JPH04302210A - Surface acoustic wave convolver - Google Patents

Abstract

PURPOSE:To reduce electrode finger resistance and to improve efficiency for convolution by providing a piezoelectric thin film having acoustic velocity higher than that of a piezoelectric substrate at an interdigital electrode for output on the piezoelectric substrate at least. CONSTITUTION:A piezoelectric thin film 7 having the acoustic velocity of Y- direction surface acoustic waves higher than that of a substrate 1 at least is provided under an interdigital electrode 5 for output on the surface of the substrate 1 at least. The film thickness of the thin film 7 is gradually made thick from the side of a waveguide 4-n in a tapered shape. When an electric signal is inputted to an interdigital electrode 2 for excitation, the surface acoustic waves are excited, and when an electric signal is inputted to an interdigital electrode 3 for excitation, the surface acoustic waves are excited, and the surface acoustic waves are respectively made incident to waveguides 4-1-4-n. For the surface acoustic waves mutually reversely propagated from the both ends of the waveguides 4-1-4-n, the surface acoustic waves propagated in + or -y axis directions are generated to the both sides by a parametric mixing phenomenon. These surface acoustic waves arrive at the interdigital electrode 5 for output, and the convolution signal of two input signals is obtained.

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, and more particularly to a split waveguide type surface acoustic wave convolver that extracts a convolution signal of two signals via a split waveguide.

0002

[Prior Art] Fig. 3 is a diagram of "Nakagawa et al., Transactions of the Institute of Electronics and Communication Engineers '86/2, Vol.j69-C, No.2, pp19.
FIG. 1 is a schematic plan view showing the configuration of a conventional segmented waveguide type surface acoustic wave convolver described in "No. 0 to 198".

[0003] The coordinate axes shown in this figure are added for convenience and do not mean the crystal axes of the substrate or the like.

In FIG. 3, 1 is a piezoelectric substrate, 2,
Reference numeral 3 denotes two comb-shaped electrodes for surface acoustic wave excitation, which are formed on the surface of the substrate 1 so as to be opposed to each other at an appropriate distance in the x direction. 4-1, 4-2,..., 4-n are the electrodes 2
, 3 extending in the x direction and parallel to each other on the surface of the substrate 1. Reference numeral 5 designates an output comb-shaped electrode formed on the surface of the substrate 1 at an appropriate distance from the waveguide in the y direction.

In this surface acoustic wave convolver, when an electrical signal with an angular frequency ω is input to the comb-shaped electrodes 2 and 3 for excitation of surface acoustic waves, a surface acoustic wave of the frequency is excited, and the surface acoustic wave is transmitted through the waveguide 4. -1, 4-2,..., 4-n propagate in opposite directions to each other in the x-axis direction, and a surface acoustic wave with an angular frequency of 2ω that propagates in the y-axis direction is generated by a parametric mixing phenomenon in the waveguide. do. This surface acoustic wave reaches the output comb-shaped electrode 5, and a convolution electric signal of the above two input signals can be obtained at the output comb-shaped electrode 5.

[0006]

However, in general, in a surface acoustic wave convolver, as the signal interaction length (integration time) becomes longer, the length of the output electrode also becomes longer.

[0007] Even in the split waveguide type surface acoustic wave convolver,
As the interaction length increases, the length of each waveguide increases. In the conventional split waveguide type surface acoustic wave convolver, the output comb-shaped electrode length is equal to the waveguide length, so as the interaction length becomes longer, the output comb-shaped electrode length also becomes longer.

The line width of the output comb-shaped electrode is determined by the frequency of the convolution signal and the propagation speed of the surface acoustic wave of the substrate, so the line width becomes narrower as the input center frequency becomes higher.

For example, 128°Y.X LiN
Input center frequency 200MHz using bO3 single crystal
, in the case of a segmented waveguide type convolver with an interaction length of 6 μs, the output comb-shaped electrode has a line width of 2 μm and a length of 20 mm.

[0010] The electrode finger resistance of this comb-shaped electrode is approximately 2 kΩ per comb-shaped electrode, and a decrease in convolution output due to this electrode finger resistance is unavoidable.

Furthermore, as mentioned above, the output comb-shaped electrode of the conventional split waveguide type surface acoustic wave convolver has a line width of several μm.
, the length is several mm to several tens of mm, and the manufacturing yield is lower than that of conventional surface acoustic wave convolvers.

(Objective of the Invention) The object of the present invention is to improve the convolution efficiency and manufacturing yield by reducing the electrode finger resistance of the output comb-shaped electrode. Our goal is to provide a wave convolver.

[0013]

[Means and operations for solving the problems] The above object is to excite at least two surface acoustic waves on a piezoelectric substrate of the present invention.
a plurality of waveguides that propagate surface acoustic waves excited from the excitation electrodes in opposite directions; and a surface acoustic wave that is generated in the waveguides and propagates in a direction transverse to the surface acoustic waves. In the surface acoustic wave convolver, the surface acoustic wave convolver has at least one output electrode that converts the output electrode into an electrical signal, and the sound velocity in the propagation direction of the surface acoustic wave generated in the waveguide is applied to at least the output electrode portion on the piezoelectric substrate. This is achieved by a surface acoustic wave convolver characterized in that a piezoelectric thin film having a higher sound velocity than the piezoelectric substrate is provided. The above object is also achieved by a surface acoustic wave convolver characterized in that the thickness of the piezoelectric thin film changes in a tapered manner from the waveguide side.

According to the configuration of the present invention, the pitch of the output comb-shaped electrodes can be increased compared to conventional ones, the line width and spacing of the comb-shaped electrodes are increased, electrode finger resistance can be reduced, and convolution efficiency can be improved. can be improved.

In the case of a single electrode, the electrode width d of the output comb-shaped electrode is determined by the sound velocity v of the surface acoustic wave of the piezoelectric body and the center frequency f0 of the surface acoustic wave.

[0016]

[Math. 1] d=v/4f0 becomes.

Therefore, when surface acoustic waves having the same center frequency are propagated, the width d of the output comb-shaped electrode becomes larger if the sound speed of the piezoelectric material is faster. Therefore, according to the present invention, since the output comb-shaped electrode section is provided with a piezoelectric thin film whose surface acoustic wave velocity is higher than that of the substrate,
The line width d and pitch (2d) of the output comb-shaped electrodes can be increased.

Therefore, compared to the conventional surface acoustic wave convolver, the resistance R per electrode finger expressed by the following equation is reduced.

[0019]

[Equation 2] (ρ: resistivity of the electrode metal, l: length of the electrode, t: thickness of the electrode, d: line width of the electrode) In addition, because the pitch of the electrodes has become wider, electrode pattern formation by the photolithography process has become more difficult. This makes it easier and improves manufacturing yield.

Furthermore, in this embodiment, since the thickness of the piezoelectric thin film gradually increases from the waveguide side in a tapered manner, the reflected wave due to the reflection of the surface acoustic wave at the end face of the piezoelectric thin film The occurrence of can be suppressed.

[0021]

Embodiment Embodiment 1 FIG. 1 is a schematic plan view showing a first embodiment of a surface acoustic wave convolver according to the present invention.

Note that the coordinate axes in the figure are added for convenience and do not mean the crystal axes of the substrate.

In FIG. 1, 1 is a piezoelectric substrate. As the piezoelectric substrate, for example, a piezoelectric substrate such as lithium niobate can be used.

Reference numerals 2 and 3 designate surface acoustic wave excitation electrodes which are formed on the surface of the substrate 1 so as to face each other at an appropriate distance in the x direction. The electrodes 2 and 3 are comb-shaped electrodes made of a conductor such as aluminum, silver, or gold, and are provided so that surface acoustic waves propagate in the ±x directions.

4-1, 4-2,..., 4-n are the electrodes 2,
The waveguides are formed by extending in the x direction between the three waveguides and being arranged parallel to each other at a constant pitch on the surface of the substrate 1.

Regarding these waveguides, please refer to “
"Surface Acoustic Wave Engineering", Institute of Electronics and Communication Engineers, pages 82-102, describes in detail, there are thin film waveguides and topographic waveguides, but in the present invention, the substrate surface is coated with a conductor such as aluminum, silver, or gold. A Δv/v waveguide with a Δv/v is preferred.

5 is the waveguide 4-1 on the surface of the substrate 1.
An output comb-shaped electrode is arranged and formed at an appropriate distance from ~4-n in the y direction, and the electrode is made of a conductor such as aluminum, silver, or gold, and has an elastic surface that propagates in the y direction. It is designed to efficiently convert waves into electrical signals.

7 is provided below at least the output comb-shaped electrode 5 on the surface of the substrate 1, and is located at least Y from the substrate 1.
This is a piezoelectric thin film with a high sound velocity of surface acoustic waves in different directions.

Further, the thickness of the piezoelectric thin film 7 is tapered gradually from the waveguide 4-n side.

In the surface acoustic wave convolver of this embodiment, the central angular frequency ω is set to one of the excitation comb-shaped electrodes 2.
When an electric signal is input, a surface acoustic wave is excited from the excitation electrode 2 and enters the waveguides 4-1 to 4-n. Similarly, when an electric signal with a center angular frequency ω is input to the other excitation comb-shaped electrode 3, a surface acoustic wave is excited from the excitation electrode 3 and enters the waveguides 4-1 to 4-n. do.

Excited by the excitation electrodes 2 and 3,
The surface acoustic waves propagating in opposite directions from both ends of the waveguides 4-1 to 4-n are caused by a parametric mixing phenomenon on the waveguides 4-1 to 4-n, resulting in a center angle that propagates in the ±y-axis direction. Surface acoustic waves with a frequency of 2ω are generated on both sides.

This surface acoustic wave then reaches the output comb-shaped electrode 5, whereby a convolution signal of the two input signals input from the excitation electrodes 2 and 3 can be obtained.

In the case of a single electrode, the electrode width d of the output comb-shaped electrode 5 is determined by the sound velocity v of the surface acoustic wave of the piezoelectric body and the center frequency f0 of the surface acoustic wave.

[0034]

[Math. 3] d=v/4f0 It is.

Therefore, when surface acoustic waves having the same center frequency are propagated, the width d of the output comb-shaped electrode becomes larger if the sound speed of the piezoelectric material is faster.

Therefore, in this embodiment, the output comb-shaped electrode 5
Since a piezoelectric thin film having a faster sound velocity of surface acoustic waves than the substrate 1 is provided under the substrate 1, the line width d and pitch (2d) of the comb-shaped electrode can be made larger than those of the conventional electrode.

Therefore, compared to the conventional surface acoustic wave convolver, the resistance R per electrode finger expressed by the following equation is reduced.

[0038]

[Equation 4] (ρ: resistivity of the electrode metal, l: length of the electrode, t: thickness of the electrode, d: line width of the electrode) In addition, because the pitch of the electrodes has become wider, electrode pattern formation by the photolithography process has become more difficult. This makes it easier and improves manufacturing yield.

Furthermore, in this embodiment, since the thickness of the thin film 7 gradually becomes thicker in a tapered manner from the waveguide 4-n side, the reflected wave due to the reflection of the surface acoustic wave at the end face of the thin film The occurrence of can be suppressed.

Further, in this embodiment, the thin film 7 is provided below the output electrode 5 of the substrate 1, but the same effect can be obtained even if it is provided above the electrode 5.

(Embodiment 2) FIG. 2 is a schematic plan view showing a second embodiment of the surface acoustic wave convolver according to the present invention.

In this figure, members similar to those in FIG. 1 are given the same reference numerals.

In this embodiment, the horn-shaped waveguides 7, 8 and the output comb-shaped electrodes 5, 6 are arranged symmetrically on both sides of the waveguides 4-1 to 4-n.

[0044] In this embodiment, the same effects as in the first embodiment described above can be obtained, but in addition, in this embodiment, the surface acoustic waves generated in the waveguide are directed in both directions of the ±y axis. Therefore, by outputting these from the two output comb-shaped electrodes 5 and 6 and combining them, it is possible to obtain an output twice that of the first embodiment. By making the distances from the waveguides 4-1 to 4-n different between the two output comb-shaped electrodes 5 and 6, the output from one output comb-shaped electrode can be transferred to the other output comb-shaped electrode. The output of the mold electrode can be delayed as appropriate.

Furthermore, by using the surface acoustic wave excitation electrodes 2 and 3 in the first and second embodiments as double electrodes (split electrodes), the surface acoustic wave in the surface acoustic wave excitation electrodes 2 and 3 is reduced. Reflections can be suppressed. Similarly, by making the output comb-shaped electrodes 5 and 6 double electrodes (split electrodes), reflection of surface acoustic waves at the comb-shaped electrodes 5 and 6 is suppressed, and the characteristics of the surface acoustic wave convolver are further improved. can be made into something.

Furthermore, in the first and second embodiments,
The substrate 1 is not limited to a piezoelectric single crystal such as lithium niobate, but may be any material and structure that has a parametric mixing effect, such as a structure in which a piezoelectric film is added to a semiconductor or glass substrate.

Furthermore, in the first and second embodiments described above, the surface acoustic wave excited by the surface acoustic wave excitation electrode is directly guided to the waveguide, but there is a horn between the excitation electrode and the waveguide. A beamwidth compressor such as a type waveguide or a multi-strip coupler may also be provided.

[0048]

As described above, according to the present invention, a piezoelectric thin film having a higher sound velocity than the piezoelectric substrate is provided on at least the output comb-shaped electrode portion on the piezoelectric substrate, thereby improving the output comb-shaped electrode. The effects of reducing electrode finger resistance and improving convolution efficiency are obtained.

Furthermore, since the output comb-shaped electrode can be manufactured easily, the manufacturing yield can also be improved.

[Brief explanation of drawings]

FIG. 1 is a schematic plan view showing a first embodiment of a surface acoustic wave convolver according to the present invention;

FIG. 2 is a schematic plan view showing a second embodiment of the surface acoustic wave convolver according to the present invention;

FIG. 3 is a schematic plan view showing a conventional example.

[Explanation of sign]

1 substrate, 2, 3 comb-shaped electrode for surface acoustic wave excitation, 4-1 to 4-n
Waveguide element, 5, 6 Output comb-shaped electrode, 7, 8 Piezoelectric thin film

Claims (2)

[Claims] 1. At least two excitation electrodes that excite surface acoustic waves on a piezoelectric substrate; a plurality of waveguides that propagate surface acoustic waves excited from the excitation electrodes in opposite directions; In the surface acoustic wave convolver, the surface acoustic wave convolver includes at least one output electrode for converting a surface acoustic wave generated by the surface acoustic wave and propagated in a direction transverse to the surface acoustic wave into an electrical signal, at least on the output electrode portion on the piezoelectric substrate. A surface acoustic wave convolver comprising a piezoelectric thin film having a higher sound velocity than the piezoelectric substrate at least in the propagation direction of the surface acoustic waves generated in the waveguide. 2. The surface acoustic wave convolver according to claim 1, wherein the thickness of the piezoelectric thin film changes in a tapered manner from the waveguide side.