JPS6145367B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention relates to a method for manufacturing a humidity sensing element, and more specifically, it improves dimensional accuracy, stabilizes the formation of a solid electrolyte layer and water vapor permeable conductive electrodes, improves yield, and improves mass productivity. It is something. BACKGROUND ART Recently, humidity control and easy measurement have become particularly desirable in industries such as air conditioning, electronic component manufacturing, agriculture and forestry, and food products. In particular, from a control point of view, a method of detecting humidity using electrical signals is required, and the current detection methods include one based on changes in the ionic conduction of deliquescent salts such as lithium chloride, one using magnetite, and one using silicon semiconductors. Resistance change type due to moisture adsorption and desorption, stress element that suppresses deformation due to moisture absorption and desorption of fibers such as hair, nylon, and styrene.
There are those that are combined with microswitches, those that utilize the resinous properties of organic resins containing conductive fine particles such as carbon and metal powder, and those that utilize α-ray absorption and transmission. However, among these, those that use ionic conduction have a large change over time and are difficult to maintain, resin-based ones have a slow response speed, those that use alpha rays are expensive, and other types will eventually deteriorate. Both have advantages and disadvantages in terms of accuracy, response, influence of environmental gases, measurable humidity range, sensitivity, heat resistance, hysteresis, change over time, price, etc. In contrast, the humidity sensing element referred to in the present invention detects changes in capacitance due to adsorption and desorption of a dielectric oxide film, and its structure and principle are based on the
It is described in detail in Publication No. 54-1897. I will give some explanation regarding this content. FIG. 1 shows a configuration diagram of a humidity sensing element according to the present invention, in which a dielectric anodic oxide film 2 is formed by anodic oxidation on an anode substrate 1 made of a valve metal such as tantalum, titanium, niobium, aluminum, or hafnium. A semiconductor metal oxide layer 3 such as manganese dioxide is formed on the entire or part of the dielectric anodic oxide film 2 by thermal decomposition of a thermally decomposable metal salt such as manganese nitrate. , and a water vapor permeable conductive electrode 4 is formed thereon using carbon and silver paint. Figure 2 shows an example of its specific structure, where 5 is a tantalum wire, 6 is a tantalum oxide film, and 7 is a tantalum wire.
1 is a manganese dioxide layer, 8 is a conductive electrode, 9 is solder, 10 is a bottomed cylindrical metal case having a through hole 11, 12 is an external lead wire connected and fixed to this metal case 11, and 13 is a hermetic seal. Department. The humidity sensing element formed in this manner adsorbs moisture in the air according to the relative humidity, and this moisture acts as a counter electrode for the dielectric anodic oxide film 2, and in the case of high humidity, this electrode Since the area increases, a high capacitance is obtained, and in the case of low humidity, a low capacitance is detected as a signal, and finally humidity detection detects changes in relative humidity in the air as changes in capacitance. Become an element. As shown in FIG. 3, this type of humidity sensing element has high measurement accuracy and sensitivity over the 0 to 100% RH range, and as shown in FIG. 4, it also has excellent moisture absorption and desorption responsiveness. Therefore, the peripheral electric circuit for signal detection is simple and the price is low. In this way, the humidity sensing element referred to in the present invention is
It is superior to any of the conventional humidity sensing elements mentioned above in terms of performance and ease of handling. The present invention relates to a method of manufacturing a humidity sensing element for stabilizing variations in capacitance characteristics, stabilizing moisture sensitivity characteristics, and improving mass productivity of such a capacitance variable humidity sensing element. Hereinafter, the contents of the present invention will be explained in detail. The humidity sensing element according to the present invention is manufactured by the manufacturing process shown in FIG. That is, after forming a dielectric anodic oxide film on an anode substrate, forming a semiconducting metal oxide, and sequentially forming a carbon layer and a cathode current collecting layer, high-humidity aging was performed to assemble this structure. It will then become a finished product. In order to manufacture such a humidity sensing element with high precision and less variation, stabilize the humidity sensing characteristics, and improve mass production, the present invention has developed an anode substrate by attaching an anode substrate to a conductive band formed and pressed into an L shape. The anode substrate attached to the conductive band is shown in FIG. 5 as a unit, that is, the dielectric anodic oxide film formation step, the semiconducting metal oxide formation step, the carbon layer formation step, and the cathode current collecting layer. This manufacturing method is characterized by separating the constituent and the conductive band after passing through each manufacturing process of a forming process and a high-humidity aging process. Here, while describing the humidity sensing mechanism of the humidity sensing element of the present invention, when considering its practicality as a humidity sensing element, in particular, the formation of a dielectric oxide film, the formation of a semiconducting metal oxide, the carbon layer, and the cathode current collection. We will discuss the important points of forming layers accurately and without variation. FIG. 6 shows the dielectric anodic oxide film 2 of FIG. 1,
This is an enlarged view of the contact portion with the semiconductor metal oxide layer 3. As shown in FIG. 6, the dielectric anodic oxide film 2 and the semiconductor metal oxide layer 3 form a non-contact area 13 in the area indicated by a, and a contact area 14 in the area indicated by b. There is. 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 layer 3
Since the moisture absorption by the dielectric film 2 is zero, the capacitance due to the dielectric anodic oxide film 2 of only the contact portion 14 shown in FIG. 6 can be detected. At this time, since the semiconductor metal oxide layer 3 has semiconductivity, it acts 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 layer 3 has hygroscopicity, the absorbed moisture is transferred to the dielectric anodic oxide film 2.
and reaches the surface of the non-contact portion 13 between the dielectric anodic oxide film 2 and the semiconductor metal oxide layer 3. Since the amount of moisture absorbed by the semiconductor metal oxide layer 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. The moisture that has reached the dielectric anodic oxide film 2 in this way contains carbon dioxide gas in the air, metal ions in the semiconductor metal oxide layer 3, and other impurities, and functions as an electrolyte in itself. Therefore, the combined capacitance of the contact portion 14 of the dielectric anodic oxide film 2 and the portion covered by moisture in the non-contact portion 13 can be extracted. In this way, the humidity sensing element of the present invention converts changes in relative humidity in the air into changes in capacitance. In order to accurately extract the concentration-capacitance conversion characteristics of the humidity sensing element of the present invention without variation, it is necessary to accurately calculate the capacitance detected between the anode substrate 1 and the conductive electrode 4. There is a need to take it out. The above-mentioned capacitance C between the two electrodes is as follows. A: Total area of the dielectric anodic oxide film 2 with which the semiconducting metal oxide layer 3 is not in contact B: Total area ε of the dielectric anodic oxide film 2 with which the semiconducting metal oxide layer 3 is in contact: Dielectric constant l of dielectric anodic oxide film 2: Thickness α of dielectric anodic oxide film 2: Coverage rate by moisture of non-contact portion 13 of dielectric anodic oxide film 2 RH: relative humidity, dielectric Moisture coverage α of anodic oxide film 2
depends on the relative humidity RH, so α∝RH, and the capacitance C is C=ε/l(B+α・A) ∴C∝ε/l(B+RH・A), and the anode substrate 1 and conductivity The capacitance C between the electrode 4 and the electrode 4 is determined uniquely and linearly with respect to the relative humidity RH. FIG. 4 shows the relationship between capacitance and relative humidity. The present invention is a method for manufacturing a humidity sensing element, which is characterized in that the capacitance between the above-described anode substrate 1 and the conductive electrode 4 of the humidity sensing element is taken out at a predetermined arbitrary value without variation, Specifically, the seventh
After attaching the anode substrate 1 to the L-shaped conductive band 15 shown in the figure, as shown in FIG. b. While controlling the dimension c of the conductive electrode 4 to an arbitrary value using the conductive band 15, the conductive electrode 4 is manufactured in sequence according to the manufacturing process diagram shown in FIG. The contact rate of the dielectric anodic oxide film 2 with the semiconducting metal oxide layer 3, that is, the ratio of the contact portion 14 between the two to the total area of the dielectric anodic oxide film 2, B/A+B can be controlled to any value. If the manufacturing method of the present invention is used, the dimensions a,
The accuracy of b and c is also extremely improved, short-circuit failures due to polymerization between the anode substrate 1 and the conductive electrode 4 are extremely reduced, and the capacitance tolerance of capacitance C is also reduced, making it possible to achieve any value of capacitance. Matching to the required electrical circuit is also significantly easier. Next, specific examples of the present invention will be described. After attaching a tantalum wire with a diameter of 1 mmφ and a length of 20 mm to the side of the pressurized stainless steel conductive band 16 shaped into an L shape as shown in FIG. An oxide film is formed by applying a voltage of 50V at ℃, and then the specific gravity becomes 1.5.
A manganese nitrate aqueous solution is applied, and a metal oxide of manganese dioxide is formed on the anodic oxide film by thermal decomposition. Furthermore, a carbon layer is formed on the manganese dioxide by impregnating and drying colloidal carbon, and a silver paint layer is formed on the carbon layer. The composition made in this way was heated to 40℃ and 90%
Hold for 50 hours under RH conditions. Comparing the structure made in this way with a structure manufactured by pressing the same tantalum wire as the one of the present invention on a stainless steel rod 18 of 1 mmφ as shown in FIG. 10 by the process shown in FIG. It looks like Table 1.

[Table] The above results are expressed as relative humidity in the humidity sensing element.
The capacitance characteristics are shown in FIGS. 12 and 13. In addition, in the method shown in FIG. 10, the immersion accuracy varies due to bending, twisting, etc. of the stainless steel rod 18, and when liquid creeps up due to immersion in each manufacturing process, etc. are added, as shown in Table 2. The capacitance width at a relative humidity of 50% RH is significantly different from that of the present invention, and at the same time, short-circuit failures are also significantly increased.

[Table] As can be seen from the above results, the humidity sensing element manufactured by the method of the present invention has very small variations as shown in Figure 12. In other words, it is possible to obtain any slope required by the electric circuit, and Matching adjustment and the like are also relatively simple, improving mass productivity and yield, and providing inexpensive and compatible humidity sensing elements. As described above, the present invention is an essential condition for producing a humidity sensing element that satisfies the above-mentioned conditions.
Its industrial value is great.

[Brief explanation of the drawing]

FIG. 1 is a cross-sectional view showing the basic structure of a humidity sensing element according to the present invention, FIG. 2 is a cross-sectional view showing a specific example of the same element, and FIG. 3 is a characteristic showing the capacitance-relative humidity characteristic of the same element. Figure 4 is a characteristic diagram showing the moisture absorption and desorption response characteristics of the same element, Figure 5 is a process diagram showing the manufacturing process of the humidity sensing element according to the present invention, and Figure 6 is a dielectric material of the humidity sensing element according to the present invention. FIG. 7 is a perspective view showing an L-shaped conductive band used in the manufacturing method of the present invention, and FIG. 8 explains the effects of the method. FIG. 9 is a schematic diagram showing the state of main steps in the manufacturing method of the present invention,
FIG. 10 is a schematic diagram showing the state of main steps in a comparative example for comparison with the manufacturing method of the present invention,
Figure 1 is a process diagram showing the steps in the same comparative example.
FIG. 2 and FIG. 13 are characteristic diagrams showing capacitance-humidity characteristics in the manufacturing method according to the present invention and a comparative example for comparison with the present invention, respectively. DESCRIPTION OF SYMBOLS 1... Anode substrate, 2... Dielectric anodic oxide film, 3... Semiconductor metal oxide layer, 4... Conductive electrode, 15... Conductive band.

Claims (1)

[Claims] 1. A plurality of anode substrates made of a valve metal are hung and attached to a conductive band formed into an L-shape,
After carrying out the steps of successively laminating a dielectric anodic oxide film, a semiconducting metal oxide layer, and a water vapor permeable conductive electrode using the plurality of anode substrates attached to this conductive band as one unit, the conductive A method for manufacturing a humidity sensing element, characterized in that it is separated from a band. 2. The method for manufacturing a humidity sensing element according to claim 1, wherein the valve metal is selected from tantalum, titanium, niobium, aluminum, and hafnium. 3. The method for manufacturing a humidity sensing element according to claim 1, wherein the anode substrate is a valve metal wire.