JPS581521B2 - Thermistor composition - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION The present invention relates to a thermistor composition for a film thermistor formed by printing and baking. Ru.

Conventional film thermistors are formed by printing and firing a thermistor paste consisting of a thermistor characteristic powder, a glass powder, and an organic vehicle on a heat-resistant insulating substrate such as alumina.

The thermistor characteristic powder in this paste is at least two selected from thermistor characteristic powders of Mn, Co, Ni, Cus Al, and Fe oxides used in individual parts such as disk-shaped thermistors or bead-shaped thermistors. It is a composite oxide powder made by firing more than one type of powder.

Further, as the glass powder, lead borosilicate glass having a softening point of 500°C to 700°C is often used.

In film thermistors, the glass content is 30wt% in order to bond the thermistor characteristic powders together and to increase the adhesive strength between the film formed by printing and firing and the substrate.
The above is necessary.

However, this film thermistor made of thermistor powder and glass is formed on an alumina substrate 1 and the alumina substrate 1 as shown in FIGS. A film thermistor with a structure similar to a thick film resistor, which consists of an electrode 2 and a thermistor layer 3 formed so that the electrodes are connected, has a resistance value of several hundred kilohms or more, and is used as a regular circuit element. It's difficult.

For this reason, a so-called sandwich-type structure in which a thermistor layer 3 is formed between a lower electrode 4 and an upper electrode 50 as shown in FIGS. 3 and 4, which has a low resistance structurally, is adopted.

However, even with this sandwich-inch film thermistor, IKΩ
In order to obtain the following low resistance value, it is necessary to use a material having thermistor characteristics with a specific resistance of 100 Ω'-cm or less.

In this way, the thermistor material with low resistivity is currently Cu.
Compositions containing these are known, but the stability of the resistance value is poor and it is difficult to form an accurate temperature sensing element.

Therefore, as a method for lowering the resistance of thermistors, in addition to the thermistor characteristic powder and glass powder, Ag and Au can be used as a third component.
It is known to add noble metal powders such as or other conductive materials.

Among these, the thermistor composition in which Ag powder and R u02 powder are added at the same time has a wide range of resistance values while having the thermistor constant of the powder material itself, which has thermistor characteristics, and the voltage dependence of the resistance value and noise current are reduced. It had many advantages such as less.

However, this thermistor characteristic powder - glass powder -
A thermistor composition consisting of Ag powder-RuO powder is. 8
If fired at a high temperature exceeding 50° C., foaming will occur in the thermistor film and the thermistor film will not be good.

This has resulted in problems such as large variations in resistance values, generation of noise current, voltage dependence of resistance values, and large changes in resistance values under temperature cycle conditions.

As described above, when it becomes difficult to bake at a temperature of 850° C. or higher, the degree of freedom in the manufacturing process of thick film module circuit boards including thick film resistors, thick film capacitors, etc. is reduced, and the board manufacturing becomes complicated.

An object of the present invention is to eliminate the above-mentioned drawbacks of the prior art, to provide a thermistor composition that can be fired at high temperatures and, when made into a thermistor, has a thermistor constant equivalent to that of the other thermistor characteristic materials.

The thermistor composition of the present invention uses at least two types of oxides selected from Mn, Co, Ni, Fe, and Al oxides in order to form a low-resistance film thermistor while using a thermistor material with a high specific resistance. consisting of a thermistor characteristic powder, a glass powder, and a RuO 2 conductive powder,
However, the content of the Ruo2 conductive powder is 2 wt% to 10 wt% based on the total powder weight of the thermistor composition.

Note that as the content of RuO2, which is a conductive powder, increases, the resistance value of the film thermistor decreases;
When the conductive powder content exceeds 10 wt%, the thermistor constant decreases and becomes much smaller than the thermistor constant of the thermistor characteristic material itself.

] Due to the hygroscopicity, the Ru02 conductive powder content is 2wt% to 1
It was set to 0 wt%.

Further, when the RuO2 conductive powder content is between 2 and 10 wt%, the resistance value changes by more than one order of magnitude, but the thermistor constant remains almost constant, which is a composition range that is very effective in practice.

Further, when the glass content is 45 wt% or less, the thermistor constant becomes larger than other glass content ranges.

The present invention will be explained below with reference to Examples.

1 Example I MnO, Co203, NiO powder at 3.5:1:0.5
A thermistor characteristic powder obtained by performing a solid phase reaction at a molar ratio of
2 powder and Table 2 No. The total weight is 10 in the ratio shown in 1 to 8.
Weigh it so that it weighs 100 g.

These powders are mixed in a stirrer for 1 hour, then 4 cc of α-terpineol solution containing 10% ethyl cellulose is added as an organic binder, and kneaded for another 1 hour to obtain a thermistor paste.

The membrane thermistor had a sandwich structure as shown in FIGS. 3 and 4.

That is, a silver/palladium conductive paste is screen printed on the alumina substrate 1 and fired at 850° C. for 10 minutes to form the lower electrode 4.

Print each of the above thermistor pastes on top of this,
After drying at 130°C for 10 minutes, silver/palladium conductive paste was printed through the dried thermistor paste so as to face the lower electrode, and this was baked at 900°C for 10 minutes to form thermistor layer 4 and upper electrode 5. and form a unique thick film thermistor.

The area where the electrodes face each other is 1 mm, and the thickness of the thermistor layer after firing is 40 μm.

The characteristics of the film thermistor thus obtained are shown in the characteristics column of thick film thermistor in Table 2.

The specific resistance of the sintered body of the thermistoric material is 720Ω.
・cm (25°C), the thermistor constant was 3290K.

Further, stability was evaluated by the rate of change in resistance after being left at 150° C. for 2000 hours.

Example 2 Mn02, Co203, Fe203 powder at 3:1.5
The thermistor characteristic powder obtained by solid phase reaction at a molar ratio of 0.2, glass powder having the composition shown in Table 1, and Ru02 powder were weighed out in the proportions shown in Tables 341 to 8, and the same procedure as in Example 1 was carried out. , a thermistor paste was prepared and a film-like thermistor was formed.

The characteristics of this thermistor are shown in the thick film thermistor characteristics column of Table 3.

The specific resistance of the sintered body of the thermistor characteristic material is 1.5K.
At Ω 1 cm (25° C.), the thermistor constant was 3850K.

Example 3 Mn02, Co203, Al203, Fe20
Table 4 No. 4 was prepared in the same manner as in Example 1 using a thermistor characteristic material in which powder was reacted in a solid phase at a molar ratio of 2.5: 1.5: 0.2: 0.2. Thick film thermistors having the compositions shown in Nos. 1 to 8 were formed.

The characteristics of this thermistor were as shown in the characteristics column of thick film thermistor in Table 4.

Note that the specific resistance of the sintered body of the thermistor characteristic material is 3. OK
When Ω was 1 cm, the thermistor constant was 4100K.

As described above, when a thermistor paste is created using the thermistor composition according to the present invention and a thick film thermistor is created using this, the thermistor layer obtained is foamed even if the paste is fired at a high temperature of around 900°C. There is no such thing as
Moreover, the obtained thick film thermistor has a resistance value as a commonly used circuit element, has improved stability, and has a large thermistor constant.

[Brief explanation of the drawing]

Fig. 1 is a plan view of a film thermistor with a thick film resistance structure, Fig. 2 is a sectional view taken along the line A-A in Fig. 1, Fig. 3 is a plan view of a film thermistor with a thick film capacitor structure, and Fig. 4 is a 3 It is an AA sectional view of the figure. 1... Alumina substrate, 3... Thermistor layer, 4... Lower electrode, 5... Upper electrode.

Claims (1)

[Claims] In a thermistor composition comprising at least two types of thermistor characteristic powders selected from oxides of IMn1Co, Ni, and FesAl, a glass powder, and a Ru02 conductive end, the amount of the Ru02 conductive powder is the thermistor. A thermistor composition characterized in that the amount is 2 wt% to 10 wt% of the total powder composition.