JPH06227861A - Dielectric ceramic composition - Google Patents

Abstract

PURPOSE:To provide a dielectric ceramic composition having high dielectric constant and small in changing ratio of volume by temperature, further capable of corresponding to the formation of thin layer having <=10mum thickness, free from secondary phase and having uniform structure. CONSTITUTION:The dielectric ceramic composition contains a main component consisting of 92.0-99.4mol% BaTiO3 having <=0.04wt.% content of an alkali metal oxide contained as impurity, 0.3-4.0mol% at least one rare earth oxide (Re2O3) selected from Tb2O3, Dy2O3, Ho2O3 and Er2O3 and 0.3-4.0mol% NiO and a subsidiary component consisting of 0.2-5.0mol% and 0.05-1.0mol% MnO based on 100mol% main component.

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, and more particularly to a dielectric ceramic composition used as a dielectric material such as a thin film-capable laminated capacitor.

[0002]

2. Description of the Related Art In general, a multilayer capacitor is formed by laminating a plurality of sheet-like dielectrics containing BaTiO ₃ as a main component and having an internal electrode paste applied on the surface thereof, and alternately forming a pair of internal electrodes of each sheet in parallel. It is formed by connecting to the external connection electrode of and sintering and integrating it. With the progress of electronics in recent years, such a multilayer capacitor is used in a wide range of electronic circuits, and its size tends to be further miniaturized.

On the other hand, various types of compositions have been heretofore proposed as a dielectric ceramic composition containing BaTiO ₃ as a main component. Among them, BaTi disclosed in Japanese Patent Application Laid-Open No. 61-275164 is disclosed as a dielectric ceramic composition having a high dielectric constant and a small rate of change in capacitance with temperature.
_{O 3 -Nb 2 O 5 -Co 2} O 3 based compositions are the most common, it is used as a basic composition of a wide multilayer capacitor. In these dielectric ceramic compositions, BaTi
O ₃ and Nb ₂ O ₅ and Co ₂ O ₃ becomes from partially diffused structure, the composition portion having a Curie point of pure BaTiO _3, and the composition part having a Curie point below room temperature or at room temperature , A composite mainly present in the central portion and the peripheral portion of the ceramic crystal grains, so-called c
The ore-shell provides flatness of the capacitance with temperature change.

As mentioned above, BaTiO ₃ is added to Nb ₂ O ₅
A dielectric porcelain composition whose main component is a dielectric having a structure in which Co ₂ O _{3 and the} like are partially diffused is 3500 to 4000 even though the temperature change rate of capacitance is small.
Because of its high dielectric constant, it is widely used as a multilayer capacitor material for small-sized and large-capacity applications.

[0005]

However, in these dielectric porcelain compositions, Nb and Co, which are likely to form a solid solution in the Ti site of BaTiO ₃ , are partially diffused in BaTiO ₃ , so that they are swept out during firing. Ti is BaTi
A low-melting-point Ti-rich phase such as BaT with O _3.
The secondary phase represented by the i ₄ O ₉ phase, the Ba ₄ Ti ₁₃ O ₃₀ phase, the Ba ₆ Ti ₁₇ O ₄₀ phase and the like was easily generated. Since these secondary phases have a low dielectric constant, there has been a problem of reduction in capacitance value. Furthermore, these Ti-rich secondary phases are likely to grow into acicular crystals, and when the element thickness is made thin to increase the size and capacity of the multilayer capacitor, the acicular crystals sometimes exceed the element thickness and extend between the internal electrodes. May exist, which has been a major problem in terms of reliability at high temperatures. Therefore, although these conventional dielectric porcelain compositions are compositional systems having a high dielectric constant, there is a limit in thinning the layer, and it is impossible to cope with further miniaturization and large capacity that will be further advanced in the future. Met.

Further, these phenomena are caused by BaTiO ₃ --N
Not only the b ₂ O ₅ —Co ₂ O ₃ system composition but also BaTiO ₃
B containing Nb ₂ O ₅ such as —Nb ₂ O ₅ —MnO system composition
This was the case for aTiO ₃ -based compositions in general.

Therefore, in order to further reduce the size and increase the capacity in the future, a dielectric porcelain composition which does not have a secondary phase and which can cope with a thin layer has been required.

Therefore, the main object of the present invention is to have a high dielectric constant and a small rate of change in capacitance with temperature.
It is an object of the present invention to provide a uniform dielectric ceramic composition having a texture that does not have a secondary phase and can be applied to a thin layer having a thickness of not more than μm.

[0009]

According to the present invention, BaTiO ₃ containing less than 0.04% by weight of an alkali metal oxide contained as an impurity, Tb ₂ O ₃ , Dy ₂ O ₃ and H.
The compounding ratio of at least one rare earth oxide (Re ₂ O ₃ ) selected from o ₂ O ₃ and Er ₂ O ₃ and NiO is BaTiO ₃ 92.0 to 99.4 mol% and Re ₂
O ₃ 0.3 to 4.0 mol% and, relative to 100 mol of the main ingredient% that ranges between NiO0.3~4.0 mol%, as an auxiliary component, and MgO0.2~5.0 mol% , MnO0.
It is a dielectric ceramic composition containing 05-1.0 mol%.

As an accessory component, SiO ₂ may be contained in an amount of 3.0 mol% or less.

Furthermore, 2.5 parts by weight or less of an oxide glass containing BaO-SrO-Li ₂ O-SiO ₂ as a main component may be contained in an amount of 100 parts by weight of all the above components.

[0012]

According to the present invention, the dielectric material containing BaTiO ₃ , rare earth oxide and NiO as the main components is added to Mg.
By adding O and MnO, it has a high dielectric constant of 3500 or more, a small temperature change rate of capacitance, and
It is possible to obtain a dielectric porcelain composition that can be applied to a thin layer of μm or less, has no secondary phase, has a uniform structure, and has excellent reliability at high temperatures. Furthermore, by adding SiO ₂ or oxide glass, the firing temperature can be lowered and the firing cost can be reduced.

Therefore, if this dielectric porcelain composition is used as a dielectric material for a monolithic ceramic capacitor, for example, it becomes possible to develop a thin layer having a thickness of 10 μm or less, which is impossible with a conventional composition system. It is possible to easily achieve further miniaturization and larger capacity of the capacitor.

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

[0015]

Example As starting materials, BaTiO ₃ , rare earth oxides, NiO, MgO, MnO, SiO ₂ and oxide glass having different contents of alkali metal oxides contained as impurities were prepared. These raw materials were weighed so that the composition ratios shown in Table 1 were obtained to obtain weighed products. Sample number 1
Nos. 21 to 21 have an alkali metal oxide content of 0.
03 Using the wt% of BaTiO _3, for sample No. 22, the content of alkali metal oxide is 0.05 wt%
Sample No. 23 containing BaTiO ₃ is used and the content of alkali metal oxide is 0.07% by weight of BaTi 3.
The O ₃ was used.

[0016]

[Table 1]

The weighed material obtained was used together with a dispersion medium for PSZ.
A raw material slurry was prepared by mixing with a ball mill using balls. Next, an organic binder and a plasticizer were added to this raw material slurry, and after sufficiently stirring, sheet forming was carried out by the doctor blade method to obtain a ceramic green sheet. The thickness of the ceramic green sheet at this time was 12 μm.

Next, a conductive paste for forming internal electrodes is applied to one surface of the thus obtained ceramic green sheet, and after drying, a plurality of ceramic green sheets are laminated and then pressure-bonded in the thickness direction to laminate. A body was obtained and cut out from this laminated body to obtain a multilayer capacitor raw unit. After removing the binder from this unit at 320 ° C. for 5 hours, remove H ₂ / N ₂
In a reducing atmosphere gas stream having a volume ratio of 3/100, it was fired at the temperature shown in Table 2 for 2 hours to obtain a sintered body. At this time, the thickness of the dielectric element of the unit after firing was 8 μm.

[0019]

[Table 2]

Silver paste for external electrodes was applied to the obtained sintered body and baked to obtain a laminated ceramic capacitor. Then, the capacitance value at room temperature of this multilayer ceramic capacitor, the dielectric loss tan δ, the insulation resistance value (IR), the temperature change rate of the capacitance (TCC), and the MTTF (mean time) in the super accelerated life test.
o failure) was measured. The results are summarized in Table 2. The capacitance value is shown in terms of the dielectric constant ε.

Regarding the dielectric constant ε and the dielectric loss tan δ,
The measurement was performed under the conditions of a temperature of 25 ° C., a frequency of 1 kHz and an AC voltage of 1V. The insulation resistance value is measured by applying a DC voltage of 16 V for 2 minutes at a temperature of 25 ° C., and the result is shown as the product of the capacitance value, that is, the CR product. Further, regarding the temperature change rate (TCC), the rate of change in capacity is the maximum between -55 ° C and 125 ° C with reference to the capacity value of 25 ° C, and between -55 ° C and + 125 ° C. The absolute value of the value, that is, the maximum rate of change is shown. As for MTTF, the electric field strength at 150 ° C. was 16.0 (kV / m) for n = 18 samples.
m) The results calculated by Weibull plot from the time until dielectric breakdown when applied are shown.

As is clear from Table 2, the laminated ceramic capacitor using the dielectric ceramic composition according to the present invention exhibits excellent characteristics even if it is a thin layer, and is very excellent in reliability at high temperatures. .

The reason for limiting the ranges of the main component and the sub-components in the present invention as described above is as follows.

First, the reason for limiting the range of the main component will be described.

The composition ratio of BaTiO _{3 as} the main component is 9
The composition ratio of 92 to 99.4 mol% is 92.
If it is less than 0 mol%, the composition ratio of the rare earth element and NiO increases, and as shown in Sample No. 4, the insulation resistance value and the dielectric constant decrease, which is not preferable. Also,
When the composition ratio of BaTiO ₃ exceeds 99.4 mol%, the effect of the addition of the rare earth element and NiO is not exerted, and as shown in Sample No. 3, the capacity-temperature change rate in the high temperature part (around the Curie point) is large. It is not preferable because it shifts to the (+) side.
Further, the content of the alkali metal oxide in BaTiO ₃ is set to 0.04% by weight or less, when the content exceeds 0.04% by weight, the dielectric constant is lowered as shown in sample numbers 22 and 23. It is not practical and is not preferable.

Next, the reason for limiting the range of subcomponents will be described.

The amount of MgO added is set to 0.2 to 5.0 mol%. When the added amount is less than 0.2 mol%, as shown in Sample No. 17, the element thickness of the multilayer capacitor is reduced. When stratified, the curve showing the capacity temperature change rate tends to have a single peak, deviates to the (-) side at a low temperature portion, and tends to deviate to the (+) side at a high temperature portion near the Curie point, It is not preferable because the insulation resistance value is lowered.
Further, if the addition amount exceeds 5.0 mol%, as shown in sample No. 15, the dielectric constant and the insulation resistance value decrease, which is not preferable.

The amount of MnO added is set to 0.05 to 1.0 mol%, when the added amount is less than 0.05 mol%, as shown in Sample No. 9, the insulation resistance is lowered and the dielectric constant is reduced. This is not preferable because it causes an increase in loss and a decrease in MTTF value. Further, when the added amount exceeds 1.0 mol%, as shown in Sample No. 12, the insulation resistance decreases and the MT
It is not preferable because the TF value decreases.

It is not preferable to set the added amount of SiO ₂ to 3.0 mol% or less, when the added amount exceeds 3.0 mol%, as shown in Sample No. 21, the dielectric constant is lowered.

[0030] _{Finally, BaO-SrO-Li 2 O} -Si
The addition amount of the oxide glass containing O ₂ as a main component is set to 2.5 parts by weight or less because when the addition amount exceeds 2.5 parts by weight, as shown in Sample No. 19, SiO ₂ As in the case, the dielectric constant is lowered, which is not preferable.

Claims (3)

[Claims] 1. BaTiO ₃ having an alkali metal oxide content of 0.04% by weight or less as an impurity, and T
b ₂ O ₃ , Dy ₂ O ₃ , Ho ₂ O ₃ , and Er ₂ O ₃ , at least one rare earth oxide (Re ₂ O 3)
And ₃₎ blending ratio of NiO is, BaTiO ₃ from 92.0 to 99.4 mol%, Re ₂ O ₃ 0.3 to 4.0 mol%, and NiO 0.3 to 4.0 mole% range A dielectric ceramic composition containing 0.2 to 5.0 mol% of MgO and 0.05 to 1.0 mol% of MnO as secondary components with respect to 100 mol% of the main component therein. 2. SiO ₂ as an auxiliary component is 3.0
The dielectric ceramic composition according to claim 1, wherein the dielectric ceramic composition is contained in an amount of not more than mol%. 3. An oxide glass containing BaO—SrO—Li ₂ O—SiO ₂ as a main component in an amount of 2.5 parts by weight or less based on 100 parts by weight of all the above components.
The dielectric ceramic composition of.