JP2001220224A - Dielectric ceramic and laminated ceramic electric part - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a dielectric ceramic having a high dielectric constant and a high insulation resistance, and further to provide a laminated ceramic capacitor good in both characteristics and reliability. SOLUTION: This dielectric ceramic consists essentially of BaTiO3, and contains dielectric ceramic particles 1, having cores 2 in a ferroelectric phase, and shells 3 formed so as to surround the core 2 and containing Mg and a rare earth element dispersed, in the BaTiO3. In short, the dielectric ceramic particle has a core-shell particle structure. The ratio d/D of the depth d from the surface of the dielectric ceramic particle 1, to the average diameter D of the dielectric ceramic particle 1 is regulated so as to be 0.03<=d/D<=0.3.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric ceramic used as a laminated body of a multilayer ceramic capacitor, and more particularly to a dielectric ceramic having a core-shell particle structure capable of obtaining a capacitor having good B temperature characteristics. The present invention relates to a dielectric ceramic having a high dielectric constant and a high insulation resistance.

[0002]

2. Description of the Related Art BaTi used for multilayer capacitors and the like
In a dielectric ceramic mainly composed of O ₃ , in order to obtain a capacitor having good B temperature characteristics, a core and a shell surrounding the core coexist in crystal grains of the dielectric ceramic. -It is considered effective to have a shell particle structure. In this core-shell particle structure, Mg or a rare earth element is added to form the shell on the surface of the dielectric ceramic particles.

[0003] Conventional cores to which Mg or rare earth elements are added
In a dielectric porcelain having a shell particle structure, Mg and rare earth elements are added at a time, and the Mg and rare earth elements are mixed and diffused in the shell. Conventionally, no special control is performed on the distribution of Mg and rare earth elements in the shell, and Mg and rare earth elements are diffused to relatively deep portions of the dielectric particles.

[0004]

However, the dielectric ceramic composed of dielectric particles having a core-shell particle structure effective for improving the B temperature characteristic as described above has a sufficiently high dielectric constant. In addition, a dielectric ceramic having good withstand voltage could not be obtained. With the increase in capacitance of multilayer ceramic capacitors, the thickness of dielectric layers has been reduced, and accordingly, the required quality level has become extremely high. However, the conventional dielectric ceramic cannot sufficiently improve the quality of the multilayer ceramic capacitor.

The present invention has been made in view of the above-mentioned problems in a conventional dielectric ceramic having a core-shell particle structure, and has been developed to obtain a dielectric ceramic having a high dielectric constant and a high insulation resistance, and having both characteristics and reliability. It is an object of the present invention to manufacture a good multilayer ceramic capacitor.

[0006]

According to the present invention, there is provided a dielectric ceramic having a core-shell particle structure for producing a multilayer ceramic capacitor having the above-mentioned B temperature characteristic. The resistance is equal to the average diameter D of the dielectric porcelain particles 1.
Was found to be related to the ratio d / D of the depth d from the surface, and this ratio d / D was set in an appropriate range.

That is, the dielectric porcelain according to the present invention has B
aTiO ₃ as a main component, a dielectric ceramic particle 1 is formed around a core 2 of a ferroelectric phase, and the core 2 is formed of BaTiO 3.
₃ has a shell _{3 in} which Mg and a rare earth element are diffused.
In short, the dielectric ceramic particles have a core-shell particle structure. In such a dielectric ceramic, the ratio d / D of the depth d of the shell 3 from the surface of the dielectric ceramic particle 1 to the average diameter D of the dielectric ceramic particle 1 is set to 0.03 ≦ d / D ≦
0.3.

The shell 3 has a higher resistance than the core 2,
If the depth is small, a dielectric ceramic having a sufficient insulation resistance cannot be obtained. In order to obtain a highly reliable multilayer ceramic capacitor even with a thin dielectric layer,
Assuming that the insulation resistance required for the dielectric porcelain is 500 MΩ or more, the ratio d / D between the depth d of the shell 3 from the surface of the dielectric porcelain particles 1 and the average diameter D of the dielectric porcelain particles 1 is 0. .
It is necessary to be 03 or more.

On the other hand, the core 2 has a higher dielectric constant than the shell 3, and the depth of the shell 3 is too deep.
Is small, a dielectric porcelain having a sufficient dielectric constant cannot be obtained. Assuming that the dielectric constant required for the dielectric ceramic is 3000 or more in order to obtain a multilayer ceramic capacitor having a required capacitance even in the case where the dielectric is made thinner, if the dielectric ceramic particles 1 of the shell 3 The ratio d / D of the average depth d from the surface to the average diameter D of the dielectric ceramic particles 1 is as follows:
It is necessary to be 0.3 or less. In other words, the average volume ratio between the shell 3 and the core 2 is 0.2 to 14.6.
It is necessary to

Further, the dielectric porcelain particles 1 having a core-shell particle structure have the following characteristics.
A grain boundary 4 where a glass component is precipitated is formed at a boundary portion of the shell 2. The vitreous grain boundaries 4 are formed in a liquid phase and have higher insulation resistance than other portions. And the core
In the dielectric porcelain having the shell particle structure, considering that the adjacent dielectric porcelain particles 1 are electrically connected in series, the grain boundary 4 having the highest resistance when an electric field is loaded.
Is locally applied with a high voltage.

Therefore, by making the grain boundaries 4 thicker,
A dielectric ceramic having high insulation resistance can be obtained. However, the grain boundary 4 has a lower dielectric constant than the core 2 and
Is too large, it is not possible to obtain a dielectric porcelain having a sufficient dielectric constant. As described above, the insulation resistance required for the dielectric porcelain is 500 MΩ or more, and the required dielectric constant is 30 MΩ.
If the ratio is not less than 00, the ratio t / D of the average thickness t of the grain boundaries 4 to the average diameter D of the dielectric ceramic particles 1 of the dielectric ceramic particles 1 is 0.005 ≦ t / D ≦ 0. .05.

Further, the multilayer ceramic electronic component according to the present invention using the above-described dielectric porcelain has a laminate 13 in which ceramic layers 17 and internal electrodes 15 and 16 are alternately laminated, and a laminate of the laminate 13. It has external electrodes 12 and 12 provided at the ends, and since the internal electrodes 15 and 16 reach the edge of the ceramic layer 17, the internal electrodes 15 and 16 are respectively led out to the end face of the laminate 13. , The same laminate 1
The internal electrodes 15, 16 led out to the end face 3 are connected to the external electrodes 12, 12, respectively. The ceramic layer 17 constituting the laminate 13 is made of the above-mentioned dielectric ceramic. As a result, a multilayer ceramic electronic component having excellent characteristics as described above can be obtained.

[0013]

Embodiments of the present invention will now be described specifically and in detail with reference to the drawings.
FIG. 1 schematically shows the state of dielectric ceramic particles 1 in a dielectric ceramic having a core-shell particle structure according to the present invention.

As mentioned above, the dielectric porcelain according to the present invention
Is BaTiO_Three, And dielectric porcelain particles 1 are strongly attracted
A core 2 of an electric phase, formed around the core 2,
TiO _ThreeHas a shell 3 in which Mg and a rare earth element are diffused.
I do. Here, the diameter of the dielectric ceramic particles 1 is D, and the induction of the core 2 is
The depth from the surface of the electric porcelain particles 1 is d. In the present invention
Is the depth of the shell 3 from the surface of the dielectric ceramic particles 1
The ratio d / D of d to the average diameter D of the dielectric ceramic particles 1 is set to 0.
03 ≦ d / D ≦ 0.3.

Assuming that the depth d of the shell 3 from the surface of the dielectric ceramic particles 1 and the average diameter D of the dielectric ceramic particles 1, the volume of the shell 3 is π {D ^3- (D-2d) ³ }. / 6. The volume core 2, π (D-2d) is a ^3/6. Assuming that the volume ratio between the shell 3 and the core 2 is γ, γ
= {D ^3- (D-2d) ³ } / (D-2d) ³ = {1 /
(1-2d / D)} ³ -1 becomes, the ratio d / D is 0.03 ≦ between the average diameter D of the depth d and the dielectric ceramic particles 1 from dielectric ceramic particles 1 of the surface of the shell 3 When d / D ≦ 0.3, 0.20 ≦ γ ≦ 14.6.

A dielectric porcelain having such a core-shell particle structure contains BaTiO ₃ (barium titanate) as a main component, and MgO (magnesium oxide) or Ho ₂
It is obtained by adding O ₃ (holmium oxide) and other additives, mixing in a wet manner, molding and firing.
The portion of the core 2 is a portion having a high purity of BaTiO ₃ and a portion to be a ferroelectric phase. On the other hand, the portion of the shell 3 is a portion in which an additive such as MgO or Ho ₂ O ₃ diffuses into BaTiO ₃ .

The depth d of the shell 3 as described above
Can be adjusted by the temperature at which the dielectric porcelain is fired and the time for maintaining the firing temperature. For example, if the temperature at which the dielectric porcelain is fired is low, additives such as Mg and rare earth elements are hardly solid-dissolved at the time of sintering, so that the diffusion of these oxides into the dielectric porcelain particles 1 is difficult. The depth d of the portion of the shell 3 having a high electric resistance is reduced.
On the other hand, if the temperature at which the dielectric porcelain is fired is high, additives such as Mg and rare earths are likely to be solid-dissolved at the time of sintering, so that the diffusion of these oxides into the dielectric porcelain particles 1 is difficult. The depth d of the portion of the shell 3 which is easy to perform and has high electric resistance is increased.

If the time during which the firing temperature is maintained during firing of the dielectric porcelain is short, it is difficult for additives such as Mg and rare earths to be solid-dissolved during firing. The depth d of the portion of the shell 3 having a high electric resistance is less likely to be diffused into the inside, and is small. In contrast,
If the time for maintaining the firing temperature when firing the dielectric porcelain is long, solidification of additives such as Mg and rare earths is likely to occur during firing, and the diffusion of these oxides into the dielectric porcelain particles 1 will occur. And the depth d of the portion of the shell 3 having high electric resistance is increased.

In the dielectric porcelain having the above-described core-shell particle structure, a grain boundary 4 having a high electric resistance in which a glass component is precipitated is formed at the boundary between the shells 2 of the adjacent dielectric porcelain particles 1. As described above, the average thickness t of the grain boundary 4
And the ratio t / D between the average diameter D of the dielectric ceramic particles 1 and
0.005 ≦ t / D ≦ 0.05.

Such a grain boundary 4 is obtained by adding a glass component such as SiO ₂ as an additive to the raw material of the dielectric porcelain,
The thickness t of the grain boundary 4 is adjusted by this addition amount. The grain boundary 4 has a high insulation resistance, but has a lower dielectric constant than the core 2.

Next, a multilayer ceramic capacitor and a method of manufacturing the same as an example of a multilayer ceramic electronic component using the above-described dielectric ceramic will be described. First, as described above, BaTiO ₃ (barium titanate) is used as a main component, and MgO (magnesium oxide) or Ho ₂ O
₃ Add (holmium oxide) and other additives, mix wet and dry. Thereafter, the mixed powder is uniformly dispersed in an organic binder such as ethyl cellulose dissolved in a solvent to prepare a ceramic slurry. This ceramic slurry is applied to a thin and uniform thickness on a base film such as a polyethylene terephthalate film or the like, and dried to form a film-shaped ceramic green sheet. Thereafter, the ceramic green sheet is cut into an appropriate size.

Next, two types of internal electrode patterns are printed on the cut ceramic green sheets using a conductive paste. For example, the conductive paste is Ni
And its alloys, Cu and its alloys, Ag, Pd, Ag-
With respect to 100% by weight of one kind of conductor powder selected from Pd and the like, ethyl cellulose, acrylic,
3 to 12% by weight of one selected from polyester or the like,
As a solvent, 80 to 120% by weight of one selected from butyl carbitol, butyl carbitol acetate, terpineol, ethyl cellosolve, hydrocarbon and the like is added,
Use what is uniformly mixed and dispersed.

Ceramic green sheets on which such internal electrode patterns are printed are alternately stacked, and ceramic green sheets on which both internal electrode patterns are not printed, so-called dummy sheets, are stacked on both sides.
These are pressed to obtain a laminate. Further, this laminate is cut into a vertical and horizontal lattice, and divided into individual unfired chip-like laminates. The internal electrodes described above are alternately led out to opposing end faces of the divided laminated body.

Next, a conductive paste for an external electrode is applied to both end surfaces of the unfired laminate from which the internal electrode patterns are led out and a part of the side surface of the laminate connected to the both end surfaces. ,dry. Then, by firing these laminates, the laminates are sintered, and the conductive paste forming the internal electrode pattern and the conductive paste applied to the ends of the laminate are baked.

Further, Sn or solder plating is applied to the conductor layer formed at the end of the laminate. Thus, a multilayer ceramic capacitor as shown in FIG. 2 is completed. This multilayer ceramic capacitor has a fired laminate 3 having a layer structure as shown in FIG. 3, and external electrodes 2 and 2 are formed at its ends as shown in FIG.

As shown in FIG. 3, the laminate 13 includes a dielectric ceramic layer 17 having internal electrodes 15 and 16.
17 are laminated, and the internal electrodes 15, 1
Are formed by stacking a plurality of ceramic layers 17 each having no 6 formed thereon. Such a laminate 13
The internal electrodes 15 and 16 facing each other via the ceramic layer 17 are alternately led out to both end surfaces of the laminate 13. Then, as shown in FIG.
The external electrodes 12 and 12 are connected to the internal electrodes 15 and 16 at both end surfaces of the laminate 13 alternately led out.
It is conducting. Here, the ceramic layers 17, 17
Are made of a dielectric ceramic having a core-shell particle structure as described above.

In the above example, a multilayer ceramic capacitor was described as the multilayer ceramic electronic component. However, the multilayer ceramic electronic component according to the present invention is also applicable to a composite component having a capacitor portion, for example, a multilayer ceramic LC composite component. And can be applied.

[0028]

Next, embodiments of the present invention will be described with specific numerical values. Example 1 In order to obtain a dielectric ceramic for a multilayer ceramic capacitor, BaTiO ₃ (barium titanate) having an average particle diameter of 0.4 μm was 94.2% by weight, MgO (magnesium oxide) was 0.8% by weight, Ho ₂ O ₃ (holmium oxide)
Of 1.0% by weight and 2.0% by weight of SiO ₂ (silicon oxide) as a sintering aid. This ceramic powder mixture was mixed in pure water for 15 hours using a ball mill and then dried. Further, water and an organic binder were added to the ceramic powder mixture to obtain a slurry.

This slurry was coated with a reverse coater to a thickness of 10 μm.
m green ceramic sheets. Next, after applying a conductive paste to this ceramic green sheet to form an internal electrode pattern, ten sheets were laminated. The obtained laminate was cut into a lattice to produce a number of laminate chips. Next, the laminated chip was fired in a reducing atmosphere at 1200 ° C. for 1.5 hours to obtain a laminated ceramic capacitor having a standard dimension length of 3.2 mm and an end face angle of 1.6 mm.

The dielectric ceramic constituting the multilayer chip of the multilayer ceramic capacitor comprises a large number of dielectric ceramic particles 1 as schematically shown in FIG. The dielectric ceramic particles 1 have a core 2 having a ferroelectric phase mainly composed of BaTiO ₃ at the center and a shell 3 of a paraelectric phase in which Mg and Ho are diffused in the surrounding BaTiO _3. It has a shell particle structure. Here, the average depth d of the shell 3 and the average diameter D of the dielectric ceramic particles 1 were measured, the ratio d / D was obtained, and the volume ratio between the core 2 and the shell 3 was obtained from this value. It is as shown in Document 4 in Table 1.

Further, as shown in Table 1, Samples 2, 3, 5 and 6 were obtained under the same conditions as Sample 4 except that only the baking temperature was changed. Further, as shown in Table 1, the dielectric ceramic was fired under the same conditions as in Sample 4 except that the firing temperature was 1050 ° C., but it was not sintered. This was designated as Sample 1 for convenience.

As shown in Table 1, the dielectric ceramics obtained as Samples 3 to 5 had a dielectric constant of 3070 to 3510, and all obtained dielectric constants of 3000 or more. Further, their insulation resistance is 520 to 810 MΩ, all of which are 500
MΩ or more. The d / D of these samples was 0.03
2 to 0.293, and is in the range of 0.03 to 0.30. The volume ratio between the shell 3 and the core 2 of these samples is
0.22 to 13.09, which is in the range of 0.20 to 14.6.

On the other hand, as shown in Table 1, Sample 1 in which the firing temperature was 1050 ° C. could not be sintered, and a sample whose characteristics were to be compared could not be obtained. Firing temperature 11
Sample 2 at 00 ° C. had a high dielectric constant of 3920, but the insulation resistance was 480 MΩ, which was less than 500 MΩ. The d / D of this sample 2 was less than 0.028 and 0.03, and the volume ratio between the shell 3 and the core 2 was 0.19,
Less than 0.20. Sample 6 at a firing temperature of 1300 ° C. had a high insulation resistance of 950 MΩ, but had a dielectric constant of 2860 or less than 3000. The d / D of this sample 2 exceeded 0.329 and 0.30, and the volume ratio between the shell 3 and the core 2 was 24.0.
It is over 14.6.

[0034]

[Table 1]

(Example 2) In the manufacturing process for obtaining the multilayer ceramic capacitor shown in Sample 1 of Table 1 of Example 1 above, as shown in Table 2, the time for maintaining the firing temperature of 1200 ° C was 0 hour, 0.5 hour,
The time was changed to 1.0 hour, 1.5 hours, 2.0 hours, and 2.5 hours, and the other conditions were the same as in the case of the multilayer ceramic capacitor shown in Sample No. 4 of Table 1 of Example 1 above. The multilayer ceramic capacitors shown as sample numbers 7 to 12 in FIG. 2 were obtained.

The structure of the dielectric ceramic constituting the multilayer chip of the multilayer ceramic capacitor has the core-shell particle structure described above with reference to FIG. Here, the average depth d of the shell 3 and the average diameter D of the dielectric ceramic particles 1 were measured,
The ratio d / D was determined, and the volume ratio between the core 2 and the shell 3 was determined from this value. The result is as shown in Table 2.

As shown in Table 2, the dielectric ceramics constituting Samples 8 to 11 have a dielectric constant of 3080 to 3910,
In each case, a dielectric constant of 3000 or more was obtained. In addition, these insulation resistances are 540 to 780 MΩ, all of which are 500 MΩ.
That was all. The d / D of these samples is between 0.033 and
0.299, which is in the range of 0.03 to 0.30.
The volume ratio between the shell 3 and the core 2 of these samples was 0.1.
23 to 14.39, which is in the range of 0.2 to 14.6.

On the other hand, as shown in Table 2, 1200
After reaching the sintering temperature of ° C., the sample 7 baked by lowering the temperature without maintaining the temperature had a high dielectric constant of 4230, but the insulation resistance was 380 MΩ, which was less than 500 MΩ. The d / D of this sample 2 was less than 0.027 and 0.03, and the volume ratio between the shell 3 and the core 2 was 0.18 and 0.1.
Less than 2. In addition, Sample 12 baked at a calcination temperature of 1200 ° C. for 2.5 hours has an insulation resistance of 900 MΩ.
High insulation resistance was obtained, but the dielectric constant was 2560 and 3
Less than 000. The d / D of this sample 2 is 0.3
21 and more than 0.30, and the volume ratio of the shell 3 to the core 2 is 20.79 and more than 14.6.

[0039]

[Table 2]

Example 3 A multilayer ceramic capacitor shown in Sample 16 of Table 3 was manufactured in the same manner as the multilayer ceramic capacitor shown in Sample No. 4 of Table 1 of Example 3 above. The amount of SiO ₂ added as a sintering aid to the ceramic mixture was 0.5% by weight, 1.0% by weight, 1.5% by weight, 2.5% by weight, 3.0% by weight, respectively.
The multilayer ceramic capacitors shown in Table 3 as Sample Nos. 13 to 15 and Sample Nos. 16 and 17 were obtained in the same manner except that the content was changed to 5.0 wt%.

The structure of the dielectric ceramic constituting the multilayer chip of the multilayer ceramic capacitor has the core-shell particle structure described above with reference to FIG. Here, the average depth d of the shell 3 and the average diameter D of the dielectric ceramic particles 1 were measured,
The ratio d / D was determined, and the volume ratio between the core 2 and the shell 3 was determined from this value. The d / D of all the samples shown in Table 3 was 0.037 to 0.2.
96, which is in the range of 0.03 to 0.30. Also,
The volume ratio of the shell 3 to the core 2 of these samples is 0.26 to
13.72, which is in the range of 0.2 to 14.6.

As shown in Table 3, the dielectric ceramics constituting Samples 14 to 17 had a dielectric constant of 3080 to 3910, and all obtained dielectric constants of 3000 or more. Further, their insulation resistance is 540 to 780 MΩ, all of which are 500
MΩ or more. The ratio t / D between the thickness of the grain boundary of these samples and the particle size of the dielectric ceramic particles is 0.005 to 0.03.
6, which is in the range of 0.005 to 0.05.

On the other hand, as shown in Table 3, in Sample 13 in which the amount of SiO ₂ added as a sintering aid was as small as 0.5% by weight, a high dielectric constant of 3840 was obtained. Was 450 MΩ, which was less than 500 MΩ. The t / D of this sample 2 is less than 0.002 and 0.005.
In addition, Sample 18 having a large amount of SiO ₂ added as a sintering aid of 5.0% by weight had a high insulation resistance of 800 MΩ, but had a dielectric constant of 2790 or less than 3000. . The t / D of this sample 2 exceeds 0.052 and 0.05.

[0044]

[Table 3]

[0045]

As described above, in the dielectric porcelain according to the present invention, when the dielectric particles have a core-shell particle structure excellent in the B temperature characteristic, a high dielectric constant and a high insulation resistance are obtained. You will be able to satisfy the request at the same time. Accordingly, it is possible to provide a multilayer ceramic capacitor having high capacitance and high reliability, which can cope with a thin ceramic layer such as a multilayer ceramic capacitor.

[Brief description of the drawings]

FIG. 1 is a cross-sectional view schematically showing a particle structure of a dielectric ceramic according to the present invention.

FIG. 2 is a partial cross-sectional perspective view showing an example of a multilayer ceramic capacitor according to the present invention made using the dielectric ceramic.

FIG. 3 is an exploded perspective view showing layers of the multilayer body of the example of the multilayer ceramic electronic component separately.

[Description of Signs] 1 porcelain particles 2 core 3 shell 4 grain boundary 12 external electrode 13 laminate 15 internal electrode 16 internal electrode 17 ceramic layer

 ────────────────────────────────────────────────── ─── Continuing on the front page (72) Inventor Kenji Yazawa 6-16-20 Ueno, Taito-ku, Tokyo Taiyo Denki Co., Ltd. F-term (reference) 4G031 AA06 AA11 BA09 BA12 CA03 CA05 5E001 AB03 AE01 AE02 AE05 AF06 5G303 AA01 AB05 AB11 CB03 CB35 CC08 DA04

Claims (4)

[Claims] 1. A core (2) mainly composed of BaTiO ₃ and having a dielectric ceramic particle (1) having a ferroelectric phase, and the core (2).
And a shell (3) formed around BaTiO ₃ and the additive diffused into BaTiO ₃ , wherein the average depth d of the shell (3) from the surface of the dielectric ceramic particles (1) is d.
And the ratio d / D of the average diameter D of the dielectric ceramic particles (1) to 0.
A dielectric ceramic, wherein 03 ≦ d / D ≦ 0.3. 2. The dielectric ceramic according to claim 1, wherein a volume ratio of the shell (3) and the core (2) is 0.20 to 14.6. 3. A grain boundary (4) in which a glass component is deposited at a boundary between shells (2) of adjacent dielectric ceramic particles (1), and an average thickness t of the grain boundary (4). The ratio t / D between the dielectric ceramic particles (1) and the average diameter D of the dielectric ceramic particles (1) satisfies 0.005 ≦ t / D ≦ 0.05. 3. The dielectric porcelain according to 2. 4. A ceramic layer (17) and an internal electrode (1).
A laminate (13) in which 5) and (16) are alternately laminated.
And external electrodes (12) and (12) provided at the ends of the laminate (13).
Since (16) reaches the edge of the ceramic layer (17), the internal electrodes (15),
A multilayer ceramic electronic component in which (16) is led out, and the internal electrodes (15) and (16) led out to the end face of the laminate (13) are connected to the external electrodes (12) and (12), respectively. 3. The multilayer ceramic electronic component according to claim 1, wherein the ceramic layer (17) constituting the multilayer body (13) is made of the dielectric ceramic according to claim 1.