JPS6151735B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to 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. Recently, various industries related to chemicals, medicine, pulp and paper, textiles, wood, tobacco, printing, etc.
Accurate and easy temperature measurement and adjustment in many fields, including agriculture, forestry and livestock industries such as greenhouses, pots, hatching, poultry and pig farming, home appliances such as cookers, air conditioners, dryers, vegetable preservers, and medical care. is strongly desired.

Currently, methods that use the change in ionic 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. In addition, the indicated value changes due to adsorbed gases other than humidity, and the response is poor. The disadvantage is that the hysteresis is large and the measurement humidity range is very limited.

There are also devices that combine the deformation of synthetic fibers such as hair, nylon, and styrene as they absorb and desorb moisture with stress elements, but these have drawbacks in response speed, hysteresis, and accuracy.

There are devices that utilize the swelling properties of synthetic resins containing conductive fine particles such as carbon and metal powder, but these devices have problems with response speed and hysteresis, and have the disadvantage of 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 detection elements and devices have various characteristics such as accuracy, sensitivity, responsiveness, hysteresis, measurement humidity range, heat resistance, influence of environmental gases, changes over time, ease of handling, price, etc. All of them have their advantages and disadvantages, and none of them were satisfactory in all aspects.

The present invention eliminates the above-mentioned conventional drawbacks, and aims to provide an inexpensive humidity sensing element that is small, easy to handle, and has stable characteristics.

Below, the humidity detection element of the present invention will be explained in Figs.
This will be explained using FIG.

First, the basic structure of the humidity detection element of the present invention will be described with reference to FIG.

In Figure 1, 1 is tantalum, titanium,
The metal base is made of a valve metal such as aluminum, an alloy thereof, silicon, or germanium, and a dielectric anodic oxide film 2 is formed on the surface of the metal base 1 by anodization or the like. A semiconductor metal oxide film 3 such as manganese dioxide is formed on the dielectric anodic oxide film 2 . However, the dielectric anodic oxide film 2 has a non-contact part 4 and a contact part 5 with the semiconductor metal oxide film 3. On this semiconductor metal oxide film 3, a carbon layer 6 and a cathode current collecting layer 7 are provided.
is provided. A cathode extraction portion 8 is formed on the cathode current collecting layer 7 by soldering or the like, if necessary.

The feature of the present invention is that the dielectric anodic oxide film 2
and semiconducting metal oxide film 3, in particular the dielectric anodic oxide film 2 or semiconducting metal oxide film 3 in the cathode extraction part, that is, the non-humidity sensitive part, and the dielectric film 3 in the other part, that is, the moisture sensitive part. The present invention relates to a humidity sensing element characterized in that it is thicker than the somatic anodic oxide film 2 or the semiconducting metal oxide film 3.

The humidity detection mechanism of the humidity detection element of the present invention will be described below, and when considering the practicality of the humidity detection element, the dielectric anodic oxide film or semiconducting metal oxide film at the cathode extraction part will be removed from other parts. The reason why it is necessary to form the film thicker than the dielectric anodic oxide film or the semiconducting metal oxide film will be explained in detail.

FIG. 2 is an enlarged schematic diagram of the contact portion between the dielectric anodic oxide film 2 and the semiconductor metal oxide film 3 shown in FIG.

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

If 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 moisture absorption by the dielectric film 2 is zero, the capacitance due to the dielectric anodic oxide film 2 only at the contact portion 5 shown in FIG. 2 can be detected. At this time, the semiconductor metal oxide film 3 is made of manganese dioxide, for example, and has semiconductivity, so it functions as an electrode for taking out the capacitance.

Next, when the humidity detecting element of the present invention is placed in humidity, since the semiconducting metal oxide film 3 has hygroscopic properties, the absorbed moisture is transferred to the dielectric anodic oxide film 2 and the semiconducting metal oxide film 3. It reaches the surface of the non-contact space 4. Since the amount of moisture absorbed by this semiconducting 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 water 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 ions, and itself acts as an electrolyte. It has the following functions. Therefore, the combined capacitance of 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 extracted.

In this way, the humidity sensing element according to the present invention
It converts changes in relative humidity in the air into changes in capacitance.

Here, the humidity sensing element according to the present invention is manufactured according to the manufacturing process diagram shown in FIG. That is,
A dielectric anodic oxide film is formed on the valve metal base, a semiconducting metal oxide film is formed, a carbon layer and a cathode current collecting layer are sequentially formed, a cathode extraction portion is formed, and if necessary, After undergoing aging treatment, it becomes a finished product.

By the way, various methods can be considered for forming a semiconductor metal oxide film. For example, a method of forming a metal nitrate such as manganese nitrate or lead nitrate by thermal decomposition at an appropriate temperature, or a method of forming it electrochemically can be considered. Furthermore, various methods can be considered for forming the cathode current collecting layer.
For example, a method in which a good electrical conductor such as gold, silver, copper, or aluminum is directly formed by vapor deposition or thermal spraying, or a method in which fine powder of a good electrical conductor such as gold, silver, platinum, copper, or aluminum is dispersed in a synthetic resin. A method of forming using a so-called conductive paste can be considered.

Furthermore, regarding the formation of the cathode lead-out portion, a method of immersing the element in molten solder, a method of directly forming metal, etc. can be considered.

However, in general, a combination of methods that are characteristically stable, easy to handle, and inexpensive are used. In other words, the semiconducting metal oxide film is formed by thermal decomposition of manganese nitrate, the carbon layer is formed by immersing the device in a colloidal carbon aqueous solution, and the cathode current collecting layer is formed by silver paint. The extraction portion is formed using a solder dip.

On the other hand, the humidity sensing element of the present invention, which converts humidity changes into capacitance changes, has various characteristics that are commonly required for other types of humidity sensing elements, such as accuracy, sensitivity, responsiveness, hysteresis, etc. In addition, high withstand voltage and no short-circuit failure are particularly required. Regarding these two points,
This comes down to the quality of the dielectric anodic oxide film. That is, the dielectric anodic oxide film is extremely thin, vulnerable to mechanical stress and electrical shock (instantaneous current flowing during charging and discharging), and easily damaged. Therefore, in order to obtain a humidity sensing element that has a high withstand voltage and is free from short-circuit failures, it is necessary to strengthen the dielectric anodic oxide film itself against mechanical stress and electrical shock, or to It is necessary to strengthen the protection of the film.

Technical methods to strengthen the dielectric anodic oxide film against mechanical stress and electrical shock, increase withstand voltage, and eliminate short circuit failures include:
Various methods are possible, but one way to strengthen the dielectric anodic oxide film is to increase the anodizing voltage, and one way to protect the dielectric anodic oxide film is to increase the amount of semiconducting metal oxide. etc. are possible.

Generally, a dielectric anodic oxide film is produced by an anodic oxidation method. There is a proportional relationship between the applied voltage and the thickness of the anodic oxide film, and high-voltage anodization results in a thicker film, which increases the withstand voltage of the device and reduces short-circuit failures.

However, as shown in FIG. 4, the capacitance change due to changes in humidity is smaller in the high voltage formation, and the accuracy as a humidity detection element is inferior. Note that curve 9 in FIG. 9 becomes curve 1 when high-voltage chemical formation is performed.
0 is the case where low voltage formation is performed.

On the other hand, in the case of semiconducting metal oxides such as manganese dioxide, there is generally a proportional relationship between the concentration of manganese nitrate aqueous solution and the amount of manganese dioxide, and if a high concentration manganese nitrate aqueous solution is used, the amount of manganese dioxide increases, making it difficult to use as an element. As the withstand voltage increases, short circuit failures decrease.

However, if the amount of manganese dioxide is large, manganese dioxide will adhere to the entire surface of the dielectric anodic oxide film. That is, most of the contact portion 5 shown in FIG. 1 is closed, the non-contact space 4 is eliminated, and it no longer functions as a humidity detection element.

To summarize the above, there is a contradictory property that if high voltage conversion and the amount of manganese dioxide are increased in order to improve reliability as a humidity detection element, the performance as a humidity detection element deteriorates.

In the present invention, despite the contradictory properties described above, it is an object to obtain an element with improved withstand voltage and less short-circuit failure without deteriorating the performance as a humidity detection element.

FIG. 5 shows a humidity detection element according to an embodiment of the present invention, and FIGS. 6a and 6b show a comparison of essential parts of a conventional humidity detection element and the humidity detection element of the present invention. In FIG. 5, part c is a humidity sensitive part as a humidity sensing element, and part d is a non-humidity sensitive part. This is because, in the portion d, the cathode extraction portion 8 is made of metal such as solder, and therefore, it is impossible to imagine moisture entering or exiting through this metal layer. In other words, the portion d is a so-called dead space that has no detection ability as a humidity sensing element.

On the other hand, mechanical stress is concentrated in this part during operations such as taking out the cathode, and current is also concentrated in this part.
That is, mechanical stress and electrical stress are concentrated in this part, and it is extremely weak compared to other parts.

In the present invention, in order to strengthen the weak point, d
Apply high-voltage chemical conversion only to the non-moisture-sensitive parts of the
A thick semiconducting metal oxide film such as manganese dioxide is formed only in the non-moisture sensitive areas. Conventional product,
The state of formation of manganese dioxide in the non-moisture sensitive part d of the product of the present invention is shown in FIGS. 6a and 6b.

As in the present invention, even if only the non-humidity-sensitive part is subjected to high-voltage chemical formation or a large amount of semiconductor metal oxide film such as manganese dioxide is formed, the humidity-sensing part remains the same as before, so the humidity detection element It is possible to obtain a humidity detection element that has the same detection performance as the above, has improved voltage resistance, and is free from short-circuit failures.

As described above, the humidity detecting element obtained by the present invention is a highly reliable humidity detecting element that is particularly sensitive, highly responsive, has a high withstand voltage, and is stable over a long period of time without short-circuit failures. It has excellent effects that cannot be obtained with conventional humidity detection elements, and has great industrial value.

[Brief explanation of the drawing]

Fig. 1 is a cross-sectional view showing the principle structure of a capacitive humidity sensing element according to the present invention, Fig. 2 is an enlarged cross-sectional view of main parts to show the operating principle of the element, and Fig. 3 is a humidity detecting element according to the present invention. FIG. 4 is a flowchart showing the manufacturing process of the sensing element, FIG. 4 is a characteristic diagram showing the capacitance change with respect to humidity change of the capacitive humidity sensing element according to the present invention, and FIG. 5 is a flow chart showing the humidity sensing element according to an embodiment of the present invention. The external perspective view and FIGS. 6a and 6b are enlarged cross-sectional views showing a comparison of the main parts of a conventional humidity detecting element and a humidity detecting element of the present invention. DESCRIPTION OF SYMBOLS 1... Metal base, 2... Dielectric anodic oxide film, 3... Semiconductor metal oxide film, 6... Carbon layer, 7... Cathode current collection layer, 8... Cathode extraction part, c
...Moisture sensing part, d...Moisture non-sensing part.

Claims (1)

[Scope of Claims] 1. A dielectric anodic oxide film obtained by anodizing a metal having a valve action such as tantalum, titanium, aluminum, zirconium, or hafnium or an alloy thereof or germanium, In a humidity detection element formed by forming a metal oxide film and then sequentially forming a carbon layer, a cathode current collecting layer, and a cathode extraction part, the portion covered by the cathode extraction part, the cathode current collection layer, and the semiconductor metal oxide film. A humidity sensing element characterized in that the dielectric anodic oxide film is thicker than the dielectric anodic oxide film covering the cathode current collecting layer and the semiconductor metal oxide film. 2. A semiconducting metal oxide film is formed on a dielectric anodic oxide film obtained by anodizing a metal having a valve action such as tantalum, titanium, aluminum, zirconium, or hafnium or an alloy thereof, or a silicon or germanium substrate. In a humidity sensing element in which a carbon layer, a depolarizing current collecting layer, and a depolarizing lead-out part are sequentially formed, the thickness of the semiconductor metal oxide film in the lower layer of the cathode lead-out part is determined by the thickness of the semiconductor metal oxide film in the lower layer of the cathode current collecting layer. 1. A humidity sensing element characterized by being formed thicker than a metal oxide film.