Filters with BAW resonators can achieve desirable insertion loss performance, such as desirable small signal insertion loss. However, second harmonic performance for BAW resonators can be degraded due to spikes in a frequency response from a lateral mode and/or a recessed frame mode of one or more BAW resonators. On the other hand, TCSAW resonators can achieve desirable second harmonic performance. However, TCSAW resonators can have higher insertion loss than BAW resonators. The higher insertion loss for TCSAW resonators can be due to degraded quality factor (Q) performance relative to BAW resonators.

Certain approaches to suppress second harmonic distortion for BAW resonators have focused on transmit filters. However, in multiplexers, a receive filter can create second harmonic distortion for a transmit filter. Embodiments disclosed herein relate to receive filter designs that can reduce harmonic distortion for one or more transmit filters in a multiplexer.

Aspects of this disclosure relate to acoustic wave filters that include different types of resonators to achieve low insertion loss and desirable second harmonic performance. A multiplexer can include a transmit filter and a receive filter. The transmit filter can include acoustic wave resonators arranged to filter a radio frequency signal. The transmit filter can and have a transmit passband. The receive filter can include BAW resonators and a shunt SAW resonator. The shunt SAW resonator can have a resonant frequency in the transmit passband. The shunt SAW resonator can be the first shunt resonator of the receive filter from a common node of the multiplexer. The shunt SAW resonator can be the only SAW resonator of the receive filter in certain applications. The shunt SAW resonator can be a TCSAW resonator, a non-temperature compensated SAW resonator, or a multilayer piezoelectric substrate (MPS) SAW resonator. With the shunt SAW resonator, the transmit filter can have better second harmonic performance than if that shunt SAW resonator were a shunt BAW resonator. The receive filter can achieve desirable insertion loss with the BAW resonators and also achieve desirable second harmonic performance with a relatively small impact on the passband of the transmit filter with the shunt SAW resonator. Accordingly, the receive filter can achieve desirable performance from features of BAW resonators and the shunt SAW resonator. Such desirable performance can also contribute to desirable second harmonic performance of the transmit filter.

FIG. 1 is a schematic block diagram of a duplexer 10. The duplexer 10 includes a first filter 12 and a second filter 14 coupled to together at a common node COM. One of the filters of the duplexer 10 can be a transmit filter and the other of the filters of the duplexer 10 can be a receive filter. In some other instances, such as in a diversity receive application, the duplexer 10 can include two receive filters. Alternatively, the duplexer 10 can include two transmit filters. The common node COM can be an antenna node.

The first filter 12 is an acoustic wave filter arranged to filter a radio frequency signal. The first filter 12 includes 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 second filter 14 can be any suitable filter arranged to filter a second radio frequency signal. The second filter 14 can be, for example, an acoustic wave filter, an LC filter, a hybrid acoustic wave LC filter, or the like. The second filter 14 is coupled between a second radio frequency node RF2 and the common node COM. The second radio frequency node RF2 can be a transmit node or a receive node.

In some applications, the first filter 12 can be a BAW filter where all acoustic wave resonators are BAW resonators. FIG. 2 is a graph illustrating second harmonic distortion for a bulk acoustic wave (BAW) filter. By using BAW technology, there can be lateral mode spikes 16 present in a frequency response of the BAW filter for the second harmonic. There can also be a recessed frame mode spike 18 in the frequency response. Suppressing the lateral mode spikes and recessed frame mode spike can be challenging. For 5G NR bands, non-linearity can be a significant specification at the system level. The spikes in the frequency response shown in FIG. 2 can undesirably increase non-linearity.

FIG. 3 is a graph illustrating that a receive filter of a duplexer can impact second harmonic performance of a transmit filter of the duplexer. FIG. 3 corresponds to frequency responses of filters of (1) a duplexer 10 with Band 3 transmit and receive filters that are each formed of BAW resonators and (2) a duplexer 10 with Band 66 transmit and receive filters that are each formed of BAW resonators. Band 3 and Band 66 have similar transmit bands (1710 megahertz (MHz) to 1785 MHz for Band 3 and 1710 MHz to 1780 MHz for Band 66). The same BAW filter was used for the Band 3 transmit filter and the Band 66 transmit filter. Band 66 has a receive band that is significantly higher than the Band 3 receive band (2110 MHz to 2200 MHz for Band 66 compared to 1805 MHz to 1880 MHz for Band 3). Accordingly, the transmit and receive bands are closer in the Band 3 duplexer than the transmit and receive bands in the Band 66 duplexer.

FIG. 3 includes two curves: a Band 3 transmit curve 26 and a Band 66 transmit curve 28. The curves 26 and 28 indicate that second harmonic performance for the Band 3 transmit band is degraded compared to the Band 66 transmit band. The Band 3 transmit curve 26 has more spikes above about 1760 MHz compared to the Band 66 transmit curve 28. This can be due to the Band 3 receive filter adding second harmonic distortion to the transmit band frequency response. The simulated Band 3 receive filter did not apply a recessed frame for shunt BAW resonators and lateral mode for such a Band 3 receive filter can be relatively strong. This can deteriorate the Band 3 transmit band second harmonic performance, particularly at a frequency range from about 1765 MHz to 1785 MHz in FIG. 3. On the other hand, the Band 66 receive filter does not have a similar impact on the Band 66 transmit filter. This can be due to the larger spacing in the frequency domain between passbands of the Band 66 transmit and receive filters.

FIG. 4 is a schematic diagram of a duplexer 30 with a receive filter 32 that includes a plurality of BAW resonators S1, S2, S3, P2, and P3 and a shunt SAW resonator P1 according to an embodiment. The shunt SAW resonator P1 can be TCSAW resonator, a non-temperature compensated SAW resonator, or a MPS SAW resonator. For example, in certain applications, the shunt SAW resonator P1 is a TCSAW resonator. As another example, in some applications, the shunt SAW resonator P1 is an MPS SAW resonator. In the receive filter 32, the shunt SAW resonator P1 is the only SAW resonator. The shunt SAW resonator P1 is the first shunt resonator from the common node COM in the receive filter 32. As illustrated, the shunt SAW resonator P1 is coupled to the common node COM by way of a single series BAW resonator S1 in the receive filter 32. The duplexer 30 also includes a transmit filter 34 with a second plurality of BAW resonators S1′, S2′, S3′, P1′, P2′, and P3′. The BAW resonators of the duplexer 30 can achieve relatively low insertion loss in the passbands of the receive filter 32 and the transmit filter 34. The common node COM of the duplexer 30 is coupled to an antenna 35. There can be one or more intervening circuit elements (not illustrated) in an antenna path between the common node COM of the duplexer 30 and the antenna 35.

In the duplexer 30, the receive filter 32 and the transmit filter 34 can be associated with the same frequency band. For duplexer bands where a transmit and receive band gap is relatively small (e.g., Band 3 or Band 25), the second harmonic performance of the first shunt resonator of the receive filter from the common node can impact the second harmonic performance of the transmit filter. The impact of the first shunt resonator from the common node can have the largest contribution to the second harmonic performance of the transmit filter of all shunt resonators of the receive filter.

Any suitable principles and advantages disclosed herein can be applied to a multiplexer where there is a relatively small band gap between passbands of two filters of the multiplexer. The relatively small band gap can be in a range from 10 MHz to 30 MHz in certain applications. In some such applications, the relatively small band gap can be in a range from 10 MHz to 20 MHz. As some examples, the relatively small band gap can be 15 MHz or 20 MHz. The relatively small band gap can be in a range from 10% to 40% of a passband of a filter of the multiplexer in certain applications. In some such applications, the relatively small band gap can be in a range from 20% to 30% of a passband of a filter of the multiplexer. As an example, the relatively small band gap can be 15 MHz and the passband of the filter can be 65 MHz. As another example, the relatively small band gap can be 20 MHz and the passband of the filter can be 75 MHz. The relatively small band gap can be, for example, in a range from 0.5% to 2% of a center frequency of a passband of a filter of the multiplexer, for example. In some such instances, the relatively small band gap can be in a range from 0.5% to 1% of a passband of a filter of the multiplexer. As an example, the relatively small band gap can be 15 MHz and the center frequency of the passband of the filter can be 1962.5 MHz. As another example, the relatively small band gap can be 20 MHz and the center frequency of passband of the filter can be 1842.5 MHz.

As shown in FIG. 4, the first shunt resonator of the receive filter 32 from the common node COM is a shunt surface acoustic wave resonator P1 and the other resonators of the receive filter 32 are BAW resonators S1, S2, S3, P2, and P3. A first filter stage of the receive filter 32 from the common node COM includes a shunt SAW resonator P1 and a series BAW resonator S1. As illustrated, the shunt SAW resonator P1 is coupled to the common node COM by way of the series BAW resonator S1. Alternatively, a first filter stage from a common node can include a first shunt SAW resonator and a series BAW resonator where the series BAW resonator is coupled between the shunt SAW resonator and a receive port of a receive filter. SAW resonators can generally have better second harmonic performance than BAW resonators. Accordingly, the shunt SAW resonator P1 of the receive filter 32 can result in better second harmonic performance for the transmit filter 34 relative to if a BAW resonator were used for the first shunt resonator from the common node COM in the receive filter 32. At the same time, the receive filter 32 can achieve relatively low insertion loss in the receive passband with the BAW resonators S1, S2, S3, P2, and P3. The better linearity of the transmit filter 34 due to the shunt SAW resonator P1 can be particularly advantageous in improving system level linearity in 5G NR applications. Moreover, the receive filter 32 can be implemented for 5G NR bands with relatively wide receive bandwidth to achieve low insertion loss in the receive passband.

FIG. 5 is a graph that illustrates passbands of example filters of the duplexer 30 of FIG. 4 and a frequency response of the shunt SAW resonator P1 of the receive filter 32. The graph of FIG. 5 corresponds to an application where the duplexer 30 is a Band 3 duplexer. This duplexer has a transmit passband B3Tx and a receive passband B3Rx. The anti-resonant frequency of the shunt SAW resonator P1 contributes to the lower band edge of the receive passband B3Rx. However, in certain applications where the transmit passband B3Tx and the receive passband B3Rx are relatively close in the frequency domain, the resonant frequency of the shunt SAW resonator P1 can impact the transmit passband B3Tx. As shown in FIG. 5, a resonant frequency fs of the shunt SAW resonator P1 is in the transmit passband B3Tx. More specifically, the illustrated resonant frequency fs of the shunt SAW resonator P1 is in an upper half of the transmit passband B3Tx. Accordingly, the second harmonic performance of the shunt SAW resonator P1 can impact second harmonic performance of the transmit passband B3Tx in the duplexer 30. This can reduce second harmonic distortion in the transmit passband B3Tx for the transmit filter 34 in the duplexer 30.

FIG. 6 is a schematic diagram of the receive filter 32 that includes a plurality of BAW resonators S1, S2, S3, P2, and P3 and a shunt SAW P1 resonator according to an embodiment. The receive filter 32 can filter a radio frequency signal propagating from an antenna port ANT to a receive port RX. The first shunt acoustic resonator from the antenna port is the shunt SAW resonator P1. The first stage of the receiver filter 32 from the antenna node ANT includes a shunt SAW resonator and a series BAW resonator. FIG. 6 illustrates that the receive filter 32 can be implemented as a standalone filter. Any of the filters disclosed herein can be implemented as a standalone filter in certain applications as suitable.

Additional embodiments of multiplexers will now be discussed. Any suitable combination of features of the multiplexers disclosed herein can be implemented together with each other.

FIG. 7 is a schematic diagram of a duplexer 40 with a first filter 42 associated with a first band and a second filter 44 associated with a second band according to an embodiment. The first filter 42 includes a plurality of BAW resonators S1, S2, S3, P2, and P3 and a shunt SAW resonator P1. The second filter 44 includes a second plurality of BAW resonators S1′, S2′, S3′, P1′, P2′, and P3′. The second filter 44 can be a transmit filter. The first filter 42 can be a receive filter in certain applications. The first filter 42 can be a transmit filter in some other applications. The band gap between respective passbands of the first filter 42 and the second filter 44 can be relatively small. Examples of such a relatively small band gap are provided herein.

The shunt SAW resonator P1 of the first filter 42 can have a resonant frequency in a passband of the second filter 44. By the shunt SAW resonator P1 being a SAW resonator instead of a BAW resonator, the shunt SAW resonator P1 can contribute to the second filter 44 achieving better second harmonic performance.

FIG. 8 is a graph that illustrates passbands of the filters 42 and 44 of the duplexer 40 of FIG. 7 and a frequency response of the shunt SAW resonator P1 of the first filter 42. The graph of FIG. 8 corresponds to an application where the second filter 44 is a Band X transmit filter and the first filter 42 is a Band Y filter. The first filter 42 can be either a Band Y transmit filter or a Band Y receive filter. As shown in FIG. 8, a resonant frequency fs of the shunt SAW resonator P1 of the first filter 42 is in the passband of the Band X transmit passband. Since the resonant frequency fs is within the Band X transmit passband, using a shunt SAW resonator P1 instead of a BAW resonator can increase second harmonic performance for the second filter 44. In the application corresponding to FIG. 8, the resonant frequency fs of the shunt SAW resonator P1 can be significantly lower than the lower frequency side skirt of the passband of the Band Y filter.

FIG. 9 is a schematic diagram of a duplexer 50 that includes a receive filter 52 and a transmit filter 34 according to an embodiment. The receive filter 52 includes a plurality of BAW resonators S2, S3, P2, and P3, a shunt SAW resonator P1, and a series SAW resonator S1″. In the receive filter 54, both the first series resonator S1″ and the first shunt resonator P1 from the common node COM are SAW resonators. Other than both the first series resonator S1″ and the first shunt resonator P1, all remaining acoustic wave resonators of the receive filter 52 can be BAW resonators. In the receive filter 52, the first filter stage from the common node includes a series SAW resonator S1″ and a shunt SAW resonator P1. The shunt SAW resonator P1 can be TCSAW resonator, a non-temperature compensated SAW resonator, or a MPS SAW resonator. The series SAW resonator S1′ can be TCSAW resonator, a non-temperature compensated SAW resonator, or a MPS SAW resonator. The shunt SAW resonator P1 can have a resonant frequency in the passband of the transmit filter 34. The first series resonator S1″ and the first shunt resonator P1 can both contribute to desirable linearity performance of the transmit filter 34. The series SAW resonator S1″ and the shunt SAW resonator P1 can both contribute to desirable linearity performance of the receive filter 52. More generally, the first series acoustic wave resonator and the first shunt acoustic wave resonator of a receive filter of a multiplexer can impact linearity and/or second harmonic performance of a transmit filter of the multiplexer.

FIG. 10 is a schematic diagram of a duplexer 60 that includes a first filter 62 and a second filter 64 according to an embodiment. The first filter 62 includes a plurality of BAW resonators S1, S2, S3, and P3, a plurality of shunt SAW resonators P1 and P2″. In the first filter 62, the first two shunt resonators P1 and P2″ from the common node COM are SAW resonators. The shunt SAW resonators P1 and P2″ can both have resonant frequencies in the passband of the second filter 64. The shunt SAW resonators P1 and P2″ can improve second harmonic performance in the duplexer 60. FIG. 10 illustrates that the second shunt resonator from the common node of a multiplexer can be a SAW resonator to improve linearity of another filter of the multiplexer. The shunt SAW resonator P2″ can be a TCSAW resonator, a non-temperature compensated SAW resonator, or a MPS SAW resonator. One or more additional shunt resonators can be SAW resonators in some applications as suitable. In certain applications, the first filter 62 is a receive filter and second filter 64 is a transmit filter. The first filter 62 and the second filter 64 can be associated with the same frequency band. Alternatively, the first filter 62 and the second filter 64 can be associated with different frequency bands.

FIG. 11 is a schematic diagram of a duplexer 70 with a first filter 72 and a second filter 74 according to an embodiment. The first filter 72 includes a plurality of acoustic wave resonators S1, S2, S3, P2, and P3 of a first type and a shunt acoustic wave resonator P1 of a second type according to an embodiment. The second filter 74 includes a plurality of acoustic wave resonators S1′, S2′, S3′, P1′, P2′, and P3′ of the first type. Acoustic wave resonators of the second type can have better second harmonic performance than acoustic wave resonators of the first type. The second harmonic performance for the acoustic wave resonators can be better in the passband of the second filter 74. In certain instances, acoustic wave resonators of the first type can have a higher Q than acoustic wave resonators of the second type. Any suitable principles and advantages disclosed herein with reference to BAW resonators and SAW resonators can be applied to acoustic wave resonators of the first type and acoustic wave resonators of the second type. The first type of acoustic wave resonators can be FBARs or BAW SMRs. The second type of acoustic wave resonator can be TCSAW, non-TC SAW, or MPS SAW.

Although example embodiments may be discussed with filters or duplexers for illustrative purposes, any suitable principles and advantages disclosed herein can be implemented 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 a shunt SAW resonator and a plurality of BAW resonators in accordance with any suitable principles and advantages disclosed herein.

FIG. 12 is a schematic diagram of a multiplexer 80 with a filter 82 that includes a plurality of BAW resonators S1, S2, S3, P2, and P3 and a shunt SAW resonator P1 according to an embodiment. The illustrated multiplexer 80 also includes filters 84 and 86. In certain embodiments, one or more of the filters 84 and 86 are transmit filters. Any shunt resonator of the filter 82 that has a resonant frequency that overlaps with a passband of any other filter of the multiplexer 80 can be a SAW resonator. For example, in FIG. 12, the shunt SAW resonator P1 of the filter 82 can have a resonant frequency in the passband of the filter 84. In this example, the filter 84 can be a transmit filter. This transmit filter can have a passband that is below the passband of the filter 82 in the frequency domain. Having the shunt resonator P1 be a SAW resonator can be preferred in certain applications because the shunt resonator closest to the common node can typically contribute most to the second harmonic performance of one or more other filters with a lower passband than the filter 82.

In some other embodiments, one or more additional shunt resonators (e.g., P2 and/or P3) of the filter 82 can be SAW resonators instead of BAW resonators when a respective resonant frequency of the one or more additional shunt resonators is in within a passband of another filter of the multiplexer 80. In certain instances, two or more shunt resonators of the filter 82 can be SAW resonators with respective resonant frequencies within the passband of one other filter. In some instances, two or more shunt resonators of the filter 82 can be SAW resonators with respective resonant frequencies within passbands of at least two other filters of the multiplexer 80. A first series acoustic wave resonator of the filter 82 from the common node can be a SAW resonator in some applications.

Compared to TCSAW resonators and non-temperature compensated SAW resonators, MPS SAW resonators can have a higher Qp, where Qp is a quality factor at anti-resonance. The higher Qp for MPS SAW resonators can lead to better receive filter insertion loss. Accordingly, the shunt SAW resonator P1 of any of the embodiments disclosed herein can be an MPS SAW resonator in applications with low receive insertion loss specifications. If a shunt MPS SAW resonator P1 has a Qp that is similar to a BAW resonator, a filter with a shunt MPS SAW resonator and BAW resonators can achieve similar insertion loss to a filter with all BAW resonators.

The filters and multiplexers disclosed herein can be implemented and packaged in a variety of different ways for certain applications. Examples of packaging such filters and multiplexers will be discussed with reference to FIGS. 13 to 15B. In these examples, a SAW die can include one or more TCSAW resonators, one or more non-temperature compensated SAW resonators, one or more MPS SAW resonators, or any suitable combination thereof. In these examples, a SAW die can include one or more TCSAW resonators, one or more non-temperature compensated SAW resonators, one or more MPS SAW resonators, or any suitable combination thereof. In these examples, a BAW die can include one or more FBARS and/or one or more SMRs.

FIG. 13 is a schematic block diagram of acoustic filter dies according to an embodiment. A SAW die 92 can include one or more shunt SAW resonators, such as shunt SAW resonator P1 of any of the embodiments discussed above. A BAW die 93 can include BAW resonators of a filter that includes shunt SAW resonator P1. In some instances, the BAW die 93 can also include BAW resonators of one or more other filters. The SAW die 92 and the BAW die 93 can be on a common package substrate 94. The SAW die 92 and the BAW die 93 can be stacked with each other in certain applications. The SAW die 92 and the BAW die 93 can be positioned laterally relative to each other in various applications. The SAW die 92 can include an electrical connection 95 to electrically connect the shunt SAW resonator P1 to BAW resonators of the same filter on the BAW die 93. The electrical connection 95 can include a bump and/or a through via. Such a through via can extend through a substrate of one of the dies 92 and/or 93.

FIG. 14 is a schematic block diagram of co-packaged acoustic filter dies according to an embodiment. As shown in FIG. 14, the SAW die 92 and the BAW die 93 can be co-packaged within a common package 96 in certain applications. A shunt SAW resonator of the SAW die 92 can be electrically connected to BAW resonators of the BAW die 93 by any suitable electrical connection 95 within the package 96.

FIGS. 15A and 15B are a schematic block diagrams of acoustic wave resonators of a multiplexer on a plurality of dies according to embodiments. As illustrated, in FIG. 15A, a multiplexer 97 can include a first filter with a shunt SAW resonator P1 on a SAW die 92 and SAW resonators of a second filter on the SAW die 92. The first filter can also include other resonators S1, S2, S3, P2, and P3 on the BAW die 93. One or more additional filters of BAW resonators can be included in the multiplexer 97 in certain applications. The one or more additional filters of BAW resonators can be implemented on the BAW die 93. For example, one additional filter of BAW resonators on the BAW die 93 is shown in FIG. 15A. As illustrated in FIG. 15B, a multiplexer 98 can include a first filter with a shunt SAW resonator P1 on a SAW die 92 and other resonators S1, S2, S3, P2, and P3 on the BAW die 93′, SAW resonators of a second filter on the SAW die 92, and a third filter on another BAW die 99. Two or more BAW dies can be included in a multiplexer in accordance with any suitable principles and advantages disclosed herein.

The shunt SAW resonators disclosed herein can be TCSAW resonators, non-temperature compensated SAW resonators, or a MPS SAW resonators in various applications. Examples of such SAW resonators will be discussed with reference to FIGS. 16A to 18.

FIG. 16A is a top view of an interdigital transducer (IDT) electrode 102 of a SAW resonator 100. FIG. 16B is a cross-sectional view of the SAW resonator 100 of FIG. 16A. The IDT electrode 102 is positioned between a first acoustic reflector 104 and a second acoustic reflector 106. The acoustic reflectors 104 and 106 are separated from the IDT electrode 102 by respective gaps. The IDT electrode 102 includes the bus bar 107 and IDT fingers 108 extending from the bus bar 107. The IDT fingers 108 have a pitch of λ. The surface acoustic wave resonator 100 can include any suitable number of IDT fingers 108. The pitch λ of the IDT fingers 108 corresponds to wavelength of a surface acoustic wave generated by the surface acoustic wave resonator 100.

The SAW resonator 100 illustrated in FIG. 16B includes a piezoelectric layer 112 and an IDT electrode 102 on the piezoelectric layer 112. The piezoelectric layer 112 can be a lithium niobate layer or a lithium tantalate layer, for example. The IDT electrode 102 can include any suitable material for an electrode, such as tungsten, aluminum, molybdenum, the like, or any suitable combination or alloy thereof. The SAW resonator 110 can be arranged as a shunt resonator in a filter in accordance with any suitable principles and advantages disclosed herein.

FIG. 17 is a cross-sectional view of a TCSAW resonator 120. The illustrated TCSAW resonator 120 includes a piezoelectric layer 112, an IDT electrode 102 on the piezoelectric layer 112, and a temperature compensation layer 122 over the IDT electrode 102. The TCSAW resonator 120 is like the SAW resonator 110, except that the TCSAW resonator 120 includes a temperature compensation layer 122 over the IDT electrode 102. The TCSAW resonator 120 can be arranged as a shunt resonator in a filter in accordance with any suitable principles and advantages disclosed herein.

The temperature compensation layer 122 can bring the temperature coefficient of frequency (TCF) of the TCSAW resonator 120 closer to zero relative to a similar SAW resonator without the temperature compensation layer 122. The temperature compensation layer 122 can have a positive TCF. This can compensate for the piezoelectric layer 112 having a negative TCF. The temperature compensation layer 122 can be a silicon dioxide (SiO₂) layer. The temperature compensation layer 122 can include any other suitable temperature compensating material including without limitation a tellurium dioxide (TeO₂) layer or a silicon oxyfluoride (SiOF layer). The temperature compensation layer 122 can include any suitable combination of SiO₂, TeO₂, and/or SiOF.

FIG. 18 is a cross-sectional view of an MPS SAW resonator 130. The illustrated MPS SAW resonator 130 includes a multilayer piezoelectric substrate including a piezoelectric layer 112 and a support substrate 132. The MPS SAW resonator 130 also includes an IDT electrode 102 on the piezoelectric layer 112. The MPS SAW resonator 130 is like the SAW resonator 110, except that the MPS SAW resonator 130 includes the support substrate 132. In certain applications, the piezoelectric layer 112 can be thinner in the MPS SAW resonator 130 compared to in the SAW resonator 110. For example, the piezoelectric layer 112 can have a thickness of less than λ in the MPS SAW resonator 130, in which A is a wavelength of a surface acoustic wave generated by the MPS SAW resonator 130. In some other instances, the piezoelectric layer 112 can have a thickness on the order of 10s of λ, in which λ is a wavelength of a surface acoustic wave generated by the MPS SAW resonator 130. The MPS SAW resonator 130 can be arranged as a shunt resonator in a filter in accordance with any suitable principles and advantages disclosed herein.

The support substrate 132 can be a silicon substrate, a quartz substrate, a sapphire substrate, a polycrystalline spinel substrate, or any other suitable carrier substrate. As one example, the MPS SAW resonator 130 can include a piezoelectric layer 112 that is lithium tantalate and a support substrate 132 that is silicon.

In some instances (not illustrated), one or more additional layers can be included in the multilayer piezoelectric substrate of an MPS SAW resonator. Non-limiting examples of a layer of the one or more additional layers include a silicon dioxide layer, a silicon nitride layer, an aluminum nitride layer, an adhesion layer, a dispersion adjustment layer, and a thermal dissipation layer. As an illustrative example, a multilayer piezoelectric substrate can include a lithium tantalate layer over a silicon dioxide layer over an aluminum nitride layer over a silicon layer. As one more illustrative example, a multilayer piezoelectric substrate can include a lithium niobate layer over a silicon dioxide layer over a high impedance layer, in which the high impedance layer has a higher acoustic impedance than the lithium niobate layer. In some instances (not illustrated), a temperature compensation layer can be included over an IDT electrode of an MPS SAW resonator.

A filter that includes a shunt SAW resonator and a plurality of BAW resonators in accordance with any suitable principles and advantages disclosed herein be arranged to filter a radio frequency signal in a fifth generation 5G NR operating band within Frequency Range 1 (FR1). FR1 can be from 410 MHz to 7.125 gigahertz (GHz), for example, as specified in a current 5G NR specification. A filter that includes a shunt SAW resonator and a plurality of BAW resonators in accordance with any suitable principles and advantages disclosed herein can be arranged to filter a radio frequency signal in a fourth generation (4G) Long Term Evolution (LTE) operating band. A filter that includes a shunt SAW resonator and a plurality of BAW resonators in accordance with any suitable principles and advantages disclosed herein can be included in a filter having a passband that includes a 4G LTE operating band and a 5G NR operating band. Such a filter can be implemented in a dual connectivity application, such as an E-UTRAN New Radio-Dual Connectivity (ENDC) application. A multiplexer including any such filters can include one or more other filters with a passband corresponding to a 5G NR operating band and/or a 4G LTE operating band.

Filters disclosed herein can be implemented in a standalone filter and/or in a filter in any suitable multiplexer. Example multiplexers will be discussed with reference to FIGS. 19A to 19C. Any suitable principles and advantages of these filters and/or multiplexers disclosed herein can be implemented together with each other.

FIG. 19A is a schematic diagram of a multiplexer 164. The multiplexer 164 includes a plurality of filters 160A to 160N coupled together at a common node COM. The plurality of filters can include any suitable number of filters including, for example, 2 filters, 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 160A to 160N 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 160A is an acoustic wave filter arranged to filter a radio frequency signal. The first filter 160A can include 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 160A includes a shunt SAW resonator and a plurality of BAW resonators in accordance with any suitable principles and advantages disclosed herein. The other filter(s) of the multiplexer 164 can include one or more acoustic wave filters, one or more acoustic wave filters that include BAW resonators, one or more acoustic wave filters that include a shunt SAW resonator and a plurality of BAW resonators, one or more LC filters, one or more hybrid acoustic wave LC filters, the like, or any suitable combination thereof.

FIG. 19B is a schematic diagram of a multiplexer 166. The multiplexer 166 is like the multiplexer 164 of FIG. 19A, except that the multiplexer 166 implements switched multiplexing. In switched multiplexing, a filter is coupled to a common node via a switch. In the multiplexer 166, the switches 167A to 167N can selectively electrically connect respective filters 160A to 160N to the common node COM. For example, the switch 167A can selectively electrically connect the first filter 160A the common node COM via the switch 167A. Any suitable number of the switches 167A to 167N can electrically a respective filters 160A to 160N to the common node COM in a given state. Similarly, any suitable number of the switches 167A to 167N can electrically isolate a respective filter 160A to 160N to the common node COM in a given state. The functionality of the switches 167A to 167N can support various carrier aggregations.

FIG. 19C is a schematic diagram of a multiplexer 168. The multiplexer 168 illustrates that a multiplexer can include any suitable combination of hard multiplexed and switched multiplexed filters. A shunt SAW resonator and a plurality of BAW resonators can be included in a filter that is hard multiplexed to the common node of a multiplexer. Alternatively or additionally, a shunt SAW resonator and a plurality of BAW resonators in accordance with any suitable principles and advantages disclosed herein can be included in a filter that is switch multiplexed to the common node of a multiplexer.

The acoustic wave filters and multiplexers 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 filters, or multiplexers 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. 20 to 24 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. 21, 22, and 24, 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. 20 is a schematic diagram of a radio frequency module 170 that includes an acoustic wave component 172 according to an embodiment. The illustrated radio frequency module 170 includes the acoustic wave component 172 and other circuitry 173. The acoustic wave component 172 can include one or more filters and/or multiplexers in accordance with any suitable combination of features of the filters and/or multiplexers disclosed herein. The acoustic wave component 172 can include an acoustic wave filter that includes a plurality of bulk acoustic wave resonators and a shunt SAW resonator, for example.

The acoustic wave component 172 shown in FIG. 20 includes acoustic wave devices 174 and terminals 175A and 175B. The acoustic wave devices 174 can include at least one shunt SAW resonator and a plurality of BAW resonators in accordance with any suitable principles and advantages disclosed herein. The terminals 175A and 174B 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 172 and the other circuitry 173 are on a common packaging substrate 176 in FIG. 20. The packaging substrate 176 can be a laminate substrate. The terminals 175A and 175B can be electrically connected to contacts 177A and 177B, respectively, on the packaging substrate 176 by way of electrical connectors 178A and 178B, respectively. The electrical connectors 178A and 178B can be bumps or wire bonds, for example.

The other circuitry 173 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 173 can be electrically connected to the one or more acoustic wave devices 174. The radio frequency module 170 can include one or more packaging structures to, for example, provide protection and/or facilitate easier handling of the radio frequency module 170. Such a packaging structure can include an overmold structure formed over the packaging substrate 176. The overmold structure can encapsulate some or all of the components of the radio frequency module 170.

FIG. 21 is a schematic block diagram of a module 180 that includes duplexers 181A to 181N and an antenna switch 182. One or more of the duplexers 181A to 181N be implemented in accordance with any suitable principles and advantages disclosed herein. Any suitable number of duplexers 181A to 181N can be implemented. The antenna switch 182 can have a number of throws corresponding to the number of duplexers 181A to 181N. The antenna switch 182 can include one or more additional throws coupled to one or more filters external to the module 180 and/or coupled to other circuitry. The antenna switch 182 can electrically couple a selected duplexer to an antenna port of the module 180.

FIG. 22 is a schematic block diagram of a module 190 that includes a power amplifier 192, a radio frequency switch 194, and duplexers 181A to 181N according to an embodiment. The power amplifier 192 can amplify a radio frequency signal. The radio frequency switch 194 can be a multi-throw radio frequency switch. The radio frequency switch 194 can electrically couple an output of the power amplifier 192 to a selected transmit filter of the duplexers 181A to 181N. One or more of the duplexers 181A to 181N can be implemented in accordance with any suitable principles and advantages disclosed herein. Any suitable number of duplexers 181A to 181N can be implemented.

FIG. 23 is a schematic block diagram of a module 200 that includes filters 202A to 202N, a radio frequency switch 204, and a low noise amplifier