JPS58173458A - Humidity sensor and its manufacture - Google Patents

Abstract

PURPOSE:To obtain a long-lived sensor capable of detecting a long range of humidity exactly, by allowing to carry at least one of meta-, ortho-, and pyro- phosphates into the pores of a porous base. CONSTITUTION:Electrodes are formed on both sides of a base 1 having fine connected pores made of alumina or quartz material, connected in parallel to form comb-type counter electrodes 3, 3, and each terminal of the electrodes 3, 3 are connected to silver terminals 5, 5, and further, to lead wires 6, 6. The electrodes may be formed on one side, but a detection range can be enlarged by forming them on both side. The electrodes 3, 3 are printed with ruthenium oxide paste on the base 1, burned, washed, then impregnated with a soln. mixture of an aq. soln. of at least one of meta-, ortho-, and pyro-phosphate, and silicate soln., and dried. A sufficient amt. of phosphate is carried into the base 1 by repeating this operation, thus obtaining a long-lived sensor extremely small in hysteresis of humidification and dehumidification and superior in humidity detection characteristics in a wide range.

Description

[Detailed Description of the Invention] Jin's invention relates to a humidity sensor that detects humidity by detecting electrical properties that change depending on humidity, and a method for manufacturing the same, and particularly to a humidity sensor that accurately detects humidity changes in a wide static environment. I am trying to make it possible.

<Background of the Invention> Humidity sensors that detect humidity play an important role in the quality control and environmental management of industrial products, and are used in the manufacturing processes of semiconductors, steel, textiles, food, paper manufacturing, electronic parts, etc., and in buildings. Widely used to control humidity in hospitals, research laboratories, greenhouses, greenhouses, living environments, etc.

Humidity sensors that utilize changes in the electrical and physical properties of substances due to ω degrees are well-known, and currently sensors such as metals, semiconductors, insulators, and hydrophilic polymer materials are used to detect stains due to humidity changes. Research and development of senna, which uses materials whose capacitance and electrical resistance change as humidity sensing elements, is active. However, currently developed humidity sensors have problems in terms of reliability for long-term use and detection humidity range, and are expensive, so their applications are limited.

That is, the well-known humidity sensor whose substrate is impregnated with lithium chloride does not have a long lifespan because lithium chloride is an electrolyte that easily dissolves in water. It is also known that porous glass impregnated with this material has poor responsiveness to changes in humidity. In a polymer sensor, it is said that even if the application of DC current is as low as 1 μA, the humidity detection characteristics will change. Ceramic thread is the first raw material! It is expensive because it is made of # and fired at high temperatures, and it is difficult to arbitrarily control the electrical resistance value with respect to humidity.

Furthermore, in the humidity sensor disclosed in JP-A-54-56199, in which a water-soluble silicate and a moisture-sensitive metal oxide are mixed, the mixture is coated on a substrate and dried, as shown in the examples of this publication. The electrical resistance of the sensor against relative humidity is high, and even at a relative humidity of 100 degrees it shows a resistance of 6MΩ, and even at a humidity of 20 degrees it only reaches 8R11Qa degrees, which shows the relationship between the relative humidity and the logarithm of the resistance value. Rounding, where the slope of the curve is gentle, has the drawbacks of poor humidity detection accuracy and expensive humidity measurement circuits.

Furthermore, there have conventionally been humidity sensors in which metaphosphate or birophosphate is used as an MS agent and attached to a substrate by plasma spraying, but it is difficult to easily obtain a desired resistance value, and the manufacturing equipment is difficult. It will be worth the price. There is also a humidity sensor in which a porous metal oxide base is impregnated with a solution of orthophosphate or pyrophosphate and then heat-treated to support a phosphorous compound in the pores of the base. This sensor has the disadvantage that it must be subjected to high temperature treatment and has a high resistance of about MΩ at a relative humidity of 30 -.

<Summary of the Invention> An object of the present invention is to provide a humidity sensor and a method for manufacturing the same that eliminates the drawbacks of conventional humidity sensors.

According to this invention, a counter electrode is provided on a porous material substrate, and one of a metaphosphate solution, an orthophosphate solution, a pyrophosphate solution, or a mixture of two or more of these salt solutions is prepared. , or a mixture of the above-mentioned one kind of salt solution or a mixture of two or more kinds and a silicate solution is occluded as an occlusion liquid in the pores of the base of the porous material, and then the liquid of the occlusion liquid is evaporated. , the salt substance present in the storage liquid is supported in the pores of the substrate.

In this invention, by selecting the phosphate solution to be occluded in the substrate, it is possible to set the relative humidity-electrical resistance value curve, which shows the relationship between humidity and electrical resistance, to a curve according to the purpose. It has a wide range and is poorly soluble, so it has a long life and can be manufactured at low cost.

The humidity sensor of the present invention and its manufacturing method will be explained below with reference to the drawings.

<Embodiment> FIG. 1 is a book showing the configuration of an example of the present invention. Substrate 1 is a mixture of a metaphosphate solution, an orthophosphate solution, a birophosphate solution, or any of these solutions or a mixture of two or more of these solutions and a silicate solution.
It is a porous material for occluding TF (hereinafter referred to as occlusion liquid), has excellent impregnation properties with occlusion liquid, and has air permeability so that when the occlusion liquid is brought into contact with a part of the substrate, it permeates through the entire TF substrate. Preferably, a porous material is used that has continuous fine pores and prevents the moisture-sensitive substance remaining in the pores of the substrate from falling off because the moisture-sensitive substance remaining in the pores of the substrate is strongly supported by the pores after the liquid outside of the storage liquid has evaporated. . A porous polymer material substrate or a porous ceramic material substrate can be used as a porous material substrate l having such performance, but alumina sintered body, glassy or quartz sintered body can be used. It is also desirable to have a ceramic material substrate having such microporous continuous pores. The reason for this is that the ceramic substrate has a smaller coefficient of thermal expansion than the polymer material substrate, and is not susceptible to erosion by solvents when cleaning the substrate. This causes the moisture-sensitive material supported in the pores of the base to crack or fall off, making the humidity detection unstable. The substrate 1 is, for example, a porous alumina sintered body, which has a rectangular size of 13 mm, a thickness of 6 m, and a distribution size of about 20 μm to 0.5 m. 0171, average diameter is 2.2μ, and porosity is 1j48-.

A pair of interlocking comb-shaped counter electrodes 3.3 are printed and baked on -rI02 of the base 1 using, for example, a ruthenium oxide-based conductive paste. Terminal part 4 of electrode 3.3
, 4 are printed with silver terminals 5, 5 to facilitate soldering, and leads @ 6, 6 are soldered to external 1.
- connection (omitted in this figure).

When the base 1 is a flat plate as shown in FIG. 1, counter electrodes can be provided on both sides of the base as shown in FIG. The reason why a plurality of opposing electrodes are provided in this way,
The aim is to lower the resistance value of the humidity sensor, and a base 1 is sandwiched between the complex terminals 5, 5 of the terminal parts 4, 4 of the counter electrodes provided on both sides, and a 917-dore wire 6.6 is attached. ,
Opposing electrodes on both sides are connected in parallel. In this way, it is possible to detect humidity in a humidity range where it was impossible to detect humidity with a single-sided counter electrode because the electrical resistance was too high.
The range of humidity detection can be expanded.

Figure 3 shows the relative relationship between a humidity sensor using a nickel phosphate (N11(PO4)l) solution as an occlusion liquid on a substrate l, in the case of a counter electrode on only one side and in the case of an electrode with counter electrodes on both sides connected in parallel. The relationship curve between humidity and resistance value is shown. Neither the characteristic curve A of the parallel connection of opposing 1L poles nor the characteristic curve B of one counter electrode shows hysteresis during humidification and dehumidification, but the electrical resistance of track 11A is lower at the same relative humidity. It shows the value.

In other words, in this case, the relative humidity is 55 for the counter electrode with only the negative side.
Although it is practically difficult to detect less than
If one pole is provided, the detection range can be expanded to a humidity range of 45%.

FIG. 4 shows a structure in which a fixed resistance element 7 is arranged in parallel with the counter electrode. Although this figure shows the case where the resistive element 7 is printed and fired, it is also possible to arrange another fixed resistive element 7 by retrofitting the base IK, or as shown in Figure 5, outside the base 1 in parallel with the counter electrode. It is also possible to connect the resistive element 7 to . The resistance elements 7 connected in parallel are preferably 10 MΩ or less, and in particular, all four resistance elements have an M range of 300Ω to 50Ω to manufacture the humidity sensor control circuit at low cost. lOM
Even if the resistance element 7 of Ω or more is connected, it has little effect on lowering the total resistance value of the humidity sensor, so the control circuit is not cheap.

By connecting the resistance element 7 as shown in Fig. 4, the maximum resistance of the humidity sensor can be controlled, and the resistance value for humidity detection in the low continuous range can be controlled. can be read as a measurable resistance value. The relative f'4#-electricity when a resistance element 7 of 105 to Ω is connected in parallel as shown in FIG. An example of a resistance bending machine is shown in FIG. In this case, an aluminum phosphate solution was used as the storage liquid, and a 7h ruthenium oxide-based resistance element was printed and fired. The curve in Figure 6 shows that at a relative humidity of <201, the resistance is 98
Ω, there is no hysteresis between the humidification curve and the dehumidification curve, and the low resistance allows external control circuits to be manufactured at low cost. Of course, the parallel resistance elements 7 can be provided on a plurality of opposing electrodes.

It is also effective to coat the substrate 10 on one or both sides with a Nesa film composed of a thin Kffi tin film to lower the humidity detection resistance in a low humidity region. It is effective to perform Wa of the Nesa membrane. Figure 7 shows the relative humidity-electrical resistance curve of a humidity sensor coated with Nesa membrane on one side and using calcium metaphosphate as the absorbing liquid.
A low resistance is shown. In addition, in the sensor used in FIG. 7, the interelectrode resistance ti250 with the Nesa film attached before calcium metaphosphate is absorbed is Ω.

The substrate IFi is first degreased with an ethyl alcohol solvent, then washed with ion-exchanged water to which ultrasonic vibrations have been applied, and then dehydrated by pyrolysis. The dried and dehydrated substrate 1 is soaked in water to which ultrasonic waves are applied, held immersed in a liquid, and then taken out and dried. The liquid content from the storage liquid impregnated into the substrate 1 is evaporated, and when drying is completed, the substrate 1 is immersed in the storage liquid again, or the storage liquid is dropped onto the surface of the substrate to impregnate it with the storage liquid and evaporated and dried. In this way, the substrate is repeatedly impregnated and evaporated with the storage liquid, and when the required resistance value is obtained, the impregnation and evaporation of the storage liquid is completed. Of course, in order to speed up the impregnation and drying of the absorption liquid into the substrate IK, it is possible to heat the substrate 1 while dropping the absorption liquid at the same time, and also to absorb the absorption liquid using the vacuum evaporation method. It is possible to remove water from the liquid.

The storage liquid used in this invention includes a metaphosphate solution, an orthophosphate solution, a pyrophosphate solution, and the like.

The metaphosphate solution is a solution of one type of salt selected from metalin wbrium, sodium metaphosphate, calcium metaphosphate, and molybdenum metaphosphate, or a mixture of solutions of two or more types of salts selected from these. be. Orthophosphate solutions include nickle phosphate, iron phosphate, and 7"
FM tin, manganese phosphate, lead phosphate, cobalt phosphate,
A solution of one type of salt selected from zinc phosphate, dium phosphate, silver phosphate, aluminum phosphate, magnesium phosphate, boron phosphate, calcium phosphate, lithium phosphate, cadium phosphate, or , a mixture of solutions of two or more groups selected from these.

The pyrophosphate solution is a solution of 91 kinds of salts selected from zinc birophosphate, calcium pyrophosphate, magnesium birophosphate, platinum birophosphate, manganese pyrophosphate, and aluminum pyrophosphate, or a solution of two or more salts selected from these. It is a mixture of base solutions. A solution obtained by mixing a solution of one kind of salt, or a mixture of solutions of two or more kinds of salts with a boundary salt solution is used as the built-in solution. Silicate solutions include calcium silicate, potassium silicate, sodium silicate,
It is a solution of one type of salt selected from calcium magnesium silicate, or a mixed solution of two or more types of salts selected from these.

The reason why the composition of the metaphosphate solution, orthophosphate solution, or birophosphate solution was limited as above is shown in Table 1.
As shown in Tables 2 and 3 (Inorganic Chemistry Hand, Book, Gihodo Publishing Co., Ltd., March 25, 1980), the above metaphosphates, phosphates, and bicarbonates are To! It is a salt that is difficult to dissolve. In this way, metaphosphate I salts, shosonosananawa, and pyrophosphates are salts that are difficult to dissolve in water, so even if the moisture-sensitive salts supported in the pores of the substrate absorb moisture, they absorb only a very small amount. does not dissociate into charge carriers,
Therefore, there is little wear and tear due to energization, and the function as a senna is maintained for a long period of time. Furthermore, even if water droplets form, the amount of the bad salt substance Fi supported in the pores that dissolves and flows out is extremely small.

Table 1 - Solubility of metaphosphate in water fJIJ2tI Solubility of metaphosphate in water The numerical value is the amount of solute dissolved in 100 f Table 3 Solubility of pyrophosphate in water Metaphosphate solution 9 Mixing □ solution of silicate with orthophosphate solution or pyrophosphate solution Butterfly, substrate When occluded and dried, the 9 pores of the substrate strongly support precipitated fine particles of phosphorescent salt, which is a salt substance (hereinafter referred to as moisture-sensitive storage), which strengthens the bonds between the particles, and as a result, the distance between the particles decreases. aI compared to not mixing the silicate solution closely.
The resistance value for WIL can be lowered, and hysteresis is eliminated in humidity-resistance-111, and the humidity detection ellipse is improved. Note that the metaphosphate solution A, orthophosphate solution Q, or pyrophosphate solution to be occluded in the substrate is hardly soluble in water, so a saturated aqueous solution or a saturated aqueous suspension solution is used as the occlusion liquid. This allows the substrate to quickly carry the required amount of moisture-sensitive material.
effective.

Example 1 The average size of pores is 1.8μ as the substrate of porous material,
An air-permeable alumina flat plate with a porosity of 4596 and a thickness of 0.6 mm was used, and a comb-shaped counter electrode was printed and fired on one side of the plate using ruthenium oxide paste, and the spacing between the counter electrodes was 0.
2■ Binding 4 of the structure shown in Fig. 1. This substrate was subjected to ultrasonic cleaning in 9696 ethyl alcohol for 5 minutes, then in ion-exchanged water for 5 minutes, and then heated at 120° C. for 1 hour to dehydrate and dry. A potassium metaphosphate solution prepared by saturated dissolving potassium metaphosphate in ion-exchanged water is used as the storage liquid, and the dehydrated and dried substrate is immersed while applying ultrasonic waves to the solution, allowing the storage liquid to penetrate into the inside of the pores. K was applied so that it was impregnated.

After 5 minutes of ultrasonic application, the substrate was taken out of the occlusion liquid and heated in a heating oven at 95°C for 5 minutes to evaporate the moisture impregnated into the pores of the substrate, and then immersed again in saturated potassium metaphosphate solution and dried. I did this. Repeat immersion and drying 20 times to fully support potassium metaphosphate in the pores of the substrate.
Figure 8 shows the S% sensitivity of the sensor. This relative 911 degrees -
The relationship between the electrical resistance values is the result of measurement at 25°C with an alternating current of IK)h, and the hysteresis of humidification and dehumidification is extremely small.
The fif detection characteristics were good at relative humidity of 40 degrees or more, and no changes were observed in this sample even after 6 months of light pollution.

Example 2゜Using a substrate with the same structure as in Example 1, using a saturated suspension of aluminum phosphate as the storage liquid, the substrate was impregnated with the storage liquid in the same manner as in Example 1, and the pores of the substrate were filled. Shun Aluminum was instructed. FIG. 9 shows a curve showing the relationship between relative humidity and electrical resistance value of this humidity sensor. The hysteresis of humidification and dehumidification is extremely small, and a relative my of 45- or more can be detected accurately. No change was observed in the curve even after 6 months had passed.

Example 3 Using a substrate with the same structure as in Example 1, using a saturated suspension of zinc pyrophosphate as the storage liquid, impregnating the mounting body with the storage liquid in the same manner as in Example 1 to fill the void in the substrate. Zinc pyrophosphate was supported in the pores. The relationship between relative concentration and electrical resistance value of this humidity sensor is shown in Figure 10. Humidification and dehumidification hysteresis is extremely small at 80m! It shows a rapid change in resistance at a relative humidity of 1 or more, and has characteristics suitable for a dew sensor. 6
No change was observed in the curve even after several months had passed.

Example 4: Electrodes were provided on both sides of the flat plate of the substrate.The substrate having the structure shown in FIG. The mixture of potassium metaphosphate and potassium silicate was supported in the pores of the substrate by impregnation with the mixed storage liquid. FIG. 11 shows a relationship curve between relative humidity and electrical resistance value of this humidity sensor. relative f
The electrical resistance value for ll[ has decreased significantly, and is less than 200 Ω even at a relative angle of 8 degrees 20 -, and the humidity detection range in the low temperature range has been expanded.
No hysteresis is observed. Further, no change was observed in the curve Fi after 6 months.

Example 5゜A substrate having the same structure as in Example 1 was used, and the storage liquid was 50% of a saturated suspension of phosphorous aluminum and 50% of a saturated solution of phosphoric acid bone.
A mixed sensitive layer material of aluminum phosphate and boron phosphate was supported in the pores of the substrate using a mixed solution of aluminum phosphate and boron phosphate. FIG. 12 shows the relative flIFIL-electrical resistance value relationship curve of this humidity sensor. As can be seen from a comparison with FIG. 9, the resistance value for the same relative humidity fK is lower than in the case of only aluminum phosphate, and the structural range of the low 9M region is expanded.

The relative immersion-electrical resistance curve did not change after 1 year.

Example 6 Using a substrate with the same structure as in Example 4, a saturated suspension of aluminum phosphate and a potassium silicate solution (Potassium silicate 2CC:
A solution prepared by mixing 100 cc of water at a ratio of 8=2 was used as the storage liquid, and a mixture of aluminum phosphate and potassium silicate was supported in the pores of the substrate. FIG. 13 shows a relationship curve between relative humidity and electrical resistance value of this humidity sensor. As can be seen from a comparison with FIG. 9, the detection range is expanded in the case of only aluminum phosphate because the electrical resistance is low in low humidity regions. No change was observed in the humidity-resistance ratio even after 6 months.゛After heating and drying, drop the mixture again and dry. In this case, the amount of dripping per substrate was 0.05ee, and this was repeated 40 times to support the mixed moisture-sensitive material of aluminum phosphate and potassium silicate in the pores of the substrate. FIG. 14 shows a relationship curve between relative humidity and electrical resistance value of this humidity sensor.

By increasing the amount of storage liquid dripped in this way, the electrical resistance against humidity becomes even lower, and even at a relative humidity of 20 inches, it falls to about 2.OMEGA., and the detection humidity range can be expanded to 0 degrees.

<Effects> As described above, according to the present invention, the resistance value is low, the measurement circuit is simplified, measurement can be performed in low humidity areas compared to conventional methods, and the life span is longer than ever before. During the selection of moisture-sensitive materials, the desired resistance value can be easily obtained depending on the number of impregnated occlusion liquids or the number of drops of mineral @ vehicle. You don't need anything expensive.

[Brief explanation of the drawing]

FIG. 1 is a perspective view showing an example of the humidity sensor according to the present invention, FIG. 2 is a perspective view showing another example of the humidity sensor according to the present invention, FIG. The relative humidity-electrical resistance value of the sensor is shown. Curve I/MA is a humidity sensor with counter electrodes on both sides and connected in parallel at the terminals. Curve B is a characteristic diagram for a turtle with counter electrodes on only one side. 4 and 5 are respectively front views showing still other examples of the humidity sensor of the present invention, and FIGS. 6 to 14 are relative temperature-electrical resistance value relationship curves of various examples of the humidity sensor of the present invention, respectively. 1: porous alumina dark blue base, 2: surface of base, 3: comb-shaped counter electrode, 4: electrode terminal, 5: silver terminal, 6: lead resistance, 7: resistance element. Patent Applicant Tokyo Cosmos Electric Co., Ltd. Agent Takuo Kusano 2 Figure 8 B Figure 3 Figure 4 Figure 5 Figure 6 Figure 1 vs. Humidity (Kario 7 Figure Relative Humidity (-) Figure O 8 Relative Humidity (0) ) O 9 Figure Relative Humidity (%) Fang 10 Figure Nu 142 degrees (°n) Su 11 Figure O Eye Su 1 No.!/i('/,) Sai 12 Figure Ome Nu:r SR Hiro(” /, ) -+ 13 'Figure 14 Figure 1 vs. 1 Procedural amendment (spontaneous) Commissioner of the Japan Patent Office 1, Indication of case Patent application No. 57-563752, Title of invention Humidity sensor and its manufacture Method 3: Relationship with the person making the amendment Patent applicant: Tokyo Cosmos Electric Co., Ltd. 4: Agent: 4-2-21 Shinjuku, Shinjuku-ku, Tokyo
Sumo Building 6615 Patent Attorney Taku Kusano 5, Subject of Amendment Claims - and Detailed Description of the Invention - 6 Contents of Amendment (1) The scope of claims will be corrected as shown in the attached sheet. (2) In the specification, page tIAJ, line 3, "metaphosphate, birophosphate" is corrected to "orthophosphate." (31 Ibid., p. 7, line 7 [t of orthophosphates and pyrophosphates] is corrected to "of kusei phosphoric acid and pyrophosphate." (5) In the same book, page 11, line 11, “birophosphoric acid solution” should be corrected as “and sparingly soluble in water.”
Beer phosphate solution” is corrected. (6) “Built-in liquid” in line 11 of page 12 of the same book is “occlusion liquid”
I am corrected. (7) On page 17 of the same book, line 19, ``I was instructed.'' is corrected to ``I was made to carry it.'' (8) On page 20 of the same book, line 4 "Vacancies K in the substrate" should be deleted. Claims (1) Metaphosphate, orthophosphate and A humidity sensor having at least one salt material of pyrophosphate supported thereon and a counter electrode formed on the porous material substrate. (2) A counter electrode is formed on a porous material substrate, and a metaphosphate solution, an orthophosphate solution, a pyrophosphate solution, or these solutions and a silicate solution are applied to the pores of the porous material substrate. Humidity that allows at least one of the mixed liquids to be occluded as an occluded liquid, and then the liquid in the occluded liquid is evaporated to support the salt substance contained in the occluded liquid in the pores of the porous material base. How to make senna. (3) The humidity sensor or the manufacturing method thereof according to claim 1 or 2, wherein the porous material has continuous air-permeable pores.

Claims (1)

[Scope of Claims] (1) At least one salt substance of methaline salt, orthophosphate, and birophosphate is supported in the pores of the porous material substrate, and is opposed to the porous material substrate. Humidity sensor with electrodes formed. ■) A counter electrode is formed on a porous material substrate, and a methaline salt solution, an orthophosphate solution, a birophosphate solution, or a solution and a silicate solution are applied to the pores of the porous material substrate. absorbing at least one of the mixed liquids as an absorbent liquid,
A method for producing a humidity sensor, in which the liquid in the storage liquid is then evaporated to support the salt substance contained in the Fj&lR liquid in the pores of the porous material base. (3) The humidity sensor or the manufacturing method thereof according to claim 1 or claim 2, wherein the porous material has continuous air-permeable pores.