Multilayer ceramic capacitor

Abstract

To provide a multilayer ceramic capacitor in which a dielectric layer is made thinner and which exhibits excellent reliability even when a voltage of high electric field strength is applied.SOLUTION: In a multilayer ceramic capacitor (1) including a plurality of first internal electrodes (4) and a plurality of second internal electrodes (5) alternately arranged in the stacking direction of a laminate (2), polarity is determined based on the direction of application of a voltage between a first external electrode (6) and a second external electrode (7) such that the first internal electrode (4) is a positive electrode and the second internal electrode (5) is a negative electrode. The first internal electrode (4) has a first metal composition containing Ni and Sn, and the second internal electrode (5) has a second metal composition containing Ni. The second metal composition may contain only Ni, or may contain Ni as the main component with at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, Ru, and Cu, which has a higher standard electrode potential than Ni, as an additive component.SELECTED DRAWING: Figure 1

Description

Technical Field

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

Background Art

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

[0003] A multilayer ceramic capacitor generally includes a laminate having a plurality of stacked 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 a voltage is applied is still insufficient in order to meet the recent demands for miniaturization and large capacitance.

[0006] This invention has been made in view of such problems, and an object thereof is to provide a multilayer ceramic capacitor in which the dielectric layer is further thinned and which exhibits excellent reliability even when a voltage with a high electric field strength is applied.

Means for Solving the Problems

[0007] The multilayer ceramic capacitor according to this invention includes a laminate having a plurality of laminated dielectric layers made of ceramic and a plurality of internal electrodes respectively 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 electrodes include a plurality of first internal electrodes and a plurality of second internal electrodes alternately arranged in the stacking direction of the laminate, and the external electrodes include a first external electrode electrically connected to the first internal electrodes and a second external electrode electrically connected to the second internal electrodes.

[0009] In order to solve the above-described technical problems, in this invention, the polarity based on the application direction of the voltage applied between the first external electrode and the second external electrode is determined such that the first internal electrode is the positive electrode and the second internal electrode is the negative electrode. The first internal electrode has a first metal composition containing Ni and Sn, the second internal electrode has a second metal composition containing Ni, and the second metal composition of the second internal electrode is characterized in that it has Ni as the main component and at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, Ru, and Cu having a standard electrode potential higher than that of Ni as an additive component.

[0010] Note that the first metal composition and the second metal composition are different from each other and are different in at least one of the types and contents of the constituent elements.

Advantages of the Invention

[0011] According to this invention, insulation degradation during voltage application of the multilayer ceramic capacitor can be suppressed, and thus a multilayer ceramic capacitor with excellent reliability can be obtained.

[0012] In addition, since the first metal composition of the first internal electrode contains Sn, the reliability of the multilayer ceramic capacitor when a voltage is applied can be further improved.

[0013] In addition, since the first internal electrode and the second internal electrode contain Ni, the melting point can be increased compared to the case where, for example, Cu is the main component. Therefore, the first internal electrode and the second internal electrode can be made thinner, so that the number of layers can be increased while maintaining the external dimensions of the multilayer ceramic capacitor, and as a result, the acquired capacitance can be increased.

Brief Description of the Drawings

[0014]

Figure 1

Figure 2

Embodiments for Carrying Out the Invention

[0015] Hereinafter, with reference to FIG. 1, the structure of a multilayer ceramic capacitor 1 according to an embodiment of the present invention will be described.

[0016] The multilayer ceramic capacitor 1 includes a laminate 2. The laminate 2 includes 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 that are alternately arranged in the stacking direction of the laminate 3. External electrodes 6 and 7 are provided on the outer surfaces of the laminate 2, more specifically, on 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.

[0017] The compositions of the internal electrodes 4 and 5 will be described later. The external electrodes 6 and 7 have, for example, Ag or Cu as the main component of the conductive component. The dielectric layer 3 is preferably made of a dielectric ceramic containing a perovskite-type compound containing Ba and Ti (however, a part of Ba may be substituted with Ca, and a part of Ti may be substituted with Zr) as the main component. In particular, when the main component of the dielectric layer 3 is BaTiO 3 it exhibits a high dielectric constant, and the multilayer ceramic capacitor 1 exhibits excellent reliability. In addition to the above main component, the dielectric layer 3 may contain, for example, rare earth elements, Mn, Mg, Si, etc. as sub-components.

[0018] The raw material powder of the dielectric ceramic is produced, for example, by a solid-phase synthesis method. Specifically, first, compound powders such as oxides and carbonates containing the constituent elements of the main component are mixed at a predetermined ratio and calcined. In addition to the solid-phase synthesis method, a hydrothermal method or the like may be applied. In the dielectric ceramic, alkali metals, transition metals, Cl, S, P, Hf, etc. may be contained within a range that does not interfere with the effects of the present invention.

[0019] The multilayer ceramic capacitor 1 is produced, for example, as follows. A ceramic slurry is produced using the raw material powder of the dielectric ceramic obtained as described above. Next, a ceramic green sheet is formed by a sheet forming method or the like. Next, a conductive paste to be each of the internal electrodes 4 and 5 is applied by printing or the like on a predetermined ceramic green sheet among the plurality of ceramic green sheets. Next, after laminating a plurality of ceramic green sheets, they are pressure-bonded to obtain a raw laminate. Next, the raw laminate is fired. In this firing step, the dielectric layer 3 made of a dielectric ceramic is obtained. Thereafter, the external electrodes 6 and 7 are formed on the end faces of the laminate 3 by baking or the like.

[0020] The multilayer ceramic capacitor 1 is characterized in that, during actual use, the polarity based on the direction of voltage applied between the first external electrode 6 and the second external electrode 7 is defined 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, it is preferable that, for example, a polarity indication mark is provided on the outer surface of the multilayer ceramic capacitor 1.

[0021] In this regard, the multilayer ceramic capacitor targeted by this invention is not limited to a two-terminal type having the first external electrode 6 and the second external electrode 7 as shown in FIG. 1, and may be a multi-terminal type having three or more external electrodes. In this case, it may be configured such that a voltage is applied between two specific sets of external electrodes selected from the three or more external electrodes so that the first internal electrode becomes the positive electrode and the second internal electrode becomes the negative electrode, that is, between at least one first external electrode and at least one second external electrode.

[0022] The multilayer ceramic capacitor 1 is characterized in that each of the first internal electrode 4 and the second internal electrode 5 is selected as follows. That is, the first internal electrode 4 serving as the positive electrode has a first metal composition containing Ni and Sn, the second internal electrode 5 serving as the negative electrode has a second metal composition containing Ni, and the second metal composition of the second internal electrode has Ni as the main component and at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, Ru, and Cu, whose standard electrode potential is higher than that of Ni, as an additive component.

[0023] The selection of each of the metal compositions of the first internal electrode 4 and the second internal electrode 5 is based on the following findings.

[0024] Although the insulation degradation mechanism of a general multilayer ceramic capacitor remains unclear, it is known that the trigger is the negative electrode segregation of oxygen ions (positive electrode segregation of oxygen vacancies) accompanying voltage application. Therefore, it is predicted that suppressing the negative electrode 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, the negative electrode segregation can be suppressed by causing a reduction reaction (release of oxygen ions) at the negative electrode.

[0025] More specifically, regarding 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 the element, and the lower the value, the more stable the oxide, and the higher the value, the more unstable the oxide.

[0026] That is, in the second internal electrode 5 on the negative electrode side, as shown in FIG. 2, it is configured to include a metal element having 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.

[0027] The standard electrode potentials of the metal elements that can be included in the metal composition of each of the internal electrodes 4 and 5 are listed in ascending order as follows: Ni is -0.26V, 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 at +1.52V.

[0028] The standard electrode potential of Ni contained in the first metal composition of the first internal electrode 4 is -0.26V, and the standard electrode potential of Sn is -0.14V. In contrast, the standard electrode potential of Ni contained in the second metal composition of the second internal electrode 5 is -0.26V. Here, Ni is easily passivated in a state where it is not oxidized, and the standard electrode potential is set to -0.26V, but actually, it can be regarded as being approximately 0V. Therefore, when comparing the standard electrode potentials between the first internal electrode 4 and the second internal electrode 5, for the first internal electrode 4, -0.14V, which is the standard electrode potential of Sn, serves as the reference, and for the second internal electrode 5, approximately 0V due to the passivation of Ni serves as the reference.

[0029] Therefore, according to this embodiment, since the standard electrode potential provided by the second internal electrode 5, which is the negative electrode, is higher than the standard electrode potential provided by the first internal electrode 4, which is the positive electrode, the negative segregation of oxygen ions (positive segregation of oxygen vacancies) accompanying voltage application is suppressed by utilizing the oxidation-reduction reaction in the internal electrodes 4 and 5. As a result, insulation degradation during voltage application of the multilayer ceramic capacitor 1 can be suppressed, and thus, a multilayer ceramic capacitor 1 with excellent reliability can be obtained.

[0030] As described above, the second metal composition of the second internal electrode 5 may contain only Ni, but it is preferably composed mainly of Ni and contains at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, Ru, and Cu, which have a higher standard electrode potential than Ni, as an additive component. Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru contained in the second metal composition are noble metals.

[0031] Regarding the metal compositions of the internal electrodes 4 and 5, the "main component" refers to the one having the highest content among metal elements, and more specifically, the one having a content of 50% or more.

[0032] In the above preferred embodiment, the standard electrode potential of Ni contained in the first metal composition of the first internal electrode 4 is -0.26V, and the standard electrode potential of Sn is -0.14V. On the other hand, Au, Pt, Ir, Pd, Os, Ag, Rh, Ru, and Cu, which are additive components of the second metal composition of the second internal electrode 5, all have a standard electrode potential higher than that of Sn.

[0033] Therefore, at least one metal element of Au, Pt, Ir, Pd, Os, Ag, Rh, Ru, and Cu added to the second metal composition of the second internal electrode 5, which is the negative electrode, can cause a reduction reaction more in the second internal electrode 5, which is the negative electrode, and can more effectively suppress the negative segregation of oxygen ions.

[0034] As described above, the higher the standard electrode potential, the more unstable the oxide. Therefore, the metal elements that may be included as additive components in the second metal composition of the second internal electrode 5 described above are in the order of increasing standard electrode potential, namely Cu, Ru, Rh, Ag, Os, Pd, Ir, Pt, Au, and the effect of suppressing the negative segregation of oxygen ions becomes higher.

[0035] Also, it is preferable that the first metal composition of the first internal electrode 4 does not contain a metal element having a standard electrode potential higher than that of Sn. This is because the relatively low standard electrode potential of the first metal composition can be advantageously maintained.

[0036] In addition, since both the first metal composition of the first internal electrode 4 and the second metal composition of the second internal electrode 5 contain Ni, the melting point can be increased compared to the case where, for example, Cu is the main component. Therefore, the first internal electrode 4 and the second internal electrode 5 can be made thinner, so that the number of layers can be increased while maintaining the external dimensions of the multilayer ceramic capacitor 1, and as a result, the acquired capacitance can be increased.

[0037] Note that Ni and Sn contained in the first metal composition of the first internal electrode 4 are included in the conductive paste applied onto the ceramic green sheet during the manufacturing process of the multilayer ceramic capacitor 1. However, they may be included in the conductive paste in the form of an alloy or an intermetallic compound containing Ni and Sn in advance, or Ni and Sn may be included in the conductive paste in separate forms. Even when the second metal composition of the second internal electrode 5 contains a plurality of metal elements, they may be included in the conductive paste in the form of an alloy or an intermetallic compound containing a plurality of metal elements in advance, or they may be included in the conductive paste in the form of separate metal elements.

[0038] Also, Ni and Sn contained in the first metal composition of the first internal electrode 4 are preferably alloyed at the stage of the multilayer ceramic capacitor 1 as a product. Similarly, when the second metal composition of the second internal electrode 5 contains a plurality of metal elements, at the stage of the multilayer ceramic capacitor 1 as a product, these plurality of metal elements are preferably alloyed.

Description of Reference Numerals

[0039] 1 Multilayer ceramic capacitor 2 Laminate 3 Dielectric layer 4 First internal electrode 5 Second internal electrode 6 First external electrode 7 Second external electrode

Claims

1. a laminate including a plurality of laminated dielectric layers made of ceramic and a plurality of internal electrodes respectively disposed along a plurality of interfaces between the dielectric layers; a plurality of external electrodes provided on an outer surface of the laminate and electrically connected to the internal electrodes; Equipped with the internal electrodes include a plurality of first internal electrodes and a plurality of second internal electrodes arranged alternately with respect to a 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, a polarity based on a direction of application of a voltage between the first external electrode and the second external electrode is determined so that the first internal electrode is a positive electrode and the second internal electrode is a negative electrode; the first internal electrode has a first metal composition including Ni and Sn; The second internal electrode has a second metal composition including only Ni. Multilayer ceramic capacitor.

2. 2. The multilayer ceramic capacitor according to claim 1, wherein the first metal composition of the first internal electrodes does not contain any metal element having a standard electrode potential higher than that of Sn.

3. 3. The multilayer ceramic capacitor according to claim 1, wherein said outer surface is provided with a mark indicating a polarity.

4. 3. The multilayer ceramic capacitor according to claim 1, wherein the multilayer ceramic capacitor is a two-terminal type having only the first external electrode and the second external electrode as the external electrodes.

5. 3. The multilayer ceramic capacitor according to claim 1, wherein the multilayer ceramic capacitor is a multi-terminal type, and further comprises, as the external electrodes, another external electrode different from the first external electrode and the second external electrode, in addition to the first external electrode and the second external electrode.

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