JPH0536561A - Manufacture of grain boundary insulating type semiconductor multilayer porcelain capacitor - Google Patents

Abstract

PURPOSE:To enhance denseness of a porcelain by using base metal as an inner electrode of a grain boundary insulating type semiconductor multilayer porcelain capacitor. CONSTITUTION:A porcelain crude sheet 1 is formed of a material in which a material containing a main ingredient of a semiconductor porcelain and a semiconductor formation accelerator is temporarily baked in an oxidative atmosphere. The sheet 1 is coated with base metal conductive paste 2 mixed with grain boundary insulating material. A laminate of the sheet 1 coated with the paste 2 is formed, and baked in a reducing atmosphere. The obtained sintered material is heat treated at 900-1200 deg.C in a weak acidic atmosphere to form the grain boundary insulating layer.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a method for manufacturing a grain boundary insulation type semiconductor multilayer ceramic capacitor.

[0002]

2. Description of the Related Art A grain boundary insulation type semiconductor ceramic comprises semiconductor crystal grains and an insulating layer interposed between the grains (grain boundaries). The grain boundary insulating layer is prepared by applying an insulating substance to the surface of the semiconductor porcelain and thermally diffusing it in an oxidizing atmosphere, or by preparing the semiconductor porcelain material mixed with the grain boundary insulating substance. Formed by firing the body.

In the case of forming a grain boundary insulation type semiconductor porcelain multilayer capacitor, a conductive paste for forming an internal electrode of the multilayer capacitor in order to enable the production of a multilayer capacitor based on the former method of thermal diffusion of an insulating material. It is possible to mix a thermal diffusion material for insulating grain boundaries into the inside of the device.
It is disclosed in Japanese Patent No. 215701.

In the method disclosed herein, a porcelain material obtained by mixing a main component such as strontium titanate and a semiconducting promoter such as niobium oxide in a reducing atmosphere at 1300 ° C.
Calcination in the range of up to 1500 ° C is performed, a porcelain raw sheet (green sheet) is formed from the porcelain material after the calcination, a conductive paste mixed with a heat diffusion substance is applied to the porcelain raw sheet, and lamination by this By forming a body and firing this laminated body in an oxidizing atmosphere, sintering and insulation of grain boundaries are performed at the same time.

[0005]

The method disclosed in the above publication uses a porcelain raw material calcined in a reducing atmosphere at a relatively high temperature of 1300 ° C. to 1500 ° C. It is difficult to obtain a sintered body. That is, since the calcinated and sintered material is crushed to be used as the material for the porcelain green sheet, the denseness of the porcelain green sheet is poor. Further, since the porcelain green sheet is fired in the air under the condition of 850 ° C to 1350 ° C, it is difficult or impossible to use a base metal such as Ni (nickel) as the internal electrode.

On the other hand, instead of thermally diffusing the insulating material,
If a method of previously mixing an insulating substance into a porcelain raw material composed of an insulating porcelain main component and a semiconducting promoter is adopted, both the semiconductor promoting agent and the insulating substance react with the main component at the same time. However, it is difficult to control the reaction, resulting in variations in characteristics. In the air, 900 ° C to 125 ° C
Oxidation treatment process at about 0 ℃ is required,
In order to prevent oxidation of the base metal, it is necessary to set the temperature of the oxidation treatment low or set the treatment time short so that the grain boundary layer can be sufficiently insulated. Was difficult.

Therefore, an object of the present invention is to provide a method for manufacturing a grain boundary insulation type semiconductor laminated ceramic capacitor which can obtain a dense sintered body. Another object of the present invention is to
It is an object of the present invention to provide a method for manufacturing a grain boundary insulation type semiconductor laminated ceramic capacitor which can use a base metal such as nickel as an internal electrode.

[0008]

In order to achieve the above object, the present invention is directed to oxidizing a porcelain raw material containing a main component for obtaining a semiconductor porcelain or a substance for obtaining the main component and a semiconducting accelerator. A step of calcination in an atmosphere, a step of forming a porcelain raw sheet using the calcinated porcelain material, a substance for insulating the grain boundaries of the semiconductor porcelain on the main surface of the porcelain raw sheet A step of applying a mixed conductive paste, a step of stacking a plurality of porcelain green sheets coated with the conductive paste to form a laminated body, and sintering the laminated body in a reducing atmosphere And a step of heat-treating the sintered body at 900 ° C. to 1200 ° C. in a weakly oxidizing atmosphere, the present invention relates to a method for manufacturing a grain boundary insulation type semiconductor multilayer ceramic capacitor. .

Further, after the heat treatment step in the weakly oxidizing atmosphere, heat treatment at 500 ° C. to 800 ° C. can be performed in an atmosphere (preferably in the air) having a stronger oxidizing property than the weakly oxidizing atmosphere. In addition, the conductive paste may be a base metal paste such as Ni in order to reduce the cost. Further, it is desirable that the conductive paste contains a glass component that diffuses into the porcelain.

For making a porcelain green sheet in the present invention
Porcelain raw material is SrTiO₃, (Sr _1-xCa_x) TiO
₃, (Sr_1-xBa_x) TiO₃Or finally these
Titanium comprising one or more of the compounds obtainable
Strontium acid-based main component and Nb₂O_Five, Ta₂
O_Five, WO₃, La₂O₃, CeO₂, Nd₂O₃, Y
₂O₃, Sm₂O₃, Pr₆O₁₁, Dy₂O₃1 of
The mixture with one or more semiconducting accelerators
Medium, calcined at 1000 ° C to 1200 ° C
Is desirable.

Insulating substances include Na ₂ O and Li
One or more of ₂ O, MnO ₂ and CuO are desirable. The conductive paste is SiO ₂ , B ₂ O ₃ , Al ₂ O
It is desirable to include a glass component containing one or more of the _three .

The weakly oxidizing atmosphere is N ₂ , He, Ne, Ar.
Impurity gas consisting of one or more of the gases, 1 to
It is desirable that oxygen (O ₂ ) of about 1000 ppm is included. In addition, H ₂ O (component) can be included in this weakly oxidizing atmosphere.

A base metal such as Ni is preferable as the electrode metal of the conductive paste from the viewpoint of cost reduction, but Pd, P
It is also possible to use a noble metal such as t or Ag-Pd.

[0014]

FUNCTION AND EFFECT OF THE INVENTION The porcelain raw material of the porcelain green sheet according to the present invention is not subjected to high temperature calcination treatment in a reducing atmosphere. Therefore, when the green porcelain sheet according to the present invention is fired in a reducing atmosphere, a dense sintered body is obtained. That is,
In the conventional method, the calcination is the first firing and the porcelain green sheet is the second firing, and a dense porcelain cannot be obtained during the second firing. On the other hand, in the present invention, since the porcelain raw material is only calcined in the oxidizing atmosphere, the sinterability during firing of the porcelain green sheet does not decrease due to calcination. In addition, since the main component and the semiconducting accelerator react with each other in the calcination, the semiconducting porcelain progresses uniformly without being significantly affected by the insulating substance by the firing in the reducing atmosphere, and the insulating substance The diffusion proceeds uniformly without being affected by the semiconducting promoter. When the sintered body is heat-treated in a weakly oxidizing atmosphere, the oxidation uniformly proceeds inside the porcelain layer, and a uniform insulating layer is formed at the crystal grain boundaries. Since firing is performed in a reducing atmosphere and insulation of grain boundaries is performed in a weakly oxidizing atmosphere, the electrode metal is hard to oxidize. Therefore, a base metal such as Ni can be used as the electrode metal.

[0015]

[First Embodiment] A method of manufacturing a grain boundary insulation type semiconductor multilayer ceramic capacitor having a varistor function (voltage-current non-linear characteristic) will be described. First, SiTiO which is the main component of porcelain
Nb ₂ O ₅ (niobium oxide) 0.5 as a semiconducting accelerator for 100 mol parts of ₃ (strontium titanate)
In order to obtain a porcelain raw material containing a molar part, SrCO
100 parts by mol of ₃ (strontium carbonate), TiO
₂ (titanium oxide) 100 parts by mole, Nb ₂ O ₅ 0.5
Molar parts were weighed and wet-mixed with a ball mill for 15 hours, and then calcined in the air (in an oxidizing atmosphere) at 1150 ° C. for 2 hours. Next, this calcined product was roughly pulverized to obtain a porcelain raw material powder.

Next, 8% by weight of polyvinyl butyral (organic binder) was added to the above porcelain raw material powder to form a slurry, and a plurality of porcelain green sheets (green sheets) having a thickness of 60 μm were prepared by the doctor blade method. .

Next, with respect to Ni (nickel) powder 100 parts by weight, 1.0 part by weight of Na ₂ O (sodium oxide) as the insulating substances, MnO ₂ (the manganese oxide) 1.
0 parts by weight, 1.0 parts by weight of Li ₂ O (lithium oxide), 5.0 parts by weight of Al ₂ O ₃ —SiO ₂ type glass as a glass component and an appropriate amount of vehicle are added and kneaded. A conductive paste mixed with an insulating substance was prepared. Next, as shown in FIGS. 1 and 2, this conductive paste was printed on the main surface of the porcelain green sheet 1 into a rectangle having a length of 3 mm and a width of 2 mm to form a paste coating layer 2. The paste coating layer 2 was formed so that only one side reaches the edge and a space of 0.3 mm is generated on the remaining three sides.

Next, 20 green sheets 1 are laminated as shown in FIG. 2 so that the paste coating layer 2 is alternately exposed on the left side surface and the right side surface, and the pressure is 800 kg / cm ² at 100 ° C. A green sheet laminate was formed by pressing.

Next, the green sheet laminate is treated with N ₂ 98% + H ₂
Heat treatment at 1300 ° C. for 2 hours in a 2% reducing atmosphere,
A sintered laminated body in which the porcelain layers 1a and the internal electrode layers 2a shown in FIG. 3 were alternately arranged was formed.

Next, the sintered laminated body was mixed with 100% oxygen (O ₂ ).
1000 ℃ in a nitrogen atmosphere (weakly oxidizing atmosphere) containing ppm
Was heat-treated for 2 hours to form an insulating layer on the crystal grain boundary.

Next, a Zn paste is applied so as to be connected to the exposed surface of the internal electrode layer 2a and baked at 500 ° C. in the atmosphere to form a pair of external electrodes 3 and 4 to form a grain boundary insulation type. A semiconductor multilayer capacitor was completed.

In the above firing step in the reducing atmosphere, N is selected from the conductive paste for forming the internal electrodes.
Insulating material consisting of a ₂ O, MnO ₂ and Li ₂ O and A
The l ₂ O ₃ —SiO ₂ glass component thermally diffuses into the porcelain, and the densification and semiconductorization of the porcelain progresses, and the insulating material and the glass component segregate in the crystal grain boundary portion to form the grain boundary insulating layer. Is formed. The glass component diffuses into the porcelain and contributes to low temperature sintering, and also serves as an inorganic binder for the conductive paste. Although the conventional grain boundary insulating treatment has been performed in the air, the present inventor has discovered that a uniform grain boundary insulating layer can be formed even by heat treatment in an oxidizing atmosphere with a low oxygen concentration.

When the electrical characteristics of the obtained grain boundary insulation type semiconductor multilayer capacitor were measured, the apparent dielectric constant ε was 1
4000, tan δ 1.3%, varistor voltage 170
The V and voltage nonlinear coefficient α was 11.

The apparent permittivity ε was calculated from the capacitance measured under the conditions of 20 ° C., frequency 1 kHz and measurement voltage 1 V and the dimensions of the multilayer capacitor.

Tan δ was measured at the same time as the capacitance.

The varistor voltage V1 was obtained by measuring the terminal voltage when a direct current of 1 mA was applied to the capacitor. This value is the value per porcelain layer having a thickness of 1 mm.

The voltage non-linearity coefficient α was determined by measuring the voltage V10 when a current of 10 mA was applied to the capacitor and determining the ratio log V10 / V1 of this to the varistor voltage V1.

The capacitor according to this embodiment has not only the electrostatic capacity but also the varistor characteristic in which the voltage-current characteristic between the pair of electrodes is non-linear. Therefore, it is suitable for surge absorption in the circuit device.

[0029]

[Second Embodiment] A grain boundary insulation type semiconductor multilayer capacitor is manufactured under the same conditions as in the first embodiment except that the heat treatment conditions (oxygen concentration, temperature, time) in a weakly oxidizing atmosphere are variously changed.
When the electrical characteristics were measured by the same method as in the first embodiment, the following results were obtained. Oxygen concentration 10ppm, temperature 90
When the condition is 0 ° C. and time is 4 hours, ε is 16000,
Tan δ was 1.1%, V1 was 140 V / mm, and α was 10. When the oxygen concentration is 1000 ppm, the temperature is 900 ° C., and the time is 2 hours, ε is 13000 and tan δ is 1.4.
%, V1 was 140 V / mm, and α was 12. When the oxygen concentration is 10 ppm, the temperature is 1000 ° C., and the time is 2 hours, ε is 15000, tan δ is 1.4%, and V1 is 180.
V / mm and α were 11. Oxygen concentration 1ppm, temperature 11
When the condition is 00 ° C. and time is 4 hours, ε is 1300.
0, tan δ 1.2%, V1 160 V / mm, α 12
Met. Under the conditions of oxygen concentration of 100 ppm, temperature of 1100 ° C. and time of 1 hour, ε was 12000, tan δ was 1.7%, V1 was 200 V / mm, and α was 13. When the oxygen concentration is 1 ppm, the temperature is 1200 ° C., and the time is 2 hours, ε is 12000, tan δ is 1.8%, and V1 is 2
It was 10 V / mm and α was 12. When the oxygen concentration is 10 ppm, the temperature is 1200 ° C., and the time is 1 hour, ε is 11
000, tan δ was 2.3%, V1 was 230 V / mm, and α was 10. Under the above seven conditions, the oxygen concentration is 1 to 1
The temperature is in the range of 000 ppm and the temperature is in the range of 900 to 1200 ° C. Although the time is 1 to 4 hours, it can be appropriately determined within a range of, for example, longer than 30 minutes. Within the above range, ε is 10,000 or more, tan δ
Can be 2.5% or less, V1 can be 100 V / mm or more, and α can be 10 or more. That is, both the capacitor characteristic and the varistor characteristic can be substantially satisfied.

For comparison, a laminated capacitor was prepared under the same conditions as in the first embodiment except that the treatment was performed in the air atmosphere at 1000 ° C. for 0.5 hours instead of the treatment in the weakly oxidizing atmosphere. When the characteristics were measured, ε was 1800
0, tan δ was 14.2%, V1 was 40 V / mm, and α was 4. In this comparative example, the treatment time is limited to 0.5 hour in order to prevent the oxidation of nickel. Therefore,
It is impossible to sufficiently form the grain boundary insulating layer, and V1
And α are lower than in the embodiment of the present invention.

The heat treatment temperature in the weakly oxidizing atmosphere is 900 to 1
In order to investigate the characteristics when the temperature is other than 200 ° C., oxygen concentration is 1000 ppm, temperature is 800 ° C., and time is 4 hours. Ε is 22000, tan δ is 11.2%, V1
Was 30 V / mm and α was 3. Also, oxygen concentration 1ppm
When the temperature was 1300 ° C. and the time was 1 hour,
ε is 6000, tan δ is 9.5%, and V1 is 270 V / m.
m and α were 7. As is clear from the above two conditions, when the processing temperature is as low as 800 ° C., it becomes impossible to form a sufficient grain boundary insulating layer, and tan δ and V1 deteriorate. Further, when the processing temperature is too high as 1300 ° C., the nickel electrode is oxidized and both the capacitor characteristic and the varistor characteristic are deteriorated.

[0032]

[Third Embodiment] In order to confirm that it is possible to add a low temperature oxidation treatment step in the atmosphere immediately after the weak oxidation atmosphere treatment step in the first embodiment, the first embodiment Weak oxidizing atmosphere treatment condition is oxidation concentration 10pp
m, the treatment temperature was 1100 ° C., the treatment time was 2 hours, and an oxidation treatment step in the atmosphere was added immediately after the treatment step in this weakly oxidizing atmosphere to make a multilayer capacitor in the same manner as in the first embodiment. When the electrical characteristics were measured, the following results were obtained. Atmospheric oxidation temperature is 500 ° C, time is 6
At 0 minutes, ε is 13000, tan δ is 1.4%,
V1 was 190 V / mm and α was 13. When the temperature of the atmospheric oxidation treatment is 600 ° C and the time is 30 minutes, ε is 1
2000, tan δ 1.5%, V1 190V / mm, α
Was 14. When the temperature of the oxidation treatment in the atmosphere is 700 ° C. and the time is 30 minutes, ε is 12000 and tan δ is 1.
5%, V1 was 210 V / mm, and α was 14. If the temperature of the atmospheric oxidation treatment is 800 ° C and the time is 30 minutes,
ε is 11000, tan δ is 1.7%, V1 is 230V /
mm and α were 13. Atmospheric oxidation temperature is 900
When ℃ and time are 30 minutes, ε is 10,000, tan δ
Was 2.8%, V1 was 250 V / mm, and α was 11.
When no atmospheric oxidation treatment is performed, ε is 13000, ta
n δ was 1.4%, V1 was 170 V / mm, and α was 12. As is clear from this example, the temperature is 800 ° C. in the atmosphere.
When heat treatment is performed at the following low temperature, V1 and α can be improved. However, the heat treatment temperature in the atmosphere is 90
At 0 ° C., oxidation of the nickel electrode begins and tan δ deteriorates.

[0033]

MODIFICATION The present invention is not limited to the above-mentioned embodiments, and the following modifications are possible. (1) The external electrode 4 can be formed of Ni, Ag, Cu or the like other than Zn. (2) The external electrode 4 can be obtained by applying a conductive paste such as Ni to the side surface of the laminate before firing and baking the same at the same time as firing. (3) SiO ₂ and B ₂ O for enabling low temperature sintering
Glass components such as ₃ , Al ₂ O _{3 and the} like can be included in the porcelain raw material. (4) It can be applied to porcelain capacitors other than strontium titanate type. (5) The firing temperature in the reducing atmosphere can be variously changed within the range of 850 ° C to 1400 ° C.

[Brief description of drawings]

FIG. 1 is a plan view showing a state in which a conductive paste is applied to a green porcelain sheet according to an example of the present invention.

FIG. 2 is a front view showing a method of laminating the green porcelain sheet of FIG.

FIG. 3 is a sectional view showing a part of the completed multilayer capacitor.

[Explanation of symbols]

1 porcelain raw sheet 2 Conductive paste coating layer

Claims (4)

[Claims] 1. A step of calcining a porcelain raw material containing a main component for obtaining a semiconductor porcelain or a substance for obtaining the main component and a semiconducting promoter in an oxidizing atmosphere, and the calcinated porcelain material. A step of forming a porcelain raw sheet using, a step of applying a conductive paste mixed with a substance for insulating the grain boundaries of the semiconductor porcelain on the main surface of the porcelain raw sheet, the conductive paste Laminating a plurality of green porcelain sheets coated with to form a laminated body, firing the laminated body in a reducing atmosphere to obtain a sintered body, and sintering the sintered body in a weakly oxidizing atmosphere. Medium, 900 ℃ ~ 1200 ℃
A method of manufacturing a grain boundary insulating type semiconductor multilayer ceramic capacitor, comprising: 2. After the step of heat-treating in the weakly oxidizing atmosphere, there is a step of further performing heat treatment in a range of 500 ° C. to 800 ° C. in an atmosphere having a stronger oxidizing property than the weakly oxidizing atmosphere. The method for manufacturing a grain boundary insulating type semiconductor multilayer ceramic capacitor according to claim 1. 3. The method for manufacturing a grain boundary insulation type semiconductor multilayer ceramic capacitor according to claim 1, wherein the conductive paste is a paste containing a base metal. 4. The method for manufacturing a grain boundary insulation type semiconductor multilayer ceramic capacitor according to claim 1, 2 or 3, wherein the conductive paste contains a glass component capable of diffusing into the porcelain.