JP2023055088A - Mems type contact combustion type gas sensor - Google Patents

Abstract

To provide a MEMS type contact combustion type gas sensor that, even when water is generated by the reaction of a gas to be detected, can prevent a reduction in the accuracy of detecting the gas to be detected.SOLUTION: A MEMS type contact combustion type gas sensor (1) comprises a gas reaction part (13) and a water scattering prevention layer (14) provided on the gas reaction part (13). The water scattering prevention layer (14) transmits a gas to be detected, and has a lower activity for the gas to be detected than the gas reaction part (13).SELECTED DRAWING: Figure 2

Description

The present disclosure relates to a MEMS type catalytic combustion gas sensor.

A catalytic combustion type gas sensor has a gas reaction part that comes into contact with a detection target gas such as hydrogen. (For example, see Patent Document 1 below.).

JP-A-2009-002888

In the catalytic combustion type gas sensor as described above, there is a demand for miniaturization and power saving. In order to satisfy such demands, development and practical use of MEMS type catalytic combustion gas sensors using MEMS (Micro Electro Mechanical System) technology capable of microfabrication are being carried out.

However, in the MEMS type catalytic combustion gas sensor as described above, there has been a problem that the detection accuracy of the detection target gas is lowered due to the water generated by the combustion (reaction) of the detection target gas.

Specifically, when a MEMS-type catalytic combustion gas sensor is constructed, the heat-generating part becomes minute compared to the conventional catalytic combustion-type gas sensor due to its miniaturization. In close proximity, water vapor produced by the combustion of hydrogen was prone to condensation. For this reason, in the conventional MEMS type catalytic combustion type gas sensor, the adhesion of water may cause the temperature of the gas reaction portion to drop and the resistance value of the gas reaction portion to fluctuate. As a result, in the conventional MEMS type catalytic combustion type gas sensor, the sensor output is not stable, and the detection accuracy of the gas to be detected may be lowered.

An object of the present disclosure is to provide a MEMS-type catalytic combustion gas sensor capable of suppressing deterioration in detection accuracy of a detection target gas even when water is generated by reaction of the detection target gas.

In order to solve the above problems, a MEMS catalytic combustion gas sensor according to one aspect of the present disclosure includes a substrate, a detection electrode provided on the substrate, and a detection electrode provided on the substrate so as to be in contact with the detection electrode. and a water-splash-suppressing layer provided on the gas reaction part, wherein the gas to be detected includes at least one gas that reacts to generate water. The water-scattering suppression layer is permeable to the detection target gas and has a lower activity with respect to the detection target gas than the gas reaction section.

According to the above configuration, the water-splashing suppression layer has a lower activity with respect to the gas to be detected than the gas reaction part. Scattering can be suppressed. As a result, even if water is generated by the reaction of the detection target gas, the generated water does not evaporate all at once, and the amount of condensation near the gas reaction part can be suppressed. It is possible to configure a MEMS type catalytic combustion gas sensor capable of suppressing the deterioration.

The gas to be detected may be hydrogen. In this case, hydrogen can be detected up to a higher concentration.

According to one aspect of the present disclosure, it is possible to provide a MEMS catalytic combustion gas sensor capable of suppressing deterioration in detection accuracy of a detection target gas even when water is produced by reaction of the detection target gas.

1 is a plan view showing a MEMS catalytic combustion gas sensor according to Embodiment 1 of the present disclosure; FIG. FIG. 2 is a sectional view taken along line II-II of FIG. 1; FIG. 2 is a circuit diagram showing a configuration example of a detection circuit included in the MEMS type catalytic combustion gas sensor; It is a graph which shows the detection result example in a comparative example. 9 is a graph showing an example of detection results of the first embodiment; FIG. 7 is a cross-sectional view showing the configuration of a main part of a MEMS catalytic combustion gas sensor according to Embodiment 2 of the present disclosure;

[Embodiment 1]
<Schematic Configuration of MEMS Type Catalytic Combustion Gas Sensor 1>
A MEMS catalytic combustion gas sensor 1 according to Embodiment 1 of the present disclosure will be described in detail below with reference to FIGS. 1 to 3. FIG. FIG. 1 is a plan view showing a MEMS catalytic combustion gas sensor 1 according to Embodiment 1 of the present disclosure. FIG. 2 is a sectional view taken along line II--II of FIG. FIG. 3 is a circuit diagram showing a configuration example of a detection circuit included in the MEMS type catalytic combustion gas sensor 1. As shown in FIG.

1 and 2, the MEMS type catalytic combustion gas sensor 1 of this embodiment includes a sensing element 10 that senses a sensing target gas and a compensating element 20 that compensates for the detection result of the sensing element 10 . The gas to be detected includes at least one gas that can generate water by reaction (combustion) in the gas reaction section 13 included in the detection element 10 . Specifically, the detection target gas is a combustible gas containing hydrogen atoms, such as hydrogen, methane, isobutane, ethane, and propane.

<Structure of detection circuit>
Further, the MEMS type catalytic combustion gas sensor 1 of this embodiment includes, for example, a detection circuit including a bridge circuit. That is, as shown in FIG. 3, the detection circuit of this embodiment includes a bridge circuit having a detection element 10, a compensation element 20, a resistor 71, and a resistor 72, a power supply 73 for supplying power to the bridge circuit, and a and a voltmeter 74 for detecting the voltage of the bridge circuit and outputting it as the sensing result of the MEMS catalytic combustion type gas sensor 1 .

Further, in the present embodiment, power is intermittently supplied from the power supply 73 to the detection element 10, and the detection element 10 receiving the power supply reaches a predetermined combustion temperature (for example, 300 ° C to 700 ° C). The compensating element 20 also compensates for changes in the resistance value of the detecting element 10 based on temperature changes other than combustion of the gas to be detected (for example, ambient temperature changes).

Further, in this embodiment, the sensing element 10 and the compensating element 20 are set to have the same resistance value. Therefore, when the detection target gas does not exist around the MEMS type catalytic combustion type gas sensor 1, the bridge circuit is in a balanced state, and the output of the voltmeter 74 (that is, the sensing result) indicates that the detection target gas does not exist. is a value of 0.

On the other hand, when the gas to be detected exists, the temperature of the detection element 10 rises due to the combustion, and the resistance value of the detection element 10 also increases. Therefore, in the detection circuit, the bridge circuit is unbalanced, and the output of the voltmeter 74 becomes greater than zero in proportion to the concentration of the gas to be detected. As a result, the MEMS type catalytic combustion gas sensor 1 of this embodiment can detect the concentration of the detection target gas.

<Main Configuration of MEMS Type Catalytic Combustion Gas Sensor 1>
As shown in FIGS. 1 and 2, the MEMS-type catalytic combustion gas sensor 1 of this embodiment includes a substrate 30 made of, for example, silicon, an insulating film 40 formed on the substrate 30, and an insulating film 40 formed on the substrate 30. and a compensating element 20 supported on a recess 32 formed in the substrate 30 .

The insulating film 40 is made of, for example, silicon oxide, silicon nitride, tantalum oxide, or a laminated film thereof, and the substrate 30 except for the surfaces of the recesses 31 and 32 is exposed to the gas to be detected. It is formed on the surface (upper surface in FIG. 2) side.

<Structure of Detecting Element 10>
The sensing element 10 includes a first supporting portion 11 that supports the sensing element 10 , heater wiring 12 provided on the first supporting portion 11 , and the above-mentioned gas heater wiring 12 provided above the heater wiring 12 so as to be in contact with the heater wiring 12 . It includes a reaction section 13 and a water-splash suppression layer 14 provided on the gas reaction section 13 .

As shown in FIGS. 1 and 2 , the first support portion 11 is attached to the substrate 30 via a plurality of, for example, four bridging portions 15 so as to float above the recess 31 . That is, one end of each of the four bridges 15 is connected to the first support 11 , and the other end of each of the four bridges 15 is connected to the substrate 30 . By separating the first support portion 11 from the substrate 30 in this manner, it is possible to suppress the heat generated by the heater wiring 12 from radiating to the substrate 30, and the temperature in the gas reaction portion 13 is reduced. The decrease can be suppressed, and power saving of the MEMS type catalytic combustion gas sensor 1 can be achieved.

The first supporting portion 11 and the bridging portion 15 are made of, for example, silicon oxide, silicon nitride, tantalum oxide, or a laminated film thereof, like the insulating film 40 .

The heater wiring 12 is made of, for example, a noble metal wire such as platinum, and also serves as a detection electrode in the bridge circuit (FIG. 3). In other words, the heater wiring 12 heats the gas reaction section 13 according to the electric power from the power source 73, and heats the gas reaction section 13 by the heater wiring 12 and combusts with the gas to be detected. Resistance value changes. A change in the resistance value of the heater wiring 12 is used as detection data for detecting the concentration of the gas to be detected.

Specifically, one end and the other end of the heater wiring 12 are connected to the thin film wirings 51 and 52 provided on the bridge portion 15, respectively. The thin-film wiring 51 is also connected to an electrode pad 61 connected to a connection point between the sensing element 10 and the resistor 72 in the bridge circuit (FIG. 3). The thin-film wiring 52 is also connected to an electrode pad 62 connected to a connection point between the sensing element 10 and the compensating element 20 in the bridge circuit.

The electrode pads 61 and 62 are connected to one end of a power supply 73 and one end of a voltmeter 74 via lead wires (not shown), respectively. As a result, the detection element 10 is supplied with power from the power source 73 and can detect the concentration of the gas to be detected.

The gas reaction unit 13 is configured by supporting, for example, a noble metal catalyst such as palladium or platinum, which is active with respect to a gas to be detected such as hydrogen, on a carrier using alumina, silica-alumina, or the like. Thus, the gas reaction unit 13 contains a noble metal catalyst that reacts with the gas to be detected and burns. Further, the gas reaction part 13 is formed by, for example, applying a coating method to the carrier supporting the noble metal catalyst on the first support part 11, and then firing the carrier in an electric furnace. 11.

The water scattering suppression layer 14 is made of an inert material that is inert to the gas to be detected, such as alumina, tin oxide, or silica-alumina. In other words, unlike the gas reaction section 13, the water scattering suppression layer 14 does not contain a noble metal catalyst that is active with respect to the detection target gas, and has a lower activity with respect to the detection target gas than the gas reaction section 13 does. Further, the water scattering suppression layer 14 is formed on the gas reaction section 13 by, for example, applying the inert material on the gas reaction section 13 by a coating method, and then firing the material in an electric furnace. be.

Moreover, the water-scattering suppression layer 14 is configured to allow the detection target gas to pass therethrough so as not to hinder the reaction with the detection target gas in the gas reaction section 13 . Specifically, the film thickness of the water scattering suppression layer 14 is, for example, approximately 10 to 40 μm. In addition, the water scattering suppression layer 14 has a small specific surface area (for example, 5 m ² /g or less), which allows permeation of the gas to be detected, and water generated in the gas reaction section 13 ( water droplets).

In addition, in the sensing element 10, the components other than the gas reaction section 13 and the water scattering suppression layer 14 are formed using MEMS (Micro Electro Mechanical System) technology.

<Structure of Compensating Element 20>
The compensating element 20 includes a second supporting portion 21 that supports the compensating element 20, a heater wiring 22 provided on the second supporting portion 21, and a compensating portion provided above the heater wiring 22 so as to contact the heater wiring 22. 23 and.

As shown in FIGS. 1 and 2 , the second support portion 21 is attached to the substrate 30 via a plurality of, for example, four bridging portions 25 so as to float above the recess 32 . That is, one end of each of the four bridges 25 is connected to the second support 21 , and the other end of each of the four bridges 25 is connected to the substrate 30 . By separating the second support portion 21 from the substrate 30 in this way, it is possible to suppress the heat generated by the heater wiring 22 from radiating to the substrate 30, and the temperature drop in the compensating portion 23 can be suppressed. can be suppressed, and power saving of the MEMS type catalytic combustion type gas sensor 1 can be achieved.

The second supporting portion 21 and the bridging portion 25 are made of, for example, silicon oxide, silicon nitride, tantalum oxide, or a laminated film thereof, like the insulating film 40 .

The heater wiring 22 is made of, for example, a noble metal wire such as platinum, and also serves as a compensating detection electrode in the bridge circuit (FIG. 3). That is, the heater wiring 22 heats the compensating portion 23 according to the electric power from the power supply 73, and the resistance value changes according to the temperature rise caused by the heating by the heater wiring 22 in the compensating portion 23. FIG. A change in the resistance value of the heater wiring 22 is used as compensation data when detecting the concentration of the gas to be detected.

Specifically, one end and the other end of the heater wiring 22 are connected to the thin film wirings 53 and 54 provided on the bridge portion 25, respectively. The thin-film wiring 53 is also connected to an electrode pad 62 connected to a connection point between the sensing element 10 and the compensating element 20 in the bridge circuit (FIG. 3). The thin-film wiring 54 is also connected to an electrode pad 63 connected to a connection point between the compensating element 20 and the resistor 71 in the bridge circuit.

The electrode pads 62 and 63 are connected to one end of the voltmeter 74 and the other end of the power source 73 via lead wires (not shown), respectively. As a result, the compensating element 20 is supplied with power from the power source 73 and can compensate for the detection of the concentration of the gas to be detected.

The compensator 23 is made of an inert material, such as alumina or silica-alumina, which is inert to the gas to be detected, and is active to the gas to be detected, such as hydrogen, such as palladium or platinum. No precious metal catalysts are included. Further, the compensating portion 23 is formed on the second supporting portion 21 by, for example, applying the inert material on the second supporting portion 21 by a coating method, and then firing the material in an electric furnace. be.

In the compensating element 20, the components other than the compensating portion 23 are formed using MEMS (Micro Electro Mechanical System) technology.

In the above description, as shown in FIG. 2, the heater wires 12 and 22 are exposed and the first support portion 11 and the second support portion are connected so as to directly contact the gas reaction portion 13 and the compensation portion 23, respectively. 21 has been described as an example. However, the present embodiment is not limited to this. For example, the heater wires 12 and 22 may be embedded inside the first support portion 11 and the second support portion 21, respectively.

In the MEMS-type catalytic combustion gas sensor 1 of the present embodiment configured as described above, the sensing element 10 includes the gas reaction section 13 and the water scattering suppression layer 14 provided on the gas reaction section 13 . In addition, since the water-splash-suppressing layer 14 has a lower activity with respect to the gas to be detected than the gas-reacting portion 13, the water-splash-suppressing layer 14 is less likely to produce water due to the reaction of the gas to be detected than the gas-reacting portion 13. Splashing of water can be suppressed. As a result, even when water is generated by the reaction of the gas to be detected, the present embodiment can suppress the amount of condensation near the gas reaction unit 13 without evaporating the generated water all at once. It is possible to configure the MEMS type catalytic combustion gas sensor 1 capable of suppressing deterioration in detection accuracy of the target gas.

In addition, in the present embodiment, the water-splash-suppressing layer 14 suppresses the splashing of water (water droplets) generated in the gas reaction section 13, so that splashing of the water droplets to the peripheral region of the sensing element 10 can be greatly suppressed. . As a result, in this embodiment, it is possible to reliably suppress fluctuations in the sensing result (sensor output) of the MEMS type catalytic combustion gas sensor 1 due to water droplets scattered in the peripheral area.

Further, in this embodiment, hydrogen is detected as the detection target gas. Thereby, in this embodiment, hydrogen can be detected up to a higher concentration.

Here, also referring to FIGS. 4 and 5, the effect of the MEMS type catalytic combustion gas sensor 1 of this embodiment will be specifically described. FIG. 4 is a graph showing an example of detection results in a comparative example. FIG. 5 is a graph showing an example of detection results of the first embodiment.

First, in the comparative example, unlike the product of the present embodiment, only the gas reaction portion is formed in the sensing element, and the water-splash-suppressing layer is not formed. For this reason, in the comparative example, it is not possible to prevent water generated by the reaction (combustion) with hydrogen (detection target gas) in the gas reaction section from scattering in the peripheral region of the detection element. As a result, in the comparative example, as shown in the graph of FIG. 4, the sensor output was not stable and fluctuated greatly.

On the other hand, in the product of the present embodiment, the water splash suppression layer 14 suppresses splashing of water to the peripheral area of the sensing element 10. Therefore, as shown in the graph of FIG. , became a constant and stable value. That is, in the product of the present embodiment, for example, the sensor output was held at a value of about 80 when the hydrogen concentration was 4%, as indicated by 100% LEL. Thus, it was demonstrated that the product of the present embodiment can detect hydrogen with high accuracy.

[Embodiment 2]
Embodiment 2 of the present disclosure will be specifically described with reference to FIG. FIG. 6 is a cross-sectional view showing a main configuration of a MEMS catalytic combustion gas sensor according to Embodiment 2 of the present disclosure. For convenience of description, members having the same functions as those of the members described in the above embodiments are denoted by the same reference numerals, and description thereof will not be repeated.

The main difference between the second embodiment and the first embodiment is that a bank window 85 is provided around the gas reaction section 83 .

In the MEMS type catalytic combustion gas sensor 1 of the present embodiment, as shown in FIG. , a gas reaction portion 83 provided so as to be in contact with the heater wiring 82, and a water scattering suppression layer 84 provided on the gas reaction portion 83. As shown in FIG.

Further, in the present embodiment, a bank window 85 having a substantially circular window (not shown) is provided on the first support portion 81 so as to surround the gas reaction portion 83 in contact with the outer peripheral portion of the gas reaction portion 83 . . The embankment window 85 is made of, for example, the same material as the first support portion 81 and is constructed using MEMS (Micro Electro Mechanical System) technology.

In addition, in this embodiment, by providing the embankment window 85, the water scattering suppression layer 84 can be formed with a more uniform film thickness. That is, the bank window 85 surrounds the outer peripheral portion of the gas reaction portion 83 so that the film thickness of the end portions of the water-scattering suppression layer 84 is uniform with the film thickness of the central portion of the water-scattering suppression layer 84 . This is because it becomes possible to easily form the end on 85 .

With the above configuration, the present embodiment has the same effects as those of the first embodiment. In addition, since the water-splashing suppression layer 84 can be formed with a more uniform film thickness, it is possible to more reliably suppress water-splashing to the peripheral region of the sensing element 80 . Fluctuations in the sensor output can be suppressed more reliably.

The present invention is not limited to the above-described embodiments, but can be modified in various ways within the scope of the claims, and can be obtained by appropriately combining technical means disclosed in different embodiments. is also included in the technical scope of the present invention.

1 MEMS type catalytic combustion type gas sensor 12, 82 heater wiring (detection electrode)
13, 83 Gas reaction section 14, 84 Water scattering suppression layer 30 Substrate

Claims (2)

A MEMS, comprising: a substrate; a sensing electrode provided on the substrate; a gas reaction section provided on the substrate so as to be in contact with the detection electrode; and a water splash suppression layer provided on the gas reaction section. A type catalytic combustion gas sensor,
The gas to be detected includes at least one gas that reacts to generate water,
The MEMS type catalytic combustion gas sensor, wherein the water scattering suppression layer is permeable to the detection target gas and has a lower activity with respect to the detection target gas than the gas reaction section. 2. The MEMS type catalytic combustion gas sensor according to claim 1, wherein the gas to be detected is hydrogen.

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