GB2247014A - Ceramic dielectric composition for multilayer capacitor - Google Patents

Abstract

A ceramic dielectric composition for multilayer capacitors consists of more than 80% of barium titanate BaTiO3, of high dielectric coefficient, as principal ingredient, and the remaining ingredients are CaSnO3, MnO2, PbTiO3, Bi2Ti2O7, ZnO and B2O3 as sintering assistant materials, so that sintering temperature is lowered and consequently lower temperature sintering is possible. Sintering is carried out at a lower temperature of 1130 DEG C-1140 DEG C while keeping higher dielectric coefficient and therefore Pd/Ag interior electrode containing more than 70% of Ag can be used which is cheaper than conventional Pd/Ag, Au.

Description

CERAMIC DIELECTRIC COMPOSITION FOR MULTILAYER CAPACITOR The present invention relates to a ceramic dielectric composition for multi layer capacitor in which lower temperature sintering is possible, and exhibiting relatively higher dielectric coefficient at vicinity of normal temperature.

Generally, a multilayer ceramic capacitor is structured in such a manner that dielectric substance layers formed by a number of thin plates and interior electrodes located between said dielectric substances are alternately piled, and the ceramic capacitor of such multi layer chip form is widely used relative to capacitors of other forms as the electrostatic capacity per unit volume can be maximized.

As a dielectric oxide material for forming dielectric layer of such a multilayer ceramic capacitor, barium titanate BaTiO3 having higher dielectric coefficient and insulation resistance are much used.

However, since the barium titanate BaTiO3 used for principal ingredient of multilayer ceramic capacitor has a high 0 sintering temperature such as 1300 C, Pd/Ag, Pd/Au or similar expensive metal, that is, precious metals should be used as a metal having high melting point but low in high temperature reactivity for an interior electrode of multilayer ceramic capacitor, and therefore it has problems in manufacturing cost.

Accordingly, as a means for solving the problem of expensive interior electrode, a dielectric composition for ceramic capacitor in which barium titanate is principal ingredient and various sintering assistant materials are added thereto 0 whereby sintering temperature is lowered to about 1100 C, is disclosed in US Patent Numbers 4,283,753; 4,335,216; and 4,530,031. However, these dielectric compositions have a disadvantage that while sintering temperature is lowered by the addition of assistant materials but dielectric coefficient which is most important property in a dielectric substance is reduced.

Therefore, it is an object of the present invention to provide a dielectric composition for multilayer ceramic capacitor in which sintering is possible at lower temperature and yet it exhibits lower dielectric loss with keeping higher dielectric coefficient of barium titanate.

The present invention provides ceramic dielectric composition for multilayer capacitor consisting of 82.603-88.118% of BaTiO3, 7.267-8.715% of CaSnO3, 0.130% of MnO2, 0.500-4.002% of pbTiO3, 0.510-4.260% of Bi2Ti207, 0.976-2.440% of ZnO, and 0.304-0.760% B203 by weight.

According to the dielectric composition of the present invention, since the sintering is carried out at the temperature range of 1130 0C-11400C, use of Pd/Ag interior electrode containing 70% of Ag which is cheaper than Pd and containing 30% of Pd, is possible.

An embodiment of the invention will now be described by way of example and with reference to the accompanying drawings in which: Fig. 1 is an enlarged photograph showing fine tissue of an example of a ceramic dielectric composition according to the present invention, and Fig. 2 is a graph showing a relation between dielectric coefficient and temperature of an example of a ceramic dielectric composition according to the present invention.

The dielectric composition for a multilayer ceramic capacitor of an embodiment of the present invention consists of 82.603-88.118% of BaTiO3, 7.267-8.267% of CaSnO3, 20.130% of MnO2, 0.500-4.002% of PbTiO3, 0.510-4.260% of Bi2Ti207, 0.976-2.440% of ZnO, and 0.304-0.760% of B203 by weight.

Since the dielectric coefficient of ceramic material exhibits a maximum value at Curie temperature, it is desirable to maintain the Curie temperature of ceramic material at about normal temperature, and according to the present invention, compound CaSnO3 is added in order to lower the Curie temperature of barium titanate to normal temperature.

As CaSnO3 is not sensitive to the addition of sintering assistant material, it has the feature that there is little property change with ununiformity of some degree in the manufacturing process.

The Curie temperature of ceramic dielectric composition of the present invention lies between 20-300C by the addition of CaSnO3, and the Curie temperature is moved to lower temperature in response to the quantity of CaSnO3 being increased, and when mole ratio of CaSnO3 and BaTiO3 is 0.1, the Curie temperature is present at normal ambient temperature.

On the other hand, according to an embodiment of the present invention, sintering assistant material of PbTiO3, Bi2Ti207, ZnO, and B203 group is used, and its adding quantity is desirable at 4-10% by weight, and 4700-5300 of dielectric coefficient and less than 2.0% dielectric loss are exhibited.

When the quantity of the sintering assistant material becomes less than 4%, sintering property becomes lowered and consequently dielectric loss becomes increased, and on the contrary, in case when it becomes more than 10%, decrease of dielectric coefficient is caused.

Particularly, the ceramic dielectric composition of the present embodiment belongs to the dielectric composition satisfying Z5U standard because it exhibits the dielectric coefficient of more than 5000 at the temperature range of 10-85 0C while it shows from +10% to -56% of temperature coefficient.

Examples according to the present invention will be described in detail as follows.

Firstly, raw material powder maintaining 1.5 p m of average particle diameter was weighed and pulverized in wet manner for 6 hours in polyethylene jar by using distilled water as distributing medium and thereafter completely dried at 0 electric dryer of 120 C. And next, completely dryed powder was pressed and moulded with one shaft by a pressure of 1500 Kg/cm by using metal mold of lcm in diameter and thereafter sintered at 1100-1140 C. Successively, Ag electrodes were doped on both surfaces of sintered sample and baked whereby ceramic capacitor was manufactured.

Table 1. Ceramic dielectric compositions of examples according to the present invention

o \ material powder Bath03 CaSnO3 Mono2 iO3 Si2Ti207 ZnO B203 Examples Example 1 82.603 7.267 0.13 4.002 2.798 2.440 0.760 Example 2 83.525 7.345 0.13 3.602 2.518 2.196 0.684 Example 3 84.444 7.426 0.13 3.202 2.238 1.962 0.608 Example 4 85.360 7.510 0.13 2.801 1.959 1.708 0.532 Example 5 86.279 7.591 0.13 2.401 1.679 1.464 0.456 Example 6 87.198 7.672 0.13 2.001 1.399 1.220 0.380 Example 7 88.118 7.752 0.13 1.601 1.119 0.976 0.304 Example 8 87.155 8.715 0.13 1.601 1.119 0.976 0.304 Example 9 87.373 8.497 0.13 1.601 1.119 0.976 0.304 Example 10 85.726 8.144 0.13 2.401 1.679 1.464 0.456 Example 11 86.639 8.231 0.13 2.001 1.399 1.220 0.380 Example 12 - 85.360 7.510 0.13 0.500 4.260 1.780 0.532 Example 13 8-.360 7.510 0.13 1.000 3.760 1.780 0.532 Example 14 85.360 7.510 0.13 1.500 3.260 1.780 0.532 Example 15 85.360 7.510 0.13 2.000 2.760 1.780 0.532 Example 16 85.360 7.510 0.13 2.500 2.260 1.780 0.532 Example 17 85.360 7.510 0.13 3.210 1.550 1.780 0.532 Example 18 85.360 7.520 0.13 3.750 1.010 1.780 0.532 Example 19 85.360 7.520 0.13 4.250 0.510 1.780 0.532 Directric properties were measured at l KHz for each example completed with sintering and positive process of composition as above table 1, and resulting values of their dielectric properties (dielectric coefficient, dielectric loss, temperature coefficient, and Curie temperature were shown as below table 2.

Table 2. Dielectric property of examples according to the present invention

Dielectric Dielectric Dielectric Temperature Curie property Coefficient loss coefficient Temperature Examples \ (max) (%, 250C) (%) (Oc) Example 1 5210 1.3 +3, -54 29 Example 2 5250 1.2 +2, -54 28 Example 3 5276 1.2 +3, -55 30 Example 4 5311 1.1 +3, -54 30 Example 5 5195 1.2 +4, -53 31 Example 6 5007 1.1 +3, -53 31 Example 7 4922 1.1 +4, -55 29 Example 8 4800 1.0 +3, -61 32 Example 9 4715 0.9 +2, -60 20 Example 10 4956 1.0 0, -59 - 22 Example 11 4788 1.0 +1, -58 - 25 Example 12 5130 1.1 +3, -60 24 Example 13 5149 1.2 +1, -60 20 Example 14 5178 1.1 +1, -65 23

Example 15 5220 1.1 +3, -57 26 Example 16 5297 1.2 +4, -58 30 Example 17 5306 1.1 +4, -54 30 Example 18 5280 1.2 +4, -54 32 Example 19 5157 1.2 +4, -50 35 On the other hand, Fig. 1 is an enlarged photograph of fine tissue for example 4 according to the present invention which is sintered for 3 hours at 11300C, and it can be seen that particle sizes are uniform, and it can be understood that composition of example 4 satisfies Z5U standard from the graph showing temperature characteristic of dielectric coefficient of Fig. 2.

Thus, the present invention relates to a composition of ceramic dielectric for multilayer capacitor, in which BaTiO3 of high dielectric coefficient is a principal ingredient and to which CaSn03, Mn02, PbTiO3, BiTi207, ZnO and B203 are added as sintering assistant materials whereby siterin temperature is lowered so that not only lower temperature sintering is possible, but also Z5U standard is satisfied.

Claims (4)

CLAIMS:

1. Ceramic dielectric composition for multilayer capacitor consisting of 82.603-88.118% of BaTiO3, 7.267-8.715% of CaSnO3, 0.130% of Mono2, 0.500-4.002% of PbTiO3, 0.510-4.260% of Bi2Ti207, 0.976-2.440% of ZnO, and 0.304-0.760% B203 by weight.

2. A method of sintering a ceramic dielectric composition for use in a multilayer capacitor, said method comprising sintering a composition according to claim 1 in a temperature range of 11300 to 1140ore

3. A ceramic dielectric composition substantially as hereinbefore described.

4. A multilayer capacitor having dielectric layers of a composition according to claim 1 or claim 3.