JP2001249099A - Electrostatic capacity humidity sensor and humidity measuring instrument - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a electrostatic capacity humidity sensor excellent in the following properties to a humidity change, environment resistance and durability and capable of accurately measuring humidity without requiring the correction of temperature. SOLUTION: In the electrostatic capacity humidity sensor 1 constituted by successively forming a lower electrode 3, a humidity-sensitive film 4 using an organic compound having a hydrophilic group and an upper electrode 5 on an insulating substrate 2, the humidity-sensitive film 4 is formed based on a fluoric organic compound.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type humidity sensor comprising a lower electrode, a moisture-sensitive film using an organic compound having a hydrophilic group, and an upper electrode formed sequentially on an insulating substrate. And a humidity measuring device provided with the capacitance type humidity sensor.

[0002]

2. Description of the Related Art As a capacitive humidity sensor of this type,
A capacitance type humidity sensor 21 shown in FIG. 3 is conventionally known. The capacitance type humidity sensor 21 includes a lower electrode 3 formed on a glass substrate 2 as an insulating substrate, a polyimide thin film 24 formed on the lower electrode 3, and a polyimide thin film 24 formed in a direction orthogonal to the lower electrode 3. And an upper electrode 5 formed on the thin film 24. When manufacturing the capacitance type humidity sensor 21, first, the lower electrode 3 is formed on the glass substrate 2 by, for example, vapor deposition of a conductive metal. Next, polyamic acid, which is a precursor of polyimide, is applied to one surface of the glass substrate 2 by spin coating, dipping, or the like, and then the polyamic acid near the edge of the glass substrate 2 is removed by a predetermined process. Thereafter, a heat treatment is performed in a heater at about 250 ° C. for about 1 hour to imidize the polyamic acid to form a polyimide thin film 24. Next, a conductive metal is deposited on the glass substrate 2 in that state to form the upper electrode 5. Thus, the capacitance type humidity sensor 21 is completed.

In the capacitance type humidity sensor 21, since the polyimide used as the moisture-sensitive film has an imide bond, the hydrophilicity is high and moisture is absorbed in a short time. In the capacitance type humidity sensor 21, the lower electrode 3
And the intersection of the upper electrode 5 is MIM (Metal-In
It functions as a sulator-metal) type capacitor. In this case, the relative dielectric constant εr of polyimide is a low value of about 3, while the relative dielectric constant εr of water is 80 at about 25 ° C.
It is a high value before and after. Therefore, when the polyimide thin film 24 absorbs moisture, the capacitance between the lower electrode 3 and the upper electrode 5 increases as compared to the dry state. Accordingly, the polyimide thin film 24 based on the measurement reference data obtained by previously measuring each capacitance of the polyimide thin film 24 in which a predetermined amount of moisture has been absorbed, and the measured capacitance between the lower electrode 3 and the upper electrode 5. Thus, it is possible to measure the amount of water absorbed, that is, the humidity at the place where the capacitance type humidity sensor 21 is installed.

[0004]

However, the conventional capacitance type humidity sensor 21 has the following problems. That is, polyimide is generally inferior in hydrophobicity. Therefore, in the capacitance type humidity sensor 21, when the humidity suddenly drops, the state that the moisture absorbed before that is still left in the polyimide thin film 24 is maintained for a long time. In such a case, a state in which excess moisture is absorbed by the polyimide thin film 24 in excess of the moisture amount corresponding to the original ambient humidity, so that the capacitance between the lower electrode 3 and the upper electrode 5 is originally measured. The value becomes larger than the capacitance to be performed. That is, the conventional capacitance type humidity sensor 21 has a hysteresis with respect to the humidity change, and as a result, there is a problem that the follow-up property with respect to the humidity change is poor. Therefore, when the humidity is measured based on the capacitance and the measurement reference data, the humidity may be erroneously measured to be higher than the actual humidity. In this case, the hydrophobicity of the polyimide thin film 24 can be improved to some extent by forming the polyimide thin film 24 thinner. However, in such a case, the polyimide thin film 24 is liable to be greatly deteriorated, so that another problem that the durability of the capacitance type humidity sensor 21 is significantly reduced occurs.

Also, a polyimide thin film 24 as a moisture-sensitive film
Has a temperature characteristic in which the relative permittivity εr varies with temperature. Therefore, when measuring humidity using the capacitance-type humidity sensor 21, the measured value must be corrected in accordance with the ambient temperature, and this temperature correction is complicated, and the measurement accuracy is reduced. There is a problem that it is. Furthermore, polyimide has poor chemical resistance, especially against alkaline chemicals, and tends to deteriorate under high temperature and high humidity. Therefore, the conventional capacitance type humidity sensor 21 has a problem that its durability is low.

The present invention has been made in view of the above problems, and has excellent follow-up characteristics to humidity changes, environmental resistance and durability, and can accurately measure humidity without requiring temperature correction. A main object is to provide a capacitance type humidity sensor and a humidity measuring device.

[0007]

According to a first aspect of the present invention, there is provided a capacitance type humidity sensor comprising: a lower electrode, a moisture-sensitive film using an organic compound having a hydrophilic group, and an upper electrode having an insulating property; In a capacitance type humidity sensor formed sequentially on a substrate, the moisture-sensitive film is formed mainly of a fluorine-based organic compound. In this case, the “hydrophilic group” in the present invention includes an imide group, a hydroxyl group, a carboxyl group, an amino group, a carbonyl group and the like.

According to a second aspect of the present invention, there is provided a capacitance type humidity sensor.
2. The capacitance-type humidity sensor according to claim 1, wherein the moisture-sensitive film is formed mainly of fluorinated polyimide.

According to a third aspect of the present invention, there is provided a humidity measuring apparatus.
Or a capacitance type humidity sensor according to item 2.

[0010]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS Preferred embodiments of a capacitance type humidity sensor according to the present invention will be described below with reference to the accompanying drawings. The conventional capacitance type humidity sensor 21
The same components as those described above are denoted by the same reference numerals, and redundant description is omitted.

First, the configuration of the capacitance type humidity sensor 1 will be described with reference to FIG.

The capacitance type humidity sensor 1 includes a glass substrate 2 corresponding to an insulating substrate in the present invention, and a lower electrode 3, a fluorinated polyimide thin film 4, and an upper electrode 5 formed on the glass substrate 2, respectively. It has. In this case, the lower electrode 3 and the upper electrode 5 are formed of a conductive metal so as to intersect at the center of the glass substrate 2 with the fluorinated polyimide thin film 4 interposed therebetween. Further, the upper electrode 5 is formed by forming countless fine air holes. For this reason, the surrounding moisture easily passes through the upper electrode 5 and is absorbed by the fluorinated polyimide thin film 4, and
The structure is such that moisture in the fluorinated polyimide thin film 4 can be easily removed. Further, the intersection of the lower electrode 3 and the upper electrode 5 functions as an MIM type capacitor in the same manner as the conventional capacitance type humidity sensor 21.
On the other hand, the fluorinated polyimide thin film 4 corresponds to the moisture-sensitive film in the present invention, and is formed in the same shape as the conventional capacitance type humidity sensor 21. In this case, in the capacitance type humidity sensor 1, the responsiveness in both the hydrophilicity and the hydrophobicity is improved by using the fluorinated polyimide thin film 4 in which the fluorinated polyimide is thinned.

Next, a method of manufacturing the capacitance type humidity sensor 1 will be described.

First, the glass substrate 2 is boiled with alcohol and washed to remove foreign matter and oil adhering to the surface. Next, a lower electrode 3 is formed on the glass substrate 2 by depositing a conductive metal such as gold in a vacuum.
Form on top. Next, a polyamic acid solution (Poly [4,4 ′) in which polyamic acid, which is a precursor of fluorinated polyimide, is dissolved in a solvent at the center of the glass substrate 2 in this state.
-(hexafluoroisopropylidene) diphthalicanhidride-co-
4,4'-oxydianiline], amic acid 15% solutionin 1-met
After applying hyl-2-pyrrolidone / aromatichydorocarbon 75/25), the glass substrate 2 is heat-treated in a heater at about 250 ° C. for about 1 hour. As a result, the fluorinated polyimide thin film 4 is formed on the glass substrate 2 by imidizing the precursor of the fluorinated polyimide.

Next, the upper electrode 5 is formed on the glass substrate 2 in that state. At this time, by placing the glass substrate 2 at an angle with respect to the deposition source, a conductive metal such as gold is deposited on the glass substrate 2 from obliquely above. As a result, the conductive metal is deposited on the projections of the fine irregularities on the surface of the fluorinated polyimide thin film 4. For this reason, fine ventilation holes are formed in the concave portions, so that moisture in the atmosphere can easily pass through the upper electrode 5. Thus, the capacitance type humidity sensor 1 is completed.

Next, the humidity detection performance and environmental resistance of the capacitance type humidity sensor 1 will be specifically described.

In the capacitance type humidity sensor 1, the fluorinated polyimide thin film 4 has the hydrophilic property of the polyimide,
It has both properties of the hydrophobic property of fluorine. In this case, in the fluorinated polyimide thin film 4 according to the embodiment of the present invention, when polyamic acid is generated as a precursor of the fluorinated polyimide, a part of hydrogen atoms in the polyamic acid molecule is replaced with fluorine atoms. I have. Therefore, at the time of generation of this precursor, the number of hydrogen atoms to be replaced with fluorine atoms is appropriately increased or decreased to control both the hydrophilicity and the hydrophobicity, thereby providing an ideal moisture-sensitive film for detecting humidity. The capacitance type humidity sensor 1 is manufactured. For this reason, the capacitance-type humidity sensor 1 has a good followability without a hysteresis to a sudden change in humidity.

More specifically, as shown in FIG. 1, the amount of change per unit time is kept constant and the humidity is changed from 0% to 80%.
When the humidity is raised to 40% and then lowered again to 40%, the capacitance when the humidity is 40% and the humidity is 40% is 12%.
04pF, and the capacitance when the humidity is reduced to 40% after the humidity is once increased to 80% is 1220.
pF. Therefore, it can be understood that the values are almost the same and the hysteresis hardly occurs. As described above, in the capacitance-type humidity sensor 1, the moisture-sensitive film is formed using the fluorinated polyimide having both the hydrophilic property and the hydrophobic property. Can be absorbed and released. Therefore, even when the humidity changes rapidly, the humidity can be accurately measured. In addition, this capacitance type humidity sensor 1
In, the relative permittivity εr of the fluorinated polyimide used as the moisture-sensitive film responds only to the relative humidity, and hardly fluctuates with respect to the temperature change. Also, the capacitance value becomes almost constant. For this reason, temperature correction at the time of humidity measurement becomes unnecessary, and humidity can be measured accurately and easily. Furthermore, the chemical stability of the fluorinated polyimide is improved by introducing fluorine. For this reason, the capacitance-type humidity sensor 1 is excellent in chemical resistance and less deteriorated under high temperature and high humidity as compared with the conventional capacitance-type humidity sensor 21 containing polyimide as a main component. Its environmental resistance and durability are improved.

Next, the humidity measuring device 11 according to the present invention will be described with reference to FIG. The humidity measuring device 11
It comprises an electrostatic capacitance type humidity sensor 1, an amplification circuit 12, an A / D conversion circuit 13, a ROM 14 for storing reference data for measuring humidity relative to a measurement capacity, and a measurement unit 15 constituted by a microcomputer, for example. I have. In the humidity measuring device 11, the amplification circuit 12 amplifies the detection signal of the capacitance type humidity sensor 1, and converts the signal into an A / D conversion circuit 13.
Converts the output signal of the amplifier circuit 12 from analog to digital. Next, the measuring unit 15 measures the humidity based on the measured capacity calculated based on the output signal of the A / D conversion circuit 13 and the reference data for measuring the humidity stored in the ROM 14. According to the humidity measuring apparatus 11, since the capacitance type humidity sensor 1 which does not need temperature correction, has no hysteresis, and is excellent in environment resistance and durability is used, it is extremely accurate, quick and long. Humidity can be measured over a period of time.

It should be noted that the present invention is not limited to the configuration shown in the above embodiment of the present invention. For example, in the embodiment of the present invention, an example in which the moisture-sensitive film of the present invention is formed using a fluorinated polyimide has been described, but the fluorine-based organic compound of the present invention is not limited to this, and various organic compounds may be formed of fluorine. A moisture-sensitive film can be formed using the converted raw material. The moisture-sensitive film may be mainly composed of a fluorine-based organic compound, and may be mixed with other various organic compounds. Furthermore, in the embodiment of the present invention, the example in which the glass substrate 2 is used as the insulating substrate in the present invention has been described. However, various types of mica substrate, epoxy substrate, alumina substrate, quartz substrate, surface-insulated silicon wafer, etc. Substrate can be used.

[0021]

As described above, according to the capacitance type humidity sensor according to the first and second aspects, the sensation is based on the fluorinated organic compound (for example, fluorinated polyimide) having excellent hydrophilicity and hydrophobicity as a main component. By forming the wet film, the humidity can be accurately measured even when the humidity changes rapidly. The fluorine-based organic compound has a relative dielectric constant εr
However, since it responds only to relative humidity and has no temperature characteristics, temperature correction at the time of humidity measurement is not required, and accurate and easy humidity measurement can be performed. Further, since the fluorine-based organic compound has excellent environmental resistance, the durability of the capacitance type humidity sensor can be improved.

According to the humidity measuring apparatus of the third aspect, it is possible to measure the humidity extremely accurately, quickly, and over a long period of time.

[Brief description of the drawings]

FIG. 1 is a characteristic diagram showing a characteristic of a capacitance with respect to a relative humidity of a capacitance type humidity sensor 1;

FIG. 2 is a block diagram of the humidity measuring device 11.

FIG. 3 is a structural diagram showing the structures of a capacitance type humidity sensor 1 according to an embodiment of the present invention and a conventional capacitance type humidity sensor 21;

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 Capacitance type humidity sensor 2 Glass substrate 3 Lower electrode 4 Fluorinated polyimide thin film 5 Upper electrode 11 Humidity measuring device

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 2G060 AA01 AB02 AE19 AF10 AG11 BA09 BB10 HA02 HC13 HC19

Claims (3)

[Claims] 1. A capacitance-type humidity sensor comprising a lower electrode, a moisture-sensitive film using an organic compound having a hydrophilic group, and an upper electrode sequentially formed on an insulating substrate, wherein the moisture-sensitive film is An electrostatic capacitance type humidity sensor characterized by being formed mainly of a fluorine organic compound. 2. The capacitance type humidity sensor according to claim 1, wherein the humidity sensitive film is formed mainly of fluorinated polyimide. 3. A humidity measuring device comprising the capacitance type humidity sensor according to claim 1.