Patent Publication Number: US-11664780-B2

Title: Rayleigh mode surface acoustic wave resonator

Description:
CROSS REFERENCE TO PRIORITY APPLICATIONS 
     This application claims the benefit of priority of U.S. Provisional Patent Application No. 62/847,552, filed May 14, 2019 and titled “RAYLEIGH MODE ACOUSTIC WAVE RESONATOR,” and U.S. Provisional Patent Application No. 62/847,535, filed May 14, 2019 and titled “RAYLEIGH MODE SURFACE ACOUSTIC WAVE RESONATOR,” the disclosures of each of which are hereby incorporated by reference in their entireties herein. 
    
    
     BACKGROUND 
     Technical Field 
     Embodiments of this disclosure relate to Rayleigh acoustic wave resonators. 
     Description of Related Technology 
     Acoustic wave filters can be implemented in radio frequency electronic systems. For instance, filters in a radio frequency front end of a mobile phone can include acoustic wave filters. An acoustic wave filter can filter a radio frequency signal. An acoustic wave filter can be a band pass filter. A plurality of acoustic wave filters can be arranged as a multiplexer. For example, two acoustic wave filters can be arranged as a duplexer. 
     An acoustic wave filter can include a plurality of resonators arranged to filter a radio frequency signal. Example acoustic wave filters include surface acoustic wave (SAW) filters and bulk acoustic wave (BAW) filters. A surface acoustic wave resonator can include an interdigital transductor electrode on a piezoelectric substrate. The surface acoustic wave resonator can generate a surface acoustic wave on a surface of the piezoelectric layer on which the interdigital transductor electrode is disposed. 
     SUMMARY OF CERTAIN INVENTIVE ASPECTS 
     The innovations described in the claims each have several aspects, no single one of which is solely responsible for its desirable attributes. Without limiting the scope of the claims, some prominent features of this disclosure will now be briefly described. 
     In one aspect, a surface acoustic wave resonator is disclosed. The surface acoustic wave resonator can include a high impedance layer, a piezoelectric layer positioned over the high impedance layer, a low impedance layer positioned between the high impedance layer and the piezoelectric layer, and an interdigital transducer electrode. The piezoelectric layer has a cut angle in a range from 115° to 135°. An acoustic impedance of the high impedance layer is greater than an acoustic impedance of the piezoelectric layer. An acoustic impedance of the low impedance layer is lower than the acoustic impedance of the high impedance layer. The surface acoustic wave resonator configured to generate a Rayleigh mode surface acoustic wave having a wavelength of λ. 
     In an embodiment, the piezoelectric layer has a thickness in a range from 0.1λ to 0.5λ. 
     In an embodiment, the low impedance layer has a thickness in a range from 0.01λ to 0.3λ. 
     In an embodiment, the low impedance layer is a silicon dioxide layer. 
     In an embodiment, the surface acoustic wave resonator further includes temperature compensating layer that is positioned over the interdigital transducer electrode. The temperature compensating layer can be a silicon dioxide layer. The surface acoustic wave resonator can further include a silicon nitride layer that is positioned over the temperature compensating layer. 
     In an embodiment, the interdigital transducer electrode includes two layers. One of the two layers can include aluminum. The other of the two layers can include molybdenum. 
     In an embodiment, the piezoelectric layer includes lithium niobate. 
     In an embodiment, the acoustic impedance of the high impedance layer is higher than an acoustic impedance of silicon dioxide, and the high impedance layer includes at least one of silicon, aluminum nitride, silicon nitride, sapphire, spinel, or high impedance glass. 
     In an embodiment, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 for a frequency range from 2 GHz to 3.75 GHz. 
     In an embodiment, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 for a frequency range from above a passband of a filter that includes the surface acoustic wave resonator to 3.75 GHz. 
     In one aspect, a surface acoustic wave resonator is disclosed. The surface acoustic wave resonator can include a high impedance layer, a lithium niobate layer that is positioned over the high impedance layer, a silicon dioxide layer that is positioned between the high impedance layer and the lithium niobate layer, and an interdigital transducer electrode that is positioned over the lithium niobate layer. The lithium niobate layer has a cut angle in a range from 115° to 135°. An acoustic impedance of the high impedance layer is greater than an acoustic impedance of the lithium niobate layer. An acoustic impedance of the silicon dioxide layer is lower than the acoustic impedance of the high impedance layer. An interdigital transducer electrode is positioned over the lithium niobate layer. The surface acoustic wave resonator is configured to generate a Rayleigh mode surface acoustic wave having a wavelength of λ. 
     In as embodiments, the piezoelectric layer has a thickness in a range from 0.1λ to 0.5λ. 
     In as embodiments, the silicon dioxide layer has a thickness in a range from 0.01λ to 0.3λ. 
     In as embodiments, the surface acoustic wave resonator further includes a temperature compensating layer over the interdigital transducer electrode, the temperature compensating layer is a second silicon dioxide layer. The surface acoustic wave resonator can further include a silicon nitride layer over the temperature compensating layer. 
     In as embodiments, the interdigital transducer electrode includes an aluminum layer and a molybdenum layer. 
     In as embodiments, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 for a frequency range from 2 GHz to 3.75 GHz. 
     In as embodiments, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 for a frequency range from above a pass band of a filter that includes the surface acoustic wave resonator to 3.75 GHz. 
     In one aspect, a surface acoustic wave resonator is disclosed. The surface acoustic wave resonator can include a high impedance layer, a piezoelectric layer that is positioned over the high impedance layer, a low impedance layer that is positioned between the high impedance layer and the piezoelectric layer, and an interdigital transducer electrode that is positioned over the piezoelectric layer. An acoustic impedance of the high impedance layer is greater than an acoustic impedance of the piezoelectric layer. An acoustic impedance of the low impedance layer is lower than the acoustic impedance of the high impedance layer. The surface acoustic wave resonator is configured to generate a Rayleigh mode surface acoustic wave having a wavelength of λ. 
     In one aspect, a Rayleigh mode surface acoustic wave resonator is disclosed. The Rayleigh mode surface acoustic wave resonator can include a high impedance layer, a piezoelectric layer that is positioned over the high impedance layer, an interdigital transducer electrode that is positioned over the piezoelectric layer, a temperature compensating layer that is positioned over the interdigital transducer electrode, and a low impedance layer that is positioned between the high impedance layer and the piezoelectric layer. An acoustic impedance of the high impedance layer is greater than an acoustic impedance of the piezoelectric layer. An acoustic impedance of the low impedance layer is lower than the acoustic impedance of the high impedance layer. The surface acoustic wave resonator is configured to generate a Rayleigh mode surface acoustic wave having a wavelength λ. 
     In an embodiment, the piezoelectric layer has a thickness in a range from 0.1λ to 0.5λ. 
     In an embodiment, the piezoelectric layer is a lithium niobate layer. The piezoelectric layer can have a cut angle in a range from 115° to 135°. 
     In an embodiment, the low impedance layer is a silicon dioxide layer. 
     In an embodiment, the low impedance layer has a thickness in a range from 0.01λ to 0.3λ. 
     In an embodiment, the high impedance layer is a silicon layer. 
     In an embodiment, wherein the temperature compensating layer is a silicon dioxide layer. The temperature compensating layer can have a thickness in a range from 0.01λ to 0.4λ. 
     In an embodiment, the Rayleigh mode surface acoustic wave resonator further includes a silicon nitride layer that is positioned over the temperature compensating layer. 
     In an embodiment, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 for a frequency range from 2 GHz to 3.75 GHz. 
     In an embodiment, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 for a frequency range from above a pass band of a filter that includes the Rayleigh mode surface acoustic wave resonator to 3.75 GHz. 
     In one aspect, a Rayleigh mode surface acoustic wave resonator is disclosed. The Rayleigh mode surface acoustic wave resonator can include a high impedance layer, a lithium niobate layer that is positioned over the high impedance layer, an interdigital transducer electrode over the piezoelectric layer, a first silicon dioxide layer that is positioned over the interdigital transducer electrode; and a second silicon dioxide layer that is positioned between the high impedance layer and the piezoelectric layer. An acoustic impedance of the high impedance layer is greater than an acoustic impedance of the lithium niobate layer. An acoustic impedance of the second silicon dioxide layer is lower than the acoustic impedance of the high impedance layer. The Rayleigh mode surface acoustic wave resonator is configured to generate a Rayleigh mode surface acoustic wave having a wavelength λ. 
     In an embodiment, the lithium niobate layer has a thickness in a range from 0.1λ to 0.5λ. 
     In an embodiment, the lithium niobate layer has a cut angle in a range from 115° to 135°. 
     In an embodiment, the second silicon dioxide layer has a thickness in a range from 0.01λ to 0.4λ. 
     In an embodiment, the high impedance layer is a silicon layer. The first silicon dioxide layer can have a thickness in a range from 0.01λ to 0.3λ. 
     In an embodiment, the Rayleigh mode surface acoustic wave resonator further includes a silicon nitride layer over the temperature compensating layer. 
     In an embodiment, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 for a frequency range from 2 GHz to 3.75 GHz. 
     In an embodiment, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 for a frequency range from above a pass band of a filter that includes the Rayleigh mode surface acoustic wave resonator to 3.75 GHz. 
     In an embodiment, the interdigital transducer electrode includes two layers. 
     In an embodiment, an acoustic wave filter includes acoustic wave resonators arranged to filter a radio frequency signal. The acoustic wave resonators includes the surface acoustic wave resonator. A front end module can include the acoustic wave filter, other circuitry, and a package that encloses the acoustic wave filter and the other circuitry. The front end module can further include a multi-throw radio frequency switch. The front end module can further include a power amplifier. A wireless communication device can include an antenna and the acoustic wave filter. The surface acoustic wave filter can be arranged to filter a radio frequency signal associated with the antenna. 
     In one aspect, a surface acoustic wave resonator is disclosed. The surface acoustic wave resonator can include a high impedance layer, a piezoelectric layer that is positioned over the high impedance layer, an interdigital transducer electrode that is positioned over the piezoelectric layer, and a temperature compensating layer that is positioned over the interdigital transducer electrode. The piezoelectric layer has a cut angle in a range from 115° to 135°. An acoustic impedance of the high impedance layer is greater than an acoustic impedance of the piezoelectric layer. The surface acoustic wave resonator is configured to generate a Rayleigh mode surface acoustic wave. 
     In an embodiment, the surface acoustic wave resonator further includes a low impedance layer that is positioned between the high impedance layer and the piezoelectric layer. An acoustic impedance of the low impedance layer is lower than the acoustic impedance of the high impedance layer. The low impedance layer can be a silicon dioxide layer. The Rayleigh mode surface acoustic wave has a wavelength of λ. The low impedance layer can have a thickness in a range from 0.01λ to 0.3λ. The low impedance layer can have a thickness in a range from 0.01λ to 0.25λ. 
     In an embodiment, the temperature compensating layer is a silicon dioxide layer and the piezoelectric layer is a lithium niobate layer. 
     In an embodiment, the Rayleigh mode surface acoustic wave has a wavelength of λ, and the piezoelectric layer has a thickness in a range from 0.1λ to 0.5λ. The temperature compensating layer can have a thickness in a range from 0.01λ to 0.4λ. 
     In an embodiment, the acoustic impedance of the high impedance layer is higher than an acoustic impedance of silicon dioxide, and the high impedance layer includes at least one of silicon, aluminum nitride, silicon nitride, sapphire, spinel, or high impedance glass. 
     In an embodiment, the interdigital transducer electrode includes two layers. One of the two layers can include aluminum. The other of the two layers can include molybdenum. 
     In an embodiment, the piezoelectric layer includes lithium niobate. 
     In an embodiment, the surface acoustic wave resonator further includes a dispersion adjustment layer that is positioned over the temperature compensating layer. The dispersion adjustment layer can be a silicon nitride layer. The dispersion adjustment layer can include a first portion and a second portion, and the first and second portions of the dispersion adjustment layer can define a trench. 
     In an embodiment, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 for a frequency range from 2 GHz to 3.75 GHz. 
     In an embodiment, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 for a frequency range from above a pass band of a filter that includes the surface acoustic wave resonator to 3.75 GHz. 
     In one aspect, a surface acoustic wave resonator is disclosed. The surface acoustic wave resonator can include a high impedance layer, a lithium niobate layer that is positioned over the high impedance layer, an interdigital transducer electrode that is positioned over the lithium niobate layer, and a silicon dioxide layer that is positioned over the interdigital transducer electrode. The lithium niobate layer has a cut angle in a range from 115° to 135°. An acoustic impedance of the high impedance layer is greater than an acoustic impedance of the lithium niobate layer. The surface acoustic wave resonator is configured to generate a Rayleigh mode surface acoustic wave. 
     In as embodiment, the surface acoustic wave resonator further includes a low impedance layer that is positioned between the high impedance layer and the piezoelectric layer. An acoustic impedance of the low impedance layer is lower than the acoustic impedance of the high impedance layer. The low impedance layer can be a second silicon dioxide layer. The Rayleigh mode surface acoustic wave has a wavelength of λ, and the low impedance layer can have a thickness in a range from 0.01λ to 0.3λ. 
     In as embodiment, the Rayleigh mode surface acoustic wave has a wavelength of λ, and the lithium niobate layer has a thickness in a range from 0.1λ to 0.5λ, and the silicon dioxide layer has a thickness in a range from 0.01λ to 0.4λ. 
     In as embodiment, the acoustic impedance of the high impedance layer is higher than an acoustic impedance of silicon dioxide, and the high impedance layer includes at least one of silicon, aluminum nitride, silicon nitride, sapphire, spinel, or high impedance glass. 
     In as embodiment, the interdigital transducer electrode includes an aluminum layer and a molybdenum layer. 
     In as embodiment, the surface acoustic wave resonator further includes a silicon nitride layer over the silicon dioxide layer. 
     In as embodiment, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 in a frequency range from 2 GHz to 3.75 GHz. 
     In as embodiment, a reflection coefficient of the surface acoustic wave resonator is at least 0.9 in a frequency range from above a pass band of a filter that includes the surface acoustic wave resonator to 3.75 GHz. 
     In one aspect, a surface acoustic wave resonator is disclosed. The surface acoustic wave resonator can include a high impedance layer, a piezoelectric layer that is positioned over the high impedance layer, an interdigital transducer electrode that is positioned over the piezoelectric layer, and a temperature compensating layer that is positioned over the interdigital transducer electrode. An acoustic impedance of the high impedance layer is greater than an acoustic impedance of the piezoelectric layer. The surface acoustic wave resonator is configured to generate a Rayleigh mode surface acoustic wave. 
     In one aspect, an acoustic wave filter is disclosed. The acoustic wave filter can include acoustic wave resonators that are arranged to filter a radio frequency signal. The acoustic wave resonators include a surface acoustic wave resonator. A front end module can include the acoustic wave filter, other circuitry, and a package that encloses the acoustic wave filter and the other circuitry. The front end module can further include a multi-throw radio frequency switch. The front end module can further include a power amplifier. A wireless communication device can include an antenna and the acoustic wave filter, The surface acoustic wave filter can be arranged to filter a radio frequency signal associated with the antenna. 
     For purposes of summarizing the disclosure, certain aspects, advantages and novel features of the innovations have been described herein. It is to be understood that not necessarily all such advantages may be achieved in accordance with any particular embodiment. Thus, the innovations may be embodied or carried out in a manner that achieves or optimizes one advantage or group of advantages as taught herein without necessarily achieving other advantages as may be taught or suggested herein. 
    
    
     
       BRIEF DESCRIPTION OF THE DRAWINGS 
       Embodiments of this disclosure will now be described, by way of non-limiting example, with reference to the accompanying drawings. 
         FIG.  1    illustrates a cross section of a surface acoustic wave (SAW) resonator. 
         FIG.  2    illustrates a cross section of a SAW resonator according to one embodiment. 
         FIG.  3    is a graph showing simulated results of reflection coefficient of the SAW resonator of  FIG.  1    and the SAW resonator of  FIG.  2   . 
         FIG.  4    illustrates a cross section of a SAW resonator. 
         FIG.  5    illustrates a cross section of a SAW resonator. 
         FIG.  6    illustrates a cross section of a SAW resonator according to one embodiment. 
         FIG.  7    includes graphs of simulation results of isolation and reflection coefficient for ladder filters using the SAW resonators of  FIGS.  4 ,  5  and  6   . 
         FIG.  8 A  illustrates a cross section of a SAW resonator. 
         FIG.  8 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  8 A . 
         FIG.  9 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  9 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  9 A . 
         FIG.  10 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  10 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  10 A . 
         FIG.  11 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  11 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  11 A . 
         FIG.  12 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  12 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  12 A . 
         FIG.  13 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  13 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  13 A . 
         FIG.  14 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  14 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  14 A . 
         FIG.  15 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  15 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  15 A . 
         FIG.  16 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  16 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  16 A . 
         FIG.  17 A  illustrates a cross section of a SAW resonator. 
         FIG.  17 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  17 A . 
         FIG.  18 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  18 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  18 A . 
         FIG.  19 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  19 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  19 A . 
         FIG.  20 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  20 B  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonator of  FIG.  20 A . 
         FIG.  21 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  21 B  illustrates graphs showing simulation results of isolation and reflection coefficient on the right for the SAW resonator of  FIG.  21 A . 
         FIG.  22 A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  22 B  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG.  22 C  illustrates graphs showing simulation results of isolation and reflection coefficient on the right for the SAW resonators of  FIGS.  22 A and  22 B . 
         FIG.  23 A  illustrates graphs showing simulation results of isolation and reflection coefficient for the SAW resonators of  FIGS.  22 A and  22 B  with a different simulation set up than for the simulations corresponding to graphs of  FIG.  22 C . 
         FIG.  23 B  illustrates transmission leakage of the SAW resonator of  FIG.  22 A  at a frequency of 4 GHz. 
         FIG.  23 C  illustrates transmission leakage of the SAW resonator of  FIG.  22 B  at a frequency of 4 GHz. 
         FIG.  24    illustrates graphs showing simulated dispersion curves of a SAW resonator having various thicknesses of silicon dioxide (SiO 2 ) layer over a molybdenum (Mo) interdigital transducer (IDT) electrode. 
         FIG.  25 A  illustrates a cross section of a surface acoustic wave resonator according to one embodiment. 
         FIG.  25 B  is a top plan view of the surface acoustic wave resonator illustrated in  FIG.  25 A . 
         FIG.  25 C  is a graph showing simulation results of admittance of the SAW resonator of  FIG.  25 A  and a similar resonator. 
         FIG.  26    is a schematic diagram of a transmit filter that includes a surface acoustic wave resonator according to an embodiment. 
         FIG.  27    is a schematic diagram of a receive filter that includes a surface acoustic wave resonator according to an embodiment. 
         FIG.  28    is a schematic diagram of a radio frequency module that includes a surface acoustic wave resonator according to an embodiment. 
         FIG.  29    is a schematic diagram of a radio frequency module that includes filters with surface acoustic wave resonators according to an embodiment. 
         FIG.  30    is a schematic block diagram of a module that includes an antenna switch and duplexers that include a surface acoustic wave resonator according to an embodiment. 
         FIG.  31    is a schematic block diagram of a module that includes a power amplifier, a radio frequency switch, and duplexers that include a surface acoustic wave resonator according to an embodiment. 
         FIG.  32 A  is a schematic block diagram of a wireless communication device that includes a filter with a surface acoustic wave resonator in accordance with one or more embodiments. 
         FIG.  32 B  is a schematic block diagram of another wireless communication device that includes a filter with a surface acoustic wave resonator in accordance with one or more embodiments. 
     
    
    
     DETAILED DESCRIPTION OF CERTAIN EMBODIMENTS 
     The following description of certain embodiments presents various descriptions of specific embodiments. However, the innovations described herein can be embodied in a multitude of different ways, for example, as defined and covered by the claims. In this description, reference is made to the drawings where like reference numerals can indicate identical or functionally similar elements. It will be understood that elements illustrated in the figures are not necessarily drawn to scale. Moreover, it will be understood that certain embodiments can include more elements than illustrated in a drawing and/or a subset of the elements illustrated in a drawing. Further, some embodiments can incorporate any suitable combination of features from two or more drawings. 
     Acoustic wave filters can filter radio frequency (RF) signals in a variety of applications, such as in an RF front end of a mobile phone. An acoustic wave filter can be implemented with surface acoustic wave (SAW) devices. Certain SAW devices may be referred as SAW resonators. A SAW resonator can be configured to generate, for example, a Rayleigh mode surface acoustic wave or a shear horizontal mode surface acoustic wave. 
     Acoustic wave filters can include SAW resonators that include a single layer piezoelectric substrate and an interdigital transducer (IDT) electrode over the single layer piezoelectric substrate. The single layer piezo substrate can consist of a piezoelectric layer. The piezoelectric layer can be a lithium niobate (LN) piezoelectric layer, for example. Such SAW resonators can degrade the reflection coefficient gamma. For example, such SAW resonators can generate higher order response at about 1.3 times and 1.8 times the main resonance. This can lower the reflection coefficient. A multiplexer that includes such SAW resonators may suffer from insertion loss (IL) degradation. 
     Multi-layer piezoelectric substrate SAW resonators can include a bonded substrate to improve a quality factor (Q) of the resonator. In various instances, such a bonded substrate has caused a reflection at a bonding interface such that a higher-order reflection may occur at a higher frequency and degrade the reflection coefficient. Degradation in the reflection coefficient can result in IL degradation in a multiplexer. 
     Aspects of this disclosure relate to a SAW resonator with a multi-layer piezoelectric substrate. Multi-layer piezoelectric substrates can provide good thermal dissipation characteristics and improved temperature coefficient of frequency (TCF) relative to certain single layer piezoelectric substrates. For example, certain SAW resonators with a piezoelectric layer on a high impedance layer, such as silicon, can achieve better temperature coefficient of frequency (TCF) and thermal dissipation compared to similar devices without the high impedance layer. 
     Embodiments of a SAW resonator disclosed herein include a piezoelectric layer that has a cut angle in a range from 115° to 135°. As used herein, a “cut angle” of N° refers to an N° rotated Y-cut in a Y-cut X-propagation piezoelectric layer. For a piezoelectric layer with Euler angles (φ, θ, ψ), the “cut angle” in degrees can be θ plus 90°. Accordingly, the second Euler angle θ can be in a range from 25° to 45° when the cut angle is in the range from 115° to 135°. The piezoelectric layer with such cut angle can provide a resonator having less reflection degradation over a relatively broad frequency range as compared to multi-layer piezoelectric substrate with a piezoelectric layer that has other cut angles (e.g., a cut angle in a range from −10° to 60°). The first Euler angle φ can be in a range from −10° to +10°. The third Euler angle ψ can be in a range from −10° to +10°. In certain embodiments, the Euler angles (φ, θ, ψ) can be (0°, 25°&lt;θ&lt;45°, 0°). 
     Embodiments of a SAW resonator disclosed herein can also include a low acoustic impedance layer that has an acoustic impedance lower than that of the high impedance layer. The low acoustic impedance layer can be disposed between the piezoelectric layer and the high impedance layer. Embodiments of a SAW resonator disclosed herein can include a temperature compensation layer over the IDT electrode in addition to or as an alternative to the low acoustic impedance layer. 
       FIG.  1    illustrates a cross section of a surface acoustic wave (SAW) resonator  1 . The illustrated SAW resonator  1  includes an LN layer  10 , IDT electrodes  12  over the LN layer  10 , and a silicon dioxide (SiO 2 ) layer  14  over the IDT electrodes  12 . The LN layer  10  has a cut angle of 122°. The IDT electrode  12  of the SAW resonator  1  has a pitch L that sets the wavelength λ of the surface acoustic wave device  1 . The pitch L of the illustrated IDT electrode  12  of the SAW resonator  1  is 2 μm. The pitch L is typically equal to the wavelength λ. A thickness of the LN layer  10  of the SAW resonator  1  can be in a range from 100 μm to 500 μm, for example. In simulations, the LN layer  10  can be modeled has having a semi-infinite thickness. A thickness of the SiO 2  layer  14  of the SAW resonator  1  is 0.3 L. The IDT electrode  12  of the SAW resonator  1  is a multi-layer IDT electrode. The IDT electrodes  12  include a molybdenum (Mo) layer and an aluminum (Al) layer over the Mo layer. The Mo layer has a thickness of 0.04 L. 
       FIG.  2    illustrates a cross section of a surface acoustic wave (SAW) resonator  2  according to one embodiment. The SAW resonator  2  includes a piezoelectric layer  20 , IDT electrodes  22  over the piezoelectric layer  20 , and a temperature compensating layer  24  over the IDT electrodes  22 . The SAW resonator  2  also includes a high impedance layer  26  under the piezoelectric layer  20 . The SAW resonator  2  can generate a Rayleigh mode surface acoustic wave. 
     The piezoelectric layer  20  can include any suitable piezoelectric material. For example, the piezoelectric layer  20  can be a lithium niobate (LN) with a cut angle in a range from 115° to 135°. With the cut angle of a piezoelectric layer  20  that is LN being within a range from 115° to 135°, the SAW resonator  2  can generate a Rayleigh mode surface acoustic wave. By contrast, a similar SAW resonator with an LN piezoelectric layer having a cut angle in a range from 20° to 30° can generate a shear horizontal surface acoustic wave and suppress a Rayleigh mode surface acoustic wave. In some embodiments, the piezoelectric layer  20  can be an LN layer with a cut angle of 122°. 
     The IDT electrodes  22  can include any suitable IDT electrode material. For example, the IDT electrodes  22  can include one or more of an aluminum (Al) layer, a molybdenum (Mo) layer, a tungsten (W) layer, a titanium (Ti) layer, a platinum (Pt) layer, a gold (Au) layer, a silver (Ag) layer, a copper (Cu) layer, a Magnesium (Mg) layer, a ruthenium (Ru) layer, or the like. The IDT electrode  22  may include alloys, such as AlMgCu, AlCu, etc. In some embodiments, the IDT electrodes  22  can be multi-layer IDT electrodes. As an example, a multi-layer IDT electrode can include an Al layer over a Mo layer, or an Al layer over a W layer. 
     The temperature compensating layer  24  can include any suitable temperature compensating material. For example, the temperature compensating layer  24  can be a silicon dioxide (SiO 2 ) layer. The temperature compensating layer  24  can be a layer of any other suitable material having a positive temperature coefficient of frequency in instances where the piezoelectric layer  20  has a negative temperature coefficient of frequency. For instance, the temperature compensating layer  24  can be a tellurium dioxide (TeO 2 ) layer or a silicon oxyfluoride (SiOF) layer in certain applications. The temperature compensating layer  24  can include any suitable combination of SiO 2 , TeO 2 , and/or SiOF. The temperature compensating layer  24  can bring the TCF of the surface acoustic wave resonator  2  closer to zero to thereby provide temperature compensation. The temperature compensating layer  24  can improve the electromechanical coupling coefficient k 2  of the SAW resonator  2  relative to a similar SAW resonator without the temperature compensating layer  24 . This advantage of the temperature compensating layer  24  can be more pronounced when the piezoelectric layer  20  includes an LN layer. 
     An acoustic impedance of the high impedance layer  26  can be higher than an acoustic impedance of the piezoelectric layer  20 . The acoustic impedance of the high impedance layer  26  can be higher than an acoustic impedance of the temperature compensating layer  24 . The high impedance layer  26  can include any suitable material so long as the acoustic impedance of the high impedance layer  26  is higher than at least one of the acoustic impedance of the piezoelectric layer  20  or the acoustic impedance of the temperature compensating layer  24 . The acoustic impedance of the high impedance layer  26  can be higher than an acoustic impedance of silicon dioxide. In certain embodiments, the high impedance layer  26  can be a silicon (Si) layer. In some other embodiments, the high impedance layer  26  can include, for example, aluminum nitride (AlN), silicon nitride (SiN), sapphire, spinel, high impedance glass, etc. As discussed with respect to  FIG.  3   , the high impedance layer  26  together with a particular cut angle of the piezoelectric layer  20  can improve the reflection coefficient of a SAW resonator. 
     The piezoelectric layer  20  has a thickness T 1 . The thickness T 1  of the piezoelectric layer  20  can be selected based on a wavelength λ or L of a surface acoustic wave generated by the surface acoustic wave resonator  2 . The IDT electrode  22  has a pitch that sets the wavelength λ or L of the surface acoustic wave device  2 . The piezoelectric layer  20  can be sufficiently thick to provide good coupling factor. A thickness T 1  of the piezoelectric layer  20  of at least 0.1 L can be sufficiently thick to mitigate degradation of the coupling factor due to a relatively thin piezoelectric layer  20 . The thickness T 1  of the piezoelectric layer  20  can be in a range from, for example, 0.1 L to 0.5 L. In some instances, the thickness T 1  of the piezoelectric layer  20  can be in a range from 0.3 L to 0.5 L. The wavelength L of the surface acoustic wave can be, for example, 2 μm and the thickness T 1  of the piezoelectric layer  20  can be, for example, 0.6 μm, in some embodiments. As noted above, the piezoelectric layer  20  can be an LN layer or any other suitable piezoelectric layer (e.g., a lithium tantalate (LT) layer). 
     The temperature compensating layer  24  has a thickness T 2 . In some embodiments, the thickness T 2  of the temperature compensating layer  24  can be in a range from 0.01 L to 0.4 L. For example, when the wavelength L is 2 μm, the thickness T 2  of the temperature compensating layer  24  can be 0.8 μm. 
     The IDT electrodes  12  has a thickness T 3 . In some embodiments, the thickness T 3  can be about 0.04 L. In some embodiments, the thickness T 3  can be in a range from 0.01 L to 0.08 L. For example, when the wavelength L is 2 μm, the thickness T 3  of the Mo layer  18  can be 80 nm. 
     The high impedance layer  26  has a thickness T 4 . In some embodiments, the thickness T 4  can be determined based at least in part on acoustic energy confirmation. In some embodiments, the thickness T 4  can be greater than 10 μm or 1 L. A thickness T 4  of at least 10 μm can provide a desired level of mechanical durability. The thickness T 4  can be in a range from 10 μm to 1000 μm. The upper bound of the thickness T 4  can be based on a final device or module height constraint. 
       FIG.  3    is a graph showing simulated results of reflection coefficient s 11  (Γ) of the SAW resonator  1  and the SAW resonator  2  illustrated in  FIGS.  1  and  2    respectively. A thickness of the LN layer  10  of the SAW resonator  1  is set to a semi-infinite condition in the simulation. The SAW resonator  2  used in the simulation has the following specification: The pitch L is 2 μm; the piezoelectric layer  20  is an LN layer with a cut angle of 122° and the thickness T 1  of 0.3 L; the IDT electrodes  22  are Mo electrodes with the thickness T 3  of 0.04 L; the temperature compensating layer  24  is a SiO 2  layer with the thickness T 2  of 0.1 L; and the high impedance layer  26  is a Si layer with the thickness T 4  of a semi-infinite condition. In certain instances, the high impedance layer  26  can be a Si layer with a thickness in a range from 10 μm to 1000 μm. 
     The simulated result of the SAW resonator  1  shows some degradations around 2.4 GHz and 3.4 GHz, while the simulated result of the SAW resonator  2  shows a clean gamma below 3.5 GHz. As shown in  FIG.  3   , the gamma for the SAW resonator  2  can be relatively high (e.g., more than 0.9 or more than 0.95) for frequencies that are below 3.5 GHz and above a passband of a filter that includes the SAW resonator  2 . This improvement in the gamma for the SAW resonator  2  can be due to the high impedance layer  26  together with the cut angle of the piezoelectric layer  20 . 
       FIG.  4    illustrates a cross section of a surface acoustic wave resonator  3 . The illustrated SAW resonator  3  includes an LN layer  30 , IDT electrodes  32  over the LN layer  30 , and a SiO 2  layer  34  over the IDT electrodes  32 . The LN layer  30  has a cut angle of 128°. The IDT electrode  32  of the SAW resonator  3  has a pitch L that sets the wavelength λ of the surface acoustic wave device  3 . The pitch L of the illustrated IDT electrode of the SAW resonator  3  is 2.5 μm. A thickness of the SiO 2  layer  34  of the SAW resonator  3  is 0.3 L. The IDT electrodes  32  of the SAW resonator  3  is a multi-layer IDS. The IDT electrodes  32  include a molybdenum (Mo) layer and an aluminum (Al) layer over the Mo layer. The Mo layer has a thickness of 0.04 L. 
       FIG.  5    illustrates a cross section of a surface acoustic wave resonator  4 . The illustrated SAW resonator  4  includes a lithium tantalate (LT) layer  40 , and IDT electrodes  42  over the LT layer  40 . The SAW resonator  4  also includes a Si layer  46  under the LT layer  40  and a SiO 2  layer  48  between the LT layer  40  and the Si layer  46 . The LT layer  40  has a cut angle of 42°. The IDT electrode  32  of the SAW resonator  4  has a pitch L that sets the wavelength λ of the surface acoustic wave device  4 . The pitch L of the illustrated IDT electrode of the SAW resonator  4  is 2.6 μm. A thickness of the LT layer  40  of the SAW resonator  4  is 0.3 L. The IDT electrodes  42  of the SAW resonator  4  are aluminum (Al) electrodes. The IDT electrodes  42  have a thickness of 0.08 L. A thickness of the SiO 2  layer  48  of the SAW resonator  4  is 0.3 L. 
       FIG.  6    illustrates a cross section of a surface acoustic wave resonator  5  according to one embodiment. The SAW resonator  5  is similar to the SAW resonator  2  illustrated in  FIG.  2   . Unless otherwise noted, the components of  FIG.  5    may be similar to or the same as like numbered components of  FIG.  2   . Like the SAW resonator  2 , the SAW resonator  5  includes a piezoelectric layer  20 , IDT electrodes  22 ′ over the piezoelectric layer  20 , a temperature compensating layer  24  over the IDT electrodes  22 , and a high impedance layer  26  under the piezoelectric layer  20 . Unlike the SAW resonator  2 , the SAW resonator  5  also includes a low impedance layer  28 . The SAW resonator  5  can generate Rayleigh mode surface acoustic waves. 
     Unlike the IDT electrodes  22  of SAW resonator  2 , the illustrated IDT electrodes  22 ′ of the SAW resonator  5  are multi-layer IDT electrodes. The IDT electrodes  22 ′ include a bottom layer  23  and an upper layer  25 . Like the IDT electrodes  22  of the SAW resonator  2 , the IDT electrodes  22 ′ of the SAW resonator  5  can include an aluminum (Al) layer, a molybdenum (Mo) layer, a tungsten (W) layer, a titanium (Ti) layer, a platinum (Pt) layer, a gold (Au) layer, a silver (Ag) layer, copper (Cu) layer, a Magnesium (Mg) layer, etc. The IDT electrode  22 ′ may include alloys, such as AlMgCu, AlCu, etc. In certain embodiments, the IDT electrodes  22 ′ can be Al/Mo multi-layer electrodes where the bottom layer  23  is a Mo layer and the upper layer  25  is an Al layer. In some other embodiments, the IDT electrodes  22 ′ can be Al/W multi-layer electrodes where the bottom layer  23  is a W layer and the upper layer  25  is an Al layer. The bottom layer  23  has a thickness T 3 ′. The thickness T 3 ′ of the bottom layer  23  can be in a range from 0.01 L to 0.08 L. 
     An acoustic impedance of the low impedance layer  28  can be lower than the acoustic impedance of the high impedance layer  26 . In some embodiments, the low impedance layer can be a silicon dioxide (SiO 2 ) layer. Some low impedance layers, such as an SiO 2  layer, can provide a greater adhesion strength between the low impedance layer and the high impedance layer  26  than a adhesion strength between the piezoelectric layer  20  and the high impedance layer  26 . As discussed with respect to  FIG.  7   , the low impedance layer  28  can contribute to improvement in the reflection coefficient of a SAW resonator. 
     The low impedance layer  28  has a thickness T 5 . In some embodiments, the thickness T 5  of the low impedance layer  28  can be in a rage from 0.01 L to 0.3 L. In some embodiments, the thickness T 5  of the low impedance layer  28  can be 0.1 L. When the wavelength is, for example, 2.3 μm, the thickness T 5  can be 230 nm. 
       FIG.  7    shows simulation results of isolation s 12  in decibels (dB) on the left and reflection coefficient s 11  (gamma or Γ) on the right for ladder filters using the SAW resonators  3 ,  4  and  5  of  FIGS.  4 ,  5  and  6   , respectively. The SAW resonator  6  used in the simulation has the following specification: The pitch L is 2.3 μm; the piezoelectric layer  20  is an LN layer with a cut angle of 124° and the thickness T 1  of 0.3 L; the IDT electrodes  22 ′ are Al/Mo multi-layer electrodes with the thickness T 3 ′ of the Al layer of 0.04 L; the temperature compensating layer  24  is a SiO 2  layer with the thickness T 2  of 0.2 L; the high impedance layer  26  is a Si layer with the thickness T 4  set to a semi-infinite condition; and the low impedance layer  28  is another SiO 2  layer with the thickness T 5  of 0.1 L. 
       FIG.  7    includes a chart  32  that shows band names with center frequencies in MHz and bandwidths in MHz. The ladder filters with the SAW resonators  3 ,  4 , and  5  for the simulation results shown in  FIG.  7    were Band 32 filters. The simulation results in  FIG.  7    indicate that the ladder filter with SAW resonators  5  has the best Γ of the simulated ladder filters.  FIG.  7    indicates that Γ for the Band 32 filter with SAW resonators  5  is relatively high for frequencies corresponding to Band 3 transmit, Band 3 receive, Band 1 transmit, Band 1 receive, Band 40, Band 66 transmit, Band 25 transmit, Band 25 receive, Band 66 receive, Band 30 transmit, and Band 30 receive. Accordingly, a Band 32 filter with SAW resonators  5  can be included in a multiplexer with one or more other filters arranged to filter any of the frequency bands shown in chart  32  without significantly degrading insertion loss. 
     As illustrated in  FIG.  7   , the Γ of the SAW resonator  3  and the Γ of the SAW resonator  4  degrades at frequency range of between about 1.7 GHz to about 2.5 GHz. On the other hand, the Γ of the SAW resonator  5  is relatively clean at the same frequency range. This improvement in the gamma Γ for the SAW resonator  5  may be due to the high impedance layer  26  and/or the low impedance layer  28  together with the cut angle of the piezoelectric layer. 
       FIGS.  8 A,  9 A,  10 A,  11 A,  12 A,  13 A,  14 A,  15 A,  16 A,  17 A,  18 A,  19 A,  20 A,  21 A, and  22 A  illustrate SAW resonators according to various embodiments.  FIGS.  8 B,  9 B,  10 B,  11 B,  12 B,  13 B,  14 B,  15 B,  16 B,  17 B,  18 B,  19 B,  20 B,  21 B, and  22 B  illustrate simulation results showing isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonators of  FIGS.  8 A,  9 A,  10 A,  11 A,  12 A,  13 A,  14 A,  15 A,  16 A,  17 A,  18 A,  19 A,  20 A,  21 A, and  22 A , respectively. 
       FIG.  8 A  illustrates a cross section of a SAW resonator  6 . Unless otherwise noted, the components of  FIG.  8 A  may be similar to or the same as like numbered components of  FIG.  2   . The SAW resonator  6  includes a piezoelectric layer  20 , IDT electrodes  22  over the piezoelectric layer  20 , and a high impedance layer  26  under the piezoelectric layer  80 . Unlike the SAW resonator  2  illustrated in  FIG.  2   , the SAW resonator  6  does not include the temperature compensating layer  24 . The SAW resonator  6  can generate Rayleigh mode surface acoustic waves. 
     The SAW resonator  6  can have a pitch L of 2 μm, for example. The piezoelectric layer  20  of the SAW resonator  6  illustrated in  FIG.  8 A  is a lithium niobate (LN) layer with a cut angle of 120°. The IDT electrodes  22  of the SAW resonator  6  are aluminum (Al) electrodes with a thickness T 3  of 0.04 L. The high impedance layer  26  of the SAW resonator  6  is a silicon (Si) layer with a thickness T 4  set to a semi-infinite condition. 
       FIG.  8 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  6  of  FIG.  8 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. 
       FIG.  9 A  illustrates a cross section of a SAW resonator  7  according to one embodiment. The SAW resonator  7  is like the SAW resonator  6  illustrated in  FIG.  8 A  except that the SAW resonator  7  also includes a low impedance layer  28 . The low impedance layer  28  of the SAW resonator  7  illustrated in  FIG.  9 A  is a silicon dioxide (SiO 2 ) layer with a thickness T 5  of 0.05 L for the simulation results shown in  FIG.  9 B . 
       FIG.  9 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  7  of  FIG.  9 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. As compared to the simulation results of the SAW resonator  6 , the Γ is improved in the simulation results of the SAW resonator  7 . Accordingly, the low impedance layer  28  can contribute to improved Γ in a Rayleigh mode SAW resonator. 
       FIG.  10 A  illustrates a cross section of a SAW resonator  8  according to one embodiment. The SAW resonator  8  is like the SAW resonator  7  illustrated in  FIG.  9 A  except that the low impedance layer  28  of the SAW resonator  8  illustrated in  FIG.  9 A  has a thickness T 5  of 0.1 L. 
       FIG.  10 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  8  of  FIG.  10 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. As compared to the simulation results of the SAW resonator  6 , the Γ is improved in the simulation results of the SAW resonator  8 . 
       FIG.  11 A  illustrates a cross section of a SAW resonator  9  according to one embodiment. The SAW resonator  9  is like the SAW resonator  7  illustrated in  FIG.  9 A  except that the low impedance layer  28  of the SAW resonator  9  illustrated in  FIG.  11 A  has a thickness T 5  of 0.2 L. 
       FIG.  11 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  9  of  FIG.  11 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. 
       FIG.  12 A  illustrates a cross section of a SAW resonator  51  according to one embodiment. The SAW resonator  51  is like the SAW resonator  7  illustrated in  FIG.  9 A  except that the low impedance layer  28  of the SAW resonator  51  illustrated in  FIG.  12 A  has a thickness T 5  of 0.3 L. 
       FIG.  12 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  51  of  FIG.  12 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. These simulations indicate that when the lower impedance layer  28  is sufficiently thick, Γ can be degraded. 
       FIG.  13 A  illustrates a cross section of a SAW resonator  52  according to one embodiment. The SAW resonator  52  is like the SAW resonator  2  illustrated in FIG.  2 A. The SAW resonator  52  can have a pitch L of 2 μm. The piezoelectric layer  20  of the SAW resonator  52  illustrated in  FIG.  13 A  is a lithium niobate (LN) layer with a cut angle of 120°. The IDT electrodes  22  of the SAW resonator  52  are aluminum (Al) electrodes with a thickness T 3  of 0.04 L. The temperature compensating layer  24  is a silicon dioxide (SiO 2 ) layer with a thickness T 2  of 0.1 L. The high impedance layer  26  of the SAW resonator  6  is a silicon (Si) layer. 
       FIG.  13 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  52  of  FIG.  13 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. 
       FIG.  14 A  illustrates a cross section of SAW resonator  53  according to one embodiment. The SAW resonator  53  is like the SAW resonator  52  illustrated in  FIG.  13 A  except that the temperature compensating layer  24  of the SAW resonator  53  illustrated in  FIG.  14 A  has a thickness T 5  of 0.2 L. 
       FIG.  14 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  53  of  FIG.  14 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. 
       FIG.  15 A  illustrates a cross section of a SAW resonator  54  according to one embodiment. The SAW resonator  54  is like the SAW resonator  52  illustrated in  FIG.  13 A  except that the temperature compensating layer  24  of the SAW resonator  54  illustrated in  FIG.  15 A  has a thickness T 5  of 0.3 L. 
       FIG.  15 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  54  of  FIG.  15 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. 
       FIG.  16 A  illustrates a cross section of a SAW resonator  55  according to one embodiment. The SAW resonator  55  is like the SAW resonator  5  illustrated in  FIG.  6   , except that the SAW resonator  55  has a single layer IDT electrodes  22  instead of the multi-layer IDT electrodes  22 ′ illustrated in  FIG.  6   . 
     The SAW resonator  55  has a pitch L of 2 μm for the simulation corresponding to  FIG.  16 B . The piezoelectric layer  20  of the SAW resonator  55  illustrated in  FIG.  16 A  is a lithium niobate (LN) layer with a cut angle of 120°. The IDT electrodes  22  of the SAW resonator  6  are aluminum (Al) electrodes with a thickness T 3  of 0.04 L for the simulation corresponding to  FIG.  16 B . The temperature compensating layer  24  is a silicon dioxide (SiO 2 ) layer with a thickness T 2  of 0.1 L. The high impedance layer  26  of the SAW resonator  55  is a silicon (Si) layer. The low impedance layer  28  of the SAW resonator  55  is a silicon dioxide (SiO 2 ) layer with a thickness T 5  of 0.1 L. 
       FIG.  16 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  55  of  FIG.  16 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. 
     When Al IDT electrodes are used as IDT electrodes  22 , an open grating may be outside of a short grating. Such stopband performance may be undesirable. On the other hand, when IDT electrodes of a material that has a higher density than Al (e.g., molybdenum (Mo), tungsten (W), etc.) are used, the stopband performance may be improved. When the temperature compensating layer  24  is a silicon dioxide (SiO 2 ) layer and has a thickness T 2  that is larger than 0.15 L, and Mo IDT electrodes are used, majority of the open grating can be within the short grating, which may indicate that the stopband performance is improved relative to the resonator with Al electrodes. Similarly, when the temperature compensating layer  24  is a silicon dioxide (SiO 2 ) layer and has a thickness T 2  that is larger than 0.1 L, and W IDT electrodes are used, majority of the open grating can be within the short grating, which may indicate that the stopband performance is improved relative to the resonator with Al electrodes. 
       FIG.  17 A  illustrates a cross section of a SAW resonator  56 . The SAW resonator  56  is like the SAW resonator  6  illustrated in  FIG.  8 A  except that the IDT electrodes  22  of the SAW resonator  56  illustrated in  FIG.  17 A  are molybdenum (Mo) IDT electrodes with a thickness T 3  of 0.4 L. 
       FIG.  17 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  56  of  FIG.  17 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. 
       FIG.  18 A  illustrates a cross section of a SAW resonator  57  according to one embodiment. The SAW resonator  57  is like the SAW resonator  56  illustrated in  FIG.  17 A  except that the SAW resonator  57  also includes a low impedance layer  28 . The low impedance layer  28  of the SAW resonator  57  illustrated in  FIG.  18 A  is a silicon dioxide (SiO 2 ) layer with a thickness T 5  of 0.1 L for the simulation corresponding to  FIG.  18 B . 
       FIG.  18 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  57  of  FIG.  18 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. As compared to the simulation results of the SAW resonator  56 , the Γ is improved in the simulation results of the SAW resonator  57 . Accordingly, the low impedance layer  28  can contribute to improved Γ in the SAW resonator  57 . 
       FIG.  19 A  illustrates a cross section of a SAW resonator  58  according to one embodiment. The SAW resonator  58  is like the SAW resonator  57  illustrated in  FIG.  18 A  except that the SAW resonator  58  illustrated in  FIG.  19 A  also includes a temperature compensating layer  24 . The temperature compensating layer  24  of the SAW resonator  58  is a silicon dioxide (SiO 2 ) layer with a thickness T 2  of 0.1 L for the simulation corresponding to  FIG.  19 B . 
       FIG.  19 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  58  of  FIG.  19 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. As compared to the simulation results of the SAW resonator  56 , the Γ is improved in the simulation results of the SAW resonator  58 . 
       FIG.  20 A  illustrates a cross section of a SAW resonator  59  according to one embodiment. The SAW resonator  59  is like the SAW resonator  58  illustrated in FIG.  19 A except that the temperature compensating layer  24  of the SAW resonator  59  illustrated in  FIG.  20 A  has a thickness T 5  of 0.2 L. 
       FIG.  20 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  59  of  FIG.  14 A . The simulation results are for five different thicknesses T 1  of the piezoelectric layer  20 . The simulations were performed with the thicknesses T 1  of 0.1 L, 0.2 L, 0.3 L, 0.4 L, and 0.5 L. As compared to the simulation results of the SAW resonator  56 , the Γ is improved in the simulation results of the SAW resonator  59 . 
       FIG.  21 A  illustrates a cross section of a SAW resonator  60  according to one embodiment. The SAW resonator  60  is like the SAW resonator  57  illustrated in  FIG.  18 A  except that the piezoelectric layer  20  of the SAW resonator  60  illustrated in  FIG.  20 A  has a thickness T 1  of 0.3 L. 
       FIG.  21 B  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonator  60  of  FIG.  21 A . The simulation results are for five different cut angles of the piezoelectric layer  20 . The simulations were performed with the cut angles of 120°, 122°, 124°, 126°, and 128°. The graph of reflection coefficient of  FIG.  21 B  indicates that spikes are affected by the cut angle of the piezoelectric layer  20 .  FIG.  21 B  indicates that the cut angle of the piezoelectric layer  20  can affect gamma. 
       FIG.  22 A  illustrates a cross section of a SAW resonator  61  according to one embodiment. The SAW resonator  61  is like the SAW resonator  5  illustrated in  FIG.  6   , except that the SAW resonator  55  has a single layer IDT electrodes  22  instead of the multi-layer IDT electrodes  22 ′ illustrated in  FIG.  6    and various features of the layers (e.g., cut angle, material and/or thickness) are indicated in  FIG.  16 A . 
     The SAW resonator  61  is illustrated with a pitch L of 2 μm. The piezoelectric layer  20  of the SAW resonator  61  illustrated in  FIG.  22 A  is a lithium niobate (LN) layer. The piezoelectric layer  20  of the SAW resonator  61  has a thickness T 1  of 0.3 L. The IDT electrodes  22  of the SAW resonator  61  have a thickness T 3  of 0.04 L. The IDT electrodes  22  of the SAW resonator  61  can be tungsten or molybdenum. The temperature compensating layer  24  of the SAW resonator  61  is a silicon dioxide (SiO 2 ) layer with a thickness T 2  of 0.2 L. The high impedance layer  26  of the SAW resonator  61  is a silicon (Si) layer. The low impedance layer  28  of the SAW resonator  61  is a silicon dioxide (SiO 2 ) layer with a thickness T 5  of 0.1 L. 
       FIG.  22 B  illustrates a cross section of a SAW resonator  62 . The illustrated SAW resonator  62  is like the SAW resonator  1  illustrated in  FIG.  1    with a single layer IDT electrode. The SAW resonator  62  includes an LN layer  10 ′, IDT electrodes  12 ′ over the LN layer  10 ′, and an SiO 2  layer  14 ′ over the IDT electrodes  12 ′. The LN layer  10 ′ has a cut angle of 126°. The pitch L of the SAW resonator  62  is 2 μm. A thickness of the SiO 2  layer  14 ′ of the SAW resonator  62  is 0.2 L. The IDT electrodes  12 ′ of the SAW resonator  62  are molybdenum (Mo) IDT electrodes. The IDT electrodes  12 ′ a thickness of 0.04 L. 
       FIG.  22 C  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonators  61  and  62  of  FIGS.  22 A and  22 B , respectively. The curves for the SAW resonator  61  have lithium niobate piezoelectric layers with cut angles of 122° and 124°. The simulations were performed with tungsten (W) IDT electrodes and molybdenum (Mo) IDT electrodes for the SAW resonator  61 . As compared to the simulation result of the SAW resonator  62 , the Γ is improved in the simulation results of the SAW resonator  61 . 
       FIG.  23 A  illustrates graphs showing simulation results of isolation s 12  on the left and reflection coefficient s 11  (Γ) on the right for the SAW resonators  61  and  62  of  FIGS.  22 A and  22 B  respectively. The simulations were performed with molybdenum (Mo) IDT electrodes and LN layers with a cut angle of 120° for the SAW resonator  61  and the SAW resonator  62 . The differences in the graphs of  FIGS.  22 C and  23 A  can be due to differences in cut angle. 
       FIG.  23 B  illustrates transmission leakage of the SAW resonator  61  illustrated in  FIG.  22 A  at a frequency of 4 GHz.  FIG.  23 C  illustrates transmission leakage of the SAW resonator  62  of  FIG.  22 B  at a frequency of 4 GHz. The acoustic leakage is reduced for the SAW resonator  61  as compared to the acoustic leakage of the SAW resonator  62 . 
       FIG.  24    illustrates graphs showing simulated dispersion curves of a SAW resonator having various thicknesses of silicon dioxide (SiO 2 ) layer over a molybdenum (Mo) IDT electrode. The simulations were performed with the SiO 2  layer having thicknesses of 0 (no SiO 2  layer over the IDT electrode), 0.01 L, 0.02 L, 0.03 L, 0.05 L, 0.1 L, 0.15 L, 0.2 L, 0.25 L, 0.3 L, 0.35 L, and 0.4 L. Each of the graphs show a short grating dispersion curve and an open grating dispersion curve. The x-axis shows frequency and the y-axis shows wave number. These graphs indicate that, when the thickness of the SiO 2  layer is more than about 0.15 L, the dispersion is better than when the thickness of the SiO 2  layer is less than about 0.15 L. 
     From these simulation results of the SAW resonators according to various embodiments, desirable resonator structures can be determined for particular operations. For example, the determination of a thickness T 1  of the piezoelectric layer  20 , a thickness T 2  of the temperature compensating layer  24 , a thickness T 4  of the high impedance layer  26 , and/or a thickness T 5  of the low impedance layer  28  can be based at least in part on the simulated reflection coefficient (Γ). For example, a material for the piezoelectric layer  20 , a cut angle of the piezoelectric layer  20 , and/or a material for the IDT electrodes  22 ,  22 ′ can be determined based at least in part on the simulated reflection coefficient (Γ). The simulated reflection coefficient (Γ) of the SAW resonators in various embodiments can be analyzed to determine a suitable structure of a SAW resonator for certain applications. 
     The simulation results indicate that the high impedance layer  26  and/or the low acoustic impedance layer  28  affect the wide range gamma. Therefore, a selection of suitable thicknesses and/or materials for the high impedance layer  26  and/or the low acoustic impedance layer  28  can improve the wide range gamma. For example, the simulation results indicate that using a silicon dioxide (SiO 2 ) layer with a thickness in a range from 0.01 L to 0.3 L, such as a thickness of about 0.1 L, as the low acoustic impedance layer  28  can improve the wide range gamma. 
     The simulation results indicate that the temperature compensating layer  24  and/or the cut angle of the piezoelectric layer  20  affect the narrow range gamma. Therefore, a selection of suitable thicknesses or materials for the temperature compensating layer  24  and/or the piezoelectric layer  20  can improve the narrow range gamma. For example, the simulation results indicate that using a silicon dioxide (SiO 2 ) layer with a thickness greater than about 0.15 L as the temperature compensating layer  24  can improve the narrow range gamma. By using such SiO 2  layer as temperature compensating layer, a resonator can obtain reflection characteristics similar to a TC-SAW resonator. 
     The simulation results indicate that a lithium niobate (LN) layer with cut angle in a range from 118° to 138°, such as a cut angle of about 128°, can be a suitable piezoelectric layer to use in embodiments disclosed herein. The simulation results indicate that an LN layer with a thickness in a range from 0.1 L to 0.5 L, such as a thickness of about 0.3 L, can be a suitable piezoelectric layer to use in various embodiments disclosed herein. The simulation results indicate that the Mo IDT electrodes or the W IDT electrodes improve an electromechanical coupling coefficient k 2  relative to the Al IDT electrodes. 
     In some instances, a SAW resonator according to one embodiment can have, referring to reference numerals used in  FIG.  6   , a silicon (Si) layer (as the high impedance layer  26 ), a silicon dioxide (SiO 2 ) layer with a thickness of 0.1 L (as the low impedance layer  28 ) over the Si layer, a lithium niobate (LN) layer with a cut angle of 124° and a thickness of 0.3 L (as the piezoelectric layer  20 ) over the SiO 2  layer, an aluminum/molybdenum (Al/Mo) IDT electrodes with a Mo thickness of 0.04 L (as the IDT electrodes  22 ′) over the LN layer, and another silicon dioxide (SiO 2 ) layer with a thickness of 0.2 L (as the temperature compensating layer  24 ) over the IDT electrodes. In some other instances, a SAW resonator according to one embodiment can have a silicon (Si) layer, a silicon dioxide (SiO 2 ) layer with a thickness of 0.1 L over the Si layer, a 120YX lithium niobate (LN) layer with a thickness of 0.3 L over the SiO 2  layer, and an aluminum/molybdenum (Al/Mo) IDT electrodes with a Mo thickness of 0.04 L over the LN layer. Such structure can be generally similar to the SAW resonator  57  illustrated in  FIG.  18 A . Such structure, unlike the IDT electrode  22  of the SAW resonator  57 , has the Al layer over the Mo layer. 
     Any of the SAW resonators with the temperature compensating layer disclosed herein may also include a dispersion adjustment layer over the temperature compensating layer. The dispersion adjustment layer can have a trench, in some embodiments. In certain applications, the dispersion adjustment layer with the trench can suppress the transverse mode. 
       FIG.  25 A  illustrates a cross section of a surface acoustic wave resonator  71  according to one embodiment. The SAW resonator  71  is similar to the SAW resonator  5  illustrated in  FIG.  6   .  FIG.  25 B  is a top plan view of the resonator  71  illustrated in  FIG.  25 A . Unless otherwise noted, the components of  FIGS.  25 A and  25 B  may be similar to or the same as like numbered components of  FIG.  6   . The SAW resonator  71  includes a piezoelectric layer  20 , IDT electrodes  22 ′ over the piezoelectric layer  20 , a temperature compensating layer  24  over the IDT electrodes  22 ′, and a high impedance layer  26  under the piezoelectric layer  20 . The SAW resonator  71  also includes a low impedance layer  28  between the piezoelectric layer  20  and the high impedance layer  26 , and a dispersion adjustment layer  80  over the temperature compensating layer  24 . 
     The illustrated dispersion adjustment layer  80  is partially disposed over an upper surface of the temperature compensation layer  24  with trenches. However, the dispersion adjustment layer  80  can be disposed entirely over the upper surface of the temperature compensation layer  24  in some other instances. The dispersion adjustment layer  80  can cause a magnitude of the velocity in the underlying region of the SAW resonator  71  to be increased. The trench can reduce velocity in the underlying region of the SAW resonator  71  relative to regions covered by the dispersion adjustment layer  80  to thereby suppress transverse modes. The dispersion adjustment layer  80  can include a SiN layer. In certain applications, the dispersion adjustment layer  80  can include any suitable material to increase the magnitude of the velocity of the underlying region of a SAW resonator. According to some applications, the dispersion adjustment layer  80  can include SiN and another material. The dispersion adjustment layer  80  has a thickness T 6 . In some embodiments, the thickness T 6  of the dispersion adjustment layer  80  can be in a range from 0.001 L to 0.05 L. 
       FIG.  25 C  is a graph showing simulation results of admittance of the SAW resonator  71  of  FIG.  25 A  and a similar resonator without the trenches in the dispersion adjustment layer  80 . In the simulation: a lithium niobate (LN) piezoelectric layer with a thickness T 1  of 0.3 L was used as the piezoelectric layer  20 ; an Al/Mo IDT electrodes with a thickness T 3 ′ of the Mo layer of 0.04 L and a thickness T 3 ″ of the Al layer of 0.04 L was used as the IDT electrodes  22 ′; a silicon dioxide (SiO 2 ) layer with a thickness T 2  of 0.2 L was used as the temperature compensating layer  24 ; a silicon (Si) layer was used as the high impedance layer  26 ; a silicon dioxide (SiO 2 ) layer with a thickness T 5  of 0.1 L was used as the low impedance layer  28 ; and a silicon nitride (SiN) layer with a thickness T 6  of 0.005 L was used as the dispersion adjustment layer  80 . 
     The trenches in the dispersion adjustment layer  80  are formed over edges of IDT fingers. A gap between a bus bar to an edge of a finger of the IDT electrode  22 ′ can be about 0.9 L. The gap can be in a range from 0.9 L to 2 L in some embodiments. A trench width between the edge of the finger of the IDT electrode to an edge of a middle portion of the dispersion adjustment layer  80  can be about 1 L. The trench width can be in a range from 0.5 L to 1.5 L, in certain embodiments. 
     The graph shown in  FIG.  25 B  indicates that the transverse mode is suppressed for the SAW resonator that includes the trench in the dispersion adjustment layer  80 , as compared to the similar resonator that does not include the trench in the dispersion adjustment layer  80 . 
       FIG.  26    is a schematic diagram of an example transmit filter  85  that includes surface acoustic wave resonators according to an embodiment. The transmit filter  85  can be a band pass filter. The illustrated transmit filter  85  is arranged to filter a radio frequency signal received at a transmit port TX and provide a filtered output signal to an antenna port ANT. Some or all of the SAW resonators TS 1  to TS 7  and/or TP 1  to TP 5  can be a SAW resonators in accordance with any suitable principles and advantages disclosed herein. For instance, one or more of the SAW resonators of the transmit filter  85  can be a surface acoustic wave resonator  2  of  FIG.  2    or a surface acoustic wave resonator  5  of  FIG.  6   . Alternatively or additionally, one or more of the SAW resonators of the transmit filter  85  can be any surface acoustic wave resonator disclosed herein. Any suitable number of series SAW resonators and shunt SAW resonators can be included in a transmit filter  85 . 
       FIG.  27    is a schematic diagram of a receive filter  90  that includes surface acoustic wave resonators according to an embodiment. The receive filter  90  can be a band pass filter. The illustrated receive filter  90  is arranged to filter a radio frequency signal received at an antenna port ANT and provide a filtered output signal to a receive port RX. Some or all of the SAW resonators RS 1  to RS 8  and/or RP 1  to RP 6  can be SAW resonators in accordance with any suitable principles and advantages disclosed herein. For instance, one or more of the SAW resonators of the receive filter  90  can be a surface acoustic wave resonator  2  of  FIG.  2    or a surface acoustic wave resonator  5  of  FIG.  6   . Alternatively or additionally, one or more of the SAW resonators of the receive filter  90  can be any surface acoustic wave resonator disclosed herein. Any suitable number of series SAW resonators and shunt SAW resonators can be included in a receive filter  90 . 
       FIG.  28    is a schematic diagram of a radio frequency module  175  that includes a surface acoustic wave component  176  according to an embodiment. The illustrated radio frequency module  175  includes the SAW component  176  and other circuitry  177 . The SAW component  176  can include one or more SAW resonators with any suitable combination of features of the SAW resonators disclosed herein. The SAW component  176  can include a SAW die that includes SAW resonators. 
     The SAW component  176  shown in  FIG.  28    includes a filter  178  and terminals  179 A and  179 B. The filter  178  includes SAW resonators. One or more of the SAW resonators can be implemented in accordance with any suitable principles and advantages of the surface acoustic wave resonator  2  of  FIG.  2   , a surface acoustic wave resonator  5  of  FIG.  6   , and/or any surface acoustic wave resonator disclosed herein. The filter  178  can be a TC-SAW filter arranged as a band pass filter to filter radio frequency signals with frequencies below about 3.5 GHz in certain applications. The terminals  179 A and  178 B can serve, for example, as an input contact and an output contact. The SAW component  176  and the other circuitry  177  are on a common packaging substrate  180  in  FIG.  28   . The package substrate  180  can be a laminate substrate. The terminals  179 A and  179 B can be electrically connected to contacts  181 A and  181 B, respectively, on the packaging substrate  180  by way of electrical connectors  182 A and  182 B, respectively. The electrical connectors  182 A and  182 B can be bumps or wire bonds, for example. The other circuitry  177  can include any suitable additional circuitry. For example, the other circuitry can include one or more one or more power amplifiers, one or more radio frequency switches, one or more additional filters, one or more low noise amplifiers, the like, or any suitable combination thereof. The radio frequency module  175  can include one or more packaging structures to, for example, provide protection and/or facilitate easier handling of the radio frequency module  175 . Such a packaging structure can include an overmold structure formed over the packaging substrate  175 . The overmold structure can encapsulate some or all of the components of the radio frequency module  175 . 
       FIG.  29    is a schematic diagram of a radio frequency module  184  that includes a surface acoustic wave component according to an embodiment. As illustrated, the radio frequency module  184  includes duplexers  185 A to  185 N that include respective transmit filters  186 A 1  to  186 N 1  and respective receive filters  186 A 2  to  186 N 2 , a power amplifier  187 , a select switch  188 , and an antenna switch  189 . In some instances, the module  184  can include one or more low noise amplifiers configured to receive a signal from one or more receive filters of the receive filters  186 A 2  to  186 N 2 . The radio frequency module  184  can include a package that encloses the illustrated elements. The illustrated elements can be disposed on a common packaging substrate  180 . The packaging substrate can be a laminate substrate, for example. 
     The duplexers  185 A to  185 N can each include two acoustic wave filters coupled to a common node. The two acoustic wave filters can be a transmit filter and a receive filter. As illustrated, the transmit filter and the receive filter can each be band pass filters arranged to filter a radio frequency signal. One or more of the transmit filters  186 A 1  to  186 N 1  can include one or more SAW resonators in accordance with any suitable principles and advantages disclosed herein. Similarly, one or more of the receive filters  186 A 2  to  186 N 2  can include one or more SAW resonators in accordance with any suitable principles and advantages disclosed herein. Although  FIG.  29    illustrates duplexers, any suitable principles and advantages disclosed herein can be implemented in other multiplexers (e.g., quadplexers, hexaplexers, octoplexers, etc.) and/or in switch-plexers. 
     The power amplifier  187  can amplify a radio frequency signal. The illustrated switch  188  is a multi-throw radio frequency switch. The switch  188  can electrically couple an output of the power amplifier  187  to a selected transmit filter of the transmit filters  186 A 1  to  186 N 1 . In some instances, the switch  188  can electrically connect the output of the power amplifier  187  to more than one of the transmit filters  186 A 1  to  186 N 1 . The antenna switch  189  can selectively couple a signal from one or more of the duplexers  185 A to  185 N to an antenna port ANT. The duplexers  185 A to  185 N can be associated with different frequency bands and/or different modes of operation (e.g., different power modes, different signaling modes, etc.). 
       FIG.  30    is a schematic block diagram of a module  190  that includes duplexers  191 A to  191 N and an antenna switch  192 . One or more filters of the duplexers  191 A to  191 N can include any suitable number of surface acoustic wave resonators in accordance with any suitable principles and advantages discussed herein. Any suitable number of duplexers  191 A to  191 N can be implemented. The antenna switch  192  can have a number of throws corresponding to the number of duplexers  191 A to  191 N. The antenna switch  192  can electrically couple a selected duplexer to an antenna port of the module  190 . 
       FIG.  31    is a schematic block diagram of a module  210  that includes a power amplifier  212 , a radio frequency switch  214 , and duplexers  191 A to  191 N in accordance with one or more embodiments. The power amplifier  212  can amplify a radio frequency signal. The radio frequency switch  214  can be a multi-throw radio frequency switch. The radio frequency switch  214  can electrically couple an output of the power amplifier  212  to a selected transmit filter of the duplexers  191 A to  191 N. One or more filters of the duplexers  191 A to  191 N can include any suitable number of surface acoustic wave resonators in accordance with any suitable principles and advantages discussed herein. Any suitable number of duplexers  191 A to  191 N can be implemented. 
       FIG.  32 A  is a schematic diagram of a wireless communication device  220  that includes filters  223  in a radio frequency front end  222  according to an embodiment. The filters  223  can include one or more SAW resonators in accordance with any suitable principles and advantages discussed herein. The wireless communication device  220  can be any suitable wireless communication device. For instance, a wireless communication device  220  can be a mobile phone, such as a smart phone. As illustrated, the wireless communication device  220  includes an antenna  221 , an RF front end  222 , a transceiver  224 , a processor  225 , a memory  226 , and a user interface  227 . The antenna  221  can transmit/receive RF signals provided by the RF front end  222 . Such RF signals can include carrier aggregation signals. Although not illustrated, the wireless communication device  220  can include a microphone and a speaker in certain applications. 
     The RF front end  222  can include one or more power amplifiers, one or more low noise amplifiers, one or more RF switches, one or more receive filters, one or more transmit filters, one or more duplex filters, one or more multiplexers, one or more frequency multiplexing circuits, the like, or any suitable combination thereof. The RF front end  222  can transmit and receive RF signals associated with any suitable communication standards. The filters  223  can include SAW resonators of a SAW component that includes any suitable combination of features discussed with reference to any embodiments discussed above. 
     The transceiver  224  can provide RF signals to the RF front end  222  for amplification and/or other processing. The transceiver  224  can also process an RF signal provided by a low noise amplifier of the RF front end  222 . The transceiver  224  is in communication with the processor  225 . The processor  225  can be a baseband processor. The processor  225  can provide any suitable base band processing functions for the wireless communication device  220 . The memory  226  can be accessed by the processor  225 . The memory  226  can store any suitable data for the wireless communication device  220 . The user interface  227  can be any suitable user interface, such as a display with touch screen capabilities. 
       FIG.  32 B  is a schematic diagram of a wireless communication device  230  that includes filters  223  in a radio frequency front end  222  and a second filter  233  in a diversity receive module  232 . The wireless communication device  230  is like the wireless communication device  200  of  FIG.  32 A , except that the wireless communication device  230  also includes diversity receive features. As illustrated in  FIG.  32 B , the wireless communication device  230  includes a diversity antenna  231 , a diversity module  232  configured to process signals received by the diversity antenna  231  and including filters  233 , and a transceiver  234  in communication with both the radio frequency front end  222  and the diversity receive module  232 . The filters  233  can include one or more SAW resonators that include any suitable combination of features discussed with reference to any embodiments discussed above. 
     Any of the embodiments described above can be implemented in association with mobile devices such as cellular handsets. The principles and advantages of the embodiments can be used for any systems or apparatus, such as any uplink wireless communication device, that could benefit from any of the embodiments described herein. The teachings herein are applicable to a variety of systems. Although this disclosure includes some example embodiments, the teachings described herein can be applied to a variety of structures. Any of the principles and advantages discussed herein can be implemented in association with RF circuits configured to process signals in a frequency range from about 30 kHz to 300 GHz, such as in a frequency range from about 450 MHz to 8.5 GHz. 
     Aspects of this disclosure can be implemented in various electronic devices. Examples of the electronic devices can include, but are not limited to, consumer electronic products, parts of the consumer electronic products such as die and/or acoustic wave filter assemblies and/or packaged radio frequency modules, uplink wireless communication devices, wireless communication infrastructure, electronic test equipment, etc. Examples of the electronic devices can include, but are not limited to, a mobile phone such as a smart phone, a wearable computing device such as a smart watch or an ear piece, a telephone, a television, a computer monitor, a computer, a modem, a hand-held computer, a laptop computer, a tablet computer, a personal digital assistant (PDA), a microwave, a refrigerator, an automobile, a stereo system, a DVD player, a CD player, a digital music player such as an MP3 player, a radio, a camcorder, a camera, a digital camera, a portable memory chip, a washer, a dryer, a washer/dryer, a copier, a facsimile machine, a scanner, a multi-functional peripheral device, a wrist watch, a clock, etc. Further, the electronic devices can include unfinished products. 
     Unless the context clearly requires otherwise, throughout the description and the claims, the words “comprise,” “comprising,” “include,” “including” and the like are to be construed in an inclusive sense, as opposed to an exclusive or exhaustive sense; that is to say, in the sense of “including, but not limited to.” The word “coupled”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Likewise, the word “connected”, as generally used herein, refers to two or more elements that may be either directly connected, or connected by way of one or more intermediate elements. Additionally, the words “herein,” “above,” “below,” and words of similar import, when used in this application, shall refer to this application as a whole and not to any particular portions of this application. Where the context permits, words in the above Detailed Description using the singular or plural number may also include the plural or singular number respectively. The word “or” in reference to a list of two or more items, that word covers all of the following interpretations of the word: any of the items in the list, all of the items in the list, and any combination of the items in the list. 
     Moreover, conditional language used herein, such as, among others, “can,” “could,” “might,” “may,” “e.g.,” “for example,” “such as” and the like, unless specifically stated otherwise, or otherwise understood within the context as used, is generally intended to convey that certain embodiments include, while other embodiments do not include, certain features, elements and/or states. Thus, such conditional language is not generally intended to imply that features, elements and/or states are in any way required for one or more embodiments. 
     While certain embodiments have been described, these embodiments have been presented by way of example only, and are not intended to limit the scope of the disclosure. Indeed, the novel apparatus, methods, and systems described herein may be embodied in a variety of other forms; furthermore, various omissions, substitutions and changes in the form of the methods and systems described herein may be made without departing from the spirit of the disclosure. For example, while blocks are presented in a given arrangement, alternative embodiments may perform similar functionalities with different components and/or circuit topologies, and some blocks may be deleted, moved, added, subdivided, combined, and/or modified. Each of these blocks may be implemented in a variety of different ways. Any suitable combination of the elements and acts of the various embodiments described above can be combined to provide further embodiments. The accompanying claims and their equivalents are intended to cover such forms or modifications as would fall within the scope and spirit of the disclosure.