KR100462871B1 - Piezoelectric Ceramic Composition Having Excellent Heat Resistance and Stability in Frequency Change and Piezoelectric Device Using the Same - Google Patents

Abstract

A piezoelectric ceramic composition having excellent heat resistance and frequency stability in which a specific material is substituted at the B site of a PZT piezoelectric composition, and a piezoelectric device using the same. CoO, Fe ₂ in the main component represented by the chemical formula Pb [(Co _1/2 W _1/2 ) _x Ti _1-xy Zr _y ] O ₃ (wherein, 0.001 ≦ x ≦ 0.04 and 0.35 ≦ _y ≦ 0.55). 0.01-2.0% by weight of at least one additive selected from the group consisting of O ₃ , Cr ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , CeO ₂ , Nb ₂ O ₅ , V ₂ O ₅ and WO ₃ Piezoelectric ceramic compositions and piezoelectric devices made therefrom are provided. The piezoelectric ceramic composition of the present invention and the piezoelectric device manufactured therewith satisfy the piezoelectric properties such as kp and Qm required for use as a piezoelectric material, and have a phase transition temperature of 320 ° C. or more, a TCF of ± 30 ppm / ° C., and a frequency after reflow. It shows excellent piezoelectric properties with a rate of change of 0.1% or less.

Description

Piezoelectric Ceramic Composition Having Excellent Heat Resistance and Stability in Frequency Change and Piezoelectric Device Using the Same}

The present invention relates to a piezoelectric ceramic composition having excellent heat resistance and frequency stability and a piezoelectric device made therefrom, and more particularly, to a piezoelectric ceramic composition having excellent heat resistance and frequency stability in which a specific material is substituted at the B site of the PZT piezoelectric composition and a preparation thereof. To a piezoelectric device.

Recently piezoelectric elements are widely used in ceramic resonators, ceramic filters, piezoelectric displacement elements, piezoelectric buzzers, ultrasonic vibrators and the like. For example, with the recent development of the information industry, the kHz SMD filter, a chip component used as one of the core parts of the digital era, is widely used as a 2-layer IF filter for various equipment such as pager, AMPS, radio, wired / wireless hands free, and wireless network. As described above, the use of piezoelectric elements is gradually increasing, and the characteristics required with the development of precision thereof are becoming more and more strict.

With the acceleration of digital, the requirements for thinning, miniaturization, high performance, and frequency stability of electronic components and the electronic component materials used therein become increasingly stringent.

In particular, as chip parts undergo reflow with accelerated SMD, a change in piezoelectric properties after reflow is required and a material having excellent heat resistance at high temperature is required.

However, the current application composition has a low Tc and low heat resistance, and the piezoelectric characteristics and frequency change after reflow are large, and thus there is a limit to manufacturing a high value-added SMD-type filter. In addition, due to the difficulty in controlling the piezoelectric properties, it is impossible to diversify the model and have no quality competitiveness.

Pb (Zr, Ti) O ₃ is the main component and additives such as Mn, Y, Dy, Er, Ho, Lu, Yb are added to secure the heat resistance of the material and to stabilize the frequency and other piezoelectric characteristics after reflow. Attempts have been made to stabilize the rate of change of frequency resistance, capacitance change, and electromechanical coupling coefficient (k) for each vibration mode after heat resistance and reflow.

For example, U. S. Patent No. 6123867 describes Pb [(M, Nb) Zr, Ti] O ₃ as a main component and adds other materials to it so that the heat resistance and frequency change after reflow, capacitance change and coupling factor (k) Disclosed is what stabilizes the change.

In Japanese Patent Laid-Open Nos. 52-17239 and 51-7318, Pb (Zn, Nb) (Sn, Nb) TiZrO ₃ -based compositions are disclosed, and in Japanese Patent Laid-Open Nos. 54-32516 and 54-36757, Pb (Sn, Sb A TiZrO ₃ -based composition is disclosed. They are characterized by excellent piezoelectric properties, small grain size, and easy removal during sintering, and are suitable for high frequency ceramic oscillators and filters. They are applied to ceramic filters, ceramic oscillators, piezoelectric transformers, and piezoelectric sensors.

Japanese Patent Application Laid-Open No. Hei 8-239269 or 9-142930 discloses a material which does not have a problem in heat resistance by adding a compound oxide such as Y and Nb to the main component PZT or adding an additive such as Cr.

However, the conventional piezoelectric composition has low heat resistance, low reliability due to thermal movement and property change, and thus has problems in mass production. That is, when the element made of a conventional piezoelectric element is heat-treated at 150 ° C. for 1 hour, the resonance frequency change immediately after the treatment reaches up to several percent.

In addition, as SMT of electronic components such as ceramic filters and ceramic oscillators is progressed, the temperature at the time of reflow is increasing and the actual thermal temperature received by the device is also increasing. Therefore, as time passes after heat treatment, the piezoelectric characteristics and the like change, and move to a different value compared with the characteristic value before treatment. In other words, in order to reflow the piezoelectric element, the piezoelectric characteristics such as the resonance frequency of the piezoelectric element before and after the heat treatment are changed when used after being heated to a temperature of about 250 ° C. and being used at the room temperature.

Accordingly, an object of the present invention is to provide a piezoelectric ceramic composition having increased heat resistance and excellent frequency stability by increasing the phase transition temperature.

Another object of the present invention is to provide a piezoelectric device made of a piezoelectric ceramic composition having excellent heat resistance and frequency stability.

According to one aspect of the invention,

CoO, Fe ₂ in the main component represented by the chemical formula Pb [(Co _1/2 W _1/2 ) _x Ti _1-xy Zr _y ] O ₃ (wherein, 0.001 ≦ x ≦ 0.04 and 0.35 ≦ _y ≦ 0.55). 0.01-2.0% by weight of at least one additive selected from the group consisting of O ₃ , Cr ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , CeO ₂ , Nb ₂ O ₅ , V ₂ O ₅ and WO ₃ Piezoelectric ceramic composition is provided.

According to another aspect of the present invention,

A piezoelectric device made of the piezoelectric ceramic composition of the present invention is provided.

EMBODIMENT OF THE INVENTION Hereinafter, this invention is demonstrated in detail.

The composite oxide, which is the main component of the piezoelectric ceramic composition of the present invention, is based on the PZT-based composite oxide and partially substituted with cobalt and tungsten in the B-site of the PZT-based composite oxide.

Pb [(Co _1/2 W _1/2 ) _x Ti _1-xy Zr _y ] O ₃

Wherein, in the formula, 0.001 ≦ x ≦ 0.04 and 0.35 ≦ y ≦ 0.55.

Furthermore, the main component of Formula 1 is selected from the group consisting of CoO, Fe ₂ O ₃ , Cr ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , CeO ₂ , Nb ₂ O ₅ , V ₂ O ₅ and WO ₃ At least one additive is added at 0.01-2.0% by weight based on the total weight of the piezoelectric ceramic composition.

PZT-based (ABO ₃ composite perovskite) ceramic compositions containing Pb (Ti, Zr) O ₃ as a main component are generally used as suitable for high frequency ceramic vibrators and filters due to their excellent piezoelectricity and small particle size.

In the piezoelectric ceramic composition of the present invention, as a main component of the PZT-based main component, a portion of the B-site of the PZT-based ceramic composition may be (Co _{1 / 2} W _1/2 ) is used. (Co _1/2 W _1/2 ) is an antiferroelectric material, which has a relatively high phase transition temperature in the antiferroelectric material.

By substituting a small amount of (Co _1/2 W _1/2 ) in the B-site of PZT, the drop in the phase transition temperature is reduced, thereby increasing the Tc, thereby preventing a decrease in heat resistance due to the Tc decrease.

In the above formula, (Co _1/2 W _1/2 ) is added so that x is 0.001 to 0.04, preferably 0.025 to 0.035. If the x value is out of the above range, the Kp value is too small or large so that the value of the desired bandwidth is not satisfied. In addition, when a large amount of (Co, W) is added, when the Tc of the material is lowered, the heat resistance rapidly decreases.

Zr is added so that y may be 0.35 to 0.55, preferably 0.46 to 0.50. If Zr does not satisfy the above range, it is out of the MPB region, and thus the TCF value is not satisfied, and the Kp value is too small to exhibit the piezoelectric effect.

As described above, Tc is increased by substituting a portion of the B-site of the PZT-based composite oxide with (Co _1/2 W _1/2 ), but frequency stability is not secured due to the increase of Tc.

That is, although the frequency change rate of the piezoelectric ceramic composition may be alleviated slightly during the heat treatment due to the increase in Tc, a specific additive is added to secure the frequency stability.

In practice, the frequency stability is affected by the domain structure formed through the forced polarization process. The domain structure is controlled by the domain behavior of how the microstructure of the material and the internal crystal structure change depending on the type of additives added to the main component, which is a PZT-based composite oxide. Therefore, the behavior of the domain can be adjusted by adding an additive suitable for the main component, which is a PZT-based composite oxide, and the stability of the frequency can be achieved by appropriately adjusting the domain structure by such physical phenomenon.

Therefore, Pb [(Co _1/2 W _1/2 ) _x Ti _1-xy Zr _y ] O ₃ (wherein 0.001 ≦ x ≦ 0.04 and 0.35 ≦ _y ≦ 0.55) of the present invention, CoO, Fe ₂ O _At least one additive selected from the group consisting of ₃ , Cr ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , CeO ₂ , Nb ₂ O ₅ , V ₂ O ₅ and WO ₃ is based on the total weight of the piezoelectric ceramic composition To 0.01-2.0% by weight. Among the additives, CoO and Cr ₂ O ₃ are particularly preferred in consideration of the frequency change amount and the capacitance change amount. If the additive is added at less than 0.01% by weight, the intended frequency stability is not exhibited and when the additive is more than 2.0% by weight, the intended properties are lowered due to the formation of the second phase.

The piezoelectric ceramic composition of the present invention is made of a piezoelectric element to satisfy the piezoelectric properties such as kp and Qm required when using a piezoelectric material such as a filter and at the same time the phase transition temperature is 320 ℃ or more, TCF ± 30ppm / ℃ and the frequency after reflow In consideration of the characteristics of each component so that the rate of change is less than 0.1%, By blending W, Ti and Zr to the above composition range and further blending specific additives in specific amounts, the mechanical and electrical properties are optimally balanced.

As described above, the piezoelectric ceramic composition in which the B-site of the ABO ₃ composite perovskite is replaced with cobalt and tungsten and a specific additive is added, is sinterable under general atmospheric pressure, and has excellent electrical properties even at reflow characteristics of 250 ° C. or higher. And thermal properties. That is, the amount of Fosc change after reflow is 0.1% or less, and has a resonant frequency temperature coefficient (TCF) of ± 30 ppm / ° C and a phase transition temperature of 320 ° C or more.

Therefore, the piezoelectric device made of such a piezoelectric ceramic composition not only has excellent heat resistance but also has excellent piezoelectric properties such that the rate of change of frequency after reflow is minimized.

Piezoelectric groups that can be produced from the piezoelectric ceramic composition of the present invention include, but are not limited to, for example, piezoelectric ceramics, ceramic resonates, piezoelectric displacement elements, piezoelectric buzzers and filters.

Hereinafter, the present invention will be described in detail through examples. The following examples illustrate the invention but do not limit the invention.

Experimental Example

To prepare a piezoelectric ceramic composition having a composition of Table 1 and to prepare a specimen for measuring the respective piezoelectric properties.

PbO, TiO ₂ , ZrO ₂ , CoO, WO ₃ used as starting materials and the additives required for each compounding were weighed so that the final composition was in the amounts shown in Table 1, followed by sufficient mixing for 24 hours using a ball mill. It was.

The sufficiently mixed slurry was dried while maintaining a powder particle diameter of 0.1-1.5 mu m. Care should be taken when drying to avoid delamination. When delamination occurs, the perovskite crystals are not formed as a single phase, but a second phase such as a pyrochlore phase is formed to have a fatal effect on piezoelectric properties and reliability.

If the average particle diameter of the powder is out of the above range, no suitable energy for forming a single phase can be supplied, so that a second phase is formed or an unreacted raw material powder is generated. The homogeneously mixed powder was then calcined at around 650-1000 ° C. for 1-4 hours. After calcination, a single phase crystal was prepared by a two-step calcination method if it was not synthesized. After calcination, the powder synthesized as a single phase was wet-pulverized so that the average particle diameter was 0.1-1.2 mu m and granulated by mixing 1.5% by weight of PVC binder.

The powder thus obtained was molded at a pressure of 1-3 ton / cm 2 and then calcined for 1 to 4 hours at a firing temperature of 1000-1350 ° C in an atmospheric atmosphere to obtain a plate-shaped sintered body of 23 mm x 18 mm.

The obtained sintered compact was polished on both sides so as to be 0.26 mm, which is the thickness used in actual application as a piezoelectric element, and the surface was cleansed and dried, and then the Ag paste was heat-treated at 600-700 ° C.

The specimens were polarized under conditions of 1-5 kV / mm and 10-30 minutes in 100-200 ° C. silicone oil. After cleaning the polarized piezoelectric specimen, the piezoelectric body was cut and processed so that the main range of the anti-resonant frequency of area vibration appeared at 455 kHz.

Using the HP419A, the prepared specimens were measured in resonant frequency (Fr), anti-resonant frequency (Fa), TCF, phase transition temperature (Tc), and frequency change rate after 250 ° C reflow in the resonant region of area vibration. It was.

The resonance frequency temperature coefficient (TCF) was calculated according to the following equation by measuring the resonance frequency (Fr) in the range of -40 ~ 90 ℃.

[Equation 1]

TABLE 1

number Pb [(Co _1/2 W _1/2 ) _x Ti _1-xy Zr _y ] O ₃ additive Additive amount (wt%) TCF (ppm / ° C) Tc (℃) ΔFr (%) x y One* 0.001 0.35 CoO 0 35 352 0.01 2 0.01 0.47 Fe ₂ O ₃ 0.01 -24 332 0.05 3 0.01 0.49 Cr ₂ O ₃ 0.05 12 324 0.03 4 0.04 0.51 Sb ₂ O ₃ One 11 294 0.02 5 * 0.1 0.57 CeO ₂ 3 82 295 0.14 6 * 0.001 0.45 Nb ₂ O ₅ 0 41 352 0.11 7 0.01 0.47 V ₂ O ₅ 0.01 10 332 0.02 8 0.01 0.49 WO ₃ 0.05 10 328 0.03 9 0.04 0.51 CoO One -22 318 0.02 10 0.04 0.53 Fe ₂ O ₃ 2 25 313 0.03 11 * 0.1 0.57 Cr ₂ O ₃ 3 45 297 0.15 12 0.01 0.47 SnO ₂ 0.01 28 332 0.04 13 0.01 0.49 CeO ₂ 0.05 -29 328 0.02 14 0.04 0.51 Nb ₂ O ₅ One 21 314 0.03 15 0.04 0.53 V ₂ O ₅ 2 23 311 0.01 16 * 0.1 0.57 WO ₃ 3 -42 295 0.18 17 * 0.001 0.45 CoO 0 37 355 0.13 18 0.01 0.47 Fe ₂ O ₃ 0.01 22 335 0.04 19 0.01 0.49 Cr ₂ O ₃ 0.05 12 325 0.02 20 0.04 0.51 Sb ₂ O ₃ One 11 318 0.02 21 0.04 0.53 SnO ₂ 2 24 314 0.02 22 * 0.1 0.57 CeO ₂ 3 46 298 0.21 23 * 0 0.45 Nb ₂ O ₅ 0 51 350 0.25 24 0.001 0.47 V ₂ O ₅ 0.01 29 330 0.05 25 0.01 0.49 WO ₃ 0.05 27 317 0.01 26 0.01 0.51 CoO One 17 312 0.04 27 0.04 0.53 Fe ₂ O ₃ 2 -22 314 0.07 28 * 0.04 0.57 Cr ₂ O ₃ 3 21 296 0.03 29 * 0.1 0.45 Sb ₂ O ₃ 0 55 314 0.12 30 * 0 0.47 SnO ₂ 0.01 60 355 0.15 31 0.001 0.49 CeO ₂ 0.05 29 322 0.02 32 0.01 0.51 Nb ₂ O ₅ One 17 312 0.01 33 0.01 0.53 CeO ₂ 2 28 302 0.03 34 * 0.04 0.57 Nb ₂ O ₅ 3 45 315 0.21 35 0.04 0.45 V ₂ O ₅ 0.05 -18 297 0.03 36 * 0.1 0.47 WO ₃ One 42 287 0.16 37 * 0.1 0.49 CoO 2 69 283 0.18

Comparative Example

As can be seen from the table, the piezoelectric composition satisfying the conditions of the present invention is 250% by satisfying the change in Fosc after reflow less than 0.1%, the resonant frequency temperature coefficient (TCF) of ± 30ppm / ℃ and the phase transition temperature of 320 ℃ or more Excellent electrical properties even in reflows above ℃

The piezoelectric ceramic composition of the present invention and the piezoelectric device manufactured therewith satisfy the piezoelectric properties such as kp and Qm required for use as a piezoelectric material, and have a phase transition temperature of 320 ° C. or more, a TCF of ± 30 ppm / ° C., and a frequency after reflow. It shows excellent piezoelectric properties with a rate of change of 0.1% or less.

Claims (6)

CoO, Fe ₂ O ₃ , Cr ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ in the main component which is a composite oxide represented by the formula Pb [(Co _1/2 W _1/2 ) _x Ti _1-xy Zr _y ] O ₃ At least one additive selected from the group consisting of CeO ₂ , Nb ₂ O ₅ , V ₂ O ₅ and WO ₃ is added at 0.01-2.0% by weight based on the total weight of the piezoelectric ceramic composition, wherein x And y is 0.001 to 0.04 and 0.35 to 0.55, respectively. The piezoelectric ceramic composition according to claim 1, wherein the x value is 0.025 to 0.035. The piezoelectric ceramic composition according to claim 1, wherein the y value is 0.46 to 0.50. The piezoelectric ceramic composition of claim 1, wherein the additive is selected from CoO and Cr ₂ O ₃ . A piezoelectric device made of the piezoelectric ceramic composition according to any one of claims 1 to 4. 6. The piezoelectric device according to claim 5, wherein the piezoelectric device includes piezoelectric ceramics, ceramic resonates, piezoelectric displacement elements, piezoelectric buzzers, and filters.