JPS637018B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention provides a compact, highly accurate, and highly responsive humidity sensing element.

Among the various basic variables in nature, such as temperature, atmospheric pressure, and humidity, humidity is still difficult to measure with high precision. On the other hand, food industry, agriculture,
Accurate and easy measurement and adjustment of humidity is becoming necessary in many other fields.

Currently, methods for detecting humidity as changes in electrical signals include a method that uses the amount of electricity required to dissociate adhering moisture by electrolysis, a method that uses changes in resistance value due to moisture adsorption, and a method that uses the present invention. There is a method that utilizes the change in capacitance due to water adsorption, which was previously developed by et al.

Among these, the humidity detection element developed by the present inventors has superior accuracy, sensitivity, responsiveness, hysteresis, aging, chemical resistance, ease of handling, measurement range, heat resistance, etc. compared to other methods. Although it is excellent in all respects, it is still not perfect, and in particular, the capacitance value with respect to humidity does not have linearity from low humidity to high humidity, that is, it changes at a completely constant rate. It had the disadvantage that it was not.

The present invention solves these conventional drawbacks, and is small and easy to assemble, and the capacitance changes at a constant rate with humidity over a wide range from low humidity to high humidity. The purpose is to provide such a stable humidity detection element at low cost. Hereinafter, regarding the humidity detection element of the present invention, the first
This will be explained using the drawings shown in FIGS.

FIG. 1 shows the basic structure of the humidity detection element of the present invention, and in the figure, 1 is a valve metal such as tantalum, aluminum, titanium, niobium, hafnium, zirconium, or an alloy thereof, or silicon, gelconium, etc. A dielectric anodic oxide film 2 is formed on the surface of the metal base 1, and a semiconductor metal oxide film such as manganese dioxide is formed on the dielectric anodic oxide film 2. 3 is formed. Between the dielectric anodic oxide film 2 and the semiconductor metal oxide film 3, there are a non-contact portion 4 and a contact portion 5. Then, on this semiconducting metal oxide film 3, an electrode 6 facing the metal substrate 1 is formed which is basically composed of a silver layer formed by a silver mirror reaction.

In such a configuration, the surface of the semiconductor metal oxide film 3 is in a very microporous state, increasing the contact area with the counter electrode 6. According to actual measurements, the diameter of this hole is several μ.
The counter electrode 6 is extremely fine, with a diameter of about 10-odd microns, and has a thickness sufficient to allow moisture in the air to pass through its entire surface.

By the way, conventionally, a carbon layer, a solder layer, a silver layer, etc. have been used as the counter electrode 6. In order to provide the counter electrode layer 6 even in the pores of the microporous semiconducting metal oxide film 3, the particle size must first be adjusted.
Carbon black of 10 μm to several hundred μm is immersed in a dispersion of a suitable solvent to form a carbon layer covering the entire surface of the hole, and then dipped in silver paint to form a silver paint layer on the surface. By doing so, it is possible to facilitate welding with the solder layer used for connection with the electrode lead, and to keep the electrical resistance of the humidity detection element low. In addition, an attempt was made to provide a silver paint layer directly on the semiconducting metal oxide film 3, but silver paint in which silver with a high specific gravity was dispersed inevitably had a high viscosity, and the pores could not be completely covered. It was impossible to cover it. In order to provide a silver layer on the carbon layer, we conducted various tests on silver paint and found that acrylic resin was used as the binder because it formed a uniform silver paint layer on the surface of the carbon layer and was easy to handle. They selected silver paint containing 0.5 to 5% of
FIG. 2 shows the structure of the conventional counter electrode part, where 6' is the counter electrode, 6a' is the carbon layer, 6b' is the silver paint layer, and 3' is the hole in the semiconducting metal oxide film 3. It is a part.

Here, the function of the silver paint layer 6b' is that the metal base 1
However, when moisture in the air passes through the silver paint layer 6b', the silver paint layer 6b'
If b′ itself absorbs and removes moisture, it will affect the linearity of humidity and capacitance, reducing the accuracy of the humidity detection element.If moisture permeation is impeded, the response will be Both of these are undesirable because they lower the water content, and the silver paint layer 6' itself must have no effect on permeated moisture.

However, in conventional humidity detection elements using such silver paint, the resin present as a binder adsorbs and desorbs moisture to a certain extent, resulting in the above-mentioned problems.

In the present invention, a silver layer is formed over the entire surface of the semiconductor metal oxide film 3, including the hole portions 3', by direct silver mirror reaction. Formation of a silver layer by silver mirror reaction will be described below with specific examples. The reagents used are prepared as follows.

That is, put 20 ml of 5% silver nitrate aqueous solution in a Teflon container, add 1 ml of 10% sodium hydroxide aqueous solution, and add 2% ammonia water while stirring until the brown silver oxide precipitate is dissolved. . The solution created in this way is called Tollen's reagent. This Tollen's reagent is heated to 30 to 60°C, and the 3 parts of the semiconductor metal oxide film of the humidity detection element, which have been formed up to the formation of the semiconductor metal oxide film 3, are immersed in this reagent, and 1 ml of formalin solution is added. and leave it for 10 minutes. In this way, the silver ammonia complex generated in the Tollens reagent is reduced to silver according to the reaction described below, and is deposited on the surface of the semiconductor metal oxide film 3 including the hole portions 3'.

HCHO+2 [Ag(NH ₃ ) ₂ )] ⁺ OH ^- →2Ag+ HCO ₂ NH ₄ +3NH ₃ +H ₂ O The silver layer formed in this way still contains nitrate roots,
Contains sodium hydroxide, ammonia, formalin, etc., which will have a negative effect on the characteristics of the humidity detection element, so after the silver layer has been formed, the element should be thoroughly washed with water.
Use dry. The silver layer formed by such a silver mirror reaction is sometimes very unstable depending on the reaction conditions, so a low-concentration silver paint may be applied on top of it through a carbon layer or directly. , a thin silver paint layer, a sprayed metal layer, a vapor deposited metal layer, etc. may be provided.

FIG. 3 shows the opposing electrode portion of the humidity sensing element according to the present invention.

According to the humidity detection element according to the present invention, the change in capacitance of the humidity detection element corresponds to a change in humidity in direct proportion from a low humidity region to a high humidity region for the following reasons. In other words, it has very good linearity, so it is possible to accurately measure humidity over a wide humidity range. That is, when the humidity detection element of the present invention is placed in humidity, moisture in the air passes through the silver layer counter electrode 6 and the semiconducting metal oxide film 3 and reaches the interface with the dielectric anodic oxide film 2. reach This interface has a contact part 5 and a non-contact part 4, and the moisture that has reached the interface is absorbed into the non-contact part 4 by the carbon dioxide in the air dissolved therein and the semiconductor metal oxide film 3. Manganese ions and other impurities act like an electrolyte, increasing the apparent contact area and increasing capacitance. In this way, the apparent contact area increases or decreases depending on the amount of moisture in the air, that is, the humidity, so changes in relative humidity in the air can be converted into changes in capacitance. Here, in the present invention, the silver layer produced by the silver mirror reaction is pure silver and can be formed very thin, so it does not have any effect on moisture permeation in the air. Instead, when a silver paint layer is provided using silver paint as in the past, the resin contained as a binder itself has a certain degree of moisture absorption and desorption effect, so it does not change the amount of moisture in the air. A properly proportional amount of moisture does not reach the interface between the semiconducting metal oxide film 3 and the dielectric anodic oxide film 2,
It is possible to solve the problem that the capacitance value does not correspond accurately to humidity.

Next, specific examples of the present invention will be given and differences in characteristics from conventional products will be explained.

As shown in Fig. 4, a tantalum oxide film 8 with a thickness of 100 to 1000 Å is provided on a part of a metal base 7 made of tantalum with a diameter of 0.1 to 1.0 mm and a length of 10 mm, and several manganese dioxide films 9 are applied thereon. A silver layer 10 is formed on it as a counter electrode by silver mirror reaction, and an electrode lead 11 is attached to a part of this silver layer 10 by a solder layer 12. They were connected to form a humidity detection element.

Regarding the humidity sensing element A of the present invention and a conventional humidity sensing element B of the same size using a carbon layer and a silver paint layer with 2% acrylic resin as a binder as a counter electrode, relative humidity and electrostatic We investigated the relationship between capacity. The results are shown in FIG. 5, and as is clear from FIG. 5, it is clear that the humidity detection element of the present invention has excellent linearity over a wide humidity range.

As described above, according to the present invention, it is possible to obtain a humidity detection element with excellent linearity in the relationship between relative humidity and capacitance over a wide humidity range.

[Brief explanation of the drawing]

FIG. 1 is a sectional view showing the basic structure of the humidity sensing element according to the present invention, FIG. 2 is an enlarged view showing the opposing electrode portion of a conventional humidity sensing element, and FIG. 3 is an opposing electrode portion of the humidity sensing element according to the present invention. FIG. 4 is a sectional view showing a humidity sensing element according to an embodiment of the present invention, and FIG. 5 is a diagram showing the characteristics of the humidity sensing element of the present invention in comparison with the characteristics of a conventional humidity sensing element. It is. DESCRIPTION OF SYMBOLS 1, 7... Metal base, 2... Dielectric anodic oxide film, 3... Semiconductor metal oxide film, 6... Counter electrode, 8... Tantalum oxide film, 9... Manganese dioxide film, 10... ...Silver layer.

Claims (1)

[Claims] 1 Tantalum, aluminum, titanium, niobium,
A dielectric anodic oxide film is formed on a valve metal such as hafnium or zirconium alone or an alloy thereof, or a metal substrate such as silicon or germanium, and a semiconducting metal oxide film is formed on the oxide film. , further comprising a counter electrode formed thereon by a single silver layer formed by silver mirror reaction or a combination of this silver layer and another conductive material.