Gas Sensor

Abstract

To provide a gas sensor capable of improving selectivity for detected gas species, improving accuracy in gas concentration measurement and achieving size reduction and lower cost.SOLUTION: A gas sensor 100 comprises: a substrate 90 including a cavity part 92; and a film-like element 1 including a first detection part 12 and second detection parts 201a, 202a, 201b, 202b above the cavity part 92. The first detection part and the second detection part include sensitive films and detection electrodes 12, 221. A catalyst part 16 thermally connected to the sensitive film is formed in at least one of the first detection part and the second detection part. A heater wire 32 capable of heating the first detection part and the second detection part is electrically isolated via the insulator film from the first detection part and the second detection part. The film-like element includes an inner peripheral part 2 having the first detection part and an outer peripheral part 3 having the second detection part. The inner peripheral part is supported via inner side beam parts 4a-4d by the outer peripheral part. The outer peripheral part is supported via outer side beam parts 5a-5d by the substrate.SELECTED DRAWING: Figure 1

Description

[Technical Field]

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

[0002] Patent Document 1 discloses a gas sensor that detects different gas species by changing the detection temperature. However, such gas sensors have issues such as large errors due to environmental changes over time. In response to this, Patent Document 2 uses multiple elements with different sensitivities to different gas species, thereby increasing the selectivity of the gas species to be detected and improving the accuracy of gas concentration measurement.

[0003] However, when a plurality of elements are used in combination, new problems arise, such as an increase in product cost and an increase in product size. [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Laid-Open No. 2007-024508 [Patent Document 2] Japanese Patent Application Publication No. 2018-036174 Summary of the Invention [Problem to be solved by the invention]

[0005] The present invention has been made in view of the above-mentioned circumstances, and an object of the present invention is to provide a gas sensor which improves the selectivity of gas species to be detected, improves the accuracy of gas concentration measurement, and also realizes miniaturization and cost reduction. [Means for solving the problem]

[0006] In order to achieve the above object, a coil device according to the present invention comprises: a substrate having a cavity; a film element having a first detection portion and a second detection portion above the cavity, the first detection unit and the second detection unit each have a sensitive membrane and a detection electrode electrically connected to the sensitive membrane; a catalyst part thermally connected to the sensitive film is formed in at least one of the first detection part and the second detection part; the film element includes a heater wiring capable of heating the first detection portion and the second detection portion, and an insulating film that insulates the heater wiring from the first detection portion and the second detection portion, the film element has an inner circumferential portion having the first detection portion and an outer circumferential portion having the second detection portion, the inner peripheral portion is supported by the outer peripheral portion via an inner beam portion, The outer periphery is supported by the substrate via outer beams.

[0007] This configuration results in a dual structure consisting of an inner and outer periphery. For example, the inner periphery can measure temperature changes due to catalytic action, while the outer periphery can measure temperature changes due to thermal conduction. In this way, the gas sensor is equipped with a dual structure of first and second detection units with different sensitivities, which allows for the gas sensor to be made smaller and less expensive. Furthermore, because it is possible to simultaneously measure temperature changes due to catalytic action and temperature changes other than those due to thermal conduction, etc., it is possible to perform highly accurate gas concentration measurements without errors over time, with high gas selectivity.

[0008] Preferably, the sensitive film is divided and arranged in the outer peripheral portion. With this configuration, it becomes possible to connect the second detection portions in a combination of series and parallel in the outer peripheral portion, and the resistance of the element can be controlled to a value appropriate for gas detection.

[0009] Preferably, an opening is formed between the outer edge of the inner periphery and the inner edge of the outer periphery. With this configuration, the opening separates the inner periphery and the outer periphery, limiting heat transfer between the inner and outer peripheries. This reduces thermal interference between the inner and outer peripheries, enabling highly accurate gas detection.

[0010] Preferably, the first detection unit outputs a signal based on a reaction in the catalyst unit, and the second detection unit outputs a signal based on a detection principle different from that of the first detection unit, The gas type and gas concentration are determined based on the determination results using the signals from the first and second detection units.

[0011] By configuring multiple detection sections within a single film element in this way, it is possible to reduce errors due to variations in detection distance, detection time, heater temperature conditions, and element shape, thereby improving the accuracy of gas detection.

[0012] The sensitive film may be a thermistor film. By using a thermistor film as the sensitive film, a high output value can be obtained.

[0013] The sensitive film may be a platinum resistor. By using a platinum resistor as the sensitive film, a highly linear change in sensitivity in response to a change in concentration can be obtained, thereby improving the accuracy of gas detection. [Brief explanation of the drawings]

[0014] [Figure 1] FIG. 1 is a plan view of a gas sensor according to one embodiment of the present invention. [Figure 2A] FIG. 2A is a cross-sectional view of the gas sensor according to FIG. 1 taken along line IIA-IIA. [Figure 2B] 2B is a cross-sectional view of the gas sensor according to FIG. 1 taken along line IIB-IIB. [Figure 2C] 2C is a cross-sectional view of the gas sensor according to FIG. 1 taken along line IIC-IIC. [Figure 3A]3A is a plan view showing the arrangement of the second detection section of the gas sensor shown in FIG. [Figure 3B] FIG. 3B is a plan view showing the arrangement of the second detection section of the gas sensor according to another embodiment. [Figure 4] FIG. 4 is a plan view showing the arrangement of the first detection portion of the gas sensor shown in FIG. [Figure 5] FIG. 5 is a plan view showing the arrangement of heaters in the gas sensor shown in FIG. [Figure 6] FIG. 6 is a graph showing the relationship between the concentration of various gases and the detected value in the first detection portion of the gas sensor according to the example. [Figure 7] FIG. 7 is a graph showing the relationship between the concentration of various gases and the detected value in the second detection portion of the gas sensor according to the example. [Figure 8] FIG. 8 is a graph showing the relationship between the temperature and the detection value at the first detection portion of the gas sensor according to the example. [Figure 9] FIG. 9 is a graph showing the relationship between the temperature and the detection value at the second detection portion of the gas sensor according to the example. DETAILED DESCRIPTION OF THE INVENTION

[0015] Hereinafter, the present invention will be described based on the embodiments shown in the drawings.

[0016] First embodiment 2A, the gas sensor 100 includes a film element 1 formed by laminating a plurality of films, and a substrate 90 having a cavity 92. The film element 1 is fixed to an upper surface 94 of the substrate 90 by a fixing portion 8.

[0017] 1, the outer edge 90a of the substrate is substantially square. As shown in FIG. 2A, a cavity 92 penetrates the substrate 90 from an upper surface 94 to a lower surface 96. The cavity 92 of the substrate has a substantially circular inner surface 93 extending in the Z-axis direction. In this embodiment, the gas sensor 100 has a symmetrical configuration with respect to a line L along the X-axis.

[0018] 2A, the film element 1 has a base insulating film 60, which is the lowest layer in the Z-axis direction. The film element 1 also has a heater 30, an intermediate insulating film 70, a first detecting electrode 12, a second detecting electrode 221, and an upper insulating film 80 above the base insulating film 60 in the Z-axis direction. As shown in FIG. 1, the first sensitive film 14 and the second sensitive films 24a1, 24a2, 24b1, and 24b2 are formed on the upper surface of the upper insulating film 80, and a catalyst part 16 is disposed on the upper surface of the first sensitive film 14.

[0019] As shown in FIG. 1, the upper surface of the film element 1 is provided with a pair of first detection pads 41a, 41b, a pair of second detection pads 42a, 42b, and a pair of heater pads 43a, 43b, which allow the first detection electrode, the second detection electrode, and the heater to be electrically connected to an external circuit (not shown). The surfaces of these pads are preferably made of gold, which is less susceptible to surface oxidation. The first detection pad 41a, the second detection pad 42a, and the heater pad 43a are arranged side by side along the X-axis. Each pair of pads is symmetrically arranged with respect to line L as the axis of symmetry. While either of the paired pads may be connected to the cathode or anode of the external circuit, for convenience, this specification may refer to one side of the Y-axis, along which the first detection pad 41a, the second detection pad 42a, and the heater pad 43a are arranged, as the anode side, and the other side as the cathode side.

[0020] In the drawings, the film stacking direction is the Z axis, and the X, Y, and Z axes are perpendicular to each other. In the specification, the direction along the Z axis in which the substrate is arranged may be referred to as "down" and the direction in which the film elements are arranged may be referred to as "up."

[0021] As shown in Fig. 2A, the film element 1 has an inner peripheral portion 2, an outer peripheral portion 3, and a fixed portion 8. The fixed portion 8 is fixed to the upper surface of the substrate. The outer edge 8a of the fixed portion 8 is formed by a base insulating film 60, an intermediate insulating film 70, and an upper insulating film 80, and as shown in Fig. 1, has four edges parallel to the X-axis or Y-axis and has a substantially rectangular shape in plan view.

[0022] The outer edge 2a of the inner circumferential portion 2 is substantially circular in a plan view taken along the Z axis. The outer circumferential portion 3 has a ring shape that surrounds the outer edge 3a of the inner circumferential portion 3. As shown in FIG. 2A , the inner circumferential portion 2 and the outer circumferential portion 3 are disposed so as to cover a portion of a cavity 92 in a substrate 90. The outer edge 3a and the inner edge 3b of the outer circumferential portion 3 are formed by an underlying insulating film 60, an intermediate insulating film 70, and an upper insulating film 80. In the specification, the direction closer to the center line O along the Z axis of the inner circumferential portion 2 may be referred to as the "inner" and the direction further away from the center line O may be referred to as the "outer."

[0023] As shown in FIG. 1, an opening 7 penetrating along the Z-axis is formed between the inner edge 8a of the fixed portion 8 and the outer edge 3a of the outer periphery 3. Outer beam portions 5a and 5b extend from the inner edge 8b of the fixed portion 8 along the Y-axis, sandwiching the outer periphery 3 therebetween, and are connected to the outer edge 3a of the outer periphery 3. In addition, outer beam portions 5c and 5d extend from the inner edge 8b of the fixed portion 8 along the X-axis, sandwiching the outer periphery 3 therebetween, and are connected to the outer edge 3a of the outer periphery 3. The outer periphery 3 is supported by the inner edge 8a of the fixed portion 8 at four locations, the outer beam portions 5a to 5d.

[0024] An opening 6 that penetrates along the Z axis is formed between the inner edge 3b of the outer peripheral portion 3 and the outer edge 2a of the inner peripheral portion 2. Inner beam portion 4a and inner beam portion 4b extend from the inner edge 3b of the outer peripheral portion 3 along the Y axis, sandwiching the inner peripheral portion 2 therebetween, and are connected to the outer edge 2a of the inner peripheral portion 2. Furthermore, inner beam portion 4c and inner beam portion 4d extend from the inner edge 3b of the outer peripheral portion 3 along the X axis, sandwiching the inner peripheral portion 2 therebetween, and are connected to the outer edge 2a of the inner peripheral portion 2. The inner peripheral portion 2 is supported by the inner edge 3b of the outer peripheral portion 3 at four locations, the inner beam portions 4a to 4d.

[0025] The number and positions of the outer beams and inner beams are not limited to those shown in FIG. 1 . For example, it is sufficient that at least two outer beams and two inner beams are formed, and the greater the number of outer beams and inner beams, the greater the mechanical strength of the outer peripheral portion 3 and the inner peripheral portion 2. However, if the number of outer beams is large, heat from the outer peripheral portion 3 is more likely to be transferred to the fixing portion 8 via the outer beams. Furthermore, if the number of inner beams is large, heat from the inner peripheral portion 2 is more likely to be transferred to the outer peripheral portion 3 via the inner beams. Therefore, the number of outer beams and inner beams is preferably two to four, and more preferably four.

[0026] In the gas sensor 100, the outer edge 2a of the inner circumferential portion 2, the inner edge 3b of the outer circumferential portion 3, the outer edge 3a of the outer circumferential portion 3, and the inner surface 93 of the cavity 92 all have a substantially circular shape in a planar view seen from the direction along the Z axis, and the diameter of the outer edge 2a of the inner circumferential portion 2 is smaller than the inner edge 3b of the outer circumferential portion 3, which is smaller than the diameter of the inner surface 93 of the cavity 92. However, the shapes of the inner circumferential portion 2, the outer circumferential portion 3, and the cavity 92 are not limited to these shapes as long as they allow an air bridge to be formed by the outer beam portion and the inner beam portion. For example, the shapes of the inner circumferential portion 2, the outer circumferential portion 3, and the cavity 92 may be rectangular, polygonal, circular, elliptical, or other shapes in a planar view.

[0027] 2C, an insulating base film 60 is formed on an upper surface 94 of the substrate 90. The lower surface in the Z-axis direction of the insulating base film 60 is flush with the XY plane and forms the lower surfaces in the Z-axis direction of the fixed portion, the second beam portion, the outer peripheral portion, the first beam portion, and the inner peripheral portion.

[0028] 2A, 2B, and 2C, a heater 30 is formed on the upper side along the Z-axis of the base insulating film 60. As shown in FIG. 5, the heater 30 has a symmetrical shape with respect to a line L along the X-axis. The heater 30 has a wiring portion 32 and end portions 34a and 34b. The end portions 34a and 34b are connected by the wiring portion 32 without branching, allowing a current to flow from the anode-side end portion 34a to the cathode-side end portion 34b.

[0029] The wiring portion 32 has a main portion 320, a second heating portion 322, and a first heating portion 321. The main portion 320 is disposed in the fixed portion, and the second heating portion 322 is disposed in the outer peripheral portion. The main portion 320 and the second heating portion 322 are connected at the outer beam portion 5d. The first heating portion 321 is disposed in the inner peripheral portion. The first heating portion 321 and the second heating portion 322 are connected at the inner beam portion 4d.

[0030] The heater 30, except for the ends 34a and 34b, is covered on the upper side in the Z-axis direction with an intermediate insulating film, and is insulated from the first and second detection units. A connecting member 35 shown in FIG. 2B is disposed above the ends 34a and 34b of the heater 30 in the Z-axis direction. The connecting member 35 is formed from the same material as the first and second detection electrodes 12 and 221, but may be formed from a different material than the first and second detection electrodes 12 and 221.

[0031] 2A, 2B, and 2C, a first detection electrode 12 and a second detection electrode 221 are formed on the upper surface of the intermediate insulating film 70. The first detection electrode 12 and the second detection electrode 221 are formed from the same material, but may be formed from different materials.

[0032] 3A, second detection electrode 221 has end portions 227a and 227b, second detection electrode lead portions 221a and 221b, and opposing portions 223a and 223b. Second detection electrode 221 has a symmetrical configuration with line L along the X-axis as the axis of symmetry. Hereinafter, explanation of the anode side will be omitted except when necessary for understanding the configuration.

[0033] The end portion 227b is disposed on the fixed portion and is connected to the main portion 221b0 of the second detection electrode lead portion 221b. The second detection electrode lead portion 221b passes through the outer beam portion 5b and extends to the outer periphery 3. The second detection electrode lead portion 221b branches into a first branch portion 221b1 and a second branch portion 221b2 at the outer periphery 3. In addition, the opposing portion 223b is disposed at the outer periphery 3.

[0034] The first branch portion 221b1 is electrically connected to the lower surface of the second sensitive membrane 24b1 and constitutes the second detection portion 201b. The first portion 223b1 of the facing portion 223b is electrically connected to the lower surface of the second sensitive membrane 24b1 and constitutes the second detection portion 201b. The first portion 223b1 of the facing portion 223b is disposed more inward than the branch portion 221b1.

[0035] The second branch portion 221b2 is electrically connected to the lower surface of the second sensitive membrane 24b2 to form the second detection portion 202b. The second portion 223b2 of the facing portion 223b is electrically connected to the lower surface of the second sensitive membrane 24b1 to form the second detection portion 202b. The second portion 223b2 of the facing portion 223b is disposed more inward than the branch portion 221b2.

[0036] The second detection electrode lead portion 221b and the facing portion 223b are electrically connected via second sensitive films 24b1 and 24b2. The second portion 223a2 of the facing portion 223a is connected to the second portion 223b2 of the facing portion 223b.

[0037] The upper side of the second detection electrode in the Z-axis direction is covered with an upper insulating film, with the exception of a portion. As shown in Fig. 2A, the upper insulating film 80 is not formed on the upper surfaces of the first branch portion 221b1, the second branch portion 221b2, and the first and second portions 223b1 and 223b2 of the opposing portion of the second detection electrode that come into contact with the second sensitive films 24b1 and 24b2. Also, as shown in Fig. 2B, the end portion 227b that comes into contact with the second detection unit pad 42b is not covered with the upper insulating film 80.

[0038] 4, first detection electrode 12 has end portions 127a and 127b and first detection electrode lead portions 12a and 12b. First detection electrode 12 has a symmetrical configuration with line L along the X-axis as the axis of symmetry. Hereinafter, explanation of the anode side will be omitted except when necessary for understanding the configuration.

[0039] End 127b is disposed on the fixed portion and is connected to main portion 12b0 of first detection electrode lead portion 12b. First detection electrode lead portion 12b passes through outer beam portion 5c, outer peripheral portion 3, and inner beam portion 4c and extends to inner peripheral portion 2. First detection electrode lead portion 12b forms contact portion 12b1 of a predetermined pattern on inner peripheral portion 2.

[0040] The contact portion 12b1 is electrically connected to the lower surface of the first sensitive film 14 and constitutes the first detection portion 12. The contact portion 12a1 and the contact portion 12b1 are electrically connected via the first sensitive film 14.

[0041] 2C, in the first detection electrode lead portions 12a and 12b, the portion of the first detection unit 12 that comes into contact with the first sensitive film 14 is not covered with the upper insulating film 80. In addition, as shown in FIG. 2B, the end portion 127b that comes into contact with the first detection unit pad 41b is not covered with the upper insulating film 80.

[0042] 1, second sensitive films 24a1, 24a2, 24b1, and 24b2 that constitute the second detection portion are formed on the outer circumferential portion 3. The second sensitive films 24a1, 24a2, 24b1, and 24b2 are electrically connected on their lower surfaces to the second detection electrode lead portion and the opposing portion, respectively.

[0043] A first sensitive film 14 that constitutes the first detection unit is formed on the inner circumferential portion 2. The first sensitive film 14 is electrically connected to the first detection lead-out unit on its underside. A catalyst portion 16 that constitutes the first detection unit is disposed on the upper surface of the first sensitive film 14, and is thermally connected to the catalyst portion 16 and the first sensitive film 14.

[0044] Next, the materials of the substrate 90 and the films included in the film element 1 will be described in detail.

[0045] The substrate 90 is not particularly limited as long as it has a mechanical strength sufficient to support the film element 1 and is made of a material suitable for microfabrication such as etching. For example, the substrate 90 may be a ferrite substrate, a silicon single crystal substrate, a sapphire single crystal substrate, a ceramic substrate, a quartz substrate, a glass substrate, or the like.

[0046] The base insulating film 60, intermediate insulating film 70, and upper insulating film 80 may be made of any material as long as they are insulating. For example, the base insulating film 60, intermediate insulating film 70, and upper insulating film 80 may be made of silicon oxide or silicon nitride, with silicon oxide being preferred. The base insulating film 60, intermediate insulating film 70, and upper insulating film 80 are constructed by controlling mechanical strength and internal stress. Using silicon oxide alone increases strength but increases internal stress, making the device more susceptible to damage. Therefore, it is desirable to use silicon nitride in combination with silicon oxide to control stress.

[0047] The thickness of the base insulating film 60 is not particularly limited as long as it is thick enough to ensure sufficient insulation between the substrate 90 and the heater 30 and to function as an etching stop layer when forming the cavity 92. For example, the thickness of the base insulating film 60 is preferably about 0.1 to 2.0 μm.

[0048] The thickness of the intermediate insulating film 70 is not particularly limited, as long as it is thick enough to reliably cover the heater 30 and ensure sufficient interlayer insulation. For example, the intermediate insulating film 70 preferably has a thickness of approximately 0.1 to 1.0 μm. The thickness of the upper insulating film 80 is not particularly limited, as long as it is thick enough to reliably cover the first detection electrode 12 and the second detection electrode 221 and ensure sufficient interlayer insulation. For example, the thickness of the upper insulating film 80 is preferably approximately 0.1 to 2.0 μm.

[0049] The heater 30 is preferably made of a material that is conductive and has a relatively high melting point. Examples of such materials include molybdenum (Mo), platinum (Pt), NiCr (Ni, Cr), tungsten (W), tantalum (Ta), palladium (Pd), iridium (Ir), or an alloy containing one or more of the above elements. Among the above materials, platinum is less susceptible to deterioration as a heater, so it is preferable to make the heater 30 from platinum. When making the heater 30 from a platinum material, it is preferable to form an adhesion layer of titanium (Ti) or the like between the base insulating film 60 and the platinum material to improve adhesion of the heater 30 to the base insulating film 60.

[0050] Both the first detection electrode 12 and the second detection electrode 221 are preferably made of a conductive material with a relatively high melting point. Like the heater 30, the first detection electrode 12 and the second detection electrode 221 can be made of molybdenum (Mo), platinum (Pt), copper (Cu), tungsten (W), tantalum (Ta), palladium (Pd), iridium (Ir), or an alloy containing one or more of the above elements, and are preferably made of platinum.

[0051] The first sensitive film 14 and the second sensitive films 24a1, 24a2, 24b1, and 24b2 may be made of a material whose resistance changes with temperature. For example, the first sensitive film 14 and the second sensitive films 24a1, 24a2, 24b1, and 24b2 may be made of a thermistor film or a platinum film, preferably a thermistor film. Examples of materials for thermistor films include composite metal oxides of Ni, Mn, Co, and Fe. The material and thickness of the first sensitive film 14 and the second sensitive films 24a1, 24a2, 24b1, and 24b2 all affect the initial resistance of the detection unit. Therefore, the material and thickness of the first sensitive film 14 and the second sensitive films 24a1, 24a2, 24b1, and 24b2 may be appropriately selected to achieve a desired initial resistance, taking into account the type of gas to be detected and the intended use of the gas sensor 100.

[0052] The catalyst section 16 may be made of a material that reacts with gases that come into contact with its surface and whose temperature changes due to the heat of reaction. From the perspective of detecting carbon monoxide, hydrogen, methane, and methanol, the catalyst section 16 may be made of Pt-supported Al2O3. Other examples of the catalyst section 16 include precious metals such as Pd, Rh, Ru, and In, and carriers such as SiO2, SnO2, Ce2O3, Zr2O3, and Y2O3. Therefore, the material and thickness of the catalyst section 16 may be appropriately selected to achieve a desired initial resistance value, taking into account the type of gas to be detected and the intended use of the gas sensor 100.

[0053] As shown in FIG. 2A, in this embodiment, the first and second detection units have heaters 30 capable of heating the first and second detection units. The heaters 30 are insulated from the detection electrodes and the sensitive membranes. The heaters 30 can heat the first and second detection units to a predetermined temperature, preferably between 100°C and 500°C, and more preferably between 200°C and 350°C. This allows the detection units to perform detection at an appropriate temperature depending on the gas type or gas concentration.

[0054] 3A, in this embodiment, the second detection electrode lead portion 221b and the facing portion 223b are electrically connected via the second sensitive films 24b1 and 24b2. The second detection electrode lead portion 221a and the facing portion 223a are electrically connected via the second sensitive films 24a1 and 24a2. The facing portions 223b and 223a are also connected.

[0055] The current flowing between the second detection unit pads from the anode side to the cathode side passes through the second sensitive films 24a1 and 24a2 arranged in parallel from the second detection electrode lead portion 221a to the facing portion 223a. Furthermore, the current flows from the facing portion 223b connected to the facing portion 223a through the second sensitive films 24b1 and 24b2 to the second detection electrode 221b. Therefore, the resistance of the second sensitive films 24a1, 24a2, 24b1, and 24b2 can be detected from the current and voltage flowing between the second detection unit pads. The resistance of the second sensitive films 24a1, 24a2, 24b1, and 24b2 changes upon contact with gas. The change in resistance of the second sensitive films 24a1, 24a2, 24b1, and 24b2 varies depending on the gas type and gas concentration, allowing the type and concentration of the gas to be detected.

[0056] 2C, in this embodiment, the catalyst portion 16 is thermally connected to the first sensitive film 14. Furthermore, the first detection electrode lead portion 12b and the first detection electrode lead portion 12a are electrically connected via the first sensitive film 14, and are not directly connected to each other.

[0057] The current flowing between the first detection unit pads from the anode side to the cathode side passes from the first detection electrode lead 12a shown in FIG. 4 through the first sensitive film 14 to the first detection electrode lead 12b. Therefore, the resistance of the first sensitive film 14 can be detected from the current and voltage flowing between the first detection unit pads. The reaction heat (combustion heat) of the gas transmitted to the catalyst unit 16 shown in FIG. 2C is transmitted to the first sensitive film 14, causing a change in the resistance of the first sensitive film 14. The change in resistance of the first sensitive film 14 varies depending on the gas species and gas concentration, making it possible to detect the reacting gas species and gas concentration.

[0058] 1, in this embodiment, the inner peripheral portion 2 is supported by the outer peripheral portion 3 via inner beam portions 4a to 4d, and the outer peripheral portion 3 is supported by the substrate via outer beam portions 5a to 5d. A first detector 10 is disposed on the inner peripheral portion 2, and second detectors 201a, 202a, 201b, and 202b are disposed on the outer peripheral portion 3.

[0059] Therefore, the film element 1 can measure temperature changes due to catalytic action and temperature changes due to thermal conduction in a single element, thereby realizing a smaller, less expensive gas sensor. In addition, because temperature changes due to catalytic action and temperature changes due to thermal conduction can be measured simultaneously, it is possible to perform highly accurate gas concentration measurements without errors over time, with high gas selectivity.

[0060] As shown in FIG. 1 , in this embodiment, an opening 6 is formed between the outer edge 2a of the inner circumferential portion 2 and the inner edge 3b of the outer circumferential portion 3. The opening 6 has a gap with a width W1. The length of the width W1 may be long enough to restrict the transfer of heat between the inner circumferential portion 2 and the outer circumferential portion 3, and the length of the width W1 is preferably, for example, 10 to 100 μm. By forming an air bridge structure in which this gap is bridged by a beam portion, thermal interference between the inner circumferential portion 2 and the outer circumferential portion 3 is suppressed, enabling highly accurate gas detection.

[0061] As shown in FIG. 1, in this embodiment, an opening 7 is formed between the outer edge 3a of the outer peripheral portion 3 and the inner edge 8b of the fixing portion 8. The opening 7 has a gap with a width W2. The length of the width W2 may be determined so as to ensure the mechanical strength of the film element 1. For example, it is preferably 20 to 150 μm. By providing an air bridge structure in which this gap is bridged by the beam portion, when the detection portion is heated by a heater, it can be heated efficiently with little power consumption.

[0062] In this embodiment, the first detection unit outputs a signal representing a change in resistance due to the heat of reaction of the gas transmitted through the catalyst unit, and the second detection unit outputs a signal representing a change in resistance due to the gas coming into contact with the second sensitive film. Because the gas type and gas concentration are calculated based on the results of signal determination using these different detection principles, it is possible to reduce errors due to variations in detection distance, detection time, heater temperature conditions, and element shape, thereby improving the accuracy of gas detection.

[0063] In this embodiment, the first and second sensitive films can be formed of a thermistor film or a platinum resistor. Using a thermistor film as the sensitive film allows for a high output value. Using a platinum resistor as the sensitive film allows for a high linearity of the resistance change relative to the concentration, thereby improving the accuracy of gas detection.

[0064] Second embodiment Hereinafter, a gas sensor according to a second embodiment will be described with reference to Fig. 3B. The gas sensor according to this embodiment is similar to that of the first embodiment except for the second detection electrode 222 shown in Fig. 3B, and therefore similar reference numerals are used, and descriptions of common configurations and effects will be omitted.

[0065] 3B, the second detection electrode 222 has a symmetrical configuration with respect to a line L along the X-axis. Hereinafter, a description of the anode side will be omitted unless necessary for understanding the configuration.

[0066] In this embodiment, the second detection electrode lead portion 222b of the second detection electrode 222 passes through the outer beam portion 5b, extends to the outer peripheral portion 3, and forms the second detection portion 201b without branching. The second detection electrode lead portion 222b is electrically connected to the lower surface of the second sensitive film 24b1.

[0067] The first portion 224b1 of the facing portion 224b is electrically connected to the lower surface of the second sensitive film 24b1 and constitutes the second detection portion 201b. The first portion 224b1 of the facing portion 224b is disposed more inward than the second detection electrode lead-out portion 222b. The second portion 224b2 of the facing portion 224b is electrically connected to the lower surface of the second sensitive film 24b2 and constitutes the second detection portion 202b.

[0068] Furthermore, the second detection electrode 222 has intermediate facing portions 225a and 225b. The intermediate facing portion 225b is disposed outside the second portion 224b2 of the facing portion 224b. The intermediate facing portion 225b is electrically connected to the lower surface of the second sensitive film 24b2 and constitutes the second detection portion 202b.

[0069] The second detection electrode lead-out portion 222b and the facing portion 224b are electrically connected via a second sensitive film 24b1. The facing portion 224b and the intermediate facing portion 225b are electrically connected via a second sensitive film 24b2. The intermediate facing portion 225a is connected to the intermediate facing portion 225b.

[0070] With this configuration, the second sensitive films 24a1, 24a2, 24b2, and 24b1 are arranged in series in this order from the anode end 227a to the cathode end 227b. Therefore, by using the second detecting electrode 222 of this embodiment, it is possible to increase the resistance of the entire second detecting section compared to the sensitive films arranged in parallel as in the first embodiment.

[0071] The present invention is not limited to the above-described embodiment, and various modifications can be made within the scope of the present invention.

[0072] For example, the inner peripheral detection section may not have a catalyst portion, and the outer peripheral detection section may have a catalyst portion. Also, a different type of catalyst portion may be provided on the outer peripheral section.

[0073] Alternatively, one of the second detection units on the cathode side and the anode side may be configured in parallel, and the other second detection unit may be configured in series as in the second embodiment. In this way, by combining a parallel second detection unit, it becomes possible to appropriately control the resistance of the element for gas detection. [Example]

[0074] The gas sensor 100 according to the first embodiment was subjected to an evaluation test to measure the sensitivity to gas concentration and heater temperature for carbon monoxide, hydrogen, methane, and methanol gases, by measuring the change in resistance at each detection element relative to the gas concentration. In the evaluation test, the gas sensor 100 was placed in a cell, and the change in resistance at each detection element between when no gas was introduced into the cell and when gas was introduced into the cell was measured.

[0075] (gas concentration) Various gases were introduced at different concentrations into a cell containing the gas sensor 100, and the change in resistance of each detection section was measured in each case. In the evaluation test, the heater temperature was controlled to be approximately constant between 200°C and 350°C. FIG. 6 shows a graph of the evaluation results for the first detection section, which is located in the inner peripheral section 2 and has a catalyst section. FIG. 7 shows a graph of the evaluation results for the second detection section, which is located in the outer peripheral section 3 and does not have a catalyst section. In FIGS. 6 and 7, the horizontal axis of the graph represents the gas concentration, and the vertical axis represents the change in resistance value at the detection section.

[0076] As shown in Figure 6, in the first detection unit having a catalyst unit, hydrogen and carbon monoxide showed a response of decreasing the resistance value, and methanol, although in trace amounts, showed a response of decreasing the resistance value. Methane, although in trace amounts, showed a response of increasing the resistance value. For each gas, the higher the concentration, the greater the change in resistance, and the change in resistance value was approximately linear. For each gas concentration, the amount of change in resistance was highest for methane, followed by methanol, carbon monoxide, and hydrogen.

[0077] As shown in Figure 7, the second detection unit, which does not have a catalyst unit, responded by increasing the resistance value to methanol and hydrogen, but showed almost no response to methane and carbon monoxide. For each gas, the resistance value changed more rapidly as the gas concentration increased, and the change in resistance was approximately linear. For each gas concentration, the amount of change in resistance was greatest for methanol, hydrogen, methane, and carbon monoxide, in descending order.

[0078] Therefore, in the gas sensor 100, since the first and second detection parts show different responses for each gas type, it is possible to identify the gas type by combining the results from each detection part. Also, since the change in resistance value at each detection part changes linearly with the concentration, it is possible to calculate the gas concentration.

[0079] (heater temperature) Various gases were introduced into the cell in which the gas sensor 100 was placed, and the change in resistance of each detection section was measured when the temperature of the heater 30 was changed. In the evaluation test, three gas concentrations were introduced: 100, 300, and 500 ppm. FIG. 8 shows a graph of the evaluation results for the first detection section, which is located in the inner peripheral section 2 and has a catalyst section. FIG. 9 shows a graph of the evaluation results for the second detection section, which is located in the outer peripheral section 3 and does not have a catalyst section. In FIGS. 8 and 9, the horizontal axis of the graph represents the heater temperature, and the vertical axis represents the change in resistance value at the detection section.

[0080] As shown in Figure 8, in the first detection unit having a catalyst, carbon monoxide and hydrogen responded by decreasing the resistance value when the heater temperature was 200°C. Carbon monoxide and hydrogen responded by decreasing the resistance value at all heater temperatures, and the resistance value decreased as the heater temperature increased, with hydrogen having a lower resistance value than carbon monoxide at all temperatures. Methane and methanol responded by increasing the resistance value when the heater temperature was 200°C. Methane responded by increasing the resistance value at all heater temperatures, and the resistance value decreased as the heater temperature increased. Methanol also responded by decreasing the resistance value when the heater temperatures were 250°C, 300°C, and 350°C.

[0081] As shown in Figure 9, the second detection unit without a catalyst responded by increasing the resistance value at all heater temperatures. For all gases, the amount of change in resistance decreased as the heater temperature increased. For methanol and hydrogen, the amount of change in resistance increased as the concentration increased, and the change in resistance was approximately linear.

[0082] Since the change in resistance value detected at each detection unit varies in different ways depending on the gas type when the heater temperature is changed, it is also possible to identify the gas type by measuring in advance the relationship between the change in resistance value of each gas type and the heater temperature.

[0083] For example, in the first detection section, both hydrogen and carbon monoxide showed a response that decreased the resistance value, whereas in the second detection section, hydrogen increased the resistance value and carbon monoxide showed almost no response, resulting in different detection results. Therefore, based on the results from both detection sections, it is possible to identify whether the gas detected by the gas sensor is hydrogen or carbon monoxide. [Explanation of symbols]

[0084] 100...Gas sensor 1...Membrane element 2…Inner circumference 2a...outer edge 3...Outer periphery 3a...outer edge 3b...Common-law marriage 4a,4b.4c,4d…Inner beam part 5a,5b.5c,5d...Outer beam part 6,7...Opening 8…Fixed part 8a...Outer edge 8b...Common edge 10...First detection unit 12...First detection electrode 12a, 12b...First detection electrode lead portion 12a0, 12b0...Main part 12a1,12b1…Contact part 127a, 127b...end 14...First sensitive membrane 16...Catalyst section 201a, 202a, 201b, 202b...Second detection unit 221, 222...Second detection electrode 221a, 221b, 222a, 222b...Second detection electrode lead portions 221a0, 221b0...Main part 221a1,221b1...1st branch 221a2,221b2…Second branch 223a, 223b, 224a, 224b...Opposing part 223a1,223b1,224a1,224b1…First part 223a2,223b2,224a2,224b2…Second part 225a, 225b...Middle opposing part 227a, 227b...end 24a1, 24a2, 24b1, 24b2...Second sensitive membrane 30...Heater 32...Wiring section 320...Main section 321...First heating section 322...Second heating section 34a, 34b...ends 35...Connecting member 41a, 41b...Pads for first detection unit 42a, 42b...Pads for second detection unit 43a, 43b...Heater pad 60...Base insulating film 70...Intermediate insulating film 80...Upper insulating film 90...Substrate 90a...outer edge 92...Cavity part 93...Inside 94…Top surface 96…Bottom surface

Claims

1. a substrate having a cavity; a membrane element having a first detection portion and a second detection portion above the cavity, the first detection unit and the second detection unit each have a sensitive membrane and a detection electrode electrically connected to the sensitive membrane; a catalyst portion thermally connected to the sensitive film is formed in at least one of the first detection portion and the second detection portion; the film element includes a heater wiring capable of heating the first detection portion and the second detection portion, and an insulating film that insulates the heater wiring from the first detection portion and the second detection portion, the film element has an inner circumferential portion having the first detection portion and an outer circumferential portion having the second detection portion, the inner peripheral portion is supported by the outer peripheral portion via an inner beam portion, The outer peripheral portion is supported by the substrate via an outer beam portion.

2. 2. The gas sensor according to claim 1, wherein the sensitive film is divided and arranged in the outer periphery.

3. 3. The gas sensor according to claim 1, wherein an opening is formed between the outer edge of said inner periphery and the inner edge of said outer periphery.

4. the first detection unit outputs a signal based on a reaction in the catalyst unit, and the second detection unit outputs a signal based on a detection principle different from that of the first detection unit, 4. The gas sensor according to claim 1, wherein the type and concentration of the gas are determined based on a determination result using the signals from the first detection section and the second detection section.

5. 5. The gas sensor according to claim 1, wherein the sensitive film is a thermistor film.

6. 5. The gas sensor according to claim 1, wherein the sensitive film is a platinum resistor.

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