JPH041965B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION (Industrial Application Field) The present invention relates to a high dielectric constant ceramic composition which is mainly composed of barium titanate and has a high dielectric constant and a dense ceramic structure.

(Structures of Conventional Examples and Their Problems) Conventionally, many compositions of ceramic capacitors mainly containing barium titanate have been known. As is well known, barium titanate is a unique substance that exhibits ferroelectricity, and has a cubic perovskite structure at high temperatures, and below 120°C, the C-axis is slightly elongated to become a tetragonal crystal. It changes to orthorhombic crystal at around 0°C and rhombohedral crystal at around -80°C.
The above-mentioned phase transition point near 120°C is particularly called the Curie point, and at higher temperatures beyond this Curie point, it exhibits paraelectricity, and at lower temperatures, it exhibits ferroelectricity. At this Curie point, the dielectric constant exhibits an extremely high value of about 10,000. Here, barium titanate alone cannot provide a high dielectric constant at room temperature. Many attempts have been made to commercialize small capacitors with appropriate capacitance near room temperature by moving the high dielectric constant of barium titanate near the Curie point to a lower temperature side. Additives that shift the temperature at which the peak value of the dielectric constant appears is called a shifter, and are used in BaSnO ₃ , SrSnO ₃ , CaSnO ₃ ,
Generally known are stannates such as PbSnO ₃ , CuSnO ₃ , ZnSnO ₃ , CdSnO ₃ , zirconates such as BaZrO ₃ , CaZrO ₃ , SrZrO ₃ and titanates such as SrTiO ₃ and PbTiO ₃ , in the above order. Great effect as a shifter.

Barium titanate using these shifters has been used in single-plate leaded type ceramic capacitors. By the way, recently, with the advancement of laminated chip technology, it has become easy to obtain dielectric sheets of about 30 to 100 μm, and so-called laminated ceramic chip capacitors, in which these thin films are laminated in many layers with electrodes sandwiched between them, are now available. have entered various electronics industries, and conventional dielectric ceramic compositions are increasingly being utilized as such laminated thin film dielectrics. However, in conventional single-plate ceramic capacitors, the dielectric thickness is 100~
Whereas multilayer ceramic chip capacitors are thick at 10,000 μm, they are thin at 10 to 20 μm, so they receive an electric field strength 5 to 10 times higher. Therefore, there is a need for a composition that has less voltage dependence than conventional single-plate capacitors. Furthermore, as the dielectric layer becomes thinner, structural defects in the ceramic become more likely to appear in the characteristics, so it is desirable that the crystal grains be uniform and fine, and that the number of pores be small and small.

Against this background, the inventors have already filed a patent application
No. 57-16809 proposes a high dielectric constant ceramic composition that has a high dielectric constant, has few structural defects in the ceramic, has low voltage dependence, and has a high breakdown voltage. That is,
This is a high dielectric constant ceramic composition consisting of 100 mol parts of BaTiO ₃ , 7±1 mol parts of CeO ₂ 2/3 and 7±1 mol parts of TiO ₂ . However, this composition had problems in terms of quality because the insulation resistance was rather low and the color was bright red, and the palladium electrodes of the multilayer ceramic chip capacitor were visible through it.

(Objective of the Invention) The present invention aims to eliminate the above-mentioned drawbacks, and is made of a high dielectric constant porcelain composition that has higher insulation resistance and at the same time prevents the palladium electrodes of the multilayer ceramic chip capacitor from being seen through the porcelain. It is something that provides something.

(Structure of the invention) In order to achieve the above object, patent application No. 57-16809
A small amount of chromium oxide (Cr ₂ O ₃ ) is added to the high dielectric constant ceramic composition proposed in the issue. With this configuration, the insulation resistance is increased, and the brightness of the coloring of the porcelain is lowered so that the palladium electrode of the multilayer ceramic chip capacitor cannot be seen through the porcelain, improving the quality.

(Description of Examples) Hereinafter, the present invention will be described in detail based on Examples.

First, barium titanate (BaTiO ₃ ) was synthesized as follows. That is, barium carbonate (BaCO ₃ )
and titanium oxide (TiO ₂ ) with a [Ba]/[Ti] ratio of
The mixture was mixed with an accuracy of 1.000±0.005, calcined at 1100 to 1150°C, and then ground. Next, this
Add CeO ₂ 2/3 (7±1) mole parts and TiO ₂ 7±1 mole parts to 100 mole parts of BaTiO ₃ , and further,
Cr ₂ O ₃ was added and mixed in various proportions. A binder was added to this mixture, the mixture was granulated, formed into a square plate shape, and fired at a temperature in the range of 1250 to 1350°C. Thereafter, a silver electrode was formed on this rectangular dielectric material to produce a capacitor.

Figure 1 shows the relationship between the amount of Cr ₂ O ₃ added and the electrical characteristics of the above capacitor. As is clear from this figure, the dielectric constant ε increases when the amount of Cr ₂ O ₃ added is 0.2 mol. There is a tendency for the number to gradually decrease in the upper divisions and above. Further, the dielectric loss angle tan〓 tends to increase when Cr ₂ O ₃ is 0.5 mole part or more. Furthermore, the insulation resistance I·R gradually increases as Cr ₂ O ₃ increases.

Next, multilayer ceramic chip capacitors as shown in FIG. 2 were experimentally manufactured with compositions containing various amounts of Cr ₂ O ₃ added. In FIG. 2, 1 is a dielectric, 2 is a palladium electrode, the thickness of the dielectric between the electrodes is 35 μm, and 3 is a silver terminal electrode. FIG. 3 shows the relationship between the amount of Cr ₂ O ₃ added and the electrical characteristics of such a laminated ceramic chip capacitor. The shaded area indicates the area where the palladium electrode can be seen through the 35 μm thick dielectric layer. As is clear from this figure, the dependence on the amount of Cr ₂ O ₃ added is relatively large compared to the electrical property values of the square plate. When 0.2 mol part or more of Cr ₂ O ₃ is added, the dielectric constant ε decreases extremely;
There is almost no change within molar parts. The insulation resistance I·R at 0.2 mol part is about 5 times that of the case without additives. The dielectric loss angle tan becomes large at 0.3 molar parts or more. From the above results, the range of the optimum amount of Cr ₂ O ₃ added is limited to between 0.05 mol part, at which the palladium electrode is not visible, and 0.2 mol part, at which the dielectric constant begins to drop suddenly.

In addition, the grain size is throughout the examples,
The average size is 2-3μm, and the pore size is also 2-3μm.
It was less than m.

(Effects of the Invention) From the above, the composition of the present invention has a dense ceramic structure with fine grains, few and small pores, as well as the composition of the patent application No. 16809/1982, and This invention greatly improves the insulation resistance characteristics of the composition of No. 16809/1982, and also improves the drawback that palladium electrodes are visible through the laminated ceramic chip capacitor. In particular, it is extremely suitable as a dielectric composition for multilayer ceramic chip capacitors with EIA specified Y5V characteristics, and it can be said that the industrial value of the present invention is extremely large.

In the examples, barium titanate was synthesized and used, but commercially available barium titanate may also be used.

[Brief explanation of drawings]

FIG. 1 is a diagram showing the amount of Cr ₂ O ₃ added and the characteristics of the square plate dielectric in the composition of the present invention, and FIG. 2 is a cross-sectional view of a multilayer ceramic chip capacitor to which the composition of the present invention is applied. FIG. 3 is a diagram showing the amount of Cr ₂ O ₃ added in the composition of the present invention and the characteristics of a multilayer ceramic chip capacitor. 1... Dielectric, 2... Palladium electrode, 3...
Silver terminal electrode.

Claims (1)

[Claims] 1 100 mol parts of barium titanate (BaTiO ₃ ),
It is characterized by adding _0.05 to 0.2 mole part of chromium oxide (Cr ₂ O ₃ ) to 2/3 (7±1) mole part of cerium oxide (CeO ₂ ) and 7±1 mole part of titanium oxide (TiO 2 ). High dielectric constant porcelain composition.