JPH0772108A - Steam sensor - Google Patents

Abstract

PURPOSE:To make a steam sensor possible to fast respond to changes in the amount of steam even in a low humidity area by using a plasma polymerization film made of spheroidal carbons (fullerene) as detector. CONSTITUTION:A plasma polymerization film made of spheroidal carbons used for a detector is an organic semiconductive thin film which is made of a compound as given by a formula of Cn (n: integer allowing the formation of a spheroidal compound geometrically) or (Cn+j) m (n: as mentioned above, j: integer of -10-10, m: positive integer). The compound has a structure in which a plurality of spheroidal carbons are polymerized by 1, 2-cycle bond added to a cyclohexatrienyl site and in the thin film, the structure is distributed in an amorphous state. The plasma polymerization film made of the spheroidal carbons is low in conductivity in the environment where no steam exists. When the steam exists, the conductivity increases 100,000 times at its maximum. The film has quick susceptibility with a high sensitivity.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a novel water vapor sensor using a plasma polymerized film of spherical carbons (so-called fullerene) as a gas detection element containing water vapor.

[0002]

2. Description of the Related Art Conventionally, inorganic materials such as ceramics are often used for humidity sensors or humidity sensors. For example, Japanese Unexamined Patent Publication No. 61-147139 discloses that a sintered body material of an organic silicon compound, metal particles, and an alkali silicate mixture is used as an element.
We have a difference of 0 ⁴ Ω.

However, the humidity sensor described in the above publication requires a process such as firing at a high temperature in order to manufacture an element, is easy to peel off, and has many problems in terms of stability and reliability.

Therefore, in order to solve these inconveniences,
Japanese Unexamined Patent Publication (Kokai) No. 3-293554 proposes to use zinc oxide whiskers as a humidity sensitive element, and as a result, it is reported that response speed and sensitivity are improved. However, when the relative humidity is 30% to 70%, the change in resistance value is about 500 times, and the response speed is only about several tens of seconds, which is not sufficient in terms of characteristics.

Further, in Japanese Patent Laid-Open No. 3-211452, a film containing a tin phosphate film as a main component and one or more of phosphate films of other metals coexisting with the film is used as a moisture sensitive material. However, the resistance change is 250
It is about double, which is insufficient in terms of sensitivity.

[0006]

As described above, in the conventional humidity sensor and humidity sensor, in addition to the complexity of the manufacturing method, there is a complaint that rapid sensing is difficult due to a sudden change in the amount of water vapor. In particular, it is difficult to apply it to a water vapor sensor that requires high-speed response and high sensitivity to changes in the amount of water vapor especially in a low humidity region.

Therefore, the present invention has been proposed in order to eliminate the drawbacks of the conventional ones,
It is an object of the present invention to provide a water vapor sensor that has excellent high-speed response to changes in the amount of water vapor even in a low humidity region, has high sensitivity, and has excellent mechanical strength, stability, and reliability.

[0008]

The inventors of the present invention have conducted extensive studies to solve the above-mentioned problems, and as a result, have found that a plasma polymerized film of spherical carbons (so-called fullerene) represented by C _n is stable. The present invention has been completed based on the finding that it has an element film structure, high mechanical strength, high speed response and high sensitivity to changes in the amount of water vapor in a low humidity region.

That is, the water vapor sensor of the present invention has a C _n
(However, n is an integer capable of geometrically forming a spherical compound.) A plasma polymerized film of spherical carbons represented by the formula (1) is used as a sensing element, and further, The plasma-polymerized film has a (Cn _{+ j} ) _m (n is an integer capable of geometrically forming a spherical compound, and j is -10.
Is an integer of 10 and m is a positive integer. ), Which is added to the cyclohexatrienyl moiety
The organic semiconducting thin film has a structure in which a plurality of spherical carbons are polymerized by cycle bonding, at least partially, and the structure is distributed in an amorphous state.

It was only in 1990 that the presence of fullerene, which is a spherical carbon compound, was clarified as the third crystalline carbon after diamond and graphite, and a macro amount synthesis method was established.

Fullerenes are a series of spheres consisting of carbon only.
Of carbonaceous compounds (Higher Fullerenes), 12
Containing 5 membered rings and 12 or more 6 membered rings
It Ie 60, 70, 76 or 84
Etc. (The carbon number is selected from the number capable of forming a geometrically spherical structure.
Is selected. ) Carbon atoms are bound to form a cluster
Spherical carbon C that constitutes (molecular assembly)_nAnd
Each C₆₀, C₇₀, C ₇₆, C₈₄And so on.

For example, C₆₀As schematically illustrated in FIG.
Then, cut off all the icosahedral vertices to produce a regular pentagon.
It has a polyhedral structure called "truncated icosahedron"
As shown in 2, all 60 vertices of this polyhedron are
A cluster that has been replaced with a carbon atom C
It has a ball-like molecular structure. Similarly, C₇₀, C₇₆, C
₈₄Etc. have a so-called rugby ball-like molecular structure.

In the present invention, the plasma polymerized film of spherical carbons (fullerene) described above is used as a sensing element.
The plasma-polymerized film of spherical carbons has an electric conductivity of 10 ^-11 S / cm or less in the absence of water vapor, and is recognized as an insulator by an ordinary measuring instrument, but the presence of water vapor causes a maximum of 10 ^-11 S / cm.
^The conductivity increases ^five times and reaches about 10 ^-6 S / cm. Also,
The sensing speed of water vapor is within 1 second, and it has high sensitivity and high sensitivity.

The plasma polymerized film is (C _{n + j} ) _m (n
Is an integer capable of forming a geometrically spherical compound selected from 60, 70, 76, 84 and the like, j is an integer of -10 to 10 and m is a positive integer. ) Is an organic semiconducting thin film represented by the composed molecule expression, as illustrated in FIG. 3, of the carbon bond constituting the cyclohexadienyl Satori enyl site (C _n on C _n, 6-membered sandwiching the 5-membered ring It refers to both ends of one ridge of the ring.) Each has a C _n polymer structure partially polymerized via a cyclobutane ring by a 1,2-cycle addition bond,
This structure has a film structure in which it is distributed amorphously.

The above C _n polymerized structure can take various forms. In addition to the structure shown in FIG. 3, as shown in FIG.
Examples include those in which _n molecules are bonded at other positions. The plasma-polymerized film may be formed only by these C _n polymerized structures, but in this case, it is considered that the C _n polymerized structures are spread over the whole in a network form by covalent bonds. Further, in the case where the C _n polymerized structure is partially present, it is presumed that the non-polymerized portions are bonded to each other by Van der Waals force. In this plasma polymerized film, C _n simple molecule such as C _{60 as} a raw material may be mixed together with the above C _n polymerized structure.

In the above-mentioned plasma polymerized film, the carbon number n of the spherical carbons C _n used as a raw material is preferably 60 and / or 70, which means that the production yield of other spherical carbons is significantly increased. From the viewpoint that it is reduced to an industrial value, it is possible to obtain a plasma polymerized film having the same characteristics even with spherical carbons having a carbon number n of 76, 84, etc., excluding the industrial value. It is possible.
Considering the availability of raw materials, C ₆₀ / C ₇₀ (mixture of C ₆₀ and C ₇₀ ) is most preferable.

Further, the plasma polymerized film is (C_{n + j})
_m(N is a geometry selected from 60, 70, 76, 84 etc.
Is an integer capable of forming a spherical compound, and j is -10 to
An integer of 10 and m is a positive integer. ) Is represented by the molecular formula
Where the value of j is C _nLack of carbon from a simple substance,
Or by addition, C₅₈, C₅₆... or C₆₂・
.. etc. are obtained and they are polymerized, so that C_n
Indicates that an integer multiple of is not the skeleton of the polymer.
It

The aforementioned plasma polymerized film, spherical carbons C _n
Polymerization with C as a sublimation source (C in the gas phase
_{The n} source material is sublimated and plasma is applied to polymerize C _n molecules. Can be used to form a film. For example,
A film formed by a method such as vapor deposition does not function as a film for sensing water vapor.

As a discharge method for plasma generation, various known methods such as direct current discharge, low frequency discharge, high frequency discharge, microwave discharge and the like can be adopted, and as the electrode type and discharge generation method, an internal electrode method, An external electrode system, a waveguide system, a capacitive coupling type, an inductive coupling type, an electrodeless oscillation type, etc. can be selected.

The plasma polymerization may be carried out in an atmosphere of spherical carbons such as C ₆₀ / C _70, but the uniformity of plasma,
A carrier gas may be used together from the viewpoint of improving stability and the like. As the carrier gas, any of those commonly used in plasma polymerization can be used,
Examples include argon, nitrogen and helium.

There are no problems in polymerization as long as the discharge conditions are in the range where the Paschen's law, which shows the relationship between the gas pressure, the electrode distance, and the voltage, is satisfied in the DC discharge and in the dischargeable range in the AC discharge. The gas pressure is preferably 13 Pascals (10 ^-1 Torr) or less.

[0022]

[Action] plasma polymerization film of spherical carbons C _n, in an environment of steam absent, or less conductivity 10 ^{-1 1} S / cm, although the conventional instrument is recognized as the insulator, there are water vapor Then, the conductivity increases up to 10 ⁵ times and reaches about 10 ^-6 S / cm. In addition, the water vapor sensing speed is within 1 second, which is a high sensitivity.

Therefore, the water vapor sensor using this plasma-polymerized film as a detection element exhibits a high-speed response to a change in the amount of water vapor even in a low humidity region, and the change in the amount of water vapor can be detected with high sensitivity. Further, the plasma-polymerized film has a stable device film structure and mechanical high strength, and does not require a baking process at a high temperature, and is therefore advantageous in terms of stability, reliability, productivity and the like.

[0024]

EXAMPLES Examples to which the present invention is applied will be described below in detail with reference to specific experimental data.

Plasma Polymerization Device FIG. 5 shows the external electrode type capacitively coupled plasma polymerization device used in this embodiment. This plasma polymerization apparatus includes a reactor 1 having a capacity of about 20 liters, and the reactor 1 is provided with gas supply pipes 2 and 3. An exhaust port 9 connected to a vacuum exhaust system including an oil diffusion pump 4, rotary pumps 5 and 6, liquid nitrogen traps 7 and 8 is provided at the bottom of the reactor 1.

Further, on the upper part of the reactor 1, the plasma generating electrodes 10 and 11 are spaced 3.5 cm apart from each other.
It is installed outside and is connected to the plasma power source 12 via an impedance matching device 13. Also, in the reactor 1, a molybdenum boat 1 for sublimation of C ₆₀ / C ₇₀ fullerene
4 and the sample substrate 15 are installed facing each other with a space of 7 cm.
Are connected.

The output of the plasma power supply 12 is AC 13.5.
The maximum output is 150W with 6MHz radio wave. Here, argon plasma is generated in a constant flow rate system of argon gas set to 25 W, 50 W, and 100 W at 13.5 Pascal, and C ₆₀ / C ₇₀ fullerene in the molybdenum boat 14 is sublimated into the plasma to generate plasma. Polymerization was carried out. The film thickness during the polymerization was continuously monitored by the sensor 17.

C ₆₀ / C ₇₀ fullerene which is a raw material is
The powder produced by arc discharge between graphite electrodes by a known method was purified by flash chromatography, and C ₆₀ : C ₇₀ was about 9: 1.

Experiment 1 A plasma-polymerized film of C ₆₀ / C ₇₀ fullerene having a thickness of 1000 was formed on the substrate shown in FIG.
The film was formed with Å. That is, as shown in FIG. 6, the substrate 21 has a comb-shaped electrode 23, 24 made of gold on the surface of the glass substrate 22.
Were formed so as to face the comb teeth 23a and 24a so as to mesh with each other, and the plasma polymerized film 25 was formed so as to cover these comb teeth 23a and 24a. The substrate is not limited to the glass substrate, and any material can be used as long as it has a conductivity sufficiently lower than that of the fullerene plasma polymerized film and can form a current collector. Good.

Therefore, as shown in FIG. 7, the plasma-polymerized film 25 is formed in the comb-tooth portion 23 of the comb-shaped electrodes 23 and 24.
a and 24a, acting as a resistor, the comb-shaped electrode 2
By passing a current at a constant voltage between 3 and 24 and measuring the current value (resistance value), the conductivity can be measured from the following formula 1.

[0031]

[Equation 1]

The conductivity of the sample prepared as described above was measured using the voltage-current characteristic measuring device shown in FIGS. 8 and 9. Note that FIG. 8 shows a cross section taken along the line FF of FIG. This voltage-current characteristic measuring device is computer-controlled, and comprises a Faraday cage type cell 30 made of copper, and a heating element 31, and a sample holder 32 on the heating element 31. The upper part of is closed by a lid 35 having vacuum valves 33 and 34. Further, coaxial cable plugs 36, 37 penetrating the cell 30 are provided at predetermined positions of the cell 30, and the comb-shaped electrodes 23, 24 formed on the surface of the glass substrate 22 via the coaxial cable plugs 36, 37. The voltage-current characteristic between them is measured. The temperature inside the cell 30 is monitored by the thermocouple 38.

In this experiment, first, 1.3
The switching characteristics between two environments in a Pa (0.01 torr) vacuum and an atmosphere introduced with air (60% relative humidity) were measured. Specifically, the cell 3 in the air atmosphere
The inside of 0 was evacuated, and then the atmosphere was rapidly introduced, and the change in current value during this period was measured. The results are shown in Fig. 10.

As is clear from FIG. 10, the current value between the comb-shaped electrodes 23 and 24 was 5 × 10 ⁻⁹ A as the vacuum was exhausted.
To 5.5 × 10 ⁻¹² A, which is converted to the conductivity of the plasma polymerized film 25 by the above equation 1,
Conductivity is 4.26 × 10 ^-6 S / cm to 4.68 × 10 ^-9 S / cm
The change in conductivity reached about 10 ³ times. When calculating the conductivity σ, the inter-electrode distance d = 0.5 × 10 ⁻³ (m) and the electrode length L = 0.12.
(M), sample film thickness e = 100 × 10 ⁻⁹ (m), and resistance value R = V / I [where voltage V = 49 (V)], and the above current value was substituted.

Further, as shown in FIG. 10, the current value gradually decreases with the evacuation, and the current value rapidly increases at the same time when the pressure is suddenly released (atmosphere is introduced). It is considered that this clearly shows that the plasma polymerized film has excellent responsiveness.

Then, when the relationship between the humidity and the element conductivity of the plasma polymerized film was measured, the results shown in FIG. 11 were obtained. As can be seen from FIG. 11, the plasma polymerized film has excellent sensitivity, especially in a low humidity region.

Experiment 2 In this experiment, the difference in characteristics between the plasma polymerized film and the vapor deposited film was examined. That is, C ₆₀ / C ₇₀ fullerene was vapor-deposited without applying plasma to form a vapor-deposited film. Then, the conductivity of this vapor-deposited film was measured and compared with the conductivity of the above plasma polymerized film. The results are shown in Table 1.

[0038]

[Table 1]

As is clear from Table 1, it is shown that the vapor deposition film has a very small change in conductivity due to water vapor and does not function as a water vapor sensor.

Experiment 3 In Experiment 1 above, the amount of water vapor (humidity) was changed by evacuation to investigate the change in the conductivity of the plasma polymerized film. However, this change in conductivity was not due to the change in pressure. In order to confirm that there was no nitrogen, nitrogen gas, argon gas, or ethylene gas was introduced instead of the atmosphere, and the same measurement as in Experiment 1 was performed.

When vacuum evacuation was performed in these nitrogen gas, argon gas and ethylene gas atmospheres, the change in conductivity was extremely small. This indicates that the change in the conductivity in Experiment 1 above is not due to the change in pressure, but is due to the change in the amount of water vapor. Further, when oxygen gas was introduced, the increase in conductivity was large as compared with each of the above gases, but it was still two orders of magnitude smaller than when introduced into the atmosphere. Therefore, it was easy to distinguish it from water vapor.

[0042]

As is apparent from the above description, in the present invention, since the plasma polymerized film of spherical carbons is used as the sensing element, the fabrication of the element is simplified, the response speed is increased, and the sensitivity is improved. This can be achieved, and the performance as a water vapor sensor can be dramatically improved.

Therefore, according to the present invention, there is provided a water vapor sensor which is excellent in high-speed response to a change in water vapor amount even in a low humidity region, has high sensitivity, and is excellent in mechanical strength, stability and reliability. It is possible.

[Brief description of drawings]

FIG. 1 is a schematic diagram showing a truncated icosahedron structure of C ₆₀ fullerene.

FIG. 2 is a schematic view showing a carbon-carbon bond state in C ₆₀ fullerene.

FIG. 3 is a schematic diagram showing an example of a C _n polymerized structure.

FIG. 4 is a schematic diagram showing another example of a C _n polymerized structure.

FIG. 5 is a schematic cross-sectional view showing one structural example of a plasma polymerization apparatus.

FIG. 6 is a schematic plan view of a measurement sample on which a plasma polymerized film is formed.

FIG. 7 is a schematic cross-sectional view of a main part of a measurement sample on which a plasma polymerized film is formed.

FIG. 8 is a schematic plan view of a conductivity measuring cell.

FIG. 9 is a schematic side view of a conductivity measuring cell.

FIG. 10 is a characteristic diagram showing a change in current value (conductivity) due to evacuation.

FIG. 11 is a characteristic diagram showing a relationship between humidity and electric conductivity in a plasma polymerized film.

Claims (3)

[Claims] 1. A water vapor characterized in that a plasma polymerized film of spherical carbons represented by C _n (where n is an integer capable of geometrically forming a spherical compound) is used as a sensing element. Sensor. 2. The plasma polymerized film is (C _{n + j} ) _m (n is an integer capable of geometrically forming a spherical compound, and j is -1.
An integer of 0 to 10 and m is a positive integer. The water vapor sensor according to claim 1, which is represented by a molecular formula: 3. The plasma polymerized film has at least partially a structure in which a plurality of spherical carbons are polymerized by 1,2-cycle bonds added to a cyclohexatrienyl site, and the structure is distributed in an amorphous state. The water vapor sensor according to claim 1, wherein the water vapor sensor is an organic semiconductive thin film.