JPH0479541B2 - - Google Patents

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 having excellent environmental resistance and good responsiveness.

[Conventional technology]

Controlling the relative humidity in the air is very important in the precision industry, food industry, textile industry, building management, etc., and the moisture sensing elements that detect it are conventionally known to use the following materials. It is being

(1) Metals or semiconductors such as Se, Ge, and Si (2) Metal oxides such as Sn, Fe, and Ti (3) Porous metal oxides such as Al ₂ O ₃ (4) Electrolyte salts such as LiCl ( 5) Polymer membranes made of organic or inorganic materials However, moisture sensing elements using these various materials are difficult to maintain, or have problems with reliability and responsiveness, so they are not satisfactory. Not in.

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 and 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 decreased 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 present inventors have previously developed a corrosion-resistant workpiece formed on an insulating substrate, preferably by sputtering. It has been found that a corrosion-resistant comb-shaped electrode obtained by forming a photoresist pattern on a thin metal film and then electrolytically etching it is suitable for use in a humidity sensor (Japanese Patent Laid-Open No. 148871/1983).

As a result of the present inventors' efforts to further improve thin film moisture-sensitive elements using such corrosion-resistant comb-shaped electrodes,
It has been found that the intended purpose can be fully achieved by covering the surface of a conductive comb-shaped electrode with a thin polymer film and then treating this with an alkyl halide.

[Means for Solving the Problems] and [Operations] Accordingly, the present invention relates to a thin film moisture sensitive element, and 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 It is covered with a thin polymer film, and the surface of the thin polymer film is further treated with alkyl iodide or alkyl bromide.

The formation of conductive interdigitated electrodes on an insulating substrate is
This is done as follows. That is, glass, quartz, alumina, etc. are generally used as the insulating substrate, and corrosion-resistant metals such as stainless steel, Hastelloy C, Inconel, and Monel, and electrode forming material metals such as silver and aluminum are applied onto the surface by sputtering. It is formed in the form of a thin film with a thickness of about 0.1 to 0.5 μm by ion plating method or the like.

A photoresist pattern is formed on the metal thin film to be compounded thus formed by applying a well-known photolithography process. That is, a photoresist coating is applied on a metal thin film, a glass dry plate on which a negative or positive image of a comb-shaped electrode pattern is printed is placed on top of the photoresist coating, and the photoresist coating is baked by light irradiation and developed.

After this, electrolytic etching is performed, for example, as shown in Figure 2, SUS304
was used as the cathode 21, and the metal thin film 23 on the glass substrate 11 was used as the anode, voltage 0 to 5 V, current 0.1 to 0.2 A.
Then, under stirring by the rotor 25 of the stirrer 24,
This is done in an etching solution 26. Electrolytic etching mainly proceeds on the surface of the anode metal thin film, so it is generally etched at a temperature of about 25 to 80°C for 60 degrees while stirring the etching solution and sinking the metal thin film at a constant rate.
Done within minutes. The etching solution used was phosphoric acid - sulfuric acid - chromic anhydride - water (weight ratio
65:15:5:15) mixed liquid, BHF (fluoric acid type), ferric chloride aqueous solution, nitric acid, phosphoric acid-nitric acid mixed liquid, etc. are used.

The surface of the conductive comb-shaped electrode thus formed on the insulating substrate is covered with a polymer thin film. The formation of this polymer thin film is generally carried out by a plasma polymerization method, and the monomer to be plasma polymerized is, for example, a silane compound having an amino group such as trimethylsilyldimethylamine or a mixture thereof with ammonia. When used as a mixture with ammonia, it is preferable to use ammonia at a partial pressure ratio of about 1/2 or less from the viewpoint of device performance.

By this plasma polymerization method, a thin polymer film of about 0.3 to 1.6 μm is formed, and the surface of this thin polymer film is treated with alkyl iodide, such as methyl iodide and ethyl iodide. By doing so, effects such as making the surface hydrophilic and improving conductivity can be further achieved.

When the treatment with alkyl iodide is compared with the treatment with alkyl bromide, which belongs to the same alkyl halide, the linearity of the relationship between element resistance and relative humidity is far superior; Together with the improved conductivity of the polymer film, this significantly improves the measurement accuracy (humidity sensitive characteristics) as a humidity sensitive element, and is also excellent in terms of reactivity and ease of handling.

After the alkyl iodide treatment is carried out in this manner, alkyl bromide such as methyl bromide or ethyl bromide is added to the alkyl bromide by contacting it in a gaseous state or dipping it in a liquid state depending on the properties of the alkyl bromide. It can also be processed using In this case, the element resistance value can be further lowered, which, together with the further improvement of the conductivity and moisture sensitivity properties of the plasma polymerized film, can be achieved over a wide humidity range from low humidity to high humidity. measurement.

FIG. 1 of the drawings is a plan view showing one embodiment of the thin film moisture sensitive element according to the present invention, in which an insulating substrate 1
Conductive comb-shaped electrodes 12, 12' are formed on 1,
Its surface is covered with a plasma polymer film 13, and lead wires 16, 16' are attached to each extraction electrode 14, 14' by soldering or silver paste 15, 15'.

〔Effect of the invention〕

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

(1) Plasma-polymerized films are generally said to be highly three-dimensionally crosslinked, but the plasma-polymerized films of the present invention can also be used in organic solvents such as acetone and methyl ethyl ketone, and inorganic acids such as hydrochloric acid and nitric acid. It does not swell or deteriorate even when exposed to relative humidity of 90%.
% atmosphere for 130 to 150 hours, so there is no problem in terms of deterioration or instability at high humidity, which is a general problem, and the environmental resistance of comb-shaped electrodes. Improving sexuality further.

(2) Polymer thin films are not only made of inexpensive materials that only require a small amount of use, but also have a simple manufacturing process, so their manufacturing costs are extremely low.

(3) Since the humidity sensing element is in the form of a thin film, it has good responsiveness and can detect high humidity with high accuracy.

(4) When the surface of a thin polymer film is sequentially treated with alkyl iodide and alkyl bromide, a commonly used moisture-sensitive element exhibits a two-digit resistance change within the relative humidity range of approximately 45% to 95%. However, it shows a resistance change value of more than three orders of magnitude, and is particularly excellent in terms of accuracy.

〔Example〕

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

Example 1 As shown in Fig. 1, a sputtered thin film of aluminum-silicon (99:1) formed on a glass substrate with dimensions of 26 x 48 x 2 mm was electrolytically etched to form a film with a width of 50 μm and an interval of 100 μm. ,thickness
A large number of 0.2μm linear teeth with a length of 13mm are formed,
A comb-shaped electrode is formed in which the linear teeth facing each other are engaged with each other in a portion corresponding to 11 mm of the length, and then a plasma polymerized film of trimethylsilylmethylamine is applied to the comb-shaped electrode portion sufficiently. Finally, it was immersed in an aqueous methyl iodide solution at 50°C for 20 hours to make the surface hydrophilic and improve conductivity.

Example 2 In Example 1, instead of trimethylsilylmethylamine, it and ammonia (partial pressure ratio 1/2) were used.
Form a plasma polymerized film using a mixture of
It was treated with methyl iodide at 20°C for 96 hours.

Example 3 The methyl iodide-treated product of Example 1 was brought into contact with methyl bromide gas at 60° C. for 48 hours to dope iodine and bromine into the plasma polymerized film.

As can be seen in the graphs of FIGS. 3 to 5 showing the measurement results for Examples 1 to 3, the thin film moisture sensitive element of the present invention constructed in this manner has a relative humidity of about 50 to 95%, In the high humidity range of about 20 to 95% or about 45 to 95%, it shows good linearity with the element resistance value, allowing the humidity to be detected with high accuracy.
In addition, the responsiveness of the moisture sensitive element is approximately 0.3 to 0.6 μm.
It was confirmed that it was very fast due to its small size and thinness.

Comparative Example In Example 1, unless immersion in the methyl iodide aqueous solution was performed, the element resistance values remained around the order of 10 ⁸ Ω in the relative humidity range of 50 to 100%.

[Brief explanation of the drawing]

FIG. 1 is a plan view showing one embodiment of a thin film moisture sensitive element according to the present invention. FIG. 2 is a schematic diagram of an electrolytic etching method for producing comb-shaped electrodes used in this thin film moisture sensitive element. Moreover, FIGS. 3 to 5 are graphs showing measurement results using the thin film moisture sensitive element of the present invention. (Explanation of symbols), 11... Insulating substrate, 12...
... Conductive comb-shaped electrode, 13 ... Polymer thin film, 21
... Cathode, 23 ... Corrosion-resistant metal thin film, 26 ... Electrolytic etching solution.

Claims (1)

[Scope of Claims] 1. A conductive comb-shaped electrode formed on an insulating substrate is covered with a polymer thin film made of a plasma polymerized film of a silane compound having an amino group or a mixture of it and ammonia, A thin film moisture sensitive element whose surface is further treated with alkyl iodide. 2 A conductive comb-shaped electrode formed on an insulating substrate is covered with a polymer thin film made of a plasma polymerized film of a silane compound having an amino group or a mixture of it and ammonia, and the surface of the polymer thin film is further coated with iodine. A thin film moisture-sensitive element sequentially treated with alkyl oxide and alkyl bromide.