JP2020057719A - Thermistor material and manufacturing method therefor - Google Patents

Abstract

To provide a thermistor material that uses few kinds of compositions as compared with a conventional one, and is capable of performing highly accurate temperature detection in a low-temperature region, and to provide a manufacturing method therefor.SOLUTION: A thermistor material comprises: matrix crystal grains made of SiN; a grain boundary phase existing between at least the matrix crystal grains; SiC crystal grains dispersed between the matrix crystal grains and/or in the grain boundary phase; Si crystal grains; and BN crystal grains. The thermistor material may further comprise TiN crystal grains and/or TiBcrystal grains in addition to these grains. Such a thermistor material has both of a proper specific resistance value and a relatively large temperature resistance change rate (B value). Such a thermistor material can be obtained by molding a mixture containing predetermined amounts of an SiNpowder, an SiC powder, a B powder or a TiBpowder, and a sintering aid and by sintering the molded mixture.SELECTED DRAWING: Figure 1

Description

  The present invention relates to a thermistor material and a method of manufacturing the same, and more particularly, to a thermistor material having a smaller number of types of constituent components than conventional and capable of detecting a temperature with high accuracy in a low temperature range, and a method of manufacturing the same.

  The thermistor refers to a resistor having a large change in electric resistance with respect to a change in temperature. The thermistors are classified into NTC thermistors whose electrical resistance decreases with increasing temperature, PTC thermistors whose electrical resistance increases with increasing temperature, and CRT thermistors whose electrical resistance sharply decreases above a certain temperature. Of these, the NTC thermistor is most used because the electric resistance value changes exponentially with temperature change at low cost, and the NTC thermistor simply refers to the NTC thermistor.

A commonly used thermistor is composed of an oxide composite containing two to four transition metal oxides such as Mn, Ni, Co, Fe, Cu, Y, and Cr. As such oxide-based thermistor materials, for example, spinel-type oxides, perovskite-type oxides, and mixtures of spinel and perovskite are known.
In an oxide thermistor, temperature detection is performed using the temperature dependence of oxygen ion diffusion. Further, in a thermistor made of a perovskite oxide, a p-type semiconductor in which more holes are introduced than holes due to oxygen vacancies is obtained by doping a divalent metal, and the electric resistance value in a low oxygen atmosphere is not improved. Stabilization has been suppressed.

Non-oxide thermistor materials are also known.
For example, Patent Document 1 discloses a general formula: (1-x) SiC-xMO (0.05 ≦ x ≦ 0.7, where MO is Al ₂ O ₃ , ZrO ₂ , Y ₂ O ₃ , or TiO ₂ ). A high temperature thermistor material having the composition represented is disclosed.
The document describes that a material having such a composition has a large thermistor constant, a small rate of change in resistance in a high temperature range, and is thermally and chemically stable.

Patent Document 2 discloses a temperature sensor in which a W wire is embedded as a resistor in a Si ₃ N ₄ sintered body.
The document describes that such a temperature sensor has excellent heat resistance even when irradiated with a high-temperature gas flame of 800 ° C. or higher, and the ignition response time is significantly shortened.

Patent Document 3 contains a conductive path forming material composed of (B ₄ C + SiC) in an amount of 13 to 15 wt%, the balance being composed of Al ₂ O ₃ , and a SiC / Al ₂ O ₃ ratio (volume ratio) of 0.044 or less. Thermistor material is disclosed.
The document describes that such a thermistor material has stability even when used at a temperature of 400 to 800 ° C., and it is easy to control the resistance value and seal the glass.

Patent Document _{4, Si 3 N 4 -8.7wt%} SiC-29.1wt% Y 2 O 3 -0.8wt% TiB 2 wide-range thermistor material consisting -0.2wt% B is disclosed .
The document describes that such a thermistor material has a low electric resistance in a wide temperature range from a low temperature to a high temperature, and the resistance value can be adjusted.

Patent Literature 5 discloses a reduction method including a matrix material made of an insulating ceramic and conductive particles made of a non-oxide conductive material and dispersed around the matrix material to form a conductive path. An atmospheric thermistor material is disclosed.
According to the document, conductive particles made of a non-oxide conductive material are arranged around a matrix material made of insulating ceramics that are stable in a reducing atmosphere, and a conductive path is formed around the matrix material. It describes that stable temperature detection is possible even in an atmosphere.

Further, Patent Document 6 includes 15 wt% or more and 30 wt% or less of α-type SiC, 0.6 wt% or more and 5.0 wt% or less of TiB ₂ , and 0.01 wt% or more and 12 wt% or less of boron, and the balance Discloses a low-temperature thermistor material comprising an insulating ceramic.
The document describes that a thermistor material having such a composition can perform temperature measurement in a temperature range of about −80 ° C. to 500 ° C. with high accuracy.

  A thermistor made of oxide ceramics performs temperature detection using ion conduction using oxygen deficiency. Therefore, when an oxide ceramics-based thermistor is used in a reducing atmosphere such as in hydrogen gas, the amount of oxygen deficiency changes, and as a result, the electric resistance value shifts significantly from its original value (the electric resistance value increases by one digit). ). To cope with this problem, at present, a structure is adopted in which the sensor element is shielded from gas by a glass seal, a metal tube, a resin coating, or the like. For this reason, there is a problem in that the cost is significantly increased by providing the seal structure, and the responsiveness is significantly reduced.

  On the other hand, in a SiC-based thermistor in which insulating ceramics and SiC are combined, there is no dependency on atmosphere and there is no problem such as an increase in electric resistance. In addition, since it has a small temperature-resistance coefficient, it is characterized by a wide range that can cover a wide temperature range from a low temperature (−80 ° C.) to a high temperature (1000 ° C. or more). However, such a wide-range thermistor has a problem that it cannot be applied to temperature detection in a short range such as only in a low-temperature range because of low detection accuracy.

On the other hand, when insulating ceramics are further compounded with TiB ₂ and B in addition to SiC and their contents are optimized, it is possible to detect the temperature with high accuracy in a low temperature range. A thermistor material can be obtained. However, the conventional low-temperature range thermistor material has many types of constituent components, and there is a problem in that it is difficult to stably manufacture the thermistor element and the manufacturing cost is increased.

JP-A-63-069203 JP-A-63-138224 JP-A-01-064202 JP 2000-348907 A JP 2009-259911 A JP 2013-197308 A

  The problem to be solved by the present invention is to provide a thermistor material having a smaller number of types of constituent components than in the past and capable of detecting a temperature with high accuracy in a low temperature range of about −50 ° C. to 500 ° C., and a method of manufacturing the same. Is to do.

In order to solve the above problems, a first aspect of the thermistor material according to the present invention has the following configuration.
(1) The thermistor material is
Matrix crystal grains composed of Si ₃ N ₄ ,
A grain boundary phase present between at least the matrix crystal grains,
SiC crystal grains, Si crystal grains, and BN crystal grains dispersed between the matrix crystal grains and / or in the grain boundary phase.
(2) The thermistor material comprises:
Si / BN ratio (strongest line peak intensity ratio) is 0.1 or more and 2.5 or less,
Si / SiC ratio (strongest line peak intensity ratio) is 0.1 or more and 2.0 or less, and
The Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) is 0.1 or more and 6.0 or less.
(3) The thermistor material comprises:
The specific resistance value at 0 ° C. is 0.5 kΩcm or more and 200 kΩcm or less, and
The rate of change in temperature resistance (B value) is 0.009 or more and 0.025 or less.

A first aspect of the method for producing a thermistor material according to the present invention has the following configuration.
(1) The method for producing the thermistor material is as follows:
A mixing step of obtaining a mixture containing Si ₃ N ₄ powder, SiC powder, B powder, and a sintering aid as main raw materials;
A forming and sintering step of forming and sintering the mixture.
(2) The mixing step comprises:
SiC compound amount becomes more than 14 vol% and less than 40 vol%,
B content becomes 2 vol% or more and 30 vol% or less,
The compounding amount of the sintering aid is 4 vol% or more and less than 15 vol%,
They consist of a mixture of these so that the remainder is Si ₃ N ₄ .
(3) The mixing step and the forming / sintering step
Si / BN ratio (strongest line peak intensity ratio) becomes 0.1 or more and 2.5 or less,
Si / SiC ratio (strongest line peak intensity ratio) becomes 0.1 or more and 2.0 or less,
Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) becomes 0.1 or more and 6.0 or less,
The specific resistance at 0 ° C. becomes 0.5 kΩcm or more and 200 kΩcm or less, and
The temperature resistance change rate (B value) is 0.009 or more and 0.025 or less,
The main material is mixed, and the mixture is molded and sintered.

A second aspect of the thermistor material according to the present invention has the following configuration.
(1) The thermistor material is
Matrix crystal grains composed of Si ₃ N ₄ ,
A grain boundary phase present between at least the matrix crystal grains,
SiC crystal grains, Si crystal grains, BN crystal grains, and TiN crystal grains dispersed between the matrix crystal grains and / or in the grain boundary phase, or TiB ₂ crystal grains in addition thereto. .
(2) The thermistor material comprises:
A Si / BN ratio (strongest line peak intensity ratio) of 0.1 or more and 1.6 or less;
A Si / SiC ratio (strongest line peak intensity ratio) of 0.1 to 0.6,
A Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) of 0.1 to 0.5, and
(TiN + TiB ₂ ) / SiC ratio (strongest line peak intensity ratio) is 0.2 or more and 1.5 or less.
(3) The thermistor material comprises:
The specific resistance value at 0 ° C. is 0.5 kΩcm or more and 200 kΩcm or less, and
The rate of change in temperature resistance (B value) is 0.009 or more and 0.025 or less.

Further, a second aspect of the method for producing a thermistor material according to the present invention has the following configuration.
(1) The method for producing the thermistor material is as follows:
A mixing step of obtaining a mixture containing Si ₃ N ₄ powder, SiC powder, TiB ₂ powder, and a sintering aid as main raw materials;
A forming and sintering step of forming and sintering the mixture.
(2) The mixing step comprises:
SiC compound amount becomes more than 14 vol% and less than 40 vol%,
TiB ₂ compounding amount becomes 4 vol% or more and 15 vol% or less,
The compounding amount of the sintering aid is 4 vol% or more and less than 15 vol%,
They consist of a mixture of these so that the remainder is Si ₃ N ₄ .
(3) The mixing step and the forming / sintering step
Si / BN ratio (strongest line peak intensity ratio) becomes 0.1 or more and 1.6 or less,
The Si / SiC ratio (strongest line peak intensity ratio) becomes 0.1 or more and 0.6 or less,
Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) becomes 0.1 or more and 0.5 or less,
(TiN + TiB ₂ ) / SiC ratio (strongest line peak intensity ratio) becomes 0.2 or more and 1.5 or less,
The specific resistance at 0 ° C. becomes 0.5 kΩcm or more and 200 kΩcm or less, and
The temperature resistance change rate (B value) is 0.009 or more and 0.025 or less,
The main material is mixed, and the mixture is molded and sintered.

In the thermistor material in which the matrix crystal grains composed of Si ₃ N ₄ and the SiC crystal grains are combined, in order to obtain a short range property, it is necessary to add both a predetermined amount of B and a predetermined amount of TiB _2. Was considered mandatory.
On the other hand, when a relatively large amount of B alone is added to the thermistor material in which the matrix crystal grains composed of Si ₃ N ₄ and the SiC crystal grains are combined, and the content of each component is optimized. Thus, a thermistor material having an appropriate specific resistance value and a relatively high rate of change in temperature resistance can be obtained. This is because Si ₃ N ₄ in the raw material reacts with B to generate Si crystal grains of an appropriate amount and an appropriate size, and the generated Si crystal grains are discretely formed between the SiC crystal grains at an appropriate interval. To form conductive paths dispersed in

Similarly, when a relatively large amount of TiB ₂ alone is added to a thermistor material in which a matrix crystal grain composed of Si ₃ N ₄ and a SiC crystal grain are combined, and the content of each component is optimized, Thus, a thermistor material having an appropriate specific resistance value and a relatively high rate of change in temperature resistance can be obtained. This is because Si ₃ N ₄ and TiB ₂ in the raw material react with each other to generate appropriate amounts and appropriate sizes of Si crystal grains and TiN crystal grains, and the generated Si crystal grains and TiN crystal grains (and TiB ₂ grains) when TiB ₂ reaction remains discretely distributed between the SiC crystal grains at moderate intervals, these crystal grains is considered to form a conductive path.

FIG. 14 is a diagram illustrating a relationship between a temperature T and a resistance value R of the thermistor element obtained in Example 6. FIG. 14 is a view showing the relationship between the temperature T and the resistance value R of the thermistor element obtained in Example 10. FIG. 9 is a diagram illustrating a relationship between a temperature T and a resistance value R of the thermistor element obtained in Comparative Example 2.

It is a figure which shows the relationship between B compounding quantity and Si / BN ratio. It is a figure which shows the relationship between B compounding quantity and Si / SiC ratio. It is a diagram showing the relationship between the B amount and the Si / Si ₃ N ₄ ratio.

It is a diagram showing the relationship between TiB ₂ amount and Si / BN ratio. Is a diagram showing the relationship between TiB ₂ amounts and Si / SiC ratio. It is a diagram showing the relationship between TiB ₂ amount and Si / Si ₃ N ₄ ratio. It is a diagram showing the relationship between TiB ₂ amount and (TiN + TiB ₂₎ / SiC ratio.

Hereinafter, an embodiment of the present invention will be described in detail.
[1. Thermistor material (1)]
The thermistor material according to the first embodiment of the present invention has the following configuration.
(1) The thermistor material is
Matrix crystal grains composed of Si ₃ N ₄ ,
A grain boundary phase present between at least the matrix crystal grains,
SiC crystal grains, Si crystal grains, and BN crystal grains dispersed between the matrix crystal grains and / or in the grain boundary phase.
(2) The thermistor material comprises:
Si / BN ratio (strongest line peak intensity ratio) is 0.1 or more and 2.5 or less,
Si / SiC ratio (strongest line peak intensity ratio) is 0.1 or more and 2.0 or less, and
The Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) is 0.1 or more and 6.0 or less.
(3) The thermistor material comprises:
The specific resistance value at 0 ° C. is 0.5 kΩcm or more and 200 kΩcm or less, and
The rate of change in temperature resistance (B value) is 0.009 or more and 0.025 or less.

[1.1. component]
[1.1.1. Matrix crystal grains]
[A. Composition of matrix grains]
The matrix crystal grains are made of insulating ceramics. “Insulating ceramics” refers to those having a specific resistance of 10 ¹² Ωcm or more. In the present embodiment, the matrix crystal grains are made of Si ₃ N ₄ .

[B. Average grain size of matrix grains]
In the present invention, the average crystal grain size of the matrix crystal grains is not particularly limited, and an optimal value can be selected according to the purpose. Generally, as the average crystal grain size of the matrix crystal grains becomes smaller, the variation in the specific resistance value becomes smaller. The average crystal grain size of the matrix crystal grains is preferably 5 μm or less. The average crystal grain size is preferably 1 μm or less, more preferably 0.75 μm or less.
Here, the “average crystal grain size” refers to a median value (diameter of a minimum circumscribed circle of crystal grains) of 10 or more crystal grains randomly selected by observation with a microscope (SEM, TEM, EPMA, etc.). It refers to the crystal grain size (d ₅₀ ) when the cumulative distribution of the sampled crystal grains becomes 50%.

[1.1.2. Grain boundary phase]
[A. Composition of Grain Boundary Phase]
The grain boundary phase exists at least between the matrix grains. The grain boundary phase may be present between SiC crystal grains, between Si crystal grains, between BN crystal grains, or between these crystal grains in addition to between matrix crystal grains. The grain boundary phase is an oxide phase, and its composition depends on the composition of the sintering aid added to the raw material. In the present invention, the composition of the grain boundary phase is not particularly limited.

As the grain boundary phase, for example,
(A) a composition used as sintering aids _{(e.g., Al 2 O 3, AlN,} Y 2 O 3, Yb 2 O 3, SiO 2, Lu 2 O 3, CeO 2, MgO, ZrO 2, SrO, HfO ₂ , Cr ₂ O ₃ ),
(B) a composition formed by the reaction of two or more sintering aids,
(C) a composition produced by reacting one or more sintering aids with other main raw materials (eg, Si ₃ N ₄ , SiC);
and so on.

[B. Grain boundary phase crystallinity]
The grain boundary phase may be crystalline or amorphous depending on the type of material added as a sintering aid and sintering conditions. In the present invention, the grain boundary phase may be crystalline or amorphous.
Generally, when the grain boundary phase is amorphous (low melting point phase), it tends to be densified at the time of sintering, but the sintered body tends to have a higher specific resistance and lower heat resistance. On the other hand, when the grain boundary phase includes a crystal phase, element diffusion in a high temperature region is suppressed, and heat resistance is improved.
[C. Grain boundary phase thickness]
If the grain boundary phase is too thick, the conductivity will decrease and the specific resistance will increase. Therefore, the thickness of the grain boundary phase is preferably 10 nm or less. The thickness of the grain boundary phase is preferably 6 nm or less, more preferably 3 nm or less.
On the other hand, when the grain boundary phase is too thin, sinterability is impaired. Therefore, the thickness of the grain boundary phase is preferably 0.5 nm or more. The thickness of the grain boundary phase is preferably at least 1 nm, more preferably at least 2 nm.

[1.1.3. SiC crystal grains]
[A. Composition of SiC crystal grains]
The SiC crystal grains are semiconductors and are dispersed between matrix crystal grains and / or in a grain boundary phase. The SiC crystal grains form a conductive path together with the Si crystal grains. The SiC crystal grains may be either α-type SiC or β-type SiC.
The specific resistance value of the SiC crystal grain changes according to the crystal structure, the type and amount of the impurity element, and the like. The specific resistance value of the SiC crystal grains is preferably 0.01 Ωcm or more and 10 ⁵ Ωcm or less, and more preferably 0.02 Ωcm or more and 10 ³ Ωcm or less.

[B. Average grain size of SiC grains]
In this embodiment, the average crystal grain size d ₅₀ of the SiC crystal grains is not limited in particular, it is possible to select an optimum value depending on the purpose. In general, the higher the d ₅₀ of the SiC crystal grains become smaller, the densification is promoted to suppress grain growth the Si ₃ N ₄ crystal that occurs during sintering, because the structure becomes finer, smaller variations in the specific resistance value Become. D ₅₀ of SiC grains is preferably not more than 5 [mu] m. d ₅₀ is preferably 2 μm or less, more preferably 1 μm or less, and further preferably 0.7 μm or less.

[1.1.4. Si crystal grains and BN crystal grains]
The Si crystal grains and the BN crystal grains are reaction products generated by the reaction between the B (boron) powder as the starting material and the Si ₃ N ₄ powder. Both the Si crystal grains and the BN crystal grains are dispersed between the matrix crystal grains or in the grain boundary phase.
Among these, the Si crystal grains are semiconductors and form a conductive path together with the SiC crystal grains described above. On the other hand, BN crystal grains are insulators, but are inevitably by-produced impurities with the generation of Si crystal grains. In the present invention, BN crystal grains hardly contribute to the development of thermistor characteristics.

The average grain size d ₅₀ of the Si crystal grains and BN grain is not particularly limited, it is possible to select an optimum value depending on the purpose. D ₅₀ of Si grains and BN grain is primarily an average particle size of B powder and Si ₃ N ₄ powder as a starting material, and depends on the sintering conditions. When a method described later is used, d _{50 of the} Si crystal grain is about 0.1 μm to 5 μm. Further, d ₅₀ of the BN crystal grains is about 0.1 m to 10 m.

[1.2. Content of each component-peak intensity ratio of strongest line]
The thermistor material according to the present embodiment includes a predetermined amount of a grain boundary phase, SiC crystal grains, Si crystal grains, and BN crystal grains, and the remainder consists of matrix crystal grains and unavoidable impurities. For the content of each component, an optimal value can be selected according to the purpose. In the present embodiment, instead of directly specifying the content of each component, the maximum intensity peak intensity ratio is used instead.

[1.2.1. Si / BN ratio]
The “Si / BN ratio” refers to the ratio (= I _Si / I _BN ) of the peak intensity (I _Si ) of the strongest line of Si to the peak intensity (I _BN ) of the strongest line of BN obtained when X-ray diffraction is performed. ).
In the present embodiment, in order to obtain an appropriate specific resistance value and a rate of change in temperature resistance (temperature detection accuracy) for exhibiting thermistor characteristics, an appropriate amount and an appropriate size are set between SiC crystal grains. Desirably, Si crystal grains are dispersed discretely. Generally, as the amount of B added to the raw material increases, the amount of Si in the sintered body increases. However, BN crystal grains are generated simultaneously with the generation of Si crystal grains. Since the BN crystal grains are insulators, the specific resistance of the sintered body is determined by the magnitude of the Si / BN ratio. As a result, as the B amount increases, the specific resistance value decreases, the rate of change in temperature resistance (B value) increases, and the temperature detection accuracy increases. Therefore, it is preferable that Si crystal grains of an appropriate size are dispersed in an appropriate amount in BN which is an insulating material. To obtain such an effect, the Si / BN ratio needs to be 0.1 or more. The Si / BN ratio is preferably at least 0.2, preferably at least 0.3, and more preferably at least 0.6.

  On the other hand, when the amount of generated Si crystal grains becomes excessive, Si liquidized at 1410 ° C. or more diffuses the crystal grain boundary phase to connect the Si crystal grains. As a result, the specific resistance value becomes excessively small, and the temperature resistance change rate (B value) becomes excessively small, so that the original characteristics of the highly accurate thermistor may be impaired. Therefore, the Si / BN ratio needs to be 2.5 or less. The Si / BN ratio is preferably 1.6 or less, more preferably 1.5 or less.

[1.2.2. Si / SiC ratio]
"Si / SiC ratio" refers to the ratio (= I _Si / I _SiC peak intensity of the strongest line of Si to the peak intensity of the strongest line of SiC obtained when performing the X-ray diffraction (I _SiC) (I _Si) ).
In the present embodiment, the amount of Si crystal grains contained in the sintered body increases as the amount of B added increases. In order to obtain an appropriate specific resistance value and a temperature resistance change rate (temperature detection accuracy) for exhibiting thermistor characteristics, an appropriate amount and an appropriate size of Si crystal grains are discretely dispersed between SiC crystal grains. It is desirable to form the microstructures that are present. In addition, a conductive path is formed by Si crystal grains and SiC crystal grains dispersed in the sintered body. Since the specific resistance value is Si <SiC, the specific resistance value decreases as the amount of generated Si crystal grains increases. Thus, in order to exhibit an appropriate specific resistance value and a high rate of change in temperature resistance (temperature detection accuracy), the Si / SiC ratio needs to be 0.1 or more. The Si / SiC ratio is preferably at least 0.2, preferably at least 0.3, and more preferably at least 0.4.
Further, for the same reason as the Si / BN ratio, the Si / SiC ratio needs to be 2.0 or less. The Si / SiC ratio is preferably at most 1.8, more preferably at most 1.6.

[1.2.3. Si / Si ₃ N ₄ ratio]
The "Si / Si ₃ N ₄ ratio", the ratio of the peak intensity of the strongest line of Si to the peak intensity of the strongest line the Si ₃ N ₄ obtained when performing the X-ray diffraction _{(I Si3N4) (I Si)} ( = I _Si / I _Si3N4 ).
In the present embodiment, in order to obtain an appropriate specific resistance value and a rate of change in temperature resistance (temperature detection accuracy), a conductive material in which an appropriate amount and an appropriate size of Si crystal grains are discretely dispersed together with SiC crystal grains. It is desirable to form a path. Since Si is mainly generated by the reaction between B added to the raw material and Si ₃ N ₄ , the Si content in the sintered body increases as the B addition amount increases, while Si ₃ N which is an insulating material ₄ amount decreases conversely. For this reason, when the amount of Si becomes too large, the amount of Si ₃ N ₄ relatively decreases, and the liquid phase Si diffuses between the Si ₃ N ₄ crystal grains, thereby breaking the discrete dispersion form. The specific resistance value is too low. For this reason, the Si / Si ₃ N ₄ ratio needs to be 0.1 or more in order to develop an appropriate specific resistance value and a rate of change in temperature resistance. The Si / Si ₃ N ₄ ratio is preferably at least 0.4, more preferably at least 0.6.
Further, for the same reason as the Si / BN ratio, the Si / Si ₃ N ₄ ratio needs to be 6.0 or less. The Si / Si ₃ N ₄ ratio is preferably 5.0 or less, more preferably 4.0 or less.

[1.3. Specific resistance]
The specific resistance value of the thermistor material depends on the amount and particle size of the SiC crystal grains and the Si crystal grains of the semiconductor, and the dispersion state of these crystal grains. In general, the specific resistance of the thermistor material decreases as the amount of crystal grains made of these conductive materials increases or as the number or area of contact points between these crystal grains increases.

Generally, when the specific resistance of the thermistor material becomes too small, the specific resistance decreases due to self-heating, and as a result, the specific resistance of the thermistor becomes unstable. Therefore, the specific resistance value of the thermistor material at 0 ° C. needs to be 0.5 kΩcm or more. The specific resistance value is preferably 0.7 kΩcm or more, more preferably 1.0 kΩcm or more.
On the other hand, if the specific resistance value of the thermistor material is too large, the current value becomes small, so that the change in current (voltage) due to a temperature change becomes small, and measurement becomes impossible. Therefore, the specific resistance value of the thermistor material at 0 ° C. needs to be 200 kΩcm or less. The specific resistance value is preferably 100 kΩcm or less, more preferably 50 kΩcm or less.

[1.4. Temperature resistance change rate (B value)]
In the present invention, the “temperature resistance change rate (B value)” refers to a constant B when the relationship between electric resistance (R) and temperature (T; Celsius temperature) is approximated by R = Aexp (−BT).
In the thermistor material according to the present embodiment, when the relationship between electric resistance (R) and temperature (T) is represented by R = Aexp (−BT), logR is T at least in a temperature range of −80 ° C. to 500 ° C. (The electrical resistance (R) changes linearly with temperature on a semilogarithmic graph). Moreover, the slope (B value) is relatively large. Therefore, the temperature can be accurately detected in the low temperature range. The B value slightly varies depending on the composition of the thermistor material, but is in the range of 0.009 or more and 0.025 or less when a method described later is used.

[2. Manufacturing method of thermistor material (1)]
The method for manufacturing a thermistor material according to the first embodiment of the present invention includes:
A mixing step of obtaining a mixture containing Si ₃ N ₄ powder, SiC powder, B powder, and a sintering aid as main raw materials;
A forming and sintering step of forming and sintering the mixture.

[2.1. Mixing process]
First, a mixture containing Si ₃ N ₄ powder, SiC powder, B powder, and a sintering aid as main raw materials is obtained (mixing step). When mixing the raw material powders, if necessary, other additives such as a binder and a dispersion stabilizer may be added to perform the granulation treatment. By performing such a process, moldability (compactness) is improved.

[2.1.1. Main raw material]
[A. Si ₃ N ₄ powder]
The Si ₃ N ₄ powder added to the raw material becomes matrix crystal grains of the sintered body. As the density of the sintered body decreases, more open pores remain, and oxygen easily diffuses inside the sintered body. In the present invention, the SiC powder is added to the raw material. However, since the SiC powder is difficult to sinter, it is likely to aggregate in the sintered body and form open pores. In order to obtain a dense sintered body, the smaller the average particle size (primary particle size) of the Si ₃ N ₄ powder, the better. Further, it is better that the particle size distribution is broad enough to improve the moldability. In order to obtain a dense sintered body, the average particle diameter (primary particle diameter) of the Si ₃ N ₄ powder is preferably 1 μm or less. The average particle size is preferably 0.7 μm or less, more preferably 0.5 μm or less.
Here, the “average particle size” refers to the median diameter (D ₅₀ ) of the particle size of the powder measured by the laser diffraction / scattering method.

[B. SiC powder]
The SiC powder added to the raw material forms a part of a conductive path in the sintered body. Although the SiC powder hardly grows during sintering, a part of the SiC powder reacts with other raw materials, and the surface of the SiC powder or another raw material (for example, Si ₃ N ₄ powder) becomes crystalline. May be formed.

The average particle diameter D ₅₀ of SiC powder can be relatively large. However, the D ₅₀ of the SiC powder is too large, decrease the density of the sintered body, or the variation of the specific resistance value becomes larger. Densifying the sintered body, and, in order to reduce variations in the specific resistance, D ₅₀ of the SiC powder is preferably not more than 5 [mu] m. D ₅₀ is preferably, 1 [mu] m or less, more preferably 0.5 [mu] m or less, more preferably, 0.2μm or less.

[C. B powder]
The B powder added to the raw material reacts with Si ₃ N ₄ during sintering to generate Si crystal grains and BN crystal grains. The Si crystal grains form a part of the conductive path in the sintered body. BN crystal grains are insulators and hardly contribute to thermistor characteristics.
B average particle diameter D ₅₀ of the powder may be relatively large. However, the D ₅₀ of the B powder is too large, the reaction the top of the Si ₃ N ₄ is locally and becomes uneven. As a result, the density of the sintered body becomes non-uniform and / or decreases, or the variation in the specific resistance value and the B value increases. The entire sintered body was densified, and, in order to reduce variations in the specific resistance value and the B value, D ₅₀ of the B powder is preferably not more than 1 [mu] m. D ₅₀ is preferably, 0.5 [mu] m or less, more preferably, 0.1μm or less.

[D. Sintering aid]
The sintering aid added to the raw material constitutes all or a part of the grain boundary phase in the sintered body. The grain boundary phase is formed when the sintering aid is substantially formed only of the sintering aid or when the sintering aid reacts with another raw material powder (for example, SiO _{2 on the} surface of Si ₃ N ₄ powder). Sometimes. In the present invention, the composition of the sintering aid is not particularly limited, and an optimum one can be selected according to the purpose. Examples of the sintering aid include Al ₂ O ₃ , AlN, Y ₂ O ₃ , Yb ₂ O ₃ , SiO ₂ , Lu ₂ O ₃ , CeO ₂ , MgO, ZrO ₂ , SrO, HfO ₂ , Cr ₂ O There are _three .

To obtain a dense sintered body, the average particle diameter D ₅₀ of the sintering aid can also be smaller. To obtain a dense sintered body, D ₅₀ of the sintering aid is preferably not more than 0.5 [mu] m. D ₅₀ is preferably 0.3 μm or less, more preferably 0.1 μm or less.

[2.1.2. Amount of each raw material]
For the amount of each raw material, an optimum value is selected according to the purpose. In order to obtain a thermistor material having an appropriate specific resistance value and a relatively high rate of change in temperature resistance (B value), the mixing step includes:
SiC compound amount becomes more than 14 vol% and less than 40 vol%,
B content becomes 2 vol% or more and 30 vol% or less,
The compounding amount of the sintering aid is 4 vol% or more and less than 15 vol%,
It is necessary to mix these so that the remainder is Si ₃ N ₄ .

[A. SiC content]
In general, as the amount of SiC compounded increases, the specific resistance value decreases, and the mechanical strength of the sintered body also increases due to particle strengthening. In order to obtain such effects, the amount of SiC must be more than 14 vol%. The compounding amount of SiC is preferably 16 vol% or more, more preferably 20 vol% or more, and further preferably 25 vol% or more.
On the other hand, when the compounding amount of SiC is excessive, the sintered density is reduced, the mechanical properties are reduced, and the specific resistance value may be excessively reduced. Further, the rate of change in temperature resistance (B value) is rather reduced. This is presumably because, when the amount of SiC compounded becomes excessive, the number and width of the conductive paths constituted by the SiC crystal grains are greatly increased and become dense. Further, the SiC crystal grains are easily aggregated, and pores are easily formed between the SiC crystal grains. Therefore, the amount of SiC needs to be less than 40 vol%. The SiC compounding amount is preferably 35 vol% or less, more preferably 30 vol% or less.

[B. B compounding amount]
As described above, the B powder added to the raw material reacts with the Si ₃ N ₄ powder during sintering to generate Si crystal grains. In general, as the B content increases, the rate of change in temperature resistance (B value) increases. This is probably because a large amount of Si crystal grains generated by the reaction are dispersed discretely between the SiC crystal grains. In order to obtain such an effect, the B content needs to be 2 vol% or more. B content is preferably 5 vol% or more, preferably 8 vol% or more, and more preferably 10 vol% or more.

  On the other hand, when the B content is excessive, the rate of change in temperature resistance (B value) is rather reduced. This is probably because Si crystal grains are excessively generated and the SiC crystal grains are connected by the Si crystal grains, or a continuous phase of a single Si phase is formed. This tendency becomes conspicuous when the amount of SiC is relatively large and the amount of B is relatively large. Therefore, the B content needs to be 30 vol% or less. B content is preferably 25 vol% or less.

[C. Amount of sintering aid]
If the amount of the sintering aid is too small, a dense sintered body cannot be obtained. Therefore, the compounding amount of the sintering aid needs to be 4 vol% or more. The amount of the sintering aid is preferably at least 5 vol%, more preferably at least 6 vol%.
On the other hand, if the amount of the sintering aid is excessive, the thickness of the grain boundary phase may increase, and the specific resistance value may increase. In addition, the diffusion of the auxiliary agent during sintering becomes remarkable, and there is a possibility that the characteristics of the sintered bodies may vary. Therefore, the compounding amount of the sintering aid needs to be less than 15 vol%. The compounding amount of the sintering aid is preferably 12 vol% or less, more preferably 10 vol% or less.

[D. Amount of other additives]
When mixing the raw material powders, a binder or a dispersion stabilizer may be added as necessary. The blending amounts of the binder and the dispersion stabilizer are not particularly limited, and an optimal blending amount can be selected according to the purpose.

[2.1.3. Mixing method]
The method of mixing the raw materials is not particularly limited, and various methods can be used. In addition, the raw materials may be ground at the time of mixing. Further, the powder mixed and pulverized may be granulated by spray drying using a spray drier or the like. By granulating the raw material powder, the fluidity in the mold is improved, and the moldability and the compactness can be improved.

[2.2. Sintering process]
Next, the mixture obtained in the mixing step is molded and sintered (molding / sintering step).

[2.2.1. Forming method and sintering method]
The molding method is not particularly limited, and an optimal method can be selected according to the purpose. Specific examples of the molding method include a press molding method, a CIP molding method, a casting molding method, a plastic molding method, an injection molding method, a slip casting molding method, a glass sealing method, an extrusion molding method, a tape molding method, and a doctor blade. There are laws. Further, in order to reduce the number of finishing processes after sintering, a green body in which a binder has been added in advance may be subjected to raw processing.
Similarly, the sintering method is not particularly limited, and an optimum method can be selected according to the purpose. In order to obtain a dense sintered body, pressure sintering such as hot press processing, SPS (Spark Plasma Sintering) processing, and HIP processing is preferable.

[2.2.2. Molding conditions and sintering conditions]
For the molding conditions and sintering conditions of the molded body, optimal conditions are selected according to the purpose. Further, the specific resistance value and the rate of change in temperature resistance (B value) depend not only on the molding conditions and sintering conditions but also on the pulverization and mixing conditions (mainly, the mixing ratio of the main raw materials and the particle size ratio).
In order to obtain a thermistor material having an appropriate specific resistance value and a relatively high rate of change in temperature resistance (B value), the mixing step and the forming / sintering step are performed as follows.
Si / BN ratio (strongest line peak intensity ratio) becomes 0.1 or more and 2.5 or less,
Si / SiC ratio (strongest line peak intensity ratio) becomes 0.1 or more and 2.0 or less,
Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) becomes 0.1 or more and 6.0 or less,
The specific resistance at 0 ° C. becomes 0.5 kΩcm or more and 200 kΩcm or less, and
The B value (temperature resistance change rate) is 0.009 or more and 0.025 or less.
It is necessary to mix the main raw materials and to mold and sinter the mixture.

The optimum sintering temperature is selected according to the material composition. In general, the higher the sintering temperature, the higher the density of the sintered body obtained, and the more the reaction between the materials proceeds. On the other hand, if the sintering temperature is too high, the grain growth of the matrix crystal grains will proceed excessively, mechanical properties such as strength and fracture toughness will decrease, and the distribution of SiC crystal grains will be non-uniform. Furthermore, the raw materials may be decomposed and sublimated. Therefore, the sintering temperature is preferably 1800 ° C. or more and less than 1900 ° C.
As for the sintering time, it is preferable to select an optimum time according to the sintering temperature. In general, when a relatively large amount of B powder is contained in a raw material, when the sintering temperature is too high and / or the sintering time is too long, an excessive Si phase (liquid phase) may be generated. There is. Si forms a liquid phase at a temperature of 1410 ° C. or higher and is easily diffused. As a result, the composition in the sintered body becomes non-uniform, and the thermistor characteristics may vary.

[3. Thermistor material (2)]
The thermistor material according to the second embodiment of the present invention has the following configuration.
(1) The thermistor material is
Matrix crystal grains composed of Si ₃ N ₄ ,
A grain boundary phase present between at least the matrix crystal grains,
SiC crystal grains, Si crystal grains, BN crystal grains, and TiN crystal grains dispersed between the matrix crystal grains and / or in the grain boundary phase, or TiB ₂ crystal grains in addition thereto. .
(2) The thermistor material comprises:
A Si / BN ratio (strongest line peak intensity ratio) of 0.1 or more and 1.6 or less;
A Si / SiC ratio (strongest line peak intensity ratio) of 0.1 to 0.6,
A Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) of 0.1 to 0.5, and
(TiN + TiB ₂ ) / SiC ratio (strongest line peak intensity ratio) is 0.2 or more and 1.5 or less.
(3) The thermistor material comprises:
The specific resistance value at 0 ° C. is 0.5 kΩcm or more and 200 kΩcm or less, and
B value (rate of change in temperature resistance) is 0.009 or more and 0.025 or less.

[3.1. component]
[3.1.1. Matrix crystal grains]
In the present embodiment, the matrix crystal grains are made of Si ₃ N ₄ . The details of the matrix crystal grains are the same as those in the first embodiment, and thus the description thereof is omitted.

[3.1.2. Grain boundary phase]
The grain boundary phase exists at least between the matrix grains. The details of the grain boundary phase are the same as those in the first embodiment, and thus description thereof is omitted.

[3.1.3. SiC crystal grains]
The SiC crystal grains are semiconductors and are dispersed between matrix crystal grains and / or in a grain boundary phase. The details of the SiC crystal grains are the same as those in the first embodiment, and thus description thereof is omitted.

[3.1.4. Si crystal grains, BN crystal grains, TiN crystal grains, and TiB ₂ crystal grains]
The Si crystal grains, the BN crystal grains, and the TiN crystal grains are reaction products generated by the reaction of the starting materials TiB ₂ powder and Si ₃ N ₄ powder. The TiB ₂ powder may react entirely with the Si ₃ N ₄ powder or may partially react with it. Si crystal grains, BN crystal grains, and TiN crystal grains, and TiB ₂ crystal grains when unreacted TiB ₂ remains, are all dispersed between matrix crystal grains or within a grain boundary phase. I have.

Among these, the Si crystal grains are semiconductors and form a conductive path together with the SiC crystal grains described above. Further, the TiN crystal grains and the TiB ₂ crystal grains are both electronic conductors, and form a conductive path together with the SiC crystal grains and the Si crystal grains to lower the specific resistance. On the other hand, BN crystal grains are insulators, but are inevitably by-produced impurities accompanying the generation of Si crystal grains and TiN crystal grains. In the present invention, BN crystal grains hardly contribute to the development of thermistor characteristics.

The average crystal grain size d ₅₀ of the Si crystal grains, BN crystal grains, TiN crystal grains, and TiB ₂ crystal grains is not particularly limited, and an optimum value can be selected according to the purpose. Si crystal grains, BN grain, and d ₅₀ of TiN grains, primarily, the average particle size of the TiB ₂ powder and Si ₃ N ₄ powder as a starting material, and depends on the sintering conditions.
When a method described later is used, d _{50 of the} Si crystal grain is about 0.1 μm to 1 μm. Further, d ₅₀ of the BN crystal grains is about 0.1 to 0.8 [mu] m. Further, d ₅₀ of TiN crystal grains becomes about 0.1 to 0.8 [mu] m. Further, d ₅₀ of the TiB ₂ grains becomes about 0.2Myuemu～1.0Myuemu.

[3.2. Content of each component-peak intensity ratio of strongest line]
The thermistor material according to the present embodiment includes a predetermined amount of a grain boundary phase, SiC crystal grains, Si crystal grains, BN crystal grains, and TiN crystal grains, or TiB ₂ crystal grains in addition thereto, and the remainder is a matrix. It consists of crystal grains and inevitable impurities. For the content of each component, an optimal value can be selected according to the purpose. In the present embodiment, instead of directly specifying the content of each component, the maximum intensity peak intensity ratio is used instead.

[3.2.1. Si / BN ratio]
The “Si / BN ratio” refers to the ratio (= I _Si / I _BN ) of the peak intensity (I _Si ) of the strongest line of Si to the peak intensity (I _BN ) of the strongest line of BN obtained when X-ray diffraction is performed. ).
In this embodiment, in order to obtain a high rate of change in temperature resistance, it is desirable that an appropriate amount of Si crystal grains are discretely dispersed between SiC crystal grains. Generally, as the amount of TiB ₂ added to the raw material increases, the amount of Si crystal grains contained in the sintered body increases. As a result, the temperature resistance change rate (B value) of the thermistor material increases. To obtain such an effect, the Si / BN ratio needs to be 0.1 or more. The Si / BN ratio is preferably at least 0.3, more preferably at least 0.5.

  On the other hand, when the generation amount of the Si crystal grains is excessive, the SiC crystal grains are connected by the Si crystal grains, or the Si crystal grains are connected to each other, and the specific resistance value is excessively reduced. In addition, a large amount of by-produced BN crystal grains serve as a starting point of destruction, and may cause deterioration of mechanical properties. Therefore, the Si / BN ratio needs to be 1.6 or less. The Si / BN ratio is preferably 1.2 or less, more preferably 0.8 or less.

[3.2.2. Si / SiC ratio]
"Si / SiC ratio" refers to the ratio (= I _Si / I _SiC peak intensity of the strongest line of Si to the peak intensity of the strongest line of SiC obtained when performing the X-ray diffraction (I _SiC) (I _Si) ).
For the same reason as the Si / BN ratio, the Si / SiC ratio needs to be 0.1 or more. The Si / SiC ratio is preferably at least 0.2, more preferably at least 0.3.
Further, for the same reason as the Si / BN ratio, the Si / SiC ratio needs to be 0.6 or less. The Si / SiC ratio is preferably 0.5 or less, more preferably 0.4 or less.

[3.2.3. Si / Si ₃ N ₄ ratio]
The "Si / Si ₃ N ₄ ratio", the ratio of the peak intensity of the strongest line of Si to the peak intensity of the strongest line the Si ₃ N ₄ obtained when performing the X-ray diffraction _{(I Si3N4) (I Si)} ( = I _Si / I _Si3N4 ).
In the present embodiment, in order to obtain an appropriate specific resistance value and a rate of change in temperature resistance (temperature detection accuracy), a conductive material in which an appropriate amount and an appropriate size of Si crystal grains are discretely dispersed together with SiC crystal grains. It is desirable to form a path. Since Si is mainly generated by the reaction between TiB ₂ and Si ₃ N ₄ added to the raw material, the larger the amount of TiB ₂ added, the larger the amount of Si in the sintered body and the larger the amount of Si, which is an insulating material. ₃ N ₄ content is reduced to the contrary. For this reason, when the amount of Si becomes too large, the amount of Si ₃ N ₄ relatively decreases, and the liquid phase Si diffuses between the Si ₃ N ₄ crystal grains, thereby breaking the discrete dispersion form. The specific resistance value is too low. For this reason, the Si / Si ₃ N ₄ ratio needs to be 0.1 or more in order to develop an appropriate specific resistance value and a rate of change in temperature resistance. The Si / Si ₃ N ₄ ratio is preferably at least 0.15, more preferably at least 0.2.
Further, for the same reason as the Si / BN ratio, the Si / Si ₃ N ₄ ratio needs to be 0.5 or less. The Si / Si ₃ N ₄ ratio is preferably 0.3 or less, more preferably 0.28 or less.

[3.2.4. (TiN + TiB ₂ ) / SiC ratio]
The “(TiN + TiB ₂ ) / SiC ratio” means the strongest line peak intensity (I _TiN ) of _TiN and the strongest line peak of TiB ₂ with respect to the strongest line peak intensity (I _SiC ) of _SiC obtained when X-ray diffraction is performed. It _means the ratio of the sum of the strengths (I _TiB2 ) (= (I _TiN + I _TiB2 ) / I _SiC ).
The TiN grains and the TiB ₂ grains form conductive paths with the SiC grains and the Si grains. Generally, as the amount of TiB ₂ added to the raw material increases, the total amount of TiN crystal grains and TiB ₂ crystal grains contained in the sintered body increases. As a result, the specific resistance value of the thermistor material increases. In order to obtain such an effect, the (TiN + TiB ₂ ) / SiC ratio needs to be 0.2 or more. Note that TiB ₂ may partially remain as TiB, but since the peak intensity of TiB is weaker than that of TiB ₂ , it may be regarded as zero.

On the other hand, when the total amount of the conductive material TiN crystal grains and TiB ₂ crystal grains becomes excessive, the SiC crystal grains are connected by Si crystal grains, TiN crystal grains and / or TiB ₂ crystal grains, and the specific resistance value becomes excessive. Become smaller. In addition, a large amount of by-produced BN crystal grains serve as a starting point of destruction, and may cause deterioration of mechanical properties. Therefore, the (TiN + TiB ₂ ) / SiC ratio needs to be 1.5 or less.

[3.3. Specific resistance]
The specific resistance of the thermistor material depends on the amount of SiC grains, Si grains, TiN grains, and TiB ₂ grains, and the state of dispersion of these grains. In general, the specific resistance of the thermistor material decreases as the amount of crystal grains made of these conductive materials increases or as the number or area of contact points between these crystal grains increases.

Generally, if the specific resistance of the thermistor material becomes too small, the specific resistance further decreases due to self-heating, and as a result, the specific resistance of the thermistor becomes unstable. Therefore, the specific resistance value of the thermistor material at 0 ° C. needs to be 0.5 kΩcm or more. The specific resistance value is preferably 0.7 kΩcm or more, more preferably 1 kΩcm or more.
On the other hand, if the specific resistance value of the thermistor material is too large, the current value will be small, so that the change in current (voltage) due to temperature change will be small, making measurement impossible. Therefore, the specific resistance value of the thermistor material at 0 ° C. needs to be 200 kΩcm or less. The specific resistance value is preferably 100 kΩcm or less, more preferably 50 kΩcm or less.

[3.4. Temperature resistance change rate (B value)]
In the thermistor material according to the present embodiment, when the relationship between electric resistance (R) and temperature (T) is represented by R = Aexp (−BT), logR is T at least in a temperature range of −80 ° C. to 500 ° C. (The electrical resistance (R) changes linearly with temperature on a semilogarithmic graph). Moreover, the slope (B value) is relatively large. Therefore, the temperature can be accurately detected in the low temperature range. The B value slightly varies depending on the composition of the thermistor material, but is in the range of 0.009 or more and 0.025 or less by using a method described later.

[4. Manufacturing method of thermistor material (2)]
The method for manufacturing a thermistor material according to the second embodiment of the present invention includes:
A mixing step of obtaining a mixture containing Si ₃ N ₄ powder, SiC powder, TiB ₂ powder, and a sintering aid as main raw materials;
A forming and sintering step of forming and sintering the mixture.

[4.1. Mixing process]
First, a mixture containing Si ₃ N ₄ powder, SiC powder, TiB ₂ powder, and a sintering aid as main raw materials is obtained (mixing step). When mixing the raw material powders, other additives such as a binder and a dispersion stabilizer may be added as necessary.

[4.1.1. Main raw material]
[A. Si ₃ N ₄ powder]
The Si ₃ N ₄ powder added to the raw material becomes matrix crystal grains of the sintered body. The details of the Si ₃ N ₄ powder are the same as those in the first embodiment, and thus the description thereof is omitted.

[B. SiC powder]
The SiC powder added to the raw material forms a part of a conductive path in the sintered body. Since the details of the SiC powder are the same as those of the first embodiment, the description is omitted.

[C. TiB ₂ powder]
All or part of the TiB ₂ powder added to the raw material reacts with Si ₃ N ₄ during sintering to generate Si crystal grains, BN crystal grains, and TiN crystal grains. The Si crystal grains, the TiN crystal grains, and the unreacted TiB ₂ crystal grains form a part of the conductive path in the sintered body. BN crystal grains are insulators and hardly contribute to thermistor characteristics.
TiB ₂ average particle diameter D ₅₀ of the powder may be relatively large. However, the TiB ₂ powder D ₅₀ becomes too large, and at the same time sintering is inhibited, the reaction the top of the Si ₃ N ₄ is locally. As a result, the density of the sintered body decreases, or the variation of the specific resistance value increases. Densifying the sintered body, and, in order to reduce variations in the specific resistance, TiB ₂ powder D ₅₀ is preferably equal to or less than 2 [mu] m. D ₅₀ is preferably, 0.6 .mu.m or less, more preferably, 0.3μm or less.

[D. Sintering aid]
The sintering aid added to the raw material forms a part of the grain boundary phase in the sintered body. The details of the sintering aid are the same as in the first embodiment, and a description thereof will not be repeated.

[4.1.2. Amount of each raw material]
For the amount of each raw material, an optimum value is selected according to the purpose. In order to obtain a thermistor material having an appropriate specific resistance value and a relatively high rate of change in temperature resistance (B value), the mixing step includes:
SiC compound amount becomes more than 14 vol% and less than 40 vol%,
TiB ₂ compounding amount becomes 4 vol% or more and 15 vol% or less,
The compounding amount of the sintering aid is 4 vol% or more and less than 15 vol%,
It is necessary to mix these so that the remainder is Si ₃ N ₄ .

[A. SiC content]
The amount of SiC is the same as in the first embodiment, and a description thereof will be omitted.

[B. TiB ₂ compounding amount]
As described above, the TiB ₂ powder added to the raw material reacts with the Si ₃ N ₄ powder during sintering to generate Si crystal grains and TiN crystal grains. As the compounding amount of the TiB ₂ powder increases, the specific resistance value of the sintered body decreases and the temperature resistance change rate (B value) increases. This is considered to be because the Si crystal grains generated by the reaction form a structure that is discretely dispersed in the conductive paths of the SiC crystal grains. In order to obtain such an effect, the amount of the TiB ₂ powder needs to be 4 vol% or more. The compounding amount of the TiB ₂ powder is preferably at least 6 vol%.

On the other hand, when the amount of the TiB ₂ powder is excessive, the rate of change in temperature resistance (B value) is rather reduced. It is considered that this is because excessively generated Si forms a large amount of liquid phase and diffuses the grain boundary phase of the sintered body to easily form a continuous phase of Si crystals. Further, TiB ₂ inhibits sintering of Si ₃ N ₄ and lowers the sintering density. Therefore, the amount of the TiB ₂ powder needs to be 15 vol% or less. B content is preferably 14 vol% or less.

[C. Amount of sintering aid]
Since the amount of the sintering aid is the same as in the first embodiment, the description is omitted.
[D. Amount of other additives]
The amounts of the other additives are the same as those in the first embodiment, and a description thereof will not be repeated.

[4.1.3. Mixing method]
The details of the method of mixing the raw materials are the same as those in the first embodiment, and thus the description thereof is omitted.

[4.2. Sintering process]
Next, the mixture obtained in the mixing step is molded and sintered (molding / sintering step).
[4.2.1. Forming method and sintering method]
The details of the forming method and the sintering method are the same as those of the first embodiment, and thus the description is omitted.

[4.2.2. Molding conditions and sintering conditions]
For the molding conditions and sintering conditions of the molded body, optimal conditions are selected according to the purpose. Further, the specific resistance value and the rate of change in temperature resistance (B value) depend not only on the molding conditions and sintering conditions but also on the pulverization and mixing conditions (mainly, the mixing ratio of the main raw materials and the particle size ratio).
In order to obtain a thermistor material having an appropriate specific resistance value and a relatively high rate of change in temperature resistance (B value), the mixing step and the forming / sintering step are performed as follows.
Si / BN ratio (strongest line peak intensity ratio) becomes 0.1 or more and 1.6 or less,
The Si / SiC ratio (strongest line peak intensity ratio) becomes 0.1 or more and 0.6 or less,
Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) becomes 0.1 or more and 0.5 or less,
(TiN + TiB ₂ ) / SiC ratio (strongest line peak intensity ratio) becomes 0.2 or more and 1.5 or less,
The specific resistance at 0 ° C. becomes 0.5 kΩcm or more and 200 kΩcm or less, and
The temperature resistance change rate (B value) is 0.009 or more and 0.025 or less,
It is necessary to mix the main raw materials and to mold and sinter the mixture.

  Other points related to the molding conditions and the sintering conditions are the same as those in the first embodiment, and thus the description thereof is omitted.

[5. Action]
In the thermistor material in which the matrix crystal grains composed of Si ₃ N ₄ and the SiC crystal grains are combined, in order to obtain a short range property, it is necessary to add both a predetermined amount of B and a predetermined amount of TiB _2. Was considered mandatory.

On the other hand, when a relatively large amount of B alone is added to the thermistor material in which the matrix crystal grains composed of Si ₃ N ₄ and the SiC crystal grains are combined, and the content of each component is optimized. Thus, a thermistor material having an appropriate specific resistance value and a relatively high rate of change in temperature resistance can be obtained. This is because Si ₃ N ₄ in the raw material reacts with B to generate Si crystal grains of an appropriate amount and an appropriate size, and the generated Si crystal grains are discretely formed between the SiC crystal grains at an appropriate interval. It is thought to be distributed to.

Similarly, when a relatively large amount of TiB ₂ alone is added to a thermistor material in which a matrix crystal grain composed of Si ₃ N ₄ and a SiC crystal grain are combined, and the content of each component is optimized, Thus, a thermistor material having an appropriate specific resistance value and a relatively high rate of change in temperature resistance can be obtained. This is because Si ₃ N ₄ and TiB ₂ in the raw material react with each other to generate appropriate amounts and appropriate sizes of Si crystal grains and TiN crystal grains, and the generated Si crystal grains and TiN crystal grains (and It is considered that the TiB ₂ crystal grains (when TiB ₂ remains in the reaction) are discretely dispersed among the SiC crystal grains at appropriate intervals.

(Examples 1 to 12, Comparative Examples 1 to 4)
[1. Preparation of sample]
Using a commercially available Si ₃ N ₄ powder (average particle size: 1 μm) as a matrix, a predetermined amount of SiC powder (α-SiC or β-SiC), Y ₂ O ₃ powder, B powder, TiB ₂ powder, and WSi ₂ Powder was added. These raw materials were mixed in ethanol, distilled and dried. Table 1 shows the composition of each sample. Table 1 also shows the B value, the specific resistance value, the Si / SiC ratio, the (TiN + TiB ₂ ) / SiC ratio, and the Si / BN ratio.

  These mixed powders were uniaxially formed at a pressure of 20 MPa, and then hot-pressed at a high temperature to produce a thermistor material. A thin chip was cut out from this thermistor material and electrodes were attached thereto to obtain a thermistor element.

[2. Test method]
[2.1. Temperature resistance change rate (B value) and specific resistance value]
The resistance value of the thermistor element when the temperature was changed using a thermo-hygrostat was measured. From the obtained relationship between the temperature and the resistance value, the temperature resistance change rate (B value) was calculated. Further, the specific resistance value was calculated from the resistance value measured at 0 ° C.

[2.2. Strongest line peak intensity ratio]
X-ray diffraction measurement was performed on the obtained sample. The strongest line peak intensity ratio was calculated from the X-ray diffraction pattern.

[3. result]
[3.1. Temperature resistance change rate (B value)]
Table 1 shows the B value of each sample. FIG. 1 shows the relationship between the temperature T and the resistance value R of the thermistor element obtained in Example 6. FIG. 2 shows the relationship between the temperature T and the resistance value R of the thermistor element obtained in Example 10. FIG. 3 shows the relationship between the temperature T and the resistance value R of the thermistor element obtained in Comparative Example 2. The following can be seen from Table 1 and FIGS.

(1) In Comparative Example 1, both the B value and the specific resistance value are low. This is considered to be related to the balance between the amount of the α-SiC powder and the amount of the B powder. That is, in Comparative Example 1, since the compounding amount of the B powder was relatively large in addition to the compounding amount of the α-SiC powder being relatively large, the liquid in which α-SiC crystal grains were formed in the sintered body was used. It is considered that they were connected by the phase Si, and thereby the B value and the specific resistance value were reduced.
(2) Comparative Examples 2 and 3 have low B values because neither B powder nor TiB ₂ powder is added. Further, in Comparative Example 4, the specific resistance could not be measured because the amount of the B powder was too small.

(3) In Examples 1 to 12 in which an appropriate amount of SiC powder and an appropriate amount of B powder or TiB ₂ powder were mixed, a high B value and an appropriate specific resistance value were obtained. The reason why Example 11 has a high B value and an appropriate specific resistance value is that although the blending amount of the B powder is relatively large, the blending amount of the α-SiC powder is relatively small. This is probably because a structure in which Si crystal grains were discretely dispersed between the crystal grains was obtained.

[3.2. Strongest line peak intensity ratio]
[3.2.1. B-based thermistor material]
FIG. 4 shows the relationship between the B content and the Si / BN ratio. FIG. 5 shows the relationship between the B content and the Si / SiC ratio. FIG. 6 shows the relationship between the B content and the Si / Si ₃ N ₄ ratio. The following can be seen from FIGS.

(1) Assuming that the B content is 2 to 30 vol%, the Si / BN ratio was about 0.1 to 2.5.
(2) Assuming that the B content is 2 to 30 vol%, the Si / SiC ratio is about 0.1 to 2.0. It is considered that the reason why the Si / SiC ratio becomes flat when the amount of B exceeds about 10% is that the amount of Si increases and the amount of liquid phase Si increases in a large amount.
(3) Assuming that the B content is 2 to 30 vol%, the Si / Si ₃ N ₄ ratio is about 0.1 to 6.0. The Si / Si ₃ N ₄ ratio monotonically increased with an increase in the B content.

[3.2.2. TiB ₂ thermistor material]
FIG. 7 shows the relationship between the amount of TiB ₂ and the Si / BN ratio. FIG. 8 shows the relationship between the amount of TiB ₂ and the Si / SiC ratio. FIG. 9 shows the relationship between the amount of TiB ₂ and the ratio of Si / Si ₃ N ₄ . FIG. 10 shows the relationship between the amount of TiB ₂ and the (TiN + TiB ₂ ) / SiC ratio. 7 to 10 show the following.

(1) When the compounding amount of TiB ₂ is 4 to 15 vol%, the Si / BN ratio is about 0.1 to 1.6.
(2) When the compounding amount of TiB ₂ is 4 to 15 vol%, the Si / SiC ratio is about 0.1 to 0.6. The Si / SiC ratio monotonically increased with an increase in the amount of TiB ₂ .
(3) When the amount of TiB ₂ is 4 to 15 vol%, the Si / Si ₃ N ₄ ratio is about 0.1 to 0.5. The Si / Si ₃ N ₄ ratio monotonically increased with an increase in the amount of the TiB ₂ powder.
(4) When the compounding amount of TiB _{2 is} 4 to 15 vol%, the (TiN + TiB ₂ ) / SiC ratio is about 0.2 to 1.5. The (TiN + TiB ₂ ) / SiC ratio monotonically increased with an increase in the amount of TiB ₂ .
(5) The TiN / SiC ratio uniformly increased with an increase in the amount of TiB ₂ .

  As described above, the embodiments of the present invention have been described in detail. However, the present invention is not limited to the above embodiments, and various modifications can be made without departing from the gist 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 500 ° C. in the atmosphere.

Claims (4)

A thermistor material having the following configuration.
(1) The thermistor material is
Matrix crystal grains composed of Si ₃ N ₄ ,
A grain boundary phase present between at least the matrix crystal grains,
SiC crystal grains, Si crystal grains, and BN crystal grains dispersed between the matrix crystal grains and / or in the grain boundary phase.
(2) The thermistor material comprises:
Si / BN ratio (strongest line peak intensity ratio) is 0.1 or more and 2.5 or less,
Si / SiC ratio (strongest line peak intensity ratio) is 0.1 or more and 2.0 or less, and
The Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) is 0.1 or more and 6.0 or less.
(3) The thermistor material comprises:
The specific resistance value at 0 ° C. is 0.5 kΩcm or more and 200 kΩcm or less, and
The rate of change in temperature resistance (B value) is 0.009 or more and 0.025 or less. A method for manufacturing a thermistor material having the following configuration.
(1) The method for producing the thermistor material is as follows:
A mixing step of obtaining a mixture containing Si ₃ N ₄ powder, SiC powder, B powder, and a sintering aid as main raw materials;
A forming and sintering step of forming and sintering the mixture.
(2) The mixing step comprises:
SiC compound amount becomes more than 14 vol% and less than 40 vol%,
B content becomes 2 vol% or more and 30 vol% or less,
The compounding amount of the sintering aid is 4 vol% or more and less than 15 vol%,
They consist of a mixture of these so that the remainder is Si ₃ N ₄ .
(3) The mixing step and the forming / sintering step
Si / BN ratio (strongest line peak intensity ratio) becomes 0.1 or more and 2.5 or less,
Si / SiC ratio (strongest line peak intensity ratio) becomes 0.1 or more and 2.0 or less,
Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) becomes 0.1 or more and 6.0 or less,
The specific resistance at 0 ° C. becomes 0.5 kΩcm or more and 200 kΩcm or less, and
The temperature resistance change rate (B value) is 0.009 or more and 0.025 or less,
The main material is mixed, and the mixture is molded and sintered. A thermistor material having the following configuration.
(1) The thermistor material is
Matrix crystal grains composed of Si ₃ N ₄ ,
A grain boundary phase present between at least the matrix crystal grains,
SiC crystal grains, Si crystal grains, BN crystal grains, and TiN crystal grains dispersed between the matrix crystal grains and / or in the grain boundary phase, or TiB ₂ crystal grains in addition thereto. .
(2) The thermistor material comprises:
A Si / BN ratio (strongest line peak intensity ratio) of 0.1 or more and 1.6 or less;
A Si / SiC ratio (strongest line peak intensity ratio) of 0.1 to 0.6,
A Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) of 0.1 to 0.5, and
(TiN + TiB ₂ ) / SiC ratio (strongest line peak intensity ratio) is 0.2 or more and 1.5 or less.
(3) The thermistor material comprises:
The specific resistance value at 0 ° C. is 0.5 kΩcm or more and 200 kΩcm or less, and
The rate of change in temperature resistance (B value) is 0.009 or more and 0.025 or less. A method for manufacturing a thermistor material having the following configuration.
(1) The method for producing the thermistor material is as follows:
A mixing step of obtaining a mixture containing Si ₃ N ₄ powder, SiC powder, TiB ₂ powder, and a sintering aid as main raw materials;
A forming and sintering step of forming and sintering the mixture.
(2) The mixing step comprises:
SiC compound amount becomes more than 14 vol% and less than 40 vol%,
TiB ₂ compounding amount becomes 4 vol% or more and 15 vol% or less,
The compounding amount of the sintering aid is 4 vol% or more and less than 15 vol%,
They consist of a mixture of these so that the remainder is Si ₃ N ₄ .
(3) The mixing step and the forming / sintering step
Si / BN ratio (strongest line peak intensity ratio) becomes 0.1 or more and 1.6 or less,
The Si / SiC ratio (strongest line peak intensity ratio) becomes 0.1 or more and 0.6 or less,
Si / Si ₃ N ₄ ratio (strongest line peak intensity ratio) becomes 0.1 or more and 0.5 or less,
(TiN + TiB ₂ ) / SiC ratio (strongest line peak intensity ratio) becomes 0.2 or more and 1.5 or less,
The specific resistance at 0 ° C. becomes 0.5 kΩcm or more and 200 kΩcm or less, and
The temperature resistance change rate (B value) is 0.009 or more and 0.025 or less,
The main material is mixed, and the mixture is molded and sintered.

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