Acoustic resonator with aspect ratio for spur reduction

Abstract

There is provided an acoustic resonator including: nanowires each including: a piezoelectric layer having a first surface and a second surface; a first electrode on the first surface; and a second electrode on the second surface. The nanowires each mainly extend from the first bus bar in a first direction such that a space is defined between a pair of nanowires of the plurality of nanowires in a second direction substantially perpendicular to the first direction such that there is no piezoelectric material between the pair of nanowires in the second direction. The nanowires each have a height in a thickness direction substantially orthogonal to the first direction and the second direction. The nanowires each have a ratio of a width of at least one of the first electrode and the second electrode in the second direction to a height of the nanowires, the ratio being less than 2.

Description

Cross - Reference to Related Applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 623,117, filed on January 19, 2024, the entire content of which is incorporated herein by reference. Technical Field

[0002] The present disclosure relates to thin - film bulk acoustic resonators and also to filters for communication devices that include thin - film bulk acoustic resonators. Background Art

[0003] A radio - frequency (RF) filter is a two - port device configured to pass some frequencies and block others, where "pass" means transmission with relatively low signal loss and "block" means blocking or significantly attenuating. The range of frequencies that a filter passes is called the "passband" of the filter. The range of frequencies that such a filter blocks is called the "stopband" of the filter. A typical RF filter has at least one passband and at least one stopband. The specific requirements for the passband or stopband can depend on the specific application. For example, in some cases, the "passband" can be defined as the frequency range in which the insertion loss of the filter is better than a defined value such as 1 dB, 2 dB, or 3 dB, while the "stopband" can be defined as the frequency range in which the rejection of the filter is greater than a defined value such as 20 dB, 30 dB, 40 dB or more (depending on the application).

[0004] RF filters are used in communication systems for transmitting information over wireless links. For example, RF filters can be found in the RF front - ends of cellular base stations, mobile phones and computing devices, satellite transceivers and ground stations, IoT (Internet of Things) devices, laptop computers and tablet computers, point - to - point radio links, and other communication systems. RF filters are also used in radar, as well as in electronic and information - warfare systems.

[0005] Performance enhancements of RF filters in wireless systems can have a wide impact on system performance. Improvements in RF filters can be used to provide system performance improvements such as larger cell sizes, longer battery life, higher data rates, greater network capacity, lower costs, enhanced security, higher reliability, etc. These improvements can be achieved individually and in combination at multiple levels of a wireless system (e.g., at the RF module, RF transceiver, mobile or fixed subsystem, or network level). As the demand for RF filters operating at higher frequencies continues to increase, there is a need for improved filters that can operate in different frequency bands, and at the same time, there is a need to improve the manufacturing processes for fabricating such filters. Summary of the Invention

[0006] As described above, resonator performance improvements (e.g., improved Q factor) also have an improvement effect on RF filters and network devices including the improved resonators as described herein. Accordingly, in an exemplary aspect, there is provided an acoustic resonator that minimizes spurious other than high frequency by setting an aspect ratio of electrode fingers of the acoustic resonator.

[0007] Specifically, in an exemplary aspect, there is provided an acoustic resonator including a plurality of nanowires, each of the plurality of nanowires including: a piezoelectric layer having a first surface and a second surface; a first electrode on the first surface of the piezoelectric layer; and a second electrode on the second surface of the piezoelectric layer. In this aspect, each of the plurality of nanowires extends mainly in a first direction from a first bus bar such that a space is defined between a pair of nanowires among the plurality of nanowires in a second direction that is substantially perpendicular to the first direction, such that there is no piezoelectric material between the pair of nanowires in the second direction. Further, each of the plurality of nanowires has a height in a thickness direction that is substantially orthogonal to the first direction and the second direction, and each of the plurality of nanowires has a ratio of a width of at least one of the first electrode and the second electrode in the second direction to the height of the nanowire, and the ratio is less than 2.

[0008] In another exemplary aspect, the acoustic resonator includes a pair of bus bars including a first bus bar and a second bus bar, the first bus bar being coupled to the first electrode of each of the plurality of nanowires, and the second bus bar being coupled to the second electrode of each of the plurality of nanowires.

[0009] In another exemplary aspect of the acoustic resonator, the second electrode of each of the plurality of nanowires is a floating electrode.

[0010] In another exemplary aspect, the acoustic resonator includes a pair of piston masses disposed on a top surface of the first electrode of each of the plurality of nanowires. In this aspect, the pair of piston masses may be disposed adjacent to a base and at a free end of each of the plurality of nanowires.

[0011] In another exemplary aspect of the acoustic resonator, the first electrode of each of the plurality of nanowires includes a multi-layer electrode in a thickness direction, and the multi-layer electrode of the first electrode includes a first electrode layer having a first acoustic impedance and a second electrode layer having a second acoustic impedance that is lower than the first acoustic impedance. Further, the second electrode of each of the plurality of nanowires includes a multi-layer electrode in a thickness direction, and the multi-layer electrode of the second electrode includes a first electrode layer having a first acoustic impedance and a second electrode layer having a second acoustic impedance, and the second acoustic impedance of the second electrode layer of the second electrode is lower than the first acoustic impedance of the first electrode layer of the second electrode.

[0012] In another exemplary aspect of the acoustic resonator, the number of multi-layer electrodes of the first electrode is 2, and the number of multi-layer electrodes of the second electrode is 2.

[0013] In another exemplary aspect of the acoustic resonator, the first electrode layer of the first electrode is disposed between the second electrode layer of the first electrode and the piezoelectric layer, and the first electrode layer of the second electrode is disposed between the second electrode layer of the second electrode and the piezoelectric layer.

[0014] In another exemplary aspect of the acoustic resonator, the ratio of the thickness of the first electrode layer of the first electrode to the thickness of the multi-layer electrodes of the first electrode is between 0.1 and 0.6. Further, the ratio of the thickness of the first electrode layer of the second electrode to the thickness of the multi-layer electrodes of the second electrode is between 0.1 and 0.6.

[0015] In another exemplary aspect of the acoustic resonator, the ratio of the thickness of the multi-layer electrodes of the first electrode to the thickness of the piezoelectric layer is between 0.1 and 0.5. Further, the ratio of the thickness of the multi-layer electrodes of the second electrode to the thickness of the piezoelectric layer is between 0.1 and 0.5.

[0016] In another exemplary aspect, an acoustic resonator is provided, the acoustic resonator including a plurality of electrode fingers, each of the plurality of electrode fingers including: a piezoelectric layer having a first surface and a second surface; a top electrode on the first surface of the piezoelectric layer; and a bottom electrode on the second surface of the piezoelectric layer. In this aspect, the top electrodes of the plurality of electrode fingers each extend mainly in a first direction from a first bus bar, wherein a space is defined between a pair of electrode fingers in a second direction that is substantially perpendicular to the first direction, such that there is no piezoelectric material between a pair of nanowires in the second direction. Further, each of the plurality of electrode fingers has a width in the second direction and a total height in a thickness direction that is substantially orthogonal to the first direction and the second direction, and the ratio of the width to the total height of at least one of the plurality of electrode fingers is less than 2.

[0017] In another exemplary aspect, a bandpass filter is provided that includes a plurality of acoustic resonators, the plurality of acoustic resonators including one or more series resonators and one or more parallel resonators, at least one of the plurality of acoustic resonators including a plurality of nanowires, each of the plurality of nanowires including: a piezoelectric layer having a first surface and a second surface; a first electrode on the first surface of the piezoelectric layer; and a second electrode on the second surface of the piezoelectric layer. In this aspect, each of the plurality of nanowires extends primarily in a first direction from a first bus bar such that a space is defined between a pair of nanowires among the plurality of nanowires in a second direction that is substantially perpendicular to the first direction, such that there is no piezoelectric material between the pair of nanowires in the second direction, the nanowires each having a height in a thickness direction that is substantially orthogonal to the first and second directions, and each of the plurality of nanowires having a ratio of the width of at least one of the first electrode and the second electrode in the second direction to the height of the nanowire that is less than 2. BRIEF DESCRIPTION OF THE DRAWINGS

[0018] The drawings incorporated in and forming a part of this specification illustrate one or more example aspects of the present disclosure and, together with the detailed description, are used to explain the principles and implementations of one or more example aspects of the present disclosure.

[0019] Figure 1 A schematic plan view and a schematic cross-sectional view of a Y-cut thin film bulk acoustic resonator (YBAR) according to an exemplary aspect are shown.

[0020] Figure 2A A schematic plan view and a schematic cross-sectional view of a YBAR according to another exemplary aspect are shown.

[0021] Figure 2B Shows according to another exemplary aspect Figure 2A A schematic plan view and a schematic cross-sectional view of a variant of the YBAR shown are shown.

[0022] Figure 3A Is a schematic cross-sectional view of a YBAR according to an exemplary aspect.

[0023] Figure 3B Is an alternative schematic cross-sectional view of a YBAR according to an exemplary aspect.

[0024] Figure 4A A schematic plan view and a perspective view of an acoustic resonator structure are shown, the acoustic resonator structure being Figure 2A A refinement of an exemplary aspect of the YBAR shown. Figure 4B Shows Figure 4A A cross-sectional view of the IDT configuration in

[0025] Figure 5 ShowsFigure 2A Schematic plan view and perspective view of another refined IDT configuration of an exemplary aspect of the YBAR shown.

[0026] Figure 6 Shows according to an exemplary aspect Figure 4A and Figure 4B Top view of the IDT configuration in

[0027] Figure 7A and Figure 7B Shows a graph of admittance [y] according to the frequency of an acoustic resonator according to an exemplary aspect.

[0028] Figure 8 Shows according to an exemplary aspect Figure 4A and Figure 4B Top view of another IDT configuration of the acoustic resonator shown.

[0029] Figure 9A and Figure 9B Shows according to an exemplary aspect according to Figure 8 Graph of admittance [y] according to the frequency of the acoustic resonator shown.

[0030] Figure 10 Shows according to an exemplary aspect Figure 4A and / or Figure 5 Cross-sectional view of the IDT fingers of the acoustic resonator configuration shown.

[0031] Figure 11A Graph of admittance [y] according to the frequency of an acoustic resonator according to an exemplary aspect.

[0032] Figure 11B Graph of coupling coefficient according to the aspect ratio of an acoustic resonator according to an exemplary aspect.

[0033] Figure 12A Shows according to an exemplary aspect Figure 8 Cross-sectional view of the IDT fingers of the acoustic resonator configuration shown.

[0034] Figure 12B and Figure 12C Graph of admittance [y] according to the frequency of an acoustic resonator according to an exemplary aspect.

[0035] Figures 13A to 13B Compares energy / acoustic damping in the metal layer according to aspects of the present disclosure.

[0036] Figure 14Shows an example of a multi-layer metal structure including a first conductor pattern disposed on a first surface of a piezoelectric layer of an acoustic resonator structure and a second conductor pattern disposed on a second surface of the piezoelectric layer, in accordance with aspects of the present disclosure.

[0037] Figures 15A to 15C Show the displacement, stress, and energy of three electrode structures, respectively, in accordance with aspects of the present disclosure.

[0038] Figures 16A to 16C Show, respectively, in accordance with aspects of the present disclosure, having Figure 14 The fd diagram, Qm diagram, and k2 diagram of the acoustic resonator ARN with the two-layer electrode structure shown.

[0039] Figure 17 Show the simulation results of the displacement (“D”), stress (“S”), and energy (“E”) of nine electrode structures, respectively, in accordance with aspects of the present disclosure.

[0040] Figure 18A Shows how the parameter fd varies with C m / C LN and ρ m / ρ LN in the fd diagram, in accordance with aspects of the present disclosure.

[0041] Figure 18B Shows how the parameter Qm varies with C m / C LN and ρ m / ρ LN in the Qm diagram, in accordance with aspects of the present disclosure.

[0042] Figure 18C Shows how the parameter k2 varies with C m / C LN and ρ m / ρ LN in the k2 diagram, in accordance with aspects of the present disclosure.

[0043] Figures 19A to 19C , Figures 20A to 20C , and Figures 21A to 21C Show the effects of different metal materials as TE1 and BE1, in accordance with aspects of the present disclosure.

[0044] Figure 22A Is a schematic block diagram of a filter using an acoustic resonator according to an exemplary aspect.

[0045] Figure 22B Is a schematic diagram of a radio frequency module of an acoustic wave filter including Figure 22A according to an exemplary aspect.

[0046] Throughout this specification, elements that appear in the drawings are assigned three - or four - digit reference numerals, where the two least - significant digits are specific to the element, and one or two of the most - significant digits are the figure number in which the element is first introduced. It is assumed that elements not described in conjunction with the drawings have the same characteristics and functions as elements with the same reference numeral previously described. Detailed Description

[0047] Aspects of the disclosed thin - film bulk acoustic resonators, filter devices, and methods of manufacturing the same are now described with reference to the drawings, where like reference numerals are used throughout to indicate like elements. In the following description, for purposes of explanation, numerous specific details are set forth to facilitate a thorough understanding of one or more aspects of the present disclosure. However, it will be apparent that any aspect described below may be practiced without the use of the specific design details described below. In other instances, well - known structures and devices are shown in block diagram form to facilitate the description of one or more aspects. A simplified summary of one or more aspects of the invention is presented below to provide a basic understanding of the invention.

[0048] Figure 1 A simplified top view and cross - sectional view of a Y - cut thin - film bulk acoustic resonator (YBAR) 100 according to an exemplary aspect are shown. According to this aspect, the YBAR 100 includes a piezoelectric layer 110 (a piezoelectric plate or a piezoelectric layer may be used interchangeably), which has front surface 112 and back surface 114 that are substantially parallel to each other. In this context, "substantially parallel" means "as close to parallel as possible" or "parallel within reasonable manufacturing tolerances". Thus, it should be understood that in the exemplary aspect, the term "parallel" generally refers to the front side 112 and the back side 114 that are opposite to each other, and the surfaces may not be strictly flat and parallel to each other. For example, due to manufacturing variations caused by deposition processes, the front side 112 and the back side 114 may have surface undulations as would be understood by those skilled in the art. Additionally, the piezoelectric layer 110 may be a thin single - crystal layer of a piezoelectric material. The term "single - crystal" does not necessarily mean a completely homogeneous crystal structure and may include impurities due to manufacturing variations, as long as the crystal structure is within acceptable tolerances.

[0049] According to an exemplary aspect, the piezoelectric layer 110 is preferably lithium niobate (LN), but may be lithium tantalate (LT), lanthanum gallium silicate, gallium nitride, or some other material. The piezoelectric layer 110 is cut such that the orientations of the X, Y, and Z crystal axes relative to the front and back surfaces are known and consistent.

[0050] In an exemplary aspect, the thickness ts of the piezoelectric layer 110 can be determined according to the following formula:

[0051] ts≈n*V SH / 2F R,

[0052] where F R is the desired operating frequency, V SH is the shear wave velocity of the piezoelectric layer, and n = 1, 3, 5, … is the desired number of modes (harmonics). In this regard, n = 1 is typically referred to as the “fundamental mode” and n>1 is referred to as a “harmonic”.

[0053] The rear side 114 of the piezoelectric layer 110 is attached to a substrate 120, which provides mechanical support to the piezoelectric layer 110. The substrate 120 can be, for example, silicon, sapphire, quartz, or some other material. The piezoelectric layer 110 can be bonded to the substrate 120 using a wafer bonding process, grown on the substrate 120, or attached to the substrate in some other manner. The piezoelectric layer 110 can be attached directly to the substrate, or can be attached to the substrate via one or more intermediate material layers, as discussed below with respect to Figure 3A and Figure 3B In other words, the rear side 114 of the piezoelectric layer 110 can be directly or indirectly coupled or connected to the surface of the substrate 120 via one or more intermediate layers (e.g., a dielectric layer). Further, as used interchangeably herein, the phrases “supported by” or “attached” can mean directly attached, indirectly attached, mechanically supported, structurally supported, or any combination thereof.

[0054] A cavity 125 is formed in the substrate 120 such that a portion of the piezoelectric layer 110 including the front side conductor pattern and the rear side conductor patterns 130, 132, 134 is suspended above the cavity 125. The portion of the piezoelectric layer 110 located above the cavity (e.g., spanning or extending above the cavity) can be referred to herein as a “diaphragm” because it is physically similar to the diaphragm of a microphone. The diaphragm can be continuous with the remainder of the piezoelectric layer 110 around all perimeters of the cavity 125. In this context, “continuous” means “continuously connected without any intermediary”. However, in an exemplary aspect, the diaphragm can be configured such that at least 50% of the edge surface of the diaphragm is coupled to the edge of the piezoelectric layer 110.

[0055] According to an exemplary aspect, a "cavity" has its conventional meaning of "an empty space within a solid body". The cavity 125 can be a hole that completely penetrates the substrate 120 (as shown in cross-section A-A) or a groove in the substrate 120 that does not extend through the substrate 120. For example, the cavity 125 can be formed by selective etching of the substrate 120 before or after attaching the piezoelectric layer 110 and the substrate 120. In some cases, the cavity 125 is not formed in the substrate 120, but rather the cavity is formed in one or more intermediate layers between the piezoelectric layer 110 and the substrate 120. In some cases, the cavity 120 is only partially formed in the substrate 120 and can also be partially formed in one or more intermediate layers between the piezoelectric layer 110 and the substrate 120. Additionally, as Figure 1 shown, the cavity 125 has a rectangular shape. However, the cavity of the YBAR 100 can have different shapes, such as regular or irregular polygons. The cavity of the YBAR 100 can have more or fewer than four sides, and these sides can be straight or curved.

[0056] The first front-side conductor pattern 130 (e.g., the first electrode) and the second front-side conductor pattern 132 (e.g., the second electrode) are formed on the front side 112 of the piezoelectric layer 110. The back-side conductor pattern 134 (e.g., the floating electrode) is formed on the second side 114 of the piezoelectric layer 110. The back-side conductor pattern 134 is a "floating" conductor pattern, which means it is not electrically connected to any other conductor. Additionally, the back-side conductor pattern 134 is capacitively coupled to the first front-side conductor pattern 130 and the second front-side conductor pattern 132. The conductor pattern can be molybdenum, aluminum, copper, gold, or some other conductive metal or alloy. The back-side conductor pattern and the front-side conductor pattern do not necessarily have to be the same material. In an exemplary aspect, the back-side conductor pattern 134 can be made of any suitable conductive material. For example, the back-side electrode can be gold to avoid corrosion. The portion of the piezoelectric layer 110 located between the first front-side conductor pattern 130 and the back-side conductor pattern 134 forms the first resonator 150. The portion of the piezoelectric layer 110 located between the second front-side conductor pattern 132 and the back-side conductor pattern 134 forms the second resonator 155. The first resonator 150 and the second resonator 155 are electrically connected in series such that an RF signal applied between the first front-side conductor pattern 130 and the second front-side conductor pattern 132 excites acoustic waves in both the first resonator 150 and the second resonator 155.

[0057] According to an exemplary aspect, the diaphragm forms a seal above the cavity 125 such that the first front-side conductor pattern 130 and the second front-side conductor pattern 134 are not exposed to the environment adjacent to the rear-side conductor pattern 134. Ideally, when an RF signal is applied between the first front-side conductor pattern 130 and the second front-side conductor pattern 132, the rear-side conductor pattern should be kept at ground potential. For this purpose, the capacitance of the first resonator 150 should be equal to the capacitance of the second resonator 155. Assuming that the piezoelectric diaphragm has a uniform thickness, if the area of the first resonator 150 (i.e., the overlapping area between the first front-side conductor pattern 130 and the rear-side conductor pattern 134) is equal to the area of the second resonator 155 (i.e., the overlapping area between the second front-side conductor pattern 132 and the rear-side conductor pattern 134), the capacitances will be equal. When a balanced signal (i.e., a signal having equal amplitudes and a 180-degree phase difference) is applied to the first conductor pattern 130 and the second conductor pattern 132, the rear-side conductor pattern 134 will be kept at ground potential. Additionally, one or more additional layers 140 may be provided on the rear-side conductor pattern 134 opposite to the piezoelectric layer 110. In an exemplary aspect, the one or more additional layers 140 may be a dielectric layer, a sensor layer, etc., which may convert the resonator into a sensor. For example, the sensing layer 140 may be provided as, for example, a thin film, a single layer, or a surface treatment, which may be directly provided on the rear-side conductor pattern 134 or may be coupled to the rear-side conductor pattern 134 via one or more additional intermediate layers (e.g., an adhesive layer).

[0058] According to an exemplary aspect, the piezoelectric layer 110 may be Y-cut (i.e., the Y crystal axis of the piezoelectric material is perpendicular to the surfaces 112, 114) or rotationally Y-cut (i.e., the Y crystal axis of the piezoelectric material is rotated by a predetermined angle with respect to the normal of the surfaces 112, 114). In this case, the RF signal applied between the first front-side conductor pattern 130 and the second front-side conductor pattern 132 will excite shear acoustic waves in both the first resonator 150 and the second resonator 155. Rotational Y-cut may be used to achieve shear displacement only in a plane parallel to the surfaces 112, 114. The choice of the rotation angle may be used to control the electromechanical coupling of the resonator. Shear displacement parallel to the surface of the piezoelectric layer does not generate a compression wave in the adjacent liquid, thereby allowing high-Q-factor operation of the resonator.

[0059] As Figure 1 shown, the first front-side conductor pattern 130, the second front-side conductor pattern 132, and the rear-side conductor pattern 134 are in a rectangular shape. However, according to an alternative aspect, the conductor patterns may be non-rectangular (e.g., trapezoidal, curved, or irregular) to suppress parasitic acoustic modes.

[0060] In a detailed cross-sectional view, the thickness of the piezoelectric layer 110 is dimension ts, and the thickness of the conductor patterns 130, 132, 134 is dimension tm. According to an exemplary aspect, the thickness ts of the piezoelectric layer 110 can be, for example, from 100 nanometers (nm) to 1000 nm. Additionally, the thickness tm of the conductor patterns 130, 132, 134 can be, for example, from 10 nm to 500 nm. In an exemplary aspect, the thicknesses of the conductor patterns can be the same, or the first front-side conductor pattern 130 and the second front-side conductor pattern 132 and the rear-side conductor pattern 134 can have different thicknesses from each other.

[0061] As further shown, the piezoelectric layer can be fully or only partially etched or otherwise removed in the region between the first front-side conductor pattern 130 and the second front-side conductor pattern 132, thereby forming a groove 115. The presence of the groove 115 can suppress lateral acoustic modes that may be excited by the electric field between the front-side conductor patterns 130, 132. The depth tg of the groove 115 can extend partially or fully through the piezoelectric layer 110.

[0062] Figure 2A A simplified top view and cross-sectional view of another YBAR 200A are shown. The YBAR 200A consists of a piezoelectric layer 210 attached to a substrate 220, as described previously. A cavity 225 (identified by the dashed line) is formed in the substrate 220 such that a portion of the piezoelectric layer 210 is suspended above the cavity 225.

[0063] The first front-side conductor pattern 230 and the second front-side conductor pattern 232 (e.g., the first electrode and the second electrode) are formed on the front side of the piezoelectric layer (the side facing away from the cavity 225). The first front-side conductor pattern 230 and the second front-side conductor pattern 232 form an interdigitated finger pattern (IFP) similar to the interdigital transducer or IDT used in a surface acoustic wave resonator. The first front-side conductor pattern 230 includes a first plurality of parallel fingers extending from a first bus bar (e.g., substantially parallel). The second front-side conductor pattern 232 includes a second plurality of parallel fingers extending from a second bus bar (e.g., substantially parallel). The first plurality of parallel fingers and the second plurality of parallel fingers are interleaved, and most or all of the interleaved parallel fingers are disposed on the portion of the piezoelectric layer 210 located above the cavity 225. The width m of each finger will be a majority of the pitch p or center-to-center spacing between at least a pair of interleaved fingers extending from different bus bars.

[0064] As shown in the detailed view, in an exemplary aspect, the slot 215 may be formed in the piezoelectric layer 210 between the interleaved fingers of the first front-side conductor pattern 230 and the second front-side conductor pattern 232. The presence of the slot 215 may suppress the lateral acoustic modes that may be excited by the electric field between the front-side conductor patterns 230, 232. The depth tg of the slot 215 may partially or fully extend through the piezoelectric layer 210. The groove also prevents the vibration energy from diffusing along the structure, thereby improving the Q factor of the resonator.

[0065] The rear-side conductor pattern 234 is formed on the rear side of the piezoelectric layer 210, which is opposite to the first front-side conductor pattern 230 and the second front-side conductor pattern 232. The first resonator is formed between the first front-side conductor pattern 230 and the rear-side conductor pattern 234. The second resonator is formed between the second front-side conductor pattern 232 and the rear-side conductor pattern 234. In an exemplary aspect, the first front-side conductor pattern and the second front-side conductor pattern may have the same number of interleaved fingers. Additionally, one or more additional layers 240 may be disposed on the rear-side conductor pattern 234 opposite to the piezoelectric layer 210. In an exemplary aspect, the one or more additional layers 240 may be a dielectric layer, a sensor layer, etc., for converting the resonator into a sensor. For example, the sensing layer 240 may be, for example, a thin film, a single layer, or a surface treatment, which may be directly disposed on the rear-side conductor pattern 234 or may be coupled to the rear-side conductor pattern 234 via one or more additional intermediate layers (e.g., an adhesive layer).

[0066] Figure 2B Shown is according to another exemplary aspect Figure 2A Schematic plan view and schematic cross-sectional view of a variant of the YBAR shown. Note that the plan view of the YBAR 200B generally includes the same elements as the YBAR 200A, which includes a piezoelectric layer 210 attached to a substrate 220 and a first front-side conductor pattern 230 and a second front-side conductor pattern 232, as described above.

[0067] However, instead of having a cavity, the YBAR 200B includes an acoustic Bragg reflector 250 between (e.g., "sandwiched between") the substrate 220 and the rear surface of the piezoelectric plate 210. The term "sandwiched between" means that the acoustic Bragg reflector 250 is disposed between the surface 322 of the substrate 220 and the rear surface 114 of the piezoelectric plate 210 and is physically connected to the surface of the substrate 220 and the rear surface of the piezoelectric plate 110. In some cases, a thin layer of additional material may be disposed between the acoustic Bragg reflector 250 and the surface of the substrate 220 and / or between the Bragg acoustic reflector 250 and the rear surface of the piezoelectric plate 210. Such an additional material layer may be present, for example, to facilitate the bonding of the piezoelectric plate 210, the acoustic Bragg reflector 250, and the substrate 220.

[0068] According to an exemplary aspect, the acoustic Bragg reflector 250 includes a plurality of layers that alternate between a material having a high acoustic impedance and a material having a low acoustic impedance. "High" and "low" are relative terms. For each layer, the standard for comparison is the adjacent layer. The acoustic impedance of each "high" acoustic impedance layer is higher than the acoustic impedance of two adjacent "low" acoustic impedance layers. The acoustic impedance of each "low" acoustic impedance layer is lower than the acoustic impedance of two adjacent "high" acoustic impedance layers. In an exemplary aspect, the thickness of each layer can be equal to or about a quarter of the acoustic wavelength at or near the resonant frequency of the SM XBAR 200. Materials having a relatively low acoustic impedance include silicon dioxide, silicon oxycarbide, aluminum, titanium, and certain plastics such as cross-linked polystyrene polymers. Materials having a relatively high acoustic impedance include silicon nitride, aluminum nitride, silicon carbide, and metals such as molybdenum, tungsten, gold, and platinum. All of the high acoustic impedance layers of the acoustic Bragg reflector 250 do not have to be the same material, and all of the low acoustic impedance layers do not have to be the same material.

[0069] An exemplary cross-sectional view along section C-C of the YBAR 200B is shown. As shown, a space 215 (e.g., a cavity) is defined or formed in the first front-side conductor pattern 230, the second front-side conductor pattern 232, and the piezoelectric plate 210 to provide acoustic isolation between adjacent fingers. The space or cavity can be formed by etching or otherwise removing to effectively form a slot as the cavity 215 in the corresponding layer. The presence of the cavity 215 suppresses the lateral acoustic modes that may be excited by the electric field between the front-side conductor patterns 230, 232.

[0070] Figure 3A and Figure 3B Two exemplary cross-sectional views along section B-B defined in Figure 2A of the YBAR 200A are shown. Note that Figure 3A and Figure 3B the configuration of the substrate 320 shown can also be implemented for the Figure 1 YBAR configuration shown. In Figure 3A , a piezoelectric layer 310 corresponding to the piezoelectric layer 210 is directly attached to the substrate 320, which can correspond to the Figure 2A substrate 220. In addition, a cavity 340 that does not completely penetrate the substrate 320 is formed in the substrate below the portion of the piezoelectric layer 310 that includes the interleaved fingers of the IDT of the YBAR (i.e., the diaphragm 315). The cavity 340 can correspond to the Figure 2A cavity 225 and / or Figure 1cavity 125. In an exemplary aspect, cavity 340 can be formed, for example, by etching substrate 320 before attaching piezoelectric layer 310. Alternatively, cavity 340 can be formed by etching substrate 320 with a selective etchant that reaches the substrate through one or more openings provided in piezoelectric layer 310.

[0071] Figure 3B An alternative aspect is shown, where substrate 320 includes a base 322 and an intermediate layer 324 disposed between piezoelectric layer 310 and base 322. Intermediate layer 324 can be, for example, a dielectric layer. Intermediate layer 324 can consist of one or more layers between base 322 and piezoelectric layer 310. For example, base 322 can be silicon (e.g., a silicon support substrate), and intermediate layer 324 can be silicon oxide or silicon dioxide or silicon nitride or some other material, e.g., an intermediate dielectric layer. That is, in this aspect, base 322 and intermediate layer 324 are collectively referred to as substrate 320. As further shown, cavity 340 is formed in intermediate layer 324 beneath the portion of piezoelectric layer 310 that includes the IDT fingers of YBAR (i.e., diaphragm 315). In some cases, the cavity can be entirely disposed within intermediate layer 324, where a portion of intermediate layer 324 is attached to the portion of piezoelectric layer 310 that is above cavity 340 (i.e., diaphragm 315). For example, cavity 340 can be formed by etching intermediate layer 324 before attaching piezoelectric layer 310. Alternatively, cavity 340 can be formed by etching intermediate layer 324. In other example embodiments, depending on whether intermediate layer 324 is etched to define cavity 340, cavity 340 can be defined in intermediate layer 324 in other ways. In some cases, etching can be performed using a selective etchant that reaches the substrate through one or more openings (not shown) provided in piezoelectric layer 310. In an exemplary aspect, a thin layer of dielectric (not shown) can also be on the underside of piezoelectric layer 310, which faces intermediate layer 324 and surrounds cavity 340.

[0072] In this case, diaphragm 315 (which can correspond to Figure 1 and / or Figure 2A the diaphragm in) can be continuous with the remainder of most of the perimeter of piezoelectric layer 310 that surrounds cavity 340. For example, diaphragm 315 can be continuous with at least 50% of the remainder of the perimeter of piezoelectric layer 310 that surrounds cavity 340. As Figure 3B shown, cavity 340 extends completely through intermediate layer 324. That is, diaphragm 315 can have an outer edge facing piezoelectric layer 310, where at least 50% of the edge surface of diaphragm 315 is coupled to the portion of piezoelectric layer 310 that faces the edge of diaphragm 315. This configuration provides increased mechanical stability of the resonator.

[0073] In other configurations, the cavity 340 may extend partially into the intermediate layer 324 but not completely through the intermediate layer 324 (i.e., the intermediate layer 324 may extend above the bottom of the cavity on top of the substrate 322) or may extend through the intermediate layer 324 and (partially or fully) into the substrate 322. As described above, it should be understood that, according to various exemplary aspects, the interleaved fingers of the IDT may be disposed on Figure 3A and Figure 3B either or both surfaces of the diaphragm 315 in Figure 2B . Also note that while the exemplary aspects contemplate a resonator structure utilizing a membrane-based resonator structure, in alternative aspects, such as using a configuration as described above with respect to Figure 2B , the resonator structure may be securely mounted on a metallic Bragg stack (mirror or reflector) to improve reliability.

[0074] Figure 4A A schematic plan view and a perspective view of an acoustic resonator structure are shown, which is a refinement of an exemplary aspect of the YBAR shown in Figure 2A . It should be understood that Figure 4A the acoustic resonator structure shown may also be configured to have an acoustic Bragg reflector configuration as described above with respect to the YBAR configuration in Figure 2B . The X-axis and Y-axis are shown relative to the plan view in Figure 4A . Figure 4B A cross-sectional view of the IDT configuration in Figure 4A is shown. Figure 4B The Z-axis in Figure 4A is orthogonal to the plane defined by the X-axis and Y-axis in Figure 4A .

[0075] As shown, electrode fingers (e.g., a pair) extend from a pair of bus bars in a similar configuration as described above. In an exemplary aspect, a plurality of electrode fingers (also referred to as nanowires) each extend from the bus bar mainly in a first direction (e.g., substantially parallel to each other). Each electrode finger includes: an electrode 436A (top or first electrode) having a first electric potential (e.g., positive electric potential) extending from the first bus bar 430, on top of (e.g., the first side of) the piezoelectric layer 410; and an electrode 436B (bottom or second electrode) having a second electric potential (e.g., negative electric potential) extending from the second bus bar 432, at the bottom of (e.g., the second side of) the piezoelectric layer / material, such that the electrode 436A at the top of the piezoelectric layer 410 at least partially overlaps with the electrode 436B at the bottom of the piezoelectric layer 410. It should be readily understood that the top electrode 436A and the bottom electrode 436B have isolating piezoelectric therebetween, such that a cavity (e.g., an air gap or some insulating material such as a dielectric) provides enhanced isolation between each adjacent pair of top and bottom electrodes and adjacent pairs of top and bottom electrodes. Below, with respect to the YBAR configuration described in Figure 5 and asFigure 8 The configurations with piston masses shown can each also have isolation between corresponding electrode fingers.

[0076] Note that although the piezoelectric layer 410 is shown as having the same width as the first and second electrodes in the X direction, in an alternative aspect, the piezoelectric layer can have a greater width in the X direction such that the electrodes (in the X direction) have a smaller width than the piezoelectric layer. In addition to the rectangular shape, the piezoelectric layer 410 can have different cross-sectional shapes, such as a hexagonal shape. Further, although the corners / edges of the piezoelectric layer 410 and the electronic device are shown as having 90 degrees or right angles, it should be understood that these corners or edges can be rounded or curved in practice, which may be caused by deposition and / or etching processes, as will be understood by those skilled in the art. Additionally, it should be understood that the electrodes 436A and / or 436B can (i.e., in the X direction) have a greater width than the piezoelectric layer 410, and the top and bottom electrodes can also have different widths from each other. It should be understood that these configurations can be applied to, for example Figure 4A , Figure 4B , Figure 5 and / or Figure 8 each of the embodiments shown.

[0077] Figure 4B shows how the electrode 436B having a second electric potential extends into the cavity (e.g., cavity 125 / 225) of the acoustic resonator, as described above. In an exemplary aspect, this configuration is described as a McBAW resonator. As described above, the cavity can be directly provided in the substrate, as Figure 3A shown. Alternatively, the cavity can be provided in an intermediate layer (e.g., a dielectric layer) between the substrate and the IDT structure, as Figure 3B shown.

[0078] Thus, according to Figure 4A and Figure 4B the exemplary aspects shown, there is provided an acoustic resonator that includes: a substrate (e.g., Figure 4Ba substrate (e.g., substrate 420); a piezoelectric layer (e.g., piezoelectric layer 410) directly coupled to the substrate or coupled to the substrate via one or more intermediate layers; a first conductor pattern forming a plurality of first electrodes 436A (having a first electric potential) disposed on a first surface of the piezoelectric layer; and a second conductor pattern forming a plurality of second electrodes 436B (having a second electric potential) disposed on a second surface of the piezoelectric layer 410 opposite the first surface. In this aspect, the corresponding electrodes of the first conductor pattern and the second conductor pattern together with the piezoelectric layer disposed therebetween form at least a pair of electrode fingers (also referred to as "acoustic resonant nanowires") that extend from a bus bar in a first direction and are acoustically isolated from each other, or at least acoustically insulated from each other, by a cavity or space disposed between adjacent nanowires (e.g., electrode fingers).

[0079] Thus, in an exemplary aspect, each of a plurality of nanowires extends from a bus bar in a first direction (e.g., Figure 4A the y-axis direction as shown), such that a space is defined between the nanowires (e.g., at least a pair of the plurality of nanowires) in a second direction that is substantially perpendicular to the first direction (e.g., Figure 4A the x-axis direction as shown). In this aspect, there is no piezoelectric material between a pair of nanowires in the second direction. In other words, as Figure 4A further shown, the conductor pattern and the piezoelectric material can be removed in the x and y regions between adjacent top and bottom electrode pairs such that the fingers (i.e., nanowires) formed by each top and bottom electrode pair are substantially acoustically isolated from each other, or at least partially acoustically isolated from each other, because the piezoelectric layer does not connect one finger to the next. Thus, top and bottom electrodes having isolated piezoelectric therebetween can be isolated from adjacent top and bottom electrodes having piezoelectric therebetween by a cavity (such as a space or air gap), some insulating material (such as a dielectric), or any other arrangement that allows enhanced isolation between each adjacent top and bottom electrode pair and adjacent top and bottom electrode pairs. For example, an exemplary YBAR configuration having this acoustic isolation configuration is described above with respect to Figure 2B this.

[0080] As described in more detail below, a pair of electrode fingers each include a width in a second direction that is substantially perpendicular to a first direction and a height in a thickness direction that is substantially orthogonal to the first and second directions. The ratio of the width to the height of each electrode finger is less than 2 to reduce spurious during excitation of the resonator device. As further shown, the acoustic resonator includes a pair of busbars (similar to the above configuration), where a first busbar of the pair is coupled to a first conductor pattern and a second busbar of the pair is coupled to a second conductor pattern. Note that the term "substantially" (e.g., "substantially perpendicular" and / or "substantially orthogonal") means that the relative directions are generally perpendicular or orthogonal, but may be slightly different (e.g., 10 degrees) to account for small tolerances in manufacturing differences.

[0081] Figure 5 is shown Figure 2A A schematic plan view and a perspective view of another refined IDT configuration of an exemplary aspect of the YBAR shown. It should be understood that Figure 5 the acoustic resonator structure shown can also be configured to have an acoustic Bragg reflector configuration as described above with respect to Figure 2B the YBAR configuration. In either case, in the Figure 5 configuration, two electrodes 536A and 536B having a positive potential and a negative potential are both on a first side (e.g., the top side or the top surface) of the piezoelectric layer 510, while the floating electrode 536C is on the opposite side (e.g., the second side) (e.g., the bottom side or the bottom surface) of the piezoelectric layer 510. A similar configuration was described above with respect to Figure 1 except that the configuration includes a plurality (e.g., a pair) of electrode fingers. Figure 5 The exemplary acoustic resonator structure shown is similar to the exemplary acoustic resonator structures described above in Figure 4A and Figure 4B except that it provides the following YBAR configuration in which a first busbar 530 of a pair of busbars is coupled to a first conductor pattern (e.g., finger 536A) and a second busbar 532 of the pair is coupled to a second conductor pattern (e.g., finger 536B). Additionally, the floating conductor pattern is a floating electrode 536C that at least partially overlaps the conductor patterns 536A and 536B. Note that while the piezoelectric layer 510 is shown as having the same width as the first and second electrodes in the X direction, in an alternative aspect, the piezoelectric layer 510 may have a greater width in the X direction.

[0082] According to Figure 4A , Figure 4B and Figure 5In an exemplary aspect, the acoustic resonator is configured such that the X-dimension (i.e., the width in the X-direction) of the fingers is reduced to a minimum to form a single pair of electrodes as shown therein. Thus, an array of electrode pairs can be arranged and, since they are separated by a vacuum, the electrode pairs are acoustically isolated from each other through the spaces or cavities between adjacent fingers, or at least partially acoustically isolated from each other, because the piezoelectric material is confined between the top and bottom electrodes or substantially between the top and bottom electrodes. According to this configuration, when the X-dimension of the electrode fingers is reduced to a minimum, the physics becomes quasi-1D and X-related strays will only occur at high operating frequencies.

[0083] Figure 6 Shows a top view of the IDT configuration according to an exemplary aspect Figure 4A and Figure 4B in. Figure 7A and Figure 7B Shows a graph of the admittance [y] according to the frequency of an acoustic resonator according to an exemplary aspect.

[0084] According to an exemplary aspect, the piezoelectric layer 410 may include lithium niobate having Euler angles (90, 90, 30 ± 4). This configuration provides a very high electromechanical coupling (i.e., k 2 ≈ 0.39), which is sufficient for Wi-Fi full band without an inductor. Figure 7A Shows a two-dimensional (2D) simulation simulated using the finite element method (FEM) simulation technique for the X-direction (2Dx), and shows the admittance of an existing series resonator for the Wi-Fi full band. Also note that the total area required for the resonator will depend on the etching process. Figure 6 Shows an estimate of the area required using a 5 µm spacing between electrode pairs.

[0085] Figure 7B Shows 2Dx FEM simulations with various line widths according to an exemplary aspect. Note that the resonance frequency is insensitive to the electrode width, which means that resonance broadening will not have an adverse effect compared to XBAR. However, strays are sensitive to the width and sidewall angle. For XBAR, the electrode dimensions should be fabricated precisely to control the effect of strays. According to an exemplary aspect, if the line width is narrow enough, all X-direction strays will only occur at high frequencies (e.g., greater than 9000 MHz). In addition, X-direction strays will also be smoothed out by normal variations in the electrode width.

[0086] Figure 8 Shows according to an exemplary aspect Figure 4A and Figure 4BTop view of another IDT configuration of the acoustic resonator shown. In this regard, piston masses 460A to 460D are respectively disposed on top of the ends of electrode fingers 436A. The piston mass can be an additional layer (e.g., metal) that is deposited adjacent to the bus bar 430 and on the free end of the electrode 436A to address strays. Thus, as shown, the acoustic resonator includes a pair of piston masses that are disposed on the top surface of a first conductor pattern forming a pair of electrode fingers. In an exemplary aspect, the first pair of piston masses 460A and 460B are disposed adjacent to the base (e.g., connected to the bus bar 430), and the second pair of piston masses 460C and 460D are respectively disposed on the free end of each of the pair of electrode fingers 436A. The piston mass can generally be considered an additional metal layer that, for example, has a rectangular or square shape when viewed from its plan view. Preferably, the piston masses 460A to 460D have the same width as the first conductor pattern and the second conductor pattern 436A (i.e., in the X direction). The pair of piston masses can be disposed on the first conductor pattern and / or on both the first conductor pattern and the second conductor pattern such that they overlap each other in the plan view (i.e., in the Z direction).

[0087] Figure 9A and Figure 9B shows according to an exemplary aspect according to Figure 8 Graphs of the admittance [y] as a function of the frequency of the acoustic resonator shown. These graphs are also simulated using the finite element method (FEM) simulation technique. According to an exemplary aspect, significant strays can exist in the aperture (i.e., the Y direction). However, the piston masses 460A to 460D are provided to suppress these strays. Figure 9A Shows a comparison of 2Dy and 2Dx simulations and additional cavity modes. According to an exemplary aspect, these lateral modes are suppressed by the piston masses 460A to 460D. Figure 9B Shows an exemplary aspect of the piston mode, which shows a reduction in strays.

[0088] Figure 10 shows according to an exemplary aspect as Figure 4A and / or Figure 5Cross-sectional view of IDT fingers (e.g., acoustic resonant nanowires) of the illustrated acoustic resonator configuration. It should be understood that the exemplary electrode fingers include a first or top electrode 1032 and a second or bottom electrode 1034, with a piezoelectric layer 1010 disposed therebetween. According to an exemplary aspect, the width of at least one (or both) electrodes (i.e., represented by the width w in the X direction) is less than twice the height in the thickness direction (i.e., represented by the height h in the Z direction), where the height h is defined as the total height of the electrode fingers (i.e., top electrode 1032, bottom electrode 1034, and piezoelectric layer 1010). In some cases, the thickness direction may be orthogonal to the top or bottom surface of the piezoelectric body. However, due to manufacturing tolerances, the top or bottom surface of the piezoelectric body may have variations, in which case the thickness direction may be substantially orthogonal (as orthogonal as possible) to the top or bottom surface of the piezoelectric body. In any case, the height h of the electrode fingers can be measured from the bottom electrode (and including the bottom electrode) to the top electrode (and including the top electrode). Figure 10 The non-limiting example shown depicts a top electrode 1032 and a bottom electrode 1034, each having a height of 96 nm and formed of aluminum. Additionally, the piezoelectric layer 1010 may be formed of lithium niobate and have a height of 354 nm.

[0089] Thus, according to an exemplary aspect, as Figure 10 shown, the ratio of x / z is less than 2. Additionally, note that the resonator performance is mainly set by the electrodes away from the piston mass (assuming they are included according to an exemplary aspect). Thus, it should be understood that if the aspect ratio x / z is less than 2, at the ends of the fingers where the piston mass is located, the aspect ratio will be even smaller (i.e., due to the increased height). According to an exemplary aspect, due to the smaller effective area, the capacitance density is much higher than that of the XBAR structure. Additionally, due to the metal covering the top and bottom surfaces of the piezoelectric layer, the thermal conductivity is much higher, and thus these effects can cancel each other out, resulting in power handling similar to that of the XBAR.

[0090] Figure 11A A graph of the admittance [y] according to the frequency of an acoustic resonator is shown according to an exemplary aspect. Figure 11B A graph of the coupling coefficient k according to the aspect ratio of an acoustic resonator is shown according to an exemplary aspect. 2 These graphs are also simulated using finite element method (FEM) simulation techniques.

[0091] According to an exemplary aspect, the aspect ratio (i.e., width / total height of the electrode structure) should be minimized to avoid strays. Figure 11AShows 2Dx FEM simulations with a fixed height and various widths. As shown, an acoustic resonator structure with a smaller aspect ratio shifts X-direction strays to higher frequencies. Thus, it should be understood that an acoustic resonator structure with an aspect ratio less than 1 according to an exemplary aspect is beneficial for minimizing strays. On the other hand, Figure 11B Shows that: for very small aspect ratios, the coupling decreases. Thus, according to an exemplary aspect, the acoustic resonator structure preferably has an aspect ratio less than 2.

[0092] Figure 12A Shows according to an exemplary aspect Figure 8 A cross-sectional view of the IDT fingers (e.g., acoustic resonator nanowires) of the acoustic resonator configuration shown. Note that Figure 12A The first cross-sectional view in the XZ plane shown generally corresponds to the configuration described above with respect to Figure 10 and the details will not be repeated herein. Additionally, Figure 12A The second cross-sectional view in the ZY plane shown can correspond to the same configuration and includes multiple pistons as described above with respect to Figure 8 In this case, the pistons can have an exemplary height of 120 nm.

[0093] Figure 12B and Figure 12C Shows a graph of the admittance [y] according to the frequency of an acoustic resonator according to an exemplary aspect. As described above with respect to Figure 8 The lateral (i.e., Y-direction) mode can be substantially and / or completely suppressed by the piston mass. Figure 12B Shows a 2Dy FEM simulation of an acoustic resonator structure without piston mass, which shows aperture-related lateral modes. Also shown is the 2Dy FEM of the same acoustic resonator structure described above with respect to Figure 8 (where piston mass is added on the top and bottom), where the lateral mode is shown to be completely suppressed. Figure 12C Shows a full 3D FEM simulation of the same acoustic resonator structure with piston mass, which also confirms the suppression of the lateral mode.

[0094] In yet another exemplary aspect, multilayer electrodes can be used for vertically field-excited resonators (e.g., YBAR, McBAW, ARN, etc.).

[0095] Specifically, Figures 13A to 13B Depicts the stress fields in the lateral and vertical excitation devices. In some examples, such as Figure 13BAs shown, for vertical excitation structures 1302 such as ARN, YBAR, and McBAW, electrodes are placed along the acoustic path (e.g., Al) 1312A to 1312B, and as shown by stress field 1322, significant acoustic energy / stress in the metal can result in significant acoustic losses in the electrodes. For a lateral excitation device 1301 (e.g., XBAR), as Figure 13A shown by stress field 1321, the metal is not placed along the acoustic path, and the acoustic energy / stress is mainly confined to the region between the metal IDTs (e.g., Al) 1311. Therefore, the acoustic energy / stress in the metal is small, and the acoustic losses in the electrodes are minimized. To reduce (e.g., minimize) the energy / acoustic damping in the electrodes (e.g., metal layers) of the vertical excitation structure, electrode materials with a higher Q factor can be used, the energy distribution within the electrodes can be reduced (e.g., minimized), and the electrode thickness can be decreased.

[0096] According to an exemplary aspect of the present disclosure, a multi-layer metal structure including multi-layer electrodes in the thickness direction (e.g., Z-axis) can be used as a vertical excitation structure. Examples of vertical excitation structures include, for example Figures 1 to 2B , Figures 4A to 4B , Figure 5 , Figure 8 and so on, as shown by acoustic resonator structures.

[0097] Figure 14 An example of a multi-layer metal structure (or multi-layer electrodes) of a first conductor pattern (TE) disposed on a first surface of a piezoelectric layer (Piezo) of an acoustic resonator structure and a second conductor pattern (BE) disposed on a second surface of the piezoelectric layer is shown according to an aspect of the present disclosure. It should be understood that Figure 14 the structure shown generally corresponds to Figure 13B the structure shown, except that the first conductor pattern (TE) may include a first electrode layer (TE1) having a first acoustic impedance (e.g., high acoustic Z) and a second electrode layer (TE2) having a second acoustic impedance (e.g., low acoustic Z), and the second acoustic impedance is lower than the first acoustic impedance. The second conductor pattern (BE) may include a first electrode layer (BE1) having a first acoustic impedance (e.g., high acoustic Z) and a second electrode layer (BE2) having a second acoustic impedance (e.g., low acoustic Z), and the second acoustic impedance is lower than the first acoustic impedance.

[0098] In an example, the multi-layer metal structure is symmetric. For example, the thickness (or height) of TE1 along the Z-axis is substantially the same as the thickness (or height) of BE1 along the Z-axis. Similarly, the thickness (or height) of TE2 along the Z-axis is substantially the same as the thickness (or height) of BE2 along the Z-axis. In addition, the materials of TE1 and BE1 are substantially the same, and the materials of TE2 and BE2 are substantially the same.

[0099] In some examples, the multi-layer metal structure is asymmetric.

[0100] In an example, as Figure 14 shown, the number of multi-layer electrodes of the first conductor pattern is two, and the number of multi-layer electrodes of the second conductor pattern is two. Therefore, the multi-layer electrodes are referred to as 2-layer electrodes or a 2-layer electrode structure.

[0101] In an example, for instance Figure 14 shown, the first electrode layer (TE1) of the first conductor pattern is disposed between the second electrode layer (TE2) of the first conductor pattern and a piezoelectric layer (e.g., made of lithium niobate (LiNbO3) or a similar synthetic salt formed by niobium, lithium, and oxygen), and the first electrode layer (BE1) of the second conductor pattern is disposed between the second electrode layer (BE2) of the second conductor pattern and the piezoelectric layer.

[0102] Referring to Figure 14 it, a 2-layer electrode (wherein a thin high-impedance metal TE1 or BE1 (e.g., tungsten (W), platinum (Pt), molybdenum (Mo), ruthenium (Ru), etc.) is placed closest to the piezoelectric layer (e.g., directly on the piezoelectric layer), and then a low-impedance metal (e.g., Al) TE2 or BE2) can be used to reduce (e.g., significantly reduce) the energy and loss within the electrode layer (e.g., TE and / or BE). Additionally, in some examples, the benefits include higher electromechanical coupling (e.g., k 2 improvement) and a reduction in the trace resistance of the IDT. In contrast, a single-layer electrode that uses a high-speed material to reduce (e.g., minimize) the energy and loss within the single-layer electrode is less effective than the 2-layer electrode described in the present disclosure. Referring below to Figures 18A to 18C to describe the high-speed material. In some examples, the high-speed material refers to a material that is relatively hard and has a relatively small density.

[0103] Figures 15A to 15C Displacements 1501, 1502, and 1503, stresses 1511, 1512, and 1513, and acoustic energies 1521, 1522, and 1523 of three different electrode structures 1531, 1502, and 1533 are shown, respectively. Electrode structure 1531 is a 1-layer electrode including Al (e.g., both TE1 and TE2 are made of Al). Electrode structure 1532 is a 1-layer electrode including W. Electrode structure 1533 is a 2-layer electrode including W as TE1 and Al as TE2. Figures 15A to 15C It is shown that using the 2-layer electrode structure 1533 (wherein a thin high-impedance metal (e.g., W, Pt, Mo, etc.) is placed closest to the piezoelectric layer, and then a low-impedance metal (e.g., Al)) can significantly reduce the energy within the electrode structure 1533 (W and Al). Referring to Figures 15A to 15C it, Figure 15CThe distribution of energy 1523 within the metal (Al and W) is less than Figure 15A and Figure 15B the distribution of energies 1521 and 1522 within the metal (Al or W) of the single-layer electrode in

[0104] For example, the multi-layer electrode structure (e.g., Figure 14 the two-layer electrode structure shown) can be optimized by manipulating the geometry and / or materials of the multi-layer electrode structure. In one aspect, certain parameters (e.g., fd, Qm, k2, etc.) indicating the performance of the multi-layer electrode structure can be used to determine this optimization. Manipulating the geometry of the multi-layer electrode structure can include controlling the thicknesses of TE1, TE2, TE, BE1, BE2, BE, and / or the piezoelectric layer. In one aspect, for example, the multi-layer electrode structure (e.g., TE the two-layer electrode structure shown) can be optimized by controlling the ratio of the thickness h piezo of TE to the thickness h TE of the piezoelectric layer (indicated by h piezo / h TE1 ), the ratio of the thickness h TE of TE1 to the thickness h TE1 of TE (indicated by h TE / h BE ), the ratio of the thickness h BE of BE to the thickness of the piezoelectric layer (indicated by h piezo / h BE1 ), the ratio of the thickness h BE1 of BE1 to the thickness of BE (indicated by h BE / h Figure 14 ), etc.

[0105] In one aspect, for an optimal electrode stack, the parameters characterizing the acoustic resonator (including the parameters fd, quality factor (Qm), and electromechanical coupling (k2)) can be relatively large. The optimal ratio h TE / h piezo and the optimal ratio h TE1 / h TE can be determined based on the fd graph, quality factor or Q-factor (Qm) graph, and / or electromechanical coupling (k2) graph to optimize the electrode stack (or multi-layer electrode). In an example, fd is the frequency constant in m / s, i.e., the frequency multiplied by the thickness h piezo of the piezoelectric layer. In an example, Qm is the motional Q-factor at resonance. In some examples, the two-layer electrode is optimized to achieve relatively large fd, Qm, and / or k2.

[0106] Figures 16A to 16C respectively show having Figure 14fd diagrams, Qm diagrams, and k2 diagrams of a 2-layer electrode structure acoustic resonator (e.g., ARN) as shown. For Figures 16A to 16C the example shown, layer TE1 and BE1 are formed of W, and layers TE2 and BE2 are formed of Al. Layer TE includes TE1 and TE2, and layer BE includes BE1 and BE2. A piezoelectric layer (e.g., having Euler angles of (90, 90, 30) and made of LiNbO3) is disposed between TE and BE. The quality factor Q piezo of the piezoelectric layer is 5000. The quality factor Q metal of the metal layer is 200. For each diagram, the x-axis (horizontal axis) indicates the ratio h TE / h piezo of the thickness of the electrode to the thickness of the piezoelectric body, and the y-axis (vertical axis) indicates the ratio h TE1 / h TE .

[0107] Reference Figure 16B , the dashed line 1601 indicates that the 2-layer electrode is substantially the same as a single-layer electrode made of TE2 (which can be aluminum) because the ratio h TE1 / h TE is close to 0. The dashed line 1602 indicates that the 2-layer electrode is substantially the same as a single-layer electrode made of TE1 (which is W) because the ratio h TE1 / h TE is close to 1. Within the dashed-line region 1605, the dashed line 1603 indicates that the 2-layer electrode is a composite electrode including the first electrode layer W and the second electrode layer Al because the ratio h TE1 / h TE is between 0 and 1. The dashed-line region 1605 indicates the acceptable range of the ratio h TE1 / h TE , generally greater than 0.1 and less than 0.6. Figure 16B It is shown that: when the ratio h TE1 / h TE increases from 0 to the optimal ratio and when the ratio h TE1 / h TE decreases from 1 to the optimal ratio, the quality factor (Qm) increases, so using a 2-layer electrode can improve Qm. In Figure 16B the example shown, the optimal ratio is within a certain range, for example, between 0.2 and 0.5 (e.g., between 0.3 and 0.4). Figures 16A to 16C It is shown that: compared with a single-layer electrode made of Al or W, the 2-layer electrode can improve Qm and k2.

[0108] The optimal ratio (e.g., h TE1 / h TEThe range in which the optimal ratio (e.g., the optimal ratio of h Figure 16B as shown) appears can depend on which one or more parameters are used to optimize the ratio. For example, whether Qm is used (as shown in Figure 16A ), whether fd is used (as shown in 2 ), and / or whether k Figure 16C is used (as shown in Figure 16B ). In an example, Qm (as shown in TE1 / h TE ) is used to optimize the range in which the optimal ratio (e.g., the optimal ratio of h

[0109] Reference Figures 16A to 16B , in the example, when h TE1 / h TE increases (indicating the use of more of the first electrode layer), Qm increases while fd decreases. Thus, a trade-off can occur when optimizing the ratio of multiple parameters.

[0110] The range in which the optimal ratio (e.g., the optimal ratio of h TE1 / h TE ) appears can depend on the material of the first electrode layer (TE1 and / or BE1) and / or the second electrode layer (TE2 and / or BE2), as shown in Figures 20A to 20C , Figures 21A to 21C , and Figures 19A to 19C .

[0111] In one aspect, the ratio h TE1 / h TE of the height (or thickness) of TE1 to the total thickness (or total height) of the multi-layer electrode (TE) can be from 0.1 to 0.6. In an exemplary aspect, the ratio h BE1 / h BE of the height (or thickness) of BE1 to the total thickness (or total height) of the multi-layer electrode (BE) can be from 0.1 to 0.6. In one aspect, the ratio h TE / h piezo of the total thickness of TE to the thickness of the piezoelectric layer can be from 0.1 to 0.5. In one aspect, the ratio h BE / h piezo of the total thickness of BE to the thickness of the piezoelectric layer can be from 0.1 to 0.5. The ratio can be determined based on a graph showing the simulation results in Figures 20A to 20C , Figures 21A to 21C , and Figures 19A to 19C .

[0112] With the appropriate electrode ratios as described above, the acoustic energy in the two metal layers (e.g., TE and / or BE) can be reduced (e.g., minimized) to reduce attenuation in the lossy metal layer, thereby improving the Q factor, and the coupling (e.g., the separation between the resonant frequency Fr and the anti-resonant frequency Fa) can be increased. Additionally, in an exemplary aspect, the TE and BE are made symmetric.

[0113] Figure 17 The simulated results of the displacement (“D”), stress (“S”), and energy (“E”) of nine electrode structures are shown respectively. Each of the nine electrode structures has one layer of electrodes. The three columns correspond to three different values (0.5, 1, and 2) of the stiffness ratio C m / C LN , where C m is the stiffness or elastic constant of the metal layer, and C LN is the stiffness or elastic constant of the piezoelectric layer. Thus, the electrodes become harder from left to right. The three rows correspond to the density ratio ρ m of the electrode to the density ρ LN of the piezoelectric layer, with three different values (0.5, 1, and 2) of ρ m / ρ LN . Thus, from the top row to the bottom row, the weight per unit volume of the electrodes becomes heavier.

[0114] Figure 17 Shows that: the energy (E) in the electrodes can be reduced (e.g., minimized) and thus the acoustic damping can be reduced by selecting a light (e.g., having a low ρ m / ρ LN ) and hard (e.g., having a high C m / C LN ) metal, which can be referred to as a high-speed metal located at the upper right corner in Figures 18A to 18C . In this example, the light and hard metal (e.g., high-speed metal) has a C m / C LN of 2 and a ρ m / ρ LN of 0.5.

[0115] Figures 18A to 18C Shows an example of the optimal material parameters (e.g., the stiffness and density indicated by C m / C LN and ρ m / ρ LN ) of a single electrode according to an aspect of the present disclosure. In the simulation used in Figures 18A to 18C , the ratio h TE / h piezo is 0.2, and the ratio h BE / h piezo is 0.2. Figure 18Ashows the fd diagram, which indicates how the parameter fd varies with C m / C LN and ρ m / ρ LN varies. Figure 18B shows the Qm diagram, which indicates how the parameter Qm varies with C m / C LN and ρ m / ρ LN varies. Figure 18B shows that higher Qm (e.g., maximum Qm) can be obtained by using a metal with high stiffness and low density (e.g., high-speed metal), which is also shown in Figure 17 as well. Figure 18C shows the k2 diagram, which indicates how the parameter k2 varies with C m / C LN and ρ m / ρ LN varies. Figure 18C shows that higher k2 (e.g., maximum k2) can be obtained by using a metal with high stiffness and high density (e.g., also known as high-impedance metal), which is also shown at the lower right corner in Figure 17 (in Figure 17 , C m / C LN is 2 and ρ m / ρ LN is 2).

[0116] Return to reference Figure 17 , when C m / C LN is lower (e.g., 0.5) and ρ m / ρ LN is higher (e.g., 2), the metal can be called a low-speed metal and can result in relatively large energy dissipation in the metal (e.g., maximum energy), which may not be optimal for many applications.

[0117] As described above, the two-layer electrode can be optimized by manipulating the geometry of the two-layer electrode (e.g., as described in Figures 16A to 16C ) and by using different metal materials in the one-layer electrode (e.g., as described in Figure 17 and Figures 18A to 18C ).

[0118] In the example, different metal materials can be used for TE1 and BE1 in the two-layer electrode. Figures 19A to 19C 、 Figures 20A to 20C , and Figures 21A to 21C show the effects of different metal materials as TE1 and BE1 in the two-layer electrode.

[0119] Figures 19A to 19CRespectively shown are the fd diagram, Qm diagram, and k2 diagram of a vertical excitation structure having a Figure 14 two-layer electrode structure as shown. In the Figures 19A to 19C example shown, TE1 and BE1 are formed of Ru, and TE2 and BE2 are formed of Al. TE includes TE1 and TE2. BE includes BE1 and BE2. A piezoelectric layer is disposed between TE and BE, where the Euler angles are [90°, 90°, 30°], and the piezoelectric layer is made of lithium niobate (e.g., LiNbO3). The quality factor Q of the piezoelectric layer piezo is 5000. The quality factor Q of the metal layer metal is 200. For each diagram, the x-axis (horizontal axis) indicates the ratio h of the thickness of the electrode to the thickness of the piezoelectric body TE / h piezo , and the y-axis (vertical axis) indicates the ratio h of the thickness of the first electrode layer Ru to the total thickness of the two-layer electrode TE1 / h TE . Figures 19A to 19C It is shown that: compared with a single-layer electrode made of Ru or W, the two-layer electrode can improve Qm and k2.

[0120] Figures 20A to 20C Respectively shown are the fd diagram, Qm diagram, and k2 diagram of a vertical excitation structure having a Figure 14 two-layer electrode structure as shown. In the Figures 20A to 20C example shown, TE1 and BE1 are formed of Pt, and TE2 and BE2 are formed of Al. TE includes TE1 and TE2. BE includes BE1 and BE2. A piezoelectric layer is disposed between TE and BE, where the Euler angles are [90°, 90°, 30°], and the piezoelectric layer is made of lithium niobate (LiNbO3). The quality factor Q of the piezoelectric layer piezo is 5000. The quality factor Q of the metal layer metal is 200. For each diagram, the x-axis (horizontal axis) indicates the ratio h of the thickness of the electrode to the thickness of the piezoelectric body TE / h piezo , and the y-axis (vertical axis) indicates the ratio h of the thickness of the first electrode layer Pt to the total thickness of the two-layer electrode TE1 / h TE . Figures 20A to 20C It is shown that: compared with a single-layer electrode made of Pt or W, the two-layer electrode can improve Qm and k2. In the example, the two-layer electrode can be used for a McBAW resonator.

[0121] Figures 21A to 21C Respectively shown are the fd diagram, Qm diagram, and k2 diagram of a vertical excitation structure having a Figure 14 two-layer electrode structure as shown. In the Figures 21A to 21CIn the example shown, TE1 and BE1 are formed of Mo, and TE2 and BE2 are formed of Al. TE includes TE1 and TE2. BE includes BE1 and BE2. A piezoelectric layer is disposed between TE and BE, where the Euler angles are [90°, 90°, 30°], and the piezoelectric layer is made of lithium niobate (LiNbO3). The quality factor Q of the piezoelectric layer piezo is 5000. The quality factor Q of the metal layer metal is 200. For each figure, the x-axis (horizontal axis) indicates the ratio h TE / h piezo of the thickness of the electrode to the thickness of the piezoelectric body, and the y-axis (vertical axis) indicates the ratio h TE1 / h TE .

[0122] Comparison Figure 16B , Figure 19B , Figure 20B and Figure 21B , the optimal ranges of the ratios h TE / h piezo and h TE1 / h TE can depend on the materials in the two-layer electrode. Figure 16B indicates that when TE1 and BE1 include W, in order to achieve a relatively large Qm, the optimal range of the ratio h TE1 / h TE is about 0.2 to 0.5 (for example, 0.3 to 0.4). Figure 19B indicates that when TE1 and BE1 include Ru, in order to achieve a relatively large Qm, the optimal range of the ratio h TE1 / h TE is about 0.3 to 0.6 (for example, 0.4 to 0.6). Figures 20B to 21B indicates that when TE1 and BE1 include Pt or Mo, in order to achieve a relatively large Qm, the optimal range of the ratio h TE1 / h TE is about 0.1 to 0.3 (for example, 0.18 to 0.25). When TE1 changes from (i) W or Ru to (ii) Pt or Mo, the thickness of TE1 will be reduced to obtain a larger Qm.

[0123] Figure 22A is a schematic block diagram of a bandpass filter using an acoustic resonator structure according to an exemplary aspect. The bandpass filter 2200 has a conventional ladder filter architecture, which includes three series resonators 2210A, 2210B, and 2210C and two parallel resonators 2220A and 2220B. The series resonators 2210A, 2210B, and 2210C are connected in series between the first port and the second port (thus called "series resonators"). InFigure 22A In it, the first port and the second port are respectively labeled as "Input (In)" and "Output (Out)". However, the filter 2200 is bi-directional and either port can be used as the input or output of the filter. At least two parallel resonators (such as parallel resonators 2220A and 2220B) are connected from the node between the series resonators to the ground connection. The filter may include Figure 22A additional reactance components (such as inductors) not shown in it. In an exemplary aspect, all the parallel resonators and series resonators are acoustic resonators. Including three series resonators and two parallel resonators is an example. The filter may have more or fewer than a total of five resonators, more or fewer than three series resonators, and more or fewer than two parallel resonators. Generally, all the series resonators are connected in series between the input and output of the filter. All the parallel resonators are generally connected between the ground and the node between the input, output, or two series resonators.

[0124] In the exemplary filter 2200, the series resonators 2210A, 2210B, and 2210C and the parallel resonators 2220A and 2220B of the filter 2200 are formed on a piezoelectric layer of at least one (and in some cases a single) piezoelectric material bonded to a silicon substrate (not visible). However, in an alternative aspect, for example, each resonator may be formed on a separate piezoelectric layer bonded to a separate substrate. Additionally, each resonator includes a corresponding IDT (not shown), where at least the fingers of the IDT are disposed above a cavity or an acoustic mirror in the substrate. In this context and similar contexts, the term "corresponding" means "relating things to each other", i.e., having a one-to-one correspondence. In Figure 22A it, the cavity is schematically shown as a dashed rectangle (e.g., rectangle 2235). In this example, each IDT is disposed above the corresponding cavity. In other filters, the IDTs of two or more resonators may be disposed above a single cavity.

[0125] Each resonator in the filter 2200 has a resonance at which the admittance of the resonator is very high and an anti-resonance at which the admittance of the resonator is very low. The resonance and anti-resonance occur at the resonance frequency and the anti-resonance frequency respectively, and for each resonator in the filter 2200, the resonance frequency and the anti-resonance frequency may be the same or different. In short, each resonator can be regarded as a short circuit at its resonance frequency and an open circuit at its anti-resonance frequency. At the resonance frequency of the parallel resonator and the anti-resonance frequency of the series resonator, the input-output transfer function will be close to zero. In a typical filter, the resonance frequency of the parallel resonator is below the lower edge of the filter passband, and the anti-resonance frequency of the series resonator is above the upper edge of the passband.

[0126] The frequency range between the resonant frequency and the anti-resonant frequency of a resonator corresponds to the coupling of the resonator. Depending on the design parameters of the filter 2200, each of the resonators can have a specific coupling parameter, and the corresponding resonator is tuned to that coupling parameter to achieve the desired frequency response of the filter 2200. According to an exemplary aspect, each of the series resonators 2210A, 2210B, and 2210C and the parallel resonators 2220A and 2220B can have an acoustic resonator configuration as described above with respect to Figures 1 to 2B , Figure 4A , Figure 4B , Figure 5 , Figure 6 and Figure 8 .

[0127] Figure 22B is a schematic diagram of a radio frequency module of an acoustic wave filter according to an exemplary aspect, including Figure 22A . Specifically, Figure 22B illustrates a radio frequency module 2240 including one or more acoustic wave filters 2244 according to an exemplary aspect. The illustrated radio frequency module 2240 also includes a radio frequency (RF) circuit (or line) 2243. In an exemplary aspect, the acoustic wave filter 2244 can include one or more filters 2200 as described above with respect to Figure 22A .

[0128] Figure 22B The illustrated acoustic wave filter 2244 includes terminals 2245A and 2245B (e.g., a first terminal and a second terminal). The terminals 2245A and 2245B can be used as, for example, an input contact portion and an output contact portion of the acoustic wave filter 2244. Although two terminals are shown, any suitable number of terminals can be implemented for a particular application. The acoustic wave filter 2244 and the RF circuit 2243 are on a package substrate 2246 (e.g., a common substrate) in Figure 22B . The package substrate 2246 can be a laminated substrate. The terminals 2245A and 2245B can be electrically connected to the contact portions 2247A and 2247B on the package substrate 2246 through electrical connectors 2248A and 2248B, respectively. For example, the electrical connectors 2248A and 2248B can be bumps or wire bonds. In an exemplary aspect, with or without using the package substrate 2246, the acoustic wave filter 2244 and the RF circuit 2243 can be packaged together in a common package.

[0129] The RF circuit 2243 may include any suitable RF circuit. For example, the RF circuit may include one or more radio frequency amplifiers (e.g., one or more power amplifiers and / or one or more low noise amplifiers), one or more radio frequency switches, one or more additional RF filters, one or more RF couplers, one or more delay lines, one or more phase shifters, or any suitable combination thereof. The RF circuit 2243 may be electrically connected to one or more acoustic wave filters 2244. The radio frequency module 2240 may include one or more encapsulation structures to, for example, provide protection and / or facilitate easier handling of the radio frequency module 2240. Such an encapsulation structure may include a overmolded structure formed above the encapsulation substrate 2246. The overmolded structure may encapsulate some or all of the components of the radio frequency module 2240.

[0130] Throughout this specification, the illustrated embodiments and examples should be considered as examples, rather than limitations of the disclosed or claimed devices and processes. Although many of the examples presented herein involve specific combinations of method acts or system elements, it should be understood that those acts and those elements may be combined in other ways to accomplish the same objective. With respect to flowcharts, additional and fewer steps may be taken, and the steps shown may be combined, or further refined, to implement the methods described herein. Acts, elements, and features discussed in conjunction with only one embodiment are not intended to be excluded from a similar role in other embodiments.

[0131] As used herein, "a plurality" means two or more. As used herein, a "set" of items may include one or more such items. As used herein, whether in the written description or claims, the terms "comprising", "including", "carrying", "having", "containing", "involving", etc. should be understood to be open-ended, i.e., meaning including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" are closed or semi-closed transitional phrases with respect to claims. The use of sequential terms such as "first", "second", "third", etc. in the claims to modify the claim elements themselves does not imply any priority, precedence, or order of one claim element with respect to another or the temporal order of acts of a method being performed, but is merely used as a label to distinguish one claim element having a particular name from another element having the same name (but using a sequential term) to distinguish claim elements. As used herein, "and / or" means that the listed items are alternatives, but the alternatives also include any combination of the listed items.

Claims

1. An acoustic resonator, comprising: A plurality of nanowires, each of the plurality of nanowires comprising: A piezoelectric layer having a first surface and a second surface; A first electrode on the first surface of the piezoelectric layer; and A second electrode on the second surface of the piezoelectric layer, wherein each of the plurality of nanowires extends mainly in a first direction from a first bus bar, such that a space is defined between a pair of nanowires among the plurality of nanowires in a second direction substantially perpendicular to the first direction, such that there is no piezoelectric material between the pair of nanowires in the second direction, wherein each of the plurality of nanowires has a height in a thickness direction substantially orthogonal to the first direction and the second direction, and wherein each of the plurality of nanowires has a ratio of the width of at least one of the first electrode and the second electrode in the second direction to the height of the nanowire, and the ratio is less than 2.

2. The acoustic resonator according to claim 1, further comprising a pair of bus bars, the pair of bus bars including a first bus bar and a second bus bar, the first bus bar being coupled to the first electrode of each of the plurality of nanowires, and the second bus bar being coupled to the second electrode of each of the plurality of nanowires.

3. The acoustic resonator according to claim 2, wherein, The second electrode of each of the plurality of nanowires is a floating electrode.

4. The acoustic resonator according to claim 1, further comprising a pair of piston masses disposed on a top surface of the first electrode of each of the plurality of nanowires.

5. The acoustic resonator according to claim 4, wherein, The pair of piston masses is disposed adjacent to a base and on a free end of each of the plurality of nanowires.

6. The acoustic resonator according to claim 1, wherein, The first electrode of each of the plurality of nanowires includes a multi-layer electrode in the thickness direction, and the multi-layer electrode of the first electrode includes a first electrode layer having a first acoustic impedance and a second electrode layer having a second acoustic impedance, and the second acoustic impedance is lower than the first acoustic impedance.

7. The acoustic resonator according to claim 6, wherein, The second electrode of each of the plurality of nanowires includes a multi-layer electrode in the thickness direction, and the multi-layer electrode of the second electrode includes a first electrode layer having a first acoustic impedance and a second electrode layer having a second acoustic impedance, and the second acoustic impedance of the second electrode layer of the second electrode is lower than the first acoustic impedance of the first electrode layer of the second electrode.

8. The acoustic resonator according to claim 7, wherein, The number of the multi-layer electrodes of the first electrode is 2, and the number of the multi-layer electrodes of the second electrode is 2.

9. The acoustic resonator according to claim 7, wherein, The first electrode layer of the first electrode is disposed between the second electrode layer of the first electrode and the piezoelectric layer, and the first electrode layer of the second electrode is disposed between the second electrode layer of the second electrode and the piezoelectric layer.

10. The acoustic resonator according to claim 6, wherein, The ratio of the thickness of the first electrode layer of the first electrode to the thickness of the multi-layer electrode of the first electrode is between 0.1 and 0.

6.

11. The acoustic resonator according to claim 7, wherein, The ratio of the thickness of the first electrode layer of the second electrode to the thickness of the multi-layer electrode of the second electrode is between 0.1 and 0.

6.

12. The acoustic resonator according to claim 6, wherein, The ratio of the thickness of the multi-layer electrode of the first electrode to the thickness of the piezoelectric layer is between 0.1 and 0.

5.

13. The acoustic resonator according to claim 7, wherein, The ratio of the thickness of the multi-layer electrode of the second electrode to the thickness of the piezoelectric layer is between 0.1 and 0.

5.

14. An acoustic resonator, comprising: A plurality of electrode fingers, each of the plurality of electrode fingers comprising: A piezoelectric layer having a first surface and a second surface; A top electrode on the first surface of the piezoelectric layer; and A bottom electrode on the second surface of the piezoelectric layer, wherein the top electrodes of the plurality of electrode fingers each mainly extend from a first bus bar in a first direction, and wherein a space is defined between a pair of electrode fingers in a second direction substantially perpendicular to the first direction, such that there is no piezoelectric material between the pair of nanowires in the second direction, wherein the plurality of electrode fingers each have a width in the second direction and a total height in a thickness direction substantially orthogonal to the first direction and the second direction, and wherein the ratio of the width to the total height of at least one of the plurality of electrode fingers is less than 2.

15. The acoustic resonator according to claim 14, wherein, The width of the plurality of electrode fingers is defined as the width in the second direction of at least one of the first electrode and the second electrode of a corresponding at least one electrode finger.

16. The acoustic resonator according to claim 14, wherein: The first electrode of each of the plurality of electrode fingers includes a multi-layer electrode in the thickness direction, and the multi-layer electrode of the first electrode includes a first electrode layer having a first acoustic impedance and a second electrode layer having a second acoustic impedance lower than the first acoustic impedance, and The second electrode of each of the plurality of electrode fingers includes a multi-layer electrode in the thickness direction, and the multi-layer electrode of the second electrode includes a first electrode layer having a first acoustic impedance and a second electrode layer having a second acoustic impedance, and the second acoustic impedance of the second electrode layer of the second electrode is lower than the first acoustic impedance of the first electrode layer of the second electrode.

17. The acoustic resonator according to claim 16, wherein, The first electrode layer of the first electrode is disposed between the second electrode layer of the first electrode and the piezoelectric layer, and the first electrode layer of the second electrode is disposed between the second electrode layer of the second electrode and the piezoelectric layer.

18. The acoustic resonator according to claim 17, wherein: The ratio of the thickness of the first electrode layer of the first electrode to the thickness of the multi-layer electrode of the first electrode is between 0.1 and 0.6, and The ratio of the thickness of the first electrode layer of the second electrode to the thickness of the multi-layer electrode of the second electrode is between 0.1 and 0.

6.

19. The acoustic resonator according to claim 17, wherein: The ratio of the thickness of the multi-layer electrode of the first electrode to the thickness of the piezoelectric layer is between 0.1 and 0.5, and The ratio of the thickness of the multi-layer electrode of the second electrode to the thickness of the piezoelectric layer is between 0.1 and 0.

5.

20. A band-pass filter, comprising: A plurality of acoustic resonators, including one or more series resonators and one or more parallel resonators, at least one of the plurality of acoustic resonators including: A plurality of nanowires, each of the plurality of nanowires comprising: A piezoelectric layer having a first surface and a second surface; A first electrode on the first surface of the piezoelectric layer; and A second electrode on the second surface of the piezoelectric layer, wherein each of the plurality of nanowires extends mainly in a first direction from a first bus bar, such that a space is defined between a pair of nanowires in the plurality of nanowires in a second direction substantially perpendicular to the first direction, such that there is no piezoelectric material between the pair of nanowires in the second direction, wherein each of the nanowires has a height in a thickness direction substantially orthogonal to the first direction and the second direction, and wherein each of the plurality of nanowires has a ratio of the width of at least one of the first electrode and the second electrode in the second direction to the height of the nanowire, the ratio being less than 2.

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