JP3469910B2 - Dielectric porcelain composition - Google Patents

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a dielectric ceramic composition containing barium titanate as a main component, and more particularly to a dielectric ceramic composition suitable for a laminated ceramic capacitor and having excellent life performance at high temperature. Regarding

[0002]

2. Description of the Related Art BaTiO ₃ has hitherto been known as a material having a high dielectric constant and is widely used as a capacitor material. However, BaTiO ₃ is not practical because it has a large temperature dependence of the relative permittivity and a large dielectric loss, and therefore the addition of various metal oxides other than BaTiO ₃ improves the characteristics. Has been done.

Specifically, as described in JP-A-3-285209, as compared with BaTiO ₃ , Nb ₂ O ₅ ,
It is described that the dielectric loss can be reduced by adding ZnO and CaZrO ₃ in appropriate amounts, and the addition of MnO further improves the dielectric loss.

On the other hand, in the multilayer ceramic capacitor, the thickness of the dielectric layer tends to become smaller as the size of the multilayer ceramic capacitor becomes smaller. It tends to increase. Therefore, the dielectric material used for the multilayer ceramic capacitor is
Further, it is required that the dielectric loss is small, and in recent years, when the dielectric layer reaches several μm, the dielectric loss (tan) of the dielectric material is increased.
δ) is required to be 0.6% or less. Further, recently, it is desired that the deterioration of characteristics with time is small.

[0005]

However, most of the dielectric ceramic compositions described in the above prior art have a dielectric loss of more than 0.6%,
It doesn't fit this purpose. Although the composition of 0.6% or less is also described in some of them, there is a limit to miniaturization of the capacitor because all of them have a small relative dielectric constant of 3000 or less.

As represented by the above-mentioned prior art, BaTi
The conventional dielectric ceramic composition containing O ₃ as a main component has a large dielectric loss, cannot be applied to downsizing, and has a problem that the relative dielectric constant becomes small even if the dielectric loss can be reduced to some extent. there were. In addition, the current situation is that sufficient consideration has not been given to extending the life of capacitors.

Therefore, it is an object of the present invention to provide a dielectric ceramic composition having a high relative dielectric constant and a small dielectric loss.

[0008]

Means for Solving the Problems The inventors of the present invention have conducted extensive studies on the above-mentioned object, and as a result, have found that Ba and Ti of BaTiO ₃ which are the main components of the dielectric ceramic composition have a stoichiometric composition. Also contains a large amount of Ba, so that the dielectric loss can be greatly reduced and the change in the relative permittivity in the high temperature region can be controlled to be small, so that the amount of other additives added can be reduced and the relative permittivity can be increased. The inventors have found that the amount of Si in the material has a great influence on the life characteristics at high temperatures, and have reached the present invention.

That is, the dielectric ceramic composition of the present invention contains at least Ba, Ti, Nb, Sm and Zn as metal components.
The composition formula of the molar ratio by the oxide of each metal component is aBa _{1 + X} TiO ₃ · bNb ₂ O ₅ ·.
When expressed as cSm ₂ O ₃ · dZnO, 0.9700 ≦ a
≤ 0.9830, 0.0105 ≤ b ≤ 0.0132,
0.0008 ≦ c ≦ 0.0025, 0.0050 ≦ d ≦
0.0150, 0.006 ≦ x ≦ 0.0180 and a
It is characterized in that + b + c + d = 1 is satisfied.

In the present invention, the value of x in Ba _{1 + X} TiO ₃ is limited to the above range. When the value of x is less than 0.006, the dielectric loss of the porcelain increases and the temperature characteristics deteriorate. This is because the porcelain density decreases when it exceeds 0.0180.

Further, the values of a, b, c and d are limited to the above ranges, because when the value of a is smaller than 0.9700, the dielectric loss becomes large and the temperature characteristic deteriorates.
This is because if it is larger than 9830, it becomes a semiconductor. Further, when the b value is smaller than 0.0105, the insulation resistance is extremely small, and the function of the capacitor is lost.
This is because if it is larger than 2, the relative dielectric constant becomes small. Furthermore, if the c value is larger than 0.0025, the temperature characteristics deteriorate. When the d value is smaller than 0.0050, the dielectric loss is large and the temperature characteristics are deteriorated, and when the d value is larger than 0.0150, the dielectric loss is large.

A more desirable range of each value of a, b, c, d and x is 0.9725≤a≤0.9807,0.0.
110 ≦ b ≦ 0.0125, 0.0008 ≦ c ≦ 0.0
025, 0.0075 ≤ d ≤ 0.0125, 0.006
≦ x ≦ 0.018.

Further, according to the present invention, it is desirable that the amount of Si as an impurity in the composition is 20 ppm or less in terms of weight of oxide. This is because when the Si amount exceeds 20 ppm, the insulation resistance tends to decrease under high temperature and high electric field.

Further in accordance with the present invention, the Mn in the composition is
Is substantially not contained, and in consideration of inclusion as an unavoidable impurity, it is preferably 300 ppm or less by weight. Mn is usually BaT as MnO
It is often used as having the effect of lowering the dielectric loss by adding it to iO ₃ , but according to the present invention,
The dielectric loss can be sufficiently reduced without adding Mn.
According to such a system of the present invention, the presence of Mn has been found to be a factor that deteriorates the life performance of porcelain. That is,
The reason for limiting the Mn amount to the above range is that if the Mn amount exceeds 300 ppm in terms of oxide weight, the insulation resistance is greatly deteriorated when exposed to a high temperature and high electric field.

The dielectric ceramic composition of the present invention comprises Ba, T
The oxide of each metal element of i, Nb, Sm, and Zn, or the mixed oxide powder of BaO and TiO ₂ which is calcined and pulverized is used to adjust the composition to the above range. Weighed and mixed powder, or 960 to 1080
The powder calcinated after calcination in an oxidizing atmosphere at ℃ is molded by a desired molding means such as a doctor blade method or a die press. When producing a laminated ceramic capacitor, it may be formed into a sheet.

The molded body can be made into a porcelain by firing it in an oxidizing atmosphere at 1300 to 1370 ° C. In the case of producing a laminated porcelain capacitor, for example, the surface of a sheet-like formed body is formed. The internal electrode forming paste such as Pd may be applied, laminated, and fired.

Further, according to the present invention, it is important to reduce the amount of Si in the composition, but Si may be mixed mainly from impurities in barium titanate or from media during mixing or crushing. Therefore, it is necessary to use a high-purity raw material powder so that the total amount of Si in the final porcelain does not exceed 20 ppm, and to prevent it from being mixed from the manufacturing process.

[0018]

According to the present invention, Ba is used as barium titanate.
The presence of more than the stoichiometric composition of
The dielectric loss of the whole porcelain can be greatly reduced.

Further, Nb ₂ added to reduce the dielectric loss of porcelain by the above-mentioned improvement of barium titanate.
The amount of O ₅ can be reduced, high specific will have a dielectric constant Although conventionally been added to CaZrO ₃ in order to increase the dielectric constant in the barium titanate from the CaZrO ₃ is a temperature characteristic Deteriorate. In the present invention, since CaZrO _{3 is} not added and has a high dielectric constant, other characteristics such as temperature characteristics are not deteriorated.

According to the dielectric porcelain composition of the present invention, the relative dielectric constant is 3000 or more, the insulation resistance is 1 × 10 ¹² Ωcm or more, and the temperature characteristic of the relative dielectric constant (−55 ° C. to + 125 ° C.) is 25 ° C. as a reference. Within ± 7.5%, aging rate 2% / dec
An excellent dielectric property equal to or less than ade is obtained.

As a result, even if the thickness of the dielectric layer in the laminated ceramic capacitor is reduced to about 5 μm, the dielectric loss is small and the dielectric constant is high, so that the capacitor can be miniaturized.

[0022]

Example 1 Barium titanol oxalate having a composition deviated from the stoichiometric composition by 0.6 to 1.8 atomic% on the Ba excess side by the oxalate method was synthesized, and 950 to 1020 was synthesized.
It was calcined at ℃ to obtain barium titanate powder, which was used as the main raw material. Nb ₂ O ₅ , Sm ₂ O ₃ and Z
Using nO powder, the ingredients were weighed and mixed so as to have the compositions shown in Table 1 and Table 2, mixed with a ball mill, and 1 part by weight of vinyl acetate resin was added to 100 parts by weight of the powder to make granules. After pressure-molding into a disc having a thickness of 1.0 mm, it was fired in the atmosphere at 1300 to 1370 ° C. for 2 hours.

After measuring the bulk density of the obtained porcelain, a silver electrode was provided to prepare a disk capacitor, which was used as an evaluation sample. Then, the capacitance and the dielectric loss (tan δ) were measured under the conditions of 1 Vrms and 1.0 KHz. Also, 50
A direct current voltage of 0 V was applied for 1 minute, and the insulation resistance was measured with an insulation resistance meter. Furthermore, the electrostatic capacity was measured in the range of -55 ° C to + 125 ° C, and the value of 25 ° C was used as a reference at -55 ° C,
The rate of change was calculated from the values at + 85 ° C and + 125 ° C. The results are shown in Table 1.

For sample No. 4 in Table 1, 150 ° C.
After heat-treating for 1 hour, the aging rate per delicate was calculated from the capacitance value immediately after standing for 100 hours at room temperature based on the capacitance value after 1 hour. The relative dielectric constant was calculated from the capacitance and the diameter of the Ag electrode and the thickness of the porcelain. These measured values and calculated values are shown in Table 1.

[0025]

[Table 1]

As shown in Table 1, all the samples whose a, b, c, d and x values satisfy the range of the present invention have a high density and a high relative dielectric constant of 3,000 or more, and 0. .6%
It had the following low dielectric loss, high insulation resistance of 1 × 10 ¹² Ωcm, and stable temperature characteristics within ± 7.5%.

Example 2 In Example 1, raw material powders having different Si contents were used, and Ba, Ti, Nb, Sm and Zn were used.
Was weighed and mixed so as to satisfy Sample No. 4, and a porcelain was manufactured in the same manner as in Example 1. IC for the obtained porcelain
The amount of Si in the porcelain was measured by P emission spectroscopy and is shown in Table 2.

The obtained porcelain had a diameter of 10 mm and a thickness of about 0.
Processed to 25mm, 30 ~ 31KV / mm on such porcelain
DC voltage is applied so that it has a potential gradient of
It was stored for 48 hours in a constant temperature bath at 27 ° C. Then, in the insulation resistance value before and after the test (500 VDC, 1 minute value), when the insulation resistance value after the test decreased to ¼ or less of that before the test, it was considered as deterioration, and the ratio is shown in Table 2. .

[0029]

[Table 2]

According to the results of Table 2, the amount of Si is 30 pp.
A decrease in insulation resistance was observed in all cases where m was exceeded. Similarly, when the same test was performed on the other samples of the present invention in Table 1, the same test results as in Table 2 were obtained, and it was confirmed that this tendency is present in all the systems of the present invention.

Example 3 In the composition system of sample No. 4, the amount of Si in the raw material was 1.2 ppm and the amount of MnO was 0.5 ppm.
70-420 pp of MnO ₂ powder to the raw material composition
After adding m and weighing and mixing, a porcelain was produced in the same manner as in Example 1. Based on the obtained porcelain, deterioration of insulation resistance under high temperature and high voltage was examined in the same manner as in Example 2, and the deterioration rate is shown in Table 3.

[0032]

[Table 3]

According to Table 3, when the Mn amount exceeds 300 ppm, a decrease in insulation resistance is observed in all cases, and by controlling the Mn amount to 300 ppm or less, deterioration of characteristics under high temperature and high voltage is suppressed. I understood it. Also, Table 1
When the same experiment was performed on the other samples of the present invention, the same results as in Table 3 were obtained.

[0034]

As described above in detail, according to the dielectric ceramic composition of the present invention, the barium titanate is allowed to exist in a larger amount than the stoichiometric composition of Ba, and Sm, N
By controlling the amounts of b and Zn within a specific range, the dielectric loss of the entire porcelain can be significantly reduced. The relative dielectric constant is 3000 or more, the insulation resistance is 1 × 10 ¹² Ωcm or more, and the temperature characteristic of the relative dielectric constant ( -55 ° C to + 125 ° C) ± 7.5
%, And a bulk density of 5.80 g / cm ³ or more, a high-density porcelain excellent in dielectric properties can be obtained.

Further, by minimizing the Si content and the Mn content, the characteristic deterioration of the porcelain under high temperature and high electric field can be prevented,
It is possible to extend the life of porcelain characteristics.

As a result, even if the thickness of the dielectric layer in the laminated ceramic capacitor is reduced to about 5 μm, the dielectric loss is small and the dielectric constant is high, so that the capacitor can be miniaturized.

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Claims (2)

(57) [Claims] 1. Ba, T as at least a metal component
It is composed of a complex metal oxide containing i, Nb, Sm, and Zn, and the composition formula of the molar ratio by the oxide of each metal component is aBa
_When expressed as _{1 + X} TiO ₃ · bNb ₂ O ₅ · cSm ₂ O ₃ · dZnO: 0.9700 ≦ a ≦ 0.9830 0.0105 ≦ b ≦ 0.0132 0.0008 ≦ c ≦ 0.00250 0.0050 ≦ d ≦ 0.0150 0.006 ≦ x ≦ 0.018 a + b + c + d = 1 is satisfied, a dielectric ceramic composition. 2. Ba, Ti, Nb, S as a metal component
A composite metal oxide containing m and Zn, wherein the oxide weight conversion of Si in the composition is 20 ppm or less, and M of Mn.
The dielectric ceramic composition according to claim 1, wherein the weight-converted amount of nO ₂ is 300 ppm or less.