JP2581754B2 - Oxide semiconductor composition for thermistor - Google Patents

Description

The present invention relates to a semiconductor for a thermistor, and more particularly to a metal oxide semiconductor composition for obtaining a thermistor having a negative temperature coefficient of resistance.

[Conventional technology]

Generally, a thermistor having a negative temperature coefficient of resistance is prepared by mixing oxides of metals such as manganese, cobalt, and nickel at an appropriate mixing ratio, molding and sintering to obtain a resistor chip, and attaching terminals and the like thereto. It is formed. The electrical characteristics of the thermistor thus obtained can be changed by variously changing the combination of metal elements contained in the material constituting the thermistor, the component ratio thereof, or the manufacturing conditions.

Such a thermistor is widely used for temperature measurement and the like by utilizing its resistance-temperature characteristic. One of the uses of a thermistor having a negative temperature coefficient of resistance (hereinafter referred to as NTC thermistor) is as follows. Some power supply circuits incorporate a thermistor to suppress the rush current that flows. A thermistor used for such a purpose is required to have a small specific resistance at room temperature. For example, a thermistor at 130 ° C. or less at 25 ° C. is preferable.

In order to obtain such an NTC thermistor with a small specific resistance value, copper oxide is added to and mixed with oxides of metals such as manganese, cobalt, and nickel, and the amount of copper oxide to be added is increased or decreased. To adjust the specific resistance to a desired range.

[Problems to be solved by the invention]

In a thermistor containing copper as described above, although the specific resistance can be reduced by increasing the amount of copper, the variation in the specific resistance increases with the reduction of the production yield, and in order to avoid this, However, there are problems with mass productivity and economic efficiency, such as the need to more strictly control the mixing ratio and production conditions. Furthermore, such a thermistor containing copper has a drawback that when used at a high temperature (for example, 200 ° C.) for a long time, the specific resistance increases and the reliability is poor.

In view of the above, an object of the present invention is to provide an NTC thermistor having a small variation in specific resistance and a small deterioration at a high temperature, and to provide an oxide semiconductor composition suitable for producing such an NTC thermistor. It is.

[Means for solving the problem]

An object of the present invention is to provide a sintered body of a metal oxide substantially consisting of a manganese oxide, a cobalt oxide, and a lanthanum oxide, wherein manganese is 10 to 80 atomic% and cobalt is 10% as a metal element. This is achieved by an oxide semiconductor composition for a thermistor, characterized in that it contains 〜80 at% and lanthanum in an amount of 1.0-45 at%.

As a raw material for producing such a semiconductor composition of the present invention, manganese, an oxide of cobalt and lanthanum, or a compound that gives an oxide of each metal element by heating and firing, for example, hydroxide, carbonate,
Alternatively, a salt of an organic acid such as oxalic acid can be used, but is not particularly limited as long as the required purity and composition stability are satisfied.

In producing the semiconductor composition of the present invention, the raw materials as described above are accurately weighed such that the mixing ratio of the contained metal elements is a desired value within the range of the present invention, for example, The mixture is sufficiently pulverized and mixed using a pulverizer such as a ball mill, appropriately molded, calcined at 600 to 1000 ° C. for 1 to 3 hours, and pulverized to adjust the particle size to obtain an oxide powder. The oxide powder thus obtained is, for example, polyvinyl alcohol, starch and other binders added to obtain a powder for granulation, and is molded under pressure at a pressure of about 1 to 3 t / cm ² and then in air.
By firing at 1200 to 1400 ° C. for 1 to 4 hours, a sintered body of the semiconductor composition of the present invention is obtained.

The sintered body thus obtained is cut into an appropriate shape as necessary, and a conductive metal film electrode such as silver for forming an ohmic contact is formed on the end face or the like by a known method to obtain a thermistor element.

The semiconductor composition of the present invention is one in which the metal element contained in the metal element oxide constituting it substantially consists of manganese, cobalt and lanthanum, and the content of manganese and cobalt as the metal element is 10% respectively. If it is out of the range of 80 at%, a semiconductor composition having a low specific resistance cannot be obtained.

If the amount of lanthanum is less than 1.0 atomic%, the specific resistance increases and the specific resistance change rate, which indicates a change in specific resistance due to high temperature storage, increases. Variations in the specific resistance of the products obtained, that is, the coefficient of variation also increases, and any product with high reliability cannot be obtained.

〔Example〕

The raw materials used are manganese tetroxide (Mn ₃ O ₄ ), cobalt tetroxide (Co ₃ O ₄ ), and lanthanum oxide (La ₂ O ₃ ), each of which has the composition shown in Table 1 Was weighed exactly as described. These raw materials are placed in a ball mill
After wet pulverization and mixing for 20 hours, the mixture was dewatered by filtration and dried at 110 ° C. to obtain a pellet-shaped dry mixture.

This dried mixture is calcined in air at 800 ° C. for 2 hours, and after cooling, polyvinyl alcohol is added as a binder to a concentration of 3% by weight and pulverized in a ball mill to obtain a granulated powder passing through a 300 μm sieve. Obtained. This granulated powder is 1.5t / c
Using a pressure of m ^2, a disk-shaped molded body having a diameter of 7 mm and a thickness of 1.2 mm was obtained. The disk-shaped compact obtained in this way is 1300 in air.
C. for 2 hours to obtain a disc-shaped sintered body composition.

Silver was baked on both sides of the disk-shaped sintered body thus obtained, and a conductive wire was soldered to form a thermistor element, and the electrical characteristics were measured.

For comparison, copper oxide (Cu) was used instead of lanthanum oxide.
O) and manganese-cobalt-
A copper-based semiconductor composition was manufactured, and the electrical characteristics were measured in the same manner.

Among the electrical characteristics of the thermistor element, the specific resistance ρ is 25
The value obtained from the measurement result of the zero load resistance value at ° C., and the B constant is a value obtained from the zero load resistance values at 25 ° C. and 85 ° C. The specific resistance change rate Δρ / ρ indicates the rate of change of the specific resistance after leaving the thermistor element at a high temperature of 200 ° C. for 500 hours, and the coefficient of variation is 25 ° C.
3 shows the ratio between the standard deviation and the average value in terms of the variation in the specific resistance in percentage.

 The obtained results are shown in Table 1.

From the results shown in Table 1, it can be seen that the semiconductor composition of the present invention has a low specific resistance, a small specific resistance change rate and a small coefficient of variation.

[Effect of the Invention] The oxide semiconductor composition for a thermistor of the present invention solves the disadvantages of the conventional manganese-cobalt-copper-based semiconductor composition, that is, both the deterioration due to high temperature use and the variation in product quality. Thus, the present invention provides a high-quality and highly reliable NTC thermistor element, and has a feature that is particularly suitable for mass-producing an NTC thermistor having a low specific resistance.

Claims (1)

(57) [Claims] 1. A sintered body of a metal oxide substantially consisting of a manganese oxide, a cobalt oxide and a lanthanum oxide, wherein manganese is 10 to 80 atomic% and cobalt is 10 to 80 atomic% as a metal element. %, And lanthanum is contained in an amount of 1.0 to 45 atomic%.