JP3106371B2 - 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 porcelain composition, and more particularly to a dielectric porcelain composition used as a material for a multilayer capacitor or the like.

[0002]

2. Description of the Related Art Conventionally, as a dielectric ceramic composition having a high dielectric constant and a small change in dielectric constant temperature, for example, BaT
iO ₃ as a main component, and Bi ₂ O ₃ —TiO ₂ , B
There are those in which a bismuth compound such as i ₂ O ₃ —SnO ₂ or Bi ₂ O ₃ —ZrO ₂ and a rare earth element are added as subcomponents. Further, a material containing BaTiO ₃ as a main component and a bismuth compound, MgO, SiO ₂ or the like added thereto as a sub component has been widely adopted.

On the other hand, apart from the dielectric ceramic composition having the above composition, BaTiO ₃ is mainly used, and Nb ₂ O ₅ ,
In some cases, Nd ₂ O ₃ and oxides of Mn, Cr, Fe, Ni, and Co are added as subcomponents (Japanese Patent Laid-Open No. 51-1
43899, JP-A-57-92575). It has been reported that even a dielectric ceramic composition having such a composition can obtain flat dielectric temperature characteristics.

Further, recent ceramic capacitors tend to be miniaturized. In particular, multilayer capacitors having a thickness of a ceramic dielectric of 5 to 15 μm are being put to practical use. Therefore, as the porcelain composition, not only a high dielectric constant but also a small grain size of the porcelain and a low voltage dependency are desired.

[0005]

However, BaT
The dielectric ceramic composition containing iO ₃ as a main component and adding a bismuth compound had a large dielectric loss tan δ at high frequencies and a low dielectric constant of 1000 to 2000. In addition, when the dielectric constant is increased, the temperature change rate of the capacitance is increased, and conversely, when the temperature change rate of the capacitance is reduced, the dielectric constant is decreased. Therefore, when this dielectric porcelain composition is used as a material for a capacitor, there has been a limit in increasing the size and capacity of the capacitor.

Further, in such a dielectric porcelain composition,
There have been problems in that Bi ₂ O ₃ evaporates during firing and distortion occurs in the porcelain, and the composition ratio changes to cause variations in required electrical characteristics. Further, when such a composition is used as a material for a multilayer capacitor, if Pd or an Ag—Pd alloy is used as an internal electrode, the Pd and Bi ₂ O ₃ react to deteriorate the characteristics of the electrode. I will. Therefore, expensive Pt that does not react with Bi ₂ O ₃
Had to be used as an internal electrode.

The dielectric ceramic composition having the composition disclosed in JP-A-51-143899 exhibits a dielectric constant temperature change rate of -27% or more even in a narrow temperature range of -25.degree. C. to + 85.degree. Was. Therefore, -55 ° C to + 125 ° C
In a wide temperature range, a flat dielectric temperature characteristic within ± 15% could not be obtained.

A dielectric porcelain composition having a composition disclosed in Japanese Patent Application Laid-Open No. 57-92575 has a temperature of -55 ° C. to + 12 ° C.
In the temperature range of 5 ° C., the temperature change rate of the dielectric constant shows a value of 15% or less, but it is necessary to satisfy the conditions of a dielectric constant of 2800 or more, a dielectric loss of 2.5% or less, and a firing temperature of 1250 ° C. Not reached.

On the other hand, a composition having a dielectric constant of 3000 to 5000 and a flat dielectric constant-temperature characteristic has been disclosed (JP-A-64-45772). However, these compositions having a large dielectric constant have a high firing temperature of 1280 ° C. or higher. Further, since these dielectric ceramic compositions have a large voltage dependency, they cannot cope with recent thinning, and a small-sized and large-capacity multilayer capacitor cannot be produced.

Therefore, the main objects of the present invention are to provide a dielectric material having a dielectric constant of 3500 or more, a small temperature change rate of capacitance over a wide temperature range, a flat surface, a small dielectric loss, a small voltage dependency, and a small grain size. An object of the present invention is to provide a dielectric ceramic composition which is as small as 1 μm or less and can be sintered at a relatively low temperature of 1250 ° C. or less.

[0011]

According to the present invention, Nb ₂ O ₅ is added to 100 parts by weight of BaTiO ₃ containing 0.03% by weight or less of alkali metal oxide as an impurity.
6 to 2.0 parts by weight, 0.1 to 0.8 parts by weight of Co ₂ O ₃ , 0.05 to 0.3 parts by weight of MnO ₂ , La ₂ O
_{3, Nd 2 O 3, CeO} 2, Pr 6 O 11, Dy 2 O 3,
Rare earth oxides RO comprising at least one of Sm ₂ O ₃
(Except when Nd ₂ O ₃ is used alone) in an amount of 0.02 to 0.5 part by weight, and BaO—B ₂ O ₃ —Li ₂
0.05 The oxide glass mainly composed of O-SiO ₂
1.0 parts by weight, and the grain size is 1 μm
The following is a dielectric porcelain composition

[0012]

In a high dielectric constant composition based on BaTiO ₃ , Nb ₂ O ₃ and Co ₂ O ₃ , alkaline earth metal oxides such as SrO and CaO present as impurities in BaTiO _{3 as} a main component, Na ₂ Among alkaline metal oxides such as O and K ₂ O, and other oxides such as Al ₂ O ₃ and SiO ₂ , particularly, the content of alkaline earth oxides such as Na ₂ O and K ₂ O is affected by the electric characteristics. Have a big impact. In addition, rare earth oxide RO and BaO—B ₂ O ₃ —Li ₂ O—Si
By containing an oxide glass containing O ₂ as a main component, a dielectric ceramic composition having good sintering properties and low voltage dependency can be obtained.

[0013] Here, Na about ₂ O, alkali metal oxides such as K ₂ O, it permittivity decreases exceeds 0.03 weight as an impurity with respect to BaTiO _3, 3
The value is 500 or less. Nb ₂ O ₅ is BaTiO ₃ 1
If the amount is less than 0.6 parts by weight with respect to 00 parts by weight, the sinterability deteriorates and the dielectric loss increases. Furthermore, the temperature change rate of the capacitance becomes large, and becomes a value larger than ± 15% in a temperature range of −55 to + 125 ° C. On the other hand, when Nb ₂ O ₅ exceeds 2.0 parts by weight, the dielectric constant decreases to a value of 3500 or less. If Co ₂ O ₃ is less than 0.1 part by weight with respect to 100 parts by weight of BaTiO ₃ , the desired flat dielectric temperature characteristic cannot be obtained. On the other hand, when Co ₂ O ₃ is 0.8
If the amount exceeds the weight part, the dielectric loss becomes extremely large, and the temperature change rate of the capacitance becomes large. MnO ₂ is BaTi
If less than 0.05 part by weight with respect to 100 parts by weight of O ₃ ,
The effect of improving the sinterability is poor, and the intended flat dielectric temperature characteristic cannot be obtained. On the other hand, when MnO ₂ is 0.1.
If it exceeds 3 parts by weight, the dielectric constant does not exceed 3500 and the dielectric loss increases. The rare earth oxide RO is BaTiO ₃
If the amount is less than 0.05 part by weight per 100 parts by weight, the effect of improving the sinterability is poor, and the AC voltage dependency becomes large. On the other hand, when RO exceeds 0.5 parts by weight, Co ₂
When the amount of O ₃ is small, the rate of change in capacitance with temperature is significantly increased, and when the amount of Co ₂ O ₃ is large, the dielectric constant is significantly reduced to 3500 or less. BaO-B ₂ O ₃ -Li ₂
The oxide glass mainly composed of O—SiO ₂ is made of BaTi
If the amount is less than 0.05 part by weight with respect to 100 parts by weight of O _3, the effect of improving the sinterability is poor and the dependency on the AC voltage becomes large. On the other hand, when the oxide glass exceeds 1.0 part by weight, the dielectric constant decreases.

[0014]

According to the present invention, when the capacitance at + 25 ° C. is used as a reference, the temperature change rate of the capacitance is flat within ± 15% over a wide temperature range from −55 ° C. to + 125 ° C. In addition, a dielectric ceramic composition having a small dielectric loss of 1.2% or less and a small voltage dependence of 3.0% or less even when an AC electric field of 200 V / mm is applied can be obtained. In addition, this composition has a high dielectric constant of 3500 or more despite having such flat temperature characteristics, and a small grain size of 1250 μm or less.
It is possible to perform sintering at a relatively low temperature of not more than ° C.

Therefore, when the dielectric ceramic composition of the present invention is used, the thickness of the ceramic dielectric layer can be reduced. And 30Ag-70Pd (the number is% by weight) can be used as the internal electrode, and a low-cost, small-sized, large-capacity multilayer ceramic capacitor having good temperature characteristics can be obtained.

The above and other objects, features and advantages of the present invention will become more apparent from the following detailed description of the embodiments.

[0017]

【Example】

(Example 1) First, as starting materials, various purity Ti
Cl ₄ and Ba (NO ₃ ) ₂ were prepared, and these raw materials were weighed such that the molar ratio of Ba ions to Ti ions became 1.000 to obtain a weighed material. The weighed material was precipitated as BaTiO (C ₂ O ₄ ) · 4H ₂ O with oxalic acid to obtain a precipitate. This precipitate was thermally decomposed at a temperature of 700 ° C. or more to synthesize BaTiO ₃ . This synthesized product was pulverized by a dry pulverizer until the average particle diameter became 1 μm or less. Thus, five types of BaTiO ₃ having different purities of A to E shown in Table 1 were obtained.

[0018]

[Table 1]

Next, Nb ₂ O ₅ , Co ₂
O ₃ , MnO ₂ , rare earth oxide RO and BaO—B ₂
Using an oxide glass containing O ₃ —Li ₂ O—SiO ₂ as a main component, the composition was weighed so as to obtain a composition having a ratio shown in Table 2, a vinyl acetate-based binder was added, and wet mixing was performed for 16 hours. The mixture was obtained.

[0020]

[Table 2]

Further, the obtained mixture was dried and granulated, and then press-formed into a disk having a diameter of 10 mm and a thickness of 0.5 mm at a pressure of 2000 kg / cm ² to obtain a formed body.
Thereafter, the molded body was fired at the firing temperature shown in Table 3 for 2 hours to obtain a disc-shaped porcelain.

The surface of the obtained porcelain was observed with a scanning electron microscope at a magnification of 1500 times, and the grain size was measured.

Then, a silver electrode is baked on the main surface of the obtained porcelain to obtain a measurement sample (capacitor). Was measured.

In this case, the dielectric constant (ε) and the dielectric loss (tan δ) were measured at a temperature of 25 ° C., 1 kHz, and 1 Vrms. The rate of change of capacitance with respect to temperature change is based on the capacitance (C ₂₅ ) at ₂₅ ° C., and the rate of change of temperature (ΔC / C at −55 ° C. and + 125 ° C.).
₂₅ ) and the absolute value of the value at which the rate of temperature change between -55 ° C and + 125 ° C is the maximum, the so-called maximum rate of change (| ΔC
/ C ₂₅ | _max ). Furthermore, dielectric loss (tan) when an electric field of 200 V / mm is applied at a frequency of 1 kHz.
δ) was measured.

The results of the above tests are shown in Table 3.

[0026]

[Table 3]

As is clear from Table 3, the porcelain compositions falling within the scope of the present invention have a dielectric constant (ε) of 3500
And high. Moreover, despite such a high dielectric constant,
The rate of change of the capacitance is small and shows a flat temperature characteristic.
It satisfies the X7R characteristics specified in the A standard. Further, the dielectric loss (tan δ) is as small as 1.2% or less, and is 200 V
/ Mm even under an AC electric field of 3.0% or less. The grain size is as small as 1.0 μm or less, and sintering is possible even at a relatively low temperature of 1250 ° C. or less.

Next, the reason why the range of the additive amount of the oxide as an additive is limited will be described. That is, the Nb ₂ O _5, to that the range as from 0.6 to 2.0 parts by weight, as in Sample No. 1, sintering temperature is high, the dielectric loss increases is less than 0.6 part by weight . Further, the temperature change rate of the capacitance becomes a value larger than ± 15% in a temperature range of −55 ° C. to + 125 ° C. In addition, as shown in sample number 4, 2.0
Exceeding parts by weight lowers the dielectric constant.

The range of Co ₂ O ₃ is 0.1 to
0.8 parts by weight was used, as in sample number 7,
When the amount is less than the weight part, the temperature change rate of the capacitance is from −55 ° C.
The value is larger than ± 15% in the temperature range of + 125 ° C. If the amount exceeds 0.8 parts by weight, as in sample No. 8, the dielectric loss becomes extremely large, and the temperature change rate of the capacitance also becomes large.

For MnO ₂ , the range is from 0.05 to
The amount of 0.3 parts by weight was 0.1% as in Sample No. 18.
If the amount is less than 05 parts by weight, the effect of improving the sinterability is poor, and the temperature change rate of the capacitance becomes large. Further, as shown in Sample No. 19, if it exceeds 0.3 parts by weight, the dielectric constant becomes 3
It does not exceed 500, and the dielectric loss increases.

La ₂ O ₃ , Nd ₂ O ₃ , CeO ₂ , Pr
Rare earth oxide RO composed of at least one of ₆ O ₁₁ , Dy ₂ O ₃ and Sm ₂ O ₃ (however, Nd ₂ O ₃ is used alone)
Use range ) of 0.02 to
0.5 parts by weight, and BaO—B ₂ O ₃ —Li ₂ O—Si
The reason why the oxide glass containing O ₂ as the main component is 0.05 to 1.0 part by weight is that the sinterability is improved and the voltage dependency is reduced within this composition range. When the addition amount of the rare earth oxide or oxide glass is small as in Examples 23 and 23, the sinterability deteriorates and the AC voltage dependency increases. Also, as in Sample No. 13, when the oxide glass exceeds 1.0 part by weight, the dielectric constant becomes lower than 3500. Further, as in Sample No. 20, when the rare earth oxide exceeds 0.3 parts by weight and the amount of Co ₂ O ₃ added is large, the dielectric constant becomes lower than 3500. Sample No. 2
When the RO exceeds 0.3 parts by weight and the addition amount of Co ₂ O ₃ is small as in 1, the temperature change rate of the capacitance is −5.
The value is larger than ± 15% in a temperature range of 5 ° C. to + 125 ° C.

Further, the content of the alkali metal is set to 0.03
% Or less, as in sample No. 24,
If it exceeds 3% by weight, the dielectric constant does not exceed 3500.

(Example 2) Dielectric ceramic raw material powders of Sample Nos. 5 and 23 of Example 1 were prepared.
To this dielectric ceramic raw material powder, add an organic solvent such as polyvinyl butyral-based binder and ethanol,
A ceramic slurry was prepared by wet mixing with a ball mill. Then, this ceramic slurry is
Sheet molded by doctor blade method, thickness 12μ
m rectangular green sheets were obtained.

Next, a conductive paste mainly composed of Pd was printed on the ceramic green sheet to form a conductive paste layer for forming internal electrodes. And
A plurality of ceramic green sheets on which the conductive paste layer was formed were laminated such that the side from which the conductive paste layer was drawn out was alternated, to obtain a laminate.

The obtained laminate was fired in air at a temperature shown in Table 4 for 2 hours. After firing, a silver paste was applied to both end surfaces of the obtained ceramic sintered body and baked at 750 ° C. in the air to form external electrodes electrically connected to the internal electrodes.

The external dimensions of the multilayer capacitor obtained as described above are 3.2 mm in width, 1.6 mm in length and 1.2 mm in thickness, and the thickness of the dielectric ceramic layer interposed between the internal electrodes is 8 μm. The total number of effective dielectric ceramic layers is 19, and the area of the counter electrode per layer is 2.1 mm ² .

The capacitance (C) and the dielectric loss (tan)
In order to measure δ), a voltage of 1 kHz and 1 Vrms was applied to the multilayer capacitor of each sample using an automatic bridge type measuring device. Next, in order to measure the insulation resistance (R) at 25 ° C. and 125 ° C., an insulation resistance meter was used to measure 16V.
Was applied for 2 minutes. Then, the product of the capacitance (C) and the insulation resistance (R), that is, the CR product was obtained.

Further, the change rate of the capacitance with respect to the temperature change was measured. Further, the rate of change in capacitance when a DC voltage of 16 V was superimposed on a voltage of 1 kHz and 1 Vrms was measured. The rate of change of the capacitance with respect to the temperature change is based on the capacitance (C ₂₅ ) at ₂₅ ° C., and the rate of change of the temperature at −55 ° C. and + 125 ° C. (Δ
C / C ₂₅ ) and the absolute value of the value at which the temperature change rate is maximum between −55 ° C. and + 125 ° C., that is, the so-called maximum change rate (| ΔC / C ₂₅ | _max ).

The results of the above tests are shown in Table 4.

[0040]

[Table 4]

As is clear from Table 4, the multilayer ceramic capacitor of Sample No. 5 within the scope of the present invention has a small capacitance change rate and a flat temperature characteristic despite obtaining a large dielectric constant. And the dielectric loss is also small. The multilayer ceramic capacitor also has excellent insulation resistance and a small rate of change in capacitance when a DC voltage is superimposed.

As described above, the multilayer ceramic capacitor according to the composition of the present invention shows good characteristics even when the dielectric ceramic layer is as thin as 8 μm, and can be expected as a small-sized and large-capacity multilayer ceramic capacitor. Furthermore, since the firing temperature is as low as 1250 ° C. or less, 30 Ag-
It is possible to use 70 Pd (the number is% by weight).

On the other hand, the multilayer ceramic capacitor of Sample No. 23 outside the scope of the present invention has a large dielectric constant when the dielectric ceramic layer is thinned to 8 μm, but has a large capacitance temperature change rate. Does not satisfy the X7R characteristics specified in the EIA standard. Further, this multilayer ceramic capacitor has a large dielectric loss and a large capacitance change rate when a DC voltage is superimposed. Further, this capacitor has a low insulation resistance at a high temperature (125 ° C.) and a high firing temperature.

In the above embodiment, BaTiO ₃ produced by the oxalic acid method was used. However, the present invention is not limited to this. BaTiO ₃ produced by the alkoxide method or the coprecipitation method, for example, BaCO 3 is used. ₃ and T
The same effect can be obtained with BaTiO ₃ produced using iO ₂ powder. Further, other additives were added as oxide powders, but Nb, Co, Mn and rare earth element R were added.
Is added so as to fall within the scope of the present invention in terms of oxides, the same effect can be obtained by addition of a solution.

────────────────────────────────────────────────── (5) References JP-A-5-6711 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01B 3/12 303 C04B 35/46 H01G 4 / 12 358

Claims (1)

(57) [Claims] 1. Nb ₂ O ₅ : 0.6 to 2.0 parts by weight, Co ₂ O _3: 100 parts by weight of BaTiO ₃ containing 0.03% by weight or less of alkali metal oxide as an impurity the 0.1 to 0.8 parts by weight, the MnO ₂ 0.05 to 0.3 parts by _{weight, La 2 O 3, Nd 2} O 3, CeO 2, Pr 6 O 11, Dy
Rare earth oxide RO composed of at least one of ₂ O ₃ and Sm ₂ O ₃ (However, when Nd ₂ O ₃ is used alone,
0.02 to 0.5 parts by weight ) and BaO-B ₂
A dielectric ceramic composition containing 0.05 to 1.0 parts by weight of an oxide glass mainly containing O ₃ —Li ₂ O—SiO ₂ and having a grain size of 1 μm or less.