JP2011132071A - Method for producing dielectric ceramic material - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a method for producing a dielectric ceramic material which has a small particle diameter and little variation in the particle diameter and is therefore suitable for the thinning of a dielectric layer. <P>SOLUTION: In the method for producing a dielectric ceramic material, barium carbonate and titanium dioxide are reacted by solid phase reaction to produce a dielectric ceramic material. The method includes: a pulverizing mixing step of pulverizing and mixing a powdery mixture containing barium carbonate powder and titanium dioxide powder in an organic solvent; and a calcining step of firing the pulverized and mixed powdery mixture to obtain the power of a barium titanate-based compound. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a method for producing a dielectric ceramic material having a small particle size and small variation in particle size and suitable for thinning a dielectric layer.

  In conventional multilayer ceramic capacitors, a green sheet is produced by forming a dielectric ceramic material containing a barium titanate compound as a main component and a metal compound for adjusting characteristics as a subcomponent into a sheet shape. It is produced by repeating the process of laminating a sheet in which electrodes are printed on a sheet.

  In recent years, with the miniaturization of electronic equipment products, the density of electronic circuits has been increasing, and as a result, there has been a strong demand for smaller and larger capacity multilayer ceramic capacitors. In order to realize this demand, attempts have been made to make the internal electrode layers and dielectric layers thinner and increase the number of layers.

  However, when the dielectric layer is thinned, if the particle size of the main component barium titanate compound is large, the characteristics after firing the green chip and the surface roughness of the dielectric layer will vary, resulting in a short circuit rate. Increases and the insulation resistance defect increases. For this reason, there is a demand for micronization of the main component barium titanate compound.

  Conventionally, as described in, for example, Patent Document 1, when a barium titanate compound is produced using a solid-phase reaction, in order to pulverize and mix barium carbonate powder and titanium dioxide powder, these are put in water. Dispersed and pulverized and mixed.

JP2007-169122

  In view of the above situation, an object of the present invention is to provide a method for producing a dielectric ceramic material having a small particle size and a small variation in particle size and suitable for thinning a dielectric layer.

  As a result of intensive studies by the present inventors, when the barium carbonate powder and the titanium dioxide powder are pulverized and mixed in an organic solvent, these raw materials can be uniformly mixed without lowering the surface activity. It was confirmed that a barium titanate phase was generated at the calcination temperature, and twins were formed in many barium titanate particles. The “twin crystal” means a crystal structure as shown in FIGS. And it was confirmed that such barium titanate hardly grows even if the calcining temperature is raised. The present invention has been completed based on such novel findings.

  Conventionally, the organic solvent is used as the dispersion medium in the solid phase reaction only when the raw material is water-soluble, and when the raw material is barium carbonate and titanium dioxide, which are hardly soluble in water. No example of using an organic solvent as the dispersion medium is known.

  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, which contains barium carbonate powder and titanium dioxide powder. A pulverizing and mixing step of pulverizing and mixing the mixed powder in an organic solvent and a calcination step of firing the pulverized and mixed mixed powder to obtain a barium titanate-based compound powder are provided.

  If this is the case, the mixed powder containing barium carbonate powder and titanium dioxide powder is pulverized and mixed in an organic solvent, and the resulting mixed powder is fired to suppress grain growth of the barium titanate compound. Therefore, control of the particle size becomes easy. As a result, it is possible to easily obtain a powder of a barium titanate compound having a small particle size and a small variation in particle size.

  As described above, by using a barium titanate compound having a small particle size and a small variation in the particle size as a main component of the dielectric layer, the short-circuit rate is low and the insulation resistance failure is suppressed, and sufficient static resistance is achieved. A multilayer ceramic capacitor having a capacitance can be obtained.

  In the present invention, the barium titanate-based compound powder obtained by the calcining step has an average particle size of 100 nm or less, and twins are present inside 10% or more of the particles. preferable.

  Moreover, it is preferable that the particle size change rate in the calcining temperature of 700-1100 degreeC is 0.3 or less as for the powder of the barium titanate type compound obtained by the said calcination process. The “particle size change rate” referred to here is a value of a slope when linearly approximating a straight line when plotting the calcining temperature 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 obtained by the manufacturing method according to the present invention is also one aspect of the present invention.

  According to the present invention, since it is possible to obtain a barium titanate compound having a small particle size and a small variation in particle size, the surface roughness of the dielectric layer mainly composed of the barium titanate compound is reduced. Variations can be suppressed, whereby the short-circuit rate and insulation resistance failure of the multilayer ceramic capacitor can be suppressed.

  Further, since the green sheet produced using the dielectric ceramic material obtained by the present invention has a dense structure, the particle size after firing is stabilized, and as a result, the electrical characteristics are stabilized and effective. The range of the firing temperature is expected to be widened.

  Furthermore, as the barium titanate compound is made finer, thinning of the dielectric layer is promoted, and the number of laminated internal electrode layers and dielectric layers can be increased. Capacitance can be increased.

  Further, the method of the present invention makes it possible to easily synthesize fine barium titanate-based compound powder having an arbitrary particle size, and facilitate temperature control in the calcination step.

The figure which shows the twin crystal structure ((a) face centered cubic lattice, (b) body centered cubic lattice). A photograph of barium titanate powder taken using a transmission electron microscope. 1 is a schematic cross-sectional view of a multilayer ceramic capacitor according to an embodiment of the present invention. 6 is a graph showing XRD measurement data obtained for Example 4. The graph which shows the relationship between the calcination temperature in each Example and a comparative example, and the average particle diameter of barium titanate powder.

  A multilayer ceramic capacitor 1 according to an embodiment of the present invention will be described below with reference to the drawings.

  As shown in FIG. 3, the multilayer ceramic capacitor 1 according to this embodiment is provided on a capacitor chip body 2 in which dielectric layers 3 and internal electrodes 4 are alternately stacked, and on the surface of the capacitor chip body 2. An external electrode 5 electrically connected to the internal electrode 4. The internal electrodes 4 are laminated so that the ends thereof are alternately exposed on the two opposing surfaces of the capacitor chip body 2, and are formed on the surfaces of the capacitor chip body 2 to form a predetermined capacitor circuit. The electrode 5 is electrically connected.

The dielectric layer 3 is made of a sintered body of a dielectric ceramic material mainly composed of a barium titanate compound. The barium titanate compound is composed of barium carbonate (BaCO ₃ ) and titanium dioxide (TiO _2). ) By a solid phase reaction.

  In the solid phase reaction, a mixed powder containing barium carbonate powder and titanium dioxide powder is pulverized and mixed in an organic solvent, and the mixed powder pulverized and mixed is fired to obtain a barium titanate compound powder. And a calcination step.

The mixed powder may contain an alkaline earth metal carbonate such as calcium carbonate (CaCO ₃ ) or strontium carbonate (SrCO ₃ ), if necessary, in addition to the barium carbonate powder and titanium dioxide powder. Good.

  Examples of the organic solvent include, but are not limited to, alcohols such as ethanol, propanol, and butanol; ketones such as acetone and methyl ethyl ethyl ketone; esters such as ethyl acetate; aromatics such as toluene, xylene, and benzene Is mentioned. These organic solvents may be used independently and 2 or more types may be used together.

  In the pulverization and mixing step, for example, a barium carbonate powder and a titanium dioxide powder are dispersed together with an organic solvent in a wet manner by using a pulverizer such as a bead mill or a ball mill or by performing a high-pressure dispersion treatment.

  In the calcination step, the pulverized and mixed powder is heated in a vacuum or in the atmosphere at, for example, 700 to 1100 ° C. for about 3 hours.

  By calcining the mixed powder in such a calcination step, a powder of a barium titanate compound having a small particle size such that the average particle size is 100 nm or less can be obtained. If the average particle size of the barium titanate compound powder exceeds 100 nm, it is difficult to make the dielectric layer 3 thinner. In addition, the said average particle diameter is measured and calculated by observation using a scanning electron microscope (SEM), for example.

  The barium titanate-based compound powder preferably has twins inside 10% or more of the particles. In such a case, grain growth is difficult even when the calcining temperature is raised, and therefore particle size control becomes easy. In addition, the abundance of twins is measured and calculated by observation using a transmission electron microscope (TEM), for example.

  Furthermore, even if the calcining temperature is changed such that the particle size change rate at a calcining temperature of 700 to 1100 ° C. is 0.3 or less by firing the mixed powder in such a calcining step. It becomes possible to obtain a powder of a barium titanate compound in which the particle size hardly changes. For this reason, according to this invention, control of a calcination temperature becomes very easy. The “particle size change rate” referred to here is a slope value when linearly approximating a straight line when plotting the calcining temperature on the x-axis and the particle size on the y-axis as described above.

  In the solid phase reaction in the present embodiment, the following steps are usually performed in addition to the pulverization and mixing step and the calcining step.

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

  In addition to the barium titanate compound powder, the dielectric ceramic material may contain a metal compound for adjusting characteristics as required. Examples of the metal compound include compounds such as oxides and carbonates containing one or more elements of Mg, Ba, Ca, Si, Mn, Al, V, Dy, Y, Ho, and Yb. It is done.

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

  The dispersant is not particularly limited. For example, polyvinyl butyral dispersant, polyvinyl acetal dispersant, polycarboxylic acid dispersant, maleic acid dispersant, polyethylene glycol dispersant, allyl ether copolymer dispersant, and the like. Is mentioned.

  A dielectric ceramic material is obtained by adding the metal compound powder or dispersant to the barium titanate-based compound powder, mixing with a homogenizer, and then pulverizing and dispersing with a bead mill. A slurry for forming a green sheet can be obtained by adding a solvent and a binder to the dielectric ceramic material thus obtained and mixing them using a ball mill or the like.

  Examples of the solvent include, but are not limited to, glycols such as ethyl carbitol, butanediol, and 2-butoxyethanol; alcohols such as methanol, ethanol, propanol, and butanol; ketones such as acetone, methyl ethyl ketone, and diacetone alcohol; Examples thereof include esters such as methyl acetate and ethyl acetate; aromatics such as toluene, xylene and benzyl acetate.

  The binder is not particularly limited, and examples thereof include acrylic resin, polyvinyl butyral resin, polyvinyl acetal resin, and ethyl cellulose resin.

  It is preferable that the binder is previously dissolved in the solvent and filtered to obtain a solution, and the dielectric ceramic material is added to the solution. A binder resin having a high degree of polymerization is difficult to dissolve in a solvent, and the dispersibility of the slurry tends to be deteriorated by an ordinary method. Dispersibility of each component in the slurry for green sheet formation can be improved by dissolving the binder resin having a high degree of polymerization in a solvent and then adding other components to the solution. Can also be suppressed. In addition, in solvents other than the said solvent, while a solid content concentration cannot be raised, it exists in the tendency for the time-dependent change of lacquer viscosity to increase.

  The green sheet is formed by applying the slurry for forming the green sheet thus produced on a base material made of polyethylene terephthalate or the like. The dielectric layer 3 is made of a sintered body obtained by firing the obtained green sheet. The thickness per three dielectric layers is preferably 2 μm or less.

  The internal electrode 4 is not particularly limited, and examples thereof include those made of metals such as Cu, Ni, W, Mo, Ag, or alloys thereof.

  The external electrode 5 is not particularly limited, and examples thereof include metals such as Cu, Ni, W, Mo, and Ag or alloys thereof; alloys such as In—Ga and Ag-10Pd; carbon, graphite, and a mixture of carbon and graphite. The thing which consists of etc. is 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 internal electrodes 4 containing the above various metals and the like is screen-printed in a predetermined shape on the green sheet to form a conductive paste film for internal electrodes 4.

  Next, a plurality of green sheets on which the conductive paste film for the internal electrode 4 is formed as described above are stacked, and a green sheet on which no conductive paste film is formed is stacked so as to sandwich the green sheets. After pressure bonding, the laminate (green chip) is obtained by cutting as necessary.

  And after performing a binder removal process to the obtained green chip, the said green chip is baked, for example in reducing environment, and the capacitor chip body 2 is obtained. In the capacitor chip body 2, dielectric layers 3 and internal electrodes 4 made of a sintered body obtained by firing a green sheet are alternately laminated.

  The obtained capacitor chip body 2 is preferably subjected to an annealing treatment to reoxidize the dielectric layer 3.

  Next, an electrode made of the above-mentioned various metals or the like on the end surface of the capacitor chip body 2 so that the external electrode 5 is electrically connected to each end edge of the internal electrode 4 exposed from the end surface of the capacitor chip body 2. The external electrode 5 is formed by coating. Then, if necessary, a coating layer is formed on the surface of the external electrode 5 by plating or the like.

  The present invention will be described in more detail with reference to the following examples. However, the present invention is not limited to these examples.

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 converted into an A / B ratio (Ba / Ti ratio) 1.002. Next, ethanol (Etha) in the examples or a toluene / ethanol mixed solution (Etha / Tolu) in which toluene and ethanol are mixed at a weight ratio of 30:70 is added to the weighed powder. Water was added, premixing was performed with a mixer, and the resulting mixed slurry was pulverized and mixed with a bead mill. Next, the mixed slurry thus pulverized and mixed was dried, and the mixed powder after drying was dry pulverized. Next, the mixed powder after dry pulverization was calcined in vacuum at the temperatures shown in Tables 1 to 5 below.

When the obtained barium titanate (BaTiO ₃ ) powder was subjected to XRD measurement, it was confirmed from the obtained XRD measurement data that it was a single phase of barium titanate (see FIG. 4). The data shown in FIG. 4 was obtained for Example 4, but similar data was obtained for other examples. Further, the obtained BaTiO ₃ powder was observed with an SEM, and the particle size was measured. 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. Further, the specific surface area (SSA) of the obtained BaTiO ₃ powder was measured by the BET method. Further, the obtained BaTiO ₃ powder was observed with a TEM, and the abundance of twins was calculated. These results are shown in Tables 1 to 5 below and FIG.

From the results obtained for each Example and Comparative Example, BaCO ₃ powder and TiO ₂ powder were pulverized and mixed in an organic solvent to suppress grain growth, and the average particle size was 100 nm at a wide range of calcining temperatures. In the following, it has become clear that a BaTiO ₃ powder with a small particle size and a small variation in particle size such that the standard deviation σ representing the variation in particle size distribution is 20 or less can be obtained. It was also confirmed that twins were formed with high probability in the BaTiO ₃ powder.

DESCRIPTION OF SYMBOLS 1 ... Multilayer ceramic capacitor 2 ... Capacitor chip body 3 ... Laminate body layer 4 ... Internal electrode 5 ... External electrode

Claims (4)

A method for producing a dielectric ceramic material by reacting barium carbonate and titanium dioxide by a solid phase reaction,
A pulverizing and mixing step of pulverizing and mixing a mixed powder containing barium carbonate powder and titanium dioxide powder in an organic solvent, and a calcination step of firing the pulverized mixed powder to obtain a barium titanate compound powder. A method for producing a dielectric ceramic material, comprising:   2. The method for producing a dielectric ceramic material according to claim 1, wherein the barium titanate-based compound powder has an average particle diameter of 100 nm or less and has twins inside 10% or more of the particles.   The method for producing a dielectric ceramic material according to claim 1 or 2, wherein the barium titanate compound powder has a particle size change rate of 0.3 or less at a calcining temperature of 700 to 1100C. A multilayer ceramic capacitor comprising a dielectric layer made of a sintered body of a dielectric ceramic material obtained by the manufacturing method according to claim 1, 2 or 3.