WO2009145152A1

WO2009145152A1 - Transparent conductive film and method for producing the same

Info

Publication number: WO2009145152A1
Application number: PCT/JP2009/059542
Authority: WO
Inventors: 崇口山; 憲治山本
Original assignee: 株式会社カネカ
Priority date: 2008-05-27
Filing date: 2009-05-25
Publication date: 2009-12-03

Abstract

When a zinc oxide-based transparent conductive oxide is formed into a thin film, the resistivity thereof is easily increased due to the air or moisture, and thus the zinc oxide-based transparent conductive oxide cannot be used as a transparent conductive film. Although the zinc oxide-based transparent conductive oxide is made to have an amorphous structure for the purpose of suppressing the resistivity increase due to grain boundary scattering, zinc oxide has good crystallinity and thus it has been difficult to form a conductive amorphous zinc oxide-based transparent conductive oxide layer. By adding silicon dioxide as an additive for amorphization and adding aluminum or gallium as a conductive doping agent, a conductive amorphous zinc oxide-based transparent conductive oxide layer can be formed. As a result, a practical transparent conductive film can be produced.

Description

Transparent conductive film and method for producing the same

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, utilization for photoacoustic materials, high temperature The present invention relates to a transparent conductive film capable of achieving high environmental variability and a method for producing the same in a heater material.

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). Non-patent document 1 describes that ZnO is excellent in transparency as compared with ITO, but is inferior in stability to moisture and heat.

Patent Documents 1 to 3 describe techniques for improving the chemical stability of ZnO by adding chromium, cobalt, silicon, or the like to ZnO. However,

Patent Documents

1 and 2 are limited to qualitative evaluation of etching characteristics, and quantitative properties are not clear regarding chemical stability, and durability in a high-temperature and high-humidity environment is not satisfactory. . On the other hand, Patent Document 3 states that the chemical stability is effective in durability in a high-temperature and high-humidity environment. However, since silicon is contained in an amount of about 5 atom%, the conductivity is lowered. In addition, it has been reported that if the silicon content is reduced in order to improve the conductivity, the durability deteriorates.

As described above, ZnO as a substitute for ITO has been widely used for transparent conductive layers, but materials superior to ITO, which is currently mainstream, have not been put into practical use.

There are many discussions on chemical stability in papers and academic societies, but one of them is that oxygen is attached to the grain boundaries, and it is assumed that charge transfer between crystal grains is hindered. Yes. On the other hand, it is assumed that the chemical stability is improved by making the zinc oxide amorphous and eliminating the grain boundaries. However, zinc oxide is a compound with good crystallinity, so far conductive and Amorphous zinc oxide transparent conductive oxide is the extent to which IZO containing indium oxide has been reported (Non-patent Document 2), and the content of zinc oxide is about 10 atom%, and the main component is indium oxide. It is. Thus, an amorphous zinc oxide transparent conductive oxide mainly composed of abundant zinc oxide as a resource has not been found so far.

Japanese Patent Laid-Open No. 2002-75061 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, by adding silicon atoms to the zinc oxide structure in the zinc oxide transparent conductive layer, amorphous zinc oxide transparent conductive oxide can be obtained. It has been found that a physical layer can be formed, and that by adding a conductive dopant, the zinc oxide transparent conductive layer can exhibit high conductivity and can improve environmental variability.

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 on at least one layer on a base material, wherein the zinc oxide transparent conductive oxide constituting the transparent conductive oxide layer is amorphous A transparent conductive material having a structure containing 0.1 to 3.0 atom% of aluminum and / or gallium with respect to zinc and further containing 3.0 to 18.0 atom% of silicon atom with respect to zinc film.

2). The ratio of the surface resistance immediately after the formation of the transparent conductive film and the surface resistance after standing for 10 days in an environment of 85 ° C./85% RH is 0.5 to 2.0. Transparent conductive film.

3). The transparent conductive film according to 1) or 2), wherein the transparent conductive oxide layer is deposited on the substrate by irradiating any one of plasma particles, electron beam, molecular beam or laser. Method.

4). The method for producing a transparent conductive film according to 3), wherein the sintered body of zinc oxide is irradiated with any of plasma particles, electron beam, molecular beam or laser.

5). The method for producing a transparent conductive film according to 4), wherein the sintered body of zinc oxide has the same composition as the transparent conductive oxide layer.

According to the present invention, it is possible to form a transparent conductive film exhibiting good 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 provides a transparent conductive film having a transparent conductive oxide layer composed mainly of at least one zinc oxide on a base material, wherein the zinc oxide has an amorphous structure, and aluminum or gallium is changed to zinc. The transparent conductive film is characterized by containing 0.1 to 3.0 atom% and further containing 3.0 to 18.0 atom% of silicon atoms with respect to zinc.

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. Secondly, it is conceivable to impart stability to zinc oxide by doping, 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 Application Laid-Open No. 10-237630 describes a method of forming a transparent conductive layer by a reactive sputtering method using a reactive gas such as carbon dioxide as a carrier gas on a metal target.

Hereinafter, typical aspects of the transparent conductive film according to the present invention will be described. FIG. 1 is a cross-sectional view of a transparent conductive film according to the present invention. A zinc oxide transparent conductive oxide layer 2 is formed on the substrate 1 (FIG. 1).

The base material 1 may be selected depending on the application, but when used as a transparent electrode, the hard or soft material is not particularly limited as long as it is a substrate that is transparent at least in the visible light region. As long as it is a hard material, a glass substrate such as alkali glass, borosilicate glass, or non-alkali glass is a typical example, but a sapphire substrate or the like can also be used.

The thickness of the glass substrate can be arbitrarily selected depending on the purpose of use, but 0.5 to 4.5 mm can be exemplified as a preferable range in consideration of the balance between handling and weight. 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.

Also, a thick substrate is not preferable in terms of transparency and cost. On the other hand, examples of soft materials include thermoplastic resins such as acrylic resins, polyesters, and polycarbonate resins, and films made of thermosetting resins such as polyurethane, but particularly excellent optical isotropy and water vapor barrier properties. A film mainly composed of a cycloolefin polymer (COP) which is excellent in the above can be used effectively.

Examples of the COP film include a norbornene polymer, a copolymer of norbornene and an olefin, and an unsaturated alicyclic hydrocarbon polymer such as cyclopentadiene. From the viewpoint of water vapor barrier properties, it is preferable that the main chain and side chain of the film constituting molecule do not contain a functional group having a large polarity, such as a carbonyl group or a hydroxyl group. The thickness of these substrates can be arbitrarily selected according to the purpose of use, but handling is easy if it is about 0.03 mm to 3.0 mm.

Thin films are difficult to handle and lack strength. Also, thick films have problems with transparency and cost, and increase the thickness of the device, making it difficult to use for portable devices. In addition, from the viewpoint of excellent heat resistance, polyethylene naphthalate (PEN), polyethersulfone (PES), and the like can also be used.

When a film substrate is used as the 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.

A method for imparting phase difference to the substrate 1 will be described. 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 preferred 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 the range of 50 to 300 nm. Thus, the vicinity of 137 nm, which is 1/4, is more preferable.

When used as an intermediate layer in a solar cell or an EL device, the zinc oxide transparent conductive oxide of the present invention can be formed thereon using a photoelectric conversion layer or a light emitting layer as a base material. In this case, the photoelectric conversion layer may be a layer made of amorphous or crystalline silicon or a multi-component compound semiconductor. For the light emitting layer, an organic metal complex having aluminum or rare earth atom as a metal center can be used.

It is an important technique of the present invention that the zinc oxide transparent conductive oxide layer 2 in the present invention is amorphous. By adopting an amorphous structure having no crystal grain boundary, it is estimated that the influence of oxygen and water adhering to the grain boundary is eliminated, and the movement of carriers becomes permanently unchanged. In order to make the zinc oxide transparent conductive oxide have an amorphous structure, it can be achieved by doping silicon dioxide. The doping amount is preferably 3.0 to 18.0 atom% of silicon atoms with respect to zinc atoms. Further, from the viewpoint of conductivity and the like, 4.0 to 16.0 atom% is preferable, and 5.0 to 15.0 atom% is more preferable. In terms of reliability testing, 9.0 to 16.0 atom% is preferable.

By doping in this range, it becomes possible to prevent the transparent conductive oxide layer from becoming an insulator while being amorphous. When the doping amount of silicon dioxide is small, the transparent conductive oxide layer becomes crystalline and the above effect cannot be expected, so that the durability under a high temperature and high humidity environment is inferior. On the other hand, when the doping amount of silicon oxide is large, an amorphous structure is obtained. However, since the conductivity is remarkably lowered and an insulator is formed, it cannot be used as a transparent conductive layer.

Silicon dioxide necessary for making the zinc oxide transparent conductive oxide into an amorphous structure is, for example, Wakabayashi, J. et al. Soc. Mat. Sci. , Japan, 49, 6, 617 (2000), requires 7 to 10 atom% or more. Further, the obtained oxide has very low conductivity and does not function as a transparent conductive oxide. However, in the present invention, by using a conductive dopant simultaneously with silicon dioxide, it becomes a transparent conductive oxide having an amorphous structure even at a lower doping amount, and can be used as a transparent conductive film.

A doping agent is added to the zinc oxide transparent conductive oxide layer 2 for the purpose of imparting conductivity. As the doping agent, aluminum or gallium is suitable. When the doping amount is 0.1 to 3.0 atom% with respect to zinc, it is possible to obtain the conductivity of the transparent conductive oxide necessary for the present invention, and 0.3 to 0.3 to exhibit higher conductivity. It is preferably 2.8 atom%, more preferably 0.4 to 2.6 atom%, and particularly preferably 0.5 to 2.5 atom%. When the doping amount is small, the conductivity is not improved due to insufficient doping. On the other hand, when the doping amount is large, the excess dopant is segregated near the crystal grain boundary of zinc oxide or enters between the lattices and hinders the movement of carriers, so that the conductivity is lowered.

As a method of forming the transparent conductive oxide layer 2 according to the present invention, the transparent conductive oxide layer can be deposited on the substrate by irradiation with any of plasma particles, electron beams, molecular beams, and lasers. . Further, the irradiation can be performed by irradiating the sintered body of zinc oxide. The sintered body of zinc oxide preferably has the same composition as the transparent conductive oxide layer.

Specific examples of plasma particle, electron beam, molecular beam, and laser irradiation means include magnetron sputtering, electron beam (EB) vapor deposition, molecular beam epitaxy (MBE), and pulsed laser deposition (PLD). . As long as it is a single-wafer type film-forming A4 size substrate, a transparent conductive film can be suitably produced by any of the above methods. For example, a large area such as a roll-to-roll film substrate In the case of continuous film formation, the magnetron sputtering method is suitable among the above methods.

The target material used for magnetron sputtering is a mixture of oxide containing zinc oxide as the main component, conductive oxide aluminum oxide or gallium oxide, and silicon dioxide for amorphous structuring. It can be produced by adhering to a backing plate. The conductivity of the transparent conductive oxide necessary for the present invention can be obtained when zinc oxide is doped with aluminum oxide or gallium oxide in an amount of 0.1 to 3.0 atom% of aluminum or gallium with respect to zinc. In order to exhibit higher conductivity, 0.3 to 2.8 atom% is preferable, 0.4 to 2.6 atom% is more preferable, and 0.5 to 2.5 atom% is particularly preferable.

When forming a film by magnetron sputtering, zinc oxide and these conductive dopants are formed with the same composition to form a transparent conductive oxide layer. Therefore, by adding the necessary doping amount to the target, It is possible to form a conductive thin film.

Since silicon is also formed at the same ratio as zinc in the magnetron sputtering film formation, the transparent conductive film necessary for the present invention can be produced by doping the thin film to be formed in a necessary amount. If the doping amount is 3.0 to 18.0 atom% of silicon with respect to zinc, the zinc oxide transparent conductive oxide has an amorphous structure, and the characteristics necessary for the present invention can be achieved. Further, from the viewpoint of conductivity and the like, 4.0 to 16.0 atom% is preferable, and 5.0 to 15.0 atom% is more preferable. In terms of reliability testing, 9.0 to 16.0 atom% is preferable.

For the formation of the transparent conductive oxide layer 2, plasma discharge can be used as necessary. The plasma power is not particularly limited, but is preferably 10 W to 600 W from the viewpoint of productivity and 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.

The film thickness of the transparent conductive oxide layer 2 is preferably 150 to 1000 mm. By using a transparent conductive oxide layer having a thickness in this range, a transparent conductive film having both high transparency and conductivity can be produced.

A method for detecting the doping amount contained in the transparent conductive oxide layer 2 will be described. The detection of the doping amount can be accurately detected by any method as long as it is a method usually used for elemental analysis. 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 doping amount can be easily calculated by the following equation by relative comparison with zinc.

(Doping amount) = (Number of atoms of doping agent) ÷ (Number of atoms of doping agent) + (Number of atoms of zinc)) × 100.

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

In the present invention, a scanning electron microscope JSM-6390-LA (manufactured by JEOL Ltd.) was used for the doping amount measurement. The crystallinity was evaluated by an X-ray diffraction method. For the surface resistance measurement, a resistivity meter Loresta GP MCT-610 (manufactured by Mitsubishi Chemical Corporation) was used.
The ratio between the surface resistance immediately after the formation of the transparent conductive film and the surface resistance after being left in an environment of 85 ° C./85% RH for 10 days was defined as a reliability test result.

The reliability test was evaluated as follows. After measuring the surface resistance of the transparent conductive film immediately after film formation, put it into a constant temperature and humidity tester set at 85 ° C / 85% RH, leave it for 10 days, take out the transparent conductive film, and cool it down to room temperature. Was measured. The evaluation was performed using the following formula.

The value of the reliability test result indicates the quality stability of the transparent conductive film, and this value is preferably 0.5 to 2.0. 0.8 to 2.0 is more preferable, 1.0 to 2.0 is more preferable, and 1.0 to 1.6 is particularly preferable. Most preferred is 1.0 to 1.3. When the value is large, the resistance is unstable, which leads to deterioration of the image for display materials, deterioration of conversion efficiency for materials such as solar cells, and deterioration of accuracy for materials such as touch panels. It is not preferable for the above reason that the value of the surface resistance increases or decreases after the reliability test.
(Reliability test result) = (Surface resistance after 10 days) ÷ (Surface resistance immediately after film formation)

Hereinafter, the present invention will be specifically described by way of examples. However, the present invention is not limited to these examples.

(Examples 1 to 10, Comparative Examples 1 to 3)
A transparent conductive oxide layer was magnetron-sputtered on alkali-free glass (trade name OA-10, film thickness 0.7 mm, manufactured by Nippon Electric Glass Co., Ltd.). As the target, sintered bodies having respective compositions were used. The film forming conditions were as follows: substrate temperature was 200 ° C., argon gas was used at 10.0 sccm as a carrier gas, DC power of 200 W was applied at a pressure of 1.5 Pa, and a film was formed for 5 minutes to form a 500-inch zinc oxide transparent conductive film. An oxide layer was produced.

Evaluation of crystallinity, surface resistance, and reliability test of the transparent conductive film thus prepared was performed. However, in the transparent conductive film of Comparative Example 3, the surface resistance was the upper limit of the measuring device, and the surface resistance and the reliability test could not be evaluated.

Table 1 shows the examination results of the above examples and comparative examples.

From this result, it was found that a transparent conductive film with excellent reliability in a high temperature and high humidity environment can be produced by making the zinc oxide transparent conductive oxide an amorphous structure and further providing conductivity. It was.

Cross-sectional explanatory drawing of the transparent conductive film according to the present invention

1 substrate 2 transparent conductive oxide layer

Claims

A transparent conductive film having a transparent conductive oxide layer composed mainly of zinc oxide on at least one layer on a base material, wherein the zinc oxide transparent conductive oxide constituting the transparent conductive oxide layer is amorphous A transparent conductive material having a structure containing 0.1 to 3.0 atom% of aluminum and / or gallium with respect to zinc and further containing 3.0 to 18.0 atom% of silicon atom with respect to zinc film.
The ratio of the surface resistance immediately after formation of the transparent conductive film and the surface resistance after standing for 10 days in an environment of 85 ° C / 85% RH is 0.5 to 2.0. Transparent conductive film.
3. The transparent conductive film according to claim 1, wherein the transparent conductive oxide layer is deposited on the substrate by irradiation with any of plasma particles, electron beam, molecular beam or laser. Method.
4. The method for producing a transparent conductive film according to claim 3, wherein the sintered body of zinc oxide is irradiated with any of plasma particles, electron beam, molecular beam or laser.
The method for producing a transparent conductive film according to claim 4, wherein the sintered body of zinc oxide has the same composition as the transparent conductive oxide layer.