JPH0227249A - Moisture sensing element - Google Patents

Abstract

PURPOSE:To achieve a reduction in hysteresis, a higher speed of a sensor reaction and a stability of an output value by forming a moisture sensing film using a high polymer crystallized. CONSTITUTION:A lower electrode 2, for example, comprising platinum is formed at a top surface of an insulating substrate 1 comprising alumina, glass or the like. A moisture sensing film 3 is applied in lamination crossing the electrode and an upper electrode 4 comprising gold is formed thereon. Leads 2a and 4a are connected to the electrodes 2 and 4 to detect a change in an electric capacity value thereof with respect to a relative humidity of the film 3. This film 3 is produced as follows: 3-15g of cellulose acetate butyrate (CAB) containing, for example, a butyryl group 17% are prepared and dissolved into 100cc of a dioxane solution to obtain a CAB solution. The CAB solution thus obtained is applied on the electrode 2 by a spin coat method and then, dried in an atmosphere at a room temperature. After the work is preheated, it is heated for one-several hours at a temperature of above a glass transition point and below a melting point of a high polymer moisture sensing material to crystallize thereby obtaining a film 3 with a thickness of 0.5-10mum.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Field of Application] The present invention relates to a moisture-sensitive element using an organic polymer as a moisture-sensitive material.

[Conventional technology]

Conventionally, this type of moisture-sensitive element uses organic polymers such as cellulose acetate petylate, cellulose acetate globionate, polyimide, or polyimide amide as a moisture-sensitive material, and the moisture-sensitive film formed from this moisture-sensitive material is A humidity-sensitive capacitive element that utilizes changes in capacitance value for humidity detection has been proposed (Japanese Patent Publication No. 1988-88951).

[Problem to be solved by the invention]

However, moisture-sensitive elements configured in this way have high hydrophilicity (the property of attracting water) and a large amount of sorbed water (water absorption rate), so water that is tightly bound to polymers due to chemical adsorption may be absorbed. remain in the This ninth, for example, temperature 4
When used for a long period of time in a high-temperature, high-humidity atmosphere with a temperature of about 0° C. 1 g and 90° C., there was a problem that the output value drifted and lacked long-term stability. Furthermore, there is a problem in that the difference in moisture sensitivity characteristics (hysteresis) between the moisture absorption process and the moisture removal process is small at low temperatures and large at high temperatures, resulting in slow sensor response.

Further, there were problems such as the occurrence of dew condensation and the output value drifting due to immersion in water.

Therefore, the present invention was made in view of the above-mentioned conventional problems, and its purpose is to
Another object of the present invention is to provide a humidity sensing element with low hysteresis and fast sensor response in the usage range from low humidity to high humidity.

Another object of the present invention is to provide a humidity sensing element that can provide a stable output value even when exposed to conditions such as high humidity, high temperature and high humidity, humidity cycles, dew condensation, or water immersion for a long period of time.

[Means to solve the problem]

The moisture-sensitive element according to the present invention forms a moisture-sensitive film using a crystallized polymer.

[Effect]

By using a crystallized polymer, the moisture-sensitive film of the present invention has a low amount of sorbed water, ensures sensitivity as a moisture-sensitive element, and improves its moisture-sensitive characteristics.

〔Example〕

Embodiments of the present invention will be described in detail below with reference to the drawings.

FIG. 1 is a perspective view showing an embodiment of a moisture-sensitive element according to the present invention, and FIG. 2 is a plan view thereof. In these figures, 1
2 is an insulating substrate made of, for example, an alumina substrate, a glass substrate, a thermally oxidized silicon substrate, etc.; 2 is a lower electrode made of, for example, platinum, formed on the upper surface of the insulating substrate 1; 3 is a lower electrode made of, for example, platinum;
4 is a moisture-sensitive film laminated and coated so as to cross this lower electrode 2, and 4 is an upper electrode formed on this moisture-sensitive film 3 and made of, for example, gold. That is, the humidity sensitive M3 is connected to the lower electrode 2.
and the upper electrode 4 in a sandwich-like manner, and in order to detect the change in the capacitance value of the moisture sensitive membrane 3 with respect to relative humidity,
Lead wires 2a and 4a are connected to the lower electrode 2 and the upper electrode 4, respectively.

The feeling of being configured like this is 0! In the device, the moisture sensitive film 3 is formed of a moisture sensitive material made of crystallized polymer.

Next, a specific method of manufacturing this moisture sensitive element will be explained.

First, 3 to 15 g of cellulose acetate butyrate (hereinafter referred to as CAB) containing, for example, 17 butyryl groups is prepared as a polymer, and this is dissolved in 100 ac of a dioxane solution to obtain a CAB solution. Next, this CAB solution is applied onto the lower electrode 2 formed on the insulating substrate 1 by a spin-coating method, and then dried in a nitrogen atmosphere at room temperature to obtain a moisture-sensitive film.

The rotation speed of the spinner at this time is 1000 to 5000 r.
p□ to obtain a film with a thickness of 0.5 to 10 μm. Next, after preheating at about 90℃ for about 1 hour, heating is performed for 1 to several hours at a temperature above the glass transition point (180 to 200℃) of the polymeric moisture-sensitive material and below the melting point to crystallize and thicken the film. 0.5
A moisture sensitive membrane 3 of ~10 μm is obtained. Next, on the insulating substrate 1 on which the moisture-sensitive film 3 is laminated and coated, gold is deposited, for example, by vapor deposition or sputtering to form an upper electrode 4 having a thickness of about 50 to 500 Å. Note that the deposited metal may be any other corrosion-resistant metal such as palladium, platinum, and chromium. The lower electrode 2 on the insulating substrate 1 is obtained by forming platinum into a thin film with a thickness of 1,000 to 10,000 Å by vapor deposition or sputtering.

According to such a configuration, the moisture-sensitive film 3 is prepared by dissolving CAB in a dioxane solution, forming it on the insulating substrate 1 in advance, coating it thinly on the lower electrode 2, and drying it.
By performing heat treatment to form the CAB, the molecular arrangement of CAB was regularly arranged and crystallized, resulting in a dense film and stable moisture sensitivity characteristics.

Figure 3 looks like this: 7! l element moisture sensitive film 4
This figure shows an Xs diffraction chart of 2. In the same figure, curve A indicates crystallization, and curve B indicates amorphization. It is clear that this has been done.

FIG. 4 shows the results of measuring the relative humidity-capacitance characteristics of the humidity sensing element constructed in this way. In addition,
An LCZ meter was used for this measurement, and the frequency was 100KH.
The test was carried out at a temperature of 25°C.

As is clear from the figure, the hysteria when measured at approximately 5 minute intervals after the humidity chamber stabilized was approximately 24 RH, which was extremely good.

Figure 5 shows the crystalline CAB moisture sensing element produced in this example.
Figure 6 shows the drift of each output at 10.30, 50.60, 70, and 90% RHK after being left in a high-temperature, high-humidity atmosphere of 0°C and 90% RH. As a comparative example, the following shows the drift of each appearance under the same conditions of a conventional amorphous CAD moisture sensitive element. As is clear from these figures, the output capacitance CIO at 10% RH of the crystalline CAB humidity sensing element according to this example is stable, and the output capacitance on the high humidity side also reaches saturation drift within 100 hours. Well, it's stable.

In the above-mentioned example, CAB containing 17 butyryl groups was used as the polymer, but it is also possible to crystallize CAH containing 38 and 504 butyryl groups in the same way, and the crystallization process is For example, the temperature range for 50% butyryl group is about 140 to 160° C., which is a temperature range of above the glass transition point (Tg) and below the Tartrange range. Table 1 below shows the glass transition points and melt ranges of three types of CAB.

Table 1 In addition, in the above-mentioned example, the crystalline CAB moisture-sensitive element was immersed in water and X-ray diffraction was performed again after about 2000 hours, but there was no difference from the initial data, indicating that it was stable. confirmed.

Further, in the ninth embodiment described above, heat treatment for crystallization is performed before forming the upper electrode 4, but this may be performed in a vacuum chamber at the time of forming the upper electrode 4, and the same effect can be obtained. can get.

In addition, in the above-mentioned embodiment, platinum was used as the lower electrode, but the material is not platinum.
Any corrosion-resistant metal such as gold, chromium, tantalum, etc. may be used. Also, Cr/Au, Cr/N
l/Au, Ti/Au, NiCr/Au.

A multilayer structure such as Cr/Pt+T'/Ptr may also be used.

Further, in the above-mentioned embodiments, a sandwich-structured moisture-sensitive element was explained as an example, but the present invention is not limited to this. It goes without saying that similar effects can be obtained even when applied to a moisture-sensitive element having a comb-shaped structure obtained by forming a comb-shaped thin film electrode and laminating a moisture-sensitive film to cover the comb-shaped thin film electrode.

Furthermore, in the ninth embodiment described above, humidity is detected by focusing on the change in the capacitance value of the humidity sensitive film with respect to the relative humidity. You may also use other methods.

Furthermore, the moisture-sensitive film in the above-described embodiment is suitable as a humidity-sensitive film for a humidity sensor that is formed on a crystal resonator and detects humidity from the shift in resonance frequency caused by adsorption of the moisture-sensitive film. Yes, a moisture-sensitive film is formed on the surface acoustic wave element, and by changing the speed of passing through the surface acoustic wave element,
It is also suitable as a humidity sensitive film of a humidity sensor configured to detect humidity.

〔Effect of the invention〕

As explained above, according to the moisture-sensitive element according to the present invention, since the moisture-sensitive film is formed using a crystallized polymer,
Since the molecular arrangement is regularly arranged to form a dense film, the amount of sorbed water is low), and stable moisture sensitivity characteristics with little drift and less hysteresis can be obtained with better response.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing one embodiment of the humidity sensing element according to the present invention, FIG. 2 is a plan view of this humidity sensing element, and FIG. 3 is a BAK of the present invention.
FIG. 4 is a diagram showing the relative humidity-capacitance characteristics of the humidity-sensing element according to the present invention, and FIG. 5 is a diagram showing the humidity-sensing characteristics of the humidity-sensing element according to the present invention. , FIG. 6 is a diagram showing the humidity sensitivity characteristics of a conventional humidity sensing element. 1... Insulating substrate, 2... Lower electrode, 3...
・Moisture sensitive membrane, 4...φ upper electrode, 2&, 4m・Fist ・
· Lead. Patent Applicant: Yamatake Honeywell Co., Ltd. Agent: Yamakawa Political Affairs (and 2 others) 1st Ward 2θ [Skin]

Claims (2)

[Claims] (1) A moisture-sensitive element comprising a moisture-sensitive film formed using a crystallized polymer. (2) The moisture-sensitive element according to claim 1, which is a moisture-sensitive film formed by crystallizing a polymer whose main component is cellulose acetate ptylate.