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US 7,679,485 B2Granted
Multilayer positive temperature coefficient thermistor
AssigneeMurata Manufacturing Co., Ltd.
InventorsAtsushi Kishimoto, Kenjirou Mihara, Hideaki Niimi
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AssigneeMurata Manufacturing Co., Ltd.
InventorsAtsushi Kishimoto, Kenjirou Mihara, Hideaki Niimi
Estimating the term…
A multilayer positive temperature coefficient thermistor that has semiconductor ceramic layers containing a BaTiO3-based ceramic material as a primary component, and at least one element selected from the group consisting of Eu, Gd, Tb, Dy, Y, Ho, Er, and Tm as a semiconductor dopant in the range of 0.1 to 0.5 molar parts with respect to 100 molar parts of Ti. The ratio of the Ba site to the Ti site is in the range of 0.998 to 1.006. Accordingly, even when the semiconductor ceramic layers have a low actual-measured sintered density in the range of 65% to 90% of a theoretical sintered density, a multilayer positive temperature coefficient thermistor having a sufficiently high rate of resistance change and a high rising coefficient of resistance at the Curie temperature or more can be realized.
A multilayer positive temperature coefficient thermistor comprising:
A multilayer positive temperature coefficient thermistor comprising:
Dependencies are inferred from the claim text.
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Having positive temperature coefficient: formed with two or more layers
Containing oxides or oxidic compounds, e.g. ferrites: perovskites, e.g. titanates
Non-adjustable resistors formed as one or more layers or coatings; Non-adjustable resistors made from powdered conducting material or powdered…:…
Resistors
Term ended 20 Sep 2026 (estimated)
The present invention relates to a multilayer positive temperature coefficient thermistor used for overcurrent protection, temperature detection, and the like, and more particularly relates to a multilayer positive temperature coefficient thermistor which has a high rate of resistance change and which improves a rising coefficient of resistance at the Curie temperature or more.
In recent years, the sizes of electronic devices have been progressively decreased, and concomitant therewith, the decreasing in size of positive temperature coefficient thermistors mounted in the above-mentioned electronic devices has also been implemented. The positive temperature coefficient thermistor described above has a positive resistance temperature characteristic, and as a decreased in size positive temperature coefficient thermistor, for example, a multilayer positive temperature coefficient thermistor is known.
This type multilayer positive temperature coefficient thermistor described above generally has a ceramic body which includes a plurality of semiconductor ceramic layers each having a positive resistance temperature characteristic and a plurality of internal electrode layers formed along interfaces between the semiconductor ceramic layers, the internal electrode layers are alternately extended to two end portions of the ceramic body, and external electrodes are also formed so as to be electrically connected to the internal electrode layers thus extended. In addition, as the semiconductor ceramic layer, a material primarily containing a BaTiO3-based ceramic material is used. Furthermore, in order to obtain a positive resistance temperature characteristic by a BaTiO3-based ceramic material, an extremely small amount of a semiconductor dopant is added thereto, and as this semiconductor dopant, in general, samarium (Sm) has been widely used.
FIG. 1 is a schematic cross-sectional view schematically showing one embodiment of a multilayer positive temperature coefficient thermistor according to the present invention.
FIG. 2 is an enlarged view of the a portion A in FIG. 1.
2 semiconductor ceramic layer 3a, 3b internal electrode layer 4 ceramic body 5a, 5b external electrode
Next, an embodiment of the present invention will be described in detail.
FIG. 1 is a schematic cross-sectional view showing one embodiment of a multilayer positive temperature coefficient thermistor of the present invention.