Multilayer ceramic capacitor

Abstract

The present application provides a laminated ceramic capacitor in which a dielectric layer is further thinned and shows excellent reliability even when a high electric field strength voltage is applied. In a laminated ceramic capacitor (1) provided with a plurality of first internal electrodes (4) and a plurality of second internal electrodes (5) alternately arranged with respect to the stacking direction of a laminate (2), the polarity of the application direction of the voltage applied between a first external electrode (6) and a second external electrode (7) is determined so that the first internal electrodes (4) are positive and the second internal electrodes (5) are negative. The first internal electrodes (4) have a first metal composition in which Ni is the main component, and the second internal electrodes (5) have a second metal composition in which Cu is the main component. The first metal composition can also include Sn as an additive component. The second metal composition can also include at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru as an additive component.

Description

Technical Field

[0001] This invention relates to multilayer ceramic capacitors, and more particularly to the metal composition of the internal electrodes in multilayer ceramic capacitors. Background Technology

[0002] With the development of electronic technology in recent years, multilayer ceramic capacitors have been required to be miniaturized and have larger capacitance. To meet these requirements, efforts have been made to thin the dielectric layers of multilayer ceramic capacitors. However, thinning the dielectric layers results in a relatively higher electric field strength applied to each layer. Therefore, it is desirable to improve the reliability when voltage is applied.

[0003] Generally, a multilayer ceramic capacitor comprises: a multilayer having multiple stacked dielectric layers and multiple internal electrodes disposed along the interfaces between the dielectric layers; and multiple external electrodes disposed on the outer surface of the multilayer and electrically connected to the internal electrodes. Here, the internal electrodes are known, for example, as described in Japanese Patent Application Publication No. 11-283867 (Patent Document 1), and are mainly composed of Ni.

[0004] Prior art literature

[0005] Patent documents

[0006] Patent Document 1: Japanese Patent Application Publication No. 11-283867 Summary of the Invention

[0007] The problem the invention aims to solve

[0008] However, when the main component of the internal electrode is set to Ni, there is still a problem that the reliability when voltage is applied is insufficient in order to meet the requirements of miniaturization and large capacitance in recent years.

[0009] The present invention was made in view of the following problems, and aims to provide a multilayer ceramic capacitor with a dielectric layer that is further thinned and exhibits excellent reliability even when subjected to voltage with high electric field strength.

[0010] Technical solutions for solving the problem

[0011] The multilayer ceramic capacitor of the present invention comprises: a multilayer having a plurality of stacked dielectric layers comprising ceramic, and a plurality of internal electrodes disposed along a plurality of interfaces between the dielectric layers; and a plurality of external electrodes disposed on the outer surface of the multilayer and electrically connected to the internal electrodes.

[0012] The internal electrodes have a plurality of first internal electrodes and a plurality of second internal electrodes arranged alternately with respect to the stacking direction of the laminate, and the external electrodes have a first external electrode electrically connected to the first internal electrodes and a second external electrode electrically connected to the second internal electrodes.

[0013] To solve the above-mentioned technical problems, in this invention, the characteristic is that, based on the polarity of the application direction of the voltage applied between the first external electrode and the second external electrode being determined, the first internal electrode is used as the positive electrode and the second internal electrode is used as the negative electrode, the first internal electrode has a first metal composition with Ni as the main component, and the second internal electrode has a second metal composition with Cu as the main component.

[0014] Furthermore, the first metal composition and the second metal composition mentioned above are different, with at least one of the constituent elements and their content being different.

[0015] Furthermore, regarding the metal composition of the internal electrodes, the term "main component" refers to the component with the highest content among metal elements, and more specifically, to the component with a content of 50% or more.

[0016] Invention Effects

[0017] According to the present invention, insulation degradation of the multilayer ceramic capacitor when voltage is applied can be suppressed, thus enabling the production of a multilayer ceramic capacitor with excellent reliability.

[0018] Furthermore, in order to provide the conductive materials for the first and second internal electrodes, commonly available and inexpensive metals such as Ni and Cu can be used, thus enabling the multilayer ceramic capacitor to achieve excellent cost efficiency. Attached Figure Description

[0019] Figure 1 This is a schematic cross-sectional view of a multilayer ceramic capacitor 1 according to an embodiment of the present invention.

[0020] Figure 2 It is used for explanation Figure 1 A diagram showing the standard electrode potentials of the metal elements contained in the first internal electrode (positive electrode) 4 and the second internal electrode (negative electrode) 5 of the stacked ceramic capacitor 1. Detailed Implementation

[0021] The following is for reference Figure 1 The structure of a multilayer ceramic capacitor 1 according to one embodiment of the present invention will be described.

[0022] A multilayer ceramic capacitor 1 includes a multilayer body 2. The multilayer body 2 includes multiple stacked dielectric layers 3 comprising ceramic, and multiple internal electrodes 4 and 5 arranged along the interfaces between the multiple dielectric layers 3. The internal electrodes 4 and 5 are classified as multiple first internal electrodes 4 and multiple second internal electrodes 5 arranged alternately with respect to the stacking direction of the multilayer body 2. External electrodes 6 and 7 are respectively provided on the outer surface of the multilayer body 2, more specifically, respectively provided on opposite end faces. The external electrodes 6 and 7 are classified as first external electrodes 6 electrically connected to the first internal electrodes 4, and second external electrodes 7 electrically connected to the second internal electrodes 5.

[0023] The composition of the internal electrodes 4 and 5 will be described later. The external electrodes 6 and 7 are, for example, composed primarily of Ag or Cu as the conductive component. The dielectric layer 3 preferably comprises a dielectric ceramic containing a perovskite-type compound containing Ba and Ti (where a portion of Ba can be replaced by Ca, and a portion of Ti can be replaced by Zr) as the main component. In particular, when the main component of the dielectric layer 3 is BaTiO3, it exhibits a high dielectric constant, and the multilayer ceramic capacitor 1 demonstrates excellent reliability. Furthermore, in addition to the aforementioned main components, the dielectric layer 3 may also contain, for example, rare earth elements, Mn, Mg, Si, etc., as secondary components.

[0024] The raw material powder for dielectric ceramics can be produced, for example, by a solid-state synthesis method. Specifically, firstly, powders of compounds such as oxides and carbonates containing the main constituent elements are mixed in a given proportion and then calcined. In addition to solid-state synthesis, hydrothermal methods can also be used. Furthermore, alkali metals, transition metals, Cl, S, P, Hf, etc., can be included in the dielectric ceramics in amounts that do not impair the effects of the present invention.

[0025] A multilayer ceramic capacitor 1 is manufactured as follows: A ceramic slurry is prepared using raw material powder of dielectric ceramic obtained as described above. Next, ceramic green sheets are formed by sheet forming or the like. Next, conductive paste, which should become internal electrodes 4 and 5, is applied to a given ceramic green sheet by printing or the like. Next, after stacking the multiple ceramic green sheets, they are pressed together to obtain an unprocessed multilayer. Next, the unprocessed multilayer is fired. In this firing process, a dielectric layer 3 made of dielectric ceramic is obtained. Then, external electrodes 6 and 7 are formed on the end faces of the multilayer 2 by firing or the like.

[0026] The multilayer ceramic capacitor 1 has the following first feature: the polarity of the voltage applied between the first external electrode 6 and the second external electrode 7 is determined such that, in practical use, the first internal electrode 4 is used as the positive electrode and the second internal electrode 5 as the negative electrode. Therefore, although not shown, it is preferable to mark the polarity on, for example, the outer surface of the multilayer ceramic capacitor 1.

[0027] In this regard, the multilayer ceramic capacitors that are the subject of this invention are not limited to, for example Figure 1 The two-terminal type multilayer ceramic capacitor shown, which includes a first external electrode 6 and a second external electrode 7, can also be a multi-terminal type multilayer ceramic capacitor with three or more external electrodes. In this case, it is sufficient to configure the capacitor such that a voltage is applied between two specific sets of external electrodes selected from the three or more external electrodes, that is, between at least one first external electrode and at least one second external electrode, so that the first internal electrode becomes the positive electrode and the second internal electrode becomes the negative electrode.

[0028] The multilayer ceramic capacitor 1 has the following second feature: the metal composition of the first internal electrode 4 and the second internal electrode 5 are selected as follows. That is, the first internal electrode 4, which serves as the positive electrode, has a first metal composition with Ni as the main component, and the second internal electrode 5, which serves as the negative electrode, has a second metal composition with Cu as the main component.

[0029] The choice of the metal composition of the first internal electrode 4 and the second internal electrode 5 is based on the following insights.

[0030] The insulation degradation mechanism of typical multilayer ceramic capacitors is not yet fully understood, but it is known to be triggered by the negative electrode segregation of oxygen ions (positive electrode segregation of oxygen vacancies) associated with voltage application. Therefore, it can be predicted that by suppressing the negative electrode segregation of oxygen ions, the insulation degradation of multilayer ceramic capacitors can be suppressed. Thus, it is possible to include elements that stabilize oxides in the positive electrode and elements that destabilize oxides in the negative electrode. Based on this consideration, by causing a reduction reaction (release of oxygen ions) at the negative electrode, it becomes possible to suppress negative electrode segregation.

[0031] More specifically, regarding the metal composition of the first internal electrode 4 and the second internal electrode 5, a metal element whose valence is easily increased (low standard electrode potential) is used on the side of the first internal electrode 4, which serves as the positive electrode, while a metal element whose valence is easily decreased (high standard electrode potential) is used on the side of the second internal electrode 5, which serves as the negative electrode. The standard electrode potential is an inherent value of an element; the lower the value, the more stable the oxide, and the higher the value, the less stable the oxide.

[0032] That is, in the second internal electrode 5 on the negative electrode side, such as Figure 2As shown, this includes metal elements whose standard electrode potential is higher than that of the metal element in the first internal electrode 4 on the positive electrode side. Figure 2 In the above, the standard electrode potential composed of the first metal of the first internal electrode 4 on the positive side only needs to be included in the range of A, and the standard electrode potential composed of the second metal of the second internal electrode 5 on the negative side only needs to be included in the range of B.

[0033] Regarding the standard electrode potentials of the metal elements that may be included in the metal composition of internal electrodes 4 and 5, if listed sequentially from the lowest, they are:

[0034] Ni is -0.26V,

[0035] Sn is -0.14V.

[0036] Cu is +0.34V.

[0037] Ru is +0.46V.

[0038] Rh is +0.76V.

[0039] Ag is +0.8V,

[0040] Os is +0.9V,

[0041] Pd is +0.92V.

[0042] Ir is +1.16V,

[0043] Pt is +1.19V,

[0044] Au is +1.52V.

[0045] The standard electrode potential of Ni, which is the main component of the first metal composition of the first internal electrode 4, is -0.26V, and that of Sn, which is sometimes an additive component, is -0.14V. In contrast, Cu, which is the main component of the second metal composition of the second internal electrode 5, and Au, Pt, Ir, Pd, Os, Ag, Rh and Ru, which are additive components, all have higher standard electrode potentials than Ni and Sn.

[0046] Therefore, at least one of the following metal elements, Cu as the main component and Au, Pt, Ir, Pd, Os, Ag, Rh and Ru as additive components, in the second metal composition of the second internal electrode 5 as the negative electrode, can cause a reduction reaction (release of oxygen ions) in the second internal electrode 5 as the negative electrode, thereby suppressing the negative electrode segregation of oxygen ions.

[0047] In this embodiment, focusing on the redox reaction in the internal electrodes 4 and 5, the negative electrode segregation of oxygen ions (positive electrode segregation of oxygen vacancies) associated with voltage application can be suppressed. As a result, the insulation degradation of the multilayer ceramic capacitor during voltage application can be suppressed, thus obtaining a multilayer ceramic capacitor with excellent reliability.

[0048] The first metal composition of the first internal electrode 4 can also include Sn as an additive. If Sn is included, the reliability of the multilayer ceramic capacitor 1 when voltage is applied can be further improved.

[0049] The second metal composition of the second internal electrode 5 can also be an additive element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru, whose standard electrode potential is higher than that of Cu. In this case, as mentioned above, the higher the standard electrode potential, the less stable the oxide is. Therefore, the aforementioned additive metal elements are selected in order of increasing standard electrode potential, i.e., in the order of Cu, Ru, Rh, Ag, Os, Pd, Ir, Pt, and Au, to achieve a higher effect in suppressing the negative electrode segregation of oxygen ions. Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru are noble metals.

[0050] In addition, when the first metal composition of the first internal electrode 4 contains multiple metal elements, or when the second metal composition of the second internal electrode 5 contains multiple metal elements, these multiple metal elements are contained in the conductive paste applied to the ceramic green sheet during the manufacturing process of the multilayer ceramic capacitor 1. However, they can be contained in the conductive paste in the form of an alloy or intermetallic compound containing multiple metal elements in advance, or they can be contained in the conductive paste in the form of separate metal elements.

[0051] Furthermore, if the first metal composition of the first internal electrode 4 contains multiple metal elements, or if the second metal composition of the second internal electrode 5 contains multiple metal elements, these multiple metal elements are preferably alloyed during the production of the multilayer ceramic capacitor 1 as a product.

[0052] Explanation of reference numerals in the attached figures

[0053] 1: Multilayer ceramic capacitor;

[0054] 2: Layered body;

[0055] 3: Dielectric layer;

[0056] 4: First internal electrode;

[0057] 5: Second internal electrode;

[0058] 6: First external electrode;

[0059] 7: Second external electrode.

Claims

1. A multilayer ceramic capacitor, comprising: A laminate having multiple stacked dielectric layers comprising ceramic, and multiple internal electrodes respectively disposed along multiple interfaces between the dielectric layers; and Multiple external electrodes are disposed on the outer surface of the laminate and are electrically connected to the internal electrodes. The internal electrodes include a plurality of first internal electrodes and a plurality of second internal electrodes arranged alternately with respect to the stacking direction of the laminate. The external electrode includes a first external electrode electrically connected to the first internal electrode and a second external electrode electrically connected to the second internal electrode. The polarity of the voltage applied between the first external electrode and the second external electrode is determined such that the first internal electrode is used as the positive electrode and the second internal electrode as the negative electrode. The first internal electrode has a first metal composition with Ni as the main component. The second internal electrode has a second metal composition with Cu as the main component.

2. The multilayer ceramic capacitor according to claim 1, wherein, The first internal electrode has a first metal composition with Sn as an added component.

3. The multilayer ceramic capacitor according to claim 1 or 2, wherein, The second internal electrode has a second metal composition consisting of at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh and Ru, whose standard electrode potential is higher than that of Cu.

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