JP3399389B2 - Multilayer ceramic capacitor and method of manufacturing the same - Google Patents

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, and more particularly to a monolithic ceramic capacitor formed by using a mixed crystal type ceramic sintered body having a plurality of dielectric phases.

[0002]

2. Description of the Related Art In manufacturing a monolithic ceramic capacitor, ceramic components constituting a dielectric phase are mixed,
A ceramic slurry or a ceramic paste is obtained, an internal electrode and a ceramic layer are laminated to obtain an unfired laminated body, and the laminated body is fired, or a part of the ceramic components is preliminarily calcined to obtain a calcined product by SiO.sub.2. After adding a sintering aid such as ₂ or glass, a ceramic slurry or ceramic paste is obtained, and then a ceramic layer is laminated with internal electrodes to obtain a laminated body, and the laminated body is fired. Has been.

In the ceramic sintered body obtained by the above method, the grain boundary layer is formed without any particular control, and the grain boundary layer is composed of SiO ₂ which is a low melting point compound or glass. It is common to have

On the other hand, a monolithic ceramic capacitor using a mixed crystal type ceramic sintered body is known. In the mixed crystal type ceramic sintered body, a plurality of dielectric phases are formed, and various temperature characteristics can be obtained by controlling the materials constituting the dielectric phases and the ratio of the dielectric phases.

[0005]

In recent years, further reduction in size and increase in capacity have been strongly demanded for laminated ceramic capacitors. In the multilayer ceramic capacitor obtained by the method described above, the grain boundary layer is made of SiO 2.
_{It is made of 2} or glass. In this case, when the ceramic sintered body has a uniform structure composed of a kind of dielectric phase, this is the case when the thickness of the ceramic layer between the internal electrodes is thinned in order to achieve miniaturization and large capacity. However, the reliability does not deteriorate so much.

However, the monolithic ceramic capacitor using the above-described mixed crystal type ceramic sintered body has a problem that reliability is deteriorated when the thickness of the ceramic layer between the internal electrodes is reduced. That is, when the ceramic sintered body is composed of a plurality of dielectric phases, the reliability as a whole depends on the dielectric phase having low reliability, so that the life of the monolithic ceramic capacitor is shortened and the reliability tends to be deteriorated. there were. In particular, as the thickness of the ceramic layer between the internal electrodes becomes thinner, the above-mentioned deterioration in reliability was more remarkable.

An object of the present invention is to improve reliability even when a mixed crystal type ceramic sintered body having two or more types of dielectric phases is used and the thickness of a ceramic layer between internal electrodes is reduced. A multilayer ceramic capacitor and a manufacturing method thereof are provided.

[0008]

A monolithic ceramic capacitor according to the present invention includes a mixed crystal type ceramic sintered body composed of a plurality of dielectric phases, and a ceramic sintered body disposed in the ceramic sintered body. A plurality of internal electrodes formed to overlap each other in the thickness direction via a body layer, and a plurality of external electrodes formed on the outer surface of the ceramic sintered body and electrically connected to any of the internal electrodes. And 10% by atom or more of the grain boundary layer between the dielectric phases in the mixed crystal type ceramic sintered body is formed of one kind of constituent components constituting a plurality of dielectric phases. Characterize.

The grain boundary layer includes any grain boundary layer between a plurality of dielectric phases, that is, between the same kind of dielectric phases and between different dielectric phases. In addition, the constituent component that constitutes the dielectric phase means one of the metal elements that constitute the dielectric phase.

In the monolithic ceramic capacitor according to the present invention, Bi is preferably used as the above-mentioned one type of component constituting the grain boundary layer. Further, in the multilayer ceramic capacitor according to the present invention, the material forming the plurality of dielectric phases forming the mixed crystal ceramic sintered body is not particularly limited, but, for example, a combination of SrTiO ₃ solid solution and TiO ₂ is used. To be

A method of manufacturing a monolithic ceramic capacitor according to the present invention is the method of manufacturing a monolithic ceramic capacitor according to claim 1, wherein a plurality of dielectric phases are used to form the mixed crystal ceramic sintered body. And a step of obtaining a calcined product by calcining the components constituting the, and as a component to be precipitated in the grain boundary layer, one of the components constituting the plurality of dielectric phases is post-added to the calcined product. And a step of obtaining a ceramic composition by kneading, and a step of using the ceramic composition to obtain an unfired ceramic laminate in which a plurality of internal electrodes are arranged so as to overlap with each other through a ceramic composition layer, Firing the ceramic laminate,
The method is characterized by including a step of obtaining a ceramic sintered body and a step of applying external electrodes to the outer surface of the ceramic sintered body.

In the method for manufacturing a monolithic ceramic capacitor according to the present invention, Bi is preferably added in the form of Bi oxide as a component to be added later to form the grain boundary layer.

In the method for producing a monolithic ceramic capacitor according to the present invention, as the material of the mixed crystal ceramic sintered body, the raw materials forming the SrTiO ₃ solid solution phase and the TiO ₂ phase are preferably used.

[0014]

BEST MODE FOR CARRYING OUT THE INVENTION The present invention will be clarified below by giving specific examples of the present invention. (Example 1) SrCO was used as a material constituting the dielectric phase.
₃ , TiO ₂ , Bi ₂ O ₃ , Pb ₃ O ₄ and CaCO ₃
The weight ratio of each powder of 33.0: 34.0: 16.0:
The mixture was mixed at a ratio of 10.0: 7.0 to obtain a raw material powder. This raw material powder was calcined at 900 ° C. for 2 hours to obtain a calcined raw material.

Bi ₂ O ₃ is further added to the above-mentioned calcination raw material so as to occupy 1% by weight of the whole calcination raw material, and glass as a sintering aid is added so as to occupy 1% by weight of the whole,
A dielectric composition was obtained by mixing.

Water and an organic binder were mixed with the above dielectric composition to obtain a ceramic slurry, and the ceramic slurry was used to obtain a ceramic green sheet having a thickness of 7.0 μm. This ceramic green sheet was punched into a rectangular shape to obtain a rectangular ceramic green sheet.

An Ag / Pd paste was screen-printed on the upper surface of the rectangular ceramic green sheet to form internal electrodes. 170 ceramic green sheets having internal electrodes formed thereon were laminated, and a plurality of plain ceramic green sheets were laminated on top and bottom to obtain a ceramic laminate. This ceramic laminate was pressed in the thickness direction and then fired in air at a temperature of 1150 ° C. for 2 hours to obtain a ceramic sintered body.

The size of the obtained ceramic sintered body is 3.1.
It was 0 × 1.55 × 1.55 mm, and when the thickness of the ceramic layer between the internal electrodes was measured, it was 4.5 μm. An Ag paste was applied to both end faces of this ceramic sintered body and baked, and a Ni plating film and a Sn plating film were laminated on the outside of the Ag film to form external electrodes.

The multilayer ceramic capacitor shown in FIG. 1 was obtained as described above. In the monolithic ceramic capacitor 1, the internal electrodes 3a to 3f are arranged in the ceramic sintered body 2 so as to overlap with each other with a ceramic layer interposed therebetween.
Further, the internal electrodes 3a, 3c, 3e are drawn out to the end face 2a. The internal electrodes 3b, 3d, 3f are drawn out to the opposite end face 2b facing the end face 2a.
Reference numerals 4 and 5 denote external electrodes, and external 4 is an internal electrode 3.
a, 3c, 3e electrically connected to the external electrode 5
Are electrically connected to the internal electrodes 3b, 3d, 3f.

In FIG. 1, the number of laminated internal electrodes 3a to 3f,
Also, although the structure of the external electrodes 4 and 5 is schematically illustrated, as described above, the number of laminated internal electrodes is 170, and the external electrodes 4 and 5 are formed on the Ag film by Ni plating film and S
It has a structure in which n-plated films are laminated.

(Example 2) Bi ₂ O added to the calcining raw material
The addition amount after ₃ was changed from 1 wt% to 3 wt% (however, as the content of Bi ₂ O ₃ in the dielectric composition is the same manner as in Example 1, the raw material powder to prepare first B
A monolithic ceramic capacitor was obtained in the same manner as in Example 1 except that the compounding ratio of i ₂ O ₃ was lowered).

(Example 3) Bi ₂ added to the calcination raw material
The post-addition amount of O ₃ was changed from 1% by weight to 5% by weight (however, in the raw material powder initially prepared so that the Bi ₂ O ₃ content in the dielectric composition was the same as in Example 1). B
A monolithic ceramic capacitor was obtained in the same manner as in Example 1 except that the compounding ratio of i ₂ O ₃ was lowered).

(Comparative Example) Bi as a calcination raw material₂O₃Add
No, but Bi in the dielectric composition₂O₃Content is
Raw material powder prepared first so that it is similar to the case of the example
Bi in the middle₂O ₃Except for increasing the blending ratio of
A monolithic ceramic capacitor was obtained in the same manner as in Example 1.
It was

(Evaluation) In order to evaluate the reliability of each of the multilayer ceramic capacitors of the examples and comparative examples obtained as described above, a voltage of 100 V was applied to the multilayer ceramic capacitors at a temperature of 150 ° C. The test was conducted. That is, when a voltage of 100 V was applied at a temperature of 150 ° C. and the insulation resistance of the laminated ceramic capacitor was 10 ⁶ Ω or less, a failure occurred, and the time until the failure occurred was defined as the failure time. At the time of evaluation, a life test was performed on 36 monolithic ceramic capacitors,
The mean time to failure (MTTF) calculated from the Weibull plot of the failure time of 36 monolithic ceramic capacitors was determined.

Further, in order to confirm the composition of the grain boundary layer in each of the laminated ceramic capacitors of Examples and Comparative Examples,
The ceramic sintered body was broken and the transmission electron microscope (TE
M) and the grain boundary composition was evaluated. At the time of evaluation, the slope m value of the plotted straight line was obtained by Weibull statistics. This m value means reliability against failure, and m
The larger the value, the higher the reliability. The results are shown in Table 1 below.

The capacitance-temperature characteristics of each of the laminated ceramic capacitors of Examples and Comparative Examples were evaluated in the following manner. That is, 20 of each monolithic ceramic capacitor
Capacitance C ₂₀ at ℃, electrostatic procedure C at 85 ℃
₈₅ and the capacitance change amount ΔC = C ₈₅ −C ₂₀ C ₂₀
Was measured. The results are also shown in Table 1 below.

[0027]

[Table 1]

As is clear from Table 1, when Bi ₂ O ₃ 3% by weight was added to the raw material powder without post-addition,
Mean failure time MTTF was as short as 38 hours. On the other hand, as in Examples 1 to _{3, when} a part of Bi ₂ O ₃ is post-added to the calcination raw material, the mean failure time MTTF becomes dramatically long.

The crystal layers of the monolithic ceramic capacitors of Examples 1 to 3 and the comparative example were confirmed by X-ray diffraction.
SrTiO ₃ solid solution containing Pb and Bi in solid solution, and Ti
It was recognized that it was composed of O ₂ .

Next, paying attention to the grain boundaries of the SrTiO ₃ phase and the TiO ₂ phase, the composition was analyzed by a transmission electron microscope. The analyzed portion is an arbitrarily extracted portion. The results are shown in Table 2. In Table 2, SrTiO ₃ —SrTiO ₃ in each multilayer ceramic capacitor
_The results of composition analysis at three points are shown for each grain boundary between the _three grains and between the SrTiO ₃ —TiO ₂ grains. The analysis area is 0.5n due to the analysis device.
The range was m × 0.5 nm.

As is clear from Table 1, the capacity-temperature characteristics TC of Examples 1 and 2 are better than those of Example 3 in which the post addition amount of Bi is 5% by weight. Therefore, in order to satisfy the JIS standard R characteristic in which the capacity-temperature characteristic TC is within ± 15%, the post-addition amount of Bi is preferably less than 5% by weight, more preferably 3% by weight or less. I find it desirable.

[0032]

[Table 2]

In addition, the analysis positions of ~ in Table 2 are
Each of the three positions shown in each grain boundary is shown. As is clear from Table 2, in the multilayer ceramic capacitor of the comparative example, the Bi abundance ratio is 8.5 atomic% or less at both the grain boundary between SrTiO ₃ —SrTiO ₃ and the grain boundary between SrTiO ₃ —TiO _2. There were few. On the other hand, in Examples 1 to 3, it can be seen that the existence ratio of Bi is 11.3 atomic% or more at any grain boundary. Comparing the results of Table 2 with the results of the life test shown in Table 1, it can be seen that the average failure time MTTF becomes longer as the Bi content ratio in the grain boundary layer increases.

Further, as in the comparative example, when Bi was not added later, it was found that although Bi was present in the grain boundary layer, its amount was small and the variation was large. Therefore,
It is considered that the effect of extending the mean failure time is hardly obtained due to the small content ratio of Bi in the grain boundary and the large variation.

In Example 1, Bi was post-added at a rate of 1% by weight, and although the mean failure time MTTF was sufficiently extended, its variation was slightly large and m
This causes the value to drop slightly. Therefore, it is desirable that the post-addition amount of Bi is 1% by weight or more, more preferably 3% by weight or more as in Examples 2 and 3, and Bi is 10 atomic% or more in the grain boundary layer. Precipitation is desirable.

In the above embodiment, SrTiO ₃ -T
Although the case of using the iO ₂ -based composition has been described, the composition of the ceramic sintered body constituting the plurality of dielectric phases in the present invention is not particularly limited, and for example, BaTiO ₃ −
Nd ₂ Ti ₂ O ₇ composition, CaTiO ₃ —La ₂ Ti
₂ O ₇ type composition etc. can be mentioned.

[0037]

The monolithic ceramic capacitor according to the present invention is constituted by using a mixed crystal type ceramic sintered body composed of a plurality of dielectric phases, and the grain boundary layer between the dielectric phases in the ceramic sintered body. 10% by atom or more is formed by one of the constituent components constituting the dielectric phase, so that it is possible to prolong the service life when a high temperature is applied and to provide a highly reliable multilayer ceramic capacitor. You can

That is, a mixed crystal type ceramic sintered body which can be constructed so as to have a temperature characteristic according to the required characteristic is used, and further, the thickness of the ceramic layer between the internal electrodes is reduced to reduce the size and increase the capacity. Even in the case of achieving the above, it becomes possible to configure a laminated ceramic capacitor having excellent reliability.

In the present invention, when Bi is used as one of the constituents of the dielectric phase constituting 10 atomic% or more of the grain boundary layer, the Bi is contained in a large amount in the grain boundary layer. As is clear from the above, the reliability can be increased.

The material forming the plurality of dielectric phases is not particularly limited, but SrTiO 3
_{When the 3} solid solution phase and the TiO ₂ phase are used, as is apparent from the above-mentioned examples, it is possible to provide a monolithic ceramic capacitor having excellent reliability when a high temperature is applied.

In the method for manufacturing a monolithic ceramic capacitor according to the present invention, the components constituting a plurality of dielectric phases are calcined to obtain a calcined product in order to form the mixed crystal ceramic sintered body, and then the grain boundary is obtained. A ceramic composition is obtained by post-adding one of the components constituting the dielectric phase as a component to be deposited in the layer to the calcined product and kneading the mixture, and using the ceramic composition, a laminated ceramic capacitor is obtained. Is configured. In this case, one of the components constituting the dielectric phase is post-added to the calcined product, so that the component is considerably high in the grain boundaries of the finally obtained mixed crystal ceramic sintered body. It is possible to deposit at a ratio, which makes it possible to provide a monolithic ceramic capacitor having excellent reliability. Therefore, in a monolithic ceramic capacitor using a mixed crystal type ceramic sintered body that can easily design the capacity-temperature characteristics according to the required characteristics, when the thickness between the internal electrodes is reduced to reduce the size and increase the capacity. Also in the above, it is possible to manufacture a laminated ceramic capacitor having excellent reliability.

In the method for producing a monolithic ceramic capacitor according to the present invention, the components to be added later are not particularly limited, but when Bi oxide is used, grain boundaries are finally obtained in the monolithic ceramic capacitor. To B
i can be deposited at a high rate, and the reliability of the monolithic ceramic capacitor can be improved.

[0043] As a material constituting the mixed crystal ceramic sintered body, when a material constituting the SrTiO ₃ solid solution phase and TiO ₂ phase, the finally obtained ceramics sintered body, SrTiO ₃ Solid solution phase and TiO ₂
The phase is formed, and the components added after the above are precipitated in the grain boundary in a high ratio. Therefore, it is possible to provide a monolithic ceramic capacitor having excellent reliability.

[Brief description of drawings]

FIG. 1 is a vertical sectional view for explaining a monolithic ceramic capacitor according to an embodiment of the present invention.

[Explanation of symbols]

1. Multilayer ceramic capacitor 2 ... Ceramic sintered body 3a to 3f ... internal electrodes 4, 5 ... External electrodes

Claims (6)

(57) [Claims] 1. A mixed crystal type ceramics sintered body composed of a plurality of dielectric phases, the ceramics sintered body is disposed inside the ceramics sintered body, and is formed so as to overlap in the thickness direction with a ceramics sintered body layer interposed therebetween. A plurality of internal electrodes, and a plurality of external electrodes formed on the outer surface of the ceramic sintered body and electrically connected to any of the internal electrodes. A monolithic ceramic capacitor, wherein 10 atomic% or more of a grain boundary layer between dielectric phases in a body is formed by one kind of constituent components constituting a plurality of dielectric phases. 2. The one of the constituents of the dielectric phase, which constitutes 10 atomic% or more of the grain boundary layer, is Bi.
The multilayer ceramic capacitor described in. 3. The multilayer ceramic capacitor according to claim 1, wherein the plurality of dielectric phases are a SrTiO ₃ solid solution phase and a TiO ₂ phase. 4. The method of manufacturing a monolithic ceramic capacitor according to claim 1, wherein components constituting a plurality of dielectric phases are calcined to form the mixed crystal ceramic sintered body. Step of obtaining a calcinated product, as a component to be precipitated in the grain boundary layer, one of the components constituting the plurality of dielectric phases is post-added to the calcined product, and the ceramic composition is kneaded. A step of obtaining, and a step of using the ceramic composition to obtain an unfired ceramic laminate in which a plurality of internal electrodes are arranged so as to overlap each other with a ceramic composition layer interposed therebetween; A method of manufacturing a monolithic ceramic capacitor, comprising: a step of obtaining a sintered body; and a step of applying an external electrode to an outer surface of the ceramic sintered body. 5. Bi is added as a component to be added later.
5. Addition in the form of i-oxide.
A method for manufacturing the multilayer ceramic capacitor described in. 6. The method for producing a monolithic ceramic capacitor according to claim 4, wherein raw materials forming a SrTiO ₃ solid solution phase and a TiO ₂ phase are used as a material of the mixed crystal ceramic sintered body.