JPS6159654B2 - - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a method for manufacturing a grain-boundary insulated semiconductor ceramic capacitor element that can easily manufacture a small capacitor with a good temperature change rate of capacitance and low dielectric loss. Grain-boundary insulated semiconductor ceramic capacitors containing strontium titanate (SrTiO ₃ ) as a main component are used in various fields because of their small size, large capacity, and good electrical characteristics. However, conventionally, developed materials have been biased towards high dielectric constant materials, and have been used as capacitors for oscillation circuits, tuning capacitors, high frequency circuits, etc.
When designing small capacitors with a small capacitance of about 1000pF, methods such as making the element smaller and making it thicker than necessary were used, but the dielectric constant was too high and the molding thickness and electrode area were small. Due to such errors, the capacitance value fluctuates greatly, and if a capacitor with small tolerance is designed, there are many disadvantages such as poor yield. In addition, high dielectric constant materials are generally used with temperature characteristics of ±10% to ±15%, but in contrast, materials with a dielectric constant of 5,000 to 35,000 are widely used for the purposes mentioned above. Moreover, capacitor materials were required to have a well-balanced dielectric loss of less than 1% and a temperature change rate of less than ±10%. The present invention was made in view of the current situation, and aims to manufacture small and small capacitors _with high accuracy and yield using strontium titanate (SrTiO ₃ ). A suitable amount of calcium titanate (CaTiO ₃ ) is combined to reduce the rate of temperature change and also change the dielectric constant. In general, SrTiO ₃ +CaTiO ₃ -based compositions are not suitable because it is difficult to convert them into semiconductors by simple methods, and it becomes particularly difficult as the amount of CaTiO ₃ added increases. However, the present invention has such disadvantages.
The main component is SrTiO ₃ +CaTiO ₃ , to which are added bismuth titanate (Bi ₂ O ₃ .2TiO ₃ ) as a subcomponent and neodymium oxide (Nd ₂ O ₃ ) as a semiconducting agent in an appropriate range, and it is also slightly stronger. By performing the firing in a reducing atmosphere, the drawbacks of the SrTiO ₃ +CaTiO ₃ system can be eliminated, thereby providing a semiconductor ceramic capacitor that can achieve the above-mentioned objectives. The semiconductor porcelain body thus obtained is coated with a reoxidizing agent containing lead oxide as a main component and heat-treated in the atmosphere to insulate the grain boundaries. In the present invention, the main components SrTiO ₃ +CaTiO ₃
The blending ratio is SrTiO ₃ 95 to 70 mol%, CaTiO ₃ 5
~30 mol%. When SrTiO ₃ exceeds 95 mol%, dielectric loss and temperature change rate increase;
If it is less than mol%, the dielectric constant becomes low, which is not preferable. In addition, when CaTiO ₃ is less than 5 mol%, the dielectric constant, dielectric loss, and temperature change rate increase;
If it exceeds 30 mol%, dielectric loss and temperature change rate will increase, which is not preferable. Furthermore, the main component
In order to understand the influence of the blending ratio of SrTiO ₃ +CaTiO ₃ on semiconductor ceramic capacitors, 0.5 parts by weight of Nd ₂ O ₃ as a subcomponent was added to 100 parts by weight of the main component,
The drawing shows the electrical characteristics when the molar ratio of SrTiO ₃ and CaTiO ₃ is varied in a composition to which 1.0 part by weight of Bi ₂ O ₃ .2TiO ₂ is added. according to this,
As the molar ratio of SrTiO ₃ decreases, the dielectric constant (ε) decreases, and the rate of change in dielectric constant with _temperature decreases.
It was found that tan δ becomes large when the amount is less than mol% (in Table 1, Experiment Nos. 15, 16, 17, 18, 19,
20, 21, 22). Therefore, the dielectric constant is wide ranging from 5000 to 35000, tan δ1% or less, and the temperature change rate of the dielectric constant is ±10%.
As mentioned above, capacitor materials that can satisfy the condition of well-balanced capacitor materials, such as
It was confirmed that this is limited to the range of 95 to 70 mol % of SrTiO ₃ + 5 to 30 mol % of CaTiO ₃ . In addition, the blending ratio of the subcomponents Nd ₂ O ₃ and _{Bi 2} O ₃ 2TiO ₂ is as follows _:
When Nd ₂ O ₃ is in the range of 0.2 to 1.0 parts by weight and Bi ₂ O ₃ 2TiO ₂ is in the range of 0.5 to 2.0 parts by weight, the conditions for a well-balanced capacitor material can be satisfied. No. 8, 9, 12, 13, 16-21, 24-29).
If Nd ₂ O ₃ is less than 0.2 parts by weight, semiconductor formation will not progress;
Satisfactory characteristics cannot be obtained. On the other hand, if it exceeds 1.0 parts by weight, dielectric loss increases, which is not preferable.
Furthermore, if Bi ₂ O ₃ .2TiO ₂ is less than 0.5 parts by weight, the dielectric loss and temperature change rate will be large, and if it exceeds 2.0 parts by weight, the dielectric loss will be large, which is not preferable. Hereinafter, the present invention will be explained in detail with reference to Examples and Comparative Examples. Example 100 parts by weight of main components consisting of 95-70 mol% SrTiO ₃ and 5-30 mol% CaTiO ₃ , 0.2-1.0 parts by weight of Nd ₂ O ₃ and Bi ₂ O ₃ 2TiO based on 100 parts by weight of main components. ₂ 0.5～
2.0 parts by weight of each of the subcomponents was weighed, pure water was added to a pot mill, and the mixture was mixed by rotation for 6 hours, dried, and passed through a sieve to obtain a finished raw material. In addition, each component was previously prepared, calcined, crushed, and manufactured.
Add an organic binder to the finished raw material and granulate it, pressure mold at approximately 500Kg/ ^cm2 , 4.0mm diameter x 0.4mm
A sample of the same thickness was prepared. This is carried out into the atmosphere using a zirconium pod.
1100℃ for 1 hour, followed by debinding, H ₂ 25%
- Semiconductorized porcelain was obtained by firing at 1380° C. for 2 hours in a reducing atmosphere of 75% N ₂ . A diffusion paste containing lead oxide as the main component and a mixture of bismuth oxide, boron oxide, silicon oxide, etc., was applied to the porcelain body in an amount of 4 to 8% by weight, and heat treated at 1100℃ for 1 hour in the atmosphere. , grain boundaries were diffused and reoxidized, and then silver electrodes were baked by a known method to form a capacitor. Table 1 shows the measurement results of the electrical characteristics of the capacitors thus obtained and the blending ratio of each composition (Experiment Nos. 8, 9, 12, 13, 16-21, 24-29). still,
The dielectric constant and dielectric loss were measured at 20°C, 1kHz, and 1V.AC, and the temperature change rate was based on 20°C. Comparative Example 100 parts by weight of the main component consisting of 100-65 mol% of SrTiO ₃ and 0-35 mol% of CaTiO ₃ , 0-1.5 parts by weight of Nd ₂ O ₃ and 0-1.5 parts by weight of Bi ₂ O ₃ 2TiO based on 100 parts by weight of the main component. ₂₀ to 2.5 parts by weight of each of the subcomponents were weighed, pure water was added to a pot mill, and semiconducting porcelain was prepared in the same manner as in the example, and a capacitor was made in the same manner. Table 1 shows the measurement results of the electrical characteristics of the capacitor thus obtained. Experiments No. 1 to 3 did not use Bi ₂ O ₃ .2TiO ₂ and had large dielectric loss and temperature change rate, and Experiment No. 3 had a low dielectric constant. Experiment Nos. 4 to 7 were in the region where the addition of subcomponents was small, and the semiconductor formation did not progress and satisfactory characteristics were not obtained. Experiment No. 10 had a large amount of Nd ₂ O ₃ and had a large loss. Experiment No. 11 is Bi ₂ O ₃・
With less 2TiO ₂ , both dielectric loss and temperature change rate were large. Experiment No. 14 contained a large amount of Bi ₂ O ₃ 2TiO ₂ and had a large dielectric loss. Experiment No. 15 is CaTiO ₃
was not added, and the dielectric constant was too large.
Experiment No. 22 had a large amount of CaTiO ₃ and the dielectric constant was too low.
In Experiment No. 23, Bi ₂ O ₃ 2TiO ₂ was small, and both the dielectric loss and temperature change rate were large. Experiments No. 30 and 31 are examples in which a large number of both subcomponents were combined, but the dielectric loss was large and the dielectric constant was lower than in other combinations with the same main component. 【table】

[Brief explanation of the drawing]

The drawing is an electrical characteristic diagram when the molar ratio of SrTiO ₃ and CaTiO ₃ is varied when Nd ₂ O _{3 is} 0.5 parts by weight and Bi ₂ O 3 .2TiO ₂ is 1.0 parts by weight.

Claims (1)

[Claims] 1 Strontium titanate ( _SrTiO3 ) 95-70
Mol%, calcium titanate (CaTiO ₃ ) 5-30
After adding 0.2 to 1.0 parts by weight of neodymium oxide (Nd ₂ O ₃ ) and 0.5 to 2.0 parts by weight of bismuth titanate (Bi ₂ O ₃ .2TiO ₂ ) to 100 parts by weight of the main component including mol%,
A method for manufacturing a semiconductor porcelain capacitor element, characterized in that the semiconductor porcelain is produced by firing in a reducing atmosphere, and then the crystal grain boundaries are reoxidized.