JPH05145368A - Surface wave device - Google Patents

Abstract

PURPOSE:To provide a device utilizing a BGS wave having less production of spurious vibration and an excellent resonance characteristic by forming a piezoelectric substrate through the use of a piezoelectric material whose electromechanical coupling coefficient of thickness-shear vibration is a specific value or over. CONSTITUTION:A piezoelectric substrate 2 is formed by using a material in which a ratio of titanium and zirconium of a lead titanate and zirconate group piezoelectric ceramics PbTi1-xO3-PbZrxO3 is selected properly and an electromechanical coupling coefficient K15 of thickness-shear vibration is selected to be 40% or over. Interdigital transducers 3, 4 are formed to the upper side of the substrate 2 to form a surface wave resonator 1 thereon. Thus, the production of spurious vibration is effectively suppressed and the resonance characteristic is made excellent.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface wave device utilizing BGS waves, and more particularly to a surface wave device having improved resonance characteristics by selecting a material for a piezoelectric substrate.

[0002]

2. Description of the Related Art FIG. 2 is a perspective view showing a conventional surface acoustic wave resonator utilizing BGS waves. The surface acoustic wave resonator 1 is configured using a piezoelectric substrate 2 made of piezoelectric ceramics such as lead zirconate titanate-based ceramics. The piezoelectric substrate 2 is polarized in the direction of arrow P. A pair of comb-teeth electrodes 3, 4 are formed on the upper surface of the piezoelectric substrate 2. Each of the comb electrodes 3 and 4 has a plurality of electrode fingers, and the plurality of electrode fingers are arranged so as to be interleaved with each other. In the surface wave resonator 1, a BGS wave is excited in the arrow X direction by applying an AC electric field between the comb-teeth electrodes 3 and 4, and the excited BGS wave is converted into the end surface 2
It is configured to be reflected between a and 2b.

[0003]

In the surface wave resonator 1 utilizing the BGS wave, the BGS wave is reflected between the end faces 2a and 2b to operate as a resonator. Therefore, the accuracy of the end faces 2a and 2b is high. Needs to be increased as much as possible. It is said that good resonance characteristics can be obtained by increasing the accuracy of the end faces 2a and 2b as much as possible. However, there is a limit to increasing the accuracy of the end faces 2a and 2b. Therefore, even if the accuracy of the end faces 2a and 2b is increased as much as possible, the resonance point-the anti-resonance point, especially the anti-resonance frequency vicinity, is limited. There was a problem that spurious vibrations of considerable strength were generated in the frequency region of.

An object of the present invention is to provide a surface acoustic wave device using BGS waves which has a good resonance characteristic with less generation of spurious vibrations.

[0005]

Means for Solving the Problems The present inventors
In a surface acoustic wave device utilizing waves, considering that there is a limit to improving the end face accuracy, as a result of diligent examination of a method of suppressing undesired spurious vibrations, if the material of the piezoelectric substrate is selected to be a specific one, The inventors have found that spurious vibrations between the resonance point and the anti-resonance point, particularly in the vicinity of the anti-resonance frequency, can be effectively suppressed, and have completed the present invention. That is, the present invention comprises a piezoelectric substrate and at least one interdigital transducer provided on the piezoelectric substrate.
A surface acoustic wave device using GS waves is characterized in that the piezoelectric substrate is made of a material having an electromechanical coupling coefficient k _{15 of} thickness shear vibration of 40% or more.

[0006]

In the present invention, since the piezoelectric substrate is made of a material having an electromechanical coupling coefficient k ₁₅ of thickness shear vibration of the piezoelectric substrate of 40% or more, as will be apparent from the examples described later,
Undesired spurious vibrations between the resonance point and the anti-resonance point, particularly near the anti-resonance frequency, can be effectively suppressed.

[0007]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Lead zirconate titanate-based piezoelectric ceramics PbTi _1-x O ₃ -PbZr _x O _{3 of} various compositions shown in Table 1 below, in which the ratio of titanium to zircon is changed.
A piezoelectric substrate was manufactured by using, and the end face reflection type surface wave resonator 1 shown in FIG. 2 was manufactured. The size of the piezoelectric substrate used was 0.92 × 0.90 × 0.80 mm, and the number of pairs of electrode fingers on the upper surface of the piezoelectric substrate was 15 pairs and the cross width was 7
A wavelength interdigital transducer was formed.

The resonance characteristics, that is, the impedance-frequency characteristics and the phase-frequency characteristics of the surface acoustic wave resonators obtained as described above were measured. The results are shown in Table 1 when the undesired spurious vibrations are hardly generated, and when the undesired spurious vibrations are generated to a considerable extent, by the cross mark. As an example, FIG. 3 shows an impedance-frequency characteristic (solid line) and a phase-frequency characteristic (broken line) of a surface wave resonator (using a piezoelectric material having a composition B) in which spurious vibration does not occur, and FIG. The impedance-frequency characteristic (solid line) and the phase-frequency characteristic (broken line) of the generated surface wave resonator (using the composition F) are shown.

[0009]

[Table 1]

As is clear from Table 1, when the piezoelectric substrates of compositions A to D are used, spurious vibrations are suppressed, whereas when the piezoelectric substrates of compositions E to G are used, the spurious vibration is suppressed. It was found that spurious vibrations occur to a considerable extent near the resonance frequency. Therefore, the compositions A to D and the compositions E to
As a result of examining the difference in the material constant of the piezoelectric substrate of G, the composition A
At ~ D, the electromechanical coupling coefficient k _{15 of} the thickness shear vibration is
To which the 40% or more, since the electromechanical coupling factor k ₁₅ of the thickness-shear vibration of the piezoelectric substrate E~G is 40% or less, the spurious vibrations, the electromechanical coupling coefficient k ₁₅
Was suppressed by using a piezoelectric substrate of 40% or more.

The electromechanical coupling coefficient k ₁₅ of the thickness-shear vibration mode has a relationship with the electromechanical coupling coefficient k _{BGS of} BGS waves shown by the following equation (1). (K _BGS ) ² = (k ₁₅ ) ² / {1+ (k ₁₅ ) ² } (1) That is, the electromechanical coupling coefficient k ₁₅ of the thickness shear vibration is
Since the electromechanical coupling coefficient k _{BGS of the} BGS wave has the above relation, the electromechanical coupling coefficient k ₁₅ is a standard for measuring the resonance characteristic in the end surface reflection type surface wave resonator 1 using the BGS wave. .. Incidentally, those used in which an index electromechanical coupling factor k ₁₅ in the thickness shear vibration as described above, it is not possible to directly measure the electromechanical coupling coefficient k _BGS of BGS waves.

A report of measuring the effective electromechanical coupling coefficient of the BGS wavefront reflection resonator (for example, 5 1976)
Published by The Acoustical Society of Japan, pp. 351-352
The electromechanical coupling coefficient is the effective electromechanical coupling coefficient k _eff of the BGS wavefront reflection resonator calculated from the curve showing the resonance characteristics, which is a direct measurement of k _BGS. This electromechanical coupling coefficient k _eff varies depending on the resonator design method, and k _BGS is 1
It should be pointed out that there is no one-to-one correlation.

FIG. 5 shows compositions A to G calculated from the electromechanical coupling coefficient k _{15 of the} thickness shear vibration according to the above equation (1).
BGS wave electromechanical coupling coefficient k _BGS of the material
The electromechanical coupling coefficient k _eff obtained from the frequency characteristics of the GS wave facet reflection resonator is indicated by a ● _symbol . As is apparent from FIG. 5, the electromechanical coupling coefficient k _BGS electromechanical coupling coefficient k ₁₅ and BGS wave of the thickness shear vibration 1: 1 it can be seen that there is no relationship. In the above embodiment, the suppression of spurious vibration is realized in the end face reflection type surface wave resonator shown in FIG. 2 by setting the electromechanical coupling coefficient k ₁₅ of the thickness shear vibration to 40% or more as described above. I have shown that
It should be pointed out that the present invention can be applied to an end-face reflection type surface wave filter using BGS waves in which two or more sets of interdigital transducers are configured.

[0014]

As described above, according to the present invention, the piezoelectric substrate has an electromechanical coupling coefficient k _{15 of} thickness shear vibration of 40%.
Since the materials described above are used, spurious vibrations can be effectively suppressed. Therefore, it is possible to provide a surface acoustic wave device using a BGS wave exhibiting excellent resonance characteristics that could not be realized only by improving the accuracy of the end surface of the piezoelectric substrate.

[Brief description of drawings]

FIG. 1 is a diagram for explaining a relationship between an electromechanical coupling coefficient k _{15 of} thickness shear vibration and resonance characteristics.

FIG. 2 is a perspective view showing an end surface reflection type surface acoustic wave resonator utilizing BGS waves.

FIG. 3 Impedance of a surface acoustic wave resonator using a piezoelectric substrate made of a material having an electromechanical coupling coefficient k ₁₅ of 40% or more-
The figure which shows a frequency characteristic and a phase-frequency characteristic.

FIG. 4 is a diagram showing impedance-frequency characteristics and phase-frequency characteristics of a surface acoustic wave resonator using a piezoelectric substrate made of a material having an electromechanical coupling coefficient k ₁₅ of 38%.

FIG. 5 shows electromechanical coupling coefficient k _BGS of BGS wave and effective electromechanical coupling coefficient k _{eff of} each piezoelectric material prepared in the example.
And FIG.

[Explanation of Codes] 1 ... Surface wave resonator 2 ... Piezoelectric substrates 2a, 2b ... End surfaces 3, 4 ... Comb-shaped electrodes constituting an interdigital transducer

Claims (1)

[Claims] 1. A surface acoustic wave device using a BGS wave, comprising a piezoelectric substrate and at least one interdigital transducer provided on the piezoelectric substrate, wherein the piezoelectric substrate has an electromechanical coupling coefficient k of thickness shear vibration.
_{15. A} surface acoustic wave device, wherein ₁₅ is composed of 40% or more of a piezoelectric material.