JP2529137B2 - Moisture-sensitive element and manufacturing method thereof - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a capacitance type moisture sensitive element using an organic polymer resin material as a moisture sensitive film and a method for manufacturing the same.

[0002]

2. Description of the Related Art Hitherto, as this type of moisture sensitive element,
Moisture-sensitive material formed by using organic polymer such as cellulose acetate butyrate, cellulose acetate propionate, polyamideimide or linear polyimide obtained by polymerizing linear high molecular weight polyamic acid as the moisture-sensitive material. A humidity-sensitive capacitive element has been proposed which utilizes a change in electric capacitance value of a film for humidity detection (Japanese Patent Laid-Open No. 62-889).
No. 51).

[0003]

However, the moisture-sensitive element thus constructed has a high hydrophilicity (a property of attracting water) and a high water absorption rate, so that it is strongly bound to the polymer by its chemical adsorption. Most of the water remains. For this reason, when used for a long time in an atmosphere of high temperature and high humidity of 40 ° C. and 90%, for example, there is a problem that the output value drifts and the long-term stability is insufficient. In addition, there is a problem that the difference (hysteresis) in the moisture sensitivity characteristics between the moisture absorption process and the dehumidification process is small on the low temperature side and increases on the high temperature side, and the sensor response is delayed. Further, when used for a long period of time in a low humidity atmosphere, there was a problem that hysteresis increased. Further, there is a problem that the output value drifts due to the generation of dew condensation and the immersion in water. Further, there is a problem in that the output value of the organic solvent drifts when exposed to an organic solvent atmosphere. Further, when the humidity sensitive element has a temperature characteristic, there is a problem that it is necessary to correct the temperature with the temperature sensitive element (temperature sensor).

Therefore, it is an object of the present invention to provide a humidity sensitive element which has a small hysteresis and a fast sensor response in a use range from low temperature to high temperature and from low humidity to high humidity. Another object of the present invention is to provide a humidity sensitive element capable of obtaining a stable output value even when exposed to conditions such as high humidity, high temperature and high humidity, low humidity exposure, organic solvent atmosphere, dew condensation or water immersion for a long period of time. There is. Another object of the present invention is to provide a humidity sensitive element that has small temperature characteristics and does not require temperature correction.

[0005]

In order to achieve such an object, the moisture-sensitive element according to the present invention comprises a moisture-sensitive film using a polymer obtained by polymerizing an acetylene end-added type polyimide oligomer and its structural isomer. To do. In addition, the method for producing a moisture-sensitive element according to the present invention comprises forming a thin film using an acetylene end-added type polyimide oligomer and its structural isomer as a starting material, and then heat-treating the moisture-sensitive film at a temperature of 200 ° C. or higher in a nitrogen atmosphere. To form.

[0006]

In the moisture-sensitive element of the present invention, the moisture-sensitive film is formed by using the polymer obtained by polymerizing the acetylene end-added type polyimide oligomer and its structural isomer, whereby the water absorption rate (adsorbed water content) becomes small, Hysteresis becomes small. Further, in the method for manufacturing a moisture sensitive element according to the present invention, the water absorption rate is suppressed to be low and the hydrophobicity is improved.

[0007]

Embodiments of the present invention will now be described in detail with reference to the drawings. 1A and 1B are diagrams showing a configuration of an embodiment of a moisture sensitive element according to the present invention. FIG. 1A is a perspective view and FIG. 1B is a plan view thereof. In these figures, 1 is an insulating substrate made of, for example, an alumina substrate, a glass substrate, or a thermally-oxidized silicon substrate, 2 is a lower electrode made of, for example, platinum formed on the upper surface of the insulating substrate 1, and 3 is a lower portion thereof. It is a moisture-sensitive film laminated and applied so as to cross the electrode 2, and this moisture-sensitive film 3 is formed of a moisture-sensitive material obtained by polymerizing an acetylene end-added type polyimide oligomer and its structural isomer. An upper electrode 4 made of, for example, gold is formed on the moisture sensitive film 3. That is, the moisture sensitive film 3 is sandwiched between the lower electrode 2 and the upper electrode 4, and the lead wire 2a is respectively attached to the lower electrode 2 and the upper electrode 4 in order to detect the change in the capacitance value of the moisture sensitive film 3 with respect to the relative humidity. And the lead wire 4a are connected.

Next, a method of manufacturing the humidity sensitive element will be described. First, 5 to 10 gr of powder of acetylene end-added polyisoimide oligomer (hereinafter referred to as polyisoimide oligomer), which is a structural isomer of acetylene end-added polyimide oligomer, is prepared, for example, dissolved in diethylene glycol dimethyl ether 10 to 50 ml. To obtain a polyisoimide oligomer solution. Next, this polyisoimide oligomer solution is applied on the lower electrode 2 formed on the insulating substrate 1 by spin coating, and then at 130 to 150 ° C. in the atmosphere or nitrogen atmosphere.
It is dried for 0.5 to 1.0 hour to obtain the moisture sensitive film 3 having a thickness of 0.5 to 5 μm. At this time, the rotation speed of the spinner is 500
~ 5000 rpm. After drying in the air or in a nitrogen atmosphere, this time in a nitrogen atmosphere at 180 ° C for 0.5 to 1 hour, 230 ° C for 1 to 2 hours, and finally at 400 ° C for 0.2.
Heat treatment is performed for 5 to 1 hour to complete the polymerization reaction.
The polyisoimide oligomer as a starting material has a structural formula as shown in Chemical formula 1, and the average degree of polymerization is defined by the number of repetitions n in [] in the formula. In the case of a polyisoimide oligomer, this average degree of polymerization n can be produced from 1 to 30, and any starting material may be used.
Mixing more than one kind is also acceptable.

[0009]

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Next, for example, gold is deposited on the insulating substrate 1 on which the moisture-sensitive film 3 is laminated and applied by a vapor deposition method or a sputtering method to form an upper electrode 4 having a film thickness of about 50 to 1000 Å.
To form. In addition to gold, the attached metal is palladium,
Any metal may be used as long as it is a corrosion-resistant metal such as platinum or chromium. The lower electrode 2 on the insulating substrate 1 is made of platinum by vapor deposition or sputtering.
It is obtained by forming a thin film with a thickness of 00 to 10000Å. Similar effects can be obtained by using a solvent such as tetrahydrofuran, ethylene glycol dimethyl ether, N-methylpyrrolidone, or a mixed solvent thereof instead of the above-mentioned diethylene glycol dimethyl ether. In the manufacturing method as described above, the starting material is not limited to the polyisoimide oligomer, and a moisture-sensitive element can be manufactured by the same method as long as it is an acetylene end-added type polyimide.

With respect to the humidity-sensitive element thus constructed, the relative humidity-electrical capacitance characteristics were measured, and as a result, the data shown in FIG. 2 was obtained. An LCZ meter was used for this measurement, and the frequency was 100 KHz and the temperature was 10 ° C and 25 ° C, respectively.
It carried out about 40 degreeC. As is clear from the figure, the temperature dependence was small and good moisture sensitivity characteristics were obtained. Therefore, since the change in the detected value (temperature characteristic) due to the temperature becomes small, the temperature correction by the circuit becomes unnecessary. Further, as is clear from the figure, the hysteresis was 1% RH or less in the measurement after about 2 minutes after stabilization in a constant humidity tank, which was extremely good.

FIG. 3 shows the humidity sensitive element manufactured in the above-described embodiment before and after being left in an acetone saturated vapor for 20 minutes at room temperature.
10% RH, 30% RH, 50% RH at 5 ° C,
It is a plot of each output at 70% RH and 90% RH. As is clear from the figure, there was no change in the output value before and after leaving, and stable (small drift) moisture sensitivity characteristics could be obtained.

FIG. 4 shows the drift of each output at 25 ° C. after the humidity sensitive element manufactured in the above-mentioned embodiment was left in a high temperature / high humidity atmosphere of about 40 ° C. and 90% RH. Further, FIG. 5 shows, as a comparative example, a humidity sensitive element having a moisture sensitive film made of a conventional polyimide moisture sensitive material obtained by polymerizing a linear high molecular weight polyamic acid at 20% RH at 25 ° C. and 40%.
The respective drifts of RH, 60% RH, and 80% RH are shown. As is clear from these figures, the output drift of the humidity sensitive element according to the present embodiment is stable, that is, the humidity drift characteristic with a small drift is stable as compared with the conventional (FIG. 5), although the measured humidity range is wider. It was obtained and good.
Also, the hysteresis was 1% RH or less when measured about 2 minutes after stabilizing in the constant humidity chamber, which has better reproducibility than before and is left in the same atmosphere for a longer period in a high temperature and high humidity atmosphere. Even after that, the capacity ratio hardly changed and it was stable. Here, the capacity ratio means 90% RH output (C ₉₀ ) and 10% RH output (C ₁₀ ) at 25 ° C.
It refers to the ratio C ₉₀ / C ₁₀ . Further, after being left in a high temperature and high humidity atmosphere and then returned to an indoor atmosphere, the initial characteristics could be reversibly restored.

In the above-mentioned embodiments, the moisture-sensitive element having a sandwich structure has been described as an example, but the present invention is not limited to this, and a pair of comb-shaped elements facing each other on the surface of the insulating substrate. It is needless to say that the same effect can be obtained by applying the thin film electrode and forming a moisture sensitive film in a laminated manner so as to cover the comb thin film electrode, to a moisture sensitive element having a comb structure.

Further, in the above-mentioned embodiment, the humidity is detected by paying attention to the change of the electric capacitance value of the humidity sensitive film with respect to the relative humidity, but paying attention to the change of the impedance with respect to the relative humidity. A method of detecting humidity may be adopted.

Further, the moisture sensitive film in the above-mentioned embodiment is
It is suitable for use as a moisture sensitive film of a humidity sensitive element that is formed on a crystal oscillator and that detects humidity from the shift in resonance frequency due to the adsorption of the moisture sensitive film. It is also suitable as a moisture-sensitive film of a humidity-sensitive element having a structure in which a humidity film is formed and humidity is detected by a change in speed of passing through the surface acoustic wave element.

[0017]

As described above, according to the moisture-sensitive element of the present invention, the moisture-sensitive film is formed by using the polymer obtained by polymerizing the acetylene end-added type polyimide oligomer and its structural isomer. The water absorption becomes small and the hysteresis becomes small. Further, the temperature characteristic becomes small, and the temperature correction becomes unnecessary. Higher temperature and humidity,
Even when exposed to conditions such as an organic solvent atmosphere and dew condensation for a long period of time, extremely excellent effects such as stable output values can be obtained. Further, according to the method for producing a moisture-sensitive element of the present invention, heat treatment at a temperature of 200 ° C. or higher in a nitrogen atmosphere using an acetylene end-added type polyimide oligomer and its structural isomer as a starting material reduces the water absorption rate. In addition, it is possible to obtain stable humidity-sensitive characteristics with less drift and less temperature dependency, with less hysteresis, and with better response. In addition, since the amount of adsorbed water is small and the hydrophilicity is low, it is possible to obtain an extremely excellent effect such that conditioning in a constant temperature / constant humidity atmosphere and conditioning such as a temperature / humidity cycle are unnecessary or easy after the production.

[Brief description of drawings]

FIG. 1A is a perspective view illustrating a configuration according to an embodiment of a moisture sensitive element of the present invention, and FIG. 1B is a plan view of FIG.

FIG. 2 is a diagram showing a relative humidity-electric capacitance characteristic of the moisture sensitive element according to the present invention.

FIG. 3 10% R each at 25 ° C. before and after leaving the humidity sensitive device according to the present invention in acetone saturated vapor for 20 minutes at room temperature.
H, 30% RH, 50% RH, 70% RH, 90% RH
It is a figure which shows each output in.

FIG. 4 shows a humidity sensitive element according to the present invention at about 40 ° C. and 90% RH.
10% RH, 30% RH, 50% RH, 70% RH at 25 ° C after being left in the high temperature and high humidity atmosphere of
It is a figure which shows the drift of each output in 90% RH.

FIG. 5: 20% RH, 40% RH, and 6% at 25 ° C., respectively, after being left in a high temperature and high humidity atmosphere of a conventional humidity sensitive element
It is a figure which shows the drift of each output in 0% RH and 80% RH.

[Explanation of symbols]

 1 Insulating substrate 2 Lower electrode 3 Moisture sensitive film 4 Upper electrode

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Toru Abe 1-12-2 Kawana, Fujisawa-shi, Kanagawa Yamatake Honeywell Co., Ltd. Fujisawa Plant (56) Reference JP 62-88951 (JP, A) Kai 63-58112 (JP, A) JP-A-54-36796 (JP, A)

Claims (3)

(57) [Claims] 1. A moisture-sensitive element comprising a acetylene-end-added type polyimide oligomer and a polymer obtained by polymerizing a structural isomer thereof as a moisture-sensitive film. 2. A method for producing a humidity-sensitive element, which comprises heat-treating at a temperature of 200 ° C. or higher in a nitrogen atmosphere after forming a thin film using an acetylene end-added type polyimide oligomer and its structural isomer as a starting material. 3. The oligomer according to claim 2, wherein the acetylene end-added type polyimide oligomer and its structural isomer have an average degree of polymerization n of n = 1 to n = 30, which is composed of a single substance or a mixture of plural types. A method of manufacturing a humidity-sensitive element, which is characterized by using a starting material.