Multi-layer ceramic capacitor and method of producing the same

A multi-layer ceramic capacitor includes a ceramic body, a first external electrode, and a second external electrode. The ceramic body includes ceramic layers laminated along a first direction, first internal electrodes and second internal electrodes that are alternately disposed between the ceramic layers, a first end surface and a second end surface that are oriented in a second direction orthogonal to the first direction, and a first inner groove and a second inner groove that are respectively formed in the first end surface and the second end surface along the first direction. The first and second external electrodes respectively cover the first and second end surfaces, the first internal electrodes being drawn to the first end surface and protruding in the first inner groove, the second internal electrodes being drawn to the second end surface and protruding in the second inner groove.

CROSS-REFERENCE TO RELATED APPLICATION

This application claims the benefit under 35 U.S.C. § 119 of Japanese Patent Application No. 2017-078764, filed Apr. 12, 2017, the disclosure of which is herein incorporated by reference in its entirety.

BACKGROUND

The present invention relates to a multi-layer ceramic capacitor and a method of producing the multi-layer ceramic capacitor.

In a multi-layer ceramic capacitor, external electrodes are provided to end surfaces of a ceramic body including internal electrodes drawn to the end surfaces, and the internal electrodes and the external electrodes are electrically connected to each other. However, when the internal electrodes are oxidized in the vicinity of the end surfaces of the ceramic body at the time of sintering or the like, electrical conduction between the internal electrodes and the external electrodes is inhibited in some cases.

In contrast to the above, there is known a technique of ensuring electrical conduction between the internal electrodes and the external electrodes by removing the oxidized end portions of the internal electrodes by a chemical solution, polishing, or the like (see, for example, Japanese Patent Application Laid-open Nos. 2016-134456 and 2010-205812).

SUMMARY

However, in the technique of removing the oxidized end portions of the internal electrodes, the performance of the multi-layer ceramic capacitor is prone to be lowered due to the influence of the residual of the chemical solution, polishing debris, or the like.

In view of the circumstances as described above, it is desirable to provide a multi-layer ceramic capacitor and a method of producing the same, which are capable of ensuring electrical conduction between an internal electrode and an external electrode.

According to an embodiment of the present invention, there is provided a multi-layer ceramic capacitor including a ceramic body, a first external electrode, and a second external electrode.

The ceramic body includes ceramic layers laminated along a first direction, first internal electrodes and second internal electrodes that are alternately disposed between the ceramic layers, a first end surface and a second end surface that are oriented in a second direction orthogonal to the first direction, and at least one first inner groove and at least one second inner groove that are respectively formed in the first end surface and the second end surface along the first direction.

The first external electrode and the second external electrode respectively cover the first end surface and the second end surface.

The first internal electrodes are drawn to the first end surface and protrude in the at least one first inner groove.

The second internal electrodes are drawn to the second end surface and protrude in the at least one second inner groove.

In this configuration, since the first internal electrodes protrude in the first inner groove and the second internal electrodes protrude in the second inner groove, the first internal electrodes and the first external electrode are electrically connected to each other at least in the first inner groove, and the second internal electrodes and the second external electrode are electrically connected to each other at least in the second inner groove. As a result, even if the first internal electrodes are oxidized in a region adjacent to the first end surface and the second internal electrodes are oxidized in a region adjacent to the second end surface, electrical conduction between the first internal electrodes and the first external electrode and between the second internal electrodes and the second external electrode can be ensured.

The at least one first inner groove may include a plurality of first inner grooves, and the at least one second inner groove may include a plurality of second inner grooves.

In this configuration, electrical conduction between the first internal electrodes and the first external electrode and between the second internal electrodes and the second external electrode can be obtained more reliably.

The first external electrode may include at least one first outer groove, the at least one first outer groove corresponding to the at least one first inner groove and being formed along the first direction. The second external electrode may include at least one second outer groove, the at least one second outer groove corresponding to the at least one second inner groove and being formed along the first direction.

In this configuration, when the multi-layer ceramic capacitor is mounted, solder wets up along the first outer groove and the second outer groove. Thus, connection strength provided by the solder is increased.

The first external electrode and the second external electrode may be each formed as a sputtering film.

In this configuration, the first external electrode and the second external electrode can be formed without using a wet process.

According to another embodiment of the present invention, there is provided a method of producing a multi-layer ceramic capacitor, the method including: producing an unsintered ceramic body including ceramic layers laminated along a first direction, first internal electrodes and second internal electrodes that are alternately disposed between the ceramic layers, and a first end surface and a second end surface that are oriented in a second direction orthogonal to the first direction, the first internal electrodes being drawn to the first end surface, the second internal electrodes being drawn to the second end surface; sintering the ceramic body; forming a first inner groove in the first end surface of the sintered ceramic body and a second inner groove in the second end surface of the sintered ceramic body along the first direction by irradiation with short-pulse laser, to cause the first internal electrodes and the second internal electrodes to respectively protrude in the first inner groove and the second inner groove; and forming a first external electrode on the first end surface and a second external electrode on the second end surface, the first end surface including the first inner groove, the second end surface including the second inner groove.

The short-pulse laser may include one of pico-second laser and femto-second laser.

In this configuration, the irradiation with short-pulse laser allows the first inner groove and the second inner groove to be formed, the first internal electrodes and the second internal electrodes respectively protruding in the first inner groove and the second inner groove. This can produce a multi-layer ceramic capacitor in which electrical conduction between the first internal electrodes and the first external electrode and between the second internal electrodes and the second external electrode is ensured.

The first external electrode and the second external electrode may be formed by sputtering.

In this configuration, the first external electrode and the second external electrode can be formed without using a wet process.

The first inner groove and the second inner groove may be formed after the sintered ceramic body is reoxidized.

In this configuration, the ceramic body is reoxidized, and thus a multi-layer ceramic capacitor having a large capacitance is easily obtained. Further, even if the first internal electrodes are oxidized in a region adjacent to the first end surface and the second internal electrodes are oxidized in a region adjacent to the second end surface at the time of reoxidation of the ceramic body, the first inner groove and the second inner groove are subsequently formed, so that the first internal electrodes and the second internal electrodes can be exposed. With this configuration, electrical conduction between the first internal electrodes and the first external electrode and between the second internal electrodes and the second external electrode can be ensured.

It is possible to provide a multi-layer ceramic capacitor and a method of producing the same, which are capable of ensuring electrical conduction between an internal electrode and an external electrode.

DETAILED DESCRIPTION OF EMBODIMENTS

In the figures, an X axis, a Y axis, and a Z axis orthogonal to one another are shown as appropriate. The X axis, the Y axis, and the Z axis are common in all figures.

1. Basic Configuration of Multi-layer Ceramic Capacitor10

FIGS. 1 to 3each show a multi-layer ceramic capacitor10according to one embodiment of the present invention.FIG. 1is a perspective view of the multi-layer ceramic capacitor10.FIG. 2is a cross-sectional view of the multi-layer ceramic capacitor10taken along the A-A′ line inFIG. 1.FIG. 3is a cross-sectional view of the multi-layer ceramic capacitor10taken along the B-B′ line inFIG. 1.

The multi-layer ceramic capacitor10includes a ceramic body11, a first external electrode14, and a second external electrode15. The ceramic body11has a first end surface E1and a second end surface E2that are oriented in an X-axis direction, two side surfaces oriented in a Y-axis direction, and two main surfaces oriented in a Z-axis direction. Ridges connecting the respective surfaces of the ceramic body11are chamfered.

It should be noted that the shape of the ceramic body11is not limited to the shape as described above. In other words, the ceramic body11does not need to have the rectangular shape as shown inFIGS. 1 to 3. For example, the surfaces of the ceramic body11may be curved surfaces, and the ceramic body11may be rounded as a whole.

The first external electrode14covers the first end surface E1of the ceramic body11. The second external electrode15covers the second end surface E2of the ceramic body11. The first external electrode14and the second external electrode15face each other in the X-axis direction with the ceramic body11therebetween and function as terminals of the multi-layer ceramic capacitor10.

The first external electrode14and the second external electrode15are each formed of a good conductor of electricity. Examples of the good conductor of electricity forming the first external electrode14and the second external electrode15include a metal mainly containing copper (Cu), nickel (Ni), tin (Sn), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), or the like, and an alloy of those metals.

The first external electrode14and the second external electrode15respectively extend from the first end surface E1and the second end surface E2of the ceramic body11and slightly come around the side surfaces. With this configuration, the first external electrode14and the second external electrode15each have a U-shaped appearance when viewed from the Y-axis direction. Further, the first external electrode14and the second external electrode15each have a U-shaped cross section parallel to an X-Z plane.

It should be noted that the shapes of the first external electrode14and the second external electrode15are not limited to the shapes shown inFIG. 1. For example, the first external electrode14and the second external electrode15may respectively extend from the first end surface E1and the second end surface E2of the ceramic body11to one of the main surfaces such that each cross section parallel to the X-Z plane has an L shape. Further, the first external electrode14and the second external electrode15may extend to the side surface(s) by the extension amount equal to the extension amount to the main surface. Furthermore, the first external electrode14and the second external electrode15may respectively remain within the first end surface E1and the second end surface E2without extending to the main and side surfaces of the ceramic body11.

The ceramic body11is formed of dielectric ceramics. The ceramic body11includes first internal electrodes12and second internal electrodes13that are covered with dielectric ceramics. The first internal electrodes12and the second internal electrodes13each have a sheet-like shape extending along an X-Y plane and are alternately disposed along the Z-axis direction.

In other words, the first internal electrode12and the second internal electrode13face each other in the Z-axis direction with the ceramic layer therebetween. The first internal electrodes12are drawn to the first end surface E1of the ceramic body11and connected to the first external electrode14. The second internal electrodes13are drawn to the second end surface E2of the ceramic body11and connected to the second external electrode15.

The first internal electrodes12and the second internal electrodes13are each formed of a good conductor of electricity and function as internal electrodes of the multi-layer ceramic capacitor10. Examples of the good conductor of electricity forming the first and second internal electrodes12and13include a metal mainly containing nickel (Ni), copper (Cu), palladium (Pd), platinum (Pt), silver (Ag), gold (Au), or the like, and an alloy of those metals.

In the ceramic body11, in order to increase capacitances of the respective ceramic layers provided between the first internal electrodes12and the second internal electrodes13, dielectric ceramics having a high dielectric constant is used. Examples of the dielectric ceramics having a high dielectric constant include a material having a Perovskite structure containing barium (Ba) and titanium (Ti), which is typified by barium titanate (BaTiO3).

It should be noted that the ceramic layers may be formed of a strontium titanate (SrTiO3) based material, a calcium titanate (CaTiO3) based material, a magnesium titanate (MgTiO3) based material, a calcium zirconate (CaZrO3) based material, a calcium zirconate titanate (Ca(Zr,Ti)O3) based material, a barium zirconate (BaZrO3) based material, a titanium oxide (TiO2) based material, or the like.

With the configuration described above, when a voltage is applied between the first external electrode14and the second external electrode15in the multi-layer ceramic capacitor10, the voltage is applied to the plurality of ceramic layers between the first internal electrodes12and the second internal electrodes13. This allows the multi-layer ceramic capacitor10to store charge corresponding to the voltage applied between the first external electrode14and the second external electrode15.

It should be noted that the basic configuration of the multi-layer ceramic capacitor10according to this embodiment is not limited to that shown inFIGS. 1 to 3and can be changed as appropriate. For example, the number of first internal electrodes12and second internal electrodes13and the thickness of each ceramic layer can be determined as appropriate according to the size and performance expected for the multi-layer ceramic capacitor10.

2. Detailed Configuration of Multi-layer Ceramic Capacitor10

FIG. 4is a perspective view of the ceramic body11of the multi-layer ceramic capacitor10. In the ceramic body11, the first end surface E1includes first inner grooves16, and the second end surface E2includes second inner grooves17. The first inner grooves16and the second inner grooves17are formed as grooves recessed in the X-axis direction and linearly extending along the Z-axis direction.

The three first inner grooves16and the three second inner grooves17are respectively disposed on the first end surface E1and the second end surface E2at mirror-symmetrical positions with intervals therebetween in the Y-axis direction. The first inner grooves16extend over the entire width of the first end surface E1in the Z-axis direction so as to pass through all the end portions of the first internal electrodes12in the first end surface E1, the end portions being in the X-axis direction. The second inner grooves17extend over the entire width of the second end surface E2in the Z-axis direction so as to pass through all the end portions of the second internal electrodes13in the second end surface E2, the end portions being in the X-axis direction.

FIG. 5is a cross-sectional view of the ceramic body11taken along the C-C′ line inFIG. 4. In other words,FIG. 5shows a cross section along the first inner groove16and the second inner groove17in the ceramic body11. Each of the first internal electrodes12includes a first protrusion12athat is formed in the first inner groove16. Each of the second internal electrodes13includes a second protrusion13athat is formed in the second inner groove17.

FIG. 6is an enlarged partial cross-sectional view of a region P surrounded by a chain line ofFIG. 5. The first protrusions12aprotrude in the X-axis direction and are exposed in the first inner groove16. In a similar manner, the second protrusions13aprotrude in the X-axis direction and are exposed in the second inner groove17.

With this configuration, the first external electrode14can be reliably electrically connected to the first protrusions12aexposed to the first end surface E1, and the second external electrode15can be reliably electrically connected to the second protrusions13aexposed to the second end surface E2. In other words, in the multi-layer ceramic capacitor10, electrical conduction between the first internal electrodes12and the first external electrode14and between the second internal electrodes13and the second external electrode15can be ensured at least in the first inner grooves16and the second inner grooves17, respectively.

Further, as shown inFIG. 1, the first external electrode14of the multi-layer ceramic capacitor10includes outer grooves18along the first inner grooves16of the ceramic body11, and the second external electrode15of the multi-layer ceramic capacitor10includes outer grooves19along the second inner grooves17of the ceramic body11. The outer grooves18emerge when the shapes of the first inner grooves16in the first end surface E1of the ceramic body11are reflected in the shape of the first external electrode14. The outer grooves19emerge when the shapes of the second inner grooves17in the second end surface E2of the ceramic body11are reflected in the shape of the second external electrode15.

FIG. 7is a diagram showing a state where the multi-layer ceramic capacitor10is mounted.FIG. 7shows a state where the multi-layer ceramic capacitor10is viewed from the first external electrode14side in the X-axis direction.FIG. 7shows the first external electrode14, but the same holds true for the second external electrode15.FIG. 7shows the position of the ceramic body11by a broken line.

The multi-layer ceramic capacitor10is mounted on a mount substrate100including a base material101and an electrode102formed thereon. The multi-layer ceramic capacitor10is heated in a reflow furnace or the like, with the first external electrode14and the second external electrode15being disposed on the electrode102of the mount substrate100via solder S.

In such a manner, the molten solder S wet-spreads on both the electrode102of the mount substrate100and the first and second external electrodes14and15of the multi-layer ceramic capacitor10. At that time, in the first external electrode14and the second external electrode15, as shown inFIG. 7, the molten solder S wets up in the Z-axis direction along the outer grooves18and19by a capillary phenomenon.

Due to such behavior of the solder5, regions connected to the solder S in the first external electrode14and the second external electrode15are expanded in the Z-axis direction. As a result, the connection strength of the solder S to the first and second external electrodes14and15is increased. Therefore, in the multi-layer ceramic capacitor10, the action of the outer grooves18and19improves mounting reliability.

Further, it is necessary to use a large amount of solder S so as to cause the solder S to sufficiently wet up in the Z-axis direction over the entire regions of the first external electrode14and the second external electrode15, but the configuration using the outer grooves18and19can improve the connection strength with a small amount of solder S. Therefore, in the multi-layer ceramic capacitor10, the improvement of the mounting reliability can be achieved at low cost.

It should be noted that in the multi-layer ceramic capacitor10, the configuration in which the first external electrode14includes the outer grooves18and the second external electrode15includes the outer grooves19is not indispensable. Therefore, if the effect as described above is not particularly expected, the first external electrode14does not need to include the outer grooves18, the second external electrode15does not need to include the outer grooves19, and the first and second external electrodes14and15can have flat and smooth surfaces.

3. Method of Producing Multi-layer Ceramic Capacitor10

FIG. 8is a flowchart showing a method of producing the multi-layer ceramic capacitor10.FIGS. 9 to 16Care views each showing a production process of the multi-layer ceramic capacitor10. Hereinafter, the method of producing the multi-layer ceramic capacitor10will be described alongFIG. 8with reference toFIGS. 9 to 16Cas appropriate.

3.1 Step S01: Production of Ceramic Body

In Step S01, an unsintered ceramic body11is produced. As shown inFIG. 9, the unsintered ceramic body11is obtained by laminating a plurality of ceramic sheets in the Z-axis direction and performing thermocompression bonding thereon. An electrically conductive paste with a predetermined pattern is printed on each of the ceramic sheets in advance, so that the first internal electrodes12and the second internal electrodes13can be disposed.

In Step S02, the unsintered ceramic body11obtained in Step S01is sintered. When a barium titanate based material is used as dielectric ceramics, the sintering temperature can be set to approximately 1,000 to 1,300° C. Further, the ceramic body11can be sintered under a reduction atmosphere or a low-oxygen partial pressure atmosphere, for example.

FIG. 10is a perspective view of the ceramic body11after sintering. The first internal electrodes12and the second internal electrodes13have a larger shrinkage amount than the dielectric ceramics at the time of sintering. For that reason, at the time of sintering, the first internal electrodes12and the second internal electrodes13are respectively recessed inward in the X-axis direction from the first end surface E1and the second end surface E2and are not exposed respectively to the first end surface E1and the second end surface E2in some cases.

In other words, as shown inFIG. 11, a void D1may be formed between each first internal electrode12and the first end surface E1. Similarly, a void D1may also be formed between each second internal electrode13and the second end surface E2. In such a case, the first external electrode14and the second external electrode15respectively have difficulty in being electrically connected to the first internal electrodes12and the second internal electrodes13in the first end surface E1and the second end surface E2.

However, in the production method according to this embodiment, even if the voids D1are formed in this Step S02, electrical conduction between the first internal electrodes12and the first external electrode14and between the second internal electrodes13and the second external electrode15can be ensured by providing the first inner grooves16and the second inner grooves17respectively to the first end surface E1and the second end surface E2of the ceramic body11in Step S04(short-pulse laser irradiation) that will be described later.

In Step S03, the ceramic body11sintered in Step S02is reoxidized. In Step S03, the dielectric ceramics forming the sintered ceramic body11is supplemented with oxygen because of the lack of oxygen. This can increase the capacitance of the multi-layer ceramic capacitor10. It should be noted that Step S03may be omitted as appropriate.

The ceramic body11can be reoxidized by heating at approximately 600 to 1,000° C. under an oxidizing atmosphere, for example. The reoxidation of the ceramic body11may lead to the oxidation of the end portions of the first and second internal electrodes12and13in the X-axis direction, the end portions being exposed to the first and second end surfaces E1and E2of the ceramic body11.

In other words, as shown inFIG. 12, oxidized regions D2may be formed at the end portions of the first internal electrodes12in the X-axis direction. Similarly, oxidized regions D2may also be formed at the end portions of the second internal electrodes13in the X-axis direction. In this case, because the oxidized regions D2do not have electrical conductivity, the first external electrode14and the second external electrode15respectively have difficulty in being electrically connected to the first internal electrodes12and the second internal electrodes13in the first end surface E1and the second end surface E2.

However, in the production method according to this embodiment, even if the oxidized regions D2are formed in this Step S03, electrical conduction between the first internal electrodes12and the first external electrode14and between the second internal electrodes13and the second external electrode15can be ensured by providing the first inner grooves16and the second inner grooves17respectively to the first end surface E1and the second end surface E2of the ceramic body11in Step S04(short-pulse laser irradiation) that will be described later.

In Step S04, the first end surface E1and the second end surface E2of the ceramic body11reoxidized in Step S03are irradiated with short-pulse laser having a short pulse width, to form the first inner grooves16and the second inner grooves17. Using the short-pulse laser, the material forming the first and second end surfaces E1and E2of the ceramic body11can be sublimated.

Specifically, the short-pulse laser used in Step S04can be selected from various types of pulse laser having a pulse width in a pico-second range or below the pico-second range. Examples of such short-pulse laser include pico-second laser having a pulse width in a pico-second range and femto-second laser having a pulse width in a femto-second range.

FIG. 13shows a state where a laser irradiation device200is irradiating the first end surface E1of the ceramic body11with short-pulse laser. The short-pulse laser is scanned as indicated by the arrow inFIG. 13, and the first inner grooves16can be formed in the first end surface E1. Further, the second inner grooves17can be formed in the second end surface E2in a similar manner to the above.

Operating conditions in the laser irradiation device200, such as a laser spot diameter, laser intensity, a scanning speed, and the number of times of repeating scanning, can be determined as appropriate such that the first inner grooves16and the second inner grooves17have the configuration shown inFIGS. 5 and 6. Specifically, the operating conditions of the laser irradiation device200can be determined such that the oxide selectively sublimates and the metal is difficult to sublimate in the first end surface E1and the second end surface E2according to the materials forming the ceramic layers and the first and second internal electrodes12and13, the shapes of the first and second end surfaces E1and E2of the ceramic body11, the width of the oxidized region D2, and the like.

Thus, in the first end surface E1and the second end surface E2, the oxidized regions D2formed in the dielectric ceramics and the first and second internal electrodes12and13selectively sublimate and are thus removed. Meanwhile, the first and second internal electrodes12and13formed of the metal are difficult to sublimate. Thus, the first protrusions12aof the first internal electrodes12and the second protrusions13aof the second internal electrodes13as shown inFIGS. 5 and 6are respectively formed in the first inner grooves16and the second inner grooves17.

It should be noted thatFIG. 13shows an example in which the short-pulse laser is scanned on the single ceramic body11. However, from the viewpoint of production efficiency,

Step S04is desirably performed in a state where the ceramic bodies11are arranged. Thus, the first inner grooves16and the second inner grooves17can be successively formed respectively in the first end surfaces E1and the second end surfaces E2of the ceramic bodies11.

3.5 Step S05: Formation of External Electrodes

In Step S05, the first external electrode14and the second external electrode15are formed on the ceramic body11in which the first inner grooves16and the second inner grooves17are formed in Step S04, to thus produce the multi-layer ceramic capacitor10shown inFIGS. 1 to 3. Hereinafter, Examples 1 to 3 of forming the first and second external electrodes14and15will be described, but the method of forming the first and second external electrodes14and15is not limited to those examples.

FIGS. 14A and 14Bare cross-sectional views showing the process of Example 1 of forming the first and second external electrodes14and15. As shown inFIG. 14A, first, a mask M is disposed in a region of the surface of the ceramic body11, in which the first external electrode14and the second external electrode15are not to be formed. As shown inFIG. 14B, sputtering is performed on the ceramic body11on which the mask M is disposed.

Thus, the first external electrode14and the second external electrode15that are formed of sputtering films are respectively formed on the first end surface E1and the second end surface E2of the ceramic body11. At that time, a metal film Ma is formed also on the mask M. The mask M is then removed from the ceramic body11together with the metal film Ma, so that the multi-layer ceramic capacitor10shown inFIGS. 1 to 3is obtained.

In the Example 1 of forming the first and second external electrodes14and15, the shapes of the first and second end surfaces E1and E2of the ceramic body11are likely to be reflected respectively in the shapes of the first and second external electrodes14and15by using sputtering. In other words, the outer grooves18and the outer grooves19(seeFIG. 1) are likely to emerge respectively on the first external electrode14and the second external electrode15where the first inner grooves16and the second inner grooves17formed on the first end surface E1and the second end surface E2of the ceramic body11are reflected.

In the Example 1 of forming the first and second external electrodes14and15, the first external electrode14and the second external electrode15are obtained by only a dry process without using a wet process such as electroplating. Therefore, since waste water or the like is not generated, an environmental load can be reduced. Additionally, in the multi-layer ceramic capacitor10, faults resulting from hydrogen absorption, infiltration or adherence of a plating solution, and the like do not occur.

Further, in the Example 1 of forming the first and second external electrodes14and15, the first external electrode14and the second external electrode15can be formed without performing heat treatment. Therefore, in the multi-layer ceramic capacitor10produced by using the Example 1 of forming the first and second external electrodes14and15, a characteristic composition distribution can be obtained, in which thermal diffusion is not caused between the first internal electrodes12and the first external electrode14and between the second internal electrodes13and the second external electrode15.

FIGS. 15A, 15B, and 15Care cross-sectional views showing the process of Example 2 of forming the first and second external electrodes14and15. First, an electrically conductive paste is applied to a region of the surface of the ceramic body11, in which the first external electrode14and the second external electrode15are to be formed. For the method of applying the electrically conductive paste, for example, a dip method or a printing method can be used.

The electrically conductive paste applied to the ceramic body11is then baked, to form an inner layer14aof the first external electrode14and an inner layer15aof the second external electrode15, which are shown inFIG. 15A. The electrically conductive paste can be baked under a reduction atmosphere or a low-oxygen partial pressure atmosphere, for example.

Next, as shown inFIG. 15B, a mask M is disposed in a region of the surface of the ceramic body11, in which the inner layers14aand15aare not formed. Subsequently, as shown inFIG. 15C, sputtering is performed on the ceramic body11on which the mask M is disposed, to form an outer layer14bof the first external electrode14and an outer layer15bof the second external electrode15.

This provides the first external electrode14having a double-layer structure of the inner layer14aand the outer layer14b, and the second external electrode15having a double-layer structure of the inner layer15aand the outer layer15b. Subsequently, the mask M is removed from the ceramic body11together with a metal film Ma formed on the mask M. Thus, the multi-layer ceramic capacitor10shown inFIGS. 1 to 3is obtained.

It should be noted that the outer layers14band15bof the first and second external electrodes14and15may be formed by a method other than sputtering and can also be formed by, for example, a wet plating method or a vapor-deposition method. Further, the first external electrode14may have a three-layer structure including an intermediate film between the inner layer14aand the outer layer14b, and the second external electrode15may have a three-layer structure including an intermediate film between the inner layer15aand the outer layer15b.Additionally, the first external electrode14and the second external electrode15may each have a structure including four layers or more.

FIGS. 16A, 16B, and 16Care cross-sectional views showing the process of Example 3 of forming the first and second external electrodes14and15. First, an electrically conductive paste is applied to regions of the first end surface E1and the second end surface E2of the ceramic body11, the first internal electrodes12and the second internal electrodes13being drawn to those regions. The electrically conductive paste applied to the ceramic body11is then baked, to form connection layers14cand15cshown inFIG. 16A.

Next, as shown inFIG. 16B, a mask M is disposed in a region of the surface of the ceramic body11, in which the first external electrode14and the second external electrode15are not to be formed, the connection layers14cand15cbeing formed on the ceramic body11. Subsequently, sputtering is performed on the ceramic body11on which the mask M is disposed, to form covering layers14dand15dshown inFIG. 16C.

This provides the first external electrode14including the connection layer14cand the covering layer14d, and the second external electrode15including the connection layer15cand the covering layer15d. Subsequently, the mask M is removed from the ceramic body11together with a metal film Ma formed on the mask M. Thus, the multi-layer ceramic capacitor10shown inFIGS. 1 to 3is obtained.

In the Example 3 of forming the first and second external electrodes14and15, the electrically conductive paste is baked to form the connection layers14cand15cbefore the covering layers14dand15dare formed. This improves connectivity of the first external electrode14to the first internal electrodes12and of the second external electrode15to the second internal electrodes13. With this configuration, electrical conduction between the first internal electrodes12and the first external electrode14and between the second internal electrodes13and the second external electrode15can be obtained more reliably.

Meanwhile, the regions where the connection layers14cand15care to be formed are limited to regions in the first and second end surfaces E1and E2of the ceramic body11, the first internal electrodes12and the second internal electrodes13being drawn to those regions. Thus, the thickness of the multi-layer ceramic capacitor10in the Z-axis direction can be suppressed. This configuration is advantageous in the increase in capacitance and the low profile of the multi-layer ceramic capacitor10.

4. Other Embodiments

While the embodiment of the present invention has been described, the present invention is not limited to the embodiment described above, and it should be appreciated that the present invention may be variously modified.

For example, in the multi-layer ceramic capacitor10, the number of first inner grooves16and second inner grooves17in the first and second end surfaces E1and E2of the ceramic body11can be optionally determined. However, from the viewpoint of reliability of electrical conduction between the first internal electrodes12and the first external electrode14and between the second internal electrodes13and the second external electrode15, the first end surface E1and the second end surface E2of the ceramic body11desirably include the plurality of first inner grooves16and the plurality of second inner grooves17, respectively.

Further, in the ceramic body11, the configuration of the first inner grooves16in the first end surface1and the configuration of the second inner grooves17in the second end surface E2may be different from each other. For example, in the ceramic body11, the number of first inner grooves16and that of second inner grooves17, the arrangement of the first inner grooves16and that of the second inner grooves17, the shapes of the first inner grooves16and those of the second inner grooves17, and the like may be different from each other.