JPH08162302A - Thermistor and its manufacture - Google Patents

Abstract

PURPOSE: To provide an excellent thermistor wherein the change of resistance value with the passage of time is small. CONSTITUTION: An element substance 1 for a thermistor is formed by adding 0.01-10 atomic % of an oxide of Zr, to 100 atomic % of a mixture of one, or at least two kinds out of oxides of Mn, Ni, Co, Cr, Fe, and Al, and electrodes 2a, 2b are formed on this thermistor element substance.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermistor used for a glass-enclosed thermistor and a method for manufacturing the thermistor.

[0002]

2. Description of the Related Art Conventionally, NTC thermistors have a thermistor element body of manganese-nickel type, manganese-nickel-type.
The electrodes were formed on this thermistor element body by using an oxide such as cobalt type.

[0003]

SUMMARY OF THE INVENTION In the above conventional configuration,
There has been a problem that the resistance value changes greatly with time due to a change in the crystal structure of the thermistor element under high temperature use. The present invention solves the above problems,
An object of the present invention is to provide a thermistor having stable characteristics with a small change in resistance value over time when used at high temperatures.

[0004]

In order to achieve this object, the thermistor of the present invention has a thermistor body of Mn, N.
The oxides of Zr are added in an amount of 0.01 atom% or more and less than 10 atom% with respect to 100 atom% of a mixture of one or two or more oxides of i, Co, Cr, Fe and Al. It is formed by using it, and an electrode is formed on it.

[0005]

According to the above structure, Zr has a valence of 4, so that Zr does not form a solid solution in the spinel phase or the NaCl phase but precipitates alone. Therefore, tetragonal-cubic transformation in the spinel single-phase region,
Spinel phase in mixed crystal region of spinel and NaCl phase-
It is possible to suppress the phase transformation of the NaCl phase, reduce the change with time of the resistance value under high temperature use, and improve the strength of the element body.

[0006]

【Example】

(Embodiment 1) Hereinafter, a first embodiment of the present invention will be described.

Compositions having metal atom compositions (Table 1), (Table 2) and (Table 3) after sintering oxides of manganese oxide, nickel oxide, cobalt oxide, chromium oxide, aluminum oxide, iron oxide and zirconium The ingredients were blended in a ratio and wet-mixed in a ball mill for 16 hours.

[0008]

[Table 1]

[0009]

[Table 2]

[0010]

[Table 3]

Then, it was dehydrated and dried at 100 ° C. to 200 ° C., and powdered using a mortar and pestle. Next, this powder is calcined at 600 ° C. to 1000 ° C. for 2 hours, and the calcined product is wet pulverized in a ball mill for 20 hours, and then 100 ° C. to 200 ° C.
Dehydrated and dried in pure water and polyvinyl alcohol (PV
8% by weight of A) is added as a binder, granulated into granules with a mortar and pestle, and the required amount is sampled, for example, a diameter of 30
mm, heat of 15 mm, block pressure 1t / cm ²
Then, pressure molding was performed to obtain a molded product. 1000 ° C in air
Sintered at a temperature of ~ 1450 ° C for 2 hours. After firing, this block was sliced into 500 μm thick wafers,
Heat treatment was performed at a temperature of 00 ° C. or higher to remove strain. Next, screen print Pt paste on both sides of this wafer,
An electrode was formed by baking at 0 ° C. After baking the electrodes,
The wafer was cut into, for example, 700 μm squares to obtain a thermistor element body 1 having electrodes 2a and 2b formed on both surfaces as shown in FIG.

Next, the electrodes 2a and 2b of the thermistor body 1
The lead wires 4a and 4b such as Dumet wires were bonded on the top with the heat resistant conductive paints 3a and 3b, and then baked at 700 to 900 ° C. The thermistor element body 1 with the lead wires 4a and 4b was housed in a lead silicate glass tube and sealed with a glass coating 5 in a tunnel furnace to obtain a glass-sealed NTC thermistor (hereinafter referred to as a thermistor element).

Each of the thermistor elements thus completed was subjected to a DC 4-terminal method to obtain a resistance value (R25) of 8 at 25.degree.
The resistance value (R85) at 5 ° C. is measured, and using (Equation 3),
The specific resistance (ρ25) at 25 ° C. and the B constant (B25 / 85) between 25 ° C. and 85 ° C. were calculated using (Equation 4).

[0014]

(Equation 3)

[0015]

[Equation 4]

The rate of change in resistance is the resistance value (R
25A) was left for 3000 hours in a high temperature bath maintained at 300 ° C., and then the resistance value (R25
B) was measured again at 25 ° C. The rate of change in resistance value before and after leaving was determined by (Equation 5).

[0017]

(Equation 5)

In (Table 1), (Table 2) and (Table 3),
The * marks are outside the scope of the present invention.

As can be seen from the table, the composition shown in the claims of the present invention has a resistance change rate of ± 5%.
Within the range, the rate of change in resistance is large in all cases outside the scope of claims of the present invention.

(Second Embodiment) The second embodiment of the present invention will be described below.

Manganese oxide, nickel oxide, cobalt oxide, chromium oxide, aluminum oxide, iron oxide, and zirconium hydroxide were mixed so that the composition of metal atoms after sintering would be the composition ratio of (Table 4). A thermistor element was prepared in the same manner as in the example.

[0022]

[Table 4]

First, after wet mixing for 16 hours in a ball mill, it was dehydrated and dried at 100 ° C. to 200 ° C., and powdered using a mortar and pestle. Next, this powder is heated to 600 ° C to 1000 ° C.
Calcined for 2 hours, wet pulverize the calcined product for 20 hours in a ball mill, dehydrate and dry at 100 ° C to 200 ° C, add 8 wt% of pure water and polyvinyl alcohol (PVA) as a binder, and use a mortar and pestle. After granulating into granules, a required amount was sampled and pressure-molded into a block mold having a diameter of 30 mm and a thickness of 15 mm at a molding pressure of 1 t / cm ² to obtain a molded product. 2 in air at a temperature of 1000 ° C to 1450 ° C
Sintered for hours. After firing, this block is 500μ thick
The wafer was sliced into a wafer of m and heat-treated at 1000 ° C. or higher to remove strain. Next, Pt paste was screen-printed on both surfaces of this wafer and baked at 980 ° C. to form electrodes. After electrode baking, the wafer is, for example, 700 μm
The thermistor element body 1 having electrodes 2a and 2b formed on both surfaces as shown in FIG.

Next, the electrodes 2a and 2b of the thermistor body 1
The lead wires 4a and 4b such as dumet wires were joined together with the heat-resistant conductive coatings 3a and 3b, and then baked at 700 to 900 ° C. This thermistor element with lead wire was placed in a lead borosilicate glass tube and sealed with a glass coating 5 in a tunnel furnace to obtain a glass-sealed NTC thermistor (hereinafter referred to as a thermistor element).

Each of the thermistor elements thus completed was subjected to a DC 4-terminal method to obtain a resistance value (R25) of 8 at 25.degree.
The resistance value (R85) at 5 ° C. is measured, and using (Equation 3),
The specific resistance (ρ25) at 25 ° C is calculated using (Equation 4) as 25
The coefficient of variation of the resistance value at 25 ° C. was calculated using the B constant (B25 / 85) between ° C and 85 ° C and (Equation 6).

[0026]

(Equation 6)

The results are shown in (Table 4). For comparison, the result of using zirconium oxide instead of zirconium hydroxide as a starting material for zirconia is shown in (Table 5).

[0028]

[Table 5]

The samples marked with * in (Table 4) and (Table 5) are outside the scope of the claims of the present invention. As can be seen from the table, if the thermistor element body 1 has the same composition, zirconium hydroxide used as a zirconia raw material has a smaller coefficient of variation than zirconium oxide.

Further, in the sample of the thermistor body 1 having a composition outside the scope of the claims of the present invention, even if zirconium hydroxide is used as the raw material, the coefficient of variation of the resistance value is as large as 3% or more, and zirconium oxide is not contained. There was no difference from the one used.

This is because zirconium hydroxide has higher activation than zirconium oxide, and therefore the use of zirconium hydroxide as the raw material of the thermistor body 1 promotes the reactivity and thermistor body. This is because 1 is homogenized.

(Embodiment 3) The third embodiment of the present invention will be described below.

The thermistor body 1 (Table 6), (Table 7),
The thermistor having the composition shown in (Table 8) has lead wires 4a and 4b.
After bonding with the heat-resistant conductive coatings 3a and 3b, a sample sealed with the glass film 5 is prepared, and the resistance value at 25 ° C (R25) and the resistance value at 85 ° C (R85) are measured by using the DC 4-terminal method. Then, using (Equation 3), the specific resistance at 25 ° C (ρ25)
By using (Equation 4), the B constant (B2
5/85) was calculated.

[0034]

[Table 6]

[0035]

[Table 7]

[0036]

[Table 8]

Then, after aging the thermistor element under actual use conditions (voltage 12 V, current 130 mA) for 100 hours, the sample was allowed to stand in a high temperature bath maintained at 300 ° C. for 3000 hours, and then the resistance value (R25B) of the sample was 25 ° C. Was measured again. The rate of change in resistance value before and after leaving was determined by (Equation 5).

The results are shown in (Table 6), (Table 7) and (Table 8). From (Table 1) to (Table 6), the samples obtained by aging the thermistor of the present invention under actual use conditions have a low rate of change in resistance with time of 5% or less. If the thermistor body 1 has the same composition, the sample that has been aged has a smaller change with time in the resistance value than the sample that has not been aged.

Further, the sample of the thermistor element 1 having a composition outside the scope of the claims of the present invention shows a large change in resistance value with time of ± 5% or more even if it is aged under actual use conditions, and there is no aging. It was no different from the one.

This is because, by aging the thermistor at an actual operating temperature, the crystal structure, the pore concentration, and the mobility are in an equilibrium state at that temperature, and the rate of change in resistance, which is a change over time, becomes small.

(Fourth Embodiment) The fourth embodiment of the present invention will be described below.

FIG. 1 shows the structure of a thermistor applied to the embodiment of the present invention. Electrodes 2 on both sides of thermistor body 1
a and 2b are formed. The electrodes 2a and 2b are P
The thermistor element body 1 is an electrode paste containing a metal frit such as t, Ag and Ag-Pd and a glass frit in a predetermined ratio.
It is formed by coating and baking on top.

The electrodes 2a and 2b thus formed are
Lead wire 4 made of heat resistant conductive paint 3a, 3b such as Au
a and 4b are connected. The thermistor element with the lead wires 4a and 4b thus formed is passed through a glass tube and then heat-welded to 800 to 1000 ° C. to form a glass coating 5.

A thermistor element having such a structure was prepared according to the present invention with the constitutions shown in (Table 9) and (Table 10), and the resistance value at 25 ° C. was measured.

[0045]

[Table 9]

[0046]

[Table 10]

Then, for these, a high temperature storage test,
And a heat cycle test was performed, and the resistance value (R2
5B) was measured again at 25 ° C., and the rate of change in resistance value before and after the test was determined by (Equation 5).

In the high temperature storage test, the measurement was performed after standing at 300 ° C. for 3000 hours.

The heat cycle test was conducted at 300 ° C. for 30 hours.
The measurement was carried out after 1000 cycles, with one cycle of immediately cooling at room temperature for 10 minutes after leaving for 1 minute.

The results are shown in (Table 9) and (Table 10).
As is clear from (Table 9) and (Table 10), the thermistor element having the constitution of the present invention has a low resistance change rate of 5% or less in the high temperature storage test and a resistance change rate of 3 after the heat cycle test. It can be seen that it has low heat resistance and high temperature stability. The thermistor element having a constitution outside the scope of the claims of the present invention shows a change in resistance value which is damaged during the high temperature storage test and the heat cycle test and cannot be used.

[0051]

As described above, in the thermistor of the present invention, the thermistor element body is composed of Mn, Ni, Co, Cr, Fe and Al.
One or a mixture of two or more of the above oxides 1
It is formed by adding 0.01 atomic% or more and less than 10 atomic% of Zr oxide to 00 atomic%.

As a result, since Zr has a tetravalent value, it does not form a solid solution in the spinel phase or the NaCl phase but precipitates alone.

Therefore, the tetragonal-cubic transformation in the spinel single-phase region and the spinel-NaCl phase transformation in the mixed crystal region of the spinel and the NaCl phase are excluded, and the change with time of the resistance value under high temperature use is eliminated. Can be made smaller.

Then, by aging the thermistor at an actual operating temperature, the crystal structure, the pore concentration, and the mobility are in an equilibrium state at that temperature, and the change in resistance with time can be further reduced.

Further, as shown in the examples, the coefficient of thermal expansion of the thermistor element body, the coefficient of thermal expansion of the lead wire, and the coefficient of thermal expansion of glass are expressed by the relational expressions of (Equation 7) and (Equation 8). By using the thermistor for a glass-filled thermistor, it is possible to reliably prevent the resistance value defect and the open defect of the thermistor.

[0056]

(Equation 7)

[0057]

(Equation 8)

[Brief description of drawings]

FIG. 1 is a sectional view of a thermistor according to an embodiment of the present invention.

[Explanation of symbols]

 1 thermistor body 2a electrode 2b electrode 4a lead wire 4b lead wire 5 glass coating

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Masahiko Miyama 1006 Kadoma, Kadoma City, Osaka Prefecture Matsushita Electric Industrial Co., Ltd.

Claims (4)

[Claims] 1. A thermistor body and an electrode provided on the thermistor body, wherein the thermistor body is Mn,
One of the oxides of Ni, Co, Cr, Fe, and Al or a mixture of two or more of them is 100 atom% and Zr is
A thermistor formed by adding 0.01 to 10 atomic% of the above oxide. 2. A thermistor body, an electrode provided on the surface of the thermistor body, a lead wire connected and fixed to the electrode, and a glass that covers the thermistor body and a part of the lead wire. A thermistor in which the relationship between the coefficient of thermal expansion αs of the thermistor body, the coefficient of thermal expansion αr of the lead wire, and the coefficient of thermal expansion αg of the glass is represented by (Equation 1) and (Equation 2). [Equation 1] [Equation 2] 3. A mixture of one or more of Mn, Ni, Co, Cr, Fe and Al oxides 10
0.01 atom% of zirconium hydroxide to 0 atom%
As described above, a method of manufacturing a thermistor in which less than 10 atomic% is added to form a thermistor body, and then an electrode is formed on the thermistor body. 4. A mixture of Mn, Ni, Co, Cr, Fe and Al oxides, or a mixture of two or more thereof.
0.01 atom% or more of Zr oxide with respect to 0 atom%,
A method for producing a thermistor, in which less than 10 atomic% is added to form a thermistor element body, and then an electrode is formed on the thermistor element body, and then aging is performed at an actual use temperature.