Gas Sensor

Abstract

To provide a gas sensor that can reduce a measurement error associated with heat deformation of a device.SOLUTION: A gas sensor has a substrate that has a cavity part, and a detection unit that is supported by two or more beam parts extending from the substrate above the cavity part. The detection unit has a laminated structure including a heater, a sensitive membrane, and a pair of counter electrodes in contact with the sensitive membrane. The pair of counter electrodes extend along a direction orthogonal to the lamination direction, and face each other at a predetermined interval in an in-plane direction of the sensitive membrane. All the beam parts extend in a direction substantially parallel to the extension direction of the counter electrodes.SELECTED DRAWING: Figure 1B

Description

[Technical Field]

[0001] The present invention relates to a gas sensor having an air bridge structure. [Background technology]

[0002] Gas sensors with an air-bridge structure, in which a membrane-shaped sensing element is supported above a cavity in a substrate, are known. In these gas sensors, the sensing element is heated to its operating temperature by a heater resistor to measure the concentration of a target gas present in the atmosphere. If the membrane-shaped sensing element deforms during measurement due to heating, the inter-electrode distance (the distance between a pair of opposing electrodes) fluctuates with the element deformation, resulting in measurement errors. Therefore, it is necessary to suppress the fluctuation of the inter-electrode distance due to thermal stress.

[0003] For example, Patent Document 1 discloses suppressing warpage of the detection unit by controlling the internal stress of the detection unit. Specifically, Patent Document 1 offsets the internal stress of the detection unit by stacking a silicon oxide film with compressive stress and a silicon nitride film with tensile stress on the detection unit. However, with the technology of Patent Document 1, the balance of internal stresses is easily disrupted due to manufacturing errors, and sufficient deformation suppression effects may not be achieved. In addition, changing the design of the detection unit, such as dimensions such as film thickness, the material of the stacked film, or the electrode pattern, also changes the balance of internal stresses, making it difficult to make design changes.

[0004] Furthermore, Patent Document 2 discloses that deformation of the detection unit is suppressed by forming holes or slits that penetrate the front and back surfaces of the detection unit. However, the technology of Patent Document 2 requires that heater resistors and electrode patterns be stacked while avoiding the holes or slits, which results in a problem of low freedom of element design. [Prior art documents] [Patent documents]

[0005] [Patent Document 1] Japanese Patent Application Publication No. 8-264844 [Patent Document 2] Patent No. 3374498 Summary of the Invention [Problem to be solved by the invention]

[0006] The present invention has been made in view of the above circumstances, and an object of the present invention is to provide a gas sensor capable of reducing measurement errors caused by thermal deformation of the element. [Means for solving the problem]

[0007] In order to achieve the above object, the gas sensor according to the present invention comprises: a substrate having a cavity; and a detection unit supported by two or more beams extending from the substrate above the cavity; the detection unit has a laminated structure including a heater, a sensitive film, and a pair of opposing electrodes in contact with the sensitive film, the pair of opposing electrodes each extend in a direction perpendicular to the stacking direction and face each other at a predetermined interval in the in-plane direction of the sensitive film, All of the beam portions extend in a direction substantially parallel to the extending direction of the counter electrode.

[0008] In a gas sensor having the above characteristics, even if the detection part is deformed by heating from a heater, the variation in the inter-electrode distance (the distance between a pair of opposing electrodes) can be suppressed, thereby reducing measurement errors due to element deformation.

[0009] A maximum width Wy0 of the detection portion in the extension direction of the counter electrode may be equal to a maximum width Wx0 of the detection portion in the opposing direction of the counter electrodes. However, preferably, a maximum width Wy0 of the detection portion in the extension direction of the counter electrodes is wider than a maximum width Wx0 of the detection portion in the opposing direction of the counter electrodes.Furthermore, it is preferable that the pair of counter electrodes and all of the beam portions extend along the longitudinal direction of the detection portion.

[0010] Preferably, the detection unit has a narrow portion in which the width of the detection unit in the opposing direction of the counter electrodes is partially narrowed. In this case, it is preferable that the narrow portion is located at the center of the detection unit in the extension direction.

[0011] Preferably, the element body has a notch in a part of an edge along the extension direction, in which case the notch is preferably located in the center of the edge.

[0012] The gas sensor according to the present invention can be used as a thermal conduction type, catalytic combustion type, semiconductor type, or solid electrolyte type gas sensor. When the thermal conduction type or catalytic combustion type is adopted as the driving method of the gas sensor, the sensitive film is preferably a thermistor film. [Brief explanation of the drawings]

[0013] [Figure 1A] FIG. 1A is an exploded perspective view showing a gas sensor 1a according to one embodiment of the present invention. [Figure 1B] FIG. 1B is a plan view of the gas sensor 1a shown in FIG. 1A. [Figure 1C] FIG. 1C is a cross-sectional view taken along line IC-IC in FIG. 1B. [Figure 1D] FIG. 1D is a cross-sectional view taken along line ID-ID in FIG. 1B. [Figure 2A] FIG. 2A is a plan view showing a conventional gas sensor 1b. [Figure 2B] FIG. 2B is a plan view showing a conventional gas sensor 1c. [Figure 3] FIG. 3 is a plan view showing a gas sensor 1d according to another embodiment of the present invention. [Figure 4] FIG. 4 is a plan view showing a gas sensor 1e according to another embodiment of the present invention. [Figure 5A] FIG. 5A is a plan view showing a modified example of the gas sensor of the present invention. [Figure 5B] FIG. 5B is a cross-sectional view taken along line VB-VB in FIG. 5A. [Figure 6] FIG. 6 is a plan view showing a modified example of the gas sensor of the present disclosure. [Figure 7A] FIG. 7A is a plan view showing a modified example of the gas sensor of the present invention. [Figure 7B] FIG. 7B is a plan view showing a modified example of the gas sensor of the present invention. [Figure 7C] FIG. 7C is a plan view showing a modified example of the gas sensor of the present invention. DETAILED DESCRIPTION OF THE INVENTION

[0014] The present invention will be described in detail below based on the embodiments shown in the drawings.

[0015] First embodiment In the first embodiment, a thermal conduction type gas sensor 1a shown in FIGS. 1A to 1D will be described as an example of a gas sensor according to the present invention.

[0016] 1A, the gas sensor 1a includes a substrate 50 and a film stack 10 formed on the substrate 50. The substrate 50 of the gas sensor 1a has a cavity 55 penetrating the front and back surfaces of the substrate 50, and has an overall shape of a hollow quadrangular prism. The substrate 50 only needs to have a structure that allows for the formation of an air bridge structure, which will be described later, and the shape and dimensions of the substrate 50 are not limited to those shown in FIG. 1A.

[0017] On the other hand, the film stack unit 10 has a first insulating film 21, a heater 3, a second insulating film 23, a pair of detection electrodes 4, a sensitive film 6, and a third insulating film 25. In the film stack unit 10, the above-mentioned multiple constituent films are stacked in the order shown along the Z axis. Four pad electrodes 8 are formed on the upper surface of the film stack unit 10, and an external circuit (not shown) can be electrically connected to the heater 3 or the detection electrodes 4 via the pad electrodes 8. In this embodiment, the pair of detection electrodes 4 may be referred to as a first detection electrode 4a and a second detection electrode 4b.

[0018] As shown in the plan view of FIG. 1B, the film stack 10 of the gas sensor 1a includes a detection section 12 that covers a portion of the upper part of the cavity 55, a peripheral section 14 that is in direct contact with the surface of the substrate 50, and four beam sections 16 that integrally connect the detection section 12 and the peripheral section 14. That is, the gas sensor 1a has an air bridge structure in which the detection section 12 is supported above the cavity 55 by the four beam sections 16 that extend from the peripheral section 14 on the surface of the substrate. Note that the four beam sections 16 may be referred to separately as a first beam section 16a to a fourth beam section 16d. When simply referring to a "beam section 16," this refers to a feature common to the first beam section 16a to the fourth beam section 16d.

[0019] The detection section 12 has four edges parallel to the X-axis or the Y-axis, and the maximum width Wx0 of the detection section 12 in the X-axis direction is equal to the maximum width Wy0 of the detection section 12 in the Y-axis direction. That is, the detection section 12 of the gas sensor 1a has a square shape in a planar view. However, the shape of the detection section 12 is not particularly limited, and the detection section 12 may have a rectangular, polygonal, circular, elliptical, or other shape in a planar view. Furthermore, the dimensions Wx0 and Wy0 are not particularly limited and may be determined appropriately depending on the application and required specifications of the gas sensor 1a.

[0020] The cavity 55 in the gas sensor 1a has a square shape in plan view that is larger than the detection unit 12. However, the shape of the cavity 55 is not limited to the shapes shown in Figures 1A and 1B as long as it can form an air bridge structure. The cavity 55 may also have a rectangular, polygonal, circular, elliptical, or other shape in plan view.

[0021] 1B is an internal perspective view, and dashed lines indicate the heater 3 and the pair of detection electrodes 4 stacked on the detection unit 12. Specifically, the heater 3 is indicated by a thin dashed line, and the pair of detection electrodes 4 is indicated by a thick dashed line.

[0022] 1B, the heater 3 preferably has a meander pattern 31 in which wiring is folded back multiple times and arranged in parallel at predetermined intervals. The meander pattern 31 of the heater 3 is layered on the detection unit 12 and serves to heat the detection unit 12 to an operating temperature when detecting a target gas. By forming the wiring pattern of the heater 3 layered on the detection unit 12 as a meander pattern, the detection unit 12 can be heated efficiently and uniformly. The end wiring 32 of the heater 3 is drawn from the end of the meander pattern 31 to the peripheral edge 14, passing through the second beam 16b or the fourth beam 16d.

[0023] The pair of detection electrodes 4 are stacked on the same plane and each have an opposing portion 41 (opposing electrode) and an extraction portion 42. The opposing portion 41 of the first detection electrode 4a and the opposing portion 41 of the second detection electrode 4b both extend in a direction parallel to the Y axis. The opposing portion 41 of the first detection electrode 4a and the opposing portion 41 of the second detection electrode 4b face each other in the X axis direction with a predetermined inter-electrode distance D0. The inter-electrode distance D0 is not particularly limited and may be set appropriately depending on the desired characteristics. For example, the ratio (D0 / Wx0) of the inter-electrode distance D0 to the maximum width Wx0 of the detection unit 12 can be 0.02 to 0.8, preferably 0.02 to 0.3. In FIGS. 1A to 1D of the first embodiment, as described above, the X axis is the opposing direction of the opposing portions 41, the Y axis is the extension direction of the opposing portions 41, and the Z axis is the stacking direction of each film in the film stack unit 10. The X-axis, Y-axis, and Z-axis are substantially perpendicular to each other.

[0024] The lead-out portion 42 of the first detection electrode 4a is led out from one end of the facing portion 41 through the first beam portion 16a to the peripheral portion 14. Similar to the first detection electrode 4a, the lead-out portion 42 of the second detection electrode 4b is led out from one end of the facing portion 41 through the third beam portion 16c to the peripheral portion 14.

[0025] In the cross section shown in FIG. 1C , the detection unit 12 is not connected to the peripheral portion 14, but is spaced apart from the peripheral portion 14 and the substrate 50. By spaced apart from the peripheral portion 14 and above the cavity 55, the heat capacity of the detection unit 12 can be made smaller than the heat capacity of the peripheral portion 14, which is in contact with the substrate 50. Furthermore, the thermal insulation between the detection unit 12 and the peripheral portion 14 can be improved. Therefore, in the gas sensor 1a having the air bridge structure, when the detection unit 12 is heated by the heater 3, the detection unit 12 can be heated efficiently with little power consumption.

[0026] 1C, the heater 3 is laminated between the first insulating film 21 and the second insulating film 23 in the detection unit 12. That is, the heater 3 is covered by the second insulating film 23 so as not to be exposed to the external atmosphere. Furthermore, by laminating the second insulating film 23 between the heater 3 and the pair of detection electrodes 4, short-circuiting between the heater 3 and the pair of detection electrodes 4 is suppressed.

[0027] 1C, each of the pair of detection electrodes 4 is laminated on the second insulating film 23. A sensitive film 6 is laminated on the pair of detection electrodes 4, and the facing portions 41 are covered by the sensitive film 6. That is, the facing portions 41 of the first detection electrode 4a and the second detection electrode 4b are both on the same plane and directly contact the sensitive film 6. A third insulating film 25 is laminated on the top layer of the detection unit 12. That is, the sensitive film 6 is covered by the third insulating film 25 so that the pair of detection electrodes 4 and the sensitive film 6 are not exposed to the external atmosphere.

[0028] 1D, a first insulating film 21, a second insulating film 23, and a third insulating film 25 are laminated in the peripheral edge portion 14. A pad electrode 8 is formed on the surface of the third insulating film 25 in the peripheral edge portion 14. A via-hole electrode 9 is formed below the pad electrode 8, penetrating the third insulating film 25. The end of the lead-out portion 42 of each of the detection electrodes 4a and 4b is electrically connected to the pad electrode 8 through the via-hole electrode 9.

[0029] Although a cross section through which the end wiring 32 of the heater 3 passes is not shown, the end of the end wiring 32 is also electrically connected to the pad electrode 8 through a via-hole electrode 9, similar to the lead-out portion 42 of the detection electrode 4. The via-hole electrode 9 connected to the end wiring 32 is an electrode that penetrates the second insulating film 23 and the third insulating film 25.

[0030] 1D, the first beam portion 16a and the third beam portion 16c are laminated with the first insulating film 21 to the third insulating film 25, the lead portion 42 of the detection electrode 4, and the sensitive film 6. Although the cross sections of the second beam portion 16b and the fourth beam portion 16d are not shown, the second beam portion 16b and the fourth beam portion 16d are laminated with the first insulating film 21 to the third insulating film 25, the end wiring 32 of the heater 3, and the sensitive film 6. As described above, the sensitive film 6 is present across from the detection portion 12 to each beam portion 16, but it is sufficient that the sensitive film 6 is laminated at least on the detection portion 12, and the beam portion 16 does not necessarily include the sensitive film 6.

[0031] In the gas sensor 1a of this embodiment, the extending direction of each of the beam portions 16a to 16d is determined based on the extending direction of the detection electrode 4. Specifically, all of the four beam portions 16a to 16d extend in a direction substantially parallel to the extending direction of the facing portion 41 (see FIG. 1B). Here, "substantially parallel" means that the angle α formed between the extending direction of the beam portion 16 and the extending direction of the facing portion 41 is less than ±45°. The angle α is preferably ±10° or less, more preferably ±3° or less, and even more preferably 0° (parallel).

[0032] Although the gas sensor 1a of this embodiment has four beams 16, the number of beams 16 is not particularly limited as long as it is two or more. The greater the number of beams 16, the greater the mechanical strength of the detection section 12 tends to be. However, if the number of beams 16 is large, heat from the detection section 12 is more likely to be transmitted to the peripheral section 14 via the beams 16. Therefore, the number of beams 16 is preferably two to four, and more preferably four.

[0033] As shown in FIG. 1B, the beams 16a-16b of the gas sensor 1a are connected to the ends of the edges of the detection unit 12 that are parallel to the X-axis. The first beam 16a and the second beam 16b form a pair and are arranged on the same line in the Y-axis direction. The third beam 16c and the fourth beam 16d form a pair and are arranged on the same line in the Y-axis direction. In this way, the multiple beams 16 are preferably arranged in positions that are symmetrical with respect to the center line along the extension direction of the facing portion 41. By arranging the multiple beams 16 in a balanced manner, the mechanical strength of the detection unit 12 is improved and deformation of the detection unit 12 can be expected to be suppressed.

[0034] The width of beam portion 16 in the X-axis direction is not particularly limited. For example, it is preferable that the width of beam portion 16 in the X-axis direction be within a range of 0.2 to 0.75 times the maximum width Wx0 of detection unit 12 in the X-axis direction. Furthermore, the length L of beam portion 16 in the Y-axis direction (see FIG. 1D) is also not particularly limited. For example, it is preferable that the length L of beam portion 16 in the Y-axis direction be within a range of 0.2 to 0.4 times the maximum width Wy0 of detection unit 12 in the Y-axis direction.

[0035] Next, the materials of the substrate 50 and the films included in the film stack portion 10 will be described in detail.

[0036] The substrate 50 is not particularly limited as long as it has a mechanical strength sufficient to support the film stack portion 10 and is made of a material suitable for microfabrication such as etching. For example, the substrate 50 may be a silicon single crystal substrate, a sapphire single crystal substrate, a ceramic substrate, a quartz substrate, a glass substrate, or the like.

[0037] The first insulating film 21, the second insulating film 23, and the third insulating film 25 may all be made of insulating materials, and are not particularly limited. For example, the first insulating film 21 to the third insulating film 25 may be made of silicon oxide or silicon nitride, with silicon oxide being preferred. The first insulating film 21 to the third insulating film 25 may be made of different materials, but are preferably made of the same material. By making the first insulating film 21 to the third insulating film 25 of the same material, adhesion between the layers is improved, and the mechanical strength of the detection unit 12 can be ensured.

[0038] The thickness of the first insulating film 21 is not particularly limited as long as it can sufficiently ensure insulation between the substrate 50 and the heater 3 and function as an etching stop layer when forming the cavity 55. For example, the thickness of the first insulating film 21 is preferably about 0.1 to 1.0 μm.

[0039] The thickness of the second insulating film 23 is not particularly limited as long as it is thick enough to reliably cover the heater 3 and ensure sufficient interlayer insulation. For example, the second insulating film 23 preferably has a thickness of about 0.06 to 1.2 μm. The thickness of the third insulating film 25 is not particularly limited as long as it is thick enough to reliably cover the sensitive film 6 and ensure sufficient interlayer insulation. For example, the third insulating film 25 preferably has a thickness of about 0.06 to 1.2 μm.

[0040] The heater 3 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), gold (Au), 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 suitable for high-precision dry etching such as ion milling and has high corrosion resistance, so it is preferable to make the heater 3 from platinum. When the heater 3 is made of platinum, it is preferable to form an adhesion layer such as titanium (Ti) between the first insulating film 21 and the platinum material to improve adhesion of the heater 3 to the first insulating film 21.

[0041] Preferably, the pair of detection electrodes 4 are both made of a material that is conductive and has a relatively high melting point. Like the heater 3, the pair of detection electrodes 4 can be made of molybdenum (Mo), platinum (Pt), gold (Au), 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.

[0042] The sensitive film 6 may be made of a material whose resistance changes with temperature. For example, the sensitive film 6 may be a thermistor film or a platinum film, with a thermistor film being preferred. Examples of materials for thermistor films include composite metal oxides, amorphous silicon, polysilicon, and germanium. The material and thickness of the sensitive film 6 are both factors that affect the initial resistance of the detection unit 12. Therefore, the material and thickness of the sensitive film 6 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 1a.

[0043] Next, an example of a method for manufacturing the gas sensor 1a will be described.

[0044] First, a substrate 50 is prepared, and a first insulating film 21 is formed on one main surface of the substrate 50. The first insulating film 21 may be formed by thermal oxidation, CVD, or the like. Then, a thin film of the conductive material (conductive thin film) contained in the heater 3 is formed on the first insulating film 21. When the heater 3 has a layered structure made of multiple conductive materials (for example, a Ti / Pt layered structure), multiple conductive thin films may be stacked. The conductive thin film may be formed using a known film formation method. Examples of known film formation methods include sputtering, CVD, and PVD. After the conductive thin film is formed, the conductive thin film is patterned by etching to form the heater 3 having a meander pattern.

[0045] Next, the second insulating film 23 is formed so as to cover the heater 3. The second insulating film 23 may be formed by the same method as the first insulating film 21. Then, a thin film of a conductive material that will form the detection electrodes 4 is formed on the second insulating film 23. The conductive thin film is patterned by etching to form a pair of detection electrodes 4 having the pattern shown in FIG. 1B.

[0046] Next, the sensitive film 6 is formed so as to cover the pair of detection electrodes 4. The sensitive film 6 may be formed by a known film formation method depending on the material of the sensitive film 6. For example, if the sensitive film 6 is a thermistor film of a complex oxide, the sensitive film 6 may be formed by a sputtering method so as to have the composition of the complex oxide. After the sensitive film 6 is formed, it is subjected to a heat treatment at a predetermined temperature for a predetermined holding time, and is etched to have a predetermined shape. Thereafter, a third insulating layer 25 is formed so as to cover the sensitive film 6 by the same method as the first and second insulating films.

[0047] The first to third insulating films are also patterned by etching to form a shape having beam portions as shown in FIGS. 1A and 1B. After the film stack portion 10 is formed by the above steps, the pad electrode 8 and the via-hole electrode 9 are formed by a known method such as a lift-off method. Thereafter, a portion of the substrate 50 is removed by etching so that the substrate 50 remains only below the peripheral edge portion 14 in the Z-axis direction, thereby forming a cavity portion 55. The substrate 50 can be etched by dry etching such as Deep-RIE, anisotropic wet etching, or the like. By the above method, the gas sensor 1a shown in FIGS. 1A to 1D is obtained.

[0048] The gas sensor 1a of this embodiment can be used as a thermal conduction gas sensor. The thermal conduction gas sensor 1a detects gases such as CO2, H2, He, and CO, which have thermal conductivities different from those of air. To measure the concentration of a target gas in a given atmosphere, the detection unit 12 is heated to its operating temperature by the heater 3. When the target gas comes into contact with the detection unit 12, the heat dissipation characteristics of the detection unit 12 change in accordance with the concentration of the target gas in the atmosphere. When the temperature of the detection unit 12 changes due to the change in heat dissipation characteristics, the resistance value of the sensitive film 6, which is formed of a thermistor film or the like, changes. This change in resistance is converted into an electrical signal by the pair of detection electrodes 4, allowing the concentration of the target gas to be determined.

[0049] (Summary of the first embodiment) The gas sensor 1a of this embodiment has an air bridge structure in which the detection unit 12 is supported above the cavity 55 by four beams 16 extending from the surface of the substrate 50. The detection unit 12 includes a heater 3, a sensitive membrane 6, and a pair of opposing electrodes (opposing portions 41) in contact with the sensitive membrane. The opposing portions 41 each extend along the Y-axis direction and oppose each other in the X-axis direction with an inter-electrode distance D0. In the gas sensor 1a having such an air bridge structure, all of the beams 16 extend in a direction substantially parallel to the extension direction of the opposing portions 41.

[0050] The gas sensor 1a has the above-described characteristics, which can suppress measurement errors caused by deformation of the detection part 12. This effect is thought to be related to the variation in the inter-electrode distance D0.

[0051] Conventionally, gas sensors with an air bridge structure generally have a structure as shown in Fig. 2A. Specifically, in gas sensor 1b of Fig. 2A, which corresponds to a comparative example, four beam portions 16' are formed along diagonal lines of detection portion 12. In this case, all of beam portions 16' extend in a direction intersecting the extending direction of opposing portion 41', and the extending direction of beam portions 16' and the extending direction of opposing portion 41' form an angle of 45°.

[0052] When the detection unit 12' is heated by the heater 3', the beams 16' block the thermal expansion of the detection unit 12'. Suppressing the thermal expansion causes stress to be applied between the beams 16', compressing the detection unit 12', resulting in deformation of the detection unit 12'. In the conventional gas sensor 1b, significant deformation occurs particularly along the diagonal of the detection unit 12, which is the extension direction of the beams 16'. This deformation causes a change in the inter-electrode distance D0 (widening of the inter-electrode distance D0). Furthermore, the inter-electrode distance D0 tends to be wider at the end portions of the opposing portions 41' than at the center, resulting in greater variation in the inter-electrode distance D0. When the inter-electrode distance D0 fluctuates due to deformation of the detection unit 12', the resistance between the electrodes (between the pair of opposing portions) changes, resulting in errors in the gas concentration measurement results.

[0053] On the other hand, in the gas sensor 1a of this embodiment, the deformation of the detection portion 12 is anisotropic and depends on the extension direction of the beam portion 16. Specifically, the detection portion 12 is easily deformed in the Y-axis direction, which is the extension direction of the beam portion 16, but is difficult to deform in the opposing direction of the opposing portion 41 (X-axis direction), in which the beam portion 16 does not extend. Therefore, even if the detection portion 12 is deformed due to thermal stress, fluctuations in the inter-electrode distance D0 can be suppressed, and the variation in the inter-electrode distance D0 can also be reduced. In other words, it is possible to reduce the change in resistance value due to deformation of the detection portion 12. As a result, the gas sensor 1a of this embodiment can suppress errors in the gas concentration measurement results.

[0054] The gas sensor 1c shown in FIG. 2B corresponds to a comparative example of this embodiment. In the gas sensor 1c shown in FIG. 2B, the first beam 16a′ and the third beam 16c′ extend parallel to the extension direction of the facing portion 41′, while the second beam 16b′ and the fourth beam 16d′ extend perpendicular to the extension direction of the facing portion 41′. In the case of this gas sensor 1c, the deformation of the detection portion 12′ is isotropic, and the detection portion 12′ deforms in the facing direction of the facing portion 41′ at approximately the same rate as in the extension direction. In other words, if a beam 16′ intersects the extension direction of the facing portion 41′ at an angle of ±45° or more, the inter-electrode distance D0 varies with the deformation of the detection portion 12′, resulting in an error in the gas concentration measurement result.

[0055] Therefore, in order to suppress fluctuations in the inter-electrode distance D0 and reduce measurement errors, it is necessary that all of the beam portions 16 extend in a direction substantially parallel to the extension direction of the opposing portions 41. Note that the closer the angle α between the extension direction of the beam portions 16 and the extension direction of the opposing portions 41 is to 0°, the less likely the inter-electrode distance D0 will change, and the smaller the measurement error can be made.

[0056] Second embodiment A gas sensor 1d according to the second embodiment will be described below with reference to Fig. 3. Note that the description of the components in the second embodiment that are common to those in the first embodiment will be omitted and the same reference numerals will be used.

[0057] As shown in FIG. 3, the gas sensor 1d also has an air bridge structure, similar to the gas sensor 1a of the first embodiment, in which the extending direction of the four beam portions 16 is substantially parallel to the extending direction of the facing portion 41.

[0058] In the gas sensor 1d, the planar shape of the detection unit 12 is different from that of the gas sensor 1a of the first embodiment. Specifically, in the gas sensor 1d, the maximum width Wy0 of the detection unit 12 in the extending direction of the opposing part 41 (the Y-axis direction in FIG. 3) is wider than the maximum width Wx0 of the detection unit 12 in the opposing direction of the opposing part 41 (the X-axis direction in FIG. 3). That is, the detection unit 12 has a rectangular planar shape with the Y-axis direction as the longitudinal direction.

[0059] When Wx0 < Wy0 is satisfied as described above, the longitudinal direction of the detection unit 12, the extending direction of the opposing part 41, and the extending direction of the beam part 16 are substantially parallel. In other words, in the gas sensor 1d, the pair of opposing parts 41 and all the beam parts 16 all extend along the longitudinal direction of the detection unit 12. Thus, not only the extending direction of the opposing part 41 and the extending direction of the beam part 16 are made to coincide, but also the longitudinal direction of the detection unit 12 is made to coincide with the extending directions of the opposing part 41 and the beam part 16, so that in the detection unit 12, deformation in the Y-axis direction becomes dominant. And in the X-axis direction, which is the opposing direction of the opposing part 41, it becomes more difficult for the detection unit 12 to deform, and fluctuations in the electrode distance D0 can be suppressed more than in the gas sensor 1a of the first embodiment. As a result, in the gas sensor 1d of the second embodiment, measurement errors due to deformation of the detection unit 12 can be further reduced.

[0060] Note that the angle β formed by the extending direction of the opposing part 41 and the longitudinal direction of the detection unit 12 is preferably ±10° or less, more preferably ±5° or less, and even more preferably 0°. Similarly, the angle γ formed by the extending direction of the beam part 16 and the longitudinal direction of the detection unit 12 is preferably ±10° or less, more preferably ±5° or less, and even more preferably 0°.

[0061] Also, the ratio (Wy0 / Wx0) of the longitudinal width to the short-side width in the detection unit 12 is preferably more than 1.0 and 2.0 or less, and more preferably 1.2 or more and 1.8 or less. By setting Wy0 / Wx0 within the above range, fluctuations in the electrode distance D0 can be suppressed while sufficiently ensuring the mechanical strength of the detection unit 12.

[0062] In the second embodiment, the shape of the detection unit 12 is not necessarily limited to a rectangle. The detection unit 12 only needs to satisfy Wx0 < Wy0, and may have a planar shape such as an ellipse or a polygon.

[0063] Third embodiment Hereinafter, based on FIG. 4, the gas sensor 1e according to the third embodiment will be described. Regarding the common configurations of the first to second embodiments in the third embodiment, the description will be omitted and the same reference numerals will be used.

[0064] As shown in FIG. 4, the gas sensor 1e has an air bridge structure in which the detection unit 12 is supported by four beam portions 16. And, similar to the gas sensor 1d of the second embodiment, in the gas sensor 1e as well, the opposing portions 41 of the detection electrodes 4 and the four beam portions 16 extend along the longitudinal direction of the detection unit 12.

[0065] In the third embodiment, the four edges of the detection unit 12 are described by distinguishing them as follows. Specifically, the edge located between the first beam portion 16a and the second beam portion 16b is defined as the first edge 12a, the edge located between the third beam portion 16c and the fourth beam portion 16d is defined as the second edge 12b, the edge located between the second beam portion 16b and the third beam portion 16c is defined as the third edge 12c, and the edge located between the first beam portion 16a and the fourth beam portion 16d is defined as the fourth edge 12d. The first edge 12a and the second edge 12b are parallel to the extending direction (Y-axis direction) of the opposing portion 41, and the third edge 12c and the fourth edge 12d are parallel to the opposing direction (X-axis direction) of the opposing portion 41. Note that the first edge 12a and the second edge 12b are also edges that intersect the opposing direction of the opposing portion 41.

[0066] The detection unit 12 of the gas sensor 1e has notch portions 71 in a part of the edges (12a, 12b) along the extending direction of the opposing portion 41. Specifically, a notch portion 71 is formed at the center of the first edge 12a, and a notch portion 71 is also formed at the center of the second edge 12b. This notch portion 71 is a region where a part of the detection unit 12 is cut off and missing.

[0067] Although the cutout 71 may be formed at a position offset from the center of the edge, it is preferable that it be located at the center of the edge as shown in Fig. 4. The cutout 71 may be formed on only one of the first edge 12a and the second edge 12b. However, as shown in Fig. 4, it is preferable to form cutouts on both the first edge 12a and the second edge 12b, and it is preferable that the cutout 71 on the first edge side and the cutout 71 on the second edge side are arranged in pairs on the same straight line in the X-axis direction.

[0068] The detection section 12 of the gas sensor 1e has a narrow width section 70 formed by a cutout portion 71. The narrow width section 70 is a region in the detection section 12 where the width in the X-axis direction is partially narrowed, and is shown by gray shading in FIG. 4. In other words, the narrow width section 70 is a region in which the detection section 12 is partially constricted toward the inside in the X-axis direction. The narrow width section 70 is preferably located at the center of the detection section 12 in the extension direction of the facing portion 41.

[0069] By forming the cutout portion 71 and the narrow width portion 70 in the detection unit 12, stress caused by thermal expansion of the detection unit 12 can be alleviated, and fluctuations in the inter-electrode distance D0 can be more effectively suppressed. Note that stress applied to the detection unit 12 tends to concentrate in the central portion between the beam portions (i.e., the central portion of the edge). Therefore, by forming the cutout portion 71 in the center of the edge, deformation of the detection unit 12 can be more effectively suppressed. Similarly, by forming the narrow width portion 70 in the center in the Y-axis direction, deformation of the detection unit 12 can be more effectively suppressed.

[0070] Furthermore, it is preferable that the cutout portion 71 has a predetermined size rather than being a linear slit. This is because a linear slit may warp and cause stress to concentrate in the slit portion. The maximum width Wx2 of the cutout portion 71 in the X-axis direction may be such that it does not reach the opposing portion 41 of the detection electrode 4. For example, the ratio Wx2 / Wx0 of Wx2 to the maximum width Wx0 of the detection portion 12 is preferably 0.05 to 0.15, and more preferably 0.05 to 0.1.

[0071] Furthermore, if the maximum width of cutout portion 71 in the Y-axis direction is Wy1, the ratio Wy1 / Wy0 of Wy1 to the maximum width Wy0 of detection unit 12 is preferably 0.15 to 0.5, and more preferably 0.15 to 0.2. Note that, although cutout portion 71 shown in FIG. 4 has a triangular, wedge-like shape in plan view, the shape of cutout portion 71 is not particularly limited. For example, cutout portion 71 may have a semicircular or semi-elliptical shape in plan view, with the edges of the cutout portion being arc-shaped.

[0072] The minimum width Wx1 of narrow portion 70 in the X-axis direction may be determined according to the set value of inter-electrode distance D0. For example, the ratio Wx1 / Wx0 of Wx1 to the maximum width Wx0 of detection unit 12 is preferably 0.85 to 0.95, and more preferably 0.90 to 0.95. The width of narrow portion 70 in the Y-axis direction may be set to the same value as the maximum width Wy1 of notch 71 in the Y-axis direction.

[0073] The cutout 71 in the first edge 12a and the cutout 71 in the second edge 12b may have different shapes and dimensions, but preferably have similar shapes and dimensions. Cutouts may also be formed in the third edge 12c and the fourth edge 12d.

[0074] Although the embodiments of the present invention have been described above, the present invention is not limited to the above-described embodiments and can be modified in various ways within the scope of the present invention.

[0075] (Variation) For example, in the above embodiment, a thermal conduction type gas sensor has been described, but the gas sensor according to the present invention may be a catalytic combustion type, a semiconductor type, or a solid electrolyte type gas sensor.

[0076] 5A and 5B is an example of a catalytic combustion gas sensor. The gas sensor 1f has a film laminate 10 with an air bridge structure, and the configuration of each film (3, 4, 6, 21 to 23) included in the film laminate 10 can be the same as that of the gas sensor 1a of the first embodiment. In the gas sensor 1f, a catalyst section 80 is formed on the detection section 12 of the film laminate 10.

[0077] The catalyst section 80 can be formed from a porous carrier material that supports a catalyst material. Examples of the carrier material that can be used include oxide materials such as aluminum oxide (such as gamma alumina), titanium oxide, silicon oxide, and cerium oxide. Examples of the catalyst material that can be used include precious metals such as platinum (Pt), gold (Au), and palladium (Pd), as well as metal oxides such as rare earth element oxides and bismuth oxide. The size of the catalyst section 80 is preferably controlled so that the volume ratio of the catalyst section 80 to the detection section 12 is 10 or more and 40 or less. The catalyst section 80 can be formed by applying a raw material paste onto the detection section 12 by screen printing or dispensing using a dispenser, and then heat-treating the paste at a predetermined temperature.

[0078] The catalytic combustion gas sensor 1f can measure the concentration of combustible gases such as CO. During measurement, the heater 3 heats the detection unit 12 to a predetermined temperature. If the combustible gas to be detected is present in the space in which the gas sensor 1f is placed, the combustible gas combines with oxygen and other gases on the catalyst unit 80, depending on the proportion of the combustible gas present, and burns. The catalyst unit 80 promotes the combination of the combustible gas and oxygen. When the combustion heat (reaction heat) generated by the combustion of the combustible gas is transmitted to the sensitive film 6, which is composed of a thermistor film or the like, the resistance value of the sensitive film 6 changes. This change in resistance is converted into an electrical signal by the pair of detection electrodes 4, allowing the concentration of the combustible gas to be determined.

[0079] In such a catalytic combustion type gas sensor 1f, by making the extension direction of the beam portion 16 substantially parallel to the extension direction of the detection electrode 4, fluctuations in the distance between the electrodes can be suppressed, and the same effects as in the first embodiment can be obtained.

[0080] When the present invention is applied to a semiconductor gas sensor, the sensitive film 6 may be a semiconductor film of a metal oxide such as SnO2, ZnO, or In2O3. When the present invention is applied to a solid electrolyte gas sensor, the sensitive film 6 may be a solid electrolyte film made of yttria-stabilized zirconia (YSZ) or a lithium ion conductive solid electrolyte. In the case of a solid electrolyte gas sensor, one of the pair of sensing electrodes 4 may be a working electrode, and the other may be a reference electrode. The working electrode contains an electronically conductive material such as platinum, gold, palladium, or silver, and an auxiliary electrode material such as an alkali metal carbonate or an alkaline earth metal carbonate, and the reference electrode may be made of an electronically conductive material such as platinum, gold, palladium, or silver.

[0081] In the first to third embodiments, the detection section 12 has a substantially rectangular shape in plan view, but the shape of the detection section in plan view may also be circular as shown in Fig. 6. In the gas sensor 1g of Fig. 6, the detection section 13 having a circular shape in plan view is supported by four beams 16. Even in the gas sensor 1g having the circular detection section 13, by making the extension direction of the beams 16 substantially parallel to the extension direction of the facing portion 41, it is possible to suppress fluctuations in the inter-electrode distance D0, and to obtain the same effect as the gas sensor 1a of the first embodiment.

[0082] The detection section 13 of the gas sensor 1g has notches 71 formed in the first and second arc-shaped edges 13a and 13b extending along the direction of extension of the facing section 41. A portion of the detection section 13 of the gas sensor 1g is constricted inward in the X-axis direction, and a narrow width section 70 is present such that the radial width of the detection section 13 is partially narrowed. Note that the "radial width" refers to the width passing through the center point of the circle, and the minimum radial width Wx3 of the narrow width section 70 is smaller than the diameter and maximum width Wx0 of the detection section 13. Wx3 may be set in the same manner as Wx1 in the third embodiment, and Wx3 / Wx0 is preferably 0.85 to 0.95, and more preferably 0.90 to 0.95. Even when the detection section 13 is circular, by forming the cutout portion 71 and / or the narrow width portion 70, deformation of the detection section 13 can be alleviated, and the same effect as that of the gas sensor 1e of the third embodiment can be obtained.

[0083] In the first to third embodiments, the number of beams 16 is four, but it is sufficient to form at least two beams 16. When the detection unit 12 is supported by two beams 16, the gas sensor can have a structure such as that shown in Fig. 7A or 7B, for example.

[0084] In the gas sensor 1h of Fig. 7A, the first beam portion 16a is connected to the center of the fourth edge 12d parallel to the opposing direction of the opposing portions 41, and the second beam portion 16b is connected to the center of the third edge 12c parallel to the opposing direction of the opposing portions 41. Even in the case where the number of beam portions 16 is two, as long as the extending direction of the beam portions 16 is parallel to the extending direction of the opposing portions 41, fluctuations in the inter-electrode distance D0 can be suppressed, and the same effects as those of the gas sensor 1a of the first embodiment can be expected. However, when the gas sensor 1a and the gas sensor 1h of Fig. 7A are compared, the gas sensor 1a can reduce fluctuations in the inter-electrode distance D0 more than the gas sensor 1h, and can also increase the mechanical strength of the detection unit 12.

[0085] 7B, the facing portion 41 of the detection electrode 4 extends in a direction intersecting the edge of the detection portion 12 at an angle of approximately 45°. The first beam portion 16a is connected to the first corner portion 12e of the detection portion 12, and the second beam portion 16b is connected to the third corner portion 12g of the detection portion 12. In the gas sensor 1i as well, the first beam portion 16a and the second beam portion 16b both extend in a direction parallel to the extending direction of the facing portion 41.

[0086] In the gas sensor 1i, the distance from the second corner 12f to the fourth corner 12h corresponds to the maximum width Wx0 of the detection part 12 in the opposing direction of the opposing part 41. Furthermore, the distance from the first corner 12e to the third corner 12g (i.e., the distance from the first beam part 16a to the second beam part 16b) corresponds to the maximum width Wy0 of the detection part 12 in the extension direction of the opposing part 41, and Wx0 ≈ Wy0 is satisfied.

[0087] 7B, even when the extending direction of the facing portion 41 intersects with the edge of the detection unit 12, the same effects as those of the gas sensor 1a of the first embodiment can be expected. However, when the gas sensor 1a is compared with the gas sensor 1i of FIG. 7B, the gas sensor 1a can reduce the variation in the inter-electrode distance D0 more effectively than the gas sensor 1i, and can also increase the mechanical strength of the detection unit 12.

[0088] As a modified example, the gas sensor may have a structure as shown in Fig. 7C. In the gas sensor 1j of Fig. 7C, the facing portions 41 extend along the diagonal direction of the detection unit 12. The four beam portions 16 are connected to the centers of the corresponding edges and extend from the centers of the edges in the extending direction of the facing portions 41. In the gas sensor 1j having such a structure, the extending direction of the facing portions 41 and the extending direction of the beam portions 16 are parallel to each other, so that the fluctuation of the inter-electrode distance D0 can be suppressed. [Explanation of symbols]

[0089] 1a~1j ... Gas sensors 10... Film stacking section 12, 13 ... Detection unit 12a~12d, 13a~13d ... (detection part) edge 12e~12h ... Corner (of the detection part) 14...periphery 16,16a~16d … Beam part 70 … Narrow part 71 ... Cutout 3...Heater 31...Meander pattern 32 … End wiring 4, 4a, 4b ... detection electrodes 41 ... opposing part (opposing electrode) 42 … Drawer part 6... Sensitive membrane 8... Pad electrode 9...Via hole electrode 21, 23, 25 ... insulating film 80... Catalyst section 50... PCB 55 … Cavity part

Claims

1. a substrate having a cavity; and a detection unit supported by two or more beams extending from the substrate above the cavity; the detection unit has a laminated structure including a heater, a sensitive film, and a pair of opposing electrodes in contact with the sensitive film, the pair of opposing electrodes each extend in a direction perpendicular to the stacking direction and face each other at a predetermined interval in the in-plane direction of the sensitive film, In a plan view, the detection unit has four corner portions corresponding to four corners of the detection unit, Each of the two or more beam portions is connected to any one of the four corner portions, A gas sensor in which all of the beam portions extend in a direction substantially parallel to the extension direction of the counter electrode and protrude from an edge of the detection portion in a direction substantially parallel to the extension direction of the counter electrode.

2. 2. The gas sensor according to claim 1, wherein a maximum width Wy0 of the detection portion in the extending direction of the counter electrode is equal to a maximum width Wx0 of the detection portion in the opposing direction of the counter electrodes.

3. a maximum width Wy0 of the detection portion in the extension direction of the counter electrode is wider than a maximum width Wx0 of the detection portion in the opposing direction of the counter electrodes; 2. The gas sensor according to claim 1, wherein the pair of opposing electrodes and all of the beam portions extend along the longitudinal direction of the detection portion.

4. 4. The gas sensor according to claim 1, wherein the detection portion has a narrow portion in which the width of the detection portion in the opposing direction of the counter electrodes is partially narrowed.

5. 5. The gas sensor according to claim 4, wherein the narrow width portion is located at a center of the detection portion in the extending direction.

6. 4. The gas sensor according to claim 1, wherein the detection portion has a notch in a part of an edge along the extending direction.

7. 7. The gas sensor according to claim 6, wherein the notch is located at the center of the edge.

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

9. A device comprising: a substrate having a hollow portion; and a detection unit supported by two or more beam portions extending from the substrate above the hollow portion; the detection unit has a laminated structure including a heater, a sensitive film, and a pair of opposing electrodes in contact with the sensitive film, the pair of opposing electrodes each extend in a direction perpendicular to the stacking direction and face each other at a predetermined interval in the in-plane direction of the sensitive film, All of the beam portions extend in a direction substantially parallel to the extending direction of the counter electrode, The gas sensor has a narrow portion where the width of the detection portion in the opposing direction of the counter electrodes is partially narrowed.

10. A gas sensor as described in Claim 9, wherein the narrow width portion is located at the center of the detection portion in the extension direction.

11. A device comprising: a substrate having a hollow portion; and a detection unit supported by two or more beam portions extending from the substrate above the hollow portion; the detection unit has a laminated structure including a heater, a sensitive film, and a pair of opposing electrodes in contact with the sensitive film, the pair of opposing electrodes each extend in a direction perpendicular to the stacking direction and face each other at a predetermined interval in the in-plane direction of the sensitive film, All of the beam portions extend in a direction substantially parallel to the extending direction of the counter electrode, The gas sensor has a notch in a part of an edge of the detection portion along the extending direction.

12. A gas sensor as described in Claim 11, wherein the cutout portion is located in the center of the edge.

13. A device comprising: a substrate having a hollow portion; and a detection unit supported by two or more beam portions extending from the substrate above the hollow portion; the detection unit has a laminated structure including a heater, a sensitive film, and a pair of opposing electrodes in contact with the sensitive film, the pair of opposing electrodes each extend in a direction perpendicular to the stacking direction and face each other at a predetermined interval in the in-plane direction of the sensitive film, In a plan view, the detection unit has a rectangular shape, Each of the two or more beam portions is connected to a center portion of any one of four edges of the detection portion, The pair of opposing electrodes extend in a direction inclined with respect to the four edges, All of the beam portions extend in a direction substantially parallel to the extending direction of the counter electrode, A gas sensor in which each of the beam portions protrudes from a center of any one of the four edges in a direction substantially parallel to an extension direction of the counter electrode.

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