KR100742239B1 - Piezoelectric ceramics - Google Patents

Abstract

Provided is a composition of piezoelectric ceramics sintered at a low temperature and being superior in piezoelectric properties to be applied to a multi layer piezoelectric transformer. The composition of piezoelectric ceramics is prepared by adding Pb[(Mn1/3Nb2/3)O3 - Pb(Zn1/3Nb2/3)O3 - Pb(Zr, Ti)O3 with at least one of Li2CO3, Bi2O3, and CuO. Preferably, the Pb[(Mn1/3Nb2/3)0.07 (Zn1/3Nb2/3)a(Zr0.48Ti0.52)1-0.07-aO3] + xwt.%Li2CO3 + ywt.%Bi2O3 + zwt.%CuO, wherein a is a value between 0.02 and 0.16, x is a value between 0 and 3, y is a value between 0 and 3, and z is a value between 0 and 3, x, y, and z not being zero. Li2CO3, Bi2O3, and CuO are used as a sintering additive for low-temperature sintering of the composition.

Description

Piezoelectric Ceramics Composition {PIEZOELECTRIC CERAMICS}

1 is a graph showing the sintered density change of the specimen according to the substitution amount and sintering temperature change of the PZN in one embodiment of the present invention.

2 is a graph showing the change in dielectric constant according to the PZN substitution amount and the sintering temperature change in one embodiment of the present invention.

Figure 3 is a graph showing the change in the electromechanical coupling coefficient according to the PZN substitution amount and the sintering temperature change in one embodiment of the present invention.

4 is a graph showing a change in the mechanical quality factor according to the PZN substitution amount and the sintering temperature change in one embodiment of the present invention.

5A is a schematic structural diagram of a laminated piezoelectric transformer manufactured in an embodiment of the present invention.

Figure 5b is a photograph of the internal electrode used when printing the internal electrode in Figure 5a.

5C is a photograph of FIG. 5A.

Figure 6 is an electron micrograph of the cross section of the multilayer transformer produced in another embodiment of the present invention.

Figure 7 is a graph showing the impedance characteristics of the multilayer piezoelectric transformer manufactured in another embodiment of the present invention.

FIG. 8 is a graph illustrating a boost ratio according to a frequency and a load resistance in a state in which an input voltage of a multilayer piezoelectric transformer is constantly maintained.

9 is a graph showing the efficiency according to the load resistance in the multilayer piezoelectric transformer manufactured in another embodiment of the present invention.

10 is a graph showing the output power according to the input voltage and the load resistance at the resonant frequency of the multilayer piezoelectric transformer manufactured in another embodiment of the present invention.

FIG. 11 is a graph illustrating a result of temperature rise measured after driving for 20 minutes at each output power according to load resistance in the multilayer piezoelectric transformer manufactured in another embodiment of the present invention. FIG.

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic composition, and more particularly, to a piezoelectric ceramic composition suitable for application to a laminated piezoelectric transformer, having excellent piezoelectric properties while having a low sintering temperature.

Recently, since the piezoelectric transformer can be applied to the TFT-LCD backlight driving inverter, research has been actively conducted on the development of the composition that can be applied to the piezoelectric transformer and evaluation methods.

These piezoelectric transformers have a wide range of applications, such as LCD displays, DC-DC converters, AC-DC converters, and other high voltage power supplies, which are growing rapidly in the IT industry.

Piezoelectric transformers have no leakage flux compared to conventional winding transformers, and use only resonant frequency. Therefore, the output waveform is close to sinusoidal waveform, so there is no harmonic noise, and it has the advantage of incombustibility. In particular, it is possible to miniaturize, slim, and lightweight, and obtain high efficiency of 90% or more.

Recently, in order to improve the output limit of a single plate piezoelectric transformer, a multilayer piezoelectric transformer capable of obtaining a high boost ratio and a high output has been proposed. However, there are various problems in manufacturing a laminated piezoelectric transformer as compared to the single plate piezoelectric transformer.

That is, high mechanical quality factor (Q _m ) and electromechanical coupling factor (k _p ) are required for practical use of piezoelectric transformers. In addition, since the structure of the stacked device includes metal electrodes therein, calcination at a high temperature is a problem in the manufacturing process. In order to perform sintering together with the internal electrodes of these metals at a high temperature of 1200 ° C. After all, an expensive electrode with high Pd content should be used.

Therefore, in order to use Ag / Pd electrode having a low Pd content, it is essential to develop a composition capable of low temperature sintering. In addition, even from an environmentally friendly point of view, low-temperature firing can suppress the volatilization of PbO, which is essential for preventing environmental pollution.

Accordingly, the present invention was devised to solve the above problems, and an object of the present invention is Pb (Mn _1/3 Nb _2/3 ) O ₃ -Pb (Zn _1/3 Nb _2/3 ) O _3- By adding at least one of Li ₂ CO ₃ , Bi ₂ O ₃ , CuO as a sintering accelerator to Pb (Zr, Ti) O ₃ -based ceramics, it has a low firing temperature and excellent piezoelectric properties. It is to provide a suitable piezoelectric ceramic composition.

In order to achieve the above object, the piezoelectric ceramic composition according to the present invention is a composition formula Pb [(Mn _1/3 Nb _2/3 ) _0.07 (Zn _1/3 Nb _2/3 ) _a (Zr _0.48 Ti _0.52 ) _{1-0.07 -a} O ₃ ] + xwt% Li ₂ CO ₃ + ywt% Bi ₂ O ₃ + zwt% CuO (where: 0.02 ≦ a ≦ 0.16, 0 <x ≦ 3, 0 <y ≦ 3, 0 <z ≦ 3) It is a ceramic composition, It is characterized by the above-mentioned.

Hereinafter, with reference to the accompanying drawings, the present invention will be described in detail.

delete

Typically, Pb (Mn _1/3 Nb _2/3 ) O ₃ (hereinafter “PMN”)-Pb (Zr _1/3 Ti _2/3 ) O ₃ (hereinafter “PZT”) based ceramics have very high mechanical quality. It is a composition known to exhibit coefficients. In addition, Pb (Zn _1/3 Nb _2/3 ) O ₃ (hereinafter “PZN”)-Pb (Zr, Ti) O ₃ based ceramics are compositions known to have high electromechanical coupling coefficients.

Therefore, according to the present invention, ceramics having improved mechanical quality coefficients and electromechanical coupling coefficients may be manufactured by synthesizing the two ceramics. This can be achieved by substituting PZN for the PMN-PZT, and the basic composition of the piezoelectric ceramic composition according to the present invention is shown in Equation 1;

_{Pb [(Mn 1/3 Nb} 2/3) 0.07 (Zn 1/3 Nb 2/3) a (Zr 0.48 Ti 0 .52) 1-0.07- a O 3] ( Equation 1)

In this case, a represents mol% of PZN to be substituted, and its value is preferably set to 0.02 to 0.16.

In the present invention, at least any one of 0 to 3.0 wt% Li ₂ CO ₃ , 0 to 3.0 wt% Bi ₂ O ₃ , and 0 to 3.0 wt% CuO as a sintering aid for low temperature sintering of the piezoelectric ceramic composition. It is preferred that one or more are added. At this time, according to a preferred embodiment of the present invention 0.1wt% Li ₂ CO ₃ and 0.3wt% Bi ₂ O ₃ and 0.3wt% CuO are added simultaneously as the sintering aid. According to the addition of such a sintering aid, the sintering temperature of 1200 ° C., which is the firing temperature of the Pb series, can be lowered to the sintering temperature of about 940 ° C. to 1000 ° C.

Hereinafter, preferred embodiments of the present invention will be described in more detail with reference to the accompanying drawings. However, the embodiments described below are provided to assist the overall understanding of the present invention, and the present invention is not limited to the above embodiments.

Example 1

In this example, each specimen was prepared by using an oxide mixing method with the following formula 2 as a composition;

_{Pb [(Mn 1/3 Nb} 2/3) 0.07 (Zn 1/3 Nb 2/3) a (Zr 0.48 Ti 0 .52) 1-0.07- a O 3] + 0.1wt% Li 2 CO 3 +0. 3wt% Bi ₂ O ₃ + 0.3wt% CuO (where a = 0.02 ~ 0.16) (Equation 2)

First, the exact molar ratio of the sample according to the base composition formula _{Pb [(Mn 1/3 Nb} 2/3) 0.07 (Zn 1/3 Nb 2/3) a (Zr 0.48 Ti 0 .52) 1-0.07- a O 3] Basis to 10 ^-4 , acetone was mixed and ground for 24 hours using a ball mill as a dispersion medium, dried in a thermostat and then calcined at 850 ℃ for 2 hours. After calcining, 0.1 wt% Li ₂ CO ₃ +0.3 wt% Bi ₂ O ₃ + 0.3 wt% CuO was added thereto, followed by remixing and grinding for 24 hours, and then 5 wt% of PVA (Polyvinyl Alcohol: 5% aqueous solution) was added as a binder. In order to prepare as a k _p mode, the mold was molded by applying a pressure of 1 [ton / cm 2] to a diameter 21 [mmφ] molder. The molded specimen was subjected to a burnout (B / O) process of the binder for 3 hours at a temperature of 600 ° C., and sintered at temperatures of 1000, 970, and 940 ° C., respectively. After sintering, the specimen was polished to a thickness of 1 [mm] for the measurement of properties, and Ag paste was applied and heat-treated at 650 ° C. for 10 minutes. The specimen on which the electrode was formed was polarized by applying an electric field of 30 [㎸ / cm] for 30 minutes in 120 degreeC silicone oil. After 24 hours, dielectric and piezoelectric properties were measured using an impedance analyzer (Agilent, 4294A) according to the resonance and antiresonance method.

1 is a graph showing the sintered density change of the specimen according to the substitution amount and the sintering temperature change of the PZN in the present embodiment.

At the sintering temperature of 940 ℃, the maximum value of 7.78 [g / cm3] was obtained at 6mol% PZN substitution, and at 970 ℃ sintering temperature, it was 7.84 [g / cm3] at 8mol% PZN substitution and 10mol% at the sintering temperature of 1000 ℃. The maximum value of 7.93 [g / cm 3] was shown for the PZN substitution. That is, as the sintering temperature increases, the solubility limit of PZN also increases, thereby increasing the sintering density. However, since PZN is oversubstituted, the density decreases.

2 is a graph showing the change in dielectric constant according to the PZN substitution amount and the sintering temperature change in the present embodiment.

At the sintering temperature of 940 ℃ and 970 ℃, the dielectric constant increased up to 8mol% PZN substitution and reached the maximum value of 1455 and 1551, respectively. At the sintering temperature of 1000 ° C, the PZN substitution amount was almost identical to the dielectric constant of the specimen sintered at 970 ° C up to 8mol% of PZN.However, the maximum value of 1733 was obtained at 14mol% substitution without increasing after that. It was.

3 is a graph showing the change of the electromechanical coupling coefficient according to the PZN substitution amount and the sintering temperature change in this embodiment.

Electromechanical coupling coefficient (k _p ) showed the same tendency as the density characteristic of FIG. In other words, the maximum value of 0.524 for 8 mol% PZN substitution at the sintering temperature of 940 ° C, the maximum value of 0.543 for the substitution of 10 mol% at the sintering temperature of 970 ° C, and the maximum value of 0.545 for 12mol% substitution at the sintering temperature of 1000 ° C Respectively. This is because the tetragonality of PMN-PZT ceramics is weakened by the substitution of PZN having a trihedral phase.

4 is a graph showing the change in the mechanical quality factor according to the PZN substitution amount and the sintering temperature change in the present embodiment.

In this embodiment, the mechanical quality factor (Q _m ) is the maximum value of 2139 when the 4 mol% substitution at sintering temperature of 940 ℃, the maximum value of 2217 when replacing 2 mol% at the sintering temperature of 970 ℃, 1000 ℃ The maximum value of 1965 was shown at 2 mol% substitution at the sintering temperature, and gradually decreased as the substitution amount of PZN increased.

Example 2

In this embodiment, the composition showing the best dielectric and piezoelectric properties in Example 1 was prepared as a powder by an oxide mixing method, and a multilayer piezoelectric transformer was manufactured using the same. In addition, after printing an internal electrode structure having a ring-dot shape on one surface, the size of the green bar was cut into 32.5 × 32.5 × 2.76㎣ and sintered. The power and the like were examined.

The structure of the multilayer piezoelectric transformer manufactured in this embodiment is shown in FIG. 5A, where P represents the polarization direction. In the stacked piezoelectric transformer according to the present embodiment, since the input side (V _in ) is in series, the input impedance is large, and the output side (V _out ) is in parallel and the capacitance is large, so that the output impedance is small and the output current can be increased. It is a structure and designed to be pushed down. Hereinafter, the manufacturing process of this embodiment is explained in full detail.

First, the ceramic sheet was manufactured using the powder manufactured by the oxide mixing method. In this case, B73305, a binder manufactured by Ferro, was used as a binder for slurry production. Then, after milling it, it was calcined at 850 ° C. for 2 hours, and the calcined powder was pulverized again and dried. Thereafter, after calcining the calcined powder for the second time, a mixture ratio of the powder and the binder solution was mixed at 70:30, and a slurry was prepared using 20 mmφ balls in a 5 Liter Jar.

Casting of the slurry (Casting) using the Doctor Blade (Doctor Blade) method, it was cast so that the thickness of the sheet 70㎛. At this time, the carrier film used was a film coated with silicone oil. In this embodiment, an internal electrode of 90Ag / 10Pd was used, and the internal electrode structure used for printing the internal electrode is shown in FIG. 5B.

Then, the upper and lower parts of the laminated ceramic sheet were preheated at 70 ° C. for 30 minutes and uniaxially molded at 3200 psi for 40 minutes. The compressed device was cut while checking the marker by stacking the sheet coated with the electrode on the same layer as the internal electrode on the uppermost layer, and preheating the lower part of the device to 70 ° C. when cutting the device.

And, in order to completely remove the binder that causes deterioration of the electrical properties of the final product, the binder B / O process was performed for 3 hours at 340 ℃ while raising the temperature at a temperature rising rate of 0.2 ℃ / min, then 1 at 950 ℃ Sintered for time. In particular, in order to suppress the occurrence of defects due to volume expansion and contraction at a high temperature of the Ag / Pd electrode material used as the internal electrode sintered by significantly lowering the temperature increase rate between 850 ℃ to 950 ℃.

After the screen printing using Ag paste as an external electrode on the input part and the driving part of the sintered stacked piezoelectric transformer, heat treatment was performed at 600 ° C. for 10 minutes to form an external electrode. 5C shows a piezoelectric transformer manufactured as described above. In addition, the input and output terminals were polarized by applying a voltage of 25 mA / cm for 10 minutes in an insulating oil at 120 ° C. In order to measure the electrical characteristics of the stacked piezoelectric transformer, the output voltage and output power according to the input voltage were measured using a power amplifier (Trek 50/750), a function generator (HP 33120A), and an oscilloscope (Oscilloscpoe: Tektronix TDS3054). ), And the temperature rise according to the output power was measured by a contact thermometer.

6 is an electron micrograph of the cross section of the multilayer transformer manufactured according to the present embodiment, which shows that the internal electrodes are integrally sintered without ceramic and delamination.

FIG. 7 is a graph showing the impedance characteristics of the multilayer piezoelectric transformer manufactured according to the present embodiment, and k _eff of the input and the output showed 0.34 and 0.23, respectively, and showed excellent piezoelectric characteristics.

  FIG. 8 is a graph showing a boost ratio according to a frequency and a load resistance in a state in which an input voltage of a multilayer piezoelectric transformer is kept constant according to the present embodiment.

As the load resistance increased, the boost ratio increased, and when the load resistance was high, the maximum boost ratio appeared at a rather high frequency. The load resistance was measured using 100 Ω, 250 Ω, 500 Ω, 750 Ω and no load. When load resistance is 100 배, 0.59 times at frequency 75㎑, when 250Ω is connected, frequency is 75㎑ 0.9 times; when 500Ω is connected, frequency is 76㎑ 1.47 times, when 750 is connected, frequency is 76㎑ to 1.88 times, At no load, the maximum boost ratio was 2.89 times.

9 is a graph showing the efficiency according to the load resistance in the multilayer piezoelectric transformer manufactured by the present embodiment.

The highest efficiency was shown at the load resistance of 250Ω and 500Ω. This result shows the maximum efficiency when the output impedance of the multilayer piezoelectric transformer matches the load resistance. Therefore, in order to obtain the maximum power transfer efficiency, the matching between the output impedance and the load resistance of the multilayer piezoelectric transformer becomes an important factor.

  10 is a graph showing the output power according to the input voltage and the load resistance at the resonance frequency of the multilayer piezoelectric transformer manufactured by the present embodiment.

The output characteristics according to the applied input voltage increased as the applied voltage increased, and showed the highest output power at 250 Ω and 500 부근 near the resonance resistance. The output power was relatively low at 500 Ω and 750 Ω, which is due to the loss caused by the heat generation as the load resistance increases.

  FIG. 11 is a graph showing a result of temperature rise measured after driving for 20 minutes at each output power according to load resistance in the multilayer piezoelectric transformer manufactured by the present embodiment.

The temperature of the multilayer piezoelectric transformer increased as the output power increased, and the increase of the load resistance increased the temperature increase. These results indicate that the magnitude of the vibration displacement, which is generally proportional to the output current, increases with the increase of the output current according to the increase of the output power, and accordingly, the mechanical loss due to the increase of the vibration speed increases. At the load resistance of 100 to 500 에서, the temperature rise was almost the same up to 6 W, and when the load resistance of 100 Ω and 500 연결 was connected, the temperature increased rapidly above 8 W. However, when the load resistance of 250 Ω was connected, the temperature increased up to 10 W. . When the allowable calorific value of the piezoelectric transformer is within the range of 20 ° C, it is judged that stable driving up to 10W is possible at a load resistance of 250 kPa.

As described above, the piezoelectric ceramic composition according to the present invention substitutes PZN to PMN-PZT ceramics having a high mechanical quality coefficient to increase the electromechanical coupling coefficient, and sinters Li ₂ CO ₃ , Bi ₂ O ₃ , CuO, and the like. The addition of the additives has a low piezoelectric property while having a low sintering temperature, which makes it well suited for application to multilayer piezoelectric transformers.

In addition, the preferred embodiment of the present invention is disclosed for the purpose of illustration, anyone of ordinary skill in the art will be possible to various modifications, changes, additions, etc. within the spirit and scope of the present invention, such modifications, changes, Additions and the like should be considered to be within the scope of the claims.

Claims (5)

Piezoelectric ceramic compositions having the following formula; Pb [(Mn _1/3 Nb _2/3 ) _0.07 (Zn _1/3 Nb _2/3 ) _a (Zr _0.48 Ti _0.52 ) _1-0.07-a O ₃ ] + xwt% Li ₂ CO ₃ + ywt% Bi ₂ O ₃ + Zwt% CuO (in this case, 0.02≤a≤0.16, 0 <x≤3, 0 <y≤3, 0 <z≤3). delete delete A multilayer piezoelectric transformer made of the piezoelectric ceramic composition of claim 1. The method of claim 4, wherein The multilayer piezoelectric transformer includes an internal electrode having a composition containing Ag and Pd, wherein the ratio of Ag and Pd is 0 <Ag / Pd≤9.

Images