Patent Publication Number: US-2022224308-A1

Title: Methods of manufacturing acoustic wave device with anti-reflection layer

Description:
CROSS REFERENCE TO PRIORITY APPLICATIONS 
     This application is a divisional of U.S. patent application Ser. No. 16/790,408, filed Feb. 13, 2020 and titled “ACOUSTIC WAVE DEVICE WITH ANTI-REFLECTION LAYER,” which claims the benefit of priority of U.S. Provisional Patent Application No. 62/806,560, filed Feb. 15, 2019 and titled “ACOUSTIC WAVE RESONATOR WITH ANTI-REFLECTION LAYER,” the disclosures of each which are hereby incorporated by reference in their entireties herein. 
    
    
     BACKGROUND 
     Technical Field 
     Embodiments of this disclosure relate to acoustic wave devices. 
     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, an acoustic wave device is disclosed. The acoustic wave device can include a piezoelectric layer, and an interdigital transducer electrode positioned over the piezoelectric layer. The interdigital transducer electrode includes a conductive layer. The acoustic wave device can also include an anti-reflection layer positioned over the conductive layer. The anti-reflection layer includes silicon. The acoustic wave device can further include a temperature compensation layer over the anti-reflection layer. 
     In an embodiment, the anti-reflection layer is a silicon oxynitride layer. The silicon oxynitride layer can have a thickness in a range from 100 nanometers to 120 nanometers. 
     In an embodiment, the anti-reflection layer is an amorphous silicon layer. The amorphous silicon layer can have a thickness in a range from 5 nanometers to 15 nanometers. 
     In an embodiment, the anti-reflection layer includes a material and has a thickness that together cause reflectivity of the acoustic wave device to be less than or equal to 0.2 for light having a wavelength of 365 nanometers. The anti-reflection layer contributes to less than 2 percent of wiring resistance of the acoustic wave device. 
     In an embodiment, the conductive layer is in physical contact with the anti-reflection layer. 
     In an embodiment, the interdigital transducer includes a metal layer positioned between the conductive layer and the piezoelectric layer. 
     In an embodiment, the acoustic wave device further including a substrate layer. The piezoelectric layer can be on the substrate layer. 
     In an embodiment, an acoustic wave filter includes acoustic wave devices arranged to filter a radio frequency signal. The acoustic wave devices include the acoustic wave device. A front end module can include the acoustic wave filter, additional circuitry, and a package enclosing the acoustic wave filter and the additional circuitry. The additional circuitry can include a multi-throw radio frequency switch. The additional circuitry can include a power amplifier. The acoustic wave filter can be included in a duplexer. A wireless communication device can include an antenna and the acoustic wave filter. The acoustic wave filter can be arranged to filter a radio frequency signal associated with the antenna. 
     In an embodiment, the conductive layer is an aluminum layer. The conductive layer can have a reflectivity of at least 0.5 for light having a wavelength of 365 nanometers. 
     The acoustic wave device can be an acoustic wave resonator. The acoustic wave resonator can be a surface acoustic wave resonator. 
     In one aspect, an acoustic wave device is disclosed. The acoustic wave device can include a piezoelectric layer, a interdigital transducer electrode positioned over the piezoelectric layer, and an anti-reflection layer over the interdigital transducer electrode. The interdigital transducer electrode can include a first interdigital transducer electrode finger extending from a first bus bar and a second interdigital transducer finger extending from a second bus bar. The first interdigital transducer electrode finger and the second interdigital transducer electrode finger can be spaced apart from each other by a gap. The anti-reflection layer can include silicon. The anti-reflection layer can be free from material of the interdigital transducer electrode. The piezoelectric layer can be free from the anti-reflection layer under the gap. 
     The acoustic wave device further includes a temperature compensation layer over the anti-reflection layer. 
     In an embodiment, the anti-reflection layer is an amorphous silicon layer. the amorphous silicon layer can have a thickness in a range from 5 nanometers to 15 nanometers. 
     The acoustic wave device of claim  8  wherein the anti-reflection layer is a silicon oxynitride layer. The silicon oxide layer can have a thickness in a range from 100 nanometers to 120 nanometers. 
     In an embodiment, the interdigital transducer electrode includes an aluminum layer. The anti-reflection layer can be in physical contact with the aluminum layer. The anti-reflection layer can have a reflectivity of 0.2 or less for light having a wavelength of 365 nanometers. 
     In an embodiment the anti-reflection layer has a reflectivity range from 0.1 to 0.2 at the wavelength of 365 nanometers. 
     In an embodiment, a line width distribution of the interdigital transducer electrode is 2% of the line width or less. 
     In an embodiment, the acoustic wave device further includes a support substrate. The piezoelectric layer can be over the support substrate. The support substrate can have a higher impedance than the piezoelectric layer. 
     The acoustic wave device can be configured to generate a surface acoustic wave. 
     In one aspect, a method of manufacturing an acoustic wave device is disclosed, the method can include providing an acoustic wave device structure with one or more interdigital transducer electrode layers on a piezoelectric layer. The one or more interdigital transducer electrode layers including a conductive layer. The method can also include forming an anti-reflection layer over the conductive layer. The anti-reflection layer includes silicon. The method further includes performing a photolithography processes to pattern an interdigital transducer electrode from one or more interdigital transducer electrode layers. The anti-reflection layer reduces reflection from the conductive layer during the photolithography process. 
     In an embodiment, the conductive layer includes aluminum. 
     In an embodiment, the anti-reflection layer is a silicon oxynitride layer. 
     In an embodiment, the anti-reflection layer is an amorphous silicon layer. 
     In an embodiment, the anti-reflection layer has a reflectivity of 0.2 or less for light having a wavelength of 365 nanometers. 
     In an embodiment, the conductive layer has a reflectivity of at least 0.5 for light having a wavelength of 365 nanometers. 
     In an embodiment, the method further includes forming a temperature compensation layer over the anti-reflection layer. 
     In an embodiment, the anti-reflection material remains distinct from the aluminum layer after a heating process. 
     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. 1A  illustrates a cross section of a surface acoustic wave (SAW) resonator structure at a stage of a manufacturing process. 
         FIG. 1B  illustrates a cross section of a surface acoustic wave resonator formed from the surface acoustic wave resonator structure illustrated in  FIG. 1A . 
         FIG. 2A  illustrates a cross section of a SAW resonator structure at a stage of a manufacturing process according to an embodiment. 
         FIG. 2B  illustrates a cross section of a SAW resonator formed from the SAW resonator structure illustrated in  FIG. 2A  according to an embodiment. 
         FIG. 3A  is a graph showing a reference wiring resistance measurement and a wiring resistance measurement of the SAW resonator illustrated in  FIG. 1B . 
         FIG. 3B  is a graph showing a reference wiring resistance measurement and a wiring resistance measurement of the SAW resonator illustrated in  FIG. 2B . 
         FIG. 4A  is a graph showing ellipsometer measurement results of reflectivity of an epoxy resin layer, a silicon oxynitride (SiON) layer, and an amorphous silicon (a-Si) layer at a wavelength of 365 nanometers (nm). 
         FIG. 4B  is a table that includes the lowest reflectivity values and corresponding thicknesses from  FIG. 4A  for the a-Si layer and the SiON layer. 
         FIG. 5A  is a graph of measurement results of line widths for different resist thicknesses of a resist film of a SAW resonator without an anti-reflection layer. 
         FIG. 5B  is a graph of measurement results of line widths for different resist thicknesses of a resist film of a SAW resonator structure with epoxy resin over an interdigital transducer (IDT) electrode. 
         FIG. 5C  is a graph of measurement results of line widths for different resist thicknesses of a resist film of a SAW resonator structure with an anti-reflection layer over an IDT electrode according to an embodiment. 
         FIG. 5D  is a graph of measurement results of line widths for different resist thicknesses of a resist film of a SAW resonator structure with an anti-reflection layer over an IDT electrode according to another embodiment. 
         FIG. 6  is a graph of swing curves of data points at the bottom sides of the measurement results illustrated in  FIGS. 5A-5D . 
         FIG. 7  illustrates a cross section of a SAW resonator according to an embodiment. 
         FIG. 8A  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG. 8B  illustrates a cross section of a SAW resonator according to another embodiment. 
         FIG. 8C  illustrates another cross section of the SAW resonator illustrated in  FIG. 8B . 
         FIG. 9A  illustrates a cross section of a Lamb wave device according to an embodiment. 
         FIG. 9B  illustrates a cross section of a Lamb wave device according to another embodiment. 
         FIG. 10A  is a schematic diagram of a transmit filter that includes a surface acoustic wave resonator according to an embodiment. 
         FIG. 10B  is a schematic diagram of a receive filter that includes a surface acoustic wave resonator according to an embodiment. 
         FIG. 11  is a schematic diagram of a radio frequency module that includes a surface acoustic wave component according to an embodiment. 
         FIG. 12  is a schematic diagram of a radio frequency module that includes duplexers with surface acoustic wave resonators according to an embodiment. 
         FIG. 13A  is a schematic block diagram of a module that includes a power amplifier, a radio frequency switch, and duplexers that include one or more surface acoustic wave resonators with an anti-reflection layer according to an embodiment. 
         FIG. 13B  is a schematic block diagram of a module that includes filters, a radio frequency switch, and a low noise amplifier according to an embodiment. 
         FIG. 14  is a schematic block diagram of a module that includes an antenna switch and duplexers that include one or more surface acoustic wave resonators with an anti-reflection layer according to an embodiment. 
         FIG. 15A  is a schematic block diagram of a wireless communication device that includes a filter in accordance with one or more embodiments. 
         FIG. 15B  is a schematic block diagram of another wireless communication device that includes a filter 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. The SAW devices include SAW resonators, SAW delay lines, and multi-mode SAW (MMS) filters (e.g., double mode SAW (DMS) filters). 
     A manufacturing process for a SAW device can include a photolithography process. In certain photolithography processes, some undesirable effects can occur. For example, light used in the photolithography process can reflect back, which can cause standing waves and/or swing curves. For SAW resonators that include an interdigital transducer (IDT) electrode with a relatively high reflectivity material, such as an aluminum IDT electrode, reflection from the IDT electrode is relatively high. Reflection from aluminum IDT electrode layers has presented technical challenges in manufacturing IDT electrode patterns with certain line widths in a photolithography process. 
     One approach to eliminate and/or mitigate such undesirable effects is to include an anti-reflection material over the aluminum IDT electrode layer. An anti-reflection epoxy resin film can suppress the reflectivity of an aluminum layer. Fixing properties of an epoxy resin anti-reflection film can involve a heating process. However, in such a heating process, the aluminum IDT electrode layer can react with the anti-reflection film to form a compound layer with carbon and aluminum. The thickness of the compound layer can be about 10 nanometers (nm) to 20 nm. This thickness can be about 10% to 15% of the thickness of the aluminum IDT electrode. The compound layer can be sparse and a wiring resistance value measured using a resistance wire test (also referred to as a wiring resistance measurement) with this structure can increase about 10% compared to a similar structure without an anti-reflection resin film. The surface of an aluminum IDT electrode with the compound film can be rough. The compound film can contribute to filter loss and/or larger frequency distribution due to the variable thickness of the compound layer with aluminum and resin throughout a wafer. 
     Aspects of this disclosure relate to an anti-reflection film over an IDT electrode layer of an acoustic wave device. For example, a SAW resonator can include a piezoelectric layer, an IDT electrode over the piezoelectric layer, and an anti-reflection layer over the IDT electrode. The anti-reflection layer can include silicon. For example, the anti-reflection layer can be a silicon oxynitride layer or an amorphous silicon layer. Anti-reflection layers disclosed herein can be free from material of an IDT electrode layer in contact with the anti-reflection layer. With such an anti-reflection layer, the wiring resistance value can be substantially the same as a similar structure without an anti-reflection layer. The anti-reflection layer can have a thickness that causes the reflectivity to satisfy a threshold. With anti-reflection layers disclosed herein, IDT electrodes of acoustic wave resonators can be patterned with line widths in a range from 0.25 micrometers (μm) to 0.4 μm in a photolithography process without significant electrical degradation in filters that include such acoustic wave resonators. 
     Although embodiments may be discussed with reference to SAW resonators, any suitable principles and advantages discussed herein can be applied to any suitable SAW device and/or any other suitable acoustic wave device. Embodiments will now be discussed with reference to drawings. Any suitable combination of features of the embodiments disclosed herein can be implemented together with each other. 
       FIG. 1A  illustrates a cross section of a surface acoustic wave resonator structure at a stage of a manufacturing process. The manufacturing process may include a photolithography process. The illustrated SAW resonator structure in  FIG. 1A  includes a piezoelectric layer  10 , an interdigital transducer (IDT) electrode  12  over the piezoelectric layer  10 , an anti-reflection epoxy resin film  14  over the IDT electrode  12 , and a resist film  16  over the epoxy resin film  14 . The IDT electrode  12  has an upper surface  12   a  in contact with the epoxy resin film  14 . The epoxy resin film  14  is subjected to a heat processing to fix its properties in another stage in the manufacturing process. The epoxy resin film  14  is heated prior to removing the resist film  16 . The resist film  16  gets removed later at a later stage in the manufacturing process. For example, the manufacturing process can include: (1) depositing an IDT electrode material layer on the piezoelectric layer  10 ; (2) coating the anti-reflection epoxy resin film  14  on the IDT electrode material layer; (3) coating the resist film  16  on the anti-reflection epoxy resin film  14 ; (4) patterning the resist film  16 ; (5) etching the IDT electrode material layer to form the IDT electrode  12 ; and (6) removing the resist film  16 . The anti-reflection epoxy resin film  14  can mitigate and/or eliminate back reflection of light from the IDT electrode  12  during the photolithography process. As discussed below, this reduction of a reflectivity of the IDT electrode  12  can make a line width range smaller. 
       FIG. 1B  illustrates a cross section of a surface acoustic wave resonator  1  formed using the surface acoustic wave resonator structure illustrated in  FIG. 1A . The illustrated SAW resonator  1  includes the piezoelectric layer  10 , the IDT electrode  12  over the piezoelectric layer  10 , a compound layer  14 ′ over the IDT electrode  12 , and a temperature compensation layer  18  over the compound layer  14 ′. 
     The piezoelectric layer  10  may include any suitable piezoelectric material, such as a lithium niobate (LN) layer or a lithium tantalate (LT) layer. A thickness t 1  of the piezoelectric layer  10  can be selected based on a wavelength λ or L of a surface acoustic wave generated by the surface acoustic wave resonator  1  in certain applications. The IDT electrode  12  has a pitch that sets the wavelength λ or L of the surface acoustic wave resonator  1 . 
     The IDT electrode  12  can be an aluminum (Al) IDT electrode. The IDT electrode  12  has a thickness t 2 . In some embodiments, the thickness t 2  of the IDT electrode  12  can be about 0.05 L. For example, when the wavelength L is 4 μm, the thickness t 2  can be 200 nm. 
     The compound layer  14 ′ is formed when the epoxy resin film  14  is heated and/or the resist film  16  is heated. Carbon included in the resist film  16  can react with a material (e.g., aluminum) of the IDT electrode  12  when heated, forming a compound that includes the material (e.g., aluminum) and carbon. Due to this reaction, relative heights of an upper surface  14   a ′ of the compound layer  14 ′ in  FIG. 1B  and an upper surface  12   a  of the IDT electrode in  FIG. 1A  can be approximately the same. The compound layer  14 ′ has a thickness t 3 . The thickness t 3  may vary along its width. The thickness t 3  of the compound layer  14 ′ may depend at least on a thickness of the epoxy resin layer  14  and/or a duration of the heat processing. The thickness t 3  of the compound layer  14 ′ can be, for example, in a range from 10 nm to 20 nm. The thickness t 3  of the compound layer  14 ′ can be, for example, in a range from 10% to 15% of thickness t 2  of the IDT electrode  12 . 
     A final thickness t 2 ′ of the IDT electrode  12  may be different from the original IDT electrode thickness t 2 . For example, the final thickness t 2 ′ of the IDT electrode  12  can be approximately the thickness t 2  of the original thickness minus the thickness t 3  of the compound layer  14 ′. In certain embodiments, the final thickness t 2 ′ can be about 180 nm. However, the IDT electrode  12  may be designed to have a thicker original thickness t 2  such that the final thickness t 2 ′ after the formation of the compound layer  14 ′ can be about 200 nm or about 0.05 L. 
     The temperature compensation layer  18  can include any suitable material. For example, the temperature compensation layer  18  can be a silicon dioxide (SiO 2 ) layer. The temperature compensation layer  18  can bring the temperature coefficient of frequency (TCF) of the SAW resonator  1  closer to zero relative to a similar SAW resonator without the temperature compensation layer  18 . The temperature compensation layer  18  has a thickness t 4 . 
       FIG. 2A  illustrates a cross section of a surface acoustic wave resonator structure at a stage of a manufacturing process according to an embodiment. The manufacturing process can include a photolithography process. The illustrated SAW resonator structure of  FIG. 2A  includes a piezoelectric layer  10 , an interdigital transducer (IDT) electrode  12  over the piezoelectric layer  10 , an anti-reflection layer  20  over the IDT electrode  12 , and a resist film  16  over the anti-reflection layer  20 . The resist film  16  can be removed at a later stage in the manufacturing process. For example, the manufacturing process can include: (1) depositing an IDT electrode material layer on the piezoelectric layer  10 ; (2) forming the anti-reflection layer  20  on the IDT electrode material layer; (3) coating the resist film  16  on the anti-reflection layer  20 ; (4) patterning the resist film  16 ; (5) etching the IDT electrode material layer to form the IDT electrode  12 ; and (6) removing the resist film  16 . 
     The anti-reflection layer  20  can include silicon. For example, the anti-reflection layer  20  can be silicon (Si), silicon oxynitride (SiON), amorphous silicon (a-Si), silicon dioxide (SiO 2 ), or another suitable silicon compound. The anti-reflection layer  20  can be a material that is similar to silicon dioxide. In certain instances, the anti-reflection layer  20  can include a non-silicon material that sufficiently mitigates back reflection in a photolithography process and does not react (e.g., does not form a compound) with the IDT electrode  12 . In certain applications, the anti-reflection material can be any suitable material having a reflectivity of 0.3 or less for light having a wavelength of 365 nm. According to some such applications, the anti-reflection material can be any suitable material having a reflectivity of 0.2 or less for light having a wavelength of 365 nm. For example, the reflectivity can be in between 0.01 to 0.2, in some embodiments. In some embodiments, the anti-reflection layer  20  does not include carbon. 
       FIG. 2B  illustrates a cross section of a surface acoustic wave resonator  2  formed using the surface acoustic wave resonator structure illustrated in  FIG. 2A  according to an embodiment. The SAW resonator  2  and other SAW resonators with a similar temperature compensation layer can be referred to as a temperature compensated SAW (TC-SAW) resonator. 
     The illustrated SAW resonator  2  includes the piezoelectric layer  10 , the IDT electrode  12  over the piezoelectric layer  10 , the anti-reflection layer  20  over the IDT electrode  12 , and a temperature compensation layer  18  over the anti-reflection layer  20 . The SAW resonator  2  illustrated in  FIG. 2B  includes some generally similar features to the SAW resonator  1  illustrated in  FIG. 1B . However, unlike the SAW resonator  1 , the SAW resonator  2  does not include the compound layer  14 ′ and includes the anti-reflection layer  20 . Unlike the anti-reflection epoxy resin film  14  of  FIG. 1A , the anti-reflection layer  20  does not react with the IDT electrode  12 . Accordingly, the anti-reflection layer  20  is distinct from the material of the IDT electrode  12 . The anti-reflection layer  20  is free from material of the IDT electrode  12 . In some embodiments, the chemical properties of the anti-reflection layer  20  can be the same in  FIGS. 2A and 2B . 
     An upper surface  20   a  of the anti-reflection layer  20  opposite the IDT electrode  12  can be relatively flat in the surface acoustic wave device  2 . A surface roughness of the upper surface  20   a  of the anti-reflection layer  20  can be about 3.5 nm. In some embodiments, the roughness of the upper surface  20   a  can be in a range from, for example, 3 nm to 4 nm. In some embodiments, the roughness of the upper surface  20   a  can be less than, for example, 4.5 nm. The smoother and/or flatter surface of upper surface  20   a  of the anti-reflection layer  20  opposite the IDT electrode  12  relative to the upper surface  14   a ′ of the anti-reflection layer  14 ′ of  FIG. 1B  can result in less variation in resistance and less electrical degradation in a filter. 
     The piezoelectric layer  10  may include any suitable piezoelectric material, such as a lithium niobate (LN) layer or a lithium tantalate (LT) layer. A thickness t 1  of the piezoelectric layer  10  can be selected based on a wavelength λ or L of a surface acoustic wave generated by the surface acoustic wave resonator  2  in certain applications. The IDT electrode  12  has a pitch that sets the wavelength λ or L of a surface acoustic wave generated by the surface acoustic wave device  2 . The piezoelectric layer  10  can be sufficiently thick to avoid significant frequency variation. 
     The IDT electrode  12  can be an aluminum (Al) IDT electrode. The IDT electrode  12  may include any other suitable IDT material. For example, the IDT electrode  12  may include copper (Cu), magnesium (Mg), titanium (Ti), etc. The IDT electrode  12  may include alloys, such as AlMgCu, AlCu, etc. The IDT electrode  12  can include a conductive layer that has a reflectivity of at least 0.3 for light having a wavelength of 365 nanometers. The IDT electrode  12  can include a conductive layer that has a reflectivity of at least 0.5 for light having a wavelength of 365 nanometers. The IDT electrode  12  can include a conductive layer that has a reflectivity of at least 0.75 for light having a wavelength of 365 nanometers. As shown in  FIG. 7 , the IDT electrode can be a multi-layer IDT in certain embodiments. 
     The IDT electrode  12  has a thickness t 2 . In some embodiments, the thickness t 2  of the IDT electrode  12  can be about 0.05 L. For example, when the wavelength L is 4 μm, the thickness t 2  can be 200 nm. Unlike the embodiment illustrated in  FIG. 1B , the original thickness and the final thickness of the IDT electrode  12  can be the same or very similar in the embodiment in  FIGS. 2A and 2B . The thickness t 5  of the anti-reflection layer  20  can be in a range from, for example, 0.004 L to 0.06 L or 8 nm to 240 nm. The thickness t 2  of the IDT electrode  12  can be about 0.05 L. For example, when the wavelength L is 4 μm, the thickness t 2  can be 200 nm. 
     The anti-reflection layer  20  can have a thickness t 5 . The thickness t 5  can vary for different materials used for the anti-reflection layer  20 . Also, the determination of the thickness t 5  can be based at least in part on reflectivity of the anti-reflection layer  20  and/or line widths, for instance, as explained below with respect to  FIGS. 4A to 6 . For example, when the anti-reflection layer  20  is an amorphous silicon layer, the thickness t 5  can be about 9 nm (e.g., 0.00225 L when the wavelength L is 4 μm), which can give a reflectivity of 0.07 in some embodiments. For example, when the anti-reflection layer  20  is a silicon oxynitride layer, the thickness t 5  can be about 110 nm, which can give a reflectivity of 0.17 in some embodiments. 
     The temperature compensation layer  18  can include any suitable material. For example, the temperature compensation layer  18  can be a silicon dioxide (SiO 2 ) layer. The temperature compensation layer  18  can be a layer of any other suitable material having a positive temperature coefficient of frequency. For instance, the temperature compensation layer  18  can be a tellurium dioxide (TeO 2 ) layer or a silicon oxyfluoride (SiOF) layer in certain applications. A temperature compensation layer can include any suitable combination of SiO 2 , TeO 2 , and/or SiOF. 
     The temperature compensation layer  18  can bring the temperature coefficient of frequency (TCF) of the SAW resonator  2  closer to zero relative to a similar SAW resonator without the temperature compensation layer  18 . The temperature compensation layer  18  together with a lithium niobate piezoelectric layer can improve the electromechanical coupling coefficient (k 2 ) of the SAW resonator  2  relative to a similar SAW resonator with a lithium tantalate piezoelectric layer and without the temperature compensation layer  18 . Improved k 2  of the temperature compensation layer  18  can be more pronounced when the SAW resonator  2  includes a lithium niobate layer as the piezoelectric layer  10 . In certain embodiments, for example, as illustrated in  FIGS. 8B and 8C , the temperature compensation layer  18  may be omitted. 
     The temperature compensation layer  18  has a thickness t 4 . In some embodiments, the thickness t 4  of the temperature compensation layer  18  can be in a range from 0.1 L to 0.5 L. For example, when the wavelength L is 4 μm, the thickness t 4  of the temperature compensation layer  14  can be 1200 nm. 
       FIG. 3A  is a graph of a reference wiring resistance measurement and a wiring resistance measurement of the SAW resonator  1  illustrated in  FIG. 1B . A wiring resistance can be measured using a resistance wire test. A wiring resistance can also be referred to as an IDT resistance or electrode resistance. The reference wiring resistance can be a wiring resistance of a SAW resonator that does not include an anti-reflective material over an IDT electrode. The wiring resistance of the SAW resonator  1  is about 1.09 (e.g., 9% increase from the reference wiring resistance). This can result from the compound layer  14 ′ degrading the performance of the SAW resonator  1  as compared to the reference SAW resonator that does not include the anti-reflective material. 
       FIG. 3B  is a graph of a reference wiring resistance measurement and a wiring resistance measurement of the SAW resonator  2  illustrated in  FIG. 2B . The wiring resistance of the SAW resonator  2  is substantially the same or very similar to the reference wiring resistance. In other words, the anti-reflection layer  20  does not noticeably degrade the wiring resistance of the SAW resonator  2  as compared to the reference SAW resonator. Therefore, the SAW resonator  2  illustrated in  FIG. 2B  may be a more desirable than the SAW resonator  1  illustrated in  FIG. 1B  in certain applications. The anti-reflection film  20  of the surface acoustic wave resonator  2  of  FIG. 2B  can contribute less than 2% of wiring resistance. 
       FIG. 4A  is a graph of ellipsometer measurement results of reflectivity of an epoxy resin layer, a silicon oxynitride (SiON) layer, and an amorphous silicon (a-Si) layer for various thicknesses at a wavelength of 365 nm. These layers were deposited on a silicon substrate and then reflectivity was measured. The graph indicates that the thickness of these anti-reflection layers impacts reflectivity. A reflectivity of 1 can mean that 100% of light emitted from a light source is reflected back. A reflectivity of 0 can mean that 0% of the light emitted from the light source is reflected. A first measurement result  30  is a result of reflectivity of the epoxy resin layer. A second measurement result  32  is a result of the SiON layer. A third measurement result  34  is a result of the a-Si layer. The first result  30  shows that the reflectivity is between about 0.1 and about 0.15 for thicknesses of the epoxy resin layer larger than about 50 nm. 
       FIG. 4B  is a table with the lowest reflectivity values of the second and third results  32  and  34 , respectively, of  FIG. 4A . The second result  32  indicates that the lowest reflectivity can be obtained when the SiON layer has a thickness of about 110 nm. The third result  34  indicates that the lowest reflectivity can be obtained when the a-Si layer has a thickness of about 9 nm. The reflectivity of the anti-reflection layer can depend on a combination of a material of the anti-reflection layer and a thickness of the anti-reflection layer. The thickness of the anti-reflection layer can be selected to achieve a reflectivity that is no greater than a threshold value. For instance, the thickness of the anti-reflection layer can be selected such that the reflectivity is 0.2 or less for a given material of the anti-reflection layer.  FIG. 4A  indicates that a reflectivity of less than about 0.2 can be obtained with an amorphous silicon anti-reflection layer with a thickness in a range from about 5 nm to about 15 nm.  FIG. 4A  indicates that a reflectivity of less than about 0.2 can be obtained with an silicon oxynitride anti-reflection layer with a thickness in a range from about 105 nm to about 115 nm. 
       FIG. 5A  is a graph of measurement results of line widths for different resist thicknesses of a resist film of a SAW resonator structure used in a lithography process. The SAW resonator structure used in the simulation of  FIG. 5A  does not include an anti-reflection layer between its IDT electrode and the resist film. A line width range r 1  from a bottom side to a top side of the measurement curve can be observed from this graph. The line width range r 1  of the measurement results of  FIG. 5A  is about 0.15 nm. 
       FIG. 5B  is a graph of measurement results of line widths for different resist thicknesses of a resist film of a SAW resonator structure used in a lithography process. The SAW resonator structure used in the measurement of  FIG. 5B  includes an epoxy resin layer between its IDT electrode and the resist film. A line width range r 2  from a bottom side to a top side of the measurement curve can be observed from this graph. The line width range r 2  of the measurement results of  FIG. 5B  is about 0.05 nm. 
       FIG. 5C  is a graph of measurement results of line width values for different resist thicknesses of a resist film of a SAW resonator structure according to an embodiment used in a lithography process. The SAW resonator structure used in the measurement of  FIG. 5C  includes an amorphous silicon (a-Si) layer between its IDT electrode and the resist film. A line width range r 3  from a bottom side to a top side of the measurement curve can be observed from this graph. The line width range r 3  of the measurement results of  FIG. 5C  is about 0.05 nm. 
       FIG. 5D  is a graph of measurement results of line width values for different resist thicknesses of a resist film of a SAW resonator structure according to an embodiment used in a lithography process. The SAW resonator structure used in the measurement of  FIG. 5D  includes a silicon oxynitride (SiON) layer between its IDT electrode and the resist film. A line width range r 4  from a bottom side to a top side of the measurement curve can be observed from this graph. The line width range r 4  of the measurement results of  FIG. 5D  is about 0.1 nm. 
       FIG. 6  is a graph of fit curves (also referred to as swing curves) of data points at the bottom sides of the measurement results curves illustrated in  FIGS. 5A-5D . The graph shows normalized line width in nanometer on y-axis and normalized resist thickness in nanometer on x-axis. These results may be used in determining the thickness t 5  of the anti-reflection layer  20  of  FIGS. 2A and 2B  that meets a desired specification. 
     For example, a specification for a SAW resonator may specify a resist thickness variation to be within 1% (e.g., +/−1% or a total variation of 2%), a frequency shift to be below 1 megahertz (MHz) at a frequency of 2 gigahertz (GHz), and a frequency shift sensitivity to be 0.85 MHz/nm. This specification can be for a Band  25  filter. In such specification, at a frequency (f) of 2 GHz and velocity (V) of 4000 m/s, line width can be calculated to be 0.5 μm. Also, to satisfy such specification, the line width distribution should be lower than about 1.18 nm (1 MHz frequency shift/0.85 MHz/nm frequency shift sensitivity), which is about 0.236% of the line width. Accordingly, with a line width distribution of 0.2% or less, stringent SAW resonator specifications can be met. 
       FIG. 7  illustrates a cross section of a surface acoustic wave resonator  3  according to an embodiment. The illustrated SAW resonator  3  includes a piezoelectric layer  10 , an interdigital transducer (IDT) electrode  12 ′ over the piezoelectric layer  10 , an anti-reflection layer  20  over the IDT electrode  12 ′, and a temperature compensation layer  18  over the anti-reflection layer  20 . The SAW resonator  3  illustrated in  FIG. 7  is generally similar to the SAW resonator  2  illustrated in  FIG. 2B . However, unlike the SAW resonator  2 , the IDT electrode  12 ′ of the SAW resonator  3  is a multi-layer IDT electrode (e.g., includes two layers). As illustrated, the IDT electrode  12 ′ includes an upper layer  24  and a lower layer  22  positioned between the upper layer  24  and the piezoelectric layer  10 . The upper layer  24  can be an aluminum layer. The lower layer  22  can be a molybdenum layer, a tungsten layer, a gold layer, a tantalum layer, a platinum layer, a silver layer, or a ruthenium layer, for example. SAW resonators can include a multi-layer IDT electrode that includes three or more layers in some other embodiments. Any suitable principles and advantages disclosed herein can be applied to single layer IDT electrodes or multi-layer IDT electrodes that include two or more IDT layers. 
       FIG. 8A  illustrates a cross section of a surface acoustic wave resonator  4  according to an embodiment. The illustrated SAW resonator  4  includes a support layer  26 , a piezoelectric layer  10  over the support layer  26 , an IDT electrode  12  over the piezoelectric layer  10 , an anti-reflection layer  20  over the IDT electrode  12 , and a temperature compensation layer  18  over the anti-reflection layer  20 .  FIG. 8A  illustrates that the anti-reflection layers disclosed herein can be implemented in acoustic wave resonators that include multi-layer piezoelectric substrates. The SAW resonator  4  illustrated in  FIG. 8A  is generally similar to the SAW resonator  2  illustrated in  FIG. 2B . However, unlike the SAW resonator  2 , the SAW resonator  4  includes the support layer  26 . By including the support layer  26 , higher order spurious modes can be suppressed. In some embodiments, the support layer  26  can have a relatively high acoustic impedance. An acoustic impedance of the support layer  26  can be higher that ac acoustic impedance of the piezoelectric layer  10 . The support layer  26  can be a silicon layer, a spinel layer, a magnesium oxide spinel layer, a quartz layer, a ceramic layer, a glass layer, a sapphire layer, a silicon nitride layer, an aluminum nitride layer, a diamond layer such as synthetic diamond layer, or the like. In some other embodiments (not illustrated), one or more additional layer can be included between the substrate layer and the piezoelectric layer. The one or more additional layers can include a silicon dioxide layer or a silicon nitride layer, for example. 
       FIG. 8B  illustrates a cross section of a surface acoustic wave resonator  5  according to an embodiment. The illustrated SAW resonator  5  includes a piezoelectric layer  10 , an IDT electrode  12  over the piezoelectric layer  10 , and an anti-reflection layer  20  over the IDT electrode  12 . The surface acoustic wave resonator  5  is like the surface acoustic wave resonator  2  of  FIG. 2B , except that the SAW resonator  5  does not include the temperature compensation layer  18 . In certain embodiments, a lithium tantalate layer may be a more suitable piezoelectric material than the lithium niobate layer when there is no temperature compensation layer present in the SAW resonator. A SAW resonator without a temperature compensation layer over an IDT electrode can include a multi-layer IDT electrode in certain instances. Alternatively or additionally, a SAW resonator without a temperature compensation layer over the IDT electrode can include a multi-layer piezoelectric substrate. 
       FIG. 8C  illustrates another cross section of the surface acoustic wave resonator  5  illustrated in  FIG. 8B . The illustrated SAW resonator  5  includes the piezoelectric layer  10 , the IDT electrode  12  over the piezoelectric layer  10 , the anti-reflection layer  20  over the IDT electrode  12 . The IDT electrode  12  includes a first IDT electrode finger  12   x  extending from a first bus bar (not shown) and a second IDT finger  12   y  extending from a second bus bar (not shown). The first IDT electrode finger  12   x  and the second IDT electrode finger  12   y  are spaced apart from each other by a gap  36 . The gap  36  can be free from the anti-reflection layer  20 . The portion of the piezoelectric layer  10  under the gap  36  is free from the anti-reflection layer  20 . 
     In some embodiments, the anti-reflection layer  20  can be patterned such that the anti-reflection layer  20  substantially covers an upper surface of IDT fingers of the IDT electrode  12 . A width W 1  of the anti-reflection layer  20  over IDT electrode finger  12   x  and a width W 2  of the IDT electrode finger  12   x  can be generally similar. In some embodiments the width W 1  of the anti-reflection layer  20  over the IDT electrode finger  12   x  can be the same as or shorter than the width W 2  of the IDT electrode finger  12   x . In some embodiments, a side wall  12   b  of the IDT electrode finger  12   x  that extends from a lower surface of the IDT electrode finger  12   x  to the upper surface of the IDT electrode finger  12   x , can be perpendicular with an upper surface of the piezoelectric layer  10 , or tapered. The side wall  12   b  of the IDT electrode finger  12   x  can be free from the anti-reflection layer  20 . The anti-reflection layer  20  can have a footprint that corresponds to a footprint of IDT electrode fingers of the IDT electrode  12  in the acoustically active part of the SAW resonator  5 . The SAW resonator  5  and/or any other SAW resonators disclosed herein can include part of the anti-reflection layer  20  over a bus bar of the IDT electrode  12 . In some other embodiments, a bus bar can be free from the anti-reflection layer  20 . In some other embodiments, a bus bar can partly covered by the anti-reflection layer  20  and partly free from the anti-reflection layer  20 . 
       FIG. 9A  illustrates a cross section of a Lamb wave device  7  according to an embodiment. The Lamb wave device  7  can be a Lamb wave resonator. The Lamb wave device  7  includes a piezoelectric layer  10 , an IDT electrode  12  over the piezoelectric layer  10 , an anti-reflection layer  20  over the IDT electrode  12 , and a temperature compensation layer  18  over the piezoelectric layer  10 . The Lamb wave device  7  also includes a substrate  35 , and an air cavity  37  between the piezoelectric layer  10  and the substrate  35 . The substrate  35  can include any suitable material. For example, the substrate  35  can be a semiconductor substrate, such as a silicon substrate. As illustrated, the Lamb wave device  7  includes part of the anti-reflection layer  20  over a bus bar of the IDT electrode  12 . In some other embodiments (not illustrated), a bus bar can be free from the anti-reflection layer. In some other embodiments (not illustrated), a bus bar can partly covered by the anti-reflection layer and partly free from the anti-reflection layer. 
       FIG. 9B  illustrates a cross section of a Lamb wave device  8  according to another embodiment. The Lamb wave device  8  can be a Lamb wave resonator. The Lamb wave device  8  is like the Lamb wave device  7  of  FIG. 9A  except that the Lamb wave device  8  includes a solid acoustic mirror  29  and a substrate  41  in place of the substrate  35  and the cavity  37 . The solid acoustic mirror  29  can include acoustic Bragg reflectors. For instance, the solid acoustic mirror  29  can include alternating layers of a low impedance layer  29   a  and a high impedance layer  29   b . As one example, the low impedance layer  29   a  can be a silicon dioxide layer and the high impedance layer  29   b  can be a tungsten layer. As another example, the low impedance layer  29   a  can be a silicon dioxide layer and the high impedance layer  29   b  can be a molybdenum layer. The substrate  41  can include any suitable material. For example, the substrate  41  can be a semiconductor substrate, such as a silicon substrate. 
     A method of manufacturing an acoustic wave device according to an embodiment will now be described. The method can include providing a piezoelectric layer and forming (e.g., depositing) an interdigital transducer electrode material over the piezoelectric layer. The interdigital transducer electrode material can include aluminum. The method can include forming (e.g., depositing) an anti-reflection layer over the interdigital transducer electrode material. The anti-reflection material can remain distinct from the interdigital transducer material after a heating process. The anti-reflection material can reduce reflections from the interdigital transducer material during photolithography. The method can include forming (e.g., depositing) a resist film over the anti-reflection layer. The resist film can be patterned, for example, by a stepper. The method can include patterning (e.g., etching) the interdigital transducer electrode material to form an interdigital transducer electrode. The method can include removing the resist film. The method can include forming (e.g., depositing) a temperature compensation layer over at least a portion of the piezoelectric layer, the interdigital transducer electrode, and/or the anti-reflection layer. 
     A SAW device including any suitable combination of features disclosed herein be included in a filter arranged to filter a radio frequency signal in a fifth generation (5G) New Radio (NR) operating band within Frequency Range 1 (FR1). A filter arranged to filter a radio frequency signal in a 5G NR operating band can include one or more SAW devices disclosed herein. FR1 can be from 410 MHz to 7.125 GHz, for example, as specified in a current 5G NR specification. One or more SAW devices in accordance with any suitable principles and advantages disclosed herein can be included in a filter arranged to filter a radio frequency signal in a 4G LTE operating band and/or in a filter having a passband that includes a fourth generation (4G) Long Term Evolution (LTE) operating band and a 5G NR operating band. 
     Acoustic wave devices disclosed herein can be implemented in a standalone filter. Acoustic wave devices disclosed herein can be implemented in one or more filters of multiplexer (e.g., a duplexer) with fixed multiplexing. Acoustic wave devices disclosed herein can be implemented in one or more filters of multiplexer with switched multiplexing. Acoustic wave devices disclosed herein can be implemented in one or more filters of a multiplexer with a combination of fixed multiplexing and switched multiplexing. 
       FIG. 10A  is a schematic diagram of an example transmit filter  45  that includes surface acoustic wave resonators of a surface acoustic wave component according to an embodiment. The transmit filter  45  can be a band pass filter. The illustrated transmit filter  45  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. The transmit filter  45  includes series SAW resonators TS 1 , TS 2 , TS 3 , TS 4 , TS 5 , TS 6 , and TS 7 , shunt SAW resonators TP 1 , TP 2 , TP 3 , TP 4 , and TP 5 , series input inductor L 1 , and shunt inductor L 2 . Some or all of the SAW resonators TS 1 , TS 2 , TS 3 , TS 4 , TS 5 , TS 6 , and TS 7  and/or TP 1 , TP 2 , TP 3 , TP 4 , and TP 5  can be a SAW resonators with an anti-reflection layer in accordance with any suitable principles and advantages disclosed herein. For instance, one or more of the SAW resonators of the transmit filter  45  can be a surface acoustic wave resonator  2  of  FIG. 2B . Alternatively or additionally, one or more of the SAW resonators of the transmit filter  45  can be any surface acoustic wave resonators disclosed herein (e.g., a surface acoustic wave resonator  3  of  FIG. 7 , a surface acoustic wave resonator  4  of  FIG. 8A , or a surface acoustic wave resonator  5  of  FIGS. 8B and 8C ). Any suitable number of series SAW resonators and shunt SAW resonators can be included in a transmit filter  45 . 
       FIG. 10B  is a schematic diagram of a receive filter  50  that includes surface acoustic wave resonators of a surface acoustic wave component according to an embodiment. The receive filter  50  can be a band pass filter. The illustrated receive filter  50  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. The receive filter  50  includes series SAW resonators RS 1 , RS 2 , RS 3 , RS 4 , RS 5 , RS 6 , RS 7 , and RS 7 , shunt SAW resonators RP 1 , RP 2 , RP 3 , RP 4 , and RP 5 , and RP 6 , shunt inductor L 2 , and series output inductor L 3 . Some or all of the SAW resonators RS 1 , RS 2 , RS 3 , RS 4 , RS 5 , RS 6 , RS 7 , and RS 8  and/or RP 1 , RP 2 , RP 3 , RP 4 , RP 5 , and RP 6  can be SAW resonators with an anti-reflection layer in accordance with any suitable principles and advantages disclosed herein. For instance, one or more of the SAW resonators of the receive filter  50  can be a surface acoustic wave resonator  2  of  FIG. 2B . Alternatively or additionally, one or more of the SAW resonators of the receive filter  50  can be any surface acoustic wave resonator disclosed herein (e.g., a surface acoustic wave resonator  3  of  FIG. 7 , a surface acoustic wave resonator  4  of  FIG. 8A , or a surface acoustic wave resonator  5  of  FIGS. 8B and 8C ). Any suitable number of series SAW resonators and shunt SAW resonators can be included in a receive filter  50 . 
       FIG. 11  is a schematic diagram of a radio frequency module  75  that includes a surface acoustic wave component  76  according to an embodiment. The illustrated radio frequency module  75  includes the SAW component  76  and other circuitry  77 . The SAW component  76  can include one or more SAW resonators with any suitable combination of features of the SAW resonators and/or acoustic wave devices disclosed herein. The SAW component  76  can include a SAW die that includes SAW resonators. 
     The SAW component  76  shown in  FIG. 11  includes a filter  78  and terminals  79 A and  79 B. The filter  78  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. 2B  and/or any surface acoustic wave resonator disclosed herein. The filter  78  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  79 A and  78 B can serve, for example, as an input contact and an output contact. The SAW component  76  and the other circuitry  77  are on a common packaging substrate  80  in  FIG. 11 . The package substrate  80  can be a laminate substrate. The terminals  79 A and  79 B can be electrically connected to contacts  81 A and  81 B, respectively, on the packaging substrate  80  by way of electrical connectors  82 A and  82 B, respectively. The electrical connectors  82 A and  82 B can be bumps or wire bonds, for example. The other circuitry  77  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  75  can include one or more packaging structures to, for example, provide protection and/or facilitate easier handling of the radio frequency module  75 . Such a packaging structure can include an overmold structure formed over the packaging substrate  75 . The overmold structure can encapsulate some or all of the components of the radio frequency module  75 . 
       FIG. 12  is a schematic diagram of a radio frequency module  84  that includes a surface acoustic wave component according to an embodiment. As illustrated, the radio frequency module  84  includes duplexers  85 A to  85 N that include respective transmit filters  86 A 1  to  86 N 1  and respective receive filters  86 A 2  to  86 N 2 , a power amplifier  87 , a select switch  88 , and an antenna switch  89 . The radio frequency module  84  can include a package that encloses the illustrated elements. The illustrated elements can be disposed on a common packaging substrate  80 . The packaging substrate can be a laminate substrate, for example. 
     The duplexers  85 A to  85 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  86 A 1  to  86 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  86 A 2  to  86 N 2  can include one or more SAW resonators in accordance with any suitable principles and advantages disclosed herein. Although  FIG. 12  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  87  can amplify a radio frequency signal. The illustrated switch  88  is a multi-throw radio frequency switch. The switch  88  can electrically couple an output of the power amplifier  87  to a selected transmit filter of the transmit filters  86 A 1  to  86 N 1 . In some instances, the switch  88  can electrically connect the output of the power amplifier  87  to more than one of the transmit filters  86 A 1  to  86 N 1 . The antenna switch  89  can selectively couple a signal from one or more of the duplexers  85 A to  85 N to an antenna port ANT. The duplexers  85 A to  85 N can be associated with different frequency bands and/or different modes of operation (e.g., different power modes, different signaling modes, etc.). 
       FIG. 13A  is a schematic block diagram of a module  90  that includes a power amplifier  92 , a radio frequency switch  93 , and duplexers  91 A to  91 N in accordance with one or more embodiments. The power amplifier  92  can amplify a radio frequency signal. The radio frequency switch  93  can be a multi-throw radio frequency switch. The radio frequency switch  93  can electrically couple an output of the power amplifier  92  to a selected transmit filter of the duplexers  91 A to  91 N. One or more filters of the duplexers  91 A to  91 N can include any suitable number of surface acoustic wave resonators with an anti-reflection layer in accordance with any suitable principles and advantages discussed herein. Any suitable number of duplexers  91 A to  91 N can be implemented. 
       FIG. 13B  is a schematic block diagram of a module  90 ′ that includes filters  91 A′ to  91 N′, a radio frequency switch  93 ′, and a low noise amplifier  96  according to an embodiment. One or more filters of the filters  91 A′ to  91 N′ can include any suitable number of acoustic wave resonators in accordance with any suitable principles and advantages disclosed herein. Any suitable number of filters  91 A′ to  91 N′ can be implemented. The illustrated filters  91 A′ to  91 N′ are receive filters. In some embodiments (not illustrated), one or more of the filters  91 A′ to  91 N′ can be included in a multiplexer that also includes a transmit filter. The radio frequency switch  93 ′ can be a multi-throw radio frequency switch. The radio frequency switch  93 ′ can electrically couple an output of a selected filter of filters  91 A′ to  91 N′ to the low noise amplifier  96 . In some embodiments (not illustrated), a plurality of low noise amplifiers can be implemented. The module  90 ′ can include diversity receive features in certain applications. 
       FIG. 14  is a schematic block diagram of a module  95  that includes duplexers  91 A to  91 N and an antenna switch  94 . One or more filters of the duplexers  91 A to  91 N can include any suitable number of surface acoustic wave resonators with an anti-reflection layer in accordance with any suitable principles and advantages discussed herein. Any suitable number of duplexers  91 A to  91 N can be implemented. The antenna switch  94  can have a number of throws corresponding to the number of duplexers  91 A to  91 N. The antenna switch  94  can electrically couple a selected duplexer to an antenna port of the module  95 . 
       FIG. 15A  is a schematic diagram of a wireless communication device  100  that includes filters  103  in a radio frequency front end  102  according to an embodiment. The filters  103  can include one or more SAW resonators in accordance with any suitable principles and advantages discussed herein. The wireless communication device  100  can be any suitable wireless communication device. For instance, a wireless communication device  100  can be a mobile phone, such as a smart phone. As illustrated, the wireless communication device  100  includes an antenna  101 , an RF front end  102 , a transceiver  104 , a processor  105 , a memory  105 , and a user interface  107 . The antenna  101  can transmit RF signals provided by the RF front end  102 . Such RF signals can include carrier aggregation signals. Although not illustrated, the wireless communication device  90  can include a microphone and a speaker in certain applications. 
     The RF front end  102  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  102  can transmit and receive RF signals associated with any suitable communication standards. The filters  103  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  104  can provide RF signals to the RF front end  102  for amplification and/or other processing. The transceiver  104  can also process an RF signal provided by a low noise amplifier of the RF front end  102 . The transceiver  104  is in communication with the processor  105 . The processor  105  can be a baseband processor. The processor  105  can provide any suitable base band processing functions for the wireless communication device  100 . The memory  106  can be accessed by the processor  105 . The memory  106  can store any suitable data for the wireless communication device  100 . The user interface  107  can be any suitable user interface, such as a display with touch screen capabilities. 
       FIG. 15B  is a schematic diagram of a wireless communication device  110  that includes filters  103  in a radio frequency front end  102  and second filters  113  in a diversity receive module  112 . The wireless communication device  110  is like the wireless communication device  100  of  FIG. 15A , except that the wireless communication device  120  also includes diversity receive features. As illustrated in  FIG. 15B , the wireless communication device  120  includes a diversity antenna  111 , a diversity module  112  configured to process signals received by the diversity antenna  111  and including filters  113 , and a transceiver  104  in communication with both the radio frequency front end  102  and the diversity receive module  112 . The filters  113  can include one or more SAW resonators that include any suitable combination of features discussed with reference to any embodiments discussed above. 
     Although embodiments disclosed herein relate to surface acoustic wave resonators, any suitable principles and advantages disclosed herein can be applied to other types of acoustic wave resonators and/or acoustic wave devices, such as Lamb wave resonators and/or boundary wave resonators. For example, any suitable combination of features of an anti-reflection layer over an IDT electrode disclosed herein can be applied to a Lamb wave resonator and/or a boundary wave resonator. 
     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 components 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.