JPH0468258B2 - - Google Patents

Description

[Detailed description of the invention]

(Industrial Application Field) The present invention relates to a dielectric ceramic composition containing barium titanate as a main component, and more particularly to a ferroelectric composition suitable for use in a capacitor. (Prior art) Conventionally, ferroelectric ceramic compositions containing barium titanate as a main component have an extremely high sintering temperature of 1300°C or higher, so when used for multilayer capacitors, high-temperature sintering is required as an internal electrode material. High-melting-point noble metals that can withstand high temperatures, such as platinum, palladium, and gold, have been used, but these noble metals are expensive, resulting in high costs for multilayer capacitors. Furthermore, since sintering is carried out at high temperatures, the design of the sintering furnace, the energy required for sintering, etc. also become problems. In other words, when manufacturing a multilayer capacitor, it is preferable to use inexpensive silver as the main component for the internal electrode material from a cost perspective, and also to facilitate the design of the furnace, it is preferable to use ferroelectric materials that can be sintered at low temperatures. There was a strong desire for a ceramic composition. Copper oxide [Trans.Brit.Ceram.
Soc., 74, 165 (1975)], lithium fluoride [J.Am.
Ceram.Soc., 66, 11, 801 (1983), Japanese Patent Application Publication No. 1987-
160963], but when dielectric ceramics are made using these sintering aids, the grain size is large and non-uniform, and in some cases, abnormal grain growth reaching several tens of micrometers may occur. It can happen. As a method to improve this drawback, Japanese Patent Application Laid-Open No. 61-251561 discloses that by adding 0.2 to 5.5 mol% of copper oxide, zinc oxide, and/or cadmium oxide,
It is disclosed that at the following sintering temperature, a sintered body having approximately the theoretical density can be obtained and its microstructure can be controlled. However, the dielectric porcelain obtained by this method can be sintered at temperatures below 1200°C, has finely uniform grains, and has relatively good electrical properties (e.g. dielectric constant, insulation resistance, dielectric loss), but has poor reliability. Some problems remained. To address this problem, it is known that adding a rare earth oxide to barium titanate improves reliability. J.Am.Ceram.Soc., 46, 5, 197
(1963) reported that adding 0.5 mol% lanthanum oxide to barium titanate improved the reliability of multilayer capacitors sintered at 1375-1500°C. In this method, the sintering temperature is high;
The grain size tends to be non-uniform, and the electrical properties are unstable in practical use. (Problem to be Solved by the Invention) Therefore, with the prior art, there has been no dielectric ceramic composition that can be sintered at a temperature of 1200°C or lower, has microuniform grains, has good electrical properties, and at the same time satisfies reliability. Not found. (Means for Solving the Problems) As a result of extensive studies, the present inventors found that when copper oxide, zinc oxide, and a specific amount of manganese oxide were added to barium titanate, the temperature We have discovered that at the sintering temperature, a sintered body with a fine microstructure and uniform grains, which is denser than 95% of the theoretical density, can be obtained, and at the same time, the reliability is dramatically improved. Reached. That is, the present invention uses 86.8 to 86.8 as the first component.
99.59 mol% barium titanate, 0.2-5.5 mol% zinc oxide as the second component, as the third component
0.01-0.7mol% manganese oxide as the fourth component
The present invention relates to a dielectric ceramic composition comprising 0.2 to 7 mol% copper oxide. A dielectric ceramic composition made by adding specific amounts of zinc oxide, manganese oxide, and copper oxide to barium titanate and firing it has a
The temperature dependence of the dielectric constant is small, the grain size is small and uniform, and the reliability is extremely high. Furthermore, by combining a specific amount of one or more selected from specific titanate, zirconate, and stannate as the fifth component, the dielectric constant near room temperature can be increased to over 9000 without impairing the above properties. It is possible to increase The barium titanate used in the present invention may be produced by either a solid phase method or a liquid phase method (for example, an oxalate method, an alkoxide method, etc.). When using particles with a small average particle size of 1 μm or less and a uniform particle size distribution, highly reliable porcelain with a more uniform microstructure and good electrical properties can be obtained. In the present invention, zinc oxide, manganese oxide, and copper oxide can be used as they are as additives, but
Inorganic acid salts such as hydroxides and carbonates, and organic salts such as oxalates and alkoxides, which decompose into oxides at or below the sintering temperature, can be used. As the copper oxide, any one of monovalent, divalent, and coexisting monovalent and divalent oxides can be used. Manganese oxide includes divalent, trivalent,
Any of tetravalent, heptavalent and their coexistence can be used. In addition, the oxides added as the fifth component in the present invention include barium stannate, calcium stannate, strontium stannate, lead stannate, strontium titanate, barium zirconate, calcium zirconate, strontium zirconate, and lead zirconate. A compound in the form of a normal composite oxide is preferably used. The proportion of barium titanate in the porcelain composition of the present invention ranges from 86.8 to 99.59 mol%. When the proportion is more than 99.59 mol%, sintering becomes difficult at temperatures below 1200°C, and when it is less than 86.8 mol%, significant deformation of the base material occurs during sintering. The preferable range for good sintering properties and hardly causing any deformation of the base material is 93.5 to 98.75 mol%. The proportion of zinc oxide is from 0.2 to 0.2 in the form of ZnO
It is in the range of 5.5 mol%. If it exceeds 5.5mol%,
It is difficult to sinter at temperatures below 1200℃, resulting in non-uniform grains and a decrease in insulation resistance. If it is less than 0.2 mol %, almost no effect of addition is observed, and dielectric loss also increases. The most preferable range that provides good sinterability and sufficiently high insulation resistance is 0.6 to 3 mol%. The proportion of manganese oxide is 0.01 in the form of Mn203
It is in the range of ~0.7 mol%. If it is more than 0.7 mol%, sintering at temperatures below 1200°C is difficult, and when manufacturing a multilayer capacitor, delamination between internal electrodes and dielectric layers is significant. Also,
When the amount is 0.01 mol% or less, almost no effect of addition is observed and reliability is low. The most preferable range in which delamination does not occur and reliability is sufficiently good is in the range of 0.05 to 0.5 mol %. The proportion of copper oxide ranges from 0.2 to 7 mol% as CuO. If it is more than 7 mol %, delamination will be significant and the dielectric loss value will also be large. Further, the grain size during sintering becomes non-uniform and large, and reliability is also extremely deteriorated. If it is less than 0.2 mol%, low temperature sintering becomes difficult. The most preferred range that does not cause delamination and provides sufficiently high reliability is 0.6 to 3 mol%. Further, in a preferred embodiment, one selected from barium stannate, calcium stannate, strontium stannate, lead stannate, strontium titanate, barium zirconate, calcium zirconate, strontium zirconate, lead zirconate. 2 or more complex oxides per 100 moles of the total of the first component, second component, third component, and fourth component.
By adding ~20 mol, it is possible to increase the dielectric constant near room temperature to 9000 or more. If the amount is less than 2 moles, the effect of addition is not so significant and the dielectric constant near room temperature is low. Moreover, if it is more than 20 mol, sintering at 1200°C or less becomes difficult. When barium stannate, calcium stannate, or a mixture thereof is used, a material with a large dielectric constant can be easily obtained. (Example) Hereinafter, the present invention will be explained in detail with reference to Examples. Example 1 Barium titanate, zinc oxide, manganese oxide, and copper oxide were weighed in the proportions shown in Table 1, pure water was added, and they were mixed in a wet ball mill (in Table 1, sample numbers 1, 4, 5, 6, 7 is a comparative example). After thoroughly drying and crushing the mixture, a paste was prepared using an acrylic resin as a binder, trichloroethane as a solvent, and zirconia as a ball medium. From the resulting paste, a green sheet with a thickness of 28 μm was created using a doctor blade method, and a multilayer capacitor with 5 effective layers was prototyped using a screen printing method. After removing the binder from this chip,
Sintering was performed 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 measured using an LCR meter.
Measured under the conditions of 1KHz, 1V, and 20℃. Insulation resistance was measured using a high insulation resistance tester and was measured by applying a voltage of 50V for 1 minute. Further, the grain size was determined by polishing the cross section of the multilayer capacitor, etching it with 1:1 hydrochloric acid, taking a scanning electron micrograph, and using the line intercept method. A high-temperature load test was conducted to evaluate reliability, and the lifespan was 125℃ and 200VDC.
It is expressed as the time required to reach a failure rate of 63% under load conditions. The measurement results are shown in Table 2. Sample numbers 1, 4, 5, 6, and 7 are comparative examples, and sample numbers 2 and 3 are inventive samples, but as is clear from Table 2, the reliability is significantly improved by adding manganese oxide. I understand that.

【table】

【table】

[Table] Example 2 As the fifth component, barium stannate and calcium stannate were weighed in the proportions shown in Table 3 (in Table 3, sample numbers 1, 6, and 8 are comparative examples), and the same method as in Example 1 was carried out. I prototyped a multilayer capacitor. Table 4 shows the measurement results.
Shown below. Sample numbers 1, 6, and 8 are comparative examples; sample numbers 2 and 8 are comparative examples;
No. 3, 4, 5, 7, and 9 are according to the present invention, but as is clear from Table 4, by adding barium stannate and calcium stannate, it is possible to increase the capacity at 20 ° C. It can be seen that a multilayer capacitor with a small grain size and high reliability can be obtained at the same time.

【table】

【table】

[Table] In the above examples, barium titanate is
The molar ratio of Ba and Ti was approximately 1, but
Even if the ratio deviates by about 0.05 mole, good characteristics can be obtained. (Effects of the Invention) From the above, the ferroelectric ceramic composition of the present invention can be sintered at a temperature of 1200°C or lower, has uniform and fine grain size, and has low dielectric loss, insulation resistance, etc. It also has good electrical properties and extremely high reliability. Furthermore, the dielectric constant at room temperature can be increased to 9000 or more without impairing these properties, making it extremely useful as a dielectric composition for multilayer ceramic capacitors, and having great industrial value.

Claims (1)

[Claims] 1 86.8 to 99.59 mol% barium titanate as the first component, 0.2 to 5.5 mol% zinc oxide as the second component, 0.01 to 0.7 mol% manganese oxide as the third component, and fourth component A dielectric ceramic composition consisting of 0.2-7 mol% copper oxide. 2 The first component is 93.5 to 98.75 mol%, the second component is
2. The dielectric ceramic composition according to claim 1, wherein the third component is 0.05 to 0.5 mol%, and the fourth component is 0.6 to 3 mol%. 3. Dielectric ceramic composition according to claim 1
For 100mol, barium stannate, calcium stannate, strontium stannate,
1 selected from lead stannate, strontium titanate, barium zirconate, calcium zirconate, strontium zirconate, lead zirconate
A dielectric ceramic composition containing 2 to 20 mol of a species or more.