gas sensor

Abstract

To provide a gas sensor that has a wide concentration range capable of detection and in which variation in a formation area of a catalyst is suppressed.SOLUTION: A gas sensor includes: a first sensor element formed on a first membrane portion; a second sensor element formed on a second membrane portion; a first detection electrode connected to the first sensor element; a second detection electrode connected to the second sensor element; a first heater portion for heating the first sensor element; a second heater portion for heating the second sensor element; a first wiring portion for connecting the first detection electrode and an external circuit; and a second wiring portion for connecting the second detection electrode and the external circuit. The first sensor element has a semiconductor material portion exposed to the outside, and the second sensor element has a catalyst material portion exposed to the outside, a protruding pattern for defining a planar view shape of the catalyst material portion, and a heat detection portion thermally connected to the catalyst material portion.SELECTED DRAWING: Figure 3A

Description

Technical Field

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

Background Art

[0002] A gas sensor is a device that detects a gas present in the atmosphere and converts information such as its type and concentration into an electrical signal for output. Such gas sensors are mounted on home appliances, industrial equipment, environmental monitoring equipment, etc., and are used to detect the concentration of specific gases that affect humans, the environment, etc.

[0003] As gas sensors, various detection methods are known depending on differences in the type of gas to be detected, the concentration range, accuracy, operating principle, constituent materials, etc. When the gas to be detected is a combustible gas, gas sensors such as catalytic combustion type, semiconductor type, and thermal conductivity type are known.

[0004] Patent Document 1 discloses a gas alarm that sets one of two semiconductor thin-film gas sensor chips for detecting low-concentration CO and the other for detecting high-concentration CO. The gas alarm described in Patent Document 1 evaluates the low-concentration CO range by the ratio of the resistance value in an atmosphere where CO is 100 ppm to the resistance value in an atmosphere where CO is 300 ppm, and evaluates the high-concentration CO range by the ratio of the resistance value in an atmosphere where CO is 300 ppm to the resistance value in an atmosphere where CO is 500 ppm.

Prior Art Documents

Patent Documents

[0005]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0006] <00However, as a guideline for preventing carbon monoxide poisoning, the permissible concentration of carbon monoxide set by TLV-TWA is 25 ppm, and the alarm range for indicating the explosion risk of carbon monoxide is, for example, 600 ppm to 3%.

[0007] Therefore, the gas alarm described in Patent Document 1 had the problem that its detectable concentration range was narrow and it could not adequately detect the risk of carbon monoxide poisoning or the risk of carbon monoxide explosion.

[0008] This invention has been made in view of the above circumstances and aims to provide a gas sensor that has a wide detectable concentration range and suppresses variations in the catalyst formation area. [Means for solving the problem]

[0009] To achieve the above objective, the embodiments of the present invention are as follows. [1] A first membrane portion and a second membrane portion, A first sensor element formed on a first membrane portion, and a second sensor element formed on a second membrane portion, A first detection electrode electrically connected to a first sensor element, and a second detection electrode electrically connected to a second sensor element, A first heater unit for heating a first sensor element, and a second heater unit for heating a second sensor element, It comprises a first wiring section that electrically connects a first detection electrode and an external circuit, and a second wiring section that electrically connects a second detection electrode and an external circuit. The first sensor element has a semiconductor material portion exposed to the outside, The second sensor element is a gas sensor having an externally exposed catalyst material portion, a convex pattern for defining the planar shape of the catalyst material portion, and a heat sensing portion thermally connected to the catalyst material portion. [2] The gas sensor described in [1], wherein the convex pattern is made of a conductor. [3] The gas sensor described in [1] or [2], wherein the outer shape of the convex pattern corresponds to a circular or nearly circular ellipse. [4] A gas sensor according to any of [1] to [3], wherein the outer shape of the semiconductor material part is circular or nearly circular elliptical. [5] A gas sensor according to any one of [1] to [4], wherein the first sensing electrode is composed of a pair of electrodes, and the planar shape of the first sensing electrode corresponds to the planar shape of the semiconductor material portion. [6] A gas sensor according to any one of [1] to [5], wherein the first sensing electrode is composed of a pair of electrodes, and the pair of electrodes are arranged to face each other in the direction toward the center of the first sensing electrode. [7] A gas sensor according to any one of [1] to [6], wherein the ratio of the area of ​​the planar shape of the semiconductor material portion to the area of ​​the planar shape of the catalyst material portion is 0.9 to 1.1. [8] A gas sensor according to any one of [1] to [7], wherein the heat sensing part includes a heat sensing material and the heat sensing material is a thermistor. [9] A gas sensor according to any one of [1] to [7], wherein the heat sensing part includes a heat sensing material, and the heat sensing material is a platinum resistor.

[10] A gas sensor according to any one of [1] to [9], further comprising a reference sensor element.

[11] A gas sensor as described in any of [1] to

[10] , wherein the range of detection standards handled by the first sensor element and the range of detection standards handled by the second sensor element are separated by 500 ppm or more.

[12] A gas sensor according to any one of [1] to

[10] having a range in which the range of detection standards handled by the first sensor element and the range of detection standards handled by the second sensor element overlap.

[13] A gas sensor according to any of [1] to

[12] , wherein the target gas to be detected is carbon monoxide gas, the first sensor element detects carbon monoxide gas with a concentration of 25 ppm or less, and the second sensor element detects carbon monoxide gas with a concentration of 0.05% or more. [Effects of the Invention]

[0010] According to the present invention, it is possible to provide a gas sensor having a wide detectable concentration range and suppressing variations in the formation area of the catalyst.

Brief Description of the Drawings

[0011] [Figure 1A] FIG. 1A is a schematic plan view of a gas sensor according to a first embodiment of the present invention. [Figure 1B] FIG. 1B is a schematic cross-sectional view of the gas sensor taken along line IB-IB in FIG. 1A. [Figure 2A] FIG. 2A is an enlarged view of the vicinity of the first sensor element in FIG. 1B. [Figure 2B] FIG. 2B is a schematic cross-sectional view of the vicinity of the first sensor element cut along the YZ plane along line IIB-IIB in FIG. 1A. [[ID=​​​​​​​​​​​​​​​​​​​​​​​​​​​Figure 4B is a wiring diagram of the third heater and third wiring section of the third sensor element shown in Figure 4A. [Figure 5A] Figure 5A is a schematic plan view of a gas sensor according to a second embodiment of the present invention. [Figure 5B] Figure 5B is a schematic cross-sectional view of the gas sensor along the VB-VB line in Figure 5A. [Figure 6A] Figure 6A is a magnified view of the vicinity of the first sensor element in Figure 5B. [Figure 6B] Figure 6B is a schematic cross-sectional view of the vicinity of the first sensor element, cut along the YZ plane along the VIB-VIB line in Figure 5A. [Figure 7A] Figure 7A is a magnified view of the vicinity of the second sensor element in Figure 5B. [Figure 7B] Figure 7B is a schematic cross-sectional view of the vicinity of the second sensor element, cut along the YZ plane parallel to the VIIB-VIIB line in Figure 5A. [Figure 7C] Figure 7C is a wiring diagram of the second heater and second wiring section of the second sensor element shown in Figure 7A. [Figure 8] Figure 8 is a graph showing the relationship between the concentration of carbon monoxide gas and the sensor sensitivity for a sample of a gas sensor prepared as an embodiment of the present invention. [Figure 9] Figure 9 is a graph showing the relationship between the concentration of carbon monoxide gas and the sensor sensitivity for gas sensor samples prepared as examples and comparative examples of the present invention. [Modes for carrying out the invention]

[0012] The present invention will be described in detail below, based on specific embodiments, in the following order. 1. Gas sensor 1.1. First Embodiment 1.1.1. Overall configuration of the gas sensor 1.1.2. First sensor element 1.1.3. Second sensor element 1.1.4. Third Sensor Element 1.2. Second Embodiment 1.3. Operation of the gas sensor 2. Method for manufacturing a gas sensor 3. Variant

[0013] (1. Gas sensor) The gas sensor according to this embodiment is a gas sensor comprising a plurality of sensor elements supported by a thin membrane. The gases to be detected are flammable gases and reducing gases, specifically exemplified by carbon monoxide (CO), methane (CH4), propane (C3H8), ethanol (C2H5OH), etc. The gas sensor according to this embodiment comprises a sensor element having a semiconductor material portion whose resistance value changes upon contact with a reducing gas, and a sensor element having a thermal sensing portion whose resistance value changes due to the heat generated by the combustion of a flammable gas in a catalyst.

[0014] The gas sensor according to this embodiment may also include a reference sensor element that does not have gas detection capabilities, other gas sensor elements for detecting different types of gases, and so on.

[0015] An example of the gas sensor according to this embodiment will be described separately as a first embodiment and a second embodiment. The configuration of the sensor element differs between the first embodiment and the second embodiment due to the difference in the material used as the heat sensing material.

[0016] (1.1. First Embodiment) An example of a gas sensor according to the first embodiment is shown in Figures 1A and 1B. Figure 1A is a schematic plan view of the gas sensor 1 according to the first embodiment, and Figure 1B is a schematic cross-sectional view of the gas sensor 1 cut along the IB-IB line in Figure 1A. In Figures 1A and 1B, the X and Y axes are perpendicular to the Z axis and perpendicular to each other. The relationship between the X, Y, and Z axes is the same in Figures 2 and onward. In the following figures, the Z axis coincides with the thickness direction of the gas sensor, and the thickness direction of the gas sensor coincides with the stacking direction of the membrane, heater, sensor element, etc., which will be described later.

[0017] (1.1.1. Overall configuration of the gas sensor) In Figures 1A and 1B, the gas sensor 1 comprises a first sensor element 10, a second sensor element 20, and a third sensor element 30 as sensor elements. Each sensor element is supported by four beams 100 connected to the substrate 90 in a cavity 93 where the substrate 90 is thinned or absent, and in areas other than the beams 100, it exists separately from the substrate 90 as shown in Figure 1B. The four beams 100 are thinned and formed by providing four openings 95 in the substrate 90 corresponding to the cavity 93.

[0018] Furthermore, the substrate portion 90 is formed with a heater terminal portion 111 for connecting to an external circuit that supplies power to the heater portion, which will be described later, and a detection terminal portion 112 for connecting to an external circuit that measures the resistance change detected by the detection electrode, which will be described later.

[0019] As shown in Figures 1A and 1B, the substrate portion 90 is composed of a support substrate 91, a coating film 92, and a cavity portion 93. In this embodiment, the coating film 92 is a thin film that extends from the support substrate 91 and constitutes the beam portion 100 and the membrane portions 41, 42, and 43 (described later) in the cavity portion 93 where the support substrate 91 is thinned or absent. That is, each sensor element is formed on the membrane portion.

[0020] In the support substrate corresponding to the planar shape (shape on the XY plane) of each sensor element, the support substrate is thinned or has a cavity where it is absent. As a result, there is almost no material other than the sensor element near each sensor element, and therefore the heat capacity of that material is reduced. Furthermore, since each sensor element is connected to the support substrate only via a thin-film beam, the heat generated from the heater is conducted only through the thin-film portion to the support substrate. Therefore, the structure insulated between each sensor element formed on the membrane and the support substrate is achieved. Consequently, the power consumption of the heater required to heat each sensor element to a predetermined temperature can be greatly reduced.

[0021] Since the coating film constitutes the membrane portion, in this embodiment, the coating film only needs to have sufficient mechanical strength to support the components (heater portion, electrode portion, wiring portion, detection portion, etc.) formed on the membrane portion.

[0022] The material constituting the coating film is preferably one that can sufficiently ensure insulation between the support substrate and the heater so that current leakage from the heater to the support substrate does not occur, as described later. Examples of such materials include silicon oxide and silicon nitride.

[0023] The thickness of the membrane portions 41, 42, and 43 is preferably such that sufficient insulation between the support substrate and the heater portion is ensured. Furthermore, the thickness is preferably such that it takes into account the mass load on the membrane portion from the sensor element formed on the membrane portion. Additionally, the thickness is preferably such that it functions as an etching stop layer when forming the cavity portion 93.

[0024] The support substrate 91 is not particularly limited, as long as it has sufficient mechanical strength to support the member formed thereon and is made of a material suitable for microfabrication such as etching. In this embodiment, examples of the support substrate 91 include a silicon single crystal substrate, a sapphire single crystal substrate, a ceramic substrate, a quartz substrate, a glass substrate, a ferrite substrate, and the like.

[0025] (1.1.2. First sensor element) Figure 2A is an enlarged view of the schematic cross-sectional diagram of the vicinity of the first sensor element 10 shown in Figure 1A. Figure 2B is a schematic cross-sectional diagram of the vicinity of the first sensor element 10, cut along the YZ plane along the line IIB-IIB in Figure 1A.

[0026] As shown in Figures 2A and 2B, a first heater section 51 and a first wiring section 61 are formed on the first membrane section 41. The first heater section 51 consists of a first heater 511, which is a resistor that generates heat when current is applied, and a first heater coating film 512. The first heater 511 is a wiring section having a predetermined resistance value that can efficiently and reliably heat the semiconductor material, which is the semiconductor material section 11. In other words, the first heater 511 is a resistive wiring section.

[0027] In this embodiment, as shown in Figure 2C, in the region corresponding to the formation region of the first sensor element 10, the first heater 511 is preferably composed of a pattern (meander pattern) in which multiple resistive wires are folded and arranged in parallel at predetermined intervals.

[0028] The material constituting the first heater is preferably a conductive material with a relatively high melting point that can withstand high-temperature processes such as the film deposition process and heat treatment process of the first sensor element. Examples of such materials include molybdenum (Mo), platinum (Pt), nickel-chromium alloy (NiCr), tungsten (W), tantalum (Ta), palladium (Pd), iridium (Ir), or alloys containing two or more of these. In this embodiment, platinum is particularly preferred because it allows for high-precision patterning such as lift-off and has high durability. When platinum is used as the material constituting the first heater, it is preferable to form an adhesion layer such as titanium (Ti) between the platinum and the first membrane to improve adhesion with the first membrane.

[0029] The first heater coating film 512 is formed to cover the first heater 511. The first heater coating film 512 is formed by being laminated on the first membrane portion 41, except for the portion that is in contact with the first heater 511. When the gas sensor according to this embodiment is in operation, the first heater formed between the first heater coating film and the first membrane portion is repeatedly subjected to thermal stress, rising to tens to hundreds of degrees Celsius and then falling back to room temperature.

[0030] To mitigate the effects of thermal stress, it is preferable that the materials of the first membrane and the first heater coating film be configured with consideration for durability against thermal stress, mechanical strength, film stress, adhesion, electrical insulation, etc. For example, the materials of the first membrane and the first heater coating film may be the same material, different materials, or composed of multiple materials.

[0031] When composed of multiple materials, for example, silicon oxide, which has excellent insulation resistance, thermal stress resistance, and mechanical strength, may be used in combination with silicon nitride to relieve stress caused by silicon oxide.

[0032] The first wiring section 61 is wiring for connecting the first detection electrode and the detection terminal section, which will be described later. As shown in Figure 2A, the first wiring section 61 and the first detection electrode 71 are connected through a through-hole TH formed in the stacking direction (Z-axis direction). Also, as shown in Figure 2C, the first wiring section 61 extends along the beam section 100 and is electrically connected to the detection terminal section.

[0033] A thermistor section 80 (thermistor 81 and thermistor coating 82) is formed on the first heater section 51 (on the first heater coating 512). In this embodiment, thermistor 81 is not electrically connected to the first wiring section 61 and the first detection electrode 71, and is not used as a detection section.

[0034] A semiconductor material portion 11 and a first detection electrode 71 are formed on the thermistor portion 80 (on the thermistor coating film 82).

[0035] The semiconductor material portion 11 is formed to be exposed to the external atmosphere, and the first sensing electrode 71 is formed to be in contact with the semiconductor material portion 11. The planar shape of the semiconductor material portion 11 is not particularly limited. In this embodiment, from the viewpoint of the semiconductor material portion formation process and the uniformity of the temperature distribution in the semiconductor material portion, the planar shape of the semiconductor material portion 11 is preferably circular or nearly circular elliptical, and more preferably circular.

[0036] In this embodiment, the semiconductor material portion has a semiconductor material exposed to the external atmosphere. Because the semiconductor material is exposed to the external atmosphere, when reducing gases present in the atmosphere come into contact with the semiconductor material, the number of free electrons on the surface of the semiconductor material increases or decreases, and the resistance value of the semiconductor material changes.

[0037] The semiconductor material included in the semiconductor material section 11 is not particularly limited as long as it is a material whose resistance changes upon contact with a reducing gas. In this embodiment, it is preferable that the material be a metal oxide from the viewpoint of thermal stability and chemical stability. Examples of metal oxides include tin oxide (SnO2), zirconium oxide (ZrO2), iron oxide (Fe2O3), tungsten oxide (WO3), and indium oxide (In2O3). Furthermore, in order to further increase the sensitivity to the gas to be detected, noble metals such as platinum (Pt) and palladium (Pd) may be supported on the metal oxide.

[0038] The first detection electrode 71 is an electrode for detecting changes in the resistance of a semiconductor material. In this embodiment, the first detection electrode 71 is composed of a pair of electrodes connected via a semiconductor material. Furthermore, in order to accurately detect even slight changes in the resistance of the semiconductor material, the first detection electrode 71 is formed so as to increase the contact area with the semiconductor material while maintaining a constant distance between the electrodes.

[0039] In this embodiment, as shown in Figures 1A and 2D, the planar shape (XY plane shape) of the first detection electrode 71 corresponds to the planar shape (XY plane shape) of the semiconductor material portion 11. As shown in Figure 2D, the first detection electrode is required to maintain a constant distance between electrodes (indicated by six double-headed arrows in Figure 2D) while electrically stably connecting the electrodes with the semiconductor material portion. Therefore, it is ideal that the planar shape of the first detection electrode 71 and the planar shape of the semiconductor material portion 11 coincide. Accordingly, as shown in Figures 1A and 2D, the relationship between the planar shape of the first detection electrode 71, which is configured with the intention of approaching the planar shape of the semiconductor material portion 11, and the planar shape of the semiconductor material portion 11 is expressed as "the planar shape of the first detection electrode 71 corresponds to the planar shape of the semiconductor material portion 11." That is, in the XY plane, the region where the pair of electrodes constituting the first detection electrode 71 are deployed and the region of the semiconductor material portion 11 almost coincide.

[0040] Because the planar shape of the first detection electrode 71 corresponds to the planar shape of the semiconductor material portion 11, the first detection electrode 71 can sufficiently and accurately detect the resistance change occurring in the semiconductor material portion 11. As a result, variations in sensitivity between individual gas sensors during gas detection can be suppressed.

[0041] As described above, the planar shape of the semiconductor material portion 11 is preferably circular or an elliptical shape close to a circle. Therefore, the planar shape of the first detection electrode 71 is also preferably a shape corresponding to a circular or an elliptical shape close to a circle.

[0042] The configuration of the first detection electrode 71 is not particularly limited as long as it is configured to correspond to the planar shape of the semiconductor material portion 11. When the first detection electrode 71 is composed of a pair of electrodes, for example, the configuration shown in Figure 2D is an example.

[0043] In Figure 2D, the first detection electrode 71 has a pair of electrodes: a first detection electrode A and a first detection electrode B. The first detection electrode A consists of an arc-shaped electrode A1, a circular electrode A2, a connecting portion A3 that connects these to a through-hole, and a connecting portion A4 formed inside the through-hole that connects the connecting portion A3 to the first wiring portion. The first detection electrode B consists of an arc-shaped electrode B1, a connecting portion B2 that connects the arc-shaped electrode B1 to a through-hole, and a connecting portion B3 formed inside the through-hole that connects the connecting portion B2 to the first wiring portion. The regions corresponding to connecting portions A4 and B3 correspond to the through-hole TH, as shown in Figure 2A, and connecting portions A4 and B3 are formed on the first wiring portion 61, not on the thermistor coating 82, and are electrically connected. The first detection electrode A and the first detection electrode B are arranged to face each other in the radial direction from the center of the first detection electrode outwards.

[0044] Here, the arc-shaped electrode A1 constitutes the outer circumference of the first detection electrode 71, with both ends facing each other across the connection portion B2 of the first detection electrode B, and arranged so that the distance between the electrodes is constant. In other words, the arc-shaped electrode A1 has a shape (C-shape) in which a part of the annular electrode is cut out, and the connection portion B2 penetrates the cut-out portion so as not to come into contact with the arc-shaped electrode A1. By configuring the pair of electrodes in this way, the pair of electrodes face each other and the contact area with the semiconductor material is increased.

[0045] Figure 2D shows an example of configuring the first detection electrode to correspond to the planar shape of the semiconductor material portion, in which one detection electrode (first detection electrode A) and the other detection electrode (first detection electrode B) are arranged alternately in concentric circles. However, the first detection electrode may be configured in an example other than that shown in Figure 2D. That is, it is preferable to divide the region corresponding to the planar shape of the semiconductor material portion so that a pair of electrodes face each other and the distance between the electrodes is constant, and furthermore, to configure it so that the area occupied by the pair of electrodes is large.

[0046] For example, as shown in Figure 2E, each concentric circle may be shared by one detection electrode (first detection electrode A) and the other detection electrode (first detection electrode B).

[0047] As shown in Figure 2A, the first detection electrode 71 is formed on the thermistor portion 80 (thermistor coating film 82) so as to protrude in the stacking direction (Z-axis direction). That is, the first detection electrode 71 has a predetermined height in the stacking direction.

[0048] As a method for forming a semiconductor material portion, a method is known in which a predetermined amount of paste containing the material constituting the semiconductor material portion (semiconductor material) is supplied onto a coating film or the like to form the semiconductor material portion. By forming the first detection electrode 71 as a pattern having a predetermined height, when a predetermined amount of paste is supplied to the region where the first detection electrode 71 is formed, the spread of the supplied paste is controlled by the first detection electrode 71. As a result, the contact area with the semiconductor material can be increased, and variations in the formation area of ​​the semiconductor material portion (area in the XY planar view) can be suppressed. As a result, variations in sensitivity between individual gas sensors during gas detection can be suppressed.

[0049] (1.1.3. Second sensor element) Figure 3A is an enlarged view of the schematic cross-sectional diagram of the vicinity of the second sensor element 20 shown in Figure 1A. Figure 3B is a schematic cross-sectional diagram of the vicinity of the second sensor element 20 cut along the YZ plane along the line IIIB-IIIB in Figure 1A. As shown in Figures 3A and 3B, the second heater portion 52 and the second detection electrode 72 are formed on the second membrane portion 42. As shown in Figure 3C, the second wiring portion 62 is also formed on the second membrane portion 42, and the second detection electrode 72 is connected to the wiring portion 62.

[0050] In this embodiment, the second heater section 52, like the first heater section, is composed of a second heater 521, which is a resistor that generates heat when energized, and a second heater coating film 522. The second heater 521 is configured with wiring having a predetermined resistance value so as to efficiently and reliably heat the thermistor, which is used as a heat sensing material. In other words, the second heater 521 is also a resistive wiring section, just like the first heater.

[0051] Furthermore, as shown in Figure 3C, in the region corresponding to the catalyst material formation region, the second heater 521 is preferably composed of a pattern (meander pattern) in which multiple resistance wires are folded and arranged in parallel at predetermined intervals. In this embodiment, the first heater and the second heater 521 are composed of the same pattern.

[0052] The material constituting the second heater is preferably the material exemplified as the material constituting the first heater. Furthermore, if the material constituting the second heater is platinum, it is preferable to form an adhesion layer between the platinum and the second membrane portion, similar to the first heater.

[0053] The second heater coating is formed to cover the second heater, the second sensing electrode, and the second wiring section. For the same reasons as the first heater coating, it is preferable that the materials constituting the second heater coating and the materials constituting the second membrane section be configured with consideration for durability against thermal stress, mechanical strength, film stress, adhesion, electrical insulation, etc.

[0054] The second detection electrode 72 is an electrode for detecting changes in the resistance value of the thermistor. In this embodiment, as shown in Figures 3A and 3C, the second detection electrode 72 is composed of a pair of opposing electrodes electrically connected via a thermistor 211, which is a thermal sensing material, in contact through a through-hole TH formed in the stacking direction (Z-axis direction). The second detection electrode may be composed of a pair of comb-shaped electrodes.

[0055] The material constituting the second detection electrode is preferably a conductive material, similar to the first detection electrode, and has a relatively high melting point that can withstand high-temperature processes such as the film deposition process and heat treatment process of the thermistor as a thermal detection material. In this embodiment, the material constituting the second detection electrode is preferably one of the materials exemplified for the material constituting the first detection electrode, and platinum is particularly preferred for the same reasons as for the first detection electrode.

[0056] As shown in Figures 3A and 3B, the heat sensing unit 21 is formed on the second heater coating film 522, except for the through-hole TH. The heat sensing unit 21 consists of a thermistor 211 as a heat sensing material and a heat sensing material coating film 212.

[0057] The thermistor has a negative temperature coefficient of resistance. The thermistor is thermally connected to the catalyst material, and thermal detection is performed by changing the resistance value of the thermistor due to temperature changes caused by the combustion of a flammable gas in the catalyst material. The material constituting the thermistor is not particularly limited as long as it is a material that can be used as a thermistor. In this embodiment, examples of the thermistor material include composite metal oxides containing metal elements such as manganese (Mn), nickel (Ni), cobalt (Co), and iron (Fe). The thickness of the thermistor can be adjusted according to the target thermistor resistance value.

[0058] When a thermal sensing material is exposed to the external atmosphere or in contact with a catalyst material, chemical degradation due to oxidation, diffusion, etc., may occur. For example, when a composite metal oxide is used as a thermistor, it is known that if the thermistor is kept at a high temperature, oxygen is removed from the composite metal oxide, causing reduction of the composite metal oxide and degradation. Therefore, in order to prevent adverse effects on thermal sensing characteristics due to such chemical degradation, it is preferable to cover the thermistor with a thermal sensing material coating film to protect the thermistor. The material constituting the thermal sensing material coating film is preferably a material that is stable at high temperatures. In this embodiment, it is preferable to use the same material as the second membrane portion and the second heater coating film described above. Therefore, silicon oxide, silicon nitride, etc., are preferred as such materials.

[0059] The thickness of the thermal sensing material coating should be such that it can reliably cover the thermistor and ensure sufficient insulation between layers.

[0060] As shown in Figures 3A, 3B, and 3D, the catalyst material portion 22 and the convex pattern 23 are formed on the surface of the heat sensing portion 21 (in this embodiment, the heat sensing material coating film 212). The convex pattern 23 is formed on the heat sensing portion 21 to have a predetermined height in the stacking direction (Z-axis direction). The convex pattern 23 is formed to define the planar shape (XY planar shape) of the catalyst material portion 22, and the catalyst material portion 22 is formed to cover the convex pattern 23. Therefore, the planar shape (XY planar shape) of the convex pattern 23 corresponds to the outer peripheral shape of the planar shape (XY planar shape) of the catalyst material portion 22.

[0061] A known method for forming a catalyst material portion involves supplying a predetermined amount of paste containing the materials constituting the catalyst material portion onto a coating film or the like. By providing a convex pattern, the spread of the paste supplied inside the convex pattern is controlled by the convex pattern, thereby suppressing variations in the formation area of ​​the catalyst material portion (area in the XY planar view). As a result, it is possible to suppress variations in sensitivity between individual gas sensors during gas detection.

[0062] The convex pattern is not particularly limited as long as it can define the planar shape of the catalyst material. It can be determined by considering the catalyst material formation process. In this embodiment, from the viewpoint of the catalyst material formation method and the uniformity of the temperature distribution in the catalyst material, it is preferable that the planar shape of the catalyst material be circular or an ellipse close to a circle. Therefore, the outer shape of the convex pattern for defining the planar shape of the catalyst material is preferably circular or an ellipse close to a circle, and more preferably circular.

[0063] For example, as shown in Figure 3D, the convex pattern 23 may consist of a continuous pattern, or as shown in Figure 3E, it may consist of intermittently formed patterns 23.

[0064] The material used to form the convex pattern is not particularly limited. In this embodiment, it is preferable that the material be a conductor for process reasons, as it can be formed simultaneously with conductors such as electrodes. A metal or alloy is preferred as the conductor. In this embodiment, the conductor is, for example, gold (Au).

[0065] The catalyst material section 22 is formed to be exposed to the outside, as shown in Figures 1A, 3A, and 3B. The catalyst material section promotes the combustion of the gas to be detected. The material constituting the catalyst material section is not particularly limited as long as it is a material known to be used as a catalyst for gas sensors. Typically, a material in which noble metal particles are supported on a carrier is used.

[0066] Furthermore, it is preferable that the area of ​​the planar shape of the catalyst material portion 22 is close to the area of ​​the planar shape of the semiconductor material portion. In this embodiment, it is preferable that the ratio of the area of ​​the planar shape of the semiconductor material portion to the area of ​​the planar shape of the catalyst material portion is 0.9 to 1.1. By having the area ratio within the above range, the thermal balance between heater heating and atmospheric heat dissipation due to the area difference and the surface areas of both sensitive components become equivalent, which has the effect of making sensor element control easier.

[0067] The carrier is a porous material formed by the aggregation and integration of multiple particles. The carrier is not particularly limited as long as it is a material commonly used as a carrier. Specifically, examples include oxide materials such as aluminum oxide (γ-alumina, etc.) and silicon oxide. In this embodiment, the carrier material is preferably aluminum oxide.

[0068] Furthermore, examples of particles used in the catalyst supported on the carrier include precious metal particles such as platinum (Pt), palladium (Pd), ruthenium (Ru), and rhodium (Rh). In this embodiment, platinum is preferred as the precious metal particle used in the catalyst.

[0069] (1.1.4. Third sensor element) The gas sensor according to this embodiment includes a first and second sensor element for detecting gas, as well as a third sensor element, which is a reference sensor element that does not have gas detection capabilities. The reference sensor element outputs the influence of the atmosphere other than the gas to be detected as a change in resistance value, and corrects the sensor element that has gas detection capabilities.

[0070] Figure 4A is an enlarged view of the schematic cross-sectional diagram of the vicinity of the third sensor element 30 shown in Figure 1A. Also, as shown in Figure 4B, the third heater 531 and the third wiring section 63 are formed on the third membrane section 43.

[0071] The third heater section 53 is formed of the same material and pattern as the first and second heater sections.

[0072] Furthermore, as shown in Figure 4B, the third wiring section 63 is electrically connected to the third heater 531, and the contact point between the third heater 531 and the third wiring section 63 becomes the third detection electrode. The third wiring section 63 extends along the beam section 100 and is electrically connected to the detection terminal section 112 shown in Figure 1A, and outputs the change in the resistance value of the third heater 531 to an external circuit connected to the detection terminal section 112.

[0073] A thermistor section 80 (thermistor 81 and thermistor coating 82) is formed on the third heater section 53, but thermistor 81 is not electrically connected to the third heater 531 and the third wiring section 63, and changes in the resistance value of the thermistor 81 are not detected.

[0074] (1.2. Second Embodiment) The gas sensor according to the second embodiment is the same as the gas sensor according to the first embodiment, except as shown below. Common components are given common component names and reference numerals, and some descriptions of common parts are omitted.

[0075] An example of the gas sensor 2 according to the second embodiment is shown in Figures 5A and 5B. Figure 5A is a schematic plan view of the gas sensor 2 according to the second embodiment, and Figure 5B is a schematic cross-sectional view of the gas sensor 2 cut along the XZ plane along the VB-VB line in Figure 5A.

[0076] As shown in Figures 5A and 5B, the gas sensor 2 according to the second embodiment, like the gas sensor according to the first embodiment, comprises a first sensor element 10, a second sensor element 20, and a third sensor element 30 formed on membrane portions 41, 42, and 43 formed by thinning the substrate portion 90.

[0077] Figure 6A is an enlarged view of the schematic cross-sectional diagram of the vicinity of the first sensor element shown in Figure 5A. Figure 6B is a schematic cross-sectional diagram of the vicinity of the first sensor element, cut along the YZ plane along the VIB-VIB line in Figure 5A.

[0078] In the second embodiment, unlike the first embodiment, the first sensor element 10 does not have a thermistor portion. That is, the first detection electrode 71 and the semiconductor material portion 11 are formed on the surface of the first heater portion 51 (first heater coating film 512). The first heater portion 51, the first detection electrode 71, the first wiring portion 61, and the semiconductor material portion 11 are configured in the same way as in the first embodiment.

[0079] In the first embodiment, the thermistor is not involved in gas detection in the first sensor element; therefore, the first sensor element in the second embodiment can also detect gas in the same way as the first sensor element in the first embodiment.

[0080] Figure 7A is an enlarged view of the schematic cross-sectional diagram of the vicinity of the second sensor element 20 shown in Figure 5A. Figure 7B is a schematic cross-sectional diagram of the vicinity of the second sensor element 20, cut along the YZ plane along the VIIB-VIIB line in Figure 5A.

[0081] In the second embodiment, unlike the second sensor element in the first embodiment, the second sensor element does not have a thermistor portion. In the second embodiment, the second heater portion also serves as the heat detection portion. That is, in the second embodiment, the second heater is the heat detection material. Therefore, in the first embodiment, the second detection electrode is electrically connected to the thermistor, which is the heat detection material, but in the second embodiment, as shown in Figure 7C, the second wiring portion 62 is connected to the second heater 521, and the contacts serve as the second detection electrode. That is, the wiring shown in Figure 7C is equivalent to the wiring shown in Figure 4B. In the second embodiment, from the viewpoint of durability against heat, the material constituting the second heater is preferably platinum (Pt).

[0082] In the second embodiment, the heat generated by the combustion of the target gas in the catalyst material causes a change in the resistance value of the second heater, which is detected by the second detection electrode (second wiring section) and output to an external circuit. The catalyst material section 22 and the convex pattern 23 are configured in the same way as in the first embodiment.

[0083] The third sensor element is a reference sensor element that does not have gas detection capability, similar to the first embodiment. In the second embodiment, the configuration of the third sensor element is the same as in the first embodiment, except that it does not have a thermistor section.

[0084] (1.3. Operation of the gas sensor) In the gas sensors according to the first and second embodiments, each heater is connected to an external circuit (not shown) via a heater terminal. The first detection electrode is also connected to an external circuit (not shown) via a detection terminal. The second and third detection electrodes are connected via a detection terminal to form a bridge circuit together with a fixed resistor. When the gas sensor is activated, power is supplied, a predetermined voltage is applied to each heater, and each sensor element is heated to a predetermined temperature.

[0085] The semiconductor material portion of the first sensor element contains a semiconductor material. When the space in which the gas sensor is placed contains the target gas, the resistance of the semiconductor material changes according to the amount of electron transfer resulting from the oxidation-reduction reaction between oxygen adsorbed on the surface of the semiconductor material and the target gas. Since the amount of electron transfer corresponds to the concentration of the target gas, the concentration of the target gas can be measured by detecting this change in resistance with the first detection electrode. Because the change in the resistance of the semiconductor material is highly sensitive even at very low concentrations of the target gas, the first sensor element is suitable for detection when the target gas is at a low concentration. However, when the target gas is at a high concentration, the change in resistance saturates, so while detection is possible, concentration measurement becomes difficult.

[0086] The second sensor element has a catalyst material section. When the space in which the gas sensor is placed contains the target gas, the combustible gas and oxygen combine and burn on the catalyst material section according to their proportion. At this time, the heat of combustion generated in the catalyst material section by the combustion of the combustible gas heats the thermal sensing material. When the change in the resistance value of the thermal sensing material caused by this temperature change due to combustion heat is input to the bridge circuit through the second sensing electrode, the balance of the bridge circuit is disrupted and a voltage is generated. Since the generated voltage corresponds to the concentration of the target gas, the concentration of the target gas can be measured by measuring the voltage. When the concentration of the target gas is low, the generated voltage is low and the sensitivity is low, but when the concentration of the target gas is high, the generated voltage is high and the sensitivity is high, so the second sensor element is suitable for detection when the target gas is at a high concentration.

[0087] Therefore, the gas sensor according to this embodiment can be configured such that the detection range of the first sensor element and the detection range of the second sensor element are different. For example, when configuring the gas sensor to take into account malfunctions due to interference regions, it is preferable that the detection range of the first sensor element and the detection range of the second sensor element are separated by 500 ppm or more. On the other hand, when configuring the gas sensor to prevent dead zones, it is preferable that the detection range of the first sensor element and the detection range of the second sensor element overlap.

[0088] Furthermore, in this embodiment, the gas concentration range detectable by the first sensor element is preferably 1 ppm to 200 ppm. Also, the gas concentration range detectable by the second sensor element is preferably 100 ppm to 4%.

[0089] Furthermore, the gas sensor according to this embodiment preferably includes carbon monoxide as the gas to be detected. In this case, the first sensor element can detect carbon monoxide gas with a concentration of 25 ppm or less, and the second sensor element can detect carbon monoxide gas with a concentration of 0.05% or more.

[0090] (2. Method for manufacturing gas sensors) Next, an example of a method for manufacturing a gas sensor according to the first and second embodiments will be described below.

[0091] First, prepare the support substrate. On one main surface of the prepared support substrate, form an insulating film that will serve as the coating (membrane portion). For forming the insulating film, any known film deposition method such as thermal oxidation or CVD (Chemical Vapor Deposition) can be used.

[0092] Next, heater sections, detection electrodes, and wiring sections are formed on the formed insulating film. In this embodiment, the predetermined pattern (heater, electrode, wiring, etc.) is formed by the lift-off method. First, a resist is applied to the entire surface on which the predetermined pattern is to be formed, and then exposed and developed to create the predetermined pattern shape. Development causes the resist corresponding to the predetermined pattern shape to dissolve, and the predetermined pattern shape is patterned. After the resist dissolves, the material constituting the pattern is deposited by a film deposition method such as sputtering or vapor deposition. After film deposition, the remaining resist is removed with a stripping solution, and the material deposited on the resist is also removed, leaving the deposited material only in the patterned area, thus forming the predetermined pattern.

[0093] After forming the heater, sensing electrode, and wiring section, a heater coating film is formed by a known film formation method, similar to the method used for forming the insulating film, so that these components are at least covered. This forms the heater section. In this embodiment, the material of the heater coating film is the same as the material of the membrane section (insulating film).

[0094] When manufacturing the gas sensor according to the first embodiment, a through-hole is formed in the second heater portion (second heater coating film) so that the second detection electrode formed in the region corresponding to the second sensor element is connected to the thermistor. The through-hole is formed by applying a resist to the second heater coating film, patterning it to the shape of a through-hole, and then using RIE (Reactive Ion Etching).

[0095] After forming the through-holes, thermistor sections are formed on each heater section. First, a thermistor, which will serve as a heat sensing material, is formed on the heater section, i.e., on the heater coating film, by a known film deposition method.

[0096] The thermistor can be formed using a known film deposition method. For example, if the thermistor is composed of the composite oxide described above, it is deposited by sputtering to achieve the composition of the composite oxide. After that, it is heat-treated at a predetermined temperature and holding time, and then etched to a predetermined shape. The formed thermistor functions as a heat sensing element in the second sensor element.

[0097] Next, a thermal sensing material coating film is formed to protect the thermistor so that it covers the thermistor. The thermal sensing material coating film is formed by a known film formation method, similar to the formation of the insulating film. This forms the thermistor portion. In this embodiment, the material of the thermal sensing material coating film is the same as the material of the insulating film.

[0098] Next, through-holes are formed in the thermistor portion (thermistor coating film) so that the first detection electrode, formed in the region corresponding to the first sensor element, is connected to the semiconductor material portion. The through-holes are formed by RIE or wet etching.

[0099] When manufacturing the gas sensor according to the second embodiment, a through-hole is formed in the first heater portion (first heater coating film) so that the first detection electrode formed in the region corresponding to the first sensor element is connected to the semiconductor material portion. The through-hole is formed by RIE.

[0100] Through the above process, in the first embodiment, a laminated structure is obtained in which an insulating film, a heater portion, and a thermistor portion are laminated on a support substrate in this order, and in the second embodiment, a laminated structure is obtained in which an insulating film and a heater portion are laminated on a support substrate in this order. On this laminated structure, a first detection electrode is formed in the region corresponding to the first sensor element, a convex pattern is formed in the region corresponding to the second sensor element, and a heater terminal portion and a detection terminal portion are formed on the substrate portion.

[0101] Since the first detection electrode, the convex pattern, and the terminal portion have a predetermined pattern shape, in this embodiment they are formed by the lift-off method, similar to the heater, wiring, etc.

[0102] Next, on the main surface of the support substrate, an etching mask is applied to a predetermined area on the main surface where no insulating film is formed, and the support substrate is etched until the insulating film formed on the other main surface is exposed, thereby forming cavities in the areas corresponding to the formation areas of each sensor element. The insulating film corresponding to the area where the cavity is formed becomes the membrane.

[0103] Furthermore, a semiconductor material portion is formed on the first sensing electrode, and a catalyst material portion is formed on a convex pattern to obtain a gas sensor. Specifically, a semiconductor material portion paste containing the raw materials for the semiconductor material portion and a catalyst material portion paste containing the raw materials for the catalyst material portion are used to form a coated body that will become the semiconductor material portion and a coated body that will become the catalyst material portion, and these are heat-treated at a predetermined temperature to form the semiconductor material portion and the catalyst material portion.

[0104] The semiconductor material paste is obtained by mixing the raw materials of the semiconductor material described above with a solvent, a binder, and additives. In this embodiment, metal oxide powder is used as the raw material for the semiconductor material. The average particle size of the metal oxide powder is not particularly limited, but is preferably 0.1 to 20 μm.

[0105] The catalyst material paste is obtained by mixing the raw materials of the catalyst material with a solvent, a binder, and additives. In this embodiment, a carrier powder on which noble metal particles are supported is used as the raw material of the catalyst material. The average particle size of the carrier powder is not particularly limited, but is preferably 0.1 to 20 μm.

[0106] The solvent used in the semiconductor material paste and the catalyst material paste is not particularly limited as long as it can dissolve the binder, etc., and any known solvent can be used. A known binder may also be used. Examples of additives include dispersants.

[0107] The prepared semiconductor material paste is applied to the first sensing electrode to form a coated body, and the prepared catalyst material paste is applied to the inside of the convex pattern to form a coated body. The method of applying the paste is not particularly limited, and known methods such as screen printing and dispensing by a dispenser are examples.

[0108] Although the applied semiconductor material paste spreads outward, the first detection electrode is formed as a pattern that protrudes in the stacking direction, so it tends to remain within the area where the first detection electrode is deployed. As a result, the planar shape of the first detection electrode corresponds to the planar shape of the coated catalyst material.

[0109] Furthermore, although the applied catalyst material paste spreads outward, it tends to remain within the convex pattern. Therefore, the planar shape of the coated body is defined by the convex pattern. As a result, the planar shape of the convex pattern corresponds to the planar shape of the coated body of the catalyst material.

[0110] The coated bodies for the semiconductor material and catalyst material are green bodies containing solvents, binders, etc. These coated bodies are subjected to heat treatment to remove the solvents, etc., forming the semiconductor material and catalyst material. During this process, the shape of the coated body is maintained, and it retains the shape of the semiconductor material and catalyst material. The heat treatment temperature is preferably between 300°C and 550°C.

[0111] By following the above steps, the gas sensors according to the first and second embodiments can be obtained.

[0112] (3. Variant) In the above-described embodiment, the gas sensor includes a third sensor element, but the third sensor element is not required.

[0113] Furthermore, in the embodiment described above, the wiring section and the heater are formed on the same plane, but they may be formed on different planes.

[0114] Furthermore, although each sensor element is supported by a beam in the embodiment described above, each sensor element may be supported by a structure other than the beam, as long as a heat insulating structure can be achieved. Also, although the number of beams is set to four, the number of beams is not particularly limited.

[0115] Although embodiments of the present invention have been described above, the present invention is not limited in any way to the embodiments described above, and may be modified in various ways within the scope of the present invention. [Examples]

[0116] The present invention will be described in more detail below with reference to examples and comparative examples. However, the present invention is not limited to the following examples.

[0117] The sample for the example was prepared as follows. First, a silicon oxide film and a silicon nitride film were deposited on the main surface of a silicon single crystal substrate, which served as a support substrate, by CVD. Next, the patterns for the heater and wiring sections were patterned using the lift-off method. After patterning, a titanium thin film (thickness 5 nm) and a platinum thin film (thickness 100 nm) were sequentially deposited by sputtering to form a Pt / Ti film. Subsequently, by removing the resist, a heater composed of Pt / Ti with a meander pattern and a wiring section composed of Pt / Ti were formed. Next, a silicon nitride film as a heater coating film was deposited on the insulating film, heater, and wiring section by CVD.

[0118] Next, a thermistor (MnNiCo-based oxide) was formed to a thickness of approximately 0.4 μm under sputtering conditions of substrate temperature 600°C, deposition pressure 0.5 Pa, O2 / Ar flow rate ratio 1%, and RF power 400 W. Subsequently, the MnNiCo-based oxide film was heat-treated in an air atmosphere at 650°C for 1 hour using a firing furnace. Next, a silicon oxide film was deposited on the thermistor by CVD as a coating film for the heat sensing material.

[0119] Next, the first detection electrode, convex pattern, heater terminal section, and detection terminal section patterns were patterned using the lift-off method. After patterning, a chromium thin film and a gold thin film (total thickness 0.5 μm) as an underlayer were sequentially deposited on the thermal sensing material coating film using the sputtering method to form a Cr / Au film. Subsequently, the first detection electrode, convex pattern, heater terminal section, and detection terminal section were formed by removing the resist. The first detection electrode had the shape shown in Figure 2D, with a pattern corresponding to a circle with a diameter of 150 μm, and the convex pattern was an annular pattern with an outer diameter of 150 μm.

[0120] Subsequently, an etching mask was applied to the main surface of the silicon single crystal substrate where no insulating film was formed, and the silicon single crystal substrate was wet-etched using Deep RIE until the insulating film was exposed, thereby forming a cavity. This created a membrane portion composed of silicon oxide and silicon nitride.

[0121] Next, SnOx powder with an average particle size of 5 μm was prepared as the raw material for the semiconductor material that constitutes the semiconductor material portion.

[0122] The above SnO x A solvent and binder were added to the powder, and the mixture was kneaded using a ball mill to form a paste, which was used to obtain a paste for semiconductor materials.

[0123] Furthermore, as raw materials for the catalyst material, Al2O3 powder with an average particle size of 2 μm and Pt powder as a catalyst were prepared. The Pt powder was supported on this Al2O3 powder by a known method. The Al2O3 powder on which the Pt is supported is the powder for the catalyst material.

[0124] A solvent and a binder were added to the above-mentioned catalyst material powder, and the mixture was kneaded in a ball mill to form a paste, thereby obtaining a catalyst material paste.

[0125] The obtained pastes for the semiconductor material portion and the catalyst material portion were applied onto a thermal sensing material coating film using a dispenser. The resulting coated bodies of the semiconductor material portion and the catalyst material portion were heat-treated at 400°C for 30 minutes to obtain a gas sensor in which the semiconductor material portion and the catalyst material portion were formed. The planar shape of both the semiconductor material portion and the catalyst material portion was circular with a diameter of 150 μm, and the thickness of both the semiconductor material portion and the catalyst material portion was 20 to 30 μm.

[0126] The resistance values ​​of the obtained gas sensors were measured under low and high concentrations of carbon monoxide gas. The measurement results are shown in Figure 8. The vertical axis of Figure 8 represents the resistance value when carbon monoxide gas is absent (Ra) versus the resistance value when carbon monoxide gas is present (Rg).

[0127] Figure 8 shows that the first sensor element responded well in the low-concentration range of carbon monoxide gas, and the second sensor element responded well in the high-concentration range of carbon monoxide gas.

[0128] Next, as a comparative example gas sensor, a gas sensor was fabricated using the same method as the gas sensor in the example, except that the pattern of the first detection electrode in the first sensor element was a comb-tooth electrode, and a convex pattern was not formed in the second sensor element.

[0129] The gas sensors from the example and the comparative example were kept in the same atmosphere, and the sensitivity variations in the low and high concentration ranges of carbon monoxide gas were measured. The sample size was 3. The measurement results are shown in Figure 9.

[0130] As shown in Figure 9, it was confirmed that the gas sensor in the embodiment with a convex pattern had less variation in the formation area of ​​the catalyst material between samples, resulting in less variation in the measured concentration of carbon monoxide gas. [Industrial applicability]

[0131] The gas sensor according to the present invention has a wide detectable concentration range for the target gas and suppresses variations in the catalyst formation area, making it suitable for use as a gas sensor for detecting a target gas. [Explanation of symbols]

[0132] 1, 2... Gas sensors 10, 20, 30... First sensor element, second sensor element, third sensor element 11… Semiconductor Materials Department 21…Thermal detection unit 211...Thermistor 212... Thermal sensing material coating film 22…Catalyst material section 23…Convex pattern 41...First membrane section 42...Second membrane section 43...Third membrane section 51, 52, 53... First heater section, second heater section, third heater section 511, 521, 531... First heater, second heater, third heater 512...First heater coating 522...Second heater coating 532...Third heater coating 61, 62, 63... First wiring section, second wiring section, third wiring section 71, 72, 73... First detection electrode, second detection electrode, third detection electrode 81...Thermistor 82...Thermistor coating 90... Circuit board section 91...Support substrate 92...Coating film 93...Cavity part 100...beam part 111, 112... Heater terminal section, detection terminal section

Claims

1. A first membrane portion and a second membrane portion are formed in a cavity where the support substrate is thinned or in a cavity where the support substrate is absent. A first sensor element formed on the first membrane portion, and a second sensor element formed on the second membrane portion, A first detection electrode electrically connected to the first sensor element, and a second detection electrode electrically connected to the second sensor element, A first heater unit for heating the first sensor element, and a second heater unit for heating the second sensor element, It comprises a first wiring section that electrically connects the first detection electrode and an external circuit, and a second wiring section that electrically connects the second detection electrode and an external circuit, The first sensor element has a semiconductor material portion exposed to the outside, The second sensor element is a gas sensor having an externally exposed catalyst material portion, a convex pattern for defining the planar shape of the catalyst material portion, and a heat sensing portion thermally connected to the catalyst material portion.

2. The gas sensor according to claim 1, wherein the convex pattern is made of a conductor.

3. The gas sensor according to claim 1 or 2, wherein the outer shape of the convex pattern corresponds to a circular or nearly circular ellipse.

4. The gas sensor according to any one of claims 1 to 3, wherein the outer periphery of the semiconductor material portion is circular or nearly circular elliptical.

5. The gas sensor according to any one of claims 1 to 4, wherein the first detection electrode is composed of a pair of electrodes, and the planar shape of the first detection electrode corresponds to the planar shape of the semiconductor material portion.

6. The gas sensor according to any one of claims 1 to 5, wherein the first detection electrode is composed of a pair of electrodes, and the pair of electrodes are arranged to face each other in a direction toward the center of the first detection electrode.

7. The gas sensor according to any one of claims 1 to 6, wherein the ratio of the area of ​​the planar shape of the semiconductor material portion to the area of ​​the planar shape of the catalyst material portion is 0.9 to 1.

1.

8. The gas sensor according to any one of claims 1 to 7, wherein the heat sensing unit includes a heat sensing material, and the heat sensing material is a thermistor.

9. The gas sensor according to any one of claims 1 to 7, wherein the heat sensing unit includes a heat sensing material, and the heat sensing material is a platinum resistor.

10. The gas sensor according to any one of claims 1 to 9, further comprising a reference sensor element.

11. The gas sensor according to any one of claims 1 to 10, wherein the range of the detection standard handled by the first sensor element and the range of the detection standard handled by the second sensor element are separated by 500 ppm or more.

12. A gas sensor according to any one of claims 1 to 10, having a range in which the range of detection standards handled by the first sensor element and the range of detection standards handled by the second sensor element overlap.

13. The gas sensor according to any one of claims 1 to 10, wherein the gas to be detected is carbon monoxide gas, the first sensor element detects carbon monoxide gas with a concentration of 25 ppm or less, and the second sensor element detects carbon monoxide gas with a concentration of 0.05% or more.

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