JP2010107446A - Surface acoustic wave element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To provide a surface acoustic wave element capable of accurately and precisely measuring the deceleration degree of the propagation speed, the degree of the phase delay and the reduction degree of the intensity of a surface acoustic wave when langasite is used as the material of a substrate including a surface acoustic wave circulating passage being a part of a spherical shape and having an annular shape. <P>SOLUTION: The surface acoustic wave element 10 is equipped with a substrate 14 formed of langasite and including an annular circulating passage 14a enabling the excited surface acoustic wave to circulate and a surface acoustic wave exciting and detecting means 16 for exciting the surface acoustic wave ASW to circulate the same to the circulating passage and detecting the circulated surface acoustic wave. In the circulating passage, the crossing line 14b wherein the crystal face around the Z-axis of langasite crosses the outer surface of the substrate becomes the maximum outer peripheral line of the outer surface of the substrate and the circulating passage is set to an annular shape along the crossing line while the surface acoustic wave exciting and detecting means 16 is arranged at a position where the attenuation of the surface acoustic wave excited to be circulated to the circulating passage most coincides with an exponential attenuation and the propagation speed of the surface acoustic wave becomes fastest in the circulating passage. <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 transmitted, 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 the change in the environment in which the surface acoustic wave circuit of the spherical surface acoustic wave element is in contact (for example, gas Proportional to the degree of concentration increase). Therefore, measuring the various degrees described above means measuring changes in the environment in which the surface acoustic wave circuit of the spherical surface acoustic wave element is in contact.
International Publication No. WO 01/45255

Materials for spherical substrates that can excite and propagate surface acoustic waves include quartz, langasite, lithium niobate (lithium niobate: LiNbO ₃ ), and lithium tantalate (lithium tantalate: LiTaO ₃ ). Piezoelectric crystal materials such as are widely known.

In these piezoelectric crystal materials, langasite is expensive compared to quartz, but cheaper than lithium niobate (lithium niobate: LiNbO ₃ ) or lithium tantalate (lithium tantalate: LiTaO ₃ ). Compared to quartz, the electromechanical coupling constant is large and the propagation speed of surface acoustic waves that are excited and propagated is relatively slow, so the degree of deceleration of the surface acoustic wave propagation speed, the degree of phase delay of surface acoustic waves, Easy observation of the degree of decrease in the intensity of the surface acoustic wave and precise observation of the degree of change in the environment (for example, increase in gas concentration) with which the surface acoustic wave circuit of the spherical surface acoustic wave element is in contact It is.

  However, when Langasite is used as a material for a spherical substrate capable of exciting and propagating a surface acoustic wave, the locus (path) of the surface acoustic wave propagating in one surface acoustic wave peripheral circuit As a result, it was found that the intensity of surface acoustic waves propagated differed and the propagation velocity differed when the surface acoustic wave orbits were different. And, naturally, the degree of environmental change (for example, increase in gas concentration) is greater when the attenuation of the intensity of the propagated surface acoustic wave matches the exponential attenuation as much as possible and the propagation velocity becomes faster. It can be observed precisely.

  SUMMARY OF THE INVENTION The present invention has been made under the above circumstances, and an object of the present invention is to provide a surface acoustic wave revolving substrate including a surface-circumferential circuit having a part of a spherical shape and an annular shape capable of exciting and propagating surface acoustic waves When Langasite is used as the material, 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 can be measured accurately and accurately. It is to provide a surface acoustic wave device.

  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 orbiting base is formed of langasite, and in the surface acoustic wave orbiting base, there is an intersecting line in which the crystal surface around one crystal axis of the langasite intersects the outer surface of the surface acoustic wave orbiting base. The surface acoustic wave circuit is set in an annular shape along the line of intersection, and the surface acoustic wave excitation detecting means excites the surface acoustic wave circuit in the surface acoustic wave circuit to circulate. The surface acoustic wave attenuation is best matched with the exponential attenuation, and the surface acoustic wave propagation velocity is the fastest.

  The surface acoustic wave device according to the present invention, which is configured as described above, has a degree of deceleration of the propagation speed of surface acoustic waves, a degree of phase lag of surface acoustic waves, and a reduction in the intensity of surface acoustic waves. Can be measured accurately and precisely.

  Hereinafter, an external environment measuring device using a surface acoustic wave device according to an embodiment of the present invention and various modifications 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 langasite, which is a crystalline material that can excite surface acoustic waves, and is defined in an annular shape by a part of a spherical surface, and is capable of circulating at least one surface acoustic wave that is excited. A surface acoustic wave substrate 14 including a surface wave circuit 14a; and a surface acoustic wave ASW excited by causing the surface acoustic wave circuit 14a of the surface wave substrate 14a to excite the surface acoustic wave ASW. And a surface acoustic wave excitation detecting means 16 for detecting the surface acoustic wave ASW that has circulated along the circumferential circuit 14a.

  Piezoelectric crystal materials such as langasite were excited when a surface acoustic wave was excited along an intersection line 14b in which the crystal surface of each spherical outer surface intersected with the spherical outer surface. It has been found that surface acoustic waves propagate along the intersection line 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.

  Langasite is known to have three crystal planes. Therefore, when langasite is used as the piezoelectric crystalline material for the surface acoustic wave rotating substrate 14, three surface acoustic wave circuit 14a can be set on the spherical outer surface.

  As the surface acoustic wave excitation detection means 16, the surface acoustic wave ASW excited by the surface acoustic wave circuit 14 a of the surface acoustic wave substrate 14 is orthogonal to the propagation direction along the surface of the surface acoustic wave substrate 14. In order to make it possible to easily set the wavelength and width satisfying the above-mentioned predetermined conditions, which can be propagated without being diffused indefinitely and circulated repeatedly, it is said to be an interdigital electrode or a comb-like electrode. Known electroacoustic transducers are usually used.

  The interdigital electrode or the comb-like electrode includes a pair of comb-like electrode portions each having a plurality of comb-like electrode branches 16a and a plurality of comb-like electrode branches 16a of one comb-like electrode portion. Each of the plurality of comb-like electrode branches 16a of the other comb-like electrode portion is arranged in the center of each of the plurality of gaps. 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 comb-like electrodes are formed on the surface acoustic wave circuit 14a of the surface acoustic wave-circulating substrate 14 with a plurality of comb-like electrode branches 16a facing the intersecting line 14b. When a high-frequency current having a frequency corresponding to the distance between the two comb-shaped electrode branches 16a facing each other is supplied to the comb-shaped electrode portion, the interdigital electrode or the comb-shaped electrode Each of the two comb-like electrode branches 16a facing each other has a frequency corresponding to the distance between the two comb-like electrode branches 16a facing each other. The surface acoustic wave ASW having the width of the length of the portion 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 wave ASW is paired with a pair of combs. A plurality of comb-like electrode branches 16a of the tooth-like electrode portion are arranged side by side That travels in a direction (that is, to propagate) causes.

  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 circulation base 14 to excite the surface acoustic wave ASW in a burst form and propagate it to the surface acoustic wave excitation detection means 16 at a desired timing and propagate it. The surface acoustic wave ASW excited and propagated by the circuit 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 surface acoustic wave ASW is excited on the burst in the surface acoustic wave circuit 14a, and the excited surface acoustic wave ASW is propagated through the surface acoustic wave circuit 14a along the aforementioned intersection line 14b and the surface acoustic wave circumference. It circulates in the circuit 14a. 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 ASW is detected by the detection / output unit 18d through the amplifier 18c at a desired timing.

  Yanagisawa, the inventor of the present application, traces the surface acoustic wave ASW propagating in the surface acoustic wave circuit 14a in the case where the surface of the surface acoustic wave orbiting substrate 14 is a trigonal piezoelectric single crystal material is a site. As a result of examining the (path) in detail, there is one main orbit 20 that can cause the surface acoustic wave ASW excited in the same surface acoustic wave circuit 14a to circulate in the same locus every round. Noticed. Even in the same surface acoustic wave circuit 14a, the surface acoustic wave ASW propagating along one main orbit 20 has an intensity attenuation that agrees well with an exponential attenuation, and the surface acoustic wave ASW has the fastest propagation speed. Become.

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

  In FIG. 1, the elastic surface along the intersection line 14b defined by the crystal plane around the Z axis, which is one crystal axis of the langasite, which is a kind of trigonal piezoelectric single crystal material. The case of the wave circuit 14a is shown as an example. The spherical surface of the spherical surface wave base 14 is assumed to be the earth, the Z axis is the earth axis, and the intersection line 14b is the equator. 20 is swung + 2 ° from the intersection line 14b.

  In the surface acoustic wave circuit 14a, the surface acoustic wave excitation detection means 16 is excited by the surface acoustic wave circuit 14a so that the attenuation of the surface acoustic wave ASW best matches the exponential attenuation, and the surface acoustic wave. If the surface acoustic wave excitation detecting means 16 is placed on the main circumference trajectory 20 if it is arranged at the position where the propagation speed of the wave ASW is fastest, it is most efficient and precise in the surface acoustic wave circuit 14a. The surface acoustic wave ASW can be propagated by controlling.

  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 through which the main circuit locus 20 passes.

  When the sensitive film 24 comes into contact with a specific substance in the external environment, the propagation speed of the surface acoustic wave ASW 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 ASW passing therethrough is reduced, and the attenuation rate is drastically reduced. The propagation speed and attenuation rate of the surface acoustic wave ASW passing through the change of hardness is changed, the propagation speed of the surface acoustic wave ASW passing through the endothermic or exothermic reaction by reacting with a specific substance, Change the attenuation factor. 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 ), and nitrogen dioxide (NO ₂ ) It has been known.

  That is, if the degree of change in the propagation speed or attenuation rate of the surface acoustic wave ASW that has passed through the sensitive film 24, that is, the change in the phase or intensity of the surface acoustic wave ASW that has passed through the sensitive film 24, is measured, It is possible to detect a change in a specific substance in the external environment that is sensitive as described above.

  When the surface acoustic wave excitation detection means 16 is placed on the main circuit locus 20, if the center of the surface acoustic wave excitation detection means 16 is made coincident with the main circuit locus 20, the elastic force can be controlled more efficiently and precisely. It is possible to propagate the surface wave ASW.

  As is clear from the above description with reference to FIG. 1, the main orbit 20 does not coincide with the intersecting line 14b, and every 120 ° rotation angle along the intersecting line 14b in the surface acoustic wave circuit 14a. In addition, the surface of the surface acoustic wave excitation detecting means 16 is meandered alternately and sinusoidally in the range of the rotation angle α of 1 ° to 3 ° in one direction and the other direction orthogonal to the intersecting line 14b. Is made to coincide with the main orbit 20, the surface acoustic wave excitation detecting means 16 is separated from the intersection line 14 b in the surface acoustic wave circuit 14 a as shown in FIG. In some cases, the line coincides with the intersection line 14b as shown in the figure.

  When the center of the surface acoustic wave excitation detection means 16 is made coincident with the main circuit locus 20, the wavefront of the surface acoustic wave ASW that the surface acoustic wave excitation detection means 16 excites and propagates in the surface acoustic wave circuit 14a becomes the main circuit locus 20. On the other hand, if they are orthogonal to each other, it is possible to propagate the surface acoustic wave ASW through more efficient and more precise control.

  In the case where the surface acoustic wave excitation detecting means 16 is an interdigital electrode or a comb-like electrode, each of the pair of comb-like electrode portions as in the surface acoustic wave excitation detecting means indicated by reference numeral 16 'in FIG. The plurality of comb-shaped electrode branches 16 ′ may be arranged so as to be as orthogonal as possible to the main circuit locus 20.

  More precisely, as shown in FIG. 2, the surface acoustic wave excitation detection means indicated by reference numeral 16 ″, the interdigital electrode or the comb-like electrode is placed on the main orbit 20 in the position where the interdigital electrode is placed. A plurality of comb-like electrode branches 16 ″ a extending in a direction orthogonal to the line 14 are sequentially shifted in the orthogonal direction corresponding to the inclination of the main circuit locus 20 with respect to the intersecting line 14 at the position. More preferably.

FIG. 1 is a schematic diagram schematically showing a configuration of an external environment measuring apparatus using a surface acoustic wave element according to an embodiment of the present invention. FIG. 2 is a schematic view schematically showing various modifications of the surface acoustic wave excitation detecting means used in the surface acoustic wave element shown in FIG.

Explanation of symbols

  DESCRIPTION OF SYMBOLS 10 ... Surface acoustic wave element, 12 ... External environment measuring apparatus, 14 ... Surface acoustic wave circulation base | substrate, 14a ... Surface acoustic wave circuit, 14b ... Intersection, 16, 16 ', 16 "... Surface acoustic wave excitation detection means 16a, 16'a, 16'a ... electrode branch, 18 ... operation control means, 18a ... input / output switching unit, 18b ... high frequency signal generating unit, 18c ... amplifier, 18d ... detection / output unit, 20 ... main circuit Trajectory, 24 ... sensitive film, ASW ... surface acoustic wave.

Claims (5)

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 orbiting substrate is formed of langasite,
In the surface acoustic wave circulating substrate, the intersection line where the crystal surface around one crystal axis of the langasite intersects the outer surface of the surface acoustic wave circulating substrate becomes the maximum outer circumferential line of the outer surface, and the surface acoustic wave circuit is connected to the surface. It is set in an annular shape along the line,
When the surface acoustic wave excitation detection means is a surface acoustic wave circuit, the attenuation of the surface acoustic wave excited and circulated by the surface acoustic wave circuit best matches the exponential attenuation, and the propagation speed of the surface acoustic wave is Placed in the fastest position,
A surface acoustic wave device.   2. The surface acoustic wave device according to claim 1, wherein the center of the surface acoustic wave excitation detecting means is disposed away from the intersecting line in the surface acoustic wave circuit.   2. The surface acoustic wave device according to claim 1, wherein the center of the surface acoustic wave excitation detecting means is disposed on the intersection line in the surface acoustic wave circuit.   4. The wavefront of a surface acoustic wave excited and propagated by a surface acoustic wave excitation circuit in a surface acoustic wave circuit is directed in a direction orthogonal to the intersecting line. 5. 2. A surface acoustic wave device according to claim 1. The surface acoustic wave excited and propagated by the surface acoustic wave excitation detecting means in the surface acoustic wave circuit is changed to the intersecting line at every 120 ° rotation angle along the intersecting line with the center of the surface acoustic wave circulating substrate as the center. Propagating on a circular trajectory having a sine wave shape that swings alternately in the range of a rotation angle of 1 ° to 3 ° to one and the other in the orthogonal direction.
The surface acoustic wave element according to claim 1, wherein the surface acoustic wave element is provided.

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