Multilayer Ceramic Capacitors

Abstract

Provided is a multilayer ceramic capacitor that exhibits excellent reliability even when a dielectric layer becomes thinner and a voltage of a high electric field intensity is applied.　The multilayer ceramic capacitor (1) comprises a plurality of first inner electrodes (4) and a plurality of second inner electrodes (5) alternatingly arranged in the lamination direction of a laminate (2). Polarity based on the application direction of a voltage applied between a first outer electrode (6) and a second outer electrode (7) is established such that the first inner electrodes (4) function as positive electrodes and the second inner electrodes (5) function as negative electrodes. Each first inner electrode (4) has a first metal composition containing Cu as a main component, and each second inner electrode (5) has a second metal composition containing Cu as a main component and containing, as an additional component, 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.

Description

[Technical field]

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

[0002] With the recent advances in electronics technology, multilayer ceramic capacitors are required to be smaller and have higher capacitance. To meet these demands, progress is being made in thinning the dielectric layers of multilayer ceramic capacitors. However, when the dielectric layers are made thinner, the electric field strength applied to each layer becomes relatively higher. Therefore, there is a demand for improved reliability when voltage is applied.

[0003] A multilayer ceramic capacitor generally comprises a laminate having a plurality of laminated dielectric layers and a plurality of internal electrodes arranged 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, it is known that the internal electrodes are mainly composed of Ni, as described in, for example, JP-A-11-283867 (Patent Document 1). [Prior art documents] [Patent documents]

[0004] [Patent Document 1] Japanese Patent Application Publication No. 11-283867 Summary of the Invention [Problem to be solved by the invention]

[0005] However, when the main component of the internal electrodes is Ni, there is a problem in that the reliability when a voltage is applied is still insufficient to meet the recent demands for miniaturization and large capacity.

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

[0007] The multilayer ceramic capacitor of the present invention comprises 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 arranged alternately with respect to 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-mentioned technical problem, in this invention, the polarity is determined based on the direction of application of a voltage between the first external electrode and the second external electrode, 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 mainly composed of Cu, and the second internal electrode has a second metal composition mainly composed 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. The first metal composition of the first internal electrode does not include a metal element having a standard electrode potential higher than that of Ni. It is characterized by the following.

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

[0011] Moreover, with regard to the metal composition of the internal electrodes, the "main component" refers to the metal element that has the largest content, more specifically, the metal element that has a content of 50% or more. Effect of the Invention

[0012] According to the present invention, it is possible to suppress deterioration of the insulation of a multilayer ceramic capacitor when a voltage is applied thereto, and therefore it is possible to obtain a multilayer ceramic capacitor with excellent reliability.

[0013] Moreover, a multilayer ceramic capacitor having good high frequency characteristics can be obtained. [Brief description of the drawings]

[0014] [Figure 1] 1 is a cross-sectional view that typically illustrates a multilayer ceramic capacitor 1 according to an embodiment of the present invention. [Diagram 2] 2 is a diagram for explaining the standard electrode potential of the metal elements contained in each of the first internal electrode (positive electrode) 4 and the second internal electrode (negative electrode) 5 in the multilayer ceramic capacitor 1 shown in FIG. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0015] Hereinafter, with reference to FIG. 1, a structure of a multilayer ceramic capacitor 1 according to one 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 laminated 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 arranged alternately in the lamination 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.

[0017] The composition of the internal electrodes 4 and 5 will be described later. The external electrodes 6 and 7 have Ag or Cu as the main conductive component. The dielectric layer 3 is preferably made of a dielectric ceramic containing a perovskite compound containing Ba and Ti as the main component (wherein Ba may be partially substituted with Ca and Ti may be partially substituted with Zr). In particular, when the main component of the dielectric layer 3 is BaTiO3, a high dielectric constant is exhibited and the multilayer ceramic capacitor 1 exhibits excellent reliability. In addition to the above main components, the dielectric layer 3 may contain, for example, rare earth elements, Mn, Mg, Si, etc. as secondary components.

[0018] The raw powder of the dielectric ceramic is prepared, for example, by a solid-phase synthesis method. Specifically, first, compound powders such as oxides and carbonates containing the constituent elements of the main components are mixed in a predetermined ratio and calcined. In addition to the solid-phase synthesis method, a hydrothermal method or the like may be applied. In addition, the dielectric ceramic may contain alkali metals, transition metals, Cl, S, P, Hf, etc., within the range of amounts that do not impair 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 dielectric ceramic raw material powder obtained as described above. Next, ceramic green sheets are formed by a sheet forming method or the like. Next, a conductive paste to become each of the internal electrodes 4 and 5 is applied by printing or the like onto a predetermined one of the plurality of ceramic green sheets. Next, the plurality of ceramic green sheets are stacked and then pressed together to obtain a green laminate. Next, the green laminate is fired. In this firing step, a dielectric layer 3 made of a dielectric ceramic is obtained. After that, the external electrodes 6 and 7 are formed on the end faces of the laminate 3 by baking or the like.

[0020] The first feature of the multilayer ceramic capacitor 1 is that the polarity is determined based on the direction of application of a voltage between the first external electrode 6 and the second external electrode 7 so that the first internal electrode 4 is a positive electrode and the second internal electrode 5 is a negative electrode during actual use. Therefore, although not shown, it is preferable that a mark indicating the polarity is provided on, for example, the outer surface of the multilayer ceramic capacitor 1.

[0021] In this regard, the multilayer ceramic capacitor to which the present invention is directed is not limited to a two-terminal type having a first external electrode 6 and a second external electrode 7 as shown in Fig. 1, but may be a multi-terminal type having three or more external electrodes. In this case, it is sufficient that the capacitor is configured so 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, so that the first internal electrode is a positive electrode and the second internal electrode is a negative electrode.

[0022] A second feature of the multilayer ceramic capacitor 1 is that the metal compositions of the first internal electrode 4 and the second internal electrode 5 are selected as follows. That is, the first internal electrode 4 serving as the positive electrode has a first metal composition mainly composed of Cu, and the second internal electrode 5 serving as the negative electrode has a second metal composition mainly composed of Cu with 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. Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru contained in the second metal composition are precious metals. Moreover, the first metal composition of the first internal electrode does not contain any metal element having a standard electrode potential higher than that of Cu.

[0023] 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.

[0024] The mechanism of insulation degradation in general multilayer ceramic capacitors has not yet been elucidated, but it is known that the trigger is the negative electrode segregation of oxygen ions (positive electrode segregation of oxygen vacancies) caused by the application of voltage. Therefore, it is predicted that insulation degradation in multilayer ceramic capacitors can be suppressed by suppressing the negative electrode segregation of oxygen ions. One possible solution is to include elements whose oxides are stable in the positive electrode and elements whose oxides are unstable in the negative electrode. Based on this idea, it would be possible to suppress negative electrode segregation by causing a reduction reaction (release of oxygen ions) at the negative electrode.

[0025] More specifically, with regard to the metal composition of each of the first internal electrode 4 and the second internal electrode 5, a metal element whose valence is likely to increase (whose standard electrode potential is low) is used on the side of the first internal electrode 4, which serves as the positive electrode, and a metal element whose valence is likely to decrease (whose standard electrode potential is high) is used on the side of the second internal electrode 5, which serves as the negative electrode. The standard electrode potential is a value specific to an element; the lower the value, the more stable the oxide, and the higher the value, the more unstable the oxide.

[0026] That is, the second internal electrode 5 on the negative electrode side contains a metal element having a standard electrode potential higher than the standard electrode potential of the metal element of the first internal electrode 4 on the positive electrode side, as shown in Fig. 2. In Fig. 2, the standard electrode potential of the first metal composition of the first internal electrode 4 on the positive electrode side may be included in the range A, and the standard electrode potential of the second metal composition of the second internal electrode 5 on the negative electrode side may be included in the range B.

[0027] The standard electrode potentials of the metal elements that may be included in the metal composition of each of the internal electrodes 4 and 5 are, in order from lowest to highest, as follows: 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 Cu, which is the main component of the first metal composition of the first internal electrode 4, is +0.34 V, whereas Au, Pt, Ir, Pd, Os, Ag, Rh and Ru, which are added to the second metal composition of the second internal electrode 5, all have a higher standard electrode potential than Cu.

[0029] Therefore, at least one metal element of Au, Pt, Ir, Pd, Os, Ag, Rh and Ru having a higher standard electrode potential than Cu, which is added to the second metal composition of the second internal electrode 5, which is the negative electrode, can cause a reduction reaction (release of oxygen ions) in the second internal electrode 5, which is the negative electrode, and suppress the segregation of oxygen ions to the negative electrode.

[0030] As described above, the higher the standard electrode potential, the more unstable the oxide is. Therefore, the metal elements that may be contained in the second metal composition of the second internal electrode 5 described above have a greater effect of suppressing the negative electrode segregation of oxygen ions in the order of increasing standard electrode potential, that is, Ru, Rh, Ag, Os, Pd, Ir, Pt, and Au.

[0031] In this manner, according to this embodiment, by focusing on the oxidation-reduction reaction in the internal electrodes 4 and 5, the negative electrode segregation of oxygen ions (positive electrode segregation of oxygen vacancies) caused by voltage application is suppressed by utilizing this oxidation-reduction reaction. As a result, insulation deterioration of the multilayer ceramic capacitor 1 when a voltage is applied thereto can be suppressed, and therefore a multilayer ceramic capacitor 1 with excellent reliability can be obtained.

[0032] As mentioned earlier, The first metal composition of the first internal electrode 4 does not include a metal element having a standard electrode potential higher than that of Cu. It is made to be This is because the relatively low standard electrode potential of the first metal composition can be advantageously maintained.

[0033] 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 are mainly composed of Cu, the high frequency characteristics of the multilayer ceramic capacitor 1 can be made good.

[0034] The multiple metal elements constituting the second metal composition of the second internal electrode 5 are contained in the conductive paste applied to the ceramic green sheet during the manufacturing process of the multilayer ceramic capacitor 1, but may be contained in the conductive paste in advance in the form of an alloy or intermetallic compound containing multiple metal elements, or may be contained in the conductive paste in the form of separate metal elements. When the first metal composition of the first internal electrode 4 contains multiple metal elements, the multiple metal elements may be contained in the conductive paste in advance in the form of an alloy or intermetallic compound containing multiple metal elements, or may be contained in the conductive paste in the form of separate metal elements.

[0035] Moreover, it is preferable that the plurality of metal elements contained in the second metal composition of the second internal electrode 5 are alloyed at the stage of the multilayer ceramic capacitor 1 as a product. [Explanation of symbols]

[0036] 1. Multilayer ceramic capacitors 2. Laminate 3 Dielectric Layer 4 1st internal electrode 5 Second internal electrode 6 1st external electrode 7 Second external electrode

Claims

[Claim 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 containing Cu as a main component, The second internal electrode has a second metal composition containing Cu as a main component and at least one metal element selected from Au, Pt, Ir, Pd, Os, Ag, Rh, and Ru having a standard electrode potential higher than that of Cu as an additive component; The first metal composition of the first internal electrode does not include a metal element having a standard electrode potential higher than that of Cu. Multilayer ceramic capacitor.

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