JP2005075714A - Method for manufacturing perovskite-type crystal particle - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for manufacturing crystal particles having an ABOx (perovskite)-type crystal structure with an average particle diameter of ≤100 nm, capable of drastically improving its productivity by lowering the processing temperature and shortening the treatment time in forming a dielectric film having an ABOx-type crystal structure. <P>SOLUTION: This method relates to manufacturing the crystal particles having the ABOx-type crystal structure with the average particle diameter of ≤100 nm and comprises a process (I) for dissolving a specific organometallic compound containing a metal species A which constitutes the crystal particles and a specific organometallic compound containing a metal species B, a hydrolysis process (II) for adding water to the solution prepared by the dissolving process and hydrolyzing a precursor in the solution to obtain the crystal particles, and a process (III) for purifying the crystal particles obtained by the hydrolysis process with an organic solvent. Crystal particles capable of manufacturing the dielectric film having good dielectric properties even under a mild condition of ≤400°C are obtainable by this method. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a method for producing crystal particles having an ABOx type (perovskite type) crystal structure and having an average particle size of 100 nm or less.

  Devices in the information industry field, including mobile phones, will require higher speed, higher capacity, and smaller size in the future, and research and development of high-functional devices to achieve this will be conducted extensively and vigorously. ing. Among them, dielectric materials having an ABOx type (perovskite type) crystal structure typified by barium titanate, barium strontium titanate, and lead zirconate titanate are widely used in the field of electronic devices including capacitors and memory materials. ing. However, in order to further reduce the size and performance of these electronic devices, it is indispensable to reduce the thickness of the element. To that end, the establishment of manufacturing technology for thin films with high-functional and high-quality dielectric properties is the key. It has become.

  Currently, thin film production methods are typically represented by PVD methods (physical vapor deposition methods) such as sputtering, chemical vapor deposition methods using organometallic compounds, and sol-gel methods. Various methods such as a liquid phase method are used.

  For example, in the case of lead zirconate titanate, a crystalline thin film having good dielectric properties can be obtained relatively easily by either the vapor phase method or the liquid phase method. On the other hand, in the case of barium titanate and barium strontium titanate, several examples have been reported that the synthesis of thin films exhibiting dielectric properties was performed using a vapor phase method or a sol-gel method. The manufacturing method is not established yet.

  As such a thin film synthesis method of barium titanate or barium strontium titanate, from the viewpoint of composition control and ease of shape formation, and further from the viewpoint of production cost, the liquid phase method is expected more than the vapor phase method. Studies on the synthesis of thin films by the gel method or coating pyrolysis method are actively conducted. The sol-gel method uses a sol solution (precursor solution) of a metal alkoxide as a starting material, synthesis from the sol state to the gel state by hydrolysis and polycondensation reaction, and finally to the metal oxide. Thin film formation by the sol-gel method refers to a process, and is less subject to restrictions on the shape and size of the substrate on which the thin film is formed, compared to other thin film formation methods such as the PVD method and the vapor phase method. In addition, there is an advantage that an expensive device is not required.

  By the way, in recent development of electronic devices, development of a technique for forming a dielectric thin film on a substrate having low heat resistance such as glass or resin is expected. However, in the conventional thin film forming method using the sol-gel method, a baking temperature of 500 ° C. or higher is required when converting an amorphous oxide coated on a substrate into an ABOx type crystal structure, Adapting to low temperature substrates is difficult.

  For example, when an amorphous coating layer is formed by applying a precursor solution containing each element of Ba, Sr, and Ti onto a substrate by a spin coating method, a dip coating method, or the like, in order to crystallize the coating layer. Requires high-temperature firing at 500 ° C. or higher. However, when firing at such a high temperature, the substrate is altered or deformed, or a reaction occurs at the interface between the substrate and the thin film layer, which causes various restrictions on the materials used for the substrate. It was.

  For this reason, in the thin film formation method by a liquid phase method, the technical innovation for reducing manufacturing process temperature is calculated | required.

  The present invention has been made in view of such circumstances. As a prior art deeply related to the present invention, for example, Patent Document 1 describes a method of producing a dielectric film having a high dielectric constant using a alkoxide of Ba, Sr, and Ti as a raw material by a coating method. However, since baking at 550 ° C. is required for crystallization, film formation on a substrate with low heat resistance is impossible.

Further, for example, in Patent Document 2, a solution obtained by partially hydrolyzing an alkoxide such as Ba or Ti is applied to a substrate, and the produced coating film is exposed to water vapor to form a crystalline BaTiO ₃ thin film at a low temperature. A method is described. However, in this method, the substrate is cooled to the temperature of liquid nitrogen and aging is required for a long time after the film formation, and the electrical characteristics of the generated crystallized film are not described.

Further, for example, Patent Document 3 describes a method for forming a crystalline gel by hydrolyzing an alkoxide such as Ba or Ti and using this to form a thin film. However, the dielectric film produced by this method has a large dielectric loss when fired at 450 ° C., and it is practically necessary to fire at a high temperature of 750 ° C. or higher.
JP-A-9-157008 Japanese Patent Laid-Open No. 2001-026421 JP 2002-275390 A

  The present invention has been made in view of the above-described circumstances, and by forming a dielectric film having an ABOx type crystal structure, the process temperature can be lowered and processing can be performed in a shorter time. An object of the present invention is to provide a method for producing crystal particles having an ABOx type crystal structure and having an average particle size of 100 nm or less, which can greatly improve productivity. That is, an object of the present invention is to provide a method for producing crystal particles having an ABOx type crystal structure and having an average particle diameter of 100 nm or less, which can form a dielectric film by low-temperature firing.

In the method for producing crystal grains according to the present invention, the metal species A is one or more metals selected from Li, Na, Ca, Sr, Ba, La, and the metal species B is selected from Ti, Zr, Ta, Nb. A method for producing crystal particles having an average particle diameter of 100 nm or less having an ABOx type crystal structure, which is one or more kinds of metals,
(I) at least one selected from metal alkoxides, metal carboxylates, and metal complexes, including metal species A constituting the crystal particles;
A dissolution step of dissolving at least one selected from a metal alkoxide, a metal carboxylate, and a metal complex, containing the metal species B constituting the crystal particles, in an organic solvent;
(II) hydrolysis step of adding crystal to the solution prepared in the dissolution step and hydrolyzing the precursor in the solution to obtain crystal particles,
(III) It is characterized by having a purification step of purifying the crystal particles obtained in the hydrolysis step with an organic solvent. In addition, in this specification, an average particle diameter means what is called a median diameter calculated | required from the median of the frequency of a particle size distribution.

  In the present invention, in the hydrolysis step, liquid water or an organic solvent containing water is preferably added dropwise to the solution.

According to the method for producing crystal grains of the present invention, crystal grains capable of producing a dielectric film having good dielectric properties even under mild conditions of 400 ° C. or lower can be obtained. By using the crystal particles, the dielectric film formation process is simplified and productivity is greatly improved as compared with a conventional process that requires crystallization by high-temperature firing in a heating furnace. Furthermore, if the crystal particles are used, a high temperature crystallization process is not required, and it is not possible to apply the conventional high temperature crystallization process to various substrates with low heat resistance that cannot be applied by the conventional sol-gel method. It is also possible to produce a crystallized film with good dielectric properties.

  Hereinafter, the present invention will be specifically described.

The method for producing crystal particles having an ABOx type crystal structure of the present invention and having an average particle size of 100 nm or less,
(I) at least one selected from metal alkoxides, metal carboxylates, and metal complexes, including metal species A constituting the crystal particles;
A dissolution step of dissolving at least one selected from a metal alkoxide, a metal carboxylate, and a metal complex, containing the metal species B constituting the crystal particles, in an organic solvent;
(II) hydrolysis step of adding crystal to the solution prepared in the dissolution step and hydrolyzing the precursor in the solution to obtain crystal particles,
(III) It is characterized by having a purification step of purifying the crystal particles obtained in the hydrolysis step with an organic solvent.

  Details will be described below.

  In the dissolution step (I), at least one selected from a metal alkoxide, a metal carboxylate, and a metal complex containing the metal species A constituting the particles having the ABOx type crystal structure as a raw material, and the ABOx type crystal Using at least one selected from metal alkoxides, metal carboxylates, and metal complexes containing metal species B constituting the particles having a structure, they are dissolved in an organic solvent by a conventional method.

  In the present invention, the metal species A constituting the particles is one or more metals selected from Li, Na, Ca, Sr, Ba, and La, and the metal species B is selected from Ti, Zr, Ta, and Nb. One or more kinds of metals are preferred. Furthermore, among these, it is more preferable that the metal species A is one or more metals selected from Sr and Ba, and the metal species B is Ti.

  At this time, the concentration of the metal species A in the solution is 0.1 to 2.0 mmol / g, preferably 0.4 to 1.5 mmol / g, more preferably 0.5 to 1.0 mmol / g. The concentration of seed B is 0.1 to 2.0 mmol / g, preferably 0.4 to 1.5 mmol / g, more preferably 0.5 to 1.0 mmol / g.

《Metal alkoxide》
The metal alkoxide is a compound in which a metal atom and an alcohol are reacted, and is represented by the following general formula (1).

M ^a (OR ¹ ) _a (1)
[In the formula (1), M is Li, Na, Ca, Sr, Ba, La, Ti, Zr, Ta, Nb.
A is an integer of 1 to 7 according to the valence of the metal M, and R ¹ is a residue excluding the OH group of the alcohol. ]
As alcohol which forms the said metal alkoxide, what is shown to following formula (2) can be mentioned as a suitable example, for example.

R ¹ OH Formula (2)
[In the formula (2), R ¹ represents a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms, or a hydrocarbon group substituted with an alkoxyl group having 1 to 6 carbon atoms. ]
In the above general formula (2), when R ¹ is a saturated or unsaturated hydrocarbon group having 1 to 6 carbon atoms, examples of the alcohol include methanol, ethanol, 1-propanol, 2-propanol, butanol, and amyl. Examples thereof include alcohol and cyclohexanol.

In the general formula (2), when R ¹ is a hydrocarbon group having 1 to 6 carbon atoms and substituted with an alkoxyl group, examples of the alcohol include methoxymethanol, methoxyethanol, ethoxymethanol, and ethoxyethanol. , Methoxypropanol, ethoxypropanol, propoxypropanol and the like.

  More specifically, in the present invention, as the metal alkoxide represented by the general formula (1), for example, dimethoxybarium, diethoxybarium, dipropoxybarium, diisopropoxybarium, dibutoxybarium, diisobutoxybarium and the like. Strontium alkoxides such as dimethoxystrontium, diethoxystrontium, dipropoxystrontium, diisopropoxystrontium, dibutoxystrontium, diisobutoxystrontium; tetramethoxytitanium, tetraethoxytitanium, tetrapropoxytitanium, tetraisopropoxytitanium, tetra Titanium alkoxides such as butoxy titanium and tetraisobutoxy titanium; and the like can be preferably used.

《Metal carboxylate》
The metal carboxylate is a compound in which a metal atom and a carboxylic acid are reacted, and is represented by the following general formula (3).

M ^a (OCOR ² ) _a (3)
[In Formula (3), M is Li, Na, Ca, Sr, Ba, La, Ti, Zr, Ta, Nb.
A is an integer of 1 to 7 according to the valence of the metal M, and R ² is a residue excluding the COOH group of the carboxylic acid. ]
As a carboxylic acid which forms the said metal carboxylate, what is shown to following formula (4) can be mentioned as a suitable example, for example.

R ² COOH Formula (4)
[In Formula (4), R ² represents a hydrocarbon group substituted with a saturated or unsaturated hydrocarbon group having 1 to 10 carbon atoms. ]
Examples of the carboxylic acid represented by the general formula (4) include acetic acid, propionic acid, 2-methylpropionic acid, pentanoic acid, 2,2-dimethylpropionic acid, butanoic acid, hexanoic acid, 2-ethylhexanoic acid, Examples include octylic acid, nonanoic acid, decanoic acid, and the like.

More specifically, in the present invention, as the metal carboxylate represented by the general formula (3), for example, barium acetate, barium propionate, barium 2-methylpropionate, barium pentanoate, 2,2-dimethyl Barium carboxylates such as barium propionate, barium butanoate, barium hexanoate, barium 2-ethylhexanoate, barium octylate, barium nonanoate, barium decanoate; strontium acetate, strontium propionate, strontium 2-methylpropionate, Strontium pentanoate, strontium 2,2-dimethylpropionate, strontium butanoate, strontium hexanoate, strontium 2-ethylhexanoate, strontium octylate, strontium nonanoate, Strontium carboxylates such as phosphate strontium; and the like can be suitably used.

《Metal complex》
The metal complex is a compound in which an organic compound is coordinated to a metal atom, and is represented by the following general formula (5).

M ^a (OR ¹ ) _b (OCOR ² ) _c R ³ _d Formula (5)
[In Formula (5), M is Li, Na, Ca, Sr, Ba, La, Ti, Zr, Ta, Nb.
A is an integer of 1 to 7 according to the valence of the metal M, b is an integer of 0 to 7, c is an integer of 0 to 7, and a = b + c Fulfill. d is an integer of 1-7. R ¹ is a residue obtained by removing the OH group of the alcohol described above, and R ² is a residue obtained by removing the COOH group of the carboxylic acid described above. R ³ is an organic compound. ]
Examples of the organic compound R ³ coordinated to the metal atom include ethers.
-1) and the compound shown to (6-2) can be mentioned.

R ⁴ (OR ⁵ ) _m Formula (6-1)
[In Formula (6-1), R ⁴ and R ⁵ each represent a saturated or unsaturated hydrocarbon group having 1 to 10 carbon atoms, and m is an integer of 1 to 4. ]
(R ⁶ O) _n Formula (6-2)
[In the formula (6-2), R ⁶ represents an alkylene group having 1 to 10 carbon atoms, and n is an integer of 1 to 3. ]
Specific examples of ethers include methylal, diethyl ether, dipropyl ether, diisopropyl ether, dibutyl ether, diamyl ether, diethyl acetal, dihexyl ether, tetrahydrofuran, tetrahydropyran, trioxane, dioxane and the like.

Examples of the organic compound R ³ coordinated to the metal atom include ketones, and examples include compounds represented by the following formulas (7) and (8).

R ⁷ R ⁸ C═O (7)
R ⁷ (C═O) (CH ₂ ) _x (C═O) R ⁸ Formula (8)
[In the formulas (7) and (8), R ⁷ and R ⁸ each have 1 carbon atom which may be substituted with a hydroxyl group.
10 to 10 saturated or unsaturated hydrocarbon groups. Moreover, in Formula (8), x is an integer of 1-10. ]
Specific ketones include, for example, acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl cyclohexyl ketone, diethyl ketone, ethyl butyl ketone, trimethylnonanone, acetonyl acetone, dimethyl oxide, phorone, Examples include cyclohexanone, diacetone alcohol, and acetylacetone.

  Examples of the organic compound coordinated to the metal atom include esters, and examples thereof include compounds represented by the following formulas (9-1) and (9-2).

R ⁹ (COOR ¹⁰ ) _y Formula (9-1)
[In formula (9-1), R ⁹ represents a hydrogen atom or a saturated or unsaturated hydrocarbon group having 1 to 10 carbon atoms which may be substituted with an oxygen atom, a hydroxyl group or an acyl group, R ¹⁰ represents a saturated or unsaturated hydrocarbon group having 1 to 10 carbon atoms which may be substituted with an alkoxy group, and y is an integer of 1 to 2. ]
(COOR ¹¹ ) ₂ Formula (9-2)
[In formula (9-2), R ¹¹ represents a saturated or unsaturated hydrocarbon group having 1 to 10 carbon atoms. ]
Specific esters include, for example, ethyl formate, methyl acetate, ethyl acetate, butyl acetate, cyclohexyl acetate, methyl propionate, ethyl butyrate, ethyl oxyisobutyrate, ethyl acetoacetate, ethyl lactate, methoxybutyl acetate, diethyl oxalate And diethyl malonate.

More specifically, in the present invention, as the metal complex represented by the general formula (5), for example, titanium allyl acetoacetate triisopropoxide, titanium dibutoxide (bis-2,4-pentanedionate), Titanium diisopropoxide (bis-2,4-pentanedionate), titanium dibutoxide bis (tetramethylheptanedionate), titanium diisopropoxide bis (tetramethylheptanedionate), titanium dibutoxide bis (ethyl) Acetoacetate), titanium diisopropoxide bis (ethyl acetoacetate),
Etc. can be used suitably.

《Organic solvent》
Examples of the organic solvent used for dissolving the metal alkoxide, metal carboxylate or metal complex include alcohol solvents, polyhydric alcohol solvents, ether solvents, ketone solvents, ester solvents and the like. it can.

  Examples of alcohol solvents include methanol, ethanol, propanol, butanol, amyl alcohol, cyclohexanol, and methylcyclohexanol.

  As the polyhydric alcohol solvent, ethylene glycol monomethyl ether, ethylene glycol monoacetate, diethylene glycol monomethyl ether, diethylene glycol monoacetate, propylene glycol monoethyl ether, propylene glycol monoacetate, dipropylene glycol monoethyl ether, propylene glycol monomethyl ether, Mention may be made of propylene glycol monopropyl ether, methoxybutanol, propylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol propyl ether, dipropylene glycol monobutyl ether and the like.

  Examples of ether solvents include methylal, diethyl ether, dipropyl ether, dibutyl ether, diamyl ether, diethyl acetal, dihexyl ether, trioxane, dioxane and the like.

  Ketone solvents include acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl cyclohexyl ketone, diethyl ketone, ethyl butyl ketone, trimethylnonanone, acetonyl acetone, dimethyl oxide, phorone, cyclohexanone, diacetone. Alcohol etc. can be mentioned.

  Ester solvents include ethyl formate, methyl acetate, ethyl acetate, butyl acetate, cyclohexyl acetate, methyl propionate, ethyl butyrate, ethyl oxyisobutyrate, ethyl acetoacetate, ethyl lactate, methoxybutyl acetate, diethyl oxalate, diethyl malonate Etc.

  1 type may be used for said solvent and it can also be used in combination of 2 or more type.

Next, in the hydrolysis step (II), the temperature of the solution prepared in the dissolution step (I) is kept at -78 to 200 ° C, preferably -20 to 100 ° C, more preferably 0 to 50 ° C. Water is usually added to the solution in an amount of 5 to 300 times mol, preferably 10 to 200 times mol, more preferably 20 to 100 times mol to 1 mol of metal species A, and the precursor in the solution is hydrolyzed. Crystallize.

  By maintaining the temperature of the solution within the above range during hydrolysis, the crystallinity of particles formed by crystallization is improved.

  Further, the amount of water added to the solution at the time of hydrolysis is optimal for obtaining particles having a high crystallinity in the above range with respect to the metal species A, and the amount of water to be added is the above lower limit. When it is less than the above value, or when it is more than the above upper limit value, the crystallinity may be lowered.

  When the crystallinity of the particles thus formed is improved, the particles can be dispersed in an organic solvent to form a uniform dielectric film having excellent dielectric properties.

  As a method for adding water to the solution in the hydrolysis step, only water may be directly added to the solution, or it may be added by mixing with water using one of the above organic solvents, Alternatively, two or more of the above organic solvents may be combined and mixed with water, but it is preferably carried out by dropping liquid water or an organic solvent containing liquid water into the solution.

  Thus, when water for hydrolysis is added by dropping into the solution using only liquid water or an organic solvent containing liquid water, hydrolysis is reproducible and efficient. This is preferable because it can be carried out automatically.

  At this time, the water to be added may contain a catalyst. Examples of usable catalysts in this case include acid catalysts such as inorganic acids (for example, hydrochloric acid, sulfuric acid, nitric acid) and organic acids (for example, acetic acid, propionic acid, butyric acid, maleic acid), sodium hydroxide, water Examples thereof include inorganic or organic alkali catalysts such as potassium oxide, barium hydroxide, ammonia, monoethanolamine, diethanolamine, and tetramethylammonium hydroxide.

  Among these, it is more preferable to use an alkali catalyst. When an organic acid such as a carboxylic acid is used, carbon dioxide generated by decomposition of the organic acid may remain in the film and affect the electrical characteristics of the formed dielectric film. In addition, when an inorganic acid such as hydrochloric acid or nitric acid is used, a part of the acid component may remain in the film, which may deteriorate the leakage current characteristics of the formed dielectric film.

  After adding water, the resulting hydrolysis / condensation product is usually at a temperature of −10 to 200 ° C., preferably 20 to 150 ° C., more preferably 30 to 100 ° C., usually 0.5 to 200 hours, preferably 1 It is desirable to hold for ˜100 hours, more preferably 3 to 20 hours.

  By passing through the dissolution step (I) and the hydrolysis step (II), particles having an average particle size of 100 nm or less, preferably an average particle size of 20 to 80 nm, having an ABOx type crystal structure can be obtained.

Then, the refinement | purification process (III) which refine | purifies this particle | grain with an organic solvent is performed, and the crystal grain of this invention is obtained.

The crystal particles produced by crystallizing the hydrolysis / condensation product as described above include unreacted metal alkoxide, metal carboxylate, metal complex (hereinafter also simply referred to as organometallic compound), and partial hydrolysis. And impurities such as metal hydroxides and metal ions generated by the complete hydrolysis of the organometallic compound and the organometallic compound.

In particular, in a composition in which such crystal particles are dispersed as they are in an organic solvent, when the concentration of metal species A in the liquid is higher than 1 mol%, a dielectric film is formed using this composition. In case,
(1) The dielectric film exhibits ionic conductivity, and leakage current increases. (2) The dielectric loss of the dielectric film increases.

In this specification, the concentration of metal species A in the liquid is defined as a value measured and calculated by the following procedures (A) to (D).
(A) Add α moles of particles having an ABOx type crystal structure and an average particle diameter of 100 nm or less to methyl cellosolve so as to be 5% by weight, and disperse by stirring or ultrasonic irradiation.
(B) The particle dispersion prepared in (A) is centrifuged at 15000 rpm for 1 hour to settle the particles, and the supernatant is separated.
(C) The amount β of metal species A and the amount γ mol of metal species B contained in the supernatant separated in (B) are measured by ICP-MS (inductively coupled plasma mass spectrometer).
(D) Based on the amount of metal species A and metal species B measured in (C), the concentration of metal species A in the liquid is calculated by the following calculation formula.

Concentration of metal species A in liquid (mol%) = (β−γ) / α × 100
In addition, a large amount of water is contained in the crystal particles produced by crystallizing the hydrolyzed / condensed product. In particular, in a composition in which such crystal particles are dispersed as they are in an organic solvent, when 1% by weight or more of water is present in the composition,
(3) Problems such as deterioration of dispersibility of particles having an ABOx type crystal structure arise. When the dispersibility of the particles in the composition is deteriorated, the average particle size of the particles is increased, which may lead to sedimentation or white turbidity of the film when the film is formed.

  Therefore, in order to obtain crystal particles capable of producing a good dielectric film, the crystal particles obtained in the hydrolysis step (II) are purified with an organic solvent, and the purified particles are washed with an organic solvent that is a washing liquid. When the composition is obtained by dispersing in a new organic solvent, the concentration of metal species A in the composition is 1 mol% or less, preferably 0.5 mol% or less, and It is important to reduce the concentration of contained water to 1% by weight or less, preferably 0.05 to 0.5% by weight.

  The concentration of the metal species A in the composition is determined by introducing an atomized sample into high-temperature argon plasma, ionizing the elements, and separating and analyzing these ions by mass. Based on the value measured by ICP-MS), it can be calculated as described above, and the concentration of water contained in the composition can be measured by the Karl Fischer coulometric titration method.

Purification step (III) for purifying the crystal particles obtained in the hydrolysis step (II) with an organic solvent
In the method of purifying crystal particles with an organic solvent, any method may be used as long as it is possible to separate the crystal particles from the organic solvent after purification. In addition, the particles are settled by decantation or centrifugation, the supernatant is removed, and the organic solvent is added again to the precipitated crystal particles, and the heating step is repeated 2-5 times to be included in the crystal particles. The above impurities and moisture can be removed to reduce their concentration. Moreover, the concentration of the impurities and water contained can be reduced by adding an organic solvent to the particles and repeating dialysis using a semipermeable membrane 2 to 5 times.

As a result, when the purified crystal particles are dispersed in an organic solvent to obtain a composition, the concentration of metal species A in the liquid and the concentration of water in the composition are reduced to the predetermined concentration. And the above problems (1) to (3) can be solved.

Examples of the organic solvent used in the purification step (III) include alcohol solvents, polyhydric alcohol solvents, ether solvents, ketone solvents, ester solvents and the like.

  Examples of alcohol solvents include methanol, ethanol, propanol, butanol, amyl alcohol, cyclohexanol, and methylcyclohexanol.

  As the polyhydric alcohol solvent, ethylene glycol monomethyl ether, ethylene glycol monoacetate, diethylene glycol monomethyl ether, diethylene glycol monoacetate, propylene glycol monoethyl ether, propylene glycol monoacetate, dipropylene glycol monoethyl ether, propylene glycol monomethyl ether, Mention may be made of propylene glycol monopropyl ether, methoxybutanol, propylene glycol monoethyl ether acetate, propylene glycol monomethyl ether acetate, dipropylene glycol propyl ether, dipropylene glycol monobutyl ether and the like.

  Examples of ether solvents include methylal, diethyl ether, dipropyl ether, dibutyl ether, diamyl ether, diethyl acetal, dihexyl ether, trioxane, dioxane and the like.

  Ketone solvents include acetone, methyl ethyl ketone, methyl propyl ketone, methyl isobutyl ketone, methyl amyl ketone, methyl cyclohexyl ketone, diethyl ketone, ethyl butyl ketone, trimethylnonanone, acetonyl acetone, dimethyl oxide, phorone, cyclohexanone, diacetone. Alcohol etc. can be mentioned.

  Ester solvents include ethyl formate, methyl acetate, ethyl acetate, butyl acetate, cyclohexyl acetate, methyl propionate, ethyl butyrate, ethyl oxyisobutyrate, ethyl acetoacetate, ethyl lactate, methoxybutyl acetate, diethyl oxalate, diethyl malonate Etc.

  1 type may be used for said solvent and it can also be used in combination of 2 or more type.

  In addition, after separating the crystal particles obtained according to the present invention from an organic solvent which is a washing solution, the composition can be added to a new organic solvent and dispersed therein to prepare a composition (particle dispersion).

  In this case, any method for dispersing the crystal particles in the organic solvent may be used as long as the particles can be uniformly dispersed in the organic solvent. For example, it is dispersed in a solvent while performing mechanical stirring or stirring using ultrasonic waves.

Examples of the organic solvent used for dispersion include the same alcohol solvents, polyhydric alcohol solvents, ether solvents, ketone solvents, ester solvents and the like as exemplified as the organic solvent used in the purification step (III). be able to.

  1 type may be used for said solvent and it can also be used in combination of 2 or more type. The organic solvent used for dispersion may be the same as or different from the organic solvent used for purification.

  1 type may be used for said solvent and it can also be used in combination of 2 or more type.

  Considering the stability of the composition, the content of crystal particles in the composition is 1 to 20% by weight, preferably 3 to 15% by weight, based on the total composition, as the solid content concentration.

In order to facilitate the dispersion of the crystal particles, a nonionic surfactant may be used as a dispersant when the purified crystal particles are dispersed in an organic solvent. For example, polyoxyethylene-polyoxypropylene glycol, polyoxypropylene-polyoxyethylene condensate of ethylenediamine (pluronic type), polyethyleneimine, polyvinylpyrrolidone, perfluoroalkyl group-containing oligomer, and the like can also be used.

  The type and amount of the dispersing agent can be appropriately selected and used depending on the type of crystal particles and the type of solvent in which the crystal particles are dispersed, but considering the dielectric properties of the obtained dielectric film, 0.001 to 10 g, preferably 0.005 to 3 g, more preferably 0.01 to 1 g.

  Further, a composition in which the crystal particles obtained by the present invention are dispersed in an organic solvent is applied to a substrate, a coating film is formed on the substrate, and this is dried as necessary, preferably further heated and fired. Thus, a dielectric film can be formed.

  Specifically, first, the composition described above is applied onto a substrate to form a coating film. Here, as a method for applying the composition onto the substrate, for example, an open spin coating method, a closed spin coating method, a mist-coating LSM-CVD method (solution vaporization chemical vapor deposition method), a dipping method, and a spray method are used. A known coating method such as a roll coating method, a printing method, an ink jet method, or an electrophoretic electrodeposition method can be used.

  The coating film is usually dried at a temperature of 50 to 300 ° C, preferably 100 to 250 ° C.

  In this way, the dielectric film finally obtained is set to a desired film thickness by repeatedly applying the composition on the substrate and repeating a series of operations until drying as necessary. Can do.

  Thereafter, the coating film is heated and baked at a temperature usually exceeding 300 ° C. and not more than 900 ° C., preferably 400 to 750 ° C., to obtain a dielectric film. That is, when the composition is used, it goes without saying that a dielectric film can be obtained by firing in a high temperature region as in the conventional case, and is fired at a temperature lower than the conventional one, for example, a temperature of 400 ° C. or lower. Therefore, a dielectric film suitable for practical use can be obtained.

  The substrate to which the composition is applied may be flat or non-planar (for example, having a step), and the form is not particularly limited as long as a desired coverage can be realized. Further, the shape of the substrate is not particularly limited, and for example, a bulk, thin plate, or film shape can be used. Specific examples of such a substrate material include semiconductors, glasses, metals, plastics, and ceramics.

  Examples of the semiconductor substrate include a silicon wafer. An electrode made of a silicon oxide film, a metal such as Pt, Ir, or Ru and a conductive metal oxide that is a metal oxide thereof may be formed on the silicon wafer. A compound semiconductor substrate such as GaAs or InP can also be used.

  As the glass substrate, for example, a substrate made of quartz glass, borosilicate glass, soda glass, lead glass, lanthanum glass, or the like can be used.

  As the metal substrate, for example, a substrate made of stainless steel other than gold, silver, copper, nickel, aluminum, iron or the like can be used.

  As the plastic substrate, for example, a substrate made of polyimide, methacrylic resin, or the like can be used. These plastic substrates may have lower heat resistance than glass substrates and metal substrates. However, in the present invention, a dielectric film (crystallized film) can be formed at a low temperature. There is no fundamental problem.

  As the ceramic substrate, for example, a substrate made of silicon oxide, aluminum oxide, titanium oxide, silicon nitride, aluminum nitride, titanium nitride, silicon carbide, titanium carbide, or the like can be used.

  Since the dielectric film thus obtained has good dielectric characteristics and leakage current characteristics, it can be suitably used as an electronic component such as a capacitor.

[Example]
EXAMPLES Hereinafter, although this invention is demonstrated further more concretely based on an Example, this invention is not limited to these Examples.

(Preparation of crystal particle 1 and composition 1)
To 25.77 g of methyl cellosolve, 25.77 g of Ba (OCH ₂ CH ₃ ) ₂ was added and dissolved, and heated at 110 ° C. for 1 hour. Thereafter, Ti (OCH (CH ₃ ) ₂ ) ₄ was added to this solution in 32
. 21 g was added and further heated at 110 ° C. for 1 hour. 58 g of methanol was added to the resulting dark brown solution to prepare a raw material solution having a Ba concentration of 0.8 mmol / g and a Ti concentration of 0.8 mmol / g.

  40 g of the above raw material solution was cooled to 0 ° C., a mixed solution of 34.56 g of water equivalent to 60 times moles of Ba and 24 g of methanol was added, and the mixture was vigorously stirred to obtain a hydrolysis / condensation product. Then, the produced hydrolyzate / condensate was allowed to stand at 60 ° C. for 3 hours for crystallization.

  After crystallization, the crystal particles and the supernatant solution were separated by decantation, 120 g of methyl cellosolve was added, and the mixture was allowed to stand again at 60 ° C. and left for 3 hours. This operation was repeated 4 times to obtain crystal particles 1.

After separating the obtained crystal particles 1 and the supernatant solution, methylcellosolve is added so that the solid content concentration in terms of BaTiO ₃ is 10% by weight, and further, polyoxypropylene-polyoxyethylene of ethylenediamine as a dispersant. Ethylene condensate was added in an amount of 0.1 with respect to the particle weight of 100, and the crystal particles 1 were dispersed with an ultrasonic disperser to prepare the composition 1.

  The concentration of barium in composition 1 in the liquid was 0.2 mol% as measured by inductively coupled plasma mass spectrometry using an inductively coupled plasma mass spectrometer ELAN DRC plus 6100 (manufactured by Perkin Elmer).

  It was 0.4 weight% when the moisture concentration of the composition 1 was measured by the Karl Fischer coulometric titration method with Hiranuma trace moisture measuring device AQ-7 (Hiranuma Sangyo Co., Ltd.).

Moreover, the result of having measured the particle size distribution of the composition 1 with the dynamic light scattering method by the dynamic light-scattering type particle size distribution measuring device LB-500 (Horiba Seisakusho) is shown in FIG. According to this, it can be seen that the particle size is a particle distribution (average particle size of about 40 nm) mainly composed of 40 nm. The dielectric-forming composition 1 could be easily filtered with a filter having a pore diameter of 200 nm to remove coarse particles.

An X-ray diffraction chart of the composition 1 dropped on a glass plate and dried at room temperature is shown in FIG. According to FIG. 2, it can be determined that the crystal particle 1 has an ABOx type crystal structure of a BaTiO ₃ composite oxide at room temperature.

[Comparative Example 1]
(Preparation of crystal particle 2 and composition 2)
To 25.77 g of methyl cellosolve, 25.77 g of Ba (OCH ₂ CH ₃ ) ₂ was added and dissolved, and heated at 110 ° C. for 1 hour. Thereafter, Ti (OCH (CH ₃ ) ₂ ) ₄ was added to this solution in 32
. 21 g was added and further heated at 110 ° C. for 1 hour. 58 g of methanol was added to the resulting dark brown solution to prepare a raw material solution having a Ba concentration of 0.8 mmol / g and a Ti concentration of 0.8 mmol / g.

  40 g of the above raw material solution was cooled to 0 ° C., a mixed solution of 34.56 g of water equivalent to 60 times moles of Ba and 24 g of methanol was added, and the mixture was vigorously stirred to obtain a hydrolysis / condensation product. Thereafter, the produced hydrolyzed / condensed product was allowed to stand at 60 ° C. for 3 hours for crystallization, whereby crystal particles 2 were produced.

After crystallization, methyl cellosolve is added to the reaction solution containing the crystal particles so that the solid content concentration in terms of BaTiO ₃ is 5% by weight, and the crystal particles are dispersed with an ultrasonic disperser. Was made.

  The water concentration of the composition 2 was measured by Karl Fischer coulometric titration with a Hiranuma trace moisture measuring device AQ-7 (Hiranuma Sangyo Co., Ltd.) and found to be 20% by weight.

  FIG. 3 shows the results of measuring the particle size distribution of the composition 2 by the dynamic scattering method using a dynamic light scattering particle size distribution measuring device LB-500 (Horiba Seisakusho). According to this, it can be seen that the particle size is a particle distribution mainly composed of 180 nm (average particle size of about 180 nm), and the dispersibility is deteriorated. Further, filtration with a filter having a pore diameter of 200 nm was attempted with respect to Composition 2, but the filter was clogged because particles having a diameter of 200 nm or more were present, and filtration was impossible.

FIG. 4 shows an X-ray diffraction chart of the composition 2 dropped on a glass plate and dried at room temperature. According to FIG. 4, it can be judged that the particles in the composition 2 have an ABOx type crystal structure of the BaTiO ₃ composite oxide at room temperature.

[Test example]
(Formation of dielectric film using compositions 1 and 2)
A lower electrode made of Pt having a thickness of 100 nm was formed by a sputtering method on a silicon wafer having a diameter of 6 inches on which a silicon oxide layer having a thickness of 1000 nm obtained by thermal oxidation was formed.

  Next, composition 1 was spin-coated on the lower electrode using a spin coater at 300 rpm for 5 seconds, then at 1000 rpm for 20 seconds, and then dried at 250 ° C. for 1 minute. After performing this operation four times, the dielectric film 1 having a film thickness of 300 nm was produced by heating and baking the coating film at 400 ° C. for 10 minutes.

On the lower electrode formed in the same manner, composition 2 was spin-coated at 300 rpm for 5 seconds and then at 1000 rpm for 20 seconds using a spin coater, and then dried at 250 ° C. for 1 minute. After performing this operation four times, the dielectric film 2 having a film thickness of 300 nm was produced by heating and baking the coating film at 400 ° C. for 10 minutes.
(Dielectric properties of dielectric film)
Next, a Pt upper electrode having a diameter of 0.2 mm and a thickness of 200 nm was formed on each of the dielectric films 1 and 2 by a sputtering method through a metal mask.

  FIG. 5 shows the result of measuring the frequency dependence of the dielectric constant and dielectric loss of the dielectric film 1. From FIG. 5, the dielectric film 1 has a dielectric constant of about 39 and a dielectric loss of 0.02 or less over a range of 100 kHz to 1 MHz, and has good dielectric properties from the composition 1 using the crystal particles 1. It can be seen that a dielectric film can be produced.

In addition, as a result of measuring the leakage current of the dielectric films 1 and 2, the dielectric film 1 is 2.7 × 10 ⁻⁸ A / cm ² at 0.2 MV / cm, and the leakage current characteristics are good. It can be seen that this is a state that can be suitably used. On the other hand, the dielectric film 2 has a leakage current exceeding 1 × 10 ⁻² A / cm ² at 0.2 MV / cm and cannot be used as a capacitor.

FIG. 1 is a chart showing the crystal particle diameter of Example 1. FIG. 2 is an X-ray diffraction chart of the crystal particles of Example 1. FIG. 3 is a chart showing the crystal particle diameter of Comparative Example 1. FIG. 4 is an X-ray diffraction chart of the crystal particles of Comparative Example 1. FIG. 5 is a graph showing the frequency dependence of the dielectric constant and dielectric loss of the dielectric film 1.

Claims (2)

ABOx type in which the metal species A is one or more metals selected from Li, Na, Ca, Sr, Ba, La, and the metal species B is one or more metals selected from Ti, Zr, Ta, Nb. A method for producing crystal particles having a crystal structure and having an average particle size of 100 nm or less,
(I) at least one selected from metal alkoxides, metal carboxylates, and metal complexes, including metal species A constituting the crystal particles;
A dissolution step of dissolving at least one selected from a metal alkoxide, a metal carboxylate, and a metal complex, containing the metal species B constituting the crystal particles, in an organic solvent;
(II) hydrolysis step of adding crystal to the solution prepared in the dissolution step and hydrolyzing the precursor in the solution to obtain crystal particles,
(III) A method for producing crystal particles, comprising a purification step of purifying the crystal particles obtained in the hydrolysis step with an organic solvent.   2. The method for producing crystal particles according to claim 1, wherein in the hydrolysis step, liquid water or an organic solvent containing water is dropped into the solution.

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