Multilayer ceramic capacitor

Abstract

To provide a multilayer ceramic capacitor that has thinner dielectric layers and exhibits excellent reliability even when a voltage of high electric field intensity is applied.SOLUTION: In a multilayer ceramic capacitor (1) including a plurality of first electrodes (4) and a plurality of second inner electrodes (5) alternately arranged with respect to a stacking direction of a multilayer body 2, a polarity based on an application direction of a voltage applied between a first outer electrode (6) and a second outer electrode (7) is determined such that the first inner electrodes (4) function as positive electrodes and the second inner electrodes (5) function as negative electrodes. The first inner electrodes (4) have a first metal composition including Cu and Sn, and the second inner electrodes (5) have a second metal composition including Cu. The second metal composition of the second inner electrodes (5) preferably includes Cu as a main component, and at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru, which have standard electrode potentials higher than that of Cu, as an additive component.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] This invention relates to a multilayer ceramic capacitor, and particularly to the metal composition of internal electrodes provided in a multilayer ceramic capacitor.

Background Art

[0002] With the recent progress of electronics technology, miniaturization and large capacitance have been required for multilayer ceramic capacitors. To meet these requirements, the dielectric layers of multilayer ceramic capacitors have been thinned. However, when the dielectric layer is thinned, the electric field strength applied to each layer becomes relatively high. Therefore, improvement in reliability when voltage is applied is required.

[0003] A multilayer ceramic capacitor generally includes a laminate having a plurality of laminated dielectric layers and a plurality of internal electrodes disposed along the interfaces between the dielectric layers, and a plurality of external electrodes provided on the outer surface of the laminate and electrically connected to the internal electrodes. Here, as described in, for example, Japanese Patent Application Laid-Open No. 11-283867 (Patent Document 1), those having Ni as a main component are known as the internal electrodes.

Prior Art Documents

Patent Documents

[0004]

Patent Document 1

Summary of the Invention

Problems to be Solved by the Invention

[0005] By the way, when the main component of the internal electrode is Ni, there is a problem that the reliability when voltage is applied is still insufficient in order to meet the recent requirements for miniaturization and large capacitance.

[0006] This invention has been made in view of the above problems, and aims to provide a multilayer ceramic capacitor in which the dielectric layer is made even thinner and exhibits excellent reliability even when a high electric field strength voltage is applied. [Means for solving the problem]

[0007] The multilayer ceramic capacitor according to this invention comprises a laminate having a plurality of stacked dielectric layers made of ceramic and a plurality of internal electrodes arranged along a plurality of interfaces between the dielectric layers, and a plurality of external electrodes provided on the outer surface of the laminate and electrically connected to the internal electrodes.

[0008] The internal electrode comprises 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 electrode comprises a first external electrode electrically connected to the first internal electrode and a second external electrode electrically connected to the second internal electrode.

[0009] To solve the technical problems described above, this invention is characterized in that the first internal electrode has a first metal composition containing Cu and Sn, and the second internal electrode has a second metal composition containing Cu, and that the first and second metal compositions are different.

[0010] Furthermore, the first metal composition and the second metal composition differ in at least one of the types and content of the constituent elements. [Effects of the Invention]

[0011] According to this invention, insulation degradation of multilayer ceramic capacitors when voltage is applied can be suppressed, and thus a highly reliable multilayer ceramic capacitor can be obtained.

[0012] Furthermore, since the first metal composition of the first internal electrode contains Sn, the reliability of the multilayer ceramic capacitor when voltage is applied can be further improved. [Brief explanation of the drawing]

[0013] [Figure 1] This is a schematic cross-sectional view showing a multilayer ceramic capacitor 1 according to one embodiment of the present invention. [Figure 2] Figure 1 is a diagram illustrating 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 multilayer ceramic capacitor 1 shown in Figure 1. [Modes for carrying out the invention]

[0014] The structure of a multilayer ceramic capacitor 1 according to one embodiment of this invention will be described below with reference to Figure 1.

[0015] The multilayer ceramic capacitor 1 comprises a laminate 2. The laminate 2 comprises a plurality of stacked dielectric layers 3 made of ceramic, and a plurality of internal electrodes 4 and 5 arranged along the interfaces between the plurality of dielectric layers 3. The internal electrodes 4 and 5 are classified into a plurality of first internal electrodes 4 and a plurality of second internal electrodes 5, which are arranged alternately with respect to the stacking direction of the laminate 3. External electrodes 6 and 7 are provided on the outer surface of the laminate 2, more specifically on each of the opposing end faces. The external electrodes 6 and 7 are classified into a first external electrode 6 electrically connected to the first internal electrode 4, and a second external electrode 7 electrically connected to the second internal electrode 5.

[0016] The composition of internal electrodes 4 and 5 will be described later. External electrodes 6 and 7 have, for example, Ag or Cu as the main conductive component. The dielectric layer 3 is preferably made of a dielectric ceramic containing a perovskite-type compound containing Ba and Ti as the main component (however, some of the Ba may be substituted with Ca, and some of the Ti may be substituted with Zr). 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 exhibits excellent reliability. In addition to the main components mentioned above, the dielectric layer 3 may also contain, for example, rare earth elements, or Mn, Mg, Si, etc. as minor components.

[0017] The raw material powder for dielectric ceramics is produced, for example, by a solid-phase synthesis method. Specifically, compound powders such as oxides and carbonates containing the main constituent elements are first mixed in a predetermined ratio and calcined. In addition to the solid-phase synthesis method, hydrothermal methods and the like may also be applied. Furthermore, alkali metals, transition metals, Cl, S, P, Hf, etc., may be included in dielectric ceramics in amounts that do not hinder the effects of the present invention.

[0018] A multilayer ceramic capacitor 1 is manufactured, for example, as follows: A ceramic slurry is prepared using the dielectric ceramic raw material powder obtained as described above. Next, a ceramic green sheet is formed by a sheet molding method or the like. Next, conductive pastes that will become the internal electrodes 4 and 5 are applied to a predetermined ceramic green sheet from among several ceramic green sheets by printing or the like. Next, the multiple ceramic green sheets are laminated and then pressed together to obtain a raw laminate. Next, the raw laminate is fired. In this firing process, a dielectric layer 3 made of dielectric ceramic is obtained. After that, external electrodes 6 and 7 are formed on the end face of the laminate 3 by baking or the like.

[0019] The first feature of the multilayer ceramic capacitor 1 is that, in actual use, the polarity is determined based on the direction of voltage application between the first external electrode 6 and the second external electrode 7, such that the first internal electrode 4 is the positive electrode and the second internal electrode 5 is the negative electrode. Therefore, although not shown in the figures, it is preferable that the outer surface of the multilayer ceramic capacitor 1, for example, is marked to indicate the polarity.

[0020] In this regard, the multilayer ceramic capacitor to which this invention applies is not limited to a two-terminal type having a first external electrode 6 and a second external electrode 7 as shown in Figure 1, but may also be a multi-terminal type having three or more external electrodes. In this case, it is sufficient that a voltage is applied between two specific pairs 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, such that the first internal electrode becomes the positive electrode and the second internal electrode becomes the negative electrode.

[0021] The multilayer ceramic capacitor 1 is characterized in that, with respect to the metal composition of each of the first internal electrode 4 and the second internal electrode 5, it is selected as follows. That is, the first internal electrode 4 serving as the positive electrode has a first metal composition containing Cu and Sn, and the second internal electrode 5 serving as the negative electrode has a second metal composition containing Cu.

[0022] The selection of the metal composition of each of the first internal electrode 4 and the second internal electrode 5 is based on the following findings.

[0023] Although the insulation degradation mechanism of a general multilayer ceramic capacitor is not yet clarified, it is known that the trigger is the negative segregation of oxygen ions (positive segregation of oxygen vacancies) accompanying voltage application. Therefore, it is predicted that suppressing the negative segregation of oxygen ions can suppress the insulation degradation of the multilayer ceramic capacitor. Thus, it is conceivable to include an element with a stable oxide in the positive electrode and an element with an unstable oxide in the negative electrode. Based on this idea, by causing a reduction reaction (release of oxygen ions) at the negative electrode, the negative segregation can be suppressed.

[0024] More specifically, with respect to the metal composition of each of the first internal electrode 4 and the second internal electrode 5, a metal element with an easily increasing valence (low standard electrode potential) is used on the side of the first internal electrode 4 serving as the positive electrode, and a metal element with an easily decreasing valence (high standard electrode potential) is used on the side of the second internal electrode 5 serving as the negative electrode. The standard electrode potential is a value inherent to an element, and the lower the value, the more stable the oxide, and the higher the value, the more unstable the oxide.

[0025] That is, in the second internal electrode 5 on the negative electrode side, as shown in FIG. 2, it is made to contain a metal element with a standard electrode potential higher than that of the metal element of the first internal electrode 4 on the positive electrode side. In FIG. 2, the standard electrode potential of the first metal composition of the first internal electrode 4 on the positive electrode side only needs to be included in the range of A, and the standard electrode potential of the second metal composition of the second internal electrode 5 on the negative electrode side only needs to be included in the range of B.

[0026] The standard electrode potentials for the metal elements that may be included in the metal composition of each of the internal electrodes 4 and 5, listed in descending order from lowest to highest, are: Sn is -0.14V, Cu is +0.34V, Ru is +0.46V, Rh is +0.76V, Ag is +0.8V, OS is +0.9V, Pd is +0.92V, Ir is +1.16V, Pt is +1.19V, Au is +1.52V.

[0027] In the multilayer ceramic capacitor 1, as described above, the first internal electrode 4, which serves as the positive electrode, has a first metal composition containing Cu and Sn, and the second internal electrode 5, which serves as the negative electrode, has a second metal composition containing Cu. The standard electrode potential of Sn included in the first metal composition of the first internal electrode 4 is -0.14V, and the standard electrode potential of Cu is +0.34V, while the standard electrode potential of Cu included in the second metal composition of the second internal electrode 5 is +0.34V. Here, the Sn included in the first internal electrode 4 acts to lower the standard electrode potential given by the first internal electrode 4 on the positive electrode side, so overall, the standard electrode potential of the second metal composition of the second internal electrode 5 is higher than that of the first metal composition of the first internal electrode 4.

[0028] Thus, according to this embodiment, by focusing on the oxidation-reduction reaction in the internal electrodes 4 and 5 and utilizing this oxidation-reduction reaction, the negative electrode segregation of oxygen ions (positive electrode segregation of oxygen vacancies) associated with voltage application is suppressed. As a result, insulation degradation of the multilayer ceramic capacitor 1 when voltage is applied can be suppressed, and thus a highly reliable multilayer ceramic capacitor 1 can be obtained. Furthermore, the Sn contained in the first internal electrode 4 also acts to further improve the reliability of the multilayer ceramic capacitor 1 when voltage is applied.

[0029] The second metal composition of the second internal electrode 5 preferably consists mainly of Cu, with at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru, which has a higher standard electrode potential than Cu, as an additive component. This is because the standard electrode potential of the second metal composition can be made higher than that of Cu alone. Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru, which are additive components of the second metal composition, are noble metals.

[0030] Regarding the metal composition of internal electrodes 4 and 5, "main component" refers to the element that is present in the highest amount among the metal elements, or more specifically, the element that is present in 50% or more of the total.

[0031] As mentioned above, the higher the standard electrode potential, the more unstable the oxide. Therefore, for the above-mentioned additive components, the effect of suppressing negative electrode segregation of oxygen ions increases in the order of increasing standard electrode potential: Cu, Ru, Rh, Ag, Os, Pd, Ir, Pt, and Au.

[0032] Furthermore, it is preferable that the first metal composition of the first internal electrode 4 does not contain any metal elements with a standard electrode potential higher than Cu. This is because it is advantageous to maintain the relatively low standard electrode potential of the first metal composition.

[0033] 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 included in the conductive paste applied to the ceramic green sheet during the manufacturing process of the multilayer ceramic capacitor 1. These elements may be included in the conductive paste in the form of an alloy or intermetallic compound containing multiple metal elements, or they may be included in the conductive paste in the form of separate metal elements.

[0034] 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, it is preferable that these multiple metal elements are alloyed at the stage of the multilayer ceramic capacitor 1 as a product. [Explanation of Symbols]

[0035] 1. Multilayer ceramic capacitor 2 Laminate 3. Dielectric layer 4 1st internal electrode 5 Second internal electrode 6 1st external electrode 7 Second external electrode

Claims

1. A laminate comprising a plurality of stacked dielectric layers made of ceramic, and a plurality of internal electrodes arranged along a plurality of interfaces between the dielectric layers, A plurality of external electrodes are provided on the outer surface of the laminate and are electrically connected to the internal electrodes, Equipped with, The internal electrode comprises 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 comprises a first external electrode electrically connected to the first internal electrode and a second external electrode electrically connected to the second internal electrode. The first internal electrode has a first metal composition including Cu and Sn, The second internal electrode has a second metallic composition containing Cu, The first metal composition and the second metal composition are different, The polarity is determined based on the direction of voltage application between the first external electrode and the second external electrode, such that the first internal electrode is the positive electrode and the second internal electrode is the negative electrode. The first metal composition of the first internal electrode is a multilayer ceramic capacitor that does not contain any metal elements whose standard electrode potential is higher than that of Cu.

2. The multilayer ceramic capacitor according to claim 1, wherein the second metal composition of the second internal electrode is mainly composed of Cu, and includes at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru, which has a higher standard electrode potential than Cu, as an additive component.

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