JP3064518B2 - 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. (JP-A-51-
(143,899, JP-A-57-92575) It has been reported that even a dielectric ceramic composition having such a composition can obtain a flat dielectric temperature characteristic.

[0004]

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.

In a dielectric porcelain composition containing a bismuth compound as a sub-component, Bi ₂ O ₃ evaporates at the time of sintering, causing distortion in the porcelain or changing the composition ratio, thereby deteriorating the required electrical characteristics. There has been a problem that variations occur. Further, when such a composition is used as a material for a multilayer capacitor, Pd or Ag-
When a Pd alloy is used, the Pd and Bi ₂ O ₃ react to deteriorate the characteristics of the electrode. Therefore, Bi
Expensive Pt that does not react with ₂ O ₃ had to be used as an internal electrode.

The dielectric ceramic composition having the composition disclosed in JP-A-51-143899 has 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, there is disclosed a composition having a dielectric constant of 3000 to 5000 and a flat dielectric constant-temperature characteristic. However, these compositions having a large dielectric constant have a high firing temperature of 1280 ° C. Further, recent ceramic capacitors tend to be miniaturized, and in particular, in multilayer capacitors, the thickness of the ceramic dielectric layer tends to be as thin as 5 μm to 15 μm in order to reduce the size and increase the capacity. Therefore, it is desired that the dielectric porcelain composition not only has a high dielectric constant but also has a small grain size of the porcelain and a small voltage dependency. However, since a composition having a large dielectric constant has a large voltage dependency, it has not been possible to cope with recent thinning, and it has not been possible to produce a small-sized and large-capacity multilayer capacitor.

Therefore, a main object of the present invention is to provide a temperature change rate of capacitance over a wide temperature range of -55 ° C. to + 125 ° C. when the dielectric constant is 3000 or more and the capacitance at + 25 ° C. is used as a reference. Is flat within ± 15%,
Another object of the present invention is to provide a dielectric ceramic composition which has a small dielectric loss of 1.2% or less, a small grain size of 1 μm or less, and can be sintered at a relatively low temperature of 1250 ° C. or less.

[0010]

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.
And 5 to 3.0 parts by weight, and the Co ₂ O ₃ 0.1 to 1.0 parts by weight, and the MnO ₂ 0.05 to 0.5 parts by weight, BaO-
The _{B 2 O 3 -Li 2 O-} SiO 2 oxide glass mainly containing a 0.05 to 2.0 parts by weight, the gray
It is a dielectric porcelain composition having a size of 1 μm or less .

[0011]

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. A dielectric ceramic composition having a small dielectric loss of 1.2% or less can be obtained. In addition, despite having such a flat temperature characteristic, this composition shows a high dielectric constant of 3000 or more, and a small grain size of 1 μm or less, and a relatively small grain size of 1250 ° C. or less. It is possible to sinter at low temperatures.

Therefore, the thickness of the ceramic dielectric layer can be reduced. And 30Ag-7 as an internal electrode
It is possible to use 0Pd (the number is% by weight), and it is possible to obtain a low-cost, small-sized, large-capacity multilayer ceramic capacitor having good temperature characteristics.

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

[0014]

EXAMPLES (Example 1) First, TiCl ₄ and Ba (NO ₃ ) _{2 of} various purities were prepared as starting materials, and these materials were prepared by adjusting the molar ratio of Ba ion to Ti ion to 1.0.
The sample was weighed to obtain 00 to obtain a weighed product. 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, A to A shown in Table 1
Five types of BaTiO ₃ having different purity of E were obtained.

[0015]

[Table 1]

Next, Nb ₂ O ₅ , Co ₂ O ₃ , MnO
₂ and an oxide glass containing _{BaO-B 2 O 3 -Li 2} O-SiO 2 as a main component were weighed so as to obtain the composition proportions shown in Table 2, the addition of vinyl acetate based binder, 16 hours wet mixing To obtain a mixture.

[0017]

[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), and its dielectric constant (ε), dielectric loss (tan δ) at room temperature, and change in capacitance with temperature change. The rate 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 ). Further, the dielectric loss (tan) when a voltage of 200 V / mm was applied at a frequency of 1 kHz.
δ) was measured.

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

[0023]

[Table 3]

Next, the reason why the range of the additive amount of the oxide as an additive is limited will be described.

That is, the range of 0.5 to 3.0 parts by weight of Nb ₂ O ₅ is that the sintering temperature is high when the amount is less than 0.5 part by weight, and the dielectric loss Becomes larger. Further, the temperature change rate of the capacitance is −55 ° C.
The value is larger than ± 15% in a temperature range of up to + 125 ° C. Further, as in Sample No. 5, when the content exceeds 3.0 parts by weight, the dielectric constant decreases.

The range of Co ₂ O ₃ is from 0.1 to
The amount of 1.0 part by weight was 0.1% as in Sample No. 12.
When the amount is less than 1 part by weight, the temperature change rate of the capacitance is −55 ° C.
The value is larger than ± 15% in a temperature range of up to + 125 ° C. If the amount exceeds 1.0 part by weight, as in Sample No. 13, the dielectric loss becomes extremely large, and the temperature change rate of the capacitance becomes large.

For MnO ₂ , the range is from 0.05 to
The amount of 0.5 part by weight was 0.1% as in Sample No. 19.
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. 20, if it exceeds 0.5 parts by weight, the dielectric constant becomes 2
It does not exceed 800, and the dielectric loss increases.

For oxide glass, the range is 0.0
The reason for setting the amount to 5 to 2.0 parts by weight is that the sinterability is improved and the voltage dependency is reduced within this composition range.
If less than 0.05 parts by weight, the sinterability becomes poor,
The AC voltage dependency increases. When the amount exceeds 2.0 parts by weight as in Sample No. 9, the dielectric constant becomes lower than 3000.

Further, the content of the alkali metal is set to 0.03
The weight percentage is set to 0.0% or less, as in Sample No. 21.
If it exceeds 3% by weight, the dielectric constant does not exceed 3000.

As described above, BaTiO ₃ , Nb ₂ O ₅ ,
In the Co ₂ O ₃ -based high dielectric constant composition, SrO, Ca present as an impurity in BaTiO _{3 as} a main component is used.
Alkaline earth metal oxides such as O, alkali metal oxides such as Na ₂ O and K ₂ O, other Al ₂ O ₃ , SiO ₂
The present inventors have found that among such oxides, the content of an alkali metal oxide such as Na ₂ O or K ₂ O greatly affects the electrical characteristics of the composition.

(Example 2) Dielectric ceramic raw material powders of Sample Nos. 8 and 16 of Example 1 were prepared. An organic solvent such as a polyvinyl butyral-based binder and ethanol was added to the dielectric ceramic raw material powder, and the mixture was wet-mixed with a ball mill to prepare a ceramic slurry. Thereafter, the ceramic slurry was formed into a sheet by a doctor blade method to obtain a rectangular green sheet having a thickness of 12 μm.

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 rate of change 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 capacitance with respect to temperature change is based on the capacitance (C ₂₅ ) at ₂₅ ° C., and the rate of change of temperature at −55 ° C. and + 125 ° C. (ΔC /
C ₂₅ ) and the absolute value of the value at which the temperature change rate between -55 ° C. and + 125 ° C. is the maximum, the so-called maximum change rate (| Δ
C / C ₂₅ | _max ).

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

[0038]

[Table 4]

As is clear from Table 4, the multilayer ceramic capacitor of Sample No. 16 falling 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 can sufficiently cope with the dielectric ceramic layer 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. 8, which is out of 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 defined 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. Also, Nb ₂ O ₅ , Co ₂ O ₃ , Mn
Additives such as O ₂ were added as oxide powder,
When b, Co, and Mn are blended so as to fall within the scope of the present invention in terms of oxides, the same effect can be obtained by adding a solution.

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-63-224105 (JP, A) JP-A-59-154704 (JP, A) JP-A-63-102105 (JP, A) (58) Survey Field (Int.Cl. ⁷ , DB name) H01B 3/00-3/14

Claims (1)

(57) [Claims] 1. Nb ₂ O ₅ is added in an amount of 0.5 to 3.0 parts by weight, and Co ₂ O ₃ is added to 100 parts by weight of BaTiO ₃ having an alkali metal oxide content of 0.03% by weight or less as an impurity. 0.1 to 1.0 part by weight, 0.05 to 0.5 part by weight of MnO ₂ , and BaO-B
_A dielectric ceramic composition containing 0.05 to 2.0 parts by weight of an oxide glass containing ₂ O ₃ —Li ₂ O—SiO ₂ as a main component and having a grain size of 1 μm or less .