WO2010021087A1

WO2010021087A1 - Dielectric ceramic and laminated ceramic capacitor

Info

Publication number: WO2010021087A1
Application number: PCT/JP2009/003458
Authority: WO
Inventors: 伴野晃一; 古賀朋美
Original assignee: 株式会社村田製作所
Priority date: 2008-08-21
Filing date: 2009-07-23
Publication date: 2010-02-25
Also published as: JP2011246284A

Abstract

Disclosed is a dielectric ceramic that has not only a high dielectric breakdown voltage but also a high permittivity ε. Also disclosed is a laminated ceramic capacitor that comprises the dielectric ceramic and is suitable for use in medium to high pressure applications. The dielectric ceramic is composed mainly of (Ba_xSr_yCa_z)TiO₃, wherein x, y, and z represent a molar ratio provided that x + y + z = 1. In a ternary composition diagram, (x, y, z) is located in a region surrounded by and on a line of a pentagon ABCDE defined by a point A (0.70, 0.00, 0.30), a point B (0.69, 0.02, 0.29), a point C (0.55, 0.10, 0.35), a point D (0.35, 0.15, 0.50), and a point E (0.50, 0.00, 0.50), provided that the point A, the point E, and the line segment AE are excluded. The laminated ceramic capacitor comprises a laminate and an external electrode provided on the outer surface of the laminate. The laminate comprises a plurality of dielectric ceramic layers and a plurality of internal electrode layers. The dielectric ceramic layers are formed of a dielectric ceramic having the above features.

Description

Dielectric ceramic and multilayer ceramic capacitors

The present invention generally relates to a dielectric ceramic and a multilayer ceramic capacitor formed using the dielectric ceramic, and more particularly to a dielectric ceramic and a multilayer ceramic capacitor suitable for use under a high electric field.

Some multilayer ceramic capacitors are used under a high voltage of, for example, 250 to 1000V. In this case, depending on the thickness of each dielectric ceramic layer, a high voltage of 25 to 100 kV / mm is applied as an electric field. Therefore, there is a concern that the dielectric ceramic layer may be dielectrically broken in such a multilayer ceramic capacitor for medium and high voltage applications.

As can be seen from the above-mentioned background, in a multilayer ceramic capacitor intended for medium and high voltage applications, the dielectric breakdown voltage (BDV: unit is kV / mm) is an important index. BDV refers to the value of an electric field that causes dielectric breakdown when the electric field is raised, and is due to a phenomenon that is completely different from the life in a load test.

An example of the dielectric ceramic is described in Japanese Patent No. 3323801 (hereinafter referred to as Patent Document 1). Patent Document 1 discloses a (Ca, Sr, Ba) (Zr, Ti) O ₃ -based dielectric ceramic. This dielectric ceramic has reduction resistance and achieves an improvement in BDV while improving the linearity of capacity-temperature characteristics and the quality factor Q.

Generally, a material having a high BDV has a low dielectric constant ε. The dielectric ceramic described in Patent Document 1 is no exception and achieves a BDV of 120 kV / mm or more, while the dielectric constant ε is as low as around 100. For this reason, it is disadvantageous for miniaturization of the multilayer ceramic capacitor.

Therefore, it is desired to develop a dielectric ceramic capable of giving high values for both BDV and dielectric constant ε.

Japanese Patent No. 3323801

Therefore, one object of the present invention is to provide a dielectric ceramic having not only a high dielectric breakdown voltage but also a high dielectric constant ε.

Another object of the present invention is to provide a multilayer ceramic capacitor configured using the above dielectric ceramic and suitable for medium to high voltage applications.

The dielectric ceramic according to the present invention, a main component _{_{_{(Ba x Sr y Ca z)}}} TiO 3 (x, y, z represent mole ratios, satisfy x + y + z = 1) , (x, y, z) in the ternary composition diagram, point A (0.70, 0.00, 0.30), point B (0.69, 0.02, 0.29), point C (0.55, 0.10, 0.35), point D (0.35, 0.15, 0.50) and within a region surrounded by a pentagon ABCDE composed of points E (0.50, 0.00, 0.50) and on a line (however, the points A, E, and AE are not included).

The dielectric ceramic of the present invention further comprises at least one rare earth selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. It is preferable to contain 1 mol part or more and 14 mol parts or less of the element with respect to 100 mol parts of the main component.

In the dielectric ceramic of the present invention, Mg, Mn and Si are further added in an amount of 0.1 mol part or more and 3.0 mol part or less, 0.5 mol part or more and 5 mol part or more with respect to 100 mol parts of the main component. It is preferable to contain 0.0 mol part or less and 1.0 mol part or more and 5.0 mol part or less.

A multilayer ceramic capacitor according to the present invention includes a multilayer body including a plurality of dielectric ceramic layers stacked, and a plurality of internal electrode layers each formed along a specific interface between the plurality of dielectric ceramic layers. And an external electrode formed on the outer surface of the laminate so as to be electrically connected to the plurality of internal electrode layers. The dielectric ceramic layer in the multilayer ceramic capacitor of the present invention is made of a dielectric ceramic having the above-described characteristics.

The multilayer ceramic capacitor of the present invention is advantageously applied to a multilayer ceramic capacitor whose electric field used is 25 kV / mm or more and 100 kV / mm or less and whose guaranteed breakdown voltage is 120 kV / mm or more.

In the dielectric ceramic according to the present invention, BaTiO ₃ , SrTiO _3, and CaTiO ₃ are not completely dissolved, and may be separated into three phases. Here, BaTiO ₃ alone has a low dielectric breakdown voltage, but has a high dielectric constant ε. On the other hand, CaTiO ₃ alone has a high dielectric breakdown voltage but a low dielectric constant ε. Therefore, by designing the composition in a region where BaTiO ₃ and CaTiO ₃ coexist, it is possible to draw out characteristics having both advantages. On the other hand, the dielectric constant ε and the breakdown voltage can be further improved by coexisting an appropriate amount of SrTiO ₃ .

As a result, according to the dielectric ceramic according to the present invention, for example, a dielectric breakdown voltage of 120 kV / mm or more can be ensured while obtaining a value of 500 or more for the dielectric constant ε.

In addition, as described above, when the dielectric ceramic according to the present invention further contains a rare earth element, the above-described dielectric constant ε and dielectric breakdown voltage can be further improved.

Furthermore, according to the dielectric ceramic according to the present invention, when a predetermined amount of Mg, Mn, and Si is contained, the above-described dielectric constant ε and dielectric breakdown voltage can be obtained even by firing in a reducing atmosphere. it can. Therefore, good characteristics can be ensured even in a multilayer ceramic capacitor including an internal electrode mainly composed of Ni.

1 is a cross-sectional view schematically showing a multilayer ceramic capacitor according to an embodiment of the present invention. It is a diagram showing the coordinates of the dielectric is a ceramic main component (Ba _x Sr _y Ca _z) in the ternary composition diagram of TiO ₃ of Ba-Sr-Ca (x, y, z) of the present invention.

As shown in FIG. 1, the multilayer ceramic capacitor 1 includes a multilayer body 2. The multilayer body 2 includes a plurality of laminated dielectric ceramic layers 3 and a plurality of

internal electrode layers

4 and 5 respectively formed along a plurality of specific interfaces between the plurality of dielectric ceramic layers 3. ing.

The

internal electrode layers

4 and 5 are preferably composed mainly of Ni. The

internal electrode layers

4 and 5 are formed so as to reach the outer surface of the multilayer body 2. The internal electrode layer 4 is drawn to the end face 6 on one side of the multilayer body 2. The internal electrode layer 5 is drawn out to the other end face 7 of the multilayer body 2. The

internal electrode layers

4 and 5 are alternately arranged inside the stacked body 2.

External electrodes 8 and 9 are formed on the outer surfaces of the laminate 2 on the end faces 6 and 7, respectively. The external electrodes 8 and 9 are formed, for example, by applying and baking a conductive paste mainly composed of Cu. One external electrode 8 is electrically connected to the internal electrode layer 4 on the end face 6, and the other external electrode 9 is electrically connected to the internal electrode layer 5 on the end face 7.

On the external electrodes 8 and 9, in order to improve the solderability, the

first plating films

10 and 11 made of Ni or the like and the second plating film made of Sn or the like thereon are further formed as necessary. 12 and 13 are formed, respectively.

In such a multilayer ceramic capacitor 1, the dielectric ceramic layer 3, a dielectric ceramic according to the present invention, _{_{_{i.e., (Ba x Sr y Ca z}}} ) TiO 3 (x, y, z represent mole ratios, x + y + z = 1) (x, y, z) in the ternary composition diagram, point A (0.70, 0.00, 0.30), point B (0.69, 0.02, 0.29), point C (0.55, 0.10, 0.35), point D (0.35, 0.15, 0.50) and point E (0.50, 0.00, 0.50) are within the region and line on the pentagon ABCDE (however, point A , Point E, and line AE are not included). Shows the (Ba _x Sr _y Ca _z) of _{TiO 3 (x, y, z} ) of the ternary composition diagram for explaining the coordinates and pentagon ABCDE in Figure 2.

In the main component of the dielectric ceramic, BaTiO ₃ , SrTiO ₃ , and CaTiO ₃ are not completely dissolved in each other and may be separated into three phases. And BaTiO ₃ alone has a low dielectric breakdown voltage (BDV) but a high dielectric constant ε. On the other hand, for CaTiO ₃ alone, BDV is high but ε is low. According to the inventor, it has been found that, when both of these coexist, both of the advantages of both can be obtained not by the average of both but by the synergistic effect of both. On the other hand, it was found that the dielectric constant ε and the dielectric breakdown voltage were further improved by coexisting an appropriate amount of SrTiO ₃ . The present invention has been made based on such knowledge of the inventors. According to the present invention, a BDV of 140 kV / mm can be obtained while obtaining a value of 500 or more for the dielectric constant ε, and a BDV of 120 kV / mm or more can be guaranteed at a minimum.

The dielectric ceramic constituting the dielectric ceramic layer 3 is further selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu. It is preferable that 1 to 14 mol parts of at least one rare earth element is contained with respect to 100 mol parts of the main component. Since such a rare earth element has an effect of enhancing the effect of the main component, both BDV and ε can be further improved by adding a predetermined amount of the rare earth element.

The dielectric ceramic constituting the dielectric ceramic layer 3 further contains Mg, Mn and Si in an amount of 0.1 to 3.0 mol parts and 0.5 to 5 mol, respectively, with respect to 100 mol parts of the main component. It is preferable to include 0.0 mol part and 1.0 to 5.0 mol part. Thus, when a predetermined amount of Mn, Mg, and Si is included, firing in a reducing atmosphere is required, and even in the multilayer ceramic capacitor 1 having Ni as a main component of the

internal electrodes

4 and 5, high BDV and high ε And good reliability can be secured.

As described above, when the dielectric ceramic constituting the dielectric ceramic layer 3 contains a rare earth element and / or Mn, Mg and Si in addition to the main component, the ceramic to be the dielectric ceramic layer 3 In the slurry prepared for forming the green sheet, in addition to BaTiO ₃ powder, SrTiO ₃ powder and CaTiO ₃ powder, rare earth oxide powder or carbonate compound powder and / or Mn, Mg and Si Powders such as oxides or carbonate compounds are added.

The dielectric ceramic according to the present invention may be substituted with Zr and / or Hf if Ti is 5 mol% or less. _{_{_{Further, (Ba x Sr y Ca z}}} ) / Ti molar ratio is 1 is around, in order to obtain stable properties, preferably about 0.950 to 1.025.

Next, experimental examples carried out to confirm the effects of the present invention will be described.

First, BaTiO ₃ powder, SrTiO ₃ powder and CaTiO ₃ powder synthesized by a solid phase method were prepared as starting materials for the main component. Also, as starting materials for the _{_{_{_{component, Y 2 O 3, La 2}}}} O 3, CeO 2, Pr 6 O 11, Nd 2 O 3, Sm 2 O 3, Eu 2 O 3, Gd 2 O 3, Tb 2 O ₃ , oxide powders of rare earth elements such as Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ and Lu ₂ O ₃ are prepared, and MgO, MnO, SiO ₂ , and (Ba _x sr _y Ca _z) / Ti were prepared BaCO ₃ powder and TiO ₂ powder for adjusting the molar ratio m of.

Next, in each sample, BaTiO ₃ powder, SrTiO ₃ powder and CaTiO ₃ powder prepared as described above were weighed so as to have the composition shown in Table 1, and these powders were mixed. Subcomponent raw material powders were added so as to have the composition shown in Table 1. In Table 1, the addition amount of each rare earth element, Mg, Mn and Si oxide powder is shown in mole parts relative to 100 mole parts of the main component. Next, the above-mentioned mixed powder was mixed in water for 16 hours with a ball mill using a PSZ medium having a diameter of 2 mm to obtain a sufficiently dispersed slurry. This slurry was dried to obtain a dielectric ceramic raw material powder.

Next, a polyvinyl butyral binder and ethanol were added to the raw material powder and mixed by a ball mill to obtain a ceramic slurry. This ceramic slurry was formed into a sheet by a doctor blade method to obtain a ceramic green sheet.

Next, a conductive paste film to be an internal electrode was formed on the ceramic green sheet by screen printing a conductive paste mainly composed of Ni. Then, the 11 ceramic green sheets on which the conductive paste film was formed were stacked so that the conductive paste films were exposed on the outer surface and the drawn sides were alternated to obtain a raw laminate. .

Next, the green laminate was heated to a temperature of 300 ° C. in a nitrogen gas atmosphere, after burning a _binder, in a reducing atmosphere composed of H 2 _-N 2 -H ₂ O gas, the 1150 ° C. The sintered laminated body was obtained by baking at temperature for 2 hours. This laminate includes a dielectric layer obtained by sintering a ceramic green sheet and an internal electrode layer obtained by sintering a conductive paste film.

Next, a conductive paste containing glass frit and containing Cu as a main component is applied to both end faces of the laminate, and is baked at a temperature of 800 ° C. in a nitrogen gas atmosphere to electrically connect the internal electrode layers. The external electrode connected to was formed, and further, the Ni plating film and the Sn plating film were formed on the external electrode, thereby obtaining each sample of the multilayer ceramic capacitor.

The outer dimensions of the multilayer ceramic capacitor of each sample thus obtained are 2.0 mm in length, 1.2 mm in width, and 0.5 mm in thickness. Met. In addition, the number of dielectric ceramic layers effective for forming a capacitance was 10, and the counter electrode area per dielectric ceramic layer was 1.3 mm ² .

The dielectric constant ε of the dielectric ceramic constituting the dielectric ceramic layer in each sample of the multilayer ceramic capacitor was determined from the capacitance of the multilayer ceramic capacitor measured under the conditions of 25 ° C., 1 kHz, and 1 V _rms . Further, the resistivity ρ of the dielectric ceramic constituting the dielectric ceramic layer was determined from the insulation resistance measured by charging a voltage of 300 V for 60 seconds at a temperature of 25 ° C. Also, a BDV (average value) was obtained by applying a DC voltage to the multilayer ceramic capacitor while increasing the voltage at a rate of 50 V / second.

Table 2 shows the dielectric constants ε, log ρ, and BDV obtained as described above. Table 2 also shows ε × (BDV) ² as an index for making it possible to quantitatively determine the compatibility between the dielectric constant ε and BDV.

As shown in Table 1, samples Nos. 1 to 11 are obtained by changing (x, y, z) in a composition not containing a rare earth element. Among these samples Nos. 1 to 11, samples (x, y, z) having sample numbers 4 to 8 in the range of the present invention obtain ε of 500 or more and BDV of 140 kV / mm or more. It can be seen that a BDV of 120 kV / mm, which is a measure for medium to high pressure, is guaranteed. As ε × (BDV) ² , it can be seen that a value of 1 × 10 ⁷ kV ² / mm ² or more is obtained. On the other hand, in the samples of sample numbers 1 to 3 and 9 to 11 where (x, y, z) is outside the scope of the present invention, both BDV and ε are not high, and ε × (BDV) ² is 1 × It can be seen that the value is less than 10 ⁷ kV ² / mm ² .

Samples Nos. 12 to 21 were evaluated by comparing the samples Nos. 4 to 8 with the effects of adding Dy as a rare earth element. According to the samples of Sample Nos. 12 to 21, both ε and BDV are improved compared to the samples of Sample Nos. 4 to 8, and this is noticeable in ε × (BDV) ² I understand.

Samples Nos. 24 to 28 are for evaluating the influence of the addition amount by changing the addition amount of the rare earth element Dy. It can be seen that ε and BDV equal to or higher than those of Samples 4 to 8 containing no rare earth element are obtained when the amount of rare earth element added is in the range of 1 to 14 mol parts.

Samples of sample numbers 22 to 23 are obtained by changing m, and samples of sample numbers 29 to 34 are obtained by changing the added amount of Mg, Mn, or Si. m is 0.95 to 1.025, Mg is 0.5 to 5.0 mol parts, Mn is 0.1 to 3.0 mol parts, Si is 1.0 to 5.0 mol parts, It can be seen that even in a multilayer ceramic capacitor fired in a reducing atmosphere, sufficient insulation and sufficient ε and BDV are obtained.

The samples with sample numbers 35 to 48 have been confirmed to be applicable to rare earth elements other than Dy.

It should be considered that the embodiments and examples disclosed herein are illustrative and non-restrictive in every respect. The scope of the present invention is shown not by the above embodiments and examples but by the scope of claims, and is intended to include all modifications and variations within the scope and meaning equivalent to the scope of claims.

Since not only a high dielectric breakdown voltage but also a dielectric ceramic having a high dielectric constant ε can be obtained, it is possible to provide a multilayer ceramic capacitor suitable for medium to high voltage applications used under a relatively high electric field.

DESCRIPTION OF SYMBOLS 1 Multilayer ceramic capacitor 2 Laminated body 3 Dielectric

ceramic layer

4,5 Internal electrode layer 8,9 External electrode

Claims

(Ba x Sr y Ca z) TiO 3 (x, y, z represent mole ratios, satisfy x + y + z = 1) as a main component, the (x, y, z) is ternary In the composition diagram, point A (0.70, 0.00, 0.30), point B (0.69, 0.02, 0.29), point C (0.55, 0.10, 0.35), point D (0.35, 0.15, 0.50), and point E (0.50) , 0.00, 0.50) in a region surrounded by a pentagon ABCDE and on a line (however, excluding point A, point E, and line segment AE).
Further, at least one rare earth element selected from the group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb and Lu is added to 100 mol of the main component. The dielectric ceramic according to claim 1, wherein the dielectric ceramic is contained in an amount of 1 mol part or more and 14 mol parts or less with respect to the part.
Further, Mg, Mn and Si are added in an amount of 0.1 mol part or more and 3.0 mol part or less, 0.5 mol part or more and 5.0 mol part or less, and 1 mol per 100 mol parts of the main component, respectively. The dielectric ceramic according to claim 1, comprising 0.0 mol part or more and 5.0 mol part or less.
A laminated body including a plurality of laminated dielectric ceramic layers, and a plurality of internal electrode layers each formed along a specific interface between the plurality of dielectric ceramic layers;
An external electrode formed on the outer surface of the laminate so as to be electrically connected to the plurality of internal electrode layers,
A multilayer ceramic capacitor, wherein the dielectric ceramic layer is made of the dielectric ceramic according to any one of claims 1 to 3.
The multilayer ceramic capacitor according to claim 4, wherein the electric field used is 25 kV / mm or more and 100 kV / mm or less, and the guaranteed breakdown voltage is 120 kV / mm or more.