Elastic wave device

Abstract

This invention relates to an elastic wave element, particularly a shear wave element, comprising a piezoelectric material (3), particularly a ferroelectric material, having a plurality of first polarization domains (3a) in a first polarization direction (13a) and a plurality of second polarization domains (3b) in a second polarization direction (13b), the first polarization direction (13a) being opposite to the second polarization direction, wherein the first and second polarization domains (3a, 3b) alternate periodically along a periodic direction (d) perpendicular to the surface normal (n) of the piezoelectric material (3), and a pair of forked comb-shaped electrodes (15a, 15b) embedded in the piezoelectric material (3), the respective comb teeth (17a1 to 17a3 and 17b1 to 17b3) extending primarily perpendicular to the periodic direction (d) and the surface normal (n).

Description

Technical Field

[0001] This invention relates to an elastic wave element and a method for manufacturing such an elastic wave element. Prior Technology

[0002] Surface acoustic wave (SAW) devices have a wide range of applications, such as filters, sensors, and delay lines. For example, SAW RF filters can be used in mobile communication devices because of their simple structure, low loss, and small size in the RF range (100 MHz – 10 GHz).

[0003] In elastic wave elements, one or more interdigitated comb transducers (IDTs) are formed on a single-crystal piezoelectric substrate. The direct piezoelectric effect converts elastic waves (typically Rayleigh waves) propagating along the surface of the piezoelectric substrate into electrical signals by electrically exciting the comb-like fingers. Conversely, an electrical signal can be applied through the finger structure of the comb electrodes to induce surface elastic waves in the piezoelectric substrate beneath the transducer.

[0004] The velocity of elastic waves is typically limited by the properties of the piezoelectric material. For lithium tantalate (LiTaO3), the Rayleigh wave phase velocity ranges from 3000 ms⁻¹ to 3500 ms⁻¹, with a maximum coupling degree of approximately 2%. On lithium niobate (LiNbO3), the Rayleigh wave phase velocity reaches as high as 3900 ms⁻¹, with a maximum coupling degree approaching 5.6%. Other modes associated with shear and compression waves are generally faster, but only partially guided by the surface and require complex guiding structures.

[0005] Piezoelectric-on-insulator (POI) wafers can achieve modes with larger phase velocities, but without radiation losses in the substrate, their velocities do not exceed 4200 ms⁻¹ on LiTaO₃ and 4500 ms⁻¹ on LiNbO₃. Summary of the Invention

[0006] Therefore, the object of the present invention is to overcome these disadvantages by providing an elastic wave element whose operating mode has a phase velocity higher than that of a guided Rayleigh wave or shear wave.

[0007] To achieve this objective, the present invention proposes an elastic wave element, particularly a shear wave element, comprising a piezoelectric material, particularly a ferroelectric material, having a plurality of first polarization domains in a first polarization direction and a plurality of second polarization domains in a second polarization direction, the first polarization direction being opposite to the second polarization direction, wherein the first and second polarization domains alternate periodically along a periodic direction (d) perpendicular to the surface normal (n) of the piezoelectric material, and a pair of forked comb-like electrodes, each of whose comb teeth extend primarily perpendicular to the periodic direction (d) and the surface normal (n), and the comb teeth being configured to be at least partially, preferably entirely, embedded in the piezoelectric material.

[0008] Due to the presence of polarization domains with opposite polarization directions, modes with phase velocities greater than 4200 ms⁻¹ emerge, and these modes primarily propagate on the surface. Since the wave propagation speed exceeds the surface skimming bulk wave (SSBW) speed, the substrate surface no longer naturally guides these modes beyond this speed; therefore, the volumetric radiation effect is less than 10⁻³ dB / λ, and thus this effect can be neglected. These modes are shear modes.

[0009] The elastic wave element according to the present invention has a wide range of applications, such as filters, especially ladder filters, or filters with acoustic coupling, such as longitudinally coupled resonator filters (LCRF), dual-mode SAW (DMS) filters, or surface cavity acoustic (SCAW) filters, as well as sensors and delay lines.

[0010] Ferroelectricity is the property of a material to spontaneously polarize. Ferroelectric materials are a subclass of piezoelectric materials. Ferroelectric properties can also be achieved artificially, for example, by creating polarization domains with different polarization directions through suitable growth conditions. Therefore, the following discussion may consider any material capable of generating polarization domains as a piezoelectric material.

[0011] According to one variation of the present invention, the comb teeth can be arranged periodically.

[0012] According to one variation of the present invention, the piezoelectric material can be disposed as a single layer on a substrate, the thickness (e1) of which is less than the wavelength (λ), preferably less than λ / 2, more preferably less than λ / 4. The substrate can be silicon, silicon oxide, silicon carbide (SiC), sapphire, silicon nitride (SiN), aluminum nitride (AlN), quartz, carbon, diamond, yttrium aluminum garnet (Yags), yttrium iron garnet (Yigs), amorphous silicon or polycrystalline silicon, or LiNbO3 and / or LiTaO3. This can be a two-layer structure or a stack of two or more layers. Therefore, energy can be confined within the piezoelectric thin layer, thereby reducing overall energy loss.

[0013] According to one variation of the invention, a dielectric layer, particularly a layer of silicon oxide, silicon nitride, Ta₂O₅, ZrO₂, HfO₂, SiON, polycrystalline silicon, or a combination of these materials, may be disposed between the piezoelectric material layer and the substrate. The thickness of the dielectric layer is preferably less than the wavelength (λ) and / or between 200 nm and 2 µm. In practice, the dielectric layer can be used during a layer transfer method to bond the piezoelectric layer to the substrate, for example, through bonding, such as by using molecular bonding, by adhesive bonding, or by eutectic bonding. The layer transfer method may be the SmartCut™ method. Using silicon oxide as the dielectric layer can further improve the temperature stability of the device because the temperature coefficients of the elastic wave velocities of silicon and silicon oxide have opposite signs. Therefore, the thickness of the dielectric layer also depends on the selected thickness of the piezoelectric layer and is preferably selected to reduce or even minimize the effect of temperature on the device.

[0014] According to one variation of the invention, a trapping layer, particularly a layer of polycrystalline silicon, polycrystalline aluminum nitride, or SiOCH, may be disposed between the piezoelectric material and the substrate, or between the dielectric layer and the substrate. The thickness of this trapping layer is preferably between 300 nm and 2 µm. The presence of the trapping layer can reduce leakage current.

[0015] According to one variation of the invention, the comb teeth extend in the region between the interface of the piezoelectric material layer and the substrate or the dielectric layer. According to another variation, the thickness of the comb teeth may be at least equal to or less than the thickness of the piezoelectric material layer. By optimizing the thickness of the comb teeth, the spectral purity of the observed mode can be improved. This allows for the fabrication of electrodes with greater thickness, enabling the use of input power of approximately 26 dBm to 33 dBm or even higher. Therefore, this type of element is suitable for filters in transmission mode (TX), where higher power is required than in receive mode. Thinner electrode comb teeth optimize the spectral purity of the observed mode.

[0016] According to an alternative variation, the comb teeth are positioned within grooves in the piezoelectric layer so that they do not extend to the interface with the substrate or the dielectric layer. Preferably, the thickness of the comb teeth is at least greater than half the thickness of the piezoelectric layer. Therefore, the coupling of the mode used can be adjusted according to the thickness of the comb teeth.

[0017] According to one variation of the invention, the comb teeth can be positioned between polarization regions with different polarization directions. In this case, the polarization regions can be created using electrodes before using electrodes in the filter, sensor, or delay line. Furthermore, an effective phase velocity greater than that of a conventional POI can be observed.

[0018] According to one variation of the invention, the comb teeth can be configured such that the polarization directions on both sides of each comb tooth are the same; specifically, the polarization directions of different electrode comb teeth are different. For this embodiment, only one mode exists, making it particularly suitable for use in filters, sensors, or delay lines, etc.

[0019] According to one variation of the present invention, the comb teeth of one of the two electrodes can be configured such that the polarization directions on both sides of each comb tooth are the same, and the comb teeth of the second electrode can be configured between polarization domains with different polarization directions.

[0020] According to one variation, the width of the comb teeth of the finger-shaped electrodes is between 40% and 60% of the width of the polarization domains, preferably between 40% and 60%, preferably 50%, and / or at least 280 nm, preferably at least 350 nm. Therefore, filters, sensors, or delay lines operating at frequencies higher than normally available frequencies can be provided by using I-line lithography.

[0021] According to one variation of the invention, the piezoelectric material can be LiTaO3 or LiNbO3. The piezoelectric material can also be ABO3-type perovskites (especially KnbO3 and PbTiO3), PZT, PMnPt, or AlScN. The modes observed in these materials (especially shear modes) possess quality factors and electromechanical coupling, enabling their industrial applications in filter or delay line types.

[0022] According to one variation, the elastic wave element may include a first electrode comprising a plurality of first switches, and a second electrode comprising a plurality of second switches. The first switches are configured to individually contact or not contact the comb teeth, and the second switches are configured to individually contact or not contact the comb teeth, forming the pair of interdigitated comb-shaped electrodes. Therefore, the excitation scheme of the comb teeth can be adjusted, for example, from a scheme where the comb teeth are alternately connected to two electrodes, to a scheme where two directly adjacent comb teeth are connected to the first electrode and then two directly adjacent comb teeth are connected to the second electrode. By changing the excitation scheme, the frequency of the mode can be changed, thereby allowing the same element to adapt to different operating parameters.

[0023] Preferably, the applied comb switching should avoid short-circuiting the first electrode and the second electrode.

[0024] According to one variation of the invention, the elastic wave element may include a supply device configured to provide a radio frequency signal with a frequency of at least 2 GHz, preferably at least 6 GHz, to the pair of interdigitated comb electrodes. Therefore, filters, sensors, or delay lines operating at frequencies higher than normally available frequencies can be provided using I-line lithography.

[0025] According to one variation of the invention, the interdigitated comb-shaped electrode may be the only conductive element in contact with the piezoelectric material. According to another variation of the invention, the elastic wave element has no electrode elements other than the interdigitated comb-shaped electrode; specifically, it has no floating electrodes. This avoids the possibility that some of the energy introduced into the system is used to form non-shear modes.

[0026] To achieve this objective, the present invention also proposes an acousto-electric device using elastic wave elements as described above (especially a comb-shaped electrode with a tooth width of at least 280 nm, preferably at least 350 nm), particularly a filter, sensor, or delay line, with an operating frequency of 2 GHz or higher, particularly 6 GHz or higher. Therefore, filters, sensors, or delay lines operating at frequencies higher than normally available frequencies can be provided by using I-line lithography.

[0027] To achieve this objective, the present invention also proposes a method for manufacturing the aforementioned elastic wave element, comprising the following steps: providing a piezoelectric material, particularly a ferroelectric material; fabricating the pair of forked comb-shaped electrodes, embedding them at least partially, preferably entirely, in the piezoelectric material; and then applying an electric field stronger than the coercive field of the piezoelectric material, particularly at least ten times stronger, to generate periodically alternating first and second polarization domains having opposite polarization directions. These electrodes can be advantageously used to create these polarization domains, thereby simplifying the manufacturing process.

[0028] According to one variation of the invention, the electric field can be applied once the temperature of the piezoelectric material is heated to at least 150°C, preferably to at least 170°C. Therefore, polarization can be achieved even without a counter electrode by applying an electric field below ambient temperature. Simple Explanation of the Diagram

[0029] The invention and its other advantages will be better understood by reading the following non-limiting description in conjunction with the accompanying drawings, wherein:

[0030] Figure 1 illustrates a summary of an elastic wave element according to a first embodiment of the present invention.

[0031] Figure 2 schematically illustrates a cross-sectional view of a portion of an elastic wave element according to a first embodiment of the present invention and a diagram of its shearing mode.

[0032] Figure 3 illustrates the harmonic conductance G and harmonic admittance Y of the elastic wave element according to the first embodiment of the present invention.

[0033] Figure 4 illustrates the harmonic conductance G and harmonic admittance Y of two dielectric layers of different thicknesses in the elastic wave element according to the first embodiment of the present invention.

[0034] Figure 5 shows a cross-sectional view of a portion of an elastic wave element 111 according to a variation of the first embodiment of the present invention.

[0035] Figure 6 illustrates the harmonic conductance G and harmonic admittance Y of three comb teeth of different thicknesses in a variation of the first embodiment of the present invention.

[0036] Figure 7 schematically illustrates a cross-sectional view of a portion of an elastic wave element according to a second variation of the first embodiment of the present invention.

[0037] Figure 8 illustrates the harmonic conductance G and harmonic admittance Y of three comb teeth of different thicknesses in an elastic wave element according to a second variation of the first embodiment of the present invention.

[0038] Figure 9 is a schematic diagram of a portion of an elastic wave element according to a second embodiment of the present invention.

[0039] Figure 10 is a diagram illustrating the harmonic conductance G and harmonic admittance Y of the elastic wave element according to the second embodiment of the present invention.

[0040] Figure 11 is a schematic diagram of a portion of an elastic wave element according to a third embodiment of the present invention.

[0041] Figure 12 illustrates the harmonic conductance G and harmonic admittance Y of the elastic wave element according to the third embodiment of the present invention for two electrical excitation schemes.

[0042] Figure 13 schematically illustrates a pair of alternating finger electrodes used to implement one of the fourth embodiments of the present invention.

[0043] Figure 14 schematically illustrates the second pair of alternating finger electrodes used to implement the fourth embodiment of the present invention.

[0044] Figure 15 illustrates the steps of a method for manufacturing an elastic wave element according to the fifth embodiment of the present invention. Implementation

[0045] The invention is described in more detail below by way of advantageous embodiments and with reference to drawings. These embodiments are merely possible configurations, and therefore the various features described may be provided independently or omitted when implementing the invention.

[0046] According to the first embodiment, the elastic wave element 1, particularly a shear mode element, includes a piezoelectric material 3, particularly a ferroelectric material, disposed on top of a piezoelectric layer 5, particularly directly on a dielectric layer 7. The dielectric layer 7 is disposed on top of, particularly directly on, a substrate 9. The piezoelectric layer 5, dielectric layer 7, and substrate 9, obtained through, for example, the SmartCut™ layer transfer method, can form a composite substrate 11. This composite substrate 11 is also referred to as a piezoelectric substrate on insulator or a POI substrate. In the layer transfer method, the dielectric layer 7 can serve as a bonding layer between the substrate 9 and the piezoelectric layer 5.

[0047] Ferroelectricity is the property of a material to spontaneously polarize. Ferroelectric materials are a subclass of piezoelectric materials. Ferroelectric properties can also be obtained artificially, for example, by creating polarization domains with different polarization directions through suitable growth conditions. Therefore, the following discussion may consider any material capable of generating polarization domains as a piezoelectric material.

[0048] According to the present invention, the piezoelectric material of the piezoelectric layer 5 includes a first polarization domain 3ai, wherein i ranges from 1 to j, the first polarization domain has a first polarization direction 13a, and a second polarization domain 3bi, wherein i ranges from 1 to j, the second polarization domain has a second polarization direction 13b, the first polarization direction 13a and the second polarization direction 13b being opposite to each other. Furthermore, the first and second polarization domains 3ai and 3bi form frequency bands of the same thickness, which alternate periodically along a periodic direction d at a spacing pf, the periodic direction d being perpendicular to the surface normal n of the piezoelectric material 3.

[0049] In this embodiment, the polarization axis Z of the polarization domain forms a non-zero angle with the normal n. Furthermore, the polarization axis Z has at least one component in the periodic direction d. This component is opposite for both types of polarization domains. The polarization axis Z preferably lies on the plane defined by the normal n and the periodic direction d, thus the angle φ is equal to 0. In this case, only sections undergoing a single defined rotation about the crystal axis X are considered without loss of generality. Specifically, for these so-called single-rotation sections, the angle φ defined about the crystal axis Z is 0.

[0050] This configuration can induce shear waves in piezoelectric layers, especially for trigonal monocrystalline materials of the 3m class, such as single-crystal lithium tantalate (LiTaO3) or lithium niobate (LiNbO3), and ABO3-type perovskite materials. These materials, due to their ferroelectric properties, meet the conditions required for inducing shear modes according to this invention. In these materials, particular attention will be paid to single polarization along the Z-axis for implementing this invention.

[0051] In this embodiment, the piezoelectric material of layer 3 can be monocrystalline lithium tantalate (LiTaO3) or monocrystalline lithium niobate (LiNbO3). Other piezoelectric materials as described above can also be used. The thickness e1 of the piezoelectric layer 5 is preferably less than the wavelength λ, preferably less than λ / 2, even more preferably less than λ / 4, and typically less than 1 μm.

[0052] For lithium tantalate (LiTaO3), according to the standard IEEE Std-176 version IRE 1949, the crystal orientation of the first polarization direction 13a of the first polarization domain 3ai of layer 3 is preferably (YXl) / θ, where the selected angle θ is between -30° and 110°. Therefore, according to the standard IEEE Std-176 version IRE 1949, the crystal orientation of the second polarization direction 13b of the second polarization domain 3bi of layer 3 is (YXl) / θ+180°. When the polarization axis is the Z-axis, if starting from the substrate oriented (YX), this axis is colinear with the width direction of the substrate. After rotating by an angle θ to obtain the orientation (YXl) / θ, this axis forms an angle θ-90° with the normal n of the substrate and an angle θ with the axis colinear with the substrate surface. Therefore, in this system, the normal n corresponds to the direction 90° - θ, and the periodic direction d is orthogonal to the normal n and forms an angle θ with the Z-axis, and in a specific mode it is collinear with the Z-axis.

[0053] For lithium niobate (LiNbO3), according to the standard IEEE Std-176 IRE 1949, the crystal orientation of the first polarization direction 13a of the first polarization domain 3ai of layer 3 is preferably (YXl) / θ, where the selected angle θ is between -40° and +110°, and preferably between -10° and +50°. Therefore, according to the standard IEEE Std-176 IRE 1949, the crystal orientation of the second polarization direction 13b of the second polarization domain 3bi of layer 3 is (YXl) / θ+180°.

[0054] For lithium tantalate and lithium niobate, the polarization direction occurs only along the Z-axis. Under the influence of an electric field exceeding the coercive field, atoms in the crystal lattice will move along this direction from the barycentre, causing the molecules to become polarized.

[0055] The dielectric layer 7 is preferably a silicon oxide layer with a thickness e2 less than the wavelength and / or between 200 nm and 2 μm. The dielectric layer may also be made of silicon nitride, Ta2O5, ZrO2, HfO2, SiON, or a combination of these materials. The dielectric layer may also include other components such as polycrystalline silicon.

[0056] The substrate 9 is preferably a silicon substrate, such as silicon (100), (110), or (111). In this structure, the orientation distance between the land regions of the two crystals, silicon and lithium tantalate, can vary between 0° and 180° without losing the generality of the basic characteristics of the converter. The same results are also observed for the three orientations of silicon. The substrate can also be made of silicon oxide, silicon carbide (SiC), sapphire, silicon nitride (SiN), aluminum nitride (AlN), quartz, carbon, diamond, yttrium aluminum garnet (Yags), yttrium iron garnet (Yigs), amorphous silicon or polycrystalline silicon, or LiNbO3 or LiTaO3.

[0057] By using silicon as the substrate 9 and silicon oxide as the dielectric layer 7, the temperature stability of the elastic wave element 1 can be improved. This is because the velocity temperature coefficient (VTC) of the shear modes has opposite signs among the stacked constituent materials, and the thickness of silicon is greater than the total thickness of the dielectric and piezoelectric layers deposited on its surface. In particular, when its thickness is 50 times the thickness of the two layers, the thermal expansion effect of the piezoelectric layer can be suppressed. Specifically, materials with a coefficient of thermal expansion of less than 10 ppm·K⁻¹ (preferably 5 ppm·K⁻¹) have proven to effectively reduce the influence of temperature on structure-guided modes.

[0058] A pair of forked comb electrodes 15a and 15b may be configured, for example, to be at least partially (preferably entirely) embedded in the piezoelectric material 3. The respective comb teeth (17a1 to 17a3 and 17b1 to 17b3) extend primarily perpendicular to the periodic direction d (i.e., parallel to the frequency bands of polarization domains 3ai and 3bi). The illustrated comb electrodes have three comb teeth, with each electrode designated to have more than three comb teeth. The comb teeth are preferably rectangular (i.e., parallelepiped) in shape. Comb teeth 17a1 to 17a3 are connected to each other via conductive strip 19a. Comb teeth 17b1 to 17b3 are connected to each other via conductive strip 19b. The two conductive strips 19a and 19b may be connected to the poles of the radio frequency source to excite modes of interest. The electrode comb teeth are periodically arranged with a mechanical spacing pe, thus their electrical periodicity is 2pe. However, according to a variation, one or more periodic interruptions may be introduced, for example, by omitting one or more comb teeth. The mechanical spacing pe of the electrodes is half the spacing pf of the polarization domains 3ai and 3bi. For example, these data can be varied to increase or even maximize the coupling effect or adjust the mode speed to achieve a specified frequency value.

[0059] The comb electrodes 15a and 15b are made of metallic materials, such as aluminum (Al), molybdenum (Mo), gold (Au), silver (Ag), or copper-aluminum alloys (AlCu), or alloys primarily based on aluminum and other metals (e.g., titanium (Ti)). Specifically, the comb electrodes 15a and 15b may be made of AlCu, AlSi, or AlTi, doped with 0.5% to 5% copper, titanium, and / or silicon, and may have sublayers of titanium, tantalum, molybdenum, palladium, or platinum, or combinations of titanium / platinum, titanium / gold, tantalum / platinum, chromium / gold, or zirconium. The thickness e3 of the comb electrodes 15a and 15b is preferably between 50 nm and 200 nm, or, according to an alternative variation, the thickness may be equal to or greater than the thickness of the piezoelectric layer 5, for example, at least 1 μm. The comb teeth 17a1 to 17a3 and 17b1 to 17b3 have a width a in the periodic direction d, which is preferably equal to or greater than 280 nm, and more preferably greater than 350 nm. Therefore, the comb electrodes 15a and 15b can be manufactured by I-line lithography.

[0060] In the metallization ratio a / pe, 'a' represents the width of the comb teeth 17a1 to 17a3 and 17b1 to 17b3, and 'pe' represents the mechanical pitch of the comb teeth, preferably between 0.25 and 0.75, and particularly between 0.4 and 0.6. This ratio a / pe and / or the thickness e3 can be adjusted to set the electromechanical coupling coefficient and / or reduce losses.

[0061] In this embodiment, the comb teeth are all the same shape; according to variations, the comb teeth can also be made to different lengths l.

[0062] The element preferably does not include any other electrode devices, such as floating electrodes or planar electrodes, and the element is neither above nor below the ferroelectric layer 5. Specifically, any electrode (more specifically, a floating electrode) will generate parasitic capacitance, which will degrade the coupling of shear modes and may degrade the spectral purity of the element.

[0063] In the embodiment of FIG1, the supply device 21 is connected to the finger comb electrodes 15a, 15b. This supply device 21 is preferably configured to provide radio frequency signals to the finger comb electrodes 15a, 15b at a frequency of at least 2 GHz, and preferably at least 6 GHz.

[0064] When the elastic wave element 1 is assembled to convert elastic waves into electrical signals, the supply device 21 will be replaced by an electrical receiver.

[0065] According to a variation of the first embodiment, the composite substrate 9 may include one or more other layers in its structure. A layer for capturing free charges (e.g., a layer of polycrystalline silicon, AlN, or polycrystalline SiOCH) may be disposed between the dielectric layer 7 and the substrate 9 to limit the average free path of free charges generated at the silicon / dielectric layer interface through an acousto-electric field associated with wave propagation, thereby reducing leakage current. Considering radio frequency applications for telecommunications (typically between 500 MHz and 6 GHz), the thickness of such capturing layer is preferably between 0.3 μm and 2 μm.

[0066] In addition to using composite substrate 11, the present invention can also be realized using a block substrate of ferroelectric material, thus eliminating the need for a dielectric layer and a base substrate.

[0067] Figure 2 schematically illustrates a cross-sectional view of a portion of the elastic wave element according to the first embodiment of the present invention, representing a periodic lattice. Figure 2 shows two halves 3a1 and 3a2 of the first polarization domain, in which a second polarization domain 3b1 with opposite polarization directions is sandwiched. Each comb-shaped electrode 15a and 15b is represented by comb teeth 17a1 and 17b1, respectively. Comb teeth 17a1 and 17b1 are embedded in the piezoelectric material layer 5. Figure 2 also shows the dielectric layer 7 and the substrate 9.

[0068] The comb teeth 17a1 are located between two opposite polarization domains, namely 3a1 and 3b1. The comb teeth 17b1 are also located between two opposite polarization domains, namely 3b1 and 3a2. In this embodiment, the comb teeth 17a1 and 17b1 extend from the surface / interface 21 of the dielectric layer 7 through the entire thickness e1 of the piezoelectric layer 5. Therefore, the thickness e3 of the comb teeth 17a1 and 17b1 is the same as the thickness e1 of the piezoelectric layer 5. The width a of the comb teeth 17a1 and 17b1 is 50% of the polarization domain width a2. In a variation, this width can be between 40% and 60% of a2.

[0069] Numerical simulations were performed using the method described by S. Ballandras et al. in "Finite element analysis of periodic piezoelectric transducers," Journal of Applied Physics 93, 702 (2003). The simulations emphasize that for the elastic wave element 1 in Figures 1 and 2, the frequencies of its fundamental modes are twice as high as those of elements without opposite polarization domains, due to the wavelength being halved. The lower half of Figure 2 illustrates the lattice deformation in the shear mode, with a wavelength of 2 µm, corresponding to the mechanical period pe of the comb teeth, not the electrical period 2pe of the element without polarization domains. This mode exists only when the electrode vibration is antisymmetric.

[0070] Figure 3 illustrates the simulation results of the elastic wave element 1 shown in Figures 1 and 2. The composite substrate used in the simulation has a silicon (100) substrate (with its connection region oriented at 45° relative to the connection region of the LiTaO3 layer), a 1 µm thick polycrystalline silicon trapping layer, a 500 nm thick silicon dioxide dielectric layer, and a 600 nm thick LiTaO3 layer. Its polarization domain is considered to be infinitely long and alternates with a period pf of 4 µm, which is consistent with the electrical period and orientation of the network (YXl) / 42° / 30° and (YXl) / 222° / 210°. In both cases, the electrodes are made of AlCu with a thickness of 150 nm, a metallization ratio a / pe of 0.5, and a mechanical spacing pe of 2 µm.

[0071] Figure 3 illustrates the simulation results, where the left axis represents the harmonic admittance modulus Y (in dB) and the right axis represents the harmonic conductance modulus G (in dB), both as a function of frequency (in MHz). A fundamental shearing mode 31 is observed to be the dominant mode at approximately 2 GHz, in addition to three other contributions at higher frequencies: mode 33 at approximately 3.3 GHz, mode 35 at approximately 5.8 GHz, and mode 37 at approximately 6.9 GHz.

[0072] Mode 33 can be reduced by decreasing the thickness of the piezoelectric layer. Modes 35 and 37 are strongly dependent on the thickness of dielectric layer 7. Figure 4 illustrates this effect by comparing simulation results for two dielectric layer thicknesses, where the left axis represents the harmonic admittance mode Y (in dB) and the right axis represents the harmonic conductance mode G (in dB), both as a function of frequency (in MHz). These modes are less pronounced when the dielectric layer 7 thickness is 300 nm instead of 500 nm. Arrow 41 indicates a decrease in harmonic conductance G for this mode at approximately 6.8 GHz, while number 43 indicates a decrease in harmonic admittance Y as the thickness decreases from 500 nm to 300 nm.

[0073] Therefore, mode 31 exhibits an apparent effective phase velocity (veff) of approximately 8 km⁻¹, which is about twice that of a piezoelectric layer without alternating polarization domains. The effective phase velocity of this mode is veff = λxf = pelxf, where λ is the coherence wavelength of the charge in the electrode, pel is the electrical period of the electrode, and f is the frequency of the mode. Thus, using a pair of finger-comb electrodes deposited on the surface of a piezoelectric layer with alternating polarization domains can improve the phase velocity while retaining an electromechanical coupling coefficient advantage of greater than 7% or even 10%, achieving quality coefficients in the thousands at frequencies exceeding 1 GHz and controlled temperature effects.

[0074] Furthermore, for an electrode configuration with the same thickness as the lithium tantalate piezoelectric layer, where the thickness is between 300 nm and 1 μm, the crystal orientation of its single rotational layer is (YXl) / θ, where θ is between +10 and +60°, and the thickness of the silicon dioxide dielectric layer is between 300 nm and 2 μm, the frequency temperature coefficient (FTC) of resonance or anti-resonance can be minimized to an absolute value of less than 20 ppm·K⁻¹, and ideally even less than 10 ppm·K⁻¹.

[0075] Figure 5 schematically illustrates a cross-sectional view of a portion of the elastic wave element 51 according to a variation of the first embodiment of the present invention. The only difference from the embodiments shown in Figures 1 and 2 is that the comb teeth 17a1 and 17b1 do not extend from the interface 21 between the dielectric layer 7 and the piezoelectric layer 5, but are incorporated into the grooves 53a and 53b of the piezoelectric layer 5. The surfaces 55a and 55b of the comb teeth 17a1 and 17b1 are aligned with the surface 57 of the piezoelectric layer 5. According to other variations, the comb teeth 17a1 and 17b1 may extend beyond the surface 57 or be recessed relative to the surface 57. Figure 5 also illustrates the dielectric layer 7 and the substrate 9. As with the first embodiment of Figures 1 or 2, Figure 5 does not show the trapping layer.

[0076] Figure 6 illustrates a variation of the elastic wave element according to the first embodiment of the present invention, with the left axis representing harmonic conductance G (in dB) and the right axis representing harmonic admittance Y (in dB), both as functions of frequency (in MHz). Mode 59 appears below 2 GHz.

[0077] For the simulation, a 600 nm thick piezoelectric layer and a 500 nm thick electrode were used. The LiTaO3 was oriented at (YXl) / 42°–222°, the dielectric layer was a 500 nm thick silicon dioxide layer, the trapping layer was 1 μm thick, and the substrate was a silicon (111) with a connection region, which was misaligned at 45° relative to the connection region of the LiTaO3 layer. The electrical period was 4 µm, which resulted in a mode with a velocity greater than 7200 ms⁻¹ and an electromechanical coupling coefficient exceeding 10%. Similar results were observed for other silicon orientations.

[0078] The 3.5 GHz contribution is related to the layer beneath the tantalate. This contribution can be reduced by adjusting the thickness ratio of different layers.

[0079] The simulation shows that if the comb teeth are completely embedded in the layer and do not reach the upper surface of the piezoelectric layer, the spectral purity and the substantially electromechanical coupling coefficient of the mode can be further improved. The resonance quality is also improved compared to the previous cases.

[0080] According to a variation, in the elastic wave element 51, the piezoelectric layer 5 portion located below the comb teeth 17a1, 17b1 remains in its initial polarization state, regardless of whether there is a polarization domain. The simulation shows that the vibration modes remain approximately the same, as shown in Figure 6.

[0081] Figure 7 schematically illustrates a cross-sectional view of a portion of the elastic wave element 61 according to a second variation of the first embodiment of the present invention. The only difference compared to the embodiments shown in Figures 1 and 2 is that the surfaces 63a and 63b of the comb teeth 17a1 and 17b1 are no longer aligned with the surface 65 of the piezoelectric layer 5, but are recessed. Therefore, e3 < e1. According to another variation, the comb teeth 17a1 and 17b1 may extend beyond the surface 65. Therefore, e3 > e1. Figure 7 also illustrates the dielectric layer 7 and the substrate 9. As with the first embodiment of Figures 1 or 2, Figure 7 does not show the trapping layer.

[0082] Figure 8 illustrates a graph of the elastic wave element 61 according to the second variation of the first embodiment of the present invention, with the left axis being the harmonic conductance G (in dB) and the right axis being the harmonic admittance Y (in dB), both as a function of frequency (in MHz).

[0083] As shown in the variation of Figure 6, simulations show that if the comb teeth do not reach the upper surface of the piezoelectric layer, the spectral purity and resonance quality are improved compared to the mode shown in Figure 3. The coupling effect is also better in this mode compared to when the electrode completely fills the cavity. Furthermore, Figure 7 shows that, due to boundary conditions, for this mode 67, the comb teeth 17a1 and 17b1 of the electrode vibrate synchronously, as shown in modes 31 and 59 in Figures 3 and 6.

[0084] Figure 9 schematically illustrates a cross-sectional view of a portion of the elastic wave element 71 according to a second embodiment of the present invention. The elastic wave element 71 has the same structure and uses the same material as the elastic wave element 1 of the first embodiment, except that the comb teeth 73a1 and 73b1 of the forked comb-shaped electrodes are positioned such that the polarization directions on both sides of each comb tooth are the same, but the polarization directions of adjacent polarization regions are different for the comb teeth 73a1 and 73b1 of different electrodes. Therefore, the comb teeth 73a1 of the first electrode 15a are located in the middle of the first polarization region 75a1, and the comb teeth 73b1 of the second electrode 15b are located in the middle of the second polarization region 75b1 with opposite polarization directions. In this embodiment, the comb teeth are positioned in the center of the polarization region; in a variation, the comb teeth may also be positioned outside the center of the polarization region. Figure 9 also illustrates the dielectric layer 7 and the substrate 9. As with the first embodiment of Figures 1 or 2, Figure 9 does not show the trapping layer.

[0085] In this embodiment, the thickness e3 of the comb teeth 73a1 and 73b1 is greater than the thickness e1 of the polarization domains 75a1 and 75b1. According to variations, e1 may also be equal to or less than e3. Furthermore, as in the first variation of the first embodiment shown in FIG5, the electrodes 73a1 and 73b1 may also be positioned in the grooves of the polarization domains 75a1 and 75b1, and do not extend toward the interface 77 between the piezoelectric layer 5 and the dielectric layer 7.

[0086] The width 'a' of the comb teeth 73a1 and 73b1 is approximately half the sum of the widths 'a2_1' and 'a2_2' of the two portions of the polarization domain 75a1 and 75b1. In other variations, the value of the width 'a' can be between 40% and 60% of the sum of the widths 'a2_1' and 'a2_2'.

[0087] The lower half of Figure 9 illustrates a vibration mode. This embodiment was obtained through simulation as described in the first embodiment above, but for the unit cell of the elastic wave element 71, the polarization domain width is 1 μm, and the orientation is LiTaO3(YXl) / 42° and (YXl) / 222°, and the substrate is silicon (111). For other silicon orientations, substantially the same results can be observed. Therefore, the mechanical spacing pe is 3 µm, and the unit cell width used for simulation is 6 µm. The wavelength λ of this vibration mode is equal to the mechanical spacing pe of the electrodes.

[0088] Figure 10 illustrates the harmonic conductance G (in dB) on the left axis and the harmonic admittance Y (in dB) on the right axis for orientations (YXl) / 42° and (YXl) / 222°, both as functions of frequency (in MHz). Only one very distinct vibration mode is observed here compared to other vibration modes.

[0089] This mode appears at approximately 1.3 GHz and can be observed in the harmonic admittance Y (see No. 81) and harmonic conductance G (see No. 83). These simulations show that the electrode motion is always in phase for the observed mode. The equivalent phase velocity is 7.8 km·s⁻¹, which is close to twice the shear mode velocity on a similar POI substrate without alternating opposite polarization domains.

[0090] These simulations also show that when the thickness e3 > e1, the spectral purity of the mode is improved compared to when the thickness is lower.

[0091] Figure 11 schematically illustrates a cross-sectional view of a portion of the elastic wave element 91 according to a third embodiment of the present invention. The elastic wave element 91 has the same structure and uses the same material as the elastic wave element 1 of the first embodiment, except that the comb teeth 93a1 and 93a2 of the first finger-shaped electrode are positioned such that the polarization directions of polarization regions 3a1 and 3b1 are opposite to those of 3b1 and 3a2 on both sides of each comb tooth 93a1 and 93a2, respectively. Simultaneously, the comb teeth 93b1 and 93a2 of the second electrode are positioned such that the polarization directions on both sides of the comb tooth are the same. In fact, comb tooth 93b1 is disposed in the middle of polarization region 3b1, and comb tooth 93b2 is disposed in the middle of polarization region 3a2. Similar to polarization region 3a2, only a portion of the first polarization region 3a1 is shown here to ensure the same edge conditions are found at the beginning and end of the unit. Figure 11 also illustrates the dielectric layer 7 and the substrate 9. As with the first embodiment of Figure 1 or Figure 2, Figure 11 does not show the capture layer.

[0092] Figure 12 illustrates the harmonic conductance G and harmonic admittance Y of two elastic wave element embodiments according to the third embodiment of the present invention (located in the upper and lower figures respectively). The difference between the two embodiments lies in the different potential schemes applied to the electrodes. These schemes are illustrated above each graph in Figure 12, indicated by the "+" and "-" symbols marked on the electrode comb teeth.

[0093] As described in the first embodiment above, simulations were performed on the unit cells of the elastic wave element 91, where the unit cell width is 6 μm, the electrode width is 750 nm, and the polarization domain widths are equal. The repetition period of this structure is 6 µm. The LiTaO3 orientations are (YXl) / 42° and (YXl) / 222°, and the substrate 9 is silicon (111). For other silicon orientations, substantially the same results were observed.

[0094] The first graph in Figure 12 shows the harmonic conductance G (in dB) on the left axis and the harmonic admittance Y (in dB) on the right axis for orientations (YXl) / 42° and (YXl) / 222°, both as functions of frequency (in MHz). These results were obtained by applying alternating +V / -V potentials to comb teeth 93a1, 93b1, 93a2, and 93b2, as shown at the top of the first graph in Figure 12.

[0095] Several modes appear in admittance and conductance. Specifically, the harmonic admittance Y of mode 951 appears at about 600 MHz, the harmonic conductance G of mode 952 appears at about 2 GHz, mode 953 appears at about 3 GHz, and mode 954 appears at about 4 GHz.

[0096] The simulation shows that Mode 951 is a Rayleigh mode with a phase velocity of approximately 3600 ms⁻¹. While there are significant radiative losses at other contributions around 2 and 3 GHz, their phase velocities are even higher.

[0097] The second mode 952 has radiation loss and a quality factor Q < 100, corresponding to the combination of shear waves and vibration modes of the electrode comb.

[0098] The effective phase velocity of the third contribution 953 at approximately 3 GHz is approximately 18 km·s⁻¹, and it exhibits lower loss than mode 952. It is also a combination of shear wave and vibration modes of the electrode comb as shown in Figure 11.

[0099] The fourth contribution 954 at approximately 4 GHz has an effective phase velocity of approximately 24 km·s⁻¹, and the simulation shows the full wavelength within the electrode. This is a second-order electrode vibratory mode.

[0100] The second graph in Figure 12 (below the first graph) illustrates the harmonic conductance G (in dB) on the left axis and the harmonic admittance Y (in dB) on the right axis for orientations (YXl) / 42° and (YXl) / 222°, both as functions of frequency (in MHz). These results were obtained by applying a +V potential to comb teeth 93a1 and 93a2' and a -V potential to comb teeth 93b1 and 93b2', as shown above the second graph in Figure 12. Three modes appear in the admittance and conductance, but at different frequencies compared to the aforementioned embodiment. Specifically, the harmonic admittance Y of mode 971 is at approximately 1.5 GHz, mode 972 at approximately 2.5 GHz, and mode 973 at approximately 3.15 GHz.

[0101] Mode 971 at 1.5 GHz has an effective phase velocity of approximately 9 km·s⁻¹, which is almost at the intersection of the SSBW frequencies. Its loss performance can be further improved by increasing the mass. The simulation shows that this is a combination of the vibration modes of the electrode comb and the conventional shear wave. According to the simulation results, only two of the four electrodes may significantly contribute to resonance.

[0102] The second mode 972 at 2.5 GHz has an effective phase velocity of approximately 15 km·s⁻¹, representing an antisymmetric shear mode generated at the electrodes, with all electrodes vibrating in phase. Indeed, as mentioned above, only two electrodes actually contribute to the electrical response. Based on simulation results, it is highly likely that only the electrode located between two opposite polarization domains can actually contribute to the resonance, while the charges of the other two electrodes should be in equilibrium.

[0103] Mode 973 at 3.15 GHz has an effective velocity of nearly 20 km·s⁻¹, which is the vibration mode of the electrode comb, as shown at the bottom of Figure 11.

[0104] Such a structure can be advantageous, particularly in cases where specific mode contributions are enhanced through coarse filtering, or in frequency source applications where only a limited segment of the spectrum is actually used. In other words, the electronic system using this component filters the spectrum in some way. The proposed solution again demonstrates its advantage by enabling an operating frequency significantly higher than that achievable with conventional nonpolar materials.

[0105] In this second embodiment, another type of finger-fork electrode pair is used, as shown in FIG13. In this case, two comb teeth with the same potential are arranged directly adjacent to each other, and then two comb teeth with opposite potentials are also arranged directly adjacent to each other. Therefore, electrode 15a' has comb teeth 13a1' and 13a2', 13a3' and 13a4', 13a5' and 13a6', and electrode 15b' has comb teeth 13b1' and 13b2', 13b3' and 13b4', 13b5' and 13b6'.

[0106] According to a variation, a control circuit can be configured to change the electrode arrangement from the configuration shown in the upper left corner to the configuration shown in the upper right corner, for example, by using a switch as shown in Figure 14.

[0107] Figure 14 illustrates a first electrode 151 with switches 153a, 153b, 153c, and 153d, located before a second electrode 155 with switches 157a, 157b, 157c, and 157d. Switches 153a, 153b, 153c, and 153d are configured to either contact or not contact electrode 151 via comb teeth 159a, 159b, 159c, and 159d, respectively. Similarly, switches 157a, 157b, 157c, and 157d are configured to either contact or not contact electrode 155 via comb teeth 159a, 159b, 159c, and 159d, respectively. Therefore, a potential application configuration as shown in the upper left and upper right corners of Figure 12 can be generated using a single element. A switching method is preferred to avoid short circuits between these electrodes. Figure 14 on the left shows comb teeth 159a to 159d, where the potential alternates between the comb teeth. On the right side of Figure 14, two adjacent comb teeth, namely 159a and 159b, and 159c and 159d, have the same potential.

[0108] Electrodes 151 and 155 can also be used in the configuration of other embodiments, allowing for changes in the electroexcitation configuration.

[0109] Figure 15 illustrates the steps of a method for manufacturing an elastic wave element (particularly the elastic wave element of the first embodiment) according to an embodiment of the present invention. The method begins at step 101, which involves providing a piezoelectric material, particularly a ferroelectric material.

[0110] This step may include providing a bulk substrate, such as a wafer made of a single-crystal piezoelectric material, or providing a composite substrate 11, which includes a piezoelectric layer 5 of the piezoelectric material 3, a dielectric layer 7 (e.g., a silicon oxide layer) and a substrate 9 (e.g., a silicon substrate, such as silicon (100), silicon (110) or silicon (111), or quartz).

[0111] The piezoelectric material of layer 3 is either single-crystal lithium tantalate (LiTaO3) or single-crystal lithium niobate (LiNbO3). Other piezoelectric materials as defined above may also be used.

[0112] For lithium tantalate (LiTaO3), according to the standard IEEE Std-176 version IRE 1949, the crystal orientation of the first polarization direction 13a of the first polarization domain 3ai of layer 3 is preferably (YXl) / θ, where the selected angle θ is between 30° and 110°. Therefore, according to the standard IEEE Std-176 version IRE 1949, the crystal orientation of the second polarization direction 13b of the second polarization domain 3bi of layer 3 is (YXl) / θ+180°. By keeping the comb teeth parallel to the polarization domain, it is also possible to set the polarization domain on an orthogonal plane, that is, relative to the situation described above, using the configurations of (YXlt) / θ / 90° and (YXlt) / θ+180° / 90°.

[0113] For lithium niobate (LiNbO3), according to the standard IEEE Std-176 IRE 1949, the crystal orientation of the first polarization direction 13a of the first polarization domain 3ai of layer 3 is preferably (YXl) / θ, where the selected angle θ is between -40° and +110°, and preferably between -10° and +50°. Therefore, according to the standard IEEE Std-176 IRE 1949, the crystal orientation of the second polarization direction 13b of the second polarization domain 3bi of layer 3 is (YXl) / θ+180°.

[0114] This composite substrate 11 can be obtained via a layer transfer method (e.g., the SmartCut™ method). In the SmartCut™ process, ions are implanted into a donor substrate (in this case, a piezoelectric substrate) to create a weakened region within the donor substrate. The donor substrate is then bonded to a base substrate. In this case, the base substrate is a single-crystal silicon substrate, such as silicon (100), silicon (110), or silicon (111), with a native oxide layer or silicon oxide with thermal or chemical vapor deposition ("CVD") or physical vapor deposition ("PVD"). This oxide layer facilitates the bonding of the two substrates, especially through molecular bonding. The orientation of the silicon plane relative to the piezoelectric layer plane can be selected to reduce or even minimize higher-than-fundamental order modes.

[0115] According to one variation, a trapping layer is first formed on the substrate before the oxide is formed. This trapping layer is usually a polycrystalline silicon layer, and its main function is to minimize the mean free path of the generated charge when an acoustic-electric wave passes through the silicon-oxide interface.

[0116] Once two substrates are bonded together, the supply of mechanical and / or thermal energy can cause the weakened area to fracture. Therefore, layers with a thickness of 1 μm or less can be transferred to the substrate.

[0117] Then, during step 103, the pair of forked comb electrodes can be fabricated on the piezoelectric material using lithography, etching, deposition, and polishing steps known to those skilled in the art, to obtain the elastic wave element of the first embodiment.

[0118] The method of step 103 can be applied to the other embodiments described above by adjusting the photomask and photomask alignment during the lithography process.

[0119] Then, during step 105, an electric field stronger than the coercive field of the piezoelectric material (especially the ferroelectric material) is applied to generate a periodically alternating first polarization domain and a second polarization domain with opposite polarization directions. The applied electric field must be higher than 22 kV·mm⁻¹, which represents the coercive field that is typically measurable for lithium niobate and lithium tantalate.

[0120] Therefore, the teeth of this pair of forked comb-shaped electrodes can also be used to manufacture structures with opposite polarization domains.

[0121] To achieve the second and third embodiments, step 105 can be performed before step 103, by using electrodes to generate an electric field in the form of parallel bands, preferably perpendicular to the surface of the piezoelectric material.

[0122] This method is exemplified in Thorlabs’ “Periodically Poled Lithium Niobate (PPLN) – Tutorial”, pages 686-687 (available at www.thorlabs.com), which uses patterned electrodes that are then removed. Other alternatives use electron beams, see: C. Restoin, C. Darraud-Taupiac, JL Decossas, JC Vareille, J. Hauden and A. Martinez: “Ferroelectric domain inversion by electron beam on LiNbO3 and Ti: LiNbO3” Journal of Applied Physics, 88:6665–6668, 2000, or M. Yamada and K. Kishima: “Fabrication of periodically reversed domain structure for SHG in LiNbO3 by direct electron beam lithography at room temperature”, Electronics Letters, 27:828–829, 1991.

[0123] 1, 51, 61, 71, 91, 111: Elastic wave element 3: Piezoelectric materials 3a1~3aj, 75a1: First polarization domain 3b1~3bj, 75b1: Second polarization domain 5: Piezoelectric layer 7: Dielectric layer 9: Substrate 11: Composite substrate 13a: First polarization direction 13b: Second polarization direction 13a1'~13a6', 13b1'~13b6', 17a1~17a3, 17b1~17b3, 73a1, 73b1, 93a1, 93a2, 93a2', 93b1, 93b2, 93b2', 159a~159d: Comb teeth 15a, 15a', 15b, 15b': Fingered comb electrodes 19a, 19b: Conductive strips 21: Supply device 31, 33, 35, 37, 41, 43, 59, 67, 81, 83, 951~954, 971~973: Pattern 53a, 53b: Grooves 55a, 55b, 57, 63a, 63b, 65: Surface 77: Interface 151: First electrode 153a~153d: First switch 155: Second electrode 157a~157d: Second switch a, a2_1, a2_2: width d: Periodic direction e1, e2, e3: Thickness n: Surface normal PE: Mechanical spacing pf: Polarization domain spacing

Claims

1. An elastic wave element, particularly a shear wave element, comprising a piezoelectric material (3), particularly a ferroelectric material, having a plurality of first polarization domains (3a) in a first polarization direction (13a) and a plurality of second polarization domains (3b) in a second polarization direction (13b), the first polarization direction (13a) being opposite to the second polarization direction (13b), wherein the first and second polarization domains (3a, 3b) are periodically alternating along a periodic direction (d) perpendicular to the surface normal (n) of the piezoelectric material (3), and a pair of finger-shaped comb electrodes (15a, 15b). Each of its comb teeth (17a1~17a3, 17b1~17b3) extends mainly perpendicular to the periodic direction (d) and the surface normal (n), and these comb teeth (17a1~17a3, 17b1~17b3) are arranged to be at least partially, preferably all, embedded in the piezoelectric material (3).

2. The elastic wave element of claim 1, wherein the comb teeth (17a1~17a3, 17b1~17b3) are arranged periodically.

3. The elastic wave element of claim 1, wherein the piezoelectric material (3) is disposed in the form of a layer (5) on a substrate (9), the thickness (e1) of the layer (5) being less than the wavelength (λ), preferably less than λ / 2, more preferably less than λ / 4, and the substrate (9) being silicon, amorphous or polycrystalline silicon, silicon oxide, silicon carbide, sapphire, silicon nitride, aluminum nitride, quartz, carbon, diamond, yttrium aluminum garnet (Yags), yttrium iron garnet (Yigs), or LiNbO3 and / or LiTaO3 substrate.

4. The elastic wave element of claim 2, wherein the piezoelectric material (3) is disposed in the form of a layer (5) on a substrate (9), the thickness (e1) of the layer (5) being less than the wavelength (λ), preferably less than λ / 2, more preferably less than λ / 4, and the substrate (9) being silicon, amorphous or polycrystalline silicon, silicon oxide, silicon carbide, sapphire, silicon nitride, aluminum nitride, quartz, carbon, diamond, yttrium aluminum garnet (Yags), yttrium iron garnet (Yigs), or LiNbO3 and / or LiTaO3 substrate.

5. The elastic wave element of claim 3, wherein a dielectric layer (7), particularly a layer of silicon oxide, silicon nitride, Ta2O5, ZrO2, HfO2, SiON, polycrystalline silicon or a combination thereof, is disposed between the piezoelectric material layer (5) and the substrate (9), wherein the thickness of the dielectric layer (7) is preferably less than the wavelength (λ) and / or between 200 nm and 2 µm.

6. The elastic wave element of claim 4, wherein a dielectric layer (7), particularly a layer of silicon oxide, silicon nitride, Ta2O5, ZrO2, HfO2, SiON, polycrystalline silicon or a combination thereof, is disposed between the piezoelectric material layer (5) and the substrate (9), wherein the thickness of the dielectric layer (7) is preferably less than the wavelength (λ) and / or between 200 nm and 2 µm.

7. The elastic wave element of any one of claims 3 to 6, wherein a trapping layer, in particular a layer of polycrystalline silicon or polycrystalline aluminum nitride or SiOCH, is disposed between the piezoelectric material (3) and the substrate (9), or between the dielectric layer (7) and the substrate (9), and the thickness of the trapping layer is preferably between 300 nm and 2 µm.

8. The elastic wave element as claimed in claim 3, wherein the comb teeth extend from the interface (21) with the substrate (9) between the regions of the piezoelectric layer (5).

9. The elastic wave element of claim 4, wherein the comb teeth extend from the interface (21) with the substrate (9) between the regions of the piezoelectric layer (5).

10. The elastic wave element of claim 5, wherein the comb teeth extend from the interface (21) with the substrate (9) or the dielectric layer (7) between the regions of the piezoelectric layer (5).

11. The elastic wave element of any one of claims 3 to 6 or 8 to 10, wherein the thickness of the comb teeth is at least equal to or less than the thickness of the layer (5) of the piezoelectric material (3).

12. The elastic wave element of any one of claims 1 to 6 or 8 to 10, wherein the comb teeth are positioned between polarization domains having different polarization directions.

13. The elastic wave element of any one of claims 1 to 6 or 8 to 10, wherein the comb teeth are configured such that the polarization directions on both sides of each comb tooth are the same, such that the polarization directions of different electrode comb teeth are different.

14. The elastic wave element of any one of claims 1 to 6 or 8 to 10, wherein the comb teeth of one of the two electrodes are configured such that the polarization directions on both sides of each comb tooth are the same, and the comb teeth of the second electrode are disposed between polarization domains with different polarization directions.

15. The elastic wave element of claim 12, wherein the width (a) of the comb teeth (15a, 15b) of the forked comb electrodes is between 40% and 60% of the width of the polarization domains (3a, 3b), preferably 50% of the width of the polarization domains, and / or is at least 280 nm, preferably at least 350 nm.

16. The elastic wave element of claim 13, wherein the width (a) of the comb teeth (15a, 15b) of the forked comb electrodes is between 40% and 60% of the width of the polarization domains (3a, 3b), preferably 50% of the width of the polarization domains, and / or is at least 280 nm, preferably at least 350 nm.

17. The elastic wave element of claim 14, wherein the width (a) of the comb teeth (15a, 15b) of the forked comb electrodes is between 40% and 60% of the width of the polarization domains (3a, 3b), preferably 50% of the width of the polarization domains, and / or is at least 280 nm, preferably at least 350 nm.

18. The elastic wave element of any one of claims 1 to 6 or 8 to 10, wherein the piezoelectric material (3) is selected from at least one of LiTaO3, LiNbO3, ABO3 type perovskite (especially KnbO3 and PbTiO3), PZT, PMnPt, or AlScN.

19. The elastic wave element of any one of claims 1 to 6 or 8 to 10, wherein a first electrode (151) includes a plurality of first switches (153a, 153b, 153c, 153d) and a second electrode (155) includes a plurality of second switches (157a, 157b, 157c, 157d), the first switches (153a, 153b, 153c, 153d) being configured to contact or not contact comb teeth (159a, 159b, 159c, 159d) respectively, and the second switches (157a, 157b, 157c, 157d) being configured to contact or not contact comb teeth (159a, 159b, 159c, 159d) respectively, to form the pair of finger-shaped comb electrodes.

20. The elastic wave element of any one of claims 1 to 6 or 8 to 10, comprising a supply device (21) configured to provide a radio frequency signal at a frequency of at least 2 GHz, preferably at least 6 GHz, to the pair of finger comb electrodes (15a, 15b).

21. The elastic wave element of any one of claims 1 to 6 or 8 to 10, wherein the pair of finger-shaped comb electrodes is the only conductive element in contact with the piezoelectric material.

22. The elastic wave element of any of claims 1 to 6 or 8 to 10 has no other electrode elements other than the pair of forked comb electrodes, specifically no floating electrodes.

23. An acoustic-electric device using the elastic wave element as claimed in claim 20, particularly a filter, sensor or delay line, having an operating frequency of 2 GHz or higher, preferably 6 GHz or higher.

24. A method for manufacturing an elastic wave element as claimed in any one of claims 1 to 22, comprising the steps of: providing a piezoelectric material, particularly a ferroelectric material; manufacturing the pair of forked comb-shaped electrodes such that at least part, preferably all, are embedded in the piezoelectric material (3); and applying an electric field stronger than the coercive field of the piezoelectric material, particularly at least ten times stronger, to generate the first and second polarization domains that are periodically alternating and have opposite polarization directions.

Images