JP3218906B2 - Thermistor element - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a thermistor element,
In particular, it relates to an improvement of a thermistor element for a temperature sensor using a thermistor.

[0002]

2. Description of the Related Art Conventionally, as a thermistor element for a temperature sensor, there is a thermistor element formed by forming an electrode on an end face of a negative characteristic thermistor element made of a sintered body containing a transition metal oxide as a main component. As a method of forming an electrode of the thermistor element, it is common to apply a paste-like electrode forming material to a thermistor body by screen printing or the like and bake it at an appropriate temperature. The electrode forming material was MnNi.
Or the MnNiCo-based thermistor element or the like, and depending on the purpose of the thermistor element, is generally used depending on the purpose, the metal powder having an electrode function, in order to enhance the bonding with the thermistor element An electrode paste in which an organic vehicle for forming a paste into an inorganic substance to which a bismuth compound such as glass frit or bismuth oxide is added is used.

[0003]

SUMMARY OF THE INVENTION A thermistor element in which an electrode is formed using a conventional electrode forming material, in particular, MnCo
In the case of using a thermistor element composed of an Fe-based material, the adhesive strength of the electrode to the element element is not sufficient, and when used for a long time in a high-temperature atmosphere, the rate of change of the resistance value with time is large. However, there is a problem that reliability is low.

The present invention solves the above-mentioned conventional problems, has a high adhesive strength of the electrode to the element body, has a small rate of change in resistance with time even when used in a high-temperature atmosphere for a long time, and has a high reliability. It is intended to provide a thermistor element having a high value.

[0005]

The thermistor element of the present invention comprises a negative characteristic thermistor element made of a sintered body containing a transition metal oxide as a main component and containing Ag, Au or Pt as a main component.
Thermistor element formed by forming a noble metal electrode
The electrode forming material contains copper and / or a copper compound, and the content of copper and / or the copper compound is 20% by weight or less of the inorganic content in the electrode forming material.

[0006] The thermistor element 請 Motomeko 2, in the thermistor element <br/> claim 1, the thermistor element is, M
It is characterized by being made of a sintered body mainly composed of oxides of n, Co and Fe.

Hereinafter, the present invention will be described in detail.

In the present invention, when a copper compound is contained in the electrode forming material, CuO,
Cu ₂ O, may be used a powder of copper oxide or copper carbonate, such as _{CuO · Fe 2 O3, Cu 2} Al 2 O 4.
When copper is contained, Cu powder or an alloy of copper and a noble metal, for example, Ag / Cu powder can be used.

[0009] The electrode forming material according to the present invention is obtained by sintering copper and / or a copper compound in air, Ag, Au or Pt.
Can be easily prepared by mixing a noble metal powder containing as a main component with a glass frit for obtaining bonding strength and further adding an organic vehicle to form a paste.

In this case, if the proportion of copper and / or copper compound is too small, the improvement effect of the present invention obtained by blending the copper component cannot be sufficiently obtained. When the content of exceeds 20% by weight,
Oxide due to copper is exposed on the electrode surface, and solderability to the electrode is reduced. For this reason, copper and / or a copper compound is preferably 20% by weight or less of the inorganic content of the electrode forming material.
Mashiku is 1 to 10 wt%, content of 20 wt% in the resulting electrode or less, preferably you blended so that 1 to 10 wt%.

It is preferable that, of the inorganic components in the electrode forming material, the content of a noble metal such as Ag is 60 to 95% by weight, and the content of the glass frit is 1 to 15% by weight.

On the other hand, in the thermistor element of the present invention,
As a transition metal oxide of a sintered body mainly composed of a transition metal oxide constituting a thermistor body, Mn, C
O and Fe oxides are represented by Mn: Co: Fe = 0 to 60:
Those containing at a ratio of 0 to 70: 0 to 70 (atomic mol%) are employed.

The thermistor element of the present invention is obtained by applying an electrode forming material having the above-mentioned composition to an end surface of a MnCoFe-based thermistor body by screen printing or the like, and then applying the same in air to 700 m.
It is easily manufactured by baking at a temperature of about 800 ° C. for about 5 to 10 minutes to form an electrode.

The obtained thermistor element has a high electrode bonding strength and a small rate of change in resistance over time even in a long-time use in a high-temperature atmosphere. Is extremely useful.

[0015]

The copper and the copper compound can easily form a transition metal oxide constituting the thermistor body, particularly a compound (spinel type) with elements such as Mn, Co, and Fe.
It is easy to alloy with noble metal elements, especially Ag, Au and the like. For this reason, by adopting the configuration of the present invention, the copper component contained in the electrode is ubiquitous in the vicinity of the interface between the electrode and the thermistor element, thereby increasing the electrode adhesion strength by chemical bonding and increasing the temperature in a high-temperature atmosphere. Therefore, even when the device is used for a long time, the rate of change of the resistance value with time can be reduced to enhance the reliability.

Particularly, in the present invention, when copper or a copper alloy is used as the copper component, an alloy effect with the noble metal is easily obtained, and the composite oxide is oxidized by baking in the air to form a composite oxide near the interface with the thermistor body. The effect of forming an object and enhancing the effect of bonding with the electrode can be obtained.

Further, when a copper compound is used as the copper component, a composite oxide is easily formed stably near the interface with the thermistor body, the chemical bonding strength is large, and the bonding strength varies. Is obtained.

[0018]

The present invention will be described more specifically with reference to the following examples.

Example 1 First, commercially available metal oxides of Mn, Co, and Fe were converted to Mn:
Co: Fe = 10: 50: 40 (atomic%) was blended so as to have a composition ratio, and the mixture was wet-mixed with a ball mill, and then the slurry was dried. Thereafter, the powder was calcined at a temperature of 900 ° C., and the calcined powder was again wet-pulverized by a ball mill, and then the slurry was dried. Next, polyvinyl alcohol was added and mixed as a binder, a required amount was fractionated, and a block-shaped pressure-formed product was fired at 1200 ° C. for 5 hours.
After slicing a 0.25 mm thick wafer from this block and forming electrodes on it, 0.7 mm x 0.7 mm
And cut into chips.

The electrode forming material includes a glass frit in an Ag paste obtained by mixing an Ag powder and an organic vehicle, and an electrode paste.
The CuO content relative to the inorganic content in the forming material was 1% (No. 1), 2% (No. 2), and 5% (No.
3) The one to which CuO powder was added so as to be 10% (No. 4) was used. Also, for comparison, a sample containing no CuO powder (No. 5) or Bi ₂ instead of CuO was used.
O ₃ 1% by weight percent (No. 6), 5% (No. 7) was used containing. Note that lead borosilicate glass was used for the glass frit, and the content was 8% by weight.

Each of these electrode forming materials was applied to the above chips and dried, and then baked at a temperature of 720 ° C. for 10 minutes to form electrodes.

A lead wire was bonded to each of the thermistor elements thus manufactured by soldering, and the bonding strength of the electrode to the thermistor element was measured by a tensile strength test. The results are shown in FIG.

From the results shown in FIG. 1, it can be seen that the thermistor element of the present invention containing a copper compound in the electrode has a bonding strength almost twice as high as that of a conventional element containing bismuth or a bismuth compound.

Further, a lead wire was bonded to the same element by soldering, and a resin mold was applied thereon, thereby producing a temperature sensor element. When these were left in a high-temperature atmosphere of 100 ° C., the rate of change in resistance over time was examined. The results are shown in FIGS.

2 to 8, it can be seen that the device of the present invention has a smaller rate of change with time in resistance value when left in a high-temperature atmosphere and is more excellent in reliability than the conventional device. In particular, when CuO was added in an amount of 5% by weight, a very good result was obtained, in which the rate of change of the resistance value with time was 1/20 or less as compared with the conventional one. Note that each of these elements exhibited electrical characteristics such as the resistivity and the B constant inherent to the thermistor material.

Further, in a device manufactured using an electrode forming material containing 2% by weight of CuO with respect to the inorganic content , an energy dispersive X-ray analyzer is used for a cross section near the interface between the element body and the electrode. FIG. 9 shows the results of elemental analysis performed using. This elemental analysis measures the percentage by weight of a specific element contained in a certain region. From FIG. 9, the copper component in the electrode is:
It can be seen that it is ubiquitous near the interface between the electrode and the element.

Example 2 A thermistor element was prepared and obtained in the same manner as in Example 1, except that a material containing Cu powder in the ratio shown in Table 1 was used instead of CuO as an electrode forming material. The adhesive strength of the electrodes of the thermistor element and the rate of change of the resistance value when left in an atmosphere at a high temperature of 100 ° C. for 1000 hours were examined. The results are shown in Table 1. Table 1 also shows the results for the case where no Cu was added (No. 5 of Example 1).

[0028]

[Table 1]

Example 3 In Example 1, CuO and further Cu were used as electrode materials.
Was prepared in the same manner except that the element containing the thermistor at the ratio shown in Table 2 was used, and the adhesive strength of the electrode of the obtained thermistor element and the case where the electrode was left for 1000 hours in a high-temperature atmosphere of 100 ° C. The rate of change of the resistance value was examined, and the results are shown in Table 2. Table 2 also shows the results for the case where no Cu was added (No. 5 of Example 1).

[0030]

[Table 2]

From Tables 1 and 2, it can be seen that, by mixing Cu or Cu and CuO into the electrode forming material, the adhesive strength of the electrode to the element body was increased, and the resistance value of the electrode when used in a high-temperature atmosphere was measured over time. It is clear that the rate of change can be reduced.

[0032]

As described above in detail, according to the thermistor element of the present invention, the adhesive strength of the electrode to the element body is high, and even when the electrode is used in a high-temperature atmosphere for a long time, the rate of change of the resistance value with time. And a highly reliable thermistor element is provided.

In particular, according to the thermistor element of the second aspect, a thermistor element having higher characteristics is provided.

[Brief description of the drawings]

FIG. 1 is a graph showing the relationship between the CuO or Bi ₂ O ₃ content and the adhesive strength of an electrode in Example 1.

FIG. 2 is a graph showing the rate of change in resistance over time when the CuO content is 1%.

FIG. 3 is a graph showing the rate of change of resistance with time when the CuO content is 2%.

FIG. 4 is a graph showing the rate of change with time of the resistance value when the CuO content is 5%.

FIG. 5 is a graph showing a change rate of a resistance value with time when the CuO content is 10%.

FIG. 6 is a graph showing the rate of change of resistance with time when CuO and Bi ₂ O _{3 are not} contained.

FIG. 7 is a graph showing a change rate of a resistance value with time when a Bi ₂ O ₃ content is 1%.

FIG. 8 is a graph showing a time-dependent change in resistance value when the Bi ₂ O ₃ content is 5%.

FIG. 9 is a graph showing a result of performing elemental analysis on a cross section near an interface between an element body and an electrode using an energy dispersive X-ray analyzer in Example 1.

Continuation of the front page (72) Inventor Hiroaki Nakajima 2270 Yokoze, Yokoze-cho, Chichibu-gun, Saitama Mitsubishi Materials Electronic Technology Laboratory (56) References JP-A-2-143502 (JP, A) JP-A-4 -334001 (JP, A) JP-A-57-180112 (JP, A) (58) Fields investigated (Int. Cl. ⁷ , DB name) H01C ^7/ 02-7/22

Claims (2)

(57) [Claims] 1. A sintered body containing a transition metal oxide as a main component.
The negative characteristic thermistor body, Ag, Au or Pt
Precious metals as main componentsThermistor element formed with electrodes
In, the electrode forming material is copperAnd / or copper compoundsContainsAnd When the content of copper and / or copper compound is inorganic in the electrode forming material
Not more than 20% by weight of the substance content Sir characterized by that
Mister element. 2. The thermistor element according to claim 1, wherein the thermistor element is made of a sintered body containing oxides of Mn, Co and Fe as main components.