JPH0623713B2 - Thin film moisture sensitive element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a thin film moisture sensitive element. More specifically, it relates to a thin film 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]

Controlling the relative humidity in the air is very important for precision industry, food industry, textile industry, building management, etc., and as a moisture sensing element for detecting it, conventionally, the following materials are used. Has been.

(1) Metals or semiconductors such as Se, Ge and Si (2) Oxides of metals such as Sn, Fe and Ti (3) Porous metal oxides such as Al ₂ O ₃ (4) Electrolyte salts such as LiCl ( 5) Polymer film made of organic or inorganic material However, the moisture sensitive element using these various materials is
None of them are in a satisfactory condition, because maintenance is difficult, or there are problems with reliability and responsiveness.

For example, when the metal oxide of (2) above is used, pressing and sintering are performed to form the metal oxide, but there are problems such as difficulty in uniform pressing and cracking during firing. Also, even if molded without problems in the process, due to the nature of the resistance change due to moisture adsorption and desorption of the moisture-sensitive element,
Since damage occurs from the grain boundaries due to the influence of water, there is a problem in durability, in other words, reliability.

Further, when the polymer film of the above (5) is used, although it is inexpensive in terms of materials, there are problems such as deterioration due to chemicals such as solvents and deterioration of reliability.

[Problems to be solved by the invention]

As a result of various investigations in order to avoid such problems, especially for an electrode material having excellent corrosion resistance, the applicant has previously found that the corrosion-resistant metal thin film to be processed is preferably formed on an insulating substrate by a sputtering method. It has been found that it is suitable to use a corrosion-resistant comb-shaped electrode obtained by electrolytic etching after forming a photoresist pattern on a humidity sensor (Japanese Patent Laid-Open No. 61-148,871). After that, the applicant of the present invention further improved the thin film moisture sensitive element using such a corrosion-resistant comb-shaped electrode, and as a result, the surface of the conductive comb-shaped electrode formed on the insulating substrate was a polymer thin film,
In general, by covering with a plasma-polymerized film of a nitrogen-containing organosilicon compound and further treating it with an alkyl halide, we succeeded in obtaining a thin film moisture-sensitive element with excellent environmental resistance and good response ( JP-A-61-200,454). As described above, in order to obtain a thin film moisture-sensitive element having better response, the surface of the conductive comb-shaped electrode formed on the insulating substrate is covered with a plasma-polymerized film of a nitrogen-containing organosilicon compound, and This is treated with alkyl halide 2
Need a process.

The inventors of the present invention have conducted various studies as to a method for obtaining a thin film moisture sensitive element having better response in one step, and as a result, formed a plasma polymerized film from a mixture of a nitrogen-containing organosilicon compound and a halogenated silane. It was found that this problem can be effectively solved.

[Means for Solving the Problems] and [Operation] Accordingly, the present invention relates to a thin film moisture sensitive element, which includes a surface of a conductive comb-shaped electrode formed on an insulating substrate. A mixture of a nitrogen organosilicon compound and a halogenated silane is covered with a plasma polymerized film.

FIG. 1 of the drawings is a plan view showing one embodiment of a thin film moisture sensitive element according to the present invention, in which conductive comb electrodes 2, 2 ′ are formed on an insulating substrate 1, and the surface thereof is generally about 500Å ~ 2000
The mixture plasma polymerized film 3 having a thickness of about 0 Å (2 μm) is covered, and the extraction electrode portion not covered with the polymerized film is soldered or silver paste is applied.
Lead wires 5, 5'are attached by 4, 4 '.

As the insulating substrate, glass, quartz, alumina, etc. are generally used. However, when it is desired that the temperature followability to the humidity sensitive element is further improved, the silicon substrate also proposed by the applicant of the present invention. Insulating film formed by oxidizing the surface (Japanese Patent Application No. 60-122,548, Japanese Patent Application Laid-Open No. 61-281958)
Etc. can also be used.

When forming a conductive comb-shaped electrode on these insulating substrates, first, on the insulating substrate, a corrosion-resistant metal such as stainless steel, Hastelloy C, Inconel, Monel, or gold, or an electrode forming material metal such as silver or aluminum. By sputtering, ion plating, 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.

In the case of aluminum, for example, 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.As the etching solution, phosphoric acid-sulfuric acid-chromic anhydride-water (weight ratio 65: 15: 5: 15) mixed solution, BHF (hydrofluoric acid system), second chloride Iron solution, nitric acid, phosphoric acid-
A nitric acid mixed solution or the like is used.

A conductive comb-shaped electrode formed on an insulating substrate is a nitrogen-containing organosilicon compound whose surface has excellent moisture sensitivity.
Covered by plasma polymerized film of halogenated silane mixture.

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} N-SiR 2 -NR 2 (R 2 N) 3 -SiR ( wherein, R is 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 the groups other than at least two hydrogen atoms are included in the molecule.) Specific examples of such compounds include trimethylsilyldimethylamine, triethylsilazane, hexamethyldisilazane, hexa Methylcyclotrisilazane, bis (dimethylamino) methylvinylsilane, bis (trimethylsilyl) acetamide, tris (dimethylamino)
Examples thereof include silane, tris (dimethylamino) methylsilane, tris (methylamino) methylsilane, tris (methylamino) ethylsilane, N, N-dimethylamino-N′-methylamino-N′-ethylaminosilane, and preferably trimethylsilyldimethyl. Amine or bis (dimethylamino) methylvinylsilane or bis (dimethylamino) dimethylsilane is used.

The halogenated silane has the general formula 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, a lower alkenyl group or a lower alkynyl group, and 1 to 3 of these are halogen atoms) Used, preferably lower alkyl substituted halogenated silanes. Some examples of such halogenated silanes are as follows.

CH ₃ SiCl ₃ CH ₃ SiH ₂ Br, CH ₃ SiHBr ₂ (CH ₃ ) ₂ SiBr ₂ plasma polymerization is performed by adding nitrogen-containing organic silicon compounds according to the shape of the plasma polymerization apparatus and the plasma generation method.
At pressures of m to a few Torr, and halogenated silane is still a few m
~ Used at pressure of several Torr and discharge output number to these mixtures ~
This is done by supplying electric power of several 100W.

Specifically, for example, when the discharge output is 10 W, the nitrogen-containing organic silicon compound is used in a ratio of about 0.15 to 0.08 Torr and the halogenated silane is used in a ratio of about 0.06 to 0.01 Torr. If the proportion of the halogenated silane is too low, the bromine content in the plasma polymerized film decreases and the moisture-sensitive property deteriorates.On the other hand, if the proportion is too high, the nitrogen content in the plasma polymerized film becomes relatively low. Moreover, the polymer film is also cured, so that the moisture-sensitive property also deteriorates.

The thin film moisture-sensitive element configured in this way has an electric resistance value that changes according to the amount of water vapor in the air. Therefore, the humidity can be measured by extracting this resistance value change from the conductive comb-shaped electrode. it can.

〔The invention's effect〕

The thin film moisture sensitive element according to the present invention has the following effects.

(1) By forming a plasma-polymerized film as a mixture of a nitrogen-containing organosilicon compound and a halogenated silane, further treatment with an alkyl halide is not required,
The process can be omitted.

(2) Since the formed plasma polymerized film has excellent water resistance and chemical resistance, the humidity-sensitive element also has good environment resistance.

(3) Since it has a sufficient function even with an extremely thin film with a film thickness of about 1000Å, it is also responsive in terms of responsiveness as compared with the conventionally used sensors such as metal oxide resistance change type and polymer capacitance change type. It is excellent.

〔Example〕

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

Examples 1 and 2 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 gold electrode patterning method.

In this lift-off method, a positive resist is applied on the glass plate surface using a spin coater, and the positive resist is applied at 80 ° C for 12 hours.
After pre-baking for 0 minutes, contact exposure with ultraviolet rays was performed using a mask, and then development was performed to form a reversed pattern of comb-shaped electrodes, and then chromium and gold with a thickness of 1000 Å were sequentially deposited there. Then, finally, the comb-shaped electrode was formed by immersing in acetone and peeling off 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 bis (dimethylamino) dimethylsilane and methyltrichlorosilane. The polymerization conditions and the film thickness of the polymer film are shown in the following table.

A lead wire is connected to the electrode by attaching a silver paste to form a moisture sensitive element, which is placed in a temperature and humidity tester and the frequency 1
Moisture-sensitive characteristics were evaluated using an LCR meter under the conditions of KHz, voltage of 1 V and temperature of 30 ° C. The relationship between the resistance value and the relative humidity is shown by curves I (Example 1) and II (Example 2) in FIG.

[Brief description of drawings]

FIG. 1 is a plan view of one mode of the thin film moisture sensitive element according to the present invention. Further, FIG. 2 is a graph showing the relationship between the relative humidity and the resistance value in Examples 1 and 2.

Claims (3)

[Claims] 1. A thin film moisture sensitive element comprising a conductive comb-shaped electrode formed on an insulating substrate, the surface of which is covered with a plasma-polymerized film of a mixture of a nitrogen-containing organosilicon compound and a silane halide. 2. The thin film moisture-sensitive element according to claim 1, wherein the nitrogen-containing organosilicon compound is bis (dimethylamino) dimethylsilane. 3. The thin film moisture sensitive element according to claim 1, wherein the halogenated silane is a lower alkyl-substituted halogenated silane.