JP4048276B2 - Conductive polypyrrole thin film and method for producing the same - Google Patents

Description

[0001]
BACKGROUND OF THE INVENTION
The present invention relates to a novel conductive polypyrrole thin film useful as, for example, a sensor element material or an electro device material that selectively responds with high sensitivity to VOC gas, and a manufacturing method thereof. By introducing a dopant consisting of alkylbenzene sulfonic acid in a vacuum atmosphere into a thin film produced by plasma polymerization of pyrrole, it is a simple method using a dry process that is dense, uniform in thickness, and has high-quality electrical conduction. The present invention relates to a method for producing a conductive polymer thin film, a conductive thin film produced by the method, a conductive member using the conductive thin film, and a chemical sensor member.
The present invention relates to a method for producing a novel conductive polymer thin film capable of producing a high-quality conductive thin film that can be used as an electro device material by a simple process, and its product, particularly in the technical field. Therefore, the present invention is useful for providing a chemical sensor member such as a high-performance VOC gas sensor having a selective and highly sensitive response characteristic to a VOC gas which is a causative substance of sick house syndrome, which is strongly demanded.
[0002]
[Prior art]
Electroconductive polymers can be expected to be applied to electrode materials, conductive thin films, capacitors, various sensors, etc. due to their high conductivity, so conventionally, for example, electron conjugated polymers such as polyacetylene, polyaniline, polythiophene, polypyrrole, etc. Development of a conductive polymer material in which an electron-donating or electron-accepting compound is added to a molecule as a dopant has been actively conducted. Among these, polypyrrole has been put to practical use as an electrolyte material for electrolytic capacitors because it has high electrical conductivity and is stable in the air, and is a particularly noted substance. Furthermore, in recent years, applications to electronic devices such as field effect transistors using conductive polypyrrole, or solar cells have been studied. However, these products have not yet achieved characteristics that surpass competitive products, and have been put to practical use. The current situation is not.
[0003]
The main cause is that a manufacturing method of a high-quality and high-stability conductive polypyrrole film that can be used for these applications has not been established. The main polymerization methods of polypyrrole are roughly classified into two methods: electrolytic polymerization and chemical polymerization. Until now, polypyrrole films have been synthesized mainly by electrolytic polymerization. However, in this technique, in order to synthesize a large-area film, a corresponding large electrode is required, and it is difficult to synthesize a film having a uniform thickness. Further, since the surface has poor smoothness and unevenness, when used as an electronic device, a problem such as an overcurrent flowing at a specific location occurs, making it difficult to control the electronic function.
[0004]
On the other hand, in the chemical polymerization method, polypyrrole is obtained as a powder, and since these are generally insoluble in a solvent, they cannot be formed into a film or film. So far, soluble polypyrrole has been synthesized by modification of pyrrole monomer (for example, see Patent Document 1) or polymerization in the presence of an appropriate dopant (for example, see Patent Document 2), and formed into a film by casting. Has been. However, these products do not have characteristics that can be used for electronic devices in terms of conductivity and film thickness uniformity. Furthermore, since these processes use a large amount of an organic solvent, it is difficult to fuse with existing semiconductor processes, which hinders high functionality by integration with semiconductors.
[0005]
On the other hand, the plasma polymerization method is widely known as a method for forming a polymer thin film, and research into practical use of various polymer thin films is also being advanced. However, if attention is paid to the conductive polymer thin film, there has been reported an example of synthesizing a conductive polymer film by vapor-phase doping iodine with a plasma polymerization film of pyrrole (see Non-Patent Document 1). ), Its conductivity remains below 10 ⁻⁸ Scm ⁻¹ . As described above, various methods for producing a conductive polypyrrole film have been conventionally studied. However, a method for producing a high-quality, high-stability conductive polypyrrole film has not yet been established. There has been a strong demand to develop a new technology capable of producing a conductive polypyrrole film.
[0006]
Recently, VOC gas, a volatile organic compound, has attracted attention as a causative agent of sick house syndrome, and various countermeasures have been developed for detecting such countermeasures as social measures are becoming a social need. Has been. However, the conventional ones are not sufficient as high-performance VOC gas sensors that exhibit high selectivity and high sensitivity to the VOC gas, and there has been a strong demand for product development in the technical field.
[0007]
[Patent Document 1]
JP-A-7-224207 [Patent Document 2]
JP 10-507225 A [Non-patent Document 1]
Thin Solid Films, 342, 119-126 (1999)
[0008]
[Problems to be solved by the invention]
Under such circumstances, the present inventors have conducted intensive research with the goal of developing a method for producing a conductive polymer film having excellent characteristics by a simple process in view of the above-described conventional technology. As a result, by adopting a method of introducing a dopant in a vacuum atmosphere into a thin film produced by plasma polymerization of pyrrole, a high-density and homogeneous polymer thin film can be obtained. It has been found that it has electrical conductivity, and the present invention has been completed.
The present invention relates to a method for efficiently producing a high-quality, high-stability conductive polypyrrole thin film having high conductivity by a dry process that does not use a solvent, the conductive polypyrrole thin film, and a conductive material containing the material as a constituent element. Another object of the present invention is to provide a chemical sensor member such as a VOC gas sensor having a selective and highly sensitive response characteristic to a VOC gas.
[0009]
[Means for Solving the Problems]
The present invention for solving the above-described problems comprises the following technical means.
(1) A method for producing a conductive polymer thin film by introducing a dopant into a polymerized film, wherein a polymer thin film produced by plasma polymerization of pyrrole is added with a dopant comprising alkylbenzene sulfonic acid in a vacuum atmosphere. A method for producing a conductive polymer thin film, comprising introducing the conductive polymer thin film.
(2) The method for producing a conductive thin film according to (1), wherein the dopant is lower alkylbenzene sulfonic acid.
(3) The method for producing a conductive thin film according to (1), wherein the dopant is an alkylbenzenesulfonic acid having a boiling point without being decomposed during heating.
[0010]
DETAILED DESCRIPTION OF THE INVENTION
Next, the present invention will be described in more detail.
As described above, the present invention is a method for producing a conductive polymer thin film by introducing a dopant into a polymerized film. The polymer thin film produced by plasma polymerization of pyrrole is subjected to alkylbenzene in a vacuum atmosphere. A conductive polymer thin film is produced by introducing a dopant made of sulfonic acid. In the present invention, pyrrole is used as a raw material monomer for producing a conductive polymer thin film. This is a hetero five-membered ring compound represented by the chemical formula C ₄ NH ₅ .
[0011]
The plasma polymerization of pyrrole in the present invention can be performed using a conventionally known plasma polymerization apparatus. The conditions for the plasma polymerization are not particularly limited. Preferably, for example, under a vacuum of 10 to 100 Pa, a high frequency of 13.56 MHz is usually applied to cause plasma discharge to cause a plasma polymerization reaction. Done. The discharge output varies depending on the polymerization apparatus, but is usually about 5 to 150 W, preferably about 10 to 120 W in view of the film forming speed or the structure of the polymer film. The polymerization time is not particularly limited, and when the polymerization time is long, a thick film is synthesized. Therefore, the polymerization time can be appropriately selected according to the required film thickness.
[0012]
In the plasma polymerization reaction, the polymerization reaction starts with radical species activated by plasma as active centers. Electrons generated by the discharge dissociate chemical bonds such as carbon-carbon of the monomer to generate radicals, and these radicals recombine to form a crosslinked polymer. For this reason, according to the polymerization method, the monomer does not necessarily require a double bond or a functional group necessary for condensation polymerization. Unlike the chain polymer synthesized by the chemical polymerization method, the produced polymer has a highly branched cross-linked structure, so that a polymer thin film having excellent mechanical properties can be produced. The dissociation of the chemical bond of the monomer and the crosslinked structure in the polymer mainly depend on the discharge output.
[0013]
In the case of the polypyrrole in the present invention, it is estimated that the pyrrole monomer having a five-membered ring structure breaks the ring structure due to the dissociation of the chemical bond and generates a polymer film having a three-dimensional crosslinked structure, but the discharge output is large. It was suggested from the infrared spectrum and elemental analysis that the degree was so large. FIG. 1 shows infrared absorption spectra of a polymer film produced with a discharge power of 110 W and a polypyrrole film synthesized by a chemical polymerization method. The absorption peak due to the five-membered ring structure seen in the polypyrrole film synthesized by the chemical polymerization method is not observed in the plasma polymerized film, indicating that the ring structure is broken. According to the plasma polymerization method described above, a polymer film having a uniform film thickness is formed on various substrate materials. The substrate material used in the present invention is not particularly limited as long as it is stable in the plasma of the above-mentioned power level. For example, Pyrex (registered trademark) glass, quartz glass, alumina, silicon, various plastics, various metals Etc. can be selected.
[0014]
In the present invention, the polymer film of pyrrole and the dopant are vacuum-sealed in a glass tube, and the dopant is introduced into the polymer film by a method of heat-treating it at an appropriate temperature. Thus, in the present invention, since the dopant is introduced in the gas phase, it is necessary that the dopant itself is not thermally decomposed and has a high vapor pressure. In order to impart conductivity to the pyrrole polymer film, it is necessary to select a dopant having a function as an electron acceptor. As an example of such a dopant, for example, lower alkylbenzene sulfonic acid typified by ethylbenzene sulfonic acid can be mentioned. Although not shown in the examples described later, benzenesulfonic acid having an alkyl group such as methyl or propyl can also be used as a dopant. However, for example, dodecylbenzenesulfonic acid having a long alkyl group does not have a boiling point and is thermally decomposed, so that it is considered not suitable for the method of the present invention. In the present invention, alkylbenzenesulfonic acid having a boiling point without being decomposed during heating is used.
[0015]
Treatment conditions such as treatment temperature and treatment time for introducing the dopant can be appropriately set depending on the film thickness of the polymer film of pyrrole to be used, the kind of dopant to be used, and the like. For example, when ethylbenzenesulfonic acid is used as the dopant, the treatment temperature is usually about 100 to 170 ° C, preferably about 120 to 150 ° C. The treatment time is about 10 to 120 hours, preferably about 20 to 60 hours. A heating means is not specifically limited, For example, arbitrary means, such as an electric heating furnace and a gas heating furnace, are employable. During the treatment, ethylbenzene sulfonic acid is doped by vaporizing in a glass sealed tube and reacting with a polymer film of pyrrole.
[0016]
The conductive polymer thin film obtained by the method of the present invention is a dense and dense film as a result of observation with an electron microscope. The film thickness varies depending on the discharge output and the reaction time during plasma polymerization, but is usually 0. Within the range of about 1 to 5 μm, in particular, a range of about 0.5 to 1 μm is preferably obtained. The polymer thin film after the doping treatment has good conductivity, and the electrical conductivity in room temperature and air measured by the DC four-terminal method in the direction parallel to the film varies depending on the synthesis conditions, etc., but is usually 10 ^−6. Scm ⁻¹ or more, more preferably 10 ⁻⁵ Scm ⁻¹ or more. According to the present invention, it is possible to form the conductive polymer thin film on an arbitrary substrate, and thereby include the polymer thin film having the good conductivity as a constituent element, for example, an electrode, an electrolyte, and an electronics All kinds of conductive members represented by devices, capacitors, and various sensors can be provided.
[0017]
In particular, the chemical sensor produced using the conductive polymer thin film has high selectivity and high sensitivity to the VOC gas of a volatile organic compound, which is attracting attention as a causative substance of sick house syndrome, and is a VOC gas sensor. As an excellent characteristic. Furthermore, the sensor exhibits excellent characteristics as a humidity sensor. Conventional resistance change type humidity sensors using a conductive polymer film have problems such as poor response linearity with respect to relative humidity and poor reliability at 90% or higher relative humidity. On the other hand, the sensor using the conductive polymer thin film obtained by the present invention can measure at a relative humidity of 0 to 100% at room temperature, and exhibits excellent linearity at a relative humidity of 40% or more. In particular, the present invention provides a chemical sensor member such as a VOC gas sensor that exhibits a specific, selective, and highly sensitive response characteristic to VOC gas, which is known as a causative agent of sick house syndrome, and provides a high-performance VOC gas sensor. It is useful as something that can be put into practical use.
[0018]
【Example】
EXAMPLES Next, although this invention is demonstrated concretely based on an Example, this invention is not limited at all by the following Examples.
Example 1
(1) Production of polymer polymer film Using an inductively coupled plasma processing apparatus using a high frequency of 13.56 MHz, a vacuum evacuated upper diameter 9 cm, lower diameter 21 cm, height 35 cm in a reaction vessel, Through a precision valve, pyrrole vapor was supplied using nitrogen gas as a carrier gas. Pyrex (registered trademark) glass cooled to room temperature was used as the substrate. There, plasma was generated at a discharge power of 110 W, and the reaction was performed for 2 hours. As a result, a polymer film having a thickness of 1 μm was obtained.
[0019]
(2) Introduction of dopant This was vacuum-sealed together with ethylbenzenesulfonic acid in an H-type Pyrex (registered trademark) glass tube having an inner diameter of 12 mm. At this time, the polymer film and ethylbenzenesulfonic acid were separately put on both sides of the H-shaped glass tube so that they were not in direct contact with each other, and the upper portions were sealed. This was heat-treated in an electric furnace at 150 ° C. for 24 hours. In this heat treatment, the heating rate was 2 ° C./min, the holding temperature was 150 ° C., and the treatment time (holding time) was 24 hours. After the treatment, in order to remove excess ethylbenzenesulfonic acid, the polymer film was washed with acetone and dried in air at 70 ° C. for 30 minutes. The obtained polymer film has an electric conductivity of 4.8 × 10 ⁻⁴ Scm ⁻¹ at room temperature and in air, which is actually about 10,000 compared to the conventionally reported thin film doped with iodine. The conductivity was about twice as high.
[0020]
(3) Fabrication of sensor and evaluation of sensor characteristics A gold thin film comb-shaped electrode was formed as a detection electrode on the surface of the obtained conductive polypyrrole film by a sputtering method to obtain a sensor element. The sensor characteristics of this sensor element with respect to hydrogen, carbon monoxide, carbon dioxide, and methane gas were evaluated by changes in electrical resistance values when exposed to each gas. The concentrations of the gases used were all 3% (air dilution), and the measurement temperatures were room temperature and 100 ° C. In the measurement, clean air (1 minute), sample gas (3 minutes), and clean air (16 minutes) were sequentially flowed, and these totaled 20 minutes as one cycle. As a result, the conductive polypyrrole sensor did not respond to these gases. On the other hand, the change of the resistance value of the sensor with respect to acetaldehyde is shown in FIG.
[0021]
For acetaldehyde, a sensor was placed in a sealed container and vaporized by supplying liquid acetaldehyde to a heater in the container, and a change in the resistance value of the sensor was measured as a predetermined concentration. As a result, for acetaldehyde, the sensor showed a response that the resistance value decreased. FIG. 3 shows sensor sensitivities (ΔR / R _air : R _air is the initial resistance value and ΔR is the amount of change in the resistance value in the gas atmosphere) for various VOC gases having a concentration of 500 ppm at room temperature obtained by the same measurement. The sensor had higher sensitivity to aldehydes and selectively responded compared to chloroform, acetone, toluene, and benzene, and among them, the highest sensitivity to formaldehyde. This indicates that the sensor according to the present invention does not respond to a combustible gas such as hydrogen, and has high selectivity and highly sensitive response characteristics with respect to the VOC gas.
[0022]
The response characteristics to humidity were measured using a sealed container as in the case of the organic gas. FIG. 4 shows the relationship between the relative humidity at room temperature and the sensor sensitivity. The sensor sensitivity was defined as the ratio of the change amount of the resistance value to the resistance value when the relative humidity was 0%. Although the resistance value of the sensor decreases as the relative humidity increases, the sensor sensitivity at 100% relative humidity is 80%, and measurement is possible over a wide range of 0-100% relative humidity. Further, excellent linearity was exhibited at a relative humidity of 40% or more.
[0023]
Example 2
A polymer thin film was produced in accordance with the method of Example 1 except that the discharge output during plasma polymerization was 10 W and the heat treatment conditions during doping were 140 ° C. for 60 hours. The electrical conductivity of the obtained polymer film at room temperature and in air was 4.0 × 10 ⁻⁴ Scm ⁻¹ .
[0024]
Example 3
A polymer thin film was produced in accordance with the method of Example 1 except that the discharge output during plasma polymerization was 10 W and the heat treatment conditions during doping were 140 ° C. for 60 hours. The electric conductivity of the obtained polymer film at room temperature and in air was 1.0 × 10 ⁻⁶ Scm ⁻¹ .
[0025]
Example 4
A polymer thin film was produced according to the method of Example 1 except that the discharge output during plasma polymerization was 50 W and the heat treatment conditions during doping were 140 ° C. for 60 hours. The electric conductivity of the obtained polymer film at room temperature and in air was 2.0 × 10 ⁻⁵ Scm ⁻¹ .
[0026]
Example 5
A polymer thin film was produced in accordance with the method of Example 1 except that the discharge output during plasma polymerization was 100 W and the heat treatment conditions during doping were 140 ° C. for 60 hours. The electrical conductivity of the obtained polymer film at room temperature and in air was 3.0 × 10 ⁻⁴ Scm ⁻¹ .
[0027]
【The invention's effect】
As described above in detail, the present invention relates to a conductive polypyrrole thin film, a manufacturing method thereof, a conductive member, and a chemical sensor member such as a VOC gas sensor, and the present invention has the following effects. Is done.
(1) According to the method for producing an electrically conductive polymer thin film of the present invention, a dense polymer thin film having excellent film thickness uniformity can be obtained.
(2) The obtained polymer thin film is appropriately doped and can be used as an electronic device material due to its high electrical conductivity.
(3) In particular, since the electroconductive polymer thin film obtained by the method of the present invention can be easily produced by a dry process, it can be integrated, and can be suitably used for various applications as a chemical sensor.
(4) It is possible to provide a conductive member including the conductive polymer thin film as a constituent element and a chemical sensor member such as a VOC gas sensor.
[Brief description of the drawings]
FIG. 1 shows an infrared absorption spectrum of polypyrrole synthesized by a plasma polymerization film and a chemical polymerization method.
FIG. 2 shows sensor characteristics of the sensor shown in Example 1 with respect to acetaldehyde.
FIG. 3 shows sensor sensitivity of the sensor shown in Example 1 to volatile organic compounds.
4 shows sensor sensitivity with respect to relative humidity of the sensor shown in Example 1. FIG.

Claims (3)

  A method for producing a conductive polymer thin film by introducing a dopant into a polymerized film, wherein a dopant comprising an alkylbenzene sulfonic acid is introduced into a polymer thin film produced by plasma polymerization of pyrrole in a vacuum atmosphere. The manufacturing method of the conductive polymer thin film characterized by these.   2. The method for producing a conductive thin film according to claim 1, wherein the dopant is lower alkylbenzene sulfonic acid.   2. The method for producing a conductive thin film according to claim 1, wherein the dopant is an alkylbenzene sulfonic acid having a boiling point without being decomposed upon heating.

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