JPH0368118A - Laminated ceramic capacitor - Google Patents

Abstract

PURPOSE:To obtain a highly economical capacitor in which the diffusion of constitution element is suppressed by a method wherein an oxide conductive material layer made of specific material for internal electrode, having specific sintering temperature characteristics, and a ceramic material layer are laminated and sintered. CONSTITUTION:A laminated ceramic capacitor is formed by laminating and sintering an oxide conductive material layer for internal electrode formed by adding CuO to an oxide having a probskite type crystal structure shown by (La, M1)CoO3-delta, and a ceramic material layer for a dielectric, in which CuO is added to a barium titanate dielectric material, having the sintering temperature lower than that of the above-mentioned conductive material layer. As a result, the element diffusion between the dielectric and the internal electrode can be suppressed effectively, sufficient characteristics are maintained, and as specific material is not used, a laminated ceramic capacitor having high economical efficiency can be formed. In the formula, M1 indicates Sr or Ba, and delta indicates 0<delta<0.5.

Description

DETAILED DESCRIPTION OF THE INVENTION Field of Industrial Application This invention relates to a multilayer ceramic capacitor widely used as a circuit component of electronic equipment.

Conventional technology Multilayer ceramic capacitors have a basic structure of a multilayer structure in which thin layers of ceramic dielectric and conductive layers of internal electrodes are alternately laminated, so they are smaller than single-plate ceramic capacitors but have larger capacitance. It has the characteristic that it can be realized. This multilayer ceramic capacitor is made by laminating and sintering a conductive material layer for internal electrodes and a ceramic material layer for a dielectric, but conventionally, because it has a high sinterability, it has been used as a conductive material with a high melting point. When performing high-rise sintering, it is necessary to select materials that do not cause an increase in electrical resistance due to oxidation. Usually, expensive platinum (Pt) and palladium (P) are used as conductor materials.
d) has been used. However, large-capacity capacitors require an increased amount of expensive conductive material, resulting in higher costs.

Ag-
The use of Pd alloys and base metals such as Ni, Fe, Co, and Cu is also being considered. However, when these base metals are used, the firing atmosphere must be strictly controlled to prevent oxidation, but this control is actually very difficult and therefore impractical.

Therefore, it has recently been proposed to use oxide conductor materials that do not have to worry about increases in electrical resistance due to oxidation even during such high-temperature sintering (World Congress on High-Tech Ceramics, June 24-28, 1986). (held in Milan, Italy).

Problems to be Solved by the Invention However, even when an oxide conductor material is used for the internal electrodes, high resistance of the internal electrodes cannot be avoided. During firing, the constituent elements mutually diffuse between the oxide conductor material layer and the dielectric ceramic material layer, particularly the constituent elements of the oxide conductor material diffuse into the ceramic material.
This is because it not only increases the resistance of the internal electrodes but also deteriorates the insulation of the dielectric. In this case, high frequency losses, equivalent series resistance.

Important capacitor characteristics such as leakage current are not sufficient.

In response to this, attempts have been made to lower the firing temperature and minimize the diffusion of the constituent elements. The goal is to lower the firing temperature by adding sintering aids and pulverizing the material. However, even this is not enough to effectively stop the spread.

In view of the above-mentioned circumstances, an object of the present invention is to provide an inexpensive multilayer ceramic capacitor with excellent characteristics in which the diffusion of constituent elements is effectively suppressed. Therefore, the multilayer ceramic capacitor according to claim 1 has a structure in which an oxide conductor material layer for internal electrodes and a ceramic material layer for a dielectric are laminated and sintered, and the layered oxide conductor material is laminated and sintered. In this case, a ceramic material whose sintering temperature is higher than that of the ceramic material is used.

As a specific oxide conductor material, for example, claim 2
As described in the invention, the oxide conductor material is an oxide having a perovskite crystal structure represented by the following formula, and CuO
Examples include (La, Ml) Coos-δ. The amount of CuO added to this oxide is
It is said to be about 10 wt% or less.

A specific ceramic material to be combined with this oxide conductor material includes, for example, a barium titanate-based dielectric material to which CuO is added, as in the third aspect of the invention. Examples of barium titanate-based dielectric materials include Zr-added barium titanate produced by hydrothermal synthesis and having a particle size of approximately 0.2 μm. The amount of CuO added to the barium titanate dielectric material is usually about 0.1-5 wt%.

In the case of the above combination, it is desirable that there is a sintering temperature difference of about 50° C. between the two materials. The oxide conductor material and dielectric ceramic material used in the present invention are not limited to the above combination.

Function: In the multilayer ceramic capacitor of the present invention, an oxide conductor material whose sintering temperature is higher than that of the ceramic material is used, so that elemental diffusion between the dielectric material and the internal electrodes is effective. It has been suppressed.

Conventionally, the sintering temperature of the oxide conductor material and the ceramic material is almost the same, and when the sintering temperature is reached, the constituent elements of both materials are in a state where they are most active and easily transferable to each other.
Mutual diffusion is likely to occur. If the sintering temperatures of the art materials 4 are approximately the same, even if the sintering temperature is low, the situation in which elements tend to diffuse into each other will not be completely eliminated.

In the case of this invention, the dielectric ceramic material is sintered first, but in this state the oxide conductor material is not yet completely sintered and the degree of activation of the elements in the material is limited. Since it is relatively weak, interdiffusion, especially problematic diffusion from the oxide conductor material to the ceramic material, is small. In this state, the sintering of the dielectric ceramic material is completed, and the temperature is increased to a point at which the oxide conductor material can be sintered. In this case, the elements of the oxide conductor material will also become fully active, but since the dielectric ceramic material has already been sintered to form a stable crystal lattice, the ceramic material of the constituent elements of the oxide conductor material Diffusion to the sides is suppressed.

Furthermore, even if there is a difference in the sintering temperature between the two materials, if the sintering temperature of the oxide conductor material is lower than the sintering temperature of the ceramic material, the element diffusion between the dielectric material and the internal electrode will be effective. cannot be suppressed. In this case, the oxide conductor material is sintered first, followed by the dielectric ceramic material at a higher temperature. The crystals of oxide conductor materials are often of the oxygen-deficient type, and the oxygen sites in the crystal lattice are vacancies, so even if sintering is completed first and the crystal lattice is constructed.

When exposed to even higher temperatures, the activated elements of the dielectric ceramic material easily diffuse into the oxide conductor, resulting in an increase in resistance.

In this way, the multilayer ceramic capacitor of this invention
Elemental diffusion between the dielectric and the internal electrodes is suppressed, preventing deterioration of the insulation of the dielectric and high resistance of the internal electrodes, making it excellent in terms of high frequency loss, equal series resistance, leakage current, etc. It has certain characteristics.

Note that CuO added to both materials has a sintering accelerating effect, lowers the sintering temperature, and functions to further suppress element diffusion.

Example Next, embodiments of the invention will be described in detail.

FIG. 1 shows an embodiment of a multilayer ceramic capacitor according to the present invention.

The basic structure of this capacitor is a laminated structure 1 in which a dielectric material 2 made of a dielectric thin layer and an internal electrode 3 made of a thin oxide conductor layer are alternately laminated. Connecting electrodes 4.4 are provided on the right and left surfaces of the laminated structure 1, and each internal electrode is distributed and connected to the left and right connecting electrodes 4, 4 at a time. Further, an outer surface electrode 5 is provided on the outside of the connection electrode 4.

The dielectric material 2 is mainly composed of barium titanate and contains zirconium oxide and rare earth oxide as a shifter for shifting the dielectric Curie point temperature, and also contains CuO as a sintering aid.
It is made of a material with added.

The internal electrode 3 is formed of a material in which CuO is added to Lao, 55r05 Coax-based oxide.

The connection electrode 4 is made of Pd, Agt, or an oxide conductor similar to the internal electrode, and the outer electrode 5 is made of Ni.

It is made of a plating thin film of Cr, solder, etc.

The laminated structure 1 is formed by laminating and sintering an oxide conductor material layer for internal electrodes and a ceramic material layer for dielectric, and the sintering temperature of the oxide conductor material is lower than the sintering temperature of the ceramic material. As mentioned above, prices are also rising.

The dielectric ceramic material used here is made by adding Cu to barium titanate powder with a Zr additive, which is produced by hydrothermal synthesis and has a uniform particle size of about 0.2 μm for low-temperature sintering.
1 wt% of O powder was added. This ceramic material is made into a green sheet by a conventional method.

On the other hand, oxide conductor materials include Laa, 5Sro, 5Co
5 wt % of CuO is added to the calcined powder having a perovskite structure with 05-δ (0 x 065). This oxide conductor material is ground into a paste using a ball mill.

The calcined powder used here is prepared by preparing an oxalate compound by a coprecipitation method in which La, Sr, and Co are adjusted to a predetermined ratio, and then calcining it in an air atmosphere at 13,000C for 12 hours.
Obtaining a calcined product with a completely perovskite crystal structure,
It is made by crushing it and it is dusted.

Using the obtained paste, a predetermined internal electrode pattern is printed on a green sheet using the same screen printing method as in the case of conventional Pd internal electrodes. After stacking a specified number of printed green sheets, they are cut into chips.
Then, after firing 10500C for 11 hours, connecting electrodes and outer electrodes were formed to complete a multilayer ceramic capacitor.

In this firing, as shown in FIG. 2, first, the ceramic material undergoes sintering shrinkage, and then the oxide conductive material undergoes sintering shrinkage at a slightly higher temperature.

The shrinkage rates of both materials are sufficiently large and a dense sintered body can be obtained. Moreover, since the shrinkage rates are about the same, the sintered body will not be distorted.

As a comparative example, by clicking on the above example, both materials are CuO.
A multilayer ceramic capacitor was obtained in the same manner except that one containing no 1 was used. In this case, the sintering temperatures of both materials are approximately equal to 1300'C.

The multilayer ceramic capacitor of the example has a high frequency loss ta
The nδ (1kHz) was 5% and the capacity achievement rate was 85%, which was superior to the comparative example's loss of 20% and achievement rate of 30%, confirming that the dielectric and internal electrodes had sufficient performance. .

Among these, the characteristics of only the above-mentioned oxide conductor material were also separately confirmed as follows.

A material obtained by adding 5 wt% of CuO to the above calcined powder was mixed and pulverized in a ball mill for 12 hours.
A pellet-shaped sintered body was obtained under the firing conditions of 12 hours at °C. This sintered body has a shrinkage rate of 18.8%, 8X10-'Ω
・It was the specific resistance of α. Therefore, it can be seen that the internal electrodes of the capacitor have low resistance. Furthermore, CuO
Pellets obtained in exactly the same manner except that no additive was added had a shrinkage rate of 0.3% and a specific resistance of 2×10 −3 Ω·(1).

The pellet-shaped sintered body obtained in the same manner except that the calcination temperature was changed from 13,000C to 10,000C (CuO was added by 5wt%) had a shrinkage rate of 15% and a 9X
The specific resistance was 10”Ω·α.

This shows that it is possible to fully control the shrinkage rate and sintering temperature by selecting the calcination temperature.

Effects of the Invention As described above, the multilayer ceramic capacitors according to claims 1 to 3 have sufficient characteristics because dielectric breakdown and elemental diffusion between internal electrodes are effectively suppressed. There is no need to use expensive materials for the internal electrodes, and firing can be carried out in an air atmosphere using a commonly used electric furnace, making it low cost and extremely practical.

[Brief explanation of drawings]

FIG. 1 is a schematic cross-sectional view of the structure of an example of a multilayer ceramic capacitor according to the present invention, and FIG. It is a graph showing a relationship. DESCRIPTION OF SYMBOLS 1... Laminated structure, 2... Dielectric, 3... Internal electrode, 4... Connection electrode, 5... External electrode. Ditch I diagram

Claims (3)

[Claims] (1) An oxide conductor material layer for internal electrodes and a ceramic material layer for dielectric are laminated and sintered, and the oxide conductor material is a laminated ceramic whose sintering temperature is higher than that of the ceramic material. capacitor. (2) The oxide conductor material for internal electrodes is obtained by adding CuO to an oxide having a perovskite crystal structure represented by the following formula (La, M1)CoO_3-δ, where M1: Sr or The multilayer ceramic capacitor according to claim 1, wherein Ba 0 < δ < 0.5. (3) The multilayer ceramic capacitor according to claim 1 or 2, wherein the dielectric ceramic material is a barium titanate dielectric material to which CuO is added.