Acoustic filter device with high edge gradient

Abstract

There is provided a filter device including a first series resonator and a second series resonator connected between a pair of ports. The device may include at least one parallel resonator connected between a ground connection and a node between the first series resonator and the second series resonator, or between one of the pair of ports and one of the first series resonator and the second series resonator, the first series resonator and the second series resonator respectively comprise a first capacitance value and a second capacitance value which are different from each other, and wherein the first series resonator and the second series resonator and the at least one parallel resonator comprise: a substrate; at least one piezoelectric layer attached to the substrate directly or via one or more intermediate layers; and an interdigital transducer (IDT) at a surface of the at least one piezoelectric layer and including a plurality of interleaved IDT fingers.

Description

Cross - Reference to Related Applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 603,529, filed on November 28, 2023, and U.S. Non - Provisional Patent Application No. 18 / 961,745, filed on November 27, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] This disclosure relates to radio frequency (RF) filters using acoustic wave resonators, and more particularly, to filters for communication devices. Background Art

[0003] An RF (radio frequency) filter is a two - port device configured to pass certain frequencies and block others, where "pass" means transmission with relatively low signal loss and "block" means blocking or significantly attenuating. The range of frequencies that the filter passes is called the "passband" of the filter. The range of frequencies that such a filter blocks is called the "stopband" of the filter. A typical RF filter has at least one passband and at least one stopband. The specific requirements for the passband or stopband can depend on the specific application. For example, in some cases, the "passband" can be defined as the frequency range where the insertion loss of the filter is better than a defined value such as 1 dB, 2 dB, or 3 dB, and the "stopband" can be defined as the frequency range where the rejection of the filter is greater than a defined value such as 20 dB, 30 dB, 40 dB, or a larger value, depending on the application.

[0004] RF filters are used in communication systems for transmitting information over wireless links. For example, RF filters can be present in the RF front - ends of cellular base stations, mobile phones and computing devices, satellite transceivers and ground stations, IoT (Internet of Things) devices, laptop computers and tablet computers, fixed - point radio links, and other communication systems. RF filters are also used in radar, electronic, and information warfare systems.

[0005] Performance enhancement of RF filters in wireless systems can have a wide - ranging impact on system performance. Improvements in RF filters can be used to provide system performance improvements such as larger cell sizes, longer battery life, higher data rates, larger network capacity, lower costs, enhanced security, higher reliability, etc. These improvements can be achieved individually and in combination at multiple levels of a wireless system (e.g., at the RF module, RF transceiver, mobile or fixed subsystem, or network level). As the demand for RF filters operating at higher frequencies continues to increase, there is a need for improved filters that can operate in different frequency bands, as well as for improved manufacturing processes for fabricating such filters.

[0006] A laterally excited thin film bulk acoustic resonator (XBAR) is an acoustic resonator structure for microwave filters. An XBAR resonator typically includes interdigital transducers (IDTs) formed on a thin floating layer or diaphragm of a single crystal piezoelectric material. The IDTs include a first set of parallel fingers extending from a first bus bar and a second set of parallel fingers extending from a second bus bar. The first set of parallel fingers and the second set of parallel fingers are interleaved. A microwave signal applied to the IDTs excites a primary shear acoustic wave in the piezoelectric diaphragm. The XBAR resonator provides very high electromechanical coupling and high frequency capabilities. The XBAR resonator can be used in various RF filters including band-stop filters, band-pass filters, diplexers, and multiplexers. The XBAR is well-suited for filters for communication bands with frequencies above 3 GHz. SUMMARY OF THE INVENTION

[0007] Currently, RF filters operating at a specific frequency (e.g., under Wi-Fi 5) require as steep an upper passband edge as possible to meet the rejection of the next adjacent operating frequency (e.g., under Wi-Fi 6). In other words, the upper passband edge is located at the end of the passband and the start of the stopband. Conventional implementations require large-scale circuits to obtain a steep upper passband edge. As described in more detail below, a technique for obtaining a steep upper passband edge without implementing large-scale circuits can be performed by further reducing the operating frequency of the lowest operating series resonator currently employed by the filter. As described further below, the area of the lowest operating series resonator of the filter is increased and / or the pitch of the electrodes is adjusted. By combinatorially adjusting these two parameters, the steepness of the upper passband can be increased while maintaining the overall circuit of the filter employed.

[0008] Accordingly, in an exemplary embodiment, there is provided a filtering device that includes: at least three series resonators connected between a pair of ports; and at least two parallel resonators, each connected between a ground connection and a node between a pair of the at least three series resonators, or connected between a ground connection and a node between one of the pair of ports and one of the at least three series resonators; in this regard, the series resonator having the lowest anti-resonant frequency among the at least three series resonators has the maximum capacitance value of the at least three series resonators, and further, each of the at least three series resonators and the at least two parallel resonators includes: a substrate; a piezoelectric layer attached to the substrate directly or via one or more intermediate layers; and an interdigital transducer (IDT) at the piezoelectric layer and including a plurality of interleaved fingers.

[0009] In another exemplary aspect, at least three series resonators include a pair of internal resonators and a pair of external resonators commonly connected in series between a pair of ports. Further, one of the pair of internal resonators has the lowest anti-resonant frequency and the maximum capacitance value. In other aspects, the pair of internal resonators includes stacks identical to each other, and the pair of external resonators includes stacks identical to each other.

[0010] In another exemplary aspect, the series resonator having the maximum capacitance includes an IDT having the largest area among the areas of the IDTs of each of the at least three series resonators.

[0011] In another exemplary aspect, the series resonator having the maximum capacitance includes an IDT having the smallest pitch among the corresponding pitches of the IDTs of each of the at least three series resonators.

[0012] In another exemplary aspect of the filtering device, at least the series resonator having the lowest anti-resonant frequency among the at least three series resonators includes a plurality of sub-resonators.

[0013] Further, in another exemplary aspect, the respective piezoelectric layers of each of the at least three series resonators and the at least two parallel resonators each form a diaphragm located above the cavity of the corresponding resonator, and the respective IDTs of each of the at least three series resonators and the at least two parallel resonators are provided on the corresponding diaphragm.

[0014] In another exemplary aspect, for each of the resonators, the piezoelectric layer and the IDT are configured such that the radio frequency signal applied to each IDT mainly excites a shear acoustic mode in the piezoelectric layer, the shear acoustic mode includes a bulk shear wave, the bulk shear wave has a propagation direction perpendicular to the direction of the main transverse excitation electric field generated by the IDT, and when the atomic motion of the bulk shear wave is mainly horizontal in the piezoelectric layer, the electric field is mainly transversely excited while the bulk shear wave propagates in a direction mainly perpendicular to the direction of the atomic motion.

[0015] According to another exemplary aspect, a filtering device is provided, the filtering device comprising: a plurality of series resonators connected between a pair of ports; and a plurality of shunt resonators each connected between a ground connection and a node between a pair of the plurality of series resonators, or connected between a ground connection and a node between one of the pair of ports and one of the plurality of series resonators; in this aspect, each of the plurality of series resonators and the plurality of shunt resonators comprises: a substrate; a piezoelectric layer attached to the substrate directly or via one or more intermediate layers; and an interdigital transducer (IDT) at the piezoelectric layer and comprising a plurality of interleaved fingers. Further, the series resonator having the lowest anti-resonant frequency among the plurality of series resonators has a characteristic value different from the corresponding characteristic values of the other series resonators among the plurality of series resonators, and the corresponding characteristic value is at least one of the area of the corresponding IDT and the pitch of the corresponding IDT.

[0016] In another exemplary aspect, the plurality of series resonators comprises a pair of internal resonators and a pair of external resonators commonly connected in series between a pair of ports. In this aspect, the corresponding characteristic value is the area of the corresponding IDT, and the internal resonator having the lowest anti-resonant frequency among the pair of internal resonators has the largest IDT area. In another aspect, the corresponding characteristic value is the pitch of the corresponding IDT, and the internal resonator having the lowest anti-resonant frequency among the pair of internal resonators has the smallest IDT pitch.

[0017] Further, in another exemplary aspect, the pair of internal resonators comprises stacks identical to each other, and the pair of external resonators comprises stacks identical to each other.

[0018] In another exemplary aspect, the internal resonator having the lowest anti-resonant frequency among the pair of internal resonators has the largest capacitance of the plurality of series resonators. In this aspect, the series resonator having the largest capacitance comprises an IDT having the smallest pitch among the corresponding pitches of the IDTs of each resonator among the plurality of series resonators. Further, the series resonator having the largest capacitance may comprise an IDT having an area larger than the corresponding areas of the IDTs of the other series resonators among the plurality of series resonators.

[0019] In another exemplary aspect, the corresponding piezoelectric layer of each resonator among the plurality of series resonators and the plurality of shunt resonators respectively forms a diaphragm located above the cavity of the corresponding resonator, and the corresponding IDT of each resonator among the plurality of series resonators and the plurality of shunt resonators is disposed on the corresponding diaphragm.

[0020] In another exemplary aspect, for each of the resonators, the piezoelectric layer and the IDT are configured such that an RF signal applied to each IDT predominantly excites a shear acoustic mode in the corresponding piezoelectric layer, the shear acoustic mode including a bulk shear wave having a propagation direction perpendicular to the direction of the predominantly transverse exciting electric field generated by the IDT, and the electric field is predominantly transversely excited when the atomic motion of the bulk shear wave is predominantly horizontal in the piezoelectric layer, while the bulk shear wave propagates in a direction predominantly perpendicular to the direction of the atomic motion.

[0021] According to another exemplary aspect, there is provided an RF module including: a filtering device including a plurality of acoustic resonators; and an RF circuit coupled to the filtering device, the filtering device and the RF circuit being packaged within a common package. In this aspect, the plurality of acoustic resonators of the filtering device include: at least three series resonators connected between a pair of ports of the filtering device; and at least two shunt resonators each connected between a ground connection and a node between a pair of the at least three series resonators, or connected between a ground connection and a node between one of the pair of ports and one of the at least three series resonators; furthermore, the series resonator having the lowest anti-resonant frequency among the at least three series resonators has the largest capacitance value of the at least three series resonators, and each of the at least three series resonators and the at least two shunt resonators includes: a substrate; a piezoelectric layer attached to the substrate directly or via one or more intermediate layers; and an interdigital transducer (IDT) at the piezoelectric layer and including a plurality of interleaved fingers, and, for each of the plurality of acoustic resonators, the piezoelectric layer and the IDT are configured such that an RF signal applied to the IDT predominantly excites a shear acoustic mode in the piezoelectric layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0022] The drawings incorporated in and forming a part of this specification illustrate one or more example aspects of the present disclosure and, together with the detailed description, are used to explain the principles and embodiments of one or more example aspects of the present disclosure.

[0023] Figure 1A Schematic plan view and schematic cross-sectional view of a laterally excited thin film bulk acoustic resonator (XBAR).

[0024] Figure 1B Schematic cross-sectional view showing an alternative configuration of the XBAR.

[0025] Figure 2A is Figure 1A An enlarged schematic cross-sectional view of a portion of the XBAR.

[0026] Figure 2B is Figure 1A An enlarged schematic cross-sectional view of an alternative configuration of the XBAR.

[0027] Figure 2C is Figure 1A an enlarged schematic cross-sectional view of another alternative configuration of the XBAR.

[0028] Figure 2D is Figure 1A an enlarged schematic cross-sectional view of another alternative configuration of the XBAR.

[0029] Figure 2E an enlarged schematic cross-sectional view of a part of a firmly mounted XBAR (SM XBAR).

[0030] Figure 3A a schematic cross-sectional view of an XBAR according to an exemplary aspect.

[0031] Figure 3B an alternative schematic cross-sectional view of an XBAR according to an exemplary aspect.

[0032] Figure 4 a graph showing the shear horizontal acoustic mode in the XBAR.

[0033] Figure 5A is using Figure 1A and / or Figure 1B a schematic block diagram of a filter of the XBAR.

[0034] Figure 5B a schematic diagram of a radio frequency module including an acoustic wave filtering device according to an exemplary aspect.

[0035] Figure 6A a circuit diagram of a filter using a resonator according to an exemplary aspect.

[0036] Figure 6B is according to an exemplary aspect of Figure 6A an exemplary graph of the filter response of the circuit diagram shown.

[0037] Figure 6C is according to an exemplary aspect of and Figure 6A an exemplary graph of resonator values corresponding to the circuit diagram shown.

[0038] Figure 7A is according to an exemplary aspect of Figure 6A an exemplary graph of the filter response of the circuit diagram shown.

[0039] Figure 7B is according to an exemplary aspect of and Figure 6A an exemplary graph of series resonator characteristics corresponding to the circuit diagram shown.

[0040] Figure 8A flowchart showing a method of manufacturing a filter as described herein according to an exemplary aspect is shown.

[0041] Throughout this specification, elements shown in the figures are assigned three - or four - digit reference numerals, where the two least - significant digits are specific to the element and one or two of the most - significant digits are the figure number in which the element is first introduced. It may be assumed that elements not described in conjunction with the figures have the same characteristics and functions as elements with the same reference numerals described previously. Detailed Description

[0042] Aspects of the disclosed acoustic resonators, filter devices, and methods of manufacturing the acoustic resonators and filter devices will now be described with reference to the accompanying drawings, where like reference numerals may be used throughout to indicate like elements. In the following description, for purposes of explanation, numerous specific details are set forth to facilitate a thorough understanding of one or more aspects of the present disclosure. However, it will be apparent that any aspect described below may be practiced without the use of the specific design details described below in some or all instances. In other instances, well - known structures and devices are shown in block diagram form to facilitate the description of one or more aspects. A simplified overview of one or more aspects of the present invention is given below to provide a basic understanding of the present invention.

[0043] Figure 1A A simplified schematic top - view and orthogonal cross - sectional view of a bulk acoustic resonator device (i.e., a laterally - excited thin - film bulk acoustic resonator (XBAR) 100) are shown. The XBAR resonator (e.g., resonator 100) can be used in various RF filters including band - reject filters, band - pass filters, diplexers, and multiplexers. The XBAR is particularly suitable for filters in communication bands with frequencies above 3 GHz.

[0044] Generally, the XBAR 100 includes conductor patterns (e.g., thin film metal layers) formed on one or both surfaces of a piezoelectric layer 110 (in this document, the piezoelectric plate or piezoelectric layer may be used interchangeably), and the piezoelectric layer 110 has parallel front side 112 and rear side 114 (which are usually also referred to as the first surface and the second surface respectively). It should be understood that the term "parallel" generally refers to the front side 112 and the rear side 114 that are opposite to each other, and these surfaces do not have to be flat and parallel to each other. For example, due to manufacturing differences caused by the deposition process, the front side 112 and the rear side 114 may have surface undulations as will be understood by those skilled in the art. In addition, the term "substantially" as used herein is used to describe a situation when components, parameters, etc. are approximately the same (i.e., "substantially constant"), but as will be understood by those skilled in the art, in practice, they may vary slightly (e.g., within an acceptable threshold or percentage) due to possible manufacturing differences. For the purposes of this disclosure, unless explicitly indicated to refer only to alternatives or if the alternatives are mutually exclusive, the use of the term "or" in the claims is used to mean "and / or".

[0045] According to an exemplary aspect, the piezoelectric layer may be a thin single crystal layer of a piezoelectric material (e.g., lithium niobate, lithium tantalate, lanthanum gallium silicate, gallium nitride, or aluminum nitride). It should be understood that the term "single crystal" does not necessarily mean a completely uniform crystal structure and may include impurities resulting from manufacturing differences as long as the crystal structure is within an acceptable tolerance. The piezoelectric layer is cut such that the orientations of the X, Y, and Z crystal axes relative to the front side and the rear side are known and consistent. In the examples described herein, the piezoelectric layer is Z-cut, i.e., the Z-axis is perpendicular to the front side 112 and the rear side 114. However, the XBAR may be fabricated on piezoelectric layers having other crystal orientations, including rotated Z-cut, Y-cut, and rotated YX-cut.

[0046] The Y-cut series (e.g., 120Y and 128Y) are generally referred to as 120YX or 128YX, where the "cutting angle" is the angle between the y-axis and the normal of the layer. The "cutting angle" is equal to β + 90°. For example, a layer having Euler angles [0°, 30°, 0°] is generally referred to as "120° rotated Y-cut" or "120Y". Thus, the Euler angles of 120YX and 128YX are [0°, 120° - 90°, 0°] and [0°, 128° - 90°, 0°] respectively. "Z-cut" is generally referred to as ZY-cut and is understood to mean that the layer surface is perpendicular to the Z-axis, but the wave propagates along the Y-axis. The Euler angle of ZY-cut is [0°, 0°, 90°].

[0047] Except for the portion of the piezoelectric layer 110 that forms the diaphragm 115 above (e.g., spanning or extending over) the cavity 140 in one or more layers (e.g., one or more intermediate layers above or in the substrate) below the piezoelectric layer 110, the rear side 114 of the piezoelectric layer 110 can be at least partially supported by the surface of the substrate 120. In other words, the rear side 114 of the piezoelectric layer 110 can be directly or indirectly coupled or connected to the surface of the substrate 120 via one or more intermediate layers (e.g., a dielectric layer such as a silicon oxide layer). Additionally, as used interchangeably herein, the phrases "supported by" or "attached to" can mean direct attachment, indirect attachment, mechanically supported, structurally supported, or any combination thereof. The portion of the piezoelectric layer located above the cavity (e.g., spanning or extending over the cavity) can be referred to herein as the "diaphragm" 115 because it is physically similar to the diaphragm of a microphone. As Figure 1A shown, the diaphragm 115 abuts the remainder of the entire perimeter 145 of the piezoelectric layer 110 surrounding the cavity 140. In this context, "abuts" means "connected continuously without any intervening substance". However, in an exemplary aspect, the diaphragm 115 can be configured such that at least 50% of the edge surface of the diaphragm 115 is coupled to the edge of the piezoelectric layer 110.

[0048] According to an exemplary aspect, the substrate 120 is configured to provide mechanical support to the piezoelectric layer 110. The substrate 120 can be, for example, silicon, sapphire, quartz, or some other material, or a combination of materials. The rear side 114 of the piezoelectric layer 110 can be bonded to the substrate 120 using a wafer bonding process. Alternatively, the piezoelectric layer 110 can be grown on the substrate 120, or otherwise supported or attached to the substrate in some other manner.

[0049] For the purposes of this disclosure, "cavity" has its conventional meaning of "an empty space within a solid body". The cavity 140 can be a hole that passes completely through the substrate 120 (as shown in cross-section A-A), a hole within a dielectric layer (as Figure 1B shown), or a groove in the substrate 120. For example, the cavity 140 can be formed by selectively etching the substrate 120 before or after directly or indirectly attaching the piezoelectric layer 110 and the substrate 120.

[0050] As shown in the figure, the conductor pattern of the XBAR 100 includes an interdigital transducer (IDT) 130. The IDT 130 includes a first plurality of parallel fingers (e.g., finger 136) extending from a first bus bar 132 and a second plurality of fingers extending from a second bus bar 134. The first plurality of parallel fingers and the second plurality of parallel fingers are interleaved with each other, and they may be "substantially" parallel to each other due to minor variations (e.g., due to manufacturing tolerances). At least a portion of the interleaved fingers overlaps a distance AP, which is generally referred to as the "aperture" of the IDT. The center-to-center distance L between the outermost fingers of the IDT 130 is the "length" of the IDT.

[0051] In Figure 1A the example of, the IDT 130 is at the surface (e.g., the first surface) of the front side 112 of the piezoelectric layer 110. However, as described below, in other configurations, the IDT 130 may be at the surface (e.g., the second surface) of the rear side 114 of the piezoelectric layer 110, or at both the surface of the front side 112 and the rear side 114 of the piezoelectric layer 110, respectively.

[0052] The first bus bar 132 and the second bus bar 134 are configured as terminals of the XBAR 100, from which a plurality of interleaved fingers extend. In operation, a radio frequency signal or a microwave signal applied between the two bus bars 132, 134 of the IDT 130 mainly excites an acoustic mode (i.e., the main shear acoustic mode) within the piezoelectric layer 110. As will be discussed further in detail, the mainly excited shear acoustic mode is a bulk shear mode or a bulk acoustic wave, in which the acoustic energy of the bulk shear acoustic wave is excited by the IDT 130 in the piezoelectric layer 110 and propagates in a direction that is substantially, dominantly, and / or mainly orthogonal to the surface of the piezoelectric layer 110, and this direction is also mainly perpendicular or transverse to the direction of the electric field generated by the IDT fingers. That is, when a radio frequency or microwave signal is applied between the two bus bars 132, 134, the RF voltage applied to each group of IDT fingers generates a time-varying electric field that is laterally excited with respect to the surface of the piezoelectric layer 110. Therefore, in some cases, the mainly excited acoustic mode can generally be referred to as a laterally excited bulk acoustic wave because, contrary to propagation, the displacement mainly occurs in the direction of the body of the piezoelectric layer, as will be discussed in more detail below with reference to Figure 4 discussed in more detail.

[0053] For the purposes of the present disclosure, a "primary acoustic mode" can generally refer to an operating mode that causes vibrational displacement in a primary thickness shear direction (e.g., the X direction), such that the wave propagates substantially and / or primarily in a direction connecting the opposing front and back surfaces of the piezoelectric layer (i.e., in the Z direction). In other words, the X-direction component of the wave is significantly less than the Z-direction component. The use of the term "primary" in "primarily excited acoustic mode" does not necessarily refer to a low-order or high-order mode. Thus, an XBAR is considered a laterally excited thin film bulk acoustic resonator. One physical constraint is that when a radio frequency or microwave signal is applied between the two busbars 132, 134 of the IDT 130, heat is generated, and this heat must be dissipated from the resonator to improve performance. Generally, heat can be dissipated through lateral conduction in the film (e.g., in the electrode itself) and through vertical conduction from the cavity to the substrate.

[0054] In either case, the IDT 130 is located at or on the piezoelectric layer 110 such that at least the fingers of the IDT extend or are on a portion of the piezoelectric layer 110 that is above the cavity 140 (e.g., the diaphragm 115), as described herein. As Figure 1A shown, the cavity 140 has a rectangular cross-section that is larger than the aperture AP and length L of the IDT 130. According to other exemplary aspects, the cavity of the XBAR can have different cross-sectional shapes, such as regular or irregular polygons. The cavity of the XBAR can have more or fewer than four sides, and these sides can be straight or curved.

[0055] According to an exemplary aspect, the area of the XBAR 100 is determined as the area of the IDT 130. For example, the area of the IDT 130 can be determined based on the product of a measured value of the length L multiplied by the width of the aperture AP of the interleaved fingers of the IDT 130. As used herein in the present disclosure, the area is in μm 2 units. Thus, as described below, the area of the XBAR 100 can be adjusted based on design choices, thereby adjusting the total capacitance of the XBAR 100.

[0056] For ease of presentation in Figure 1A the geometry pitch and width of the IDT fingers are greatly magnified relative to the length (dimension L) and aperture (dimension AP) of the XBAR. A typical XBAR has more than ten parallel fingers in the IDT. For example, according to an exemplary aspect, an XBAR can have hundreds or even thousands of parallel fingers in the IDT. Similarly, the thickness of the fingers in the cross-sectional view is greatly magnified.

[0057] Figure 1B A schematic cross-sectional view of an alternative XBAR configuration 100' is shown. In Figure 1BIn, the cavity 140 of the resonator 100' (which can generally correspond to Figure 1A 's cavity 140) is completely formed within a dielectric layer 124 (such as, for example, silicon oxide or silica, as Figure 1B shown), and this dielectric layer 124 is located between a substrate 120 (designated as Si in Figure 1B ) and a piezoelectric layer 110 (designated as LN in Figure 1B ). Although a single dielectric layer 124 is shown as having a cavity 140 formed therein (e.g., by etching), it should be understood that the dielectric layer 124 can be formed from a plurality of individual dielectric layers formed on top of each other to provide a stack of materials.

[0058] Furthermore, in the example of Figure 1B , all sides of the cavity 140 are defined by the dielectric layer 124. However, in other exemplary embodiments, one or more sides of the cavity 140 can be defined by the substrate 120 and / or the piezoelectric layer 110. In the example of Figure 1B , the cavity 140 has a trapezoidal shape. However, as described above, the cavity shape is not limited and can be rectangular, oval, or other shapes.

[0059] Figure 2A Shows a detailed schematic cross-sectional view (labeled Detail C) of the XBAR 100 of Figure 1A or Figure 1B . The piezoelectric layer 110 is a single-crystal layer of piezoelectric material having a thickness ts. Ts can be, for example, from 100 nm to 1500 nm. When used in filters for the 5G NR and Wi-Fi TM frequency bands from 3.4 GHz to 7 GHz, the thickness ts can be, for example, from 150 nm to 500 nm. In an exemplary aspect, the thickness ts can be measured in a direction substantially perpendicular or orthogonal to the surface of the piezoelectric layer.

[0060] In this aspect, a front-side dielectric layer 212 (such as, for example, a first dielectric coating or material) can be formed on the front side 112 of the piezoelectric layer 110. By definition, the "front side" of the XBAR is the surface facing away from the substrate. The front-side dielectric layer 212 has a thickness tfd. As Figure 2A shown, the front-side dielectric layer 212 covers the IDT fingers 238a, 238b, which can correspond to the fingers 136 as described above with respect to Figure 1A . Although not shown in Figure 2A , the front-side dielectric layer 212 can also be deposited only between the IDT fingers 238a, 238b. In this case, an additional thin dielectric layer (not shown) can be deposited on the IDT fingers to seal and passivate the fingers. Furthermore, although Figure 2AAlthough not shown either, the front dielectric layer 212 may also be deposited, for example, only on the selected IDT fingers 238a.

[0061] The back dielectric layer 214 (e.g., a second dielectric coating or material) may also be formed on the back side of the back side 114 of the piezoelectric layer 110. Generally speaking, for the purposes of the present disclosure, the term "back side" refers to the side opposite to the conductor pattern of the IDT structure and / or the side opposite to the front dielectric layer 212. In addition, the back dielectric layer 214 has a thickness tbd. The front dielectric layer 212 and the back dielectric layer 214 may be non-piezoelectric dielectric materials, such as silicon oxide, silicon dioxide, or silicon nitride. Tfd and tbd may be, for example, from 0 to 500 nm. Tfd and tbd may be less than the thickness ts of the piezoelectric layer. Tfd and tbd are not necessarily equal, and the front dielectric layer 212 and the back dielectric layer 214 are not necessarily the same material. In an exemplary aspect, according to various exemplary aspects, either or both of the front dielectric layer 212 and the back dielectric layer 214 may be formed of multiple layers of two or more materials.

[0062] The IDT fingers 238a, 238b may include aluminum, substantially (i.e., mainly) aluminum alloy, copper, substantially (i.e., mainly) copper alloy, beryllium, gold, or some other conductive material. Thin (relative to the total thickness of the conductor) layers of other metals, such as chromium or titanium, may be formed below and / or above these fingers to improve the adhesion between the fingers and the piezoelectric layer 110, and / or passivate or encapsulate these fingers. The bus bars of the IDT ( Figure 1A 132, 134 in) may be made of the same or different materials as these fingers. In various exemplary aspects, the cross-sectional shape of the IDT fingers may be trapezoidal (finger 238a), rectangular (finger 238b), or some other shape. Generally speaking, note that the terms "comprising", "having", "including", and "containing" (and their variants) used herein are open conjunctions and allow the addition of other elements when used in claims. In addition, unless the context otherwise provides, "a" or "an" when used in a claim or specification in conjunction with the term "comprising" means one or more than one.

[0063] The dimension p (i.e., "pitch") may be considered as the center-to-center spacing between adjacent IDT fingers (e.g., Figures 2A to 2D the IDT fingers 238a, 238b in). As Figure 2AAs shown, the center-to-center spacing center point can be measured at the center of the width "w" of the finger. In some cases, if the width of a given finger changes along the length of the finger, if the width and the extending direction change, or any of their variations, the center-to-center spacing can change. In such cases, for a given position along AP, the center-to-center spacing can be measured as the average center-to-center spacing, the maximum center-to-center spacing, the minimum center-to-center spacing, or any of their variations. Adjacent fingers can each extend from different bus bars, and the center-to-center spacing can be measured from the center of the first finger extending from the first bus bar to the center of the second finger adjacent to the first finger and extending from the second bus bar. The center-to-center spacing can be constant along the length of the IDT. In this case, the dimension p can be referred to as the pitch of the IDT and / or the pitch of the XBAR. However, in an alternative exemplary aspect, the center-to-center spacing varies along the length of the IDT. In this case, the pitch of the IDT can be the average value of the dimension p along the length of the IDT. When compared to other adjacent fingers, the center-to-center spacing from one finger to an adjacent finger can vary continuously in discrete portions of multiple adjacent pairs or any combination thereof. Each IDT finger (e.g., Figures 2A to 2D the IDT fingers 238a, 238b in Figure 1A ) has a width w measured perpendicular to the long direction of each finger. The width w can also be referred to herein as a "mark". Generally, the width of the IDT finger can be constant along the length of the IDT. In this case, the dimension w can be the width of each IDT finger. However, in another exemplary aspect as will be discussed below, the widths of the individual IDT fingers vary along the length of the IDT 130. In this case, the dimension w can be the average value of the widths of the IDT fingers along the length of the IDT. Note that the pitch p and the width w of the IDT finger are measured in a direction substantially parallel to the length L of the IDT, as defined in

[0064] Generally, the IDT of the XBAR is significantly different from the IDT used in surface acoustic wave (SAW) resonators, mainly in that the IDT of the XBAR excites as described below with respect to Figure 4The main shear acoustic mode (also known as the main shear mode, main shear thickness mode, etc.) is described in more detail, where the SAW resonator excites surface waves during operation. Additionally, in the SAW resonator, the pitch of the IDT is one-half of the acoustic wavelength at the resonant frequency. Further, the mark-to-pitch ratio of the SAW resonator IDT is typically close to 0.5 (i.e., the width of the mark or finger is approximately one-fourth of the acoustic wavelength at resonance). In an XBAR, the pitch p of the IDT is typically 2 to 20 times the width w of the finger. Additionally, the pitch p of the IDT is typically 2 to 20 times the thickness ts of the piezoelectric layer 110. Further, the width of the IDT fingers in the XBAR is not limited to one-fourth of the acoustic wavelength at resonance. For example, the width of the XBAR IDT fingers can be 500 nm or greater, such that the IDT can be fabricated using optical lithography. The thickness tm of the IDT fingers can range from 100 nm to approximately equal to the width w, as lithography processes generally cannot support configurations where the thickness is greater than the width. The thickness of the bus bars ( Figure 1A 132, 134 in

[0065] can be equal to the thickness tm of the IDT fingers, less than the thickness tm of the IDT fingers, greater than the thickness tm of the IDT fingers, or any combination thereof. Note that the XBAR devices described herein are not limited to the size ranges described herein.

[0066] Return reference Figure 2A , the thickness tfd of the front-side dielectric layer 212 above the IDT fingers 238a, 238b can be greater than or equal to the minimum thickness required to cover and passivate the IDT fingers and other conductors on the front side 112 of the piezoelectric layer 110. According to an exemplary aspect, depending on the material of the front-side dielectric layer and the deposition method, the minimum thickness can be, for example, 10 nm to 50 nm. The thickness of the back-side dielectric layer 214 can be configured to a specific thickness to adjust the resonant frequency of the resonator, as will be described in more detail below.

[0067] Although Figure 2A the configuration of the IDT fingers 238a and 238b at the front side 112 of the piezoelectric layer 110 is disclosed, alternative configurations can be provided. For example, Figure 2BAn alternative configuration (labeled Detail C') is shown, where the IDT fingers 238a, 238b are at the rear side 114 of the piezoelectric layer 110 (i.e., facing the cavity) and are covered by the rear dielectric layer 214. The front dielectric layer 212 may cover the front side 112 of the piezoelectric layer 110. In an exemplary aspect, the dielectric layer disposed on the diaphragm of each resonator may be trimmed or etched to adjust the resonant frequency. However, if the dielectric layer is on the side of the diaphragm facing the cavity, there may be variations in spurious modes (e.g., caused by a coating on the fingers). Additionally, the markings are changed by the passivation layer coated on the top of the IDT, which can also cause spurious. Thus, as Figure 2B shown, by disposing the IDT fingers 238a, 238b at the rear side 114 of the piezoelectric layer 110, the variation in the resolved frequency and its impact on spurious can be eliminated compared to when the IDT fingers 238a and 238b are on the front side 112 of the piezoelectric layer 110.

[0068] Figure 2C An alternative configuration (labeled Detail C'') is shown, where the IDT fingers 238a, 238b are on the front side 112 of the piezoelectric layer 110 and are covered by the front dielectric layer 212. The IDT fingers 238c, 238d are also on the rear side 114 of the piezoelectric layer 110 and are also covered by the rear dielectric layer 214. As previously described, the front dielectric layer 212 and the rear dielectric layer 214 are not necessarily of the same thickness or the same material.

[0069] Figure 2D Another alternative configuration (labeled Detail C''') is shown, where the IDT fingers 238a, 238b are on the front side 112 of the piezoelectric layer 110 and are covered by the front dielectric layer 212. The surface of the front dielectric layer is planarized. The front dielectric layer can be planarized, for example, by polishing or some other method. A thin layer of dielectric material with a thickness tp may cover the IDT fingers 238a, 238b to seal and passivate the fingers. The dimension tp can be, for example, 10 nm to 50 nm.

[0070] As described above regarding Figures 2A to 2D each XBAR configuration in the XBAR configuration described includes a diaphragm spanning the cavity. However, in an alternative aspect, the bulk acoustic resonator can be firmly mounted, where the diaphragm with the IDT fingers is mounted on or above a Bragg reflector, which in turn can be mounted on a substrate.

[0071] Specifically, Figure 2E a detailed schematic cross-sectional view of a firmly mounted XBAR (SM-XBAR) is shown. Note that, in addition to having a firmly mounted configuration, Figure 2E is generally disclosed in relation to Figure 1AA cross-section similar to the cross-section. In this regard, the SM-XBAR includes a piezoelectric layer 110 and an IDT (where only two fingers 236 are visible), and a dielectric layer 212 is disposed on the piezoelectric layer 110 and the IDT fingers 236. Similar to the above configuration, the piezoelectric layer 110 has parallel front and back surfaces. The dimension ts is the thickness of the piezoelectric layer 110. The width of the IDT fingers 236 is the dimension w, the thickness of the IDT fingers is the dimension tm, and the IDT pitch is the dimension p.

[0072] Contrary to Figure 1A the XBAR device shown, Figure 2E the IDT of the SM XBAR in [] is not formed on a diaphragm spanning a cavity in the substrate. Instead, an acoustic Bragg reflector 240 is sandwiched between the surface 222 of the substrate 220 and the back surface of the piezoelectric layer 110. The term "sandwiched between" means that the acoustic Bragg reflector 240 is disposed between the surface 222 of the substrate 220 and the back surface of the piezoelectric layer 110 and is mechanically attached to both the surface 222 of the substrate 220 and the back surface of the piezoelectric layer 110. In some cases, additional material layers (e.g., one or more dielectric layers) may be disposed between the acoustic Bragg reflector 240 and the surface 222 of the substrate 220 and / or between the Bragg reflector 240 and the back surface of the piezoelectric layer 110. Such additional material layers may be present, for example, to facilitate bonding of the piezoelectric layer 110, the acoustic Bragg reflector 240, and the substrate 220.

[0073] The acoustic Bragg reflector 240 may be an acoustic mirror configured to reflect at least a portion of the primary acoustic mode excited in the piezoelectric body and includes a plurality of dielectric layers alternating between a material having a high acoustic impedance and a material having a low acoustic impedance. The acoustic impedance of a material is the product of the shear wave velocity and the density of the material. "High" and "low" are relative terms. For each layer, the standard for comparison is the adjacent layer. The acoustic impedance of each "high" acoustic impedance layer is higher than the acoustic impedance of two adjacent "low" acoustic impedance layers. The acoustic impedance of each "low" acoustic impedance layer is lower than the acoustic impedance of two adjacent "high" acoustic impedance layers. As discussed above, the primary acoustic mode in the XBAR piezoelectric layer is a shear body wave. In an exemplary aspect, the thickness of each layer of the acoustic Bragg reflector 240 is equal to or approximately one-quarter of the wavelength in a layer of shear body waves having the same polarization as the primary acoustic mode at or near the resonant frequency of the SM XBAR. Dielectric materials having a relatively low acoustic impedance include silicon dioxide, carbon-containing silicon oxide, and certain plastics such as cross-linked polyphenylene polymers. Materials having a relatively high acoustic impedance include hafnium oxide, silicon nitride, aluminum nitride, and silicon carbide. All of the high acoustic impedance layers of the acoustic Bragg reflector 240 do not have to be the same material, and all of the low acoustic impedance layers do not have to be the same material. In Figure 2EIn the example, the acoustic Bragg reflector 240 has a total of six layers, but the acoustic Bragg reflector may have more or fewer than six layers in alternative configurations.

[0074] IDT fingers (e.g., IDT fingers 236, 238a, and 238b) may be disposed on the surface of the front side 112 of the piezoelectric layer 110. Alternatively, the IDT fingers (e.g., IDT fingers 236, 238a, and 238b) may be disposed in a groove formed in the surface of the front side 112. The groove may extend partially through the piezoelectric layer. Alternatively, the groove may extend completely through the piezoelectric layer.

[0075] Figure 3A and Figure 3B shows two exemplary cross-sectional views of the XBAR 100 along Figure 1A section A-A defined in Figure 3A In Figure 1A the piezoelectric layer 310 corresponding to the piezoelectric layer 110 is directly attached to a substrate 320, which may correspond to Figure 1A and / or Figure 1B the substrate 120 of

[0076] Figure 3BAn alternative aspect is shown, where the substrate 320 includes a base 322 and an intermediate layer 324 disposed between the piezoelectric layer 310 and the base 322. For example, the base 322 can be silicon (e.g., a silicon support substrate), and the intermediate layer 324 can be silicon dioxide or silicon nitride or some other material, such as an intermediate dielectric layer. That is, in this aspect, the base 322 and the intermediate layer 324 are collectively referred to as the substrate 320. As further shown, a cavity 340 is formed in the intermediate layer 324 below the portion of the IDT fingers of the piezoelectric layer 310 that includes the XBAR (i.e., the diaphragm 315). The cavity 340 can be formed, for example, by etching the intermediate layer 324 before attaching the piezoelectric layer 310. Alternatively, the cavity 340 can be formed by etching the intermediate layer 324. In other exemplary embodiments, the cavity 340 can be defined in the intermediate layer 324 in other ways that are different from whether the intermediate layer 324 is etched to define the cavity 340. In some cases, etching can be performed using a selective etchant that reaches the substrate through one or more openings (not shown) provided in the piezoelectric layer 310.

[0077] In this case, the diaphragm 315 (which can correspond to, for example, Figure 1A the diaphragm 115 in the exemplary aspect) can be adjacent to the remainder of the piezoelectric layer 310 (i.e., the remainder that surrounds most of the perimeter of the cavity 340). For example, the diaphragm 315 can be adjacent to the remainder of the piezoelectric layer 310 that surrounds at least 50% of the perimeter of the cavity 340. As Figure 3B shown, the cavity 340 extends completely through the intermediate layer 324. That is, the diaphragm 315 can have an outer edge facing the piezoelectric layer 310, where at least 50% of the edge surface of the diaphragm 315 is coupled to the edge of the piezoelectric layer 310 facing the diaphragm 315. This configuration provides increased mechanical stability of the resonator.

[0078] In other configurations, the cavity 340 can extend partially into the intermediate layer 324 but not completely through the intermediate layer 324 (i.e., the intermediate layer 324 can extend above the bottom of the cavity on top of the base 322) or can extend through the intermediate layer 324 and (partially or fully) into the base 322. As described above, it should be understood that according to the various exemplary aspects, the interleaved fingers of the IDT can be disposed on Figure 3A and Figure 3B either or both surfaces of the diaphragm 315 in

[0079] Figure 4 is a graphical illustration of the main excited acoustic mode of interest in the XBAR. Figure 4A small portion of an XBAR 400 is shown, which includes a piezoelectric layer 410 and three interleaved IDT fingers 430. In general, according to exemplary aspects, the exemplary configuration of the XBAR 400 may correspond to that described above and in Figures 2A to 2D Thus, it should be understood that piezoelectric layer 410 may correspond to piezoelectric layer 110 and IDT fingers 430 may be implemented according to any configuration of fingers 238a and 238b, for example.

[0080] In operation, an RF voltage is applied to the interlaced fingers 430. This voltage produces a time-varying electric field between these fingers. The direction of the electric field is transverse (i.e., transversely excited) or primarily parallel to the surface of the piezoelectric layer 410, as indicated by the arrow labeled "Electric Field." Due to the high dielectric constant of the piezoelectric layer 410, the electric field is highly concentrated in the piezoelectric layer relative to air. The transverse electric field induces shear deformation in the piezoelectric layer 410, thereby strongly exciting shear acoustic modes in the piezoelectric layer 410. In this context, "shear deformation" is defined as a deformation in which parallel planes in a material remain parallel and maintain a constant distance while translating relative to each other. In other words, parallel planes of the material are displaced laterally relative to each other. "Shear acoustic modes" are defined as acoustic vibration modes in a medium that cause shear deformation of the medium. The shear deformation in the XBAR 400 is represented by curve 460, where the adjacent small arrows provide a schematic indication of the direction and amplitude of the atomic motion. Note that for ease of illustration in Figure 4 In the visualization in FIG. 4 , the extent of atomic motion and the thickness of the piezoelectric layer 410 have been exaggerated. Although the atomic motion is primarily lateral (i.e., Figure 4 ), but the direction of the acoustic energy flow of the primarily excited shear acoustic mode is substantially and / or primarily normal to the surface of the piezoelectric layer, as indicated by arrow 465.

[0081] BARs based on shear acoustic wave resonances can achieve better performance than the current state-of-the-art film bulk acoustic resonator (FBAR) and firmly mounted resonator bulk acoustic wave (SMR BAW) devices with an electric field applied in the thickness direction. In such devices, the acoustic mode is compressed, with atomic motion and acoustic energy flow in the thickness direction. In addition, the piezoelectric coupling of shear wave XBAR resonances can be high (>20%) compared to other acoustic resonators. Therefore, the high piezoelectric coupling enables the design and implementation of microwave and millimeter wave filters with considerable bandwidth.

[0082] Figure 5ASchematic circuit diagram and layout of a high-frequency bandpass filter 500 using an XBAR, such as the general XBAR configuration 100 described above (e.g., a bulk acoustic resonator). The filter 500 has a conventional ladder filter architecture (which may include a split ladder filter architecture where the filter is split between multiple chips), which has a plurality of bulk acoustic resonators, including four resonators 510A, 510B, 510C, and 510D and three shunt resonators 520A, 520B, and 520C. The series resonators 510A, 510B, 510C, and 510D are connected in series between a first port and a second port (and are thus referred to by the term "series resonator"). In Figure 5A , the first port and the second port are labeled "In" and "Out", respectively. However, the filter 500 is bidirectional and either port can be used as the input or output of the filter. At least two shunt resonators (such as shunt resonators 520A and 520B) are connected from a node between the series resonators to a ground connection. The filter may include Figure 5A additional reactance components not shown in

[0083] , such as inductors. In an exemplary aspect, all shunt resonators and series resonators are XBARs (e.g., any one of the XBAR configurations 100 and / or 100' described above). As an example, four series resonators and three shunt resonators are included. The filter may have more or fewer than a total of seven resonators, more or fewer than four series resonators, and more or fewer than three shunt resonators. Generally, for both split ladder filter and non-split ladder filter architectures, all series resonators are connected in series between the input and output of the filter, and all shunt resonators are generally connected between ground and the input, output, or a node between two series resonators.In an exemplary filter 500, the series resonators 510A, 510B, 510C, and 510D and the parallel resonators 520A, 520B, and 520C of the filter 500 may be formed on at least one piezoelectric material layer 530 (and in some cases on a single piezoelectric material layer 530) bonded to a silicon substrate (not visible). However, in an alternative aspect, each resonator may be formed on a separate respective piezoelectric layer of each resonator, where all the resonators are located on the same chip. However, in some cases, for example, different resonators of the filter may be bonded to separate substrates. This may result in a segmented ladder architecture that may include one or more separate chips that include separate piezoelectric layers and IDTs of one or more bulk acoustic resonators, and then these separate piezoelectric layers and IDTs are configured together to form the entire segmented ladder filter. Additionally, each resonator includes a respective IDT (not shown), where at least the fingers of the IDT are disposed above a cavity or an acoustic mirror in the substrate. In this context and similar contexts, the term "respective" means "relating things to each other", i.e., having a one-to-one correspondence. In Figure 5A , the cavity is schematically shown as a dashed rectangle (e.g., rectangle 535). In this example, each IDT is disposed above a respective cavity. In other filters, the IDTs of two or more resonators may be disposed above a single cavity.

[0084] Each of the resonators 510A, 510B, 510C, 510D, 520A, 520B, and 520C in the filter 500 has a resonance where the admittance of the resonator (also interchangeably referred to as the Y-parameter) is very high and an anti-resonance where the admittance of the resonator is very low. The resonance and anti-resonance occur at the resonance frequency and the anti-resonance frequency, respectively, and for the various resonators in the filter 500, the resonance frequency and the anti-resonance frequency may be the same or different. In short, each resonator can be considered a short circuit at its resonance frequency and an open circuit at its anti-resonance frequency. At the resonance frequency of the parallel resonator and the anti-resonance frequency of the series resonator, the input-output transfer function will be close to zero. In a typical filter, the resonance frequency of the parallel resonator is below the lower edge of the filter passband, and the anti-resonance frequency of the series resonator is above the upper edge of the passband.

[0085] The frequency range between the resonance frequency and the anti-resonance frequency of the resonator corresponds to the coupling of the resonator. Depending on the design parameters of the filter 500, each of the resonators 510A, 510B, 510C, 510D, 520A, 520B, and 520C may have a specific coupling parameter to which the respective resonator is tuned in order to achieve the desired frequency response of the filter 500.

[0086] According to an exemplary aspect, each of the series resonators 510A, 510B, 510C, and 510D and the shunt resonators 520A, 520B, and 520C can have an XBAR configuration as described above with respect to Figures 1A to 2D wherein a diaphragm having IDT fingers spans over a cavity. Alternatively, each of the series resonators 510A, 510B, 510C, 510D and the shunt resonators 520A, 520B, and 520C can have an XBAR configuration, wherein the series resonators 510A, 510B, 510C, 510D and / or the shunt resonators 520A, 520B, and 520C can be fixedly mounted on or above a Bragg reflector (e.g., as Figure 2E shown), and the Bragg reflector can in turn be mounted on a substrate.

[0087] Figure 5B FIG. is a schematic diagram of a radio frequency module including an acoustic wave filtering device according to an exemplary aspect. Specifically, Figure 5B FIG. shows a radio frequency module 540 including one or more acoustic wave filters 544 according to an exemplary aspect. The illustrated radio frequency module 540 also includes a radio frequency (RF) circuit (or RF circuitry) 543. In an exemplary aspect, as described above with reference to Figure 5A the acoustic wave filter 544 can include one or more filters 500 that include an XBAR (e.g., a bulk acoustic resonator as described herein).

[0088] Figure 5B The acoustic wave filter 544 shown in FIG. includes terminals 545A and 545B (e.g., a first terminal and a second terminal). The terminals 545A and 545B can be used as, for example, an input contact and an output contact of the acoustic wave filter 544. Although two terminals are shown, any suitable number of terminals can be implemented for a particular application. The acoustic wave filter 544 and the RF circuit 543 are on Figure 5B a package substrate 546 (e.g., a common substrate) in. The package substrate 546 can be a laminated substrate. The terminals 545A and 545B can be electrically connected to contacts 547A and 547B on the package substrate 546 through electrical connectors 548A and 548B, respectively. For example, the electrical connectors 548A and 548B can be bumps or wire bonds. In an exemplary aspect, with or without the package substrate 546, the acoustic wave filter 544 and the RF circuit 543 can be packaged together in a common package.

[0089] The RF circuit 543 may include any suitable RF circuit. For example, the RF circuit may include one or more radio frequency amplifiers (e.g., one or more power amplifiers and / or one or more low noise amplifiers), one or more radio frequency switches, one or more additional RF filters, one or more RF couplers, one or more delay lines, one or more phase shifters, or any suitable combination thereof. The RF circuit 543 may be electrically connected to one or more acoustic wave filters 544. The radio frequency module 540 may include one or more encapsulation structures to, for example, provide protection and / or facilitate easier handling of the radio frequency module 540. Such encapsulation structures may include a molding structure formed above the encapsulation substrate 546. The molding structure may encapsulate some or all of the components of the radio frequency module 540.

[0090] According to an exemplary aspect, an RF filtering device (e.g., the filter 500 described above with respect to Figure 5B is configured to use a grounded inductor in series with a parallel resonator to create a transmission zero (Tz) at a desired frequency, thereby improving rejection of the frequency response. Figure 6A A circuit diagram 600 of a filter (or a portion of a filter) using a resonator with a series grounded inductor is shown in accordance with an exemplary aspect.

[0091] Specifically, Figure 6A A schematic circuit diagram and layout of a filter 600 using resonators (e.g., XBARs, such as the general XBAR configuration 100 and / or 100' described above) are shown. The filter 600 has a filter architecture that includes series resonators 610A (SE2), 610B (SE4), 610C (SE6), and 610D (SE8). In one aspect of the present disclosure, the series resonators 610A and 610D may be referred to as a pair of external resonators, and the series resonators 610B and 610C may be referred to as a pair of internal resonators based on their series arrangement in the circuit. Additionally, one or more (or all) of the series resonators may be composed of multiple sub-resonators arranged in a parallel configuration. For example, as Figure 6A shown, the series resonators 610A, 610B, and 610C may each include four individual series sub-resonators (indicated by "x4"), and the series resonator 610D may include two individual series sub-resonators (indicated by "x2"). Further, in an exemplary aspect, a pair of internal resonators (e.g., resonators 610B and 610C) includes stacks that are identical to each other, and a pair of external resonators (e.g., resonators 610A and 610D) includes stacks that are identical to each other.

[0092] A major benefit of dividing the XBARs described herein into multiple sub-resonators is to reduce the peak stress that would occur when each XBAR has a single large diaphragm. That is, at least two sub-resonators can share the same diaphragm over a single cavity, which effectively reduces the mechanical stress. It should be understood that for a resonator having four separate series-connected sub-resonators, all four or some (but not all) of the sub-resonators can share the same cavity. In some cases, the sub-resonators may not share the same cavity, but can share an etched hole through the piezoelectric layer, thereby allowing the corresponding cavity to be etched. The etched hole can be disposed outside the IDT region of each sub-resonator, but shared between two sub-resonators, such that one etched hole can be used to access the cavity of each corresponding sub-resonator.

[0093] In an additional exemplary aspect of the present disclosure, each of the series resonators can include a stack that is identical to each other. For the purposes of the present disclosure, the term "stack" as used herein refers to the construction in the thickness direction (e.g., the Z-axis direction) of the respective resonators. Thus, as described herein, a pair of resonators having the same stack will have the same layers (e.g., piezoelectric layer, dielectric layer, substrate layer), etc. These layers will also have the same thickness (taking into account possible manufacturing variations). As described according to the exemplary aspect, a pair of internal resonators (e.g., series resonators 610B and 610C) can thus have the same stack, but the IDT area and / or IDT pitch of one of these series resonators (e.g., series resonator 610C) can be varied to increase the capacitance of a particular series resonator as described herein.

[0094] Additionally, the filter 600 has a filter architecture that includes parallel resonators 620A (SH1), 620B (SH3), 620C (SH5), 620D (SH7), and 620E (SH9). One, some, or all of the parallel resonators can be composed of multiple parallel sub-resonators that are arranged in a parallel configuration with ground "Gnd" (e.g., a ground connection). For example, as Figure 6A shown, in the exemplary aspect, each of the parallel resonators 620A, 620B, 620C, 620D, and 620E can include two separate parallel sub-resonators (indicated by "x2").

[0095] As shown, the series resonators 610A, 610B, 610C, and 610D are connected in series between a first port (e.g., "In") and a second port (e.g., "Out"), and the first port and the second port can be the input and output of the filter 600. That is, in Figure 6AIn this case, the first port and the second port are labeled "In" and "Out" of 600. Note that the filter 600 can be configured to be bidirectional, and either port can serve as the input or output of the filter. The parallel resonators 620A, 620B, 620C, 620D, and 620E are connected from the nodes between the series resonators to ground (Gnd) and / or from ground to the node between one of the first port and the second port and one of the external resonators (e.g., series resonator 610A or 610D).

[0096] As further shown and described below, the parallel resonators and the series resonators can be XBARs, and four series resonators and five parallel resonators are included in the filter 600 as an example. The filter can have more or fewer than a total of nine resonators, more or fewer than four series resonators, and more or fewer than five parallel resonators. For example, the filtering device 600 can include at least three or more series resonators that are connected between a pair of ports and at least two or more parallel resonators, and each of the at least two or more parallel resonators is connected between the ground connection and the node between a pair of series resonators, or between the ground connection and the node between one of a pair of ports and one of the series resonators. As described in detail below, one of the series resonators having the lowest anti-resonant frequency among the at least three series resonators (e.g., the resonator falling at the upper frequency band edge of the filter 600) is configured (e.g., by increasing the IDT area and / or decreasing the IDT pitch, as described herein) to have the highest capacitance value among the three series resonators of the filter 600. Thus, in this configuration, all the series resonators 610A to 610D are connected in series between the input and output of the filter, and all the parallel resonators 620A to 620E are generally connected between ground (Gnd) and the input, output, or the node between two (e.g., a pair of) series resonators.

[0097] As described above, the filtering device (e.g., filter 600) is configured to pass certain frequencies and block other frequencies. Figure 6B is according to an exemplary aspect Figure 6A Exemplary graph 600' of the filter response of the circuit diagram shown. More specifically, Figure 6B shows the admittance (in dB) of the filter 600 as a function of frequency (GHz), which is simulated using the finite element method (FEM) simulation technique.

[0098] As shown in the figure, the filter 600 has a filter response as shown in 684, which indicates Figure 6A the resonator response of the combination of the total resonators of the filter 600 shown. Note that although Figure 6BOnly additionally indicates the resonator response of 682 as that of XBAR 610C, but for clarity, the remaining resonator responses of resonators 610A, 610B, 610D, 620A, 620B, 620C, 620D, and 620E are also shown in the graph but not individually labeled. Additionally, the resonator response 682 also indicates the lowest admittance (dB) at 686, approximately -69 dB.

[0099] According to Figure 6B the frequency response graph shown, the characteristic values of the resonators of filter 600 are shown as examples in Figure 6C It should be understood that Figure 6C the values shown are relative values of capacitance C0 (in picofarads) and IDT area (in microns). That is, the capacitance of each resonator is a defined value X that is offset by a value, where the series resonator 610C has the maximum capacitance value as described herein. Accordingly, the IDT area is a defined value Y that is again offset by a value relative to each resonator. It should be understood that a larger IDT area corresponds to a larger capacitance, as shown in the table of Figure 6C Therefore, in an exemplary aspect, the series resonator 610C can have an IDT that has the largest area among the IDT areas of each series resonator in filter 600, such that it has the maximum capacitance value.

[0100] Additionally, in one aspect of the present disclosure, the characteristic value of the resonator can be any one of capacitance value (in pF), surface area (in (µm) 2 ), and pitch of the IDT, as described above. Adjusting any one of these characteristic values individually or in combination can adjust the operating frequency of the resonator. For example, reducing the pitch of the IDT will increase the operating frequency of the resonator. In other words, the larger the pitch, the lower the frequency, and the smaller the pitch, the higher the frequency. In another aspect, reducing the resonator area (and thus reducing the capacitance) will change the resonant frequency of the resonator. In other words, the smaller the area of the resonator IDT, the smaller the capacitance; the larger the area, the larger the capacitance. Therefore, in an exemplary aspect, the series resonator 610C can have an IDT that has the smallest pitch among the IDT pitches of each series resonator in filter 600, such that it has the maximum capacitance value.

[0101] Thus, according to an exemplary aspect, the filtering device 600 may include a plurality of series resonators (e.g., three or more series resonators) and a plurality of parallel resonators (e.g., two or more parallel resonators), the plurality of series resonators being connected between a pair of ports, and each of the plurality of parallel resonators being connected between a ground connection and a node between a pair of series resonators, or between a ground connection and a node between one of the pair of ports and one of the series resonators. In this aspect, each of the plurality of series resonators and the plurality of parallel resonators may include: a substrate; a piezoelectric layer attached to the substrate directly or via one or more intermediate layers; and an interdigital transducer (IDT) at the piezoelectric layer and including a plurality of interleaved fingers. As further described herein, one of the series resonators having the lowest anti-resonant frequency among the plurality of series resonators will have characteristic values different from the corresponding characteristic values of the other series resonators among the plurality of series resonators. Additionally, in an exemplary aspect, the characteristic value may be at least one of the area of the corresponding IDT and the pitch of the corresponding IDT.

[0102] Specifically, resonators 620A, 610A, 620B, 610B, 620C, 610C, 620D, 610D, and 620E are set to have a capacitance value (in pF) and a surface area (in square micrometers, i.e., (μm) 2 as the unit), and will be further discussed below. Note that, as described in detail below, the series resonator 610C (the resonator having the lowest anti-resonant frequency among the series resonators of a pair of internal resonators of the filter 600) is also configured to: based on having the maximum area at Y + 34420 μm 2 and having the maximum and / or highest capacitance value at X + 0.535 pF. In other words, the filter 600 is configured such that the resonator having the lowest frequency among the series resonators (e.g., resonator 610C) is configured to (i) set an improved steepness starting from the anti-resonance at the upper frequency band edge of the filter 600, and (2) is configured such that a larger C0 value restores the matching (i.e., return loss) of the filter, e.g., as described herein Figure 7A as shown.

[0103] As described above, the "area" described herein is the area of the IDT of the corresponding resonator. For example, referring to Figure 1A , the area is the area of the IDT 130, which is based on the length L of the IDT 130 multiplied by the aperture AP. Thus, the area (in order to increase capacitance) can be increased by increasing the length L of a specific resonator (e.g., the series resonator 610C) and / or increasing the aperture AP.

[0104] Referring to Figure 6B, the filter response 684 has a passband in the range of approximately 5.1 GHz to 6.1 GHz. As generally described above, the passband includes a low edge at approximately 5.1 GHz (indicated as 690) and a high edge at approximately 6.1 GHz (indicated as 688). Additionally, frequencies outside of these indicated frequencies, e.g., below 5.1 GHz and above 6.1 GHz, are considered the stopband or rejection band of the filter 600. Note that for ease of illustration, the frequency values listed herein are approximate only, as the filter response 684 does not exhibit perfectly vertical high edge 688 and low edge 690 responses. The relatively steep slope in the passband of the high edge 688 undesirably allows unwanted frequencies to leak or pass through the filter. To better tune the high edge 688 of the passband, the slope and / or steepness must be increased, i.e., made more vertical. According to an exemplary aspect, increasing the steepness of the high edge passband or upper frequency band edge improves the effectiveness of the filter 600.

[0105] In one aspect of the present disclosure, the steepness of the high edge passband can be increased by further changing the frequency of the lowest frequency series resonator by increasing its capacitance (pF). That is, the series resonator having the lowest frequency can be identified as having the lowest anti-resonance, lowest resonance, or both. In one aspect of the present disclosure, increasing the area of the IDT of the series resonator having the lowest operating frequency or decreasing the pitch of the IDT of the lowest operating frequency series resonator increases the capacitance of the series resonator. In another aspect of the present disclosure, increasing the area of the series resonator having the lowest operating frequency and decreasing the pitch (minimum pitch) of the lowest operating frequency series resonator increases the capacitance.

[0106] Furthermore, by adjusting the area and / or pitch of one of the internal series resonators in a pair of internal series resonators (e.g., series resonator 610B or 610C of filter 600), the steepness of the high-end passband of the filter 600 is improved. Specifically, the frequency of the corresponding series resonator (e.g., series resonator 610C) is adjusted to clearly illustrate the improvement effect of the filter 600 (and more specifically, the improved high-end steepness), as series resonator 610C is the lowest frequency series resonator.

[0107] Turning Figure 7A and Figure 7B , the capacitance of series resonator 610C has been increased to shift its resonance frequency 24 MHz to the left (or down). More specifically, Figure 7A FIG. 700 shows a graph of the admittance (in dB) of filter 600 as a function of frequency (GHz), which is simulated using the finite element method (FEM) simulation technique. Figure 7B FIG. shows exemplary series resonator characteristics corresponding to series resonator 610C of filter 600 according to an exemplary aspect.

[0108] In this example, based on the adjustment of the area and / or pitch, the resonant frequency of the series resonator 610C is reduced by increasing the capacitance value from 0.685 pF to 0.8 pF, as described above. Figure 7A Indicating 682 (e.g., peak admittance) as the resonator response of XBAR 610C with respect to Figure 6C the capacitance value shown, and also indicating 782 as the resonator response (e.g., peak admittance) of XBAR 610C with respect to Figure 7B the increased value shown. As Figure 7A shown, compared to the response 682, the response 782 has shifted to the left (i.e., lower frequency). In addition, the resonator response 682 has the lowest admittance (dB), indicated at 686 as approximately -69 dB, as described above with respect to Figure 6C the value. In addition, the resonator response 782 has the lowest admittance (dB), indicated at 786 as approximately -68 dB, as described above with respect to Figure 7B the value.

[0109] According to an exemplary aspect, compared to the filter response 684 described above, Figure 7A it is clearly shown that by responding to the increase in the capacitance value of 610C with respect to Figure 7B the value, the frequency of the lowest frequency series resonator is reduced, thereby improving the high-end steepness of the passband of the filter 600, as shown at 784. Specifically, according to an exemplary aspect, the slope of the high-end steepness increases from 0.46 db / MHz to 0.54 db / MHz. In fact, the series resonator with the lowest anti-resonant frequency (e.g., series resonator 610C) generates a zero of the filter response, i.e., the high-side transition. In fact, to meet the Wi-Fi 6 GHz suppression, the anti-resonance of this resonator 610C is configured to be as low as possible while meeting the Wi-Fi 5 GHz bandwidth, loss, and return loss requirements.

[0110] Figure 8 is a simplified flowchart outlining process 800 for manufacturing a filtering device including an XBAR according to an exemplary aspect. It should be understood that although Figure 8 generally describes the process for manufacturing a single filtering device, multiple filtering devices can be manufactured simultaneously on a common wafer (composed of a piezoelectric layer bonded to a substrate). In this case, each step of process 800 can be performed simultaneously on all the filtering devices on the wafer.

[0111] As shown, process 800 is for manufacturing a filtering device including multiple XBARs, such as the filter 600 described above. Process 800 begins at 805, where a device substrate and a thin layer of piezoelectric material are disposed on a sacrificial substrate. Process 800 ends at 895: the filtering device is completed. Note thatFigure 8 The flowchart of Figure 8 only includes the main process steps. Various conventional process steps (e.g., surface preparation, cleaning, inspection, baking, annealing, monitoring, testing, etc.) can be performed before, between, after, and during the steps shown in Figure 8 Figure 8 .

[0112] Figure 8 The flowchart of

[0112] captures three variants of process 800 for manufacturing an XBAR, which differ in whether and how a cavity is formed in the device substrate. A cavity can be formed at step 810A, 810B, or 810C, or no cavity is formed at all. It should be understood that only one of steps 810A, 810B, and 810C or none of steps 810A, 810B, and 810C is performed in each of the three variants of process 800. To produce an SM XBAR with a Bragg stack layer thickness determined according to the present disclosure, a firmly mounted XBAR can be fabricated without forming any cavity in the device substrate. Examples of firmly mounted XBARs are described above with reference to Figure 2E Figure 2E .

[0113] The piezoelectric layer can be, for example, a lithium niobate plate or a lithium tantalate plate, either of which can be Z-cut, rotated Z-cut, Y-cut, rotated Y-cut, or rotated YX-cut. Due to historical reasons, the rotated Y-cut plate configuration is generally referred to as "Y-cut", where the "cutting angle" is the angle between the y-axis and the normal of the plate. The "cutting angle" is equal to β + 90°. For example, a plate with Euler angles [0°, 30°, 0°] is generally referred to as "120° rotated Y-cut". In some embodiments, the z-axis of the piezoelectric layer can be perpendicular to the plate surface, and the y-axis can be orthogonal to the IDT fingers. Such a piezoelectric plate has Euler angles [0°, 0°, 90°]. Further embodiments can include a piezoelectric layer with Euler angles of [0°, β, 90°], where β is in the range of -15° to +5°, 0° ≤ β ≤ 60°, or any combination thereof. The piezoelectric layer can be some other materials and / or some other cuts. The device substrate can preferably be silicon. The device substrate can be some other materials that allow the formation of deep cavities by etching or other processes.

[0114] In one variant of process 800, one or more cavities are formed in the device substrate at 810 before the piezoelectric layer is bonded to the substrate at 815A. Separate cavities can be formed for each resonator in the filtering device. Conventional lithography and etching techniques can be used to form one or more cavities. Generally, the cavities formed at 810A will not penetrate the device substrate. As described above, the cavities can be in the substrate base (e.g., silicon). Alternatively, the cavities can be in an intermediate layer of the substrate (e.g., silicon dioxide).

[0115] At 815, a piezoelectric layer is bonded to a device substrate. The piezoelectric layer and the device substrate can be bonded by a wafer bonding process. Generally, the mating surfaces of the device substrate and the piezoelectric layer are highly polished. One or more layers of an intermediate material (e.g., an oxide or a metal) can be formed or deposited on the mating surface of one or both of the piezoelectric layer and the device substrate. For example, a Bragg stack of high acoustic impedance layers and low acoustic impedance layers can be formed or deposited on the mating surface of one or both of the piezoelectric layer and the device substrate. One or both of the mating surfaces can be activated using, for example, a plasma process. Then the mating surfaces can be pressed together with a substantial force to establish a molecular bond between the piezoelectric layer and the device substrate or the intermediate material layer.

[0116] At 820, the sacrificial substrate can be removed. For example, the piezoelectric layer and the sacrificial substrate can be wafers of a piezoelectric material that have been ion implanted to create defects in the crystal structure along a plane that defines the boundary between the piezoelectric layer and the sacrificial substrate. At 820, the wafer can be split along the plane of the defects, for example, by thermal shock, separating the sacrificial substrate and leaving the piezoelectric layer bonded to the device substrate. After the sacrificial substrate is separated, the exposed surface of the piezoelectric layer can be polished or processed in some way.

[0117] Thin layers of single crystal piezoelectric materials laminated to non-piezoelectric substrates are commercially available. In this application, both lithium niobate layers and lithium tantalate layers can be bonded to various substrates including silicon, quartz, and fused quartz. Thin layers of other piezoelectric materials may become available now or in the future. The thickness of the piezoelectric layer can be between 300 nm and 1000 nm. When the substrate is silicon, a SiO 2 layer can be provided between the piezoelectric layer and the substrate. In an exemplary aspect, when using a commercially available piezoelectric layer / device substrate laminate, steps 810A, 815, and 820 of process 800 are not performed.

[0118] At 830, a first conductor pattern including an IDT for each XBAR is formed by depositing and patterning one or more conductor layers on the front side of the piezoelectric layer (e.g., piezoelectric layer 110 as described above). The conductor layer can be, for example, aluminum, an aluminum alloy, copper, a copper alloy, or some other conductive metal. One or more layers of other materials can be provided under the conductor layer (i.e., between the conductor layer and the piezoelectric layer) and / or on top of the conductor layer. For example, thin films of titanium, chromium, or other metals can be used to improve the adhesion between the conductor layer and the piezoelectric layer. A second conductor pattern of gold, aluminum, copper, or other higher conductivity metal can be formed over portions of the first conductor pattern (e.g., the IDT busbars and the interconnects between the IDTs). It should be understood that at 830, the area and / or pitch of each resonator of the filter 600 can be defined in order to set the capacitance of each corresponding resonator.

[0119] In addition, at 830, each conductor pattern can be formed by sequentially depositing a conductor layer and optionally one or more other metal layers on the surface of the piezoelectric layer. The excess metal can then be removed by etching through the patterned photoresist. For example, the conductor layer can be etched by plasma etching, reactive ion etching, wet chemical etching, or other etching techniques.

[0120] Alternatively, at 830, a lift-off process can be used to form each conductor pattern. The photoresist can be deposited over the piezoelectric layer and patterned to define the conductor pattern. The conductor layer and optionally one or more other layers can be sequentially deposited over the surface of the piezoelectric layer. Then, the photoresist can be removed, which removes the excess material, leaving the conductor pattern. In either case, the conductor pattern can be formed to include grating elements as described herein.

[0121] At 840, one or more frequency-setting dielectric layers can be formed by depositing one or more layers of dielectric material on the front side of the piezoelectric layer. For example, a dielectric layer can be formed over the parallel resonator to lower the frequency of the parallel resonator relative to the frequency of the series resonator. Conventional deposition techniques such as physical vapor deposition, atomic layer deposition, chemical vapor deposition, or some other method can be used to deposit the one or more dielectric layers. One or more photolithography processes (using photomasks) can be used to confine the deposition of the dielectric layer to selected regions of the piezoelectric layer. For example, a mask can be used to confine the dielectric layer to cover only the parallel resonator.

[0122] At 850, a passivation / tuning dielectric layer can be deposited over the piezoelectric layer and the conductor pattern. The passivation / tuning dielectric layer can cover the entire surface of the filter except for the pads used for electrical connection to circuitry located outside the filter. In some instances of process 800, the passivation / tuning dielectric layer can be formed after the cavities in the substrate of the device substrate and / or an intermediate layer of the substrate are etched at 810B or 810C.

[0123] More specifically, in a second variant of process 800, at 810B, one or more cavities are formed in the back surface of the substrate of the device substrate and / or an intermediate layer of the substrate. Separate cavities can be formed for each resonator in the filtering device. Anisotropic or orientation-dependent dry or wet etching can be used to open holes through the back side of the device substrate down to the piezoelectric layer to form the one or more cavities. In this case, the resulting resonant device will have a cross-section as Figure 1A or Figure 1B shown.

[0124] In a third variation of process 800, at 810C, one or more cavities in the form of grooves can be formed in the device substrate by etching the substrate using an etchant introduced through an opening in the piezoelectric layer. Separate cavities can be formed for each resonator in the filtering device. The one or more cavities formed at 810C will not penetrate the device substrate.

[0125] Ideally, most or all of the filtering devices on the wafer will meet the set of performance requirements. However, normal process tolerances will result in variations in parameters such as the thickness of the dielectric layers formed at 840 and 850, variations in the thickness and line width of the conductors and IDT fingers formed at 830, and variations in the thickness of the piezoelectric layer. These variations cause the performance of the filtering devices to deviate from the set of performance requirements.

[0126] To increase the yield of filtering devices that meet the performance requirements, frequency tuning can be performed by selectively adjusting the thickness of the passivation / tuning layer deposited over the resonators at 850. The frequency of the passband of the filtering device can be decreased by adding material to the passivation / tuning layer, and the frequency of the passband of the filtering device can be increased by removing material from the passivation / tuning layer. Typically, process 800 is biased to produce filtering devices having a passband that initially is below the desired frequency range but can be tuned to the desired frequency range by removing material from the surface of the passivation / tuning layer.

[0127] At 860, a probe card or other device can be used to electrically connect to the filter to allow radio frequency (RF) testing and measurement of filter characteristics such as the input-output transfer function. Typically, RF measurements are made on all or most of the filtering devices fabricated simultaneously on the common piezoelectric layer and substrate.

[0128] At 865, global frequency tuning can be performed by removing material from the surface of the passivation / tuning layer using a selective material removal tool (e.g., a scanning ion mill as described previously). The "global" tuning is performed at a spatial resolution equal to or greater than that of an individual filtering device. The purpose of global tuning is to shift the passband of each filtering device towards the desired frequency range. The test results from 860 can be processed to generate a global contour map that indicates the amount of material to be removed as a function of the two-dimensional position on the wafer. The material is then removed using the selective material removal tool according to the contour map.

[0129] At 870, local frequency tuning may be performed in addition to or instead of the global frequency tuning performed at 865. The “local” frequency tuning is performed at a spatial resolution less than that of a single filtering device. The test results from 860 may be processed to generate a map indicating the amount of material to be removed at each filtering device. Local frequency tuning may require the use of masks to limit the size of the area where material is removed. For example, a first mask may be used to limit the tuning to only the parallel resonators, and then a second mask may be used to limit the tuning to only the series resonators (or vice versa). This will allow for independent tuning of the lower band edge (by tuning the parallel resonators) and the upper band edge (by tuning the series resonators) of the filtering device.

[0130] After frequency tuning at 865 and / or 870, the filtering device is completed at 875. Actions that may occur at 875 include: forming an interleaved inductor configuration, forming bond pads or solder bumps or other devices for connection between the device and an external circuit (if such pads were not formed at 830); singulating the individual filtering devices from a wafer containing multiple filtering devices; other packaging steps; and additional testing. After each filtering device is completed, the process ends at 895.

[0131] As used herein, “plurality” means two or more. As used herein, a “set” of items may include one or more such items. As used herein, whether in the written description or claims, the terms “comprising,” “including,” “carrying,” “having,” “containing,” “involving,” etc. shall be understood to be open-ended, i.e., meaning including but not limited to. Only the transitional phrases “consisting of” and “consisting essentially of” are closed or semi-closed transitional phrases for claims. The use of ordinal terms such as “first,” “second,” “third,” etc. in the claims to modify the claim elements themselves does not imply any priority, precedence, or order of one claim element with respect to another claim element or the temporal order of acts of a method of performing, but is only used as a label to distinguish one claim element having a particular name from another element having the same name (but using an ordinal term) to distinguish the claim elements. As used herein, “and / or” means that the listed items are alternatives, but the alternatives also include any combination of the listed items.

Claims

1. A filter device, comprising: at least three series resonators connected between a pair of ports; as well as at least two parallel resonators, each connected between a ground connection and a node between a pair of series resonators among the at least three series resonators or between the ground connection and a node between one of the pair of ports and one of the at least three series resonators; wherein the series resonator having the lowest anti-resonance frequency among the at least three series resonators has the largest capacitance value among the at least three series resonators, and Wherein, the at least three series resonators and the at least two parallel resonators each include: substrate; a piezoelectric layer, attached to the substrate directly or via one or more intermediate layers, and An interdigital transducer (IDT) is at the piezoelectric layer and includes a plurality of interlaced fingers.

2. The filter device according to claim 1, wherein: The at least three series resonators include a pair of internal resonators and a pair of external resonators commonly connected in series between the pair of ports.

3. The filter device according to claim 2, wherein: One of the pair of internal resonators has the lowest anti-resonance frequency and the maximum capacitance value.

4. The filter device according to claim 2, wherein: The pair of inner resonators include identical stacks to each other, and the pair of outer resonators include identical stacks to each other.

5. The filter device according to claim 1, wherein: The series resonator having the maximum capacitance includes an IDT having the largest area among areas of the IDTs of each of the at least three series resonators.

6. The filter device according to claim 1, wherein: The series resonator having the maximum capacitance includes an IDT having a smallest pitch among corresponding pitches of the IDTs of each of the at least three series resonators.

7. The filter device according to claim 1, wherein: At least the series resonator having the lowest anti-resonance frequency among the at least three series resonators includes a plurality of sub-resonators.

8. The filter device according to claim 1, in, The corresponding piezoelectric layer of each of the at least three series resonators and the at least two parallel resonators each forms a diaphragm located above the cavity of the corresponding resonator, and Wherein, a corresponding IDT of each of the at least three series resonators and the at least two parallel resonators is arranged on a corresponding diaphragm.

9. The filter device according to claim 1, wherein: For each of the resonators, the piezoelectric layer and the IDT are configured so that the RF signal applied to each IDT mainly excites a shear acoustic mode in the piezoelectric layer, the shear acoustic mode including a bulk shear wave having a propagation direction perpendicular to the direction of a main transverse excitation electric field generated by the IDT, and when the atomic motion of the bulk shear wave is mainly horizontal in the piezoelectric layer, the electric field is mainly excited laterally, and the bulk shear wave propagates in a direction mainly perpendicular to the direction of the atomic motion.

10. A filter device comprising: A plurality of series resonators connected between a pair of ports; as well as a plurality of parallel resonators, each connected between a ground connection and a node between a pair of series resonators among the plurality of series resonators or between a ground connection and a node between one of a pair of ports and one of the plurality of series resonators; Wherein, the plurality of series resonators and the plurality of parallel resonators each include: substrate; a piezoelectric layer, attached to the substrate directly or via one or more intermediate layers, and an interdigital transducer IDT at the piezoelectric layer and comprising a plurality of interleaved fingers, wherein a series resonator having a lowest anti-resonance frequency among the plurality of series resonators has a corresponding characteristic value different from characteristic values ​​of other series resonators among the plurality of series resonators, and The corresponding characteristic value is at least one of an area of ​​a corresponding IDT and a pitch of a corresponding IDT.

11. The filter device according to claim 10, wherein: The plurality of series resonators include a pair of internal resonators and a pair of external resonators commonly connected in series between the pair of ports.

12. The filter device according to claim 11, wherein: The corresponding characteristic value is an area of ​​a corresponding IDT, and the internal resonator having the lowest anti-resonance frequency of the pair of internal resonators has the largest IDT area.

13. The filter device according to claim 11, wherein: The corresponding characteristic value is a pitch of a corresponding IDT, and the internal resonator having the lowest anti-resonance frequency of the pair of internal resonators has a smallest IDT pitch.

14. The filter device according to claim 11, wherein: The pair of inner resonators include identical stacks to each other, and the pair of outer resonators include identical stacks to each other.

15. The filter device according to claim 11, wherein The internal resonator having the lowest anti-resonance frequency among the pair of internal resonators has the largest capacitance among the plurality of series resonators.

16. The filter device according to claim 15, wherein: The series resonator having the maximum capacitance includes an IDT having a smallest pitch among corresponding pitches of the IDTs of each of the plurality of series resonators.

17. The filter device according to claim 15, wherein: The series resonator having the maximum capacitance includes an IDT having the largest area among corresponding areas of the IDTs of each of the plurality of series resonators.

18. The filter device according to claim 10, in, The corresponding piezoelectric layer of each resonator of the plurality of series resonators and the plurality of parallel resonators each forms a diaphragm located above a cavity of the corresponding resonator, and The corresponding IDT of each resonator of the plurality of series resonators and the plurality of parallel resonators is arranged on the corresponding diaphragm.

19. The filter device according to claim 18, wherein: For each of the resonators, the piezoelectric layer and the IDT are configured so that the RF signal applied to each IDT mainly excites a shear acoustic mode in the corresponding piezoelectric layer, and the shear acoustic mode includes a bulk shear wave, which has a propagation direction perpendicular to the direction of the main transverse excitation electric field generated by the IDT, and when the atomic motion of the bulk shear wave is mainly horizontal in the piezoelectric layer, the electric field is mainly excited laterally, and the bulk shear wave propagates in a direction mainly perpendicular to the direction of the atomic motion.

20. A radio frequency module, comprising: A filter device including a plurality of acoustic resonators; as well as a radio frequency circuit coupled to the filter device, the filter device and the radio frequency circuit being enclosed in a common package, Wherein, the plurality of acoustic resonators of the filter device include: at least three series resonators connected between a pair of ports of the filter device; and at least two parallel resonators, each connected between a ground connection and a node between a pair of series resonators among the at least three series resonators or between the ground connection and a node between one of the pair of ports and one of the at least three series resonators; wherein the series resonator having the lowest anti-resonance frequency among the at least three series resonators has the largest capacitance value among the at least three series resonators, wherein the at least three series resonators and the at least two parallel resonators each comprise: a substrate; a piezoelectric layer attached to the substrate directly or via one or more intermediate layers; and an interdigital transducer IDT at the piezoelectric layer and comprising a plurality of interlaced fingers, and For each of the plurality of acoustic resonators, the piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT primarily excites a shear acoustic mode in the piezoelectric layer.

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