JP2518282B2 - Moisture sensitive element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a humidity sensitive element. More specifically, the present invention relates to a moisture sensitive element in which the surface of a conductive comb-shaped electrode formed on an insulating substrate is covered with a plasma polymerized film.

[Conventional technology]

The present applicant has previously proposed a moisture sensitive element in which the surface of a conductive comb-shaped electrode formed on an insulating substrate is covered with various plasma polymerized films. As a plasma polymerized film,
Plasma polymerized film of chlorine-containing polymer, preferably vinylidene chloride (Japanese Patent Publication No. 5-25064), plasma polymerized film of bis (trimethylsilyl) acetamide (Japanese Patent Publication No. 5-33)
741), a plasma-polymerized film of a mixture of a nitrogen-containing organic silicon compound and a halogenated hydrocarbon (Japanese Patent Publication No. 6-23712), a plasma-polymerized film of a mixture of a nitrogen-containing organic silicon compound and a silane halide (special Japanese Patent Publication No. 6-23713),
Mixture of organic amine and halogenated hydrocarbon or silane, plasma polymerized film (Japanese Patent Publication No. 7-104311) or nitrogen-containing organic silicon compound plasma polymerized film surface-treated with alkyl halide (Japanese Patent Publication 6). −
No. 68476) is used.

Some of these plasma-polymerized membranes have a quaternary ammonium salt formed in the membrane, which shows excellent moisture-sensitive properties. This is a polymer electrolyte-type humidity sensor currently widely studied. It has a function similar to.

By the way, although the polymer electrolyte type humidity sensor can be used in a high humidity region, it has a common problem that the membrane and the salt in the membrane easily flow out when it is condensed for a long time or immersed in water. There are spots. For this reason, the instruction manuals of commercially available polymer electrolyte type humidity sensors often describe that storage and use in high humidity conditions should be avoided.

[Problems to be solved by the invention]

The present inventor has improved the water resistance of a humidity sensitive element having a plasma polymerized film having a function similar to that of the polymer electrolyte type as described above, particularly a plasma polymerized film containing a quaternary ammonium salt as a humidity sensor. As a result of various studies to fully exhibit its function even when exposed to dew condensation, it is possible to achieve the intended purpose by coating the moisture-sensitive plasma polymerized film with another specific plasma polymerized film. I was able to.

[Means for solving the problem]

Therefore, the present invention relates to a moisture sensitive element, which is
The moisture-sensitive plasma-polymerized film directly covering the surface of the conductive comb-shaped electrode formed on the insulating substrate is further covered with a plasma-polymerized film of nitrogen-free organosilicon compound or hydrocarbon.

As the insulating substrate, glass, quartz, alumina, etc. are generally used, but an insulating film (Japanese Patent Publication No. 5-28340) formed by oxidizing the surface of a silicon substrate, which is also proposed by the applicant, is also available. Can be used.

When forming a conductive comb-shaped electrode on such an insulating substrate, first, on the insulating substrate, a corrosion-resistant metal such as stainless steel, Hastelloy C, Inconel, Monel, or gold, or an electrode forming material such as silver or aluminum. By sputtering metal, ion plating method, etc.
A thin film having a thickness of about 0.1 to 0.5 μm is formed, and then a photoresist pattern is formed thereon.

For example, in the case of aluminum, the photoresist pattern is formed on the electrode forming material metal thin film thus formed by applying a well-known photolithography process. That is, a photoresist coating is applied on the metal thin film, a glass plate having a negative or positive image of the pattern of the comb-shaped electrode printed thereon is placed thereon, and baking and development by light irradiation are carried out. After this, wet chemical etching is performed, and as an etching solution, phosphoric acid-sulfuric acid-chromic anhydride-water (weight ratio 65: 15: 5:
15) A mixed solution, BHF (hydrofluoric acid type), ferric chloride aqueous solution, nitric acid, phosphoric acid-nitric acid mixed solution and the like are used.

The surface of the conductive comb-shaped electrode formed on the insulating substrate is covered with the plasma-polymerized film having various moisture-sensitive characteristics as described above. As the monomer used for forming the moisture-sensitive plasma-polymerized film, various monomers are used as described above, but preferably a mixture of a nitrogen-containing organosilicon compound and a halogenated silane, an organic amine or a nitrogen-containing heterocyclic group. Mixtures of compounds with halogenated hydrocarbons or halogenated silanes are used.

As the nitrogen-containing organic silicon compound, for example, a compound represented by the following general formula is used.

_{R 3 Si-NR 2 R 2} -SiR 2 -NR 2 (R 2 N) 3 -SiR ( wherein, R represents a hydrogen atom, a methyl group, an ethyl group, a vinyl group or an acetylene group, R ₂ or R ₃ Are the same or different R groups, and groups other than at least two hydrogen atoms are included in the molecule. Specific examples of such compounds include trimethylsilyldimethylamine, triethylsilazane, hexamethyldisilazane, and hexamethyl. Cyclotrisilazane, bis (dimethylamino) methylvinylsilane, bis (trimethylsilyl) acetamide, tris (dimethylamino) silane, tris (dimethylamino) methylsilane,
Tris (methylamino) methylsilane, tris (methylamino) ethylsilane, N, N-dimethylamino-N'-
Examples thereof include methylamino-N'-ethylaminosilane, and preferably trimethylsilyldimethylamine or bis (dimethylamino) methylvinylsilane or bis (dimethylamino) dimethylsilane.

As the organic amine, aliphatic or aromatic first to third
Amine can be used, but preferably a secondary to tertiary amine substituted with an alkyl group, for example (substituted) monoamine such as n-butylamine, secondary butylamine, isopropylamine, dimethylethylamine, diethylamine, dimethylallylamine, N, (Substituted) diamines such as N-dimethyl-1,3-propanediamine, N, N, N ', N'-tetramethylethylenediamine, and cycloalkyl-substituted monoamines such as pentamethyleneimine and hexamethyleneimine, N, N Cycloalkyl-substituted diamines such as'-dimethylpiperazine, aromatic amines such as aniline and its derivatives are used.

Examples of the nitrogen-containing heterocyclic compound include pyridine and 2
-Methylpyridine, 4-vinylpyridine, 2-methylpyrazine, dimethylpyrazole and the like are used.

As halogenated hydrocarbons preferably alkyl halides are used, the halogen substituents may be one or more. Specifically, methylene bromide, methane bromide, tribromide methane, ethylene bromide, ethylene dibromide,
Propane bromide, propane dibromide, butane bromide, butane dibromide, methylene chloride, methylene bromide chloride, ethyl iodide and the like are used. Further, the halogenated hydrocarbon group may be a chain saturated bond or an aromatic nucleus.

Examples of the halogenated silane include SiX ₁ X ₂ X ₃ X ₄ (wherein X _{1 to} X ₄ are a halogen atom, a hydrogen atom, a lower alkyl group or a lower alkenyl group or a lower alkynyl group, and among these, 1 to 3 are halogen atoms), and preferably a lower alkyl-substituted halogenated silane is used. Some examples of such halogenated silanes are as follows.

CH ₃ SiCH ₃ CH ₃ SiH ₂ Br, CH ₃ SiHBr ₂ (CH ₃ ) ₂ SiBr ₂ plasma polymerization is a nitrogen-containing organosilicon compound depending on the shape of the plasma polymerization apparatus and the plasma generation method.
Several meters to several Torr of organic amine or nitrogen-containing heterocyclic compound
And the halogenated hydrocarbon or silane is also used at a pressure of a few m to a few Torr, and the mixture is supplied with electric power of a discharge output of a few 100 W.

Specifically, for example, when the discharge output is 20 W in a mode where an organic amine is used, the organic amine is about 0.04 to 0.2 To.
It is used in a ratio of about 0.01 to 0.1 Torr of halogenated hydrocarbon or silane halide to rr. If the proportion of the halogenated hydrocarbon or the silane halide is too small, the halogen content in the plasma polymerized film will be reduced and the moisture-sensitive property will be poor. Since the nitrogen content decreases and the polymerized film also hardens, the moisture-sensitive property also deteriorates.

In the present invention, this moisture-sensitive plasma-polymerized film is further coated with a plasma-polymerized film of a nitrogen-free organosilicon compound or hydrocarbon. Examples of nitrogen-free organosilicon compounds include tetramethylsilane, hexamethyldisilane, hexamethylkiloxane, tetramethylsiloxane, methyltrimethoxysilane, methyltriethoxysilane, methyldiethoxysilane, vinyltriethoxysilane, and vinylmethyl. Diethoxysilane, vinyltriethoxysilane, etc. are used, and the hydrocarbon is C _1-
Saturated or unsaturated hydrocarbons such as C ₇ alkanes, ethylene, propylene, styrene and benzene are used.
Plasma polymerization using these monomers is carried out under the same plasma polymerization conditions as above, and generally has a thickness of about 2000-
Form a 10000Å polymer film.

The moisture sensitive element is then manufactured by attaching a lead wire to the extraction electrode portion which is not covered with any plasma polymerized film by soldering or silver paste.

〔The invention's effect〕

When the plasma-polymerized film as a humidity sensor is further covered with a plasma-polymerized film of nitrogen-free organosilicon compound or hydrocarbon, the latter plasma-polymerized film is highly crosslinked and has excellent solvent resistance and hydrophobicity. No direct contact of moisture with the moisture-sensitive plasma-polymerized film is observed, and the water resistance is greatly improved with almost no influence on the response of the moisture-sensitive element.

As a result, the applicable range of the moisture-sensitive element is greatly expanded, and it becomes possible to use the moisture-sensitive element for a long time in a dew condensation state, store it, and use it in a solution.

〔Example〕

 Next, the present invention will be described with reference to examples.

Example 1 A glass plate was used as an insulating substrate, and a comb-shaped electrode having an electrode width of 500 μm and an electrode interval of 250 μm was formed on the surface of the glass plate by a lift-off method generally used as a patterning method of gold electrodes.

In this lift-off method, a positive resist is applied on the glass plate surface using a spin coater, and the temperature is increased to 85 ° C.
After pre-baking for 30 minutes, a mask was used to carry out contact exposure with ultraviolet light, and then development was carried out to form a transfer pattern of comb-shaped electrodes.
Comb-shaped electrodes were formed by sequentially depositing 00Å chromium and gold, and finally dipping in acetone to remove the remaining resist.

The surface of the comb-shaped electrode on the surface of the glass plate thus formed was covered with a plasma polymerized film of N, N, N ', N'-tetramethylethylenediamine and methylene bromide. The plasma polymerization was carried out using a mixed gas of 0.08 Torr of N, N, N ', N'-tetramethylethylenediamine and 0.01 Torr of methylene bromide under a discharge condition of 20 W for 20 minutes.

With the moisture-sensitive element on which the moisture-sensitive plasma-polymerized film has been formed in this manner, the inside of the reactor is kept inside the plasma reactor.
The pressure was reduced to 10 ^-4 Torr, and methyltrimethoxysilane was introduced at a pressure of 0.06 Torr to carry out plasma polymerization for 30 minutes at a discharge power of 60 W.
Å) was formed.

After connecting a lead wire to this moisture sensitive element for forming a protective film by attaching silver paste, it was installed in a humidity generator (manufactured by Shinei), and under the conditions of frequency 1KHz, voltage 1V, temperature 30 ° C, LCR meter (YHP When the moisture sensitivity characteristics were evaluated using a product manufactured by K.K., a resistance change of about 3 digits or more was shown in the relative humidity range of 40 to 98%.

Further, the water resistance of the moisture sensitive element having a protective film formed thereon was evaluated by a dew condensation cycle test. The test is a humidifier (Hitachi, Ltd.) for 1 minute and a humidity / humidity tester (30 degrees, 10%)
Drying for 10 minutes by RH) was set as one cycle, and the change in resistivity up to 20 cycles was measured under the conditions of 30 ° C. and 60% RH.
The obtained results are shown in the graph of FIG. 1, and it can be seen from the results that the moisture-sensitive element of the present invention has good water resistance as compared with the one without a protective film (Comparative Example). It

Example 2 In Example 1, the formation of the plasma polymerization protective film was 0.06.
Torr styrene was used under the conditions of discharge power of 50 W and time of 10 minutes to form a protective film with a thickness of 4000 Å.

This protective film-forming dry / wet element showing a resistance change of about 3 digits or more in the relative humidity range of 40 to 98% is evaluated for water resistance in the same manner as in Example 1, and the result is shown in the graph of FIG. The result is as follows. From this result, it can be seen that the water resistance is also good.

Example 3 In Example 1, the formation of the moisture-sensitive plasma polymerized film was 0.1.
A mixed gas of 07 Torr of pyridine and 0.01 Torr of methylene bromide was used under the discharge condition of an output of 20 W and a time of 20 minutes, and 0.06 Torr was continuously formed on the formed moisture-sensitive plasma polymerized film having a film thickness of 9000 Å. Output of methyltrimethoxysilane
Under the discharge condition of 60 W for 30 minutes, a plasma polymerization protective film was formed with a film thickness of 5100Å.

When the water resistance test was conducted on this moisture sensitive element with protective film formed in the same manner as in Example 1, the results shown in the graph of FIG. 2 were obtained. The case where no protective film is provided is also shown as a corresponding comparative example.

Example 4 In Example 3, instead of pyridine, 0.07 Torr of 2-
Using methylpyridine, the discharge time was changed to 10 minutes to form a moisture-sensitive plasma polymerized film having a film thickness of 4500Å, and subsequently a plasma polymerized protective film was similarly formed.

When the water resistance test was conducted on this moisture sensitive element with protective film formation in the same manner as in Example 1, the results shown in the graph of FIG. 3 were obtained. The case where no protective film is provided is also shown as a corresponding comparative example.

Example 5 In Example 3, the pyridine was replaced by 0.03 Torr of 4-
Using vinylpyridine, the discharge time was changed to 10 minutes to form a moisture-sensitive plasma-polymerized film having a film thickness of 2000 Å, and subsequently a plasma-polymerized protective film was similarly formed.

Example 6 In Example 3, the pyridine was replaced by 0.06 Torr of 2-
Using methyl pyridine, the discharge time was changed to 10 minutes to form a moisture-sensitive plasma polymerized film with a film thickness of 4100Å, and was continuously adjusted to 0.
Output of 60 torr vinyltriethoxysilane 60W, time 20
Under a discharge condition of 1 minute, a plasma polymerization protective film was formed with a thickness of 1800Å.

Example 7 In Example 1, the formation of the moisture-sensitive plasma-polymerized film was 0.
A mixed gas of 014 Torr of aniline and 0.006 Torr of methylene bromide was used under the discharge condition of an output of 8 W and a time of 30 minutes, and 0.06 Torr was continuously formed on the formed moisture-sensitive plasma polymerized film having a film thickness of 700 Å. Output of methyltrimethoxysilane
Under the discharge condition of 60 W for 10 minutes, a plasma polymerization protective film was formed with a thickness of 1800 Å.

With respect to the protective film forming moisture-sensitive elements obtained in each of Examples 3 to 5, Example 6 and Example 7, the electrical resistance with respect to the relative humidity was measured in the same manner as in Example 1, and the results shown in FIGS. As shown in the graph, it was confirmed that the humidity-sensitive property in which a resistance change of three digits or more was observed.

[Brief description of drawings]

1 to 3 are graphs showing the data of the dew condensation cycle of the moisture-sensitive elements obtained in Examples 1 to 2, Example 3 and Example 4, respectively. 4 to 6 are graphs showing the relationship between the relative humidity and the electric resistance of the humidity sensitive elements obtained in Examples 3 to 5, Example 6 and Example 7, respectively.

Claims (1)

(57) [Claims] 1. A plasma-polymerized film of a mixture of a nitrogen-containing organosilicon compound and a halogenated silane or an organic amine or a nitrogen-containing heterocyclic compound and a halogen on the surface of a conductive comb-shaped electrode formed on an insulating substrate. A mixture of dehydrogenated hydrocarbon or halogenated silane Plasma-polymerized film which is a plasma-polymerized film is directly covered, and further the moisture-sensitive plasma-polymerized film is covered with a plasma-polymerized film of nitrogen-free organosilicon compound or hydrocarbon. Moisture sensitive element.