KR100372687B1 - A method for manufacturing multilayer ceramic capacitor having low deviation in dielectric properties - Google Patents

Abstract

The present invention relates to the manufacture of multilayer ceramic capacitors; The purpose is to provide a method of manufacturing a multilayer ceramic capacitor which satisfies the X7R characteristics but has excellent dielectric properties and further has a very small variation in dielectric characteristics, thereby providing high reliability.

The present invention for achieving the above object is MgO: 0.5-4 mol, MnO: 0.01-0.5 mol, BaO: 0.1-2 mol, CaO: 0.1-2 mol, SiO ₂ : 1-4 mol per 100 mol of barium calcium titanate, V ₂ O ₅ and Cr ₂ O ₃ alone or in combination: 0.4 mol or less, and at least one component selected from the group consisting of Y ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ 0 ₃ and Er ₂ O ₃ : 0.1 to Prepare a powder to be formulated within a range of 3 moles, mix at least two or more of the powders, calcinate the mixed powder, pulverize the calcined powder and the pulverized powder and the remaining components of the barium calcium titanate BaCa _x After making a plurality of sheets by mixing with TiO ₃ (0.001≤x ≤0.02) and forming the inner electrode of Ni or Ni-based alloy in some sheets, and then alternately stacked between the sheet with the inner electrode and the sheet without the inner electrode Multilayer ceramic capacitance, which is formed by firing a ceramic laminate formed by And that the relates to a process for the preparation as a technological base.

Description

A method of manufacturing a multilayer ceramic capacitor having a low variation in dielectric characteristics {A METHOD FOR MANUFACTURING MULTILAYER CERAMIC CAPACITOR HAVING LOW DEVIATION IN DIELECTRIC PROPERTIES}

The present invention relates to the manufacture of a multilayer ceramic capacitor, and more particularly, to a method of manufacturing a multilayer ceramic capacitor having a very low reliability due to a very small variation in dielectric characteristics.

In general, as shown in FIG. 1, a multilayer ceramic capacitor is formed by stacking a ceramic dielectric layer 2a and a plurality of ceramic dielectric layers 2a and 2b on which an internal electrode 3 is printed, and at both ends thereof an external electrode 4. This is formed and configured. In order to reduce production cost, multilayer ceramic capacitors having such a structure have recently used base metals such as inexpensive Ni such as Ag and Pd instead of expensive precious metals such as Ag and Pd.

Recently, with the development of electronic technology, miniaturization of electronic components is rapidly progressing, and even in the case of multilayer ceramic capacitors having Ni internal electrodes, a large capacity and temperature stability of capacitance are required. In order for a multilayer ceramic capacitor using Ni as an electrode to satisfy large capacity and miniaturization, the dielectric layer must be further thinned and multilayered. However, when the dielectric layer is thinned, more high voltage is applied to the dielectric material, and when the conventional dielectric material is used, the lowering of the dielectric constant, the increase of the temperature dependence of the capacitance, and the stability of other characteristics often lead to deterioration. In particular, when the thickness of the dielectric layer is reduced to 5 μm or less, the number of ceramic particles between the internal electrodes decreases to 10 or less, making it difficult to assure stable characteristics.

On the other hand, barium titanate has been mostly used as a dielectric composition used in the dielectric layer of a capacitor. However, if barium titanate is fired in a reducing atmosphere, it is semiconducted during firing and loses its insulation resistance. Therefore, if the shell component having reduction resistance is not uniformly formed in all particles in the capacitor, the insulation resistance of the product may decrease and the life may be drastically reduced. Can be. In addition, even if a large shell is formed, when the thickness is very small, the barium titanate in the particles may be semiconductorized, thereby lowering the insulation resistance of the product and rapidly reducing the life.

In order to solve this problem, Korean Patent Laid-Open Publication No. 2000-17250 provides a capacitor having a Ni internal electrode using a starting material including barium calcium titanate, which has greatly improved reduction resistance compared to conventional barium titanate. Since barium calcium titanate has reduction resistance due to lattice defects formed by Ca replacing Ti sites, there is an advantage of maintaining high insulation resistance even when a shell is not formed or is thinly formed during the reduction atmosphere firing. The multilayer ceramic capacitor disclosed in the Korean patent publication uses a dielectric composition containing glass oxide as a subsidiary component of a starting material including (Ba _1-x Ca _x ) _m TiO ₂ . A multilayer ceramic capacitor is provided that satisfies the X7R characteristics specified in the standard and uses Ni as the internal electrode. In addition, the dielectric ceramic disclosed in the Republic of Korea Patent (Ba _1-x Ca _x ) _m TiO ₂ Re component (wherein Re is at least one or more selected from Y, Gd, Tb, Dy, Ho, Er and Yb) ), The core-shell structure present near the particle boundary and at the particle boundary is obtained by diffusion during firing.

However, since the multilayer ceramic capacitor uses a glass component as a subcomponent of the dielectric layer, it is difficult to control the rate at which the composition forming the shell having a high dielectric resistance but a low dielectric constant diffuses into the core, and thus the multilayer ceramic capacitor is laminated using such a dielectric composition. The dielectric property of the ceramic capacitor is rather low. In particular, the patent discloses Li ₂ O— (Si, Ti) O ₂ —MO based oxides (wherein MO is at least one selected from Al ₂ O ₃ and ZrO ₂ ), or SiO ₂ —TiO ₂ —XO. Oxide (XO is at least one selected from BaO, CaO, SrO, MgO, ZnO, and MnO), or Li ₂ OB ₂ O _3- (Si, Ti) O ₂ based, Al ₂ O ₃ -MO-B ₂ O Sintering aids are used, such as the _third system (MO is at least one selected from BaO, CaO, SrO, MgO, ZnO, MnO), and since these sintering aids form a liquid phase at low temperatures, almost all of them have a dielectric constant of less than 2000. There is a problem that can not provide a reliable large capacity multilayer ceramic capacitor. Furthermore, in manufacturing a multilayer ceramic capacitor that satisfies the X7R characteristic, when a plurality of subcomponents are mixed with a main component alone, a shell component formed in the particles in the product may be different. There is a problem in that the yield of the product is reduced because the deviation of the electrical characteristics is increased.

Therefore, the present invention has been proposed to solve such a conventional problem, and its object is to pretreat the sub-materials to more advantageously control the diffusion rate of the dielectric ceramic when manufacturing a multilayer ceramic capacitor using barium calcium titanate having excellent reduction resistance. Accordingly, the present invention provides a method of manufacturing a multilayer ceramic capacitor that satisfies the X7R characteristic and has excellent dielectric characteristics, and further has a very small variation in dielectric characteristics and high reliability.

1 is a cross-sectional view of a multilayer ceramic capacitor

Figure 2 is an exploded perspective view of the ceramic dielectric layer of Figure 1

Explanation of symbols on the main parts of the drawings

1 ..... multilayer ceramic capacitors 2a, 2b ..... ceramic dielectric layer

3 ..... Internal Electrode 4 ........... External Electrode

In the present invention for achieving the above object in the method of manufacturing a multilayer ceramic capacitor using barium calcium titanate as a starting material,

MgO: 0.5-4 mol, MnO: 0.01-0.5 mol, BaO: 0.1-2 mol, CaO: 0.1-2 mol, SiO ₂ : 1-4 mol, V ₂ O ₅ and Cr ₂ O per 100 mol of the barium calcium titanate ₃ alone or in combination: 0.4 mol or less, and at least one component selected from the group consisting of Y ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ 0 _3, and Er ₂ O ₃ : composition in the range of 0.1 to 3 mol Preparing a powder so as to mix at least two or more of the powders, and then calcining the mixed powder;

Pulverizing the calcined powder to mix the pulverized powder and the remaining components with the barium calcium titanate BaCa _x TiO ₃ (0.001 ≦ _x ≦ 0.02), and adding a binder and a solvent to prepare a slurry;

Forming a plurality of sheets by molding the prepared slurry, and then forming internal electrodes of Ni or Ni-based alloys on some sheets;

Alternately stacking the sheet on which the internal electrodes are formed and the sheet on which the internal electrodes are not formed to form a ceramic laminate, and firing the laminate; And

And forming an external electrode at both ends of the fired laminate to electrically connect with the internal electrode.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The manufacturing method of the capacitor according to the present invention can be applied regardless of the production of the multilayer ceramic capacitor, but is preferably very effective when applied to the production of a multilayer ceramic capacitor having a dielectric layer containing barium calcium titanate. Since barium calcium titanate forms a core-shell structure, the barium titanate has an advantage of greatly improving dielectric properties than conventional barium titanate.

Firstly, the present invention relates to Y ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ 0 ₃ and MgO, MnO, and CaO, SiO ₂ , and V ₂ O ₅ and Cr ₂ O ₃ powders as barium calcium titanate powder and its subsidiary materials. It is necessary to prepare at least one starting material powder selected from the group consisting of Er ₂ O ₃ . Specifically, in the present invention, MgO: 0.5-4 mol, MnO: 0.01-0.5 mol, BaO: 0.1-2 mol, CaO: 0.1-2 mol, SiO ₂ : 1-4 mol and V ₂ O ₅ per 100 mol of barium calcium titanate. And Cr ₂ O ₃ alone or in combination: 0.4 mol or less, and at least one component selected from the group consisting of Y ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ 0 _3, and Er ₂ O ₃ : 0.1-3 mol The powder is prepared to be formulated within the range.

Powders having these ingredients and compositions facilitate diffusion control in the shell of the capacitor dielectric layer and can significantly improve dielectric properties, in particular. Therefore, in the case of manufacturing a large-capacity multilayer ceramic capacitor using the dielectric ceramic composition of the present invention, the insulation resistance may be greatly improved and the dielectric constant of at least 2000 may be satisfied while satisfying the X7R characteristic.

Specifically, the reason for allowing the powders constituting the dielectric layer composition in the capacitor of the present invention to have the above composition is as follows.

First, in BaCa _x TiO ₃ which is a powder raw material for forming the dielectric layer in the capacitor according to the present invention, x is preferably used having a range of 0.001 to 0.02. This composition range is very advantageous for improving the reduction resistance of barium calcium titanate.

In the MgO powder contained in the dielectric layer of the capacitor of the present invention, the change of the capacitor capacity with temperature serves to satisfy the X7R characteristic. However, if too little MgO component is added, the X7R characteristic cannot be satisfied, and the change of capacitor capacity becomes large, and if a large amount is added, plasticity of the capacitor becomes difficult. For this reason, the MgO component is preferably added in the range of 0.5 to 4 mol based on 100 mol of barium calcium titanate. More preferably, the MgO component is added within the range of 0.5 to 3 mol based on 100 mol of barium calcium titanate.

In addition, the MnO powder acts on the change in the insulation resistance and capacitance of the capacitor over time, but if it is added too little, the insulation resistance of the capacitor is lowered. For the above reason, the MnO content is suitably added within the range of 0.01 to 0.5 mol per 100 mol of barium calcium titanate. More preferably, MnO content is added in the range of 0.05-0.2 mol per 100 mol of barium calcium titanate.

In addition, the BaO powder serves to control the rate at which the shell-forming compositions diffuse into the barium calcium titanate, and remain together in the shell portion to greatly improve dielectric resistance as well as dielectric resistance. In the present invention, the BaO content is suitably added within the range of 0.1 to 2.0 mol per 100 mol of barium calcium titanate. If the content of BaO is small, the insulation resistance of the capacitor is lowered. If the content of BaO is large, the firing of the capacitor is not preferable. More preferably, the BaO content is added within the range of 0.5 to 1.5 mol per 100 mol of barium calcium titanate.

In the manufacture of the capacitor of the present invention, CaO serves to control the rate at which the shell-forming compositions with BaO diffuse into the barium calcium titanate, and remain together in the shell portion to greatly improve dielectric resistance as well as dielectric resistance. At this time, the content of CaO is suitably added within the range of 0.1 to 2.0 mol per 100 mol of barium calcium titanate. If a small amount of CaO is added, the insulation resistance of the capacitor is lowered, and if a large amount of CaO is added, it is not preferable because plasticity of the capacitor is difficult. More preferably, the CaO content is added in the range of 0.5 to 1.5 mol per 100 mol of barium calcium titanate.

One of the other sintering aids, the SiO ₂ component, also serves to carry and retain the shell-forming composition in the shell portion of the barium calcium titanate. The content of SiO ₂ is suitably added within the range of 1 to 4 mol per 100 mol of barium calcium titanate. If a small amount of SiO ₂ is added, the firing of the capacitor is difficult, and if a large amount is added, the insulation resistance of the capacitor is lowered, which is not preferable. More preferably, the content of SiO ₂ is added within the range of 1.5 to 3 mol per 100 mol of barium calcium titanate.

The components of Y ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ or Er ₂ O ₃ contained in the dielectric layer of the capacitor of the present invention contribute to the extension of the accelerated life of the capacitor. Each of the above components is preferably added in the range of 0.1 to 3 moles based on 100 moles of barium calcium titanate. If less components are added, the life of the capacitor is shorter and the DC bias characteristics are worse. If more components are added, the dielectric constant is not only lowered but also difficult to fire. More preferably, the components are each added within the range of 0.5 to 2 mol per 100 mol of barium calcium titanate.

In addition, the V ₂ O ₅ and Cr ₂ O ₃ components contained in the dielectric layer in the capacitor of the present invention reduce the change in capacitor capacity with time. In the present invention, the V ₂ O ₅ and Cr ₂ O ₃ may be contained alone or in combination at 0.4 mol or less per 100 mol of barium calcium titanate. If more V ₂ O ₅ and Cr ₂ O ₃ are added, the insulation resistance of the capacitor is significantly lowered. More preferably, the V ₂ O ₅ and Cr ₂ O ₃ alone or in combination are contained in the range of 0.05 to 0.3 mol per 100 mol of barium calcium titanate.

The present invention is characterized by mixing at least two or more kinds of the powders prepared as described above and preliminary calcination. As in the present invention, if the starting material powder is calcined in advance, the dielectric composition remaining in the shell portion can be more uniformly distributed as compared with the conventional method of adding sub-materials without pretreatment, thereby greatly increasing the dielectric characteristic variation of the capacitor. Can be reduced.

In the case of the present invention, the calcination of the starting material powder may be calcined after mixing some powders of the raw material powder and then mixing the remaining powders as it is or mixing all the starting material powders. However, calcination of the starting material powder in the present invention is preferably performed at a temperature of 1000 ~ 1100 ℃. If the calcination temperature for the starting material is too low, the effect is insufficient, and if it is too high, there is a high possibility that the powder will partially melt and vitrify.

Then, the calcined powder is pulverized, and then the pulverized calcined raw powder and the barium calcium titanate are mixed, and an organic binder is added thereto to make a slurry.

Then, the slurry is molded into a sheet to prepare a green sheet.

Then, an internal electrode is formed of Ni or a Ni-based alloy on one surface of the green sheet, and the green sheet having the internal electrode is laminated as many as necessary.

Thereafter, the dielectric layer on which the internal electrode is formed and the dielectric layer on which the internal electrode is not formed are alternately laminated and pressurized to form a laminate, and the ceramic chip can be obtained by baking the laminate at a predetermined temperature in a reducing atmosphere. At this time, it is preferable to perform the temperature which bakes a ceramic chip in the range of 1250-1350 degreeC.

Finally, a pair of external electrodes are formed at both ends of the chip to electrically connect with the internal electrodes. In general, the external electrode is formed by baking or baking after applying the metal powder paste on both ends of the chip.

Hereinafter, the present invention will be described in detail through examples.

EXAMPLE

Each powder was mixed in a ratio of 1 mol of BaCO _{3, at} least 99.5% purity CaCO _{3, and} 0.001 to 0.02 mol of TiO ₂ , and then calcined at 1100 ° C. for 2 hours to prepare barium calcium titanate.

Comparative Example (1-12)

12 kinds of dielectric powders were prepared by simply mixing subsidiary ingredients in 100 mol of prepared barium calcium titanate as shown in Table 1, and a polyvinyl butyral binder and a solvent such as ethanol were added to the mixture to make a slurry.

division Chemical composition (mol%) BaCa _x TiO ₃ MgO MnO BaO CaO SiO ₂ Y ₂ O ₃ Dy ₂ O ₃ Ho ₂ O ₃ Er ₂ O ₃ V ₂ O ₅ Cr ₂ O ₃ Dielectric a x = 0.001 2 0.1 0.5 0.5 2 1.0 - - - 0.07 0.2 Dielectric b x = 0.001 One 0.1 0.5 0.5 2 1.0 - - - 0.07 0.2 Dielectric c x = 0.001 2 0.1 0.5 1.0 2 1.0 - - - 0.07 0.2 Dielectric x = 0.005 2 0.1 0.5 0.1 2 1.0 - - - 0.07 0.2 Dielectric x = 0.005 4 0.1 0.5 0.1 2 1.0 - - - 0.07 0.2 Dielectric x = 0.005 2 0.1 0.5 0.5 2 1.0 - - - 0.07 0.2 Dielectric g x = 0.005 2 0.1 0.5 0.5 2 - 1.0 - - 0.07 0.2 Dielectric x = 0.005 2 0.1 0.5 0.5 2 - - 1.0 - 0.07 0.2 Dielectric i x = 0.005 2 0.1 0.5 0.5 2 - - - 1.0 0.07 0.2 Dielectric j x = 0.01 2 0.1 0.5 0.1 2 1.0 - - - 0.07 0.2 Dielectric k x = 0.01 2 0.1 0.5 0.5 2 1.0 - - - 0.07 0.2 Dielectric x = 0.02 2 0.1 0.5 0.1 2 1.0 - - - 0.07 0.2

After the slurry was molded into a sheet having a thickness of 20 µm, Ni internal electrodes were printed on the molded sheets, and chips were manufactured to have a capacity of about 100 GPa after firing in consideration of the dielectric constant of each composition. Then, after removing the part of the binder by heat-treating the prepared chip at 230 ~ 320 ℃, the heat-treated chip was fired for 2 hours at a temperature between 1250 ℃ to 1350 ℃. During firing, the Ni electrode was not oxidized by using a mixed gas of nitrogen, hydrogen, and water vapor. Then, the calcined chip was heat treated at a temperature of 900 ° C to 1100 ° C. Thereafter, both ends of the manufactured chip were polished, and external electrodes were applied to both ends of the chip to prepare a multilayer ceramic capacitor. The capacitance, dielectric loss, and insulation resistance of the multilayer ceramic capacitor thus prepared were measured, and the results are shown in Table 2.

The capacitance and dielectric loss were measured by applying an AC 1V of 1kHz at room temperature using an LCR meter, and the insulation resistance was measured by applying 50V, which is a DC rated voltage of the product, for 10 seconds.

division Dielectric type Capacitance Dielectric loss (%) Insulation Resistance Remarks Average Standard Deviation Average Standard Deviation Average Standard Deviation Comparative Example 1 a 103.9 5.00 1.42 0.17 7517 912 Simple mixing Comparative Example 2 b 103.6 4.58 1.53 0.17 7181 1420 Simple mixing Comparative Example 3 c 104.4 5.40 1.41 0.15 5434 1551 Simple mixing Comparative Example 4 d 106.4 5.34 1.41 0.11 7495 1473 Simple mixing Comparative Example 5 e 102.9 5.85 1.48 0.18 7188 2052 Simple mixing Comparative Example 6 f 105.8 5.49 1.40 0.15 6094 1427 Simple mixing Comparative Example 7 g 107.5 4.79 1.40 0.14 6243 1526 Simple mixing Comparative Example 8 h 104.8 5.10 1.39 0.18 5571 1313 Simple mixing Comparative Example 9 i 106.8 4.58 1.36 0.14 6155 1151 Simple mixing Comparative Example 10 j 103.5 4.90 1.41 0.15 7019 1328 Simple mixing Comparative Example 11 k 102.3 4.86 1.39 0.16 4616 1178 Simple mixing Comparative Example 12 l 104.4 4.65 1.28 0.16 7104 1420 Simple mixing

As can be seen from Table 2, the multilayer ceramic capacitor satisfies the X7R characteristic specification defined by the EIA standard, but shows a slight variation in capacitance, dielectric loss, and insulation resistance.

Invention Example (1-14)

To 100 mol of the barium calcium titanate prepared above were mixed the sub-materials in the ratio as shown in Table 1, and the mixture was calcined for 2 hours at 1050 ℃ in advance. Then, the calcined powder was ground and mixed with the remaining uncalcined powder and barium calcium titanate, and a slurry was prepared by putting a polyvinyl butyral binder and a solvent such as ethanol into the mixture to form a slurry. A multilayer ceramic capacitor was manufactured by the method. In Table 3, Inventive Examples (1) (2) (5) (6) and (12-14) were calcined by mixing only MgO, BaO, CaO, and SiO ₂ powders, and the other powders were not calcined. Honor (3) (4) and (7-11) are cases where all of the subsidiary powder is calcined.

division Dielectric type Capacitance (Cp) Dielectric loss (DF) Insulation Resistance Remarks Average Standard Deviation Average Standard Deviation Average Standard Deviation Inventive Example 1 a 104.9 3.35 1.39 0.12 7130 697 Some calcination Inventive Example 2 b 103.1 3.26 1.33 0.20 7203 835 Some calcination Inventive Example 3 a 105.5 4.56 1.35 0.13 6286 1032 Calculate all Inventive Example 4 c 108.8 4.06 1.42 0.15 6039 915 Calculate all Inventive Example 5 d 105.2 3.11 1.40 0.10 7549 1053 Some calcination Inventive Example 6 e 101.4 3.42 1.39 0.10 7363 930 Some calcination Inventive Example 7 d 106.7 4.09 1.35 0.11 5670 1160 Calculate all Inventive Example 8 f 104.0 4.07 1.39 0.17 6021 806 Calculate all Inventive Example 9 g 104.8 2.92 1.39 0.14 5974 860 Calculate all Inventive Example 10 h 107.3 3.76 1.39 0.14 6229 1037 Calculate all Inventive Example 11 i 106.5 3.93 1.38 0.14 5913 1252 Calculate all Inventive Example 12 j 102.7 2.92 1.39 0.15 6630 747 Some calcination Inventive Example 13 k 103.5 3.47 1.31 0.16 4428 811 Some calcination Inventive Example 14 l 104.2 2.81 1.40 0.15 6696 794 Some calcination

As can be seen from Table 3, the multilayer ceramic capacitor according to the present invention is manufactured by the conventional method, which satisfies the X7R characteristic specification defined by the EIA standard, but the variation in capacitance, dielectric constant, and insulation resistance does not apply the present invention. It is very small compared to the case. That is, as in the present invention, when the calcined or partially calcined powder is used for the dielectric powder containing barium calcium titanate, the distribution of the composition of the dielectric shell can be uniformed, and as a result, the variation in the dielectric properties of the capacitor can be greatly reduced. have.

As described above, according to the manufacturing method according to the present invention, in the case of manufacturing a multilayer ceramic capacitor using barium calcium titanate having excellent reduction resistance, by pre-treating a part or all of the sub-materials to more advantageously control the diffusion rate of the dielectric ceramic In addition, it satisfies the X7R characteristic, but also has excellent dielectric properties, and further, a very small variation in dielectric properties provides an effective multilayer ceramic capacitor.

Claims (3)

In the method of manufacturing a multilayer ceramic capacitor using barium calcium titanate as a starting material, MgO: 0.5-4 mol, MnO: 0.01-0.5 mol, BaO: 0.1-2 mol, CaO: 0.1-2 mol, SiO ₂ : 1-4 mol, V ₂ O ₅ and Cr ₂ O per 100 mol of the barium calcium titanate ₃ alone or in combination: 0.4 mol or less, and at least one component selected from the group consisting of Y ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ 0 _3, and Er ₂ O ₃ : composition in the range of 0.1 to 3 mol Preparing a powder so as to mix at least two or more of the powders, and then calcining the mixed powder; Pulverizing the calcined powder to mix the pulverized powder and the remaining components with the barium calcium titanate BaCa _x TiO ₃ (0.001 ≦ _x ≦ 0.02), and adding a binder and a solvent to prepare a slurry; Forming a plurality of sheets by molding the prepared slurry, and then forming internal electrodes of Ni or Ni-based alloys on some sheets; Alternately stacking the sheet on which the internal electrodes are formed and the sheet on which the internal electrodes are not formed to form a ceramic laminate, and firing the laminate; And Forming an external electrode at both ends of the fired laminate so as to be electrically connected with the internal electrode. The method of claim 1, wherein the calcination of the powder is performed at a temperature of 1000 ~ 1100 ℃. The method according to claim 1, wherein the laminate is fired at a temperature of 1250 to 1350 ° C.