Murata Manufacturing Co., Ltd.

Kenjirou Mihara

Hideaki Niimi

Atsushi Kishimoto

Yuichi Takaoka

Hayato Katsu

Kenji Nagareda

A multilayer positive temperature coefficient thermistor includes a ceramic body having semiconductor ceramic layers and internal electrodes, the semiconductor ceramic layers being mainly composed of BaTiOand containing semiconductor-forming agents, the semiconductor ceramic layers and the internal electrodes being alternately stacked, and the outermost layers of the ceramic body being formed of the semiconductor ceramic layers. The outermost layers serve as protective layers. The semiconductor ceramic layers arranged between the internal electrodesandserve as effective layers. The protective layers contain a semiconductor-forming agent having a larger ionic radius than that of a semiconductor-forming agent contained in the effective layers. The protective layers have a lower porosity than that of the effective layers.

Multilayer positive temperature coefficient thermistor

A barium titanate-based semiconductor ceramic composition and a PTC element that have a high Curie temperature and a low electrical resistivity at room temperature and that exhibit a desired rate of change in resistance are provided. The barium titanate-based semiconductor ceramic composition is a ceramic composition having a perovskite structure containing at least barium and titanium, wherein some of the barium is replaced with an alkali metal element, bismuth, and a rare earth element, and when the content of the titanium is assumed to be 100 parts by mole, a ratio of the content of the alkali metal element to the content of the bismuth plus the content of the rare earth element represented by parts by mole, is 1.00 or more and 1.06 or less. A PTC thermistor includes a ceramic body composed of the barium titanate-based semiconductor ceramic composition having the above feature and electrodes disposed on both side faces of the ceramic body.

Barium titanate-based semiconductor porcelain composition and PTC element including the same

A multilayer positive temperature coefficient thermistor that has semiconductor ceramic layers containing a BaTiO-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 that has a BaTiO-based ceramic material contained as a primary component in semiconductor ceramic layers, the ratio of the Ba site to the Ti site is in the range of 0.998 to 1.006, and at least one element selected from the group consisting of La, Ce, Pr, Nd, and Pm is contained as a semiconductor dopant. In this multilayer positive temperature coefficient thermistor, a thickness d of internal electrodes layer and a thickness D of the semiconductor ceramic layers satisfy d&#x2267;0.6 &#x3bc;m and d/D&#x3c;0.2. Accordingly, even when the semiconductor ceramic layers have a low sintered density such that an actual-measured sintered density is 65% to 90% of a theoretical sintered density, a multilayer positive temperature coefficient thermistor having a low rate of temporal change in room-temperature resistance can be obtained without performing any complicated processes, such as a heat treatment. When the content of the semiconductor dopant is 0.1 to 0.5 molar parts with respect to 100 molar parts of Ti, a low-temperature firing at 1,150&#xb0; C. can be realized, and a low room-temperature resistance and a sufficiently high rate of resistance change can be obtained.

A method of producing a laminated PTC thermistor involves alternately laminating electroconductive pastes to form internal electrodes and ceramic green sheets to form semiconductor ceramic layers with a positive resistance-temperature characteristic to form a laminate, firing the laminate to form a ceramic piece, and forming external electrodes on both of the end-faces of the ceramic piece, and heat-treating the ceramic piece having the external electrodes formed thereon at a temperature between about 60&#xb0; C. and 200&#xb0; C.

Method of producing laminated PTC thermistor

A semiconductor ceramic for thermistors contains zinc oxide and titanium oxide as main components and a predetermined content of manganese. Also, a chip-type thermistor including the semiconductor ceramic is provided. By adding manganese, the resistance-temperature characteristic is controllable in the range of positive temperature coefficient to negative temperature coefficient. Also, by adding nickel, the resistivity is controllable. As a result, a thermistor material which provides a series of semiconductor ceramics having various resistivities and various B constants in a low range, for example 0 to 1,000 K, is available.

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Higashiomo, Japan

Kenjirou Mihara