Barium titanate precursor dispersion and method for producing same

Abstract

To provide a dispersion liquid of a barium titanate precursor, from which a barium titanate thin film can be produced by a simple method, and a method of producing the same.SOLUTION: The dispersion liquid of a barium titanate precursor includes a titanium element, a barium element, and lactic acid.SELECTED DRAWING: None

Description

[Technical Field]

[0001] The present invention relates to a barium titanate precursor dispersion and a method for producing the same. [Background technology]

[0002] Barium titanate (BaTiO3) is a compound that exhibits a high dielectric constant and is widely used in electronic components such as multilayer ceramic capacitors and piezoelectric elements. Furthermore, as electronic devices become smaller and their performance improves, there is a demand for the formation of fine barium titanate thin films. For example, thin film formation by laminating fine barium titanate particles and thin film formation by the sol-gel method have been studied (e.g., Patent Documents 1 and 2). [Prior art documents] [Patent documents]

[0003] [Patent Document 1] Japanese Patent Application Laid-Open No. 2002-255552 [Patent Document 2] Japanese Patent Application Laid-Open No. 2009-227542 Summary of the Invention [Problem to be solved by the invention]

[0004] Thin film formation by laminating fine barium titanate particles has the problem that the particles tend to aggregate, making it difficult to obtain a thin film of uniform thickness. Furthermore, thin film formation by the sol-gel method often uses expensive and unstable titanium alkoxides as water-soluble titanium salts, making it difficult to reduce production costs.

[0005] In view of the above, the present invention provides a barium titanate precursor dispersion that can produce a barium titanate thin film in a simple manner, and a method for producing the same. [Means for solving the problem]

[0006] The barium titanate precursor dispersion of the present invention is characterized by containing titanium element, barium element, and lactic acid.

[0007] The barium titanate precursor dispersion of the present invention preferably has a pH of 8 or higher.

[0008] The barium titanate thin film precursor of the present invention is characterized by comprising a dried product of the above-mentioned barium titanate precursor dispersion.

[0009] The barium titanate thin film of the present invention is characterized by comprising a fired product of the above-mentioned barium titanate thin film precursor.

[0010] The method for producing a barium titanate thin film of the present invention is characterized by comprising a mixing step of mixing solutions containing titanium element, barium element, and lactic acid to form a barium titanate precursor dispersion, a step of applying the barium titanate precursor dispersion onto an inorganic substrate to form a barium titanate thin film precursor, and a step of firing the barium titanate thin film precursor. [Effects of the Invention]

[0011] According to the present invention, it is possible to provide a barium titanate precursor dispersion liquid that can produce a barium titanate thin film by a simple method, and a method for producing the same. DETAILED DESCRIPTION OF THE INVENTION

[0012] The barium titanate precursor dispersion of the present invention is characterized by containing elemental titanium, elemental barium, and lactic acid. Also, the method for producing a barium titanate thin film of the present invention is characterized by comprising a mixing step of mixing solutions containing elemental titanium, elemental barium, and lactic acid to form a barium titanate precursor dispersion, a step of applying the barium titanate precursor dispersion onto an inorganic substrate to form a barium titanate thin film precursor, and a step of firing the barium titanate thin film precursor.

[0013] <Method of manufacturing barium titanate thin film> First, a solution containing titanium element, barium element, and lactic acid is mixed to prepare a barium titanate precursor dispersion. More specifically, a titanium source solution containing titanium element and lactic acid is mixed with a barium source.

[0014] The titanium element source solution contains elemental titanium and lactic acid. Metallic titanium is preferably used as the titanium element source. Metallic titanium can be used as a water-soluble titanium element source by dissolving it in a mixed solution of H2O2 and NH3 (peroxotitanium solution). The titanium element source may contain, in addition to metallic titanium, a metal salt (e.g., a water-soluble metal salt) that is soluble in the solvent used. For example, titanium chloride may be used as the metal salt.

[0015] It is preferable to add a hydroxycarboxylic acid, particularly an α-hydroxycarboxylic acid, to the peroxotitanium solution, as this allows the peroxotitanate ions to form a peroxohydroxycarboxylic acid titanium complex, which is more likely to be stabilized.

[0016] The barium titanate precursor dispersion of the present invention contains lactic acid, a hydroxycarboxylic acid, as an essential component. This stabilizes the titanium ions in the peroxotitanium solution, making it easier to use as a suitable titanium element source solution. Furthermore, as described below, it also facilitates increasing the viscosity of the resulting barium titanate precursor dispersion. The barium titanate precursor dispersion of the present invention is sufficient as long as it contains at least lactic acid, and may further contain other hydroxycarboxylic acids. Specifically, it may contain, for example, glycolic acid, tartaric acid, malic acid, etc.

[0017] The amount of lactic acid added is preferably 0.25 or more, 0.50 or more, or 0.75 or more in terms of molar ratio (lactic acid / titanium ion) relative to the titanium ions contained in the peroxotitanium solution. This facilitates favorable stabilization of the titanium ions in the peroxotitanium solution. The upper limit is preferably 4 or less, 3 or less, 2 or less, and particularly 1.5 or less. If the amount of lactic acid added is too large, the amount of lactic acid polymer increases, making the viscosity of the dispersion too high and making film formation difficult. Note that when hydroxycarboxylic acids other than lactic acid are contained, the total amount of hydroxycarboxylic acids is preferably 0.25 or more, 0.50 or more, or 0.75 or more in terms of molar ratio (hydroxycarboxylic acid / titanium ion) relative to the titanium ions contained in the peroxotitanium solution. The upper limit is preferably 4 or less, 3 or less, and particularly 2 or less.

[0018] As the barium element source, it is preferable to use a metal salt (e.g., a water-soluble metal salt) that is soluble in the solvent used. For example, it is preferable to use barium hydroxide, barium nitrate, barium acetate, or barium chloride, and it is particularly preferable to use barium acetate. Barium acetate has high solubility in water and can be easily mixed with the titanium element source solution described above. These raw materials may be used alone or in combination of two or more compounds.

[0019] To adjust the properties of barium titanate, salts of other metals may be dissolved in the solvent and added. Examples of other metals include tin, zirconium, calcium, strontium, magnesium, and nickel. When adding these metals, it is preferable to substitute titanium with tin or zirconium, and barium with calcium, strontium, magnesium, and nickel, in equivalent amounts of metal ions. This method allows for mixing in solution, making it easy to uniformly disperse the added metals.

[0020] In addition to the H2O2 and NH3 mixed solution, any other solution such as a dispersant may be added to the barium titanate precursor dispersion. For example, water, ethanol, polyethylene glycol, glycerin, etc. may be added. The amount added is preferably 0.01% or more, 0.05% or more, 0.1% or more, and particularly 0.2% or more, based on the weight of the peroxotitanium solution. The upper limit is, for example, 5% or less, 4% or less, or 3% or less. Preferably, it is 2% or less, and particularly 1.5% or less.

[0021] The barium titanate precursor dispersion of the present invention preferably has a pH of 8 or higher, particularly 9 or higher. This facilitates the promotion of polymerization of the added lactic acid, making it possible to provide a dispersion with adjustable viscosity.

[0022] Next, the barium titanate precursor dispersion is applied to an inorganic substrate and dried. This allows a barium titanate thin film precursor to be formed from the dried barium titanate precursor dispersion. Examples of coating methods that can be used include spin coating, dip coating, and spray coating.

[0023] As described above, the barium titanate precursor dispersion of the present invention is a dispersion containing lactic acid, and its viscosity can be adjusted by polymerization of lactic acid. Generally, when coating is performed using a low-viscosity solution, the film thickness formed in one run tends to be too small. Therefore, multiple coatings of the solution are required to achieve the desired film thickness. On the other hand, by appropriately adjusting the viscosity of the barium titanate precursor dispersion of the present invention, the desired film thickness can be easily achieved in a single coating run. In other words, the thickness of the barium titanate thin film precursor and barium titanate thin film formed in one run can be easily controlled, reducing the number of coatings and thereby reducing film formation costs. Specifically, the thickness of the barium titanate thin film obtained in a single film formation can be 0.05 μm or more, 0.1 μm or more, and particularly 0.2 μm or more. The upper limit can be, for example, 2 μm or less, particularly 1 μm or less.

[0024] The inorganic substrate is not particularly limited, but examples thereof include glass substrates, glass ceramic substrates, alumina substrates, silicon nitride substrates, and aluminum nitride substrates.

[0025] Next, the barium titanate thin film precursor is fired to form a barium titanate thin film. The firing temperature is, for example, preferably 600°C or higher, 700°C or higher, and particularly preferably 800°C or higher. The upper limit is, for example, preferably 1200°C or lower, 1100°C or lower, and particularly preferably 1000°C or lower. If the firing temperature is too low, firing may not proceed sufficiently. If the firing temperature is too high, production costs tend to be high.

[0026] The firing is preferably carried out in an air atmosphere to prevent residual lactic acid, but may be carried out in combination with firing in an inert atmosphere, a reducing atmosphere, or a vacuum.

[0027] The firing time is not particularly limited, but is preferably 1 to 10 hours, particularly 2 to 5 hours. If the firing time is too short, firing may not proceed sufficiently. If the firing time is too long, production costs tend to increase.

[0028] As described above, the barium titanate precursor dispersion of the present invention contains titanium element, barium element, and lactic acid. This configuration stabilizes titanium ions in the peroxotitanium solution. Furthermore, it becomes easier to control the thickness of the barium titanate thin film precursor and barium titanate thin film formed at one time, reducing the number of coatings and thereby reducing film formation costs. Therefore, the barium titanate precursor dispersion of the present invention enables the production of a barium titanate thin film by a simple method, thereby reducing the film formation costs of the barium titanate thin film. [Example]

[0029] The present invention will be described below based on examples, but the present invention is not limited to these examples.

[0030] Tables 1 and 2 show Examples 1 to 7 of the present invention and Comparative Examples 8 and 9.

[0031] [Table 1]

[0032] [Table 2]

[0033] Examples 1 to 7 were prepared as follows. First, 0.03 g of metallic titanium powder was weighed as a titanium element source and added to 6 g of a 31 wt % H2O2 aqueous solution, followed by stirring in a water bath. Next, 1.5 g of a 28 wt % NH3 aqueous solution was added to the aqueous solution, followed by stirring until the metallic titanium powder was completely dissolved, yielding a yellowish-white mixed aqueous solution (step a). Next, the amount of L(+)-lactic acid shown in Table 1 was added to the mixed aqueous solution (step b). Next, the aqueous solution was heated and degassed on a hot plate at 100°C, yielding a yellowish-white suspended titanium element source solution (step c).

[0034] After the titanium element source solution was allowed to stand until it reached room temperature, 0.15 g of barium acetate Ba(CH3COO)2 was added as a barium element source and stirred to obtain a barium titanate precursor dispersion liquid as a white suspension (step d).

[0035] The pH of the solution was measured in steps (a) to (d) of Examples 1 to 3. The barium titanate precursor dispersion was applied to an Al2O3 substrate by spin coating, and then fired in air for 5 hours at the temperature shown in Table 1. The obtained thin film was also subjected to XRD measurement to confirm the deposition of crystals.

[0036] In Comparative Example 8, a barium titanate precursor dispersion was prepared, applied, and fired under the same conditions as in Example 1, except that L(+)-tartaric acid was used (same molar amount) instead of L(+)-lactic acid.

[0037] In Comparative Example 9, heating was continued in step c to obtain a dried salt, and then the dried salt was dissolved in water and barium acetate Ba(CH3COO)2 was added. The obtained solution was applied and fired under the same conditions as in Example 2. The pH of the solution was measured in steps (a), (b), and (d).

[0038] As shown in Table 1, barium titanate was formed in the samples of Examples 1 to 7. The thickness of the obtained barium titanate thin film was 0.39 μm or more. On the other hand, as shown in Table 2, in the sample of Comparative Example 8, BaTi2O5 was precipitated as a crystal other than barium titanate (BaTiO3). In the sample of Comparative Example 9, only barium titanate was precipitated, but the thickness of the obtained thin film was very thin at 0.01 μm. [Industrial Applicability]

[0039] The barium titanate precursor dispersion of the present invention can be suitably used for producing a barium titanate thin film.

Claims

1. A barium titanate precursor dispersion liquid containing titanium element, barium element and lactic acid, wherein the molar ratio of (lactic acid / titanium ion) is 0.25 to 2.

2. The barium titanate precursor dispersion according to claim 1 , having a pH of 8 or more.

3. A barium titanate thin film precursor comprising a dried product of the barium titanate precursor dispersion liquid according to claim 1 or 2.

4. A barium titanate thin film comprising a fired product of the barium titanate thin film precursor according to claim 3.

5. A method for producing a barium titanate thin film, comprising: a mixing step of mixing solutions containing titanium element, barium element, and lactic acid, the molar ratio of lactic acid / titanium ion being 0.25 to 2, to form a barium titanate precursor dispersion; applying the barium titanate precursor dispersion onto an inorganic substrate to form a barium titanate thin film precursor; calcining the barium titanate thin film precursor; A method for producing a barium titanate thin film, comprising:

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