JP2005294384A - Manufacturing method of dielectric material ceramic composition and ceramic capacitor using the same - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To obtain a dielectric material ceramic composition which can prevent localization of elements in the dielectric material layer by uniformly covering barium titanic acid powder with an additive. <P>SOLUTION: The barium titanic acid suspension is formed by blowing the carbonic acid gas into a dispersion liquid obtained by dispersing manganese carbonate into water, dissolving the manganese carbonate as manganese bicarbonate into water, and inputting barium titanic acid powder into the aqueous solution of this manganese bicarbonate. Moreover, the suspension is heated up to 70°C or higher to obtain manganese bicarbonate as a precipitation substance of manganese carbonate. In this case, the precipitation substance of manganese carbonate is caused to adhere to the surface of the barium titanic acid powder. The precipitation substance obtained is baked in the temperature equal to or higher than 550°C but under 1,000°C in the atmospheric condition or in the oxidizing atmosphere to change manganese carbonate into manganese trioxide. Consequently, the barium titanic acid powder covered with manganese trioxide can be obtained as the dielectric material ceramic powder. <P>COPYRIGHT: (C)2006,JPO&NCIPI

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 problems, the invention according to claim 1 is a method for producing a dielectric ceramic composition, wherein carbon dioxide gas is blown into a dispersion in which manganese carbonate is dispersed in water, and the manganese carbonate is converted into hydrogen carbonate. Dissolving manganese in water as manganese;
Adding a barium titanate powder to this manganese hydrogen carbonate aqueous solution to obtain a barium titanate suspension;
Heating the suspension to 50 ° C. or higher to precipitate the dissolved manganese hydrogen carbonate as manganese carbonate so that the surface of the barium titanate powder adheres;
After the precipitation reaction, the precipitate is baked in air or in an oxidizing atmosphere at a temperature of 550 ° C. or higher and lower than 1000 ° C. to convert manganese carbonate to dimanganese trioxide,
It is characterized in that barium titanate powder coated with dimanganese trioxide is obtained as a dielectric ceramic powder.

  The invention according to claim 2 is characterized in that the barium titanate suspension is heated to 70 ° C. or higher and lower than the boiling temperature.

  Further, 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 claim 1 or 2.

  Since manganese oxide can be uniformly coated on the surface of the barium titanate powder, the barium titanate component and the manganese oxide 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, the inventions of claims 1 and 2 will be described.
This invention is a method of coating a barium titanate powder with dimanganese trioxide by the following process as a dielectric ceramic composition.
1. 1. A step of blowing carbon dioxide into a dispersion in which manganese carbonate is dispersed in water to dissolve the manganese carbonate in water as manganese hydrogen carbonate. 2. Step of charging barium titanate powder into this manganese hydrogen carbonate aqueous solution to obtain a barium titanate suspension. 3. The suspension is heated to 50 ° C. or higher to precipitate the dissolved manganese hydrogen carbonate as manganese carbonate so that the surface of the barium titanate powder adheres. After the precipitation reaction is completed, the precipitate is baked in air or in an oxidizing atmosphere at a temperature of 550 ° C. or higher and lower than 1000 ° C. to convert manganese carbonate to dimanganese trioxide

  Below, the detail in each process is demonstrated.

  Manganese carbonate is insoluble in water. However, when manganese carbonate is introduced into water and carbon dioxide gas is blown into it, it becomes manganese hydrogen carbonate as shown in the following formula 1 and dissolves in water.

(Formula 1)
MnCO ₃ + CO ₂ + H ₂ O → Mg (HCO ₃ ) ₂ (1)

  And barium titanate powder is thrown into this aqueous solution. The barium titanate powder is insoluble in the aqueous solution, and the aqueous solution becomes a suspension.

  It should be noted that even if manganese carbonate and barium titanate powder are simultaneously poured into water and carbon dioxide gas is blown in, the resulting suspension is the same.

  Therefore, when this suspension is heated to 50 ° C. or higher, carbon dioxide is desorbed from the aqueous solution according to the following formula 2, and manganese carbonate is precipitated.

(Formula 2)
Mn (HCO ₃ ) ₂ → MnCO ₃ + CO ₂ + H ₂ O (2)

  The rate of the precipitation reaction varies depending on the manganese ion concentration of the starting solution and the heating temperature, but in order to precipitate so that manganese carbonate adheres to the surface of the barium titanate powder, the rate of precipitation is somewhat slow. It is preferable.

  A method of spontaneously generating a precipitate from a solution without adding a precipitating agent from the outside is called a uniform precipitation method, and the use of this uniform precipitation method can slow the rate of precipitate formation. In the present invention, by using this uniform precipitation method, the produced manganese carbonate precipitates while adhering to the surface of the barium titanate powder. Therefore, uniform mixing of manganese carbonate and barium titanate is achieved.

  As such a condition, it is necessary to heat the temperature of the aqueous solution to 50 ° C. or higher. When the temperature is lower than 50 ° C., the precipitation reaction of manganese carbonate is extremely slow and is not practical.

  Especially, it is suitable when the temperature of aqueous solution shall be 70 degreeC or more and less than boiling temperature. As described above, the precipitation reaction of manganese carbonate is greatly affected by the heating temperature, and the higher the temperature, the faster the precipitation reaction rate. However, if the above-mentioned suspension is boiled, the precipitation reaction of manganese carbonate is too fast, so that some precipitates without adhering to the surface of the barium titanate powder. Therefore, it is preferable to maintain the suspension at a temperature below the boiling temperature. In addition, the precipitation reaction of manganese carbonate proceeds by heating the suspension at 50 ° C. or higher, but in the range of 50 to 60 ° C., the rate of the precipitation reaction is too slow and it takes too much time to complete the precipitation reaction. Therefore, it is not practical.

  Therefore, the optimum temperature range has been experimentally found to be 70 ° C. or higher and lower than the boiling point temperature.

  Further, after the precipitation reaction, when the precipitate is baked at a temperature of 550 ° C. or higher and lower than 1000 ° C. in air or in an oxidizing atmosphere, manganese carbonate changes to dimanganese trioxide. Here, if the firing temperature is too high (1000 ° C. or higher), sintering of the powders proceeds, which is not preferable. On the other hand, when it is lower than 550 ° C., the change from manganese carbonate to dimanganese trioxide is not completed.

  Through the above process, barium titanate powder coated with dimanganese trioxide can be obtained as a dielectric ceramic composition powder.

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. Into 300 ml of water, 30 g of barium titanate powder and 0.296 g of manganese carbonate were added to make 0.002 mol of manganese oxide (MnO equivalent) coated with 1 mol of barium titanate. Carbon dioxide gas was blown at a rate of 50 ml per minute for 6 hours. Manganese carbonate was dissolved as manganese bicarbonate.
Although some manganese carbonate remained undissolved, when the solution was left in an environment of about 20 ° C. for 6 hours, the manganese carbonate was completely dissolved.
Since the barium titanate powder was insoluble in water, the aqueous solution became a suspension of barium titanate.

2. When this suspension was heated and allowed to stand for 5 hours or more while maintaining a temperature of about 100 ° C., precipitation of manganese carbonate occurred.
In this heating step, a solution was collected every 1 hour, and the concentration of manganese ions dissolved in the supernatant was quantified by inductively coupled plasma emission spectroscopy.
In the above process, the concentration of manganese ions before heating was 45 ppm, but gradually decreased with heating time, and decreased to 0.1 ppm or less after 3 hours.
Therefore, it was confirmed that all manganese ions in the aqueous solution were precipitated as manganese carbonate by heating for about 3 hours. This means that 0.002 mol of manganese oxide is coated on 1 mol of barium titanate.

  3. After finishing the heating, the precipitated powder was filtered and the precipitate was taken out. This precipitate is obtained by coating barium titanate with a MnO precursor.

  4). In order to make the MnO precursor dimanganese trioxide, firing was performed at 600 ° C. for 1 hour to obtain a dielectric ceramic composition powder.

  5). After this firing, the composition of the dielectric ceramic powder and the distribution of manganese in the powder were analyzed by EDX analysis, and it was confirmed that manganese was evenly distributed in the powder.

  Through the above process, a dielectric ceramic powder made of barium titanate powder coated with dimanganese trioxide could be 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 the dielectric base material, a dielectric ceramic composition in which BaTiO ₃ having an average particle diameter of 0.7 μm was coated with manganese trioxide 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 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 the insulation resistance when 25 V was applied were measured for 1 minute, 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)

Blowing carbon dioxide into a dispersion in which manganese carbonate is dispersed in water, and dissolving the manganese carbonate in water as manganese hydrogen carbonate;
Adding a barium titanate powder to this manganese hydrogen carbonate aqueous solution to obtain a barium titanate suspension;
Heating the suspension to 50 ° C. or higher to precipitate the dissolved manganese hydrogen carbonate as manganese carbonate so as to adhere to the surface of the barium titanate powder;
After the precipitation reaction, the precipitate is baked in air or in an oxidizing atmosphere at a temperature of 550 ° C. or higher and lower than 1000 ° C. to convert manganese carbonate to dimanganese trioxide,
A method for producing a dielectric ceramic composition, comprising obtaining barium titanate powder coated with dimanganese trioxide as a dielectric ceramic powder. The method for producing a dielectric ceramic composition according to claim 1, wherein the barium titanate suspension is heated to 70 ° C or higher and lower than a boiling temperature. A ceramic capacitor manufactured using the dielectric ceramic composition obtained by the method for manufacturing a dielectric ceramic composition according to claim 1.