JP2001307939A - Laminated ceramic capacitor and its manufacturing method - Google Patents

Abstract

PROBLEM TO BE SOLVED: To solve a problem in which an electric field is increased in intensity per layer when dielectric layers are each lessened in thickness and increased in number of layers so as to enable a laminated ceramic capacitor to be enhanced in capacitance and lessened in size at the same time, and therefore a dielectric breakdown is liable to occur between inner electrodes, so that the laminated ceramic capacitor is shortened in service life and deteriorated in reliability of electrical properties. SOLUTION: Dielectric layers and inner electrode layers are laminated into a laminated ceramic capacitor of integral structure, where the dielectric layer is formed of dielectric porcelain composition composed of ceramic particles and glassy grain boundaries linking and covering the ceramic particles. The grain boundaries contain one or more elements selected out of Mn, V, Cr, Mo, Cu, Ni, Fe and Co. At this point, it is preferable that the grain boundaries are formed of glass. It is preferable that the inner electrode layers come into contact with the ceramic particles through the intermediary of the grain boundary.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a monolithic ceramic capacitor having improved life characteristics and capable of achieving further miniaturization and large capacity by thinning and multilayering, and a method of manufacturing the same.

[0002]

2. Description of the Related Art FIG. 3 is an explanatory view of a multilayer ceramic capacitor. As shown in FIG. 1, the multilayer ceramic capacitor includes a chip-shaped element body 10 and a pair of external electrodes 12 formed on both ends of the element body 10. The element body 10 is generally formed of a laminate in which a large number of dielectric layers 14 and internal electrodes 16 are alternately laminated. Among the internal electrodes 16, the adjacent internal electrodes 16 and 16 face each other via the dielectric layer 14,
It is electrically connected to separate external electrodes 12 and 12.

Here, as a material for the dielectric layer 14, for example, a reduction-resistant dielectric ceramic composition containing barium titanate as a main component and an oxide of a rare earth element added thereto is used. This dielectric ceramic composition is composed of ceramic particles 18 and grain boundaries 20, as shown in FIG. Further, as a material of the internal electrode 16, for example, a material obtained by sintering a conductive paste containing Ni metal powder as a main component is used.

[0004] The element body 10 is obtained by removing a chip-like laminate in which ceramic green sheets and internal electrode patterns are alternately and integrally laminated, and then subjecting the chip body to a high temperature of about 1200 to 1300 ° C in a non-oxidizing atmosphere. It is manufactured by firing and then reoxidizing in an oxidizing atmosphere.

[0005]

With the recent trend of miniaturization and high density of electronic circuits, multilayer ceramic capacitors are also required to have a small size and a large capacity.
To increase the size and the capacity, the number of stacked dielectric layers is further increased, and the thickness of each dielectric layer is further reduced.

However, when the thickness of the dielectric layer is reduced, the electric field strength per one layer increases, and the life of the multilayer ceramic capacitor is shortened, so that a multilayer ceramic capacitor having a desired life cannot be obtained. .

SUMMARY OF THE INVENTION It is an object of the present invention to provide a multilayer ceramic capacitor which has a desired life even when the dielectric layers are multilayered and thinned, and which can be reduced in size and capacity, and a method of manufacturing the same.

[0008]

A multilayer ceramic capacitor according to the present invention is formed by integrally laminating a plurality of dielectric layers and a plurality of internal electrodes, and the dielectric layers are made of a dielectric ceramic composition. The dielectric porcelain composition comprises ceramic particles and a vitreous grain boundary portion (a portion between adjacent ceramic particles) connecting and covering the ceramic particles, and the grain boundary portion is Mn, V, Cr, Mo. , Cu, Ni, Fe and C
It contains one or more elements selected from o.

Here, the internal electrode may be in contact with the ceramic particles via the grain boundary portion. Further, the grain boundary portion may be a glass containing one or more elements selected from Mn, V, Cr, Mo, Cu, Ni, Fe and Co.

It is preferable that the grain boundary part occupies 0.2 to 3 wt% of the dielectric ceramic composition. If the grain boundary portion is less than 0.2 wt% of the dielectric ceramic composition, a desired life cannot be obtained, and if it exceeds 3 wt%, the dielectric constant of the dielectric layer is excessively lowered.

Further, Mn, V, Cr, Mo, Cu, N
It is preferable that a compound of one or more elements selected from i, Fe and Co is contained in the grain boundary at a ratio of 0.05 to 20 wt%. If the compound of these elements is less than 0.05 wt%, the desired life cannot be obtained,
This is because if it exceeds wt%, the dielectric constant of the dielectric layer will be too low.

The grain boundary may include a crystalline secondary phase. When a crystalline secondary phase is contained, the decrease in the dielectric constant of the dielectric layer is reduced. Further, the grain boundary part is preferably made of a composition having reduction resistance.

[0013] Further, a method of manufacturing a multilayer ceramic capacitor according to the present invention includes a raw material step of preparing a ceramic raw material, a sheet forming step of forming a ceramic green sheet using the ceramic raw material, and a conductive paste on the ceramic green sheet. A printing step of printing an internal electrode pattern at, a laminating step of laminating the ceramic green sheets after the printing step to form a laminated body, and cutting the laminated body for each internal electrode pattern to form a chip-shaped laminated body. And a firing step of firing the chip-like laminate obtained in the cutting step, wherein the ceramic raw material contains a grain boundary forming component, and the grain boundary forming component is Mn, V, C
1 selected from r, Mo, Cu, Ni, Fe and Co
It contains a species or a compound of two or more elements.

The term "grain boundary forming component" as used herein refers to a mixture of compounds which melt when fired to form a vitreous melt. For example, Li ₂ O--SiO ₂ --MO (M is Ba, Ca , Sr, Mg, Zn) and B ₂ O ₃ —SiO ₂
Although what is shown by -MO can be mentioned, it is not limited to these and glass-forming components other than these may be sufficient. .

Preferably, the grain boundary forming component accounts for 0.2 to 3% by weight of the ceramic raw material. If the content of the grain boundary forming component is less than 0.2 wt%, a multilayer ceramic capacitor having a desired life cannot be obtained, and if it exceeds 3 wt%, the dielectric constant of the dielectric layer of the multilayer ceramic capacitor is excessively lowered.

Also, Mn, V, Cr, Mo, Cu, N
i, a compound of one or more elements selected from Fe and Co is contained in the grain boundary forming component in an amount of 0.05 to 20 wt.
% Is preferred. If the compound of these elements is less than 0.05 wt%, a laminated ceramic capacitor having a desired life cannot be obtained, and if it exceeds 20 wt%, the dielectric constant of the dielectric layer of the laminated ceramic capacitor is excessively lowered.

Further, the conductive paste may include the grain boundary forming component. In this case, the conductive paste preferably contains 1 to 20 vol% of the component for forming the grain boundary. If the content is less than 1 vol%, the effect of extending the life of the multilayer ceramic capacitor is not recognized, and if it exceeds 20 vol%, the electrical resistance of the internal electrodes of the multilayer ceramic capacitor becomes too large.

[0018]

EXAMPLE First, 0.96 mol part of BaCO ₃ and MgO were used.
0.05 mol part, SrO 0.01 mol part, TiO ₂
0.99 mol part and Yb ₂ O ₃ 0.005 mol part,
Each was weighed, and these compounds were put into a pot mill together with alumina balls and 2.5 liters of water and stirred and mixed for 15 hours to obtain a raw material mixture.

Next, the raw material mixture is placed in a stainless steel pot, dried at 150 ° C. using a hot air drier, and the dried raw material mixture is coarsely pulverized. About 1200 ° C in air
For 2 hours to obtain a powder of the first basic component.

Further, BaCO ₃ and ZrO ₂ were weighed so as to be equimolar, mixed, dried and pulverized, and calcined in the atmosphere at about 1250 ° C. for 2 hours. A powder of the second basic component was obtained. Then, 98 mol parts (976.28 g) of the powder of the first basic component and 2 mol parts (23.85 g) of the powder of the second basic component were mixed to obtain 1000 g of the basic component.

Also, 1 mol part of Li ₂ O and 8 mol of SiO ₂
0 mol parts, 3.8 mol parts of BaCO ₃ , 9.5 mol parts of CaCO ₃ , 4.7 mol parts of MgO, and 1.0 mol part of TiO ₂ were weighed, and with respect to 100 parts by weight, 8 parts by weight of MnO ₂ was further added and mixed, and 300 ml of alcohol was added to this mixture, and 1 part of the mixture was placed in a polyethylene pot using alumina balls.
Stir for 0 hours, then in air at 1000 ° C for 2 hours.
It was calcined for hours.

Next, what was obtained by the above calcination was
Put in an alumina pot with 00 ml of water,
The powder was pulverized with an alumina ball for 15 hours and then dried at 150 ° C. for 4 hours to obtain a powder of the first additive component.

Next, 2 parts by weight (20 g) of the first additive component is added to 100 parts by weight (1000 g) of the basic component, and the average particle size is 0.5 μm and the purity is good. 99.0% or more of Cr ₂ O ₃ and Al ₂ O ₃
0.1 parts by weight (1 g) were added as additive components, and 15% by weight of an organic binder composed of an aqueous solution of an acrylate polymer, glycerin, and condensed phosphate was added.
Further, 50% by weight of water was added, and these were put into a ball mill, pulverized and mixed to prepare a slurry of a porcelain raw material.

Next, the ceramic slurry is placed in a vacuum defoaming machine to remove bubbles, and the ceramic slurry is placed in a reverse roll coater, and a thin film formed therefrom is continuously received on a long polyester film. At the same time, the film was heated to 100 ° C. and dried on the same film to obtain a square ceramic green sheet having a thickness of about 5 μm and a square of 10 cm.

On the other hand, 10 g of nickel powder having an average particle size of 1.5 μm and 0.9 g of ethyl cellulose dissolved in 9.1 g of butyl carbitol were placed in a stirrer and placed in a stirrer.
By stirring for a time, a conductive paste for an internal electrode was obtained. Then, using this conductive paste, a length of 14 m
An internal electrode pattern was printed on one side of the ceramic green sheet through a screen having 50 m and 7 mm wide patterns, and this was dried.

Next, eleven ceramic green sheets on which the internal electrode patterns were printed were laminated with the internal electrode patterns facing upward. At this time, the printed surfaces of the adjacent upper and lower ceramic green sheets were arranged so as to be shifted by about half in the longitudinal direction of the internal electrode pattern. Furthermore,
On the upper and lower surfaces of the laminate, ceramic green sheets for a protective layer on which no internal electrode pattern was printed were laminated with a thickness of 200 μm.

Next, the laminate is pressed at a temperature of about 50 ° C. by applying a load of about 40 tons in a thickness direction, and thereafter,
This laminate is cut into a lattice shape for each internal electrode pattern,
Fifty 3.2 × 1.6 mm chip-shaped laminates were obtained.

Next, this chip-shaped laminate is placed in a furnace capable of firing in an atmosphere, and is heated at 100 ° C./h in an air atmosphere.
The temperature was raised to 600 ° C. at a rate of to burn off the organic binder.

After that, the atmosphere of the furnace was changed from the air atmosphere to H2.
The atmosphere was changed to a reducing atmosphere of (2% by volume) + N2 (98% by volume). Then, while keeping the furnace in the reducing atmosphere, the heating temperature of the laminated chip was raised from 600 ° C. to the sintering temperature of 1130 ° C. at a rate of 100 ° C./h, and 11
30 ° C. (maximum temperature) was maintained for 3 hours.

Then, the temperature was lowered to 600 ° C. at a rate of 100 ° C./h, the atmosphere was changed to the air atmosphere (oxidizing atmosphere), and the oxidation treatment was carried out at 600 ° C. for 30 minutes.
Thereafter, the resultant was cooled to room temperature to obtain a body of a multilayer ceramic capacitor.

Next, zinc, glass frit and vehicle (v) are applied to the side surfaces of the element where the ends of the internal electrodes are exposed.
ehicle) and dried.
This is baked in the air at a temperature of 550 ° C. for 15 minutes to form a zinc electrode layer, a copper layer is further formed thereon by an electroless plating method, and a Pb—Sn solder layer is further formed thereon by an electroplating method. To form a pair of external electrodes.

When the cross section of the dielectric layer of the multilayer ceramic capacitor was observed with a microscope, it was found that the ceramic particles 18 were coated on the vitreous grain boundary 20 as shown extremely in the model in FIG. Then, when the components of the grain boundary portion 20 were analyzed by point analysis using a TEM (transmission electron microscope), it was found that Mn was contained in the range of 0.05 to 5 wt%.

The life of the multilayer ceramic capacitor thus produced and the dielectric constant (ε) of the dielectric layer
Was as shown in Table 1.

Here, the life was determined by applying a voltage of 70 V to the multilayer ceramic capacitor in a constant temperature bath at 170 ° C. and measuring the breakdown time. In addition,
The values of the life in Table 1 are shown in Sample No. It is represented by the magnification when the value of 1 is set to 1.

The dielectric constant (ε) is obtained by measuring the capacitance of a multilayer ceramic capacitor under the conditions of a temperature of 20 ° C., a frequency of 1 kHz and a voltage of 1.0 V. It was calculated from the thickness of the dielectric layer.

[0036]

[Table 1]

From the above results, the grain boundary forming component was 0.2 w
With the addition of t% or more, an increase in the life of the multilayer ceramic capacitor was observed. However, it has also been found that when the grain boundary forming component exceeds 3 wt%, the dielectric constant of the dielectric layer is excessively reduced. The grain boundary forming component is B ₂ O ₃ —Si
O ₂ -MO-TiO ₂ Similar results as were obtained.
Similar results were obtained when Sr or Zn was used as the M component of MO.

Further, when the additive element was added in an amount of 0.05 wt% or more, the life of the multilayer ceramic capacitor was increased. However, it has also been found that when the additive element exceeds 5 wt%, the dielectric constant of the dielectric layer is excessively reduced. The additional elements are V, Cr, Mo, Co, Cu, Ni,
Similar results were obtained for Fe.

Also, when the above-mentioned grain boundary forming component was added to the conductive paste for forming the internal electrode in the range of 1 to 20 vol%, the life was improved.

The above-mentioned increase in life is due to the following reasons.
It seems to be due to. That is, as shown in FIG.
Oxygen vacancies (V_o) Is the internal electrode
When DC is applied between 16 and 16, (V_o) → (V_o
⁺⁺) + 2e⁻And charge positively, and on the cathode side
Move and accumulate. Then, a certain amount or more (V _o
⁺⁺) Can no longer maintain the crystal structure
As a result, the crystal is destroyed, the life is exhausted, and dielectric breakdown occurs.

However, as shown in FIG. 2, when the ceramic particles 18 are covered with the grain boundary portions 20, the movement of (V _o ⁺⁺ ) is first blocked at the grain boundary portions, and the (V _o ⁺⁺ ) is not accumulated on the cathode side. It is considered that a similar phenomenon occurs between the internal electrode 16 and the ceramic particles 18. For this reason, it is considered that the destruction is prevented without leading to local concentration of oxygen vacancies, and the life is extended.

[0042]

According to the present invention, since the ceramic particles in the dielectric ceramic composition forming the dielectric layer are covered with the vitreous grain boundaries, oxygen defects (V _o ) in the ceramic particles are obtained.
Of the multilayer ceramic capacitor, especially when the dielectric layer is made thinner, improves the life characteristics of the multilayer ceramic capacitor. There is an effect that it becomes possible.

[Brief description of the drawings]

FIG. 1 is an explanatory diagram of a fine structure of a porcelain composition forming a dielectric layer of a multilayer ceramic capacitor according to the present invention.

FIG. 2 is an enlarged view of a portion A in FIG.

FIG. 3 is an explanatory diagram of a multilayer ceramic capacitor.

FIG. 4 is an explanatory diagram of a fine structure of a porcelain composition forming a dielectric layer of a conventional multilayer ceramic capacitor.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 10 Element body 12 External electrode 14 Dielectric layer 16 Internal electrode 18 Ceramic particle 20 Grain boundary part

──────────────────────────────────────────────────の Continued on the front page (51) Int.Cl. ⁷ Identification symbol FI Theme court ゛ (Reference) H01G 4/30 311 H01G 4/30 311D (72) Inventor Hiroshi Kishi 6-16-20 Ueno, Taito-ku, Tokyo No. Taiyo Denki Co., Ltd. F-term (reference) 5E001 AB03 AC09 AD00 AE05 AH01 AH06 AH09 AJ01 AJ02 5E082 AA01 AB03 BC39 EE04 EE22 EE35 FG06 FG25 FG26 FG54 LL01 LL02 LL03 MM24 PP03

Claims (13)

[Claims] 1. A plurality of dielectric layers and a plurality of internal electrodes are integrally laminated, wherein the dielectric layers are composed of a dielectric ceramic composition, and the dielectric ceramic composition comprises ceramic particles and the ceramic. And a vitreous grain boundary that connects and covers the particles, and the grain boundary is Mn, V, Cr, Mo, Cu, Ni, F
A multilayer ceramic capacitor comprising one or more elements selected from e and Co. 2. The method according to claim 1, wherein the internal electrode is in contact with the ceramic particles via the grain boundary.
3. The multilayer ceramic capacitor according to item 1. 3. The method according to claim 1, wherein the grain boundary part is Mn, V, Cr, Mo, C.
3. The multilayer ceramic capacitor according to claim 1, comprising a glass containing one or more elements selected from u, Ni, Fe and Co. 4. 4. The multilayer ceramic capacitor according to claim 1, wherein said grain boundary portion occupies 0.2 to 3% by weight of said dielectric ceramic composition. 5. The method according to claim 1, wherein Mn, V, Cr, Mo,
The compound of one or more elements selected from Cu, Ni, Fe and Co is contained at a ratio of 0.05 to 20% by weight. Multilayer ceramic capacitors. 6. The multilayer ceramic capacitor according to claim 1, wherein a crystalline secondary phase is contained in the grain boundary part. 7. The multilayer ceramic capacitor according to claim 1, wherein the grain boundary part is made of a composition having reduction resistance. 8. A raw material step for preparing a ceramic raw material,
A sheet forming step of forming a ceramic green sheet using the ceramic raw material, a printing step of printing an internal electrode pattern on the ceramic green sheet with a conductive paste, and laminating the ceramic green sheets after the printing step to form a laminate A laminating step of forming, a cutting step of cutting the laminated body for each internal electrode pattern to obtain a chip-shaped laminated body, and a firing step of firing the chip-shaped laminated body obtained in the cutting step, The ceramic raw material contains a grain boundary forming component, and the grain boundary forming component is Mn, V, Cr, M
A method for manufacturing a multilayer ceramic capacitor, comprising a compound of one or more elements selected from o, Cu, Ni, Fe and Co. 9. The method according to claim 8, wherein the grain boundary forming component is Mn, V, Cr, M.
The method for manufacturing a multilayer ceramic capacitor according to claim 8, comprising a glass-forming component containing one or more elements selected from o, Cu, Ni, Fe, and Co. 10. The method for manufacturing a multilayer ceramic capacitor according to claim 8, wherein the grain boundary forming component accounts for 0.2 to 3 wt% of the ceramic raw material. 11. Mn, V, C in the grain boundary forming component
1 selected from r, Mo, Cu, Ni, Fe and Co
0.05 to 20 wt% of a compound of a species or two or more elements
11. The composition according to claim 8, wherein
The method for manufacturing a multilayer ceramic capacitor according to any one of the above. 12. The method according to claim 8, wherein the conductive paste contains the grain boundary forming component. 13. The method according to claim 1, wherein the conductive paste is 1 to 20 vol%.
13. The method for manufacturing a multilayer ceramic capacitor according to claim 12, comprising the grain boundary forming component.