JP3178083B2 - Barium titanate-based ceramic semiconductor and method for producing the same - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a barium titanate-based ceramic semiconductor exhibiting PTC characteristics (positive temperature coefficient characteristics) and a method for producing the same.

[0002]

2. Description of the Related Art A barium titanate-based ceramic semiconductor in which a small amount of Bi, Nb, W, Ta, Sb or a rare earth element is added to barium titanate (BaTiO ₃ ) is a P-based semiconductor.
It is conventionally known to have TC characteristics.

For example, JP-A-53-59888 discloses that barium titanate is added with a rare earth element, Ta, Nb or Sb, silicon dioxide (SiO ₂ ) is added, and firing is performed in the presence of oxygen. It is disclosed that a barium titanate-based ceramic semiconductor having excellent electric characteristics can be obtained by this.

Japanese Patent Application Laid-Open No. 53-75495 discloses that the above barium titanate-based ceramic semiconductor contains 1.0 to 5.0 mol% of excess titanium oxide (TiO ₂ ) and 0.5 to 10.0 mol% of silicon dioxide. It is described that the addition of mol% increases the breakdown voltage and makes it difficult to break even when subjected to a thermal shock.

In Japanese Patent Application Laid-Open No. 57-53902, the excess amount of titanium oxide is set to 0.5 to 2.0 mol%, and the addition amount of silicon dioxide is set to 0.5 to 2.5 mol%. It is disclosed that a barium titanate-based ceramic semiconductor having a double structure (a crystal structure in which large and small particles are mixed) can be obtained.
It is described that the withstand voltage is high and the current fluctuation is reduced.

[0006]

However, in the above-mentioned conventional structure, the structure particles have a large difference in particle diameter, and when a voltage is applied to the barium titanate-based ceramic semiconductor, the current density locally increases. As a result, there is a problem that local heating occurs and the barium titanate-based ceramic semiconductor may be destroyed by thermal stress at that time.

[0007]

According to a first aspect of the present invention, there is provided a barium titanate-based ceramic semiconductor, comprising: a semiconductor agent such as Bi or a rare earth element; In the barium titanate-based ceramic semiconductor containing titanium oxide, the sum of the added amount of silicon dioxide and the excess amount of titanium oxide is set to 2.0 to 4.0 mol%, and the porosity is 2%. It is characterized in that it is controlled as follows.

According to a second aspect of the present invention, there is provided a method for manufacturing a barium titanate-based ceramic semiconductor, wherein at least barium carbonate as a raw material and Bi
Or a semiconducting agent such as a rare earth element, and silicon dioxide,
A method for producing a barium titanate-based ceramic semiconductor by mixing and firing an excess titanium oxide, wherein the average particle diameter of the silicon dioxide is set to 10 μm or less.

[0009]

According to the first aspect of the present invention, in a barium titanate-based ceramic semiconductor containing a semiconducting agent such as Bi or a rare earth element, silicon dioxide, and excess titanium oxide, the amount of silicon dioxide added and the amount of titanium oxide Is set to 2.0 to 4.0 mol% and the porosity is controlled to 2% or less, resulting in a dense particle structure. Accordingly, since the particles constituting the structure have a uniform and fine particle diameter, local increase of the current density at the time of applying a voltage is less likely to occur, so that breakdown due to thermal stress up to a high voltage is less likely to occur.

According to the second aspect of the present invention, at least barium carbonate, a semiconducting agent such as Bi or a rare earth element, silicon dioxide, and excess titanium oxide are mixed as raw materials, and the mixture is calcined to obtain barium titanate. In the method for producing a ceramic ceramic semiconductor, a dense barium titanate ceramic semiconductor having a porosity of 2% or less can be produced since the average particle diameter of the silicon dioxide is set to 10 μm or less.

[0011]

DESCRIPTION OF THE PREFERRED EMBODIMENTS One embodiment of the present invention will be described below with reference to FIGS.

In this embodiment, barium carbonate (BaC)
O ₃ ), strontium carbonate (SrCO ₃ ), titanium oxide (TiO ₂ ), silicon dioxide (SiO ₂ ), manganese carbonate (MnCO ₃ ), dysprosium oxide (Dy ₂ O)
₃ ) was blended with the compositions (mol%) of Tables 1 to 5 to prepare barium titanate-based ceramic semiconductor samples.

Barium carbonate and titanium oxide are main components of a barium titanate-based ceramic semiconductor, and these constitute a skeleton of barium titanate. Excess titanium oxide stabilizes the barium titanate-based ceramic semiconductor.

Sr, a component of strontium carbonate, is
By substituting with Ba of the barium titanate skeleton, the Curie point of the barium titanate-based ceramic semiconductor can be shifted. Silicon dioxide stabilizes a barium titanate-based ceramic semiconductor, like excess titanium oxide. Mn, which is a component of manganese carbonate, acts as a so-called mineralizer for increasing the grain boundary barrier. Thereby, the specific resistance at room temperature can be controlled. Dy, which is a component of dysprosium oxide, acts as an impurity for converting barium titanate into a semiconductor, and can control the specific resistance at room temperature, like Mn.

[0015]

[Table 1]

[0016]

[Table 2]

[0017]

[Table 3]

[0018]

[Table 4]

[0019]

[Table 5] Next, a method of manufacturing the barium titanate-based ceramic semiconductor sample will be described.

First, the above-mentioned composition was put into a ball mill together with ion-exchanged water and an iron ball coated with nylon, and wet-mixed for 24 hours. Then, this was filtered, dried, and calcined at a temperature of 1100 to 1150 ° C for 1 to 5 hours. Next, the calcined sample was crushed, and an aqueous solution containing 2% by weight of polyvinyl alcohol (PVA) as a binder was added to the crushed sample to form a slurry, which was then granulated and dried by a spray drier.

The granulated powder is filled in a disc-shaped molding machine, and is pressed at a pressure of 1.0 ton / cm ² to form a powder having a diameter of 1 ton / cm ^2.
It was formed into a 6.4 mm, 2.5 mm thick disk. Then, the molded product is packed in a sintering sheath, heated in an electric furnace at a rate of 3 ° C./min, held at 1300 to 1380 ° C. for 0 to 10 hours, and then baked at a temperature of 3 to 0.5 ° C./min. Cooled at speed.

As described above, the diameter is 13.5 mm and the thickness is
A 2.0 mm disc-shaped sample was prepared.

A silver paste and a silver paste for a cover were baked on both surfaces of the sample to form ohmic contact electrodes, and the specific resistance, breakdown voltage, PTC characteristics, and porosity were measured.

The measuring methods are as follows.

(1) Measuring method of specific resistance A sample was attached to a sample holder for measurement, and a measuring tank (MINI-SUBZERO M manufactured by Tabi Espec Co., Ltd.) kept at 25 ° C.
C-810P), and the electric resistance was measured using a DC resistance meter (multimeter 3878A) manufactured by Yokogawa Hewlett-Packard Company.

The diameter and thickness of the sample were measured in advance, and the specific resistance (ρ) was calculated by the following equation. ρ = RS · t / ρ: Specific resistance (Ωcm) R: Measured value of electric resistance (Ω) S: Area of electrode (cm ² ) t: Thickness of sample (cm) (2) Measuring method of breakdown voltage Attach the sample to the sample holder for measurement, and use the Takasago AC stabilized power supply (FREQU-ENCY CONVERSION AC POWER SUPPL).
Y AA330F, FR-EQUENCY / VOLTAGE CONTROLLER FOA1MG),
Hewlett-Packard AC resistance meter (multimeter 3457A) and AC ammeter (multimeter AD
VANTEST), and the current was measured while gradually increasing the applied voltage from 100 mV.

Then, the current value was plotted against the applied voltage, and the voltage showing the minimum value of the current was defined as the breakdown voltage.

(3) Method of Measuring PTC Characteristics A sample is mounted on a sample holder for measurement and mounted in the above-mentioned measuring tank, and the change in the electrical resistance of the sample with respect to a temperature change from −50 to 180 ° C. is measured as described above. It was measured using a DC resistance meter.

Then, similarly to the above (1), the specific resistance was calculated, and the specific resistance was plotted against the temperature. And
The specific resistance when rising sharply near the Curie point,
Find the ratio with the specific resistance at 25 ° C,
The scale was used to evaluate the effect. The larger this is,
This indicates that the rise width of the specific resistance is large.

(4) Method of Measuring Porosity True density was measured by a dry automatic densitometer manufactured by Shimadzu Corporation, and the porosity was determined by the following equation. P = ((ρ _t −ρ _a ) / ρ _t ) × 100 [%] P: Porosity ρ _t : True density ρ _a : Bulk density For the samples having the compositions shown in Tables 1 to 5, the above-mentioned measurement method is used. Tables 6 to 10 show the measurement results of the specific resistance, the breakdown voltage, the PTC effect, and the porosity obtained by the method. Further, based on the measurement results, the suitability as a barium titanate-based ceramic semiconductor was determined, and the results were shown in three stages of △, Δ, and × in order from the most suitable one.

Table 6 shows that, as is clear from the composition of Table 1,
It shows changes in various physical properties when the amount of dysprosium oxide added was changed.

Samples Nos. 1 to 7 are comparative examples. In these samples, although the specific resistance is low, PT
C effect and breakdown voltage are not enough. At the time of sintering, if the cooling rate is reduced, the specific resistance can be controlled to 30 to 50 Ωcm, but the PTC effect and the breakdown voltage are not significantly improved.

FIG. 3 shows an electron micrograph showing the particle structure of Sample No. 7. The magnification is 500 times.

[0034]

[Table 6] Table 7 shows changes in various physical properties when the excess amount of titanium oxide was changed, as is clear from the composition in Table 2.

[0035]

[Table 7] Sample No. 8 shows a comparative example, which is not practical because both the PTC effect and the breakdown voltage are low despite the high specific resistance.

On the other hand, in samples Nos. 10 to 14 in which the excess amount of titanium oxide was increased, both the PTC effect and the breakdown voltage were greatly improved. However, when the excess amount of titanium oxide is too large, the characteristics are deteriorated as in the sample of sample No. 15.

Table 8 shows that, as is clear from the composition of Table 3,
The graph shows changes in various physical properties when the addition amount of silicon dioxide is changed.

[0038]

[Table 8] Sample No. 16 shows a comparative example, which is not practical because both the PTC effect and the breakdown voltage are low despite the high specific resistance.

On the other hand, in the samples of Sample Nos. 18 to 21 in which the excess amount of titanium oxide was increased, both the PTC effect and the breakdown voltage were greatly improved. However, when the addition amount of silicon dioxide was set to 3.5 mol% or more, Sample No. 22
In contrast, only the specific resistance is increased as in the sample (1), and conversely, the characteristics are deteriorated.

FIGS. 1 and 2 show electron micrographs showing the particle structure of Sample No. 19. The magnification of FIG. 1 is 500 times and the magnification of FIG. 2 is 1000 times.

Table 9 shows changes in various physical properties when the amount of manganese added was changed, as is apparent from Table 4.

It can be seen that when the amount of manganese added is 0.08 mol% or more, the specific resistance sharply increases as in the sample of sample No. 26, making it impractical.

[0043]

[Table 9] Table 10 shows changes in various physical properties when the average particle diameter of silicon dioxide was changed, as is clear from Table 5.

A comparison was made between the sample No. 19 using silicon dioxide having an average particle diameter of 5 μm as a raw material and the sample No. 27 using silicon dioxide having an average particle diameter of 40 μm as a raw material. As the resistance decreased, the breakdown voltage decreased, and the porosity greatly increased. Also, comparing the sample of sample No. 19 with the sample of sample No. 28 using silicon dioxide having an average particle diameter of 0.012 μm as a raw material, the sample of sample No. 28 has a higher breakdown voltage with respect to the specific resistance, and has a lower porosity. Significantly reduced.

It is also found that the porosity of the barium titanate-based ceramic semiconductor can be controlled to 2% or less when silicon dioxide having an average particle diameter of 10 μm or less is used as a compounding material.

[0046]

[Table 10] From the above results, in the raw material of the barium titanate-based ceramic semiconductor, the excess amount of titanium oxide was set to 0.8 to 3.5 mol%, and the addition amount of silicon dioxide was set to 0.5 to 3.0 mol%. And the total amount of both is set to be 2.0 to 4.0 mol%, and the amount of manganese added is set to 0.04 to 0.4 mol%.
By setting the molar ratio to 07 mol%, the liquid phase component can be optimized. That is, a sufficient liquid phase is generated at a high temperature. This allows each particle to intervene without contact
Can be sintered.

Further, by setting the average particle size of silicon dioxide as a raw material to 10 μm or less, the porosity becomes 2% or less, and a barium titanate-based ceramic semiconductor having a uniform particle size can be obtained.

For this reason, the barium titanate-based ceramic semiconductor of this embodiment has a low specific resistance and
The PTC effect and breakdown voltage become very high. Also, the current-
Voltage characteristics are stable, do not show varistor characteristics, and the reproducibility of resistance-temperature characteristics is high. Therefore, it can withstand use under a high voltage and use under a condition of a large thermal shock.

Further, at the time of firing, if the temperature decreasing rate is reduced,
Since the diffusion of oxygen to the grain boundaries is promoted, the potential barrier is increased. For this reason, although the specific resistance increases, the breakdown voltage can be further increased.

[0050]

As described above, in the barium titanate-based ceramic semiconductor according to the first aspect of the present invention, the sum of the added amount of silicon dioxide and the excess amount of titanium oxide is set to 2.0 to 4.0 mol%. And the porosity is controlled to 2% or less, resulting in a dense particle structure. As a result, local increase in current density during voltage application is less likely to occur, so that there is an effect that breakdown due to thermal stress does not easily occur up to a high voltage.

In the method for producing a barium titanate-based ceramic semiconductor according to the first aspect of the present invention, as described above, since the average particle diameter of the raw material silicon dioxide is set to 10 μm or less, the porosity is 2%. The following barium titanate-based ceramic semiconductor can be produced.

[Brief description of the drawings]

FIG. 1 is an electron micrograph showing a particle structure of a barium titanate-based ceramic semiconductor of Sample No. 19 of the present invention.

FIG. 2 is an electron micrograph showing the particle structure of a barium titanate-based ceramic semiconductor in which the particle structure of FIG. 1 is magnified twice.

FIG. 3, which shows a comparative example, is an electron micrograph showing the particle structure of a barium titanate-based ceramic semiconductor of Sample No. 7.

 ──────────────────────────────────────────────────続 き Continuation of front page (56) References JP-A-53-75495 (JP, A) JP-A-2-142101 (JP, A) JP-A 64-22001 (JP, A)

Claims (2)

(57) [Claims] 1. A semiconducting agent such as Bi or a rare earth element,
In a barium titanate-based ceramic semiconductor containing silicon dioxide and excess titanium oxide, the sum of the added amount of silicon dioxide and the excess amount of titanium oxide is 2.
0 to 4.0 mol%, and the porosity is 2%
A barium titanate-based ceramic semiconductor which is controlled as follows. 2. A raw material comprising at least barium carbonate and B
a method for producing a barium titanate-based ceramic semiconductor by mixing and firing a semiconductor agent such as i or a rare earth element, silicon dioxide, and an excess of titanium oxide, wherein the silicon dioxide has an average particle size of 10 μm A method for producing a barium titanate-based ceramic semiconductor, which is set as follows.