JP2000344529A - Composition for forming lsco conductive thin film, and formation of lsco conductive thin film - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a composition for LSCO conductive thin film excellent in long-term preservation stability, and to provide the method for forming the LSCO conductive thin film by using the composition. SOLUTION: In this composition for forming the perovskite type LSCO conductive thin film containing metallic alkoxides of La, Sr and Co, the partially hydrolyzed material and/or an organic acid salt, the particles having >=0.5 μm is <=50 pieces/ml. The LSCO conductive thin film is formed by repeating a process that the composition is applied on a heat resistant substrate and heated in the air, an oxidizing atmosphere or a steam-containing atmosphere until a film having a desirable film thickness is obtained and firing the film at least during heating or after heating in the final process at a temp. equal to or above the crystallization temp.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

The present invention relates to a composition and a method for forming an LSCO conductive thin film expected to be applied to various devices due to its electrical properties.

[0002]

2. Description of the Related Art LSCO thin films are attracting attention as electrode materials and the like because of their excellent conductive properties, and are expected to be applied to various devices. As a method of forming the LSCO conductive thin film, there are a sputtering method, an MOCVD method, and the like. As a relatively inexpensive and simple thin film forming method, there is a sol-gel method. The sol-gel method is described in US Pat. Filing No. 09/061
As described in 362, a method for forming a thin film by applying a thin film forming composition comprising a solution of an organometallic compound to a substrate, hydrolyzing the coated film to form an oxide thin film, and then firing and crystallizing the oxide thin film In general, a metal alkoxide, a partial hydrolyzate thereof, or an organic acid salt is used as an organic metal compound as a raw material.

[0003]

SUMMARY OF THE INVENTION Conventionally used L
When the composition for forming an SCO conductive thin film is stored for a long period of time, there is a problem of an increase in particles and generation of a precipitate due to a polymerization reaction in the liquid and the like, and thus the composition cannot be used stably for a long period of time.

The present invention solves the above-mentioned conventional problems, and provides a composition for forming an LSCO conductive thin film having excellent long-term storage stability and an LSC using the composition for forming an LSCO conductive thin film.
An object of the present invention is to provide a method for forming an O conductive thin film.

[0005]

SUMMARY OF THE INVENTION The composition for forming an LSCO conductive thin film of the present invention comprises an LSCO solution comprising an organometallic compound solution for forming a perovskite-type LSCO conductive thin film.
In the composition for forming a CO conductive thin film, the particle size is 0.5 μm
The present invention is characterized in that the abundance of the particles is 50 particles / mL or less.

That is, the present inventors have intensively studied to improve the long-term storage stability of the composition for forming an LSCO conductive thin film, and as a result, the composition of the composition for forming an LSCO conductive thin film in an organometallic compound solution was found. The present inventors have found that by minimizing the number of initial particles serving as initial nuclei for the generation of sediment as much as possible, it is possible to drastically reduce the increase in particles and the generation of sediment during long-term storage, and have reached the present invention.

In the method for forming an LSCO conductive thin film of the present invention, such a composition for forming an LSCO conductive thin film of the present invention is applied to a heat-resistant substrate and heated in air, an oxidizing atmosphere or a steam-containing atmosphere. This step is repeated until a film having a desired thickness is obtained, and the film is fired at or above a crystallization temperature at least during or after heating in the final step. Even after the composition for forming a conductive thin film has been stored for a long period of time, a good LSCO conductive thin film having a uniform and high film quality can be formed.

[0008]

Embodiments of the present invention will be described below in detail.

The raw material of the organometallic compound used in the present invention is, specifically, a metal alkoxide of La, Sr and Co, a partial hydrolyzate thereof and / or an organic acid salt. Alkoxides such as 2-methoxyethoxide are exemplified. Organic acid salts such as strontium 2-ethylhexanoate as the Sr compound,
Alkoxides such as strontium-2-methoxyethoxide are exemplified. Examples of the Co compound include an organic acid salt such as cobalt octylate. The metal alkoxide may be used as it is, or its partial hydrolyzate may be used to accelerate the decomposition.

In order to prepare the composition for forming an LSCO conductive thin film of the present invention, these starting organometallic compounds are dissolved in an appropriate solvent in a ratio corresponding to a desired LSCO conductive thin film composition, and the composition is applied. Adjust to an appropriate concentration.

The solvent of the LSCO conductive thin film forming composition used here is appropriately determined according to the starting organometallic compound. Generally, carboxylic acids, alcohols, esters, ketones (for example, acetone, Methyl ethyl ketone), ethers (e.g., dimethyl ether, diethyl ether), cycloalkanes (e.g., cyclohexane, cyclohexanol), aromatics (e.g., benzene, toluene, xylene), tetrahydrofuran, and the like, or two or more of these A mixed solvent can be used.

Specific examples of the carboxylic acid include n-butyric acid, α-methylbutyric acid, i-valeric acid, 2-ethylbutyric acid,
2,2-dimethylbutyric acid, 3,3-dimethylbutyric acid, 2,3
-Dimethylbutyric acid, 3-methylpentanoic acid, 4-methylpentanoic acid, 2-ethylpentanoic acid, 3-ethylpentanoic acid, 2,2-dimethylpentanoic acid, 3,3-dimethylpentanoic acid, 2,3-dimethylpentane It is preferable to use an acid, 2-ethylhexanoic acid, or 3-ethylhexanoic acid.

Examples of the ester include ethyl acetate, propyl acetate, n-butyl acetate, sec-butyl acetate, tert-butyl acetate, isobutyl acetate, n-amyl acetate, sec-amyl acetate, tert-amyl acetate, and isoamyl acetate. It is preferable to use 1-propanol, 2-propanol, 1-butanol, 2-butanol, iso-butyl alcohol, 1-propanol.
It is preferable to use pentanol, 2-pentanol, 2-methyl-2-pentanol, and 2-methoxyethanol.

The total concentration of the organometallic compound in the organometallic compound solution of the composition for forming an LSCO conductive thin film is as follows:
It is preferable to be about 0.1 to 20% by weight in terms of metal oxide.

In this organometallic compound solution, if necessary, β-diketones (eg, acetylacetone, heptafluorobutanoylpivaloylmethane, dipivaloylmethane, trifluoroacetylacetone, benzoyl) may be used as a stabilizer. Acetone, etc.), ketone acids (eg, acetoacetic acid, propionylacetic acid, benzoylacetic acid, etc.), lower alkyl esters of these ketone acids such as methyl, propyl, butyl, etc., and oxyacids (eg, lactic acid, glycolic acid, α-oxy acid) Butyric acid, salicylic acid, etc.), lower alkyl esters of these oxyacids, oxyketones (eg, diacetone alcohol, acetoin, etc.), α-amino acids (eg, glycine, alanine, etc.), alkanolamines (eg, jetanol) Amine, triethanolamine, mono The ethanolamine) or the like, may be added from 0.2 to 3 approximately at (stabilizer number of molecules) / (number of metal atoms).

In the present invention, the organometallic compound solution thus prepared is filtered to remove particles, and the number of particles having a particle size of 0.5 μm or more is 50 particles / mL or less per 1 mL of the solution. So that

When the number of particles having a particle size of 0.5 μm or more in the organometallic compound solution exceeds 50 particles / mL, the long-term storage stability becomes poor. The number of particles having a particle size of 0.5 μm or more in this organometallic compound solution is preferably as small as possible, and particularly preferably 30 particles / mL or less.

The method for treating the prepared organometallic compound solution so that the number of particles is as described above is not particularly limited, but specific examples include the following methods. A filtration method in which a commercially available membrane filter having a pore size of 0.2 μm is used and the solution is pumped by a syringe. A pressure filtration method combining a commercially available membrane filter with a pore size of 0.05 μm and a pressure tank. A circulation filtration method combining the above filter and a solution circulation tank.

In any of the methods, the particle capture rate by the filter differs depending on the solution pressure.
It is generally known that the lower the pressure, the higher the trapping rate. In particular, in order to achieve the condition of 50 particles or less according to the present invention, it is necessary to pass the filter very slowly at a low pressure. There is. In the embodiments described later, the method of (1) does not realize 50 particles or less, but naturally the condition of the present invention can be achieved by lowering the pressure.

In order to form an LSCO conductive thin film according to the method of the present invention from such a composition for forming an LSCO conductive thin film, the above-described composition for forming an LSCO conductive thin film of the present invention is spin-coated and dipped. Coat, LSMC
D (Liquid Source Misted Ch)
It is applied onto a substrate by a coating method such as an electronic deposition method, and is dried (temporarily baked) and baked.

As a specific example of the substrate used, monocrystalline Si, polycrystalline Si, Pt, Pt (top layer) / Ti, Pt (top layer) / Ta, Ru, RuO ₂ ,
Ru (top layer) / RuO ₂ , RuO ₂ (top layer) / Ru,
Perovskite-type conductivity such as Ir, IrO ₂ , Ir (top layer) / IrO ₂ , Pt (top layer) / Ir, Pt (top layer) / IrO ₂ , SrRuO ₃ or (La _x Sr _{1 -x} ) CoO ₃ A substrate using an oxide or the like can be given, but not limited thereto.

If the desired film thickness cannot be obtained by one coating, the steps of coating and drying are repeated a plurality of times, followed by main baking.

Here, the calcination is performed in air, in an oxidizing atmosphere, or in a steam-containing atmosphere since the calcination is performed to remove the solvent and hydrolyze the organic metal compound to convert it to a complex oxide. Even when heated in the air, the water required for hydrolysis is sufficiently ensured by the humidity in the air. This heating may be performed in two stages of low-temperature heating for removing the solvent and high-temperature heating for decomposing the organometallic compound.

[0024] The main firing is a step for firing the thin film obtained by the preliminary firing at a temperature higher than the crystallization temperature to crystallize, thereby obtaining an LSCO conductive thin film.

Generally, the calcination is performed at 150 to 550 ° C., and the main calcination is performed at 450 to 800 ° C.

[0026]

The present invention will be described more specifically below with reference to examples and comparative examples.

In the following Examples and Comparative Examples,
The following were used as organometallic compound raw materials. La compound: lanthanum-2-methoxyethoxide Sr compound: strontium-2-methoxyethoxide Co compound: cobalt octylate Examples 1-3, Comparative Examples 1-12 Toluene was used as an organic solvent, and the above metal compound was used for this. Was dissolved and refluxed at a solvent boiling point for 24 hours to carry out a complexing reaction. Further, for the purpose of stabilizing the solution, acetylacetone was added in a molar amount of 1.5 times the total number of moles of La and Sr, and the reaction was performed under reflux for 1 hour. The total concentration of the organometallic compound in this solution was about 8% by weight in terms of metal oxide.

The obtained solution was filtered by the following method, and the number of particles having a particle size of 0.5 μm or more in the solution after the filtration was measured by a submerged particle counter. The results are shown in Table 1. Was. However, Comparative Example 1,
In Nos. 5 and 9, the number of particles was measured without filtering.

[Filtration method] A: 9: 1 mixture of the liquid filtered by the filtration method and the stock solution B: The filtration method C: The filtration method D: The filtration method Then, each solution is shielded from light at room temperature. When stored for a long time, the number of particles having a particle size of 0.5 μm or more in the solution is measured by a submerged particle counter,
The changes over time are shown in Table 1.

In Examples 1 to 3, each solution was stored for 3 months after filtration, and then a thin film was formed by the sol-gel method according to the following method.

That is, each solution was applied on a 6-inch silicon substrate by spin coating at 3000 rpm for 15 seconds. The film quality of the surface of the obtained coating film was confirmed by examining the presence or absence of striation by optical microscopic observation, and evaluated according to the following criteria. The results are shown in Table 1. ：: good △: almost good ×: bad Also, as described above, after application, drying was performed at 400 ° C. for 10 minutes. This application and drying were repeated four times, and then RTA (rapid) was performed in an oxygen atmosphere at 800 ° C. for 1 minute. LSCO conductive thin film having a thickness of 2800 ° was formed by baking with a heat treatment device).
The conductive properties of this LSCO conductive thin film were examined with a four-probe surface resistance meter, and the results are shown in Table 1.

[0032]

[Table 1]

From Table 1, it can be seen that the storage stability can be maintained for more than 3 months by setting the number of initial particles (particles having a particle size of 0.5 μm or more) in the solution to 50 particles / mL or less. It can be seen that a composition for forming an LSCO conductive thin film having excellent properties is provided. Further, by using such a composition for forming an LSCO conductive thin film,
It can be seen that a high-quality coating film can be formed even after long-term storage, whereby a LSCO conductive thin film having excellent conductive properties and its reproducibility can be formed.

[0034]

As described in detail above, according to the present invention, LS which has no problem of generation of precipitates and increase of particles even after long-term storage, has extremely good long-term storage stability, and has high practicality.
A composition for forming a CO conductive thin film is provided.
Using the composition for forming an SCO conductive thin film, a LSCO conductive thin film having high quality and excellent conductive properties can be formed with good reproducibility.

Claims (2)

[Claims] 1. A composition for forming an LSCO conductive thin film comprising an organometallic compound solution for forming a perovskite-type LSCO conductive thin film, wherein an amount of particles having a particle diameter of 0.5 μm or more is 50 particles /
mL or less, a composition for forming an LSCO conductive thin film. 2. The step of applying the composition for forming an LSCO conductive thin film according to claim 1 to a heat-resistant substrate and heating the composition in air, an oxidizing atmosphere, or a steam-containing atmosphere to form a film having a desired thickness. A method for forming an LSCO conductive thin film, characterized in that the film is repeatedly fired at or above a crystallization temperature during or after heating in a final step at least until obtained.