JP3189467B2 - Elastic convolver - Google Patents

Description

DETAILED DESCRIPTION OF THE INVENTION

[0001]

BACKGROUND OF THE INVENTION 1. Field of the Invention The present invention relates to an elastic convolver utilizing the nonlinearity of a surface acoustic wave, and more particularly, to an L-shaped convolver.
The present invention relates to an elastic convolver using a structure in which a ZnO piezoelectric thin film is laminated on a piezoelectric substrate made of iNbO ₃ piezoelectric single crystal.

[0002]

2. Description of the Related Art An elastic convolver is a type of signal processing device utilizing the nonlinear behavior of a piezoelectric material.
An arithmetic element that performs convolution integration of two input signals.
As this elastic convolver, a structure incorporating a multistrip coupler (hereinafter abbreviated as MSC) is conventionally known. An example of this known elastic convolver is shown in FIG.

The elastic convolver 1 is configured by using a rectangular piezoelectric substrate 2 made of a LiNbO ₃ piezoelectric single crystal as a piezoelectric body. Both end faces 2a of the piezoelectric substrate 2,
In the vicinity of 2b, input interdigital transducers (hereinafter abbreviated as input IDTs) 3 are formed. The input IDT 3 is constituted by a pair of comb teeth having electrode fingers interposed therebetween.

At the center of the region between the input IDTs 3, 3, a waveguide 4 extending parallel to the propagation direction of the surface wave is provided.
Are formed. An MSC 5 is formed between the waveguide 4 and each input IDT 3.

In the elastic convolver 1, when an input signal is applied to the input IDTs 3 and 3, the surface acoustic wave excited by the input signal is propagated along the directions of arrows A and B. Are respectively compressed in the MSC 5 and then superimposed in the waveguide 4 to extract the output signal.

[0006]

The performance of the convolver is as follows:
In general, the efficiency F and the BT product (B indicates the bandwidth, and T indicates the integration or the process time) are shown.

Since the elastic convolver utilizes the surface acoustic wave as described above, it is considered that the efficiency F can be increased by using the piezoelectric substrate 2 having a large electromechanical coupling coefficient and a large nonlinearity. .

On the other hand, when an IDT is formed on a piezoelectric substrate made of a LiNbO ₃ piezoelectric single crystal to excite a surface acoustic wave, a ZnO piezoelectric thin film is further laminated on the surface of the LiNbO ₃ piezoelectric substrate, thereby increasing the size. It is reported that an electromechanical coupling coefficient can be obtained (A. Armst
long. et al. Proc. 1972 IEEE
E Ultrason. Symp. 370-372 (1972) and Nakamura et al .: Proceedings of the Acoustical Society of Japan, October 1991, pp. 953-954.

Therefore, in the elastic convolver 1 shown in FIG.
When an elastic convolver having a ZnO piezoelectric thin film formed on the entire surface so as to cover 3, 3 and the MSCs 5 and 5 and the waveguide 4 was manufactured, a conventional elastic convolver 1 was formed.
It was confirmed that the efficiency was improved as compared with.

However, although the efficiency is improved,
Bandwidth, especially the width of the band where the attenuation is attenuated to 3 dB (3
(dB attenuation bandwidth) was considerably narrowed. In other words, the convolver is required to have a wider bandwidth because a wider bandwidth can process a signal having a wider spectrum, but the efficiency is increased when the ZnO insulating thin film is formed on the entire surface as described above. However, the bandwidth was narrowed, which proved to be undesirable. SUMMARY OF THE INVENTION It is an object of the present invention to provide an elastic convolver having a structure capable of increasing the efficiency without reducing the bandwidth.

[0011]

SUMMARY OF THE INVENTION The present invention provides a LiNbO ₃
A piezoelectric substrate made of a single crystal, a pair of input IDTs arranged at a predetermined distance from each other on the piezoelectric substrate, a waveguide arranged between the pair of input IDTs, and multi-strip couplers formed respectively between the IDT, said waveguides on said piezoelectric substrate
An elastic convolver, comprising: a formed portion and a ZnO piezoelectric thin film formed on the entire remaining region except the vicinity thereof , thereby achieving the above object.

[0012]

According to the present invention, the efficiency of the elastic convolver is improved at least by the IDT as described above.
It is considered that the ZnO thin film is formed on the piezoelectric substrate made of LiNbO ₃ in the region where is formed, thereby increasing the electromechanical coupling coefficient.

The reason why the efficiency of the elastic convolver according to the present invention is higher than that in the case where the ZnO thin film is formed on the entire surface of the piezoelectric substrate is considered as follows. That is, the loss of attenuation in the conventional elastic convolver 1 (FIG. 5) is determined by the input IDT3 and the input IDT3.
3 and the loss in the MSCs 5 and 5 and the loss in the surface acoustic wave path (including the portion where the waveguide 4 is formed). To reduce the loss in each portion, the ZnO thin film Is preferably not formed.

On the other hand, since the region where the IDT and the MSC are formed is a portion that positively utilizes the piezoelectric phenomenon, it is preferable to increase the surface acoustic wave excitation efficiency by laminating a ZnO thin film. Conceivable.

Therefore, in the present invention, at least the input I
By forming the above-mentioned ZnO piezoelectric thin film on the DT, the excitation efficiency of the surface acoustic wave is enhanced, and on the other hand, the ZnO piezoelectric thin film is formed on the surface wave propagation path, which is not preferably covered with the ZnO piezoelectric thin film, especially on the waveguide Therefore, it is considered that the propagation loss of the surface wave is reduced, the efficiency is further increased as compared with the case where the entire surface is covered with ZnO, and the bandwidth can be prevented from being narrowed at the same time.

[0016]

DESCRIPTION OF THE PREFERRED EMBODIMENTS Hereinafter, the present invention will be clarified by describing non-limiting embodiments of the present invention. FIG. 1 is a plan view showing an elastic convolver according to a first reference example on which the present invention is based . The elastic convolver 11 is configured using a piezoelectric substrate 12 having a rectangular planar shape. The piezoelectric substrate 12 is composed of a LiNbO ₃ piezoelectric single crystal substrate.

Input IDTs 13, 13 are formed near the end faces 12a, 12b of the piezoelectric substrate 12. Each of the input IDTs 13 is constituted by a pair of comb-shaped electrodes having electrode fingers interposed therebetween.
In the center between the input IDTs 13, 13, a waveguide 14 extending parallel to the surface wave propagation direction is formed. MS between the waveguide 14 and each input IDT 13
C15 and 15 are formed. Up to this point, it is the same as the conventional elastic convolver 1 shown in FIG.

[0018] Features of the present embodiment, the piezoelectric substrate 12 described above
Input IDTs 13, 13 and MSC
That is, the ZnO piezoelectric thin films 16 and 16 are formed so as to cover portions where the layers 15 and 15 are formed.

[0019] Therefore, the elastic convolver 11 of this reference example, since the ZnO film 16, 16 is coated formed on the piezoelectric substrate 12, enhanced the excitation efficiency of the surface acoustic wave, and in the waveguide on 14 ZnO piezoelectric thin film 1
Since no coating 6 is formed, the propagation loss on the surface wave propagation path, especially on the waveguide 14 is reduced. Therefore, not only the efficiency is improved as compared with the conventional elastic convolver 1, but also the bandwidth is not reduced. This will be described with reference to FIG.

FIG. 2 is a diagram showing efficiency-frequency characteristics of elastic convolvers having various structures manufactured by the present inventors. 2, the dashed line A indicates the characteristic of the conventional elastic convolver 1 shown in FIG. 5, and the broken line B indicates the case where the ZnO thin film is formed on the entire upper surface of the piezoelectric substrate 2 in the conventional elastic convolver 1. The solid line C shows the characteristic of the elastic convolver 11 of the first reference example. As is clear from FIG. 2, in the structure in which the ZnO piezoelectric thin film is formed on the entire upper surface of the piezoelectric substrate as compared with the conventional elastic convolver 1, although the efficiency is improved, the bandwidth is narrowed (broken line). B). On the other hand, in the elastic convolver of the first reference example, it can be seen that not only the efficiency is further improved but also the 3 dB attenuation bandwidth is sufficiently large.

[0021] FIG. 3 is a plan view showing an elastic convolver 21 according to the second embodiment. The elastic convolver 21 is composed of piezoelectric thin films 26, 26 made of ZnO.
Except that the region in which
Is configured similarly to the elastic convolver 11 of the reference example. Therefore, the same reference numerals are given to the same components, and the description thereof will be omitted.

[0022] In elastic convolver 21 of the second reference example, the piezoelectric thin film 26 and 26, the upper surface of the piezoelectric substrate 12 is formed so as to cover only an area input IDT13,13 is formed .

Indicated by the solid line D the frequency characteristics in FIG. 2 - The efficiency of the elastic convolver 21 of the second reference example. As is clear from FIG. 2, the elastic convolver 21 of the second reference example also has higher efficiency and does not have a narrower bandwidth than the conventional elastic convolver 1. Therefore, it is understood that the efficiency can be increased without reducing the bandwidth by forming the ZnO piezoelectric thin films 26 so as to cover at least the input IDTs 23 as in the present reference example.

FIG. 4 is a plan view showing an elastic convolver according to actual施例of the present invention. In the elastic convolver 31, the piezoelectric thin film 36 made of ZnO is formed so as to cover the entire area except the portion where the waveguide 14 is formed and the vicinity thereof. Other structures are the same as those of the elastic convolver 11 of the first reference example, and the same parts are denoted by the same reference numerals.

[0025] In the present invention as described above, ZnO piezoelectric thin film is coated formed in all the regions of the remaining region excluding the upper waveguide 14, first, similarly in the conventional second reference example Compared to the elastic convolver 1, the efficiency can be increased without reducing the bandwidth. ZnO / Li
In the NbO ₃ stacked structure, the conversion efficiency of the surface wave in the IDT and the MSC is higher than that of the piezoelectric substrate made only of LiNbO _3, however, on the contrary, because of the high conversion efficiency, between the two MSCs 15 and 15 Interference between leaked surface waves becomes a problem, or IDTs 13 and 13
From the surface of the piezoelectric substrate, which may cause a problem. However, in the elastic convolver 31 of this embodiment, the surface waves slightly leaking from the MSCs 15, 15 indicated by arrows E, E in FIG. 4 can be attenuated by the ZnO piezoelectric thin film 36. Therefore, interference between both MSCs 15 and 15 can be reduced. In addition, the surface waves reflected by the end faces indicated by arrows F and F in FIG. Can be reduced.

[0026]

According to the present invention, the ZnO thin film is formed so as to cover at least the input IDT except on the waveguide on the piezoelectric substrate made of LiNbO ₃ .
It is possible to provide a highly efficient elastic convolver without reducing the bandwidth.

[Brief description of the drawings]

FIG. 1 is a plan view showing an elastic convolver according to a first reference example.

FIG. 2 is a diagram showing efficiency-frequency characteristics of elastic convolvers according to a conventional example and a reference example.

FIG. 3 is a plan view showing an elastic convolver according to a second reference example.

[Figure 4] gills plan view showing a stick combo Luba real施例.

FIG. 5 is a plan view showing a conventional elastic convolver.

[Explanation of symbols]

 11 Elastic convolver 12 Piezoelectric substrate 13, 13 Input IDT 14 Waveguide 15, 15 MSC

──────────────────────────────────────────────────続 き Continuation of the front page (56) References JP-A-54-66792 (JP, A) JP-A-4-35211 (JP, A) PROCEEDINGS OF THE IEEE, VOL. 64, NO. 5, MAY 1976, p. 748 ~ 751 (58) Fields investigated (Int. Cl. ⁷ , DB name) H03H 9/72 H03H 9/25

Claims (1)

(57) [Claims] 1. A piezoelectric substrate made of LiNbO ₃ single crystal, a pair of input interdigital transducers arranged at a predetermined distance on the piezoelectric substrate, and a pair of input interdigital transducers arranged between the pair of input interdigital transducers A waveguide, a multistrip coupler formed between the waveguide, and each input interdigital transducer, and a portion of the piezoelectric substrate on which the waveguide is formed; and
An elastic convolver comprising: a ZnO piezoelectric thin film formed on the entire remaining area except the vicinity thereof .