KR100481717B1 - Piezoelectric ceramic composition and piezoelectric device using the same - Google Patents

Abstract

In the present invention, a general formula is represented by [Pb _{(1-1.5x) ± (0 to 0.2)} La _x ] [Ti _(1-y) Mn _y ] O ₃ , and the subscripts of the general formula are 0.03 ≦ x ≦, respectively. 0.13, 0.0001 ≤ y ≤ 0.1, and as an additive CuO: 0.01wt% or more and 2wt% or less, CoO, MgO, ZnO, Al ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ , Sb ₂ O ₃ , SnO Provided is a piezoceramic composition in which at least one component of the group consisting of ₂ , CeO ₂ , Nb ₂ O ₅ , V ₂ O _5, and WO ₃ is added in an amount of 0.01 wt% or more and 2 wt% or less.

The piezoelectric ceramic composition of the present invention is capable of stable sintering at atmospheric pressure in an atmosphere having an oxygen partial pressure of 80% or more, and has excellent piezoelectric properties as well as thermal stability. Therefore, a composition having excellent piezoelectric characteristics of thickness longitudinal vibration 3 harmonics capable of high frequency of 15 MHz or more even in a ceramic resonator having a small electrode formation area can be obtained.

Description

Piezoelectric ceramic composition and piezoelectric element using the piezoelectric ceramic composition {PIEZOELECTRIC CERAMIC COMPOSITION AND PIEZOELECTRIC DEVICE USING THE SAME}

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 having excellent piezoelectric properties exhibiting high D / R (dynamic ratio) values by substituting a conventional piezoelectric ceramic component with another component, and a piezoelectric ceramic device using the same. .

With the recent development of the information industry, hard disk drives (HDD). HHP. CD-ROM. CD-RW. Nearly all home appliances and equipment, such as DVDs, DVD-RWs, wireless keyboards, optical mice, etc., use surface mount resonators that generate clock frequencies as one of the key components of the digital era. . These resonators continue to develop while pursuing high frequency and light and small size reduction in accordance with the performance and small size of digital products. Accordingly, there is a need for piezoelectric ceramic compositions having better piezoelectric properties and temperature stability to produce more high frequency and miniaturized resonators. do.

Piezoelectric ceramic compositions which are widely used in recent years can be roughly classified into two types, Pb (Zr, Ti) O ₃ and PbTiO ₃ . A typical vibration mode of such piezoelectric ceramic composition is a thickness vibration mode. It uses energy traps during vibration, and there is a method using vibration of fundamental wave and a method using higher order vibration.

In the case of Pb (Zr, Ti) O ₃ system, it is very good in vibration of fundamental wave, but in high order vibration, piezoelectric characteristics are relatively inferior and the resonant frequency constant is relatively small. Therefore, it is difficult to obtain high frequency. In contrast, the PbTiO ₃ system has a low dielectric constant, small particle size, and high phase transition temperature. In addition, since the lattice anisotropy is large in the C-axis direction, it is difficult to trap energy in the vibration of the fundamental wave, but energy trapping is easy in the case of higher-order vibrations in which high frequencies can be obtained. Due to these characteristics, the PbTiO ₃ system has better piezoelectric properties and temperature stability than the Pb (Zr, Ti) O ₃ system, and thus is known as a suitable material for high frequency band oscillators.

However, since PbTiO ₃ system has a large crystallographic anisotropy, cracking easily occurs due to spontaneous stress caused by phase transition during cooling, so that sintering is poor, and various components are replaced with A-site and B-site. In order to minimize the spontaneous stress caused by phase transition when cooling by using other additives, studies are being actively conducted.

As a representative example of this, Japanese Patent Laid-Open No. 7-206517 (published on August 8,199, Applicant: Matsushita Electric Co., Ltd.) has a piezoelectric ceramic composition using CuO, ZrO ₂ , and MnO ₂ as an additive to a (Pb, La) TiO ₃ -based main component. Presenting. According to this document, the new piezoelectric ceramic composition has an effect of having a high dynamic ratio (D / R) at high operating frequencies and resonance. However, the piezoelectric ceramic composition should be sintered in an atmosphere with an oxygen partial pressure of 80% or more, and when evaluating its properties, an element having a straight line of 15 to 18 mm is used, which is 2.5 mm × 2.0 in diameter recently used in ceramic oscillators for driving hard disks. There is a limit to application to ceramic resonators exceeding 40 MHz of mm. In addition, when miniaturization thereof, there is a problem in that the D / R at resonance decreases and spurious phenomenon occurs in the third harmonic.

SUMMARY OF THE INVENTION The present invention has been made to solve the above problems, and one object of the present invention is to sinter even at atmospheric pressure even when the electrode formation area is reduced to 2.5 mm x 2.0 mm or less when applied to piezoelectric elements. To provide a piezoelectric ceramic composition having excellent electrical properties (D / R 60 or more) and thermal properties in the above reflow, and excellent piezoelectric properties of the third longitudinal harmonics of thickness vibration.

In addition, another object of the present invention is to provide a piezoelectric ceramic device which is surface mountable at high temperature while being advantageous for high frequency and miniaturization.

In the present invention, a general formula is represented by [Pb _{(1-1.5x) ± (0 to 0.2)} La _x ] [Ti _(1-y) Mn _y ] O ₃ , and the subscripts of the general formula are 0.03 ≦ x ≦, respectively. 0.13, 0.0001 ≤ y ≤ 0.1, and as an additive CuO: 0.01wt% or more and 2wt% or less, CoO, MgO, ZnO, Al ₂ O ₃ , 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 to provide a piezoceramic composition comprising at least one component: 0.01wt% or more and 2wt% or less.

In addition, the present invention provides a piezoelectric ceramic device that can be surface-mounted at a high temperature while being advantageous for high frequency and miniaturization using the piezoelectric ceramic composition.

In the piezoelectric ceramic composition of the present invention, in the composition of ABO ₃ perovskite, the component of A site is composed of PbO and La ₂ O ₃ , and the component of B site is composed of TiO ₂ and MnO ₂ . Pb _{(1-1.5x) ± (0 to 0.2)} La _x ] [Ti _(1-y) Mn _y ] O ₃ , and as an additive, CuO and CoO, MgO, ZnO, Al ₂ O ₃ , Fe ₂ It contains at least one component of 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 .

As such, unlike conventional piezoelectric ceramic compositions, manganese (Mn) is not added as an additive, but instead of titanium (Ti) in a matrix composition, the crystallization and chemical stability together with crystal structure and chemical stability are more stable. Adjust with In addition, as an additive, CuO of 0.01wt% or more and 2wt% or less, CoO, MgO, ZnO, Al ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , CeO ₂ , Nb ₂ The piezoelectric properties can be further improved by adding 0.01 wt% or more and 2 wt% or less to at least one component consisting of O ₅ , V ₂ O _5, and WO ₃ .

In the general formula, lanthanum (La), which is a constituent element of the A site, is included so that the subscript x is in the range of 0.03 to 0.13. When lanthanum (La) is added to 0.03 or more, a cavity is formed at some sites occupied by lead (Pb) to maintain charge neutrality. As a result, the diffusion of atoms may be promoted to alleviate internal stress due to crystallographic anisotropy during sintering and to prevent cracking. However, when the lanthanum content is less than the above range, such an effect is inferior. When the lanthanum content exceeds the above range, the oscillation stability and thermal stability tend to be lowered.

In addition, in the general formula, manganese (Mn), which is a component of B-site, serves to improve the electrical properties and thermal stability of the piezoelectric ceramic composition by minute changes. Manganese is included such that the subscript y is in the range 0.0001 to 0.1. If it exceeds the above range, there is a problem that the insulating property of the sintered compact and acts as an electron acceptor and the amount of leakage current is rapidly increased, so that polarization is impossible or the piezoelectric properties are degraded.

On the other hand, by adding CuO as a base additive in the range of 0.01wt% or more and 2wt% or less, by providing a cavity as the base additive in the composition to lower the resonance resistance value to control the leakage current. If it exceeds the above range, there is a problem that the piezoelectric properties are lowered and the thermal stability is lowered. Also, among the group consisting of CoO, MgO, ZnO, Al ₂ O ₃ , 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 By selecting and adding any selected component, the piezoelectric characteristic can be improved more. Although there was a difference according to the selected composition, the piezoelectric properties tended to be improved in the range of about 0.01 wt% or more and 2 wt% or less. In particular, when the additive is more than 2wt%, the insulation of the sintered compact is lowered, so that polarization is impossible or the piezoelectric characteristics are sharply degraded.

Since the piezoelectric ceramic composition of the present invention is excellent in sintering property, it is possible not only to sinter in an atmosphere having a predetermined oxygen partial pressure but to be stable sintering under atmospheric pressure, and to have excellent electrical properties even in a reflow of 250 ° C. or higher for surface mounting. The thermal stability is excellent even after furnace. Therefore, it is possible to provide a composition that can be manufactured from a piezoelectric ceramic device having an electrode-forming surface having a planar dimension of 2.5 mm x 2.0 mm or less, as well as exhibiting excellent piezoelectric properties of the thickness longitudinal vibration 3 harmonics capable of high frequency.

Hereinafter, the present invention will be described in more detail with reference to the following tables. Experimental Examples

Starting materials PbO, La ₂ O ₃ , TiO ₂ , MnO ₂ , CuO, CoO, MgO, ZnO, Al ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , CeO ₂ , The components of at least one of the group consisting of Nb ₂ O ₅ , V ₂ O ₅ and WO ₃ were weighed respectively. It was mixed using a ball mill so as to have the composition shown in the table. The sufficiently mixed slurry is dried while maintaining the particle size of the powder to 0.1-1.5 탆. Care should be taken when drying to avoid delamination. When delamination occurs, the perovskite crystals are not formed in a single phase, but are formed in two phases and have a fatal effect on the piezoelectric properties, and when the average particle diameter of the powder is out of the above range, suitable energy for forming a single phase is obtained. Since the second phase is not formed, unreacted raw material powder is generated.

The powder was then calcined at 650-1000 ° C. for 1-4 hours. The two step calcination method was chosen such that no single phase was formed. The obtained calcined powder was mixed with a small amount of binder and wet pulverized to an average particle size of 0.1-1.2 탆, and then calcined at 1000-1350 DEG C for 1 to 4 hours in an atmospheric condition to be 23 mm x 18 mm A plate-shaped sintered compact was obtained. After the obtained sintered body was first polished on both sides with a thickness of 0.5 mm, it was secondarily processed into a piezoelectric material having excellent surface roughness so that the thickness longitudinal vibration third mode had a range of 20 MHz to 60 MHz. Next, the piezoelectric sample was prepared by forming electrodes having a diameter of 0.5-1.5 mm on both surfaces of the obtained piezoelectric body. This sample was subjected to polarization treatment by applying an electric field of 3-10 μm for 10-30 minutes in 100-250 ° C. silicone oil.

Each specimen prepared as described above was subjected to an impedance analyzer (product name: HP4194A) using the energy trap, and the resonance frequency (F _r ), the anti-resonance frequency (F _a ), and the resonance resistance (Z) near the resonance frequency of the three longitudinal harmonics of the thickness longitudinal vibration. _r ) and antiresonance resistance (Z _a ) were measured.

In this experiment, resonance, which is an important factor of D / R (dynamic ratio) and oscillation stability, is used to determine the output level of oscillation circuit in the actual oscillator rather than the dielectric constant, electromechanical coupling coefficient (k _t ) and mechanical quality coefficient (Q _m ). The temperature coefficient (TCF) and phase transition temperature of the frequency and the rate of change of the oscillation frequency ( _{ΔF osc} ) after the surface mount reflow at the temperature were evaluated.

The D / R value is a factor that determines the output level expressed as the following equation. In this experiment, it was measured by the standard circuit of I.R.E.

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

The piezoelectric and temperature characteristics obtained as described above are summarized together with the piezoelectric specimens having different composition ratios, respectively, and are shown in Tables 1 and 2.

Table 1 shows the basic additives CuO and CoO, MgO, ZnO, Al ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , CeO ₂ , Nb ₂ O ₅ , V ₂ O ₅ In order to examine the effect on the additive selected from the group consisting of and WO ₃ , it is the result of evaluating the specimen prepared with the remaining components in the same composition ratio.

         (Comparative example is marked with *)

As shown in Table 1, in the D / R value showing the piezoelectric characteristics, the D / R value is lower than the specimens 1 and 2 of Comparative Examples in which only CuO as the base additive (A) or only the additive (B) is added It can be seen that the increase. The degree of improvement varies depending on the amount of CuO added and the type and amount of group B additives. However, when the additives of CoO, Fe ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , CeO ₂ and WO ₃ are added as additives, It was big. CuO, which is a basic additive, serves to control the leakage current by providing a cavity in the crystal of the piezoelectric composition to reduce resonance resistance, and the group B additive, as shown in Table 1, affects crystallographic anisotropy and piezoelectric characteristics. Subject D / R characteristics increase in a certain range.

Also, the resonant frequency temperature coefficient tends to decrease slightly. However, the reduced resonant frequency temperature coefficient has a value within the range of 30ppm / ℃ did not appear to have a significant effect on the desired oscillation stability.

As shown in Table 1, the addition amount of such a basic additive CuO and B group additive is preferably added in the range of 0.01 to 2wt%.

If the added amount of CuO is less than 0.01wt%, the effect is insignificant. If it exceeds 2wt%, the D / R value is rather lowered, and the resonance frequency temperature coefficient is increased. As a result, the piezoelectric composition having a CuO content of more than 2 wt% has a problem in that piezoelectric properties are lowered and thermal stability is lowered. On the other hand, when the amount of the group B additive is 0.01wt%, the effect is insignificant, and when it exceeds 2wt%, the insulation of the sintered body is lowered and polarization is impossible or the piezoelectric characteristic is sharply lowered.

Table 2 and Table 3 show the basic additives CuO and other additives CoO, MgO, ZnO, Al ₂ O ₃ , 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 is an additive of one of the group consisting of 0.01wt% or more in an amount of less than 2wt%, but the evaluation result of the specimen prepared by varying the basic composition range.

        (Comparative example is marked with *)

        (Comparative example is marked with *)

As shown in Tables 2 and 3, x, the number of moles of lanthanum substituted with lead components is in the range of 0.01 to 0.2, and t and u, the number of moles of manganese and copper substituted with titanium components, are in the range of 0.0001 to 0.1. At this time, stable sintering was possible even under atmospheric pressure, and excellent piezoelectric properties and temperature stability of the thickness longitudinal vibration 3 harmonics capable of high frequency of 15 MHz or more were shown.

Lanthanum prevents cracking by relaxing internal stress in the range of 3 to 13 mol% Do it. When the lanthanum content was 1 mol% or more, the sinterability improved and the D / R value increased. However, when the lanthanum content exceeded 20 mol%, the resonance frequency temperature coefficient (TCF) exceeded 60 ppm / ° C and the phase transition temperature was also increased. It tends to decrease.

Manganese lowers the resonance resistance in the range of 0.01 to 10 mol%, thereby improving piezoelectric properties and improving heat resistance to impart thermal stability. If the manganese content is less than 0.01 mol%, the effect is insignificant. If it exceeds 10 mol%, the insulation resistance is increased and the amount of leakage current rapidly increases, making polarization impossible.

In this way, even if the size of the electrode formation surface is reduced to a size of 2.5 mm x 2.0 mm, the D / R value is maintained at 60 dB or more, and the phase transition temperature T _c of each composition and the oscillation frequency change amount after reflow (ΔF) _osc ) is ± 1%, and the resonant frequency temperature coefficient (TCF) is 60ppm / ℃ or less.

The present invention described above is not limited by the above-described embodiment and the accompanying drawings, but by the appended claims. Therefore, it will be apparent to those skilled in the art that various forms of substitution, modification, and alteration are possible without departing from the technical spirit of the present invention described in the claims.

As described above, the piezoelectric ceramic composition according to the present invention has an oxygen partial pressure of 80% or less. Stable sintering is possible in the atmospheric phase, not in the atmosphere of the phase, and it exhibits not only high electrical properties of 60 dB or more even in a reflow of 250 ° C. or more, but also has excellent thermal stability. In other words, it is possible to obtain an excellent piezoelectric ceramic composition exhibiting an oscillation frequency change amount of about 1% after reflow and having a resonance frequency temperature coefficient of 30 ppm / ° C or less.

Therefore, a composition having excellent piezoelectric characteristics of thickness longitudinal vibration 3 harmonics capable of high frequency of 15 MHz or more even in a ceramic resonator having a small electrode formation area can be obtained.

Claims (2)

The general formula is represented by [Pb _{(1-1.5x) ± (0 to 0.2)} La _x ] [Ti _(1-y) Mn _y ] O ₃ , and the subscripts of the general formula are 0.03 ≦ x ≦ 0.13 and 0.0001 ≦, respectively. satisfies y≤0.1, CuO: 0.01wt% or more and 2wt% or less, CoO, MgO, ZnO, Al ₂ O ₃ , Fe ₂ O ₃ , Cr ₂ O ₃ , Sb ₂ O ₃ , SnO ₂ , CeO ₂ At least one component of the group consisting of: Nb ₂ O ₅ , V ₂ O _5, and WO ₃ : a piezoceramic composition to which 0.01 wt% or more and 2 wt% or less are added. The piezoelectric ceramic element manufactured using the piezoelectric ceramic composition of Claim 1.