Element, electronic device, electronic instrument, and system

Abstract

To provide a surface acoustic wave element having excellent accuracy and sensitivity, and to provide an electronic device, an electronic instrument, and a system using the surface acoustic wave element.SOLUTION: The surface acoustic wave element includes a circular or roughly circular piezoelectric body and an electrode. One or more interdigital electrodes are provided on the piezoelectric body so that surface acoustic waves can be made to propagate in the circumferential or roughly circumferential direction. The electrode is provided on a surface of the piezoelectric body of the surface acoustic wave element that is parallel to the circumferential or roughly circumferential direction of the piezoelectric body to make detection of a bulk wave resulting from a surface acoustic wave propagated from the interdigital electrode. Thereby, a high-precision sensor using bulk waves is produced.SELECTED DRAWING: Figure 1

Description

Technical Field

[0001] The present invention relates to an element using a piezoelectric body, an electronic device, an electronic apparatus, and a system.

Background Art

[0002] One type of piezoelectric element, a surface acoustic wave (SAW) element, includes interdigital electrodes (IDT) on a piezoelectric substrate such as a quartz substrate. The interdigital electrodes are paired and formed on the piezoelectric substrate so that the comb-shaped electrodes face each other without contact. By applying an alternating voltage to the interdigital electrodes, the piezoelectric effect and the inverse piezoelectric effect of the piezoelectric substrate can vibrate the surface and the vicinity of the surface of the piezoelectric substrate in a frequency band. SAW elements are widely used in electronic circuits that make up various electronic devices, such as oscillators, band filters, and gyroscopes, depending on the combination and configuration of the interdigital electrodes.

[0003] In recent years, for example, with the miniaturization and weight reduction of mobile communication terminal devices used in mobile communication, and in order to achieve high communication quality, elastic wave elements with even higher accuracy have been demanded. To meet such requirements, spherical SAW sensors (ball SAW sensors) and the like have been studied (Patent Document 1). The ball SAW sensor can significantly increase the interaction distance compared to planar sensors by utilizing the phenomenon of multiple round-trips of the natural collimated beam of SAW, and thus is useful for high-sensitivity improvement. However, when used in, for example, gas sensors, the sensitive film used in the gas sensor increases the attenuation of SAW, which hinders high-sensitivity improvement. Also, there are many problems with SAW devices regarding high-frequency characteristics and correction methods for high-sensitivity improvement, and they are still not satisfactory. Furthermore, the demand for energy conservation for environmental problems and the like has been added, and a new SAW element that solves these problems has been awaited.

Prior Art Documents

Patent Documents

[0004] [Patent Document 1] Japanese Patent Publication No. 2014-115084 [Overview of the project] [Problems that the invention aims to solve]

[0005] The present invention aims to provide a surface acoustic wave element having excellent accuracy and sensitivity, as well as electronic devices, electronic equipment, and systems using the surface acoustic wave element. [Means for solving the problem]

[0006] As a result of diligent research to achieve the above objective, the present inventors have discovered that when an electrode for detecting bulk waves caused by surface acoustic waves propagating from the curtain-like electrodes is provided on a surface of the piezoelectric material parallel to the circumferential or substantially circumferential direction, in an element that includes a circular or substantially circular piezoelectric material and has one or more curtain-like electrodes provided on the piezoelectric material so that surface acoustic waves can propagate in the circumferential or substantially circumferential direction, it is possible to easily convert the bulk wave signal generated by the optical path difference into angular velocity, which is useful for correcting the sensor. Furthermore, by using a reflector, they have succeeded in further improving accuracy and sensitivity through the Sagnac effect while also saving energy, and have found that such an element can solve the above-mentioned conventional problems all at once. Furthermore, after obtaining the above findings, the inventors conducted further studies and completed the present invention.

[0007] In other words, the present invention relates to the following invention. [1] An element comprising a circular or substantially circular piezoelectric body, wherein one or more curtain-like electrodes are provided on the piezoelectric body so that surface acoustic waves can propagate in the circumferential or substantially circumferential direction, The element is characterized in that electrodes for detecting bulk waves caused by surface acoustic waves propagating from the blind-shaped electrodes are provided on a surface of the piezoelectric body parallel to the circumferential direction or substantially circumferential direction. [2] The element according to [1], wherein the bulk wave is an SH bulk wave that propagates in a direction perpendicular to the propagation direction of the surface acoustic wave. [3] The element according to [1] or [2], wherein the piezoelectric body is cylindrical, substantially cylindrical, barrel-shaped, or substantially barrel-shaped. [4] The element according to any one of [1] to [3], wherein a reflector is provided on the piezoelectric body which is in the propagation path of the surface acoustic wave. [5] The element according to [4], wherein two or more of the curtain-shaped electrodes are provided on either side of the reflector. [6] The element according to any one of [1] to [5], wherein the curtain-shaped electrode comprises a SAW generating means for generating surface acoustic waves and a SAW receiving means for receiving surface acoustic waves. [7] The device according to any one of [1] to [6], wherein the piezoelectric material is a single crystal made of a piezoelectric material having a trigonal or hexagonal crystal structure. [8] The element according to [7], wherein the surface acoustic wave propagates on the c-plane of the single crystal. [9] The device according to [7] or [8], further comprising an electrode provided on the a-plane or m-plane of the single crystal for reading bulk waves propagating on the a-plane or m-plane.

[10] The element according to any one of [1] to [9], wherein the piezoelectric material is laminated on a crystal substrate via a buffer layer by an epitaxial crystal growth method.

[11] The device according to

[10] , wherein the buffer layer comprises a metal oxide containing Hf or Zr.

[12] An electronic device comprising a piezoelectric element, wherein the piezoelectric element is the element described in any of [1] to

[11] above.

[13] The electronic device described in

[12] above, which is a sensor.

[14] Electronic equipment including an electronic device, wherein the electronic device is the electronic device described in

[12] or

[13] above.

[15] A system including electronic equipment, wherein the electronic equipment is the electronic equipment described in

[14] . [Effects of the Invention]

[0008] The element of the present invention is a surface acoustic wave element having excellent accuracy and sensitivity, and the electronic device, electronic equipment and system of the present invention are equipped with the surface acoustic wave element and can exhibit the high sensitivity and high accuracy characteristics of the surface acoustic wave element. [Brief explanation of the drawing]

[0009] [Figure 1] This figure schematically shows an example of a preferred embodiment of the element of the present invention. [Figure 2] This figure schematically shows an example of a reflector suitably used in the element of the present invention. [Figure 3] This figure schematically shows an example of another preferred embodiment of the element of the present invention. [Figure 4] This figure schematically illustrates the propagation direction of surface acoustic waves in the element of the present invention, their perpendicular direction, and corrections utilizing these. [Figure 5] This figure schematically shows a film deposition apparatus preferably used in the examples. [Modes for carrying out the invention]

[0010] The present invention provides an element comprising a circular or substantially circular piezoelectric body, wherein one or more curtain-like electrodes are provided on the piezoelectric body so that surface acoustic waves can propagate in the circumferential or substantially circumferential direction, and is characterized in that electrodes for detecting bulk waves caused by surface acoustic waves propagating from the curtain-like electrodes are provided on a surface of the piezoelectric body parallel to the circumferential or substantially circumferential direction.

[0011] The electrode is provided on a surface parallel to the circumferential direction or the substantially circumferential direction of the piezoelectric body, and is not particularly limited as long as it is an electrode for detecting a bulk wave caused by an elastic surface wave propagated from the comb-shaped electrode, and the electrode may also be a known excitation electrode. The bulk wave is not particularly limited as long as it is a bulk wave caused by an elastic surface wave propagated from the comb-shaped electrode, and the frequency for detecting the bulk wave as a signal is not particularly limited either. In the present invention, it is preferable that the bulk wave is an SH bulk wave propagating in a direction perpendicular to the propagation direction of the elastic surface wave. By detecting such a preferable bulk wave, it can be more easily converted into an angular velocity and applied to correction for high-precision.

[0012] Also, in the present invention, it is preferable that a reflector is provided on the piezoelectric body within the propagation path of the surface elastic wave. The reflector is not particularly limited as long as it is provided on the piezoelectric body within the propagation path of the surface elastic wave (hereinafter also referred to as "SAW"), and may be a known reflector. In the present invention, for example, as shown in FIG. 1, it is preferably positioned adjacent to the comb-shaped electrode (hereinafter also referred to as "IDT electrode") in the propagation direction of the SAW. The reflector may be, for example, an electrode formed in a lattice shape. In the present invention, as shown in FIG. 2, it preferably has a pair of reflection bus bars 21 facing each other and a plurality of reflection electrode fingers 23 extending between the pair of reflection bus bars 21.

[0013] The shape and dimensions of the reflective bus bar 21 and the reflective electrode fingers 23 in FIG. 2 may be basically the same as those of the bus bar and electrode fingers of the IDT electrode, except that both ends of each reflective electrode finger 23 are connected to a pair of reflective bus bars 21. For example, each reflective electrode finger 23 has an elongated shape extending linearly in a direction (D2 direction) orthogonal to the propagation direction of the SAW with a constant width, and they have the same length as each other. These plurality of reflective electrode fingers 23 are arranged side by side in the propagation direction of the SAW, for example. The number of the plurality of reflective electrode fingers 23 is usually set so that the reflectivity of the SAW in the intended mode is approximately 100% or more. The theoretically required minimum number is, for example, several to about 10 as a preferred example, and the number of the reflective electrode fingers 23 is preferably 20 or more.

[0014] The reflector is usually not electrically connected to the IDT electrode and may be in an electrically floating state (a state where no potential is applied from the outside), or a reference potential or the like may be applied. In the present invention, the reflector may be electrically connected to one of the electrode portions of the IDT electrode, but it is preferably in an electrically floating state (a state where no potential is applied from the outside).

[0015] Furthermore, in the present invention, it is preferable that the element comprises a SAW generating means for generating surface acoustic waves and a SAW receiving means for receiving the surface acoustic waves, and it is also preferable that electrodes for detecting signals caused by surface acoustic waves propagating from the SAW electrodes are provided on a surface of the piezoelectric body parallel to the circumferential direction or substantially circumferential direction. The signal is not particularly limited as long as it is a signal caused by the surface acoustic waves, and is usually a signal that propagates in a direction perpendicular to the propagation direction of the surface acoustic waves, but in the present invention, it is preferable that it is an SH bulk wave that propagates in a direction perpendicular to the propagation direction of the surface acoustic waves. With such a preferred range, the accuracy by correction using the signal can be more easily improved, and a more sensitive sensor can be realized. Furthermore, in the present invention, it is more preferable that two or more SAW electrodes are provided on either side of the reflector, as shown in Figure 3, for example, and with this configuration, the accuracy by correction using the signal can be further improved, and a more sensitive sensor can be realized more easily.

[0016] Here, a preferred example of a correction method using the aforementioned signal is shown. As shown in Figure 4, when a voltage is applied to the curtain-shaped electrodes 13a and 13b, the electrode fingers of the curtain-shaped electrodes apply a voltage to the piezoelectric body 3, exciting a predetermined mode of SAW that propagates along the piezoelectric body 3 in the D1 and D2 directions. The excited SAW is mechanically reflected by the electrode fingers of the curtain-shaped electrodes 13a and 13b and the reflector 9, forming a standing wave with a pitch of half a wavelength between the electrode fingers. The standing wave is converted into an electrical signal of the same frequency as the standing wave and extracted by the electrode fingers of the curtain-shaped electrodes. Here, a phase difference occurs between the wave in the D1 direction and the wave in the D2 direction propagating with rotational angular velocity applied to the SAW, so, for example, correction using the following equation (1) that represents the phase difference becomes possible.

number

[0017] Furthermore, the reflector 9 causes strong standing waves at the IDT electrodes 13a and 13b, improving their function as resonators. Additionally, for example, at the boundary between the IDT electrodes 13a and 13b and the reflector 9, a portion of the SAW is converted into a bulk wave and enters the piezoelectric body 3, allowing for the extraction of signals propagating in a direction perpendicular to the propagation direction of the surface acoustic waves, i.e., in the D3 direction. This also enables corrections using these signals.

[0018] The piezoelectric element is not particularly limited as long as it includes a circular or substantially circular piezoelectric element, and may have any shape. However, in the present invention, it is preferable that the piezoelectric element is cylindrical, substantially cylindrical, barrel-shaped, or substantially barrel-shaped. These preferred shapes can also be obtained by processing according to conventional methods. The material of the piezoelectric element is also not particularly limited as long as it is made of a piezoelectric material, and may be a known piezoelectric material. However, in the present invention, it is preferable that it is a piezoelectric material having a trigonal or hexagonal crystal structure. Furthermore, in the present invention, it is preferable that the piezoelectric element is a single crystal, and more preferably a single crystal made of a piezoelectric material having a trigonal or hexagonal crystal structure. By following these preferred ranges, higher sensitivity can be achieved, and the element can be made more environmentally friendly. Furthermore, if the piezoelectric material is a single crystal made of a piezoelectric material having a trigonal or hexagonal crystal structure, it is preferable that the element is configured such that the surface acoustic wave propagates on the c-plane of the single crystal, and it is also preferable that electrodes for reading bulk waves propagating on the a-plane or m-plane of the single crystal are provided on the a-plane or m-plane. Within this preferred range, further increases in sensitivity of the element can be easily achieved.

[0019] In the present invention, the piezoelectric material is preferably laminated on a crystalline substrate via a buffer layer using an epitaxial crystal growth method. The buffer layer is not particularly limited as long as it does not hinder the objectives of the present invention, but it is preferably a metal oxide containing Hf or Zr. The metal compound is not particularly limited as long as it does not hinder the objectives of the present invention and may be a known metal compound. It may be an oxide or a nitride. In the present invention, the metal oxide is usually a crystalline metal oxide, but it is also preferable that the crystalline metal oxide contains 50 atomic% or more of Hf and / or Zr in the constituent metal and 0.1 atomic% to 50 atomic% of one or more metals selected from Al, Ti, Y, and Ce. Such a preferred mixed crystal not only improves the stress relaxation effect of the buffer layer but also improves the piezoelectric properties of the piezoelectric material.

[0020] The crystalline substrate (hereinafter also simply referred to as "substrate") is not particularly limited as long as it does not hinder the objectives of the present invention, and may be a known crystalline substrate. It may be an organic compound or an inorganic compound. In the present invention, it is preferable that the crystalline substrate contains an inorganic compound. In the present invention, it is preferable that the substrate has crystals on part or all of its surface, more preferably that it is a crystalline substrate having crystals on all or part of the main surface on the crystal growth side, and most preferably that it is a crystalline substrate having crystals on all of the main surface on the crystal growth side. The crystal is not particularly limited as long as it does not hinder the objectives of the present invention, and the crystal structure is not particularly limited, but it is preferable that it is a cubic, tetragonal, trigonal, hexagonal, orthorhombic, or monoclinic crystal, and more preferably a trigonal or hexagonal crystal. The crystalline substrate may also have an off-angle, and examples of the off-angle include an off-angle of 0.2° to 12.0°. Here, "off-angle" refers to the angle between the substrate surface and the crystal growth surface. The substrate shape is not particularly limited, but is plate-shaped and serves as a support for the buffer layer. It may be an insulating substrate or a semiconductor substrate, but in the present invention, the substrate is preferably a Si substrate, more preferably a crystalline Si substrate, and most preferably a crystalline Si substrate oriented to (100). Examples of the substrate material include, in addition to a Si substrate, one or more metals belonging to groups 3 to 15 of the periodic table or oxides of these metals. The shape of the substrate is not particularly limited, and may be substantially circular (e.g., circular, elliptical, etc.) or polygonal (e.g., triangular, square, rectangular, pentagonal, hexagonal, heptagonal, octagonal, nonagonal, etc.), and various shapes can be suitably used. Furthermore, in the present invention, a large-area substrate can also be used.

[0021] Furthermore, in the present invention, it is preferable that the crystal substrate has a flat surface, but it is also preferable that the crystal substrate has an uneven shape on part or all of its surface, as this can improve the quality of crystal growth of the epitaxial film. The crystal substrate having the uneven shape only needs to have an uneven portion consisting of recesses or protrusions on part or all of its surface, and the uneven portion is not particularly limited as long as it consists of protrusions or recesses, and may be an uneven portion consisting of protrusions, an uneven portion consisting of recesses, or an uneven portion consisting of both protrusions and recesses. In addition, the uneven portion may be formed from regular protrusions or recesses, or from irregular protrusions or recesses. In the present invention, it is preferable that the uneven portion is formed periodically, and more preferably that it is patterned periodically and regularly. The shape of the uneven portion is not particularly limited, and examples include stripe-like, dot-like, mesh-like, or random-like, but in the present invention, dot-like or stripe-like is preferred, and dot-like is more preferred. Furthermore, if the uneven surfaces are patterned periodically and regularly, it is preferable that the pattern shape of the uneven surfaces be a polygonal shape such as a triangle, quadrilateral (e.g., square, rectangle, or trapezoid), pentagon or hexagon, circular, or elliptical. When the uneven surfaces are formed in a dot shape, it is preferable that the lattice shape of the dots be a grid shape such as a square grid, rhombic grid, triangular grid, or hexagonal grid, and more preferably a triangular grid. The cross-sectional shape of the recesses or protrusions of the uneven surfaces is not particularly limited, but examples include a U-shape, inverted U-shape, wave shape, or a polygonal shape such as a triangle, quadrilateral (e.g., square, rectangle, or trapezoid), pentagon or hexagon. The thickness of the crystal substrate is not particularly limited, but is preferably 50 to 2000 μm, and more preferably 100 to 1000 μm.

[0022] Preferred embodiments of the present invention will be described below with reference to the drawings, but the present invention is not limited to these preferred embodiments.

[0023] Figure 1 shows an example of a preferred element of the present invention. In the element of Figure 1, a buffer layer 2 is formed on a crystal substrate 1 by epitaxial crystal growth, and a piezoelectric body 3 is formed on the buffer layer 2. The piezoelectric body 3 is processed into a cylindrical shape, and a curtain-like electrode 13 and a reflector 9 are formed on its side surface. An extraction electrode 15 is also formed on the upper surface of the piezoelectric body 3. The extraction electrode 15 is an electrode for detecting a signal caused by surface acoustic waves propagating from the curtain-like electrode, and is connected to a detector that detects SH bulk waves, etc., propagating in a direction perpendicular to the propagation direction of the surface acoustic waves. The curtain-like electrode 13, the reflector 9, and the extraction electrode may be formed using known means. When a voltage is applied to the curtain-like electrode 13, strain is generated on the piezoelectric body between adjacent electrode fingers of the curtain-like electrode 13 due to the piezoelectric effect of the piezoelectric body 3, and surface waves are excited. In a curtain-like electrode configuration, electrode fingers are arranged periodically, and the surface wave is most strongly excited when its wavelength is equal to the period of the electrode fingers. Since the frequency is determined by the spacing of the electrodes formed on the surface, it can easily be adapted to high frequencies by photolithography or other processes.

[0024] The element can be suitably used in electronic devices according to conventional methods. For example, by connecting the element as a piezoelectric element to a power supply or electrical / electronic circuit and mounting it on a circuit board or packaging it, various electronic devices can be constructed. In the present invention, it is preferable that the electronic device is a piezoelectric device, and it can be used as a piezoelectric device in electronic devices such as gyroscopes and motion sensors. Furthermore, for example, by connecting an amplifier and a rectifier circuit and packaging it, it can be used in various sensors such as magnetic sensors.

[0025] The aforementioned electronic device is suitably used in electronic devices in accordance with conventional methods. Besides the electronic devices described above, the device can be applied to a variety of other electronic devices. More specifically, suitable examples include liquid dispensing heads, liquid dispensing devices, vibration wave motors, optical instruments, vibration devices, imaging devices, piezoelectric acoustic components, and audio playback devices, audio recording devices, mobile phones, and various information terminals.

[0026] Furthermore, the aforementioned electronic devices can also be applied to systems in accordance with conventional laws, and such systems include, for example, sensor systems. [Examples]

[0027] (Examples of piezoelectric material fabrication) The crystal growth surface of the Si substrate (100) was treated with RIE, and after heating in the presence of oxygen to form a thermal oxide film, a single crystal of crystalline metal oxide was formed on the Si substrate by a vapor deposition method without using oxygen, causing a thermal reaction between the metal of the deposition source and the oxygen in the oxide film on the Si substrate. Then, by flowing oxygen, lowering the temperature, and increasing the pressure, a single crystal film of crystalline metal oxide was deposited as the aforementioned crystal by vapor deposition. The conditions for the vapor deposition method during this film formation were as follows. Vapor deposition source: Hf, Zr Voltage: 3.5~4.75V Pressure: 3 × 10 -2 ~6×10 -2 Pa Substrate temperature: 450~700℃

[0028] Figure 5 shows a deposition apparatus used for depositing single-crystal films of crystalline metal oxides. The deposition apparatus in Figure 5 is equipped with at least a crucible containing metal sources 1101a to 1101b, grounds 1102a to 1102h, ICP electrodes 1103a to 1103b, cut filters 1104a to 1104b, DC power supplies 1105a to 1105b, RF power supplies 1106a to 1106b, lamps 1107a to 1107b, Ar source 1108, reactive gas source 1109, power supply 1110, substrate holder 1111, substrate 1112, cut filter 1113, ICP ring 1114, vacuum chamber 1115, and rotating shaft 1116. Note that the ICP electrodes 1103a to 1103b in Figure 13 have a substantially concave or parabolic shape that curves toward the center of the substrate 1112.

[0029] As shown in Figure 5, the substrate 1112 is secured on the substrate holder 1111. Then, the rotating shaft 1116 is rotated using the power supply 1110 and a rotating mechanism (not shown) to rotate the substrate 1112. The substrate 112 is also heated by lamps 1107a to 1107b, and the inside of the vacuum chamber 1115 is evacuated to create a vacuum or reduced pressure using a vacuum pump (not shown). After that, Ar gas is introduced into the vacuum chamber 1115 from the Ar source 1108, and the surface of the substrate 1112 is cleaned by forming argon plasma on the substrate 1112 using DC power supplies 1105a to 1105b, RF power supplies 1106a to 1106b, ICP electrodes 1103a to 1103b, cut filters 1104a to 1104b, and grounds 1102a to 1102h.

[0030] Ar gas is introduced into the vacuum chamber 1115, and a reactive gas is also introduced using the reactive gas source 1109. At this time, the lamp heaters, lamps 1107a to 1107b, are alternately turned on and off, which allows for the formation of a higher quality crystal growth film.

[0031] Next, a platinum (Pt) metal film was formed as a conductive film on a single crystal film of crystalline metal oxide by sputtering. The conditions used for this process are shown below. Equipment: ULVAC QAM-4 sputtering system Pressure: 1.20 × 10 -1 Pa Target: Pt Power: 100W(DC) Thickness: 100nm Substrate temperature: 450~600℃

[0032] Next, an SRO film was formed on the conductive film by sputtering. The conditions used for this process are shown below. Equipment: ULVAC QAM-4 sputtering system Power: 150W (RF) Gas: Ar Pressure: 1.8 Pa Substrate temperature: 600℃ Thickness: 20nm

[0033] Next, on the SRO film, a piezoelectric film of Pb(Zr) 0.52 Ti 0.48 The O3 film (PZT film) was formed by a coating method. The conditions used are as follows.

[0034] Lead acetate was used as the raw material for Pb, zirconium nitrate for Zr, and titanium isopropoxide for Ti. The raw materials for Pb, Zr, and Ti were mixed in a composition ratio of Pb:Zr:Ti = 100 + δ:52:48. Pure water was used as the solvent, considering the solubility of the raw materials, and acetic acid was added to control hydrolysis. Furthermore, ethanol mixed with polyvinylpyrrolidone powder (0.5 to 3.0 mol per 1 mol of PZT) was added to adjust viscosity. Finally, an appropriate amount of 2n butoxyethanol was mixed in to adjust wettability during coating, and a sol-gel solution was prepared as the raw material solution.

[0035] Next, the prepared sol-gel solution was dropped onto the substrate and rotated at 2000 rpm for 1 minute to spin-coat (apply) the sol-gel solution onto the substrate, thereby forming a film containing the precursor. Then, the substrate was placed on a hot plate at 150°C, and then on a hot plate at 350°C to evaporate the solvent and dry the film. This process was repeated 5 times to build up 5 layers under the same conditions, and then the precursor was oxidized and crystallized by heat treatment at 650°C for 3 minutes in an oxygen (O2) atmosphere. The above process was repeated 10 times to obtain Pb(Zr 0.52 Ti 0.48 An O3 film (PZT film) was fabricated. The total film thickness at this time was 10 μm.

[0036] Examples of applications of the obtained piezoelectric material to elements will be described in more detail below with reference to the figures, but the present invention is not limited to these examples. In the present invention, unless otherwise specified, elements and electronic devices can be manufactured from the piezoelectric material using known means.

[0037] Figure 3 shows an example of an element representing a preferred embodiment of the present invention. The element in Figure 3 differs from that in Figure 1 in that two curtain-like electrodes are provided flanking the reflector. The element in Figure 3 also includes an SH bulk wave detector for detecting SH bulk waves and a SAW receiver for detecting SAW. In the element in Figure 3, the piezoelectric body 3 is processed into a cylindrical shape, and curtain-like electrodes 13a, 13b and a reflector 9 are formed on its side surface using known means. An extraction electrode 15 is formed on the upper surface of the piezoelectric body 3 according to a conventional method. The extraction electrode 15 is connected to an SH bulk wave detector 18 that detects SH bulk waves propagating in a direction perpendicular to the propagation direction of the surface acoustic wave. The formation of the curtain-like electrodes 13a, 13b and the reflector 9, as well as the extraction electrode, may be carried out using known means. When a voltage is applied to the curtain-shaped electrodes 13a and 13b, the piezoelectric effect of the piezoelectric body 3 causes strain to be generated on the piezoelectric body between adjacent electrode fingers of the curtain-shaped electrodes 13a and 13b, exciting a surface wave. A SAW receiver 19 is connected to the curtain-shaped electrode 13a and is configured to detect surface acoustic waves propagating in the SAW propagation path. The surface acoustic waves propagate across the surface of the piezoelectric body 3 in the D1 and D2 directions shown in Figure 4, respectively, due to the reflector 9. In other words, the surface acoustic waves propagate in opposing directions, creating a phase difference. By extracting the bulk wave generated between the curtain-shaped electrodes 13a and 13b and the reflector 9, and detecting it via electrode 15, an environmentally friendly, high-precision, and high-sensitivity sensor utilizing both surface acoustic waves and bulk waves can be manufactured. [Industrial applicability]

[0038] The element of the present invention is applicable to various uses, but is particularly suitable for use in piezoelectric sensors, and is applied, for example, to electronic devices for sensor systems. [Explanation of Symbols]

[0039] 1. Crystal substrate 2 buffer layers 3 Piezoelectric material 9 reflector 10 elements 13. Bamboo blind-shaped electrodes 13a Bamboo blind-shaped electrode 13b Bamboo blind-shaped electrode 15. Removal electrode 18 SH bulk wave detector 19 SAW receiver 21 Reflective busbars 23 Reflector electrode finger 1101a~101b Metal source 1102a~102j Earth 1103a~103b ICP electrode 1104a~104b Cut Filter 1105a~105b DC power supply 1106a~106b RF power supply 1107a~107b Lamp 1108 Ar source 1109 Reactive gas source 1110 Power supply 1111 Circuit board holder 1112 circuit board 1113 Cut Filter 1114 ICP ring 1115 Vacuum chamber 1116 Rotation axis

Claims

1. An element including a circular or approximately circular piezoelectric body, and one or more interdigital transducers provided on the piezoelectric body so that surface acoustic waves can propagate in a circumferential direction or an approximately circumferential direction, An element characterized in that an electrode for detecting bulk waves resulting from surface acoustic waves propagating from the interdigital electrode is provided on a surface of the piezoelectric body that is parallel to the circumferential direction or approximately the circumferential direction.

2. 2. The element according to claim 1, wherein the bulk wave is an SH bulk wave that propagates in a direction perpendicular to the propagation direction of the surface acoustic wave.

3. The element according to claim 1 , wherein the piezoelectric body is cylindrical, approximately cylindrical, barrel-shaped, or approximately barrel-shaped.

4. 4. The element according to claim 1, wherein a reflector is provided on the piezoelectric body located within a propagation path of the surface acoustic wave.

5. 5. The element according to claim 4, wherein two or more interdigital transducers are provided with the reflector therebetween.

6. 4. The device according to claim 1, wherein the interdigital transducer comprises a SAW generating means for generating the surface acoustic waves and a SAW receiving means for receiving the surface acoustic waves.

7. 4. The element according to claim 1, wherein the piezoelectric body is a single crystal made of a piezoelectric material having a trigonal or hexagonal crystal structure.

8. 8. The element according to claim 7, wherein the surface acoustic wave is propagated on the c-plane of the single crystal.

9. 8. The element according to claim 7, further comprising an electrode on the a-plane or m-plane of the single crystal for reading bulk waves propagating on the a-plane or m-plane.

10. 4. The element according to claim 1, wherein the piezoelectric body is layered on a crystal substrate via a buffer layer by epitaxial crystal growth.

11. The device of claim 10 , wherein the buffer layer comprises a metal oxide containing Hf or Zr.

12. An electronic device, an electronic equipment or a system including a piezoelectric element, wherein the piezoelectric element is an element according to any one of claims 1 to 3.

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