JPH08310862A - Piezoelectric porcelain composition - Google Patents

Abstract

PURPOSE: To obtain a piezoelectric porcelain compsn. maintaining high piezoelectric property in a compsn. region close to MPB and having superior thermal stability. CONSTITUTION: In a piezoelectric porcelain compsn. consisting of perovskite type oxides each represented by the general formula ABO3 and having XPb(Mn1/3 Nb2/3 )O3 -YPbZrO3 -ZPbTiO3 as the basic compsn., X, Y and Z are regulated to 0.01<=X<=0.20, 0.30<=Y<=0.60 and 0.20<=Z<=0.69 (X+Y+Z=1.0), and Co and Mg are added as additives by 0.1-2.0wt.% (expressed in terms of CoO) and 0.1-0.5wt.% (expressed in terms of MgO), respectively.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a piezoelectric ceramic composition, and more specifically, to elasticity using SH type surface waves, such as BGS waves, which mainly have a displacement in a direction perpendicular to the propagation direction of surface waves. The present invention relates to a piezoelectric ceramic composition for surface acoustic wave devices.

[0002]

2. Description of the Related Art Among surface waves propagating in a piezoelectric substrate (surface acoustic wave substrate), as an SH type surface wave mainly composed of displacement in a direction perpendicular to the propagation direction of the surface wave, BG is
S waves and love waves are known.

Of these, the BGS wave is excited when a surface wave resonator 14 as shown in FIG. 3 is formed using a material such as piezoelectric ceramics.

This surface acoustic wave resonator 14 is formed by disposing comb-teeth electrodes 12, 13 on a piezoelectric substrate 11 polarized in the direction of the polarization axis indicated by arrow P. , 13 are a plurality of electrode fingers 12 which are inserted into each other.
a and 13a.

When an alternating electric field is applied from the comb-teeth electrodes 12 and 13 to the surface acoustic wave resonator 14 thus constructed, only the displacement in the direction perpendicular to the surface acoustic wave propagation direction indicated by the arrow A occurs. That is, BG having only transverse wave components
The S wave is excited.

In such a surface wave resonator 14, the BGS
The waves are completely reflected by the free ends 11a and 11b of the piezoelectric substrate 11, and the vibration is confined. Therefore, the surface wave resonator 14 operates as an end surface reflection type surface wave resonator.

Further, in the conventional surface wave resonator utilizing the Rayleigh wave, it was necessary to form a reflector on the side of the comb-teeth electrode, but in the surface wave resonator 14 utilizing the BGS wave, Since such a reflector can be omitted, the chip size can be reduced to about 1/10.

[0008]

By the way, in the case of a surface wave resonator using a BGS wave, a surface wave resonator used for an application requiring a wide band such as a VCO (voltage controlled oscillator circuit). , The piezoelectric ceramic itself is required to have a large electromechanical coupling coefficient (k _BGS ).

Therefore, in order to meet this requirement, PZT
A piezoelectric ceramic with a large electromechanical coupling coefficient such as (lead zirconate titanate) is used, and MPB (Morphotropin
The composition region near the ic phase boundary) is used.

However, a piezoelectric ceramic such as PZT having a large electromechanical coupling coefficient has poor thermal stability in the composition region near MPB, and must guarantee performance in applications requiring high reliability and in a wide temperature range. However, there is a problem in that it is difficult to apply it to the required applications.

The present invention solves the above-mentioned problems, and particularly when it is used for a surface acoustic wave device which maintains high piezoelectricity in a composition region near MPB and has excellent thermal stability. The object is to provide a meaningful piezoelectric ceramic composition.

[0012]

[Means for Solving the Problems] To achieve the above object
In addition, the piezoelectric ceramic composition of the present invention has XPb (Mn_1/3N
b_2/3) O₃-YPbZrO₃-ZPbTiO₃The basic composition
And the general symbol ABO Of the perovskite type represented by 3
An oxide piezoelectric ceramic composition, wherein X, Y and Z are each
0.01 ≦ X ≦ 0.20, 0.30 ≦ Y ≦ 0.6
0, 0.20 ≦ Z ≦ 0.69, and X
+ Y + Z = 1.0, and Co is added as an additive.
0.1 to 2.0% by weight in terms of CoO, Mg to MgO
It is added at a rate of 0.1 to 0.5% by weight
It is characterized by the following.

[0013]

In the piezoelectric ceramic composition of the present invention, the detailed mechanism by which the thermal stability is brought about is not clear, but Co and Mg added as additives are not considered to be the perovskite phase in the ceramics sintering process. The formation of different spinel phases cancels out the instability of the crystal structure due to the phase transition in the perovskite single phase in some way, so that high piezoelectricity is maintained in the composition region near MPB and excellent thermal stability. Will be realized.

[0014]

EXAMPLES Examples of the present invention will be shown below to more specifically describe the features thereof.

First, as starting materials, Pb ₃ O ₄ and TiO 2 are used.
₂ , powders of ZrO ₂ , MnCO ₃ , Nb ₂ O ₅ , CoO, and MgO were prepared, and these starting materials (powder) were weighed so as to have the composition shown in Table 1 and wetted using a ball mill. After mixing, it was calcined at 700 to 900 ° C. for 2 hours and pulverized to obtain a calcined powder. Then, a vinyl acetate-based binder is added to the calcined powder, the mixture is further wet-mixed, dried and granulated, and then molded into a predetermined shape at a pressure of 1000 to 2000 kg / cm ² , which is fired at 1200 to 1300 ° C. Then, a sintered body (piezoelectric ceramic) was obtained.

Using this sintered body, a surface wave resonator 4 as shown in FIGS. 1 (a) and 1 (b) was manufactured according to a general method for manufacturing a surface wave resonator. This surface wave resonator 4 is formed by disposing comb-teeth electrodes 2 and 3 on a piezoelectric substrate 1 polarized in the polarization axis direction indicated by arrow P, and the comb-teeth electrodes 2 and 3 are , And has a plurality of electrode fingers 2a and 3a which are inserted into each other. In the surface acoustic wave resonator 4 configured as above, when an alternating electric field is applied from the comb-teeth electrodes 2 and 3, only the displacement in the direction perpendicular to the surface acoustic wave propagation direction indicated by the arrow A (that is, the transverse wave component). BGS wave is excited. Further, in such a surface wave resonator 4, the BGS wave is generated by the free end 1 of the piezoelectric substrate 1.
As a result of being completely reflected by a and 1b, and confinement of vibration is realized, it operates as an end face reflection type surface wave resonator.

Then, regarding this surface wave resonator 4, B
The characteristics in the GS wave were evaluated. Table 1 shows the results.

[0018]

[Table 1]

In Table 1, the sample numbers marked with * indicate samples having compositions outside the scope of the present invention.

Further, in Table 1, Δf represents the rate of change of the resonance frequency (fr) in the BGS wave resonator after 24 hours have passed after the heat treatment (250 ° C., 3 minutes). There is. The value of Δf was calculated by the following formula.

Δf (%) = {(f−f ₀ ) / f ₀ } × 100 f: Resonance frequency before heat treatment f ₀ : Resonance frequency after 24 hours have passed after heat treatment

As shown in Table 1, in each sample having a composition within the range of the present invention, the relative permittivity (ε ₁₁ /
It can be seen that, regarding ε ₀ ), the electromechanical coupling coefficient (k _BGS ), and the frequency stability (Δf), almost good results are obtained.

Next, the reasons for limiting the composition of the piezoelectric ceramic composition of the present invention will be described.

X (that is, Pb (Mn _1/3 Nb _2/3 ) O ₃
Ratio of less than 0.01 mol, the evaporation of PbO during sintering is severe, and it becomes difficult to obtain a stable sintered body peculiar to the three-component piezoelectric ceramic. Note that FIG. 2 shows Pb (Mn
_1/3 Nb _2/3 ) O ₃ in a proportion of 0.10 mol and P
It is a diagram which shows the difference in the amount of evaporation of PbO at the time of baking when b (Mn _1/3 Nb _2/3 ) O ₃ is not contained. Also,
When X exceeds 0.20 mol, the Curie point (Tc) is 25.
The temperature becomes 0 ° C. or less, and the temperature stability of the resonance frequency near room temperature decreases. Therefore, X is 0.01 ≦ X ≦ 0.20
Is preferable, and 0.03 ≦ X ≦
More preferably, it is in the range of 0.10.

Further, when Y (that is, the ratio of PbZrO ₃ ) is less than 0.30 mol away from MPB or exceeds 0.60 mol, the piezoelectricity becomes small,
It cannot be applied to applications such as VCOs that require a high electromechanical coupling coefficient ( _KBGS ). Therefore, Y is
Preferably, it is in the range of 0.30 ≦ Y ≦ 0.60,
Further, it is more preferable that the range is 0.35 ≦ Y ≦ 0.50.

Further, Z is defined in the range of 0.20≤Z≤0.69 in order to satisfy the relation of X + Y + Z = 1.0.

Further, regarding the amount of Co added, the amount of Co
As can be seen in the comparison between o.3 and Sample No. 4, when the amount of Co added is less than 0.1 wt% in terms of CoO (Sample N
The stability (Δf) of the resonance frequency after the heat treatment is poor for o.3 (no addition of CoO), and the addition amount of Co is converted to CoO as shown in sample No. 8. If it exceeds 0% by weight, there is a problem that the electromechanical coupling coefficient K _BGS becomes too small. Therefore, the amount of Co added is preferably in the range of 0.1 to 2.0 wt% in terms of CoO, and more preferably in the range of 0.3 to 1.0 wt%. .

Regarding the amount of addition of Mg, sample No.
As can be seen from the comparison between Sample No. 1 and Sample No. 2, when the added amount of Mg is less than 0.1 wt% in terms of MgO (Sample No.
Nos. 1 and 2 do not include MgO), and even if Co is added within the range of the present invention, stability of resonance frequency after heat treatment (Δ
f) is not improved. Further, when the added amount of Mg exceeds 0.5 wt% in terms of MgO, MgO begins to precipitate on the surface of the sintered body, causing a problem of breakdown voltage deterioration in the polarization step. Therefore, the addition amount of Mg is preferably in the range of 0.1 to 0.5% by weight in terms of MgO, and more preferably in the range of 0.2 to 0.4% by weight. .

The present invention is not limited to the above-mentioned embodiments, and various applications and modifications can be made within the scope of the gist of the invention with regard to its composition, manufacturing method and the like.

[0030]

As described above, the piezoelectric ceramic composition of the present invention is XPb (Mn _1/3 Nb _2/3 ) O ₃ -YPbZrO _3-.
The ZPbTiO ₃ as a basic composition, the general symbols ABO oxide piezoelectric ceramic composition of the perovskite type represented by ₃ X,
Y and Z are 0.01 ≦ X ≦ 0.20 and 0.30, respectively.
≦ Y ≦ 0.60, 0.20 ≦ Z ≦ 0.69, and as an additive, Co is converted to CoO to be 0.1.
˜2.0 wt%, 0.1 to 0.
Since it is added in a proportion of 5% by weight, it becomes possible to secure a large electromechanical coupling coefficient ( _KBGS ) while maintaining high thermal stability in a piezoelectric ceramic using a composition region near MPB.

Therefore, for example, 5 MHz to 70 MH
In the high frequency band of z, it becomes possible to use the BGS wave resonator for applications requiring a large electromechanical coupling coefficient such as a VCO.

The application of the piezoelectric ceramic composition of the present invention is not limited to the piezoelectric ceramics for surface acoustic wave devices using SH type surface waves, but the conventional surface acoustic wave using Rayleigh waves is used. It can also be applied to a piezoelectric ceramic for an element.

[Brief description of drawings]

1A and 1B are views showing a surface acoustic wave resonator formed using a piezoelectric ceramic composition according to an embodiment of the present invention, wherein FIG. 1A is a perspective view and FIG. 1B is a sectional view.

FIG. 2 is a diagram showing the difference in the amount of PbO evaporated during firing, with and without Pb (Mn _1/3 Nb _2/3 ).

FIG. 3 is a perspective view showing a conventional surface acoustic wave resonator.

[Explanation of symbols]

 1 Piezoelectric Substrate 1a, 1b Free End of Piezoelectric Substrate 2,3 Comb Tooth Electrode 2a, 3a Electrode Finger 4 Surface Wave Resonator

Claims (1)

[Claims] 1. XPb (Mn _1/3 Nb _2/3 ) O ₃ -YPb
ZrO ₃ —ZPbTiO ₃ is used as a basic composition, and a general symbol AB
A perovskite-type oxide piezoelectric ceramic composition represented by O ₃ , wherein X, Y, and Z are 0.01 ≦ X ≦ 0.20, 0.30 ≦ Y ≦ 0.60, and 0.20, respectively. ≦ Z ≦ 0.69, and X + Y + Z = 1.0, and as an additive, Co is converted into CoO by 0.1 to 2.0% by weight, and Mg is converted into MgO. 0.1 to 0.5% by weight, and a piezoelectric ceramic composition characterized by being added.