Metal-piezoelectric-metal capacitor

Abstract

There is provided an acoustic resonator including: a substrate; a piezoelectric layer coupled to the substrate through the one or more dielectric layers, and having a first surface and a second surface opposite to each other; an interdigital transducer on at least one of the first surface and the second surface of the piezoelectric layer, and including interleaved fingers; and a capacitor electrically coupled in parallel to the interdigital transducer and including at least one first electrode on a first surface of the piezoelectric layer and a metal layer on a second surface of the piezoelectric layer such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Provisional Patent Application No. 63 / 529,541 filed on July 28, 2023 and U.S. Patent Application No. 18 / 781,233 filed on July 23, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to radio frequency filters using acoustic wave resonators, and more particularly, to filters for communication devices using capacitors connected in parallel with acoustic wave resonators. Background Art

[0004] A radio frequency (RF) filter is a two-port device that is configured to pass certain frequencies and block other frequencies, where "pass" means transmitting with relatively low signal loss, and "blocking" means blocking or significantly attenuating. The range of frequencies passed by a filter is called the "passband" of the filter. The range of frequencies blocked by such a filter 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, a "passband" can be defined as a frequency range where the insertion loss of the filter is better than a defined value such as 1dB, 2dB, or 3dB, while a "stopband" can be defined as a frequency range where the rejection of the filter is greater than a defined value such as 20dB, 30dB, 40dB, or more, depending on the application.

[0005] RF filters are used in communication systems that transmit information over wireless links. For example, RF filters can be found in the RF front end of cellular base stations, mobile phones and computing devices, satellite transceivers and ground stations, IoT (Internet of Things) devices, laptops and tablets, fixed-point radio links, and other communication systems. RF filters are also used in radar, as well as electronic and information warfare systems.

[0006] Performance enhancements of RF filters in wireless systems can have a wide range of impacts on system performance. Improvements in RF filters can be used to provide system performance improvements, such as larger unit sizes, longer battery life, higher data rates, greater network capacity, lower costs, enhanced security, higher reliability, etc. These improvements can be implemented individually or in combination at multiple levels of the wireless system, for example, at the RF module, RF transceiver, mobile or fixed subsystem, or network level.

[0007] In addition, the expectation for wider communication channel bandwidth will inevitably lead to the use of higher frequency communication bands. The radio access technology for mobile phone networks has been standardized by 3GPP (3rd Generation Partnership Project). The radio access technology for the fifth generation of mobile networks is defined in the 5G NR (New Radio) standard. The 5G NR standard defines several new communication bands. Two of these new communication bands are: n77, which uses a frequency range from 3300MHz to 4200MHz; and n79, which uses a frequency range from 4400MHz to 5000MHz. The bandpass filters for bands n77 and n79 must be able to handle the transmission power of the communication equipment. However, current acoustic resonators have too much coupling for narrow bands (e.g., n79), so it is necessary to improve filters that can operate in narrow bands, while also improving the manufacturing process for manufacturing such filters. Summary of the invention

[0008] Thus, as described herein, an acoustic resonator and a filter device incorporating the same are provided wherein a capacitor is coupled in parallel with an acoustic (XBAR) resonator to reduce the effective coupling of the resonator by lowering the frequency of the anti-resonance (Fa).

[0009] Therefore, according to an exemplary embodiment, an acoustic resonator is provided, which includes: a substrate; a piezoelectric layer coupled to the substrate through one or more dielectric layers and having a first surface and a second surface opposite to each other; an interdigital transducer (IDT) on at least one of the first surface and the second surface of the piezoelectric layer and including interlaced fingers; and a capacitor electrically coupled to the IDT in parallel and including at least one first electrode on the first surface of the piezoelectric layer and a metal layer on the second surface of the piezoelectric layer, such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer.

[0010] In another exemplary aspect of the acoustic resonator, the at least one first electrode is an anode of a capacitor and the metal layer is a cathode of the capacitor.

[0011] In another exemplary aspect of the acoustic resonator, the at least one first electrode comprises a pair of electrodes, the pair of electrodes comprising an anode and a cathode of a capacitor. Further, in this aspect, the metal layer can be a floating metal.

[0012] In another exemplary aspect of the acoustic resonator, a portion of the piezoelectric layer forms a diaphragm that is above a cavity that extends at least partially in one or more dielectric layers. In this aspect, an IDT can be disposed on a second surface of the piezoelectric layer that faces the cavity. In addition, the IDT can be configured such that a radio frequency signal applied to the IDT excites a bulk shear acoustic wave in the diaphragm, wherein the acoustic energy propagates in a direction substantially orthogonal to a surface of the piezoelectric layer that is transverse to a direction of an electric field generated by interlaced fingers of the IDT.

[0013] In another exemplary aspect, the acoustic resonator can include a Bragg mirror disposed between the piezoelectric layer and the substrate.

[0014] In another exemplary aspect of the acoustic resonator, each IDT includes: a first busbar and a second busbar, each extending in a first direction from a first end to a second end thereof: a first plurality of electrode fingers extending from the first busbar toward the second busbar in a second direction, wherein the second direction intersects the first direction; and a second plurality of electrode fingers extending from the second busbar toward the first busbar in the second direction, such that the first plurality of electrode fingers and the second plurality of electrode fingers form interlaced fingers of the IDT. In addition, in this aspect, the at least one first electrode includes: an anode of a capacitor coupled to the first busbar and extending in parallel with the first plurality of electrode fingers; and a cathode of the capacitor coupled to the second busbar and extending in parallel with the second plurality of electrode fingers.

[0015] In another exemplary aspect of the acoustic resonator, the piezoelectric layer includes a pair of through holes extending along a side surface of the at least one first electrode of the capacitor in a thickness direction of the piezoelectric layer.

[0016] In another exemplary aspect of the acoustic resonator, the piezoelectric layer includes: a first piezoelectric layer including a first cut material having a first crystal orientation; and a second piezoelectric layer attached to the first piezoelectric layer and including a second cut material having a second crystal orientation, such that the polarity of the piezoelectric tensor of the second piezoelectric layer is opposite to the polarity of the piezoelectric tensor of the first piezoelectric layer.

[0017] In yet another exemplary aspect, a filter device including a plurality of BAW resonators is provided. In this aspect, at least one BAW resonator of the plurality of BAW resonators includes: a substrate; a piezoelectric layer coupled to the substrate via one or more dielectric layers and having a first surface and a second surface opposite to each other; an interdigital transducer (IDT) on at least one of the first surface and the second surface of the piezoelectric layer and including interlaced fingers; and a capacitor electrically coupled to the IDT in parallel and including at least one first electrode on the first surface of the piezoelectric layer and a metal layer on the second surface of the piezoelectric layer, such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer.

[0018] In yet another exemplary aspect, a radio frequency module is provided that includes a filter device, the filter device including a plurality of bulk acoustic wave resonators connected in parallel; and a radio frequency circuit coupled to the filter device, the filter device and the radio frequency circuit being packaged in a common package. In this aspect, at least one of the plurality of bulk acoustic wave resonators of the filter device includes: a substrate; a piezoelectric layer coupled to the substrate through one or more dielectric layers and having a first surface and a second surface opposite to each other; an interdigital transducer (IDT) on at least one of the first surface and the second surface of the piezoelectric layer and including interlaced fingers; and a capacitor electrically coupled to the IDT in parallel and including at least one first electrode on a first surface of the piezoelectric layer and a metal layer on a second surface of the piezoelectric layer, such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer.

[0019] The simplified overview of the above exemplary aspects is used to provide a basic understanding of the present disclosure. This overview is not an extensive overview of all conceived aspects, and is neither intended to identify the key or decisive elements of all aspects, nor to delimit the scope of any or all aspects of the present disclosure. Its sole purpose is to present one or more aspects in a simplified form as a preface to a more detailed description of the present disclosure that follows. In order to achieve the aforementioned objectives, one or more aspects of the present disclosure include the features described in the claims and exemplarily pointed out. BRIEF DESCRIPTION OF THE DRAWINGS

[0020] The accompanying drawings, which are incorporated in and form a part of this specification, illustrate one or more example aspects of the present disclosure and, together with the detailed description, serve to explain principles and embodiments of one or more example aspects of the present disclosure.

[0021] Figure 1A Schematic plan view and schematic cross-sectional view of a film bulk acoustic resonator (XBAR) including lateral excitation.

[0022] Figure 1B Schematic cross-sectional views showing alternative configurations of XBARs.

[0023] Figure 2A yes Figure 1A An enlarged schematic cross-sectional view of a portion of an XBAR.

[0024] Figure 2B yes Figure 1A An enlarged schematic cross-sectional view of an alternative configuration of an XBAR.

[0025] Figure 2C yes Figure 1A An enlarged schematic cross-sectional view of another alternative configuration of an XBAR.

[0026] Figure 2D yes Figure 1AAn enlarged schematic cross-sectional view of another alternative configuration of an XBAR.

[0027] Figure 2E is an enlarged schematic cross-sectional view of a portion of a securely mounted XBAR (SM XBAR).

[0028] Figure 3A is a schematic cross-sectional view of an XBAR according to an exemplary aspect.

[0029] Figure 3B is an alternative schematic cross-sectional view of an XBAR according to an exemplary aspect.

[0030] Figure 4 is a graph showing the shear horizontal acoustic modes in the XBAR.

[0031] Figure 5A is used Figure 1A and / or Figure 1B Schematic block diagram of the XBAR filter.

[0032] Figure 5B is a schematic diagram of a radio frequency module including an acoustic wave filter device according to an exemplary aspect.

[0033] Fig. 6A is a schematic cross-sectional view of a portion of a filter device including an XBAR having a capacitor coupled in parallel with a resonator according to an exemplary aspect.

[0034] Figure 6B According to the exemplary aspects Fig. 6A The circuit of the filter device is shown.

[0035] Figure 6C is a graph of admittance as a function of frequency for an XBAR device having an MPM capacitor coupled thereto according to an exemplary aspect.

[0036] 7A to 7C An enlarged schematic cross-sectional view of an MPM capacitor structure according to an exemplary aspect is shown.

[0037] FIG. 7D to FIG. 7E An enlarged schematic top view of an MPM capacitor structure is shown according to an exemplary aspect.

[0038] Figure 7F An enlarged schematic cross-sectional view of an MPM capacitor structure according to an exemplary aspect is shown.

[0039] Figure 7G An enlarged schematic top view of an MPM capacitor structure is shown according to an exemplary aspect.

[0040] Fig. 8A and Figure 8BA conventional interleaved capacitor (IDC) structure is shown.

[0041] Figure 8C and Fig.8D yes Fig. 8A and Figure 8B A plot of the frequency varying admittance of the IDC structure shown.

[0042] Fig.9A , Fig. 9C , Fig.9E , Figure 9G and Fig.9I An enlarged schematic cross-sectional view of an MPM capacitor structure according to an exemplary aspect is shown.

[0043] Fig. 9B , Fig.9D , Fig.9F and Figure 9H They are Fig.9A , Fig. 9C , Fig.9E and Figure 9G A plot of the frequency varying admittance of the MPM IDC capacitor structure shown.

[0044] Fig.10 A flow chart of a method of manufacturing an acoustic resonator device as described herein is shown according to an exemplary aspect.

[0045] Fig.11A is a graph of electric field as a function of rotation relative to the Z-cut according to an exemplary aspect.

[0046] Fig. 11B yes Figure 7B A plot of the frequency-dependent admittance of the MPM capacitor structure shown.

[0047] Fig. 12A and Fig. 12B is a graph of admittance as a function of frequency comparing an exemplary aspect MPM capacitor structure to a conventional IDC capacitor.

[0048] Throughout this specification, elements appearing in the figures are assigned three-digit or four-digit reference numerals, wherein 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. Elements not described in conjunction with a figure may be assumed to have the same properties and functions as previously described elements having the same reference numeral. DETAILED DESCRIPTION

[0049] Various aspects of the disclosed bulk acoustic resonator, filter device, radio frequency module, and method of manufacturing the bulk acoustic resonator, filter device, and radio frequency module are now described with reference to the accompanying drawings, wherein the same reference numerals may be used to represent the same elements throughout. In the following description, for the purpose of illustration, many specific details are set forth to facilitate a thorough understanding of one or more aspects of the present disclosure. However, it is apparent in some or all instances that any aspect described below can be practiced without adopting the specific design details described below. In other instances, known structures and devices are shown in block diagram form to facilitate 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.

[0050] Figure 1A Simplified schematic top view and orthogonal cross-sectional views of a bulk acoustic resonator device, i.e., a laterally excited film bulk acoustic resonator (XBAR) 100, are shown. XBAR resonators, such as resonator 100, can be used in various RF filters including band-stop filters, band-pass filters, duplexers, and multiplexers. XBARs are particularly suitable for filters for communication bands with frequencies above 3 GHz.

[0051] In general, the XBAR 100 includes a conductor pattern (e.g., a thin film metal layer) formed at one or both surfaces of a piezoelectric layer 110 (piezoelectric plate or piezoelectric layer may be used interchangeably herein), the piezoelectric layer 110 having a parallel front side 112 and a rear side 114 (also commonly referred to as a first surface and a second surface, respectively). It should be understood that the term "parallel" generally refers to the front side 112 and the rear side 114 being opposite to each other, and these surfaces are not necessarily flat and completely parallel to each other. For example, due to manufacturing differences caused by the deposition process, the front side 112 and the rear side 114 may have surface undulations as will be understood by those skilled in the art. In addition, the term "substantially" as used herein is used to describe the situation when components, parameters, etc. are approximately the same (i.e., "substantially constant"), but may vary slightly in practice (e.g., within an acceptable threshold or percentage) due to possible manufacturing differences, as will be understood by those skilled in the art. For the purposes of this disclosure, the use of the term "or" in the claims is used to mean "and / or" unless it is explicitly indicated that only alternatives are pointed to or if the alternatives are mutually exclusive.

[0052] According to an exemplary aspect, the piezoelectric layer can 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 differences as long as the crystal structure is within acceptable tolerances. The piezoelectric layer is cut so that the orientation of the X, Y, and Z crystal axes relative to the front and back sides 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, the XBAR can be manufactured on piezoelectric layers with other crystal orientations, including rotated Z-cut, Y-cut, and rotated YX-cut.

[0053] The Y-cut series (e.g., 120Y and 128Y) is often referred to as 120YX or 128YX, where the "cut angle" is the angle between the y-axis and the normal to the layer. The "cut angle" is equal to β+90°. For example, a layer with Euler angles [0°, 30°, 0°] is often referred to as a "120° rotated Y-cut" or "120Y". Therefore, the Euler angles for 120YX and 128YX are (0, 120-90, 0) and (0, 128-90, 0), respectively. "Z-cut" is often referred to as ZY-cut and is understood to mean that the layer surface is perpendicular to the Z-axis, but the waves propagate along the Y-axis. The Euler angles for ZY-cut are (0, 0, 90).

[0054] In addition to the portion of the piezoelectric layer 110 that forms the diaphragm 115, the back side 114 of the piezoelectric layer 110 can be at least partially supported by the surface of the substrate 120, wherein the diaphragm 115 is above the cavity 140 (e.g., spanning the cavity 140 or extending above the cavity 140), and the cavity 140 is in one or more layers below the piezoelectric layer 110 (such as one or more intermediate layers above or in the substrate). In other words, the back side 114 of the piezoelectric layer 110 can be directly or indirectly coupled or connected to the surface of the substrate 120 via one or more intermediate layers (e.g., a dielectric layer, such as a silicon oxide layer). In addition, as used interchangeably herein, the phrases "supported by..." or "attached" can mean directly attached, indirectly attached, mechanically supported, structurally supported, or any combination thereof. The portion of the piezoelectric layer located above the cavity (e.g., spanning the cavity 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 As shown, the diaphragm 115 is adjacent to the rest of the piezoelectric layer 110 around the entire perimeter 145 of the cavity 140. In this context, "adjacent" means "continuously connected without any intermediate." However, in an exemplary aspect, the diaphragm 115 can be configured such that at least 50% of the edge surface of the diaphragm 115 is coupled to the edge of the piezoelectric layer 110.

[0055] According to an exemplary aspect, substrate 120 is configured to provide mechanical support to piezoelectric layer 110. Substrate 120 may be, for example, silicon, sapphire, quartz, or some other material, or combination of materials. Back side 114 of piezoelectric layer 110 may be bonded to substrate 120 using a wafer bonding process. Alternatively, piezoelectric layer 110 may be grown on substrate 120, or supported by or attached to the substrate in some other manner.

[0056] For the purposes of this disclosure, "cavity" has the conventional meaning of "empty space within a solid body". Cavity 140 may be a hole that passes completely through substrate 120 (as shown in section AA), a hole that is completely or partially within a dielectric layer (as shown in section AA), or a hole that is completely or partially within a dielectric layer (as shown in section AA). Figure 1B 1) or a groove in the substrate 120. For example, the cavity 140 may be formed by selectively etching the substrate 120 before or after directly or indirectly attaching the piezoelectric layer 110 and the substrate 120.

[0057] As shown, the conductor pattern of XBAR 100 includes an interdigital transducer (IDT) 130. IDT 130 includes a first plurality of parallel fingers (e.g., finger 136) extending from a first busbar 132 and a second plurality of fingers extending from a second busbar 134. The first plurality of parallel fingers and the second plurality of parallel fingers are staggered with each other, and they may be "substantially" parallel to each other, for example, due to minor variations (such as minor variations due to manufacturing tolerances). At least a portion of the staggered fingers overlap 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 IDT 130 is the "length" of the IDT.

[0058] exist Figure 1A In the example of FIG. 1 , the IDT 130 is at a surface (e.g., a first surface) of the front side 112 of the piezoelectric layer 110. However, as described below, in other configurations, the IDT 130 may be at a surface (e.g., a second surface) of the back side 114 of the piezoelectric layer 110, or at both surfaces of the front side 112 and the back side 114 of the piezoelectric layer 110, respectively.

[0059] The first busbar 132 and the second busbar 134 are configured as terminals of the XBAR 100, from which a plurality of interlaced fingers extend. In operation, an RF signal or a microwave signal applied between the two busbars 132, 134 of the IDT 130 predominantly excites an acoustic mode (i.e., a primary shear acoustic mode) within the piezoelectric layer 110. As will be discussed in further detail, the predominantly excited shear acoustic mode is a bulk shear mode or 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 orthogonal, predominantly orthogonal, and / or predominantly orthogonal to the surface of the piezoelectric layer 110, which is also substantially perpendicular or transverse to the direction of the electric field generated by the IDT fingers. That is, when an RF or microwave signal is applied between the two busbars 132, 134, the RF voltage applied to each set of IDT fingers generates a time-varying electric field that is excited laterally relative to the surface of the piezoelectric layer 110. Therefore, in some cases, the predominantly excited acoustic mode can often be referred to as a transversely excited bulk acoustic wave, since the displacement occurs primarily in the direction of the bulk of the piezoelectric layer, as opposed to propagation, as described below with reference to Figure 4 discussed in more detail.

[0060] For the purposes of this disclosure, a "primary acoustic mode" may generally refer to an operating mode that causes vibration displacement in a primary thickness shear direction (e.g., the X direction), so that the wave propagates substantially / primarily in the direction connecting the relative front and rear surfaces of the piezoelectric layer (i.e., 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 "primarily" in "primarily excited acoustic mode" does not necessarily refer to low-order or high-order modes. Therefore, an XBAR is considered to be a laterally excited thin film bulk wave resonator. One physical constraint is that when an RF or microwave signal is applied between the two busbars 132, 134 of the IDT 130, heat is generated, which must be dissipated from the resonator to improve performance. In general, the heat can be dissipated by lateral conduction on the diaphragm (e.g., in the electrode itself) and vertical conduction through the cavity to the substrate.

[0061] 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 at or on a portion of the piezoelectric layer 110 that is located above the cavity 140 (e.g., the diaphragm 115), as described herein. Figure 1A As shown, the cavity 140 has a rectangular cross-section, which is larger than the aperture AP and length L of the IDT 130. According to other exemplary aspects, the cavity of the XBAR can have different cross-sectional shapes, such as regular or irregular polygons. The cavity of the XBAR can have more or less than four sides, which can be straight or curved.

[0062] According to an exemplary aspect, the area of ​​XBAR 100 is determined as the area of ​​IDT 130. For example, the area of ​​IDT 130 may be determined based on a measurement of the length L of IDT 130 multiplied by the width of the aperture AP of the interleaved fingers. As used in this disclosure, area is measured in μm. 2 Therefore, as described below, the area of ​​XBAR 100, and thus the total capacitance of XBAR 100, can be adjusted based on design choices.

[0063] In order to facilitate Figure 1A As presented in the cross-sectional view, the geometric pitch and width of the IDT fingers are greatly exaggerated 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 exemplary aspects, an XBAR may have hundreds or even thousands of parallel fingers in the IDT. Similarly, the thickness of the fingers in the cross-sectional view is greatly exaggerated.

[0064] Figure 1B A schematic cross-sectional view of an alternative XBAR configuration 100' is shown. Figure 1B In the resonator 100', the cavity 140 (which may generally correspond to Figure 1A The cavity 140 is formed completely in the dielectric layer 124 (eg, silicon oxide or silicon dioxide, such as Figure 1B As shown), the dielectric layer 124 is located on the substrate 120 (in Figure 1B and the piezoelectric layer 110 (indicated as Si in Figure 1B Although a single dielectric layer 124 is shown having a cavity 140 formed therein (eg, by etching), it should be understood that the dielectric layer 124 may be formed of multiple individual dielectric layers that are formed on top of each other to provide a stack of materials.

[0065] In addition, Figure 1B In the example of FIG. 1 , 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 may be defined by the substrate 120 and / or the piezoelectric layer 110. Figure 1B In the example of FIG. 1 , the cavity 140 has a trapezoidal shape. However, as described above, the cavity shape is not limited and may be a rectangular, elliptical, or other shapes.

[0066] Figure 2A Shows Figure 1A or Figure 1BDetailed schematic cross-sectional view of XBAR 100 (labeled as detail C). Piezoelectric layer 110 is a single crystalline layer of piezoelectric material having a thickness ts. ts may be, for example, 100 nanometers (nm) to 1500 nm. When used for 5G NR and Wi-Fi for 3.4 GHz to 7 GHz TM When the filter has a frequency band of 100,0 ...

[0067] In this aspect, a front dielectric layer 212 (eg, a first dielectric coating or material) may 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 dielectric layer 212 has a thickness tfd. Figure 2A As shown, the front side dielectric layer 212 covers the IDT fingers 238a, 238b, which may correspond to the above with respect to Figure 1A The finger 136 described. Although not in Figure 2A , the front side dielectric layer 212 may also be deposited only between the IDT fingers 238a, 238b. In this case, an additional thin dielectric layer (not shown) may be deposited on the IDT fingers to seal and passivate the fingers. Figure 2A Also not shown in FIG. 2 , the front-side dielectric layer 212 may, for example, also be deposited only on selected IDT fingers 238 a .

[0068] A backside dielectric layer 214 (e.g., a second dielectric coating or material) may also be formed on the back side 114 of the piezoelectric layer 110. Generally, for the purposes of this disclosure, the term "backside" refers to the side opposite to the conductor pattern of the IDT structure and / or opposite to the front side dielectric layer 212. In addition, the backside dielectric layer 214 has a thickness tbd. The front side dielectric layer 212 and the back side dielectric layer 214 may be non-piezoelectric dielectric materials, such as silicon oxide, silicon dioxide, or silicon nitride. Tfd and tbd may be, for example, 0 to 500 nm. Tfd and tbd may be less than the thickness ts of the piezoelectric layer. Tfd and tbd are not necessarily equal, and the front side dielectric layer 212 and the back side dielectric layer 214 are not necessarily the same material. In exemplary aspects, either or both of the front side dielectric layer 212 and the back side dielectric layer 214 may be formed of multiple layers of two or more materials according to various exemplary aspects.

[0069] The IDT fingers 238a, 238b may include aluminum, an aluminum alloy that is substantially (i.e., primarily) aluminum, copper, a copper alloy that is substantially (i.e., primarily) copper, beryllium, gold, or some other conductive material. A thin (relative to the total thickness of the conductor) layer of other metals (e.g., 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, it is noted that the terms "include," "have," "include," and "contain" (and variations thereof) as used herein are open conjunctions and allow for the addition of other units 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.

[0070] The dimension p (ie, “pitch”) can be considered as the distance between adjacent IDT fingers (eg, FIG. 2A to FIG. 2D The center-to-center spacing between the IDT fingers 238a, 238b in FIG. Figure 2A As shown, the measurement of the center point of the center-to-center spacing can be 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 extending from a second busbar adjacent to the first finger. 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 in the length direction 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 any combination thereof. FIG. 2A to FIG. 2DThe IDT fingers 238a, 238b) in the IDT 130 have a width w measured perpendicular to the long direction of each finger. The width w may also be referred to as a "mark" herein. In general, the width of the IDT fingers can be constant over 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 the individual IDT fingers varies along the length of the IDT 130, in which case the dimension w can be the average of the widths of the IDT fingers over 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 shown in FIG. Figure 1A As defined in .

[0071] In general, the IDT of an XBAR is significantly different from the IDT used in a surface acoustic wave (SAW) resonator, mainly in that the IDT excitation of an XBAR is as follows: Figure 4 The main shear acoustic mode (also referred to as the main shear mode, main shear thickness mode, etc.) described in more detail, in which the SAW resonator excites surface waves during operation. In addition, in a SAW resonator, the pitch of the IDT is one-half the wavelength of the acoustic wave at the resonant frequency. In addition, the mark-to-pitch ratio of the SAW resonator IDT is typically close to 0.5 (i.e., the mark or finger width is approximately one-quarter the wavelength of the acoustic wave at resonance). In an XBAR, the pitch p of the IDT is typically 2 to 20 times the width w of the finger. 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 the wavelength of the acoustic wave at resonance. For example, the width of the XBAR IDT fingers can be 500nm or greater, so that the IDT can be manufactured using optical lithography. The thickness tm of the IDT fingers can be from 100nm to approximately equal to the width w, because the lithography process generally cannot support a configuration where the thickness is greater than the width. The busbar of the IDT ( Figure 1A The thickness of 132, 134) in the IDT finger can be equal to the thickness tm of the IDT finger, less than the thickness tm of the IDT finger, greater than the thickness tm of the IDT finger, or any combination thereof. Note that the XBAR device described herein is not limited to the size range described herein.

[0072] In addition, unlike SAW filters, the resonant frequency of an XBAR depends on the total thickness (i.e., in the vertical or thickness direction) of its diaphragm, including the piezoelectric layer 110 and the front dielectric layer 212 and the back dielectric layer 214 disposed thereon. In an exemplary aspect, the thickness of one or both dielectric layers (i.e., the dielectric layers on the opposite surfaces of the piezoelectric layer) can be varied to change the resonant frequency of various XBARs in the filter. For example, a parallel resonator in a ladder filter circuit can include a thicker dielectric layer to reduce the resonant frequency of the parallel resonator relative to a series resonator having a thinner dielectric layer, thereby reducing the overall thickness.

[0073] Return to reference Figure 2A , the thickness tfd of the front 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, the minimum thickness can be, for example, 10nm to 50nm, depending on the material of the front dielectric layer and the method of deposition. The thickness of the back 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.

[0074] although Figure 2A The configuration of the IDT fingers 238a and 238b at the front side 112 of the piezoelectric layer 110 is disclosed, but alternative configurations may be provided. For example, Figure 2B An alternative configuration is shown (labeled as detail C') 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 will be changes in the stray modes (e.g., caused by the coating on the fingers). In addition, the markings will change due to the passivation layer coated on top of the IDT, which may also cause strays. Therefore, if Figure 2B As shown, by positioning the IDT fingers 238a, 238b at the back side 114 of the piezoelectric layer 110, the need to account for frequency variations and their impact on spurs may be eliminated compared to when the IDT fingers 238a and 238b are on the front side 112 of the piezoelectric layer 110.

[0075] Figure 2CAn alternative configuration (labeled as detail C") is shown in which 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 the same thickness or the same material.

[0076] Figure 2D Another alternative configuration is shown (labeled as detail C'"), in which 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 layer of dielectric material with a thickness tp can cover the IDT fingers 238a, 238b to seal and passivate the fingers. The dimension TP can be, for example, 10nm to 50nm.

[0077] Above about FIG. 2A to FIG. 2D Each of the described XBAR configurations includes a diaphragm spanning a cavity. However, in alternative aspects, the bulk acoustic resonator may be rigidly mounted, with the diaphragm having IDT fingers mounted on or over a Bragg mirror, which in turn may be mounted on a substrate.

[0078] Specifically, Figure 2E A detailed schematic cross-sectional view of a securely mounted XBAR (SM XBAR) is shown. Note that in addition to having a securely mounted configuration, Figure 2E Generally speaking, Figure 1A . In this aspect, the SM-XBAR includes a piezoelectric layer 110 and an IDT (of which only two fingers 236 are visible), wherein the dielectric layer 212 is disposed on the piezoelectric layer 110 and the IDT fingers 236. Similar to the above configuration, the piezoelectric layer 110 has parallel front and rear surfaces. Dimension ts is the thickness of the piezoelectric layer 110. The width of the IDT fingers 236 is dimension w, the thickness of the IDT fingers is dimension tm, and the IDT pitch is dimension p.

[0079] and Figure 1A The XBAR device shown is opposite, Figure 2EThe IDT of the SMXBAR in the embodiment of the present invention is not formed on the diaphragm across the cavity in the substrate. Instead, the acoustic Bragg reflector 240 is sandwiched between the surface 222 of the substrate 220 and the back surface of the piezoelectric layer 110. The term "sandwiched between" means that the acoustic Bragg reflector 240 is disposed between the surface 222 of the substrate 220 and the back surface of the piezoelectric layer 110 and is mechanically attached to both the surface 222 of the substrate 220 and the back surface of the piezoelectric layer 110. In some cases, a layer 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 back surface of the piezoelectric layer 110. Such additional material layers may be present, for example, to facilitate bonding of the piezoelectric layer 110, the acoustic Bragg reflector 240, and the substrate 220.

[0080] The acoustic Bragg reflector 240 may be an acoustic reflector 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 density of the material. "High" and "low" are relative terms. For each layer, the standard for comparison is the adjacent layer. The acoustic impedance of each "high" acoustic impedance layer is higher than the acoustic impedance of two adjacent low acoustic impedance layers. The acoustic impedance of each "low" acoustic impedance layer is lower than the acoustic impedance of two adjacent high acoustic impedance layers. As discussed above, the primary acoustic mode in the XBAR piezoelectric layer is a shear bulk wave. In an exemplary aspect, the thickness of each layer of the acoustic Bragg reflector 240 is equal to or about one-quarter of the wavelength in the layer of a shear bulk wave having the same polarization as the primary acoustic mode at or near the resonant frequency of the SM XBAR. Dielectric materials with relatively low acoustic impedance include silicon dioxide, carbon-containing silicon oxide, and certain plastics such as cross-linked polyphenylene polymers. Materials with relatively high acoustic impedance include hafnium oxide, silicon nitride, aluminum nitride, silicon carbide. All high acoustic impedance layers of the acoustic Bragg reflector 240 do not have to be the same material, and all low acoustic impedance layers do not have to be the same material. Figure 2E In the example of , the acoustic Bragg reflector 240 has a total of six layers, but the acoustic Bragg reflector may have more or less than six layers in alternative configurations.

[0081] The IDT fingers (e.g., IDT fingers 236, 238a, and 238b) may be disposed on the surface of the front side 112 of the piezoelectric layer 110. Alternatively, the IDT fingers (e.g., IDT fingers 236, 238a, and 238b) may be disposed in a groove formed in the surface of the front side 112. The groove may extend partially through the piezoelectric layer. Alternatively, the groove may extend completely through the piezoelectric layer.

[0082] Figure 3A and Figure 3B The XBAR 100 is shown along Figure 1A Two exemplary cross-sectional views of the section AA defined in FIG. Figure 3A In the embodiment, the piezoelectric layer 310 corresponding to the piezoelectric layer 110 is directly attached to the substrate 320, which may correspond to Figure 1A 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 (ie, the diaphragm 315). In an exemplary aspect, the cavity 340 may correspond to Figure 1A and / or Figure 1B In an exemplary aspect, the cavity 340 can be formed, for example, by etching the substrate 320 before attaching the piezoelectric layer 310. Alternatively, the cavity 340 can 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.

[0083] Figure 3B An alternative aspect is shown, in which the substrate 320 includes a substrate 322, and an intermediate layer 324 disposed between the piezoelectric layer 310 and the substrate 322. For example, the substrate 322 can be silicon (e.g., a silicon support substrate), and the intermediate layer 324 can be silicon dioxide or silicon nitride or some other material, such as an intermediate dielectric layer. That is, in this aspect, the substrate 322 and the intermediate layer 324 are collectively referred to as the substrate 320. As further shown, the cavity 340 is formed in the intermediate layer 324 below the portion of the piezoelectric layer 310 that contains the IDT fingers of the XBAR (i.e., the diaphragm 315). The cavity 340 can be formed, for example, by etching the intermediate layer 324 before attaching the piezoelectric layer 310. Alternatively, the cavity 340 can be formed by etching the intermediate layer 324. In other example embodiments, the cavity 340 can be defined in the intermediate layer 324 by other means, which is different from whether the intermediate layer 324 is etched 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 .

[0084] In this case, the diaphragm 315 (which in exemplary aspects may correspond to, for example, Figure 1A The diaphragm 115 of the piezoelectric layer 310 may be adjacent to the remaining portion of the piezoelectric layer 310 around most of the periphery of the cavity 340. For example, the diaphragm 315 may be adjacent to the remaining portion of the piezoelectric layer 310 around at least 50% of the periphery of the cavity 340. Figure 3BAs shown, cavity 340 extends completely through intermediate layer 324. That is, diaphragm 315 may have an outer edge facing piezoelectric layer 310, wherein at least 50% of the edge surface of diaphragm 315 is coupled to the edge of piezoelectric layer 310 facing diaphragm 315. This configuration provides increased mechanical stability of the resonator.

[0085] 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 over the bottom of the cavity on top of the substrate 322) or may extend through the intermediate layer 324 and (partially or completely) into the substrate 322. As described above, it should be understood that the interleaved fingers of the IDT may be arranged in accordance with various exemplary aspects. Figure 3A and Figure 3B On either surface or both surfaces of the diaphragm 315.

[0086] Figure 4 is a graphical illustration of the main excited acoustic modes of interest in the XBAR. Figure 4 A small portion of an XBAR 400 is shown, including a piezoelectric layer 410 and three interleaved IDT fingers 430. In general, according to exemplary aspects, an exemplary configuration of the XBAR 400 may correspond to that described above and in FIG. 2A to FIG. 2D Thus, it should be understood that piezoelectric layer 410 may correspond to piezoelectric layer 110 and IDT fingers 430 may be implemented according to any configuration of fingers 238a and 238b, for example.

[0087] In operation, an RF voltage is applied to the interlaced fingers 430. This voltage produces a time-varying electric field between these fingers. The direction of the electric field is transverse (i.e., laterally excited) or primarily parallel to the surface of the piezoelectric layer 410, as indicated by the arrow labeled "Electric Field." Due to the high dielectric constant of the piezoelectric layer 410, the electric field is highly concentrated in the piezoelectric layer relative to air. The transverse electric field induces shear deformation in the piezoelectric layer 410, thereby strongly exciting shear acoustic modes in the piezoelectric layer 410. In this context, "shear deformation" is defined as a deformation in which parallel planes in a material remain parallel and maintain a constant distance while translating relative to each other. In other words, parallel planes of the material are displaced laterally relative to each other. "Shear acoustic modes" are defined as acoustic vibration modes in a medium that cause shear deformation of the medium. The shear deformation in the XBAR 400 is represented by curve 460, where the adjacent small arrows provide a schematic indication of the direction and amplitude of the atomic motion. Note that for ease of illustration in Figure 4 In the visualization in FIG. 4 , the extent of atomic motion and the thickness of the piezoelectric layer 410 have been exaggerated. Although the atomic motion is primarily lateral (i.e., Figure 4), but the direction of the acoustic energy flow of the primarily excited shear acoustic mode is substantially and / or primarily normal to the surface of the piezoelectric layer, as indicated by arrow 465.

[0088] Bulk acoustic resonators based on shear acoustic wave resonances can achieve better performance than the current state-of-the-art film bulk acoustic resonator (FBAR) and firmly mounted resonator bulk acoustic wave (SMR BAW) devices with an electric field applied in the thickness direction. In such devices, the acoustic mode is compressed, with atomic motion and acoustic energy flow in the thickness direction. In addition, the piezoelectric coupling of shear wave XBAR resonances can be high (>20%) compared to other acoustic resonators. Therefore, the high voltage electric coupling enables the design and realization of microwave and millimeter wave filters with considerable bandwidth.

[0089] Figure 5A is a schematic circuit diagram and layout of a high frequency bandpass filter 500 using multiple bulk acoustic wave resonators (e.g., XBARs), such as the general XBAR configuration 100 (e.g., bulk acoustic wave resonators) described above. The filter 500 has a conventional ladder filter architecture (which may include a split ladder filter architecture in which the filter is split between multiple chips) having multiple bulk acoustic resonators, including four resonators 510A, 510B, 510C, and 510D and three parallel 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 (hence the term "series resonators"). In Figure 5A In FIG. 5 , the first port and the second port are labeled “In” and “Out”, respectively. However, the filter 500 is bidirectional and either port can be used as the input or output of the filter. At least two parallel resonators (e.g., parallel resonators 520A and 520B) are connected from the node between the series resonators to the ground connection. The filter may include Figure 5A Additional reactive components not shown in the filter, such as inductors. In an exemplary aspect, all parallel resonators and series resonators are XBARs (e.g., any of the XBAR configurations 100 and / or 100' as described above). Including three series resonators and two parallel resonators is an example. The filter can have more or less than five total resonators, more or less than three series resonators, and more or less than two parallel resonators. Typically, 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 parallel resonators are typically connected between ground and the input, output, or a node between two series resonators.

[0090] In the exemplary filter 500, the series resonators 510A, 510B, 510C, and 510D and the parallel resonators 520A, 520B, and 520C of the filter 500 can be formed on at least one piezoelectric material layer 530 (and in some cases, a single piezoelectric material layer 530) bonded to a silicon substrate (not visible). However, in alternative aspects, each resonator can be formed on a separate corresponding piezoelectric layer of each resonator, wherein all resonators are located on the same chip. However, in some cases, for example, different resonators of the filter can be bonded to separate substrates. This can produce a split ladder architecture that can include one or more separate chips that include separate piezoelectric layers and IDTs for one or more bulk acoustic resonators, which are then configured together to form the entire split ladder filter. In addition, each resonator includes a corresponding IDT (not shown), wherein at least the fingers of the IDT are disposed above a cavity or acoustic reflector in the substrate. In this and similar contexts, the term "corresponding" means "relating things to one another," that is, having a one-to-one correspondence. Figure 5A In FIG. 5 , the cavity is schematically shown as a dashed rectangle (e.g., rectangle 535). In this example, each IDT is disposed above a corresponding cavity. In other filters, the IDTs of two or more resonators may be disposed above a single cavity.

[0091] Each of the resonators 510A, 510B, 510C, 510D, 520A, 520B, and 520C in the filter 500 has a resonance where the admittance of the resonator (also interchangeably referred to as the Y parameter) is very high and an anti-resonance where the admittance of the resonator is very low. The resonance and anti-resonance occur at the resonant frequency and the anti-resonance frequency, respectively, and the resonant frequency and the anti-resonance frequency can be the same or different for the various resonators in the filter 500. In short, each resonator can be regarded as a short circuit at its resonant frequency and an open circuit at its anti-resonance frequency. At the resonant frequency of the parallel resonator and the anti-resonance frequency of the series resonator, the input-output transfer function will be close to zero. In a typical filter, the resonant 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.

[0092] The frequency range between the resonant frequency and the anti-resonant 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 can have a specific coupling parameter to which the corresponding resonator is tuned in order to achieve the desired frequency response of the filter 500.

[0093] 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 a configuration as described above with respect to Figures 1A to 2D 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 securely mounted on or above a Bragg reflector (e.g., as Figure 2E As shown), the Bragg reflector can be mounted on a substrate. In addition, as will be described below, exemplary aspects include a resonator having a plate capacitor that is coupled in parallel with the resonator to reduce the coupling coefficient. Therefore, the filter 500 may include a plurality of capacitors that are electrically coupled in parallel with a plurality of IDTs, respectively, as will be apparent to those skilled in the art. In addition, as described in detail below, each capacitor includes at least one first electrode on a first major surface of the piezoelectric layer and a metal layer (e.g., a second electrode) on a second major surface of the piezoelectric layer, such that at least one piezoelectric layer is sandwiched between the first electrode and the metal layer. Details of the exemplary capacitor structure will be described below.

[0094] Figure 5B is a schematic diagram of a radio frequency module including an acoustic wave filter device according to an exemplary aspect. Specifically, Figure 5B 540 is shown including one or more acoustic wave filters 544 according to an exemplary aspect. The illustrated RF module 540 also includes a radio frequency (RF) circuit (or radio frequency "RF" circuit) 543. In an exemplary aspect, as described above with reference to Figure 5A As depicted, acoustic wave filter 544 may include one or more filters 500 including an XBAR (eg, a bulk acoustic resonator as described herein).

[0095] Figure 5B The acoustic wave filter 544 shown includes terminals 545A and 545B (e.g., a first terminal and a second terminal). Terminals 545A and 545B can be used, for example, as input contacts and output contacts 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 connected to each other. Figure 5B546 (e.g., a common substrate). The package substrate 546 may be a laminate substrate. The terminals 545A and 545B may be electrically connected to the contact portions 547A and 547B on the package substrate 546, respectively, through electrical connectors 548A and 548B, respectively. For example, the electrical connectors 548A and 548B may be bumps or wiring 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.

[0096] The RF circuit 543 may include any suitable RF circuit. For example, the RF circuit may include one or more RF amplifiers (e.g., one or more power amplifiers and / or one or more low noise amplifiers), one or more RF 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 RF module 540 may include one or more packaging structures to, for example, provide protection and / or facilitate easier handling of the RF module 540. Such a packaging structure may include an overmolded structure formed above the packaging substrate 546. The overmolded structure may encapsulate some or all components of the RF module 540.

[0097] Fig. 6A 600A is a schematic cross-sectional view of a portion of a filter device including an XBAR according to an exemplary aspect, the XBAR having a capacitor coupled in parallel with the resonator. Specifically, the resonator structure 600A includes 6 metal-piezoelectric-metal ("MPM") capacitors 650, which are capacitors coupled in parallel with the acoustic resonator, providing high capacitance density while providing size reduction compared to conventional interleaved capacitors (IDC) or metal-insulator-metal ("MIM") capacitor structures. In an exemplary aspect, the capacitor can be configured as a parallel plate capacitor, but it is also noted that the term "parallel" generally refers to two or more opposing metal plates forming a capacitor, and the surfaces of the individual metal plates are not necessarily planar and completely parallel to each other. In contrast, the plates of the capacitor may have slight variations due to, for example, manufacturing tolerances.

[0098] Typically, the coupling coefficient K of the XBAR resonator is eff The bandwidth of the filter device including such an XBAR resonator is greatly affected. In addition, it is well known that the introduction of series or parallel passive components (e.g., IDC and MIM capacitor structures) may reduce the coupling coefficient K of the filter device. effHowever, the two conventional capacitor structures (ie, the MIM structure and the IDC structure) have a negative impact on the Q factor of the filter device and greatly increase the overall volume of the filter, making practical applications difficult.

[0099] To overcome these limitations, the resonator structure 600A of the exemplary aspect utilizes a vertical electric field ("E field"), wherein metal electrodes are disposed on opposing surfaces of the piezoelectric layer to create a capacitor 650 (e.g., a parallel plate capacitor), which for purposes of this disclosure may be referred to as an MPM structure or MPM capacitor. In general, Figure 6B According to the exemplary aspects Fig. 6A As shown, the XBAR 100 (e.g., as described above with respect to FIG. 1 and FIG. 2 ) is a circuit 600B of the resonator structure 600A. FIG. 2A to FIG. 2E 6) is coupled in parallel to capacitor 650. In practice, parallel plate MPM capacitor 650 can be implemented to provide higher capacitance density and size reduction compared to conventional IDC or MIM capacitor structures, as will be described in detail below.

[0100] Return to reference Fig. 6A , the resonator structure 600A may generally correspond to, for example, the above Figure 1B The structure shown in FIG. 1 , wherein the substrate (also referred to as a supporting substrate) includes a base 622 (e.g., silicon) and an intermediate layer 624 (e.g., silicon oxide or silicon dioxide) is disposed on the base 622. It should be understood that in exemplary aspects, the base 622 and the intermediate layer 624 may be collectively referred to as, for example, as described above with respect to Figure 3B In either case, the piezoelectric layer 610 (e.g., lithium niobate or lithium tantalate) can be supported by the substrate 622, for example, coupled to the intermediate layer 624, wherein the cavity 640 is formed above the base 622 supporting the substrate. It should be understood that the substrate 622 can correspond to the substrate 120, and the intermediate layer 624 can correspond to the intermediate layer 124 described above. In addition, the piezoelectric layer 610 can correspond to the piezoelectric layer 110 described above.

[0101] As further shown, the piezoelectric layer 610 is disposed above the cavity 640 to form a diaphragm thereon, as described above. The IDT can be disposed on one or both surfaces on opposite sides of the piezoelectric layer 610. As generally described herein, the IDT can include: a first busbar and a second busbar, each extending along the length of the diaphragm in a first direction from a first end to a second end thereof. In addition, the IDT can include a first plurality of electrode fingers extending from the first busbar toward the second busbar in a second direction, wherein the second direction intersects the first direction. Fig. 6AIn the example shown, IDT electrode finger 638a (which may correspond to the above-mentioned IDT finger 238a) may extend from a first bus bar (not shown). Similarly, the IDT may also include a second plurality of electrode fingers extending from the second bus bar toward the first bus bar in a second direction. IDT electrode finger 638b (which may correspond to the above-mentioned IDT finger 238b) may extend from a second bus bar (not shown). According to this configuration, the first plurality of electrode fingers and the second plurality of electrode fingers form staggered fingers of the IDT. Fig. 6A In the example, only two first electrode fingers 638a (e.g., positive potential) and two second electrode fingers 638b (e.g., negative potential) are shown to represent the ends of the resonator (e.g., XBAR 100) in the length direction across the diaphragm, but it should be reiterated that the XBAR can have many (e.g., multiple) interlaced electrode fingers and is not limited to only two pairs of electrode fingers.

[0102] As described above, the MPM capacitor structure 650 (also commonly referred to as capacitor 650) is coupled in parallel to the resonator end of the XBAR 100. As shown, the capacitor 650 includes one or more first electrodes 652 and 654 on the first major surface 612 of the piezoelectric layer 610 and a metal layer 656 on the second major surface 614 of the piezoelectric layer 610, which is opposite to the first major surface 612 (i.e., the first and second surfaces 612 and 614 are opposite to each other). In an exemplary aspect, the first electrodes 652 and 654 correspond to a pair of electrodes on the first major surface 612, which include an anode 652 (e.g., a positive potential) and a cathode 654 (e.g., a negative potential). In addition, the metal layer 656 can be a floating metal disposed on the second major surface 614 of the piezoelectric layer 610. Thus, the piezoelectric layer 610 is sandwiched between one or more first electrodes 652 and 654 of the capacitor 650 and the floating metal (ie, metal layer 656) of the capacitor 650, which effectively forms an MPM capacitor on opposing surfaces of the piezoelectric layer 610, as described herein.

[0103] Thus, according to an exemplary aspect, one or more first electrodes include an anode 652 of capacitor 650, which is coupled to a first busbar (not shown) and extends in parallel with a first plurality of electrode fingers (e.g., finger 638a) at the resonator end. In addition, one or more first electrodes include a cathode 654 of capacitor 650, which is coupled to a second busbar (not shown) and extends in parallel with a second plurality of electrode fingers (e.g., finger 638b) at the resonator end.

[0104] Figure 6Cis a graph of the frequency-varying admittance of an XBAR device having an MPM capacitor coupled thereto according to an exemplary aspect. More specifically, graph 600C illustrates the frequency-varying admittance (in dB) of an XBAR device having an MPM capacitor structure having different capacitances coupled thereto, which is simulated using a finite element method (FEM) simulation technique. As described above, capacitor 650 is coupled in parallel with XBAR resonator 100 to reduce the effective coupling of the resonator by lowering the frequency of the anti-resonance (Fa).

[0105] As shown, an XBAR acoustic resonator (e.g., XBAR 100) without a parallel plate capacitor as described above has an anti-resonance frequency (fa) of about 6.57 GHz. For example, by coupling MPM capacitors with capacitance values ​​of 0.1 pf C, 0.2 pf C, and 0.4 pf C in parallel therewith, the anti-resonance frequency (fa) will be shifted downward (i.e., to the left), which effectively reduces the effective coupling. Doing so is very important for XBAR devices operating in a narrow passband (e.g., n79 as described herein).

[0106] In general, the MPM capacitor structure 650 can be implemented according to various aspects and coupled in parallel to the XBAR resonator 100 . 7A to 7C An enlarged schematic cross-sectional view of an MPM capacitor structure according to an exemplary aspect is shown.

[0107] Specifically, Fig. 7A An MPM capacitor 700A is shown, which generally corresponds to the above description of Fig. 6A 650. As shown, capacitor 700A includes an anode 652 and a cathode 654, which may generally correspond to one or more first electrodes as described herein and are disposed on a first major surface 612 of piezoelectric layer 610, and a metal layer 656 is disposed on a second major surface 614 of piezoelectric layer 610, the second major surface 614 being opposite to the first major surface 612. As shown, a first capacitance is formed across piezoelectric layer 610 between anode 652 and floating metal (i.e., metal layer 656), while a second capacitance is formed across piezoelectric layer 610 between floating metal (i.e., metal layer 656) and cathode 654. Thus, an electric field (E field) flows from a positive potential (anode 652) to a negative potential (cathode 654) 656 through the metal layer.

[0108] Figure 7B FIG. 7 shows an MPM capacitor 700B according to another exemplary aspect. It should be understood that the MPM capacitor 700B can replace the above Fig. 6A700B. As shown, capacitor 700B includes an anode 652 on a first major surface 612 of piezoelectric layer 610 and a cathode 654 disposed on a second major surface 614 of piezoelectric layer 610, the second major surface 614 being opposite to the first major surface 612. As shown, a capacitance is formed across piezoelectric layer 610 between anode 652 and cathode 654 in a vertical direction. Therefore, an electric field (E field) flows in a vertical direction from a positive potential (anode 652) to a negative potential (cathode 654).

[0109] Figure 7C FIG. 2 shows another MPM capacitor 700C according to another exemplary aspect. It should be understood that the MPM capacitor 700C can replace the above Fig. 6A 6. In this example, the MPM capacitor is coupled in parallel to the SM XBAR, e.g. Figure 2E As shown, capacitor 700C includes an anode 652 and a cathode 654, which may generally correspond to one or more first electrodes as described herein and are disposed on a first major surface 612 of piezoelectric layer 610, and a metal layer 656 is disposed on a second major surface 614 of piezoelectric layer 610, the second major surface 614 being opposite to the first major surface 612. As further shown, metal layer 656 is disposed on a Bragg reflector or Bragg mirror 660. In this regard, Bragg reflector 660 may be disposed on a supporting substrate (e.g., substrate 622 (e.g., silicon)) and may correspond to the above description of Figure 2E The acoustic Bragg reflector 240 described above. Thus, the Bragg reflector 660 may include a plurality of dielectric layers that alternate between a material having a high acoustic impedance and a material having a low acoustic impedance. As described above, "high" and "low" are relative terms such that for each layer, the standard for comparison is the adjacent layer. The acoustic impedance of each "high" acoustic impedance layer is higher than the acoustic impedance of two adjacent low acoustic impedance layers. The acoustic impedance of each "low" acoustic impedance layer is lower than the acoustic impedance of two adjacent high acoustic impedance layers.

[0110] according to Figure 7C In the exemplary aspect shown, a first capacitance of the capacitor structure 700C is formed across the piezoelectric layer 610 between the anode 652 and the floating metal (i.e., the metal layer 656), and a second capacitance is formed across the piezoelectric layer 610 between the floating metal (i.e., the metal layer 656) and the cathode 654. Thus, an electric field (E field) flows through the metal layer 656 from a positive potential (anode 652) to a negative potential (cathode 654).

[0111] FIG. 7D to FIG. 7EAn enlarged schematic top view of an MPM capacitor structure according to an exemplary aspect is shown. Specifically, the illustrated top view shows alternative exemplary aspects of capacitor structures 700A and / or 700C, each of which includes an anode 652 and a cathode 654 on a first major surface (e.g., top surface) of a piezoelectric layer 610. In addition, a floating metal layer 656 is disposed on a second major surface. Fig.7D and Fig. 7E In each of the embodiments shown, the anode 652 and cathode 654 are coupled to the respective busbars 132 and 134 of the IDT conductor pattern, as described above with respect to FIG. Figure 1A Thus, as described above, the anode 652 will extend in a direction parallel to the direction of the first electrode fingers extending from the bus bar 132, and the cathode 654 will extend in a direction parallel to the direction of the second electrode fingers extending from the bus bar 134.

[0112] In each embodiment, the anode 652 and cathode 654 extend toward each other. Fig.7D In the embodiment of FIG. 6 , the anode 652 and the cathode 654 are arranged in an offset and asymmetrical configuration, but they overlap each other in the length direction of the IDT. In contrast, in Fig. 7E In the embodiment of the present invention, the anode 652 and the cathode 654 extend directly toward each other in a symmetrical configuration with a gap therebetween. It should be understood that in each embodiment, the metal layer 656 overlaps (at least partially) both the anode 652 and the cathode 654 in the thickness direction of the capacitor structure so as to sandwich the piezoelectric layer 610 and form the above-mentioned MPM capacitor structure. In addition, metal traces 702 and 704 can be provided and electrically coupled to the corresponding busbars 132 and 134 to generate positive and negative potentials, thereby generating an electric field between the capacitor plates.

[0113] Figure 7F An enlarged schematic cross-sectional view of an MPM capacitor structure according to an exemplary aspect is shown. In addition, Figure 7G An enlarged schematic top view of an MPM capacitor structure according to an exemplary aspect is shown. Specifically, Figure 7F and Figure 7G The figure shown may illustrate exemplary aspects of the above capacitor structure 700B, which includes an anode 652 (e.g., metal M1) on a first major surface of the piezoelectric layer 610 and a cathode 654 (e.g., metal M1) on a second major surface of the piezoelectric layer 610. In this embodiment, the anode 652 is (electrically) coupled to the bus bar 132 and the cathode 654 is (electrically) coupled to the bus bar 134 of the IDT conductor pattern, as described above with respect to Figure 1A As described.

[0114] In addition, a metal via 706 (e.g., filled with a conductive metal M2 such as aluminum) extends through the piezoelectric layer 610 to couple the bus bar 134 to a cathode 654 disposed on a lower surface of the piezoelectric layer 610. The metal trace 702 (also represented as M2) and the conductive via 706 (or a trace coupled thereto) can be configured as capacitor terminals coupled to the anode 652 and the cathode 654, respectively. In an exemplary embodiment, a through hole 708 can be etched or otherwise provided in the piezoelectric layer 610 on each side of the anode 652 and the cathode 654 along the thickness direction (e.g., vertical direction) of the piezoelectric layer 610. In this regard, the through hole 708 provides a defined area of ​​capacitance (wherein the electric field is confined to the electrode region of the capacitor), electrical isolation of the MPM capacitor structure from adjacent structures, and acoustic isolation from adjacent structures.

[0115] Fig. 8A and Figure 8B A conventional interleaved capacitor (IDC) structure is shown. More specifically, Fig. 8A A release structure 800A for an IDC structure is shown (eg, on a diaphragm suspended above a cavity). Figure 8B The unreleased structure 800B (e.g., substrate and / or dielectric layer) of the IDC structure is shown. In either case, a pair of positive potential electrodes 852 are each capacitively coupled to a negative potential electrode 854. The electrode pair 852 and the electrode 854 are disposed on the piezoelectric plate 810, and an electric field (i.e., an E field) flows from the electrode pair 852 to the electrode 854. In addition, Figure 8B The unreleased structures include a dielectric layer 824 (eg, silicon dioxide) and a support substrate 822 (eg, silicon) that supports the capacitor structure.

[0116] Figure 8C and Fig.8D They are Fig. 8A and Figure 8B Graphs of the admittance of the IDC structures shown vary with frequency. Specifically, graph 800C shows a graph of the admittance of the released structure 800A, while graph 800D shows a graph of the admittance of the unreleased structure 800B.

[0117] Generally speaking, capacitance density (C d ) is a function of the thickness and dielectric constant of the insulating material:

[0118]

[0119] In addition, the sensitivity of capacitance to the thickness change of insulating material is dC = -dt / t 2 For IDC structures (e.g., structures 800A and 800B), the capacitance density (C d ) will be a function of the pitch (which is the spacing between the capacitor electrodes) and the thickness of each layer. Figure 8C and Fig.8D As shown in the figure, the transverse field will limit the capacitance density. Therefore, although it is noted that Figure 8B The unreleased structure in can suppress some acoustic activity near the passband, but both configurations exhibit poor capacitor performance and significant acoustic activity (e.g., spurious activity) at frequencies near the passband of the audio frequency.

[0120] Fig.9A , Fig. 9C , Fig.9E , Figure 9G and Fig.9I An enlarged schematic cross-sectional view of an MPM capacitor structure according to an exemplary aspect is shown. Fig. 9B , Fig.9D , Fig.9F and Figure 9H They are Fig.9A , Fig. 9C , Fig.9E and Figure 9G Graph of the frequency-dependent admittance of the MPM IDC capacitor structure shown. Note that the reference numerals used above with respect to the exemplary embodiments are the same as those used above. Fig.9A , Fig. 9C , Fig.9E and Figure 9G The features shown have the same reference numerals and will not be described in detail below.

[0121] In an exemplary aspect, Fig.9A FIG. 1 shows a release structure of an MPM structure (eg, on a diaphragm suspended above a cavity) according to an exemplary embodiment. In this example, the total capacitance C total Equal to C L (Linear Capacitance) plus C v (vertical capacitance) divided by 2. That is, C total =C L +C v / 2. The capacitance density is C d =182[pF / mm 2 ].

[0122] Fig. 9B shows shows Fig.9A A graph of the frequency-dependent admittance (in dB) of the XBAR device coupled in parallel with the MPM capacitor structure shown, which was simulated using the finite element method (FEM) simulation technique. The simulation parameters are: the piezoelectric plate has a height of 350 nm, the aluminum fingers have a height of 100 nm and a mark (e.g., width) of 1.99 μm, a pitch of 4 μm, and the Euler angles of the piezoelectric plate are [0, 30°, 0]. As shown in the figure, with Figure 8C and Fig.8DCompared to the figures in FIG. , the exemplary MPM capacitor structure provides higher capacitor performance and reduced acoustic activity (eg, spurious activity) at frequencies near the passband of the audio frequencies.

[0123] In addition to the unreleased structure, Fig. 9C Shown with Fig.9A The configuration shown is similar to that shown in FIG. 1 , where the MPM capacitor structure is coupled to a dielectric layer 624 (e.g., silicon oxide or silicon dioxide) on a support structure (e.g., substrate 622 (e.g., silicon)). Again, the total capacitance is C total =C L +C v / 2, and the capacitance density is C d =182[pF / mm 2 ]. Using the same simulation parameters as above, Fig.9D The diagrams shown illustrate that the unreleased structures are configured to suppress and / or attenuate most of the acoustic activity near the passband. Additionally, in alternative exemplary aspects, other parameters including pitch, marks, IDT thickness, and piezoelectric thickness may be varied to mitigate stray noise.

[0124] Fig.9E and Figure 9G The release MPM capacitor described herein is shown Fig.9E ) and unreleased MPM capacitors ( Figure 9G ), wherein the anode 652 is disposed on a first (or top) surface of the piezoelectric layer 610, and the cathode 654 is disposed on a second (or bottom) surface of the piezoelectric layer 610. As further shown, the E field flows from the anode 652 to the cathode 654 in a vertical direction. As further shown, the anode 652 has a TE (top electrode) width in a horizontal direction (i.e., parallel to the top surface of the piezoelectric layer 610). Similarly, the cathode 654 has a BE (bottom electrode) width in a horizontal direction (i.e., parallel to the bottom surface of the piezoelectric layer 610).

[0125] exist Fig.9E and Figure 9G In the exemplary aspect shown, the capacitance density is C d =990[pF / mm 2 ]. In this case, a larger capacity density is achieved due to the vertical electric field (E field). In addition, the electrode ratio (Elect_Ratio) is defined as the ratio of BE (bottom electrode width) to TE (top electrode width). Fig.9F and Figure 9H The release structures under different electrode ratios are shown ( Fig.9E ) and unreleased structures ( Figure 9G). The simulation parameters for these figures are: the piezoelectric plate has a height of 350nm, the aluminum fingers have a height of 100nm, and the mark (e.g., width) is 0.6μm. Note that when the top / bottom electrodes are not aligned, significant acoustic activity will be observed. In addition, Figure 9G The diagrams shown illustrate that the unreleased structures are configured to suppress and / or attenuate most of the acoustic activity near the passband. As described above, in alternative exemplary aspects, other parameters including pitch, marks, IDT thickness, and piezoelectric thickness may be varied to mitigate stray.

[0126] Fig.9I Shows the Fig.9A The exemplary aspects shown and described above Fig. 6A Except that the piezoelectric layer is a multilayer complementary oriented piezoelectric ("COP") structure (which may include a dielectric coating to achieve high coupling of high-order modes (e.g., A3 mode)), Fig.9I Embodiments of generally include the same components as described above.

[0127] According to this exemplary aspect, the COP structure can include a joining of piezoelectric materials (e.g., layers or plates) having complementary cuts. These cuts have crystal orientations relative to each other so that the corresponding piezoelectric tensors have opposite polarities within the additional one or more COP layers. Although this exemplary aspect contemplates a COP structure having two piezoelectric layers 910A and 910B, it is noted that in alternative aspects, the number of piezoelectric layers within the COP structure is not limited to two layers. Specifically, the number of piezoelectric layers can be determined based on the mode order and the desired coupling k2.

[0128] Fig.9Iis a schematic cross-sectional view of an acoustic wave resonator having a complementary oriented piezoelectric structure according to an exemplary aspect. As shown, a pair of piezoelectric layers 910A and 910B (e.g., piezoelectric plates) are provided. In an exemplary aspect, a first piezoelectric layer (e.g., piezoelectric layer 910A, which can be considered a COP layer) is formed of and includes a material having a first cut (e.g., lithium niobate or lithium tantalate), the first cut having a first crystal orientation. In addition, a second piezoelectric layer (e.g., piezoelectric layer 910B, which can be considered a standard layer) is coupled to the first piezoelectric layer (e.g., piezoelectric layer 910A) and is formed of and includes a material having a second cut (e.g., lithium niobate or lithium tantalate), the second cut having a second crystal orientation. The first cut and the second cut are configured such that the polarity of the piezoelectric tensor of the second piezoelectric layer 910B is opposite to the polarity of the piezoelectric tensor of the first piezoelectric layer 910A to increase the coupling k2 of the resonator. In an embodiment similar to the above, the first electrode 652 and the second electrode 654 can correspond to an electrode pair including an anode 652 (e.g., positive potential) and a cathode 654 (e.g., negative potential), and can be disposed on opposite sides of a COP structure including a first piezoelectric layer 910A and a second piezoelectric layer 910B.

[0129] Advantageously, the COP structure provides a configuration in which an MPM capacitor may be configured without offsetting any benefits that may occur associated with using the COP structure in a resonator (eg, any benefits that may occur with respect to higher order modes of the resonator when using the COP structure).

[0130] In an exemplary aspect, the piezoelectric layers 910A and 910B can be, for example, lithium niobate (LN) plates or lithium tantalate (LT) plates. The crystal structure of LN and LT belongs to the 3m point group because it exhibits a three-fold rotational symmetry around the c-axis (usually defined as the Z-axis). In addition, the crystal structure of the 3m point group exhibits a single-fold symmetry around the a / b axis (usually defined as the X / Y axis). The materials of different piezoelectric layers 910A and 910B (e.g., LN or LT) will have different Euler angles to define the cut of the material. For example, the Euler angles can be [0°, β, 0°], which can be referred to as a "Y cut", where the "cut angle" is the angle between the y-axis and the normal of the plate. The "cut angle" is equal to β+90°. For example, a plate with Euler angles [0°, 30°, 0°] is typically referred to as a "120° rotated Y cut". Thus, in an exemplary aspect, the material of the first piezoelectric layer 910A can be a 60° rotated Y-cut lithium tantalate, while the material of the second piezoelectric layer 910B can be a 120° rotated Y-cut lithium tantalate. In practice, these cuts are oriented so that the corresponding piezoelectric tensors have opposite polarities within the additional COP layer (e.g., piezoelectric layer 910A).

[0131] Fig.10A flow chart of a method 1000 for manufacturing a filter as described herein is shown according to exemplary aspects. Specifically, method 1000 summarizes an exemplary manufacturing process for manufacturing a filter device including an XBAR coupled in parallel to an MPM capacitor structure as described herein. Specifically, process 1000 is used to manufacture a filter device including a plurality of XBARs having a parallel plate MPM capacitor as described herein. Process 1000 begins at 1005, wherein a device substrate and a thin layer of piezoelectric material are disposed on a sacrificial substrate. Process 1000 ends at 1095, wherein the filter device is completed. Fig.10 The flow chart only includes the main process steps. Fig.10 Various conventional process steps (e.g., surface preparation, cleaning, inspection, baking, annealing, monitoring, testing, etc.) are performed before, between, after, and during the steps shown. Note that at 1005, a material layer (e.g., a floating metal layer for a capacitor as described above) can be deposited on the piezoelectric material before coupling the piezoelectric material to the sacrificial substrate.

[0132] In addition, note that although Fig.10 Generally described for manufacturing a single filter device process, but can be a common wafer (including the piezoelectric layer bonded to the substrate) on a plurality of filter devices simultaneously manufactured. In this case, can be with respect to all filter devices on the wafer at the same time perform each step of process 1000.

[0133] Fig.10 The flowchart of FIG. 1 captures three variations of a process 1000 for making an XBAR that differ in when and how the cavity is formed in the device substrate. The cavity may be formed at step 1010A, 1010B, or 1010C. Only one of these steps is performed in each of the three variations of process 1000. It should be understood that these steps may be omitted, for example, if the filter device includes only an SM XBAR configuration. In such an embodiment, a separate step (not shown) for forming the layers of the Bragg mirror may be incorporated into the exemplary manufacturing method.

[0134] In one exemplary aspect, the piezoelectric layer can be, for example, a lithium niobate plate or a lithium tantalate plate, any of which can be Z-cut, rotated Z-cut, Y-cut, or rotated YX-cut. For historical reasons, a rotated Y-cut plate configuration can be generally referred to as a "Y-cut", where the "cut angle" is the angle between the y-axis and the normal to the plate. The "cut angle" is equal to β+90°. For example, a plate with Euler angles of [0°, 30°, 0°] is generally 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 of 0°, 0°, 90°. Additional embodiments may include a piezoelectric layer with Euler angles of 0°, β, 90°, where β is in the range of from -15° to +5° (such as Y82 discussed in more detail below), 0°≤β≤60 (such as Y120 and / or Y128 discussed in more detail below), or any combination thereof. The piezoelectric layer may be some other material and / or some other cut. The device substrate may preferably be silicon. The device substrate may be some other material that allows deep cavities to be formed by etching or other processes.

[0135] In a variation of process 1000, one or more cavities are formed in the device substrate at 1010A before at least one piezoelectric layer is bonded to the substrate at 1015. A separate cavity can be formed for each resonator in the filter device. In addition, the cavity can be shaped and formed so that two or more resonators can be on one diaphragm above one cavity. These resonators sharing the diaphragm are acoustically coupled on the sound track. Conventional photolithography and etching techniques can be used to form one or more cavities. Typically, the cavity formed at 1010A will not penetrate the device substrate.

[0136] At 1015, at least one piezoelectric layer is bonded to a device substrate or indirectly to a dielectric layer, as described above. The at least one piezoelectric layer and the device substrate may be bonded by a wafer bonding process. Typically, 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 metal) may be formed or deposited on the mating surfaces of one or both of the piezoelectric layer and the device substrate. One or both mating surfaces may be activated using, for example, a plasma process. The mating surfaces may then be pressed together with considerable force to establish a molecular bond between the piezoelectric layer and the device substrate or the intermediate material layer.

[0137] At 1020, 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 a defect in the crystal structure along a plane that defines a boundary between what will become the piezoelectric layer and the sacrificial substrate. At 1020, the wafer can be singulated along the defect plane, 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 manner.

[0138] At 1030, a first conductor pattern is formed by depositing and patterning one or more conductor layers on the front side of the piezoelectric layer, which includes the IDT of each XBAR and the capacitor electrode. The conductor layer can be, for example, aluminum, aluminum alloy, copper, copper alloy, or some other conductive metal. In some aspects, one or more layers of other materials can be arranged below the conductor layer (i.e., between the conductor layer and the piezoelectric layer) and / or on the top of the conductor layer. For example, a thin film of titanium, chromium or other metal can be used to improve the adhesion between the conductor layer and the piezoelectric layer. A second conductor pattern of gold, aluminum, copper or other higher conductivity metal can be formed above a portion of the first conductor pattern (e.g., an IDT busbar and the interconnection between the IDTs).

[0139] At 1030, each conductor pattern can be formed by sequentially depositing a conductor layer and (in some aspects) one or more other metal layers on the surface of the piezoelectric layer. Excess metal can then be removed by etching through the patterned photoresist. For example, the conductor layer can be etched by plasma etching, reactive ion etching, wet chemical etching, or other etching techniques.

[0140] Alternatively, at 1030, 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. It should be understood that the photoresist for the conductor pattern can be defined to achieve the desired chirp configuration as described above. In addition, the conductor layer and one or more other layers under some aspects can be sequentially deposited on the surface of the piezoelectric layer. The photoresist can then be removed, which removes excess material, leaving the conductor pattern. It should also be understood that in alternative exemplary aspects, a metal layer (e.g., an electrode of a capacitor) can be deposited on the piezoelectric layer before the piezoelectric layer is bonded to the substrate at step 1015, as will be understood by those skilled in the art.

[0141] At 1040, one or more dielectric layers may be formed on one or both surfaces of the piezoelectric layer and the conductor pattern. According to an exemplary aspect, these layers may be deposited and trimmed to configure the resonant frequency.

[0142] At 1050, a passivation layer / 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 pads for electrical connection to circuits located outside the filter. In some examples of process 1000, the passivation / tuning dielectric layer can be formed after etching the cavity in the device substrate and / or the intermediate layer at 1010B or 1010C.

[0143] In a second variation of process 1000, at 1010B, one or more cavities are formed in the back surface of the device substrate and / or intermediate layer. A separate cavity can be formed for each resonator in the filter device. In addition, the cavity can be shaped and formed so that multiple resonators can be on one diaphragm above one cavity. These resonators sharing the diaphragm are acoustically coupled on the acoustic track. Anisotropic or orientation-dependent dry or wet etching can be used to open holes through the back side of the device substrate to the piezoelectric layer to form one or more cavities. In this case, the resulting resonant device will have a structure such as Figure 1A Cross section shown.

[0144] In a third variation of process 1000, at 1010C, one or more cavities in the form of grooves can be formed in the device substrate by etching the substrate using an etchant introduced through an opening in the piezoelectric layer. A separate cavity can be formed for each resonator in the filter device. In addition, the cavity can be shaped and formed so that two or more resonators can be on one diaphragm above one cavity. These resonators that share a diaphragm are acoustically coupled on the sound track. The one or more cavities formed at 1010C will not penetrate the device substrate.

[0145] Ideally, after forming the cavity at 1010B or 1010C, most or all filter devices on the wafer will meet the performance requirement set. However, normal process tolerances will result in variations in parameters (e.g., thickness of the dielectric layer formed at 1040 and 1050), variations in thickness and line width of the conductor and IDT fingers formed at 1030, and variations in thickness of the piezoelectric layer. These variations cause the performance of the filter devices to deviate from the performance requirement set.

[0146] To increase the yield of filter devices that meet performance requirements, frequency tuning can be performed by selectively adjusting the thickness of the passivation / tuning layer deposited above the resonator at 1050. The frequency of the filter device passband can be reduced by adding material to the passivation / tuning layer, and the frequency of the filter device passband can be increased by removing material from the passivation / tuning layer. In general, process 1000 is biased to produce a filter device with 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.

[0147] At 1060, a probe card or other device may be used to make electrical connections to the filter to allow radio frequency (RF) testing and measurement of the filter characteristics (e.g., input-output transfer function). Typically, RF measurements are performed on all or most of the filter components fabricated simultaneously on a common piezoelectric layer and substrate.

[0148] At 1065, 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., scanning ion mill as described above). "Global" tuning is performed with a spatial resolution equal to or greater than that of a single filter device. The purpose of global tuning is to move the passband of each filter device to a desired frequency range. The test results from 1060 can be processed to generate a global contour map, which 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.

[0149] At 1070, as a supplement or alternative to the global frequency tuning performed at 1065, local frequency tuning can also be performed. "Local" frequency tuning is performed with a spatial resolution less than that of a single filter device. The test results from 1060 can be processed to generate a graph indicating the amount of material to be removed at each filter device. Local frequency tuning may require the use of a mask to limit the size of the area where the material is removed. For example, a first mask can be used to limit tuning to only parallel resonators, then a second mask can be used to limit tuning to only series resonators, and then a third mask can be used to limit tuning to only extraction pole resonators. This will allow the lower band edge and upper band edge of the filter device to be independently tuned.

[0150] After frequency tuning at 1065 and / or 1070, the filter device is completed at 1075. Actions that may occur at 1075 include: forming bonding pads, metal traces, and / or solder bumps or other means for establishing connections between the device and external circuits (if such pads were not formed at 1030); cutting individual filter devices from a wafer containing multiple filter devices; other packaging steps; and additional testing. After each filter device is completed, the process ends at 1095.

[0151] Referring back to the exemplary aspects described above, it is noted that the excitation of fast and slow shear thickness modes should be mitigated to prevent large acoustic activity at frequencies near the filter passband.

[0152] Fig.11Ais a graph of the electric field as a function of rotation relative to the Z-cut according to an exemplary aspect. The graph shown was simulated using a finite element method (FEM) simulation technique. As shown, based on the e34 fast shear response, a range of rotational cut angles (Y82 to Y130) can be achieved for the piezoelectric layer to use the MPM capacitor structure described herein, where the associated piezoelectric tensor is small (i.e., close to 0 for minimum excitation) and the slow and fast shear modes are not effectively excited by the vertical electric field. In other words, unlike a standard IDC capacitor structure, the electric field remains fairly constant for a large range of rotational cuts of the piezoelectric plate (including Y120, Y128, Y82, and Z-cut).

[0153] also, Fig. 11B yes Figure 7B The graph shown is a graph of the frequency-dependent admittance of the MPM capacitor structure shown. The graph shown is simulated using a finite element method (FEM) simulation technique, which shows the above Figure 7B The described MPM capacitor has good capacitive behavior in the lower frequency range (e.g., n79 passband). In addition, although the 82Y cut shows that the fast shear mode is weakly excited, its corresponding resonant frequency f is far below the filter passband (i.e., n79 passband), so this effect does not affect the filter's admittance in the passband.

[0154] Fig. 12A and Fig. 12B are graphs of admittance as a function of frequency comparing an exemplary aspect of an MPM capacitor structure to a conventional IDC capacitor. These graphs were simulated using a finite element method (FEM) simulation technique. The simulation parameters for the MPM capacitor structure are: the piezoelectric plates have a height of 350 nm, the aluminum fingers have a mark (e.g., width) of 3.78 μm, the top electrode has a thickness of 100 nm, and W is 30 μm. In addition, the simulation parameters for a conventional IDC structure (for comparison) are: the piezoelectric plates have a height of 350 nm, a pitch of 1.5 μm, an electrode mark (e.g., width) of 0.6 μm, the top electrode has a thickness of 100 nm, and W is 45 μm. As Fig. 12A As shown, the exemplary aspect of the MPM capacitor provides a more ideal capacitive behavior across the filter passband, which means that there is limited acoustic activity at these frequencies. In addition, Fig. 12B The MPM capacitor of the exemplary embodiment shows similar admittance at the passband to a conventional IDC capacitor, but the MPM area is 113 μm 2 , which is 1309μm with IDC capacitor area 2 Thus, the exemplary configuration provides an additional technical advantage that the overall size of the resonator and filter can be reduced accordingly.

[0155] Based on the foregoing disclosure, an acoustic resonator is provided, the acoustic resonator comprising: a substrate; a piezoelectric layer supported by the substrate and having a first major surface and a second major surface opposite to each other; and an interdigital transducer (IDT) disposed on a surface of the piezoelectric layer and comprising interlaced fingers. In addition, the acoustic resonator comprises a capacitor electrically coupled to the IDT in parallel and comprising at least one first electrode on a first major surface of the piezoelectric layer and a metal layer on a second major surface of the piezoelectric layer, such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer. Advantageously, the MPM capacitor provides a much higher capacitance density (which can reduce the coupling coefficient) while also providing a significant size reduction compared to conventional IDC or MIM structures.

[0156] In general, it should be noted that throughout this specification, the illustrated embodiments and examples should be considered as examples, rather than limitations on the disclosed or claimed devices and processes. Although many of the examples presented herein relate to specific combinations of method actions or system elements, it should be understood that these actions and these elements can be combined in other ways to achieve the same goals. With respect to the flow charts, additional steps and fewer steps can be taken, and the steps shown can be combined or further refined to achieve the methods described herein. The actions, elements, and features discussed only in conjunction with one embodiment are not intended to exclude similar effects in other embodiments.

[0157] As used herein, the paired terms "top" and "bottom" can be interchanged with the paired "front" and "back". 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 a written specification or in a claim, the terms "comprise", "include", "carry", "have", "contain", "involve", etc. should be understood as open, i.e., meaning including but not limited to. With respect to the claims, only the transition phrases "consisting of..." and "consisting essentially of..." are closed or semi-closed transition phrases, respectively. The use of sequential terms such as "first", "second", "third" and the like in the claims to modify the claim elements themselves does not imply any priority, priority or order of one claim element relative to another claim element or the time sequence of the actions of the execution method, but is only used as a label to distinguish a claim element with a specific name from another element with the same name (but using sequential terms) to distinguish the claim elements. As used herein, "and / or" means that the listed items are alternatives, but the alternatives also include any combination of the listed items.

Claims

1. An acoustic resonator, comprising: substrate; a piezoelectric layer coupled to the substrate via one or more dielectric layers and having a first surface and a second surface opposite to each other; an interdigital transducer (IDT) on at least one of the first and second surfaces of the piezoelectric layer and comprising interlaced fingers; as well as A capacitor is electrically coupled in parallel to the IDT and includes at least one first electrode on a first surface of the piezoelectric layer and a metal layer on a second surface of the piezoelectric layer such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer.

2. The acoustic resonator according to claim 1, wherein The at least one first electrode is an anode of the capacitor and the metal layer is a cathode of the capacitor.

3. The acoustic resonator according to claim 1, wherein: The at least one first electrode includes a pair of electrodes including an anode and a cathode of the capacitor.

4. The acoustic resonator according to claim 3, wherein: The metal layer is a floating metal.

5. The acoustic resonator according to claim 1, wherein A portion of the piezoelectric layer forms a diaphragm over a cavity extending at least partially within the one or more dielectric layers.

6. The acoustic resonator according to claim 5, wherein: The IDT is disposed on a second surface of the piezoelectric layer facing the cavity.

7. The acoustic resonator according to claim 6, wherein: The IDT is configured such that a radio frequency signal applied to the IDT excites bulk shear acoustic waves in the diaphragm, wherein acoustic energy propagates in a direction substantially orthogonal to a surface of the piezoelectric layer, the direction being transverse to a direction of an electric field generated by interlaced fingers of the IDT.

8. The acoustic resonator of claim 1, further comprising a Bragg mirror disposed between the piezoelectric layer and the substrate.

9. The acoustic resonator according to claim 1, wherein: The IDT includes: A first busbar and a second busbar each extending in a first direction from a first end to a second end thereof, a first plurality of electrode fingers extending from the first busbar toward the second busbar in a second direction, wherein the second direction intersects the first direction, and A second plurality of electrode fingers extend from the second bus bar toward the first bus bar in the second direction such that the first plurality of electrode fingers and the second plurality of electrode fingers form interleaved fingers of the IDT.

10. The acoustic resonator according to claim 9, wherein: The at least one first electrode comprises: an anode of the capacitor coupled to the first bus bar and extending in parallel with the first plurality of electrode fingers; and A cathode of the capacitor is coupled to the second bus bar and extends in parallel with the second plurality of electrode fingers.

11. The acoustic resonator according to claim 1, wherein: The piezoelectric layer includes a pair of through holes extending along a side surface of the at least one first electrode of the capacitor in a thickness direction of the piezoelectric layer.

12. The acoustic resonator according to claim 1, wherein The piezoelectric layer comprises: a first piezoelectric layer comprising a first cut material having a first crystal orientation; and A second piezoelectric layer is attached to the first piezoelectric layer and includes a second cleaved material having a second crystal orientation such that a polarity of a piezoelectric tensor of the second piezoelectric layer is opposite to a polarity of a piezoelectric tensor of the first piezoelectric layer.

13. A filter device, comprising: A plurality of BAW resonators, wherein at least one BAW resonator of the plurality of BAW resonators comprises: substrate; a piezoelectric layer coupled to the substrate via one or more dielectric layers and having a first surface and a second surface opposite to each other; an interdigital transducer (IDT) on at least one of the first and second surfaces of the piezoelectric layer and comprising interlaced fingers; and A capacitor is electrically coupled in parallel to the IDT and includes at least one first electrode on a first surface of the piezoelectric layer and a metal layer on a second surface of the piezoelectric layer such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer.

14. The filter device according to claim 13, wherein: The at least one first electrode is an anode of the capacitor and the metal layer is a cathode of the capacitor.

15. The filter device according to claim 13, wherein: The at least one first electrode includes a pair of electrodes including an anode and a cathode of the capacitor, and the metal layer is a floating metal.

16. The filter device according to claim 13, wherein: A portion of the piezoelectric layer forms a diaphragm, the diaphragm being above a cavity, the cavity extending at least partially in the one or more dielectric layers, and the IDT being disposed on a second surface of the piezoelectric layer facing the cavity.

17. The filter device according to claim 16, wherein: The IDT of at least one BAW resonator is configured such that a radio frequency signal applied to the IDT excites bulk shear acoustic waves in the diaphragm, wherein acoustic energy propagates in a direction substantially orthogonal to a surface of the piezoelectric layer, the direction being transverse to a direction of an electric field generated by the interlaced fingers of the IDT.

18. The filter device according to claim 13, wherein: The IDT of the at least one BAW resonator comprises: A first busbar and a second busbar each extending in a first direction from a first end to a second end thereof, a first plurality of electrode fingers extending from the first busbar toward the second busbar in a second direction, wherein the second direction intersects the first direction, and A second plurality of electrode fingers extend from the second bus bar toward the first bus bar in the second direction such that the first plurality of electrode fingers and the second plurality of electrode fingers form interleaved fingers of the IDT.

19. The filter device according to claim 18, wherein: The at least one first electrode comprises: an anode of the capacitor coupled to the first bus bar and extending in parallel with the first plurality of electrode fingers; and A cathode of the capacitor is coupled to the second bus bar and extends in parallel with the second plurality of electrode fingers.

20. A radio frequency module, comprising: A filter device comprising a plurality of bulk acoustic wave resonators connected in parallel; as well as A radio frequency circuit is coupled to the filter device, the filter device and the radio frequency circuit are enclosed in a common package, wherein at least one of the plurality of bulk acoustic wave resonators of the filter device comprises: substrate; a piezoelectric layer coupled to the substrate via one or more dielectric layers and having a first surface and a second surface opposite to each other; an interdigital transducer (IDT) on at least one of the first and second surfaces of the piezoelectric layer and comprising interlaced fingers; and A capacitor is electrically coupled in parallel to the IDT and includes at least one first electrode on a first surface of the piezoelectric layer and a metal layer on a second surface of the piezoelectric layer such that the piezoelectric layer is sandwiched between the at least one first electrode and the metal layer.

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