JPH05198407A - Thick film thermistor composition - Google Patents

Abstract

PURPOSE:To obtain a product whose resistance variation is small, whose cost is low and whose quality is excellent by a method wherein oxide powder which is obtained by the thermal decomposition of the precipitate of oxalate at a specific temperature and has a spinel structure is employed. CONSTITUTION:Oxalic acid solution is added to solution in which ions of Mn, Co, Ni and Cu are mixed so as to form coprecipitate whose composition is expressed by a formula MnpCoqNirCusO4, wherein p+q+r+s=3, pnot equal to 0 and q, r and s are not simultaneously zero to obtain oxalate precipitate. The oxalate precipitate is refined and thermally decomposed at a temperature about 600-800 deg.C to obtain oxide powder having a spinel structure. 60-98wt.% of the oxide powder and 2-40wt.% of glass powder are mixed and baked to obtain a thick film thermistor element. With this constitution, the product whose resistance variation is small, whose cost is low and whose quality is excellent can be obtained without using a trimming process and a thermal aging treatment.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thick film thermistor composition having little variation in properties and excellent stability against heat.

[0002]

As a conventional thick film thermistor composition,
There are the following (1) to (3).

(1) Oxide powders of chemical formula 2, CoO, NiO, CuO, etc. are mixed so as to form a composition having a predetermined spinel structure, and then they are synthesized by a solid phase reaction at a high temperature and pulverized. Powder (average particle diameter of about 2 μm) and glass powder are used.

[Chemical 2]

(2) Fine powder 3, CoO, NiO, Cu
An oxide powder having an average particle diameter of 1 μm or less and glass powder such as O is used to generate an oxide having a spinel structure during thick film firing.

[Chemical 3]

(3) An alkaline aqueous solution is added to a mixed aqueous solution of hydrochlorides or nitrates of Mn, Co, Ni, and Cu to coprecipitate, the precipitate is purified, and the spinel structure obtained by thermal decomposition is oxidized. Material powder and glass powder are used.

Further, in order to lower the resistance value, a method of adding a metal conductive material such as Chemical formula 4 to these is also adopted.

[Chemical 4]

However, the thermistor elements made of these thermistor compositions have large variations in resistance value and B constant, and are stable to heat (eg, 15).
The change in resistance value when left at 0 ° C.) was also poor, and the product lacked reliability.

That is, since the powder obtained by the solid-phase reaction of the above (1) has a large particle size and is non-uniform, the sinterability during thick film firing is poor, and the thick film structure is non-uniform. As a result, the variation in the resistance value increases. Furthermore, since the reaction temperature during powder synthesis is high, a high temperature phase remains depending on the composition, and a phase change occurs when left at high temperature, resulting in poor thermal stability.

Further, in the method (2) using the finely powdered oxide, the spinel formation reaction during thick film firing is unstable (the temperature dependence and the atmosphere dependence are large). There is a thick film dependency, and the variation in the resistance value becomes large.

Further, in the method (3) of using hydroxide precipitation, since the precipitate is fine, it is difficult to carry out filtration and purification, and there is a possibility that alkaline elements may be mixed. In addition, since the oxide powder obtained by thermal decomposition is too fine, it may rather agglomerate or the sinterability may deteriorate, resulting in a relatively small variation in resistance value, but lacking in thermal stability.

For the above-mentioned reasons, 1200 ° C. to 1500 ° C. after the organic vehicle is added to the metal oxide powder and press-molded.
At present, thick film type thermistors are not used much as compared with so-called bulk sintered body type thermistors obtained by sintering at ° C.

[0012]

By the way, in the case of manufacturing a thick film thermistor, usually, a large number of elements are manufactured on an alumina substrate by printing once, but the resistance of each thermistor element on one substrate is increased. Since the variation in the value was about ± 15% in the conventional one, it was necessary to make the resistance value to a predetermined value by performing resistance trimming by laser processing or the like. Moreover, since the resistance value of the thermistor element, which is a temperature-sensitive resistance element, changes due to the temperature change caused by the heat received during the trimming process, it is necessary to perform trimming in consideration of the change. Compared with the case of the thick film fixed resistor, it takes time to perform the trimming process accurately, and the manufacturing process becomes complicated.

Therefore, one of the objects of the present invention is to eliminate the trimming process during the manufacturing process and to suppress the variation in the resistance value to ± 5% or less, thereby obtaining an inexpensive and excellent quality product. A thick film thermistor composition is provided.

In the conventional case, the resistance value changes about 10% in 1000 hours when left at 150 ° C.,
There is also the complexity of making the product after the heat aging treatment in advance.

Therefore, another object of the present invention is to
It is an object of the present invention to provide a thick film thermistor composition capable of achieving a resistance change of 3% or less in 1000 hours even if it is left at 0 ° C. without performing a heat aging treatment in advance.

[0016]

[Means for Solving the Problems] Various chemical raw material powder synthesizing methods have been studied in order to sinter a high-performance sintered body at a low temperature. As a result of various research experiments, the present inventors have found that among these, oxalate precipitates
Focusing on the oxide powder having a spinel structure obtained by thermal decomposition at 00 ° C. to 800 ° C., it has been found that this is extremely excellent in liquid phase sinterability particularly in the presence of glass powder. Furthermore, they have found that this is far more effective when used in the composition of a thick film thermistor, rather than in a normal bulk sintered body thermistor, and finally completed the invention.

That is, it has been already known that the chemically synthesized powder has excellent solid-phase sinterability and sinters at about 1160 ° C., whereby a bulk sintered body thermistor can be obtained. Is likely to be unstable with respect to heat because phases other than the spinel phase are generated even at the above-mentioned firing temperature. Therefore, in order to obtain a stable one against heat, the range of B constant is limited. Become.

However, an oxalic acid aqueous solution is added to a mixed aqueous solution of Mn, Co, Ni, and Cu ions, and Mn is mixed with Co,
General formula 5 comprising at least one of Ni and Cu
(However, p + q + r + s = 3, at least one of p ≠ 0, q, r, and s is not 0).
The oxide powder obtained by thermal decomposition at 800 ° C. has an appropriate particle size distribution, and since the liquid phase sinterability is extremely excellent especially in the presence of glass powder, only the spinel phase is present in a wide composition range. , Which is very stable to heat, was obtained over a wide range of B constants.

[Chemical 5]

Actually, it showed sufficient sinterability as a thick film at 800 ° C. to 950 ° C., both the resistance value and the B constant had good reproducibility, and the variation was extremely small. And 60 to 98% by weight of the oxide powder having the spinel structure
The composition of the thick film thermistor obtained by mixing the glass powder in the ratio of 2 to 40% by weight and the remaining ratio was extremely small and the electrical characteristics were excellent.

[0020]

EFFECT OF THE INVENTION According to the composition of the present invention, a uniform thick film thermistor having a small variation in resistance value and excellent stability against heat can be simplified without trimming treatment or heat aging treatment. It can be obtained at a low cost by the changed manufacturing process. In particular, in the current situation where electronic devices are becoming smaller, it can be effectively used as a thick film thermistor such as a chip type which is strongly demanded.

[0021]

EXAMPLES Example 1 Chemical formulas 6 and 7 were weighed so as to give a predetermined composition having a spinel structure, and dissolved in water to prepare a 0.5 mol / 1 aqueous solution. A predetermined amount of 0.2 mol / 1 ammonium oxalate aqueous solution is added thereto, and the mixture is stirred at room temperature to coprecipitate oxalate. The precipitate is suction filtered, dried at 120 ° C., and then pyrolyzed in air at 800 ° C. for 2 hours.

[Chemical 6]

[Chemical 7]

A predetermined amount of binder glass and an organic vehicle are added to the spinel oxide powder thus obtained, and the mixture is kneaded with an automatic mixer to prepare a printable thick film thermistor paste.

The prepared paste was applied to an alumina substrate (purity 9
(6%) was printed in a state of bridging between the Ag / pd-based electrodes burned on top, and this was baked at a predetermined temperature of 800 ° C. to 950 ° C. for 10 minutes to produce a thick film thermistor element.

The characteristics of the thick film thermistor device thus obtained are shown in Table 1 below.

[0025]

[Table 1]

Table 2 shows conventional ones.

[0027]

[Table 2]

From Tables 1 and 2, it can be seen that the sheet according to the present invention has a much smaller variation in sheet resistance value than the conventional sheet. Also, from Table 1, there is a tendency for the variation in the resistance value to increase as the mixing amount of the glass powder increases, and as in the case of No. 7, the mixing amount is 50 wt%.
Then, the variation of the resistance value greatly exceeds 5%. Furthermore, as in the case of No. 9, even when the synthesis temperature of the spinel structure oxide powder reaches 900 ° C., the variation in resistance value exceeds 5%.

Example 2 Depending on the composition, it may not be possible to obtain a quantitative precipitate with one aqueous solution of oxalate. In such a case, a spinel oxide powder obtained by preparing a plurality of precipitates with a plurality of aqueous oxalate solutions having different pHs, mixing them, and then thermally decomposing them can be used. As a result, a wide range of compositions can be used, and a thick film thermistor with a wide range of characteristics can be obtained.

Further, it is possible to obtain a material having a lower resistance by adding a material having a metal conductivity such as Chemical formula 8 below.

[Chemical 8]

Table 3 shows various characteristics of the thick film thermistor thus obtained.

[0032]

[Table 3]

Table 4 shows the conventional one.

[0034]

[Table 4]

From Tables 3 and 4, the composition according to the present invention has a sheet resistance lower than that of the conventional composition.
It is possible to obtain a device having a small variation in resistance value. Further, by selecting the composition of the spinel structure oxide and the mixing ratio of the chemical formula 9, it is possible to obtain one having a small variation in the resistance value in a wide range of characteristics.

[Chemical 9]

From FIG. 1 showing the measurement results concerning the thermal stability, the product C of the present invention (No. 4 in Table 3) and the product B of the present invention
The one according to (No. 6 in Table 3) is the conventional product A (in Table 4).
It can be seen that the thermal stability is far superior to that of No. 1).

[Brief description of drawings]

FIG. 1 is an explanatory diagram showing, in the form of a graph, a comparison result regarding thermal stability between a product of the present invention and a conventional product.

Front Page Continuation (72) Inventor Tei Tei 3-6 Tsukioka-cho, Toyama City, Toyama Prefecture Tateyama Science Co., Ltd. Minami Plant (72) Inventor Takaaki Hotta 3-6 Tsukioka-cho, Toyama City, Toyama Prefecture Industrial Co., Ltd. Minami Factory (72) Inventor Ken Ken Honda 3-6 Tsukioka-cho, Toyama City, Toyama Prefecture Tateyama Science Co., Ltd. Minami Factory (72) Inventor Hiroto Nakamura 3-6 Tsukioka-cho, Toyama City, Toyama Prefecture Address Tateyama Kagaku Kogyo Co., Ltd. South factory

Claims (1)

[Claims] 1. An oxalic acid aqueous solution is added to a mixed aqueous solution of respective ions of Mn, Co, Ni, and Cu to add Mn, Co, Ni, and
Coprecipitated to a ratio of at least one of Cu, represented by the general formula 1 (provided that p + q + r + s = 3, p ≠ 0, at least one of q, r, and s is not 0). The precipitate was purified and it was heated to 600 ° C-80 ° C.
The oxide powder having a spinel structure obtained by thermal decomposition at 0 ° C. is contained in a proportion of 60 to 98% by weight, and the remaining 2 to 4
A thick film thermistor composition characterized in that 0% by weight contains glass powder so that the B constant does not depend on the film thickness after firing. [Chemical 1]