JPS623771B2 - - Google Patents

Description

[Detailed description of the invention]

INDUSTRIAL APPLICATION FIELD The present invention relates to a method for producing thick film dielectric powder for obtaining dense film capacitor porcelain with few defects. Conventional configuration and its problems In order to miniaturize the capacitor element and increase its capacity,
Thick-film dielectric ceramics in which dielectric layers and electrode layers are alternately laminated have been put into practical use. Possible methods for obtaining a small-sized, large-capacitance capacitor element include a method of using a dielectric material with a high relative dielectric constant, and a method of reducing the thickness of the dielectric layer. However, a dielectric material having a large dielectric constant at room temperature cannot be put to practical use if there is a large temperature change. On the other hand, the method of reducing the thickness of the dielectric has the problem of lowering the withstand voltage.
It is said that in order to obtain a rated voltage of 50V in a thick film capacitor, a film thickness of 25 to 30 μm is required. In general, thick-film porcelain that has a high withstand voltage has fewer pores and has a uniform and small fired grain size. In order to obtain such porcelain, it is desirable that the raw material powder has a fine particle size and a narrow particle size distribution width. It is difficult to reduce the particle size to 1 μm or less with the raw material powder obtained from the conventional solid-phase reaction, and the particle size distribution width is also large. Dielectric powders that are fine and have a narrow particle size distribution are obtained by hydrolysis of metal alkoxides, and the synthesis of SrTiO ₃ and BaTiO ₃ is known in the literature. SrTiO ₃ has a dielectric constant of about 200, so it is not suitable for small, large-capacity capacitors. BaTiO ₃ has a high dielectric constant of about 1800,
The fine structure of fired porcelain is 20 to 30 μm in some parts.
It is difficult to create a thick film capacitor with a film thickness of 30 μm or less and a high withstand voltage because it tends to have a double structure with abnormally grown particles. Therefore,
In order to obtain excellent thick-film capacitors, a raw material powder that achieves magnetism with a uniform and small fired particle size and a dielectric constant of 1500 or more is required. Purpose of the Invention The present invention provides the following methods:
This provides a method for producing fine powder of dielectric material that satisfies the above conditions, and by using this fine powder as a raw material, the dielectric constant at room temperature is 1500 or more, and the fired particle size is uniform. It can be made less than 1 μm. Therefore, it has become possible to create a small, large-capacity, thick-film porcelain capacitor that has a withstand voltage of 150 V or more even when the film thickness is 10 μm. Structure of the Invention In order to achieve the above object, the method for producing a thick film dielectric powder of the present invention includes a method for obtaining a fine powder of an oxide by hydrolysis of a metal alkoxide.
48.50-49.92 mol% barium dialkoxide,
45.5 to 49.78 mol% of titanium tetraalkoxide and 0.3 to 6 mol% of tantalum pentaalkoxide are dissolved and mixed in isopropyl alcohol of more than 5 times their weight, and the mixed solution is mixed with 40 to 85 mol% of titanium tetraalkoxide.
Water is poured into the solution while stirring and maintained at a temperature of °C.
Isopropyl alcohol mixed solution (weight ratio 1:10
2:1) to form a precipitate of tantalum-doped BaTiO ₃ , the precipitate is separated from the water-alcohol mixed solution, dried, and heat-treated at a temperature of 400 to 1000°C. DESCRIPTION OF EMBODIMENTS Hereinafter, embodiments of the present invention will be described based on the drawings. In order to synthesize a system in which a small amount of Ba1/2 TaO ₃ is dissolved in BaTiO ₃ as a solid solution, a predetermined amount of barium dipropoxide, titanium tetrabutoxide or titanium tetrapropoxide, tantalum pentabutoxide or tantalum pentapropoxide is weighed, and the total weight of
Add 20 times the weight of isopropyl alcohol to 80
Keep at ℃ and stir. After stirring for about 2 hours,
Solid barium dipropoxide is dissolved. After continuing stirring for an additional 4 to 8 hours, a solution of water and isopropyl alcohol mixed at a ratio of 1:1 is added dropwise while maintaining the temperature at 80°C. The amount of solution added dropwise was set so that three times the amount of water required for hydrolyzing all the metal alkoxides was added. When the water-isopropyl alcohol solution is added dropwise, the metal alkoxide solution forms a precipitate and becomes opaque. After dropping the set amount of water-isopropyl alcohol solution, stirring was continued for another 6 hours while maintaining the temperature at 80℃.
Aging is performed so that no unreacted metal alkoxide remains. After aging, the precipitate and solution are separated using a centrifuge or evaporative drying. It was confirmed by X-ray that the precipitate had a perovskite structure. Further, since the particle size of the precipitate particles is several tens of Å and occludes 5 to 10% by weight of alcohol, the heat treatment was performed at 400 to 1000°C. By heat treatment, the precipitate becomes fine particles with a particle size of several hundred to 1,000 angstroms. Next, we will discuss the results of various studies regarding the synthesis conditions for fine powder. When dissolving metal alkoxide in isopropyl alcohol, if the temperature of the solution is stirred at 40℃ or lower, barium dipropoxide will remain undissolved even after 2 hours, so the temperature of the solution will be 40℃ or lower.
It is necessary to heat the product to a higher level. Furthermore, since the boiling point of isopropyl alcohol is 85°C, it is not preferable to raise the temperature above this temperature. If the temperature during hydrolysis is set to 40°C or lower, the precipitate will contain a large amount of amorphous and contain 5 to 10% by weight of water groups, so the temperature during hydrolysis must also be 40 to 85°C. be. If the weight percentage of metal alkoxide in isopropyl alcohol exceeds 20%, it is extremely difficult to dissolve the metal alkoxide, so the concentration of metal alkoxide needs to be below 20% by weight. When the water concentration of the water-isopropyl alcohol solution dropped for the hydrolysis reaction becomes 67% by weight or more, an amorphous substance is formed. Further, if the content is less than 10%, the concentration change of the metal alkoxide cannot be ignored during the progress of the hydrolysis reaction, and the particle size distribution width of the precipitate widens. Therefore, the weight ratio of water to isopropyl alcohol is suitably 2:1 to 1:10. If aging is not performed after the hydrolysis reaction, uniformity of the doped tantalum cannot be obtained.
If the heat treatment temperature of the precipitated and dry powder is below 400°C, occluded alcohols will remain and the porosity will increase when fired. Furthermore, if the temperature exceeds 1000°C, the particle size will grow significantly and the reactivity will decrease, making it unsuitable for the purpose of producing fine particles by hydrolyzing metal alkoxides. The synthesis conditions described above are summarized. The dissolution and hydrolysis reaction of the metal alkoxide is carried out at 40-85°C. The concentration of the isopropyl alcohol solution of water used in the hydrolysis reaction is 10 to 67%, and after dropping a predetermined amount of this solution, it is aged at 40 to 85°C. After drying the precipitate, heat treatment is performed at 400-1000°C. The heat-treated fine powder was granulated by adding a polyvinyl alcohol aqueous solution, press-molded into a disc shape, and then fired at 1300°C for 2 hours. As a result of observing the microstructure of the dielectric ceramic after firing using a scanning electron microscope, it was found that when the amount of tantalum alkoxide is 0.1 mol% or less, it has a double structure containing abnormally sized particles, like BaTiO ₃ without tantalum doping. and
As the amount of tantalum doped increases, the fired grain size becomes smaller, and becomes 1 μm or less at 0.3 mol % or more. Moreover, at 0.15 to 0.25 mol %, the dielectric becomes a semiconductor and cannot be used as a capacitor. Silver electrodes were baked on both sides of the fired disk-shaped sample, and the dielectric constant and its temperature change were measured. These results obtained from various compositions, including comparative examples, are shown in the following table and in Section 1.
As shown in the figure.

[Table] Also, an organic binder such as polyvinyl butyrate or rosin, a dispersant, and an organic solvent are added to the heat-treated fine powder and kneaded to form a paste. This paste and the platinum paste that forms the electrodes are alternately screen printed to form five dielectric layers 1...
was formed and fired at 1300°C for 2 hours to obtain a multilayer capacitor. In the figure, 2 is an internal electrode made of platinum, 3 is an external electrode made of silver, and 4 is an ineffective dielectric layer. The thickness of the dielectric layer 1 after firing is 10 μm. The withstand voltage characteristics of this capacitor are also shown in the table. As is clear from the table and Figure 1, the thick film dielectrics obtained from the compositions of sample numbers 14 to 19 have a dielectric constant of 1500 or more and a withstand voltage of 150 V or more even when the film thickness is 10 μm. It is possible to obtain a thick film capacitor having . Effects of the Invention As described above, the thick film capacitor obtained from the dielectric powder produced by the manufacturing method provided by the present invention has excellent dielectric strength characteristics and dielectric strength compared to those produced by the conventional method. Since the rate is over 1500, it can be made small and large capacity.

[Brief explanation of the drawing]

The drawings show one embodiment of the present invention, and Figure 1 shows the relative dielectric constant and temperature change from -25°C to +85°C when dielectric powder produced by the manufacturing method of the present invention is fired. A graph showing the relationship, FIG. 2, is a cross-sectional view of a thick film multilayer capacitor made using dielectric powder. 1... Dielectric layer, 2... Internal electrode, 3... External electrode.

Claims (1)

[Claims] 1. A method for obtaining a fine powder of an oxide by hydrolysis of a metal alkoxide, comprising 48.50 to 49.92 mol%.
barium dialkoxide, 45.5-49.78 mol%
of titanium tetraalkoxide and 0.3 to 6 mol% of tantalum pentaalkoxide are dissolved and mixed in isopropyl alcohol of more than 5 times their weight, and the mixed solution is maintained at a temperature of 40 to 85 ° C. while stirring. Add a water-isopropyl alcohol mixed solution (weight ratio 1:10 to 2:1) dropwise to
After generating a precipitate of tantalum-doped BaTiO ₃ , the precipitate is separated from the water-alcohol mixed solution.
A method for producing dielectric powder for thick films, which is dried and heat treated at a temperature of 400 to 1000°C. 2. The method for producing a thick film dielectric powder according to claim 1, wherein the barium dialkoxide is barium dipropoxide. 3. The method for producing a dielectric powder for thick films according to claim 1, wherein the titanium tetraalkoxide is titanium tetrapropoxide or titanium tetrabutoxide. 4. The method for producing a dielectric powder for thick films according to claim 1, wherein the tantalum pentaalkoxide is tantalum pentapropoxide or tantalum pentabutoxide.