JP2015004537A - Gas detection element driving method and gas detection device - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a gas detection element driving method and a gas detection device capable of improving durability to high-temperature use and long-term service, and stabilizing gas detection sensitivity.SOLUTION: Provided is the gas detection element driving method for applying with switching polarity at a desired timing to a gas detection element X on which a gas sensitivity part for contacting to gas to be detected is provided, in which the gas sensitivity part is mainly formed of a metal oxide formed by sintered with covering a noble metal wire. A gas detection device Y comprising: the gas detection element X; polarity inversion means 40 for applying with switching polarity at desired timing to the gas detection element X; and a current generation device 50 for feeding pulse current to the gas detection element X, is also provided.

Description

  The present invention relates to a method for driving a gas detection element having a gas sensitive portion that is in contact with a gas to be detected, the main component of which is a metal oxide that covers and sinters a noble metal wire, and a gas detection device including the gas detection element. About.

  As a gas detection element having a gas sensitive part of a sintered body, for example, a semiconductor type is known. Since such a gas detection element normally performs gas detection in a state where the gas sensitive part is maintained at 300 ° C. to 700 ° C., 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 reduce the battery cost and reduce the frequency of battery replacement as much as possible, it is desirable to reduce the power consumption of the gas sensor.
By utilizing MEMS (Micro Electro Mechanical System) technology capable of microfabrication, a minute member can be processed, and a gas detection element that is reduced in size and consumes less power can be manufactured. The average power consumption can be further reduced by pulse-driving this downsized gas detection element to detect gas intermittently. Since the gas detection elements can be mass-produced by using the MEMS technology, the cost of the gas detection elements can be reduced.

However, in order to put such a gas detection element into practical use, it is necessary to improve characteristics such as thermal shock resistance and durability.
As a gas detection element having a supported substrate portion manufactured by MEMS technology, there is one disclosed in Patent Document 1. In this type of element, a supported substrate portion provided with a gas sensitive portion and a heating means is supported on a supporting substrate portion by a plurality of bridging portions, and is excellent in thermal insulation.

  When a thermal cycle is applied to the gas detection element over a room temperature and a driving temperature (for example, 500 ° C.), a thermal shock is repeatedly applied to the gas detection element. This thermal shock causes thermal deterioration of members constituting the gas detection element.

JP 2007-132814 A

  For example, in the case of a sensor for detecting methane, it is necessary to raise the temperature of the substrate to a high temperature of about 500 ° C. Therefore, it is important for the sensor for detecting methane to improve the heat resistance of the substrate. For example, the MEMS type sensor described in Patent Document 1 has a low substrate durability when a voltage is continuously applied, and thus the voltage is intermittently applied to extend the life. However, when the substrate needs to be heated like a methane detection sensor, further measures against the high temperature are necessary.

  In the case of a two-terminal type thermal linear semiconductor sensor, the temperature distribution of the gas detection element due to DC voltage application is high in the semiconductor part on the positive side and low in the semiconductor part on the negative side. There is a temperature difference. As a result, by using the thermal linear semiconductor sensor for a long time, grain growth is likely to occur in the semiconductor portion on the plus side, and even if a precious metal catalyst or the like is uniformly added to the entire gas sensing element, the plus side Aggregation in the semiconductor portion of this was likely to occur. Therefore, long-term use of the thermal linear semiconductor sensor has deteriorated the catalyst activity, which has been a factor in changing the gas detection sensitivity.

  Accordingly, an object of the present invention is to provide a gas detection element driving method and a gas detection device capable of improving durability in high temperature use and long-term use and stabilizing gas detection sensitivity.

  The first characteristic means of the driving method of the gas detection element according to the present invention for achieving the above object is a gas sensitive part mainly comprising a metal oxide covered and sintered over a noble metal wire and in contact with the gas to be detected. The point is that the polarity is switched and applied to the gas detection element provided with the desired timing.

The temperature distribution of the gas detection element by voltage application is usually high in the positive semiconductor part and low in the negative semiconductor part. For this reason, if a driving voltage is applied with the polarity fixed to the gas detection element, the temperature distribution of the gas detection element is biased only to one side of the gas detection element. Is easily deteriorated by heat.
On the other hand, as in the present means, by applying the polarity to the gas detection element at a desired timing, it is possible to prevent the temperature distribution of the gas detection element from being biased to only one side of the gas detection element. Can do. Therefore, it is difficult to generate a part that is heated unevenly in the gas detection element, and it is possible to prevent the gas detection element from being deteriorated by heat. Therefore, the gas detection element driving method of the present invention has excellent durability even when the gas detection element is used at a high temperature and for a long time.

  In addition, in this means, it is possible to prevent the temperature distribution of the gas detection element from being biased toward only one side of the gas detection element, and thus it is possible to prevent uneven grain growth.

  Furthermore, as shown in the examples described later, this means can suppress a change in gas detection sensitivity even when the gas detection element is used at a high temperature and for a long period of time, so that stable gas detection can be performed. it can.

  The 2nd characteristic means of the drive method of the gas detection element which concerns on this invention exists in the point which replaces polarity every predetermined time.

  According to the present means, since the polarity of the applied voltage periodically applied to the gas detection element is reversed, it is more difficult to generate an unevenly heated portion in the gas detection element. Therefore, it is possible to effectively prevent the gas detection element from being deteriorated by heat.

  The third characteristic means of the driving method of the gas detection element according to the present invention is that it is executed by supplying a pulse current.

  According to this means, it is possible to intermittently detect the gas by pulse driving, so that the average power consumption can be reduced.

  A first characteristic configuration of a gas detection device according to the present invention includes a gas detection element having a gas sensitive portion that is in contact with a gas to be detected, the main component being a metal oxide that covers and sinters a noble metal wire, and the gas. A polarity inversion means for switching the polarity at a desired timing and applying it to the detection element, and a current generator for supplying a pulse current to the gas detection element are provided.

  According to this configuration, it is possible to prevent the temperature distribution of the gas detection element from being biased toward only one side of the gas detection element by switching the polarity and applying the gas detection element at a desired timing. . Therefore, it is difficult to generate a part that is heated unevenly in the gas detection element, and it is possible to prevent the gas detection element from being deteriorated by heat. Therefore, the gas detection device of the present invention has excellent durability even when the gas detection element is used at a high temperature and for a long time.

  Furthermore, in the gas detection device of the present invention, it is possible to prevent the temperature distribution of the gas detection element from being biased to only one side of the gas detection element. Even when the gas is used at a high temperature and for a long time, the change in gas detection sensitivity can be suppressed.

  The second characteristic configuration of the gas detector according to the present invention is that the gas sensitive part is formed on a supported substrate part, and the supported substrate part is formed by a MEMS technique.

  According to this configuration, since the MEMS technology capable of microfabrication is applied, it is possible to manufacture an extremely small gas detection element. Thereby, a gas detection element with little average power consumption can be obtained.

It is sectional drawing of the gas detection element in the gas detection apparatus of this invention. It is the schematic of the gas detection apparatus of this invention. It is the graph which showed the result of having investigated durability of a gas detector. It is the graph which showed the result of having investigated the stability of the gas detection sensitivity of a gas detection apparatus.

Hereinafter, embodiments of the present invention will be described with reference to the drawings.
The method for driving a gas detection element according to the present invention has a desired timing for a gas detection element having a gas sensitive part that is mainly composed of a metal oxide covered with a noble metal wire and is in contact with a gas to be detected. And drive so that the polarity is changed.

This method can be implemented by the gas detection device Y shown in FIGS. In the present embodiment, a mode in which the gas sensitive portion 11 is formed on the supported substrate portion 10 and the supported substrate portion 10 is formed by the MEMS technology will be described.
That is, in the gas detection element X, the supported substrate portion 10 provided with the gas sensitive portion 11 is supported by the support substrate portion 30. The supported substrate portion 10 and the supporting substrate portion 30 are formed of one member and are attached to another Si base material 31.

  An insulating film 13 is formed on the supported substrate part 10, and a laminated body A is formed in which a gas sensitive part 11 and a detection electrode (noble metal wire: also used as a heater) 12 are laminated. In addition, when the to-be-supported board | substrate part 10 has a function of an insulating film, the said insulating film 13 does not need to be provided. Each structure except the gas sensitive part 11 among the laminated bodies A is produced using the MEMS technology. The MEMS technology is a technology for manufacturing an electronic device system having an ultrafine structure. With this technique, fine circuits can be processed. Laminate A can be formed by a known method using MEMS technology.

  The gas detection element X is connected to the polarity inversion means 40 by a lead wire a, and the polarity inversion means 40 is connected to the current generator 50 by a lead wire b.

  The polarity inversion means 40 may be in any form as long as it has a function of inverting the polarity of the drive voltage applied by the current generator 50 at a desired timing.

The temperature distribution of the gas detection element X by voltage application is usually high in the positive semiconductor part and low in the negative semiconductor part. Therefore, if the driving voltage is applied with the polarity fixed to the gas detection element X, the temperature distribution of the gas detection element X is biased only to one side of the gas detection element X, and thus the gas detection element X is biased. The heated part is easily deteriorated by heat.
On the other hand, the temperature distribution of the gas detection element X is biased to only one side of the gas detection element X by applying the polarity to the gas detection element X at a desired timing as in this configuration. Can be prevented. Therefore, it is difficult to generate a portion that is heated unevenly in the gas detection element X, and it is possible to prevent the gas detection element X from being deteriorated by heat. Therefore, the driving method of the gas detection element X of the present invention has excellent durability even when the gas detection element X is used at a high temperature and for a long time.

  The timing of polarity inversion is preferably controlled so that the inversion is performed every predetermined time (for example, every 30 seconds to 10 minutes). In this configuration, since the polarity of the applied voltage that is periodically applied to the gas detection element X is reversed, a part that is biased and heated in the gas detection element X is less likely to occur. Therefore, it is possible to effectively prevent the gas detection element X from being deteriorated by heat.

  The current generator 50 may be configured to receive a power supply from the battery and convert it into a pulse current. By applying a pulse current and applying the gas detection element X as in this configuration, the gas can be intermittently detected by driving the pulse, so that the average power consumption can be reduced.

[Example 1]
Examples of the present invention will be described.
The durability of the gas detector X of the present invention was examined. That is, the durability of the supported substrate portion 10 was evaluated when a pulse voltage (application period: 0.3 seconds, application time: 0.1 seconds) was applied to the gas detection element X and the polarity was changed. . The temperature at the time of application with respect to the gas detection element X was 550 degreeC. In this investigation, acceleration was applied 100 times as compared with normal use, and the number of days required for disconnection in 25 gas detectors was examined. The results are shown in FIG.

  As a result, in the conventional gas detection device (the polarity is not reversed), disconnection occurred after 30 days, but in the gas detection device of the present invention, it was confirmed that disconnection occurred after 80 days. That is, it was recognized that the durability of the gas detection element driving method of the present invention was improved by about 2.7 times.

[Example 2]
The stability of the gas detection sensitivity of the gas detector X of the present invention was examined. In this embodiment, 10 times acceleration application (application period 3 seconds, application time 0.1 seconds) is applied to the gas detection element X as compared with the normal use, and how the alarm concentrations for methane gas and hydrogen gas change. Evaluated what to do. The results are shown in FIG. 4 ((a) conventional gas detection device (b) gas detection device of the present invention).

As a result, in the conventional gas detection device, the alarm concentration of methane gas hardly changed even after the number of days applied, but the alarm concentration of hydrogen gas gradually decreased to about half after 200 days. On the other hand, in the gas detector of the present invention, it was found that the alarm concentration of methane gas hardly changed even when the number of applied days passed, and the alarm concentration of hydrogen gas could be suppressed to a decrease of about 15%.
As described above, in the method of driving the gas detection element, it was recognized that the gas detection sensitivity can be stabilized even when used at a high temperature and for a long period of time.

[Another embodiment]
The gas detection element driving method and the gas detection device of the present invention is a gas detection element having a gas sensitive portion that is mainly composed of a metal oxide covered with a noble metal wire and is in contact with the gas to be detected. It is not limited to the above-described embodiment. For example, as a gas detection element, a metal oxide semiconductor mainly composed of a metal oxide such as indium oxide, tungsten oxide or tin oxide is coated on a noble metal wire such as platinum, platinum-rhodium alloy, etc. A hot-wire semiconductor sensor having a gas-sensitive part that has been formed can be used.

  The present invention relates to a method for driving a gas detection element having a gas sensitive portion that is in contact with a gas to be detected, the main component of which is a metal oxide that covers and sinters a noble metal wire, and a gas detection device including the gas detection element. Available to:

X gas detection element 10 supported substrate part 11 gas sensitive part 40 polarity inversion means 50 current generator

Claims (5)

  A gas sensing element that is made of a metal oxide that covers and sinters a noble metal wire, and that has a gas sensitive part that comes into contact with the gas to be sensed. Driving method.   The method for driving a gas detection element according to claim 1, wherein the polarity is switched every predetermined time.   The method for driving a gas detection element according to claim 1, wherein the method is performed by applying a pulse current. A gas detection element comprising a metal oxide that covers and sinters a noble metal wire as a main component, and is provided with a gas sensitive portion that comes into contact with the gas to be detected;
Polarity reversing means for switching and applying the polarity at a desired timing to the gas detection element;
And a current generator that provides a pulse current to the gas detection element.   The gas detection device according to claim 4, wherein the gas sensitive part is formed on a supported substrate part, and the supported substrate part is formed by a MEMS technique.

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