JPS61144909A - Surface acoustic wave transducer - Google Patents

Abstract

PURPOSE:To improve the characteristic by making a combined vector of acoustic reflection between the 1st type electrode finger pairs and the 2nd type electrode finger pairs in opposite phase to the overall electric reflection so as to suppress a reflection spurious wave thereby suppressing generation of a ripple due to a bulk spurious. CONSTITUTION:The width of the 1st type electrode finger pairs A is designed to nearly 1/8 of the wavelength lambda of a surface acoustic wave propagating a piezoelectric substrate 1 and the width of the 2nd type electrode finger pairs B is designed to be nearly 1/8 and nearly 1/4 of the wavelength lambda. When a surface acoustic wave R is made incident on the 2nd tupe electrode finger pairs B of a surface acoustic wave transducer, a sound reflection 16 shown in arrows 11-16 is generated at the edge of comb-line electrodes 2, 3, and the reflection is completely opposite inn phase to the electric reflection. Then the phase of the remaining acoustic reflections 11-12, 14, 15 is in the direction of 11-12, 14, 15. On the other hand, when the surface acoustic wave R propagates toward the 1st type electrode finger pairs A, since the width of all the electrode fingers is formed as 1/8lambda and arranged at a period of 1/4lambda, the acoustic reflection is cancelled together and no reflection remains.

Description

DETAILED DESCRIPTION OF THE INVENTION [Technical Field of the Invention] The present invention relates to a surface acoustic wave transducer with improved reflection spurious.

[Technical background of the invention and its problems]

A surface acoustic wave device in which interdigital electrodes are formed on a piezoelectric substrate has a pair of electrode fingers in which a first AI tooth-shaped electrode and a second comb-shaped electrode are intermeshed with each other. By changing , various frequency characteristics can be realized.

In such a surface acoustic wave device, spurious (hereinafter referred to as reflected spurious) occurs due to reflection of the surface acoustic wave by the comb-shaped electrode. This reflected spurious appears in the form of triple transit echo ('ITE) when a filter or delay line is actually constructed, causing a significant deterioration of the characteristics. The reflection spurious is caused by the reflection component (
(hereinafter referred to as acoustic reflection) and the reflected component caused by electrical re-excitation of the comb-shaped electrode (hereinafter referred to as electrical reflection).
It is known that there is one.

Therefore, by focusing on these two reflected components, the applicant of the present application has developed a surface acoustic wave transducer that is configured to remove the reflected spurious by canceling out the acoustic and electrical reflections in opposite phases. ζ has been published separately (Japanese Unexamined Patent Publication No. 56-10724).

This surface acoustic wave transducer is shown in FIG. In the figure, 61 is a piezoelectric substrate, and 62 is an interdigital electrode! It is extreme. The interdigital electrode 62 is composed of a $1 comb-shaped electrode 63 and a second comb-shaped electrode 64. The first &i tooth-shaped electrode 63 has an electrode finger 63a with a width of 1/8λ (λ is the wavelength of the surface acoustic wave) and an electrode finger 63b with a width of 3Aλ.
Particularly along the direction of incidence of surface acoustic waves, an electrode finger 63b having a width of 3/8λ is arranged after an electrode finger 63H having a width of 1/8λ with a gap width of 1/8λ. After a gap width of 3/8λ width from the right end of the finger 63b, the electrode finger 63a of 1/8λ width and the electrode finger 63 of 3/8λ width
b are arranged repeatedly. In addition, a second comb-shaped electrode 6
4 is constructed by arranging electrode fingers 64a each having a width of 1/8λ at a predetermined gap width.

As shown in the figure, the first comb-shaped electrode 63 and the second comb-shaped electrode 64 are interlocked to form an interdigital electrode 62. [63a.

The gap widths of 63b and 64a are all set to 1/8λ.

When a surface acoustic wave R is incident on this surface acoustic wave device from the left in the figure, the surface acoustic wave waveform becomes 71 in the figure due to the mismatch of acoustic impedance at the edge of each comb-shaped electrode.
It is reflected as shown by the arrow ˜76. For example, when the X plane in FIG. 7 is used as the reference phase plane for electrical reflection, the surface acoustic waves reflected at the electrode finger edges located on the right side of this reference phase plane X are delayed in phase with respect to the electrically reflected waves. Moreover, the surface acoustic wave reflected by the electrode finger edge located on the left side leads in phase to the electrically reflected wave. FIG. 8 shows the phases of the acoustic reflected waves 71 to 76 with the phase of the electrical reflected waves as a reference (0 degree). For example, the acoustic reflected wave 76 will be delayed in phase by 9Aλ in the round trip with respect to the reference phase plane X, and will have a positive phase with respect to the electrical reflected wave (45°
The phase is delayed by ×9) degrees. Also, the phase of the acoustic reflected wave 75 is delayed by 7/8λ during the round trip, but since it has an opposite phase relationship t with that of the electrical reflected wave, the overall phase is (7/8λ).
8λ-λ/2), for electrically reflected waves, (
The phase is delayed by 45° x 3) degrees. In addition, the acoustic reflected wave 7
Phases 1 to 74 can be considered in the same way.

Therefore, as shown in Figure @8, the composite vector 77 of all the acoustic reflected waves 71 to 76 is opposite in phase to the electrical reflected waves, so they cancel each other out, and as a result, the reflected spurious can be reduced. can.

The following problems have been pointed out in this surface acoustic wave device. That is, the amount of electrical reflection of the surface acoustic wave device is the load R,l! connected to it. , it is necessary to generate an amount of acoustic reflection commensurate with the amount of electrical reflection. In this case, the amount of acoustic reflection is adjusted using the electrode fingers 63a, 63b of the comb-shaped electrodes 63, 64,
This is done by changing the acoustic reflectance by the action of the mass effect of the metal film 64a. Therefore, the load RI! When the amount of electrical reflection increases due to the value of , the electrode fingers 63a and 63b.

It is necessary to increase the thickness of 64a to increase the mass effect and increase the amount of acoustic reflection.

Therefore, when the electrode metal film is formed thickly, a portion of the surface wave energy is converted into the bulk wave mode at a higher rate, and ripples appear in the output signal due to so-called pulse spurious, and this phenomenon is caused by the comb-shaped electrode 3. There was a problem that occurred more noticeably as the film thickness of No. 4 increased.

[Purpose of the invention]

This invention was made to solve the above problems, and provides a surface acoustic wave transducer that can suppress ripples caused by bulk spurious signals, suppress reflected spurious signals over a wide band, and significantly improve characteristics. The purpose is to provide.

[Summary of the invention]

This invention is the first method in which only electrical reflection occurs and acoustic reflection is zero.
The type of electrode finger pair is formed by electrode fingers having at least approximately 1/8 human width of approximately 5/8 λ width and approximately 1/8 λ width, and a second electrode finger pair that causes both electrical reflection and acoustic reflection.
By forming a type of electrode finger pair with electrode fingers of approximately IAλ width and approximately 1/4λ width, the composite vector of acoustic reflections of the first type electrode finger pair and the second type electrode finger pair is integrated. It is characterized by suppressing reflected spurious by making the phase opposite to that of electrical reflection.

〔Effect of the invention〕

According to this invention, the maximum acoustic reflection amount per pair of toothed electrodes can be set larger than that of conventional ones, so the metal film thickness of the comb-shaped electrodes can be made thinner to obtain the desired amount of acoustic reflection. This makes it possible to reduce the rate at which surface wave energy is exchanged with the bulk wave mode, thereby reducing bulk wave spurious. Moreover, since the maximum acoustic reflection of the transducer can be increased, the amount of electrical reflection can be increased and a surface wave transducer with low loss can be easily realized.

[Embodiments of the invention]

Hereinafter, one embodiment of the present invention will be described with reference to the drawings.

In FIG. 1, reference numeral 1 denotes a piezoelectric substrate, and on the elastic surface propagation surface of this substrate 1 are provided a first comb-shaped electrode 2, a second comb-shaped electrode 3. , and the respective pairs of electrode fingers are engaged to form a surface acoustic wave transducer. The electrode finger pairs of this transducer consist of a first type of electrode finger pair that causes only electrical reflection and zero acoustic reflection, and a second type of electrode finger pair B that causes electrical and acoustic reflection. standing.

The intersection width of this second type of electrode finger pair B is varied triangularly along the propagation direction of the surface acoustic wave so that electrical reflection and acoustic reflection become zero at all points on the time axis. Then, on both sides of this fa2 type electrode finger pair B, there are first electrodes.
A pair of electrode fingers A of the type is provided.

The first type of electrode finger pair B is provided with a width dimension that is approximately 1/8 of the wavelength λ of the surface acoustic wave propagating through the piezoelectric substrate 1, and the second type electrode finger pair B is provided with a width dimension that is approximately 1/8 of the wavelength λ of the surface acoustic wave propagating on the piezoelectric substrate 1. 8 and about 1
/4 width dimension. In the illustrated example, the first comb-shaped ′:4L pole 2 has electrode fingers 2a and 2b having a width of approximately IAλ along the direction in which the surface acoustic wave R is incident.

2C are arranged with a gap width of IAλ, and furthermore, an electrode finger pair 2d having a width of approximately 1/4λ is arranged between the electrode finger pairs 2b and 2c.
is arranged to electrically short-circuit the electrode finger pair 2b, 2C. At this time, the electrode finger 2d with a width of 1/4λ is l/
Arranged at a position approximately 1/16λ distance from the left end of the electrode finger 2b having a width of 8λ! It is shi. In addition, the comb-shaped electrode 3 of $2 has a structure in which electrode fingers 3a having a width of about 14λ are repeated, and in particular, the electrode fingers 3a having a width of 1/8λ are connected to the first comb-shaped electrode 2.
are adjacent to each other with a gap width of 1/8λ.

Now, when a surface acoustic wave is incident on the second type of electrode finger pair B of this surface acoustic wave transducer, acoustic reflection occurs at the edges of the comb-shaped electrodes 2 and 3 as shown by arrows 11 to 16 in the figure. occurs. When the phases of the acoustic reflections 11 to 16 are expressed with respect to the electrical reflection reference phase plane (reference phase plane X), it becomes as shown in FIG. For example, acoustic reflection 16
The V8λ phase is delayed with respect to the reference phase plane X in the round trip. Also, the acoustic reflection 13 is V8λ in round trip with respect to the acoustic reflection 16.
The phase advances, and further phase reversal causes 180 degrees (1/2λ
) are added, resulting in a relationship in which the phase is advanced by 13/8λ as a whole. At this time, the acoustic reflection 16 is in the direction shown by 16 in FIG. 2, and has a completely opposite phase to the electrical reflection. Based on the same concept, the remaining acoustic reflections 11 to 12 and 14.15 have the same phase as 11 to 12°14.15 in Figure 2.
The direction will be

On the other hand, when the surface acoustic wave R enters the first type of electrode finger pair A, the electrode fingers in this region are all formed with a width of IAλ and are arranged at a period of 1/4λ, so that acoustic reflections occur from each other. Nothing remains because they cancel each other out.

Therefore, within the region of the second type electrode finger pair B, the composite vector 17 of all the acoustic reflections 11 to 16 is the acoustic reflection at the edge of the electrode finger 2d of the first a-tooth-shaped electrode 2, as shown in FIG. 13. ! :14 resultant vectors of acoustic reflections remain.

In this example, the maximum amount of acoustic reflection per pair of electrodes in the shield is made to match the overall electrical reflection characteristic, so if the magnitude of acoustic reflection and electrical reflection are made the same, reflected spurious over a wide band can be suppressed. It can be suppressed. Moreover, since the composite vector 17 of all the acoustic reflections 11-16 is a composite of the acoustic reflections 13 and 14, the maximum acoustic reflection amount per pair of comb-shaped electrodes is approximately 1.
It can be set to 4 times.

Therefore, the metal film having the polar tooth shape ti can be formed thinly to obtain the desired amount of acoustic reflection.

Bulk wave spurious can be improved by suppressing surface wave propagation loss. Thereby, the characteristics of the surface acoustic wave transducer can be significantly improved.

Other embodiments of this invention will be shown below.

FIG. 3 shows a modification of the above embodiment, in which the acoustic reflection regions indicated by broken lines 20 in FIG. 3 are dispersed in the cross width direction. The first type W electrode finger pair A is provided with a width dimension of approximately V8 of the wavelength λ of the surface acoustic wave propagating through the piezoelectric substrate 21, and the second type electrode finger pair B is provided with a width dimension of approximately V8 of the wavelength λ of the surface acoustic wave propagating on the piezoelectric substrate 21.
The width dimension is approximately 1/8 and approximately 1/4 of the width.

Therefore, even with such a configuration, the same effects as described above can be achieved.

In FIG. 4, a first comb-shaped electrode 32 and a comb-shaped electrode 33 of t42 are formed on the elastic surface propagation surface of a piezoelectric substrate 31, and each pair of electrode fingers is engaged to form a surface acoustic wave transducer. The electrode finger pair of this transducer is of the second type 1! as shown in the figure. The crossing width of the polar finger pair B is changed in a triangular shape along the propagation direction of the surface acoustic wave so that the electrical reflection and acoustic reflection become zero at all points on the time axis,
A first type of electrode finger pair is provided on both sides of this second type of electrode finger pair B. The width dimensions of the first type of electrode finger to person are approximately 1/8 and approximately 5/8 of the wavelength λ of the surface acoustic wave (
ζ, and the width dimensions of the second type electrode finger pair B are set to approximately 1/8 and approximately 1/4 of the wavelength λ.

Now, when a surface acoustic wave is incident on the second type of electrode finger pair B of this surface acoustic wave transducer, acoustic reflection occurs at the edges of the comb-shaped electrodes as shown by arrows 41 to 46 in the figure. The phases of the acoustic reflections 41 to 46 are expressed with respect to the electrical reflection reference phase plane (reference phase plane X) as shown in FIG.

For example, the acoustic reflection 46 is 9 times round trip to the reference phase plane X.
/8 λ phase is delayed. Also, the acoustic reflection 43 is the acoustic reflection 4
For 6, the μλ phase advances in the round trip, and 180 degrees (1/2λ) is added due to this phase reversal, resulting in a total of 1
The relationship is such that the 3/8λ phase is advanced.

Therefore, the acoustic reflection 43 is in the direction shown by 43 in FIG. 5, which is completely opposite in phase to the electric reflection.

The remaining acoustic anti-N41, 42, and 44.45 phases are also considered to be 41, 42, 44 in Fig. 5 based on the same idea.
．． 45 direction. Therefore, within the region of the second type electrode finger pair B, the composite vector 47 of all the acoustic reflections 41 to 46 is the acoustic reflection 43 at the edge of the electrode finger 33a of the first comb-shaped electrode, as shown in FIG. This means that acoustic reflections for 44 combined vectors remain.

Therefore, with such a configuration, the same effects as the embodiment shown in FIG. 1 can be achieved.

FIG. 6 shows a modification of the embodiment shown in FIG.
The acoustic reflection regions indicated by broken lines 50 in FIG. 6 are dispersed in the cross width direction.

Therefore, even with such a configuration, the same effects as described above can be achieved.

Note that the present invention is not limited to the above-mentioned embodiments, and can be implemented with various modifications without changing the gist.

[Brief explanation of drawings]

Fig. 1 is a configuration diagram showing an embodiment of the present invention, Fig. 2 is a reflection synthesis vector diagram for explaining the implementation, w, Fig. 3,
4 and 6 are block diagrams showing other embodiments of the present invention, FIG. 5 is a reflection synthesis vector diagram for explaining the embodiment of FIG. 4, and FIG. 7 is a conventional surface acoustic wave FIG. 8 is a configuration diagram showing a transducer, and is a reflection synthesis vector diagram for explaining this transducer. 1.21.31... Piezoelectric substrate 2.32... First comb-shaped electrodes 2a, 2b, 2C, 3a, 33a... Electrode fingers 3.3
3...Second comb tooth shape'? ! 11-16.41-46...Acoustic reflection 17...Synthetic vector A...First type of electrode finger pair B...Second type of electrode finger pair R...Surface acoustic wave X...Electrical reflection reference phase plane 20.50...Acoustic reflection area 61...Pressure 1Ti, plate 62...Interdigital electrode 63...First handle I tooth-shaped electrode 63a, 63b, 64a - ffi pole finger pole fat...Second m tooth shaped electrodes 71-76...Acoustic reflection 77...Synthetic vector R1! ···load

Claims (4)

[Claims] (1) Formed by combining a first type of electrode finger pair that causes only electrical reflection and zero acoustic reflection on the piezoelectric substrate and a second type of electrode finger pair that causes both electrical and acoustic reflection. The first type of electrode finger pair is formed by electrode fingers having a width approximately 1/8 of the wavelength of the surface acoustic wave propagating through the piezoelectric substrate, and the second type of electrode finger pair is Formed by electrode fingers having a combination of width dimensions of approximately 1/8 and approximately 1/4 of the wavelength of the surface acoustic wave, and intersecting the first type electrode finger pair and the second type electrode finger pair. A surface acoustic wave transducer characterized by being distributed alternately in the width direction. (2) A patent characterized in that the first type of electrode finger pair is formed by combining electrode fingers with a width dimension of approximately 1/8 and approximately 5/8 of the wavelength of the surface acoustic wave propagating through the piezoelectric substrate. A surface acoustic wave transducer according to claim 1. (3) Claims characterized in that the 1/4 width electrode fingers of the second type of electrode finger pair are formed to have a width dimension of approximately 1/4±1/8 of the wavelength of the surface acoustic wave. 2. The surface acoustic wave transducer according to claim 1. (4) The surface acoustic wave transducer according to claim 1, wherein the intersection width of the second type electrode finger pair changes in a substantially triangular shape along the propagation direction of the surface acoustic wave. .