JP3255658B2 - Surface acoustic wave convolver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to a surface acoustic wave convolver in which surface acoustic wave transducers having interdigital electrodes having different electrode widths and periods in the direction of surface acoustic wave propagation are combined.

[0002]

2. Description of the Related Art Conventionally, interdigital transducers comprising positive and negative electrodes provided on a piezoelectric substrate (including a piezoelectric thin film substrate) or an electrostrictive substrate.
In general, the surface acoustic wave converter having the above-mentioned structure has an electrode arrangement having a regular period structure. FIG. 5A is a plan view showing a surface acoustic wave convolver using a conventional surface acoustic wave converter, and FIG. 5B is an XY cross-sectional view thereof. 51 is a first surface acoustic wave converter for converting an electric signal into a surface acoustic wave, 52 is a second surface acoustic wave converter for converting a similar electric signal into a surface acoustic wave, and 53 is a surface acoustic wave converter 51 , 52 are output electrodes for detecting the advanced surface acoustic waves generated and extracting the convolution output as an electric signal. Each of the interdigital transducers of the surface acoustic wave converters 51 and 52 has an electrode arrangement structure having an equal period. That is, when the electrode width of the interdigital transducer is m and the period is p, p is constant.
m / p was a constant (mostly “0.5”) everywhere.

In a surface acoustic wave converter having such a periodic electrode arrangement, the generated surface acoustic wave propagates with substantially the same amplitude in both the left and right directions. Therefore, it can be said that it has the same surface acoustic wave radiation characteristics in both directions, so to say, has bidirectional characteristics. Also, to obtain broadband characteristics
In addition, the number of electrode pairs is reduced,
The excitation efficiency was also small.

Incidentally, a surface acoustic wave convolutor shown in FIG.
To improve convolution efficiency
, The elastic waves excited by the surface acoustic wave converters 51 and 52
The excitation efficiency of the surface acoustic wave is increased, and the central output electrode 5
The strength of surface acoustic waves going to 3 is higher than the strength going to the outside
You just need to increase it. On the other hand, it has a periodic electrode arrangement and emits surface acoustic waves strongly in one direction to the propagation direction.
Conventionally, techniques for obtaining a unidirectional surface acoustic wave converter include, for example, a method using a 120-degree phase shifter, a method using a 90-degree phase shifter, and an asymmetrical reflection electrode between the positive and negative electrodes at regular intervals. There is a method of providing an internal reflection type one-way converter that obtains one-way characteristics by arranging them in a single direction.

[0005]

Surface acoustic wave transducer having an electrode arrangement structure of such period [0008] has a bi-directional characteristic, characteristic you strongly excited in one direction can not be obtained. More broadband
To obtain the characteristics, the number of electrode pairs must be reduced
However, the excitation efficiency is further reduced. Therefore, even if a surface acoustic wave convolver is configured using such a surface acoustic wave converter, a convolver with high convolution efficiency cannot be obtained. In the technique of obtaining a unidirectional surface acoustic wave transducer described above, the characteristics you strongly excited in one direction is obtained, because of the use of surface acoustic wave transducer having an electrode arrangement of an equal period again , Broadband characteristics cannot be obtained. Therefore, even when applied to a surface acoustic wave convolver, wideband characteristics cannot be obtained.

An object of the present invention is to provide a surface acoustic wave convolver having high convolution efficiency and wide band characteristics in view of the above-mentioned problems in the conventional example.

[0007]

In order to achieve the above object, the present invention provides first and second interdigital electrodes for exciting a surface acoustic wave on a piezoelectric or electrostrictive substrate. And an output electrode for detecting a surface acoustic wave of the above and extracting a convolution output as an electric signal, wherein the first and second interdigital electrodes have a predetermined thickness, and the first and second interdigital electrodes have a predetermined thickness. The interdigital transducer has positive and negative electrodes whose electrode width and cycle gradually decrease toward the output electrode, and the second interdigital transducer gradually changes the electrode width and cycle toward the output electrode. Are alternately arranged, and one of the first and second interdigital electrodes is a single electrode.
It has an electrode structure, and the other has a double electrode structure. And the sound of the metal film of the interdigital transducer
Impedance Zm, acoustic impedance of electrode gap
If Zm / Zg is smaller than 1,
Then, the first interdigital transducer has a single electrode structure.
Then, the second IDT may have a double electrode structure.
No.

[0008]

Function: The electrode width m and the period p gradually change in the propagation direction
Single positive and negative electrodes having the electrode structure is a large number arranged, when wave thickness is excited in the electrode is thick <br/> to the extent to cause reflection, anti-phase with the wave of the wave by direct excitation is the electrode <br that /> and elevation and wave generated by the phase becomes the same phase in one propagation direction, the other in the propagation direction can be such that the opposite phase, straight
The phase of the wave generated by the contact excitation and the wave
Surface acoustic wave is strongly excited so that the phase of the
A surface acoustic wave converter with one-way vibration characteristics was obtained.
It is. In addition, the electrode width at both ends, the number of electrode pairs, and the electrode width
And the rate of change of the cycle
A highly efficient surface acoustic wave converter in a band can be obtained.
A surface acoustic wave convolver having high convolution efficiency can be obtained by facing the directionality of the surface acoustic wave converter having such unidirectional and broadband characteristics and forming an output electrode therebetween. But as above
Face the positive and negative electrodes whose electrode width and period gradually change
If they are arranged together, the delay characteristics due to frequency may change
A little dispersibility comes out. To eliminate this dispersibility
Are the surface acoustic wave transducers on both sides of the output electrode
Pole) is the width and width in the propagation direction (direction toward the output electrode).
It is necessary to reverse the directions of change of the period and the period. This
A first interdigital electrode and a second interdigital electrode
Have a single electrode structure and are manufactured in the same process
So that either of the interdigital transducers
Has the opposite direction to the electrode, for example, the first interdigital
If the direction of the electrode is directed to the output electrode, the second interdigital
Because the pole direction is away from the output electrode ,
No improvement in solution efficiency can be expected. Therefore,
In the bright and to have a double electrode structure to the second interdigital electrode
I have. In other words, a single in which the electrode width and period gradually change
Direct excitation by double electrode structure
Wave phase and the position of the wave generated by reflection of the wave on the electrode
Phase is the same phase in the propagation direction.
In both directions, there is a bidirectional characteristic that surface acoustic waves are excited.
A surface acoustic wave converter is obtained. As a result, the second interdigital transducer has bidirectional characteristics, and a convolver having a relatively wide band and relatively high convolution efficiency can be obtained.

[0009]

Embodiments of the present invention will be described below with reference to the drawings.

FIG. 1 is a plan view of a surface acoustic wave convolver according to one embodiment of the present invention. Reference numeral 2 denotes an excitation-side first surface acoustic wave converter disposed on the piezoelectric substrate, and reference numeral 3 denotes an excitation-side second surface acoustic wave converter disposed on the piezoelectric substrate. The first surface acoustic wave converter 2 has a positive electrode 4 and a negative electrode 5 (first interdigital electrode). The second surface acoustic wave converter 3 has a positive electrode 6 and a negative electrode 7 (second interdigital electrode). Reference numeral 8 denotes an output electrode. The positive electrode 4 and the negative electrode 5 are alternately arranged so that the electrode width m and the period p gradually become shorter toward the output electrode. This first interdigital transducer is a single electrode with m / p = 0.5. The positive electrode 6 and the negative electrode 7 are alternately arranged so that the electrode width m and the period p gradually increase toward the output electrode. Further, the second interdigital transducer has a double electrode structure, and one positive electrode 6 is composed of two electrodes 6a and 6a.
b, and one negative electrode 7 has two electrodes 7a and 7b, respectively. This second interdigital electrode has m / p =
0.25. In other words, the second interdigital electrode is m
Each of the interdigital transducers having a single electrode structure with /p=0.8 was divided into two to form a double electrode structure. The piezoelectric substrate 1 is made of Y-cut Z-propagated lithium niobate, and the electrodes 4, 5, 6, and 7 are made of thickness.
An aluminum film of about 2000 angstroms was used.

By using such an electrode, the first
The interdigital transducer and the second interdigital transducer are both
Elasticity table excited in the direction of the output electrode while having broadband characteristics
A surface wave can be emitted. In particular, the first interdigital transducer can strongly radiate surface acoustic waves in the direction of the output electrode.
And the second interdigital transducer has a double electrode structure.
Output while maintaining the same dispersion as the first IDT
Since a surface acoustic wave can be radiated in the direction of the electrode, a convolver having a wide band and high convolution efficiency can be obtained. By adopting the double electrode structure, the electrode width in this embodiment is λ / 8, but it can be manufactured without any problem at a practical frequency. In this case, 0 ≦ m / p <0.5 is also included in the present patent as m / p.

The present invention relates to a so-called chirp type solder.
Found for the first time to impart directionality to the surface acoustic wave transducer actively using reflection at the electrode disposed on the piezoelectric substrate while maintaining a characteristic of wide band in which electrodes, a wide band utilizing this characteristic A surface acoustic wave convolver having a wide width and high convolution efficiency is configured. In this case, electrodes must have a certain thickness. Assuming that the thickness of the electrode is H and the wavelength of the surface acoustic wave is λ, it is preferable that about 0.01 ≦ H / λ ≦ 0.10.

Next , when Zm is the acoustic impedance of the electrode metal and Zg is the acoustic impedance of the electrode gap, the electrode width and the period gradually change in the propagation direction.
Surface acoustic wave converter with a single electrode structure
It indicates that the radiation direction of the surface acoustic wave of the chirp electrode having a so-called single electrode structure is determined by Zm / Zg
You . Here, the value of Zm / Zg depends on the electrode material, electrode film thickness, electrode
It is determined by the pole width and the substrate material.

FIG. 2 shows that the thickness of the electrode made of Al is 200
FIG. 7 is a diagram showing frequency characteristics and electrode arrangement for explaining the directionality of a chirp electrode having a single electrode structure by an equivalent circuit analysis when 0 angstrom and Zm / Zg = 0.98. is there. As shown in FIG. 2 (b), a down- chirped blind in which the density of the arrangement of the positive and negative electrodes gradually increases toward the IDT 24 having a pair of positive and negative electrodes. Electrode 23
Are adjacent to each other, a frequency characteristic as shown by a solid line 21 in FIG. Conversely, as shown in FIG. 2 (c), the toward the IDT 26 having a pair of positive and negative electrodes, Interdigital up tea <br/>-loop, such as the density of the arrangement of the positive and negative electrodes gradually becomes rough In the configuration in which the electrodes 25 are adjacent to each other, FIG.
The frequency characteristic is as shown by the broken line 22 in FIG. As a frequency characteristic, the solid line 21 is better than the broken line 22. Therefore, it can be seen that the interdigital electrode 23 has a direction indicated by an arrow 23D, and the interdigital electrode 25 has a direction indicated by an arrow 25D.

FIG. 3 shows that the thickness of the electrode made of Al is 200
FIG. 7 is a diagram showing frequency characteristics and electrode arrangement for explaining the directionality of a chirp electrode having a single electrode structure by an equivalent circuit analysis when Zm / Zg = 1.00 when 0 angstrom is set and Zm / Zg = 1.00. is there. As shown in FIG. 3B, a down- chirped interdigital electrode 33 whose density of arrangement of the positive and negative electrodes gradually increases is adjacent to an interdigital electrode 34 having a pair of positive and negative electrodes. In the configuration shown in FIG.
The frequency characteristic is as shown by the solid line 31 in FIG. Further, as shown in FIG. 3 (c), an up- chirped interdigital electrode 35 is provided adjacent to an interdigital electrode 36 having a pair of positive and negative electrodes so that the density of the arrangement of the positive and negative electrodes gradually becomes smaller. However, similarly, the frequency characteristic shown by the solid line 31 in FIG. Therefore, it can be seen that both the interdigital transducer 33 and the interdigital transducer 35 have no directionality.

FIG. 4 shows that the thickness of the electrode made of Al is set to 200.
FIG. 7 is a diagram showing frequency characteristics and electrode arrangement for explaining the directionality of a chirp electrode having a single electrode structure by equivalent circuit analysis when 0 Angstrom and Zm / Zg = 1.02. is there. As shown in FIG. 4 (b), a down- chirped interdigital electrode 43 in which the density of the arrangement of the positive and negative electrodes gradually increases toward the interdigital electrode 44 having a pair of positive and negative electrodes. In the configuration shown in FIG.
The frequency characteristic is as shown by the solid line 41 in FIG. Conversely, as shown in FIG. 4 (c), an up- chirped interdigital electrode 45 is arranged adjacent to an interdigital electrode 46 having a pair of positive and negative electrodes so that the density of the positive and negative electrodes is gradually reduced. In the configuration, the frequency characteristics are as shown by a broken line 42 in FIG. As a frequency characteristic, the broken line 42 is better than the solid line 41. Accordingly, it can be seen that the interdigital transducer 43 has a direction indicated by an arrow 43D, and the interdigital electrode 45 has a direction indicated by an arrow 45D.

Single electrode under various conditions as described above
As a result of investigating the directionality of a chirped electrode having a structure ,
In a chirp type electrode having a single electrode structure,
When Zm / Zg <1, there is a direction in which the arrangement density of the positive and negative electrodes is changed from coarse to dense, when Zm / Zg = 1, there is no directionality, and when Zm / Zg> 1, It has been found that the arrangement density of the positive and negative electrodes has a direction in which the density changes from dense to coarse. Therefore, while keeping a wide band characteristic be configured to convolver considering the direction of the electrode Combo
A surface acoustic wave convolver with high solution efficiency can be obtained. Originally, each of the interdigital transducers was unidirectional and the output electrode
The direction in which the surface acoustic wave is radiated is best . However , from the viewpoint of eliminating dispersion , both sides of the output electrode
Down-chirp and up-chirp electrodes
And both must be directed toward the output electrode.
In order to provide
With Zm / Zg <1
The chirped electrode has a single electrode structure and Zm / Zg
> 1. For that purpose, the electrode material
Material, electrode thickness, electrode width, substrate material, etc.
Absent. In that case, the other interdigital electrode may have bidirectionality. In other words, one of the interdigital electrode has a directionality toward the output electrode, the other interdigital transducer to lever better to have a bi-directional. Chirped electrode
In order to provide bidirectionality, the electrode structure must be a double electrode
Only because it does not affect Zm / Zg
The other (opposite direction) chirp with electrode structure
By making the mold electrode a double electrode as it is,
Maintains dispersibility of chirped electrode with
With bidirectional characteristics and elastic in the direction of the output electrode
Surface waves can be excited.

[0018]

As described above, according to the present invention,
A pair of thick interdigital electrodes is provided on a piezoelectric or electrostrictive substrate , and an output is provided between the interdigital electrodes.
In the surface acoustic wave convolver having a electrode, in consideration of the directionality while maintaining the wide bandwidth of interdigital electrodes, one sheet
Single electrode structure with directivity toward output electrode
To the output electrode if the other single electrode structure remains
IDT becomes to have cormorants direction opposite to the direction in eliminating the directionality as da <br/> Bull electrode structure. By this
As a result, a surface acoustic wave convolver having high convolution efficiency and wide band characteristics can be obtained. In addition, only one of the interdigital electrodes needs to consider the directionality, and the design and manufacture are simple.

[Brief description of the drawings]

FIG. 1 is a plan view of a surface acoustic wave convolver according to an embodiment of the present invention.

FIG. 2 is a diagram showing a frequency characteristic and an electrode arrangement for explaining the directionality of a chirped electrode in which Zm / Zg = 0.98.

FIG. 3 is a diagram showing frequency characteristics and electrode arrangement for explaining the directionality of a chirped electrode with Zm / Zg = 1.00.

FIG. 4 is a diagram showing frequency characteristics and electrode arrangement for explaining the directionality of a chirped electrode with Zm / Zg = 1.02.

FIG. 5 is a plan view and a cross-sectional view of a filter using a conventional surface acoustic wave converter.

[Explanation of symbols]

2, 51: first surface acoustic wave converter, 3, 52: second surface acoustic wave converter, 4: positive electrode, 5: negative electrode, 6: double-electrode positive electrode, 7: double electrode structure Negative electrode,
8, 53 ... output electrode.

 ────────────────────────────────────────────────── ─── Continued on the front page (72) Inventor Shunji Kato 5-30-3 Nakazuma, Ageo City, Saitama Prefecture Oak Hills 202

Claims (1)

(57) [Claims] 1. A first or second interdigital electrode for exciting a surface acoustic wave on a piezoelectric or electrostrictive substrate, and detecting these surface acoustic waves to extract a convolution output as an electric signal. A surface acoustic wave convolver provided with an output electrode, wherein the first and second interdigital electrodes have a predetermined thickness, and the first interdigital electrode gradually has an electrode width and a period toward the output electrode. The second interdigital transducer is configured by alternately arranging positive and negative electrodes whose electrode width and period gradually increase toward the output electrode . One interdigital electrode has a single electrode structure, and the second
The interdigital transducer has a double electrode structure, and
The acoustic impedance of the metal film of the electrode is Zm,
When the acoustic impedance of the tip is Zg,
Zm / Zg of IDT is less than 1
Surface acoustic wave convolver.