JPS6140124B2 - - 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. Accurate and easy measurement and adjustment of humidity is becoming necessary in the food industry, agriculture, and many other fields.

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

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. Furthermore, the response, hysteresis, and measurement humidity range were extremely limited.

There are other methods that combine the deformation of synthetic fibers such as hair, nylon, and styrene with stress elements as they absorb and desorb moisture, but they also reduce response speed, hysteresis,
There is a problem with accuracy.

Elements that utilize the swelling properties of synthetic resins containing conductive fine particles such as carbon and metal powder have problems in that they are excessively swellable and suffer from 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.

Furthermore, although hygrometers that utilize α-ray absorption and transmission have very high accuracy, they require large-scale equipment and are very expensive, making them impossible to use for general purposes.

In this way, currently developed or commercially available humidity sensing elements and devices have high accuracy, responsiveness,
There are advantages and disadvantages in terms of the influence of environmental gases, measurement range, sensitivity and heat resistance, hysteresis, changes 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 an inexpensive humidity sensing element that is small, easy to handle, and has stable characteristics.

Embodiments of the present invention will be described below with reference to the accompanying drawings.
This will be explained using Figure 0.

First, the basic structure of the humidity detecting element of the present invention is shown in FIG.

1 is a metal base made of a valve metal such as tantalum, aluminum, or titanium, and a dielectric anodic oxide film 2 is formed on the surface of this metal base 1, and this dielectric anodic oxide film 2 is made of manganese dioxide. A semiconductor metal oxide film 3 is formed as shown in FIG. 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 . On this semiconducting metal oxide film 3, an electrode 6 facing the metal substrate 1 is provided.
is provided.

The feature of the present invention is related to the optimum contact ratio range between the dielectric anodic oxide film 2 and the semiconducting metal oxide film 3, and the contact portion 5 is 20% of the total area of the dielectric anodic oxide film 2. The present invention relates to a humidity detection element characterized in that the humidity is within the range of ~98%.

The humidity detection mechanism of the humidity detection element of the present invention will be described below, and when practicality as a humidity detection element is taken into account, it will be shown that the contact coverage of the dielectric anodic oxide film 2 is optimally 20 to 98%. Explain in detail.

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 area 5 in the range indicated by b, and a non-contact space 4 in the range indicated by a.
It is becoming.

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 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 detection element of the present invention is placed in humidity, since the semiconductor metal oxide film 3 has hygroscopicity, the absorbed moisture reaches the surface of the dielectric anodic oxide film 2, causing the dielectric property to deteriorate. The surface of the non-contact space 4 between the anodic oxide film 2 and the semiconducting metal oxide film 3 is reached. 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.

Hereinafter, humidity-capacitance conversion will be explained in more detail.

The electrostatic capacitance C detected between the metal base 1 and the counter electrode 6 is as follows.

A: Total area of the dielectric anodic oxide film 2 that is not in contact with the semiconducting metal oxide film 3 B: Total area ε of the dielectric anodic oxide film 2 that is in contact with the semiconducting metal oxide film 3: Dielectric constant l of dielectric anodic oxide film 2: Thickness α of dielectric anodic oxide film 2: Coverage rate of moisture in the non-contact space 4 portion of dielectric anodic oxide film 2 HR: Relative humidity. Since the moisture coverage α of the dielectric anodic oxide film 2 depends on the relative humidity HR, α∝HR Also, the capacitance C is C=ε/l(B+α・A) ∴C∝ε/l(B+HR・A) The capacitance C between the metal base 1 and the counter electrode 6 is uniquely and directly determined by the relative humidity HR. FIG. 3 shows the relationship between capacity and relative humidity, and shows linearity between 0 and 100% relative humidity.

By the way, the above-mentioned contact ratio of the dielectric anodic oxide film 2 to the semiconductor metal oxide film layer 3, that is, the ratio of the contact portion 5 between the two to the total area of the dielectric anodic oxide film 2, B/A+B is the humidity detection element. It has an important correlation with characteristics such as accuracy, sensitivity, and responsiveness. FIG. 4 shows the relationship between relative humidity and capacitance change depending on the contact ratio B/A+B between the dielectric anodic oxide film 2 and the semiconductor metal oxide layer 3. That is, when B/A+B is small, the capacitance change due to moisture adsorption and desorption is large, and as B/A+B becomes large, the capacitance change with respect to humidity changes becomes small.
Also, the smaller B/A+B, the smaller the capacitance value at 0% relative humidity, so the ratio of capacitance C ₀ at 0% humidity to the capacitance change from 0% to 100%
C ₁₀₀ −C ₀ /C ₀ becomes larger as B/A+B is smaller, and the accuracy as a humidity detection element becomes better. (However, C ₁₀₀ is the capacitance value when R・H=100%) Figure 5 shows the relationship between B/A+B and C ₁₀₀ -C ₀ /C ₀ , but as mentioned above, B/ A+B
As C ₁₀₀ −C ₀ /C 0 becomes larger, C 100 −C 0 /C ₀ becomes smaller. In other words, it can be seen that the accuracy as a humidity detection element deteriorates.

Figure 6 shows the response of capacitance change to a sudden change in atmosphere from 30% to 90% relative humidity, B/A+B.
It is shown separately. In this case as well, the smaller B/A+B is, the larger the rate of change is, so when detecting a change in capacitance as an electrical signal, the response is excellent and the element becomes sensitive.

Figure 7 shows the hysteresis of the humidity detection element during dehumidification and moisture absorption by B/A+B.
It can be seen that when B/A+B is too small, the hysteresis tends to increase. In other words, the moisture present in the non-contact area 4 of the dielectric anodic oxide film 2 with the semiconducting metal oxide film 3 must pass through the contact area 5 between the two to form the non-contact dielectric material. It reaches the anodic oxide film and spreads. As a result, if the number of contact parts 5 between the two is too small, that is, if B becomes too small, there will be fewer relay points for adsorption and desorption of moisture onto the dielectric anodic oxide film 2, and the upper and lower atmospheric humidity will increase. Greater hysteresis to changes.

Figure 8 shows the relationship between the difference in capacitance values during moisture absorption and dehumidification and the contact ratio B/A+B when the RH is 50%.

Considering the contact ratio between the dielectric anodic oxide film 2 and the semiconducting metal oxide film 3 as described above in terms of practical use as a humidity detection element, [] When B/A+B>0.98, the contact ratio between the two is large. If it is too high, the capacitance change due to relative humidity change will be small, and the accuracy C ₁₀₀ −
C ₀ /C ₀ becomes smaller. As can be seen from Figure 5, when B/A+B is greater than 0.98, C ₁₀₀ −
C ₀ /C ₀ becomes extremely small, making it impractical as a humidity detection element.

[] When B/A+B<0.2, the smaller B/A+B is, the higher the accuracy C ₁₀₀ −C ₀ /C ₀
can yield excellent results, but as mentioned above,
If the hysteresis of the capacitance change with respect to the relative humidity change becomes large and B/A+B becomes smaller than 0.2 as shown in FIG. 8, the humidity detection element becomes unsuitable in consideration of its practicality.

In this way, when considering the accuracy, responsiveness, and hysteresis as a humidity detection element, the contact ratio B/A+B between the dielectric anodic oxide film 2 and the semiconductor metal oxide film 3 is 0.2<B/A+B< 0.98 is appropriate.

As described above, according to the humidity detection element of the present invention, it is possible to convert changes in relative humidity into capacitance values.

Next, the response, accuracy, hysteresis, change over time, etc. of the humidity detection element of the present invention will be described.

(A) Responsiveness As mentioned above, the responsiveness is determined by the moisture absorption effect of the semiconducting metal oxide film 3, and the thickness of the semiconducting metal oxide film 3 is several tens of microns to
When the contact rate is several hundred microns, the capacitance change due to humidity change is within a few seconds, and the saturation value is still reached within a few minutes. FIG. 9 shows the response speed of various conventional hygrometers, but the response speed of the present invention is extremely high.

(B) Accuracy In order to extract microscopic adsorption and desorption of moisture on the dielectric anodic oxide film 2 as a capacitance signal, it has higher accuracy than conventional humidity detection elements such as resistance change type and mechanical displacement type. .

(C) Sensitivity As mentioned above, within the range of the contact rate of the present invention,
The amount of capacitance change is very large and the sensitivity is excellent.

(D) Hysteresis Since the response is excellent as described above, there is almost no hysteresis, and the linear relationship between capacitance and relative humidity is always maintained.

(E) Change over time The dielectric anodic oxide film 2 such as tantalum oxide film is a very stable film thermally, electrically, and chemically, and its properties hardly change over time.
The same can be said of the semiconductor metal oxide film 3 such as manganese dioxide. It was confirmed that there was almost no change over time in the contact ratio between the two, and the moisture adsorption/desorption reaction through these was also very stable.

(F) Heat Resistance Conventional humidity detection elements were composed of deliquescent salts, organic films, hair, etc., making them difficult to use at high temperatures, and could only be used at temperatures up to 50°C. The humidity detection element can be used in an atmosphere of about 150 to 200 degrees Celsius, considering its constituent materials.

(G) Chemical resistance and gas resistance Tantalum and other metals are corrosion-resistant metals, and are superior to conventional metals in this respect as well.

(H) Price and cost performance Tantalum oxide ε = 28, aluminum oxide ε = 10, and titanium oxide ε = 100, all of which have high dielectric constants, making them highly sensitive to humidity changes and large capacitance changes even in a very small size. It can be converted and the price is significantly lower. Furthermore, handling and maintenance are much easier than with conventional humidity detection elements.

Furthermore, in conventional humidity detection elements such as variable resistance type, when dehumidifying moisture that has been absorbed, it is necessary to accelerate the dehumidification by some means such as heating with a heater, which is difficult due to the electrical circuit and element configuration. However, in the device of the present invention, as mentioned above, both moisture absorption and dehumidification can be quickly performed by the unique action of the semiconducting metal oxide film 3. No additional auxiliary equipment required.

Next, specific examples of the present invention will be described.

Example: A tantalum oxide film 2 is applied to a part of a metal base 1 made of tantalum with a diameter of 0.1 to 1.0 mm and a length of 10 mm.
100 to 1000 Å and a manganese dioxide film 3 on top of it.
Form a thickness of several to several hundred microns. However, the contact area between manganese dioxide and tantalum oxide at this time is 20 to 98% of the total area of tantalum oxide.
so that it becomes Further, a carbon layer 6 is formed as a counter electrode, and an electrode lead 7 is connected to a part of this carbon layer 6 with a solder layer 8. FIG. 10 is a sectional view of the device of this example.

The relationship between relative humidity and capacitance of the humidity detection element thus obtained is as shown in FIG.

As the valve metal base of the present invention, tantalum, titanium, and aluminum are suitable because of their chemical, thermal, and electrical stability, and the high dielectric constant of oxides as described above, and their shapes Also, rod-shaped, plate-shaped, thin film, sintered body, sprayed layer, etc. can be considered. Further, as the semiconducting metal oxide, manganese dioxide, lead oxide, nickel oxide, ruthenium oxide, and mixtures thereof can be considered.

As described above, the humidity sensing element of the present invention, in which the contact area between the dielectric anodic oxide film and the semiconducting metal oxide layer is 20 to 98% of the total area of the dielectric anodic oxide film, has excellent accuracy and sensitivity. , responsiveness, hysteresis, aging, chemical resistance, ease of handling, measurement range,
It is superior to conventional products in all respects such as heat resistance, and has great industrial value.

[Brief explanation of the drawing]

Fig. 1 is a sectional view showing the principle structure of the humidity detection element of the present invention, Fig. 2 is an enlarged sectional view of the main part to show the principle of operation, and Fig. 3 is the relative humidity and electrostatic charge of the humidity detection element. A characteristic diagram showing the relationship between capacitance and Figure 4 shows the relationship between relative humidity and capacitance change based on the contact ratio B/A+ between the dielectric anodic oxide film and the semiconducting metal oxide film.
Characteristic diagram shown separately for B, Figure 5 is also B/A+B
Figure 6 is a characteristic diagram showing the relationship between C ₁₀₀ -C ₀ /C ₀ , Figure 6 is a characteristic diagram showing the response of capacitance change for each B/A+B, and Figure 7 is a diagram showing the hysteresis of capacitance-relative humidity as B/A+B. Characteristic diagram shown separately for A+B, Figure 8 shows relative humidity
A characteristic diagram showing the difference in capacitance value during moisture absorption and dehumidification at 50% with respect to the contact ratio B/A+B. Figure 9 shows the response speed of various conventional humidity detection elements and the response speed of the present invention. FIG. 10 is a cross-sectional view showing an example of a specific configuration of the humidity detecting element of the present invention. DESCRIPTION OF SYMBOLS 1... Metal base, 2... Dielectric anodic oxide film, 3... Semiconductor metal oxide film, 4... Non-contact space, 5... Contact portion, 6... Counter electrode, 7...
...electrode lead.

Claims (1)

[Claims] 1. A dielectric anodic oxide film is provided on a valve metal base, and 20% of the total area of the dielectric anodic oxide film is
1. A humidity sensing element, characterized in that ~98% of the humidity sensing element is coated with a semiconductor metal oxide layer so as to be in contact therewith, and a current collecting counter electrode is provided on a part or all of the semiconductor metal oxide layer. 2. The humidity sensing element according to claim 1, wherein the semiconductor metal oxide is made of one or more of manganese dioxide, lead oxide, nickel oxide, and ruthenium oxide.