JP2001006971A - Multilayered dielectric element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a multilayered dielectric element which has a superior insulation characteristic even when its dielectric layers are relatively thin. SOLUTION: A multilayered dielectric element 10 is constituted by laminating many dielectric layers 14 upon another with metallic thin film electrodes 16 in between. The electrodes 16 are made of a base metal, such as the nickel, etc., which is relatively easily oxidized and each dielectric layer 14 has a thickness of <=4.0 μm. In addition, the coverage of each electrode 16 is 58-78%. The coverage is defined as the ratio of the actual area of the electrode 16 reduced by many pores uniformly distributed on the electrode 16 to the nominal area of the electrode 16.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a multilayer dielectric element comprising a plurality of dielectric layers laminated with electrodes interposed therebetween.
More specifically, the present invention relates to a multilayer dielectric element having improved insulation resistance.

[0002]

2. Description of the Related Art In recent years, with the spread of mobile communication devices and the increase in component mounting density in various electronic devices, demand for small multilayer dielectric elements such as multilayer dielectric capacitors or multilayer dielectric filters has increased. I have. Further, in this type of multilayer dielectric element, further miniaturization is achieved by reducing the thickness of the dielectric layer (so-called thinning). In particular, in the field of multilayer dielectric capacitors, miniaturization and increase in capacity are progressing due to further reduction in the number of layers and the number of layers.

A multilayer dielectric capacitor using a base metal such as Ni, which is relatively easily oxidized, as an electrode material,
In the manufacturing process, firing is usually performed in a reducing atmosphere in order to prevent oxidation of the electrodes. However, the firing process in such a reducing atmosphere also tends to reduce the dielectric material itself. It is known that the insulating properties of the layers are deteriorated. In order to cope with such deterioration of the insulation properties, usually, a baking step as described above is followed by a process of injecting oxygen into the dielectric layer called a reoxidation process.

However, as described above, when the thickness of the dielectric layer is further reduced and the layer thickness is reduced to several μm or less, it becomes difficult to improve the insulation characteristics of the dielectric layer by reoxidation. This is probably because the extremely thin dielectric layers result in a relatively large number of traps of oxygen by the Ni electrodes sandwiching each layer, making it difficult to perform sufficient oxygen injection into the entire dielectric layers. .

[0005]

SUMMARY OF THE INVENTION Accordingly, one object of the present invention is to provide a multilayer dielectric device having excellent insulating properties even when the dielectric layer is relatively thin.

In order to achieve the above object, a multilayer dielectric element according to the present invention, comprising a plurality of dielectric layers laminated with a metal thin film electrode interposed therebetween,

The material of the metal thin film electrode contains a base metal which is relatively easily oxidized,

The dielectric layer has a thickness of 4.0 μm or less;

The above metal thin film electrode has a coverage of 58% or more and 7% or more.
8% or less. Here, the coverage is defined as the area of the electrode when the metal thin film is formed in a perfect shape without generating micropores or the like.
It is defined by the ratio of the actual effective area obtained by subtracting the total area of micropores and the like uniformly distributed on the metal thin film of the electrode.

[0010] In the multilayer dielectric element having such a configuration, during the reoxidation process in the manufacturing process, oxygen is diffused throughout the dielectric layer through micropores and the like uniformly distributed in the electrodes. While the insulating properties of the dielectric layer are improved, the desired properties (eg, capacitance) of the device are hardly affected. In this case, when the thickness of the dielectric layer exceeds 4 μm, the insulation resistance of the dielectric layer hardly decreases even if the coverage is higher than 78%. On the other hand, if the coverage is less than 58%, the desired characteristics cannot be achieved.

[0011] Further, in such a multilayer dielectric element,
When the number of the dielectric layers is 50 or more, the improvement of the insulating properties is particularly effective. Further, the base metal material is Ni
This makes it possible to obtain a multilayer dielectric element which is inexpensive and has excellent insulation properties. Further, the dielectric layer is usually formed from a ceramic material, and a multilayer ceramic capacitor can be manufactured using such a ceramic material.

Further, a method of manufacturing a multi-layer dielectric element comprising a plurality of dielectric layers according to the present invention laminated with a metal thin film electrode interposed between the respective layers,

A metal thin film electrode containing a base metal material is formed on a plurality of green sheets having a predetermined thickness containing a dielectric material, respectively.

These green sheets are laminated to form a laminate,

Firing the laminate in a reducing atmosphere;

The fired laminate is reoxidized by heating in an oxidizing atmosphere.

Each of the steps has the steps described above, whereby the thickness of each of the dielectric layers formed from each of the green sheets becomes approximately 4.0 μm or less, and the coverage of the metal thin film electrode is between 58% and 78%. It is characterized by the following.

[0018]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS An embodiment in which a multilayer dielectric element according to the present invention is applied to a multilayer ceramic capacitor will be described below in detail with reference to the drawings.

FIG. 1 to FIG. 4 show a multilayer ceramic capacitor 10 according to the present invention. This capacitor 1
Reference numeral 0 denotes a so-called chip-type multilayer ceramic capacitor formed by providing terminal electrodes 12a and 12b at both ends in the longitudinal direction of a substantially rectangular parallelepiped main body 11. 1 to 4 are conceptual drawings for understanding the present invention, and do not show actual capacitors according to the dimensions.

The main body 11 of the capacitor 10 has a large number (for example, 100) of ceramic layers 14, 1 each having a rectangular shape in plan view.
Are formed by sandwiching internal electrodes 16, 16, which have the same rectangular shape in plan view, between the respective layers, and such a lamination mode itself is known. In FIG. 2, only seven ceramic layers and six internal electrodes are shown for ease of explanation. Each ceramic layer 14
Is made of a ceramic material containing, for example, barium titanate (BaTiO ₃ ) as a main component, and has a thickness of, for example, 3.5 μm. Each internal electrode 16 is formed of a metal thin film, and is formed of a relatively oxidizable base metal such as Ni.

Among the internal electrodes 16, for example, odd-numbered internal electrodes 16 -o located on even-numbered ceramic layers 14-e have, as shown in FIG.
2a, and has dimensions slightly smaller than the ceramic layer 14-e, so that
A margin of a fixed width is provided on both side edges of 4-e and an edge on the side of the terminal electrode 12b. Also, as shown in FIG. 4, one end of the even-numbered internal electrode 16-e located on the odd-numbered ceramic layer 14-o has the other terminal electrode 1
2b and the odd-numbered internal electrodes 16-
o having substantially the same dimensions as the ceramic layer 1
A margin of a fixed width is provided on both side edges of 4-o and the edge on the side of the terminal electrode 12a.

The terminal electrode 12 is formed by baking a paste of a metal having good conductivity, such as copper, at a predetermined temperature, and covers the entire corresponding end face of the main body 11 and the main body 1.
1 has an extension of a fixed length extending along the upper and lower surfaces and both side surfaces. In this case, as described above, one terminal electrode 12a is connected to each odd-numbered internal electrode 16-o, and the other terminal electrode 12b is connected to each even-numbered internal electrode 16-o.
e (see FIG. 2).

According to the present invention, the ratio of the actual area to the nominal area of each internal electrode 16 of the capacitor 10 (this ratio is defined as coverage in the present invention) is
It is selected from 58% to 78%. More specifically, according to the present invention, a metal thin film formed as an internal electrode 16 over the entire area defining the above-mentioned nominal area has micropores (FIG. 5) distributed substantially uniformly over the thin film. ) Is formed, and the area of the internal electrode 16 is reduced by an amount corresponding to the total area of these pores, so that the actual area of the electrode 16 is 58% to 78% as compared with the nominal area.
Within the range of.

The inventor of the present application has found that when the coverage of the internal electrode 16 is within the above-mentioned specific range, the capacitance of the capacitor is maintained at a value corresponding to the above-mentioned nominal area, and actually decreases. Experiments have confirmed that there is no such problem. In addition, since each internal electrode 16 has a very large number of fine holes uniformly distributed in this manner, in the above-described reoxidation treatment, injected oxygen can be spread over the entire ceramic layer through these fine holes. This indicates that the insulating properties of the ceramic layer 14 are improved.

[0025]

[Experimental example] A number of ceramic green sheets having a predetermined thickness mainly composed of barium titanate (BaTiO ₃ ) are prepared, and screen printing is performed on these green sheets using a metal paste mainly composed of Ni. A metal thin film electrode having a constant thickness was formed, thereby obtaining a number of green sheets 24 having a metal thin film electrode 26 on the upper surface as shown in FIGS. 6 (a) and 6 (b).

Next, 100 green sheets 24 are alternately stacked in a positional relationship as shown in FIGS. 6 (a) and 6 (b), and green sheets having no electrodes formed on the uppermost and lowermost sides. Was arranged, and the whole was pressed to obtain a chip-shaped laminate. In this case, the electrode 26 corresponds to the internal electrode 16.

Next, such a chip-shaped laminate was heated to about 300 ° C. in a furnace to firstly perform a binder removal treatment.
Next, the chip-like laminate is fired at about 1200 ° C. for about 2 hours in a reducing atmosphere obtained by introducing a gas such as N ₂ + H ₂ into the furnace, and subsequently O ₂ is introduced. Change the inside of the furnace to an oxidizing atmosphere.
The re-oxidation treatment was carried out by continuing the heating at the same temperature for about 30 minutes.

Next, after cooling each chip-shaped laminate (that is, the capacitor main body 11) obtained as described above, a copper paste is applied to both ends of each main body 11 by dipping, and then these coated pastes are applied. About 800 ° C
The terminal electrodes 12a and 12b were formed by baking.

The capacitor 1 formed as described above
After extracting some of the sample groups of No. 0, cutting these samples along the surface of the internal electrode 16, and observing the cut surfaces with an electron microscope, the average coverage of the internal electrode 16 was about 66%. (See FIG. 5B). Also,
For each of these capacitors 10, a double terminal electrode 12
When a voltage of, for example, 10 volts was applied between a and 12b to determine the quality of the insulation resistance, the yield related to the insulation resistance was 100%. The capacitance of these capacitors 10 was about 10 μF.

[0030]

COMPARATIVE EXPERIMENTS Next, according to substantially the same process as described above, various sample groups were prepared by slightly differentiating only the film thickness of the metal thin film electrode 26 formed on the green sheet 24. For these sample groups, the coverage of the internal electrode 16, the yield of insulation resistance, and the capacitance were measured in the same manner as described above. The results are shown in the graph of FIG. In this graph, the horizontal axis represents the average coverage of the internal electrode 16 in each sample group in%, and the solid line represents 50%.
%, The yield (%) of the insulation resistance of the sample group is plotted along the right vertical axis for each coverage rate, and the broken line plots the capacity (μF) of the sample group for each coverage rate along the left vertical axis. It was done.

As is clear from this graph, when the coverage of the internal electrode 16 is 78% or less, the yield concerning the insulation resistance becomes 100%, and when the coverage is 58% or more, a decrease in the capacity is recognized. I understand that there is no.

In the comparative example, the thickness of the metal thin film electrode formed by screen printing on the green sheet is changed in order to obtain various coverages. Other methods are also conceivable. For example, a method of changing a method of forming a metal thin film on a green sheet itself, a method of mixing a dielectric material with a metal paste for a metal thin film electrode, and a method of changing a firing temperature can be considered.

The base metal material of the internal electrode in the present invention is not limited to Ni but may be another metal.

[Brief description of the drawings]

FIG. 1 shows a multilayer ceramic capacitor according to one embodiment of the present invention, wherein (A) is a front view, (B) is a side view, and (C) is a plan view.

FIG. 2 is a cross-sectional view taken along line-of FIG.

FIG. 3 is a cross-sectional view taken along line-of FIG.

FIG. 4 is a sectional view taken along the line − in FIG. 2;

FIG. 5 is a photomicrograph of an internal electrode in the multilayer ceramic capacitor of the present invention, showing various coverages of the internal electrode.

FIG. 6 is a conceptual diagram for explaining a manufacturing process of the multilayer ceramic capacitor according to the present invention.

FIG. 7 is a graph showing a change in the yield of insulation resistance and a change in capacitance with respect to various coverages of the internal electrodes in the multilayer ceramic capacitor of the present invention.

[Explanation of symbols]

 10: Multilayer ceramic capacitor 11: Capacitor body 12: Terminal electrode 14: Ceramic layer 16: Internal electrode 24: Ceramic green sheet 26: Metal thin film electrode

 ──────────────────────────────────────────────────続 き Continued on the front page F term (reference) 5E001 AB03 AC01 AC09 AD00 AH00 AH03 AH09 AJ01 5E082 AA01 AB03 BC14 BC38 EE05 EE23 FG06 FG26 FG54 GG10 GG28 JJ03 JJ23 MM24 PP08 PP09 PP10

Claims (10)

[Claims] 1. A multilayer dielectric element comprising a plurality of dielectric layers laminated with a metal thin film electrode interposed therebetween, wherein the material of the metal thin film electrode includes a base metal material which is relatively easily oxidized. A multilayer dielectric element, wherein a layer thickness of the layer is 4.0 μm or less, and a coverage of the metal thin film electrode is 58% or more and 78% or less. 2. The multilayer dielectric device according to claim 1, wherein the number of said dielectric layers is 50 or more. 3. The multilayer dielectric device according to claim 1, wherein said base metal material is Ni. 4. The multilayer dielectric device according to claim 1, wherein said dielectric layer is formed of a ceramic material. 5. The multilayer dielectric device according to claim 4, wherein said multilayer dielectric device is a multilayer ceramic capacitor. 6. A method of manufacturing a multilayer dielectric element comprising a plurality of dielectric layers laminated with a metal thin film electrode interposed between the respective layers, wherein a base metal is formed on a plurality of green sheets having a predetermined thickness containing a dielectric material. By forming a metal thin film electrode including a material, laminating these green sheets to form a laminate, firing the laminate in a reducing atmosphere, and heating the fired laminate in an oxidizing atmosphere. Performing a re-oxidation process, whereby the thickness of each dielectric layer formed from each of the green sheets is approximately 4.0 μm.
m, and the coverage of the metal thin-film electrode is 58% or more and 78% or less. 7. The method of manufacturing a multilayer dielectric device according to claim 6, wherein the number of said dielectric layers is 50 or more. 8. The method for manufacturing a multilayer dielectric device according to claim 6, wherein the base metal material is Ni. 9. The method for manufacturing a multilayer dielectric device according to claim 6, wherein the dielectric material is a ceramic material. 10. The method for manufacturing a multilayer dielectric device according to claim 9, wherein said multilayer dielectric device is a multilayer ceramic capacitor.