Bolometer and manufacturing method thereof

Abstract

To provide a bolometer having a high TCR value and low resistance and a method for manufacturing the same.SOLUTION: According to the present invention, a method for manufacturing a bolometer is provided that includes the processes of fabricating an intermediate layer on a substrate in a predetermined shape that functions to enhance the bonding between the substrate and carbon nanotubes, and moving a semiconductor-type carbon nanotube dispersion in one direction relative to the intermediate layer on the fabricated intermediate layer.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] The present invention relates to a bolometer using carbon nanotubes and a method for manufacturing the same. [Background technology]

[0002] Quantum infrared sensors made of HgCdTe have been widely used as infrared sensors, but they require the element to be cooled to a temperature below liquid nitrogen, which limits the miniaturization of the equipment.In recent years, therefore, uncooled infrared sensors, which do not require the element to be cooled to low temperatures, have attracted attention, and bolometers, which detect changes in electrical resistance due to changes in the element's temperature, have become widely used. The temperature coefficient of resistance (TCR) and resistivity are particularly important performance factors for a bolometer. As the absolute value of TCR increases, the temperature resolution of the infrared sensor decreases and its sensitivity improves. Furthermore, resistivity must be reduced to reduce noise. Conventionally, vanadium oxide thin films have been used as uncooled bolometers, but because their TCR is small (approximately -2.0% / K), improvements to the TCR have been widely studied. To improve the TCR, materials with semiconducting properties and a high carrier density are required, and so it is expected that semiconducting single-walled carbon nanotubes will be used as bolometers. Patent document 1 proposes the fabrication of a bolometer using a thin-film process in which ordinary single-walled carbon nanotubes are used in the bolometer section, a dispersion of single-walled carbon nanotubes mixed in an organic solvent is cast onto an electrode, and the single-walled carbon nanotubes are annealed in air. Patent Document 2 proposes the production of a bolometer in which, since single-walled carbon nanotubes contain a mixture of metallic and semiconducting components, semiconducting single-walled carbon nanotubes are extracted using an ionic surfactant and applied to the bolometer section. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] WO2012 / 049801 issue [Patent Document 2] Patent No. 6455910 Summary of the Invention [Problem to be solved by the invention]

[0004] However, the carbon nanotube thin film used in the infrared sensor described in Patent Document 1 has a low TCR because metallic carbon nanotubes are mixed with carbon nanotubes, which limits the improvement of the infrared sensor's performance. The infrared sensor using semiconducting carbon nanotubes described in Patent Document 2 has the problem that the ionic surfactant used for separation cannot be easily removed, resulting in high resistance.

[0005] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a bolometer having a high TCR value and low resistance, and a method for manufacturing the same. [Means for solving the problem]

[0006] The present invention solves the above problems and has the following features.

[0007] One aspect of the present invention is The present invention relates to a method for manufacturing a bolometer, which includes the steps of: forming an intermediate layer having a predetermined shape on a substrate, the intermediate layer having a function of enhancing the bonding between the substrate and carbon nanotubes; and moving a semiconducting carbon nanotube dispersion liquid on the formed intermediate layer in one direction relative to the intermediate layer. [Effects of the Invention]

[0008] According to the invention of this application, it is possible to provide a bolometer having a high TCR value and low resistance by including a carbon nanotube layer with a high degree of orientation, and a method for manufacturing the same. [Brief explanation of the drawings]

[0009] [Figure 1] Cross-sectional schematic diagram of the bolometer section [Figure 2] Schematic diagram of forming a line-shaped APTES film on a substrate (top) and a schematic diagram of forming a carbon nanotube film on the APTES film and arranging electrodes (bottom). [Figure 3] SEM image of carbon nanotube film on APTES line. [Figure 4] An example of a carbon nanotube film formed on a linear APTES film arranged in an electrode array [Figure 5] Schematic diagram showing an example of the positional relationship between an electrode pair and a carbon nanotube film. [Figure 6] Schematic diagram of forming a square-shaped APTES film on a substrate. [Figure 7] Schematic diagram of a carbon nanotube film formed on a square APTES film and electrodes arranged on it. DETAILED DESCRIPTION OF THE INVENTION

[0010] The bolometer manufacturing method of this embodiment will be described in detail below.

[0011] The bolometer manufacturing method of this embodiment includes the steps of: forming (patterning) an intermediate layer having a predetermined shape on a substrate, the intermediate layer having the function of enhancing the bonding between the substrate and the carbon nanotubes; and moving a semiconducting carbon nanotube dispersion liquid on the formed intermediate layer in one direction relative to the intermediate layer. Specifically, an intermediate layer having a function of enhancing the bonding between the substrate and the carbon nanotubes is formed on the substrate in a linear or rectangular shape so as to straddle the first and second electrodes approximately perpendicularly. Alternatively, the intermediate layer is formed in a linear or rectangular shape so that a portion of the intermediate layer straddles the first and second electrodes approximately perpendicularly. Thereafter, a semiconductor carbon nanotube dispersion liquid is provided to the intermediate layer forming section so that the dispersion liquid moves in one direction from one end of the line or rectangle, and then dried, thereby providing a method for manufacturing a bolometer in which the carbon nanotubes are oriented perpendicularly to the electrodes.

[0012] In this way, by patterning an intermediate layer on a substrate that has the function of increasing the bonding strength between the substrate and the carbon nanotubes, it is possible to easily form a carbon nanotube film of the desired shape and size, such as a line or square, on the substrate. Furthermore, in the bolometer manufacturing method of this embodiment, by moving the carbon nanotube dispersion liquid relatively in one direction on the patterned intermediate layer, it is possible to easily form a highly oriented carbon nanotube film in which the carbon nanotubes are oriented along the direction in which the dispersion liquid moves.

[0013] According to this method, a bolometer having a high TCR value and low resistance can be manufactured by providing a carbon nanotube layer with a high degree of orientation. In one embodiment, a minute semiconducting carbon nanotube aligned film and a bolometer using the same can be manufactured by the above-described simple method. Furthermore, in one embodiment, the highly oriented carbon nanotube layer can be made smaller, which allows the bolometer element to be made smaller. Furthermore, the manufacturing method of this embodiment has the advantage of being low cost and suitable for mass production.

[0014] In the manufacturing method of this embodiment, the intermediate layer is not particularly limited as long as it is made of a material that enhances the bonding between the substrate and the carbon nanotubes. The material for the intermediate layer is preferably a compound having both a partial structure that bonds or adheres to the substrate surface and a partial structure that bonds or adheres to the carbon nanotubes. This allows the intermediate layer to function as a mediator between the substrate and the carbon nanotubes. The bonds between the substrate and the intermediate layer and between the intermediate layer and the carbon nanotubes can utilize not only chemical bonds but also various intermolecular interactions such as electrostatic interactions, surface adsorption, hydrophobic interactions, van der Waals forces, and hydrogen bonds. The material of the intermediate layer is also preferably a compound that increases the lyophilicity of the substrate surface. By treating with such a compound, droplets of the carbon nanotube dispersion can be provided and held mainly only on the portion where the intermediate layer is formed, and / or the carbon nanotubes in the dispersion can be attached mainly only on the portion where the intermediate layer is formed. This allows the shape and size of the carbon nanotube film to be easily controlled by patterning the intermediate layer.

[0015] Examples of the partial structure in the intermediate layer material that bonds to or adheres to the substrate surface include an alkoxysilyl group (SiOR), SiOH, a hydrophobic moiety or hydrophobic group, etc. Examples of the hydrophobic moiety or hydrophobic group include a methylene group (methylene chain) or alkyl group having preferably 1 or more, more preferably 2 or more, and preferably 20 or less, more preferably 10 or less carbon atoms. Examples of the partial structure in the intermediate layer material that bonds to or adheres to the carbon nanotubes include amino groups such as a primary amino group (-NH2), a secondary amino group (-NHR1), and a tertiary amino group (-NR1R2), an ammonium group (-NH4), an imino group (=NH), an imide group (-C(=O)-NH-C(=O)-), an amide group (-C(=O)NH-), an epoxy group, an isocyanurate group, an isocyanate group, a ureido group, a sulfide group, and a mercapto group.

[0016] The material for such an intermediate layer is not particularly limited, and examples thereof include silane coupling agents. Silane coupling agents have both a reactive group that bonds to or interacts with inorganic materials and a reactive group that bonds to or interacts with organic materials in their molecules, and function to bond organic materials and inorganic materials. In this embodiment, for example, by using a silane coupling agent that has both a reactive group that bonds to a substrate such as a Si substrate and a reactive group that bonds to carbon nanotubes, a monolayer polymolecular film that presents reactive groups that bond to carbon nanotubes can be formed on the substrate, thereby immobilizing carbon nanotubes on the substrate.

[0017] Examples of silane coupling agents include: Silane coupling agents having an amino group and an alkoxysilyl group (aminosilane compounds), such as 3-aminopropyltrimethoxysilane, 3-aminopropylmethyltriethoxysilane, 3-aminopropylmethyltrimethoxysilane, 3-aminopropyltriethoxysilane (APTES), 3-(2-aminoethyl)aminopropyltrimethoxysilane, N-(2-aminoethyl)-3-aminopropyltrimethoxysilane, N-2-(aminoethyl)-3-aminopropylmethyltrimethoxysilane, and N-(2-aminoethyl)-3-aminopropylmethyldimethoxysilane; silane coupling agents having an epoxy group and an alkoxysilyl group, such as 3-glycidoxypropyltrimethoxysilane, 3-glycidoxypropyltriethoxysilane, 3-glycidoxypropylmethyldimethoxysilane, 3-glycidoxypropylmethyldiethoxysilane, 2-(3,4-epoxycyclohexyl)ethyltrimethoxysilane, 3-glycidoxypropyldiethoxysilane, and triethoxy(3-glycidyloxypropyl)silane; Isocyanurate-based silane coupling agents such as tris-(trimethoxysilylpropyl) isocyanurate; ureido-based silane coupling agents such as 3-ureidopropyltrialkoxysilane; mercapto-based silane coupling agents such as 3-mercaptopropylmethyldimethoxysilane, 3-mercaptopropyltrimethoxysilane, and 3-mercaptopropyltriethoxysilane; Sulfide-based silane coupling agents such as bis(triethoxysilylpropyl)tetrasulfide; and Isocyanate-based silane coupling agents such as 3-isocyanatepropyltriethoxysilane; Examples include:

[0018] In particular, a silane coupling agent having an amino group (aminosilane compound) is preferred because of its good bonding property with carbon nanotubes.

[0019] Other examples of materials for the intermediate layer include polymers, such as cationic polymers, that have moieties that can bond or attach to a substrate, such as a plastic substrate, and reactive groups that bond to carbon nanotubes.

[0020] Examples of such polymers include poly(N-methylvinylamine), polyvinylamine, polyallylamine, polyallyldimethylamine, polydiallylmethylamine, polydiallyldimethylammonium chloride, polydiallyldimethylammonium trifluoromethanesulfonate, polydiallyldimethylammonium nitrate, polydiallyldimethylammonium perchlorate, polyvinylpyridinium chloride, poly(2-vinylpyridine), poly(4-vinylpyridine), polyvinylimidazole, poly(4-aminomethylstyrene), poly(4-aminostyrene), polyvinyl(acrylamide-co-dimethylaminopropylacrylamide), polyvinyl(acrylamide-co-dimethylaminoethylmethacrylate ... acrylates), polyethyleneimine (PEI), DAB-Am and polyamidoamine dendrimers, polyaminoamides, polyhexamethylene biguanide, polydimethylamine-epichlorohydrin, products of alkylation of polyethyleneimine with methyl chloride, products of alkylation of polyaminoamides with epichlorohydrin, cationic polyacrylamides with cationic monomers, formalin condensation products of dicyandiamide, dicyandiamide, polyalkylenepolyamine polycondensates, naturally-based cationic polymers (e.g., partially deacetylated chitin, chitosan, and chitosan salts), synthetic polypeptides (e.g., polyasparagine, polylysine, polyglutamine, and polyarginine).

[0021] Among these polymers, cationic polymers having an amino group and a hydrophobic group or a hydrophobic portion are preferred from the viewpoint of immobilizing carbon nanotubes on a substrate.

[0022] By using such a polymer, an intermediate layer presenting multiple reactive groups that bond or attach to carbon nanotubes can be formed on the substrate. Although there are no particular limitations on the intermediate layer, a monolayer is desirable from the viewpoint of uniform attachment, and the thickness can be 1 nm to 1 μm, preferably 2 nm to 100 nm.

[0023] The material of the intermediate layer can be appropriately selected taking into consideration the material of the substrate to be used. Here, the material constituting the substrate may be an inorganic material or an organic material, and any material commonly used in the art can be used without particular limitation. Examples of inorganic materials include, but are not limited to, glass, Si, SiO2, SiN, etc., and examples of organic materials include, but are not limited to, plastics, rubber, etc., such as polyimide, polyethylene, polypropylene, polystyrene, polyvinyl chloride, polyethylene terephthalate, acrylonitrile styrene resin, acrylonitrile butadiene styrene resin, fluororesin, methacrylic resin, polycarbonate, etc. In one embodiment, materials used for flexible substrates are preferred.

[0024] The invention of this application has the above-mentioned characteristics, and the following embodiments will be described. However, although the embodiments described below have technically preferable limitations for carrying out the invention, they do not limit the scope of the invention to the following.

[0025] In the following embodiments, an example will be described in which an APTES layer or a polylysine layer is used as the intermediate layer, and a Si substrate or a plastic substrate is used as the substrate, but the intermediate layer and substrate are not limited to these.

[0026] Furthermore, in the method for manufacturing a bolometer, processes other than the process of forming a carbon nanotube layer on a substrate are not limited to those exemplified below, and any process used in the technical field can be used without particular restrictions.

[0027] In this specification, the term "substantially perpendicular" includes both completely perpendicular and a state deviated from completely perpendicular by 30° or less, preferably 20° or less, for example, 10° or less. The term "substantially parallel" includes both completely parallel and a state deviated from completely parallel by 30° or less, preferably 20° or less, for example, 10° or less. In this specification, the terms "APTES-attached portion," "APTES-applied portion," "APTES portion," etc. are synonymous and refer to a region in which an intermediate layer is formed by APTES. Furthermore, "APTES layer" may be referred to as "APTES film," etc. In this specification, the terms "carbon nanotube layer" and "carbon nanotube film" can be used synonymously, and the "carbon nanotube alignment film" may be simply referred to as the "carbon nanotube layer" or the like. Furthermore, the bolometer according to this embodiment can be used to detect not only infrared light but also electromagnetic waves having a wavelength of, for example, 0.7 μm to 1 mm, such as terahertz waves. In one embodiment, the bolometer is an infrared sensor.

[0028] First Embodiment FIG. 1 shows a cross-sectional schematic diagram of a bolometer unit according to one embodiment of the present invention. A 3-aminopropyltriethoxysilane (APTES) layer 2 is disposed on a Si substrate 1. A carbon nanotube layer 3, a first electrode 4, and a second electrode 5 are disposed on the APTES layer 2, with the electrodes 4 and 5 connected by the carbon nanotube layer 3 between them. The arrangement of the APTES layer 2, the carbon nanotube layer 3, and the electrodes 4 and 5 on the substrate 1 is not limited to that shown in FIG. 1; the electrodes 4 and 5 may be disposed on the APTES layer or directly on the Si substrate 1. Furthermore, the carbon nanotube layer 3 may be disposed either below or above both electrodes, as long as at least a portion of the carbon nanotube layer 3 is on the APTES layer and connected to the electrodes 4 and 5. The carbon nanotube layer 3 is primarily composed of a plurality of semiconducting carbon nanotubes, preferably separated using a nonionic surfactant, as described below.

[0029] FIG. 2 (top) shows a schematic plan view of an APTES layer 2 according to one embodiment of the present invention, fabricated in a line shape. The SiO2-coated Si substrate is washed sequentially with acetone, isopropyl alcohol, and water, and organic matter on the surface is removed by oxygen plasma treatment. After masking the areas other than the linear APTES portions shown in FIG. 2 (top), the substrate is immersed in an aqueous APTES solution or sprayed with the aqueous APTES solution, washed with water, and then dried. The mask is then removed from the substrate. The linear APTES portions may be coated using a dispenser, inkjet printer, or printer, and optionally washed with water and then dried.

[0030] The width of the line shape is preferably 1 μm to 10 cm, more preferably 2 μm to 1 cm, and more preferably 5 μm to 2 mm. For miniaturization, it is also preferable that it be 100 μm or less. Furthermore, in order to maximize the area through which current flows through the carbon nanotube film, the width of the line shape is also preferably equal to or greater than the electrode length of the portion between the facing electrodes where the device length is minimum. For example, in the case of a parallel electrode pair, the electrode length of the portion between the facing electrodes where the device length is minimum is the length of the parallel opposing portions. For the parallel electrode pair shown in Figure 5, this corresponds to the length indicated as "electrode length through which current flows in the CNT film" in the figure.

[0031] The concentration of the APTES aqueous solution is preferably 0.001% by volume to 30% by volume, more preferably 0.01% by volume to 10% by volume, and even more preferably 0.05% by volume to 5% by volume. When a compound other than APTES is used for the intermediate layer, the concentration and solvent may be appropriately changed depending on the compound used.

[0032] When the substrate is immersed in the APTES aqueous solution, the mask for the portions other than the line shape can be, for example, tapes such as Kapton tape or masking tape, adhesive sheets, or masking materials such as resist.When the APTES aqueous solution is sprayed, a metal mask or stencil mask that comes into contact with the substrate can be used.

[0033] When a dispersion of semiconducting carbon nanotubes dispersed in an aqueous solution of a polyoxyethylene alkyl ether, such as polyoxyethylene (100) stearyl ether or polyoxyethylene (23) lauryl ether, which is a nonionic surfactant, is introduced from one end of the linear APTES attachment portion, the portion where APTES is not attached (masked portion) repels the dispersion, allowing the carbon nanotube dispersion to flow only to the APTES attachment portion, and / or allowing the carbon nanotubes in the dispersion to be attached only to the portion where the intermediate layer is formed. The method for introducing the carbon nanotube dispersion is not particularly limited, and any method may be used as long as the dispersion moves unidirectionally on the APTES film relative to the APTES film, as shown by the arrows in Figure 2. For example, when providing the dispersion unidirectionally on the APTES film, the dispersion can be flowed from the end of the line using a syringe or pump, or droplets can be dropped onto the end of the line and the substrate can be tilted to allow the dispersion to flow. The tilt angle of the substrate is not particularly limited, but can be, for example, 5° or more, preferably 10° or more, and for example, 90° or less, preferably 60° or less. Furthermore, when moving the dispersion on the APTES film, for example, the dispersion or the substrate can be moved within the dispersion, or both the dispersion and the substrate can be moved, so that the dispersion moves unidirectionally on the APTES line. The supply amount and concentration of the carbon nanotube dispersion liquid can be appropriately set within a range in which the desired density is obtained when the carbon nanotube film is formed, and the carbon nanotube dispersion liquid is provided mainly on the APTES line, and / or the carbon nanotubes in the dispersion liquid adhere mainly only to the APTES layer forming portion.

[0034] The method for moving the dispersion or the substrate unidirectionally through the dispersion is not particularly limited. For example, the substrate with the APTES film attached can be placed in a jig with a moving means such as a belt conveyor or that can be moved by pulling or pushing, and moved unidirectionally through a tank of carbon nanotube dispersion to produce a carbon nanotube film on the APTES. The substrate or dispersion can be moved horizontally or tilted. The substrate can also be tilted vertically, and the substrate can be immersed in the dispersion and then pulled up, as in dip coating, to allow the dispersion to move unidirectionally over the substrate. Furthermore, in this method, the substrate can be tilted and pulled up as described above.

[0035] The carbon nanotube dispersion preferably contains a surfactant. In this case, if the dispersion has a flow direction, the carbon nanotubes will move oriented in the flow direction without entanglement. At this time, because the APTES has amino groups exposed, when some of the carbon nanotubes bond with the amino groups of the APTES, the carbon nanotubes will remain on the APTES and will be adsorbed in an oriented state in the flow. Once the first layer of carbon nanotubes is adsorbed by the APTES, the second and subsequent layers will deposit aligned carbon nanotubes in bundles, resulting in the creation of a carbon nanotube film oriented in the direction of the APTES line, which is the flow of droplets.

[0036] Figure 3 shows a scanning electron microscope (SEM) image of carbon nanotubes deposited on the APTES-coated area. The direction of the arrow in the SEM image (diagonally upward to the left) is parallel to the direction of the APTES line. The carbon nanotubes are oriented approximately parallel to the APTES line. The carbon nanotube film is deposited almost uniformly across the width of the line shape.

[0037] The thickness of the carbon nanotube layer is not particularly limited, but is, for example, preferably 1 nm or more, more preferably 2 nm or more, and even more preferably 5 nm or more, and is preferably 1 μm or less, more preferably 500 nm or less, and even more preferably 100 nm or less. The thickness of the carbon nanotube layer can be measured at any 10 points using a laser microscope, and the average value of the measured values ​​can be used.

[0038] To increase the degree of orientation, the temperatures of the substrate and dispersion are desirably, for example, 5° C. to 60° C., and preferably 10° C. to 40° C. The relative humidity is preferably 15% RH to 80% RH. The degree of orientation of carbon nanotubes was measured by a frequency of -1 μm from the center in a plane FFT image, which was obtained by performing two-dimensional fast Fourier transform on an SEM image of the carbon nanotube film to express the distribution of unevenness in each direction as a frequency distribution. -1 +1μm from -1 When an integrated value f of the amplitude up to the point where the integrated value f is greatest is calculated and the integrated value in the direction x where the integrated value f is greatest is defined as fx and the integrated value in the direction y perpendicular to the direction x is defined as fy, the degree of orientation of the carbon nanotubes can be expressed as fx / fy, and it is preferable that fx / fy ≥ 2. Note that the SEM image on which the FFT image is based needs to show unevenness for calculation by Fourier transform, and from the viewpoint of observing the carbon nanotubes, the field of view range is preferably about 0.05 to 10 μm in both length and width. This definition of the degree of orientation can also be applied to the orientation film in the embodiments described below.

[0039] The speed at which the carbon nanotube dispersion moves on the substrate is not particularly limited, but since CNTs must adhere to the APTES, it is, for example, 10 mm / sec or less, preferably 1 mm / sec or less, more preferably 100 μm / sec or less, and even more preferably 10 μm / sec or less. A moderately fast moving speed is advantageous for the orientation of carbon nanotubes, but since the amount of adhesion to the APTES decreases, if the amount of adhesion is small, carbon nanotubes can be more easily adhered by repeating the process or continuously supplying the dispersion.

[0040] The carbon nanotube layer preferably contains semiconducting carbon nanotubes in a proportion of 90% by mass or more, more preferably 95% by mass or more, and in some cases even more preferably 98% by mass or more, of the total amount of carbon nanotubes. To produce such a carbon nanotube layer, it is desirable to use a dispersion liquid with a high concentration of semiconducting carbon nanotubes obtained by separating metallic carbon nanotubes from semiconducting carbon nanotubes using, for example, an electric-field-induced layer formation method. The diameter of the carbon nanotubes is preferably 0.6 to 1.5 nm, more preferably 0.6 to 1.2 nm, and more preferably 0.6 to 1.0 nm. The length of the carbon nanotubes is preferably within the range of 100 nm to 5 μm, as this facilitates dispersion and droplet formation. From the viewpoint of the conductivity of the carbon nanotubes, the length is preferably 100 nm or more, and from the viewpoint of reduced aggregation, the length is preferably 5 μm or less. The range is more preferably 500 nm to 3 μm, and even more preferably 700 nm to 1.5 μm. It is preferable that 70% or more (by number) of the carbon nanotubes have diameters and lengths within the above ranges.

[0041] When the diameter and length of the carbon nanotube are within the above ranges, the semiconducting effect is greater when semiconducting carbon nanotubes are used, and a large current value can be obtained, so that a high TCR value is likely to be obtained when used in a bolometer.

[0042] An example of a carbon nanotube dispersion liquid that can be used in the manufacturing method of this embodiment will be described.

[0043] The carbon nanotube dispersion contains the above-mentioned carbon nanotubes. The concentration of the carbon nanotubes in the dispersion and the amount of droplets can be appropriately selected depending on the density and thickness of the carbon nanotube layer to be formed. Although not particularly limited, the concentration of the carbon nanotubes in the dispersion can be, for example, 0.0003% by mass or more, preferably 0.001% by mass or more, more preferably 0.003% by mass or more, and 10% by mass or less, preferably 3% by mass or less, more preferably 0.3% by mass or less.

[0044] The carbon nanotube dispersion preferably contains a surfactant in addition to the carbon nanotubes. The concentration of the surfactant in the dispersion is not particularly limited, but is preferably, for example, above the critical micelle concentration to approximately 5% by mass, more preferably 0.001% to 3% by mass, and particularly preferably 0.01% to 1% by mass. The surfactant contained in the carbon nanotube dispersion is preferably a nonionic surfactant. Unlike ionic surfactants, nonionic surfactants have a weak interaction with carbon nanotubes and can be easily removed after the dispersion is applied to a substrate. This allows for the formation of stable carbon nanotube conductive paths and the attainment of excellent TCR values. Furthermore, nonionic surfactants with long molecular lengths are preferred because they increase the distance between carbon nanotubes when the dispersion is applied to a substrate and are less likely to re-aggregate after water evaporation, allowing for the maintenance of an aligned state. By aligning the carbon nanotubes, the contact area between the carbon nanotubes increases, increasing the number of conductive paths and lowering resistance. This allows for a large change in resistance with temperature.

[0045] The nonionic surfactant can be appropriately selected, but it is preferable to use one or a combination of multiple nonionic surfactants having a polyethylene glycol structure, such as polyoxyethylene alkyl ethers.

[0046] The solvent for the carbon nanotube dispersion is not particularly limited as long as it can disperse and suspend carbon nanotubes. Examples include water, heavy water, organic solvents, and mixtures thereof, with water being preferred.

[0047] The method for separating and preparing a carbon nanotube dispersion liquid having a high ratio of semiconducting carbon nanotubes, and the nonionic surfactant used in the method, can be, for example, that described in WO2020 / 158455, which is incorporated herein by reference.

[0048] The bolometer of this embodiment can be manufactured, for example, as follows, after forming a linearly oriented film of semiconducting carbon nanotubes on a substrate. The carbon nanotubes are deposited oriented parallel to the lines, so the oriented film is made linear. First and second electrodes are fabricated by gold vapor deposition or the like on top of this carbon nanotube oriented film. The electrodes are then placed so that the orientation direction of the carbon nanotubes and the direction of the current flowing between the first and second electrodes are approximately parallel.

[0049] The electrode material is not particularly limited as long as it is conductive, and gold, platinum, titanium, etc. can be used alone or in combination. The electrode fabrication method is not particularly limited, and examples include vapor deposition, sputtering, and printing. The thickness can be adjusted as appropriate, but is preferably 10 nm to 1 mm, and more preferably 50 nm to 1 μm.

[0050] In the bolometer of this embodiment, the distance (channel length) between the first electrode and the second electrode is preferably 1 μm to 500 μm, more preferably 10 μm to 300 μm. Furthermore, for miniaturization, 1 μm to 200 μm is more preferable. When the distance between the electrodes is 1 μm or more, degradation of the TCR characteristics can be suppressed even when a small amount of metallic carbon nanotubes is included. Furthermore, when the distance between the electrodes is 100 μm or less, for example, 50 μm or less, it is advantageous for application to an image sensor in a two-dimensional array. The lengths of electrodes 4 and 5 are preferably short as long as the carbon nanotubes can be connected to both electrodes and conduct electricity, and when the connection portion with the carbon nanotubes is 100 μm or less, for example, 50 μm or less, it is advantageous for application to an image sensor in a two-dimensional array.

[0051] As shown in Figure 4, when the carbon nanotube alignment film is linear (extending across multiple electrode pairs) and therefore carbon nanotubes are connected to adjacent electrode pairs, unnecessary carbon nanotubes can be removed, for example, by the following method. An acrylic resin solution such as polymethyl methacrylate (PMMA) is applied to the region 6 between the electrodes on the carbon nanotube alignment film to form a PMMA protective layer. After heating at 200°C in the atmosphere to remove excess solvent, impurities, etc., the entire substrate is subjected to oxygen plasma treatment to remove excess carbon nanotubes and other materials in the carbon nanotube layer 3 in regions other than the region 6 covered by the PMMA layer.

[0052] Furthermore, as shown in FIG. 4, by forming a plurality of lines of APTES-coated portions in approximately parallel fashion in accordance with the spacing between the electrode pairs, an array can be easily formed.

[0053] If necessary, a protective layer may be provided on the surface of the carbon nanotube layer. When the bolometer is used as an infrared sensor, the protective layer is preferably made of a material that is highly transparent in the infrared wavelength range to be detected, such as an acrylic resin such as PMMA, an epoxy resin, or Teflon (registered trademark).

[0054] The above embodiment describes a method for fabricating a bolometer element in the order of forming an APTES film on a Si substrate, fabricating a carbon nanotube layer, and then fabricating electrodes. However, the following fabrication order may be reversed. First, a first electrode and a second electrode are fabricated on a cleaned Si substrate using titanium and gold or gold vapor deposition, and then APTES is applied thereon. The APTES coating is performed by masking the areas other than the line-shaped portions, immersing the substrate in an APTES aqueous solution, or spraying the APTES aqueous solution, and then drying. The mask is then removed. APTES may be applied using a dispenser, inkjet printer, or printer, and optionally washed with water and then dried. Although the APTES film is an insulating film, it does not adhere to the gold electrode because it bonds with the silicon oxide film surface of the substrate and presents amino groups on the surface. When a carbon nanotube dispersion is poured onto the APTES film, the carbon nanotubes are aligned and deposited on the APTES film, and both ends of the aligned film are directly connected to the electrodes. If carbon nanotubes are connected between adjacent electrode pairs, unnecessary carbon nanotubes can be removed using the same method as above.

[0055] <Second embodiment> FIG. 6 shows a schematic plan view of an APTES layer 2 according to one embodiment of the present invention, fabricated in the form of a square or a linear arrangement of multiple squares, as shown by dashed lines. A Si substrate is cleaned in the same manner as in the first embodiment, and the portions other than the square APTES portions shown in FIG. 6 are masked. The substrate is then immersed in an aqueous APTES solution or sprayed with the aqueous APTES solution, washed with water, and dried. The mask is then removed from the substrate. The square APTES portions may be applied using a dispenser, inkjet printer, or printer, and then dried after washing with water.

[0056] As shown in FIG. 7, the length (width b) of the rectangular shape, which is approximately parallel to the first and second electrodes, is, for example, 1 μm to 1 cm, preferably 10 μm to 1 cm, more preferably 20 μm to 1 mm, and more preferably 30 μm to 300 μm. Furthermore, in order to maximize the area through which current flows through the carbon nanotube film, it is also preferable that the length b of the rectangular shape is equal to or greater than the electrode length of the portion between the facing electrodes that provides the minimum device length. The length (width c) of the rectangular shape, which is approximately perpendicular to the electrodes, is, for example, 1 μm to 1 cm, preferably 10 μm to 1 cm, more preferably 20 μm to 1 mm, and more preferably 30 μm to 300 μm. Furthermore, for miniaturization, 10 μm to 300 μm is more preferable. Furthermore, the length c (width c) of the rectangular shape is preferably longer than the device length of the electrode pair, which will be described later. Furthermore, either width b or width c may be shorter depending on the desired device shape.

[0057] When the carbon nanotube dispersion liquid is moved in one direction over the square-shaped APTES attachment area as in the first embodiment, the carbon nanotubes adhere to the square-shaped area and accumulate, oriented approximately parallel to the direction of movement.

[0058] The bolometer of this embodiment can be manufactured, for example, as follows after forming a rectangular alignment film of semiconducting carbon nanotubes on a substrate. The dashed line portion in FIG. 6 is shown in FIG. 7. The carbon nanotubes are attached and aligned parallel to the direction of dispersion movement (indicated by the arrow in FIG. 6), and an alignment film is formed over the entire rectangular portion. Electrodes are fabricated by gold vapor deposition on top of this carbon nanotube alignment film so that both the first electrode 4 and the second electrode 5 are in contact with the alignment film. Because the alignment film is rectangular, it is preferable that one pair of sides be under the electrodes and the other pair of sides be approximately parallel to the direction of current flowing between the first electrode 4 and the second electrode 5, as shown in FIG. 7. Furthermore, to maximize the area through which current flows through the carbon nanotube film, it is preferable that the alignment film be positioned in a region that includes the entire length of the electrodes between the opposing electrode pairs, as shown in FIG. 7.

[0059] In the bolometer of this embodiment, the distance between the first electrode and the second electrode is preferably 1 μm to 500 μm, more preferably 5 μm to 300 μm. Furthermore, for miniaturization, 1 μm to 200 μm is more preferable. When the distance between the electrodes is 1 μm or more, degradation of the TCR characteristics can be suppressed even when a small amount of metallic carbon nanotubes is contained. Furthermore, when the distance between the electrodes is 100 μm or less, for example, 50 μm or less, it is advantageous for application to an image sensor in a two-dimensional array. The lengths of electrodes 4 and 5 are preferably short as long as the carbon nanotubes can be connected to both electrodes and conduct electricity, and when the connection portion with the carbon nanotubes is 100 μm or less, for example, 50 μm or less, it is advantageous for application to an image sensor in a two-dimensional array.

[0060] In this embodiment, as shown in Figure 6, the carbon nanotube alignment film is in a dashed line shape, so the electrodes can be placed so that the carbon nanotubes are connected between the electrodes of an electrode pair. In this case, there are areas between adjacent electrode pairs where no carbon nanotubes are present, so a process for removing unnecessary carbon nanotubes is not necessary. Excess solvent, surfactant, etc. can be removed by heating at 200°C in the atmosphere.

[0061] In this embodiment, too, a protective layer may be provided on the surface of the carbon nanotube layer, if necessary. When the bolometer is used as an infrared sensor, the protective layer is preferably made of a material that is highly transparent in the infrared wavelength range to be detected, such as an acrylic resin such as PMMA, an epoxy resin, or Teflon (registered trademark).

[0062] The above embodiment describes a method for fabricating a bolometer element in the order of forming an APTES film on a Si substrate, fabricating a carbon nanotube layer, and then fabricating electrodes. However, the following fabrication order may be reversed. First, a first electrode and a second electrode are fabricated on a cleaned Si substrate by gold vapor deposition or the like, and then APTES is applied thereon. The APTES coating is performed by masking the substrate so that a rectangular APTES film is formed between each pair of electrodes and that there is a region between adjacent pairs of electrodes that is not coated with APTES. The substrate is then immersed in an APTES aqueous solution or sprayed with the APTES aqueous solution and dried. The mask is then removed. The rectangular APTES portions may be applied using a dispenser, inkjet printer, or printer, and optionally washed with water and dried. Although the APTES film is an insulating film, it does not adhere to the gold electrode because it bonds with the silicon oxide film surface and presents amino groups on the surface. When the carbon nanotube dispersion is moved in one direction over the square-shaped APTES-attached portion in the same manner as in the first embodiment, the carbon nanotubes are attached to the square-shaped portion, oriented approximately parallel to the direction of movement, and both ends of the alignment film are directly connected to the electrodes. Since the carbon nanotubes are not connected between adjacent electrode pairs, there is no need for an unnecessary carbon nanotube removal process using PMMA or the like.

[0063] Unless otherwise specified, the components and manufacturing process of the bolometer other than the formation of the APTES attachment portion in a square shape can be appropriately applied from those described in the first embodiment.

[0064] <Third embodiment> The bolometer according to this embodiment has the same structure as that shown in FIG. 1, but uses a plastic substrate instead of the Si substrate 1. Also, polylysine is used instead of the APTES layer 2. Polylysine easily bonds to the surface of the plastic substrate and, like APTES, presents amino groups on its surface. Therefore, the polylysine film does not repel the carbon nanotube dispersion liquid and easily adsorbs the dispersion droplets. The method for applying the polylysine film and the method for manufacturing the bolometer can be the same as those described in the first and second embodiments. Since the substrate in this embodiment can be made flexible, it can be used in flexible image sensors, etc.

[0065] Some or all of the above embodiments can be described as, but are not limited to, the following supplementary notes. [Appendix 1] A method for manufacturing a bolometer, comprising the steps of: preparing an intermediate layer in a predetermined shape on a substrate, the intermediate layer having the function of enhancing the bonding between the substrate and carbon nanotubes; and moving a semiconducting carbon nanotube dispersion liquid on the prepared intermediate layer in one direction relative to the intermediate layer. [Appendix 2] 2. A method for manufacturing a bolometer according to claim 1, comprising the step of forming the intermediate layer in a line shape or a square shape. [Appendix 3] A method for producing a bolometer according to Appendix 2, comprising a step of providing or moving a semiconducting carbon nanotube dispersion liquid in one direction multiple times from one end of the linear or rectangular intermediate layer. [Appendix 4] 4. The method for manufacturing a bolometer according to claim 2 or 3, wherein the width of the line shape is 1 μm to 10 cm. [Appendix 5] 4. The method for manufacturing a bolometer according to claim 2 or 3, wherein one shorter side of the rectangular shape is 1 μm to 1 cm. [Appendix 6] 6. The method for manufacturing a bolometer according to any one of claims 1 to 5, wherein the carbon nanotubes deposited on the intermediate layer have an average thickness of 500 nm or less. [Appendix 7] 7. The method for manufacturing a bolometer according to any one of claims 1 to 6, wherein the intermediate layer is a layer of a silane coupling agent, and the substrate is a Si substrate. [Appendix 8] 8. A method for manufacturing a bolometer according to any one of claims 1 to 7, comprising forming the intermediate layer using an aqueous solution of an aminosilane compound having a concentration of 0.001% by volume or more and 30% by volume or less, and wherein the substrate is a Si substrate. [Appendix 9] 9. The method for producing a bolometer according to claim 8, wherein the aminosilane compound is 3-aminopropyltriethoxysilane (APTES). [Appendix 10] 7. A method for manufacturing a bolometer according to any one of claims 1 to 6, wherein the intermediate layer is a cationic polymer layer and the substrate is a plastic substrate. [Appendix 11] 11. The method for manufacturing a bolometer according to claim 10, wherein the intermediate layer is a layer of a cationic polymer having an amino group, and the substrate is a plastic substrate. [Appendix 12] 12. The method for producing a bolometer according to any one of claims 1 to 11, wherein the dispersion of semiconducting carbon nanotubes contains semiconducting carbon nanotubes in an amount of 90 mass % or more of the total amount of carbon nanotubes. [Appendix 13] 13. The method for manufacturing a bolometer according to any one of claims 1 to 12, wherein the bolometer is an infrared sensor. [Appendix 14] 14. The method for manufacturing a bolometer according to any one of claims 1 to 13, wherein the bolometer is a bolometer array. [Example]

[0066] The present invention will be illustrated in more detail below with reference to examples, but the present invention is not limited to these examples.

[0067] Example 1 100 mg of single-walled carbon nanotubes (Meijo Nanocarbon Co., Ltd., EC1.0 (diameter: approximately 1.1 to 1.5 nm, average diameter 1.2 nm) were placed in a quartz boat and heat-treated in an electric furnace under a vacuum atmosphere. The heat treatment was carried out at 900°C for 2 hours. After the heat treatment, the weight was reduced to 80 mg, indicating that surface functional groups and impurities had been removed. The obtained single-walled carbon nanotubes were crushed with tweezers, and 12 mg of them were immersed in 40 ml of a 1 wt% aqueous solution of surfactant (polyoxyethylene (100) stearyl ether) and thoroughly submerged. Then, ultrasonic dispersion treatment (BRANSON ADVANCED-DIGITAL The solution was then heated in a SONIFIER device (50 W output) for 3 hours. This removed any carbon nanotube aggregates. This procedure removed bundles and residual catalyst, yielding a carbon nanotube dispersion. To observe the length and diameter of the carbon nanotubes, this dispersion was applied to an SiO2 substrate, dried at 100°C, and observed with an atomic force microscope (AFM). The results showed that 70% of the single-walled carbon nanotubes had lengths in the range of 500 nm to 1.5 μm, with an average length of approximately 800 nm.

[0068] The carbon nanotube dispersion obtained as described above was introduced into a double-tube separation device. Approximately 15 ml of water, approximately 70 ml of carbon nanotube dispersion, and approximately 10 ml of a 2 wt% surfactant solution were placed in the outer tube of the double-tube separation device, and approximately 20 ml of a 2 wt% surfactant solution was placed in the inner tube. The bottom lid of the inner tube was then opened, creating a three-layer structure with different surfactant concentrations. A voltage of 120 V was applied, with the lower side of the inner tube acting as the anode and the upper side of the outer tube acting as the cathode. Semiconducting carbon nanotubes migrated to the anode side. Meanwhile, metallic carbon nanotubes migrated to the cathode side. Semiconducting and metallic carbon nanotubes were successfully separated approximately 80 hours after the start of separation. The separation process was carried out at room temperature (approximately 25°C). The semiconducting carbon nanotube dispersion that had migrated to the anode side was collected and analyzed by optical absorption spectroscopy, revealing that the metallic carbon nanotubes had been removed. Furthermore, Raman spectroscopy revealed that 99 wt% of the carbon nanotubes in the carbon nanotube dispersion that migrated to the anode side were semiconducting carbon nanotubes. The diameter of the single-walled carbon nanotubes was approximately 1.2 nm, accounting for the majority (70% or more), and the average diameter was 1.2 nm.

[0069] The surfactant was partially removed from the carbon nanotube dispersion liquid containing 99 wt% of the semiconducting carbon nanotubes (the carbon nanotube dispersion liquid moved to the anode side) to adjust the surfactant concentration to 0.05 wt%. Then, carbon nanotube dispersion liquid A (referred to as dispersion liquid A) was adjusted so that the concentration of carbon nanotubes in the dispersion liquid was 0.01 wt%. This dispersion liquid A was used to form the carbon nanotube layer.

[0070] The SiO2-coated Si substrate was washed with acetone, isopropyl alcohol, and water in that order, and then the organic matter on the surface was removed by oxygen plasma treatment. As shown in Figure 2 (top), after masking with Kapton tape all areas except for the approximately 300 μm-wide linear APTES region, the substrate was immersed in a 0.1% by volume APTES aqueous solution for 30 minutes, the Kapton tape was peeled off from the substrate, and the substrate was dried.

[0071] The substrate was tilted approximately 15°, and carbon nanotube dispersion A was dripped from one end of the APTES line using a syringe. The droplets flowed in one direction along the APTES line. The masked area (where no APTES was attached) repelled the dispersion, allowing the carbon nanotube dispersion to flow only along the APTES line. This process of collecting the dispersion and re-dropping it was repeated, resulting in the deposition of carbon nanotubes onto the APTES surface. This process was carried out at 23°C and 60% relative humidity. After washing with water, ethanol, and isopropyl alcohol, the substrate was dried at 110°C. The substrate was then heated in air at 200°C to remove nonionic surfactants and other contaminants from dispersion A. SEM observation of the carbon nanotube film on the APTES revealed that the carbon nanotubes were aligned parallel to the APTES line, as shown in Figure 3. In addition, the SEM image was subjected to two-dimensional Fourier transform processing, and a frequency of -1 μm was measured in one direction from the center. -1 +1μm from -1 The integrated value f of the amplitude up to the point where the integrated value f was maximum was defined as fx, and the integrated value fy was defined as the integrated value in the direction x perpendicular to the direction x. The ratio fx / fy was calculated to be 2.2. The thickness of the carbon nanotube layer was measured using a laser microscope and found to be approximately 20 nm on average (average value of 10 random points).

[0072] Gold was deposited onto the carbon nanotube alignment film to form the first and second electrodes, 300 nm thick and 100 μm apart. The electrodes were positioned so that the APTES lines, i.e., the orientation of the aligned carbon nanotubes, were approximately parallel to the direction of current flow between the electrodes. Next, the carbon nanotubes and the areas containing the connections between the first and second electrodes and the carbon nanotubes were protected by applying a PMMA-anisole solution. The film was then dried in air at 200°C for 1 hour, and unnecessary carbon nanotubes connected to adjacent electrode pairs were removed using oxygen plasma treatment.

[0073] (Comparative Example 1) Carbon nanotube dispersion A was prepared in the same manner as in Example 1. After cleaning a Si substrate in the same manner as in Example 1, APTES was applied to the entire surface of the substrate without a mask. When approximately 200 μL of dispersion A was dropped onto the substrate, dispersion A spread over the entire surface of the substrate. After cleaning with water, ethanol, and isopropyl alcohol, the substrate was dried at 110°C and then heated in air at 200°C to remove nonionic surfactants and the like. When the substrate was observed using an SEM, carbon nanotubes were found to be attached in a random network pattern. The thickness of the carbon nanotube layer was measured using a laser microscope and found to be approximately 10 nm on average.

[0074] Next, gold was deposited on the carbon nanotube layer to form the first and second electrodes, with a thickness of 300 nm and a distance of 100 μm between the electrodes. The carbon nanotubes and the first and second electrodes were protected with PMMA of the same area as in Example 1, dried in air at 200°C for 1 hour, and unnecessary carbon nanotubes were removed by oxygen plasma treatment.

[0075] (Comparison between Example 1 and Comparative Example 1) Table 1 shows the film resistance measurement results at 300 K and the TCR values ​​in the range of 20°C to 40°C for the bolometers fabricated from the carbon nanotube films obtained in Example 1 and Comparative Example 1. It was found that the oriented carbon nanotube film of Example 1 had a resistance one order of magnitude lower than that of Comparative Example 1. This is because the carbon nanotubes in Example 1 were oriented, increasing the contact area of ​​the conductive paths between the carbon nanotubes. As a result, noise was reduced during sensor fabrication, and sensitivity was improved. [Table 1] [Explanation of symbols]

[0076] 1. Si substrate 2 APTES layer 3 carbon nanotube layers 4 1st electrode 5 Second electrode 6 PMMA layers

Claims

1. A method for manufacturing a bolometer, comprising the steps of: preparing a linear or rectangular intermediate layer on a substrate, the intermediate layer having the function of enhancing the bonding between the substrate and carbon nanotubes; and providing or moving a semiconducting carbon nanotube dispersion liquid in one direction on the prepared intermediate layer multiple times from one end of the linear or rectangular intermediate layer.

2. 2. The method for manufacturing a bolometer according to claim 1, wherein the width of the line shape is 1 μm to 10 cm.

3. 2. The method for manufacturing a bolometer according to claim 1, wherein one of the shorter sides of the rectangular shape is 1 μm to 1 cm.

4. 2. The method for manufacturing a bolometer according to claim 1, wherein the carbon nanotubes deposited on the intermediate layer have an average thickness of 500 nm or less.

5. 2. The method for manufacturing a bolometer according to claim 1, wherein the intermediate layer is a layer of a silane coupling agent, and the substrate is a Si substrate.

6. 2. The method for producing a bolometer according to claim 1, further comprising the step of forming the intermediate layer using an aqueous solution of an aminosilane compound having a concentration of 0.001% by volume or more and 30% by volume or less, and wherein the substrate is a Si substrate.

7. 2. The method for manufacturing a bolometer according to claim 1, wherein the intermediate layer is a cationic polymer layer and the substrate is a plastic substrate.

8. 2. The method for producing a bolometer according to claim 1, wherein the semiconducting carbon nanotube dispersion liquid contains semiconducting carbon nanotubes in an amount of 90 mass % or more of the total amount of carbon nanotubes.

Images