JPH01321601A - Moisture sensitive substance film and manufacture thereof - Google Patents

Abstract

PURPOSE:To speed up responsiveness in case of using the title film for a humidity sensor and make it excellent also in environmental resistance by making indium oxide contain alkaline metal or alkaline earth metal so as to form the film. CONSTITUTION:Solution containing alkaline earth metal, etc., and indium compound is applied onto a substrate and is dried, and then it is heat-treated so as to produce a humidity sensitive film. When water molecules are absorbed on the indium oxide film that contain alkaline metal, etc., the water molecules are partially dissociated and protons are created. Since the absorption amounts of water molecules change according to the change of the relative humidity, proton concentration also changes according to it and sufficient impedance change in accordance with the change of the relative humidity arises, so the film can be used as a moisture sensitive substance. The moisture sensitive substance film obtained in this way is fact in responsiveness and also excellent in environmental resistance, and it has sufficient long-term stability as long as it is used as a humidity sensor.

Description

DETAILED DESCRIPTION OF THE INVENTION [Industrial Application Field] The present invention relates to a moisture sensitive thin film for a humidity sensor and a method for manufacturing the same.

[Conventional technology/problems to be solved by the invention] Up until now, humidity sensors for humidity sensors have been made using the expansion caused by moisture absorption, such as hair, while porous ceramic sintered bodies and polymeric thin films have been used as humidity sensors. There are known methods that utilize alternating current impedance (hereinafter referred to as impedance) changes and capacitance changes.

However, devices that utilize the expansion of hair or the like have problems such as slow response speed and low accuracy and reliability.

In addition, although porous ceramic sintered bodies have excellent environmental resistance due to the characteristics of the ceramic material, they have slow response times, chemical adsorption of adsorbed water, and deterioration due to an accompanying increase in element impedance. There are problems such as the possibility of small size compounding or multifunctionalization by combining with other sensors.

Furthermore, the response speed of polymeric thin films is relatively fast, and moisture-sensitive materials with excellent sensitivity are beginning to be commercially available, but they have the disadvantages of being organic, such as poor environmental resistance and a narrow operating temperature range. There's a problem.

[Means for Solving the Problem] In view of the above circumstances, the inventors of the present invention have conducted extensive research and have found that an indium oxide thin film containing an alkali metal and/or an alkaline earth metal has a high resistance to changes in relative humidity. It was discovered that the film exhibits sufficient impedance change and can be used as a high-performance moisture-sensitive thin film for humidity sensors.

In other words, when indium oxide contains an alkali metal and/or an alkaline earth metal to form a thin film, the impedance of the thin film increases and the impedance change due to moisture adsorption becomes large, making it easier to detect and making it useful as a humidity sensor. The present inventors have discovered that the response speed when used is much faster than that of conventional humidity sensors, and the humidity sensor has superior environmental resistance, leading to the completion of the present invention.

The present invention relates to a moisture sensitive thin film made of indium oxide containing an alkali metal and/or alkaline earth metal (hereinafter also referred to as alkali metal, etc.) provided on a substrate, and an alkali metal compound and/or alkaline earth metal compound and/or alkaline earth metal. The present invention relates to a method of manufacturing the moisture-sensitive thin film by applying a solution containing a similar metal compound (hereinafter also referred to as an alkali metal compound) and an indium compound onto a substrate, drying it, and then heat-treating it.

[Function] In a moisture sensitive element that utilizes the change in impedance of the thin film of the moisture sensitive body due to moisture adsorption, the amount of protons changes as protons are generated by the dissociation of adsorbed water molecules, and the conductivity changes with the change in the amount of protons. In order to do this, the impedance of the moisture-sensitive thin film changes in response to changes in relative humidity.

However, when using an indium oxide thin film as a moisture-sensitive thin film, indium oxide alone has a low resistivity;
It becomes difficult to detect a decrease in impedance due to adsorption of water molecules, that is, a change in conductivity due to a change in the amount of protons.

Therefore, in order to use an indium oxide thin film as a moisture-sensitive thin film, it is necessary to increase its electrical resistivity, which can be achieved by adding an alkali metal or the like.

According to the experimental results of the present inventors, the resistivity of an indium oxide thin film that actually contains an alkali metal or the like increases rapidly.

When water molecules are adsorbed onto this indium oxide thin film containing an alkali metal or the like, the water molecules partially dissociate to generate protons. Since the amount of adsorbed water molecules changes in accordance with changes in relative humidity, the proton concentration also changes accordingly, and a sufficient change in impedance occurs in response to changes in relative humidity, so indium oxide thin films containing alkali metals, etc. Can be used as a moisture sensitive body.

[Example] The moisture sensitive thin film of the present invention consists of an indium oxide thin film containing an alkali metal and/or an alkaline earth metal (alkali metal, etc.).

The alkali metals, etc. in the indium oxide containing alkali metals, etc. include not only those existing in a metallic state, but also those existing in an oxide state, a hydroxide state, or a hydrated state thereof. It is a concept. In addition, "contained" refers to a state in which indium oxide and an alkali metal, etc. are mutually diffused, dispersed, or dissolved in solid solution, a state in which alkali metal, etc. is segregated at the grain boundaries of indium oxide particles, or a state in which alkali metals, etc. are segregated at the grain boundaries of alkali metal, etc. particles. In a state in which indium oxide is segregated, and furthermore, the general formula: M3 In03 (M is an alkali metal),
M” In204 (F is an upper alkali metal)
204, etc.) is formed in whole or in part, and as long as the thin film finally formed on the substrate is in this state, it is limited to the manufacturing method etc. Instead, it can be used as indium oxide containing an alkali metal or the like used in the present invention.

The alkali metals and alkaline earth metals include the alkali metals and alkaline earth metals shown in the periodic table, namely lithium, sodium, potassium, rubidium,
Any of cesium, beryllium, magnesium, calcium, strontium, and barium can be used. These may be used alone or in combination of two or more. Among these alkali metals and alkaline earth metals, lithium, sodium, potassium, magnesium, calcium, strontium, barium, and these two metals are preferred because they are easy to form a uniform thin film and have good moisture sensitivity characteristics. A combination of the above is preferred.

The content of the alkali metal etc. is such that the resistivity of the indium oxide thin film is higher than a certain level, for example, 104Ω・(2
), so it is preferably 5 mol % or more based on indium. In addition, in order to obtain a homogeneous moisture-sensitive thin film, it is preferable that the amount is 500 mol% or less based on indium, although it depends on the alkali metal added. For good vines, 5 to 200 mol%, more preferably 10 to 20
Preferably it is 0 mol%.

There are no particular limitations on the purity of the alkali metal, etc. and indium oxide constituting the indium oxide containing the alkali metal, etc., and any purity that is commercially available or manufactured may be used.

The thin film of the moisture sensitive body made of indium oxide containing an alkali metal etc. of the present invention may contain other substances in an amount of 10 mol% or less relative to indium, as long as it does not adversely affect the performance as a moisture sensitive body. metals may be included.

Specific examples of the above-mentioned metal include TI.

■, C", Mns Fes 00% Niq CL1%
Zn5B% AI% 91%Ge, P, Pb
, Zr, Nbs No., Sn, etc.

Next, regarding the thickness of the indium oxide moisture-sensitive body thin film containing alkali metals, etc., the thicker it is, the lower the impedance of the moisture-sensitive body, which is advantageous in broadening the measurement humidity range. When an indium oxide thin film containing an alkali metal or the like is formed, cracks and peeling tend to occur, making it difficult to form a homogeneous thin film. therefore,
A film thickness of about 0.02 to 5 um, more preferably about 0.05 to 2 ρ, is preferable.

In the present invention, an indium oxide thin film containing an alkali metal or the like as described above is provided on a substrate.

The substrate is not particularly limited as long as it is capable of forming and holding an indium oxide thin film containing alkali metals, etc., but glass substrates such as soda glass and quartz glass, ceramic substrates such as alumina, stainless steel, silicon, and polyimide films may be used. A substrate manufactured by E.g., etc. is preferable because it has good heat resistance and surface smoothness.

Next, a method for manufacturing the moisture sensitive thin film of the present invention will be explained.

There is no particular limitation on the method for obtaining the indium oxide moisture-sensitive thin film containing alkali metals, etc. of the present invention, and it can be obtained by a method similar to the method for obtaining a normal indium oxide thin film.
CVD method (chemical vapor deposition method) is a method to more easily obtain indium oxide thin film containing alkali metal etc.
, alkali metal compounds and/or alkaline earth metals, rather than thin film formation techniques using vacuum techniques such as sputtering and vacuum evaporation, or spray methods in which a metal compound solution is sprayed onto a high-temperature substrate and thermally decomposed. The coating and thermal decomposition method of a solution containing a compound (alkali metal compound, etc.) and indium compound is relatively easier to add alkali metals, etc., and is suitable for humidity sensors that have the surface porosity necessary for adsorption of water molecules. It is preferable as a moisture-sensitive thin film and is excellent in that it is easy to change.

In addition, indium oxide thin films containing no alkali metals are formed on substrates containing alkali metals such as soda glass using film forming techniques such as CVD, sputtering, vacuum evaporation, coating and thermal decomposition, and spraying. However, it is also possible to adopt a method in which an alkali metal or the like is diffused and contained in the indium oxide thin film from the substrate by thermal diffusion by subsequently performing a heat treatment. However, as a method for easily obtaining a moisture sensitive thin film having good and reproducible moisture sensitive characteristics, the above-mentioned coating thermal decomposition method is excellent.

As an organic indium compound which is a type of indium compound used in the coating thermal decomposition method of a solution containing an alkali metal compound and an indium compound, for example, the general formula (■): I n (OR1) 3 (1) (in the formula , R1 is a hydrocarbon group having 1 to 20 carbon atoms), general formula (■): In(OR1) Y [I
I) Indium partial alkoxides represented by 3-a a (wherein R1 is the same as above, Y is a functional group having chelating ability or a halogen atom, and a is an integer of 1 to 2), general formula f1 ), a condensed polyester of the compound represented by the general formula [11), the general formula (I[D .

I n (OCOR2)3 (I[D
Indium carboxylates represented by (wherein, R2 is a hydrogen atom or a hydrocarbon group having 1 to 30 carbon atoms), β-diketone complexes that are reactants of indium with acetylacetone, benzoylacetone, etc., trimethyl Examples include alkylindiums such as indium, organic indium compounds such as triphenylindium, but are not limited to these.

Specific examples of the compound represented by the general formula (1) include:
Specific examples of compounds represented by general formula (It) such as triethoxyindium and tripropoxyindium include compounds represented by general formula (III) such as indium dibutoxy chloride.
Specific examples of compounds represented by include indium acetate,
Examples include indium oxalate, indium tartrate, indium octylate, indium oleate, indium linoleate, indium stearate, and indium naphthenate. In addition to these organic indium compounds, inorganic indium compounds such as indium nitrate may also be used. These compounds may be used alone,
Two or more types may be used as a mixture, but they are soluble in organic solvents,
Particularly preferred are those that decompose into indium oxide when heated to 350°C or higher.

Examples of the organic solvent include monohydric alcohols such as methyl alcohol, ethyl alcohol, isopropyl alcohol, butyl alcohol, and pentanol; polyhydric alcohols such as ethylene glycol, glycerin, and 1,4-butanediol; ethyl acetate and acetic acid. Carboxylic acid esters such as propyl, isoamyl acetate, and propyl formate; Ketones such as acetone, acetylacetone, diethyl ketone, and methyl ethyl ketone; Aromatic solvents such as benzene, toluene, and xylene; Ethers such as dioxane and tetrahydrofuran; Methyl cellosolve, Examples include, but are not limited to, glycol ethers such as ethyl cellosolve, nitrogen-containing organic solvents such as N-methyl-2-pyrrolidone, dimethylformamide, and dimethylacetamide. These organic solvents may be used alone or in combination of two or more.

In the case of containing alkali metals, etc., any compound may be used, as long as it is soluble in the above organic solvent among organic compounds and inorganic compounds containing alkali metals. For example, hydroxylation of alkali metals, etc. alkoxides of alkali metals and alkaline earth metals such as sodium methylate, sodium ethylate, and magnesium jetoxide; alkoxides of alkali metals and alkaline earth metals such as sodium octylate, lithium octylate, and magnesium octylate. Organic compounds such as carboxylic acid salts are preferred because they are easy to use and easy to contain.

The metal content in the solution may be selected as appropriate to achieve an appropriate hydrolysis rate during application and to adjust the film thickness, but is usually 0.5 to 20% by weight, preferably 3 to 10% by weight.
The i amount is 96.

Further, in the present invention, inorganic metal salts, organic metal salts, thickeners, stabilizers, etc. may be added that do not impede the purpose of the present invention.

There are no particular limitations on the method for applying the solution containing the alkali metal compound and the indium compound onto the substrate, and any commonly used methods such as dip coating, spraying, and spin coating may be used.

There is no particular limitation on the temperature at which the solvent is dried after being applied onto the substrate, as long as the temperature is such that the solvent evaporates. Therefore, although it varies depending on the solvent used, it is usually 50 to 300℃.
It is.

The heat treatment temperature after drying should be at least the temperature at which the organic indium compound turns into indium oxide through thermal decomposition, and usually requires a temperature of about 350°C or higher, but in order to obtain a moisture-sensitive thin film with excellent reproducibility, It is desirable to bake at a temperature of about 400°C or higher. However, if the firing temperature is too high, the densification of the thin film will be promoted and it will be difficult to maintain good moisture sensitivity characteristics. is preferred.

As the atmosphere during firing, an atmosphere containing an inert gas such as nitrogen or oxygen can be used.

The moisture-sensitive thin film of the present invention obtained in this way increases the impedance of the thin film itself, and the impedance change due to moisture adsorption becomes large, making it easier to detect and exhibiting a very high response speed when used as a humidity sensor. It is fast, has excellent environmental resistance, and has sufficient long-term stability for use as a humidity sensor. Furthermore, if a moisture sensitive element is manufactured using this moisture sensitive thin film, it can be made smaller and more intelligent.

Next, the present invention will be explained based on Examples, but the present invention is not limited by these Examples.

Example 1 and Comparative Example 1 5 g of indium 2-ethylhexanoate (In content: 8.6% by weight) was dissolved in 100 g of benzene, 5 g of linoleic acid was added, and then sodium bovine 2-ethyl hexanoate was dissolved. 10 sides of (Na content Q 6.3ffiffi%)
% ethanol solution was added and thoroughly stirred while heating to obtain a homogeneous transparent solution (Na is approximately
146 mol%).

This solution was applied onto an alumina substrate on which gold comb-shaped electrodes (electrode spacing 0.2 mm, electrode length 200 ma+) were formed.
After drying in air at 120°C, in a Matsufuru oven,
By heating at 00° C. for 1 hour, a moisture-sensitive element containing a transparent indium oxide thin film containing sodium was obtained.

The resulting sodium-containing indium oxide thin film was transparent, and as a result of observation using a scanning electron microscope, the film thickness was approximately 0.41! It was m.

When we measured the moisture sensitivity characteristics of this moisture sensitive element at room temperature, that is, the change in impedance with respect to changes in relative humidity, the impedance changed by about three orders of magnitude when the relative humidity was between 10 and 95% R1+ (see FIG. 1).

In addition, we investigated the responsiveness during humidification from 50% R11 to 90% R1+ and the responsiveness during dehumidification from 90% R11 to 50% R1+ at 25°C. The response speed is faster compared to
It was a good moisture-sensitive element (see Figure 2).

Example 2 20 g of indium acetylacetonate was dissolved in 100 g of a 1:1 solution of ethanol and acetone, and then 5 g of magnesium acetylacetonate was added and thoroughly stirred to form a homogeneous transparent solution (about 46 mol of Mg relative to In). %)
The resulting solution was dip coated onto a soda glass substrate at a pulling rate of 30 cm/min, dried in air at 100°C, and then heated in a Matsufuru furnace to 500°C at a heating rate of 10°C/min. The temperature was raised, maintained for 1 hour, and then allowed to cool to obtain a homogeneous magnesium-containing indium oxide thin film (0.1 lacquer film thickness).

A gold comb-shaped electrode similar to that in Example 1 was formed on this thin film-F by vacuum evaporation to produce a moisture-sensitive element.

When the moisture sensitive characteristics and responsiveness of the obtained moisture sensitive element were measured, it showed almost the same characteristics as in Example 1.

[Effects of the Invention] A moisture-sensitive element using the moisture-sensitive thin film of the present invention has faster response than conventional moisture-sensitive elements, and because it is a thin film-based element, it can be made smaller. It has the characteristics that it can be combined with other sensors to make it multi-functional. Moreover, it can be easily produced by the method of the present invention.

[Brief explanation of the drawing]

FIG. 1 is a graph showing the relationship between relative humidity and impedance value measured using the moisture sensitive element containing the alkali metal etc.-containing indium oxide thin film of the present invention obtained in Example 1 as a humidity sensor; The figure shows the responsivity when the moisture-sensitive element having the indium oxide thin film containing alkali metal etc. of the present invention obtained in Example 1 is used as a humidity sensor and the responsivity when a conventional ceramic humidity sensor is used. This is a graph showing. Patent applicant Kanebuchi Chemical Industry Co., Ltd. Relative humidity (5', RH”1

Claims (1)

[Claims] 1. Alkali metal and/or provided on the substrate
A moisture-sensitive thin film made of indium oxide containing alkaline earth metals. 2. Claim 1, wherein the thin film has a thickness of 0.02 to 5 μm.
The moisture sensitive thin film described. 3. The moisture sensitive thin film according to claim 1, wherein the content of the alkali metal and/or alkaline earth metal is 5 to 500 mol% based on indium. 4. A method for producing a moisture-sensitive thin film according to claim 1, wherein a solution containing an alkali metal compound and/or an alkaline earth metal compound and an indium compound is applied onto a substrate, dried, and then heat-treated. 5. The ratio of the alkali metal compound and/or alkaline earth metal compound to the indium compound in the solution is 5 to 500 mol% of the alkali metal and/or alkaline earth metal to indium. the method of.