JP2019027991A - Gas sensor - Google Patents

Abstract

To provide a gas sensor capable of improving responsibility to humidity change.SOLUTION: A gas sensor detects gas in a detected atmosphere. The gas sensor includes a gas detection element having a resistor of which a resistance value varies depending on its temperature change. The gas detection element has a substrate in which a resistor is arranged, and a cover. The cover is attached to the surface of the substrate so as to form an internal space between the cover and the substrate in a region overlapping the resistor in a thickness direction of the substrate. The cover has an opening which communicates the internal space and is blocked with a film body that permeates water vapor and prevents permeation of detected gas.SELECTED DRAWING: Figure 2

Description

  The present disclosure relates to a gas sensor.

  A gas sensor that is not affected by moisture is known as a gas sensor that detects flammable gas or the like (see Patent Document 1). In the gas sensor of Patent Document 1, one gas detection element is disposed in a space opened to a detection target gas, and another gas detection element is disposed in a space covered with a film body that transmits water vapor and does not transmit a gas to be detected. The

  Thereby, in the gas sensor of patent document 1, since the humidity conditions of a pair of gas detection elements become the same, gas can be detected without being influenced by humidity.

JP 2001-124716 A

  In the gas sensor, for example, if a gas detection element is arranged on a pedestal and a space is formed by fixing a cap to the pedestal, an increase in the volume of the space is inevitable. As a result, there arises a disadvantage that the responsiveness of the gas sensor to the humidity change is lowered.

  An object of one aspect of the present disclosure is to provide a gas sensor that can improve responsiveness to changes in humidity.

  One embodiment of the present disclosure is a gas sensor for detecting a gas in a detection target atmosphere. The gas sensor includes a gas detection element having a resistor whose resistance value changes according to its own temperature change. The gas detection element includes a substrate on which a resistor is disposed and a cover. The cover is attached to the surface of the substrate so as to form an internal space between the cover and the substrate in a region overlapping the resistor in the thickness direction of the substrate. In addition, the cover has an opening that is in communication with the internal space and is blocked by a film body that transmits water vapor and does not transmit the gas to be detected.

  According to such a configuration, since the cover that forms the internal space is directly attached to the substrate of the gas detection element, the volume of the internal space can be reduced. As a result, it is possible to improve responsiveness to changes in humidity. In addition, the overall size of the gas sensor can be reduced by reducing the internal space.

  In one embodiment of the present disclosure, the opening may be provided at a position facing the resistor. According to such a configuration, since the distance between the outside of the internal space and the resistor is reduced, the responsiveness to changes in humidity can be further increased.

  In one aspect of the present disclosure, the cover may have a plurality of openings. According to such a structure, the permeability | transmittance to the internal space of water vapor | steam can be improved, maintaining the intensity | strength of a cover or a film body. As a result, the responsiveness to humidity changes can be further increased.

  In one embodiment of the present disclosure, the membrane body may be a fluororesin ion exchange membrane. According to such a configuration, the gas to be detected can be prevented from being transmitted while the water vapor is transmitted more reliably.

  In one aspect of the present disclosure, the membrane body may be directly fixed to the cover without any other substance. According to such a configuration, since the film body can be directly formed in the opening of the cover, the manufacturing cost can be reduced.

  In one aspect of the present disclosure, the resistor may be a heating resistor whose resistance value changes due to a temperature change. Further, the gas detection element may be a heat conduction type detection element. According to such a configuration, the advantages of the present disclosure can be used effectively.

It is a typical sectional view showing a gas sensor of an embodiment. It is a typical partial expanded sectional view of the 1st gas detection element and 2nd gas detection element vicinity of the gas sensor of FIG. It is a typical fragmentary expanded sectional view of the 1st gas detection element and cover in the gas sensor of FIG. It is a typical top view of the board | substrate of the 1st gas detection element in the gas sensor of FIG. It is typical sectional drawing in the VV line | wire of FIG. It is a flowchart which shows the manufacturing method of the gas sensor of FIG. It is a typical fragmentary expanded sectional view which shows the gas sensor of embodiment different from FIG.

Hereinafter, embodiments to which the present disclosure is applied will be described with reference to the drawings.
[1. First Embodiment]
[1-1. Constitution]
A gas sensor 1 shown in FIG. 1 is a gas sensor for detecting a specific gas in an atmosphere to be detected.

Examples of the gas to be detected detected by the gas sensor 1 include flammable gases such as hydrogen, ammonia, carbon monoxide (CO), and hydrocarbon (HC).
As shown in FIG. 1, the gas sensor 1 includes a first gas detection element 2, a second gas detection element 3, a casing 4, a circuit board 10, and a calculation unit 12.

<First gas detection element>
The first gas detection element 2 is a heat conduction type detection element.
As shown in FIGS. 2 and 3, the first gas detection element 2 includes a heating resistor 21, a substrate 22, and a cover 23.

(Heating resistor)
As shown in FIG. 4, the heating resistor 21 is a conductor patterned in a spiral shape in plan view (that is, viewed from the thickness direction of the element), and is embedded in the central portion of the substrate 22. Specifically, the heating resistor 21 is disposed between the first compressive stress layer 22D and the second compressive stress layer 22E constituting the substrate 22, as shown in FIG.

  The heating resistor 21 is a member whose resistance value changes according to its own temperature change, and is made of a conductive material having a large temperature resistance coefficient. As a material of the heating resistor 21, for example, platinum (Pt) can be used. The resistance value of the heating resistor 21 changes due to the change in the temperature of the diaphragm structure of the substrate 22 on which the heating resistor 21 is arranged due to the presence of the gas to be detected.

  As shown in FIG. 4, wiring 25 embedded in the substrate 22 is electrically connected to the heating resistor 21. Both ends of the wiring 25 are electrically connected to the electrode pads 26A and 26B. That is, the heating resistor 21 is electrically connected to the electrode pads 26A and 26B.

  The electrode pads 26A and 26B are formed on the surface of the substrate 22 as shown in FIG. The electrode pads 26A and 26B have protrusions that protrude to the second compressive stress layer 22E. The wiring 25 is connected to this protrusion.

(substrate)
The substrate 22 supports the heating resistor 21, the wiring 25, and the electrode pads 26A and 26B.
The substrate 22 has a six-layer structure in this embodiment. Specifically, the substrate 22 includes a base material layer 22A, a first tensile stress layer 22B, a second tensile stress layer 22C, a first compressive stress layer 22D, a second compressive stress layer 22E, and a third tensile stress layer. And a stress layer 22F.

The base material layer 22A is a substrate made of silicon or glass and has a front surface and a back surface.
The first tensile stress layer 22B is laminated on the surface of the base material layer 22A (that is, the surface on the side where the heating resistor 21 is disposed). The second tensile stress layer 22C is laminated on the back surface of the base material layer 22A. The second tensile stress layer 22 </ b> C constitutes the outermost layer on the side opposite to the cover 23 of the substrate 22.

The first tensile stress layer 22B and the second tensile stress layer 22C are films that generate tensile stress. Specific examples of the first tensile stress layer 22B and the second tensile stress layer 22C include, for example, a silicon nitride (Si ₃ N ₄ ) film formed by LP (Low Pressure) -CVD (chemical vapor deposition) method. Can be mentioned.

  The first compressive stress layer 22D is laminated on the surface of the first tensile stress layer 22B. The second compressive stress layer 22E is laminated on the surface of the first compressive stress layer 22D. Further, the heating resistor 21 and the wiring 25 are disposed between the first compressive stress layer 22D and the second compressive stress layer 22E so as to be embedded in these layers.

The first compressive stress layer 22D and the second compressive stress layer 22E are films that generate compressive stress. Specific examples of the first compressive stress layer 22D and the second compressive stress layer 22E include a silicon oxide (SiO ₂ ) film formed by a plasma CVD (chemical vapor deposition) method, for example.

  The third tensile stress layer 22F is laminated on the surface of the second compressive stress layer 22E. The third tensile stress layer 22F constitutes the outermost layer on the cover 23 side of the substrate 22. The third tensile stress layer 22F is the same type of film as the first tensile stress layer 22B and the second tensile stress layer 22C.

  The layer structures of the third tensile stress layer 22F, the second compressive stress layer 22E, the first compressive stress layer 22D, and the first tensile stress layer 22B are symmetrical in the thickness direction (vertical direction in the figure) with the heating resistor 21 interposed therebetween. It has become.

  As shown in FIG. 5, the substrate 22 has a recess 22 </ b> G formed by removing the second tensile stress layer 22 </ b> C and the base material layer 22 </ b> A in a region where the heating resistor 21 is disposed. That is, the board | substrate 22 has a diaphragm structure by the recessed part 22G.

  As shown in FIG. 4, the recess 22G overlaps with a region where the heating resistor 21 is arranged in the thickness direction of the substrate 22, and the second tensile stress layer 22C and the base material layer 22A do not exist in this region. Accordingly, the first tensile stress layer 22B is exposed as the back surface of the substrate 22 in the recess 22G.

(cover)
As shown in FIG. 3, the cover 23 is attached to the surface of the substrate 22 so as to form an internal space 24 between the substrate 22 and the heating resistor 21 in a region overlapping the heating resistor 21 in the thickness direction of the substrate 22.

  The cover 23 includes a plurality of openings 23A, a film body 23B, a base material layer 23C, a first tensile stress layer 23D, and a second tensile stress layer 23E. The cover 23 has a configuration in which a film body 23B is provided on a sheet-like member having a three-layer structure.

The base material layer 23C is a silicon or glass substrate similar to the base material layer 22A of the substrate 22 and has a front surface and a back surface.
The first tensile stress layer 23D is laminated on the surface of the base material layer 23C (that is, the surface opposite to the substrate 22). The second tensile stress layer 23E is laminated on the back surface of the base material layer 23C. The first tensile stress layer 23 </ b> D constitutes the outermost layer on the side opposite to the substrate 22 of the cover 23. The second tensile stress layer 23E constitutes the outermost layer on the substrate 22 side of the cover 23.

  The first tensile stress layer 23 </ b> D and the second tensile stress layer 23 </ b> E are films that generate tensile stress, and are the same type of films as the first tensile stress layer 22 </ b> B and the second tensile stress layer 22 </ b> C of the substrate 22. Further, the second tensile stress layer 23E is laminated on the surface of the substrate 22.

  A region of the cover 23 that faces the heating resistor 21 in plan view is formed with a recess from which the second tensile stress layer 23E and a part of the base material layer 23C are removed. An internal space 24 is formed by the recess and the surface of the substrate 22. The internal space 24 overlaps with a region where the heating resistor 21 is arranged in plan view. In the internal space 24, the base material layer 23C of the cover 23 is exposed.

  The plurality of openings 23 </ b> A communicate with the internal space 24. Therefore, the plurality of openings 23A penetrates the first tensile stress layer 23D and the base material layer 23C in the thickness direction. The plurality of openings 23 </ b> A are provided at positions facing the heating resistor 21.

  The film body 23B is disposed so as to cover the whole of the plurality of openings 23A. In the present embodiment, the film body 23B is disposed on the surface of the cover 23 (that is, the surface of the first tensile stress layer 23D) so as to straddle the plurality of openings 23A. The film body 23B is directly fixed to the cover 23 without any other substance such as an adhesive.

  The film body 23B has a property of transmitting water vapor and not detecting gas to be detected. As such a membrane body 23B, a fluororesin ion exchange membrane can be preferably used. Specific examples include Nafion (registered trademark), Flemion (registered trademark), and Aciplex (registered trademark). Moreover, you may use the hollow fiber membrane which can isolate | separate to-be-detected gas and water vapor | steam as the membrane body 23B.

  The gas to be detected is not supplied to the internal space 24 by the film body 23B. Therefore, the first gas detection element 2 functions as a reference element in which the heating resistor 21 is not affected by the gas to be detected. On the other hand, since the film body 23 </ b> B transmits water vapor, the humidity condition in the gas detection of the first gas detection element 2 is the same as that of the second gas detection element 3. The internal space 24 has no openings other than the plurality of openings 23A.

<Second gas detection element>
Similar to the first gas detection element 2, the second gas detection element 3 includes a heating resistor 31 whose resistance value changes due to a temperature change, and a substrate 32. On the other hand, the second gas detection element 3 does not have a cover attached to the surface of the substrate 32 unlike the first gas detection element 2.

  Since the configuration of the heating resistor 31 and the substrate 32 of the second gas detection element 3 is the same as that of the heating resistor 21 and the substrate 22 of the first gas detection element 2, detailed description thereof is omitted. The heating resistor 21 of the first gas detection element 2 and the heating resistor 31 of the second gas detection element 3 preferably have the same resistance value.

<Casing>
The casing 4 accommodates the first gas detection element 2 and the second gas detection element 3. As shown in FIG. 2, the casing 4 has an opening 4 </ b> A for introducing the gas to be detected therein, and a filter 4 </ b> B disposed in the opening 4 </ b> A.

  Specifically, the first gas detection element 2 and the second gas detection element 3 are accommodated in an internal space 4 </ b> C provided inside the casing 4. The internal space 4 </ b> C is formed by fixing the circuit board 10 to the inner frame 4 </ b> D protruding inside the casing 4 via the seal member 11.

  The opening 4A is formed to communicate the detected atmosphere and the internal space 4C. The filter 4B is a water repellent filter that transmits the gas to be detected and does not transmit liquid water (that is, removes water droplets contained in the gas to be detected). The filter 4B suppresses water droplets from entering the internal space 4C from the opening 4A. In the present embodiment, the filter 4B is attached to the inner surface of the casing 4 so as to close the opening 4A.

<Circuit board>
The circuit board 10 is disposed in the casing 4 and forms a circuit for calculating the gas concentration with the calculation unit 12. The circuit board 10 applies a voltage to the heating resistor 21 of the first gas detection element 2 and the heating resistor 31 of the second gas detection element 3.

<Calculation unit>
The computing unit 12 computes the concentration of gas in the atmosphere to be detected. Specifically, the computing unit 12 is configured to apply the first voltage when a constant voltage is applied to the heating resistor 21 of the first gas detection element 2 and the heating resistor 31 of the second gas detection element 3 connected in series. The concentration is calculated from the respective voltages (that is, partial pressures) of the heating resistor 21 of the gas detection element 2 and the heating resistor 31 of the second gas detection element 3.

  More specifically, the operational amplifier outputs a difference in partial pressure between the heating resistor 21 of the first gas detection element 2 and the heating resistor 31 of the second gas detection element 3, and is calculated from the difference in partial pressure. The density is output by the calculation unit 12.

[1-2. Production method]
Next, a method for manufacturing the gas sensor 1 will be described.
As shown in FIG. 6, the manufacturing method of the gas sensor 1 includes a substrate forming step S10, a cover forming step S20, a cover attaching step S30, and an in-casing arrangement step S40.

<Substrate formation process>
In this step, the substrate 22 of the first gas detection element 2 and the substrate 32 (so-called micro heater) of the second gas detection element 3 are formed. Hereinafter, a specific formation procedure for the substrate 22 of the first gas detection element 2 will be described, but the formation procedure of the substrate 32 of the second gas detection element 3 is also the same.

First, the first tensile stress layer 22B and the second tensile stress layer 22C are formed on the front and back surfaces of the base material layer 22A by, for example, the LP-CVD method.
Next, a first compressive stress layer 22D is formed on the surface of the first tensile stress layer 22B by, for example, a plasma CVD method.

  After the formation of the first compressive stress layer 22D, a metal film serving as a heater layer including the heating resistor 21 and the wiring 25 and a metal film serving as an adhesion layer are formed on the surface of the first compressive stress layer 22D by sputtering. Film. For example, tantalum (Ta) or niobium (Nb) can be used as the adhesion layer. The heating resistor 21 and the wiring 25 are formed by patterning these metal films.

  Further, a second compressive stress layer 22E is formed on the surface of the heating resistor 21 and the wiring 25 by a plasma CVD method. Thereafter, a third tensile stress layer 22F is formed on the surface of the second compressive stress layer 22E by the LP-CVD method.

Contact holes for connecting the electrode pads 26A and 26B to the wiring 25 of the heater layer are provided in the formed third tensile stress layer 22F and second compressive stress layer 22E.
After the contact hole is formed, a contact metal such as gold (Au) is deposited by sputtering and further patterned to form electrode pads 26A and 26B.

  Next, in order to form the diaphragm structure of the substrate 22, the back surface of the second tensile stress layer 22C is patterned. After the patterning, the substrate 22 on which the diaphragm structure is formed is obtained by etching the second tensile stress layer 22C and the base material layer 22A.

  Etching is performed with an anisotropic etching solution such as tetramethylammonium hydroxide (TMAH). Note that when an anisotropic etching solution is used, etching proceeds along the crystal plane, so that the etching plane is inclined with respect to the thickness direction as shown in FIG. In addition, when a glass substrate is used as the base material layer 22A, the concave portion may be formed using sand blasting.

<Cover forming process>
In this step, the cover 23 of the first gas detection element 2 is formed.
First, the first tensile stress layer 23D and the second tensile stress layer 23E are formed on the front and back surfaces of the base material layer 23C by, for example, the LP-CVD method.

  Next, the surface of the first tensile stress layer 23D and the back surface of the second tensile stress layer 23E are patterned in order to provide recesses for forming the internal space 24 and through holes that form a plurality of openings 23A. After the patterning, the first tensile stress layer 23D, the second tensile stress layer 23E, and the base material layer 23C are etched. Thereby, the said recessed part and several opening 23A are formed. Etching is performed with an anisotropic etching solution such as TMAH. In addition, when a glass substrate is used as the base material layer 23C, a concave portion or a through hole may be formed using, for example, sand blasting.

  Next, the liquid raw material of the film body 23B is placed on the surface of the first tensile stress layer 23D so as to close the plurality of openings 23A with, for example, a micropipette. The film body 23B is formed by drying the liquid raw material after mounting. When the liquid raw material is used in this way, the thickness of the film body 23B can be easily adjusted. Therefore, the responsiveness of the gas sensor 1 can be improved.

<Cover installation process>
In this step, the cover 23 is attached to the substrate 22 of the first gas detection element 2 to obtain the first gas detection element 2.

  Specifically, first, the superposition is performed so that the back surface of the cover 23 comes into contact with the front surface of the substrate 22. At this time, positioning is performed so that the concave portion of the cover 23 overlaps the heating resistor 21 in the thickness direction of the substrate 22.

  After the cover 23 is overlaid, the third tensile stress layer 22F of the substrate 22 and the second tensile stress layer 23E of the cover 23 are bonded by, for example, an anodic bonding apparatus. Thereby, the first gas detection element 2 having the internal space 24 is formed. In addition, you may adhere | attach the board | substrate 22 and the cover 23 using thermosetting resin.

<Inside casing arrangement process>
In this step, the first gas detection element 2 and the second gas detection element 3 are arranged in the internal space 4 </ b> C of the casing 4. Thereby, the gas sensor 1 is obtained.

[1-3. effect]
According to the embodiment detailed above, the following effects can be obtained.
(1a) Since the cover 23 forming the internal space 24 is directly attached to the substrate 22 of the first gas detection element 2, the volume of the internal space 24 with which the heating resistor 21 reacts can be reduced. As a result, it is possible to improve responsiveness to changes in humidity. Further, the size of the gas sensor 1 as a whole can be reduced by the reduction of the internal space 24.

  (1b) Since the plurality of openings 23A are provided at positions facing the heating resistor 21, the distance between the outside of the internal space 24 and the heating resistor 21 is reduced. As a result, the responsiveness to humidity changes can be further increased.

  (1c) Since the cover 23 has a plurality of openings 23A, the permeability of water vapor to the internal space 24 can be increased while maintaining the strength of the cover 23 or the film body 23B. As a result, the responsiveness to humidity changes can be further increased.

  (1d) The film body 23B is directly fixed to the cover 23 without any other substance. That is, the film body 23 </ b> B is directly formed in the opening 23 </ b> A of the cover 23. Therefore, the manufacturing cost of the gas sensor 1 can be reduced.

[2. Other Embodiments]
As mentioned above, although embodiment of this indication was described, it cannot be overemphasized that this indication can take various forms, without being limited to the above-mentioned embodiment.

  (2a) In the gas sensor 1 of the above embodiment, as shown in FIG. 7, the first gas detection element 2 and the second gas detection element 3 may be placed on the pedestal 5 provided on the surface of the circuit board 10. Good. The base 5 is made of ceramic and is made of alumina, for example.

  (2b) In the gas sensor 1 of the above embodiment, the cover 23 may have one opening 23A. Further, the opening 23 </ b> A does not necessarily have to face the heating resistor 21.

  (2c) In the gas sensor 1 of the above embodiment, the film body 23B does not necessarily have to be directly fixed to the cover 23. Therefore, the film body 23B may be fixed to the cover 23 with an adhesive or the like. In this case, the film body 23 </ b> B previously formed when the cover 23 is formed is used. In addition, the film body 23B may be filled in each through hole constituting the opening 23A. That is, the film body 23 </ b> B is not necessarily arranged on the surface of the cover 23.

  (2d) In the gas sensor 1 of the above embodiment, the structure of the substrate 22 is not limited to the above-described one. Therefore, the board | substrate 22 does not need to be provided with all the layers mentioned above, and may be provided with layers other than the above-mentioned.

  (2e) In the gas sensor 1 of the above embodiment, the structure of the cover 23 is not limited to the above-described one. Therefore, the cover 23 may not include all the layers described above, or may include layers other than those described above. Moreover, since the cover 23 should just be attached directly to the board | substrate 22, it may be metal.

  (2f) In the gas sensor 1 of the above embodiment, the casing 4 does not necessarily include the filter 4B. Moreover, the shape of the casing 4 shown in FIG.1 and FIG.2 is an example, and can be changed suitably.

  (2g) In the gas sensor 1 of the above embodiment, the first gas detection element 2 and the second gas detection element 3 are not limited to the heat conduction type. Therefore, the first gas detection element 2 and the second gas detection element 3 may be a contact combustion type detection element that burns the detection target gas using a combustion catalyst such as a noble metal. The first gas detection element 2 and the second gas detection element 3 may be detection elements using a metal oxide semiconductor as a resistor.

  (2h) The functions of one component in the above embodiment may be distributed as a plurality of components, or the functions of a plurality of components may be integrated into one component. Moreover, you may abbreviate | omit a part of structure of the said embodiment. In addition, at least a part of the configuration of the above embodiment may be added to or replaced with the configuration of the other embodiment. In addition, all the aspects included in the technical idea specified from the wording described in the claims are embodiments of the present disclosure.

DESCRIPTION OF SYMBOLS 1 ... Gas sensor, 2 ... 1st gas detection element, 3 ... 2nd gas detection element, 4 ... Casing,
4A ... opening, 4B ... filter, 4C ... internal space, 4D ... inner frame, 5 ... pedestal,
DESCRIPTION OF SYMBOLS 10 ... Circuit board, 11 ... Sealing member, 12 ... Operation part, 21 ... Heating resistor, 22 ... Board | substrate,
22A ... base material layer, 22B ... first tensile stress layer, 22C ... second tensile stress layer,
22D ... 1st compressive stress layer, 22E ... 2nd compressive stress layer, 22F ... 3rd tensile stress layer,
22G ... concave portion, 23 ... cover, 23A ... opening, 23B ... film body, 23C ... base material layer,
23D: first tensile stress layer, 23E: second tensile stress layer, 24: internal space, 25: wiring,
26A, 26B ... electrode pads, 31 ... heating resistor, 32 ... substrate.

Claims (6)

A gas sensor for detecting a gas in an atmosphere to be detected,
It has a gas detection element having a resistor whose resistance value changes due to its own temperature change,
The gas detection element is
A substrate on which the resistor is disposed;
A cover attached to the surface of the substrate so as to form an internal space with the substrate in a region overlapping the resistor in the thickness direction of the substrate;
Have
The cover is a gas sensor which has an opening which is in communication with the internal space and which is closed with a film body which transmits water vapor and does not transmit a gas to be detected.   The gas sensor according to claim 1, wherein the opening is provided at a position facing the resistor.   The gas sensor according to claim 1, wherein the cover has a plurality of the openings.   The gas sensor according to any one of claims 1 to 3, wherein the film body is a fluororesin-based ion exchange membrane.   The gas sensor according to any one of claims 1 to 4, wherein the film body is directly fixed to the cover without any other substance.   The gas sensor according to any one of claims 1 to 5, wherein the gas detection element is a heat conduction type detection element.

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