Transparent conductive film and method for manufacturing same

Abstract

Provided is a transparent conductive film capable of achieving a low resistance value by maintaining a low resistivity even when the thickness of a transparent electrode layer made of a conductive oxide is increased.　A transparent conductive film 1 has a transparent electrode layer 40 containing indium oxide as a main component formed on a substrate 30. The transparent electrode layer 40 has a thickness of 80 nm or more. The half-value width of a diffraction peak corresponding to the (222) plane of indium oxide as measured by in-plane X-ray diffraction is 0.60° or less.

Description

Transparent conductive film and method for producing the same

[0001] The present invention relates to a transparent conductive film in which a transparent electrode layer is formed on a substrate, and a method for producing the same.

[0002] Transparent conductive films have traditionally been widely used in touch panels, solar cells, light-control devices, and other devices. However, in recent years, there has been a demand for lower resistance due to the need for larger device areas and faster response times.

[0003] In response to such demands for lower resistance in transparent conductive films, attempts have been made to lower resistance by combining a transparent electrode material made of conductive oxide with a metal material such as a metal mesh of silver or copper, but the use of a metal material in combination with the film sometimes limits its applications due to the deterioration of reliability and durability.

[0004] International Publication No. 2016 / 163323

[0005] In view of the above, increasing the thickness of the transparent electrode layer made of a conductive oxide was considered as a means of reducing the resistance of the transparent conductive film without using a metal material. However, simply increasing the thickness of the transparent electrode layer resulted in an increase in resistivity as the thickness increased, and the expected low resistance value could not be obtained.

[0006] The present invention aims to provide a transparent conductive film that can achieve a low resistance value by maintaining low resistivity even when the film thickness of a transparent electrode layer made of a conductive oxide is increased.

[0007] Specific means for solving the above problems include the following embodiments. <1> A transparent conductive film having a transparent electrode layer mainly composed of indium oxide formed on a substrate, wherein the transparent electrode layer has a thickness of 80 nm or more, and a half-width of a diffraction peak corresponding to the (222) plane of indium oxide measured by in-plane X-ray diffraction is 0.60° or less. <2> A transparent conductive film having a transparent electrode layer mainly composed of indium oxide formed on a substrate, wherein the transparent electrode layer has a thickness of 80 nm or more, and a detection angle 2θ of a diffraction peak corresponding to the (222) plane of indium oxide measured by in-plane X-ray diffraction is 30.75° or less. <3> The method for producing a transparent conductive film according to <1> or <2>, wherein the transparent electrode layer is a multilayer formed by three or more sputtering steps, the sputtering is performed under two or more different discharge power conditions and two or more different pressure conditions, the discharge power is lowest when forming a bottom layer, and two or more sputtering steps are performed under a lower pressure condition prior to the highest pressure condition. <4> The method for producing a transparent conductive film according to <3>, wherein the two or more different pressure conditions include a condition of 0.1 Pa or more and less than 0.4 Pa and a condition of 0.4 Pa or more and less than 1.0 Pa. <5> The method for producing a transparent conductive film according to <3> or <4>, wherein the layer formed in one sputtering step has a thickness of 30 nm or less, and the thickness of the bottom layer is 10 nm or less.

[0008] According to the present invention, it is possible to provide a transparent conductive film that can achieve a low resistance value by maintaining low resistivity even when the film thickness of the transparent electrode layer made of a conductive oxide is increased.

[0009] 1 is a schematic cross-sectional view of one embodiment of the transparent conductive film of the present invention. 2 is a diagram showing spectra measured in an evaluation test.

[0010] Preferred embodiments of the present invention will be described below, but the present invention is not limited to these embodiments.

[0011] (Transparent Conductive Film 1) A transparent conductive film 1 as one embodiment of the transparent conductive film of the present invention is formed by laminating a transparent electrode layer 40 on a substrate 30, as shown in FIG.

[0012] (Substrate 30) The substrate 30 can be formed by laminating a functional layer 20 such as a hard coat layer or an optical adjustment layer on one or both surfaces of the transparent resin substrate 10.

[0013] (Transparent Resin Substrate 10) The transparent resin substrate 10 is a substrate that ensures the strength of the transparent conductive film 1. The transparent resin substrate 10 can be a flexible, transparent resin film. Examples of materials for the transparent resin substrate include polyester resin, polyolefin resin, acrylic resin, polycarbonate resin, polyethersulfone resin, polyarylate resin, melamine resin, polyamide resin, polyimide resin, cellulose resin, and polystyrene resin. Examples of polyester resins include polyethylene terephthalate (PET), polybutylene terephthalate, and polyethylene naphthalate. Examples of polyolefin resins include polyethylene, polypropylene, and cycloolefin polymer. Examples of acrylic resins include polymethacrylate. As the material for the transparent resin substrate, polyester resin is preferably used, and PET is more preferably used, from the viewpoints of transparency and strength, for example.

[0014] The surface of the transparent resin substrate 10 may be subjected to a surface modification treatment. Examples of surface modification treatments include corona treatment, plasma treatment, ozone treatment, primer treatment, glow treatment, and coupling agent treatment.

[0015] The thickness of the transparent resin substrate 10 is preferably 10 μm or more, more preferably 50 μm or more, and even more preferably 100 μm or more, from the viewpoint of ensuring the strength of the transparent conductive film 1. The thickness of the transparent resin substrate 10 is preferably 500 μm or less, more preferably 300 μm or less, and even more preferably 200 μm or less, from the viewpoint of ensuring the handleability of the transparent resin substrate 10 in a roll-to-roll system.

[0016] (Functional Layer 20) The substrate 30 can have a functional layer 20 on one or both sides of the transparent resin substrate 10. The functional layer 20 may be a single layer or multiple layers. Examples of layers that constitute the functional layer 20 include an optical adjustment layer, an antireflection layer, an antiglare layer, an easy-adhesion layer, a stress buffer layer, a hard coat layer, an easy-slip layer, an antistatic layer, a crystallization promotion layer, a crystallization rate adjustment layer, and a coating layer.

[0017] An example of a case where the functional layer 20 is a multi-layer structure is a combination of a hard coat layer 11 and an optical adjustment layer 12. The hard coat layer 11 may be laminated on at least one side of the transparent resin substrate 10, and may be laminated on both sides as needed. The hard coat layer 11 can impart good chemical resistance and contamination resistance. The optical adjustment layer 12 is a layer that adjusts the optical properties of the transparent conductive film 1 to suppress pattern visibility of the transparent conductive layer 40 and ensure excellent transparency in the transparent conductive film 1. The optical adjustment layer 12 can be formed on a hard coat layer 11a, as shown in FIG. 1 .

[0018] (Transparent Electrode Layer 40) The transparent electrode layer 40 is a transparent layer that exhibits excellent conductivity. The transparent electrode layer 40 is formed on the substrate 30. In the embodiment shown in FIG. 1 , the transparent electrode layer 40 is formed on the optical adjustment layer 12.

[0019] The transparent electrode layer 40 contains indium oxide as a main component. Examples of compounds containing indium oxide include indium-containing oxides such as indium tin composite oxide (ITO), indium gallium composite oxide (IGO), indium zinc composite oxide (IZO), and indium gallium zinc composite oxide (IGZO). These composite oxides can impart uniform conductivity to the entire surface of the transparent electrode layer 40 and are preferable from the standpoint of a balance between transparency and resistance value. The main component refers to the component that is contained in the transparent electrode layer 40 at the highest ratio.

[0020] When the transparent electrode layer 40 contains ITO formed from indium oxide and tin oxide, the content of tin oxide in the ITO is preferably 8% by mass or more, and more preferably 10% by mass or more, relative to the total amount of tin oxide and indium oxide, from the viewpoint of low resistivity and stable film quality. To achieve low resistance through crystallization of the ITO, the content is preferably 20% by mass or less, and more preferably 15% by mass or less. Furthermore, from the viewpoint of improving crystallinity, a portion of the transparent electrode layer having a tin oxide content of 10% by mass or less or 8% by mass or less may be provided.

[0021] Materials other than those mentioned above may be combined for the transparent electrode layer 40. Materials to be combined with the transparent electrode layer 40 include, without particular limitation, inorganic materials containing oxides or nitrides of tin, zinc, titanium, aluminum, or the like as components, carbon-based materials such as graphene, carbon nanotubes, fullerene, and diamond-like carbon, and organic transparent conductive materials such as PEDOT, as long as they satisfy the required characteristics of the device.

[0022] The film thickness of the transparent electrode layer 40 is 80 nm or more, preferably 130 nm or more, more preferably 145 nm or more, and particularly preferably 180 nm or more, from the viewpoint of ensuring high conductivity. On the other hand, from the viewpoint of optical properties and crack resistance, it is preferably 500 nm or less, more preferably 350 nm or less, and particularly preferably 250 nm or less. Therefore, the film thickness of the transparent electrode layer 40 is preferably 80 nm or more and 500 nm or less, more preferably 130 nm or more and 350 nm or less, and particularly preferably 145 nm or more and 250 nm or less. The film thickness of the transparent conductive layer 40 can be measured by cross-sectional observation using, for example, a transmission electron microscope (TEM).

[0023] (In-plane X-ray diffraction (XRD)) In-plane X-ray diffraction (XRD) is an analytical technique in which X-rays are incident on a sample at a shallow angle and a detector is rotated in a direction parallel to the substrate surface to obtain information on the in-plane orientation of a thin film, i.e., information on the crystal planes parallel to the substrate. By performing in-plane X-ray diffraction, the crystalline state of the thin film and the orientation of the crystal planes parallel to the substrate surface can be measured from the diffraction peaks from the thin film.

[0024] The transparent electrode layer 40 has a diffraction peak corresponding to the (222) plane of indium oxide measured by in-plane X-ray diffraction that has a half-width of 0.60° or less. The diffraction peak corresponding to the (222) plane of indium oxide indicates the physical properties of the transparent electrode layer 40. When the half-width of the diffraction peak is 0.60° or less, the transparent electrode layer 40 has high crystallinity and can have a low resistivity.

[0025] Furthermore, the transparent electrode layer 40 has a detection angle 2θ of 30.75° or less of the diffraction peak corresponding to the (222) plane of indium oxide measured by in-plane X-ray diffraction. The detection angle 2θ of the diffraction peak corresponding to the (222) plane of indium oxide varies depending on the crystalline state of the transparent electrode layer 40, but by having the detection angle 2θ of 30.75° or less, it is possible to keep the resistivity of the transparent electrode layer 40 low.

[0026] (Method of Forming Transparent Electrode Layer 40) The transparent electrode layer 40 is formed by sputtering using a target containing indium oxide as a main component.

[0027] When transparent electrode layer 40 is formed using ITO as a target, the sintered density of ITO is preferably 99% or more from the viewpoint of discharge stability.

[0028] The sputtering system used can be a batch system, a roll-to-roll system, or the like, without any particular limitation, but from the viewpoint of productivity, it is preferable to use a take-up sputtering system and perform the sputtering in a roll-to-roll system. The power source used for sputtering film formation is not particularly limited, and a DC power source, an MF power source, an RF power source, or the like can be used, but from the viewpoint of improving productivity, a DC power source or an MF power source is preferred, and a DC power source is particularly preferred.

[0029] It is known that water molecules are adsorbed in a chamber that is open to the atmosphere. The water molecules in the chamber are taken into the film during the formation of the transparent electrode layer, and can be a factor in increasing the resistance. Therefore, after placing the film substrate in the sputtering deposition apparatus, it is preferable to evacuate the chamber and reduce the water pressure in the chamber before depositing the transparent electrode layer. The water pressure in the chamber is 1×10 －３ Pa or less is preferable, and 1×10－４ Pa or less is more preferable.

[0030] The substrate may be heated or cooled during sputtering depending on the purpose. If the thermal load on the substrate due to sputtering is large, the substrate may be cooled, or sputtering may be performed while heating the substrate in order to improve the film quality of the transparent electrode layer.

[0031] The transparent electrode layer 40 is composed of multiple layers formed by three or more sputtering processes, and the sputtering processes are performed under two or more different discharge power conditions and two or more different pressure conditions. The discharge power is set to the lowest when forming the bottom layer, and sputtering is performed two or more times under the lower pressure condition before the highest pressure condition. Sputtering of multiple layers may be performed by repeatedly discharging using the same target, or may be performed by using an apparatus comprising multiple targets and transporting them in a single process. When using an apparatus comprising multiple targets, pressure control is facilitated by placing the targets in separate deposition chambers.

[0032] The transparent electrode layer 40 is formed while introducing an inert gas such as argon or a carrier gas containing an inert gas such as argon and oxygen gas into the film formation chamber. The sputtering pressure can be adjusted by adjusting the amount of carrier gas introduced into the film formation chamber.

[0033] For example, if the transparent electrode layer 40 is formed of three layers, sputtering can be performed at low discharge power and low pressure to promote surface diffusion of sputtered particles in the formation of the first layer, which is the bottom layer, and at low pressure and high discharge power to promote the generation of crystal nuclei in the formation of the second layer. Furthermore, sputtering can be performed at high pressure while maintaining the discharge power in the formation of the third layer, reducing plasma damage to the second layer and forming a dense layer. Furthermore, by repeating sputtering multiple times in this way, new interfaces are generated for each layer, making it possible to form a homogeneous amorphous layer overall.

[0034] The two different discharge power conditions can be, for example, 0.1 kW or more and less than 0.5 kW, and 0.5 kW or more and less than 1.5 kW. For example, in the case of a plate-type target, 0.3 W / cm ２ 1.5W / cm or more ２ Less than 1.5 W / cm ２ 6.0W / cm or more ２ For a cylindrical target, the discharge power can be set to 0.3 kW / m or more and less than 4.0 kW / m, and for a cylindrical target, the discharge power can be set to 4.0 kW / m or more and less than 15 kW / m. By performing sputtering under these conditions, a transparent electrode layer with low resistivity can be formed. Furthermore, by setting the discharge power conditions more precisely, a transparent electrode layer with low resistivity can be smoothly formed.

[0035] The two different pressure conditions are preferably 0.1 Pa or more and less than 0.4 Pa and 0.4 Pa or more and less than 1.0 Pa, more preferably 0.3 Pa or more and less than 0.4 Pa and 0.4 Pa or more and less than 0.7 Pa, and particularly preferably 0.3 Pa or more and less than 0.4 Pa and 0.5 Pa or more and less than 0.6 Pa. By performing sputtering under such conditions, a transparent electrode layer with low resistivity can be formed. Furthermore, by setting the pressure conditions more precisely, a transparent electrode layer with low resistivity can be smoothly formed.

[0036] The transparent electrode layer 40 is formed as multiple layers by repeated sputtering, and it is preferable that the thickness of the bottom layer be 10 nm or less, and that sputtering be performed three or more times so that each time a deposition thickness of 30 nm or less is achieved. By repeating sputtering multiple times at such a thickness, deposition at new interfaces is repeated, making it possible to form a homogeneous amorphous layer as a whole.

[0037] The transparent electrode layer 40 formed by sputtering is primarily an amorphous layer, but annealing is preferred because it increases the crystallinity, thereby reducing resistivity and improving transmittance. The annealing temperature is preferably 120 to 220°C, and more preferably 130 to 180°C. If the annealing temperature is too low, the time required for crystallization will be long, reducing productivity, while if it is too high, the temperature will exceed the heat resistance temperature of the substrate, making it impossible to maintain the shape of the film.

[0038] (Uses of Transparent Conductive Film) The transparent conductive film of the present invention can be used as a transparent electrode for displays, light-emitting devices, photoelectric conversion devices, and the like.

[0039] Example 1 A 125 μm thick optical PET film (Lumirror, manufactured by Toray Industries, Inc.) was used as a substrate, and a 2 μm thick hard coat layer was formed on both sides of the substrate using an ultraviolet curable resin (Lioduras TYAB, manufactured by Toyochem Co., Ltd.). The hard coat layer was formed by applying a UV curable resin coating solution diluted with methyl isobutyl ketone (MIBK) using a bar coater, drying in a hot air drying oven at 80° C. for 1 minute, and then irradiating the substrate with 400 mJ / cm using a high-pressure mercury lamp. ２ This process was carried out on both sides of the substrate to obtain a film with a hard coat layer, in which a hard coat layer was formed on both sides of the substrate.

[0040] Subsequently, an optical adjustment layer was formed on one side of the PET film with the hard coat layer. A UV-curable resin coating liquid for the optical adjustment layer (Lioduras TYZ, manufactured by Toyochem Co., Ltd.) with a refractive index of 1.65 was diluted with MIBK and applied by bar coating. The coating was dried in a hot air drying oven at 80°C for 1 minute, and then irradiated with 600 mJ / cm using a high-pressure mercury lamp. ２ The coating film was cured by irradiation with ultraviolet light at 1000 kJ / cm. The optical adjustment layer thus obtained had a film thickness of 40 nm.

[0041] Subsequently, a transparent electrode layer made of ITO was formed on the optical adjustment layer of the film with the optical adjustment layer by sputtering. After the film with the optical adjustment layer was placed in a roll-to-roll sputtering device, it was transported at room temperature while the water pressure in the chamber was 1×10 －４The chamber was then evacuated to a vacuum of 0.3 Pa. Next, using ITO (tin oxide content 10.0% by mass) as a target, only argon was introduced so that the pressure inside the chamber was 0.3 Pa, and pre-sputtering was performed for 15 minutes at a discharge power of 1.0 kW. After that, while the film was being transported so that the film thickness of the first transparent electrode layer was 3 nm, sputtering was performed using a DC power supply at a discharge power of 0.2 kW, thereby forming a first transparent electrode layer.

[0042] Next, argon and oxygen were supplied at a ratio of 100:1, and under conditions of a chamber pressure of 0.3 Pa, deposition of 24 nm per deposition was repeated four times while transporting the film so that the total thickness of the multiple layers formed by multiple sputtering (hereinafter referred to as the "total film thickness") was 96 nm, and sputtering was performed using a DC power supply with a discharge power of 1.0 kW to form a second transparent electrode layer.

[0043] Next, oxygen was supplied so that the ratio of argon to oxygen was 200:1, and under conditions of a chamber pressure of 0.6 Pa, the film was transported so that the total film thickness of the third transparent electrode layer was 96 nm, and deposition of 24 nm per deposition was repeated four times, and sputtering was performed using a DC power supply with a discharge power of 1.0 kW to form a third transparent electrode layer.

[0044] The obtained transparent conductive film was further annealed in a hot air drying oven at 140° C. for 90 minutes, and then evaluated.

[0045] Example 2 A transparent conductive film was produced in the same manner as in Example 1, except that deposition of 24 nm was repeated three times so that the total film thickness of the second transparent electrode layer and the third transparent electrode layer was 72 nm.

[0046] (Example 3) A transparent conductive film was produced in the same manner as in Example 1, except that deposition of 24 nm was repeated three times so that the total thickness of the second transparent electrode layer was 72 nm, and deposition of 19 nm was repeated three times so that the total thickness of the third transparent electrode layer was 57 nm.

[0047] (Example 4) A transparent conductive film was produced in the same manner as in Example 1, except that the second transparent electrode layer was deposited in a single transport so as to have a thickness of 100 nm, and the third transparent electrode layer was deposited in a single transport so as to have a thickness of 100 nm.

[0048] Example 5 A transparent conductive film was produced in the same manner as in Example 4, except that the thickness of the third transparent electrode layer was set to 80 nm.

[0049] Example 6 A transparent conductive film was produced in the same manner as in Example 4, except that the thickness of the third transparent electrode layer was set to 55 nm.

[0050] Reference Example 1 A transparent conductive film was produced in the same manner as in Example 1, except that the second transparent electrode layer was deposited to a thickness of 75 nm in one transfer, and the third transparent electrode layer was not formed.

[0051] Comparative Example 1 A transparent conductive film was produced in the same manner as in Example 1, except that a second transparent electrode layer was deposited to a thickness of 200 nm in a single transfer, and a third transparent electrode layer was not formed. The produced film had many cracks in the transparent electrode layer, and therefore could not be evaluated.

[0052] Comparative Example 2 A transparent conductive film was produced in the same manner as in Comparative Example 1, except that deposition of 100 nm was repeated twice so that the total thickness of the second transparent electrode layer became 200 nm.

[0053] Comparative Example 3 A transparent conductive film was produced in the same manner as in Example 1, except that the third transparent electrode layer was deposited to a thickness of 200 nm in one transfer, and the second transparent electrode layer was not formed.

[0054] Comparative Example 4 A transparent conductive film was produced in the same manner as in Comparative Example 3, except that deposition of 100 nm was repeated twice so that the total film thickness of the third transparent electrode layer was 200 nm.

[0055] Comparative Example 5 A transparent conductive film was produced in the same manner as in Comparative Example 1, except that the second transparent electrode layer was deposited to a thickness of 150 nm in a single transfer.

[0056] (Evaluation Methods) The transparent conductive films of Examples 1 to 6 and Comparative Examples 1 to 5 were evaluated by the following evaluation methods.

[0057] Measurements by in-plane X-ray diffraction (XRD) were performed using a RIGAKU SmartLab X-ray diffractometer. A Cu source was used, with a tube output of 40 kV and 30 mA. A HiPix-3000 detector was used. The optical system was a parallel optical system, with an incident-side Soller slit of in-plane PSC 0.5°, a receiving-side Soller slit of in-plane PSA 0.5°, and an incident slit width of 0.1 mm. Neither a monochromator nor a CuKβ filter was used.

[0058] The sample was a 5 cm square cut transparent conductive film, with the side without the transparent conductive layer attached to a 1 mm thick glass using 3M OCA8146-1, and was placed horizontally on a 4-inch wafer sample plate.

[0059] Measurements were performed using the in-plane 2θχ / φ method, with a measurement range of 2θ = 29.5 to 32.0°, a step width of 0.12°, and a scan speed of 0.5° / min, with the vector difference between the incident X-rays and the diffracted X-rays aligned in the in-plane MD direction of the film. Prior to measurement, the sample position was adjusted using the automatic sample position adjustment function provided by the instrument to maximize the reflected X-ray intensity.

[0060] From the obtained XRD spectrum, the peak position and half-width were calculated by fitting. Processing was performed using the analysis program SmartLab Studio II attached to the instrument, using B-spline as the background type and a divided pseudo-Voigt function as the peak shape.

[0061] The film thickness of the transparent conductive layer was measured by cross-sectional TEM analysis and an indium calibration curve method using a scanning X-ray fluorescence analyzer ZSX Primus III+ manufactured by RIGAKU.

[0062] The sheet resistance of the transparent conductive film was calculated in accordance with JIS K7194 using Loresta GP manufactured by Mitsubishi Chemical Corporation.

[0063] The resistivity was calculated from the above sheet resistance value and film thickness value.

[0064]

[0065] As shown in Table 1, Examples 1 to 6 exhibited good resistivity, and it was confirmed that Examples 1 to 3, in which sputtering was performed three or more times so that each deposition was 30 nm or less, exhibited particularly excellent resistivity.

[0066] The transparent conductive film of the present invention can be suitably used in applications requiring low resistance, such as light control elements, touch sensors, liquid crystal elements, photoelectric conversion elements, heat ray control members, antennas, electromagnetic wave shielding members, and image display devices.

[0067] REFERENCE SIGNS LIST 1 transparent conductive film 10 transparent resin substrate 11 hard coat layer 11a hard coat layer 11b hard coat layer 12 optical adjustment layer 20 functional layer 30 substrate 40 transparent electrode layer

Claims

1. A transparent conductive film comprising a substrate and a transparent electrode layer formed on the substrate, the transparent electrode layer having a thickness of 80 nm or more, and a half-width of a diffraction peak corresponding to the (222) plane of indium oxide measured by in-plane X-ray diffraction of 0.60° or less.

2. A transparent conductive film comprising a substrate and a transparent electrode layer formed on the substrate, the transparent electrode layer having a thickness of 80 nm or more, and a detection angle 2θ of a diffraction peak corresponding to the (222) plane of indium oxide measured by in-plane X-ray diffraction of 30.75° or less.

3. A method for producing a transparent conductive film according to claim 1 or 2, wherein the transparent electrode layer is a multi-layer formed by three or more sputtering operations, the sputtering is carried out under two or more different discharge power conditions and two or more different pressure conditions, the discharge power is lowest when forming the bottom layer, and two or more sputtering operations are carried out under the lower pressure conditions before the highest pressure conditions.

4. The method for producing a transparent conductive film according to claim 3, wherein the two or more different pressure conditions include a condition of 0.1 Pa or more and less than 0.4 Pa and a condition of 0.4 Pa or more and less than 1.0 Pa.

5. The method for producing a transparent conductive film according to claim 3, wherein the thickness of the layers formed by one sputtering is 30 nm or less, and the thickness of the bottom layer is 10 nm or less.

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