Gas sensor, gas sensor assembly, detection method, and chemical substance identification method

Abstract

This gas sensor (100) is provided with: a sensitive part (30); and a pair of electrodes, i.e., a first electrode (20) and a second electrode (25), which are electrically connected to the sensitive part (30). The sensitive part (30) comprises an electrically conductive material and a polymer having a siloxane bond as a main chain structure thereof. The polymer has a cyano group in a side chain thereof.

Description

Technical Field

[0001] The present disclosure relates to a gas sensor, a gas sensor assembly, and a chemical substance identification method.

Background Art

[0002] Conventionally, gas sensors that detect chemical substances such as volatile organic compounds in a gas by detecting the characteristics of a sensitive part associated with adsorption to the sensitive part composed of an adsorbent made of a polymer or the like are known (for example, Patent Document 1 and Patent Document 2).

Prior Art Documents

Patent Documents

[0003]

Patent Document 1

Patent Document 2

Summary of the Invention

Problems to be Solved by the Invention

[0004] When identifying chemical substances such as volatile organic compounds or odors in a gas using a gas sensor, a gas sensor with high identification accuracy is required.

[0005] The present disclosure provides a gas sensor or the like that can improve the identification accuracy when used for identifying chemical substances or the like.

Means for Solving the Problems

[0006] A gas sensor according to one aspect of the present disclosure includes a sensitive part and a pair of electrodes each electrically connected to the sensitive part, the sensitive part having a conductive material and a polymer having a siloxane bond as a main chain structure, and the polymer having a cyano group in a side chain.

[0007] In addition, a gas sensor assembly according to one aspect of the present disclosure includes a plurality of gas sensors, and at least one of the plurality of gas sensors is the above gas sensor.

[0008] Further, a chemical substance identification method according to one aspect of the present disclosure is a chemical substance identification method using the above gas sensor assembly, and includes a step of acquiring a signal output from the gas sensor assembly exposed to a gas containing a chemical substance, a step of calculating a feature amount from the acquired signal, and a step of identifying the chemical substance contained in the gas based on the calculated feature amount.

Advantages of the Invention

[0009] According to a gas sensor or the like according to one aspect of the present disclosure, the identification accuracy when used for identifying a chemical substance or the like can be improved.

Brief Description of the Drawings

[0010]

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DETAILED DESCRIPTION OF THE INVENTION

[0011] (Background Leading to an Aspect of the Present Disclosure) In a gas sensor including a sensitive part composed of an adsorbent or the like, for example, when the sensitive part adsorbs a chemical substance in a gas and expands, electrical characteristics such as the electrical resistance of the sensitive part change. By detecting such electrical characteristics such as electrical resistance using an electrode electrically connected to the sensitive part, a chemical substance in the gas is detected.

[0012] Patent Document 1 discloses a chemical sensor element including a detection material containing a polysiloxane compound. When a polysiloxane compound is used for the adsorbent of the sensitive part of a gas sensor as in the chemical sensor element described in the examples of Patent Document 1, for example, a polysiloxane compound having a hydrocarbon group such as a methyl group and a phenyl group in the side chain is used for the adsorbent. However, in a gas sensor including a sensitive part having a polysiloxane compound having a hydrocarbon group in the side chain as an adsorbent, when identifying a chemical substance using the gas sensor, there are also chemical substances that are difficult to identify. The inventors of the present invention have found that when identifying a chemical substance using a gas sensor including a sensitive part having a polysiloxane compound having a hydrocarbon group in the side chain as an adsorbent, although the identification accuracy of hydrogen bond acceptor molecules is high among chemical substances, the identification accuracy of hydrogen bond donor molecules is low. The identification accuracy of a chemical substance by a gas sensor is considered to be related to the magnitude of the change in the electrical characteristics of the sensitive part. For example, when the interaction between a hydrogen bond donor molecule and the sensitive part is weak, it is difficult for the hydrogen bond donor molecule to be adsorbed to the sensitive part. As a result, the change in the electrical characteristics of the sensitive part becomes small, and it is considered that the identification accuracy when identifying a hydrogen bond donor molecule using the gas sensor decreases.

[0013] Therefore, the present disclosure provides a gas sensor capable of improving the identification accuracy by improving the identification accuracy of hydrogen bond donor molecules when used for identifying chemical substances and the like.

[0014] (Summary of the Present Disclosure) The summary of one aspect of the present disclosure is as follows.

[0015] A gas sensor according to one aspect of the present disclosure includes a sensing part and a pair of electrodes each electrically connected to the sensing part. The sensing part has a conductive material and a polymer having a siloxane bond as a main chain structure, and the polymer has a cyano group in a side chain.

[0016] Thereby, since the cyano group is a hydrogen bond acceptor, the cyano group easily interacts with a hydrogen bond donor molecule. As a result, when the gas contains a hydrogen bond donor molecule, the electrical characteristics such as the electrical resistance of the sensing part easily change. Therefore, the gas sensor can improve the discrimination accuracy when used for discriminating chemical substances and the like.

[0017] Further, for example, the polymer may have an alkylene group located between the cyano group and the main chain in the side chain.

[0018] Since the alkylene group is located between the cyano group and the main chain, the cyano group can be separated from the main chain of the polysiloxane compound, so that the cyano group and the hydrogen bond donor molecule more easily interact. Therefore, the discrimination accuracy when used for discriminating chemical substances and the like is further improved.

[0019] Further, for example, the polymer may have a cyanopropyl group in the side chain.

[0020] Thereby, since the distance between the main chain and the cyano group in the polymer is appropriately maintained, a gas sensor that achieves both the stability of the polysiloxane compound and the discrimination accuracy when used for discriminating chemical substances and the like can be realized.

[0021] Further, for example, the polymer may have at least one selected from the group consisting of a biscyanopropyl polysiloxane structure, a cyanopropylmethyl-dimethyl polysiloxane structure, a biscyanopropyl-cyanopropylphenyl polysiloxane structure, a cyanopropylphenyl-dimethyl polysiloxane structure, and a cyanopropylmethyl-phenylmethyl polysiloxane structure.

[0022] Thereby, a sensitive part can be realized with a polymer that is easy to synthesize.

[0023] Further, for example, in the thermogravimetric analysis of the polymer in an air atmosphere, the temperature at which a weight loss of 5% or more occurs with respect to the weight of the polymer at 35°C may be 250°C or higher.

[0024] Thereby, since the polymer has excellent thermal stability, deterioration of the detection accuracy of the gas sensor over time is less likely to occur.

[0025] Further, for example, the gas sensor may further include a detector that detects the electrical resistance of the sensitive part.

[0026] Thereby, the gas sensor can detect a chemical substance by detecting the electrical resistance, and the detected electrical resistance can be used to identify the chemical substance or the like.

[0027] Further, for example, the conductive material is conductive particles, and the average particle diameter of the conductive particles may be in the range of 10 nm or more and 300 nm or less.

[0028] Thereby, electrical properties such as the electrical resistance of the sensitive part are likely to change.

[0029] Further, for example, the ratio of the weight of the conductive material to the weight of the sensitive part may be in the range of 0.05 or more and 0.95 or less.

[0030] Thereby, since an electric current easily flows through the sensitive part, electrical properties such as the electrical resistance of the sensitive part can be easily detected.

[0031] Further, for example, the sensing part is in the form of a film.

[0032] Thereby, when a chemical substance is adsorbed on the sensing part, the electrical characteristics are likely to change.

[0033] Moreover, the gas sensor assembly according to one aspect of the present disclosure includes a plurality of gas sensors, and at least one of the plurality of gas sensors is the above gas sensor.

[0034] Thereby, since the gas sensor assembly includes the above gas sensor, the identification accuracy when used for identifying a chemical substance or the like can be improved.

[0035] In addition, the chemical substance identification method according to one aspect of the present disclosure is a chemical substance identification method using the above gas sensor assembly, and includes a step of acquiring a signal output from the gas sensor assembly exposed to a gas containing a chemical substance, a step of calculating a feature amount from the acquired signal, and a step of identifying the chemical substance contained in the gas based on the calculated feature amount.

[0036] Thereby, the chemical substance can be identified with high accuracy using the above gas sensor assembly.

[0037] It should be noted that the embodiments described below all show comprehensive or specific examples. The numerical values, shapes, materials, components, arrangement positions and connection forms of the components, steps, order of steps, etc. shown in the following embodiments are merely examples and are not intended to limit the present disclosure. In addition, among the components in the following embodiments, the components not described in the independent claims are described as optional components.

[0038] In addition, in this specification, terms indicating the relationship between elements such as parallel, terms indicating the shape of elements, and numerical ranges are not expressions representing only strict meanings, but are expressions meaning substantially equivalent ranges, for example, including differences of about several percent.

[0039] Also, each figure is not necessarily drawn precisely. In each figure, substantially the same configurations are denoted by the same reference numerals, and redundant descriptions are omitted or simplified.

[0040] Also, in this specification, "plan view" means the case where the gas sensor is viewed along the thickness direction of the substrate (in other words, the normal direction to the main surface of the substrate).

[0041] Also, in this specification, the terms "upper" and "lower" do not refer to the upward direction (e.g., vertically upward) and the downward direction (e.g., vertically downward) in absolute spatial recognition, but are used as terms defined by the relative positional relationship based on the arrangement configuration of each component member on the substrate. The same applies to the terms "upper surface" and "lower surface" of each component member.

[0042] (Embodiment) First, the gas sensor according to the embodiment will be described.

[0043] FIG. 1 is a plan view showing a schematic configuration of the gas sensor according to the present embodiment. FIG. 2 is a cross-sectional view of the gas sensor according to the present embodiment at the position indicated by line II-II in FIG. 1.

[0044] As shown in FIGS. 1 and 2, the gas sensor 100 according to the present embodiment includes a substrate 10, a first electrode 20 and a second electrode 25 which are a pair of electrodes, a sensitive portion 30, and an insulating layer 40. In FIG. 1, the planar view shapes of the first electrode 20 and the second electrode 25 covered by the sensitive portion 30 and the insulating layer 40 are indicated by broken lines.

[0045] The substrate 10 is a substrate that supports the first electrode 20 and the second electrode 25, the insulating layer 40, and the sensitive portion 30. The substrate 10 is, for example, plate-shaped. The substrate 10 has, for example, a rectangular or circular shape in plan view. In the present embodiment, the substrate 10 has a circular shape in plan view. The material of the substrate 10 is not particularly limited as long as it can maintain the shape of the gas sensor 100. The substrate 10 is, for example, a silicon substrate, a metal plate, a glass plate, or a polymer film.

[0046] The first electrode 20 is disposed on the substrate 10. The lower surface of the first electrode 20 is in contact with the upper surface of the substrate 10. The shape of the first electrode 20 is not particularly limited. The first electrode 20 has, for example, an arc or ring shape in plan view. In the present embodiment, the first electrode 20 has an arc shape in plan view and also has a strip shape.

[0047] The first electrode 20 includes a terminal portion 20a that is exposed outside the gas sensor 100. In FIG. 1, the terminal portion 20a extends outside the substrate 10 beyond the outer peripheral surface of the substrate 10. Note that the first electrode 20 may not have a portion that extends outside the substrate 10 beyond the outer peripheral surface of the substrate 10. For example, a through hole may be provided in the substrate 10, and a part of the lower surface of the first electrode 20 may be exposed outside the gas sensor 100 through the through hole. In this case, a part of the lower surface of the first electrode 20 corresponds to the terminal portion 20a.

[0048] The second electrode 25 is disposed on the substrate 10. The lower surface of the second electrode 25 is in contact with the upper surface of the substrate 10. The shape of the second electrode 25 is not particularly limited. The second electrode 25 surrounds, for example, the first electrode 20. The second electrode 25 is not in contact with the first electrode 20. The second electrode 25 has, for example, an arc or ring shape in plan view. In the present embodiment, the second electrode 25 has an arc shape in plan view and also has a strip shape.

[0049] The second electrode 25 includes a terminal portion 25a that is exposed outside the gas sensor 100. In FIG. 1, the terminal portion 25a extends outside the substrate 10 beyond the outer peripheral surface of the substrate 10. Note that the second electrode 25 may not have a portion that extends outside the substrate 10 beyond the outer peripheral surface of the substrate 10. For example, a through hole may be provided in the substrate 10, and a part of the lower surface of the second electrode 25 may be exposed outside the gas sensor 100 through the through hole. In this case, a part of the lower surface of the second electrode 25 corresponds to the terminal portion 25a.

[0050] Of the pair of electrodes, the first electrode 20 and the second electrode 25, the first electrode 20 is electrically connected to the sensing portion 30 through a first opening 45 described later, and the second electrode 25 is electrically connected to the sensing portion 30 through a second opening 46 described later. The first electrode 20 and the second electrode 25 are disposed opposite to each other with an insulating layer 40 interposed therebetween. Note that the insulating layer 40 may not be disposed between the first electrode 20 and the second electrode 25, and the sensing portion 30 may be disposed therebetween, and the first electrode 20 and the second electrode 25 may be disposed opposite to each other with the sensing portion 30 interposed therebetween.

[0051] The material of the first electrode 20 and the material of the second electrode 25 are not particularly limited as long as they are conductive materials. Each of the first electrode 20 and the second electrode 25 contains, for example, at least one metal selected from the group consisting of silver, gold, copper, platinum, and aluminum. The material of the first electrode 20 may be the same as the material of the second electrode 25.

[0052] Note that the shape of each of the first electrode 20 and the second electrode 25 is not limited to an arc shape in plan view, and may be, for example, a rod shape having an elongated rectangular shape in plan view or a comb shape in plan view. When the shape of each of the first electrode 20 and the second electrode 25 is a comb shape in plan view, for example, in the first electrode 20 and the second electrode 25, the teeth of one may be located between the teeth of the other.

[0053] The sensing portion 30 is an adsorption layer disposed above the substrate 10 so as to cover the first electrode 20, the second electrode 25, and the insulating layer 40. The sensing portion 30 is composed of members whose electrical characteristics such as electrical resistance change by adsorbing chemical substances such as volatile organic compounds in a gas. The sensing portion 30 covers the entire upper surface and the entire side surface of the insulating layer 40. The sensing portion 30 may only partially cover the upper surface and the side surface of the insulating layer 40. The sensing portion 30 may cover the entire upper surface of the substrate 10 or may partially cover the upper surface of the substrate 10. The sensing portion 30 may be in contact with the substrate 10 or may not be in contact with the substrate 10.

[0054] The sensing part 30 is in contact with the first electrode 20 through the first opening 45 and is in contact with the second electrode 25 through the second opening 46. Therefore, when a voltage is applied to the first electrode 20 and the second electrode 25, a current flows through the sensing part 30. Thereby, electrical characteristics such as the electrical resistance of the sensing part 30 can be detected.

[0055] The sensing part 30 is, for example, in a film shape. Thereby, when a chemical substance is adsorbed on the sensing part 30, the electrical characteristics are likely to change. The surface of the sensing part 30 on the side opposite to the substrate 10 side, that is, the upper surface of the sensing part 30 is exposed. The upper surface of the sensing part 30 is, for example, a flat plane, but may also be a curved surface. The thickness of the sensing part 30 is determined according to the type of gas to be detected, the composition of the sensing part 30, and the like. The thickness of the sensing part 30 is, for example, in the range of 0.1 μm or more and 10 μm or less. The shape of the sensing part 30 is not particularly limited. The sensing part 30 has, for example, a circular or ring shape in plan view. In the present embodiment, the sensing part 30 has a ring shape in plan view. Also, the sensing part 30 may be porous. The area of the sensing part 30 in plan view is, for example, 0.002 mm 2 or more and 50 mm 2 or less.

[0056] The sensing part 30 has a polysiloxane compound as a conductive material and an adsorbent. In this specification, the polysiloxane compound is an example of a polymer. Since the sensing part 30 has a conductive material, a current can flow through the sensing part 30. By flowing a current through the sensing part 30, electrical characteristics such as the electrical resistance of the sensing part 30 can be detected. In the sensing part 30, for example, the conductive material is dispersed in the adsorbent.

[0057] The conductive material contained in the sensing unit 30 is, for example, particles of a conductive material (i.e., conductive particles). The average particle size of the conductive material particles may be in the range of 10 nm or more and 300 nm or less. The "average particle size" can be measured by the following method. Observe the surface or cross-section of the sensing unit 30 with an electron microscope, and measure the diameters of any number of particles (e.g., 50 particles) contained in the sensing unit 30. The average particle size is determined by the average value calculated using the obtained measurement values. The diameter of a circle having an area equal to the area of the particles observed with the electron microscope can be regarded as the particle size. Note that the conductive material may be a conductive material having a shape other than particles, such as fibers of the conductive material.

[0058] The conductive material is not particularly limited as long as it has conductivity. The conductive material includes, for example, at least one selected from the group consisting of carbon materials, conductive polymers, metal materials, metal oxides, semiconductor materials, superconductors, and complex compounds.

[0059] The carbon material includes, for example, at least one selected from the group consisting of carbon black, graphite, coke, carbon nanotubes, graphene, and fullerenes. The conductive polymer includes, for example, at least one selected from the group consisting of polyaniline, polythiophene, polypyrrole, and polyacetylene. The metal material includes, for example, at least one selected from the group consisting of silver, gold, copper, platinum, and aluminum. The metal oxide includes, for example, at least one selected from the group consisting of indium oxide, tin oxide, tungsten oxide, zinc oxide, and titanium oxide. The semiconductor material includes, for example, at least one selected from the group consisting of silicon, gallium arsenide, indium phosphide, and molybdenum sulfide. The superconductor includes, for example, at least one selected from the group consisting of YBa2Cu3O7 and Tl2Ba2Ca2Cu3O 10 and at least one selected from the group consisting of. The complex compound includes, for example, at least one selected from the group consisting of a complex compound of tetramethyl paraphenylenediamine and chloranil, a complex compound of tetracyanoquinodimethane and an alkali metal, a complex compound of tetrathiafulvalene and a halogen, a complex compound of iridium and a halocarbonyl compound, and tetracyano platinum.

[0060] The conductive material includes, for example, carbon black. When the conductive material includes carbon black, the electrical properties such as the electrical resistance of the sensing portion 30 are likely to change. Therefore, when the gas sensor 100 is used for identifying chemical substances, the identification accuracy can be improved.

[0061] The ratio of the weight of the conductive material to the weight of the sensing portion 30 may be any ratio as long as a current can flow through the sensing portion 30 by a pair of electrodes due to the continuity of the conductive material. For example, it may be in the range of 0.05 or more and 0.95 or less, or may be in the range of 0.25 or more and 0.95 or less. Thereby, current can easily flow from the first electrode 20 or the second electrode 25 to the sensing portion 30. Therefore, the electrical properties such as the electrical resistance of the sensing portion 30 can be easily detected.

[0062] The polysiloxane compound adsorbs chemical substances such as volatile organic compounds in the gas. When the polysiloxane compound adsorbs the chemical substance in the gas, the volume of the sensing portion 30 changes. The polysiloxane compound has a siloxane bond as a main chain structure. That is, the polysiloxane compound has a polysiloxane structure as a main chain structure. The polysiloxane compound may have a linear polysiloxane structure as a main chain structure.

[0063] In addition, the polysiloxane compound has a cyano group in the side chain. Since the cyano group is a hydrogen bond acceptor, the cyano group easily interacts with a hydrogen bond donor molecule, and when the gas contains a hydrogen bond donor molecule, the electrical properties such as the electrical resistance of the sensing portion 30 are likely to change. Therefore, when the gas sensor 100 is used to identify chemical substances or the like, the identification accuracy can be improved.

[0064] The hydrogen bond donor molecule is, for example, a molecule having hydrogen capable of forming a hydrogen bond. The hydrogen bond donor molecule is, for example, an organic compound having at least one of an O-H bond, an N-H bond, and an S-H bond.

[0065] In addition, the polysiloxane compound has an alkylene group in the side chain that is located between the cyano group and the main chain of the polysiloxane compound. For example, one end of the alkylene group is bonded to the silicon atom of the main chain of the polysiloxane compound, and the other end of the alkylene group is bonded to the cyano group. Thereby, since the cyano group can be separated from the main chain of the polysiloxane compound, the cyano group and the hydrogen bond donor molecule can more easily interact with each other. Also, generally, the main chain of a linear polysiloxane structure is a helical structure, and the side chain of the polysiloxane compound extends outside the helical structure. Since the polysiloxane compound has a linear polysiloxane structure as the main chain structure and has an alkylene group in the side chain, the cyano group is further extended outside the helical structure, so that the cyano group and the hydrogen bond donor molecule can more easily interact with each other. Note that the polysiloxane compound may not have an alkylene group in the side chain.

[0066] The number of carbon atoms of the alkylene group is 1 or more, and may be 1 or more and 10 or less, or may be 2 or more and 5 or less. Also, the number of carbon atoms of the alkylene group may be 3. That is, the polysiloxane compound may have a cyanopropyl group in the side chain. Thereby, since the distance between the main chain and the cyano group in the polysiloxane compound is appropriately maintained, the gas sensor 100 that achieves both the stability of the polysiloxane compound and the discrimination accuracy when used for discrimination of chemical substances and the like can be realized. Examples of the siloxane structure (repeating unit structure in the polysiloxane structure) included in such a polysiloxane compound having a side chain include a biscyanopropylsiloxane structure, a cyanopropylmethyl structure, and a cyanopropylphenylsiloxane structure.

[0067] Note that the polysiloxane compound only needs to have a cyano group and an alkylene group in at least a part of the side chains, and the polysiloxane compound may have other substituents such as a hydrocarbon group in a part of the side chains. Also, at least one hydrogen atom of the alkylene group may be substituted with a substituent such as a hydrocarbon group or a functional group containing a hetero element or an atom other than a hydrogen atom such as a halogen atom.

[0068] Such a polysiloxane compound having a cyano group and an alkylene group in the side chain may specifically have at least one selected from the group consisting of a biscyanopropyl polysiloxane structure, a cyanopropylmethyl-dimethyl polysiloxane structure, a biscyanopropyl-cyanopropylphenyl polysiloxane structure, a cyanopropylphenyl-dimethyl polysiloxane structure, and a cyanopropylmethyl-phenylmethyl polysiloxane structure. Thereby, the sensitive part 30 can be realized by a polysiloxane compound that is easy to synthesize.

[0069] Here, the description of the "cyanopropylmethyl-dimethyl polysiloxane structure" means the polysiloxane structure of a copolymer of cyanopropylmethylsiloxane and dimethylsiloxane, and the same applies to other polysiloxane structures. When the polysiloxane structure includes a copolymer, the copolymer may be a random copolymer, a block copolymer, or an alternating copolymer.

[0070] The polysiloxane compound may be a commercially available material. Also, the polysiloxane compound may be synthesized by polymerizing alkoxysilanes such as dialkoxysilane, which is a unit of the siloxane bond of the polysiloxane compound, by a condensation reaction.

[0071] In the thermogravimetric analysis of the polysiloxane compound in an air atmosphere, the temperature at which a weight loss of 5% or more occurs with respect to the weight of the polysiloxane compound at 35°C may be 250°C or higher. As a result, since the polysiloxane compound has excellent thermal stability, it is less likely to cause deterioration of the detection accuracy of the gas sensor 100 over time, for example, an increase in noise in the detection signal. Also, even when heated during the drying of the solvent in the formation of the sensing part 30 described later, the sensing part 30 is less likely to deteriorate, and the detection accuracy of the gas sensor 100 can be improved. From the viewpoint of further enhancing the thermal stability of the polysiloxane compound, in the thermogravimetric analysis of the polysiloxane compound in an air atmosphere, the temperature at which a weight loss of 5% or more occurs with respect to the weight of the polysiloxane compound at 35°C may be 300°C or higher. The thermogravimetric analysis is performed, for example, using a thermogravimetric analyzer under an air atmosphere at a heating rate of 10°C / min from 35°C to 400°C.

[0072] The ratio of the weight of the polysiloxane compound to the weight of the sensing part 30 is determined according to the type of gas to be detected, the type of conductive material, etc. The ratio of the weight of the polysiloxane compound to the weight of the sensing part 30 may be in the range of 0.05 or more and 0.95 or less.

[0073] The sensing part 30 may have an adsorbent that adsorbs chemical substances in the gas in addition to the polysiloxane compound.

[0074] Examples of the adsorbent other than the polysiloxane compound include materials commercially available as the stationary phase of a column for gas chromatography. The adsorbent other than the polysiloxane compound contains, for example, at least one selected from the group consisting of polymer materials and low molecular weight materials. The organic adsorbent contains, for example, at least one selected from the group consisting of polyalkylene glycols, polyesters, silicones other than the polysiloxane compounds exemplified above, glycerols, nitriles, dicarboxylic acid monoesters, and aliphatic amines.

[0075] Polyalkylene glycols include, for example, polyethylene glycol. Polyesters include at least one selected from the group consisting of, for example, poly(diethylene glycol adipate) and poly(ethylene succinate). Silicones include at least one selected from the group consisting of, for example, dimethylpolysiloxane, phenylmethylpolysiloxane, diphenylpolysiloxane, phenylmethyl-dimethylpolysiloxane, phenylmethyl-diphenylpolysiloxane, trifluoropropylmethylpolysiloxane, and cyanopolysiloxane. Glycerols include, for example, diglycerol. Nitriles include at least one selected from the group consisting of, for example, N,N-bis(2-cyanoethyl)formamide and 1,2,3-tris(2-cyanoethoxy)propane. Dicarboxylic acid monoesters include at least one selected from the group consisting of, for example, nitroterephthalic acid-modified polyethylene glycol and diethylene glycol succinate. Aliphatic amines include, for example, tetrahydroxyethylethylenediamine.

[0076] The sensitive part 30 may further contain an additive. Examples of the additive include a dispersant for improving the dispersibility of the conductive material.

[0077] The ratio of the weight of the polysiloxane compound to the weight of the sensitive part 30 excluding the conductive material may be 0.85 or more, or may be 0.95 or more.

[0078] The insulating layer 40 covers each of the first electrode 20 and the second electrode 25. The insulating layer 40 is in contact with each of the first electrode 20 and the second electrode 25. The insulating layer 40 may cover the entire upper surface of the substrate 10. The insulating layer 40 may partially cover the upper surface of the substrate 10.

[0079] The insulating layer 40 has a first opening 45 and a second opening 46. The first opening 45 exposes a part of the surface of the first electrode 20. The first opening 45 overlaps the first electrode 20 in a plan view. For example, the entire first opening 45 overlaps the first electrode 20 in a plan view. The first opening 45 penetrates the insulating layer 40 in the thickness direction. Except for the first opening 45, the insulating layer 40 covers the entire upper surface and the entire side surface of the first electrode 20.

[0080] The insulating layer 40 may have a plurality of first openings 45. The number of the plurality of first openings 45 is not particularly limited.

[0081] The second opening 46 exposes a part of the surface of the second electrode 25. The second opening 46 overlaps the second electrode 25 in a plan view. For example, the entire second opening 46 overlaps the second electrode 25 in a plan view. The second opening 46 penetrates the insulating layer 40 in the thickness direction. Except for the second opening 46, the insulating layer 40 covers the entire upper surface and the entire side surface of the second electrode 25.

[0082] The insulating layer 40 may have a plurality of second openings 46. The number of the plurality of second openings 46 is not particularly limited.

[0083] The shape of each of the first opening 45 and the second opening 46 is not particularly limited. Each of the first opening 45 and the second opening 46 has, for example, a circular or rectangular shape in a plan view. As described above, the first electrode 20 and the second electrode 25, which are a pair of electrodes, are each covered by the insulating layer 40 and are electrically connected to the sensing portion 30 through the first opening 45 and the second opening 46. In this way, since the first electrode 20 and the second electrode 25 are covered by the insulating layer 40, the current path in the sensing portion 30 is reduced, and thus the electrical characteristics such as the electrical resistance of the sensing portion 30 detected change more significantly due to the change in the current path.

[0084] The material of the insulating layer 40 is not particularly limited as long as it has insulating properties. The material of the insulating layer 40 includes, for example, at least one selected from the group consisting of insulating polymer materials, ceramics, and glass. The insulating polymer material includes, for example, at least one selected from the group consisting of polyethylene, polypropylene, polystyrene, polybutadiene, epoxy resin, fluororesin, polyvinyl chloride, polymethyl methacrylate, polyamide, polyimide, polycarbonate, cellulose acetate, polyethylene terephthalate, polyethylene naphthalate, polyethersulfone, polyphenylene sulfide, and polyetherimide. The ceramics includes, for example, at least one selected from the group consisting of SiO2, Si3N4, Al2O3, Zr2O3, and MgO.

[0085] Note that the gas sensor 100 may not include the insulating layer 40. In this case, for example, the upper surfaces and side surfaces of the first electrode 20 and the second electrode 25 are in contact with and cover the sensitive portion 30.

[0086] As shown in FIGS. 1 and 2, the gas sensor 100 may further include a first wall portion 11. The first wall portion 11 surrounds the surface of the substrate 10. The first wall portion 11 has a ring shape in plan view. The first wall portion 11 extends upward (in the thickness direction of the substrate 10) from the substrate 10. The surface of the substrate 10 surrounded by the first wall portion 11 has, for example, a circular shape. The first wall portion 11 is connected to the outer peripheral edge of the substrate 10. The first wall portion 11 may be integrated with the substrate 10. In other words, the first wall portion 11 may be a part of the substrate 10. The first wall portion 11 extends above the sensitive portion 30. The inner peripheral surface of the first wall portion 11 is in contact with the sensitive portion 30.

[0087] Further, the gas sensor 100 may further include a second wall portion 12. The second wall portion 12 extends upward from a part of the surface of the substrate 10. The shape of the second wall portion 12 is, for example, cylindrical or tubular. The second wall portion 12 is connected to a part of the surface of the substrate 10. The second wall portion 12 may be integrated with the substrate 10. In other words, the second wall portion 12 may be a part of the substrate 10. The second wall portion 12 is surrounded by the first electrode 20 and the second electrode 25. The second wall portion 12 extends above the sensing portion 30. The outer peripheral surface of the second wall portion 12 is in contact with the sensing portion 30. The sensing portion 30 is disposed between the first wall portion 11 and the second wall portion 12.

[0088] The material of each of the first wall portion 11 and the second wall portion 12 is not particularly limited. Each of the material of the first wall portion 11 and the material of the second wall portion 12 may have hydrophobicity. Each of the material of the first wall portion 11 and the material of the second wall portion 12 includes, for example, a hydrophobic polymer material. The hydrophobic polymer material includes, for example, at least one selected from the group consisting of polyethylene, polypropylene, polystyrene, polybutadiene, epoxy resin, and fluororesin. The material of the first wall portion 11 may be the same as the material of the second wall portion 12. Each of the material of the first wall portion 11 and the material of the second wall portion 12 may be the same as the material of the substrate 10.

[0089] Next, a method for manufacturing the gas sensor 100 will be described.

[0090] First, each of the first electrode 20 and the second electrode 25 is disposed on the substrate 10. The method for disposing each of the first electrode 20 and the second electrode 25 on the substrate 10 is not particularly limited. For example, by depositing a metal on the substrate 10, each of the first electrode 20 and the second electrode 25 can be disposed on the substrate 10. Examples of the method for depositing the metal include sputtering method, ion plating method, electron beam evaporation method, vacuum evaporation method, chemical vapor deposition method, chemical vapor phase method, and the like.

[0091] Next, an insulating layer 40 is formed. The method for forming the insulating layer 40 is not particularly limited. The insulating layer 40 can be formed, for example, by the following method. A dispersion containing an insulating polymer material is prepared. The dispersion is obtained by dispersing the insulating polymer material in a coating solvent. The coating solvent contains at least one selected from the group consisting of, for example, water and organic solvents.

[0092] The dispersion is applied onto the substrate 10 in a desired pattern so as to cover each of the first electrode 20 and the second electrode 25, thereby forming a coating film. Examples of the method for forming the coating film include a printing method. By drying the coating film, a precursor layer of the insulating layer 40 is formed.

[0093] Next, a first opening 45 and a second opening 46 are formed in the precursor layer of the insulating layer 40. Thereby, the insulating layer 40 can be formed. The method for forming the first opening 45 and the second opening 46 is not particularly limited. The first opening 45 and the second opening 46 can be formed, for example, by irradiating an ion beam onto the precursor layer of the insulating layer 40. The first opening 45 and the second opening 46 can also be formed, for example, by etching the precursor layer of the insulating layer 40.

[0094] Next, the sensing unit 30 is fabricated. First, a coating solution containing a conductive material and a polysiloxane compound is prepared. The coating solution is obtained by dispersing the conductive material and the polysiloxane compound in a coating solvent. Also, from the viewpoint of forming a uniform coating film, the polysiloxane compound may be dissolved in the coating solvent. Further, the conductive material may be dissolved in the coating solvent. The coating solvent used in fabricating the sensing unit 30 contains at least one selected from the group consisting of, for example, water and organic solvents. The organic solvent contains at least one selected from the group consisting of, for example, dimethyl sulfoxide, dimethylformamide, toluene, chloroform, acetone, acetonitrile, methanol, ethanol, isopropanol, tetrahydrofuran, ethyl acetate, butyl acetate, and hexyl acetate. Next, the coating solution is applied onto the insulating layer 40 to form a coating film. The sensing unit 30 is formed by drying the coating film. The coating film is dried, for example, by heating at 50°C or higher and 200°C or lower.

[0095] The sensing unit 30 formed by the above method usually has a uniform thickness in the circumferential direction on the surface of the substrate 10. In the gas sensor 100 according to the present embodiment, the first electrode 20 and the second electrode 25 have an arc or ring shape in plan view. Therefore, the sensing unit 30 has a uniform thickness along the first electrode 20. Similarly, the sensing unit 30 has a uniform thickness along the second electrode 25. Thereby, the electrical resistance of the sensing unit 30 can be stably detected.

[0096] When the gas sensor 100 includes the first wall portion 11 and the second wall portion 12, the dispersion liquid can be uniformly applied. That is, the thickness of the sensing unit 30 can be made uniform. When each of the first wall portion 11 and the second wall portion 12 has hydrophobicity, the surface tension generated between the dispersion liquid and each of the first wall portion 11 and the second wall portion 12 is low. Therefore, the thickness of the sensing unit 30 can be made more uniform.

[0097] Next, an example of a method for detecting a chemical substance in a gas using the gas sensor 100 will be described.

[0098] FIG. 3 is a block diagram showing a characteristic configuration of the gas sensor 100. As shown in FIG. 3, the gas sensor 100 may further include a detector 60.

[0099] The detector 60 is, for example, an electric resistance meter. Each of the terminal portions 20a of the first electrode 20 and the terminal portion 25a of the second electrode 25 is connected to the detector 60. The detector 60 can apply a voltage to the first electrode 20 and the second electrode 25, for example. When the detector 60 applies a voltage to the first electrode 20 and the second electrode 25, a current flows through the sensing portion 30. The detector 60 detects (or measures, in other words) the electrical resistance of the sensing portion 30 based on the current flowing through the sensing portion 30. The detector 60 outputs the detected result to an external device as a detection signal, for example. Further, the detector 60 may have a display unit such as a display or a meter that displays the detected result.

[0100] In the detection of chemical substances using the gas sensor 100, first, the gas sensor 100 is placed in a gas atmosphere. The gas contains, for example, a chemical substance including at least one selected from the group consisting of volatile organic compounds and inorganic gases. Examples of volatile organic compounds include ketones, amines, alcohols, aromatic hydrocarbons, aldehydes, esters, organic acids, methyl mercaptan, disulfides, and pyrrole. Examples of inorganic gases include hydrogen sulfide, sulfur dioxide, and carbon disulfide.

[0101] When a chemical substance in the gas comes into contact with the gas sensor 100, the polysiloxane compound in the sensitive part 30 adsorbs the chemical substance. When the polysiloxane compound adsorbs the chemical substance, the volume of the sensitive part 30 changes. Specifically, the sensitive part 30 expands or contracts. When the volume of the sensitive part 30 changes, the positional relationship between the conductive materials in the sensitive part 30 changes. When the positional relationship between the conductive materials changes, the current path changes, and the electrical characteristics such as electrical resistance change. For example, when the sensitive part 30 adsorbs a chemical substance, the sensitive part 30 expands, the contact between the conductive materials decreases, and the electrical resistance of the sensitive part 30 increases. The detector 60 detects the electrical characteristics such as the electrical resistance of the sensitive part 30. Thereby, the gas sensor 100 can detect the chemical substance in the gas.

[0102] Note that the gas sensor 100 may not include the detector 60, and the terminal part 20a of the first electrode 20 and the terminal part 25a of the second electrode 25 may be connected to an external detector to detect the chemical substance in the gas as described above.

[0103] Note that the gas sensor 100 may detect the chemical substance from the value of the current flowing between the first electrode 20 and the second electrode 25 in a state where a constant voltage is applied between the first electrode 20 and the second electrode 25. The gas sensor 100 may detect the chemical substance from the amount of voltage drop between the first electrode 20 and the second electrode 25 in a state where a constant current is passed through the sensitive part 30. The detector 60 is, for example, a current measuring device or a voltage measuring device that measures current or voltage as described above. The detector 60 may output an index of the electrical resistance of the sensitive part 30 as a current signal or a voltage signal. That is, the gas sensor 100 may detect the chemical substance based on an index that changes according to the change in the electrical resistance of the sensitive part 30.

[0104] Next, the gas sensor assembly according to the present embodiment will be described.

[0105] FIG. 4 is a plan view showing a schematic configuration of the gas sensor assembly according to the present embodiment. As shown in FIG. 4, the gas sensor assembly 200 includes a plurality of gas sensors 100 and a substrate 210.

[0106] The substrate 210 is, for example, plate-shaped. The substrate 210 has, for example, a rectangular shape in plan view. The substrate 210 has two pairs of end faces facing each other.

[0107] A plurality of the above gas sensors 100 are arranged on the substrate 210. At least two gas sensors 100 selected from the plurality of gas sensors 100 may each have a sensitive portion 30 made of a different material. Specifically, the types of polysiloxane compounds contained in the sensitive portions 30 of at least two gas sensors 100 selected from the plurality of gas sensors 100 may be different from each other. Also, the types of polysiloxane compounds contained in the sensitive portions 30 of all the plurality of gas sensors 100 may be different from each other. In this case, two or more gas sensors 100 each having a sensitive portion 30 containing polysiloxane compounds of different types exhibit different behaviors with respect to a specific chemical substance. For example, a chemical substance that is difficult to adsorb to a specific gas sensor 100 is likely to be adsorbed to another gas sensor 100. Thereby, the discrimination accuracy when using the gas sensor assembly 200 (that is, a plurality of gas sensors 100) for discriminating chemical substances or the like can be improved.

[0108] The number of the plurality of gas sensors 100 included in the gas sensor assembly 200 is not particularly limited. The number of the plurality of gas sensors 100 included in the gas sensor assembly 200 is set according to the type of chemical substance to be detected or discriminated. As shown in FIG. 4, the number of the plurality of gas sensors 100 is, for example, 16. In FIG. 4, four gas sensors 100 are arranged in a row in the direction from one end face to the other end face of the substrate 210. Four gas sensors 100 are arranged in a row in the direction from one end face to the other end face of the other pair of end faces of the substrate 210. That is, the plurality of gas sensors 100 are arranged in a 4×4 matrix. Note that the arrangement of the plurality of gas sensors 100 is not particularly limited.

[0109] In addition, the plurality of gas sensors provided in the gas sensor assembly 200 only needs to include at least one gas sensor 100. For example, in addition to the gas sensor 100, the gas sensor assembly 200 may include a gas sensor having a sensitive part with an adsorbent other than the polysiloxane compound instead of the above polysiloxane compound of the gas sensor 100. Examples of the adsorbent other than the polysiloxane compound include the adsorbents other than the polysiloxane compound exemplified above.

[0110] Next, an example of a method for identifying chemical substances in a gas using the gas sensor assembly 200 according to the present embodiment will be described. FIG. 5 is a flowchart of a chemical substance identification method using the gas sensor assembly 200 according to the present embodiment.

[0111] First, the gas sensor assembly 200 is exposed to a gas containing a chemical substance (step S11). For example, the gas sensor assembly 200 is placed in a stream of an inert gas such as nitrogen. Then, a chemical substance is mixed into the stream for a certain period of time. Alternatively, the gas sensor assembly 200 may be placed in a sealed container connected to a pipe, and an inert gas such as nitrogen and a gas containing a chemical substance may be exclusively introduced into the sealed container through the pipe. In this way, the gas sensor assembly 200 is exposed to the gas containing the chemical substance. The gas contains, for example, a volatile organic compound as the chemical substance. The volatile organic compound may be a hydrogen bond donor molecule.

[0112] Next, time-varying data output from the gas sensor assembly 200 exposed to the gas containing the chemical substance is acquired (step S12). The time-varying data is an example of a signal output from the gas sensor assembly. For example, the detector 60 acquires the electrical resistance or the like of the sensitive part 30 in a period including before and after mixing the chemical substance, and outputs it as a signal including the time-varying data. The output signal is, for example, a voltage signal or a current signal. Thereby, for example, the time-varying data of the electrical resistance or the like of the sensitive part 30 output from the detector 60 for each of the plurality of gas sensors 100 can be acquired.

[0113] Next, feature quantities for identifying the chemical substance are calculated from the time-dependent change data obtained in step S12 (step S13). Specifically, feature quantities of the time-dependent change data corresponding to each of the plurality of gas sensors 100 are calculated from the obtained time-dependent change data. The feature quantity is, for example, the difference or ratio between the electrical resistance while the chemical substance is mixed in and the electrical resistance while the chemical substance is not mixed in. The feature quantity is not limited to the difference or ratio of the electrical resistance, and may be the amount of change per unit time of the electrical resistance when the mixing of the chemical substance starts or when the mixing of the chemical substance ends, that is, the slope of the electrical resistance in the time-dependent change data. Further, a feature quantity based on the waveform of the time-dependent change data obtained when the chemical substance is mixed in (for example, an eigenvalue obtained by principal component analysis of the time-dependent change data) may be used. Further, depending on the type of the output signal, a value such as voltage or current may be used for calculating the feature quantity instead of the electrical resistance. The number of calculated feature quantities is not particularly limited, and may be one for each gas sensor 100, or may be a plurality for each gas sensor 100. Thus, for identifying the chemical substance, feature quantities related to the change in the electrical characteristics of the sensitive portion 30 of the gas sensor 100 due to the mixing of the chemical substance can be used.

[0114] Next, using a logical model for identifying the chemical substance, the chemical substance contained in the gas is identified based on the feature quantity calculated in step S13 (step S14). For example, using a computer or the like, the feature quantity calculated from the time-dependent change data which is the detection result of the gas sensor assembly 200 (that is, the feature quantity corresponding to each of the plurality of gas sensors 100) is input to the logical model used for identifying the chemical substance, thereby identifying the chemical substance. The logical model is a learned logical model learned in advance by machine learning. The logical model outputs, for example, which chemical substance among a plurality of chemical substances to be identified as the identification result. The plurality of chemical substances to be identified include, for example, hydrogen bond donor molecules.

[0115] The logical model used for identifying chemical substances is constructed, for example, by machine learning using feature quantities calculated for known chemical substances with the use of a computer or the like. For example, for each of a plurality of chemical substances to be identified, feature quantities corresponding to each of the plurality of gas sensors 100 are calculated in the same manner as in step S13 described above. That is, for each chemical substance, the number of feature quantities equal to the number of the plurality of gas sensors 100 is calculated. Then, the logical model is constructed by performing machine learning using the calculated feature quantities as explanatory variables in teacher data. The method used for constructing the logical model in machine learning is not particularly limited. For example, random forest is used for constructing the logical model in machine learning. A neural network, a support vector machine, or a self-organizing map may be used for constructing the logical model in machine learning.

[0116] Note that the method for identifying chemical substances is not limited to the above method, and a discriminant analysis method other than machine learning such as cluster analysis, genetic algorithm, and k-means method may be used. Further, the above-described identification method may be applied to odor identification or intensity detection using the gas sensor assembly 200.

[0117] Further, the gas sensor assembly 200 may include a processing unit that performs the processing from step S12 to step S14. The processing unit is realized by a microcomputer or a processor or the like that incorporates a program for performing the above processing.

[0118] Further, instead of the gas sensor assembly 200, one or more gas sensors 100 may be used to identify chemical substances by the above-described method.

Example

[0119] The present disclosure will be specifically described based on examples. However, the present disclosure is not limited by the following examples in any way. In the following description of the examples, benzaldehyde may be denoted as "Bz", nonanal may be denoted as "Nn", and pyrrole may be denoted as "Pr".

[0120] (Fabrication of Gas Sensor) [Sample 1] A gas sensor of Sample 1 was fabricated to have the same structure as the gas sensor 100 shown in FIGS. 1 and 2. Specifically, first, each of the first electrode and the second electrode was disposed on a substrate having a circular shape in plan view. Platinum was used for each of the first electrode and the second electrode, and a silicon substrate was used as the substrate.

[0121] Next, each of the first electrode and the second electrode was coated with a precursor layer of an insulating layer. SiO2 was used as the material of the precursor layer. By providing four first openings and four second openings in the precursor layer, an insulating layer was fabricated. Each of the first opening and the second opening had a circular shape in plan view. The diameters of the first opening and the second opening in plan view were each 5 μm.

[0122] Next, a coating liquid containing a conductive material and an adsorbent as materials of the sensitive portion was applied to the insulating layer in a circular shape to form a coating film. As the solvent of the coating liquid, hexyl acetate and dimethylformamide were used. As the conductive material, carbon black was used. As the adsorbent, cyanopropylmethyl-dimethylpolysiloxane (manufactured by GL Sciences Inc., trade name OV-105), which is a polysiloxane compound having a cyanopropyl group in the side chain, was used. The sensitive portion was formed by drying the coating film at 140°C. The ratio of the weight of the conductive material to the weight of the sensitive portion was 0.5. Also, the diameter of the sensitive portion was 900 μm. In this way, the gas sensor of Sample 1 was obtained.

[0123] [Sample 2] A gas sensor was fabricated in the same manner as Sample 1 except that cyanopropylphenyl-dimethylpolysiloxane (manufactured by GL Sciences Inc., trade name OV-1701), which is a polysiloxane compound having a cyanopropyl group in the side chain, was used as the adsorbent of the sensitive portion, and the gas sensor of Sample 2 was obtained.

[0124] [Sample 3] A gas sensor was fabricated in the same manner as in Sample 1, except that cyanopropylmethyl-phenylmethylpolysiloxane (manufactured by GL Sciences Inc., trade name OV-225), which is a polysiloxane compound having a cyanopropyl group in the side chain, was used as the adsorbent of the sensing part, and the gas sensor of Sample 3 was obtained.

[0125] [Sample 4] A gas sensor was fabricated in the same manner as in Sample 1, except that bis(cyanopropyl)-cyanopropylphenylpolysiloxane (manufactured by Sigma-Aldrich, trade name SP-2330), which is a polysiloxane compound having a cyanopropyl group in the side chain, was used as the adsorbent of the sensing part, and the gas sensor of Sample 4 was obtained.

[0126] [Sample 5] A gas sensor was fabricated in the same manner as in Sample 1, except that bis(cyanopropyl)polysiloxane (manufactured by Sigma-Aldrich, trade name SP-2340), which is a polysiloxane compound having a cyanopropyl group in the side chain, was used as the adsorbent of the sensing part, and the gas sensor of Sample 5 was obtained.

[0127] [Sample 6] A gas sensor was fabricated in the same manner as in Sample 1, except that bis(cyanopropyl)polysiloxane (manufactured by GL Sciences Inc., trade name OV-275), which is a polysiloxane compound having a cyanopropyl group in the side chain, was used as the adsorbent of the sensing part, and the gas sensor of Sample 6 was obtained.

[0128] [Sample 7] A gas sensor was fabricated in the same manner as in Sample 1, except that dimethylpolysiloxane (manufactured by GL Sciences Inc., trade name OV-101), which is a polysiloxane compound whose side chain is composed of a hydrocarbon group, was used as the adsorbent of the sensing part, and the gas sensor of Sample 7 was obtained.

[0129] [Sample 8] A gas sensor was fabricated in the same manner as Sample 1, except that phenylmethyl-dimethylpolysiloxane (manufactured by GL Sciences Inc., phenyl ratio 10%, trade name OV-3), which is a polysiloxane compound having a hydrocarbon group as a side chain, was used as the adsorbent of the sensing part, and the gas sensor of Sample 8 was obtained.

[0130] [Sample 9] A gas sensor was fabricated in the same manner as Sample 1, except that phenylmethyl-dimethylpolysiloxane (manufactured by GL Sciences Inc., phenyl ratio 20%, trade name OV-7), which is a polysiloxane compound having a hydrocarbon group as a side chain, was used as the adsorbent of the sensing part, and the gas sensor of Sample 9 was obtained.

[0131] [Sample 10] A gas sensor was fabricated in the same manner as Sample 1, except that phenylmethyl-dimethylpolysiloxane (manufactured by GL Sciences Inc., phenyl ratio 50%, trade name OV-17), which is a polysiloxane compound having a hydrocarbon group as a side chain, was used as the adsorbent of the sensing part, and the gas sensor of Sample 10 was obtained.

[0132] [Sample 11] A gas sensor was fabricated in the same manner as Sample 1, except that phenylmethyl-diphenylpolysiloxane (manufactured by GL Sciences Inc., phenyl ratio 65%, trade name OV-22), which is a polysiloxane compound having a hydrocarbon group as a side chain, was used as the adsorbent of the sensing part, and the gas sensor of Sample 11 was obtained.

[0133] [Sample 12] A gas sensor was fabricated in the same manner as Sample 1, except that phenylmethyl-diphenylpolysiloxane (manufactured by GL Sciences Inc., phenyl ratio 75%, trade name OV-25), which is a polysiloxane compound having a hydrocarbon group as a side chain, was used as the adsorbent of the sensing part, and the gas sensor of Sample 12 was obtained.

[0134] [Sample 13] A gas sensor was fabricated in the same manner as in Sample 1, except that N,N-bis(2-cyanoethyl)formamide was used as the adsorbent for the sensitive part, and a gas sensor of Sample 13 was obtained.

[0135] (Thermogravimetric analysis) Thermogravimetric analysis was performed on the adsorbents of the sensitive parts in the gas sensors of Samples 1 to 13. Specifically, using a thermogravimetric analyzer, thermogravimetric analysis was carried out under an air atmosphere at a heating rate of 10 °C / min from 35 °C to 400 °C. The thermogravimetric analysis results for the adsorbents of the sensitive parts in the gas sensors of Samples 1 to 6 are shown in Figure 6. Also, the thermogravimetric analysis results for the adsorbents of the sensitive parts in the gas sensors of Samples 7 to 13 are shown in Figure 7. In Figures 6 and 7, the horizontal axis represents temperature, and the vertical axis represents the weight ratio with respect to the weight of the adsorbent at 35 °C.

[0136] As shown in Figures 6 and 7, for the adsorbents of the sensitive parts in the gas sensors of Samples 1 to 12, in all cases, the temperature at which a weight loss of 5% or more occurred with respect to the weight of the adsorbent at 35 °C was 250 °C or higher. In contrast, for the adsorbent of the sensitive part in the gas sensor of Sample 13, the temperature at which a weight loss of 5% or more occurred with respect to the weight of the adsorbent at 35 °C was less than 250 °C. Thus, the result was obtained that the polysiloxane compound, which is the adsorbent of the sensitive part in the gas sensors of Samples 1 to 12, has high thermal stability.

[0137] (Evaluation of changes in detection results) Regarding the gas sensor of Sample 5 and the gas sensor of Sample 13, the changes in the detection results of chemical substances in the gas were evaluated at 0 days (i.e., the day of gas sensor fabrication) and 6 months after gas sensor fabrication. The gas sensors were stored at room temperature under the atmosphere.

[0138] In the evaluation of the detection results, a detector for detecting the electrical resistance was connected to the gas sensor, and a detection signal of the electrical resistance of the gas sensor was obtained. Specifically, the gas sensor was placed in a nitrogen gas stream, and benzaldehyde was mixed as a chemical substance in the gas stream at a concentration of 2 ppm for 15 seconds, and the detection signal of the electrical resistance of the gas sensor was obtained from the detector while repeating flowing a nitrogen-only gas stream for 15 seconds. That is, data on the change over time of the electrical resistance of the gas sensor was obtained. The detection results of the gas sensor of Sample 5 are shown in FIG. 8, and the detection results of the gas sensor of Sample 13 are shown in FIG. 9. In FIGS. 8 and 9, the horizontal axis represents the elapsed time, and the vertical axis represents the intensity of the normalized detection signal (that is, an index of the electrical resistance of the sensitive part). Also, in FIGS. 8 and 9, the dashed-line graph shows the detection results on the 0th day after the production of the gas sensor, and the solid-line graph shows the detection results 6 months after the production of the gas sensor. Note that in FIGS. 8 and 9, for ease of viewing, the graph of the detection results 6 months later is shown slid upward.

[0139] As shown in FIG. 8, in the gas sensor of Sample 5, data on the change over time with little noise was obtained in both the detection results on the 0th day and 6 months after the production of the gas sensor. On the other hand, as shown in FIG. 9, in the gas sensor of Sample 13, data on the change over time with large noise was obtained in the detection results 6 months after the production of the gas sensor. Thus, it was found that the gas sensor of Sample 5 having a sensitive part including an adsorbent in which the temperature at which a weight loss of 5% or more occurs with respect to the weight of the adsorbent at 35 °C is 250 °C or higher can obtain detection results with little noise even when stored for a long period.

[0140] (Fabrication of Gas Sensor Assembly) Using the gas sensors of Samples 1 to 12 described above, a gas sensor assembly was fabricated.

[0141] [Sample 14] On a silicon substrate having a rectangular shape in plan view, one gas sensor each of Samples 1 to 6, that is, a total of six gas sensors, were arranged in a 2-row and 3-column matrix. In this way, a gas sensor assembly of Sample 14 was obtained. Further, a detector for detecting the electrical resistance was connected to each of the six gas sensors (that is, the gas sensors of Samples 1 to 6) provided in the gas sensor assembly of Sample 14. One detector was connected to one gas sensor.

[0142] [Sample 15] On a silicon substrate having a rectangular shape in plan view, one gas sensor each of Samples 7 to 12, that is, a total of six gas sensors, were arranged in a 2-row and 3-column matrix. In this way, a gas sensor assembly of Sample 15 was obtained. Further, a detector for detecting the electrical resistance was connected to each of the six gas sensors (that is, the gas sensors of Samples 7 to 12) provided in the gas sensor assembly of Sample 15. One detector was connected to one gas sensor.

[0143] (Identification of Chemical Substances) [Example 1] (1) Acquisition of Feature Quantities First, the gas sensor assembly of Sample 14 was placed in a nitrogen gas stream, and benzaldehyde was mixed as a chemical substance into the gas stream at a concentration of 2 ppm for 30 seconds. The electrical resistance of the gas sensor was acquired from the detector from 30 seconds before the start of the chemical substance mixing to 30 seconds after the end of the chemical substance mixing. As a result, for each of the sensitive parts of the gas sensors of Samples 1 to 6, time-dependent change data of the electrical resistance was acquired. For each of the six acquired time-dependent change data, the electrical resistance value a before the start of the chemical substance mixing, the electrical resistance value b during the chemical substance mixing, and the electrical resistance value c when a predetermined time had elapsed after the end of the chemical substance mixing were acquired. From the acquired electrical resistance values a, b, and c, a feature quantity R (R = b / (a / 2 + c / 2)), which is the ratio of the average value of the electrical resistance values a and b to the electrical resistance value c, was calculated. That is, for benzaldehyde, six feature quantities R were acquired as one set corresponding to each of the gas sensors of Samples 1 to 6.

[0144] The operation of obtaining this time-dependent change data was repeated 30 times, and for benzaldehyde, 30 sets of feature quantity R corresponding to each of the gas sensors from sample 1 to sample 6 were obtained.

[0145] Next, instead of benzaldehyde as the chemical substance, nonanal and pyrrole were used respectively, and the same operations as above were performed. As a result, for nonanal, 30 sets of feature quantity R corresponding to each of the gas sensors from sample 1 to sample 6 were obtained, and for pyrrole, 30 sets of feature quantity R corresponding to each of the gas sensors from sample 1 to sample 6 were obtained.

[0146] Among benzaldehyde, nonanal and pyrrole, benzaldehyde and nonanal are hydrogen bond acceptor molecules, and pyrrole is a hydrogen bond donor molecule.

[0147] (2) Construction of logical model Among the 30 sets of feature quantity R for each of benzaldehyde, nonanal and pyrrole obtained in the above “(1) Acquisition of feature quantity”, 5 randomly selected sets of feature quantity R were used to construct a logical model by machine learning. For the construction of the logical model in machine learning, a random forest using 6 feature quantity R corresponding to each of the gas sensors from sample 1 to sample 6 for conditional branching was used. In this way, by performing machine learning using 5 sets of feature quantity R for each of benzaldehyde, nonanal and pyrrole as explanatory variables in the training data, a random forest logical model for identifying chemical substances was constructed.

[0148] (3) Identification of chemical substances Of the 30 sets of feature quantities R for each of benzaldehyde, nonanal, and pyrrole obtained in the above “(1) Acquisition of feature quantities”, 25 sets of feature quantities R not used in the above “(2) Construction of logical model” were used to identify chemical substances. Specifically, the chemical substances were identified using the constructed logical model from the 25 sets of feature quantities R for each of benzaldehyde, nonanal, and pyrrole. That is, for each of benzaldehyde, nonanal, and pyrrole, the chemical substances were identified 25 times. The results of the identification are shown in Table 1.

[0149] In Table 1, in each cell, when the feature quantity R calculated from the detection result mixed with the chemical substance (Bz, Nn, or Pr) described at the top of the column where the cell is located was input, the number of times the cell was identified as the chemical substance (Bz, Nn, or Pr) described at the leftmost part of the row where the cell is located by the constructed logical model is described. That is, the numerical value of the cell where the chemical substances described at the top and the leftmost part are the same is the number of times the identification was correct, and the numerical value of the cell where the chemical substances described at the top and the leftmost part are different is the number of times the identification was incorrect. The same applies to Table 2 described later.

[0150]

Table 1

[0151] As shown in Table 1, in Example 1, for each of all three types of chemical substances, the mixed chemical substance and the identified chemical substance all matched 25 times. The ratio of the number of times a correct identification result was obtained (75 times) to the total number of times the chemical substances were identified (75 times) was 100%. Thus, when identifying chemical substances using the gas sensors of Samples 1 to 6 containing a polysiloxane compound having a cyanopropyl group in the side chain as the adsorbent of the sensitive part, good identification results were obtained. That is, in Example 1, by using the gas sensor assembly of Sample 14 (that is, the gas sensors of Samples 1 to 6), the identification accuracy when identifying chemical substances was high.

[0152] [Comparative Example 1] As the gas sensor assembly, the gas sensor assembly of Sample 15 was placed in a nitrogen gas stream, and the chemical substance was identified by the same operations from "(1) Acquisition of characteristic amounts" to "(3) Identification of chemical substances" as in Example 1. The results of the identification are shown in Table 2.

[0153] [Table 2]

[0154] In Comparative Example 1, when pyrrole was mixed as the chemical substance, it was identified as benzaldehyde 16 times out of 25 times, and was identified as pyrrole only 9 times. The ratio of the number of times the correct identification result was obtained (59 times) to the total number of times of identifying each chemical substance (75 times) was 79%. Thus, when identifying chemical substances using the gas sensors of Samples 7 to 12 containing a polysiloxane compound whose side chain is composed of a hydrocarbon group as the adsorbent of the sensitive part, good identification results were not obtained for pyrrole, which is a hydrogen bond donor molecule.

[0155] As described above, the gas sensor and the like according to the present disclosure have been described based on the embodiments and examples. However, the present disclosure is not limited to these embodiments and examples. As long as the gist of the present disclosure is not deviated from, various modifications conceived by those skilled in the art applied to the embodiments and examples, as well as other forms constructed by combining some constituent elements in the embodiments and examples, are also included in the scope of the present disclosure. [Industrial Applicability]

[0156] The gas sensor, gas sensor assembly, and chemical substance identification method according to the present disclosure are useful for detecting or identifying chemical substances in a gas and the like. [Description of Reference Numerals]

[0157] 10, 210 Substrate 11 First wall portion 12 Second wall portion 20 First electrode 20a, 25a Terminal portion 25 Second electrode 30 Sensing portion 40 Insulating layer 45 First opening 46 Second opening 60 Detector 100 Gas sensor 200 Gas sensor assembly

Claims

1. A gas sensor, comprising: a sensing part; a pair of electrodes each electrically connected to the sensing part; The sensing part has a conductive material and a polymer having a siloxane bond as a main chain structure; The polymer has a cyano group and an alkylene group located between the cyano group and the main chain in a side chain; The gas sensor is used for detecting a hydrogen bond donor molecule. Gas sensor.

2. The polymer has a cyanopropyl group in the side chain; The gas sensor according to claim 1.

3. The polymer has at least one selected from the group consisting of a biscyanopropylpolysiloxane structure, a cyanopropylmethyldimethylpolysiloxane structure, a biscyanopropylcyanopropylphenylpolysiloxane structure, a cyanopropylphenyldimethylpolysiloxane structure, and a cyanopropylmethylphenylmethylpolysiloxane structure; The gas sensor according to claim 1 or 2.

4. In the thermogravimetric analysis of the polymer in an air atmosphere, the temperature at which a weight loss of 5% or more occurs with respect to the weight of the polymer at 35°C is 250°C or higher; The gas sensor according to any one of claims 1 to 3.

5. Further comprising a detector for detecting the electrical resistance of the sensing part; The gas sensor according to any one of claims 1 to 4.

6. The conductive material is conductive particles; The average particle size of the conductive particles is in the range of 10 nm or more and 300 nm or less; The gas sensor according to any one of claims 1 to 5.

7. The ratio of the weight of the conductive material to the weight of the sensing part is in the range of 0.05 or more and 0.95 or less. The gas sensor according to any one of claims 1 to 6.

8. The sensing part is in the form of a film. The gas sensor according to any one of claims 1 to 7.

9. Comprising a plurality of gas sensors, At least one of the plurality of gas sensors is the gas sensor according to any one of claims 1 to 8. Gas sensor assembly.

10. Detecting a hydrogen bond donor molecule using the gas sensor according to any one of claims 1 to 8. Detection method.

11. A chemical substance identification method using the gas sensor assembly according to claim 9, comprising: obtaining a signal output from the gas sensor assembly exposed to a gas containing a hydrogen bond donor molecule as a chemical substance; calculating a feature quantity from the obtained signal; and identifying the hydrogen bond donor molecule contained in the gas based on the calculated feature quantity. Chemical substance identification method.

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