Transducer structure for an acoustic wave device

Abstract

The invention relates to a transducer structure (200) of a surface acoustic device, comprising a composite substrate comprising a piezoelectric layer (212), a pair of interdigital comb electrodes (206, 208) comprising a plurality of electrode means (206-1, 206-2... 208-1, 208-2...) having a pitch p satisfying the Bragg condition, wherein the interdigital comb electrodes are embedded in the piezoelectric layer (212) such that, in use, an excitation of a wave propagation mode in the volume of the electrode means occurs and is the main propagation mode of the structure. The invention also relates to an acoustic wave device comprising at least one transducer structure as described above and to a method of manufacturing said transducer structure. The invention also relates to the use of the frequency of the bulk wave propagating in the electrode means of said transducer structure in an acoustic wave device to generate a contribution at high frequencies and in particular above 3 GHz.

Description

Technical Field

[0001] This invention relates to acoustic wave devices, and more particularly to the transducer structure of acoustic wave devices. Background Technology

[0002] In recent years, surface acoustic wave (SAW) devices have been used in an increasing number of practical applications, such as filters, sensors, and delay lines. In particular, SAW filters are of particular interest in mobile phone applications because they can be formed into low-loss, high-order bandpass filters without employing complex circuitry with unprecedented compactness. Therefore, SAW filters offer significant advantages over other filter technologies in terms of performance and size.

[0003] In typical surface acoustic wave (SAW) devices, one or more interdigitated transducers (IDTs) are formed on a surface propagation substrate. These IDTs are used to convert acoustic waves into electrical signals and vice versa by utilizing the piezoelectric effect of the substrate. An IDT comprises opposing "electrode combs" in which interdigitated metal fingers are disposed on a piezoelectric substrate. Rayleigh surface acoustic waves are formed on the substrate by electrically exciting the fingers. Other wave types, shear waves, and longitudinally polarized waves travel through the volume and are absorbed, thus requiring optimized metal grid thickness for filter applications. Conversely, electrical signals can be generated across the fingers by surface acoustic waves propagating in the piezoelectric substrate material beneath the transducer.

[0004] SAW devices typically use a wafer made of monolithic quartz, LiNbO3, or LiTaO3 crystal as the piezoelectric material. However, depending on the piezoelectric material used, the use of a piezoelectric substrate in the case of LiNbO3 or LiTaO3 leads to high temperature sensitivity, or in the case of quartz, it results in weak electromechanical coupling.

[0005] Furthermore, the velocity of elastic waves is generally limited by the properties of single-crystal materials, especially considering that the phase velocity remains between 3000 m / s and 4000 m / s for most of the time. In fact, in the case of quartz, Rayleigh surface acoustic waves are the most commonly used mode, and their phase velocities range from 3000 m / s. -1 Change to 3500m.s -1 The use of shear waves allows for speeds up to 5100 m / s. -1 The phase velocity. In quartz, coupling is limited to 0.5%. In the case of lithium tantalate, Rayleigh waves exhibit a velocity at 3000 m·s. -1 Up to 3500m.s -1 The phase velocity is within a certain range, but mode coupling is almost non-existent at 2%. Rayleigh waves on lithium niobate reach as high as 3900 m / s.-1 The phase velocity, with a coupling factor of 5.6%, can reach 8% when a SiO2 passivation layer is used on the IDT.

[0006] Shear waves (also known as pseudomodes) on LiTaO3 and LiNbO3 exhibit radiation leakage (so-called leakage modes). In this case, the surface partially guides the wave. Therefore, the electrode grid plays a major role in capturing energy near the surface. The phase velocity of both materials is 4000 m / s. -1 Up to 4500m.s -1 Within the range.

[0007] Finally, compression modes can also be excited along certain crystal cuts on LiTaO3 and LiNbO3 substrates. However, these modes are inherently leaky, thus requiring a specific relationship between electrode thickness and frequency to minimize leakage effects caused by wave radiation into the bulk.

[0008] One method to overcome leakage effects has led to the use of composite substrates. Composite substrates comprise a piezoelectric layer formed on a base substrate. Composite substrates offer a wide range of material choices for the base substrate, including base substrate materials with high acoustic wave propagation speeds, such as diamond, sapphire, silicon carbide, or silicon. Similar to optical devices, the use of such base substrates enables the guidance of modes.

[0009] Composite substrates can combine strong electromechanical coupling (i.e., an electromechanical coefficient k greater than 1%). s 2 It improves the performance of SAW devices and provides design flexibility by enhancing temperature stability (i.e., a frequency temperature coefficient (TCF) of less than 20 ppm / K).

[0010] However, acoustic wave devices are limited to operating frequencies from approximately 1 GHz to 3 GHz. For a given phase velocity, the electrode pitch or mechanical period p of the comb electrode determines the acoustic wavelength λ, given by the relationship p = λ / n, where n ≥ 2, and is typically equal to 2. Operating at frequencies above 2 GHz requires metal dimensions and thicknesses of approximately 100 nm or less, which presents structural stability issues. Therefore, in practice, it is difficult to further miniaturize the comb electrode when higher operating frequencies are required. This is partly due to the need for lithography techniques with higher resolution than the I-line lithography currently used in the SAW industry, and partly due to electrical losses inherent in this structure.

[0011] Therefore, a great deal of technical effort is required to create SAW devices above 3 GHz. Summary of the Invention

[0012] Therefore, the object of the present invention is to overcome the aforementioned disadvantages by providing an interdigitated transducer structure with improved parameters for an acoustic wave device, and to provide an acoustic wave device that can operate at frequencies exceeding 3 GHz but can still be manufactured using standard I-line lithography. Furthermore, a second object of the present invention is to provide a transducer structure in which the transfer function can be adapted to specific needs.

[0013] The second objective of the present invention is achieved by a transducer structure for an acoustic device according to claim 1, the transducer structure comprising: a piezoelectric layer; a pair of interdigitated comb electrodes, the pair of interdigitated comb electrodes comprising a plurality of electrode devices having a pitch p, characterized in that the interdigitated comb electrodes are embedded in the piezoelectric layer, and wherein the pair of interdigitated comb electrodes comprises adjacent electrode devices belonging to different comb electrodes, and the pair of interdigitated comb electrodes comprises a second region or more regions in which two or more adjacent electrode devices belong to the same comb electrode, and the distance between them is the same as the distance between adjacent electrode devices belonging to different comb electrodes.

[0014] According to a variant, the two or more adjacent electrode devices belonging to the same comb electrode have the same geometry as adjacent electrode devices belonging to different comb electrodes.

[0015] By linking adjacent electrode devices to the same potential while maintaining the same mechanical cycle, the sound source is removed from the system, thereby reducing electromechanical coupling. This can be used to customize electromechanical coupling, thus adjusting the filter's transfer function when forming a filter, i.e., by fine-tuning the bandpass width. Further stability of the electrode can be obtained by embedding it.

[0016] According to a variant, the acoustic impedance of the electrode device can be less than the acoustic impedance of the piezoelectric layer.

[0017] Here, since the electrode device is embedded in the piezoelectric layer, and the acoustic impedance of the electrode device is less than that of the piezoelectric layer, a shear wave-like propagation mode (electrode mode) that is essentially confined to the volume of the electrode device can be excited. In fact, the boundary conditions are those that allow this shear mode to be excited within the electrode device. Due to the acoustic impedance contrast, the reflection at the lateral edges of the electrode device is sufficiently large to essentially confine the energy within the electrode. Due to the grid configuration of the interdigitated comb electrodes and the presence of alternating polarity, a vibration is still induced within the piezoelectric layer, leading to coherence between the electrode vibrations. This results in a resonant phenomenon where one electrode opposite the next adjacent electrode undergoes phase vibration. The operating acoustic wavelength λ of the transducer and the resonant frequency f of the transducer structure are related. r Related to, fr =v / 2p = v / λ, where v is the velocity of sound waves propagating in the substrate. Therefore, in a given geometry, a much higher equivalent phase velocity than described above can be observed, for example, even approximately 10000 m / s. -1 Since the bulk acoustic waves inside the electrode device resonate at a higher frequency compared to the guided waves in the piezoelectric layer of the aforementioned prior art, this mode allows the transducer structure to operate at higher frequencies above 3 GHz, and is not limited by the manufacturing technology of I-line lithography compared to prior art transducer structures.

[0018] In particular, the ratio between the acoustic impedance of the electrode assembly and the acoustic impedance of the piezoelectric layer is preferably less than 0.5. Material combinations that produce electromechanical coupling of greater than 2%, and preferably greater than 3%, are beneficial for establishing modes within the electrodes and coherent coupling between the electrodes.

[0019] According to a variant, the pitch p satisfies the Bragg condition given by p = λ / 2, where λ is the operating acoustic wavelength of the transducer. Under this condition, the electrode modes are excited more efficiently.

[0020] According to a variation of the invention, the metallization ratio a / p of the electrode device can be between 0.3 and 0.75, and particularly between 0.4 and 0.65, where "a" is the width of the electrode device and "p" is the pitch of the electrode device. Using an a / p ratio within this range is beneficial for forming excitation acoustic waves in the electrode device and for reducing or suppressing the contribution of the acoustic surface modes of the piezoelectric layer.

[0021] According to a variation of the invention, the piezoelectric layer can be disposed on a base substrate. Using a base substrate is advantageous for confining energy to the vicinity of the surface, and particularly to the interior of the electrode device.

[0022] According to a variant, the transducer structure may also include an attachment layer, particularly silicon dioxide (SiO2) located between the piezoelectric layer and the base substrate. Various materials can be used as the piezoelectric layer and the underlying base substrate via the attachment layer to optimize the transducer structure. Silicon dioxide can be used to improve the temperature coefficient of frequency (TCF).

[0023] According to a variant, the transducer structure may further include a high-speed layer located between the piezoelectric layer and the base substrate, wherein the high-speed layer is made of a material whose material and crystal orientation allow for a higher shear wave phase velocity compared to the piezoelectric layer. This allows for the acceleration of the fundamental shear mode, whose phase velocity can be greater than the slow shear bulk wave (also known as surface skimming bulk wave (SSBW)) velocity of the base substrate. In this case, the fundamental shear mode cannot be guided in the piezoelectric layer, but will instead be dissipated in the base substrate.

[0024] According to a variant, the high-speed layer can be positioned between the attachment layer and the base substrate. By positioning the attachment layer between the piezoelectric layer and the high-speed layer, acceleration characteristics can be utilized without changing the attachment process of the piezoelectric layer to the underlying structure, thus enabling the high-quality piezoelectric layer to be obtained independently of the material selection of the high-speed layer.

[0025] According to a variant, the transducer structure may also include a trap enrichment layer, particularly a polysilicon trap enrichment layer, located between the piezoelectric layer and the base substrate. The trap enrichment layer can suppress leakage current.

[0026] According to a variant, the trap enrichment layer can be positioned between the high-speed layer and the base substrate. This order allows the individual advantages of each layer to be maintained within the overall structure.

[0027] According to a variant, the transducer structure may also include a capping layer located above the embedded electrode devices and the piezoelectric layer. This further improves the guidance of shear modes in the electrodes and further reduces the possibility of electromigration.

[0028] According to a variant, the capping layer can be made of a material that allows for a higher shear wave phase velocity compared to the material of the piezoelectric layer and / or has a crystal orientation that allows for a higher shear wave phase velocity compared to the crystal orientation of the piezoelectric layer. Therefore, the material of the capping layer can be selected such that the velocity of the fundamental shear mode is increased compared to its velocity in the piezoelectric layer. This facilitates dissipation into the volume of the base substrate, so that essentially only electrode modes are retained in the guiding domain of the piezoelectric layer.

[0029] According to a variation of the invention, the transducer structure may further include a Bragg mirror located below the piezoelectric layer and / or below the embedded electrode device. The Bragg mirror reduces energy loss toward the base substrate and can increase the mechanical stability of the device structure.

[0030] According to a variation of the invention, the thickness of the embedded electrode device can be less than or equal to the thickness of the piezoelectric layer. Therefore, using electrodes thicker than those in prior art transducer structures not only allows for the establishment of shear modes within the electrodes but also increases electrode stability and reduces ohmic losses.

[0031] According to a variation of the present invention, the thickness t of the electrode device e Satisfying λ>t e >0.1*λ. Within this thickness range, the electromechanical field near the surface can be concentrated in a region with a thickness comparable to the electrode thickness in the single-crystal case or the piezoelectric layer plus electrode thickness in the composite wafer case. This will result in improved electromechanical coupling and spectral purity, thereby allowing for single or at least a limited number of mode contributions to the device response.

[0032] According to a variation of the invention, the acoustic impedance of the base substrate of the composite substrate is approximately equal to the acoustic impedance of the piezoelectric layer, particularly within ±25% of the acoustic impedance of the piezoelectric layer, and more particularly within ±15% of the acoustic impedance of the piezoelectric layer. Specifically, when the electrodes have the same thickness as the piezoelectric layer, impedance matching allows for the limitation of shear modes in the electrodes.

[0033] According to a variation, the embedded electrode device can be filled into a groove in the piezoelectric layer. The cross-section of the groove can be pyramidal, trapezoidal, V-shaped, or U-shaped, and / or the sidewalls and / or bottom of the groove can be convex, concave, or scalloped. In particular, a pyramidal or trapezoidal shape with shorter parallel sides at the surface of the transducer structure results in an improved quality factor compared to a groove with vertical walls.

[0034] According to a variation of the invention, a dielectric layer may be provided on the bottom of the groove. According to another variation of the invention, the sidewalls and bottom wall of the groove may be covered with a conductive material, and the remainder of the groove may be filled with a dielectric material. According to another variation of the invention, the groove may extend through a piezoelectric layer, and the sidewalls of the groove may be covered with a conductive material, and the remainder of the groove may be filled with a dielectric material. According to another variation of the invention, only the sidewalls facing the piezoelectric layer may be covered with a conductive material. According to another variation of the invention, the dielectric material may be a material having a higher shear wave phase velocity than the conductive material. As already explained, this will allow for a faster phase velocity of the fundamental shear wave, enabling it to exceed the SSBW velocity and thus allowing it to dissipate in the base substrate.

[0035] According to a variation of the invention, the sign of the temperature coefficient of frequency of the dielectric material can be opposite to that of the temperature coefficient of frequency of the conductive material. Therefore, the device can be used over a wider temperature range.

[0036] According to a variation of the invention, the dielectric material of the cover layer and the dielectric material filled in the groove can be the same. Therefore, two advantageous features can be achieved in a single process step.

[0037] According to a variant, the electrode device can be made of a material lighter than manganese, particularly aluminum or aluminum alloys including Cu, Si, or Ti. In particular, the combination of aluminum and lithium tantalate produces a coupling factor greater than 3%, while the fundamental shear mode in the piezoelectric layer is absent.

[0038] According to variations, the piezoelectric layer can be lithium tantalate (LiTaO3) or lithium niobate (LiNbO3). For both materials, composite substrates, especially so-called piezoelectric on insulator (POI) substrates, can be obtained on an industrial scale.

[0039] According to variations, the base substrate can be silicon, silicon dioxide, glass, quartz, fused silica, glass, LiTaO3, LiNbO3, or silicon, particularly Si(111). Using these substrates, the shear modes within the electrode device remain, while the fundamental shear modes in the piezoelectric layer can be suppressed. In Si(111), the SSBW speed is particularly low compared to Si(100). Meanwhile, for example, by using a piezoelectric on insulator (POI) substrate, piezoelectric layers on glass or SiO2 substrates can be obtained on an industrial scale.

[0040] According to a variation, the high-speed layer is one of AlN, Al2O3, Si3N4, SiC, or a carbon-based material, particularly single-crystal diamond, amorphous carbide, or nanocrystalline polycrystalline diamond. According to a variation, the capping layer can be one of AlN, Al2O3, Si3N4, SiC, or a carbon-based material, particularly single-crystal diamond, amorphous carbide, or nanocrystalline polycrystalline diamond. According to a variation, the dielectric material can be a carbon-based material (particularly single-crystal diamond, amorphous carbide, or nanocrystalline polycrystalline diamond) or AlN or SiO2. These materials allow for a reduction in the contribution of the fundamental shear mode. Using SiO2 can improve TCF characteristics.

[0041] According to a variant, regions having two or more, and particularly at least three, adjacent electrode devices that may belong to the same comb electrode are not periodically distributed, but rather randomly distributed. Specifically, they are characterized in that adjacent regions have different distances relative to each other within the extension of the transducer structure. By reducing the symmetry of the system, spurious contributions from higher-order periodicity can be reduced or even suppressed.

[0042] According to a variant, a region having two or more adjacent electrode devices belonging to the same comb electrode can have different numbers of adjacent electrode devices belonging to the same comb electrode. By connecting regions with different numbers of adjacent electrode devices to the same potential, spurious contributions can be further reduced.

[0043] According to a variant, the electrode device of the transducer structure can have dimensions achievable by I-line lithography, particularly a width greater than 350 nm. Therefore, compared to lithography tools using 248 nm or 193 nm or even shorter wavelengths, cheaper lithography equipment can be used to manufacture devices that can be used at frequencies higher than 3 GHz.

[0044] The object of this invention is also achieved using an acoustic device comprising at least one transducer structure as described above, and particularly an acoustic resonator and / or an acoustic filter and / or an acoustic sensor. Acoustic devices capable of operating at frequencies greater than 3 GHz can be fabricated using I-line lithography without the use of more advanced and therefore more expensive lithography tools. Therefore, the use of electrode shear wave modes allows for an extended frequency range without altering the patterning technique, compared to Rayleigh surface waves using SAW devices whose frequencies are limited to a maximum of 2 GHz. When using a composite substrate, a reduced first-order frequency temperature coefficient (TCF) of less than 20 ppm / K can be achieved, resulting in temperature-stable device performance. Using this invention, acoustic bandpass filters with relative bandwidths greater than 5% or even 10% and up to 15% can be achieved.

[0045] According to a variant, the acoustic device may include a radio frequency (RF) supply device configured to drive the transducer structure using an RF signal higher than 3 GHz. Therefore, it is possible to implement an I-line lithography apparatus operating at frequencies higher than 3 GHz.

[0046] According to a variant, the acoustic device may include the input and output transducer structures as described above.

[0047] The object of the present invention is also achieved using a method employing the transducer structure described above, the method comprising the steps of: applying an alternating potential to two interdigitated electrodes to excite shear modes that, compared to the piezoelectric layer, occur primarily or exclusively within the electrode device and have an equivalent velocity higher than the fundamental shear wave mode of the piezoelectric layer. The vibration amplitude in the electrode device is at least greater than that in the piezoelectric layer. Using higher frequencies of the shear waves propagating in the electrode device of the transducer structure described above (particularly for ladder filters and / or impedance filters and / or coupling filters), devices operating above 3 GHz and more particularly above 3.5 GHz are obtained. Simultaneously, the devices can be formed using I-line lithography.

[0048] The object of the present invention is also achieved using a method employing a transducer structure as described above, the method comprising the steps of: applying an alternating potential to two interdigitated electrodes to excite shear modes in the electrode arrangement using a pair of neutral lines without exhibiting shear movement within the electrodes, and having an equivalent velocity higher than the fundamental shear wave mode of the piezoelectric layer. This mode allows for the use of higher resonant frequencies, enabling the realization of devices that function above 3 GHz, and particularly above 3.5 GHz, similar to ladder filters and / or impedance filters and / or coupling filters, while using I-line lithography to pattern the device. Attached Figure Description

[0049] The invention can be understood from the following description taken in conjunction with the accompanying drawings, wherein reference numerals identify features of the invention.

[0050] Figure 1 An example is shown of an interdigitated transducer structure on a composite substrate of an acoustic device according to a first embodiment of the present invention.

[0051] Figure 2 The illustration demonstrates the use of Figure 1 The pattern obtained by the illustrated transducer structure.

[0052] Figure 3a The simulated broadband harmonic admittance of an example excitation mode according to a first embodiment of the present invention is shown.

[0053] Figure 3b A grid view illustrating the vibrations of the observed patterns is shown.

[0054] Figure 3c A grid view illustrating vibrations in modes with opposite phases is shown.

[0055] Figure 3d As shown Figure 3a An enlarged view of the simulated broadband harmonic admittance of the excitation mode is shown.

[0056] Figure 3e The conductance and resistance of the excitation mode are shown.

[0057] Figure 3f The dispersion characteristics of the excitation mode are shown.

[0058] Figures 4a to 4c Three different electrode shapes within the piezoelectric layer are illustrated. Figure 4a According to the second embodiment, Figure 4b According to the first embodiment, and Figure 4cAccording to the third embodiment.

[0059] Figure 4d The harmonic susceptance corresponding to three different electrode geometries is illustrated.

[0060] Figure 4e The harmonic conductance corresponding to three different electrode geometries is illustrated.

[0061] Figures 4f to 4h Further examples of electrode shapes with concave, convex, or serrated sidewalls are shown.

[0062] Figure 4i and Figure 4j Two further variations of the electrode shape are illustrated, wherein a dielectric layer is present in the groove.

[0063] Figure 5 The effect of electrode thickness on the occurrence of shear vibration modes confined within the electrode is illustrated.

[0064] Figure 6 An interdigitated transducer structure of an acoustic device according to a fourth embodiment of the present invention is illustrated.

[0065] Figure 7a An interdigitated transducer structure of an acoustic device according to a fifth embodiment of the present invention is illustrated.

[0066] Figure 7b A simulated broadband harmonic admittance of the excitation mode according to a fifth embodiment of the present invention is shown.

[0067] Figure 7c The simulated broadband harmonic admittance of the excitation mode of a variant example according to the fifth embodiment of the present invention is shown.

[0068] Figure 7d The simulated broadband harmonic admittance of the excitation mode of a variant example according to the fifth embodiment of the present invention is shown.

[0069] Figure 8 A sixth embodiment of the transducer structure according to any one of the first to fifth embodiments of the present invention is shown.

[0070] Figure 9a A seventh embodiment of the present invention is illustrated, and it relates to a filter at 5 GHz.

[0071] Figure 9b Examples are given based on Figure 9a The transfer function of the filter.

[0072] Figure 10a A higher-order mode according to the present invention is illustrated.

[0073] Figure 10b The harmonic conductance and resistance of this mode are illustrated for LiTaO3 substrates and SiO2 substrates.

[0074] Figure 10c The harmonic conductance and resistance of this mode are illustrated for Al2O3 substrates and Si substrates.

[0075] Figure 11 An eighth embodiment of the present invention with a suppressed sound source is illustrated.

[0076] Figures 12a to 12c Three variations of the ninth embodiment of the present invention are illustrated.

[0077] Figures 13a to 13d Examples of obtaining such Figure 12a The process for the illustrated electrode shape.

[0078] Figure 14a and Figure 14b The admittance and impedance of the transducer structure according to the ninth embodiment are illustrated when diamond-like carbon is used as the dielectric.

[0079] Figure 14c A grid view illustrating the vibration patterns observed in a transducer structure according to the ninth embodiment is shown.

[0080] Figure 15a and Figure 15b The admittance and impedance of the transducer structure according to the ninth embodiment are illustrated when aluminum nitride is used as the dielectric.

[0081] Figure 16a The conductivity G and resistance R of the transducer structure according to the ninth embodiment are illustrated when silicon dioxide is used as the dielectric. Figure 16b The amplification of the resonance of the aforementioned transducer structure is illustrated. Figure 16c An example of the anti-resonance amplification of the transducer structure is illustrated.

[0082] Figure 16d A fourth variation of the transducer according to the ninth embodiment is illustrated.

[0083] Figure 17a and Figure 17b Two variations of the transducer structure according to the tenth embodiment are illustrated.

[0084] Figure 18a and Figure 18b Two images taken with an electron microscope are shown, illustrating a practical example of a transducer according to the present invention.

[0085] Figure 18c Examples are shown that are used in simulation Figure 18aand Figure 18b The finite element mesh shows the behavior of a real-world example.

[0086] Figure 19a Experimental measurements of susceptance and resistance are illustrated in practical examples.

[0087] Figure 19b Examples are given by Figure 18c The results of susceptance and resistance obtained by numerical simulation of the structure shown are shown. Detailed Implementation

[0088] The invention will now be described in more detail using advantageous embodiments, with reference to the accompanying drawings. The described embodiments are merely possible configurations according to the invention, and it should be remembered that the individual features described above can be provided independently or in combination to achieve other embodiments according to the invention.

[0089] Figure 1 An interdigitated transducer structure of an acoustic device according to a first embodiment of the present invention is illustrated.

[0090] The transducer structure 100 includes an acoustic wave propagation substrate 102. The acoustic wave propagation substrate 102 may be a composite substrate 102 including a piezoelectric layer 104 formed on a base substrate 106. The composite substrate may be a so-called piezoelectric substrate on insulator (PBI) or a POI substrate. In other embodiments, the piezoelectric layer may be thick enough to form a bulk material.

[0091] The piezoelectric layer 104 described herein by way of example may be lithium niobate (LiNbO3) or lithium tantalate (LiTaO3). The piezoelectric material layer 104 can be directly bonded (e.g., using SmartCut). TM The piezoelectric layer 104 formed on the base substrate 106 is attached to the base substrate 106 using a layer transfer technique. The thickness of the piezoelectric layer 104 formed on the base substrate 106 is about one wavelength λ or less, particularly about 2 μm or less, particularly less than 0.5λ, and even particularly less than 0.4λ.

[0092] The piezoelectric layers described by way of example in this article can be: lithium niobate (LiNbO3), particularly LiNbO3 with a crystal orientation as defined in standard IEEE 1949Std-176: (YXl) / θ in the case of 36°<θ<52° or 60°<θ<68° or 120°<θ<140°, and (YXt) / Ψ in the case of 85°<Ψ<95°, and (YXwlt) / ΦθΨ in the case of Φ=90°, -30°<θ<+45° and 0°<Ψ<45°; or lithium tantalate (LiTaO3), particularly LiTaO3 with a crystal orientation as defined in standard IEEE 1949Std-176 ((YXl) / θ in the case of 36°<θ<52°), more particularly with a 42° Y-cut, X-propagated orientation as defined in standard IEEE 1949Std-176. 1949Std-176 is defined as LiTaO3 with a (YXl) / 42° cut.

[0093] As already mentioned, according to a variant, the thickness of the piezoelectric layer 104 can be greater than the wavelength λ, so that the piezoelectric layer thickness can also be equivalent to that of a bulk piezoelectric material.

[0094] The base substrate 106 used in the first embodiment of the present invention is a silicon substrate, silicon, quartz, fused silica, or glass. For such a substrate, the slow shear volume wave velocity (SSBW) is lower than one of the basic acoustic volume shear modes in the piezoelectric layer, so that the volume shear modes of the piezoelectric layer are diffused and radiation from the surface to the volume is suppressed.

[0095] Other substrates with high acoustic propagation speeds equal to or greater than 4500 m / s, such as silicon, diamond, sapphire, silicon carbide, silicon nitride, or aluminum nitride, can be used. However, in this case, a basic guided shear mode can exist, which corresponds to the shear mode excited when the electrode is positioned on the piezoelectric layer.

[0096] In this embodiment, the thickness of the base substrate 106 is greater than the thickness of the piezoelectric layer 104. A preferred case corresponds to a base substrate thickness that is at least ten times, and particularly 50 to 100 times, greater than the thickness of the piezoelectric layer 104.

[0097] Furthermore, the acoustic impedance of the base substrate 106 of the composite substrate 102 is approximately the acoustic impedance of the piezoelectric layer, particularly within a range of ±25%, and more specifically within a range of ±15%. According to a variant, these are identical.

[0098] In a variant of the invention, the base substrate 106 may further include a trap enrichment layer adjacent to the piezoelectric material layer above it. This trap enrichment layer can improve the isolation properties of the base substrate 106 and can be formed from at least one of a polycrystalline material, an amorphous material, or a porous material (such as polycrystalline silicon, amorphous silicon, or porous silicon). The term "trap enrichment" should be understood as a layer that can absorb charge but does not form a conductive layer.

[0099] Composite substrates can be obtained by transferring piezoelectric layers to a base substrate using layer transfer methods. Methods such as bonding and thinning, or smart-cut methods that allow for subwavelength layer transfer, can be used. TM The layer transfer method. Such composite substrates may include additional layers or stacked layers, such as bonding layers or attachment layers (especially SiO2), or other functional layers, such as trap enrichment layers, Bragg mirrors, low-speed / high-speed stacks.

[0100] In a variant, the base substrate 106 may be a semiconductor-on-insulator (SOI) substrate. SOI substrates are obtained through molecular adhesion, for example using an intermediate SiO2 (bonding) layer and a transferred silicon layer, such as the Smart-Cut described above. TM Process.

[0101] The transducer structure 100 also includes a pair of opposing interdigitated comb electrodes 108 and 110, each comb electrode having a plurality of electrode devices 112_i and 114_j (here 1≤i, j≤4), the plurality of electrode devices extending from their respective conductive portions 116 and 118 and interdigitated with each other. The comb electrodes 108 and 110, and in particular the electrode devices 112_i, 114_j, are formed of any suitable conductive metal, provided that the acoustic impedance is lower than that in the piezoelectric layer 104, for example, pure aluminum or an alloy of Al such as doped with Cu, Si, or Ti. Typically, electrode materials lighter than manganese, thus starting with chromium or lighter elements, are suitable. According to this embodiment, the aspect ratio a / p of the electrode devices 112_i, 114_j is between 0.3 and 0.75, and particularly between 0.4 and 0.65, where a is the width of the electrode device and p is the pitch of the electrode device. The metallization ratio or aspect ratio a / p and thickness t of electrode devices 112_i and 114_j e These are parameters related to radiation loss and electromechanical coupling in control devices.

[0102] The electrical load 120 is illustrated as being coupled across the comb electrodes 108, 110. However, it will be understood that the source potential 120 may also be coupled across the electrodes 108, 110, depending on whether the transducer 100 is used to excite acoustic waves in the substrate 102 or to convert the received acoustic waves into electrical signals or both.

[0103] The electrode arrays (e.g., 112_1 to 112_4 and 114_1 to 114_4) are interdigitated and connected to an alternating potential via their respective comb electrodes 108 and 110. The alternating potential can be +V and -V as shown, or mass and load / source potentials.

[0104] In this embodiment, electrode devices 112_i and 114_j all have the same length l, width a, and thickness t. e According to a variation of the invention, the electrode devices 112_i and 114_j may also have different lengths l and / or widths a and / or thicknesses t. e .

[0105] Electrode devices 112_i and 114_j, and their corresponding comb electrodes 108 and 110, are disposed in the same plane. According to a variant, electrode devices 112_i and 114_j are embedded in piezoelectric layer 104, and comb electrodes 108 and 110 that provide electrical connections between the electrode devices can be placed on piezoelectric layer 104.

[0106] Furthermore, corresponding to the Bragg condition, the electrode pitch p will be defined as λ / 2 for the transducer structure 100, where λ is the operating wavelength of the acoustic wave. The electrode pitch p corresponds to the distance between two adjacent electrode devices from opposing comb electrodes 108 and 110, for example, the distance between 112_3 and 114_3. In this case, the wavelength λ corresponds to the distance between two adjacent electrode devices from the same comb electrode 108 or 110, for example, the distance between 112_3 and 112_4. Under this Bragg condition, the transducer is said to operate at a frequency f. r The transducer operates in synchronous mode, where all excitation acoustic waves within the transducer structure are coherent and in phase. Therefore, the electrode pitch p defines the operating frequency of the transducer structure. The operating frequency f... r Fixed according to the phase consistency condition given by v / 2p, where v is the effective phase velocity of the acoustic wave propagating in the transducer structure 100 and p is the electrode pitch of the transducer structure 100.

[0107] Electrode devices 112_i and 114_j are embedded in the piezoelectric layer 104, preferably completely embedded in the piezoelectric layer 104, such that their thickness t e The thickness t is equal to or less than that of the piezoelectric layer 104.

[0108] The thickness of electrode devices 112_i to 114_j should satisfy the following relationship with respect to wavelength λ: 0.1 <t e / λ<1.

[0109] Therefore, electrode devices 112_i to 114_j are thicker than electrodes in prior art interdigitated transducer structures having interdigitated electrodes formed on a piezoelectric substrate. Consequently, electrode devices 112_i to 114_j offer better stability and reduced electrical losses. Furthermore, power handling is improved because the embedded electrodes limit the possibility of acoustic and electromigration due to power effects. Positioning the metal in the grooves prevents direct metal contact due to surface diffusion and metal migration.

[0110] The conductive portions 116 and 118 of the comb electrodes 108 and 110 can be disposed on the piezoelectric layer 104 and / or the embedded electrode devices 112_i and 114_j.

[0111] The charge distribution in electrodes 108 and 110 of transducer structure 100 excites sound waves along the electric field direction. This means that the extension direction z of electrode devices 112_i and 114_j perpendicular to electrodes 108 and 110, such as... Figure 1 As shown by arrow E in the diagram.

[0112] In existing SAW devices, different modes can exist, such as Rayleigh surface acoustic waves, Lamb waves, or shear waves. In contrast, the transducer structure 100 of the present invention enables the realization of a new mode that results in a shear-like mode primarily concentrated within the electrodes, which will be referred to below as the electrode mode.

[0113] This is because the electrode device is embedded in the piezoelectric layer and the acoustic impedance of the electrode device is less than that of the piezoelectric layer. In fact, the boundary conditions make it possible to excite shear modes within the electrode device. The maximum value of the vibration occurs at the center of the electrode, and the sign changes from one electrode device to the next adjacent electrode device.

[0114] Due to the acoustic impedance contrast, the reflections at the lateral edges of the electrode assembly are large enough to essentially confine the energy within the electrodes. The grid configuration of the interdigitated comb electrodes, and the presence of alternating polarity, still induces a vibration within the piezoelectric layer. This vibration leads to coherence between the electrode vibrations, resulting in resonance, but the mode can still be guided.

[0115] The operating acoustic wavelength λ of the transducer and the resonant frequency f of the transducer structure r Related to, f r =v / 2p =v / λ, where v is the speed of sound wave propagation in the substrate.

[0116] Figure 2The mode is schematically illustrated in the figure, which is a top view of transducer structure 100a and two adjacent electrode devices 112_3 and 114_3. Numerical simulations were performed, see S. Ballandras et al., Finite-element analysis of periodic piezoelectric transducers, Journal of Applied Physics 93, 702 (2003); https: / / doi.org / 10.1063 / 1.1524711, and the excitation of this mode, in which shear movement is concentrated within the electrode devices, has been demonstrated. Indeed, shear motion also exists in piezoelectric layer 104; however, the vibration amplitude is larger in the electrodes with alternating vibration directions from one electrode to another compared to the vibration amplitude in piezoelectric layer 104.

[0117] Figure 3a The simulated broadband harmonic admittance of the excitation mode of a first example according to a first embodiment of the present invention is shown.

[0118] In this embodiment, the transducer structure includes an Al-Cu electrode embedded in a LiTaO3 piezoelectric layer on a silicon substrate. The wavelength λ of the transducer structure is equal to 2.8 μm, therefore p = 1.4 μm, and the aspect ratio a / p of the electrode is equal to 0.43. In this embodiment, as... Figure 1 As illustrated, electrodes 112_i and 114_j are embedded in piezoelectric layer 104 and represent continuous material from a geometric point of view, although the physical properties of the resulting layer are periodically distributed.

[0119] As can be seen from the results illustrated below, the pattern's signature is similar to that at approximately 9850 m.s -1 The equivalent phase velocity propagation leakage-SAW is therefore higher than that of the swept volume wave (SSBW) in silicon dioxide, which is typically around 3750 m / s. -1 In fact, considering a metallization ratio of approximately 0.43 a / p and a resonant frequency of 3.45 GHz, the electrical cycle of the structure is 2.8 μm, achieving approximately 9850 m·s. -1 The equivalent speed was obtained by multiplying the resonant frequency of 3.45 GHz by the electrical period of 2.8 μm. The mode speed was calculated as the sum of the frequencies at the beginning and end of the stopband multiplied by the mechanical period, as further explained below.

[0120] Figure 3a The shear mode for the excited electrode is shown (as already shown in the diagram). Figure 2The simulation data obtained using the configuration illustrated in the figure. The graph shows the conductance G (in s) on the left Y-axis and the susceptance B (in s) on the right Y-axis as a function of frequency in MHz for both the G and B harmonics. As can be seen, broadband harmonic admittance is observed, with shear resonance at 3.45 GHz. Shear resonance at 3.45 GHz is the dominant excitation mode. Furthermore, two much smaller contributions are observed around 1.5 GHz and around 7 GHz.

[0121] Figure 3b and Figure 3c The deformation within the transducer structure is illustrated. This movement is concentrated only in the region of the interdigitated electrodes 108 and 110. Vibration in the piezoelectric layer 104 is barely visible in the simulation.

[0122] According to the present invention, the parameters mentioned above cause the shear body acoustic wave mode to be excited primarily within the metal electrode devices 112_i, 114_j, polarized along the y-direction, and displaced along the z-direction. The useful E-field extends along the x-direction. Therefore, the vibration is mainly located within the electrodes, where the deformation is close to the fundamental shear body wave of the electrode itself. Although shear motion is also observed within the piezoelectric layer 104, the largest vibration amplitude occurs in the electrodes 112_i, 114_j, which have alternating vibration directions.

[0123] When transducer 100 is excited by the +V / -V polarization structure, the shear displacement direction alternates from one electrode to the other. This phase reversal of the electrodes increases charge accumulation at the electrode edges, thereby increasing the excitation of volume modes in electrodes 112_i and 114_j. The piezoelectric layer 104 confines the stress on the electrode edges, and because the transducer structure operates under Bragg conditions, coherent vibrations occur when the boundary conditions are satisfied along the grid. Although shear motion is also present in the piezoelectric layer 104, the largest vibration amplitudes occur in the electrodes with alternating vibration directions from one electrode to the other.

[0124] Therefore, the main acoustic wave propagating in the transducer structure is a bulk shear wave that is essentially confined within electrodes 112_i and 114_j. The resonant frequency f of the transducer structure 100 is... r By f r =v / 2p=v / λ is given, where v is the propagation speed of the sound wave in the sound wave propagation substrate, and λ is the operating sound wave wavelength of the transducer.

[0125] Because the bulk acoustic waves in the electrode device resonate at frequencies higher than the pilot wave of the fundamental shear mode in the piezoelectric layer, this transducer structure can operate at higher frequencies, particularly above 3 GHz. Therefore, higher frequencies than existing devices can be utilized without the need for more complex lithography tools, especially I-line lithography steppers, used to move to features smaller than those currently used in the SAW industry.

[0126] Therefore, a key aspect of the invention is that this type of structure enables the excitation of shear modes primarily located within the electrodes, similar to the shear body modes confined within the electrode assembly as described above. Electrode modes can be adapted to function as pseudo-modes or leakage modes, confined by reduced but not completely suppressed leakage, resulting in synchronization between the electrodes. This mode exhibits a significantly higher equivalent velocity than that achievable with prior art interdigitated transducer structures on composite substrates utilizing shear modes in piezoelectric layers. Other modes are much weaker or even suppressed, primarily due to the use of a silicon substrate with a low SSBW velocity, thus allowing dissipation of standard shear modes.

[0127] The configuration of the present invention can be understood as a separate network or grid of resonators, wherein the resonators are coupled via a piezoelectric layer, so that even if the phase velocity is higher than that of the fundamental shear mode, dissipation into the substrate is at least largely prevented, thus being comparable to the leakage mode.

[0128] Figure 3d The first embodiment of the present invention is shown. Figure 3a The amplification of the simulated broadband harmonic admittance of the excitation mode is shown.

[0129] Figure 3d The graph shown represents the conductance in s (S) on the left Y-axis and the susceptance in s (S) on the right Y-axis for both the G and B harmonics, within the frequency range of 3400 MHz to 3600 MHz on the X-axis. A resonance at approximately 3.475 GHz and an anti-resonance at approximately 3.525 GHz can be observed. The resonance and anti-resonance are well separated, giving a coupling factor of approximately 3%. The resonance also occurs at the beginning of the stopband.

[0130] In this specific case, a reflection coefficient of approximately 9%, a resonance quality factor of approximately 500, and an anti-resonance of approximately 1000 were achieved.

[0131] The coupling factor can be improved by modifying the characteristics of the transducer structure (such as the aspect ratio a / p, electrode thickness, and materials used). In particular, the aspect ratio a / p and thickness of the electrodes allow for control over velocity, electromechanical coupling, quality factor, or radiation loss and reflection coefficient.

[0132] Figure 3eThe conductivity and resistance of the excitation mode of a variant of the first embodiment obtained with the same material selection but an aspect ratio a / p of 0.57 are shown.

[0133] In the same configuration, shear modes concentrated within the electrodes are excited. The graph shows the conductance in s (S) on the left Y-axis and the susceptance in s (S) on the right Y-axis for both G and R harmonics, within the frequency range of 3450 MHz to 3750 MHz on the X-axis. Resonance at approximately 3.55 GHz and anti-resonance at approximately 3.7 GHz are obtained.

[0134] In this scenario, the increase in aspect ratio a / p from 0.43 to 0.57 results in an increase in the equivalent phase velocity of the propagation mode to greater than 10 km / s. -1 This causes the coupling factor to increase to greater than 10%. However, the reflection coefficient is now less than 5%. At resonance, the Q factor is still equal to 500, but at anti-resonance, the Q factor is now equal to 350.

[0135] Figure 3f An example is shown according to the first embodiment of the present invention. Figure 3a The dispersion characteristics of the illustrated excitation modes are shown. In this case, admittance is calculated for various normalized wavelengths around a value of 0.5, corresponding to the edge of the first Brillouin zone, which is also identified as the Bragg condition. For normalized wavelengths less than 0.5, as can be seen on the curve and at lower frequencies, the modes are excited less efficiently. Taking this into account and by plotting the evolution of the maximum admittance module relative to frequency and normalized wavelength, a projected 2D representation is obtained, which then invokes the classical dispersion curve for any wave propagation in a periodic lattice. As can be seen, resonance occurs at the beginning of the stopband.

[0136] The choice of substrate is important when modes other than the shear mode concentrated in the electrodes must be suppressed, or at least weakened compared to the desired mode. As mentioned above, this condition is achieved when the SSBW velocity in the substrate is lower than the velocity of the fundamental shear mode in the piezoelectric layer. In this case, the fundamental shear mode will penetrate the substrate and its energy will be dissipated.

[0137] Furthermore, the acoustic impedance should be close to that of the piezoelectric layer to facilitate the mode.

[0138] It is still possible to use a value equal to or greater than 4500m.s -1 Other substrates with high acoustic propagation speeds (such as silicon, diamond, sapphire, silicon carbide, or aluminum nitride) may also have volume shear modes in addition to the modes of interest concentrated in the electrodes.

[0139] This is why the use of composite substrates is not mandatory. Even bulk piezoelectric substrates made of lithium tantalate or lithium niobate can be used with electrodes embedded in the surface region. Even in this case, electrode patterns can be observed.

[0140] Figure 3g and Figure 3h Another example of internal deformation according to the first embodiment is illustrated. Here, shear movement is less concentrated in the regions of the interdigitated electrodes 108, 110, although it is still dominant. Vibration in the piezoelectric layer 104 is barely visible in the simulation.

[0141] In this example of the implementation, the transducer structure includes an Al-Cu (2% Cu) electrode embedded in a LiTaO3(YXI) / 42° piezoelectric layer on a silicon substrate. The wavelength λ of the transducer structure is equal to 2.8 μm, therefore p = 1.4 μm, and the aspect ratio a / p of the electrode is equal to 0.5, wherein the groove depth is t. e / λ = 20%. In this embodiment, for example, regarding Figure 1 In the first example shown, electrodes 112_i and 114_j are embedded in the piezoelectric layer 104.

[0142] Figure 3h This is a view of the mode in the xz-plane, illustrating that the electrode mode satisfies the synchronization condition f = v / 2p mentioned above, as indicated by reference numeral 130 in the figure. Figure 3h The shear movement within electrodes 108 and 110 is characterized by two neutral vibration points 132 within each electrode 108 and 110. Furthermore, the edges 134a, 134b, 136a, and 136b of each electrode 108 and 110 move synchronously. This indicates that within an electrode 108 or 110, charges of the same sign exist at both interfaces.

[0143] Figures 4a to 4c Three variations of this implementation are illustrated, in which three different electrode shapes are considered for the excitation of electrode resonant modes. These figures illustrate... Figure 1 A cross-sectional view in the xy-plane passing through an electrode assembly 112-i or 114-j. In all three figures, a mechanical cycle is represented. The embedded electrodes are filled into the grooves of the piezoelectric layer. For simulation purposes ( Figure 4d and Figure 4f (The results are illustrated) assuming the grid is infinitely long and excited by harmonic +V / -V excitation. The electrode radiates energy from its bottom interface with the substrate into the bulk substrate.

[0144] Al electrodes 201a, 201b, and 201c are represented by horizontal shaded lines, piezoelectric layer 203 (here, LiTaO3) is represented by slanted shaded lines, and bottom layer 205 is represented by vertical shaded lines. This bottom layer can be SiO2, another interface material, or the same material as piezoelectric layer 203.

[0145] Figure 4a A second embodiment of the invention is illustrated. Here, the groove in the piezoelectric layer 203 has a conical or trapezoidal cross-section. According to the second embodiment of the invention, the cross-section of the electrode 201a filled in the groove has a conical or trapezoidal shape. In this embodiment, the shorter side of the parallel sides of the trapezoid is aligned with the upper surface of the piezoelectric layer 203.

[0146] according to Figure 1 In the first embodiment illustrated, electrode 201b has Figure 4b The vertical type is shown.

[0147] According to a third embodiment of the invention, the electrode 201c is filled into a groove having a trapezoidal shape, but unlike the second embodiment, the shorter side of the parallel sides is arranged inside the piezoelectric layer 203 rather than on the surface of the piezoelectric layer. Therefore, the electrode 201c has a truncated V-shape.

[0148] Therefore, the electrodes fill grooves of different shapes inside the piezoelectric layer 203, which behave like bulk materials depending on the thickness of the piezoelectric layer.

[0149] Figure 4d and Figure 4e The simulation results are illustrated, and a comparison of the excitation efficiency of the electrode resonant modes for three electrode shapes is provided:

[0150] Figure 4d Harmonic susceptance is illustrated, and Figure 4e The harmonic conductance is illustrated.

[0151] The simulation results clearly show that the cone shape is of more interest than the other two shapes; however, its coupling efficiency is lower.

[0152] exist Figures 4f to 4h The examples illustrate other design options. These variations are based on Figure 4b The design is illustrated, but it can also be adapted to other implementations.

[0153] Figure 4f An electrode 201d is illustrated inside a groove in a piezoelectric layer 203, the sidewall 207a of which has a concave shape. Figure 4g An electrode 201e is illustrated inside a groove in a piezoelectric layer 203, the sidewall 207b of which has a convex shape. Figure 4hAn electrode 201f is illustrated within a groove in the piezoelectric layer 203, the sidewalls 207c of which have a serrated shape. By increasing the surface area of ​​the sidewalls, more charges of the same sign can exist at the interface, thereby improving the charge distribution that contributes to the distinctive characteristics of the mode and thus increasing the intensity of mode excitation. It can also be noted that the Q-factor of the mode (e.g., capture efficiency) depends on the shape of the electrode. Therefore, it is preferable to optimize both the working surface and the aspect ratio to improve the operating conditions of the electrode mode.

[0154] Alternatively, or as an alternative, the bottom of the groove may also have a convex shape, a concave shape, or a toothed shape.

[0155] Figure 4i Examples based on Figure 4b Further variations of the illustrated first embodiment can also be adapted to other embodiments and variations. A dielectric layer 211, for example, Si3N4, is provided on the bottom 215 of the groove in the piezoelectric layer 203. Then, a conductive layer 213 for the electrode is provided to fill the groove. Due to the presence of the dielectric layer 211, there is no charge at the bottom of the electrode. Using a dielectric with a higher shear rate than the conductive material can accelerate the basic shear mode so that the phase velocity of the dielectric exceeds the SSBW velocity of the underlying layer, allowing it to be better absorbed in the underlying layer 205. This phenomenon is described in more detail below with reference to Figures 7 and 12.

[0156] Figure 4j Another variation based on the previous variation is illustrated. Here, the conductive layer 217 is in contact with the bottom layer 205. The dielectric layer 211 again shields the conductive layer 217 towards the piezoelectric layer 203, such that the conductive layer 215 is in contact with the piezoelectric layer only via the sidewalls 219 and 221.

[0157] It has been found that when the conductive material of the electrode is not in direct contact with the piezoelectric material (e.g., ... Figure 4i and Figure 4j As illustrated, compared to a comparison structure without this feature, parameters such as phase velocity, resonant Q-factor, reflection coefficient, and coupling factor k can be optimized. 2 .

[0158] The above about Figures 4a to 4h All the variant examples described can be based on Figure 4j The variant shown is implemented in which the electrode is connected to the bottom layer 205.

[0159] Figure 5The effect of the thickness of electrode devices 112_i and 114_j on the shear vibration modes within the electrodes is shown. Here, harmonic analysis of an aluminum electrode in a (YXl) / 42° lithium tantalate piezoelectric layer embedded in a 325nm thick silicon dioxide layer on Si(100) is illustrated for a 1μm pitch, and a metal / piezoelectric a / p ratio set to 0.35 is presented. Figure 5 This shows the effect on the relative metal layer height t e / λ admittance from 5% to 15%. It can be identified that only at t e Resonance is only observed when the ratio / λ is greater than 0.1.

[0160] Compared to the other examples illustrated above, the resonance occurs at a higher frequency of approximately 5.15 GHz, due to the smaller pitch.

[0161] Figure 6 An interdigitated transducer structure of an acoustic device according to a fourth embodiment of the present invention is illustrated.

[0162] The transducer structure 300 includes a different acoustic wave propagation substrate 302 compared to the substrate 102 of the transducer structure 100 of the first embodiment; this is the only difference with respect to the first embodiment. All other features are the same and will therefore not be described in detail again, but will be referred to the description above.

[0163] The transducer structure 300 includes a composite substrate 302, such as composite substrate 102, which includes a piezoelectric layer 104 formed on a base substrate 306, but also includes an acoustic reflector 304, also known as a Bragg reflector, formed on the base substrate 306 and under the piezoelectric layer 104.

[0164] The Bragg reflector 304 comprises multiple stacked layers 306 to 309, wherein the layers with even-numbered reference numerals 306 and 308 are made of a first material, and the layers with odd-numbered reference numerals 307 and 309 are made of a second material. The first and second materials have different acoustic impedances, such that the Bragg reflector 304 comprises alternating stacks of high-impedance and low-impedance layers.

[0165] The Bragg reflector 304 has a pair of periodically repeating layers, each approximately one-quarter the thickness of the wavelength, with alternating high / low impedance to ensure reflection.

[0166] The first and second materials can be selected from tungsten, molybdenum, LiTaO3, Al2O3, AlN, LiNbO3, Si3N4, and any combination of SiO2 and Si3N4 (referred to as silicon oxynitride and denoted as SiO2). x N y (where x and y control the amount of various elements in the compound), as well as ZnO, aluminum, or SiO2.

[0167] In a variant, the first material and the second material can be interchanged so that the first material has low impedance and the second material has high impedance.

[0168] In this embodiment, the Bragg reflector 304 is represented as having four layers 306 to 309 forming a stack of alternating high-impedance and low-impedance layers. However, in another variation, the Bragg reflector 304 may also have more or fewer than four layers forming a stack of alternating high-impedance and low-impedance layers.

[0169] Increasing the number of pairs in a 304 Bragg mirror increases its reflectivity, and increasing the impedance ratio between the materials in the Bragg pair increases both reflectivity and bandwidth. Common choices for the laminated materials include, for example, titanium dioxide and silica.

[0170] According to the present invention, the piezoelectric layer 104 and the Bragg reflector 304 are arranged to reduce the contribution of additional modes present in the structure to promote unique modes within the transducer structure 100, thereby ensuring the spectral purity of the acoustic device based on such transducer structure 100 and thus preventing spectral contamination.

[0171] One approach is to optimize the thickness of the stack of Bragg reflectors 304 to facilitate unique modes within the transducer structure and achieve a high-efficiency reflection coefficient for those modes. Bragg reflectors 304 will thus acoustically isolate vibrations generated within the electrode devices 112, 114 from the base substrate 106.

[0172] Figure 7a An interdigitated transducer structure of an acoustic device according to a fifth embodiment of the present invention is illustrated.

[0173] The transducer structure 400 includes a cover layer 402 over the transducer structure 100 of the first embodiment, which is the only difference with respect to the first embodiment. All other features are the same and will therefore not be described in detail again, but will be referred to the description above.

[0174] The transducer structure 400 includes a composite substrate 102, which includes a piezoelectric layer 104 formed on a base substrate 106.

[0175] In this embodiment of the invention, layer 402 exists above the embedded electrodes 108, 110 and the piezoelectric layer 104. Layer 402 may be a passivation layer or a guiding substrate, comprising high-speed, low-loss materials such as silicon, sapphire, Al2O3, garnet (i.e., yttrium-based materials), aluminum nitride (AlN), silicon carbide (SiC), and silicon nitride (Si3N4).

[0176] According to another variation, layer 402 can also be a carbon substrate, such as a single-crystal diamond, an amorphous carbide layer, nanocrystalline polycrystalline diamond (NCD), or a carbon layer of any diamond-like material, which can drive compressed wave velocities exceeding 15 km / s. -1 And the shear wave velocity exceeds 7 km / s. -1 In another variation, the SiO2 layer can be used as layer 402. SiO2 can act as a TCF corrector to improve the overall TCF value of the structure.

[0177] The capping layer 402 can also be made of glass, for example, as a TCF corrector, and is typically a silicon-based substrate.

[0178] The phase velocity of the basic shear wave mode is accelerated to a speed higher than or further higher than the SSBW speed of the base substrate by using high-speed, low-loss materials, so that unwanted modes can be suppressed by dissipation into the base substrate 106.

[0179] exist Figure 7a In the illustrated embodiment, the cover layer 402 is made of the same material as the base substrate 106 of the composite substrate 102. However, the cover layer 402 may be different from the base substrate of the composite substrate.

[0180] According to another variation, layer 402 may exist only on electrode devices 108, 110, or only on piezoelectric layer 104.

[0181] Figures 7b to 7d A simulated broadband harmonic admittance is shown for an excitation mode according to a fifth embodiment of the present invention with an acoustic wavelength of 2.8 μm, an a / p ratio of 0.5, and an aluminum electrode and (YXl / 42°) lithium tantalate as a piezoelectric layer 104.

[0182] for Figure 7b The capping layer 402 and the base substrate 106 are silicon dioxide. The excitation mode appears at 3.5 GHz. Figure 7c The capping layer 402, the base substrate 106, and the piezoelectric layer 104 are (YX1 / 42°) lithium tantalate. The excitation mode also appears at approximately 3.5 GHz. An additional contribution is visible at approximately 6.5 GHz, which can be attributed to the third harmonic. However, it is essentially present in the conductance, and the corresponding susceptance shows no sign change, indicating low coupling.

[0183] for Figure 7d The capping layer 402 and the base substrate 106 are silicon substrates. The excitation mode appears at 3.5 GHz, but here, the fundamental shear mode in the piezoelectric layer is also excited and is visible at a lower frequency (i.e., at about 1.8 GHz).

[0184] The present invention also relates to an acoustic device comprising two transducer structures, each of which is an embodiment of any one of the first to fifth embodiments of the present invention.

[0185] In another example, only one of the two transducer structures may be a surface acoustic device according to the present invention, while the other transducer structure may be a transducer structure according to the prior art.

[0186] The acoustic device may be an acoustic resonator and / or an acoustic filter and / or an acoustic sensor and / or a high-frequency source. The acoustic device may include a radio frequency (RF) supply device configured to drive the transducer structure using an RF signal higher than 3 GHz.

[0187] Figure 8 A sixth embodiment of the transducer structure is shown.

[0188] Figure 8 The transducer structure 500 and Figure 1 The difference in the transducer structure is that the interdigitated electrodes 512 and 514 only partially fill the groove 510 in the piezoelectric region 504.

[0189] Depending on the manufacturing process, the thickness of the metal layer is not constant throughout the removal region 510. Due to surface energy properties, the metal layer thickness at the sidewall 508 is greater than that in the central portion.

[0190] The transducer structure 500 functions in the same manner as the transducer structure described above.

[0191] The frequency of the bulk wave propagating in the electrode device using the transducer structure described above in the acoustic device (especially for ladder filters and / or impedance filters and / or coupling filters) allows for the generation of contributions at high frequencies, particularly above 3 GHz, and more particularly above 3.5 GHz.

[0192] Compared to bulk piezoelectric substrates, using this embedded electrode device in the transducer structure can improve the performance and application range of acoustic wave devices without changing the manufacturing tools (i.e., I-line lithography).

[0193] Figure 9a and Figure 9b A practical example of a filter is illustrated as a seventh embodiment, demonstrating an efficient implementation of the invention according to typical market demands (e.g., for 5G sub-6-GHz (C-band) filtering). This practical example is based on an Al electrode in LiTaO3 embedded in silicon with the following parameters: pitch p = 1 μm, thereby generating a wavelength λ of 2 μm, thus providing resonance close to 5 GHz, as... Figure 5As illustrated, and with the electrode and piezoelectric layer thicknesses at 700 nm, therefore t e The ratio of / λ is 0.35. According to common methods in SAW ladder filter design, the resonance of the series branch occurs at the anti-resonance point of the parallel branch.

[0194] This example according to the invention can be manufactured in a single batch using standard SAW manufacturing techniques (e.g., using I-line lithography and single metal layer deposition). It is possible to use grid pitch p and / or aspect ratio a / p and / or t. e / λ is used to fine-tune the resonant frequency. Alternatively, methods such as... Figure 7a and Figure 6 The illustrated passivation layer or Bragg mirror is used to improve the properties.

[0195] The filters in the practical example are based on, for example, Figure 1 The illustrated basic transducer structure. Based on this method, resonators are formed and combined in series and parallel to form units, which can be arranged in a cascaded manner or as a ladder filter structure known in the art.

[0196] In the practical example, two 35% grids are used, with corresponding material ratios a / p = 0.6 and 0.65. In both cases, the harmonic admittance and impedance are calculated, and... Figure 9a An example is provided. The resonance of the grid with a / p = 0.65 is close to the anti-resonance of the grid with a / p = 0.6, which is a prerequisite for designing the ladder filter as mentioned above.

[0197] By combining the responses, the transfer function of a known 4π-type unit filter can be calculated. Figure 9b The results are illustrated. This transfer function illustrates the improved power handling allowed by an ultra-compact filter operating above 5 GHz with electrodes up to 700 nm thick when embedded according to the invention. In this configuration, there is no physical migration. The filter of the present invention provides a coupling factor k of over 10% for LiTaO3. s 2 Considering the scaling between the two materials, this can be improved by using LiNbO3.

[0198] The proposed design demonstrates a bandwidth of 300 MHz. Improved matching, achieved through tuning the resonant-anti-resonant conditions, can also result in a high bandwidth of approximately 400 MHz. As mentioned above, tuning can include adjusting the pitch and / or the a / p ratio.

[0199] Figure 10a The higher harmonic modes of the electrode shear mode, which can also be excited by the electrode, are illustrated. Figure 10aThis actually illustrates the shear shift of the third harmonic. In this mode, four neutral vibration points or lines are observed in each electrode. For a transducer structure with a 700 nm thick Al vertical electrode, a metal ratio a / p of 0.5, a pitch of 1.4 μm, and a piezoelectric layer of LiTaO3(YXl) / 42°, the following results were obtained: Figure 10a The electrode shear vibration mode is shown. (Compared to...) Figure 7b Conversely, here, the third harmonic generates significant vibrations at the edges of the electrodes, thus producing distinct features that characterize the coupling modes. Figure 10b In this study, comparisons were made between LTO, Si, SiO2, and sapphire substrates, taking into account the cone shape of the electrodes (like...). Figure 4a As illustrated, this cone shape produces a better Q than other types of electrodes. For Figure 10a The other parameters are the same.

[0200] Figure 10b and Figure 10c Examples of corresponding harmonic conductances G and susceptance B for various base substrates, including LiTaO3, SiO2, Si, and sapphire, are shown. These modes are of interest due to their high resonant frequency of around 8.75 GHz, exhibiting high equivalent velocity. Exciting the corresponding modes using the transducer structure according to the invention can be advantageously used for the development of high-frequency sources. The sign variation of the susceptance is illustrated. Figure 10c This indicates that the coupling of patterns is effective.

[0201] Figure 11 An eighth embodiment of the invention related to the second objective of the invention is illustrated. The figure illustrates an interdigitated transducer structure 200 of a surface acoustic wave device according to a first embodiment of the invention. The interdigitated transducer structure 200 includes a pair of interdigitated comb electrodes 202 and 204, each comb electrode including a plurality of electrode devices 206 and 208 embedded in a piezoelectric layer 212.

[0202] In the first embodiment, electrode devices 206 and 208 have the shape of fingers 206 and 208. In a variant of this embodiment, the electrode devices may also have split fingers 206 and 208, each comprising two or more directly adjacent electrode fingers belonging to the same comb electrode.

[0203] The piezoelectric layer 212 is part of the composite substrate 210, which also includes the base substrate 214. The piezoelectric layer has the same material as described in other embodiments and has the same properties regarding thickness.

[0204] The thickness of the base substrate 214 can be greater than the thickness of the piezoelectric layer 212 to apply its thermal expansion to the piezoelectric layer 212 and reduce the transducer's sensitivity to temperature changes. A preferred case corresponds to a base substrate thickness that is at least ten times greater than the thickness of the piezoelectric layer 212.

[0205] The base substrate 214 has the same material as in the first embodiment.

[0206] By using different materials for the base substrate 214, design flexibility can be enhanced.

[0207] The interdigitated comb electrodes 202 and 204 include multiple electrode fingers 1206 and 1208. The electrode fingers (e.g., 206_1, 208_1 to 206_4, 208_4 and 208_5, 206_7 to 208_8, 206_10, respectively) are interdigitated and connected to an alternating potential via their comb electrodes 202 and 204, and are embedded in the piezoelectric layer 212. The alternating potential can be +V and -V as shown, or in a variant, mass and load / source potentials. The electrode fingers are metallic and all have the same length l, width w, and thickness t. Furthermore, an electrode pitch p, defined herein as λ / 2, is also used in the transducer structure 200. The number of electrode fingers is not fixed, and the device may include more than... Figure 11 The example shows more or fewer electrode fingers.

[0208] According to a variation of the present invention, electrode fingers 206 and 208 may also have different lengths l, widths w, and thicknesses t. e .

[0209] As in the first embodiment, the thickness t e The thickness is equal to or less than that of the piezoelectric layer 212.

[0210] The eighth embodiment is unique in that the transducer structure 200 further includes a region 218 (also referred to as the second region) in which two adjacent electrode fingers 208_4 and 208_5 (also referring to directly adjacent electrode fingers) are connected to the same potential (here, +V), and there are no electrode fingers 206 from the opposing interdigitated comb electrodes 202 between these two adjacent electrode fingers. The two adjacent electrode fingers 208_4 and 208_5 can also be connected to -V, or mass, or load / source potential V. IN (Not shown). In this context, one or more first regions are part of the transducer structure, wherein directly adjacent electrodes refer to different comb electrodes.

[0211] In a variant where electrode devices 206 and 208 are represented by split fingers 206 and 208 among two or more adjacent fingers at the same potential, the two adjacent electrode devices 206 and 208 connected to the same potential can refer to all fingers of the split fingers 206 that are connected to the same potential of the split fingers 208. However, it is also possible that at least one electrode finger of the split fingers 206 is connected to the same potential of the split fingers 208.

[0212] exist Figure 11 In this embodiment, the region or second region 218 is actually located in the middle of the transducer structure 200, such that there are eight electrode fingers or four electrode finger pairs on each side (left and right) of the region 218. In a variant of this embodiment, the region 218 can be placed at different locations in the transducer structure so that the electrode finger pairs are unevenly distributed on either side of the region 218. The region 218 can also be placed at either end of the transducer structure 200.

[0213] As previously mentioned, electrode fingers 206_1, 208_1 to 206_4, 208_4 and 208_5, 206_5 to 208_8, 206_8 are interdigitated and have alternating potentials. In fact, it can be seen that, due to the presence of region 218, on the left side of region 218, the interdigitated electrode fingers 206_1, 208_1 to 206_4, 208_4 are at alternating potentials of -V / +V, while on the right side of region 218, the interdigitated electrode fingers 208_5, 206_5 to 208_8, 206_8 are at alternating potentials of +V / -V.

[0214] A pair of adjacent electrodes connected to an alternating potential defines an electroacoustic source. For example, here... Figure 11 In this configuration, adjacent interdigitated electrode fingers 206_1 and 208_1, located at alternating potentials -V / +V, define an electroacoustic source 220. However, adjacent interdigitated electrode fingers 208_1 and 206_2, located at alternating potentials +V / -V, also define an electroacoustic source 222. Therefore, each pair of adjacent interdigitated electrode fingers 206_2, 208_2 to 206_4, 208_4 further defines an electroacoustic source 220, and correspondingly, each pair of adjacent interdigitated electrode fingers 208_2, 206_3 and 208_3, 206_4 further defines an electroacoustic source 220. In particular, here, on the left side of region 218, there are four active electroacoustic sources 220 and three active electroacoustic sources 222, and a total of eight interdigitated electrode fingers 206_1, 208_1 to 206_4, 208_4 exist.

[0215] To the right of region 218, a pair of adjacent interdigital electrode fingers (e.g., 208_5 and 206_5) connected to alternating potentials +V / -V also define electroacoustic source 222, and adjacent interdigital electrode fingers at alternating potentials -V / +V, 206_5 and 208_6, define electroacoustic source 220. To the right of region 218, there are four active electroacoustic sources 222 and three active electroacoustic sources 220, for a total of eight interdigital electrode fingers 208_5, 206_5 to 208_8, 206_8. However, here, the electroacoustic sources 220 and 222 on the left side of region 218 are in opposite phase to the electroacoustic sources 222 and 220 on the right side of region 218, specifically π.

[0216] However, since the electrode pitch p is defined as λ / 2, this means that the transducer structure 200 operates in synchronous mode under Bragg conditions. Therefore, the multiple electroacoustic sources 220, 222 on the left side of region 218 are in phase and coherent with each other, while the multiple electroacoustic sources 222, 220 on the right side of region 218 are in phase and coherent with each other.

[0217] In region 218, there is no electroacoustic source 220 or 222 between the two adjacent electrode fingers 208_4 and 208_5 because they are both connected to the same potential.

[0218] According to a variant, the polarity of the potential can be exchanged between the first interdigital comb electrode 206 and the second interdigital comb electrode 208, or one comb electrode can be connected to the mass and the other comb electrode can be connected to the load / source potential V. IN .

[0219] Because of the presence of a second region 218 in the transducer structure 200, the phase of the electroacoustic sources within the transducer is reversed by π, as the electroacoustic sources to the left of region 218 are in opposite phase to those to the right of region 218. Therefore, by combining the energy emitted from each side of the two electrode fingers connected to the same comb electrode toward the transducer, destructive interference occurs between the electroacoustic sources within the transducer, while the energy emitted toward the outside of the transducer is effectively emitted and reflected by mirrors located on either side of the transducer structure within the SAW device.

[0220] Therefore, a transducer structure of the same size, in which all electrodes are at alternating potentials (for example, such as...) Figure 1 Compared to (as shown), this reduces the amount of coherent and in-phase electroacoustic sources present in transducer structure 200. As a result, the electromechanical coupling coefficient k in the transducer structure is reduced. s 2 .

[0221] Here, in this particular embodiment, since region 218 is located in the middle of transducer structure 200, the left and right sides of region 218 in transducer structure 200 have exactly the same number (i.e., 8) of interdigitated electrode fingers 206 and 208, resulting in 7 active electroacoustic sources. Here, the electromechanical coupling coefficient k in transducer structure 200 is... s 2 The efficiency decreases by a factor of 2. Again, by combining the energy emitted from each side of the two electrode fingers connected to the same comb electrode towards the transducer, destructive interference occurs between the electroacoustic sources within the transducer structure, while the energy emitted towards the outside of the transducer is actually emitted and reflected by the mirrors. Therefore, the transducer efficiency decreases by a factor of 2.

[0222] Furthermore, compared to existing technologies, the possibility of phase coherence of the mode of reflection at interface 216 of composite substrate 212 is also modified. If a phase shift occurs within the transducer structure, there is no opportunity to detect waves that do not match the phase matching condition. Therefore, reducing the detection of reflected acoustic waves from interface 216 will, in turn, reduce parasitic resonances at unwanted frequencies due to these reflections in the filter performance of the SAW device based on transducer structure 200.

[0223] Therefore, the generation and / or detection of acoustic waves in the transducer structure 200 according to the present invention is controlled based on the amount of in-phase electroacoustic sources present in the transducer structure 200. By connecting two adjacent electrode fingers to the same potential, a phase transition π occurs within the structure, which has a positive effect on the efficiency of the transducer structure in rejecting parasitic modes. It is not necessary to change the dimensions of the transducer (such as the width or length of the electrode fingers or the distance between the electrodes), as changing the transducer dimensions would otherwise affect the manufacturing technology of such a structure and could significantly reduce the resonant quality of the resonator utilizing the above-described transducer structure.

[0224] According to a variant of the eighth embodiment, more than one region 218 can exist in the transducer structure, thus increasing the number of suppressed electroacoustic sources in the transducer structure and further reducing the electromechanical coupling coefficient k. s 2 This is an efficient way to control filter bandwidth, thus giving more freedom to work with various filter frequency bands.

[0225] According to another variation, more than two adjacent electrode devices 208_4 and 208_5 (e.g., three or more) can be connected to the same potential, thereby suppressing more sources. Alternatively, according to another variation, there can be more than one region with suppressed sources. In this case, it is advantageous to distribute these regions randomly across the extension of the transducer structure. With more regions present, the number of adjacent electrode devices associated with the same potential is different.

[0226] Figures 12a to 12c Three variations of the ninth embodiment of the present invention are illustrated. Unlike the above, for example, such as... Figure 1 or Figures 4a to 4c As illustrated, the grooves within the piezoelectric layer are exclusively filled with a conductive material, particularly a metal similar to Al or an Al alloy. A variant of the transducer structure in the ninth embodiment also includes a dielectric material located within the grooves of the piezoelectric layer. Apart from this difference, the variant of the sixth embodiment has the same structural features and characteristics as the first embodiment and can be combined with any of the other embodiments from the second to the eighth embodiments, or combinations thereof.

[0227] Figure 12a A partial cross-sectional view of a transducer structure 600 of a first variant of the ninth embodiment is shown, the transducer structure having two adjacent electrode devices 612 and 614, each belonging to a different comb electrode. Electrode devices 612 and 614 are embedded in grooves 616 and 618 in a piezoelectric layer 604 disposed on a base substrate 606 via an attachment layer 608. In this embodiment, the sidewalls and bottom walls of grooves 616 and 618 are covered with conductive materials 620 and 622, for example, Al or an Al alloy as described above. The remaining portions of grooves 616 and 618 are at least partially filled with dielectric materials 624 and 626, particularly diamond carbon.

[0228] Figure 12b A transducer structure 650 according to a variant of the ninth embodiment is illustrated. Elements having the same reference numerals as those used in the first variant example 600 will no longer be described, but will be referred to instead.

[0229] In this variant, grooves 652 and 654 extend through the entire piezoelectric layer to the attachment layer 608. Again, the sidewalls of grooves 652 and 654, as well as the bottom of the grooves that now contact the base layer 606 and attachment layer 608, are covered with conductive materials 656 and 658. The remaining portions of grooves 652 and 654 are at least partially filled with dielectric materials 660 and 662. The same materials as in the first variant can be used.

[0230] The focus of this embodiment is to allow the use of materials with phase velocities greater than those of metallic materials, particularly aluminum-based metals. As a result, this embodiment can achieve higher frequencies compared to Embodiment 1.

[0231] Figure 12c A third variation of the transducer structure 690 is illustrated. The only difference from the second variation is that dielectric materials 692 and 694 extend through the entire thickness of grooves 696 and 698 to reach attachment layer 608, so that only the sidewalls of grooves 696 and 698 are covered with conductive materials 656 and 658.

[0232] Figures 13a to 13d An example of obtaining a first variant of the ninth embodiment is illustrated.

[0233] The grooves 616 and 618 are etched into the piezoelectric layer 604, such as Figure 13a As illustrated. Then, as... Figure 13b As illustrated, a metal deposition step is performed to cover the piezoelectric layer 604 and the walls of the recesses 616 and 618 with a metal layer 700. Subsequently, a dielectric layer 702 is deposited onto the metal layer 700, such that the recesses 616 and 618 are at least partially filled with the dielectric material. This... Figure 13c An example is provided. Finally, a polishing step (e.g., a CMP polishing step) is performed to obtain the transducer structure 600.

[0234] A second variation of the transducer structure 650 can be obtained by adjusting the etching steps so that the groove extends through the piezoelectric layer 604 to the base substrate 606.

[0235] Figure 14a Examples are shown as follows Figure 12b Numerical simulation results of the conductance G and susceptance B of the structure shown. Figure 14b The conductivity G and susceptance B, as well as the resistance R and reactance X, are illustrated. In the simulation, diamond carbon is used as the dielectric material, and aluminum is used as the metal within the groove. The piezoelectric layer 604 is LiTaO3(YXl) / 42°. The base substrate 606 is also lithium tantalate (with the same crystal cut) bonded to the piezoelectric layer 604 via an attachment layer 608 of silicon SiO2.

[0236] This structure (also known as isomorphic bonding) means using the same material as the substrate and employing SiO2 to bond the piezoelectric layer. SiO2 can be used as an etch stop layer to control the thickness of the piezoelectric layer and thus the excitation layer. SiO2 also helps reduce TCF. The structural portion beneath the silicon attachment layer is also referred to as the radiation domain, where undesired modes dissipate, while desired modes remain in the guiding domain on the attachment layer 608.

[0237] The mechanical cycle or electrode pitch p is 1.4 μm, and the embedded electrode thickness is 500 nm, with 100 nm thick metal layers 656 and 658 and 400 nm thick AlN / carbon diamond as dielectric filling materials 660 and 662. For simulation, a piezoelectric / electrode ratio close to a / p = 0.5 was used. The observed mode corresponds to leakage waves, but for a phase velocity of 12 km / s... -1 With a coupling factor of 2.2% in the case of resonance, the quality factor Q at resonance was found. r The quality factor Q at anti-resonance a They are equal to 400 and 670 respectively.

[0238] Figure 14c An example of an electrode mode obtained through numerical simulation is shown, in which the shear vibration mode is similar to the vibration present in the electrodes (i.e., the metal portion 656 and the dielectric portion 660), while the piezoelectric layer 604 moves very little. Figure 14c The finite element mesh of the piezoelectric layer 604, the embedded electrodes, and the attachment layer 608 is illustrated. In the simulation, the boundary conditions take into account the wave behavior in the radiation domain beneath the attachment layer 608. Figure 15a Examples are shown as follows Figure 12b Numerical simulation results of harmonic conductance G and susceptance B of the structure shown. Figure 15b Examples of harmonic conductance G and susceptance B, as well as harmonic resistance R and reactance X, are shown, with aluminum nitride (AlN) serving as dielectrics 660 and 662. All other structural parameters are identical except for the dielectric material. Compared to diamond-like carbon, the phase velocity of AlN is reduced to 11.3 km / s. -1 In this variant, a coupling factor of 4.4% and a quality factor Q can be observed. r =1850 and Q a =990.

[0239] Figure 16a Numerical simulation results for harmonic conductance G and resistance R are shown. Figure 16b An example of amplifying resonance is shown. Figure 16c An example of amplification for anti-resonance is illustrated. In this variant, dielectrics 660 and 662 are as follows: Figure 12b The structure shown is silicon dioxide (SiO2). Except for the dielectric material, all other structural parameters are the same as those in the first and second variations of the ninth embodiment.

[0240] Compared to the transducer structure of the observed mode, which has grooves exclusively filled with metallic material, the use of SiO2 improved the TCF. This is due to the fact that SiO2 has a K+ of +80 ppm. -1 The TCF coefficient of the metal is opposite to that of the metal.

[0241] In fact, here, when SiO2 is used as the dielectric 660 and 662, -11 ppm.K was observed. -1 The resonant TCF value and -14.7 ppm.K -1 The TCF value of the anti-resonance. The coupling factor is 6.7%, and the quality factor Q of the resonance is... R Greater than 5000. Q Ar It is relatively small, around 650, but this can be improved by optimizing the structural parameters of the design.

[0242] When in such Figure 16d When an additional layer of SiO2 is provided on the illustrated transducer structure 650, the observed TCF value can be further improved. This figure illustrates a transducer structure 670 according to a fourth variant of the ninth embodiment. Except for the presence of the additional SiO2 layer 672, the transducer structure 670 corresponds to... Figure 12b The transducer structure 650. The dielectric material can also extend downwards through to the attachment layer 608, just like... Figure 12c exemplified.

[0243] Another aspect of providing such a layer is to accelerate the phase velocity of the mode, as described above with respect to Figure 7, so as to accelerate the fundamental shear mode beyond the SSBW velocity of the substrate 606 when it is necessary to dissipate the observed fundamental mode.

[0244] Instead of using the same dielectric material to fill the groove and provide the additional layer 672, two different materials can be used to further optimize the TCF and phase velocity.

[0245] Figure 17a and Figure 17b Two variations of the tenth embodiment of the present invention are illustrated. It is possible that the electrode mode can be observed simultaneously with the standard guided shear mode (e.g., the basic guided shear mode), for example, such as... Figure 7d exemplified.

[0246] This also occurs when using a POI composite substrate with a LiTaO3 piezoelectric layer on SiO2. A typical example of such a POI substrate is a 500nm thick SiO2 layer enriched with 1μm traps on a Si(100) base substrate, on which a 600nm thick LiTaO3 layer is formed. In this configuration, at a speed between 3800m·s -1 With 4200m.s -1 The persistence of the basic guided shear mode was observed at the phase velocity between the two phase velocities, and thus, potential problems arise when the electrode mode is used to target the high-frequency band at frequencies approximately two and a half times higher than the electrode mode.

[0247] As already mentioned, see the section on Figures 3a to 3f The choice of base substrates 106, 205, 306, 406, 506, and 606 plays a crucial role in this description. In fact, when the SSBW velocity of the substrate is less than the velocity of the basic acoustic bulk shear mode in the piezoelectric layer, the bulk shear mode will enter the base substrate and become dissipated therein.

[0248] The contribution of the basic guided shear mode can be reduced by using a Si(111) base substrate, which exhibits the advantage of a lower SSBW velocity than that on Si(100), typically 4700 m / s. -1 Even smaller, rather than 5650m.s -1 The Si orientation corresponding to (YXw) / 45° is of particular interest in this objective. However, in this case, we still retain the distinct characteristics of the fundamental shear-guided mode, which can still be observed, even though we suppress a pair of higher-order modes as already described.

[0249] To further reduce the residual contribution of the basic guided shear wave, the transducer structure according to the tenth embodiment includes at least one additional layer within the stack. This additional layer is selected to accelerate the basic guided shear wave, thereby further pushing its velocity beyond the SSBW velocity of the substrate.

[0250] like Figure 17a The illustrated transducer structure 700 includes a LiTaO3 piezoelectric layer 704 on a SiO2 layer 706 having embedded electrodes 712, 714, 716 (here these electrodes are made of aluminum). The structure also includes a trap-enriched multi-Si layer 708 on a Si (111) base substrate 710.

[0251] The transducer structure 700 also includes an additional layer 718, also known as the high-speed, low-loss layer, sandwiched between the SiO2 layer 706 and the trap-enriched layer 708. The high-speed layer 718 is one of AlN, Al2O3, Si3N4, or SiC layers. All these materials exhibit speeds greater than 10 km / s. -1 The compressed body wave velocity value is greater than 5 km / s. -1 The shear wave velocity. Alternatively, the high-speed layer 718 can be based on carbon: single-crystal diamond, amorphous carbide layers, nanocrystalline polycrystalline diamond (NCD), or any diamond-like carbon layer, which can drive compression wave velocities exceeding 15 km / s. -1 And the shear wave velocity exceeds 7 km / s. -1 .

[0252] Figure 17bA second variation of the tenth embodiment is illustrated. This figure is based on the first variation, but additionally includes a second additional layer 720 (also a high-speed, low-loss layer), which may be made of the same or different material as the first additional layer 718. The two layers 718 and 720 will accelerate the speed of the basic guided shear mode. Figure 18a An image taken with an electron microscope shows a practical example of a transducer according to the present invention. The image shows a side sectional view of transducer structure 800, corresponding to, for example... Figure 1 The illustrated first embodiment of the transducer structure 800 has an aluminum electrode 802 embedded in a LiTaO3(YXl) / 42° body substrate 804. After measuring the transducer's characteristics, a layer 806 has been added to the surfaces of the electrode 802 and the body substrate 804, and this layer serves as a contrast enhancement layer for imaging purposes. The pitch is p = 3.4 μm, and the height of the electrode 802 is h = 510 nm. The aspect ratio a / p is 0.5. This structure has 50 pairs of electrode arrangements.

[0253] Figure 18b This is an enlarged view of the area highlighted by rectangle 808, thus illustrating the shape of electrode 806. The recess in the body substrate 804 has a trapezoidal shape, wherein the longer side of the parallel sides is aligned with the surface 810 of the body substrate 804. The sidewalls 812 and 814 are slightly concave, and the bottom surface 814 is convex.

[0254] Figure 18c A finite element mesh 820 illustrating the shape of an electrode 802 embedded in a real-world example piezoelectric substrate 804 is used for simulation. Figure 18a and Figure 18b The behavior of the actual example shown.

[0255] Figure 19a Experimental measurements of conductance and resistance are illustrated in practical examples. Figure 19b Examples are given for such Figure 18c The conductivity and resistance results were obtained from numerical simulation of the structure shown.

[0256] like Figure 18a and Figure 18b The fabricated device shown exhibits a phase velocity of 10950 m / s. -1 Coupling factor K s 2 The percentage is 1.85% and the quality factor is Q. ar =350. This mode was observed at a frequency of approximately 1.6 GHz, which is therefore much higher than the 580 MHz of the fundamental shear mode. Figure 19a Examples of the measured conductance and resistance are shown.

[0257] Use such as Figure 18cThe simulation results, presented with the FEM mesh and considering an infinitely long transducer structure, are consistent with the experimental results for the electrode mode described above. A velocity of 10862 m / s was observed. -1 Coupling factor K s 2 It is 0.62% and the quality factor Q ar It is approximately 100. Additionally, this pattern appears at approximately 1.6 GHz and exhibits similar behavior in terms of conductance and resistance correlation.

[0258] Many embodiments of the invention have been described. However, it should be understood that various modifications and enhancements can be made without departing from the appended claims. In particular, Figure 11 The implementation method can be with Figures 1 to 1 Combinations of features 0 and any features or combinations thereof illustrated in the embodiments of Figures 12 to 19, and / or evident from the combination of claims.

Claims

1. A transducer structure (100, 200, 300, 408, 410) for an acoustic device, said transducer structure comprising: A piezoelectric layer (104) is disposed on a base substrate (106). A pair of interdigitated comb electrodes (108, 110, 412, 414), the pair of interdigitated comb electrodes comprising having a pitch p Multiple electrode devices (112_i, 114_j, 418, 420). Its features are, The interdigitated comb-shaped electrodes (108, 110, 412, 414) are embedded in the piezoelectric layer (104), and The pair of interdigitated comb electrodes (202, 204) includes adjacent electrode devices (206, 208) belonging to different comb electrodes (202, 204), and The pair of interdigitated comb electrodes (202, 204) includes one or more regions (218) in which two or more adjacent electrode devices (206, 208) belong to the same comb electrode (202, 204) and are at the same distance from each other as adjacent electrode devices belonging to different comb electrodes are at the same distance from each other. The thickness of the embedded electrode devices (112_i, 114_j, 418, 420) is equal to the thickness of the piezoelectric layer (104), and The acoustic impedance of the base substrate (106) is within ±25% of the acoustic impedance of the piezoelectric layer (104).

2. The transducer structure according to claim 1, wherein, The two or more adjacent electrode devices belonging to the same comb electrode have the same geometry as adjacent electrode devices belonging to different comb electrodes.

3. The transducer structure according to claim 1 or 2, wherein, The acoustic impedance of the electrode device is less than that of the piezoelectric layer.

4. The transducer structure according to claim 1 or 2, wherein, The pitch p satisfies the condition that... p=λ / 2 Given the Bragg conditions, λ It is the operating acoustic wavelength of the transducer.

5. The transducer structure according to claim 1 or 2, wherein, The aspect ratio a / p of the electrode devices (112_i, 114_j, 418, 420) is between 0.3 and 0.75, where "a" is the width of the electrode devices (112_i, 114_j, 418, 420) and "p" is the pitch of the electrode devices (112_i, 114_j, 418, 420).

6. The transducer structure according to claim 5, wherein, The aspect ratio of the electrode devices (112_i, 114_j, 418, 420) is between 0.4 and 0.

65.

7. The transducer structure according to claim 1, wherein the transducer structure further comprises an attachment layer (608, 706) located between the piezoelectric layer (604, 704) and the base substrate (606, 710).

8. The transducer structure according to claim 7, wherein, The attachment layer is silicon dioxide (SiO2).

9. The transducer structure according to claim 7 or 8, wherein the transducer structure further comprises a high-speed layer (718) located between the piezoelectric layer (704) and the base substrate (710), wherein, The high-speed layer is made of a material whose material and crystal orientation allow for a higher shear wave phase velocity compared to the piezoelectric layer (104).

10. The transducer structure according to claim 9, wherein, The high-speed layer (718) is positioned between the attachment layer (706) and the base substrate (710).

11. The transducer structure according to claim 9, wherein the transducer structure further comprises a trap enrichment layer (708) located between the piezoelectric layer (704) and the base substrate (710).

12. The transducer structure according to claim 11, wherein, The trap enrichment layer is a polycrystalline silicon trap enrichment layer.

13. The transducer structure according to claim 11 or 12, wherein, The trap enrichment layer (708) is positioned between the high-speed layer (718) and the base substrate (710).

14. The transducer structure according to claim 1 or 2, wherein the transducer structure further comprises a cover layer (302) located above the embedded electrode devices (112_i, 114_j, 418, 420) and the piezoelectric layer (104).

15. The transducer structure according to claim 14, wherein, The capping layer (302) is made of a material that allows for a higher shear wave phase velocity compared to the material of the piezoelectric layer (104) and / or has a crystal orientation that allows for a higher shear wave phase velocity compared to the crystal orientation of the piezoelectric layer (104).

16. The transducer structure according to claim 1 or 2, wherein the transducer structure further comprises a Bragg reflector (304) located below the piezoelectric layer (104) and / or the electrode device.

17. The transducer structure according to claim 1, wherein, The thickness t of the electrode device e satisfy λ>t e >0.1 λ , λ It is the operating acoustic wavelength of the transducer.

18. The transducer structure according to claim 1, wherein, The acoustic impedance of the base substrate is within ±15% of the acoustic impedance of the piezoelectric layer (104).

19. The transducer structure according to claim 1 or 2, wherein, The embedded electrode device is filled into the grooves of the piezoelectric layer (104, 203).

20. The transducer structure according to claim 19, wherein, The cross-section of the groove is conical or trapezoidal (201a) or V-shaped or U-shaped (201c), and / or the sidewalls and / or bottom of the groove are convex (207b) or concave (207a) or serrated (207c).

21. The transducer structure according to claim 19, wherein, A dielectric layer (211) is provided on the bottom (215) of the groove.

22. The transducer structure according to claim 20, wherein, The sidewalls and bottomwalls of the grooves (616, 618) are covered with conductive material (620, 622), and the remaining portion of the grooves (616, 618) is filled with dielectric material (624, 626).

23. The transducer structure according to claim 20, wherein, The grooves (696, 698) extend through the piezoelectric layer (604), and the sidewalls of the grooves (696, 698) are covered with conductive material (656, 658), and the remaining portions of the grooves (696, 698) are filled with dielectric material (692, 694).

24. The transducer structure according to claim 23, wherein, The conductive material (656, 658) is only covered on the sidewalls of the piezoelectric layer (604).

25. The transducer structure according to any one of claims 22 to 24, wherein, The dielectric material is a material that has a higher shear wave phase velocity than the conductive material.

26. The transducer structure according to any one of claims 22 to 24, wherein, The sign of the temperature coefficient of frequency of the dielectric material is opposite to that of the temperature coefficient of frequency of the conductive material.

27. The transducer structure according to any one of claims 21 to 24, the transducer structure further comprising a capping layer (302) located above the embedded electrode devices (112_i, 114_j, 418, 420) and the piezoelectric layer (104), wherein, The dielectric material of the cover layer (672) is the same as the dielectric material (660, 662) filled in the grooves (652, 654).

28. The transducer structure according to claim 1 or 2, wherein, The electrode device is made of a material that is lighter than manganese.

29. The transducer structure according to claim 28, wherein, The electrode device is made of aluminum or an aluminum alloy including Cu, Si or Ti.

30. The transducer structure according to claim 1 or 2, wherein, The piezoelectric layer is lithium tantalate or lithium niobate.

31. The transducer structure according to claim 1 or 2, wherein, The base substrate (106) is one of silica, quartz, fused silica, glass, LiTaO3, LiNbO3, or silicon.

32. The transducer structure according to claim 31, wherein, The base substrate is Si(111).

33. The transducer structure according to claim 9, wherein, The high-speed layer (718) is one of AlN, Al2O3, Si3N4, SiC or carbon-based materials.

34. The transducer structure according to claim 33, wherein, The high-speed layer is made of single-crystal diamond, amorphous carbide, or nanocrystalline polycrystalline diamond.

35. The transducer structure according to claim 14, wherein, The capping layer (302, 672) is one of AlN, Al2O3, Si3N4, SiC or a carbon-based material.

36. The transducer structure according to claim 35, wherein, The coating layer is made of single-crystal diamond, amorphous carbide, or nanocrystalline polycrystalline diamond.

37. The transducer structure according to claim 22 or 23, wherein, The dielectric material is a carbon-based material or AlN or SiO2.

38. The transducer structure according to claim 37, wherein, The carbon-based material is single-crystal diamond, amorphous carbide, or nanocrystalline polycrystalline diamond.

39. The transducer structure according to claim 35 or 36, wherein the transducer structure has three or more regions (218): the three or more regions have two or more adjacent electrode devices (206) belonging to the same comb electrode (202, 204), characterized in that, Neighboring areas are at different distances from each other.

40. The transducer structure according to claim 39, wherein, The adjacent region is randomly distributed within the extension range of the transducer structure.

41. The transducer structure according to claim 35 or 36, wherein, These regions (218) having two or more adjacent electrode devices (206, 208) belonging to the same comb electrode (202, 204) have different numbers of adjacent electrode devices belonging to the same comb electrode.

42. The transducer structure according to claim 1 or 2, wherein, The electrode device has a size that can be achieved by I-line lithography.

43. The transducer structure according to claim 42, wherein, The electrode device has a width greater than 350 nm.

44. An acoustic wave device (400), said acoustic wave device comprising at least one transducer structure (100, 200, 300, 408, 410) according to any one of claims 1 to 43, wherein, The device (400) is an acoustic resonator and / or an acoustic filter and / or an acoustic sensor and / or a frequency source.

45. The acoustic device of claim 44, further comprising a radio frequency (RF) supply device configured to drive the transducer structure using an RF signal higher than 3 GHz.

46. ​​A method of using a transducer structure according to any one of claims 1 to 43, the method comprising the steps of: An alternating potential is applied to the two interdigitated electrodes to excite shear modes, which have a larger vibration amplitude in the electrode arrangement than in the piezoelectric layer, and have an equivalent velocity higher than the fundamental shear wave mode of the piezoelectric layer.

47. The method according to claim 46, wherein, Compared to the piezoelectric layer, the shear vibration mode mainly occurs within the electrode device.

48. The method according to claim 46 or 47, wherein, The transducer structure is part of a filter, resonator, delay line, or sensor.

49. The method according to claim 48, wherein, The filter is a ladder filter and / or an impedance filter and / or a coupling filter.

50. A method of using a transducer structure according to any one of claims 1 to 43, the method comprising the steps of: An alternating potential is applied to the two interdigitated electrodes to excite shear modes in the electrode arrangement using a pair of neutral lines. These shear modes do not exhibit shear movement within the electrodes and have an equivalent velocity higher than the fundamental shear wave mode of the piezoelectric layer.

51. The method according to claim 50, wherein, The transducer structure is part of a filter, resonator, delay line, or sensor.

52. The method according to claim 51, wherein, The filter is a ladder filter and / or an impedance filter and / or a coupling filter.

53. The method according to claim 51 or 52, wherein, The filter is used at frequencies above 3 GHz.

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