JP2014072374A - Barium titanate-based semiconductor porcelain composition and ptc thermistor using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a barium titanate-based semiconductor porcelain composition which has a low Curie point, is operable to work at a low temperature, and shows a low resistance at a room temperature and a high resistance-temperature curve, and to provide a PTC thermistor using such a composition.SOLUTION: A barium titanate-based semiconductor porcelain composition comprises: barium; titanium; strontium; calcium; and manganese. In the barium titanate-based semiconductor porcelain composition, the molar ratio Ti-site/Ba-site of Ti sites to Ba sites is equal to or larger than 0.985, and the contents of Sr, Ca and Mn are as follows: 7.0 mol%≤Sr≤17.0 mol%; 12.5 mol%≤Ca≤19.0 mol%; and 0.035 mol%≤Mn≤0.074 mol%. The molar ratio Ti-site/Ba-site of Ti sites to Ba sites falls in a range between 0.985 and 1.005 inclusive.

Description

  The present invention relates to a barium titanate-based semiconductor ceramic composition having positive resistance-temperature characteristics, and a PTC thermistor using the semiconductor ceramic composition.

  As a barium titanate semiconductor porcelain having positive resistance-temperature characteristics, for example, a semiconductor porcelain composition as shown in Patent Document 1 is known.

  The barium titanate-based semiconductor ceramic composition disclosed in Patent Document 1 contains barium and titanium, and prepares a raw material powder with an increased titanium blending amount relative to the stoichiometric ratio of titanium and barium, The barium in the raw material powder was replaced with 10 to 15 mol% strontium and 13 to 18 mol% calcium, and 0.08 to 0.15 mol% manganese and 1.5 to 2.2. After obtaining a mixture obtained by mixing 5 mol% of silicon and at least one semiconducting agent powder from the semiconducting agent group consisting of Bi, Nb, W, Ta, Sb and rare earth elements, the mixture was subjected to an oxidizing atmosphere. Primary firing within a temperature range of 1150 ° C. to 1240 ° C. to obtain a primary firing product, and the primary firing product is subjected to secondary firing at 1300 to 1380 ° C. in an oxidizing atmosphere. A barium titanate type semiconducting ceramic obtained by the method of.

To summarize, the barium titanate-based semiconductor ceramic disclosed in Patent Document 1 is
Ti / Ba ratio is 1.00 or more,
10-15 mol% of Ba is replaced with Sr, and
While replacing 13 to 18 mol% of Ba with Ca,
Titanic acid mixed with 0.08 to 0.15 mol% of Mn and 1.5 to 2.5 mol% of Si and mixed with at least one kind of semiconducting agent composed of Bi, Nb, W, Ta, Sb and rare earth It is a barium-based semiconductor ceramic composition.

  According to the invention of Patent Document 1, since the primary fired product obtained by primary firing of the mixture is sufficiently oxidized to the inside, the powder obtained by pulverizing the primary fired product has a homogeneous composition up to the inside. In addition, it is said that a barium titanate-based semiconductor ceramic with small variation in specific resistance value at room temperature can be obtained by molding the powder and performing secondary firing.

  By the way, in recent years, chip-type devices such as current control devices and temperature sensing devices are required to be capable of low temperature operation with a lower Curie point, low room temperature resistance, and high resistance-temperature characteristics. Similar demands are increasing for semiconductor ceramics having positive resistance-temperature characteristics used in such elements.

  Furthermore, when mounting elements such as current control elements and temperature sensing elements on a substrate, mounting is performed by soldering by reflow or the like, but there is a problem that the resistance value of the element is likely to change due to thermal effects during mounting. is there.

  If the change in the resistance value of the element due to mounting becomes large, the resistance value of the element may deviate from the standard value after mounting, resulting in a defective product. For this reason, a semiconductor ceramic having positive resistance-temperature characteristics used for such an element is required to have a small change in resistance value due to mounting.

  In addition, it is estimated that the change in resistance value due to mounting is caused by an increase in resistance due to minute peeling of the electrode interface or a decrease in the resistance of the material due to a reducing atmosphere generated by the combustion of organic components.

  Under such circumstances, in the case of the barium titanate-based semiconductor ceramic disclosed in Patent Document 1, the above-mentioned requirement may not be sufficiently satisfied, and the semiconductor ceramic having positive resistance-temperature characteristics with better characteristics. The fact is that the development of

JP-A-7-183104

  The present invention solves the above-described problems, and can realize low-temperature operation, has a low room temperature resistance, and has a high resistance-temperature characteristic. It is an object of the present invention to provide a barium titanate-based semiconductor ceramic composition having a small resistance change due to heat resistance and a PTC thermistor using them. Here, as an application to operate at a temperature near room temperature, for example, there is an overheat detection element for preventing the device from becoming too hot and causing a human burn or damage to the device.

In order to solve the above problems, the barium titanate-based semiconductor ceramic composition of the present invention has a molar ratio of Ba site to Ti site of 0.985 ≦ Ti site / Ba site,
Sr, Ca, and Mn 7.0 mol% ≦ Sr ≦ 17.0 mol% 12.5 mol% ≦ Ca ≦ 19.0 mol% 0.035 mol% ≦ Mn ≦ 0.074 mol%
It is characterized by containing at a ratio of

In the present invention, the Ti site is the total amount (molar amount) of Ti and Mn, and the Ba site is the total amount (molar amount) of Ba, Sr, Ca and a donor (when a donor such as rare earth is included). The molar ratio of Ba site to Ti site (Ti site / Ba site) is expressed by the formula: (Ti + Mn) / (Ba + Sr + Ca + donor)
It is the value (compounding ratio) calculated | required by (1).

In the barium titanate-based semiconductor ceramic composition of the present invention, the molar ratio of Ba site to Ti site is
0.985 ≦ Ti site / Ba site ≦ 1.005
It is preferable that it exists in the range.

The molar ratio of Ba site to Ti site (Ti site / Ba site)
0.985 ≦ Ti site / Ba site ≦ 1.005
By setting it as the range, it becomes possible to realize a low room temperature resistance and a high resistance-temperature characteristic, and to provide a barium titanate-based semiconductor ceramic composition having a small resistance change due to mounting.

The PTC thermistor of the present invention is
The barium titanate-based semiconductor ceramic composition of the present invention is used as a thermistor element having positive resistance-temperature characteristics.

The barium titanate-based semiconductor ceramic composition of the present invention is
The molar ratio of Ba site to Ti site (Ti site / Ba site) is 0.985 or more, and
Sr is 7.0 mol% or more and 17.0 mol% or less,
Ca 12.5 mol% or more, 19.0 mol% or less,
Since Mn is contained in a ratio of 0.035 mol% or more and 0.074 mol% or less, in a barium titanate-based semiconductor ceramic composition not containing lead, it has been difficult to realize conventionally, It becomes possible to simultaneously realize a Curie point, a low room temperature resistance, and a high resistance-temperature characteristic.

  The present invention achieves the above-mentioned effect because of the valence of ions, the Ca atom that should replace the site where the Ba atom originally exists replaces the site where the Ti atom exists, and thus from the charge balance. By designing the composition intended to express the acceptor effect and to adjust the crystal lattice constant in detail, both the site where the Ba element exists and the site where the Ti element exist are both Ca atoms. It is presumed that by making the region that can be replaced in a self-controlling manner, a significant increase in resistance at room temperature is suppressed.

  In the barium titanate semiconductor ceramic composition of the present invention, the rare earth element is mainly blended as a donor, and Mn is blended mainly as an acceptor.

  The PTC thermistor of the present invention is a semiconductor ceramic composition used as a thermistor element having a positive resistance-temperature characteristic, has a low resistance near room temperature, can be operated at a low temperature, and has a resistance-temperature characteristic. For example, it can be suitably used as a protective element for a personal computer.

It is a perspective view which shows the structure of the PTC thermistor concerning one Embodiment of this invention produced using the barium titanate semiconductor ceramic composition concerning this invention.

  Embodiments of the present invention will be described below to describe the features of the present invention in more detail.

FIG. 1 is a perspective view showing a PTC thermistor (positive temperature coefficient thermistor) manufactured using the barium titanate semiconductor ceramic composition according to the present invention.
This PTC thermistor 1 is provided with a pair of electrodes 3 a and 3 b on the front and back surfaces of a semiconductor ceramic body (thermistor body having positive resistance-temperature characteristics) 2.

  The semiconductor ceramic constituting the semiconductor ceramic body 2 is manufactured by the method described below using the semiconductor ceramic composition according to the present invention.

  The electrodes 3a and 3b are electrodes having a two-layer structure in which an Ni layer is formed on both the front and back main surfaces of the semiconductor ceramic body 2, and then an Ag layer is further formed on the Ni layer as an outermost electrode layer. is there.

<Manufacturing method of PTC thermistor>
Hereinafter, a method for manufacturing the PTC thermistor will be described.
First, the following raw materials were prepared as raw materials for the semiconductor ceramic composition for the semiconductor ceramic body 2.
BaCO ₃ , TiO ₂ , SrCO ₃ , and CaCO ₃ were prepared as main component materials, and Er ₂ O ₃ was prepared as a semiconducting agent.
However, as a semiconducting agent, a group consisting of Y, La, Ce, Pr, Nd, Sm, Eu, Gd, Tb, Dy, Ho, Er, Tm, Yb, and Lu instead of Er (Er ₂ O ₃₎ It is also possible to use an oxide of at least one kind of rare earth element selected from the above.

Further, as other additives, MnCO ₃ (resistance-temperature coefficient improver) and SiO ₂ (sintering aid) were prepared.

Each above-mentioned raw material was prepared in a desired ratio and wet-pulverized and mixed with pure water and zirconia balls in a polyethylene pot to obtain a mixture slurry.
Next, the obtained mixture slurry was dehydrated and dried, and calcined at 1200 ° C.

  Thereafter, the binder was mixed and granulated, and the resulting granulated particles were molded by uniaxial pressing to obtain a disk-shaped molded body having a thickness of 2 mm and a diameter of 14 mm.

Next, the obtained molded body is placed in a sheath made of a material mainly composed of Al ₂ O ₃ , SiO ₂ , and ZrO, and fired (main firing) at 1380 ° C. for 1.5 hours in the air. Thus, a semiconductor ceramic body (a thermistor body having a positive resistance-temperature characteristic) was obtained.

Then, a pair of electrodes (Ni-Ag electrodes) 3a and 3b were formed on the front and back surfaces of the semiconductor ceramic body.
The Ni-Ag electrodes 3a and 3b were formed through a process of forming an Ni layer as an ohmic electrode layer and further forming an Ag layer as an outermost electrode layer on the Ni layer.

<Evaluation of resistance-temperature characteristics>
For each sample (PTC thermistor) thus prepared, the specific resistance (ρ _{25 °} C.) at room temperature (25 ° _C. ) and the resistance-temperature characteristics are measured, and the resistance is approximately double that shows a value close to the Curie temperature. The temperature (double point) and the resistance-temperature coefficient (α), which is an index of resistance-temperature characteristics, were clarified.

Note that the specific resistance value of the material (semiconductor ceramic body) varies greatly by changing the amount of addition of Er as a donor. Therefore, in order to enable comparison on the same standard, the specific resistance is set to a minimum value. The characteristics of the samples at the indicated Er amount (Er-ρ _min ) were compared.

Also, the resistance-temperature coefficient has an inclination of 10 to 100 times the resistance: α _10-100 as an index, and the resistivity generally changes exponentially. The higher the resistivity, the more the resistance-temperature coefficient. _Therefore , {α _10-100 / Log (ρ _{25 ° C.} )} was quantified and compared.

Table 1A, Table 1B, Table 1C, Table 1D, and Table 1E show the measurement results for each of the above samples. The ratio of Ti site to Ba site (Ti site / Ba site) (molar ratio) of each sample of Table 1A, Table 1B, Table 1C, Table 1D, and Table 1E is 1.00.
The ratio of Ti site to Ba site (Ti site / Ba site) is a mixing ratio determined by the formula: (Ti + Mn) / (Ba + Sr + Ca + donor (rare earth)).
Moreover, in Table 1A, Table 1B, Table 1C, Table 1D, and Table 1E, samples with “*” added to the sample numbers are samples of comparative examples that do not have the requirements of the present invention.

The following can be seen from Tables 1A to 1E showing the characteristics of the samples of each composition.
As shown in Table 1A, in the case of the samples Nos. 101 to 106 in which the Sr content in the semiconductor ceramic constituting the semiconductor ceramic body is 6.5 mol%, the Sr content is too small and {α _{10− 100} / Log (ρ _{25 ° C.} )} is not preferable in that the value is small (<10).

Moreover, as shown in Table 1E, among the samples Nos. 501 to 506 having a Sr content of 17.5 mol%, the Ca Nos. 501 to 503 having a Ca content (substitution amount) of 12.5 mol% In this case, the value of {α _10-100 / Log (ρ _{25 ° C.} )} is small (<10), and in the case of the samples of sample numbers 504 to 506 having a Ca content of 19.0 mol%, The specific resistance (ρ _{25 ° C.} ) at _{25 ° C.} is a high value, which is not preferable.

Further, in the case of samples Nos. 201 to 203, 217 to 219, 401 to 403, and 417 to 419 in which the Ca content is outside the range of the present invention, {α _10-100 / Log (ρ _{25 ° C.} ) } Is small, or the specific resistance (ρ _{25 °} C.) at room temperature (25 ° _C. ) is high.

Further, in the case of samples Nos. 204, 212, 404, and 412 whose Mn content (substitution amount) is lower than the range of the present invention, the value of {α _10-100 / Log (ρ _{25 ° C.} )} becomes small. Therefore, it is not preferable.

In addition, in the case of samples Nos. 208, 216, 408, and 416 in which the Mn content exceeds the range of the present invention, the specific resistance (ρ _{25 °} C.) at room temperature (25 ° _C. ) is a high value, which is not preferable. .

<Measurement of resistance change by mounting>
Further, in the composition of typical Sr amount, Ca amount, and Mn amount, as shown in Table 2A, Table 2B, and Table 2C, a predetermined Sr content (7.0 mol%, 12.0 mol%, 17.0 mol%) ), The Ti / Ba site ratio (molar ratio) was changed in the range of 0.980, 0.985, 1.000, 1.005, 1.010, and barium titanate semiconductor ceramics were produced. The Ti / Ba site ratio (molar ratio) is a blending ratio determined by the formula: (Ti + Mn) / (Ba + Sr + Ca + donor (rare earth)) as described above.

  And the positive characteristic thermistor (sample) of the size of a rectangular parallelepiped shape of 1.6 * 0.8 * 0.8mm was produced using the produced barium titanate semiconductor ceramic. The positive temperature coefficient thermistor (sample) is a single plate type PTC thermistor formed by providing external electrodes at both ends of a semiconductor ceramic.

And about each sample, after measuring each resistance, it mounted in the board | substrate. Then, the resistance after mounting was measured, and the rate of change in resistance before and after mounting (mounting ΔR) (%) was examined.
The mounting on the substrate was performed by a method of placing the sample on the substrate and performing reflow soldering at 260 ° C.

Tables 2A, 2B, and 2C show measurement results of the rate of change in resistance (mounting ΔR) (%) before and after mounting. In Tables 2A, 2B, and 2C, the Ti / Ba site ratio, Er-ρ _min , ρ _{25 ° C.} , double point, α _10-100 , and {α _10-100 / Log (ρ _{25 ° C.} )} Are also shown. In Tables 2A, 2B, and 2C, the samples with “*” in the sample numbers are comparative samples that do not have the requirements of the present invention.

As shown in Table 2A, Table 2B, and Table 2C, each sample number 601, 611, 621, 631, 641, 651, 661, 671, 681 has a Ti / Ba site ratio as small as 0.980, The sample was outside the scope of the present invention, and ρ25 _{° C.} was a high value (> 100 Ω · cm), which was confirmed to be undesirable.

In addition, each of the sample numbers 602 to 604, 612 to 614, 622 to 624, 632 to 634, 642 to 644, 652 to 654, 662 to 664, 672 to 674, 682 to 684 has a Ti / Ba site ratio. There is a sample having an appropriate value within a range of 0.985 to 1.005, the absolute value of mounting ΔR is as small as 10% or less, and the specific resistance (ρ _{25 °} C.) at room temperature (25 ° _C. ) is 100Ω. _-It was confirmed that the excellent characteristic that the value of {α _10-100 / Log (ρ _{25 ° C.} )} was 10 or more at a cm or less was realized.

In addition, each sample number 605, 615, 625, 635, 645, 655, 665, 675, 685 with a Ti / Ba site ratio of 1.010 has a resistance change rate (mounting ΔR) before and after mounting. The absolute value was 12.1 to 15.7%, which was a practical range, but was confirmed to be a little larger.
From the above results, it is preferable that the Ti / Ba site ratio is greater than 0.985 from the viewpoint of keeping the rate of change in resistance before and after mounting (mounting ΔR) low, and further, the Ti / Ba site ratio is 1. It can be seen that it is preferable not to exceed 010.

From the above embodiment, the barium titanate-based semiconductor ceramic according to the present invention can realize low room temperature resistance and high resistance and one temperature characteristic, and adjust the Ti / Ba site ratio to an appropriate range. Thus, it can be seen that the rate of change in resistance (mounting ΔR) before and after mounting can be reduced.
Therefore, by using the semiconductor ceramic composition of the present invention, a PTC thermistor with good characteristics can be provided.

  In the above embodiment, a single plate type PTC thermistor having a structure in which electrodes are formed on both main surfaces of a disk-shaped semiconductor ceramic body has been described as an example. However, there are no particular restrictions on the specific configuration of the PTC thermistor. However, various modifications can be made.

  The present invention is not limited to the above-described embodiment in other points, and various applications and modifications can be made within the scope of the present invention.

1 PTC thermistor 2 Semiconductor ceramic body 3a, 3b Electrode

Claims (3)

The molar ratio of Ba site to Ti site is 0.985 ≦ Ti site / Ba site,
Sr, Ca, and Mn 7.0 mol% ≦ Sr ≦ 17.0 mol% 12.5 mol% ≦ Ca ≦ 19.0 mol% 0.035 mol% ≦ Mn ≦ 0.074 mol%
A barium titanate-based semiconductor ceramic composition characterized by comprising: The molar ratio of Ba site to Ti site is
0.985 ≦ Ti site / Ba site ≦ 1.005
The barium titanate-based semiconductor ceramic composition according to claim 1, wherein the composition is in the range of   A PTC thermistor using the barium titanate-based semiconductor ceramic composition according to claim 1 or 2 as a thermistor element having a positive resistance-temperature characteristic.

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