MEMS type semiconductor gas sensor

Abstract

This MEMS-type semiconductor gas sensor is provided with: a MEMS-type semiconductor gas detection element that detects a gas to be detected included in a gas to be measured; a housing that houses the gas detection element and has an opening through which the gas to be measured can flow; and a filter member provided between the opening and the gas detection element, the filter member being provided with a first filter member for removing siloxane and a second filter member for removing sulfur-based gas, the first filter member having a higher siloxane removal capacity than the second filter member, and the second filter member having a higher sulfur-based gas removal capacity than the first filter member. The second filter member has a higher chalcogenide gas removal capacity than the first filter member, and the filter members do not contain a noble metal.

Description

Technical Field

[0001] This invention relates to a MEMS semiconductor gas sensor. Background Technology

[0002] Conventionally, gas detection elements used to detect target gases contained in the atmosphere or other target gases have employed semiconductor gas detection elements manufactured using MEMS (Micro Electro Mechanical System) technology, as disclosed in Patent Document 1. MEMS-type semiconductor gas detection elements are miniaturized through MEMS technology, thus enabling low power consumption through intermittent operation. However, the intermittent operation of MEMS-type semiconductor gas detection elements results in shorter high-temperature periods. Therefore, if the target gas contains siloxanes (such as octamethylcyclotetrasiloxane) or sulfur-based gases (such as hydrogen sulfide), the possibility of poisoning and sensitivity variations increases. Consequently, MEMS-type semiconductor gas detection elements require more advanced poisoning countermeasures compared to other types of gas detection elements.

[0003] To suppress poisoning of gas detection elements caused by siloxanes and sulfur-based gases, for example, Patent Document 2 uses a filter containing activated carbon and a noble metal catalyst. As shown in Patent Document 2, the noble metal catalyst adsorbs siloxanes and sulfur-based gases; however, when the target gas contains ethanol, the ethanol is oxidized to produce acetic acid. Acetic acid, like siloxanes and sulfur-based gases, poisons the gas detection element, causing changes in its sensitivity. Therefore, Patent Document 2 proposes a method to neutralize the acetic acid generated by the noble metal catalyst using calcium carbonate or the like to suppress gas detection element poisoning caused by acetic acid.

[0004] Existing technical documents

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 2014-041164

[0007] Patent Document 2: Japanese Patent Application Publication No. 2018-211233 Summary of the Invention

[0008] As mentioned above, in gas detection elements such as MEMS-type semiconductor gas detection elements, which are intermittently driven and have shorter high-temperature periods, more advanced poisoning countermeasures are required compared to other types of gas detection elements. As in Patent Document 2, in structures that utilize noble metal catalysts to generate acetic acid, there is a problem that if acetic acid is generated in excess of a permissible amount, it cannot be adequately neutralized. Therefore, in MEMS-type semiconductor gas detection elements, it is difficult to sufficiently suppress sensitivity fluctuations caused by poisoning using the filter in Patent Document 2.

[0009] The present invention was made in view of the above-mentioned problems, and its object is to provide a MEMS type semiconductor gas sensor that can suppress the sensitivity variation of MEMS type semiconductor gas detection element even when siloxane, sulfur series gas and ethanol are present in the gas to be measured.

[0010] The MEMS-type semiconductor gas sensor of the present invention comprises: a MEMS-type semiconductor gas detection element for detecting a target gas contained in a target gas; a housing for housing the MEMS-type semiconductor gas detection element and having an opening for the target gas to flow through; and a filter member disposed within the housing between the opening and the MEMS-type semiconductor gas detection element, wherein the filter member comprises a first filter member for removing siloxanes and a second filter member for removing sulfur-based gases, the first filter member having a higher siloxane removal capacity than the second filter member, the second filter member having a higher sulfur-based gas removal capacity than the first filter member, and the filter member not containing precious metals. Attached Figure Description

[0011] Figure 1 This is a schematic cross-sectional view illustrating a MEMS-type semiconductor gas sensor according to an embodiment of the present invention.

[0012] Figure 2 It is a schematic representation Figure 1 A cross-sectional view of the MEMS-type semiconductor gas detection element contained in the MEMS-type semiconductor gas sensor. Detailed Implementation

[0013] Hereinafter, with reference to the accompanying drawings, a MEMS-type semiconductor gas sensor (hereinafter simply referred to as "gas sensor") according to an embodiment of the present invention will be described. However, the embodiment shown below is an example, and the gas sensor of the present invention is not limited to the following example.

[0014] The gas sensor of this embodiment is used to detect a target gas in a measurement target gas that may contain the target gas, such as an ambient atmosphere like the atmosphere. The target gas refers to any gas that can be detected by the MEMS-type semiconductor gas detection element 2 described later. The target gas is not particularly limited; examples include flammable gases such as methane, butane, isobutane, propane, and hydrogen, with isobutane and propane being particularly examples. The detection of the target gas includes determining whether the target gas is present in the measurement target gas and determining the concentration of the target gas in the measurement target gas.

[0015] like Figure 1As shown, the gas sensor 1 includes: a MEMS-type semiconductor gas detection element (hereinafter referred to as "gas detection element") 2; a housing 3 that houses the gas detection element 2; and a filter component 4 disposed within the housing 3. The gas sensor 1 is assembled to a detection circuit (e.g., a known bridge circuit) via leads 5 and electrodes 6, and can be used in a gas detector. The gas detector includes a control unit, a display unit, and a notification unit. The control unit controls the voltage applied in the detection circuit, calculates the gas concentration of the target gas based on the sensor output from the detection circuit, displays the gas concentration of the target gas, and issues a warning if the calculated gas concentration exceeds a predetermined threshold.

[0016] Gas detection element 2 detects the target gas contained within the target gas. Gas detection element 2 is configured as a known semiconductor type, detecting the target gas by utilizing the change in resistance (or conductivity) with the chemical reaction with the target gas. Furthermore, as... Figure 2 As shown, the gas detection element 2 is formed as a MEMS (Micro Electromechanical System). MEMS refers to a device structure in which at least a portion of the component elements are integrated on a substrate such as a silicon substrate using microfabrication techniques. By forming the gas detection element 2 as a MEMS, compared to forming it as a coil, miniaturization and low-power operation can be achieved.

[0017] The gas detection element 2 can be configured as a known MEMS-type semiconductor, and its specific structure is not particularly limited. In this embodiment, the gas detection element 2 is configured to detect isobutane and propane. Figure 2 As shown, the gas detection element 2 includes a substrate 21 such as a silicon substrate, a gas sensing part 22 disposed on the substrate 21, and a catalyst protective layer 23 covering the gas sensing part 22. The gas detection element 2 also includes a resistor 24 disposed on the substrate 21 such that it is covered by the gas sensing part 22.

[0018] The substrate 21 supports the gas sensing unit 22, the catalyst protective layer 23, and the resistor 24. For example... Figure 2As shown, 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 in contact with its lower surface and a portion disposed on a cavity 21c of the substrate body 21a, separate from the substrate body 21a. The gas sensing element 22, the catalyst protection layer 23, and the resistor 24 are disposed on the portion of the insulating support film 21b disposed on 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 silicon oxide films, respectively.

[0019] The gas sensing unit 22 is a portion whose resistance changes with the chemical reaction with the target gas, primarily composed of a metal oxide semiconductor. The gas sensing unit 22 can be formed, for example, by adding metals such as antimony or niobium as donors to a metal oxide semiconductor such as tin oxide or indium oxide. The gas sensing unit 22 may also include a noble metal catalyst such as platinum or palladium. In this embodiment, the gas sensing unit 22 includes tin oxide as the metal oxide semiconductor, antimony as a donor, and platinum as a noble metal catalyst.

[0020] The catalyst protective layer 23 is a region that suppresses the reaction between interfering gases that hinder the detection of the target gas and the surface of the gas sensing unit 22. To suppress the reaction between the gas sensing unit 22 and the interfering gas, the catalyst protective layer 23 can be appropriately structured according to the interfering gas. For example, the catalyst protective layer 23 can be formed by coating the surface of the gas sensing unit 22 with a metal oxide such as alumina or silica, on which a noble metal catalyst such as platinum or palladium is supported. In this embodiment, the catalyst protective layer 23 comprises palladium-supported alumina.

[0021] The resistive element 24 functions as a heating electrode that heats the gas sensing element 22 (and the catalyst protective layer 23) to a predetermined temperature (e.g., 400°C to 600°C) suitable for detecting the target gas by applying a predetermined voltage. Additionally, the resistive element 24 also functions as a resistance detection electrode that detects changes in the resistance value of the gas sensing element 22. The gas detection element 2 detects the target gas based on the change in the resistance value of the gas sensing element 22 detected by the resistive element 24. The resistive element 24 can be formed, for example, by depositing a film of a precious metal such as platinum or a platinum-rhodium alloy on a substrate 21 (insulating support film 21b) using a known film deposition method such as sputtering. It should be noted that in this embodiment, the resistive element 24 serves as both a heating electrode and a resistance detection electrode, but the heating electrode and the resistance detection electrode may also be provided separately.

[0022] like Figure 1As shown, the housing 3 has an internal space capable of housing the gas detection element 2, and an opening 31 for the gas to be measured is provided to guide the gas to be measured into this space. In this embodiment, the opening 31 is provided on one side of the housing 3 (in...). Figure 1 The opening is a portion of the center of the end of the housing (the upper side). However, the size and location of the opening are not particularly limited as long as it allows the gas to be measured to flow through. For example, the opening may be provided throughout one end of the housing or in other parts of the housing. In addition, in this embodiment, the housing 3 is located on the other side of the space inside the housing 3 (in the upper side). Figure 1 The gas detection element 2 is housed in the lower part of the housing. However, the housing only needs to be able to accommodate the gas detection element within the housing space; its storage location is not particularly limited and it can also be stored in other parts of the housing space.

[0023] The housing 3 only needs to have an opening 31 that can accommodate the gas detection element 2 and allow the gas to be measured to flow through; its structure is not particularly limited. In this embodiment, such as Figure 1 As shown, the housing 3 includes a base 32 on which a gas detection element 2 is disposed, and a cover 33 fixed to the base 32 in a manner surrounding the gas detection element 2. Leads 5 and electrodes 6 for connecting the gas detection element 2 to a detection circuit (e.g., a known bridge circuit) are also provided on the base 32. The cover 33 is formed on one side (in... Figure 1 The end of the middle (upper side) has an opening 31, and on the other side (in the middle) Figure 1 The lower end of the cover 33 has an opening closed by the base 32, forming a generally cylindrical shape. The other end of the cover 33 is fixed to the base 32, and the opening at the other end of the cover 33 is closed by the base 32, thereby forming a space inside the cover 33 that can accommodate the gas detection element 2. It should be noted that in this embodiment, the housing 3 has a single-layer structure with one cover 33, but it may also have a multi-layer structure with multiple covers, one of which is covered by other covers.

[0024] like Figure 1As shown, the filter assembly 4 includes a first filter assembly 41 for removing siloxanes and a second filter assembly 42 for removing sulfur-based gases. The filter assembly 4 is disposed within the housing 3 between the opening 31 and the gas detection element 2. The filter assembly 4 is disposed between the opening 31 and the gas detection element 2, thereby removing siloxanes and sulfur-based gases from the target gas reaching the gas detection element 2 through the opening 31. Here, in this specification, removing siloxanes / sulfur-based gases means removing at least partially, preferably completely, siloxanes / sulfur-based gases from the target gas. Furthermore, removing siloxanes / sulfur-based gases includes: adsorbing siloxanes / sulfur-based gases onto the filter assembly 4 to remove them from the target gas reaching the gas detection element 2; decomposing siloxanes / sulfur-based gases in the filter assembly 4 to remove them from the target gas reaching the gas detection element 2, etc. In the gas sensor 1, even if the target gas contains siloxanes and sulfur-based gases, the poisoning of the gas detection element 2 caused by siloxanes and sulfur-based gases can be suppressed by using the filter component 4 to remove the siloxanes and sulfur-based gases, thereby suppressing the sensitivity variation of the gas detection element 2.

[0025] The first filter element 41 is made of a material with a higher siloxane removal capacity than the second filter element 42. The first filter element 41 removes siloxanes from the target gas that reaches the gas detection element 2 through the opening 31. The siloxanes removed by the first filter element 41 refer to gases composed of compounds having siloxane bonds, such as hexamethylcyclotrisiloxane (D3), octamethylcyclotetrasiloxane (D4), decamethylcyclopentasiloxane (D5), and dodecylcyclohexasiloxane (D6).

[0026] The first filter element 41 can be made of a material whose siloxane removal capacity is at least higher than that of the second filter element 42. The material is not particularly limited, but silica gel is preferred. The inclusion of silica gel in the first filter element 41 further enhances its siloxane removal capacity, thereby further suppressing sensitivity fluctuations in the gas detection element 2. Silica gel is not particularly limited; organic sulfonic acid-supported silica gel with a higher siloxane removal capacity can be used appropriately. It should be noted that silica gel can also be appropriately used because it is capable of adsorbing and removing moisture that may cause fluctuations in the sensitivity of the gas detection element 2.

[0027] The first filter component 41 is not particularly limited as long as its removal capacity for siloxanes is at least higher than that of the second filter component 42, and can be formed from materials having shapes such as granular, powdery, fibrous, flake, or disc. For example, the first filter component 41 can be formed by filling the housing 3 with granular filter material.

[0028] The second filter element 42 is made of a material with a higher removal capacity for sulfur-based gases than the first filter element 41. The second filter element 42 removes sulfur-based gases from the target gas that reaches the gas detection element 2 through the opening 31. The sulfur-based gases removed by the second filter element 42 refer to gases containing sulfur, such as hydrogen sulfide and sulfur dioxide.

[0029] The second filter element 42 can be made of a material with a higher removal capacity for sulfur-based gases than the first filter element 41. The material is not particularly limited, but preferably includes any one of zinc aluminosilicate, diatomite, and manganese oxide. From the viewpoint of further suppressing the formation of ethanol oxidation products described later, the second filter element 42 preferably includes zinc aluminosilicate or diatomite. Zinc aluminosilicate is a composite oxide containing aluminum oxide (Al₂O₃, etc.), silicon oxide (SiO₂, etc.), and zinc oxide (ZnO, etc.), and also contains substances known as zinc aluminosilicate minerals. Zinc aluminosilicate preferably has a structure in which zinc dioxide particles are encapsulated within a silica-alumina gel. Diatomite, on the other hand, is a quasi-mineral composed of amorphous or low-crystallinity hydrated aluminosilicates.

[0030] The second filter element 42 is not particularly limited as long as its removal capacity for sulfur-based gases is higher than that of the first filter element 41, and it can be formed from materials having granular, powdery, fibrous, flake, or disc-shaped forms. For example, the second filter element 42 can be formed by filling the housing 3 with granular filter material.

[0031] like Figure 1 As shown, the filter component 4 is disposed within the housing 3 between the opening 31 and the gas detection element 2, configured such that part or all of the target gas flowing into the housing 3 through the opening 31 passes through both the first filter component 41 and the second filter component 42 before reaching the gas detection element 2. In the gas sensor 1, the target gas passes through both the first filter component 41 and the second filter component 42, thereby removing siloxanes and sulfur-based gases contained in the target gas. The first filter component 41 and the second filter component 42 need only be configured to allow at least the target gas to pass through both, but... Figure 1As shown, preferably, the first filter member 41 and the second filter member 42 are arranged sequentially from the opening 31 of the housing 3 toward the gas detection element 2. That is, the first filter member 41 and the second filter member 42 are preferably configured such that the target gas flowing into the housing 3 from the opening 31 and reaching the gas detection element 2 first passes through the first filter member 41 and then through the second filter member 42. In the gas sensor 1, by arranging the filter members 41 and 42 in the order of the first filter member 41 and the second filter member 42 from the upstream side to the downstream side of the target gas flow, poisoning caused by siloxanes and sulfur-based gases can be further suppressed, and the influence of ethanol (described later) can also be further suppressed, thereby further suppressing the sensitivity variation of the gas detection element 2. However, the first filter member 41 and the second filter member 42 can be arranged either sequentially from the opening 31 toward the gas detection element 2 in the order of the second filter member 42 and the first filter member 41, or they can be arranged alternately.

[0032] In this embodiment, such as Figure 1 As shown, the first filter member 41 is disposed adjacent to the opening 31 of the housing 3 via a breathable material (e.g., metal mesh 7 and non-woven fabric 8) that is 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., non-woven fabric 8) disposed in the middle between one side and the other side of the housing 3. The first filter member 41 and the second filter member 42 are fixed by the breathable material (e.g., non-woven fabric 8 and metal mesh 7) disposed on the other side of the housing 3 in a manner that prevents them from moving toward the gas detection element 2. It should be noted that the first filter member 41 and the second filter member 42 are not limited to the example shown. The first filter member 41 may be disposed in one cover, and the second filter member 42 may be disposed in another cover. The cover containing the second filter member 42 may be inserted into the cover containing the first filter member 41, thus forming a double-layered housing.

[0033] Here, the filter component 4 does not contain precious metals such as gold, platinum, or palladium. Precious metals oxidize ethanol to produce ethanol oxidation products (acetaldehyde, acetic acid). Ethanol oxidation products, like siloxanes and sulfur-based gases, can poison the gas detection element 2, causing variations in its sensitivity. In the gas sensor 1, even if the target gas contains ethanol, by ensuring that the filter component 4 does not contain precious metals, the formation of ethanol oxidation products can be suppressed. Therefore, poisoning of the gas detection element 2 caused by ethanol oxidation products can be suppressed, and variations in the sensitivity of the gas detection element 2 can be suppressed.

[0034] The embodiments of the present invention have been described above, but the present invention is not limited to the above embodiments. It should be noted that the above embodiments are mainly described based on an invention having the following structure.

[0035] (1) A MEMS semiconductor gas sensor, comprising:

[0036] MEMS type semiconductor gas detection element, which detects the target gas contained in the target gas;

[0037] A housing that houses the MEMS-type semiconductor gas detection element, having an opening for the gas to be measured to flow through; and

[0038] A filter component is disposed within the housing between the opening and the MEMS-type semiconductor gas detection element, wherein...

[0039] The filter assembly includes a first filter assembly for removing siloxanes and a second filter assembly for removing sulfur-based gases.

[0040] The first filter element has a higher siloxane removal capacity than the second filter element, and the second filter element has a higher sulfur-based gas removal capacity than the first filter element.

[0041] The filter components do not contain precious metals.

[0042] Based on the above structure, even if siloxanes, sulfur-based gases, and ethanol are present in the target gas, the sensitivity variation of the MEMS-type semiconductor gas detection element can be suppressed.

[0043] (2) According to the MEMS semiconductor gas sensor described in (1), the first filter component and the second filter component are arranged in the order of the first filter component and the second filter component from the opening toward the MEMS semiconductor gas detection element.

[0044] Based on the above structure, even if siloxanes, sulfur-based gases, and ethanol are present in the target gas, the sensitivity variation of the MEMS-type semiconductor gas detection element can be further suppressed.

[0045] (3) The MEMS semiconductor gas sensor according to (1) or (2), wherein the second filter component comprises zinc aluminosilicate or hydrated aluminosilicate.

[0046] Based on the above structure, even if siloxanes, sulfur-based gases, and ethanol are present in the target gas, the sensitivity variation of the MEMS-type semiconductor gas detection element can be further suppressed.

[0047] (4) The MEMS semiconductor gas sensor according to any one of (1) to (3), wherein the first filter component comprises silicone.

[0048] Based on the above structure, even if siloxanes, sulfur-based gases, and ethanol are present in the target gas, the sensitivity variation of the MEMS-type semiconductor gas detection element can be further suppressed.

[0049] Example

[0050] The superior effects of the gas sensor of this embodiment will be described below based on examples. However, the gas sensor of the present invention is not limited to the following examples.

[0051] (Gas sensor)

[0052] As a gas sensor, it was fabricated in Figure 1 The gas sensor is shown in a schematic diagram. The gas sensor is manufactured by welding a cover with a filter component to a base with a gas detection element. The cover is formed with a height of 12 mm, an outer diameter of 8.3 mmφ, an inner diameter of 7.7 mm, and an opening diameter of 2 mmφ.

[0053] As a gas detection element, it was manufactured in Figure 2 The gas detection element is schematically shown in the diagram. In this case, a silicon substrate is used as the substrate, and a silicon oxide film is used as the insulating support film. A resistive element is formed on the insulating support film by sputtering platinum. The gas sensing element is formed by coating the resistive element with a paste containing microparticles of tin oxide semiconductor with antimony as a donor and microparticles of platinum, followed by drying, heating, and sintering. The catalyst protective layer is formed by coating the gas sensing element with a paste containing palladium-supported alumina microparticles, followed by drying and heating. Other known methods are employed.

[0054] As a filter component, in Figure 1 The first and second filter components shown are respectively positioned with an upstream filter component and a downstream filter component containing the filter materials shown in Tables 1 to 4 below. The upstream and downstream filter components are formed by filling a cover with the filter materials shown in Tables 1 to 4 below, which are formed in granular form. The acid-supported silica gel in Tables 1 to 4 refers to organic sulfonic acid-supported silica gel, which is an example of the material constituting the first filter component. Additionally, zinc aluminosilicate, diaspore, and manganese oxide in Tables 1 to 4 are examples of the materials constituting the second filter component.

[0055] (Exposure test)

[0056] The gas sensors were exposed to siloxanes, sulfur series gases, ethanol, and a combination of siloxanes and ethanol, and the changes in the sensitivity of the gas detection element were 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 series 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 intermittently driven, alternating between 0.1 seconds of energization (heated to 500°C) and 29.9 seconds of de-energization.

[0057] (Measurement conditions)

[0058] A gas sensor was assembled into a known bridge circuit, and the potential difference generated in the bridge circuit as the resistance of the gas detection element changed was measured as the sensor output. The driving conditions for measuring the gas detection element were set to alternately repeat a detection action of 0.1 seconds of energizing the resistive element (heating at 500°C) and a 29.9-second intermittent drive without energizing. The sensor output was measured in an atmosphere free of the target gas before and after the exposure test. The change in the sensitivity of the gas detection element was evaluated by the increase in the 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, in a gas detector configured to issue an alarm when 2000 ppm propane is detected in the atmosphere, if the normalized sensor output exceeds 100 due to the exposure test, an alarm will be issued even if propane is not present in the atmosphere.

[0059] (Results of siloxane exposure test)

[0060] Table 1 shows the changes in sensor output when siloxanes are exposed to the gas sensor. First, in Table 1, regardless of the examples or comparative examples, when the filter contains acid-supported silica gel (Examples 1-6, Comparative Examples 2-6), the increase in sensor output is significantly suppressed compared to the case without acid-supported silica gel (Comparative Examples 1, 7-10). This indicates that acid-supported silica gel removes siloxanes from the target gas and suppresses poisoning of the gas detection element. Next, when focusing on Comparative Examples 2-6 and Comparative Examples 7-10 in Table 1, the increase in sensor output is suppressed when the filter contains acid-supported silica gel, but the sensor output increases significantly when the filter does not contain acid-supported silica gel but contains any one of zinc aluminosilicate, borosilicate, manganese oxide, or platinum-supported alumina. This indicates that acid-supported silica gel has a stronger ability to remove siloxanes compared to zinc aluminosilicate, borosilicate, manganese oxide, and platinum-supported alumina. Furthermore, when focusing on Examples 1-3 and Examples 4-6 in Table 1, the increase in sensor output was slightly suppressed when the acid-supported silica gel was disposed on the upstream side compared to when it was disposed on the downstream side. Therefore, it can be concluded that, in order to remove siloxanes from the target gas, it is preferable to dispose of the acid-supported silica gel on the upstream side.

[0061] [Table 1]

[0062] Table 1: Results of Siloxane Exposure Tests

[0063]

[0064]

[0065] (Results of hydrogen sulfide exposure test)

[0066] Table 2 shows the changes in sensor output when hydrogen sulfide is exposed to the gas sensor. First, in Table 2, regardless of the examples or comparative examples, when the filter contains any one of zinc aluminosilicate, borosilicate, manganese oxide, or platinum-supported alumina (Examples 1-6, Comparative Examples 2, 7-10), the increase in sensor output is significantly suppressed compared to the case where none of these three substances is present (Comparative Examples 1, 3-6). This indicates that zinc aluminosilicate, borosilicate, manganese oxide, and platinum-supported alumina remove hydrogen sulfide from the target gas and suppress poisoning of the gas detection element. Next, when focusing on Comparative Examples 3-6 and 7-10 in Table 2, the increase in sensor output was suppressed when the filter contained any one of zinc aluminosilicate, diatomite, manganese oxide, or platinum-supported alumina. However, when the filter did not contain any one of zinc aluminosilicate, diatomite, manganese oxide, or platinum-supported alumina, but contained acid-supported silica gel, the sensor output increased significantly. This indicates that zinc aluminosilicate, diatomite, manganese oxide, and platinum-supported alumina have a higher ability to remove hydrogen sulfide compared to acid-supported silica gel. Furthermore, when focusing on Examples 1-3 and 4-6 in Table 2, the increase in sensor output was slightly suppressed when any one of zinc aluminosilicate, diatomite, or manganese oxide was disposed on the downstream side compared to when it was disposed on the upstream side. This indicates that, for removing hydrogen sulfide from the target gas, it is preferable to dispose of any one of zinc aluminosilicate, diatomite, or manganese oxide on the downstream side.

[0067] [Table 2]

[0068] Table 2: Results of Hydrogen Sulfide Exposure Tests

[0069]

[0070]

[0071] (Results of ethanol exposure test)

[0072] Table 3 shows the changes in sensor output when ethanol is exposed to the gas sensor. First, in Table 3, regardless of the examples or comparative examples, when the filter contains platinum-supported alumina (Comparative Examples 2 and 7), the sensor output increases significantly compared to when it does not contain platinum-supported alumina (Examples 1-6, Comparative Examples 1, 3-6, 8-9). In particular, when the filter contains platinum-supported alumina (Comparative Examples 2 and 7), the sensor output increases significantly compared to when it contains alumina or silica alumina instead of platinum-supported alumina (Comparative Examples 3-4). This indicates that platinum-supported alumina, by including platinum, promotes poisoning of the gas detection element caused by the influence of ethanol. It is believed that platinum oxidizes ethanol to generate ethanol oxidation products, which in turn promote poisoning of the gas detection element. In contrast, in any example, by not including platinum in the filter, the increase in sensor output and the poisoning of the gas detection element can be suppressed. Furthermore, when focusing on Examples 1-3 and Examples 4-6 in Table 3, the increase in sensor output is slightly suppressed when any one of acid-supported silica gel is configured on the upstream side and zinc aluminosilicate, hydrated borosilicate, or manganese oxide is configured on the downstream side, compared to the opposite configuration. Therefore, to suppress the influence of ethanol, it is preferable to configure acid-supported silica gel on the upstream side and any one of zinc aluminosilicate, hydrated borosilicate, or manganese oxide on the downstream side. Additionally, in the examples, when the filter contains manganese oxide (Examples 3 and 6), the sensor output increases slightly compared to the case where zinc aluminosilicate or hydrated borosilicate is used instead of manganese oxide (Examples 1-2 and 4-5). Therefore, to further suppress the influence of ethanol, it is even more preferable to include zinc aluminosilicate or hydrated borosilicate in the filter instead of manganese oxide. This is believed to be because manganese oxide, although present in trace amounts, has the ability to oxidize ethanol, generating trace amounts of ethanol oxidation products.

[0073] [Table 3]

[0074] Table 3: Results of Ethanol Exposure Tests

[0075]

[0076]

[0077] (Results of siloxane + ethanol exposure test)

[0078] Table 4 shows the changes in sensor output when siloxane + ethanol is exposed to the gas sensor. First, in Table 4, regardless of the examples or comparative examples, when the filter contains acid-supported silica gel but not platinum-supported alumina (Examples 1-6, Comparative Examples 3-6), the increase in sensor output is significantly suppressed compared to cases without acid-supported silica gel or containing platinum-supported alumina (Comparative Examples 1-2, 7-10). This indicates that acid-supported silica gel removes siloxanes from the target gas, suppressing poisoning of the gas detection element, and the filter does not contain platinum, thereby suppressing poisoning of the gas detection element. For example, in Comparative Examples 1 and 7-10, since the filter does not contain acid-supported silica gel, siloxanes cannot be removed from the target gas; in Comparative Examples 2 and 7, the filter contains platinum-supported alumina, resulting in the generation of ethanol oxidation products, which promotes poisoning of the gas detection element. In contrast, it is believed that in any of the embodiments, siloxanes are removed by including acid-supported silica gel in the filter, and the generation of ethanol oxidation products is suppressed by not including platinum in the filter, thereby suppressing poisoning of the gas detection element. Next, when focusing on Examples 1-3 and Examples 4-6 in Table 1, the increase in sensor output is slightly suppressed when acid-supported silica gel is arranged on the upstream side and any one of zinc aluminosilicate, hydrated borosilicate, or manganese oxide is arranged on the downstream side, compared to the opposite configuration. Therefore, it can be seen that in order to suppress the increase in sensor output in the presence of siloxanes and ethanol, it is preferable to arrange acid-supported silica gel on the upstream side and any one of zinc aluminosilicate, hydrated borosilicate, or manganese oxide on the downstream side.

[0079] [Table 4]

[0080] Table 4: Results of Siloxane + Ethanol Exposure Test

[0081]

[0082] Explanation of reference numerals in the attached figures

[0083] 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 sensing part; 23. Catalyst protective layer; 24. Resistor; 3. Housing; 31. Opening; 32. Base; 33. Cover; 4. Filter component; 41. First filter component; 42. Second filter component; 5. Lead wire; 6. Electrode; 7. Metal mesh; 8. Non-woven fabric.

Claims

1. A MEMS-type semiconductor gas sensor, comprising: MEMS type semiconductor gas detection element, which detects the target gas contained in the target gas; A housing that houses the MEMS-type semiconductor gas detection element, having an opening for the gas to be measured to flow through; and A filter component is disposed within the housing between the opening and the MEMS-type semiconductor gas detection element, wherein... The filter assembly includes a first filter assembly for removing siloxanes and a second filter assembly for removing sulfur-based gases. The first filter element has a higher siloxane removal capacity than the second filter element, and the second filter element has a higher sulfur-based gas removal capacity than the first filter element. The filter components do not contain precious metals. The second filter component comprises zinc aluminosilicate or hydrated aluminosilicate.

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

3. The MEMS semiconductor gas sensor according to claim 1, wherein, The first filter component contains silicone.

Images