JP2019015521A - Contact combustion type gas sensor - Google Patents

Abstract

To provide a contact combustion type gas sensor capable of suppressing influence of water generated by combustion of a combustible gas.SOLUTION: The contact combustion type gas sensor includes a detection element 1 with a resistance value changing in accordance with combustion heat of a combustible gas, and a heater 40 that is removal means for removing water generated by combustion of the combustible gas. The gas sensor further includes a silicon substrate 31 on which the detection element 1 is supported, and the heater 40 is arranged on the silicon substrate 31.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a contact combustion type gas sensor that detects a combustible gas.

  As a gas sensor having a gas sensitive part of a sintered body, a semiconductor type, a catalytic combustion type, a solid electrolyte, and the like are known. These usually perform gas detection in a state where the gas sensitive part is maintained at 300 ° C. to 700 ° C., so that the power consumption is required to be several hundred mW or more.

  In recent years, there is an increasing demand for driving gas sensors with batteries for a long period of time. In order to suppress the power consumption of the battery and reduce the frequency of battery replacement as much as possible, it is desirable to reduce the power consumption of the gas sensor.

  Therefore, if a MEMS (Micro Electro Mechanical System) technology capable of microfabrication is used, a minute member can be processed, and a gas detection element that is reduced in size and consumes less power can be manufactured.

  As a gas detection element having a supported substrate portion manufactured by the MEMS technology, for example, a suspension bridge type catalytic combustion type gas detection element is known (for example, see Patent Document 1).

  In this type of catalytic combustion type gas detection element, a supported substrate portion provided with a gas sensitive portion and a heating means is called a plurality of bridge portions (including a supported substrate portion and a bridge portion, also referred to as “membrane” or “diaphragm”). ) Is supported in a hollow state so that it floats in the air on a supporting substrate portion such as a silicon substrate, and mutual heat transfer between the supporting substrate portion and the supported substrate portion can be suppressed, so that heat insulation is excellent. . As a result, the suspension bridge type catalytic combustion type gas detection element can prevent a temperature drop due to heat dissipation and realize low power consumption.

  The contact combustion type gas detection element has two elements, a detection element that performs a combustion reaction with respect to the combustible gas and a compensation element that does not perform the combustion reaction, and if there is a combustible gas, it burns on the detection element side. The sensing element temperature increases and the resistance of the sensing element increases. By measuring this resistance change amount, combustible gas can be detected. In the contact combustion type gas detection element, for example, when hydrogen is present as an example of a combustible gas, the detection element burns to generate water.

JP 2009-58389 A

  For example, in the catalytic combustion type gas detection element that has been reduced in size by the MEMS technology, water droplets generated by combustion adhere to the periphery of the detection element at a predetermined hydrogen gas concentration. It has been found that the resistance of the sensing element is changed, causing variations in the output value of the sensing element. This is a problem peculiar to the catalytic combustion type gas detection element reduced in size for low power consumption as described above. Therefore, a technology for suppressing the influence of water generated by combustion of combustible gas is desired in the catalytic combustion type gas detection element.

  Then, this invention is made | formed in view of the said subject, and it aims at providing the contact combustion type gas sensor which can suppress the influence of the water produced | generated by combustion of combustible gas.

  The problem to be solved by the present invention is as described above. Next, means for solving the problem will be described.

  That is, the catalytic combustion type gas sensor of the present invention comprises a detection element whose resistance value changes according to the combustion heat of the combustible gas, and a removing means for removing water generated by the combustion of the combustible gas. It is a thing.

  According to such a configuration, as the flammable gas, for example, water generated by combustion of flammable gas such as hydrogen can be removed by the removing means. It can be detected accurately.

  The contact combustion gas sensor of the present invention further includes a substrate on which the detection element is supported, and the removing means is provided on the substrate.

  According to such a structure, the water produced | generated on a board | substrate can be removed efficiently.

  In the catalytic combustion gas sensor of the present invention, the detection element is supported by the substrate in a hollow state.

  According to such a configuration, since the detection element is supported in a hollow state, the thermal insulation is excellent.

  The catalytic combustion type gas sensor of the present invention further includes a compensation element connected in parallel with the detection element, and the removing means is provided at least around the detection element.

  According to such a configuration, it is possible to efficiently remove water by providing the removing means at least on the detection element that generates water by the combustion of the combustible gas.

  In the catalytic combustion gas sensor of the present invention, the removing means is a heater that removes water by heating.

  According to such a configuration, water can be removed with a simple configuration.

  In the catalytic combustion type gas sensor of the present invention, the removing means is arranged on the exposed surface side of the combustible gas in the substrate.

  According to such a configuration, water can be efficiently removed by providing the removing means on the exposed surface side of the combustible gas, which is the side where water is easily generated by the combustion of the combustible gas in the substrate. .

  The catalytic combustion type gas sensor of the present invention is formed by MEMS technology.

  According to such a configuration, since the MEMS technology capable of fine processing is applied, it is possible to manufacture an extremely small sensing element. Thereby, a contact combustion type gas sensor with low average power consumption can be obtained.

  According to the present invention, as the flammable gas, for example, water generated by combustion of a flammable gas such as hydrogen can be removed by the removing means. Can be detected.

The top view which shows the whole structure of the gas detection element with which the catalytic combustion type gas sensor which concerns on one Embodiment of this invention is provided. AA sectional drawing in FIG. Schematic which shows the bridge circuit with which a contact combustion type gas sensor is provided. It is a figure which shows the measurement result in the predetermined environment in the conventional MEMS type contact combustion type gas sensor, (a) is a figure which shows the response waveform of the sensor output at the time of hydrogen exposure, (b) is hydrogen in a high temperature and low humidity environment The figure which shows the response waveform of the sensor output at the time of exposure.

  Next, a catalytic combustion type gas sensor 100 according to an embodiment of the present invention will be described with reference to the drawings.

The catalytic combustion type gas sensor 100 is a gas sensor including a catalytic combustion type gas detection element 60 that detects flammable gas, and is a small gas sensor formed by MEMS technology.
In addition, the combustible gas in this embodiment is the gas which water produces | generates by a combustion reaction, for example, hydrogen, methane, isobutane, ethane, propane etc. are mentioned.

  As shown in FIG. 3, the contact combustion type gas sensor 100 includes a detection element 1 that detects by burning a combustible gas such as hydrogen gas that is a gas to be detected, and a temperature other than the combustion of the combustible gas such as an environmental change. A compensation element 2 for correcting a change in the resistance value of the sensing element 1 based on the change and fixed resistances R1 and R2 are included, and a bridge circuit is configured by these elements. The detection element 1 changes its resistance value according to the combustion heat of the combustible gas. The detection element 1 and the compensation element 2 are connected in parallel to form a bridge circuit. The bridge circuit constantly supplies a predetermined current by the power source E, and holds the detection element 1 at a temperature at which the combustible gas is easy to contact and burn.

  The sensing element 1 and the compensating element 2 are set so that the resistance values are equal. For this reason, when there is no flammable gas, the bridge circuit is in an equilibrium state and the sensor output V is not generated. On the other hand, if flammable gas exists, the temperature of the sensing element 1 rises due to the combustion and the resistance value increases, so the balance of the bridge circuit is lost and the sensor output V is generated. Since the sensor output V is proportional to the concentration of the combustible gas, the contact combustion type gas sensor 100 can measure the concentration of the combustible gas in the air.

  As shown in FIG. 2, the catalytic combustion type gas detection element 60 is disposed on a silicon (Si) substrate 31, an insulating film F formed on the silicon substrate 31, and spaced apart on the insulating film F. The detection element 1 and the compensation element 2, and the heater 40 disposed around the detection element 1 and the compensation element 2 are included.

  The silicon substrate 31 is a substrate for supporting the detection element 1 and the compensation element 2. The silicon substrate 31 is provided with a pair of concave spaces S at positions corresponding to the detection element 1 and the compensation element 2.

The insulating film F is a member obtained by processing a thin insulating member in a predetermined pattern shape, and is attached on the silicon substrate 31. The insulating film F includes a supported substrate portion 10 having a rectangular shape in a top view for providing the gas sensitive portion 11 and the heating means 12, and a plurality (four in this embodiment) of which one end is connected to the supported substrate portion 10. It is comprised by the bridge | crosslinking part 20 and the support substrate part 30 with which the other end of the said bridge | crosslinking part 20 is connected. The supported substrate portion 10 is disposed above the space S of the silicon substrate 31 by the plurality of bridging portions 20 and is held on the support substrate portion 30 in a suspension bridge shape. Accordingly, the detection element 1 is supported in a state of being positioned above the space S, that is, in a hollow state on the silicon substrate 31.
Note that the shape of the supported substrate unit 10 in a top view is not limited to this embodiment, and may be a circular shape or an elliptical shape.
For example, when the supported substrate part 10 is a square, the size of one side is 100 to 200 μm.

  The sensing element 1 has a gas sensitive part 11 and a heating means 12 made of a noble metal wire such as Pt for heating the gas sensitive part 11. The gas sensitive part 11 is a sintered body whose main component is a metal oxide which is covered with the heating means 12 and sintered. The gas sensitive part 11 is configured by supporting a noble metal catalyst on a catalyst carrier. Platinum, palladium, etc. can be used as the noble metal catalyst. Although it does not specifically limit as a catalyst support | carrier, For example, an alumina, a silica alumina, etc. can be used.

  The compensation element 2 has substantially the same configuration as that of the detection element 1, and includes a compensation unit 13 that does not include a noble metal catalyst in the gas sensitive part 11 of the detection element 1. That is, the compensation unit 13 is configured only by the same catalyst carrier as that used in the detection element 1.

The heating means 12 is also used as a detection electrode in the block circuit. The heating means 12 is connected to pads 51, 52, 53 disposed on the support substrate portion 30 via a thin film wiring 14 formed on the bridging portions 20, 20, and leads ( Wire bonding). A signal sensed by the gas sensitive unit 11 is transmitted to the control unit (not shown) of the catalytic combustion type gas sensor 100 via the lead and the thin film wiring 14, and power is supplied to the heating unit 12 by the power source E. Can do.
In addition, after confirming presence of combustible gas by the control part of the contact combustion type gas sensor 100, you may control so that the heater 40 may be driven for a fixed time, and you may comprise so that power consumption may be suppressed.

  The supported substrate part 10, the heating means 12, and the gas sensitive part 11 are laminated in order to constitute a laminated body. Each structure except the gas sensitive part 11 among the said laminated body is produced using the MEMS technique. The MEMS technology is a technology for manufacturing an electronic device system having an ultrafine structure. With this technique, fine circuits can be processed. The laminate can be formed by a known method using MEMS technology.

The heater 40 is a removing unit that is provided on the exposed surface side of the combustible gas of the silicon substrate 31 and removes water generated by the combustion reaction of the combustible gas. Specifically, the heater 40 is a heating means made of a platinum thin film, and is formed in a predetermined pattern around each of the detection element 1 and the compensation element 2, and the periphery of each of the detection element 1 and the compensation element 2 is predetermined. Water is vaporized and removed by heating to a temperature of. The heater 40 in this embodiment is mainly disposed in a portion excluding the portion where the pads 51, 52, 53 are disposed on the upper end surface of the silicon substrate 31.
The heater 40 is not limited to the pattern shape of the present embodiment, and may have any pattern shape as long as it can heat the surroundings of the detection element 1 and the compensation element 2. For example, a configuration may be adopted in which a heater is partially provided in a portion where the temperature tends to be relatively low around each of the detection element 1 and the compensation element 2.
The heater 40 may be provided at least around the detection element 1 that generates water by a combustion reaction.
Moreover, the heating temperature by the heater 40 should just be more than the temperature which water vaporizes, for example, 80 degreeC or more is preferable.
Further, the heating temperature by the heater 40 may be equal to or higher than the temperature at which water vaporizes as described above, but the heating temperature is preferably as low as possible from the viewpoint of power saving.
In addition, the range in which the heater 40 is disposed is preferably as narrow as possible from the viewpoint of power saving.
Heating by the heater 40 may be performed constantly or at predetermined intervals (intermittent heating), but from the viewpoint of power saving, when a combustible gas such as hydrogen is detected (water The heating may be performed only when there is a high possibility of the occurrence of.

  In addition to the heater 40, as a removing means for removing water, for example, the surface of the silicon substrate 31 may be subjected to water repellent treatment, or the water repellent treatment and the heater 40 may be combined.

Next, measurement results when a high-concentration combustible gas is exposed using a conventional MEMS-type catalytic combustion gas sensor will be described.
In the graph shown in FIG. 4, the vertical axis represents the sensor output (mV) of a conventional catalytic combustion gas sensor, the horizontal axis represents time (sec.), And the temperature of the gas sensitive part is maintained at 300 ° C. The concentration of the combustible gas up to the lower explosion limit (LEL) is increased every elapse of a predetermined time.

  When high-concentration hydrogen was exposed to a conventional MEMS-type catalytic combustion gas sensor in a predetermined environment (set environmental condition: 20 ° C./60% RH), a phenomenon in which the response waveform was disturbed was observed (FIG. 4A). reference). However, it was found that the disturbance of the response waveform can be improved as shown in FIG. 4B by measuring in an environment of high temperature and low humidity (setting environment condition: 80 ° C./0% RH). When high-concentration hydrogen is exposed to a conventional MEMS type catalytic combustion gas sensor, it has been confirmed that water is generated around the sensing element due to the combustion reaction of the sensing element. These phenomena are presumed to be due to the heat of adsorption / evaporation when water generated by hydrogen combustion is adsorbed / desorbed (vaporized) around the sensing element.

  In the catalytic combustion type gas detection element 60 according to this embodiment, the heater 40 is formed in a predetermined pattern so as to cover the periphery of the detection element 1 and the compensation element 2, thereby preventing the generated water from being adsorbed and having a high concentration. Disturbance of response waveform at the time of hydrogen exposure can be solved.

  As described above, the catalytic combustion type gas sensor 100 according to the present embodiment includes the detection element 1 whose resistance value changes according to the combustion heat of the combustible gas, and the removing unit that removes the water generated by the combustion of the combustible gas. And. As a result, for example, water generated by combustion of a combustible gas such as hydrogen can be removed by the removing means as the combustible gas, so that the adverse effect of water is suppressed and the combustible gas is accurately detected. Can do.

  The catalytic combustion gas sensor 100 of the present embodiment further includes a silicon substrate 31 on which the detection element 1 is supported, and a removing means is provided on the silicon substrate 31. Thereby, the water produced | generated on the silicon substrate 31 can be removed efficiently.

  Further, the catalytic combustion type gas sensor 100 of the present embodiment is excellent in thermal insulation because the sensing element 1 is supported by the silicon substrate 31 in a hollow state.

  Further, the catalytic combustion gas sensor 100 of the present embodiment further includes a compensation element 2 connected in parallel with the detection element 1, and the removing means is provided at least around the detection element 1. Thereby, water can be efficiently removed by providing a removing means in the detection element 1 that generates water by combustion of combustible gas.

  Moreover, the contact combustion type gas sensor 100 of this embodiment is the heater 40 from which a removal means removes water by heating. Thereby, water can be removed with a simple configuration.

  Further, in the catalytic combustion type gas sensor 100 of the present embodiment, the removing means is arranged on the exposed surface side of the combustible gas in the silicon substrate 31.

  According to such a configuration, the water can be efficiently removed by providing the removing means on the exposed surface side of the combustible gas, which is the side where water is easily generated by the combustion of the combustible gas in the silicon substrate 31. Can do.

  Moreover, the catalytic combustion type gas sensor 100 of this embodiment is formed by MEMS technology. Thereby, since the MEMS technology capable of fine processing is applied, it is possible to manufacture an extremely small catalytic combustion type gas detection element 60. Thereby, the contact combustion type gas sensor 100 with low average power consumption can be obtained.

  INDUSTRIAL APPLICABILITY The present invention can be used for a contact combustion type gas sensor including a detection element whose resistance value changes according to the combustion heat of combustible gas.

DESCRIPTION OF SYMBOLS 1 Detection element 31 Silicon substrate 40 Heater 60 Contact combustion type gas detection element 100 Contact combustion type gas sensor

Claims (7)

A sensing element whose resistance value changes according to the combustion heat of the combustible gas;
A contact combustion type gas sensor comprising: removal means for removing water generated by combustion of the combustible gas. A substrate on which the sensing element is supported;
The catalytic combustion gas sensor according to claim 1, wherein the removing unit is provided on the substrate.   The catalytic combustion gas sensor according to claim 1, wherein the detection element is supported by the substrate in a hollow state. A compensation element connected in parallel with the sensing element;
The catalytic combustion gas sensor according to any one of claims 1 to 3, wherein the removing means is provided at least around the sensing element.   The catalytic combustion gas sensor according to any one of claims 1 to 4, wherein the removing means is a heater that removes water by heating.   The catalytic combustion type gas sensor according to any one of claims 1 to 5, wherein the removing means is disposed on the exposed surface side of the combustible gas in the substrate.   The catalytic combustion type gas sensor according to any one of claims 1 to 6, formed by MEMS technology.

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