JPH09330805A - Positive characteristic thermistor and manufacture thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a positive characteristic thermistor which has a positive temperature coefficient of resistance and is used as a heater or a switching element, and which is low in its resistive value and large in its breakdown voltage, in particular, at room temperature. SOLUTION: In a method for preparing a composition contains barium titanate or its solid solution as its main component and at least one of rate earth elements and Nb, Bi, Sb oxides and SiO2 , Al2 O3 , and MnTiO3 as its subcomponents; MnTiO3 is added and mixed after being calcined and controlled, so that an average particle diameter ratio between the calcined crushed powder and MnTiO3 is 0.5-1.0, thereby forming a positive characteristic thermistor.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive temperature coefficient thermistor having a low resistance value at room temperature and a high withstand voltage, and a manufacturing method thereof.

[0002]

2. Description of the Related Art In order to improve resistance temperature coefficient while achieving low resistance, a positive temperature coefficient thermistor is prepared by immersing a sintered body containing barium titanate as a main component in a solution containing transition elements such as Mn and Fe. Was being made.

[0003]

When a transition element such as Mn or Fe is localized near the grain boundary where the PTC characteristic develops, it acts as an acceptor element and the potential barrier at the grain boundary becomes large, so the PTC characteristic is increased. Is believed to improve. If these elements do not localize at the grain boundaries and exist in the grains, valence compensation with the intragranular components occurs and the resistivity increases, so the issue is how to localize these elements near the grain boundaries. is there. However, in the above method, since the solution does not sufficiently penetrate into the inside of the sintered body, there is a difference in PTC characteristics between the inside and the surface of the sintered body, which causes a decrease in withstand voltage and a large variation in characteristics. Had.

Therefore, an object of the present invention is to provide a positive temperature coefficient thermistor having a small resistance value at room temperature and an improved temperature coefficient and withstand voltage.

[0005]

To achieve this object, a positive temperature coefficient thermistor of the present invention comprises a main component containing barium titanate and a rare earth element, Nb, S as a subcomponent.
At least one of the oxides of b and Bi, and SiO
_An element is formed from ₂ , Al ₂ O ₃ , and MnTiO _3, and the above object can be achieved by this.

[0006]

BEST MODE FOR CARRYING OUT THE INVENTION The invention according to claim 1 of the present invention is characterized in that a rare earth element or Nb, Sb, B as a main component comprising barium titanate or a solid solution thereof is added as a subcomponent.
at least one of the oxides of i, SiO ₂ ,
A positive temperature coefficient thermistor including an element containing Al ₂ O ₃ and MnTiO ₃ and at least a pair of electrodes formed on the surface of the element, which has a low resistance because Mn can be suppressed from diffusing into the grain. Moreover, it is possible to obtain an element having a large PTC characteristic.

The invention according to claim 2 is directed to MnTiO 3.
₃ is the positive temperature coefficient thermistor according to claim 1, which is contained in an amount of 0.03 to 0.2 mol based on 100 mol of the main component,
It is possible to prevent the specific resistance from becoming extremely large and obtain sufficient PTC characteristics.

According to a third aspect of the present invention, the main component containing barium titanate, at least one of rare earth elements or oxides of Nb, Sb, Bi as a sub-component, and SiO ₂ , Al ₂ O _{3 are used.} The raw material added with is calcined, then MnTiO ₃ is added to the raw material and crushed, and then the raw material is molded and fired to obtain a sintered body, and then at least a pair of electrodes is formed on the surface of the sintered body. This is a method of manufacturing a characteristic thermistor to be formed, and Mn can be localized near the grain boundary, so that a positive characteristic thermistor having a high PTC effect can be obtained.

The invention according to claim 4 is the MnT after pulverization.
The average particle size of iO ₃ is D _B , and the average particle size of raw materials other than MnTiO ₃ is D _A , D _A / D _B is set to 0.5 to 1.0. This is a method of manufacturing a characteristic thermistor, in which the reaction between intragranular components and MnTiO ₃ is suppressed, and a positive temperature coefficient thermistor having a lower resistance and a large PTC effect can be obtained.

According to a fifth aspect of the present invention, the amount of MnTiO ₃ added is 0.03 to 0.2 with respect to 100 mol of the main component.
The method for producing a positive temperature coefficient thermistor according to claim 3, wherein the molar ratio is molar, and it is possible to prevent the specific resistance from becoming extremely large and obtain sufficient PTC characteristics.

An embodiment of the present invention will be described below. (Embodiment 1) First, (Ba _0.68 Pb _0.22 Ca _0.10 )
TiO ₃ + 0.002Y ₂ O ₃ + 0.01Al ₂ O ₃ +0.
02CO ₂ + MnTiO ₃ so that the composition is BaCO
₃ , PbO, CaCO ₃ , TiO ₂ , Y ₂ O ₃ , Al ₂ O ₃ ,
Each SiO ₂ is weighed, and for MnTiO ₃ , 1 mol of the main component (Ba _0.68 Pb _0.22 Ca _0.10 ) TiO ₃ is weighed as shown in (Table 1) and wet-mixed with a ball mill.

[0012]

[Table 1]

Next, after drying this mixture,
And calcine for 2 hours. After that, it is wet-milled again with a ball mill and dried. Next, a binder made of polyvinyl alcohol was added to this dry pulverized powder and granulated, and the pressure was 800 kg per square centimeter, the diameter was 20 mm, and the thickness was 2.
It was molded into a 5 mm disk shape. Next, main firing was performed at 1300 ° C. for 2 hours to obtain a sintered body. After Ni plating was formed on this sintered body, a silver paste was applied by printing and baked to form an electrode. Next, the room temperature resistance value R ₂₅ , the temperature coefficient of resistance α, and the withstand voltage V _BD were measured as the evaluation of the sample thus manufactured. The results are shown in (Table 1).

Here, the temperature coefficient of resistance was determined according to the following equation. _{[In (R 2 / R 1)} / (T 2 -T 1) ] × 100 (% /
However, R ₁ and T ₁ ; resistance value twice that of R ₂₅ and temperature at that time R ₂ and T ₂ ; resistance value of (T ₁ +30) ° C. and temperature thereof.

As is clear from (Table 1), MnTiO
Amount of ₃ Sample No. 3 is within the scope of the present invention
No. 7 has a low room temperature resistance value, a large resistance temperature coefficient, and a large withstand voltage. On the contrary, Sample Nos. 1, 2, 8 and 9 which are outside the scope of claims of the present invention have high room temperature resistance values, and no improvement in the temperature coefficient of resistance is observed.

(Embodiment 2) Raw materials are blended so as to have the same composition as in Embodiment 1 and wet mixed in a ball mill. However, at this time, MnTiO ₃ is excluded from the composition. Next, the mixture was dried and calcined at 1050 ° C. for 2 hours. Furthermore, MnTiO ₃ is the main component (B
a _0.68 Pb _0.22 Ca _0.10 ) TiO ₃ (1 mol) was added at the addition amount shown in (Table 2) and wet-mixed with a ball mill.

[0017]

[Table 2]

The average particle size of the calcined powder at this time was D _A , and the average particle size of MnTiO ₃ was D _B.

[0019] was prepared in this case, D _A and D _B and the ratio D _A / D _B (Table 2) grinding time so as to become a. Further, this pulverized powder was granulated, molded and fired in the same manner as in (Embodiment 1) to form an electrode. Next, various electrical characteristics of the sample thus manufactured are measured. From the resistance temperature characteristics, R ₂₅ , α, and V _BD are evaluated in the same manner as in (Embodiment 1). The evaluation results are shown in (Table 2).

As is clear from (Table 2), MnTiO
By adding ₃ after calcination, the room temperature resistance value is low,
It is possible to obtain a positive temperature coefficient thermistor with high withstand voltage,
If the amount of MnTiO ₃ added is outside the scope of the claims of the present invention as in Sample Nos. 10 and 16, the effect is not recognized.
On the other hand, in sample numbers 18 to 20 in which D _A / D _B is within the range of 0.5 to 1.0, sample numbers 11 to 15 and 17,
It is possible to obtain a positive temperature coefficient thermistor which has a lower room temperature resistance value and a higher withstand voltage than those in which the amount of MnTiO ₃ is specified as in No. 21.

As described above (Embodiment 1) and (Embodiment 2), by using the method for manufacturing the positive temperature coefficient thermistor of the present invention, the resistance value at room temperature is low, the temperature coefficient of resistance is large, and the withstand voltage is high. It is possible to obtain a device with high efficiency.

In the first and second embodiments, Y ₂ O ₃ is used as the semiconductor element, but at least one of other rare earth elements or oxides of Nb, Sb and Bi is used. As a result, the same effect can be obtained.

The amount of semiconducting element in the present invention is 0.1 to 0.4 mol based on 100 mol of the main component, SiO ₂
The amount is preferably 1 to 5 mol, and the Al ₂ O ₃ amount is preferably 0.05 to 0.2 mol. This is because if the temperature is outside these ranges, the resistance value at room temperature greatly increases or the temperature coefficient of resistance decreases, so that the object of the present invention cannot be achieved.

[0024]

As is apparent from the above description, the present invention is based on barium titanate or its solid solution as a main component and at least one of rare earth elements or oxides of Nb, Sb, and Bi as a secondary component and SiO ₂ And Al ₂ O ₃ and MnTiO ₃ are added, and in the manufacturing method thereof, in particular, MnTiO ₃ is added and mixed after calcination,
Further, a positive temperature coefficient thermistor is formed by controlling the ratio of the average particle size of the calcined pulverized powder to MnTiO ₃ to be 0.5 to 1.0. As a result, it is possible to obtain a positive temperature coefficient thermistor having a low resistance value at room temperature and a high withstand voltage, and it is expected that the product can be miniaturized and applied to a high power circuit, so that its industrial value is great.

Claims (5)

[Claims] 1. A main component comprising barium titanate or a solid solution thereof, a rare earth element or Nb,
At least one of oxides of Sb and Bi, and S
an element containing iO ₂ , Al ₂ O ₃ and MnTiO ₃ ,
A positive temperature coefficient thermistor comprising at least a pair of electrodes formed on the surface of this element. 2. The positive temperature coefficient thermistor according to claim 1, wherein MnTiO ₃ is contained in an amount of 0.03 to 0.2 mol based on 100 mol of the main component. 3. A raw material obtained by adding SiO ₂ and Al ₂ O ₃ to a main component containing barium titanate and at least one of rare earth elements or oxides of Nb, Sb and Bi as auxiliary components, and SiO ₂ and Al ₂ O ₃ . Then, MnTiO ₃ is added to this raw material and pulverized, and then this raw material is molded and fired to obtain a sintered body, and thereafter, a positive temperature coefficient thermistor in which at least a pair of electrodes is formed on the surface of this sintered body Method. 4. When the average particle size of MnTiO ₃ after pulverization is D _B and the average particle size of raw materials other than MnTiO ₃ is D _A , D _A / D _B becomes 0.5 to 1.0. The method for manufacturing a positive temperature coefficient thermistor according to claim 3. 5. The addition amount of MnTiO ₃ is 100
The method for producing a positive temperature coefficient thermistor according to claim 3, wherein the molar ratio is 0.03 to 0.2 mol.