JP5857570B2 - Multilayer ceramic capacitor - Google Patents

Description

  The present invention relates to a dielectric ceramic and a multilayer ceramic capacitor, and more particularly to a multilayer ceramic capacitor having a strength capable of withstanding an impact during mounting.

  With the recent progress of electronics technology, the degree of integration of surface mount type small chip components represented by multilayer ceramic capacitors is increasing. For this reason, the multilayer ceramic capacitor is required to have a low profile.

  When the height of the multilayer ceramic capacitor is reduced, there is a risk that the multilayer ceramic capacitor will break due to an impact during mounting. Therefore, a high bending strength is desired for the multilayer ceramic capacitor.

  On the other hand, in order to reduce the height of the multilayer ceramic capacitor, the thickness per layer of the ceramic layer has been reduced in order to ensure the capacitance with a small occupied volume. At this time, the electric field strength applied per ceramic layer is relatively high, and relatively large electrostriction occurs particularly in the medium-high pressure type application.

  At this time, in order to prevent the multilayer ceramic capacitor from being broken by electrostriction, the multilayer ceramic capacitor is required to have a high bending strength.

  In Patent Document 1, in order to increase the bending strength, a multilayer ceramic capacitor having a configuration in which dielectric layers and internal electrode layers are alternately stacked has the following characteristics. That is, one or more internal electrode layers on both sides in the stacking direction including two internal electrode layers positioned at both ends in the stacking direction among the plurality of internal electrode layers are substantially oxidized and do not function as the internal electrode layers. The capacitance is determined by the remaining internal electrode layers that are not oxidized.

JP 2007-35848 A

  However, in patent document 1, since the area | region which does not contribute to an electrostatic capacitance increases in a laminated body, it was unpreferable from a viewpoint of size reduction. In addition, since only specific internal electrodes require special management, there is a problem that the process becomes complicated.

  Accordingly, an object of the present invention is to solve the above-described problems by providing characteristics of the crystal particles and composition of the dielectric ceramic layer, thereby achieving excellent bending strength without special element design. An object of the present invention is to provide a multilayer ceramic capacitor.

  That is, the present invention provides a laminate having a dielectric ceramic layer including crystal grains and crystal grain boundaries, and an internal electrode layer, and an internal electrode layer formed on the surface of the laminate and exposed on the surface of the laminate. And a multilayer ceramic capacitor comprising an external electrode electrically connected to each other, wherein the composition of the laminate includes a perovskite-type compound containing Ba, Ti, and Zr as main components, and the laminate is dissolved The Zr / (Ti + Zr) molar ratio at the center of the crystal grain when the cross-section of the dielectric ceramic layer was observed when the Zr-containing molar part was 10 or more and 40 or less when Ba was 100 parts by mole. Is TA, and the number ratio of crystal grains B having a Ti / (Ti + Zr) molar ratio of 0.005 or less at the center of the crystal grains is T. When the, TB is equal to or less than 0.1.

  The present invention also provides a laminate having a dielectric ceramic layer including crystal grains and crystal grain boundaries, and an internal electrode layer, and an internal electrode formed on the surface of the laminate and exposed on the surface of the laminate. And a dielectric ceramic layer comprising a perovskite-type compound containing Ba, Ti and Zr as a main component, wherein the dielectric ceramic layer comprises: Zr / (Ti + Zr) mol at the center of the crystal grain when the cross-section of the dielectric ceramic layer is 10 to 40 and the cross-section of the dielectric ceramic layer is 10 to 40 mol. TA is the number ratio of crystal grains A having a ratio of 0.005 or less, and the number of crystal grains B having a Ti / (Ti + Zr) molar ratio of 0.005 or less at the center of the crystal grains. When the engagement TB, and, TB is 0.1 or more, and wherein the.

  Furthermore, the composition of the laminate or dielectric ceramic in the present invention is Mn, Mg, R (R is Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb. And at least one selected from Lu), and when the laminated body is dissolved, or when the dielectric ceramic layer contains Ba in an amount of 100 parts by mole, the contained mole part of each element is Mn: 0 1 or more and 3.5 or less, Mg: 0.1 or more and 15 or less, R: 2 or more and 30 or less, Si: 0.8 or more and 5 or less, and TA is preferably 0.5 or more.

1 is a cross-sectional view schematically showing a multilayer ceramic capacitor 1 configured using a dielectric ceramic according to the present invention.

  With reference to FIG. 1, first, an example of a multilayer ceramic capacitor 1 to which the dielectric ceramic according to the present invention is applied will be described.

  The multilayer ceramic capacitor 1 includes a multilayer body 5 including a plurality of dielectric ceramic layers 2 and a plurality of internal electrodes 3 and 4 formed along an interface between the dielectric ceramic layers 2. Yes. The internal electrodes 3 and 4 are mainly composed of Ni, for example.

  First and second external electrodes 6 and 7 are formed at different positions on the outer surface of the laminate 5. The external electrodes 6 and 7 are mainly composed of Ag or Cu, for example. Although not shown, a plating film is formed on the external electrodes 6 and 7 as necessary. The plating film is composed of, for example, a Ni plating film and a Sn plating film formed thereon.

  In the monolithic ceramic capacitor 1 shown in FIG. 1, the first and second external electrodes 6 and 7 are formed on the end surfaces of the capacitor body 5 facing each other. The internal electrodes 3 and 4 are a plurality of first internal electrodes 3 electrically connected to the first external electrode 6 and a plurality of second internal electrodes 4 electrically connected to the second external electrode 7. The first and second internal electrodes 3 and 4 are alternately arranged as viewed in the stacking direction.

  The multilayer ceramic capacitor 1 may be a two-terminal type including two external electrodes 6 and 7 or a multi-terminal type including a large number of external electrodes.

  In such a multilayer ceramic capacitor 1, the dielectric ceramic layer 2 including crystal grains and grain boundaries occupies most of the multilayer body 5 and is basically an oxide ceramic.

  The composition of the laminated body 5 or the composition of the dielectric ceramic layer 2 includes a perovskite type compound containing Ba, Ti, and Zr as main components. The Zr-containing mole part is 10 or more and 40 or less when Ba is 100 mole parts. When it is within this range, the bending strength is increased.

  Whether the main component of the laminate 5 or the main component of the dielectric ceramic layer 2 is a perovskite type compound can be confirmed by a method such as XRD, for example.

When the cross section of the dielectric ceramic layer was observed, the number ratio of crystal grains A having a Zr / (Ti + Zr) molar ratio of 0.005 or less at the crystal grain center was TA, and the Ti / (Ti + Zr) molar ratio was at the crystal grain center. When the ratio of the number of crystal grains B having a particle size of 0.005 or less is TB, TB is 0.1 or more. That is, the number of crystal grains mainly containing BaZrO ₃ is 10% or more of the whole. At this time, the bending strength is increased.

Moreover, preferably, TA is 0.5 or more. That is, the number of crystal grains mainly composed of BaTiO ₃ is 50% or more of the whole. At this time, the temperature characteristics of the capacitance can be kept good while keeping the bending strength high.

In the crystal particles, unless the object of the present invention is impaired, there is a crystal particle that does not apply to either the crystal particle A or the crystal particle B, for example, a crystal particle mainly composed of Ba (Ti, Zr) O _3. It doesn't matter. However, in order to increase the TB to 0.1 or more, it is preferable to suppress the generation of crystal grains mainly composed of Ba (Ti, Zr) O ₃ as much as possible.

  Next, as a subcomponent, the composition of the laminate or dielectric ceramic is Mn, Mg, R (R is Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm. , Yb, and Lu), and Si.

  Moreover, the presence form of these subcomponents is not ask | required. For example, an oxide such as MgO may be present at a crystal grain boundary or a triple point, or a secondary phase particle may be formed as a composite oxide containing a plurality of elements. Moreover, a part may exist in the crystal grain. In particular, it may be present only in the surface layer portion (shell portion) of the crystal particles.

  In addition, regarding the content ratio of each element in the composition of the laminated body 5, the laminated body can be dissolved and quantitatively analyzed by, for example, ICP (Emission Spectroscopic Plasma Analysis). In essence, it is preferable to define the composition of only the dielectric ceramic layer 2. However, as described above, since most of the multilayer body 5 is occupied by the capacitance forming portion of the dielectric ceramic layer 2, it is sufficient to define the composition of the multilayer body 5.

  That is, regarding the content of each element, in the laminate or dielectric ceramic layer, the content mole part of each element when Ba is 100 mole parts is Mn: 0.1 to 3.5, Mg: When it is 0.1 or more and 15 or less, R: 2 or more and 30 or less, and Si: 0.8 or more and 5 or less, the dielectric constant and the capacitance temperature characteristic are improved.

  Next, an example is described below about the manufacturing method of a multilayer ceramic capacitor.

First, a powder mainly composed of BaTiO ₃ and a powder mainly composed of BaZrO ₃ are prepared. These may be prepared by a general solid phase synthesis method, or may be prepared by a wet synthesis method such as a hydrothermal synthesis method, a hydrolysis method, or an oxalic acid method. .

At this time, in the powder mainly composed of BaTiO ₃ and the powder mainly composed of BaZrO ₃ , the respective particle sizes and crystallization degrees affect the values of TA and TB in the sintered body.

  Next, an Mn compound, an Mg compound, and an Si compound R compound as auxiliary components are prepared. The form of these compounds is not particularly limited, and may be oxide powder or carbonate powder, or sol or organic metal.

Next, powder containing BaTiO ₃ as a main component, powder containing BaZrO ₃ as a main component, Mn compound, Mg compound, R compound, and Si compound are mixed. At this time, another element may be added as a subcomponent. Further, the mixing form of the subcomponents is not particularly limited. For example, a plurality of subcomponents may be mixed in advance, or may be further synthesized by heat treatment. Moreover, you may mix a specific subcomponent in two steps or more. Furthermore, as long as the object of the present invention is not impaired, a part of the subcomponents may be mixed in advance when the main component is synthesized.

  A binder or the like may be mixed into the ceramic slurry when the subcomponents are mixed into the main component powder, and the process may proceed to sheet forming. Alternatively, the subcomponents may be mixed with the main component powder and then dried to obtain a ceramic raw material, and then mixed with a solvent again to obtain a ceramic slurry. If necessary, the ceramic raw material powder may be heat treated to cause the main component powder and the subcomponent to react.

  Next, a ceramic green sheet is obtained by sheet-forming this ceramic slurry. By stacking this ceramic green sheet and the internal electrode layer, a laminate before firing is obtained. Specifically, a conductive paste containing metal particles that are components of internal electrodes and an organic vehicle is applied and formed on the surface of the ceramic green sheet, and these are stacked and crimped so that the internal electrode lead-out directions are staggered. The method of doing is mentioned.

  The obtained raw laminate is baked in an atmosphere showing an oxygen partial pressure to such an extent that the internal electrode is not oxidized and the dielectric is not reduced after removing the binder. By this firing, a laminate 5 including a dielectric ceramic 2 having crystal grains and crystal grain boundaries and internal electrodes 3 and 4 is obtained. At this time, firing conditions such as the firing temperature affect the values of TA and TB in the sintered body.

  A multilayer ceramic capacitor 1 is obtained by forming an external electrode in a portion of the multilayer body 5 where the internal electrode layer is exposed. In addition, the formation of the external electrode includes a method in which a conductive paste is applied and formed in advance on the surface of the laminate before firing, and the conductive paste is baked in accordance with the firing of the laminate.

Below, the experiment example implemented based on this invention is demonstrated.
[Example 1]
(A) Production of Ceramic Raw Material First, high-purity BaCO ₃ , TiO _2, and ZrO ₂ powders were prepared as starting materials for BaTiO ₃ and BaZrO ₃ , which are main components, and each was prepared. This blended powder was wet-mixed using a ball mill, uniformly dispersed, and then dried to obtain a mixed powder. The obtained mixed powder was calcined to obtain BaTiO ₃ powder and BaZrO ₃ powder. At this time, BaTiO ₃ powder and BaZrO ₃ powder having various particle sizes were obtained by changing the particle size of the starting material and the calcining temperature.

Next, as starting materials for subcomponents, MnCO ₃ , MgCO ₃ , SiO ₂ , Y ₂ O ₃ , La ₂ O ₃ , CeO ₂ , Pr ₅ O ₁₁ , Nd ₂ O ₃ , Sm ₂ O ₃ , Eu ₂ O ₃ , Gd ₂ O ₃ , Tb ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , Er ₂ O ₃ , Tm ₂ O ₃ , Yb ₂ O ₃ and Lu ₂ O ₃ powders were prepared.

Subsequently, the BaTiO ₃ powder and the BaZrO ₃ powder were mixed so as to satisfy a ratio satisfying x in Table 1 when BaTiO ₃ : BaZrO ₃ = (100−x): x. The BaTiO ₃ powder and the BaZrO ₃ powder were selected so that the ratio of the particle size of the BaZrO ₃ powder to the particle size of the BaTiO ₃ powder was the value shown in Table 1. Furthermore, the starting materials of the subcomponents were mixed so that the molar parts of Mn, Mg, Si, and R with respect to 100 parts by mol of Ba had the values shown in Table 1. A mixed powder was obtained as described above.

(B) Production of Multilayer Ceramic Capacitor Next, an organic solvent and a dispersing agent were added to the mixed powder, and wet mixed by a ball mill and uniformly dispersed. Furthermore, a polyvinyl butyral binder and a plasticizer were added and mixed to obtain a ceramic slurry.

    Next, this ceramic slurry was formed into a sheet by a lip method to obtain a rectangular ceramic green sheet having a thickness of 14 μm.

  Next, a conductive paste containing Ni was screen-printed on the ceramic green sheet to form a conductive paste film to be an internal electrode.

  Next, a plurality of ceramic green sheets on which the conductive paste film was formed were stacked so that the side from which the conductive paste film was drawn was staggered to obtain a raw laminate that would become the capacitor body.

Next, this laminate was heated in a N ₂ atmosphere at a temperature of 350 ° C. for 3 hours to burn the binder, and then H ₂ —N ₂ — with an oxygen partial pressure of 10 ⁻⁹ to 10 ⁻¹² MPa. In a reducing atmosphere composed of H ₂ O gas, firing was performed at 1100 to 1200 ° C. for 2 hours to obtain a sintered laminate.

  When this laminated body was melt | dissolved and ICP analysis was carried out, it was confirmed that the above-mentioned preparation composition was substantially maintained except Ni of the internal electrode component.

  Next, an XRD structural analysis of this laminate was performed, and it was revealed that the main component has a perovskite structure.

  Next, Ag paste containing glass frit is applied to both end faces of the capacitor body, and the external electrode electrically connected to the internal electrode is formed by baking at 600 ° C. in the atmosphere. A multilayer ceramic capacitor was obtained.

The outer dimensions of the multilayer ceramic capacitor thus obtained were 4.5 mm in length, 3.2 mm in width and 1.2 mm in thickness, and the thickness of the dielectric ceramic layer interposed between the internal electrodes was 10 μm. . The number of effective dielectric ceramic layers was 100, and the counter electrode area per one dielectric ceramic layer was 2.5 mm ² .

(C) Characteristic evaluation Next, the following evaluation was performed about the multilayer ceramic capacitor concerning each sample.
(1) Measurement of TA and TB After the laminated body in each sample number was polished and sliced, 100 crystal particles were observed with a TEM, and the contents of Ti and Zr were determined by EDX near the center of the crystal particles. Quantified. Of these, crystal grains having a Zr / (Ti + Zr) molar ratio of 0.005 or less were regarded as crystal grains mainly composed of BaTiO ₃ , and the counted result was TA. Similarly, crystal grains having a Ti / (Ti + Zr) molar ratio of 0.005 or less were regarded as crystal grains mainly composed of BaZrO ₃ , and the counted result was taken as TB. The results are shown in Table 2.
(2) Measurement of dielectric constant The capacitance of the multilayer ceramic capacitor was measured under the conditions of 1 Vrms and 1 kHz at 25 ° C. using an automatic bridge type measuring machine. The dielectric constant was calculated from the obtained measured value. Values are shown in Table 2. Here, 400 or more were regarded as non-defective products.
(3) Measurement of capacitance temperature characteristics The change in capacitance was measured in the range of -55 ° C to 125 ° C. Table 2 shows the values of the rate of change when the rate of change is the largest when the capacitance at 25 ° C. is used as a reference. Here, the X7S characteristic, that is, within ± 22% was regarded as a non-defective product.
(4) Measurement of bending strength On the surface of the multilayer ceramic capacitor sample between the length direction and the width direction, stress is applied to the middle position in the length direction, and a three-point bending test is performed to determine the bending strength. Calculated. The results are shown in Table 2. Here, 180 MPa or more was regarded as a good product.

  Like sample number 1, when TB was less than 0.1, the bending strength was low. In addition, as in sample number 3, a sample having x less than 10 also had a low bending strength.

  For samples Nos. 2 and 3-39, TB was 0.1 or more and x was 0.1 or more, so that a high bending strength was obtained.

  In addition, when TA is 0.5 or more and Ba is 100 mol parts, the contained mol parts of each element are Mn: 0.1 or more and 3.5 or less, Mg: 0.1 or more and 15 or less, Samples having a composition of R: 2 to 30 and Si: 0.8 to 5 (ie, sample numbers 13 to 39) satisfied a dielectric constant of 400 or more and X7S characteristics.

DESCRIPTION OF SYMBOLS 1 Multilayer ceramic capacitor 2 Dielectric ceramic layer 3, 4 Internal electrode 5 Laminated body 6,7 External electrode

Claims (5)

A laminate having a dielectric ceramic layer including crystal grains and crystal grain boundaries, and an internal electrode layer;
An external electrode formed on the surface of the laminate and electrically connecting the internal electrode layer exposed on the surface of the laminate;
In a multilayer ceramic capacitor comprising:
The composition of the laminate includes a perovskite type compound containing Ba, Ti and Zr as main components,
When the laminate is dissolved, the Zr-containing mole part when Ba is 100 mole parts is 10 or more and 40 or less, and
When the cross section of the dielectric ceramic layer was observed, the number ratio of crystal grains A having a Zr / (Ti + Zr) molar ratio of 0.005 or less at the crystal grain center was TA, and the Ti / (Ti + Zr) molar ratio was at the crystal grain center. when the number ratio of the crystal grains B but 0.005 or less TB, a state, and are TB is 0.1 or more,
The dielectric ceramic layer raw material includes BaTiO ₃ powder and BaZrO ₃ powder, and the ratio of the particle size of the BaZrO ₃ powder to the particle size of the BaTiO ₃ powder is 1.1 or more and 3.1 or less , Multilayer ceramic capacitor. Further, the composition of the laminate is at least selected from Mn, Mg, R (R is Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) One kind), and Si,
When the laminated body is dissolved, the content mole parts of each element when Ba is 100 mole parts,
Mn: 0.1 or more and 3.5 or less Mg: 0.1 or more and 15 or less R: 2 or more and 30 or less Si: 0.8 or more and 5 or less, and
TA is 0.5 or more,
The multilayer ceramic capacitor according to claim 1, wherein: A laminate having a dielectric ceramic layer including crystal grains and crystal grain boundaries, and an internal electrode layer;
An external electrode formed on the surface of the laminate and electrically connecting the internal electrode layer exposed on the surface of the laminate;
In a multilayer ceramic capacitor comprising:
The composition of the dielectric ceramic layer includes a perovskite type compound containing Ba, Ti and Zr as main components,
The dielectric ceramic layer has a Zr-containing molar part of 10 or more and 40 or less when Ba is 100 parts by mole, and
When the cross section of the dielectric ceramic layer was observed, the number ratio of crystal grains A having a Zr / (Ti + Zr) molar ratio of 0.005 or less at the crystal grain center was TA, and the Ti / (Ti + Zr) molar ratio was at the crystal grain center. when the number ratio of the crystal grains B but 0.005 or less TB, a state, and are TB is 0.1 or more,
The dielectric ceramic layer raw material includes BaTiO ₃ powder and BaZrO ₃ powder, and the ratio of the particle size of the BaZrO ₃ powder to the particle size of the BaTiO ₃ powder is 1.1 or more and 3.1 or less , Multilayer ceramic capacitor. Furthermore, the composition of the dielectric ceramic layer is selected from Mn, Mg, R (R is Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, Lu) At least one type), and Si,
When the Ba in the dielectric ceramic layer is 100 mol parts, the contained mol parts of each element are:
Mn: 0.1 or more and 3.5 or less Mg: 0.1 or more and 15 or less R: 2 or more and 30 or less Si: 0.8 or more and 5 or less, and
TA is 0.5 or more,
The multilayer ceramic capacitor according to claim 3, wherein: A method for producing a multilayer ceramic capacitor according to any one of claims 1 to 4,
BaTiO ₃ Powder and BaZrO ₃ Including a step of obtaining the dielectric ceramic layer by firing a ceramic green sheet containing powder;
  BaZrO ₃ The BaTiO particle size of the powder ₃ The manufacturing method whose ratio with respect to the particle size of a powder is 1.1 or more and 3.1 or less.

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