JPS6130410B2 - - Google Patents

Description

[Detailed description of the invention]

This invention has features such as high dielectric constant, flat temperature characteristics, excellent withstand voltage characteristics, low dielectric loss, particularly low firing temperature, and less sticking of porcelain pieces to each other during firing. This opens the door to grain boundary insulated semiconductor ceramic capacitors. Conventionally, by forming an insulating layer at the grain boundaries of barium titanate-based semiconductor porcelain, we have increased the apparent permittivity compared to conventional porcelain dielectrics.
It is known that so-called grain boundary insulated semiconductor ceramic capacitors can be obtained. However, although this type of material can obtain a large apparent dielectric constant, it has the drawbacks of a large temperature change rate and a large dielectric loss. A grain boundary insulated semiconducting capacitor based on strontium titanate has been developed to overcome these drawbacks. This semiconductor ceramic capacitor contains strontium titanate or its solid solution, Y,
Semiconductor porcelain is created by adding a small amount of a semiconducting agent such as Nb or W and firing in a neutral or reducing atmosphere.Then, a metal oxide base such as CuO or Bi ₂ O ₃ is applied, and this is heated in air. An insulating layer is formed at the grain boundaries by heat treatment inside the crystal. This semiconductor ceramic capacitor has features such as high dielectric constant, low dielectric loss, small change in apparent dielectric constant with respect to temperature, excellent DC bias characteristics, and low distortion. However, in general, high-purity raw materials are required, and the manufacturing process is complicated, resulting in high costs. There is a desire to reduce the size and cost of ceramic capacitors. In addition, although conventional products using Y, Nb, W, etc. as semiconducting agents can obtain a high dielectric constant, about 30% of the fired porcelains cause sticking between the porcelains during the firing process. This requires a troublesome process in which the fired porcelain must be peeled off, which takes time and is a factor in increasing costs. Furthermore, when oxides such as Y, Nb, and W are used as semiconducting agents, the firing temperature in a neutral or reducing atmosphere is as high as 1,420 to 1,460°C, which can cause deterioration of refractories, heating elements, etc. It was significant. Means for lowering the firing temperature include adding metal powders such as Y, Nb, and W, or adding mineralizers such as Al ₂ O ₃ and SiO ₂ . However, the former method cannot be said to be effective in normal mass production processes. In other words, in the mass production process, it is necessary to burn the binder in air at 500 to 1000℃ before starting the firing process, and in this process, the metals such as Y, Nb, and W mentioned above turn into oxides, and the firing temperature eventually changes. will end up being expensive. The latter method was also not an effective method because Al ₂ O ₃ , SiO _{2 ,} etc. were precipitated at the grain boundaries, resulting in a decrease in the apparent dielectric constant. This invention improves the above-mentioned problems by using praseodymium oxide as a semiconducting agent, but strontium titanate contains praseodymium oxide and copper oxide and is fired at 1430°C in a reducing atmosphere. 1050 later in the atmosphere
It is known that boundary layer type porcelain dielectrics exist which can be obtained by heat treatment at temperatures of .degree. However, this product does not contain praseodymium oxide alone, but coexists with copper oxide, and the firing temperature is as high as 1430℃, and the crystal grain boundaries are not made into insulators by metal oxides such as Cu and Bi. Also the apparent permittivity
36000-37300, which is not a very large value. This invention has solved all of the above-mentioned problems, and its gist is that strontium titanate or strontium titanate with a part of strontium replaced with calcium or barium is 98.6 to 99.93% by weight, and praseodymium oxide is 98.6-99.93% by weight. Bismuth oxide and copper oxide are diffused into the grain boundaries of the semiconductor porcelain consisting of 0.07 to 1.4% by weight to make the grain boundaries an insulator, and electrodes are formed on the surface of the semiconductor porcelain. This is a characteristic feature. Among the compositions described above, strontium titanate includes strontium titanate in which a portion of strontium is replaced with calcium or barium. Strontium titanate substituted in this way is also disclosed in Research and Practical Report Special Issue No. 28, page 221, Table 35, published in 1975, and in this invention, strontium is replaced with 20
Up to mol% of calcium, barium may be substituted. Partial substitution with calcium can improve the breakdown voltage without impairing the characteristics of semiconductor ceramic capacitors made of strontium titanate. In addition, partial substitution with barium makes it possible to obtain a large dielectric constant by changing the Curie point without impairing the characteristics of semiconductor ceramics made of strontium titanate. In addition,
Simultaneous substitution with calcium and barium is also possible within a range of up to 20 mol%. Here, the reason why the amount of substitution is up to 20 mol % is because if it exceeds 20 mol %, the apparent dielectric constant becomes small. Praseodymium oxide contained in semiconductor porcelain promotes the conversion of strontium titanate, which is the main component of the insulator, or strontium titanate, in which a portion of the strontium is replaced with calcium or barium, into a semiconductor. For this praseodymium oxide, oxides, chlorides, metals, etc. may be used as raw materials, and the point is that it can be present as praseodymium oxide in the semiconductor porcelain obtained by firing. Semiconductor porcelain made of strontium titanate containing praseodymium oxide or strontium titanate substituted with calcium or barium has a particle size large enough to obtain a large capacity when fired in a neutral or reducing atmosphere. . In addition, SiO ₂ , GeO ₂ , ZnO,
The properties can be further improved by containing small amounts of CuO and TiO ₂ . A mixture of bismuth oxide and copper oxide is used to make the grain boundaries of semiconductor porcelain into an insulator. These substances that make the grain boundaries of semiconductor ceramics into insulators are added to the surface of semiconductor ceramics and are exposed to air.
When heat treated at 1000 to 1300°C, it diffuses into the semiconductor porcelain and exists as an insulating layer at grain boundaries. Further, although the amount applied to semiconductor ceramics makes the characteristics constant over a fairly wide range, if the amount is outside the appropriate range, the characteristics will be adversely affected, such as dielectric loss worsening. Further, the amount applied varies depending on each metal or its compound. Furthermore, any method such as coating, dipping, spraying, vapor deposition, etc. can be used as a method of application. The reason why the composition of the semiconductor ceramic is limited in this invention is that when praseodymium oxide is less than 0.07% by weight, the apparent dielectric constant becomes small and the dielectric loss becomes bad. Moreover, when praseodymium oxide exceeds 1.4% by weight, the apparent dielectric constant becomes small. Therefore, the amount of strontium titanate or strontium titanate substituted with calcium or barium is also limited to a range of 98.6 to 99.93% by weight. The present invention will be described in detail below with reference to Examples. Example In order to obtain semiconductor porcelain having the composition ratio shown in Table 1, first, main raw materials such as SrTiO ₃ , CaTiO ₃ , BaTiO ₃ and Pr ₂ O ₃ were prepared, and these raw materials were blended and milled in a wet ball mill. After pulverizing for 10 hours, 10% by weight of vinyl acetate resin was added as a binder, and the
Granulated into 50 mesh pieces, 10.0mm in diameter using a hydraulic press.
It was molded into a disc with a wall thickness of 0.5 mm. Next, the molded disk was calcined in the air at 1150℃ for 2 hours to heat the binder, and then heated to 1340 to 1370℃ in a reducing atmosphere consisting of 10% by volume hydrogen and 90% by volume nitrogen.
C. for 2 hours to obtain strontium titanate semiconductor porcelain having a diameter of 8 mm and a wall thickness of 0.4 mm. A paste consisting of 45% by weight of bismuth oxide, 5% by weight of copper oxide and 50% by weight of varnish was applied to the surface of this semiconductor porcelain. The amount applied was approximately 10 mgr. Semiconductor porcelain coated with paste is exposed to air at 1150°C.
Heat treatment was performed at ℃ for 1 hour. This treatment converts the grain boundaries of the semiconductor ceramic into an insulator. Furthermore, silver paste was applied to both surfaces of the semiconductor porcelain and baked at 800°C for 30 minutes to form electrodes and create a semiconductor porcelain capacitor. The apparent dielectric constant, dielectric loss (tanδ) and its standard deviation (σ), insulation resistance (IR), and breakdown voltage (BDV) of the semiconductor ceramic capacitor obtained in this way were measured, and the results were are shown in Table 1. In addition, the apparent permittivity and dielectric loss are +25℃, 1K
This is a value measured under the condition of Hz - 0.3V. Also, those marked with * in the table are outside the scope of this invention, and all others are within the scope of this invention.

[Table] Reference Example Semiconductor ceramics having the composition ratios shown in Table 2 were prepared in the same manner as in the above-mentioned Examples, and the crystal grain boundaries were made into insulators to prepare semiconductor ceramic capacitors. Various characteristics of the semiconductor ceramic capacitor obtained in this way were measured in the same manner as in the above example,
It is also shown in Table 2.

[Table] As is clear from a comparison of Tables 1 and 2, the grain boundary insulated semiconductor ceramic capacitor obtained by containing praseodymium oxide as a semiconducting agent as in the present invention has an apparent permittivity of The BDV is 1.5 times higher than the conventional one, and the apparent permittivity is 1.5 times higher when the BDV is the same, so it is possible to improve the characteristics and reduce the size. It has the effect of making you look like someone. Furthermore, for those within the scope of the invention in the examples, reference examples, and conventional examples in which strontium titanate contains praseodymium oxide and copper oxide at the same time, the rate of change in apparent permittivity with respect to temperature change (-
35°C to +85°C), the results were as shown in Figure 1. Area A in the figure indicates what is within the scope of this invention,
Area B shows a reference example and a conventional example. From the figure, the values within the range of this invention are +10% to -8%, while those of the reference and conventional examples are in the range of +23 to -20%, and those within the range of this invention have excellent temperature characteristics. It can be seen that In FIG. 1, area A shows the temperature change rate of the apparent permittivity of sample numbers 2, 3, and 6 among the samples shown in Table 1. In addition, in region B, the temperature change rate of the apparent dielectric constant is shown for Reference Examples 1, 2, and 3 shown in Table 2, and the conventional example. In addition, with conventional products, the porcelain caused a reaction between each other and exhibited a pecking phenomenon, and the rate reached 30% on average, but with this invention, the rate has been reduced to an extremely small 4% on average, and the porcelain peels off. This has the effect that almost no work is required and workability is greatly improved. Furthermore, grain boundary insulated semiconductor ceramic capacitors obtained by containing praseodymium oxide as a semiconducting agent have small variations in dielectric loss, can be produced in large quantities with stable quality in the mass production process, and can be fired at low temperatures. It has great value in industrial applications.

[Brief explanation of the drawing]

FIG. 1 is a diagram showing the rate of change in the apparent dielectric constant with respect to temperature change.

Claims (1)

[Claims] 1 Strontium titanate or strontium titanate with a part of strontium replaced with calcium or barium is 98.6 to 99.93% by weight,
Bismuth oxide and copper oxide are diffused into the grain boundaries of semiconductor porcelain containing 0.07 to 1.4% by weight of praseodymium oxide, and the grain boundaries are made into an insulator.
A grain boundary insulated semiconductor ceramic capacitor, characterized in that an electrode is formed on the surface of the semiconductor ceramic.