Patent Publication Number: US-2023163746-A1

Title: Laterally excited bulk wave device with acoustic mirrors

Description:
INCORPORATION BY REFERENCE TO ANY PRIORITY APPLICATIONS 
     Any and all applications for which a foreign or domestic priority claim is identified in the Application Data Sheet as filed with the present application, including U.S. Provisional Patent Application No. 62/943,092, filed Dec. 3, 2019, titled “LATERALLY EXCITED BULK WAVE DEVICE WITH ACOUSTIC MIRRORS,” are hereby incorporated by reference under 37 CFR 1.57 in their entirety. 
    
    
     BACKGROUND 
     Technical Field 
     Embodiments of this disclosure relate to acoustic wave devices. 
     Description of Related Technology 
     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. In BAW resonators, acoustic waves propagate in a bulk of a piezoelectric layer. Example BAW resonators include film bulk acoustic wave resonators (FBARs) and solidly mounted resonators (SMRs). Certain acoustic resonators can include features of SAW resonators and features of BAW resonators. 
     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 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. As another example, four acoustic wave filters can be arranged as a quadplexer. 
     SUMMARY 
     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 embodiment, a laterally excited bulk acoustic wave device is disclosed. The laterally excited bulk acoustic wave device can include a first solid acoustic mirror, a second solid acoustic mirror, a piezoelectric layer positioned between the first solid acoustic mirror and the second solid acoustic mirror, an interdigital transducer electrode on the piezoelectric layer, and a support substrate arranged to dissipate heat associated with the bulk acoustic wave. The interdigital transducer electrode is arranged to laterally excite a bulk acoustic wave. The first solid acoustic mirror and the second solid acoustic mirror are arranged to confine acoustic energy of the bulk acoustic wave. The first solid acoustic mirror is positioned on the support substrate. 
     In one embodiment, the laterally excited bulk acoustic wave device further includes a second substrate that is configured to dissipate heat associated with the bulk acoustic wave. The first solid acoustic mirror and the second solid acoustic mirror both can be positioned between the support substrate and the second substrate. 
     In one embodiment, the first solid acoustic mirror is arranged to confine acoustic energy such that the support substrate is free from acoustic energy during operation of the laterally excited bulk acoustic wave device. 
     In one embodiment, the first solid acoustic mirror is an acoustic Bragg reflector that includes alternating low impedance and high impedance layers. At least one of the low impedance layers and at least one of the high impedance layers can be free from acoustic energy during operation of the laterally excited bulk acoustic wave device. The high impedance layers can each have a thickness in a range from about 0.14λ p  to 0.30λ p  or from about 0.35λ p  to 0.45λ p , in which λ p  is a wave length of longitudinal wave velocity. 
     In one embodiment, the support substrate is a silicon substrate. 
     In one embodiment, the piezoelectric layer has a thickness in a range from 0.2 micrometers to 0.4 micrometers. 
     In one embodiment, the piezoelectric layer has a thickness in a range from 0.2 micrometers to 0.3 micrometers. 
     In one embodiment, the piezoelectric layer is an aluminum nitride layer. 
     In one embodiment, the piezoelectric layer is a lithium niobate layer. 
     In one embodiment, the piezoelectric layer is a lithium tantalate layer. 
     In one embodiment, the laterally exited bulk acoustic wave device has a resonant frequency in a range from 4.5 gigahertz to 10 gigahertz. 
     In one embodiment, the laterally exited bulk acoustic wave device has a resonant frequency in a range from 5 gigahertz to 10 gigahertz. 
     In one embodiment, the laterally exited bulk acoustic wave device has a resonant frequency in a range from 10 gigahertz to 25 gigahertz. 
     In one embodiment, the laterally exited bulk acoustic wave device has a resonant frequency in a range from 3 gigahertz to 5 gigahertz. 
     In one aspect, a laterally excited bulk acoustic wave device is disclosed. The laterally excited bulk acoustic wave device can include a piezoelectric layer and an interdigital transducer electrode on the piezoelectric layer. The interdigital transducer electrode is configured to laterally excite a bulk acoustic wave. The laterally excited bulk acoustic wave device can also include a pair of solid acoustic mirrors on opposing sides of the piezoelectric layer. The pair of solid acoustic mirrors are configured to confine acoustic energy of the bulk acoustic wave. The laterally excited bulk acoustic wave device can further include a support substrate. One solid acoustic mirror of the pair of solid acoustic mirrors is positions between the support substrate and the piezoelectric layer. 
     In one embodiment, the laterally excited bulk acoustic wave device further includes one or more suitable features disclosed herein. 
     In one aspect, a laterally excited bulk acoustic wave component is disclosed. The laterally excited bulk acoustic wave component can include a first substrate, a first solid acoustic mirror on the first substrate, a piezoelectric layer on the first solid acoustic mirror, and an interdigital transducer electrode on the piezoelectric layer. The interdigital transducer electrode that is arranged to laterally excite a bulk acoustic wave. The laterally excited bulk acoustic wave component can also include a second solid acoustic mirror on the piezoelectric layer and the interdigital transducer electrode. The first solid acoustic mirror and the second solid acoustic mirror are together arranged to confine acoustic energy of the bulk acoustic wave. The laterally excited bulk acoustic wave component can further include a second substrate on the second solid acoustic mirror. The first and second solid acoustic mirrors are positioned between the first and second substrates. The first and second substrates are arranged to dissipate heat associated with the bulk acoustic wave. 
     In one embodiment, the laterally excited bulk acoustic wave component further includes a conductive via extending through the second substrate. The conductive via can be electrically connected to a laterally excited bulk acoustic wave resonator that includes the interdigital transducer electrode. The laterally excited bulk acoustic wave component can further include an input/output contact that is electrically connected to the conductive via. 
     In one embodiment, the laterally excited bulk acoustic wave component further includes a third solid acoustic mirror on the second substrate, a second piezoelectric layer on the third solid acoustic mirror, and a second interdigital transducer electrode on the second piezoelectric layer. The laterally excited bulk acoustic wave component can further include an adhesion layer positioned between the second substrate and the third solid acoustic mirror. The laterally excited bulk acoustic wave component can further include a fourth solid acoustic mirror over the second piezoelectric layer. The laterally excited bulk acoustic wave component can further include a third substrate over the fourth solid acoustic mirror. The laterally excited bulk acoustic wave component can further include a third substrate over the second interdigital transducer electrode. 
     In one embodiment, the laterally excited bulk acoustic wave component further includes circuitry on the second substrate. The circuitry can include a transistor. The circuitry can include a passive impedance element. The circuitry can include an acoustic wave device. 
     In one embodiment, the second substrate is a silicon substrate. 
     In one embodiment, the laterally excited bulk acoustic wave component can further include one or more suitable features disclosed herein. 
     In one aspect, a stacked acoustic wave device assembly is disclosed. The stacked acoustic wave device assembly can include a first support substrate and a first laterally excited bulk acoustic wave stack on the first support substrate. The first laterally excited bulk acoustic wave stack includes a first piezoelectric layer, a first interdigital transducer electrode on the first piezoelectric layer, and a pair of solid acoustic mirrors on opposing sides of the first piezoelectric layer. The stacked acoustic wave device assembly can further include a second support substrate positioned on the first laterally excited bulk acoustic wave stack, and a second laterally excited bulk acoustic wave stack on the second support substrate. The second laterally excited bulk acoustic wave stack includes a second piezoelectric layer, a second interdigital transducer electrode on the second piezoelectric layer, and a solid acoustic mirror positioned between the second piezoelectric layer and the second support substrate. 
     In one embodiment, the solid acoustic mirror is included in a second pair of solid acoustic mirrors. The second pair of solid acoustic mirrors can be on opposing sides of the second piezoelectric layer. 
     In one embodiment, the stacked acoustic wave device assembly further includes a third substrate over the second laterally excited bulk acoustic wave stack. 
     In one embodiment, the stacked acoustic wave device assembly further include an adhesion layer positioned between the second support substrate and the solid acoustic mirror. 
     In one embodiment, the first laterally excited bulk acoustic wave stack and the second laterally excited bulk acoustic wave stack are included in a single acoustic wave filter arranged to filter a radio frequency signal. 
     In one embodiment, the first laterally excited bulk acoustic wave stack and the second laterally excited bulk acoustic wave stack are included in different acoustic wave filters. The different acoustic wave filters can be included in a multiplexer. 
     In one embodiment, the first piezoelectric layer has a thickness in a range from 0.2 micrometers to 0.4 micrometers. 
     In one embodiment, the first piezoelectric layer has a thickness in a range from 0.2 micrometers to 0.3 micrometers. 
     In one embodiment, the laterally exited bulk acoustic wave stack is included in a resonator having a resonant frequency in a range from 4.5 gigahertz to 10 gigahertz. 
     In one embodiment, the laterally exited bulk acoustic wave stack is included in a resonator having a resonant frequency in a range from 5 gigahertz to 10 gigahertz. The laterally exited bulk acoustic wave stack included in a resonator can have a resonant frequency in a range from 10 gigahertz to 25 gigahertz. 
     In one embodiment, the stacked acoustic wave device assembly further includes one or more suitable features disclosed herein. 
     In one aspect, an acoustic wave filter is disclosed. The acoustic wave filter can include a laterally excited bulk acoustic wave resonator that includes a first solid acoustic mirror on a first substrate, a piezoelectric layer on the first solid acoustic mirror, an interdigital transducer electrode on the piezoelectric layer, and a second solid acoustic mirror on the piezoelectric layer and the interdigital transducer electrode. The acoustic wave filter can also include a plurality of acoustic wave resonators. The laterally excited bulk acoustic wave resonator and the plurality of acoustic wave resonators are together configured to filter a radio frequency signal. 
     In one embodiment, the acoustic wave filter is a band pass filter. 
     In one embodiment, the plurality of acoustic wave resonators include a second laterally excited bulk acoustic wave resonator. The second laterally excited bulk acoustic wave resonator can include a third solid acoustic mirror on a second substrate, a second piezoelectric layer on the third solid acoustic mirror, and a second interdigital transducer electrode on the second piezoelectric layer. The second laterally excited bulk acoustic wave resonator can further include a fourth solid acoustic mirror on the second piezoelectric layer and the second interdigital transducer electrode. The second substrate can be positioned between the second solid acoustic mirror and the third solid acoustic mirror. An adhesion layer can be positioned between the second substrate and the third solid acoustic mirror. 
     In one embodiment, the laterally excited bulk acoustic wave resonator has a resonant frequency in a range from 4.5 gigahertz to 10 gigahertz. 
     In one embodiment, the laterally excited bulk acoustic wave resonator has a resonant frequency in a range from 5 gigahertz to 10 gigahertz. 
     In one embodiment, the laterally excited bulk acoustic wave resonator has a resonant frequency in a range from 10 gigahertz to 25 gigahertz. 
     In one embodiment, the piezoelectric layer has a thickness in a range from 0.2 micrometers to 0.4 micrometers. 
     In one embodiment, the piezoelectric layer has a thickness in a range from 0.2 micrometers to 0.3 micrometers. 
     In one embodiment, the acoustic wave filter further includes one or more suitable features disclosed herein. 
     In one aspect, a radio frequency module is disclosed. The radio frequency module can include any acoustic wave filter disclosed herein and a radio frequency circuit element that is coupled to the acoustic wave filter. The acoustic wave filter and the radio frequency circuit element can be enclosed within a common package. 
     In one embodiment, the radio frequency circuit element is a radio frequency amplifier arranged to amplify a radio frequency signal. The radio frequency amplifier can be a low noise amplifier. The radio frequency amplifier can be a power amplifier. The radio frequency module can further includes a switch that is configured to selectively couple a terminal of the acoustic wave filter to an antenna port of the radio frequency module. 
     In one embodiment, the radio frequency circuit element is a switch that is configured to selectively couple the acoustic wave filter to an antenna port of the radio frequency module. 
     In one aspect, a wireless communication device is disclosed. The wireless communication device can include an acoustic wave filter disclosed herein, an antenna that is operatively coupled to the acoustic wave filter, a radio frequency amplifier that is operatively coupled to the acoustic wave filter and configured to amplify a radio frequency signal, and a transceiver that is in communication with the radio frequency amplifier. 
     In one embodiment, the wireless communication device further includes a baseband processor that is in communication with the transceiver. 
     In one embodiment, the acoustic wave filter is included in a radio frequency front end. 
     In one embodiment, the acoustic wave filter is included in a diversity receive module. 
     In one aspect, a method of filtering a radio frequency signal is disclosed. The method can include receiving a radio frequency signal at a port of an acoustic wave filter disclosed herein, and filtering the radio frequency signal with the acoustic wave filter. 
    
    
     
       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 A  is cross sectional diagram of a laterally excited bulk acoustic wave device according to an embodiment. 
         FIG.  1 B  is a plan view of an interdigital transducer (IDT) electrode of the laterally excited bulk acoustic wave device of  FIG.  1 A . 
         FIG.  2 A  is a cross sectional diagram of a laterally excited bulk acoustic wave device with a solid acoustic mirror according to an embodiment. 
         FIG.  2 B  is a cross sectional view showing heat flow in the laterally excited bulk acoustic wave device of  FIG.  2 A . 
         FIG.  3    is a cross sectional diagram of a baseline laterally excited bulk acoustic wave device. 
         FIG.  4 A  is graph of admittance of the baseline laterally excited bulk acoustic wave device of  FIG.  3   . 
         FIG.  4 B  illustrates displacement at a resonant frequency for the baseline laterally excited bulk acoustic wave device of  FIG.  3   . 
         FIG.  4 C  illustrates displacement at an anti-resonant frequency for the baseline laterally excited bulk acoustic wave device of  FIG.  3   . 
         FIG.  5    is a cross sectional diagram of a laterally excited bulk acoustic wave device with a support substrate in contact with a piezoelectric layer. 
         FIG.  6 A  is graph of admittance of the laterally excited bulk acoustic wave device of  FIG.  5   . 
         FIG.  6 B  illustrates displacement at a resonant frequency for the laterally excited bulk acoustic wave device of  FIG.  5   . 
         FIG.  6 C  illustrates displacement at an anti-resonant frequency for the laterally excited bulk acoustic wave device of  FIG.  5   . 
         FIG.  7    is a cross sectional diagram of a laterally excited bulk acoustic wave device with a solid acoustic mirror according to an embodiment before design refinement. 
         FIG.  8 A  is graph of admittance of the laterally excited bulk acoustic wave device of  FIG.  7   . 
         FIG.  8 B  illustrates displacement at a resonant frequency for the laterally excited bulk acoustic wave device of  FIG.  7   . 
         FIG.  8 C  illustrates displacement at an anti-resonant frequency for the laterally excited bulk acoustic wave device of  FIG.  7   . 
         FIG.  9    is a cross sectional diagram of a laterally excited bulk acoustic wave device with a solid acoustic mirror according to an embodiment. 
         FIG.  10 A  is graph of admittance of the laterally excited bulk acoustic wave device of  FIG.  9   . 
         FIG.  10 B  illustrates displacement at a resonant frequency for the laterally excited bulk acoustic wave device of  FIG.  9   . 
         FIG.  10 C  illustrates displacement at an anti-resonant frequency for the laterally excited bulk acoustic wave device of  FIG.  9   . 
         FIG.  10 D  is a graph corresponding to different thicknesses of the piezoelectric layer for the laterally excited bulk acoustic wave device of  FIG.  9   . 
         FIG.  10 E  is a graph corresponding to different thicknesses of the interdigital transducer electrode for the laterally excited bulk acoustic wave device of  FIG.  9   . 
         FIG.  10 F  is a cross sectional diagram of a laterally excited bulk acoustic wave device with a solid acoustic mirror and silicon dioxide between interdigital transducer electrode fingers according to an embodiment. 
         FIG.  10 G  is a graph corresponding to different thicknesses of the interdigital transducer electrode for the laterally excited bulk acoustic wave device of  FIG.  10 F . 
         FIG.  11 A  is a cross sectional diagram of a laterally excited bulk acoustic wave device with a double solid acoustic mirror structure according to an embodiment. 
         FIG.  11 B  is a cross sectional view showing heat flow in the laterally excited bulk acoustic wave device of  FIG.  11 A . 
         FIG.  12 A  is graph of admittance of the laterally excited bulk acoustic wave device with a double solid acoustic mirror structure of  FIG.  11 A . 
         FIG.  12 B  illustrates displacement at a resonant frequency for the laterally excited bulk acoustic wave device with a double solid acoustic mirror structure of  FIG.  11 A . 
         FIG.  12 C  illustrates displacement at an anti-resonant frequency for the laterally excited bulk acoustic wave device with a double solid acoustic mirror structure of  FIG.  11 A . 
         FIG.  12 D  is a graph corresponding to different thicknesses of the piezoelectric layer for the laterally excited bulk acoustic wave device of  FIG.  11 A . 
         FIG.  12 E  is a graph corresponding to different thicknesses of the interdigital transducer electrode for the laterally excited bulk acoustic wave device of  FIG.  11 A . 
         FIG.  12 F  is a graph corresponding to different thicknesses of a low impedance layer of a solid acoustic mirror over the interdigital transducer electrode for the laterally excited bulk acoustic wave device of  FIG.  11 A . 
         FIG.  13    is a cross sectional diagram of an acoustic wave component with a laterally excited bulk acoustic wave device with a double solid acoustic mirror structure according to an embodiment. 
         FIG.  14    is a group comparing admittance of the laterally excited bulk acoustic wave devices of  FIGS.  2 A,  3 , and  11 A . 
         FIG.  15    illustrates a thermal simulation result of a laterally excited bulk acoustic wave device with a membrane structure. 
         FIG.  16    illustrates a thermal simulation result of a laterally excited bulk acoustic wave device with a single solid acoustic mirror structure according to an embodiment. 
         FIG.  17    illustrates a thermal simulation result of a laterally excited bulk acoustic wave device with a double solid acoustic mirror structure according to an embodiment. 
         FIG.  18    is a cross sectional diagram of a stacked laterally excited bulk acoustic wave device structure according to an embodiment. 
         FIG.  19    is a cross sectional diagram of a stacked laterally excited bulk acoustic wave device structure according to another embodiment. 
         FIG.  20    is a cross sectional diagram of a stacked device structure with a laterally excited bulk acoustic wave device structure stacked with other circuitry according to another embodiment. 
         FIG.  21    is a schematic diagram of a ladder filter that includes a laterally excited bulk acoustic wave resonator according to an embodiment. 
         FIG.  22    is a schematic diagram of a lattice filter that includes a laterally excited bulk acoustic wave resonator according to an embodiment. 
         FIG.  23    is a schematic diagram of a hybrid ladder lattice filter that includes a laterally excited bulk acoustic wave resonator according to an embodiment. 
         FIG.  24 A  is a schematic diagram of an acoustic wave filter. 
         FIG.  24 B  is a schematic diagram of a duplexer. 
         FIG.  24 C  is a schematic diagram of a multiplexer with hard multiplexing. 
         FIG.  24 D  is a schematic diagram of a multiplexer with switched multiplexing. 
         FIG.  24 E  is a schematic diagram of a multiplexer with a combination of hard multiplexing and switched multiplexing. 
         FIG.  25    is a schematic diagram of a radio frequency module that includes an acoustic wave filter according to an embodiment. 
         FIG.  26    is a schematic block diagram of a module that includes an antenna switch and duplexers according to an embodiment. 
         FIG.  27    is a schematic block diagram of a module that includes a power amplifier, a radio frequency switch, and duplexers according to an embodiment. 
         FIG.  28    is a schematic block diagram of a module that includes a low noise amplifier, a radio frequency switch, and filters according to an embodiment. 
         FIG.  29    is a schematic diagram of a radio frequency module that includes an acoustic wave filter according to an embodiment. 
         FIG.  30    is a schematic block diagram of a wireless communication device that includes a filter according to an embodiment. 
     
    
    
     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. 
     Laterally excited bulk acoustic wave resonators can be include in acoustic wave filters for high frequency bands, such as frequency bands above 3 gigahertz (GHz) and/or frequency bands above 5 GHz. Such frequency bands can include a fifth generation (5G) New Radio (NR) operating band. Certain laterally excited bulk acoustic wave resonators can include an interdigital transducer (IDT) electrode on a relatively thin piezoelectric layer. A bulk acoustic wave (BAW) mode excited by the IDT electrode is not strongly affected by the pitch of IDT electrode in certain applications. Accordingly, such a resonator to have a higher operating frequency than certain conventional surface acoustic wave (SAW) resonators. Certain laterally excited bulk acoustic wave resonators can be free standing. However, heat dissipation can be undesirable for such free standing laterally excited bulk acoustic wave resonators. Power durability and/or mechanical ruggedness of such laterally excited bulk acoustic wave resonators can be a technical concern. Free standing laterally excited bulk acoustic wave resonators with lithium niobate or lithium tantalate piezoelectric layers can encounter problems related to power durability in transmit filter applications. 
     Heat dissipation and mechanical ruggedness can be improved by bonding a piezoelectric layer to a support substrate with a relatively high thermal conductivity. By bonding the piezoelectric layer directly to the support substrate, resonant characteristics can be degraded by leakage into support substrate. 
     Aspects of this disclosure relate to a laterally excited bulk acoustic wave resonator with a solid acoustic mirror positioned between a piezoelectric layer and a support substrate. An IDT electrode can be positioned on the piezoelectric layer. The support substrate can have a relatively high thermal conductivity. For example, the support substrate can be a silicon support substrate. The solid acoustic mirror, which can be an acoustic Bragg reflector, can reduce and/or eliminate leakage into the support substrate. With such a structure, acoustic energy can be confined over the solid acoustic mirror effectively and heat can flow though the support substrate with the relatively high thermal conductivity. Mechanical ruggedness of such a laterally exited bulk acoustic wave resonator can be improved by avoiding an air cavity. At the same time, a relatively high frequency resonance can be achieved with desirable power durability. 
     Aspects of this disclosure relate to a laterally excited bulk acoustic wave resonator with a piezoelectric layer positioned between a double solid acoustic mirror structure on a support substrate. A second substrate can be positioned on an opposite side of the double solid acoustic mirror structure than the support substrate. An IDT electrode can be positioned on the piezoelectric layer. Such a laterally excited bulk acoustic wave resonator can achieve desirable heat dissipation and mechanical ruggedness. At the same time, the laterally excited bulk acoustic wave resonator can achieve a relatively high frequency resonance and desirable power durability. The package structure can also be less complex relative to a laterally excited bulk acoustic wave resonator with an air cavity. 
     A laterally excited bulk acoustic wave 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 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 laterally excited bulk acoustic wave device disclosed herein. FR1 can be from 410 MHz to 7.125 GHz, for example, as specified in a current 5G NR specification. 
     A laterally excited bulk acoustic wave device disclosed herein can be included in a filter arranged to filter a radio frequency signal having a frequency above FR1. For example, a laterally excited bulk acoustic wave device can be included in a filter arranged to filter radio frequency signals in a range from 10 GHz to 25 GHz. In applications where such high frequency signals are being transmitted, higher transmit powers can be used to account for higher loss in communication channels at higher frequencies. Accordingly, thermal dissipation at high frequencies of laterally excited bulk acoustic wave devices disclosed herein can be desirable. 
     In certain 5G applications, the thermal dissipation of the acoustic wave disclosed herein can be advantageous. For example, such thermal dissipation can be desirable in 5G applications with a higher time-division duplexing (TDD) duty cycle compared to fourth generation (4G) Long Term Evolution (LTE) applications. As another example, there can be more ganging of filters and carrier aggregation in 5G applications than 4G LTE applications. Accordingly, signals can have higher power to account for losses associated with such ganging of filters and/or carrier aggregation. Thermal dissipation of laterally excited bulk acoustic wave devices disclosed can be implemented in these example applications to improve performance of filters. 
     One or more laterally excited bulk acoustic wave 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 4G LTE operating band and a 5G NR operating band. 
       FIG.  1 A  is cross sectional diagram of a laterally excited bulk acoustic wave device  10  according to an embodiment. The laterally excited bulk acoustic wave device  10  can be a laterally excited bulk acoustic wave resonator included in a filter. The laterally excited bulk acoustic wave device  10  can be any other suitable laterally excited bulk acoustic wave device, such as a device in a delay line. The laterally excited bulk acoustic wave device  10  can be implemented in relatively high frequency acoustic wave filters. Such acoustic wave filters can filter radio frequency signals having a frequencies above 3 GHz and/over above 5 GHz. As illustrated, the laterally excited bulk acoustic wave device  10  includes a piezoelectric layer  12 , an IDT electrode  14 , a first solid acoustic mirror  15 , a second solid acoustic mirror  16 , a first substrate  17 , and a second substrate  18 . The solid acoustic mirrors  15  and  16  can confine acoustic energy in the piezoelectric layer  12 . The substrates  17  and  18  can function like heat sinks. The substrates  17  and  18  can provide thermal dissipation and improve power durability of the laterally excited bulk acoustic wave device  10 . 
     The piezoelectric layer  12  can be a lithium based piezoelectric layer. For example, the piezoelectric layer  12  can be a lithium niobate layer. As another example, the piezoelectric layer  12  can be a lithium tantalate layer. In certain applications, the piezoelectric layer  12  can be an aluminum nitride layer. The piezoelectric layer  12  can be any other suitable piezoelectric layer. 
     In certain surface acoustic wave resonators, there can be horizontal acoustic wave propagation. In such surface acoustic wave resonators, IDT electrode pitch can set the resonant frequency. Limitations of photolithography can set a lower bound on IDT electrode pitch and, consequently, resonant frequency of certain surface acoustic wave resonators. 
     The laterally excited bulk acoustic wave device  10  can generate a Lamb wave that is laterally excited. A resonant frequency of the laterally excited bulk acoustic wave device  10  can depend on a thickness H1 of the piezoelectric layer  12 . The thickness H1 of the piezoelectric layer  12  can be a dominant factor in determining the resonant frequency for the laterally excited bulk acoustic wave device  10 . The pitch of the IDT electrode  14  can be a second order factor in determining resonant frequency of the laterally excited bulk acoustic wave device  10 . A thickness of a low impedance layer, such as a silicon dioxide layer, directly over the piezoelectric layer  12  and the IDT electrode and/or directly under the piezoelectric layer  12  can have a secondary impact on the resonant frequency of the laterally excited bulk acoustic wave device  10 . The thickness of such a low impedance layer can be sufficient to adjust resonant frequency for a shunt resonator and a series resonator of a filter. 
     The resonant frequency of the laterally excited bulk acoustic wave device  10  can be approximated based on Equations 1 and/or 2. 
     
       
         
           
             
               
                 
                   v 
                   = 
                   
                     f 
                     * 
                     λ 
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                         
                     1 
                   
                   ) 
                 
               
             
           
         
       
       
         
           
             
               
                 
                   f 
                   = 
                   
                     v 
                     
                       2 
                       ⁢ 
                       λ 
                     
                   
                 
               
               
                 
                   ( 
                   
                     Equation 
                     ⁢ 
                         
                     2 
                   
                   ) 
                 
               
             
           
         
       
     
     In Equations 1 and 2, v can represent acoustic velocity in a piezoelectric material, f can represent resonant frequency, and λ can represent 2 times the thickness H1 of the piezoelectric layer  12 . Accordingly, a combination of the thickness H1 of the piezoelectric layer  12  and the acoustic velocity in the piezoelectric layer  12  can determine the approximate resonant frequency of the laterally excited bulk acoustic wave device  10 . The resonant frequency can be increased by making the piezoelectric layer  12  thinner and/or by using a piezoelectric layer  12  with a higher acoustic velocity. 
     The piezoelectric layer  12  can be manufactured with a thickness H1 that is 0.2 micrometers or higher from the fabrication point of view. In certain applications, the piezoelectric layer can have a thickness H1&gt;0.04 L from the electrical performance (K 2 ) point of view, in which L is IDT electrode pitch. 
     The laterally excited bulk acoustic wave device  10  with a 0.2 micrometer thick aluminum nitride piezoelectric layer  12  can have a resonant frequency of approximately 25 GHz based on Equations 1 and 2. Similarly, the laterally excited bulk acoustic wave device  10  with a 0.2 micrometer thick lithium niobate piezoelectric layer  12  can have a resonant frequency of approximately 10 GHz. The laterally excited bulk acoustic wave device  10  with a 0.4 micrometer thick lithium niobate piezoelectric layer  12  can have a resonant frequency of approximately 5 GHz. Based on the piezoelectric materials and thickness of the piezoelectric layer, the resonant frequency of the laterally excited bulk acoustic wave device  10  can be designed for filtering an RF signal having a particular frequency. 
     Odd harmonics for a laterally excited bulk acoustic wave resonator can have a k 2  that is sufficiently large for a ladder filter in certain applications. Such odd harmonics (e.g., a 3 rd  harmonic) can have a k 2  that is proportional to fundamental mode k 2 . A laterally excited bulk acoustic wave resonator using an odd harmonic can have a lithium niobate piezoelectric layer. 
     Filters that include one or more laterally excited bulk acoustic wave devices  10  can filter radio frequency signals up to about 10 GHz with a relatively wide bandwidth. Filters that include one or more laterally excited bulk acoustic wave devices  10  can filter radio frequency signals having a frequency in a range from 10 GHz to 25 GHz. In some instances, a filter that include one or more laterally excited bulk acoustic wave devices  10  can filter an RF signal having a frequency in a range from 3 GHz to 5 GHz, a range from 4.5 GHz to 10 GHz, a range from 5 GHz to 10 GHz, or a range from 10 GHz to 25 GHz. 
     In the laterally excited bulk acoustic wave device  10 , the IDT electrode  14  is over the piezoelectric layer  12 . As illustrated, the IDT electrode  14  has a first side in physical contact with the piezoelectric layer  12  and a second side in physical contact with a layer of the solid acoustic mirror  16 . The IDT electrode  14  can include aluminum (Al), molybdenum (Mo), tungsten (W), gold (Au), silver (Ag), copper (Cu), platinum (Pt), ruthenium (Ru), titanium (Ti), the like, or any suitable combination or alloy thereof. The IDT electrode  14  can be a multi-layer IDT electrode in some applications. 
     The first solid acoustic mirror  15  includes alternating low impedance layers  20 A and high impedance layers  22 A. Accordingly, the first solid acoustic mirror  15  is an acoustic Bragg reflector. The second solid acoustic mirror  16  includes alternating low impedance layers  20 B and high impedance layers  22 B. Accordingly, the second solid acoustic mirror  16  is an acoustic Bragg reflector. The low impedance layers  20 A and/or  20 B can be any suitable low impedance material such as silicon dioxide (SiO 2 ) or the like. The low impedance layers  20 A and  20 B can be the same material as each other in certain applications. The high impedance layers  22 A and/or  22 B can be any suitable high impedance material such as platinum (Pt), tungsten (W), iridium (Ir), aluminum nitride (AlN), molybdenum (Mo), or the like. The high impedance layers  22 A and  22 B can be the same material as each other in certain applications. 
     As illustrated, the layer of the first solid acoustic mirror  15  closest to the piezoelectric layer  12  is a low impedance layer  20 A. Having a low impedance layer  20 A closest to the piezoelectric layer  12  can increase an electromechanical coupling coefficient (k 2 ) of the laterally excited bulk acoustic wave device  10  and/or bring a temperature coefficient of frequency (TCF) of the laterally excited bulk acoustic wave device  10  closer to 0 in certain instances. 
     As illustrated, the layer of the first solid acoustic mirror  15  closest to the first substrate  17  is a high impedance layer  22 A. Having a high impedance layer  22 A closest to the first substrate  17  can increase reflection of the layer of the first solid acoustic mirror  15  closest to the first substrate  17 . Alternatively, a solid acoustic mirror (not illustrated) with a low impedance layer  20 A closest to the first substrate  17  can have a higher adhesion with the first substrate  17 . For example, when the first substrate  17  is a silicon substrate, the first substrate should have a higher adhesion with a solid acoustic mirror with a silicon dioxide low impedance layer  20 A that is closest to the support substrate (not illustrated) relative to the having a platinum high impedance layer  22 A closest to the first substrate  17 . A low impedance layer of an acoustic mirror in contact with the first substrate  17  can have a reduced thickness compared to other low impedance layers of the acoustic mirror in certain applications. 
     As illustrated, the layer of the second solid acoustic mirror  16  closest to the piezoelectric layer  12  is a low impedance layer  20 B. Having a low impedance layer  20 B closest to the piezoelectric layer  12  can increase an electromechanical coupling coefficient of the laterally excited bulk acoustic wave device  10  and/or bring a TCF of the laterally excited bulk acoustic wave device  10  closer to 0 in certain instances. 
     As illustrated, the layer of the second solid acoustic mirror  16  closest to the second substrate  18  is a high impedance layer  22 B. Having a high impedance layer  22 B closest to the second substrate  18  can increase reflection of the layer of the second solid acoustic mirror  16  closest to the second substrate  18 . Alternatively, a solid acoustic mirror (not illustrated) with a low impedance layer  20 B closest to the second substrate  18  can have a higher adhesion with the first substrate  18 . A low impedance layer of an acoustic mirror in contact with the second substrate  18  can have a reduced thickness compared to other low impedance layers of the acoustic mirror in certain applications. 
     The first substrate  17  can be any suitable support substrate. The first substrate  17  can have a relatively high thermal conductivity to dissipate heat associated with operation of the laterally excited bulk acoustic wave device  10 . The first substrate  17  can be a silicon substrate. The first substrate  17  being a silicon substrate can be advantageous for processing during manufacture of the laterally excited bulk acoustic wave device  10  and provide desirable thermal conductivity. Silicon is also a relatively inexpensive material. The first substrate  17  can be an aluminum nitride substrate. In some other applications, the first substrate  17  can be a quartz substrate, a ceramic substrate, a glass substrate, a spinel substrate, a magnesium oxide spinel substrate, a sapphire substrate, a diamond substrate, a diamond like carbon substrate, a silicon carbide substrate, a silicon nitride substrate, or the like. 
     The second substrate  18  can be any suitable substrate. The second substrate  18  can have a relatively high thermal conductivity to dissipate heat associated with operation of the laterally excited bulk acoustic wave device  10 . The second substrate  18  can be a silicon substrate. The second substrate  18  can be an aluminum nitride substrate. In some other applications, the second substrate  18  can be a quartz substrate, a ceramic substrate, a glass substrate, a spinel substrate, a magnesium oxide spinel substrate, a sapphire substrate, a diamond substrate, a diamond like carbon substrate, a silicon carbide substrate, a silicon nitride substrate, or the like. 
     In certain instances, the first substrate  17  and the second substrate  18  can have similar thicknesses to account for thermal expansion. The first substrate  17  and the second substrate  18  can be of the same material in certain applications. 
       FIG.  1 B  illustrates the IDT electrode  14  of the laterally excited bulk acoustic wave device  10  of  FIG.  1 A  in plan view. Only the IDT electrode  14  of the laterally excited bulk acoustic wave device  10  is shown in  FIG.  1 B . The IDT electrode  14  includes a bus bar  24  and IDT fingers  26  extending from the bus bar  24 . The IDT fingers  26  have a pitch of λ. As discussed above, the pitch λ can have less impact than the thickness of the piezoelectric layer  12  in the laterally excited bulk acoustic wave device  10 . The laterally excited bulk acoustic wave device  10  can include any suitable number of IDT fingers  26 . 
       FIG.  2 A  is a cross sectional diagram of a laterally excited bulk acoustic wave device  28  with a solid acoustic mirror  15  according to an embodiment. The laterally excited bulk acoustic wave device  28  can be a laterally excited bulk acoustic wave resonator included in a filter. The laterally excited bulk acoustic wave device  28  can be any other suitable laterally excited bulk acoustic wave device, such as a device in a delay line.  FIG.  2 A  illustrates that a single solid acoustic mirror  15  can be implemented in certain applications. As illustrated, the laterally excited bulk acoustic wave device  28  includes a support substrate  17 , a solid acoustic mirror  15  on the support substrate  17 , a piezoelectric layer  12  on the solid acoustic mirror  15 , and an IDT electrode  14  on the piezoelectric layer  12 . The IDT electrode  14  is arranged to laterally excite a bulk acoustic wave. 
     The piezoelectric layer  12  can have a thickness in a range from 0.2 micrometers to 0.4 micrometers in certain applications. The piezoelectric layer can have a thickness in a range from 0.2 micrometers to 0.3 micrometers. 
     The solid acoustic mirror  15  can confine acoustic energy. The solid acoustic mirror  15  can confine acoustic energy such that the support substrate  17  is free from acoustic energy during operation of the laterally excited bulk acoustic wave device  28 . At least one of the low impedance layers  20  and/or at least one of the high impedance layers  22  can be free from acoustic energy during operation of the laterally excited bulk acoustic wave device  28 . 
     The support substrate  17  can dissipate heat associated with generating a laterally excited bulk acoustic wave. The support substrate  17  has a thermal conductivity that is higher than a thermal conductivity of the piezoelectric layer  12 . The support substrate  17  can be a silicon substrate. 
     Filters that include one or more laterally excited bulk acoustic wave devices  28  can filter an RF signal having a frequency in a range from 3 GHz to 5 GHz, a range from 4.5 GHz to 10 GHz, a range from 5 GHz to 10 GHz, or a range from 10 GHz to 25 GHz. 
       FIG.  2 B  is a cross sectional view showing heat flow in the laterally excited bulk acoustic wave device  28  of  FIG.  2 A . During operation, heat can be generated by the IDT electrode  14 . This heat can flow through the piezoelectric layer  12  and the solid acoustic mirror  15  to the substrate  17 . Accordingly, the solid acoustic mirror  15  can provide a heat flow path from the piezoelectric layer  12  to the substrate  17 . The substrate  17  can have a relatively high thermal conductivity and provide heat dissipation. The substrate  17  can increase mechanical durability. 
       FIG.  3    is a cross sectional diagram of a baseline laterally excited bulk acoustic wave device  30 . As illustrated, the baseline laterally excited bulk acoustic wave device  30  includes a piezoelectric layer  12  and an IDT electrode  14  on the piezoelectric layer  12 . The laterally excited bulk acoustic wave device  30  can be a free standing device supported over a support substrate. There can be an air cavity positioned between the piezoelectric layer  12  and the support substrate. 
       FIG.  4 A  is graph of admittance of the baseline laterally excited bulk acoustic wave device  30  of  FIG.  3   . This graph shows a relatively clean frequency response with a resonant frequency at around 4.8 GHz and an anti-resonant frequency around 5.4 GHz. 
       FIG.  4 B  illustrates displacement at a resonant frequency for the baseline laterally excited bulk acoustic wave device  30  of  FIG.  3   .  FIG.  4 B  indicates displacement in the piezoelectric layer  12  at the resonant frequency. 
       FIG.  4 C  illustrates displacement at an anti-resonant frequency for the baseline laterally excited bulk acoustic wave device  30  of  FIG.  3   .  FIG.  4 C  indicates displacement in the piezoelectric layer  12  at the anti-resonant frequency. 
       FIG.  5    is a cross sectional diagram of a laterally excited bulk acoustic wave device  50  with a support substrate in contact with a piezoelectric layer. As illustrated, the laterally excited bulk acoustic wave device  50  includes a piezoelectric layer  12 , an IDT electrode  14  on a first side of the piezoelectric layer  12 , and a support substrate  17  in contact with a second side of the piezoelectric layer  12  that is opposite to the first side. The support substrate  17  can be a silicon substrate. The support substrate  17  can dissipate heat associated with operation of the laterally excited bulk acoustic wave device  50 . 
       FIG.  6 A  is graph of admittance of the laterally excited bulk acoustic wave device  50  of  FIG.  5   , in which the support substrate  17  is a silicon substrate. This graph indicates that the laterally excited bulk acoustic wave device  50  produces a low quality factor (Q) that is generally undesirable for an acoustic wave filter. 
       FIG.  6 B  illustrates displacement at a resonant frequency for the laterally excited bulk acoustic wave device  50  of  FIG.  5   , in which the support substrate  17  is a silicon substrate.  FIG.  6 B  indicates acoustic energy leakage into the silicon substrate at the resonant frequency. 
       FIG.  6 C  illustrates displacement at an anti-resonant frequency for the laterally excited bulk acoustic wave device  50  of  FIG.  5   , in which the support substrate  17  is a silicon substrate.  FIG.  6 B  indicates acoustic energy leakage into the silicon substrate at the anti-resonant frequency. 
       FIG.  7    is a cross sectional diagram of a laterally excited bulk acoustic wave device  70  with a solid acoustic mirror according to an embodiment before design refinement and/or optimization. The laterally excited bulk acoustic wave device  70  includes a piezoelectric layer  12 , an interdigital transducer electrode  14  on the piezoelectric layer  12 , a solid acoustic mirror  15  including alternating low impedance layers  20  and high impedance layers  22 , and a support substrate  17 . The solid acoustic mirror  15  is positioned between the support substrate  17  and the piezoelectric layer  12 . The solid acoustic mirror  15  is not optimized in the laterally excited bulk acoustic wave device  70 . In  FIG.  7   , the support substrate  17  is not necessarily shown to scale. The support substrate  17  can be the thickest element illustrated in the laterally excited bulk acoustic wave device  70 . 
     In the simulations for  FIGS.  8 A to  8 C , the acoustic mirror includes silicon dioxide low impedance layers having a thickness of 0.1λ and platinum (Pt) high impedance layers having a thickness of 0.1λ. The performance of the laterally excited bulk acoustic wave device  70  in these simulations is degraded. This can be due to the high impedance layers having a thickness that is away from range that leads to better performance. 
       FIG.  8 A  is graph of admittance of the laterally excited bulk acoustic wave device  70  of  FIG.  7   . This graph shows a generally undesirable frequency response. 
       FIG.  8 B  illustrates displacement at a resonant frequency for the laterally excited bulk acoustic wave device  70  of  FIG.  7   .  FIG.  8 B  indicates some acoustic energy leakage into the middle layers of the solid acoustic mirror  15  at the resonant frequency. 
       FIG.  8 C  illustrates displacement at an anti-resonant frequency for the laterally excited bulk acoustic wave device  70  of  FIG.  7   .  FIG.  8 C  indicates acoustic energy leakage into the middle and lower layers of the solid acoustic mirror  15  at the anti-resonant frequency. 
       FIG.  9    is a cross sectional diagram of a laterally excited bulk acoustic wave device  90  with a solid acoustic mirror according to an embodiment. The laterally excited bulk acoustic wave device  90  is like the laterally excited bulk acoustic wave device  70  of  FIG.  7   , except that the laterally excited bulk acoustic wave device  90  is modified to increase confinement of acoustic energy and produce a cleaner frequency response. In  FIG.  9   , the support substrate  17  is not necessarily shown to scale. The support substrate  17  can be the thickest element illustrated in the laterally excited bulk acoustic wave device  90 . 
     The piezoelectric layer  12  can have a thickness to increase performance of the laterally excited bulk acoustic wave device  90 . For example, the piezoelectric layer  12  can have a thickness in a range from about 0.04λ to 0.5λ, in which λ is IDT electrode pitch. As one example, the piezoelectric layer  12  can have a thickness of about 0.08λ. 
     The layers of the solid acoustic mirror  15  can each have a thickness to increase performance of the laterally excited bulk acoustic wave device  90 . For example, the low impedance layers  20  can be silicon dioxide layers having a thickness in a range from 0.02λ, to 0.10λ. The high impedance layers can be platinum layers having a thickness in a range from 0.01λ, to 0.03λ, or 0.04λ, to 0.06λ. As one example, the low impedance layers  20  and high impedance layers  22  can each have a thickness of about 0.05λ. Preferred mirror layer thickness can vary for material. For example, in the case with high impedance layers that are tungsten, preferred thickness of the high impedance layer can be in a range from 0.017λ to 0.027λ or from 0.049λ to 0.059λ. For molybdenum high impedance layers, preferred thickness of each high impedance layer can be in a range from 0.040λ to 0.050λ or 0.010λ to 0.011λ. Normalized by wave length of longitudinal wave velocity λ p  in each material, preferred low impedance layer thickness for each silicon dioxide low impedance layer can be in a range from 0.1λ p  to 0.3λ p  and each high impedance layer thickness can be in a range from about 0.14λ p  to 0.30λ p  or from about 0.35λ p  to 0.45λ p . In certain applications, the low impedance layers  20  and the high impedance layers  22  can have similar and/or approximately the same thicknesses. In some other applications, the low impedance layers  20  can have different thickness than the high impedance layers  22 . 
     The simulations in  FIGS.  10 A to  10 C  correspond to a piezoelectric layer thickness of 0.08λ and low impedance and high impedance layers  20  and  22 , respectively, each having a thickness of 0.05λ. 
       FIG.  10 A  is graph of admittance of the laterally excited bulk acoustic wave device of  FIG.  9   . This graph shows a relatively clean frequency response with a resonant frequency at around 4.6 GHz and an anti-resonant frequency around 5.0 GHz. 
       FIG.  10 B  illustrates displacement at a resonant frequency for the laterally excited bulk acoustic wave device  FIG.  9   .  FIG.  10 B  indicates that the acoustic energy in confined near the piezoelectric layer  12  at the resonant frequency in the laterally excited bulk acoustic wave device  90 .  FIG.  10 B  shows improve acoustic energy confinement relative to  FIG.  8 B . 
       FIG.  10 C  illustrates displacement at an anti-resonant frequency for the laterally excited bulk acoustic wave device of  FIG.  9   .  FIG.  10 C  indicates that the acoustic energy in confined near the piezoelectric layer  12  at the anti-resonant frequency in the laterally excited bulk acoustic wave device  90 .  FIG.  10 C  shows improve acoustic energy confinement relative to  FIG.  8 C . 
       FIG.  10 D  is a graph corresponding to different thicknesses of the piezoelectric layer for the laterally excited bulk acoustic wave device  90  of  FIG.  9   . The different curves correspond to different thicknesses H1 for a lithium niobate piezoelectric layer  12 .  FIG.  10 D  indicates that the thickness H1 of the lithium niobate piezoelectric layer  12  can be at least 0.06 L to achieve a preferred electrical performance (k 2 ). The thickness H1 of lithium niobate piezoelectric layer  12  can be at least 200 nanometers from a fabrication point of view. 
       FIG.  10 E  is a graph corresponding to different thicknesses of the interdigital transducer electrode for the laterally excited bulk acoustic wave device  90  of  FIG.  9   . The different curves correspond to different thicknesses H2 for the IDT electrode  14 . This graph indicates that an IDT electrode thickness H2 of greater than 0.02 L can excite a spurious mode. The simulations in  FIG.  10 E  do not include the effect of IDT electrode resistivity. 
       FIG.  10 F  is a cross sectional diagram of a laterally excited bulk acoustic wave device  100  with a solid acoustic mirror  15  and silicon dioxide  102  between fingers of the IDT electrode  14  according to an embodiment. The laterally excited bulk acoustic wave device  100  is like the laterally excited bulk acoustic wave device  90  of  FIG.  9   , except that silicon dioxide  102  is included between fingers of the IDT electrode  14 . In some other instances (not illustrated), silicon dioxide and/or another temperature compensation layer can cover fingers of the IDT electrode  14 . 
     Including silicon dioxide  102  between fingers of the IDT electrode  14  can suppress a spurious mode by thicker IDT electrodes. Resonant frequency can be dominated by total thickness of the piezoelectric layer  12  and silicon dioxide  102 . An upper silicon dioxide layer (e.g., the silicon dioxide  102 ) can provide frequency tuning. A trimming range can be sufficient to cover series and parallel arms in a ladder type filter. 
       FIG.  10 G  is a graph corresponding to different thicknesses of the IDT electrode  14  for the laterally excited bulk acoustic wave device  100  of  FIG.  10 F . The simulations in  FIG.  10 G  do not include the effect of IDT electrode resistivity. 
       FIG.  11 A  is a cross sectional diagram of a laterally excited bulk acoustic wave device  110  with a double solid acoustic mirror structure according to an embodiment. With the double solid acoustic mirror structure, a more complex package structure can be avoided. The laterally excited bulk acoustic wave device  110  can includes a pair of solid acoustic mirrors including a first solid acoustic mirror  15  and a second solid acoustic mirror  16 , a piezoelectric layer  12  positioned between the first solid acoustic mirror  15  and the second solid acoustic mirror  16 , an IDT electrode  14  on the piezoelectric layer  12 , a first substrate  17  on which the first solid acoustic mirror  15  is positioned, and a second substrate  18  over the second solid acoustic mirror  16 . The IDT electrode  14  is arranged to laterally excite a bulk acoustic wave. The first solid acoustic mirror  15  and the second solid acoustic mirror  16  are arranged to confine acoustic energy of the bulk acoustic wave. The first substrate  17  and the second substrate  18  are arranged to dissipate heat associated with the bulk acoustic wave. The laterally excited bulk acoustic wave device  110  can perform as described with reference to  FIGS.  1 A and/or  1 B . 
       FIG.  11 B  is a cross sectional view showing heat flow in the laterally excited bulk acoustic wave device  110  of  FIG.  11 A . During operation, heat can be generated by the IDT electrode  14 . This heat can flow through the piezoelectric layer  12  and the first solid acoustic mirror  15  to the first substrate  17 . Accordingly, the first solid acoustic mirror  15  can provide a heat flow path from the piezoelectric layer  12  to the first substrate  17 . The first substrate  17  can dissipate heat. Similarly, heat generated by the IDT electrode  14  can flow through the second solid acoustic mirror  16  to the second substrate  18 . Accordingly, the second solid acoustic mirror  16  can provide a heat flow path from the IDT electrode  14  to the second substrate  18 . The second substrate  18  can dissipate heat. The first solid acoustic mirror  15  and the second solid acoustic mirror  16  can confine acoustic energy during operation. 
       FIG.  12 A  is graph of admittance of the laterally excited bulk acoustic wave device  110  of  FIG.  11 A . This graph shows a desirable frequency response.  FIG.  12 A  indicates that the simulated laterally excited bulk acoustic wave device  110  has a resonant frequency at around 4.5 GHz and an anti-resonant frequency around 4.8 GHz. 
       FIG.  12 B  illustrates displacement at a resonant frequency for the laterally excited bulk acoustic wave device  110  of  FIG.  11 A .  FIG.  12 B  indicates that the acoustic energy in confined near the piezoelectric layer  12  at the resonant frequency in the laterally excited bulk acoustic wave device  110 . 
       FIG.  12 C  illustrates displacement at an anti-resonant frequency for the laterally excited bulk acoustic wave device  110  of  FIG.  11 A .  FIG.  12 C  indicates that the acoustic energy in confined near the piezoelectric layer  12  at the anti-resonant frequency in the laterally excited bulk acoustic wave device  110 . 
       FIG.  12 D  is a graph corresponding to different thicknesses of the piezoelectric layer for the laterally excited bulk acoustic wave device  110  of  FIG.  11 A . The different curves correspond to different thicknesses H1 for a lithium niobate piezoelectric layer  12 .  FIG.  12 D  indicates that the thickness H1 of the lithium niobate piezoelectric layer  12  can be at least 0.04 L to achieve a preferred electrical performance (e.g., k 2 ). The thickness H1 of lithium niobate piezoelectric layer  12  can be at least 200 nanometers from a fabrication point of view. 
       FIG.  12 E  is a graph corresponding to different thicknesses of the interdigital transducer electrode for the laterally excited bulk acoustic wave device  110  of  FIG.  11 A . The different curves correspond to different thicknesses H2 for the IDT electrode layer  14 . In the laterally excited bulk acoustic wave device  110 , a low impedance layer (e.g., a silicon dioxide layer) overcoats the IDT electrode  14 . This can make the laterally excited bulk acoustic wave device  110  robust for IDT electrode thickness H2. The simulations in  FIG.  12 E  do not include the effect of IDT electrode resistivity. 
       FIG.  12 F  is a graph corresponding to different thicknesses of a silicon dioxide low impedance layer  20 A of a solid acoustic mirror  16  over the interdigital transducer electrode  14  for the laterally excited bulk acoustic wave device  110  of  FIG.  11 A . Height H3 of the low impedance layer  20 A in physical contact with the IDT electrode is varied for the different curves in  FIG.  12 F . Frequency can be adjusted and/or trimmed by changing thickness H3 of the silicon dioxide low impedance layer  20 A that is in physical contact with the IDT electrode  14 . A range for frequency adjustment and/or trimming can be sufficient to cover series and parallel arms in a ladder type filter. 
       FIG.  13    is a cross sectional diagram of an acoustic wave component  130  with a laterally excited bulk acoustic wave device with a double solid acoustic mirror structure according to an embodiment. The acoustic wave component  130  can be referred to as a laterally excited bulk acoustic wave component. The acoustic wave component  130  includes a first substrate  17 , a first solid acoustic mirror  15  on the first substrate  17 , a piezoelectric layer  12  on the first solid acoustic mirror  15 , an IDT electrode  14  on the piezoelectric layer  12 , a second solid acoustic mirror  16  on the piezoelectric layer  12  and the IDT electrode  14 , and a second substrate  18  on the second solid acoustic mirror  16 . The acoustic wave component  130  also includes input/output contacts  132  and conductive vias  134 . 
     The input/output contacts  132  can be pins, for example. An input/output contact  132  can be electrically connected to one or more laterally excited bulk acoustic wave devices of the acoustic wave component by way of a conductive via  134 . 
     As illustrated, the conductive vias  134  extend through the second substrate  18  and the second solid acoustic mirror  16 . In some other instances (not illustrated), one or more conductive vias can extend through the first substrate  17 . In such instances, there can be one or more input/output contact on a side of the first substrate  17  opposite to the piezoelectric layer that are electrically connected to the one or more conductive vias. 
     The acoustic wave component  130  can include a plurality of laterally excited bulk acoustic wave resonators. For example, the acoustic wave component  130  can include 10 to 20 laterally excited bulk acoustic wave resonators. The laterally excited bulk acoustic wave resonators of the acoustic wave component  130  can be included in a single filter or two or more filters. 
       FIG.  14    is a group comparing admittance of the laterally excited bulk acoustic wave devices of  FIGS.  2 A,  3 , and  11 A . A relatively small amount of acoustic energy in a solid acoustic mirror or solid acoustic mirrors during operation of a laterally excited bulk acoustic wave device can reduce electromechanical coupling coefficient (k 2 ). The electromechanical coupling coefficient can be proportional to the difference between the resonant frequency and the anti-resonant frequency of an acoustic resonator.  FIG.  14    indicates that an electromechanical coupling coefficient of about 20% can be achieved with a double mirror laterally exited bulk acoustic wave device. This electromechanical coupling coefficient can still be desirable. For example, this electromechanical coupling coefficient can be higher than for temperature compensated surface acoustic wave resonators. The single mirror laterally exited bulk acoustic wave device can achieve a higher electromechanical coupling coefficient than the double mirror laterally exited bulk acoustic wave device. 
       FIG.  15    illustrates a thermal simulation result of a laterally excited bulk acoustic wave device with a membrane structure. The laterally excited bulk acoustic wave device with a membrane structure of  FIG.  15    includes a piezoelectric layer  12 , an IDT electrode  14  on the piezoelectric layer  12 , an air cavity  152  under the piezoelectric layer  12 , and a support substrate  154 . Although not shown in  FIG.  15   , the support substrate  154  extends below the air cavity  154  such that the air cavity  152  is between a portion of the support substrate  154  and the piezoelectric layer  12 . The IDT electrode  14  generates heat during operation. This generated heat dissipates thought the relatively thin piezoelectric layer  12  to the support substrate  154  laterally from the IDT electrode  14 . This can cause the piezoelectric layer  12  to heat up to a high temperature. The piezoelectric layer  12  and the IDT electrode  14  are hotter than the maximum value on the temperature scale in the thermal simulation. The thermal simulation indicates that the laterally excited bulk acoustic wave device with a membrane structure can heat up to about 124° C. 
       FIG.  16    illustrates a thermal simulation result of a laterally excited bulk acoustic wave device with a single solid acoustic mirror structure according to an embodiment. The laterally excited bulk acoustic wave device with the single solid acoustic mirror structure is generally similar to the laterally excited bulk acoustic wave device  28  of  FIGS.  2 A- 2 B  and the laterally excited bulk acoustic wave device  90  of  FIG.  9   . Heat can flow as illustrated in  FIG.  2 B . The IDT electrode  14  generates heat during operation. The thermal simulation indicates that heat is dissipated into the support substrate  17 . The highest temperature during operation can be at the IDT electrode  14 . The thermal simulation indicates that the laterally excited bulk acoustic wave device with a single solid acoustic mirror can heat up to about 37° C. This is a significant improvement relative to the laterally excited bulk acoustic wave device with a membrane structure of  FIG.  15   . 
       FIG.  17    illustrates a thermal simulation result of a laterally excited bulk acoustic wave device with a double solid acoustic mirror structure according to an embodiment. The laterally excited bulk acoustic wave devices with the double solid acoustic mirror structure is generally similar to the laterally excited bulk acoustic wave device  10  of  FIGS.  1 A- 1 B  and the laterally excited bulk acoustic wave device  110  of  FIGS.  11 A- 11 B . Heat can flow as illustrated in  FIG.  11 B . The IDT electrode  14  generates heat during operation. Heat can be dissipated into support substrates  17  and  18  on opposing sides of the IDT electrode  14 . The highest temperature during operation can be at the IDT electrode  14 . The thermal simulation of indicates that the laterally excited bulk acoustic wave device with the double solid acoustic mirror can heat up to about 31° C. This is an improvement relative to the laterally excited bulk acoustic wave device with the single solid acoustic mirror of  FIG.  16   . 
       FIG.  18    is a cross sectional diagram of a stacked laterally excited bulk acoustic wave device assembly  180  according to an embodiment.  FIG.  18    illustrates that laterally excited bulk acoustic wave devices can be stacked. The stacked laterally excited bulk acoustic wave device assembly  180  can implement a plurality of laterally excited bulk acoustic wave devices in a relatively small sized component. Such a component can have a relatively small vertical height and/or footprint for implementing a plurality of acoustic wave devices. 
     As illustrated, the stacked laterally excited bulk acoustic wave device assembly  180  includes a first support substrate  17 , a first laterally excited bulk acoustic wave stack on the first support substrate  17 , a second support substrate  18  positioned on the first laterally excited bulk acoustic wave stack, a second laterally excited bulk acoustic wave stack on the second support substrate  18 , and a third substrate  188 . 
     The first laterally excited bulk acoustic wave stack includes a first piezoelectric layer  12 , a IDT electrode  14  on the first piezoelectric layer  12 , and a first pair of solid acoustic mirrors on opposing sides of the first piezoelectric layer  12 . The first pair of solid acoustic mirrors includes a first solid acoustic mirror  15  and a second solid acoustic mirror  16 . 
     The second laterally excited bulk acoustic wave stack includes a second piezoelectric layer  182 , a second IDT electrode  184  on the second piezoelectric layer  182 , and a second pair of solid acoustic mirrors on opposing sides of the first piezoelectric layer  182 . The second pair of second solid acoustic mirrors includes a third solid acoustic mirror  185  and a fourth solid acoustic mirror  186 . The second piezoelectric layer  182  can be implemented in accordance with any suitable principles and advantages of the piezoelectric layers disclosed herein. The second IDT electrode  184  can be implemented in accordance with any suitable principles and advantages of the IDT electrodes disclosed herein. The solid acoustic mirrors  185  and  186  include respective low impedance layers  20 C and  20 D and respective high impedance layers  22 C and  22 D. The solid acoustic mirrors  185  and  186  can be implemented in accordance with any suitable principles and advantages of the solid acoustic mirrors disclosed herein. The third substrate  188  can be implemented in accordance with any suitable principles and advantages of the substrates disclosed herein. 
     In the stacked laterally excited bulk acoustic wave device assembly  180 , the second support substrate  18  is implemented as a single support substrate between solid acoustic mirrors of the laterally excited bulk acoustic wave stacks. The substrates  17 ,  18 , and  188  can each include the same material in certain applications. Two or more of the substrates  17 ,  18 , and  188  can include different materials in some other applications. 
     The stacked laterally excited bulk acoustic wave device assembly  180  can include devices of one or more filters arranged to filter RF signals. The first laterally excited bulk acoustic wave stack and the second laterally excited bulk acoustic wave stack can implement devices in the same filter in certain applications. The first laterally excited bulk acoustic wave stack and the second laterally excited bulk acoustic wave stack can implement devices in different filter in various applications. In some such applications, the different filters can be included in a multiplexer. 
     Although two devices are stacked in  FIG.  18   , three or more laterally excited bulk acoustic wave devices can be stacked in some other applications. Moreover, although two double mirror laterally excited bulk acoustic devices are shown in  FIG.  18   , a single mirror laterally excited bulk acoustic device can be stacked on a double mirror laterally excited bulk acoustic devices in some other applications. 
       FIG.  19    is a cross sectional diagram of a stacked laterally excited bulk acoustic wave device assembly  190  according to another embodiment. With stacked structures, firm mechanical connections may not be needed. Accordingly, an adhesion layer can be implemented between layers. The stacked laterally excited bulk acoustic wave device assembly  190  is like the stacked laterally excited bulk acoustic wave device assembly  180  of  FIG.  18   , except that an adhesion layer  192  is included in the stacked laterally excited bulk acoustic wave device assembly  190 . The adhesion layer  192  can be an epoxy layer. The adhesion layer  192  can be any other suitable layer arranged to increase adhesion between the second substrate  18  and the third solid acoustic mirror  185 . 
     A laterally excited bulk acoustic wave can be stacked with other circuitry.  FIG.  20    is a cross sectional diagram of a stacked device assembly  200  with a laterally excited bulk acoustic wave device  110  stacked with other circuitry  202  according to another embodiment. As shown in  FIG.  20   , other circuitry  202  can be implemented on the second substrate  18 . Implementing the other circuitry  202  on the second substrate  18  can enable more integration of electrical components in a module. This can reduce physical size of the module. 
     The second substrate  18  can be a semiconductor substrate. The second substrate  18  can be a silicon substrate. A variety of other circuitry  202  can be implemented on such a second substrate  18 . The other circuitry  202  can include one or more transistors, one or more passive impedance elements, one or more other acoustic wave devices, the like, or any suitable combination thereof. 
     For example, the other circuitry  202  can include one or more transistors, such as one or more of a semiconductor-on-insulator transistor, a silicon-on-insulator transistor, a complementary metal oxide semiconductor transistor, or the like. 
     Alternatively or additionally, the other circuitry can include one or more passive impedance elements, such as one or more of a capacitor, an inductor, a resistor, a transformer, or a diode. In certain instances, a filter can include the laterally excited bulk acoustic wave device  110  and an inductor capacitor circuit of the other circuitry. 
     As one more example, the other circuitry can include an acoustic wave device on the second substrate  18 . Such an acoustic wave device, can a surface acoustic wave device such as a multi-layer piezoelectric substrate surface acoustic wave device, a bulk acoustic wave device such as a film bulk acoustic wave resonator or s solidly mounted resonator, a boundary wave device, or the like. The laterally excited bulk acoustic wave device  110  can be included in the same filter as the acoustic wave device of the other circuitry  202 . Alternatively, the laterally excited bulk acoustic wave device  110  can be included in a different filter as the acoustic wave device of the other circuitry  202 . The different filters can be included in a multiplexer in some instances. 
     One or more vias and/or other conductive structures (not shown) in the stacked device assembly  200  can provide an electrical connection between the laterally excited bulk acoustic wave device  110  and the other circuitry  202 . Such electrical connections in the stacked device assembly  200  can reduce an impact of electrical connections between the laterally excited bulk acoustic wave device  110 . 
     Acoustic wave devices disclosed herein can be implemented in a variety of different filter topologies. Example filter topologies include without limitation, ladder filters, lattice filters, hybrid ladder lattice filters, filters that include ladder stages and a multi-mode surface acoustic wave filter, and the like. Such filters can be band pass filters. In some other applications, such filters include band stop filters. In some instances, acoustic wave devices disclosed herein can be implemented in filters with one or more other types of resonators and/or with passive impedance elements, such as one or more inductors and/or one or more capacitors. Some example filter topologies will now be discussed with reference to  FIGS.  21  to  23   . Any suitable combination of features of the filter topologies of  FIGS.  21  to  23    can be implemented together with each other and/or with other filter topologies. 
       FIG.  21    is a schematic diagram of a ladder filter  201  that includes a laterally excited bulk acoustic wave resonator according to an embodiment. The ladder filter  201  is an example topology that can implement a band pass filter formed from acoustic wave resonators. In a band pass filter with a ladder filter topology, the shunt resonators can have lower resonant frequencies than the series resonators. The ladder filter  201  can be arranged to filter a radio frequency signal. As illustrated, the ladder filter  201  includes series acoustic wave resonators R1 R3, R5, and R7 and shunt acoustic wave resonators R2, R4, R6, and R8 coupled between a first input/output port I/O 1  and a second input/output port I/O 2 . Any suitable number of series acoustic wave resonators can be included in a ladder filter. Any suitable number of shunt acoustic wave resonators can be included in a ladder filter. 
     One or more of the acoustic wave resonators of the ladder filter  201  can include a laterally excited bulk acoustic wave filter according to an embodiment. In certain applications, all acoustic resonators of the ladder filter  201  can be laterally excited bulk acoustic wave resonators in accordance with any suitable principles and advantages disclosed herein. According to some applications, the ladder filter  201  can include at least one laterally excited bulk acoustic wave device according to one embodiment and at least one other laterally excited bulk acoustic wave device according to another embodiment. 
     The first input/output port I/O 1  can a transmit port and the second input/output port I/O 2  can be an antenna port. Alternatively, first input/output port I/O 1  can a receive port and the second input/output port I/O 2  can be an antenna port. 
       FIG.  22    is a schematic diagram of a lattice filter  210  that includes a laterally excited bulk acoustic wave resonator according to an embodiment. The lattice filter  210  is an example topology of a band pass filter formed from acoustic wave resonators. The lattice filter  210  can be arranged to filter an RF signal. As illustrated, the lattice filter  210  includes acoustic wave resonators RL1, RL2, RL3, and RL4. The acoustic wave resonators RL1 and RL2 are series resonators. The acoustic wave resonators RL3 and RL4 are shunt resonators. The illustrated lattice filter  210  has a balanced input and a balanced output. One or more of the illustrated acoustic wave resonators RL1 to RL4 can be a laterally excited bulk acoustic wave resonator in accordance with any suitable principles and advantages disclosed herein. 
       FIG.  23    is a schematic diagram of a hybrid ladder and lattice filter  220  that includes a laterally excited bulk acoustic wave resonator according to an embodiment. The illustrated hybrid ladder and lattice filter  220  includes series acoustic resonators RL1, RL2, RH3, and RH4 and shunt acoustic resonators RL3, RL4, RH1, and RH2. The hybrid ladder and lattice filter  220  includes one or more laterally excited bulk acoustic wave resonators in accordance with any suitable principles and advantages disclosed herein. For example, the series resonators RL1, RL2, RH3, and RH4 and the shunt resonators RL3, RL4, RH1, and RH2 can each be a laterally excited bulk acoustic wave resonator according to an embodiment. 
     According to certain applications, a laterally excited bulk acoustic wave resonator can be included in filter that also includes one or more inductors and one or more capacitors. 
     The laterally excited bulk acoustic wave resonators disclosed herein can be implemented in a standalone filter and/or in a filter in any suitable multiplexer. Such filters can be any suitable topology, such as any filter topology of  FIGS.  21  to  23   . The filter can be a band pass filter arranged to filter a 4G LTE band and/or 5G NR band. Examples of a standalone filter and multiplexers will be discussed with reference to  FIGS.  24 A to  24 E . Any suitable principles and advantages of these filters and/or multiplexers can be implemented together with each other. 
       FIG.  24 A  is schematic diagram of an acoustic wave filter  230 . The acoustic wave filter  230  is a band pass filter. The acoustic wave filter  230  is arranged to filter a radio frequency. The acoustic wave filter  230  includes one or more acoustic wave devices coupled between a first input/output port RF_IN and a second input/output port RF OUT. The acoustic wave filter  230  includes a laterally excited bulk acoustic wave resonator according to an embodiment. 
       FIG.  24 B  is a schematic diagram of a duplexer  232  that includes an acoustic wave filter according to an embodiment. The duplexer  232  includes a first filter  230 A and a second filter  230 B coupled to together at a common node COM. One of the filters of the duplexer  232  can be a transmit filter and the other of the filters of the duplexer  232  can be a receive filter. In some other instances, such as in a diversity receive application, the duplexer  232  can include two receive filters. Alternatively, the duplexer  232  can include two transmit filters. The common node COM can be an antenna node. 
     The first filter  230 A is an acoustic wave filter arranged to filter a radio frequency signal. The first filter  230 A includes one or more acoustic wave resonators coupled between a first radio frequency node RF1 and the common node COM. The first radio frequency node RF1 can be a transmit node or a receive node. The first filter  230 A includes a laterally excited bulk acoustic wave resonator in accordance with any suitable principles and advantages disclosed herein. 
     The second filter  230 B can be any suitable filter arranged to filter a second radio frequency signal. The second filter  230 B can be, for example, an acoustic wave filter, an acoustic wave filter that includes a laterally exited bulk acoustic wave resonator, an LC filter, a hybrid acoustic wave LC filter, or the like. The second filter  230 B is coupled between a second radio frequency node RF2 and the common node. The second radio frequency node RF2 can be a transmit node or a receive node 
     Although example embodiments may be discussed with filters or duplexers for illustrative purposes, any suitable principles and advantages disclosed herein can be implement in a multiplexer that includes a plurality of filters coupled together at a common node. Examples of multiplexers include but are not limited to a duplexer with two filters coupled together at a common node, a triplexer with three filters coupled together at a common node, a quadplexer with four filters coupled together at a common node, a hexaplexer with six filters coupled together at a common node, an octoplexer with eight filters coupled together at a common node, or the like. Multiplexers can include filters having different passbands. Multiplexers can include any suitable number of transmit filters and any suitable number of receive filters. For example, a multiplexer can include all receive filters, all transmit filters, or one or more transmit filters and one or more receive filters. One or more filters of a multiplexer can include any suitable number of laterally excited bulk acoustic wave devices. 
       FIG.  24 C  is a schematic diagram of a multiplexer  234  that includes an acoustic wave filter according to an embodiment. The multiplexer  234  includes a plurality of filters  230 A to  230 N coupled together at a common node COM. The plurality of filters can include any suitable number of filters including, for example, 3 filters, 4 filters, 5 filters, 6 filters, 7 filters, 8 filters, or more filters. Some or all of the plurality of acoustic wave filters can be acoustic wave filters. As illustrated, the filters  230 A to  230 N each have a fixed electrical connection to the common node COM. This can be referred to as hard multiplexing or fixed multiplexing. Filters have fixed electrical connections to the common node in hard multiplexing applications. 
     The first filter  230 A is an acoustic wave filter arranged to filter a radio frequency signal. The first filter  230 A can include one or more acoustic wave devices coupled between a first radio frequency node RF1 and the common node COM. The first radio frequency node RF1 can be a transmit node or a receive node. The first filter  230 A includes a laterally excited bulk acoustic wave resonator in accordance with any suitable principles and advantages disclosed herein. The other filter(s) of the multiplexer  234  can include one or more acoustic wave filters, one or more acoustic wave filters that include a laterally excited bulk acoustic wave resonator, one or more LC filters, one or more hybrid acoustic wave LC filters, or any suitable combination thereof. 
       FIG.  24 D  is a schematic diagram of a multiplexer  236  that includes an acoustic wave filter according to an embodiment. The multiplexer  236  is like the multiplexer  234  of  FIG.  24 C , except that the multiplexer  236  implements switched multiplexing. In switched multiplexing, a filter is coupled to a common node via a switch. In the multiplexer  236 , the switch  237 A to  237 N can selectively electrically connect respective filters  230 A to  230 N to the common node COM. For example, the switch  237 A can selectively electrically connect the first filter  230 A the common node COM via the switch  237 A. Any suitable number of the switches  237 A to  237 N can electrically a respective filters  230 A to  230 N to the common node COM in a given state. Similarly, any suitable number of the switches  237 A to  237 N can electrically isolate a respective filter  230 A to  230 N to the common node COM in a given state. The functionality of the switches  237 A to  237 N can support various carrier aggregations. 
       FIG.  24 E  is a schematic diagram of a multiplexer  238  that includes an acoustic wave filter according to an embodiment. The multiplexer  238  illustrates that a multiplexer can include any suitable combination of hard multiplexed and switched multiplexed filters. One or more laterally excited bulk acoustic wave devices can be included in a filter that is hard multiplexed to the common node of a multiplexer. Alternatively or additionally, one or more laterally excited bulk acoustic wave devices can be included in a filter that is switch multiplexed to the common node of a multiplexer 
     The acoustic wave devices disclosed herein can be implemented in a variety of packaged modules. Some example packaged modules will now be disclosed in which any suitable principles and advantages of the acoustic wave devices, acoustic wave components, or stacked acoustic wave device assemblies disclosed herein can be implemented. The example packaged modules can include a package that encloses the illustrated circuit elements. A module that includes a radio frequency component can be referred to as a radio frequency module. The illustrated circuit elements can be disposed on a common packaging substrate. The packaging substrate can be a laminate substrate, for example.  FIGS.  25  to  29    are schematic block diagrams of illustrative packaged modules according to certain embodiments. Any suitable combination of features of these packaged modules can be implemented with each other. While duplexers are illustrated in the example packaged modules of  FIGS.  26 ,  27 , and  29   , any other suitable multiplexer that includes a plurality of filters coupled to a common node and/or standalone filter can be implemented instead of one or more duplexers. For example, a quadplexer can be implemented in certain applications. As another example, one or more filters of a packaged module can be arranged as a transmit filter or a receive filter that is not included in a multiplexer. 
       FIG.  25    is a schematic diagram of a radio frequency module  240  that includes an acoustic wave component  242  according to an embodiment. The illustrated radio frequency module  240  includes the acoustic wave component  242  and other circuitry  243 . The acoustic wave component  242  can include one or more acoustic wave devices in accordance with any suitable combination of features of the acoustic wave filters disclosed herein. The acoustic wave component  242  can include an acoustic wave filter that includes a plurality of laterally excited bulk acoustic wave resonators, for example. 
     The acoustic wave component  242  shown in  FIG.  25    includes one or more acoustic wave devices  244  and terminals  245 A and  245 B. The one or more acoustic wave devices  244  includes an acoustic wave device implemented in accordance with any suitable principles and advantages disclosed herein. The terminals  245 A and  244 B can serve, for example, as an input contact and an output contact. Although two terminals are illustrated, any suitable number of terminals can be implemented for a particular application. The acoustic wave component  242  and the other circuitry  243  are on a common packaging substrate  246  in  FIG.  25   . The package substrate  246  can be a laminate substrate. The terminals  245 A and  245 B can be electrically connected to contacts  247 A and  247 B, respectively, on the packaging substrate  246  by way of electrical connectors  248 A and  248 B, respectively. The electrical connectors  248 A and  248 B can be bumps or wire bonds, for example. 
     The other circuitry  243  can include any suitable additional circuitry. For example, the other circuitry can include one or more radio frequency amplifiers (e.g., one or more power amplifiers and/or one or more low noise amplifiers), one or more radio frequency switches, one or more additional filters, one or more RF couplers, one or more delay lines, one or more phase shifters, the like, or any suitable combination thereof. The other circuitry  243  can be electrically connected to the one or more acoustic wave devices  244 . The radio frequency module  240  can include one or more packaging structures to, for example, provide protection and/or facilitate easier handling of the radio frequency module  240 . Such a packaging structure can include an overmold structure formed over the packaging substrate  246 . The overmold structure can encapsulate some or all of the components of the radio frequency module  240 . 
       FIG.  26    is a schematic block diagram of a module  250  that includes duplexers  251 A to  251 N and an antenna switch  252 . One or more filters of the duplexers  251 A to  251 N can include an acoustic wave device in accordance with any suitable principles and advantages disclosed herein. Any suitable number of duplexers  251 A to  251 N can be implemented. The antenna switch  252  can have a number of throws corresponding to the number of duplexers  251 A to  251 N. The antenna switch  252  can include one or more additional throws coupled to one or more filters external to the module  250  and/or coupled to other circuitry. The antenna switch  252  can electrically couple a selected duplexer to an antenna port of the module  250 . 
       FIG.  27    is a schematic block diagram of a module  260  that includes a power amplifier  262 , a radio frequency switch  264 , and duplexers  251 A to  251 N according to an embodiment. The power amplifier  262  can amplify a radio frequency signal. The radio frequency switch  264  can be a multi-throw radio frequency switch. The radio frequency switch  264  can electrically couple an output of the power amplifier  262  to a selected transmit filter of the duplexers  251 A to  251 N. One or more filters of the duplexers  251 A to  251 N can include an acoustic wave device in accordance with any suitable principles and advantages disclosed herein. Any suitable number of duplexers  251 A to  251 N can be implemented. 
       FIG.  28    is a schematic block diagram of a module  270  that includes filters  272 A to  272 N, a radio frequency switch  274 , and a low noise amplifier  276  according to an embodiment. One or more filters of the filters  272 A to  272 N can include any suitable number of acoustic wave devices in accordance with any suitable principles and advantages disclosed herein. Any suitable number of filters  272 A to  272 N can be implemented. The illustrated filters  272 A to  272 N are receive filters. In some embodiments (not illustrated), one or more of the filters  272 A to  272 N can be included in a multiplexer that also includes a transmit filter. The radio frequency switch  274  can be a multi-throw radio frequency switch. The radio frequency switch  274  can electrically couple an output of a selected filter of filters  272 A to  272 N to the low noise amplifier  276 . In some embodiments (not illustrated), a plurality of low noise amplifiers can be implemented. The module  270  can include diversity receive features in certain applications. 
       FIG.  29    is a schematic diagram of a radio frequency module  280  that includes an acoustic wave filter according to an embodiment. As illustrated, the radio frequency module  280  includes duplexers  251 A to  251 N, a power amplifier  262 , a select switch  264 , and an antenna switch  252 . The radio frequency module  280  can include a package that encloses the illustrated elements. The illustrated elements can be disposed on a common packaging substrate  287 . The packaging substrate  287  can be a laminate substrate, for example. A radio frequency module that includes a power amplifier can be referred to as a power amplifier module. A radio frequency module can include a subset of the elements illustrated in  FIG.  29    and/or additional elements. The radio frequency module  280  may include any one of the acoustic wave filters in accordance with any suitable principles and advantages disclosed herein. 
     The duplexers  251 A to  251 N can each include two acoustic wave filters coupled to a common node. For example, 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 a band pass filter arranged to filter a radio frequency signal. One or more of the transmit filters can include an acoustic wave device in accordance with any suitable principles and advantages disclosed herein. Similarly, one or more of the receive filters can include an acoustic wave device 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 and/or with standalone filters. 
     The power amplifier  262  can amplify a radio frequency signal. The illustrated switch  264  is a multi-throw radio frequency switch. The switch  264  can electrically couple an output of the power amplifier  262  to a selected transmit filter of the transmit filters of the duplexers  251 A to  251 N. In some instances, the switch  264  can electrically connect the output of the power amplifier  262  to more than one of the transmit filters. The antenna switch  252  can selectively couple a signal from one or more of the duplexers  251 A to  251 N to an antenna port ANT. The duplexers  251 A to  251 N can be associated with different frequency bands and/or different modes of operation (e.g., different power modes, different signaling modes, etc.). 
     The acoustic wave devices disclosed herein can be implemented in wireless communication devices.  FIG.  30    is a schematic block diagram of a wireless communication device  290  that includes a filter according to an embodiment. The wireless communication device  290  can be a mobile device. The wireless communication device  290  can be any suitable wireless communication device. For instance, a wireless communication device  290  can be a mobile phone, such as a smart phone. As illustrated, the wireless communication device  290  includes a baseband system  291 , a transceiver  292 , a front end system  293 , antennas  294 , a power management system  295 , a memory  296 , a user interface  297 , and a battery  298 . 
     The wireless communication device  290  can be used communicate using a wide variety of communications technologies, including, but not limited to, 2G, 3G, 4G (including LTE, LTE-Advanced, and LTE-Advanced Pro), 5G NR, WLAN (for instance, WiFi), WPAN (for instance, Bluetooth and ZigBee), WMAN (for instance, WiMax), and/or GPS technologies. 
     The transceiver  292  generates RF signals for transmission and processes incoming RF signals received from the antennas  294 . Various functionalities associated with the transmission and receiving of RF signals can be achieved by one or more components that are collectively represented in  FIG.  30    as the transceiver  292 . In one example, separate components (for instance, separate circuits or dies) can be provided for handling certain types of RF signals. 
     The front end system  293  aids in conditioning signals transmitted to and/or received from the antennas  294 . In the illustrated embodiment, the front end system  293  includes antenna tuning circuitry  300 , power amplifiers (PAs)  301 , low noise amplifiers (LNAs)  302 , filters  303 , switches  304 , and signal splitting/combining circuitry  305 . However, other implementations are possible. The filters  303  can include one or more acoustic wave filters that include any suitable number of laterally excited bulk acoustic wave devices in accordance with any suitable principles and advantages disclosed herein. 
     For example, the front end system  293  can provide a number of functionalities, including, but not limited to, amplifying signals for transmission, amplifying received signals, filtering signals, switching between different bands, switching between different power modes, switching between transmission and receiving modes, duplexing of signals, multiplexing of signals, or any suitable combination thereof. 
     In certain implementations, the wireless communication device  290  supports carrier aggregation, thereby providing flexibility to increase peak data rates. Carrier aggregation can be used for Frequency Division Duplexing (FDD) and/or Time Division Duplexing (TDD), and may be used to aggregate a plurality of carriers and/or channels. Carrier aggregation includes contiguous aggregation, in which contiguous carriers within the same operating frequency band are aggregated. Carrier aggregation can also be non-contiguous, and can include carriers separated in frequency within a common band or in different bands. 
     The antennas  294  can include antennas used for a wide variety of types of communications. For example, the antennas  294  can include antennas for transmitting and/or receiving signals associated with a wide variety of frequencies and communications standards. 
     In certain implementations, the antennas  294  support MIMO communications and/or switched diversity communications. For example, MIMO communications use multiple antennas for communicating multiple data streams over a single radio frequency channel. MIMO communications benefit from higher signal to noise ratio, improved coding, and/or reduced signal interference due to spatial multiplexing differences of the radio environment. Switched diversity refers to communications in which a particular antenna is selected for operation at a particular time. For example, a switch can be used to select a particular antenna from a group of antennas based on a variety of factors, such as an observed bit error rate and/or a signal strength indicator. 
     The wireless communication device  290  can operate with beamforming in certain implementations. For example, the front end system  293  can include amplifiers having controllable gain and phase shifters having controllable phase to provide beam formation and directivity for transmission and/or reception of signals using the antennas  294 . For example, in the context of signal transmission, the amplitude and phases of the transmit signals provided to the antennas  294  are controlled such that radiated signals from the antennas  294  combine using constructive and destructive interference to generate an aggregate transmit signal exhibiting beam-like qualities with more signal strength propagating in a given direction. In the context of signal reception, the amplitude and phases are controlled such that more signal energy is received when the signal is arriving to the antennas  294  from a particular direction. In certain implementations, the antennas  294  include one or more arrays of antenna elements to enhance beamforming. 
     The baseband system  291  is coupled to the user interface  297  to facilitate processing of various user input and output (I/O), such as voice and data. The baseband system  291  provides the transceiver  292  with digital representations of transmit signals, which the transceiver  292  processes to generate RF signals for transmission. The baseband system  291  also processes digital representations of received signals provided by the transceiver  292 . As shown in  FIG.  30   , the baseband system  291  is coupled to the memory  296  of facilitate operation of the wireless communication device  290 . 
     The memory  296  can be used for a wide variety of purposes, such as storing data and/or instructions to facilitate the operation of the wireless communication device  290  and/or to provide storage of user information. 
     The power management system  295  provides a number of power management functions of the wireless communication device  290 . In certain implementations, the power management system  295  includes a PA supply control circuit that controls the supply voltages of the power amplifiers  301 . For example, the power management system  295  can be configured to change the supply voltage(s) provided to one or more of the power amplifiers  301  to improve efficiency, such as power added efficiency (PAE). 
     As shown in  FIG.  30   , the power management system  295  receives a battery voltage from the battery  298 . The battery  298  can be any suitable battery for use in the wireless communication device  290 , including, for example, a lithium-ion battery. 
     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 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 having a frequency in a range from about 30λ Hz to 300 GHz, such as in a frequency range from about 400 MHz to 25 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 packaged radio frequency modules, radio frequency filter die, 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 microwave, a refrigerator, a vehicular electronics system such as an automotive electronics system, a robot such as an industrial robot, an Internet of things device, a stereo system, a digital music player, a radio, a camera such as a digital camera, a portable memory chip, a home appliance such as a washer or a dryer, a peripheral device, a wrist watch, a clock, etc. Further, the electronic devices can include unfinished products. 
     Unless the context indicates otherwise, throughout the description and the claims, the words “comprise,” “comprising,” “include,” “including” and the like are to generally 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.” 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. The word “coupled”, as generally used herein, refers to two or more elements that may be either directly coupled, or coupled 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. 
     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 filters, multiplexer, devices, modules, wireless communication devices, 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 filters, multiplexer, devices, modules, wireless communication devices, apparatus, 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/or 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.