Beat mode suppression in power bars and quaternary bars

Abstract

The invention relates to beat mode suppression in power bars and quaternary bars. A resonator includes a substrate including a top surface, a bottom electrode disposed on the top surface of the substrate, a piezoelectric layer disposed on the bottom electrode, and a top electrode disposed on the piezoelectric layer. The bottom electrode includes a first elongate member configured to extend longitudinally along the top surface on a first side of the substrate.

Description

[0001] Copyright Notice

[0002] A portion of the disclosure of this patent document contains material which is subject to copyright protection. The copyright owner has no objection to the facsimile reproduction by anyone of the patent document or the patent disclosure, as it appears in the Patent and Trademark Office patent file or records, but otherwise reserves all copyright rights whatsoever. Technical Field

[0003] The present disclosure generally relates to methods, systems, and apparatus for beat mode suppression in bulk acoustic wave resonators. Background Art

[0004] Bulk acoustic wave (BAW) resonators, such as film bulk acoustic resonators (FBARs), are often implemented as radio frequency (RF) filters, also called BAW filters. In the acoustic frequency regime, a BAW resonator has a series resonant frequency (f s ) and parallel resonant frequency (f p ). Outside of this acoustic mechanism, the BAW resonator behaves like a capacitor. To mitigate the effects of the second harmonic (H2) in a BAW resonator, two flipped BAW resonators are placed in a series configuration, called a "powerbar" (or two pairs of flipped BAW resonators, called a "quadbar") and in a shunt configuration, called a "split-bar". In a typical ladder filter, the powerbar is used to compensate for the series path of the ladder filter, while the split-bar is used to compensate for the shunt, because f p and f s falls outside the passband.

[0005] When the BAW resonator exhibits acoustic and electromagnetic asymmetries, the f of the individual power bars / split bars s / f p The difference in frequency can lead to a beat frequency mode (for example, at two frequencies f s With f p In the ultra-high band (UHB) operation (5 to 7 GHz), the shunt resonators cannot be placed in a split-strip configuration because they become too small. Within the UHB regime, the shunt resonators are placed in a power-strip configuration and at f p The beat mode generated under this condition falls within the passband. This causes undesirable peaks in the linear response (e.g., insertion loss, group delay), H2 response, and thermal response.

[0006] Thus, methods, systems, and apparatus are provided for beat mode suppression in power bars and quad bars. Summary of the invention

[0007] Various embodiments describe power bar and / or quad bar configurations of BAW resonators.

[0008] In some embodiments, an apparatus for beat frequency suppression in a bulk acoustic wave resonator is provided. The apparatus includes: one or more first resonators, each first resonator having a corresponding parasitic capacitance; and a second resonator having a second parasitic capacitance. The second resonator includes a substrate, a bottom electrode disposed on the substrate, a piezoelectric layer disposed on the bottom electrode, and a top electrode disposed on the piezoelectric layer. In a first region, the bottom electrode overlaps with a top electrode without a piezoelectric layer between the bottom electrode and the top electrode, wherein an area of ​​the first region is determined at least in part based on a difference between the second parasitic capacitance and the corresponding parasitic capacitance of at least one of the one or more first resonators.

[0009] In a further embodiment, a resonator having an architecture for beat frequency suppression is provided. The resonator includes a substrate including a top surface, a bottom electrode disposed on the top surface of the substrate, a piezoelectric layer disposed on the bottom electrode, and a top electrode disposed on the piezoelectric layer. The bottom electrode includes a first elongated member configured to extend longitudinally along the top surface on a first side of the substrate.

[0010] In a further embodiment, an apparatus for beat frequency suppression in a bulk acoustic wave resonator is provided. The apparatus includes a first external resonator having a first parasitic resonance. The first external resonator includes a substrate including a top surface, a bottom electrode disposed on the top surface of the substrate, a piezoelectric layer disposed on the bottom electrode, and a top electrode disposed on the piezoelectric layer. The apparatus includes a first center resonator coupled to the first external resonator, a second center resonator coupled to the first center resonator, and a second external resonator coupled to the second center resonator. The bottom electrode includes a first elongated member configured to extend longitudinally along the top surface of the substrate at least partially around a first side of at least one of the second center resonator, the first center resonator, or the second external resonator. BRIEF DESCRIPTION OF THE DRAWINGS

[0011] A further understanding of the nature and advantages of certain embodiments may be achieved by reference to the remainder of the specification and the accompanying drawings, in which like reference numerals are used to refer to similar components. In some instances, a sub-label is associated with a reference numeral to denote one of multiple similar components. When reference is made to a reference numeral without specifying an existing sub-label, it is intended to refer to all such multiple similar components.

[0012] Figure 1Ais a schematic top view of a pair of bulk acoustic wave resonators according to various embodiments;

[0013] Figure 1B is a schematic diagram of a cross section of a bulk acoustic wave resonator pair according to various embodiments;

[0014] Figure 1C is a schematic circuit diagram of a bulk acoustic wave resonator pair in a power strip configuration according to various embodiments;

[0015] Figure 2A is a schematic diagram of a quaternary strip with a BAW resonator shielding structure according to various embodiments;

[0016] Figure 2B is a schematic diagram of a quaternary strip having a BAW resonator with an alternative first shielding structure according to various embodiments; and

[0017] Figure 2C is a schematic diagram of a quaternary strip having a BAW resonator with a second alternative shielding structure according to various embodiments. DETAILED DESCRIPTION

[0018] In the following description, for the purpose of explanation, many details are set forth to provide a thorough understanding of the described embodiments. However, it will be appreciated by those skilled in the art that other embodiments may be practiced without some of these details. Several embodiments are described herein, and although various features are attributed to different embodiments, it should be understood that features described with respect to one embodiment may also be combined with other embodiments. However, by the same token, any single feature or multiple features of any described embodiment should not be considered as necessary for every embodiment of the present invention, as other embodiments of the present invention may omit such features.

[0019] When an element is referred to herein as being "connected" or "coupled" to another element, it is understood that the element may be directly connected to the other element, or that there may be intervening elements between the elements. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, it is understood that there may be no intervening elements in a "direct" connection between the elements. However, the presence of a direct connection does not exclude other connections in which there may be intervening elements.

[0020] When an element is referred to herein as being "disposed" in some manner relative to another element (e.g., disposed on, between, below, adjacent, or in some other relative manner), it is understood that the element may be disposed directly relative to the other element (e.g., disposed directly on the other element) or that there may be intervening elements between the elements. In contrast, when an element is referred to as being "directly disposed" relative to another element, it is understood that there are no intervening elements in the "direct" instance. However, the presence of a direct placement does not exclude other instances in which there may be intervening elements.

[0021] Likewise, when an element is referred to herein as a "layer," it is understood that the layer may be a single layer or may include multiple layers. For example, a conductive layer may include a plurality of different conductive materials or multiple layers of different conductive materials, and a dielectric layer may include a plurality of dielectric materials or multiple layers of dielectric materials. When a layer is described as being coupled or connected to another layer, it is understood that the coupled or connected layer may include an intervening element that is present between the coupled or connected layers. In contrast, when a layer is referred to as being "directly" connected or coupled to another layer, it is understood that there are no intervening elements between the layers. However, the presence of a directly coupled or connected layer does not exclude other connections in which an intervening element may be present.

[0022] In addition, the terms left, right, front, back, top, bottom, forward, reverse, clockwise, and counterclockwise are used for explanation purposes only and are not limited to any fixed direction or orientation. Instead, they are only used to indicate the relative position and / or direction between the various parts of an object and / or component.

[0023] In addition, for ease of description, the methods and processes described herein may be described in a particular order. However, it should be understood that unless the context dictates otherwise, intervening processes may occur before and / or after any portion of the described processes, and further various processes may be reordered, added, and / or omitted according to various embodiments.

[0024] Unless otherwise indicated, all numbers used herein to express quantities, sizes, etc. should be understood to be modified by the term "approximately" in all instances. In this application, unless otherwise specifically stated, the use of the singular includes the plural, and unless otherwise indicated, the use of the terms "and" and "or" means "and / or". In addition, the use of the terms "including" and "having" and other forms (such as "includes, included", "has, have and had") should be considered non-exclusive. Moreover, unless otherwise specifically stated, terms such as "element" or "component" cover both elements and components including one unit and elements and components including more than one unit.

[0025] As used herein, the phrase "at least one of..." preceding a list of items (where the terms "and" or "or" are used to separate any of the items) modifies the entire list, rather than each member of the list (i.e., each item). The phrase "at least one of..." does not require selection of at least one of each item listed; rather, the phrase allows for a meaning that includes at least one of any of the items and / or at least one of any combination of items. For example, the phrase "at least one of A, B, and C" or "at least one of A, B, or C" each refers to only A, only B, or only C; and / or any combination of A, B, and C. In instances where the selection is intended to be "at least one of each of A, B, and C," or, alternatively, "at least one of A, at least one of B, and at least one of C," it is explicitly described as such.

[0026] In a conventional split-bar arrangement, two BAW resonators are placed in parallel, but oriented to face in opposite directions (e.g., the axis of the piezoelectric acoustic material is flipped). To maintain the capacitance, and therefore impedance, of the stage, the size of each individual BAW resonator is halved. However, in UHB operation, the size of the resonators becomes too small to be implemented as a split-bar. Therefore, in UHB, due to size constraints, BAW filters (e.g., ladder filters) utilize power bars or quad bars, where the size of each individual resonator is doubled or quadrupled in size to maintain capacitance in the series path. In a quad bar configuration, each individual resonator is placed in series facing alternating directions. However, in f p The beat frequency mode falls within the passband of the BAW filter and causes unwanted peaks in the linear response.

[0027] The power bar and quaternary bar configurations described below provide a new architecture for beat mode suppression. Specifically, the capacitive loading of individual resonators within the power bar and / or quaternary bar is used to compensate for the difference in parasitic capacitance of the individual resonators. Another aspect of the configuration is provided by equipotentialization via a shielding structure on one or more of the outer resonators of the quaternary bar.

[0028] Figure 1A is a schematic top view of a pair of BAW resonators 100 according to various embodiments. Figure 1Bis a schematic diagram of a cross section of a BAW resonator pair 100 taken across line xx. The BAW resonator pair 100 includes a first BAW resonator 105a (hereinafter, "first resonator 105a") and a second BAW resonator 105b (hereinafter, "second resonator 105b"), wherein the first resonator 105a includes a first bottom electrode 110, a first top electrode 115, and a first piezoelectric layer 130, and wherein the second resonator 105b includes a second bottom electrode 120, a second top electrode 125, and a second piezoelectric layer 135. It should be noted that the various parts and components of the BAW resonator 100 are shown in FIG. Figure 1A and 1B 1 and modifications to various components and other arrangements of the BAW resonator 100 pair may be possible and in accordance with various embodiments.

[0029] refer to Figure 1A and 1B , the BAW resonators 105a, 105b may include FBARs or other types of BAW resonators. The first resonator 105a and the second resonator 105b may be part of a power bar and / or a quaternary bar arrangement. In a power bar arrangement, the first and second resonators 105a, 105b are placed in series but flipped in orientation. As used herein, the orientation of a resonator may refer to the piezoelectric orientation (e.g., crystal or grain orientation) of the piezoelectric material within the piezoelectric layer. However, for visualization purposes, Figure 1A The first resonator 105a and the second resonator 105b are depicted oriented in the same direction (eg, with the connecting edge on the right).

[0030] In various examples, the overlap area of ​​the first bottom electrode 110 and the first top electrode 115 (e.g., the area where the first top electrode 115 overlaps the first bottom electrode 110) determines the capacitance of the first resonator 105a. Therefore, the capacitance of the first resonator 105a can be determined and / or adjusted by controlling the overlap area of ​​the first bottom electrode 110 and the first top electrode 115. For example, a larger overlap area results in a larger capacitance, while a smaller overlap area results in a smaller capacitance.

[0031] In various examples, the first and second bottom electrodes 110, 120 may be deposited above a substrate, respectively. Suitable substrates may include, but are not limited to, ceramic, silicon, glass, or other suitable dielectric materials. Thus, the bottom electrodes 110, 120 of the respective resonators 105a, 105b may be disposed on a top surface of the substrate (including as will be referred to below). Figures 2A to 2C105a, 105b). The top electrodes 115, 125 may be disposed on the top of the respective piezoelectric layers 130, 135.

[0032] Therefore, in some embodiments, the overlapping region of the first resonator 105a can be configured to mitigate the mismatch of the capacitance (or parasitic capacitance) of the second resonator 105b. Specifically, the difference in the parasitic capacitance of the individual resonators will result in a corresponding parallel resonant frequency f of the corresponding resonator. p and the corresponding series resonant frequency f s Therefore, the difference in parasitic capacitance can be mitigated by capacitive loading of one or more of the resonators in the power strip and / or the quad strip, as shown in FIG. Figure 1C visible. Figure 1C is a schematic circuit diagram of a bulk acoustic wave resonator pair in a power strip configuration 100C according to various embodiments. In the above example, the first resonator 105a is capacitively loaded using a larger first top electrode 115, thereby creating a larger overlap area with the first bottom electrode 110. Therefore, the overlap area can be determined at least in part based on the difference in parasitic capacitance of the first and second resonators 105a, 105b.

[0033] In some examples, the overlapping region can be an overlapping region along a connecting edge. The connecting edge can be a region where the top and bottom electrodes overlap at the connecting edge, where the resonator is not acoustically active (e.g., not over the piezoelectric layer and / or the cavity between the bottom electrode and the substrate).

[0034] In various embodiments, the overlap region may refer to the surface area of ​​the top electrode that is in direct contact with the bottom electrode in an acoustically inactive region (or "dead zone"). Thus, in some examples, the overlap region may be a two-dimensional area where the top and bottom electrodes directly overlap.

[0035] In various embodiments, the first and second bottom electrodes 110, 120, the first and second top electrodes 115, 125, and the first and second piezoelectric layers 130, 135 may be planar structures. In some examples, the bottom and top electrodes 110, 115, 120, 125 may be formed of a conductive material, such as a metal (e.g., copper (Cu), silver (Ag), gold (Au), aluminum (Al), etc.) or other suitable conductive materials. In various embodiments, the piezoelectric layers 130, 135 may be thin film piezoelectric layers made of piezoelectric materials. In some examples, the piezoelectric layers 130, 135 are aluminum nitride (AlN) piezoelectric materials. In other examples, other materials may be used, such as zinc oxide (ZnO) or other suitable piezoelectric crystal materials. In some embodiments, individual resonators that are part of the same quaternary bar (or power bar) may have piezoelectric layers of the same size (e.g., within the tolerance of the corresponding manufacturing process).

[0036] Conventional methods of capacitive loading, such as adjusting frame elements, also called "outies," also change the acoustic behavior of the resonator. Thus, by increasing the bottom electrode-top electrode overlap, and in some embodiments, increasing the overlap of the bottom and top electrodes at the connecting edges of the respective resonators, the mismatch of parasitic capacitances can be mitigated via capacitive loading without affecting the acoustic properties of the resonator.

[0037] In further embodiments, shielding and / or equipotentialization may also be used to reduce beat modes in the quad strips. Figures 2A to 2C A quad strip configuration is described in which a shielding structure is provided. Figures 2A to 2C Schematic diagrams of quaternary strips 200A to 200C having a BAW resonator with a shielding structure according to various embodiments are shown. The quaternary strips 200A to 200C include a first BAW resonator 205a (hereinafter, "first resonator 205a"), a second BAW resonator 205b (hereinafter, "second resonator 205b"), a third BAW resonator 205c (hereinafter, "third resonator 205c"), and a fourth BAW resonator 205d (hereinafter, "fourth resonator 205d"). The first resonator 205a includes a first bottom electrode 210a and a first top electrode 215a. The second resonator 205b includes a second bottom electrode 210b and a second top electrode 215b. The third resonator 205c includes a third bottom electrode 210c and a third top electrode 215c. The fourth resonator 205d includes a fourth bottom electrode 210d and a fourth top electrode 215d. It should be noted that the various parts and components of the quaternary strips 200A to 200C are Figures 2A to 2C 2 is schematically illustrated in FIG. 2 , and modifications to the various components and other arrangements of the quaternary strips 200A- 200C may be possible and in accordance with various embodiments.

[0038] Each of the first, second, third and fourth resonators 205a to 205d may be coupled in series to form a quad strip 200A. Thus, the quad strip 200A includes a central resonator 220, which includes a second resonator 205b and a third resonator 205c. Accordingly, the outer resonators include a first resonator 205a and a fourth resonator 205d.

[0039] refer to Figure 2A , the first bottom electrode 210a includes a shield structure 225 that is configured to extend around the center resonator 220. In some examples, the shield structure 225 is an extension of the first bottom electrode 210a that extends around both sides (e.g., top and bottom) of the center resonator 220. For example, the shield structure 225 may include a bottom member 225a and a top member 225b, where each member is an elongated structure (e.g., an "elongated member") extending from the first bottom electrode 210a. In various examples, the elongated structure may be referred to as having a length extending in a "longitudinal direction" and a width extending in a "lateral direction."

[0040] Figure 2B is a schematic diagram of a quad bar 200B having a BAW resonator with an alternative first shielding structure according to various embodiments. Figure 2A In contrast, Figure 2B The first shield structure 225 and the second shield structure 230 are included. The first shield structure 225 can be formed by the first bottom electrode 210a and extend around both sides of at least one of the central resonators 220. The second shield structure 230 can be formed by the fourth bottom electrode 210d and extend around both sides of at least one of the central resonators 220. In this way, both the first and second shield structures 225, 230 can include top and bottom components, such as in Figure 2A of the quaternary bar 200A.

[0041] In the depicted example, the bottom member of the first shield structure 225 extends beyond the bottom side of the second resonator 205b and at least a portion of the third resonator 205c. The top member of the first shield structure 225 extends at least partially along the top side of the second resonator 205b. The top member of the second shield structure 230, in turn, extends beyond the top side of the third resonator 205c and at least a portion of the second resonator 205b. The bottom member of the second shield structure 230 extends at least partially along the bottom side of the third resonator 205c. In this way, both the first shield structure 225 and the second shield structure 230 are asymmetric structures in which the top and bottom members have different sizes. In other examples, the first and second shield structures 225, 230 may include top and bottom members that are symmetrical or nearly symmetrical (e.g., within the tolerances of the respective manufacturing processes).

[0042] Figure 2C 2 is a schematic diagram of a quaternary bar 200C having a bulk acoustic wave resonator with a second alternative shielding structure according to various embodiments. The quaternary bar 200C includes a first shielding structure 225 and a second shielding structure 230. The first shielding structure 225 can be formed by the first bottom electrode 210a and extends around one side (either the top side or the bottom side) of the central resonator 220. In the depicted example, the first shielding structure 225 extends around the top side of the central resonator 220. The second shielding structure 230 can be formed by the fourth bottom electrode 210d and extends around a side of the central resonator 220 opposite the first shielding structure 225. In the depicted example, the second shielding structure 230 extends along the bottom side of the central resonator 220.

[0043] In the depicted example, the first shielding structure 225 extends beyond the top side of the third resonator 205c. It should be understood that in other embodiments, the first shielding structure 225 may extend at least partially along the top side of at least one of the second or third resonators 205b, 205c. In further embodiments, the first shielding structure 225 may extend around the top side of the center resonator 220 and at least partially along the top side of the fourth resonator 205d. Similarly, the second shielding structure 230 may extend at least partially along the bottom side of at least one of the second or third resonators 205b, 205c. In further embodiments, the first shielding structure 225 may extend around the bottom side of the center resonator 220 and at least partially along the bottom side of the first resonator 205a.

[0044] In further embodiments, the first shielding structure 225 may instead extend along the bottom side of the center resonator 220 and / or the fourth resonator 205d. The second shielding structure 230 may in turn extend along the top side of the center resonator 220 and / or the first resonator 205a.

[0045] Therefore, in various embodiments, reference Figures 2A to 2C , shielding structures 225, 230 shield the quaternary strips 200A-200C and / or the center resonator 220 on both the bottom and top sides. The shielding structures 225, 230 provide an equipotential reference for each of the center resonators 220, isolating the center resonator 220 from its surroundings, thereby mitigating the effects of parasitic capacitance and / or reducing beat modes.

[0046] In some embodiments, the shielding structures 225, 230 may be utilized in combination with capacitive loading of individual resonators, as described above with respect to Figures 1A to 1CFor example, individual resonator pairs may be configured such that differences in parasitic capacitance are minimized, wherein at least one of a pair of resonators is capacitively loaded as previously described (e.g., via overlap of bottom and top electrodes). A resonator pair (e.g., two pairs of resonators in a quad strip) may further include a shielding structure on at least one of the resonators to provide shielding for a center resonator of the quad strip.

[0047] Although some features and aspects have been described with respect to embodiments, those skilled in the art will recognize that many modifications are possible. For example, the methods and processes described herein may be implemented using hardware components, custom integrated circuits (ICs), programmable logic, and / or any combination thereof. In addition, although the various methods and processes described herein may be described with respect to specific structural and / or functional components for ease of description, the methods provided by the various embodiments are not limited to any specific structural and / or functional architecture, but may be implemented in any suitable hardware configuration. Similarly, although some functionality is attributed to one or more system components, unless the context dictates otherwise, according to several embodiments, this functionality may be distributed among various other system components.

[0048] In addition, although the procedures of the methods and processes described herein are described in a particular order for ease of description, unless the context dictates otherwise, various procedures may be reordered, added, and / or omitted according to various embodiments. In addition, the procedures described with respect to a method or process may be incorporated into other described methods or processes; similarly, system components described according to a particular structural architecture and / or with respect to one system may be organized in an alternative structural architecture and / or incorporated into other described systems. Therefore, although various embodiments with or without some features are described to facilitate description and explanation of aspects of these embodiments, various components and / or features described herein with respect to specific embodiments may be replaced, added, and / or subtracted from other described embodiments, unless the context dictates otherwise. Therefore, although several embodiments are described above, it will be understood that the present invention is intended to cover all modifications and equivalents within the scope of the appended claims.

Claims

1. A device comprising: one or more first resonators, each first resonator having a corresponding parasitic capacitance; A second resonator having a second parasitic capacitance, the second resonator comprising: substrate; a bottom electrode disposed on the substrate; a piezoelectric layer disposed on the bottom electrode; a top electrode disposed on the piezoelectric layer; wherein in a first region, the bottom electrode overlaps a top electrode, wherein there is no piezoelectric layer between the bottom electrode and the top electrode, wherein an area of ​​the first region is determined at least in part based on a difference between the second parasitic capacitance and the corresponding parasitic capacitance of at least one of the one or more first resonators.

2. The device of claim 1, wherein at least one first resonator has a first piezoelectric orientation, wherein the second resonator has a second piezoelectric orientation opposite to the first piezoelectric orientation.

3. The apparatus of claim 2, wherein the at least one first resonator and a second resonator are placed in a parallel configuration.

4. The apparatus of claim 2, wherein the at least one first resonator and a second resonator are placed in a series configuration.

5. The apparatus of claim 1, wherein the one or more first resonators include a first center resonator, a second center resonator, and an outer resonator, wherein the one or more first resonators and the second resonator are placed in a four-element strip configuration.

6. The apparatus of claim 5, wherein the bottom electrode of the second resonator comprises a first elongated member configured to extend longitudinally at least partially around a first side of at least one of the one or more first resonators.

7. The apparatus of claim 6, wherein the bottom electrode comprises a second elongated member configured to extend longitudinally at least partially around a second side of at least one of the one or more first resonators.

8. The apparatus of claim 5, wherein a second bottom electrode of the outer resonator comprises a second elongated member configured to extend longitudinally at least partially around a second side of at least one of the first or second center resonators.

9. The apparatus of claim 1, wherein the first zone is a dead zone.

10. A resonator, comprising: The substrate including a top surface; a bottom electrode disposed on the top surface of the substrate; a piezoelectric layer disposed on the bottom electrode; a top electrode disposed on the piezoelectric layer; Wherein the bottom electrode includes a first elongated member configured to extend longitudinally along the top surface on a first side of the substrate.

11. The resonator of claim 10, wherein the first elongated member is configured to extend longitudinally at least partially around a first side of at least one second resonator.

12. The resonator of claim 10, wherein the bottom electrode comprises a second elongated member configured to extend longitudinally along the top surface on a second side of the at least one second resonator.

13. The resonator of claim 12, wherein the second elongated member is configured to extend longitudinally at least partially around the first side of at least one second resonator.

14. The resonator of claim 10, wherein in a first region, the bottom electrode overlaps a top electrode, wherein there is no piezoelectric layer between the top and bottom electrodes, wherein a surface area of ​​the first region is determined at least in part based on a difference in parasitic capacitance with a second resonator.

15. An apparatus comprising: A first external resonator having a first parasitic resonance, the first external resonator comprising: a substrate comprising a top surface; a bottom electrode disposed on the top surface of the substrate; a piezoelectric layer disposed on the bottom electrode; a top electrode disposed on the piezoelectric layer; a first central resonator coupled to the first outer resonator; a second central resonator coupled to the first central resonator; a second outer resonator coupled to the second central resonator; Wherein the bottom electrode includes a first elongated member configured to extend longitudinally along the top surface of the substrate at least partially around a first side of at least one of the second center resonator, the first center resonator, or the second outer resonator.

16. The apparatus of claim 15, wherein the first outer resonator, the first center resonator, the second center resonator, and the second outer resonator are placed in a four-element strip configuration.

17. The apparatus of claim 15, wherein the bottom electrode comprises a second elongated member configured to extend longitudinally along the top surface of the substrate at least partially around a second side of at least one of the second central resonator, the first central resonator, or the first outer resonator.

18. The apparatus of claim 15, wherein the second outer resonator comprises a second bottom electrode, wherein the second bottom electrode includes a second elongated member configured to extend longitudinally along the top surface of the substrate at least partially around a second side of at least one of the first center resonator, the second center resonator, or the first outer resonator.

19. The apparatus of claim 15, wherein in a dead region, the bottom electrode overlaps a top electrode without the piezoelectric layer being present above and between the bottom electrodes.

20. The apparatus of claim 19, wherein an area of ​​the dead zone is determined based in part on a difference in parasitic capacitance between the first parasitic capacitance and a corresponding parasitic capacitance of at least one of the first center resonator, a second center resonator, and a second outer resonator.

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