JPH0458507A - Dielectric porcelain capacitor - Google Patents

Abstract

PURPOSE:To get a porcelain capacitor of high permittivity by adding and admixing a specific additive to and in the composition of a specific barium titanate, a tantalum oxide, and a samarium oxide, and forming a baked electrode mainly composed of copper. CONSTITUTION:An additive is added to the composition of 94.0-99.5 mole % barium titanate, 0.2-0.3 mole % tantalum oxide, and 0.2-3.0 mole % samarium oxide, and those are wetly mixed in a pot mill. As the additive, at least one kind among a cobalt oxide, a zine oxide, and a nickel oxide, by 0.05-0.07wt.%, and at least, one kind among a silicon oxide and an aluminum oxide, by 0.05-0.5wt.%, are used. And the composition being wetly mixed is dehydrated and calcined, and after smashing, an organic binder is added to granulate it, and this is compacted. This compact is baked in an air atmosphere for about two hours in the range of 1300-1400 deg.C so as to bake copper electrodes on both sides.

Description

DETAILED DESCRIPTION OF THE INVENTION [Field of Industrial Application] The present invention relates to a ceramic capacitor having a high dielectric constant, a small temperature change in the dielectric constant, a small change over time, and a small dielectric loss.

[Conventional technology]

Conventionally, ceramic capacitors using barium titanate with a bismuth compound such as bismuth stannate added, or Nb2O5, Ta2es, and rare earth oxides have been put into practical use as compositions with small temperature changes in dielectric constant. It has been.

By the way, silver electrodes have conventionally been used as electrodes in such ceramic capacitors, but silver is expensive.

For this reason, inexpensive copper and nickel have recently been used as electrode materials for ceramic capacitors instead of silver, which has traditionally been widely used.

Among these, copper is considered a promising electrode material because it does not suffer from electromigration, which is a disadvantage of silver electrodes, has high reliability, and can be formed into electrodes at a relatively low cost.

However, the formation of copper electrodes requires baking in a neutral or reducing atmosphere to prevent oxidation, so the dielectric composition as described above is easily reduced by the reducing atmosphere during baking and does not have the desired properties. However, there is a problem in that it is not possible to obtain the same characteristics as described above, and a method of adding MnO or a compound thereof as a reduction inhibitor is known.

Dielectric compositions containing barium titanate, tantalum oxide, and samarium oxide as main components are well known (Japanese Unexamined Patent Application Publication No. 1983-1998).
143895), which uses silver as an electrode for the reasons mentioned above, and is expensive.

[Problem to be solved by the invention]

By the way, when MnO or the like is added as a reduction inhibitor to the composition, there is a problem that the temperature characteristic change rate of the dielectric constant and its change over time are large, which is not desirable.

Therefore, it is an object of the present invention to provide a highly reliable ceramic capacitor that has copper electrodes on opposing surfaces of dielectric ceramic with excellent reduction resistance, has a high dielectric constant, and has a small rate of change in dielectric constant with temperature and change over time. This is what we provide.

[Means to solve the problem]

In order to achieve the above object, the present inventors conducted extensive research and found that 94.0 to 99.5 mol% of BaTiO3 and Ta20
0.2 to 3.0 mol% of Sm2O3 and 0.2 to 3.0 mol% of Sm2O3.
With respect to 100 parts of a blended composition of 2 to 3.0 mol%, as additives: (1) 0.0% of at least one of Coo, ZnO, and NiO;
By adding 0.05 to 0.7% by weight of at least one of SiOx and Aj2zO3, a copper electrode can be formed and a ceramic capacitor having desired characteristics can be obtained. I found out.

〔Example〕

The present invention will be explained in detail based on examples.

Barium carbonate BaCO3, tantalum oxide Ta as raw materials
2ks, samarium oxide S+l+203, and each additive are weighed and blended so that the composition after sintering has the composition ratio shown in Table 1 below, and wet-mixed in a bot mill.

After sowing, it is dehydrated and pre-fired at 1150-1250''C.

Next, this is pulverized, an organic binder is added thereto, granulated, and then pressure molded to a diameter of 16 fl and a thickness of 0.6 tn.

This molded product is fired in an air atmosphere at a temperature of 1300 to 1400°C for 2 hours.

Dielectric ceramic capacitors are prepared by baking copper electrodes on both sides of the ceramic fired body thus obtained, and used as measurement samples to measure the electrical characteristics of each.

The measurement results are shown in Table 1.

Note that the measurement conditions for the measured values in Table 1 are as shown below.

The dielectric constant (ε,) is the value at IKHz at room temperature, and the rate of change in dielectric constant temperature characteristics (ΔC/C) is the rate of change between the permittivity at -25℃ and +85℃, based on the dielectric constant at 20℃ ( %), the capacitance change rate over time is 1000
It shows the capacitance change rate (%) after time.

In addition, in Table 1, sample No. 5.6.12.14
．． 15.17.18.19.22.23.24.25.
26.27.28.30.31 are outside the scope of this invention.

As is clear from Table 1 below, samples having the composition range of the present invention have good characteristics such as a high dielectric constant, a small rate of change in dielectric constant temperature characteristics, and a small rate of change in capacitance over time.

Next, the reason for limiting the composition range in the present invention will be explained.

If BaTiOs exceeds 99.5 mol%, the dielectric constant will be low and the dielectric loss will be large (for example, sample No. 1 in Table 1).
, 19).

BaTi0 again! If l is less than 94.0 mol%, the rate of change in dielectric constant temperature characteristics will increase, and the rate of change in capacitance over time will also increase (for example, Sample No. in Table 1).

(see 18).

When Taxes exceeds 3.0 mol%, the dielectric constant becomes small, the rate of change in dielectric constant temperature characteristics increases, and the rate of change in capacitance over time also increases (for example, sample No. 14.1 in Table 1).
8).

If Ta2es is less than 0.2 mol%, the dielectric constant is still small, the rate of change in dielectric constant temperature characteristics is large, and the rate of change in capacitance over time is also large (for example, sample No. 1 in Table 1,
12).

When 3111209 exceeds 3.0 mol%, the rate of change in dielectric constant temperature characteristics becomes large (for example, sample N0017 in Table 1).
reference).

If Sn+s03 is less than 0.2 mol%, the dielectric constant will be small and the rate of change in dielectric constant temperature characteristics will be large (for example, the first
(See table sample No. 15).

Further, at least one of Coo, ZnO, and NiO is 0.
When it exceeds 7% by weight, the dielectric constant becomes low (see, for example, sample No. 5.22.23 in Table 1) or the dielectric loss increases (see, for example, sample No. 0027 in Table 1).

If at least one of Coo, ZnO, and NiO is less than 0.05% by weight, both the rate of change in dielectric constant temperature characteristics and the rate of change in capacitance over time become large (for example, sample N in Table 1).
o, see 30.31).

Furthermore, at least one of '5ins and Altos is 0.
If it exceeds 5% by weight, the dielectric constant is low (see, for example, sample No. 26.28 in Table 1).

Also, SiO! , at least one of Alx03 is 0.0
If it is less than 5% by weight, the dielectric loss becomes large (see, for example, Sample No. 6.24.25.27 in Table 1).

In addition, in the conventional example (sample No., bottom column) in Table 1, BaT
An example is shown in which MnO is added as a reduction inhibitor to a composition consisting of iO3, Ta205, and Sm1O3.
If added, the change over time in the dielectric constant and its rate of change in temperature characteristics increases, making it impractical.

C. Effects of the Invention] By using the composition of the present invention, tAT is applied to the opposing surface.
By forming a magnetic capacitor with poles H,
A dielectric ceramic capacitor with excellent reduction resistance can be obtained. This capacitor not only has a high dielectric constant but also
A ceramic capacitor having a small rate of change in temperature characteristics and a small change over time can be obtained with high multiplicity.

Claims (1)

[Claims] Barium titanate (BaTiO_3) 94.0 to 99.5 mol% Tantalum oxide (Ta_2O_5) 0.2 to 3.0 mol% Samarium oxide (Sm_2O_3) 0.2 to 3.0 mol% Additives (1) cobalt oxide (CoO), zinc oxide (ZnO),
At least one kind of nickel oxide (NiO) from 0.05 to
(2) at least one of silicon oxide (SiO_2) and aluminum oxide (Al_2O_3) at 0.05 to 0.7% by weight;
A dielectric ceramic capacitor characterized in that baked electrodes mainly made of copper (Cu) are formed in a ceramic dielectric composition to which 5% by weight of Cu is added.