JPH0943186A - Moisture sensor and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To improve response and long-term reliability by improving the correlation linearity between a moisture and a capacitance value by filling a moisture- sensing material consisting of hydrophilic macromolecule in an insulation porous ceramic with upper and lower electrodes. SOLUTION: A paste made of precious metal is subjected to thick-film printing on a lower electrode on an insulation substrate, ceramic thick film is formed by paste made of, for example, iron oxide, further an upper electrode is formed on it by the same paste as that of the lower electrode and is baked at approximately 700 deg.C, and an insulation porous ceramic is formed between opposite electrodes. Then, a hydrophilic macromolecule, for example, phthalic hydrogen acetic acid cellulose of cellulose macromolecule is dissolved into acetone to prepare a moisture-sensing liquid, and it is dipped into porous ceramic. In this manner, a capacitance-type sensor element has improved linear correlation property between moisture and capacitance and an improved response and the capacitance value is within a practical measuring range from 100 to 200pF, thus achieving a reliable measurement.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a humidity sensor and its manufacturing method. More specifically, the present invention relates to a capacitive humidity sensor having good linearity in the correlation between humidity and capacitance value, and a method for manufacturing the same.

[0002]

2. Description of the Related Art A humidity sensor is a method of detecting a change in humidity. It is classified as a capacitive humidity sensor that detects the capacitance value.

Here, as the resistance type humidity sensor, an inexpensive sensor using an organic polymer as a moisture sensitive material has been already commercialized, but the linearity of the correlation between humidity and electric resistance is poor and has become a problem. It was Further, since the responsiveness and the long-term reliability are inferior, it is required to improve the characteristics.

Further, as a capacitive humidity sensor, when a ceramic material is used as a moisture sensitive material, there is a problem of deterioration with time. Therefore, it is inferior in mass productivity. Therefore, it is expensive and has been popular only in some industrial fields such as measurement.

[0005]

SUMMARY OF THE INVENTION It is an object of the present invention to simply provide a capacitive humidity sensor having good linearity in the correlation between humidity and capacitance value, excellent responsiveness and long-term reliability. is there.

[0006]

The above-mentioned object of the present invention comprises a constitution in which a moisture sensitive material made of a hydrophilic polymer is filled in an insulating porous ceramic having an upper electrode and a lower electrode. Is achieved by the capacitive humidity sensor.

Further, a lower electrode is provided on the insulating substrate by a thick film printing method, a ceramic thick film is formed on the lower electrode, and an upper electrode is formed on the lower electrode so as to face the lower electrode. The method for manufacturing a capacitive humidity sensor is characterized in that an insulating porous ceramics formed between opposing electrodes is impregnated with a moisture sensitive material made of a hydrophilic polymer.

[0008]

BEST MODE FOR CARRYING OUT THE INVENTION The insulating porous ceramics of the present invention include iron oxide, aluminum oxide, chromium oxide,
Examples thereof include oxides such as tin oxide and zinc oxide, and porous glass.

As the hydrophilic polymer, a cellulose-based polymer such as cellulose acetate hydrogen phthalate, cellulose acetate and cellulose propionate, polyvinyl alcohol, polyvinyl acetate, polyethylene glycol,
Examples include polymers such as polypropylene glycol and polyamide. Among these, cellulose hydrogen phthalate, which is a cellulosic polymer, is preferable in terms of linearity of correlation between humidity and capacitance value. Furthermore, phenol resin, cross-linked polymer of methacrylate monomer, cross-linked polymer of fluorinated polyimide, polymer obtained by polymerizing reactive cationic monomer, polymer obtained by crosslinking cationic monomer with vinyl monomer, thermosetting resin, etc. Alternatively, a copolymer obtained by graft-polymerizing a hydrophilic polymer and a hydrophobic polymer, a mixture of an ionene polymer and another polymer, or copolymerization resistance may be used.

[0010]

The present invention will now be described by way of Examples and Comparative Examples.
This will be described in more detail. Example 1 Using a thick film printing method, a lower electrode is printed on an insulating substrate with a paste made of a noble metal, a ceramic thick film is formed on the upper portion with a paste made of iron oxide, and the same paste as the lower electrode is formed on the upper electrode. An upper electrode was formed and fired at 700 ° C. to obtain an element made of insulating porous ceramics. next,
2.0 g of cellulose hydrogen phthalate, which is a cellulosic polymer as a hydrophilic polymer, is dissolved in 30 g of acetone as a solvent to prepare an impregnating solution, and the impregnating solution is impregnated with the element made of the insulating porous ceramics. A capacitive humidity sensor was manufactured.

Example 2 A capacitive humidity sensor was obtained in the same manner as in Example 1 except that 2.0 g of cellulose acetate, which is a cellulosic polymer as a hydrophilic polymer, was dissolved in 30 g of acetone as a solvent to prepare an impregnating liquid. .

Example 3 A capacitive humidity sensor was obtained in the same manner as in Example 1 except that 0.5 g of cellulose propionate, which is a cellulosic polymer as a hydrophilic polymer, was dissolved in 30 g of acetone as a solvent to prepare an impregnating solution. It was

Comparative Example Using a thick film printing method, a lower electrode is printed on an insulating substrate with a paste made of a noble metal, and a ceramic thick film is formed on the upper portion with a paste made of iron oxide. An upper electrode was formed from the paste and baked at 700 ° C. to obtain a humidity sensor.

FIG. 1 shows the humidity sensors obtained in the examples and comparative examples at a temperature of 25 V under the measurement conditions of 1 V and 100 KHz.
The results measured in an atmosphere of ℃ and relative humidity of 30 to 90% RH are shown.

From the results shown in FIG. 1, the capacitance type humidity sensor of the present invention is superior in linearity of the correlation between humidity and capacitance as compared with the comparative example, and the capacitance value is practically measured in the range of 100 pF to 200 pF. It turned out to be inside. In addition, the responsiveness to humidity changes was good, and it was confirmed from the results of various reliability tests that the capacitive humidity sensor according to the present invention has excellent reliability.

[0016]

According to the present invention, it is possible to easily obtain a capacitive humidity sensor having excellent linearity of the correlation between humidity and capacitance.

[Brief description of drawings]

FIG. 1 is a diagram showing a relationship between electrostatic capacitance and relative humidity of humidity sensors obtained according to the present invention and a comparative example.

Claims (2)

[Claims] 1. A capacitance type humidity sensor, characterized in that a moisture sensitive material made of a hydrophilic polymer is filled in an insulating porous ceramic having an upper electrode and a lower electrode. 2. A lower electrode is provided on an insulating substrate by a thick film printing method, and a ceramic thick film is formed on the lower electrode.
Further, an upper electrode is formed thereon so as to face the lower electrode, and after firing, the insulating porous ceramics formed between the opposing electrodes are impregnated with a moisture-sensitive material made of a hydrophilic polymer. The method for manufacturing the capacitive humidity sensor according to claim 1.