Barium titanate-based semiconductive ceramic composition

Details Barium titanate-based semiconductive ceramic composition Barium titanate-based semiconductive ceramic composition

1999-05-20

2001-02-13

Brunsman, David (Department: 1755)

Compositions: ceramic

Ceramic compositions

Titanate, zirconate, stannate, niobate, or tantalate or...

Reexamination Certificate

active

06187707

ABSTRACT:

TECHNICAL FIELD
The present invention generally relates to semiconductive ceramic compositions, and more specifically to a barium titanate-based semiconductive ceramic composition.
BACKGROUND ART
The following conventional barium titanate-based semiconductive ceramic compositions are known. Japanese Patent Publication No. 62-43522 discloses a barium titanate-based semiconductive ceramic composition, which is substantially composed of BaTiO
3
or in which Pb is partly substituted for Ba, and which contains 0.00035 to 0.0072 percent by weight of magnesium when the weight of the composition is 100, for the purpose of increasing withstand voltage.
Japanese Patent Publication No. 63-28324 discloses a barium titanate-based semiconductive ceramic composition containing 30 to 95 mole percent of BaTiO
3
as the major component, 3 to 25 mole percent of CaTiO
3
, 1 to 30 mole percent of SrTiO
3
, and 1 to 50 mole percent of PbTiO
3
, in which a fraction of Ba is replaced with Ca, Sr and Pb in order to improve withstand voltage and rush current resistance characteristics.
Furthermore, Japanese Patent Publication No. 62-58642 discloses a semiconductive ceramic composition having a rush current which is not large, and a positive resistance-versus-temperature property with a small change over time in an intermittent test, in which Ba in barium titanate is replaced with 1 to 50 mole percent of Pb and 0.1 to 1.0 mole percent of Mg.
Japanese Patent Application Laid-Open No. 2-48464 discloses a semiconductive ceramic composition, in which a fraction of the Ba in BaTiO
3
is replaced with 0.001 to 0.1 atomic percent of Mg and 0.01 to 2.0 atomic percent of Ca, a fraction of Ba is replaced with 0.01 to 5.0 atomic percent of Pb and 0.01 to 20 atomic percent of Ca, or a fraction of Ba is replaced with 0.001 to 0.1 atomic percent of Mg, 0.01 to 5.0 atomic percent of Pb, and 0.01 to 2.0 atomic percent of Ca to reduce a change in resistance with temperature within an operational environment temperature range and to reduce specific resistance at ordinary temperatures.
Japanese Patent Application Laid-Open No. 2-48465 discloses a barium titanate-based semiconductive ceramic composition, in which a fraction of the Ba in BaTiO
3
is replaced with 0.001 to 0.1 atomic percent of Mg, a fraction of Ba is replaced with 0.01 to 5.0 atomic percent of Pb, or a fraction of Ba is replaced with 0.001 to 0.1 atomic percent of Mg and 0.01 to 5.0 atomic percent of Pb to reduce a change in resistance with temperature within an operational environment temperature range.
With miniaturization and high-density trends in recent electronic devices, miniaturization of positive coefficient thermistor devices composed of barium titanate-based semiconductive ceramic compositions used in the electronic devices has also progressed. However, miniaturization of positive coefficient thermistors causes deterioration of rush current resistance characteristics (flash withstand voltage characteristics); hence, no conventional positive coefficient thermistor meets commercial miniaturization requirements.
DISCLOSURE OF INVENTION
It is an object of the present invention to provide a barium titanate-based semiconductive ceramic composition having improved rush current resistance characteristics, thus facilitating miniaturization of positive coefficient thermistor devices.
The present invention has been completed to achieve such an object.
A barium titanate-based semiconductive ceramic composition in accordance with the present invention comprises a major component composed of barium titanate or a solid solution thereof, a semiconductivity-imparting agent, and an additive, wherein a fraction of the Ba in BaTiO
3
as the major component is replaced with 1 to 25 mole percent of Ca, 1 to 30 mole percent of Sr, and 1 to 50 mole percent of Pb, and wherein to 100 mole percent of the major component, the semiconductivity-imparting agent is added in an amount of 0.2 to 1.0 mole percent as a converted element content, and the additive comprises manganese oxide in an amount of 0.01 to 0.10 mole percent as a converted Mn content, silica in an amount of 0.5 to 5 mole percent as a converted SiO
2
content, and magnesium oxide in an amount of 0.028 to 0.093 mole percent as a converted Mg content.
In the barium titanate-based semiconductive ceramic composition in accordance with the present invention, the semiconductivity-imparting agent is preferably at least one element selected from the group consisting of Y, La, Ce, Nb, Bi, Sb, W, Th, Ta, Dy, Gd, Nd, and Sm.


REFERENCES:
patent: 55-046524 (1980-04-01), None
patent: 4042501 (1992-02-01), None
patent: 4104951 (1992-04-01), None
patent: 5051254 (1993-03-01), None
patent: 5070223 (1993-03-01), None

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