Method of manufacturing a bolometer

Abstract

To provide a method of manufacturing a bolometer which has a small resistance value.SOLUTION: A method of manufacturing a bolometer includes: a process (A) of forming one or more electrode pairs on a substrate; a process (B) of forming an intermediate layer between the electrode pairs on the substrate; and a process (C) of forming a carbon nanotube layer, wherein the process includes a process (c1) of applying a carbon nanotube fluid dispersion stationarily over the intermediate layer between the electrode pairs to form a carbon nanotube preparatory layer, a process (c2) of cleaning the carbon nanotube preparatory layer with a cleaning solvent, and a process (c3) of drying the cleaning solvent while applying centrifugal force, a vertical component of relative centrifugal acceleration to at least one of a first electrode wall and a second electrode wall of an electrode pair which face each other being 50 to 900×g.SELECTED DRAWING: Figure 2

Description

[Technical Field]

[0001] This invention relates to a method for manufacturing a bolometer using carbon nanotubes. [Background technology]

[0002] Infrared sensors are classified into cooled (quantum) and uncooled (thermal) types based on the detector they contain. Cooled infrared sensors require a cooling device, making miniaturization difficult and resulting in high manufacturing costs. In contrast, uncooled infrared sensors can operate at room temperature, eliminating the need for a cooler. This allows for easy miniaturization and lower manufacturing costs, leading to expanded applications in areas such as security and thermography.

[0003] Bolometers are widely used as uncooled infrared sensors. To increase the sensitivity of bolometers, it is necessary to improve the absolute value of the temperature coefficient of resistance (TCR) of the bolometer material and reduce its resistance.

[0004] Currently, vanadium oxide and amorphous silicon are used as element materials for bolometers. However, vanadium oxide has a low TCR, which limits its performance. Amorphous silicon, on the other hand, has high resistance and has not yet achieved performance superior to that of vanadium oxide.

[0005] Against this technological backdrop, the use of carbon nanotubes (CNTs) with high absolute TCR values ​​in the bolometer portion is being considered. For example, Patent Document 1 applies semiconductor-type single-walled carbon nanotubes to the bolometer portion. [Prior art documents] [Patent Documents]

[0006] [Patent Document 1] Japanese Patent Publication No. 2015-49207 [Overview of the project] [Problems that the invention aims to solve]

[0007] However, for the practical application of infrared sensors using carbon nanotubes (uncooled CNT infrared sensors), improvements in characteristics such as low resistance are necessary in addition to improving the TCR (Transmission Cycle). The resistance of a CNT bolometer is the sum of the bulk resistance of the bolometer film and the connection resistance between the bolometer film and the electrode. Therefore, in order to reduce the resistance value of a CNT bolometer, it is important to reduce the connection resistance with the electrode in addition to lowering the bulk resistance of the bolometer film.

[0008] The present invention aims to provide a method for manufacturing a bolometer with low resistance. [Means for solving the problem]

[0009] To achieve the above objective, the method for manufacturing a bolometer of the present invention is as follows: (A) A step of forming one or more electrode pairs on a substrate, (B) A step of forming an intermediate layer between the electrode pairs on the substrate, (C) Following steps (c1)~(c3): (c1) A step of applying a carbon nanotube dispersion onto the intermediate layer between the electrode pair and letting it stand to form a carbon nanotube preliminary layer. (c2) A step of washing the carbon nanotube preliminary layer with a washing solvent, and (c3) A step of drying the washing solvent while applying centrifugal force, wherein the vertical component of the relative centrifugal acceleration with respect to at least one of the opposing first electrode wall and second electrode wall of the electrode pair is in the range of 50 × g to 900 × g. A process of forming a carbon nanotube layer, including, This is a method for manufacturing a bolometer, which includes [the following]. [Effects of the Invention]

[0010] As described above, the invention according to the present application can provide a method for manufacturing a bolometer with a low resistance value. It has such an effect.

Brief Description of the Drawings

[0011] [Figure 1] The left figure of FIG. 1 is a top view showing an embodiment of the bolometer of the present invention, and the right figure of FIG. 1 is a cross-sectional view taken along the line I-I' in the left figure of FIG. 1. [Figure 2] FIG. 2 is a cross-sectional view showing an embodiment of the manufacturing process of the bolometer of the present invention. [Figure 3] FIG. 3 is a top view showing a bolometer array in which bolometer cells are arranged in an array. [Figure 4] FIG. 4 is a diagram showing the orientation of the bolometer array with respect to centrifugal force. [Figure 5] FIG. 5 is a diagram showing that the orientations of the electrode walls with respect to centrifugal force are parallel. [Figure 6] FIG. 6 is a diagram showing that the orientations of the electrode walls with respect to centrifugal force are perpendicular. [Figure 7] FIG. 7 is a diagram showing that the orientations of the electrode walls with respect to centrifugal force are 45°. [Figure 8] FIG. 8 is a diagram showing that the orientations of the electrode walls with respect to centrifugal force are in two perpendicular directions. [Figure 9] FIG. 9 is a cross-sectional view of a bolometer manufactured by the method described in JP-A-2018-148138. [Figure 10] FIG. 10 is a SEM image of the joint between the carbon nanotube film and the electrode wall.

Embodiments for Carrying Out the Invention

[0012] [Bolometer] Figure 1 shows the structure of one embodiment of the bolometer of the present invention manufactured by the manufacturing method described later, and is a bolometer comprising an electrode pair 110 provided on a substrate 100, an intermediate layer 120 provided between the electrode pair 110 on the substrate 100, and a carbon nanotube layer 140 provided on the intermediate layer 120. The carbon nanotube layer 140 is located between the electrode pair 110 and is electrically connected by contact with the opposing side walls of the electrode pair.

[0013] In the bolometer of the present invention, the carbon nanotube layer formed between the electrode pair is not formed to span across the two electrodes (electrode pair), but is only provided between the electrode pair (Figure 10). Therefore, in order to lower the resistance value of the bolometer, the contact state between the opposing side walls of the electrode pair and the CNT film is important. The inventors presume that, according to the manufacturing method of the present invention, the CNT film makes good contact with the electrode wall, thereby enabling the production of a bolometer with a low resistance value. For example, the bolometer of the present invention has a resistance value of 1.0 × 10⁻¹⁰ at a voltage of 3V. 10 Ω or less, preferably 1.0 × 10⁻⁶ 9 It is less than or equal to Ω.

[0014] [Method for manufacturing a bolometer] Figure 2 shows one embodiment of the manufacturing process for the bolometer of the present invention. A method for manufacturing a bolometer 10 according to one embodiment of the present invention is: (A) A step of forming one or more electrode pairs 110 on a substrate 100, (B) A step of forming an intermediate layer 120 between the electrode pairs 110 on the substrate 100, (C) Following steps (c1)~(c3): (c1) A step of applying a carbon nanotube dispersion onto the intermediate layer 120 between the electrode pair 110 and letting it stand to form a carbon nanotube preliminary layer. (c2) A step of washing the carbon nanotube preliminary layer with a washing solvent, and (c3) A step of drying the washing solvent while applying centrifugal force, wherein the vertical component of the relative centrifugal acceleration with respect to at least one of the opposing first electrode wall 113a and second electrode wall 113b of the electrode pair 110 is in the range of 50 × g to 900 × g. A step of forming a carbon nanotube layer 140, including, This is a method for manufacturing a bolometer, which includes [the following].

[0015] (A) Process for forming electrode pairs Two electrodes (electrode pair 110) are formed on the substrate 100 with a gap between them. The method for fabricating the electrode pair 110 is not particularly limited, but it can be formed by vapor deposition, sputtering, printing, pressing, etc. Alternatively, it may be formed into a desired shape using a photomask, metal mask, etc. Alternatively, a pre-formed metal thin film may be used. The electrode pair 110 may be a single pair, but multiple electrode pairs may be formed on the substrate in the vertical and horizontal directions to form an array.

[0016] The materials constituting the substrate may be inorganic or organic, and any materials used in the art can be used without particular limitation. Examples of inorganic materials, though not limited to them, include glass, Si, SiO2, SiN, etc. Examples of organic materials, though not limited to them, include 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. The substrate may be either a flexible substrate or a rigid substrate, but a flexible substrate is preferred.

[0017] The electrodes are not limited to conductive materials, but for example, gold, platinum, titanium, etc. can be used. The height of the electrode pair can be adjusted as appropriate, but 10 nm to 1 mm is preferred, 50 nm to 1 μm is more preferred, and 50 nm to 200 nm is particularly preferred. The distance between the electrode pair 110 is preferably 1 μm to 500 μm, and 5 to 200 μm is more preferred for miniaturization.

[0018] (B) Intermediate layer formation process An intermediate layer 120 is formed between electrode pairs 110 on the substrate 100. In the bolometer 10 of the present invention, the intermediate layer 120 has the function of enhancing the bonding between the substrate 100 and the carbon nanotube layer 140. The intermediate layer can be formed by coating a solution of the intermediate layer material onto the substrate, and, if necessary, washing with water and drying. Coating of the intermediate layer material in the solution may be done by immersing the substrate in the solution, or by spraying the solution onto the substrate. Before coating the solution, areas other than the area where the intermediate layer is to be formed may be protected with various masking materials.

[0019] The material of the intermediate layer 120 is not particularly limited, but it is preferably a compound having both a substructure that bonds to or adheres to the substrate surface and a substructure that bonds to or adheres to the carbon nanotubes. This allows the intermediate layer to function as an intermediary in bonding the substrate and the carbon nanotube layer. Here, the bonding between the substrate and the intermediate layer, and the bonding between the intermediate layer and the carbon nanotube layer, can utilize not only chemical bonding but also various intermolecular interactions such as electrostatic interactions, surface adsorption, hydrophobic interactions, van der Waals forces, and hydrogen bonding.

[0020] Examples of substructures that bond to or adhere to the substrate surface in the intermediate layer material include alkoxysilyl groups (SiOR), OHCl, hydrophobic moieties, or hydrophobic groups. Examples of hydrophobic moieties or hydrophobic groups include methylene groups (methylene chains) with 1 or more carbon atoms, preferably 2 or more, preferably 20 or less, and more preferably 10 or less, and alkyl groups.

[0021] Examples of substructures that bond to or adhere to the carbon nanotube layer in the intermediate layer material include primary amino groups (-NH2) and secondary amino groups (-NH2). 1 ), tertiary amino group (-NR 1 R 2 Examples include amino groups such as ), ammonium groups (-NH4), imino groups (=NH), imide groups (-C(=O)-NH-C(=O)-), amide groups (-C(=O)NH-), epoxy groups, isocyanurate groups, isocyanate groups, ureido groups, sulfide groups, and mercapto groups.

[0022] Examples of materials for such an intermediate layer include silane coupling agents. Silane coupling agents have both reactive groups that bind to or interact with inorganic materials and reactive groups that bind to or interact with organic materials within their molecules, and have the function of binding organic materials and inorganic materials. In this embodiment, for example, a silane coupling agent having both reactive groups that bind to a substrate such as a Si substrate and reactive groups that bind to carbon nanotubes can be used to form a single-layer multi-molecular film on the substrate that presents reactive groups that bind to carbon nanotubes, thereby immobilizing carbon nanotubes on the substrate.

[0023] Examples of silane coupling agents include: Silane coupling agents (aminosilane compounds) having an amino group and an alkoxysilyl group, 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 epoxy groups and alkoxysilyl groups, 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; Ureidopropyltrialkoxysilane and other ureido-based silane coupling agents; Mercaptopropyl 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-isocyanate-propyltriethoxysilane; These are some examples.

[0024] The intermediate layer material described above can be appropriately selected considering the material of the substrate used, but a silane coupling agent (aminosilane compound) having an amino group is preferred due to its good bonding properties with carbon nanotubes, and 3-aminopropyltriethoxysilane (APTES) is particularly preferred.

[0025] The concentration of the intermediate layer material in the solution is not particularly limited and may be appropriately changed depending on the compound used, but for example, 0.001% to 30% by volume is preferred, 0.01% to 10% by volume is more preferred, and 0.05% to 5% by volume or less is particularly preferred. Furthermore, the solvent for the solution of the intermediate layer material is not particularly limited, as long as it can dissolve the intermediate layer material and can be easily removed after coating the substrate, such as water.

[0026] The thickness of the intermediate layer is not particularly limited, but from the viewpoint of uniform adhesion, it can be 5 nm to 10 μm, preferably 10 nm to 1 μm.

[0027] (C) Process for forming a carbon nanotube layer A carbon nanotube dispersion is applied to the intermediate layer 120 and allowed to stand to form a carbon nanotube preliminary layer (c1). The carbon nanotube preliminary layer is then washed with a solvent (c2), and the washing solvent is dried (c3) to form a carbon nanotube layer 140 (also referred to as a "carbon nanotube film" or "CNT film").

[0028] The carbon nanotube layer is composed of multiple carbon nanotubes that form conductive paths that electrically connect the electrodes, and preferably has a highly uniform network structure.

[0029] The thickness of the carbon nanotube layer is not particularly limited, but for example, it is in the range of 1 nm to 100 μm, preferably 10 nm to 10 μm, and more preferably 50 nm to 10 μm. The carbon nanotube layer may be a single layer or multiple layers. In the bolometer of the present invention, the carbon nanotube layer may be formed on the upper surface of the electrodes in addition to between the electrode pairs, but since the carbon nanotube layer on the upper surface of the electrodes and the carbon nanotube layer between the electrodes are not connected, the carbon nanotubes on the upper surface of the electrodes do not contribute as a component of the bolometer film.

[0030] (c1) Process for forming a carbon nanotube reserve layer, A carbon nanotube dispersion is dropped onto the intermediate layer 120, and the carbon nanotube prelayer is formed by allowing the droplets of the carbon nanotube dispersion to stand.

[0031] The carbon nanotubes used in the carbon nanotube dispersion may be heat-treated in an inert atmosphere or vacuum to remove surface functional groups, amorphous carbon, and other impurities, as well as catalysts. The heat treatment temperature can be selected as appropriate, but 800 to 2000°C is preferred, and 800 to 1200°C is more preferred.

[0032] As carbon nanotubes, single-walled, double-walled, and multi-walled carbon nanotubes can be used, but it is preferable that single-walled carbon nanotubes make up 80% by mass or more, and more preferably 90% by mass or more (including 100% by mass).

[0033] The diameter of the carbon nanotube is not particularly limited, but is preferably between 0.6 and 1.5 nm, more preferably between 0.6 nm and 1.2 nm, and even more preferably between 0.7 and 1.1 nm. If the diameter is 0.6 nm or greater, the carbon nanotube is easier to manufacture, and if it is 1.5 nm or less, it is easier to maintain the band gap within an appropriate range, and a high TCR can be obtained.

[0034] The length of the carbon nanotubes is not particularly limited, but a length of 100 nm to 5 μm is preferable because it disperses easily and has excellent coating properties. From the viewpoint of the conductivity of the carbon nanotubes, a length of 100 nm or more is also preferable. Furthermore, if the length is 5 μm or less, aggregation on the substrate is easily suppressed. The length of the carbon nanotubes is more preferably 500 nm to 3 μm, and even more preferably 700 nm to 1.5 μm.

[0035] As the carbon nanotubes, it is preferable to use semiconducting carbon nanotubes that have a large band gap and carrier mobility. The proportion of semiconducting carbon nanotubes in the carbon nanotubes is generally 67% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more, particularly 90% by mass or more, more preferably 95% by mass or more, and even more preferably 99% by mass or more (including 100% by mass).

[0036] The concentration of carbon nanotubes in the carbon nanotube dispersion is not particularly limited, but for example, it can be 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.

[0037] The carbon nanotube dispersion preferably contains a surfactant in addition to carbon nanotubes. The surfactant contained in the carbon nanotube dispersion is preferably a nonionic surfactant. Unlike ionic surfactants, nonionic surfactants have weak interactions with carbon nanotubes and can be easily removed after the dispersion is provided on the substrate. Therefore, a stable carbon nanotube conductive path can be formed, and an excellent TCR value can be obtained. Furthermore, nonionic surfactants with long molecular lengths are preferable because when the dispersion is provided on the substrate, the distance between carbon nanotubes increases, making it less likely for re-aggregation to occur after the evaporation of water, thus maintaining the network state.

[0038] Nonionic surfactants can be appropriately selected. It is preferable to use one or a combination of multiple nonionic surfactants composed of a hydrophilic moiety that does not ionize and a hydrophobic moiety such as an alkyl chain, such as nonionic surfactants having a polyethylene glycol structure typified by polyoxyethylene alkyl ethers and alkyl glucoside-based nonionic surfactants. As such nonionic surfactants, polyoxyethylene alkyl ethers are preferably used. Also, the alkyl moiety may contain one or more unsaturated bonds. Particularly, polyoxyethylene (23) lauryl ether, polyoxyethylene (20) cetyl ether, polyoxyethylene (20) stearyl ether, polyoxyethylene (10) oleyl ether, polyoxyethylene (10) cetyl ether, polyoxyethylene (10) stearyl ether, polyoxyethylene (20) oleyl ether, polyoxyethylene (100) stearyl ether, etc. are more preferable. Also, N,N-bis[3-(D-gluconamido)propyl]deoxycholamide, n-dodecyl β-D-maltoside, octyl β-D-glucopyranoside, digitonin can also be used.

[0039] As nonionic surfactants, polyoxyethylene sorbitan monostearate (molecular formula: C 64 H 126 O 26 , trade name: Tween 60, manufactured by Sigma-Aldrich, etc.), polyoxyethylene sorbitan trioleate (molecular formula: C 24 H 44 O6, trade name: Tween 85, manufactured by Sigma-Aldrich, etc.), octylphenol ethoxylate (molecular formula: C 14 H 22 O(C2H4O) n , n = 1 to 10, trade name: Triton X-100, manufactured by Sigma-Aldrich, etc.), polyoxyethylene (40) isooctylphenyl ether (molecular formula: C8H 17 C6H40(CH2CH20) 40 H, trade name: Triton X-405, manufactured by Sigma-Aldrich, etc.), poloxamer (molecular formula: C5H 10O2 (trade name: Pluronic, manufactured by Sigma-Aldrich, etc.), polyvinylpyrrolidone (molecular formula: (C6H9NO)n, n=5~100, manufactured by Sigma-Aldrich, etc.) can also be used.

[0040] The concentration of the surfactant in the carbon nanotube dispersion can be controlled as appropriate. A critical micelle concentration of approximately 5% by mass is preferred, more preferably 0.001% to 3% by mass, and particularly preferred to be 0.01% to 1% by mass in order to suppress re-aggregation after coating. A concentration below the critical micelle concentration is undesirable because dispersion is not possible. In this specification, the critical micelle concentration refers to the concentration at which the surface tension is measured at atmospheric pressure and 25°C using a surface tension meter such as a Wilhelmy surface tension meter, while varying the concentration of the surfactant aqueous solution.

[0041] The dispersion medium for the carbon nanotube dispersion is not particularly limited as long as it can disperse and suspend the carbon nanotubes, but examples include water, heavy water, organic solvents, or mixtures thereof, with water being preferred.

[0042] The method for obtaining a carbon nanotube dispersion is not particularly limited, and conventionally known methods can be applied. For example, a solution containing carbon nanotubes can be prepared by mixing a carbon nanotube mixture, a dispersion medium, and a nonionic surfactant, and the carbon nanotubes can be dispersed by sonication of this solution to prepare a carbon nanotube dispersion (micelle dispersion solution). In addition to or instead of the sonication, a carbon nanotube dispersion method using mechanical shear force may be used. Mechanical shearing may be performed in the gas phase. In a micelle dispersion aqueous solution of carbon nanotubes and a nonionic surfactant, it is preferable that the carbon nanotubes are in an isolated state. Therefore, if necessary, bundles, amorphous carbon, impurity catalysts, etc., may be removed using ultracentrifugation. During the dispersion process, the carbon nanotubes can be cut, and their length can be controlled by changing the crushing conditions of the carbon nanotubes, ultrasonic power, sonication time, etc. For example, the aggregate size can be controlled by crushing untreated carbon nanotubes with tweezers, a ball mill, etc. After these processes, the length can be controlled to 100 nm to 5 μm by using an ultrasonic homogenizer with an output of 40 to 600 W, sometimes 100 to 550 W, at 20 to 100 kHz, and a processing time of 1 to 5 hours, preferably 1 to 3 hours. If the processing time is shorter than 1 hour, under certain conditions, the material may hardly disperse and remain almost the same length as before. Furthermore, from the viewpoint of reducing the dispersion processing time and cost, a processing time of 3 hours or less is preferable.

[0043] Dispersion and scission of carbon nanotubes generate surface functional groups on the surface or edges of the carbon nanotubes. The functional groups generated include carboxyl groups, carbonyl groups, and hydroxyl groups. If the treatment is in the liquid phase, carboxyl groups and hydroxyl groups are generated, while if the treatment is in the gas phase, carbonyl groups are generated.

[0044] There are no particular limitations on the method of applying the carbon nanotube dispersion, but it is preferable to form it using printing technology. Examples of printing methods include coating (dispenser, inkjet) and transfer (microcontact printing, gravure printing). The amount of carbon nanotube dispersion applied can be appropriately selected depending on the density and thickness of the carbon nanotube layer to be formed.

[0045] The standing time after applying the carbon nanotube dispersion is not particularly limited, but for example, it is 1 minute to 24 hours, preferably 5 minutes to 18 hours, and more preferably 30 minutes to 12 hours. The amount of carbon nanotube adhesion can also be controlled by the standing time.

[0046] (c2) Cleaning process The formed carbon nanotube preliminary layer is washed with a washing solvent. The washing solvent is preferably an alcohol such as ethanol or isopropyl alcohol, or water, and it is preferable to perform the washing multiple times.

[0047] (c3) Drying process In this invention, the drying of the washing solvent is performed by centrifugal drying. Examples of centrifugal drying apparatus include spin coaters and other devices having a turntable that rotates around a rotation axis along a horizontal plane. Centrifugal drying is performed under conditions in which the vertical component of the relative centrifugal acceleration with respect to at least one of the opposing first electrode wall 113a and second electrode wall 113b of the electrode pair 110 is in the range of 50 × g to 900 × g, preferably 100 × g to 900 × g, and particularly preferably 100 × g to 800 × g. If the vertical component of the relative centrifugal acceleration with respect to the electrode wall is less than 50 × g or more than 900 × g, the resistance value of the bolometer becomes high, which is undesirable. In this invention, the "vertical component of relative centrifugal acceleration" is the same as the relative centrifugal acceleration when the orientation of the electrode wall is perpendicular to the centrifugal force, 1 / 1.414 of the relative centrifugal acceleration when the orientation of the electrode wall is 45° to the centrifugal force, and 0 when the orientation of the electrode wall is parallel to the centrifugal force.

[0048] Relative centrifugal acceleration (RCF) is calculated using the following formula and is usually expressed with "×g" or "G" attached (1.0×g = 9.8 m / s²). 2 ). RCF = 1.118 × 10 -5 ×N 2 ×r (In the formula, N is the rotational speed per minute (rpm), and r is the radius of rotation (cm).)

[0049] The washing solvent can be dried by applying a centrifugal force in a direction having a perpendicular component of the relative centrifugal acceleration to at least one of the opposing first electrode wall 113a and second electrode wall 113b of the electrode pair 110. However, it is preferable to apply both a centrifugal force in a direction having a perpendicular component to the first electrode wall and a centrifugal force in a direction having a perpendicular component to the second electrode wall. In particular, it is preferable to alternately reverse the direction of the centrifugal force and perform drying multiple times. Figure 4 shows the orientation of the bolometer array with respect to centrifugal force (parallel, 45°, and perpendicular directions).

[0050] In the drying process of the washing solvent, the vertical component of the relative centrifugal acceleration (×g) / electrode pair height (nm) is preferably less than 4, more preferably between 0.5 and 3.5, and particularly preferably between 1 and 3. If the vertical component of the relative centrifugal acceleration (×g) / electrode pair height (nm) exceeds 4, the resistance value of the bolometer may increase.

[0051] Furthermore, in a method for forming a carbon nanotube film by applying a carbon nanotube dispersion by centrifugal force such as spin coating, as described in Japanese Patent Publication No. 2018-148138, the carbon nanotube film 21 is formed so that it extends over the electrode 11 and spans the electrode pair, as shown in Figure 3 of Japanese Patent Publication No. 2018-148138, thus forming a bolometer with a different structure from that of the present invention (Figure 9).

[0052] The carbon nanotube layer may be heat-treated to remove surfactants and solvents. The heat treatment temperature can be set appropriately above the decomposition temperature of the surfactant, but 150 to 400°C is preferred, and 200 to 400°C is more preferred. Temperatures above 150°C are preferable because they help suppress the residue of surfactant decomposition products, while temperatures below 400°C are preferable because they help suppress substrate alteration, decomposition and size changes of carbon nanotubes, and detachment of functional groups.

[0053] A protective layer may be provided on the carbon nanotube layer. The protective layer can function as an insulating protective layer, and a protective layer located above the carbon nanotube layer may have an effect of suppressing doping of carbon nanotubes by adsorption of oxygen, etc. The protective layer can be any material used as a protective layer in a bolometer, and examples include silicon nitride, silicon oxide (SiO2), resins, such as parylene, PMMA, PMMA anisole and other acrylic resins, epoxy resins, and Teflon® films.

[0054] In the bolometer of the present invention, a predetermined carbon nanotube layer with high light absorption is used as the bolometer film, so an infrared absorption layer (light absorption layer) is not necessarily required, but an infrared absorption layer may be provided if desired. The infrared absorption layer may be provided directly on the carbon nanotube layer or on top of the protective layer.

[0055] When an infrared absorbing layer is directly placed on a carbon nanotube layer, it can be, but is not limited to, a polyimide coating film. When an infrared absorbing layer is placed on a protective layer, it can be, but is not limited to, a titanium nitride thin film. The thickness of the infrared absorbing layer can be appropriately set depending on the material, but can be, for example, 50 nm to 1 μm.

[0056] In the bolometer of the present invention, a light-reflecting layer for reflecting infrared light transmitted through the bolometer film is not necessarily required, but a light-reflecting layer may be provided between the carbon nanotube layer and the substrate, for example, on the substrate, if desired. However, from the viewpoint of simplifying the device structure, it is preferable not to provide a light-reflecting layer.

[0057] Although the above shows a single cell (single element) of a bolometer, there are no particular restrictions on the element structure and array structure that can be used in a bolometer. For example, bolometer elements can be arranged in an array to form a bolometer array (Figure 3). An array of multiple elements arranged in two dimensions, similar to those used in image sensors, may also be used. Furthermore, the bolometer of this embodiment is not limited to the structure shown in Figure 1, but can be applied without any particular restrictions to element structures commonly used in bolometers, such as elements having a diaphragm structure, or elements having a desired thermal insulation structure such as a thermal insulation layer made of thermal insulation resin instead of a diaphragm structure.

[0058] Furthermore, the bolometer according to this embodiment can be used not only for detecting infrared light but also for detecting electromagnetic waves having wavelengths of, for example, 0.7 μm to 1 mm, such as terahertz waves. [Examples]

[0059] The present invention will be further illustrated with examples below, but the present invention is not limited to these examples.

[0060] [Example 1] (1) A Si substrate coated with SiO2 was sequentially cleaned with acetone, isopropyl alcohol, and water. An electrode pair was then formed on the substrate by depositing 5 nm titanium and 195 nm gold onto it to a height of 200 nm with a distance of 100 μm between the electrodes. (2) The substrate on which the electrodes were formed was cleaned sequentially with acetone and isopropyl alcohol, and organic matter on the surface was removed by oxygen plasma treatment. (3) An intermediate layer was formed between the electrode pairs by coating them with a 0.1 volume% aqueous APTES solution. (4) 100 mg of single-walled carbon nanotubes (Meijo Nanocarbon Co., Ltd., EC1.0 (diameter: approximately 1.1-1.5 nm, average diameter 1.2 nm)) were placed in a quartz boat and heat-treated in an electric furnace under a vacuum atmosphere (900°C, 2 hours). After heat treatment, the nanotubes were crushed with tweezers, and 12 mg were immersed in 40 ml of 1% by mass aqueous solution of surfactant (polyoxyethylene (100) stearyl ether). After being fully submerged, ultrasonic dispersion treatment (BRANSON ADVANCED-DIGITAL SONIFIER device, output 50 W) was performed for 3 hours to obtain a carbon nanotube dispersion. (5) The carbon nanotube dispersion was dropped onto the intermediate layer and left to stand for 2 hours, then washed with water, ethanol, and isopropyl alcohol. (6) Drying was performed by applying a relative centrifugal acceleration of 200 × g such that the orientation of the first electrode wall of the opposing electrode wall of the electrode pair was parallel to the centrifugal force (Figure 5), perpendicular to it (Figure 6), or at 45° (Figure 7). (7) The carbon nanotube film was washed again with water, ethanol, and isopropyl alcohol, and dried by applying centrifugal force in the same direction as in (6) to obtain a bolometer.

[0061] (Method for measuring resistance) The resistance value of the bolometer was measured using a Cascade Microtech probe (product name SUMMIT 12000B-Series) under a measurement environment of an applied voltage of 3V, 300K, and dry air flow (approximately 5%RH or less).

[0062] The resistance value at 3V is 1.0 × 10⁻⁶. 10 A resistance of Ω or less is desirable, and the lower the resistance value, the better the carbon nanotubes are bonded to the electrode wall. Table 1 shows the orientation of the electrode wall relative to the centrifugal force during drying and the resulting bolometer resistance values.

[0063] [Table 1]

[0064] In the drying process after washing the CNT film, when the orientation of the electrode wall was parallel to the centrifugal force direction of the spin coat (Figure 5), the resistance value was high (4.9 × 10⁻⁶). 10 Ω). In contrast, when the electrode wall is oriented perpendicular to the direction of centrifugal force (Figure 6), the resistance value is significantly reduced (2.5 × 10⁻⁶). 7 It was found that Ω). This is thought to be because, when the direction of centrifugal force is parallel to the electrode wall, the CNT film between the electrodes moves in a way that is parallel to the electrode due to the centrifugal force, weakening the force with which the ends of the CNT film adhere to the electrode wall. On the other hand, when the direction of centrifugal force is perpendicular to the electrode wall, the CNTs at the ends of the CNT film adhere firmly to the electrode wall due to the centrifugal force. Furthermore, it is also thought that when centrifugal force is applied perpendicular to the electrode wall, the effect of removing surfactants in the carbon nanotube dispersion is enhanced.

[0065] Furthermore, when the centrifugal force direction was 45° to the electrode wall (Figure 7), the resistance value was significantly reduced compared to when it was parallel (8.5 × 10⁻⁶). 7 Ω). This is thought to be because, even at 45°, a component of centrifugal force perpendicular to the electrode wall is still present.

[0066] [Example 2] In the drying step (6) of Example 1, the electrode wall was positioned perpendicular to the centrifugal force direction and drying was performed. Then, in the drying step (7), the direction of the centrifugal force was reversed from that in (6), and drying was performed in two perpendicular directions (Figure 8). Table 2 shows the orientation of the electrode wall relative to the centrifugal force during drying and the corresponding resistance value.

[0067] [Table 2]

[0068] In the drying process after washing the CNT film, we discovered that reversing the direction of the centrifugal force between the first and second drying cycles (Figure 8) further reduced the resistance value (5.7 × 10⁻¹⁰). 6Ω). This is thought to be because the edges of the CNT film were more closely bonded not only to the first electrode wall but also to the opposite second electrode wall. Furthermore, the method of applying centrifugal force in two directions was also confirmed to be effective when multiple layers of CNT film were formed (2.2 × 10⁻¹⁰). 6 Ω). Thus, it was found that the resistance can be further reduced by drying with centrifugal force in both directions relative to the electrode walls (applying both centrifugal force with a component perpendicular to the first electrode wall and centrifugal force with a component perpendicular to the second electrode wall).

[0069] [Example 3] In the drying process of Example 1 (6), the electrode wall was positioned perpendicular to the direction of centrifugal force, and drying was performed by varying the relative centrifugal acceleration from 50 × g to 1000 × g. Table 3 shows the relative centrifugal acceleration and bolometer resistance values ​​during drying.

[0070] [Table 3]

[0071] In the drying process after washing the CNT film, if the relative centrifugal acceleration acting on the electrode wall is 100×g, 150×g, 200×g, 500×g, and 700×g, the resistance value is 1.0×10 10 The following results were obtained: It was found that a reduction in resistance can be achieved when the vertical component of the relative centrifugal acceleration acting on the electrode wall during the drying process is in the range of 50 × g to 900 × g.

[0072] [Example 4] In Example 1 (2), the height of the electrode pair formed was varied from 50 nm to 200 nm, and in the drying step (6), the electrode wall was positioned perpendicular to the centrifugal force direction, and the relative centrifugal acceleration was varied from 50 × g to 1000 × g while drying was performed. Table 4 shows the relative centrifugal acceleration and bolometer resistance values ​​at each electrode height.

[0073] [Table 4]

[0074] Although the range of the vertical component of relative centrifugal acceleration that yields a resistance reduction effect is 50 × g to 900 × g, it was found that the effective range of relative centrifugal acceleration (especially the preferred upper limit of relative centrifugal acceleration) depends on the height of the electrodes. This is because if the centrifugal force during drying is strong, the moisture-containing CNTs will exceed the electrode thickness, preventing them from firmly bonding to the electrodes, or if moisture is removed beyond the electrodes in the initial stages of drying, the surfactant removal effect at the ends of the CNTs will decrease. From these results, it was found that it is preferable for the vertical component of relative centrifugal acceleration (× g) / the height of the electrode pair (nm) to be less than 4.

[0075] Although the present invention has been described above with reference to embodiments and examples, the present invention is not limited to the above embodiments and examples. Various modifications to the configuration and details of the present invention can be made that can be understood by those skilled in the art within the scope of the present invention.

[0076] (Note 1) (A) A step of forming one or more electrode pairs on a substrate, (B) A step of forming an intermediate layer between the electrode pairs on the substrate, (C) Following steps (c1)~(c3): (c1) A step of applying a carbon nanotube dispersion onto the intermediate layer between the electrode pair and letting it stand to form a carbon nanotube preliminary layer. (c2) A step of washing the carbon nanotube preliminary layer with a washing solvent, and (c3) A step of drying the washing solvent while applying centrifugal force, wherein the vertical component of the relative centrifugal acceleration with respect to at least one of the opposing first electrode wall and second electrode wall of the electrode pair is in the range of 50 × g to 900 × g. A process of forming a carbon nanotube layer, including, A method for manufacturing a bolometer, including (Note 2) The method according to Appendix (1), wherein the drying of the washing solvent is performed by applying a centrifugal force having a component perpendicular to the first electrode wall and a centrifugal force having a component perpendicular to the second electrode wall. (Note 3) The method according to any of the preceding appendices, wherein the vertical component of the relative centrifugal acceleration with respect to the first electrode wall and / or the second electrode wall (×g) / the height of the electrode pair (nm) is less than 4. (Note 4) The method according to any of the preceding appendices, wherein multiple carbon nanotube layers are formed. (Note 5) The method according to any of the preceding appendices, wherein the step of forming the intermediate layer is the step of applying a silane coupling agent. (Note 6) The method according to Appendix 5, wherein the silane coupling agent is 3-aminopropyltriethoxysilane. [Explanation of Symbols]

[0077] 10 bolometers 20 bolometer arrays 100 circuit boards 110 electrode pairs 113a First electrode wall 113b Second electrode wall 120 Middle Class 140 Carbon nanotube layer 150 Direction of centrifugal force 152 Direction of the centrifugal force during the first cycle 154 Direction of the second centrifugal force

Claims

1. (A) A step of forming one or more electrode pairs on a substrate, (B) A step of forming an intermediate layer between the electrode pairs on the substrate, (C) The following steps (c1) to (c3): (c1) A step of applying a carbon nanotube dispersion onto the intermediate layer between the electrode pair and letting it stand to form a carbon nanotube preliminary layer. (c2) A step of washing the carbon nanotube preliminary layer with a washing solvent, and (c3) A step of drying the washing solvent while applying centrifugal force, wherein the vertical component of the relative centrifugal acceleration with respect to at least one of the opposing first electrode wall and second electrode wall of the electrode pair is in the range of 50 × g to 900 × g. A process of forming a carbon nanotube layer, including, A method for manufacturing a bolometer, including

2. The method according to claim 1, wherein the drying of the washing solvent is performed by applying a centrifugal force having a component perpendicular to the first electrode wall and by applying a centrifugal force having a component perpendicular to the second electrode wall.

3. The method according to claim 1 or 2, wherein the vertical component of the relative centrifugal acceleration with respect to the first electrode wall and / or the second electrode wall (×g) / the height of the electrode pair (nm) is less than 4.

4. The method according to claim 1 or 2, wherein multiple carbon nanotube layers are formed.

5. The method according to claim 1 or 2, wherein the step of forming the intermediate layer is the step of applying a silane coupling agent.

6. The method according to claim 5, wherein the silane coupling agent is 3-aminopropyltriethoxysilane.

Images