JPS637013B2 - - Google Patents

Description

[Detailed description of the invention]

The present invention uses strontium titanate (SrTiO ₃ )
A dielectric layer is provided in the grain boundary region by thermally diffusing a diffusing agent mainly composed of bismuth oxide (Bi ₂ O ₃ ) and copper oxide (Cu ₂ O) into the grain boundaries of semiconductor ceramics mainly composed of The present invention relates to a capacitor material, that is, a grain boundary dielectric layer type semiconductor ceramic composition obtained by the method. The composition of the grain boundary dielectric layer type semiconductor porcelain as a capacitor material consists of a composition of the semiconductor porcelain and a grain boundary diffusion material for increasing the resistance of the grain boundary region of the semiconductor porcelain and providing a dielectric layer at the grain boundaries. The composition consists of both. 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. BACKGROUND ART Niobium oxide-containing strontium titanate semiconductor porcelain is already known. (Unexamined Japanese Patent Publication No. 129896/1973, No. 8099/1973)
However, the grain boundary diffusing agent for providing a dielectric layer at the grain boundaries of these semiconductor ceramics is Bi 2 O 3 as an example in JP-A No. 49-129896, and Bi ₂ O ₃ as an example in JP-A No. 50-8099.
The issue only discloses a composition consisting of Nb ₂ O ₃ and ZnO. The grain boundary diffusing agent according to the present invention is characterized in that it is a composition containing at least Bi ₂ O ₃ and Cu ₂ O, especially the above-mentioned Bi ₂ O ₃ and Cu ₂ O.
Compositions containing MnO ₂ and B ₂ O ₃ in addition to the above
In addition to Bi ₂ O ₃ , Cu ₂ O, MnO ₂ and B ₂ O ₃
A preferred example is a composition containing Li ₂ O.
On the other hand, compositions containing Bi ₂ O ₃ and Cu ₂ O as grain boundary diffusing agents are disclosed in JP-A-54-78494 and JP-A-52-88799; The semiconductor ceramic composition described is strontium titanate containing manganese oxide and niobium oxide, and is different from the semiconductor ceramic composition according to the present invention. Furthermore, the semiconductor ceramic composition described in JP-A-52-88799 is strontium titanate containing only niobium oxide, which is different from the semiconductor ceramic composition according to the present invention, and has a lower apparent dielectric constant. The dielectric breakdown voltage is low and its variation is large. Furthermore, the grain boundary diffusing agent is Bi ₂ O ₃ ,
A composition consisting of a four-component system of Cu ₂ O, MnO ₂ and Li ₂ O is disclosed in JP-A-52-111698;
The semiconductor ceramic composition used here is strontium titanate containing bismuth oxide and niobium oxide, which is also different from the semiconductor ceramic composition according to the present invention. The semiconductor ceramic composition according to the present invention includes silicon oxide,
selected from the group consisting of aluminum oxide, barium oxide, calcium oxide, lead oxide, magnesium oxide, tin oxide, zirconium oxide, chromium oxide, iron oxide, cobalt oxide, nickel oxide, copper oxide, silver oxide, sodium oxide, potassium oxide It is strontium titanate containing at least one component and a niobium oxide component. The composition according to the first invention has a SrO component of 52.32 to 40.27 mol%,
TiO ₂ component is 47.63-50.23 mol%, Nb ₂ O ₅ component is
0.05-0.5 mol%, furthermore, 1.00 mol% or less _SiO2
Ingredients, 0.40 mol% or less Al ₂ O ₃ components, total amount 5.00
Each component of BaO, CaO, PbO is 1.00 mol% or less, MgO component is 1.00 mol% or less, and the total amount is 1.00 mol% or less.
The total amount of each component of SnO ₂ and ZrO ₂ is 0.50 mol% or less
At least one of the following components: Cr ₂ O ₃ , Fe ₂ O ₃ , CoO, NiO, Cu ₂ O, Ag _{2 O, Na 2 O} , K ₂ O in a total amount of 0.10 mol% or less Consisting of ingredients. In addition, the composition according to the second invention has a SrO component of 51.02 to 42.87 mol% and a TiO ₂ component of 48.93 to 48.93 mol%.
50.23 mol%, Nb ₂ O ₅ component is 0.05-0.50 mol%,
_SiO2 component is 0.10-1.00 mol% or less, _Al2O3 is _0.02
~0.40 mol% or less, and 3 of BaO, CaO, and PbO
The total amount of at least one selected from among the components is 0.05 to 0.50 mol % or less. The Nb ₂ O ₅ component is a component necessary to convert SrTiO ₃ or its solid solution, which is composed of an SrO component and a TiO ₂ component, into a semiconductor based on the principle of valence control, and its amount is 0.05 mol% (SrTiO For _tri- based solid solutions, there is no effect on semiconductor formation when the amount of the component is less than 0.10 mol%), while on the other hand, when the amount of the component is 0.50 mol%
(approximately 1.00 mol% for SrHiO ₃ -based solid solution) is not desirable because grain growth of SrTiO ₃ -based solid solution porcelain is suppressed to less than 10 μm. As a result of research related to the present invention, the desirable crystal grain size of the grain boundary dielectric layer type semiconductor ceramic composition is 10 to 30 μm on average. The apparent dielectric constant ε _a and the breakdown voltage (direct current applied) V _b , which are important characteristics of a capacitor, strongly depend on the average particle size of the porcelain. As the particle size increases, ε _a increases, but V _b decreases. When the average particle size is 10 μm, V _b
can obtain 3500V/mm, but ε _a can only obtain 10000. On the other hand, when the average particle size is 30 μm, ε _a is 70,000, but V _b is only 500 V/mm. ε _a required for a practical capacitor is 10,000 or more, and V _b is
Since it is 500 V/mm or more, the average crystal grain size required for semiconductor porcelain is 10 to 30 μm. This crystal grain size is further influenced by the molar ratio between the total amount of each component of SrO, BaO, CaO, and PbO and the amount of the _two TiO components.
The above molar ratio range that provides an average particle size of 10 to 30 μm is 1.005 to 0.990. Even if the molar ratio exceeds 1.005 or is less than 0.990, the average particle size will be less than 10 μm, and ε _a will be less than 10,000, which is not desirable as a capacitor material that requires a high dielectric constant. The above molar ratio that gives the largest average particle size is approximately
0.996, and the average particle size at this time is 0.05 to 0.50.
Select an appropriate amount of Nb ₂ O ₅ within the range of mol%, and
_SiO2 amount below 1.00 mol%, below 0.40 mol%
By selecting the amount of Al ₂ O ₃ , the thickness can be suppressed to 30 μm or less. SiO ₂ content of 1.00 mol % or less promotes sintering of SrTiO ₃ semiconductor porcelain and has the effect of slightly reducing dielectric loss tan δ, but if the content exceeds 1.00 mol %, grain growth suppressing effect is large, An average particle size of 10 μm or more cannot be obtained. A similar grain growth inhibitory effect is
It is undesirable because it is observed in the amount of Al ₂ O ₃ exceeding 0.40 mol %, and in the total amount of CaO, BaO, and PbO exceeding 5.00 mol %. Also exceeds 1.00 mol%
A similar effect occurs when MgO is contained, which is undesirable since an average particle size of less than 10 μm can be obtained. The inclusion of small amounts of SnO ₂ and ZrO ₂ has the effect of slightly reducing the rate of temperature change of capacitor capacitance (85°C to -25°C), but the total content is
If it exceeds 1.00 mol%, the sintered grain size of the SrTiO ₃ semiconductor porcelain becomes non-uniform, which increases the variation in properties, which is not desirable. The inclusion of trace amounts of each of Cr ₂ O ₃ , Fe ₂ O ₃ , CoO, NiO, Cu ₂ O, and Ag ₂ O has the effect of increasing the breakdown voltage of the capacitor element, but the total amount of each of these components
If it exceeds 0.50 mol%, it is undesirable because it becomes difficult to convert the SrTiO ₃ solid solution into a semiconductor by controlling the valence. Na ₂ O and K ₂ O components have the effect of increasing tan δ, and if the total amount of these components exceeds 0.10 mol %, tan δ of 0.01 or less cannot be obtained, which is not desirable. Next, the composition of the grain boundary diffusing agent according to the present invention mainly has a Bi ₂ O ₃ component and a Cu ₂ O component in a ratio of 9:1 to 1:6.
Basically, it consists of a mixture containing Bi ₂ O ₃ and Cu ₂ O in a molar ratio in the range of 4.00 mol % or less of the _MnO component and 6.00 mol % or less of B ₂ O. 4-component mixtures substituted with ₃ components, and furthermore, a portion of said mixture is substituted with 4.00 mol% or less of
A preferred example is a five-component mixture substituted with _two MnO components, 6.00 mol % or less of B ₂ O ₃ components, and 20.00 mol % or less of Li ₂ O components. As a result of research related to the present invention, Bi ₂ O ₃ in the grain boundary diffusion component after thermal diffusion
As the number of components increases, ε _a increases, but V _b decreases and the capacitance temperature change rate (85° C. to −25° C.) increases. Conversely, as the Cu ₂ O component increases, the capacitance temperature change rate decreases, V _b increases, but ε _a decreases.
The dielectric loss tan δ is the smallest (0.0045) when the mole percentage of each component is 65.00-35.00 in the Bi ₂ O ₃ -Cu ₂ O binary system, and even if the Bi ₂ O ₃ component is larger than this composition ratio, the Cu ₂ Even if the O component increases, tanδ increases. When the molar ratio of Bi ₂ O ₃ and Cu ₂ O exceeds 9:1
This is not desirable because it is not possible to obtain characteristics with V _b of 500 V/mm or more. Furthermore, if the molar ratio of Bi ₂ O ₃ to Cu ₂ O is less than 1:6, it is not preferable because even if semiconductor porcelain with an average grain size of 24 μm is used, a characteristic of ε _a of 10.000 or more cannot be obtained. Further addition of MnO ₂ to this two-component diffusion component has the effect of increasing the value of V _b , but on the other hand, ε _a tends to decrease slightly and tan δ increases.
When the amount of MnO _two components exceeds 4.00 mol%, tanδ is 0.01
The amount of MnO ₂ contained is desirably 4.00 mol % or less because the following characteristics cannot be obtained. moreover
Addition of B ₂ O ₃ has the effect of reducing tan δ, but on the other hand tends to reduce V _b . If the B ₂ O ₃ component exceeds 6.00 mol %, the characteristic of V _b of 500 V/mm cannot be obtained, so it is desirable that the content of the B ₂ O ₃ component is 6.00 mol % or less. Furthermore, by adding a Li ₂ O component to the four-component diffusion component consisting of Bi ₂ O ₃ , Cu ₂ O, MnO ₂ and B ₂ O ₃ , ε _a can be increased without increasing the capacitance temperature change rate. Although it is effective, if the content exceeds 20.00 mol %, V _b decreases and tan δ increases, and in particular, characteristics with V _b of 500 V/mm or more cannot be obtained, which is not desirable. This will be explained below with reference to examples. Example 1 Commercially available industrial raw materials SrCO ₃ powder (purity 99.0% or higher), TiO ₂ powder (anatase type, purity 99.5% or higher), Nb ₂ O ₅ powder (purity 99.0% or higher), and a commercially available prototype special grade product. _SiO2 , _{Al2O3 ,} BaO, CaO,
MgO, PbO, _SnO2 , _ZrO2 , _{Cr2O3 , Fe2O3 ,}
Using CoO, NiO, Cu ₂ O, Ag ₂ O, Na ₂ CO ₃ and K ₂ CO ₃ powders (purity 99.5% or more), they were mixed to have the composition ratio of the semiconductor ceramic composition shown in Table 1, After wet mixing, drying and calcination at a temperature of 1200℃, the average
It was ground to a powder of 2.5 μm. After that, polyvinyl alcohol aqueous solution is added as a binder and mixed, the sized powder is sized to 32 mesh passes, and the sized powder is
It was molded into a disc shape of 15 mm x 0.5 mm thick with a pressure of about 1 ton/cm ² , and after heat-treating these molded bodies in air at 1000°C, it was heated to 90% N ₂ -10% H ₂ . Approximately 12mm in diameter after firing for 4 hours at 1390℃ in a mixed gas stream.
A disk-shaped semiconductor porcelain with a thickness of 0.4 mm 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.

【table】

【table】

[Table] * is a comparative example ↓ is the same as above The average grain size of the sintered body is set at a main firing temperature of 1380~
There was no change even when the temperature was changed within the range of 1410℃. Further, the specific resistance (In-Ga electrode) of the obtained semiconductor ceramics was all in the range of 0.2 to 0.5 Ωcm except for samples 11, 72, and 73. However, sample number 11 with Nb ₂ O ₅ component content of less than 0.05 mol % has a resistance of 2 Ωcm, Cr ₂ O ₃ , Fe ₂ O ₃ , Cu ₂ O
Sample number 73 with a total amount of more than 0.50 mol% is
It exhibited a high specific resistance of 1.5 Ωcm, indicating that valence-controlled semiconductor formation was insufficient. On the other hand, the amount of Nb ₂ O ₅ component is
In sample No. 29, in which the content exceeded 0.50 mol %, grain growth was suppressed and the grain size was as small as 8 μm on average. In addition, sample numbers 12 and 23 are SrO + BaO + CaO + PbO/TiO ₂
Since the molar ratio of is over 1.005, the average particle size is 10μ
It was less than In addition, sample numbers 16 and 28 are SrO+
The average particle size was also less than 10 μm because the molar ratio of BaO+CaO+PbO/TiO ₂ was less than 0.990. Furthermore, sample number 45, in which the total amount of each component of BaO, CaO, and PbO exceeded 5.00 mol%, and the amount of _two components of SiO
Sample number 49, Al ₂ O ₃ component amount exceeding 1.00 mol%
The average particle diameter was also less than 10 μm in Sample No. 51, in which the MgO content exceeded 0.40 mol%, and in Sample No. 63, in which the MgO content exceeded 1.00 mol%. In addition, as the total amount of SnO ₂ components and ZrO ₂ components increases, the variation in average particle size increases accordingly, and when the total amount exceeds 1.00 mol%, the average particle size will change from undesirable particles with an average particle size of less than 10 μm. Particles with a particle size of up to 30 μm are appearing. Next, a paste-like diffusing agent was applied to these semiconductor ceramics of sample numbers 11 to 76 (Table 1), 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 65.00 mol % Bi ₂ O ₃ component - 35.00 mol % Cu ₂ O component.
The raw material powder used was a commercially available special grade reagent. Coating amount is per semiconductor porcelain element (250mg)
It was 1.2 mg. In addition, 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 make a capacitor element, and the capacitor characteristics were determined as follows: ε _a (1KHz),
tanε (1KHz) and _Vb were measured. Table 2 shows these results.

【table】

[Table] *Comparative examples Sample numbers 111, 112, 116, 123, 128, 129, 145,
All the samples according to the present invention other than 149, 151, 163, 167, 173 and 176 have characteristics of ε _{a of} 10000 or more, tan δ of 0.01 or less, and V _b of 500 V/mm or more. Example 2 Commercially available special grade reagents 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 diffusion composition shown in Table 3, dry mixed, and further mixed with appropriate amounts of pine tar, turpentine oil, etc.
A paste-like diffusing agent was created. This paste-like diffusing agent was applied to a semiconductor ceramic element (average particle size: 23 μm) of sample number 20 shown in Table 1 of Example 1. The amount of the diffusing agent applied was 1.2 mg per element (approximately 250 mg) in terms of oxide powder. A semiconductor device coated with this paste-like diffusing agent was heated to 1190°C for 2 hours.
Heat treatment was performed for a period of time. In this thermal diffusion treatment, care was taken to ensure that the applied diffusion component was not lost to the outside of the sample due to evaporation, melting, or diffusion to the outside of the sample. Ag electrodes are 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, and the capacitor characteristic ε _a
(1KHz), tanδ (1KHz), V _b and capacitance change rate (85
℃ to -25℃). These results are shown in Table 3.

[Table] * indicates comparative example. In Table 3, sample numbers 201, 211, 256, 262
All samples according to the present invention other than 279 have ε _a
10,000 or more, tan δ is 0.01 or less, and V _b is 500 V/mm or more. As described above, according to the present invention, a grain boundary dielectric that satisfies the characteristics required for practical capacitors: apparent permittivity ε _a of 10,000 or more, breakdown voltage V _b of 500 V/mm or more, and dielectric loss tan δ of 0.01 or less. A layered semiconductor ceramic composition can be provided, and in a preferred example, ε _a =40000~
50000, V _b =2000~1000V/mm, tanδ=0.002~
0.005, capacitance change rate (85 to -25°C) = within ±15%, and can provide capacitors with excellent characteristics.

Claims (1)

[Claims] 1 SrO component is 52.32 to 40.27 mol%, TiO ₂ component is
47.63 to 50.23 mol%, 0.05 to 0.50 mol% of Nb ₂ O ₅ components, and at least one component among the components A to G shown below. Both Bi ₂ O ₃ and Ca ₂ O 9 to 1 to 1
1. A grain boundary dielectric layer type semiconductor ceramic composition, characterized in that a dielectric layer is formed at the grain boundaries of the composition by thermally diffusing a composition containing the composition at a molar ratio of 6 to 6. A: 1.00 mol% or less of SiO ₂ components B: 0.40 mol% or less of Al ₂ O ₃ components C: Each component of BaO, CaO, and PbO with a total amount of 5.00 mol% or less D: MgO component E of 1.00 mol% or less : Each component of SnO ₂ and ZrO ₂ with a total amount of 1.00 mol% or less F: Cr ₂ O ₃ , Fe ₂ O ₃ with a total amount of 0.50 mol% or less,
Each component G of CoO, NiO, Cu ₂ O, and Ag ₂ O: Each component 2 of Na ₂ O and K ₂ O with a total amount of 1.10 mol % or less To form a dielectric layer at the crystal grain boundaries of the semiconductor ceramic The composition that thermally diffuses into the grain boundaries is
90.00-12.90 mol% _Bi2O3 , _10.00-77.10 mol%
_CuO2 , 4.00 mol% _MnO2 and 6.00 mol%
The grain boundary dielectric layer type semiconductor ceramic composition according to claim 1, characterized in that it is made of the following B ₂ O ₃ . 3. A composition to be thermally diffused to the grain boundaries of the semiconductor device to form a dielectric layer at the grain boundaries of the semiconductor device,
90.00-10.00 mol% _{Bi2O3 ,} 10.00-60.00 mol%
of Cu ₂ O, 4.00 mol % or less of MnO ₂ , 6.00 mol % or less of B ₂ O ₃ and 20.00 mol % or less of Li ₂ O. Body layered semiconductor porcelain composition. 4 SrO component is 51.02 to 42.87 mol%, TiO ₂ component is
48.93-50.23 mol%, Nb ₂ O ₅ component is 0.05-0.50 mol%, SiO ₂ component is 0.10-1.00 mol%, Al ₂ O ₃ component is
0.02 to 0.40 mol%, at least one selected from the three components BaO, CaO, and PbO in the total amount
A composition containing at least Bi ₂ O ₃ and Cu ₂ O in a molar ratio of 9:1 to 1:6 is thermally diffused into the grain boundaries of semiconductor ceramic having a composition containing 0.50 to 5.00 mol%. A grain boundary dielectric layer type semiconductor ceramic composition characterized in that a dielectric layer is formed at the grain boundaries. 5. A composition is thermally diffused into the grain boundaries of the semiconductor ceramic to form a dielectric layer at the grain boundaries.
90.00-12.90 mol% _Bi2O3 , _10.00-77.10 mol%
_Cu2O , 4.00 mol% _MnO2 and 6.00 mol%
The grain boundary dielectric layer type semiconductor ceramic composition according to claim 4, characterized in that it consists of the following B ₂ O ₃ . 6. A composition that is thermally diffused into the grain boundaries of the semiconductor ceramic to form a dielectric layer at the grain boundaries.
90.00-10.00 mol% _{Bi2O3 ,} 10.00-60.00 mol%
of Cu ₂ O, 4.00 mol% or less of MnO ₂ , 6.00 mol% or less of B ₂ O ₃ and 20.00 mol% or less of Li ₂ O. Body layered semiconductor porcelain composition.