JP2004177405A - Humidity detecting device of electrical capacitance type and method of manufacturing the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide an electrical capacitance type humidity detecting device and a method of manufacturing the same with high volume productivity in which a humidity-sensitive film is formed at a low temperature and in a short time. <P>SOLUTION: The electrical capacitance type humidity detecting device comprises a substrate 1 and the humidity-sensitive film 3 having a first electrode layer 2 and a second electrode layer 4. The humidity-sensitive film 3 has polyimide as the main ingredient made by the polymerization of biphenylsulfone tetracarboxylic dianhydride and aromatic diamine. An example of biphenylsulfone tetracarboxylic dianhydride is 3,3',4,4'-diphenylsulfone tetracarboxylic dianhydride. <P>COPYRIGHT: (C)2004,JPO

Description

  The present invention relates to a capacitance type humidity sensing element using an organic polymer resin material as a moisture-sensitive film and a method for manufacturing the same.

  The capacitance-type humidity sensing element uses a dielectric whose dielectric constant changes as a function of adsorbed water molecules as a moisture-sensitive film, and arranges a pair of electrode layers facing each other with the dielectric interposed therebetween to reduce the capacitance of the moisture-sensitive film. The change is detected, and the humidity is detected based on the change in the electric capacity.

As a humidity detecting element of this type, a capacitive humidity detecting element using a polyimide film soluble in an organic polar solvent as a moisture-sensitive film has been proposed.A polyimide film is composed of a biphenyltetracarboxylic acid component and an aromatic diamine. It is obtained by polymerizing and imidizing a component (for example, see Patent Documents 1 and 2).
JP-A-4-250352 Japanese Patent Publication No. Hei 8-23542 (Japanese Unexamined Patent Publication No. Hei 6-148122)

However, in the conventional capacitive humidity sensing element, it is necessary to polymerize and imidize a biphenyltetracarboxylic acid component and an aromatic diamine component on a substrate in order to obtain a polyimide film. The heat treatment temperature (heat hardening temperature) becomes as high as 300 to 350 ° C., and it takes 30 minutes or more. Therefore, the substrate may be deteriorated in the process of forming the moisture-sensitive film, and the mass productivity is low. In particular, when producing the above polyimide film, the homogeneity of the obtained moisture-sensitive film is reduced, and undulation is generated on the surface of the moisture-sensitive film. Had low quality.
Further, in the case of the humidity detecting element obtained in this way, the reliability as the humidity detecting element is also reduced, and the output value with respect to the relative humidity fluctuates depending on the temperature, or the output value drifts due to being left in a high temperature and high humidity environment. Inconveniences, such as occurrence, also occurred.

  The present invention solves such a problem, a method of manufacturing a humidity sensor capable of forming a moisture-sensitive film at a relatively low temperature and in a short time, and excellent in mass productivity, and a method of producing an output value. An object of the present invention is to provide a highly reliable capacitance-type humidity detecting element having a small temperature dependency and a small drift change even in a high-temperature and high-humidity environment.

  In order to achieve the above object, a capacitance-type humidity detecting element of the present invention includes a substrate and a moisture-sensitive film provided with at least two electrode layers, wherein the moisture-sensitive film is biphenylsulfonetetracarboxylic dianhydride. And a polyimide obtained by polymerizing an aromatic diamine. In the present invention, “having polyimide as a main component” means that the moisture-sensitive film contains 50% by mass or more of polyimide.

  The polyimide used in the present invention can be formed by dissolving in an organic polar solvent, adjusting the composition, applying the composition to a substrate, and then performing heat treatment at a relatively low temperature of 100 to 280 ° C. for several minutes to about twenty minutes. is there. Therefore, the capacitance type humidity detecting element of the present invention can prevent thermal deterioration of the substrate and has high mass productivity. Further, according to the capacitance type humidity detecting element of the present invention, the swelling of the moisture-sensitive film is sufficiently prevented even in a high-temperature and high-humidity environment. Therefore, a change in the thickness of the moisture-sensitive film is sufficiently prevented, and a change in the capacitance due to the change in the thickness is also sufficiently prevented. Therefore, according to the capacitance type humidity detecting element of the present invention, it is possible to accurately indicate the original humidity even under a high temperature and high humidity environment. That is, even under a high-temperature and high-humidity environment, the drift change of the output value with respect to the relative humidity can be sufficiently reduced. Further, the temperature dependency of the output value with respect to the relative humidity can be reduced.

  The heat treatment temperature for forming the moisture-sensitive film is preferably 200 to 250C. The heat treatment time is preferably from 10 minutes to 20 minutes. The higher the heat treatment temperature, the shorter the heat treatment time.

  As the biphenylsulfonetetracarboxylic dianhydride used in the present invention, preferably, 3,3 ', 4,4'-diphenylsulfonetetracarboxylic dianhydride can be used. In this case, heat resistance is higher than in the case where biphenylsulfonetetracarboxylic dianhydride other than 3,3 ', 4,4'-diphenylsulfonetetracarboxylic dianhydride is used.

（上記式中、Ｒ^０は、単結合、−ＳＯ_２−、−ＣＯ−、−Ｏ−、−Ｓ−、アルキレン基又はアリーレン基を表し、Ｒ^１、Ｒ^２は、それぞれ独立にアルキル基又はハロゲン原子を表し、ｐ、ｑはそれぞれ０〜４の整数を表す）
で表されるものであってもよい。この場合、ポリイミドが有機極性溶媒に可溶になる。 Further, as the aromatic diamine used in the above invention, a compound having a hydrogen atom, a halogen element, or two phenyl groups which may contain a substituent having 0 to 4 carbon atoms is preferable. When the number of phenyl groups becomes four or more and the polymer unit becomes longer, the heat resistance decreases. Specifically, p-phenylenediamine, m-phenylenediamine, 4,4′-diaminodiphenylmethane, 4,4′-diaminodiphenyl ether, 4,4′-diaminodiphenyl sulfide, diaminotoluene, diaminodiphenylsulfone, bis ( Those having at least one of (aminophenoxy-phenyl) sulfones are more preferred. By using such an aromatic diamine, it becomes soluble in an organic solvent even after polyimide, and the residual stress is reduced compared with the case where it is polymerized on a substrate. Capacitance drift can be reduced. The aromatic diamine has the following structural formula (1):

(In the above formula, R ⁰ represents a single bond, —SO ₂ —, —CO—, —O—, —S—, an alkylene group or an arylene group, and R ¹ and R ² each independently represent an alkyl group or Represents a halogen atom, p and q each represent an integer of 0 to 4)
May be represented by In this case, the polyimide becomes soluble in the organic polar solvent.

  In the humidity sensing element according to the present invention, when at least one of the at least two electrode layers is formed on the surface of the moisture-sensitive film on the substrate side, at least one of the surfaces of the electrode layer in contact with the moisture-sensitive film is provided. The part is desirably surface-treated with a silane coupling agent. Thereby, the interface strength between the moisture-sensitive film and the electrode layer is enhanced, and the adhesiveness is enhanced. As a result, peeling of the moisture-sensitive film from the first electrode layer is sufficiently prevented for a long period of time, penetration of moisture into the interface is reduced, and a change in capacitance drift under a high-temperature and high-humidity environment is effective for a long period of time. Can be suppressed.

  As the silane coupling agent, a silane coupling agent of an organic functional silane having one or more functional terminal groups at the terminal can be used. Examples of the functional terminal group include a phenyl group, an amino group, and a ureido group. Examples of the silane coupling agent for the organic functional silane having a functional terminal group include γ-anilinopropyltrimethoxysilane (AnPS), γ-aminopropyltriethoxysilane, γ-aminopropyltrimethoxysilane, N-β-aminoethyl-γ-aminopropyltrimethoxysilane and γ-ureidopropyltriethoxysilane can be used.

  As a method of surface treatment, for example, a method of immersing the substrate on which the electrode layer is formed in a silane coupling agent, or a method of dropping a silane coupling agent on the electrode layer, followed by drying and heat treatment. No.

  Further, of the at least two electrode layers, the first electrode layer is formed on the surface of the moisture-sensitive film on the substrate side, and the second electrode layer is formed on the surface of the moisture-sensitive film opposite to the substrate. In this case, the second electrode layer desirably has moisture permeability. When the second electrode layer has moisture permeability, the sensitivity of the humidity detecting element to a change in humidity becomes sufficiently higher than when the second electrode layer does not have moisture permeability.

  Further, more preferably, the second electrode layer can be formed in a mesh shape. By forming the electrode into a mesh shape, sufficient air permeability can be ensured and the thickness of the second electrode layer can be increased, so that the adhesion between the moisture-sensitive film and the second electrode layer and the mechanical properties are improved. Target strength is increased.

  The mesh-shaped electrode layer can be formed in a comb shape or a mesh shape by using, for example, a vacuum evaporation method.

  More preferably, the substrate can be based on a plastic material. By using a substrate containing a plastic material as a main component, it is possible to reduce the weight of the humidity detecting element and improve impact resistance as compared with a case where a substrate containing a material other than the plastic material as a main component is used.

  As the plastic material, a known material can be used as long as the heat-resistant temperature is equal to or higher than the heat treatment temperature of the moisture-sensitive film. For example, polyimide, a fluoropolymer, or the like can be used. In order to increase the sensitivity of the humidity detecting element, it is preferable that the plastic material has lower hygroscopicity than the moisture-sensitive film.

（上記式中、Ｒ^３は−ＳＯ_２−又は又は下記構造式（３）：

で表される基を表し、Ｒ^４，Ｒ^５はそれぞれ独立に、水素原子、−ＳＯ_２Ｒ^６又は上記構造式（３）で表される基を表し、Ｒ^６はアリール基又は炭化水素基を表す）
で表されるものであることが好ましい。ビフェニルスルホンテトラカルボン酸二無水物として、上記一般構造式（２）で表されるものが用いられることにより、ポリイミドが有機極性溶媒に可溶となる。そのため基板上でポリイミド化することなく、ポリイミド化後に基板上に塗布することができ、感湿膜の均質性がより向上する。このため、感湿膜が不均質であることに起因する感湿膜への加工が不要となり、歩留まりの低下を十分に防止することができる。 The biphenylsulfonetetracarboxylic dianhydride has the following general structural formula (2):

(In the above formula, R ³ is —SO ₂ — or or the following structural formula (3):

Wherein R ⁴ and R ⁵ each independently represent a hydrogen atom, —SO ₂ R ⁶ or a group represented by the above structural formula (3), and R ⁶ is an aryl group or a hydrocarbon group Represents)
It is preferably represented by By using the biphenylsulfonetetracarboxylic dianhydride represented by the general structural formula (2), the polyimide becomes soluble in an organic polar solvent. Therefore, it can be applied on the substrate after the polyimide, without the polyimide on the substrate, and the uniformity of the moisture sensitive film is further improved. Therefore, it is not necessary to process the moisture-sensitive film due to the non-uniformity of the moisture-sensitive film, and it is possible to sufficiently prevent the yield from decreasing.

  Further, a method of manufacturing the capacitance-type humidity sensing element of the present invention for achieving the above object includes a step of sequentially forming an electrode layer and a moisture-sensitive film on a substrate, wherein the step of forming a moisture-sensitive film comprises: Dissolving a polyimide obtained by polymerizing biphenylsulfonetetracarboxylic dianhydride and an aromatic diamine in an organic polar solvent to obtain a polyimide solution; applying the polyimide solution onto the electrode layer; and Heating the solution.

  According to the production method of the present invention, since the moisture-sensitive film is formed by removing the solvent from the polyimide solution on the substrate, the moisture-sensitive film can be formed at a relatively low temperature in a short time. For this reason, mass productivity of the humidity detecting element can be improved. Further, thermal deterioration of the substrate can be prevented. Furthermore, since the moisture-sensitive film is formed by removing the solvent from the polyimide solution on the substrate, the homogeneity of the obtained moisture-sensitive film is lower than when the moisture-sensitive film is formed by polymerization and imidization on the substrate. The undulation on the surface of the moisture-sensitive film is sufficiently prevented. For this reason, it is not necessary to process the moisture-sensitive film due to the undulation, and the mass productivity can be sufficiently improved. Further, according to the method of manufacturing the capacitance-type humidity detection element of the present invention, it is possible to obtain the capacitance-type humidity detection element capable of accurately indicating the original humidity even in a high-temperature and high-humidity environment.

  The temperature at which the polyimide solution is heated is preferably from 100 to 280 ° C, more preferably from 200 to 250 ° C. If the heating temperature of the polyimide solution is lower than 100 ° C., the solvent tends to remain and cause a change with time in the dielectric constant.

  The heating time is preferably several minutes to twenty and several minutes, and more preferably 10 minutes to 20 minutes.

  Furthermore, it is preferable to use a substrate mainly composed of a plastic material having a high heat-resistant temperature as the substrate. In this case, it is possible to obtain a humidity detecting element having improved lightness and impact resistance as compared with a case where a substrate mainly containing a material other than the plastic material is used. As the plastic material, a known material can be used as long as the heat resistance temperature is equal to or higher than the heat treatment temperature of the moisture-sensitive film. For example, polyimide, a fluoropolymer, or the like can be used. In order to further increase the sensitivity of the humidity detecting element, it is preferable that the plastic material has a lower hygroscopic property than the moisture-sensitive film.

  In order to further strengthen the adhesion between the moisture-sensitive film and the electrode layer, the surface of the electrode layer on which the moisture-sensitive film is to be formed is formed after the step of forming the electrode layer and before the step of forming the moisture-sensitive film. It is desirable to have a step of at least partially treating the surface with a silane coupling agent. Thereby, the interface strength between the moisture-sensitive film and the electrode layer is enhanced, and the adhesiveness is enhanced. As a result, in the obtained humidity detecting element, the intrusion of moisture into the interface is reduced, and the change in the capacity drift under a high-temperature and high-humidity environment can be effectively suppressed for a long period of time.

Advantageous Effects of Invention According to the present invention, it is possible to provide a capacitance-type moisture-sensitive element and a method for manufacturing the capacitance-type moisture-sensitive element which can be formed at a relatively low temperature in a short time and have high mass productivity.
Note that the present invention does not depend on these effects.

  Hereinafter, an embodiment of the present invention will be described with reference to the drawings. FIG. 1 is a partially cutaway perspective view of a capacitance type humidity detecting element according to a first embodiment of the present invention. In FIG. 1, the moisture-sensitive film 3 is sandwiched between a first electrode layer 2 and a second electrode layer 4. Lead wires 5 are connected to the first electrode layer 2 and the second electrode layer 4, respectively, so that a change in the capacitance value corresponding to the relative humidity of the moisture-sensitive film 3 can be detected. Therefore, the relative humidity can be determined based on the detected change in the capacitance value of the moisture-sensitive film 3 and the correlation between the previously determined capacitance value and the relative humidity.

  The first electrode layer 2, the moisture-sensitive film 3, and the second electrode layer 4 form a humidity detecting element main body, and the humidity detecting element main body is provided on the substrate 1. Here, the first electrode layer 2 of the humidity sensing element main body is directed to the substrate 1 side, and the second electrode layer 4 is directed to the opposite side to the substrate 1. That is, in the humidity sensing element, the first electrode layer 2 is formed on the substrate 1 side of the moisture sensitive film 3 and the second electrode layer 4 is formed on the surface of the moisture sensitive film 3 opposite to the substrate 1. ing.

（上記式中、Ｒ^０は、単結合、−ＳＯ_２−、−ＣＯ−、−Ｏ−、−Ｓ−、アルキレン基又はアリーレン基を表し、Ｒ^１、Ｒ^２は、それぞれ独立にアルキル基又はハロゲン原子を表し、ｐ、ｑはそれぞれ０〜４の整数を表す）で表されるものであってもよい。この芳香族ジアミンを用いることで、ポリイミドが有機極性溶媒に可溶になる。上記一般構造式（１）で表される芳香族ジアミンとしては、例えば４、４’−ジアミノジフェニルスルホン等が用いられる。 The moisture-sensitive film 3 contains, as a main component, a polyimide obtained by polymerizing biphenylsulfonetetracarboxylic dianhydride and an aromatic diamine. With such a configuration of the moisture-sensitive film 3, the drift change of the output value with respect to the relative humidity can be sufficiently reduced even in a high-temperature and high-humidity environment. Further, the temperature dependency of the output value with respect to the relative humidity can be reduced. Here, as the biphenylsulfonetetracarboxylic dianhydride, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride is preferably used because of its high heat resistance. Further, when a polyimide is polymerized by using this biphenylsulfonetetracarboxylic dianhydride, the aromatic diamine may be a polyimide containing a hydrogen atom, a halogen element, or a substituent having 0 to 4 carbon atoms. Compounds having two good phenyl groups are preferred. With such a compound, Tg (glass transition point) tends to be high, and as a result, the drift of the element tends to be small and the temperature dependency tends to be small. And among such compounds, p-phenylenediamine, m-phenylenediamine, 4,4'-diaminodiphenylmethane, 4,4'-diaminodiphenylether, 4,4'-diaminodiphenyl sulfide, diaminotoluene, diaminodiphenylsulfone And at least one of bis (aminophenoxy-phenyl) sulfone are more preferably used. By using such an aromatic diamine, even a polyimide after polymerization becomes soluble in an organic polar solvent. The drift can be reduced by reducing the residual stress in the moisture-sensitive film as compared with the conventional process of polymerizing and imidizing on the substrate. The aromatic diamine is represented by the following structural formula (1):

(In the above formula, R ⁰ represents a single bond, —SO ₂ —, —CO—, —O—, —S—, an alkylene group or an arylene group, and R ¹ and R ² each independently represent an alkyl group or A halogen atom, and p and q each represent an integer of 0 to 4). By using this aromatic diamine, the polyimide becomes soluble in the organic polar solvent. As the aromatic diamine represented by the general structural formula (1), for example, 4,4′-diaminodiphenyl sulfone or the like is used.

  It is preferable that at least a part of the surface of the first electrode layer 2 is surface-treated with a silane coupling agent. In this case, the interfacial strength between the moisture-sensitive film 3 and the first electrode layer 2 is enhanced, the peeling of the moisture-sensitive film 3 and the first electrode layer 2 is sufficiently prevented for a long period of time, and the penetration of moisture into the interface is prevented. And a change in drift of the capacity under a high-temperature and high-humidity environment can be effectively suppressed over a long period of time.

  Further, as shown in FIG. 1, in the capacitance type humidity detecting element of the present embodiment, the second electrode layer 4 has a mesh shape. That is, the second electrode layer 4 has a large number of through holes 4a. By forming the second electrode layer 4 in a mesh shape in this manner, sufficient air permeability can be ensured, and the thickness of the second electrode layer 4 can be increased. For this reason, the adhesiveness and mechanical strength between the moisture-sensitive film 3 and the second electrode layer 4 are sufficiently increased as compared with the case where the second electrode layer 4 is not mesh-shaped, that is, the case where there are not many through holes. be able to.

  The material of the first electrode layer 2 is not particularly limited as long as it is a conductive material. Examples of the material of the first electrode layer 2 include nickel, chromium, titanium, tantalum, molybdenum, silicon, and the like. The above can be used in combination.

  The material of the second electrode layer 4 may be any material that can form a moisture-permeable electrode layer, that is, any conductive material having moisture permeability. Such a conductive material may be appropriately selected from the viewpoint of corrosion resistance and adhesion, and for example, gold, platinum, aluminum, chromium, carbon, or the like, or a combination of two or more thereof can be used.

  As the substrate 1, for example, a glass substrate, an alumina substrate, a quartz substrate, a substrate made of thermally oxidized silicon, a substrate mainly composed of a plastic material, or the like can be used. Among them, a substrate mainly composed of a plastic material is preferable. By using a substrate containing a plastic material as a main component, it is possible to reduce the weight of the humidity detecting element and improve impact resistance as compared with a case where a substrate containing a material other than the plastic material as a main component is used. As the plastic material, a known material can be used as long as the weight of the humidity detecting element can be reduced and the impact resistance can be improved and the heat resistance temperature is equal to or higher than the heat treatment temperature of the moisture sensitive film 3. Polyimide, fluoropolymer, or the like can be used. In order to increase the sensitivity of the humidity detecting element, it is preferable that this plastic material has lower hygroscopicity than the moisture sensitive film 3.

  For example, a chromium electrode is used as a first electrode layer on a glass substrate, and a moisture-sensitive film is formed of 3,3 ′, 4,4′-biphenylsulfonetetracarboxylic dianhydride and 4,4′-diaminodiphenyl ether. By using an element having a configuration in which polymerized polyimide is used and the second electrode layer is made of gold, the adhesion between the electrode and the moisture-sensitive film is particularly improved, and a highly reliable capacitance-type humidity detecting element is obtained.

  The method for manufacturing the humidity sensing element in the present embodiment is as follows.

  First, a first electrode layer 2 is formed on a substrate 1. As described above, as the substrate 1, for example, a glass substrate, an alumina substrate, a quartz substrate, a substrate made of thermally oxidized silicon, a substrate mainly composed of a plastic material, or the like can be used. Here, a substrate mainly composed of a plastic material is preferably the same as described above. As described above, as the plastic material, a plastic material whose heat-resistant temperature is equal to or higher than the heat treatment temperature of the moisture-sensitive film 3, for example, polyimide, fluoropolymer, or the like can also be used.

  The first electrode layer 2 can be formed by an evaporation method, a sputtering method, or the like. The patterning of the first electrode layer 2 can be performed by forming a resist pattern by photolithography and etching. As a material of the first electrode layer 2, for example, chromium, titanium, tantalum, or the like can be used as described above.

  Here, when surface treatment is performed on the first electrode layer 2 with a silane-based coupling agent, the surface treatment is performed after the formation of the first electrode layer 2. By this surface treatment, the interface strength between the moisture-sensitive film 3 and the first electrode layer 2 by the silane coupling agent is enhanced, and the adhesion between the moisture-sensitive film 3 and the first electrode layer 2 is sufficiently increased. Can be. As a result, in the obtained humidity detecting element, the peeling of the moisture-sensitive film 3 and the first electrode layer 2 is sufficiently prevented for a long period of time, the penetration of moisture into the interface is reduced, and the capacity in a high-temperature and high-humidity environment is reduced. Can effectively be suppressed from changing over a long period of time. In the surface treatment, for example, the substrate 1 on which the first electrode layer 2 is formed is immersed in a silane coupling agent and subjected to drying and heat treatment, or the silane coupling agent is dropped on the first electrode layer 2 Then, drying and heat treatment are performed.

  Next, the moisture-sensitive film 3 is formed on the first electrode layer 2. The moisture-sensitive layer 3 can be formed by spin-coating a polyimide solution obtained by dissolving polyimide in an organic polar solvent on the first electrode layer 2, and then heating the polyimide solution. The heating temperature of the polyimide solution is preferably 100 to 280C, more preferably 200 to 250C. If the heating temperature is lower than 100 ° C., the solvent tends to remain and cause a change with time in the dielectric constant. The heating time is preferably from several minutes to twenty and several minutes, more preferably from 10 minutes to 20 minutes.

  The organic polar solvent is not particularly limited as long as it can dissolve the polyimide. As such an organic polar solvent, for example, N-methyl-2-pyrroline can be used.

  The patterning of the moisture-sensitive layer 3 can be performed by forming a resist pattern by photolithography and etching. In order to increase the adhesion between the first electrode layer 2 and the moisture-sensitive film 3, it is preferable to perform heat treatment again after removing the resist.

  Next, a second electrode layer 4 is formed on the moisture-sensitive film 3. As described above, the material of the second electrode layer 4 may be any material that can form a moisture-permeable electrode layer, and for example, gold, platinum, aluminum, chromium, or the like can be used. The formation of the second electrode layer 4 can be performed by an evaporation method, a sputtering method, or the like. The patterning of the second electrode layer 4 can be performed by forming a resist pattern by photolithography and etching.

  In order to strengthen the adhesion between the moisture-sensitive film 3 and the second electrode layer 4, as shown in FIG. 1, the second electrode layer 4 is formed in a mesh shape. In this case, the second electrode layer 4 can be formed by evaporation using a resist pattern or a comb-shaped or mesh-shaped mask.

  In the above manufacturing method, a moisture-sensitive film 3 is formed by applying a polyimide solution containing a polyimide which is a polymer on the substrate 1 and removing the organic polar solvent from the solution. The wet film 3 can be formed. For this reason, mass productivity of the humidity detecting element can be improved. In addition, it is possible to prevent thermal deterioration of the substrate 1. Furthermore, since the moisture-sensitive film 3 is formed by removing the solvent from the polyimide solution on the substrate 1, the obtained moisture-sensitive film 3 can be compared with the case where the moisture-sensitive film 3 is formed on the substrate 1 by polymerization and imidization. 3 becomes more uniform, and the occurrence of undulation on the surface of the moisture-sensitive film 3 is sufficiently prevented. For this reason, it is not necessary to process the moisture-sensitive film 3 due to the undulation, and the mass productivity can be sufficiently increased. Further, by the above manufacturing method, it is possible to obtain a capacitance type humidity detecting element capable of accurately indicating the original humidity even under a high temperature and high humidity environment.

  Next, a second embodiment of the capacitance type humidity detecting element of the present invention will be described with reference to FIG.

  FIG. 2 is an exploded perspective view of the capacitance type humidity detecting element according to the second embodiment of the present invention. Note that, in FIG. 2, the same or equivalent components as those of the humidity detecting element according to the first embodiment are denoted by the same reference numerals.

  As shown in FIG. 2, in the capacitance type humidity detecting element of the present embodiment, the electrode layer 6 as the second electrode layer is provided on the surface of the moisture sensitive layer 3 on the side opposite to the substrate 1 side. However, the second embodiment differs from the first humidity sensing element in that the first moisture sensing element is provided on the surface of the moisture sensitive layer 3 on the substrate 1 side. That is, in the present embodiment, the electrode layer 6 as the first electrode layer and the electrode layer 7 as the second electrode layer are provided on the same side as the substrate 1 with respect to the moisture-sensitive film 3. The electrode layer 6 and the electrode layer 7 are sandwiched between the moisture-sensitive film 3 and the substrate 1. A lead wire 5 is connected to each of the electrode layers 6 and 7 so that a change in the capacitance value corresponding to the relative humidity of the moisture-sensitive film 3 can be detected. Therefore, the relative humidity can be determined based on the detected change in the capacitance value of the moisture-sensitive film 3 and the correlation between the previously determined capacitance value and the relative humidity.

  The method of manufacturing the humidity detecting element of the present embodiment is similar to that of the first embodiment except that the second electrode layer 4 is formed on the substrate 1 together with the first electrode layer 2 before the formation of the moisture-sensitive film 3. This is the same as the method for manufacturing the humidity detecting element according to the above.

で表されるものであってもよい。 The present invention is not limited to the embodiments described above. For example, in the above embodiment, 3,3 ′, 4,4′-diphenylsulfonetetracarboxylic dianhydride is used as biphenylsulfonetetracarboxylic dianhydride. And the following general structural formula (2):

May be represented by

で表される基を表し、Ｒ^４，Ｒ^５はそれぞれ独立に、水素原子、−ＳＯ_２Ｒ^６又は前記構造式（３）で表される基を表し、Ｒ^６はアリール基又は炭化水素基を表す。 However, in the above formula, R ³ is —SO ₂ — or the following structural formula (3):

Wherein R ⁴ and R ⁵ each independently represent a hydrogen atom, —SO ₂ R ⁶ or a group represented by the structural formula (3), and R ⁶ represents an aryl group or a hydrocarbon group. Represents

  By using the biphenylsulfonetetracarboxylic dianhydride represented by the general structural formula (2), the homogeneity of the moisture-sensitive film 3 is further improved. For this reason, processing on the moisture-sensitive film 3 due to the non-uniformity of the moisture-sensitive film 3 becomes unnecessary, and it is possible to sufficiently prevent a decrease in the yield, thereby achieving cost reduction.

As biphenylsulfonetetracarboxylic dianhydride represented by the above structural formula, R ³ is —SO ₂ — or a compound represented by the above structural formula (3), and R ⁴ and R ⁵ are each a hydrogen atom. However, it is also possible to use those in which R ³ is —SO ₂ — and R ⁴ and R ⁵ are —SO ₂ R ⁶ .

  Hereinafter, the present invention will be described in more detail with reference to Examples and Comparative Examples.

(Example 1)
In Example 1, the variable-capacitance humidity element was prepared as follows. First, a first electrode layer 2 (0.2 μm thick) was formed on a glass substrate by masking with a metal mask and chromium was deposited by a vacuum deposition method. Thereafter, a polyimide obtained by polymerizing 3,3 ′, 4,4′-biphenylsulfonetetracarboxylic dianhydride and 4,4′-diaminodiphenyl ether was dissolved in N-methyl-2-pyrrolidone as an organic polar solvent. Then, a polyimide solution was prepared, and the polyimide solution was spin-coated on the first electrode layer 2 and baked at 200 ° C. for 10 minutes. Next, a positive type photoresist was spin-coated, prebaked, exposed, developed, and resist-removed to form a moisture-sensitive film 3 (2 μm thick). Finally, masking was performed using a mesh-shaped metal mask, and gold was deposited by a vacuum deposition method to form a second electrode layer 4 (1 μm in thickness).

で表されるγ−アニリノプロピルトリメトキシシラン（ＡｎＰＳ）及び酢酸を、水とイソプロピルアルコール（ＩＰＡ）とを１０：９０の割合で混合した混合溶媒にそれぞれ溶解した溶液を作成した。このとき、ＡｎＰＳ及び酢酸の濃度はそれぞれ1質量％となるようにした。そして、その溶液を第１の電極層を形成したガラス基板上に滴下し、１２０℃のオーブンにて２０分間熱処理して、第１の電極層の全体をシラン系カップリング剤で表面処理した。その他の湿度検知素子の製造条件、即ち感湿膜の形成条件及びその後の第２の電極層の形成条件は、実施例１と同様とした。 (Example 2)
The following structural formula (4):

Were prepared by dissolving γ-anilinopropyltrimethoxysilane (AnPS) and acetic acid, respectively, in a mixed solvent of water and isopropyl alcohol (IPA) at a ratio of 10:90. At this time, the concentrations of AnPS and acetic acid were each set to 1% by mass. Then, the solution was dropped on the glass substrate on which the first electrode layer was formed, and heat-treated in an oven at 120 ° C. for 20 minutes, and the entire first electrode layer was surface-treated with a silane coupling agent. The other manufacturing conditions for the humidity detecting element, that is, the conditions for forming the moisture-sensitive film and the subsequent conditions for forming the second electrode layer were the same as those in Example 1.

(Comparative Example 1)
For comparison with Example 1, instead of 3,3 ′, 4,4′-biphenylsulfonetetracarboxylic dianhydride used in producing the moisture-sensitive film 3 of Example 1, 3,3 ′, It was polymerized with 4,4'-diaminodiphenyl ether using 4,4'-pyromellitic dianhydride to prepare a polyamic acid requiring imidization treatment. This polyamic acid was spin-coated on the first electrode layer 2 and prebaked at 140 ° C. for 10 minutes. Next, a positive photoresist was spin-coated, and prebaking, exposure, development, and resist removal were performed. Thereafter, heat treatment was performed at 350 ° C. for 1 hour to form a moisture-sensitive film 3 having a thickness of 2 μm. The other manufacturing conditions of the humidity detecting element, that is, the material of the substrate used, the conditions for forming the first electrode layer, and the conditions for forming the second electrode layer were the same as those in Example 1.

(Comparative Example 2)
For comparison with Example 1, instead of the moisture-sensitive film 3 of Example 1, 3,3 ′, 4,4′-biphenyltetracarboxylic dianhydride and 4,4′-diaminodiphenyl ether were polymerized. The resulting polyimide was used. Other manufacturing conditions of the humidity detecting element, that is, the material of the substrate used, the forming condition of the first electrode layer, the forming condition of the moisture sensitive film, and the forming condition of the second electrode layer were the same as those of the first embodiment.

で表される化合物とを重合してなるポリイミドを用いた。その他の湿度検知素子の製造条件、即ち使用した基板の材質、第１の電極層の形成条件、感湿膜の形成条件及び第２の電極層の形成条件は、実施例１と同様とした。 (Comparative Example 3)
For comparison with Example 1, instead of the moisture-sensitive film 3 of Example 1, 3,3 ′, 4,4′-biphenylsulfonetetracarboxylic dianhydride and the following structural formula (5):

A polyimide obtained by polymerizing a compound represented by the following formula was used. Other manufacturing conditions of the humidity detecting element, that is, the material of the substrate used, the forming condition of the first electrode layer, the forming condition of the moisture sensitive film, and the forming condition of the second electrode layer were the same as those of the first embodiment.

  With respect to the humidity detecting elements of Examples 1 and 2 and Comparative Examples 1, 2 and 3 manufactured as described above, the moisture sensitivity was evaluated as follows.

  The conditions for evaluating the humidity sensitivity are as follows. First, the capacitance value of the device obtained in Example 1 was measured at 5 ° C., 25 ° C., and 45 ° C. in a relative humidity range of 5 to 95%. FIG. 3 shows the measurement results.

  In addition, a predetermined humidity atmosphere was created using a split flow type precision humidity generator (manufactured by Shinei). The electric capacity was measured at a frequency of 10 KHz using an LCR meter (manufactured by HEWLETT PACKARD).

  From the above measurement results, it was found that the humidity dependency of the humidity detecting element of Example 1 was within ± 2% at any relative humidity, and that the humidity sensing element had low temperature dependency and good moisture sensitivity was obtained.

  Further, for Example 1, Example 2, and Comparative Examples 1, 2, and 3, the drift amount of the capacity under a high-temperature and high-humidity environment (60 ° C., 95% RH, 1000 hours) was measured in terms of relative humidity.

  As a result, the drift amount of the capacitance was 3% RH relative to the initial value in terms of relative humidity in the humidity detecting element of Example 1 and 2% RH in the humidity detecting element of Example 2, The humidity detecting element of Comparative Example 1 has an initial value of 18% RH, the humidity detecting element of Comparative Example 2 has an initial value of 6% RH, and the humidity detecting element of Comparative Example 3 has an initial value of 18% RH. It was 5% RH for the value. In other words, the humidity sensing elements in Examples 1 and 2 had less capacitance drift under high temperature and high humidity than the humidity sensing elements in Comparative Examples 1, 2 and 3. Therefore, it was found that the humidity detecting elements in Examples 1 and 2 were superior to the humidity detecting elements in Comparative Examples 1, 2 and 3 in recoverability to the initial value.

  As described above, according to the present invention, it is possible to form a film by heat treatment at a relatively low temperature of 200 ° C. and several minutes to about several tens of minutes in order to improve the moisture sensitivity of the moisture sensitive film. Do you get it. From this, it was found that a humidity detecting element which can prevent thermal deterioration of the substrate and has high mass productivity can be obtained. Further, from the evaluation results of the temperature dependence of the humidity sensitivity characteristics of Example 1, according to the capacitance-type humidity detecting element of the present invention, the drift amount of 3% or less, which is a practical target, even in a high-temperature and high-humidity environment. It was found that it was possible to accurately indicate the original humidity.

  Further, in the humidity detecting element of the first embodiment and the humidity detecting element of the second embodiment, the humidity detecting element of the second embodiment has a smaller capacitance drift amount. It has been found that when surface treatment is performed with a coupling agent, an increase in the capacitance value can be suppressed even when left for a long time in a high-temperature, high-humidity atmosphere. This is presumably because the surface treatment of the first electrode layer with the silane coupling agent improved the adhesion between the moisture-sensitive film and the metal electrode.

  Although the present invention has been described with reference to the embodiment and the examples, those skilled in the art can arrive at various changes or modifications within the scope of the technical idea described in the claims. It is obvious that they belong to the technical scope of the present invention.

1 is a partially cutaway perspective view showing a configuration of a humidity detecting element according to a first embodiment of the present invention. It is an exploded perspective view showing the composition by the 2nd embodiment of the humidity sensing element by the present invention. FIG. 4 is a diagram illustrating humidity sensitivity characteristics according to an embodiment of the humidity detecting element according to the present invention.

Explanation of reference numerals

DESCRIPTION OF SYMBOLS 1 ... Substrate 2 ... 1st electrode layer 3 ... Moisture sensitive film 4 ... 2nd electrode layer 5 ... Lead wire 6, 7 ... Electrode layer

Claims (11)

A substrate, and a moisture-sensitive film having at least two electrode layers,
The humidity sensor according to claim 1, wherein the moisture-sensitive film is mainly composed of polyimide obtained by polymerizing biphenylsulfonetetracarboxylic dianhydride and aromatic diamine.   The capacitance type humidity sensing element according to claim 1, wherein the biphenylsulfonetetracarboxylic dianhydride is 3,3 ', 4,4'-biphenylsulfonetetracarboxylic dianhydride. The capacitance-type humidity sensing element according to claim 1, wherein the aromatic diamine has at least one of the following (a) to (h).
(A) p-phenylenediamine (b) m-phenylenediamine (c) 4,4'-diaminodiphenylmethane (d) 4,4'-diaminodiphenyl ether (e) 4,4'-diaminodiphenyl sulfide (f) diaminotoluene (G) diaminodiphenyl sulfone (h) bis (aminophenoxy-phenyl) sulfone The aromatic diamine has the following structural formula (1):

(In the above formula, R ⁰ represents a single bond, —SO ₂ —, —CO—, —O—, —S—, an alkylene group or an arylene group, and R ¹ and R ² each independently represent an alkyl group or Represents a halogen atom, p and q each represent an integer of 0 to 4)
The capacitance-type humidity detecting element according to claim 1 or 2, wherein:   At least one of the at least two electrode layers is formed on a surface of the moisture-sensitive film on the substrate side, and at least a part of a surface of the electrode layer that contacts the moisture-sensitive film is a silane-based cup. The capacitance-type humidity detecting element according to any one of claims 1 to 4, which is surface-treated with a ring agent.   Of the at least two electrode layers, a first electrode layer is formed on a surface of the moisture-sensitive film on the substrate side, and a second electrode layer is formed on a surface of the moisture-sensitive film on the opposite side to the substrate. The capacitance type humidity sensing element according to claim 1, wherein the second electrode layer has moisture permeability.   The capacitance type humidity sensing element according to claim 6, wherein the second electrode layer is formed in a mesh shape.   The capacitance-type humidity detecting element according to claim 1, wherein the substrate is mainly composed of a plastic material. The biphenylsulfonetetracarboxylic dianhydride has the following general structural formula (2):

(In the above formula, R ³ is —SO ₂ — or the following structural formula (3):

Wherein R ⁴ and R ⁵ each independently represent a hydrogen atom, —SO ₂ R ⁶ or a group represented by the structural formula (3), and R ⁶ represents an aryl group or a hydrocarbon group. Represents)
The capacitance-type humidity detecting element according to claim 1, wherein the element is represented by: A method for manufacturing a capacitance-type humidity sensing element including a step of sequentially forming an electrode layer and a moisture-sensitive film on a substrate,
The step of forming the moisture-sensitive film, dissolving a polyimide obtained by polymerizing biphenylsulfonetetracarboxylic dianhydride and an aromatic diamine in an organic polar solvent to obtain a polyimide solution,
Applying the polyimide solution on the electrode layer,
Heating the polyimide solution,
A method for manufacturing a capacitance-type humidity detecting element, comprising:   After the step of forming the electrode layer and before the step of forming the moisture-sensitive film, a step of surface-treating at least a part of the surface of the electrode layer on which the moisture-sensitive film is formed with a silane coupling agent. The method for manufacturing a capacitance-type humidity sensing element according to claim 10, further comprising:

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