JPS6130211B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method of manufacturing a small-sized, highly accurate, and highly responsive humidity sensing element.

Among the basic variables in the natural world, such as temperature, pressure, and humidity, humidity is still difficult to measure with high precision, but humidity can be measured easily and accurately in the food industry, agriculture, and many other fields. There is a growing need for accurate measurements and adjustments.

Currently, methods that use the change in ion conduction of deliquescent salts such as lithium chloride to detect humidity as an electrical signal, and methods that use resistance changes due to moisture adsorption and desorption of magnetite and silicon semiconductors are widely used. ing.

However, all of these methods utilize ionic conduction, and change over time due to polarization is large, and the indicated value also changes due to adsorbed gases other than humidity. Also, the responsiveness is poor,
The hysteresis was also large, and the measurement humidity range was extremely limited.

It combines the deformation caused by moisture adsorption and desorption of other synthetic fibers such as hair, nylon, and styrene with stress elements, etc., but the response speed, hysteresis,
There is a problem with accuracy.

Furthermore, elements that utilize the swelling properties of synthetic resins containing conductive fine particles such as carbon and metal powder have problems in terms of sensitivity and are subject to significant humidity deterioration.

Furthermore, there is a method that detects water adsorption and desorption in the pores of aluminum oxide as a change in capacitance, but this method has the drawback of large changes over time.

Further, a hygrometer that uses α-ray absorption and transmission has very high accuracy, but the device is large-scale and very expensive, so it cannot be used for general purpose.

As described above, currently developed or commercially available humidity sensing elements and devices have various characteristics such as accuracy, responsiveness, influence of environmental gas, measurement humidity range, sensitivity, heat resistance,
All of them have advantages and disadvantages in terms of hysteresis, change over time, ease of handling, price, etc., and there was no one that was satisfactory in all respects.

The present invention eliminates the above-mentioned conventional drawbacks, and aims to provide a small, easy-to-handle, inexpensive humidity sensing element with stable characteristics, and in particular, a method for manufacturing the same.

First, the basic structure of the humidity sensing element of the present invention and the principle of humidity sensing will be described.

FIG. 1 is an enlarged view of the configuration of a humidity sensing element according to the present invention, in which valve metals such as tantalum, aluminum, niobium, titanium, zirconium, and hafnium or alloys thereof, silicon, and germanium are coated on the surface of a metal base 1. A dielectric anodic oxide film 2 is formed, and a semiconductor metal oxide film 3 such as manganese dioxide, lead oxide, nickel oxide, or ruthenium oxide is formed on the dielectric anodic oxide film 2. . However, the dielectric anodic oxide film 2 and the semiconductor metal oxide film 3 are adjacent to each other at the contact portion 5 and the non-contact space portion 4 . A carbon layer 6 and a cathode current collecting layer 7 are provided on this semiconducting metal oxide film 3.

FIG. 2 shows the dielectric anodic oxide film 2 of FIG. 1,
This is an enlarged view of the contact portion with the semiconductor metal oxide film 3.

As shown in FIG. 2, dielectric anodic oxide film 2
The semiconductor metal oxide film 3 forms a contact portion 5 in the range indicated by b, and a non-contact space 4 in the range indicated by a.

Now, when the humidity sensing element of the present invention is placed in an atmosphere with a relative humidity of 0%, the semiconductor metal oxide film 3
Since the water absorption by the contact portion 5 is zero, the capacitance due to the dielectric anodic oxide film 2 only on the contact portion 5 in FIG. 2 can be detected. At this time, since the semiconductor metal oxide film 3 has semiconductivity, it functions as an electrode for taking out the capacitance.

Next, when the humidity sensing element of the present invention is placed in humidity, since the semiconductor metal oxide film 3 has hygroscopicity, the absorbed moisture is transferred to the dielectric anodic oxide film 2.
and reaches the surface of the non-contact space 4 between the dielectric anodic oxide film 2 and the semiconductor metal oxide film 3. Since the amount of moisture absorbed by the semiconductor metal oxide film 3 is proportional to the relative humidity in the air, the moisture coverage in the dielectric anodic oxide film 2 is proportional to the relative humidity.

In this way, the moisture that has reached the dielectric anodic oxide film 2 contains carbon dioxide gas in the air, manganese ions in the semiconductor metal oxide film 3, and other impurities, and itself functions as an electrolyte. Therefore, the capacitance due to the contact portion 5 of the dielectric anodic oxide film 2 and the portion covered by moisture in the non-contact space 4 can be taken out.

In this way, changes in relative humidity in the air are converted into changes in capacitance.

Generally, the humidity sensing element according to the present invention is manufactured according to the manufacturing process diagram shown in FIG. . That is,
Forming a dielectric anodic oxide film on the surface of the metal base of the valve metal, forming a semiconducting metal oxide film,
Furthermore, a carbon layer and a cathode current collecting layer are sequentially formed, and a finished product is obtained through high temperature and high humidity treatment.

By the way, various methods can be considered for forming the cathode current collecting layer. For example, a method of directly forming a good electrical conductor such as gold, silver, or copper by vapor deposition or thermal spraying, or a method of dispersing fine powder of a good electrical conductor such as gold, silver, platinum, copper, or aluminum in a synthetic resin.
Although a method of forming the cathode current collecting layer using so-called conductive paint is considered, the latter method is generally used because it is easy to handle and inexpensive, that is, forming the cathode current collecting layer using conductive paint.

As mentioned above, conductive paint is made by dispersing good electrical conductors such as gold, silver, platinum, copper, and aluminum into synthetic resins such as acrylic resin, epoxy resin, vinylidene fluoride resin, and fluorine resin. Alternatively, a conductive layer is formed by curing a synthetic resin with light or the like. For example, commercially available silver paint is made by dispersing silver powder in acrylic resin.
It is heat-cured at 100-150°C.

By the way, in the humidity sensing element according to the present invention, a cathode current collecting layer is formed and a finished product can be obtained that fully satisfies the function as a humidity sensing element, but as shown in characteristic A in FIG. The drawback was that the capacity decreased when left in a high-temperature, high-humidity atmosphere for a long time.

Therefore, the present invention was developed to eliminate this drawback of capacity reduction. After forming a cathode current collecting layer with conductive paint, the device was placed in boiling water for 10 minutes.
It is immersed for ~180 minutes, and has characteristic B in Figure 4.
As shown in Figure 3, it is possible to obtain a product with significantly less capacity loss even when left in a high-temperature, high-humidity atmosphere for a long time.

The reason why the capacity decreases when the humidity sensing element according to the present invention is left in a high temperature and high humidity atmosphere for a long time will be explained in detail.

As mentioned above, the medium of conductive paint is synthetic resin, and this synthetic resin swells in a high-temperature, high-humidity atmosphere, and as a result, the semiconducting metal oxide film 3 separates from the dielectric anodic oxide film 2. It is. In other words, when comparing the adhesion strength of each of the cathode current collecting layer 7, carbon layer 6, and semiconducting metal oxide film 3 with the adhesion strength of the semiconducting metal oxide film 3 and dielectric anodic oxide film 2, the former The adhesive strength is much stronger than the latter adhesive strength, and therefore, when the conductive paint absorbs moisture, the non-contact space 4 gradually increases due to its swelling and the capacity decreases.

Therefore, if the conductive paint is treated in boiling water for 10 to 180 minutes as in the manufacturing method of the present invention, the swelling of the conductive paint is completed uniformly and in a short period of time, resulting in an element with significantly small subsequent changes in capacitance. .

As described above, the humidity sensing element obtained by the manufacturing method of the present invention is a long-term stable humidity sensing element with particularly small changes over time, and has excellent effects that cannot be obtained with conventional humidity sensing elements. It is of great industrial value that it can be equipped with

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the principle structure of the humidity sensing element according to the present invention, FIG. 2 is an enlarged cross-sectional view of the main parts to show the principle of operation, and FIG. 3 is the manufacturing of the humidity sensing element according to the present invention. A process diagram showing the manufacturing steps in the method,
FIG. 4 is a characteristic diagram showing changes in capacitance characteristics over time to explain the effects of the present invention. DESCRIPTION OF SYMBOLS 1... Valve metal base, 2... Dielectric electrode oxide film, 3... Semiconductor metal oxide film, 6... Carbon layer, 7... Cathode current collecting layer.

Claims (1)

[Claims] 1. Tantalum, aluminum, niobium, titanium,
A step of forming a dielectric anodic oxide film on the surface of a valve metal such as zirconium or hafnium or an alloy thereof or a metal substrate of silicon or germanium, and forming a semiconductor metal oxide film on the dielectric anodic oxide film. a step of forming carbon on the semiconducting metal oxide film; a step of forming a cathode current collecting layer on the carbon layer; and after forming the cathode current collecting layer, immersion in boiling water 1. A method for manufacturing a humidity sensing element, comprising a treatment step of immersing it in water. 2. The method for manufacturing a humidity sensing element according to claim 1, wherein the semiconducting metal oxide film is made of at least one of manganese dioxide, lead oxide, nickel oxide, and ruthenium oxide. 3. The method for manufacturing a humidity sensing element according to claim 1, wherein the cathode current collecting layer is made by dispersing metal powder in a synthetic resin. 4. The method for manufacturing a humidity sensing element according to claim 3, wherein the metal powder is at least one of gold, silver, platinum, copper, and aluminum.