JPS6150371B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention incorporates a mixture of bismuth oxide (Bi ₂ O ₃ ), copper oxide (Cu ₂ O), and boron oxide (B ₂ O ₃ ) mainly at the grain boundaries of semiconductor porcelain mainly composed of strontium titanate (SrTiO ₃ ). The present invention relates to a capacitor material obtained by thermally diffusing a diffusing agent and providing a dielectric layer in the grain boundary region, that is, a composition of grain boundary dielectric layer type porcelain. The composition of the grain boundary dielectric layer type semiconductor porcelain used as a capacitor material consists of the composition of the semiconductor porcelain and the grain boundary diffusing agent for increasing the resistance of the grain boundary region of the semiconductor porcelain and providing a dielectric layer at the grain boundaries. It consists of both a composition and a composition. The selection of these two determines various characteristics of the capacitor. The semiconductor ceramic composition according to the present invention is mainly composed of strontium titanate containing niobium oxide. Conventionally, niobium oxide-containing strontium titanate semiconductor ceramics are already known.
(Japanese Patent Application Laid-open No. 49-129896, JP-A No. 50-8099,
(Japanese Patent Application Laid-Open No. 52-88799). However, the grain boundary diffusing agent for providing a dielectric layer at the grain boundaries of these semiconductor ceramics is Bi ₂ O ₃ in JP-A-49-129896, and Nb ₂ O ₅ and ZnO in JP-A-508099. In JP-A No. 52-88799, the composition consists of Bi ₂ O ₃ and
Only a composition consisting of Cu ₂ O ₃ is disclosed. The grain boundary diffusing agent in the present invention is Bi ₂ O ₃ and Cu ₂ O.
A composition consisting of B ₂ O ₃ or Bi ₂ O ₃ and Cu ₂ O
The composition is characterized by containing at least one component of MnO ₂ and Zi ₂ O in addition to B ₂ O ₃ and B 2 O 3 .
On the other hand, a composition containing Bi ₂ O ₃ and Cu ₂ O as a grain boundary diffusing agent is disclosed in JP-A-54-78494;
The semiconductor ceramic composition used here is strontium titanate containing manganese oxide and niobium oxide, and is different from the semiconductor ceramic composition according to the present invention. In addition, grain boundary diffusing agents include Bi ₂ O ₃ , Cu ₂ O,
A composition consisting of a four-component system of MnO ₂ and Li ₂ O is disclosed in JP-A-52-111698, and a composition consisting of a three-component system of Bi ₂ O ₃ , Cu ₂ O, and MnO ₂ is disclosed in JP-A-52-111698. 52
The semiconductor ceramic composition disclosed in Japanese Patent No. 124200 is strontium titanate containing bismuth oxide and niobium oxide, and is different from the semiconductor ceramic composition according to the present invention. The semiconductor ceramic composition according to the present invention is strontium titanate containing niobium oxide and strontium oxide, strontium titanate containing niobium oxide and titanium oxide, or strontium titanate containing only niobium oxide. The semiconductor ceramic composition according to the present invention has a SrO component.
50.23 to 49.47 mol%, TiO ₂ component is 49.72 to 50.23 mol%, and Nb ₂ O ₅ component is 0.05 to 0.3 mol%. Nb ₂ O ₅ is a component necessary to convert SrTiO ₃ , which _is composed of SrO component and TiO ₂ component, into a semiconductor based on the principle of valence control, and its component amount is 0.05 mol% (approximately If the amount of the component is less than 0.1 mol%), there will be no effect on semiconductor formation;
If it exceeds mol % (approximately 0.6 mol % for SrTiO ₃ ), grain growth of SrTiO ₃ porcelain will be suppressed to less than 10 μm, which is not desirable. As a result of research conducted by the inventors, the desirable crystal grain size of grain boundary dielectric layer type porcelain is on average 10 to 30 μm.
It is. The apparent dielectric constant εa and breakdown voltage (DC) Vb, which are important characteristics of a capacitor, strongly depend on the average particle size of the ceramic. As the particle size increases, ε
_a increases, but Vb decreases. Average particle size 10μ
m, Vb can be obtained as 3500V/mm, but εa is
You can only get 10000. On the other hand, the average particle size is 30μm
Then, ε _a can be obtained as 70000, but Vb can only be obtained as 500V/mm. ε _a required for practical capacitors
is 10,000 or more, and Vb is 500 V/mm, so the average crystal grain size required for semiconductor porcelain is 10 to 30 μm. The molar ratio of the SrO component and the TiO ₂ component influences this average particle size. The SrO/ _TiO2 molar ratio range is 1.005 to 0.990, giving an average particle size of 10 to 30 μm. Even if the SrO/TiO ₂ molar ratio exceeds 1.005 or less than 0.990, the average particle size will be less than 10 μm.
ε _a is less than 10,000, which is undesirable as a capacitor material that requires a high dielectric constant. The molar ratio of SrO/TiO ₂ that gives the largest average particle size is approximately 0.996, and the average particle size at this time is Nb ₂ O ₅
By selecting the amount, it can be suppressed to 30 μm. Next, the composition of the grain boundary diffusing agent in the present invention is 90%
~14.3 mol% _{Bi2O3 component} and 10~85.7 mol%
Based on a three-component mixture consisting of a Cu ₂ O component and 0.5 to 6 mol% B ₂ O ₃ , a part of this mixture is further added with ₂ components of MnO of up to 4 mol% or 20 mol%.
A four-component mixture substituted with any of the following Li ₂ O components, and furthermore, 4 mol % or less of MnO ₂ components and 20
It is characterized by being a five-component mixture substituted with less than mol % of Li ₂ O. As a result of research related to the present invention, as the Bi ₂ O ₃ component increases in the grain boundary diffusion component after thermal diffusion, ε _a increases, but Vb decreases, and the capacitance temperature change rate (85℃ to -25℃) decreases. growing. Conversely, as the Cu ₂ O component increases, the capacitance temperature change rate decreases, Vb increases, but ε _a decreases. The dielectric loss tan δ is the lowest (0.0045) when the respective molar ratios are approximately 65:35 in a binary system of Bi ₂ O ₃ - Cu ₂ O, and the Bi ₂ O ₃ component is larger than this composition ratio. Also, even if the Cu ₂ O component increases, tanδ
increases. When the Bi ₂ O ₃ component exceeds 90 mol%,
This is undesirable because characteristics with Vb of 500 V/mm or higher cannot be obtained. Furthermore, if the Bi ₂ O ₃ component is less than 14.3 mol%, even if semiconductor porcelain with an average grain size of 24 μm is used, ε
_This is not desirable because it is not possible to obtain characteristics with a of 10,000 or more. Further addition of MnO ₂ to this two-component diffusion component has the effect of increasing the value of Vb, but on the other hand, ε _a tends to decrease slightly and tan δ increases. When the amount of MnO _two components exceeds 4 mol%, tanδ
Since properties of 0.01 or less cannot be obtained, the inclusion
It is desirable that the amount of MnO ₂ is 4 moles or less. In addition, Bi ₂ O ₃ ―Cu ₂ O diffused components and Bi ₂ O ₃ ―Cu ₂ O―
Adding B ₂ O ₃ to the MnO ₂ -based diffusion component has the effect of reducing tan δ, but on the other hand tends to reduce Vb. When the B ₂ O ₃ component exceeds 6 mol%, Vb
Since the characteristics of 500V/mm cannot be obtained, the inclusion
It is desirable that the amount of B ₂ O ₃ component is 6 mol % or less. Furthermore, adding Li ₂ O component to the diffusion component of these two-component, three-component, and four-component systems has the effect of increasing ε _a without increasing the capacitance temperature change rate. If the content exceeds 20 mol %, Vb decreases and tan δ increases, and in particular, characteristics with Vb of 500 V/mm or more cannot be obtained, which is undesirable. As described above, the grain boundary dielectric layer type semiconductor ceramic composition according to the present invention has an apparent dielectric constant of 10,000 or more, a breakdown voltage of 500 V/mm, and a breakdown voltage of 500 V/mm, which are required for practical capacitor elements.
It satisfies the characteristics of dielectric loss of 0.01 or less, for example, ε _a is 40,000 to 50,000, Vb is 2,000 to
It provides excellent capacitor characteristics of 1000V/mm, tan δ of 0.002 to 0.005, and capacitance temperature change rate (85 to -25°C) within ±15%. This will be explained below with reference to examples. Example 1 Using commercially available industrial raw materials SrCO ₃ powder (purity 97.5% or more), TiO ₂ powder (anatase type, purity 98.5% or more), and Nb ₂ O ₅ powder (purity 98% or more), The semiconductor ceramic composition was blended to have the composition ratio shown below, wet mixed, dried, pre-fired at a temperature of 1200°C, and ground to a powder with an average size of 2.5 μm. Polyvinyl alcohol aqueous solution was added as a binder and mixed. , sized to 32 mesh passes, and the sized powder is shaped into a disk with a diameter of 15 mm and a thickness of 0.5 mm.
After molding with a pressure of ton/cm ² and heat-treating these molded bodies at 1000°C in air, 90% N ₂
- Sintered at a temperature of 1390℃ for 4 hours in a mixed gas flow of 10% _H2 , with a diameter of approximately 12.5 mm and a thickness of approximately 0.4 mm.
A disk-shaped semiconductor porcelain was obtained. The fractured surfaces of these semiconductor ceramics were polished and etched, and the average particle size was observed and measured. Table 1 shows the results. Note that the average grain size of the sintered body did not change even if the main firing temperature was changed within the range of 1370 to 1410°C.

[Table] *marked is sample for comparison.Resistivity of obtained semiconductor ceramic (In-Ga electrode)
were all in the range of 0.2 to 0.4 Ωcm except for sample 11. However, only sample 11 showed a high specific resistance of 2 Ωcm, and not only was the valence control type semiconductor insufficient, but also the sintered grain size was small at an average of 8 μm. On the other hand, in sample 31 in which the Nb ₂ O ₅ content exceeded 0.30 mol %, grain growth was suppressed and the average grain size was as small as 7 μm. In addition, Samples 12 and 25 had a SrO/TiO ₂ molar ratio of more than 1.005, so the average particle size was also less than 10 μm. In addition, in sample 30, SrO/
The average particle size was less than 10 μm because the TiO ₂ molar ratio was less than 0.990. Samples 11, 12, 25, 30,
All samples other than No. 31 had an average particle size of 10 μm or more. Next, a paste-like diffusing agent was applied to the semiconductor ceramics of Samples 11 to 31, and heat treatment was performed at a temperature of 1190° C. for 2 hours to form a dielectric layer at the grain boundaries.
The composition of the diffusing agent at this time was two components, Bi ₂ O ₃ and Cu ₂ O, and the respective component ratios were 65 mol % and 35 mol % (the difference between Bi ₂ O ₃ and Cu ₂ O used) was 65 mol % and 35 mol %. The raw material powder is a commercially available reagent grade). The coating amount was 1.2 mg per semiconductor ceramic element (250 mg). Furthermore, during thermal diffusion, care was taken to prevent the applied diffusion components Bi ₂ O ₃ and Cu ₂ O from scattering outside the sample due to evaporation, diffusion, etc. Ag electrodes were baked on both sides of the disk-shaped element of the grain boundary dielectric layer type semiconductor porcelain obtained _in this way to form a capacitor element.
(1KHz), and Vb were measured. These results are shown in Table 2. Samples 111, 112, 125, 130, and
All the samples of the present invention other than No. 131 have the following characteristics: ε _a of 10,000 or more, tan δ of 0.01 or less, and Vb of 500 V/mm or more.

[Table] Example 2 Commercially available reagent special grade Bi ₂ O ₃ , Cu ₂ O, MnO ₂ , B ₂ O ₃ ,
and Li ₂ CO ₃ powders were blended to have the composition ratio of the diffusing agent composition shown in Table 3, and dry mixed.
Furthermore, an appropriate amount of turpentine oil, etc. was added to the pine resin and mixed to prepare a paste-like dispersing agent. This paste-like diffusing agent was applied to a semiconductor ceramic element (average particle size: 24 μm) of Sample 22 shown in Table 1 of Example 1. The amount of the diffusing agent applied is 1.2 mg per element (approximately 250 mg) in terms of oxide powder. The semiconductor ceramic element coated with this paste-like diffusing agent was heat-treated at a temperature of 1190° C. for 2 hours. In this thermal diffusion treatment, care was taken to prevent the applied diffusion component from being lost to the outside of the sample due to evaporation, melting, or diffusion to the outside of the sample. Ag electrodes were baked on both sides of the disk-shaped element of the grain boundary dielectric layered semiconductor porcelain obtained in this way to form a capacitor element, and ε _a (1KHz),
tanδ (1KHz), Vb and capacitance temperature change rate (85℃
-25℃) was measured. These results are shown in Table 3. All samples according to the present invention other than comparative samples 201, 211, 256, 262, and 279 have ε _a of 10000 or more and tan
It has the characteristics that δ is 0.01 or less and Vb is 500V/mm or more.

【table】

Claims (1)

[Claims] 1. Strontium oxide (SrO) component is 50.23~
49.47 mol%, titanium oxide (TiO ₂ ) component is 49.72~
50.23 mol%, and niobium oxide (Nb ₂ O ₅ ) component
Bismuth oxide (Bi ₂ O ₃ ) component is 90 to 14.3 mol %, copper oxide (Cu ₂ O) component is 10 to 85.7 mol %, and boron oxide is present in the grain boundaries of semiconductor porcelain with a composition of 0.05 to 0.3 mol %. A grain boundary dielectric layer type ceramic composition, characterized in that it contains a composition consisting of 0.5 to 6 mol % of the (B ₂ O ₃ ) component to form a dielectric layer at the grain boundaries. 2. Claim 1, characterized in that the molar ratio between the strontium oxide (SrO) component and the titanium oxide (TiO ₂ ) component constituting the composition of the semiconductor ceramic is within the range of 1.005 to 0.990. Grain boundary dielectric layer type porcelain composition. 3 Strontium oxide (SrO) component is 50.23~
49.47 mol%, titanium oxide (TiO ₂ ) component is 49.72~
50.23 mol%, and niobium oxide (Nb ₂ O ₅ ) component
At the grain boundaries of semiconductor porcelain with a composition of 0.05 to 0.3 mol%, bismuth oxide (Bi ₂ O ₃ ) component is 90 to 14.3 mol%, copper oxide (Cu ₂ O) component is 10 to 85.7 mol%, boron oxide ( A dielectric layer is formed at the grain boundaries by containing a composition consisting of four components: 0.5 to 6 mol% of B ₂ O ₃ ) component and 4 mol% or less of manganese oxide (MnO ₂ ) component. A grain boundary dielectric layer type ceramic composition characterized by the following. 4. Claim 3, characterized in that the molar ratio between the strontium oxide (SrO) component and the titanium oxide (TiO ₂ ) component constituting the composition of the semiconductor ceramic is within the range of 1.005 to 0.990. The grain boundary dielectric layer type ceramic composition described above. 5 Strontium oxide (SrO) component is 50.23~
49.47 mol%, titanium oxide (TiO ₂ ) component is 49.72~
50.23 mol%, and niobium oxide (Nb ₂ O ₅ ) component
At the grain boundaries of semiconductor porcelain with a composition of 0.05 to 0.3 mol%, bismuth oxide (Bi ₂ O ₃ ) component is 90 to 14.3 mol%, copper oxide (Cu ₂ O) component is 10 to 85.7 mol%, boron oxide ( A dielectric layer is formed at the grain boundaries by containing a four-component composition of 0.5 to 6 mol% of B ₂ O ₃ ) component and 20 mol% or less of lithium oxide (Li ₂ O) component. A grain boundary dielectric layer type ceramic composition characterized by the following. 6. Claim 5, characterized in that the molar ratio between the strontium oxide (SrO) component and the titanium oxide (TiO ₂ ) component constituting the composition of the semiconductor ceramic is within the range of 1.005 to 0.990. The grain boundary dielectric layer type ceramic composition described above. 7 Strontium oxide (SrO) component is 50.23~
49.47 mol%, titanium oxide (TiO ₂ ) component is 49.72~
50.23 mol%, and niobium oxide (Nb ₂ O ₅ ) component
At the grain boundaries of semiconductor porcelain with a composition of 0.05 to 0.3 mol%, bismuth oxide (Bi ₂ O ₃ ) component is 90 to 14.3 mol%, copper oxide (Cu ₂ O) component is 10 to 85.7 mol%, boron oxide ( Contains a composition consisting of five components: 0.5 to 6 mol% of B ₂ O ₃ ) component, 4 mol% or less of manganese oxide (MnO ₂ ) component, and 20 mol% or less of lithium oxide (Li ₂ O) component. A grain boundary dielectric layer type ceramic composition, characterized in that a dielectric layer is formed at the grain boundaries. 8. Claim 7, characterized in that the molar ratio between the strontium oxide (SrO) component and the titanium oxide (TiO ₂ ) component constituting the composition of the semiconductor ceramic is within the range of 1.005 to 0.990. The grain boundary dielectric layer type ceramic composition described above.