JPS62255860A - Thin film moisture sensitive element - Google Patents

Abstract

PURPOSE:To obtain a thin film moisture sensitive element having good environmental resistance and responsiveness by covering the surface of comb-shaped electrodes formed on an insulating substrate with a mixed plasma-polymerized film composed of a nitrogenous org. silicon compd. and halogenated silane. CONSTITUTION:The conductive comb-shaped electrodes 2, 2' are formed on the insulating substrate 1 and the surfaces thereof are coated with the plasma- polymerized film 3. Lead wires 5, 5' are attached by soldering or silver pastes 4, 4' to taking-out electrode parts. The polymerized film 3 consists of the mixed plasma-polymerized film composed of the nitrogenous org. silicon compd. such as bis(dimethylamino)dimethyl silane and the halogenated silane (more preferably lower alkyl-substd. halogenated silane). The electric resistance value of the resulted thin film moisture sensitive element changes according to the quantity of the steam in the air. The humidity is measured by taking out such change of the resistance value from the electrodes 2, 2'.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a thin film moisture sensitive element. More specifically, the present invention relates to a thin film moisture sensitive element in which the surface of conductive comb-shaped electrodes formed on an insulating substrate is covered with a plasma polymerized film.

[Conventional technology]

Controlling the relative humidity in the air is very important in the precision industry, food industry, textile industry, building management, etc., and there are currently no known moisture sensing elements that use conventional materials to detect this. It is being

(1) Metals or semiconductors such as Ss, Ge, SL, etc. (2) Metal oxides such as Sn, Fe, Ti, etc. (3)
1,0. porous metal oxides such as (4) electrolyte salts such as LiCfi, (5) polymer membranes made of organic or inorganic materials.However, moisture sensing elements using these various materials are difficult to maintain, Or, there are problems with reliability or responsiveness, and the system is not in a satisfactory state.

For example, when using the metal oxide of (2) above, pressing and sintering are performed to shape it, but there are problems such as difficulty in homogeneous pressing or cracking during firing. Furthermore, even if molded without any problems during the process, moisture-sensitive elements utilize resistance changes caused by desorption of moisture, and as a result, fractures occur at grain boundaries due to the influence of moisture, resulting in poor durability and, in other words, reliability. There are also problems with sexuality.

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

[Problem that the invention seeks to solve]

As a result of various studies to avoid these problems and to find a material with particularly excellent corrosion resistance as an electrode material, the applicant has previously developed a corrosion-resistant workpiece metal thin film formed on an insulating substrate, preferably by sputtering. It has been found that it is suitable to use a corrosion-resistant comb-shaped electrode obtained by electrolytically etching a photoresist pattern after forming a photoresist pattern in a humidity sensor (Japanese Patent Application No. 59-270,456).

Subsequently, the present applicant attempted to further improve the thin film moisture-sensitive element using such corrosion-resistant comb-shaped electrodes, and as a result, the surface of the conductive comb-shaped electrode formed on an insulating substrate was coated with a thin polymer film.
In general, by covering with a plasma polymerized film of nitrogen-containing organosilicon compound and further treating this with an alkyl halide, we succeeded in obtaining a thin film moisture-sensitive element with excellent environmental resistance and good response ( Patent application 1986-40,786
issue).

In this way, in order to obtain a thin film moisture-sensitive element with better response, the surface of the conductive comb-shaped electrode formed on an insulating substrate is covered with a plasma polymerized film of a nitrogen-containing organosilicon compound, and Two steps are required: treating this with an alkyl halide.

The present inventors conducted various studies in search of a method for obtaining a thin-film moisture-sensitive element with better responsiveness in one step, and found that a plasma polymerized film was formed from a mixture of a nitrogen-containing organosilicon compound and a halogenated silane. It has been found that this problem can be effectively solved by doing so.

[Means for Solving the Problem] and [Operation] Therefore, the present invention relates to a thin film moisture sensitive element, and this thin film moisture sensitive element has the following features:
The surface of a conductive comb-shaped electrode formed on an insulating substrate is covered with a plasma polymerized film of a mixture of a nitrogen-containing organosilicon compound and a halogenated silane.

FIG. 1 of the drawings is a plan view showing one embodiment of a thin film moisture sensitive device according to the present invention, in which conductive comb-shaped electrodes 2, 2' are formed on an insulating substrate l, the surface of which is generally approximately It is covered with the above-mentioned mixture plasma polymerized film 3 having a thickness of about 500 to 20,000 nanometers (2 μm), and the lead-out electrode portion not covered by this polymer film is soldered or with silver paste 4, 4'. .

A lead wire 5.5' is attached.

Generally, glass, quartz, alumina, etc. are used as the insulating substrate, but in cases where even better temperature tracking is desired for the moisture-sensitive element, a silicon substrate, which has been proposed by the applicant, may be used. An insulating film formed by oxidizing the surface (Japanese Patent Application No. 60-122.548) can also be used.

When forming conductive comb-shaped electrodes on these insulating substrates, first, 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 is placed on the insulating substrate. A thin film having a thickness of about 0.1 to 0.5 μm is formed by sputtering, ion blasting, or the like, and then a photoresist pattern is formed thereon.

For example, in the case of aluminum, the formation of a photoresist pattern on the thus formed electrode forming material gold is performed by applying a well-known photolithography process. That is, a photoresist coating is applied on the metal thin film.

A glass dry plate on which a negative or positive image of the comb-shaped electrode pattern has been printed is placed on top of this, and the process is carried out by printing with light irradiation and development. After this, wet chemical etching is performed, and the etching liquid used is a mixed solution of phosphoric acid-sulfuric acid-chromic anhydride-water (weight ratio 65:15:5:15), BH
F (hydrofluoric acid), ferric chloride aqueous solution, nitric acid, phosphoric acid-nitric acid mixed solution, etc. are used.

The conductive comb-shaped electrode formed on the insulating substrate is further coated with a nitrogen-containing organosilicon compound, which has excellent moisture-sensing properties, on its surface.
Covered by a plasma polymerized film of halogenated silane mixture.

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

R,Si-NR2 R,N-8iR2-NR.

(R,N), -3iR (wherein, R is a hydrogen atom, a methyl group, an ethyl group, a vinyl group, or an acetylene group, and R2 or R1 are the same or different R groups, and at least two Examples of such compounds include trimethylsilyldimethylamine, triethylsilazane, hexamethyldisilazane, hexamethylcyclotrisilazane, bis(dimethylamino)methylvinylsilane, and bis(trimethylsilyl). Acetamide, Tris (dimethylamino)
silane, tris(dimethylamino)methylsilane, tris(methylamino)methylsilane, tris(methylamino)ethylsilane, N,N-dimethylamino-N'-methylamino-N'-ditylaminosilane, etc., preferably trimethylsilyl Dimethylamine or bis(dimethylamino)methylvinylsilane or bis(
dimethylamino)dimethylsilane is used.

As the halogenated silane, general formula SiX, X is used.

X, X4 (where, A lower alkyl-substituted halogenated silane is preferably used. Some examples of such halogenated silanes are as follows.

CH,5iC1゜ CH, SiH, Br, CH, 5iHBr.

(CH,)2SiBr.

In plasma polymerization, a nitrogen-containing organosilicon compound is used at a pressure of several m to several Torr, and a halogenated silane is used at a pressure of several m to several Torr, depending on the shape of the plasma polymerization apparatus and the plasma generation method. .

This is carried out by supplying electric power of several to several hundred units of discharge power to these mixtures.

Specifically, for example, when the discharge output is 100 W, the nitrogen-containing organosilicon compound is about 0.15 to 0.08 Torr, while the halogenated silane is about 0.06 to 0.01 Torr.
used at a rate of If the proportion of halogenated silane is too small, the bromine content in the plasma polymerized film will decrease, resulting in poor moisture sensitivity properties, while if this proportion is too large.

Since the nitrogen content in the plasma polymerized film is relatively reduced and the polymerized film is also hardened, the moisture sensitivity properties are also reduced.

The electrical resistance of the thin film humidity sensing element constructed in this way changes depending on the amount of water vapor in the air, so humidity can be measured by measuring this change in resistance through a conductive comb-shaped electrode. Can be done.

〔Effect of the invention〕

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,
Furthermore, there is no need for treatment with an alkyl halide, resulting in labor saving in the process.

(2) Since the formed plasma polymerized film has excellent water resistance and chemical resistance, the moisture sensitive element has good ring resistance and immersion resistance.

(3) Even an extremely thin film with a film thickness of approximately 1,000 people has sufficient functionality, so it has improved responsiveness compared to conventionally used sensors such as metal oxide variable resistance type and polymer capacitance variable type. But it's excellent.

〔Example〕

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

Examples 1 to 2 A glass plate is used as an insulating substrate, and the electrode width is 500 μm and the electrode spacing is 250 μm by the lift-off method, which is commonly used as a patterning method for gold electrodes on the surface of the glass plate.
A comb-shaped electrode was formed.

In this lift-off method, a positive resist is applied on the surface of the glass plate using a spin coater and prebaked at 80° C. for 120 minutes.

Close exposure to ultraviolet rays was carried out using a mask, followed by development to form an inverted pattern of comb-shaped electrodes, followed by successive vapor deposition of chromium 11 and gold, each with a thickness of 1000 nm, and finally immersion in acetone. By stripping the remaining resist, a comb-shaped electrode was formed.

The surface of the comb-shaped electrode on 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 polymerized film are shown in the following table.

Table 1 Bis(dimethylamino)dimethylsilane (Torr)
0.07 0.065 Methyltrichlorosilane (
Torr) 0.01 0.015 Output (W
) 20 10
Time (minutes) 2
0 30 Immediate film thickness (people) 6
Connect the lead wires to the 900 and 9000 electrodes with silver paste to form a humidity sensing element, place this in a temperature/humidity tester, and test it with an LCR meter under the conditions of frequency I K Hz, pressure I V, and temperature 30°C. The moisture sensitivity characteristics were evaluated using The relationship between the resistance value and the relative humidity is shown in curves ■ (Example 1) and ■ (Example 2) in FIG.

[Brief explanation of drawings]

FIG. 1 is an iZ plane view of one embodiment of a single-film moisture-sensitive element according to the present invention. Moreover, FIG. 2 is a graph showing the relationship between relative humidity and resistance value in Examples 1 and 2.

Claims (3)

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