DE102014217742A1 - DIELECTRIC MATERIAL FOR TEMPERATURE COMPENSATION AND METHOD FOR THE PRODUCTION THEREOF - Google Patents

Abstract

The present invention provides a dielectric material for temperature compensation of Chemical Formula 1 and a process for its production. Chemical Formula 1 (Ba1-a-b-3c / 2SraMgbLac) (Ti1-x Snx) O3 In the above Chemical Formula 1, a is 0 ≦ a <0.20; b is 0 <b <0.05; c is 0 <c <0.01; and x is 0 <x <0.20 as defined in the detailed description.

Description

RELATED APPLICATIONS

This application claims priority to and the benefit of Korean Patent Application No. 10-2013-0152539 filed in the Korean Intellectual Property Office on Dec. 9, 2013, the entire contents of which are incorporated herein by reference.

TECHNICAL PART

The present invention relates to a dielectric material having a comparatively high temperature coefficient and a relatively high relative permittivity for temperature compensation without containing lead, and a method for producing the same.

BACKGROUND

A set LC circuit including an inductance is mainly used as a drive circuit in a piezoelectric ultrasonic wave sensor. However, a change in the electrostatic capacitance of the piezoelectric sensor based on a temperature must be compensated to maintain a drive waveform and drive efficiency in the adjusted LC driver circuit when the adjusted LC drive circuit is in a wide temperature range of about -40 ° C to about 80 ° ° C is used, for example in an ultrasonic wave sensor for a parking aid for vehicles.

A temperature coefficient of capacitance (TCC) denotes a temperature compensation rate of a temperature compensation material having electrostatic capacity up to a reference temperature of 25 ° C and is provided as follows: TCC (ppm / ° C) = 10 ⁶ × (C _T - C ₂₅ / C ₂₅ ) / (T - 25) where T denotes a temperature in Celsius (° C) and C _T and C ₂₅ respectively denote the electrostatic capacity at each temperature T and about 25 ° C.

A piezoelectric material used for the piezoelectric ultrasonic wave sensor typically includes a lead zirconium titanate (or PZT) 5-based soft piezoelectric material having a high piezoelectric constant and a low frequency of aging. However, the PZT-5-based soft piezoelectric material may have a relatively high TCC in the range of about 2,500 to about 4,000 ppm / ° C at a temperature of about -40 to about 25 ° C and about 25 to about 80 ° C and also a have relatively high relative permittivity of about 2,000 or more.

A piezoelectric device for the ultrasonic wave sensor can be usually adhered to a material such as aluminum, a polymer plastic and the like using an adhesive such as epoxy and the like. Thus, such a piezoelectric device may have a significantly higher TCC due to a change in hardness depending on a temperature of the adhesive. For example, the TCC, which depends on the temperature characteristics of an adhesive, can range from about 6,000 to about 10,000 ppm / ° C. The piezoelectric device may be connected in parallel with a temperature compensation device in the ultrasonic wave sensor. Accordingly, a compensation device having an electrostatic capacitance may have a range of electrostatic capacitance appropriately selected in view of a compensation rate so as to minimize a transmission-type oscillation reduction characteristic and to maintain the reception sensitivity of the ultrasonic wave sensor. Therefore, the compensation device may have an electrostatic capacity in a range of about 30% to about 70% of the electrostatic capacity of the piezoelectric device.

The temperature compensation device in an ultrasonic wave sensor for a vehicle has been constantly developed. In one example, such a temperature compensation device may be internally incorporated into a sensor structure, and a wire may be directly soldered thereto. Since the ultrasonic wave sensor requires a driving voltage of about 400 to about 600 V / mm, increasing the electrostatic capacitance can be limited by reducing a thickness when the relative permittivity in view of an internal insulation pressure, a separation distance of successive surfaces for insulation and the like is small. In addition, when the electrostatic capacitance is increased by reducing the thickness, the temperature compensating device may have a substantially small thickness, and its handling and further the formation of an integrated body with the ultrasonic wave sensor may become difficult.

Accordingly, in order to downsize and easily handle or fabricate the temperature compensation device or to obtain effective temperature compensation of the ultrasonic piezoelectric wave sensor in a wide temperature range, dielectric material having a temperature compensation rate of about -5,000 to about -30,000 ppm / ° C and a relative permittivity of more than or equal to about 1000 may be required.

The currently used dielectric materials for temperature compensation for a conventional circuit may include a calcium titanate (CaTiO ₃ ) zirconium titanate (ZrTiO ₃ ) strontium titanate (SrTiO ₃ ) based material, but have a temperature compensation rate of about -5,000 to at most about -6,000 ppm / ° C and a relative permittivity of about 200 to about 800. In some examples, a barium titanate (BaTiO ₃ ) calcium zirconate (CaZrO ₃ ) zinc oxide (ZnO) silicate (SiO ₃ ) -based material having a temperature coefficient of capacitance (TCC) of about -5,000 to about -15,000 ppm / ° C, however, whose relative permittivity may be about 700 to about 1,100. In another example, a lead oxide (Pb ₃ O ₄ ) -strontium oxide (SrO) -calcium oxide (CaO) -titanium oxide (TiO ₂ -) bismuth oxide (Bi ₂ O ₃ -) magnesia (MgO) -based material was used with a temperature coefficient of capacitance (TCC) of about -2,500 ppm / ° C and a relative permittivity of less than or equal to about 500. However, such materials may include toxic lead (Pb). In another example, a calcium titanate (CaTiO ₃ ) lead titanate (PbTiO ₃ ) lanthanum oxide (La ₂ O ₃ ) titanium oxide (TiO ₂ ) -based material having a temperature coefficient of capacitance of about -8,700 ppm / ° C mentioned. However, its relative permittivity may be less than or equal to about 1,000, and Pb may also be included.

The above information disclosed in this section is only for the better understanding of the background of the invention and therefore may contain information that does not form the prior art, which is already known in this country to a person skilled in the art.

SUMMARY

An exemplary embodiment of the present invention provides a dielectric material for temperature compensation with a high dielectric constant and a high temperature compensation rate without containing lead; and further, the dielectric material can optimize the temperature compensation of a piezoelectric ultrasonic wave sensor in a wide temperature range, whereby it can downsize a temperature compensation device.

An exemplary embodiment of the present invention provides a dielectric material for temperature compensation with Chemical Formula 1.

Chemical formula 1

• (Ba _{lab-3c / 2} Sr _a Mg _b La _c ) (Ti _1-x Sn _x ) O ₃

In the above chemical formula 1, a is 0 ≦ a <0.20; b is 0 <b <0.05; c is 0 <c <0.01; and x is 0 <x <0.20.

In another exemplary embodiment, the dielectric material for temperature compensation may have a negative (-) value of a temperature coefficient of capacitance (TCC), which is from Equation 1 in the two temperature ranges from about -40 to about 25 ° C and about 25 to about 80 ° C was obtained. In addition, the temperature coefficient of the capacitance may be about -5,000 to about -30,000 ppm / ° C.

Equation 1

• Temperature coefficient of capacitance (TCC) (ppm / ° C) = 10 ⁶ × (C _T - C ₂₅ / C ₂₅ ) / (T - 25)

In Equation 1, T denotes a temperature in Celsius (° C), and C _T and C ₂₅ respectively denote the electrostatic capacity at each temperature T and approximately 25 ° C.

In another exemplary embodiment, the temperature compensation dielectric material may have a relative permittivity in the range of about 1,000 to about 3,000 according to [Equation 2 (at a reference temperature of 25 ° C).

Equation 2

• Relative permittivity (K) = ε / ε ₀

In Equation 2, ε denotes a dielectric constant of a dielectric material for temperature compensation, and ε ₀ denotes a dielectric constant of the vacuum.

Another exemplary embodiment of the present invention provides a method of making a dielectric material for temperature compensation which comprises preparing a mixture including barium carbonate (BaCO ₃ ), titanium dioxide (TiO ₂ ), tin dioxide (SnO ₂ ), lanthanum oxide (La ₂ O ₃ ). and magnesium oxide (MgO) and optionally strontium carbonate (SrCO ₃ ) corresponding to a composition ratio provided in Chemical Formula 1; and sintering the mixture at a temperature in the range of about 1280 to about 1360 ° C for about 1 to about 3 hours.

The present invention provides the dielectric material for temperature compensation which contains no lead but has a high dielectric constant and a high temperature compensation rate. Thus, the dielectric material of the present invention can control the temperature compensation of the piezoelectric ultrasonic wave sensor in a wide temperature range without using a limited material, i. H. Lead, optimize and further reduce the temperature compensation device.

DETAILED DESCRIPTION

It should be understood that the term "vehicle" or "vehicle-related" or other similar term as used herein includes motor vehicles in general, such as, for example, motor vehicles. Passenger cars including all-terrain sports cars (SUV), buses, trucks, various commercial vehicles, watercraft including a variety of boats and ships, aircraft and the like, and hybrid vehicles, electric vehicles, plug-in hybrid electric vehicles, hydrogen powered vehicles, and others vehicles fueled by alternative fuels (eg fuels derived from resources other than oil).

The terminology used herein is for the purpose of describing specific embodiments only and is not intended to limit the invention. As used herein, the singular forms "a, a" and "the" are also meant to include the plural forms unless the context clearly indicates otherwise. It will further be understood that the terms "comprises" and / or "comprising" when used in this specification specify the presence of the specified features, integers, steps, operations, elements and / or components, but not the presence or absence thereof Add one or more features, integers, steps, operations, elements, components, and / or their groups. The term "and / or" as used herein includes all combinations of one or more of the associated listed terms.

Unless specifically stated or obvious from context, the term "about" as used herein is to be understood as within a range of normal tolerance in the art, for example, within 2 standard deviations of the mean. "About" can be considered within 10%, 9%, 8%, 7%, 6%, 5%, 4%, 3%, 2%, 1%, 0.5%, 0.1%, 0.05% or 0.01% of the listed value. Unless otherwise apparent from the context, all numerical values provided herein are modified by the term "about".

Hereinafter, embodiments will be described in detail. However, these embodiments are exemplary, and the disclosure is not limited thereto.

In an exemplary embodiment of the present invention, a temperature compensation dielectric material may be a material represented by Chemical Formula I.

Chemical formula 1

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

In Chemical Formula 1, a is 0 ≤ a <0.20, b is 0 <b <0.05; c is 0 <c <0.01; and x is 0 <x <0.20. An ultrasonic wave sensor for a vehicle is operated in a temperature range of about -40 to about 80 ° C. To compensate for a substantially lower temperature reduction in temperature using BaTiO ₃ -based material, a Curie temperature (Tc) of the BaTiO _{3 can be} reduced to less than or equal to about -40 ° C. When the Tc is reduced by using strontium (Sr), a dielectric constant at room temperature may decrease. Therefore, in an exemplary embodiment of the present invention, the BaTiO ₃ -based material may be used together with tin (Sn) and lanthanum (La). Thus, the Tc can be reduced, and a reduction effect of a dielectric constant can be reduced. Furthermore, toxic material such as lead (Pb) must not be used, thereby providing environmentally friendly dielectric materials for temperature compensation.

In another exemplary embodiment, the temperature compensation dielectric material having the composition of the Chemical Formula I may have a negative (-) value of the temperature coefficient of capacitance in a temperature range of about -40 to about 25 ° C and about 25 to about 80 ° C , In particular, the temperature coefficient of the capacitance may be about -5,000 to about -30,000 ppm / ° C. When the temperature compensation dielectric material has a temperature coefficient within the range, it can have excellent temperature compensation characteristics in a wide temperature range between about -40 to about 80 ° C. Accordingly, the dielectric material of the present invention can optimize temperature compensation of a piezoelectric ultrasonic wave sensor and further reduce the temperature compensation device.

In addition, the temperature coefficient of the capacitance can be obtained according to Equation 1.

Equation 1

• Temperature coefficient of capacity (ppm / ° C) = 10 ⁶ × (C _T - C ₂₅ / C ₂₅ ) / (T - 25)

In Equation 1, T denotes a temperature (° C), and C _T and C ₂₅ respectively denote the electrostatic capacity at each temperature T and about 25 ° C.

In addition, the temperature compensation dielectric material may have a relative permittivity in a range of about 1,000 to about 3,000 (at a reference temperature of 25 ° C). When the temperature compensation dielectric material has a relative permittivity within the range, it can have improved temperature compensation characteristics in a wide temperature range of about -40 to about 80 ° C. Accordingly, the dielectric material of the present invention can optimize the temperature compensation of a piezoelectric ultrasonic wave sensor and further reduce the temperature compensation device.

Further, the relative permittivity according to Equation 2 can be obtained at a reference temperature of 25 ° C.

Equation 2

• Relative permittivity (K) = ε / ε ₀

In Equation 2, ε denotes a dielectric constant of the dielectric material for temperature compensation, and ε ₀ denotes a dielectric constant of the vacuum.

In the following Table 1, compositions 7, 8 and 10 to 12 correspond to examples according to exemplary embodiments of the present invention, while compositions 1 to 6 and 9 correspond to comparative examples according to conventional materials. In addition, a, b, c and x in Table 1 each denote a composition ratio corresponding respectively to the content of Sr, Mg, La and Sn of Chemical Formula 1.

As shown in the following Table 2, the respective contents of Sn, Sr, Mg, and La within a range according to an exemplary embodiment may be set to have a relative permittivity of about 1,500 to about 2,500 at room temperature; and a temperature coefficient of capacitance (TCC) of about -9,200 to about -30,000 ppm / ° C at a temperature of about -40 to about 25 ° C. The relative permittivity at room temperature and the temperature coefficient of capacity can be adjusted by increasing or decreasing the content of Sn or Sr within a range according to an exemplary embodiment, if necessary. Accordingly, the temperature compensation dielectric material according to an exemplary embodiment may not include Pb, but may have such a high dielectric constant and a high TCC of about -40 to about 80 ° C that compares the decrease in the electrostatic capacity of a piezoelectric sensor in a wide temperature range can be effectively compensated with conventional dielectric materials.

As shown in Tables 1 and 2, Tc is not sufficiently low when only Sr is used as in Compositions 1 and 2; however, the TCC may be relatively high (eg, above a threshold) even when a is about 0.5 or about 0.6. However, when the content of Sr as in the composition 2 is increased, the dielectric constant at room temperature may deteriorate considerably and may not be suitable for the compensation material of the piezoelectric device. When only Sn is included as in compositions 3 to 5, the compositions containing only Sn may have a relatively high TCC or a significantly deteriorated dielectric constant, similar to the composition containing only Sr.

The addition of La can suppress particle growth during sintering and, in addition to reducing Tc, can prevent the substantial deterioration of a dielectric constant. When La is added, the content of La, c, is greater than or equal to about 0.01; a sintering property may deteriorate significantly, causing a very high dielectric loss. However, when a sintering temperature is increased, most of the La may solidify into a particle and have a very small effect. Accordingly, the content of La according to an exemplary embodiment of the present invention may be in a range of 0 <c <0.01.

The addition of Mg can lower the Tc, increase a sintering property, and lower the TCC. If Mg is not included as in the composition 6, a sintering density may decrease and a dielectric loss may increase. Accordingly, the content of Mg may be in a range of about 0 <b <0.05 to prevent a marked decrease in relative permittivity. The dielectric material for temperature compensation can be manufactured according to the following method.

The mixture comprising BaCO ₃ , TiO ₂ , SnO ₂ , La ₂ O ₃ and MgO, and optionally SrCO ₃ can be prepared according to the range of the composition ratio provided in Chemical Formula 1. The resulting mixture may be dried and calcined to produce synthesized powder and then molded and sintered. In particular, the sintering may be carried out at a temperature of about 1280 to about 1360 ° C for about 1 to about 3 hours. In particular, a temperature compensation dielectric material as provided in Table 1 can be prepared. A mixture containing BaCO ₃ , TiO ₂ , SnO ₂ , SrCO ₃ , La ₂ O ₃ and MgO can be uniformly prepared according to the composition ratio as provided in Table 1 in a friction mill by adding deionized water and a dispersant. The mixture may be vacuum filtered and dried at about 80 to about 120 ° C. The dispersant may contain a non-ion-based dispersant and the like in a weight ratio of about 0.25%. The dried cake is broken and calcined at about 1100 ° C for about 2 hours to synthesize the raw materials. After the crushing of the calcined cake, deionized water and the dispersing agent are added, and the mixture may be pulverized, filtered and dried in the attrition mill, thereby preparing a synthesized powder. A polyvinyl alcohol (PVA) solution of about 10 w / w% can be added to the synthesized powder.

The mixture may be spray granulated for molding into granules, and the granules may be pressed and shaped to have a diameter of about 12 mm and a thickness of about 1 mm. Then, the granulated mixture may be sintered at about 1300 ° C or about 1340 ° C for 2 hours to prepare a pellet. Both sides of the pellet can be printed with silver paste; the printed pellet can be dried and heated at about 820 ° C for about 15 minutes to place a silver electrode thereon; and the properties of the electrode are measured. The electrostatic capacity and the dielectric loss of the electrode are used at 1 kHz and 1V of an LCR meter (Agilent, 4263B), and the rate of compensation of the dielectric material is measured at a temperature in a range of about -40 to about 80 ° C in a thermostatic oven. Table 1 Composition no. a b c x annotation 1 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 8th 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 Example3 11 0.08 0.005 0.0065 0,125 Example4 12 0.08 0.005 0.0065 0.15 Example5 Table 2

Since Comparative Example 1 has a very high Tc of about -27 ° C, the TCCs in Table 1 can not be provided. Further, since Comparative Examples 6 and 7 show insufficient sintering properties, their TCC was not measured. In addition, the TCC values in Table 2 can be calculated according to Equation 1, and the K values can be calculated according to Equation 2.

With reference to Tables 1 and 2, in contrast to Comparative Examples 1 to 7, each of Examples 1 to 10 using a temperature compensation dielectric material according to an exemplary embodiment of the present invention exhibits the temperature coefficient of capacitance in the range of approximately -5,000 to approximately -30,000 ppm / ° C in the two temperature ranges from about -40 to about 25 ° C and about 25 to about 80 ° C and a relative permittivity of about 1,000 to about 3,000. Accordingly, Examples 1 to 10 can optimize the temperature compensation of a piezoelectric ultrasonic wave sensor in a wide temperature range and further reduce the temperature compensation device.

In addition, if the sintering temperature is more than about 1360 ° C, a new phase can be formed and the TCC increases. However, if the sintering temperature is less than about 1280 ° C, the sintering may be insufficient and cause an unduly high dielectric loss.

While this disclosure has been described in conjunction with what is presently considered exemplary embodiments, it is to be understood that the invention is not limited to the disclosed embodiments, but on the contrary, is intended to cover various modifications and equivalent arrangements within the spirit and scope of the appended claims ,

Claims (5)

Dielectric material for temperature compensation of Chemical Formula 1: (Ba _{1-ab-3c / 2} Sr _a Mg _b La _c ) (Ti ₁ -x Sn _x ) O ₃ wherein in Chemical Formula 1 a is 0 ≤ a <0.20; b is 0 <b <0.05; c is 0 <c <0.01; and x is 0 <x <0.20. The dielectric material for temperature compensation of claim 1, wherein the dielectric material has a negative (-) value of a temperature coefficient of capacitance (TCC) according to Equation 1 in the two temperature ranges of about -40 to about 25 ° C and about 25 to about 80 ° C having; Temperature coefficient of capacitance (TCC) (ppm / ° C) = 10 ⁶ × (C _T - C ₂₅ / C ₂₅ ) / (T - 25); and wherein in equation 1 T denotes a temperature (° C) and C _T and C ₂₅ respectively denote the electrostatic capacity at each temperature T and 25 ° C. The dielectric material for temperature compensation according to claim 2, wherein the dielectric material has the temperature coefficient of capacitance (TCC) of about -5,000 to about -30,000 ppm / ° C according to equation 1 in the two temperature ranges of about -40 to about 25 ° C and about 25 to about 80 ° C. The dielectric material for temperature compensation of claim 1, wherein the dielectric material has a relative permittivity of about 1,000 to about 3,000 according to equation 2 at a reference temperature of 25 ° C: Relative permittivity (K) = ε / ε ₀ ; wherein in equation 2 ε denotes a dielectric constant of the dielectric material for temperature compensation and ε ₀ denotes a dielectric constant of the vacuum. A method of making a temperature compensating dielectric material comprising: preparing a mixture comprising barium carbonate (BaCO ₃ ), titanium dioxide (TiO ₂ ), tin dioxide (SnO ₂ ), lanthanum oxide (La ₂ O ₃ ), and magnesium oxide (MgO) and optionally strontium carbonate ( SrCO ₃ ) in a composition ratio provided in Chemical Formula 1; and sintering the mixture at a temperature of about 1280 to about 1360 ° C for about 1 to 3 hours: (Ba _{1 -ab-3c / 2} Sr _a Mg _b La _c ) (Ti ₁ -x Sn _x ) O ₃ wherein a is 0 ≤ a <0.20; b is 0 <b <0.05; c is 0 <c <0.01; and x is 0 <x <0.20.