JPS58191514A - Surface acoustic wave device - Google Patents

Abstract

PURPOSE:To suppress the generation of spurious radiation, by changing the shape of a track separating section of a multi-strip coupler and replacing the section with a photoconductive film. CONSTITUTION:A surface acoustic wave device consists of a piezoelectric substance 1, an input interdigital ID electrode 2, an output ID electrode 3, the multi- strip coupler 4', track sections 5, 7 and a track separating section 6. The coupler 4' is provided in the surface acoustic wave propagation path, and consists of electrode groups cross-linking the track sections 5, 7 and being narrowered for the part corresponding to the track separation section 6. Since the section 6 is formed narrower, the spurious radiation is suppressed. Further, similar effect is obtained by replacing the section 6 with a photoconductive film 12.

Description

Detailed Description of the Invention The present invention provides an interdigital electrode and a multi-strip coupler on the surface of a piezoelectric thin film, and changes the shape of the track separation portion of the multi-strip coupler, replaces it with a photoconductive film, or The present invention relates to a surface acoustic wave device in which the connecting portion between the teeth and the base of an interdigital electrode is replaced with a photoconductive film.

Figure 1 is a perspective view of a surface acoustic wave device.
A piezoelectric material made of lithium niobate (L + NO3) single crystal, quartz, or the like may be used. 2 is a manual interdigital electrode (hereinafter referred to as input transducer), and 3 is an output interdigital electrode (hereinafter referred to as output transducer), both of which are made of aluminum (Al) and gold (Au).
Made of metals such as

4 is a multi-strip coupler. The transnausers 2.3 have conventional electrical connections to external circuits, but the multistrip couplers 4 need not have external connections and must be electrically isolated from each other. Next, a conventional surface acoustic wave device using the multi-strip coupler 4 will be described in detail with reference to FIG. Typical applications for multistrip couplers 4 at present include filters and delay lines. First, FIG. 2 shows the configuration of the filter. 2' is an apodized interdigital electrode as an input transducer, 3' is an apodized interdigital electrode as an output transducer, 5 is a track A, 6 is a track separation portion, and 7 is a track B.

If the propagation path of the surface wave excited by the input quadrature transducer 2' is called track A5, and the propagation path of the surface wave incident on the output quadrature transducer 3' is called track B7, the function of the multi-strip coupler 4 is as follows from track A5. Track B7
This is the energy conversion of surface waves into . In other words, the multi-strip coupler 4 where the surface wave cuts through the track separation part 6 from the track A5 and extends to the track B7.
When coupled in an array, an alternating electric field is created between adjacent conductors. This electric field causes the multi-strip coupler 4 to
A surface wave is induced from track A5 to track BT. Furthermore, since the IJ tube coupler 4 has the effect of homogenizing spatially non-uniform surface waves during this conversion process, apodized interdigital electric coils can be used for both the input and output transducers. , the product form H(ω)-H of the respective frequencies H1(ω) and H2(ω)
A filter characteristic can be realized by l(ω)・H2((O). Also, as is clear from the configuration shown in FIG. It is customary to provide a slight gap or trunk separation portion 6 between the trunk and the truck BT.

However, the excitation of surface waves in the conventional track separation section 6 has had problems, such as causing insertion loss and unpredictable generation of other spurious.

In order to solve the above-mentioned drawbacks, the present invention aims to suppress the generation of spurious waves by making the track separation portion 6 of the multi-strike 11 tube coupler 4 narrower or replacing it with a photoconductive film. It is.

Next, a preferred embodiment of the surface acoustic wave device shown in FIGS. 1, 2, and 3 will be described in detail. and input Katranos, rUsa 2.2' and output Katranosu 3
．． 3', a multi-strip coupler 4', a track section 5.7 and a track separation section 6. The interdigital poles 2.2', 3.3' as input and output transducers are formed in such a way that the teeth are arranged alternately and do not overlap, and/or: 9 Dechiru. The plurality of track portions 5.7 are surface wave propagation paths formed of a thin electrolyte film. Furthermore, the track separation portion 6 is a joining area of the track portions. The multi-strip coupler 4' is provided in the surface wave propagation path and consists of a group of electrodes that bridge the track portions 5 and I and have a narrow portion corresponding to the track separation portion 6. Since the configuration is as described above, the following effects occur. In other words, since the electrode widths are different, the excitation efficiency of spurious waves is
can be kept small. The reason for this is that when the electrode width of the multi-strip coupler 4 is constant from top to bottom, a surface wave with the same intensity is generated in the track separation portion 6 and the track portion BT by the signal of the track A5. In this case, since there is a phase difference between the original signal and the generated signal, spurious signals are likely to occur. However, since the electrode widths of the multi-strip coupler 4' are different in the track separation part 6, the intensity of the signal generated in this part is smaller than in other parts, resulting in an interference effect.

Next, a conventional example in which a photoconductive film is provided on the trunk portion of the IJ knob coupler 4 will be described based on FIGS. 4 and 5. This is Japanese Patent Application Publication No. 53-1
2252 and an excerpt from JP-A-53-19741. 2
is an input transducer, 3" is an output transducer, 4 is a multi-strip coupler, and 11 is a photoconductive film. The transmission characteristics of the surface acoustic waves transmitted and received between the human output transducers 2 and 3" are , is determined by the product of the transfer function of each electrode and the distance between the electrodes. Overall transmission characteristic F(ω)
is expressed by the following equation.

where, fe: Transfer function fr of input quadrature transducer 2, : Transfer function L of a portion located on region 5 of quadrature transducer 3'' fr2: Transfer function L of a portion located above region 7 of quadrature transducer 3'' : Distance between centers of electrodes 2.3'' ■1, ■2: When surface wave velocity light is irradiated onto the photoconductive film 11..11' and the multi-strip coupler 4 is short-circuited, the photoconductor transducer Since surface waves are not received in the portion of the region T of 3", the above equation can be expressed as follows.

Therefore, by controlling the irradiation of the input signal, it is possible to easily vary the phase of the input signal, select the delay time, vary the width of the input signal, and perform encoding.

Next, the track separation portion 6 shown in FIGS. 2, 6, and 7
Describing in detail a preferred embodiment of a surface acoustic wave device using multi-strip couplers 4'' substituted with gold photoconductive films 12.12-1 to 12-M, the surface acoustic wave device of the present invention has an insulating substrate 1 and , IE conductive thin film, input quadrature transducer 2', catalytic transducer 3', track portion 5.7, track separation portion 6, multi-strip coupler 4'', photoconductive film 12. 12-1~1
2-M. Interdigital tm as input transducer and output transducer
2' and 3' are formed such that the tooth portions are arranged alternately and do not overlap. The multi-strip coupler 4'' is cut at the track separation portion 6 and replaced with a photoconductive film 12 or different photoconductive films 12-1 to 12-M. Further, the plurality of track portions 5.7 are surface wave propagation paths formed of piezoelectric thin films.Furthermore, the track separation portion 6 is a bonding region of the track portions 5.7.Furthermore, the photoconductive film 12. 12-1 to 12-41 are made of cadmium sulfide (CdS), zinc oxide (ZnO), or the like.

In the case of No. 61:4, by changing the intensity of the irradiated light or the irradiated area, the surface wave energy conversion rate between tracks by the multi-strip coupler 4'' can be directly controlled. When irradiating, if the number of complete energy conversion is NT, the energy conversion rate when there are M multi-strip couplers is PA −= Pin cos (πM/ 2N
T ) P B = P in sin (1tM/
2NT). Therefore, the oscillation frequency can be made variable by combining two different amplitudes. That is, when the photoconductive film 12 is provided on the track separation portion 6 of the multi-strip coupler 4'' and light is irradiated thereon, the following will occur.When the light is irradiated, the resistance of the photoconductive film 12 increases. Since the value is high, it is the same as if there were no electrode. However, when light is irradiated, the resistance value decreases and becomes the same as if there was an electrode. By changing the so-called light intensity or irradiation area, The multi-strip coupler 4" has a switch function and can be turned on or off.

Further, in the case of FIG. 7, since each of the photoconductive films 12-1 to 12-M is made of a plurality of types of photoconductive materials, they perform various operations depending on the wavelength of the irradiated light. L'l]
By irradiating light with a wavelength sensitive only to each photoconductive film, only any electrode of the multi-strip coupler 4'' has a low resistance value.

Therefore, it can have a switch function.

Next, a preferred embodiment of a surface acoustic wave device in which a part of the input/output quadrant transducer shown in FIG. 2, FIG. 8, and FIG. 9 is replaced with a photoconductive film will be described in detail. , an insulating substrate, a piezoelectric thin film, an input/output quadrant transducer 13.13', a photoconductive film 14.15, a multi-strip coupler 4, a track portion 5.7, and a track separation portion 6. The multi-strip coupler 4 induces a surface wave from track A to track B. The track portion 5.7 is a surface wave propagation path formed of a piezoelectric thin film. Furthermore, the trunk separation section 6 is the joining region of the track section 5,T. The turn-out quadrant transducer has its southern part 13' separated from the Z section 13. and photoconductive film 14.
15 is cadmium sulfide (CrlS) and zinc oxide (ZnO
), etc. Further, since the structure is configured as described above, the following effects occur. FIG. 9 shows the photoconductive film 14.15 of FIG. , R2. First, when only the photoconductive film 14 is irradiated with light, the resistance value becomes R, <EL2, and surface wave excitation and reception with a wavelength of λ becomes possible. Also at this time 1 (,, ~R2
If so, it becomes possible to manipulate surface waves with a wavelength of 1/3. In other words, by irradiating R1 with light of different intensities depending on the location, a resistance division variable weighting transducer can be constructed. That is, a switching function can be provided by changing the intensity of light irradiated to the photoconductive film at the joint portion between the base and the teeth of the turntable 13, 13'.

As a result, the interval between the comb teeth of the input and output quadrature transducers changes, so the incident wavelength of the surface wave can be selected.

As is clear from the above examples, first, the width of the track separation part is narrower than the track part.
A surface acoustic wave device using a tube coupler can keep the surface wave excitation efficiency small at the track separation portion. Therefore, spurious characteristics and insertion loss can be improved. For example, if the ratio of the width of the track separation part to the width of the track part d1 and d2 is about d1/d2"0.2, IL!, i
, spurious level about 6 dB, insertion loss 1-2 d
It has the effect of improving the level of B. The track separation portion of the multi-strip coupler is then cut and replaced with a photoconductive film./:1 The surface acoustic wave device can vary the intensity of the irradiated light, the irradiated area, or the wavelength of the incident light.

Therefore, there is an effect that the surface wave energy conversion rate between tracks can be directly controlled. Furthermore, a surface acoustic wave device in which the base and teeth of the input/output transducer are cut off and replaced with a photoconductive film can change the intensity or area of the irradiated light. Therefore, if the light guiding film is irradiated with light of different intensities depending on the location, the resistive division variable weighting has the effect of forming a transducer.

[Brief explanation of the drawing]

FIG. 1 is a perspective view of a surface acoustic wave device, FIG. 2 is a plan view of a conventional surface acoustic wave filter, and FIG. A plan view of a coupler, FIG. 6 is a plan view of a multi-strip coupler in which twIL corresponding to the track separation portion of the present invention is replaced with a photoconductive film, and FIG. 7 is a plan view of a multi-strip coupler in which a plurality of photoconductive films of FIG. FIG. 8 is a plan view of a multi-strip coupler filled with photoconductive material of the type shown in FIG. 8 figure light n 礒('l
! i'! FIGS. 4 and 5 are plan views of a conventional example in which a photoconductive film is applied to the track portion of a multi-strip coupler. FIGS. 1...Piezoelectric body 2...Input/tertiary electrode 2'
...Apodized interdigital electrode 3.3" as input transducer, ...output interdigital electrode 3' ・
...Apodized interdigital electrode 4 as an output transducer ...Multi-strip coupler 4'
...Multi-strip coupler 4 with a narrow track separation part...Cut off the track separation part.Xed multi-strip coupler 5...Track A part 6... ......Track separation part 7...Trough 28 part 11.11', 12.12-1 to 12-jψ, 14.1
5...Photoconductive film 13...Base 13' of interdigital electrode
・・・・・・Interdigital electrode teeth representative Patent attorney Moritani-Yu No. t Publication 2nd Ward 43 Figure 61- 4 Figure 弗 5 Sono 〃' 6 Figure

Claims (1)

[Claims] 1. An insulating substrate, a piezoelectric thin film provided on the substrate,
interdigital electrodes as input quadrature transducers and catalytic transducers formed on the piezoelectric thin film so that their teeth are alternately arranged and do not overlap; and a surface formed of the piezoelectric thin film. A plurality of track portions as wave propagation paths, a track separation portion that is a joining area of the track portions, and a portion provided in the surface wave propagation path and bridging the trunk portions and corresponding to the track separation portion. A surface acoustic wave device comprising a multi-strip coupler comprising a group of narrow electrodes. 2. The surface acoustic wave device according to claim 1, wherein the portion where the tooth portion of the interdigital electrode and the base portion are joined is made of a photoconductive film. 3. The surface acoustic wave device according to claim 1 or 2, wherein the track separation portion of the multi-strip coupler is made of a photoconductive film.