JP3393157B2 - Polycrystalline semiconductor fiber and method for producing the same - Google Patents

Description

Detailed Description of the Invention

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a polycrystalline semiconductor fiber containing a TiO ₂ -based perovskite compound as a main component, which is useful as a raw material for semiconductor ceramics, and a method for producing the same.

[0002] With the recent progress in size and weight reduction of electronic equipment,
The electronic components used therein are also required to have a significantly small size and high reliability. T
The same applies to ferroelectric ceramics using an iO ₂ -based perovskite compound, and various studies have been conducted in terms of compounding technology, molding technology, sintering technology, etc. for the purpose of miniaturization and high performance. In addition, in order to improve the characteristics of the material itself, 1
A fine powder of a spherical TiO ₂ -based perovskite compound having a diameter of μm or less, preferably 0.5 μm or less, a narrow particle size distribution, has been developed. However, in reality, such a technique cannot satisfy the demand for downsizing in the market.

That is, although the conventional ceramics capacitor has excellent high frequency characteristics as compared with the tantalum capacitor and the film capacitor, the capacitance value obtained in the same size is small, so that the conventional product has a tantalum capacitor and a film capacitor. Could not be a substitute for. However, in the grain boundary insulation type semiconductor ceramic capacitor, since the boundary between particles in ceramics is used as a dielectric layer or an insulating layer, the effective dielectric thickness with respect to the thickness of the ceramic becomes a fraction to a few tenths. It can be made much smaller than conventional ceramic capacitors. Further, the surface-insulating semiconductor ceramics uses a glass-diffused layer formed at the interface between the semiconductor ceramics and the electrode as an insulating layer, and has a higher apparent dielectric constant than that of the grain boundary insulating type.

For the above reasons, various attempts have been made to use the semiconductor ceramic capacitor as a substitute for a tantalum capacitor or a film capacitor. In the current semiconductor ceramic capacitor, first, a semiconductor porcelain is manufactured and then electrodes are attached. It was manufactured by the above method, and there was a problem in the manufacturing technology that it was difficult to stack, which is an important point for downsizing and large capacity. For this reason, there is a limit to the use as a substitute for a tantalum capacitor or a film capacitor.

DISCLOSURE OF THE INVENTION Problems to be Solved by the Invention The present invention provides a polycrystalline semiconductor fiber capable of producing a laminated semiconductor ceramic capacitor utilizing anisotropy by a manufacturing process similar to that of a laminated ceramic capacitor, and a manufacturing method thereof. With the goal.

Means for Solving the Problems The present invention relates to a polycrystalline semiconductor fiber containing a TiO ₂ -based perovskite-type compound as a main component, the crystal semiconductor axis of which is composed of fine crystal grains whose crystal axes are oriented in the fiber extension direction. It is a reduction product of the TiO ₂ -based perovskite-type compound, and provides the polycrystalline semiconductor fiber characterized by having a powder specific resistance of 500 Ω · cm or less. The fiber length of the fiber is 5 to 100 μm, and the fiber diameter is 0.2 to 2 μm.
It is preferably m. Further, it is preferable to further provide an insulating layer on the surface of the semiconductor fiber.

Depending on the reducing conditions such as temperature, time, kind and amount of added metal, etc., the powder resistivity of the reduced powder is 10 ⁶
It is possible to control in the range of -10 ^-1 Ω · cm, but it is necessary for the raw material powder for semiconductor ceramic capacitors to have low powder resistance in order to reduce loss, and this powder resistance value is It is preferably 500 Ω · cm or less, and more preferably 400 Ω · cm or less.

The polycrystalline semiconductor fiber according to the present invention can be typically manufactured by the following method.

That is, the formula: TiO ₂ .nH ₂ O (however,
In the formula, n is a titanic acid fiber represented by 1 to 6), and an amount of alkaline earth metal such that the molar ratio with TiO ₂ contained therein is MO / TiO ₂ > 1 (M is an alkaline earth metal). An oxide or an alkaline earth metal compound that decomposes at high temperature to form an alkaline earth metal oxide, and an amount of NaCl-KCl corresponding to 150 wt% or less based on TiO _2.
After spray-drying the mixed slurry mixed with the system flux, it is fired at 500 to 800 ° C. to produce alkaline earth metal titanate, and then the excess alkaline earth metal raw material compound and flux remaining in the fired product are removed. It can be manufactured by dissolving and removing with water or an acid and then reducing at 1100 ° C to 1400 ° C.

Upon reduction, Nd ₂ O ₃ , La ₂ O ₃ , Dy
_At least 1 selected from the group consisting of trivalent metal oxides of ₂ O ₃ , Sm ₂ O ₃ , Pr ₂ O ₃ , Gd ₂ O ₃ and Ho ₂ O _3.
Species of the metal oxide, or Nb ₂ O _5, and 5 of Ta ₂ O ₅
It is preferable to add and mix at least one metal oxide selected from the group consisting of valent metal oxides.

The titanic acid fiber used in the present invention is K ₂
The layered structure potassium titanate represented by the composition of O.4TiO ₂ is treated with an acid to elute and remove potassium ions between layers by an acid, and the hydrous titanium oxide is heat-aged in a sodium hydroxide aqueous solution and then acidified. And the like. With respect to the obtained titanic acid fiber, an amount of an alkaline earth metal oxide that corresponds to the amount of MO / TiO ₂ > 1 in molar ratio or a compound that decomposes at high temperature to form an alkaline earth metal oxide ( For example, carbonate, nitrate, hydroxide, oxalate, etc.) and 150 wt% with respect to the amount of TiO _2.
These are dispersed and mixed in water by adding an amount of NaCl-KCl based flux corresponding to the following. Here, the ratio of the amounts of the alkaline earth metal raw material compound and TiO ₂ may be any value larger than 1, but is preferably 1.1 to 2.0. This is because an excess amount of the alkaline earth metal raw material compound needs to be removed with water or an acid after firing, so that making the molar ratio too large unnecessarily increases the manufacturing cost, while the molar ratio of 1. If it is less than 1, it is necessary to bake at a higher temperature in order to complete the reaction, and it becomes impossible to avoid the formation of granular TiO ₂ -based perovskite-type compounds. If the amount of the flux is too large, it causes the formation of granular TiO ₂ -based perovskite-type compounds, so the range of 3 to 150 wt% is preferable, and the range of 5 to 120 wt% is more preferable. The composition of the flux is 30 to 70 mol% NaCl
It is preferable that the calcination temperature be high in order to obtain a single-phase TiO ₂ -based perovskite-type compound because the melting point of the flux becomes high when the composition is out of this range. However, it becomes impossible to avoid the formation of granular TiO ₂ -based perovskite-type compounds. Next, after spray-drying the obtained slurry, 500-80
By firing at 0 ° C., preferably 600 to 750 ° C., a TiO ₂ based perovskite type compound is produced.
The firing time is 0.1 to 4 hours. Firing for a long time leads to the collapse of the fiber morphology due to the fact that the microcrystalline particles in the fiber become too large. Also, if firing is too short, Ti
The formation reaction of the O ₂ based perovskite type compound cannot be completed. The calcined product is dispersed in water or an aqueous acid solution to dissolve the flux and excess alkaline earth metal raw material compound, and then washed and dried to obtain TiO ₂ -based perovskite compound fiber.

The TiO ₂ type perovskite type compound includes barium titanate and strontium titanate. In the case of barium titanate, Ba is Ca, Sr
And Mg may be partially substituted by one or more elements selected from Mg. Also in the case of strontium titanate, Sr can be partially replaced by one or more elements selected from Ba, Ca and Mg. The amount of substitution at this time varies depending on the required properties, but usually a substitution amount up to about 30 mol% will sufficiently improve the properties. Also,
It is also possible to replace part of Ti with Zr.

Reduction is a known method, that is, a forced reduction method,
It can be carried out by a valence control method, a combination method thereof, or the like, and the temperature is suitably in the range of 1100 to 1400 ° C. That is, when the amount is lower than this range, the reduction does not proceed, and when the amount is higher than this range, the fibers are sintered with each other to form a lump, or the fiber form is broken.

When the reduction is carried out by the valence control method, an oxide such as Nd added during the manufacture of semiconductor porcelain is used.
₂ O ₃ , La ₂ O ₃ , Dy ₂ O ₃ , Sm ₂ O ₃ , Pr ₂ O ₃ , Gd
Addition of at least one trivalent metal oxide selected from the group consisting of ₂ O ₃ and Ho ₂ O ₃ , or Nb ₂ O ₅ , Ta ₂ O ₅ at least one pentavalent metal oxide, etc. Is effective,
It is also effective to add at least one kind of oxide selected from the group consisting of ZnO and SiO ₂ together with the oxide of the trivalent or pentavalent element.

The insulating layer is formed on the surface of the semiconductor fiber of the present invention by MnO ₂ , CuO, Bi ₂ O ₃ , PbO and Tl.
_At least one oxide selected from the group consisting of ₂ O ₃ , Sb ₂ O ₃ , Fe ₂ O _{3 and the} like is added together with the oxide of the trivalent or pentavalent element to reduce it, and then heat treatment is performed. Alternatively, the reducing powder may be added with the above-described additive for forming an insulator phase and then baked.
During the reduction, the shape of the semiconductor fiber produced does not change even if the above-mentioned elements are added, and the shape of the titanate fiber is maintained. Furthermore, after the reduction is completed, the insulating layer can be formed by reoxidizing in an oxidizing atmosphere and forming an oxide film on the surface.

The semiconductor fiber of the present invention is a polycrystal fiber having microscopic particles having the form of a titanic acid fiber and having a perovskite type compound as a main component, and the crystal axes of the microcrystalline particles are fiber growth. Since it is oriented in the direction, the anisotropy can be advantageously utilized. This feature is effectively utilized in the manufacture of any of the grain boundary insulation type, reoxidation type, surface insulation type, etc. semiconductor ceramic capacitors, and in particular, high capacity multilayer semiconductor ceramic capacitors with the same manufacturing process as multilayer capacitors. Is effectively used in manufacturing.

The present invention will be described in more detail below with reference to examples. The following examples are given for illustrative purposes only and the scope of the invention is not limited thereby. Example 1 3200 g of anatase-type titanium dioxide and 1700 g of potassium carbonate powder were dry-mixed, then transferred to an alumina crucible, heated to 1100 ° C. at a heating rate of 250 ° C./hour in an electric furnace, and calcined at the temperature for 5 hours. After that, the temperature was lowered at a rate of 200 ° C./hour.

The fired product was put into 40 liters of warm water in a stainless steel container and immersed for 7 hours, and then 3 minutes at 600 rpm.
Stir for hours. The pH of the slurry was dropped by adding 5N-hydrochloric acid.
Was adjusted to 0.5, filtered and washed to obtain titanic acid fiber.

2040 g of titanic acid fiber, 5075 g of barium carbonate corresponding to 1.2 times the number of moles of TiO ₂ contained therein, and 560 g of NaCl and 550 g of KCl as flux corresponding to 65 wt% of TiO _2.
Was added, water was added to this to make a total volume of 75 liters, and the mixture was stirred for 30 minutes. The slurry was heated to an inlet temperature of 270-2
Spray-dry under the conditions of 80 ° C and an outlet temperature of 92 to 95 ° C, put the obtained dried product in an alumina crucible, and set at 700 ° C for 1
Burned for hours. The calcined product was dispersed in warm water, and 1N-hydrochloric acid was added to adjust the pH of the slurry to 4 to dissolve excess barium carbonate. The residue was filtered, washed and dried to obtain barium titanate fiber.

The powder obtained was treated with N ₂ (90% by volume) + H
₂ (10% by volume) was reduced in a gas stream at 1350 ° C. for 8 hours to obtain a black powder. 280 kg / cm of the reduced powder
^When the direct current resistance of the molded body was measured by using a universal bridge manufactured by Yokogawa Hewlett Packard after compression molding in ² and the powder resistance value was calculated by the following formula:
It was 1 Ω · cm.

Powder resistance (Ω · cm) = DC resistance (Ω)
x (cross-sectional area (cm ² ) / thickness (cm)) When the powder was observed with an electron microscope, a length of 0.5 to
0.7 μm, diameter 0.2-, fiber length is 15-4
The diameter was 0 μm and the diameter was 0.5 to 1.5 μm. Barium titanate was identified by X-ray diffraction, and it was confirmed by electron X-ray diffraction that the crystal axes of the microcrystalline particles were oriented in the fiber extension direction. BaO investigated by chemical analysis
The / TiO ₂ molar ratio was 0.992.

Example 2 1500 g of titanic acid fiber used in Example 1, 2560 g of strontium carbonate, 450 g of NaCl, KCl
560 g was mixed, water was added to this to make the total volume 50 liters, and the mixture was stirred for 40 minutes. At the inlet temperature 27
Spray drying under conditions of 0 to 280 ° C. and an outlet temperature of 85 to 87 ° C., and the obtained dried product is put into an alumina crucible, and 720
Calcination was performed for 1 hour. After dispersing the fired product in warm water, 1
Excess strontium carbonate was dissolved by adding N-acetic acid to adjust the pH of the slurry to 6. After filtering and washing the residue, it is slurried and has an average particle size of 0.6 μm.
110 g of Nb ₂ O ₅ powder and Z having an average particle size of 0.8 μm
12 g of nO powder was added, mixed and dried.

The powder obtained was treated with N ₂ (90% by volume) + H
₂ (10% by volume) was reduced in a gas stream at 1200 ° C. for 1 hour to obtain a black powder. When the powder resistance value of the reduced powder was measured in the same manner as in Example 1, it was 135 Ω · cm.

When the powder was observed with an electron microscope, it was the same polycrystalline fiber as in Example 1. Strontium titanate was identified by X-ray diffraction, and it was confirmed by electron X-ray diffraction that the crystal axes of the microcrystalline particles were oriented in the fiber extension direction. SrO investigated by chemical analysis
The / TiO ₂ molar ratio was 1.010.

Example 3 1500 g of titanate fiber used in Example 1, 3440 g of barium carbonate and 280 g of strontium carbonate, Na
310 g of Cl and 540 g of KCl were mixed, water was added to the mixture to bring the total volume to 50 liters, and the mixture was stirred for 30 minutes. The slurry was spray-dried under conditions of an inlet temperature of 270 to 280 ° C and an outlet temperature of 85 to 87 ° C, and the obtained dried product was put in an alumina crucible and calcined at 700 ° C for 1 hour.
The calcined product was dispersed in warm water, and 1N-acetic acid was added to adjust the pH of the slurry to 6, whereby unreacted barium carbonate and strontium carbonate were dissolved. Filter the residue,
After washing, it is slurried and La with an average particle size of 0.6 μm
95 g of ₂ O ₃ powder and 10 g of SiO ₂ powder having an average particle diameter of 0.01 μm were added, mixed and dried.

The powder obtained was treated with N ₂ (90% by volume) + H
₂ (10% by volume) was reduced in a gas stream at 1170 ° C. for 1 hour to obtain a black powder. When the powder resistance value of the reduced powder was measured in the same manner as in Example 1, it was 350 Ω · cm.

When the powder was observed with an electron microscope, it was the same polycrystalline fiber as in Example 1. It was found by X-ray diffraction that barium titanate was a solid solution of strontium. Checked by chemical analysis (BaO + SrO)
The / TiO ₂ molar ratio was 1.008.

Example 4 1500 g of titanic acid fiber used in Example 1, 2600 g of strontium carbonate and 310 g of calcium carbonate, N
380 g of aCl and 480 g of KCl were mixed, water was added to the mixture to make the total volume 50 liters, and the mixture was stirred for 30 minutes. The slurry was spray-dried under conditions of an inlet temperature of 270 to 280 ° C and an outlet temperature of 85 to 87 ° C, and the obtained dried product was placed in an alumina crucible and calcined at 650 ° C for 30 minutes. After the calcined product was dispersed in warm water, 1N-hydrochloric acid was added to adjust the pH of the slurry to 3 to dissolve unreacted strontium carbonate and calcium carbonate. The residue is filtered and washed, then slurried, and the average particle size is 0.5 μm.
Of Ta ₂ O ₅ powder 90g dried after addition mixing.

The obtained powder was added to N ₂ (90% by volume) + H
₂ (10% by volume) was reduced in a gas stream at 1230 ° C. for 1 hour to obtain a black reduced powder. When the powder resistance value of the reduced powder was measured in the same manner as in Example 1, it was 190 Ω · cm.

When the powder was observed with an electron microscope, it was the same polycrystalline fiber as in Example 1. It was found by X-ray diffraction that it was strontium titanate in which calcium was in solid solution. Investigated by chemical analysis (SrO + Ca
The O) / TiO ₂ molar ratio was 0.991.

Example 5 1500 g of titanate fiber used in Example 1, 3300 g of barium carbonate and 340 g of magnesium carbonate, NaC
410 g of Kl and 430 g of KCl were mixed, water was added to this to make a total volume of 50 liters, and the mixture was stirred for 30 minutes.
The slurry was treated at an inlet temperature of 270 to 280 ° C. and an outlet temperature of 9
Spray drying was carried out under the condition of 2 to 95 ° C., and the obtained dried product was put into an alumina crucible and calcined at 700 ° C. for 1 hour. After the calcined product was dispersed in warm water, 1N-hydrochloric acid was added to adjust the pH of the slurry to 6, thereby dissolving unreacted barium carbonate and magnesium carbonate. The residue is filtered, washed and slurried to give 50 g of Ta ₂ O ₅ powder having an average particle size of 0.6 μm and 70 g of Nb ₂ O ₅ powder having an average particle size of 0.6 μm.
Was mixed and dried.

The powder obtained was treated with N ₂ (85% by volume) + H
₂ (15% by volume) was reduced in a gas stream at 1200 ° C. for 1 hour to obtain a black reduced powder. When the powder resistance value of the reduced powder was measured in the same manner as in Example 1, it was 20 Ω · cm.

When the powder was observed with an electron microscope, it was found to be the same polycrystalline fiber as in Example 1. It was found by X-ray diffraction that the solid solution was barium titanate containing magnesium. Chemically analyzed (BaO + MgO) /
The TiO ₂ molar ratio was 1.018.

Example 6 100 g of the reduced powder obtained in Example 1 was slurried with toluene, and then 5 g of PbO powder was added and mixed. After drying the slurry, it was heated in air at 800 ° C. for 15 minutes to obtain a powder in which an insulating layer was formed on the fiber surface. The powder resistance value calculated in the same manner as in Example 1 was 1.5.
It was x10 ⁴ Ω · cm.

Comparative Example 1 In Example 1, the powder resistance of barium titanate fiber before reduction was measured in the same manner as in Example 1,
It was 1.8 × 10 ⁸ Ω · cm.

Comparative Example 2 In Example 2, the powder resistance value of the strontium titanate fiber before reduction was measured in the same manner as in Example 1 and found to be 0.9 × 10 ⁹ Ω · cm.

─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Chisato Kariyama 25 Chitan Kogyo Co., Ltd., 1978, Kogushi, Ube City, Yamaguchi Prefecture (56) Reference JP-A-2-164800 (JP, A) JP-A-63 -155504 (JP, A) JP-A 63-12760 (JP, A) JP-A 61-55218 (JP, A) JP-A 58-135129 (JP, A) JP-A 58-135130 (JP, A) ) JP-A-57-183324 (JP, A) JP-A-3-237100 (JP, A) JP-A-3-69511 (JP, A) JP-A-55-113623 (JP, A) JP-A-62- 21799 (JP, A) (58) Fields surveyed (Int.Cl. ⁷ , DB name) C30B 1/00-35/00 C01G 23/00

Claims (5)

(57) [Claims] 1. A polycrystalline semiconductor fiber comprising a TiO ₂ -based perovskite-type compound as a main component, which is composed of fine crystal grains whose crystal axes are oriented in the fiber extension direction, and comprises titanate fiber and alkaline earth metal. Oxide or an alkaline earth metal compound that decomposes at high temperature to form an alkaline earth metal oxide at a molar ratio of MO / TiO ₂ > 1 (M is an alkaline earth metal), and calcined. A reduction product of the above-mentioned TiO ₂ -based perovskite-type compound, which is composed of a fibrous TiO ₂ -based perovskite-type compound and whose surface is reduced at 1100 ° C. to 1400 ° C., and further 280 kg / cm ² A polycrystalline semiconductor fiber having a powder specific resistance of 500 Ω · cm or less when compression-molded under pressure. 2. A coated polycrystalline semiconductor fiber, further comprising an insulating layer on the surface of the polycrystalline semiconductor fiber according to claim 1. 3. A length of 5 to 100 μm and a diameter of 0.
It is 2-2 micrometers, The polycrystalline semiconductor fiber of Claim 1 or 2 characterized by the above-mentioned. 4. A titanic acid fiber represented by the formula TiO ₂ .nH ₂ O (where n in the formula is 1 to 6), and Ti contained therein.
An oxide of an alkaline earth metal in an amount such that the molar ratio with O ₂ is MO / TiO ₂ > 1 (M is an alkaline earth metal) or an alkaline earth that decomposes at high temperature to form an oxide of an alkaline earth metal. Compounds of group metals, and based on TiO ₂ 15
After spray-drying the mixed slurry mixed with an amount of NaCl-KC1 based flux in an amount corresponding to 0 wt% or less, 50
After baking at 0 to 800 ° C. to produce alkaline earth metal titanate, and then removing excess alkaline earth metal starting compound and flux remaining in the baked product with water or acid, 1100 ° C. to 1400 ° C. The method for producing a polycrystalline semiconductor fiber according to claim 1, wherein the reduction is carried out with. 5. When reducing, Nd ₂ O ₃ , La
_At least one metal oxide selected from the group consisting of trivalent metal oxides of ₂ O ₃ , Dy ₂ O ₃ , Sm ₂ O ₃ , Pr ₂ O ₃ , Gd ₂ O 3 and Ho ₂ O ₃ , or The production method according to claim 4, wherein at least one metal oxide selected from the group consisting of pentavalent metal oxides of Nb ₂ O ₅ and Ta ₂ O ₅ is added and mixed.