JP2583091B2 - Dielectric ceramic composition - Google Patents

Description

Description: TECHNICAL FIELD The present invention relates to a dielectric ceramic composition containing barium titanate as a main component.
The present invention relates to a ferroelectric composition suitable for use in a capacitor.

(Prior art) Conventionally, ferroelectric ceramic compositions containing barium titanate as a main component have a very high sintering temperature of 1300 ° C. or higher. High melting point noble metal that can withstand sintering temperature,
For example, platinum, palladium, gold and the like have been used. Since these noble metals are expensive, the cost of the multilayer capacitor is also high. In addition, since sintering is performed at a high temperature, the design of a sintering furnace, the energy required for sintering, and the like also pose problems. That is, in the case of manufacturing a multilayer capacitor, it is preferable to use inexpensive silver as a main component as an internal electrode material from the viewpoint of cost, and also that sintering can be performed at a low temperature because the furnace design is easy. Ferroelectric ceramic compositions have been strongly desired.

Copper oxide (Trans.Brit. Ceram. Soc., 74, 165) as a sintering aid for lowering the sintering temperature of barium titanate.
(1975)], lithium fluoride [J. Am. Ceram. Soc., 66, 11,
801 (1983), JP-A-57-160963] and the like. However, when dielectric porcelain is prepared using these sintering aids, the grain size is large and non-uniform. As a result, abnormal grain growth reaching several tens of μm may occur. As a method for remedying this drawback, JP-A-61-251561 discloses that copper oxide, zinc oxide and / or cadmium oxide are used in an amount of 0.2 to 0.2%.
It is disclosed that by adding 5.5 mol%, a sintered body having a substantially theoretical density can be obtained at a sintering temperature of 1200 ° C. or lower, and the microstructure thereof can be controlled. However, the dielectric porcelain obtained by this method can be sintered at 1200 ° C or lower, has a fine and uniform grain, and has relatively good electrical characteristics (for example, permittivity, insulation resistance, and dielectric loss). Had some problems.

It is known that the reliability is improved by adding a rare earth oxide to barium titanate. J.
Am. Ceram., 46, 5, 197 (1963) states that barium titanate
It is reported that the reliability of a multilayer capacitor sintered at 1375 to 1500 ° C. by adding 0.5 mol% of lanthanum oxide is improved. In this method, since the sintering temperature is high, the grain size tends to be non-uniform, and the electrical characteristics are unstable in practical use.

(Problems to be Solved by the Invention) Therefore, in the prior art, a dielectric ceramic composition which can be sintered at a temperature of 1200 ° C. or less, has a uniform grain, has good electric characteristics and satisfies reliability at the same time has been found. Not.

(Means for Solving the Problems) As a result of intensive studies, the present inventors have selected barium titanate from copper oxide, zinc oxide, rare earth oxide, iron oxide, cobalt oxide, and nickel oxide. At a sintering temperature of 1200 ° C or less,
It has been found that a sintered body having a uniform microstructure and densified to 95% or more of the theoretical density can be obtained, and at the same time, reliability has been dramatically improved, and the present invention has been achieved.

That is, the present invention provides, as the first component, 85.6 to 99.49 mol.
% Barium titanate, 0.2-5.5 mol% as the second component
Zinc oxide, as a third component 0.01-0.7 mol% of iron oxide,
The present invention relates to a dielectric ceramic composition comprising at least one selected from cobalt oxide and nickel oxide, 0.1 to 1.2 mol% of a rare earth oxide as a fourth component, and 0.2 to 7 mol% of copper oxide as a fifth component. is there.

A dielectric ceramic composition obtained by adding a specific amount of zinc oxide, rare earth oxide, copper oxide, and at least one selected from iron oxide, cobalt oxide, and nickel oxide to barium titanate, followed by firing, has a rare earth oxide Compared with the case of addition, the dielectric constant is high, the grain size is uniform, and the reliability is extremely high.

Further, by combining at least one specific amount selected from titanates, zirconates, and stannates as the sixth component, the dielectric constant near room temperature can be increased to 12000 or more without deteriorating the above characteristics. It is possible.

The barium titanate used in the present invention may be produced by any method such as a solid phase method and a liquid phase method (for example, oxalate method, alkoxide method). When an average particle size as small as 1 μm or less and having a uniform particle size distribution is used, a highly reliable porcelain having a more uniform microstructure and good electric characteristics can be obtained.

In the present invention, as additives zinc oxide, rare earth oxide,
Copper oxide, iron oxide, cobalt oxide and nickel oxide can be used as they are, but inorganic acid salts such as hydroxides and carbonates, organic acids such as oxalates and alkoxides, etc. Any substance can be used as long as it decomposes to form an oxide. Monovalent, divalent, as copper oxide
Any of monovalent and divalent coexisting materials can be used. As manganese oxide, any of divalent, trivalent, tetravalent, and heptavalent and those coexisting therewith can be used. As the rare earth oxide, any of neodymium oxide, samarium oxide, gadolinium oxide, dysprosium oxide, holmium oxide, erbium oxide, thulium oxide and the like can be used.

The oxide added as the sixth component in the present invention is preferably in the form of an ordinary composite oxide of stannate, titanate and zirconate.

The proportion of barium titanate in the porcelain composition of the present invention,
It is in the range of 85.6 to 99.49 mol%. The ratio is 99.49mol%
If it is larger, sintering becomes difficult at temperatures below 1200 ° C,
If the amount is less than 5.6 mol%, significant deformation of the substrate occurs during sintering. A preferable range in which sinterability is good and deformation of the substrate hardly occurs is 92.8 to 98.45 mol%.

The proportion of zinc oxide is in the range from 0.2 to 5.5 mol% in the form of ZnO. If it exceeds 5.5 mol%, sintering at 1200 ° C. or less is difficult, resulting in non-uniform grain and lower insulation resistance. If it is less than 0.2 mol%, the effect of addition is hardly recognized, and the dielectric loss increases. The most preferable range which provides good sinterability and sufficiently high insulation resistance is 0.6 to 3 mol%.
Range.

The ratio of iron oxide, cobalt oxide, and nickel oxide is in the range of 0.01 to 0.7 mol% as Fe203, Co304, and Ni203, respectively. If it is more than 0.7 mol%, sintering at 1200 ° C or less is difficult.
The delamination between the internal electrode and the dielectric layer is remarkable.
In addition, when the content is 0.01 mol% or less, the effect of addition is hardly recognized, and the reliability is low. The most preferable range in which delamination does not occur and the reliability is sufficiently good is 0.05
0.50.5 mol%.

The ratio of the rare earth oxide is Me203 (Me = La, Nd, Sm, G
d, Dy, Ho, Er, Tm, etc.) in the range of 0.1 to 1.2 mol%. The reliability increases as the amount added increases,
If it exceeds 1.2 mol%, the microstructure tends to be non-uniform, and abnormal grain growth is also observed. If it further increases, sintering at 1200 ° C. or lower becomes difficult. If it is less than 0.1 mol%, the effect of addition is hardly recognized and the reliability is low. The most preferable range in which high reliability can be obtained without impairing the sinterability is 0.3 to 0.7 mol%.
It is.

The proportion of copper oxide is in the range of 0.2 to 7 mol% as CuO. When it is more than 7 mol%, delamination is remarkable, and the value of dielectric loss becomes large. In addition, the grain size during sintering becomes uneven and large, and the reliability is extremely deteriorated. If it is less than 0.2 mol%, low-temperature sintering becomes difficult. The most preferable range where delamination does not occur and which provides sufficiently high reliability is 0.6 to 3 mol%.

Further, in a preferred embodiment, one or more complex oxides selected from stannate, titanate, and zirconate are combined with the first component, the second component, the third component, and the fourth component. Ten
By adding 2 to 20 mol per 0 mol, the dielectric constant near room temperature can be increased to 12000 or more. If the amount is less than 2 mol, the effect of addition is not so remarkable,
The dielectric constant near room temperature is also low. Also, if it exceeds 20 moles, 12
Sintering at or below 00 ° C. becomes difficult. When using barium stannate or calcium stannate or a mixture thereof,
A material having a large dielectric constant is easily obtained.

(Examples) Hereinafter, the present invention will be described in detail with reference to examples.

Example 1 Barium titanate, zinc oxide, copper oxide, and iron oxide, cobalt oxide, nickel oxide and neodymium oxide, samarium oxide, dysprosium oxide, holmium oxide,
Erbium oxide and thulium oxide were weighed at the ratios shown in Table 1, pure water was added, and mixed by a wet ball mill. After the mixture was sufficiently dried and crushed, a paste was prepared using zirconia as a ball medium and trichloroethane as a solvent using an acrylic resin as a binder. A green sheet having a thickness of 28 μm was prepared from the obtained paste by a doctor blade method, and a multilayer capacitor having five effective layers was prototyped by a screen printing method. As an internal electrode
Ag / Pd = 70/30 material was used. After debinding the chip, the chip was sintered at 1100 ° C. for 3 hours. The obtained multilayer capacitor has a dielectric layer thickness of 18 μm and an effective internal electrode area of 0.009 cm ² . Next, a silver electrode was baked as an external electrode, and the electrical characteristics were measured. Dielectric constant and dielectric loss are LCR
The measurement was performed using a meter under the conditions of 1 KHz, 1 V, and 20 ° C. For insulation resistance, use a high insulation resistance meter and apply 50V voltage 1
The value was shown in minutes. The grain size was determined by polishing the cross section of the multilayer capacitor, performing an etching treatment with 1: 1 hydrochloric acid, photographing a scanning electron microscope photograph, and determining the grain size by a line intercept method. A high-temperature load test was performed as an evaluation of reliability, and the life was expressed as the time to reach a failure rate of 63% under the conditions of 125 ° C and 200 VDC load. Table 2 shows the measurement results.

In Table 2, sample numbers 9, 10, and 11 are comparative examples in which the third component, the fourth component, or both were not added. In this case, although the electrical characteristics of the capacitor do not deteriorate, the high temperature load life is as short as 106, 121, and 23 hours.

On the other hand, when any one of iron oxide, cobalt oxide, and nickel oxide is added as the third component and neodymium oxide, samarium oxide, dysprosium oxide, holmium oxide, erbium oxide, and thulium oxide are added as the fourth component, It can be seen that high-temperature load characteristics are significantly improved without lowering electrical characteristics such as dielectric loss and insulation resistance.

Example 2 As an additive for shifting the Curie point, barium stannate and calcium stannate were used in Table 3 with respect to 100 mol of the sum of the first, second, third, fourth and fifth components. Was weighed so as to have the ratio shown in Table 2, and added as the sixth component. A multilayer capacitor was prototyped in the same manner as in Example 1, and the electrical properties were measured. Table 4 shows the results.

In Table 3, Sample Nos. 2 and 6 are Comparative Examples in which the amount of the third component added is different from that of the present invention. As can be seen from Table 4, the sintered body density is low and the electrical characteristics cannot be measured. Sample Nos. 1, 3, 4, and 5 are of the present invention and include barium stannate,
It is possible to increase the capacity at 20 ° C. by adding calcium stannate. Similar effects can be obtained by using strontium stannate, lead stannate, strontium titanate, barium zirconate, calcium zirconate, strontium zirconate, lead zirconate, or the like as a shifter to be added. The element body has a uniform microstructure with a grain size of about 4 μm, and no deterioration in electrical characteristics such as dielectric loss and insulation resistance is observed. It can be seen that a long life under a high temperature load condition and a highly reliable multilayer capacitor can be obtained.

In the above embodiments, barium titanate having a molar ratio of Ba to Ti of approximately 1 was used, but good characteristics can be obtained even if the ratio is shifted by about 0.05 mol.

(Effects of the Invention) As described above, the ferroelectric ceramic composition of the present invention can be sintered at a temperature of 1200 ° C. or less, has a uniform grain size, and has electrical properties such as dielectric loss and insulation resistance. It is good and has extremely high reliability. Furthermore, without impairing these properties, the dielectric constant near room temperature can be increased to 12000 or more, which is extremely useful as a dielectric composition for a multilayer ceramic capacitor,
Its industrial value is great.

Claims (6)

(57) [Claims] 1. A first component comprising 85.6 to 99.49 mol% of barium titanate, a second component comprising 0.2 to 5.5 mol% of zinc oxide, and a third component comprising 0.01 to 0.7 mol% of iron oxide, cobalt oxide and nickel oxide. A dielectric ceramic composition comprising 0.1 to 1.2 mol% of a rare earth oxide as a fourth component and 0.2 to 7 mol% of a copper oxide as a fifth component. 2. The composition according to claim 1, wherein the first component is 92.8 to 98.45 mol%, and the second component is
0.6-3mol%, the third component is 0.05-0.5mol%, the fourth component is
3. The composition according to claim 1, wherein the third component is 0.3 to 0.7 mol%, and the fifth component is 0.6 to 3 mol%.
The dielectric ceramic composition as described in the above. 3. The dielectric ceramic composition according to claim 1, wherein the third component is cobalt oxide. 4. The dielectric ceramic composition according to claim 1, wherein the fourth component is at least one selected from samarium oxide, dysprosium oxide, holmium oxide, and erbium oxide. 5. The dielectric ceramic composition according to claim 1,
For 0 mol, as the sixth component, stannate, titanate,
A dielectric ceramic composition containing 2 to 20 mol of at least one selected from zirconates. 6. The dielectric ceramic composition according to claim 5, wherein the sixth component is barium stannate and / or calcium stannate.