KR20150067807A - Dielectric material for temperature compensation and method of preparing the same - Google Patents

Abstract

Provided are a dielectric material for temperature compensation represented by the following formula 1 and a preparing method thereof. [Formula 1] (Ba_1-a-b-3c/2Sr_aMg_bLa_c)(Ti_1-xSn_x)O_3 (Each of a, b, c and x in the formula 1 is as defined in the specification.)

Description

TECHNICAL FIELD [0001] The present invention relates to a dielectric material for temperature compensation and a manufacturing method thereof. BACKGROUND OF THE INVENTION < RTI ID = 0.0 >

The present invention relates to a temperature-compensating dielectric material having a large temperature coefficient and a large relative dielectric constant, but not containing lead, and a method for producing the same.

An LC tuned circuit including an inductor is mainly used as a driving circuit of a piezoelectric ultrasonic sensor. However, in order to maintain the driving waveform and driving efficiency in the LC synchronous driving circuit when the operating temperature range is as wide as -40 ° C to 80 ° C, such as an ultrasonic sensor for car parking assist, it is necessary to compensate for the capacitance change according to the temperature of the piezoelectric sensor Measures are needed.

The temperature coefficient of capacitance (TCC), which represents the temperature compensation factor of the capacitance temperature compensating material, is given at 25 ° C as follows.

TCC (ppm / ° C) = 10 ⁶ X (C _T -C ₂₅ / C ₂₅ ) / (T-25)

(T is the temperature, C _T and C ₂₅ are the capacitance at temperature T and 25 ° C, respectively).

PZT-5 soft piezoelectric materials are widely used as piezoelectric materials for piezoelectric ultrasonic sensors, which have a large piezoelectric constant and a small change over time. However, the material has a very large TCC of 2500 and 4000 ppm / DEG C in the range of -40 to 25 DEG C and 25 to 80 DEG C, and the relative dielectric constant is also very large, about 2,000 or so.

Most of piezoelectric elements for ultrasonic sensors are bonded to materials such as aluminum or polymer plastic with an adhesive such as epoxy. The TCC of the piezoelectric element thus bonded becomes larger due to the hardness change depending on the temperature of the adhesive. For example, the TCC according to the temperature characteristics of the adhesive may range from 6,000 to 10,000 ppm / ° C.

In the ultrasonic sensor, the temperature compensation element is mainly connected in parallel to the piezoelectric element. Therefore, in order to properly maintain the reception sensitivity of the ultrasonic sensor and to maintain the vibration attenuation characteristic of the transmission waveform, the size of the capacitance of the capacitance compensation element Should be selected accordingly. The capacitance of the compensating element is mainly set to about 30% to 70% of the capacitance of the piezoelectric element.

In a vehicle ultrasonic sensor, the temperature compensating element is built in the sensor structure mainly as in US Pat. No. 5,987,992 and the wires are soldered directly. The driving voltage of the ultrasonic sensor reaches 400 to 600 V / mm, and when the dielectric constant and the insulation distance for insulation are taken into consideration, there is a limit to increase the capacitance by reducing the thickness when the dielectric constant is small. Also, if the capacitance is increased by decreasing the thickness, the strength of the compensating element becomes weak, which makes handling difficult, and it becomes difficult to manufacture an ultrasonic sensor in which the temperature compensating element is integrated.

Therefore, in order to effectively reduce the size of the temperature-compensating device, ease of handling and manufacture, and effectively compensate the temperature of the piezoelectric ultrasonic sensor in a wide temperature range, a material having a temperature compensation ratio of about -5,000 to -30,000 ppm / .

Currently, materials for CaTiO ₃ -ZrTiO ₃ -SrTiO ₃ system are used as temperature-compensating dielectric materials for general circuits, but the temperature compensation ratio is from -5,000 to -6,000 ppm / ° C. and the relative dielectric constant is as small as about 200 to 800. US Patent 6,251,816 is BaTiO ₃ -CaZrO ₃ -ZnO-SiO has stopped the temperature coefficient of -5,000 to -15,000 ppm / ℃ degree in the composition the relative dielectric constant of 700 to 1,100 degree, but seen in the material of the _third series. US Patent No. 4,388,416 discloses a composition having a temperature coefficient of about -2,500 ppm / ° C in a material system based on Pb ₃ O ₄ -SrO-CaO-TiO ₂ -Bi ₂ O ₃ -MgO, but has a relative dielectric constant of less than 500 And contains Pb which is a harmful substance. U.S. Patent No. 3,660,124 shows a composition with a temperature coefficient of -8,700 ppm / ° C in a CaTiO ₃ -PbTiO ₃ -La ₂ O ₃ -TiO ₂ system, but has a relative dielectric constant of 1,000 or less and also contains Pb.

The present invention aims to provide a temperature-compensating dielectric material which does not use lead and which is capable of miniaturizing the temperature-compensating device and optimizing the temperature compensation of the piezoelectric ultrasonic sensor in a wide temperature range.

One embodiment provides a dielectric material for temperature compensation represented by the following formula (1).

[Chemical Formula 1]

(Ba _{1 -ab-3c / 2} Sr _a Mg _b La _c ) (Ti _{1 - x} Sn _x ) O ₃

(In the formula 1,

a, b, c and x are 0? a <0.20, 0 <b <0.05, 0 <c <0.01 and 0 <x <0.20, respectively.

The dielectric constant of the dielectric material for temperature compensation is such that the temperature coefficient of the dielectric constant obtained by the following formula (1) has a negative value in a temperature range of -40 to 25 占 폚 and a temperature range of 25 to 80 占 폚, 30,000 ppm / ° C.

[Equation 1]

Temperature coefficient of dielectric constant (TCC) (ppm / ° C) = 10 ⁶ X (C _T -C ₂₅ / C ₂₅ ) / (T-25)

(Where T is the temperature and C _T and C ₂₅ are the capacitance at the temperature T and 25 ° C, respectively, in the above equation (1)).

The temperature-compensating dielectric material may have a dielectric constant (based on 25 ° C) of 1,000 to 3,000, which is obtained from the following formula (2).

&Quot; (2) &quot;

Relative dielectric constant (K) =? /? ₀

(In the above equation (2),? Is the dielectric constant of the temperature-compensating dielectric material and? ₀ is the dielectric constant of the vacuum.)

According to another embodiment, the raw material containing BaCO ₃ , TiO ₂ , SnO ₂ , La ₂ O ₃ and MgO and optionally SrCO ₃ is mixed according to the composition ratio of Formula 1 to obtain a mixture; And sintering the mixture at a temperature of 1280 to 1360 캜 for 1 to 3 hours.

It is possible to optimize the temperature compensation of a piezoelectric ultrasonic sensor over a wide temperature range without using lead, which is a regulating material, by providing a dielectric material for temperature compensation that does not include lead and has a high dielectric constant and a high temperature compensation ratio. It can be downsized.

Hereinafter, embodiments of the present invention will be described in detail. However, it should be understood that the present invention is not limited thereto, and the present invention is only defined by the scope of the following claims.

The dielectric material for temperature compensation according to one embodiment may be a substance represented by the following formula (1).

[Chemical Formula 1]

(Ba _{1 -ab-3c / 2} Sr _a Mg _b La _c ) (Ti _{1 - x} Sn _x ) O ₃

(In the formula 1,

a, b, c and x are 0? a <0.20, 0 <b <0.05, 0 <c <0.01 and 0 <x <0.20, respectively.

The operating temperature of the ultrasonic sensor for automobile is -40 to 80 캜. In order to perform temperature compensation to the low temperature by using a BaTiO ₃ -based material, it is required to lower the Curie temperature (Tc) of BaTiO ₃ to below -40 ° C. When only strontium (Sr), which is mainly used for lowering Tc, is used, the dielectric constant at room temperature becomes too low. In one embodiment, the use of tin (Sn) and lanthanum (La) together with a BaTiO ₃ -based material not only reduces the effect of decreasing the dielectric constant while lowering the Tc, but also does not use lead (Pb) to be.

The temperature-compensating dielectric material having the above composition may have a negative temperature coefficient in a temperature range of -40 to 25 占 폚 and a temperature range of 25 to 80 占 폚, specifically, -5,000 to -30,000 ppm / [deg.] C. When the temperature-compensating dielectric material has a temperature coefficient within the above-mentioned range, it can have an excellent temperature compensation characteristic in a wide temperature range of -40 to 80 ° C, thereby optimizing the temperature compensation of the piezoelectric ultrasonic sensor, It is possible to downsize the size.

The temperature coefficient of the dielectric constant can be obtained from the following equation (1).

[Equation 1]

Temperature coefficient of dielectric constant (TCC) (ppm / ° C) = 10 ⁶ X (C _T -C ₂₅ / C ₂₅ ) / (T-25)

(Where T is the temperature and C _T and C ₂₅ are the capacitance at the temperature T and 25 ° C, respectively, in the above equation (1)).

The temperature-compensating dielectric material may have a dielectric constant (based on 25 ° C) of 1,000 to 3,000. When the temperature-compensating dielectric material has a relative dielectric constant within the range, it can have an excellent temperature compensation characteristic in a wide temperature range of -40 to 80 ° C, thereby optimizing the temperature compensation of the piezoelectric ultrasonic sensor, It is possible to downsize the size.

The relative dielectric constant can be obtained from the following equation (2) on the basis of 25 ° C.

&Quot; (2) &quot;

Relative dielectric constant (K) =? /? ₀

(In the above equation (2),? Is the dielectric constant of the temperature-compensating dielectric material and? ₀ is the dielectric constant of the vacuum.)

Compositions # 7 and # 8 and # 10 to # 12 in Table 1 correspond to the embodiment according to one embodiment, and Compositions # 1 to # 6 and # 9 are comparative examples. In Table 1, a, b, c, and x represent the composition ratios corresponding to the contents of Sr, Mg, La, and Sn in the above Formula 1, respectively.

As shown in the following Table 2, the specific dielectric constant at room temperature (25 ° C) is in the range of 1,500 to 2,500 as the contents of Sn, Sr, Mg and La are appropriately controlled within the range of one embodiment, The temperature coefficient of dielectric constant (TCC) can be about -9,200 to -30,000 ppm / DEG C. It can be understood that the temperature coefficient of normal temperature relative dielectric constant and permittivity can be adjusted as needed as the Sn content or the Sr content is increased or decreased within the range according to one embodiment. Compared with the prior art, the dielectric constant is high and the TCC is high without containing Pb, so that it is possible to effectively compensate the capacitance decrease of the piezoelectric sensor in a wide temperature range of -40 to 80 캜.

As shown in the following Tables 1 and 2, when only Sr is added as in the compositions 1 and 2, even when a is 0.5 or 0.6, Tc is not sufficiently low and TCC is too large, and Sr If the content is further increased, the dielectric constant at room temperature sharply decreases and it is not suitable as a piezoelectric element compensation material.

When Sn alone is added as in the compositions 3 to 5, the TCC is large or the dielectric constant is drastically decreased as in the case of adding only TCC.

The addition of La suppresses grain growth during sintering and can prevent a rapid decrease in dielectric constant while lowering Tc. When La is added, that is, when the content of La, that is, c is 0.01 or more, the sinterability is drastically lowered and the dielectric loss becomes too large, which makes the application difficult. However, if the sintering temperature is raised for sintering, all the La is solved into the particles, and the addition effect becomes insignificant. Accordingly, in one embodiment, the content of La and the range of c are limited to 0 < c < 0.01.

Addition of Mg has the effect of lowering Tc, increasing sinterability and decreasing TCC. As in the case of composition No. 6, when Mg was not added, the sintered density was low and the dielectric loss was large, which made it impossible to use. Accordingly, in one embodiment, the content of Mg and the range of b are limited to 0 < b < 0.05 in order to prevent a drastic decrease in the relative dielectric constant due to the addition of Mg.

The temperature-compensating dielectric material can be produced by the following method.

BaCO ₃ , TiO ₂ , SnO ₂ , La ₂ O ₃ and MgO, and optionally SrCO ₃ can be used as the base raw materials, and the base raw materials can be mixed in the composition ratio range of the above formula (1). Drying the mixture obtained by mixing, calcining the mixture, preparing a synthetic powder, and molding and sintering the mixture. The sintering may be carried out at a temperature of 1280 to 1360 캜 for 1 to 3 hours.

Specifically, the temperature-compensating dielectric materials shown in Table 1 were prepared in the following manner.

BaCO ₃ , TiO ₂ , SnO ₂ , SrCO ₃ , La ₂ O ₃ and MgO as basic raw materials were mixed with the deionized water and the dispersing agent in an artificial mill, Followed by vacuum filtration and drying at 80 to 120 ° C. As the dispersing agent, a nonionic dispersing agent and the like can be used and they are added in an amount of about 0.25% by weight. The dried cake was crushed and calcined at 1,100 ° C for 2 hours to synthesize the raw material. After crushing the calcined cake, the deionized water and the dispersant were added, and further pulverized, filtered and dried using an art mill to prepare a synthetic powder. 10% polyvinyl alcohol (PVA) solution was added to the synthetic powder and granulated by spraying to prepare granules for molding. The granules were molded into a 12 mm diameter and 1 mm thick by pressing, and then sintered at 1,300 ° C and 1,340 ° C for 2 hours, respectively To prepare a sintered body. Silver paste was printed on both sides of the sintered body, dried, and then heated at 820 ° C for 15 minutes to coat the silver electrode and measure its characteristics. Capacitance and dielectric loss were measured at 1 kHz, 1 V using an LCR meter and the compensation factor was measured in the range of -40 to 80 ° C using a constant temperature oven.

Composition number a b c x Remarks One 0.50 0 0 0 Comparative Example 1 2 0.60 0 0 0 Comparative Example 2 3 0 0 0 0.20 Comparative Example 3 4 0 0 0 0.25 Comparative Example 4 5 0 0 0 0.30 Comparative Example 5 6 0.08 0 0.006 0.10 Comparative Example 6 7 0.08 0.005 0.005 0.10 Example 1 8 0.08 0.005 0.0075 0.10 Example 2 9 0.08 0.005 0.01 0.10 Comparative Example 7 10 0.08 0.005 0.0083 0.10 Example 3 11 0.08 0.005 0.0065 0.125 Example 4 12 0.08 0.005 0.0065 0.15 Example 5

Composition number K (25 캜) tan? (25 占 폚) TCC (ppm / ° C) (-40 to 25 ° C) TCC (ppm / DEG C)
(25 to 80 ° C) Sintering temperature (℃) Remarks One 1,500 0.002 - - 1,300 Comparative Example 1 2 850 0.003  - 60,000 -3,600 1,300 Comparative Example 2 3 3,000 0.002 -61,000 -7,000 1,300 Comparative Example 3 4 1,400 0.003 -45,000 -7,300 1,300 Comparative Example 4 5 850 0.004 -16,000 -7,000 1,300 Comparative Example 5 6 1,100 0.25 - - 1,300 Comparative Example 6 7 1,700 0.003 -19,000 -8,600 1,300 Example 1 8 2,400 0.001 -30,000 -8,200 1,300 Example 2 9 1,160 0.155 - - 1,300 Comparative Example 7 10 1,500 0.004 -19,000 -8,500 1,300 Example 3 11 1,500 0.004 -9,200 -6,360 1,300 Example 4 12 2,300 0.003 -30,000 -10,000 1,300 Example 5 7 2,250 0.005 -21,500 -9,100 1,340 Example 6 8 2,250 0.004 -28,000 -10,000 1,340 Example 7 10 1,700 0.006 -15,000 -7,300 1,340 Example 8 11 1,630 0.005 -11,500 -6,400 1,340 Example 9 12 1,500 0.005 -20,000 -8,200 1,340 Example 10

In Table 2, in Comparative Example 1, the Tc was as high as -27 deg. C, so that it was not usable and data were not shown. In Comparative Examples 6 and 7, TCC was not measured because sinterability was poor. Also, in Table 2, the TCC was calculated from Equation (1), and K was calculated from Equation (2).

Through the above Tables 1 and 2, in the case of Examples 1 to 10 using the temperature-compensating dielectric material having the composition according to one embodiment, unlike Comparative Examples 1 to 7, the temperature coefficient of the dielectric constant ranges from -40 to 25 占 폚 And a value of -5,000 to -30,000 ppm / 占 폚 both in the temperature range of 25 to 80 占 폚, and has a relative dielectric constant of 1,000 to 3,000. As a result, it can be seen that the temperature compensation of the piezoelectric ultrasonic sensor can be optimized in a wide temperature range and the miniaturization of the temperature compensation element can be realized.

If the sintering temperature exceeds 1360 DEG C, a new phase is formed and TCC becomes excessively large. If the sintering temperature is lower than 1280 DEG C, the sintering is insufficient and the dielectric loss becomes large and the use becomes unsuitable.

While the present invention has been particularly shown and described with reference to exemplary embodiments thereof, it is to be understood that the invention is not limited to the disclosed exemplary embodiments, And falls within the scope of the invention.

Claims (5)

1. A temperature-compensating dielectric material represented by the following formula (1).
[Chemical Formula 1]
(Ba _{1 -ab-3c / 2} Sr _a Mg _b La _c ) (Ti _{1 - x} Sn _x ) O ₃
(In the formula 1,
a, b, c and x are 0? a <0.20, 0 <b <0.05, 0 <c <0.01 and 0 <x <0.20, respectively.
The method according to claim 1,
Wherein the temperature coefficient dielectric constant of the dielectric material for temperature compensation has a negative value in a temperature range of -40 to 25 占 폚 and a temperature range of 25 to 80 占 폚.
[Equation 1]
Temperature coefficient of dielectric constant (TCC) (ppm / ° C) = 10 ⁶ X (C _T -C ₂₅ / C ₂₅ ) / (T-25)
(Where T is the temperature and C _T and C ₂₅ are the capacitance at the temperature T and 25 ° C, respectively, in the above equation (1)).
The method according to claim 1,
The dielectric material for temperature compensation is a dielectric material for temperature compensation having a temperature coefficient of the dielectric constant obtained by the following formula (1) and having a value in the range of -40 to 25 占 폚 and a temperature range of 25 to 80 占 폚 in the range of -5,000 to -30,000 ppm / material.
[Equation 1]
Temperature coefficient of dielectric constant (TCC) (ppm / ° C) = 10 ⁶ X (C _T -C ₂₅ / C ₂₅ ) / (T-25)
(Where T is the temperature and C _T and C ₂₅ are the capacitance at the temperature T and 25 ° C, respectively, in the above equation (1)).
The method according to claim 1,
Wherein the temperature-compensating dielectric material has a relative dielectric constant (25 deg. C) obtained from the following formula (2): 1,000 to 3,000.
&Quot; (2) &quot;
Relative dielectric constant (K) =? /? ₀
(In the above equation (2),? Is the dielectric constant of the temperature-compensating dielectric material and? ₀ is the dielectric constant of the vacuum.)
Mixing a raw material containing BaCO ₃ , TiO ₂ , SnO ₂ , La ₂ O ₃ and MgO and optionally SrCO _{3 according} to a composition ratio of the following formula 1 to obtain a mixture; And
Sintering the mixture at a temperature of 1280 to 1360 DEG C for 1 to 3 hours
Of the dielectric material.
[Chemical Formula 1]
(Ba _{1 -ab-3c / 2} Sr _a Mg _b La _c ) (Ti _{1 - x} Sn _x ) O ₃
(In the formula 1,
a, b, c and x are 0? a <0.20, 0 <b <0.05, 0 <c <0.01 and 0 <x <0.20, respectively.