JP2508143B2 - Thin film moisture sensitive element - Google Patents

Description

TECHNICAL FIELD The present invention relates to a thin film moisture sensitive element. More specifically, it relates to a thin film moisture sensitive element having improved moisture sensitive characteristics.

[Prior Art] Control of relative humidity in the air is very important in precision industry, food industry, textile industry, building management, etc. The one used is known.

(1) Metals or semiconductors such as Se, Ge, Si (2) Oxides of metals such as Sn, Fe, Ti (3) Porous metal oxides such as Al ₂ O ₃ (4) Electrolyte salts such as LiCl ( 5) Polymer film made of organic or inorganic material However, the moisture-sensitive elements using these various materials are in a satisfactory condition such as difficult maintenance or problems in reliability and responsiveness. Not in.

For example, when the metal oxide of (2) above is used,
Although pressing and sintering are performed to form it, there are problems such as difficulty in uniform pressing and cracking during firing. In addition, even if molded in the process without any problem, because the sensitive element utilizes the resistance change caused by the desorption of moisture, since the fracture occurs from the grain boundary under the influence of moisture, the durability,
In other words, there is also a problem with reliability.

Further, when the polymer film of the above (5) is used, although it is inexpensive in terms of materials, there are problems such as deterioration due to chemicals such as solvents and deterioration of reliability.

[Problems to be solved by the invention]

As a result of various investigations in order to avoid such problems and particularly to obtain a material having excellent corrosion resistance as an electrode material, the applicant first found that the corrosion-resistant processed metal thin film formed on the insulating substrate, preferably by the sputtering method. It has been found that it is suitable to use a corrosion-resistant comb-shaped electrode obtained by electrolytically etching after forming a photoresist pattern on the humidity sensor for a humidity sensor (JP-A-61-148,871).

After that, the applicant has made further improvement of the thin film sensitive element using such a corrosion-resistant comb-shaped electrode, and as a result, the surface of the conductive comb-shaped electrode formed on the insulating substrate is a polymer thin film, generally By covering it with a plasma-polymerized film of a nitrogen-containing organosilicon compound and further treating it with an alkyl halide, we succeeded in obtaining a thin film moisture-sensitive element having excellent environmental resistance and good responsiveness. 61-200,454).

As described above, in order to obtain a thin film moisture-sensitive element having better response, the surface of the conductive comb-shaped electrode formed on the insulating substrate is covered with a plasma-polymerized film of a nitrogen-containing organosilicon compound, and 2 to treat this with an alkyl halide
Needs a process.

Therefore, as a result of various investigations by the applicant for a method of obtaining a thin film moisture-sensitive element having better responsiveness in one step, as a result, a plasma-polymerized film was formed using a nitrogen-containing organosilicon compound and a halogenated hydrocarbon or silane. It was subsequently found that such a problem can be effectively solved by forming it from a mixture with (JP-A-62-28225).
5 and 61-98318 (JP-A-62-255860), and it was subsequently found that similar results could be obtained by using an organic amine compound instead of the nitrogen-containing organic silicon compound. (Japanese Patent Application No. 61-104678 (JP-A-62-261946)
issue)).

However, in each of the thin film moisture sensitive elements described above, since the electric resistance value changes in accordance with the amount of water vapor in the air, by taking out the change in the resistance value from the conductive comb-shaped electrode, it is possible to measure the humidity. Has become.

For this reason, when the relative humidity (RH) is 40% or less, the electric resistance value becomes 10 ⁶ Ω or more, and it is difficult to measure with a normal inexpensive measuring device. That is, in each of the thin film moisture sensitive elements described above, a change in relative humidity is taken out as a change in electrical resistance, which makes measurement in a low humidity region difficult.

Therefore, the present invention does not catch the change in the relative humidity as an electric resistance, but as the change in the capacitance corresponding to the change in the relative humidity over a wide range, and enables the measurement in the low humidity region of 40% or less of the relative humidity. As a result of various investigations for a thin film moisture sensitive element to be used, a lower electrode and an upper electrode are respectively placed on a plasma polymerized film acting as a moisture sensitive film, and the upper electrode is formed of a moisture permeable material. Has been found to be effectively resolved.

[Means for solving the problem]

Therefore, the present invention relates to a thin film moisture sensitive element having improved moisture sensitive characteristics, and this thin film moisture sensitive element preferably has an insulating inorganic thin film formed on the surface of a lower electrode formed on an insulating substrate. After that, a mixture plasma-polymerized film of an organic amine compound and a halogenated hydrocarbon or a silane halide is formed, and a moisture-permeable upper electrode is provided on the plasma-polymerized film.

FIG. 1 is a perspective view showing a basic mode of a thin film moisture sensitive element according to the present invention, and FIG. 2 is a perspective view of a mode in which an insulating inorganic thin film is provided.

In these modes, the lower electrode 2 and the upper electrode take-out electrode 3 are formed on the upper surface of the insulating substrate 1 so as to be partially and isolated from each other. A plasma-polymerized film 4 is formed on the upper surface of the plasma-polymerized film 4 so as to extend over both of them, and a moisture-permeable upper electrode 5 extending to the upper electrode extraction electrode 3 is formed on the upper surface of the plasma-polymerized film 4. In the embodiment shown in FIG. 2, the insulating inorganic thin film 6 is formed on the lower surface side of the plasma polymerized film 4. Further, lead wires 8 and 8'are attached to the upper surface of the lower electrode not covered with the plasma polymerized film 4 and the upper surface of the upper electrode on the extraction electrode 3 for the upper electrode by soldering or silver paste 7,7 ', respectively. ing.

As the insulating substrate, glass, quartz, alumina, ceramics, etc. are generally used, but when the temperature followability to the humidity sensitive element is desired to be further improved, it is also proposed by the present applicant. An insulating film formed by oxidizing the surface of a silicon substrate (Japanese Patent Laid-Open No. 61-281,958) can also be used.

In forming the lower electrode and the upper electrode lead-out electrode on these insulating substrates, first, a resin adhesive tape, preferably a heat-resistant adhesive tape, having a width equal to the distance between these two electrodes is formed on the insulating substrate. It is attached to a position corresponding to the separated portion of both electrodes. Next, a corrosion-resistant metal such as stainless steel, Hastelloy C, Inconel, Monel, or gold, or an electrode forming material metal such as silver or aluminum is formed by a sputtering method or an ion plating method to about 0.1.
A thin film having a thickness of about 0.5 μm is formed. After that,
When the adhesive tape is peeled off, the formed metal thin film is separated into a lower electrode and an upper electrode extraction electrode.

In forming these electrodes, when the element shape is further miniaturized and a large number of elements are to be formed on the same insulating substrate, these two electrodes can be formed by a well-known photolithography process.

In the case of aluminum, for example, a photoresist coating is applied onto the thin film, a glass plate having a negative or positive image of the electrode pattern baked thereon is placed thereon, and baking and development by light irradiation are carried out. After this, wet chemical etching is performed.
Phosphoric acid-sulfuric acid-chromic anhydride-water (weight ratio 65: 15: 5: 15)
Mixed solution, BHF (hydrofluoric acid type), ferric chloride aqueous solution, nitric acid,
A phosphoric acid-nitric acid mixed solution or the like is used.

Thus, for example, by applying a photolithographic method on a glass substrate or by applying a screen printing method using a gold paste on a ceramic substrate, both electrodes formed on the insulating substrate are The surface is covered with a plasma polymerized film of a mixture of an organic amine compound and a halogenated hydrocarbon or a silane halide having excellent moisture-sensitive properties.

As the organic amine compound, primary to tertiary amino compounds can be used, preferably secondary to tertiary amino compounds substituted with an alkyl group, such as n-butylamine,
Substituted monoamino compounds such as secondary butylamine, isopropylamine, dimethylethylamine, diethylamine and dimethylallylamine, substituted diamino such as N, N-dimethyl-1,3-propanediamine and N, N, N ', N'-tetramethylethylenediamine Compounds, further, cycloalkyl-substituted monoamino compounds such as pentamethyleneimine and hexamethyleneimine, cycloalkyl-substituted diamino compounds such as N, N'-dimethylpiperazine are used,
Other than these, dimethylpyrazole and the like can be used.

As halogenated hydrocarbons preferably alkyl halides are used, the halogen substituents may be one or more. Specifically, methylene bromide, methane bromide, tribromide methane, ethylene bromide, ethylene dibromide,
Propane bromide, propane dibromide, butane bromide, butane dibromide, methylene chloride, methylene bromide chloride, ethyl iodide and the like are used. Further, the halogenated hydrocarbon group may be a chain unsaturated bond or an aromatic nucleus.

The halogenated silane, the general formula SiX ₁ X ₂ X ₃ X ₄ (wherein X _{1 to} X ₄ is a halogen atom, a hydrogen atom, a lower alkyl group, a lower alkenyl group or a lower alkynyl group,
Those in which 1 to 3 of these are halogen atoms) are used, and lower alkyl-substituted halogenated silanes are preferably used. Some examples of such halogenated silanes are as follows.

CH ₃ SiCl ₃ CH ₃ SiH ₂ Br, CH ₃ SiHBr ₂ (CH ₃ ) ₂ SiBr ₂ plasma polymerization is performed by adding an organic amine compound of several meters to several meters depending on the shape of the plasma polymerization apparatus and the plasma generation method.
It is carried out at a pressure of a few Torr, and also using a halogenated hydrocarbon or a halogenated silane at a pressure of a few m to a few Torr, and supplying the mixture with electric power having a discharge output of several 100 W.

Specifically, for example, when the discharge output is 20 W, the halogenated hydrocarbon or silane is used at a ratio of about 0.01 to 0.1 Torr with respect to the organic amine compound of about 0.04 to 0.2 Torr. If the proportion of the halogenated hydrocarbon or the silane halide is too small, the halogen content in the plasma polymerized film decreases and the moisture-sensitive property deteriorates. On the other hand, if the proportion is too large, the relative content in the plasma polymerized film becomes relatively small. Since the nitrogen content decreases and the polymerized film also hardens, the moisture-sensitive property also deteriorates.

The upper electrode is formed on the upper surface of the plasma polymerized film thus formed to a thickness of about 500 to 20000Å in a state of being extended to the extraction electrode for the upper electrode. The upper electrode is preferably formed of gold or platinum having excellent corrosion resistance, but it is required to have moisture permeability so that water vapor in the air can reach the plasma polymerized film.

Therefore, the upper electrode is formed by the vacuum evaporation method,
If the film thickness becomes thinner than about 250Å, it becomes porous, so it is desirable to set it in the range of about 50 to 250Å. When forming such a porous electrode, a method of introducing a small amount of an inert gas such as argon or nitrogen into the vacuum vapor atmosphere is also effective means.

Further, when forming an insulating inorganic thin film on the lower surface side of the plasma polymerized film, prior to the formation of the plasma polymerized film,
A thin film is formed from a nitride such as silicon nitride or an oxide such as silicon oxide, aluminum oxide, and tantalum oxide, which have excellent insulating properties and chemical stability.

These thin films can be formed by using various conventional
Although any method such as the CVD method and the sputtering method can be used, the plasma CVD method and the sputtering method, which are carried out at a relatively low temperature, are suitable in consideration of the influence on the substrate and the electrodes. An example of processing conditions in the case of the plasma CVD method is as follows.

The production rate of these films is generally about 20 to 200 nm / min, although it varies depending on the discharge output and the gas mixing ratio in addition to the above factors.

The insulating inorganic thin film thus formed to a thickness of about 500 to 10000Å is once formed so as to cover the entire lower electrode surface on the substrate, but to expose the connection part with the external lead wire. Then, the insulating film in that portion is removed by a normal photolithography method.

That is, a photoresist is coated on the surface of the substrate, a positive image or a negative image is exposed so that only the connecting portion is exposed, contact exposure is performed, and after development processing, the insulating film at the connecting portion is removed by etching. The etching may be performed by either a wet method or a dry method, but it is preferable that the dry etching is performed so that the electrode surface does not contaminate or corrode the substrate. As the dry etching, a commonly used plasma etching method, reactive ion etching method, or the like is used. In the case of plasma etching, for example, CF ₄ containing about 5 to 10% oxygen is used as an etching gas, and the pressure is about 0.1 to 10 Torr.
r, high frequency (13.56MHz) with power of about 50-400W, the etching rate varies depending on the mating material,
When the mating material is SiN or SiO, it is generally about 50 to 400Å / min.

[Operation] and [Effect of the Invention] In the thin film moisture-sensitive element according to the present invention, the moisture-sensitive film formed of the plasma-polymerized film is sandwiched by the upper and lower electrodes that act as counter electrodes, and Since the body capacitor is formed there, it becomes possible to detect the dielectric constant of the plasma polymerized film, which changes depending on the relative humidity, as a change in capacitance.

For this reason, the capacitance value changes in response to changes in relative humidity over a wide humidity range, so that it is possible to measure humidity in a wide range from a low humidity range to a high humidity range. Further, at this time, the capacitance value can be controlled by variously changing the type and mixing ratio of the plasma-polymerized monomer, the supplied power, and the like.

Furthermore, when an insulating inorganic thin film is formed on the lower electrode, insulation failure is less likely to occur between the upper and lower electrodes, and the linearity of the graph showing the relationship of the capacitance value with respect to relative humidity is significantly improved. Has the effect.

〔Example〕

 Next, the present invention will be described with reference to examples.

Example 1 A glass plate was used as an insulating substrate, and a heat-resistant adhesive tape having a width of 2 mm was attached to the surface of the glass plate at a position corresponding to a separation portion between the lower electrode and the upper electrode extraction electrode. Next, after vacuum-depositing chromium and gold on this surface with a film thickness of 300 Å and 700 Å respectively, by peeling the adhesive tape,
The vapor-deposited film was separately formed on the lower electrode and the extraction electrode for the upper electrode.

On the electrode thus formed on the surface of the glass plate, using a monomer mixture of N, N, N ', N'-tetramethylethylenediamine (0.07 Torr) and methylene bromide (0.01 Torr), discharge output Plasma polymerization was carried out under the conditions of 40 W, 30 minutes and 30 ° C. temperature.

On the formed plasma polymerized film with a thickness of about 5000 Å, a stainless steel plate evaporation mask (0.4 mm thick) with a window corresponding to the upper electrode size was overlaid, and gold was vacuum evaporated through the mask there. The upper electrode was formed. At this time, the thickness of the gold vapor-deposited film should be adjusted to give the upper electrode moisture permeability.
It was 200Å.

Humidity sensors are constructed by connecting lead wires to the surfaces of the lower electrode surface and the surface of the extraction electrode for the upper electrode where the plasma polymerized film was not formed, by connecting silver paste to each, and put this in a temperature / humidity tester and apply a voltage of 1V. , Temperature 30 ℃, frequency 12
Under the measurement condition of 0 to 10 KHz, the LCR meter was used to evaluate the winning humidity characteristics. The measurement result shown as a capacitance value with respect to relative humidity is shown in the graph of FIG.

Example 2 In Example 1, prior to the formation of the plasma polymerized film, on both electrodes of the lower electrode and the extraction electrode for the upper electrode,
The plasma CVD method was applied according to the following conditions to form an insulating SiN thin film (film thickness of about 5000 to 6000Å).

Gas: SiH ₄ 15SCCM NH ₃ 30SCCM N ₂ 150SCCM Pressure: 0.5Torr Substrate temperature: 250 ° C Discharge output: 150W Time: 20 minutes After that, the electrode covered with the above insulating film is connected to an external lead wire. In order to selectively remove the insulating film in the portion to be a portion, plasma etching, which is a kind of dry etching method, was performed as follows.

First, coat a positive type photoresist on the substrate, overlay a photomask with a positive image so that the insulating film at the lead wire junction is exposed, perform contact exposure with ultraviolet light, and etch the insulating film under the following plasma etching conditions. Then, the resist was dissolved and removed.

Gas: CF ₄ 90SCCM containing 5% oxygen Pressure: 0.5 Torr Discharge output: 200 W Time: 12 minutes The steps after the formation of the plasma polymerized film on the insulating inorganic thin film thus formed are Evaluation of the humidity sensitivity characteristics (frequency: 120 Hz) of the obtained humidity sensor, which was performed in the same manner as in Example 1, was performed in the same manner as in Example 1, and the result is shown in the graph of FIG.

[Brief description of drawings]

1 and 2 are perspective views of an embodiment of the thin film moisture sensitive element according to the present invention. Further, FIGS. 3 to 4 are graphs showing the moisture sensitivity characteristics of the humidity sensors obtained in Examples 1 and 2, respectively. (Explanation of symbols) 1 ... Insulating substrate 2 ... Lower electrode 3 ... Extraction electrode for upper electrode 4 ... Plasma polymerized film 5 ... Upper electrode 6 ... Insulating inorganic thin film

Claims (7)

(57) [Claims] 1. A plasma polymerized film of a mixture of an organic amine compound and a halogenated hydrocarbon or a silane halide is formed on the surface of a lower electrode formed on an insulating substrate, and the upper surface of the plasma polymerized film has moisture permeability. A thin film moisture sensitive element with an upper electrode installed. 2. The thin film moisture-sensitive element according to claim 1, wherein the organic amine compound is an alkyl-substituted amino compound. 3. The thin film moisture-sensitive element according to claim 1, wherein the halogenated hydrocarbon is a lower alkyl halide or a lower alkenyl halide. 4. The thin film moisture-sensitive element according to claim 1, wherein the halogenated silane is a lower alkyl-substituted halogenated silane. 5. The moisture permeable upper electrode has a thickness of about 250Å
The thin film moisture sensitive element according to claim 1, which is formed of the following noble metal vacuum deposited film. 6. A plasma-polymerized film of a mixture of an insulating inorganic thin film and an organic amine compound and a halogenated hydrocarbon or a halogenated silane is sequentially formed on the surface of a lower electrode formed on an insulating substrate, and the plasma polymerization is performed. A thin film moisture sensitive element having a moisture permeable upper electrode provided on the upper surface of the film. 7. The thin film moisture sensitive element according to claim 6, wherein the insulating inorganic thin film is a nitride film or an oxide film formed by a plasma CVD method or a sputtering method.