JPH045801A - Thermistor material and thermistor chip - Google Patents

Abstract

PURPOSE:To obtain a thermistor element which is stable at 400 to 800 deg.C, which can easily control a glass sealing operation and a resistance value and whose characteristic is good by a method wherein the particle diameter of B4C as a substance to form a conductive route is made uniform at a prescribed diameter and the substance is dispersed uniformly inside a sintered body. CONSTITUTION:A thermistor material is constituted of a sintered body which contains the following: B4C as a substance to form a conductive route; and a matrix substance containing one or more kinds of oxides of Al, Mg, Ca, Sr and Ba. In a state that 300 to 5000 particles of B4C exist inside the angle of field of an electron microscope, the cross section of the sintered body is observed and their particle diameters are measured. The distribution of the particles diameters is computed, and it is accumulated from small particle diameters. The particle diameters of the particles of B4C containing 10%, 50% and 90% out of the total expressed in terms of the number of pieces are designated as (D10)B, (D50)B and (D90)B; the thermistor material is constituted of the sintered body whose (D10)B/(D50)B is 0.1 to 1 and whose (D90)B/(D50)B is 1 to 2. At this time, it is possible to obtain the thermistor material which is stable even at 400 to 800 deg.C and in which the distribution of a sheet resistance value in a fine region is uniform. When the material is applied, it is possible to obtain a thermistor element whose characteristic is good.

Description

DETAILED DESCRIPTION OF THE INVENTION <Industrial Application Field> The present invention relates to a thermistor material and a thermistor chip 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 for the temperature-sensitive resistor of the conventional high-temperature thermistor element, that is, the thermistor material, is fluorite type (Zr02-
zirconia type such as Ca0-Y2O2-Nd203-ThO), spinel type (MgO-NiO-Ag2O3-Cr
20s-Fe20a etc.; Co0-Mn0-Ni0-
Ag2O3-Cr20a-CaSiOa etc.; Ni0z
-CoO-Aj20a etc.; Mg0-Ag2O3-Cr
203-L a to r Oa, etc.) mycorandom type (A
fi20a-CrJa-MnO□-(:aO-3iO3
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 of the chip 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 Q, 7vol or less of 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 trace amount of impurities.

However, these thin-film type thermistors have low productivity and high manufacturing costs like single crystal thermistors. Furthermore, glass sealing cannot be performed.

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) With silicon carbide as the main component, Be, Bed, B,
20w of B2O3, BN, B4C in terms of element
A polycrystalline silicon carbide sintered body containing t% or less (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.

Further, when examining the relationship between the composition ratio and resistivity (p) of the thermistor materials, it is found that in these materials, ρ changes rapidly even with a slight change in composition ratio, making it difficult to control the resistance. Furthermore, JP-A No. 55-140201 discloses that SiC is the main component, 2 to 15 wt% Rub, and 20
Thick film thermistors containing ~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.

But, for example, 50×501! When looking at the electrical resistance value using a micro region of about I11 as a reference, there still exists positional variation in the electrical resistance value.

Therefore, the sintered body wafer is, for example, 0.75xO, 75X
When cutting the thermistor chips into chips with dimensions of about 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.

<Means for Solving the Problems> Such objects are achieved by the following inventions (1) to (6).

(1) A sintered body containing boron carbide as a conductive path-forming material and a matrix material containing one or more of oxides of aluminum, magnesium, calcium, strontium, and barium, wherein the Observe the cross section of the sintered body with 300 to 5,000 boron carbide grains present in the field of view, measure the grain size of boron carbide, calculate the grain size distribution of the grains, and select small grains. The grain sizes at which 10%, 50%, and 90% of the boron carbide grains exist in terms of number are respectively (D, ,)B, (
D. )B and (D9°)B, (D +oLs/(D60)B is 0.1 to 1,
(D9°1B/(D,.) A thermistor material comprising a sintered body in which B is 1 to 2.

(2) When the cross section of the sintered body is observed with 100 to 500 boron carbide grains present in one field of view, the ratio of the total area SB of boron carbide grains to the total area SA of the matrix material The coefficient of variation C■ of SB/SA is 10
% or less, the thermistor material according to (1) above.

(3) The thermistor material according to (1) or (2) above, wherein (D, .)B is 0.5 to 5μ.

(4) The thermistor material according to any one of (1) to 3) above, wherein the density of the sintered body is 75% or more of the theoretical density.

(5) A thermistor chip formed by dividing the thermistor material according to any one of (1) to 4) above into a plurality of pieces.

(6) The thermistor chip according to (5) above, wherein the thermistor chip has a resistivity variation coefficient C2 of 2% or less at 25°C.

Effect> In the thermistor material of the present invention, the grain size of boron carbide as a conductive path forming substance is made uniform to a predetermined diameter.

More preferably, boron carbide is uniformly dispersed within the sintered body.

The thermistor material of the present invention having such a configuration has a uniform in-plane resistance value distribution at the microregion level.

More specifically, for example, when using a micro area of about 50×50 as a reference, positional variations in electrical resistance values occurring within the sintered wafer are significantly reduced.

As a result, the sintered body wafer is, for example, 0.75X0.75X
When cutting the thermistor chip into a size of about 0.5 mm, the thermistor chip can be obtained having a constant electric resistance value regardless of the cutting position.

<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 an oxide matrix material.

Boron carbide in the sintered body is represented by the chemical formula B4C, and the stoichiometric composition may be slightly different.

In addition, the grain diameters, , D@o and I)so are defined as follows.

After mirror-finishing the cut surface of the sintered body, it was observed with an electron microscope with 300 to 5,000 boron carbide grains present in the field of view, and the grain size was determined by converting the area of the boron carbide grains into a circle. Calculate (using circle equivalent diameter).

Then, when calculating the grain size distribution of boron carbide, the number of grains is accumulated starting from the smallest particle size, and when there are 10%, 50%, and 90% of the total number of boron carbide grains, The grain size is Dlo
sDso and Dg. shall be.

The grain size (Dso)++ of boron carbide is 0.5 to
It is preferable that the number of units is 5, more preferably 1 to 3μ.

Within the above range, boron carbide grains are more evenly dispersed in the sintered body.

Further, (Dlo)B/(D, o)B is 0.1 to 1, and 0.4 to 0.8 for the shell.

If it is less than the above range, the positional variation in electrical resistance value that occurs within the sintered wafer at the level of a minute area of, for example, 50×50) IJI becomes large.

However, if it is too large, it is difficult to manufacture.

Also, (D oo) a/ (D 50) R is 1 to 2
, generally between 1.2 and 1.5.

If it exceeds the above range, the positional variation in electrical resistance value that occurs within the sintered wafer at the level of a micro area of, for example, 50×50p becomes large.

However, if it is too small, it is difficult to manufacture.

Matrix materials are Aβ, Mg, Ca, Sr and Ba
It is a sintered body of one or more types selected from the group consisting of oxides, and is usually polycrystalline.

By using such an oxide sintered body as the matrix material, it has high stability in the temperature range of 400 to 800°C,
Resistance value can be easily controlled, glass sealing is easy, and chip processability is improved.

Such oxides include aluminum oxide (Anz
oa, in particular a AAz Os ) (and also in addition to or in addition to aluminum oxide, one or more of the oxides of Mg, Ca, Sr and Ba).

Oxides of Mg, Ca, Sr and Ba are usually magnesium oxide (MgO), calcium oxide (Cab), strontium oxide (SrO), barium oxide (Bad).
Contained in the form of

The amounts of Mg, Ca, Sr, and Ba oxides may be appropriately determined within the range of 0 to 100% of the matrix material depending on the desired electrical resistance value.

However, among the above-mentioned oxides, aluminum oxide is particularly preferred in terms of high-temperature stability.

In addition to the above-mentioned oxides, particularly aluminum oxide, the matrix material may contain one or more selected from simple elements of group 4A elements and compounds such as oxides, borides, carbides, and nitrides. preferable.

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 (TiO□) and titanium boride (T i B 2
), titanium carbide (TiC), titanium nitride (Ti
N), zirconium oxide (ZrOt), zirconium boride (ZrBz), zirconium carbide (ZrC), and zirconium nitride (ZrN) are preferred.

Of these, Ti alone, titanium oxide (T
), titanium boride (TiB2), titanium carbide (T
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 grain size D go of the matrix material is usually 0.
The number ranges from 1 to 250 units.

The boron carbide forms a conductive path in the matrix material and exhibits thermistor characteristics.

The conductive path formed from these is stable at high temperatures of 400° C. or higher and has good thermistor characteristics.

It is preferable that boron carbide is uniformly dispersed in the sintered body.

If boron carbide is uniformly dispersed, the effects of the present invention will be further improved.

Quantitative evaluation of dispersibility may be performed, for example, by the following method.

After mirror-finishing the cut surface of the sintered body, 1
Observe with 100 to 500 boron carbide grains present in the field of view, and calculate the total area S of boron carbide grains,
and the total area SA of the matrix material, the ratio SB/SA is determined.

Then, calculate the average value S of SB/SA and the standard deviation 0 of SB/SA, and use the following formula to calculate the coefficient of variation CV of SB/SA.
Find (%).

(Formula) CV=(σ/5)X100 In the present invention, the CV is 10% or less, especially 0. It is preferably 1 to 5%.

Next, as a preferred example, a case where aluminum oxide (cz-Aρ203) is used as the oxide sintered body of the matrix material will be described in more detail. 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-Aρ203) and boron carbide (B4.C) is 5 to 95 wt%, more preferably 5 to 50 wt%, still more preferably 5 to 20 wt%, particularly preferably is 10~
Preferably it is 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 (TiO2),
Titanium boride (T i B 2 ) and titanium carbide (
It is preferable to contain one or more types of T i C).

Elements and compounds of group 4A elements are usually added in the form of elemental elements or oxides (TiO2, Zr0z, Hf02), but some may be changed into borides, carbides, nitrides, etc.

The content of the Group 4A 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 (Z r B 2 ) is preferred, and TiBz is particularly optimal.

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

Their presence can be confirmed using an analytical electron microscope, and their content may be measured by quantitative analysis using X-ray diffraction.

In the above, α-Aβ20 is used as the matrix material.
The preferred composition range when No. 3 is used alone has been described.

When using one or more matrix materials selected from oxides of Mg%Ca, Sr, and Ba in place of α-AρXOS, the theoretical density of the other matrix material is ρ0,
If the theoretical density ρa of α-A2□03, α-AI2゜o3 content is xwt%, and the content of 84G is ywt%, then A=100/(9m x/ρa+y), the matrix material is Axρ . 708 parts by weight may be used for B4C, and Ay parts by weight may be used for B4C. Then, A corresponding to the a-AilzO8 content xwt% and the B4C content ywt%
The composition range determined by ρ×/ρawt% and Aywt% is the preferred content weight range of both components.

In such a case, the theoretical density of each component is, for example, “E
ngineering Properties of
CeramicsDatabook to Guide
e Materials 5election f'o
rStructural Applications
” Battele Memorial Institute
te Columbus Laboratory
s and can be easily calculated from it.

In addition, a A 1220 a is pa=3.98g/c
m", B4C has p = 2, 52 g/cm".

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 into an oxide (boron oxide), and a part of the oxide may be changed into a carbide, a boride, or the like.

However, the content of boron oxide and the complex oxide containing boron oxide is 0 to 1 wt%, especially 0.5 wt% in terms of boron element.
It is preferably 1 to 0.5 wt%. The reason for this is that boron oxide, especially B2O3, becomes glassy, so 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, Ce0z) or carbides are preferred.

Preferably 0.01 to 10 wt of Group 3A elements in elemental terms
%, the electrical resistance value can be easily controlled and positional variations in the electrical resistance value within the sintered wafer can be reduced.

In addition, 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 (Fe203
), 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 Co, Ni, Ru, etc., the amount of oxygen vacancies tends to change at operating temperatures of 500°C or higher, and if the content is large (if the content is large, electrical resistance will deteriorate over time. Although the inclusion of elemental metals, oxides, carbides, etc. of Group 8 elements other than iron is not excluded, it is preferably 1 wt% or less, particularly O to 0.5 wt%, in terms of element.

The above-mentioned effects of group 3A elements and Fe are similar to those of oxides of AJ2, Mg, Ca, Sr, and Ba, as well as 4
This can also be achieved with oxides of group A elements. As described above, the preferred content of these components is all or part of the matrix material, and is preferably 0.01 wt% or more in terms of element.

Furthermore, these elements, preferably Mg.

One or more of Ca, Sr%Ba, Ti, and Zr may be a single element or a carbide, etc., and preferably at a content of 0.01 to 10 wt% in terms of element, it increases the resistance value. Control becomes easier and variations become smaller.

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

First, although the inclusion of Group 5A and Group 6A 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, when the glass is sealed, these particles tend to diffuse into the glass, which tends to cause characteristic deterioration.

The content of the Group IA element is preferably 0 to 1 wt%, particularly O to O,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 tend to change over time.

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

Furthermore, since group IB elements and group 2B elements are also susceptible to changes over time, they are 0 to 1 wt% in terms of element, especially O to 0.05 wt%.
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 C10 and N
Since group B elements and the like are unfavorable in terms of characteristics, the content is preferably 0 to 1 wt%.

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

Further, the grain particle size I)so of the subcomponent is usually about 1 to 5 μm in the case of an elemental metal, and usually about 0.1 to 5 μm in the case of a compound.

Note that since the content of the subcomponents is very small, there is no particular restriction on the grain size distribution of the subcomponents.

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

Such a sintered body can be obtained as follows.

Predetermined amounts of powder of a matrix material such as aluminum oxide and 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.

The raw material powder of the above-mentioned oxide such as aluminum oxide (AI220.) is generally preferably one having a D5 of 0.1 to 5 and a relatively sharp particle size distribution.

The particle size may be measured by electron microscopy in the same manner as the grain size described above. Then, from the measured area converted into yen, D lo and D so% are calculated in the same way as above.
Find D9° for each.

In addition to the oxide, the raw material for the 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).

Generally, boron carbide (B, C) powder has I) so of 0.
, 5-101m, D to/D so is 0.
3-1, D9o/DIIo is 1-1.5,
Use one with a purity of 97 wt% or higher.

By using such a starting material, boron carbide is uniformly dispersed, and in addition, the grain size of the boron carbide is also made uniform.

Elements or compounds of group 4A elements may be added, for example, as T i O2 powder, and generally D s
It is sufficient to use a material having o of 0.1 to 5- and a purity of 98 wt% or more.

The boride of Group 4A element may be added, for example, as T i B 2 powder, and generally has a Dso of 0. 1~5pm
Therefore, a material with 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, etc., as described above.

At this time, by controlling the sintering conditions as described below, for example, B4C and T i 02 react, and for example, T
i B t generates.

In such a case, for example, Aρ203 is mixed with 84C of the conductive path forming material as a matrix material, and 4A is added to this.
When T i O2 is added as a group element source and fired, 9 (Aβ20g) is generated simultaneously with the production of T i B z.
2 (B, O), B+iCz, TiC%Tia
A12, Ti may be formed as a by-product.

These by-products may be contained in an amount of about 10 wt% or less, particularly about 1 wt% 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.

As the dispersant, a surfactant is preferable, and by adding a surfactant, the dispersibility of boron carbide is further improved.

In addition, when wet mixing the above-mentioned raw materials in a ball mill, the mixing time is preferably about 5 to 15 hours.

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

The pressure during pressure molding is 500 to 2000 7 cm.
That's about it.

The non-oxidizing atmosphere during sintering may be various atmospheres such as inert gases such as N2, Ar, and He, H, Co, various hydrocarbons, mixed atmospheres thereof, and even vacuum.

In the case of pressureless sintering method, atmospheric pressure is sufficient, and the sintering temperature is 1400℃.
-1900°C1, particularly 1600-1900°C, more preferably 1750-1800°C.

If the temperature is lower than 1400°C, it will not be sufficiently densified even if sintered for a long time, and if the temperature is higher than 1900°C, A
The interaction between oxides such as 2203 and B10 becomes intense.

Sintering time is usually 0.5 to 20 hours.

For HP sintering method, press pressure is 150-250 kg
/cm2, 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 1800C, the interaction between the matrix material such as A I2t Os 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
°C, sintering time is 1-50 hours, pressure is l OOO-15
00 kg/cm2, and may be carried out in an oxygen atmosphere or an inert atmosphere such as Ar.

In this case, oxygen gas, Ar gas, etc. are heated at 30 C) to
Pressure is increased to 400 kg/cm2, and then pressure is applied by heating as described above.

The above sintering conditions are common to both 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 occasionally generate borides of Group 4A elements, the following profile may be used.

In the cold sintering method, Temperature increase rate 1-100°C/min, 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 to 100°C/min.

Sintering temperature 1400-1800℃, Holding time at sintering temperature 1-30 hours shall be.

Furthermore, in the HIP method, Temperature increase rate: 1 to 100°C/min.

Pre-sintering temperature 1400-1650℃, holding time at pre-sintering temperature 1-50 hours, sintering temperature 12
The holding time at the sintering temperature is 1 to 50 hours.

In this way, especially by increasing the holding time at the sintering temperature, 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, resulting in the chipping. Improves workability.

The thermistor material produced in this way has a resistivity ρ of 50
It is about 102 to 107 Ωcm at 0℃, and 50
There is almost no positional variation in resistivity at the micro-area level of about X50)+n+.

More specifically, the sintered body wafer is 0.75XO175X
When formed into a chip with a size of about 0.5 mm, the coefficient of variation C■ of the resistivity ρ at 25° C. of the thermistor chip is 2% or less, particularly 0.1 to 1%.

In addition, there is almost no change in resistance value even when used or stored in a temperature range of 400 to 800°C. Further, the value of the thermistor constant B is also 1000 to 5000 at 25 to 500°C.

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 chipped into a predetermined size and applied to a thermistor element as the thermistor chip of the present invention.

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 is no particular limit to the dimensions of the thermistor chip, but it is usually 0.5 to 1. Omm, width 0.5-1, Omm, thickness 0.
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.

0 of Example 1 and the following starting materials were weighed in the proportions shown in Table 1, surfactant Tsurpone S-85 (manufactured by Toho Chemical Industry Co., Ltd.) was added as a dispersant, and the mixture was mixed in a ball mill using acetone. Mixing was carried out for 10 hours.

In addition, starting materials D+o, Ds. Andri,. are values measured by electron microscopy observation.

・AA□03 (Purity 99.9wt% or more) Dio: 3
Press, ・B4C (purity 98 wt% or more) B6C: 2) zm, Dlo/Dao: o, 7 D,, /D,. : 1. 2.TiO□ (purity 99 wt% or more) Dso: 1 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/cm2.

The sintering conditions were a sintering temperature of about 1680° C. and a holding time of about 2 hours. And after cooling, 50X50X0.5m
A sintered body of m was obtained.

In addition, a comparative sample was prepared in the same manner except that B4C was replaced with the one shown below and the mixing time was changed to 20 hours.

・B4C (purity 98wt% or more) D,,: 2μ, D+o/D50: o, 2D, o/D60: 3 As a result of X-ray diffraction of each obtained sintered body, 8ρ208 and 84G were present. It was confirmed that

In addition, each sample has the composition shown in Table 1, No. 3
．． 4, at the same time as the production of T i B 2, a small amount of Ti
C, Ti, Ti3Aρ, B , 3C2, 9 (Aj22
By-products such as 0-)2 (B20i) were observed.

Next, after mirror-finishing the cut surface of each sample, scanning electron microscopy (SEM) observation was performed to determine the grain size of B and C grains in the sintered body (D5°)ll, (D,.)B/ (D,,)
, (D9o)B/(D6o)B and B4C grains were evaluated.

FIG. 2 is a scanning electron microscope (SEM) photograph of sample No. 4 at a magnification of 1500 times, and the grains that appear black are B4C grains.

The B4C grains (DIO), (Dso), and (Deo)s each contain 1000 B4C grains in the field of view.
It was measured and calculated by SEM observation in the presence of 4C grains.

Moreover, the dispersibility of B4C was evaluated as follows.

By SEM observation, the ratio SIl/SA of the total area S6 of B4C grains and the total area SA of Aρ203 is determined in a state where 200 B and C grains are present.

Then, the process was repeated 50 times at random, and the coefficient of variation CV (%) of SB/SA was calculated.

The results are shown in Table 1.

Both sides of the obtained composite sintered body are electroless plated to a thickness of 3.
．． A 5 μm N1-B electrode layer was formed and a wafer was prepared.

The obtained wafer was sliced with a diamond blade using a peripheral slicing machine of 0.75 x 0.75 x 0.5 on each side.
The thermistor chip was obtained by cutting into a square of mm.

Such a thermistor chip has a diameter of 0.3 mm and a length of 6
A 5 mm Kovar lead wire was connected by parallel gap welding.

Then, the thermistor constant B at 25 to 500°C was measured, and the average value was determined.

In addition, the average value ρ of resistivity at No. 25 and the coefficient of variation CV (%) of resistivity ρ were determined.

The results are shown in Table 2.

The thus obtained product was inserted into a borosilicate glass having a diameter of 2.5 mm and a length of 4 mm, and the glass was sealed at 850° C. in an Ar gas atmosphere. This was subjected to aging treatment to produce various thermistor element samples as shown in FIG.

For these, initial and 5000 at 500°C
The change in resistance value after time storage was measured.

The evaluation was calculated as (ΔR/Ro)X100 (%), where Ro is the initial resistance value of ΔR1 when the resistance value changes.

The results are shown in Table 2.

Table 2 Sample Sample B ρ CVNO, No
, (K) (Ω・Cm) (%) Resistance value change (%) l (comparison) 1 2050 3. lX10
' 12.02 (present invention) 2 2050
3.1xlO' 1.53 (comparison) 3 2
050 3. lXl0' 3.54 (invention)
4 2050 3.1 Mowing 0' 0.8 The effects of the present invention are clear from these results.

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

Further, as a matrix material, Ar1.0. Instead, or in addition to 8β203, samples containing other oxides were prepared and the same measurements as in Example 1 were performed, and the same results were obtained.

<Effects of the Invention> The thermistor material of the present invention has, for example, 50×50 tffl
The positional variation in the electrical resistance value is extremely small based on a micro area of about 1.

Furthermore, it is stable 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 we examine the relationship between composition ratio and resistivity, we find that the change in resistivity is not steep (but resistance can be controlled by changing the composition ratio. Therefore, the composition range of the target resistance range is widened. , 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 joining and bonding other materials by heating under pressure, the dimensional accuracy will be good, and dimensional changes will not occur like when raw materials are integrated by sintering. and variations in characteristics are extremely reduced.

[Brief explanation of drawings]

FIG. 1 is a sectional view showing an example of the thermistor element of the present invention. FIG. 2 is a photograph substituted for a drawing showing the grain structure, and is a scanning electron micrograph showing boron carbide grains in the thermistor material of the present invention. Explanation of symbols 1...Thermistor element 5...Glass 11...Thermistor depth 33.35...Electrode layer 43.45...Lead body

Claims (6)

[Claims] (1) A sintered body containing boron carbide as a conductive path-forming material and a matrix material containing one or more of oxides of aluminum, magnesium, calcium, strontium, and barium, wherein the Observe the cross section of the sintered body with 300 to 5,000 boron carbide grains present in the field of view, measure the grain size of boron carbide, calculate the grain size distribution of the grains, and select small grains. The grain sizes at which 10%, 50%, and 90% of the boron carbide grains exist, respectively, are (D_1_0)_B, (D_5_0)_B, and (D_
When 9_0)_B, (D_1_0)_B/(D_5_0)_B is 0.1 to 1
and (D_9_0)_B/(D_5_0)_B is 1
A thermistor material characterized in that it is composed of a sintered body having the following properties. (2) When the cross section of the sintered body is observed with 100 to 500 boron carbide grains present in one field of view, the ratio of the total area S_B of boron carbide grains to the total area S_A of the matrix material Coefficient of variation C of S_B/S_A
The thermistor material according to claim 1, wherein V is 10% or less. (3) The thermistor material according to claim 1 or 2, wherein (D_5_0)_B is 0.5 to 5 μm. (4) The thermistor material according to any one of claims 1 to 3, wherein the density of the sintered body is 75% or more of the theoretical density. (5) A thermistor chip formed by dividing the thermistor material according to any one of claims 1 to 4 into a plurality of parts. (6) The thermistor chip according to claim 5, wherein the thermistor chip has a resistivity variation coefficient CV of 2% or less at 25°C.