KR20110074486A - Method for manufacturing dielectric ceramic material - Google Patents

Abstract

PURPOSE: A manufacturing method of dielectric ceramic material is provided to easily manufacture a titanate-based barium compound with 'a small grain size and low unbalance of grain' by controlling grain growth of the titanate-based barium compound in the rising of a calcining temperature. CONSTITUTION: The manufacturing method of dielectric ceramic material includes following steps.(a) A compound powder 'containing barium carbonate powder and titanium dioxide powder' is pulverized and mixed in an organic solvent.(b) The pulverized and mixed compound powder is plasticized, and the titanate-based barium compound is manufactured. The titanate-based barium compound powder has a particle average of below 100nm. A twin crystal exists inside more than 10% of particle. The titanate-based barium compound powder has a particle change rate of below 0.3 at the calcining temperature of 700-1100°C.

Description

Method for manufacturing dielectric ceramic material

The present invention relates to a method for producing a dielectric ceramic material suitable for the thinning of a dielectric layer having a small particle size and a low imbalance of the particle size.

In the conventional multilayer ceramic capacitor, a green sheet is produced by molding a dielectric ceramic material containing a barium titanate-based compound as a main component and a metal compound for property adjustment as a secondary component to form a sheet, and printing an electrode on the green sheet. It is produced by repeating the laminating process.

In recent years, with the miniaturization of electronic device products, the densification of electronic circuits has progressed, and as a result, there is a strong demand for miniaturization of multilayer ceramic capacitors. In order to realize such a demand, thinning of the internal electrode layers and the dielectric layers and increasing the number of stacked layers have been attempted.

However, in the case where the dielectric layer is thinned, when the particle size of the barium titanate compound as a main component is large, an unbalance occurs in the characteristics after the green chip firing or the surface roughness of the dielectric layer, resulting in an increase in short circuit rate and poor insulation resistance. For this reason, the granulation of the barium titanate type compound which is a main component is calculated | required.

Conventionally, as described, for example, in Patent Document 1, in the case of producing a barium titanate-based compound using a solid phase reaction, in order to pulverize and mix barium carbonate powder and titanium dioxide powder, they are dispersed in water and pulverized and mixed. .

Japanese Laid-Open Patent 2007-169122

An object of the present invention is to provide a method for producing a dielectric ceramic material suitable for the thinning of a dielectric layer having a small particle size and a low imbalance of the particle size in view of the above phenomenon.

As a result of earnest examination by the present inventors, when barium carbonate powder and titanium dioxide powder are pulverized and mixed in an organic solvent, these raw materials can be mixed uniformly without reducing surface activity, and titanic acid is carried out at low calcining temperature. In addition to the formation of the barium phase, it was confirmed that twins were formed in many barium titanate particles. In addition, "twin" means the crystal structure shown to FIG. 1 and FIG. And it was confirmed that such barium titanate did not grow well even if the plasticization temperature was raised. The present invention has been completed based on these novel findings.

In addition, conventionally, the use of an organic solvent as a dispersion medium in a solid phase reaction is only possible when the raw material is water-soluble, and an example of using an organic solvent as the dispersion medium is known when barium carbonate and titanium dioxide which are insoluble in water are used as the raw material. Not.

That is, the method for producing a dielectric ceramic material according to the present invention is a method for producing a dielectric ceramic material by reacting barium carbonate and titanium dioxide by a solid phase reaction, wherein the mixed powder containing barium carbonate powder and titanium dioxide powder is organically produced. And a calcining step of pulverizing and mixing the solvent in the solvent, and calcining and mixing the powder mixed with the barium titanate compound.

According to the above method, the mixed powder containing barium carbonate powder and titanium dioxide powder is pulverized and mixed in an organic solvent, and the grain growth of the barium titanate compound is suppressed by firing the prepared mixed powder, so that the particle size can be easily controlled. As a result, the powder of the barium titanate-based compound having a small particle size and a small imbalance of the particle size can be easily produced.

Thus, by using the barium titanate-based compound having a small particle size and a small imbalance of the particle size as a main component of the dielectric layer, a multilayer ceramic capacitor having a low short circuit rate, an insulation resistance defect can be suppressed, and a sufficient capacitance can be formed.

In the present invention, it is preferable that the powder of the barium titanate-based compound produced by the calcination step has twin particles in the particles having an average particle diameter of 100 nm or less and 10% or more.

In addition, the powder of the barium titanate-based compound produced by the calcination step preferably has a particle size change rate of 0.3 or less at a calcination temperature of 700 to 1100 ° C. The "particle size change rate" here is the inclination value at the time of linear approximation of the straight line when the plastic temperature is plotted on the x-axis and the particle size on the y-axis.

A multilayer ceramic capacitor having a dielectric layer made of a sintered body of a dielectric material produced by the manufacturing method according to the present invention is also one of the present inventions.

According to the present invention, since the barium titanate compound having a small particle size and a small imbalance of the particle size can be produced, an unbalance of the surface roughness of the dielectric layer mainly containing such a barium titanate compound can be suppressed, whereby the multilayer ceramic capacitor The defect of a short circuit rate and an insulation resistance can be suppressed.

In addition, the green sheet fabricated using the dielectric ceramic material produced by the present invention is expected to have a stable structure and thus have a stable particle diameter after firing, thereby to stabilize the electrical properties and widen the range of effective firing temperatures.

In addition, as the barium titanate-based compound becomes finer, the thinning of the dielectric layer may be promoted to increase the number of stacked layers of the internal electrode layer and the dielectric layer, thereby increasing the capacitance per unit volume of the multilayer ceramic capacitor.

Further, according to the method of the present invention, it is possible to easily synthesize a powder of the barium titanate-based compound having a particle size of an arbitrary particle size, thereby facilitating temperature management in the calcination step.

BRIEF DESCRIPTION OF THE DRAWINGS It is a figure which shows twin crystal structure ((a) face-centered cubic lattice, (b) body centered cubic lattice).
Fig. 2 is a photograph of barium titanate powder taken using a transmission electron microscope.
3 is a schematic cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention.
4 is a graph showing XRD measurement data measured for Example 4. FIG.
5 is a graph showing the relationship between the calcining temperature of each Example and Comparative Example and the average particle diameter of the barium titanate powder.

EMBODIMENT OF THE INVENTION Hereinafter, the multilayer ceramic capacitor 1 which concerns on one Embodiment of this invention is demonstrated with reference to drawings.

As shown in FIG. 3, the multilayer ceramic capacitor 1 according to the present embodiment is formed on the surface of the capacitor chip body 2 and the capacitor chip body 2 in which the dielectric layers 3 and the internal electrodes 4 are alternately stacked. It is provided with the external electrode 5 which is provided and is conductive with the internal electrode 4. The internal electrodes 4 are laminated so that their ends are alternately exposed on two opposite surfaces of the capacitor chip body 2, and are formed on the surface of the capacitor chip body 2 to form an external capacitor ( Electrically connect with 5).

The dielectric layer 3 is composed of a sintered body of a dielectric ceramic material containing a barium titanate-based compound as a main component, and the barium titanate-based compound is prepared by reacting barium carbonate (BaCO ₃ ) with titanium dioxide (TiO ₂ ) by a solid phase reaction. Can be.

The solid phase reaction is a pulverized mixing process of pulverizing and mixing a mixed powder containing barium carbonate powder and titanium dioxide powder in an organic solvent, and calcining the pulverized mixed powder to produce a powder of a barium titanate-based compound. Process.

The mixed powder may further contain, in addition to barium carbonate powder and titanium dioxide powder, alkaline earth metal carbonates such as calcium carbonate (CaCO ₃ ) and strontium carbonate (SrCO ₃ ).

It does not specifically limit as said organic solvent, For example, Alcohol, such as ethanol, a propanol, butanol; Ketones, such as acetone and methyl ethyl ethyl ketone; Ester, such as ethyl acetate; Aromatics, such as toluene, xylene, benzene, etc. Can be mentioned. These organic solvents may be used alone, or two or more thereof may be used in combination.

In the above pulverized mixing process, barium carbonate powder and titanium dioxide powder are wet-dispersed with an organic solvent, for example, using a mill such as a bead mill or a ball mill, or performing a high pressure dispersion treatment.

The calcining step heats the mixed powder, which is pulverized and mixed, in vacuum or in the air, for example, at about 700 to 1100 ° C. for about 3 hours.

By firing the mixed powder in such a calcination step, it is possible to produce a powder of a barium titanate compound having a small particle size with an average particle diameter of 100 nm or less. When the average particle diameter of the barium titanate-based powder exceeds 100 nm, it is difficult to thin the dielectric layer 3. In addition, the said average particle diameter is measured and calculated by observation, for example using a scanning electron microscope (SEM).

In addition, in the powder of the barium titanate-based compound, twins are preferably present within 10% or more of the particles. As a result, even if the plasticization temperature is increased, the grain growth is not easy, and thus the particle size control is facilitated. In addition, the abundance of twins is measured and calculated by observation, for example using a transmission electron microscope (TEM).

In addition, by firing the mixed powder in such a calcination process, it is possible to produce a powder of a barium titanate-based compound whose particle size does not change well even when the calcination temperature of which the particle size change rate is lower than 0.3 at a calcination temperature of 700 to 1100 ° C. is changed. . Thus, according to the present invention, control of the firing temperature becomes very easy. In addition, the "particle size change rate" here is the inclination value at the time of linear approximation of the straight line at the time of plotting plastic temperature on the x-axis and particle size on the y-axis as mentioned above.

In addition, in addition to the said pulverization mixing process and the said calcination process, each of the following processes is normally performed for the solid-phase reaction of this embodiment.

First, after a predetermined amount of barium carbonate powder and titanium dioxide powder is weighed, an organic solvent is added to the weighed barium carbonate powder and titanium dioxide powder and mixed with a mixer. Subsequently, the prepared mixed powder is pulverized and mixed as above. Then, the ground mixed powder is dried and then dry ground. Then, the mixed powder after the dry grinding is fired as described above to prepare a powder of the barium titanate compound.

In addition to the powder of the barium titanate-based compound, the dielectric ceramic material may contain a metal compound for adjusting properties as necessary. Examples of the metal compound include compounds such as oxides and carbonates containing one or a plurality of elements of Mg, Ba, Ca, Si, Mn, Al, V, Dy, Y, Ho, and Yb.

When adding the powder of the metal compound to the powder of the barium titanate-based compound, it is preferable to add a dispersant together.

It does not specifically limit as said dispersing agent, For example, a polyvinyl butyl al type dispersing agent, a polyvinyl acetal type dispersing agent, a polycarboxylic acid type dispersing agent, a maleic acid type dispersing agent, a polyethylene glycol type dispersing agent, an aryl ether copolymer type dispersing agent, etc. are mentioned.

A dielectric ceramic material can be produced by adding a powder or dispersant of the metal compound to the powder of the barium titanate-based compound, for example, mixing with a homogenizer, and then grinding / dispersing with a bead mill. The slurry for green sheet formation can be manufactured by adding a solvent and a binder to the dielectric ceramic material thus prepared, and mixing using a ball mill etc.

The solvent is not particularly limited, and for example, glycols such as ethyl calbitol, butanediol and 2-butoxyethanol; alcohols such as methanol, ethanol, propanol and butanol; acetone, methyl ethyl ketone, diacetone alcohol and the like Ketones; esters such as methyl acetate and ethyl acetate; aromatics such as toluene, xylene, benzyl acetate, and the like.

It does not specifically limit as said binder, For example, an acrylic resin, a polyvinyl butylal resin, a polyvinyl acetal resin, an ethyl cellulose resin, etc. are mentioned.

It is preferable to melt | dissolve the said binder beforehand in the said solvent, make it a solution, and to add the said dielectric ceramic material to this solution. The binder resin of high polymerization degree does not melt | dissolve easily in a solvent, and there exists a tendency for the dispersibility of a slurry to deteriorate by a conventional method. By dissolving the binder resin of high polymerization degree in a solvent and adding another component to the solution, the dispersibility of each component of the slurry for green sheet formation can be improved, and generation | occurrence | production of undissolved binder resin can also be suppressed. In addition, the solid content concentration cannot be increased by solvents other than the above solvent, and there is a tendency that the change over time of the lacquer viscosity increases.

The green sheet is formed by applying the green sheet forming slurry thus prepared in a sheet form onto a substrate made of polyethylene terephthalate or the like. The dielectric layer 3 consists of a sintered compact formed by baking the manufactured green sheet. It is preferable that the thickness per one dielectric layer 3 is 2 micrometers or less.

It does not specifically limit as the internal electrode 4, For example, what consists of metals, such as Cu, Ni, W, Mo, Ag, these alloys, etc. is mentioned.

It does not specifically limit as the external electrode 5, For example, metals, such as Cu, Ni, W, Mo, Ag, or these alloys; Alloys, such as In-Ga, Ag-10 Pd; Carbon, graphite, carbon; The thing which consists of mixtures of graphite, etc. are mentioned.

Although it does not specifically limit as a manufacturing method of the multilayer ceramic capacitor which concerns on this embodiment, For example, it manufactures as follows. First, the conductive paste for the internal electrode 4 containing the above-described various metals and the like is screen printed on the green sheet in a predetermined shape to form a conductive paste film for the internal electrode 4.

Next, after laminating a plurality of green sheets with the conductive paste film for the internal electrode 4 and the above-described one, laminating and pressing the green sheet without the conductive paste film so as to interpose the green sheet, A laminate (green chip) is formed by cutting according to the above.

Then, after the binder removal process is performed on the formed green chip, the green chip is baked in a reducing atmosphere, for example, to form the capacitor chip body 2. In the capacitor chip body 2, a dielectric layer 3 made of a sintered body obtained by firing a green sheet and an internal electrode 4 are alternately stacked.

It is preferable to perform an annealing treatment on the formed capacitor chip body 2 in order to reoxidize the dielectric layer 3.

Next, the above-mentioned various types on the end surface of the capacitor chip body 2 are electrically connected to the respective edges of the internal electrode 4 exposed at the end face of the capacitor chip body 2. The external electrode 5 is formed by applying an electrode made of metal or the like. Then, a coating layer is formed on the surface of the external electrode 5 through plating or the like as necessary.

[Example]

Hereinafter, although an Example is given and this invention is demonstrated in more detail, this invention is not limited only to this Example.

BaCO ₃ powder (specific surface area; 30 m 2 / g or 50 m 2 / g) and TiO ₂ powder (specific surface area; 50 m ² / g or 100 m ² / g) were prepared, and the prepared powder was subjected to A / B ratio (Ba / Ti ratio). Next, ethanol (Etha) or toluene / ethanol mixed solution (Etha / Tolu) obtained by mixing toluene and ethanol in a weight ratio of 30:70 was added to the weighed powder, and water was added for the comparative example. The mixed slurry produced by premixing with the furnace was ground and mixed with a bead mill. Then, the mixed slurry which was pulverized and mixed was dried, and the mixed powder after drying was dry pulverized. Next, the mixed powder after dry grinding was vacuum-fired at the temperature of following Tables 1-5.

As a result of performing XRD measurement on the produced barium titanate (BaTiO ₃ ) powder, it was confirmed from the obtained XRD measurement data that it was a barium titanate single phase (see FIG. 4). In addition, although the data shown in FIG. 4 was measured about Example 4, the same data could be obtained about another Example. Furthermore, SEM observation of the produced BaTiO ₃ powder was carried out to measure the particle size. At this time, the particle size of 100 or more particles was measured, and the standard deviation σ was calculated together with the average particle size. In addition, the specific surface area (SSA) was measured by the BET method with respect to the manufactured BaTiO ₃ powder. In addition, the abundance of twins was calculated by TEM observation of the prepared BaTiO ₃ powder. The results are shown in Tables 1 to 5 and FIG. 5.

From the results according to the examples and the comparative examples, by pulverizing and mixing BaCO ₃ powder and TiO ₂ powder in an organic solvent, grain growth is suppressed, and standard deviation showing an unbalance in particle size distribution with an average particle diameter of 100 nm or less at a wide range of calcination temperatures It was found that BaTiO ₃ powder having a particle size of 20 or less and a small particle size with little unbalance in particle size could be produced. It was also confirmed that twins were formed in the BaTiO ₃ powder with a high probability.

1: multilayer ceramic capacitor
2: condenser chip
3: laminate layer
4: internal electrode
5: external electrode

Claims (4)

In a method of producing a dielectric ceramic material by reacting barium carbonate and titanium dioxide by a solid phase reaction,
A pulverized mixing process of pulverizing and mixing a mixed powder containing barium carbonate powder and titanium dioxide powder in an organic solvent,
And a calcining step of calcining and mixing the mixed powder to produce a powder of a barium titanate compound.
The method of claim 1,
The powder of the barium titanate-based compound is a method of producing a dielectric ceramic material, the average particle diameter is 100nm or less and twins are present in the particles 10% or more.
The method according to claim 1 or 2,
The powder of the barium titanate-based compound is a method for producing a dielectric ceramic material having a particle size change rate of 0.3 or less at a calcination temperature of 700 ~ 1100 ℃.
A multilayer ceramic capacitor comprising a dielectric layer made of a sintered body of a dielectric ceramic material produced by the manufacturing method according to any one of claims 1 to 3.

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