Gas sensor

Abstract

A gas sensor capable of improving durability can be provided.　This gas sensor (10) comprises: a gas sensor element (20); a substrate (30); and a support part (40) that joins the gas sensor element (20) and the substrate (30). The gas sensor element (20) has: a heater (24); and an element-side electrode pad (22) and a heater-side electrode pad (23). When the outer shape of the gas sensor is viewed from the plate thickness direction of the substrate (30), the support part (40) overlaps a section of the gas sensor element (20) and a section of the substrate (30), and the support part (40) is disposed at a position closer to the center of gravity (G) of the gas sensor element (20) than to the element-side electrode pad (22) and the heater-side electrode pad (23).

Description

gas sensor

[0001] This disclosure relates to a gas sensor.

[0002] The gas sensor disclosed in Patent Document 1 comprises a base substrate made of glass, a sensor substrate mainly made of alumina, and a sensor support substrate portion that supports the sensor substrate with respect to the base substrate.

[0003] Japanese Patent Publication No. 2024-150267

[0004] In the gas sensor configuration described in Patent Document 1, the sensor support substrate is joined to the entire back surface of the sensor substrate and to the areas overlapping with the pads provided at the four corners. As a result, thermal distortion is likely to occur in the sensor support substrate due to the difference between the thermal expansion coefficient of the sensor substrate and the thermal expansion coefficient of the base substrate. This thermal distortion in the sensor support substrate can put stress on the sensor substrate and the base substrate, potentially compromising the durability of the gas sensor.

[0005] This disclosure is made in view of the above circumstances and aims to provide a gas sensor that can improve durability. This disclosure can be implemented in the following forms.

[0006] The gas sensor of this disclosure comprises a gas sensor element, a substrate, and a support portion that joins the gas sensor element and the substrate, wherein the gas sensor element has a heater and an electrode pad, and the support portion, in its outer shape as viewed from the thickness direction of the substrate, overlaps with a part of the gas sensor element and a part of the substrate, and is positioned closer to the center of gravity of the gas sensor element than the electrode pad.

[0007] This disclosure can provide a gas sensor that may have improved durability.

[0008] This is a side cross-sectional view of the gas sensor of the first embodiment of the present disclosure. This is a plan view of the gas sensor of Figure 1. This is a plan view of the gas sensor element portion of the gas sensor of the second embodiment of the present disclosure. This is a plan view of the gas sensor element portion of the gas sensor of the third embodiment of the present disclosure. This is a plan view of the gas sensor element portion of the gas sensor of the fourth embodiment of the present disclosure. This is a plan view of the gas sensor element portion of the gas sensor of another embodiment of the present disclosure. This is a plan view of the gas sensor element portion of the gas sensor of another embodiment of the present disclosure. This is a side cross-sectional view of the gas sensor element portion of the gas sensor of another embodiment of the present disclosure. This is a plan view of the gas sensor of Figure 9.

[0009] Embodiments of the present disclosure are listed and illustrated below. [1] A gas sensor comprising a gas sensor element, a substrate, and a support portion for joining the gas sensor element and the substrate, wherein the gas sensor element has a heater and an electrode pad, and the support portion, in its outer shape as viewed from the thickness direction of the substrate, overlaps with a part of the gas sensor element and a part of the substrate, and is positioned closer to the center of gravity of the gas sensor element than the electrode pad.

[0010] According to the gas sensor described in [1] above, the support portion does not overlap with the entire gas sensor element or the entire substrate, and thermal strain of the support portion due to the difference in thermal expansion coefficients between the gas sensor element and the substrate can be suppressed. Furthermore, because it is positioned closer to the center of gravity of the gas sensor element than the electrode pads, uneven thermal strain in the support portion is less likely to occur compared to configurations where it overlaps with the electrode pads or is positioned further from the center of gravity of the gas sensor element than the electrode pads. Therefore, stress is less likely to be placed on the gas sensor element and the substrate, and consequently, the durability of the gas sensor can be improved.

[0011] [2] The gas sensor according to [1], wherein it comprises only one support portion, and the support portion is aligned with the center of gravity of the gas sensor element when viewed from the thickness direction of the substrate.

[0012] According to the gas sensor described in [2] above, the gas sensor element and the substrate can expand and contract freely from the support portion without being constrained by each other, and thermal distortion is less likely to occur in the support portion.

[0013] [3] The gas sensor according to [1], comprising two or more support portions, wherein, when viewed from the thickness direction of the substrate, at least one entire support portion is arranged in each of the regions on both sides of a straight line passing through the center of gravity of the gas sensor element and perpendicular to the thickness direction of the substrate.

[0014] According to the gas sensor described in [3] above, the support parts can be dispersed to reduce their size and suppress thermal distortion, while the stability of the support of the gas sensor element on the substrate can be improved by the use of multiple support parts.

[0015] [4] The gas sensor according to [3], comprising four or more support portions, wherein, when viewed from the thickness direction of the substrate, at least one entire support portion is arranged in each of four regions divided by a first straight line passing through the center of gravity of the gas sensor element and perpendicular to the thickness direction of the substrate, and a second straight line passing through the center of gravity of the gas sensor element and perpendicular to the thickness direction of the substrate and perpendicular to the first straight line.

[0016] According to the gas sensor described in [4] above, the support parts are dispersed to reduce their size and further suppress thermal distortion, while the stability of the support of the gas sensor element to the substrate can be further improved by the use of multiple support parts.

[0017] [5] The gas sensor according to any one of [1] to [4], wherein the substrate comprises a frame and a membrane, the membrane is fixed to the frame so as to cover a cavity surrounded by the frame, and the gas sensor element is arranged on the side of the membrane opposite to the cavity.

[0018] According to the gas sensor described in [5] above, by providing a cavity in the substrate, the conduction of heat generated by the heater to the substrate can be suppressed.

[0019] <First Embodiment> 1. Configuration of the Gas Sensor 10 Below, a gas sensor 10 of the first embodiment embodying the present invention will be described with reference to Figures 1 and 2. The gas sensor 10 of the first embodiment shown in Figure 1 is an example of the gas sensor of this disclosure. In the following description, for the sake of explanation, the vertical direction shown in Figure 1 will be defined as the vertical direction, but it does not have to coincide with the vertical direction in the actual arrangement of the gas sensor 10. The vertical direction corresponds to the thickness direction of the substrate 30.

[0020] As shown in Figures 1 and 2, the gas sensor 10 comprises a gas sensor element 20, a substrate 30, and a support portion 40 that joins the gas sensor element 20 and the substrate 30. The gas sensor 10 measures the gas concentration of a target gas, such as oxygen.

[0021] 1-1. Configuration of Substrate 30 The substrate 30 shown in Figures 1 and 2 is, for example, a MEMS (Micro Electro Mechanical Systems) chip. Figure 1 is a cross-section of line A-A in Figure 2. The substrate 30 has a frame 31 and a membrane 32. The frame 31 is, for example, a rectangular ring. A rectangular parallelepiped cavity 31A is formed inside the frame 31. The membrane 32 is fixed to the upper surface of the frame 31. The membrane 32 is a plate-like structure with a rectangular (for example, square) shape in plan view. The membrane 32 covers the cavity 31A surrounded by the frame 31 from above. The frame 31 and the membrane 32 form a diaphragm structure in which the central part of the membrane 32 forms a diaphragm film.

[0022] Specifically, as shown in Figure 1, the substrate 30 has a semiconductor substrate 33A and insulating layers 33B-33F. The substrate 30 further has a pair of signal leads 34, a pair of signal pads 35, a pair of signal electrodes 36 (see Figure 2), a pair of heater leads 37, a pair of heater pads 38, and a pair of heater electrodes 39 (see Figure 2). In Figure 1, one signal lead 34, one signal pad 35, one signal electrode 36, one heater lead 37, one heater pad 38, and one heater electrode 39 are shown.

[0023] The semiconductor substrate 33A is made of, for example, silicon (Si). The semiconductor substrate 33A has openings 33G that penetrate through both the upper and lower surfaces. The shape of the openings 33G is, for example, a rectangle in plan view. A portion of the insulating layer 33B is exposed within the openings 33G.

[0024] The insulating layers 33B-33F only need to have sufficient insulating properties, and their material is not particularly limited. The insulating layers 33B-33E are laminated on the upper surface of the semiconductor substrate 33A. From the upper side of the semiconductor substrate 33A, the insulating layer 33B, insulating layer 33C, insulating layer 33D, and insulating layer 33E are laminated in that order. The material of insulating layers 33B and 33D is, for example, silicon oxide (SiO₂ ２ The insulating layer 33B is formed, for example, by thermal oxidation (thermal oxidation of the silicon substrate, etc.). The material of the insulating layers 33C and 33E is, for example, silicon nitride (Si ３ N ４ The insulating layers 33C and 33E are formed, for example, by reduced-pressure CVD. The insulating layer 33D is formed, for example, by TEOS (Si(OC ２ H ５ ) ４ The insulating layer 33D is formed by plasma CVD using ) as a liquid source. The insulating layer 33D is formed by two film deposition steps, for example, with the formation of a pair of signal leads 34 and a pair of heater leads 37 in between.

[0025] The insulating layer 33F is laminated on the lower surface of the semiconductor substrate 33A. The material of the insulating layer 33F is, for example, silicon oxide (SiO ２ The insulating layer 33F is formed, for example, by thermal oxidation (thermal oxidation of the silicon substrate, etc.).

[0026] A pair of signal leads 34 and a pair of heater leads 37 are embedded in the insulating layer 33D. The pair of signal leads 34 and the pair of heater leads 37 extend horizontally from the outside to the inside of the insulating layer 33D when viewed from above.

[0027] The signal lead 34 is connected to a signal pad 35 and a signal electrode 36. The signal lead 34 is a conductive path for extracting electrical signals such as current from the gas sensor element 20 that measures gas concentration. For example, the signal lead 34 has a two-layer structure including a layer made of titanium (Ti) and a layer made of platinum (Pt) formed thereon.

[0028] A signal pad 35 is connected to one end (outer end) of the signal lead 34. For example, the signal pad 35 has a two-layer structure including a layer made of chromium (Cr) and a layer made of gold (Au) formed thereon. A wiring (not shown) for exchanging power with an external circuit is connected to the signal pad 35. The signal pad 35 is formed at a position overlapping the semiconductor substrate 33A (frame body 31) in the vertical direction.

[0029] A signal electrode 36 is connected to the other end (inner end) of the signal lead 34. The material of the signal electrode 36 is, for example, gold (Au). The signal electrode 36 is disposed in a hole 30A formed on the upper surface side of the substrate 30. The hole 30A penetrates through insulating layers 33D and 33E, and the other end of the signal lead 34 is exposed at the bottom of the hole. The thickness of the signal electrode 36 is, for example, the same as the thickness of the insulating layer 33D. A conduction part 25, which will be described later, is connected to the signal electrode 36.

[0030] The heater lead 37 is connected to a heater pad 38 and a heater electrode 39. The heater lead 37 is a conductive path for supplying current to a heater 24 of the gas sensor element 20, which will be described later. For example, the heater lead 37 has a two-layer structure including a layer made of titanium (Ti) and a layer made of platinum (Pt) formed thereon.

[0031] A heater pad 38 is connected to one end (outer end) of the heater lead 37. For example, the heater pad 38 has a two-layer structure including a layer made of chromium (Cr) and a layer made of gold (Au) formed thereon. A wiring (not shown) for supplying power from an external circuit is connected to the heater pad 38. The heater pad 38 is formed at a position overlapping the semiconductor substrate 33A (frame body 31) in the vertical direction.

[0032] A heater electrode 39 is connected to the other end (inner end) of the heater lead 37. The material of the heater electrode 39 is, for example, gold (Au). The heater electrode 39 is disposed in a hole 30B formed on the upper surface side of the substrate 30. The hole 30B penetrates through the insulating layers 33D and 33E, and the other end of the heater lead 37 is exposed at the bottom of the hole. The thickness of the heater electrode 39 is, for example, the same as the thickness of the insulating layer 33D. A conduction portion 25, which will be described later, is connected to the heater electrode 39.

[0033] The pair of signal pads 35 and the pair of heater pads 38 are located at rotationally symmetric positions centered on the center line C (a line passing through the center of gravity and parallel to the vertical direction) of the gas sensor 10 (specifically, the gas sensor element 20 and the substrate 30) when viewed in plan from the plate thickness direction (vertical direction) of the substrate 30. As shown in FIG. 1, the pair of signal electrodes 36 and the pair of heater electrodes 39 are located at rotationally symmetric positions centered on the center line C (a line passing through the center of gravity and parallel to the vertical direction) of the gas sensor 10 (specifically, the gas sensor element 20 and the substrate 30) when viewed in plan from the plate thickness direction (vertical direction) of the substrate 30.

[0034] The frame body 31 is constituted by a semiconductor substrate 33A and an insulating layer 33F. The membrane 32 is constituted by the inner portion (the portion excluding the portion overlapping the frame body 31 in the vertical direction) of the region constituted by the insulating layers 33B to 33E, the pair of signal electrodes 36, and the pair of heater electrodes 39.

[0035] 1-2. Configuration of Gas Sensor Element 20 As shown in FIG. 1, the gas sensor element 20 is disposed on the surface side (upper surface side) of the membrane 32 opposite to the cavity 31A. The gas sensor element 20 shown in FIGS. 1 and 2 includes a main body 21, a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23. The element-side electrode pads 22 and the heater-side electrode pads 23 correspond to an example of "electrode pads" in the present disclosure. The main body 21 is formed using a ceramic material. The gas sensor element 20 has, for example, a plate shape of a quadrangle (square) in plan view.

[0036] The main body portion 21 includes, for example, a solid electrolyte body (not shown), a detection electrode, and a reference electrode. The solid electrolyte body contains a material that is activated at high temperatures to exhibit ionic conductivity. The solid electrolyte body contains zirconia (ZrO ２ ) and is preferably made thereof. The solid electrolyte body includes, for example, stabilized zirconia. The stabilized zirconia is, for example, yttria-stabilized zirconia (YSZ). The detection electrode and the reference electrode are electrodes mainly composed of metal formed on the surface of the solid electrolyte body. The material of the detection electrode and the reference electrode is, for example, platinum (Pt). The solid electrolyte body is sandwiched between the detection electrode and the reference electrode. The detection electrode is exposed to the measurement target gas. A reference gas (oxygen, etc.) with a predetermined concentration is introduced into the reference electrode.

[0037] The main body portion 21 includes, for example, an insulating layer (not shown). The insulating layer constitutes, for example, the lower end side portion of the main body portion 21. The material of the insulating layer is, for example, a metal oxide, such as aluminum oxide (Al ２ O ３ ), or the like.

[0038] The main body portion 21 is provided with a heater 24. The heater 24 is embedded in, for example, the insulating layer. The heater 24 has, for example, a strip plate shape. When viewed from the vertical direction, the heater 24 has, for example, a square spiral shape, a meandering shape, or the like. The material of the heater 24 is, for example, platinum (Pt). The heater 24 generates heat for activating the solid electrolyte body when energized.

[0039] As shown in FIG. 2, the pair of element-side electrode pads 22 and the pair of heater-side electrode pads 23 are disposed, for example, at four corners on the upper surface of the gas sensor element 20. The element-side electrode pads 22 and the heater-side electrode pads 23 have, for example, a two-layer structure including a layer made of gold (Au) and a layer made of platinum (Pt) formed thereunder.

[0040] One of the element-side electrode pads 22 is a pad for extracting a signal obtained from the detection electrode (not shown). Although not illustrated in the drawings, conduction between the one element-side electrode pad 22 and the detection electrode (not shown) is ensured via a through hole formed in the gas sensor element 20 (insulating layer, etc.).

[0041] The other element-side electrode pad 22 is a pad that extracts the signal obtained from the reference electrode (not shown). Although not shown, the other element-side electrode pad 22 is electrically connected to the reference electrode (not shown) through a through-hole formed in the gas sensor element 20 (insulating layer, etc.).

[0042] The pair of heater-side electrode pads 23 are electrodes for supplying current to the heater 24. One heater-side electrode pad 23 is connected to one end of the heater 24. The other heater-side electrode pad 23 is connected to the other end of the heater 24. The pair of heater-side electrode pads 23 are connected to the heater 24 via through holes formed in the gas sensor element 20 (insulating layer, etc.).

[0043] The gas sensor 10 has four conductive portions 25 between the gas sensor element 20 and the substrate 30. The conductive portions 25 are, for example, conductive wires. The material of the conductive portions 25 is, for example, gold (Au), copper (Cu), aluminum (Al), etc. One pair of conductive portions 25 are connected to the signal electrode 36 of the substrate 30 and the element-side electrode pad 22 of the gas sensor element 20, respectively. The other pair of conductive portions 25 are connected to the heater electrode 39 of the substrate 30 and the heater-side electrode pad 23 of the gas sensor element 20, respectively.

[0044] The gas sensor element 20 is formed, for example, using a sheet molding process and a printing process. For example, the gas sensor element 20 can be formed by preparing a sheet made from ceramic raw materials that will serve as the base for a solid electrolyte, a sheet that will serve as the base for an insulating layer, printing various electrodes on it, and then sintering it.

[0045] The gas sensor element 20 outputs a signal (voltage signal) based on the difference between the concentration of the target gas to which the detection electrode (not shown) is exposed and the concentration of the reference gas introduced to the reference electrode (not shown). For example, if the target gas is oxygen, the solid electrolyte (not shown) can be made ionic conductive by keeping it at a high temperature, and oxygen ions conduct from the reference electrode side, where the oxygen concentration is high, to the detection electrode side, generating an electric current. Since oxygen ions have a negative charge, an electromotive force is generated between the two electrodes.

[0046] The driving temperature of the gas sensor element 20 (surface temperature of the solid electrolyte when heated by the heater 24) is preferably, for example, 550°C to 800°C, more preferably 600°C to 750°C, and even more preferably 650°C to 700°C. The surface temperature of the frame 31 (semiconductor substrate 33A) when the gas sensor element 20 is driven is preferably, for example, room temperature (e.g., 25°C) to 50°C.

[0047] 1-3. Support portion 40 As shown in Figure 1, the support portion 40 connects the gas sensor element 20 and the substrate 30. In this first embodiment, the gas sensor 10 is provided with only one support portion 40. The gas sensor element 20 and the substrate 30 are connected via the support portion 40, and the entire gas sensor element 20, excluding the portion in contact with the support portion 40, is positioned to face and be separated from the substrate 30.

[0048] The support portion 40 is, for example, rectangular (cube) in shape. The support portion 40 has the same shape as each electrode pad (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23) when viewed from the thickness direction (vertical direction) of the substrate 30. The material of the support portion 40 is, for example, gold (Au).

[0049] The support portion 40 is solid. Here, "solid" means that the porosity (the ratio of the volume of all pores to the total volume) of the support portion 40 is 10% or less. Porosity can be derived, for example, by observing a cross-section of the support portion 40 with an SEM (scanning electron microscope) and expressing the ratio of the total area of ​​all pores to the area of ​​non-pores in the observation area as a percentage.

[0050] The vertical thickness of the support portion 40 is, for example, smaller than the plate thickness of the gas sensor element 20 (main body portion 21), larger than the plate thickness of the membrane 32, and larger than the vertical thickness of each electrode pad (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23).

[0051] The horizontal width of the support portion 40 (the length of one side when viewed from the thickness direction of the substrate 30) is, for example, half or one-third of the distance (shortest distance) between adjacent electrodes (for example, a pair of element-side electrode pads 22).

[0052] As shown in Figure 2, the support portion 40 overlaps with a part of the gas sensor element 20 (central portion) and a part of the substrate 30 (central portion) in terms of its outer shape when viewed from the thickness direction (vertical direction) of the substrate 30.

[0053] The support portion 40 is positioned closer to the center of gravity G of the gas sensor element 20 than each of the electrode pads of the gas sensor element 20 (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23) when viewed from the thickness direction (vertical direction) of the substrate 30. The center of gravity G of the gas sensor element 20 is the center of the rectangular (square) outer shape of the gas sensor element 20 when viewed from the thickness direction of the substrate 30 (the position where the two diagonals intersect). Here, a position closer to the center of gravity G of the gas sensor element 20 than each electrode pad is a position where the furthest distance between the center of gravity G and the support portion 40 is smaller than the shortest distance between the center of gravity G and each electrode pad. In Figure 2, the shortest distances between the center of gravity G and each electrode pad are the same.

[0054] As shown in Figure 2, the bonding region R is defined as the area enclosed by each electrode pad (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23) when viewed from the thickness direction (vertical direction) of the substrate 30. The bonding region R is the area enclosed by a rectangular frame formed by connecting the inner corners (towards the center of the gas sensor element 20) of adjacent electrode pads in the circumferential direction with straight lines. When viewed from the thickness direction of the substrate 30, the center of gravity G of the gas sensor element 20 is contained within the bonding region R. More specifically, when viewed from the thickness direction of the substrate 30, the support portion 40 coincides with the center of gravity G of the gas sensor element 20 and the center of the bonding region R. When viewed from the thickness direction of the substrate 30, the support portion 40 is contained within the bonding region R.

[0055] The support portion 40 is aligned with the center of gravity G of the gas sensor element 20 when viewed from the thickness direction (vertical direction) of the substrate 30. More specifically, the center of gravity of the support portion 40 is aligned with the center of gravity G of the gas sensor element 20 when viewed from the thickness direction of the substrate 30.

[0056] The support portion 40 is spaced apart from each electrode pad of the gas sensor element 20 (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23) when viewed from the thickness direction (vertical direction) of the substrate 30. For example, the support portion 40 is spaced apart from each electrode pad by the same width as itself (the length of the diagonal of the support portion 40).

[0057] In the external view of the substrate 30 from the thickness direction (vertical direction), the four edges of the support portion 40 are parallel to the four edges of the gas sensor element 20. The four edges of the support portion 40 are parallel to the four edges of each electrode pad (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23).

[0058] The support portion 40 can be formed on the substrate 30 using MEMS processing technology. Then, the gas sensor 10 is manufactured by joining a separately formed gas sensor element 20 to the support portion 40.

[0059] 2. Effects of the First Embodiment The gas sensor 10 of the first embodiment comprises a gas sensor element 20, a substrate 30, and a support portion 40 that joins the gas sensor element 20 and the substrate 30. The gas sensor element 20 has a heater 24 and electrode pads (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23). In terms of its external shape when viewed from the thickness direction (vertical direction) of the substrate 30, the support portion 40 overlaps with a part of the gas sensor element 20 and a part of the substrate 30, and is positioned closer to the center of gravity G of the gas sensor element 20 than the electrode pads (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23).

[0060] With this gas sensor 10, the support portion 40 does not overlap with the entire gas sensor element 20 or the entire substrate 30, and thermal strain of the support portion 40 due to the difference in thermal expansion coefficients between the gas sensor element 20 and the substrate 30 can be suppressed. Furthermore, since it is positioned closer to the center of gravity G of the gas sensor element 20 than the electrode pads (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23), uneven thermal strain in the support portion 40 is less likely to occur compared to configurations where it overlaps with the electrode pads (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23) or where it is positioned further from the center of gravity G of the gas sensor element 20 than the electrode pads. Therefore, stress is less likely to be placed on the gas sensor element 20 and the substrate 30, and consequently, the durability of the gas sensor 10 can be improved.

[0061] For example, the insulating layer constituting the gas sensor element 20 is aluminum oxide (Al ２ O ３ When using aluminum oxide (Al) as the material, ２ O ３ The thermal expansion coefficient of ) is 7.3 × 10 －６ The temperature is approximately / °C, and the thermal expansion coefficient of the entire gas sensor element 20 is 8 × 10 －６ It is approximately / °C. On the other hand, the material of the insulating layers 33B and 33D that make up the membrane 32 is silicon oxide (SiO ２ ) and the material of the insulating layers 33C and 33E is silicon nitride (Si ３ N ４ ) If so, silicon oxide (SiO ２ The coefficient of thermal expansion of ) is 0.51 × 10 －６ / ℃ -0.58 × 10 －６ It is around / °C, and silicon nitride (Si ３ N ４ The coefficient of thermal expansion of ) is 2.6 × 10 －６ / ℃ -3.5 × 10 －６ The temperature is approximately / °C, and the thermal expansion coefficient of the entire membrane 32 is 3 × 10⁻⁶. －６ It is approximately / °C. Thus, although the gas sensor element 20 has a larger coefficient of thermal expansion than the membrane 32, the support portion 40 overlaps only a part of the gas sensor element 20 and only a part of the substrate 30, so that thermal strain of the support portion 40 due to the difference in the coefficient of thermal expansion between the gas sensor element 20 and the substrate 30 can be suppressed.

[0062] Since the substrate 30 can be easily formed to a thickness of several micrometers using MEMS processing technology, the thermal insulation design between the gas sensor element 20 and the substrate 30 becomes easier.

[0063] The gas sensor 10 of the first embodiment is equipped with only one support portion 40. The support portion 40 is positioned so as to coincide with the center of gravity G of the gas sensor element 20 when viewed from the thickness direction (vertical direction) of the substrate 30. With this configuration, the gas sensor element 20 and the substrate 30 can expand and contract freely from the support portion 40 without being constrained by each other, and thermal distortion is less likely to occur in the support portion 40.

[0064] In the gas sensor 10 of the first embodiment, the substrate 30 has a frame 31 and a membrane 32. The membrane 32 is fixed to the frame 31 so as to cover the cavity 31A surrounded by the frame 31. The gas sensor element 20 is arranged on the side of the membrane 32 opposite to the cavity 31A. With this configuration, by providing a cavity 31A in the substrate 30, the conduction of heat generated by the heater 24 to the substrate 30 can be suppressed.

[0065] <Second Embodiment> A second embodiment embodying the present disclosure will be described below with reference to Figure 3. The gas sensor of the second embodiment differs from that of the first embodiment in the configuration of the support portion, but is otherwise common. Components identical to those of the first embodiment are denoted by the same reference numerals, and detailed explanations are omitted. Figure 3 is a plan view of the gas sensor element portion of the gas sensor of the second embodiment.

[0066] As shown in Figure 3, the gas sensor of the second embodiment includes two support portions 240. The support portions 240 connect the gas sensor element 20 and the substrate 30. The support portions 240 are, for example, rectangular parallelepipeds. The material, solid structure, and vertical thickness of the support portions 240 are the same as those of the support portion 40 of the first embodiment.

[0067] Viewed from the thickness direction (vertical direction) of the substrate 30, one entire support portion 240 is positioned in each of the regions (region A1, region A2) on either side of a straight line L1 that passes through the centroid G of the gas sensor element 20 and is perpendicular to the thickness direction of the substrate 30. Regions A1 and A2 are the regions enclosed by the straight line L1 and the outline of the gas sensor element 20 when viewed from the thickness direction of the substrate 30. The straight line L1 is parallel to a pair of parallel sides of the gas sensor element 20 when viewed from the thickness direction of the substrate 30, and is the axis of symmetry of the gas sensor element 20.

[0068] The support portion 240 is positioned closer to the center of gravity G of the gas sensor element 20 than each electrode pad of the gas sensor element 20 (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23) when viewed from the thickness direction (vertical direction) of the substrate 30. The two support portions 240 are at the same distance (shortest distance) from the center of gravity G of the gas sensor element 20. The two support portions 240 are contained within the bonding region R.

[0069] In the configuration of the gas sensor of the second embodiment, the two support parts 240 are dispersed to reduce their size and suppress thermal distortion, while the stability of the support of the gas sensor element 20 to the substrate 30 can be improved by the multiple support parts 240.

[0070] <Third Embodiment> A third embodiment embodying the present disclosure will be described below with reference to Figure 4. The gas sensor of the third embodiment differs from that of the first embodiment in the configuration of the support portion, but is otherwise common. Components identical to those of the first embodiment are denoted by the same reference numerals, and detailed explanations are omitted. Figure 4 is a plan view of the gas sensor element portion of the gas sensor of the third embodiment.

[0071] As shown in Figure 4, the gas sensor of the third embodiment includes four support portions 340. The support portions 340 connect the gas sensor element 20 to the substrate 30. The support portions 340 are, for example, rectangular parallelepiped (cube) shaped. The material, solid construction, and vertical thickness of the support portions 340 are the same as those of the support portion 40 of the first embodiment.

[0072] When viewed from the thickness direction (vertical direction) of the substrate 30, the substrate 30 is divided into four regions (regions A3-A6) by a straight line L1 that passes through the centroid G of the gas sensor element 20 and is perpendicular to the thickness direction of the substrate 30, and a straight line (second straight line) L2 that passes through the centroid G of the gas sensor element 20 and is perpendicular to the thickness direction of the substrate 30 and perpendicular to the straight line (first straight line) L1. When viewed from the thickness direction of the substrate 30, the straight lines L1 and L2 are parallel to a pair of parallel sides of the gas sensor element 20 and are axes of symmetry of the gas sensor element 20. When viewed from the thickness direction of the substrate 30, regions A3-A6 are regions enclosed by the straight lines L1 and L2 and the outline of the gas sensor element 20. The entirety of one support part 340 is arranged in each of the four regions (regions A3-A6). The four support parts 340 are each arranged in the corners on the centroid G side of the gas sensor element 20 in regions A3-A6. The four support parts 340 are positioned in a rotationally symmetrical position with respect to the center line C (a line passing through the center of gravity and parallel to the vertical direction) of the gas sensor 10 (specifically, the gas sensor element 20 and the substrate 30) when viewed from the thickness direction of the substrate 30.

[0073] The support portion 340 is positioned closer to the center of gravity G of the gas sensor element 20 than each electrode pad of the gas sensor element 20 (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23) when viewed from the thickness direction (vertical direction) of the substrate 30. The four support portions 340 are all at the same distance (shortest distance) from the center of gravity G of the gas sensor element 20. The four support portions 340 are contained within the bonding region R.

[0074] In the configuration of the gas sensor of the third embodiment, the four support parts 340 are dispersed to reduce their size and suppress thermal distortion, while the stability of the support of the gas sensor element 20 to the substrate 30 can be improved by the multiple support parts 340.

[0075] <Fourth Embodiment> A fourth embodiment embodying the present disclosure will be described below with reference to Figure 5. The gas sensor of the fourth embodiment differs from that of the first embodiment in the configuration of the support portion, but is otherwise common. Components identical to those of the first embodiment are denoted by the same reference numerals, and detailed explanations are omitted. Figure 5 is a plan view of the gas sensor element portion of the gas sensor of the fourth embodiment.

[0076] As shown in Figure 5, the gas sensor of the fourth embodiment includes four support portions 440. The support portions 440 connect the gas sensor element 20 to the substrate 30. The support portions 440 are, for example, rectangular parallelepiped (cube) shaped. The material, solid construction, and vertical thickness of the support portions 440 are the same as those of the support portion 40 of the first embodiment.

[0077] When viewed from the thickness direction (vertical direction) of the substrate 30, the substrate 30 is divided into four regions (regions A7-A10) by a straight line L3 that passes through the centroid G of the gas sensor element 20 and is perpendicular to the thickness direction of the substrate 30, and a straight line L4 that passes through the centroid G of the gas sensor element 20 and is perpendicular to the thickness direction of the substrate 30 and also perpendicular to the straight line (first straight line) L3. Straight lines L3 and L4 are the diagonals of the gas sensor element 20 when viewed from the thickness direction of the substrate 30, and are the axes of symmetry of the gas sensor element 20. Regions A7-A10 are the regions enclosed by straight lines L3 and L4 and the outline of the gas sensor element 20 when viewed from the thickness direction of the substrate 30. The entirety of one support part 440 is arranged in each of the four regions (regions A7-A10). The four support portions 440 are each positioned near the corners of the gas sensor element 20 on the side of its center of gravity G within regions A7-A10. The four support portions 440 are rotationally symmetrical with respect to the center line C (a line passing through the center of gravity and parallel to the vertical direction) of the gas sensor 10 (specifically, the gas sensor element 20 and the substrate 30) when viewed from the thickness direction of the substrate 30. For example, the four support portions 440 are all at the same distance from the center of gravity G of the gas sensor element 20.

[0078] Even with this configuration, the four support parts 440 can be distributed to reduce their size and suppress thermal distortion, while the stability of the support of the gas sensor element 20 to the substrate 30 can be improved by the multiple support parts 440.

[0079] <Other Embodiments> This disclosure is not limited to the embodiments described above and in the drawings. For example, any combination of the features of the embodiments described above or below is possible as long as it does not contradict the original. Furthermore, any feature of the embodiments described above or below may be omitted unless explicitly stated as essential. In addition, the embodiments described above may be modified as follows.

[0080] In the first embodiment described above, the other end (inner end) of the signal lead 34 and the signal electrode 36 were located inside the substrate 30 (frame 31) (towards the center line C), but as shown in Figures 9 and 10, they may be located in a position that overlaps the substrate 30 (frame 31) in the vertical direction. Similarly, in the first embodiment described above, the other end (inner end) of the heater lead 37 and the heater electrode 39 were located inside the substrate 30 (frame 31) (towards the center line C), but as shown in Figures 9 and 10, they may be located in a position that overlaps the substrate 30 (frame 31) in the vertical direction.

[0081] In the first embodiment described above, as shown in Figure 2, the center of gravity of the support portion 40, when viewed from the thickness direction (vertical direction) of the substrate 30, coincided with the center of gravity G of the gas sensor element 20. However, as shown in Figure 6, the center of gravity of the support portion 40 may be offset from the center of gravity G of the gas sensor element 20 if it is positioned closer to the center of gravity G of the gas sensor element 20 (within the bonding region R) than each electrode pad (a pair of element-side electrode pads 22 and a pair of heater-side electrode pads 23).

[0082] In the third embodiment described above, as shown in Figure 4, the distance from the center of gravity G of the gas sensor element 20 of each support portion 340 was the same when viewed from the thickness direction (vertical direction) of the substrate 30, but as shown in Figure 7, they may be different.

[0083] In the fourth embodiment described above, as shown in Figure 5, the distance from the center of gravity G of the gas sensor element 20 of each support portion 440 was the same when viewed from the thickness direction (vertical direction) of the substrate 30, but as shown in Figure 8, they may be different.

[0084] In the second embodiment described above, as shown in Figure 3, one entire support portion 240 was arranged in each of the regions (region A1 and region A2) on both sides of the straight line L1, but two or more entire support portions 240 may be arranged in each region.

[0085] In the third embodiment described above, as shown in Figure 4, one entire support portion 340 was arranged in each of the four regions (regions A3-A6) separated by the straight lines L1 and L2, but two or more entire support portions 340 may be arranged in each region.

[0086] In the first to fourth embodiments described above, the pair of element-side electrode pads 22 and the pair of heater-side electrode pads 23 were arranged at the four corners on the upper surface of the gas sensor element 20, but they may be arranged at other positions, such as positions closer to the center of gravity G.

[0087] 10: Gas sensor 20: Gas sensor element 21: Main body 22: Element-side electrode pad (electrode pad) 23: Heater-side electrode pad (electrode pad) 24: Heater 25: Conductive part 30: Substrate 30A: Hole 30B: Hole 31: Frame 31A: Cavity 32: Membrane 33A: Semiconductor substrate 33B-33F: Insulating layer 33G: Opening 34: Signal lead 35: Signal pad 36: Signal electrode 37: Heater lead 38: Heater pad 39: Heater electrode 40: Support part 240: Support part 340: Support part 440: Support part A1-A10: Region C: Centerline of gas sensor element G: Center of gravity of gas sensor element L1, L3: Straight line (first straight line) L2, L4: Straight line (second straight line) R: Joint area

Claims

A gas sensor comprising a gas sensor element, a substrate, and a support portion that joins the gas sensor element and the substrate, The gas sensor element comprises a heater and an electrode pad. The support portion, when viewed from the thickness direction of the substrate, overlaps with a part of the gas sensor element and a part of the substrate, and is positioned closer to the center of gravity of the gas sensor element than the electrode pad, in the gas sensor. 　 The aforementioned support portion comprises only one, The gas sensor according to claim 1, wherein the support portion is aligned with the center of gravity of the gas sensor element when viewed from the thickness direction of the substrate. 　 The system comprises two or more of the aforementioned support parts, The gas sensor according to claim 1, wherein, when viewed from the thickness direction of the substrate, at least one entire support portion is arranged in each of the regions on both sides of a straight line passing through the center of gravity of the gas sensor element and perpendicular to the thickness direction of the substrate. 　 The system comprises four or more of the aforementioned support parts, The gas sensor according to claim 3, wherein, when viewed from the thickness direction of the substrate, at least one entire support portion is disposed in each of four regions divided by a first straight line passing through the center of gravity of the gas sensor element and perpendicular to the thickness direction of the substrate, and a second straight line passing through the center of gravity of the gas sensor element and perpendicular to the thickness direction of the substrate and perpendicular to the first straight line. 　 The substrate comprises a frame and a membrane. The membrane is fixed to the frame so as to cover the cavity enclosed by the frame, The gas sensor according to any one of claims 1 to 4, wherein the gas sensor element is arranged on the side of the membrane opposite to the cavity.

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