TWI397932B - Multi-layer ceramic capacitor - Google Patents

Description

Multilayer ceramic capacitor

The present invention relates to a multi-layer ceramic capacitor, in particular, in which the capacitance reliability is improved, and the absence of such as electrical short-circuit and cracking is reduced.

Recently, the trend toward smaller electronic devices has led to a demand for ultra-capacity multilayer ceramic capacitors. For this purpose, the multilayer ceramic capacitor must have a higher capacitance without increasing the size. This requires a thinner ceramic layer, a thinner cover layer, and a thinner inner electrode layer.

Fig. 1 is a side cross-sectional view showing an example of a conventional multilayer ceramic capacitor.

Referring to Fig. 1, a multilayer ceramic capacitor 10 includes a cover layer provided as an outermost layer on the upper surface and the lower surface of the multilayer ceramic capacitor 10, and a ceramic sintered body 11 having a plurality of ceramic layers disposed between the cover layers.

The first and second internal electrodes 12a and 12b are alternately disposed between one of the corresponding ones of the ceramic layers. The first and second external electrodes 15a and 15b are formed on the opposite side faces of the ceramic sintered body 11, and are connected to the first and second internal electrodes 12a and 12b, respectively.

In this configuration, in order to increase the capacitance of the capacitor without increasing the size, it is necessary to thin the ceramic cover layer and the internal electrodes 12a and 12b located at the outermost portions. But this The stable electrical properties of the internal electrodes 12a and 12b are not ensured. Therefore, in order to suppress the stable electrical characteristics of the internal electrodes in order to suppress the oxidation of the internal electrodes, sintering should be performed in a reducing atmosphere in which the reduction is performed. The oxygen partial pressure at the atmosphere can be adjusted.

When performed in a reducing atmosphere (which has a regulated partial pressure of oxygen), sintering beneficially affects high temperature reliability such as 150 °C IR characteristics. However, it was observed that the innermost electrode adjacent to the outermost side of the relatively thin cover layer had been oxidized.

2A and 2B are graphs showing the results of electron probe micro analysis (EPMA) for analyzing the oxidation mode of the internal electrodes in the conventional multilayer ceramic capacitor, which is obtained by a reducing atmosphere (which has The adjusted oxygen partial pressure is initiated by sintering.

Referring to the EPMA results of Figures 2A and 2B, it is observed that an oxide layer (indicated by A and B) formed by the Mg-Ni-O phase has been formed adjacent to the outermost side of the internal electrode containing, for example, Ni. On the area.

As described above, these oxide layers are formed by performing sintering in a reducing atmosphere having a regulated partial pressure of oxygen. The oxide layer can trigger structural defects, such as cracking within the covered portion, i.e., covering the crack, and degrading electrical characteristics. Therefore, the reliability and yield of the multilayer ceramic capacitor will be infringed.

One aspect of the present invention provides a multilayer ceramic capacitor having an oxidation resistant structure, although in a reducing atmosphere (which has a regulated partial pressure of oxygen) Sintering, the anti-oxidation structure can still prevent the loss due to oxidation of the internal electrodes.

According to another aspect of the present invention, there is provided a multilayer ceramic capacitor comprising: a ceramic sintered body having a cover layer disposed on an upper surface and a lower surface of the ceramic sintered body as an outermost layer, and a plurality of layers disposed thereon a ceramic layer covering the interlayer; the first and second internal electrodes are formed on the ceramic layers, the first and second internal electrodes are stacked to insert one of the ceramic layers; the first and second external electrodes Forming on opposite sides of the ceramic sintered body to respectively connect to the first and second internal electrodes; and a plurality of layers of antioxidant electrode layers respectively formed adjacent to the cover layers and the ceramic layers Between these, the antioxidant electrode layers are disposed so as not to affect the capacitance.

The antioxidant electrode layers may be formed of the same material as that used for the first and second internal electrodes. Each of the antioxidant electrode layers has at least one oxidized portion.

Each of the first and second internal electrodes and the antioxidant electrode layers may be formed of a Ni layer. The oxidized portion of the antioxidant electrode layer may be a Mg-Ni-O phase.

Each of the antioxidant electrode layers may have a width equal to or greater than a width of the first and second internal electrodes, and the antioxidant electrode layers may extend in a length direction without respectively corresponding to the first and second External electrode contact.

The antioxidant electrode layers may be spaced apart from the first and second external electrodes by a distance of at least 5 μm.

Alternatively, each of the antioxidant electrode layers may be connected to one of the external electrodes having the same polarity as the adjacent one of the first and second internal electrodes. The antioxidant electrode layer may have the same or larger area than the adjacent ones of the first and second internal electrodes, and the antioxidant electrode layer may be superposed on the adjacent ones of the first and second internal electrodes .

The antioxidant electrode layer may be spaced apart from the corresponding electrode of the first and second external electrodes that is not connected to the antioxidant electrode layer by a distance of at least 5 μm.

The antioxidant electrode layers adjacent to the first and second internal electrodes, respectively, may comprise a plurality of layers of antioxidant electrode layers to further prevent oxidation.

Each of the cover layers may comprise BaTiO ₃ and MgO, wherein MgO is 0.5 mol or less than 100 mol of BaTiO ₃ .

Exemplary embodiments of the present invention will now be described in detail with reference to the drawings.

Fig. 3 is a side sectional view showing a multilayer ceramic capacitor according to an exemplary embodiment of the present invention.

Referring to Fig. 3, the multilayer ceramic capacitor 30 includes a ceramic sintered body 31 having first and second internal electrodes 32a and 32b.

Although not clearly illustrated in Fig. 3, the ceramic sintered body 31 is understood to include a cover layer formed on the upper surface and the lower surface of the ceramic sintered body 31 as the outermost layer, and a plurality of layers disposed between the cover layers. .

The ceramic sintered body 31 includes first and second external electrodes 35a and 35b formed on opposite sides, and the first and second internal electrodes 32a and 32b are connected to the first and second external electrodes 35a and 35b, respectively. Between one of the ceramic layers.

The multilayer ceramic capacitor 30 includes antioxidant electrode layers 34a and 34b disposed between the outermost layers (cover layers) and adjacent to the ceramic layers. As described above, when the sintering is performed in a reducing atmosphere having a regulated oxygen partial pressure to control oxidation and electrical characteristics of the internal electrodes, the antioxidant electrode layers 34a and 34b prevent the first outermost portion The first and second internal electrodes are oxidized.

The antioxidant electrode layers 34a and 34b of the present embodiment are not connected to any of the first and second external electrodes 35a and 35b so as not to affect the capacitance. In this case, in order to prevent oxidation more effectively, the width of each of the antioxidant electrode layers 34a and 34b may be the same as or larger than the width of the first and second internal electrodes 32a and 32b, and may extend in the longitudinal direction to The first and second external electrodes 35a and 35b are not in contact. Here, even if it is not required in the present embodiment, each of the antioxidant electrode layers 34a and 34b may be spaced apart from the first and second external electrodes 35a and 35b by a distance of at least 5 μm, respectively, to effectively prevent the first And the second internal electrodes 32a and 32b are oxidized, and the influence of the electrodes on electrical characteristics is minimized.

The antioxidant electrode layers 34a and 34b of the present embodiment may be formed of a metal material, particularly the same material as that used for the first and second internal electrodes 32a and 32b. In general, internal electrodes made of nickel are sintered in a reducing atmosphere (which has a regulated partial pressure of oxygen). Here, antioxidant electricity The pole layers 34a and 34b may be made of nickel.

In fact, in the multilayer ceramic capacitor 30 of the present embodiment, the antioxidant electrode layers 34a and 34b can maintain local oxidation in a sintering process. As described above, in the case where the antioxidant electrode layers 34a and 34b are formed of the Ni layer, the oxidized portion of the antioxidant electrode layers 34a and 34b may exist as the Mg-Ni-O phase.

Meanwhile, in order to prevent the Mg-Ni-O phase from being formed in the first and second internal electrodes 32a and 32b in addition to the antioxidant electrode layers 34a and 34b, the ratio of the minor component in the cover layer can be adjusted. In general, for example, in the case where the cover layers contain BaTiO ₃ as a main component and MgO as a secondary component, MgO may represent equal to or less than 0.5 mol with respect to 100 mol of BaTiO ₃ .

4A and 4B are side cross-sectional and exploded perspective views respectively illustrating a multilayer ceramic capacitor structure according to an exemplary embodiment of the present invention.

Referring to Fig. 4, the multilayer ceramic capacitor 40 includes a ceramic sintered body 41 having first and second internal electrodes 42a and 42b.

As shown in the exploded perspective view of FIG. 4B, the ceramic sintered body 41 of FIG. 4A includes a cover layer formed on the upper surface and the lower surface of the ceramic sintered body 41 as the outermost layer, and a plurality of layers disposed between the cover layers. Ceramic layer. Furthermore, one of the first and second internal electrodes 42a and 42b is alternately disposed while being inserted into one of the corresponding ones of the ceramic layers to be respectively connected to the first and second external electrodes 45a and 45b. First and second internal electrodes 42a and 42b disposed to be inserted into corresponding ones of the ceramic layers are respectively connected to the first and second external electrodes formed on the opposite sides 45a and 45b, as shown in Figure 4A.

Furthermore, the multilayer ceramic capacitor 40 includes the cover layers 41a and 41b and the antioxidant electrode layers 44a and 44b which are respectively inserted between the cover layer 41a and the adjacent ones of the ceramic layers.

As shown in FIG. 4A, each of the antioxidant electrode layers 44a and 44b in the present embodiment is connected to the first and second external electrodes 45a and 45b and has the same as the adjacent ones of the first and second internal electrodes. The external electrode of the polarity, thereby not affecting the capacitance. In this configuration, as shown in FIG. 4, each of the antioxidant electrode layers 44a and 44b may be formed to have an area substantially the same as or larger than one of the first and second internal electrodes to be protected, while being substantially Superimposed on the corresponding internal electrode. This ensures that the antioxidant electrode layers 44a and 44b are more sufficient to prevent oxidation.

The antioxidant electrode layers 44a and 44b may be spaced apart from the unconnected electrodes (45a or 45b) of the first and second external electrodes by a distance of at least 5 μm to effectively prevent the first and second internal electrodes 42a and 42b. Oxidize and minimize the effects of the electrodes on electrical characteristics.

The antioxidant electrode layers 44a and 44b of the present embodiment may be formed of a metal material, particularly the same material as that used for the first and second internal electrodes 42a and 42b. Similarly, referring to Fig. 3, in the multilayer ceramic capacitor 40 of the present embodiment, the antioxidant electrode layers 44a and 44b can maintain local oxidation during the sintering process. As described above, in the case where the antioxidant electrode layers 44a and 44b are formed of the Ni layer, the oxidized portion of the antioxidant electrode layers 44a and 44b may exist as the Mg-Ni-O phase, for example. This can be confirmed by the following examples and Figures 5A and 5B.

In the embodiment shown in Figures 3 and 4A, an antioxidant electrode layer is employed at each corresponding location. However, multilayer ceramic capacitors may require a greater resistance to oxidation, depending on the nature of the reducing atmosphere or the thickness of the overlay. Here, an additional antioxidant electrode layer may be disposed after additionally providing an additional ceramic layer adjacent to the innermost electrode located at the outermost side. That means that a plurality of layers of antioxidant electrodes can be used.

Hereinafter, the operation and effects of the present invention will be described in more detail by the following examples.

Invention example

In order to confirm the improved effect of the antioxidant electrode layer of the present invention, 120 multilayer ceramic capacitors (having a size of X5R 1.6 mm × 0.8 mm and having the same results as shown in Figures 4A and 4B, that is, several layers of resistance Each of the oxidant electrode layers are connected to the corresponding same polarity) and are designed to have a capacitance of 22 μF. Here, the internal electrode is formed of nickel, and the antioxidant electrode layer is formed of nickel.

As described above, for the multilayer ceramic capacitor, the sintering system is performed in a reducing atmosphere having a regulated partial pressure of oxygen. One of the completed multilayer ceramic capacitors was selected and subjected to scanning electron microscope (SEM) photography of the cross section. 5A and 5B are photographs of a scanning electron microscope (SEM) illustrating a cross section of a multilayer ceramic capacitor fabricated in accordance with the present invention.

Referring to Fig. 5A, only the antioxidant electrode layer was partially formed with an oxide layer thereon, and it was observed that the electrodes located under the (antioxidant electrode layer) in the internal electrodes were not oxidized. However, it was slightly observed that the oxide layer was present around the edge of the antioxidant electrode layer, as shown in Fig. 5B. But this part The edge regions of the internal electrodes are separated and therefore do not directly affect the electrical characteristics such as capacitance.

Comparison example

In order to confirm the effect of the improvement of the antioxidant electrode layer of the present invention, 120 multilayer chip capacitors having the conventional structure (shown in Fig. 1) were fabricated under the same design as the above-described inventive example. Here, however, none of the multilayer wafer capacitors is provided with an antioxidant electrode layer connected to an external electrode having the same polarity as the adjacent internal electrodes. For multilayer ceramic capacitors fabricated according to the comparative example description, in a similar manner to the inventive example, the sintering is performed in a reducing atmosphere having a regulated partial pressure of oxygen.

For a multilayer ceramic capacitor manufactured according to the inventive examples and conventional examples, the capacitance and various defect rates such as a short occurrence rate, a flash defect rate, and a coverage rupture rate are measured ( Cover crack occurrence rate). The measurement results are recorded in Table 1 below.

As can be seen from the first table, the multilayer ceramic capacitor of the inventive example has a significant portion in terms of short circuit occurrence rate, flash missing rate, and coverage crack occurrence rate. Improvement. As such, the inventive examples show better capacitance than the comparative examples. Because of the comparison example, the internal electrode is locally oxidized, so the capacitance cannot be increased. In the invention example, the internal electrode that contributes to the capacitance is protected by the antioxidant electrode layer, thereby preventing oxidation-induced loss. As described above, the antioxidant electrode layer of the inventive example ensures that the internal electrode has a stable electrical characteristic of at least 80%, thereby preventing a decrease in capacitance.

As described above, according to an exemplary embodiment of the present invention, when sintering is performed in a reducing atmosphere having a regulated oxygen partial pressure, in order to suppress internal electrode oxidation and enhance electrical characteristics thereof (the internal electrode), the respective configurations do not affect The resistive electrode layer of the capacitance is adjacent to the outermost inner electrode to significantly reduce the loss caused by oxidation of the internal electrode.

The present invention has been shown and described with respect to the embodiments of the present invention, and modifications and changes may be readily made by those skilled in the art without departing from the spirit and scope of the invention.

10‧‧‧Multilayer Ceramic Capacitors

11‧‧‧Ceramic sintered body

12a‧‧‧First internal electrode

12b‧‧‧Second internal electrode

15a‧‧‧First external electrode

15b‧‧‧Second external electrode

30, 40‧‧‧Multilayer ceramic capacitors

31, 41‧‧‧Ceramic sintered body

32a, 42a‧‧‧ first and

32b, 42b‧‧‧second internal electrode

34a, 34b, 44a, 44b‧‧‧Antioxidant electrode layer

35a, 45a‧‧‧first external electrode

35b, 45b‧‧‧Second external electrode

41a, 41b‧‧ Cover

A, B‧‧‧ oxide layer

The above and other aspects, features, and other advantages of the present invention will be more clearly understood from the aspects of the accompanying drawings in which <RTIgt; And FIG. 2B illustrates an electron probe microanalysis (EPMA) result of analyzing an oxidation mode of an internal electrode in a conventional multilayer ceramic capacitor; FIG. 3 is a side cross-sectional view illustrating a multilayer ceramic capacitor according to an exemplary embodiment of the present invention; FIGS. 4A and 4B BRIEF DESCRIPTION OF THE DRAWINGS FIG. 1 is a side cross-sectional view and an exploded perspective view, respectively, illustrating a multilayer ceramic capacitor structure in accordance with an exemplary embodiment of the present invention; 5A and 5B are photographs of a scanning electron microscopy (SEM) illustrating a partial cross-section of different portions of a multilayer ceramic capacitor structure fabricated in accordance with an exemplary embodiment of the present invention.

30‧‧‧Multilayer ceramic capacitors

31‧‧‧Ceramic sintered body

32a‧‧‧First internal electrode

32b‧‧‧Second internal electrode

34a, 34b‧‧‧Antioxidant electrode layer

35a‧‧‧First external electrode

35b‧‧‧Second external electrode

Claims (12)

A multilayer ceramic capacitor comprising: a ceramic sintered body having a cover layer disposed on an upper surface and a lower surface of the ceramic sintered body as an outermost layer, and a plurality of ceramic layers disposed between the cover layers; Two internal electrodes are formed on the ceramic layers, the first and second internal electrodes are plural to insert one of the ceramic layers; the first and second external electrodes are formed on the ceramic sintered body a side surface connected to the first and second internal electrodes, respectively; and a plurality of antioxidant electrode layers respectively formed between the cover layer and an adjacent one of the ceramic layers, the antioxidant electrode layer It is installed so as not to affect the capacitance. The multilayer ceramic capacitor of claim 1, wherein the antioxidant electrode layers comprise the same material as that used for the first and second internal electrodes. The multilayer ceramic capacitor of claim 2, wherein each of the first and second internal electrodes and the antioxidant electrode layer comprises a Ni layer. The multilayer ceramic capacitor of claim 1, wherein each of the antioxidant electrode layers has at least one oxidized portion. The multilayer ceramic capacitor of claim 4, wherein the oxidized portion of the antioxidant electrode layer is a Mg-Ni-O phase. The multilayer ceramic capacitor of claim 1, wherein each of the antioxidant electrode layers has a width equal to or greater than a width of the first and second internal electrodes, and the antioxidant electrode layers are The length direction extends while not contacting the first and second external electrodes, respectively. The multilayer ceramic capacitor of claim 6, wherein each of the antioxidant electrode layers is separated from the first and second external electrodes by a distance of at least 5 μm. The multilayer ceramic capacitor of claim 1, wherein each of the antioxidant electrode layers is connected to the external electrodes and has the same polarity as the adjacent one of the first and second internal electrodes Corresponding to one (polarity). The multilayer ceramic capacitor of claim 8, wherein the antioxidant electrode layer is spaced apart from a corresponding one of the first and second external electrodes that is not connected to the antioxidant electrode layer by a distance of at least 5 μm. The multilayer ceramic capacitor of claim 8, wherein the area of the antioxidant electrode layer is the same as or larger than an area of an adjacent one of the first and second internal electrodes, and the antioxidant electrode layer is Superimposed on an adjacent one of the first and second internal electrodes. The multilayer ceramic capacitor of claim 1, wherein the antioxidant electrode layers adjacent to the first and second internal electrodes respectively comprise a plurality of antioxidant electrode layers. The multilayer ceramic capacitor of claim 1, wherein each of the cover layers comprises BaTiO ₃ and MgO, wherein the MgO system represents equal to or less than 0.5 mol with respect to 100 mol of BaTiO ₃ .