unlike the microcrystalline structure in which the surface is amorphous, there is no crystal grain boundary. Therefore, it is considered that the barrier property against air and water molecules is enhanced. Further, it is considered that the transparent conductive oxide layer 3 becomes a compound having a strong covalent bond by introducing silicon dioxide, and has a higher durability against zinc oxide having a strong ionic bond.

  The content of silicon dioxide is 7 wt. % Or more is preferable. More preferably, 7 to 45 wt. % Or 8-35 wt. %, In particular 8-25 wt. % Is preferred. When the content of silicon dioxide is small, the transparent conductive oxide layer 3 is unlikely to be amorphous, and in this case, the durability improvement effect is small. On the other hand, when there is too much silicon dioxide, the transparent conductive oxide layer 3 becomes a dielectric, and surface resistance becomes large, which is not preferable.

  The film thickness of the transparent conductive oxide layer 3 can be arbitrarily adjusted within a range that does not adversely affect the transparent conductive film, but a film of 60 mm or more, more preferably 80 mm or more is preferable, and an effect on the barrier property can be expected. . If the thickness is less than that, the transparent conductive oxide layer 3 may be striped and the effect of the barrier property is reduced. The film thickness of the transparent conductive oxide 3 is preferably 500 mm or less, and more preferably 300 mm or less. When this film thickness is too thick, there is a possibility of a decrease in conductivity.

  As a method for detecting the doping amount, any method that is usually used for elemental analysis can be detected with high accuracy. For example, in addition to elemental analysis means such as atomic absorption analysis and fluorescent X-ray analysis, there are spectroscopic techniques such as X-ray photoelectron spectroscopy, Auger electron spectroscopy, electron beam microanalyzer, and secondary ion mass spectrometry.

  In particular, energy dispersive X-ray analysis (EDX) is a relatively simple technique that can perform elemental analysis with high accuracy simultaneously with shape observation using a scanning electron microscope (SEM) or transmission electron microscope (TEM). When these methods are used, the silicon doping amount can be easily calculated by the following formula by relative comparison with zinc.

(Silicon doping amount) = (number of silicon atoms) ÷ ((number of silicon atoms) + (number of zinc atoms))
The crystallinity of the transparent conductive oxide layer 3 can be easily determined by X-ray diffraction measurement.

  The carbon layer 4 is used for the purpose of enabling protection of the zinc oxide transparent conductive oxide layer against air and moisture, improving durability against physical impact on the surface of the transparent conductive layer, and high light transmittance. For these carbon layers, hydrocarbons containing hydrogen in the structure are preferable, and amorphous hydrocarbons and tetrahedral amorphous hydrocarbons are more preferably used from the viewpoint of physical strength and transparency.

  Further, the refractive index of the carbon layer according to the present invention is in the range of 1.25 to 1.80, more preferably 1.25 to 1.75, especially 1.25 to 1.70. Preferably there is. By having such a carbon layer, the light transmittance can be improved. These carbon layers are generally formed by a known technique such as a CVD method, a sputtering method, an ion plating method, or an evaporation method, but the carbon layer according to the present invention is formed by a high frequency plasma CVD method or a magnetron sputtering method. Is preferably used.

  There are various types of high-frequency power sources to be used, such as RF, VHF, and microwave, but a desired carbon layer can be obtained by using any power source. When the carbon layer is formed by the high-frequency plasma CVD method, a raw material that is usually used can be used, and depending on the structure of the desired carbon layer, there may be a case where only methane gas is used or a film is diluted with hydrogen. The plasma power is not particularly limited, but is preferably 5 W to 600 W. When it is low, the film is not formed, and when it is high, the transparent conductive layer 2 may be etched by plasma.

  When the carbon layer is formed by magnetron sputtering, a carbon target can be used and a carrier gas mixed with argon, hydrogen, or carbon dioxide can be used. Among them, it is preferable to use a mixed gas of argon and carbon dioxide, and it is more preferable to use a carrier gas having an amount of carbon dioxide of less than 50 volumes. Specifically, it is preferable to use a carrier gas in which the partial pressure of argon: partial pressure of carbon dioxide = 9: 1 to 6: 4, and further 8.5: 1.5 to 7: 3.

  Regarding the power source to be used, a carbon layer necessary for the present invention can be formed without any particular limitation. The power can be arbitrarily set as long as the film forming speed with productivity is obtained and the power is such that the already formed transparent conductive oxide layer is not etched.

  Even if the carbon layer 4 is formed as a single layer, the effects necessary for the present invention can be sufficiently obtained, but from the viewpoint of improvement in physical durability, a multilayer laminated structure can be obtained. In this case, if the refractive index is in the above range in at least one carbon layer in the multilayer film, it is possible to contribute to high light transmittance.

  The film thickness of the carbon layer 4 is preferably 200 to 1600 mm, more preferably 250 to 1300 mm, and particularly preferably 250 to 1000 mm as a whole in both a single layer and a multilayer. If it is too thick, there is a possibility that the function of the transparent conductive film will be reduced, such as a decrease in transmittance due to absorption loss and a decrease in conductivity. If it is too thin, the layer becomes optically meaningless, and effects such as improvement in light transmittance cannot be obtained.

  The surface resistance of the transparent conductive film to be produced varies depending on the intended use. For example, it is preferably about 10 to 20Ω / □ in the case of a solar cell or an EL element, and 200 to 1000Ω / □ in the case of a touch panel. Is preferably 25 to 600Ω / □.

  EXAMPLES The present invention will be specifically described below with reference to examples, but the present invention is not limited to these examples.

Silicon dioxide content: A scanning electron microscope JSM-6390-LA (manufactured by JEOL Ltd.) was used.
Surface resistance: Measured using a resistivity meter Loresta GP MCT-610 (manufactured by Mitsubishi Chemical Corporation).
Light transmittance: A spectrophotometer U-4000 (manufactured by Hitachi High-Technologies Corporation) was used.

Refractive index: Measured and measured using a spectroscopic ellipsometry M2000 (manufactured by JA Woollam).
X-ray diffraction: The crystallinity was judged from the presence or absence of a peak using an X-ray commentary for thin film evaluation manufactured by Rigaku Corporation.

  Durability: The transparent conductive film after film formation was put into a high-temperature and high-humidity device set in an environment of 85 ° C./85% RH and left for 10 days. The surface resistance before and after the durability test was measured, and the ratio was evaluated as the degree of change.

(Examples 1-3)
To alkali-free glass (trade name OA-10, film thickness 0.7 mm, manufactured by Nippon Electric Glass Co., Ltd.), 2 wt. Sputtering of zinc oxide doped with% aluminum oxide was performed. The film formation was performed according to the magnetron sputtering method, and a transparent conductive oxide layer 2 of 400 で was formed at a film formation rate of 3.6 Å / sec using a high frequency power source of 10 W / cm ⁻² .

A transparent conductive oxide layer 3 was formed thereon. A magnetron sputtering method was used for forming the layer, and 10 wt. % (Example 1), 20 wt. % (Example 2), 40 wt. % (Example 3) Using the contained target, a film thickness of 100 mm was formed using a high frequency power source of 10 W / cm ⁻² at a film forming speed of 3.0 kg / sec.

(Examples 4 to 5)
A carbon layer was formed on the transparent conductive oxide layer 3 formed in the same manner as in Example 1. The film forming conditions for the carbon layer were as follows.

(Example 4) A carbon target was used as a sputter target, the argon / carbon dioxide partial pressure ratio was 8/2, the total pressure was 8.0 Pa, and a high frequency power source of 0.15 W / cm ^-2 was used for 2.5Å. A carbon layer 4 (carbon layer 1 in Table 1) having a thickness of 600 kg was formed at a film forming speed of / sec. The carbon layer had a refractive index of 1.26 at 550 nm.

(Example 5) A carbon target was used as a sputtering target, the hydrogen / carbon dioxide partial pressure ratio was 8/2, the total pressure was 8.0 Pa, and a high frequency power source of 0.15 W / cm ^-2 was used for 1.5Å. A carbon layer 4 (carbon layer 2 in Table 1) having a thickness of 600 kg was formed at a film forming speed of / sec. The refractive index of this carbon layer at 550 nm was 1.65.

(Examples 6 to 7)
A carbon layer 4 is formed in the same manner as in Examples 4 and 5 on the layer formed up to the transparent conductive oxide layer 2 in the same manner as in Example 1, and further transparent conductive in the same manner as in Example 1. The oxide layer 3 was formed (Example 6 and Example 7 in order).

(Examples 8 to 9)
The transparent conductive oxide layer 3 was formed in the same manner as in Examples 6 and 7 except that the film thickness of the carbon layer was changed to 300 mm, and a carbon layer of 300 mm was formed thereon as in Examples 4 and 5 ( Example 8 and Example 9 in this order.

(Comparative Example 1)
The silicon dioxide content of the transparent conductive oxide layer 3 is 5 wt. A transparent conductive film was prepared in the same manner as in Example 1 except that the zinc oxide target was set to be%.

(Comparative Example 2)
In the same manner as in Example 1, a 400-mm transparent conductive oxide layer 2 was formed.

  In the above transparent conductive film, the kind of carbon layer, the content of silicon dioxide in the transparent conductive oxide layer 3, crystallinity judged from X-ray diffraction, light transmittance at 550 nm, surface resistance, surface resistance by durability test Table 1 shows the degree of change and the quality judgment of durability, and Table 2 shows the unit of each item in Table 1.

  From this result, in a transparent conductive film using a zinc oxide transparent conductive oxide layer, the surface side zinc oxide transparent conductive oxide contains silicon dioxide and has an amorphous structure, thereby improving conductivity and durability. It was found that an excellent transparent conductive film can be produced.

Cross-sectional explanatory drawing of transparent conductive film (Claim 1) Cross-sectional explanatory drawing of a transparent conductive film (Claim 2) Cross-sectional explanatory drawing of a transparent conductive film (Claim 2) Cross-sectional explanatory drawing of a transparent conductive film (Claim 2)

Explanation of symbols

1 substrate 2 transparent conductive oxide layer 3 transparent conductive oxide layer (amorphous)
4 Carbon layer

Claims (5)

  A transparent conductive film having a transparent conductive oxide layer composed mainly of zinc oxide composed of two or more layers on a transparent substrate, wherein the transparent conductive oxide layer formed far from the transparent substrate is amorphous. A transparent conductive film.   2. The transparent conductive film according to claim 1, wherein a carbon layer is formed on one side or both sides of the amorphous transparent conductive oxide layer.   The amorphous transparent conductive oxide layer is composed of 7 wt. % Or more is contained, The transparent conductive film of Claim 1 or 2 characterized by the above-mentioned.   The transparent conductive film according to claim 2, wherein the carbon layer has a refractive index of 1.25 to 1.80.   The transparent conductive film according to any one of claims 1 to 4, wherein the ratio of surface resistance before and after standing for 10 days in an environment of 85 ° C / 85% RH is 1.0 to 1.5.