JPH03268303A - Thermistor material and thermistor element - Google Patents

Abstract

PURPOSE:To obtain a thermistor material which has stability at a high temperature and is free from positional irregularities of electric resistance value generated in a sintered wafer, by containing carbon in the form of simple substance in a sintered body containing boron carbide as conduction path forming material and matrix material containing aluminum oxide. CONSTITUTION:The title material is constituted of sintered body containing matrix material of boron carbide and aluminum oxide as conducting path forming material and simple substance of carbon element. The boron carbide in the sintered body is expressed by a chemical formula B4C, and may deviate stoichiometrically from its composition to some extent. The matrix material is desirable to contain, in addition to aluminum oxide, one or more kinds selected out of single substances of 4A group elements and compounds like oxide and boride. The carbon is made to exist in the form of element simple substance. Thereby thermistor material which has stability at a high temperature and uniform resistance value distribution in the surface of minute region level can be obtained.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a thermistor material and a thermistor element that are effective when applied to a thermistor element having negative resistance temperature characteristics for high temperatures.

<Prior Art> A thermistor is a temperature sensor that utilizes the temperature dependence of the electrical resistance of a temperature-sensitive resistor, and is widely used for temperature measurement, temperature control, and the like. Particularly for high-temperature applications, they are used, for example, in automobile exhaust gas temperature detection sensors, oil and gas combustion control sensors, and the like.

The material of the temperature-sensitive resistor of the conventional high-temperature thermistor element, that is, the thermistor material, is fluorite type (Zr0z-
zirconia type such as CaO-Y*0a-NdzOa-ThO), spinel type (MgO-NiO-Aj!0l-Cr
103-FexOx etc.; Co0-Mn0-Ni0-
AjiOx-CrzOs-CaSiOx etc.; Ni0z
-COO-AlzOz etc.; Mg0-AjJs-Cr2
0s-LaCrO, etc.), corundum type (AlzOz-
CrxOs-Mn02-CaO-3iOa, etc.), perovskite type, rutile type, and other complex oxide sintered bodies are used.

Since these materials are composite oxide sintered bodies, they do not change significantly over time due to factors such as 1) having a crystal transformation point below 1000°C, and 2) forming barriers between particles. Many are stable. In particular, since zirconia is an oxygen ion conductor, it undergoes redox reactions and changes significantly over time.

Furthermore, since it is a multi-component composite oxide, there are large variations in properties such as resistance value.

Furthermore, in these devices, the value of the thermistor constant B is large, and the temperature coefficient of resistance of the thermistor is too large, making it impossible to provide a thermistor that covers a wide temperature range from room temperature to high temperature. In particular, it could not withstand use at temperatures above 500°C.

On the other hand, various thermistor elements whose main components are silicon carbide or boron carbide are known.

For example, Japanese Patent Publication No. 42-19061 describes a thermistor element in which a trace amount of a group 3B or 5B element is added to single crystal silicon carbide as a p-type or n-type impurity.

However, since this method involves single crystal production, productivity is low (manufacturing cost is high).

Further, although this material exhibits a very stable electrical resistance value at high temperatures, when the device is used in the atmosphere at high temperatures, it is subject to surface oxidation, particularly at temperatures above 400°C. Therefore, a protective film is required. As a method for forming this protective film, sealing the depth with glass is preferable since it is the easiest to manufacture.

However, in the above-mentioned thermistor element, silicon carbide tends to foam due to reaction with glass in the step of glass sealing, and glass sealing cannot be performed.

Further, US Pat. No. 4,086,559 describes a thermistor element using thermally decomposed polycrystalline equiaxed silicon carbide to which 0.7 vol. % or less of an n-type impurity is added.

Also, U.S. Patent Nos. 4,359,372 and 44,245
No. 07 describes a sputter thin film thermistor element made of silicon carbide or boron carbide containing a small amount of impurities.

However, these thin-film thermistors have low productivity and high manufacturing costs (similar to single crystals), and cannot be sealed with glass.

Therefore, in the latter sputtered thin film, glass is vapor-deposited as a protective film to suppress foaming, but in this case, productivity is further reduced.

On the other hand, composite sintered bodies of oxide and non-oxide materials are also known. This material has higher productivity than single crystals or thin films.

As such a composite sintered body, the following composite sintered body mainly composed of silicon carbide is known.

(A) Be containing silicon carbide as a main component.

A polycrystalline silicon carbide sintered body containing 20 wt% or less of any of Beo, B, B*Os, BN, and B4C (US Pat. No. 4,467,309).

(B) Add 0.5 to 10 wt of one or more types of aluminum compounds such as aluminum and aluminum oxide to silicon carbide.
% of polycrystalline sintered body (Japanese Unexamined Patent Publication No. 60-49607).

(C) A silicon carbide sintered body obtained by thermally diffusing B into silicon carbide and adding a small amount of B (Japanese Patent Publication No. 60-52562).

However, since these have a high SiC content, glass sealing is difficult due to foaming as described above.

Furthermore, if silicon carbide is used as the main material, it is difficult to process, and cutting into a thermistor chip is difficult.

Furthermore, there is a drawback that the value of B increases to 10,0OOK or more, and the temperature coefficient of the thermistor becomes too large to cover a wide temperature range.

Furthermore, when examining the relationship between the composition ratio and resistivity (ρ) of the thermistor materials, it is found that with these materials, ρ changes rapidly even with a slight change in the composition ratio, making it difficult to control the resistance. Furthermore, JP-A-55-140201 discloses that SiC is the main component, 2 to 15 wt% Ru0a and 2
Thick film thermistors containing 0-50 wt% glass have been described. However, in this case as well, the powdered SiC and glass foam violently during the printing and firing steps, and it is very difficult to control this.

Therefore, the present inventors have previously developed a thermistor material that is stable even when used at high temperatures, especially temperatures of 400 to 800°C, has easy control of resistance, and is easy to seal with glass. It contains silicon carbide and/or boron carbide as a conductive path forming material, and a matrix material containing one or more of oxides of aluminum, silicon, magnesium, calcium, strontium, and barium, and the content of silicon carbide is as described above. We have proposed a thermistor material composed of a sintered body whose volume ratio to the content of the matrix substance is 1.24 or less (Japanese Patent Application Laid-Open No. 1983-1999).
-64202).

Compared to previous thermistor materials, this material has reduced positional variations in electrical resistance within the sintered wafer.

However, when looking at the electrical resistance value microscopically, there are still positional variations in the electrical resistance value.

As a result, the sintered wafer is, for example, 0.75xQ, 75
When cutting the thermistor chips into chips with a size of approximately 0.5 mm, the electrical resistance value of each chip differs depending on the cutting position, making it impossible to obtain thermistor chips with constant characteristics.

<Problems to be Solved by the Invention> The object of the present invention is to provide a material that is stable even when used at high temperatures, particularly at temperatures of 400 to 800°C, is easy to seal with glass, and is easy to control the resistance value. The object of the present invention is to provide a thermistor material having a uniform in-plane resistance value distribution at the level of a minute area, and a thermistor element with excellent characteristics by applying this material.

(3) The thermistor material according to (1) or (2) above, which further contains a group 4A element as the matrix material, and the content of the group 4A element relative to the content of boron carbide is 5 wt% or less.

(4) A thermistor element having a thermistor chip formed from the thermistor material according to any one of (1) to 3) above.

<Means for Solving the Problems> Such objects are achieved by the following inventions (1) to (4).

(1) A sintered body containing boron carbide as a conductive path forming material and further containing a matrix material containing aluminum oxide, characterized in that carbon is present in the form of an element in the sintered body. thermistor material.

(2) The thermistor material according to (1) above, wherein the content of carbon existing in the form of a simple element is 3 wt% or less based on boron carbide.

Effect> In the thermistor material of the present invention, carbon exists in the form of an elemental element.

Therefore, a thermistor material having a uniform in-plane resistance value distribution when viewed microscopically is realized.

As a result, the sintered body wafer of thermistor material can be
．． When manufacturing a thermistor element by chipping it into a thermistor chip with dimensions of approximately 75 x 0.75 x 0.5 mm, a thermistor element having a constant electrical resistance value can be obtained.

<Specific structure of the invention> Hereinafter, a specific configuration of the present invention will be explained in detail.

The thermistor material of the present invention is composed of a sintered body containing boron carbide as a conductive path-forming material and a matrix material of aluminum oxide, and further containing an elemental carbon element.

Boron carbide in the sintered body is represented by chemical formulas B and C, and the stoichiometric composition may be slightly different.

In addition, the average grain size of boron carbide is usually 0.1~
It is in the range of 15-.

The matrix material is a sintered body of aluminum oxide (Al2O2, especially α-8),
Usually polycrystalline.

By using a sintered body of aluminum oxide as the matrix material and a sintered body of boron carbide as the conductive path forming material,
It has high stability in the temperature range of 400 to 800°C, easy control of resistance, easy glass sealing, and improved chip processability.

In addition to aluminum oxide, the matrix material is
It is preferable to contain one or more types selected from simple substances of Group 4A elements and compounds such as oxides, borides, carbides, and nitrides.

By containing a simple substance or a compound of a group 4A element, the electrical resistance value can be easily controlled, its variation within the sintered body is reduced, and cutting workability is also improved.

Compounds of group 4A elements (Ti, Zr, Hf) include titanium oxide (TiOz), titanium boride (TiB2),
Titanium carbide (T i C) Titanium nitride (TiN), Zirconium oxide (ZrC2), Zirconium boride (Zr
Bz), zirconium carbide (ZrC), and zirconium nitride (ZrN) are preferred.

Of these, Ti alone, titanium oxide (T
iO++), titanium boride (TiB*), titanium carbide (
It is preferable to contain one or more of titanium nitride (T i N) and titanium nitride (T i N).

The chemical formulas of these compounds are shown in parentheses, but the stoichiometric composition may be slightly different.

The average grain size of the matrix material is usually 0.1~
It is in the range of 250-.

Boron carbide forms a conductive path in the matrix material and exhibits thermistor properties. The conductive path formed from these is stable at high temperatures of 400° C. or higher and has good thermistor characteristics.

The compositions in the following description are expressed in weight percentages obtained by chemically analyzing the sintered body.

The content of boron carbide relative to the total amount of aluminum oxide (α-A Q *Os) and boron carbide (B4C) is 5 to 95 wt%, more preferably 5 to 50 wt%.
, more preferably 5 to 2 wt%, particularly preferably 1
It is preferably 0 to 15 wt%.

If it is less than the above range, a conductive path tends not to be formed, and if it exceeds the above range, sintering etc. tend to become difficult.

As mentioned above, one or more elements and compounds of group 4A elements, especially titanium oxide (Tie),
Titanium boride (TiB) and titanium carbide (TiC)
It is preferable to contain one or more of the following.

Single elements and compounds of group 4A elements are usually added in the form of single elements or oxides (TiO2, Zr0g, Hfoz), but some may be converted into borides, carbides, nitrides, etc. .

The content of the 4A group element is preferably 5 wt% or less, particularly 0.1 to 2 wt%, based on boron carbide.

If it exceeds the above range, the thermistor characteristics and stability at high temperatures will deteriorate.

However, if it is too small, the above effects tend not to be obtained.

In this case, if the thermistor material contains a boride of a group 4A element, the occurrence of chipping will be significantly reduced.
The lifespan of diamond grinding wheels during machining is dramatically improved.

As a boride of group 4A element, titanium boride (TiB
, ), zirconium boride (ZrB, ) are preferred, and T i B t is particularly optimal.

Borides of group 4A elements usually exist at grain boundaries or within grains.

The presence of these can be confirmed using an analytical electron microscope, and the content is X! ! ! It may be measured by quantitative analysis using a diffraction method.

In the thermistor material of the present invention, carbon is further present in the form of an elemental element.

When carbon is contained in the form of a single element, the in-plane resistance value distribution of the thermistor material becomes uniform, and positional variations in resistance value occurring within the sintered wafer are reduced.

The presence of carbon element is confirmed by transmission electron microscopy (TEM). The carbon element in the sintered body may be clustered or thinly precipitated at grain boundaries. Most of the carbon element is crystallized (graphite) and can be observed by electron diffraction images.

Further, impurities may be included in the carbon.

Further, the content of carbon existing in the form of a simple element is preferably 3 wt % or less based on boron carbide.

The presence of carbon beyond the above range is unnecessary.

However, if the amount is too low, the effects of the present invention tend not to be obtained.
More preferably 100 ppm (weight ratio) to 1 wt%
is preferred.

The carbon content may be measured by preparing a calibration curve and using an X-ray diffraction method.

In addition, the actual density of the sintered body is 75% of the theoretical density of the sintered body.
or more, preferably 90 to 100%, particularly 95%
Most preferably, it is between 100% and 100%. This results in
The temporal change characteristics of the electrical resistance value of the element are improved.

Note that during sintering, a part of boron carbide may be changed to an oxide (boron oxide), and a part of the oxide may be changed to a carbide, a boride, etc., but the present invention Since carbon exists in the form of a simple element, the surface of boron carbide reacts with boron oxide (especially B-Ox > or with AQwOs in the matrix, forming 9 (Al2O,
)2(B□0.) and other double oxides can be suppressed.

The content of boron oxide and complex oxide containing boron oxide is 0 to 1 wt%, especially 0.1 wt% in terms of boron element.
It is preferably 0.5 wt%. The reason for this is
Boron oxide, especially B20. This is because, since it becomes glassy, the glass phase increases and the melting point becomes low, making it difficult to control the electrical resistance and the particle size of the sintered body.

The thermistor material may further contain one or more group 3A elements as a subcomponent.

The Group 3A element may be contained as an elemental metal, a compound, or a composite of these elements.

As group 3A elements, Y and Ce are particularly preferable, and when contained as a compound, oxides of these elements (Y2
03, Cent) or carbides are preferred.

Group 3A elements are preferably o, oi to 10wt in terms of element.
%, the electrical resistance value can be easily controlled and the positional variation in the electrical resistance value within the sintered wafer can be reduced.

Also, instead of or in addition to the Group 3A elements, iron may be used as a subcomponent, preferably as an elemental metal or as an oxide (Fe*os).
), may be contained in the form of one or more types of carbides.

Fe also has the same effect as the Group 3A elements.

The content of Fe is preferably 0.01 to 10 wt% in terms of element.

In Group 8 elements other than iron, such as CO1Ni and Ru, the amount of oxygen vacancies tends to change at operating temperatures of 500° C. or higher, and as the content increases, electrical resistance deteriorates over time. For this reason, the content of elemental metals, oxides, carbides, etc. of Group 8 elements other than iron is not excluded, but it is preferably 1 wt % or less, particularly 0 to 0.5 wt % in terms of element.

The above-mentioned effects of Group 3A elements and Fe can also be achieved with elemental elements such as Aρ, carbides, and elemental elements, oxides, and carbides of Mg, Ca, Sr, and Ba.

These subcomponents preferably have an elemental equivalent of 0.
At a content of 01 to 10 wt%, the resistance value can be easily controlled and its variation becomes small.

Furthermore, if necessary, other subcomponents may also be contained in the form of simple substances, oxides, carbides, etc.

First, although the inclusion of SA group and 6A group elements has no effect, their inclusion is not necessarily excluded. However, since addition of a large amount deteriorates the thermistor characteristics, it is preferable not to exceed 10 wt% in terms of element, and particularly preferably not to exceed 1 wt%.

Next, it is particularly preferable that group IA elements such as Na and Li are not contained. This is because when a voltage is applied to the thermistor element, these ions move and diffuse, and the resistance tends to deteriorate over time. Further, during glass sealing, these materials tend to diffuse into the glass (and tend to cause characteristic deterioration).

The content of the Group IA element is preferably 0 to 1 wt%, particularly O to 0.001 wt% in terms of element.

Furthermore, the inclusion of Group 7A elements is also not preferred.

This is because the valence of group 7A elements tends to change (and their properties change over time).

The content of the Group 7A element is preferably 0 to 1 wt%, particularly 0 to 0.05 wt% in terms of element.

Furthermore, since group IB elements and group 2B elements tend to change over time, O = 1wt% in terms of element, especially O ~ 0.05w.
Preferably, it is t%.

In addition, Ga, In, which are group 3B elements other than B and Aρ,
Tj2 may also be contained in an amount of about 0 to 1 wt% or less.

However, groups 4B, 5B, 6B, and 7 other than C, O, and N
Group B elements etc. are unfavorable due to their characteristics, so 0 to 1 wt%
It is preferable that the content is .

When these subcomponents in the sintered body are contained as compounds, their stoichiometric compositions may be slightly different.

In addition, the average grain size of the subcomponents is usually in the range of 1 to 5 in the case of an elemental metal, and in the case of a compound, it is usually in the range of O
It is in the range of 01 to 5-.

Furthermore, if necessary, the above-mentioned subcomponents or compounds that change into these by sintering, such as carbonates, organometallic compounds, etc., are added.

Next, a method for manufacturing the thermistor material of the present invention will be explained.

Predetermined amounts of raw material powder of aluminum oxide and raw material powder of boron carbide are each prepared, a solvent such as ethanol or acetone is added thereto, and the mixture is wet-mixed using a ball mill or the like.

As raw material powder for aluminum oxide (Al2O,),
Generally, average particle size is 0.1-5, purity is 99.5wt%
Use the above.

In addition to aluminum oxide, the raw material powder for the aluminum oxide may be a compound that becomes an oxide by sintering, such as a carbonate or an organometallic compound, or a combination of these may be used.

The raw material powder of boron carbide (B4C) generally has an average particle size of 0.5 to 10 particles and a purity of 97 wt% or more.

Note that as the boron carbide raw material powder, in addition to the boron carbide powder, a carbon raw material powder and a boron raw material powder may be used, or they may be used in combination.

Further, in the method for manufacturing a thermistor material of the present invention, the resistance value is finely adjusted as described below.

Generally commercially available B and C have slightly different stoichiometric compositions.

Therefore, even if a plurality of thermistor materials are manufactured using the same method, the resistance values of the thermistor materials differ depending on the boron carbide used.

Therefore, in the present invention, two or more types of boron carbide having different stoichiometric compositions are mixed to adjust the atomic ratio B/C of boron and carbon. Then, the atomic ratio B/corresponding to the desired resistance value is
A raw material powder of boron carbide of C is obtained.

This atomic ratio B/C is preferably 3.5 to 4.0 degrees.

Alternatively, B/C may be adjusted by adding carbon or boron to one or more types of boron carbide, or even B/C may be adjusted using carbon and boron without using boron carbide. It may also be used as a raw material powder of boron carbide.

In this way, when carbon is contained in the form of an elemental element in the boron carbide raw material powder, a part of it remains in the form of an elemental element after sintering.

Alternatively, when sintering is performed using a boron carbide raw material powder with B/C adjusted as described above, some of the added carbon may remain in the form of a single element.

Alternatively, part of boron carbide may decompose and carbon may exist in the form of an elemental element.

In addition, although boron may exist in the form of a single element,
There is no particular effect on the characteristics of the thermistor.

The simple substance or compound of the 4A group element may be added, for example, as T i Oa powder, and generally the average particle size is 0.1 to 5-5 and the purity is 98 wt % or more.

The boride of the Group 4A element may be added, for example, as T i B 2 powder (generally, one with an average particle size of 0.1 to 5 μm and a purity of 98 wt % or more may be used).

Further, the boride of the Group 4A element may be added in the form of its oxide, simple substance, or the like.

At this time, by controlling the sintering conditions as described below, for example, B4C and TiOZ react, and for example, Ti
B is generated.

In such a case, for example, Al2O is mixed as a matrix material with conductive path forming materials B and C, and 4A is added to this.
When TiO□ is added as a group element source and fired, T
Simultaneously with the generation of iB*, B+sCa, Tic%
Tis AI2, Ti, etc. may be formed as by-products.

These by-products may be contained in an amount of 10 wt% or less, particularly Iwt% or less.

The amount of solvent is approximately 100 to 120 wt% of the powder.

Further, a dispersant or the like may be further added as necessary.

Thereafter, the above mixture is pressure molded at room temperature, and then sintered in an oxygen atmosphere or a non-oxidizing atmosphere by a pressureless sintering method, a hot press (HP) sintering method, a hot isostatic pressing (HIP) method, etc. This molded body is sintered and left to cool to obtain a thermistor material.

The pressure during pressure molding is 500 to 2000 kg/cm2
That's about it.

The non-oxidizing atmosphere during sintering may be various atmospheres such as an inert gas such as N2Ar or He, H, Co, various hydrocarbons, a mixed atmosphere thereof, or even a vacuum.

In the case of pressureless sintering method, atmospheric pressure is sufficient, and the sintering temperature is 1400℃.
It is effective at temperatures between 1900°C and 1900°C, particularly between 1600 and 1900°C, more preferably between 1750 and 1800°C.

If the temperature is lower than 1400°C, even if sintered for a long time, it will not be sufficiently densified, and if the temperature is higher than 1900°C, Al
The mutual reaction between oxides such as 2O2 and B4C becomes intense.

Sintering time is usually 0.5 to 20 hours.

For HP sintering method, press pressure is 150-250 kg
/cm", firing temperature is 1400-1800℃, especially 15
00~1800℃, more preferably 1650~1750℃
°C is preferred.

If the temperature is lower than 1400°C, a dense sintered body cannot be obtained, and if the temperature is higher than 1800°C, the mutual reaction between Al2O2 and B and C becomes intense.

Sintering time is generally 1 to 30 hours.

In the case of the HIP sintering method, a compact of raw material powder is pre-sintered in an oxygen atmosphere or a non-oxidizing atmosphere (for example, in a vacuum up to 1200°C, and then preferably in an Ar atmosphere), and then in a HIP furnace. This preliminary sintered body is sintered.

The temperature of the preliminary sintering is preferably 1400 to 1650°C, and the time is preferably 1 to 50 hours.

In addition, the sintering temperature in the HIP method is 1200 to 1500
℃, sintering time is 1-50 hours, pressure is 1000-150
0 kg/am'' and may be carried out in an oxygen atmosphere or an inert atmosphere such as Ar.

In this case, at room temperature, oxygen gas, Ar gas, etc.
Pressurize to 0 kg/cm'' and then apply pressure by heating as described above.

The above sintering conditions are common to all cases, including cases in which borides of group 4A elements are used in advance and cases in which borides of group 4A elements are generated. In order to generate a boride of a group 4A element during crystallization, the following profile may be used.

In the cold sintering method, Temperature increase rate 1~1OO℃/win, Sintering temperature 1600-1900℃, The holding time at the sintering temperature is 0.5 to 20 hours.

In addition, in the HP method, Temperature increase rate 1-100°C/rnin, Sintering temperature 1400-1800℃, Holding time at sintering temperature 1-30 hours shall be.

Furthermore, in the HIP method, the temperature increase rate is 1 to 100 °C/min, the pre-sintering temperature is 1400 to 1650 °C, the holding time at the pre-sintering temperature is 1 to 50 hours, and the sintering temperature is 12
The holding time at the sintering temperature is 1 to 50 hours.

In this way, by increasing the holding time at the sintering temperature in particular, the formation of borides of group 4A elements is promoted, and the grain size of the matrix material becomes coarser in the range of about 10 times or less, making it difficult to process chips. Improves sex.

The thermistor material produced in this way has a resistivity ρ of 50
It is about 102 to 107 Ωcm at 0°C, and there is almost no positional variation in resistance value or resistivity.
Then, a thermistor material having a desired resistance value can be manufactured with good reproducibility. In addition, there is almost no change in resistance value even when used or stored in a temperature range of 400 to 800°C. In addition, the value of the thermistor constant B is also 1 at 25 to 500°C.
It is from 000 to 5000.

In such a thermistor material, chip processability is dramatically improved by containing 0.01 to 10 wt % of a group 4A element boride, as described above.

The thermistor characteristics, glass sealing characteristics, etc. can be changed to the same characteristics as those described in JP-A-64-64202.

The thermistor material produced as described above is applied to the thermistor element of the present invention as a thermistor chip.

As the thermistor element of the present invention, a so-called glass-sealed thermistor element can be particularly preferred.

Such a glass-sealed thermistor element 1, for example, as shown in FIG. It has a structure in which the two parts are connected and sealed with glass 5.

There are no particular restrictions on the dimensions of the thermistor chip, but it is usually 0.5 to 1.0 ma+ in length, 0.5 to 1.0 mm in width, and 0 mm in thickness.
．． It is about 5 to 1.0 mm.

Regarding various thermistor elements, please refer to Japanese Patent Application Laid-Open No. 64-6420.
This is detailed in Publication No. 2.

<Examples> Hereinafter, specific examples of the present invention will be shown, and the present invention will be explained in detail.

Example 1 and the starting materials were weighed in the proportions shown below, and mixed using acetone in a ball mill for 20 hours. In this case, carbon is added to increase the atomic ratio B of boron and carbon in the starting material.
/C was finely adjusted. Note that the average particle size is a value measured by electron microscopic observation.

・Ax*os (purity 99.9 wt% or more) = 86 parts by weight Average particle size: 3-1 ・B,,,C (purity 98 wt% or more) = 14 parts by weight Average particle size: 2 units, ・TiO□ ( (Purity: 99 wt% or more) 20.2 parts by weight (0.84 wt% in terms of Ti, based on boron carbide) Average particle size: 1-1 ・C (Purity: 99 wt% or more): 0.16 parts by weight Average particle size: 0.5-1 B/C (atomic ratio): 3.9 The mixed slurry was dried and granulated, and filled into a graphite mold with an inner diameter of 77 mm.

This was pressed in an Ar atmosphere at a pressure of 200 to 300 K.
Hot press sintering was carried out at "g/cm".

The firing conditions were a firing temperature of about 1680° C. and a holding time of about 2 hours. And after cooling, 50X50X0.5m
A sintered body of m (sample No. 1) was obtained.

As a result of electron beam diffraction by TEM, the obtained sintered body showed
It was confirmed that carbon exists in the form of a simple element.

Then, a calibration curve was prepared and measured by an X-ray diffraction method. As a result, the content of carbon existing in the form of a simple element was 0.14 wt% based on boron carbide.

In addition, some of the added TiO snow remains as it is, and at the same time as T i B z is generated, trace amounts of Tic and T
By-products such as i, Tin Ar2, B+sCz, etc. were observed.

Comparative sample No. 12 was prepared in the same manner as above except that B and C were used as boron carbide and no carbon element was added.
was manufactured.

As a result of performing electron beam diffraction using a TEM on the obtained thermistor material, it was confirmed that carbon does not exist in the form of an elemental element.

In addition, similar to the generation of T i B *, a trace amount of Tic,
In addition to by-products such as Ti, Tis Ar2, B+sC-, 9
The by-formation of (AntOs)2(BtOx) was observed.

Both sides of each sintered body obtained are electroless plated to a thickness of 0.
A 1.0 μm thick N1-B electrode layer was formed, and a 1.0 μm thick platinum electrode layer was further formed thereon by plating to prepare a wafer.

The obtained wafer was sliced with a diamond blade using a peripheral slicing machine with a side of 0.75 x Q and 75 x 0.5
A thermistor chip was obtained by cutting into a +a+o square.

Such a thermistor chip has a diameter of 0.3 mm and a length of 6
Kovar lead wires of 5a+m were connected by parallel gap welding.

Then, the average thermistor constant B of the thermistor chip at 25 to 500°C was measured.

In addition, the average resistivity ρ at 25° C. and the coefficient of variation CV (%) of the resistivity ρ were determined.

The results are shown in Table 1.

The material obtained in this way has a diameter of 2.511QI,
It was inserted into borosilicate glass having a length of 4 s+m, and the glass was sealed at 850° C. in an Ar gas atmosphere. This was subjected to an aging treatment to produce a thermistor element sample as shown in FIG.

For these products, changes in resistance values were measured at the initial stage and after storage at 500° C. for 5000 hours.

The evaluation was calculated by calculating the change in resistance value as (ΔR/R0)XIOQ (%), with the initial resistance value of ΔR1 being Ro.

The results are shown in Table 1.

The effects of the present invention are clear from the results shown in Table 1.

Note that the thermistor material of the present invention also had good chip processability.

<Effects of the Invention> When viewed microscopically, the thermistor material of the present invention has extremely small positional variations in electrical resistance that occur within the sintered wafer.

Furthermore, it has stability even when used at high temperatures, particularly at temperatures of 400 to 800°C. Furthermore, since the B value can be made considerably low, the temperature coefficient of the thermistor is also small, and the applicable temperature range can be widened. Furthermore, when examining the relationship between the composition ratio and resistivity, the change in resistivity is not steep, and resistance can be controlled by changing the composition ratio. Therefore, the composition range of the target resistance range is expanded, and mass productivity and quality are improved.

When such thermistor material is applied to a glass-sealed thermistor element, it has good characteristics,
Moreover, a thermistor element having a uniform electrical resistance value can be manufactured.

In addition, if a so-called integrated thermistor element is formed by bonding with other materials by applying heat under pressure, the dimensional accuracy will be good, and dimensional changes such as when raw materials are integrated by sintering will be avoided. There is very little variation in properties and characteristics.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the thermistor element of the present invention. Explanation of symbols 1...Thermistor element 5...Glass 11...Thermistor chip 33.35...Electrode layer 43.45...Lead body FIG, 1 Submitted by TDC Co., Ltd. Patent attorney Yo Ishii

Claims (4)

[Claims] (1) A sintered body containing boron carbide as a conductive path forming material and further containing a matrix material containing aluminum oxide, characterized in that carbon is present in the form of an element in the sintered body. thermistor material. (2) The thermistor material according to claim 1, wherein the content of carbon present in the form of a simple element is 3 wt% or less based on boron carbide. (3) The thermistor material according to claim 1 or 2, further comprising a group 4A element as the matrix material, and the content of the group 4A element relative to the content of boron carbide is 5 wt% or less. (4) A thermistor element having a thermistor chip formed from the thermistor material according to any one of claims 1 to 3.