JPH07297009A - Positive temperature coefficient thermistor and manufacturing method thereof - Google Patents

Abstract

PURPOSE:To obtain a positive temperature coefficient thermistor especially in high resistance temperature coefficient and wider resistance fluctuation width out of the electric characteristics thereof within the positive temperature coefficient thermistor having positive resistance temperature characteristics used as a heating element and a switching element. CONSTITUTION:Within the positive temperature coefficient thermistor, the thermistor is formed of a composition A comprising fine amount of semiconductor element Si, Mn, Al added thereto as the principal component of barium titanate, another composition B represented by BaTinO2n+1 (n=2, 3, 4) is added in the ratio of 0.1-4.0mol% to 1mol% of the composition A and then electrode is to be provided.

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 large resistance temperature coefficient and a large resistance change width, and a method for manufacturing the thermistor.

[0002]

2. Description of the Related Art A small amount of a rare earth element such as Y, La or Ce or a transition metal such as Nb or Ta is added to barium titanate to become a semiconductor, and a positive temperature coefficient (Positive Temperature Coefficient; PTC
It is widely known in the past to exhibit the characteristics. That P
Utilizing the TC characteristics, it has been applied to various applications such as an overcurrent protection element, a temperature control element, a motor starting element, and a heater element.

On the other hand, as a method of manufacturing such a positive temperature coefficient thermistor, the following method is generally used. First, the blended raw materials are mixed using a ball mill, a disper mill or the like, dehydrated and dried with a filter press, a drum dryer or the like, and then these mixed powders are calcined. Next, the calcined powder is pulverized by a ball mill or the like, a binder such as polyvinyl alcohol is added to form a slurry, and the slurry is granulated by a spray dryer or the like to form a desired shape. Furthermore, this molded body is usually placed in the air at 1300 to 1400 ° C.
The main firing is performed at a high temperature, and electrodes are applied to the obtained sintered body to form a positive temperature coefficient thermistor.

[0004]

The characteristics required of such a positive temperature coefficient thermistor are roughly classified into (1) low resistance (2) from the viewpoint of large current control, withstand voltage, heat generation amount and the like.
There is a high Curie point.

However, if it is attempted to satisfy these, there are the following problems, so that they have not been put to practical use.

(1) Problems of low resistance In a general synthesis method by solid-phase reaction, the room temperature resistivity is currently limited to about 5 Ωcm. However, although a liquid crystal reaction such as the sol-gel method or a positive temperature coefficient thermistor made of an organic material has been obtained at 1 Ωcm or less, it is difficult to put it into practical use in terms of cost or mass productivity. The biggest problem in such a low resistance element is a decrease in withstand voltage. This is because the temperature coefficient of resistance or the range of resistance change in the PTC characteristic decreases as the resistance decreases.

(2) Problem of High Curie Point For increasing the Curie point in a positive temperature coefficient thermistor, it is general to use Pb as a shifter at the present time. Therefore, the problem in increasing the Curie point is highlighted as a problem related to Pb. In particular,
There is a problem in that compositional deviation due to evaporation of Pb during firing causes a large variation in characteristics, and because sintering is difficult, mechanical strength cannot be sufficiently obtained.

Under these circumstances, the high Curie point that has been put to practical use is around 300 ° C. The two major problems of the positive temperature coefficient thermistor have been described above. In particular, the present invention provides a positive temperature coefficient thermistor having a large resistance temperature coefficient and a large resistance change width, which is described as a problem for reducing the resistance in the above (1). It is intended for. Especially when these are used for degaussing or for preventing overcurrent, the effect of reducing the inrush current can be obtained.

[0009]

Means for achieving the above object will be described.

First, the composition of the thermistor element of the present invention comprises a main component made of barium titanate and a rare earth element such as Y, La, Sm or Nb, S as a semiconductor element.
a composition A containing at least one kind of oxides of b and Bi and further added with a small amount of SiO ₂ , MnO ₂ , and Al ₂ O ₃ , and BaTi _n O _{2n + 1} (n = 2, 3, 4) ) And the composition B represented by this.

Further, in the manufacturing method thereof, BaT
After mixing i _n O _{2n + 1} other than the composition, calcining a mixture of the resulting composition A and BaTi _n O _{2n + 1} composition B to obtain a thermistor element and then the main firing, then An electrode is formed on the surface of the thermistor element.

[0012]

With the above structure, the temperature coefficient of resistance and the range of resistance change in the PTC characteristic are greatly improved. The detailed mechanism thereof is not clear at present, but it is considered as follows.

It is considered that the improvement of the temperature coefficient of resistance is due to the suppression of the production of a compound or the like which reduces the phase transition rate from the tetragonal system to the cubic system in the crystal structure described above. That is, when a trace amount of additive component moves to the vicinity of the grain boundary during sintering, it is generally considered that the composition near the grain boundary, which is a part where the PTC characteristics are expressed, changes, and for example, Ba ₂ TiSi ₂ It is considered that compounds such as O ₈ are generated and disturb the crystal structure, thereby inhibiting the phase transition. Therefore by the present invention of adding BaTi _n O _{2n + 1} component is believed that turbulence generation and crystal structure of the phase transition inhibitor in the vicinity of the grain boundary is suppressed.

On the other hand, considering that the resistance change width depends on the potential barrier height at the grain boundary, BaTi _n O
Ti slightly increased by adding _{2n + 1} component
Since the component acts as an acceptor element, oxygen defects are generated by the reaction with Mn and Al that have moved to the vicinity of grain boundaries during firing, resulting in a higher hole concentration and a lower electron concentration, resulting in a higher potential barrier and a resistance change. It is considered that the width has increased. Furthermore, it is considered that these actions occur more effectively near the grain boundaries by using the production method of the present invention.

[0015]

EXAMPLE The mechanism of expression of PTC characteristics has long been known.
As pointed out by Heywang, it is thought to be due to the potential barrier at the grain boundary.

It is explained that at temperatures above the Curie point, the potential barrier exponentially increases with increasing temperature. The grain boundary resistance is shown by the following equation.

Ρ = ρ ₀ exp (φ / kT) (1) However, ρ ₀ , k; constant φ; potential barrier height T; absolute temperature Further, in forming this potential barrier, a grain boundary portion is formed. The adsorbed oxygen is said to be involved.

On the other hand, it has been confirmed that the crystal structure is a tetragonal perovskite structure below the Curie point and a cubic system above the Curie point.

Therefore, in order to obtain a positive temperature coefficient thermistor having a large resistance temperature coefficient and a large resistance change width, the phase transition rate from the tetragonal system to the cubic system is high and the height of the potential barrier per grain boundary is high. It seems necessary to be large.

Based on such a viewpoint, the present invention has been achieved as a result of earnest research on the composition side and the process side.

Examples of the present invention will be described below. Example 1 (Ba _0.8 Pb _0.1 Ca _0.1 ) TiO ₃ +0.
002Y ₂ O ₃ + 0.03SiO ₂ +0.0005 MnO ₂
In order to have a composition of + 0.01Al ₂ O ₃ , barium carbonate (BaCO ₃ ) and titanium oxide (Ti
O ₂ ), lead oxide (PbO), calcium carbonate (CaC
O ₃ ), yttrium oxide (Y ₂ O ₃ ), silicon dioxide (S
iO ₂ ), manganese dioxide (MnO ₂ ), and aluminum oxide (Al ₂ O ₃ ) are weighed, and BaTi ₂ O ₅ is weighed as shown in (Table 1).

[0022]

[Table 1]

Next, these are wet mixed in a ball mill, dried and calcined at 1100 ° C. for 2 hours. Then, the calcined powder is wet pulverized with a ball mill and dried.

Next, 5% of polyvinyl alcohol as a binder was added to this pulverized powder, and the mixture was granulated and press-molded at a pressure of 80 kg / cm ² . This molded product was fired in air at about 1350 ° C. for 1 hour to obtain a disk-shaped sintered body having a diameter of 20 mm and a thickness of 2.0 mm. Further, this sintered body was plated with Ni, and then silver paste was applied and baked to form an electrode to obtain a positive temperature coefficient thermistor.

Next, various electrical characteristics of the sample thus obtained are measured. From the resistance temperature characteristic curve, the room temperature resistance value (R ₂₅ ), the resistance temperature coefficient (α), and the resistance change width (Ψ) are evaluated. The results are shown in (Table 1).

From these results, BaTi of the present invention
It is recognized that the sample added with ₂ O ₅ added has a room temperature resistance value which is almost the same as that of the case without addition, but the temperature coefficient of resistance and the range of resistance change are greatly improved.

Example 2 Using the same raw material as in Example 1, (Ba _0.8 Pb _0.1 Ca _0.1 ) TiO ₃ + 0.002Y ₂
O ₃ +0.03 SiO ₂ +0.0005 MnO ₂ +0.0
Each raw material is weighed so as to have a composition of 1Al ₂ O ₃ and wet-mixed in a ball mill.

Next, this mixture is dried, calcined at 1100 ° C. for 2 hours, and then wet pulverized by a ball mill (the particle size of the calcined pulverized particles is D _A ). Further, the calcined pulverized powder and BaTi ₂ O ₅ (whose particle size is D _B ) are simultaneously wet mixed. At this time, the addition amount of BaTi ₂ O ₅ and D
_{The A} / D _B ratio is as shown in (Table 2).

[0029]

[Table 2]

The subsequent sample preparation process after granulation was the same as in Example 1, and the evaluation of electrical characteristics was also the same. The results are shown in (Table 2).

Looking at (Table 2), the D _A / D _B ratio is 2.0.
From the above, it can be seen that the resistance temperature characteristics and the resistance change width in the PTC characteristics are significantly improved.

In Example 1 and Example 2, barium carbonate and titanium oxide were used in the production of the calcined and ground powder, but the same effect can be obtained even if a solid solution of barium titanate is used. Is.

Further, although the case of adding Y ₂ O ₃ is a rare earth oxide as a sub-component of the composition A, the Y ₂ O ₃
The same effect can be obtained by adding other rare earth oxides, oxides of Nb, Sb, Bi, or these oxides containing Y ₂ O ₃ in combination instead of.

Further, as composition B, BaTi _n O _{2n + 1}
Although only the case of n = 2 is shown, the same effect can be obtained in the case of n = 3, 4 or the combination of n = 2, 3, 4.

[0035]

As described above in detail, the present invention is a PTC.
Without changing the initial electrical characteristics of the characteristics
The temperature coefficient of resistance and the range of resistance change can be greatly improved. Further, when the positive temperature coefficient thermistor of the present invention is used for a degaussing circuit of a cathode ray tube or for preventing overcurrent, the inrush current can be reduced.

Claims (4)

[Claims] 1. A thermistor element and at least a pair of electrodes provided on the surface of the thermistor element, wherein the thermistor element comprises a barium titanate main component as a main component and a rare earth element or Nb, Sb, Bi as a secondary component. At least one of the above oxides and SiO ₂ , Mn
Composition A containing O ₂ and Al ₂ O ₃ added, and BaTi _n
A positive temperature coefficient thermistor comprising the composition B represented by O _{2n + 1} (n = 2, 3, 4). 2. The content of the composition B is 1 mol of the composition A.
The positive temperature coefficient thermistor according to claim 1, which is 0.1 to 4.0 mol%. 3. A main component composed of barium titanate, and at least one or more of rare earth elements or oxides of Nb, Sb, Bi as secondary components, and SiO ₂ , Mn.
O _2, Al ₂ O ₃ and after addition of mixed, calcined to obtain a composition A, then BaTi the composition _{A n O 2n + 1 (n} = 2,
A method for producing a positive temperature coefficient thermistor in which the composition B represented by 3, 4) is mixed, and then main-baked to form a thermistor element, and electrodes are provided on the surface of the thermistor element. 4. The particle size ratio D _A / D _B of the average particle size (D _A ) of the powder of composition _A and the average particle size (D _B ) of the powder of composition _B is 2.0 or more. Composition 3 and composition B are used.
A method for manufacturing the described positive temperature coefficient thermistor.