Patent ID: 12231111

DETAILED DESCRIPTION

The detailed description set forth below in connection with the appended drawings is intended as a description of exemplary implementations and is not intended to represent the only implementations in which the invention may be practiced. The term “exemplary” used throughout this description means “serving as an example, instance, or illustration,” and should not necessarily be construed as preferred or advantageous over other exemplary implementations. The detailed description includes specific details for the purpose of providing a thorough understanding of the exemplary implementations. In some instances, some devices are shown in block diagram form. Drawing elements that are common among the following figures may be identified using the same reference numerals.

Electroacoustic devices such as surface acoustic wave (SAW) resonators, which employ electrode structures on a surface of a piezoelectric material, are being designed to cover more frequency ranges (e.g., 500 MHz to 6 GHz), to have higher bandwidths (e.g., up to 25%), and to have improved efficiency and performance. In general, certain SAW resonators are designed to cause propagation of an acoustic wave in a particular direction through the piezoelectric material (e.g., main acoustic wave mode). However, due to the nature of the particular piezoelectric material used and the way the piezoelectric material is excited by the electrode structure, at least some undesired acoustic wave modes in other directions may be generated. For example, transversal acoustic wave modes that are transverse to the direction of the main (e.g., fundamental) acoustic wave mode may be excited in the piezoelectric material. These transversal acoustic wave modes may be undesirable and have an adverse impact on filter performance (e.g., introducing ripples in the passband of the filter). By adjusting characteristics of the electrode structure, acoustic velocities in various transversal regions may be controlled in a manner to reduce transversal acoustic wave modes. The characteristics that are adjusted may depend on the type of piezoelectric material and other characteristics of the SAW resonator. Aspects of the present disclosure are directed to particular electrode structure configurations that reduce transversal acoustic wave modes. In particular, the electrode structure configurations described herein include introducing conductive structures that are disposed between busbars and electrode fingers of the electrode structure. The conductive structures are connected to and between at least portion of the electrode fingers and have a height that is less than a height of the electrode fingers to control an acoustic velocity in certain regions to reduce transversal modes.

FIG.1Ais a diagram of a perspective view of an example of an electroacoustic device100. The electroacoustic device100may be configured as or be a portion of a SAW resonator. In certain descriptions herein, the electroacoustic device100may be referred to as a SAW resonator. However, there may be other electroacoustic device types that may be constructed based on the principles described herein. The electroacoustic device100includes an electrode structure104, that may be referred to as an interdigital transducer (IDT), on the surface of a piezoelectric material102. The electrode structure104generally includes first and second comb shaped electrode structures (conductive and generally metallic) with electrode fingers extending from two busbars towards each other arranged in an interlocking manner in between two busbars (e.g., arranged in an interdigitated manner). An electrical signal excited in the electrode structure104(e.g., applying an AC voltage) is transformed into an acoustic wave106that propagates in a particular direction via the piezoelectric material102. The acoustic wave106is transformed back into an electrical signal and provided as an output. In many applications, the piezoelectric material102has a particular crystal orientation such that when the electrode structure104is arranged relative to the crystal orientation of the piezoelectric material102, the acoustic wave mainly propagates in a direction perpendicular to the direction of the fingers (e.g., parallel to the busbars).

FIG.1Bis a diagram of a side view of the electroacoustic device100ofFIG.1Aalong a cross-section107shown inFIG.1A. The electroacoustic device100is illustrated by a simplified layer stack including a piezoelectric material102with an electrode structure104disposed on the piezoelectric material102. The electrode structure104is conductive and generally formed from metallic materials. The piezoelectric material may be formed from a variety of materials such as quartz, lithium tantalate (LiTaO3), lithium niobite (LiNbO3), doped variants of these, or other piezoelectric materials. It should be appreciated that more complicated layer stacks including layers of various materials may be possible within the stack. For example, optionally, a temperature compensation layer108denoted by the dashed lines may be disposed above the electrode structure104. The piezoelectric material102may be extended with multiple interconnected electrode structures disposed thereon to form a multi-resonator filter or to provide multiple filters. While not illustrated, when provided as an integrated circuit component, a cap layer may be provided over the electrode structure104. The cap layer is applied so that a cavity is formed between the electrode structure104and an under surface of the cap layer. Electrical vias or bumps that allow the component to be electrically connected to connections on a substrate (e.g., via flip-chip or other techniques) may also be included.

FIG.2Ais a diagram of a top view of an example of an electrode structure204aof an electroacoustic device100. The electrode structure204ahas an IDT205that includes a first busbar222(e.g., first conductive segment or rail) electrically connected to a first terminal220and a second busbar224(e.g., second conductive segment or rail) spaced from the first busbar222and connected to a second terminal230. A plurality of conductive fingers226are connected to either the first busbar222or the second busbar224in an interdigitated manner. Fingers226connected to the first busbar222extend towards the second busbar224but do not connect to the second busbar224so that there is a small gap between the ends of these fingers226and the second busbar224. Likewise, fingers226connected to the second busbar224extend towards the first busbar222but do not connect to the first busbar222so that there is a small gap between the ends of these fingers226and the first busbar222.

In the direction along the busbars, there is an overlap region including a central region where a portion of one finger overlaps with a portion of an adjacent finger as illustrated by the central region225. This central region225including the overlap may be referred to as the aperture, track, or active region where electric fields are produced between fingers226to cause an acoustic wave to propagate in this region of the piezoelectric material102. The periodicity of the fingers226is referred to as the pitch of the IDT. The pitch may be indicted in various ways. For example, in certain aspects, the pitch may correspond to a magnitude of a distance between fingers in the central region225. This distance may be defined, for example, as the distance between center points of each of the fingers (and may be generally measured between a right (or left) edge of one finger and the right (or left) edge of an adjacent finger when the fingers have uniform thickness). In certain aspects, an average of distances between adjacent fingers may be used for the pitch. The frequency at which the piezoelectric material vibrates is a self-resonance (also called a “main-resonance”) frequency of the electrode structure204a. The frequency is determined at least in part by the pitch of the IDT205and other properties of the electroacoustic device100.

The IDT205is arranged between two reflectors228which reflect the acoustic wave back towards the IDT205for the conversion of the acoustic wave into an electrical signal via the IDT205in the configuration shown and to prevent losses (e.g., confine and prevent escaping acoustic waves). Each reflector228has two busbars and a grating structure of conductive fingers that each connect to both busbars. The pitch of the reflector may be similar to or the same as the pitch of the IDT205to reflect acoustic waves in the resonant frequency range. But many configurations are possible.

When converted back to an electrical signal, the converted electrical signal may be provided as an output such as one of the first terminal220or the second terminal230while the other terminal may function as an input.

A variety of electrode structures are possible.FIG.2Amay generally illustrate a one-port configuration. Other 2-port configurations are also possible. For example, the electrode structure204amay have an input IDT205where each terminal220and230functions as an input. In this event, an adjacent output IDT (not illustrated) that is positioned between the reflectors228and adjacent to the input IDT205may be provided to convert the acoustic wave propagating in the piezoelectric material102to an electrical signal to be provided at output terminals of the output IDT.

FIG.2Bis a diagram of a top view of another example of an electrode structure204bof an electroacoustic device100. In this case, a dual-mode SAW (DMS) electrode structure204bis illustrated that is a structure which may induce multiple resonances. The electrode structure204bincludes multiple IDTs along with reflectors228connected as illustrated. The electrode structure204bis provided to illustrate the variety of electrode structures that principles described herein may be applied to including the electrode structures204aand204bofFIGS.2A and2B.

It should be appreciated that while a certain number of fingers226are illustrated, the number of actual fingers and lengths and width of the fingers226and busbars may be different in an actual implementation. Such parameters depend on the particular application and desired frequency of the filter. In addition, a SAW filter may include multiple interconnected electrode structures each including multiple IDTs to achieve a desired passband (e.g., multiple interconnected resonators or IDTs to form a desired filter transfer function).

FIG.3Ais a diagram of a perspective view of another example of an electroacoustic device300. The electroacoustic device300(e.g., that may be configured as or be a part of a SAW resonator) is similar to the electroacoustic device100ofFIG.1Abut has a different layer stack. In particular, the electroacoustic device300includes a thin piezoelectric material302that is provided on a substrate310(e.g., silicon). The electroacoustic device300may be referred to as a thin-film SAW resonator (TF-SAW) in some cases. Based on the type of piezoelectric material302used (e.g., typically having higher coupling factors relative to the electroacoustic device100ofFIG.1) and a controlled thickness of the piezoelectric material302, the particular acoustic wave modes excited may be slightly different than those in the electroacoustic device100ofFIG.1A. Based on the design (thicknesses of the layers, and selection of materials, etc.), the electroacoustic device300may have a higher Q-factor as compared to the electroacoustic device100ofFIG.1A. The piezoelectric material302, for example, may be Lithium tantalate (LiTa03) or some doped variant. Another example of a piezoelectric material302forFIG.3may be Lithium niobite (LiNbO3). In general, the substrate310may be substantially thicker than the piezoelectric material302(e.g., potentially on the order of 50 to 100 times thicker as one example—or more). The substrate310may include other layers (or other layers may be included between the substrate310and the piezoelectric material302).

FIG.3Bis a diagram of a side view of the electroacoustic device300ofFIG.3Ashowing an exemplary layer stack (along a cross-section307). In the example shown inFIG.3B, the substrate310may include sublayers such as a substrate sublayer310-1(e.g., of silicon) that may have a higher resistance (e.g., relative to the other layers—high resistivity layer). The substrate310may further include a trap rich layer310-2(e.g., poly-silicon). The substrate310may further include a compensation layer310-3(e.g., silicon dioxide (SiO2) or another dielectric material) that may provide temperature compensation and other properties. These sub-layers may be considered part of the substrate310or their own separate layers. A relatively thin piezoelectric material302is provided on the substrate310with a particular thickness for providing a particular acoustic wave mode (e.g., as compared to the electroacoustic device100ofFIG.1Awhere the thickness of the piezoelectric material102may not be a significant design parameter beyond a certain thickness and may be generally thicker as compared to the piezoelectric material302of the electroacoustic device300ofFIGS.3A and3B). The electrode structure304is positioned above the piezoelectric material302. In addition, in some aspects, there may be one or more layers (not shown) possible above the electrode structure304(e.g., such as a thin passivation layer).

Based on the type of piezoelectric material, the thickness, and the overall layer stack, the coupling to the electrode structure304and acoustic velocities within the piezoelectric material in different regions of the electrode structure304may differ between different types of electroacoustic devices such as between the electroacoustic device100ofFIG.1Aand the electroacoustic device300ofFIGS.3A and3B.

With respect to the electroacoustic device100and electroacoustic device300ofFIGS.1A and3A, one source of potential losses that are desirable to be reduced are spurious acoustic wave modes that may include transversal acoustic modes. These transversal acoustic wave modes may result in undesired ripples in the passband of the filter. In general, the electroacoustic devices are designed to confine or guide the acoustic wave in the central region225(e.g., active region as indicted inFIG.2A) to avoid radiation into the bulk (e.g., in a z-direction that is perpendicular to the surface) or laterally. Confinement of the acoustic wave may lead to generation of a series of transversal acoustic wave modes (e.g., generally in a direction towards the busbars and more parallel to the fingers226). In particular, the acoustic wave excited propagates perpendicular to the fingers226but also at certain angles to the main propagation direction which may correspond to various transversal acoustic wave modes. It is desirable to reduce these transversal acoustic wave modes as they lead to sharp, deep, dips in a filter passband when corresponding electroacoustic device tracks are electrically connected.

FIG.4is a diagram of a portion of an electrode structure404of an electroacoustic device aligned with a plot illustrating acoustic velocity profiles in different regions of the electroacoustic device. The electrode structure404ofFIG.4shows a portion of an IDT405similar to that described with reference toFIG.2Awith a first busbar422, a second busbar424, and interdigitated fingers426. As the angles and frequency position of the transversal acoustic wave modes depend on the directional acoustic wave velocity, in an aspect, the transversal velocity profile within the acoustic track can designed in such a way to reduce transversal acoustic wave modes and promote excitation of the main or fundamental mode. In particular, the electrode structure404(and potentially other layers) can be adjusted in different regions of the electrode structure404to adjust the transversal velocity profile within the acoustic track to reduce transversal acoustic modes (e.g., effectively forming a transversal acoustic waveguide). In certain aspects, an acoustic velocity may correspond to an acoustic velocity of the fundamental mode of the electroacoustic device, although the velocity may be understood more generally in certain respects to capture or relate to different modes.

FIG.4illustrates different regions of the electrode structure404that may be designed or structurally altered to adjust the transversal velocity profile. As described with respect toFIG.2A, a central region425(or active track region or aperture) is defined where interdigitated fingers overlap (e.g., in the direction parallel to the busbar) and is where the main or fundamental mode is generally intended and designed to propagate perpendicular to the fingers426.

In an aspect, barrier regions429(e.g., gap regions) are defined outside the central region425that include regions between the first busbar422and fingers426aconnected to the opposite second busbar424. More particularly, the barrier regions429include a first barrier region429aand a second barrier region429b. The first barrier region429ais defined between the first busbar422and unconnected ends of a first set of fingers426aconnected to the second busbar424. The second barrier region429bis defined between the second busbar424and unconnected ends of a second set of fingers426bconnected to the first busbar422. The barrier regions429may sometimes correspond to or be referred to as a transversal gap which is included in IDTs to separate metal structures of different potentials (i.e., separate fingers connected to opposite busbars where the busbars have different potentials).

To adjust the transversal velocity profile, the number of fingers per wavelength within the barrier regions429(e.g., one finger instead of the two fingers as illustrated in the central region425) along with the distance or size of the barrier regions429are selected (and/or with adjustment of other characteristics within the barrier regions429) so that there is a higher acoustic wave velocity, particularly higher than in the central region425. The plot440to the right of the electrode structure404illustrates relative velocities of each region of the electrode structure404where the y-axis represents and is aligned with different regions of the electrode structure404along the direction the fingers426extend. As illustrated by line450(see dashed line portions), the acoustic velocity along the x-axis is higher in the barrier regions429as compared to the acoustic velocity in the central region425(e.g., active track). In general, as an acoustic wave may tend to propagate more easily where velocity is lower, a relative higher wave velocity may be a barrier for the acoustic wave. A distance/width of the barrier regions429(e.g., at least 2-3 wavelengths for certain applications), which may be wider than what may be required to sufficiently separate metal structures of different potentials, provides a sufficient barrier and prevents acoustic waves from coupling to outside regions.

In addition to the barrier regions429, further regions referred to as a trap regions427are provided at either outer boundary of the central region425(e.g., bound on each end) where the fingers426overlap. In particular, a first trap region427ais positioned towards or at a first end (e.g., boundary) of the central region425(e.g., active region) and between the first barrier region429aand the central region425(e.g., in a region of the fingers426that is towards an end of the first set of fingers426athat are connected to the second busbar424where the region is distal from the second busbar424). A second trap region427bis positioned towards or at a second end of the central region425(opposite the first end) and between the second barrier region429band the central region425(e.g., in a region of the fingers that is towards an end of the second set of fingers426bthat are connected to the first busbar422where the region is distal from the first busbar422). The trap regions427may correspond to outer edges or outer regions of the central region425. A structural characteristic in the trap regions427different than in the central region425is provided to create a region of the electroacoustic device aligned with the trap regions427that has a reduced acoustic wave velocity, in particular to be lower than an acoustic wave velocity in a region defined by the central region425. Such structural characteristics may include widening the electrode fingers426in the trap regions427or increasing the height of the electrode fingers426in the trap regions427, but many implementations are possible. In general, an acoustic wave may tend to propagate more easily where velocity is lower. The trap regions427with a lower acoustic wave velocity may thereby provide a way to shape the transversal amplitude profile of the fundamental acoustic wave mode.

As a result of designing and selecting sizes for the barrier regions429, the trap regions427, and the central region425, the fundamental acoustic wave mode amplitude in the transversal directions (e.g., in the direction of the fingers426) may be conformed towards a rectangular profile as indicated by line444of the plot440. The rectangular profile caused by the different acoustic wave velocities in the different regions corresponds to a mode where undesired transversal modes are suppressed. Line442in the plot440corresponds to the fundamental mode amplitude in the transversal direction without trap regions which may lead to undesired transversal modes. Line446in the plot440corresponds to the fundamental mode amplitude in the transversal direction where the trap regions427are insufficiently deep (e.g., acoustic wave is not sufficiently slowed within that region). Although improved, undesired transversal modes may continue to impact performance. Line448in the plot440corresponds to the fundamental mode amplitude in the transversal direction where the trap regions427are too deep. This may also result in undesired transversal acoustic wave modes. By adjusting the characteristics of the barrier regions429and the trap regions427, the fundamental mode amplitude in the transversal direction can be adjusted to conform towards the rectangular profile indicated by line444and transversal modes are effectively suppressed. The techniques for providing the barrier regions429and the trap regions427in such configurations are sometimes referred to a piston mode.

FIGS.5A and5Bare diagrams of examples of electrode structures504aand504bthat illustrate examples of different implementations of trap regions527-1and527-2as defined with reference toFIG.4. Barrier regions529are denoted but are not particularly illustrated or drawn to scale. Rather, the electrode structures504aand504bare provided to illustrate implementations of the trap regions527-1(FIG.5A) and527-2(FIG.5B). For example, in the electrode structure504aofFIG.5A, the trap regions527-1are illustrated with a portion509of the electrode structure504ahaving an increased thickness relative to other portions of the active region. A side view is shown on right along a cross-section531. The increased height may result in a slower acoustic velocity in the trap regions527-1. In another implementation, as illustrated by the electrode structure504bofFIG.5B, the electrode structure504bwithin the trap regions527-2has a width that is wider as compared to the active region. These wider widths may result in a slower acoustic velocity in the trap regions527-2. In some implementations, the trap regions527-2may have both a width that is wider as compared to the active region along with an increased height (e.g., thickness) as illustrated inFIG.5A. As such, any techniques described herein for the trap regions527-2may be combined. In other implementations, other materials (e.g., a layer of dielectric material) may be positioned over the trap regions427(FIG.4) to reduce an acoustic velocity in the trap regions427(e.g., or other types of mass loading). In addition, one or more trimming operations may adjust or have a structural effect in the various regions so that the relative acoustic velocity in the trap regions427are reduced relative to the central region425. Other implementations using different techniques may also be employed such that structural characteristics in the trap regions427are adjusted and different than in the central region425so that there is reduced acoustic velocity in trap regions427.

In certain electroacoustic device designs, the barrier regions429may be a sufficient parameter that can be adjusted to create the desired transversal acoustic velocity profile to work in conjunction with the trap regions427to suppress transversal acoustic modes (e.g., achieve relatively higher acoustic velocity than in the active region). However, for certain other electroacoustic devices desired using different materials, configuring the size of the barrier regions429may not create a transversal mode acoustic profile that causes the acoustic velocity in the barrier regions429to be sufficiently high to create the desired transversal velocity profile. For example,FIGS.3A and3Billustrate a thin-film type of electroacoustic device300. In some implementations, the piezoelectric material302in this electroacoustic device300may be formed from Lithium tantalate (LiTaO3). The acoustic velocity profile for Lithium tantalate may be different than other systems based on the coupling factor (and may be due in part to the particular layer stack and thickness of Lithium tantalate such as for the thin-film type shown inFIGS.3A and3B). For example, for a Lithium tantalate based device, the difference in velocity between the central region425and the barrier regions429may be lower and therefore transversal modes may not be as easily confined over the entire stopband width of the electroacoustic device300. In addition, for a Lithium tantalate based electroacoustic device, in the central region425, increased frequency may correspond to increasing angles from the main acoustic wave propagation direction (e.g., sometimes referred to as a “convex slowness”). However, for a Lithium tantalate based system, in the barrier regions429, mode frequency decreases with increasing propagation angles (a “concave slowness” in barrier regions429). A concave slowness may be attractive for the acoustic wave and spurious modes may be formed. Having a concave slowness in the barrier regions429may therefore result in undesired modes to be excited within the barrier regions429. As such, it is desirable to provide a structure that achieves a convex slowness in the barrier regions429to reduce unwanted modes in the barrier regions429along with providing a desired higher acoustic velocity within the barrier regions429.

Certain techniques to address these issues for such electroacoustic devices may be difficult to implement for higher metallization ratios and higher metal heights (and due to other manufacturing difficulties of such solution) and may increase ohmic losses. In addition, barrier regions429as described with reference toFIG.4(e.g., including 1 strip per wavelength) may lead to concave slowness for certain configurations such as when using Lithium tantalate based devices as described above with reference toFIG.3A. Aspects of the disclosure described herein relate to implementations for the barrier regions429to suppress transversal modes while being easier to manufacture and design for. These techniques may apply to a variety of different types of electroacoustic devices, but may have particular advantages for thin-film electroacoustic devices using Lithium tantalate.

FIG.6Ais a diagram of an example of an electrode structure604of an electroacoustic device (e.g., a SAW resonator) that reduces transversal acoustic modes according to aspects of the present disclosure. The electrode structure604may be disposed on or above a piezoelectric material602(or be arranged relative to the piezoelectric material602so that there is an electroacoustic coupling between the piezoelectric material602and the electrode structure604). The electrode structure604(which may be in the form of or include an IDT605) includes a first busbar622and a second busbar624. In some aspects, the first busbar622and the second busbar624may be referred to as conductive connection structures more generally. In certain aspects, the first busbar622and the second busbar624extend along a direction and are in parallel or to each other (although certain differences in angles between the busbars may be possible).

The electrode structure604further includes electrode fingers626arranged in an interdigitated manner and connected to either the first busbar622or the second busbar624. In particular, the electrode fingers626include a first plurality of fingers626aconnected to the first busbar622and extending towards the second busbar624. In addition, the electrode fingers626include a second plurality of fingers626bconnected to the second busbar624and extending towards the first busbar622. The electrode fingers626have a pitch652. Similarly as described above with reference toFIG.2, in certain aspects, the pitch652may correspond to a periodicity of the electrode fingers626. In certain aspects, the pitch652may be indicated by a distance between centers of adjacent electrode fingers626. When the electrode fingers626are generally of the same width, then this distance may also be defined by the distance between left edges of adjacent electrode fingers626(or right edges). In addition, in certain aspects where the electrode fingers626are not uniformly distributed, the pitch652may be indicated by an average of the distances between centers of adjacent electrode fingers626. Other ways to measure or indicate the pitch652may also be possible. In certain aspects, the electrode fingers626extend in a direction normal to a direction of the first busbar622and the second busbar624(although certain other angles are possible).

The electrode structure604includes a first conductive structure629adisposed between each of the first plurality of fingers626a. In certain aspects, the first conductive structure629ais connected to each of the first plurality of fingers. The first conductive structure629ahas a height that is less than a height of the first plurality of fingers626a. This is illustrated inFIG.6B.

FIG.6Bis a diagram of a side view of the electrode structure604ofFIG.6Aalong a cross-section654. As illustrated, the height of the first conductive structure629ais less than the height of the first plurality of electrode fingers626a.

The first conductive structure629ais disposed between the first busbar622and the second plurality of electrode fingers626b(e.g., in the first barrier region429aas described with reference toFIG.4A). There is a gap between the first conductive structure629aand the second plurality of electrode fingers626bin a direction along which the second plurality of electrode fingers626bextend. In certain aspects, the first conductive structure629ais connected to the first busbar622. However, in certain implementations it is possible that the first conductive structure629bis unconnected to the first busbar622(e.g., there is a gap between the first busbar622and one or more portions of the first conductive structure629a).

The electrode structure604includes a second conductive structure629bdisposed between each of the second plurality of fingers626b. In certain aspects, the second conductive structure629bis connected to each of the second plurality of fingers. The second conductive structure629bhas a height that is less than a height of the second plurality of fingers626b(e.g., similarly as illustrated with respect to the side view shown inFIG.6B). The second conductive structure629bis disposed between the second busbar624and the first plurality of electrode fingers626a(e.g., in the second barrier region429bas described with reference toFIG.4A). There is a gap between the second conductive structure629band the first plurality of electrode fingers626ain a direction along which the first plurality of electrode fingers626aextend. In certain aspects, the second conductive structure629bis connected to the second busbar624. However, in certain implementations it is possible that the second conductive structure629bis unconnected to the second busbar624(e.g., there is a gap between the second busbar624and one or more portions of the second conductive structure629b). Together, the first conductive structure629aand the second conductive structure629bmay be referred to as conductive structure629. In some aspects, the conductive structures629extend in a same direction as the first busbar622and the second busbar624.

The height of the conductive structures629may vary based on the application and height of the electrode fingers626but may be generally substantially lower than the height of the electrode fingers626. A variety of heights may be possible. As one example only, the height of the conductive structures629may be 5-20 nm relative to a 150 nm height of the electrode fingers626. In general there should be some reflection from the electrode fingers626. Stated another way, if the height of the conductive structures629is close to the height of the busbars622and624then the conductive structures629would functionally merge into the busbar. In another example, the height (e.g., thickness) of the conductive structures629is between a few nanometers and a few ten nanometers. Other exemplary ranges may be between 10-25 nm although higher is also possible. In an example, the height of the conductive structures629is at least less than half of a height of the electrode fingers626. In another example, the height of the conductive structures629is less than ten to fifteen percent of a wavelength for an operating frequency of the electroacoustic device.

In certain aspects, the conductive structures629include different conductive portions between each of the respective fingers. For example, the first conductive structure629amay include multiple conductive portions between each of the first plurality of fingers626a.

As illustrated, and similar to that described with reference toFIG.4, the electrode fingers626have a central region625that may correspond to or include an active region (also referred to as a track or aperture). In this region, the first plurality of fingers626aand the second plurality of fingers626boverlap in the direction along which the first busbar622and the second busbar624extend. A first trap region627aand a second trap region627b, together trap regions627, are defined that are located on boundaries of the central region625(see also description of the trap regions427described with reference toFIG.4). In some aspects, the first trap region627amay be positioned in a region of the electrode fingers626aligned with a portion that is towards or at an end portion of the second plurality of fingers626bthat is proximate to the first conductive structure629a(where there is a gap between the first conductive structure629aand the second plurality of fingers626b). In accordance with this, the second trap region627bmay be positioned in a region of the electrode fingers626aligned with a portion that is towards an end portion of the first plurality of fingers626athat is proximate to the second conductive structure629b(where there is a gap between the second conductive structure629band the first plurality of fingers626a). As described above with reference toFIGS.4,5A, and5B, a structural characteristic of the electroacoustic device is different in the first trap region427aand the second trap region627brelative to the central region625. For example, the structural characteristic may correspond to a portion of the electrode fingers626having an increased width or increased height within the first and second trap regions627or any other characteristic as described above with reference toFIGS.4,5A, and5B. In particular, the structural characteristic causes an acoustic velocity in a region defined by the trap regions627to be lower relative to acoustic velocities in the central region625(and also lower than the barrier regions including the conductive structures629). In certain aspects, a dimension of the trap regions627in the direction in which the electrode fingers626extend may be between one-half of the pitch652of the electrode fingers626and twice the pitch of the electrode fingers626(although amounts may vary based on the application).

As noted, the conductive structures629correspond to an implementation of barrier regions429as described with reference toFIG.4. The conductive structures629are configured so that an acoustic velocity is higher in the region of the conductive structures629relative to in the central region625. In addition, the height of the conductive structures629may be adjusted to achieve a particular transversal velocity profile to better suppress transversal acoustic wave modes (e.g., achieve something close the rectangular profile shown by line444inFIG.4for the particular piezoelectric material602and layer stack of the electroacoustic device).

The acoustic wave velocity in the region of the conductive structures629is maintained higher than the central region625to be an effective barrier. As described above with reference toFIG.4, the difference in transversal acoustic wave velocity between the regions (in conjunction with the trap regions627) suppresses transversal acoustic wave modes. In addition, the conductive structures629may provide for convex slowness within the region of the conductive structures629that may be desirable for reducing acoustic modes excited in this region (particularly for certain piezoelectric materials such as Lithium tantalate). In addition, manufacturability of the conductive structures629may be easier relative to other implementations (e.g., the same process used to increase the thickness in the trap regions627may be used to deposit the metal conductive structures629with the particular height—although many manufacturing techniques are possible). In addition, the uniform metallization of the conductive structures629may reduce ohmic losses. In addition, the gap between the conductive structures629and unconnected fingers626may be kept large enough to avoid peaks in the electric field strength to increase power durability.

A dimension of the conductive structures629along a direction in which the electrode fingers626extend may also be made smaller as compared to certain other implementations (e.g., for another structure or for where a dimension of the barrier regions429are increased to provide the desired acoustic velocity). In certain aspects, the dimension may be between 1.25 times the wavelength and 4 times the wavelength for an operating frequency of the electroacoustic device. As one example, 125 nm may be sufficient for this dimension (e.g., length). Other dimension amounts are possible. Having smaller barrier regions, or in other words using the conductive structures629, may allow for saving chip area. This may be particularly valuable for implementations involving cascaded tracks with multiple barrier regions and may allow for smaller chip sizes.

The first busbar622, the second busbar624, the conductive structures629and electrode fingers626may be generally metallic or be made from some other conductive material. In some aspects, they can be formed from at least some of the same materials and may be implemented with a variety of different metallic stacks.

FIGS.6C and6Dare diagrams of an example of an implementation of the electrode structure604ofFIGS.6A and6B. The electrode structure604cofFIGS.6C and6Dillustrate a configuration where the conductive structures629are not connected to the electrode fingers626(e.g., there is a gap between portions of the conductive structures629and electrode fingers626in the direction along which the busbars extend). While in many implementations the conductive structures629are connected to the electrode fingers626, the electrode structure604cillustrates an alternative configuration. In this case, the first conductive structure629ais disposed between the first busbar622and the second plurality of fingers626bwhere the first conductive structure629ahas a height that is less than a height of the first plurality of fingers626a. A second conductive structure629bis disposed between the second busbar624and the first plurality of fingers626awhere the second conductive structure629bhas a height that is less than a height of the second plurality of fingers626b. In addition, as mentioned above, while the conductive structures629are illustrated as connected to the busbars622and624, in some configurations based on the electrode structure604cofFIGS.6C and6D, there may be a gap between the busbars622and624and the conductive structures629.

FIGS.7A and7Bare diagrams of an example of an implementation of the electrode structure604ofFIGS.6A and6B. The electrode structure704ofFIGS.7A and7Bis similar to the electrode structure604ofFIGS.6A and6Bbut illustrates a different implementation for the trap regions727. The trap regions727are implemented to have a wider electrode portion relative to the central region725(see description above with reference toFIG.5B). As described above, there may be a variety of different implementations for the trap regions727.

FIG.8Ais a plot800aillustrating a measure of propagation angles versus frequency for different regions of the electrode structure604ofFIG.6A. In the y-axis an indicator kywith a value of zero corresponds to a main propagation direction where increasing kyvalues correspond to increasing propagation angles (e.g., that may correspond to transversal acoustic modes). In the x-direction is frequency. The curves represented by the plot700are sometimes referred to as slowness curves. Line862corresponds to the curve for the central region625sometimes referred to as the track. Line864corresponds to the curve for the conductive structures629. Line866correspond to the curve for the busbars622and624. Line868correspond to the curve for an implementation using a gap rather than the conductive structures629. The line864illustrates that the slowness curve for the conductive structures629may correspond to a convex slowness which is desirable for suppressing acoustic modes that could be generated in barrier regions. In addition, the difference in velocity between the central region625and the region of the conductive structures629increases.

FIG.8Bis a plot800billustrating electroacoustic device admittance values versus frequency of an electroacoustic device including the electrode structure604ofFIG.6Aversus an alternative electrode structure along with corresponding slowness curves. The top portion includes the slowness curves ofFIG.8Aincluding the curve862for the central region625, a curve864for the conductive structures629, and a curve866for the busbars622and624. The bottom plot includes a line872corresponding to admittance values versus frequency of an electroacoustic device using the electrode structure604ofFIG.6A. The line874corresponds to admittance values versus frequency of an electroacoustic device that does not include conductive structures629but just an extended gap in the barrier regions429. As illustrated, the line874includes multiple significant ripples caused by transversal acoustic modes which reduce performance. The line872corresponding to the electrode structure604ofFIG.6includes significantly less ripples as illustrated which indicates the effectiveness of the suppression of transversal acoustic modes.

Example Operations

FIG.9is a flow chart illustrating an example of a method900for forming an electroacoustic device including a piezoelectric material602(FIG.6A) and the electrode structure604ofFIG.6Aaccording to certain aspects of the present disclosure. The method900is described in the form of a set of blocks that specify operations that can be performed. However, operations are not necessarily limited to the order shown inFIG.9or described herein, for the operations may be implemented in alternative orders or in fully or partially overlapping manners. Also, more, fewer, and/or different operations may be implemented to perform the method900, or an alternative approach. At block902, the method900includes forming a layer of piezoelectric material602. At block904, the method900further includes forming an electrode structure604on or above the piezoelectric material602. Forming the electrode structure604of block904includes, at block906, forming a first busbar622and a second busbar624. Forming the electrode structure of block904further includes, at block908, forming electrode fingers626arranged in an interdigitated manner, where forming the electrode fingers626includes forming a first plurality of fingers626aconnected to the first busbar622and forming a second plurality of fingers626bconnected to the second busbar624. Forming the electrode structure of block904further includes, at block910, forming a first conductive structure629adisposed between each of the first plurality of fingers626a, the first conductive structure629aformed with a height that is less than a height of the first plurality of fingers626a. Forming the electrode structure of block904further includes, at block912, forming a second conductive structure629bdisposed between each of the second plurality of fingers626b, the second conductive structure629bformed with a height that is less than a height of the second plurality of fingers626b.

As described above, the electrode fingers626have a central region625with a first trap region627aand a second trap region627brespectively located on boundaries of the central region625. In certain aspects, the method900, at block914, may further include adjusting or forming a structural characteristic of the electroacoustic device in the first and second trap regions627to reduce an acoustic velocity.

In certain aspects, with reference toFIG.6A, a method for filtering an electrical signal via an electroacoustic device including a piezoelectric material602and an interdigital transducer605may be provided. The method includes providing the electrical signal to a terminal of the interdigital transducer605. The method further includes reducing a transversal acoustic wave mode via conductive structures629respectively connected between a respective busbar (622or624) and electrode fingers626of the interdigital transducer605where a height of the conductive structures629are less than a height of the electrode fingers626.

The electroacoustic devices with the electrode structure604ofFIG.6Amay be used in a variety of applications.

FIG.10is a schematic diagram of an electroacoustic filter circuit1000that may include the electrode structure604ofFIG.6A. The filter circuit1000provides one example of where the electrode structure604may be used. The filter circuit1000includes an input terminal1002and an output terminal1014. Between the input terminal1002and the output terminal1014a ladder network of SAW resonators is provided. The filter circuit1000includes a first SAW resonator1004, a second SAW resonator1006, and a third SAW resonator1008all electrically connected in series between the input terminal1002and the output terminal1014. A fourth SAW resonator1010(e.g., shunt resonator) has a first terminal connected between the first SAW resonator1004and the second SAW resonator1006and a second terminal connected to a ground potential. A fifth SAW resonator1012(e.g., shunt resonator) has a first terminal connected between the second SAW resonator1006and the third SAW resonator1008and a second terminal connected to a ground potential. The electroacoustic filter circuit1000may, for example, be a bandpass circuit having a passband with a selected frequency range (e.g., on the order between 100 MHz and 3.5 GHz). WhileFIG.10illustrates one example of a ladder network, as described above, the electrode structure604ofFIG.6Amay be incorporated into other resonator configurations such as within a DMS design.

FIG.11is a functional block diagram of at least a portion of an example of a simplified wireless transceiver circuit1100in which the filter circuit1000ofFIG.10including the electrode structure604ofFIG.6Amay be employed. The transceiver circuit1100is configured to receive signals/information for transmission (shown as I and Q values) which is provided to one or more base band filters1112. The filtered output is provided to one or more mixers1114. The output from the one or more mixers1114is provided to a driver amplifier1116whose output is provided to a power amplifier1118to produce an amplified signal for transmission. The amplified signal is output to the antenna1122through one or more filters1120(e.g., duplexers if used as a frequency division duplex transceiver or other filters). The one or more filters1120may include the filter circuit1000ofFIG.10and may include the electrode structure604ofFIG.6A. The antenna1122may be used for both wirelessly transmitting and receiving data. The transceiver circuit1100includes a receive path through the one or more filters1120to be provided to a low noise amplifier (LNA)1124and a further filter1126and then down-converted from the receive frequency to a baseband frequency through one or more mixer circuits1128before the signal is further processed (e.g., provided to an analog digital converter and then demodulated or otherwise processed in the digital domain). There may be separate filters for the receive circuit (e.g., may have a separate antenna or have separate receive filters) that may be implemented using the filter circuit1000ofFIG.10. Furthermore, the transceiver circuit1100illustrated represents one simplified example of a transceiver architecture and that other architectures (e.g., sharing or without sharing antennas) with other filter configurations are possible.

FIG.12is a diagram of an environment1200that includes an electronic device1202that includes a wireless transceiver1296such as the transceiver circuit1100ofFIG.11(and that may incorporate filters that use the electrode structure604ofFIG.6A). In the environment1200, the electronic device1202communicates with a base station1204through a wireless link1206. As shown, the electronic device1202is depicted as a smart phone. However, the electronic device1202may be implemented as any suitable computing or other electronic device, such as a cellular base station, broadband router, access point, cellular or mobile phone, gaming device, navigation device, media device, laptop computer, desktop computer, tablet computer, server computer, network-attached storage (NAS) device, smart appliance, vehicle-based communication system, Internet of Things (IoT) device, sensor or security device, asset tracker, and so forth.

The base station1204communicates with the electronic device1202via the wireless link1206, which may be implemented as any suitable type of wireless link. Although depicted as a base station tower of a cellular radio network, the base station1204may represent or be implemented as another device, such as a satellite, terrestrial broadcast tower, access point, peer to peer device, mesh network node, fiber optic line, another electronic device generally as described above, and so forth. Hence, the electronic device1202may communicate with the base station1204or another device via a wired connection, a wireless connection, or a combination thereof. The wireless link1206can include a downlink of data or control information communicated from the base station1204to the electronic device1202and an uplink of other data or control information communicated from the electronic device1202to the base station1204. The wireless link1206may be implemented using any suitable communication protocol or standard, such as 3rd Generation Partnership Project Long-Term Evolution (3GPP LTE, 3GPP NR 5G), IEEE 802.11, IEEE 802.16, Bluetooth™, and so forth.

The electronic device1202includes a processor1280and a memory1282. The memory1282may be or form a portion of a computer readable storage medium. The processor1280may include any type of processor, such as an application processor or a multi-core processor, that is configured to execute processor-executable instructions (e.g., code) stored by the memory1282. The memory1282may include any suitable type of data storage media, such as volatile memory (e.g., random access memory (RAM)), non-volatile memory (e.g., Flash memory), optical media, magnetic media (e.g., disk or tape), and so forth. In the context of this disclosure, the memory1282is implemented to store instructions1284, data1286, and other information of the electronic device1202, and thus when configured as or part of a computer readable storage medium, the memory1282does not include transitory propagating signals or carrier waves.

The electronic device1202may also include input/output ports1290(I/O ports116). The I/O ports1290enable data exchanges or interaction with other devices, networks, or users or between components of the device.

The electronic device1202may further include a signal processor (SP)1292(e.g., such as a digital signal processor (DSP)). The signal processor1292may function similar to the processor and may be capable executing instructions and/or processing information in conjunction with the memory1282.

For communication purposes, the electronic device1202also includes a modem1294, a wireless transceiver1296, and an antenna (not shown). The wireless transceiver1296provides connectivity to respective networks and other electronic devices connected therewith using radio-frequency (RF) wireless signals and may include the transceiver circuit1100ofFIG.11. The wireless transceiver1296may facilitate communication over any suitable type of wireless network, such as a wireless local area network (LAN) (WLAN), a peer to peer (P2P) network, a mesh network, a cellular network, a wireless wide area network (WWAN), a navigational network (e.g., the Global Positioning System (GPS) of North America or another Global Navigation Satellite System (GNSS)), and/or a wireless personal area network (WPAN).

Implementation examples are described in the following numbered clauses:

1. An electroacoustic device, comprising:a piezoelectric material; andan electrode structure, comprising:a first busbar and a second busbar;electrode fingers arranged in an interdigitated manner and comprising a first plurality of fingers connected to the first busbar and a second plurality of fingers connected to the second busbar;a first conductive structure disposed between each of the first plurality of fingers and disposed between the first busbar and the second plurality of fingers, the first conductive structure having a height that is less than a height of the first plurality of fingers; anda second conductive structure disposed between each of the second plurality of fingers and disposed between the second busbar and the first plurality of fingers, the second conductive structure having a height that is less than a height of the second plurality of fingers.

2. The electroacoustic device of clause 1, wherein the height of the first conductive structure is less than half of the height of the first plurality of fingers, wherein the height of the second conductive structure is less than half of the height of the second plurality of fingers.

3. The electroacoustic device of any of clauses 1 to 2, wherein the height of the first conductive structure is between 5 and 20 nanometers, wherein the height of the second conductive structure is between 5 and 20 nanometers.

4. The electroacoustic device of any of clauses 1 to 3, wherein the first conductive structure is connected to the first busbar, wherein the second conductive structure is connected to the second busbar.

5. The electroacoustic device of any of clauses 1 to 4, wherein the electrode fingers have a central region with a first trap region and a second trap region respectively located on boundaries of the central region, wherein a structural characteristic of the electroacoustic device is different in the first trap region and the second trap region relative to the central region.

6. The electroacoustic device of clause 5, wherein the structural characteristic corresponds to a portion of each of the electrode fingers having an increased width or increased height within the first trap region and the second trap region relative to the within the central region.

7. The electroacoustic device of clause 5, wherein the structural characteristic corresponds to at least one of a dielectric material positioned over the trap regions, a mass loading within the trap regions, or a structural effect of a trimming operation.

8. The electroacoustic device of any of clauses 5 to 7, wherein an acoustic velocity in a region of the electroacoustic device defined by the first conductive structure and the second conductive structure is higher than in a region of the electroacoustic device defined by the first trap region, the second trap region, and the central region.

9. The electroacoustic device of clause 8, wherein the acoustic velocity in the first trap region and the second trap region is lower than the acoustic velocity in the central region.

10. The electroacoustic device of clause 5, wherein a dimension of the trap region in the direction in which the electrode fingers extend is between one-half of a pitch of the electrode fingers and twice the pitch of the electrode fingers.

11. The electroacoustic device of clause 1, wherein the electrode fingers have a central region with a first trap region and a second trap region respectively located on boundaries of the central region, wherein an acoustic velocity in a region of the electroacoustic device defined by the first trap region and the second trap region is lower than in a region of the electroacoustic device defined by the central region.

12. The electroacoustic device of any of clauses 1 to 11, wherein a dimension of the first conductive structure in the direction in which the electrode fingers extend is between 1.25 times and 4 times a wavelength for an operating frequency of the electroacoustic device.

13. The electroacoustic device of any of clauses 1 to 12, wherein the electrode fingers extend in a direction normal to a direction of the first busbar and the second busbar.

14. The electroacoustic device of any of clauses 1 to 13, wherein the electrode fingers extend in a direction normal to a direction of the first conductive structure and the second conductive structure.

15. The electroacoustic device of any of clauses 1 to 14, wherein the piezoelectric material comprises lithium tantalate (LiTa03).

16. The electroacoustic device of any of clauses 1 to 15, further comprising:a substrate;a trap rich layer forming a portion of or being disposed on the substrate; anda layer of dielectric material disposed on the substrate, the piezoelectric material disposed on the layer of dielectric material.

17. The electroacoustic device of any of clauses 1 to 15, further comprising:a substrate; anda compensation layer disposed on the substrate, the piezoelectric material disposed between the electrode structure and the compensation layer.

18. The electroacoustic device of any of clauses 1 to 17, wherein the electroacoustic device is at least a part of a SAW resonator that forms part of a filter circuit.

19. The electroacoustic device of clause 18, wherein the filter circuit is part of a transceiver.

20. A method for forming an electroacoustic device, comprising:forming a layer of a piezoelectric material; andforming an electrode structure on or above the piezoelectric material, forming the electrode structure comprising:forming a first busbar and a second busbar;forming electrode fingers arranged in an interdigitated manner, where forming the electrode fingers comprises forming a first plurality of fingers connected to the first busbar and forming a second plurality of fingers connected to the second busbar;forming a first conductive structure disposed between each of the first plurality of fingers, the first conductive structure formed with a height that is less than a height of the first plurality of fingers; andforming a second conductive structure disposed between each of the second plurality of fingers, the second conductive structure formed with a height that is less than a height of the second plurality of fingers.

21. The method of clause 20, wherein the electrode fingers have a central region and a first trap region and a second trap region respectively located on boundaries of the central region, wherein the method further comprises adjusting or forming a structural characteristic of the electroacoustic device in the first and second trap regions to reduce an acoustic velocity.

22. An electroacoustic device, comprising:a piezoelectric material; andan electrode structure, comprising:a first busbar and a second busbar;electrode fingers arranged in an interdigitated manner and connected to either the first busbar or the second busbar; andmeans for controlling an acoustic velocity in a first region between the first busbar and the electrode fingers and in a second region between the second busbar and the electrode fingers, the means for controlling an acoustic velocity having a height that is less than a height of the electrode fingers.

23. The electroacoustic device of clause 22, wherein the means for controlling an acoustic velocity has a height that is less than half of the height of the electrode fingers.

24. The electroacoustic device of any of clauses 22 to 23, wherein the electrode fingers have a central region with a first trap region and a second trap region respectively located on boundaries of the central region, wherein a structural characteristic of the electroacoustic device is different in the first trap region and the second trap region relative to the central region.

25. An electrode structure of an electroacoustic device, comprising:a first busbar and a second busbar;electrode fingers arranged in an interdigitated manner and comprising a first plurality of fingers connected to the first busbar and a second plurality of fingers connected to the second busbar;a first conductive structure disposed between the first busbar and ends of the second plurality of fingers, the first conductive structure having a height that is less than a height of the first plurality of fingers; anda second conductive structure disposed between the second busbar and ends of the first plurality of fingers, the second conductive structure having a height that is less than a height of the second plurality of fingers.

26. The electrode structure of clause 25, wherein the height of the first conductive structure is less than half of the height of the first plurality of fingers, wherein the height of the second conductive structure is less than half of the height of the second plurality of fingers.

27. The electrode structure of any of clauses 25 to 26, wherein the first conductive structure is connected to the first busbar, wherein the second conductive structure is connected to the second busbar.

28. The electrode structure of any of clauses 25 to 27, wherein the electrode fingers have a central region with a first trap region and a second trap region respectively located on boundaries of the central region, wherein a structural characteristic of the electroacoustic device is different in the first trap region and the second trap region relative to the central region.

29. The electrode structure of any of clauses 25 to 28, wherein the electrode structure is disposed on a piezoelectric material that comprises lithium tantalate (LiTa03).

30. A wireless communication apparatus comprising the electroacoustic device of claim1.

31. A method for filtering an electrical signal via an electroacoustic device comprising a piezoelectric material and an interdigital transducer, the method comprising:providing the electrical signal to a terminal of the interdigital transducer; andreducing a transversal acoustic wave mode via conductive structures respectively connected between a respective busbar and electrode fingers of the interdigital transducer, a height of the conductive structures being less than a height of the electrode fingers.

32. An electroacoustic device, comprising:a piezoelectric material; andan electrode structure, comprising:electrode fingers arranged in an interdigitated manner and comprising a first plurality of fingers and a second plurality of fingers;a first conductive structure connected to and between each of the first plurality of fingers, the first conductive structure having a height that is less than a height of the first plurality of fingers; anda second conductive structure connected to and between each of the second plurality of fingers, the second conductive structure having a height that is less than a height of the second plurality of fingers.

The various operations of methods described above may be performed by any suitable means capable of performing the corresponding functions. The means may include various hardware and/or software component(s) and/or module(s), including, but not limited to a circuit, an application-specific integrated circuit (ASIC), or processor.

By way of example, an element, or any portion of an element, or any combination of elements described herein may be implemented as a “processing system” that includes one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems on a chip (SoC), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gated logic, discrete hardware circuits, and other suitable hardware configured to perform the various functionality described throughout this disclosure. One or more processors in the processing system may execute software. Software shall be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executables, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

Accordingly, in one or more example embodiments, the functions or circuitry blocks described may be implemented in hardware, software, or any combination thereof. If implemented in software, the functions may be stored on or encoded as one or more instructions or code on a computer-readable medium. Computer-readable media includes computer storage media. Storage media may be any available media that can be accessed by a computer. By way of example, and not limitation, such computer-readable media can comprise a random-access memory (RAM), a read-only memory (ROM), an electrically erasable programmable ROM (EEPROM), optical disk storage, magnetic disk storage, other magnetic storage devices, combinations of the aforementioned types of computer-readable media, or any other medium that can be used to store computer executable code in the form of instructions or data structures that can be accessed by a computer. In some aspects, components described with circuitry may be implemented by hardware, software, or any combination thereof.

Generally, where there are operations illustrated in figures, those operations may have corresponding counterpart means-plus-function components with similar numbering.

As used herein, the term “determining” encompasses a wide variety of actions. For example, “determining” may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, a database, or another data structure), ascertaining, and the like. Also, “determining” may include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), and the like. Also, “determining” may include resolving, selecting, choosing, establishing, and the like.

As used herein, a phrase referring to “at least one of” a list of items refers to any combination of those items, including single members. As an example, “at least one of: a, b, or c” is intended to cover: a, b, c, a-b, a-c, b-c, and a-b-c, as well as any combination with multiples of the same element (e.g., a-a, a-a-a, a-a-b, a-a-c, a-b-b, a-c-c, b-b, b-b-b, b-b-c, c-c, and c-c-c or any other ordering of a, b, and c).

The methods disclosed herein comprise one or more steps or actions for achieving the described method. The method steps and/or actions may be interchanged with one another without departing from the scope of the claims. In other words, unless a specific order of steps or actions is specified, the order and/or use of specific steps and/or actions may be modified without departing from the scope of the claims.

It is to be understood that the claims are not limited to the precise configuration and components illustrated above. Various modifications, changes and variations may be made in the arrangement, operation and details of the methods and apparatus described above without departing from the scope of the claims.