JPH11273904A - Positive temperature coefficient thermistor element - Google Patents

Abstract

PROBLEM TO BE SOLVED: To enhance resistance to flash voltage, by dividing an element body into two region, an outer region and an inner region so that the outer region has lower Curie point than the inner region, while at least a portion of the periphery is thicker than the center in each opposite principal surface of the element body. SOLUTION: A positive temperature coefficient thermistor element has a disc shape and comprises a ceramic element body 12 with positive temperature coefficient thermistor characteristics. A protrusion 13 is formed on the whole periphery of each principal surface in the element body 12 and a recess 14 is formed on a region surrounded with the protrusion 13. Ohmic contact electrodes 15 and 16 are also formed on each principal surface of the element body 12. An inner region 18 of the element body 12 is located at the center in the thickness direction and an outer region 18 is located at both ends in the thickness direction so that the inner region 18 is inserted into the outer region 17 in the thickness direction. The outer region 17 has lower Curie point than the inner region 18.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a PTC thermistor element, and more particularly to an improvement for improving a flash breakdown voltage.

[0002]

2. Description of the Related Art Positive temperature coefficient thermistors are used in fields such as overcurrent protection, demagnetization, and motor starters. FIG. 5 is a perspective view showing a conventional typical PTC thermistor element 1. Referring to FIG. 5, a positive temperature coefficient thermistor element 1 includes an element body 2 made of ceramic having a thermistor characteristic having a positive temperature coefficient. Each of the opposing main surfaces of the element body 2 has an electrode 3
And 4 are formed. These electrodes 3 and 4 are formed of, for example, In-Ga, and are brought into ohmic contact with element body 2.

Further, a positive temperature coefficient thermistor 5 shown in a sectional view in FIG. 6 is sometimes used. The PTC thermistor element 5 shown in FIG. 6 differs from the PTC thermistor element 1 shown in FIG. 5 in the structure of the electrodes 7 and 8 formed on each main surface of the element body 6. That is, electrodes 7 and 8 are each composed of two layers: lower layers 7a and 8a containing, for example, nickel and upper layers 7b and 8b containing, for example, silver. Also, upper layers 7b and 8b are formed leaving a gap on the periphery of lower layers 7a and 8a, so that the periphery of lower layers 7a and 8a is exposed.

The positive temperature coefficient thermistor element 1 shown in FIG. 5 has a disk shape, and the positive temperature coefficient thermistor element 5 shown in FIG. 6 is also intended to have a disk shape. For such an outer shape, for example, a square-plate-shaped positive characteristic thermistor element may be used.

[0005]

A positive temperature coefficient thermistor element for use in applications such as overcurrent protection, demagnetization, or a motor starter as described above is required to have a high flash breakdown voltage of, for example, 600 V. .
In addition, the flash withstand voltage referred to here is a flash withstand voltage in a state where current is not limited. For example, in a public standard of an element for a communication device, a specific resistance is connected in series to a positive characteristic thermistor element, and It is also required that the flash withstand voltage in a state where the current flowing through the characteristic thermistor element is limited is high. For example, it is required to have a flash withstand voltage as high as 600 V while limiting the current to 2.2 A.

However, as far as the positive temperature coefficient thermistor element 1 or 5 described above has been concerned, it has been difficult to increase both the flash breakdown voltage without limiting the current and the flash breakdown voltage with limiting the current. SUMMARY OF THE INVENTION It is an object of the present invention to provide a positive temperature coefficient thermistor element capable of increasing not only a flash withstand voltage that does not limit current but also a flash withstand current that limits current.

[0007]

SUMMARY OF THE INVENTION The present invention is directed to a positive temperature coefficient thermistor element including a ceramic element body having a thermistor characteristic having a positive temperature coefficient, and solves the above-mentioned technical problem. Therefore, the element body has a shape in which the thickness at at least a part of the peripheral portion of each of the opposing main surfaces is thicker than the thickness at the central portion, and the element body has an outer region and an inner region. The outer region has a lower Curie point than the inner region.

In the present invention, with respect to the arrangement of the external region and the internal region described above, typically, the internal region is located at the center in the thickness direction of the element body, and the external region is formed by connecting the internal region in the thickness direction. A first aspect, which is located at both ends in the thickness direction of the element body so as to sandwich the element body;
A second region located at a central portion in the main surface direction of the element body, and an outer region located at a peripheral portion in the main surface direction of the element body so as to surround the inner region from the periphery.
There is a mode of.

Further, in the positive temperature coefficient thermistor element according to the present invention, an electrode may be formed on each main surface.

[0010]

FIG. 1 shows a PTC thermistor element 11 according to an embodiment of the present invention. In FIG. 1, (1) is a plan view, and (2) is a sectional front view. The positive-characteristic thermistor element 11 has an element body 12 made of, for example, ceramic containing BaTiO ₃ as a main component and having a thermistor characteristic having a positive temperature coefficient as a whole, for example. Element body 1
2 has opposing main surfaces, and has a shape in which the thickness of at least a part of the peripheral portion of each main surface is thicker than the thickness of the central portion. In this embodiment, on each main surface of the element main body 12, a convex portion 13 is formed on the entire periphery thereof, and the concave portion 1 is formed in a region surrounded by the convex portion 13.
4 are formed.

On each main surface of the element main body 12, electrodes 15 and 16 made of, for example, In-Ga and in ohmic contact with the element main body 12 are formed. The element body 12 is partitioned into an outer region 17 and an inner region 18. In this embodiment, the inner region 18 is
Is located at the center in the thickness direction of the outer region 17.
The element body 12 is sandwiched so that the inner region 18 is sandwiched in the thickness direction.
Are located at both ends in the thickness direction.

In the element body 12 having such a structure,
As a characteristic configuration, the outer region 17 is
Also have a low Curie point. Curie point like this
Between the outer region 17 and the inner region 18
Therefore, for example, BaTiO _ThreeThermist mainly composed of
The composition of the material is changed. FIG. 2 shows a second embodiment of the present invention.
1 shows a positive temperature coefficient thermistor element 21 according to an embodiment.
You.

The positive temperature coefficient thermistor element 21 shown in FIG.
Is provided with an element main body 22 having the same outer shape as the element main body 12 provided in the above-described PTC thermistor element 11. That is, the element body 22 has the convex portions 23 formed on the entire periphery of each main surface, and the concave portions 24 in the region surrounded by the convex portions 23. Electrodes 25 and 26 are formed on each main surface of the element main body 22, respectively.

In such a PTC thermistor element 21, the form of the outer region 27 and the inner region 28 of the element body 22 is different from that of the PTC thermistor element 11 described above. That is, the inner region 28 is located at the central portion in the main surface direction of the element body 22, and the outer region 27 having a lower Curie point is located at the peripheral portion of the element body 22 in the main surface direction so as to surround the inner region 28 from the periphery. It is located in.

FIG. 3 shows a PTC thermistor element 11a according to a third embodiment of the present invention. This positive temperature coefficient thermistor element 11a has many elements common to the positive temperature coefficient thermistor element 11 shown in FIG.
In FIG. 7, elements corresponding to the elements shown in FIG. 1 are denoted by the same reference numerals, and redundant description will be omitted.

The positive temperature coefficient thermistor element 11a shown in FIG.
Is characterized by the manner in which the electrodes 15 and 16 are formed. That is, the electrodes 15 and 16 are formed of two layers, for example, lower layers 15a and 16a containing nickel and upper layers 15b and 16b containing silver, for example, as in the case of the positive temperature coefficient thermistor element 5 shown in FIG. Be composed. The upper layers 15b and 16b are formed leaving a gap around the lower layers 15a and 16a.
The edges of 5a and 16a are exposed.

FIG. 4 shows a PTC thermistor element 21a according to a fourth embodiment of the present invention. This positive temperature coefficient thermistor element 21a includes many elements common to the positive temperature coefficient thermistor element 21 shown in FIG. 2, and therefore, in FIG. 4, the elements corresponding to the elements shown in FIG. , And duplicate description will be omitted.

The positive temperature coefficient thermistor element 21a shown in FIG.
Also, similarly to the case of the positive temperature coefficient thermistor element 11a shown in FIG. 3, the electrodes 25 and 26 have a two-layer structure. In other words, electrodes 25 and 26 are each composed of two layers of lower layers 25a and 26a containing, for example, nickel and upper layers 25b and 26b containing, for example, silver.
5b and 26b are formed to form lower layers 25a and 26a
Is exposed.

In the positive temperature coefficient thermistor elements 11, 11a, 21 and 21a according to the above-described embodiments, the presence of the protrusions 13 or 23 provided on the periphery of each main surface of the element body 12 or 22; The fact that the Curie point of the external region 17 or 27 in the element body 12 or 22 is lower than the Curie point of the internal region 18 or 28 contributes to the improvement of both the flash breakdown voltage that does not limit the current and the flash breakdown voltage that limits the current. doing. An example of an experiment conducted to confirm such an improvement in the breakdown voltage of both flashes will be described below.

[0020]

[Experimental Example 1] In Experimental Example 1, as an embodiment of the present invention,
The PTC thermistor element 11 (Example 1) shown in FIG. 1 and the PTC thermistor element 21 (Example 2) shown in FIG. 2 were employed. Further, as comparative examples, the positive temperature coefficient thermistor element 1 (comparative example 1) shown in FIG. 5, the positive temperature coefficient thermistor element 31 (comparative example 2) shown in FIG. 7, and the positive temperature coefficient thermistor element 41 shown in FIG. Comparative Example 3) was employed.

The positive temperature coefficient thermistor element 31 shown in FIG. 7 includes an element body 32 and electrodes 33 and 34 formed on the main surfaces of the element body 32, respectively. In the element main body 32, no convex portion is formed at the peripheral edge of each main surface, but the element main body 32 has an outer region 35 and an inner region 36.
The internal region 36 is located at the center in the thickness direction of the element body 32, and the external region 35 is located at both ends in the thickness direction of the element body 32 so as to sandwich the internal region 36 in the thickness direction. You. Then, the external area 35
Has a lower Curie point than the inner region 36.

The PTC thermistor element 41 shown in FIG. 9 includes an element body 42 and electrodes 43 and 44 formed on the main surfaces of the element body 42, respectively. The element body 42 is made of a uniform material without being divided into an outer region and an inner region.
A convex portion 45 is formed on the periphery of each of the main surfaces of No. 2 and a concave portion 46 is formed in a region surrounded by the convex portion 45.

Examples 1 and 2 and Comparative Example 1
3 to 3, the ceramic material having a thermistor characteristic having a positive temperature coefficient and constituting the element body is
For a sample using aTiO ₃ as a main component and having a device body made of a uniform material as in Comparative Examples 1 and 3, the Curie point was set to 100 ° C., and Examples 1 and 2 were used. Further, as in Comparative Example 2, for a sample in which the element body is partitioned into an outer region and an inner region, the Curie point of the outer region is set to 100 ° C., the Curie point of the inner region is set to 105 ° C., and the Curie point of the outer region is set. It was made lower than the Curie point of the inner area. The electrodes were formed of In-Ga.

As for the dimensions of the respective parts shown in FIGS. 1 (2), 2 (2), 5, 7 and 9, a is 8.2 mm, b is 1 mm, and c is 3.5 mm. , D
Is 1 mm, e is 1 mm, f is 1 mm, g is 8.2 mm,
h is 1 mm, i is 3.5 mm, j is 3 mm, and k is 8.2.
mm, m is 3 mm, n is 8.2 mm, p is 1 mm, q is 1 mm, r is 1 mm, s is 8.2 mm, t is 1 mm, u
Was set to 3.5 mm and v was set to 3 mm, respectively, so that the resistance value at room temperature was 23Ω.

Examples 1 and 2 thus obtained
In addition, the flash withstand voltage and the current which do not limit the current of the PTC thermistor elements according to Comparative Examples 1 to 3 are set to 2.2.
The flash withstand voltage limited to A was measured. The results of these measurements are shown in Table 1 below.

[0026]

[Table 1]

The flash withstand voltage, which does not limit the current, was measured up to 810 V. Samples withstanding up to 810 V were indicated as “over” in Table 1 above. The flash withstand voltage at which the current was limited was measured up to 658 V.
Above is 658 for all samples.
It means that you endured V.

As can be seen from Table 1, Examples 1 and 2
As for the flash withstand voltage that does not limit the current and the flash withstand voltage that limits the current, a remarkable improvement has been achieved. As for the flash breakdown voltage which does not limit the current, the comparative example 2 is more excellent than the comparative example 1, the comparative example 3 is more excellent, and in the case of the comparative example 3, the results are almost the same as those of the examples 1 and 2. Has been obtained. However, when looking at the flash breakdown voltage with the current limited, all of Comparative Examples 1 to 3 are inferior to Examples 1 and 2.

[0029]

[Experimental Example 2] In Experimental Example 2, as an embodiment of the present invention,
PTC thermistor element 11a shown in FIG. 3 (Example 3)
The positive-characteristic thermistor element 21a (Example 4) shown in FIG. 4 and FIG. 4 are employed. As a comparative example, the positive-characteristic thermistor element 5 (Comparative Example 4) shown in FIG. 6 and the positive-characteristic thermistor shown in FIG. The element 31a (Comparative Example 5) and the positive temperature coefficient thermistor element 41a (Comparative Example 6) shown in FIG. 10 were employed.

The positive temperature coefficient thermistor element 31a shown in FIG.
Compared with the positive temperature coefficient thermistor element 31 shown in FIG. 7, the electrodes 33 and 34 are respectively composed of two layers of lower layers 33a and 34a and upper layers 33b and 34b, and the lower layers 33a and 34a The only difference is that the upper layers 33b and 34b are formed leaving a gap at the periphery.

Also, in the positive temperature coefficient thermistor element 41a shown in FIG. 10, the electrodes 43 and 44 are different from the positive temperature coefficient thermistor element 41 shown in FIG.
It is composed of two layers, lower layers 43a and 44a and upper layers 43b and 44b.
The only difference is that upper layers 43b and 44b are formed leaving a gap at the periphery of a.

Examples 3 and 4 and Comparative Example 4
In each of Nos. 6 to 6, the same as in Experimental Example 1 described above, except that nickel was used as the lower layer of the electrode, silver was used as the upper layer, and the upper layer was formed leaving a gap of 1 mm from the periphery of the lower layer. Positive temperature coefficient thermistor elements according to the respective samples having a material and dimensions and a resistance value of 23Ω at room temperature were manufactured.

When the Curie point is repeated, as in Comparative Examples 4 and 6, the Curie point of the sample whose element body is made of a uniform material is set to 100 ° C. For a sample in which the element body is divided into an outer region and an inner region as in Comparative Example 5, the Curie point of the outer region is 100 ° C., the Curie point of the inner region is 105 ° C., and the Curie point of the outer region is It was made lower than the Curie point of the inner area.

For each of the obtained positive temperature coefficient thermistor elements, the flash withstand voltage without limiting the current and the flash withstand voltage with the current limited to 2.2 A were measured in the same manner as in Experimental Example 1. The results of these measurements are shown in Table 2 below.

[0035]

[Table 2]

As can be seen from Table 2, the same tendency as in the above-described Experimental Example 1 was observed in Experimental Example 2, and according to Examples 3 and 4, the flash breakdown voltage and current, which did not limit the current, were limited. Significant improvements have been made in both the flash breakdown voltage. The optimum values of the dimensions a,... Of the respective parts defined in the above-mentioned respective experimental examples vary depending on the Curie point to be obtained. However, it is not limited to those having typical dimensions.

[0037]

As described above, according to the present invention, as can be seen from the above-mentioned experimental examples, both flash withstand voltages, that is, both the flash withstand voltage without limiting the current and the flash withstand voltage with the current limited, are significantly improved. Can be planned. The reason can be considered as follows. First, since the thickness of at least a part of the peripheral portion of each main surface of the element body is thicker than the thickness of the central portion, the resistance value at the peripheral portion becomes larger than the resistance value at the central portion. In particular, particularly at the beginning of heat generation, the temperature rise at the peripheral portion occurs faster than the temperature rise at the central portion. In addition, since the outer region of the element body has a lower Curie point than the inner region, this also makes the resistance value in the outer region larger than the resistance value in the inner region, especially in the early stage of heat generation, and It acts so that the temperature rise in the region occurs faster than in the internal region. From these facts, despite the large amount of heat dissipation at the peripheral portion or the external region of the element body, the temperature difference between the peripheral portion or the external region and the central portion or the internal region becomes small, and therefore, the positive temperature coefficient thermistor device It is considered that both flash breakdown voltages are improved.

The positive temperature coefficient thermistor element according to the present invention comprises:
An electrode is not formed on each main surface of the element body itself, and for example, a terminal member having a spring property may be brought into contact with each main surface, but when an electrode is formed on each main surface, The characteristics of the element main body having the above-described protrusions, the outer region, and the inner region can be more effectively brought out.

[Brief description of the drawings]

FIG. 1 shows a positive temperature coefficient thermistor element 11 according to a first embodiment of the present invention, wherein (1) is a plan view and (2) is a sectional front view.

FIG. 2 shows a positive temperature coefficient thermistor element 21 according to a second embodiment of the present invention, wherein (1) is a plan view and (2) is a sectional front view.

FIG. 3 shows a positive temperature coefficient thermistor element 11a according to a third embodiment of the present invention, wherein (1) is a plan view and (2)
Is a sectional front view.

FIG. 4 shows a positive temperature coefficient thermistor element 21a according to a fourth embodiment of the present invention, wherein (1) is a plan view and (2)
Is a sectional front view.

FIG. 5 is a perspective view showing the appearance of a typical conventional PTC thermistor element 1;

FIG. 6 is a cross-sectional front view showing another typical conventional PTC thermistor element 5;

FIG. 7 is a cross-sectional front view showing a positive temperature coefficient thermistor element 31 as Comparative Example 2 employed in an experimental example conducted to confirm the effect of the present invention.

FIG. 8 is a cross-sectional front view showing a positive temperature coefficient thermistor element 31a as Comparative Example 5 employed in an experimental example conducted to confirm the effect of the present invention.

FIG. 9 is a cross-sectional front view showing a positive temperature coefficient thermistor element 41 as Comparative Example 3 adopted in an experimental example conducted to confirm the effect of the present invention.

FIG. 10 is a cross-sectional front view showing a positive-characteristic thermistor element 41a as Comparative Example 6 employed in an experimental example performed to confirm the effect of the present invention.

[Explanation of symbols]

 11,11a, 21,21a Positive temperature coefficient thermistor element 12,22 Element body 13,23 Convex part 15,16,25,26 Electrode 17,27 External area 18,28 Internal area

 ──────────────────────────────────────────────────続 き Continued on the front page (72) Inventor Takeo Haga 2-26-10 Tenjin, Nagaokakyo-shi, Kyoto Inside Murata Manufacturing Co., Ltd.

Claims (4)

[Claims] 1. A ceramic material having a thermistor characteristic having a positive temperature coefficient, having main surfaces opposed to each other, wherein a thickness of at least a part of a peripheral portion of each of the main surfaces is smaller than a thickness of a central portion. A positive temperature coefficient thermistor, comprising: an element body having a thickened shape; wherein said element body is partitioned into an outer region and an inner region, wherein said outer region has a lower Curie point than said inner region. element. 2. The internal region is located at a central portion in the thickness direction of the element body, and the external region is located at both ends in the thickness direction of the element body so as to sandwich the internal region in the thickness direction. The positive temperature coefficient thermistor element according to claim 1. 3. The device according to claim 1, wherein the inner region is located at a central portion of the element body in a main surface direction, and the outer region is located at a peripheral portion of the element body in a main surface direction so as to surround the inner region from the periphery. The positive temperature coefficient thermistor element according to claim 1, wherein 4. The positive temperature coefficient thermistor element according to claim 1, further comprising an electrode formed on each of said main surfaces.