JPH0212047A - Capacity change type moisture sensitive element and production thereof - Google Patents

Abstract

PURPOSE:To form the microstructure of an electrode having excellent moisture permeability with good reproducibility by forming the electrode to be exposed to a measuring atmosphere of a physically vapor deposited film of a noble metal and scattering gold thread pattern-shaped through-holes having the same size as the size of the particles of the noble metal or above into this vapor deposited film. CONSTITUTION:The lower electrode 2 is formed on an insulating substrate 1 and a moisture sensitive high-polymer film 3 is formed on the electrode 2. The upper electrode 4 which consists of the physically vapor deposited film of the noble metal formed in a low vacuum and is scattered with the gold thread pattern-shaped through-holes having about the same size as the size of the secondary particles of the noble metal or above is formed on this moisture sensitive film 3. The moisture permeability is imparted by the through-holes to this upper electrode 4. The electrode provided with the microstructure having the excellent moisture permeability is formed in this way by the relatively easy stage and the moisture sensitive element having excellent characteristics is stably obtd.

Description

DETAILED DESCRIPTION OF THE INVENTION [Object of the Invention] (Industrial Application Field) The present invention relates to a capacitance variable humidity sensing element using an organic polymer thin film as a humidity sensitive material and a method for manufacturing the same.

(Prior Art) As a method for detecting humidity in an atmosphere, a method that utilizes changes in the electrical characteristics of a moisture-sensitive material is well known.

Materials whose properties change due to adsorption and desorption of moisture include metal oxide ceramics, electrolytes such as lithium chloride, hygroscopic organic polymers and polymer electrolytes, and polymer composite materials containing conductive fillers. is known, and many types have already been put into practical use.

The detection principle of a moisture-sensitive element using these moisture-sensitive materials is
11 Detects changes in the electrical conductivity and dielectric constant of the material before adsorption and desorption of moisture into the abrasive material as changes in impedance, electrical resistance, or capacitance between electrodes formed in an appropriate shape. It is something to do.

Among the moisture-sensitive materials mentioned above, capacitance-variable moisture-sensing elements using hygroscopic polymer thin films have a wide moisture-sensing range and fast response speed, and their structure is relatively simple, making them easy to manufacture. Because it is easy, it is easy to mass produce and has low cost.

Cellulose derivatives, polyvinyl alcohol-based resins, polyamide-based resins, polyimide-based resins, acrylic-based resins, polyester-based resins, etc. are known as polymeric moisture-sensitive film materials used in such moisture-sensitive elements. A commonly used device configuration is a three-layer parallel plate capacitor structure in which the upper and lower surfaces of a polymer moisture-sensitive film are sandwiched between electrodes.

A typical example of such a moisture-sensitive element is one in which a lower electrode is provided on an insulating substrate such as a glass substrate, and a polymer moisture-sensitive film and an upper electrode are sequentially laminated thereon.

In a moisture-sensitive element having this structure, in order to improve responsiveness and increase capacitance, the polymeric moisture-sensitive film is formed as thin as possible, and is usually about lμIl to 2μm. In addition, since the upper electrode is directly exposed to the measurement atmosphere, it must have corrosion resistance of 6, allow moisture in the atmosphere to freely pass through, and do not prevent water molecules from entering the moisture-sensitive membrane. It won't happen.

Therefore, for this upper electrode, a precious metal thin film whose electrode layer itself has moisture permeability, or, if the electrode layer itself is not moisture permeable, a mesh-like or comb-shaped noble metal film with gaps through which water molecules can pass through is recommended. electrodes are used. Comparing the two, we find that with a mesh-shaped or comb-shaped upper electrode, it is difficult to make the gaps formed in the electrode layer sufficiently small compared to the thickness of the moisture-sensitive membrane, so water molecules that enter through the gaps are This prevents rapid penetration into all parts of the moisture sensitive membrane. Therefore, a moisture-permeable metal thin film electrode, in which the electrode layer itself is porous and only the permeation of water molecules in the thickness direction of the moisture-sensitive membrane needs to be considered, is superior in terms of sensitivity and the like.

This moisture-permeable metal thin film electrode is formed by a vapor deposition method or a sputtering method, and the electrode layer itself is made porous.
In addition, it is common to use a thin film with a thickness of several 100 layers or less, and to ensure permeability to water molecules with the appearance of main holes formed therein.

(Three problems to be solved by the invention) However, depending on the type and surface properties of the polymer moisture-sensitive membrane, it may not be possible to obtain a porous precious metal thin film, or even if the electrode film thickness is made sufficiently thin, it may not be possible to obtain a porous precious metal thin film. There was a problem that the scope of application was narrow, such as not being able to obtain. In addition, if the thickness of the electrode layer was made too thin, the precious metal particles generated on the moisture-sensitive film would become discontinuous, resulting in a significant increase in the impedance of the electrode layer, making it impossible to measure capacitance. .

In this way, for moisture-permeable electrodes in capacitive moisture-sensing elements, it is not enough to simply control the thickness of the electrode layer; it is necessary to control the microstructure of the electrode layer.
The type and surface properties of the polymer moisture-sensitive membrane used as the base material also had to be considered.

The present invention was made in order to address the problems related to moisture-permeable thin film electrodes, which are one of the components of such capacitance-variable moisture-sensing elements. The purpose of the present invention is to provide a capacitance-variable moisture-sensing element with excellent characteristics such as sensitivity and responsiveness, and a method for manufacturing the same.

[Structure of the Invention] (Means for Solving the Problems) That is, the capacitive humidity-sensitive element of the present invention has at least a pair of electrodes on the surface of a smooth polymeric moisture-sensitive film so as to sandwich the polymeric moisture-sensitive film. In a capacitive humidity sensing element in which electrodes are formed, the electrode of the pair of electrodes that is exposed to the measurement atmosphere is made of a physically deposited film of a noble metal, and the physically deposited film contains particles of the noble metal. It is characterized by a scattering of through-holes in the shape of a gold thread pattern, the size of which is about the same or larger than the size of the pores.

In addition, in the method for manufacturing a capacitive humidity sensing element of the present invention, at least one pair of electrodes is formed on the surface of a smooth polymeric moisture sensitive film so as to sandwich the polymeric moisture sensitive film. In manufacturing the wet element, the electrode exposed to the measurement atmosphere of the pair of electrodes is formed by vapor deposition or sputtering of a noble metal in a low vacuum.

(Function) The humidity-sensitive element of the present invention detects the humidity in the atmosphere by measuring the capacitance that changes depending on the amount of water molecules adsorbed and desorbed by the polymeric moisture-sensitive membrane. At least one electrode for detecting capacitance f;1 is exposed to the measurement atmosphere and needs to be a thin film electrode with moisture permeability so that water molecules can freely pass through the electrode. If the size of the pores in this thin film electrode is too large, the response will be affected, so it is desirable to make the pores as small as possible without hindering the permeation of water molecules. Further, it is desirable that the electrode itself has low impedance.

In the present invention, the electrode is constituted by a physically vapor-deposited film of a noble metal, and a gold thread pattern is formed in the thickness direction of the film, which has a size comparable to or larger than that of the noble metal particles (secondary particles). Since the through holes are scattered, the electrode itself has a continuous structure and low impedance can be achieved, and the diameter of the noble metal secondary particles formed by normal physical vapor deposition is several tens of angstroms or more. It becomes possible for water molecules to sufficiently permeate through the pores.

Further, the above-mentioned physical vapor deposition film is formed by vapor depositing or sputtering a noble metal in a low vacuum, in other words, under a relatively high gas pressure range. The formation mechanism is not necessarily clear, but when the gas pressure is high, there is a high probability that noble metal atoms (-order particles) collide with gas molecules before reaching the base material, and noble metal particles are continuously supplied onto the base material. Therefore, as the crystal grains become smaller,
As a continuous --like noble metal film grows, gaps are created at various locations. In addition, in the configuration of the present invention, the fact that the base material has a smooth polymer membrane surface is considered to be one of the reasons why such gaps occur.

(Example) Hereinafter, an example of the present invention will be described with reference to the drawings.

FIG. 1 is a diagram showing the configuration of a capacitive humidity sensing element according to an embodiment of the present invention, and FIG. 1(a) is a plan view thereof, and FIG.
b) is a sectional view taken along the line XX. In the figure, 1 is an insulating substrate such as a glass substrate or an 81 substrate coated with 5I02, 5I3N, etc., and a lower electrode 2 is formed on this insulating substrate 1. The lower electrode 2 may be divided into a plurality of pieces, for example.

A polymer moisture-sensitive film 3 is formed on the lower electrode 2 . As a material for forming this polymeric moisture-sensitive material 113, various known capacitive moisture-sensitive material R'F4 such as cellulose derivatives, polyamide resins, polyimide resins, etc. can be used. In particular, cellulose 1 transparent conductors, such as ethyl cellulose, ethyl hydroxyethyl cellulose, cellulose acetate, and cellulose acetate butyrate obtained by etherification or esterification, have excellent film forming properties, and have various characteristics other than moisture sensitivity. It is suitable because the composition can be used. In addition, polyimide resin has heat resistance and excellent film formability and mechanical strength, and can be said to be a suitable material like cellulose derivatives.

On this polymer moisture sensitive @ 3, there are gold thread pattern-shaped through holes which are made of a physically deposited precious metal film formed in a low vacuum and have a size comparable to or larger than the secondary particles of the precious metal. Scattered upper electrodes 4 are formed, and the upper electrodes 4 are provided with moisture permeability by the above-mentioned through holes. Since this upper electrode 4 is exposed to the n1 constant atmosphere, corrosion resistance is essential.
It is made of an alloy having I[a. Further, the thickness of the upper electrode 4 varies depending on the material of the polymer moisture-sensitive film 3, but is preferably 100 Å or more. This is because when forming a physically deposited noble metal film on the polymer moisture sensitive film 3 under low vacuum, noble metal particles do not form as a single layer film on the base material, and crystal grains of a certain size are formed. It grows as a.

Therefore, the electrode layer is originally an aggregate of noble metal particles, and 1
This is because if the film thickness is less than 00 Å, the impedance of the electrode layer is too large, making it difficult to detect capacitance.

A lead wire 5 is connected from the lower electrode 2 and the upper electrode 4.
is pulled out to form a capacitance-variable humidity sensing element.

Such a capacitance-variable humidity sensing element is manufactured, for example, as follows.

That is, first, a lower electrode 2 is formed on an insulating substrate 1 by a thin film forming method such as evaporation or sputtering, or a thick film forming method, and a capacitance-variable polymer-based sensor as described above is formed on this lower electrode 2. The polymer moisture-sensitive film 3 is formed by applying a wet material solution or a precursor solution, drying, and thermally curing.

Next, an upper electrode 4 is formed on this polymeric moisture-sensitive film 3 by physical vapor deposition in a low vacuum.

The physical vapor deposition method referred to here refers to the use of a vacuum system to
This is a method of physically forming a thin film thereon, and a vacuum evaporation method including an ion blasting method or a sputtering method is applied.

As the vacuum evaporation method, any one of a resistance heating evaporation source, a high frequency heating evaporation source, an electron beam evaporation source, etc. can be used as the evaporation source. Also, in the ion brating method, any commonly used method such as a direct current method, a high frequency method, a cluster ion beam method, etc. can be used.

Moreover, various methods such as bipolar sputtering, high frequency sputtering, and magnetron sputtering can be used in the sputtering method.

Then, using these physical vapor deposition methods, the upper electrode 4 made of a noble metal thin film is formed under a low vacuum. "Low vacuum" during the formation of this physical vapor deposition film is not a specific range, but varies depending on the vapor deposition or sputtering method, the material of the noble metal for the upper electrode 4, the material of the polymer moisture sensitive @ 3, etc. An appropriate gas pressure range must be selected for the combination, but in the vapor deposition method, 1O-2
A rough guideline is about 1 Pa or more, and in the case of sputtering, about 1 Pa or more. The upper limit of the atmospheric pressure in these physical vapor deposition methods is about 5 Pa for vapor deposition method and 30 Pa for sputtering method, which is the upper limit of general atmospheric pressure.
degree.

Further, the type of gas used is not particularly limited, and argon, air (nitrogen + oxygen), etc. can be used.

Furthermore, the arrangement of each element within the apparatus, the temperature of the substrate, and other conditions shall be appropriately selected depending on the gas pressure.

By forming the physical vapor deposition method in this way,
An upper electrode 4 is obtained in which through-holes in a gold thread pattern are scattered in the film and have a size comparable to or larger than that of the noble metal secondary particles. Note that the size of the through hole herein refers to the gap distance in the width direction of the through hole.

For example, FIG. 2 shows a sputtering device using a DC two-pole sputtering method, using gold as a sputtering source, and changing the gas pressure to 2.5 argon during sputtering. OPa, sputtering power DC85ν
, a transmission electron microscope (TEM) 11 schematically showing an upper electrode made of gold having a thickness of approximately 300 mm formed on a polyimide moisture sensitive film under conditions of a film formation rate of 60 mm/1 nm. As is clear from this figure, in a continuous layer consisting of fine crystal grains 6 with a width of 50 to 300 particles,
It can be seen that discontinuous through holes 7 in the shape of a 200-meter gold thread pattern are almost uniformly present. The through holes 7 allow moisture in the atmosphere to be uniformly supplied to the polymer moisture sensitive membrane.

In addition, for comparison with the present invention, FIG. 3 shows that about 32 cm
FIG. 3 is a diagram schematically showing a TEM image of an upper electrode formed with a film thickness of 0. Compared to FIG. 2, the crystal grains are slightly thicker and coarse grains of 100 Å or more are observed, and in FIG. 2, no clearly recognized through holes are observed.

Further, the relative relationship at an ambient temperature of 25° C. and a measurement frequency of 10 kllz between the humidity sensing element A in which the upper electrode 4 was formed according to the above-mentioned manufacturing method of the present invention and the humidity sensing element B in which the upper electrode 4 was formed by changing the gas pressure. Humidity and capacitance ratio (
Fig. 4 shows the results of a constant relationship with humidity characteristics. The capacitance ratio referred to here is the capacitance ratio C/C1 based on the capacitance ff1c1o at 10% relative humidity.
o, which corresponds to the sensitivity. As is clear from FIG. 4, although there is some hysteresis, the humidity sensing element A of the present invention changes almost linearly with respect to relative humidity, and has practically sufficient sensitivity and accuracy. The response was also good when the value suddenly changed. On the other hand, moisture sensitive element B had almost no sensitivity, and its response was extremely slow and its characteristics were poor. This is because, as can be seen from the TEM image, the four upper electrode layers have a dense structure that even water molecules cannot pass through.

Furthermore, FIG. 5 shows a sputtering device using the same DC bipolar sputtering method as that used to form the upper electrode of the moisture-sensitive element A described above, which sputters argon or pure air onto the polyimide moisture-sensitive film at various pressures. Gas pressure and sensitivity (relative humidity 10%) of the humidity-sensitive element with electrodes formed by sputtering gold
The relationship between the capacitance ratio (C9o/C1o) and relative humidity of 90% is shown. Although sputtering conditions change when the pressure of argon or pure air changes, the film formation rate was kept as constant as possible, and the electrode layer thickness was about 280 to 320.

As is clear from Figure 5, the gas pressure is set to a certain value (approximately
When the pressure was 1 Pa) or more, the sensitivity was almost constant and good moisture sensitivity was obtained, and below that, almost no sensitivity was exhibited. TEM observation of the microstructure of the electrode under each condition revealed that the electrode formed under the high gas pressure condition had a microstructure similar to that shown in FIG. 2, with clear pores present.

However, the case where the gas pressure was low and there was no sensitivity was similar to that shown in FIG. 3, and no through holes were observed. Furthermore, almost no effect was observed due to the difference in gas between argon and pure air.

Next, an example will be described in which humidity-sensitive elements were manufactured under various manufacturing conditions and their humidity-sensitive characteristics were measured.

Example 1 Chromium and gold were sequentially vapor-deposited and patterned on a glass substrate to form a lower electrode (thickness: 1,500 mm), and an ethyl cellulose solution was spin-coded thereon and dried at 120° C. to form a layer with a thickness of 1.5 mm. An 8 μm polymer moisture sensitive film was formed.

Next, gold was sputtered onto this polymer moisture-sensitive film through a metal mask using a DC bipolar sputtering device under the conditions of a gas pressure of argon of 2.0Pa and a film formation rate of 60 people/+In. A moisture-permeable upper electrode with a thickness equal to that of a human body was formed, and a moisture-sensitive element having the same structure as that shown in FIG. 1 was fabricated.

Comparative Example 1 A moisture-sensitive element was fabricated by forming an upper electrode with a film thickness of about 300 on an ethyl cellulose moisture-sensitive membrane formed in the same manner as in Example 1 using the same apparatus at a gas pressure of 0.5 Pa with argon.

Example 2 An ethyl cellulose moisture-sensitive membrane formed in the same manner as in Example 1 was coated with an argon gas pressure of 2. OPa,
Platinum was sputtered at a deposition rate of 50 gln/+gln to form an upper electrode with a film thickness of about 250 gln, thereby producing a moisture-sensitive element.

Comparative Example 2 In the same manner as in Example 2 above, platinum was sputtered on the ethyl cellulose moisture-sensitive membrane to a thickness of approximately 280 mm using the same equipment at an argon gas pressure of 0.87 Pa to form a lower electrode and form a moisture-sensitive element. Created.

Example 3 A polyimide precursor (polyamic acid) solution was spin-coded onto the substrate with the lower electrode prepared in Example 1, and
Dry by heating for 20 minutes at ℃
50℃×30 minutes, 250”CX 60 minutes, 350℃×6
The mixture was cured by heating for 0 minutes to form a polyimide moisture-sensitive film having a thickness of 1.7 μm.

Next, using the same apparatus as in Example 1, argon gas pressure 1. A moisture-sensitive element was fabricated by sputtering gold using OPa to form an upper electrode with a thickness of approximately 280 mm.

Comparative Example 3 The argon gas pressure in Example 3 was set to o, 67 Pa.
, under the same conditions except that the film thickness of the upper electrode was approximately 300 mm.
A moisture sensing element was fabricated.

Example 4 Using pure air as the gas during sputtering in Example 3 above,
A moisture sensitive element was manufactured under the same conditions except that the pressure was 2.2 Pa and the thickness of the upper electrode was approximately 250 mm.

Comparative Example 4 A moisture-sensitive element was manufactured under the same conditions as in Example 4 except that the gas pressure was 0.3 Pa and the thickness of the upper electrode was approximately 260 mm.

Example 5 On a polyimide moisture sensitive film formed in the same manner as in Example 3,
Using a vacuum evaporation apparatus equipped with a resistance heating evaporation source, the gas pressure during evaporation was set to 1.0 × 10' Pas, and the film thickness was approximately 320 mm, and a gold upper electrode was formed through a metal mask to detect moisture. The device was fabricated.

Comparative Example 5 In Example 5 above, the gas pressure during vapor deposition was changed to 1.2×10
A moisture-sensitive element was produced under the same conditions except that the film thickness was set to -' Pa and the film thickness was set to about 310.

Using the moisture-sensitive elements of each example and comparative example thus obtained, the capacitance-relative humidity characteristics (humidity characteristics) were measured at a temperature of 25° C. and a measurement frequency of 10 kllz. Table 1 shows the sensitivity (ratio of capacitance C9o/C1o at relative humidity 1O% and relative humidity 90%) as the measurement results. Also,
The microstructure of the upper electrode was observed using TEM.

(Margin below) Book 1: Based on TEM observation.

As is clear from the results in Table 1, regardless of the type of polymer moisture-sensitive film, the type of noble metal used as the upper electrode, and the method of forming the upper electrode, vapor deposition in a low vacuum as defined in the present invention Alternatively, by forming the upper electrode using sputtering, an upper electrode with fine through holes can be formed.
A moisture sensitive element exhibiting good humidity characteristics was obtained.

[Effects of the Invention] As explained above, according to the present invention, an electrode having a microstructure with excellent moisture permeability can be formed with good reproducibility through a relatively easy process, and a moisture-sensitive element with excellent characteristics can be obtained. It becomes possible to stably provide the following.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the configuration of a moisture-sensitive element according to an embodiment of the present invention, FIG. 1(a) is a top view thereof, and FIG. 1(b) is a cross-sectional view taken along the line 2 is a diagram schematically showing a TEM image of a moisture permeable electrode in an example of the present invention, FIG. 3 is a diagram schematically showing a TEM image of a moisture permeable electrode in a comparative example, and FIG. FIG. 5 is a graph showing the humidity-sensitive characteristics of the moisture-sensitive element in Examples and Comparative Examples of the invention, and FIG. 5 is a graph showing the relationship between the gas pressure and the sensitivity of the moisture-sensitive element when forming a moisture-permeable electrode by sputtering. It is a diagram. 1...Insulating substrate 2...Lower electrode 3...Polymer moisture sensitive film 4... Moisture permeable upper electrode 5...Lead wire 6...Precious metal particles 7...Through hole Applicant Toshiba Corporation Patent attorney Su Yamasa - Figure 2 1 ○ 2COOA Figure 3 Onshin mark (C90/Csu) Piece (' Yaden atmosphere + 9 (C/C1o) Oko>

Claims (2)

[Claims] (1) In a capacitive humidity sensing element in which at least one pair of electrodes are formed on the surface of a smooth polymeric moisture sensitive membrane so as to sandwich the polymeric moisture sensitive membrane, one of the pair of electrodes is connected to the measuring atmosphere. The exposed electrode is made of a physical vapor deposited film of a noble metal, and this physical vapor deposited film is scattered with gold thread pattern-like through holes having a size comparable to or larger than the noble metal particles. A capacitance-variable humidity sensing element characterized by: (2) At least one pair of electrodes are formed on the surface of a smooth polymeric moisture-sensitive membrane so as to sandwich the polymeric moisture-sensitive membrane, and when manufacturing a capacitance-variable moisture-sensitive element, measurements are made among the pair of electrodes. A method for manufacturing a capacitance-variable moisture-sensitive element, characterized in that electrodes exposed to the atmosphere are formed by vapor deposition or sputtering of a noble metal in a low vacuum.