Patent Application
20230288262
The present invention relates to a bolometer material, an infrared sensor, and a method for manufacturing the same.
Infrared sensors have a very wide range of applications such as not only monitoring cameras for security, but also thermography for human body, in-vehicle cameras, and inspection of structures, foods, and the like, and are thus actively used in industrial applications in recent years. In particular, development of a low-cost and high-performance uncooled infrared sensor capable of obtaining biological information in cooperation with IoT (Internet of Things) is expected. In conventional uncooled infrared sensors, VOx (vanadium oxide) has been mainly used in the bolometer unit, but high process cost because of the necessity of heat treatment under vacuum, and low temperature coefficient resistance (TCR) (about −2.0%/K) are problems.
For TCR improvement, a material that has a large resistivity change with respect to temperature increase, and also has a high conductivity, and therefore, semiconducting single-walled carbon nanotubes having a large band gap and carrier mobility are expected to be applied to the bolometer unit. In addition, since carbon nanotubes are chemically stable, an inexpensive device manufacturing processes such as a printing technique can be applied, and there is a possibility that a low cost/high performance infrared sensor can be realized. However, single-walled carbon nanotubes typically contain nanotubes with semiconducting properties and nanotubes with metallic properties in a ratio of 2:1, and separation is thus required.
In addition, in order to further increase sensitivity, in addition to improving the band gap of carbon nanotubes, a structure and a conductive mechanism in which the resistivity reduction increases with temperature rising need to be achieved as a carbon nanotube thin film.
Patent Document 1 suggests applying typical single-walled carbon nanotubes to a bolometer unit, and producing a bolometer by a low-cost thin film process in which a dispersion liquid is prepared by mixing single-walled carbon nanotubes in an organic solvent utilizing their chemical stability and then is applied on an electrode. In this case, TCR is successfully improved to about −1.8%/K by subjecting single-walled carbon nanotubes to annealing treatment in the air.
In Patent Document 2, since metallic and semiconducting components are present in a mixed state in single-walled carbon nanotubes, semiconducting single-walled carbon nanotubes of uniform chirality are extracted using an ionic surfactant and applied to the bolometer unit, and TCR of −2.6%/K is thereby successfully achieved.
However, in the carbon nanotube thin film used for the infrared sensor described in Patent Document 1, since many metallic carbon nanotubes are present in a mixed state in carbon nanotubes, TCR is low at room temperature range and the improvement of the performance of the infrared sensor is limited. In addition, the TCR value of the infrared sensor using semiconducting carbon nanotubes described in Patent Document 2 cannot be said sufficient from the view point of high sensitivity, and further improvement of the carbon nanotube film is required.
In view of the above-described problems, an object of the present invention is to provide a bolometer material and an infrared sensor using semiconducting carbon nanotubes and having a high TCR value, and a method for manufacturing the same.
According to an aspect of the present invention, there is provided a bolometer material which is a thin film comprising semiconducting carbon nanotubes and a negative thermal expansion material.
According to an aspect of the present invention, there is provided a method for manufacturing a bolometer material, comprising mixing carbon nanotubes, a nonionic surfactant, and a dispersion medium to prepare a solution comprising carbon nanotubes;
According to an aspect of the present invention, there is provided a method for manufacturing an infrared sensor,
wherein the infrared sensor comprises
According to an aspect of the present invention, there is also provided an infrared sensor comprising
According to an aspect of the present invention, there is also provided an infrared sensor comprising
According to an aspect of the present invention, there is also provided a method for manufacturing an infrared sensor comprising
According to an aspect of the present invention, there is also provided a method for manufacturing an infrared sensor comprising
According to the present invention, a bolometer material, an infrared sensor, and an infrared sensor array having a high TCR value, and a method for manufacturing the same can be provided.
The inventor found that a high TCR value can be obtained by applying a thin film in which semiconducting carbon nanotubes and a negative thermal expansion material are mixed to a bolometer material.
The bolometer material according to the present embodiment is a carbon nanotube composite material in which a negative thermal expansion material is dispersed in a carbon nanotube aggregate formed by the aggregation of a plurality of semiconducting carbon nanotubes, wherein the carbon nanotube aggregate has a three-dimensional mesh structure that forms a network structure formed of dispersed carbon nanotubes intertwined with each other into an aggregate. In such a three-dimensional electrically conductive network formed of carbon nanotubes, the carbon nanotubes are not necessarily all connected to each other to contribute to electric conductivity in the bolometer material, but part of the carbon nanotubes does not contribute to the electrical conduction mechanism. These carbon nanotubes build a new electrically conductive path resulting from the effect of reduction in the volume of the negative thermal expansion material exhibited by an increase in temperature. Or, the effect of reduction in the volume further increases the contact area between the carbon nanotubes, and moreover, the number of electrically conductive paths also increases. As a result, a larger increase in current occurs as the temperature increases, resulting in an improvement in a TCR value. That is, the negative thermal expansion material mixed with the semiconducting carbon nanotubes shrinks as the temperature rises, creating an additional network of carbon nanotubes previously separate from each other, resulting in an increase in the number of electrically conductive paths, whereby a greater amount of current flows. Furthermore, in an embodiment, using a negative thermal expansion material having resistance greater than that of the semiconducting carbon nanotubes allows more efficient formation of electrically conductive paths formed of the semiconducting carbon nanotubes.
In addition, in an embodiment, it is preferable to apply a thin film in which carbon nanotubes having a predetermined diameter and length and a negative thermal expansion material to the bolometer material.
Furthermore, in an embodiment, it is also possible that the carbon nanotubes and the negative thermal expansion material forming the bolometer thin film are connected by molecular chains. This has the effects of reducing hysteresis upon temperature increase and decrease of the bolometer thin film, and improving durability.
Furthermore, in an embodiment, a TCR value and the structure can be controlled by combining negative thermal expansion materials having large and small thermal expansion coefficients, or having anisotropy and no anisotropy.
In an embodiment, it is also preferable to use a nonionic surfactant for the separation of semiconducting carbon nanotubes from untreated carbon nanotubes, and it is also preferable to use a nonionic surfactant having a long molecular length as the noninic surfactant. Such a nonionic surfactant has a weak interaction with the carbon nanotubes and can be easily removed after applying a dispersion liquid. Therefore, a stable carbon nanotube conductive network can be formed and an excellent TCR value can be obtained.
The bolometer thin film in which semiconducting carbon nanotubes and a negative thermal expansion material are mixed described above can be suitably used in a MEMS-type bolometer element, a printed-type bolometer element, or a bolometer array using thereof as described below. The bolometer film of the present embodiment has a high light absorption rate (infrared absorption rate). Therefore, in one embodiment, it is possible to simplify the manufacturing process and reduce the cost by omitting elements such as the light reflection layer and the infrared absorption layer in some cases.
The present invention has the characteristics as described above, and examples of embodiments will be described below.
In the following embodiments, a bolometer that detects infrared light (i.e., an infrared sensor) will be used as an example for explanation, but the bolometer of the present embodiment can also be used to detect, for example, terahertz waves in addition to infrared light. Therefore, as used herein, the terms “infrared ray” and “infrared light” can be read as appropriate for a desired electromagnetic wave to be detected. The bolometer of the present embodiment using a bolometer film comprising carbon nanotubes and a negative thermal expansion material can be particularly preferably used for detecting an electromagnetic wave having a wavelength of 0.7 pin to 1 mm. The electromagnetic waves included in this wavelength range include, in addition to infrared ray, terahertz wave.
The bolometer of the present embodiment is preferably an infrared sensor.
The infrared sensor with the bolometer thin film 1 can be manufactured as described below. A dispersion liquid comprising semiconducting carbon nanotubes is applied on a substrate, dried and heat treated. Through these procedures, a bolometer thin film layer is formed on the substrate. Thereafter, a first and a second electrodes are produced by vapor deposition or application at an interval of 50 μm over the bolometer thin film. The obtained infrared sensor detection unit of
The infrared sensor with the bolometer thin film 1 can also be manufactured as follows. SiO2-coated Si is used as a substrate, and is sequentially washed with acetone, isopropyl alcohol, and water, and is then subjected to oxygen plasma treatment to remove the organics and the like on the surface. Next, the substrate is immersed in an aqueous 3-aminopropyltriethoxysilane (APTES) solution, and dried. A mixed liquid is prepared with semiconducting carbon nanotubes dispersed in a polyoxyethylene alkyl ether solution such as polyoxyethylene (100) stearyl ether or polyoxyethylene (23) lauryl ether, which is a nonionic surfactant, and a negative thermal expansion material, and the mixed liquid is applied on the substrate and dried. The nonionic surfactant and the like are removed by heating the substrate in an air atmosphere at 200° C. or higher. As a result of these procedures, a bolometer thin layer 1 is formed on the substrate. Thereafter, a first and a second electrodes are produced over the bolometer thin layer at an interval of 50 μm by vapor deposition or application. An acrylic resin (PMMA) solution is applied to the region between the electrodes on the bolometer thin layer formed to form a protective layer of PMMA. Thereafter, the entire substrate is subjected to oxygen plasma treatment to remove the excess carbon nanotubes and the like on the region other than bolometer thin film layer. Excess solvents, impurities, and the like are removed by heating in an air atmosphere at 200° C.
As used herein, the term “bolometer thin film” or “bolometer film” is a thin film constituted by a plurality of carbon nanotubes forming conductive paths which electrically connect the first electrode and the second electrode, and a negative thermal expansion material. The plurality of carbon nanotubes may form a structure such as, for example, parallel, fibrous, and network, and preferably form a three-dimensional network structure in which aggregation is less likely to occur and uniform conductive paths can be obtained. As used herein, the term “bolometer material” may refers to a “bolometer thin film.”
As the carbon nanotubes, single-walled, double-walled, and multi-walled carbon nanotubes may be used, but when semiconducting carbon nanotubes are separated, single-walled or few-walled (for example, double-walled or triple-walled) carbon nanotubes are preferred, and single-walled carbon nanotubes are more preferred. The carbon nanotubes preferably comprise single-walled carbon nanotubes in an amount of 80% by mass or more, and more preferably 90% by mass or more (including 100% by mass).
The diameter of the carbon nanotubes is preferably between 0.6 and 1.5 nm, more preferably 0.6 nm to 1.2 nm, and further preferably 0.7 to 1.1 nm, from the viewpoint of increasing the band gap to improve TCR. In one embodiment, the diameter of 1 nm or less may be particularly preferred in some cases. When the diameter is 0.6 nm or more, the manufacture of carbon nanotubes becomes much easier. When the diameter is 1.5 nm or less, the band gap is easily maintained in an appropriate range and a high TCR can be obtained.
As used herein, the diameter of the carbon nanotubes means that when the carbon nanotubes on a substrate (or on any predetermined base material such as the heat insulating layer described later) or of a formed thin film are observed using an atomic force microscope (AFM) and the diameter thereof is measured at about 100 positions, 60% or more, preferably 70% or more, optionally preferably 80% or more, more preferably 100% thereof is within a range of 0.6 to 1.5 nm. It is preferred that 60% or more, preferably 70% or more, optionally preferably 80% or more, and more preferably 100% thereof be within a range of 0.6 to 1.2 nm, and further preferably within a range of 0.7 to 1.1 nm. In one embodiment, 60% or more, preferably 70% or more, optionally preferably 80% or more, and more preferably 100% thereof is within a range of 0.6 to 1 nm.
Radial breathing mode (RBM) of Raman spectra can also be used to evaluate the diameter of single-walled carbon nanotubes.
The length of the carbon nanotubes is preferably between 100 nm to 5 μm because dispersion is easy and application properties are excellent. Also, from the viewpoint of conductivity of the carbon nanotubes, the length is preferably 100 nm or more. When the length is 5 μm or less, aggregation on a substrate or on a predetermined base material, and/or upon forming a film is easily suppressed. The length of the carbon nanotubes is more preferably 500 nm to 3 μm, and further preferably 700 nm to 1.5 μm.
As used herein, the length of the carbon nanotubes means that, when at least 100 carbon nanotubes are observed using an atomic force microscope (AFM) and enumerated to measure the distribution of the length of the carbon nanotubes, 60% or more, preferably 70% or more, optionally preferably 80% or more, and more preferably 100% thereof is within a range of 100 nm to 5 μm. It is preferred that 60% or more, preferably 70% or more, optionally preferably 80% or more, and more preferably 100% thereof be within a range of 500 nm to 3 μm. It is more preferred that 60% or more, preferably 70% or more, optionally preferably 80% or more, and more preferably 100% thereof be within a range of 700 nm to 1.5 μm.
When the diameter and length of the carbon nanotubes are within the above range, the influence of semiconductive properties becomes large and a large current value can also be obtained, and thus, a high TCR value is likely to be obtained when the carbon nanotubes are used in an infrared sensor.
For the bolometer film, semiconducting carbon nanotubes having a large band gap and carrier mobility are preferably used. The content of the semiconducting carbon nanotubes, preferably single-walled semiconducting carbon nanotubes in carbon nanotubes is generally 67% by mass or more, more preferably 70% by mass or more, particularly preferably 80% by mass or more, and in particular, preferably 90% by mass or more, more preferably 95% by mass or more, and further preferably 99% by mass or more (the upper limit may be 100% by mass). In the present specification, the ratio (mass %) of semiconducting carbon nanotubes in carbon nanotubes may also be referred to as “semiconductor purity.”
In the present specification, the negative thermal expansion material means a material that has a negative coefficient of expansion and contracts as the temperature rises. Examples of the negative thermal expansion material include a material having a coefficient of linear thermal expansion ΔL/L ((length after expansion−length before expansion)/length before expansion) per temperature difference of 1K preferably ranging from −1×10−6/K to −1×10−3/K, more preferably from −1×10−5/K to −1×10−3/K, in any temperature range from −100 to +200° C., for example, the range from −100 to +100° C., preferably in the temperature range over which the infrared sensor is used, for example, at least in the range from −50 to 100° C.
The coefficient of thermal expansion can be measured in accordance, for example, with JIS Z 2285 (method for measuring coefficient of linear expansion of metallic materials) or JIS R 1618 (method for measuring thermal expansion of fine ceramics based on thermo-mechanical analysis).
In an embodiment, the negative thermal expansion material is preferably a material that exhibits sufficient negative thermal expansion in the environment in which the infrared sensor is used. The temperatures of the environment in which the infrared sensor is used range, for example, from −350° C. to 100° C., preferably from −40° C. to 80° C., more preferably in some cases from 20° C. to 30° C., for example, from 21° C. to 30° C.
The humidity in the environment in which the infrared sensor is used, for example, in a case where the bolometer part of the infrared sensor is used in a structure in which the bolometer part is exposed to the atmosphere, may be the ambient humidity, preferably, for example, 75% RH or lower. When the bolometer is vacuum-packaged or used in a structure in which the package is filled with an inert gas, the humidity is preferably, for example, 5% RH or lower, and may not fall within the range described above depending on the degree of vacuum and other factors. From the viewpoint of long-term stability of the device, lower humidity is preferable, so that the lower limit is not limited to a specific value in either case, and the humidity is 0% RH or higher, for example, higher than 0% RH.
The resistivity of the negative thermal expansion material described above is not limited to a specific value, and can range from 10−1 Ωcm to 108 Ωcm, preferably from 10 Ωcm to 108 Ωcm, more preferably 102 Ωcm to 107 Ωcm, further more preferably 106 Ωcm or less in any temperature range from −100 to +100° C., preferably at the temperature at which the infrared sensor is used, for example, at room temperature (about 23° C.). The resistivity can be measured in accordance with standard methods, for example, JIS K 7194 and JIS K 6911.
In the present specification, the negative thermal expansion material may include oxides, nitrides, sulphides or multi-element compounds containing one or two or more of Li, Al, Fe, Ni, Co, Mn, Bi, La, Cu, Sn, Zn, V, Zr, Pb, Sm, Y, W, Si, P, Ru, Ti, Ge, Ca, Ga, Cr, Cd, but not limited thereto. A mixture of two or more compounds may be used.
The negative thermal expansion material may include, but not limited thereto, vanadium oxides, β-eucryptite, bismuth-nickel oxides, zirconium tungstate, ruthenium oxides, manganese nitrides, lead titanate, samarium monosulphide and others (including those in which one or more of the elements of these compounds have been replaced by the above elements). For example, LiAlSiO4, ZrW2O8, Zr2WO4(PO4)2, BiNi1-xFexO3 (0.05≤x≤0.5), such as BiNi0.85Fe0.15O3, Bi1.95La0.05NiO3, Pb0.76La0.04Bi0.20VO3, Sm0.78Y0.22S, Cu1.8Zn0.2V2O7, Cu2V2O7, 0.4PbTiO3-0.6BiFeO3, MnCo0.98Cr0.02Ge, Ca2RuO3.74, Mn3Ga0.7Ge0.3N0.88C0.12, Cd(CN)2-XCCl4, LaFe10.5Co1.0Si1.5, Ca2RuO4, MnxSnyZnzN (3≤x≤4, 0.1≤y≤0.5, 0.1≤z≤0.8), such as Mn3.27Zn0.45Sn0.28N, Mn3Ga0.9Sn0.1N0.9, Mn3ZnN are suitable.
In one embodiment, among the negative thermal expansion materials, oxides, nitrides, and sulphides are preferable from the view point of ease of synthesis and availability.
In particular, when an oxide is used as the negative thermal expansion material, it has good binding property with the surface functional groups of the carbon nanotubes (—COOH, —OH, etc.), which also has the advantage of suppressing structural degradation caused by temperature cycling, reducing hysteresis upon temperature increase and decrease of the bolometer thin film, and improving durability.
In an embodiment, a material with high stability during the manufacturing processes is preferred, such as an oxide with low solubility in water or the like.
In the present specification, the size of the negative thermal expansion material can be selected as appropriate. Preferably, it is between 10 nm and 100 μm, more preferably 15 nm to 10 μm, and in some cases, it is also preferred to be between 50 nm and 5 μm, and it is particularly preferred to be 1 μm or less.
The form of the negative thermal expansion material is not particularly limited, but may be, for example, spherical, needle, rod, plate, fibre, scale and the like, with spherical being preferred in terms of film formability.
As used herein, the thickness of the bolometer thin film is not particularly limited, but in the range of, for example, 1 nm or more, for example a few nm to 100 nm, preferably 10 nm to 10 μm, more preferably 50 nm to 1 μm. In an embodiment, it is preferably 20 nm to 500 nm, more preferably 50 nm to 200 nm.
When the thickness of the bolometer film is 1 nm or more, a good infrared absorption rate can be achieved.
When the thickness of the bolometer film is 10 nm or more, preferably 50 nm or more, the element structure can be made simpler because an adequate infrared absorption rate is obtained even without comprising a light reflection layer (infrared reflection layer) or a light absorbing structure/infrared absorbing layer (light absorbing layer).
In addition, from the view point of simplifying the manufacturing method, it is preferred that the thickness of the bolometer film is 1 μm or less, preferably 500 nm or less. Also, when the bolometer film is too thick, the contact electrode deposited from above may not fully contact the carbon nanotubes at the bottom side of the bolometer film, and the effective resistance value becomes higher, but when the thickness is within the above range, increase of the resistance value can be suppressed.
Also, in the case of comprising an infrared absorbing layer, it is also possible to make the bolometer film thinner than the above range in order to further simplify the manufacturing process and improve the resistance value.
Also, when the thickness of the bolometer film is in the range of 10 nm to 1 μm as described above, it is also preferable in that printing techniques can be suitably applied to the manufacturing method of the bolometer film.
The thickness of the bolometer film can be determined as an average value of the thickness of the carbon nanotube film measured at arbitrary 10 positions.
The density of the bolometer film is, for example, 0.3 g/cm3 or more, preferably 0.8 g/cm3 or more, more preferably 1.1 g/cm3 or more. The upper limit thereof is not particularly limited, but can be the upper limit of the true density of the carbon nanotube used (for example, about 1.4 g/cm3).
When the density of the bolometer film is 0.3 g/cm3 or more, a good infrared absorbing rate can be achieved.
When the density of the bolometer film is 0.5 g/cm3 or more, it is preferred in that the element structure can be simplified because an adequate infrared absorption rate is obtained even without comprising a light reflection layer or an infrared absorbing layer.
Also, when an infrared absorbing layer is comprised, the density of the bolometer film of lower than the above-described density may be appropriately employed.
The density of the bolometer film can be calculated from weight, area, and the thickness obtained as above of the carbon nanotube film.
In addition to the above-mentioned components described above, ionic conductors (surfactants, ammonium salts, inorganic salts), resins, organic binders, and the like may also be appropriately used in the bolometer thin film.
In the infrared sensor of the present embodiment, the distance between its electrodes is preferably 1 μm to 500 μm, and for miniaturization, it is more preferably 5 to 200 μm. When the distance is 5 μm or more, for example, a reduction in the nature of TCR can be suppressed, even in the case of containing a small amount of metallic carbon nanotubes. In addition, the distance of 500 μm or less is advantageous when the infrared sensor is applied to an image sensor by two-dimensionally arraying the infrared sensors. The electrodes may by formed on the upper side of the bolometer film, or may be formed below the bolometer film.
The content of carbon nanotubes in the bolometer thin film connecting the first electrode and the second electrode can be selected appropriately, and preferably more than 0.1% by mass or more based on the total mass of the thin film is effective, more preferably 1% by mass or more is effective, for example 30% by mass, and even 50% by mass or more may also be preferred, and in some cases 60% by mass or more may be preferred.
The amount of negative thermal expansion material in the bolometer thin film (i.e., the thin film comprising semiconducting carbon nanotubes and a negative thermal expansion material) can be selected as appropriate, but it is preferable that it is contained in the semiconducting carbon nanotubes in an amount of 1 to 99% by mass based on the total mass of the thin film, with 1 to 70% by mass being more preferable, for example, 1 to 50% by mass, in some cases 10 to 50% by mass, and optionally 40% by mass or less may also be preferred.
In addition to the carbon nanotubes and the negative thermal expansion material, the bolometer thin film may also comprise a binder described later and, if desired, other components, but it is preferred that the total mass of the carbon nanotubes and the negative thermal expansion material is 70% by mass or more, more preferably 90% by mass or more, and even more preferably 95% by mass or more, based on the mass of the bolometer thin film.
As the constitutions of the substrate, electrode, and the like, those mentioned below may be used.
The infrared sensor with the bolometer thin film comprising carbon nanotubes and a negative thermal expansion material as mentioned above may be manufactured by, for example, a method comprising a cutting and dispersion step and a separation step of carbon nanotubes comprising a nonionic surfactant as described below, and a mixing step of the separated carbon nanotubes and the negative thermal expansion material, but may also be manufactured using other methods.
An example of the method for manufacturing a bolometer thin film and an infrared sensor according to one embodiment of the present invention will be described in detail below.
From the carbon nanotubes, surface functional groups and impurities such as amorphous carbon, catalysts, and the like may be removed by performing a heat treatment under an inert atmosphere, in a vacuum. The heat treatment temperature may be appropriately selected and is preferably 800 to 2000° C., and more preferably 800 to 1200° C.
The nonionic surfactant may be appropriately selected, and it is preferred to use nonionic surfactants constituted by a hydrophilic portion which is not ionized and a hydrophobic portion such as an alkyl chain, for example, nonionic surfactants having a polyethylene glycol structure exemplified by polyoxyethylene alkyl ethers, and alkyl glucoside based nonionic surfactants, singly or in combination. As such a nonionic surfactant, polyoxyethylene alkyl ether represented by Formula (1) is preferably used. In addition, the alkyl moiety may have one or a plurality of unsaturated bonds.
CnH2n+1(OCH2CH2)mOH (1)
wherein, n=preferably 12 to 18, and m=10 to 100, and preferably 20 to 100.
In particular, a nonionic surfactant specified by polyoxyethylene (n) alkyl ether (wherein n=20 or more and 100 or less, and the alkyl chain length is C12 or more and C18 or less) such as 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 is more preferred. In addition, N,N-bis[3-(D-gluconamido)propyl]deoxycholamide, n-dodecyl β-D-maltoside, octyl β-D-glucopyranoside, and digitonin may also be used.
As the nonionic surfactant, polyoxyethylene sorbitan monostearate (molecular formula: C64H126O26, trade name: Tween 60, manufactured by Sigma-Aldrich, etc.), polyoxyethylene sorbitan trioleate (molecular formula: C24H44O6, trade name: Tween 85, manufactured by Sigma-Aldrich, etc.), octylphenol ethoxylate (molecular formula: C14H22O(C2H4O)n, n=1 to 10, trade name: Triton X-100, manufactured by Sigma-Aldrich, etc.), polyoxyethylene (40) isooctylphenyl ether (molecular formula: C8H17C6H4O(CH2CH2O)40H, trade name: Triton X-405, manufactured by Sigma-Aldrich, etc.), poloxamer (molecular formula: C5H10O2, trade name: Pluronic, manufactured by Sigma-Aldrich, etc.), polyvinyl pyrrolidone (molecular formula: (C6H9NO)n, n=5 to 100, manufactured by Sigma-Aldrich, etc.) and the like may be used.
The method for obtaining a dispersion solution of carbon nanotubes is not particularly limited, and conventionally known methods can be applied. For example, a carbon nanotube mixture, a dispersion medium, and a nonionic surfactant are mixed to prepare a solution containing carbon nanotubes, and this solution is subjected to sonication to disperse the carbon nanotubes, thereby preparing a carbon nanotube dispersion liquid (micelle dispersion solution). The dispersion medium is not particularly limited, as long as it is a solvent that allows carbon nanotubes to disperse and suspend during the separation step, and for example, water, heavy water, an organic solvent, an ionic liquid, or a mixture thereof may be used, and water and heavy water are preferred. In addition to or instead of the sonication mentioned above, a technique of dispersing carbon nanotubes by a mechanical shear force may be used. The mechanical shearing may be performed in a gas phase. In a micelle dispersion aqueous solution of the carbon nanotubes and the nonionic surfactant, the carbon nanotubes are preferably in an isolated state. Thus, if necessary, bundles, amorphous carbon, impurity catalysts, and the like may be removed using an ultracentrifugation treatment. During the dispersion treatment, the carbon nanotubes can be cut, and the length thereof can be controlled by changing the grinding conditions of the carbon nanotubes, ultrasonic output, ultrasonic treatment time, and the like. For example, the aggregate size can be controlled by grinding the untreated carbon nanotubes using tweezers, a ball mill, or the like. After these treatments, the length can be controlled to 100 nm to 5 μm using an ultrasonic homogenizer by setting the output to 40 to 600 W, optionally 100 to 550 W, 20 to 100 KHz, the treatment time to 1 to 5 hours, preferably up to 3 hours. When the treatment time is shorter than 1 hour, the carbon nanotubes may be hardly dispersible depending on the conditions, and may remain almost the original length in some cases. From the viewpoint of shortening the dispersion treatment time and reducing the cost, the treatment time is preferably 3 hours or less. The present embodiment may also have the advantage of ease of adjustment of cutting due to use of a nonionic surfactant. In addition, the infrared sensor according to the present embodiment manufactured using the carbon nanotubes prepared by a method using a nonionic surfactant has the advantage of containing no ionic surfactant which is difficult to be removed.
Dispersion and cutting of the carbon nanotubes generate a surface functional group at the surface or the end of the carbon nanotube. Functional groups such as carboxyl group, carbonyl group, and hydroxyl group are generated. When the treatment is performed in a liquid phase, a carboxyl group and a hydroxyl group are generated, and when the treatment is performed in a gas phase, a carbonyl group is generated.
When these surface functional groups are present and an oxide is used as the negative thermal expansion material, structural deterioration of the infrared sensor due to temperature cycle can be suppressed in some cases as these functional groups have good binding properties to the oxide, and can enhance the binding between carbon nanotubes via a compound having an amino group, and can also express an anchor effect to the substrate.
The concentration of the surfactant in the liquid comprising heavy water or water and a nonionic surfactant mentioned above is preferably from the critical micelle concentration to 10% by mass, and more preferably from the critical micelle concentration to 3% by mass. The concentration of the critical micelle concentration or less is not preferred because dispersion is impossible. When the concentration is 10% by mass or less, a sufficient density of carbon nanotubes can be applied after separation, while reducing the amount of surfactant. As used herein, the critical micelle concentration (CMC) refers to the concentration serving as an inflection point of the surface tension measured by, for example, changing the concentration of an aqueous surfactant solution using a surface tensiometer such as a Wilhelmy surface tensiometer at a constant temperature. As used herein, the “critical micelle concentration” is a value under atmospheric pressure at 25° C.
The concentration of the carbon nanotubes in the above cutting and dispersion step (the weight of the carbon nanotubes/(the total weight with the dispersion medium and the surfactant)×100) is not particularly limited, and for example, may be 0.0003 to 10% by mass, preferably 0.001 to 3% by mass, and more preferably 0.003 to 0.3% by mass.
The dispersion liquid obtained through the aforementioned cutting and dispersion step may be used as it is in the separation step mentioned below, or steps such as concentration and dilution may be performed before the separation step.
Separation of the carbon nanotubes can be performed by, for example, the electric-field-induced layer formation method (ELF method: see, for example, K. Ihara et al. J. Phys. Chem. C. 2011, 115, 22827 to 22832 and Japanese Patent No. 5717233, which are incorporated herein by reference). One example of the separation method using the ELF method will be described. Carbon nanotubes, preferably single-walled carbon nanotubes are dispersed by a nonionic surfactant, and the dispersion liquid is put into a vertical separation apparatus, and then a voltage is applied to the electrodes arranged above and below, so that the carbon nanotubes are separated by free flow electrophoresis. The mechanism of separation can be inferred as follows for example. When the carbon nanotubes are dispersed by the nonionic surfactant, the micelle of the semiconducting carbon nanotubes has a negative zeta potential, whereas the micelle of the metallic carbon nanotubes has an opposite (positive) zeta potential (in recent years, it is considered that the metallic carbon nanotubes have a slightly negative zeta potential or are barely charged). Thus, when an electric field is applied to the carbon nanotube dispersion liquid, the micelle of the semiconducting carbon nanotubes is electrophoresed toward the anode (+) direction, and the micelle of the metallic carbon nanotubes is electrophoresed toward the cathode (−) direction by the difference between the zeta potentials, and the like. Eventually, the layer in which the semiconducting carbon nanotubes are concentrated is formed near the anode, and the layer in which the metallic carbon nanotubes are concentrated is formed near the cathode in the separation tank. The voltage for separation may be appropriately set in consideration of the composition of the dispersion medium, the charge amount of carbon nanotubes, and the like, and is preferably 1 V or more and 200 V or less, and more preferably 10 V or more and 200 V or less. It is preferably 100 V or more from the viewpoint of shortening the time for the separation step. It is preferably 200 V or less from the viewpoint of suppressing the generation of bubbles during separation and maintaining the separation efficiency. The purity is improved by repeating separation. The same separation procedure may be performed by resetting the dispersion liquid after separation to the initial concentration. As a result, the purity can be further increased.
Through the aforementioned dispersion and cutting step and separation step of the carbon nanotubes, a dispersion liquid in which the semiconducting carbon nanotubes having the desired diameter and length are concentrated can be obtained. As used herein, the carbon nanotube dispersion liquid in which semiconducting carbon nanotubes are concentrated may be referred to as the “semiconducting carbon nanotube dispersion liquid”. The semiconducting carbon nanotube dispersion liquid obtained by the separation step comprises semiconducting carbon nanotubes generally 67% by mass or more, preferably 70% by mass or more, more preferably 80% by mass or more in the total amount of carbon nanotubes, and it is particularly preferably 90% by mass or more, more preferably 95% by mass or more, further preferably 99% by mass or more (the upper limit may be 100% by mass). The separation tendency of the metallic and semiconducting carbon nanotubes can be analyzed by microscopic Raman spectroscopy and ultraviolet-visible near-infrared absorptiometry.
The centrifugation treatment may be performed to remove the bundles, amorphous carbon, metal impurities, and the like in the carbon nanotube dispersion liquid after the aforementioned dispersion and cutting step of the carbon nanotubes and before the separation step. The centrifugal acceleration may be appropriately adjusted, and is preferably 10000×g to 500000×g, more preferably 50000×g to 300000×g, and optionally 100000×g to 300000×g. The centrifugation time is preferably 0.5 hours to 12 hours, and more preferably 1 to 3 hours. The centrifugation temperature may be appropriately adjusted, and is preferably 4° C. to room temperature, and more preferably 10° C. to room temperature.
The concentration of the surfactant in the carbon nanotube dispersion liquid after separation may be appropriately controlled. The concentration of the surfactant in the carbon nanotube dispersion liquid is preferably from the critical micelle concentration to about 5% by mass, more preferably, 0.001% by mass to 3% by mass, and particularly preferably 0.01 to 1% by mass to suppress the reaggregation after application and the like.
A mixed dispersion liquid comprising semiconducting carbon nanotubes and a negative thermal expansion material (semiconducting carbon nanotubes/negative thermal expansion material dispersion liquid) can be obtained by mixing a negative thermal expansion material into the semiconducting carbon nanotube dispersion liquid comprising obtained by the above steps.
The mixing ratio of the semiconducting carbon nanotubes and the negative thermal expansion material in the dispersion liquid can be selected as appropriate, but the semiconducting carbon nanotubes is preferably 0.01% by mass to 99% by mass, more preferably 0.1% by mass to 90% by mass, for example, 30% by mass or more, and furthermore, 50% by mass to 85% by mass is also preferred, based on the total mass of the semiconducting carbon nanotubes and the negative thermal expansion material.
When mixing the negative thermal expansion material into the semiconducting carbon nanotube dispersion liquid obtained by the above steps, a binder or the like may also be added. By adding a binder, the viscosity can be more easily adjusted, and the dispersion liquid can be more easily applied. It also prevents the semiconducting carbon nanotubes and thermal expansion material from agglomerating or settling after application, making it easier to produce a more uniform coating film. The type of the binder can be appropriately selected, examples of which include polyvinylidene fluoride, acrylic resin, styrene butadiene rubber, imide resin, imideamide resin, polytetrafluoroethylene resin, polyamic acid, vinylidene fluoride-hexafluoropropylene, vinylidene fluoride-tetrafluoroethylene, polypropylene, polyethylene, polyimide, polyamideimide, methyl(meth)acrylate, ethyl(meth)acrylate, butyl(meth)acrylate, (meth)acrylonitrile, isoprene rubber, butadiene rubber, and fluoro rubber. Mixtures of two or more binders may be used. When a binder is used, the content is not particularly limited, but, for example, more than 0% by mass, preferably 0.01% by mass or more, for example, 0.1% by mass or more, and 30% by mass or less, preferably 10% by mass or less, preferably 5% by mass or less based on the total mass of semiconducting carbon nanotubes and negative thermal expansion material.
The semiconducting carbon nanotube/negative thermal expansion material dispersion liquid obtained by the processes described above can be applied on the substrate or on a predetermined base material, dried, and, optionally heat treated to form a bolometer thin film.
The substrate may be either a flexible substrate or a rigid substrate, and may be appropriately selected, and those in which at least the element forming surface has insulating property or semiconducting property are preferred. For examples, Si, SiO2-coated Si, SiO2, SiN, parylene, polymers, resins, plastics, and the like, but is not limited thereto.
The method for applying the semiconducting carbon nanotube/negative thermal expansion material dispersion liquid to the substrate or a predetermined base material is not particularly limited, and examples thereof include dropping method, spin coating, printing, inkjet, spray coating, dip coating, and the like. From the viewpoint of reducing the manufacturing cost of infrared sensor, a printing method is preferred. The printing methods can include application (dispenser, inkjet or the like), transferring (microcontact print, gravure printing, or the like) and the like.
The semiconducting carbon nanotubes/negative thermal expansion material dispersion liquid applied on the substrate or a predetermined based material may be subjected to a heat treatment to remove the surfactant and the solvent. The temperature of the heat treatment may be appropriately set as long as it is equal to or higher than the decomposition temperature of the surfactant, and it is preferably 150 to 500° C., and more preferably 200 to 500° C., for example 200 to 400° C. A temperature of 200° C. or more is preferred because the remaining of the decomposition product of the surfactant can be easily suppressed. A temperature of 500° C. or less, for example 400° C. or less is preferred because the change in the quality of the substrate or other components can be suppressed. Also, the decomposition of carbon nanotubes, the change in size, the leaving of functional groups, and the like can be suppressed.
The first electrode and the second electrode on the substrate can be produced using, for example, gold, platinum, and titanium singly or in combination. The method for producing the electrode is not particularly limited, and examples thereof include vapor deposition, sputtering, and printing method. The thickness may be appropriately adjusted and is preferably 10 nm to 1 mm, and more preferably 50 nm to 1 μm. The above dispersion liquid may be applied to the substrate on which the electrodes are provided in advance, or the electrode may be produced after the dispersion liquid is applied, before or after the heat treatment.
A protective film may be provided on the surface of the bolometer thin film, if necessary. The protective film is preferably a material with high transparency in the infrared wavelength range to be detected. Examples thereof include acrylic resins such as PMMA and PMMA anisole, epoxy resins, and Teflon®.
The infrared sensor according to the present embodiment may be a single element or may be an array in which a plurality of elements are two-dimensionally arranged such as those used in an image sensor.
As for the structure of the element and array of the infrared sensor, the structure used for infrared sensors can be adopted without any particular restriction. Examples of suitable elements and array structures are described below, but are not limited to these.
An example of a cell structure of the bolometer will be explained with reference to the figures.
The bolometer thin film comprising semiconducting carbon nanotubes and a negative thermal expansion material according to the present embodiment described above has a higher infrared absorption rate than the conventional bolometer film. Therefore, one or both of the light reflection layer and the infrared absorbing layer are not necessary to be provided, and one or both of these may be omitted as shown in
When a light reflection layer 109 is comprised as shown in
Hereinafter, elements constituting the bolometer element according to the present embodiment will be each described in detail.
A bolometer thin film comprising the above-described semiconducting carbon nanotubes and a negative thermal expansion can be used as the bolometer film.
In the bolometer of the present embodiment, a gap 102 is provided between the infrared detection unit (light detection unit) 110 comprising the above-described bolometer film 104 and the substrate 101. In a bolometer equipped with a light reflecting layer 109 as shown in
The insulation between the infrared detection unit and the substrate can also be improved by vacuum packaging the entire infrared element and keeping the gap 102 in vacuum.
In the bolometer of the present embodiment, as a component other than the above-described bolometer film 104 and the gap 102, those used in bolometers can be used without limitation, and an example thereof will be described below. As the substrate and the electrodes, those described above can be used for example.
The bolometer of the present embodiment may comprise an infrared absorbing structure.
For example, an infrared absorbing structure 107 in a form of eave can be provided in order to efficiently absorb the incident infrared rays and further increase the fill factor as shown in
Also, as shown in
The thickness of the infrared absorbing layer depends on its material, and for example, may be from 50 nm to 1 μm.
In a case where an infrared absorbing layer 107 is provided directly on the bolometer film 104, the example thereof includes, but not limited thereto, a coating film of polyimide and the like. An example of the infrared absorbing layer 107 to be provided on a protection layer includes, but not limited thereto, a thin film of silicon nitrate and the like.
As shown in
As shown in
Although a bolometer of a single cell (single element) is shown in the above embodiment, a bolometer array can be made by arranging a plurality of elements in an array configuration.
For the method for manufacturing the bolometer and bolometer array according to the present embodiment, any manufacturing process typically used for manufacturing a bolometer can be used without limitation, except that a predetermined bolometer film is used. Examples of the element structure of a bolometer array and the manufacturing method thereof will be described below.
The silicon MEMS (Micro Electro Mechanical Systems) process is usually used to fabricate elements such as those shown in
The light reflection layer may also be omitted in the above-described processes. In this case, the thickness of the sacrificial layer, namely the distance d between the light reflection layer 109 and the bolometer film 104 can be set freely without taking into account the wavelength of electromagnetic waves to be absorbed, and the manufacturing processes can be further simplified.
When an infrared absorbing layer 107 is provided in addition to the above components, it may be formed on the above bolometer film 104 or on the silicon nitrate film using a printing method or the like, or an infrared absorbing layer formed in advance may be layered.
It is also desirable to apply a transistor array to the bolometer array of the present embodiment. The application of a transistor array is advantageous in that, for example, it makes a high-speed scanning possible. The form of the transistor array is not limited, and any form used in the art can be applied without a particular limitation, for example, by building in the transistor array under the photosensitive area.
Another example of the cell structure of the bolometer is described with reference to the figures.
In the bolometer of the present embodiment, the bolometer film 204 and the substrate 201 are thermally separated by the heat insulating layer 202, which prevents heat from escaping from the bolometer film 204 and improves detection sensitivity. Furthermore, the element structure is simpler than that of a bolometer of a diaphragm-type structure having a gap between the substrate 201 and the bolometer film 204, and there is also an advantage that vacuum packaging to evacuate the gap is not required.
Furthermore, since the bolometer film 204 and the heat insulating layer 202 can be fabricated using printing technology, there is also an advantage that the manufacturing cost can be lowered as compared to the case of using the MEMS process.
In the present embodiment, as shown in
Also, as shown in
The bolometer thin film comprising semiconducting carbon nanotubes and a negative thermal expansion material according to the present embodiment described above has a higher infrared absorption rate than the conventional bolometer film. Therefore, one or both of the light reflection layer and the infrared absorbing layer are not necessary to be provided, and one or both of these may be omitted. This makes it possible to more simplify the element structure and lowering the cost of the manufacturing process.
Hereinafter, elements constituting the bolometer element according to the present embodiment will be each described in detail.
A bolometer thin film comprising semiconducting carbon nanotubes and a negative thermal expansion described above can be used as the bolometer film.
The heat insulating layer 202 is a layer interrupting the heat transmission from the carbon nanotube film 204 to the substrate 201. In the conventional bolometers, a gap is provided to serve as a structure interrupting the heat transmission from a bolometer film to a substrate, and complicated production processes are required to form such a gap. However, since the heat insulating layer in the present embodiment can be formed using a printing process and the like, and complicated production processes are thus not required. In addition, while in the conventional bolometers, the entire element is need to be vacuum packaged in order to keep the gap in vacuum, the bolometer of the present embodiment has an advantage of not requiring such vacuum packaging.
A resin component with a low heat conductivity is preferably used for the heat insulating layer. The heat conductivity of the resin component to be used for the heat insulating layer is lower than the heat conductivity of the substrate 201, and for example, is in the range of 0.02 to 0.3 (W/mK), preferably 0.05 to 0.15 (W/mK). Examples of such resin component include parylene, but not limited thereto. Parylene is a generic term for paraxylene-based polymers, and has a structure in which benzene rings are linked via CH2. Parylene includes parylene N, parylene C, parylene D, parylene HT and the like, and among them, parylene C (heat conductivity: 0.084 (W/mK)) having the lowest heat conductivity is suitable.
The thickness of the heat insulating layer can be appropriately set in considering the heat conductivity of the component to use, and in a case of using parylene C for example, it is preferably in the range of 5 μm to 50 μm, and more preferably in the range of 10 μm to 20 μm.
When a light reflection layer is comprised to improve infrared absorption, it is preferable to set the distance d=λ/4 between the bolometer film 204 and the light reflection layer, taking into account the wavelength λ of the infrared rays to be absorbed as described above. On the other hand, when the light reflection layer is omitted, the thickness of the heat insulation layer can be set freely within the range where a desired heat insulation properties can be obtained without taking into account the wavelength λ of the infrared rays to be absorbed. In this case, there is also the advantage that the bolometer can be used to detect electromagnetic waves in a wider wavelength range.
In the bolometer of the present embodiment, as a component other than the above-described bolometer film 204 and heat insulating layer 202, those typically used in bolometers can be used without limitation, and an example thereof will be described below. As the substrate and the electrodes, those described above can be used.
When an infrared absorbing layer 209 is provided as shown in
For example, in the embodiment shown in
The protection layer is preferably made of a material having a high transparency in the infrared wavelength range to be detected, and examples thereof include resins used for the above-described heat insulating layer, such as parylene, and also acrylic resins such as PMMA and PMMA anisole, epoxy resins, Teflon®, silicon nitrate and the like, but not limited thereto. The thickness of the protection layer depends on its material, and may be for example 5 nm to 50 nm.
As shown in
Furthermore, although a bolometer of a single cell (single element) is shown above, a bolometer array can be made by arranging a plurality of elements in an array configuration.
The method for manufacturing the bolometer according to the present embodiment is not particularly limited and any method used for manufacturing a bolometer can be appropriately employed. From the view point of simplifying the manufacturing processes and lowering the cost, it is preferred to form a heat insulating layer and a bolometer film on a desired substrate using a printing method or the like, but the method is not limited to the printing method.
The bolometer film can be formed by applying the semiconducting carbon nanotubes/negative thermal expansion material dispersion liquid obtained by the aforementioned processes on the aforementioned heat insulating layer, and drying the resultant. Alternatively, the semiconducting carbon nanotubes/negative thermal expansion material dispersion liquid may be applied on a desired base material to form a film, and the resulting bolometer film may be layered on the aforementioned heat insulating layer.
The manufacturing method of the heat insulating layer is not particularly limited as long as the method can produce the heat insulating layer described above. For example, when a parylene film is used as the heat insulating layer, the parylene film can be formed by coating a desired area with parylene using a vacuum vapor deposition apparatus. Specifically, when solid dimer is heated under vacuum, it vaporizes to become dimer gas. This gas is thermally decomposed and the dimer is cleaved to a monomer form. In the vapor deposition chamber at room temperature, this monomer gas polymerizes on all surfaces to form a thin, transparent polymer film.
If necessary, pre-treatment of the substrate, cleaning of the substrate, and masking of the areas that should not be deposited may be performed before the vapor deposition process is performed.
An example of the structure and the manufacturing method of a bolometer array will be described with reference to the figures, but the structure and the manufacturing method of the bolometer array are not limited thereto.
In
Next, as shown in
Then, as shown in
Then, as shown in
Thereafter, bolometer film 204 is formed. Bolometer film 204 is preferably formed by a printing method, for example, by applying the carbon nanotubes/negative thermal expansion material dispersion liquid described above by a dispenser apparatus. Here, the thickness and the density of the bolometer film are, for example, the thickness of 100 nm and the density of 1.1 g/cm3, respectively.
In the case of comprising a light reflection layer, a parylene film is formed as the heat insulation layer 202, on which a light reflection layer 210 is formed by vapor deposition of aluminum (1000 Å), on which a second heat insulation layer 202 is formed with a thickness of about 2.5 μm (distance d) by the evaporation of Parylene.
If a protective film 208 is to be provided in addition to the above components, for example, a protection layer can be formed by applying a resin solution used for the protection layer on the formed bolometer film 204. Thereafter, the entire substrate may be subjected to an oxygen plasma treatment to remove excess carbon nanotube and the like present in the areas other than the bolometer film 204.
When an infrared absorbing layer 209 is provided in addition to the above components, it may be formed on the above bolometer film 204 or on a protection film 208 using a printing method or the like, or an infrared absorbing layer formed in advance may be layered or transferred.
The following example shows an example of the method for manufacturing a bolometer that does not have a light reflection layer, an infrared absorption layer, or a protective layer. Of course, however, the manufacturing method may additionally include steps of forming a light reflection layer, an infrared absorption layer, a protective layer, and the like.
Another example will be explained with reference to
First, as shown in
Next, insulating film 211 is formed to insulate a part of row wiring 206 that intersects with a row wiring in a later process. A method of forming the insulating film includes coating polyimide to form a film using a printing method.
Next, as shown in
Next, as shown in
According to such a method, a bolometer array as shown in
Another example will be explained with reference to
In the bolometer array of
Another example will be explained with reference to
A TFT (thin-film transistor) array is also preferably applied to the array sensor according to the present embodiment. The application of a TFT array makes possible high-speed scanning. The form of the TFT array is not particularly limited, and one example thereof is shown in
The present invention will be described further in detail by way of Examples below. Of course, the present invention should not be limited by the following examples.
100 mg of single-walled carbon nanotubes (Meijo Nano Carbon Co., Ltd., EC 1.0 (diameter: about 1.1 to 1.5 nm (average diameter 1.2 nm)) was put in a quartz boat and inserted into an electric furnace and heat treatment was performed at 900° C. for two hours under a vacuum atmosphere. The surface functional groups and impurities were removed, and the weight after heat treatment was 80 mg. 12 mg of the obtained single-walled carbon nanotubes was immersed in 40 ml of an aqueous solution of 1 wt % surfactant (polyoxyethylene (100) stearyl ether) and ultrasonic dispersion treatment (BRANSON ADVANCED-DIGITAL SONIFIER apparatus (output: 50 W)) was performed for three hours. Through this step, aggregates of the carbon nanotubes in the solution were eliminated. The obtained solution was subjected to ultracentrifugation treatment under conditions of 50000 rpm at 10° C. for 60 minutes. Through this procedure, bundles, remaining catalysts, and the like were removed to obtain a carbon nanotube dispersion liquid.
The carbon nanotube dispersion liquid was introduced into the separation apparatus to extract semiconducting carbon nanotubes by ELF method. Their analysis by optical absorption spectra showed that the metallic carbon nanotube component was removed. The Raman spectra also showed that 99 wt % was semiconducting carbon nanotubes.
Negative thermal electrical material (negative thermal expansion material) (Cu1.8Zn0.2V2O7, thermal expansion coefficient: −14 ppm/K, resistivity: 105 Ωcm, size: 20 nm, shape: spherical) was mixed to the semiconducting carbon nanotube dispersion liquid so that the ratio by weight of the semiconducting carbon nanotubes was 70%. A dispersion liquid of semiconducting carbon nanotubes/negative thermal electrical material was prepared by ultrasonic treatment.
A substrate in which a silicon substrate is coated with 100 nm of SiO2 was prepared. The substrate was washed, and immersed in a 0.1% APTES aqueous solution for 30 minutes. After washing, the substrate was dried at 105° C. A semiconducting carbon nanotubes/negative thermal electrical material dispersion liquid was added dropwise on the obtained substrate, and dried at 110° C. The substrate was heated in an air atmosphere at 200° C. to remove the nonionic surfactant and the like. Thereafter, gold was vapor deposited to a thickness of 50 nm at two positions on the substrate at an interval of 100 μm. Then, a PMMA anisole solution was applied between the electrodes to protect the carbon nanotubes between the electrodes, and then, excess carbon nanotubes and the like near the electrodes were removed by oxygen plasma treatment. Thereafter, the substrate was dried at 200° C. for one hour to produce an infrared sensor. The AFM observation showed that at least 70% of carbon nanotubes had a diameter within the range of 0.9 to 1.5 nm and a length within the range of 700 nm to 1.5 μm.
The change in resistance value when the temperature of the infrared sensor produced in step 4 was changed from 20° C. to 40° C. was measured. The results showed that the TCR value (dR/RdT) was about −10.5%/K at 300K. It was found that this value largely exceeds that of Comparative Example 1 and −2%/K of the conventionally used vanadium oxide. This is not only because semiconducting carbon nanotubes in the bolometer thin film had a small diameter and a large band gap, but also because the negative thermal expansion material gradually reduced in volume with the temperature rising, resulting the increase of the density of the bolometer thin film, and the number of conductive paths between carbon nanotubes was gradually increased.
Negative thermal expansion material (BiNi0.85Fe0.15O3, thermal expansion coefficient: about −180 ppm/K, resistivity: 5 Ωcm, shape: spherical) was mixed to the semiconducting carbon nanotube dispersion liquid, which is same as that of steps 1 to 2 of Example 1, so that the ratio by weight of the semiconducting carbon nanotubes was 60%. A dispersion liquid of semiconducting carbon nanotubes/negative thermal electrical material was prepared by ultrasonic treatment.
A substrate in which a silicon substrate is coated with 100 nm of SiO2 was prepared. The substrate was washed, and immersed in a 0.1% APTES aqueous solution for 30 minutes. After washing, the substrate was dried at 105° C. A dispersion liquid of semiconducting carbon nanotubes/negative electrical material was added dropwise on the obtained substrate, and dried at 110° C. The substrate was heated in an air atmosphere at 180° C. to remove the nonionic surfactant and the like. Thereafter, gold was vapor deposited to a thickness of 200 nm at two positions on the substrate at an interval of 100 μm. Then, a PMMA anisole solution was applied between the electrodes to protect the carbon nanotubes between the electrodes, and then, excess carbon nanotubes and the like near the electrodes were removed by oxygen plasma treatment. Thereafter, the substrate was dried at 180° C. for one hour to produce an infrared sensor.
The change in resistance value at 0.6 V when the temperature of the infrared sensor produced in step 4 was changed from 293K to 303K was measured (
Negative thermal expansion material (Mn3.27Sn0.28Zn0.45N, thermal expansion coefficient: about −40 ppm/K, resistivity: 0.3 Ωcm, shape: spherical) was mixed to the semiconducting carbon nanotube dispersion liquid, which is same as that of steps 1 to 2 of Example 1, so that the ratio by weight of the semiconducting carbon nanotubes was 60%. A dispersion liquid of semiconducting carbon nanotubes/negative thermal electrical material was prepared by ultrasonic treatment.
A substrate in which a silicon substrate is coated with 100 nm of SiO2 was prepared. The substrate was washed, and immersed in a 0.1% APTES aqueous solution for 30 minutes. After washing, the substrate was dried at 105° C. A semiconducting carbon nanotubes/negative thermal electrical material dispersion liquid was added dropwise on the obtained substrate, and dried at 110° C. The substrate was heated in an air atmosphere at 180° C. to remove the nonionic surfactant and the like. Thereafter, gold was vapor deposited to a thickness of 200 nm at two positions on the substrate at an interval of 100 μm. Then, a PMMA anisole solution was applied between the electrodes to protect the carbon nanotubes between the electrodes, and then, excess carbon nanotubes and the like near the electrodes were removed by oxygen plasma treatment. Thereafter, the substrate was dried at 180° C. for one hour to produce an infrared sensor.
The change of resistance at 0.6V when the temperature of the infrared sensor manufactured in step 4 was changed from 293K to 303K was measured. The resulted TCR value (dR/RdT) was about −6.4%/K at 293K. This value was higher than Comparison example 1. The TCR value was lower as compared to Examples 1 and 2. This may be due to the slight solubility of MnxSnyZnzN in water, and the negative expansion effect may not be sufficiently obtained due to the dissolution of the particles during the ink preparation process.
An infrared sensor was produced using a semiconducting carbon nanotube dispersion liquid in the same manner as in step 1 of Example 1 and in the same manner as in step 4 except for not performing the mixing step in step 3. The TCR value at this time was about −5.5%/K. The TCR value is lower as compared to Example 1 because the conductive paths between carbon nanotubes do not change with respect to the temperature change.
The whole or part of the example embodiments disclosed above can be described as, but not limited to, the following supplementary notes.
A bolometer material which is a thin film comprising semiconducting carbon nanotubes and a negative thermal expansion material.
The bolometer material according to supplementary note 1, wherein the thin film comprising semiconducting carbon nanotubes and a negative thermal expansion material comprises the negative thermal expansion material in the semiconducting carbon nanotubes in an amount of from 1 to 99% by mass based on the total mass of the thin film.
The bolometer material according to supplementary note 1 or 2, wherein the semiconducting carbon nanotubes have a semiconductor purity of 67% by mass, a diameter within the range of 0.6 to 1.5 nm and a length within the range of 100 nm to 5 μm.
The bolometer material according to any one of supplementary notes 1 to 3, wherein the negative thermal expansion material is an oxide, a nitride, a sulphide or a multi-element compound comprising one or two or more selected from the group consisting of Fe, Ni, Co, Mn, Bi, La, Cu, Sn, Zn, V, Zr, Pb, Sm, Y, W, P, Ru, Ti, Ge, Ca, Ga, Cr and Cd, or a mixture thereof.
The bolometer material according to supplementary note 4, wherein the negative thermal expansion material is one or more types of oxide.
The bolometer material according to any one of supplementary notes 1 to 5, wherein the negative thermal expansion material has a coefficient of linear thermal expansion ΔL/L ((length after expansion−length before expansion)/length before expansion) per 1K ranging from −1×10−6/K to −1×10−3/K in a temperature range of from −100 to +100° C.
The bolometer material according to any one of supplementary notes 1 to 6, wherein the resistivity of the negative thermal expansion material is in the range from 10−1 Ωcm to 108 Ωcm in a temperature range of from −100 to +100° C.
An infrared sensor, comprising
An infrared sensor according to supplementary note 8, wherein the electrode distance between the first electrode and the second electrode is 10 μm to 500 μm.
An infrared sensor, comprising
The infrared sensor according to supplementary note 10, comprising no light reflection layer.
An infrared sensor, comprising
The infrared sensor according to supplementary note 12, comprising no light reflection layer.
The infrared sensor according to any one of claims 8 to 13, which is a bolometer array in which a plurality of elements comprising a bolometer thin film comprising semiconducting carbon nanotubes and a negative thermal expansion material are formed on a substrate.
A method for manufacturing a bolometer material, comprising
A method for manufacturing an infrared sensor,
wherein the infrared sensor comprises
A method for manufacturing an infrared sensor, comprising
A method for manufacturing an infrared sensor, comprising
While the invention has been described with reference to example embodiments and examples thereof, the invention is not limited to these embodiments and examples. Various changes that can be understood by those of ordinary skill in the art may be made to form and details of the present invention without departing from the spirit and scope of the present invention.
This application claims priority based on PCT/JP2020/20795 filed on May 26, 2020 and Japanese patent application No. 2020-218851 filed on Dec. 28, 2020, the entire disclosures of which are incorporated herein.
| Number | Date | Country | Kind |
|---|---|---|---|
| PCT/JP2020/020795 | May 2020 | WO | international |
| 2020-218851 | Dec 2020 | JP | national |
| Filing Document | Filing Date | Country | Kind |
|---|---|---|---|
| PCT/JP2021/019796 | 5/25/2021 | WO |
