JPH0137806B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a ceramic composition, particularly a dielectric ceramic composition that can be sintered at a low temperature of 950° C. or lower and has a high product of dielectric constant and specific resistance.

It is well known that porcelain containing barium titanate (BaTiO ₃ ) as a main component has been widely put into practical use as a dielectric porcelain composition. However, the sintering temperature of materials whose main component is BaTiO ₃ or the like is usually as high as 1300 to 1400°C. Therefore, when using this material in multilayer capacitors, materials that can withstand this sintering temperature must be used for the internal electrodes, such as expensive noble metals such as platinum and palladium, which increases manufacturing costs. There are drawbacks. In order to make multilayer capacitors cheaply, it is desirable to use porcelain that can be sintered at as low a temperature as possible, especially at a temperature lower than 960°C, which is the melting point of silver, and which allows the use of inexpensive metals mainly composed of silver and nickel. ing.

For this reason, Pb (Fe _2/3
W _1/3 ) O _{3 −Pb} (Fe _1/2 Nb _1/2 )
See Publication No. 34962. ) and (Sr/Pb) TiO ₃ −Pb (Mg _1/2 W _1/2 ) O ₃ system (JP-A-Sho
See Publication No. 52-21699. ) have been proposed.
By the way, when creating a practical multilayer capacitor using a ceramic composition, many items must be evaluated as the characteristics of the ceramic composition. Basically, it is required that the dielectric constant be as large as possible, the dielectric loss as small as possible, the resistivity as large as possible, and the rate of change of the dielectric constant with temperature as small as possible. Here, the capacitance of a multilayer capacitor is proportional to the dielectric constant of the porcelain, but inversely proportional to the thickness of the porcelain, and proportional to the area of overlapping electrodes and the number of laminated layers, so the value of the dielectric constant is not an absolute factor in practice. Furthermore, there are various allowable ranges for the temperature change rate of dielectric constant depending on the application.
This is also not an absolute factor. Dielectric loss (tanδ) is limited to a certain value depending on the application, and the maximum value is at room temperature.
5.0%, preferably 2.5% or less, is generally desired.

Regarding resistivity, for example, as stated in the EIAJ standard (Japan Electronics Industry Association's Multilayer Ceramic Capacitors (Chip Type) RC-3698B), the insulation resistance of a multilayer capacitor is 10000MΩ.
or more than 500μF・MΩ in capacitance/resistance product (CXR)
It is defined as the smaller of the above.
In other words, unless the product of the permittivity and resistivity of the ceramic composition exceeds a certain absolute value, a capacitor of any capacitance, especially a large capacitance, cannot be made to meet practical standards, and its uses are extremely limited and it is not practical. It loses its meaning. This point will be explained in detail as follows. A multilayer capacitor has a structure in which single-layer capacitors are stacked, generally consisting of n layers of the same thickness and forming n+1 internal electrodes. In this case, the capacitance per single layer is C ₀ and the insulation resistance is R ₀
Then, C of the multilayer capacitor becomes n times _C0 ,
The insulation resistance R is 1/n of R ₀ . Here, if the permittivity of the ceramic composition is ε, the permittivity of vacuum is ε ₀ , the specific resistance of the ceramic composition is ρ, the thickness of the ceramic of the single-layer capacitor is d, and the area of the weighted electrode is S, then C ₀ of a single layer capacitor becomes (ε ₀ εS)/d, and R ₀ becomes (ρ ^d )/s. Therefore, the product C×R of capacitance and insulation resistance of a multilayer capacitor consisting of n layers is [(ρ ^d )/
(ns)]×[nε ₀ εS)/d]=ε ₀ ερ. That is, C×R of a multilayer capacitor of any capacity is normalized to a constant value obtained by multiplying the product of ε and ρ of the ceramic composition by ε ₀ . C×R is 500μF・MΩ, that is, 500F・
Ω or more means that ε ₀ = 8.855×10 ^-14 F/cm, so 8.855×10 ^-14 ×ε×ρ (F/cm)≧500F・Ω, and therefore ερ≧5.65×10 ¹⁵ Ω・cm. There is. For example, when ε=10000, ρ≧5.65×10 ¹¹ Ω・cm, ε=3000
Then, ρ≧1.88×10 ¹² Ω・cm, and when ε=500, ρ≧1.13
×10 ¹³ Ω・cm is required. Any large capacitance multilayer capacitor of porcelain composition with ρ greater than these values depending on the dielectric constant is 500μF・MΩ.
satisfy. If ε is 3000 and ρ is 1.88×10 ¹¹ Ω・cm, which is one order of magnitude lower than the required value, then ε ₀ ερ=50μF・MΩ
500μF・MΩ is not satisfied, and the insulation resistance is
In order to satisfy 10000 MΩ, that is, 10 ¹⁰ Ω or more, the capacitance C must be limited to 0.005 μF or less.
That is, the C×R of this multilayer capacitor is always
Since it shows 50μF・MΩ, when R is 10000MΩ, C will be 0.005μF, and if C is larger than this, R will be smaller than 10000MΩ. 0.005μF is the highest capacitance that meets the standard. Therefore, if the specific resistance of the ceramic composition is low, the practicality of the material, especially the features of multilayer capacitors such as small size and large capacity, cannot be taken advantage of, and it is completely meaningless. Therefore, it is extremely important from a practical standpoint that the product of resistivity and dielectric constant of the ceramic composition is greater than a certain value.

By the way, Pb (Mg _1/2 W _1/2 ) O ₃ −PbTiO ₃ based porcelain compositions have already been reported by NNKrainik and AI.
Aqranovskaya (Fiziko Tverdoqo Tela, Vo.2,
No. 1, pp70-72, Janoary 1960), there is a proposal: (Sr _x Pb _1-x TiO ₃ ) _a (PbMg _0.5 W _0.5 O ₃ ) _b 0.5;
It is disclosed in Japanese Patent Laid-Open No. 21662, and also disclosed as a dielectric powder composition in Japanese Patent Application Laid-open No. 21699/1983.
Furthermore, it is a composition mainly composed of Pb(Mg _1/2 W _1/2 ) O ₃ and PbTiO ₃ , in which Pb(Mg _1/2 W _1/2 ) O ₃ is 20.0 to 70.0 mol%, and PbTiO ₃ is A high dielectric constant porcelain composition characterized by containing an amount of MgO of 30% or less of the calculated value in a composition in the range of 30.0 to 80.0 mol% was disclosed in Japanese Patent Application Laid-Open No. 1983-1999.
-Disclosed as Publication No. 144609. However, none of them disclosed any specific resistance, and the practicality of the Pb(Mg _1/2 W _1/2 )O ₃ --PbTiO ₃ ceramic composition was clear.

The object of the present invention is that it can be sintered at a temperature of 910℃ to 950℃, the product ερ of electrostatic constant and specific resistance is 5.65×10 ¹⁵ Ω・cm,
That is, the object is to provide a ceramic composition having a value of _{ε 0} ερ of 500 F·Ω or more.

The present invention consists of a binary component of Pb(Mg _1/2 W _1/2 )O ₃ -PbTiO ₃ , which is combined into [Pb(Mg _1/2 W _1/2 )O ₃ ] _x
[PbTiO ₃ ] When expressed as _1-x , it is in the range of 0.7<x≦1.00, can be sintered at a temperature of 910℃ to 950℃, and has a product of dielectric constant and specific resistance of 5.65×10 ¹⁵ Ω・cm or more. It is a porcelain composition that is characterized by having

Next, the present invention, which exhibits excellent characteristics, will be explained in detail with reference to Examples.

Example Using lead oxide (PbO), magnesium oxide (MgO), tungsten oxide (WO ₃ ) and oxide (TiO ₂ ) with a purity of 99.9% or more as starting materials,
Weigh to the predetermined mixing ratio. Next, after wet mixing in a ball mill, the mixture was pre-baked at 750-800°C. Thereafter, it was ground in a ball mill, separated and dried, and an organic binder was added thereto for sizing and pressing to produce four discs each having a diameter of 16 mm and a thickness of about 2 mm. Next, 1 at 910-950℃ in air.
Sintered for hours. Silver electrodes were baked on the top and bottom surfaces of the sintered disk, and a frequency of 1KHz was measured using a digital LCR meter.
The capacitance and dielectric loss (tan δ) were measured at a voltage of 1 Vr.ms, and the dielectric constant was calculated. Next, check 50V using a super insulation resistance tester.
The voltage was applied for 1 minute, the insulation resistance was measured, and the specific resistance was calculated. The average value of the four samples was taken, and that value was taken as the representative value of the blending ratio x. Figure 1 shows the results of dielectric constant (ε), and Figure 2 shows dielectric loss (tanδ).
Figure 3 shows the results of dielectric constant (ε) and specific resistance (ρ).
The results of multiplying the product by the vacuum dielectric constant (ε ₀ ) are shown using the sintering temperature as a parameter.

From FIG. 1, as x decreases, ε increases. x is
At 0.6, it can be seen that the value of ε varies greatly depending on the sintering temperature. From Figure 2, tan δ increases as x decreases. From FIG. 3, ε ₀ ερ reaches its maximum when x is around 0.9, and decreases rapidly especially as x becomes smaller. If x is larger than 0.65, even if sintered at 910 to 950°C, a value of 500MΩ・μF or more will always be achieved.
That is, the composition of the present invention can be sintered at a low temperature of 910 to 950°C, has a high product of dielectric constant and specific resistance, achieves ε ₀ ερ of 500 MΩ・μF or more, and has a small tan δ.
It has excellent features as a ceramic composition for multilayer capacitors. Note that the porcelain composition of the present invention contains Pb
(Mg _1/2 Ti _1/2 ) _x Ti _1-x O ₃ and is limited to 0.7<x≦1.00.

The reason is that ε ₀ ερ becomes small when x≦0.7.

As described above, the porcelain composition of the present invention can be sintered at a low temperature of 910 to 950°C, and low-cost metals such as silver and nickel can be used. It is an extremely practical material from the viewpoint of its characteristics, such as its high product density.

[Brief explanation of drawings]

Figures 1 to 3 respectively show the relationship between the blending ratio and various properties of the porcelain composition of the present invention.
The figure shows the dielectric constant (ε), and the figure 2 shows the dielectric loss (tanδ).
FIG. 3 shows the product of the dielectric constant (ε) and specific resistance (ρ) multiplied by the vacuum permittivity (ε ₀ ), each with the sintering temperature as a parameter.

Claims (1)

[Claims] 1 Magnesium lead tungstate [Pb
(Mg ^1/2 W ^1/2 )O ₃ ] and lead titanate [PbTiO ₃ ], [Pb(Mg ^1/2 W ^1/2 )O ₃ ] _x
[PbTiO ₃ ] When expressed as _1-x , x is 0.7<x≦1.00
is in the range of , and the product of permittivity and resistivity is 5.65×
A porcelain composition characterized by having a resistance of 10 ^{to 15} Ω·cm or more.