JP2010107445A - Surface acoustic wave element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave element capable of circling a plurality of surface acoustic waves many times at the same time using one circulating passage and capable of accurately and precisely measuring the deceleration of the propagation speed, phase delay or intensity reducing degree of the surface acoustic waves accompanying an increase in the circulating number of times of a plurality of the surface acoustic waves. <P>SOLUTION: The surface acoustic wave element 10 is equipped with a substrate 14 formed of a surface acoustic wave excitable crystal material and containing at least one annular circulating passage 14a capable of circulating the excited surface acoustic waves and a surface elastic wave exciting and detecting means 16 for exciting the surface acoustic waves to circulate the same to the circulating passage and detecting the circulated surface acoustic waves. This circulating passage includes one main circulating locus 20 capable of circulating the excited surface acoustic waves along the same locus at every round and at least one sub-circulating locus 22 allowing the excited surface acoustic waves to circulate along mutually different loci below a predetermined circulating number of times and coinciding with the first circulating locus in a predetermined circulating number of times. The exciting and detecting means excites the surface acoustic waves in the sub-circulating locus to detect the same circulated along the sub-circulating locus. <P>COPYRIGHT: (C)2010,JPO&INPIT

Description

  The present invention relates to a surface acoustic wave device.

  A plate-like surface acoustic wave element in which surface acoustic wave excitation means and surface acoustic wave detection means are arranged opposite to each other at two positions on the upper surface of a flat piezoelectric body arranged on a flat substrate. Is well known in the art.

  In such a conventional plate-shaped surface acoustic wave element, interdigital electrodes (also called comb-shaped electrodes) are used as the surface acoustic wave excitation means and the surface acoustic wave detection means, respectively. When a high-frequency current is supplied to the surface acoustic wave excitation means, the surface acoustic wave excitation means excites the surface acoustic wave on the upper surface of the piezoelectric body, and the excited surface acoustic wave is detected along the upper surface of the flat piezoelectric body. And is detected by the surface acoustic wave detection means.

  Such conventional plate-like surface acoustic wave devices are used in delay lines, oscillation and resonance devices for oscillators, frequency selective filters, chemical sensors, biosensors, remote tags, and the like. The longer the distance between the surface acoustic wave excitation means and the surface acoustic wave detection means on the upper surface of the piezoelectric body, the higher the accuracy of these various devices using surface acoustic wave elements.

  However, in such a conventional plate-shaped surface acoustic wave element, since the piezoelectric body disposed on the flat substrate is flat, the surface acoustic wave excited by the surface acoustic wave excitation means on the upper surface of the piezoelectric body is provided. Diffuses in a direction perpendicular to the propagation direction while propagating toward the surface acoustic wave detecting means along the upper surface of the flat piezoelectric body, and loses its energy. Accordingly, the distance between the surface acoustic wave excitation means and the surface acoustic wave detection means that can be set on the upper surface of the flat piezoelectric body is naturally limited.

  If the surface area of the flat substrate is increased by increasing the energy of the high-frequency current supplied to the surface acoustic wave excitation means, the distance can be increased, but the power required for driving the surface acoustic wave element increases and the elasticity is increased. The external dimensions of the surface acoustic wave device are increased.

  International Publication No. WO 01/45255 (Patent Document 1) places interdigital electrodes as surface acoustic wave excitation detection means on the surface of a spherical substrate capable of exciting and propagating surface acoustic waves. Surface radius and frequency of surface acoustic wave excited on the surface of the substrate by the interdigital electrode (size of surface acoustic wave in a direction perpendicular to the surface of the substrate along the surface of the surface) Is set to a predetermined condition, and surface acoustic waves excited on the surface of the substrate by the interdigital electrode are diffused infinitely in a direction orthogonal to the direction of propagation along the surface of the substrate. It has been clarified that it can be propagated without being repeated, and thus can be repeatedly circulated.

  The trajectory of the surface acoustic wave that circulates around the surface of the spherical substrate is within a region where a part of the sphere including the maximum outer circumference of the spherical substrate is continuous in an annular shape on the surface of the spherical substrate. This area is called a surface acoustic wave circuit. Such a conventional surface acoustic wave device using a spherical base body generates a large number of surface acoustic waves along the surface acoustic wave circuit without diffusing in the direction intersecting the extending direction of the surface acoustic wave circuit. (I.e., the surface of the elastic surface has not yet been detected until the interdigital electrode can accurately detect the surface acoustic wave that circulates the surface acoustic wave circuit after the interdigital electrode excites the surface acoustic wave.) Therefore, it is necessary to accurately measure the degree of deceleration of the surface acoustic wave propagation speed, the degree of phase lag of the surface acoustic wave, and the degree of reduction of the intensity of the surface acoustic wave. I can do it.

  The degree of deceleration of the propagation velocity, the degree of phase lag of the surface acoustic wave, and the degree of decrease in the intensity of the surface acoustic wave depend on changes in the environment in which the surface acoustic wave circuit of the surface acoustic wave element is in contact (for example, gas concentration Increase). Accordingly, measuring the various degrees described above means measuring changes in the environment in which the surface acoustic wave circuit of the surface acoustic wave element is in contact.

  The above measurement is performed a plurality of times under the same environmental conditions, and the accuracy is further increased by averaging the measurement results of the plurality of times. However, if a plurality of measurements are performed using only one surface acoustic wave circuit, it takes time to measure between them, and the probability that the environmental conditions change during that time will also increase.

For this purpose, Japanese Patent Application Laid-Open No. 2006-121234 (Patent Document 2) describes setting a plurality of surface acoustic wave circuits on the outer surface of one spherical base.
International Publication WO 01/45255 JP 2006-121234 A

  However, a base material that can set a plurality of surface acoustic wave circuits on its outer surface is relatively expensive, such as lithium niobate or lithium tantalate, and a plurality of elastic surfaces on the outer surface of one spherical substrate. Even if the wave circuit can be set, the surface acoustic wave propagation characteristics are slightly different in each of the surface acoustic wave circuits, so even if they are measured under the same environmental conditions in each surface wave circuit The average of the measurement results does not necessarily increase the accuracy of the measurement results.

  The present invention has been made under the circumstances described above, and the object of the present invention is to allow a plurality of surface acoustic waves to rotate at the same time using only one surface acoustic wave circuit, and therefore, in a plurality of surface acoustic waves. A surface acoustic wave that can accurately and accurately measure the degree of deceleration of the surface acoustic wave propagation speed, the degree of phase delay of the surface acoustic wave, and the degree of decrease in the intensity of the surface acoustic wave as the number of turns increases. It is to provide an element.

  In order to achieve the object of the present invention described above, a surface acoustic wave device according to the present invention is formed of a crystal material capable of exciting surface acoustic waves, and is defined and excited in an annular shape by a part of a spherical surface. A surface acoustic wave circuit including at least one surface acoustic wave circuit capable of circulating the surface acoustic wave; and the elasticity excited by exciting the surface wave in the surface wave circuit of the surface wave circuit And surface acoustic wave excitation detecting means for detecting surface acoustic waves that circulate along the surface acoustic wave circuit and detect the surface acoustic waves that have circulated. The surface acoustic wave circuit is different from each other in that the main surface trajectory capable of circulating the excited surface acoustic wave along the same trajectory every round and the excited surface acoustic wave less than a predetermined number of times. And at least one sub-circulation trajectory that circulates along the trajectory and coincides with the trajectory of the first circulation at a predetermined number of turns, and the surface acoustic wave excitation detection means includes a sub-circulation trajectory of the surface acoustic wave circuit. The surface acoustic wave is excited and the surface acoustic wave that circulates in the secondary circulation locus is detected.

  The surface acoustic wave device according to the present invention, which is configured as described above, can simultaneously rotate a plurality of surface acoustic waves many times using only one surface acoustic wave circuit, and therefore Accurately and accurately measure the degree of deceleration of the surface acoustic wave propagation speed, the degree of phase lag of the surface acoustic wave, and the degree of decrease in the intensity of the surface acoustic wave with the increase in the number of rounds of the surface acoustic wave. I can do it.

  Hereinafter, an external environment measuring apparatus using a surface acoustic wave device according to an embodiment of the present invention will be described in detail with reference to the accompanying drawings.

  FIG. 1 schematically shows a basic configuration of an external environment measuring apparatus 12 using a surface acoustic wave element 10 according to an embodiment of the present invention.

  The surface acoustic wave element 10 is formed of a crystal material capable of exciting a surface acoustic wave, and is defined as an annular shape by a part of a spherical surface, and is capable of circulating an excited surface acoustic wave. A surface acoustic wave substrate 14 including 14a; and a surface acoustic wave that is excited by exciting a surface acoustic wave in the surface acoustic wave circuit 14a of the surface acoustic wave substrate 14 along the surface acoustic wave circuit 14a. And a surface acoustic wave excitation detecting means 16 for detecting the surface acoustic wave that has circulated.

Examples of crystal materials that can excite surface acoustic waves include piezoelectric crystal materials such as quartz, langasite, lithium niobate (lithium niobate: LiNbO ₃ ), and lithium tantalate (lithium tantalate: LiTaO ₃ ). I can do it. When these crystal materials excite a surface acoustic wave along an intersection line 14b where the crystal plane of each spherical outer surface intersects the spherical outer surface, the excited surface acoustic waves are It is known that the light propagates along the line of intersection 14b. According to International Publication No. WO 01/45255 (Patent Document 1), the radius of the spherical surface acoustic wave substrate 14 capable of exciting and propagating the surface acoustic wave and the outer surface of the surface acoustic wave substrate 14 are determined. Frequency and width of surface acoustic wave excited on the surface (size of surface acoustic wave in a direction perpendicular to the surface of surface acoustic wave orbiting substrate 14 along the surface of surface acoustic wave orbiting substrate 14) Are set to predetermined conditions so that the surface acoustic wave excited on the surface of the surface acoustic wave substrate 14 is orthogonal to the direction of propagation along the surface of the surface acoustic wave substrate 14 along the surface of the substrate. It has been clarified that it can be propagated without being infinitely diffused in the direction, and can be repeatedly circulated.

  The intersecting line 14b is a line that becomes the outer periphery of the maximum diameter on the outer surface of the surface acoustic wave circulating substrate 14, and is formed into an annular shape by a part of the spherical surface on which the surface acoustic wave excited along the intersecting line 14a propagates. The region defined by is the surface acoustic wave circuit 14a.

  Each of quartz and langasite is known to have three crystal planes. Accordingly, when each of quartz crystal and langasite is used as the piezoelectric crystal material for the surface acoustic wave revolving substrate 14, three surface acoustic wave circuits 14a can be set on the spherical outer surface. become.

  Each of lithium niobate and lithium tantalate is known to have 10 crystal planes. Therefore, when each of lithium niobate and lithium tantalite is used as the piezoelectric crystalline material for the surface acoustic wave revolving substrate 14, ten surface acoustic wave circuits 14a can be set on the spherical outer surface. It will be.

  As the surface acoustic wave excitation detecting means 16, the surface acoustic wave excited by the surface acoustic wave circuit 14a of the surface acoustic wave circulating substrate 14 is infinite in the direction orthogonal to the propagation direction along the surface of the surface acoustic wave circulating substrate 14. In order to make it possible to easily set the wavelength and width satisfying the above-mentioned predetermined conditions, it is said to be an interdigital electrode or a comb-like electrode. A known electroacoustic transducer is usually used.

  A comb-like electrode or a comb-like electrode comprises a pair of comb-like electrode portions each having a plurality of comb-like electrode branches, and a plurality of comb-like electrode branches of one comb-like electrode portion. Each of the plurality of comb-like electrode branches of the other comb-like electrode portion is arranged in the center of each gap. The interdigital electrode or the comb-like electrode having such a configuration is easily and precisely formed by a known forming method (for example, photolithography) at a desired position of the surface acoustic wave circuit 14a of the surface acoustic wave substrate 14. Is possible. A pair of interdigital electrodes or interdigital electrodes are formed on the surface acoustic wave circuit 14a of the surface acoustic wave circuit 14a in a state where a plurality of comb-like electrode branches are directed in a direction crossing the intersection line 14b. When a high-frequency current having a frequency corresponding to the distance between the two comb-shaped electrode branches facing each other is supplied to the comb-shaped electrode portion, the interdigital electrode or the comb-shaped electrode faces each other. The lengths of the two mutually facing portions of the two comb-like electrode branches that have a frequency corresponding to the distance between the two comb-like electrode branches and that are opposed to each other The surface acoustic wave having a certain width is excited at the desired position of the surface acoustic wave circuit 14a of the surface acoustic wave circulating substrate 14, and the excited surface acoustic waves are generated in a plurality of pairs of comb-like electrode portions. In the direction in which the comb-like electrode branches are arranged (that is, propagated).

  Note that the surface acoustic wave is an elastic wave that concentrates and propagates much of its energy on the material surface, unlike the longitudinal and transverse waves called normal bulk waves. Rayleigh waves, Sezawa waves, and pseudo Sezawa waves , Love waves and the like.

  The surface acoustic wave excitation detection means 16 is connected to an operation control means 18 for controlling the operation of the surface acoustic wave excitation detection means 16. The operation control means 18 causes the surface acoustic wave circuit 14a of the surface acoustic wave circulating substrate 14 to excite and propagate the surface acoustic wave in a burst form to the surface acoustic wave excitation detection means 16 at a desired timing and propagates the surface acoustic wave circuit. The surface acoustic wave excited and propagated by 14a is detected by the surface acoustic wave excitation detecting means 16 at a desired timing. For example, the operation control unit 18 includes an input / output switching unit 18a connected to one of a pair of comb-shaped electrode portions of the interdigital electrode or the comb-shaped electrode constituting the surface acoustic wave excitation detecting unit 16, and A high-frequency signal generation unit 18b connected to the input terminal of the input / output switching unit 18a, and a detection / output unit 18d connected to the output terminal of the input / output switching unit 18b via an amplifier 18c. The other of the pair of interdigital electrodes or the interdigital electrodes constituting the surface acoustic wave excitation detecting means 16 is grounded.

  The surface acoustic wave excitation detecting means 16 is connected to the high frequency signal generating section 18b by the input / output switching section 18a at a desired timing, so that the high frequency signal supplied from the high frequency signal generating section 18b to the surface acoustic wave excitation detecting means 16 is changed. The elastic surface is excited on the burst in the surface acoustic wave circuit 14a, and the excited burst-shaped surface acoustic wave propagates in the surface acoustic wave circuit 14a along the above-mentioned intersection line 14b and propagates along the surface acoustic wave circuit 14a. Go around the inside. The surface acoustic wave excitation detection means 16 is connected to the detection / output unit 18d via the amplifier 18c by the input / output switching unit 18a at a desired timing, so that the surface acoustic wave excitation circuit 16a circulates in the surface acoustic wave circuit 14a. The surface acoustic wave is detected by the detection / output unit 18d through the amplifier 18c at a desired timing.

  The research group including Yanagisawa, the inventor of the present application, examined in detail the trajectory (path) of the surface acoustic wave propagating in the surface acoustic wave circuit 14a. When the surface acoustic wave substrate 14 is a trigonal piezoelectric single crystal material, it is noticed that there is one main circuit track 20 capable of rotating the surface wave with the same track every round. This is described in the specification of Japanese Patent Application No. 2008-0667408. Even in the same surface acoustic wave circuit 14a, the surface acoustic wave propagating along one main orbit 20 has an intensity attenuation that agrees well with an exponential attenuation, and the propagation speed of the surface acoustic wave is the fastest.

  The main orbit 20 is a surface acoustic wave that passes through the piezoelectric single crystal material of the surface acoustic wave orbiting substrate 14 at each of a plurality of positions along the intersection line 14b. Since the propagation speed, electromechanical coupling constant, and power flow angle are slightly different from each other, the surface acoustic wave orbiting substrate 14 is not a coincident line 14b, and the surface acoustic wave orbiting substrate 14 is a trigonal piezoelectric single crystal. In the case of a material, as shown in FIG. 1, one direction orthogonal to the intersecting line 14b and the other in every 120 ° rotation angle along the intersecting line 14b in the surface acoustic wave circuit 14a. In the direction of the rotation angle α in the range of 1 ° to 3 °, the sine wave oscillates alternately and sinusoidally.

  FIG. 1 shows an example of a surface acoustic wave circuit 14a along an intersecting line 14b defined by a crystal plane around the Z axis of quartz crystal, which is a kind of trigonal piezoelectric single crystal material. Assuming the spherical surface acoustic wave orbiting substrate 14 as the earth, the main orbit 20 is +2 from the intersecting line 14b in the latitude direction of the -Y axis direction when the intersecting line 14b is the equator with the Z axis as the ground axis. ° Swing.

  Next, a more detailed configuration of the external environment measuring device 12 using the surface acoustic wave device 10 according to the embodiment of the present invention will be described with reference to FIG.

  Yanagisawa, the inventor of the present application, examined in more detail the locus (path) of the surface acoustic wave propagating in the surface acoustic wave circuit 14a. As a result, one main circuit locus 20 in the same surface acoustic wave circuit 14a. In addition to this, it is noticed that the excited surface acoustic wave circulates along different trajectories that are less than a predetermined number of revolutions, and that there is at least one sub-circulation locus 22 that coincides with the trajectory of the first revolution at the predetermined number of laps. It was. The predetermined number of turns of the sub-circular trajectory 22 depends on the crystal symmetry of the piezoelectric single crystal material of the surface acoustic wave substrate 14, and the surface acoustic wave substrate 14 shown in FIG. In the case of quartz, which is a kind of trigonal piezoelectric single crystal material, the number is 3, and in FIG. 1, the subcircular trajectory 22 of the second round is given a reference symbol 22a to the secondary round trajectory 22 of the first round. Is attached with a reference sign 22b, and a reference sign 22c is attached to the sub-circular trajectory 22 of the third round.

  In the subcirculation trajectory 22, the surface acoustic wave excitation detection means 16 is installed at a position that does not overlap with the main circulation trajectory 20 in the same manner as the main circulation trajectory 20. The surface wave excitation detecting means 16 is connected to the same operation control means 18 as the operation control means 18 for the surface acoustic wave excitation detecting means 16 installed on the main orbit 20.

  The surface acoustic wave that is excited and propagated by the surface acoustic wave excitation detection means 16 to the subcircular trajectory 22 is not attenuated exponentially as well as the surface acoustic wave that propagates the main circular trajectory 20, but the main circular trajectory. For the purpose of calibrating the change of the propagation characteristics of the surface acoustic wave propagating through the surface 20 due to the influence of the temperature surrounding the surface acoustic wave element 10, it is sufficiently useful.

  For example, in one surface acoustic wave circuit 14a, a sensitive film 24 for detecting a change in the external environment surrounding the surface acoustic wave element 10 is provided in a region where only the main circular locus 20 passes and the secondary circular locus 22 does not pass.

  When the sensitive film 24 comes into contact with a specific substance in the external environment, the propagation speed of the surface acoustic wave passing therethrough is changed according to the amount of the specific substance in contact. For example, by adsorbing a specific substance, due to its mass effect, the propagation speed of the surface acoustic wave passing therethrough is reduced, and the attenuation rate is drastically reduced. Changes the propagation speed and attenuation rate of surface acoustic waves that pass through it, or generates endothermic or exothermic reactions by reacting with specific substances to change the propagation speed and attenuation rate of surface acoustic waves that pass through it. Change it. And it is preferable that the sensitive film | membrane 24 produces the reversible reaction with respect to a specific substance.

As such a sensitive film 24, palladium (Pd), which absorbs hydrogen (H ₂ ) to form a hydride and changes mechanical characteristics, platinum (Pt) having high adsorptivity to ammonia (NH ₃ ), Tungsten oxide (WO ₃ ) that adsorbs hydride, phthalocyanine (Phthalocyanine) that selectively adsorbs carbon monoxide (CO), carbon dioxide (CO ₂ ), sulfur dioxide (SO ₂ ), nitrogen dioxide (NO ₂ ), etc. It has been known.

  In the above-described embodiment, the surface acoustic wave excitation detecting means 16 is installed in each of one main circuit locus 20 and one sub circuit locus 22 in one surface acoustic wave circuit 14a. When a plurality of sub-circulation trajectories 22 are included in one surface acoustic wave circuit 14a, the surface acoustic wave excitation detection means 16 is installed in at least two of the plurality of sub-circulation trajectories 22, and one main circuit The surface acoustic wave excitation detecting means 16 may be omitted from the locus 20.

FIG. 1 is a schematic diagram schematically showing a basic configuration of an external environment measuring apparatus using a surface acoustic wave device according to an embodiment of the present invention. FIG. 2 is a schematic view schematically showing a more detailed configuration of the external environment measuring apparatus using the surface acoustic wave element shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Surface acoustic wave element, 12 ... External environment measuring device, 14 ... Surface acoustic wave circulation base | substrate, 14a ... Surface acoustic wave circuit, 14b ... Intersection, 16 ... Surface acoustic wave excitation detection means, 18 ... Operation control means, 18a ... Input / output switching unit, 18b ... High frequency signal generator, 18c ... Amplifier, 18d ... Detection / output unit, 20 ... Main circuit locus, 22 ... Sub circuit track, 22a ... First circuit (sub circuit 22), 22b ... 2nd lap (secondary track 22), 22c ... 3rd lap (secondary track 22), 24 ... sensitive membrane.

Claims (6)

A surface acoustic wave circuit substrate including at least one surface acoustic wave circuit that is formed of a crystal material capable of exciting surface acoustic waves, and is circularly defined by a part of a spherical surface and capable of circulating the excited surface wave And; and
A surface acoustic wave excitation detection means for detecting a surface acoustic wave that is caused to circulate along the surface acoustic wave circuit by exciting the surface acoustic wave by exciting the surface acoustic wave in the surface acoustic wave circuit of the surface acoustic wave circuit. When;
With
The surface acoustic wave circuit is different from each other in that the main surface trajectory capable of circulating the excited surface acoustic wave along the same trajectory every round and the excited surface acoustic wave less than a predetermined number of times. Including at least one sub-circulation trajectory that circulates in a trajectory and that coincides with the trajectory of the first lap in a predetermined number of laps,
The surface acoustic wave excitation detection means excites a surface acoustic wave in the secondary circulation locus of the surface acoustic wave circuit and detects the surface acoustic wave that circulates in the secondary circulation locus.
A surface acoustic wave device. One surface acoustic wave circuit includes a plurality of sub-circulation trajectories, and the surface acoustic wave excitation detecting means excites surface acoustic waves in at least two of the plurality of plural trajectories and circulates at least two sub-circulation trajectories. Detect surface acoustic waves,
The surface acoustic wave device according to claim 1. The surface acoustic wave excitation detection means detects surface acoustic waves that have excited the surface acoustic wave in the main circuit trajectory and the sub circuit trajectory of the surface acoustic wave circuit and circulated the main circuit trajectory and the sub circuit trajectory.
The surface acoustic wave device according to claim 1, wherein the surface acoustic wave device is provided. The surface acoustic wave excitation detection means includes one electroacoustic transducer for each of the main orbit and one sub orbit,
The surface acoustic wave device according to claim 3.   4. The surface acoustic wave device according to claim 1, wherein the surface acoustic wave revolving base is one of quartz, langasite, lithium niobate, and lithium tantalate. 5. . The surface acoustic wave orbiting substrate is quartz,
The surface acoustic wave circuit of the surface acoustic wave circuit substrate has an annular shape including a maximum outer diameter line centering on the Z axis of the crystal,
The main circular trajectory of the surface acoustic wave circuit is 1 ° to 3 ° in one direction and the other direction orthogonal to the maximum outer diameter line every 120 ° along the maximum outer diameter line in the surface acoustic wave circuit. Within the range of rotation angle
The surface acoustic wave device according to claim 5.

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