JPH10178329A - Piezoelectric resonator - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a piezoelectric resonator employing a thickness-shear 3-multiple wave energy confinement resonator used for a filter and an oscillator or the like where oscillation at a thickness-shear fundamental wave is prevented. SOLUTION: A vibration electrode 2 is formed opposite to both sides of a piezoelectric substrate 1, a terminal electrode 4 is formed across the piezoelectric substrate 1 and the vibration electrode 2 and the terminal electrode 4 are connected by a lead electrode 3 in the piezoelectric resonator. The vibration electrode 2 is formed elliptic, and let a major diameter of the vibration electrode 2 be L1 , the minor diameter be L2 , then accept ratio (L1 /L2 ) is selected to satisfy a relation of 1.10-1.75, and the lead electrode 3 is connected to the minor diameter side of the vibration electrode 2 and the width of the lead electrode 3 is selected to be a multiple of 0.9-1.1 of the major diameter of the vibration electrode 2.

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an energy trapping type in which a pair of electrodes are formed substantially at the center on both sides of a piezoelectric substrate, and vibration energy is confined and used in a vibrating portion sandwiched between the pair of electrodes. The present invention relates to a piezoelectric oscillator, for example, to an energy trap type piezoelectric resonator applied to a resonator, a filter, or the like.

[0002]

2. Description of the Related Art As shown in FIG. 8, a conventional thickness longitudinal harmonic energy trapping type resonator has a circular vibrating electrode 2 formed as a pair of front and back faces at the center of a main plane of a piezoelectric substrate 1.
And an extraction electrode 3 derived from these vibrating electrodes 2,
One end of each of the extraction electrodes 3 is connected to a terminal electrode 4 provided at an end of the piezoelectric substrate 1.

As shown in FIG. 9, such a piezoelectric resonator is formed by molding the entire surface portion with an exterior resin 5, and
A free vibration space 6 is formed on the vibrating electrode 2 and in the vicinity thereof (for example, see Japanese Patent Application Laid-Open No. 4-216208).

In the piezoelectric resonator configured as described above,
Due to the free vibration space 6 formed on the vibrating electrode 2 and in the vicinity thereof, the oscillation performance is efficiently performed without inhibiting the vibration of the vibrating electrode 2.

[0005]

However, the piezoelectric resonator shown in FIG. 8 has a large PV value of the fundamental wave of the thickness longitudinal vibration,
There is a problem that oscillation occurs due to the fundamental wave of the thickness longitudinal vibration. As a result, there is a possibility that an oscillator or a filter incorporating such a resonator may malfunction.

An object of the present invention is to provide a piezoelectric resonator that can prevent oscillation due to a fundamental wave of thickness longitudinal vibration.

[0007]

According to the present invention, there is provided a piezoelectric resonator comprising:
Vibration electrodes are formed facing the substantially central portions of both surfaces of the piezoelectric substrate, and terminal electrodes are formed at both ends of the piezoelectric substrate,
Further, in a piezoelectric resonator in which the vibrating electrode and the terminal electrode are respectively connected by extraction electrodes, the vibrating electrode has an elliptical shape, and the major axis of the vibrating electrode is L ₁ and the minor axis is L.
When a _2, accept ratio (L ₁ / L ₂₎ is 1.10
With satisfying 1.75 which, the lead-out electrode connected to the major axis side of the vibrating electrode, and the width of the cited exit electrode was 0.9 to 1.1 times the minor axis L ₂ of the vibrating electrode It is.

[0008]

In the piezoelectric resonator of the present invention, when the vibrating electrode has an elliptical shape and the major axis of the vibrating electrode is L ₁ and the minor axis is L ₂ , the accept ratio (L ₁ / L ₂ ) is 1.10 to 1 .75, in the frequency band of the fundamental wave of thickness longitudinal vibration,
The harmonics of the spreading vibration mode occurring in the vibrating electrode overlap, effectively suppressing the fundamental vibration of the thickness longitudinal vibration. As a result, the resonator using the third harmonic of the thickness longitudinal vibration suppresses the fundamental vibration. It is possible to improve the oscillation performance at the third harmonic of the thickness longitudinal vibration. Further, by making the width of the lead electrode and the 0.9 to 1.1 times the major axis L ₁ of the vibrating electrode, since also occur resonance of thickness shear vibration mode as well as expansion vibration mode, the fundamental wave of thickness longitudinal vibration Unnecessary vibration occurring adjacent to the frequency band increases, and the effect of suppressing the fundamental wave vibration increases.

[0009]

DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS As shown in FIGS. 1 and 2, a piezoelectric resonator according to the present invention has a vibrating electrode 2 formed opposite to a substantially central portion on both front and back surfaces of a piezoelectric substrate 1, and a piezoelectric substrate 1 having the same structure. The terminal electrodes 4 are formed at both ends, and the vibration electrodes 2 and the terminal electrodes 4 are connected by the extraction electrodes 3 respectively.

The piezoelectric substrate 1 is made of Pb polarized in the thickness direction.
It consists of a TiO ₃ -based piezoelectric ceramic, for example, PbT
There is a composition of iO ₃ —Pb (Nb _2/3 Fe _1/3 ) O ₃ . In such a PbTiO ₃ -based piezoelectric ceramic, the Poisson's ratio is 0.24 to 0.26.

A central portion on both sides of the piezoelectric substrate 1 has A
A vibrating electrode 2 made of u, Ag or Cu is formed by vapor deposition, sputtering, photoresist or the like. Similarly, the extraction electrode 3 and the terminal electrode 4 are formed by vapor deposition, sputtering, photoresist, or the like. The electrodes 2, 3, and 4 are produced simultaneously by vapor deposition or the like. The pair of extraction electrodes 3 and the pair of terminal electrodes 4 are arranged so that they do not overlap.

The vibrating electrode 2 of the present invention is formed in an elliptical shape, and its short diameter portion is connected to one end of the extraction electrode 3. Further, as shown in FIG.
When the major axis is L ₁ and the minor axis is L ₂ , the accept ratio (L
₁ / L ₂ ) satisfies 1.10 to 1.75.

Thus, the accept ratio (L ₁ / L ₂ )
Is set to 1.10 to 1.75, if within this range,
This is because the fundamental wave vibration of the thickness longitudinal vibration can be effectively suppressed. On the other hand, when the accept ratio (L ₁ / L ₂ ) is smaller than 1.10, the effect of suppressing the fundamental vibration of the thickness longitudinal vibration is small, and the P of the third harmonic of the thickness longitudinal vibration is small.
This is because the V value becomes smaller, and when it is larger than 1.75, the fundamental wave vibration of the thickness longitudinal vibration becomes larger. Accept ratio (L ₁ / L ₂₎ is to increase the PV value of the third harmonic, from the viewpoint of reducing the PV value of the fundamental wave, it is desirable that 1.2 to 1.5.

Further, the major axis L ₁ of the vibrating electrode 2 from the viewpoint of increasing the PV value of the third-order wave of a thickness extensional vibration, the dimensions of the piezoelectric substrate 1, vertically 1.0 to 1.2 mm, lateral 4.0 ~ 5.
0m, thickness 0.22-0.24mm,
0.6~0.7mm is desirable, 0.4 to 0.6 mm is preferable for the same reason minor L _2.

[0015] The width B of the lead electrode 3 of the present invention is 0.9 to 1.1 times the major axis L ₁ of the vibrating electrode 2. This is because, within this range, the PV value of the third harmonic is increased, in combination with the effect of limiting the accept ratio (L ₁ / L ₂ ),
This is because the PV value of the fundamental wave can be reduced.
On the other hand, 0 width B of the lead electrode 3 is the major axis L ₁ of the vibrating electrode 2.
This is because the PV value of the third harmonic becomes smaller when it is smaller than nine times, and the PV value of the fundamental wave becomes larger when it is larger than 1.1. The width B of the extraction electrode 3 is the vibration electrode 2
And most preferably the same as that of the major axis L _1.

In the piezoelectric resonator configured as described above,
The harmonics of the spreading vibration corresponding to the major axis L ₁ and the minor axis L ₂ of the elliptical shape are adjacent to the frequency band of the fundamental wave of the thickness longitudinal vibration, the PV value of the fundamental wave can be reduced, and the oscillation by the fundamental wave of the thickness longitudinal vibration Can be eliminated.

[0017] 0 the width B of the lead electrode 3 of the major axis L _1.
Since the resonance of the thickness shear vibration mode as well as the spread vibration mode occurs by setting the thickness to 9 to 1.1 times, unnecessary vibration occurring adjacent to the frequency band of the fundamental wave of the thickness longitudinal vibration increases,
The PV value of the fundamental wave can be reduced, oscillation due to the fundamental wave can be prevented, and the oscillation performance at the third harmonic of the thickness longitudinal vibration can be improved.

The piezoelectric resonator of the present invention can be used, for example, as shown in FIG. 3, fixed on a dielectric substrate 7 with an adhesive. A case 8 that forms a free vibration space 6 is provided on and near the vibration electrode 2.

With such a piezoelectric resonator,
The heat resistance can be improved as compared with the conventional resin mold type, and downsizing can be promoted. In particular, in the case of the type in which the piezoelectric resonator is arranged on the dielectric substrate 7, since the fundamental wave of the thickness longitudinal vibration is not absorbed by the resin in the energy trapping mode in comparison with the resin mold type, the thickness longitudinal vibration When a piezoelectric resonator using only the harmonic energy confinement mode is used as the oscillation element, it is easy to oscillate with the fundamental wave of the thickness longitudinal vibration, but the configuration of the present invention makes it possible to effectively oscillate with the fundamental wave. Can be prevented.

In addition, as shown in FIG.
A free vibration space 6 may be formed on the vibration electrode 2 and in the vicinity thereof.

[0021]

EXAMPLE The composition was Pb _0.80 La _0.08 Sr _0.05 (Nb _2/3
A PbTiO ₃ -based piezoelectric substrate represented by Fe _1/3 ) _0.02 Mn _0.02 Ti _0.96 O ₃ and polarized in the thickness direction and having a length of 1.1 mm, a width of 4.5 mm, and a thickness of 0.22 mm was prepared.
The Poisson's ratio of the piezoelectric ceramic was 0.25.

As shown in FIG. 2, an elliptical vibrating electrode, terminal electrodes at both ends of the piezoelectric substrate, and lead electrodes for connecting the vibrating electrode and the terminal electrode are provided substantially at the center of both sides of the piezoelectric substrate, as shown in FIG.
It was formed in the dimensions shown in Table 1 by evaporating Cu. The thickness of the electrode was 0.6 μm. The width B of the terminal electrode was 0.5 mm, and the length L of the extraction electrode was 1.4.
mm.

The frequency dependence of the impedance of such an energy trapping type piezoelectric resonator is determined using an impedance analyzer (YHP4194A) in a measurement frequency range of 1 to 40 MHz, and the logarithm of the maximum value Zmax and the minimum value Zmin of the impedance is obtained. The ratio was defined as the PV value. The PV value is PV = 20 × log (Zmax / Z
min) (unit: dB). The PV value of the fundamental wave is obtained by using the maximum value Zmax and the minimum value Zmin of the impedance in the measurement frequency range of 10 to 15 MHz, and the PV value of the third harmonic is the maximum value Zmax and the minimum value of the impedance in the measurement frequency range of 33 to 36 MHz. It was determined using the value Zmin. Table 1 shows the results.

[0024]

[Table 1]

From Table 1, it can be seen that in the case of the conventional product (sample Nos. 1 and 8 when the accept ratio is 1), the PV value of the fundamental vibration of the thickness longitudinal vibration is as large as 35 dB or more, and the PV of the thickness longitudinal vibration is 3 dB or more. The PV value at the harmonic vibration was as small as 58.3 dB or less. In sample No. 11, the PV value at the fundamental vibration was 2
Although it is 7.5 dB, the PV value at the third harmonic vibration is 5
It was as small as 8.4 dB. On the other hand, when the accept ratio is 2 (sample No. 7), the PV value at the fundamental wave oscillation is 38 d
B was big.

The width B of the extraction electrode is equal to the major axis L of the vibration electrode.
_In the case of 0.8 times ₁ (sample No. 12), the third harmonic P
It can be seen that the V value decreases to 58.9 dB, and when the value is 1.2 times (sample No. 15), the PV value of the fundamental wave increases to 33 dB.

On the other hand, the samples Nos. 2 to 6 of the present invention
In 9, 10, 13, and 14, the PV value is 63 dB or more in the third harmonic vibration of the thickness longitudinal vibration and 29 d in the fundamental vibration.
B or less.

FIG. 4 shows a 1 MHz sample No. 5 of the present invention.
FIG. 5 shows the frequency characteristics of the resonance impedance in the thickness longitudinal vibration mode at 〜40 MHz, and FIG. 5 shows the frequency characteristics near the frequency of the fundamental wave vibration in the thickness longitudinal vibration mode at 10 to 15 MHz.

FIG. 6 shows the 1M sample No. 8 of the comparative example.
FIG. 7 shows the frequency characteristic of the resonance impedance in the thickness longitudinal vibration mode in the range of Hz to 40 MHz, and FIG.
The frequency characteristics near the frequency of the fundamental wave vibration in the thickness longitudinal vibration mode at 14.5 MHz are shown.

[0030]

As described above, in the piezoelectric resonator of the present invention, the vibrating electrode has an elliptical shape, and the major axis of the vibrating electrode is L ₁ ,
When the short diameter L _2, accept ratio (L ₁ / L ₂₎ is 1.
Satisfy 10 to 1.75, by the width of the lead electrode is 0.9 to 1.1 times the major axis L ₁ of the vibrating electrode, near the frequency band of the thickness extensional fundamental vibration, the other vibration modes Since the harmonics are superimposed and resonance of the thickness shear vibration is generated, the fundamental wave vibration can be suppressed, and the oscillation in the thickness longitudinal fundamental wave can be effectively prevented.

[Brief description of the drawings]

FIG. 1 is a perspective view showing a piezoelectric resonator of the present invention.

FIG. 2 is a plan view showing the vibrating electrode of FIG. 1 and its vicinity.

FIG. 3 is a perspective view showing an example in which the piezoelectric resonator of FIG. 1 is mounted on a dielectric substrate and a case is covered.

FIG. 4 shows a frequency characteristic of a resonance impedance of a sample No. 5 of the present invention in a thickness longitudinal vibration mode at 1 MHz to 40 MHz.

FIG. 5 shows frequency characteristics of the sample No. 5 of the present invention in the vicinity of the frequency of the fundamental vibration in the thickness longitudinal vibration mode at 10 to 15 MHz.

FIG. 6 shows a frequency characteristic of a resonance impedance in a thickness longitudinal vibration mode at 1 MHz to 40 MHz of a sample No. 8 of a comparative example.

FIG. 7 shows 9.5 to 14.5 MHz of sample No. 8 of a comparative example.
5 shows the frequency characteristics near the frequency of the fundamental wave vibration in the thickness longitudinal vibration mode in FIG.

FIG. 8 is a plan view showing a conventional piezoelectric resonator.

FIG. 9 is a cross-sectional view showing an example in which a conventional piezoelectric resonator is molded with resin.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... Piezoelectric substrate 2 ... Vibration electrode 3 ... Leader electrode 4 ... Terminal electrode

Claims (1)

[Claims] A vibration electrode is formed opposite to a substantially central portion of both surfaces of a piezoelectric substrate, and terminal electrodes are formed at both ends of the piezoelectric substrate. Further, the vibration electrode and the terminal electrode are respectively connected by extraction electrodes. In the connected piezoelectric resonator, when the vibrating electrode has an elliptical shape and the major axis of the vibrating electrode is L ₁ and the minor axis is L ₂ , the accept ratio (L ₁ /
L ₂ ) satisfies 1.10 to 1.75, and the extraction electrode is connected to the minor diameter side of the vibration electrode, and the width of the extraction electrode is 0.9 of the major diameter L ₁ of the vibration electrode. ~ 1.1
A piezo-resonator characterized in that it is twice as large.