Metal layer between electrode and piezoelectric layer for controlling coupling

Abstract

There is provided an acoustic resonator device including: a piezoelectric layer; an interdigital transducer on a surface of the piezoelectric layer and including interleaved IDT fingers extending from the first bus bar and the second bus bar, respectively; and a metal layer disposed between the fingers interleaved with the IDT fingers and the piezoelectric layer in a thickness direction measured in a direction perpendicular to a surface of the piezoelectric layer. In this aspect, a ratio of a width of the metal layer to a pitch of the interleaved IDT fingers is greater than or equal to 0.45, the width of the metal layer being measured in a width direction parallel to a surface of the piezoelectric layer. In addition, the thickness of the metal layer in the thickness direction is less than one third of the thickness of the fingers in the thickness direction.

Description

[0001] CROSS-REFERENCE TO RELATED APPLICATIONS

[0002] This application claims priority to U.S. Patent Application No. 18 / 775,010, filed on July 17, 2024, which claims priority to U.S. Provisional Patent Application No. 63 / 529,220, filed on July 27, 2023, the entire contents of each of which are incorporated herein by reference. Technical Field

[0003] The present disclosure relates to a radio frequency filter using an acoustic wave resonator, and in particular, to an acoustic wave resonator and a filter used for a communication device and having a metal layer between an electrode and a piezoelectric layer for controlling coupling. 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 to transmit with relatively low signal loss, and "block" means to block or significantly attenuate. 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 depend on the specific application. For example, 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. 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, 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 and in combination at multiple levels of the wireless system (e.g., at the RF module, RF transceiver, mobile or fixed subsystem, or network level). As the demand for RF filters operating at higher frequencies continues to increase, there is a need for improved filters that can operate at different frequency bands, as well as a need for improved manufacturing processes for making such filters.

[0007] A laterally excited film bulk acoustic resonator (XBAR) is an acoustic resonator structure used in microwave filters. An XBAR resonator includes an interdigital transducer (IDT) formed on a thin floating layer or diaphragm of a single crystal piezoelectric material. The IDT includes a first set of parallel fingers extending from a first busbar and a second set of parallel fingers extending from a second busbar. The first set of parallel fingers and the second set of parallel fingers are interlaced. A microwave signal applied to the IDT excites a primary shear acoustic wave in the piezoelectric film. XBAR resonators provide very high electromechanical coupling and high frequency capabilities. XBAR resonators can be used in a variety of RF filters including band-stop filters, bandpass filters, duplexers, and multiplexers. XBARs are well suited for filters targeting communication bands with frequencies above 3 GHz.

[0008] However, in order to provide the type of advanced performance required for the above-mentioned communications applications, resonator coupling is an important parameter that requires tuning within a narrow range for optimal filter design. Resonator coupling is a measure of the separation between the resonant frequency and the anti-resonant frequency of a resonator.

[0009] If the coupling of the resonators in the filter is less than the value required by the design parameters of the filter, the desired bandwidth of the filter cannot be achieved. On the other hand, if the coupling of the resonators is greater than the value required by the design parameters of the filter, the selectivity of the filter will be reduced.

[0010] Various resonator parameters affect coupling, including crystal cut, dielectric thickness above and below the piezoelectric layer, pitch of the IDT fingers, and marks of the IDT fingers. However, since modulation of these parameters also affects other important resonator characteristics, such as resonant frequency and spurious position and amplitude, these parameters cannot be used to independently tune resonator coupling without affecting other resonator characteristics. Summary of the invention

[0011] In view of the foregoing, a resonator structure that allows independent tuning of resonator coupling while minimizing changes to the characteristics of other resonators would improve the performance of XBAR devices and, by extension, the performance of filters that include such devices.

[0012] Thus, in an exemplary aspect, an acoustic resonator device is provided, comprising: a piezoelectric layer; an interdigital transducer (IDT), on a surface of the piezoelectric layer, the IDT comprising staggered IDT fingers extending from a first busbar and a second busbar, respectively; and a metal layer disposed between the fingers of the staggered IDT fingers and the piezoelectric layer in a thickness direction, the thickness direction being measured in a direction perpendicular to the surface of the piezoelectric layer. According to an exemplary aspect, a ratio of a width of the metal layer to a pitch of the staggered IDT fingers is greater than or equal to 0.45, the width of the metal layer being measured in a width direction parallel to the surface of the piezoelectric layer. In addition, a thickness of the metal layer in the thickness direction is less than one-third of a thickness of the fingers in the thickness direction.

[0013] In another exemplary aspect, the acoustic resonator device further includes: a substrate; and a dielectric layer having a cavity disposed therein. In this aspect, the piezoelectric layer is on the dielectric layer and includes a portion forming a diaphragm over the cavity in the dielectric layer.

[0014] In another exemplary aspect of the acoustic resonator device, the width of the metal layer is greater than the width of each of the staggered IDT fingers measured in the width direction, and the fingers are centrally positioned relative to the metal layer in the width direction so that the metal layer extends beyond opposite sides of the fingers in the width direction.

[0015] In another exemplary aspect of the acoustic resonator device, the thickness of the metal layer in the thickness direction is less than 20 nanometers.

[0016] In another exemplary aspect of the acoustic resonator device, a thickness of the metal layer in the thickness direction is less than 10% of a thickness of the piezoelectric layer in the thickness direction.

[0017] In another exemplary aspect of the acoustic resonator device, the metal layer includes a first metal layer and a second metal layer, the first metal layer is positioned closer to the piezoelectric layer than the second metal layer in the thickness direction and has a higher conductivity than the second metal layer, and the second metal layer contacts the fingers of the interleaved IDT fingers, and the second metal layer has a higher degree of adhesion to the fingers of the interleaved IDT fingers than the first metal layer. In addition, the first metal layer can be titanium, and the second metal layer can be aluminum.

[0018] In another exemplary aspect of the acoustic resonator device, a ratio of the width of the metal layer to the pitch of the staggered IDT fingers is less than 1.0. In addition, a ratio of the width of the metal layer to the pitch of the staggered IDT fingers can be greater than or equal to 0.45 and less than 1.0, wherein the ratio corresponds to a desired coupling between the resonant frequency and the anti-resonant frequency of the acoustic resonator device.

[0019] In another exemplary aspect of the acoustic resonator device, the piezoelectric layer is a lithium niobate plate having Euler angles of [0, 30, 0].

[0020] In another exemplary aspect of the acoustic resonator device, the IDT is configured such that a radio frequency signal applied to the IDT excites bulk shear acoustic waves in the piezoelectric layer, wherein the acoustic energy propagates in a direction substantially orthogonal to a surface of the piezoelectric layer and transverse to a direction of an electric field generated by the interlaced IDT fingers.

[0021] In yet another exemplary aspect, a filter device is provided that includes a plurality of BAW resonators, wherein at least one of the plurality of BAW resonators includes: a piezoelectric layer; an interdigital transducer (IDT), on a surface of the piezoelectric layer, the IDT including staggered IDT fingers extending from a first busbar and a second busbar, respectively; and a metal layer disposed between the fingers of the staggered IDT fingers and the piezoelectric layer in a thickness direction, the thickness direction being measured in a direction perpendicular to the surface of the piezoelectric layer. In this aspect, a ratio of a width of the metal layer to a pitch of the staggered IDT fingers is greater than or equal to 0.45, the width of the metal layer being measured in a width direction parallel to the surface of the piezoelectric layer. In addition, a thickness of the metal layer in the thickness direction is less than one-third of a thickness of the fingers in the thickness direction.

[0022] In yet another exemplary aspect, there is provided a radio frequency module including a filter device, the filter device including a plurality of bulk acoustic resonators connected in parallel, and a radio frequency circuit coupled to the filter device, the filter device and the radio frequency circuit being enclosed in a common package. In this aspect, at least one bulk acoustic resonator of the filter device includes: a piezoelectric layer; an interdigital transducer (IDT), on the surface of the piezoelectric layer, the IDT includes staggered IDT fingers extending from a first busbar and a second busbar, respectively; and a metal layer, disposed between the fingers of the staggered IDT fingers and the piezoelectric layer in a thickness direction, the thickness direction being measured in a direction perpendicular to the surface of the piezoelectric layer. In addition, the ratio of the width of the metal layer to the pitch of the staggered IDT fingers is greater than or equal to 0.45, and the width of the metal layer is measured in a width direction parallel to the surface of the piezoelectric layer. In addition, the thickness of the metal layer in the thickness direction is less than one-third of the thickness of the fingers in the thickness direction.

[0023] 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

[0024] 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.

[0025] Figure 1A Schematic plan view and schematic cross-sectional view of a film bulk acoustic resonator (XBAR) including lateral excitation.

[0026] Figure 1B Schematic cross-sectional views showing alternative configurations of XBARs.

[0027] Figure 2A yes Figure 1A An enlarged schematic cross-sectional view of a portion of an XBAR.

[0028] Figure 2B yes Figure 1A An enlarged schematic cross-sectional view of an alternative configuration of an XBAR.

[0029] Figure 2C yes Figure 1A An enlarged schematic cross-sectional view of another alternative configuration of an XBAR.

[0030] Figure 2D yes Figure 1A An enlarged schematic cross-sectional view of another alternative configuration of an XBAR.

[0031] Figure 2E is an enlarged schematic cross-sectional view of a portion of a solidly-mounted XBAR (SM XBAR).

[0032] Figure 3A is a schematic cross-sectional view of an XBAR according to an exemplary aspect.

[0033] Figure 3B is an alternative schematic cross-sectional view of an XBAR according to an exemplary aspect.

[0034] Figure 4 is a graph showing the shear horizontal acoustic modes in the XBAR.

[0035] Figure 5A is used Figure 1A and / or Figure 1B Schematic block diagram of the XBAR filter.

[0036] Figure 5B is a schematic diagram of a radio frequency module including an acoustic wave filter device according to an exemplary aspect.

[0037] Figure 6 is a schematic cross-sectional view of two XBARs showing the frequency setting dielectric layer.

[0038] Figure 7 is a cross-sectional view of an XBAR having a metal pedestal layer between each IDT finger and the piezoelectric layer.

[0039] Figure 8 is a graph showing the effect of different values ​​of the ratio between the width of the metal pedestal layer and the pitch of the IDT fingers on the coupling.

[0040] Fig. 9 is a graph showing the shift of the anti-resonance frequency and the resulting frequency band between the resonant frequency and the anti-resonance frequency as the ratio between the width of the metal pedestal layer and the pitch of the IDT fingers increases.

[0041] Fig.10 is a flow chart of a method for manufacturing an XBAR or a filter using an XBAR.

[0042] 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

[0043] 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, well-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.

[0044] 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 a variety of RF filters including band-stop filters, band-pass filters, duplexers, and multiplexers. XBARs are particularly suitable for filters in the communication bands with frequencies above 3 GHz.

[0045] In general, the XBAR 100 includes a conductor pattern (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 when a component, parameter, etc. is dominant in view of other comparable features or even compared to the absence of the same features, or is substantially the same (i.e., "substantially constant"), but as will be understood by those skilled in the art, may vary slightly in practice (e.g., within an acceptable threshold or percentage) due to possible manufacturing differences. For purposes of this disclosure, use of the term "or" in the claims is intended to mean "and / or" unless explicitly indicated to refer to only alternatives or if the alternatives are mutually exclusive.

[0046] 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.

[0047] 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 the Euler angles [0°, 30°, 0°] is often referred to as a "120° rotated Y-cut" or "120Y". Therefore, the Euler angles of 120YX and 128YX are (0, 120 to 90, 0) and (0, 128 to 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 wave propagates along the Y axis. The Euler angles of ZY cut are (0, 0, 90).

[0048] In addition to the portion of the piezoelectric layer 110 that forms a diaphragm 115 located above the cavity 140 (e.g., spanning the cavity 140 or extending above the cavity 140) in one or more layers below the piezoelectric layer 110 (e.g., one or more intermediate layers above or in the substrate), the back side 114 of the piezoelectric layer 110 can be at least partially supported by the surface of the substrate 120. 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). Furthermore, 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) can be referred to herein as a "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.

[0049] 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. The 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 or attached to the substrate in some other manner.

[0050] 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 sections AA and BB), or a groove in substrate 120 (as shown in the following sections). Figure 3A and Figure 3B For example, the cavity 140 may be formed by selectively etching the substrate 120 before or after the piezoelectric layer 110 and the substrate 120 are directly or indirectly attached.

[0051] 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, which may be "substantially" parallel to each other due to minor variations (such as due to manufacturing tolerances, for example). 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.

[0052] exist Figure 1A to Figure 1B , Figure 3A and Figure 3B In the example of FIG. 1 , the IDT 130 is on the front surface 112 (e.g., the first surface) of the piezoelectric layer 110. However, as described below, in other configurations, the IDT 130 may be at the surface (e.g., the second surface) of the back side 114 of the piezoelectric layer 110, or at both the surfaces of the front side 112 and the back side 114 of the piezoelectric layer 110, respectively.

[0053] 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, a radio frequency signal or a microwave signal applied between the two busbars 132, 134 of the IDT 130 primarily excites an acoustic mode (i.e., a primary shear acoustic mode and / or a primary shear acoustic wave) within the piezoelectric layer 110. As will be discussed in further detail, the primary 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, predominantly, and / or primarily orthogonal to the surface of the piezoelectric layer 110, which direction is also primarily perpendicular or transverse to the direction of the electric field generated by the IDT fingers. That is, when a radio frequency or microwave signal is applied between the two 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.

[0054] 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 "primary" in "primary excited acoustic mode" does not necessarily refer to low-order or high-order modes. Therefore, the XBAR is considered to be a laterally excited thin film bulk wave resonator. One physical constraint is that when a radio frequency or microwave signal is applied between the two busbars 132, 134 of the IDT 130, heat is generated, which must be dissipated from the resonator to improve performance. In general, the heat can be dissipated by lateral conduction across the membrane (e.g., in the electrode itself) and vertical conduction through the cavity to the substrate.

[0055] 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 side surfaces, which can be straight or curved.

[0056] 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 can be determined based on the product of the measured value of length L multiplied by the width of the aperture AP of the interleaved fingers of IDT 130. As used herein in the present disclosure, for example, 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.

[0057] In order to facilitate Figure 1A As presented in the sectional views, the geometric spacing 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 views is greatly exaggerated.

[0058] Figure 1B A schematic cross-sectional view of an alternative XBAR configuration 100' is shown. Figure 1BIn the resonator 100', the cavity 140 (which may generally correspond to Figure 1A The cavity 140 is completely formed 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 as 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 formed on top of each other to provide a stack of materials.

[0059] 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.

[0060] Figure 2A Shows Figure 1A or Figure 1B Detailed 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 can be, for example, 100 nanometers (nm) to 1500 nm. When used for filters for 5G NR and Wi-FiTM bands from 3.4 GHZ to 7 GHz, the thickness ts can be, for example, 150 nm to 500 nm. In an exemplary aspect, the thickness ts can be measured in a direction substantially perpendicular or orthogonal to the surface of the piezoelectric layer.

[0061] 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 .

[0062] A backside dielectric layer 214 (e.g., a second dielectric coating or material) may also be formed on the back side of the back side 114 of the piezoelectric layer 110. Generally, for the purposes of this disclosure, the term "backside" refers to the side opposite to the conductor pattern of the IDT structure and / or the side 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, according to various 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.

[0063] The IDT fingers 238a, 238b may include aluminum, substantially (i.e., primarily) aluminum alloys, copper, substantially (i.e., primarily) copper alloys, beryllium, gold, or some other conductive material. A thin (relative to the total thickness of the conductor) layer of other metals such as chromium or titanium may be formed under and / or over the fingers to improve adhesion between the fingers and the piezoelectric layer 110 and / or to passivate or encapsulate the fingers. The busbars ( Figure 1A 132, 134 in the claims) can be made of the same or different materials as these fingers. In various exemplary aspects, the cross-sectional shape of the IDT fingers can be trapezoidal (finger 238a), rectangular (finger 238b), or some other shape. In general, 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 elements when used in the claims. In addition, unless the context dictates otherwise, "a" or "an" when used in conjunction with the term "comprising" in a claim or specification means one or more than one.

[0064] As described below, a thin metal pedestal layer may be formed between the IDT fingers and the piezoelectric layer to accommodate coupling.

[0065] The dimension p (ie, “pitch”) can be considered to be 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 2AAs shown, the center point of the center-to-center spacing can be measured at the center of the width "w" of the finger. In some cases, the center-to-center spacing can change if the width of a given finger changes along the length of the finger, if the width and extension direction change, or any variation thereof. In this case, for a given position along the AP, the center-to-center spacing can be measured as an average center-to-center spacing, a maximum center-to-center spacing, a minimum center-to-center spacing, or any variation thereof. Adjacent fingers can each extend from a different busbar, and the center-to-center spacing can be measured from the center of a first finger extending from a first busbar to the center of a second finger adjacent to the first finger and extending from a second busbar. The center-to-center spacing can be constant over the length of the IDT, in which case the dimension p can be referred to as the pitch of the IDT and / or the pitch of the XBAR. However, in alternative exemplary aspects, the center-to-center spacing varies along the length of the IDT, in which case the pitch of the IDT can be the average value of the dimension p over the length of the IDT. The center-to-center spacing from one finger to an adjacent finger when compared to other adjacent fingers may vary continuously in discrete portions of a plurality of adjacent pairs or any combination thereof. FIG. 2A to FIG. 2D The 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 .

[0066] 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 4The main shear acoustic mode (also called the main shear mode, main shear thickness mode, etc.) described in more detail, in which the SAW resonator excites surface waves in 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 these fingers. In addition, the pitch p of the IDT is typically 2 to 20 times the thickness ts of the piezoelectric layer 110. In addition, the width of the IDT fingers in the XBAR is not limited to one-quarter 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.

[0067] Furthermore, unlike a SAW filter, 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., on 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.

[0068] 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.

[0069] 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 (marked as detail C') may be provided. For example, Figure 2BAn alternative configuration is shown in which the IDT fingers 238a, 238b are at the back side 114 of the piezoelectric layer 110 (i.e., facing the cavity) and are covered by the back side dielectric layer 214. The front side dielectric layer 212 can cover the front side 112 of the piezoelectric layer 110. In an exemplary aspect, the dielectric layer disposed on the diaphragm of each resonator can be trimmed or etched to adjust the resonant frequency. However, if the dielectric layer is on the side of the diaphragm facing the cavity, there will be changes in the stray modes (e.g., caused by the coating on the fingers). In addition, the signature will change with the passivation layer coated on top of the IDT, which can 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.

[0070] Figure 2C An 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.

[0071] Figure 2D Another alternative configuration is shown (marked 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.

[0072] 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.

[0073] 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 1AThe SMXBAR includes a piezoelectric layer 110 and an IDT (of which only two fingers 236 are visible), wherein a dielectric layer 212 is disposed on the piezoelectric layer 110 and the IDT fingers 236. Similar to the above configuration, the piezoelectric layer 110 has parallel front and back surfaces. 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.

[0074] and Figure 1A The XBAR device shown is opposite, Figure 2E The 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.

[0075] 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 polyphenyl 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 2EIn 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.

[0076] The IDT fingers (e.g., IDT fingers 236, 238a, and 238b) can be disposed on the surface of the front side 112 of the piezoelectric layer 110. Alternatively, the IDT fingers (e.g., IDT fingers 236, 238a, and 238b) can be disposed in a groove formed in the surface of the front side 112. The groove can extend partially through the piezoelectric layer. Alternatively, the groove can extend completely through the piezoelectric layer.

[0077] Figure 3A and Figure 3B Shown along Figure 1A An alternative exemplary cross-sectional view of the section AA defined in FIG. Figure 3A As shown, 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.

[0078] Figure 3BAn 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, a 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). For example, the cavity 340 can be formed 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 .

[0079] 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 3B As 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.

[0080] 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.

[0081] Figure 4 is a graphical illustration of the principal excited acoustic modes of interest in the XBAR. Figure 4 A small portion of XBAR 400 is shown, including piezoelectric layer 410 and three interleaved IDT fingers 430. In general, according to exemplary aspects, the exemplary configuration of XBAR 400 may correspond to that described above and in FIG. 2A to FIG. 2D as well as FIG. 3A to FIG. 3B Thus, it should be understood that piezoelectric layer 410 may correspond to piezoelectric layer 110 and / or 130 and IDT finger 430 may be implemented according to any configuration of fingers 238a and 238b and / or 338, for example.

[0082] In operation, an RF voltage is applied to the interlaced fingers 430. This voltage produces a time-varying electric field between these fingers. The direction of the electric field is transverse (i.e., transversely excited) or primarily parallel to the surface of the piezoelectric layer 410, as indicated by the arrow labeled "Electric Field." Due to the high dielectric constant of the piezoelectric layer 410, the electric field is highly concentrated in the piezoelectric layer relative to air. The transverse electric field induces shear deformation in the piezoelectric layer 410, thereby strongly exciting shear acoustic modes in the piezoelectric layer 410. In this context, "shear deformation" is defined as a deformation in which parallel planes in a material remain parallel and maintain a constant distance while translating relative to each other. In other words, parallel planes of the material are displaced laterally relative to each other. "Shear acoustic modes" are defined as acoustic vibration modes in a medium that cause shear deformation of the medium. The shear deformation in the XBAR 400 is represented by curve 460, where the adjacent small arrows provide a schematic indication of the direction and amplitude of the atomic motion. Note that for ease of illustration in Figure 4 In the visualization in FIG. 4 , the extent of atomic motion and the thickness of the piezoelectric layer 410 have been exaggerated. Although the atomic motion is primarily lateral (i.e., Figure 4 ), but the direction of the acoustic energy flow of the primarily excited shear acoustic mode is substantially and / or primarily normal to the surface of the piezoelectric layer, as indicated by arrow 465.

[0083] 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, where the atomic motion and the direction of acoustic energy flow are 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.

[0084] Figure 5Ais 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 described above (e.g., bulk acoustic resonators). 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.

[0085] 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 "respective" means "relating things to one another," that is, having a one-to-one correspondence. Figure 5A In the example, 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 can be disposed above a single cavity.

[0086] Each of the resonators 510A, 510B, 510C, 510D, 520A, 520B, and 520C in the filter 500 has a resonance in which the admittance of the resonator (also interchangeably referred to as the Y parameter) is very high and an anti-resonance in which 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.

[0087] 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.

[0088] According to an exemplary aspect, at least one and / or 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 as well as FIG. 3A to FIG. 3B The XBAR configuration described above, wherein the diaphragm with IDT fingers spans over the cavity. Alternatively, at least one and / or 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 Figure 2E An XBAR configuration is described having a securely mounted XBAR configuration.

[0089] 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 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).

[0090] 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 5B The package substrate 546 (e.g., a common substrate) in the embodiment of the present invention is a package substrate 546. The package substrate 546 can be a laminate substrate. The terminals 545A and 545B can be electrically connected to the contact portions 547A and 547B on the package substrate 546 respectively through electrical connectors 548A and 548B. For example, the electrical connectors 548A and 548B can be bumps or wiring joints. In an exemplary aspect, by using or not using the package substrate 546, the acoustic wave filter 544 and the RF circuit 543 can be packaged together in a common package.

[0091] 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, for example, to provide protection and / or to 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.

[0092] Figure 6 6 is a schematic cross-sectional view through a parallel resonator and a series resonator of a filter 600 that uses a dielectric frequency setting layer to separate the resonant frequencies of the parallel resonator and the series resonator. As shown, a piezoelectric layer 610 is attached to a substrate 620. A portion of the piezoelectric layer 610 forms a diaphragm above a cavity 640 in the substrate 620. In an exemplary aspect, Figure 6 6 shows a single piezoelectric layer 610 spanning across a plurality of cavities 640. In another exemplary aspect, a plurality of separate piezoelectric layers may span respective cavities 640. The piezoelectric layer 610 may correspond to the piezoelectric layer 110 described above, for example.

[0093] In either case, staggered IDT fingers (e.g., fingers 630) are formed on the diaphragm. Staggered IDT fingers 630 may correspond to, for example, fingers 136, 238a, 238b, and are shown on the surface of the piezoelectric plate 610 opposite the cavity 640, while in an alternative aspect, the staggered IDT fingers 630 may be disposed on the surface of the piezoelectric plate 610 facing the cavity 640.

[0094] In either case, a first dielectric layer 650 having a thickness t1 is formed over the IDT of the parallel resonator. The first dielectric layer 650 can be considered a "frequency setting dielectric layer," which is a layer of dielectric material applied to the first subset of resonators in the filter to shift the resonant frequency of the first subset of resonators relative to the resonant frequency of the resonators that do not receive the frequency setting dielectric layer. The frequency setting dielectric layer is typically silicon dioxide (i.e., SiO 2 ), but can be silicon oxide, silicon nitride, aluminum oxide, aluminum nitride, beryllium oxide, tantalum oxide, tungsten oxide, or some other dielectric material. The frequency setting dielectric layer can be a laminate or composite of two or more dielectric materials.

[0095] A second dielectric layer 655 having a thickness t2 may be deposited over both the parallel resonator and the series resonator. The second dielectric layer 655 is used to seal and passivate the surface of the filter 600. The second dielectric layer may be the same material as the first dielectric layer or a different material. The second dielectric layer may be a laminate or composite of two or more different dielectric materials. In addition, as will be described later, the thickness of the second dielectric layer may be locally adjusted to fine tune the frequency of the filter 600. Therefore, the second dielectric layer may be referred to as a "passivation and tuning layer".

[0096] The resonant frequency of the XBAR is roughly proportional to the inverse of the total thickness of the diaphragm including the piezoelectric layer 610 and the dielectric layers 650, 655. That is, a thinner XBAR will have a higher resonant frequency than a thicker XBAR with the same configuration. The diaphragm (or overall stack) of the parallel resonator is thicker than the diaphragm (or overall stack) of the series resonator by the thickness t1 of the dielectric frequency setting layer 650. Therefore, the parallel resonator will have a lower resonant frequency than the series resonator. The difference in resonant frequency between the series resonator and the parallel resonator is determined by the thickness t1.

[0097] In addition to adjusting for a desired resonant frequency, the coupling of each resonator in the filter can also be adjusted to achieve a specified performance of the filter. As described above, the resonant characteristics can be adjusted by selecting appropriate thicknesses of the first dielectric layer and the second dielectric layer. Other parameters (e.g., crystal cut, pitch of the IDT fingers, and marking of the IDT fingers) can also be used to affect both resonant frequency and coupling.

[0098] However, since the above-mentioned resonator parameters affect both resonant frequency and coupling, as well as spurious location and amplitude, it is difficult to independently tune the coupling of the resonators because other properties of the resonators are typically also changed at the same time. In some related systems and resonator configurations, capacitors connected in parallel with each resonator can be used to independently adjust or reduce coupling. Such capacitors can be interleaved capacitors or metal-insulator-metal (MIM) capacitors, both of which may take up additional space on the die. Therefore, there is a need for structural variables that can be used to independently tune the resonator coupling without consuming additional space on the die.

[0099] To achieve this independent tuning, Figure 7An exemplary aspect of forming a thin metal layer (also referred to herein as a "pedestal layer") between the IDT fingers and the piezoelectric layer is shown. In an exemplary aspect, the thickness of the thin metal pedestal layer is, for example, ten percent (i.e., 10%) or less (e.g., 20 nm or less) of the thickness of the piezoelectric layer 710. By further adjusting the ratio of the width of the pedestal metal layer to the pitch of the IDT fingers, the coupling of the resonator can be changed (e.g., reduced) while minimizing changes in other resonator properties (including the acoustic properties of the resonator). Further still, the thickness of the pedestal metal layer in the thickness direction is preferably less than one-third of the thickness of the IDT fingers in the thickness direction so that the coupling of the resonator can also be independently controlled without affecting the acoustic properties of the resonator.

[0100] According to an exemplary aspect, Figure 7 A piezoelectric layer 710 and IDT fingers 736 and 738 supported on the piezoelectric layer 710 are shown. In an exemplary aspect, the piezoelectric layer 710 can be, for example, a lithium niobate plate with Euler angles of [0, 30, 0]. Between the piezoelectric layer 710 and each of the IDT fingers 736, 738, there is a corresponding thin metal pedestal layer (e.g., a metal layer). That is, a corresponding pedestal metal layer 770 is between the IDT finger 736 and the piezoelectric layer 710, and a corresponding pedestal metal layer 780 is between the IDT finger 738 and the piezoelectric layer 710. Although Figure 7 The exemplary aspect of shows two pedestal layers, but there may be at least one pedestal layer between the piezoelectric layer 710 and the IDT finger. In an exemplary aspect, the pedestal layer 770 is centrally symmetric relative to its corresponding IDT finger 736, such that the IDT finger 736 is centrally located in the width direction relative to the pedestal layer 770. In other words, the portion of the pedestal layer 770 that extends beyond the opposite sides of the IDT finger 736 in the width direction (i.e., parallel to the surface of the piezoelectric layer 710) is equal in length on both sides (i.e., the opposite sides to the left and right of the IDT finger 736). Similarly, the IDT finger 738 is centrally located in the width direction relative to its corresponding pedestal layer 780. Other IDT fingers (not shown) supported by the piezoelectric layer 710 may similarly have a corresponding pedestal layer located between each IDT finger and the piezoelectric layer 710.

[0101] Although Figure 7The exemplary aspects of show that the IDT fingers 736 and 738 are centered relative to their corresponding pedestal layers 770 and 780 (e.g., symmetrically aligned in the vertical direction), but other aspects can include asymmetrical arrangements of the IDT fingers and pedestal layers. For example, one or more IDT fingers can be positioned closer to one outer edge of their corresponding pedestal layer (e.g., offset in the horizontal direction) and farther away from another outer edge of their corresponding pedestal layer. In such aspects, the outer edges of the IDT fingers are located within the outer edges of their corresponding pedestal layers in a plan view. For example, the offset in the vertical alignment between the IDT fingers and the pedestal layer can be a design choice, or caused by misalignment due to manufacturing differences.

[0102] It should be understood that the piezoelectric layer 710 may generally correspond to the piezoelectric layers 110, 310, 410, and / or 610 described above. Similarly, the IDT fingers 736 and 738 may correspond to Figure 1A IDT finger 136, FIG. 2A to FIG. 2E IDT fingers 238a and 238b, and / or Figure 4 IDT finger 430. However, according to Figure 7 In an exemplary aspect of the present invention, an additional base-like layer (eg, at least one metal layer) may be disposed between one or more piezoelectric layers and each corresponding IDT finger. In addition, Figure 7 A close-up view of only the diaphragm and IDT fingers is shown, and it should be understood that this configuration can be implemented with the IDT fingers facing (e.g., Figure 2B ) or deviate from (e.g. Figure 2A ) corresponding cavity. Alternatively, Figure 7 This configuration can be, for example, Figure 5B As shown and implemented in the SM XBAR described above. That is, in reference Figure 5B In the Bragg mirror arrangement of the described SMXBAR configuration, one or more pedestal layers may be disposed between the one or more piezoelectric layers and the corresponding IDT fingers.

[0103] Furthermore, in an exemplary aspect, the IDT fingers 736, 738 are formed of aluminum and the pedestal layers 770, 780 are formed of titanium. In other exemplary aspects, different conductive materials can be used to form the IDT fingers 736, 738 and the pedestal layers 770, 780. The IDT fingers 736, 738 and the pedestal layers 770, 780 can be formed of the same material or of different materials. For example, in one aspect, each IDT finger and its corresponding pedestal layer can be a single continuous material formed, for example, by photoresist and etching.

[0104] In an exemplary aspect, each pedestal layer 770, 780 can be formed of multiple layers of the same or different metals. For example, each pedestal layer can be formed of an upper layer and a lower layer, the upper layer being closer to the corresponding IDT finger and having high adhesion to the IDT finger, and the lower layer being closer to the piezoelectric layer and having higher conductivity than the upper layer. That is, the upper layer can have higher adhesion to the corresponding IDT finger than the lower layer, and the lower layer can have higher conductivity than the upper layer. In an exemplary aspect, where the IDT fingers are formed of aluminum, the upper layer of each pedestal layer can also be formed of aluminum to achieve higher conductivity to the IDT fingers, and the lower layer can be formed of titanium to achieve higher adhesion (e.g., coupling / attachment to the piezoelectric layer). Note again that although in the exemplary aspect, the lower layer is formed of a thin layer of titanium (relative to the total thickness of the conductor), other metals (e.g., chromium) can also be used with or in place of titanium to improve adhesion between the fingers and the piezoelectric layer.

[0105] exist Figure 7 , the center-to-center distance between IDT fingers 736 and 738 is shown as pitch p, and the width / mark of the IDT fingers is shown as m. a , and the height / thickness of the piezoelectric layer 710 is shown as h LN As described above, in an exemplary aspect, the thickness of the thin metal pedestal layers 770 and 780 may be, for example, the thickness h of the piezoelectric layer 710. LN 10% or less (eg, 20 nm or less) to minimize the impact on the acoustic properties of the resonator. In addition, the width / mark of the pedestal layers 770, 780 is shown as m p , the height / thickness of the electrode structure including the IDT fingers and the pedestal layer is shown as h m , and the height / thickness of the pedestal layer is h p .

[0106] like Figure 7 As shown, the thickness (or height) is measured in a direction perpendicular or normal to the surface of the piezoelectric layer 710 supporting the IDT fingers (i.e., the height or thickness direction). The width (or mark) and pitch of the IDT fingers are measured in a direction parallel to the surface of the piezoelectric layer 710 on which the IDT fingers are disposed (i.e., the width direction). In an exemplary aspect, the height / thickness h of the metal layer 770 (and / or 780) in the thickness direction is p Less than the thickness h of the finger 736 (and / or 738) in the thickness direction m In practice, the acoustic resonator utilizes one or more very thin metal layers (which are essentially configured as capacitors) to independently control the coupling of the resonators without affecting the acoustic properties of the resonators.

[0107] When the width of the pedestal layers 770, 780 is equal to the width of the IDT fingers 736, 738, m p Equal to m a , and the effect on coupling is small. In this case, the IDT fingers 736, 738 are only raised by the pedestal layer without any change in width. On the other hand, when the width of the pedestal layers 770, 780 is increased to the extent that the adjacent pedestal layers almost touch each other, m p The ratio to the pitch p approaches 1.0 and the coupling decreases to zero.

[0108] Width of the base layer m p In the above m a Certain values ​​between the lower limit of and the upper limit of p correspond to various coupling parameters of the resonator, such as Figure 8 shown. Figure 8 The simulated resonant frequency value (f r ), anti-resonance frequency value (f a ) and coupling value (k 2 ) is the ratio of the width to the pitch of the pedestal layer on the abscissa (x) axis (m p / p). Figure 8 The data for and all subsequent graphs are obtained from simulations of an exemplary XBAR device using finite element three-dimensional simulation techniques.

[0109] Generate by simulating a resonator formed on a 120Y piezoelectric layer with a thickness of 350nm Figure 8 The f r 、f a and k 2 The simulated resonator has a thickness h of 385 nm for the electrode structure (including IDT fingers and pedestal layer). m , a pitch of the IDT fingers of 3.4 μm, and a mark of the IDT fingers of 0.76 μm. The simulated resonator also has a front-side dielectric layer with a thickness of 66 nm.

[0110] f r and f a The value of Figure 8 The left-hand axis of the graph is defined as frequency (in MHz), while k 2 The values ​​of are defined on the right-hand axis of the graph. 2 =1-f r 2 / f a 2 , the coupling value k is calculated as a function of the resonance value and the antiresonance value 2 .

[0111] like Figure 8 As highlighted by the ellipse, when the ratio of the width to the pitch of the base layer (m p When the value of / p) increases between the values ​​of 0.45 and 1.0, the coupling value decreases. The decrease in coupling value is caused by the antiresonance frequency value f a The corresponding decrease of Figure 8 On the other hand, the ratio of the width to the pitch of the base layer (m p / p) value is in the range of 0.45 to 1.0, the resonance value f r Keep it basically constant.

[0112] Therefore, if Figure 8 As shown, the ratio of the width to the pitch of the base layer (m p / p) and the coupling value, assuming a predetermined pitch p of the IDT fingers, can be obtained by selecting an appropriate width m of the pedestal layer. p , the resonant coupling is tuned in a range of values ​​between 0.18 and 0.07. That is, as long as the ratio of the width to the pitch of the pedestal layer (m p / p) is greater than or equal to 0.45, the width of the pedestal layer can be adjusted to tune the resonant coupling to a desired (eg, predetermined) coupling of the acoustic resonator without affecting the resonant frequency.

[0113] Fig. 9 Additional graphs are shown which show the effect of adjusting the ratio of the width to the pitch of the pedestal layer (m p / p) occurs when the anti-resonance frequency shifts. Fig. 9 As shown in FIG. 1 , the resonant frequency at the position where the admittance peak appears is substantially constant at 3800 MHz in all curves. Fig. 9 For each curve, the ratio m of change p / p does not affect the resonant frequency.

[0114] On the other hand, in the case of different ratios m equal to or greater than 0.45 p On the / p curve, it can be seen that the anti-resonance frequency at the lower admittance is shifted downward from 4250MHz to about 3950MHz. Fig. 9 As can be seen from the figure, relative to the ratio m representing 0.45 p The solid curve of / p represents a ratio m of 0.22 (which is not higher than 0.45). p The dashed curve for / p has a moderate shift in resonant frequency, while the anti-resonant frequency does not change.

[0115] therefore, Fig. 9 The ratio m is shown pValues ​​of / p below 0.45 do not allow independent tuning of the coupling without affecting the resonant frequency. Fig. 9 It is shown that for the ratio m p / p is 0.22, the resonant frequency shifts, but for m p When the value of / p is equal to or greater than 0.45, the resonance frequency is kept constant.

[0116] Exemplary aspects of the present disclosure may combine adjustment of the width of the pedestal layer with other resonator parameters to optimize coupling characteristics across multiple modes. For example, coupling of the S2 and A3 modes may be minimized by selecting thickness values ​​for the front and back dielectric layers. However, the thickness values ​​selected for the dielectric layers may result in A1 mode coupling that is too high to meet the filter design parameters.

[0117] In this case, the width of the pedestal layer can be adjusted to reduce the A1 mode coupling to an acceptable range while maintaining the minimized coupling of the S2 and A3 modes achieved by the selected thickness values ​​of the front and back dielectric layers. In other scenarios, other resonator parameters such as crystal cut, IDT finger pitch, or IDT finger markings can be optimized for various resonator characteristics in a way that causes coupling to be out of the range of the filter design. In this case, the width of the pedestal layer can be used as an independent tuning parameter to adjust the coupling without affecting the resonant frequency. Fig.10 1 is a simplified flow chart summarizing a process 1000 for making a filter device including an XBAR. Specifically, the process 1000 is used to make a filter device including a plurality of XBARs, some of which include the pedestal-like layer described above. The process 1000 begins at 1005, where a device substrate and a thin layer of piezoelectric material are disposed on a sacrificial substrate. The process 1000 ends at 1095, where the filter device is completed. Fig.10 The flow chart only includes the main process steps. Fig.10 Various conventional processing steps (eg, surface preparation, cleaning, inspection, baking, annealing, monitoring, testing, etc.) are performed before, between, after, and during the steps shown.

[0118] Although Fig.10 The process for making a single filter device is generally described, but multiple filter devices can be made simultaneously on a common wafer (composed of a piezoelectric layer bonded to a substrate). In this case, each step of process 1000 can be performed simultaneously on all filter devices on the wafer.

[0119] Fig.10The flowchart of FIG. 1 captures three variations of process 1000 for fabricating 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. In another variation of process 1000, a securely mounted XBAR may be fabricated without forming any cavity in the device substrate. Figure 2E An example of a securely mounted XBAR is described.

[0120] 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, rotated Y-cut or rotated YX-cut. For historical reasons, the rotated Y-cut plate configuration is often 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 [0°, 30°, 0°] is often referred to as a "120° rotated Y-cut". In some embodiments, the z-axis of the piezoelectric layer can be perpendicular to the plate surface, and the y-axis can be orthogonal to the IDT fingers. Such a piezoelectric plate has Euler angles 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 -15° to +5°, 0°≤β≤60 or any combination thereof. The piezoelectric layer can be some other material and / or some other cut. The device substrate can preferably be silicon. The device substrate may be some other material that allows for the formation of deep cavities by etching or other processes.

[0121] In one variation of process 1000, before bonding the piezoelectric layer to the substrate at 1015, one or more cavities are formed in the device substrate at 1010A. A separate cavity can be formed for each resonator in the filter device. Conventional photolithography and etching techniques can be used to form the one or more cavities. Typically, the cavity formed at 1010A does not penetrate the device substrate. As described above, the cavity can be in the base (e.g., silicon) of the substrate. Alternatively, the cavity can be in an intermediate layer (e.g., silicon dioxide) of the substrate.

[0122] At 1015, the piezoelectric layer is bonded to the device substrate. The 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.

[0123] 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.

[0124] Thin layers of single crystal piezoelectric material laminated to non-piezoelectric substrates are commercially available. At the time of this application, both lithium niobate and lithium tantalate layers are available for bonding to a variety of substrates including silicon, quartz, and fused quartz. Thin layers of other piezoelectric materials are available now or in the future. The thickness of the piezoelectric layer can be between 300nm and 1000nm. When the substrate is silicon, SiO 2 The layer may be disposed between the piezoelectric layer and the substrate. When a commercially available piezoelectric layer / device substrate laminate is used, steps 1010A, 1015, and 1020 of process 1000 are not performed.

[0125] 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 and the pedestal metal layer of each XBAR. The conductor layer can be, for example, aluminum, aluminum alloy, copper, copper alloy, or some other conductive metal. 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 and / or act as the above-mentioned pedestal metal layer. A second conductor pattern of gold, aluminum, copper or other higher conductivity metals can be formed on a portion of the first conductor pattern (e.g., an IDT busbar and the interconnection between the IDTs).

[0126] At 1030, each conductor pattern can be formed by sequentially depositing a conductor layer and optionally one or more other metal layers on the surface of the piezoelectric layer. 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.

[0127] Alternatively, at 1030, each conductor pattern may be formed using a lift-off process. A photoresist may be deposited over the piezoelectric layer and patterned to define the conductor pattern. The conductor layer and optionally one or more other layers may be sequentially deposited over the surface of the piezoelectric layer. The photoresist may then be removed, which removes excess material, leaving the conductor pattern. In either case, the conductor pattern may be formed to include a grating element as described herein.

[0128] At 1050, one or more frequency setting dielectric layers may be formed by depositing one or more layers of dielectric material on the front side of the piezoelectric layer. For example, a dielectric layer may be formed on a parallel resonator to reduce the frequency of the parallel resonator relative to the frequency of the series resonator. The one or more dielectric layers may be deposited using conventional deposition techniques such as physical vapor deposition, atomic layer deposition, chemical vapor deposition, or some other method. One or more photolithography processes (using photomasks) may be used to limit the deposition of the dielectric layer to selected areas of the piezoelectric layer. For example, a mask may be used to limit the dielectric layer to only cover the parallel resonator.

[0129] At 1055, a passivation / tuning dielectric layer can be deposited over the piezoelectric layer and the conductor pattern. The passivation / tuning dielectric layer can cover the entire surface of the filter except for pads for electrical connection to circuits external to the filter. In some examples of process 1000, the passivation / tuning dielectric layer can be formed after etching a cavity in a base of the device substrate and / or an intermediate layer of the substrate at 1010B or 1010C.

[0130] In a second variation of process 1000, at 1010B, one or more cavities are formed in the back surface of the base of the device substrate and / or an intermediate layer of the substrate. A separate cavity may be formed for each resonator in the filter device. An anisotropic or orientation-dependent dry or wet etch may be used to open a hole through the back side of the device substrate to the piezoelectric layer to form the one or more cavities. In this case, the resulting resonator device will have a structure such as Figure 1B Cross section shown.

[0131] In a third variation of process 1000, at 1010C, one or more cavities in the form of recesses may be formed in the device substrate by etching the substrate using an etchant introduced through the openings in the piezoelectric layer. A separate cavity may be formed for each resonator in the filter device. The one or more cavities formed at 1010C will not penetrate the device substrate.

[0132] 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 such as the thickness of the dielectric layers formed at 1050 and 1055, variations in the thickness and line width of the conductors and IDT fingers formed at 1030, and variations in the thickness of the piezoelectric layer. These variations cause the filter device performance to deviate from the performance requirement set.

[0133] 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 over the resonator at 1055. The frequency of the filter device passband can be lowered 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 a desired frequency range, but can be tuned to a desired frequency range by removing material from the surface of the passivation / tuning layer.

[0134] 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 filter devices fabricated simultaneously on a common piezoelectric layer and substrate.

[0135] 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., a 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 shift the passband of each filter device toward a desired frequency range. The test results from 1060 can be processed to generate a global contour map that indicates the amount of material to be removed as a function of two-dimensional location on the wafer. The selective material removal tool is then used to remove material according to the contour map.

[0136] At 1070, local frequency tuning may be performed in addition to or in lieu of the global frequency tuning performed at 1065. "Local" frequency tuning is performed at a spatial resolution less than that of a single filter device. The test results from 1060 may 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 from which material is removed. For example, a first mask may be used to limit tuning to only parallel resonators, and then a second mask may be used to limit tuning to only series resonators (or vice versa). This will allow independent tuning of the lower band edge of the filter device (by tuning the parallel resonators) and the upper band edge (by tuning the series resonators).

[0137] After frequency tuning at 1065 and / or 1070, the filter devices are completed at 1075. Actions that may occur at 1075 include: forming bonding pads or solder bumps or other means for connecting between the device and external circuitry (if such pads were not formed at 1045); 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.

[0138] 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.

[0139] 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-ended, i.e., meaning including but not limited to. Only the transition phrases "consisting of..." and "consisting essentially of..." are closed or semi-closed transition phrases for the claims, respectively. The use of sequential terms such as "first", "second", "third", etc. 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 device, comprising: Piezoelectric layer; An interdigital transducer (IDT), on the surface of the piezoelectric layer, the IDT comprising staggered IDT fingers extending from a first busbar and a second busbar, respectively; as well as a metal layer disposed between the fingers of the interlaced IDT fingers and the piezoelectric layer in a thickness direction, the thickness direction being measured in a direction perpendicular to a surface of the piezoelectric layer, wherein a ratio of a width of the metal layer to a pitch of the staggered IDT fingers is greater than or equal to 0.45, the width of the metal layer being measured in a width direction parallel to a surface of the piezoelectric layer, and Wherein, the thickness of the metal layer in the thickness direction is less than one third of the thickness of the finger in the thickness direction.

2. The acoustic resonator device according to claim 1, further comprising: substrate; as well as a dielectric layer having a cavity disposed in the dielectric layer, The piezoelectric layer is on the dielectric layer and includes a portion forming a diaphragm, wherein the diaphragm is above the cavity in the dielectric layer.

3. The acoustic resonator device of claim 1, wherein: The metal layer has a width greater than a width of each of the staggered IDT fingers measured in the width direction, and The finger is centrally positioned relative to the metal layer in the width direction such that the metal layer extends beyond opposite sides of the finger in the width direction.

4. The acoustic resonator device according to claim 1, wherein The thickness of the metal layer in the thickness direction is less than 20 nanometers.

5. The acoustic resonator device according to claim 1, wherein The thickness of the metal layer in the thickness direction is less than 10% of the thickness of the piezoelectric layer in the thickness direction.

6. The acoustic resonator device of claim 1, wherein: The metal layer includes a first metal layer and a second metal layer, The first metal layer is positioned closer to the piezoelectric layer than the second metal layer in the thickness direction and has a higher electrical conductivity than the second metal layer, and The second metal layer contacts the fingers of the staggered IDT fingers and has a higher degree of adhesion to the fingers of the staggered IDT fingers than the first metal layer.

7. The acoustic resonator device according to claim 6, wherein: The first metal layer includes titanium, and the second metal layer includes aluminum.

8. The acoustic resonator device according to claim 1, wherein: A ratio of the width of the metal layer to the pitch of the staggered IDT fingers is less than 1.

0.

9. The acoustic resonator device according to claim 8, wherein: A ratio of the width of the metal layer to the pitch of the interleaved IDT fingers is greater than or equal to 0.45 and less than 1.0, the ratio corresponding to a desired coupling between a resonant frequency and an anti-resonant frequency of the acoustic resonator device.

10. The acoustic resonator device of claim 1, wherein: The piezoelectric layer is a lithium niobate plate with Euler angles of [0, 30, 0].

11. The acoustic resonator device according to claim 1, wherein: The IDT is configured such that a radio frequency signal applied to the IDT excites bulk shear acoustic waves in the piezoelectric layer, wherein acoustic energy propagates in a direction substantially orthogonal to a surface of the piezoelectric layer and transverse to a direction of an electric field generated by the interlaced IDT fingers.

12. A filter device, comprising: A plurality of BAW resonators, wherein at least one BAW resonator of the plurality of BAW resonators comprises: Piezoelectric layer; an interdigital transducer (IDT), wherein on the surface of the piezoelectric layer, the IDT comprises staggered IDT fingers extending from a first busbar and a second busbar, respectively; and a metal layer disposed between the fingers of the interleaved IDT fingers and the piezoelectric layer in a thickness direction, the thickness direction being measured in a direction perpendicular to the surface of the piezoelectric layer, wherein a ratio of a width of the metal layer to a pitch of the staggered IDT fingers is greater than or equal to 0.45, the width of the metal layer being measured in a width direction parallel to a surface of the piezoelectric layer, and Wherein, the thickness of the metal layer in the thickness direction is less than one third of the thickness of the finger in the thickness direction.

13. The filter device according to claim 12, wherein: The at least one BAW resonator further comprises: substrate; and a dielectric layer having a cavity disposed in the dielectric layer, The piezoelectric layer is on the dielectric layer and includes a portion forming a diaphragm, wherein the diaphragm is above the cavity in the dielectric layer.

14. The filter device according to claim 12, wherein: The metal layer has a width greater than a width of each of the staggered IDT fingers measured in the width direction, and The finger is centrally positioned relative to the metal layer in the width direction such that the metal layer extends beyond opposite sides of the finger in the width direction.

15. The filter device according to claim 12, wherein: The thickness of the metal layer in the thickness direction is less than 10% of the thickness of the piezoelectric layer in the thickness direction.

16. The filter device according to claim 12, wherein: The metal layer includes a first metal layer and a second metal layer, The first metal layer is positioned closer to the piezoelectric layer than the second metal layer in the thickness direction and has a higher electrical conductivity than the second metal layer, and The second metal layer contacts the fingers of the staggered IDT fingers and has a higher degree of adhesion to the fingers of the staggered IDT fingers than the first metal layer.

17. The filter device according to claim 12, wherein: A ratio of the width of the metal layer to the pitch of the staggered IDT fingers is less than 1.

0.

18. The filter device according to claim 17, wherein: A ratio of the width of the metal layer to the pitch of the interleaved IDT fingers is greater than or equal to 0.45 and less than 1.0, the ratio corresponding to a desired coupling between a resonant frequency and an antiresonant frequency of the at least one BAW resonator.

19. The filter device according to claim 12, wherein: The IDT is configured such that a radio frequency signal applied to the IDT excites bulk shear acoustic waves in the piezoelectric layer, wherein acoustic energy propagates in a direction substantially orthogonal to a surface of the piezoelectric layer and transverse to a direction of an electric field generated by the interlaced IDT fingers.

20. A radio frequency module, comprising: A filter device comprising a plurality of bulk acoustic resonators connected in parallel; as well as a radio frequency circuit coupled to the filter device, the filter device and the radio frequency circuit being enclosed in a common package, wherein at least one bulk acoustic resonator of the filter device comprises: Piezoelectric layer; an interdigital transducer (IDT), wherein on the surface of the piezoelectric layer, the IDT comprises staggered IDT fingers extending from a first busbar and a second busbar, respectively; and a metal layer disposed between the fingers of the interleaved IDT fingers and the piezoelectric layer in a thickness direction, the thickness direction being measured in a direction perpendicular to the surface of the piezoelectric layer, wherein a ratio of a width of the metal layer to a pitch of the staggered IDT fingers is greater than or equal to 0.45, the width of the metal layer being measured in a width direction parallel to a surface of the piezoelectric layer, and Wherein, the thickness of the metal layer in the thickness direction is less than one third of the thickness of the finger in the thickness direction.

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