JP2007099541A - Method of manufacturing dielectric ceramic composition, and ceramic capacitor using the manufactured dielectric ceramic composition - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a dielectric ceramic composition capable of preventing the localization of a component in the dielectric layer by uniformly coating barium titanate powder with additives. <P>SOLUTION: A barium titanate suspension is obtained by feeding barium titanate powder to an aqueous solution in which ammonium polyacrylate is dissolved and mixing to prepare barium titanate slurry, dissolving citric acid or ammonium citrate, ethylene glycol and various kinds of metal acetates in water in another vessel to obtain an aqueous solution having pH adjusted to 8.0-9.5 and feeding the barium titanate slurry and silica sol into the aqueous solution. The barium titanate suspension is heated and concentrated to chemically bond the citric acid with metal ion and to dehydration-condense the citric acid with ethylene glycol. After concentration, the solidified material is fired to obtain an oxide of the metal ion and the metal oxide fine particles are applied on the barium titanate powder to obtain the barium titanate powder coated with the metal oxide fine particle as the dielectric ceramic powder. <P>COPYRIGHT: (C)2007,JPO&INPIT

Description

  The present invention relates to a method for producing a dielectric ceramic composition used for a ceramic capacitor or the like and a ceramic capacitor.

Since barium titanate (BaTiO ₃ ) -based dielectric materials have excellent dielectric properties, they are widely used in various applications such as multilayer capacitors. However, the conventional barium titanate-based dielectric ceramic material has a problem that when it is fired in a neutral or reducing atmosphere, it is reduced and becomes a semiconductor. Therefore, firing is required to be performed under an oxidizing high oxygen partial pressure. In this case, for example, when a base metal material such as nickel (Ni) is used as an internal electrode in a multilayer capacitor, the internal electrode (nickel) is used in the firing step. ) Will be oxidized. Therefore, as the electrode material, for example, a noble metal such as palladium (Pd) or platinum (Pt) that does not melt at a high firing temperature and is not oxidized even when fired in an oxidizing atmosphere must be used. This is a major factor that increases the cost of multilayer capacitors.

  Therefore, the base metal electrode material such as nickel is not oxidized in the firing process, and is not reduced and becomes a semiconductor even when fired in a neutral or reducing atmosphere with a low oxygen partial pressure. The need for a non-reducing dielectric ceramic material having sufficient resistivity and excellent dielectric properties for use as a dielectric material has been strongly recognized.

For satisfying these conditions, for example, a BaTiO ₃ — (Mg, Zn, Sr, Ca) O—B ₂ O ₃ —SiO ₂ based material disclosed in Japanese Patent Publication No. 61-14611 is proposed. Has been. It is also known that the same effect can be obtained by using barium titanate powder to which MnO is added.

Japanese Patent Publication No. 61-14611

  In order to produce such a material, generally, a powder of a predetermined additive component is added to a powder of barium titanate, pulverized and mixed with a ball mill or the like, and then a binder is added to form a slurry. It is manufactured by firing as a green sheet.

  As an industrial mixing method of the raw material powder for forming these dielectric ceramic compositions, an oxide or carbonate of a metal element constituting the additive element (as described above) is added to the main component barium titanate powder. In this method, the added powder cannot be uniformly adhered and fixed to the surface of the barium titanate powder, and has stable characteristics. There is a problem that it is difficult to obtain a dielectric ceramic composition powder.

  Therefore, when a ceramic capacitor is produced using a dielectric ceramic composition in which barium titanate powder and additives are mixed, the additive components in the dielectric layer are localized, and the characteristics of the dielectric layer are uniform. It was difficult to do.

  Therefore, barium titanate powder is dispersed in an aqueous solution in which the salt of the additive element is dissolved, and an aqueous solution containing a precipitant is supplied to this to precipitate precipitated particles of oxide and carbonate of the additive element. A method of mixing with barium powder is also known, but in this method, since the formation of a precipitate containing an additive element is completed instantaneously, precipitation is always performed while covering the surface of the barium titanate powder. Does not necessarily precipitate. For this reason, it is difficult to uniformly coat the surface of the barium titanate powder with the additive.

  Accordingly, the present invention provides a dielectric ceramic composition capable of preventing the localization of components in the dielectric layer by coating the barium titanate powder uniformly with additives.

  It is another object of the present invention to provide a ceramic capacitor having good characteristics using the above dielectric ceramic composition.

In order to solve the above-mentioned problem, the invention according to claim 1 is a process of preparing a barium titanate slurry by adding barium titanate powder to water in which ammonium polyacrylate is dissolved and stirring the powder. ,
Dissolving citric acid or ammonium citrate, ethylene glycol, yttrium acetate, manganese acetate, magnesium acetate, calcium acetate and barium acetate in water to obtain an aqueous solution having a pH adjusted to a range of 8.0 to 9.5;
Adding a barium titanate slurry and silica sol to the aqueous solution to obtain a barium titanate suspension;
A step of thermally concentrating the suspension to chemically bond citric acid and metal ions, and dehydrating condensation of citric acid and ethylene glycol;
By baking the solidified product after the concentration in air or in an oxidizing atmosphere at a temperature of 550 ° C. or higher and lower than 1000 ° C. to obtain the metal ion oxide,
It is characterized in that barium titanate powder coated with metal oxide fine particles is obtained as dielectric ceramic powder.

  Further, in the invention according to claim 2, in the aqueous solution in which the citric acid or ammonium citrate, ethylene glycol, and acetate described in claim 1 are dissolved, the amount of citric acid or ammonium citrate and ethylene glycol is a metal It is characterized by being 1.5 to 5 times the total amount of ions.

  The invention according to claim 3 is characterized in that a ceramic capacitor is formed using the dielectric ceramic composition obtained by the manufacturing method according to claims 1 and 2.

  Since the additive component can be uniformly coated on the surface of the barium titanate powder, the barium titanate component and the additive component can be uniformly dispersed when the powder is slurried.

  For this reason, when a green sheet is prepared from this slurry and further formed into a ceramic capacitor, the localization of additive components in the dielectric layer is eliminated, and a ceramic capacitor having stable characteristics can be obtained.

  Next, an embodiment of the present invention will be described.

First, claim 1 will be described.
This invention is a method of coating a barium titanate powder with an additive component as a dielectric ceramic composition by the following steps.
1. 1. Step of preparing a barium titanate slurry having a pH of 8.0 to 9.5 by adding barium titanate powder to water in which ammonium polyacrylate is dissolved and stirring the powder. An aqueous solution in which citric acid or ammonium citrate, ethylene glycol, yttrium acetate, manganese acetate, magnesium acetate, calcium acetate, and barium acetate was dissolved in water in another container was adjusted to pH 8.0 to 9.5 with aqueous ammonia. 2. adjusting to the range of 3. A step of adding a barium titanate slurry and silica sol to an aqueous solution to obtain a barium titanate suspension. 4. Condensing citric acid and metal ions by heating and concentrating the suspension, and dehydrating condensation of citric acid and ethylene glycol A step of firing the solidified product after concentration in air or in an oxidizing atmosphere at a temperature of 550 ° C. or higher and lower than 1000 ° C. to obtain an oxide of the metal ion

  Below, the detail in each process is demonstrated.

  Barium powder is put into water in which ammonium polyacrylate is dissolved, and this is stirred. Ammonium polyacrylate ionizes into polyacrylate ions in water, which is adsorbed on the surface of the barium titanate powder particles, preventing the barium titanate particles from aggregating with each other due to the steric hindrance effect of polyacrylic acid. it can. Thereby, a slurry in which barium titanate is dispersed in water can be obtained. Due to the ionization of ammonium polyacrylate, the pH of the slurry is usually in the range of 8.0 to 9.5.

  On the other hand, citric acid or ammonium citrate, ethylene glycol, yttrium acetate, manganese acetate, magnesium acetate, calcium acetate, and barium acetate are dissolved in water in another container, and the pH is 8.0 to 9.5 with aqueous ammonia. Adjust to the range. The reason for using acetate is to facilitate the combination of metal ions and citric acid as will be described later. The reason for adjusting the pH to the range of 8.0 to 9.5 by adding ammonia water is to prevent the barium titanate particles from aggregating again when the barium titanate slurry is added.

  The barium titanate slurry and silica sol are added to the aqueous solution. Silica sol is silica fine particles dispersed in water. Since there is no water-soluble silicon acetate, silicon must be added as a silica sol among the additive components. With these inputs, a suspension in which barium titanate and silica particles are suspended in an aqueous solution is obtained.

  The suspension is then concentrated by heating. Specifically, the suspension put in the container is heated or concentrated by heating using a rotary evaporator. By this heating, the combination of the metal ion derived from the acetate and the citrate ion is promoted, and the metal citrate is formed in the suspension.

At the same time, as water is removed from the suspension, the metal citrate and ethylene glycol are sequentially dehydrated and condensed according to the formula 1 to form a polymer combined with the metal ions.
Here, M ^{n +} represents an n-valent metal ion combined with citric acid.
The dehydration condensation does not end with the formula (1), but further the dehydration condensation takes place between the products of the formula (1).

  The polymer produced by the progress of dehydration condensation adheres to and covers the surface of the barium titanate powder particles and silica sol particles dispersed in the suspension. As the dehydration condensation further proceeds, the suspension goes through a viscous liquid and finally becomes a solidified product.

  The solidified product is a state in which barium titanate powder, silica powder, and a polymer combined with metal ions are uniformly mixed.

  When this solidified product is baked in air or in an oxidizing atmosphere at a temperature of 550 ° C. or higher and lower than 1000 ° C., the polymer is burned and removed, and the metal ions combined with citric acid are changed into fine metal oxides. . As a result, fine particles of yttrium oxide, manganese oxide, magnesium oxide, barium oxide and silica are coated on the surface of the barium titanate powder particles. If the calcination temperature is less than 550 ° C., combustion removal of the polymer is not completed, and if it is 1000 ° C. or more, the sintering of the barium titanate particles proceeds.

  Citric acid and ethylene glycol are preferably 1.5 times or more and 5 times or less, respectively, with respect to the total amount of acetate salt first dissolved in water. If it is less than 1.5 times, not all of the metal ions can combine with citric acid, and eventually the additive components are localized. Also, adding more than 5 times is uneconomical.

  By the above process, barium titanate powder coated with yttrium oxide, manganese oxide, magnesium oxide, calcium oxide, barium oxide and silica is synthesized.

The invention will now be described with more detailed examples.
[Example 1]
In Example 1, a method for producing a dielectric ceramic composition by the method described in claims 1 and 2 will be described.
(1) 0.01 mole of yttrium oxide (converted to Y2O3), 0.002 mole of manganese oxide (converted to MnO), 0.01 mole of magnesium oxide (converted to MgO) to 0.01 mole of barium titanate, 0.01 Commercially available in 30 ml water with the intention of making a powder coated with mol calcium oxide (CaO equivalent), 0.015 mol barium oxide (BaO equivalent), 0.015 mol silica (SiO2 equivalent). The polyacrylic acid ammonium salt 0.21g was melt | dissolved, the barium titanate powder 30g was thrown into this, and it stirred for 1 hour with the high-speed stirrer, and prepared the barium titanate slurry. The pH of the slurry was 9.1.

  (2) Take 30 ml of water in another container and add 0.874 g of yttrium acetate tetrahydrate, 0.064 g of manganese acetate tetrahydrate, 0.227 g of magnesium acetate tetrahydrate, calcium acetate monohydrate. 0.278 g, barium acetate 0.495 g, citric acid 3.09 g, and ethylene glycol 2.78 ml were dissolved, and concentrated aqueous ammonia was added thereto to adjust the pH to 9.1.

  (3) Put the aqueous solution and barium titanate slurry in a eggplant-shaped flask attached to the rotary evaporator, and add 0.390 g of commercial silica sol (manufactured by Nissan Chemical Industries, trade name: methanol silica sol, containing SiO 2 at 30% by weight). A barium titanate suspension was obtained.

  (4) When the suspension was concentrated under reduced pressure for 3 hours while being heated to 70 ° C., the suspension gradually increased in viscosity and finally a white solid was obtained.

  (5) The solidified product was recovered from the eggplant-shaped flask, placed in a platinum crucible, and baked at 800 ° C. for 2 hours in an air atmosphere. As a result, a slightly brownish powder was obtained.

  (6) After this firing, the composition of the dielectric porcelain powder and the distribution of yttrium, manganese, magnesium, calcium, barium and silica in the powder were analyzed by EDX analysis. These additive components were found in the powder. It was confirmed that it was uniformly distributed.

  Through the process described above, a dielectric ceramic powder made of barium titanate powder coated with yttrium oxide, manganese oxide, magnesium oxide, calcium oxide, barium oxide and silica was obtained.

[Example 2]
Next, examples of ceramic capacitors using the dielectric ceramic composition prepared by the above method will be described.

[1. Manufacturing process]
[1-1. Preparation of dielectric slurry]
As a dielectric base material, a dielectric ceramic composition in which BaTiO ₃ having an average particle diameter of 0.7 μm was coated with a MnO precursor by the above-described method was used. In addition, this BaTiO ₃ used what was obtained by the oxalate coprecipitation method. The oxides of the main additive (MgO + Y ₂ O ₃ ) and the second sub-additive (WO ₃ , MoO ₃ ) were weighed in predetermined amounts according to the compositions shown in Table 1, respectively.

The oxide glass represented by BaSiO ₃ is obtained by wet-mixing BaCO ₃ and SiO ₂ with a ball mill for 24 hours, drying, firing in air at 1150 ° C., and pulverizing using a fine pulverizer such as a jet mill or an attritor mill. Was manufactured.

  A dielectric material was prepared from the dielectric base material, oxide powder, and oxide glass obtained as described above. That is, 850 g of a solvent in which water, ethyl alcohol, and a dispersant were mixed at a ratio of 80: 19: 1 was added to 1200 g of each dielectric material, and dispersed using a homogenizer. This mixture was dispersed for 10 hours using a ball mill, which is an ordinary well-known dispersion method, and then a solution containing a butyral resin and a plasticizer was added to prepare a dielectric slurry. The viscosity of these slurries was adjusted to about 200 cps.

[1-2. Green chip production]
Using the dielectric slurry obtained as described above, a green sheet having a thickness of 10 μm was formed on a PET film by a die coater, and an internal electrode paste was formed on the green sheet at a thickness of 2 μm. Printed. The internal electrode paste includes 100 parts by weight of Ni particles having an average particle diameter of 0.5 μm, 40 parts by weight of an organic vehicle (8 parts by weight of ethyl cellulose resin dissolved in 92 parts by weight of butyl carbitol), and butyl carbyl. A paste obtained by kneading 10 parts by weight of tall with three rolls was used.

Next, the sheet was peeled off from the PET film, laminated, and pressure bonded using a hydrostatic pressure of 1 ton / cm ² at 80 ° C. to obtain a green chip. The effective number of layers was 200. Next, this green chip was cut into a predetermined size, mounted on a metal plate setter, and subjected to binder removal processing, firing and annealing continuously under the following conditions to produce a capacitor element. The conditions for debinding, firing and annealing are as follows. Moreover, a wetter was used for humidifying each atmospheric gas.

(Binder removal)
Temperature increase rate: 20 ° C / hour Holding temperature: 300 ° C
Temperature holding time: 12 hours Atmospheric gas: In air (firing)
Temperature rising rate: 200 ° C./hour Holding temperature: 1200 ° C. to 1300 ° C.
Temperature holding time: 4 hours Cooling rate: 200 ° C./hour Atmospheric gas: Mixed gas of humidified N ₂ and H ₂ Oxygen partial pressure: 1 × 10 ⁻¹⁰ atm
(Annealing)
Holding temperature: 950 ° C
Temperature holding time: 8 hours Temperature rising / falling rate: 200 ° C./hour Atmospheric gas: N ₂ gas Oxygen partial pressure: 2 × 10 ⁻⁵ atm

[1-3. Barrel treatment / formation of external electrodes]
After polishing the end face of the obtained capacitor element by barrel treatment, 100 parts by weight of Cu particles having an average particle diameter of 0.5 μm and an organic vehicle (8 parts by weight of ethyl cellulose resin dissolved in 92 parts by weight of butyl carbitol) 35 Part by weight, 3 parts by weight of zinc borosilicate glass powder, and 7 parts by weight of butyl carbitol were kneaded, and the paste for external electrode was transferred to the end face, and then at 850 ° C. for 10 minutes in N ₂ atmosphere. The external electrode was formed by firing to obtain a multilayer ceramic capacitor having a configuration as shown in FIG. In the figure, 1 is a dielectric layer, 2 is an internal electrode, and 3 is an external electrode. The size of the sample manufactured as described above is 3.2 × 2.5 × 2.0 mm, the thickness of the effective dielectric layer is 7 μm × 200 layers, and the thickness of the internal electrode layer is about 1.5 μm. Met.

(Conventional example 1)
As a conventional example, as a method for dispersing MnO, a method by mixing oxide powder was used as Conventional Example 1.

  The characteristics shown below were evaluated for each sample.

(Capacitance temperature characteristics)
It was examined whether the temperature characteristic of the capacity satisfied EIA X7R. Specifically, the capacity was measured with a measurement voltage of 1 V at −55 to 125 ° C. using an LCR meter, and it was examined whether or not the capacity change rate satisfied within ± 15% (reference temperature 25 ° C.).

(Relative permittivity ε)
The capacitance at 20 ° C. was measured, and the relative dielectric constant was measured from the electrode area and the thickness of the dielectric. For the dielectric constant and dielectric loss, values at 1 vrms and 1.0 kHz were used.

(Capacitance resistance product)
The element was allowed to stand in a constant temperature bath at 25 ° C., and after 10 minutes, the capacitance and 1 minute value of insulation resistance when 25 V was applied were measured, and the product of the value and the capacitance was taken as the CR product.

(Accelerated life test)
As an accelerated life test, a DC voltage of 100 V was applied at a temperature of 150 ° C., and the change over time in the insulation resistance was measured. In the accelerated life test, the time when the insulation resistance of each sample became 10 ⁵ or less and IR lifetime to determine the mean life time for a plurality of samples.

The results are shown in Table 2 below.

[Test results]
In the dispersion by mixing the MnO powder of Conventional Example 1 shown in Table 2, the accelerated lifetime is shortened. Also, the temperature characteristic shows a large change at −55 ° C., and CR also shows a low value. This is presumably because the dispersion by mixing localizes the MnO powder and makes uniform dispersion difficult.

  In the examples of the present invention shown in Table 2, the CR was large and the accelerated life test result was good, and it was confirmed that sufficient reliability could be secured.

As is apparent from Table 2, when the technique of coating the surface of BaTiO ₃ according to the present invention with manganese oxide is used, an MLC excellent in withstand voltage can be manufactured and the reliability is high.

It is sectional drawing which shows the structure of a multilayer ceramic capacitor.

Explanation of symbols

1 Dielectric layer 2 Internal electrode 3 External electrode

Claims (3)

A step of preparing a barium titanate slurry by adding barium titanate powder to water in which poly (ammonium acrylate) is dissolved, and stirring the powder;
Dissolving citric acid or ammonium citrate, ethylene glycol, yttrium acetate, manganese acetate, magnesium acetate, calcium acetate and barium acetate in water to obtain an aqueous solution having a pH adjusted to a range of 8.0 to 9.5;
Adding a barium titanate slurry and silica sol to the aqueous solution to obtain a barium titanate suspension;
A step of thermally concentrating the suspension to chemically bond citric acid and metal ions, and dehydrating condensation of citric acid and ethylene glycol;
By baking the solidified product after the concentration in air or in an oxidizing atmosphere at a temperature of 550 ° C. or higher and lower than 1000 ° C. to obtain the metal ion oxide,
A method for producing a dielectric ceramic composition, comprising obtaining barium titanate powder coated with metal oxide fine particles as a dielectric ceramic powder. In the aqueous solution in which citric acid or ammonium citrate, ethylene glycol, yttrium acetate, manganese acetate, magnesium acetate, calcium acetate, and barium acetate are dissolved, the amount of citric acid or ammonium citrate and ethylene glycol is the total amount of metal ions. The method for producing a dielectric ceramic composition according to claim 1, wherein the dielectric ceramic composition is 1.5 times or more and 5 times or less. A ceramic capacitor manufactured using the dielectric ceramic composition obtained by the method for manufacturing a dielectric ceramic composition according to claim 1.