JP2007263982A - Method for manufacturing gas measuring device - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide various gas sensors differed in gas responding characteristics. <P>SOLUTION: The gas measuring device includes two or more gas sensors differed in gas responding characteristics. Each gas sensor includes a sensitive membrane 7 of a conductive polymer provided between two or more electrodes 3 and 3 formed on an insulating substrate 1, and measures a measuring object component by an electric change between the electrodes 3 and 3 caused by adhesion of the measuring object component in gas to the sensitive membrane 7. To at least one of the gas sensors, a gas responding characteristic differed from those of other gas sensors is given by adjusting, in the process of polymerizing a conductive polymer membrane in the manufacturing process, the polymerization condition. <P>COPYRIGHT: (C)2008,JPO&INPIT

Description

  The present invention relates to a method for manufacturing a gas measuring device using a plurality of gas sensors that detect a component to be measured in a gas using a sensitive film made of a conductive polymer. The present invention can also be used for an odor sensor for identifying an odor.

The gas sensor is also used to electrically measure a physical change of the sensor caused by an odorous substance contained in air or a supplied sample gas adhering to a sensitive surface of the sensor.
A gas sensor using an oxide semiconductor is commercially available.

  A gas measuring device called an artificial electronic nose using a plurality of oxide semiconductor gas sensors has also been commercially available. Artificial electronic noses are used as systems for detecting "odor", such as quality inspections of foods and fragrances, quantitative standards for bad odor pollution, and fire alarms using burnt odor detection. If it becomes even more sensitive and matches the dog's nose, it can also be used in areas such as human tracking, identification, authentication and drug testing.

  However, the measurement target of an odor sensor using an oxide semiconductor is limited to a substance that causes a redox reaction on the sensitive surface. In addition, since the sensor unit does not operate unless the temperature is high, a substance that undergoes thermal decomposition by the heat is not a measurement target. Further, in the analysis, it is necessary to wait until the temperature of the sensor rises to the operating temperature and stabilizes, and there is a problem that it takes time for repeated measurement, and there is a drawback that there is a change with time depending on the surface state of the sensor.

  As another gas sensor, there is one using a sensitive film made of a conductive polymer such as polypyrrole or polythiophene. In a gas sensor using a conductive polymer film, when a gas component such as an odor substance adheres to a sensitive surface, the conductivity of the conductive polymer changes due to the direct or indirect participation of molecules. Therefore, the gas component can be detected by measuring a change in resistance or impedance between the electrodes provided with the sensitive film interposed therebetween.

  In addition, since the gas sensor using the conductive polymer film operates at room temperature, it is possible to detect an odorous substance as it is without thermally decomposing the measurement target, and to raise the temperature of the sensor unit to a predetermined temperature. No extra time is required.

  A gas sensor using a conductive polymer film is not specifically sensitive only to a specific component, and generally has sensitivity to a plurality of components, although there are differences in sensitivity. Therefore, if an odor discriminating apparatus is to be constructed, a plurality of gas sensors having different gas response characteristics are required. In order to increase the types of gas sensors, it is common to increase the types of sensitive film compositions of the gas sensor. There are a relatively large number of types of conductive polymers, but the types are limited as long as they are gas responsive and stable conductive polymers that can be used as sensitive films for gas sensors. Moreover, enormous time and effort are required to synthesize conductive polymers having a new structure.

  Therefore, the present invention has an object of realizing various gas sensors having different gas response characteristics when a gas measuring device is constituted by a gas sensor using a conductive polymer film.

  A gas measuring device as an object of the present invention includes two or more gas sensors having different gas response characteristics. In these gas sensors, a sensitive film made of a conductive polymer is provided between two or more electrodes formed on an insulating substrate, and the electric current between the electrodes when a measurement target component in the gas adheres to the sensitive film. The component to be measured is measured by a change in the environment.

  The production method of the present invention for producing gas sensors having different gas response characteristics is to adjust the polymerization conditions in the process of polymerizing the conductive polymer film in the production process. The conductive polymer is likely to be a linear conductive polymer under conditions where the polymerization reaction is difficult to proceed, such as polymerization under low temperature, short-time polymerization, or a small amount of oxidizing agent used. Conversely, a conductive polymer having a network structure is easily obtained under conditions where the polymerization reaction easily proceeds, for example, polymerization at a high temperature, polymerization for a long time, and a large amount of an oxidizing agent used. Thus, the higher order structure of the conductive polymer differs depending on the polymerization conditions. One possible mechanism for changing the conductivity of the conductive polymer is swelling of the conductive polymer film due to gas. Since the swelling ratio varies depending on the higher order structure of the conductive polymer, the amount of change in conductivity also varies. That is, gas sensors having different gas response characteristics can be created by adjusting the polymerization conditions.

  As described above, even with a limited conductive polymer, a gas measuring device including a gas sensor having various types of gas response characteristics can be created.

  According to the present invention, the gas response characteristic of the gas sensor can be changed by changing the polymerization conditions of the conductive polymer film.

  In this way, even with a limited conductive polymer, it becomes possible to create a gas measuring device equipped with a gas sensor having various types of gas response characteristics. This can contribute to the realization of a device for quantification.

FIG. 1 shows an example of a gas sensor to which the present invention is applied. (A) is a plan view, and (B) is a partially enlarged view of the electrode portion.
On the glass substrate 1, two gold electrodes 3 and 3 are formed in a comb shape with a space of 5 μm in an area of 2 mm × 3 mm, and these electrodes 3 and 3 are 0.5 mm wide terminals 5 made of the same material. , 5 are respectively connected. The electrode 3 and the terminal 5 are formed by patterning a gold thin film by, for example, a lift-off method. A sensitive film 7 made of a conductive polymer is formed on the upper surface of the electrode 3 so as to cover the entire electrode 3. A sensitive film 7 is present between the opposing electrode pairs, and the electric resistance value of the sensitive film 7 between the electrode pairs is measured between the terminals 5 and 5.

  FIG. 2 shows an example of a gas measuring apparatus to which the present invention is applied. A valve 9 and a flow cell 11 are provided on the flow path of the dry nitrogen gas supplied from the cylinder, and the dry nitrogen gas flows through the flow path by suction of a pump (not shown). A gas flow path connected to the odor substance container 13 is connected to the valve 9, and an appropriate amount of odor substance is mixed into the dry nitrogen gas by the operation of the valve 9. A sensor 15 is installed in the flow cell 11. The sensor 15 includes a plurality of gas sensors shown in FIG. 1, and these gas sensors have different gas response characteristics. Each gas sensor is connected to an ohmmeter 17 for measuring a resistance value between the electrodes 3 and 3.

  Next, the operation of this gas measuring device will be described. First, dry nitrogen gas is allowed to flow through the flow cell 11, the valve 9 is switched, and the odorous substance is sent from the odorous substance container 13 to the flow cell 11. When molecules of various components contained in the odorous substance adhere to the sensitive film 7 of the sensor 15, the conductivity of the sensitive film 7 of the conductive polymer changes due to the direct or indirect involvement of the molecules, and the resistance meter 17 The resistance change between 3 and 3 is measured. The odor substance includes a plurality of components, and these components are detected simultaneously by a plurality of gas sensors included in the sensor 15. The detection output of each gas sensor does not correspond to any component, but each gas sensor has sensitivity to multiple components, so each gas sensor detects multiple components simultaneously with sensitivity corresponding to each gas response characteristic And output. Although not shown in the figure, the data processing apparatus performs multivariate analysis based on the outputs of those gas sensors and simultaneously quantifies a plurality of components.

(Reference Example 1)
Sensitive membrane made of multiple types of conductive polymer membranes:
As shown in FIG. 1, two comb-shaped electrodes 3 and 3 are formed on a glass substrate 1, and poly (3-hexylthiophene) and poly (3-octylpyrrole) are formed on the upper surfaces of the electrodes 3 and 3. A mixed conductive polymer film is formed as the sensitive film 7. The conductive polymer film is doped with 12 tungsto (IV) phosphoric acid as a dopant. The structural formulas of poly (3-hexylthiophene) and poly (3-octylpyrrole) are shown in the following chemical formulas (A) and (B), respectively.

The manufacturing method of this gas sensor is shown.
An electrode 3 and a terminal 5 are formed on the glass substrate 1 by a lift-off method. In order to form a conductive polymer film, 3-hexylthiophene and 3-octylpyrrole as raw materials are dissolved in chloroform as a solvent so that the respective monomer equivalent concentrations are 0.05 M, and the solution is glass at a rotational speed of 1500 rpm. A film was formed by spin coating on the substrate 1 for 10 seconds.

  Next, the dopant is doped by immersing the glass substrate 1 on which the conductive polymer film is formed in a solution in which 12 tungsto (IV) phosphoric acid serving as a dopant is dissolved in nitromethane at a concentration of 10 mM for 60 minutes. A sensitive film 7 was formed.

  In order to evaluate the characteristics of this gas sensor, this gas sensor was installed as the sensor 15 of the gas measuring device of FIG. First, dry nitrogen gas was passed at a flow rate of 200 ml / min for 10 seconds, and then butyl acetate gas diluted with dry nitrogen gas was passed at the same flow rate for 30 seconds. Finally, dry nitrogen gas was flowed again. The resistance value of the gas sensor was measured every 2 seconds.

The response curve at this time is shown in FIG. The vertical axis represents resistance value (le), and the horizontal axis represents time (seconds).
From this result, it can be confirmed that this gas sensor has a very fast response and high sensitivity.

In this reference example, a film in which two kinds of conductive polymers are mixed is used as a sensitive film. The gas response characteristics are compared with the gas response characteristics of a gas sensor using each conductive polymer film as a sensitive film. The results are shown in Table 1. Each of the mixed film, the poly (3-hexylthiophene) film, and the poly (3-octylpyrrole) film is doped with 12 tungsten (IV) phosphoric acid having the same concentration as a dopant. The measured gases are butyl acetate, butyric acid, water vapor, and trimethylamine. The response rate for each gas is shown. The response rate was calculated by the following formula. The same applies to the following examples or reference examples.
Response rate (%) = (change in resistance value / resistance value before change) × 100

表１中で、アミンはトリメチルアミン（以下の表でも同じ）、単一膜１はポリ（３−ヘキシルチオフェン）、単一膜２はポリ（３−オクチルピロール）を表わす。

In Table 1, amine represents trimethylamine (the same applies to the following tables), single film 1 represents poly (3-hexylthiophene), and single film 2 represents poly (3-octylpyrrole).

  According to this result, the mixed film does not show the average characteristics of the poly (3-hexylthiophene) film and the poly (3-octylpyrrole) film contained in the mixed film, but different gas response characteristics from the single film. Indicates. For example, in this case, the poly (3-hexylthiophene) film and the poly (3-octylpyrrole) film alone have poor sensitivity to amines, but the mixed film increases the sensitivity to amines by about 5 times. It has been improved. Thus, by forming a sensitive film by mixing a plurality of types of conductive polymers, it is possible to obtain a gas sensor having gas response characteristics different from those of a single film. A plurality of gas sensors having different gas response characteristics can be obtained by changing the combination and composition of the conductive polymers to be mixed.

(Reference Example 2)
Multi-layered soluble conductive polymer film made into a sensitive film:
As the sensitive film, a polyaniline layer laminated on a poly (3-hexylthiophene) layer was used. The structural formula of polyaniline is shown below.

  A method for producing this sensitive film will be described. On the glass substrate 1 on which the electrode 3 was formed, a solution obtained by dissolving poly (3-hexylthiophene) in chloroform as a solvent was spin-coated at a rotation speed of 1500 rpm for 10 seconds to form a film. The substrate 1 was immersed in a nitromethane solution of 12 tungsto (IV) phosphoric acid serving as a dopant for 60 minutes to dope the poly (3-hexylthiophene) film.

Next, a polyaniline aqueous solution was similarly spin-coated on the film, and the polyaniline film was doped with paratoluenesulfonic acid.
In order to evaluate the characteristics of this gas sensor, this gas sensor is installed as the sensor 15 of the gas measuring device in FIG. 2, and after passing dry nitrogen gas at a flow rate of 200 ml / min for 10 seconds, it is diluted with dry nitrogen gas. The butyl acetate gas was passed at the same flow rate for 30 seconds, and finally, dry nitrogen gas was passed again. The resistance value of the gas sensor was measured every 2 seconds.
The response curve at this time is shown in FIG. The vertical axis represents resistance value (le), and the horizontal axis represents time (seconds). From this result, it can be confirmed that the response is very fast and the sensitivity is large.

  In this reference example, two layers of conductive polymer films were laminated to form a sensitive film. The gas response characteristics were compared with the gas response characteristics of a gas sensor using each conductive polymer film as a sensitive film. The results are shown in Table 2. The single film 1 is a poly (3-hexylthiophene) film doped with 12 tungsto (IV) phosphoric acid as a dopant, and the single film 2 is a polyaniline film doped with paratoluenesulfonic acid as a dopant.

表１中でアミンはトリメチルアミンを表わす。

In Table 1, amine represents trimethylamine.

  If different conductive polymers do not dissolve in the same solvent, or if one conductive polymer has poor solubility in another conductive polymer, separate each conductive polymer from a separate solvent. It is possible to form a situation in which a plurality of different conductive polymers are present on the same sensor by dissolving them in a layer and forming them as separate layers by the dip method or spin coating method and then laminating them.

  By laminating a plurality of types of conductive polymer films to form a sensitive film, it is possible to obtain a gas sensor different from the gas response characteristics of a gas sensor using a single film as the sensitive film. A plurality of gas sensors having different gas response characteristics can be obtained by changing the combination of the conductive polymer films to be stacked and the film thickness ratio.

(Reference Example 3)
Gas sensors containing multiple types of dopants:
In the gas sensor shown in FIG. 1, two types of dopants were introduced into a single conductive polymer film as the sensitive film 7. Poly (3-hexylthiophene) was used as the conductive polymer film, and BF ₄ and PF ₆ were used as the dopant.

In order to prepare the sensitive film, electrolytic polymerization was performed on a substrate on which an electrode was formed in a monomer solution of 3-hexylthiophene containing BF ₄ and PF ₆ .
The method for producing the sensitive film 7 is not limited to the above, and after the conductive polymer film is formed on the substrate, it is immersed in a solution containing a plurality of types of dopants, and only a voltage is applied or immersed. Plural kinds of dopants can be introduced into the conductive polymer film.

Table 3 shows an example in which the gas selectivity of the gas sensor changes depending on the type of dopant in the sensitive film. A gas sensor was prepared by electropolymerization in a monomer solution of 3-hexylthiophene containing BF ₄ or PF ₆ and using a poly (3-hexylthiophene) film having BF ₄ and PF ₆ as dopants as a sensitive film. The result of Table 3 is the sensitivity ratio of each gas sensor.

これ以外に、ヘプタンのように、ＢＦ₄には感じるが、ＰＦ₆には感じない対象物もある。

In addition to this, there is an object such as heptane that is felt by BF ₄ but not by PF ₆ .

  From this result, it can be seen that the gas selectivity of the gas sensor varies depending on the type of dopant in the sensitive film. And the gas response characteristic of a gas sensor changes by introduce | transducing a multiple types of dopant into a sensitive film | membrane. A plurality of gas sensors having different gas response characteristics can be obtained by changing the kind and composition of the dopant introduced into the sensitive film.

(Reference Example 4)
Gas sensor with different dopant concentrations:
In the gas sensor shown in FIG. 1, a sensitive film 7 in which Sc (CF ₃ SO ₃ ) ₃ is introduced as a dopant to poly (3-hexylthiophene) was used. And 2 types of gas sensors provided with the sensitive film | membrane from which dopant concentration differs were produced.

  In order to prepare the sensitive film, 3-hexylthiophene was polymerized by an oxidative polymerization method and dissolved in chloroform to obtain a solution having a concentration of 0.1M in terms of monomer concentration. Using the solution, a film was formed by spin coating on a substrate on which an electrode was formed at a rotation speed of 1500 rpm for 10 seconds.

Next, a solution in which Sc (CF ₃ SO ₃ ) _{3 serving} as a dopant is dissolved in nitromethane at concentrations of 5 mM and 0.5 mM is prepared, and a poly (3-hexylthiophene) film is formed in each solution. The substrate under film formation was immersed for 60 minutes for dopant doping.

  In order to evaluate the characteristics of this gas sensor, this gas sensor is installed as the sensor 15 of the gas measuring device in FIG. 2, and after passing dry nitrogen gas at a flow rate of 200 ml / min for 10 seconds, it is diluted with dry nitrogen gas. The various gases were passed at the same flow rate for 30 seconds, and finally dry nitrogen gas was flowed again. The resistance value of the gas sensor was measured every 2 seconds. The results are shown in Table 4. The measured gases are butyl acetate, butyric acid, water vapor, and trimethylamine.

  From this result, it can be seen that even when the same conductive polymer and the same dopant are used, the gas response characteristics of the sensitive film differ by changing the dopant concentration. Thus, a plurality of gas sensors having different gas response characteristics can be obtained by changing the dopant concentration.

  In this reference example, only the dopant concentration at the time of introducing the dopant is changed, but the amount of the dopant introduced into the sensitive film can also be changed by changing the dopant introduction time and temperature.

(Reference Example 5)
How to change the gas response characteristics depending on the amount of oxygen and moisture during doping:
In the gas sensor shown in FIG. 1, a sensitive film 7 in which 12 tungsto (IV) phosphoric acid was introduced as a dopant to poly (3-hexylthiophene) was used. And 2 types of gas sensors provided with the sensitive film | membrane from which dopant concentration differs were produced.

  In order to prepare the sensitive film, 3-hexylthiophene was polymerized by an oxidative polymerization method and dissolved in chloroform to obtain a solution having a concentration of 0.1M in terms of monomer concentration. Using the solution, a film was formed by spin coating on a substrate on which an electrode was formed at a rotation speed of 1500 rpm for 10 seconds.

  Next, doping operation was performed in two kinds of environments. On the other hand, 12 tungsto (IV) phosphoric acid was dissolved in water-containing nitromethane at a concentration of 10 mM, and was immersed in the solution for 60 minutes in the atmosphere for doping. In this way, a gas sensor provided with a sensitive film doped in the atmosphere under water content was obtained.

  On the other hand, a 12-tungsto (IV) phosphoric acid dissolved in dehydrated distilled nitromethane at a concentration of 10 mM and a substrate on which a poly (3-hexylthiophene) film is formed are placed in the solution under a dry nitrogen atmosphere. Doping was performed by immersing for a minute. Thus, the gas sensor 1 provided with the sensitive film | membrane doped under nitrogen and anhydrous was obtained.

  In order to evaluate the characteristics of these gas sensors, these gas sensors are separately installed as the sensor 15 of the gas measuring device in FIG. 2, and first, dry nitrogen gas is passed at a flow rate of 200 ml / min for 10 seconds, followed by drying. Various gases diluted with nitrogen gas were passed at the same flow rate for 30 seconds, and finally, dry nitrogen gas was flowed again. The resistance value of the gas sensor was measured every 2 seconds. The results are shown in Table 5. The measured gases are butyl acetate, butyric acid, water vapor, and trimethylamine.

  From this result, it can be seen that even when the same conductive polymer film and the same dopant are used, the gas response characteristics of the obtained gas sensor differ by forming the sensitive film by changing the environment during the doping. Thus, a plurality of gas sensors having different gas response characteristics can be obtained by changing the doping environment.

Example 1
Method to change gas response characteristics depending on polymerization conditions of conductive polymer film:
In the gas sensor shown in FIG. 1, a sensitive film 7 in which 12 tungsto (IV) phosphoric acid was introduced as a dopant to poly (3-hexylthiophene) was used. And two types of gas sensors provided with the sensitive film | membrane from which the polymerization conditions of a conductive polymer film differ were created.

In order to prepare the sensitive film, 3-hexylthiophene was polymerized by an oxidation polymerization method. The conditions for the polymerization reaction at this time were two types of −20 ° C. and 30 ° C. by changing the reaction temperature.
Polymerized poly (3-hexylthiophene) was dissolved in chloroform to obtain a solution having a concentration of 0.1M in terms of monomer concentration. Using the solution, a film was formed by spin coating on a substrate on which an electrode was formed at a rotation speed of 1500 rpm for 10 seconds.

  Doping was performed by dissolving 12 tungsto (IV) phosphoric acid in nitromethane at a concentration of 10 mM and immersing the substrate on which poly (3-hexylthiophene) was formed in the solution for 60 minutes.

  In order to evaluate the characteristics of these gas sensors, these gas sensors are separately installed as the sensor 15 of the gas measuring device in FIG. 2, and first, dry nitrogen gas is passed at a flow rate of 200 ml / min for 10 seconds, followed by drying. Various gases diluted with nitrogen gas were passed at the same flow rate for 30 seconds, and finally, dry nitrogen gas was flowed again. The resistance value of the gas sensor was measured every 2 seconds. The results are shown in Table 6. The measured gases are butyl acetate, butyric acid, water vapor, trimethylamine and methanol.

From this result, even if the same conductive polymer film and the same dopant are used, by changing the polymerization reaction temperature of the conductive polymer film and forming the conductive polymer film, the gas response characteristics of the obtained gas sensor can be improved. I can see that they are different.
Thus, by changing the polymerization reaction temperature of the conductive polymer film, a plurality of gas sensors having different gas response characteristics can be obtained.

  In this example, only the temperature is changed as the polymerization condition of the conductive polymer, but the higher order structure of the conductive polymer film can be changed even if the conditions such as the polymerization time and the amount of the oxidizing agent are changed. The gas response characteristics of the gas sensor can be changed.

(Reference Example 6)
Method to change the gas response characteristics depending on the solvent when forming the conductive polymer film:
In the gas sensor shown in FIG. 1, a sensitive film 7 in which 12 tungsto (IV) phosphoric acid was introduced as a dopant to poly (3-hexylthiophene) was used. Then, two types of gas sensors were prepared in which different solvents were used to form a poly (3-hexylthiophene) film.

  In order to prepare the sensitive film, 3-hexylthiophene was polymerized by an oxidative polymerization method and dissolved in chloroform and anisole, respectively, to prepare two types of solutions having a concentration of 0.05M in terms of monomer concentration. Each solution was spin-coated on a substrate on which an electrode was formed at a rotation speed of 1500 rpm for 10 seconds to form a film.

  Doping was performed by dissolving 12 tungsto (IV) phosphoric acid in nitromethane at a concentration of 10 mM and immersing two types of substrates on which poly (3-hexylthiophene) was formed in the solution for 60 minutes.

  In order to evaluate the characteristics of these gas sensors, these gas sensors are separately installed as the sensor 15 of the gas measuring device in FIG. 2, and first, dry nitrogen gas is passed at a flow rate of 200 ml / min for 10 seconds, followed by drying. Various gases diluted with nitrogen gas were passed at the same flow rate for 30 seconds, and finally, dry nitrogen gas was flowed again. The resistance value of the gas sensor was measured every 2 seconds. The results are shown in Table 7. The measured gases are butyl acetate, butyric acid, water vapor, and trimethylamine.

From this result, even if the same conductive polymer film and the same dopant are used, the gas response characteristics of the obtained gas sensor can be improved by forming a sensitive film by changing the solvent when forming the conductive polymer film. I can see that they are different.
Thus, by changing the solvent when forming the conductive polymer film, a plurality of gas sensors having different gas response characteristics can be obtained.
A plurality of gas sensors having different gas response characteristics can be obtained by the method shown in the above embodiments. By providing the plurality of gas sensors as sensors of the gas measuring device, a plurality of components such as odor components can be quantified simultaneously.

It is a figure which shows the gas sensor which this invention makes object, (A) is a top view, (B) is the elements on larger scale of the electrode part. It is a block diagram of the gas measuring apparatus using the gas sensor of FIG. It is a figure which shows a response curve when butyl acetate is detected in Reference Example 1. It is a figure which shows a response curve when butyl acetate is detected in Reference Example 2.

Explanation of symbols

DESCRIPTION OF SYMBOLS 1 Glass substrate 3 Comb-shaped electrode 7 Sensitive membrane 9 Valve 11 Flow cell 13 Odor substance container 15 Sensor 17 Resistance meter

Claims (1)

The gas sensor includes two or more gas sensors having different gas response characteristics, and the gas sensor is provided with a sensitive film made of a conductive polymer between two or more electrodes formed on an insulating substrate, and measurement in gas is performed on the sensitive film. In the method of manufacturing a gas measuring device that measures a measurement target component by an electrical change between the electrodes when the target component adheres,
At least one of the gas sensors has a gas response characteristic different from that of other gas sensors by adjusting the polymerization conditions in the process of polymerizing the conductive polymer film in the manufacturing process. Manufacturing method.

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