Multilayer ceramic capacitor

Abstract

Provided is a layered ceramic capacitor that has even thinner dielectric layers and demonstrates excellent reliability, even when voltage that has a high field intensity is applied.　A layered ceramic capacitor (1) comprises a plurality of first internal electrodes (4) and a plurality of second internal electrodes (5) that alternate in the layering direction of a layered body (2). The polarity based on the application direction of voltage applied between a first external electrode (6) and a second external electrode (7) is set such that the first internal electrodes (4) are positive electrodes and the second internal electrodes (5) are negative electrodes. The first internal electrodes (4) have a first metal composition that includes Ni as a principal component, and the second internal electrodes (5) have a second metal composition that includes Cu as a principal component. The first metal composition may include Sn as an added component. The second metal composition may include at least one metal element selected from among Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru as an added component.

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 thinned, 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 has been 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 stacked dielectric layers made of ceramic and a plurality of internal electrodes respectively disposed 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 mainly composed of Ni, and the second internal electrode has a second metal composition mainly composed of Cu. Moreover, the first metal composition of the first internal electrode has Sn as an additive component. It is characterized by this.

[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.

[0011] Regarding the metal composition of the internal electrodes, the “main component” refers to the one having the largest content among the metal elements, and more specifically, the one having a content of 50% or more.

Effects of the Invention

[0012] According to the present invention, it is possible to suppress insulation degradation when a voltage is applied to a multilayer ceramic capacitor, and thus, a multilayer ceramic capacitor with excellent reliability can be obtained.

[0013] Further, in order to provide each of the conductive materials of the first internal electrode and the second internal electrode, it is possible to use metals such as Ni and Cu, which are currently widely used and inexpensive, and thus, the cost efficiency of the multilayer ceramic capacitor can be made excellent.

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 disposed 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 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 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.

[0017] The compositions of the internal electrodes 4 and 5 will be described later. The external electrodes 6 and 7 mainly contain, for example, Ag or Cu as 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). 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 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 green laminate. Next, the green laminate is fired. In this firing step, the dielectric layer 3 made of the 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] In actual use, the multilayer ceramic capacitor 1 is characterized in that the polarity is determined based on the direction of voltage applied 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, it is preferable that, for example, a polarity 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 including the first external electrode 6 and the second external electrode 7 as shown in FIG. 1, and may be a multi-terminal type including 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, 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.

[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 mainly composed of Ni, and the second internal electrode 5 serving as the negative electrode has a second metal composition mainly composed of Cu. Moreover, the first metal composition of the first internal electrode having Sn as an additive component is the second feature.

[0023] The selection of the metal composition of each of the first internal electrode 4 and the second internal electrode 5 as described above 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 segregation of oxygen ions (positive segregation of oxygen vacancies) accompanying voltage application. Therefore, it is predicted that the insulation degradation of the multilayer ceramic capacitor can be suppressed by suppressing the negative segregation of oxygen ions. Thus, it is considered to include an element with stable oxide in the positive electrode and an element with unstable oxide in the negative electrode. Based on this idea, the negative 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. The lower the value, the more stable the oxide, and the higher the value, the less stable the oxide.

[0026] 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 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 +1.52V.

[0028] 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 Sn, which may be an additive component, is -0.14V. On the other hand, Cu, which is the main component of the second metal composition of the second internal electrode 5, as well as Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru, which may be additive components, all have a standard electrode potential higher than that of Ni and Sn.

[0029] Therefore, at least one metal element of Cu, which is the main component of the second metal composition of the second internal electrode 5 serving as the negative electrode, and Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru, which are additive components, can cause a reduction reaction (release of oxygen ions) in the second internal electrode 5 serving as the negative electrode and suppress the segregation of oxygen ions to the negative electrode.

[0030] 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 segregation of oxygen ions to the negative electrode (segregation of oxygen vacancies to the positive electrode) accompanying voltage application is suppressed. As a result, 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.

[0031] The first metal composition of the first internal electrode 4 includes Sn as an additive component exist . When Sn is included, the reliability of the multilayer ceramic capacitor 1 during voltage application can be further improved.

[0032] The second metal composition of the second internal electrode 5 may include at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru, which have a higher standard electrode potential than Cu, as an additive component. In this case, as described above, the higher the standard electrode potential, the more unstable the oxide is. Therefore, the metal elements serving as the above-described additive components 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 segregation of oxygen ions to the negative electrode becomes higher. Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru are noble metals.

[0033] In addition, when the first metal composition of the first internal electrode 4 contains a plurality of metal elements, or when the second metal composition of the second internal electrode 5 contains a plurality of metal elements, these plurality of metal elements are contained in the conductive paste applied onto the ceramic green sheet during the manufacturing process of the multilayer ceramic capacitor 1. However, they may be contained in the conductive paste in the form of an alloy or an intermetallic compound containing a plurality of metal elements in advance, or may be contained in the conductive paste in the form of separate metal elements.

[0034] Also, when the first metal composition of the first internal electrode 4 contains a plurality of metal elements, or 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, it is preferable that these plurality of metal elements are alloyed.

Explanation of Reference Numerals

[0035] 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 having a plurality of stacked 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; Comprising; 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; The external electrodes include a first external electrode electrically connected to the first internal electrode and a second external electrode electrically connected to the second internal electrode; Based on the application direction of the voltage applied between the first external electrode and the second external electrode, the polarity 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 mainly composed of Ni; The second internal electrode has a second metal composition mainly composed of Cu; A multilayer ceramic capacitor.

2. The multilayer ceramic capacitor according to Claim 1, wherein the first metal composition of the first internal electrode contains Sn as an additive component.

3. The multilayer ceramic capacitor according to Claim 1 or 2, wherein the second metal composition of the second internal electrode contains 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, as an additive component.

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