JPH04144961A - Porcelain composition and production thereof - Google Patents

Abstract

PURPOSE:To obtain the title composition excellent in both capacitor and varistor characteristics by forming, with electrical insulating layer consisting of an oxide containing Bi, Cu, Mn and Na, the crystal grain boundaries of a sintered compact comprising, as the chief components, SrTiO3 and CaTiO3 and, as minor components, Nb2O5 or Sb2O5 and CuO or MnO2. CONSTITUTION:The objective porcelain composition consisting of a sintered compact comprising (A) as the chief components, a total of 100mols of (1) 99-70mol% of SrTiO3 and (2) 1-30mol% of CaTiO3 and (B) as the minor components (3) 0.001-1.0mol of one or both of Nb2O5 and Sb2O5 and (4) 0.001-1.0mol of one or both of CuO and MnO2. For the present composition, the crystal grain boundaries and region close thereto are formed by electrical insulating layer consisting of an oxide containing Bi, Na and Mn, or Na, Mn and Cu, or Na and Mn. To produce the present composition, the surface of the above-mentioned sintered compact is coated with a pasty composition prepared by adding a solvent to a mixture of (a) 0-70mol% of Bi2O3 or CuO, (b) 1-70mol% of Na carbonate or oxide and (c) 1-70mol% of Mn carbonate or oxide into a pasty form, followed by calcining.

Description

[Detailed Description of the Invention] The present invention relates to a porcelain composition and a method for producing the same, and more specifically, the present invention relates to a porcelain composition and a method for producing the same. The present invention relates to a ceramic composition for forming an electronic component called a varistor, which is used to protect semiconductor components and circuits from abnormal high voltage, noise, pulses, static electricity, etc., and a method for manufacturing the same.

With the spread of information processing devices such as computers and OA equipment, the noise generated by these digital devices has increased
Malfunctions of semiconductor components such as transistors and transistors have become a problem, and semiconductor components also have the disadvantage of being easily destroyed by high voltages such as surges, pulses, and static electricity, so varistor elements are incorporated into electronic circuits. protection of the parts is being carried out.

A varistor is a functional element whose resistance value changes non-linearly depending on the applied voltage, and its voltage-current characteristic is I = kVc
It is represented by t. Here, ■ is the current value flowing through the element, k
is a varistor-specific coefficient, ■ is a voltage value applied to both ends of the varistor, and α is a coefficient indicating nonlinearity (nonlinear coefficient).

The evaluation of a varistor is expressed by a nonlinear coefficient α, and the larger the nonlinear coefficient α, the greater the varistor effect. The nonlinear coefficient α of the SiC varistor is 3 to 7, and the ZnO
The nonlinear coefficient α of the system varistor is as high as 50 to 100. However, conventional varistors such as SiC and ZnO type varistors have low capacitance and are therefore unable to absorb almost any noise having high frequency components.

On the other hand, ceramic capacitors have an apparent dielectric constant εap
It has a high p value, about 10 to 20 times that of ZnO-based varistors, and is therefore used to absorb and remove the above-mentioned noise, but on the other hand, it has the disadvantage of being weak against high voltage and being destroyed by surges, etc. Was. Therefore, a parallel circuit was constructed by combining a ZnO-based varistor and a capacitor, and the capacitor absorbed high-frequency noise, while the varistor absorbed and removed high voltage. However, it was very disadvantageous in terms of implementation. Therefore, a capacitive varistor, which has both capacitor and varistor characteristics in one element and whose main component is 5rTiOs, has been developed and put into practical use.

For capacitive varistors, 5rTi03 series (Japanese Patent Application Laid-Open No. 56-3
6103) or (Sr+-++Cax1T
There are xO3 series (Japanese Unexamined Patent Publication No. 57-187906) and the like. These capacitive varistors have Sr as the main component, and semiconducting agents such as Nb, Y, and La in addition to Ca as subcomponents.
, W, Ta, Dy, etc., and C as a nonlinear coefficient improver.
After adding a combination of u, Co, Mn, Ni, V, etc., and sintering aids such as Si, Aj, B, etc. and firing in a reducing atmosphere to obtain a porcelain sintered body, this porcelain sintered body is In order to form an insulating layer at the grain boundaries of , Na compounds and B2O3, SbgOs, Bi2O5,
Ti0z, MoOs, WO3, etc. are used (Japanese Patent Laid-Open No. 131501/1983).

As mentioned above, the conventional 5rTiOa-based varistor is a multi-functional element that has both varistor characteristics and capacitor characteristics, and is characterized by being small.
Suitable for protecting small electronic devices in which ICs, LSIs, etc. are incorporated. However, with the development of higher density electronic circuits and lower rated voltage technology, varistors with larger nonlinear coefficient α and lower varistor voltage, and capacitors with higher capacitance and lower dielectric loss have become available. desired.

Up to now, in order to obtain high capacitance and low varistor voltage, methods have been used to either reduce the thickness of the element body or to increase the size of crystal grains. but,
The method of reducing the thickness of the element body has its limits because the strength decreases, making the element more likely to break down electrically, and the withstand voltage decreases.Also, the method of increasing the size of the crystal grains causes abnormal grain growth during firing. Since this occurs and a uniform particle size cannot be obtained, there is a problem in that the nonlinear coefficient α decreases, the device becomes more likely to be electrically destroyed, and the withstand voltage decreases.

The present invention was invented in view of the above-mentioned problems, and
A ceramic composition for a high dielectric constant varistor that can obtain a functional element with a large apparent dielectric constant, that is, high capacitance, high breakdown voltage, large nonlinear coefficient a, and small dielectric loss and varistor voltage. The purpose is to provide products and methods of manufacturing them.

In order to achieve the above-mentioned objects, the porcelain composition according to the present invention contains 99-70 mol% of 5rTiOs, CaTiO3
For 100 mol of the main component consisting of 1-31-3O%, a small amount of NbzOs or 5bzOs (both 1
Seed 0.001-1.0mot and CuO or M
0.001 to 1.0 mo of at least one of nO□
A sintered body containing Bi, Na and Mn or Na, Mn at the grain boundaries and the vicinity of the grain boundaries.
and an insulating layer of an oxide containing Cu or Na and Mn.
a is 99-70 mol%, CaTiOs is 1-31-3
O! %, Nb2O
5 or at least one of Sb2O5 at 0.00
1-1.001-1.0 mol and CuO or M
0.001 to 1.0 mo of at least one of nO□
0 to 70 mol% of B12O3 or CuO, 1 to 70 may% of Na carbonate or oxide, and 1 to 70 mol% of Mn carbonate or oxide, on the surface of the sintered body containing 1 to 1 mol% of B12O3 or CuO.
The method is characterized in that a paste composition prepared by adding a solvent to a mixture at a ratio of 70 mol % is applied and then fired.

Placed porcelain is created through sintering in which solid-state diffusion is the main process, and crystal grains grow due to reactions between crystal grains accompanying this sintering. Among the characteristics of a varistor having capacitance, the characteristics as a varistor mainly utilize the characteristics of the grain boundaries between the crystal grains. Therefore, the varistor voltage ■1□ and the nonlinear coefficient α are determined by the nature and number of grain boundaries existing between the two electrodes.

On the other hand, the apparent dielectric constant ε1, which is a characteristic of a capacitor. Alternatively, using the grain boundary permittivity ε1, ε, p, = 81・
r/l, and the total capacitance C is given by C=ε,,p-S/d. Here, r: crystal grain size, t: thickness of grain boundary layer, S: electrode area, d: distance between electrodes, respectively.

Therefore, the capacitance C is proportional to the crystal grain diameter r and inversely proportional to the grain boundary layer thickness t.

In a 5rTiOs-based varistor with such a structure, when the crystal grain size is increased, the number of grain boundaries existing between the electrodes decreases, the varistor voltage decreases, and the apparent dielectric constant and capacitance decrease. growing. However, in general, 5rTiOa porcelain tends to cause abnormal grain growth and become a mixed grain structure, so in a structure with large crystal grains, the number of grain boundaries in the direction of current flow varies depending on the location, and the thickness of each grain boundary layer and This causes variations in component distribution. the result,
Variations occur in the voltage applied to each grain boundary and the height of the grain boundary barrier of each grain boundary. In such a structure, the nonlinear coefficient α, which is an index representing the sharpness of the rise of the current with respect to the applied voltage, and the breakdown voltage decrease. Therefore, in order to satisfy all the requirements of high capacitance, low varistor voltage, high nonlinear coefficient, high withstand voltage, and low dielectric loss, it is necessary to suppress abnormal grain growth and create a structure with uniform and large crystal grain size. At the same time, it is necessary to select a composition that creates grain boundaries in which oxygen, which contributes to the formation of grain boundary barriers, can easily diffuse uniformly at an appropriate concentration.

In the present invention described above, 5rTiOs is 99-mol%,
Main component 100 consisting of 1-31 to 3 g% of CaTi0a
NbJs or 5, which is a semiconducting agent,
At least one type of bzOs from 0.001 to 1.0m
ol, CuO or Mn0, which is a nonlinear coefficient improver
A sintered body containing 0.001 to 1.0 mol of at least one of g, Bi, Na, and M, which are grain boundary insulating diffusing agent substances, at and near the grain boundaries of the sintered body.
n or Na, lAn and Cu or Na and M
By forming an insulating layer of oxide containing n,
A ceramic composition for a high dielectric constant varistor having good dielectric properties, varistor properties, and electrical properties such as withstand voltage can be obtained. In addition, Biass or CuO is applied to the surface of the sintered body at 0-70-
70%, Na carbonate or oxide 1-70 mol%
, Mn carbonate or oxide in a ratio of 1 to 70 mol % by adding a solvent to a paste-like composition, and then baking it.
The above porcelain composition is easily obtained.

In addition, when the main component CaTiOs is less than 1 mol%,
The nonlinear coefficient α was not improved and was 3001 to 1.0 mol%.
If the varistor voltage exceeds
The preferred range is 1-3g% of l-30ml.

In addition, the content of NbzOs or sb, o is 0.0
If it is less than 0.01 mol, semiconductor formation will not proceed sufficiently, and the
When the amount exceeds mol, unreacted semiconducting agent segregates at grain boundaries,
The preferred content range of NbzOs or 5bzOs is 0.001 to 1.0 mol, since it significantly hinders the increase in resistance of grain boundaries in the diffusion process.

Furthermore, the content of CuO or Mn0t is 0.001
If it is less than mol, oxygen diffusion becomes non-uniform and the non-linear coefficient α is not improved. If it exceeds 1.0 mof, the apparent dielectric constant will decrease, so the preferred content range of CuO or MnO□ is 0.001 to 1.0 mol.

BiJ3, CuO, and carbonates or oxides of Na and Mn diffuse into the grain boundaries to make them highly resistive, and mainly contribute to improving the nonlinear coefficient α and breakdown voltage.

Examples of the porcelain composition for high dielectric constant varistors and the method for producing the same according to the present invention will be described below.

First, 5rC with a purity of 99% or more is adjusted so that the main components of 5rTiOa and CaTiOz are as shown in Table 1.
03, CaCO5 and TiO□ were weighed and blended,
Next, for the main component 100 moj, the purity is 99.
More than 9% Nb2O6.5biOs CuO and Mn0
The metal oxide powders of No. 2 were weighed and blended in the composition shown in Table 1, and mixed in a ball mill for 24 hours. After mixing, drying and pulverizing, 3 it% of a 10wt% polyvinyl alcohol aqueous solution was added and mixed as binggu, and the granulated powder was granulated into 80 mesh passes.
It was press-molded into a disk shape with a thickness of 0.8 mm and a thickness of 0.8 mm. After degreasing these molded bodies in air at a temperature of 1000°C, N2 (80-99voffi%)
1 to 20 voj%) in a reducing atmosphere of 1400 to 1
Firing was performed in a temperature range of 560° C. for 2 to 10 hours to obtain a sintered body.

On the other hand, BiJa, CuO, Mn2COx or N
A2O was weighed and mixed to have the composition shown in Table 1.

An equal amount of 100 parts by weight of an organic solvent containing ethyl cellulose as a main component was mixed with 100 parts by weight of this mixture, and the mixture was kneaded for 3 hours to obtain a diffusing agent paste.

Next, the diffusing agent paste was applied to one surface of the sintered body and dried. After that, heat treatment is performed at 1100°C for 1 hour in air or oxygen atmosphere to thermally diffuse oxides containing Bi, Cu, Mn or Na into the grain boundaries of the sintered body, creating a high dielectric constant porcelain. A composition was obtained. Here, Na2COs becomes NazO, and MnCO3 becomes Mn
It becomes O or MnO2 and diffuses into the grain boundaries.

Furthermore, in order to investigate the characteristics of the semiconductor ceramic composition,
Silver paste was applied to both sides and baked at a temperature of 800°C to form electrodes and complete the device.

In the above embodiments, for example, AQ, which is a mineralizer, is used within a range that does not impair the properties of the barista according to the present invention
20s, SiO□, etc. may be added.

Also, 5rTxOs, CaTiOs, Nb2O5.5b
205, CuO, MnO□, etc. are shown in the form of metal oxides corresponding to each component of the porcelain composition after firing, but it is sufficient if the desired metal oxide can be finally obtained, and the starting components are: Metal elements, carbonates, hydroxides, phosphates, nitrates,
Alternatively, oxalate may be used.

Further, although silver electrodes were formed on both surfaces of the sintered body, electrodes made of other known materials may be used. Further, the sintering conditions are not limited to those in the examples, but may be any conditions as long as the sintered body can be sufficiently converted into a semiconductor and the grain boundaries can be sufficiently insulated.

Regarding the semiconductor ceramic composition obtained with the composition shown in Table 1, the characteristics of the device were evaluated by nonlinear coefficient α, varistor voltage V + ma, apparent dielectric constant εapp, and dielectric loss t.
and[delta] was measured, and the results are shown in Table 1.

Note that the nonlinear coefficient α is the terminal voltage V when a current of ImA flows, and the terminal voltage V when a current of 10 mA flows. , and were determined by the following equation.

Further, the apparent dielectric constant ε, p9, and dielectric loss tan δ are values measured by applying IKH, ACIV.

(Margin below) In the table, those marked with * indicate those within the scope of the present invention, and all others indicate those outside the scope of the present invention.

As is clear from the table, the semiconductor ceramic composition for varistors within the scope of the present invention has a nonlinear coefficient a of 2.
6 or more, the varistor voltage V 1mA is 100V or less, the apparent dielectric constant εapp is large at 40,000 or more, the dielectric loss tan δ is low at almost 6% or less, and the withstand voltage is all 250V/mm or more, making it an excellent capacitor and varistor. It has multiple functions and pressure resistance.

As is clear from the above explanation, in the ceramic composition according to the present invention, 5rTiOs is 99-mol%, C
Main component 100 consisting of aTi0a of 1 to 31 to 30%
mol, Nb2O. Alternatively, by containing at least one kind of 5bzOs in a proportion of 0.001 to 1.0 moj, semiconductor formation is promoted, and at least one kind of CuO or MnO2 is contained in a proportion of 0.001 to 1.0 moj.
1. By containing it in a proportion of Omoj, a semiconductor ceramic composition having a grain boundary layer that promotes uniform diffusion of oxygen can be obtained, and the nonlinear coefficient α and breakdown voltage can be improved. In addition, the grain boundaries are Bi, Cu, Mn, Na
By forming the insulating layer of an oxide containing , it is possible to increase the resistance of the grain boundaries and further improve the nonlinear coefficient α and breakdown voltage.

Further, according to the method for producing a ceramic composition according to the present invention, a ceramic composition having excellent both capacitor properties and varistor properties can be obtained without impairing the processes of the prior art, and in particular, a ceramic composition with a high dielectric constant can be obtained. Also, a material having a large nonlinear coefficient α and exhibiting high pressure resistance was obtained. Therefore, not only can it be used as a single capacitor or a varistor, but it can also be used as a single element with the functions and voltage resistance of both a capacitor and a varistor, making it extremely effective for downsizing electrical and electronic equipment. It is possible to manufacture products with extremely high utility value in electrical and electronic equipment.

Patent applicant: Sumitomo Metal Industries, Ltd. Agent: Patent attorney Ryuji Iuchi

Claims (2)

[Claims] (1) SrTiO_3 is 99-70 mol%, CaTi
100 mol of main component consisting of 1 to 30 mol% O_3
0.001 to 1.0 mol of at least one of Nb_2O_5 or Sb_2O_5 and Cu
0.00 of at least one of O or MnO_2
A sintered body containing at a ratio of 1 to 1.0 mol, the grain boundaries and the vicinity of the grain boundaries being formed of an insulating layer of Bi, Na and Mn, or Na, Mn and Cu, or an oxide containing Na and Mn. A porcelain composition characterized by: (2) SrTiO_3 is 99 to 70 mol%, CaTi
100 mol of main component consisting of 1 to 30 mol% O_3
0.001 to 1.0 mol of at least one of Nb_2O_5 or Sb_2O_5 and Cu
0.00 of at least one of O or MnO_2
Bi_
Add a solvent to a mixture of 0 to 70 mol% of 2O_3 or CuO, 1 to 70 mol% of Na carbonate or oxide, and 1 to 70 mol% of Mn carbonate or oxide to form a paste. 2. The method for producing a porcelain composition according to claim 1, wherein the paste-like composition is applied and then fired.