JP2020056726A - Gas sensor - Google Patents

Abstract

To meet a demand for a gas sensor that can selectively and accurately detect a gas to be detected with higher sensitivity.SOLUTION: A gas sensor comprises: an adsorption layer 53 that adsorbs a gas containing a gas to be detected and a gas not to be detected; and a sensing layer 52 that is covered with the adsorption layer 53 and has electrical characteristics changing according to concentration of the gas to be detected passing through the adsorption layer 53. The adsorption layer contains a catalyst component that includes gold particles and metal oxide carriers carrying the gold particles. An average particle diameter of the gold particles is 10 nm or less, and when taking a total mass of the catalyst component as 100%, the gold particles are included by an amount of 0.02 mass% or more and 12 mass% or less.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a gas sensor. In particular, the present invention relates to a gas sensor that can selectively detect a gas to be detected with high sensitivity.

  2. Description of the Related Art Conventionally, there has been known a gas sensor capable of accurately detecting a detection target gas even in an atmosphere containing a detection target gas and a non-detection target gas (for example, see Patent Document 1).

JP 2017-223557 A

  There is a need for a gas sensor that has higher sensitivity and can selectively and accurately detect a gas to be detected.

  The present inventors have completed the present invention by examining the catalytic components of the adsorption layer of the gas sensor and finding that the target gas can be selectively detected by including a specific active component in a specific amount. I came to.

  According to an embodiment of the present invention, there is provided a gas sensor, wherein an adsorption layer that adsorbs a gas containing a detection target gas and a non-detection target gas, and the detection that is covered by the adsorption layer and passes through the adsorption layer. A sensing layer whose electrical characteristics change according to the concentration of the target gas, wherein the adsorption layer includes a catalyst component including gold particles and a metal oxide carrier supporting the gold particles, The average particle diameter is 10 nm or less, and the gold particles are contained in an amount of 0.02% by mass or more and 12% by mass or less when the total mass of the catalyst component is 100%.

In the gas sensor, the catalyst _{components, Fe 2 O 3, MnO 2} , CeO 2, Co 3 O 4, NiO, may further include one or more co-catalysts selected from the group consisting of ZrO 2, CuO.

  In the gas sensor containing the co-catalyst, it is preferable that the co-catalyst is contained in an amount of 0.1% by mass or more and 10% by mass or less when the total mass of the catalyst components is 100%. .

  The gas sensor preferably further includes a heater layer for heating the adsorption layer.

In the gas sensor, the metal oxide carrier may include at least one metal oxide selected from the group consisting of Al ₂ O ₃ , ZrO ₂ , CeO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , and NiO. preferable.

  In the gas sensor, it is preferable that the sensing layer includes a metal oxide semiconductor.

In the gas sensor, the metal oxide semiconductor preferably includes at least one metal oxide selected from the group consisting of SnO ₂ , In ₂ O ₃ , WO ₃ , ZnO, and TiO ₂ .

  In the gas sensor, preferably, the detection target gas is ketone, and the non-detection target gas is alcohol.

  According to another embodiment, the present invention provides a gas detection method using the gas sensor according to any of the above, wherein the adsorption layer is heated to 200 to 400 ° C. A method comprising a detection step of obtaining a property.

  The gas detection method preferably includes a cleaning step of heating the adsorption layer and the sensing layer to 370 ° C. to 500 ° C. before the detection step.

  According to the present invention, a gas to be detected can be accurately detected.

FIG. 1 is a conceptual diagram showing a cross-sectional structure of a gas sensor according to one embodiment of the present invention. FIG. 2 is a graph showing sensitivity characteristics of the gas sensor of Example 1-1. FIG. 3 is a graph showing the sensitivity characteristics of the gas sensor of Example 1-2. FIG. 4 is a graph showing the sensitivity characteristics of the gas sensor of Example 1-3. FIG. 5 is a graph showing the sensitivity characteristics of the gas sensor of Example 1-4. FIG. 6 is a graph showing the sensitivity characteristics of the gas sensor of Example 1-5. FIG. 7 is a graph illustrating sensitivity characteristics of the gas sensor according to the second embodiment. FIG. 8 is a graph showing the sensitivity characteristics of the gas sensor of Comparative Example 1. FIG. 9 is a graph showing the sensitivity characteristics of the gas sensor of Comparative Example 2. FIG. 10 shows a plot of the sensitivity ratio of the gas sensor of Example 1 at 300 ° C. FIG. 11 is a graph showing the results of testing the conversion of gas components using the catalyst components of the gas sensor according to the present invention, and showing the relationship between the amount of supported gold, the ethanol conversion, and the acetone conversion. . FIG. 12 shows the results of testing the conversion of gas components using the catalyst components of the gas sensor according to the present invention, and shows the relationship among the amount of gold carried, the reaction temperature, the conversion of ethanol, and the conversion of acetone. It is a graph. FIG. 13 is a graph showing the results of testing the conversion of gas components using the catalyst component of the gas sensor according to the present invention, and showing the relationship between the particle size of gold, the ethanol conversion, and the acetone conversion. . FIG. 14 shows the results of testing the conversion of the gas component using the catalyst component of the gas sensor according to the present invention, and shows the amount of the co-catalyst Fe ₂ O ₃ when the amount of gold supported was substantially constant. It is the graph which showed the relationship between the ethanol conversion rate and the acetone conversion rate. FIG. 15 shows the results of testing the conversion rate of the gas component using the catalyst component of the gas sensor according to the present invention, and shows the amount of the supported catalyst ZrO ₂ and the ethanol conversion when the supported amount of gold is substantially constant. 5 is a graph showing the relationship between the conversion rate and the acetone conversion rate.

  Hereinafter, embodiments of the present invention will be described with reference to the drawings. However, the present invention is not limited by the embodiments described below.

  A gas sensor according to one embodiment of the present invention is a gas sensor that can accurately detect a detection target gas even in an atmosphere containing a detection target gas and a non-detection target gas.

  Hereinafter, a semiconductor type gas sensor capable of accurately detecting acetone in a gas atmosphere containing acetone as an example of a detection target gas and ethanol as an example of a non-detection target gas will be described as an example. . A gas sensor capable of accurately detecting acetone can be suitably used for, for example, a breath meter that detects acetone in breath and performs physical condition management. The detection target gas may be a ketone gas other than acetone, and the non-detection target gas may be an alcohol gas other than ethanol. Ketone gases to be detected other than acetone include, but are not limited to, ethyl methyl ketone, diethyl ketone, 2-butanone, and the like. Non-detection target alcohol gases other than ethanol include, but are not limited to, methanol, 1-propanol, 2-propanol, and the like.

(Gas sensor)
The present invention, according to one embodiment, is a gas sensor. A gas sensor according to the present embodiment will be described with reference to FIG. FIG. 1 is a schematic sectional view of a gas sensor according to one embodiment.

  As shown in FIG. 1, the gas sensor may be a semiconductor type gas sensor having a diaphragm structure, and includes a substrate 10, a heat insulating support layer 20, a heater layer 30, an insulating layer 40, and a gas detection layer 50. It has. The heater layer 30 is electrically connected to a drive processing unit (not shown), and the drive processing unit drives the heater layer 30 with a heater. The gas detection layer 50 is electrically connected to a drive processing unit (not shown), and the drive processing unit reads out the electrical characteristics of the sensing layer 52 of the gas detection layer 50.

  The substrate 10 may be a member formed of a semiconductor material, for example, silicon (Si). A through hole 11 penetrating through the substrate 10 is formed in a central portion of the substrate 10.

  The heat insulating support layer 20 is formed on the substrate 10 and has a diaphragm structure. The thermal insulating support layer 20 includes a thermal oxide film 21, a support film 22, and a thermal insulating film 23.

The thermal oxide film 21 is formed on the substrate 10 and is formed of, for example, a thermal oxide SiO ₂ film. The thermal oxide film 21 reduces the thermal conductivity so that the heat generated in the heater layer 30 is not conducted to the substrate 10 side. Further, the thermal oxide film 21 has a high etching selectivity with respect to the substrate 10.

Supporting film 22 is formed on the thermal oxide film 21, for example, formed by _CVD-Si 3 _{N 4} film. The support film 22 functions as a support film having a diaphragm structure.

The heat insulating film 23 is formed on the support film 22 and can be formed by, for example, a CVD-SiO ₂ film. The heat insulating film 23 has a high adhesiveness with the heater layer 30 and electrically insulates the substrate 10 from the heater layer 30.

  The heater layer 30 can be formed on the heat insulating support layer 20 at the center of the position where the through-hole 11 is formed in plan view. Thereby, the heater layer 30 is thermally separated from the substrate 10. The heater layer 30 is connected to a power supply (not shown), and generates heat when supplied with power from the power supply to heat the gas detection layer 50. More specifically, the heater layer 30 is heated to a temperature at which ethanol is oxidized to reduce the amount of ethanol reaching the sensing layer 52, which will be described later, and a temperature required for cleaning, for example, 200 ° C. to 500 ° C. In addition, the adsorption layer 53 can be heated. At this time, since the heater layer 30 is thermally separated from the substrate 10, the heat generated in the heater layer 30 hardly diffuses to the surroundings. For this reason, the temperature of the gas detection layer 50 and the sensing layer 52 can be efficiently increased. The heater layer 30 can be formed of, for example, an alloy film of platinum (Pt) and tungsten (W) (hereinafter, also referred to as a “Pt-W film”). If the gas detection layer 50 including the sensing layer 52 and the adsorption layer 53 can be heated to a predetermined temperature, another heating device can be provided instead of the heater layer 30.

The insulating layer 40 is formed on the heat insulating support layer 20 so as to cover the heater layer 30, and can be formed by, for example, a sputtered SiO ₂ film. The insulating layer 40 electrically insulates the heater layer 30 from the gas detection layer 50. Further, the insulating layer 40 has a high adhesiveness with the gas detection layer 50.

  The gas detection layer 50 is formed on the insulating layer 40 at the center of the position where the through hole 11 is formed in plan view. That is, the gas detection layer 50 is formed on the insulating layer 40 so as to correspond to the position where the heater layer 30 is formed in a plan view. The gas detection layer 50 includes an electrode layer 51, a sensing layer 52, and an adsorption layer 53. If the adhesion between the insulating layer 40 and the electrode layer 51 is not sufficient, a film of, for example, a tantalum (Ta) film or a titanium (Ti) film is formed between the insulating layer 40 and the electrode layer 51. May be provided.

  The electrode layer 51 is a pair of metal films formed on the insulating layer 40 at both ends of the sensing layer 52 in plan view, and can be formed of, for example, a Pt film or a gold (Au) film.

The sensing layer 52 is formed on the insulating layer 40 so as to be in contact with the pair of electrode layers 51. The sensing layer 52 is formed of a metal oxide, and can be formed of, for example, SnO ₂ . The sensing layer 52 changes its electrical characteristics such as resistance according to the concentration of acetone that has passed through the adsorption layer 53. The sensing layer 52 may be formed of a material other than SnO ₂ , for example, a material mainly containing a metal oxide semiconductor such as In ₂ O ₃ , WO ₃ , ZnO, and TiO ₂ . Further, the “main component” in this specification means that 50% by mass or more is contained when the total mass of the components constituting the layer is 100%.

  The adsorption layer 53 is formed on the electrode layer 51 and the sensing layer 52 so as to cover the surface of the sensing layer 52, and can adsorb a gas containing acetone and ethanol. The adsorption layer 53 contains a metal oxide carrier supporting gold particles as a main component. The definition of the principal component is the same as above. The adsorption layer 53 may be formed by being stacked on the upper surface of the sensing layer 52, and the side surface of the sensing layer does not necessarily need to be covered with the adsorption layer.

The metal oxide carrier is preferably Al ₂ O ₃ , ZrO ₂ , CeO ₂ , Cr ₂ O ₃ , Fe ₂ O ₃ , NiO, or an insulator in which two or more of these are mixed. It may be Al ₂ O ₃ , but is not limited thereto.

  The gold particles have an average particle diameter of 10 nm or less, preferably 5 nm or less. This is because in such an average particle size range, the catalytic effect of promoting the selective oxidation reaction (combustion reaction) of ethanol is high. The activity of the gold particles for the reaction is larger as the particle size is smaller, and shows catalytic activity even in an atomic state. Therefore, the lower limit of the average particle size of the gold particles is not particularly limited, but may be, for example, about 0.3 nm or more. The average particle diameter of the gold particles refers to an average particle diameter measured by a transmission electron microscope.

  The gold particles are contained in an amount of 0.02% by mass or more and 12% by mass or less when the total mass of the catalyst component is 100%, and 5% by mass or more and 12% by mass or less. Is more preferable. Here, the total mass of the catalyst component refers to the total mass of the gold particles, the metal oxide carrier, and, if present, the cocatalyst which is an optional component described later.

The adsorption layer 53 preferably contains a promoter as an optional component. This is because the addition of the cocatalyst can impart other characteristics such as durability while maintaining the sensitivity characteristics. The co-catalyst is preferably a metal oxide selected from Fe ₂ O ₃ , MnO ₂ , CeO ₂ , Co ₃ O ₄ , NiO, ZrO ₂ , CuO, or a mixture of two or more thereof, for example, ethanol From the viewpoint of the activity of selectively converting and converting acetone, Fe ₂ O ₃ and ZrO ₂ can be preferably used, but are not limited thereto.

  The cocatalyst is preferably contained in an amount of 0.1% by mass or more and 10% by mass or less when the total mass of the catalyst components is 100%, and more preferably 0.1% by mass or more. More preferably, it is contained in an amount of 8% by mass or less. This is because the effect is remarkable in this addition range. If the added amount of the co-catalyst is less than 0.1% by mass, the above effect may not be sufficiently exhibited.

  In addition, the adsorption layer 53 may include a binder, an aggregate, and other usual additive components. For example, the silica sol binder may be contained in an amount of 5% by mass or more and 20% by mass or less based on the total mass of the adsorption layer, but is not limited to a specific content. In some cases, it is preferable that the adsorption layer 53 of the present invention does not contain platinum (Pt) or palladium (Pd). The total mass of the adsorption layer is the total mass of the catalyst component, the binder, the aggregate, the additive, and the like, and refers to the mass of the adsorption layer after being sintered and dried and mounted on the gas sensor.

  The gas sensor having such a diaphragm structure is a structure that can have high heat insulation and low heat capacity. In the gas sensor, the heat capacity of each component of the electrode, the sensing layer, and the heater layer can be reduced by a technique such as MEMS (micro electro mechanical system). Therefore, the time change of the temperature at the time of driving the heater is fast, and the thermal desorption can be caused in a very short time. Note that the present invention is not limited to a gas sensor having a diaphragm structure, but includes any gas sensor that includes the adsorption layer and the sensing layer described in this specification and can detect gas.

(Method of manufacturing gas sensor)
A method for manufacturing a gas sensor according to one embodiment of the present invention will be described. First, the heat insulating support layer 20 is formed on the substrate 10. Specifically, by thermally oxidizing the substrate 10, the thermal oxide film 21 can be formed on the substrate 10. Subsequently, silicon nitride (Si ₃ N ₄ ) is deposited on the thermal oxide film 21 by a plasma CVD method to form a support film 22. Subsequently, silicon oxide (SiO ₂ ) is deposited on the support film 22 by a plasma CVD method, so that the heat insulating film 23 can be formed.

  Next, the heater layer 30 is formed on the heat insulating support layer 20. Specifically, a Pt-W film is formed on the heat insulating film 23 by a sputtering method at a central portion of the position where the through hole 11 is formed in a plan view, and the heater layer 30 can be formed. . At this time, for example, a metal mask or the like having an opening at the position where the Pt-W film is formed can be used.

Next, an insulating layer 40 is formed on the heat insulating support layer 20 so as to cover the heater layer 30. Specifically, the insulating layer 40 can be formed on the heat insulating support layer 20 by depositing SiO ₂ so as to cover the surface of the heater layer 30 by a sputtering method.

Next, the gas detection layer 50 is formed on the insulating layer 40. Specifically, a pair of electrode layers 51 can be formed by forming Pt on the insulating layer 40 by a sputtering method. Subsequently, SnO ₂ is formed on the insulating layer 40 by a sputtering method so as to be in contact with the pair of electrode layers 51 to form the sensing layer 52.

Subsequently, an adsorption layer 53 is formed on the electrode layer 51 and the sensing layer 52. In forming the adsorbing layer 53, an adsorbing layer composition containing at least the gold particles and the metal oxide carrier and optionally containing a co-catalyst, a binder and the like is prepared. The adsorption layer composition can be prepared by first depositing the catalyst component by a precipitation method, specifically, the following method. A metal oxide carrier is dispersed in an aqueous solution containing HAlCl ₄ , a precursor of gold particles, and optionally a nitrate of a metal element constituting a co-catalyst, and adjusted to an appropriate pH, for example, about pH 6 to 8. Adjust and stir for a certain time. This is washed, filtered, dried and calcined at about 350 to 450 ° C. for 3 to 5 hours. Prepared by adding an organic solvent of the same mass as the total amount of these to the thus obtained metal oxide supporting gold particles and optionally a promoter, and further adding a binder such as a silica sol binder. can do. Examples of the organic solvent include ethylene glycol and glycerin, but are not limited thereto. In addition, in the preparation of the catalyst component, the content of the gold particles can be changed by changing the addition amount of the precursor of the gold particles. The paste of the adsorption layer composition thus obtained is formed on the electrode layer 51 and the sensing layer 52 to a predetermined thickness by a screen printing method or the like to form an adsorption layer 53. By firing for a time, the adsorption layer 53 can be formed. The adsorption layer 53 may be formed so as to be laminated on the surface of the sensing layer 52 or may be formed so as to cover the surfaces of the electrode layer 51 and the sensing layer 52.

  Next, a through hole 11 is formed in the substrate 10. Specifically, the substrate 10 is etched from the rear surface side (the side where the gas detection layer 50 is not formed) by plasma etching, and Si in a portion including the position where the gas detection layer 50 is formed in plan view is removed. Thus, the through hole 11 can be formed. At this time, since the thermal oxide film 21 has high etching selectivity with respect to the substrate 10, only the substrate 10 can be etched without etching the thermal oxide film 21. That is, the thermal oxide film 21 functions as an etching stop film when etching the substrate 10.

  As described above, as shown in FIG. 1, a gas sensor having a diaphragm structure can be manufactured. Note that the method for manufacturing the gas sensor is an example, and the present invention is not limited to this. For example, after forming the electrode layer 51 and the sensing layer 52, the through hole 11 may be formed in the substrate 10, and then the adsorption layer 53 may be formed so as to cover the sensing layer 52.

(Gas detection method)
According to another embodiment, the present invention relates to a gas detection method using the gas sensor according to the above embodiment. Such a gas detection method can also be called an operation method of a gas sensor. The gas detection method according to the present embodiment includes a detection step of heating the adsorption layer of the gas sensor to 200 ° C. to 400 ° C. to obtain the electrical characteristics of the sensing layer.

The heating of the adsorption layer can be performed by heating the adsorption layer 53 to 200 ° C. to 400 ° C. with a heater layer or another heating device. When heating is performed by the heater layer 30 shown in FIG. 1, the heater temperature can be set in this range. This is because the sensitivity of acetone and ethanol tends to be different in such a temperature range, so that ethanol can be selectively removed from the adsorption layer 53 and the acetone can reach the sensing layer 52. A suitable temperature range may vary depending on the composition of the adsorption layer. For example, when the adsorption layer 53 does not contain a cocatalyst, the adsorption layer 53 is preferably heated to 250 to 350 ° C, and 280 to 320 ° C. It is more preferable to heat the mixture. This is because a high sensitivity ratio between acetone and ethanol can be achieved at about 300 ° C. regardless of the concentration of the gold particles. When the adsorption layer contains Fe ₂ O ₃ as a promoter, the adsorption layer is preferably heated to 300 ° C. above 200 ° C., and more preferably to 230 ° C. to 270 ° C. This is because a high sensitivity ratio between acetone and ethanol can be achieved at about 250 ° C.

  The electrical characteristics of the sensing layer 52 can be obtained by reading out the electrical resistance value of the sensing layer 52 by the drive processing unit. In this case, the temperature of the sensing layer 52 is substantially the same as the temperature of the adsorption layer 53.

  According to such a detection step, by setting the temperature within a predetermined temperature range, the oxidation reaction (combustion reaction) of ethanol is promoted in the adsorption layer 53, but acetone is hardly oxidized. This allows the adsorption layer 53 to selectively oxidize and remove ethanol with respect to acetone. Then, in the adsorption layer 53, the amount of ethanol that reaches the sensing layer 52 can be reduced, and acetone can selectively reach the sensing layer 52. As a result, acetone and ethanol can be separately detected in the sensing layer 52, and acetone can be accurately detected.

  It is preferable to include a cleaning step of heating the sensing layer 52 and the adsorption layer 53 to 370 ° C. to 500 ° C. before the detection step. When heating is performed by the heater layer 30 shown in FIG. 1, the heater temperature can be set in this range. By heating to 370 ° C. or higher, adsorbed substances on the surface of the sensing layer can be removed, and oxygen can be chemically adsorbed on the surface of the metal oxide semiconductor forming the sensing layer. If the temperature is 370 ° C. or higher, the above-described action can be performed, and the gas sensor can be cleaned in a state suitable for detection. The cleaning step can be performed, for example, by intermittently driving for 0.5 to 2 seconds at a cycle of 20 to 40 seconds and continuing for 5 to 15 minutes. The range is not limited. As another example of the cleaning step, for example, the driving can be performed by continuously driving for several tens of seconds to several minutes.

  According to the gas detection method according to the present embodiment, alcohol such as ethanol can be removed from the adsorption layer, and ketone such as acetone can be accurately detected. It becomes possible.

(Example 1)
In this example, the gas sensor shown in FIG. 1 was manufactured, and gas sensitivity characteristics were evaluated. First, a thermally oxidized SiO ₂ film to be a thermally oxidized film 21 was formed on the Si substrate by thermally oxidizing the Si substrate used as the substrate 10. Subsequently, on the thermal oxide SiO ₂ film by a plasma CVD method, a CVD SiO ₂ film serving as a support film 22 to become _CVD-Si 3 _{N 4} film and the thermally insulating layer 23 is formed in this order, the heat insulating support layer 20.

Next, a Pt-W film to be the heater layer 30 was formed on the CVD-SiO ₂ film by a sputtering method using an RF magnetron sputtering device. Subsequently, an SiO ₂ film serving as the insulating layer 40 was formed on the Pt-W film by a sputtering method using an RF magnetron sputtering device.

Next, an electrode layer having a thickness of 200 nm was formed on the SiO ₂ film by sputtering using an RF magnetron sputtering apparatus under the conditions of an Ar gas pressure of 1 Pa, a substrate temperature of 300 ° C., and an RF power of 2 W / cm 2. A 51 Pt film was formed.

Next, on the SiO ₂ film, an Ar + O ₂ gas pressure is 2 Pa, a substrate temperature is 150 ° C. to 300 ° C., and an RF power is 2 W / cm ² by a reactive sputtering method using an RF magnetron sputtering device. An SnO ₂ film to be the sensing layer 52 having a thickness of 400 nm was formed. At this time, SnO ₂ containing 0.1% by mass of antimony (Sb) was used as a target material.

Next, the adsorption layer 53 was prepared. Gold was added to γ-Al ₂ O ₃ (average particle size: 1 μm to ₂ μm) by a precipitation method. That is, HAuCl ₄ as a precursor was dissolved in water, and Al ₂ O ₃ was added. After adjusting the pH to 7 and stirring for 1 hour, washing, filtration and drying were performed, and calcination was performed at 400 ° C. for 4 hours. Thus prepared, _Al 2 _{O 3} in the catalyst (Au / _Al 2 _{O 3} catalyst) having an average particle size in the metal oxide support mainly is was supported gold particles 2.5~3.5nm the , An organic solvent is added by the same weight, and a silica sol binder is added in an amount of 13% by mass in Example 1-1 and 12% by mass in Examples 1-2 to 1-5 based on the total mass of the adsorption layer. To produce pastes with different gold concentrations. Subsequently, a paste was applied on the Pt film and the SnO ₂ film by screen printing so as to form a circular shape having a thickness of about 30 μm and a diameter of about 250 μm, and was baked at 400 ° C. for 12 hours. Thereby, as the adsorption layer 53, the amount of gold added was 2.2% by mass (Example 1-1), 4.8% by mass (Example 1-2), and 9.9% by mass (Example 1). 3) Five kinds of Au—Al ₂ O ₃ films different from 10.2% by mass (Example 1-4) and 10.4% by mass (Example 1-5) were formed. The amount of gold added (% by mass) refers to the amount of gold, including γ-Al ₂ O ₃ , when the total mass of the calcined catalyst component is 100%.

Next, the Si substrate is etched from the back surface side by a plasma etching method, and Si in a portion including a position where the Pt-W film, the Pt film, the SnO ₂ film, and the Au—Al ₂ O ₃ film are formed in plan view is removed. By removing, the through-hole 11 was formed. As described above, a gas sensor having a diaphragm structure was manufactured as shown in FIG.

(Example 2)
In Example 2, a gas sensor was manufactured in the same manner as in Example 1 except that the adsorbing layer was formed using a material and a method different from those in Example 1. Specifically, an organic solvent is added to γ-Al ₂ O ₃ (average particle size: 1 μm to ₂ μm) to which 8% by mass of gold particles having an average particle size of 2.5 nm and 0.5% by mass of Fe ₂ O ₃ are added. And the same weight, and further 12% by mass of a silica sol binder were added to form a paste. Subsequently, a paste formed to have a circular shape with a thickness of about 30 μm and a diameter of about 250 μm is applied on the Pt film and the SnO ₂ film by a screen printing method, and baked at 400 ° C. for 12 hours. As a result, an Au / Fe—Al ₂ O ₃ film carrying gold particles and Fe ₂ O ₃ in the adsorption layer was formed.

(Comparative Example 1)
In Comparative Example 1, a gas sensor was manufactured in the same manner as in Example 1 except that the adsorption layer was formed without using gold. Specifically, diethylene glycol monoethyl ether is added to γ-Al ₂ O ₃ (average particle size: ₂ μm to ₃ μm) to which 7.0 mass% of palladium (Pd) is added, and 11 mass% of silica sol binder is further added. To produce a paste. Subsequently, a paste formed to have a circular shape with a thickness of about 30 μm and a diameter of about 250 μm was applied on the Pt film and the SnO ₂ film by screen printing, and baked at 500 ° C. for 12 hours. Thus, an Al ₂ O ₃ (Pd-Al ₂ O ₃ ) film carrying Pd particles on the adsorption layer was formed.

(Comparative Example 2)
In Comparative Example 2, a gas sensor was manufactured in the same manner as in Example 1 except that an adsorption layer containing no catalyst was formed. Specifically, a paste was formed by adding γ-Al ₂ O ₃ (average particle size: ₂ μm to ₃ μm) alone with the same weight of diethylene glycol monoethyl ether and further adding 15% by mass of a silica sol binder without adding a catalyst. . Subsequently, a paste formed to a thickness of about 30 μm and a diameter of about 250 μm was applied on the Pt film and the SnO ₂ film by screen printing, and baked at 500 ° C. for 12 hours. Thus, an Al ₂ O ₃ film containing no catalyst was formed in the adsorption layer.

(Evaluation)
Next, after intermittently driving the gas sensors manufactured in Examples 1 and 2 and Comparative Examples 1 and 2 at a cycle of 30 seconds for 1 second at a heater temperature of the gas sensor of 400 ° C. for 10 minutes, the heater temperature was changed. Then, the resistance value of the gas sensor (sensing layer 52) in a state where the resistance value was stabilized was measured. The gas sensitivity was calculated from the measured resistance value. The sensitivity is the resistance of the gas sensor in clean air atmosphere containing no acetone and ethanol R _air, the resistance value of the gas sensor in a gas atmosphere containing acetone or ethanol predetermined concentration when the R _gas, R _{air /} R It is a value calculated by _gas .

2 to 7 are graphs for explaining the sensitivity characteristics of the gas sensor of the embodiment, FIG. 8 is a graph for explaining the sensitivity characteristics of the gas sensor of Comparative Example 1, and FIG. 9 is a graph for explaining the sensitivity characteristics of the gas sensor of Comparative Example 2. The graph shows the temperature dependence of the sensitivity in a gas atmosphere containing 1 ppm of acetone and the temperature dependence of the sensitivity in a gas atmosphere containing 1 ppm of ethanol. The horizontal axis shows the heater temperature (° C.) of the gas sensor, and the vertical axis shows the sensitivity R _air / R _gas of the _gas sensor. The white circles in the graph show the temperature dependence of the sensitivity of acetone, and the black circles show the temperature dependence of the sensitivity of ethanol.

2 to 6 show the sensitivity characteristics of the gas sensor according to the first embodiment. As shown in FIG. 2, when the heater of the gas sensor is in a range of 250 ° C. to 350 ° C., the sensitivity of acetone and the sensitivity of ethanol tend to be different, and the sensitivity of acetone is higher than the sensitivity of ethanol. I understand. This is considered to be because ethanol is oxidized in the range of 250 ° C. to 350 ° C. by γ-Al ₂ O ₃ to which gold particles having an average particle diameter of 5 nm or less are added, and acetone is hardly oxidized. Therefore, in the gas sensor according to the first embodiment, the difference between the sensitivity of acetone and the sensitivity of ethanol can be used to distinguish and detect acetone and ethanol.

  FIGS. 3 to 6 show that the difference between the acetone sensitivity and the ethanol sensitivity tends to increase particularly with the increase in the amount of gold particles added, and the effect of ethanol is further increased by increasing the amount of gold particles added. Acetone can be detected without receiving the noise. Table 1 shows the ratio of the sensitivity of acetone to the sensitivity of ethanol in the gas sensor of Example 1. The sensitivity ratio tended to increase between 250 ° C. and 350 ° C. regardless of the amount of gold particles added.

  A plot of the sensitivity ratio at 300 ° C. in Table 1 is shown in FIG. The sensitivity ratio tended to be increased by increasing the amount of gold particles added.

  FIG. 7 is a graph illustrating the sensitivity characteristics of the gas sensor according to the second embodiment. As shown in FIG. 7, when the heater temperature of the gas sensor was in the range of 200 ° C. to 400 ° C., the sensitivity of acetone and the sensitivity of ethanol tended to be different, and the sensitivity of acetone became higher than the sensitivity of ethanol.

  Table 2 shows the ratio between the acetone sensitivity and the ethanol sensitivity of Example 2. As in the second embodiment, by using a sensing layer having a composition containing a promoter in addition to the gold particles, the heater temperature at the time of gas detection can be lower than in the first embodiment.

  FIG. 8 is a diagram for explaining the sensitivity characteristics of the gas sensor of Comparative Example 1. As shown in FIG. 8, it can be seen that the sensitivity of acetone and the sensitivity of ethanol show almost the same tendency in a temperature range where the heater temperature of the gas sensor is high in sensitivity to acetone (100 ° C. to 300 ° C.). This is considered to be because although Pd was added to the adsorption layer as a catalyst, in the temperature range where the sensitivity to acetone was high, neither the oxidation reaction of acetone nor the oxidation reaction of ethanol almost occurred. Therefore, the gas sensor of Comparative Example 1 cannot detect acetone and ethanol separately.

  FIG. 9 is a diagram for explaining the sensitivity characteristics of the gas sensor of Comparative Example 2. 9, it can be seen that, similarly to FIG. 8, in the temperature range where the heater temperature of the gas sensor is high in sensitivity to acetone (100 ° C. to 300 ° C.), the sensitivity of acetone and the sensitivity of ethanol show almost the same tendency. . This is considered to be because both the oxidation reaction of acetone and the oxidation reaction of ethanol hardly occur because the adsorption layer contains no catalyst. Therefore, the gas sensor of Comparative Example 2 cannot detect acetone and ethanol separately.

(Test example)
In this test example, the conversion ratio of acetone and ethanol was verified using the catalyst component used for the sensor according to the present invention.

(Test Example 1. Relationship between gold carrying amount and conversion of ethanol and acetone)
A catalyst (Au / Al ₂ O ₃ catalyst) in which gold was supported on a metal oxide carrier containing Al ₂ O ₃ as a main component was prepared by a precipitation precipitation method (DP). An Al ₂ O ₃ carrier was added to the aqueous solution in which the precursor HAuCl ₄ was dissolved, the pH was adjusted to 7 using an aqueous NaOH solution, and the mixture was stirred for 1 h, followed by washing, filtration, and drying. The obtained catalyst was calcined at 400 ° C. for 4 hours. As the Al ₂ O ₃ support, a product obtained by calcining Hygilite (Showa Denko H43M) at 800 ° C. for 5 hours was used. The amount of the aqueous solution was 50 mL per 1 g of Al ₂ O ₃ . The aqueous solution of the gold precursor was prepared by dissolving HAuCl ₄ in a 50 mL aqueous solution to a predetermined charged weight.

In a gas-phase flow reactor, 50 mL min of a gas containing 2000 ppm of ethanol, 400 ppm of acetone, 20 vol% of oxygen and nitrogen as a balance gas was added to 0.048 g of the Au / Al ₂ O ₃ catalyst prepared by the above method. ^{-1 and} the gas after passing was analyzed by a gas chromatograph equipped with a flame ionization detector (FID). The temperature of the catalyst was 250 ° C. By this experimental method, it is possible to simulate the gas component passing through the adsorption layer 53 shown in FIG. 1 of the present invention, and the values of the ethanol conversion and the acetone conversion obtained are correlated with the gas sensor sensitivity. There is.

  Table 3 and FIG. 11 show the supported amounts of gold in the catalyst components, ethanol conversion, and acetone conversion. The ethanol conversion% is a value determined by [(initial ethanol concentration-ethanol concentration after passing through catalyst) / initial ethanol concentration] * 100. The acetone conversion% is a value determined by [(initial acetone concentration-acetone concentration after passing through catalyst) / initial acetone concentration] * 100. In the range of the supported amount of gold of the present invention, the ethanol conversion rate is higher and the acetone conversion rate can be kept low as compared with the case where gold is not used. It was suggested that it was possible.

(Test Example 2. Relationship between gold loading, ethanol and acetone conversion, and temperature)
Ethanol conversion% and acetone conversion were measured under the same experimental conditions as in Test Example 1 except that the catalyst temperature was changed using Catalyst Examples a, b, and i above. The result is shown in FIG. From this result, the temperature range where the difference between the acetone conversion rate and the ethanol conversion rate is large and the ethanol conversion rate is sufficiently large depends on the amount of gold supported on the catalyst. It was suggested that selective detection of is possible.

(Test Example 3. Gold particle size and conversion of ethanol and acetone)
In the same manner as in Test Example 1, an Au / Al ₂ O ₃ catalyst with a supported gold amount of 2.1% by mass was prepared, and used as Catalyst Example j. The Au / Al ₂ O ₃ catalyst obtained in the same manner as in Catalyst Example j was refired at 600 ° C. for 4 hours, and the catalyst was refired at 700 ° C. for 4 hours. After recalcining for 4 hours, this was designated as catalyst example n. In each case, the charged amount was 4% by mass, and the gold carrying amount was 2.1% by mass. Next, using these catalysts, under the same experimental conditions as in Test Example 1, the catalyst temperature was set to 250 ° C., and the conversions of ethanol and acetone were measured.

  Table 4 and FIG. 12 show the gold particle diameter, ethanol conversion, and acetone conversion in the catalyst components. Within the range of the gold particle diameter according to the present invention, the activity with a low ethanol conversion and a low acetone conversion could be obtained.

(Test Example 4. Effect of adding cocatalyst Fe ₂ O ₃ )
A catalyst component containing Fe ₂ O ₃ was prepared as a promoter. γ-Al ₂ O ₃ (product name: H43M Hygilite) is dispersed in an aqueous solution in which a predetermined amount of a metal nitrate (iron (III) nitrate nonahydrate) is dissolved, and the resultant powder is evaporated to dryness. By firing at 600 ° C. for 4 hours, the co-catalyst was impregnated and supported on a metal oxide carrier mainly composed of Al ₂ O ₃ . Next, an Al ₂ O ₃ carrier (Fe ₂ O ₃ / Al ₂ O ₃ ) supporting a co-catalyst Fe ₂ O ₃ was added to the aqueous solution in which the precursor HAuCl ₄ was dissolved, and the pH was adjusted to 7 using an aqueous NaOH solution. After adjusting and stirring for 1 h, washing, filtration and drying were performed. The obtained catalyst was calcined at 400 ° C. for 4 hours. The amount of the aqueous solution was 50 mL per gram of Al ₂ O ₃ , and the aqueous gold precursor solution was prepared by dissolving HAuCl ₄ in a 50 mL aqueous solution so as to have a predetermined charged weight. Next, using these catalyst components, under the same experimental conditions as in Test Example 1, the catalyst temperature was set to 250 ° C., and the conversions of ethanol and acetone were measured.

  Table 5 and FIG. 13 show the relationship between the content of the cocatalyst in the catalyst components, the ethanol conversion, and the acetone conversion. When the content of the cocatalyst was within a predetermined range, the activity could be reduced to an ethanol conversion rate and an acetone conversion rate.

(Test Example 5. Effect of Cocatalyst Addition of ZrO ₂ )
A catalyst component containing ZrO ₂ as a promoter was prepared in the same manner as in Test Example 4 except that zirconium oxynitrate was used as the metal nitrate. The aqueous solution of the gold precursor was prepared by dissolving HAuCl ₄ in a 50 mL aqueous solution to a predetermined charged weight. Next, using these catalyst components, under the same experimental conditions as in Test Example 1, the catalyst temperature was set to 250 ° C., and the conversions of ethanol and acetone were measured.

  Table 6 and FIG. 14 show the relationship between the content of the cocatalyst in the catalyst components, the ethanol conversion, and the acetone conversion. When the content of the cocatalyst was within a predetermined range, the activity could be reduced to an ethanol conversion rate and an acetone conversion rate.

(Test Example 6. Effect of Cocatalyst Addition)
Catalyst components containing each cocatalyst were prepared in the same manner as in Test Examples 4 and 5, except that nitrates of metals constituting metal oxides shown in the following table were used as metal nitrates. The aqueous solution of the gold precursor was prepared by dissolving HAuCl ₄ in a 50 mL aqueous solution to a predetermined charged weight. Next, the conversion of ethanol and acetone was measured using these catalyst components under the same experimental conditions as in Test Example 1. The catalyst temperature was 250 ° C., and the conversion of ethanol and acetone at a catalyst temperature of 213 ° C. was also measured for the catalyst example vi supporting 1% by mass of CuO as a promoter.

Table 7 shows the relationship between the type and content of the co-catalyst in the catalyst component, the ethanol conversion, the acetone conversion, and the catalyst temperature. Even when each of the cocatalysts shown in the table was added, the difference between the ethanol conversion rate and the acetone conversion rate was observed, indicating that the catalyst could function as an adsorption layer component of the gas sensor.

  The preferred embodiment of the present invention has been described above. However, the present invention is not limited to the specific embodiment, and various modifications may be made within the scope of the present invention described in the appended claims.・ Change is possible.

  INDUSTRIAL APPLICABILITY The gas sensor according to the present invention is useful as a low-power-consumption type MEMS solid-state gas sensor with battery driving in mind.

DESCRIPTION OF SYMBOLS 10 Substrate 11 Through-hole 20 Thermal insulation support layer 21 Thermal oxide film 22 Support film 23 Thermal insulation film 30 Heater layer 40 Insulation layer 50 Gas detection layer 51 Electrode layer 52 Sensing layer 53 Adsorption layer

Claims (10)

An adsorption layer that adsorbs a gas containing a detection target gas and a non-detection target gas,
A sensing layer that is covered by the adsorption layer and has an electrical characteristic that changes according to the concentration of the detection target gas that has passed through the adsorption layer;
The adsorption layer includes a catalyst component including gold particles and a metal oxide carrier supporting the gold particles,
The average particle diameter of the gold particles is 10 nm or less, and the gold particles are contained in an amount of 0.02% by mass or more and 12% by mass or less when the total mass of the catalyst component is 100%. Have a gas sensor. Said catalyst _{component, Fe 2 O 3, MnO 2} , CeO 2, Co 3 O 4, NiO, further comprising one or more co-catalysts selected from the group consisting of ZrO 2, CuO, gas sensor according to claim 1 .   3. The gas sensor according to claim 2, wherein the cocatalyst is contained in an amount of 0.1% by mass or more and 10% by mass or less when the total mass of the catalyst component is 100%.   The gas sensor according to claim 1, further comprising a heater layer that heats the adsorption layer. The metal oxide support _{comprises Al 2 O 3, ZrO 2,} CeO 2, Cr 2 O 3, Fe 2 O 3, 1 or more metal oxide selected from the group consisting of NiO, claims 1 to 4 The gas sensor according to claim 1.   The gas sensor according to claim 1, wherein the sensing layer includes a metal oxide semiconductor. The metal oxide semiconductor according to claim 1, wherein the metal oxide semiconductor includes one or more metal oxides selected from the group consisting of SnO ₂ , In ₂ O ₃ , WO ₃ , ZnO, and TiO _2. Gas sensor.   The gas sensor according to claim 1, wherein the detection target gas is ketone, and the non-detection target gas is alcohol. A gas detection method using the gas sensor according to any one of claims 1 to 8,
A method comprising heating the adsorbing layer to 200 ° C. to 400 ° C. to obtain electrical characteristics of the sensing layer.   The gas detection method according to claim 9, further comprising a cleaning step of heating the adsorption layer and the sensing layer to 370 ° C. to 500 ° C. before the detection step.