Acoustic filter device with low edge gradient

Abstract

There is provided a filter device including: a series resonator connected between a pair of ports; and parallel resonators each connected between a ground connection and a node between the series resonators. The parallel resonator having the highest resonance frequency among the parallel resonators has a minimum capacitance value of the parallel resonator. Further, the resonators each include: 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.

Description

Cross - Reference to Related Applications

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 603,528, filed on November 28, 2023, and U.S. Non-Provisional Patent Application No. 18 / 953,865, filed on November 20, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present 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, while 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 enhancements of RF filters in wireless systems can have a wide 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, greater network capacity, lower costs, enhanced security, higher reliability, etc. These improvements can be achieved individually and in combination at multiple levels of the 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, and at the same time, there is a need to improve the manufacturing processes for making such filters.

[0006] A laterally excited thin film bulk acoustic resonator (XBAR) is an acoustic resonator structure for microwave filters. The XBAR resonator typically includes interdigital transducers (IDTs) formed on a thin floating layer or diaphragm of a single crystal piezoelectric material. The IDT includes 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 IDT excites a primary shear acoustic wave in the piezoelectric film. The XBAR resonator provides very high electromechanical coupling and high frequency capabilities. The XBAR resonator can be used in various RF filters including bandstop filters, bandpass 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 6) require as steep a lower passband edge as possible to meet the suppression of the next adjacent operating frequency (e.g., under Wi-Fi 5). In other words, the lower passband edge is located at the position where the passband starts and the stopband ends. Conventional implementations require large-scale circuits to obtain a steep lower passband edge. As described in more detail below, a technique for obtaining a steep lower passband edge without implementing large-scale circuits can be performed by further increasing the operating frequency of the currently employed shunt resonator located in the middle of the filter topology. As described further below, the area of the shunt resonator of the filter is reduced and / or the static capacitance C0 is reduced. By a combination of adjustments, the steepness of the lower passband edge can be increased while maintaining the overall circuit of the filter employed.

[0008] Accordingly, in an exemplary embodiment, the techniques described herein relate to a filtering device that includes: at least two series resonators connected between a pair of ports; and at least three shunt resonators, each connected between a ground connection and a node between the pair of the at least two series resonators, or connected between a ground connection and a node between one of the pair of ports and one of the at least two series resonators; wherein the shunt resonator having the highest resonant frequency among the at least three shunt resonators has the smallest capacitance value of the at least three shunt resonators, and wherein the at least two series resonators and the at least three shunt resonators each 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.

[0009] In another exemplary aspect, the filtering device further includes at least five shunt resonators commonly connected in parallel between a pair of ports, the at least five shunt resonators including a plurality of internal shunt resonators and a pair of external shunt resonators.

[0010] In another exemplary aspect of the filtering device, one of the plurality of internal parallel resonators has the highest resonance frequency and the smallest capacitance value.

[0011] In another exemplary aspect of the filtering device, the plurality of internal parallel resonators include stacks that are identical to each other, and a pair of external parallel resonators include stacks that are identical to each other.

[0012] In another exemplary aspect of the filtering device, when viewed in a plan view, the middle parallel resonator among the plurality of internal parallel resonators has the highest resonance frequency and the smallest capacitance value.

[0013] In another exemplary aspect of the filtering device, the parallel resonator having the smallest capacitance includes an IDT, and the area of the IDT is at least 50% smaller than the corresponding area of the IDTs of the other parallel resonators among the plurality of parallel resonators.

[0014] In another exemplary aspect of the filtering device, among at least three parallel resonators, the parallel resonator having the highest resonance frequency includes a plurality of sub-resonators.

[0015] In another exemplary aspect of the filtering device, for each of the at least three parallel resonators and the at least two series resonators, the respective piezoelectric layers each form a diaphragm located above the cavity of the corresponding resonator, and wherein the respective IDTs of the at least three parallel resonators and the at least two series resonators are disposed on the corresponding diaphragms.

[0016] In another exemplary aspect of the filtering device, for each resonator, 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.

[0017] According to another exemplary embodiment, the techniques described herein relate to a filtering device that includes: 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 between a ground connection and a node between one of the pair of ports and one of the plurality of series resonators; wherein the plurality of series resonators and the plurality of shunt resonators each 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, wherein the shunt resonator having the highest resonance frequency among the plurality of shunt resonators has an eigenvalue different from the corresponding eigenvalues of the other shunt resonators among the plurality of shunt resonators, and wherein the corresponding eigenvalue is at least one of the area and capacitance of the corresponding IDT.

[0018] In another exemplary aspect of the filtering device, the plurality of shunt resonators include a plurality of internal shunt resonators commonly connected in parallel between a pair of ports and a pair of external shunt resonators, and wherein the plurality of internal shunt resonators include three shunt resonators.

[0019] In another exemplary aspect of the filtering device, the corresponding eigenvalue is the area of the corresponding IDT, and the internal shunt resonator having the highest resonance frequency among the plurality of internal shunt resonators has the smallest area of the IDT.

[0020] In another exemplary aspect of the filtering device, when viewed in a plan view, the intermediate shunt resonator among the plurality of internal shunt resonators has the highest resonance frequency and the smallest capacitance value.

[0021] In another exemplary aspect of the filtering device, the plurality of internal shunt resonators include stacks identical to each other, and the pair of external resonators include stacks identical to each other.

[0022] In another exemplary aspect of the filtering device, the internal shunt resonator having the highest resonance frequency among the plurality of internal shunt resonators has the smallest capacitance among the plurality of shunt resonators.

[0023] In another exemplary aspect of the filtering device, the shunt resonator having the smallest capacitance includes an IDT, the area of which is at least 50% smaller than the corresponding areas of the IDTs of the other shunt resonators among the plurality of shunt resonators.

[0024] In another exemplary aspect of the filtering device, the corresponding piezoelectric layer of each of the plurality of series resonators and the plurality of shunt resonators respectively forms a diaphragm located above the cavity of the corresponding resonator, and wherein the corresponding IDT of each of the plurality of series resonators and the plurality of shunt resonators is disposed on the corresponding diaphragm.

[0025] In another exemplary aspect of the filtering device, for each resonator, the piezoelectric layer and the IDT are configured such that a radio frequency signal applied to the IDT predominantly excites a shear acoustic mode in the piezoelectric layer.

[0026] In another exemplary aspect of the filtering device, each of the plurality of parallel resonators includes a plurality of sub-resonators.

[0027] According to another exemplary embodiment, the techniques described herein relate to a radio frequency module that includes: a filtering device including a plurality of acoustic resonators; and a radio frequency circuit coupled to the filtering device, the filtering device and the radio frequency circuit being encapsulated within a common package, wherein the plurality of acoustic resonators of the filtering device include: at least two series resonators connected between a pair of ports of the filtering device; and at least three 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; wherein the parallel resonator having the highest resonance frequency among the at least three parallel resonators has the minimum capacitance value of the at least three parallel resonators, wherein the at least two series resonators and the at least three parallel resonators each 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, and wherein, 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 predominantly excites a shear acoustic mode in the piezoelectric layer. BRIEF DESCRIPTION OF THE DRAWINGS

[0028] 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, serve to explain the principles and implementations of one or more example aspects of the present disclosure.

[0029] Figure 1A Schematic plan view and schematic cross-sectional view including a laterally excited thin film bulk acoustic resonator (XBAR).

[0030] Figure 1B Schematic cross-sectional view showing an alternative configuration of the XBAR.

[0031] Figure 2A is Figure 1A An enlarged schematic cross-sectional view of a portion of the XBAR.

[0032] Figure 2B is Figure 1A An enlarged schematic cross-sectional view of an alternative configuration of the XBAR.

[0033] Figure 2C is Figure 1AAn enlarged schematic cross-sectional view of another alternative configuration of the XBAR.

[0034] Figure 2D Is Figure 1A An enlarged schematic cross-sectional view of another alternative configuration of the XBAR.

[0035] Figure 2E An enlarged schematic cross-sectional view of a part of a solidly-mounted XBAR (SM-XBAR).

[0036] Figure 3A A schematic cross-sectional view of an XBAR according to an exemplary aspect.

[0037] Figure 3B An alternative schematic cross-sectional view of an XBAR according to an exemplary aspect.

[0038] Figure 4 A graph showing the shear horizontal acoustic mode in the XBAR.

[0039] Figure 5A Is using Figure 1A And / or Figure 1B A schematic block diagram of a filter of an XBAR.

[0040] Figure 5B A schematic diagram of a radio frequency module including an acoustic wave filtering device according to an exemplary aspect.

[0041] Figure 6 A circuit diagram of a filter using a resonator according to an exemplary aspect.

[0042] Figure 7A Is according to an exemplary aspect of Figure 6 An exemplary graph of the filter response of the circuit diagram shown.

[0043] Figure 7B Is according to an exemplary aspect of Figure 6 An exemplary graph of the filter response of the circuit diagram shown.

[0044] Figure 7C Is according to an exemplary aspect of Figure 6 An exemplary enlarged graph of the filter response of the circuit diagram shown.

[0045] Figure 8 Shows a flowchart of a method for manufacturing a filter as described herein according to an exemplary aspect.

[0046] 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 the one or two most significant digits are the figure number in which the element is first introduced. It may be assumed that elements not described in connection with the figures have the same characteristics and functions as elements with the same reference numerals described previously. Detailed Description

[0047] Aspects of the disclosed acoustic resonators, filter devices, and methods of manufacturing bulk acoustic resonators, filter devices, and radio frequency modules will now be described with reference to the drawings, where like reference numerals may be used throughout to denote 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 other instances, well-known structures and devices are shown in block diagram form in order 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.

[0048] Figure 1A A simplified schematic top view and an 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 bandstop filters, bandpass filters, diplexers, and multiplexers. The XBAR is particularly suitable for filters in communication bands with frequencies above 3 GHz.

[0049] Generally, the XBAR 100 includes conductor patterns (e.g., thin film metal layers) formed on one or both surfaces of a piezoelectric layer 110 (herein, piezoelectric plate or piezoelectric layer may be used interchangeably), the piezoelectric layer 110 having parallel front side 112 and back side 114 (which are also commonly 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 back side 114 that face each other, and these surfaces are not necessarily flat and perfectly parallel to each other. For example, due to manufacturing variations caused by deposition processes, the front side 112 and the back side 114 may have surface undulations as would be understood by those skilled in the art. Additionally, the term "substantially" as used herein is used to describe situations when components, parameters, etc. are approximately the same (i.e., "substantially constant"), but as would be understood by those skilled in the art, may vary slightly in practice (e.g., within an acceptable threshold or percentage) due to possible manufacturing variations. For the purposes of the present 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".

[0050] According to an exemplary aspect, the piezoelectric layer may be a thin single crystal layer of a piezoelectric material such as 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 due to manufacturing variations, as long as the crystal structure is within acceptable tolerances. The piezoelectric layer is cut such that the orientations of the X, Y, and Z crystal axes relative to the front side and the back side are known and consistent. In the examples described herein, the piezoelectric layer is Z-cut, that is, the Z-axis is perpendicular to the front side 112 and the back side 114. However, XBAR may be fabricated on piezoelectric layers having other crystal orientations, including rotated Z-cut, Y-cut, and rotated YX cut.

[0051] Y-cut series (e.g., 120Y and 128Y) are typically referred to as 120YX or 128YX, where the "cutting angle" is the angle between the y-axis and the normal to the layer. The "cutting angle" is equal to β + 90°. For example, a layer having Euler angles [0°, 30°, 0°] is typically referred to as "120° rotated Y-cut" or "120Y". Thus, the Euler angles of 120YX and 128YX are (0, 120 to 90, 0) and (0, 128 to 90, 0), respectively. "Z-cut" is typically 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).

[0052] In addition to the portion of the piezoelectric layer 110 that forms a diaphragm 115 above (e.g., spanning or extending above) the cavity 140 in one or more layers below the piezoelectric layer 110 (e.g., one or more intermediate layers above or within the substrate), the back side 114 of the piezoelectric layer 110 may be at least partially supported by the surface of the substrate 120. In other words, the back side 114 of the piezoelectric layer 110 may 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). Further, as used interchangeably herein, the phrases "supported by" or "attached to" may 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 above the cavity) may 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 piezoelectric layer 110 all around the perimeter 145 of the cavity 140. In this context, "abuts" means "connected continuously without any intervening substance". However, in an exemplary aspect, the diaphragm 115 may 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.

[0053] 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 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 by some other means.

[0054] For the purposes of the present disclosure, "cavity" has its conventional meaning of "an empty space within a solid body". The cavity 140 can be a hole that completely passes 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.

[0055] As shown, the conductor pattern of the XBAR 100 includes interdigital transducers (IDTs) 130. The IDT 130 includes a first plurality of parallel fingers (e.g., fingers 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 can 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.

[0056] In Figure 1A the example, 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 can be at the surface (e.g., the second surface) of the rear side 114 of the piezoelectric layer 110, or at the surfaces of both the front side 112 and the rear side 114 of the piezoelectric layer 110, respectively.

[0057] 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 acoustic modes (i.e., the main shear acoustic mode and / or the main shear acoustic wave) within the piezoelectric layer 110. As will be discussed in further detail, the mainly excited shear acoustic mode is a bulk shear mode or a bulk acoustic wave, wherein 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, predominantly, and / or mainly orthogonal to the surface of the piezoelectric layer 110, which 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. Thus, in some cases, the mainly excited acoustic mode can generally be referred to as a laterally excited bulk acoustic wave because, as opposed to propagation, the displacement mainly occurs in the direction of the bulk of the piezoelectric layer, as discussed in further detail below with reference to Figure 4 discussed in more detail.

[0058] For the purposes of the present disclosure, a "main acoustic mode" can generally refer to an operating mode that causes vibrational displacement in the main thickness shear direction (e.g., the X direction), such that the wave propagates substantially / mainly in the direction connecting the opposite 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 smaller than the Z-direction component. The use of the term "mainly" in "mainly excited acoustic mode" does not necessarily refer to a low-order or high-order mode. Thus, the XBAR is regarded as a laterally excited thin-film bulk acoustic wave resonator. One physical constraint is that when a radio frequency or microwave signal is applied between the two bus bars 132, 134 of the IDT 130, heat is generated, and the heat must be dissipated from the resonator to improve performance. Generally speaking, the heat can be dissipated through lateral conduction on the film (e.g., in the electrodes themselves) and through vertical conduction from the cavity to the substrate.

[0059] 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 the portion of the piezoelectric layer 110 located 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 the 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 side surfaces, and these side surfaces can be straight or curved.

[0060] According to an exemplary aspect, the area of the XBAR 100 is determined to be the area of the IDT 130. For example, the area of the IDT 130 can be determined based on the product of the 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, for example, 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.

[0061] For ease of presentation in Figure 1A , the geometric 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, the 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.

[0062] Figure 1B A schematic cross-sectional view of an alternative XBAR configuration 100' is shown. In Figure 1B , the cavity 140 of the resonator 100' (which can generally correspond to Figure 1A 's cavity 140) is formed entirely within the dielectric layer 124 (such as silicon oxide or silica, as Figure 1B shown), which is located between the substrate 120 (indicated as Si in Figure 1B ) and the piezoelectric layer 110 (indicated as LN in Figure 1B ). Although a single dielectric layer 124 is shown as having the cavity 140 formed therein (e.g., by etching), it should be understood that the dielectric layer 124 can be formed of multiple individual dielectric layers formed on top of each other to provide a stack of materials.

[0063] Furthermore, in the Figure 1B example, 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 Figure 1B example, 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.

[0064] Figure 2A Shows Figure 1A or Figure 1BDetailed schematic cross-sectional view of the XBAR 100 (marked as Detail C). The piezoelectric layer 110 is a single crystal layer of a piezoelectric material having a thickness ts. Ts can be, for example, 100 nm to 1500 nm. The thickness ts can be, for example, 150 nm to 500 nm when used in filters for 5G NR and Wi-FiTM bands from 3.4 GHz to 7 GHz. In an exemplary aspect, the thickness ts can be measured in a direction substantially perpendicular or orthogonal to the surface of the piezoelectric layer.

[0065] In this aspect, a front-side dielectric layer 212 (e.g., 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 the description. Although not shown in Figure 2A it, 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. In addition, although Figure 2A not shown in

[0066] it either, the front-side dielectric layer 212 can also be deposited, for example, only on the selected IDT finger 238a.

[0067] The IDT fingers 238a, 238b may include aluminum, substantially (i.e., primarily) aluminum alloys, copper, substantially (i.e., primarily) copper alloys, beryllium, gold, or some other conductive material. A thin (relative to the total thickness of the conductor) layer of other metals such as chromium or titanium may be formed under and / or over the fingers to improve adhesion between the fingers and the piezoelectric layer 110 and / or to passivate or encapsulate the fingers. The busbars ( Figure 1A 132, 134 in the claims) can be made of the same or different materials as these fingers. In various exemplary aspects, the cross-sectional shape of the IDT fingers can be trapezoidal (finger 238a), rectangular (finger 238b), or some other shape. In general, note that the terms "include," "have," "include," and "contain" (and variations thereof) as used herein are open conjunctions and allow for the addition of other elements when used in the claims. In addition, unless the context dictates otherwise, "a" or "an" when used in conjunction with the term "comprising" in a claim or specification means one or more than one.

[0068] The dimension p (i.e., “pitch”) can be considered as the distance between adjacent IDT fingers (e.g., Figures 2A to 2D The center-to-center spacing between the IDT fingers 238a, 238b. Figure 2A As shown, the center point of the center-to-center spacing can be measured at the center of the width "w" of the finger. In some cases, the center-to-center spacing can change if the width of a given finger changes along the length of the finger, if the width and extension direction change, or any variation thereof. In this case, for a given position along the AP, the center-to-center spacing can be measured as an average center-to-center spacing, a maximum center-to-center spacing, a minimum center-to-center spacing, or any variation thereof. Adjacent fingers can each extend from a different busbar, and the center-to-center spacing can be measured from the center of a first finger extending from a first busbar to the center of a second finger adjacent to the first finger and extending from a second busbar. The center-to-center spacing can be constant over the length of the IDT, in which case the dimension p can be referred to as the pitch of the IDT and / or the pitch of the XBAR. However, in alternative exemplary aspects, the center-to-center spacing varies along the length of the IDT, in which case the pitch of the IDT can be the average value of the dimension p over the length of the IDT. The center-to-center spacing from one finger to an adjacent finger when compared to other adjacent fingers may vary continuously in discrete portions of a plurality of adjacent pairs or in any combination thereof. Each IDT finger (e.g., Figures 2A to 2DThe IDT fingers 238a, 238b) in [it] have a width w measured perpendicular to the long direction of each finger. The width w can also be referred to as a "mark" herein. Generally, the width of the IDT fingers can be constant along the length of the IDT, in which case the dimension w can be the width of each IDT finger. However, in another exemplary aspect as will be discussed below, the width of each IDT finger varies along the length of the IDT 130, in which 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 width w of the IDT fingers are measured in a direction substantially parallel to the length L of the IDT, as Figure 1A defined in.

[0069] 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 the main shear acoustic mode (also referred to as the main shear mode, main shear thickness mode, etc.) described in more detail below with respect to Figure 4 wherein the SAW resonator excites surface waves during operation. In addition, in a SAW resonator, the pitch of the IDT is one-half of the acoustic wavelength at the resonant frequency. In addition, the mark pitch ratio of the SAW resonator IDT is typically close to 0.5 (i.e., the mark or finger width is approximately one-quarter of the acoustic wavelength at resonance). In the XBAR, the pitch p of the IDT is typically 2 to 20 times the width w of these fingers. In addition, the pitch p of the IDT is typically 2 to 20 times the thickness ts of the piezoelectric layer 110. In addition, the width of the IDT fingers in the XBAR is not limited to one-quarter 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, since the lithography process generally cannot support a configuration where the thickness is greater than the width. The thickness of the bus bars ( Figure 1A 132, 134) in [it] can be equal to, less than, greater than, or any combination of the thickness tm of the IDT fingers. Note that the XBAR devices described herein are not limited to the size ranges described herein.

[0070] In addition, different from SAW filters, the resonant frequency of an XBAR depends on the total thickness of its diaphragm (i.e., in the vertical or thickness direction), including the piezoelectric layer 110 and the front-side dielectric layer 212 and the back-side dielectric layer 214 disposed thereon. In an exemplary aspect, the thickness of one or both dielectric layers (i.e., on opposite surfaces of the piezoelectric layer) can be changed to change the resonant frequencies of various XBARs in the filter. For example, the shunt resonators in a ladder filter circuit can include a thicker dielectric layer to lower the resonant frequency of the shunt resonators relative to the series resonators having a thinner dielectric layer, thereby reducing the total thickness.

[0071] 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.

[0072] 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 2B an alternative configuration (labeled as Detail C’) is shown, in which the IDT fingers 238a, 238b are at the back side 114 of the piezoelectric layer 110 (i.e., facing the cavity) and are covered by the back-side dielectric layer 214. The front-side dielectric layer 212 can cover the front side 112 of the piezoelectric layer 110. In an exemplary aspect, the dielectric layer disposed on the diaphragm of each resonator can 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 are variations in the spurious modes (e.g., generated by the coating on the fingers). In addition, the markings are changed by the passivation layer coated on the top of the IDT, which can also cause spurious. Therefore, as Figure 2B shown, by disposing the IDT fingers 238a, 238b at the back side 114 of the piezoelectric layer 110, the need to address the frequency variations and their 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.

[0073] Figure 2CAn alternative configuration (labeled as 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-side dielectric layer 212. The IDT fingers 238c, 238d are also on the back side 114 of the piezoelectric layer 110 and are also covered by the back-side dielectric layer 214. As previously described, the front-side dielectric layer 212 and the back-side dielectric layer 214 are not necessarily of the same thickness or the same material.

[0074] Figure 2D Another alternative configuration (labeled as 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-side dielectric layer 212. The surface of the front-side dielectric layer is planarized. The front-side dielectric layer can be planarized, for example, by polishing or some other method. A thin dielectric material layer with a thickness tp can cover the IDT fingers 238a, 238b to seal and passivate the fingers. The dimension TP can be, for example, 10 nm to 50 nm.

[0075] As described above regarding Figures 2A to 2D each XBAR configuration in the described XBAR configuration includes a diaphragm spanning a 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 mirror, and the acoustic mirror can in turn be mounted on a substrate.

[0076] 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 a cross-section similar to that of Figure 1A In this regard, the SM-XBAR includes a piezoelectric layer 110 and an IDT (where only two fingers 236 are visible), where a dielectric layer 212 is disposed on the piezoelectric layer 110 and the IDT fingers 236. Similar to the above-described 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 finger 236 is the dimension w, the thickness of the IDT finger is the dimension tm, and the IDT pitch is the dimension p.

[0077] Unlike Figure 1A the XBAR device shown, Figure 2EThe IDT of the SM-XBAR in [the relevant context] is not formed on a diaphragm that spans a cavity in the substrate. Instead, the acoustic Bragg reflector 240 is sandwiched between the surface 222 of the substrate 220 and the rear 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 rear surface of the piezoelectric layer 110 and is mechanically attached to both the surface 222 of the substrate 220 and the rear surface of the piezoelectric layer 110. In some cases, layers of additional material (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 rear surface of the piezoelectric layer 110. Such additional material layers may be present, for example, to facilitate the bonding of the piezoelectric layer 110, the acoustic Bragg reflector 240, and the substrate 220.

[0078] The acoustic Bragg reflector 240 can 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 layers. The acoustic impedance of each "high" acoustic impedance layer is higher than the acoustic impedance of the two adjacent "low" acoustic impedance layers. The acoustic impedance of each "low" acoustic impedance layer is lower than the acoustic impedance of the two adjacent "high" acoustic impedance layers. As discussed above, the primary acoustic mode in the XBAR piezoelectric layer is a shear bulk 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 bulk 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 polystyrene polymers. Materials having a relatively high acoustic impedance include hafnium oxide, silicon nitride, aluminum nitride, 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 2E the example, the acoustic Bragg reflector 240 has a total of six layers, but the acoustic Bragg reflector can have more or fewer than six layers in alternative configurations.

[0079] IDT fingers (e.g., IDT fingers 236, 238a, and 238b) can 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) can be disposed in a groove that is formed in the surface of the front side 112. The groove can extend partially through the piezoelectric layer. Alternatively, the groove can extend completely through the piezoelectric layer.

[0080] Figure 3A and Figure 3B shows two exemplary cross-sectional views of XBAR 100 along the Figure 1A cross-section A-A defined in. In Figure 3A , the piezoelectric layer 310 corresponding to the piezoelectric layer 110 is directly attached to the substrate 320, which may correspond to the Figure 1A substrate 120. In addition, a cavity 340 that does not completely penetrate the substrate 320 is formed in the substrate below the portion of the piezoelectric layer 310 that includes the IDT of the XBAR (i.e., the diaphragm 315). In an exemplary aspect, the cavity 340 may correspond to the Figure 1A and / or Figure 1B cavity 140. In an exemplary aspect, the cavity 340 may be formed, for example, by etching the substrate 320 before attaching the piezoelectric layer 310. Alternatively, the cavity 340 may be formed by etching the substrate 320 with a selective etchant that reaches the substrate through one or more openings provided in the piezoelectric layer 310.

[0081] Figure 3B shows an alternative aspect, in which 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 may be silicon (e.g., a silicon support substrate), and the intermediate layer 324 may 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 piezoelectric layer 310 that includes the IDT fingers of the XBAR (i.e., the diaphragm 315). The cavity 340 may be formed, for example, by etching the intermediate layer 324 before attaching the piezoelectric layer 310. Alternatively, the cavity 340 may be formed by etching the intermediate layer 324. In other example embodiments, the cavity 340 may be defined in the intermediate layer 324 in other ways that are different from whether to etch the intermediate layer 324 to define the cavity 340. In some cases, etching may be performed using a selective etchant that reaches the substrate through one or more openings (not shown) provided in the piezoelectric layer 310.

[0082] In this case, the diaphragm 315 (which may correspond to, for example, the Figure 1A diaphragm 115 in) may be adjacent to the remainder of the piezoelectric layer 310 around most of the perimeter of the cavity 340. For example, the diaphragm 315 may be adjacent to the remainder of the piezoelectric layer 310 around at least 50% of the perimeter of the cavity 340. As Figure 3BAs shown, the cavity 340 extends completely through the intermediate layer 324. That is, the diaphragm 315 may 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.

[0083] In other configurations, the cavity 340 may extend partially into the intermediate layer 324 but not completely through the intermediate layer 324 (i.e., the intermediate layer 324 may extend above the bottom of the cavity on top of the substrate 322), or may extend through the intermediate layer 324 and (partially or fully) into the substrate 322. As described above, it should be understood that according to various exemplary aspects, the interleaved fingers of the IDT may be provided on Figure 3A and Figure 3B either or both surfaces of the diaphragm 315 in

[0084] Figure 4 is a graphical illustration of the primary excited acoustic modes of interest in the XBAR. Figure 4 Shows a small portion of the XBAR 400, including the piezoelectric layer 410 and three interleaved IDT fingers 430. Generally, according to an exemplary aspect, the exemplary configuration of the XBAR 400 may correspond to any of the configurations described above and shown in Figures 2A to 2D Thus, it should be understood that the piezoelectric layer 410 may correspond to the piezoelectric layer 110, and the IDT fingers 430 may be implemented according to any of the configurations of, for example, the fingers 238a and 238b.

[0085] In operation, an RF voltage is applied to the interleaved fingers 430. This voltage creates a time-varying electric field between these fingers. The direction of the electric field is transverse to (i.e., transversely excited) or predominantly 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 introduces shear deformation in the piezoelectric layer 410, and thus strongly excites 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 translate relative to each other while remaining parallel and maintaining a constant distance. In other words, the parallel planes of the material are laterally displaced relative to each other. "Shear acoustic mode" is defined as an acoustic vibration mode in a medium that causes shear deformation of the medium. The shear deformation in the XBAR 400 is represented by the curve 460, where the adjacent small arrows provide a schematic indication of the direction and magnitude of atomic motion. Note that for ease of visualization in Figure 4 the degree of atomic motion and the thickness of the piezoelectric layer 410 have been magnified. Although the atomic motion is predominantly lateral (i.e., as in Figure 4in the horizontal direction shown), but the direction of the acoustic energy flow of the predominantly excited shear acoustic mode is substantially and / or predominantly orthogonal to the surface of the piezoelectric layer, as indicated by arrow 465.

[0086] Bulk acoustic resonators based on shear acoustic wave resonance can achieve better performance than the currently state-of-the-art thin film bulk acoustic resonators (FBARs) and solidly mounted resonator bulk acoustic wave (SMR BAW) devices that apply an electric field in the thickness direction. In such devices, the acoustic mode is compressive, where the atomic motion and the direction of the acoustic energy flow are in the thickness direction. Additionally, the piezoelectric coupling of shear wave XBAR resonance can be relatively high (>20%) compared to other acoustic resonators. Thus, the high piezoelectric coupling enables the design and implementation of microwave and millimeter wave filters with appreciable bandwidths.

[0087] Figure 5A is a schematic 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 can 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 it, the first port and the second port are labeled "In" and "Out", respectively. However, the filter 500 is bi-directional and either port can be used as the input or output of the filter. At least two shunt resonators (e.g., shunt resonators 520A and 520B) are connected from nodes between the series resonators to a ground connection. The filter can include Figure 5A additional reactive components not shown in it, 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). The inclusion of four series resonators and three shunt resonators is an example. The filter can have more or fewer than seven total resonators, more or fewer than four series resonators, and more or fewer than three shunt resonators. Generally, for 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.

[0088] 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 split ladder architecture, which may include one or more separate chips that include separate piezoelectric layers and IDTs of one or more bulk acoustic resonators, and then these are configured together to form the entire split 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.

[0089] Each of the resonators 510A, 510B, 510C, 510D, 520A, 520B, and 520C in the filter 500 has a resonance where the admittance (also interchangeably referred to as the Y-parameter) of the resonator 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 approach 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.

[0090] 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.

[0091] According to an exemplary aspect, each of the series resonators 510A, 510B, 510C, and 510D and the parallel resonators 520A, 520B, and 520C may 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 parallel resonators 520A, 520B, and 520C may have an XBAR configuration, wherein the series resonators 510A, 510B, 510C, 510D and / or the parallel resonators 520A, 520B, and 520C may be firmly mounted on or above a Bragg reflector (e.g., as Figure 2E shown), and the Bragg reflector may in turn be mounted on a substrate.

[0092] Figure 5B is a schematic diagram of a radio frequency module including an acoustic wave filtering device according to an exemplary aspect. Specifically, Figure 5B 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 may include one or more filters 500 that include an XBAR (e.g., a bulk acoustic resonator described herein).

[0093] Figure 5B The illustrated acoustic wave filter 544 includes terminals 545A and 545B (e.g., a first terminal and a second terminal). The terminals 545A and 545B may 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 may 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 may be a laminated substrate. The terminals 545A and 545B may 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 may 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 may be packaged together in a common package.

[0094] 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 an encapsulation structure 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.

[0095] According to an exemplary aspect, for an RF filtering device (e.g., the filter 500 described above with respect to Figure 5A ), the capacitance of one of the parallel resonators is configured to increase the steepness of the lower edge of the passband of the filter, thereby improving the rejection of the frequency response. Figure 6 A circuit diagram 600 of a filter (or a portion of a filter) using resonators according to an exemplary aspect is shown.

[0096] Specifically, Figure 6 A schematic circuit diagram and layout of a filter 600 using resonators (e.g., XBAR, such as the general XBAR configuration 100 and / or 100' as described above) are shown. As shown, the filter 600 has a filter architecture that includes series resonators 610A (SE2), 610B (SE4), 610C (SE6), and 610D (SE8). Additionally, each of the series resonators may be composed of a plurality of sub-resonators arranged in a parallel configuration. For example, as Figure 6 shown and referenced, the series resonators 610A, 610B, 610C, and 610D may each include four individual series sub-resonators (indicated by "x4"). It should be noted that in other exemplary aspects, the series resonators may be composed of other numbers of series sub-resonators (e.g., two sub-resonators).

[0097] The main 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 above 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 set 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.

[0098] 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). Thus, according to an exemplary aspect, multiple series resonators can have the same stack, and multiple parallel resonators can have the same stack. However, as described below, the IDT area of one of these parallel resonators (e.g., parallel resonator 620C) can be changed to reduce the capacitance, as described herein.

[0099] Specifically, as further shown, the filter 600 has a filter architecture that includes parallel resonators 620A (SH1), 620B (SH3), 620C (SH5), 620D (SH7), and 620E (SH9). In one aspect of the present disclosure, parallel resonators 620A and 620E can be referred to as a pair of external resonators, and parallel resonators 620B, 620C, and 620D can be referred to as a group or multiple internal resonators based on their parallel arrangement in the circuit (e.g., as Figure 6 shown, from left to right, and vice versa). Additionally, each of the parallel resonators can be composed of multiple parallel sub-resonators that are arranged in a parallel configuration with "Gnd" (e.g., a ground connection). For example, as Figure 6 shown and referenced, parallel resonators 620A, 620B, 620C, 620D, and 620E can each include two separate parallel sub-resonators (indicated by x2) that are identical to each other in configuration, although other numbers of parallel sub-resonators can also be provided. As described above, in one aspect of the present disclosure, each of the parallel resonators can include a stack that is identical to each other, and in another aspect of the present disclosure, each of the parallel resonators can include a stack that is different from each other.

[0100] As shown, 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 and second ports can be the input and output of filter 600. That is, in Figure 6 it, the first and second ports of filter 600 are labeled "In" and "Out". Note that filter 600 can be configured to be bi-directional, and either port can serve as the input or output of the filter. As further shown, a plurality of parallel resonators 620A, 620B, 620C, 620D, and 620E are connected from nodes between the series resonators to ground (Gnd) and / or from ground to a node between one of the first and second ports and one of the external resonators (e.g., series resonator 610A or 610D). For example, parallel resonator 620A is connected between a ground connection and a node between the first port (e.g., "IN") and series resonator 610A. Similarly, parallel resonator 620E is connected between a ground connection and a node between the second port (e.g., "OUT") and series resonator 610D. Each of the other three (internal) parallel resonators (e.g., resonators 620B, 620C, and 620D) is connected between a ground connection and a node between a pair of series resonators (e.g., a pair of directly adjacent series resonators).

[0101] As further shown and described below, the parallel and series resonators can be XBARs, and as an example, filter 600 includes four series resonators and five parallel resonators. 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. As described above, all series resonators 610A to 610D are connected in series between the input and output of the filter, and all parallel resonators 620A to 620E are generally connected between ground (Gnd) and a node between the input, output, or two (e.g., a pair of) series resonators.

[0102] Thus, according to another exemplary aspect, the filter 600 generally may include at least two series resonators connected between the pair of ports; and at least three shunt resonators, each connected between a ground connection and a node between a pair of the at least two series resonators, or between a ground connection and a node between one of the pair of ports and one of the at least two series resonators; as described in more detail below, the shunt resonator having the highest resonant frequency among the shunt resonators (e.g., shunt resonator 620C) is configured to have the minimum capacitance value of the shunt resonators. In an exemplary aspect, the capacitance of the "intermediate" shunt resonator is configured by reducing the IDT area relative to the other shunt resonators.

[0103] As described above, the filtering device (e.g., filter 600) is configured to pass certain frequencies and block other frequencies. Figure 7A is according to an exemplary aspect Figure 6 Exemplary graph 700 of the filter response of the circuit diagram shown. More specifically, Figure 7A shows the admittance (in dB) of filter 600 as a function of frequency (GHz), which is simulated using a finite element method (FEM) simulation technique.

[0104] As shown, filter 600 has a filter response (i.e., passband) as shown at 702, which indicates Figure 6 the resonator response of the combination of the total resonators of filter 600 shown. Note that although Figure 7A only additionally indicates 704 as the resonator response of shunt resonator 620C, for clarity, the other remaining resonator responses of resonators 610A, 610B, 610C, 610D, 620A, 620B, 620D, and 620E are also shown in the graph but not individually labeled. Additionally, the resonator response 704 also indicates the highest admittance (dB) 706 (e.g., peak admittance), which is -5 dB at approximately 5.75 GHz.

[0105] According to Figure 7A the frequency response graph shown, the characteristic values of the resonators of filter 600 are set as a baseline, e.g., a capacitance of approximately 0.21 pF, an IDT area between 2000 µm 2 and 9000 µm 2 and a pitch of 2.57 µm. In this aspect, the IDT area of 2000 µm 2 will be only the area of the IDT fingers, while the IDT area of 9000 µm 2 includes the space between the IDT fingers (e.g., filled with dielectric). Additionally, in aspects of the present disclosure, the characteristic values of the resonators may be capacitance values (in pF) and / or surface areas (in (µm)2 Any one of them (in units of), as described above. Adjusting any one of these characteristic values, either alone or in combination, provides an adjustment to the operating frequency of the resonators of the filtering device 600. For example, a change in the IDT pitch can be provided to adjust or shift the resonant frequency of each resonator of the filter 600.

[0106] Specifically, the resonators 620A, 610A, 620B, 610B, 620C, 610C, 620D, 610D, and 620E are configured to have a specific surface area (in square micrometers, i.e., (µm) 2 as the unit), which in turn sets the capacitance value (in pF) of the corresponding resonator. Note that, as described in detail below, the parallel resonator 620C (one of the internal resonator groups of the filter 600) has the highest operating frequency among the parallel resonators, and thus has the smallest and / or lowest capacitance value (based on having the smallest area).

[0107] Specifically, the resonance of the parallel resonator (e.g., parallel resonator 620C) "in the middle" of the filter 600 topology is configured to be relatively closer to the low edge of the filter passband (e.g., in an exemplary aspect, +2%, +100 MHz), such that the low edge transition (e.g., 2 dB to 40 dB) is strictly defined / controlled by this resonator. To recover from the degradation of the insertion / return loss (about 2 dB) at the low edge passband, the IDT area (and effectively the capacitance C0) of the parallel resonator 620C is significantly reduced (e.g., reduced by 50% of the IDT area of other parallel resonators) in order to maintain a similar actual admittance (Y). In other words, the IDT area of the parallel resonator 620C (tracked as the capacitance C0) is reduced in order to bring the actual admittance (Y) back to the original level at a specific frequency (e.g., about 6.025 GHz), resulting in a similar return loss at the lower edge of the passband. This is because the resonant frequency has shifted, and thus the actual (Y) curve has shifted. Intersecting at the low frequency band edge (e.g., about 6.025 GHz) is the optimal position in the exemplary aspect because it balances the insertion loss recovery and steepness retention. It is also generally noted that the relationship between C0 and Y is given by described. In this configuration, the parallel resonator at the center of the topology (i.e., parallel resonator 620C) provides a balancing effect on the return loss. Based on this offset transition and the insertion / return loss of the recovery, the low edge steepness of the filter 600 can be greatly improved, for example, from 0.37 to 0.53 dB / MHz.

[0108] Thus, according to an exemplary aspect and using capacitance (C0) as a measured value, the capacitance C0 of a higher-frequency shunt resonator (e.g., shunt resonator 620C) is reduced by 50% to 75% compared to other shunt resonators (e.g., shunt resonators 610A, 620C, 620D, and 620E). In other words, the capacitance C0 of the higher-frequency shunt resonator (shunt_high) is, for example, 25% to 50% of the shunt resonator nominal value. This reduction in the capacitance of this "intermediate" shunt resonator significantly improves the steepness of the lower edge of the passband of filter 600, as described in more detail below.

[0109] 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 IDT 130, which is based on the length L of IDT 130 multiplied by the aperture AP. Thus, according to various exemplary aspects, the area (and thus the capacitance) can be reduced by reducing the length L and / or reducing the aperture AP of a particular resonator (e.g., shunt resonator 620C).

[0110] Referring to Figure 7A , the filter response 702 has a passband starting at approximately 5.6 GHz (i.e., the lower edge). As generally described above, the passband includes a lower edge (indicated as 708) and an upper edge (not shown) at approximately 5.7 GHz. Frequencies outside of these indicated frequencies, e.g., below 5.6 GHz and above the upper edge, are considered the stopband or rejection band of filter 600. Note that for ease of illustration, the frequency values listed herein are only approximate, as the filter response 702 does not exhibit a perfectly vertical upper edge (not shown) and lower edge 708 response. The relative steepness in the passband of the lower edge 708 undesirably allows unwanted frequencies to leak through or pass through the filter. To better tune the lower edge 708 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 lower edge passband or lower frequency band edge improves the effectiveness of filter 600.

[0111] In one aspect of the present disclosure, the steepness of the lower edge passband can be increased by further shifting the frequency of the shunt resonator having the highest operating resonance frequency based on reducing capacitance (pF) and / or IDT pitch. In one aspect, the shunt resonator having the highest frequency can be identified as having the highest anti-resonance, the highest resonance, or both among the shunt resonators. In one aspect of the present disclosure, reducing the area of the IDT of the shunt resonator having the highest operating frequency reduces the capacitance of the shunt resonator. This configuration in turn improves the steepness of the lower edge frequency band 708.

[0112] Thus, according to an exemplary aspect, configuring the IDT area of one of the plurality of internal parallel resonators (e.g., any one of the parallel resonators 620B, 620C, or 620D of the filter 600) can improve the steepness of the low-end passband of the filter 600. Specifically, reducing the IDT area of the corresponding parallel resonator (e.g., the parallel resonator 620C) effectively reduces its capacitance, thereby improving the effectiveness of the filter 600, and more specifically, improving the low-edge steepness because the parallel resonator 620C is the highest-frequency parallel resonator and is located in the middle of the filter topology. Thus, according to an exemplary aspect, when observing the filter 600 in a plan view, the middle parallel resonator (e.g., the parallel resonator 620C) among the plurality of internal parallel resonators (e.g., the parallel resonators 620B, 620C, and 620D) has the highest resonance frequency and the smallest capacitance value.

[0113] Turning Figure 7B and Figure 7C , and according to aspects of the present disclosure, the IDT pitch of the parallel resonator 620C has been reduced (compared to the resonators 620B and 620D), e.g., by about 400 nm to 500 nm, to shift its resonance frequency to the right (or up) by about 100 MHz. Additionally, the reduced capacitance of the parallel resonator 620C shifts the admittance level, where Figure 7B FIG. 700' shows a graph of the admittance (in dB) of the filter 600 as a function of frequency (GHz), which is simulated using a finite element method (FEM) simulation technique.

[0114] In this example, the capacitance value of the parallel resonator 620C is reduced by adjusting (i.e., reducing) the area of the IDT of the parallel resonator 620C, as described above. Figure 7B Indicator 706' represents the resonator response of XBAR 620C with respect to the reduced capacitance value, and indicator 706 represents the resonator response of the parallel resonator 620C with respect to Figure 7A the value shown. As Figure 7B shown, compared to the response 706 (e.g., the peak admittance), the response 706' (e.g., the peak admittance) has shifted to the right (i.e., higher frequency). Additionally, compared to 708, the filter response 702' has a steeper (e.g., more vertical) lower edge 708'.

[0115] Furthermore, according to an exemplary aspect, FIG. 700'' shows Figure 7C which is Figure 7BThe enlarged view clearly shows that in response to reducing the capacitance value 620C based on the reduced area, the low-edge steepness of the passband of the filter 600 is improved by increasing the frequency of the highest-frequency parallel resonator. The graph 700’’ is also simulated using the finite element method (FEM) simulation technique. Advantageously, according to an exemplary aspect, the slope of the low-edge steepness increases from 0.37 dB / MHz to 0.53 dB / MHz. In fact, to meet the Wi-Fi 5GHz suppression, the resonance of the parallel resonator 620C is configured to be as high as possible while meeting the Wi-Fi 6GHz bandwidth, loss, and return loss requirements. Therefore, according to an exemplary aspect, the capacitance of one of the parallel resonators is configured to increase the steepness of the lower edge of the passband of the filter, thereby improving the suppression of the frequency response.

[0116] Figure 8 is a simplified flowchart summarizing the 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 substrate). In this case, the steps of process 800 can be performed simultaneously on all the filtering devices on the wafer.

[0117] As shown, the process 800 is used to manufacture a filtering device including multiple XBARs, such as the filter 600 described above. The process 800 starts at 805, where a device substrate and a thin layer of piezoelectric material are disposed on a sacrificial substrate. The process 800 ends at 895, completing the filtering device. Note that Figure 8 the flowchart 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 Figure 8 shown.

[0118] Figure 8 The flowchart captures three variants of the process 800 for manufacturing an XBAR, which differ in whether and how a cavity is formed in the device substrate. The 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 these steps 810A, 810B, and 810C or none of these steps is performed in each of the three variants of the 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 manufactured without forming any cavity in the device substrate. An example of a firmly mounted XBAR was described above with reference to Figure 2E

[0119] ​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 often 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 often referred to as a "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°]. Additional embodiments can include a piezoelectric layer with Euler angles [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 material and / or some other cut. The device substrate can preferably be silicon. The device substrate can be some other material that allows the formation of deep cavities by etching or other processes.

[0120] In one variant of process 800, before bonding the piezoelectric layer to the substrate at 815, at 810A, one or more cavities are formed in the device substrate. 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's base (e.g., silicon). Alternatively, the cavities can be in an intermediate layer of the substrate (e.g., silica).

[0121] At 815, the piezoelectric layer is bonded to the 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 significant force to establish a molecular bond between the piezoelectric layer and the device substrate or the intermediate material layer.

[0122] At 820, the sacrificial substrate can be removed. For example, the piezoelectric layer and the sacrificial substrate can be a wafer of piezoelectric material that has been ion implanted to create defects in the crystal structure along a plane defining the boundary between the portion that will become 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 treated in some way.

[0123] Thin layers of single crystal piezoelectric materials laminated to non-piezoelectric substrates are commercially available. At the time of this application, both lithium niobate and lithium tantalate layers can be used to bond to various substrates including silicon, quartz, and fused quartz. Other thin layers of piezoelectric materials may be 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.

[0124] At 830, a first conductor pattern 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), including the IDT of each XBAR. 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 metal with higher conductivity can be formed on portions of the first conductor pattern (e.g., the IDT busbars and the interconnects between the IDTs). As described above, according to the exemplary aspects described herein, 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 (e.g., parallel resonator 620C), thereby increasing the steepness of the lower frequency band edge of the filter response described herein.

[0125] 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 a patterned photoresist. For example, the conductor layer can be etched by plasma etching, reactive ion etching, wet chemical etching, or other etching techniques.

[0126] Alternatively, at 830, a lift-off process can be used to form each conductor pattern. A 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.

[0127] 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 lithography processes (using a photomask) 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.

[0128] At 850, a passivation / tuning dielectric layer can be deposited over the piezoelectric layer and the conductor pattern. The passivation layer / tuning dielectric layer can cover the entire surface of the filter except for the pads used for electrical connection to circuitry external to the filter. In some instances of process 800, after etching the cavities in the substrate of the device substrate and / or the intermediate layer of the substrate at 810B or 810C, the passivation / tuning dielectric layer can be formed.

[0129] In a second variant of process 800, at 810B, one or more cavities are formed in the rear surface of the substrate of the device substrate and / or the 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 rear 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.

[0130] In a third variant of process 800, at 810C, one or more cavities in a recessed form can be formed in the device substrate by etching the substrate using an etchant introduced through openings 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.

[0131] 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 (e.g., the thickness of the dielectric layer formed at 840), variations in the thickness and linewidth 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.

[0132] 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 on the resonator 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 is initially 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.

[0133] At 860, a probe card or other device can be used to make electrical contact with the filter to allow radio frequency (RF) testing and measurement of filter characteristics (e.g., the input-output transfer function). Typically, RF measurements are made on all or most of the filtering devices fabricated simultaneously on a common piezoelectric layer and substrate.

[0134] 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 according to the two-dimensional position on the wafer. The selective material removal tool is then used to remove the material according to the contour map.

[0135] At 870, in addition to or instead of the global frequency tuning performed at 865, local frequency tuning can be performed. The "local" frequency tuning is performed at a spatial resolution less than that of an individual filtering device. The test results from 860 can be processed to generate a map that indicates 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 can be used to limit the tuning to only the parallel resonators, and subsequently a second mask can be used to limit the tuning to only the series resonators (and vice versa). This will allow independent tuning of the lower frequency band edge of the filtering device (by tuning the parallel resonators) and the upper frequency band edge (by tuning the series resonators).

[0136] 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 means for connection between the device and an external circuit (if such pads were not formed at 830); singulating 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.

[0137] 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," and the like are to be understood to be open-ended, i.e., to mean including but not limited to. Only the transitional phrases "consisting of" and "consisting essentially of" are closed or semi-closed transitional phrases for claims, respectively. The use of ordinal terms such as "first," "second," "third," etc. in the claims to modify the claim elements themselves does not imply any precedence, priority, 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 merely used as a label to distinguish one claim element having a particular name from another element having the same name (but using the ordinal term) to distinguish 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 two series resonators connected between a pair of ports; as well as at least three parallel resonators, each connected between a ground connection and a node between a pair of series resonators of the at least two series resonators or between the ground connection and a node between one of the pair of ports and one of the at least two series resonators; wherein the parallel resonator with the highest resonance frequency among the at least three parallel resonators has the smallest capacitance value among the at least three parallel resonators, and Wherein, the at least two series resonators and the at least three 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 , further comprising at least five parallel resonators commonly connected in parallel between the pair of ports, the at least five parallel resonators comprising a plurality of inner parallel resonators and a pair of outer parallel resonators.

3. The filter device according to claim 2, wherein: One of the plurality of internal parallel resonators has the highest resonant frequency and the smallest capacitance value.

4. The filter device according to claim 2, wherein: The plurality of inner parallel resonators include identical stacks to one another, and the pair of outer parallel resonators include identical stacks to one another.

5. The filter device according to claim 2, wherein: When viewed in a plan view, a middle parallel resonator among the plurality of inner parallel resonators has the highest resonance frequency and the smallest capacitance value.

6. The filter device according to claim 1, wherein: The parallel resonator having the minimum capacitance includes an IDT having an area at least 50% smaller than an area of ​​each of the IDTs of the other parallel resonators of the at least three parallel resonators.

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

8. The filter device according to claim 1, in, The piezoelectric layer of each of the at least three parallel resonators and the at least two series resonators each forms a diaphragm located above the cavity of the resonator, and The IDT of each of the at least three parallel resonators and the at least two series resonators is arranged on the 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 the ground connection and a node between one of the 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 parallel resonator having a highest resonance frequency among the plurality of parallel resonators has a characteristic value different from characteristic values ​​of other parallel resonators among the plurality of parallel resonators, and The corresponding characteristic value is at least one of an area and a capacitance of a corresponding IDT.

11. The filter device according to claim 10, in, The plurality of parallel resonators include a plurality of inner parallel resonators and a pair of outer parallel resonators commonly connected in parallel between the pair of ports, and Wherein, the plurality of internal parallel resonators include three parallel resonators.

12. The filter device according to claim 11, wherein: The characteristic value is an area of ​​an IDT, and an internal parallel resonator having the highest resonance frequency among the plurality of internal parallel resonators has a smallest IDT area.

13. The filter device according to claim 11, wherein: When viewed in a plan view, a middle parallel resonator among the plurality of inner parallel resonators has the highest resonance frequency and the smallest capacitance value.

14. The filter device according to claim 11, wherein: The plurality of inner parallel resonators include identical stacks to one another, and the pair of outer resonators include identical stacks to one another.

15. The filter device according to claim 11, wherein An internal parallel resonator having the highest resonance frequency among the plurality of internal parallel resonators has a smallest capacitance among the plurality of parallel resonators.

16. The filter device according to claim 15, wherein: The parallel resonator having the smallest capacitance includes an IDT having an area that is at least 50% smaller than corresponding areas of IDTs of other parallel resonators of the plurality of parallel resonators.

17. The filter device according to claim 10, in, The corresponding piezoelectric layer of each 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 Wherein, a corresponding IDT of each of the plurality of series resonators and the plurality of parallel resonators is disposed on a corresponding diaphragm.

18. The filter device according to claim 10, 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.

19. The filter device according to claim 10, wherein: At least a parallel resonator having the highest resonance frequency among the plurality of parallel resonators includes a plurality of sub-resonators.

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 two series resonators connected between a pair of ports of the filter device; and at least three 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 parallel resonator with the highest resonance frequency among the at least three parallel resonators has the smallest capacitance value of the at least three parallel resonators, wherein the at least two series resonators and the at least three 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.

Images