JP2001114559A - Dielectric composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To obtain a reduction resistant dielectric composition low in rate of change of capacitance in wide temperature range having a long high temperature load life and a large dielectric constant at normal temperature. SOLUTION: This dielectric composition has composition ratio of Nb2O3: 1.0-5.0 mole, ZnO: 1.0-5.0 mole, MgO: 0-3.0 mole, R2O3: 0.5-5.0 mole (R is a rare earth element), BaSiO3: 1.0-10 mole and MnO: 0.1-0.5 mole based on 100 mole of BaTiO3. A multilayer porcelain capacitor having a Ni internal electrode is produced by using the composition.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric such as a multilayer ceramic capacitor in which Ni or a Ni alloy can be used for an internal electrode. More specifically, the present invention relates to a reduction-resistant dielectric composition used for a ceramic capacitor.

[0002]

2. Description of the Related Art A ceramic capacitor using a ceramic mainly composed of titanate such as barium titanate as a dielectric has a small size, a large capacity, good high frequency characteristics, excellent heat resistance, and mass production. From the features such as possible,
In recent years, it has become an indispensable component for industrial and consumer electronic devices. The structure of the capacitor is also
There is also a single-plate type with two electrodes attached, but with the demand for high-density mounting of electronic devices, with the aim of miniaturization and large capacity,
Many laminated types in which a dielectric is thinned and an area of a counter electrode is increased, and a dielectric and a counter electrode are alternately stacked are also manufactured. This multilayer ceramic capacitor prints or applies a paste of conductive metal powder to be an internal electrode on a thin ceramic green sheet, stacks a large number of these and fires and integrates them. It is made by attaching external electrodes that conduct.

[0003] In order to increase the relative dielectric constant of ceramics, it is necessary to perform sufficient firing at a high temperature of about 1300 ° C. At this time, if a part of the oxygen of the ceramic is released or reduced, the dielectric becomes a semiconductor and the insulating property as a capacitor is reduced. Therefore, firing is usually performed in an oxidizing atmosphere containing oxygen. As the internal electrode, if the melting point is low, it may flow out during firing, so a metal that has a melting point higher than the firing temperature of the ceramic, is sintered at the same temperature as the ceramic, and is not oxidized in the oxidizing atmosphere at that temperature is required. It is. Conventionally, Pt, Pd, or an alloy thereof has been used as a suitable metal for the internal electrode. However, these materials are extremely expensive, and as the number of layers increases and the thickness of the ceramic layer decreases, the usage ratio to the total weight of the capacitor increases, and the cost of the capacitor increases. Therefore, Ni and Ni alloys have been applied to electrode materials because of their low specific resistance, high melting point and low cost.

[0004] Ni is oxidized by high-temperature firing in an oxidizing atmosphere. If the oxygen partial pressure is reduced or an atmosphere containing hydrogen is used to prevent the oxidation of Ni, there is a problem that the ceramic is reduced. The reduction of ceramic
It is said that the oxygen bonded to the silicon is released to generate trivalent Ti ions, and the electrical conductivity is increased by the popping conduction through the ions. As a result, not only the relative permittivity is reduced but also the insulation resistance is reduced. This leads to a decrease in breakdown voltage and breakdown voltage. Therefore, there is no practical use of ceramics that have sufficient reduction resistance and good characteristics as a dielectric so that they do not turn into semiconductors or deteriorate in insulation resistance even when fired in an atmosphere of reducing or low oxygen partial pressure. Has been promoted.

[0005] For example, as disclosed in US Patent No. 3920781 (1975), cations having a large ionic radius (divalent ions such as Ba and Ca) of barium titanate ceramics
There is an invention in which the molar ratio between a small cation (a tetravalent ion such as Ti and Zr) is 0.95 or more and less than 1.0. In this case, a base metal such as Ni is used for
If firing at 1400 ° C is performed in an atmosphere with a low oxygen partial pressure, the electrode will not be oxidized, and electrical characteristics equivalent to or better than those using a platinum electrode fired in air will be obtained .

Then, a divalent ion such as Ba, Ti
It has been clarified that it is preferable to slightly increase the molar ratio with respect to the tetravalent ions to 1 for improvement of the reduction resistance. At present, when Ni or the like is used as the internal electrode, the molar ratio is reduced to such a value. It is common to use conductive ceramic dielectrics.

With the improvement of the ceramic dielectric as described above, a base metal such as Ni has been used for the internal electrode. However, when compared with a multilayer capacitor using Pd or the like for the electrode, the stability of the characteristics is still low. Inferior and low reliability.

On the other hand, various improvements have been proposed, such as improvement in performance as well as improvement in reliability. For example,
In the invention disclosed in JP-A-3-133166, part of Ba is replaced by Ca or Sr, part of Ti is replaced by Zr,
After setting the molar ratio to the former to 1.000 to 1.020, Y, Gd, Tb, Dy, Zr, V, Mo, Zn, C
0.005 or more of one or more oxides of d, Tl, Sn and P
There is a multilayer ceramic chip capacitor in which a ceramic to which 0.5% by weight is added is used as a dielectric and Ni or a Ni alloy is used as an internal electrode. It is stated that by adding an oxide such as Y, the life of the insulation resistance is greatly increased as compared with the case where no oxide is added. As similar improvements, the composition molar ratio of BaO system exceeds slightly 1.0 to TiO ₂ system, M
Japanese Patent Application Laid-Open No. 4-367559 discloses an invention of a reduction-resistant dielectric ceramic in which an oxide of n or Cr, an oxide of Si and an oxide of Y are added in an amount of 0.05 to 1.0% by weight, respectively. And further, JP-A-6-45182 and JP-A-6-275
Japanese Patent No. 459 also discloses an invention in which, in addition to the oxides of Y and Mn, oxides of V and W, SiO ₂ , Al ₂ O _{3, and the} like are also included, and the life thereof is increased.

In addition, the molar ratio of BaO-based and TiO ₂ -based is set to 1, and the molar ratio of Y ₂ O ₃ , MnO, Al ₂ O ₃ and NiO
By adding an appropriate amount of, even at a low oxygen partial pressure for making Ni an internal electrode, an invention that a ceramic composition of a capacitor having sufficient reduction resistance can be obtained is also disclosed in JP-A-6-78189. It has been disclosed.

As described above, instead of expensive noble metals such as Pt and Pd, Ni electrodes are used for the internal electrodes of the ceramic capacitor.
In order to use inexpensive base metals such as Ni and Ni alloys, many development studies have been made on ceramic dielectrics whose characteristics do not deteriorate even when the integrated firing is performed in a reducing atmosphere.
However, there is still a strong demand for ceramic capacitors to have a small size and a large capacity, to improve performance and reliability, and to further reduce the manufacturing cost.

One of the problems is that, for example, as in the case of X7R of the EIA standard, the capacitance change ΔC / C (%) due to temperature in a wide temperature range from −55 ° C. to + 125 ° C. is ± 15.
% Or less. If an attempt is made to satisfy such a standard and to obtain a material having a long high-temperature load life, the dielectric constant of the reduction-resistant dielectric will be low at room temperature, making it difficult to reduce the size and capacitance of the capacitor.

[0012]

SUMMARY OF THE INVENTION An object of the present invention is to provide Ni
Or, it can be applied to ceramic capacitors manufactured by integrally firing with Ni alloy as internal electrodes. Especially, the reduction rate of the capacitance is small over a wide temperature range, the high temperature load life is long, and the relative dielectric constant at room temperature is large. It is to obtain a body composition.

[0013]

SUMMARY OF THE INVENTION In general, a reduction-resistant dielectric has a molar ratio of Ba-based divalent ions to Ti-based tetravalent ions slightly larger than 1. In this case, part of Ba is replaced by Sr or the like and part of Ti is replaced by Zr or the like in order to improve the relative dielectric constant at room temperature. On the other hand, to satisfy, for example, X7R of the EIA standard which requires a small capacity change rate in a wide temperature range, and to extend the high-temperature load life, addition of CaO or MgO for improving the temperature characteristics, rare earth element Oxides are required. However, when the molar ratio of divalent / tetravalent ions is made slightly larger than 1, and addition of CaO, MgO, or the like,
As a result, the relative dielectric constant is greatly reduced, and it becomes difficult to obtain a dielectric having a relative dielectric constant exceeding 3000.

The present inventors have conducted various studies in order to obtain a reduction-resistant dielectric material which satisfies the EIA standard X7R, has a long high-temperature load life, and has a relative dielectric constant as high as possible. First, since the relative dielectric constant is high, the molar ratio of divalent / tetravalent ions was set to 1, and the effect of the added component was investigated using BaTiO ₃ . It is known that when CaO or MnO is added to a BaTiO ₃ -based ceramic, reduction resistance is improved. Then, when examining the effect of CaO, the effects of improving the temperature characteristics and improving the reduction resistance described above were recognized, but the relative permittivity dropped significantly, making it difficult to secure a sufficient relative permittivity. Met. MnO also improves the reduction resistance, but also lowers the relative permittivity. However, it has the effect of improving the heat resistance and the sintering density, and it is considered that the use of the minimum necessary is rather desirable.

Further, the effect of various additives was investigated. When Nb ₂ O ₅ and ZnO were added in combination, reduction resistance was improved even if the molar ratio of divalent / tetravalent ions was 1. It has been found that the temperature can be controlled without lowering the relative permittivity, and that good temperature characteristics can be secured. The reasons for these effects are not always clear. However, it seems that the presence of Nb ₂ O ₅ and ZnO suppresses the release of oxygen from BaTiO ₃ when heated at a high temperature and improves the reduction resistance. Nb ₂ O ₅ is said to inhibit grain growth during ceramic sintering, but this is considered to be effective for improving temperature characteristics.

When a reduction-resistant ceramic is used for a multilayer capacitor, it is generally considered that its high-temperature load life is short and its reliability is low. Therefore, there is a case where a rare-earth element Y or an oxide of a lanthanoid is added to improve it. Many. Nb ₂ O ₅ and ZnO
The addition of these elements was effective in prolonging the high temperature load life also in the ceramics to which both were added. Further, since these Y and lanthanoid oxides lower the Curie temperature, they are also effective in improving the relative dielectric constant at room temperature.

However, the addition of Nb ₂ O ₅ or ZnO, and further, the oxides of Y and lanthanoids cause deterioration of sinterability,
In other words, the sintering density of the ceramic decreases and the strength is insufficient. Therefore, as a result of examining an additive which improves the sinterability to reduce the adverse effects of these oxides and does not deteriorate the performance as a capacitor, it has been found that BaSiO ₃ is most suitable.

The EIA standard X7R requires that the temperature characteristic ΔC / C be small over a wide temperature range.
Many of the ceramic compositions discussed above satisfy this temperature characteristic, but depending on the amount of the composition, there may be cases where the standard is deviated. On the other hand, it was also found that the content of ZnO improved the temperature characteristics, and that it was effective to add a small amount of MgO as needed.

As described above, by adding Nb ₂ O ₅ and ZnO to the base material of BaTiO ₃ ,
It has been found that even if the molar ratio of tetravalent ions is 1, sufficient reduction resistance can be obtained and temperature characteristics can be improved. Based on this, a small amount of MnO, Y, lanthanoid oxide, BaSiO ₃ By adding MgO as needed, various other performances were improved, and a nearly desired dielectric composition having a high relative dielectric constant could be obtained. Furthermore, the limits of the contents of each composition were clarified, and the present invention was completed. The gist of the present invention is as follows.

A composition mainly comprising BaTiO ₃ ,
When the composition ratio is 100 mol of BaTiO ₃ , Nb ₂ O ₃ : 1.0 to 5.0 mol ZnO: 1.0 to 5.0 mol R ₂ O ₃ : 0.5 to 5.0 mol (where R is a rare earth element) M
gO: 0 to 3.0 mole BaSiO _3: 1.0 to 10 mol MnO: reduction-resistant dielectric composition characterized in that 0.1 to 0.5 mol.

[0021]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS The basic component of the ceramic dielectric of the capacitor of the present invention is Ba having a perovskite crystal structure.
Barium titanate having a molar ratio of O / TiO ₂ of 1. When this is 100 mol, each composition is included in the following range.

Nb ₂ O ₃ is contained in an amount of 1.0 to 5.0 mol. Nb
By containing ₂ O ₃ at the same time as ZnO, the reduction resistance of the ceramic is improved and its temperature characteristics are improved. When the content is less than 1.0 mol, these effects are not sufficiently obtained.When the content is more than 5.0 mol, the relative dielectric constant at room temperature is lowered, and the sintering density is lowered. The load life decreases.

The content of ZnO is 1.0 to 5.0 mol. N
By containing it together with b ₂ O ₃ , reduction resistance is improved. As a result, the reduction resistance can be improved without making the molar ratio of the oxide: (BaO-based oxide) / (TiO ₂ -based oxide) slightly larger than 1. Also, there is an effect of improving temperature characteristics without lowering the dielectric constant. If the content is less than 1.0 mol, sufficient reduction resistance and temperature characteristic improvement effects cannot be obtained, and if it exceeds 5.0 mol, the specific permittivity decreases and the high-temperature load life decreases.

Y represented by R ₂ O ₃ (R is a rare earth element)
And the content of the oxide of the lanthanoid element is 0.5 to 5.0 mol. The inclusion of these rare earth element oxides greatly improves the high temperature load life. However, with a content of less than 0.5 mol,
A sufficient high temperature load life improvement effect cannot be obtained, while a content exceeding 5.0 mol results in greatly impaired sinterability.
0.5 to 5.0 mol. Desirably, it is 1.0 to 3.0 mol.

It is not necessary to add MgO, but when it is added, the amount is up to 3.0 mol. Since MgO reduces the temperature characteristics, that is, the ratio of ΔC / C depending on the temperature, MgO is contained particularly when it is necessary to improve the temperature characteristics. In the case where the effect is to be obtained by containing it, the content is preferably 0.5 mol or more. However, the relative permittivity at room temperature is greatly reduced, so that it is at most 3.0 mol. Preferably, the amount is 0.6 to 1.0 mol.

BaSiO ₃ is contained in an amount of 1.0 to 10 mol. This is to compensate for the deterioration of sinterability due to the addition of Nb ₂ O ₃ , ZnO, and rare earth element oxides. Although the addition of SiO ₂ is good for improving the sinterability, the high temperature load life is deteriorated. On the other hand, BaSiO ₃ can improve the sinterability without deteriorating the high temperature load life. In order to obtain this effect, it is necessary to contain at least 1.0 mol, but if it is contained too much, the relative permittivity is lowered.

The content of MnO is 0.1 to 0.5 mol. M
The content of nO, in addition to the improvement of reduction resistance, improvement of heat resistance,
Although there are various effects such as improvement of insulation properties and improvement of sinterability, the specific permittivity is lowered. Therefore, a small amount is contained within a range that does not significantly affect the relative permittivity. Ie
If the amount is less than 0.1 mol, the effect is not sufficient, and if it exceeds 0.5 mol, the decrease in the relative dielectric constant becomes remarkable.

The production of the dielectric composition, or the production of a multilayer ceramic capacitor using this dielectric composition, may be a commonly applied method. That is, each material having the above composition is subjected to a pretreatment such as mixing and calcining and pulverizing, if necessary, for example, BaTiO ₃ and the like, mixed in a required amount, appropriately added with a binder, and pulverized and kneaded in a ball mill or the like.
Then, it is formed into a sheet shape, and a paste such as Ni serving as an internal electrode is applied, and after lamination, cut into a predetermined shape.
In an atmosphere that is reducing against, it is fired and sintered at 1200 to 1400 ° C, and then 900 to 1100 in an oxidizing atmosphere.
A reoxidation treatment is performed at a temperature of ° C. to obtain a required dielectric composition.

[0029]

EXAMPLES As shown in Table 1, the molar ratio of each of Nb ₂ O ₃ , ZnO, MgO, rare earth element oxide (R ₂ O ₃ ), BaSiO ₃ and MnO when BaTiO ₃ is 100 mol. Compositions of varying amounts were made. In this case, first, as a raw material, BaTiO ₃ is a calcined material, BaSi ₃
O ₃ was hexahydrate, and MnO was carbonate. A predetermined amount of each raw material was weighed, an organic binder was added, and the mixture was pulverized and kneaded using a ball mill. This is molded into a sheet so that the size after firing is 10 μm, printed with a Ni paste to be an internal electrode, and laminated and pressed on 10 layers, and the size after firing becomes 2.0 mm in length and 1.25 mm in width Cut into green chips. The obtained green chips were subjected to a binder removal treatment at 300 ° C., and baked at 1300 ° C. for 2 hours in a nitrogen atmosphere containing 3% of hydrogen humidified with water at 30 ° C. Then, in a nitrogen atmosphere humidified with water at 30 ° C, 10
A reoxidation treatment was performed at 00 ° C. for 2 hours, and Cu connection terminal electrodes were baked thereon. The relative dielectric constant measurement, the temperature characteristic measurement, and the high-temperature load life test were performed on the capacitor specimen thus obtained to evaluate the performance of the dielectric. In the high-temperature load test, the time until the insulation resistance decreased at a temperature of 200 ° C. and a DC voltage of 150 V was measured.

[0030]

[Table 1]

Table 1 also shows the results of measurement of relative permittivity, temperature characteristics and high temperature load life. As is clear from the results in this table, when the composition ratio satisfies the range defined by the present invention, the relative dielectric constant is high, and ΔC / C over a wide temperature range.
Is within a narrow range, and a capacitor having excellent high-temperature load life can be obtained.

[0032]

According to a ceramic capacitor using a reduction-resistant dielectric, conventionally, if the temperature characteristic ΔC / C is restricted within a narrow range over a wide temperature range, for example, X7R of the EIA standard or the like should be satisfied. It was difficult to sufficiently increase the dielectric constant. According to the present invention, it is possible to obtain a reduction-resistant dielectric material that satisfies such temperature characteristics by sufficiently increasing the relative dielectric constant and has a high high-temperature load life, thereby allowing Ni or a Ni alloy to be contained inside. This makes it possible to manufacture a small-sized, high-capacity capacitor with excellent temperature characteristics at low cost.

Claims (1)

[Claims] 1. A composition mainly comprising BaTiO ₃ ,
When the composition ratio is 100 mol of BaTiO ₃ , Nb ₂ O ₃ : 1.0 to 5.0 mol ZnO: 1.0 to 5.0 mol MgO: 0 to 3.0 mol R ₂ O ₃ : 0.5 to 5.0 mol (where R is a rare earth element) BaSiO _3: 1.0 to 10 mol MnO: dielectric composition characterized in that 0.1 to 0.5 mol.