JPH0745403A - Semiconductor ceramic element - Google Patents

Abstract

PURPOSE:To acquire a semiconductor ceramic element of good reliability test characteristics wherein the rise of the resistance value at a low temperature is high, a resistance value in a temperature rise state is small, a current consumption amount can be reduced and it is possible to correspond to a large current. CONSTITUTION:A ceramic element body comprised of rare earth transition element oxide such as LaCo oxide is used and porosity of the ceramic element body is made 3 to 20vol%.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a semiconductor ceramic device using a ceramic body having a negative temperature coefficient of resistance.

[0002]

2. Description of the Related Art For example, a so-called NTC thermistor element is used as an element for absorbing an initial rush current because an overcurrent flows in a switching power supply at the moment when the switch is turned on. This NTC thermistor element has a high resistance value at room temperature and has a function of decreasing the resistance value as the temperature rises, which suppresses the initial inrush current, and then raises the temperature by self-heating to reduce the resistance. Therefore, the power consumption can be reduced in the steady state. Spinel oxide has been conventionally used as the ceramic body of such an NTC thermistor element.

[0003]

When such an NTC thermistor element is used for preventing an inrush current, the resistance value must be small in the temperature rising state due to self-heating as described above. However, in the conventional NTC thermistor element using spinel oxide, the B constant tends to decrease as the specific resistance decreases, and the resistance value in the temperature rising state cannot be sufficiently decreased. There is a problem that the power consumption cannot be reduced.

Further, in the conventional NTC thermistor element,
There is a problem that the initial resistance value varies depending on the change of the outside air temperature, and the rise of the resistance value is delayed particularly at a low temperature of 0 ° C. or less. To remedy such problems,
It is necessary that the B constant be small near room temperature and the B constant be large at high temperature.

The object of the present invention is to improve the rise of the resistance value at a low temperature, reduce the resistance value in a temperature rising state to reduce the power consumption, and also to cope with a large current, and to improve the reliability. Another object of the present invention is to provide an excellent semiconductor ceramic device.

[0006]

In order to achieve the above object, the inventors of the present invention have made earnest studies on a ceramic composition exhibiting a negative resistance-temperature characteristic in which the B constant is small at room temperature and large at high temperature. The oxide ceramic composition of elements has such characteristics, and the porosity of such a ceramic element body of rare earth transition element oxide is set to 3 to 20% by volume, so that a highly reliable semiconductor can be obtained. The inventors have found that a ceramic element can be obtained, and completed the present invention.

That is, the semiconductor ceramic element of the present invention is characterized in that the ceramic body is made of a rare earth element oxide and the porosity of the ceramic body is 3 to 20% by volume.

The rare earth transition element oxide used in the present invention is not particularly limited as long as it is an oxide composed of a rare earth element and a transition element. For example, a rare earth transition element oxide such as LaCo type or NdCoO ₃ is used. Can be used. In particular, LaCo-based oxides have a large increase in B constant due to temperature increase and a small B constant at room temperature, and therefore excellent properties can be obtained.

[0009]

With respect to the characteristics that the rare earth transition element oxide has a low resistance, a small B constant at room temperature, and a large B constant at high temperature, for example, V.I. G. Bhide, D.A. S. Ra
-Joria reference (Phys. Rev. B6
[3] 1021 (1972)) and the like. As a result of various trials of practical tests on whether or not such characteristics can be actually applied to the element, the present inventors did not break even when a large current was flowed, but showed a sufficient current suppressing effect,
It was found that the rate of change of the resistance value was greatly influenced by the manufacturing conditions, and the cause was largely dependent on the molding filling pressure, the firing temperature, or the porosity of the fired body determined by the binder content. In the present invention, such a ceramic body has a porosity of 3 to 20% by volume, and is a semiconductor ceramic element exhibiting reliable and stable characteristics.
When the porosity of the ceramic body becomes smaller than 3% by volume,
Since the oxidation does not proceed easily, the B constant becomes small, and when it exceeds 20% by volume, the reliability decreases.

According to the present invention, by using a ceramic body made of a rare earth transition element oxide and having a porosity of 3 to 20% by volume, reliability and stability of room temperature resistance value can be improved, It is possible to reduce the resistance in the room temperature state, reduce the power consumption in the steady state, and increase the allowable current value.

[0011]

EXAMPLES The present invention will be described in detail below with reference to examples. Examples La _X Co _Y O ₃ (X /
Y = 0.9 to 1.1) so that Co ₃ O ₄ , La
₂ O ₃ powder is weighed and mixed. The powder is wet mixed with pure water in a ball mill for 16 hours, dried, and calcined at 1000 ° C. for 2 hours. 5% by weight of a binder was added to the calcined powder, the mixture was again wet mixed in a ball mill for 5 hours, pulverized, filtered, dried, and then pressure-molded into a disk shape so that the room temperature resistance value was 10Ω. The molded body is fired in the atmosphere at 1400 ° C. for 2 hours to obtain a fired body (8.2% by volume). Next, after applying a silver paste on both sides of this fired body, it is baked at 650 ° C. to form an electrode, and an NTC thermistor element is obtained.

[0012]Comparative example For comparison, a conventional NTC thermistor element is manufactured.
Co₃O_Four, Mn₃O _FourAnd CuCO₃Each weight
Weigh this powder to a ratio of 6: 3: 1 and
Using the NTC thermistor element as in the above embodiment
To manufacture.

FIG. 1 is a characteristic diagram showing the temperature dependence of the specific resistance of the NTC thermistor elements of the above-mentioned Examples and Comparative Examples. As shown in FIG. 1, in the NTC element of the comparative example,
The specific resistance at 25 ° C. is as high as 100 Ω · cm, and the increase in B constant due to temperature rise is small. On the other hand, in the NTC element of the example according to the present invention, the specific resistance at 25 ° C. is 20Ω.
It is shown that the resistance is smaller than that of the NTC element of the comparative example at a high temperature, which is small as cm or less and further increases the B constant due to the temperature rise.

The NTC element of the example and the NTC element of the comparative example were respectively connected in series to a switching power supply, and the time change of the current value of the switching power supply when the power was turned on was measured. The results are shown in Table 1.

[0015]

[Table 1]

As is clear from Table 1, the device of the comparative example also has the current delay effect, but the outside air temperature is 60 ° C. and −30.
At ℃, the current value after 1 second was 9.1 A and 1.3, respectively.
A indicates that there is a large variation in the rising characteristics.

FIG. 2 is a diagram showing the results of the repeated energization test of the NTC element of the example. In the test, a heat cycle of conducting a current for 1 minute, turning off the power for 30 minutes and cooling to 25 ° C. was performed 10,000 times. FIG. 2 shows the characteristics of the first time and the characteristics of the 10,000th time.
It can be seen that no change in the characteristics was observed even after the operation was repeated 100 times.

Further, as a result of conducting a practical test to 100 NTC elements of the embodiment by applying 20 A to them, it was confirmed that they can be applied to a large current without destroying any element.

Next, by changing the amount of the binder added to the calcined powder in the above-mentioned examples to 0 to 15% by weight, fired bodies having different porosities as shown in Table 2 below were prepared, and these were prepared. From the fired body to NT as in the above embodiment
A C thermistor element was manufactured. A high-temperature storage test (200
℃, 1000 hours) and energization test (10A, 1000
The rate of change in resistance value over time was measured, and the results are shown in Table 2. The B constant was measured and is shown in Table 2. Here, B constant is B (T) = {Lnρ (T ₀ ) −Lnρ (T)} / (T ₀ where T is temperature, ρ is resistivity, and Ln is natural logarithm.
It is a constant defined by −T) and indicates a resistance change with temperature. The larger this value, the larger the resistance change with temperature. The B constant shown here is a constant when the temperature is raised from 25 ° C. to 200 ° C.

In Table 2, the sample numbers with * are comparative examples in which the porosity is outside the range of the present invention.

[0021]

[Table 2]

As is clear from Table 2, in Sample Nos. 1 and 2 having a porosity smaller than the range of the present invention, B at high temperature
The constant is getting smaller. In Sample Nos. 9 and 10 having a porosity larger than the range of the present invention, the resistance change rate in the high temperature storage test and the resistance change rate in the current application test were -1.
A change of 0% or more is shown, indicating that the reliability is low.

Although the disk-shaped NTC thermistor element is manufactured and described in the above embodiment, the semiconductor ceramic element of the present invention is not limited to such a shape.
It is also applied to other element shapes such as a laminated element and a cylindrical element. Further, although Ag is used as the electrode of the element in the above-mentioned embodiment, similar characteristics can be obtained by using other electrode materials such as Pd, Pt or alloys thereof.

[0024]

As described above, according to the present invention, by using the ceramic body made of rare earth transition element oxide, B
An element having a small constant and a large B constant due to temperature rise can be formed, a steady state can be achieved, power consumption can be reduced, and a large current can be applied. Further, by setting the porosity of the ceramic body to 3 to 20% by volume, it is possible to remarkably improve the B constant at high temperature and the stability of characteristic values in reliability tests such as high temperature storage test and energization test. it can.

[Brief description of drawings]

FIG. 1 is a diagram showing the temperature dependence of the specific resistance of an NTC thermistor element in an example of the present invention.

FIG. 2 Time of heat cycle test of Example of the present invention-
The figure which shows a current characteristic.

Claims (2)

[Claims] 1. A semiconductor ceramic device using a ceramic body having a negative temperature coefficient of resistance, wherein the ceramic body is made of a rare earth transition element oxide and the porosity of the ceramic body is 3 to 20% by volume. A semiconductor ceramic device characterized in that 2. The rare earth transition element oxide is LaCo
The semiconductor ceramic device according to claim 1, which is a system oxide.