MEMS semiconductor gas sensor

Abstract

A MEMS semiconductor gas sensor according to the present disclosure comprises: a MEMS semiconductor gas detection element that detects a gas to be detected that is contained in a gas to be measured; a housing containing the gas detection element and having an opening through which the gas to be measured can circulate; and a filter member provided between the opening and the gas detection element, wherein the filter member comprises a first filter member that removes siloxanes and a second filter member that removes sulfuric gases, the first filter member has a higher siloxane removal capacity than the second filter member, the second filter member has a higher sulfuric gas removal capacity than the first filter member, and the filter member is free of precious metals.

Description

MEMS semiconductor gas sensor

[0001] The present invention relates to a MEMS semiconductor gas sensor.

[0002] Conventionally, semiconductor gas detection elements manufactured using MEMS (Micro Electro Mechanical System) technology, such as that disclosed in Patent Document 1, have been used as gas detection elements for detecting target gases contained in target gases such as the atmosphere. MEMS-type semiconductor gas detection elements are miniaturized using MEMS technology, allowing for intermittent operation to achieve low power consumption. However, because intermittent operation shortens the time required for MEMS-type semiconductor gas detection elements to reach high temperatures, they are more likely to be poisoned and their sensitivity may fluctuate if the target gas contains siloxanes (e.g., octamethylcyclotetrasiloxane) or sulfur-based gases (e.g., hydrogen sulfide). Therefore, MEMS-type semiconductor gas detection elements require more advanced poisoning prevention measures than other types of gas detection elements.

[0003] To prevent gas detection elements from being poisoned by siloxanes and sulfur-based gases, for example, Patent Document 2 uses a filter containing activated carbon and a precious metal catalyst. As shown in Patent Document 2, the precious metal catalyst adsorbs siloxanes and sulfur-based gases, and when the gas to be measured contains ethanol, it oxidizes the ethanol to produce acetic acid. Like siloxanes and sulfur-based gases, acetic acid poisons the gas detection element, causing its sensitivity to fluctuate. Therefore, Patent Document 2 proposes neutralizing the acetic acid produced by the precious metal catalyst with calcium carbonate or the like to prevent the gas detection element from being poisoned by acetic acid.

[0004] JP 2014-041164 A JP 2018-211233 A

[0005] As described above, gas detection elements such as MEMS semiconductor gas detection elements, which are driven intermittently and reach high temperatures for a short period of time, require more advanced poisoning prevention measures than other types of gas detection elements. In a configuration in which acetic acid is generated by a precious metal catalyst, as in Patent Document 2, there is a problem that if acetic acid is generated in excess of the allowable amount, the acetic acid cannot be sufficiently neutralized. Therefore, with MEMS semiconductor gas detection elements, it is difficult to sufficiently suppress fluctuations in sensitivity due to poisoning using the filter in Patent Document 2.

[0006] The present invention has been made in consideration of the above problems, and aims to provide a MEMS semiconductor gas sensor that can suppress fluctuations in the sensitivity of the MEMS semiconductor gas detection element even when siloxane, sulfur-based gases, and ethanol are present in the gas to be measured.

[0007] The MEMS type semiconductor gas sensor of the present invention is a MEMS type semiconductor gas sensor comprising: a MEMS type semiconductor gas detection element that detects a target gas contained in a target gas; a housing that houses the MEMS type semiconductor gas detection element and has an opening through which the target gas can flow; and a filter member that is provided within the housing between the opening and the MEMS type semiconductor gas detection element, wherein the filter member comprises a first filter member that removes siloxane and a second filter member that removes sulfur-based gases, the first filter member having a higher siloxane removal ability than the second filter member, the second filter member having a higher sulfur-based gas removal ability than the first filter member, and the filter member does not contain precious metals.

[0008] While the present invention has been described with reference to exemplary embodiments, it is to be understood that the invention is not limited to the disclosed exemplary embodiments and is not to be construed as limiting the invention.

[0009] A MEMS semiconductor gas sensor (hereinafter simply referred to as a "gas sensor") according to one embodiment of the present invention will be described below with reference to the accompanying drawings. However, the embodiment shown below is merely an example, and the gas sensor of the present invention is not limited to the following example.

[0010] The gas sensor of this embodiment is used to detect a target gas in a target gas that may contain the target gas, such as an ambient atmosphere such as the air. The target gas is a gas that can be detected by the MEMS semiconductor gas detection element 2 described below and is the target of detection. The target gas is not particularly limited, and examples include combustible gases such as methane, butane, isobutane, propane, and hydrogen, with isobutane and propane being particularly preferred. Detection of the target gas includes determining whether the target gas is present in the target gas and determining the concentration of the target gas in the target gas.

[0011] 1, the gas sensor 1 includes a MEMS semiconductor gas detection element (hereinafter simply referred to as the "gas detection element") 2, a housing 3 that houses the gas detection element 2, and a filter member 4 provided within the housing 3. The gas sensor 1 can be incorporated into a detection circuit (for example, a well-known bridge circuit) via lead wires 5 and electrodes 6, and can be used by being incorporated into a gas detector that includes a control unit that controls the voltage applied in the detection circuit and calculates the gas concentration of the target gas from the sensor output output by the detection circuit, a display unit that displays the gas concentration of the target gas, and a notification unit that issues a warning when the calculated gas concentration is higher than a predetermined threshold.

[0012] The gas detection element 2 detects a target gas contained in a measurement target gas. The gas detection element 2 is configured as a known semiconductor type and detects the target gas by utilizing a change in electrical resistance (or electrical conductivity) that occurs in response to a chemical reaction with the target gas. As shown in FIG. 2 , the gas detection element 2 is formed as a MEMS (Micro Electro Mechanical System) type. The MEMS type refers to a device structure in which at least some of the element components are integrated on a substrate such as a silicon substrate using microfabrication technology. Because the gas detection element 2 is formed as a MEMS type, it can be made smaller and can be driven with lower power consumption than a coil type.

[0013] The gas detection element 2 may be configured as a known MEMS semiconductor, and its specific configuration is not particularly limited. In this embodiment, the gas detection element 2 is configured to detect isobutane and propane. As shown in FIG. 2 , the gas detection element 2 includes a substrate 21 such as a silicon substrate, a gas sensitive portion 22 provided on the substrate 21, and a catalyst protection layer 23 covering the gas sensitive portion 22. The gas detection element 2 further includes a resistor 24 provided on the substrate 21 so as to be covered by the gas sensitive portion 22.

[0014] The substrate 21 supports the gas sensitive part 22, the catalyst protective layer 23, and the resistor 24. As shown in FIG. 2 , the substrate 21 includes a substrate body 21a and an insulating support film 21b formed on the substrate body 21a. The insulating support film 21b includes a portion formed on the substrate body 21a and in contact with the substrate body 21a at its underside, and a portion spaced apart from the substrate body 21a and provided above a cavity 21c in the substrate body 21a. The gas sensitive part 22, the catalyst protective layer 23, and the resistor 24 are provided on the portion of the insulating support film 21b provided above the cavity 21c. The substrate 21 can be made of, for example, a silicon substrate, and the substrate body 21a and the insulating support film 21b can be made of silicon and a silicon oxide film, respectively.

[0015] The gas sensing part 22 is primarily composed of a metal oxide semiconductor, and its electrical resistance changes in response to a chemical reaction with the target gas. The gas sensing part 22 can be formed, for example, by adding a metal such as antimony or niobium as a donor to a metal oxide semiconductor such as tin oxide or indium oxide. The gas sensing part 22 may further include a noble metal catalyst such as platinum or palladium. In this embodiment, the gas sensing part 22 includes tin oxide as the metal oxide semiconductor, antimony as the donor, and platinum as the noble metal catalyst.

[0016] The catalyst protective layer 23 is a portion that suppresses interfering gases that impede detection of the target gas from reacting with the surface of the gas sensitive part 22. The catalyst protective layer 23 can have an appropriate layer structure designed depending on the interfering gas in order to suppress reaction between the gas sensitive part 22 and the interfering gas. The catalyst protective layer 23 can be formed, for example, by coating the surface of the gas sensitive part 22 with a support in which a noble metal catalyst such as platinum or palladium is supported on a metal oxide such as alumina or silica. In this embodiment, the catalyst protective layer 23 includes palladium-supported alumina.

[0017] When a predetermined voltage is applied to the resistor 24, the resistor 24 functions as a heating electrode that heats the gas sensing portion 22 (and the catalyst protective layer 23) to a predetermined temperature (e.g., 400 to 600°C) suitable for detecting the target gas. The resistor 24 also functions as a resistance detection electrode that detects changes in the electrical resistance of the gas sensing portion 22. The gas detection element 2 detects the target gas through changes in the electrical resistance of the gas sensing portion 22 detected by the resistor 24. The resistor 24 can be formed by depositing a film of a precious metal, such as platinum or a platinum-rhodium alloy, on the substrate 21 (insulating support film 21b) by a known film deposition method, such as sputtering. In this embodiment, the resistor 24 serves as both a heating electrode and a resistance detection electrode, but the heating electrode and the resistance detection electrode may be provided separately.

[0018] As shown in FIG. 1 , the housing 3 has an internal space capable of accommodating the gas detection element 2, and has an opening 31 through which the gas to be measured can flow in order to introduce the gas to be measured into the space. In this embodiment, the opening 31 is provided in a central portion of the end of one side (the upper side in FIG. 1 ) of the housing 3. However, the size and location of the opening are not particularly limited as long as the opening is configured to allow the gas to be measured to flow through it. For example, the opening may be provided over the entire end of one side of the housing, or may be provided in another portion of the housing. In this embodiment, the housing 3 accommodates the gas detection element 2 on the other side (the lower side in FIG. 1 ) of the space within the housing 3. However, the location of the opening is not particularly limited as long as the gas detection element can be accommodated in the space within the housing, and the opening may be located in another portion of the space within the housing.

[0019] The configuration of the housing 3 is not particularly limited as long as it can accommodate the gas detection element 2 and has an opening 31 through which the gas to be measured can flow. In this embodiment, as shown in FIG. 1 , the housing 3 includes a base 32 on which the gas detection element 2 is mounted and a cap 33 fixed to the base 32 so as to surround the gas detection element 2. The base 32 is further provided with lead wires 5 and electrodes 6 for connecting the gas detection element 2 to a detection circuit (for example, a known bridge circuit). The cap 33 is formed in a generally cylindrical shape having an opening 31 at one end (upper side in FIG. 1 ) and an opening at the other end (lower side in FIG. 1 ) that is closed by the base 32. When the other end of the cap 33 is fixed to the base 32 and the opening at the other end of the cap 33 is closed by the base 32, a space capable of accommodating the gas detection element 2 is formed inside the cap 33. In this embodiment, the housing 3 has a single-layer structure with one cap 33, but it may also have a multi-layer structure with multiple caps, with one cap covered by another cap.

[0020] As shown in FIG. 1 , the filter member 4 includes a first filter member 41 that removes siloxane and a second filter member 42 that removes sulfur-based gases. The filter member 4 is disposed within the housing 3 between the opening 31 and the gas detection element 2. By being disposed between the opening 31 and the gas detection element 2, the filter member 4 removes siloxane and sulfur-based gases from the measurement target gas that reaches the gas detection element 2 through the opening 31. Here, in this specification, "removing siloxane / sulfur-based gases" means at least partially, and preferably entirely, removing the siloxane / sulfur-based gases from the measurement target gas that reaches the gas detection element 2. Removing the siloxane / sulfur-based gases includes, for example, adsorbing the siloxane / sulfur-based gases onto the filter member 4 to remove the siloxane / sulfur-based gases from the measurement target gas that reaches the gas detection element 2, or decomposing the siloxane / sulfur-based gases using the filter member 4 to remove the siloxane / sulfur-based gases from the measurement target gas that reaches the gas detection element 2. In the gas sensor 1, even if the gas to be measured contains siloxane and sulfur-based gases, the siloxane and sulfur-based gases are removed by the filter member 4, thereby preventing the gas detection element 2 from being poisoned by the siloxane and sulfur-based gases and suppressing fluctuations in the sensitivity of the gas detection element 2.

[0021] The first filter member 41 is made of a material that has a higher ability to remove siloxane than the second filter member 42. The first filter member 41 removes siloxane from the measurement target gas that reaches the gas detection element 2 through the opening 31. The siloxane removed by the first filter member 41 is a gas composed of compounds having siloxane bonds, and examples thereof include hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecamethylcyclohexasiloxane (D6).

[0022] The first filter member 41 may be made of any material that has a higher siloxane removal ability than the second filter member 42, but preferably contains silica gel. By including silica gel in the first filter member 41, the siloxane removal ability is further enhanced, and fluctuations in the sensitivity of the gas detection element 2 can be further suppressed. Although the silica gel is not particularly limited, organic sulfonic acid-supported silica gel, which has a higher siloxane removal ability, is preferably used. Note that silica gel is also preferably used in that it can adsorb and remove moisture, which may cause fluctuations in the sensitivity of the gas detection element 2.

[0023] The first filter member 41 is not particularly limited as long as it is configured to have a higher siloxane removal capability than at least the second filter member 42, and can be formed from a material having a shape such as granular, powdery, fibrous, sheet-like, or disc-like. The first filter member 41 can be formed, for example, by filling the housing 3 with a granular filter material.

[0024] The second filter member 42 is made of a material that has a higher sulfur-based gas removal capability than the first filter member 41. The second filter member 42 removes sulfur-based gases from the measurement target gas that reaches the gas detection element 2 through the opening 31. The sulfur-based gases removed by the second filter member 42 are gases that contain sulfur, such as hydrogen sulfide and sulfur dioxide.

[0025] The second filter member 42 may be made of any material having at least a higher sulfur-based gas removal capability than the first filter member 41. However, the material preferably contains zinc aluminosilicate, allophane, or manganese oxide. From the perspective of further suppressing the generation of ethanol oxidation products (described later), the second filter member 42 preferably contains zinc aluminosilicate or allophane. Zinc aluminosilicate is a composite oxide containing aluminum oxide (e.g., Al2O3), silicon oxide (e.g., SiO2), and zinc oxide (e.g., ZnO), and includes what are also known as zinc aluminosilicate minerals. Zinc aluminosilicate preferably has a structure in which silica-zinc particles are encapsulated within a silica-alumina gel. Allophane is a clay mineral composed of amorphous or hydrated aluminum silicate with low crystallinity.

[0026] The second filter member 42 is not particularly limited as long as it is configured to have a higher sulfur-based gas removal capability than at least the first filter member 41, and can be formed from a material having a shape such as granular, powdery, fibrous, sheet-like, or disk-like. The second filter member 42 can be formed, for example, by filling the housing 3 with a granular filter material.

[0027] As shown in FIG. 1 , the filter member 4 is provided within the housing 3 between the opening 31 and the gas detection element 2, and is arranged so that some or all of the target gas that flows into the housing 3 through the opening 31 passes through both the first filter member 41 and the second filter member 42 before reaching the gas detection element 2. In the gas sensor 1, the target gas passes through both the first filter member 41 and the second filter member 42, thereby removing siloxanes and sulfur-based gases contained in the target gas. The first filter member 41 and the second filter member 42 may be arranged so that at least the target gas can pass through both of them. However, as shown in FIG. 1 , it is preferable that the first filter member 41 and the second filter member 42 are arranged in this order from the opening 31 of the housing 3 toward the gas detection element 2. In other words, the first filter member 41 and the second filter member 42 are preferably arranged so that the target gas that flows into the housing 3 from the opening 31 and reaches the gas detection element 2 first passes through the first filter member 41 and then the second filter member 42. In the gas sensor 1, the filter members 4 are provided in the order of the first filter member 41 and the second filter member 42 from upstream to downstream in the flow of the gas to be measured, thereby further suppressing poisoning by siloxane and sulfur-based gases and further suppressing the influence of ethanol, which will be described later, and thereby further suppressing fluctuations in the sensitivity of the gas detection element 2. However, the first filter member 41 and the second filter member 42 may be provided in this order from the opening 31 toward the gas detection element 2: second filter member 42 then first filter member 41, or they may be provided alternately.

[0028] 1 , the first filter member 41 is disposed adjacent to the opening 31 of the housing 3 via a breathable material (e.g., wire mesh 7 and nonwoven fabric 8) disposed in contact with one end of the housing 3. The second filter member 42 is disposed adjacent to the first filter member 41 via a breathable material (e.g., nonwoven fabric 8) disposed midway between the one and other sides of the housing 3. The first filter member 41 and the second filter member 42 are fixed so as not to move toward the gas detection element 2 by the breathable material (e.g., nonwoven fabric 8 and wire mesh 7) disposed on the other side of the housing 3. Note that the first filter member 41 and the second filter member 42 are not limited to the example shown in the figure. Alternatively, the first filter member 41 may be disposed in one cap and the second filter member 42 in another cap, and the cap containing the second filter member 42 may be inserted into the cap containing the first filter member 41 to form a two-layer structure within the housing.

[0029] Here, the filter member 4 does not contain precious metals such as gold, platinum, or palladium. Precious metals oxidize ethanol to produce ethanol oxidation products (acetaldehyde and acetic acid). Like siloxane and sulfur-based gases, the ethanol oxidation products poison the gas detection element 2 and cause fluctuations in the sensitivity of the gas detection element 2. In the gas sensor 1, even if the measurement target gas contains ethanol, the absence of precious metals in the filter member 4 suppresses the production of ethanol oxidation products, thereby suppressing poisoning of the gas detection element 2 by the ethanol oxidation products and suppressing fluctuations in the sensitivity of the gas detection element 2.

[0030] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments. Note that the above-described embodiments mainly describe the invention having the following configurations.

[0031] (1) A MEMS type semiconductor gas sensor comprising: a MEMS type semiconductor gas detection element that detects a target gas contained in a target gas; a housing that houses the MEMS type semiconductor gas detection element and has an opening through which the target gas can flow; and a filter member that is provided in the housing between the opening and the MEMS type semiconductor gas detection element, wherein the filter member comprises a first filter member that removes siloxane and a second filter member that removes sulfur-based gases, the first filter member having a higher siloxane removal ability than the second filter member, and the second filter member having a higher sulfur-based gas removal ability than the first filter member, and the filter member does not contain a precious metal.

[0032] According to the above configuration, even if siloxane, sulfur-based gas, and ethanol are present in the gas to be measured, fluctuations in the sensitivity of the MEMS semiconductor gas detection element can be suppressed.

[0033] (2) The MEMS semiconductor gas sensor according to (1), wherein the first filter member and the second filter member are arranged in this order from the opening toward the MEMS semiconductor gas detection element.

[0034] According to the above configuration, even if siloxane, sulfur-based gas, and ethanol are present in the gas to be measured, the fluctuation in sensitivity of the MEMS semiconductor gas detection element can be further suppressed.

[0035] (3) The MEMS type semiconductor gas sensor according to (1) or (2), wherein the second filter member contains zinc aluminosilicate or allophane.

[0036] According to the above configuration, even if siloxane, sulfur-based gas, and ethanol are present in the gas to be measured, the fluctuation in sensitivity of the MEMS semiconductor gas detection element can be further suppressed.

[0037] (4) The MEMS type semiconductor gas sensor according to any one of (1) to (3), wherein the first filter member contains silica gel.

[0038] According to the above configuration, even if siloxane, sulfur-based gas, and ethanol are present in the gas to be measured, the fluctuation in sensitivity of the MEMS semiconductor gas detection element can be further suppressed.

[0039] The excellent effects of the gas sensor of this embodiment will be described below based on examples, but the gas sensor of the present invention is not limited to the following examples.

[0040] (Gas Sensor) A gas sensor as shown in Fig. 1 was fabricated. The gas sensor was fabricated by welding a cap with a filter member disposed therein to a base with a gas detection element disposed therein. The cap was formed to have a height of 12 mm, an outer diameter of 8.3 mm, an inner diameter of 7.7 mm, and an opening diameter of 2 mm.

[0041] The gas detection element shown schematically in Figure 2 was fabricated. A silicon substrate was used as the substrate, a silicon oxide film was used as the insulating support film, and a platinum film was sputtered onto the insulating support film to form a resistor. The gas sensing section was formed by applying a paste containing platinum powder and fine powder of tin oxide semiconductor with antimony added as a donor to the insulating support film, covering the resistor, followed by drying, heating, and sintering. The catalyst protection layer was formed by applying a paste containing fine particles of palladium-loaded alumina to the gas sensing section, followed by drying and heating. Other processes were performed using known methods.

[0042] As filter elements, an upstream filter element and a downstream filter element containing the filter material shown in Tables 1 to 4 below were disposed at the respective positions of the first filter element and the second filter element shown in FIG. 1 . The upstream filter element and the downstream filter element were each formed by filling a cap with the granular filter material shown in Tables 1 to 4 below. Among the filter materials in Tables 1 to 4, acid-supported silica gel refers to organic sulfonic acid-supported silica gel, and is an example of a material that constitutes the first filter element described above. Furthermore, among the filter materials in Tables 1 to 4, zinc aluminosilicate, allophane, and manganese oxide are examples of materials that constitute the second filter element described above.

[0043] (Exposure Test) The gas sensor was exposed to siloxane, sulfur-based gas, ethanol, and siloxane + ethanol, and the change in sensitivity of the gas detection element was measured. In the siloxane exposure test (Table 1), the gas sensor was exposed to an atmosphere containing 10 ppm of octamethylcyclotetrasiloxane (D4) for 90 days. In the sulfur-based gas exposure test (Table 2), the gas sensor was exposed to an atmosphere containing 5 ppm of hydrogen sulfide for 24 hours. In the ethanol exposure test (Table 3), the gas sensor was exposed to an atmosphere containing 250 ppm of ethanol for 90 days. In the siloxane + ethanol exposure test (Table 4), the gas sensor was exposed to an atmosphere containing 10 ppm of octamethylcyclotetrasiloxane (D4) and 250 ppm of ethanol for 90 days. During the exposure period, the gas detection element was subjected to intermittent driving in which the resistor was alternately energized for 0.1 seconds (heated to 500° C.) and deenergized for 29.9 seconds.

[0044] (Measurement Conditions) The gas sensor was incorporated into a known bridge circuit, and the potential difference generated in the bridge circuit due to changes in the electrical resistance of the gas detection element was measured as the sensor output. The gas detection element was driven intermittently during measurement, alternating between a 0.1-second detection operation (heating to 500°C) and a 29.9-second de-energization operation. Sensor output measurements were performed in an atmosphere containing no target gas before and after the exposure test. Changes in the sensitivity of the gas detection element were evaluated by the increase in sensor output from before to after the exposure test. The sensor output was normalized to 100, with the sensor output obtained in an atmosphere containing 2000 ppm propane. Incidentally, a gas detector designed to issue an alarm when detecting 2000 ppm propane in the atmosphere would issue an alarm even when no propane was present in the atmosphere if the normalized sensor output exceeded 100 during the exposure test.

[0045] (Siloxane Exposure Test Results) Table 1 shows the change in sensor output when the gas sensor was exposed to siloxane. First, Table 1 shows that, regardless of whether it was an Example or Comparative Example, when the filter contained acid-supported silica gel (Examples 1 to 6, Comparative Examples 2 to 6), the increase in sensor output was significantly suppressed compared to when it did not contain acid-supported silica gel (Comparative Examples 1, 7 to 10). This indicates that acid-supported silica gel removes siloxane from the gas to be measured and suppresses poisoning of the gas detection element. Next, looking at Comparative Examples 2 to 6 and 7 to 10 in Table 1, the increase in sensor output was suppressed when the filter contained acid-supported silica gel, but when the filter did not contain acid-supported silica gel but contained zinc aluminosilicate, allophane, manganese oxide, or platinum-supported alumina, the sensor output significantly increased. This indicates that acid-supported silica gel has a higher ability to remove siloxane than zinc aluminosilicate, allophane, manganese oxide, or platinum-supported alumina. Furthermore, looking at Examples 1 to 3 and Examples 4 to 6 in Table 1, when the acid-supported silica gel is placed on the upstream side, the increase in sensor output is slightly suppressed compared to when it is placed on the downstream side. This shows that in order to remove siloxane from the measurement target gas, it is preferable to place the acid-supported silica gel on the upstream side.

[0046]

[0047] (Hydrogen Sulfide Exposure Test Results) Table 2 shows the change in sensor output when the gas sensor was exposed to hydrogen sulfide. First, Table 2 shows that, regardless of whether it was an Example or Comparative Example, when the filter contained any of zinc aluminosilicate, allophane, manganese oxide, or platinum-supported alumina (Examples 1 to 6, Comparative Examples 2, 7 to 10), the increase in sensor output was significantly suppressed compared to when the filter did not contain any of zinc aluminosilicate, allophane, manganese oxide, or platinum-supported alumina (Comparative Examples 1, 3 to 6). This shows that zinc aluminosilicate, allophane, manganese oxide, and platinum-supported alumina remove hydrogen sulfide from the gas to be measured and suppress poisoning of the gas detection element. Next, looking at Comparative Examples 3 to 6 and Comparative Examples 7 to 10 in Table 2, the increase in sensor output was suppressed when the filter contained any of zinc aluminosilicate, allophane, manganese oxide, and platinum-supported alumina. However, when the filter did not contain any of zinc aluminosilicate, allophane, manganese oxide, and platinum-supported alumina, but contained acid-supported silica gel, the sensor output significantly increased. This indicates that zinc aluminosilicate, allophane, manganese oxide, and platinum-supported alumina have a higher ability to remove hydrogen sulfide than acid-supported silica gel. Furthermore, looking at Examples 1 to 3 and Examples 4 to 6 in Table 2, the increase in sensor output was slightly suppressed when zinc aluminosilicate, allophane, or manganese oxide was located downstream compared to when it was located upstream. This indicates that, in order to remove hydrogen sulfide from the gas to be measured, it is preferable to locate any of zinc aluminosilicate, allophane, and manganese oxide downstream.

[0048]

[0049] (Ethanol Exposure Test Results) Table 3 shows the change in sensor output when the gas sensor was exposed to ethanol. First, Table 3 shows that, regardless of whether the example or comparative example was used, when the filter contained platinum-supported alumina (Comparative Examples 2 and 7), the sensor output increased significantly compared to when the filter did not contain platinum-supported alumina (Examples 1 to 6, Comparative Examples 1, 3 to 6, and 8 to 9). In particular, when the filter contained platinum-supported alumina (Comparative Examples 2 and 7), the sensor output increased significantly compared to when the filter contained alumina or silica-alumina instead of platinum-supported alumina (Comparative Examples 3 and 4). This indicates that the platinum content of platinum-supported alumina promotes poisoning of the gas detection element due to the effects of ethanol. This is thought to be because platinum oxidizes ethanol to generate ethanol oxidation products, and the generated ethanol oxidation products promote poisoning of the gas detection element. In contrast, in all of the examples, the absence of platinum in the filter suppressed the increase in sensor output and suppressed poisoning of the gas detection element. Furthermore, looking at Examples 1 to 3 and Examples 4 to 6 in Table 3, when acid-supported silica gel was placed upstream and zinc aluminosilicate, allophane, or manganese oxide was placed downstream, the increase in sensor output was slightly suppressed compared to the reverse arrangement. This indicates that, in order to suppress the effects of ethanol, it is preferable to place acid-supported silica gel upstream and zinc aluminosilicate, allophane, or manganese oxide downstream. Furthermore, in the examples, when the filter contained manganese oxide (Examples 3 and 6), the sensor output increased slightly compared to when zinc aluminosilicate or allophane was used instead of manganese oxide (Examples 1 to 2, 4 to 5). This indicates that, in order to further suppress the effects of ethanol, it is even more preferable to include zinc aluminosilicate or allophane in the filter instead of manganese oxide. This is thought to be because manganese oxide has the ability to oxidize ethanol, albeit slightly, and produces a small amount of ethanol oxidation products.

[0050]

[0051] (Siloxane + Ethanol Exposure Test Results) Table 4 shows the change in sensor output when the gas sensor was exposed to siloxane + ethanol. First, Table 4 shows that, regardless of whether it was an example or a comparative example, when the filter contained acid-supported silica gel but not platinum-supported alumina (Examples 1-6, Comparative Examples 3-6), the increase in sensor output was significantly suppressed compared to when the filter did not contain acid-supported silica gel or contained platinum-supported alumina (Comparative Examples 1-2, 7-10). This indicates that the acid-supported silica gel removes siloxane from the gas to be measured and suppresses poisoning of the gas detection element, while the absence of platinum in the filter suppresses poisoning of the gas detection element. For example, in Comparative Examples 1 and 7-10, the absence of acid-supported silica gel in the filter prevented siloxane from being removed from the gas to be measured. In Comparative Examples 2 and 7, the presence of platinum-supported alumina in the filter likely led to the generation of ethanol oxidation products, which accelerated poisoning of the gas detection element. In contrast, in all of the examples, the filter containing acid-supported silica gel removes siloxane, and the filter not containing platinum suppresses the production of ethanol oxidation products, which is thought to suppress poisoning of the gas detection element. Next, looking at Examples 1 to 3 and Examples 4 to 6 in Table 1, when acid-supported silica gel is placed upstream and zinc aluminosilicate, allophane, or manganese oxide is placed downstream, the increase in sensor output is slightly suppressed compared to the reverse arrangement. This shows that in order to suppress the increase in sensor output in the presence of siloxane and ethanol, it is preferable to place acid-supported silica gel upstream and zinc aluminosilicate, allophane, or manganese oxide downstream.

[0052]

[0053] REFERENCE SIGNS LIST 1 MEMS semiconductor gas sensor (gas sensor) 2 MEMS semiconductor gas detection element (gas detection element) 21 Substrate 21a Substrate body 21b Insulating support film 21c Cavity 22 Gas sensitive part 23 Catalyst protective layer 24 Resistor 3 Housing 31 Opening 32 Base 33 Cap 4 Filter member 41 First filter member 42 Second filter member 5 Lead wire 6 Electrode 7 Wire mesh 8 Nonwoven fabric

Claims

1. A MEMS type semiconductor gas sensor comprising: a MEMS type semiconductor gas detection element that detects a target gas contained in a target gas; a housing that contains the MEMS type semiconductor gas detection element and has an opening through which the target gas can flow; and a filter member provided within the housing between the opening and the MEMS type semiconductor gas detection element, wherein the filter member comprises a first filter member that removes siloxane and a second filter member that removes sulfur-based gases, the first filter member has a higher siloxane removal ability than the second filter member, and the second filter member has a higher sulfur-based gas removal ability than the first filter member, the filter member does not contain a precious metal, and the second filter member contains zinc aluminosilicate or allophane.

2. The MEMS type semiconductor gas sensor according to claim 1, wherein the first filter member and the second filter member are provided in the order of the first filter member and the second filter member from the opening toward the MEMS type semiconductor gas detection element.

3. The MEMS type semiconductor gas sensor according to claim 1, wherein the first filter member includes silica gel.

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