JP2000103671A - Dielectric ceramic composition - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enable a dielectric ceramic composition to be baked at a comparatively low temperature at which an internal electrode is not eluted and further to improve temperature characteristics such as X7R and B-characteristic, a ceramic density, and a relative dielectric constant by externally adding Nb2DO3, ZnO, Tb4O7, SiO2 and B2O3 in specific proportions to BaTiO3. SOLUTION: This dielectric ceramic composition is obtained by externally adding 0.8-2.0 pts.wt. Nb2O3, 0.3-0.8 pt.wt. ZnO, 0.2-0.9 pt. wt. Tb4O7, and 0.1-2.0 pts.wt. (SiO2+B2O3), preferably in a proportion satisfying the equation 0<B2 O3/(SiO2+B2O3)<=0.3. The composition can be baked at <=1,200 deg.C at which the internal electrode is not eluted when producing a laminated type ceramic capacitor by using the internal electrode of silver or the like. The composition has good sintering properties and can provide a high ceramic density of about >=5.72 g/cm3. Further, the ceramic composition has a small rate of change by the temperature, satisfying X7R and B-characteristic within the temperature range of (-55)-125 deg.C, and a high relative dielectric constant of about 3,300 or more.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

TECHNICAL FIELD The present invention relates to a dielectric porcelain composition. The dielectric ceramic composition of the present invention can be suitably used for a laminated ceramic capacitor.

[0002]

2. Description of the Related Art A dielectric ceramic composition used for a porcelain (ceramic) capacitor has a high relative dielectric constant εr and a small dielectric loss tan δ, and furthermore has excellent temperature characteristics of relative dielectric constant, that is, temperature change. It is desired that the change in the relative dielectric constant with respect to is small.

For this reason, various dielectric ceramic compositions containing BaTiO ₃ as a main component having a high relative dielectric constant have been frequently used as dielectric materials for ceramic capacitors. Above all, Nb ₂ O ₅ in _{BaTiO 3, Ta 2 O 5,} Zn
0.1 to 3% by weight of components such as O, CoO, and rare earth oxides
The dielectric porcelain composition which is added at a time is widely used because it has a high relative dielectric constant and excellent temperature characteristics such as X7R and B characteristics.

However, this dielectric ceramic composition is not suitable for use in a laminated ceramic capacitor. This is because, in the case of a multilayer ceramic capacitor, it is necessary to fire in a state in which plate-shaped porcelain and plate-shaped internal electrodes are alternately stacked at the time of manufacturing, but the firing temperature of the dielectric composition is 1,200.
Ag which is usually used as an internal electrode
Is eluted during firing.

As one means for solving this problem, it is conceivable to use an Ag-Pd alloy having a large Pd ratio as an internal electrode material to improve the heat resistance of the internal electrode. However, Pd is expensive. Also, when the Pd ratio is large, the specific resistance value of the electrode becomes large, so that there is a disadvantage that the capacitor generates heat during use. Therefore, in the case of a laminated ceramic capacitor, it is desired to use a dielectric ceramic composition that can be fired even at a low temperature of 1200 ° C. or less.

[0006] In order to satisfy this demand, a dielectric porcelain composition is disclosed in JP-A-8-337470. This dielectric porcelain composition is based on 100 parts by weight of BaTiO ₃ and Nb.
The ₂ O ₅ 0.8 to 2.0 parts by weight, 0.3 to 0.8 parts by weight of ZnO, Tb ₄ O ₇ and 0.2 to 0.9 parts by weight, the SiO ₂ 0.1 ~
Contains 2.0 parts by weight. This dielectric composition can be fired even at 1,200 ° C. or lower, and has good sinterability with a porcelain density of 5.70 g / cm ³ or more. Further, the relative dielectric constant at room temperature is as high as 3,200 to 3,820, and the temperature characteristic is X7R, B in the temperature range of -55 ° C to + 125 ° C.
Meet the characteristics.

[0007]

However, in order to obtain a higher performance laminated ceramic capacitor, it is desirable that the ceramic density and the relative dielectric constant are higher. However, it is difficult to increase both the porcelain density and the relative permittivity. For example,
In the dielectric porcelain composition described in No. 8-337470, SiO 2
_It is possible to increase the density of the porcelain by increasing the ratio of ₂ , but instead, the relative dielectric constant is reduced.

Therefore, the present invention is to provide a dielectric ceramic composition which can be fired even at 1,200 ° C. or less, has excellent temperature characteristics, and has a higher ceramic density and relative dielectric constant than conventional compositions. It is an object.

[0009]

According to the dielectric ceramic composition of the present invention, Nb ₂ O ₅ is added to 100 parts by weight of BaTiO ₃ in an amount of 0.1% by weight.
8 to 2.0 parts by weight, ZnO 0.3 to 0.8 parts by weight, Tb ₄ O
₇ 0.2 to 0.9 parts by weight, and wherein SiO _2, B ₂ O ₃ and that it has from 0.1 to 2.0 part by weight externally added together.

In the dielectric ceramic composition of the present invention (hereinafter abbreviated as the present composition), a low-melting glass having a melting point of 577 ° C. of B ₂ O ₃ is contained together with SiO ₂ as a sintering aid. The wettability to BaTiO ₃ is improved. As a result, the composition of the present invention can be fired even at 1200 ° C. or lower, and has a small temperature change rate, and the temperature characteristics in the temperature range of −55 ° C. to + 125 ° C. satisfy the X7R, B characteristics.
Moreover, the porcelain density is 5.72 g / cm ³ or more and the relative dielectric constant is 3,
At 300 or more, it is higher than the conventional dielectric ceramic composition. In the composition of the present invention, the weight of SiO ₂ and B ₂ O ₃ is 0%.
When <B ₂ O ₃ / (SiO ₂ + B ₂ O ₃ ) ≦ 0.3, the porcelain density and the relative dielectric constant are further increased.

In the composition of the present invention, the composition ratio of each oxide to 100 parts by weight of BaTiO ₃ is determined as described above for the following reasons.

The reason why the ratio of Nb ₂ O ₅ is set to 0.8 to 2.0 parts by weight is that when Nb ₂ O ₅ is less than 0.8 parts by weight, the temperature change rate of the relative dielectric constant becomes large and the desired temperature characteristics cannot be obtained. On the other hand, if it exceeds 2.0 parts by weight, the dielectric ceramic does not sufficiently sinter at a firing temperature of 1200 ° C. or less, and the relative dielectric constant tends to decrease.

The reason why the ratio of ZnO is set to 0.3 to 0.8 parts by weight is that when ZnO is less than 0.3 parts by weight, the temperature change rate of the relative dielectric constant becomes large and the desired temperature characteristics cannot be obtained.
At a sintering temperature of 1200 ° C or less, the dielectric porcelain does not tend to sinter.
This is because the dielectric ceramic does not sufficiently sinter at a firing temperature of not more than ℃, and the relative dielectric constant tends to decrease.

The reason why the proportion of Tb ₄ O ₇ is set to 0.2 to 0.9 parts by weight is that when Tb ₄ O ₇ is less than 0.2 parts by weight, the sinterability of the dielectric ceramic decreases, and at a firing temperature of 1,200 ° C. or less, This is because the body porcelain tends to be unable to be sintered, and when it exceeds 0.9 parts by weight, the sinterability of the dielectric porcelain tends to decrease, and the relative permittivity tends to decrease.

The total ratio of SiO ₂ and B ₂ O ₃ is 0.1
When the total amount is less than 0.1 part by weight, the sinterability of the dielectric porcelain is significantly reduced, and the electrical and temperature characteristics tend to be significantly reduced. If the amount exceeds part by weight, the dielectric constant tends to decrease, the rate of temperature change tends to increase, and the number of porcelain pores increases, and the withstand voltage tends to decrease.

The weight of SiO ₂ and B ₂ O ₃ is 0 <
B ₂ O ₃ / to that more preferably the relation of _{(SiO 2 + B 2 O 3} ) ≦ 0.3 is the SiO ₂ even slightly B ₂
Substitution with O ₃ increases the relative permittivity, while B ₂ O ₃
If the substitution ratio exceeds 30%, the sinterability deteriorates and the relative dielectric constant also decreases.

Furthermore, by adding MnO to the composition of the present invention at a predetermined ratio, the insulation resistance of the dielectric ceramic can be further increased in addition to the above-mentioned excellent characteristics. And the reliability can be improved. When MnO is contained, it is preferable that the ratio to 100 parts by weight of BaTiO _{3 be} 0.3 parts by weight or less. If over 0.3 parts by weight, 1,200
It is not preferable because the sinterability of the dielectric porcelain at a sintering temperature of not higher than ℃ tends to decrease, and the relative dielectric constant of the dielectric porcelain tends to decrease due to aging. Note that Mn compounds other than MnO, for example, Mn (OH) ₂ , Mn (CO
Similar effects can be obtained even if O) ₂ , Mn (NO ₃ ) _2, etc. are contained.

As described above, the composition of the present invention has a relative dielectric constant εr
, High sinterability, and the temperature change rate in the temperature range of -55 ° C to + 125 ° C satisfies the X7R and B characteristics.
It is a dielectric ceramic composition that can be fired even at a low temperature of 1,200 ° C or less. Further, according to the composition of the present invention, it is possible to obtain a highly reliable dielectric porcelain having sufficiently high insulation resistance. Therefore, when the composition of the present invention is applied to a multilayer ceramic capacitor, a high-performance multilayer ceramic capacitor can be obtained. In addition, since low-temperature firing is possible, material costs can be reduced by using an Ag-Pd alloy having a small Pd ratio as an internal electrode material, and at the same time, power and fuel costs for firing can be reduced. Therefore, the laminated ceramic capacitor can be manufactured at low cost.

[0019]

BEST MODE FOR CARRYING OUT THE INVENTION The dielectric ceramic composition of the present invention will be described below in detail based on examples.

BaTiO is used as a raw material of the composition of the present invention.
_3, and oxide powders of Nb ₂ O ₅ , ZnO, Tb ₄ O ₇ , and SiO ₂ were prepared. Each oxide used had a purity of 99.5% or more.

Each of these oxide powders was weighed so as to have the composition shown in Table 1 with respect to 100 parts by weight of BaTiO ₃ and mixed by a ball mill to prepare a mixture. Each composition in Table 1 is shown in parts by weight, and one star attached to the sample number indicates that the sample is out of the scope of Claim 1. Further, two star marks indicate that the sample belongs to claim 1 but is outside the scope of claim 2.

[0022]

[Table 1]

Next, ammonium polycarboxylate as a dispersant was added to each of the prepared powders, and the mixture was placed in a polyethylene pot and wet-pulverized for 20 hours. A binder obtained by adding a binder to this pulverized material is molded into a tape having a thickness of 50 μm, and laminated and laminated.
Pressed and punched into a disk shape, and the disk-shaped molded body was fired in the atmosphere at 1,190 ° C. for 2 hours, each having a diameter of about 20 mm,
A disc-shaped sintered body having a thickness of 850 to 900 μm was obtained. Ag paste was applied to both principal surfaces of each of the disk-shaped sintered bodies thus obtained and baked at 800 ° C. to form Ag electrodes, thereby manufacturing disk-shaped capacitor samples 1 to 21.

The following tests were conducted to evaluate the characteristics of each capacitor sample.

First, the porcelain density was calculated by measuring the diameter, thickness and weight of the porcelain. Also, to evaluate the electrical characteristics,
At a reference temperature of 25 ° C, a signal of 1 kHz frequency and 1.0 Vrms measurement voltage is input and a digital LCR meter (4274 manufactured by YHP) is input.
The capacitance and the dielectric loss tan δ were measured using A). Next, the relative permittivity εr was calculated in consideration of the dimensions of the sample. Further, the relative permittivity εr was measured in the temperature range of -55 ° C to + 125 ° C, and the temperature change rate was determined based on the value at + 25 ° C.

The following values were used as evaluation criteria for these measurement results.

The porcelain density is an important property that is most important in withstanding voltage characteristics by evaluating the sinterability of the dielectric porcelain, and that of 5.70 g / cm ³ or more is regarded as good. The relative dielectric constant εr is an important characteristic for producing a small-sized and high-dielectric-constant capacitor. The temperature change rate of the relative permittivity εr is from −55 ° C. to + 125 ° C.
X7R, B within ± 10% within the temperature range of
Since the characteristics were satisfied, it was evaluated as good. Note that the dielectric loss tan δ
Is an important characteristic for realizing a thinner green sheet of a dielectric ceramic to produce a small and large-capacity laminated ceramic capacitor, and a small value is desirable. For example, in order to manufacture a laminated ceramic capacitor in which the thickness of the dielectric between the electrodes is 10 μm, it is desirable that the tan δ of the dielectric single plate be about 0.70% or less. did.

Table 2 shows the results of these measurements. In the table, all the results of the εr temperature change rate are from −55 ° C. to + 125 ° C.
The minimum and maximum values in the temperature range of ° C. are expressed as percentages based on the value of + 25 ° C. In the table, those with one star and two stars of the sample numbers are samples outside the scope of claims 1 and 2 as in Table 1.

[0029]

[Table 2]

As can be seen from the results in Table 2, the capacitors of Sample Nos. 2 to 4, 7, 8, 11, 12, 15, 16, 19 to 21, that is, the capacitors produced by the composition of the present invention, And good results were obtained in all the characteristics. In particular, for the porcelain density and relative permittivity εr, the porcelain density is
The relative permittivity εr was 5.348 g / cm ³ or more, and the relative dielectric constant εr was a value of 3,348 to 4,003, which was clearly higher than that of the capacitor made by the dielectric ceramic composition described in JP-A-8-337470.
That is, according to the composition of the present invention, the composition can be fired even at 1200 ° C. or lower, the temperature characteristics in the temperature range of −55 ° C. to + 125 ° C. satisfy the X7R and B characteristics, the dielectric loss is small, and the ceramic density is low. In addition, it is possible to obtain a laminated ceramic capacitor having a relative dielectric constant εr higher than that of the conventional one.

As can be seen from Table 1, each of the capacitors of Sample Nos. 18 to 21 is composed of Nb ₂ O with respect to 100 parts by weight of BaTiO _3.
5 , parts by weight of ZnO and Tb ₄ O ₇ and SiO ₂ and B
_Although the total weight parts of ₂ O ₃ are common,
Ratio of the weight of the weight and B ₂ O ₃ of O ₂ are different. And
According to the results shown in Table 2, the relative dielectric constant εr of the capacitor of Sample No. 19 containing a small amount of B ₂ O ₃ was higher than that of the capacitor of Sample No. 18 containing no B ₂ O ₃ . The sample number containing more B ₂ O ₃
The capacitor 20 has a higher relative dielectric constant εr. However, in the capacitor of Sample No. 21, which contains much more, the density is low, and the porcelain density is also significantly reduced. From this, it was found that it is preferable that the weights of SiO ₂ and B ₂ O ₃ have a relationship of 0 <B ₂ O ₃ / (SiO ₂ + B ₂ O ₃ ) ≦ 0.3.

With respect to the sample capacitors in which the composition ratio of each oxide was out of the range of the present invention, except for Sample No. 18, any of the characteristics could not meet the evaluation criteria. When the amount of Nb ₂ O ₅ is small as in Sample No. 1, there was a tendency that tan δ deteriorated and the temperature change rate of the relative dielectric constant increased. On the other hand, when the amount of Nb ₂ O ₅ was large as in Sample No. 5, the dielectric porcelain did not sufficiently sinter at a low temperature, and the specific permittivity tended to decrease.

When the amount of ZnO is small as in sample No. 6, the dielectric porcelain no longer sinters at a low temperature and ta
There is a tendency that the temperature change rate of nδ and the relative dielectric constant is deteriorated. On the other hand, when the amount of ZnO is large as in Sample No. 9, the dielectric ceramic is not sufficiently sintered at a low temperature and the relative dielectric constant is also low. There was a tendency to decrease.

When the amount of Tb ₄ O ₇ is small as in Sample No. 10, the sinterability of the dielectric ceramic at a low temperature is lowered and tan δ is deteriorated.
_{When the} amount of ₄ O ₇ was large, the specific permittivity tended to decrease.

When the amount of SiO ₂ is small as in sample No. 14, the sinterability of the dielectric porcelain at a low temperature is remarkably reduced, and at the same time, the relative permittivity, tan δ and relative permittivity change with temperature. On the other hand, when the amount of SiO ₂ is large as in Sample No. 17, the porcelain density and the relative permittivity tend to decrease, and the temperature change rate tends to increase.

[0036]

As described in detail above, the composition of the present invention comprises:
High relative permittivity εr, good sinterability, -55 ° C to +125
It is a dielectric ceramic composition which satisfies the X7R and B characteristics at a temperature change rate in the temperature range of ℃ and which can be fired even at a low temperature of 1,200 ℃ or less. Therefore, when the composition of the present invention is applied to a multilayer ceramic capacitor, a high-performance multilayer ceramic capacitor can be obtained at low cost.

Claims (2)

[Claims] 1. An amount of N based on 100 parts by weight of BaTiO ₃
0.8 to 2.0 parts by weight of b ₂ O ₅ and 0.3 to
0.8 parts by weight, a Tb ₄ O ₇ 0.2 to 0.9 parts by weight, S
iO ₂ and B ₂ O ₃ and the dielectric ceramic composition, characterized in 0.1-2.0 parts by weight that externally added together. _2. The weight of SiO ₂ and B ₂ O ₃ is 0 <B _2
2. The dielectric ceramic composition according to claim 1, wherein a relationship of O ₃ / (SiO ₂ + B ₂ O ₃ ) ≦ 0.3 is satisfied.