JPH07131283A - End surface reflection type surface wave device - Google Patents

Abstract

PURPOSE:To obtain the end surface reflection type surface wave device which can reduce an unnecessary ripple on the lower frequency side than a resonance point and has superior resonance characteristics. CONSTITUTION:On the top surface 2a of a piezoelectric substrate 2 whose plane shape is quadrangular, a couple of inter-digital electrodes 3 and 4 are arranged so that plural electrode fingers 3a-3c and 4a-4c are put between one another; and the outermost electrode fingers 3c and 4a are formed along the end surfaces 2b and 2c of the piezoelectric substrate 2 to constitute the end surface reflection type surface wave device 1 which utilize an SH type surface wave. The outermost electrode fingers 3c and 4c are so cut that the end surfaces are positioned lambda/64-7lambda/64 inside, thereby determining the width of the outermost electrode fingers.

Description

Detailed Description of the Invention

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an end surface reflection type surface acoustic wave device, and in particular, it utilizes an SH type surface acoustic wave whose displacement such as BGS wave and Love wave is mainly perpendicular to the surface wave propagation direction. The present invention relates to an end surface reflection type surface acoustic wave device.

[0002]

2. Description of the Related Art As a conventional end surface reflection type surface acoustic wave device, B
An end face reflection type surface wave resonator utilizing GS waves is known (for example, Proceedings of the Acoustical Society of Japan, Spring 1976, pp. 351 to 352, published in May 1976).

An end surface reflection type surface acoustic wave resonator utilizing BGS waves is constructed by using a piezoelectric substrate having a rectangular planar shape made of a piezoelectric single crystal such as lead zirconate titanate type piezoelectric ceramics or LiNbO _3. There is. Here, on the piezoelectric substrate, a pair of comb-teeth electrodes arranged so that a plurality of electrode fingers of each other are interleaved are formed. When the wavelength of the excited BGS wave is λ, the electrode fingers are
The width is set to λ / 4 excluding the outermost electrode fingers, and the width between the adjacent electrode fingers is also set to λ / 4. Further, the electrode fingers on both sides located on the outermost side are formed along the edge of the piezoelectric substrate and have a width of λ / 8. That is, the pair of outermost electrode fingers has a width of 1 compared to other electrode fingers.
The size is / 2.

In the end face reflection type surface wave resonator, the BGS wave is completely reflected by the end faces of the piezoelectric substrate facing each other, and
The S wave is confined between both end faces and resonates. by the way,
Proceedings of the Acoustical Society of Japan, 1976, mentioned above, No. 3
On pages 51 to 352, unless the width of the outermost electrode finger is accurately set to λ / 8, undesired spurious is generated in the resonance characteristic.
It has been pointed out that it is necessary to form it accurately so as to have a width of / 8.

[0005]

As described above, in the related art, the end face reflection type surface wave resonator utilizing the BGS wave is
It was thought that the width of the electrode fingers at both ends had to be exactly λ / 8.

By the way, the edge reflection type surface acoustic wave resonator has been manufactured through the following steps. That is, first, a pair of comb-shaped electrodes having a plurality of electrode fingers each having a width of λ / 4 are formed on a piezoelectric substrate so that the electrode fingers are inserted into each other. Thereafter, the piezoelectric substrate is cut in the thickness direction so that the outermost electrode fingers have a width of λ / 8, the outermost electrode fingers have a width of λ / 8, and an end face on which a surface wave is reflected. Cut out.

Therefore, in the above cutting, the electrode fingers located on both sides are cut exactly at the center to form the electrode fingers having a width of λ / 8. When the resonance characteristics of the end surface reflection type surface acoustic wave resonator obtained by cutting the outermost electrode finger accurately at the center as described above were measured, the results shown in FIG. 4 were obtained.

The resonance characteristic shown in FIG.
PZT with dimensions of 850 x 800 x 500 mm
This is a characteristic of a surface acoustic wave resonator configured by forming a pair of comb-teeth electrodes so that the number N of pairs of electrode fingers is 15 on the upper surface of a piezoelectric substrate made of piezoelectric ceramics. The width of the electrode fingers is λ except for the outermost electrode fingers.
/4=14.2 μm, and the width of the pair of outermost electrode fingers was set to λ / 8 = 7.2 μm.

In FIG. 4, the solid line A shows the impedance-frequency characteristic of the end face reflection type surface wave resonator obtained as described above, and the broken line B shows the phase-frequency characteristic. As is clear from FIG. 4, in this end face reflection type resonator, a considerably large ripple is generated in the portion indicated by the arrow A on the low frequency side of the resonance point.

An object of the present invention is to provide an end surface reflection type surface acoustic wave device having a structure capable of effectively reducing ripples generated in the lower frequency region than the resonance frequency and having excellent resonance characteristics.

[0011]

The present invention utilizes SH-type surface waves propagating in a piezoelectric substrate, which is provided on the piezoelectric substrate and the piezoelectric substrate and which are interleaved with each other. A pair of comb-teeth electrodes having electrode fingers,
In the end surface reflection type surface acoustic wave device in which the outermost electrode fingers are arranged along the end surface of the piezoelectric substrate, after forming the plurality of electrode fingers, the surface wave of the surface acoustic wave is more than the center line of the outermost electrode fingers. When the wavelength is λ, the width of the outermost electrode finger is determined by cutting so that the end face is located inside by λ / 64 to 7λ / 64, and the end face reflection type surface is characterized. It is a wave device.

[0012]

The inventor of the present application, in an end surface reflection type surface acoustic wave device utilizing SH type surface waves, has various angles with respect to the end surface reflection type surface acoustic wave device in order to suppress the ripple generated in the low frequency side from the resonance point. As a result of the investigation, it was found that the outermost electrode fingers, that is, the widths of the electrode fingers on both sides may be made somewhat thinner as described above, and the present invention has been completed.

That is, in the prior art, in the end surface reflection type surface acoustic wave device utilizing the SH type surface wave, for example, when the width of the remaining electrode fingers is λ / 4, the electrode fingers on both sides along the end surface to be the reflection surface are formed. It was thought that the width of λ must be exactly λ / 8, but in reality it is λ / 64 rather than λ / 8.
It has been found that it is better to make the thickness as thin as ˜7λ / 64, and thereby it is possible to effectively reduce the occurrence of ripples on the low frequency side of the resonance point. Therefore, as described above, in determining the width of the outermost electrode finger, after forming the comb-teeth electrode, λ / 64 is larger than the center line of the outermost electrode finger.
The end face is cut out and the width of the outermost electrode finger is determined by cutting ~ 7λ / 64 inside.

As described above, the widths of the electrode fingers on both sides may be made narrower than 1/2 of the widths of the other electrode fingers, and the position and the position of the end face may be determined as described above. Although confirmed experimentally by the inventor of the present application,
The reason is considered as follows.

First, the frequency calculated by the wavelength of the electrode is
Approximately, when the acoustic velocity when the surface of the substrate is electrically opened is Vf, and the acoustic velocity when electrically shorted is Vm.

[0016]

[Equation 1]

Is given by On the other hand, the frequency determined by the length L between the end faces is f when the sound velocity of the entire substrate is V.
It is given by _L = V / L.

[0018]

[Equation 2]

However, since V largely contributes to Vm due to the effect of the electric field,

[0020]

[Equation 3]

And to match f _E = f _L

[0022]

[Equation 4]

This is because it is necessary to set

[0024]

DESCRIPTION OF THE PREFERRED EMBODIMENTS The present invention will be clarified by describing embodiments with reference to the drawings.

FIG. 1 is a perspective view showing an end surface reflection type surface acoustic wave device using BGS waves to which the present invention is applied.
FIG. 3 is a schematic cross-sectional view showing an enlarged main part thereof. The end surface reflection type surface acoustic wave device 1 is an embodiment as an end surface reflection type surface wave resonator, and is configured by using a piezoelectric substrate 2 having a quadrangular planar shape. The piezoelectric substrate 2 is made of, for example, a piezoelectric material such as lead zirconate titanate-based piezoelectric ceramics or a LiNbO ₃ piezoelectric single crystal, and is polarized in the P direction shown. On the upper surface 2a of the piezoelectric substrate 2, a pair of comb-teeth electrodes 3 and 4 are formed. Comb electrode 3,
4 is a plurality of electrode fingers 3a-3c and 4a-, respectively.
4c. The plurality of electrode fingers 3a to 3c and the plurality of electrode fingers 4a to 4c are arranged so as to be inserted into each other as illustrated.

Of the plurality of electrode fingers 3a to 3c and 4a to 4c, the electrode fingers 4a and 3c located on the outermost side have a narrower width than the other electrode fingers 3a, 3b, 4b and 4c. There is.

Conventionally, the electrode finger 3 among the plurality of electrode fingers 3
The widths of a, 3b, 4b, and 4c are λ / 4, and the width of the region between the plurality of electrode fingers is also λ / 4, and the widths of the electrode fingers 3c and 4a on both sides are λ / 8. It was thought necessary to do.

However, as described above, when the end surface reflection type surface acoustic wave resonator having the electrode fingers 3c and 4a having the width of λ / 8 is formed, a large number of relatively large ripples are generated on the low frequency side from the resonance point. Had occurred.

The inventors of the present invention have proposed an end surface reflection type surface acoustic wave resonator 1
In, the widths of the electrode fingers 3c and 4a on the both sides were variously changed, and the magnitude of the ripple on the low frequency side from the resonance point was measured. The results are shown in Fig. 3.

The end surface reflection type surface acoustic wave resonator 1 having the electrode fingers 3c and 4a having various widths is formed on a piezoelectric substrate made of PZT and having a quadrangular planar shape. By forming a comb-shaped electrode, and then cutting the piezoelectric substrate in the thickness direction so that the width of the electrode fingers on both sides is narrower than that of the other electrode fingers, and cutting out both end faces 2b, 2c of FIG. Obtained. The width of the electrode fingers was λ / 4 = 14.2 μm except for the outermost electrode fingers, and the width of the region between the electrode fingers was λ / 4 = 7.1 μm.

The horizontal axis in FIG. 3 indicates the electrode fingers 4a on both sides,
The cutting position in 3c is shown, and the case of cutting at the center of the first formed λ / 4 electrode finger is set to zero, and the distance from the center position to the cutting position is expressed as the distance from the electrode center. Regarding the positive and negative of the distance from the center of the electrode, the case inside the center of the electrode was negative and the case outside the center was positive. That is, when the distance from the electrode center in FIG. 3 is −λ / 16, for example, the cutting position is λ / 4.
The position of the outermost electrode finger is shifted by −λ / 16 to the center side from the center of the electrode finger of, and the width of the outermost electrode finger formed by cutting is (λ / 8−λ / 16) = 4λ / 64. Become.

In FIG. 3, a broken line C indicates a case where the number N of electrode fingers is 7.5, a solid line D indicates a case where the number N of electrode fingers is 15, and a broken line E indicates a case where the number N of electrode fingers is 30. The results are shown. In addition, the vertical axis in FIG. 3, that is, the magnitude of the ripple, shows a relative value when the Q of the vibrator is constant.

As is apparent from FIG. 3, the outermost electrode finger is accurately cut at the center regardless of the number of pairs of electrode fingers, that is, the outermost electrode finger having a width of λ / 8 is formed. Shows that the ripple is not so small. That is, as shown in the result shown in FIG. 4, a relatively large ripple was generated in the low frequency side of the resonance point.

On the other hand, when the outermost electrode fingers are made thinner than λ / 8, that is, the cutting position is brought closer to the center side,
It can be seen that the ripple can be reduced when the distance from the electrode center in FIG. 3 is set to a certain range on the − side. Specifically, as is clear from FIG. 3, the cutting position is set within the range of λ / 64 to 7λ / 64 from the center of the original electrode finger to the − side, in other words, the width of the outermost electrode finger. Λ
It can be seen that the ripple can be effectively reduced by making λ / 64 to 7λ / 64 thinner than / 8.

Therefore, as is clear from the result of FIG.
The width of the electrode fingers on both sides is λ / 64 to 7λ / 6 rather than λ / 8.
By making it thinner by 4, the ripple on the lower frequency side than the resonance point can be effectively reduced.

In the description of the above embodiment, BG
Although the end surface reflection type surface wave resonator using the S wave has been described, the present invention can also be applied to an end surface reflection type surface wave resonator using other SH type surface waves such as a Love wave.

Further, although the end surface reflection type surface wave resonator has been described as the above embodiment, the present invention can be applied to the end surface reflection type surface wave filter. Further, in the above embodiment, the pair of comb-teeth electrodes are formed on the piezoelectric substrate, but another thin film such as ZnO or CdS may be further formed on the comb-teeth electrodes.

[0038]

According to the present invention, in the end surface reflection type surface acoustic wave device using SH type surface waves, the width of the outermost electrode finger is cut by λ / 64 to 7λ / 64 inside the center line. Since the width is determined, the unnecessary ripple on the low frequency side of the resonance point can be effectively reduced. Therefore, it becomes possible to provide an end surface reflection type surface acoustic wave device having excellent resonance characteristics.

[Brief description of drawings]

FIG. 1 is a perspective view showing an end surface reflection type surface acoustic wave device to which the present invention is applied.

FIG. 2 is an enlarged cross-sectional view showing a part of the end surface reflection type surface acoustic wave device shown in FIG.

FIG. 3 is a diagram showing the relationship between the distance from the electrode center and the magnitude of ripple when cutting to define the width of the outermost electrode finger.

FIG. 4 is a diagram showing impedance-frequency characteristics and phase-frequency characteristics in a conventional end surface reflection type surface acoustic wave device.

[Explanation of symbols]

 DESCRIPTION OF SYMBOLS 1 ... End surface reflection type surface acoustic wave device 2 ... Piezoelectric substrate 3, 4 ... Comb-shaped electrode 3a-3c, 4a-4c ... Electrode finger

 ─────────────────────────────────────────────────── ─── Continuation of the front page (72) Inventor Yasutaka Takakuwa 2-26-10 Tenjin Tenjin, Nagaokakyo, Kyoto Prefecture Murata Manufacturing Co., Ltd. (72) Inventor Seigo Hayashi 2-26-10 Tenjin, Nagaokakyo, Kyoto Stock Company Murata Manufacturing

Claims (1)

[Claims] 1. A pair of comb teeth that utilizes SH type surface waves propagating through a piezoelectric substrate and that has a piezoelectric substrate and a plurality of electrode fingers that are provided on the piezoelectric substrate and that are interleaved with each other. An end face reflection type surface acoustic wave device comprising an electrode and an outermost electrode finger arranged along an end face of the piezoelectric substrate, wherein after forming the plurality of electrode fingers, a center line of the outermost electrode finger. Λ / 64, where λ is the wavelength of the surface wave
The end surface reflection type surface acoustic wave device, wherein the width of the outermost electrode finger is defined by cutting the end surface so that the end surface is located inside by ˜7λ / 64.