JP2020161759A - Thermistor material - Google Patents

Abstract

To provide a new thermistor material, having fewer types of components than before, capable of highly accurate temperature detection in a low temperature range of about -50°C to 500°C.SOLUTION: The thermistor material includes: matrix crystal grains composed of insulating ceramics; conductive particles dispersed between the matrix crystal grains; and a grain boundary phase. The conductive particles are composed of α-SiC doped with B, Al, and/or N. The thermistor material has a carrier concentration at room temperature of 1×1014 cm-3 or more and 1×1019 cm-3 or less. The mobility of the thermistor material is preferably 1×10-4 cm2/V s or more and 1 cm2/V s or less.SELECTED DRAWING: Figure 1

Description

The present invention relates to a thermistor material, and more particularly to a thermistor material which has fewer kinds of constituents than the conventional one and can detect a temperature with high accuracy in a low temperature range.

A thermistor is a resistor that has a large change in electrical resistance with respect to temperature changes. 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 decreases sharply when a certain temperature is exceeded. Of these, the NTC thermistor is the most used because it is low cost and the electrical resistance value changes exponentially with respect to temperature changes. The term thermistor simply refers to the NTC thermistor.

A commonly used thermistor consists of an oxide composite containing 2 to 4 types of transition metal oxides such as Mn, Ni, Co, Fe, Cu, Y, and Cr. As such an oxide-based thermistor material, for example, a spinel-type oxide, a perovskite-type oxide, a mixture of spinel and perovskite, and the like are known.
In the oxide thermistor, the temperature is detected by utilizing the temperature dependence of oxygen ion diffusion. Further, in a thermistor made of a perovskite-type oxide, a p-type semiconductor in which more holes than holes due to oxygen defects are introduced by doping with a divalent metal, and the electrical resistance value is not high in a low oxygen atmosphere. Stabilization is suppressed.

Non-oxide thermistor materials are also known.
For example, Patent Document 1 discloses a thermistor material obtained by mixing a predetermined amount of Si ₃ N ₄ , α-type SiC, Y ₂ O ₃ , B, and TiB ₂ and molding and sintering the mixture. Has been done.
The document describes that such a method can obtain a thermistor material suitable for high-precision temperature measurement for a low temperature range.

In a thermistor material in which α-type SiC is dispersed in an insulation matrix made of Si ₃ N ₄ , when B and TiB ₂ are further added, the thermistor material capable of highly accurate temperature detection in a low temperature range (resistance change with respect to temperature change). Large thermistor material) is obtained.
However, when B or TiB ₂ is added to the raw material, these may react with Si ₃ N ₄ to form Si or BN. Since the BN generated in the material becomes the starting point of fracture, the material strength may be lowered. Further, Si generated in the material is a semiconductor and functions as a part of the conductive path, but its melting point (1414 ° C.) is lower than the sintering temperature (1800 ° C. or higher), and it becomes liquid phase during sintering. Since it diffuses, it may cause composition variation in the sintered body, which in turn causes variation in resistance value.

Japanese Patent No. 5765277

The problem to be solved by the present invention is to provide a novel thermistor material which has fewer kinds of constituents than the conventional one and can detect a temperature with high accuracy in a low temperature range of about -50 ° C to 500 ° C. It is in.
Another problem to be solved by the present invention is to provide a novel thermistor material having high strength and substantially free of free Si, BN, or boron compounds.

The thermistor material according to the present invention in order to solve the above problems has the following constitution.
(1) The thermistor material is
Matrix crystal grains made of insulating ceramics and
Conductive particles dispersed between the matrix crystal particles and
Grain boundary phase and
Is equipped with.
(2) The conductive particles are made of α-SiC doped with B, Al, and / or N.
(3) The thermistor material has a carrier concentration of 1 × 10 ¹⁴ cm ^-3 or more and 1 × 10 ¹⁹ cm ^-3 or less at room temperature.

When α-SiC containing an appropriate amount of p-type dopant and / or n-type dopant is dispersed as conductive particles in the insulating ceramic, the temperature resistance coefficient (B value) of B, TiB _2, etc. is increased in the raw material. A thermistor material capable of highly accurate temperature detection in a low temperature range can be obtained without adding a component for this purpose.
This is because the carrier concentration-optimized α-SiC is dispersed in the matrix, so that the influence of the mobility of the thermistor material is greatly reduced, while the temperature dependence of the carrier concentration of the thermistor material becomes dominant. Therefore, it is considered that the temperature resistance change rate (B value) becomes large.

It is a figure which shows the relationship between the temperature T of the thermistor element obtained in Example 1 and the specific resistance value ρ. It is a figure which shows the relationship between the distance from the center of the wafer obtained in Example 1 and the specific resistance value ρ.

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 constitution.
(1) The thermistor material is
Matrix crystal grains made of insulating ceramics and
Conductive particles dispersed between the matrix crystal particles and
Grain boundary phase and
Is equipped with.
(2) The conductive particles are made of α-SiC doped with B, Al, and / or N.
(3) The thermistor material has a carrier concentration of 1 × 10 ¹⁴ cm ^-3 or more and 1 × 10 ¹⁹ cm ^-3 or less at room temperature.

[1.1. component]
[1.1.1. Matrix crystal grains]
[A. Matrix crystal grain composition]
The matrix crystal grains are made of insulating ceramics. “Insulating ceramics” means ceramics having a specific resistance value of 10 ¹² Ωcm or more. The composition of the insulating ceramics constituting the matrix crystal grains is not particularly limited as long as the properties required for the thermistor can be obtained.
Examples of the insulating ceramics include Si ₃ N ₄ , SiALON, Al N, Al ₂ O ₃ , Y ₂ Si ₂ O ₇ . The matrix crystal grains may be made of any one of these insulating ceramics, or may be made of two or more kinds.

[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 optimum value can be selected according to the intended purpose. In general, the smaller the average crystal grain size of the matrix, the smaller the variation in resistivity value. 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" is a median value (diameter of the minimum circumscribing circle of crystal grains) of 10 or more crystal grains randomly selected by observation with a microscope (SEM, TEM, EPMA, etc.). The size of the crystal grains (d ₅₀ ) when the cumulative distribution of the sizes of the sampled crystal grains is 50%).

[1.1.2. Conductive particles]
Conductive particles are dispersed between the matrix crystal particles. In the present invention, the conductive particles are made of α-SiC doped with B, Al, and / or N.

[A. Dopant]
The dopant consists of B, Al, and / or N. Of these, B and Al are p-type dopants, and N is an n-type dopant. In the present invention, α-SiC may be doped with either a p-type dopant or an n-type dopant, or may be doped with both.

Doping α-SiC with a p-type dopant and / or an n-type dopant introduces carriers at a predetermined concentration into α-SiC. Of these, the p-type dopant has a greater action of increasing the temperature resistance coefficient (B value) than the action of lowering the resistance value of the thermistor material. On the other hand, the n-type dopant has a greater action of lowering the resistance value than an action of increasing the temperature resistance coefficient (B value) of the thermistor material.
Therefore, by optimizing the type and amount of dopant according to the purpose, the temperature-resistance characteristics required for a thermistor capable of highly accurate temperature detection in a low temperature range can be obtained.

[B. Carrier concentration]
The carrier concentration of the thermistor material affects the temperature-resistance properties of the thermistor material. If the carrier concentration is too low, the resistance value of the thermistor material becomes too high, which may increase the cost of the measurement circuit. Therefore, the carrier concentration at room temperature is preferably 1 × 10 ¹⁴ cm ^-3 or more. The carrier concentration at room temperature is preferably 5 × 10 ¹⁴ cm ^-3 or more, more preferably 1 × 10 ¹⁵ cm ^-3 or more.
On the other hand, when the carrier concentration at room temperature becomes excessive, the resistance value becomes too low, and the influence of the carrier concentration change due to the temperature change on the resistance value change becomes small, that is, the temperature sensitivity may become small. Therefore, the carrier concentration at room temperature is preferably 1 × 10 ¹⁹ cm ^-3 or less. The carrier concentration at room temperature is preferably 5 × 10 ¹⁸ cm ^-3 or less, more preferably 1 × 10 ¹⁸ cm ^-3 or less.

[C. Mobility]
The mobility of the thermistor material affects the resistance value. If the mobility is too small, the resistance value becomes too large, and conversely, if the mobility is too large, the temperature sensitivity cannot be determined only by the carrier concentration. Therefore, the mobility of the thermistor material is preferably 1 × 10 ^-4 cm ² / V · s or more and 1 cm ² / V · s or less, and 1 × 10 ^-3 cm ² / V · s or more 1 × 10 ^-1 cm ² It is more preferably / V · s or less.

[D. Dopant concentration]
It is preferable to select the optimum dopant concentration so that the carrier concentration and mobility are within the above ranges.

If the concentrations of B, Al, and N are too low, the resistance value of α-SiC becomes too high, and the measurement circuit becomes expensive when used as a thermistor material. On the other hand, if the concentrations of B, Al, and N are too high, the carrier concentration of α-SiC becomes large and the resistance value becomes too low, and the temperature sensitivity of the thermistor material decreases. Therefore, the concentrations of B, Al, and N are preferably 1 × 10 ¹⁶ cm ^-3 or more and 1 × 10 ²⁰ cm ^-3 or less, and more preferably 1 × 10 ¹⁷ cm ^-3 or more and 1 × 10 ¹⁹ cm ^-3 or less.

[E. Average crystal grain size of conductive particles]
In the present embodiment, the average crystal grain size d ₅₀ of the conductive particles is not particularly limited, and an optimum value can be selected depending on the intended purpose. In general, the smaller the d ₅₀ of the conductive particles, the more the densification is promoted, the grain growth of the matrix crystal grains that occurs during sintering is suppressed, and the structure becomes finer. Therefore, the variation in the specific resistance value becomes small. The d ₅₀ of the conductive particles is preferably 5 μm or less. d ₅₀ is preferably 2 μm or less, more preferably 1 μm or less, still more preferably 0.7 μm or less.

[1.1.3. Grain boundary phase]
[A. Grain boundary phase composition]
The grain boundary phase exists at least between the matrix crystal grains. The grain boundary phase may be present between the conductive particles in addition to the 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) Compositions used as sintering aids (eg, Al ₂ O ₃ , Al N, 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, etc.),
(B) A composition produced by the reaction of two or more kinds of sintering aids.
(C) A composition produced by reacting one or more kinds of sintering aids with other main raw materials (for example, Si ₃ N ₄ , SiC).
and so on.

[B. Crystallinity of grain boundary phase]
The grain boundary phase may be crystalline or amorphous depending on the type of material added as the sintering aid and the 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 during sintering, but the resistivity value of the sintered body tends to increase, and the heat resistance also decreases. On the other hand, when the grain boundary phase contains 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 decreases and the resistivity value increases. 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, if the grain boundary phase is too thin, the 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 1 nm or more, more preferably 2 nm or more.

[1.2. Content]
The thermistor material according to the present invention contains a predetermined amount of conductive particles and grain boundary phases, and the balance consists of insulating ceramics and unavoidable impurities.

[1.2.1. Content of conductive particles]
In general, as the content of conductive particles increases, the resistivity value decreases, and the mechanical strength of the sintered body also increases due to particle strengthening. In order to obtain such an effect, the content of the conductive particles is preferably more than 14 vol%. The content of the conductive particles is preferably 16 vol% or more, more preferably 20 vol% or more, still more preferably 25 vol% or more.

On the other hand, if the content of the conductive particles is excessive, the sintering density is lowered and the mechanical properties are lowered, and at the same time, the specific resistance value may be excessively reduced. In addition, the rate of change in temperature resistance (B value) is rather small. It is considered that this is because when the content of the conductive particles is excessive, the number and width of the conductive paths composed of the conductive particles are greatly increased and the particles become dense. In addition, the conductive particles are likely to aggregate, and pores are likely to be formed between the conductive particles. Therefore, the content of the conductive particles is preferably less than 40 vol%. The content of the conductive particles is preferably 35 vol% or less, more preferably 30 vol% or less.

[1.2.2. Grain boundary phase content]
If the content of the grain boundary phase (that is, the sintering aid) is too small, a dense sintered body cannot be obtained. Therefore, the content of the grain boundary phase is preferably 4 vol% or more. The content of the grain boundary phase is preferably 5 vol% or more, more preferably 6 vol% or more.
On the other hand, if the content of the grain boundary phase becomes excessive, the thickness of the grain boundary phase may increase and the resistivity value may increase. In addition, the diffusion of the auxiliary agent becomes remarkable during the sintering, and there is a possibility that the characteristics of the sintered body may vary. Therefore, the content of the grain boundary phase is preferably less than 15 vol%. The content of the grain boundary phase is preferably 12 vol% or less, more preferably 10 vol% or less.

[12.3. Impurity content]
Conventionally, it has been considered essential to add B or a boron compound (for example, TiB ₂ ) to the raw material in order to perform highly accurate temperature detection in a low temperature range. However, in the present invention, only α-SiC in which the type and amount of the dopant are optimized is used as the conductive particles, and B and a boron compound are not added to the raw material.
Therefore, the thermister material according to the present invention includes unreacted B and boron compounds, and B and boron compounds and nitride ceramics used as raw materials even when nitride ceramics are used as insulating ceramics. It is substantially free of reaction products with (ie, Si and BN).

Specifically, the thermistor material according to the present invention has a Si, boron compound, and BN content of 0.1% or less, respectively.
Here, the "content of X (%)" is the content (% by weight) obtained by pulverizing the thermistor material to obtain a powder X-ray diffraction pattern and quantifying the composition of X by the Rietveld method. Say.

[1.3. Properties of thermistor material]
[13.1. Strength]
When the insulating ceramic is a nitride-based ceramic containing Si such as Si ₃ N ₄ , when B or a boron compound is added to the raw material, these react to form BN. BN causes a decrease in the strength of the thermistor material.
On the other hand, since the thermistor material according to the present invention does not use B or a boron compound as a raw material, BN is not generated in the material even when a nitride ceramic is used as the insulating ceramic. .. Therefore, the strength is higher than that of the conventional thermistor material for low temperature range.

Specifically, the thermistor material according to the present invention has a bending strength of 300 MPa or more and 900 MPa or less. When the manufacturing conditions are optimized, the bending strength is 350 MPa or more, or 400 MPa or more.

[1.3.2. 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 the electrical resistance (R) and the temperature (T; Celsius temperature) is approximated by R = Aexp (−BT).
In the thermistor material according to the present invention, when the relationship between the electric resistance (R) and the temperature (T) is expressed by R = Aexp (−BT), the logR is relative to T in the temperature range of at least −80 ° C. to 500 ° C. (Electrical resistance (R) changes linearly with temperature on a semi-log graph). Moreover, the slope (B value) is relatively large. Therefore, the temperature can be accurately detected in the low temperature range. The B value varies slightly depending on the composition of the thermistor material, but it is in the range of 0.01 or more and 0.025 or less when the method described later is used.

[1.3.3. Specific resistance value]
The resistivity value of the thermistor material depends on the amount, particle size, and dispersed state of the conductive particles that are semiconductors. In general, as the amount of conductive particles increases, or as the number and area of contact points between these crystal grains increase, the resistivity value of the thermistor material decreases.

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

[2. Thermistor material manufacturing method]
The method for producing a thermistor material according to the present invention is as follows.
A mixing step of obtaining a mixture containing an insulating ceramic powder, an α-SiC powder containing a predetermined amount of a dopant, and a sintering aid as a main raw material.
It is provided with a molding / sintering step of molding and sintering the mixture.

[2.1. Mixing process]
First, as a main raw material, an insulating ceramic powder, an α-SiC powder containing a predetermined amount of dopant, and a mixture containing a sintering aid are 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 carry out the granulation treatment. By performing such a treatment, the moldability (compacting property) is improved.

[2.1.1. Main raw material]
[A. Insulating ceramic powder]
The insulating ceramic powder added to the raw material becomes matrix crystal grains of the sintered body. The lower the density of the sintered body, the more open pores remain, and the easier it is for oxygen to diffuse inside the sintered body. In the present invention, SiC powder is added to the raw material, but since SiC powder is difficult to sinter, it tends 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 insulating ceramic 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 size (primary particle size) of the insulating ceramic 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]
As a raw material for the conductive particles, α-SiC powder containing a predetermined amount of dopant is used. The type and amount of the dopant are as described above, and thus the description thereof will be omitted.
The SiC powder added to the raw material forms part of the conductive path in the sintered body. The SiC powder rarely grows during sintering, but a part of it reacts with other raw materials and becomes crystalline on the surface of the SiC powder or the surface of other raw materials (for example, insulating ceramic powder). Inorganic compounds may be produced.

The average particle size D ₅₀ of the SiC powder may be relatively large. However, if the D _{50 of} the SiC powder becomes too large, the density of the sintered body decreases, or the variation in the specific resistance value becomes large. In order to densify the sintered body and reduce the variation in the specific resistance value, the D ₅₀ of the SiC powder is preferably 5 μm or less. D ₅₀ is preferably 1 μm or less, more preferably 0.5 μm or less, still more preferably 0.2 μm or less.

[C. Sintering aid]
The sintering aid added to the raw material constitutes all or part of the grain boundary phase in the sintered body. When the grain boundary phase is formed substantially only from the sintering aid, the sintering aid reacts with other raw material powders (for example, oxides on the surface of the insulating ceramic powder (for example, SiO ₂ )). In the present invention, the composition of the sintering aid is not particularly limited, and the optimum one can be selected according to the purpose. As the sintering aid. For example, there are Al ₂ O ₃ , Al N, 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 .

In order to obtain a dense sintered body, the smaller the average particle size D ₅₀ of the sintering aid is, the better. In order to obtain a dense sintered body, the D ₅₀ of the sintering aid is preferably 0.5 μm or less. D ₅₀ is preferably 0.3 μm or less, more preferably 0.1 μm or less.

[2.1.2. Blending amount of each raw material]
Each raw material is blended so as to obtain a thermistor material having a desired composition. To obtain a thermistor material with the composition described above, the mixing step is
The amount of SiC powder blended is more than 14 vol% and less than 40 vol%.
The blending amount of the sintering aid is 4 vol% or more and less than 15 vol%.
It is preferable to mix these so that the balance becomes an insulating ceramic powder.

[2.1.3. Mixing method]
The method for mixing the raw materials is not particularly limited, and various methods can be used. Moreover, you may also grind the raw material at the time of mixing. Further, the mixed / crushed powder may be granulated by spray drying with a spray dryer or the like. By granulating the raw material powder, the fluidity in the mold can be 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. Molding method and sintering method]
The molding method is not particularly limited, and the optimum 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 cast molding method, a glass sealing method, an extrusion molding method, a tape molding method, and a doctor blade. There is a law and so on. Further, in order to reduce the man-hours for finishing after sintering, the molded product containing the binder in advance may be subjected to raw processing.
Similarly, the sintering method is not particularly limited, and the optimum method can be selected according to the purpose. In order to obtain a dense sintered body, pressure sintering such as hot press treatment, SPS (Spark Plasma Sintering) treatment, and HIP treatment is preferable.

[2.2.2. Molding conditions and sintering conditions]
The optimum molding conditions and sintering conditions for the molded product are selected according to the purpose. Further, the specific resistance value and the temperature resistivity change rate (B value) depend not only on the molding conditions and the sintering conditions but also on the pulverization / mixing conditions (mainly the mixing ratio of the main raw materials and the particle size ratio).

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, 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 progresses excessively, the mechanical properties such as strength and fracture toughness deteriorate, and the distribution of the SiC crystal grains becomes non-uniform. Furthermore, the raw material may be decomposed and sublimated. Therefore, the sintering temperature is preferably 1800 ° C. or higher and lower than 1900 ° C.

It is preferable to select the optimum sintering time according to the sintering temperature. Generally, when a relatively large amount of B powder is contained in the raw material, when the sintering temperature is too high and / or the sintering time is too long, an excess Si phase (liquid phase) may be generated. There is. Si forms a liquid phase at 1410 ° C. or higher and easily diffuses. As a result, the composition in the sintered body becomes non-uniform, and the thermistor characteristics may vary.

[3. Action]
When α-SiC containing an appropriate amount of p-type dopant and / or n-type dopant is dispersed as conductive particles in the insulating ceramic, the temperature resistance coefficient (B value) of B, TiB _2, etc. is increased in the raw material. A thermistor material capable of highly accurate temperature detection in a low temperature range can be obtained without adding a component for this purpose.
This is because the carrier concentration-optimized α-SiC is dispersed in the matrix, so that the influence of the mobility of the thermistor material is greatly reduced, while the temperature dependence of the carrier concentration of the thermistor material becomes dominant. Therefore, it is considered that the temperature resistance change rate (B value) becomes large.

(Example 1)
[1. Preparation of sample]
Si ₃ N ₄ powder was used as a raw material for the insulating ceramics. The raw material of the conductive particles, B to 1 × 10 ¹⁸ cm ^-3, with ^{1 × 10 17 cm -3 α-} SiC powder containing N. Y ₂ O ₃ powder was used as the sintering aid. Weighed so that Si ₃ N ₄ powder: α-SiC powder: Y ₂ O ₃ powder = 60 vol%: 35 vol%: 5 vol%, and these raw materials were mixed in ethanol and dried.

The obtained mixed powder was sintered by hot pressing to obtain a disk-shaped sintered body (wafer). The pressing force was 20 MPa, and the sintering temperature was 1850 ° C. A 2 mm square × 0.8 mm thick sample was cut out from the obtained wafer, and Ni electrodes were formed on the upper and lower surfaces. This was further heat-treated to obtain a chip element.

[2. Test method and results]
[2.1. B value]
The thermistor characteristics of the chip element were evaluated. FIG. 1 shows the relationship between the temperature T of the thermistor element obtained in Example 1 and the specific resistance value ρ. The obtained chip element had thermistor characteristics with a specific resistance value ρ = 7.90exp (−0.018T) (T: temperature). That is, the specific resistance value at 0 ° C. was 7.9 kΩcm, and the temperature detection sensitivity (temperature resistivity change rate) showed a high value of 0.018.

[2.2. Resistance value variation]
Next, a plurality of samples were cut out from different positions on the wafer to prepare a chip element. The specific resistance value of each chip element was measured at −40 ° C. From the obtained specific resistance value, the resistance value variation (= standard deviation of the specific resistance value × 100 / average value of the specific resistance value) was calculated.
FIG. 2 shows the relationship between the distance from the center of the wafer obtained in Example 1 and the resistivity value ρ. From FIG. 2, it can be seen that the obtained wafer has a stable resistivity distribution in the radial direction. In the case of the wafer obtained in Example 1, the resistance value variation was about 0.6%.

[2.3. Carrier concentration and mobility]
A 4 mm square × 0.8 mm thick sample was cut out from the wafer, and 1 mm square Ni electrodes were formed at the four corners. Hall measurements were performed at room temperature to determine the carrier concentration and mobility of the thermistor substrate. The carrier concentration was 5 × 10 ¹⁵ cm ^-3 , and the mobility was 2 × ^10-2 cm ² / V · s.

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 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 (7)

Thermistor material with the following configurations.
(1) The thermistor material is
Matrix crystal grains made of insulating ceramics and
Conductive particles dispersed between the matrix crystal particles and
Grain boundary phase and
Is equipped with.
(2) The conductive particles are made of α-SiC doped with B, Al, and / or N.
(3) The thermistor material has a carrier concentration of 1 × 10 ¹⁴ cm ^-3 or more and 1 × 10 ¹⁹ cm ^-3 or less at room temperature. The thermistor material according to claim 1, wherein the thermistor material has a mobility of 1 × 10 ^-4 cm ² / V · s or more and 1 cm ² / V · s or less. The thermistor material according to claim 1 or 2, wherein the bending strength is 300 MPa or more and 900 MPa or less. The thermistor material according to any one of claims 1 to 3, wherein the Si content is 0.1% or less. The thermistor material according to any one of claims 1 to 4, wherein the content of the boron compound is 0.1% or less. The thermistor material according to any one of claims 1 to 5, wherein the BN content is 0.1% or less. The insulating ceramic is any one of claims 1 to 6 including any one or more selected from the group consisting of Si ₃ N ₄ , Si ALON, Al N, Al ₂ O ₃ , and Y ₂ Si ₂ O _7. Thermistor material described in section.

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