Gas sensor and gas alarm with gas sensor

Abstract

To provide a gas sensor capable of detecting detection object gas with high accuracy.SOLUTION: A gas sensor 2 comprises: a first detection element 3 including a first gas sensing part, a first heating part for heating the first gas sensing part, and a first detection electrode for detecting a change in a resistance value of the first gas sensing part; and a second detection element 4 including a second gas sensing part, a second heating part for heating the second gas sensing part and a second detection electrode for detecting a change in a resistance value of the second gas sensing part and having different detection sensitivity for the detection object gas from that of the first detection element 3. The gas sensor 2 is configured to detect the detection object gas on the basis of the difference in the detection sensitivity for the detection object gas between the first detection element 3 and the second detection element 4.SELECTED DRAWING: Figure 1

Description

[Technical field]

[0001] The present invention relates to a gas sensor and a gas alarm equipped with the gas sensor. [Background technology]

[0002] For example, hydride gases such as silane are used in semiconductor factories. Hydride gases are highly toxic and therefore require highly accurate detection. Conventionally, electrochemical gas sensors such as those disclosed in Patent Document 1 have been used to detect hydride gases. However, electrochemical gas sensors have difficulty in extending their lifespan because the amount of electrolyte used increases or decreases over time, causing sensitivity fluctuations. In addition, there is a problem that the amount of electrolyte increases or decreases with humidity fluctuations in the usage environment, causing sensitivity fluctuations. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] JP 2005-134248 A [Patent Document 2] JP 2014-202478 A Summary of the Invention [Problem to be solved by the invention]

[0004] On the other hand, as a gas sensor that does not use an electrolyte, for example, a semiconductor gas sensor as disclosed in Patent Document 2 is used. However, the semiconductor gas sensor has high detection sensitivity to interference gases such as alcohol used in semiconductor factories. Therefore, when a detection target gas such as a hydride gas and an interference gas such as alcohol are mixed in the measurement environment, the semiconductor gas sensor is affected by the interference gas, making it difficult to detect the detection target gas with high accuracy.

[0005] The present invention has been made in consideration of the above problems, and has an object to provide a gas sensor capable of detecting a target gas with high accuracy, and a gas alarm equipped with the gas sensor. [Means for solving the problem]

[0006] The gas sensor of the present invention comprises a first detection element having a first gas sensing part mainly composed of tin oxide or indium oxide, a first heating part for heating the first gas sensing part, and a first detection electrode for detecting a change in resistance value of the first gas sensing part, and a second detection element having a second gas sensing part mainly composed of tin oxide or indium oxide, a second heating part for heating the second gas sensing part, and a second detection electrode for detecting a change in resistance value of the second gas sensing part, the second gas sensing element having a detection sensitivity to a target gas different from that of the first detection element, characterized in that the gas sensor is configured to detect the target gas based on a difference in detection sensitivity to the target gas between the first detection element and the second detection element.

[0007] In addition, it is preferable that a difference in detection sensitivity for the target gas between the first detection element and the second detection element is larger than a difference in detection sensitivity for an interference gas between the first detection element and the second detection element.

[0008] It is also preferable that the second sensing element comprises a second catalytic layer covering the second gas sensitive portion, and the first sensing element does not comprise a catalytic layer covering the first gas sensitive portion, or comprises a first catalytic layer different from the second catalytic layer covering the first gas sensitive portion.

[0009] The difference in detection sensitivity to the target gas is preferably a difference in detection sensitivity to a silicon-hydrogen bond-containing gas.

[0010] The second catalyst layer preferably contains alumina.

[0011] It is also preferable that the first detection element includes a first catalyst layer covering the first gas sensitive portion, and the first catalyst layer contains any one of silica, silica alumina, and zeolite.

[0012] It is also preferable that the gas sensor in which the first sensing element and the second sensing element are incorporated is configured as a single gas sensor.

[0013] A gas alarm of the present invention is characterized by comprising the above-mentioned gas sensor. Effect of the Invention

[0014] According to the present invention, it is possible to provide a gas sensor capable of detecting a detection target gas with high accuracy, and a gas alarm equipped with the gas sensor. [Brief description of the drawings]

[0015] [Figure 1] 1 is a schematic diagram showing the configuration of a gas alarm including a gas sensor according to one embodiment of the present invention. [Diagram 2] 2 is a schematic diagram of a first sensing element and a second sensing element included in the gas sensor of FIG. 1. [Diagram 3] 5A and 5B are diagrams showing changes in element output of a sensing element relative to changes in gas concentration, where (a) shows changes in element output of a first sensing element, and (b) shows changes in element output of a second sensing element. [Figure 4] FIG. 13 is a graph showing a change in the difference between the element output of a first sensing element and the element output of a second sensing element with respect to a change in gas concentration. [Diagram 5] FIG. 13 is a graph showing the change in element output of a sensing element obtained from 1 ppm of silane with respect to the change in the amount of molybdenum oxide added. [Figure 6] FIG. 13 shows a change in the element output of a sensing element obtained from 1 ppm of silane with respect to a change in the amount of lanthanum oxide added, and a change in the ratio of the element output of a first sensing element obtained from 100 ppm of hydrogen to the element output of a first sensing element obtained from 1 ppm of silane. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0016] A gas sensor 2 according to one embodiment of the present invention will be described below with reference to the accompanying drawings. In particular, as shown in FIG. 1, the gas sensor 2 of this embodiment will be described by taking an example in which the gas sensor 2 is incorporated into a gas alarm 1. However, the embodiment described below is merely an example, and the gas sensor of the present invention is not limited to the following example. Furthermore, the gas sensor of the present invention can also be incorporated and used in known gas alarms and gas detectors other than the gas alarms described below.

[0017] As shown in FIG. 1, the gas alarm device 1 is equipped with a gas sensor 2 that detects a target gas. The gas alarm device 1 is configured to notify the user that a target gas has been detected by the gas sensor 2. In this embodiment, in addition to the gas sensor 2, the gas alarm device 1 further comprises a power source 6 that supplies power to the components of the gas alarm device 1, an input section 7 such as a button that accepts user input, a storage section 8 such as a memory that stores the sensitivity characteristics (calibration curve) of the detection element included in the gas sensor 2 and the detection results of the target gas, and an output section 9 such as a display or speaker that outputs the detection results of the target gas. The gas alarm device 1 is configured to notify the user of a warning by the output section 9 using a warning display or warning sound, for example, when a target gas of a predetermined concentration or higher is detected by the gas sensor 2. It is sufficient that the gas alarm device 1 is equipped with at least the gas sensor 2, and the power source 6, input section 7, storage section 8 and output section 9 may be provided separately from the gas alarm device 1 and connected to the gas alarm device 1.

[0018] The gas sensor 2 detects a target gas contained in a target gas constituting an environmental atmosphere, such as atmospheric gas. The gas sensor 2 determines the presence or absence of the target gas in the target gas and / or determines the concentration of the target gas in the target gas. The target gas detected by the gas sensor 2 is not particularly limited, but examples thereof include silicon-hydrogen bond-containing gases such as silane, disilane, trisilane, chlorosilane, dichlorosilane, and trichlorosilane. However, the gas sensor 2 may be configured to detect gases other than silicon-hydrogen bond-containing gases.

[0019] As shown in FIG. 1, the gas sensor 2 includes a first sensing element 3 and a second sensing element 4 having a detection sensitivity to a target gas different from that of the first sensing element 3. The gas sensor 2 further includes a control unit 5 that processes detection signals obtained by the first sensing element 3 and the second sensing element 4. The gas sensor 2 is configured to detect the target gas using the control unit 5 based on the difference in detection sensitivity to the target gas between the first sensing element 3 and the second sensing element 4. Here, the detection signals obtained by the first and second sensing elements 3 and 4 include not only the detection signal of the target gas, but also the detection signal of interference gases (ethanol, hydrogen, etc.) other than the target gas contained in the target gas. The interference gas is a gas that is not a target of detection by the gas sensor 2 but can be inevitably detected by the first and second sensing elements 3 and 4. In the gas sensor 2, the first and second detection elements 3, 4 are configured to have different detection sensitivities to the target gas, so that, for example, by calculating the difference between the detection signals obtained by the first and second detection elements 3, 4, it is possible to reduce the detection signal strength of the interference gas while maintaining the detection signal strength of the target gas. As a result, the gas sensor 2 can reduce the relative strength of the detection signal of the interference gas to the detection signal of the target gas, so that the effect of the interference gas can be suppressed and the target gas can be detected with high accuracy. From this perspective, it is preferable that the difference in detection sensitivity to the target gas between the first detection element 3 and the second detection element 4 is larger than the difference in detection sensitivity to the interference gas between the first detection element 3 and the second detection element 4. However, it is sufficient that the first and second detection elements 3, 4 have different detection sensitivities for the target gas, and even if the difference in detection sensitivity for the target gas between the first detection element 3 and the second detection element 4 is the same as or smaller than the difference in detection sensitivity for the interference gas between the first detection element 3 and the second detection element 4, the target gas can be detected with high accuracy as long as the type and concentration of the interference gas are known, or the ratio of the concentration of the interference gas to the concentration of the target gas is known. Note that, as an example of the difference in detection sensitivity for the target gas, the difference in detection sensitivity for a silicon-hydrogen bond-containing gas is exemplified, but it may also be a difference in detection sensitivity for other gases.

[0020] The first detection element 3 is a semiconductor gas detection element having a higher detection sensitivity to the target gas than the second detection element 4. The first detection element 3 may have a higher detection sensitivity to the target gas than the second detection element 4, and the structure thereof is not particularly limited. In this embodiment, as shown in FIG. 2, the first detection element 3 includes a first gas sensing part 31, a first heating part 32 for heating the first gas sensing part 31, and a first detection electrode 33 for detecting a change in resistance value of the first gas sensing part 31. The first detection element 3 detects the target gas and / or interference gas contained in the target gas by detecting the change in resistance value with the first detection electrode 33, utilizing a phenomenon in which the resistance value of the first gas sensing part 31 changes when the target gas contains the target gas and / or interference gas.

[0021] In this embodiment, as shown in FIG. 1, the first sensing element 3 is incorporated into a first bridge circuit BC1 via a first sensing electrode 33 together with a power source E and fixed resistors R0, R1, and R2 in order to detect a change in the resistance value of the first gas sensing part 31. The first bridge circuit BC1 measures a change in potential difference in the circuit caused by a change in the resistance value of the first gas sensing part 31 in the first sensing element 3 using a potentiometer V, and outputs the change in potential difference as a detection signal for the detection target gas and / or interference gas. The output change in potential difference is transmitted to the control unit 5. However, the first sensing element 3 is not limited to the first bridge circuit BC1, and may be incorporated into a circuit other than the first bridge circuit BC1 as long as it can detect a change in the resistance value of the first gas sensing part 31.

[0022] The first gas sensitive section 31 is a section whose resistance value changes when the target gas contains a detection target gas and / or an interference gas. The change in the resistance value of the first gas sensitive section 31 is considered to occur when the target gas and / or the interference gas reacts with oxygen adsorbed on the surface of the first gas sensitive section 31. The first gas sensitive section 31 may be doped with a metal element such as antimony or cerium as a donor, for example, by using a metal oxide in order to adjust the electrical resistance. The first gas sensitive section 31 may be formed with tin oxide or indium oxide as the main component, and the method of forming the first gas sensitive section 31 is not particularly limited. The first gas sensitive section 31 may be formed, for example, by mixing fine powder of tin oxide or indium oxide with a dispersion medium such as ethylene glycol to form a paste, and applying the paste to the application target (in this embodiment, the first heating section 32 and the first detection electrode 33) and drying it. The term "main component" refers to a main component among the components constituting the first gas sensing part 31, and means, for example, a component contained in the first gas sensing part 31 at a concentration of more than 50 mol %.

[0023] The first gas sensing part 31 may contain molybdenum oxide (such as MoO3) and / or lanthanoid oxide (such as La2O3, Pr2O3, Nd2O3, etc.) in addition to the main component tin oxide or indium oxide. The first gas sensing part 31 contains molybdenum oxide, which improves the detection sensitivity to the detection target gas, particularly the silicon-hydrogen bond-containing gas. The first gas sensing part 31 contains lanthanoid oxide, which improves the detection sensitivity to the detection target gas, particularly the silicon-hydrogen bond-containing gas, and improves the selectivity to interference gases such as hydrogen. The amount of molybdenum oxide added is not particularly limited, but is preferably 0.01 to 1 mol %, more preferably 0.05 to 0.5 mol %, and even more preferably 0.1 to 0.3 mol %, relative to the main component tin oxide or indium oxide. The amount of lanthanoid oxide added is not particularly limited, but is preferably 0.01 to 1 mol %, more preferably 0.05 to 0.5 mol %, and even more preferably 0.1 to 0.3 mol % relative to the main component tin oxide or indium oxide. Molybdenum oxide and lanthanoid oxide are not particularly limited, and can be added to tin oxide or indium oxide by impregnating tin oxide or indium oxide with a molybdenum-based aqueous solution such as an aqueous ammonium molybdate solution or a lanthanoid-based aqueous solution such as an aqueous lanthanum nitrate solution, respectively, and subjecting the tin oxide or indium oxide to a thermal decomposition treatment.

[0024] The first heating section 32 is a section for heating the first gas sensitive section 31. The heating temperature of the first gas sensitive section 31 may be any temperature suitable for detecting the gas to be detected, and is not particularly limited, but may be set to, for example, 300 to 600°C, preferably 350 to 550°C, and more preferably 400 to 500°C. In this embodiment, the first heating section 32 is formed in a coil shape using a platinum wire or the like, as shown in FIG. 2, and the first gas sensitive section 31 is provided so as to cover its outer periphery. As a result, the first sensing element 3 is formed as a coil type (or hot wire type, two-terminal type) semiconductor type gas sensing element. The first heating section 32 heats the first gas sensitive section 31 and also functions as the first sensing electrode 33 for detecting a change in the resistance value of the first gas sensitive section 31. The coil constituting the first heating section 32 and the first sensing electrode 33 is made of a material, a wire diameter, a coil diameter, and a number of coil turns that are generally used in coil type semiconductor type gas sensing elements. The first detection element 3 is not limited to a coil type, but may be a MEMS type or a substrate type, and is not limited to being integral with the heating portion and the detection electrode, but may be another type of semiconductor gas detection element in which the heating portion and the detection electrode are provided separately.

[0025] As shown in FIG. 2, the first detection element 3 may include a first catalyst layer 34 covering the first gas sensitive portion 31. The first catalyst layer 34 partially or entirely covers the first gas sensitive portion 31, thereby reducing the detection sensitivity of the first detection element 3 to interference gases contained in the measurement target gas. This is believed to be because the interference gas is burned by the catalytic action of the first catalyst layer 34, and the interference gas is prevented from reaching the surface of the first gas sensitive portion 31 beyond the first catalyst layer 34. The first catalyst layer 34 may be any material capable of reducing the detection sensitivity of the first detection element 3 to interference gases, and is not particularly limited, but preferably contains any of silica, silica alumina, and zeolite. By containing any of silica, silica alumina, and zeolite, the first catalyst layer 34 can reduce the detection sensitivity of the first detection element 3 to interference gases while suppressing the reduction in the detection sensitivity of the first detection element 3 to the detection target gas. It is preferable that the first catalyst layer does not contain alumina from the viewpoint of suppressing a decrease in the detection sensitivity of the first detection element 3 to the detection target gas, particularly to the silicon-hydrogen bond-containing gas.

[0026] From the viewpoint of further reducing the detection sensitivity of the first detection element 3 to interference gases, the first catalyst layer 34 may be formed by supporting tungsten oxide and / or molybdenum oxide on a carrier containing any one of silica, silica alumina, and zeolite. The first detection element 3 has a reduced detection sensitivity to alcohol, which is an interference gas, when the first catalyst layer 34 contains tungsten oxide and / or molybdenum oxide. This is considered to be because tungsten oxide and / or molybdenum oxide promote the decomposition of alcohol as a dehydration catalyst for alcohol. The contents of tungsten oxide and molybdenum oxide in the first catalyst layer 34 are not particularly limited, but are preferably 0.5 to 5.0 mol%, more preferably 1.0 to 4.0 mol%, and even more preferably 1.5 to 3.0 mol%, respectively, relative to the carrier containing any one of silica, silica alumina, and zeolite.

[0027] The method of forming the first catalytic layer 34 is not particularly limited as long as it can be formed to have the above-mentioned functions. The first catalytic layer 34 can be formed, for example, by mixing fine powders of silica, silica alumina, zeolite, or the like to which tungsten oxide, molybdenum oxide, or the like has been added with a dispersion medium such as water to form a paste, applying the paste to the surface of the first gas sensitive part 31, and then sintering the paste by heating.

[0028] The second detection element 4 is a semiconductor gas detection element having a detection sensitivity to the detection target gas lower than that of the first detection element 3. The second detection element 4 only needs to have a detection sensitivity to the detection target gas lower than that of the first detection element 3, and the structure thereof is not particularly limited. In this embodiment, as shown in FIG. 2, the second detection element 4 includes a second gas sensing part 41, a second heating part 42 for heating the second gas sensing part 41, and a second detection electrode 43 for detecting a change in the resistance value of the second gas sensing part 41. The second detection element 4 detects the detection target gas and / or interference gas by detecting the change in the resistance value with the second detection electrode 43, utilizing the phenomenon that the resistance value of the second gas sensing part 41 changes when the detection target gas and / or interference gas is contained in the measurement target gas.

[0029] In this embodiment, the second sensing element 4 is incorporated into a second bridge circuit BC2 via a second sensing electrode 43 together with a power source E and fixed resistors R0, R1, and R2, as shown in FIG. 1, in order to detect a change in the resistance value of the second gas sensing part 41. The second bridge circuit BC2 measures a change in the potential difference in the circuit caused by a change in the resistance value of the second gas sensing part 41 in the second sensing element 4 using a potentiometer V, and outputs the change in the potential difference as a detection signal for the target gas and / or interference gas. The output change in the potential difference is transmitted to the control unit 5. In this embodiment, the second sensing element 4 is incorporated into a second bridge circuit BC2 separate from the first bridge circuit BC1 in which the first sensing element 3 is incorporated, but may be incorporated into the bridge circuit in which the first sensing element 3 is incorporated together with the first sensing element 3. Furthermore, the first bridge circuit BC1 incorporating the first sensing element 3 and the second bridge circuit BC2 incorporating the second sensing element 4 may be connected to a differential circuit, so that the first sensing element 3 and the second sensing element 4 are incorporated in one circuit. In this manner, the gas sensor 2 incorporating the first sensing element 3 and the second sensing element 4 can be configured as a single gas sensor. However, the second sensing element 4 is not limited to being incorporated in the second bridge circuit BC2, and may be incorporated in a circuit different from the second bridge circuit BC2 as long as it can detect a change in the resistance value of the second gas sensing portion 41.

[0030] The second gas sensitive part 41 is a part whose resistance value changes when the gas to be measured contains a metal oxide semiconductor of tin oxide or indium oxide. It is considered that the change in the resistance value of the second gas sensitive part 41 occurs when the gas to be detected and / or the interference gas reacts with oxygen adsorbed on the surface of the second gas sensitive part 41. The second gas sensitive part 41 may be doped with a metal element such as antimony or cerium as a donor in order to adjust the electrical resistance. The second gas sensitive part 41 may be formed by any method as long as it can be formed with tin oxide or indium oxide as the main component. The second gas sensitive part 41 can be formed, for example, by mixing fine powder of tin oxide or indium oxide with a dispersion medium such as ethylene glycol to form a paste, and applying the paste to the application target (in this embodiment, the second heating part 42 and the second detection electrode 43) and drying it. The term "main component" refers to a main component among the components constituting the second gas sensing part 41, and means, for example, a component contained in the second gas sensing part 41 at a concentration of more than 50 mol %.

[0031] The second gas sensing part 41 may contain molybdenum oxide (such as MoO3) and / or lanthanoid oxide (such as La2O3, Pr2O3, Nd2O3, etc.) in addition to the main component tin oxide or indium oxide. The second gas sensing part 41 contains molybdenum oxide, which improves the detection sensitivity to the detection target gas, particularly the silicon-hydrogen bond-containing gas. The second gas sensing part 41 contains lanthanoid oxide, which improves the detection sensitivity to the detection target gas, particularly the silicon-hydrogen bond-containing gas, and improves the selectivity to interference gases such as hydrogen. The amount of molybdenum oxide added is not particularly limited, but is preferably 0.01 to 1 mol %, more preferably 0.05 to 0.5 mol %, and even more preferably 0.1 to 0.3 mol %, relative to the main component tin oxide or indium oxide. The amount of lanthanoid oxide added is not particularly limited, but is preferably 0.01 to 1 mol %, more preferably 0.05 to 0.5 mol %, and even more preferably 0.1 to 0.3 mol % relative to the main component tin oxide or indium oxide. Molybdenum oxide and lanthanoid oxide are not particularly limited, and can be added to tin oxide or indium oxide by impregnating tin oxide or indium oxide with a molybdenum-based aqueous solution such as an aqueous ammonium molybdate solution or a lanthanoid-based aqueous solution such as an aqueous lanthanum nitrate solution, respectively, and subjecting the tin oxide or indium oxide to a thermal decomposition treatment.

[0032] The second heating section 42 is a section for heating the second gas sensing section 41. The heating temperature of the second gas sensing section 41 may be a temperature suitable for detecting the gas to be detected, and is not particularly limited, but may be set to, for example, 300 to 600°C, preferably 350 to 550°C, and more preferably 400 to 500°C. In this embodiment, the second heating section 42 is formed in a coil shape using a platinum wire or the like, as shown in FIG. 2, and the second gas sensing section 41 is provided so as to cover the outer periphery of the second heating section 42. As a result, the second sensing element 4 is formed as a coil-type (or hot wire type, two-terminal type) semiconductor gas sensing element. The second heating section 42 heats the second gas sensing section 41 and also functions as a second sensing electrode 43 for detecting a change in the resistance value of the second gas sensing section 41. The coil constituting the second heating section 42 and the second sensing electrode 43 is made of a material, a wire diameter, a coil diameter, and a number of coil turns that are generally used in coil-type semiconductor gas sensing elements. The second detection element 4 is not limited to a coil type, but may be a MEMS type or a substrate type. Furthermore, it is not limited to one in which the heating portion and the detection electrode are integrally provided, but may be another type of semiconductor gas detection element in which the heating portion and the detection electrode are provided separately.

[0033] As described above, the second detection element 4 is formed so as to have a lower detection sensitivity to the target gas than the first detection element 3. For that purpose, in this embodiment, the second detection element 4 is provided with a second catalyst layer 44 covering the second gas sensitive portion 41. The second catalyst layer 44 reduces the detection sensitivity of the second detection element 4 to the target gas by partially or entirely covering the second gas sensitive portion 41. When the second detection element 4 is provided with the second catalyst layer 44, the first detection element 3 does not include a catalyst layer covering the first gas sensitive portion 31, or includes a first catalyst layer 34 that covers the first gas sensitive portion 31 and is different from the second catalyst layer 44, in order to realize a detection sensitivity to the target gas higher than that of the second detection element 4. The first catalyst layer 34 is configured to suppress the decrease in the detection sensitivity of the first detection element 3 to the target gas at least more than the second catalyst layer 44.

[0034] The second catalyst layer 44 is not particularly limited as long as it can reduce the detection sensitivity of the second detection element 4 to the target gas, but preferably contains alumina. When the second catalyst layer 44 contains alumina, the detection sensitivity of the second detection element 4 to the target gas is reduced. This is considered to be because the target gas, particularly the silicon-hydrogen bond-containing gas, is adsorbed to the alumina of the second catalyst layer 44, and is prevented from passing through the second catalyst layer 44 and reaching the surface of the second gas sensitive part 41. If alumina is provided in at least a part of the second catalyst layer 44, it can reduce the detection sensitivity of the second detection element 4 to the target gas, but from the viewpoint of further reducing the detection sensitivity to the target gas, it is preferable to contain alumina as a main component (more than 50 mol%) of the second catalyst layer 44. Note that alumina as used here does not include aluminum oxide containing silicon oxide such as silica alumina and zeolite.

[0035] From the viewpoint of reducing the detection sensitivity of the second detection element 4 to interference gases, the second catalyst layer 44 may be formed by supporting tungsten oxide and / or molybdenum oxide on a support containing alumina. The second detection element 4 has a reduced detection sensitivity to alcohol, which is an interference gas, when the second catalyst layer 44 contains tungsten oxide and / or molybdenum oxide. This is believed to be because tungsten oxide and / or molybdenum oxide promote the decomposition of alcohol as a dehydration catalyst for alcohol. The contents of tungsten oxide and molybdenum oxide in the second catalyst layer 44 are not particularly limited, but are preferably 0.5 to 5.0 mol %, more preferably 1.0 to 4.0 mol %, and even more preferably 1.5 to 3.0 mol %, respectively, relative to the support containing alumina.

[0036] The method of forming the second catalytic layer 44 is not particularly limited as long as it can be formed to have the above-mentioned functions. The second catalytic layer 44 can be formed, for example, by mixing fine powder such as alumina to which tungsten oxide, molybdenum oxide, etc. have been added with a dispersion medium such as water to form a paste, applying the paste to the surface of the second gas sensitive part 41, and then sintering the paste by heating.

[0037] In this embodiment, as described above, in order to increase the detection sensitivity of the first detection element 3 to the target gas more than that of the second detection element 4, the first gas sensitive portion 31 of the first detection element 3 and the second gas sensitive portion 41 of the second detection element 4 are configured the same, and the respective catalytic layers are configured differently. However, for the same purpose, for example, the respective gas sensitive portions may be configured differently and the respective catalytic layers may be configured the same, or the respective gas sensitive portions and catalytic layers may be configured the same, and the respective element temperatures during measurement may be different. In addition, the detection sensitivity of the first detection element 3 to the target gas may be increased more than that of the second detection element 4 by making the composition of the respective gas sensitive portions and / or catalytic layers the same, and changing the firing temperature of the respective gas sensitive portions and / or catalytic layers.

[0038] The control unit 5 processes the detection signals obtained by the first detection element 3 and the second detection element 4. In this embodiment, as shown in FIG. 1, the control unit 5 is communicatively connected to a first bridge circuit BC1 in which the first detection element 3 is incorporated, and a second bridge circuit BC2 in which the second detection element 4 is incorporated. The control unit 5 calculates a difference between the detection signal of the first detection element 3 transmitted from the first bridge circuit BC1 and the detection signal of the second detection element 4 transmitted from the second bridge circuit BC2. The control unit 5 determines the presence or absence of the target gas based on the calculated difference, and / or determines the concentration of the target gas using a calibration curve prepared in advance. In this way, the gas sensor 2 is configured to process the detection signals of the two first and second detection elements 3 and 4 by the single control unit 5, thereby constituting a single gas sensor. Note that the control unit 5 does not need to perform a step of calculating the difference between the detection signals when the first and second detection elements 3 and 4 are arranged in a single circuit and the difference between the detection signals is calculated by the single circuit. The control unit 5 is not particularly limited and is formed by a known CPU. The control unit 5 may be provided in the gas alarm 1 separately from the gas sensor 2.

[0039] A gas sensor and a gas alarm equipped with a gas sensor according to one embodiment of the present invention have been described above. However, the gas sensor and gas alarm of the present invention are not limited to the above-described embodiment. The above-described embodiment mainly describes an invention having the following configuration.

[0040] (1) a first sensing element including a first gas sensing part mainly composed of tin oxide or indium oxide, a first heating part for heating the first gas sensing part, and a first sensing electrode for detecting a change in resistance value of the first gas sensing part; a second gas sensing element including a second gas sensing part mainly composed of tin oxide or indium oxide, a second heating part for heating the second gas sensing part, and a second sensing electrode for detecting a change in resistance value of the second gas sensing part, the second gas sensing element having a detection sensitivity to a detection target gas different from that of the first sensing element; A gas sensor comprising: The gas sensor is configured to detect the target gas based on a difference in detection sensitivity for the target gas between the first detection element and the second detection element. Gas sensor.

[0041] (2) a difference in detection sensitivity for the target gas between the first detection element and the second detection element is larger than a difference in detection sensitivity for an interference gas between the first detection element and the second detection element; The gas sensor according to (1).

[0042] (3) the second detection element includes a second catalyst layer covering the second gas sensitive portion, The first sensing element does not include a catalyst layer covering the first gas sensitive portion, or includes a first catalyst layer covering the first gas sensitive portion and different from the second catalyst layer. A gas sensor according to (1) or (2).

[0043] (4) The difference in detection sensitivity for the detection target gas is a difference in detection sensitivity for a silicon-hydrogen bond-containing gas, The gas sensor according to any one of (1) to (3).

[0044] (5) The second catalyst layer contains alumina. The gas sensor according to (3).

[0045] (6) The first detection element includes a first catalyst layer covering the first gas sensitive portion, The first catalyst layer contains any one of silica, silica alumina, and zeolite. The gas sensor according to (3) or (5).

[0046] (7) The gas sensor in which the first sensing element and the second sensing element are incorporated is configured as a single gas sensor. The gas sensor according to any one of (1) to (6).

[0047] (8) A gas alarm comprising the gas sensor according to any one of (1) to (7). EXAMPLES

[0048] The excellent effects of the gas sensor of this embodiment will be described below with reference to examples, although the gas sensor of the present invention is not limited to the following examples.

[0049] (First sensing element) As the first sensing element, a first sensing element 3 shown in Fig. 2 was produced. The components of the first sensing element were formed in the following manner.

[0050] The first gas sensing part was formed into a roughly spherical shape with a diameter of about 0.5 mm by mixing a fine powder of tin oxide semiconductor doped with antimony to obtain a predetermined electrical conductivity with a dispersion medium (ethylene glycol) to make a paste, which was applied around the platinum coil (first heating part and first detection electrode) and dried by heating at 600°C for 1 hour. Furthermore, the roughly spherical tin oxide semiconductor was impregnated with droplets of a 0.1 mol / L aqueous solution of lanthanum nitrate, subjected to a thermal decomposition treatment at 600°C for 1 hour, and further impregnated with droplets of a 0.2 mol / L aqueous solution of ammonium molybdate, subjected to a thermal decomposition treatment at 600°C for 1 hour, and supported by lanthanum oxide and molybdenum oxide on the tin oxide semiconductor. The amounts of lanthanum oxide and molybdenum oxide added were 0.1 mol% and 0.2 mol% relative to the tin oxide semiconductor, respectively.

[0051] The first catalytic layer was formed by mixing fine silica-alumina powder with 2 mol% tungsten oxide with a dispersion medium (water) to form a paste, which was then applied to the entire surface of the first gas sensing part, heated at 600°C for 1 hour, and sintered.

[0052] (Second sensing element) As the second sensing element, a second sensing element 4 shown in Fig. 2 was produced. The components of the second sensing element were formed in the following manner.

[0053] The second gas sensitive part was prepared in the same manner as the first gas sensitive part of the first detection element.

[0054] The second catalytic layer was formed by mixing fine alumina powder with 2 mol% tungsten oxide added with a dispersion medium (water) to form a paste, which was then applied to the entire surface of the second gas sensing part, heated at 600°C for 1 hour, and sintered.

[0055] (Element output of the first and second detector elements) The first and second sensing elements were incorporated into a first and second bridge circuit, as shown in FIG. 1, and the element outputs (changes in the potential difference in the bridge circuit, corresponding to the above-mentioned detection signal) of the first and second sensing elements were measured in an environment in which the target gas, silane, and interference gases, ethanol and hydrogen, were contained in the air. The temperatures of the first gas-sensing part of the first sensing element and the second gas-sensing part of the second sensing element during measurement were set to 400°C by passing a predetermined amount of current through the first heating part and the second heating part. FIG. 3(a) shows the changes in the element output of the first sensing element with respect to the respective concentrations of silane, ethanol, and hydrogen, and FIG. 3(b) shows the changes in the element output of the second sensing element with respect to the respective concentrations of silane, ethanol, and hydrogen. FIG. 4 shows the changes in the element output, obtained by subtracting the element output of the second sensing element of FIG. 3(b) from the element output of the first sensing element of FIG. 3(a), with respect to the gas concentration.

[0056] In Fig. 3(a) and Fig. 3(b), in both the first and second sensing elements, the element output increases with an increase in the respective concentrations of silane, ethanol, and hydrogen. Also, the element output for silane in the first sensing element, which has a relatively high detection sensitivity to silane (Fig. 3(a)), is much larger than the element output for silane in the second sensing element, which has a relatively low detection sensitivity to silane (Fig. 3(b)). On the other hand, the element output for ethanol and hydrogen in the first sensing element (Fig. 3(a)) is only slightly larger than the element output for ethanol and hydrogen in the second sensing element (Fig. 3(b)). As a result, the difference in element output obtained for silane, which is the detection target gas, between the first and second sensing elements is larger than the difference in element output obtained for alcohol and hydrogen, which are interference gases. When the element output of the second detection element is subtracted from the element output of the first detection element, the element output for silane is significantly larger than the element outputs for ethanol and hydrogen relative to the element outputs for ethanol and hydrogen, while the tendency for the element output to increase with increasing concentrations of silane, ethanol, and hydrogen is maintained, as shown in Figure 4. This result shows that by determining the difference between the element outputs obtained by the first and second detection elements, which have different detection sensitivities to the target gas, the effect of interference gases on the element output can be suppressed, thereby enabling the target gas to be detected with high accuracy.

[0057] (Effect of adding molybdenum oxide to the gas sensing element) In the above-mentioned first sensing element, the concentration of the ammonium molybdate aqueous solution used in forming the first gas sensing part was changed to form a first gas sensing part with a different amount of molybdenum oxide added. At this time, the amount of lanthanum oxide added was set to 0.1 mol %. The first sensing element thus prepared was incorporated into a first bridge circuit as shown in FIG. 1, and the element output of the first sensing element was measured in an environment containing 1 ppm of silane in the air. The temperature of the first gas sensing part of the first sensing element during measurement was set to 400° C. by passing a predetermined amount of current through the first heating part. FIG. 5 shows the change in the element output of the first sensing element with respect to the amount of molybdenum oxide added.

[0058] In Fig. 5, the element output of the first detection element increases with increasing amount of molybdenum oxide when the amount of molybdenum oxide added is from 0.05 mol% to 0.2 mol%, and decreases with increasing amount of molybdenum oxide added when the amount of molybdenum oxide added is from 0.2 mol% to 2 mol%. When the element output exceeds 100mV, it can be said that the sensitivity is sufficient to accurately detect silane, which is the detection target gas, and from that viewpoint, it is preferable that the amount of molybdenum oxide added is 0.01 to 1 mol%. Among them, it is more preferable that the amount of molybdenum oxide added is 0.05 to 0.5 mol%, and even more preferable that it is 0.1 to 0.3 mol%.

[0059] (Effect of adding lanthanum oxide to the gas sensing element) In the above-mentioned first sensing element, the concentration of the lanthanum nitrate aqueous solution used for forming the first gas sensing part was changed to form a first gas sensing part with a different amount of lanthanum oxide added. At this time, the amount of molybdenum oxide added was set to 0.2 mol %. The fabricated first sensing element was incorporated into a first bridge circuit as shown in FIG. 1, and the element output of the first sensing element was measured in an environment where 1 ppm of silane was contained in the air. Separately, the element output of the first sensing element was measured in an environment where 100 ppm of hydrogen was contained in the air. The temperature of the first gas sensing part of the first sensing element during measurement was set to 400° C. by passing a predetermined amount of current through the first heating part. FIG. 6 shows the change in the element output (1 ppm silane) and element output ratio (100 ppm hydrogen / 1 ppm silane) of the first sensing element with respect to the amount of lanthanum oxide added.

[0060] In FIG. 6, the element output of the first sensing element obtained from 1 ppm silane decreases with an increase in the amount of lanthanum oxide added. When the element output exceeds 100 mV, it can be said that the sensitivity is sufficient to accurately detect silane, which is the target gas, and from that viewpoint, it is preferable that the amount of lanthanum oxide added is 1 mol% or less. Among them, it is more preferable that the amount of lanthanum oxide added is 0.5 mol% or less, and even more preferable that the amount of lanthanum oxide added is 0.3 mol% or less. Also, in FIG. 6, the ratio of the element output of the first sensing element obtained from 1 ppm silane to the element output of the first sensing element obtained from 100 ppm hydrogen decreases with an increase in the amount of lanthanum oxide added. When the element output ratio (100 ppm hydrogen / 1 ppm silane) is smaller than 1, it can be said that there is sufficient selectivity to accurately detect silane, which is the target gas, while suppressing the influence of hydrogen, which is an interference gas, and from that viewpoint, it is preferable that the amount of lanthanum oxide added is 0.01 mol% or more. It can be seen that, among these, the amount of lanthanum oxide added is more preferably 0.05 mol % or more, and even more preferably 0.1 mol % or more. [Explanation of symbols]

[0061] 1 Gas alarm 2 Gas Sensor 3 First sensing element 31 First gas sensor 32 1st heating section 33 First sensing electrode 34 1st catalyst layer 4 Second sensing element 41 Second gas sensor 42 2nd heating section 43 Second sensing electrode 44 Second catalyst layer 5. Control section 6 Power supply 7 Input section 8 Memory section 9 Output section BC1 First bridge circuit BC2 Second bridge circuit E Power R0, R1, R2 fixed resistance V Potentiometer

Claims

1. a first detection element including a first gas sensitive part containing tin oxide or indium oxide as a main component, a first heating part for heating the first gas sensitive part, and a first detection electrode for detecting a change in resistance value of the first gas sensitive part; a second detection element including a second gas sensitive part mainly composed of tin oxide or indium oxide, a second heating part for heating the second gas sensitive part, and a second detection electrode for detecting a change in resistance value of the second gas sensitive part, the second detection element having a detection sensitivity to a detection target gas different from that of the first detection element; A gas sensor comprising: the gas sensor is configured to detect the target gas based on a difference in detection sensitivity for the target gas between the first detection element and the second detection element; The difference in detection sensitivity for the detection target gas is a difference in detection sensitivity for a silicon-hydrogen bond-containing gas. Gas sensor.

2. A first detection element including a first gas sensitive part whose main component is tin oxide or indium oxide, a first heating part for heating the first gas sensitive part, and a first detection electrode for detecting a change in the resistance value of the first gas sensitive part; a second detection element including a second gas sensitive part mainly composed of tin oxide or indium oxide, a second heating part for heating the second gas sensitive part, and a second detection electrode for detecting a change in resistance value of the second gas sensitive part, the second detection element having a detection sensitivity to a detection target gas different from that of the first detection element; A gas sensor comprising: the gas sensor is configured to detect the target gas based on a difference in detection sensitivity for the target gas between the first detection element and the second detection element; the first sensing element includes a first catalyst layer covering the first gas sensitive portion, the second detection element includes a second catalyst layer covering the second gas sensitive portion, the first catalyst layer and the second catalyst layer have different structures such that the detection sensitivity of the first detection element for the target gas is higher than the detection sensitivity of the second detection element for the target gas. Gas sensor.

3. a difference in detection sensitivity between the first detection element and the second detection element for the target gas is larger than a difference in detection sensitivity between the first detection element and the second detection element for an interference gas; 3. The gas sensor according to claim 1.

4. the second detection element includes a second catalyst layer covering the second gas sensitive portion, the first sensing element does not include a catalyst layer covering the first gas sensitive portion, or includes a first catalyst layer covering the first gas sensitive portion and different from the second catalyst layer; 2. The gas sensor according to claim 1.

5. The difference in detection sensitivity for the detection target gas is a difference in detection sensitivity for a silicon-hydrogen bond-containing gas.

3. The gas sensor according to claim 2.

6. the second catalyst layer contains alumina; 5. The gas sensor according to claim 2 or 4.

7. the first sensing element includes a first catalyst layer covering the first gas sensitive portion, the first catalyst layer contains any one of silica, silica alumina, and zeolite; 5. The gas sensor according to claim 2 or 4.

8. the gas sensor incorporating the first sensing element and the second sensing element is configured as a single gas sensor; 3. The gas sensor according to claim 1.

9. A gas alarm comprising the gas sensor according to claim 1 or 2.

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