JP2864731B2 - Positive characteristic thermistor and manufacturing method thereof - Google Patents

Description

Description: BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a positive temperature coefficient thermistor whose resistance value sharply increases at a specific temperature, and a method of manufacturing the same, particularly when used in a reducing gas atmosphere. The present invention relates to a highly reliable positive temperature coefficient thermistor with less characteristic deterioration and a method of manufacturing the same.

2. Description of the Related Art As is well known, a positive temperature coefficient thermistor containing barium titanate as a main component and made into a semiconductor with niobium or a rare earth element has an abrupt resistance value above a specific temperature, which is usually called a switching temperature. Indicates an increase. Utilizing this characteristic, it is used for a wide range of applications such as a heating element or a switching element of a degaussing circuit of a television receiver.

Problems to be Solved by the Invention It has long been pointed out that the characteristics of such a positive temperature coefficient thermistor depend on crystal grain boundaries, but when used in a reducing atmosphere or a neutral atmosphere, This causes a characteristic change such as a large decrease in the resistance value and a remarkable decrease in the temperature coefficient of resistance. Therefore, it was necessary to devise a device so that the element did not directly come into contact with such an atmosphere.
In addition, it is necessary to prevent contact with substances that are composed of organic components such as gasoline, machine oil, edible oil, and seasonings, and that cause a reducing action when adhered to the element, thus limiting its use.

It is an object of the present invention to provide a highly reliable positive temperature coefficient thermistor with a small characteristic deterioration particularly when used in a reducing atmosphere, and a method of manufacturing the same.

Means for Solving the Problems In order to solve such problems and reduce characteristic deterioration even when used in a reducing atmosphere, the present invention employs a semiconductor ceramic having a positive resistance temperature characteristic other than the electrode forming surface. Is formed by forming an insulator layer on the surface.

Further, the insulator layer is formed by adding an excessive amount of a semiconductor element of the semiconductor composition.

Further, the insulator layer is formed on the outer peripheral portion of the semiconductor porcelain at the time of molding the powder, and becomes an insulator layer by firing.

According to the present invention, by forming an insulator layer on a surface other than the electrode forming surface of a semiconductor porcelain having a positive resistance temperature characteristic, that is, on an outer peripheral portion, contact between the semiconductor porcelain and the surrounding atmosphere is prevented, and a reducing atmosphere is formed. It is possible to prevent the characteristic deterioration due to a reducing substance or the like.

In addition, since the main component of the insulator layer is the same as that of semiconductor porcelain, it does not peel or crack during thermal expansion and contraction due to heat generation and cooling of the element, so it can withstand long-term use. It is a good thing.

Furthermore, the insulator layer is formed in a powder state on the outer peripheral portion of the semiconductor porcelain at the time of molding the powder, and becomes an insulator layer by subsequent firing, so that a strong bonding is obtained and can withstand long-term use. It will be.

Example Hereinafter, an example of the present invention will be described.

First, (Ba _0.73 Pb _0.22 Ca _0.05 ) TiO ₃ + 0.001Nb ₂ O ₅ +0.
02 BaCO ₃ , PbO, Ti so that the composition becomes SiO ₂ + 0.0033MnO ₂
O ₂ , Nb ₂ O ₅ , SiO ₂ , and MnO ₂ were weighed, mixed using a usual method, calcined and pulverized to obtain a semiconductor ceramic powder. In the above composition, the amount of Nb ₂ O ₅ is 0.005, 0.010, 0.050,
BaCo ₃ , PbO, TiO ₂ , Nb ₂ O ₅ , SiO ₂ , MnO
₂ were weighed and mixed, calcined, and pulverized using a conventional method to obtain four types of powders for an insulator layer.

Next, a binder made of polyvinyl alcohol was added to the semiconductor porcelain powder, and the powder was pressed under a pressure of 300 kg per square centimeter to a diameter of 35 mm and a thickness of 3.2 mm.
It was formed into a disk shape.

Next, this compact was placed in the center of a powder pressure molding die having a diameter of 38 mm, and Nb ₂ O ₅ in the above-mentioned insulator layer powder was mixed with a powder having 0.005 mol of Nb ₂ O _{5 at} the periphery of the compact. Was added thereto, and the mixture was press-molded at a pressure of 1000 kg per square centimeter to obtain a molded body having a diameter of 38 mm and a thickness of 3 mm.

When this molding was fired at 1290 ° C, the diameter after firing was 32.
mm and a thickness of 2.5 mm, a crack-free flat porcelain was obtained. Next, after forming a Ni plating on the porcelain, a silver paste was applied and baked to form electrodes, and the electrodes on the side surfaces were deleted to prepare a sample. In addition, samples were prepared in the same manner for the other three types of insulator layer powders.

In addition, as a comparative example, a molded body was prepared using only the semiconductor ceramic powder, and an electrode was formed in the same manner as described above.

1 and 2 are a perspective view and an oblique view of the positive temperature coefficient thermistor according to the present invention manufactured as described above.
In the figure, 1 is a semiconductor ceramic, 2 is an insulator layer, and 3 is an electrode.

After measuring the resistance and temperature characteristics of the above sample, a voltage of 100 V was applied in nitrogen gas for 100 hours, the sample was taken out, and the resistance and temperature characteristics were measured again in a normal atmosphere. The results are shown in Table 1 below.

In the sample numbers 1 and 5 of the comparative examples, as shown in Table 1, the resistance value after the energization in nitrogen gas and the range of change in the resistance value were significantly reduced, whereas the sample numbers of the examples of the present invention were reduced. In the numbers 2 and 3, the characteristics hardly change.

This is because the side of the semiconductor porcelain is covered with a dense insulator layer made of fine crystal grains, and the electrode formation surface is also covered with dense Ni plating, so it is hardly affected by the external atmosphere It is thought to be.

In the present invention, the reason why the addition amount of niobium pentoxide (Nb ₂ O ₅ ) in the insulator material is 0.01 mol or more and less than 0.1 mol is that if it is less than 0.01 mol, the crystal grains are not sufficiently refined.
Therefore, the effect of the present invention cannot be exhibited due to insufficient densification of the insulator layer. This is because when the amount of niobium pentoxide added is 0.01 mol or more, the particle size of the insulator layer is 2 μm.
m and a porosity of 0.1% or less, whereas a porosity of less than 0.01 mol is almost the same as the particle size and porosity of the semiconductor porcelain, with a particle size of 5 μm and a porosity of 0.5% or more. Conceivable.

Also, if the amount of niobium pentoxide exceeds 0.1 mol,
This is because, as shown in Table 1, there is a disadvantage that excessive niobium pentoxide diffuses into the semiconductor ceramic and causes an increase in the resistance value.

In the above embodiment, a barium titanate-based compound containing lead titanate and calcium titanate was described. However, the barium titanate-based compound is not limited thereto, and a part of barium titanate may be replaced with titanium. Compounds substituted with strontium acid, barium stannate, barium zirconate, calcium zirconate, etc. may be used.

As a method of forming the insulator layer, any method may be used as long as powder pressure molding is used.For example, a disk molded body made of a semiconductor porcelain material and an inner diameter having the same dimension as the diameter of the disk may be used. A ring-shaped molded body made of an insulating material may be prepared, and after fitting both, they may be integrated and fired by a method such as hydrostatic molding.

Effect of the Invention As described in detail above, by using the present invention, it is possible to obtain a positive temperature coefficient thermistor having a small characteristic change even when used in a neutral atmosphere or a reducing atmosphere, and its utility value is great. .

[Brief description of the drawings]

1 and 2 are a perspective view and a sectional view, respectively, showing an embodiment of a positive temperature coefficient thermistor according to the present invention. 1 ... Semiconductor ceramic, 2 ... Insulator layer, 3 ... Electrode.

Claims (2)

(57) [Claims] (1) a barium titanate-based compound as a main component,
An insulator layer is formed on a surface other than the electrode forming surface of the semiconductor porcelain having a positive resistance temperature characteristic containing at least niobium pentoxide, and the insulator layer is made of a barium titanate compound 1
A positive temperature coefficient thermistor comprising an insulating material containing 0.01 mol or more and less than 0.1 mol of niobium pentoxide based on mol. 2. A barium titanate-based compound as a main component,
The semiconductor magnetic composition powder having at least a positive resistance temperature characteristic containing at least niobium pentoxide is subjected to powder pressure molding, and simultaneously, niobium pentoxide is added to 1 mol of the barium titanate-based compound.
A method for producing a positive temperature coefficient thermistor, comprising: forming an insulator layer by subjecting an insulator powder containing 0.01 mol or more and less than 0.1 mol to an outer peripheral portion, followed by powder pressing and firing to form an insulator layer.