JP2004300013A - Metal oxide ultrafine particle dispersed solution and metal oxide ultrafine particle thin film - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a metal oxide ultrafine particle dispersed solution in which crystallized metal oxide ultrafine particles with a uniform diameter and a uniform shape are highly dispersed, and a dense metal oxide ultrafine particle thin film with a small particle diameter. <P>SOLUTION: As to the metal oxide ultrafine particle dispersed solution prepared by a hydrolysis reaction of a raw material in a microemulsion containing a hydrophobic dispersion medium 6, water 4, and a surfactant 2, the raw material comprises a combined metal alkoxide and the amount of water contained in the microemulsion is 0.95-3 times the amount of water required for the hydrolysis of the complex metal alkoxide. <P>COPYRIGHT: (C)2005,JPO&NCIPI

Description

  The present invention relates to a metal oxide ultrafine particle dispersion solution in which metal oxide ultrafine particles are dispersed, in particular, a metal oxide ultrafine particle dispersion solution suitable for producing a composite metal oxide ultrafine particle thin film, and a nano-sized metal oxide ultrafine particle. The present invention relates to a metal oxide ultrafine particle thin film composed of fine particles and having excellent dielectric properties.

  In recent years, with the demand for miniaturization of devices, research and development of increasingly sophisticated devices have been vigorously performed. For example, composite metal oxides such as barium titanate and lead zirconate titanate are widely used in multilayer capacitors, actuators, and the like because of their excellent dielectric properties and piezoelectric properties. For further miniaturization and higher performance, thinning of the element is indispensable. For this purpose, it is important to establish a high-quality thin-film manufacturing technology composed of finer ultrafine particles.

  However, on the other hand, it is said that ferroelectric material loses ferroelectricity at a certain critical particle size due to a size effect. For example, in the case of barium titanate used for a multilayer capacitor, it is said that the ferroelectricity disappears at about 50 nm. It cannot be applied to

  Therefore, in general, in a multilayer capacitor, for example, barium titanate of about 50 nm synthesized by a hydrolysis method is grown to 100 nm or more by heat treatment to improve crystallinity, and then mixed and pulverized with a binder, a dispersant, and the like. After the slurry is formed, the sheets are formed, stacked, stacked, and further subjected to a binder removal process and a firing process.

  However, in the multilayer capacitor, the element thickness has been reduced to about 1 μm. In this case, in order to obtain sufficient reliability, assuming, for example, ten particles in one layer in the thickness direction, 100 nm per particle is assumed. It is necessary to miniaturize to the extent. Further, assuming an element thickness of 0.5 μm as a next-generation multilayer capacitor, it is necessary to reduce the size of particles to about 50 nm. That is, there is a demand for miniaturization of particles by thinning, while suppressing the size effect to its limit.

However, as a matter of fact, accurate experimental data at such a nano-level particle size has not been obtained, and ferroelectric properties in a nano-range are hardly clarified. this is,
1) It was difficult to obtain fine, narrow particle size distribution, and highly crystalline ceramic nanoparticles. 2) Due to the difficulty in obtaining a dense sample while maintaining the fine particle size. ing. Also, when the powder sample and the thin film sample are compared even if they have the same particle size, the critical particle size of the thin film sample may change compared to the powder sample due to the stress from the substrate surface, etc. Although there are reports of ceramic nanoparticle thin films that exhibit some ferroelectric properties at the nanoparticle level, ceramics with an average particle size of 50 nm or less and ferroelectricity, and exhibiting sufficiently good dielectric properties are produced by practical production methods. No nanoparticle thin film was obtained.

  As a method of producing a thin film, first, as a method of forming a ceramic thin film having excellent orientation, a vapor phase method such as a molecular beam epitaxy method (MBE), a chemical vapor deposition method (CVD), and a physical vapor deposition method (PVD) is used. It has been known. However, in these methods, enormous cost is increased, and when two or more kinds of composite metal oxide ultrafine particles are produced, a difference in vapor pressure, sublimability, chemical reactivity, etc. of each metal, The fact is that it is difficult to adjust the composition, and it has not yet been put to practical use.

  On the other hand, thin film formation using a liquid phase method represented by a sol-gel method is more advantageous than a gas phase method from the viewpoints of composition controllability and cost, and has been extensively studied.

  Here, when a thin film is formed by the sol-gel method, generally, a metal alkoxide solution is used as a raw material, and water is not added, or a precursor solution that has been partially hydrolyzed by adding a small amount of water is prepared. The film is formed by a spin coating method or a dip coating method.

  However, these gel thin films obtained by the sol-gel method need to proceed with the hydrolysis reaction very slowly to form the target oxide after film formation. Many cracks are formed on the surface, and a good quality thin film cannot be obtained. Therefore, aging had to be performed for a long time to obtain a good quality thin film without cracks.

  Further, the film thus formed is generally amorphous containing an organic compound, and it is necessary to further bake after forming the film in order to obtain a crystalline film. However, in this case, the amorphous phase of the film may form an intermediate phase during firing, which causes problems such as hindering densification and increasing surface roughness, and formation of a different phase at the interface with the substrate. As a result, there is a problem that the characteristics are deteriorated. In this case, since it is necessary to perform firing at a relatively high temperature, grain growth occurs by firing, and it has been difficult to obtain a dense thin film while maintaining a sufficiently small particle size.

  Therefore, in order to solve these problems, if it is possible to prepare a composite metal oxide ultrafine particle dispersion in which highly crystallized composite metal oxide ultrafine particles are already highly dispersed in a solvent, the prepared dispersion solution may be used. By performing film formation by, for example, a spin coating method, drying, and performing heat treatment at a relatively low temperature, a dense thin film can be obtained while maintaining a sufficiently small particle size.

  In order to prepare such a composite metal oxide ultrafine particle dispersion solution, it is necessary to synthesize ultrafine composite metal oxide particles having a uniform composition, a uniform particle size, and crystallized, and to disperse them in a solvent to a high degree. It is necessary to make it. However, it is said that as the miniaturization proceeds, it becomes difficult to control the aggregation of the ceramic fine particles, and that the presence of water causes hard aggregation of the ceramic fine particles (see Non-Patent Document 1).

  That is, if water is present on the powder surface, as shown in FIG. 1, adjacent fine particles are cross-linked by hydrogen bonding via water, and aggregation proceeds. If the agglomeration occurs, it is very difficult to crush the agglomerated ceramic fine particles and re-disperse them again to a high degree.

  Therefore, the key is to first synthesize ultrafine composite metal oxide particles having high crystallinity while avoiding aggregation, and then to keep the ultrafine particles once synthesized in a dispersed state without agglomeration.

  Here, Patent Document 1 discloses production of ultrafine metal oxide particles which have recently been reported, such as a metal colloid method, a microemulsion method (reverse micelle method), a polymer complex method, a metal alcoholate hydrolysis method, and a Grignard method. The methods are listed.

  Among them, in the W / O (Water in Oil) microemulsion method, water is added to a hydrophobic liquid together with a surfactant to disperse as fine water droplets, and the water is introduced by a reaction such as hydrolysis in the fine water droplets. This is a method of reacting raw materials to obtain ultrafine metal oxide particles. In this W / O microemulsion method, it is known that the particle size and surface structure of metal oxide fine particles are controlled on a nanoscale (see Non-Patent Document 2).

However, generally, after the synthesis, fine particles obtained by further adding a precipitant or the like are completely precipitated, and the precipitate is taken out by a centrifuge. The target fine particles are separated and obtained by washing the mixture of the fine particles, which are taken out precipitates, and the surfactant with an organic solvent or the like (see Patent Document 2).
Chemical Industry, April 1995, Item 45 Chem.Phys.Lett.125, 299, etc. JP 2001-163617 A JP-A-9-255331

  Here, if the ultrafine particles synthesized by the microemulsion method can be dispersed in a solution without being aggregated, they can be used as a solution for forming a metal oxide ultrafine particle thin film.

  The water droplets of the emulsion are thermodynamically stable and present in a dispersed state. However, the individual droplets 1 and 1 repeat bonding and dissociation as shown in FIG. Therefore, when the composite metal oxide ultrafine particles are synthesized by the microemulsion method, while the above-mentioned bonding and dissociation are repeated, the synthesized fine particles gradually aggregate and precipitate.

  Further, as described above, in the ultrafine metal oxide thin film used for the dielectric device, there is a problem that when the crystal grain size is reduced, the ferroelectric characteristics disappear at a certain critical grain size. Therefore, it is required to further reduce the thickness and improve the performance while suppressing the size effect that the ferroelectric characteristic disappears depending on the size to the limit.

  The present invention has been made in view of the above points, and has a uniform composition, uniform particle diameter and shape, and highly dispersed metal oxide ultrafine particles in which crystallized metal oxide ultrafine particles are highly dispersed. Along with providing the dispersion solution, the main purpose is to provide a fine metal oxide ultrafine particle thin film having a small particle size by using the obtained composite metal oxide ultrafine particle dispersion solution, and further, has excellent dielectric properties. It is an object of the present invention to provide a thin film of metal oxide ultrafine particles having a nanoparticle size.

  Therefore, the present inventors have conducted intensive studies to achieve the above object, and as a result, when synthesizing ultrafine metal oxide particles by the microemulsion method, as a raw material that consumes water in the emulsion in the reaction process, for example, metal By using an alkoxide and minimizing the amount of water in the microemulsion solution, water is almost consumed after the reaction, and a solution in which the synthesized ultrafine metal oxide particles are highly dispersed in the solvent after the reaction can be obtained. We have found that we can do this and completed the present invention.

  That is, the metal oxide ultrafine particle dispersion solution of the present invention is a metal oxide ultrafine particle dispersion solution produced by a hydrolysis reaction of raw materials in a microemulsion containing a dispersion medium which is a hydrophobic liquid, water and a surfactant. Wherein the raw material is a composite metal alkoxide solution obtained by mixing and mixing a plurality of metal alkoxides in alcohol, and the amount of water contained in the microemulsion is 0.95 of the amount of water required for hydrolysis of the raw material. More than twice and less than three times.

  Here, the ultrafine particles refer to, for example, particles having an average particle diameter of 100 nm or less.

  According to the present invention, the amount of water contained in the microemulsion is 0.95 times or more the amount of water required for hydrolysis of the raw material, so that undecomposed raw material without hydrolysis and non-sufficient crystallinity are not used. While the ratio of the crystalline ultrafine particles can be reduced, the amount of water contained in the microemulsion is not more than three times the amount of water required for hydrolysis of the raw material, so that aggregation of the metal oxide ultrafine particles generated after the reaction is suppressed. , Resulting in a highly dispersed transparent metal oxide ultrafine particle dispersion solution.

  Further, according to the present invention, since the metal alkoxide solution serving as the raw material solution is a composite metal alkoxide solution in which a plurality of metal alkoxides are compounded, the generated ultrafine particles are very fine, the composition is uniform, and the particle diameter is large. In addition, the composite metal oxide single phase fine particles having a uniform and crystallized shape are obtained.

  In another embodiment of the present invention, at least one of the plurality of metal alkoxides is a barium alkoxide, and the composite metal alkoxide solution contains a polymerization inhibitor that suppresses polymerization of the barium alkoxide.

  As the polymerization inhibitor, for example, benzene is preferable.

  According to this embodiment, since a polymerization inhibitor such as benzene which suppresses the polymerization of barium alkoxide is contained, polymerization of barium alkoxide is suppressed, and a homogeneous composite metal alkoxide of barium alkoxide and another metal alkoxide is obtained. Can be.

  The metal oxide ultrafine particle thin film according to the present invention is produced using the metal oxide ultrafine particle dispersion prepared by the method of the present invention.

  According to the present invention, a dense metal oxide ultrafine particle thin film having a small particle diameter can be obtained.

Further, the metal oxide ultrafine particle thin film according to the present invention is composed of metal oxide ultrafine particles having an average particle diameter of 15 nm or more and 50 nm or less, and has a ferroelectric property of ² Pr of ² μC / cm ² or more in remanent polarization (Pr). And a dielectric constant at a measurement frequency of 1 kHz is 300 or more.

According to the present invention, since the average particle diameter is 50 nm or less, it is possible to further reduce the thickness. On the other hand, even if it is composed of ultrafine particles of 15 to 50 nm, the ferroelectric properties of ² Pr of ² μC / cm ² or more are obtained. And an excellent thin film having a relative dielectric constant of 300 or more at a measurement frequency of 1 kHz can be obtained.

Further, it is preferable that the metal oxide ultrafine particles constituting the metal oxide ultrafine particle thin film of the present invention are perovskite oxides containing titanium and barium. As described above, even a composite oxide such as a perovskite-type oxide containing titanium and barium has an average particle diameter of 50 nm or less, so that it is possible to further reduce the thickness. Even when composed of fine particles, an excellent thin film having a ferroelectric property of 2Pr of ² μC / cm ² or more and a relative dielectric constant of 300 or more at a measurement frequency of 1 kHz can be obtained.

  As described above, according to the present invention, since the amount of water contained in the microemulsion is limited, the composition is homogeneous, the particle diameter and shape are uniform, and the crystallized metal oxide ultrafine particles are highly dispersed. A fine particle dispersion solution can be easily obtained. In addition, a dense metal oxide ultrafine particle thin film having a small particle diameter can be produced using the obtained metal oxide ultrafine particle dispersion solution.

  In addition, since the composite metal alkoxide is used as a raw material, a composite metal oxide ultrafine particle dispersion solution in which the composite metal oxide ultrafine particles are highly dispersed and a thin composite metal oxide ultrafine particle thin film having a small particle size can be obtained. .

  Further, according to the metal oxide ultrafine particle thin film of the present invention, the average particle diameter is 50 nm or less, so that when used for a device, it is possible to reduce the size and thickness and to suppress the size effect. And excellent dielectric properties can be obtained.

  Hereinafter, the present invention will be described in more detail.

  The microemulsion according to the present invention is a W / O microemulsion comprising a dispersion medium, which is a hydrophobic liquid, water, and a surfactant.

  Examples of the dispersion medium that is a hydrophobic liquid include petroleum hydrocarbons such as kerosene, nonpolar hydrocarbons such as cyclohexane, hexane, cyclopentane, benzene, and octane, and ethers such as diethyl ether and isopropyl ether.

Surfactants include ionic surfactants such as AOT (sodium bis (2-ethylhexyl) sulfosucciate) and SDS: CH ₃ (CH ₂ ) ₁₁ OSO ₃ Na, and NP-n (n = 1 to 10). _{) :( p-C 9 H 19} ) -C 6 H 4 -O- (CH 2 CH 2 O) n CH 2 CH 2 OH and _{polyoxyethylene (n) 1aury1ether: C 12} H 25 (OCH 2 CH 2) n OH Any nonionic surfactant such as ionic surfactant can be used. However, in the case of ionic surfactant, an extra component remains in the membrane component, and thus nonionic surfactant is preferable.

  The raw material of the present invention is a composite metal alkoxide.

  This is obtained by mixing a plurality of metal alkoxides in an alcohol to form a composite. As the alcohol used here, ethanol, propanol, butanol, isopropyl alcohol and the like can be appropriately used. Note that it is preferable to use an alcohol corresponding to each metal alkoxide.

  Examples of the composite metal alkoxide include, but are not particularly limited to, for example, barium titanium methoxide, barium titanium ethoxide, barium titanium propoxide, barium titanium butoxide, strontium titanium methoxide, strotium titanium ethoxide, and magnesium titanium methoxide. , Magnesium titanium ethoxide and the like.

  The amount of water in the microemulsion of the present invention is preferably 0.95 times or more and 3 times or less the amount of water required for hydrolysis of the metal alkoxide as a raw material.

The amount of water required for the hydrolysis is defined by a chemical reaction formula. For example, taking the hydrolysis reaction between barium isopropoxide Ba (isop) ₂ and titanium isopropoxide Ti (isop) ₄ as an example , As follows:

Ba (isop) ₂ + Ti (isop) ₄ + 3H ₂ O
→ BaTiO ₃ + 6isopropanol
Therefore, in this case, 3 mol of water is required for hydrolysis with respect to 1 mol of each of barium isopropoxide and titanium isopropoxide. In this case, the amount of water contained in the microemulsion needs to be 0.95 to 3 times the amount of water required for hydrolysis, that is, 2.85 to 9 mol.

  When the amount of water is less than 1 time, water is completely consumed after the reaction, so that a very clear dispersion solution can be obtained. Some of the particles are not sufficient. However, these phases may enter between the ultrafine particles that form a film at the time of film formation and act as a sintering aid to improve the film density. In some cases, it may be better to adjust to include an amorphous portion.

  However, since the proportion of the crystalline phase decreases as the undecomposed or non-crystalline phase increases, it is preferable to contain at least 0.95 times of water. Further, when the amount of water is 1.05 times or more and 1.2 times or less, it is more preferable because a clear, highly dispersible, and highly crystalline composite metal oxide ultrafine particle dispersion solution can be obtained. By minimizing the amount of residual water after the reaction, there is also an effect of preventing a deviation in the composition of the synthesized composite metal oxide.

  For example, in the case of barium titanate, the Ba / Ti ratio in a substance is an important factor in characteristics, but it is known that barium partially elutes in water. Generally, when synthesis is performed by a hydrolysis method, synthesis is performed using a raw material adjusted in excess of barium. On the other hand, when there is almost no water remaining after the reaction as in the present invention, barium ions do not dissolve in water, so that uniform target ultrafine particles can be obtained with the adjusted raw material composition. . Therefore, by making the amount of water contained in the microemulsion 0.95 times or more and 3 times or less, preferably 1.05 times or more and 1.2 times or less the amount of water required for hydrolysis, There is also an advantage that the composition shift due to the remaining easily soluble components can be almost eliminated.

  In the microemulsion, it is preferable to add one or more alcohols as another surfactant, so-called cosurfactant.

  FIG. 3 is a schematic diagram showing, in an enlarged manner, the vicinity of a microemulsion solution and a part of droplets thereof, and also shows a state after a hydrolysis reaction by adding a composite metal alkoxide. In the figure, 2 is a surfactant, 3 is a cosurfactant, 4 is water, 5 is a reaction product, and 6 is a dispersion medium such as cyclohexane.

  By adding one or more alcohols as a cosurfactant, water droplets can be made to exist more stably at the time of preparing the microemulsion. Further, when the water in the emulsion is consumed after the reaction to produce the composite metal oxide, the composite metal oxide enters between the interface of the composite oxide and the surfactant, and the surfactant surrounds the periphery of the composite oxide ultrafine particles as it is. It can be considered that the synthesized composite oxide ultrafine particles can stably maintain dispersion as in the case of water because they can exist in a form.

  It is considered that the cosurfactant has an effect of entering the hydrophilic part of the surfactant, lowering the interfacial energy with water, and reducing the steric hindrance of the long carbon chain of the hydrophilic part of the surfactant. The appropriate number of carbon atoms of the alcohol also depends on the length of the carbon chain of the hydrophilic portion of the surfactant, but is preferably about 4 to 10. If it is 4 or less, the hydrophilicity is too high, so that it is considered to be dissolved in water and not exist only at the water-surfactant interface. On the other hand, when it is larger than 10, the hydrophobicity becomes too large and the steric hindrance becomes large, so that it is not so preferable.

  It is preferable that a metal alkoxide is used as a raw material, and that each metal alkoxide is mixed and complexed before hydrolysis.

Barium alkoxide is known to be easily polymerized in alcohol. Here, J. Am. Ceram. Soc, 77 [2], pp. 603-605 and Jpn. J. Appl. Phys. Vo136, 5 939-5942 states that BaTi (OCH (CH ₃ ) ₂ ) -C ₆ H ₆ crystals can be obtained by aging an iso-propanol solution of barium and titanium in benzene. I have. In this, benzene hardly dissolves the metal alkoxide, helps stabilize and precipitate BaTi (OCH (CH ₃ ) ₂ ) -C ₆ H ₆ crystals, and has the effect of suppressing the polymerization of barium alkoxide. Is suggested.

  Therefore, it is considered that by adding benzene within a range in which no crystal is precipitated, polymerization of barium alkoxide is suppressed, and a uniform barium titanium double alkoxide is easily obtained. For this reason, benzene having a function of suppressing the polymerization of barium alkoxide is partially added to the alcohol solvent to adjust and use the barium-containing composite alkoxide raw material solution to obtain uniform barium-containing composite oxide ultrafine particles. Is preferred. In addition, as long as it has the same kind of effect, it can be used without being limited to benzene.

  The metal oxide ultrafine particle thin film of the present invention is produced using the metal oxide ultrafine particle dispersion prepared by the method of the present invention.

  Since the ultrafine particles of the metal oxide ultrafine particle dispersion solution have high crystallinity, they can be heat-treated at a relatively low temperature, for example, at 600 ° C. or lower.

  The metal oxide ultrafine particle thin film of the present invention is composed of metal oxide ultrafine particles having an average particle diameter of 15 nm or more and 50 nm or less and has ferroelectric properties.

As the ferroelectric properties, in terms of remanent polarization (Pr), 2Pr preferably has a ferroelectric property of ² μC / cm ² or more, and a relative dielectric constant at a measurement frequency of 1 kHz (room temperature) is preferably 300 or more.

A metal oxide ultrafine particle thin film composed of 15 to 50 μm ultrafine particles as in the present invention, wherein 2Pr has a ferroelectric property of ² μC / cm ² or more in remanent polarization (Pr), and When the dielectric constant is 300 or more, the device sufficiently functions as a ferroelectric device such as a thin film capacitor or a multilayer capacitor. Therefore, by using a metal oxide ultrafine particle thin film composed of ultrafine particles of 15 to 50 nm as in the present invention, it is possible to further reduce the thickness and size. Further, when the metal oxide ultrafine particle thin film of the present invention is used as a thin film capacitor, it is composed of fine particles of 15 to 50 nm, so that the number of particles per layer can be increased and reliability is greatly improved. In addition, it is possible to further reduce the thickness and size.

  The metal oxide ultrafine particle thin film of the present invention is highly dispersible as it is after synthesizing the finest possible and crystallized metal oxide ultrafine particles, for example, ceramic nanoparticles composed of perovskite-type oxide containing titanate. It is preferable to manufacture the film by keeping it in a state, forming a film on a substrate, and then growing the particles to a size of 15 nm or more and 50 nm or less by adding energy such as heat treatment to further promote densification and crystallization.

  As such a film forming method, for example, a solution in which ultrafine metal oxide particles having a nano-size and a uniform particle size distribution are kept in a highly dispersed state as they are by the microemulsion (ME) method, for example, the metal oxide of the present invention is used. A thin film is formed by a method of directly forming a film by a spin coating method or the like using the material ultrafine particle dispersion solution as a raw material solution, and further performing a heat treatment using an RTA (Rapid Thermal Annealing) furnace or the like. be able to.

  The metal oxide ultrafine particle thin film of the present invention has an average particle diameter of, for example, 30 nm or less, metal oxide ultrafine particles, for example, a process of synthesizing ceramic nanoparticles composed of perovskite oxide containing titanate, A process of keeping the synthesized ceramic nanoparticles in a medium in a highly dispersed state as it is and a series of processes of forming the highly dispersed ceramic nanoparticles on a substrate are used to further heat-treat the ceramic nanoparticle thin film. It is preferable to produce the particles by growing the particles to 15 nm to 50 nm by adding energy.

  As described above, ceramic fine particles, that is, ceramic nanoparticles, are highly agglomerated, and once aggregated, it is extremely difficult to re-disperse them separately. It is necessary to keep a high dispersion state inside. For this purpose, it is necessary to produce the desired nanoparticles by reacting the raw materials in a fine reaction space partitioned into nano-sizes in a medium, and to keep them in a state where they are not aggregated. Is a desirable method. As described above, the W / O microemulsion is composed of a dispersion medium, which is a hydrophobic liquid, water, and a surfactant, and thermally stabilizes water droplets having a droplet diameter of several nm to several tens nm in a hydrophobic solvent. Can be dispersed.

  For example, in the case of barium titanate used for a multilayer capacitor, a crystallized barium titanate nanometer having a very fine and uniform particle size corresponding to a water droplet diameter is dropped by dropping a Ba, Ti composite alkoxide raw material solution therein. Particles can be synthesized.

  In addition, by adjusting the amount of water in the microemulsion composition to 0.95 times or more and 3 times or less the amount of water required for hydrolysis as described above, the synthesized barium titanate nanoparticles are stable without aggregation. Is obtained.

  Here, since the synthesized nanoparticles need to be subsequently grown to a particle size of 50 nm or less by heat treatment, the synthesized nanoparticles should be as small as possible, and the average particle size should be at least 30 nm or less. Preferably, it is 10 nm or less. The nanoparticle dispersion solution prepared in this manner is applied to a substrate by using, for example, a spin coating method, a dip coating method, a screen printing method, and the like. In order to increase the density, a step of performing a heat treatment is performed to produce a dense barium titanate nanoparticle thin film.

  Adjustment of the average particle size after film formation can be performed using an electric furnace, an infrared furnace, an RTA furnace, or the like. In particular, in an infrared furnace or an RTA furnace, high-speed temperature rise is possible, and grain growth can be suppressed to a small value even at the same temperature by high-speed temperature rise and short-time heat treatment.

  Ultrafine metal oxide particles synthesized by the microemulsion method are deposited in a highly dispersed state, so that even a nanoparticle is a dense thin film, and since it has already been crystallized, heat treatment etc. Even if it is performed, no intermediate layer is formed, and densification is not hindered, and the surface roughness does not greatly increase. Further, there is no possibility that a different phase is formed at the interface with the substrate to deteriorate the electric characteristics. Furthermore, since the nanoparticles that are as fine and crystallized as possible are grown by heat treatment or the like, even if the average particle diameter is as small as 50 nm or less, the densification and crystallization are progressing, and excellent dielectric properties are achieved. And reliability can be expected.

  In addition, unlike the powder sample, the thus obtained metal oxide ultrafine particle thin film is strong even with nanoparticles having an average particle size smaller than the generally known critical size due to the influence of stress from the substrate and the like. May exhibit dielectric properties. It was confirmed that the metal oxide ultrafine particle thin film of the present invention actually obtained exhibited ferroelectricity even when the average particle diameter was 50 nm or less, and had excellent dielectric properties.

  In addition, since the metal oxide ultrafine particle thin film formed in this manner is formed in a series of steps of synthesis → dispersion → film formation, there is an advantage that the steps are not multi-step, and the apparatus and the manufacturing process are not complicated. Have.

Next, an example in which the metal oxide ultrafine particle thin film of the present invention is applied to an electronic device will be described.
The metal oxide ultrafine particle thin film of the present invention can be used for various electronic devices. For example, FIG. 4 shows an example of a configuration when applied to a multilayer capacitor.

As shown in FIG. 2B, a ceramic layer 8 is formed on a substrate 7 such as an alumina substrate shown in FIG. 2A, and a first-layer conductor electrode 9a is formed thereon. A ceramic layer 8 is formed thereon, a second-layer conductor electrode 9b is further formed, a ceramic layer 8 is further formed, and a third-layer conductor electrode 9a is formed thereon.
By repeating such a process, the conductor electrodes 9a and 9b and the ceramic layer 8 are alternately stacked on the surface of the substrate 7 by a plurality of layers, respectively, and the plurality of conductor electrodes 9a and 9b and the plurality of ceramic layers are stacked. 8 is formed.

  Here, each of the ceramic layers 8 is formed by the method for producing a metal oxide ultrafine particle thin film of the present invention, and each of the conductor electrodes 9a and 9b is formed by using any one of a CVD method, a vapor deposition method, and a sputtering method. The thickness of each ceramic layer 8 and each conductor electrode 9a, 9b is, for example, 1 μm or less. The conductor electrodes 9a and 9b serving as internal electrodes are patterned using a mask, and the conductor electrodes 9a of the odd-numbered layers and the conductor electrodes 9b of the even-numbered layers are alternately arranged at opposite ends. Has been pulled out to.

  Thereafter, when the substrate 7 is selectively removed by etching or the like, only the ceramic-metal laminate 10 as shown in FIG. Next, when the external electrodes 11a and 11b are formed at both ends by dipping, sputtering, or the like, the odd-numbered-layer conductor electrodes 9a are electrically connected to one of the external electrodes 11a, and the even-numbered-layer conductor electrodes 9b are connected to the other external electrodes 11b. , And an ultra-compact multilayer ceramic capacitor 12 as shown in FIG.

  FIG. 5 shows an example of a configuration in which the metal oxide ultrafine particle thin film of the present invention is applied to a dielectric thin film element.

  First, a substrate 13 constituting a lower layer of a dielectric thin film element and a platinum film 14 as a lower electrode formed thereon were prepared as follows. On the single-crystal silicon plate 15, a silicon oxide film 16 was formed as a buffer layer by forcibly oxidizing the surface of the silicon plate 15 in order to prevent diffusion of silicon into the platinum film 14 serving as a lower electrode. Then, an aluminum oxide film 17 was formed thereon by 1000 angstrom sputtering in order to improve the adhesion between the silicon plate 15 and the platinum film 14. A platinum film 14 as a lower electrode was formed on the substrate 13 composed of the silicon plate 15, the silicon oxide film 16, and the aluminum oxide film 17 thus formed by sputtering at 3000 Å.

  Next, on this platinum film 14, a dielectric thin film 18 composed of ultrafine metal oxide particles having an average particle diameter of 15 to 50 nm of the present invention was formed. On this, a platinum electrode 19 was provided as an upper electrode by sputtering.

  Next, the present invention will be described more specifically with reference to examples, but the present invention is not limited to these examples.

(Example 1)
In the following examples, a method for preparing an ultrafine particle dispersion solution of barium titanate used for producing the metal oxide ultrafine particle thin film of the present invention and a barium titanate ultrafine particle thin film produced by the dispersion solution are taken as examples. This will be specifically described.

  First, as a preparation of a raw material alkoxide solution, 4 g of barium isopropoxide was mixed and dissolved in a mixed solvent of 160 ml of isopropyl alcohol and 40 ml of benzene in a glove box in an Ar atmosphere to form a barium alkoxide solution, and an equimolar amount thereof was added thereto. The titanium isopropoxide solution was added dropwise and mixed overnight to obtain a pale yellow transparent barium-titanium composite alkoxide raw material solution.

Next, the W / O microemulsion solution was prepared by using cyclohexane as a dispersion medium and NP-10: (p-C ₉ H ₁₉ ) -C ₆ H ₄ -O- (CH ₂ CH ₂ O) ₁₀ CH _{2 as} a surfactant. CH ₂ OH, using 1-octanol as a cosurfactant and bubbling with Ar gas, mixing at a ratio of water: 1-octanol: NP-10: cyclohexane = 0.2: 9: 7.5: 150 to W / O microemulsion solution.

  The barium-titanium composite alkoxide solution was added to the prepared microemulsion solution so that the amount of water in the microemulsion was 0.95, 1.2, and 3 times the amount of water required for hydrolysis of the barium-titanium composite alkoxide. Each sample was collected using a pipette, and introduced into each microemulsion solution using a tube pump. The mixture was stirred and mixed for 1 day in a glove box in an Ar atmosphere to obtain a barium titanate ultrafine particle dispersion solution.

  The obtained barium titanate ultrafine particle dispersion solution was light brown and transparent, and it was confirmed that the barium titanate ultrafine particles generated by hydrolysis were highly dispersed. Further, a part of the dispersion solution was collected, precipitated by adding acetone, centrifuged, and then the crystal phase of the sample washed with an organic solvent was identified by powder X-ray diffraction method. It was confirmed that the titanium oxide / barium was converted into a single phase. Further, when the particle shape was observed by high-resolution SEM, it was found to be ultrafine particles having a very fine size of about 8 nm and a uniform particle size distribution.

  Next, a barium titanate ultrafine particle thin film was prepared by spin coating using the obtained barium titanate ultrafine particle dispersion solution. The ultrafine particle dispersion solution is transparent in the visible light region because the ultrafine particles crystallized at about 8 nm are highly dispersed from the results of the powder X-ray diffraction and the results of SEM observation. It was found to have applicability. In addition, the concentration of ultrafine particles in the liquid can be freely adjusted by partially evaporating an organic dispersion medium occupying a volume ratio of about 90% using an evaporator or the like, or adding the organic dispersion medium in the reverse direction. Can be.

  After performing spin coating using a barium titanate ultrafine particle dispersion solution having a concentration of 0.07 mol / l, heat treatment was performed at 450 ° C. in air to obtain a barium titanate ultrafine particle thin film. From the SEM photograph of the surface of the barium titanate ultrafine particle thin film, it was confirmed that fine barium titanate ultrafine particles of about 10 nm were formed at a high density. Further, it was confirmed that by performing heat treatment at 600 ° C., a similarly high-density thin film having a grain growth of about 20 nm was obtained.

(Example 2)
While performing bubbling with Ar gas, water / 1-octanol: NP-4: cyclohexane was mixed at a ratio of 0.2: 9: 7.5: 150 to obtain a W / O microemulsion solution. Next, a barium-titanium composite alkoxide solution prepared in the same manner as in Example 1 was dispensed into this microemulsion solution using a micropipette such that the amount of water in the microemulsion was three times the amount of water required for hydrolysis of the alkoxide raw material. Then, the mixture was introduced into each microemulsion solution using a tube pump. The mixture was stirred and mixed for 1 day in a glove box in an Ar atmosphere to obtain a barium titanate ultrafine particle dispersion solution.

(Comparative Example 1)
A barium-titanium composite alkoxide solution and a microemulsion solution were prepared in the same manner as in Example 1. The barium-titanium composite alkoxide solution is separated into the prepared microemulsion solution using a micropipette such that the amount of water in the microemulsion is five times the amount of water required for hydrolysis of the barium-titanium composite alkoxide, and a tube pump is used. And introduced into the microemulsion solution. The mixture was stirred and mixed for 1 day in a glove box under an Ar atmosphere to obtain a barium titanate ultrafine particle dispersion solution.

(Comparative Example 2)
While performing bubbling with Ar gas, water / 1-octanol: NP-10: cyclohexane = 5: 9: 7.5: 150 was mixed to obtain a W / O microemulsion solution. The barium-titanium composite alkoxide solution is separated into the prepared microemulsion solution using a micropipette such that the amount of water in the microemulsion is 50 times the amount of water required for hydrolysis of the barium-titanium composite alkoxide, and a tube pump is used. And introduced into the microemulsion solution. The mixture was stirred and mixed for 1 day in a glove box under an Ar atmosphere to obtain a barium titanate ultrafine particle dispersion solution.
(Comparative Example 3)
While bubbling with Ar gas, water / 1-octanol: NP-10: cyclohexane = 0.2: 9: 7.5: 150 was mixed to obtain a W / O microemulsion solution. In the adjusted microemulsion solution, a barium-titanium composite alkoxide solution is fractionated using a micropipette such that the water amount in the microemulsion is 0.75 times the water amount required for hydrolysis of the barium-titanium composite alkoxide, It was introduced into the microemulsion solution using a tube pump. The mixture was stirred and mixed for 1 day in a glove box under an Ar atmosphere to obtain a barium titanate ultrafine particle dispersion solution.

(Comparative Example 4)
Barium acetate powder was dissolved in water to prepare a 0.1 mol / l barium acetate aqueous solution. The adjusted barium acetate aqueous solution: 1-octanol: NP-10: cyclohexane = 5: 9: 7.5: 150 was mixed to obtain a W / O microemulsion solution. An equivalent amount of titanium isopropoxide was added dropwise with a micropipette, and the mixture was stirred and mixed for 1 day in a glove box under an Ar atmosphere to obtain a barium titanate ultrafine particle dispersion solution.

(Comparative Example 5)
While bubbling with Ar gas, water / NP-4: cyclohexane was mixed at a ratio of 5: 7.5: 150 to form a W / O microemulsion solution. Next, a barium-titanium composite alkoxide solution prepared in the same manner as in Example 1 was dispensed into this microemulsion solution using a micropipette such that the amount of water in the microemulsion was 50 times the amount of water required for hydrolysis of the alkoxide raw material. Then, it was introduced into the microemulsion solution using a tube pump. The mixture was stirred and mixed for 1 day in a glove box under an Ar atmosphere to obtain a barium titanate ultrafine particle dispersion solution.

  Table 1 shows the dispersion state and the crystal phase of the obtained barium titanate ultrafine particle dispersion solution.

表１において、分散状態の評価は、目視による評価であって、◎は完全透明な状態を、○は透明な状態を、△は白濁した状態を、×は、沈殿が生じた状態をそれぞれ示している。

In Table 1, the evaluation of the dispersion state is a visual evaluation, in which ◎ indicates a completely transparent state, は indicates a transparent state, Δ indicates a cloudy state, and × indicates a state in which precipitation occurs. ing.

  First, barium titanate ultrafine particles prepared by using a raw material solution subjected to complex alkoxidation and using a W / O microemulsion adjusted to 0.95 times to 3 times the amount of water required for hydrolysis of the raw material solution Examples of the dispersion solution are shown in Examples 1 and 2.

  As described above, by setting the amount of water to be 0.95 times or more and 3 times or less the amount of water required for alkoxide hydrolysis, aggregation of the composite metal oxide ultrafine particles generated after the reaction is suppressed, and a highly dispersed transparent composite is obtained. A dispersion solution of ultrafine metal oxide particles can be obtained. The generated ultrafine particles are very fine and uniform in composition, and have a uniform particle diameter and shape and are crystallized single-phase ultrafine particles of a composite metal oxide.

  On the other hand, when the amount of water is larger than that, as shown in Comparative Example 1, the generated ultrafine particles aggregate and precipitate. Further, when the amount of water becomes 50 times, precipitation due to aggregation occurs. In addition, it was found that when the amount of water was 0.75 times, hydrolysis was not sufficiently performed, so that an amorphous phase was generated in the ultrafine particles. In Comparative Examples 2 and 5, the barium carbonate phase was confirmed by powder X-ray diffraction in addition to the barium titanate phase. When the solubility of the constituent elements of the composite metal oxide in water was high, some of Therefore, composition deviation and reduction in composition uniformity occur.

Further, when the composite material was not subjected to complex alkoxide conversion, as shown in Comparative Example 4, an amorphous phase was obtained after the reaction, and was not crystallized. The sample subjected to heat treatment after centrifugation and washing was confirmed to be composed of a BaTiO ₃ phase and a BaTi ₂ O ₄ phase as a result of powder X-ray diffraction, and that titanium was excessive. That is, in this case, it is considered that titanium was excessive due to removal of barium remaining in water at the time of washing, and not only a crystal phase was not obtained, but also a problem in terms of composition deviation and uniformity. Become.

  Next, examples of the metal oxide ultrafine particle thin film of the present invention will be described.

(Examples A to C)
In the following examples, a barium titanate ultrafine particle thin film produced using a barium titanate dispersion solution synthesized by the above-described microemulsion will be specifically described.

  First, as a preparation of a raw material alkoxide solution, 4 g of barium isopropoxide was mixed and dissolved in a mixed solvent of 160 ml of isopropyl alcohol and 40 ml of benzene in a glove box in an Ar atmosphere to form a barium alkoxide solution, and an equimolar amount thereof was added thereto. The titanium isopropoxide solution was added dropwise and mixed overnight to obtain a pale yellow transparent barium-titanium composite alkoxide raw material solution.

Next, the W / O microemulsion solution is prepared by adding cyclohexane as a dispersion medium and NP-10: (p-C ₉ H ₁₉ ) -C ₆ H ₄ -O- (CH ₂ CH ₂ O) ₁₀ CH _{2 as} a surfactant. CH ₂ OH, 1-octanol as a cosurfactant, and bubbling with Ar gas, mixing at a ratio of water: -octanol: NP-10: cyclohexane = 0.2: 9: 7.5: 150 and W / An O microemulsion solution was obtained.

  The barium-titanium composite alkoxide solution was introduced into the microemulsion solution so that the amount of water in the microemulsion was 1.5 times the amount of water required for the hydrolysis of the barium-titanium composite alkoxide. The mixture was stirred and mixed in a glove box to obtain a barium titanate ultrafine particle dispersion solution. Barium titanate in the dispersion solution was confirmed by TEM observation to be crystallized fine nanoparticles of about 8 nm.

Next, using the obtained barium titanate ultrafine particle dispersion solution, it is applied several times onto a Si / SiO ₂ / Al ₂ O ₃ / Pt substrate to be described later by a spin coating method, and heat-treated at 450 ° C. in the air. After that, heat treatment was performed at 600 ° C. to 900 ° C. in an RTA furnace to obtain barium titanate ultrafine particle thin films of Examples A to C having average particle diameters of 15.2 nm, 19.6 nm, and 48.9 nm, respectively. . That is, Example A is a barium titanate ultrafine particle thin film having an average particle diameter of 15.2 nm that has been heat-treated at 600 ° C., and Example B is a titanium alloy having an average particle diameter of 19.6 nm that has been heat-treated at 800 ° C. Example C is a barium titanate ultrafine particle thin film having an average particle size of 48.9 nm, which was heat-treated at 900 ° C.

  The average particle size of the obtained barium titanate ultrafine particle thin film was determined from a digitizer measurement of 100 particles from a SEM photograph of the thin film surface, and obtained from the average. FIG. 6 is a particle size distribution diagram showing the particle size distribution of Example B. This particle size distribution is obtained by measuring the particle size of arbitrary 100 particles from an SEM photograph and calculating the standard deviation (σ) from the distribution. As can be seen from FIG. 6, the standard deviation (σ) when the heat treatment temperature average particle size at 800 ° C. is 19.6 nm is as narrow as 1.21. Also in Examples A and C, it was found that the standard deviation (σ) was as narrow as 1.24 to 1.33.

  In addition, it was confirmed by SEM observation and SPM observation that a dense nanoparticle thin film having a small surface roughness was obtained. FIG. 7 shows an SEM photograph of Example B.

  In addition, XRD measurement confirmed that the thin film was a crystalline barium titanate single phase.

  The electrical characteristics were evaluated by forming an upper electrode on the surface of the obtained barium titanate nanoparticles by Pt sputtering, measuring the relative permittivity and dielectric loss at room temperature and a measurement frequency of 1 kHz with an LCR meter, and measuring the hysteresis by: Evaluation of ferroelectricity was performed. In the evaluation of the withstand voltage, when the sample used for the measurement of the dielectric loss was applied with a current of 200 kV / cm by applying a current from the electrode and the sample was destroyed, the sample was broken. The case was marked as ○.

  FIG. 8 shows the structure of the sample used for the evaluation of the electrical characteristics.

The substrate with SiO ₂ as an insulating layer on Si, the Al ₂ O ₃ was deposited as a buffer layer, further, the above laminated with Pt21 as a lower electrode _{Si / SiO 2 / Al 2 O} 3 / Pt substrate 20 Using. A barium titanate ultrafine particle thin film 22 is formed on the Si / SiO ₂ / Al ₂ O ₃ / Pt substrate 20 by film formation by spin coating and heat treatment, and Pt 23 of 0.5φ is formed as an upper electrode by sputtering. To prepare a sample.

(Comparative Example A)
A barium titanate ultrafine particle dispersion solution was obtained in the same manner as in Example A. Next, the obtained barium titanate ultrafine particle dispersion solution is applied several times on a Si / SiO ₂ / Al ₂ O ₃ / Pt substrate by a spin coating method, and heat-treated at 300 ° C. in air, and then RTA. Heat treatment was performed in a furnace at 500 ° C. to obtain a barium titanate ultrafine particle thin film of Comparative Example A having an average particle size of 12.6 nm.

  The obtained barium titanate ultrafine particle thin film was confirmed by SEM observation and SPM observation to be a dense nanoparticle thin film having a small surface roughness. In addition, XRD measurement confirmed that the thin film was a barium titanate single phase.

(Comparative Examples B and C)
After obtaining a barium-titanium composite alkoxide raw material solution in the same manner as in Example A, it was directly applied on a Si / SiO ₂ / Al ₂ O ₃ / Pt substrate by a spin coat method in a dry atmosphere, and at 120 ° C. Drying was performed for 15 minutes. After repeating this spin coating and drying several times, heat treatment was performed in an RTA furnace at 500 ° C. and 700 ° C., and barium titanate ultrafine particle thin films of Comparative Examples B and C having average particle diameters of 33.2 nm and 45.6 nm, respectively. Got. That is, Comparative Example B is a barium titanate ultrafine particle thin film having an average particle size of 33.2 nm subjected to heat treatment at 500 ° C., and Comparative Example C is a titanium particle having an average particle size of 45.6 nm subjected to heat treatment at 700 ° C. It is a barium acid ultrafine particle thin film. As a result of SEM observation and SPM observation of the obtained barium titanate ultrafine particle thin film, the surface roughness was larger than that of the thin film surface prepared in Example A, and many gaps were observed between the particles, and the compactness was also high. It was confirmed that it was small. According to the XRD measurement, only the halo peak was observed in the thin film subjected to the heat treatment at 500 ° C., and the thin film was not crystallized. In addition, although the thin film subjected to the heat treatment at 700 ° C. had a peak due to barium titanate, a halo peak was also observed, indicating that the thin film also contained an amorphous phase.

(Comparative Example D)
As an adjustment of the raw material alkoxide solution, 4 g of barium isopropoxide was mixed and dissolved in 200 ml of 2-methoxyethanol in a glove box under an Ar atmosphere to form a barium alkoxide solution, and an equimolar titanium isopropoxide solution was added thereto. The mixture was dropped and mixed overnight to obtain a barium-titanium composite alkoxide raw material solution. The obtained solution was aged for 3 days while stirring in the presence of steam to produce a partially hydrolyzed raw material solution. This raw material solution was applied several times on a Si / SiO ₂ / Al ₂ O ₃ / Pt substrate by a spin coat method and heat-treated at 450 ° C. in air, and further heat-treated at 700 ° C. in an RTA furnace. As a result, a barium titanate ultrafine particle thin film having an average particle size of 48.9 nm was obtained.

  Table 2 shows the surface state, dielectric properties and crystal phase of the obtained barium titanate ultrafine particle thin film, and Table 3 shows the relative dielectric constant, dielectric loss and remanent polarization Pr × 2 at room temperature of each sample. Is shown.

まず、マイクロエマルジョン（ＭＥ）法により合成したチタン酸バリウム超微粒子が高分散状態に保たれた透明原料溶液を用いて成膜を行い、その後熱処理により粒成長させて、平均粒径を１５〜５０ｎｍに調整されたチタン酸バリウム超微粒子薄膜が、実施例Ａ〜Ｃに示されている。

First, film formation is performed using a transparent raw material solution in which barium titanate ultrafine particles synthesized by a microemulsion (ME) method are kept in a highly dispersed state, and then the particles are grown by heat treatment to have an average particle diameter of 15 to 50 nm. Examples of the barium titanate ultrafine particle thin film adjusted to the above are shown in Examples A to C.

  In this way, by forming a film from the metal oxide ultrafine particle dispersion solution kept in a highly dispersed state, even a nanoparticle becomes a uniform and dense thin film, and since it is already well crystallized, Even if heat treatment is performed, the surface roughness does not greatly increase due to the reaction, and the film quality does not significantly decrease due to cracks, etc. Rather, the heat treatment causes fine nanoparticles to grow, so further densification and crystallization Is promoted.

In addition, the electrical characteristics are sufficiently obtained. Therefore, in the barium titanate ultrafine particle thin film composed of particles grown to have an average particle diameter of 15 nm or more, as can be seen from the hysteresis curve of Example B in FIG. 9, the ferroelectricity is ² Pr> 2.0 μC / cm ^2. As shown, a dielectric constant of 300 or more was obtained. In addition, a thin film element using such a thin film as an element shows good dielectric properties with a dielectric loss of less than 4%. Also, the withstand voltage is preferably 200 kV / cm or more, which is preferable.

On the other hand, in Comparative Example A having an average particle size of 15 nm or less, ferroelectric properties were not obtained at ² Pr <2.0 μC / cm ² , and the relative dielectric constant was 300 or less, and sufficient ferroelectric properties were not obtained. Was.

  Next, as shown in Comparative Examples B and C, when a film was formed by a general sol-gel method, there was a problem in crystallinity. In Comparative Example C in which heat treatment was performed at 500 ° C., amorphous Phase. In addition, electrical measurement was not possible. Even in Comparative Example B which was heat-treated at 700 ° C., the crystallinity was poor, and although partly still contained an amorphous phase, barium titanate was crystallized, but the series of reactions greatly increased the surface roughness. At the same time, cracks were observed in some places, and the film quality was greatly reduced. Also, due to cracks, the leakage current becomes large, a dielectric hysteresis curve cannot be obtained, and the amorphous phase reacts with the substrate to form a low dielectric constant intermediate phase. It became smaller as follows. As a result, it was found that the dielectric loss was large and the withstand voltage was not sufficiently obtained.

  Furthermore, in the case of Comparative Example D in which a film was formed using a raw material solution that had been partially hydrolyzed in advance by a sol-gel method, the reaction amount after film formation was reduced, or a slight improvement in surface roughness was observed, After the heat treatment at 700 ° C., the barium titanate becomes a single phase. However, the dispersion and the crystallinity of the nanoparticles generated by the partial hydrolysis are still insufficient, and the surface roughness is smaller than that of the thin films shown in Examples A to C. In addition, the dielectric loss was increased and the relative dielectric constant was reduced to 300 or less, probably due to the inclusion of the low dielectric constant phase as in Comparative Examples B and C.

It is a schematic diagram of the aggregation mode of ceramic fine particles through water. It is a schematic diagram of the dispersion association mode of the emulsion water droplet in a dispersion medium. It is a schematic diagram of a microemulsion and an ultrafine particle dispersion mode after hydrolysis. It is sectional drawing which shows the manufacturing process of the laminated capacitor using the metal oxide ultrafine particle thin film of this invention. FIG. 3 is a cross-sectional view of a thin film element using the present invention. FIG. 3 is a particle size distribution diagram showing a particle size distribution of Example B of the present invention. 4 is an SEM photograph of an example of the present invention. It is sectional drawing of a measurement sample. FIG. 4 is a diagram illustrating hysteresis characteristics of the example of the present invention.

Explanation of reference numerals

1 drop 2 surfactant 3 cosurfactant 4 water 5 reaction product 6 dispersant 7,13 substrate 8 ceramic layer 18 dielectric film _{20 Si / SiO 2 / Al 2} O 3 / Pt substrate

Claims (5)

A dispersion liquid of metal oxide ultrafine particles produced by a hydrolysis reaction of a raw material in a microemulsion containing a dispersion medium that is a hydrophobic liquid, water and a surfactant,
The raw material is a composite metal alkoxide solution in which a plurality of metal alkoxides are mixed in alcohol to form a composite,
A dispersion of ultrafine metal oxide particles, wherein the amount of water contained in the microemulsion is 0.95 times or more and 3 times or less the amount of water required for hydrolysis of the raw material.   The metal oxide ultrafine particle dispersion according to claim 1, wherein at least one of the plurality of metal alkoxides is a barium alkoxide, and the composite metal alkoxide solution includes a polymerization inhibitor that suppresses polymerization of the barium alkoxide.   A metal oxide ultrafine particle thin film obtained by using the metal oxide ultrafine particle dispersion solution according to claim 1 or 2. It is composed of ultrafine metal oxide particles having an average particle size of 15 nm or more and 50 nm or less, has 2Pr or more ferroelectric properties in remanent polarization (Pr) of ² μC / cm ² or more, and has a relative dielectric constant of 300 or more at a measurement frequency of 1 kHz. A metal oxide ultrafine particle thin film characterized by the following.   The metal oxide ultrafine particle thin film according to claim 4, wherein the metal oxide ultrafine particles are a perovskite oxide containing titanium and barium.

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