JP2014050095A - Surface acoustic wave transducer and electronic system using the same - Google Patents

Abstract

PROBLEM TO BE SOLVED: To provide a unidirectional surface acoustic wave transducer to solve such a problem that conventional surface acoustic wave transducers have bidirectionality, and both low loss and flat characteristics cannot be achieved, while low loss, excellent phase characteristics and flat frequency characteristics are required for a surface acoustic wave filter using a surface acoustic wave transducer including an interdigital electrode provided on a surface of a piezoelectric substrate.SOLUTION: In the present invention, a unidirectional transducer high in conversion efficiency and small in spurious characteristics can be obtained by asymmetrically arranging short circuit type floating electrodes between positive and negative electrodes of interdigital electrodes, the short circuit type floating electrode having a distance between the centers of λ/2, an electrode width thereof of λ/4 width, and a gap of λ/4.

Description

Detailed Description of the Invention

    The present invention relates to a transducer using surface acoustic waves and an electronic device using the same, and is a one-way configuration in which a short-circuited reflective electrode is disposed between positive and negative electrodes of a comb electrode transducer (interdigital transducer, IDT). The present invention relates to a surface acoustic wave transducer and an electronic device using the surface acoustic wave transducer.

    A device that excites and receives normal surface acoustic waves, that is, a transversal type that is used as a converter that transmits and receives (input / output) waves in which surface acoustic waves excited by interdigital electrodes propagate evenly in the left and right directions of the device. Various unidirectional surface acoustic wave converters have been proposed in the past in order to reduce the 6 dB loss that is basically present in a type surface acoustic wave filter and an electronic device using the same.

  These unidirectional surface acoustic wave transducers are roughly classified as follows: (a) a three-phase unidirectional device that applies signals having phase differences of 0 degree, 120 degrees, and 240 degrees to three types of IDT electrode fingers, respectively ( b) A group-type unidirectional converter that applies a signal having a phase difference of 90 degrees by using a common interdigital electrode finger to sew a meander line and setting it as an installation electrode, and (c) an aluminum interdigital electrode finger Internal reflection unidirectionality as 1/8 of the wavelength of the excited wave with the distance between the center of excitation of the surface acoustic wave and the center of reflection as a pair with an electrode finger of a high density metal such as gold (for surface acoustic wave reflection) There are three types of converters, but the three-phase unidirectional converter in (a) maintains the unidirectionality of wave propagation over a wide frequency range, but on one of the three bus bars. It is necessary to let it overbridge and it is extremely manufactured Difficult, therefore there is a defect of requiring complex phaser not only be expensive. In addition, the group-type unidirectional converter (b) also requires a 90-degree phase shifter (specifically, a coil), and the total extension of the meander line becomes long, so that the insertion loss of the filter based on ohmic loss is reduced. There was a flaw that became large. The internal reflection type unidirectional converter (c) is a unidirectional interdigital transducer that does not require a phase shifter by disposing the excitation position and the reflection position by λ / 8. Excellent properties are expected. In a conventional converter, a positive electrode is formed of a double electrode structure in which the electrode gap is divided into λ / 8 and the positive and negative electrodes are divided into λ / 8. One-way using the mass addition effect with added is proposed. This converter has defects such as the fact that it cannot be used for a high-frequency element because it uses a double electrode, and that mask alignment exposure is required.

  On the other hand, after making one of the double electrodes on the substrate using a double electrode, and then attaching a dielectric film having a uniform thickness H, the other of the double electrodes is attached on the electromechanical coupling. An internal reflection type unidirectional interdigital transducer has been proposed that uses the difference in the magnitude of the coefficients, but this converter is also complicated in its manufacturing method and has a conversion efficiency because it uses a double electrode. There are defects such as badness and use of high-frequency elements because of the use of λ / 8 interdigital electrodes.

(1) C.I. S. Hartmann, et al, 1982 IEEE Ultrasonic Symposium Proceedings, pp. 40-45), (2) K.M. Yamanouchi et al, Electronics Letters, Vol. 20, NO. 20, pp. 819-821, Sept. (1982)

Problems to be solved by the invention

    As described above, the conventional unidirectional changer requires a phase shifter and has a defect such that it is difficult to obtain a high-frequency device because it has a narrow electrode width and is difficult to manufacture.

    In addition, in order to obtain the desired frequency characteristics, an apodized method (weighting method) in which the crossing width of the interdigital electrodes is changed has been proposed, but defects such as weighting loss cannot be applied to the interdigital transducer electrodes. There is.

Means for Solving the Invention

    The present invention has been made to eliminate the drawbacks of the conventional unidirectional surface acoustic wave transducer as described above, and the device manufacturing process is simple and does not require an external circuit such as a phase shifter. In addition, the present invention provides an internal reflection type unidirectional surface acoustic wave transducer with low loss and excellent conversion efficiency. It also proposes a new weighting method.

Effect of the invention

The unidirectional transducer according to the present invention has a structure in which an excitation electric field is applied by placing a short-circuited floating electrode between positive and negative electrodes, and a surface acoustic wave transducer with efficient conversion characteristics and low spurious is provided. can get.
By using this unidirectional transducer, a surface acoustic wave filter and a surface acoustic wave functional element having a wide bandwidth and low loss can be obtained. Moreover, a low insertion loss filter with excellent cut-off characteristics can be obtained by weighting the electrodes in a distributed manner for both transmission and reception.
Fig. 4 is a diagram. This is an example of the characteristics of the unidirectional filter having the structure 1, and low-loss and high-efficiency conversion characteristics are obtained. FIG. 5 shows the experimental results of the unidirectional characteristics of this electrode. A directionality of about 7 dB is obtained per converter.

Cross section and plan view of transducer with short-circuited floating electrode inserted between positive and negative electrodes (A) Cross section, (B) Plan view (C) Converter with positive and negative electrodes as one cycle Cross section and plan view of transducer with short-circuited floating electrode inserted between positive and negative electrodes (A) Cross section, (B) Plan view, Cross section and plan view of transducer with short-circuited floating electrode inserted between positive and negative electrodes (A) Cross section, (B) Plan view Filter characteristics using unidirectional interdigital electrodes Experimental results of directivity per converter for unidirectional interdigital transducers (A) Forward wave characteristics, (B) Backward wave characteristics

  1. ... Substrate, 2. ... + bus bar, 3 ...- bus bar, 4 ... positive electrode, 5 ... short-circuited floating electrode, 6 ... connection electrode, 7 ... short-circuited floating electrode, 8 ... negative electrode, 9 ... positive electrode, 10 ... short-circuited floating electrode, 11 Connection electrode 12 Short-circuit floating electrode 13 Negative electrode 14 Positive electrode 15 Short-circuit floating electrode 16 Connection electrode 17 Short-circuit floating electrode 18 Negative electrode 19 Forward wave characteristics 20 ... reverse wave characteristic, 21 ... forward wave characteristic, 22 ... reverse wave characteristic

Hereinafter, the present invention will be described in detail based on embodiments shown in the drawings.
In Example 1, the surface acoustic wave conversion in which interdigital electrodes are arranged on the surface of the piezoelectric / electrostrictive material substrate 1 or the piezoelectric thin film substrate and the surface acoustic wave that receives or propagates the surface acoustic wave is received in FIG. In the electronic device and the electronic device using the same, the wavelength at the basic operating frequency is λ, the distance between the electrodes between the positive electrode 4 and the negative electrode 8 on the surface of the substrate 1 is approximately λ / 2, and the width is A structure in which electrodes of approximately λ / 4, 5 and 7 are connected by a conductive thin film 6, and short-circuited floating electrodes 5 and 7 which are not connected are arranged asymmetrically between positive and negative electrodes on the bus bars 2 and 3. The surface acoustic wave converter having a structure in which these electrodes are periodically arranged from the positive electrode to the positive electrode, or the period from the positive electrode 4 to the negative electrode 8 as one cycle, as shown in FIG. Surface acoustic waves with a structure in which these electrodes are periodically arranged A converter, or a surface acoustic wave transducer having a structure in which the width of the electrodes 4, 8, 5, 7, and 0.5 is in the range of 0.5 to 1.5 times, and an electronic device using these transducers are implemented. One of the examples.
Example 2 is shown in FIG. 1. As described above, a surface acoustic wave converter for receiving a surface acoustic wave that has excited or propagated a surface acoustic wave by disposing an interdigital electrode on the surface of the electrostrictive material substrate 1 or a piezoelectric thin film substrate, and an electronic device using the same , The wavelength at the fundamental operating frequency is λ, and the positive electrode 4 and its width are disposed on the surface of the substrate 1 between the positive electrode 4 whose width is λ / 4 and the negative electrode 8 whose width is λ / 4. Is λ / 8, the gap is λ / 4, the gap is λ / 4, and then the width of the electrode 7 is λ / 4. The electrode 5 and the electrode 7 are connected by the conductor 6, The bus bars 2 and 3 are provided with short-circuited floating electrodes 5 and 7 that are not connected, and then the gap between the electrode 7 and the negative electrode 8 is 3λ / 8, and then the negative electrode 8 with λ / 4, Next, a surface acoustic wave having a structure in which the electrodes composed of positive electrodes 3 having a gap of λ / 4 and then λ / 4 are defined as one period and these electrodes are periodically arranged. As shown in FIG. 1C, a surface acoustic wave transducer having a structure in which the positive electrode 4 to the negative electrode 8 are set as one cycle and these electrodes are periodically arranged as shown in FIG. , 8 are the same, and the surface width of these electrodes is in the range of 0.3 times to 1.7 times the previous value, or the gap between the electrodes is 0. The converter in the range of .5 times to 1.5 times, and the electronic device using these converters are the second embodiment.
Example 3 is shown in FIG. As shown in FIG. 2, a surface acoustic wave transducer for receiving a surface acoustic wave that has been excited or propagated by arranging interdigital electrodes on the surface of the piezoelectric / electrostrictive material substrate 1 or the piezoelectric thin film substrate, and the same In the electronic device, the wavelength at the basic operating frequency is λ, and the width of the substrate 1 is between the positive electrode 9 having a width of 5λ / 16 and the negative electrode 13 having a width of 5λ / 16. An electrode 10 having 3λ / 16 and a gap of λ / 4, an electrode distance of λ / 4, and an electrode 12 having an electrode width of 3λ / 16 are connected by a conductor 11 and connected to the bus bars 2 and 3. The short-circuited floating electrodes 10 and 12 are arranged, then the negative electrode 13 with a gap of λ / 4, then 5λ / 16, and then the positive electrode 9 with a gap of λ / 4 and then 5λ / 16. A surface acoustic wave transducer having a structure in which these electrodes are periodically arranged, Alternatively, a surface acoustic wave transducer having a structure in which the positive electrode 9 to the negative electrode 13 are set as one cycle and these electrodes are periodically arranged, or the positions of the electrodes 9, 10, 12, 13, and 9 are the same, and the electrode width Is a surface acoustic wave transducer having a value between 0.3 times and 1.7 times the previous value, a transducer having a gap between the above electrodes in a range between 0.5 times and 1.5 times, and these An electronic apparatus using the converter is the third embodiment.
As shown in FIG. 3, the fourth embodiment is an elastic surface that receives a surface acoustic wave that has excited or propagated a surface acoustic wave by disposing an interdigital electrode on the surface of the piezoelectric / electrostrictive material substrate 1 or the piezoelectric thin film substrate. In a wave converter and an electronic device using the same, a wavelength at a basic operating frequency is λ, and a positive electrode 14 having a width of 7λ / 32 and a negative electrode 18 having a width of 9λ / 32 are formed on the surface of the substrate 1. The electrode 15 having a gap of 3λ / 16 and then having a width of 7λ / 32, and then the electrode 17 having a gap of λ / 4 and then having a width of 9λ / 32 is connected by a conductor 16, and the bus bar 2 and 3 are arranged short-circuited floating electrodes 15 and 17 which are not connected, then the negative electrode 18 having a gap of 5λ / 16, then 9λ / 32, then the gap of λ / 4, and then One electrode is composed of 7λ / 32 positive electrodes 14, and these electrodes are arranged periodically. The surface acoustic wave transducer having the structure described above, or the surface acoustic wave transducer having the structure in which these electrodes are periodically arranged with the period from the positive electrode 14 to the negative electrode 18 being one cycle, or the electrodes 14, 15, 17, 18 Surface acoustic wave transducer with the same position and electrode width in the range of 0.3 to 1.7 times the previous value, the gap between the above electrodes in the range of 0.5 to 1.5 times 4 and the electronic device using these converters is the fourth embodiment.
In the fifth embodiment, according to the first, second, third, and fourth claims, the periodic structure includes one, two, three short-circuit floating electrodes between the positive and negative electrodes. Or the structure near the center, one with two, three, etc. distributed as the distance from the center is distributed, or the structure of these electrodes is changed. In the fifth embodiment, a unidirectional surface acoustic wave transducer and an electronic device using the transducer are obtained, and a filter having a steep characteristic is obtained by weighting transmission / reception electrodes.
Example 6 is an example in which the electrode and the metal film are Al, Cu, Mo, Au, Ag, W in the claims, the first, second, third, fourth, and fifth claims. , Ti, etc., or alloys thereof, and interdigital electrodes having a structure in which a thin film such as SiO ₂ , SiO, ZnO, LiNbO ₃ , Ta ₂ O ₅ , PZT, or glass is attached as a dielectric film on the above electrode Example 6 is to obtain a surface acoustic wave converter and an electronic device using the surface acoustic wave converter and having excellent temperature characteristics.

Claims (6)

    In a surface acoustic wave transducer for receiving a surface acoustic wave that has been excited or propagated by disposing interdigital electrodes on the surface of a piezoelectric / electrostrictive material substrate 1 or a piezoelectric thin film substrate, and an electronic device using the surface acoustic wave converter, With the wavelength at the fundamental operating frequency being λ, electrodes on the surface of the substrate 1 between the positive electrode 4 and the negative electrode 8 and having an interelectrode distance of approximately λ / 2 and a width of approximately λ / 4, 5, 7 However, a short-circuit type floating electrode 5, 7 that is not connected to the bus bars 2, 3 is arranged asymmetrically between the positive and negative electrodes on the bus bars 2, 3. As one period, a surface acoustic wave transducer having a structure in which these electrodes are periodically arranged, or one period from the positive electrode 4 to the negative electrode 8, and as shown in FIG. Surface acoustic wave transducers or electrodes 4, 8, 5 7, the width of and the surface acoustic wave transducer structure in the range of 1.5 times to 0.5 times, an electronic device using the transducers.     Basic operation of a surface acoustic wave transducer for receiving a surface acoustic wave that has been excited or propagated by arranging interdigital electrodes on the surface of an electrostrictive material substrate 1 or a piezoelectric thin film substrate, and an electronic device using the surface acoustic wave transducer The wavelength at the frequency is λ, and the positive electrode 4 and its width are λ / 4 on the surface of the substrate 1 between the positive electrode 4 whose width is λ / 4 and the negative electrode 8 whose width is λ / 4. An electrode 7 having a gap of λ / 8, a gap of λ / 4, and a width of λ / 4 is then disposed between the electrode 5 and the electrode 5, the electrode 5 and the electrode 7 are connected by a conductor 6, and the bus bar 2, 3, short-circuit type floating electrodes 5 and 7 that are not connected are arranged, and then the gap between the electrode 7 and the negative electrode 8 is 3λ / 8, then the negative electrode 8 of λ / 4, and then the gap A surface acoustic wave transducer having a structure in which an electrode composed of positive electrodes 3 of λ / 4 and then λ / 4 is taken as one period, and these electrodes are periodically arranged, or Alternatively, as shown in FIG. 1C, a surface acoustic wave transducer having a structure in which the positive electrode 4 to the negative electrode 8 are defined as one cycle and these electrodes are periodically arranged, or the electrodes 4, 5, 7, 8 Are the same, and the surface width of these electrodes is in the range of 0.3 to 1.7 times the previous value, or the gap between the electrodes is 0.5. Converters in the range of 1 to 1.5 times, and electronic devices using these converters.     In a surface acoustic wave transducer for receiving a surface acoustic wave that has been excited or propagated by disposing interdigital electrodes on the surface of a piezoelectric / electrostrictive material substrate 1 or a piezoelectric thin film substrate, and an electronic device using the surface acoustic wave converter, The wavelength at the basic operating frequency is λ, and the width of the substrate 1 is 3λ / 16, the gap between the positive electrode 9 having a width of 5λ / 16 and the negative electrode 13 having a width of 5λ / 16. Is an electrode 10 having a wavelength of λ / 4, an electrode 12 having an interelectrode distance of λ / 4, and an electrode 12 having an electrode width of 3λ / 16 is connected by a conductor 11 and is not connected to the bus bars 2 and 3. The floating electrodes 10 and 12 are arranged, and then an electrode composed of a negative electrode 13 having a gap of λ / 4 and then 5λ / 16, and then a positive electrode 9 having a gap of λ / 4 and then 5λ / 16 is set to 1 As a period, a surface acoustic wave converter having a structure in which these electrodes are periodically arranged, or a positive electrode 9 to the negative electrode 13 as one cycle, the surface acoustic wave transducer having a structure in which these electrodes are periodically arranged, or the positions of the electrodes 9, 10, 12, 13, and 9 are the same, and the electrode width is the previous one. Surface acoustic wave transducers in the range of 0.3 to 1.7 times the value, transducers in which the gap between the electrodes is in the range of 0.5 to 1.5 times, and these transducers Electronic device using.     In a surface acoustic wave transducer for receiving a surface acoustic wave that has been excited or propagated by disposing interdigital electrodes on the surface of a piezoelectric / electrostrictive material substrate 1 or a piezoelectric thin film substrate, and an electronic device using the surface acoustic wave converter, The wavelength at the fundamental operating frequency is λ, and the gap between the positive electrode 14 having a width of 7λ / 32 and the negative electrode 18 having a width of 9λ / 32 on the surface of the substrate 1 is 3λ / 16, and then An electrode 15 having a width of 7λ / 32, then a gap of λ / 4, and then an electrode 17 having a width of 9λ / 32 is connected by a conductor 16 and is not connected to the bus bars 2 and 3. The floating electrodes 15 and 17 are arranged, then the negative electrode 18 having a gap of 5λ / 16, then 9λ / 32, and then the positive electrode 14 having a gap of λ / 4 and then 7λ / 32 is set to 1 As a period, a surface acoustic wave transducer having a structure in which these electrodes are periodically arranged, or Alternatively, a surface acoustic wave transducer having a structure in which the positive electrode 14 to the negative electrode 18 are taken as one period and these electrodes are periodically arranged, or the positions of the electrodes 14, 15, 17, and 18 are the same, and the electrode width is the same. Surface acoustic wave transducers in the range of 0.3 to 1.7 times the previous value, transducers in which the gap between the electrodes is in the range of 0.5 to 1.5 times, and these transformations Electronic device using a container.     In claim 1, 2, 3, 4, as a periodic structure, a structure in which one, two, three, etc., short-circuit type floating electrodes are inserted between positive and negative electrodes, or The unidirectional surface acoustic wave in the vicinity of the center is one, and as the distance from the center is two, three, etc., the structure in which these electrodes are distributed or the period of these electrodes is changed. CONVERTER AND ELECTRONIC DEVICE USING THE CONVERTER In the claims, the first term, the second term, the third term, the fourth term, and the fifth term, the electrode and the metal film may be made of Al, Cu, Mo, Au, Ag, W, Ti, etc. Interdigital surface acoustic wave conversion with a structure in which a thin film such as SiO ₂ , SiO, ZnO, LiNbO ₃ , Ta ₂ O ₅ , PZT, or glass is adhered as a dielectric film on the above-mentioned electrodes. And electronic device using the same.

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