JP3198876B2 - Semiconductor porcelain, manufacturing method thereof, and positive temperature coefficient thermistor - 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 semiconductor porcelain and a method for producing the same.

[0002]

2. Description of the Related Art A barium titanate-based semiconductor porcelain having a positive resistance temperature characteristic (hereinafter referred to as a semiconductor porcelain) has a characteristic that the resistance value rapidly increases above the Curie point and is used for starting a motor. It is widely used for degaussing CRTs, heaters, and other uses of color television receivers. However, this type of semiconductor porcelain has a problem in that when an inrush current that exceeds a destruction characteristic with respect to an inrush current when a voltage is applied (hereinafter, referred to as an inrush withstand voltage characteristic) flows, the semiconductor ceramic is broken down into layers.

[0003] Such a phenomenon occurs because the outside portion of the semiconductor porcelain is in contact with the outside air, so that the heat diffusion is fast, and the temperature of the portion becomes low, resulting in low resistance. This is because heat diffusion is slower in the portion than in the outer portion, resulting in high resistance, and the semiconductor porcelain generates heat unevenly. Therefore, as a method for manufacturing a semiconductor porcelain that does not cause such porcelain destruction, as described in JP-A-4-154661, after firing in air, reduction is performed, and reoxidation is performed in air. A method was proposed.

[0004]

However, in the method of reducing and reoxidizing semiconductor porcelain, if the reoxidation is insufficient, the withstand voltage is low, and if the reoxidation proceeds, the specific resistance at room temperature increases. There was a problem.

An object of the present invention is to provide a semiconductor porcelain which has excellent inrush withstand voltage characteristics and hardly causes porcelain destruction, and a method of manufacturing the same.

According to a first aspect of the present invention, in a barium titanate-based semiconductor porcelain having a positive resistance temperature characteristic, a resistance value between a surface portion and a center portion of the semiconductor porcelain is equal to a surface portion and a center portion of the semiconductor porcelain. Semiconductor porcelain having a resistance value higher than

According to a second aspect of the present invention, there is provided a semiconductor porcelain wherein the resistance between the surface and the center of the semiconductor porcelain is 15 to 68% higher than the resistance of the surface and the center.

According to a third aspect of the present invention, the semiconductor porcelain is a barium titanate-based semiconductor porcelain containing lead oxide, strontium oxide, and calcium oxide.

According to a fourth aspect of the present invention, in the step of firing a barium titanate-based semiconductor porcelain having a positive resistance temperature characteristic, the temperature is lowered by 110 ° C. after reaching the maximum firing temperature.
The holding temperature is set between 0 and 1200 ° C. and 0.4 to 10
Hold for a while and from the maximum firing temperature to the holding temperature.
The temperature lowering process and the subsequent temperature lowering process from the holding temperature
This is a method for manufacturing a semiconductor porcelain that lowers the temperature at an arbitrary rate .

According to a fifth aspect of the present invention, in the step of firing a barium titanate-based semiconductor porcelain having a positive resistance temperature characteristic, the temperature is lowered by 110 ° C.
The temperature is lowered from 0 to 1200 ° C. at a slow cooling rate of 1.0 ° C./min or less, and the temperature is lowered from the maximum firing temperature to 1200 ° C.
The temperature process and the subsequent cooling process from 1100 ° C are gradually cooled.
This is a method for manufacturing a semiconductor porcelain in which the temperature is lowered at a higher rate than the rate . The invention according to claim 6 provides at least claim 1
4. The semiconductor porcelain according to claim 3, wherein
Consists of a pair of terminal electrodes formed on the surface of conductive porcelain
Is a positive characteristic thermistor .

[0011]

According to the semiconductor porcelain of the present invention, the inrush breakdown voltage characteristics can be improved by making the distribution of resistance values different in the thickness direction. According to the method for manufacturing a semiconductor porcelain of the present invention, by gradually cooling or holding the semiconductor porcelain in the temperature decreasing process, the distribution of the resistance value can be varied in the thickness direction of the semiconductor porcelain, thereby improving the inrush breakdown voltage characteristics. Can be planned.

[0012]

EXAMPLE First, (Ba _0.536 Pb _0.08 Sr _0.20 Ca
_0.18 Er _0.004 ) TiO ₃ + 0.0004Mn + 0.02
As a composition of _{SiO 2, BaCO 3, SrCO 3} ,
Pb ₃ O ₄ , CaCO ₃ , TiO ₂ , Er ₂ O ₃ , MnCO ₃
And SiO ₂ were weighed. Put these in a polyethylene pot together with pure water and zirconia balls,
After crushing and mixing for hours, dehydration and drying were performed and calcined at 1150 ° C. for 2 hours to obtain a calcined powder. Put this calcined powder together with pure water and zirconia balls into a polyethylene pot
Crushed for hours. Thereafter, a vinyl acetate-based binder was mixed with the mixture and granulated.

Next, the diameter is 18 mm and the thickness is 3.
A 6 mm compact was prepared, baked at 1360 ° C. for 1 hour, and cooled under the conditions shown in Table 1 to obtain a semiconductor porcelain. A nickel layer exhibiting ohmic properties to be terminal electrodes was formed on both surfaces of the obtained semiconductor ceramic by electroless plating, a silver paste was applied to the outermost layer, and baked at 600 ° C. for 30 minutes to obtain a positive temperature coefficient thermistor. .

The cooling conditions shown in Table 1 indicate the conditions for cooling from the highest firing temperature to room temperature.
Is cooled from the maximum firing temperature to the holding temperature at a rate of the temperature decreasing rate, the holding temperature is maintained at the holding temperature for the holding time, and the temperature is cooled from the holding temperature to room temperature. In addition, sample numbers 27 to 30
Is cooled from the highest firing temperature to 1200 ° C. at a temperature decreasing rate, and is cooled at a rate of a slow cooling rate from 1200 to 1100 ° C., and is cooled from 1100 ° C. to room temperature. Further, the sample numbers 31 and 32 are cooled from the maximum firing temperature to the room temperature at a constant cooling rate.

[0015]

[Table 1]

Using this positive temperature coefficient thermistor, specific resistance,
The resistance value per unit thickness, the inrush withstand voltage characteristic, and the resistance value ratio were measured. Here, the inrush withstand voltage characteristic is a value obtained from the following equation, and the resistance value ratio is a resistance value (maximum resistance value) that is the maximum between the surface portion and the center portion of the positive temperature coefficient thermistor. It is a value obtained from the ratio of the minimum resistance value (minimum resistance value) at the center of the positive characteristic thermistor. Inrush withstand voltage characteristics = (breakdown voltage) ² / normal temperature resistance Table 2 shows the measurement results. The * marks are outside the scope of the present invention, and those without the * marks are within the scope of the present invention.

[0017]

[Table 2]

FIG. 1 schematically shows a change in resistance per unit thickness from one main surface to the other main surface of the positive temperature coefficient thermistor of the present invention. As can be seen from FIG. 1, it is understood that the positive temperature coefficient thermistor has a low resistance value between the central portion and both surface portions and a high resistance value between the central portion and the surface portion.

FIG. 2 shows the relationship between the resistance value ratio and the inrush withstand voltage characteristics. From FIG. 2, the resistance value between the surface portion and the central portion is 15 to 68% of the resistance value at the central portion.
The results show that the semiconductor porcelain having a high region (resistance ratio = 1.15 to 1.68) has excellent inrush withstand voltage characteristics.

FIG. 3 shows the relationship between the holding temperature and the inrush withstand voltage characteristic in the temperature decreasing process. FIG.
Thus, the rush withstand voltage characteristics are good in the temperature holding range of 1100 to 1200 ° C. in the temperature decreasing process. In addition, even when the temperature is gradually cooled in the temperature range, a material having excellent inrush withstand voltage characteristics is obtained.

[0021]

The semiconductor porcelain according to the present invention has an excellent rush withstand voltage characteristic by making the resistance value distribution per unit thickness different, and exhibits an effect of not being destroyed even at a high voltage.

The resistance between the surface and the center of the semiconductor porcelain is 15 to 68 times smaller than the resistance of the surface and the center.
By being higher, porcelain breakage does not occur at a high voltage, and is suitable for use in overcurrent protection of a circuit.

Further, by using a barium titanate-based semiconductor porcelain containing lead oxide, strontium oxide, and calcium oxide, the resistance between the surface and the center of the semiconductor porcelain is higher than the resistance of the surface and the center. Also 15-68
% Can be made more remarkable, and can be widely used for overcurrent protection, degaussing, and the like of a circuit, which does not cause porcelain breakdown at a high voltage.

According to the method for manufacturing a semiconductor porcelain of the present invention, the resistance value per unit thickness of the semiconductor porcelain is changed by gradually cooling or maintaining the temperature in the process of lowering the temperature, thereby applying a high voltage. In addition, it is possible to obtain a semiconductor porcelain which is less likely to cause porcelain destruction and has excellent inrush withstand voltage characteristics.

[Brief description of the drawings]

FIG. 1 schematically shows a change in resistance value per unit thickness from one main surface to another main surface of a positive temperature coefficient thermistor obtained by a semiconductor ceramic according to the present invention.

FIG. 2 shows the relationship between the resistance value ratio and the inrush withstand voltage characteristic of the semiconductor ceramic of the present invention.

FIG. 3 shows the relationship between the temperature and the inrush withstand voltage characteristic of the semiconductor porcelain of the present invention during the temperature drop process.

────────────────────────────────────────────────── ─── Continuation of the front page (56) References JP-A-4-154661 (JP, A) JP-A-5-294625 (JP, A) JP-A-5-254928 (JP, A) (58) Field (Int.Cl. ⁷ , DB name) C04B 35/42-35/49 H01C ⁷ /02-7/22 C04B 35/00-35/22

Claims (6)

(57) [Claims] 1. A semiconductive ceramic barium titanate having a positive resistance-temperature characteristic, the resistance value between the surface portion and the central portion of the semiconductor porcelain, Oyo surface portion of the semiconductor ceramic
Semiconducting ceramic, wherein the higher than the resistance value of the fine center. 2. A resistance value between a surface portion and a center portion of the semiconductor porcelain is 1 more than a resistance value of the surface portion and the center portion.
The semiconductor porcelain according to claim 1, wherein the height is 5 to 68% higher. 3. The semiconductor porcelain according to claim 1, wherein the semiconductor porcelain is a barium titanate containing lead oxide, strontium oxide, and calcium oxide. 4. In a step of firing a barium titanate-based semiconductor porcelain having a positive resistance temperature characteristic, a holding temperature is set between 1100 and 1200 ° C. in a temperature decreasing process after reaching a maximum firing temperature. A method for manufacturing a semiconductor porcelain, wherein the temperature is maintained at 4 to 10 hours, and the temperature is decreased at an arbitrary rate in a temperature decreasing process from the maximum firing temperature to the holding temperature and a subsequent temperature decreasing process from the holding temperature. 5. A step of firing a barium titanate-based semiconductor porcelain having a positive resistance temperature characteristic, wherein a temperature between 1100 and 1200 ° C. is 1.0 ° C./min or less in a temperature decreasing process after reaching a maximum firing temperature. The temperature is lowered at a slow cooling rate, and the temperature is lowered from the maximum firing temperature to 1200 ° C. and 1100
A method for manufacturing semiconductor porcelain, wherein the temperature is lowered at a temperature lowering rate than the slow cooling rate in a subsequent temperature lowering process from a temperature of ° C. 6. A positive temperature coefficient thermistor comprising at least the semiconductor porcelain according to claim 1 and a pair of terminal electrodes formed on a surface of said semiconductor porcelain. .