JP2021067552A - Method of manufacturing composite metal oxide particle, method of manufacturing gas sensing layer, composite metal oxide particle, gas sensing layer, and gas sensor - Google Patents

Abstract

To provide a method of manufacturing a composite metal oxide particle capable of manufacturing the composite metal oxide used for a gas sensor capable of easily obtaining gas sensitivity with high accuracy while enhancing detection performance of detection gas.SOLUTION: A method of manufacturing composite metal oxide particles according to the present invention is a method for manufacturing the composite metal oxide particle used in a gas sensitive layer of a gas sensor. This includes a composite step of obtaining the composite metal oxide particle composited by fixing a second particle to the surface of a first particle by applying mechanical treatment to the first particle containing SnO2 having an average particle diameter of 1 μm to 10 μm, and the second particle containing SnO2 having the average particle diameter of 10nm-300nm.SELECTED DRAWING: Figure 1

Description

The present invention relates to a method for producing composite metal oxide particles, a method for producing a gas sensitive layer, composite metal oxide particles, a gas sensitive layer, and a gas sensor.

Gas sensors that detect a specific gas (detection gas) contained in the gas to be detected (gas to be inspected) are used in various applications such as gas leak alarms in buildings and the like.

As the detection gas, for example, toxic gas such as carbon monoxide (CO) and nitrogen oxide (NOx), flammable gas such as methane (CH ₄ ), propane (C ₃ H ₈ ) and butane (C ₄ H ₁₀ ). , And volatile organic compounds (VOC) such as ethanol (C ₂ H ₅ OH), formaldehyde (HCHO), acetone (C ₃ H ₆ O), chloroform (CHCl _{3) and the like are used.}

In the gas sensor that detects the gas, a thin film of a metal oxide such as _{SnO 2 is used for the gas sensitive layer.} As such a gas sensor, for example, a thin film gas sensor having a gas sensitive layer formed of _two porous SnO layers doped with antimony (Sb) on the upper surface of the electrically insulating layer has been proposed (for example, Patent Document). 1). In this thin film gas sensor, the gas sensitive layer is formed by an aggregate of a large number of columnar crystals, a plurality of gaps are formed between the large number of columnar crystals, and a plurality of pores are formed on the surface and inside of the columnar crystals. Is formed to increase the surface area of the gas sensitive layer.

Japanese Unexamined Patent Publication No. 2010-60481

However, in the thin film gas sensor of Patent Document 1, if the columnar crystals are not sufficiently grown, the surface area of the gas sensitive layer cannot be increased, and the gas sensitivity of the detected gas cannot be increased. Further, it is difficult to uniformly control the growth of columnar crystals, and it is difficult to stably secure the specific surface area of the gas-sensitive layer. Further, if the columnar crystals are grown too high, the columnar crystals tend to aggregate with each other, which may lead to a decrease in the specific surface area of the gas-sensitive layer.

One aspect of the present invention provides a method for producing composite metal oxide particles capable of producing a composite metal oxide used in a gas sensor capable of obtaining highly accurate gas sensitivity while improving the detection performance of the detected gas. The purpose is.

One aspect of the method for producing composite metal oxide particles according to the present invention is a method for producing composite metal oxide particles used for a gas-sensitive layer of a gas sensor, which comprises _{SnO 2 having an average particle diameter of 1 μm to 10 μm. A composite metal in which the first particles and the second particles containing SnO 2} having an average particle diameter of 10 nm to 300 nm are mechanochemically treated to fix the second particles on the surface of the first particles and composite them. Includes a complex step of obtaining oxide particles.

One aspect of the method for producing composite metal oxide particles according to the present invention can produce a composite metal oxide used for a gas sensor capable of obtaining highly accurate gas sensitivity while improving the detection performance of the detected gas.

It is explanatory drawing which shows an example of the structure of the composite metal oxide particle. It is a flowchart which shows the manufacturing method of the gas sensitive layer which concerns on one Embodiment. It is a conceptual cross-sectional view which shows an example of the structure of a gas sensor.

Hereinafter, embodiments of the present invention will be described in detail. In addition, in order to facilitate understanding of the description, the same components are designated by the same reference numerals in each drawing, and duplicate description will be omitted. In addition, the scale of each member in the drawing may differ from the actual scale. Unless otherwise specified, the tilde "~" indicating a numerical range in the present specification means that the numerical values described before and after the tilde are included as the lower limit value and the upper limit value.

<Manufacturing method of composite metal oxide particles>
A method for producing composite metal oxide particles according to an embodiment will be described. The method for producing composite metal oxide particles according to one embodiment includes a composite step of mixing the first particles and the second particles to composite the first particles and the second particles. The composite metal oxide particles produced by the method for producing composite metal oxide particles according to one embodiment can be used for a gas sensitive layer of a gas sensor that detects a detection gas contained in a gas to be inspected.

The detected gas is, for example, VOC; _{flammable gas such as methane (CH 4} ), propane (C ₃ H ₈ ), butane (C ₄ H ₁₀ ); carbon monoxide (CO), nitrogen oxide (NOx), etc. Toxic gas; malodorous gas such as sulfur compound (SOx). VOCs are aldehydes such as formaldehyde, acetaldehyde, propionaldehyde, butanal, pentanal, hexanal, heptanal, octanal, nonanal and glutanal aldehyde; alcohols such as ethanol, methanol and n-butanol; acetone, toluene, xylene and ethyl acetate, Refers to chloroform, paradichlorobenzene, etc.

The first particle is a particle _{containing tin dioxide (SnO 2} ).

The average particle size of the first particles is 1 μm to 10 μm, preferably 1.2 μm to 5 μm, and more preferably 1.5 μm to 2 μm. When the average particle size of the first particles is 1 μm to 10 μm, it is possible to prevent the first particles from aggregating too much.

The average particle size means a volume average particle size based on an effective diameter, and the average particle size is measured by, for example, a laser diffraction / scattering method or a dynamic light scattering method.

The second particle is a particle containing _{SnO 2 like the first particle.}

The average particle size of the second particles is 10 nm to 300 nm, preferably 15 nm to 200 nm, and more preferably 30 nm to 100 nm. When the average particle size of the second particles is 10 nm to 300 nm, the second particles are smaller than the first particles, so that they can be easily attached to the surface of the first particles and the aggregation of the second particles can be suppressed. ..

The second particle consists of a group consisting of diphosphorus pentoxide (P ₂ O ₅ ), niobium pentoxide (Nb ₂ O ₅ ), antimony (Sb), phosphorus (P) and niobium (Nb) _{in addition to SnO 2.} It may contain one or more selected components. By including Sb ₂ O ₃ , PO ₅ , Nb ₂ O ₅ , Sb, P and Nb in the second particle, the conductivity of the second particle can be enhanced. Further, since the second particle has a smaller average particle size than the first particle, when Sb ₂ O ₃ , PO ₅ , Nb ₂ O ₅ , Sb, P, Nb, etc. are included, Sb ₂ O ₃ , PO ₅ , Nb, etc. are included. ₂ O ₅ , Sb, P, Nb and the like are more likely to be mixed uniformly with the second particles having a small average particle size than with the first particles, which is preferable.

In addition, the second particle may contain one or more components selected from the group consisting of Pt and Pd. Pt and Pd can function as catalysts and promote the reaction between the first particles and the second particles and the detection gas. Further, since the second particle has a smaller average particle size than the first particle, when Pt or Pd is included, it is better to mix Pt and Pd with the second particle having a smaller average particle size than to mix with the first particle. It is preferable because it is easy to mix uniformly.

_{In addition to SnO 2} , the first particle or the second particle may contain indium oxide (In ₂ O ₃ ), tungsten oxide (WO ₃ ), zinc oxide (ZnO), and titanium oxide (TiO ₂ ).

The method of mixing the first particles and the second particles may be a dry method using no water or a solvent, or a wet method using water or a solvent, but the dry method is preferable.

The first particles and the second particles are preferably mixed so as to have a weight ratio in the range of 9.8: 0.2 to 7.0: 3.0, preferably 9.5: 0.5 to 9.5: 0.5. 7.5: 2.5 is more preferable, and 9.0: 1.0 to 8.0: 2.0 is even more preferable.

In the compounding step, a mixed powder obtained by mixing the first particles and the second particles is treated with a mechanochemical substance to form a composite.

The mechanochemical treatment is a treatment that causes a mechanochemical reaction. The mechanochemical reaction is a chemical reaction that causes solid dissolution or the like by utilizing high energy locally generated by mechanical energy such as friction or compression in the crushing process of the first particle and the second particle.

Examples of the apparatus for performing mechanochemical treatment include crushers / dispersers such as convergence mills, ball mills, bead mills, vibration mills, turbo mills, mechanofusions, and disc mills. Among these, the converge mill is preferable from the viewpoints of a large amount of pulverization in a short time, easy suppression of aggregation of the first and second particles, and high recovery rate.

By fixing the second particle to the surface of the first particle by the mechanochemical treatment, the first particle and the second particle are composited, and a composite metal oxide particle is obtained.

The method for producing composite metal oxide particles according to one embodiment has a first particle having a large average particle diameter and a micron size, and a nano-sized particle having a small average particle diameter by a composite step. The second particle is treated with mechanochemical. As a result, as shown in FIG. 1, the composite metal oxide particles 10 can be produced by firmly adhering the second particles 12 having a small average particle size to the surface of the first particles 11 having a large average particle size. it can.

When the composite metal oxide particles are sintered as described later, the second particles having a small average particle size are preferentially melted, and the first particles can be three-dimensionally bonded to each other. Thereby, the sintered body of the composite metal oxide particles can have a porous structure having a gap inside. Since the detection gas easily passes through the sintered body of the obtained composite metal oxide particles, the detection gas easily comes into contact with the sintered body. By using the obtained sintered body of the composite metal oxide particles for the gas-sensitive layer of the gas sensor, the gas-sensitive layer can increase the detection sensitivity of the detected gas and can have high-precision gas sensitivity. .. Therefore, by using the method for producing composite metal oxide particles according to one embodiment, it is possible to manufacture composite metal oxide for use in a gas sensor having high accuracy gas sensitivity while improving the detection performance of the detected gas. it can.

Further, since the obtained composite metal oxide particles are composite particles in which the second particles are firmly fixed to the surface of the first particles, agglomeration of only the first particles and agglomeration of only the second particles in the compositing step. Is suppressed. Therefore, even if the composite metal oxide particles are immersed in a liquid such as a solvent, it is possible to prevent the composite metal oxide particles from separating into a layer having many first particles and a layer having many second particles in the liquid. The particles can be uniformly dispersed in the solution. Therefore, when the solution containing the composite metal oxide particles is heated to evaporate the solution, the composite metal oxide particles can be deposited substantially uniformly on the substrate, so that the composite metal oxide particles can be deposited on the gas sensitive layer of the gas sensor. When used in the above, a gas-sensitive layer having a substantially uniform thickness can be stably formed. Further, even if the solution containing the composite metal oxide particles is stored for a long period of time, the composite metal oxide particles can be maintained in a uniformly dispersed state in the solution, so that a gas-sensitive layer of the composite metal oxide particles is formed. At that time, even if the solution is removed, the gas-sensitive layer can be manufactured while stably controlling the film thickness.

The method for producing composite metal oxide particles according to one embodiment is to mix the first particles and the second particles so as to be in the range of 9.8: 0.2 to 8.0: 2.0. Therefore, it becomes easy to fix the second particle on the surface of the first particle. Therefore, it becomes easy to produce composite metal oxide particles in which the second particles are fixed to the surface of the first particles and composited substantially uniformly. Since the obtained sintered body of the composite metal oxide particles tends to have a large number of gaps inside, when the sintered body of the composite metal oxide particles is used as the gas sensitive layer of the gas sensor, the gas sensitive layer is a detection gas. The detection performance of the gas can be further improved. Further, the composite metal oxide particles constituting the gas-sensitive layer are composited by fixing the second particles to the surface of the first particles, and the aggregation between the first particles is suppressed, so that the composite metal The gas-sensitive layer formed of the oxide particles can enhance the adhesion to the substrate on which the gas-sensitive layer is installed.

In general, particles having a large particle size are difficult to sinter, and therefore tend to have low adhesion to a substrate on which the particles are placed. On the other hand, since particles having a small particle size are easily sintered, they tend to have higher adhesion to a substrate on which the particles are placed than particles having a large particle size. Therefore, it can be said that the second particle having a small particle size has higher adhesion to the substrate than the first particle having a large particle size. In addition, the first particles tend to form voids between the particles, so that a porous structure is easily formed. In the present embodiment, when the sintered body of the composite metal oxide particles is used for the gas-sensitive layer of the gas sensor, the gas-sensitive layer is formed by fixing the second particles to the surface of the first particles, and the second particles. Is easy to contact with the substrate on which the gas-sensitive layer is installed, so that the gas-sensitive layer can improve the adhesion to the substrate.

In the method for producing composite metal oxide particles according to one embodiment, one or more components selected from the group consisting of _{Sb 2} O ₃ , PO ₅ , Nb ₂ O _{5, Sb, P and Nb are added to the second particles.} By including it, the conductivity of the obtained composite metal oxide particles can be enhanced.

The method for producing composite metal oxide particles according to one embodiment is to detect that the composite metal oxide particles are sintered bodies by including one or more components selected from the group consisting of Pt and Pd in the second particles. The reactivity with gas can be enhanced. Therefore, when the sintered body of the composite metal oxide particles is used for the gas-sensitive layer of the gas sensor, the gas-sensitive layer can enhance the detection performance of the detected gas.

In the method for producing composite metal oxide particles according to the present embodiment, the first particles consist of a group consisting of _{Sb 2} O ₃ , PO ₅ , Nb ₂ O ₅ , Sb, P and Nb in addition to _{SnO 2.} It may contain one or more selected components. Both the first and second particles may contain one or more components selected from the group consisting of _{Sb 2} O ₃ , PO ₅ , Nb ₂ O _{5, Sb, P and Nb.}

In this embodiment, the first particle may contain one or more components selected from the group consisting of Pt and Pd. Both the first and second particles may contain one or more components selected from the group consisting of Pt and Pd.

<Composite metal oxide particles>
Composite metal oxide particles can be obtained by the method for producing composite metal oxide particles according to one embodiment. As described above, the composite metal oxide particles include the first particles and the second particles, and the second particles having a small average particle size are fixed and composited on the surface of the first particles having a large average particle size. Is.

In the composite metal oxide particles according to one embodiment, as described above, the first particles have an average particle diameter of 1 μm to 10 μm, which are larger than the second particles. Therefore, since the composite metal oxide particles contain the first particles, the sintered body of the composite metal oxide particles can have a porous structure in which gaps are formed therein. Therefore, the detection gas can easily pass through the inside of the sintered body, the detection sensitivity of the detection gas can be increased, and the gas sensitivity with high accuracy can be obtained. Therefore, when the sintered body of the composite metal oxide particles according to one embodiment is used as a gas sensitive layer of a gas sensor, it is a gas reaction layer having high detection gas detection performance and high precision gas sensitivity. be able to.

Further, as the composite metal oxide particles, particles having a nano-sized size having an average particle diameter of 10 nm to 300 nm are used as the second particles. Since the composite metal oxide particles contain the second particles, the second particles can be preferentially melted in the firing step when the gas-sensitive layer is formed by using the sintered body of the composite metal oxide particles. , The sintering temperature in the firing process can be lowered. Therefore, when the gas-sensitive layer is formed by using the composite metal oxide particles, the influence on the electrodes and wiring arranged on the substrate which is the base of the gas-sensitive layer can be reduced, so that the gas sensor including the gas-sensitive layer can be reduced. Is easier to manufacture.

In the composite metal oxide particles according to one embodiment, it is preferable to mix the first particles and the second particles so as to be in the range of 9.8: 0.2 to 7.0: 3.0. The composite metal oxide particles include the first particles and the second particles so as to be in the range of 9.8: 0.2 to 7.0: 3.0, so that the second particles are on the surface of the first particles. It becomes easier to fix the particles. Therefore, the composite metal oxide particles can be made into particles having a substantially uniform size in a state in which the second particles are fixed to the surface of the first particles and composited. Since the sintered body of the composite metal oxide particles formed by using the obtained composite metal oxide particles tends to have a large number of gaps inside, the sintered body of the composite metal oxide particles is used as the gas sensitive layer of the gas sensor. At this time, the gas sensitive layer can enhance the detection performance of the detected gas. Further, the composite metal oxide particles are composited by fixing the second particles to the surface of the first particles, and the aggregation of the first particles is suppressed. Therefore, the composite metal oxide particles are sintered. The gas-sensitive layer formed by the body can have high adhesion to the substrate on which the gas-sensitive layer is installed.

As described above, the composite metal oxide particles according to the embodiment can be suitably used as a gas sensitive layer of a gas sensor because the sintered body can have a porous structure in which a large number of voids are formed. ..

<Manufacturing method of gas sensitive layer>
A method for producing a gas-sensitive layer to which the composite metal oxide particles according to the embodiment is applied will be described. FIG. 2 is a flowchart showing a method for manufacturing a gas-sensitive layer according to an embodiment. As shown in FIG. 2, the method for producing the gas-sensitive layer includes an ink manufacturing step (step S11), a coating step (step S12), and a firing step (step S13).

The composite metal oxide particles produced by using the above method for producing composite metal oxide particles are dispersed in a solvent to produce a paste-like ink (ink preparation step (step S11)).

As the solvent, water, an organic solvent and the like can be used. Examples of the organic solvent include alcohols such as methanol, ethanol, 1-propanol, 2-propanol (isopropyl alcohol: IPA), butanol, pentanol, hexanol, octanol and diacetone alcohol, ethyl acetate, butyl acetate and ethyl lactate. , Esters such as propylene glycol monomethyl ether acetate, propylene glycol monoethyl ether acetate and γ-butyrolactone; diethyl ether, ethylene glycol monomethyl ether, ethylene glycol monoethyl ether, ethylene glycol monobutyl ether, propylene glycol monomethyl ether, diethylene glycol Ethers such as monomethyl ether and diethylene glycol monoethyl ether; ketones such as acetone, methyl ethyl ketone (MEK), methyl isobutyl ketone (MIBK), acetylacetone and cyclohexanone; N, N-dimethylformamide, N, N-dimethylacetoacetamide and N -Amids such as methylpyrrolidone; glycols such as ethylene glycol, diethylene glycol and propylene glycol can be mentioned. These solvents may be used alone or in combination of two or more.

The blending ratio of the composite metal oxide particles and the solvent contained in the ink can be appropriately designed, but for example, it is preferably 30 parts by weight to 90 parts by weight, preferably 40 parts by weight, based on 100 parts by mass of the solvent. It is more preferably parts to 80 parts by weight, and even more preferably 50 parts by weight to 70 parts by weight.

Further, as the composite metal oxide particles, those in which the second particles having a small average particle size are fixed to the surface of the first particles having a large average particle size and composited are used. Therefore, when the composite metal oxide particles are dispersed in the solvent, the first particles having a large average particle size and the second particles having a small average particle size do not separate from each other. Therefore, the gas-sensitive layer obtained through the coating step (step S12) and the firing step (step S13) can have a porous structure in which voids are formed substantially uniformly.

Next, the obtained ink is applied to the substrate in a desired pattern and dried to form a film having a desired pattern shape on the substrate (coating step (step S12)).

The substrate is not particularly limited, and for example, a substrate having a surface made of a metal oxide, having an insulating property, and having a heating function is preferable. As the substrate, for example, a material or the like used for an insulating layer in which a gas reaction layer is installed in a gas sensor, which will be described later, can be used.

The method of applying the ink to the substrate is not particularly limited, and known methods such as screen printing, roller coating, spin coating, spray coating, inkjet method, and dispenser method can be used. When the ink is in the form of a paste, screen printing is preferably used, and when the ink is in the form of a liquid, spray coating is preferably used.

The thickness of the film can be appropriately designed according to the thickness of the gas reaction layer described later.

Next, the film formed in the pattern shape is fired to prepare a gas-sensitive layer (firing step (step S13).

The coating is preferably fired in an oxidizing atmosphere while introducing dry air into the furnace. _{Further, dry air such as oxygen (O 2} ) may be introduced for the purpose of removing the organic component evaporated during the heat treatment.

The firing temperature of the film is preferably, for example, 400 ° C. to 800 ° C., more preferably 500 ° C. to 600 ° C. By firing in such a temperature range, the first particles and the second particles can be stably sintered, and the second particles can be fixed to the surface of the first particles, so that the gas-sensitive film can be stabilized. Can be made.

The firing time of the gas-sensitive film can be appropriately designed, and is preferably 10 minutes to 1 hour, for example.

By firing the film, the solvent in the film evaporates and the composite metal oxide is sintered, so that a gas-sensitive layer made of a sintered body of the composite metal oxide as shown in FIG. 1 is formed. ..

In the method for producing a gas-sensitive layer according to one embodiment, the paste-like ink is heated by the firing step (step S13) to remove the solvent contained in the ink and the composite metal oxide particles are sintered. .. This makes it possible to obtain a gas-sensitive layer formed of a sintered body of composite metal oxide particles. Since the gas-sensitive layer has a porous structure in which voids are formed inside, the detection gas can easily pass through the inside, and the contact area with the detection gas can be increased, so that the detection performance of the detection gas can be increased. Can have high precision gas sensitivity.

Further, in the firing step (step S13), when the ink is fired, the second particles are particles having a small average particle size and a nano-sized size, so that the sintering temperature can be lowered. Therefore, when the gas-sensitive layer of the composite metal oxide is formed and the electrodes, wirings, etc. are arranged on the substrate as the base, the influence on these electrodes, wirings, etc. can be reduced, and thus the gas. A gas sensor having a sensitive layer can be easily manufactured.

Further, the gas-sensitive layer is composited with the second particles fixed to the surface of the first particles, and the aggregation of the first particles is suppressed, so that the gas-sensitive layer adheres to the substrate on which the gas-sensitive layer is installed. Highly sex. Therefore, by firing the gas-sensitive film to evaporate the solvent in the gas-sensitive film and depositing the composite metal oxide particles on the substrate, it is possible to improve the adhesion to the substrate on which the gas-sensitive layer is formed. ..

Further, in the method for producing a gas-sensitive layer according to one embodiment, the ink produced in the ink production step (step S11) can contain composite metal oxide particles in a state of being uniformly dispersed in a solvent. Therefore, in the firing step (step S13), the composite metal oxide particles can be deposited on the substrate substantially uniformly by evaporating the solvent in the gas-sensitive film, so that the composite metal oxide particles are generated in the firing step (step S13). The gas-sensitive layer can stably have a substantially uniform layer. Further, even if the ink is stored for a long period of time, the composite metal oxide particles in the ink can be maintained in a uniformly dispersed state in the ink. Therefore, in the firing step (step S13), the ink is heat-treated to remove the solvent. However, the gas-sensitive layer can be manufactured while stably controlling the film thickness.

<Gas sensitive layer>
A gas-sensitive layer produced by using the method for producing a gas-sensitive layer according to an embodiment will be described. As described above, the gas-sensitive layer is formed of a sintered body of composite metal oxide particles produced by firing an ink containing composite metal oxide particles.

_{SnO 2} constituting the first particles and the second particles contained in the sintered body of the composite metal oxide particles is a metal oxide semiconductor, and its electric resistance value changes when it comes into contact with the detection gas. When the gas-sensitive layer is heated to a high temperature (for example, about 200 ° C. to 500 ° C.), its conductivity changes depending on the gas concentration of the detected gas. Metal oxide semiconductors adsorb oxygen in the air at room temperature to increase resistance, but when left in a flammable gas at a high temperature (for example, about 200 ° C to 500 ° C), the flammable gas is released. Combustion (desorption by reacting with adsorbed oxygen) reduces resistance.

Since SnO _{2 and the} like are n-type metal oxide semiconductors, when the gas-sensitive layer is in the air, oxygen and the like are adsorbed on the surface of the gas-sensitive layer. Since oxygen has strong electron acceptability and adsorbs negative charges, a space charge layer is formed on the surface of the gas-sensitive layer. As a result, the conductivity of the gas-sensitive layer is lowered and the resistance is increased. On the other hand, when the gas-sensitive layer in the electron-donating reducing gas such as flammable gas is heated to a high temperature (for example, about 200 ° C. to 500 ° C.), a combustion reaction of the flammable gas occurs. At this time, the adsorbed oxygen on the surface of the gas-sensitive layer is consumed, and the electrons captured by the adsorbed oxygen are returned to the gas-sensitive layer, so that the electron density in the gas-sensitive layer increases. As a result, the conductivity of the gas-sensitive layer is increased and the resistance is lowered.

As described above, the gas-sensitive layer is formed of a sintered body of composite metal oxide particles and has a porous structure, so that the detected gas easily passes through the gas-sensitive layer and easily contacts the gas-sensitive layer. Therefore, the gas-sensitive layer can have high detection performance of the detected gas and high-precision gas sensitivity. Further, the composite metal oxide particles constituting the gas-sensitive layer are composited by fixing the second particles to the surface of the first particles, and the agglomeration of the first particles is suppressed, so that they are gas-sensitive. The layer can enhance the adhesion to the substrate on which the gas-sensitive layer is formed.

<Gas sensor>
A gas sensor to which the gas sensitive layer according to the embodiment is applied will be described. The gas sensor according to one embodiment is a gas sensor that detects a detected gas, and has a gas sensitive layer that detects the detected gas. The gas sensor is a thin film semiconductor type sensor. FIG. 3 is a conceptual cross-sectional view showing an example of the configuration of the gas sensor. As shown in FIG. 3, the gas sensor 20 includes a substrate 21, a heat insulating support layer 22, a heater layer 23, an insulating layer 24, and a gas detection layer 25. The gas detection layer 25 has a gas-sensitive layer 25c for detecting the detected gas and an electrode (sensing layer electrode 25b described later) connected to the gas-sensitive layer 25c. The heater layer 23 is connected to a power supply unit (not shown), and the gas detection layer 25 is connected to a detector (not shown).

The substrate 21 is a flat plate, and as a material for forming the substrate 21, metallic silicon, metal oxides such as alumina, mullite, forsterite, steatite, and cordierite can be used.

The substrate 21 has a through hole 21a at a position where the gas detection layer 25 is formed in a plan view.

The surface of the substrate 21 is preferably flat, and the surface roughness of the substrate is preferably, for example, between 0.01 μm and 1.0 μm.

The heat insulating support layer 22 is provided on the upper surface of the substrate 21 (upward in FIG. 3), and is formed in the through hole 21a like a diaphragm. In the present embodiment, the thermal insulating supporting layer 22 is composed of a three-layer structure of the first SiO ₂ layer 22a, _Si 3 _{N 4} layer 22b and the second SiO ₂ layer 22c.

The first SiO ₂ layer 22a can be formed by thermal oxidation at a thermal oxidation temperature of 800 ° C. to 1100 ° C. The first SiO ₂ layer 22a functions as a heat insulating layer, and has a function of reducing the heat capacity by preventing heat transfer generated in the heater layer 23 to the substrate 21 side. Further, the first SiO ₂ layer 22a exhibits high resistance to plasma etching, and can facilitate the formation of through holes in the substrate 21 by plasma etching.

The Si ₃ N ₄ layer 22b is formed on _{the upper surface (upward direction in FIG. 3) of the first SiO 2} layer 22a by using a chemical vapor deposition (CVD) method.

The second SiO ₂ layer 22c can be formed by a CVD method, and can improve the adhesion with the heater layer 23 and secure the insulating property. _{Since the second SiO 2} layer formed by the CVD method has a small internal stress, it is possible to reduce the occurrence of distortion in the heat insulating support layer 22.

The heater layer 23 is provided substantially in the center of the upper surface (upward direction in FIG. 3) of the heat insulating support layer 22. The heater layer 23 is a thin film and can be formed of, for example, a Pt-W film containing Pt and W. The heater layer 23 is electrically connected to a power supply unit (not shown) via a terminal (not shown) to supply power.

The insulating layer 24 is provided so as to cover the heat insulating support layer 22 and the heater layer 23. The insulating layer 24 can be formed of, for example, _{two SiO layers.} The insulating layer 24 can secure electrical insulation between the heater layer 23 and the sensing layer electrode 25b, which is an electrode, and improves the adhesion to the gas-sensitive layer 25c.

The gas detection layer 25 includes a pair of bonding layers 25a, a pair of sensing layer electrodes 25b, a gas sensitive layer 25c, and an adsorption layer 25d.

The bonding layer 25a can be formed of, for example, a tantalum film (Ta film) or a titanium film (Ti film), and is provided on the insulating layer 24. The bonding layer 25a can increase the bonding strength between the sensing layer electrode 25b and the insulating layer 24.

The sensing layer electrode 25b can be formed of, for example, a platinum film (Pt film) or a gold film (Au film). The sensing layer electrode 25b is provided on the pair of bonding layers 25a and serves as a sensing electrode for the gas sensitive layer 25c. The sensing layer electrode 25b is electrically connected to a detector (not shown) via a terminal (not shown).

The gas sensitive layer 25c is formed on the insulating layer 24 so as to connect the pair of sensing layer electrodes 25b.

As described above, the gas sensitive layer 25c uses the gas sensing layer according to the present embodiment, and thus details thereof will be omitted.

The thickness of the gas-sensitive layer 25c can be appropriately designed, and is preferably, for example, 10 μm to 40 μm, preferably 7 μm to 30 μm, and even more preferably 5 μm to 20 μm. If the thickness of the gas-sensitive layer 25c is, for example, 5 μm to 20 μm, both the detection performance and the sensitivity can be improved.

The adsorption layer 25d is provided so as to cover the surfaces of the insulating layer 24, the pair of bonding layers 25a, the pair of sensing layer electrodes 25b, and the gas sensitive layer 25c.

As the adsorption layer 25d, a sintered body supported on a carrier having a porous structure can be used using at least one of noble metal elements such as palladium (Pd) and platinum (Pt) as a catalyst. As the carrier, for example, alumina (Al ₂ O ₃ ), chromium oxide (Cr ₂ O ₃ ), iron oxide (Fe ₂ O ₃ ), nickel oxide (Ni ₂ O ₃ ), zirconium oxide (ZrO ₂ ), silica ( Metal oxides such as SiO ₂ ) and zeolite can be used. These may be used alone or in combination of two or more. Since the carrier such as alumina has a porous structure, the area where the gas to be inspected passing through the pores comes into contact with the catalyst can be increased. Further, when the atmosphere contains a reducing gas having a stronger oxidizing activity than the inspection target gas in addition to the inspection target gas, the combustion reaction of the reducing gas can be promoted and the selectivity of the inspection target gas can be enhanced. .. As a result, the gas concentration of the gas to be inspected reaching the gas sensitive layer 25c increases, and the sensitivity of the gas sensor 20 can be further increased.

The gas sensor 20 has a diaphragm structure with high heat insulation and low heat capacity. In the gas sensor 20, the heater layer 23 is connected to a power supply unit (not shown), and the gas detection layer 25 is connected to a detector (not shown). The heater layer 23 is connected so as to be driven by electricity sent from a power supply unit (not shown). The gas-sensitive layer 25c is connected via a sensing layer electrode 25b so as to detect a change in the resistance value of the gas-sensitive layer 25c.

As described above, the gas sensor 20 includes the gas sensitive layer 25c. As described above, the gas-sensitive layer 25c is formed of a sintered body of composite metal oxide particles and has a porous structure, so that the detected gas easily passes through the inside of the gas-sensitive layer 25c and easily comes into contact with the gas-sensitive layer 25c. Therefore, the gas sensor 20 can improve the detection performance of the detected gas and can have high-precision gas sensitivity. Further, as described above, the gas-sensitive layer 25c is formed of a sintered body of composite metal oxide particles, and the sintered body of the composite metal oxide particles is composited by fixing the second particles to the surface of the first particles. Therefore, aggregation of the first particles is suppressed. Therefore, since the gas sensor 20 can improve the adhesion between the gas sensitive layer 25c and the insulating layer 24, the gas sensitive layer 25c can be stably installed on the insulating layer 24, and the detection of the detected gas is stable. Can be done.

In this embodiment, the gas sensor 20 does not have to have a diaphragm structure.

Although the embodiments have been described above, the above-described embodiments are presented as examples, and the present invention is not limited to the above-described embodiments. The above-described embodiment can be implemented in various other forms, and various combinations, omissions, replacements, changes, and the like can be made without departing from the gist of the invention. These embodiments and modifications thereof are included in the scope and gist of the invention, and are also included in the scope of the invention described in the claims and the equivalent scope thereof.

10 Composite metal oxide particles 11 First particles 12 Second particles 20 Gas sensor 25 Gas detection layer 25c Gas sensitive layer

Claims (9)

A method for producing composite metal oxide particles used in the gas sensitive layer of a gas sensor.
By mechanochemical treatment of _{the first particle containing SnO 2} having an average particle diameter of 1 μm to 10 μm and _{the second particle containing SnO 2} having an average particle diameter of 10 nm to 300 nm, the surface of the first particle is formed. A method for producing composite metal oxide particles, which comprises a composite step of fixing the second particles to obtain composite composite metal oxide particles. The method for producing a composite metal oxide particle according to claim 1, wherein the first particle and the second particle are contained in the range of 9.8: 0.2 to 7.0: 3.0. Claim that one or both of the first particle and the second particle contains one or more components selected from the group consisting of _{Sb 2} O ₃ , PO ₅ , Nb ₂ O _{5, Sb, P and Nb.} The method for producing composite metal oxide particles according to 1 or 2. The composite metal oxide according to any one of claims 1 to 3, wherein either one or both of the first particle and the second particle contains one or more components selected from the group consisting of Pt and Pd. How to make particles. Ink production for producing a liquid or paste-like ink by dispersing the composite metal oxide particles produced by the method for producing a composite metal oxide particle according to any one of claims 1 to 4 in a solvent. Process and
A firing step of firing the ink to produce a gas-sensitive layer, and
A method for manufacturing a gas-sensitive layer including. Composite metal oxide particles used in the gas sensitive layer of gas sensors.
The surface of the first particles is subjected to mechanochemical treatment of the first particles containing SnO ₂ having an average particle size of 1 μm to 10 μm and _{the second particles containing SnO 2 having an average particle size of 10 nm to 300 nm.} Composite metal oxide particles in which the second particles are fixed and composited. The composite metal oxide particle according to claim 6, wherein the first particle and the second particle are contained in the range of 9.8: 0.2 to 7.0: 3.0. A gas-sensitive layer formed by using the composite metal oxide particles according to claim 6 or 7. A gas sensor that detects the detected gas,
A gas-sensitive layer that detects the detected gas,
With an electrode connected to the gas sensitive layer,
A gas sensor in which the gas sensitive layer uses the gas sensitive layer according to claim 8.

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