JP2012020909A - Pyroelectric ceramic material - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a pyroelectric ceramic material which has a low dielectric constant εand a high Curie point Tc and achieves low-temperature sintering at 1,100°C or lower.SOLUTION: SiOof 0.1 mass% or more and 10 mass% or less is added as an accessory component to a principal component whose composition formula is represented by (Pb, Ca)(Ti, (SbNb))O(wherein, 0.08≤x≤0.24, and 0.001≤y≤0.5).

Description

  The present invention relates to a pyroelectric material, and more particularly to a pyroelectric material suitable for use in a surface-mounting pyroelectric infrared sensor.

  Conventionally, pyroelectric infrared sensors capable of detecting human movement have been widely applied in various fields such as crime prevention devices and home appliances. In recent years, awareness of environmental issues has increased worldwide, and human detection using pyroelectric infrared sensors has become an indispensable technology from the viewpoint of energy saving.

  Pyroelectric infrared sensor used as a part of functions of home appliances, etc., is required for downsizing and high sensitivity, and the pyroelectric device for pyroelectric infrared sensor has the performance of pyroelectric infrared sensor The sensitivity characteristic of the material is a very important parameter.

The detection sensitivity of the pyroelectric infrared sensor increases as the relative permittivity ε _r of the pyroelectric material decreases. For this reason, a pyroelectric material having a small relative dielectric constant ε _r such as lead titanate is required rather than a pyroelectric material having a large relative dielectric constant ε _r such as lead zirconate titanate.

In Patent Document 1, at least one selected from MnO, NiO, and Nb ₂ O ₅ is added to a composite perovskite structure represented by (Pb _1-x Ca _x ) TiO ₃ as a pyroelectric infrared detection element. A ceramic sintered body obtained by blending has been proposed. This ceramic sintered body has a large pyroelectric coefficient and a low relative dielectric constant, and has excellent characteristics as an infrared detecting element.

  Further, since the pyroelectric infrared sensor is often used in combination with other electronic devices, it is often used by being mounted on a printed circuit board simultaneously with other electronic components by a surface mounting technique. Therefore, since the pyroelectric infrared sensor passes through the reflow furnace and is used as a part of the electrical appliance or electronic device, the sensor sensitivity does not deteriorate even when heated to about 300 ° C., which is the lead solder melting temperature of the reflow furnace. It is demanded.

  Furthermore, in recent years, from the viewpoint of environmental protection, lead-free solder paste has been used, and the temperature of the reflow furnace needs to be higher than the conventional lead solder melting temperature.

  Normally, lead-free solder has a reflow furnace peak temperature set at about 280 ° C, but depending on the heat distribution of the reflow furnace, there are areas that can reach up to 300 ° C. The device is required to have a heat resistance of 300 ° C. or higher, preferably 340 ° C. or higher.

Japanese Unexamined Patent Publication No. 60-191054

  Conventional pyroelectric elements for pyroelectric infrared sensors generally have a Curie point Tc, which is a temperature at which polarization is depolarized, in the range of 200 ° C. When heat is applied in a reflow furnace during surface mounting, There is a problem that the polarization deteriorates and the characteristics deteriorate.

In such a background, there is an urgent need to develop a material that has a low relative dielectric constant ε _r and does not deteriorate the polarization of the pyroelectric element even at a high temperature of about 340 ° C.

  In the pyroelectric infrared detecting element of Patent Document 1, if the Ca substitution amount is increased in order to increase the detection sensitivity, the Curie point Tc decreases, and the polarization deteriorates due to the heat of the reflow furnace during surface mounting, resulting in a decrease in characteristics. Therefore, it is not suitable for a surface mount pyroelectric infrared sensor.

  In addition, lead titanate is usually sintered at a temperature of 1200 ° C. or higher, but at such temperatures, lead transpiration is remarkably different from the desired pyroelectric composition. Furthermore, since lead titanate has strong anisotropy, it is a material that cracks during sintering and sometimes breaks during standing after sintering. Considering these problems and mass productivity, it is desired to lower the sintering temperature, in particular, low temperature sintering at 1100 ° C. or lower.

The present invention has been made to solve the above-described problems, and provides a pyroelectric material that has a low relative dielectric constant ε _r and a high Curie point Tc and realizes low-temperature sintering at 1100 ° C. or lower. For the purpose.

To solve the problems described above, the present invention provides a composition formula _{(Pb (1-x),} Ca x) (Ti (1-y), (Sb 1/2 Nb 1/2) y) O 3 ( where , 0.08 ≦ x ≦ 0.24, 0.001 ≦ y ≦ 0.5), and a pyromagnetic component in which SiO ₂ is added in an amount of 0.1% by mass to 10% by mass as a subcomponent. an equipment cost, relative permittivity epsilon _r low, high Curie point Tc, the pyroelectric ceramic material is obtained that realizes low-temperature sintering at 1100 ° C. or less.

That is, according to the present invention, composition formula _{(Pb (1-x),} Ca x) (Ti (1-y), (Sb 1/2 Nb 1/2) y) O 3 ( where 0.08 ≦ x ≦ 0.24, 0.001 ≦ y ≦ 0.5), and SiO ₂ is added in an amount of 0.1% by mass to 10% by mass as a subcomponent. A ceramic material is obtained.

In the present invention, it is possible to provide a pyroelectric material that has a low relative dielectric constant ε _r and a high Curie point Tc and realizes low-temperature sintering at 1100 ° C. or lower.

The figure which shows the dielectric constant (epsilon) _r when Ca substitution amount x is changed. The figure which shows the Curie point Tc when changing Ca substitution amount x. The figure which shows the relationship between sintering temperature and density.

The pyroelectric material of the present invention has a composition formula of (Pb _(1-x) , Ca _x ) (Ti _(1-y) , (Sb _1/2 Nb _1/2 ) _y ) O ₃ (where 0. The main component represented by (08 ≦ x ≦ 0.24, 0.001 ≦ y ≦ 0.5) is characterized in that 0.1% by mass or more and 10% by mass or less of SiO ₂ is added as a subcomponent. . The value of x is the amount of Ca substitution for Pb. By increasing the amount of Ca substitution, the relative dielectric constant can be reduced. The value of y is the substitution amount of Sb _1/2 Nb _1/2 for Ti, and the Curie point Tc can be increased by increasing the substitution amount of Sb _1/2 Nb _1/2 . By increasing the amount of SiO ₂ added, the sinterability of the pyroelectric material is improved, the density peak of the sintered body is shifted to the low temperature side, and low temperature sintering becomes possible.

PbO, TiO ₂ , CaO, Nb ₂ O ₅ , Sb ₂ O ₃ , and SiO ₂ were weighed so as to have a target composition as the main component materials. This raw material powder was put into a nylon pot together with zirconia balls and wet mixed for 46 hours. This mixed powder was dehydrated and dried, and then pre-fired at 950 ° C. for 2 hours in an alumina bowl. This pre-baked powder was wet pulverized with zirconia balls in a nylon pot for 20 hours. Subsequently, it was dehydrated and dried, and a binder was mixed with the obtained pre-fired pulverized powder and pressed to form φ20 × 10 mm. This molded body was sintered at 1000 to 1250 ° C. and cut into a thickness of 1 mm with an outer peripheral blade cutter to obtain a disc. And silver paste was apply | coated to both surfaces of the processed disc, it baked at 450 degreeC, the electrode was formed, and it was set as the sample. The sample thus obtained was subjected to a polarization treatment in silicon oil at 180 ° C., 4 kV / mm for 15 minutes, and then returned to an environment at room temperature of 25 ° C.

FIG. 1 is a graph showing the relative dielectric constant ε _r when the Ca substitution amount x is changed. Here, the relative dielectric constant ε _r was determined when y = 0.01, the amount of SiO ₂ added was 0.1% by mass, and x was 0.07, 0.08, 0.10, 0.14. . The value of x is the molar ratio in terms of the amount of Ca substitution with respect to Pb. When this amount of Ca substitution is 0.14, the relative dielectric constant ε _r is as small as about 300. As the Ca substitution amount is increased from 0.07 to 0.14, the relative dielectric constant ε _r decreases, and it becomes a promising material from the viewpoint of detection sensitivity as a pyroelectric infrared sensor. It can be seen that as a pyroelectric material normally used as a pyroelectric infrared sensor, the relative dielectric constant ε _r is preferably 500 or less, and therefore x needs to be 0.08 or more.

FIG. 2 is a diagram showing the Curie point Tc when the Ca substitution amount x is changed. Here, the amount of SiO ₂ added is 0.1 mass%, the value of y is changed from 0 to 0.01, and the curie when x is 0.08, 0.15, 0.24, 0.40. A point Tc was determined. The value of y is the molar ratio of the substitution amount of Sb _1/2 Nb _{1/2 to} Ti. As shown in FIG. 2, the Curie point Tc decreases as the Ca substitution amount increases. In order to use as a pyroelectric infrared sensor corresponding to surface mounting, it is necessary that Tc is 340 ° C. or higher shown by a broken line in FIG. 2 so that polarization does not deteriorate even by heat of reflow. Therefore, x needs to be 0.24 or less.

Further, in FIG. 2, it can be seen that the Curie point Tc increases as y, which is the substitution amount of (Sb _1/2 Nb _1/2 ), is increased. Since the Curie point Tc needs to be 340 ° C. or higher, y needs to be 0.001 or higher. When the substitution amount of (Sb _1/2 Nb _1/2 ) is excessively blended, polarization tends to deteriorate and the pyroelectric effect tends to disappear. For this reason, y is required to be 0.5 or less, and is preferably 0.01 or less in consideration of application to a practical pyroelectric infrared sensor.

Further, by adding SiO ₂ to the above-described pyroelectric material, the sinterability of the pyroelectric material is improved, and low-temperature sintering becomes possible. FIG. 3 is a diagram showing the relationship between the firing temperature and the density. Here, the composition of the main component was x = 0.14 and y = 0.01. The density was shown when the addition amount of SiO ₂ was 0.1 mass% and 0.5 mass% and when SiO ₂ was not added (0 mass%). As shown in FIG. 3, the addition of SiO ₂ shifts the density peak to the low temperature side, and enables low temperature sintering at 1100 ° C. or lower. Here, in the case where SiO ₂ is not added in FIG. 3 (0% by mass), the density peak is taken at 1100 ° C., and therefore, the sintering is performed at a high temperature of 1100 ° C. or higher in consideration of variation in characteristics in the mass production process. There is a need to. For this reason, in order to perform low-temperature sintering at 1100 ° C., the addition amount of SiO ₂ needs to be 0.1 mass% or more. On the other hand, if SiO ₂ is added too much, the polarization tends to deteriorate and the pyroelectric effect tends to disappear. For this reason, the addition amount of SiO ₂ needs to be 10% by mass or less, and preferably 0.5% by mass or less in consideration of application as a practical pyroelectric infrared sensor.

Thus, according to the present invention, an excellent pyroelectric ceramic used for a surface-mounting pyroelectric infrared sensor that has a low relative dielectric constant ε _r and a high Curie point Tc and realizes low-temperature sintering at 1100 ° C. or lower. Material was obtained.

Claims (1)

The composition formula is (Pb _(1-x) , Ca _x ) (Ti _(1-y) , (Sb _1/2 Nb _1/2 ) _y ) O ₃ (where 0.08 ≦ x ≦ 0.24, 0 A pyroelectric material, wherein SiO ₂ is added in an amount of 0.1% by mass or more and 10% by mass or less as a subcomponent to the main component represented by .001 ≦ y ≦ 0.5).

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