Gas sensor

Abstract

To provide a gas sensor that offers good detection response.SOLUTION: A gas sensor is provided comprising a substrate having an opening formed therethrough, an insulation film provided at a position overlapping the opening in plan view, and a gas detection unit provided on an upper surface of the insulation film, where the insulation film is warped to protrude upward when the gas detection unit is ready to detect gas.SELECTED DRAWING: Figure 6

Description

[Technical Field]

[0001] The present disclosure relates to gas sensors. [Background technology]

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

[0003] As a gas sensor, one has been disclosed in which an opening is formed in a substrate and a detection part is disposed on a flat insulating film disposed in the opening (see Patent Document 1, etc.). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Patent No. 5100733 specification Summary of the Invention [Problem to be solved by the invention]

[0005] However, in conventional gas sensors in which the detection part is placed on a flat insulating film, there are cases in which the detection part does not have sufficient contact with the gas flow. For example, when a gas flow parallel to the flat insulating film occurs around the gas sensor, the area of ​​the detection part that has contact with the gas flow is limited, which can cause problems in terms of high-speed response.

[0006] The present disclosure has been made in view of the above circumstances, and provides a gas sensor that can increase the chance of a gas detection portion coming into contact with a gas flow and has favorable responsiveness. [Means for solving the problem]

[0007] The gas sensor according to the present disclosure comprises: a substrate in which an opening is formed; an insulating film disposed at a position overlapping the opening in a plan view; a gas detection unit provided on an upper surface of the insulating film, When the gas detection unit is capable of detecting a gas, the insulating film has a curved shape that protrudes upward.

[0008] In this type of gas sensor, the insulating film on which the gas detection unit is mounted is curved upward, which increases the chance of the gas detection unit coming into contact with a gas flow approaching from the side, thereby providing favorable responsiveness.

[0009] Furthermore, for example, the insulating film may be a multilayer film having a first insulating film, a second insulating film provided below the first insulating film, and a third insulating film provided below the second insulating film, The gas detection unit may be provided on an upper surface of the first insulating film, a first heater wiring provided between the first insulating film and the second insulating film; a second heater wiring provided between the second insulating film and the third insulating film, The first heater wiring and the second heater wiring may be electrically connected in series, and a resistance value of the first heater wiring may be greater than a resistance value of the second heater wiring.

[0010] In this gas sensor, the heat generated by the first heater wire is made larger than that generated by the second heater wire, and the heat generated by these heater wires can deform the insulating film into a warped shape that protrudes upward. Furthermore, in this gas sensor, the heat used to heat the gas detection unit is diverted to deform the insulating film into a warped shape, thereby achieving efficient energy utilization.

[0011] Furthermore, for example, the insulating film may be a multilayer film having a first insulating film, a second insulating film provided below the first insulating film, and a third insulating film provided below the second insulating film, The gas detection unit may be provided on an upper surface of the first insulating film, a first heater wiring provided between the first insulating film and the second insulating film; a second heater wiring provided between the second insulating film and the third insulating film, The first heater wiring and the second heater wiring may be electrically connected in parallel, and a resistance value of the first heater wiring may be smaller than a resistance value of the second heater wiring.

[0012] In this gas sensor, the heat generated by the first heater wire is made larger than that generated by the second heater wire, and the heat generated by these heater wires can deform the insulating film into a warped shape that protrudes upward. Furthermore, in this gas sensor, the heat used to heat the gas detection unit is diverted to deform the insulating film into a warped shape, thereby achieving efficient energy utilization.

[0013] Furthermore, for example, the insulating film may be a multilayer film having a first insulating film, a second insulating film provided below the first insulating film, and a third insulating film provided below the second insulating film, The gas detection unit may be provided on an upper surface of the first insulating film, a first heater wiring provided between the first insulating film and the second insulating film; a second heater wiring provided between the second insulating film and the third insulating film, The amount of expansion of the first heater wire in the film surface direction when heated relative to when not heated may be larger than the amount of expansion of the second heater wire in the film surface direction when heated relative to when not heated.

[0014] In this gas sensor, by setting the expansion amounts of the first heater wire and the second heater wire in the film surface direction to a predetermined relationship, the insulating film can be warped to protrude upward as these heater wires deform when heated. Furthermore, in this gas sensor, the heat used to heat the gas detection unit is diverted to warp the insulating film, thereby achieving efficient energy utilization.

[0015] Furthermore, for example, the insulating film may be a multilayer film having a first insulating film, a second insulating film provided below the first insulating film, and a third insulating film provided below the second insulating film, The gas detection unit may be provided on an upper surface of the first insulating film, a first heater wiring provided between the first insulating film and the second insulating film; a second heater wiring provided between the second insulating film and the third insulating film, The first heater wiring and the second heater wiring may be electrically independent.

[0016] In this gas sensor, the current or voltage applied to the first heater wire and the second heater wire can be independently controlled to generate heat from the heater wires, causing the insulating film to warp and protrude upward. Furthermore, in this gas sensor, the heat used to heat the gas detection unit is diverted to warp the insulating film, thereby achieving efficient energy utilization. [Brief explanation of the drawings]

[0017] [Figure 1] FIG. 1 is a schematic plan view of a gas sensor according to a first embodiment of the present disclosure. [Figure 2] FIG. 2 is a schematic cross-sectional view of the gas sensor shown in FIG. 1 taken along line II-II. [Figure 3] FIG. 3 is a schematic cross-sectional view of the gas sensor shown in FIG. 1 taken along line III-III. [Figure 4]FIG. 4 is a schematic cross-sectional view of the gas sensor shown in FIG. 1 taken along line IV-IV. [Figure 5] FIG. 5 is an enlarged cross-sectional view of the insulating film and the gas detection portion of the gas sensor shown in FIG. 1, showing the state before gas detection. [Figure 6] FIG. 6 is a conceptual diagram showing the insulating film and the gas detection section shown in FIG. 5 in a state during gas detection. [Figure 7] FIG. 7 is a plan view showing the shape of the substrate of the gas sensor shown in FIG. [Figure 8] FIG. 8 is a plan view showing the shape of the third insulating film of the gas sensor shown in FIG. [Figure 9] FIG. 9 is a plan view showing the shape of the second heater wire of the gas sensor shown in FIG. [Figure 10] FIG. 10 is a plan view showing the shape of the second insulating film of the gas sensor shown in FIG. [Figure 11] FIG. 11 is a plan view showing the shape of the first heater wire of the gas sensor shown in FIG. [Figure 12] FIG. 12 is a plan view showing the shape of the first insulating film of the gas sensor shown in FIG. [Figure 13] FIG. 13 is a plan view showing the shape of the detection electrode of the gas sensor shown in FIG. [Figure 14] FIG. 14 is a plan view showing the shape of the thermistor film of the gas sensor shown in FIG. [Figure 15] FIG. 15 is a conceptual diagram showing the shape of the gas sensor according to the first embodiment and the flow of gas around the gas sensor during gas detection. [Figure 16] FIG. 16 is a plan view showing the shape of the gas detection part of the gas sensor according to the second embodiment of the present disclosure. [Figure 17] FIG. 17(a) is a plan view showing the shapes of the heater wiring and the insulating film in the gas sensor according to the third embodiment of the present disclosure, and FIG. 17(b) is an enlarged cross-sectional view of the heater wiring, the insulating film, etc. shown in FIG. 17(a). [Figure 18]FIG. 18(a) is a plan view showing the shapes of the heater wiring and the insulating film in the gas sensor according to the fourth embodiment of the present disclosure, and FIG. 18(b) is an enlarged cross-sectional view of the heater wiring and the insulating film shown in FIG. 18(a). [Figure 19] FIG. 19(a) is a plan view showing the shapes of a heater wiring and an insulating film in a gas sensor according to a fifth embodiment of the present disclosure, and FIG. 19(b) is an enlarged cross-sectional view of the heater wiring and the insulating film shown in FIG. 19(a). DETAILED DESCRIPTION OF THE INVENTION

[0018] The present disclosure will be described in detail below based on specific embodiments in the following order. 1. First embodiment 1.1. Overall structure 1.2. Base material 1.3.Insulating Film 1.4.Heater wiring 1.5.Gas detection unit 1.6. Manufacturing method 1.8. Effect 2. Second embodiment 3. Third embodiment 4. Fourth embodiment 5. Fifth embodiment

[0019] (1. First embodiment) 1 is a schematic plan view showing a gas sensor 10 according to a first embodiment, as viewed from above. In FIG. 1, of the components included in the gas sensor 10, only the substrate 20 and the third insulating film 33 are shown opaque, and the other components are shown with outlines superimposed so that the shapes of the components below can be seen.

[0020] Fig. 2 is a cross-sectional view of the gas sensor 10 taken along the cross-sectional line II-II shown in Fig. 1. As shown in Fig. 1 and Fig. 2, the gas sensor 10 has a substrate 20 in which an opening 22 is formed, an insulating film 30 disposed at a position overlapping the opening 22 in a plan view from a direction perpendicular to an upper surface 24 of the substrate, and a gas detection unit 60 provided on the upper surface of the insulating film 30. The gas to be detected by the gas detection unit 60 can be, for example, carbon dioxide (CO2).

[0021] As will be described in detail later, the gas detection unit 60 of the gas sensor 10 has a thermistor film 61 whose resistance value changes upon contact with a gas to be detected. A change in the concentration of the gas to be detected changes the thermal conductivity of the gas in contact with the thermistor film 61, which in turn changes the temperature of the thermistor film 61 and the resistance value of the thermistor film 61. The gas detection unit 60 also has at least one pair of electrodes 62a, 62b in contact with the thermistor film 61. The gas sensor 10 detects the gas concentration based on the change in resistance of the thermistor film 61 connecting the electrodes 62a, 62b.

[0022] The gas detection unit 60 of the gas sensor according to the present disclosure is not limited to one having a thermistor film 61 and a pair of electrodes 62a, 62b, but also includes one using a thin film of MOx (metal oxide) instead of the thermistor film 61 (see the second embodiment, etc.). In particular, the gas sensor according to the present disclosure preferably has a thin film portion that contacts and reacts with gas. However, the gas sensor according to the present disclosure also includes any gas detection unit, such as one having a reference element that does not directly have gas detection capability or one having multiple different gas detection units. Other examples of the gas detection unit 60 of the gas sensor according to the present disclosure include a thermal conduction type that uses Pt wires instead of a thermistor film and electrodes, and a catalytic combustion type that uses a catalyst material and electrodes. Examples of catalyst materials include those in which precious metal particles such as platinum (Pt), palladium (Pd), ruthenium (Ru), rhodium (Rh), etc. are supported on a carrier of an oxide material such as aluminum oxide (such as gamma alumina) or silicon oxide.

[0023] (1.1. Overall structure) Fig. 3 is a schematic cross-sectional view of the gas sensor 10 taken along a plane along line III-III in Fig. 1, and Fig. 4 is a schematic cross-sectional view of the gas sensor 10 taken along a plane along line IV-IV in Fig. 1. In the description of the gas sensor 10, a direction perpendicular to the substrate upper surface 24 is referred to as the up-down direction D1, and a direction parallel to the substrate upper surface 24 is referred to as the film surface direction D2. In addition, with respect to the up-down direction D1, a direction away from the substrate 20 with respect to the substrate upper surface 24 on which the insulating film peripheral portion 35 is formed is referred to as the upper side, and a direction into the substrate 20 with respect to the substrate upper surface 24 is referred to as the lower side.

[0024] 1 and 2, the gas sensor 10 has a substrate 20 in which an opening 22 is formed. Other components of the gas sensor 10 are arranged at positions overlapping the opening 22 of the substrate 20 in a plan view and on an upper surface 24 of the substrate that extends around the opening 22. The other components of the gas sensor 10 other than the substrate 20 include an insulating film 30, a first heater wiring 40, a second heater wiring 50, and a gas detection unit 60 that are arranged at positions overlapping the opening 22 in a plan view, and an insulating film peripheral portion 35, a first heater terminal portion 46, a second heater terminal portion 56, and electrode terminal portions 66a and 66b that are arranged on the upper surface 24 of the substrate.

[0025] (1.2. Base material) Fig. 7 is a plan view showing the shape of the substrate 20 of the gas sensor 10. As shown in Figs. 1 and 7, the opening 22 is formed near the center of the substrate 20. As shown in Fig. 2, an insulating film 30 and the like are disposed in the region above the opening 22. As shown in Figs. 1 and 2, the insulating film 30 is disposed so as to overlap the opening 22 when viewed from the up-down direction D1.

[0026] 1, 2, and 7, the opening 22 in the substrate 20 is configured as a through-hole having a substantially rectangular shape in a plan view of the substrate 20, but the shape of the opening 22 in a plan view is not limited to a rectangle. Furthermore, the opening 22 is not limited to a through-hole as shown in FIGS. 2 and 4, and the opening 22 may be configured as a recess recessed downward from the upper surface 24 of the substrate.

[0027] The material of the substrate 20 is not particularly limited as long as it has sufficient mechanical strength to support components formed at positions overlapping the opening 22 in a plan view and on the substrate upper surface 24, and is made of a material suitable for microfabrication such as etching. In this embodiment, examples of the substrate 20 include a silicon single crystal substrate, a sapphire single crystal substrate, a ceramic substrate, a quartz substrate, a glass substrate, and a ferrite substrate.

[0028] (1.3. Insulating film) 1 and 2, in the gas sensor 10, an insulating film 30 is disposed at a position overlapping with an opening 22 formed in the center of a substrate 20 in a plan view. A gas detection unit 60 is provided on the upper surface of the insulating film 30. The insulating film 30 is a multilayer film in which a first insulating film 31, a second insulating film 32, and a third insulating film 33 are overlapped. A first heater wiring 40 is provided between the first insulating film 31 and the second insulating film 32, and a second heater wiring 50 is provided between the second insulating film 32 and the third insulating film 33.

[0029] Fig. 5 is an enlarged cross-sectional view showing the gas detection unit 60, the insulating film 30, the first heater wire 40, and the second heater wire 50 in the gas sensor 10 shown in Fig. 2. As shown in Fig. 5, the insulating film 30 has a first insulating film 31, a second insulating film 32 provided below the first insulating film 31, and a third insulating film 33 provided below the second insulating film 32.

[0030] 8(a) is a plan view of the third insulating film 33 and a third insulating film peripheral portion 38 formed of a film in the same layer as the third insulating film 33, and FIG. 8(b) is a partial enlarged view showing the periphery of the third insulating film 33 in FIG. 8(a). The third insulating film 33 is disposed at the lowest of the first insulating film 31, second insulating film 32, and third insulating film 33 that form the insulating film 30. As shown in FIGS. 2 to 4, the third insulating film peripheral portion 38 is disposed below the first insulating film peripheral portion 36 and the second insulating film peripheral portion 37.

[0031] 8(a) and 1, the third insulating film 33 is disposed at a position overlapping the opening 22 of the substrate 20 in a plan view, and the third insulating film peripheral portion 38 is provided on the substrate upper surface 24 of the substrate 20. The third insulating film 33 and the third insulating film peripheral portion 38 are formed as an integrated film that is deposited simultaneously. As shown in FIG. 2, the lower surface of the third insulating film peripheral portion 38 is in direct contact with the substrate upper surface 24.

[0032] 8(b), the third insulating film 33 has a substantially rectangular central portion 33e and a plurality of beam portions 33a, 33b, 33c, and 33d (four beam portions in this embodiment) connecting the central portion 33e and a third insulating film peripheral portion 38. The beam portions 33a, 33b, 33c, and 33d are provided at the four corners of the central portion 33e. Peripheral holes 33f, 33g, 33h, and 33i are formed in the portions of the central portion 33e other than the four corners to surround the central portion 33e. By arranging the third insulating film 33 at a position overlapping the opening 22 in a plan view and surrounding the central portion 33e with the peripheral holes 33f, 33g, 33h, and 33i, heat transfer between the third insulating film 33 and the third insulating film peripheral portion 36 can be suppressed.

[0033] 10(a) is a plan view of the second insulating film 32 and a second insulating film peripheral portion 37 formed of a film in the same layer as the second insulating film 32, and FIG. 10(b) is a partial enlarged view showing the periphery of the second insulating film 32 in FIG. 10(a). The second insulating film 32 is disposed between the first insulating film 31 and the third insulating film 33 among the first insulating film 31, the second insulating film 32, and the third insulating film 33 that form the insulating film 30. As shown in FIGS. 2 to 4, the second insulating film peripheral portion 37 is disposed between the first insulating film peripheral portion 36 and the third insulating film peripheral portion 38.

[0034] As can be seen from a comparison of FIG. 10(a) with FIG. 8(a), the planar shape of the second insulating film 32 is similar to that of the third insulating film 33, except that a heater connection hole 32j is formed in the central portion 32e. Furthermore, the planar shape of the second insulating film peripheral portion 37 is similar to that of the third insulating film peripheral portion 38, except that a heater insertion hole 32k is formed therein. As can be seen from a comparison of FIG. 10(a) with FIG. 1, the second insulating film 32 is disposed in a position overlapping the opening 22 of the substrate 20 in a planar view, and the second insulating film peripheral portion 37 is provided above the substrate upper surface 24 of the substrate 20 and the third insulating film peripheral portion 38. The second insulating film 32 and the second insulating film peripheral portion 37 are formed as an integral film that is deposited simultaneously. As shown in FIG. 2, the lower surface of the second insulating film peripheral portion 37 directly contacts the upper surface of the third insulating film peripheral portion 38.

[0035] 10(b), the second insulating film 32 has a substantially rectangular central portion 32e and a plurality of beam portions 32a, 32b, 32c, and 32d (four beam portions in this embodiment) that connect the central portion 32e and the second insulating film peripheral portion 37. The beam portions 32a, 32b, 32c, and 32d are provided at the four corners of the central portion 32e. In addition, peripheral holes 32f, 32g, 32h, and 32i are formed in the portions of the central portion 32e other than the four corners so as to surround the central portion 32e. By surrounding the central portion 32e with the peripheral holes 32f, 32g, 32h, and 32i in this manner, heat transfer between the second insulating film 32 and the second insulating film peripheral portion 37 can be suppressed.

[0036] 12(a) is a plan view of the first insulating film 31 and a first insulating film peripheral portion 36 formed of a film in the same layer as the first insulating film 31, and FIG. 12(b) is a partial enlarged view showing the periphery of the first insulating film 31 in FIG. 12(a). The first insulating film 31 is arranged at the uppermost position among the first insulating film 31, second insulating film 32, and third insulating film 33 that form the insulating film 30. As shown in FIGS. 2 to 4, the first insulating film peripheral portion 36 is arranged above the second insulating film peripheral portion 37 and the third insulating film peripheral portion 38.

[0037] As can be seen from a comparison of FIG. 12(a) and FIG. 8(a), the planar shape of the first insulating film 31 is similar to that of the third insulating film 33. Furthermore, the planar shape of the first insulating film peripheral portion 36 is similar to that of the third insulating film peripheral portion 38, except for the heater insertion holes 31k and 31l. As can be seen from a comparison of FIG. 12(a) and FIG. 1, the first insulating film 31 is disposed in a position overlapping the opening 22 of the substrate 20 in a planar view, and the first insulating film peripheral portion 36 is provided above the substrate upper surface 24 of the substrate 20, the third insulating film peripheral portion 38, and the second insulating film peripheral portion 37. The first insulating film 31 and the first insulating film peripheral portion 36 are formed as an integrated film that is deposited simultaneously. As shown in FIG. 2, the lower surface of the first insulating film peripheral portion 36 directly contacts the upper surface of the second insulating film peripheral portion 37.

[0038] 12(b), the first insulating film 31 has a substantially rectangular central portion 31e and multiple (four in this embodiment) beam portions 31a, 31b, 31c, and 31d connecting the central portion 31e and the first insulating film peripheral portion 36. The beam portions 31a, 31b, 31c, and 31d are provided at the four corners of the central portion 31e. In addition, peripheral holes 31f, 31g, 31h, and 31i are formed in the portions of the central portion 31e other than the four corners to surround the central portion 31e. By surrounding the central portion 31e with the peripheral holes 31f, 31g, 31h, and 31i in this manner, heat transfer between the first insulating film 31 and the first insulating film peripheral portion 36 can be suppressed.

[0039] As described above, the insulating film 30 is a multilayer film including the first insulating film 31, the second insulating film 32, and the third insulating film 33. As shown in FIGS. 1, 8, 10, and 12, the insulating film 30 is connected to the first to third insulating film peripheral portions 36-38 provided on the upper surface 24 of the substrate via the beam portions 31a-31d, 32a-32d, and 33a-33d of the first to third insulating films 31-33. Therefore, the insulating film 30 is supported by the first to third insulating film peripheral portions 36-38 and the substrate 20 via the beam portions 31a-31d, 32a-32d, and 33a-33d, and is thereby held at a position overlapping with the opening 22 in a plan view, as shown in FIG.

[0040] As shown in FIG. 5, the first insulating film 31, the second insulating film 32, and the third insulating film 33 may have different thicknesses. When the first insulating film 31, the second insulating film 32, and the third insulating film 33 have different thicknesses, it is preferable to make the third insulating film 33 thicker than the first insulating film 31 and the second insulating film 32 in order to ensure the strength of the gas sensor 10 and to deform the insulating film 30 into a warped shape that protrudes upward as shown in FIG. 6. It is also preferable to make the second insulating film 32 thinner than the third insulating film 33 and the first insulating film 31 in order to reduce a step that occurs in the flat portion 40b where the first heater wiring 40 and the second heater wiring 50 are connected. However, the first insulating film 31, the second insulating film 32, and the third insulating film 33 may have the same thickness.

[0041] The materials of the first insulating film 31, the second insulating film 32, and the third insulating film 33 are not particularly limited as long as they are insulating films, and examples thereof include SiO2 (silicon oxide) and SiNx (silicon nitride).

[0042] (1.4. Heater wiring) 5, the gas sensor 10 has a first heater wire 40 provided between the first insulating film 31 and the second insulating film 32, and a second heater wire 50 provided between the second insulating film 32 and the third insulating film 33. Fig. 9(a) is a plan view of the second heater wire 50 and a second heater lead-out portion 54 and a second heater terminal portion 56 formed of a film in the same layer as the second heater wire 50, and Fig. 9(b) is a partial enlarged view showing an enlarged view of the periphery of the second heater wire 50 in Fig. 9(a).

[0043] 9(a) with FIG. 1, the second heater wiring 50 is disposed in a position overlapping the opening 22 of the substrate 20 in a plan view, and the second heater terminal portion 56 is provided on the upper side of the substrate upper surface 24 of the substrate 20. The second heater lead portion 54 connects the second heater wiring 50 and the second heater terminal portion 56. A portion of the second heater lead portion 54 is disposed in a position overlapping the opening 22 in a plan view and is provided between the second insulating film 32 and the third insulating film 33. In addition, another portion of the second heater lead portion 54 is provided on the upper side of the substrate upper surface 24, between the second insulating film peripheral portion 37 (see FIG. 10(a)) and the third insulating film peripheral portion 38 (see FIG. 8(a)).

[0044] 9(b) and 5, the second heater wiring 50 has a flat portion 50b disposed in the center of the insulating film 30 and a heat generating portion 50a formed in a spiral shape around the flat portion 50b. The heat generating portion 50a has a smaller cross-sectional area perpendicular to the electrical conduction direction than the flat portion 50b and the second heater lead portion 54. Therefore, by passing a current through the second heater wiring 50 and the second heater lead portion 54, the heat generating portion 50a generates heat effectively.

[0045] 11(a) is a plan view of the first heater wire 40, as well as the first heater lead-out portion 44, the first heater terminal portion 46, and the discontinuous portion 45, which are made of the same film layer as the first heater wire 40, and Fig. 11(b) is a partially enlarged view showing the periphery of the first heater wire 40 in Fig. 11(a). As can be seen from a comparison of Fig. 11(a) with Fig. 9(a), the planar shape of the first heater wire 40 is similar to that of the second heater wire 50.

[0046] 11(a) and 1, the first heater wiring 40 is disposed in a position overlapping the opening 22 of the substrate 20 in a plan view, and the first heater terminal 46 is provided above the substrate upper surface 24 of the substrate 20. The first heater lead 44 connects the first heater wiring 40 and the first heater terminal 46. A portion of the first heater lead 44 is disposed in a position overlapping the opening 22 in a plan view and is provided between the first insulating film 31 and the second insulating film 32. Another portion of the first heater lead 44 is provided above the substrate upper surface 24, between the first insulating film peripheral portion 36 (see FIG. 12(a)) and the second insulating film peripheral portion 37 (see FIG. 10(a)). The discontinuous portion 45 is formed on the second heater terminal 56 (see FIG. 9) and connects the surface electrode portion 74 (see FIG. 1) exposed on the surface to the second heater terminal 56 (see FIG. 3).

[0047] As shown in FIG. 5, the flat portion 40b of the first heater wiring 40 and the flat portion 50b of the second heater wiring 50 are in direct contact with each other, and the first heater wiring 40 and the second heater wiring 50 are electrically connected in series. That is, as shown in FIGS. 10(a) and 10(b), a heater connection hole 32j is formed in the second insulating film 32 disposed between the first heater wiring 40 and the second heater wiring 50. As shown in FIG. 5, the second insulating film 32 insulates the heat-generating portion 40a of the first heater wiring 40 from the heat-generating portion 50a of the second heater wiring 50, but the flat portions 40b, 50b of the first heater wiring 40 and the second heater wiring 50 are in contact with each other via the heater connection hole 32j. Therefore, when a potential difference is generated between the first heater terminal 46 and the second heater terminal 56 shown in FIG. 1, a current flows through the first heater wiring 40 and the second heater wiring 50, which are connected in series.

[0048] 11(b) is greater than the resistance value of the second heater wiring 50 shown in FIG. 9(b). That is, as shown in FIG. 5, the film thickness of the first heater wiring 40 is thinner than the film thickness of the second heater wiring 50, and therefore the heat-generating portion 40a of the first heater wiring 40 has a smaller cross-sectional area perpendicular to the electrical conduction direction than the heat-generating portion 50a of the second heater wiring 50. When a current is passed through such first heater wiring 40 and second heater wiring 50, the amount of heat generated in the first heater wiring 40 is greater than the amount of heat generated in the second heater wiring 50.

[0049] As shown in FIG. 5, the insulating film 30 sandwiching the first heater wiring 40 and the second heater wiring 50 is substantially flat when the first heater wiring 40 and the second heater wiring 50 are not energized. On the other hand, when energization of the first heater wiring 40 and the second heater wiring 50 is started during gas detection, the insulating film 30 and the first heater wiring 40 and the second heater wiring 50 undergo thermal expansion according to the amount of heat generated. At this time, the amount of thermal expansion of the first heater wiring 40 and its surroundings, which is relatively higher, becomes larger than the amount of thermal expansion of the second heater wiring 50 and its surroundings, which is relatively lower. Therefore, as shown in FIG. 6, the insulating film 30 warps and protrudes upward during gas detection.

[0050] The method for making the resistance value of the first heater wiring 40 greater than the resistance value of the second heater wiring 50 is not limited to making the film thicknesses of the first heater wiring 40 and the second heater wiring 50 different. For example, other possible methods include making the widths or wiring lengths of the heat generating portions 50a, 40a in the film surface direction D2 different between the first heater wiring 40 and the second heater wiring 50, or making the materials of the first heater wiring 40 and the second heater wiring 50 different.

[0051] The materials for the first heater wire 40, first heater lead portion 44, first heater terminal portion 46, discontinuous portion 45, second heater wire 50, second heater lead portion 54, and second heater terminal portion 56 are not particularly limited as long as they are conductive. However, a material with a relatively high melting point is preferable from the viewpoint of enabling high-temperature processes in the formation of the gas detection unit 60. Examples of such materials include molybdenum (Mo), platinum (Pt), nickel (Ni), chromium (Cr), tungsten (W), tantalum (Ta), palladium (Pd), iridium (Ir), and alloys containing two or more of these (e.g., nickel-chromium alloy (NiCr)). In this embodiment, platinum (Pt) is particularly preferable because it allows high-precision patterning such as lift-off and has high durability. The first heater wire 40 and the second heater wire 50 may be made of the same material or different materials.

[0052] (1.5. Gas detection unit) 2, the gas detection unit 60 is provided on the upper surface of the insulating film 30. As shown in Fig. 5, in the gas sensor 10 in which the insulating film 30 is a multilayer film made up of first to third insulating films 31, 32, and 33, the gas detection unit 60 is provided on the upper surface of the first insulating film 31 located above the first heater wiring 40. The gas detection unit 60 has a thermistor film 61 and electrodes 62a and 62b that detect a change in resistance of the thermistor film 61.

[0053] Figure 13(a) is a plan view of electrode portions 62a, 62b and electrode lead portions 64a, 64b and electrode terminal portions 66a, 66b which are made of the same film as electrode portions 62a, 62b, and Figure 13(b) is a partially enlarged view showing the area around electrode portions 62a, 62b in Figure 13(a).

[0054] As shown in FIG. 13(a), the electrode terminals 66a and 66b are disposed above the upper surface 24 of the substrate 20. The electrode lead-out portion 64a connects the electrode terminal 66a to the electrode portion 62a provided on the first insulating film 31. The electrode lead-out portion 64b connects the electrode terminal 66b to the electrode portion 62b provided on the first insulating film 31. As shown in FIG. 13(b), the electrode portion 62a and the electrode portion 62b are formed on the first insulating film 31 with a predetermined distance between them.

[0055] Fig. 14(a) is a plan view showing the planar shape of the thermistor film 61 and its arrangement on the substrate 20, and Fig. 14(b) is a partially enlarged view showing the periphery of the thermistor film 61 in Fig. 14(a). The thermistor film 61 is provided on the upper side of the insulating film 30, and in particular, as shown in Fig. 5, it is provided on the first insulating film 31 in the central portion thereof so as to connect the electrode portion 62b and the electrode terminal portion 66b. As shown in Figs. 1 and 5, the thermistor film 61 and the flat portions 40b, 50b of the first heater wiring 40 and the second heater wiring 50 are arranged so as to at least partially overlap each other when viewed from above.

[0056] When the gas detection unit 60 is detecting a gas that can be detected, the first heater wiring 40 and the second heater wiring 50 are energized to generate heat, thereby heating the gas detection unit 60 to a temperature at which the gas detection unit 60 can properly detect the gas. The thermistor film 61 in the gas detection unit 60 may be made of a material such as CoNiMnOx, but may also be made of other materials whose resistance value changes when in contact with a specific gas. The electrodes 62a, 62b, the electrode leads 64a, 64b, and the electrode terminals 66a, 66b may be made of conductive materials such as platinum (Pt), silver (Ag), gold (Au), and aluminum (Al).

[0057] 1 and 3, surface electrodes 71, 72, 73, and 74 are formed on the uppermost layers of the electrode terminals 66a and 66b and the first and second heater terminals 46 and 56. Examples of materials for the surface electrodes 71, 72, 73, and 74 include conductive materials such as platinum (Pt), silver (Ag), gold (Au), and aluminum (Al).

[0058] (1.6. Manufacturing method) An example of a method for manufacturing the gas sensor 10 will be described below. However, the method for manufacturing the gas sensor 10 is not limited to the manufacturing method described below. In manufacturing the gas sensor 10, first, a substrate material that will be the raw material for the substrate 20 is prepared. The substrate material is flat and has no openings 22 formed therein. Next, a third insulating film 33, a third insulating film peripheral portion 38, etc. (see FIG. 8 ) are formed on a substrate upper surface 24, which is one of the main surfaces of the prepared substrate material. The third insulating film 33 and the third insulating film peripheral portion 38 may be formed by a known film formation method such as thermal oxidation or CVD (Chemical Vapor Deposition).

[0059] Next, the second heater wiring 50 is formed on the third insulating film 33. In the process of forming the second heater wiring 50, the second heater lead portion 54 and the second heater terminal portion 56, which are made of the same film as the second heater wiring 50, are also formed at the same time (see FIG. 9(a)). The shapes of the second heater wiring 50, the second heater lead portion 54, and the second heater terminal portion 56 are formed, for example, by a lift-off process. In the lift-off process, first, a resist is applied to the entire surface on which a predetermined pattern is to be formed, and then the resist is exposed and developed to form the predetermined pattern. By development, the resist corresponding to the predetermined pattern shape is dissolved, and the predetermined pattern shape is patterned. After the resist is dissolved, a film of material that constitutes the pattern is formed by a film formation method such as sputtering or vapor deposition. After film formation, the remaining resist is removed with a stripper, thereby removing the material formed on the resist, and the material formed on the resist remains only in the patterned area, forming the predetermined pattern.

[0060] Next, the second insulating film 32 is formed on the second heater wiring 50. In the process of forming the second insulating film 32, a second insulating film peripheral portion 37 made of the same film as the second insulating film 32 is also formed at the same time (see FIG. 10(a)). In the process of forming the second insulating film 32 and the second insulating film peripheral portion 37, they are formed using a known film formation method or the like, similar to the formation of the first insulating film 31.

[0061] Next, the first heater wiring 40 is formed on the second insulating film 32. In the process of forming the first heater wiring 40, the first heater lead-out portion 44, the first heater terminal portion 46, and the discontinuous portion 45, which are made of the same film as the first heater wiring 40, are also formed at the same time (see FIG. 11(a)). The method of forming the first heater wiring 40, etc. is the same as the method of forming the second heater wiring 50 described above.

[0062] Next, the first insulating film 31 is formed on the first heater wiring 40. In the process of forming the first insulating film 31, a first insulating film peripheral portion 36 made of the same film as the first insulating film 31 is also formed at the same time (see FIG. 12(a)). In the process of forming the first insulating film 31 and the first insulating film peripheral portion 36, a known film formation method or the like can be used, as in the process of forming the third insulating film 33 and the second insulating film 32.

[0063] Next, the gas detection unit 60 is formed on the first insulating film 31. In the process of forming the gas detection unit 60, the electrode portions 62a, 62b, electrode lead portions 64a, 64b, and electrode terminal portions 66a, 66b shown in FIG. 13(a) are formed in the same film formation process, and then the thermistor film 61 (see FIG. 14) is formed on the electrode portions 62a, 62b. The shapes of the electrode portions 62a, 62b, etc. are formed by a lift-off method or the like, similar to the first and second heater wirings 40, 50. Furthermore, surface electrode portions 71-74 are formed on the upper sides of the first and second heater terminal portions 46, 56 and the electrode terminal portions 66a, 66b. The thermistor film 61 may be formed on the electrode portions 62a, 62b after the process of forming the surface electrode portions 71-74 and the process of forming the opening portion 22, which will be described later.

[0064] Next, an etching mask is applied to a predetermined region of the main surface of the substrate material on which the third insulating film 33, the third insulating film peripheral portion 38, etc. are not formed, and the substrate material is etched until the third insulating film 33, etc. formed on the opposite main surface (substrate upper surface 24) is exposed, thereby forming the opening 22. This results in the gas sensor 10 having the insulating film 30 arranged at a position overlapping the opening 22 in a plan view, as shown in FIG.

[0065] (1.7.Operation) In the gas sensor 10, the first heater wiring 40 and the second heater wiring 50 are connected to an external circuit (not shown) via the first and second heater lead-out portions 44, 54, the first and second heater terminal portions 46, 56, the surface electrode portions 71, 72, etc. Furthermore, the electrode portions 62a, 62b of the gas detection unit 60 are connected to an external circuit (not shown) via the electrode lead-out portions 64a, 64b, the electrode terminal portions 66a, 66b, the surface electrode portions 73, 74, etc. When the gas sensor 10 is operated, current is applied from the control unit and the external circuit to the first and second heater wirings 40, 50, and the gas detection unit 60 and its surrounding area are heated to a predetermined temperature, thereby enabling the gas detection unit 60 to detect gas.

[0066] 5, the insulating film 30 sandwiching the first heater wiring 40 and the second heater wiring 50 is substantially flat when the first heater wiring 40 and the second heater wiring 50 are not energized. However, after energization of the first and second heater wirings 40, 50 begins, when the gas detection unit 60 is capable of detecting a gas, the insulating film 30 becomes warped and protrudes upward as shown in FIG. 6. This is because, in the first and second heater wirings 40, 50 that are directly connected, the resistance value of the first heater wiring 40 is greater than the resistance value of the second heater wiring 50, and the amount of heat generated in the first heater wiring 40 is greater than the amount of heat generated in the second heater wiring 50.

[0067] 15 is a conceptual diagram showing the shape of the gas sensor 10 during gas detection and the flow of gas through the gas sensor 10. As shown in Fig. 15, during gas detection, gas may flow in the vertical direction D1 as indicated by arrow 91, or in the film surface direction D2 as indicated by arrows 92 and 93. If the insulating film 30 of the gas sensor 10 were flat even during gas detection, the gas detection unit 60 of the gas sensor 10 would have fewer opportunities to detect the gas flow in the film surface direction D2 as indicated by arrows 92 and 93, which could result in a delay in the detection output.

[0068] 15, the insulating film 30 of the gas sensor 10 is warped upward during gas detection. Therefore, in the gas sensor 10, the gas detection unit 60 has a greater chance of detecting a gas flow in the film surface direction D2 as indicated by arrows 92 and 93 than when the insulating film 30 is flat. This allows the gas sensor 10 to exhibit high-speed response even to a gas flow in the film surface direction D2. Note that the gas sensor 10 exhibits the same response to a gas flow in the up-down direction D1 as when the insulating film 30 is flat.

[0069] (2. Second Embodiment) FIG. 16(a) is a plan view showing the shape of the gas detection unit 160 in the gas sensor 110 according to the second embodiment of the present disclosure, and FIG. 16(b) is a partially enlarged view showing the periphery of the MOx material film 161 shown in FIG. 16(a). The gas sensor 110 differs from the gas sensor 10 according to the first embodiment in that the gas detection unit 160 has the MOx material film 161, which is a metal oxide film, instead of the thermistor film 61. However, the gas sensor 110 is otherwise similar to the gas sensor 10 shown in FIG. 1. When the gas detection unit 160 comes into contact with a gas to be detected, an oxidation-reduction reaction occurs, causing a change in the resistance value of the metal oxide film. The gas to be detected by the gas detection unit 160 can be, for example, a combustible gas or a reducing gas, such as carbon monoxide (CO), methane (CH), propane (C3H8), ethanol (C2H5OH), or hydrogen (H2). Examples of the MOx material film 161, which is a metal oxide film, include tin oxide (SnO2), zirconium oxide (ZrO2), iron oxide (Fe2O3), tungsten oxide (WO3), indium oxide (In2O3), cobalt oxide (Co3O4), etc. The MOx material film 161 may carry particles of a noble metal such as platinum (Pt) or palladium (Pd).

[0070] The MOx material film 161 shown in Fig. 16(a) is provided on the upper surface of the insulating film 30 (see Fig. 5), similar to the thermistor film 61 shown in Fig. 14(a). In particular, as shown in Figs. 5 and 16, the MOx material film 161 is provided on the first insulating film 31 in the center of the first insulating film 31 so as to connect the electrode portion 62b and the electrode terminal portion 66b.

[0071] 1, the gas sensor 110 has a first heater wiring 40 and a second heater wiring 50 provided in a multilayer insulating film 30. Similar to the gas sensor 10, the gas sensor 110 is heated to a temperature at which the gas detection unit 160 can properly detect gas by the first heater wiring 40 and the second heater wiring 50 being energized and generating heat during gas detection.

[0072] 15, the gas sensor 110 has a curved shape in which the insulating film 30 protrudes upward during gas detection, and has a fast response speed during gas detection. In addition, the gas sensor 110 shown in Fig. 16 has the same common features as the gas sensor 10 shown in Fig. 1 and the like, and exhibits the same effects as the gas sensor 10.

[0073] (3. Third Embodiment) FIG. 17(a) is a plan view showing the planar shapes of the first heater wire 240, first heater lead-out portions 244a and 244b, first heater terminal portions 246a and 246b, the second insulating film 232, and the second insulating film peripheral portion 237 in a gas sensor 210 according to a third embodiment of the present disclosure. FIG. 16(b) is a cross-sectional view showing the first insulating film 31, the second insulating film 232, the third insulating film 33, the first heater wire 240, and the second heater wire 250 in the gas sensor 210. Note that in FIG. 17(a), the outlines of the components are overlapped so that the shape of the underlying second insulating film 232 can be seen. In FIGS. 17(a) and 17(b), the gas detection unit, substrate, and the like of the gas sensor 210 are omitted.

[0074] The gas sensor 210 according to the third embodiment differs from the gas sensor 10 in that the first heater wiring 240 and the second heater wiring 250 are electrically connected in parallel and the resistance value of the first heater wiring 240 is smaller than the resistance value of the second heater wiring 250. However, the gas sensor 210 is similar to the gas sensor 10 according to the first embodiment except for the connection method between the first heater wiring 240 and the second heater wiring 250. The following description of the gas sensor 210 will focus on the differences from the gas sensor 10, and a description of the commonalities with the gas sensor 10 will be omitted.

[0075] The insulating film 230 of the gas sensor 210 is a multilayer film having a first insulating film 31, a second insulating film 232 provided below the first insulating film 31, and a third insulating film 33 provided below the second insulating film 232. The planar shapes of the first insulating film 31 and the third insulating film 33 are the same as those of the gas sensor 10. Although not shown in FIG. 17 , the planar shapes of the first insulating film peripheral portion 36 made of the same film as the first insulating film 31 and the third insulating film peripheral portion 38 made of the same film as the third insulating film 33 are also the same as those of the gas sensor 10.

[0076] On the other hand, unlike the second insulating film 32 shown in Fig. 10(a), the second insulating film 232 of the gas sensor 210 shown in Fig. 17(a) does not have a heater connection hole 32j formed in the center. That is, as shown in Fig. 17(b), no through-hole is formed in the center 232e of the second insulating film 232, and the second insulating film 232 electrically insulates the first heater wiring 240 on the upper side from the second heater wiring 250 on the lower side.

[0077] 17(b), heater insertion holes 232l and 232k are formed in a second insulating film peripheral portion 237 that is made of the same film as the second insulating film 232. As will be described later, the first heater wiring 240 is drawn out from the center of the opening 22 (see FIG. 1) to two first heater terminal portions 246a and 246b that are formed in two locations on the upper side of the base material upper surface 24. Two heater insertion holes 232l and 232k that correspond to the two first heater terminal portions 246a and 246b are formed in the second insulating film peripheral portion 237.

[0078] 17(a) and 17(b) is provided between the first insulating film 31 and the second insulating film 232, similar to the first heater wiring 40 shown in FIGS. 11(a) and 5. When viewed from above, the first heater wiring 240 is disposed in the opening 22 of the substrate 20, and first heater terminal portions 246a and 246b are provided on the upper side of the substrate upper surface 24 of the substrate 20. The first heater wiring 240 has a central flat portion 240b and heat-generating portions 240a and 240c formed in a spiral shape so as to surround the flat portion 240b.

[0079] The heat generating units 240a and 240c have two spiral-like planar shapes that do not overlap each other when viewed from above, with the central flat portion 240b at the center. The outer end of the heat generating unit 240a is connected to the first heater lead-out portion 244a at the bottom right of Figure 17(a) and is connected to the first heater terminal portion 246a via the first heater lead-out portion 244a. Meanwhile, the outer end of the heat generating unit 240c is connected to the first heater lead-out portion 244b at the top left of Figure 17(a) and is connected to the first heater terminal portion 246g via the first heater lead-out portion 244b.

[0080] 9(a) and 5, the second heater wiring 250 shown in FIG. 17(b) is provided between the second insulating film 232 and the third insulating film 33. Although not shown in FIG. 17(a), the second heater wiring 250 has a planar shape similar to that of the first heater wiring 240, and includes a central flat portion 250b and heat-generating portions 250a and 250c formed in a spiral shape surrounding the flat portion 250b. Similarly to the first heater wiring 240, the second heater wiring 250 is connected to two second heater terminals located below the first heater terminals 246a and 246b via two second heater lead portions.

[0081] As described above, no heater connection hole is formed in the second insulating film 232 between the first heater wiring 240 and the second heater wiring 250. Therefore, the first heater wiring 240 and the second heater wiring 250 are electrically insulated from each other within the insulating film 30 shown in FIG.

[0082] 17(a), the first heater terminal 246a is electrically connected to the second heater terminal located below it, and the first heater terminal 246b is electrically connected to the second heater terminal located below it. In this way, the first heater wiring 240 and the second heater wiring 250 of the gas sensor 210 are electrically connected in parallel.

[0083] 17(b), unlike the first heater wiring 40 and the second heater wiring 50 of the gas sensor 10 shown in FIG. 5, the resistance value of the first heater wiring 240 is smaller than the resistance value of the second heater wiring 250. When a current is passed through such first heater wiring 240 and second heater wiring 250, the amount of heat generated in the first heater wiring 240 is greater than the amount of heat generated in the second heater wiring 250.

[0084] 5, the gas sensor 210 also has a gas detection unit provided on the upper surface of the first insulating film 31. Therefore, similar to the gas sensor 10, when the gas detection unit detects a gas that can be detected, the insulating film 230 of the gas sensor 210 also has a warped shape that protrudes upward, similar to the insulating film 30 shown in FIG. 6, thereby increasing the chance of detecting the target gas. In addition, the gas sensor 210 shown in FIG. 17 has similar features to the gas sensor 10 shown in FIG. 1 and the like, and thus exhibits the same effects as the gas sensor 10.

[0085] (4. Fourth Embodiment) FIG. 18(a) is a plan view showing the planar shapes of the substrate 20, insulating film 30, insulating film peripheral portion 35, first heater wiring 340, first heater lead portion 44, first heater terminal portion 46, second heater wiring 350, second heater lead portion 54, and second heater terminal portion 56 in a gas sensor 310 according to a fourth embodiment of the present disclosure. FIG. 18(b) is a cross-sectional view showing the first insulating film 31, second insulating film 32, third insulating film 33, first heater wiring 340, and second heater wiring 350 in the gas sensor 310. Note that in FIG. 18(a), only the substrate 20 and third insulating film 33 are shown opaque, and the other components are shown with outlines superimposed so that the shapes of the underlying components can be seen. In FIGS. 18(a) and 18(b), the gas detection unit and other components of the gas sensor 310 are omitted.

[0086] As shown in FIG. 18( b), the insulating film 30 of the gas sensor 310 is a multilayer film including a first insulating film 31, a second insulating film 32 provided below the first insulating film 31, and a third insulating film 33 provided below the second insulating film 32. The planar shape of the insulating film 30 is similar to that of the gas sensor 10. However, the first insulating film 31 and the second insulating film 32 of the gas sensor 310 are flattened to prevent irregularities from forming on the upper surfaces of these films that trace the irregularities on the lower surfaces on which the films are formed. In the gas sensors of the respective embodiments, whether or not the upper surfaces of the first insulating film 31 and the second insulating film 32 are flattened is optional. The upper surfaces of the first insulating film 31 and the second insulating film 32 of the gas sensor 10 may be flattened, while the upper surfaces of the first insulating film 31 and the second insulating film 32 of the gas sensor 310 may not be flattened. The following description of the gas sensor 310 will focus on the differences from the gas sensor 10, and a description of the commonalities between the gas sensor 10 and the gas sensor 10 will be omitted.

[0087] 11(a) and 5, the first heater wiring 340 shown in Figures 18(a) and 18(b) is provided between the first insulating film 31 and the second insulating film 32. When viewed from above, the first heater wiring 340 is disposed in the opening 22 of the substrate 20, and the first heater terminal portion 46 is provided above the substrate upper surface 24 of the substrate 20. The first heater wiring 340 has a central flat portion 340b and a heat-generating portion 340a formed in a spiral shape so as to surround the flat portion 340b.

[0088] 9(a) and 5, the second heater wiring 350 is provided between the second insulating film 32 and the third insulating film 33. When viewed from above, the second heater wiring 350 is disposed in the opening 22 of the substrate 20, and the second heater terminal portion 56 is provided above the substrate upper surface 24 of the substrate 20. The second heater wiring 50 has a central flat portion 350b and a heat-generating portion 350a formed in a spiral shape so as to surround the flat portion 350b.

[0089] 18(b), the flat portion 340b of the first heater wiring 340 and the flat portion 350b of the second heater wiring 350 are in direct contact with each other, and the first heater wiring 340 and the second heater wiring 350 are electrically connected in series. That is, a heater connection hole 32j is formed in the second insulating film 32 disposed between the first heater wiring 340 and the second heater wiring 350, and the flat portion 340b of the first heater wiring 340 and the flat portion 350b of the second heater wiring 350 are connected via the heater connection hole 32j.

[0090] 18(b), the heat generating portion 340a of the first heater wiring 340 and the heat generating portion 350a of the second heater wiring 350 have different cross-sectional shapes in a cross section passing through the center of the opening 22 and perpendicular to the upper surface 24a of the substrate. That is, the heat generating portion 340a of the first heater wiring 340 is thinner in the up-down direction D1 and wider in the film surface direction D2 than the heat generating portion 350a of the second heater wiring 350.

[0091] In the gas sensor 310, the amount of expansion of the first heater wire 340 in the film surface direction D2 when heated relative to when not heated is larger than the amount of expansion of the second heater wire 350 in the film surface direction D2 when heated relative to when not heated. This is because the amount of expansion of the heat generating parts 340a, 350a in the film surface direction D2 is proportional to the width of the heat generating parts 340a, 350a in the film surface direction D2.

[0092] 18(a) and 18(b), the gas detection unit of the gas sensor 310 is provided on the upper surface of the first insulating film 31, similar to the gas detection unit 60 of the gas sensor 10 shown in FIG. 2 etc. When the gas sensor 350 detects gas, if the first heater wiring 340 and the second heater wiring 350 are energized to generate heat, the insulating film 30 of the gas sensor 310 will be warped and protrude upward due to the difference in the amount of expansion described above (see FIGS. 6 and 15).

[0093] Therefore, in the gas sensor 310, the gas detection unit has more opportunities to detect a gas flow in the film surface direction D2, and the response speed of the output is improved. In the gas sensor 310, even if the resistance values ​​of the first heater wiring 340 and the second heater wiring 350 are the same, by making the aspect ratios, which are the ratios of the thickness in the up-down direction D1 to the width in the film surface direction D2, of the heat generating parts 340a, 350a different from each other, it is possible to cause the heat generating parts 340a, 350a to warp and protrude upward relative to the insulating film 30. In addition, the gas sensor 310 shown in FIG. 18 has similar effects to the gas sensor 10 shown in FIG. 1 etc. in terms of commonalities.

[0094] (5. Fifth Embodiment) FIG. 19(a) is a plan view showing the planar shapes of the substrate 20, insulating film 230, insulating film peripheral portion 435, first heater wire 240, first heater lead portions 244a and 244b, first heater terminal portions 246a and 246b, second heater wire 250, second heater lead portions 454a and 454b, and second heater terminal portions 456a and 456b in a gas sensor 410 according to a fifth embodiment of the present disclosure. FIG. 18(b) is a cross-sectional view showing the first insulating film 31, second insulating film 232, third insulating film 33, first heater wire 240, and second heater wire 250 in the gas sensor 410. Note that in FIG. 18(a), only the substrate 20 and third insulating film 33 are shown opaque, and the other components are shown with outlines superimposed so that the shapes of the underlying components can be seen. In FIGS. 19(a) and 19(b), the gas detection unit and other components of the gas sensor 410 are omitted.

[0095] 19(b) and 17(b), the shapes of the insulating film 230, the first heater wiring 240, and the second heater wiring 250 of the gas sensor 410 are similar to those of the gas sensor 210 according to the third embodiment. However, the gas sensor 410 differs from the gas sensor 210 in that the second heater wiring 250 of the gas sensor 410 is connected to second heater terminals 456a and 456b that are provided independently of the first heater terminals 246a and 246b to which the first heater wiring 240 is connected. The following description of the gas sensor 410 will focus on the differences from the gas sensor 210, and a description of the commonalities with the gas sensor 210 will be omitted.

[0096] 19(b), the insulating film 230 of the gas sensor 410 is a multilayer film including a first insulating film 31, a second insulating film 232 provided below the first insulating film 31, and a third insulating film 33 provided below the second insulating film 232. The second insulating film 232 of the gas sensor 410 does not have a through-hole formed in a central portion 232e, similar to the second insulating film 232 shown in FIG. 17(a), and electrically insulates the first heater wiring 240 on the upper side from the second heater wiring 250 on the lower side.

[0097] 19(a), in the gas sensor 410, the positions of the first heater terminals 246a, 246b do not overlap the positions of the second heater terminals 456a, 456b when viewed from above. Furthermore, the second heater drawer 454a, which connects the heat generating unit 250a and the second heater terminal 456a, has a different shape from the first heater drawer 244a. Furthermore, the second heater drawer 454b, which connects the heat generating unit 250c and the second heater terminal 456b, has a different shape from the first heater drawer 244b.

[0098] 19(a), heater insertion holes 431k, 431l, etc., which enable electrical connection to the second heater terminals 456a, 456b, are formed in the first insulating film peripheral portion and the second insulating film peripheral portion 435 provided on the second heater terminals 456a, 456b. In the gas sensor 410, the first heater wiring 240, the first heater lead-out portions 244a, 244b, and the first heater terminals 246a, 246b connected thereto, are insulated from the second heater wiring 250, the second heater lead-out portions 454a, 454b, and the second heater terminals 456a, 246b connected thereto. Therefore, the first heater wiring 240 and the second heater wiring 250 are electrically independent.

[0099] 19(a), the first heater wiring 240 and the second heater wiring 250 are independently connected to a controller and an external circuit via first heater terminals 246a and 246b and second heater terminals 456a and 456b, respectively. Therefore, the current or voltage applied to the first heater wiring 240 and the current or voltage applied to the second heater wiring 250 can be independently controlled by, for example, independent control signals transmitted from a controller.

[0100] In this gas sensor 410, even if the first heater wiring 240 and the second heater wiring 250 are made of the same material and have the same shape, the heat generation amounts of the first heater wiring 240 and the second heater wiring 250 can be controlled arbitrarily. Therefore, the gas sensor 410 can control the current value and the like so that the heat generation amount of the first heater wiring 240 is greater than that of the second heater wiring 250, thereby enabling the insulating film 230 to be curved upwardly, as shown in FIG. 6 . This allows the gas sensor 410 to improve the response speed when detecting a target gas. Furthermore, the gas sensor 410 shown in FIG. 18 has similar features to the gas sensor 210 shown in FIG. 17 and other figures, and thus provides the same effects as the gas sensor 210.

[0101] Although the gas sensor according to the present disclosure has been described above using embodiments, it goes without saying that the gas sensor according to the present disclosure is not limited to these embodiments and includes many other embodiments and modifications. For example, the insulating film of the gas sensor is not limited to the three-layer multilayer film shown in the embodiments, but may be a two-layer or four-layer or more multilayer film. Furthermore, the installation direction of the gas sensor is arbitrary, and the up-down direction D1 of the gas sensor when installed may be different from or may be the same as the vertical direction.

[0102] Furthermore, the gas sensor according to the present disclosure is not limited to the first to fifth embodiments in which the insulating film warps upward when the heater is energized. It is also possible to consider embodiments in which the insulating film warps upward and protrudes even before the heater is energized. For example, by setting the formation temperature (substrate temperature during film formation) of the first insulating film 31, which is the upper insulating film, higher than the formation temperature of the third insulating film 33, which is the lower insulating film, stress is generated in the third insulating film 33 and the first insulating film 31, causing the insulating films to warp upward and protrude even before the heater is energized. Since the stress on the insulating film is supported by the substrate 20 before the opening 22 is formed, the third insulating film 33 and the first insulating film 31 do not warp during the manufacturing stage before the opening 22 is formed, and this does not interfere with the formation of the heater wiring and the gas detection unit. In addition, in such a gas sensor, the heater wiring can be formed as a single-layer structure using the second heater wiring 50, thereby omitting the first heater wiring 40. Alternatively, the insulating film can be formed as a two-layer structure using the first and third insulating films 31 and 33, thereby omitting the second insulating film 32.

[0103] Another example of an embodiment in which the insulating films are warped upward when current is applied to the heater is to increase the film density of the first insulating film 31, which is the upper insulating film, to a value higher than that of the third insulating film 33, which is the lower insulating film. The film densities of the first and third insulating films 31, 33 can be adjusted, for example, by varying the gas pressures during the deposition of the first and third insulating films 31, 33 to thereby vary the amounts of gas components absorbed into the first and third insulating films 31, 33. For example, a relatively low gas pressure during deposition results in a relatively high film density, whereas a relatively high gas pressure during deposition results in a relatively low film density. In this gas sensor, the heater wiring can be configured as a single-layer structure using the second heater wiring 50, thereby omitting the first heater wiring 40. Alternatively, the insulating film can be configured as a two-layer structure using the first and third insulating films 31, 33, thereby omitting the second insulating film 32.

[0104] Furthermore, in the gas sensor according to the present disclosure, there is no particular limitation on how much the insulating film 30 is warped to protrude upward, but it is preferable that the amount of upward protrusion (protrusion height H1) of the insulating film 30 during gas detection be, for example, 1% or more of the maximum width W1 in the film surface direction D2 of the insulating film 30 that overlaps with the opening 22 in a planar view (see Figure 15). [Explanation of symbols]

[0105] 10, 110, 210, 310, 410...Gas sensor 20...Base material 22...Opening 24…Top surface of base material 30, 230...insulating film 31a, 31b, 31c, 31d, 32a, 32b, 32c, 32d, 33a, 33b, 33c, 33d...beam section 33e, 32e, 31e, 232e...Central part 31f, 31g, 31h, 31i, 32f, 32g, 32h, 32i, 33f, 33g 33h, 33i...Peripheral hole 31...First insulating film 32, 232...Second insulating film 33...Third insulating film 32j...Heater connection hole 32k, 232k, 232l, 431k, 431l...Heater insertion hole 35...Insulating film peripheral portion 36...periphery of first insulating film 37, 237...periphery of second insulating film 38...periphery of third insulating film 40, 240, 340...1st heater wiring 40a, 50a, 250a, 250c, 240a, 240c, 350a, 340a...heat generating part 40b, 50b, 250b, 240b, 350b, 340b...Flat area 44, 244a, 244b...First heater drawer 45...Discontinuous section 46, 246a, 246b...First heater terminal 50, 250, 350...Second heater wiring 54, 454a, 454b...Second heater drawer 56, 454a, 456b...Second heater terminal 60, 160...Gas detector 61...Thermistor film 62a, 62b...electrode part 64a, 64b...electrode extraction part 66a, 66b...electrode terminal section 71, 72, 73, 74...Surface electrode part 91, 92, 93...Arrows D1…Vertical direction D2…Membrane surface direction 161…MOx material film

Claims

1. a substrate in which an opening is formed; an insulating film disposed at a position overlapping the opening in a plan view; a gas detection unit provided on an upper surface of the insulating film, The gas sensor has a configuration in which, when the gas detection unit is capable of detecting a gas, the insulating film is warped so as to protrude upward.

2. the insulating film is a multilayer film having a first insulating film, a second insulating film provided below the first insulating film, and a third insulating film provided below the second insulating film; the gas detection unit is provided on an upper surface of the first insulating film, a first heater wiring provided between the first insulating film and the second insulating film; a second heater wiring provided between the second insulating film and the third insulating film; 2. The gas sensor according to claim 1, wherein the first heater wire and the second heater wire are electrically connected in series, and the resistance value of the first heater wire is greater than the resistance value of the second heater wire.

3. the insulating film is a multilayer film having a first insulating film, a second insulating film provided below the first insulating film, and a third insulating film provided below the second insulating film; the gas detection unit is provided on an upper surface of the first insulating film, a first heater wiring provided between the first insulating film and the second insulating film; a second heater wiring provided between the second insulating film and the third insulating film; 2. The gas sensor according to claim 1, wherein the first heater wiring and the second heater wiring are electrically connected in parallel, and the resistance value of the first heater wiring is smaller than the resistance value of the second heater wiring.

4. the insulating film is a multilayer film having a first insulating film, a second insulating film provided below the first insulating film, and a third insulating film provided below the second insulating film; the gas detection unit is provided on an upper surface of the first insulating film, a first heater wiring provided between the first insulating film and the second insulating film; a second heater wiring provided between the second insulating film and the third insulating film; 2. The gas sensor according to claim 1, wherein the amount of expansion of the first heater wire in the film surface direction when heated compared to when not heated is larger than the amount of expansion of the second heater wire in the film surface direction when heated compared to when not heated.

5. the insulating film is a multilayer film having a first insulating film, a second insulating film provided below the first insulating film, and a third insulating film provided below the second insulating film; the gas detection unit is provided on an upper surface of the first insulating film, a first heater wiring provided between the first insulating film and the second insulating film; a second heater wiring provided between the second insulating film and the third insulating film; 2. The gas sensor according to claim 1, wherein the first heater wiring and the second heater wiring are electrically independent from each other.

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