JP2017188492A - Thermistor material and production method thereof - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a thermistor material which is usable under a reduction atmosphere and has small variation in an electric resistance value, and a production method thereof.SOLUTION: The thermistor material comprises first-phase particles, each composed of insulating material and second-phase particles, each composed of a semiconductor material and a conductive material. The insulating material includes an Si-N based ceramic, the semiconductor material includes SiC and Si, and the conductive material includes metal boride, metal nitride, metal silicate and/or metal carbide. The first-phase particles and the second-phase particles are uniformly dispersed and an average crystal particle diameter (d) of each of the first-phase and the second-phase particles is equal to or smaller than 5 μm. An average crystal particle diameter of SiC and Si is 0.5 μm or larger and 1 μm or smaller. The thermistor material can be obtained by first preparing an SiC fine powder, next adding Si-N based ceramic, boron, conductive material and, as needed, a powder of sintering aid to the prepared SiC fine powder, crushing and mixing them, molding and sintering the crushed and mixed powder.SELECTED DRAWING: Figure 4

Description

  The present invention relates to a thermistor material and a method for producing the thermistor, and more specifically, can be used in a reducing atmosphere, can accurately detect a temperature in a low temperature range of about -80 ° C to 200 ° C, and The present invention relates to a thermistor material having a small variation in resistance value and a manufacturing method thereof.

  The thermistor is a resistor having a large resistance change with respect to a temperature change. The thermistor is classified into an NTC thermistor whose resistance decreases with increasing temperature, a PTC thermistor whose resistance increases with increasing temperature, and a CRT thermistor whose resistance decreases rapidly when exceeding a certain temperature. Among these, the NTC thermistor is most often used because the change in temperature and resistance value is proportional, and the term “thermistor” refers to the NTC thermistor.

The thermistor generally used is composed of an oxide composite containing 2 to 4 kinds of transition metal oxides such as Mn, Ni, Co, Fe, and Cu. As such an oxide-based thermistor material, for example, a spinel oxide (Patent Document 1), a perovskite oxide (Patent Documents 2 to 5), a mixture of spinel and perovskite (Patent Document 6), and the like are known. ing.
In the oxide thermistor, temperature detection is performed by utilizing the temperature dependence of oxygen ion diffusion. In a thermistor made of a perovskite oxide, a p-type semiconductor in which more holes than oxygen defects are introduced is obtained by doping a divalent metal, and the resistance value is unstable in a low oxygen atmosphere. Suppression is carried out.

Non-oxide type thermistor materials are also known.
For example, Patent Document 7 discloses a reduction obtained by adding 30 wt% SiC powder and 6 wt% Y ₂ O ₃ to a Si ₃ N ₄ powder, mixing them, and molding and sintering the mixture. An atmospheric thermistor material is disclosed.
This document describes that this thermistor material for reducing atmosphere has a resistance change rate of 1% or less when exposed to a hydrogen atmosphere at 120 ° C. × 10 atm for 1000 hours.

Further, in Patent Document 8, 15-30 wt% α-type SiC, 6 wt% Y ₂ O ₃ , 0-20 wt% B, and 0-5 wt% TiB ₂ are added to Si ₃ N ₄ powder. A thermistor material for low temperature obtained by mixing and sintering the mixture is disclosed.
In this document, when a thermistor material comprising a matrix material made of insulating ceramics and conductive particles made of α-type SiC, a predetermined amount of boron and second conductive particles (particularly TiB ₂ ) are further added. It describes that a thermistor material suitable for high-accuracy temperature measurement for a low temperature range can be obtained.

  In the oxide-based thermistor material, holes are generated by introducing oxygen vacancies or doping with a metal, and therefore the operation tends to be unstable when used in a low oxygen atmosphere. Further, when exposed to a reducing atmosphere such as hydrogen, there is a problem that the resistance value increases by 2 to 3 orders of magnitude from the normal value. In order to solve this problem, the temperature detection unit is glass-sealed, or a metal cover is attached to the temperature detection unit, thereby preventing the influence of reducing gas. However, this method leads to an increase in cost and a decrease in responsiveness. In addition, there is a problem that it is difficult to assure the quality because hydrogen easily enters from the cracks or gaps of the glass or metal cover.

  On the other hand, the non-oxide type thermistor material has an advantage that the operation is stable even in a reducing atmosphere and a glass seal or a metal cover is not necessarily required. However, in the conventional non-oxide type thermistor material, it is necessary to make the particle size of the matrix material larger than that of the conductive material in order to easily form a network structure. Therefore, there is a problem that it is difficult to form a network structure with a uniform cell size, and the resistance value is likely to vary.

JP 05-275206 A Japanese Patent Laid-Open No. 06-325907 Japanese Patent Laid-Open No. 06-338402 Japanese Patent Application Laid-Open No. 07-099103 Japanese Patent Laid-Open No. 07-201528 Japanese Patent Laid-Open No. 10-070011 JP 2009-259911 A JP 2013-197308 A

  The problem to be solved by the present invention is that it can be used in a reducing atmosphere without using a glass seal or a metal cover, and the temperature can be accurately detected in a low temperature range of −80 ° C. to 200 ° C. An object of the present invention is to provide a thermistor material that can be manufactured and has a small variation in electric resistance value, and a method for manufacturing the thermistor material.

In order to solve the above problems, the thermistor material according to the present invention is summarized as having the following configuration.
(1) The thermistor material is
First phase particles made of an insulating material;
Second phase particles made of a semiconductor material and a conductive material,
The insulating material includes Si-N ceramics,
The semiconductor material includes SiC and Si,
The conductive material includes one or more metal compounds selected from the group consisting of metal borides, metal nitrides, metal silicides, and metal carbides.
(2) The thermistor material exhibits a structure in which the first phase particles and the second phase particles are uniformly dispersed;
Each of the first phase particles and the second phase particles has an average crystal grain size (d) of 5 μm or less,
The SiC has an average crystal grain size (d _SC ) of 0.5 μm or less,
The average crystal grain size (d _SI ) of the Si is 1 μm or less.

The thermistor material manufacturing method according to the present invention includes:
A SiC fine powder preparation step for preparing SiC powder having an average particle size (D _SC ) of 0.5 μm or less;
A pulverization and mixing step of adding Si-N ceramics, boron, a conductive material, and, if necessary, a powder of a sintering aid to the prepared SiC powder and pulverizing and mixing,
The gist of the present invention is to provide a molding / sintering step of molding and sintering the powder obtained in the pulverization and mixing step to obtain the thermistor material according to the present invention.

  When manufacturing a thermistor material having a first phase made of an insulating material and a second phase made of a semiconductor material and a conductive material, a fine SiC powder is used as a main semiconductor material, and the remaining raw material powder is used for this. In addition, when pulverized and mixed, a thermistor material in which both the first phase particles and the second phase particles are fine and the first phase particles and the second phase particles are uniformly dispersed is obtained.

The thermistor element using the material thus obtained exhibits a stable resistance value even in a reducing atmosphere, and has little variation in electric resistance value. this is,
(A) Since the semiconductor material and the conductive material forming the conductive path are electronic conductors, both of which have a stable resistance value in a reducing atmosphere, and
(B) By miniaturizing the entire structure and at the same time making the conductive path structure sufficiently small with respect to the element size, the uniformity of the composition in the element was promoted.
it is conceivable that.

2 is a TEM image of the thermistor material obtained in Example 1. FIG. 2 is an absorption current image of the thermistor material obtained in Example 1. FIG. 3 is a diagram showing temperature-resistance characteristics of the thermistor material obtained in Example 1. It is a figure which shows the dispersion | variation in the electrical resistance value of the thermistor material obtained in Example 1 and Comparative Examples 1 and 2. FIG.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Thermistor material]
The thermistor material according to the present invention has the following configuration.
(1) The thermistor material is
First phase particles made of an insulating material;
Second phase particles made of a semiconductor material and a conductive material,
The insulating material includes Si-N ceramics,
The semiconductor material includes SiC and Si,
The conductive material includes one or more metal compounds selected from the group consisting of metal borides, metal nitrides, metal silicides, and metal carbides.
(2) The thermistor material exhibits a structure in which the first phase particles and the second phase particles are uniformly dispersed;
Each of the first phase particles and the second phase particles has an average crystal grain size (d) of 5 μm or less,
The SiC has an average crystal grain size (d _SC ) of 0.5 μm or less,
The average crystal grain size of Si is 1 μm or less.

[1.1. First phase particles]
[1.1.1. composition]
The first phase particles are made of an insulating material. The insulating material preferably has an electrical specific resistance of 10 ¹² Ωcm or more. In the present invention, the insulating material constituting the first phase particles includes at least Si—N ceramics. "Si-N ceramics"
(A) Si ₃ N ₄ or
(B) Compounds in which various elements are dissolved in Si ₃ N ₄ (for example, SiALON)
Say.

The insulating material may be made of only Si—N ceramics or may contain other materials. As other materials constituting the first phase particles, for example,
(A) BN produced by a reaction between Si-N ceramics and boron,
(B) There is a grain boundary phase derived from the sintering aid.

[1.1.2. Average crystal grain size of first phase particles]
In the present invention, the average crystal grain size (d) of the first phase particles is 5 μm or less. In general, the smaller the average crystal grain size of the first phase particles (and the average crystal grain size of the second phase particles), the smaller the variation in electrical resistance value. The average crystal grain size of the first phase particles is preferably 1 μm or less, and more preferably 0.75 μm or less.
Here, the “average crystal grain size” means the median value (sampled) of the size of 10 or more crystal grains (diameter of the minimum circumscribed circle of crystal grains) randomly selected by observation with a microscope (SEM, TEM, etc.) Particle size corresponding to 50% of the particles).
Since the size of the grain boundary phase is usually about several nanometers, the term “average crystal grain size of the first phase” refers to the average crystal grain size of Si—N ceramics and BN.

[1.2. Second phase particles]
The second phase particles are made of a semiconductor material and a conductive material. The first phase particles made of an insulating material and the second phase particles made of a semiconductor material and a conductive material are uniformly dispersed.
The semiconductor particles mainly have an effect of increasing the temperature resistance coefficient (B). On the other hand, the conductive particles mainly have an effect of lowering the electric resistance value of the material.
In the present invention, the constant B when the relationship between the resistance (R) and the temperature (T) is approximated by R = Aexp (−BT) is defined as a “temperature resistance coefficient”.

[1.2.1. Semiconductor materials]
The semiconductor material contains at least SiC and Si. The semiconductor material may be composed only of SiC and Si, or may contain other materials.

  SiC is added to the starting material. SiC is preferably α-type SiC. SiC may be a mixture of α-type SiC and β-type SiC. SiC may be undoped with boron or may be doped with SiC. Further, other impurity elements (for example, N, P, Al, etc.) may be doped into SiC to increase the temperature resistance coefficient. SiC is suitable as a semiconductor particle because of its high durability under a reducing atmosphere and a large temperature resistance coefficient (B value).

As will be described later, Si is mainly formed by the reaction of Si—N ceramics with free carbon in SiC and / or boron added to the raw material.
Si can also be added to the starting material. However, since the melting point of Si (1414 ° C.) is usually lower than the sintering temperature of the material (1700 to 1800 ° C.), it is difficult to control the amount of Si in the method of adding Si to the starting material. Therefore, Si is preferably generated by reacting starting materials.

[1.2.2. Conductive material]
The thermistor material according to the present invention further includes a conductive material in addition to the insulating material and the semiconductor material. When particles made of a conductive material are further added to the thermistor material,
(A) Control of specific resistance value is facilitated.
(B) Durability is improved compared to the case of SiC alone.
(C) The temperature-resistance coefficient (sensitivity to temperature) increases and the measurement accuracy improves.
Effects such as can be obtained.

The “conductive material” refers to a metal compound having a specific resistance value at room temperature lower than that of SiC and Si and a melting point of 1700 ° C. or higher. The particles made of a conductive material constitute a part of the conductive path together with the particles made of a semiconductor material.
In the present invention, the conductive material is made of a metal compound such as a metal boride, metal nitride, metal silicide, or metal carbide. The conductive material may be composed of any one of these metal compounds, or may be a mixture or solid solution of two or more. Specific examples of the conductive material include borides, nitrides, carbides, silicides, and the like of groups 4A, 5A, and 6A in the periodic table.
The conductive material is preferably a boride-based metal compound. Of the boride-based metal compounds, TiB ₂ and TiB are particularly preferable. Since these materials have a thermal expansion coefficient close to that of SiC, and even if these are added to the material together with SiC, the residual stress is small, so that there is an advantage that the material is not easily cracked and is resistant to thermal shock.

[1.2.3. Average crystal grain size of second phase particles]
In the present invention, the average crystal grain size (d) of the second phase particles is 5 μm or less. In general, the smaller the average crystal grain size of the second phase particles, the smaller the variation in electrical resistance value. The average crystal grain size of the second phase particles is preferably 1 μm or less, more preferably 0.5 μm or less, and still more preferably 0.3 μm or less.
Of the second phase particles, the average crystal grain size of SiC is preferably 0.5 μm or less. The average crystal grain size of Si is preferably 1 μm or less.

[1.2.4. Particle size ratio]
The average crystal grain size of the second phase particles (especially SiC) and the first phase particles (especially Si—N-based ceramics) and the ratio thereof affect the variation in the electrical resistance value of the thermistor material. In general, as the average crystal grain size of SiC (d _SC) is reduced, and / or the ratio (= d the average crystal grain size of the Si-N ceramics to the average crystal grain size of _{SiC (d SC) (d m} ) _The smaller the _m / d _SC ), the smaller the variation in electrical resistance value.
In order to reduce the variation of the electric resistance value as compared with the conventional material, d _SC is preferably 0.5 μm or less, more preferably 0.3 μm or less. The _dm / d _SC ratio is preferably less than 4, more preferably less than 3. Such a d _SC and d _m / d _SC ratio can be obtained by using fine SiC as a starting material and pulverizing and mixing the raw material or by pulverizing the starting material in two stages. This point will be described later.

Of the second phase particles, the conductive particles may be coarser than the SiC particles as long as the average crystal grain size (d) is within the above range. This is because the conductive particles have a smaller additive amount than the semiconductor particles and are less affected by the particle size.
However, if the average crystal grain size of the conductive particles becomes too large, the strength may decrease. Therefore, the average crystal grain size of the conductive particles is preferably 5 μm or less. The average crystal grain size of the conductive particles is preferably 2 μm or less.

[1.3. Content of each component]
In general, the thermistor material having a smaller electric resistance value is obtained as the content of the second phase particles is increased. On the other hand, when the content of the second phase particles becomes excessive, the electric resistance value becomes excessively small, and the temperature range that can be measured with high accuracy becomes narrow.
Furthermore, when the amount of the conductive particles in the second phase particles becomes excessive, the temperature resistance coefficient (B) becomes excessively small, and the temperature range that can be measured with high accuracy becomes narrow.

The content of each component is selected in accordance with the composition of the first phase particles and the second phase particles and the purpose. In order to detect the temperature accurately in the temperature range of −80 ° C. to 200 ° C.,
The SiC content is 20 wt% or more and 40 wt% or less,
The Si content is 5 wt% or more and 20 wt% or less,
The content of the conductive material is 1 wt% or more and 15 wt% or less,
The balance is preferably made of the insulating material and inevitable impurities.
Here, the “content” of each component contained in the thermistor material refers to a value calculated by the Rietveld method.

The SiC content affects the electrical resistance value, temperature resistance coefficient (B value) and strength (denseness) of the material. In general, if the SiC content is too small, it is difficult to form a conductive path, and the resistance value tends to increase. That is, the particle spacing is widened, or the density of conductive paths is reduced, so that the electrical resistance value of the material becomes too large. In order to obtain an appropriate electric resistance value and high strength, the content of SiC is preferably 20 wt% or more. The content of SiC is more preferably 25 wt% or more.
On the other hand, when the content of SiC becomes excessive, not only the electric resistance value of the material becomes excessively small but also SiC tends to form aggregates. When SiC forms an aggregate, the aggregate becomes a starting point of fracture and becomes insufficiently densified, so that the strength is decreased and the temperature resistance coefficient (B value) is decreased. In order to obtain an appropriate electric resistance value and temperature resistance coefficient (B value) and high strength, the content of SiC is preferably 40 wt% or less. The content of SiC is more preferably 35 wt% or less.

If the Si content is too small, the B value becomes small. Accordingly, the content of Si is preferably 5 wt% or more. The content of Si is preferably 10 wt% or more.
On the other hand, when the Si content is excessive, the amount of liquid phase generated during sintering increases, and the variation in resistance value increases, the temperature characteristics become unstable, and the strength may decrease. Accordingly, the Si content is preferably 20 wt% or less. The Si content is preferably 15 wt% or less.

The conductive material mainly affects the specific resistance value of the thermistor material. When no conductive material is added at all, the specific resistance value is often excessively large. In addition, Si may be difficult to generate.
In order to obtain an appropriate specific resistance value, the content of the conductive material is preferably 1 wt% or more. The content of conductive particles is more preferably 5 wt% or more.
On the other hand, when the content of the conductive material is excessive, the specific resistance value is excessively decreased and the temperature resistance coefficient (B value) is decreased. Accordingly, the content of the conductive material is preferably 15 wt% or less. The content of the conductive material is more preferably 12 wt% or less.

For example, when a thermistor material is manufactured using TiB ₂ as a raw material for the conductive material, TiB is generated in the thermistor material. Although the details of the reason are unknown, it is considered that a part of TiB ₂ reacts with these when Si—N ceramics and B react to produce BN. TiB constitutes a part of the conductive material. When the conductive material is composed of TiB ₂ and TiB, the content of the semiconductor material and the conductive material (content calculated by the Rietveld method) particularly satisfies the relationship of the following formulas (1) to (3): It is preferable.
50 ≦ x × 100 / (x + y + z + w) ≦ 70 (1)
5 ≦ y × 100 / (x + y + z + w) ≦ 30 (2)
1 ≦ (z + w) × 100 / (x + y + z + w) ≦ 15 (3)
However,
x is the weight of SiC, y is the weight of Si,
z is the weight of TiB ₂ and w is the weight of TiB.

[1.3. Uniformity (electrical resistance variation)]
In the thermistor material according to the present invention, fine first phase particles and second phase particles are uniformly dispersed. The average crystal grain size and the uniformity of dispersion of the first phase particles and the second phase particles affect the variation in the electric resistance value. In general, the higher the uniformity of the dispersion of the first phase particles and the second phase particles, the smaller the variation in the electric resistance value.
When a method described later is used, a thermistor material having a small variation in electric resistance value (= standard deviation of electric resistance value × 100 / average value of electric resistance values) can be obtained. Specifically, by optimizing the manufacturing conditions, the variation in the electric resistance value is 10% or less, 7% or less, or 5% or less.

[1.4. Application]
SiC and Si used as semiconductor materials and metal compounds used as conductive materials all have high stability of electric resistance values in a reducing atmosphere. Therefore, the thermistor material according to the present invention is suitable as a material for a thermistor element for measuring temperature in a reducing atmosphere.

[2. Method for manufacturing thermistor material]
The thermistor material manufacturing method according to the present invention includes:
A SiC fine powder preparation step for preparing SiC powder having an average particle size (D _SC ) of 0.5 μm or less;
A pulverization and mixing step of adding Si-N ceramics, boron, a conductive material, and, if necessary, a powder of a sintering aid to the prepared SiC powder and pulverizing and mixing,
Forming and sintering the powder obtained in the pulverization and mixing step to obtain the thermistor material according to the present invention.

[2.1. SiC fine powder preparation process]
First, an SiC powder having an average particle diameter (D _SC ) of 0.5 μm or less is prepared (SiC fine powder preparation step).
When a commercially available SiC powder can be used to produce a material with little variation in electrical resistance, the commercially available SiC powder can be used as a starting material as it is. However, commercially available SiC powder usually has a predetermined particle size and particle size distribution. Even if such commercially available SiC powder is used as a raw material as it is, a thermistor material with small variation in electric resistance value cannot often be obtained. In such a case, it is preferable to pre-grind only the SiC powder among the starting materials. If the SiC powder is preliminarily pulverized in advance, the variation in the electric resistance value can be reduced.

When SiC powder is preliminarily pulverized, the average particle size of the SiC powder before pulverization is not particularly limited. In order to obtain a fine powder having a uniform particle size by pulverization in a short time, the average particle size of the SiC powder is preferably 0.5 μm or less.
Here, the “average particle diameter” of the powder refers to the median diameter (D ₅₀ ) of the particles measured by a laser diffraction / scattering method.

As the pulverization conditions, optimum conditions are selected according to the average particle diameter of the SiC powder, the pulverization method, and the like. In general, the greater the force applied to the powder during pulverization, the more thermistor material with less variation in electrical resistance value can be obtained by pulverization in a short time. On the other hand, pulverization more than necessary has no difference in effect and has no profit.
The optimum pulverization condition varies depending on the average particle diameter of the SiC powder, the pulverization method, and the like. For example, when SiC powder having an average particle diameter of about 1 μm is pulverized by a ball mill, the peripheral speed is preferably 40 m / min or more and 100 m / min or less in order to obtain a thermistor material having an electric resistance variation of 10% or less. . The pulverization time is preferably 12 hours or more and 200 hours or less. If the grinding time is too long, the amount of impurity components may be increased.

[2.2. Crushing and mixing process]
Next, the prepared SiC powder is further pulverized and mixed by adding Si—N ceramics, boron, a conductive material, and, if necessary, a sintering aid (pulverization and mixing step).

[2.2.1. Compounding amount]
[A. SiC powder]
Since SiC hardly reacts with other raw materials during sintering, the charged composition of the raw materials almost corresponds to the Si content in the sintered body. Therefore, the ratio of the weight of the SiC powder to the total weight of the raw materials is selected so that a sintered body having a target composition can be obtained.
In order to detect the temperature accurately in the temperature range of −80 ° C. to 200 ° C., the blending amount of the SiC powder is preferably 20 wt% or more and 40 wt% or less. More preferably, the blending amount of the SiC powder is not less than 24 wt% and not more than 35 wt%.

[B. Si-N ceramics]
Si-N ceramics react with boron to produce BN and Si. Si-N ceramics may react with the conductive material and / or the sintering aid. For example, when Si ₃ N ₄ is used as a starting material and Al ₂ O ₃ is used as a sintering aid, a part of Al ₂ O ₃ is dissolved in Si ₃ N ₄ to produce SiALON.

Therefore, the ratio of the weight of the Si—N-based ceramic powder to the total weight of the raw materials is selected so as to obtain a sintered body having the desired composition in consideration of the reaction between the raw materials.
In order to detect the temperature accurately in the temperature range of −80 ° C. to 200 ° C., the blending amount of the Si—N ceramic is preferably 40 wt% or more and 70 wt% or less. The blending amount of the Si—N ceramic is more preferably 45 wt% or more and 60 wt% or less.

[C. Boron]
Boron reacts with Si-N ceramics. Boron may react with the conductive material or suppress decomposition of the metal boride. Furthermore, the amount of boron added to the raw material affects the amount of Si contained in the sintered body. Therefore, the ratio of the weight of boron to the total weight of the raw materials is selected so as to obtain a sintered body having the desired composition in consideration of the reaction between the raw materials.
When no boron is added, the temperature resistance coefficient (B value) is often less than 0.01. In order to obtain a high temperature resistance coefficient (B value), the amount of boron is preferably 2 wt% or more.
On the other hand, when the amount of boron is excessive, the temperature resistance coefficient (B value) is lowered. Accordingly, the blending amount of boron is preferably 15 wt% or less. The amount of boron is preferably 10 wt% or less.

[D. Conductive material]
The conductive material may or may not react with other raw materials. Therefore, the ratio of the weight of the conductive material to the total weight of the raw materials is selected so as to obtain a sintered body having a target composition in consideration of the reaction between the raw materials.
In order to detect the temperature accurately in the temperature range of −80 ° C. to 200 ° C., the blending amount of the conductive material is preferably 1 wt% or more and 15 wt% or less. The blending amount of the conductive material is more preferably 4 wt% or more and 10 wt% or less.

[E. Sintering aid]
The sintering aid can be added as necessary. The composition of the sintering aid is selected in accordance with the composition of the starting material. Examples of the sintering aid include Y ₂ O ₃ , AlN, Al ₂ O ₃ , MgO, Cr ₂ O ₃ , MgAl ₂ O ₄ , Yb ₂ O ₃ , HfO, and La ₂ O ₃ . Any one of these sintering aids may be used, or two or more thereof may be used in combination. The sintering aid is particularly preferably Y ₂ O ₃ , Y ₂ O ₃ —MgAl ₂ O ₄ , or Y ₂ O ₃ —Al ₂ O ₃ .

The sintering aid may or may not react with other raw materials. Therefore, the ratio of the weight of the sintering aid to the total weight of the raw materials is selected in consideration of the reaction between the raw materials so as to obtain a sintered body having the desired composition.
In order to detect the temperature accurately in the temperature range of −80 ° C. to 200 ° C., the blending amount of the sintering aid is preferably 4 wt% or more and 20 wt% or less. More preferably, the amount of the sintering aid is 6 wt% or more and 10 wt% or less.

[F. Binder, dispersion stabilizer]
When the raw material powder is pulverized and mixed, a binder or a dispersion stabilizer may be added as necessary. The blending amount of the binder and the dispersion stabilizer is not particularly limited, and an optimum blending amount can be selected according to the purpose.

[2.2.2. Average particle size of raw material]
The average particle diameter of the powders of Si—N ceramics, boron, conductive material, and sintering aid, which are starting materials, is not particularly limited. In order to obtain a fine mixed powder having a uniform particle size by pulverization in a short time, the average particle size of the raw material powder is preferably 1 μm or less.

[2.2.3. Grinding conditions]
As the pulverization conditions, optimum conditions are selected according to the average particle diameter of each raw material powder, the pulverization method, and the like. In general, the greater the force applied to the powder during pulverization, the more thermistor material with less variation in electrical resistance value can be obtained by pulverization in a short time. On the other hand, pulverization more than necessary has no difference in effect and has no profit.
The optimum pulverization condition varies depending on the average particle diameter of each raw material powder, the pulverization method, and the like. For example, when a raw material powder having an average particle diameter of about 1 μm is pulverized by a ball mill, the peripheral speed is preferably 40 m / min or more and 100 m / min or less in order to obtain a thermistor material having an electric resistance variation of 10% or less. . The pulverization time is preferably 12 hours or more and 200 hours or less.

[2.3. Molding / sintering process]
Next, the powder obtained in the pulverization and mixing step is molded and sintered to obtain the thermistor material according to the present invention (molding and sintering step).
The molding method is not particularly limited, and an optimal method may be selected according to the purpose. Specific examples of the molding method include a press molding method, a CIP molding method, a cast molding method, a plastic molding method, an injection molding method, and a slip cast molding method. Moreover, in order to reduce the man-hour of the finishing process after sintering, you may perform a raw process with respect to the molded object which put the binder previously.

As the sintering temperature, an optimum temperature is selected according to the material composition. In general, the higher the sintering temperature is, the higher the density sintered body is obtained. On the other hand, when the sintering temperature is too high, the grain growth of the first phase crystal grains proceeds excessively, and the distribution of the semiconductor particles and the conductive particles becomes non-uniform.
For example, when the blending amount of SiC powder is 20 to 40 wt%, the sintering temperature is preferably 1750 to 1880 ° C., although it depends on the composition of the sintering aid.
As the sintering time, an optimum time is selected according to the sintering temperature.
The sintering method is not particularly limited. In order to obtain a dense sintered body, pressure sintering such as hot pressing or HIP is preferable.

  A thermistor element can be obtained by cutting the obtained sintered body into an appropriate size and joining electrodes on both sides. The material of the electrode is not particularly limited, and various materials can be used depending on the purpose. The electrode is preferably a material made of a metal or a compound having a thermal expansion coefficient close to that of the first phase.

[3. Operation of thermistor material and its manufacturing method]
In the thermistor material according to the present invention, two types of semiconductor materials having different band gaps (ie, SiC and Si) and second phase particles made of a conductive material are uniformly dispersed in the first phase made of an insulating material. In addition, the second phase particles have a fine structure in which a fine conductive path layer is formed. Such a thermistor material can be obtained by first using SiC fine powder as a main semiconductor material, adding the remaining raw material powder to this, pulverizing and mixing, and molding and sintering the pulverized mixed powder.

  When such a thermistor material is energized, the current flows through the second phase particles. In the thermistor material in which such a conductive path is formed, a large resistance change can be obtained with respect to the temperature change, and the temperature can be accurately detected in a low temperature range of −80 ° C. to 200 ° C. Furthermore, by forming a uniform and fine structure, variation in electrical resistance value between lots is reduced, and industrial productivity (robustness) is increased.

Although the details of the principle of obtaining such an effect are unknown, the temperature resistance changes more greatly depending on the temperature due to the superposition effect of the conductive paths of SiC and Si, which are semiconductor materials having a large resistance change with respect to temperature. It is presumed that can be expressed.
Further, by homogenizing the composition by miniaturizing the entire structure and at the same time making the conductive path structure sufficiently small with respect to the element size. Therefore, it is presumed that the resistance value in the thermistor element is also made uniform, and as a result, the resistance value variation between lots is also suppressed.
Furthermore, since the resistance values of the semiconductor material and the conductive material forming the conductive path are stable even in a reducing atmosphere, the thermistor element using the material according to the present invention has a stable resistance value even in the reducing atmosphere. Show.

(Example 1, Comparative Examples 1-2)
[1. Preparation of sample]
[1.1. Example 1]
Commercially available SiC raw material powder (average particle size D _50: 0.7 [mu] m) by a ball mill, rotation speed: 125 rpm (peripheral velocity: 55m / min), grinding time: pre pulverized under the conditions of 150 hr, an average particle diameter D ₅₀ SiC powder having a thickness of 0.2 μm was obtained.
Next, for pre-ground SiC powder: 65 g (32.8 wt%),
Si ₃ N ₄ powder (average particle size D ₅₀ : 1 μm): 95 g
Al ₂ O ₃ powder (average particle diameter D ₅₀ : 0.6 μm): 6 g,
AlN powder (average particle diameter D ₅₀ : 0.8 μm): 2 g
TiB ₂ powder (average particle diameter D ₅₀ : 1.5 μm): 14 g and B powder (average particle diameter D ₅₀ : 4.5 μm): 16 g were added.
This mixed powder was pulverized and mixed by a ball mill under the conditions of a rotational speed of 125 rpm (peripheral speed: 55 m / min) and a pulverization time of 72 hours. The obtained pulverized mixed powder was sintered in Ar at 1800 ° C. to prepare a thermistor substrate having a diameter of 40 mm.

[1.2. Comparative Example 1]
To the commercially available SiC raw material powder, Si ₃ N ₄ powder, Al ₂ O ₃ powder, AlN powder, TiB ₂ powder and B powder were added so as to have the same blending ratio as in Example 1. This mixed powder was mixed with a ball mill under the conditions of a rotational speed of 45 rpm (peripheral speed: 20 m / min) and a mixing time of 72 hours. The obtained mixed powder was sintered in Ar at 1800 ° C. to prepare a thermistor substrate having a diameter of 40 mm.

[1.3. Comparative Example 2]
In the same manner as in Example 1, SiC powder was pre-ground to obtain SiC powder having an average particle diameter D ₅₀ of 0.2 μm. Next, Si ₃ N ₄ powder, Al ₂ O ₃ powder, AlN powder, TiB ₂ powder and B powder were added to the pre-ground SiC powder so as to have the same blending ratio as in Example 1. This mixed powder was mixed with a ball mill under the conditions of a rotational speed of 45 rpm (peripheral speed: 20 m / min) and a mixing time of 72 hours. The obtained mixed powder was sintered in Ar at 1800 ° C. to prepare a thermistor substrate having a diameter of 40 mm.

[2. Test method and results]
[2.1. TEM observation]
FIG. 1 shows a TEM image of the thermistor material obtained in Example 1. It is found that the material contains Si and BN in addition to SiC crystal grains, Si-Al-N-based (SiALON) crystal grains, and Y-Al-O-based crystal grains derived from the sintering aid. It was. Si and BN are considered to be mainly produced by the reaction of Si ₃ N ₄ and B. The contents of the semiconductor material and the conductive material (values of the formulas (1) to (3)) determined by the Rietveld method were SiC: 65 wt%, Si: 24 wt%, and TiB ₂ + TiB: 11 wt%. D _SC = 0.3 μm and d _m / d _SC ratio was about 3.

[2.2. Absorption current image]
FIG. 2 shows an absorption current image of the thermistor material obtained in Example 1. In FIG. 2, the white portion represents the second phase. FIG. 2 shows that the second phase particles form a fine conductive path in the material.

[2.3. Resistance value]
A total of 13 chip-type elements of 2 mm square and 0.8 mm thickness were cut out from the vertical and horizontal radial directions of the thermistor substrate. The resistance value was measured for each chip-type element. FIG. 3 shows the temperature-resistance characteristics of the thermistor material obtained in Example 1. FIG. 3 shows that the material according to the present invention exhibits linear temperature resistance characteristics and high temperature sensitivity.

  Moreover, the variation in resistance value was evaluated from the resistance value of each chip-type element. FIG. 4 shows variations in resistance values of the thermistor materials obtained in Example 1 and Comparative Examples 1 and 2. All of the materials obtained in Comparative Examples 1 and 2 had a resistance value variation exceeding 30%. On the other hand, the resistance value variation of the material obtained in Example 1 was about 5%.

(Examples 2-3)
A thermistor base material was produced in the same manner as in Example 1 except that the blending amount of the SiC powder was 24 wt% (Example 2) or 32 wt% (Example 3). The resistance value variation of the thermistor base material obtained was 5% or less.

  Although the embodiments of the present invention have been described in detail above, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the scope of the present invention.

  The thermistor material according to the present invention can be used as a temperature sensor used in a temperature range of about −80 ° C. to 200 ° C. in a reducing atmosphere.

Claims (9)

Thermistor material with the following configuration.
(1) The thermistor material is
First phase particles made of an insulating material;
Second phase particles made of a semiconductor material and a conductive material,
The insulating material includes Si-N ceramics,
The semiconductor material includes SiC and Si,
The conductive material includes one or more metal compounds selected from the group consisting of metal borides, metal nitrides, metal silicides, and metal carbides.
(2) The thermistor material exhibits a structure in which the first phase particles and the second phase particles are uniformly dispersed;
Each of the first phase particles and the second phase particles has an average crystal grain size (d) of 5 μm or less,
The SiC has an average crystal grain size (d _SC ) of 0.5 μm or less,
The average crystal grain size (d _SI ) of the Si is 1 μm or less. 2. The thermistor material according to claim 1, wherein a ratio (= d _m / d _SC ) of an average crystal grain size (d _m ) of the Si—N-based ceramics to an average crystal grain size (d _SC ) of the SiC is less than 4. 3. . The content of SiC (content calculated by Rietveld method; hereinafter the same) is 20 wt% or more and 40 wt% or less,
The Si content is 5 wt% or more and 20 wt% or less,
The content of the conductive material is 1 wt% or more and 15 wt% or less,
The thermistor material according to claim 1 or 2, wherein the balance is made of the insulating material and inevitable impurities. The thermistor material according to any one of claims 1 to 3, wherein the conductive material is made of TiB ₂ and TiB. The thermistor material of Claim 4 with which content (content computed by the Rietveld method) of the said semiconductor material and the said electroconductive material satisfy | fills the relationship of following Formula (1)-Formula (3).
50 ≦ x × 100 / (x + y + z + w) ≦ 70 (1)
5 ≦ y × 100 / (x + y + z + w) ≦ 30 (2)
1 ≦ (z + w) × 100 / (x + y + z + w) ≦ 15 (3)
However,
x is the weight of the SiC, y is the weight of the Si,
z is the weight of TiB ₂ and w is the weight of TiB.   The thermistor material according to any one of claims 1 to 5, wherein variation in electric resistance value (= standard deviation of electric resistance value x 100 / average value of electric resistance value) is 10% or less.   The thermistor material according to any one of claims 1 to 6, wherein the thermistor material is used for temperature measurement under a reducing atmosphere. A SiC fine powder preparation step for preparing SiC powder having an average particle size (D _SC ) of 0.5 μm or less;
A pulverization and mixing step of adding Si-N ceramics, boron, a conductive material, and, if necessary, a powder of a sintering aid to the prepared SiC powder and pulverizing and mixing,
A method for producing a thermistor material, comprising: forming and sintering the powder obtained in the pulverization and mixing step to obtain the thermistor material according to any one of claims 1 to 7.   The method for producing the thermistor material according to claim 8, wherein the SiC fine powder preparation step includes a step of obtaining the SiC powder by preliminary pulverization.

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