阅读说明：本技术 层叠陶瓷电容器及其制造方法 (Multilayer ceramic capacitor and method for manufacturing same ) 是由 加藤洋一 于 2020-02-13 设计创作，主要内容包括：本发明提供能够确保高耐久性、并且实现小型化和大电容化的层叠陶瓷电容器及其制造方法。层叠陶瓷电容器包括电容形成部和保护部。电容形成部包括：在第一方向上层叠的多个陶瓷层；和配置在多个陶瓷层之间的多个内部电极。保护部包括覆盖部、侧边缘部和棱部,其中,覆盖部覆盖电容形成部、且构成朝向第一方向的主面,侧边缘部构成朝向与第一方向正交的第二方向的侧面,棱部构成用于连接主面和侧面的连接部。多个陶瓷层由第一陶瓷形成,棱部由第二陶瓷形成。第一陶瓷为以不包含晶内孔隙的结晶颗粒为主成分的多晶体。第二陶瓷为以包含晶内孔隙的结晶颗粒为主成分的多晶体,并且第二陶瓷的硅的含量比第一陶瓷多。(The invention provides a laminated ceramic capacitor which can ensure high durability and realize miniaturization and large capacitance and a manufacturing method thereof. The multilayer ceramic capacitor includes a capacitance forming portion and a protection portion. The capacitance forming portion includes: a plurality of ceramic layers laminated in a first direction; and a plurality of internal electrodes disposed between the plurality of ceramic layers. The protective portion includes a covering portion that covers the capacitor forming portion and constitutes a main surface facing a first direction, side edge portions that constitute side surfaces facing a second direction orthogonal to the first direction, and ridge portions that constitute a connecting portion for connecting the main surface and the side surfaces. The plurality of ceramic layers are formed of a first ceramic, and the ridge portions are formed of a second ceramic. The first ceramic is a polycrystalline body mainly composed of crystal grains containing no intracrystalline pores. The second ceramic is a polycrystalline body having crystal grains containing intracrystalline pores as a main component, and the second ceramic has a larger silicon content than the first ceramic.)

1. A laminated ceramic capacitor, comprising:

a capacitor forming portion including a plurality of ceramic layers stacked in a first direction, and a plurality of internal electrodes arranged between the plurality of ceramic layers; and

a protective portion including a covering portion that covers the capacitor forming portion and that constitutes a main surface facing the first direction, a side edge portion that constitutes a side surface facing a second direction orthogonal to the first direction, and a ridge portion that constitutes a connecting portion for connecting the main surface and the side surface,

the plurality of ceramic layers are formed of a first ceramic, the ridge portions are formed of a second ceramic,

the first ceramic is a polycrystalline body having crystal grains containing no intracrystalline pores as a main component,

the second ceramic is a polycrystalline body having crystal grains containing intracrystalline pores as a main component, and the second ceramic has a larger silicon content than the first ceramic.

2. The laminated ceramic capacitor according to claim 1, wherein:

the second ceramic has a silicon content of 0.5 mol% or more.

3. The laminated ceramic capacitor as claimed in claim 1 or 2, wherein:

the side edge portion is formed of the second ceramic.

4. The laminated ceramic capacitor according to claim 3, wherein:

the dimension of the side edge portion in the second direction is 30 μm or less.

5. The laminated ceramic capacitor as claimed in claim 3 or 4, wherein:

the protective portion is entirely formed of the second ceramic.

6. The laminated ceramic capacitor as claimed in claim 1 or 2, wherein:

the cover is formed of the second ceramic.

7. The laminated ceramic capacitor according to any one of claims 1 to 6, wherein:

the first ceramic and the second ceramic are both polycrystalline bodies having perovskite structures containing barium and titanium.

8. A method of manufacturing a laminated ceramic capacitor, comprising:

a step of preparing a first powder containing, as a main component, ceramic particles containing no intracrystalline pores;

a step of preparing a second powder having a perovskite structure with an axial ratio c/a of 1.008 or less and containing ceramic particles containing intracrystalline pores as a main component;

a step of producing an unfired laminate including a capacitor forming portion including a plurality of ceramic layers containing the first powder as a main component and stacked in a first direction, and a covering portion that covers the capacitor forming portion from the first direction, the plurality of internal electrodes being arranged between the plurality of ceramic layers;

forming a side edge portion containing the second powder as a main component and having a larger silicon content than the plurality of ceramic layers on a side surface of the laminate facing a second direction orthogonal to the first direction, to produce an unfired ceramic body; and

and firing the ceramic body.

9. The method of manufacturing a laminated ceramic capacitor according to claim 8, wherein:

the side edge portions are formed by attaching ceramic sheets to the side surfaces.

10. A method of manufacturing a laminated ceramic capacitor, comprising:

a step of preparing a first powder containing, as a main component, ceramic particles containing no intracrystalline pores;

a step of preparing a second powder having a perovskite structure with an axial ratio c/a of 1.008 or less and containing ceramic particles containing intracrystalline pores as a main component;

a step of producing an unfired ceramic body including a laminated portion including a plurality of ceramic layers mainly composed of the first powder laminated in a first direction, a plurality of internal electrodes arranged between the plurality of ceramic layers, and side edge portions covering the plurality of internal electrodes from a second direction orthogonal to the first direction, and a covering portion covering the laminated portion from the first direction, mainly composed of the second powder, and having a larger content of silicon than the plurality of ceramic layers; and

and firing the ceramic body.

11. The method for manufacturing a laminated ceramic capacitor as claimed in any one of claims 8 to 10, wherein:

the second powder is made by a hydrothermal process.

12. The method for manufacturing a laminated ceramic capacitor as claimed in any one of claims 8 to 11, wherein:

the second powder has an average particle diameter of 5nm to 500 nm.

13. The method for manufacturing a laminated ceramic capacitor as claimed in any one of claims 8 to 12, wherein:

the first powder is made by a solid phase method.

Technical Field

The present invention relates to a laminated ceramic capacitor and a method for manufacturing the same.

Background

The multilayer ceramic capacitor is provided with a protective portion for protecting the periphery of the internal electrode. In order to reduce the size and increase the capacitance of the multilayer ceramic capacitor, it is advantageous to make the protective portion that does not contribute to the formation of the capacitance as thin as possible. Patent document 1 discloses a technique capable of making a protective portion thin.

In the technique disclosed in patent document 1, a laminate in which internal electrodes are exposed on the side surfaces is produced, and protective portions (side edge portions) are provided on the side surfaces of the laminate. In this multilayer ceramic capacitor, even if the side edge portions are made thin to achieve miniaturization and large capacitance, the side surface of the multilayer body where the internal electrodes are exposed can be appropriately protected by the side edge portions.

Disclosure of Invention

Technical problem to be solved by the invention

However, in the multilayer ceramic capacitor, as the protective portion becomes thinner, insulation failure due to cracks generated in the protective portion reaching the internal electrode is more likely to occur. Therefore, a technique for realizing miniaturization and large capacitance while ensuring high durability is required for the multilayer ceramic capacitor.

In view of the above circumstances, an object of the present invention is to provide a multilayer ceramic capacitor and a method for manufacturing the same, which can secure high durability and realize miniaturization and large capacitance.

Means for solving the problems

In order to achieve the above object, a multilayer ceramic capacitor according to one embodiment of the present invention includes a capacitance forming portion and a protection portion.

The capacitance forming part includes: a plurality of ceramic layers laminated in a first direction; and a plurality of internal electrodes disposed between the plurality of ceramic layers.

The protective portion includes a covering portion that covers the capacitor forming portion and forms a main surface facing the first direction, a side edge portion that forms a side surface facing a second direction orthogonal to the first direction, and a ridge portion that forms a connecting portion for connecting the main surface and the side surface.

The plurality of ceramic layers are formed of a first ceramic, and the ridge portions are formed of a second ceramic.

The first ceramic is a polycrystalline body mainly composed of crystal grains containing no intracrystalline pores.

The second ceramic is a polycrystalline body mainly composed of crystal grains containing intracrystalline pores, and the second ceramic has a higher silicon content than the first ceramic.

The second ceramic may have a silicon content of 0.5 mol% or more.

In the multilayer ceramic capacitor, a first ceramic and a second ceramic having different configurations are provided. The first ceramic does not contain intragranular pores and excessive silicon which cause a decrease in capacitance, unlike the second ceramic. Therefore, the capacitance of the laminated ceramic capacitor can be ensured by forming at least the plurality of ceramic layers from the first ceramic.

The second ceramic is capable of inhibiting the development of cracks by utilizing a structure comprising intracrystalline pores and excess silicon. Therefore, by forming the ridge portion of the protective portion, which is particularly likely to receive an external impact, with the second ceramic, it is possible to suppress an insulation failure caused by a crack generated in the protective portion reaching the capacitor forming portion.

More specifically, in the second ceramic containing an excessive amount of silicon, silicon segregates at grain boundaries, and the mechanical strength at the grain boundaries between crystal grains can be improved. Therefore, in the second ceramic, the development of cracks along the grain boundaries, which is likely to occur in a general polycrystalline body, is less likely to occur.

Thus, in the second ceramic, cracks can be caused to develop on a path along the intragranular pores. In this process, each time the crack reaches the intracrystalline pore, the stress of the tip portion, which is the propulsive force of the crack, is weakened. Therefore, in the second ceramic, the intragranular pores can hinder the development of cracks, and therefore, the development of cracks can be suppressed.

As described above, in the above configuration, insulation failure can be suppressed without accompanying a decrease in capacitance. In addition, in the above configuration, since the progress of the crack generated in the protection portion can be suppressed, the protection portion can be formed thinner. Thus, the multilayer ceramic capacitor can be further reduced in size and increased in capacitance.

The side edge portion may be formed of the second ceramic.

The dimension of the side edge portion in the second direction may be 30 μm or less.

In the protective portion having these structures, not only the development of cracks in the ridge portion but also the development of cracks in the side edge portion can be suppressed. Therefore, the multilayer ceramic capacitor can ensure higher durability. Therefore, even when the thickness of the side edge portion is reduced to 30 μm or less, insulation failure can be prevented.

The entire protection portion may be formed of the second ceramic.

In the protection portion having this structure, the progress of cracks can be suppressed in the entire protection portion. Therefore, the multilayer ceramic capacitor can ensure higher durability.

The covering portion may be formed of the second ceramic.

In the protective portion having this structure, not only the development of cracks in the ridge portion but also the development of cracks in the covering portion can be suppressed. Therefore, the multilayer ceramic capacitor can ensure higher durability.

The first ceramic and the second ceramic may be both polycrystalline bodies having a perovskite structure containing barium and titanium.

In a method for manufacturing a laminated ceramic capacitor according to an embodiment of the present invention, a first powder is prepared, the first powder containing, as a main component, ceramic particles containing no intracrystalline pores.

A second powder having a perovskite structure with an axial ratio c/a of 1.008 or less and containing ceramic particles containing intracrystalline pores as a main component is prepared.

An unfired laminate is produced, wherein the unfired laminate includes a capacitor-forming portion including a plurality of ceramic layers, which are stacked in a first direction and have the first powder as a main component, and a plurality of internal electrodes arranged between the plurality of ceramic layers, and a covering portion that covers the capacitor-forming portion from the first direction.

And forming an unfired ceramic body by forming side edge portions, which are mainly composed of the second powder and contain a larger amount of silicon than the plurality of ceramic layers, on a side surface of the laminate facing a second direction perpendicular to the first direction.

And firing the ceramic body.

The side edge may be formed by attaching a ceramic sheet to the side surface.

With this configuration, a multilayer ceramic capacitor in which the development of cracks in the ridge portion and the side edge portion of the protective portion can be suppressed can be manufactured.

In a method for manufacturing a laminated ceramic capacitor according to another aspect of the present invention, a first powder is prepared, the first powder containing, as a main component, ceramic particles containing no intracrystalline pores.

A second powder having a perovskite structure with an axial ratio c/a of 1.008 or less and containing ceramic particles containing intracrystalline pores as a main component is prepared.

An unfired ceramic body is produced, wherein the unfired ceramic body includes a laminated portion including a plurality of ceramic layers laminated in a first direction and containing the first powder as a main component, a plurality of internal electrodes arranged between the plurality of ceramic layers, and side edge portions covering the plurality of internal electrodes from a second direction orthogonal to the first direction, and a covering portion covering the laminated portion from the first direction, containing the second powder as a main component, and containing a larger amount of silicon than the plurality of ceramic layers.

And firing the ceramic body.

With this configuration, a multilayer ceramic capacitor in which the development of cracks in the ridge portion and the side edge portion of the protective portion can be suppressed can be manufactured.

The second powder may be prepared by hydrothermal method.

The second powder may have an average particle diameter of 5nm to 500 nm.

With these technical means, the second ceramic containing the crystal grains containing the intracrystalline pores as the main component in the laminated ceramic capacitor can be formed satisfactorily.

The first powder may be prepared by a solid phase method.

In the multilayer ceramic capacitor having this structure, a large capacitance can be easily obtained.

Effects of the invention

As described above, the present invention can provide a multilayer ceramic capacitor and a method for manufacturing the same, which can ensure high durability and realize miniaturization and large capacitance.

Drawings

Fig. 1 is a perspective view of a multilayer ceramic capacitor according to an embodiment of the present invention.

Fig. 2 is a sectional view of the laminated ceramic capacitor taken along line a-a' of fig. 1.

Fig. 3 is a sectional view of the laminated ceramic capacitor taken along line B-B' of fig. 1.

Fig. 4 is a partial cross-sectional view showing a microstructure of the first ceramic of the multilayer ceramic capacitor.

FIG. 5 is a partial cross-sectional view showing the microstructure of the second ceramic of the multilayer ceramic capacitor.

Fig. 6 is a diagram showing the path of crack propagation in the first ceramic.

Fig. 7 is a diagram showing the path of the crack of the second ceramic.

Fig. 8 is a sectional view showing a first configuration example of the multilayer ceramic capacitor.

Fig. 9 is a flowchart showing a manufacturing method of the first configuration example.

Fig. 10 is a plan view showing a manufacturing process of the first configuration example.

Fig. 11 is a perspective view showing a manufacturing process of the first configuration example.

Fig. 12 is a plan view showing a manufacturing process of the first configuration example.

Fig. 13 is a perspective view showing a manufacturing process of the first configuration example.

Fig. 14 is a perspective view showing a manufacturing process of the first configuration example.

Fig. 15 is a sectional view showing a second configuration example of the multilayer ceramic capacitor.

Fig. 16 is a flowchart showing a manufacturing method of the second configuration example.

Fig. 17 is a plan view showing a manufacturing process of the second configuration example.

Fig. 18 is a perspective view showing a manufacturing process of the second configuration example.

Fig. 19 is a perspective view showing a manufacturing process of the second configuration example.

FIG. 20 is a sectional view showing another example of the structure of the multilayer ceramic capacitor.

Description of the reference numerals

10. 10a, 10b, 10 a' … … laminated ceramic capacitor

11 … … ceramic body

12. 13 … … external electrode

16 … … laminate

17 … … laminated part

20 … … capacitance forming part

21 … … ceramic layer

22. 23 … … internal electrode

30 … … protection part

31 … … cover

32 … … side edge

33 … … corner part

R1 … … first ceramic

R2 … … second ceramic

P … … intracrystalline porosity

M … … major face

Side surface of S … …

Q … … connection part

Detailed Description

Embodiments of the present invention will be described below with reference to the drawings.

The X, Y and Z axes are shown as being orthogonal to each other as appropriate in the drawings. The X, Y and Z axes are the same in all figures.

Monolithic structure of I-laminated ceramic capacitor 10

1. Schematic structure

Fig. 1 to 3 show a multilayer ceramic capacitor 10 according to an embodiment of the present invention. Fig. 1 is a perspective view of a multilayer ceramic capacitor 10. Fig. 2 is a sectional view of the laminated ceramic capacitor 10 taken along line a-a' of fig. 1. Fig. 3 is a sectional view of the laminated ceramic capacitor 10 taken along line B-B' of fig. 1.

The laminated ceramic capacitor 10 includes a ceramic main body 11, a first external electrode 12, and a second external electrode 13. The first external electrode 12 is provided at one end of the ceramic body 11 in the X-axis direction, and the second external electrode 13 is provided at the other end of the ceramic body 11 in the X-axis direction. That is, the external electrodes 12 and 13 are opposed to each other in the X-axis direction.

The ceramic body 11 has: 2 end faces E facing the X-axis direction; 2 side faces S facing to the Y-axis direction; 2 main surfaces M facing the Z-axis direction; and a connecting portion Q connecting the main surface M and the side surface S. The connecting portion Q is typically configured as a convex curved surface extending in the X-axis direction formed by chamfering.

The external electrodes 12 and 13 cover the end faces E of the ceramic body 11 and extend in the X-axis direction from the end faces E. The external electrodes 12, 13 are spaced apart from each other on the side surface S, the main surface M, and the connection portion Q. Therefore, in both the external electrodes 12 and 13, the cross section parallel to the X-Z plane and the cross section parallel to the X-Y plane have U-shapes.

The ceramic main body 11 includes a capacitance forming portion 20 and a protection portion 30. The capacitance forming portion 20 is disposed in the center portion in the Y-axis and Z-axis directions. The protection unit 30 covers the capacitive formation unit 20 from the Y-axis and Z-axis directions, and physically protects and electrically protects the capacitive formation unit 20. The protective portion 30 includes a covering portion 31, side edge portions 32, and ridge portions 33.

The capacitance forming portion 20 includes a plurality of ceramic layers 21, a plurality of first internal electrodes 22, and a plurality of second internal electrodes 23. The ceramic layers 21 are sheet-like and extend parallel to the X-Y plane, and are stacked in the Z-axis direction. The internal electrodes 22 and 23 are alternately arranged in the Z-axis direction between the ceramic layers 21.

The first internal electrode 22 is connected to the first external electrode 12 at one end face E, and is spaced apart from the other end face E covered with the second external electrode 13. The second internal electrode 23 is connected to the second external electrode 13 at the other end face E, and is spaced apart from the other end face E covered with the first external electrode 12.

The covering portion 31 of the protective portion 30 covers the capacitance forming portion 20 from both sides in the Z-axis direction, and constitutes the main surface M of the ceramic body 11. The side edge portion 32 of the protective portion 30 covers the capacitance forming portion 20 from both sides in the Y axis direction, and constitutes a side surface S of the ceramic main body 11. The ridge 33 of the protector 30 constitutes the connection portion Q of the ceramic main body 11.

With the above-described structure, in the multilayer ceramic capacitor 10, when a voltage is applied between the first external electrode 12 and the second external electrode 13, the voltage is applied to the plurality of ceramic layers 21 between the first internal electrode 22 and the second internal electrode 23. Accordingly, in the multilayer ceramic capacitor 10, electric charges corresponding to the voltage between the external electrodes 12 and 13 can be accumulated.

The internal electrodes 22 and 23 of the capacitor-forming portion 20 are each formed of a conductive material and function as internal electrodes of the multilayer ceramic capacitor 10. As the conductive material, for example, a metal material containing nickel (Ni), copper (Cu), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), or an alloy thereof can be used.

The capacitor-forming portion 20 is formed of a dielectric ceramic in a region other than the internal electrodes 22 and 23 including the ceramic layer 21. In the multilayer ceramic capacitor 10, in order to increase the capacitance of the capacitance forming portion 20, it is advantageous to form the ceramic layers 21 with a dielectric ceramic having a high dielectric constant.

Therefore, in the multilayer ceramic capacitor 10, barium titanate (BaTiO) can be used as the high-permittivity dielectric ceramic constituting the capacitor forming portion 20₃) Polycrystalline bodies of the material-like, i.e., perovskite-structured polycrystalline bodies containing barium (Ba) and titanium (Ti). Thus, a large capacitance can be obtained in the laminated ceramic capacitor 10.

The capacitance forming part 20 may be formed ofStrontium titanate (SrTiO)₃) Calcium titanate (CaTiO)₃) Magnesium titanate (MgTiO)₃) Calcium zirconate (CaZrO)₃) Calcium zirconate titanate (Ca (Zr, Ti) O₃) Barium zirconate (BaZrO)₃) Titanium oxide (TiO)₂) And the like.

The covering portion 31, the side edge portion 32, and the ridge portion 33 of the protective portion 30 are also formed of a dielectric ceramic of the same composition as the ceramic main body 11. That is, in the multilayer ceramic capacitor 10, barium titanate (BaTiO) is used as the dielectric ceramic constituting the protective portion 30₃) Polycrystalline like materials.

The structure of the multilayer ceramic capacitor 10 of the present embodiment is not limited to the structure shown in fig. 1 to 3, and can be modified as appropriate. For example, the number of internal electrodes 22 and 23 and the thickness of the ceramic layer 21 may be appropriately determined according to the size and performance required for the laminated ceramic capacitor 10.

2. Detailed structure

The region formed of the dielectric ceramic other than the internal electrodes 22, 23 in the ceramic main body 11 includes the first ceramic R1 and the second ceramic R2 having microstructures different from each other. Fig. 4 is a partial sectional view schematically showing the microstructure of the first ceramic R1. Fig. 5 is a partial sectional view schematically showing the microstructure of the second ceramic R2.

The first ceramic R1 and the second ceramic R2 are polycrystalline bodies having the first crystal grains G1 and the second crystal grains G2 of different structures as main components. Specifically, the first crystalline particles G1 constituting the first ceramic R1 do not contain intracrystalline pores (intraparticle pores) P, and the second crystalline particles G2 constituting the second ceramic R2 contain intracrystalline pores P.

The intracrystalline pores P included in the second crystal grains G2 constituting the second ceramic R2 constitute minute spaces existing in the second crystal grains G2. That is, the intracrystalline pores P are different from the grain boundary pores which are generally observed in the polycrystalline body as spaces formed at boundaries between adjacent crystal grains, i.e., grain boundaries.

In the second ceramic R2, the content of silicon is large, i.e., an excess amount of silicon is contained, compared to the first ceramic R1. In the second ceramic R2 containing silicon in excess, silicon segregates at grain boundaries, so that high mechanical strength can be obtained at the grain boundaries between the second crystal grains G2.

On the other hand, unlike the second ceramic R2, the first ceramic R1 does not contain intracrystalline pores P and excessive silicon, which cause a decrease in capacitance. In the laminated ceramic capacitor 10, at least the plurality of ceramic layers 21 are formed of the first ceramic R1. Accordingly, a large capacitance can be ensured in the multilayer ceramic capacitor 10.

In the second ceramic R2, the development of cracks can be effectively suppressed by a structure including an excess amount of silicon and intracrystalline pores P which cause a decrease in capacitance, and details thereof will be described later. In the laminated ceramic capacitor 10, at least the ridge 33 of the protective part 30 that does not contribute to the formation of capacitance, which is indicated by a dense dot pattern in fig. 3, is formed of the second ceramic R2.

The protection portion 30 is exposed at the center in the X axis direction without being covered with the external electrodes 12 and 13, and is therefore susceptible to external impact. In the multilayer ceramic capacitor 10, at least a part of the protection portion 30 is made of the second ceramic R2, whereby insulation failure caused by cracks generated in the protection portion 30 reaching the capacitance forming portion 20 can be suppressed.

In particular, the projecting ridge 33 of the protector 30 is susceptible to a strong impact from the outside. Therefore, in the multilayer ceramic capacitor 10, at least the ridge portion 33 of the protective portion 30 is made of the second ceramic R2, whereby cracks occurring in the protective portion 30 can be effectively prevented from reaching the capacitance forming portion 20.

Thus, in the multilayer ceramic capacitor 10, insulation failure can be suppressed without accompanying a decrease in capacitance. In addition, in the laminated ceramic capacitor 10, since the development of cracks generated in the protection portion 30 can be suppressed, further downsizing and large capacitance can be achieved by forming the protection portion 30 thinner.

Next, a mechanism of the crack development in the first ceramic R1 and the second ceramic R2 will be described with reference to fig. 6 and 7. Fig. 6 and 7 are diagrams schematically showing the paths of the cracks generated in the first ceramic R1 and the second ceramic R2 by the impact from the outside by arrows. Fig. 6 shows the first ceramic R1, and fig. 7 shows the second ceramic R2.

In the first ceramic R1 shown in fig. 6, cracks generated in the first crystal grains G1 by an external impact progress toward the grain boundaries (or grain boundary triple points) between the first crystal grains G1 while breaking the grain boundaries having low mechanical strength. Therefore, cracks generated in the first ceramic R1 easily progress deep on the path along the grain boundaries between the first crystal grains G1.

In the second ceramic R2, on the other hand, the grain boundaries between the second crystal grains G2 have high mechanical strength due to the action of silicon as described above. Accordingly, in the second ceramic R2, cracks generated in the second crystal grains G2 by an external impact can be made to progress not on a path along the grain boundaries between the second crystal grains G2 but on a path along the intracrystalline pores P.

More specifically, in the second ceramic R2 shown in fig. 7, cracks generated in the second crystal grains G2 by an external impact first move to the intracrystalline pores P in the second crystal grains G2. Then, the crack reaching the intracrystalline pore P progresses toward the adjacent intracrystalline pore P. That is, in the second ceramic R2, cracks develop along the adjacent intracrystalline pores P.

The crack progresses with a stress concentrated on the tip portion having a large curvature as a propulsive force. In this regard, in the second ceramic R2, the intracrystalline pores P having a small curvature function to hinder the development of cracks. That is, in the second ceramic R2, when the crack reaches the intracrystalline pore P, the curvature sharply decreases at the tip of the crack, and the stress is dispersed.

Therefore, in the second ceramic R2, the stress at the tip portion, which is the propulsive force of the crack, is weakened each time the crack reaches the intracrystalline pore P during the progress. That is, in the second ceramic R2, the intracrystalline pores P in the second crystal grains G2 function to stop the development of cracks, so that the cracks become difficult to develop.

In the second ceramic R2, in order to effectively suppress the development of cracks along the grain boundaries between the second crystal grains G2, the content of silicon is preferably 0.5 mol% or more. On the other hand, in order to suppress adverse effects caused by excessive silicon, such as a decrease in capacitance of the capacitance forming portion 20 due to diffusion during firing, the content of silicon is preferably limited to 10 mol% or less.

The first ceramic R1 is substantially composed of only the first crystalline particles G1 not containing the intracrystalline pores P, but may contain a small amount of the second crystalline particles G2 containing the intracrystalline pores P. The second ceramic R2 is substantially composed of only the second crystal grains G2 containing the intracrystalline pores P, but may contain a small amount of the first crystal grains G1 not containing the intracrystalline pores P.

The amount of the second crystalline particles G2 containing the intracrystalline pores P can be evaluated by the intracrystalline porosity existence. The intracrystalline porosity can be obtained, for example, as the following ratio: in all crystal grains observed in a predetermined region in a photograph taken at 5 ten thousand times by a scanning electron microscope of a cross section, the proportion of crystal grains having voids with a maximum diameter of 5nm or more was observed as intracrystalline pores P.

In the second ceramic R2, among all the second crystal grains G2 including the intracrystalline pores P, the second crystal grains G2 in which the intracrystalline pores P do not appear in a specific cross section are present at a certain ratio. When this ratio is considered, the second ceramic R2 substantially composed of only the second crystal grains G2 containing the intracrystalline pores P has an intracrystalline pore existence rate of 2.5% or more.

On the other hand, in the first ceramic R1 substantially composed of only the first crystal grains G1 not containing the intracrystalline pores P, the intracrystalline pores existence rate is infinitely close to 0%. Specifically, in the first ceramic R1, even in the case where the second crystal grains G2 including the intracrystalline pores P are occasionally contained, the intracrystalline pores existence rate is limited to 0.001% or less.

II multilayer ceramic capacitor 10a of the first configuration example

1. Integral structure

Fig. 8 is a diagram showing a multilayer ceramic capacitor 10a according to a first configuration example of the above embodiment. The laminated ceramic capacitor 10a has the following structure: a side edge portion 32 formed continuously with the ridge portion 33 is provided on a side surface of the laminated body 16 including the capacitor forming portion 20 and the covering portion 31 in the Y axis direction.

In the protective portion 30 of the multilayer ceramic capacitor 10a, as shown by the dense dot pattern in fig. 8, the side edge portion 32 is also formed of the second ceramic R2 in addition to the ridge portion 33. Therefore, in the protection portion 30, not only the ridge portion 33 but also the side edge portion 32 can suppress the development of cracks. Further, the laminated body 16 is formed of the first ceramic R1.

In the multilayer ceramic capacitor 10a, since the development of cracks in the side edge portion 32 can be suppressed, the side edge portion 32 can be further thinned. Specifically, in the multilayer ceramic capacitor 10a, insulation failure can be prevented even when the dimension of the side edge portion 32 in the Y axis direction is 30 μm or less.

2. Manufacturing method

Fig. 9 is a flowchart showing a method for manufacturing the multilayer ceramic capacitor 10 a. FIGS. 10 to 14 show a process for manufacturing the multilayer ceramic capacitor 10 a. Next, a method for manufacturing the multilayer ceramic capacitor 10a will be described with reference to fig. 9 and fig. 10 to 14 as appropriate.

2.1 step S11: preparing the first powder

In step S11, a first powder, which is a ceramic powder for forming the laminated body 16, is prepared. The first powder is produced by a method other than the hydrothermal method, and in the present embodiment, is a solid-phase powder produced by a solid-phase method. For example, a solid-phase powder of barium titanate can be obtained by heating a mixed powder of titanium oxide and barium carbonate to cause a solid-phase reaction of them.

2.2 step S12: preparing the second powder

In step S12, a second powder is prepared, which is a ceramic powder for forming the side edge portions 32 and the ridge portions 33 of the protector 30. The second powder is a hydrothermal powder prepared by a hydrothermal method. The hydrothermal powder produced by the hydrothermal method is obtained mainly from ceramic particles containing intracrystalline pores P.

Therefore, the side edge portions 32 and the ridge portions 33 formed by the hydrothermal powder become a polycrystal containing the second crystal grains G2 containing the intracrystalline pores P generated by the hydrothermal powder as a main component after firing. For example, hydrothermal powder of barium titanate can be obtained by synthesizing titanium oxide and barium hydroxide by a hydrothermal method in an autoclave filled with hot water.

Since the ceramic powder can be produced at low cost by the hydrothermal method, the production cost of the multilayer ceramic capacitor 10a can be reduced by forming the side edge portion 32 and the ridge portion 33 using the hydrothermal powder. The hydrothermal powder is obtained as a substantially spherical fine powder having a uniform particle diameter, and has an average particle diameter of, for example, 5nm to 500 nm.

The crystallinity of the perovskite structure can be evaluated by an axial ratio c/a which is a ratio of the length of the c-axis to the length of the a-axis in the unit lattice. In an ideal crystal structure, the axial ratio c/a is about 1.01, and in the case of using hydrothermal powder, the axial ratio c/a is 1.008 or less. The axial ratio c/a can be calculated from a spectrum obtained by X-ray diffraction, for example.

2.3 step S13: manufacture of ceramic wafer

In step S13, a: a first ceramic sheet 101 and a second ceramic sheet 102 for forming the capacitance forming part 20; a third ceramic sheet 103 for forming the cover 31; and a fourth ceramic sheet 104 (not shown) for forming the side edge portion 32 and the ridge portion 33.

The ceramic sheets 101, 102, 103, and 104 are formed as unfired dielectric green sheets in a sheet form using a solvent and a binder, with ceramic powder as a main component. The ceramic sheets 101, 102, 103, 104 may be formed by, for example, a roll coater, a doctor blade, or the like.

More specifically, the first powder, which is the solid-phase powder prepared in step S11, is used in the production of the ceramic sheets 101, 102, 103 for forming the laminated body 16. On the other hand, in the production of the fourth ceramic sheet 104 for forming the side edge portion 32 and the ridge portion 33, the second powder, which is the hydrothermal powder prepared in step S12, is used.

As described above, the hydrothermal powder is a substantially spherical fine powder having a uniform particle diameter. Therefore, the hydrothermal powder is easily dispersed in the solvent. Furthermore, the slurry of the hydrothermal powder dispersed in the solvent and the binder is soft and deformable, and therefore has high moldability. Therefore, by using the hydrothermal powder, the fourth ceramic sheet 104 of high quality can be obtained.

In the fourth ceramic sheet 104 for forming the side edge portion 32 and the ridge portion 33, the content of silicon is larger than the ceramic sheets 101, 102, 103. By using a hydrothermal powder having high sinterability and containing a large amount of silicon which is likely to form a liquid phase in the ceramic sheet 104, the sinterability of the side edge portions 32 and the ridge portions 33 can be improved.

Fig. 10 is a plan view of the ceramic sheets 101, 102, 103. At this stage, the ceramic sheets 101, 102, and 103 are configured as large sheets that are not singulated. Fig. 10 shows cutting lines Lx, Ly when the laminated bodies 16 are singulated. The cutting line Lx is parallel to the X-axis, and the cutting line Ly is parallel to the Y-axis.

As shown in fig. 10, unfired first inner electrodes 122 corresponding to the first inner electrodes 22 are formed on the first ceramic sheet 101, and unfired second inner electrodes 123 corresponding to the second inner electrodes 23 are formed on the second ceramic sheet 102. No internal electrode is formed on the third ceramic sheet 103 corresponding to the covering portion 31.

The internal electrodes 122 and 123 may be formed by applying an arbitrary conductive paste on the ceramic sheets 101 and 102. The method of applying the conductive paste can be arbitrarily selected from known techniques. For example, when the conductive paste is applied, a screen printing method or a gravure printing method can be used.

In the internal electrodes 122 and 123, a gap is formed along the X-axis direction of the cutting line Ly every 1 cutting line Ly. The gaps of the first inner electrodes 122 and the gaps of the second inner electrodes 123 are arranged alternately in the X-axis direction. That is, the cutting lines Ly passing through the gaps of the first internal electrodes 122 and the cutting lines Ly passing through the gaps of the second internal electrodes 123 are alternately arranged.

2.4 step S14: lamination of layers

In step S14, the ceramic sheets 101, 102, and 103 produced in step S13 are laminated as shown in fig. 11 to produce a laminated sheet 105. In the laminated sheet 105, the first ceramic sheet 101 and the second ceramic sheet 102 corresponding to the capacitance forming portion 20 are alternately laminated in the Z-axis direction.

In the laminated sheet 105, the third ceramic sheet 103 corresponding to the covering section 31 is laminated on the upper and lower surfaces in the Z-axis direction of the ceramic sheets 101 and 102 alternately laminated. In the example shown in fig. 11, 3 third ceramic sheets 103 are laminated, respectively, but the number of the third ceramic sheets 103 may be changed as appropriate.

The laminated sheet 105 is integrated by pressure-bonding the ceramic sheets 101, 102, 103. For the press-bonding of the ceramic sheets 101, 102, 103, for example, hydrostatic pressing, uniaxial pressing, or the like is preferably used. Thus, the density of the laminated sheet 105 can be increased.

2.5 step S15: cutting off

In step S15, the laminate sheet 105 obtained in step S14 is cut along cutting lines Lx, Ly as shown in fig. 12, thereby producing an unfired laminate 116. The laminate 116 corresponds to the fired laminate 16. For example, a rotary cutter, a press cutter, or the like can be used to cut the laminated sheet 105.

More specifically, the laminated sheet 105 is cut along the cutting lines Lx, Ly while being held by the holding member C. Thus, the laminated sheet 105 is singulated to obtain a laminated body 116. At this time, the holding member C is not cut, and the stacked bodies 116 are connected by the holding member C.

Fig. 13 is a perspective view of the laminate 116 obtained in step S15. The stacked body 116 has a capacitor forming portion 120 and a covering portion 131. In the laminate 116, the internal electrodes 122 and 123 are exposed on both side surfaces facing the Y-axis direction as cut surfaces. A ceramic layer 121 is formed between the internal electrodes 122, 123.

2.6 step S16: forming side edge portions and ridge portions

In step S16, unfired side edge portions 132 and ridge portions 133 are formed by pasting the fourth ceramic sheet 104 prepared in step S13 on the laminated body 116 obtained in step S15. Thus, an unfired ceramic body 111 shown in fig. 14 is obtained.

More specifically, in step S16, the fourth ceramic sheet 104 is bonded to both side surfaces of the laminated body 116, which are cut surfaces in step S15, in the Y-axis direction. Therefore, in step S16, the stacked body 116 is preferably peeled from the holding member C in advance, and the direction of the stacked body 116 is preferably rotated by 90 degrees.

In step S16, for example, the fourth ceramic sheets 104 cut in accordance with the outer shape of the side surfaces of the laminated body 116 may be bonded to both side surfaces of the laminated body 116. Accordingly, the fourth ceramic sheets 104 bonded to both side surfaces of the laminated body 116 become unfired side edge portions 132 and ridge portions 133 as shown in fig. 14.

The fourth ceramic sheet 104, which mainly contains hydrothermal powder having a uniform particle diameter, can flexibly deform following the fine uneven shape of the side surface of the laminate 116, and can therefore be brought into close contact (close contact) along the side surface of the laminate 116. Therefore, in the ceramic main body 111, the side edge portion 132 and the ridge portion 133 are not easily peeled off from the laminated body 116.

The method of forming the unfired side edge portions 132 and the ridge portions 133 is not limited to the above method. For example, the fourth ceramic sheet 104 may be bonded to the side surface of the laminated body 116 and then cut in accordance with the contour of the side surface of the laminated body 116. The fourth ceramic sheet 104 may be punched out on the side surface of the laminated body 116.

2.7 step S17: firing

In step S17, the unfired ceramic body 111 obtained in step S16 is fired to produce the ceramic body 11 of the multilayer ceramic capacitor 10a shown in fig. 8. That is, in step S17, the laminate 116 becomes the laminate 16, the side edge 132 becomes the side edge 32, and the ridge 133 becomes the ridge 33.

The firing temperature in step S17 may be determined according to the sintering temperature of the ceramic body 111. For example, when a barium titanate-based material is used as the dielectric ceramic, the firing temperature can be set to about 1000 to 1300 ℃. The firing may be performed, for example, in a reducing atmosphere or in an atmosphere with a low oxygen partial pressure.

In the multilayer ceramic capacitor 10a, since the side edge portions 132 and the ridge portions 133 are in close contact (close contact) with the multilayer body 116 without any gap as described above, in the ceramic body 11 after firing, gaps are less likely to occur between the side edge portions 32 and the ridge portions 33 and the multilayer body 16. Thus, the laminated ceramic capacitor 10a can obtain high moisture resistance.

2.8 step S18: forming external electrodes

In step S18, the external electrodes 12 and 13 are formed on the ceramic body 11 obtained in step S17, whereby the multilayer ceramic capacitor 10a shown in fig. 8 is produced. In step S18, for example, a base film, an intermediate film, and a surface film constituting the external electrodes 12 and 13 are formed on the X-axis direction end face of the ceramic body 11.

More specifically, in step S18, first, the unfired electrode material is applied so as to cover both end surfaces of the ceramic body 11 in the X-axis direction. For example, the base films of the external electrodes 12 and 13 are formed on the ceramic body 11 by sintering the applied unfired electrode material in a reducing atmosphere or a low oxygen partial pressure atmosphere.

Then, an intermediate film of the external electrodes 12 and 13 is formed on the base film of the external electrodes 12 and 13 sintered on the ceramic body 11, and further, surface films of the external electrodes 12 and 13 are formed. For example, plating treatment such as electrolytic plating can be used for forming the intermediate film and the surface film of the external electrodes 12 and 13.

Part of the processing in step S18 may be performed before step S17. For example, an unfired electrode material may be applied to both end surfaces of the unfired ceramic body 111 in the X axis direction before step S17. Accordingly, in step S17, firing of the unfired ceramic body 111 and sintering of the electrode material can be performed simultaneously.