JP2011160091A - Spherical surface acoustic wave element - Google Patents

Abstract

<P>PROBLEM TO BE SOLVED: To further improve operation precision of a spherical surface acoustic wave element, and further improve the operation precision of various devices using the spherical surface acoustic wave element as a result. <P>SOLUTION: In the spherical surface acoustic wave element 10, a center C of an electroacoustic transducer 22 is in a range of 15 degree or less with respect to a linearly extending direction of an outer circle line 14 of the maximum diameter from a cross point with +Y crystal axis in a surface area 16, further, when crystal or langasite is dextrorotatory, the center C of the electroacoustic transducer 22 is in a position rotated by an angle of 1 degree or more and 3 degree or less in +Z direction with respect to the outer circle line 14 of the maximum diameter from the cross point with the +Y crystal axis in the surface area 16, on the other hand, when the crystal or the langasite is levorotatory, the center C of the electroacoustic transducer 22 is in a position rotated by an angle of 1 degree or more and 3 degree or less in -Z direction with respect to the outer circle line 14 of the maximum diameter from the cross point with the +Y crystal axis in the surface area 16. <P>COPYRIGHT: (C)2011,JPO&INPIT

Description

  The present invention relates to a spherical surface acoustic wave device.

  Conventionally, a surface acoustic wave element in which electroacoustic transducers are provided at two positions apart from each other on the surface of a substrate having a flat surface made of a piezoelectric material is known. The electroacoustic transducer is usually a high-frequency excitation / high-frequency receiving means such as an interdigital electrode.

  In this conventional surface acoustic wave device, when a high frequency current is supplied to one electroacoustic transducer, the one electroacoustic transducer generates a surface acoustic wave (SAW) on the surface of the substrate. Can propagate in the direction. The other electroacoustic transducer can receive a surface acoustic wave from one electroacoustic transducer on the surface and generate a high-frequency current corresponding to the received surface acoustic wave. When the electroacoustic transducer is an interdigital electrode, the direction in which multiple electrode branches of the interdigital electrode are aligned is the direction in which the surface acoustic wave generated by the interdigital electrode propagates, and the surface acoustic wave is efficiently used. It becomes the direction to receive well.

  A surface acoustic wave is a surface acoustic wave that propagates while concentrating much of its energy on a material surface, unlike a longitudinal wave or a transverse wave called a normal bulk wave. Examples of surface acoustic waves include Rayleigh waves, Sezawa waves, pseudo Sezawa waves, Love waves, and the like, and can also exist on the surface of anisotropic materials.

  Such conventional surface acoustic wave devices are used for delay lines, oscillation and resonance devices for transmitters, filters for selecting frequencies, chemical sensors, biosensors, remote tags, and the like.

  The width of the surface acoustic wave immediately after the interdigital transducer is excited (the dimension in the direction orthogonal to the propagation direction of the surface acoustic wave) is such that two adjacent electrode branches face each other in the interdigital electrodes. It is equal to the length (referred to as overlap width).

  However, in the conventional surface acoustic wave device as described above in which the surface of the substrate on which the surface acoustic wave propagates is flat, the surface acoustic wave excited by one electroacoustic transducer and propagated from one electroacoustic transducer is As it moves away from one electroacoustic transducer, it continues to diffuse in the width direction and weakens the energy it has. Accordingly, there is a limit to the distance that the electroacoustic transducer for surface acoustic wave excitation and the electroacoustic transducer for receiving surface acoustic waves can be placed apart from each other. As a result, the conventional surface acoustic wave as described above is limited. There has been a limit to the improvement of the operation accuracy of various devices as described above using wave elements.

  In contrast to such a conventional surface acoustic wave element, in Non-Patent Document 1, surface acoustic waves are generated under predetermined conditions on the spherical surface of a substrate having a spherical surface capable of exciting and propagating surface acoustic waves. It is disclosed that by exciting and propagating, the excited surface acoustic wave can be circulated many times along the outermost line of the maximum diameter of the spherical surface without continuing to diffuse in the direction intersecting the propagation direction. .

  Patent Document 1 discloses a spherical surface acoustic wave element that can be used practically. In this practical spherical surface acoustic wave device, a part of the spherical surface including the outermost line of the maximum diameter that can excite the surface acoustic wave and propagate and circulate without infinite diffusion in the direction intersecting the propagation direction. An interdigital electrode is installed as an electroacoustic transducer on the surface region of a spherical or disk-shaped substrate having an annular surface region formed on the outer surface, and on the outer surface of the substrate A region other than the surface region (that is, a region where no surface acoustic wave is propagated) is supported by the support member. Such a spherical surface acoustic wave element is also referred to as a ball SAW device.

  In a spherical surface acoustic wave element, the surface acoustic wave is diffused in a direction intersecting the propagation direction of an annular surface region composed of a part of the spherical surface including the outermost line of the maximum diameter on the outer surface of the substrate. Many rounds are possible without continuing (ie, without continuing to lose energy). And such conditions are W = √ (2aλ), where a is the radius of a part of the sphere of the surface region, λ is the wavelength of the surface acoustic wave, and W is the elastic surface The width of the wave.

  Therefore, in comparison with the various devices as described above using the conventional surface acoustic wave device as described above, the various devices as described above using the spherical surface acoustic wave device instead of the conventional surface acoustic wave device as described above, Furthermore, it is possible to dramatically improve the operation accuracy.

International Publication WO01 / 45255 Pamphlet

Technical Report of Institute of Electronics, Information and Communication Engineers, US2000, Volume 14 (2000), Technical Report of Institute of Electronics, Information and Communication Engineers

In the case of using a piezoelectric single crystal including quartz, for example, which can be procured most inexpensively as the base material of the spherical surface acoustic wave element, the piezoelectric single crystal is a plane including the Y axis and perpendicular to the Z axis ( Z-axis crystal plane) is processed into a spherical shape centered on the position where it intersects the Z-axis, and the circle of the line where the plane intersects on the outer surface of the spherical substrate (maximum on the outer surface of the spherical substrate) It is known that the excited surface acoustic wave can be rotated many times by exciting and propagating the surface acoustic wave under the conditions described above along the outer circumferential circle.
In the present invention, a right-handed XYZ coordinate axis is assumed. The crystal orientation of crystal langasite crystal is defined in terms of piezoelectric material and crystallography, and in particular, the + X axis is defined by the existence of an equivalent orientation clearly in three directions because of the crystal's objectivity, and it is adopted. .

  Furthermore, the surface acoustic wave excited on the outer surface of the spherical base material along the maximum outer peripheral circle under the above-described conditions is caused by the electromechanical coupling constant different from the position on the outer surface, so that the maximum outer peripheral circle is It has been found that meandering so as to wave at predetermined intervals on both sides of the maximum outer circumference circle while propagating along the maximum outer circumference circle in a ring-shaped surface region centered on. This is due to the anisotropy of the piezoelectric single crystal.

  Moreover, the meandering surface acoustic wave propagation path is peculiar to the material of the base material, and when the surface acoustic wave is excited at a position away from the meandering surface acoustic wave propagation path in the annular surface region, It has been found that such surface acoustic waves have a faster attenuation of the intensity during the circulation, and the attenuation of the intensity during the rotation is not a geometric series but is an attenuation while generating a wave.

  Such a situation lowers the operation accuracy of the spherical surface acoustic wave element, and consequently reduces the operation accuracy of various devices using the spherical surface acoustic wave element.

  The present invention has been made under the above circumstances, and an object of the present invention is to further improve the operation accuracy of the spherical surface acoustic wave element, and further improve the operation accuracy of various devices using the spherical surface acoustic wave element. is there.

  One embodiment of the present invention is formed of quartz or langasite, and is formed of a part of a spherical surface centered on a point that includes a + Y crystal axis and is perpendicular to the + Z crystal axis and intersects the Z crystal axis. The surface includes a surface area extending on an annulus including the outermost line of the maximum diameter intersecting a part of the spherical surface, and the surface area is along an annular extending direction of the surface area. A substrate in which the excited surface acoustic wave circulates while meandering along the outer peripheral line at a predetermined cycle: exciting the surface acoustic wave along the annular extending direction of the surface region on the surface region of the substrate And the center of the electroacoustic transducer is within a range of 15 degrees or less from the intersection with the + Y crystal axis in the surface region in the extending direction of the outermost line of the maximum diameter. In addition, the crystal or the Rangasai However, when it is dextrorotatory, the center of the acoustic transducer is at an angle of not less than 1 degree and not more than 3 degrees in the + Z direction with respect to the outermost line of the maximum diameter from the intersection with the + Y crystal axis in the surface region. When the crystal or the langasite is levorotatory in the rotated position, the center of the acoustic transducer is from the intersection with the + Y crystal axis in the surface region to the outermost line of the maximum diameter. A spherical surface acoustic wave device characterized by being in a position rotated at an angle of not less than 1 degree and not more than 3 degrees in the -Z direction.

  In the spherical surface acoustic wave element, the center of the electroacoustic transducer may coincide with the + Y crystal axis direction or the −Y crystal axis direction in the surface region.

  According to the spherical surface acoustic wave device according to the present invention, characterized in that it is configured as described above, it is excited and propagated to the surface region of a predetermined annular shape on the piezoelectric single crystal substrate. It is possible to reduce the surface acoustic wave intensity in a geometric series and to improve the operation accuracy of the spherical surface acoustic wave element by enabling multiple wraparound by suppressing the attenuation rate. As a result, the operation accuracy of various devices using the spherical surface acoustic wave element can be further improved.

1 is a diagram schematically showing a spherical surface acoustic wave device according to an embodiment of the present invention. FIG. In the spherical surface acoustic wave element shown in FIG. 1, the surface acoustic wave excited and propagated along the maximum outer peripheral line at the center of the surface region in the surface region of the predetermined annular shape on the base material propagates best. FIG. 3 is a diagram schematically showing a surface acoustic wave propagation path meandering with a period in a flat shape. (A) is a point P in FIG. 2 on the maximum outer peripheral line that is the center of the surface area in the surface area of the predetermined annular shape in FIG. 1 (the −Y crystal axis of the base material in the spherical surface acoustic wave device in FIG. 1). 2) on the maximum outer perimeter line at a predetermined intensity and a predetermined frequency centering on the point K where the surface acoustic wave propagation path meandering at a predetermined period in FIG. 2 intersects the maximum outer perimeter line. FIG. 2 is a diagram schematically showing a change in amplitude (intensity) accompanying an increase in the number of rounds of a predetermined surface acoustic wave excited and propagated along the maximum outer peripheral line; FIG. 2 at a predetermined intensity and a predetermined frequency centering on the point P of FIG. 2 that is farthest from the surface acoustic wave propagation path meandering with the predetermined period of FIG. Increase in the number of rounds of a given surface acoustic wave excited and propagated along It is a figure which shows schematically the change of the amplitude (intensity) which accompanies; (C) is with respect to the said largest outer periphery line from the P point of FIG. It was excited and propagated along the maximum perimeter line at a predetermined intensity and a predetermined frequency around a point H located on the surface acoustic wave propagation path meandering at a predetermined cycle in FIG. It is a figure which shows roughly the change of the amplitude (intensity) accompanying the increase in the frequency | count of a predetermined surface acoustic wave. (A) shows that the surface acoustic wave circulation path through which the surface acoustic wave excited and propagated along the extending direction of the surface region in the predetermined annular surface region of FIG. In the case of meandering with the maximum amplitude at a position deviated by −1.5 degrees in the direction orthogonal to the maximum outer peripheral line from the central maximum outer peripheral line, the surface acoustic wave circulation path from the maximum outer peripheral line. The same as the maximum amplitude position of the wave is shifted by +3.0 degrees in the orthogonal direction, and is excited and propagated along the maximum outer periphery line at a predetermined intensity and a predetermined frequency around a position away from the maximum amplitude position of the surface acoustic wave circulation path. FIG. 2 is a diagram schematically showing a change in amplitude (intensity) accompanying an increase in the number of rounds of a predetermined surface acoustic wave generated; (B) is a diagram of the surface region in the surface region of the predetermined annular shape in FIG. 1; Excited and propagated along the extension direction The surface acoustic wave circulation path through which the surface acoustic wave propagates best has a maximum amplitude at a position deviated by −1.5 degrees in the direction perpendicular to the maximum outer peripheral line from the maximum outer peripheral line which is the center of the surface region. The meandering position is shifted by +1.5 degrees in the same orthogonal direction as the maximum amplitude position of the surface acoustic wave circulation path from the maximum outer circumference line, and a position away from the maximum amplitude position of the surface acoustic wave circulation path. FIG. 6 is a diagram schematically showing a change in amplitude (intensity) accompanying an increase in the number of rounds of a predetermined surface acoustic wave excited at a predetermined intensity and a predetermined frequency in the center and propagated along the maximum outer peripheral line; ) Indicates that the surface acoustic wave circulation path through which the surface acoustic wave excited and propagated along the extending direction of the surface region in the predetermined annular surface region of FIG. 1 propagates best is the center of the surface region. Above the maximum perimeter line The same orthogonality as the maximum amplitude position of the surface acoustic wave circulation path from the maximum outer periphery line when meandering with the maximum amplitude at a position shifted by -1.5 degrees in the direction orthogonal to the maximum outer periphery line The number of rounds of a predetermined surface acoustic wave that is excited at a predetermined intensity and a predetermined frequency around a position away from the maximum amplitude position of the surface acoustic wave circulation path without being displaced It is a figure which shows schematically the change of the amplitude (intensity) accompanying an increase; (D) is the elasticity which was excited and propagated along the extension direction of the said surface region in the surface region of the predetermined annular shape of FIG. The surface acoustic wave circulation path through which the surface wave propagates best has a maximum amplitude at a position deviated by −1.5 degrees in the direction orthogonal to the maximum outer peripheral line from the maximum outer peripheral line which is the center of the surface region. If meandering, Predetermined intensity and predetermined centering on a position on the maximum amplitude position of the surface acoustic wave orbital path shifted by -1.5 degrees in the same orthogonal direction as the maximum amplitude position of the surface acoustic wave orbital path from the large outer circumference line FIG. 2 is a diagram schematically showing a change in amplitude (intensity) accompanying an increase in the number of rounds of a predetermined surface acoustic wave excited at a frequency of and propagated along the maximum outer peripheral line; FIG. The surface acoustic wave circulation path through which the surface acoustic wave excited and propagated along the extending direction of the surface region in the ring-shaped surface region of the surface is the best from the maximum outer peripheral line at the center of the surface region. In the case of meandering with the maximum amplitude at a position shifted by -1.5 degrees in the direction orthogonal to the outer circumferential line, the orthogonality is the same as the maximum amplitude position of the surface acoustic wave circulation path from the maximum outer circumferential line. -3.0 degree offset in the direction above Amplitude (intensity) associated with an increase in the number of rounds of a predetermined surface acoustic wave excited at a predetermined intensity and a predetermined frequency around a position away from the maximum amplitude position of the surface wave circulation path and propagated along the maximum outer peripheral line. FIG.

  An overall configuration of a spherical surface acoustic wave device according to an embodiment of the present invention will be schematically described with reference to FIG.

  The spherical surface acoustic wave element 10 includes a base material 12 of a trigonal piezoelectric single crystal such as quartz or langasite. In this example, dextrorotatory quartz was used. In left-handed quartz and langasite, the SAW meandering phase is shifted 60 degrees around the Z axis and the meandering is reversed north-south (Z direction). The difference is that the direction of shifting (rotating) the conversion element 22 (interdigital electrode) is reversed. The substrate 12 is formed of a part of a spherical surface having a center C at a point where a plane including the Y crystal axis and perpendicular to the Z crystal axis (crystal plane around the Z axis) intersects the + Z crystal axis. A surface region 16 including an outer peripheral line 14 having a maximum diameter intersecting a part of the spherical surface and extending in an annular shape is included. The base material 12 is supported by a pedestal (not shown) via a support column 18 fixed to a region excluding the annular surface region 16. In this embodiment, the base material 12 has a spherical shape, but may be a disk shape in which a portion excluding the annular surface region 16 is deleted.

  The trigonal piezoelectric single crystal has six Y crystal axes in total because of the three-fold symmetry of the crystal plane, but one -Y crystal in order to avoid complication of the drawing. Only the axes are shown, and these six Y crystal axes intersect with the outermost perimeter line 14 of the maximum diameter every 60 degrees around the center C.

  It is possible to excite and propagate the surface acoustic wave 20 along the outer peripheral line 14 having the maximum diameter in the surface region 16. As described above in the “Background Art” section of this specification, by setting the wavelength and width of the surface acoustic wave 20 to meet the above-described conditions based on the radius of a part of the spherical surface of the surface region 16, The surface acoustic wave 20 excited and propagated along the outer circumferential line 14 having the maximum diameter in the surface region 16 is circulated many times without continuing to diffuse in a direction intersecting the propagation direction (that is, without continuing to lose energy). It is possible.

  The spherical surface acoustic wave element 10 further excites and propagates the surface acoustic wave 20 along the extending direction of the annular surface region 16 (maximum outer peripheral line 14) to the annular surface region 16 of the substrate 12. The electroacoustic transducer 22 is provided. In this embodiment, the electroacoustic transducer 22 includes an alternite phase array, which is a so-called interdigital electrode, which is a kind of high-frequency excitation / high-frequency reception / means. It is provided in a predetermined range on the surface region 16 in a state of extending in a direction orthogonal to the line 14 as described later.

  The interdigital electrode can be easily formed at a desired position of the annular surface region 16 of the substrate 12 by a known photoetching technique, and in this embodiment, has a two-layer structure of gold and chromium.

  In this embodiment, the diameter of the outer circumferential line 14 of the annular surface region 16 of the base material 12 is 3.3 mm, and the annular surface region 16 is 150 MHz along the extending direction of the annular surface region 16. In order to excite the surface acoustic wave 20, the dimensions of the interdigital electrode are: When the substrate 12 is a langasite, the array period of the plurality of electrode branches is about 15.88 microns, and each of the plurality of electrode branches is The length (overlap width) facing each other is set to about 228.9 microns, and the length between both sides along the extending direction in the plurality of electrode branches is set to about 167 microns; When 12 is quartz, the arrangement period of the plurality of electrode branches is about 21.38 microns, and the length (overlap width) facing each other in the plurality of electrode branches is about 265.6 microns, And in the multiple electrode branches The length between the extending two sides along the direction is set to about 225 microns.

  The electroacoustic transducer 22 is electrically connected to a combination of a high-frequency signal generator 26, an amplifier 28, and a detection / output unit 30 via a switching unit 24. The high-frequency signal generator 26 applies a high-frequency signal to the electroacoustic transducer 22 via the switching unit 24 for a very short time, so that the circular surface region 16 of the base material 12 of the trigonal piezoelectric single crystal 12 has a circular shape. The surface acoustic wave 20 can be excited and propagated along the extending direction of the annular surface region 16. Thereafter, the switching unit 24 receives the surface acoustic wave 20 that has propagated and circulated along the extending direction of the annular surface region 16 before the electroacoustic conversion element 22 receives the amplifier 28 and the detection / output unit 30. The high-frequency signal corresponding to the surface acoustic wave 20 received by the electroacoustic transducer 22 being propagated along the annular surface region 16 and circulated is received via the switching unit 24 and detected / output. Sent to the combination of parts 30.

  Examples of piezoelectric crystals that can be used for the substrate 12 include lithium niobate (LiNbO3) and lithium tantalate (LiTaO3) in addition to quartz and langasite. Even when the substrate 12 is formed of a piezoelectric crystal other than quartz or langasite, the predetermined ring-shaped surface region 16 that can circulate the surface acoustic wave 20 on the outer surface of the substrate 12 is the substrate 12. Is the surface region of the outer surface of the base material 12 along the outer circumferential line of the maximum diameter of the annular shape intersecting with the spherical outer surface of the base material 12.

  Instead of the switching unit 24, the high-frequency signal is transmitted from the high-frequency signal generating unit 26 only to the electroacoustic transducer 22 in one direction, and the high-frequency signal converted from the surface acoustic wave 20 received by the electroacoustic transducer 22 is A known directional coupling circuit that transmits only to the combination of the amplifier 28 and the detection / output unit 30 can also be used.

  When the spherical surface acoustic wave element 10 is used as a gas sensor, a sensitive film 32 sensitive to a specific gas is provided in the annular surface region 16. The sensitive film 32 may reduce the propagation speed of the surface acoustic wave 20 propagating along the annular surface region 16 according to the amount of mass increased by adsorbing a specific gas on the surface, for example. The surface acoustic wave propagating through the annular surface region 16 can be obtained by storing a specific gas in the sensitive film 32 and changing the mechanical rigidity of the sensitive film 32 in accordance with the amount of occlusion. The propagation speed and attenuation rate of 20 may be changed. Furthermore, an endothermic or exothermic reaction is caused according to the amount of the specific gas reacted by reacting with the specific gas, and the surface acoustic wave propagating through the annular surface region 16 according to the amount of the endothermic or exothermic reaction. The propagation speed of 20 may be changed. The sensitive film 32 is desirably a material that causes a reversible reaction.

  For example, as such a sensitive film 32, palladium (Pd), which absorbs hydrogen (H2) to form a hydride to change mechanical properties, platinum (Pt) having high adsorptivity to ammonia (NH3), hydride Oxidized tungsten oxide (WO3), carbon monoxide (CO), carbon dioxide (CO2), sulfur dioxide (SO2), nitrogen dioxide (NO2), etc. are selectively adsorbed, such as phthalocyanine. .

  Many of the piezoelectric crystals used for the substrate 12 have anisotropy, and due to this, the electromechanical coupling constant varies depending on the position in the annular surface region 16. Therefore, in the case where the surface acoustic wave 20 is excited along the extending direction of the annular surface region 16 (maximum outer peripheral line 14) by the electroacoustic transducer 22 in the annular surface region 16, the surface acoustic wave 20 is excited. The sound velocity and the power flow angle are varied while propagating along the extending direction. Then, the surface acoustic wave 20 propagates best (that is, the surface acoustic wave 20 is excited by the electroacoustic transducer 22, and the intensity of the surface acoustic wave 20 is clean and smooth until it becomes undetectable after many rounds. It is known that the circuit path CT meanders in such a way that waves are struck at predetermined intervals on both sides of the outer diameter line 14 of the maximum diameter.

  In other words, the surface acoustic wave 20 is excited in the annular surface region 16 of the substrate 12 by the electroacoustic transducer 22 along the extending direction of the annular surface region 16 (maximum diameter outer peripheral line 14). In this case, if the center of the surface acoustic wave 20 is positioned on such a circular path CT and the direction in which the surface acoustic wave 20 propagates is made to coincide with the direction of the circular path CT, the surface acoustic wave 20 is the most. It can be propagated well.

  When the substrate 12 is a trigonal piezoelectric single crystal such as quartz or langasite as in this embodiment, it extends along the extending direction of the annular surface region 16 (maximum diameter outer peripheral line 14). The circular path CT through which the surface acoustic wave 20 propagates best is 120 degrees along the outer circumferential line 14 of the maximum diameter that can be virtually assumed as the equator when the spherical base material 12 is regarded as the earth and the Z crystal axis is assumed as the earth axis. Waves meander like a sine wave on both sides of the outer circumferential line 14 having the maximum diameter in a cycle. The six maximum amplitude positions of the circular path CT have six Y crystal axes (only one in FIG. 1) in the direction along the maximum diameter outer peripheral line 14 and the above-mentioned + · − on the maximum diameter outer peripheral line 14. This corresponds to the direction perpendicular to the outermost peripheral line 14 with respect to the position where the cross section (shown) intersects.

  The crystal axis of the piezoelectric crystal can be known by, for example, the X-ray diffraction method. Further, the above-described circulation path CT extends the annular surface region 16 by bringing the external independent electroacoustic transducer 22 close to each of a plurality of preset positions of the annular surface region 16 of the base 12. It is possible to know experimentally by actually exciting, propagating and circulating a surface acoustic wave of a predetermined strength along the direction, and observing the attenuation state of the surface acoustic wave after having rotated a predetermined number of times.

  FIG. 2 shows that the surface acoustic wave 20 propagates best when the intersection P with one + Y crystal axis (see FIG. 1) on the outermost circumferential line 14 of the annular surface region 16 is 0 degree. The circular path CT is illustrated, and the power flow angle at the position (maximum amplitude position) where the wave of the circular path CT is farthest from the outer circumferential line 14 having the maximum diameter is zero. A person skilled in the art can easily obtain the power flow angle by a known elasticity theory using the elastic constant of the material constituting the substrate 12. An example of such a theory of elasticity is A. Auld. “Acoustic Fields and Waves in solids” vol. 1 and 2, 2nd edition, Krieger Publishing Company (1990) Page 135-161.

  FIG. 3A shows the center of the electroacoustic transducer 22 in which the plurality of electrode branches 22a are oriented in a direction perpendicular to the outermost peripheral line 14 of the annular surface region 16 in this embodiment. 2 is arranged at a point K deviated by +30 degrees on the outermost circumferential line 14 from the point P on the outermost circumferential line 14 in FIG. 2, and after the high frequency signal of 150 MHz is input for 1 microsecond, the annular surface It is shown that the surface acoustic wave 20 that is excited along the extending direction of the surface region 16 along the extending direction of the surface region 16 (the outermost circumference line 14), propagates, and circulates changes the intensity (decibel) as the number of turns increases. . Here, the intensity is displayed logarithmically.

  The point K is on the circular path CT through which the surface acoustic wave 20 propagates best, but the arrangement direction of the plurality of electrode branches 22a of the interdigital electrodes of the electroacoustic transducer 22 arranged at the point K (that is, the point K) The direction in which the surface acoustic wave 20 generated by the electroacoustic transducer 22 is first separated from the electroacoustic transducer 22) does not coincide with the direction of the circular path CT at the point K.

  From (A) of FIG. 3, the intensity of the surface acoustic wave 20 becomes 1/10 at 38 laps, and after that, it is attenuated cleanly in a geometric series until 60 laps. It can be seen that there is a wave. This means that when the center of the electroacoustic transducer 22 is arranged at the point K in FIG. 2, the surface acoustic wave 20 exceeding 60 laps increases the accuracy of various measurement results based on the surface acoustic wave 20. It turns out to reduce.

  FIG. 3B shows the center of the electroacoustic transducer 22 in which the plurality of electrode branches 22a are oriented in a direction perpendicular to the outermost line 14 having the maximum diameter of the annular surface region 16 in this embodiment. 2 is arranged at the point P on the outer peripheral line 14 with the maximum diameter in FIG. 2, and after the high frequency signal of 150 MHz is input for 1 microsecond, the extending direction of the surface area 16 (the maximum diameter It is shown that the surface acoustic wave 20 that is excited along the outer circumferential line 14), propagates, and circulates changes the intensity (decibel) as the number of laps increases. Here, the intensity is displayed logarithmically.

  Although the point P is on the outermost line 14 having the maximum diameter of the annular surface region 16, the surface acoustic wave 20 is generated when the outermost line 14 having the maximum diameter is viewed on the equator with the spherical base material 12 viewed on the earth. The circular path CT that propagates best is approximately -2 degrees away from the P point in latitude at the same longitude as the P point. Therefore, the plurality of interdigital electrodes 22a of the interdigital electrode of the electroacoustic transducer 22 arranged at the point P is out of the circulation path CT through which the surface acoustic wave 20 propagates best.

  From FIG. 3B, an annular shape is obtained by the electroacoustic transducer 22 arranged at the point P deviated from the circular path CT in which the surface acoustic wave 20 propagates best in the annular surface region 16. The surface acoustic wave 20 excited along the extending direction of the surface region 16 is arranged at a point K on the circular path CT where the surface acoustic wave 20 propagates best as shown in FIG. Compared with the surface acoustic wave 20 excited along the extending direction of the annular surface region 16 by the electroacoustic conversion element 22, the intensity is small, and further, the sound is attenuated while generating a wave over the entire number of turns. I understand that. This means that, when the center of the electroacoustic transducer 22 is arranged at the point P in FIG. 2, the accuracy of various measurement results based on the surface acoustic wave 20 is reduced over the entire number of turns. I understand.

  FIG. 3C shows the center of the electroacoustic transducer 22 in which the plurality of electrode branches 22a are oriented in a direction orthogonal to the outermost circumferential line 14 of the annular surface region 16 in this embodiment. 2 is the same longitude as the point P on the outermost line 14 having the maximum diameter in FIG. 2, but is placed at the point H approximately -2 degrees apart from the point P, and a high frequency signal of 150 MHz is input for 1 microsecond. A state in which the surface acoustic wave 20 that is excited, propagated, and circulated on the annular surface region 16 along the extending direction of the surface region 16 (the outermost line 14 of the maximum diameter) changes the intensity (decibel) as the number of turns increases. It is shown. Here, the intensity is displayed logarithmically.

  At point H, the maximum amplitude position of the circular path CT through which the surface acoustic wave 20 propagates best intersects, and at the point H, the power flow angle of the circular path CT is zero, and the tangent of the circular path CT is It faces the same direction as the outer circumferential line 14 of the maximum diameter of the annular surface region 16. That is, the extending direction of the tangent line of the circulation path CT at the H point is the same direction as the arrangement direction of the plurality of electrode branches 22a of the interdigital electrode of the electroacoustic transducer 22 centered at the H point. As a result, it is the same as the propagation direction of the surface acoustic wave 20 when it is excited by the plurality of electrode branches 22a and leaves the plurality of electrode branches 22a.

  From FIG. 3C, the annular surface region 16 is arranged at the point H on the circular path CT where the surface acoustic wave 20 propagates best, and the tangent of the circular path CT at the point H is extended. The surface acoustic wave 20 excited by the electroacoustic transducer 22 having the arrangement direction of the plurality of interdigital branches 22a in the same direction as the outgoing direction and excited along the extending direction of the annular surface region 16 is excited. As shown in FIG. 3A, the ring-shaped surface region 16 is formed by the electroacoustic transducer 22 arranged at the point K on the circulation path CT through which the surface acoustic wave 20 propagates best. Compared to the surface acoustic wave 20 excited along the extending direction, it can be seen that the initial intensity is the same, but it is attenuated cleanly and exponentially without generating a wave over a longer number of rounds. This shows that the surface acoustic wave 20 improves the accuracy of various measurement results based on the surface acoustic wave 20 when the center of the electroacoustic transducer 22 is arranged at the point H in FIG. .

  From (A) to (C) of FIG. 3, an electroacoustic transducer of interdigital electrodes in which a plurality of electrode branches 22 a are oriented in a direction orthogonal to the outer peripheral line 14 having the maximum diameter of the annular surface region 16. The center of 22 is from the intersection P with the Y crystal axis on the outermost line 14 of the maximum diameter in the annular surface region 16 of the spherical base material 12 of a trigonal piezoelectric single crystal such as quartz or langasite. If within the range of 15 degrees or less in the extending direction of the outermost line 14 having the maximum diameter, the surface acoustic wave 20 is excited, propagated and circulated by the electroacoustic transducer 22 along the extending direction of the annular surface region 16. It can be seen that it attenuates geometrically without producing a large wave as a whole over the entire number of laps. As a result, the operation accuracy of various devices that perform various operations based on the surface acoustic wave 20 can be further improved.

  Further, the direction in which the center of the electroacoustic transducer 22 is orthogonal to the maximum diameter outer peripheral line 14 from the intersection P with the −Y crystal axis on the maximum outer peripheral line 14 in the annular surface region 16 of the substrate 12. If the position is within the range of 1 degree or more and 3 degrees or less in the -Z direction, and if it is within the range of 1.5 degree or more and 3 degrees or less, the electroacoustic transducer 22 can more reliably extend the annular surface region 16 in the extending direction. It can be seen that the surface acoustic wave 20 excited along, propagated and circulated attenuates geometrically without producing a large wave as a whole over the entire number of laps. As a result, the operation accuracy of various devices that perform various operations based on the surface acoustic wave 20 can be further improved. Although not shown in the drawing, such a phenomenon that the attenuation is reduced may be within a range of not less than 3 degrees and not less than 1.5 degrees and 3 degrees in the + Z direction when there is an electroacoustic transducer in the + Y direction. If it is, the effect can be expected more reliably. The crystal system of crystal or langasite crystal is equivalent to specifying the position of the electroacoustic transducer with respect to the + Y direction, if the position of the electroacoustic transducer is defined with respect to the −Y direction, and conversely, the + Y direction. If the position of the electroacoustic transducer is defined with respect to the -Y direction, it is known in crystallography that it is equivalent to specifying the location of the electroacoustic transducer with respect to the -Y direction. It is assumed that the explanation of the case has been made and the description of the explanation is omitted.

  Further, the center of the electroacoustic transducer 22 extends in a direction orthogonal to the outermost line 14 having the maximum diameter from the intersection P with the Y crystal axis on the outermost line 14 having the maximum diameter in the annular surface region 16 of the substrate 12. +2 degrees (when the maximum amplitude position of the circular path CT corresponding to the Y crystal axis is on the + side in the latitude direction: +/− 60 degrees position and +/− 180 degrees position in the longitude direction in FIG. 2), or −2 3 degrees (when the maximum amplitude position of the circular path CT corresponding to the Y crystal axis is on the minus side in the latitude direction: 0 degree position and +/- 120 degree position in the longitude direction in FIG. 2) ( The surface acoustic wave 20 excited, propagated and circulated along the extending direction of the annular surface region 16 by the electroacoustic transducer 22 is the same as that shown in FIG. It turns out that it attenuates in a series. As a result, the operation accuracy of various devices that perform various operations based on the surface acoustic wave 20 can be most improved.

  4A to 4E, the power flow angle of the meandering path CT shown in FIG. 2 in which the surface acoustic wave 20 propagates best in the annular surface region 16 is zero. The position in which the extending direction of the tangent line coincides with the arrangement direction of the plurality of electrode branches 22a of the interdigital electrode of the electroacoustic transducer 22 (that is, the maximum diameter from the outer peripheral line 14 having the maximum diameter of the annular surface region 16). One of the largest amplitude positions farthest in the direction orthogonal to the outer circumferential line 14 passes through a position at a latitude of −1.5 degrees from a position of 0 degrees longitude along the outermost circumferential line 14 of the maximum diameter. A plurality of interdigital electrodes of the electroacoustic transducer 22 at positions of latitude +3 degrees, +1.5 degrees, 0 degrees, −1.5 degrees, and −3 degrees on a longitude line of 0 degrees longitude. The surface of the surface of the electrode branch 22a is arranged under the same conditions with the center of the electrode branch 22a. Schematically shows a state of attenuation of the intensity of the surface acoustic wave 20 for the resulting elapsed time when allowed to orbit is propagated to excite.

  4D, the center of the plurality of electrode branches 22a of the interdigital electrode of the electroacoustic transducer 22 is illustrated in FIG. 2 where the surface acoustic wave 20 propagates best in the annular surface region 16. The outer peripheral line of the maximum diameter of the surface region 16 is located on the maximum amplitude position of the meandering circular path CT and the power flow angle on the circular path CT at that position is zero and the tangential extension direction is the annular surface region 16 14, that is, the arrangement direction of the plurality of electrode branches 22 a of the interdigital electrode of the electroacoustic transducer 22.

  Here, the surface acoustic wave 20 excited in a predetermined condition along the extending direction of the annular surface region 16 in the annular surface region 16 by the interdigital electrode of the electroacoustic transducer 22 is formed into an annular surface. In the region 16, the surface acoustic wave 20 propagates best and propagates along the meandering circulation path CT shown in FIG. 2, so that the elapsed time (number of revolutions) from the start of the circulation increases. As a result, it can be seen that the strength is reduced cleanly in a geometric series.

  4C and 4E, the surface acoustic wave 20 propagates best in the annular surface region 16 at the center of the plurality of electrode branches 22a of the interdigital electrode of the electroacoustic transducer 22. The power flow angle on the meandering circular path CT illustrated in FIG. 2 is zero, and the tangential extension direction is the extension direction of the outermost peripheral line 14 of the annular surface region 16, that is, electroacoustic conversion. The arrangement direction of the plurality of electrode branches 22a of the interdigital electrodes of the element 22 and the maximum amplitude position of −1.5 degrees latitude on the longitude line that coincides with the longitude line of 0 degrees, respectively +1.5 on the longitude line of the same longitude And latitudes of -1.5 degrees apart (i.e., 0 degrees latitude and -3 degrees latitude).

  Here, the surface acoustic wave 20 excited in a predetermined condition along the extending direction of the annular surface region 16 in the annular surface region 16 by the interdigital electrode of the electroacoustic transducer 22 is formed into an annular surface. While the region 16 propagates in the extending direction of the annular surface region 16 and circulates, its strength is accompanied by some wave with an increase in elapsed time (number of laps) after starting the lap. It can be seen that the overall trend is to reduce geometrically.

  4A and 4B, the surface acoustic wave 20 propagates best in the annular surface region 16 at the center of the plurality of electrode branches 22a of the interdigital electrode of the electroacoustic transducer 22. The power flow angle on the meandering circular path CT illustrated in FIG. 2 is zero, and the tangential extension direction is the extension direction of the outermost peripheral line 14 of the annular surface region 16, that is, electroacoustic conversion. The alignment direction of the plurality of electrode branches 22a of the interdigital electrodes of the element 22 and the maximum amplitude position of latitude -1.5 degrees on the longitude line that coincides with the longitude line of 0 degrees, respectively +3.0 on the longitude line of the same longitude And latitudes of +4.5 degrees apart (i.e., latitude +1.5 degrees and latitude +3.0 degrees).

  Here, the surface acoustic wave 20 excited in a predetermined condition along the extending direction of the annular surface region 16 in the annular surface region 16 by the interdigital electrode of the electroacoustic transducer 22 is formed into an annular surface. In the region 16, it propagates in the extending direction of the annular surface region 16 and circulates. As the elapsed time (number of laps) after starting the lap increases, its strength is increased as a whole tendency with a large wave. It can be seen that is reduced geometrically.

  4A to 4E, the surface acoustic wave 20 propagates best in the annular surface region 16 from the center of the plurality of electrode branches 22a of the interdigital electrode of the electroacoustic transducer 22. The power flow angle on the meandering circular path CT illustrated in FIG. 2 is zero, and the tangential extension direction is the extension direction of the outermost peripheral line 14 of the annular surface region 16, that is, electroacoustic conversion. Electroacoustics within the range of −1.5 degrees latitude and −3.0 degrees latitude on the meridian of the longitude 0 degrees coincident with the arrangement direction of the plurality of electrode branches 22a of the interdigital electrodes of the element 22 The surface acoustic wave 20 excited in a predetermined condition along the extending direction of the annular surface region 16 in the annular surface region 16 by the interdigital electrode of the conversion element 22 is formed in the annular surface region 16 in an annular shape. Propagated in the extending direction of the surface region 16 In the meantime, it can be seen that as the elapsed time (number of laps) from the start of the lap increases, the intensity is accompanied by some waves but the overall trend is reduced geometrically. .

  This signal is further subjected to frequency analysis to extract a 150 MHz component, and the Q value (a value representing the magnitude of attenuation, which is known as an evaluation parameter of the vibration device, is described based on the attenuation rate associated with the circulation of the 150 MHz surface acoustic wave. (Don't need), the case of (A), (B), (C) was about 32,000 compared to about 32,000, compared to about 36,000 in (D), (E), It was confirmed that the attenuation was smaller.

10 ... Spherical surface acoustic wave element,
12 ... base material,
C ... Center,
14 ... the maximum diameter outer circumference,
16 ... surface area,
18 ... posts,
20 ... surface acoustic wave,
22 ... electroacoustic transducer,
22a ... electrode branch,
24 ... switching part,
26 ... high frequency signal generator,
28 ... Amplifier,
30: Detection / output unit,
32 ... Sensitive membrane,
CT ... Circumference route,
P: Y crystal axis crossing position.

Claims (2)

A plane formed of quartz or langasite, including a + Y crystal axis and perpendicular to the + Z crystal axis is formed as a part of a spherical surface centered on a point intersecting the Z crystal axis, and the orthogonal plane is defined as a part of the spherical surface. A surface region including an outer circumferential line of the maximum diameter intersecting and extending on a ring, and the surface acoustic wave excited along the ring-shaped extending direction of the surface region is formed on the surface region. A base material that circulates while meandering along a peripheral line at a predetermined cycle:
An electroacoustic transducer that excites a surface acoustic wave along the annular extending direction of the surface region on the surface region of the substrate;
With
The center of the electroacoustic transducer is within a range of 15 degrees or less in the extending direction of the outermost line of the maximum diameter from the intersection with the + Y crystal axis in the surface region,
Furthermore, when the crystal or langasite is dextrorotatory, the center of the acoustic transducer is once in the + Z direction with respect to the outermost line of the maximum diameter from the intersection with the + Y crystal axis in the surface region. At a position rotated at an angle within 3 degrees,
On the other hand, when the crystal or langasite is levorotatory, the center of the acoustic transducer is once in the −Z direction with respect to the outermost line of the maximum diameter from the intersection with the + Y crystal axis in the surface region. A spherical surface acoustic wave device characterized by being in a position rotated at an angle of 3 degrees or more. 2. The spherical surface acoustic wave device according to claim 1, wherein the center of the electroacoustic transducer is coincident with the + Y crystal axis direction or the -Y crystal axis direction in the surface region.

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