Bragg stack structure for spurious mode suppression in solid state assembled acoustic resonators

Abstract

There is provided an acoustic resonator device, the acoustic resonator device including: a substrate; a piezoelectric layer at least partially supported by the substrate; an interdigital transducer (IDT) at the piezoelectric layer; and an acoustic Bragg reflector between the substrate and the piezoelectric layer. The acoustic Bragg reflector includes alternating layers of a first material and a second material having a higher acoustic impedance than the first material. The thicknesses of the first material and the second material of the acoustic Bragg reflector are configured to produce a reflection band centered on a shift frequency f0'shifted with respect to a resonant frequency fr of the acoustic resonator device based on harmonic spurs of the resonant frequency fr. In this aspect, the thicknesses of the first material and the second material are measured in a direction perpendicular to the substrate.

Description

CROSS-REFERENCE TO RELATED APPLICATIONS

[0001] This application claims priority to U.S. Provisional Patent Application No. 63 / 585,053 filed on September 25, 2023 and U.S. Patent Application No. 18 / 889,894 filed on September 19, 2024, the entire contents of which are incorporated herein by reference. Technical Field

[0002] The present disclosure relates to radio frequency filters using acoustic wave resonators, and in particular, to filters for communication devices. Background Art

[0003] 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 a passband or stopband may depend on the specific application. For example, in some cases, a "passband" may be defined as a frequency range where the insertion loss of the filter is better than a defined value such as 1dB, 2dB, or 3dB, while a "stopband" may 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.

[0004] 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.

[0005] 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.

[0006] 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 interleaved. 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 capability. XBAR resonators can be used in a variety of RF filters including band-stop filters, band-pass filters, duplexers, and multiplexers. XBARs are well suited for filters targeting communication bands with frequencies above 3 GHz.

[0007] One type of XBAR is a solid-state fabricated XBAR (SM XBAR), which uses a Bragg stack or Bragg mirror to support the piezoelectric layer instead of a piezoelectric film. The Bragg stack is located between the substrate and the piezoelectric layer and includes alternating high and low acoustic impedance layers that define the reflectivity of the Bragg stack at various frequencies. That is, each Bragg stack has a corresponding frequency response, including a broadband with good reflection and a stopband with poor reflection (i.e., high transmittance).

[0008] Reflection and transmission in the context of a Bragg stack refers to the reflection of energy moving down from the piezoelectric layer back toward the piezoelectric layer and the transmission of energy moving down from the piezoelectric layer toward the substrate. The frequency response of each Bragg stack is a result of the materials and thicknesses of the high and low acoustic impedance layers of the Bragg stack.

[0009] That is, the overall device performance of the SM XBAR is affected by the structure and frequency response of the Bragg stack, because these factors affect the energy reflected to and transmitted from the transducer structure of the SM XBAR. If the frequency response of the Bragg stack is optimized to maximize the energy / waves of the XBAR resonant modes reflected by the Bragg stack and also maximize the energy / waves of the spurious modes transmitted through the Bragg stack toward the substrate and away from the transducer structure of the XBAR, the performance can be improved. Summary of the invention

[0010] Therefore, SM XBAR performance will benefit from a Bragg stack structure optimized to maximize the energy / waves of the XBAR resonant modes reflected by the Bragg stack and to maximize the energy / waves of the spurious modes of the transducer structure transmitted through the Bragg stack towards the substrate and away from the XBAR.

[0011] Therefore, in an exemplary embodiment, a bulk acoustic resonator device is provided, the bulk acoustic resonator device including a substrate; a piezoelectric layer, at least partially supported by the substrate; an interdigital transducer (IDT) on a surface of the piezoelectric layer, the IDT including interlaced fingers extending from a first busbar and a second busbar, respectively; and an acoustic Bragg reflector between the substrate and the piezoelectric layer, the acoustic Bragg reflector including alternating layers of a first material and a second material, the second material having a higher acoustic impedance than the first material. The thicknesses of the first material and the second material of the acoustic Bragg reflector are configured to produce a reflection frequency band centered at a shift frequency f0', the shift frequency f0' being based on a resonant frequency f0 of the bulk acoustic resonator device. r The harmonic spurious relative to the resonant frequency f r Furthermore, the thickness of the first material and the second material is measured along a direction substantially perpendicular to the substrate.

[0012] In another exemplary aspect, the resonant frequency f r The harmonic spurs include 3f r The corresponding A3 harmonic spurious.

[0013] In another exemplary aspect, the shift frequency f0′ is higher than f r .

[0014] In another exemplary aspect, the shift frequency f0′ is lower than f r .

[0015] In another exemplary aspect, the thickness of the first material and the second material of the acoustic Bragg reflector are defined by the following formula: in, Corresponding to the generation of f r a thickness of one of the first material and the second material centered at the reflection band, corresponds to the thickness of one of the first material and the second material that produces a reflection band centered at the shift frequency f0', m corresponds to the order of harmonic spurious, and r represents the ratio of the acoustic impedance of the first material to the acoustic impedance of the second material.

[0016] In another exemplary aspect, the thickness of the first material and the second material of the acoustic Bragg reflector are defined by the following formula: In this regard, the harmonic spur is a third-order harmonic spur, and This is done by taking into account the non-infinite steepness of the reflection band of the acoustic Bragg reflector and the harmonic spurs relative to f r The error component in the case of frequency positioning.

[0017] In another exemplary aspect, m is equal to 3, such that the harmonic spur is a third order harmonic spur.

[0018] In another exemplary aspect of the bulk acoustic resonator device, the reflection band of the Bragg reflector covers the resonant frequency f of the bulk acoustic resonator device. r and the anti-resonance frequency f a .

[0019] In another exemplary aspect of the bulk acoustic resonator device, the reflection band of the acoustic Bragg reflector is greater than the resonant frequency f of the bulk acoustic resonator device. r and the anti-resonance frequency f a The frequency bandwidth between.

[0020] In another exemplary aspect of the bulk acoustic resonator device, the first material and the second material are dielectric materials.

[0021] In another exemplary aspect of the bulk acoustic resonator device, a thickness of each of the alternating layers of the acoustic Bragg reflector is in a range of 75% to 125% of a quarter of a wavelength of an acoustic wave corresponding to the shift frequency f0′, the wavelength of the acoustic wave propagating in a corresponding alternating layer of the alternating layers of the acoustic Bragg reflector.

[0022] Furthermore, in an exemplary aspect of the bulk acoustic resonator device, the piezoelectric layer is one of a lithium niobate plate and a lithium tantalate plate.

[0023] In another exemplary aspect, the bulk acoustic resonator device further includes at least one of: a front-side dielectric layer at a front side of the piezoelectric layer; or a back-side dielectric layer at a back side of the piezoelectric layer.

[0024] In another exemplary aspect of the bulk acoustic resonator device, the piezoelectric layer and the IDT are configured to excite a bulk shear wave having a propagation direction perpendicular to the direction of a primary lateral excitation electric field generated by the IDT, and when the atomic motion of the bulk shear wave is primarily horizontal in the piezoelectric layer, the electric field is primarily excited laterally, and the bulk shear wave propagates in a direction primarily perpendicular to the direction of atomic motion.

[0025] In another exemplary aspect, a filtering device comprising a plurality of bulk acoustic resonators is provided. In this aspect, at least one of the plurality of bulk acoustic resonators comprises a substrate; a piezoelectric layer at least partially supported by the substrate; an interdigital transducer (IDT) on a surface of the piezoelectric layer, the IDT comprising interlaced fingers extending from a first busbar and a second busbar, respectively; and an acoustic Bragg reflector between the substrate and the piezoelectric layer, the acoustic Bragg reflector comprising alternating layers of a first material and a second material, the second material having a higher acoustic impedance than the first material. In addition, the thicknesses of the first material and the second material of the acoustic Bragg reflector are configured to produce a reflection frequency band centered at a shift frequency f0', the shift frequency f0' being based on a resonant frequency f0 of the at least one of the plurality of bulk acoustic resonators.r The harmonic spurs are relative to the resonant frequency f r The thickness of the first material and the second material is measured along a direction substantially perpendicular to the substrate.

[0026] In yet another exemplary aspect, a radio frequency module is provided, the radio frequency module comprising: a filter device having a plurality of bulk acoustic wave resonators, one or more of the plurality of bulk acoustic wave resonators comprising an acoustic Bragg reflector between a substrate and a piezoelectric layer, on which an interdigital transducer (IDT) is configured to excite a bulk acoustic wave in the piezoelectric layer; and a radio frequency circuit coupled to the filter device, the filter device and the radio frequency circuit being packaged in a common package. In this aspect, the acoustic Bragg reflector comprises alternating layers of a first material and a second material, the second material having a higher acoustic impedance than the first material, and further, the thicknesses of the first material and the second material of the acoustic Bragg reflector are configured to produce a reflection frequency band centered at a shift frequency f0', the shift frequency f0' being based on a resonant frequency f0 of the one or more bulk acoustic wave resonators. r The harmonic spurs are relative to the resonant frequency f r The thickness of the first material and the second material is measured along a direction substantially perpendicular to the substrate.

[0027] The above simplified overview of the exemplary aspects is intended to provide a basic understanding of the present disclosure. This overview is not an extensive overview of all contemplated 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

[0028] 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.

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

[0030] Figure 1B Schematic cross-sectional views showing alternative configurations of XBARs.

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

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

[0033] Figure 2C yes Figure 1A An enlarged schematic cross-sectional view of another alternative configuration of an XBAR.

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

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

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

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

[0038] Figure 4 is a graph showing the shear horizontal acoustic modes in the XBAR.

[0039] Figure 5A is used Figure 1A and / or Figure 1B Schematic block diagram of the XBAR filter.

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

[0041] Figure 6 is a graph illustrating a filter passband response and an image response of a SMXBAR according to an exemplary aspect.

[0042] Figure 7 is an exemplary graph illustrating resonator admittance and Bragg reflectivity versus frequency values ​​according to an exemplary aspect.

[0043] 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

[0044] Various aspects of the disclosed bulk acoustic resonator, filter device, radio frequency module, and method of manufacturing the bulk acoustic resonator, filter device, and radio frequency module are now described with reference to the accompanying drawings, wherein the same reference numerals may be used to represent the same elements throughout. In the following description, for the purpose of illustration, many specific details are set forth to facilitate a thorough understanding of one or more aspects of the present disclosure. However, it is apparent in some or all instances that any aspect described below can be practiced without adopting the specific design details described below. In other instances, known structures and devices are shown in block diagram form to facilitate description of one or more aspects. A simplified overview of one or more aspects of the present invention is given below to provide a basic understanding of the present invention.

[0045] 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 communication bands with frequencies above 3 GHz.

[0046] In general, the XBAR 100 includes a conductor pattern (e.g., a thin film metal layer) formed at one or both surfaces of a piezoelectric layer 110 (piezoelectric plate or piezoelectric layer may be used interchangeably herein), respectively, and the piezoelectric layer 110 has a parallel front side 112 and a rear side 114 (also commonly referred to as a first surface and a second surface, respectively). It should be understood that the term "parallel" generally refers to the front side 112 and the rear side 114 being opposite to each other, and these surfaces are not necessarily flat and completely parallel to each other. For example, due to manufacturing differences caused by the deposition process, the front side 112 and the rear side 114 may have surface undulations as will be understood by those skilled in the art. In addition, the term "substantially" as used herein is used to describe the situation when components, parameters, etc. are generally the same (i.e., "substantially constant") but may be slightly different (e.g., within an acceptable threshold or percentage) in practice due to possible manufacturing differences as will be understood by those skilled in the art. For the purpose of this disclosure, the use of the term "or" in the claims is used to mean "and / or" unless it is explicitly indicated to refer only to alternatives or if the alternatives are mutually exclusive.

[0047] 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.

[0048] The Y-cut series (e.g., 120Y and 128Y) is often referred to as 120YX or 128YX, where the "cut angle" is the angle between the y-axis and the normal to the layer. The "cut angle" is equal to β+90°. For example, a layer with Euler angles [0°, 30°, 0°] is often referred to as a "120° rotated Y-cut" or "120Y". Therefore, the Euler angles for 120YX and 128YX are (0, 120 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 for ZY cut are (0, 0, 90).

[0049] 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.

[0050] 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.

[0051] For the purposes of this disclosure, "cavity" has the conventional meaning of "empty space within a solid body". Cavity 140 may be a hole that passes completely through substrate 120 (as shown in section AA), a hole in a dielectric layer (as shown in section AA), or a hole in a dielectric layer (as shown in section AA). Figure 1B 1) or a groove in the substrate 120. For example, the cavity 140 may be formed by selectively etching the substrate 120 before or after the piezoelectric layer 110 and the substrate 120 are attached directly or indirectly.

[0052] As shown, the conductor pattern of XBAR 100 includes an interdigital transducer (IDT) 130. IDT 130 includes a first plurality of parallel fingers (e.g., finger 136) extending from a first busbar 132 and a second plurality of fingers extending from a second busbar 134. The first plurality of parallel fingers and the second plurality of parallel fingers are staggered with each other, and they may be "substantially" parallel to each other, for example, due to minor variations (such as minor variations due to manufacturing tolerances). At least a portion of the staggered fingers overlap a distance AP, which is generally referred to as the "aperture" of the IDT. The center-to-center distance L between the outermost fingers of IDT 130 is the "length" of the IDT.

[0053] exist Figure 1A In the example of FIG. 1 , the IDT 130 is at a surface (e.g., a first surface) of the front side 112 of the piezoelectric layer 110. However, as described below, in other configurations, the IDT 130 may be at a surface (e.g., a second surface) of the back side 114 of the piezoelectric layer 110, or at both surfaces of the front side 112 and the back side 114 of the piezoelectric layer 110, respectively.

[0054] 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.

[0055] For the purposes of this disclosure, a "primary acoustic mode" may generally refer to an operating mode that causes a vibration displacement in the 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.

[0056] 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 (eg, 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.

[0057] 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.

[0058] In order to facilitate Figure 1A As presented in the cross-sectional view, 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, the XBAR may have hundreds or even thousands of parallel fingers in the IDT. Similarly, the thickness of the fingers in the cross-sectional view is greatly exaggerated.

[0059] Figure 1B A schematic cross-sectional view of an alternative XBAR configuration 100' is shown. Figure 1B In the resonator 100', the cavity 140 (which may generally correspond to Figure 1A The cavity 140 is 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 dielectric layer 124 may be formed of multiple separate dielectric layers formed on top of each other to provide a stack of materials.

[0060] 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.

[0061] Figure 2A Shows Figure 1A or Figure 1BDetailed schematic cross-sectional view of XBAR 100 (labeled as detail C). Piezoelectric layer 110 is a single crystalline layer of piezoelectric material having a thickness ts. ts can be, for example, 100 nanometers (nm) to 1500 nm. Thickness ts can be, for example, 150 nm to 500 nm when used for filters for 5G NR and Wi-Fi™ bands from 3.4 GHZ to 7 GHz. In an exemplary aspect, thickness ts can be measured in a direction substantially perpendicular or orthogonal to a surface of the piezoelectric layer.

[0062] 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 .

[0063] 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.

[0064] The IDT fingers 238a, 238b may include aluminum, substantially (i.e., primarily) aluminum alloys, copper, substantially (i.e., primarily) copper alloys, beryllium, gold, or some other conductive material. A thin (relative to the total thickness of the conductor) layer of other metals such as chromium or titanium may be formed under and / or over the fingers to improve adhesion between the fingers and the piezoelectric layer 110 and / or to passivate or encapsulate the fingers. The busbars ( Figure 1A 132, 134 in the claims) can be made of the same or different materials as these fingers. In various exemplary aspects, the cross-sectional shape of the IDT fingers can be trapezoidal (finger 238a), rectangular (finger 238b), or some other shape. In general, note that the terms "include," "have," "include," and "contain" (and variations thereof) as used herein are open conjunctions and allow for the addition of other elements when used in the claims. In addition, "a" or "an" when used in conjunction with the term "comprising" in a claim or specification means one or more than one unless the context dictates otherwise.

[0065] The dimension p (i.e., “pitch”) can be considered as the distance between adjacent IDT fingers (e.g., FIG. 2A to FIG. 2D The center-to-center spacing between the IDT fingers 238a, 238b. Figure 2A As shown, the center point of the center-to-center spacing can be measured at the center of the width "w" of the finger. In some cases, the center-to-center spacing can change if the width of a given finger changes along the length of the finger, if the width and extension direction change, or any variation thereof. In this case, for a given position along the AP, the center-to-center spacing can be measured as an average center-to-center spacing, a maximum center-to-center spacing, a minimum center-to-center spacing, or any variation thereof. Adjacent fingers can each extend from a different busbar, and the center-to-center spacing can be measured from the center of a first finger extending from a first busbar to the center of a second finger adjacent to the first finger and extending from a second busbar. The center-to-center spacing can be constant over the length of the IDT, in which case the dimension p can be referred to as the pitch of the IDT and / or the pitch of the XBAR. However, in alternative exemplary aspects, the center-to-center spacing varies along the length of the IDT, in which case the pitch of the IDT can be the average value of the dimension p over the length of the IDT. The center-to-center spacing from one finger to an adjacent finger when compared to other adjacent fingers may vary continuously in discrete portions of a plurality of adjacent pairs or in any combination thereof. Each IDT finger (e.g., FIG. 2A to FIG. 2DThe IDT fingers 238a, 238b in the IDT 130 have a width w measured perpendicular to the long direction of each finger. The width w may also be referred to as a "mark" herein. In general, the width of the IDT fingers can be constant over the length of the IDT, in which case the dimension w can be the width of each IDT finger. However, in another exemplary aspect as will be discussed below, the width of the individual IDT fingers varies along the length of the IDT 130, in which case the dimension w can be the average of the widths of the IDT fingers over the length of the IDT. Note that the pitch p and width w of the IDT fingers are measured in a direction substantially parallel to the length L of the IDT, as shown in FIG. Figure 1A As defined in .

[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 4 The principal shear acoustic mode (also called principal shear mode, principal shear thickness mode, etc.) described in more detail is where the SAW resonator excites surface waves during operation. In addition, in a SAW resonator, the pitch of the IDT is one-half the wavelength of the acoustic wave at the resonant frequency. In addition, the mark-to-pitch ratio of the SAW resonator IDT is typically close to 0.5 (i.e., the mark or finger width is approximately one-quarter the wavelength of the acoustic wave at resonance). In an XBAR, the pitch p of the IDT is typically 2 to 20 times the width w of 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 an 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 about 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 the IDT fingers 132, 134) may be equal to the thickness tm of the IDT fingers, less than the thickness tm of the IDT fingers, greater than the thickness tm of the IDT fingers, or any combination thereof. Note that the XBAR devices described herein are not limited to the size ranges described herein.

[0067] Furthermore, unlike SAW filters, the resonant frequency of an XBAR depends on the total thickness (i.e., in the vertical or thickness direction) of its diaphragm, including the piezoelectric layer 110 and the front dielectric layer 212 and the back dielectric layer 214 disposed thereon. In an exemplary aspect, the thickness of one or both dielectric layers (i.e., on the opposite surfaces of the piezoelectric layer) can be varied to change the resonant frequency of various XBARs in the filter. For example, a parallel resonator in a ladder filter circuit can include a thicker dielectric layer to reduce the resonant frequency of the parallel resonator relative to a series resonator having a thinner dielectric layer, thereby reducing the overall thickness.

[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 (labeled as detail C'), but alternative configurations may be provided. For example, Figure 2B An 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, as 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 2CAn alternative configuration is shown (labeled as detail C"), in which the IDT fingers 238a, 238b are on the front side 112 of the piezoelectric layer 110 and are covered by the front side dielectric layer 212. The 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 (labeled as detail C''') in which the IDT fingers 238a, 238b are on the front side 112 of the piezoelectric layer 110 and are covered by the front side dielectric layer 212. The surface of the front side dielectric layer is planarized. The front side dielectric layer may be planarized, for example, by polishing or some other method. A thin layer of dielectric material having a thickness tp may cover the IDT fingers 238a, 238b to seal and passivate the fingers. The dimension TP may be, for example, 10 nm to 50 nm.

[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 solid-state mounted XBAR (SM XBAR) is shown. Note that in addition to having a solid-state mounted configuration, Figure 2E Generally speaking, Figure 1A . In this aspect, the 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 rear surfaces. Dimension ts is the thickness of the piezoelectric layer 110. The width of the IDT fingers 236 is dimension w, the thickness of the IDT fingers is dimension tm, and the IDT pitch is dimension p.

[0074] and Figure 1A In contrast to the XBAR device shown, Figure 2EThe IDT of the SMXBAR in the embodiment of the present invention is not formed on the diaphragm that spans 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 a primary acoustic mode excited in a 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. More generally, the acoustic Bragg reflector 240 includes alternating layers of a first material and a second material, the second material having a higher acoustic impedance than the first material. The acoustic impedance of each of the first material and the second material is the product of the shear wave velocity and the density of the material. "High" and "low" are relative terms relative to each other. For each layer, the standard for comparison is the adjacent layer. The acoustic impedance of each "high" acoustic impedance layer is higher than the acoustic impedance of two adjacent low acoustic impedance layers. The acoustic impedance of each "low" acoustic impedance layer is lower than the acoustic impedance of two adjacent high acoustic impedance layers. As discussed above, the primary acoustic mode in the XBAR piezoelectric layer is a shear body wave. In an exemplary aspect, the thickness of each layer of the acoustic Bragg reflector 240 is equal to or approximately one-quarter of the wavelength in the layer of a sheared bulk wave having the same polarization as the principal acoustic mode at or near the resonant frequency of the SMXBAR. Dielectric materials with relatively low acoustic impedance include silicon dioxide, carbon-containing silicon oxides, and certain plastics such as cross-linked polyphenylene polymers. Materials with relatively high acoustic impedance include hafnium oxide, silicon nitride, aluminum nitride, silicon carbide. All high acoustic impedance layers of the acoustic Bragg reflector 240 need not be the same material, and all low acoustic impedance layers need not be the same material. In Figure 2E In the example of , the acoustic Bragg reflector 240 has a total of six layers, but the acoustic Bragg reflector may have more or less than six layers in alternative configurations.

[0076] As will be discussed in detail below, according to exemplary aspects, the thicknesses of the first and second materials (e.g., alternating low-Z and high-Z layers) of the acoustic Bragg reflector are configured to produce a reflection band centered around a shift frequency f0′. The shift frequency f0′ is based on the resonant frequency f0 of the acoustic resonator device. r The harmonic spurious relative to the resonant frequency f r The first material and the second material are displaced a certain distance. In addition, the thickness of the first material and the second material is usually measured in a direction perpendicular to the substrate. Advantageously, this configuration maximizes the energy / wave of the XBAR resonant mode reflected by the Bragg stack and maximizes the energy / wave of the stray mode of the transducer structure transmitted through the Bragg stack toward the substrate and away from the XBAR.

[0077] The IDT fingers (e.g., IDT fingers 236, 238a, and 238b) may be disposed on the surface of the front side 112 of the piezoelectric layer 110. Alternatively, the IDT fingers (e.g., IDT fingers 236, 238a, and 238b) may be disposed in a groove formed in the surface of the front side 112. The groove may extend partially through the piezoelectric layer. Alternatively, the groove may extend completely through the piezoelectric layer. In addition, the IDT fingers may be disposed on the back side 114 of the piezoelectric layer 110 and embedded in one or more top layers of the Bragg reflector 240 and / or embedded in one or more intermediate layers (e.g., dielectric layers) between the Bragg reflector 240 and the piezoelectric layer 110.

[0078] Figure 3A and Figure 3B The XBAR 100 is shown along Figure 1A Two exemplary cross-sectional views of the section AA defined in FIG. Figure 3A In the embodiment, the piezoelectric layer 310 corresponding to the piezoelectric layer 110 is directly attached to the substrate 320, which may correspond to Figure 1A In addition, a cavity 340 that does not completely penetrate the substrate 320 is formed in the substrate below the portion of the piezoelectric layer 310 that includes the IDT of the XBAR (ie, the diaphragm 315). In an exemplary aspect, the cavity 340 may correspond to Figure 1A and / or Figure 1B In an exemplary aspect, the cavity 340 can be formed, for example, by etching the substrate 320 before attaching the piezoelectric layer 310. Alternatively, the cavity 340 can be formed by etching the substrate 320 with a selective etchant that reaches the substrate through one or more openings provided in the piezoelectric layer 310.

[0079] 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 piezoelectric layer 310 .

[0080] 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.

[0081] 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.

[0082] 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 Thus, it should be understood that piezoelectric layer 410 may correspond to piezoelectric layer 110 and IDT fingers 430 may be implemented according to any configuration of fingers 238a and 238b, for example.

[0083] In operation, an RF voltage is applied to the interlaced fingers 430. This voltage generates 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, and therefore strongly excites shear acoustic modes in the piezoelectric layer 410. In this context, "shear deformation" is defined as a deformation in which parallel planes in a material remain parallel and maintain a constant distance while translating relative to each other. In other words, parallel planes of the material are laterally displaced relative to each other. "Shear acoustic modes" are defined as acoustic vibration modes in a medium that cause shear deformation of the medium. In this configuration, the piezoelectric layer and the IDT excite bulk shear waves that have a propagation direction perpendicular to the direction of the primary transverse excitation electric field generated by the IDT. When the atomic motion of the bulk shear wave is mainly horizontal in the piezoelectric layer, the electric field is mainly excited in the transverse direction, and the bulk shear wave propagates in a direction mainly perpendicular to the direction of atomic motion.

[0084] Thus, as further shown, the shear deformation in XBAR 400 is represented by curve 460, wherein the adjacent small arrows provide a schematic indication of the direction and magnitude of atomic motion. 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.

[0085] 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 solid-state 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 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.

[0086] Figure 5Ais a schematic circuit diagram and layout of a high frequency bandpass filter 500 using 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, 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.

[0087] 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 an acoustic reflector (such as the exemplary Bragg reflector structure described herein). That is, the alternating first material and second material of the Bragg reflectors of one or more bulk acoustic wave resonators of the acoustic wave filter 544 can be configured to produce a reflection frequency band centered on a shifted frequency f0′, which is shifted a certain distance relative to the center frequency f0 of the acoustic wave filter 544 based on the harmonic spurs of the acoustic wave filter 544.

[0088] Furthermore, 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 cavities are schematically shown as dashed rectangles (eg, rectangle 535). In this example, each IDT is disposed above a corresponding cavity. In other filters, the IDTs of two or more resonators may be disposed above a single cavity.

[0089] 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.

[0090] 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.

[0091] According to an exemplary aspect, each of the series resonators 510A, 510B, 510C, and 510D and the parallel resonators 520A, 520B, and 520C may have a configuration as described above with respect to Figures 1A to 2D The XBAR configuration described above, wherein the diaphragm with the IDT fingers spans over the cavity. Alternatively, each of the series resonators 510A, 510B, 510C, 510D and the parallel resonators 520A, 520B, and 520C can have an XBAR configuration, wherein the series resonators 510A, 510B, 510C, 510D and / or the parallel resonators 520A, 520B, and 520C can be securely mounted on or above a Bragg reflector (e.g., as Figure 2E As shown), the Bragg reflector can then be mounted on a substrate.

[0092] 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 A radio frequency module 540 is shown including one or more acoustic wave filters 544 according to an exemplary aspect. The illustrated radio frequency module 540 also includes a radio frequency (RF) circuit (eg, radio frequency circuit / 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).

[0093] 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 Figure 5BThe 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 through electrical connectors 548A and 548B, respectively. For example, the electrical connectors 548A and 548B can be bumps or wiring bonds. 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.

[0094] The RF circuit 543 may include any suitable RF circuit. For example, the RF circuit may include one or more RF amplifiers (e.g., one or more power amplifiers and / or one or more low noise amplifiers), one or more RF switches, one or more additional RF filters, one or more RF couplers, one or more delay lines, one or more phase shifters, or any suitable combination thereof. The RF circuit 543 may be electrically connected to one or more acoustic wave filters 544. The RF module 540 may include one or more packaging structures to, for example, provide protection and / or facilitate easier handling of the RF module 540. Such a packaging structure may include an overmolded structure formed above the packaging substrate 546. The overmolded structure may encapsulate some or all components of the RF module 540.

[0095] Figure 6 The frequency response of a filter implemented using one or more SMXBARs and the frequency response of a Bragg stack of SMXBARs according to an exemplary aspect are shown. In general, the frequency response of a Bragg stack need not be the same as the frequency response of a filter device using the Bragg stack. However, if the frequency response of the Bragg stack is narrower than the filter bandwidth, the performance of the filter will be affected. On the other hand, having a frequency response of a Bragg stack that is wider than the filter bandwidth allows flexibility in designing a Bragg stack to suppress spurious modes of a filter device without affecting filter performance.

[0096] As described above, there is a relationship between the thickness of the layers of the Bragg stack and the center frequency of the frequency response of the Bragg stack, such that the thickness of each layer of the acoustic Bragg stack is equal to or approximately one-quarter of the wavelength corresponding to the center frequency. Due to this relationship, the center frequency of the frequency response of the Bragg stack can be tuned by varying the thickness of the layers of the Bragg stack. Note (and also mentioned above) that the terms "about" or "approximately" as used herein take into account minor variations in dimensions (such as thickness) that may be due to differences in manufacturing variations, etc.

[0097] In an exemplary aspect, a generalized Bragg stack can be composed of alternating layers having acoustic impedances Z1 and Z2, respectively, and the thickness of the alternating layers can be set to be 1 / 400 using a standard quarter-wave configuration. , where c is the wave speed in each corresponding layer, and the reflection is centered at frequency f0. Thus, such an infinite Bragg mirror of alternating layers will have a reflectivity centered at f0, where the fractional bandwidth is given by (Equation 1) gives.

[0098] Fractional Bandwidth represents the ratio of the bandwidth of the Bragg stack to its center frequency. Figure 6 middle, corresponds to the bandwidth (or reflection band) M_BW of the Bragg stack, and the center frequency corresponds to the center frequency M_f0 of the Bragg stack reflection band. Although Equation 1 above represents the fractional bandwidth of an infinite Bragg mirror, a finite mirror or Bragg stack will have a slightly different reflectivity, depending on the design and fabrication precision.

[0099] Furthermore, an ideal / infinite Bragg stack will have a harmonic passband of odd harmonics denoted as , where m is an odd number. The harmonic passbands will have the same bandwidth , but due to the frequency Higher, and therefore has a lower fractional bandwidth As mentioned above, a finite or non-ideal Bragg stack may have a harmonic passband that is slightly different from the above-mentioned harmonic passband.

[0100] Figure 6 An example of a filter frequency response and a Bragg stack frequency response according to an exemplary aspect is shown. As described above, M_BW represents the bandwidth of the Bragg stack frequency response, and M_f0 (e.g., a vertical small dashed line) represents the center frequency of the Bragg stack frequency response. Similarly, F_BW represents the bandwidth of the overall filter frequency response, and F_f0 (e.g., a vertical large dashed line) represents the center frequency of the filter passband. According to an exemplary aspect, the shift frequency (e.g., frequency f0' as described herein) is higher than the resonant frequency f of the acoustic resonator in this example. r In an alternative aspect, the shift frequency (eg, frequency f0') can be lower than the resonant frequency f r .exist Figure 6 In the context of the overall filter frequency response shown, the shift frequency (e.g., frequency f0') can be shifted relative to the center frequency of the filter passband and can be above or below the center frequency of the filter passband (e.g., Figure 6 In addition, in an exemplary aspect, the reflection frequency band of the Bragg reflector can be configured to cover the resonant frequency f of the acoustic resonator device. r and the anti-resonance frequency f aIn this regard, the reflection frequency band of the Bragg reflector may be greater than the resonance frequency f of the acoustic resonator device. r and the anti-resonance frequency f a The frequency bandwidth between.

[0101] In accordance with Figure 6 In any such case of the exemplary aspects shown, the center frequencies of the filter and the Bragg stack are offset from each other and the bandwidth of the Bragg stack is wider than the bandwidth of the filter. According to aspects of the present disclosure, the filter response is maintained as long as the Bragg stack bandwidth completely encompasses the filter passband.

[0102] The condition that the Bragg stack bandwidth covers the filter passband can be expressed by the inequality By combining these conditions with Equation 1 described above for the fractional bandwidth of the Bragg mirror, the frequency response of the Bragg stack can be tuned according to the following bounds: (Equation 2)

[0103] In Equation 2, the variable and represents the upper and lower limits of the filter passband (e.g., the upper edge frequency and the lower edge frequency of the band), is the center frequency of the Bragg stack frequency response, and r is the ratio of the respective acoustic impedances Z1 and Z2 of the Bragg stack. According to aspects of the present disclosure, following the boundary conditions outlined by Equation 2 when designing the Bragg stack frequency response ensures that the main mode filter passband is maintained.

[0104] In terms of thickness, Equation 2 can be modified and expressed as Equation 3 as follows: c z / 4t z (Equation 3)

[0105] In this aspect of Equation 3, the center frequency of a quarter wavelength Bragg reflector is defined by Mf0=c / 4t, where c is the speed of sound, t is the thickness of the particular impedance layer, and Z can indicate a high-Z or low-Z material.

[0106] so far, Figure 6 The description of has indicated that the center frequency of the Bragg stack frequency response can be offset relative to the center frequency of the filter passband. In addition, the above equation 2 defines the limits within which the center frequency of the Bragg stack frequency response can be adjusted. Based on these constraints, according to exemplary aspects, the center frequency of the Bragg stack frequency response can be adjusted to suppress spurious modes of the XBAR device, such as A3 harmonic spurs.

[0107] The location of the A3 harmonic spur of the XBAR device can be determined by To approximate, is the resonant frequency of the main XBAR mode. That is, the A3 harmonic spur corresponds to approximately three times the XBAR resonant frequency (i.e., “3f r The center frequency of the Bragg frequency response can be changed from Move to a new (or shifted) center Bragg stack frequency To minimize the approximate frequency Spurious harmonic modes under .

[0108] For example, the new center Bragg stack frequency is chosen to minimize the spurious A3 harmonic mode can be defined such that (Equation 4). As described above, tuning the frequency response of the Bragg stack is achieved by changing the thickness of the alternating layers of the Bragg stack. Therefore, using Equation 4, the ratio of the new Bragg layer thickness to the original Bragg layer thickness can be expressed as (Equation 5).

[0109] In equation 5, and represents the original Bragg stack center frequency and layer thickness centered on the main resonant frequency of the XBAR. represents the new (or shifted) thickness of the corresponding Bragg layer that is shifted relative to the main resonant frequency of the XBAR to suppress the spurious A3 harmonic mode of the XBAR. Although the above equations 3 and 4 are for A3 harmonic spurs, the suppression of A3 spurs is used as an example. Other asymmetric spurious modes can be suppressed in the same way by moving the center frequency of the Bragg frequency response while complying with the constraints of equation 2.

[0110] Additionally, an error component can be introduced into Equation 5 to account for the non-infinite steepness of the Bragg mirror reflectivity roll-off and for assumptions made when calculating Equation 5 (such as and ), these are approximate values ​​in practice. That is, the error component can be used to compensate for the approximate harmonic spurs relative to f r The error in frequency positioning, etc. , Equation 5 is modified as follows: .

[0111] In some exemplary aspects, the error component Can be approximately equal to 0.005. In other exemplary aspects, It can be equal to the ratio of the new Bragg layer thickness to the original Bragg layer thickness The error component The exact value of can be determined by simulation (eg, finite element method (FEM) simulation).

[0112] Although Equations 3 and 4 are intended to minimize the A3 harmonic spur, their expressions can be generalized to suppress the mth harmonic. For example, the ratio of the new Bragg layer thickness to the original Bragg layer thickness can be expressed as (Equation 6), where m represents the order of the target harmonic. Thus, in an exemplary aspect, m can be equal to 3, since the harmonic spur can be a third-order harmonic spur (ie, an A3 harmonic spur in the observed A3 mode).

[0113] The above error components The consideration of also applies to Equation 6, so that the right-hand side of Equation 6 can be considered as an approximation without the error component. In addition, the approximation accuracy of the right-hand side of Equation 6 becomes lower as the frequency / order of the target harmonic increases. Accordingly, the error component The uncertainty will increase accordingly with the increase of m.

[0114] It should be understood that the The operator indicates that the thickness of the Bragg stack layer can be increased or decreased to minimize the impact of stray modes on the performance of the SMXBAR. In an exemplary aspect, the determination to increase or decrease the thickness of a given Bragg stack layer can be made based on design and / or manufacturing factors (such as actual material loss, manufacturing tolerances, etc.). In addition, depending on the frequency response of the resulting Bragg stack, the thickness of the Bragg stack layer can be increased or decreased by selecting operators to suppress multiple spurious modes simultaneously.

[0115] Figure 7 is an exemplary graph showing resonator admittance and Bragg reflectivity versus frequency values ​​according to an exemplary aspect. Figure 7 In FIG. 5 , the solid curve represents the resonator admittance, while the dashed curve represents the Bragg reflectivity. Figure 7 The diagram shown is simulated using the Finite Element Method (FEM) simulation technique. In addition, Figure 7 The dotted and dashed curves in FIG. 5 show the simulation results when the frequency response of the Bragg stack is centered at 5.5 GHz (i.e., approximately equal to the resonant frequency of the filter), while the solid and dashed curves show the simulation results when the center frequency of the frequency response of the Bragg stack is moved (or shifted) below the resonant frequency of the filter to 4.4 GHz.

[0116] like Figure 7As shown by the arrows in the figure, the resonator admittance in the solid curve is improved, indicating that moving the center frequency of the Bragg stack's frequency response suppresses the spurious modes at 7 GHz and 16 GHz. This is evidenced by the lower spurs at these frequencies in the solid curve (compared to the dashed curve, which shows the filter performance when the center frequency of the Bragg stack is approximately equal to the resonant frequency of the filter).

[0117] Typically, minimizing out-of-band spurious modes can be achieved by strategically shifting the center frequency of the Bragg stack using, for example, equations 4 or 5 above, such as Figure 7 2. The spurs at 7 GHz and 16 GHz in the filter are shown in Figure 2. Such out-of-band spurs will affect the out-of-band rejection metric of the filter. On the other hand, strategically moving the Bragg stack center frequency to minimize the out-of-band spurs will maintain the in-band filter performance as long as the conditions in Equation 2 are met.

[0118] By using Figure 7 Based on the example center frequencies (5.5 GHz and 4.4 GHz) of the Bragg stack simulated in FIG, the Bragg stack layer thickness of each of the low acoustic impedance layer and the high acoustic impedance layer of the Bragg stack can be determined. For example, for a center frequency of 5.5 GHz, the low acoustic impedance (low-Z) layer thickness can be 132 nm, while the high acoustic impedance (high-Z) layer thickness can be 105 nm. More generally, the thickness of the low acoustic impedance (low-Z) layer can be greater than the thickness of the high acoustic impedance (high-Z) layer.

[0119] As another example, for a center frequency of 4.4 GHz, the low Z layer thickness may be 165 nm and the high Z layer thickness may be 131 nm. Exemplary Bragg stack thickness values ​​are based on the ratio of the acoustic impedance values ​​of the low Z layer and the high Z layer, as shown in Equations 4 and 5 above.

[0120] In one example, the thickness of each of the alternating low-Z and high-Z layers of the Bragg stack is in a range corresponding to the shift frequency The corresponding one-quarter wavelength of the acoustic wave is in the range of 75% to 125%, where the acoustic wave wavelength is the wavelength propagating in the low-Z layer and the high-Z layer, respectively. This configuration is shown in Figure 6 The shift frequency in the figure is shifted, and the out-of-band spurious modes are minimized in the exemplary configuration of the SM XBAR described herein. In addition, due to the original thickness quarter frequency calculation , the materials used for the low-Z and high-Z layers affect the Bragg stack layer thickness.

[0121] 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 temporal order of the actions of the method of execution, 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. A bulk acoustic resonance device, comprising: substrate; a piezoelectric layer at least partially supported by the substrate; an interdigital transducer (IDT), on the surface of the piezoelectric layer, the IDT comprising interlaced fingers extending from a first busbar and a second busbar, respectively; as well as an acoustic Bragg reflector between the substrate and the piezoelectric layer, the acoustic Bragg reflector comprising alternating layers of a first material and a second material, the second material having a higher acoustic impedance than the first material, The thicknesses of the first material and the second material of the acoustic Bragg reflector are configured to produce a reflection frequency band centered at a shift frequency f0', wherein the shift frequency f0' is based on the resonant frequency f of the bulk acoustic resonator. r The harmonic spurs are relative to the resonant frequency f r shift occurs, and The thickness of the first material and the second material are measured along a direction substantially perpendicular to the substrate.

2. The bulk acoustic resonator device according to claim 1, wherein: The resonant frequency f r The harmonic spurs include 3f r The corresponding A3 harmonic spurious.

3. The bulk acoustic resonator device according to claim 1, wherein: The shift frequency f0' is higher than f r .

4. The bulk acoustic resonator device according to claim 1, wherein: The shift frequency f0' is lower than f r .

5. The bulk acoustic resonator device according to claim 1, wherein: The thickness of the first material and the second material of the acoustic Bragg reflector are defined by the following formula: in, Corresponding to the generation of f r a thickness of one of the first material and the second material centered at a reflection band, corresponds to the thickness of one of the first material and the second material that produces a reflection band centered on the shift frequency f0', m corresponds to the order of the harmonic spurious, and r represents the ratio of the acoustic impedance of the first material to the acoustic impedance of the second material.

6. The bulk acoustic resonator device according to claim 5, wherein: The thickness of the first material and the second material of the acoustic Bragg reflector are further defined by the following formula: ， wherein the harmonic spur is a third-order harmonic spur, and is taken into account the non-infinite steepness of the reflection band of the acoustic Bragg reflector and the harmonic spurs relative to f r The error component in the case of frequency positioning.

7. The bulk acoustic resonator device according to claim 5, wherein: m is equal to 3, so that the harmonic spur is a third-order harmonic spur.

8. The bulk acoustic resonator device according to claim 1, wherein: The reflection frequency band of the Bragg reflector covers the resonance frequency f of the bulk acoustic resonator. r and the anti-resonance frequency f a .

9. The bulk acoustic resonator device according to claim 8, wherein: The reflection frequency band of the acoustic Bragg reflector is larger than the resonance frequency f of the bulk acoustic resonator. r and the anti-resonance frequency f a The frequency bandwidth between.

10. The bulk acoustic resonator device according to claim 1, wherein: The first material and the second material are dielectric materials.

11. The bulk acoustic resonator device according to claim 1, wherein: The thickness of each of the alternating layers of the acoustic Bragg reflector is in the range of 75% to 125% of a quarter of a wavelength of an acoustic wave corresponding to the shift frequency f0', the wavelength of the acoustic wave propagating in a corresponding one of the alternating layers of the acoustic Bragg reflector.

12. The bulk acoustic resonator device according to claim 1, wherein: The piezoelectric layer is one of a lithium niobate plate and a lithium tantalate plate.

13. The bulk acoustic resonator device according to claim 1, further comprising at least one of the following: a front dielectric layer at the front side of the piezoelectric layer; or A backside dielectric layer is at the back side of the piezoelectric layer.

14. The bulk acoustic resonator device according to claim 1, wherein: The piezoelectric layer and the IDT are configured to excite a bulk shear wave having a propagation direction perpendicular to the direction of a main transverse excitation electric field generated by the IDT. When the atomic motion of the bulk shear wave is mainly horizontal in the piezoelectric layer, the electric field is mainly excited laterally, and the bulk shear wave propagates in a direction mainly perpendicular to the direction of atomic motion.

15. A filter device comprising: A plurality of bulk acoustic resonators, at least one of the plurality of bulk acoustic resonators comprising: substrate; a piezoelectric layer at least partially supported by the substrate; an interdigital transducer (IDT) comprising interlaced fingers extending from a first busbar and a second busbar, respectively, on a surface of the piezoelectric layer; and an acoustic Bragg reflector between the substrate and the piezoelectric layer, the acoustic Bragg reflector comprising alternating layers of the first material and the second material, the second material having a higher acoustic impedance than the first material, wherein the thicknesses of the first material and the second material of the acoustic Bragg reflector are configured to produce a reflection frequency band centered at a shift frequency f0′, wherein the shift frequency f0′ is based on a resonant frequency f0 of the at least one bulk acoustic resonator of the plurality of bulk acoustic resonators. r The harmonic spurs are relative to the resonant frequency f r shift occurs, and The thickness of the first material and the second material are measured along a direction substantially perpendicular to the substrate.

16. The filter device according to claim 15, wherein: The harmonic spurs of the filtering device include A3 harmonic spurs.

17. The filter device according to claim 15, wherein: The shift frequency f0' is higher than f0.

18. The filter device according to claim 15, wherein: The shift frequency f0' is lower than f0.

19. The filter device according to claim 15, wherein: The thickness of the first material and the second material of the acoustic Bragg reflector are defined by the following formula: in, Corresponding to the generation of f r a thickness of one of the first material and the second material centered at a reflection band, corresponds to the thickness of one of the first material and the second material that produces a reflection band centered on the shift frequency f0', m corresponds to the order of the harmonic spurious, and r represents the ratio of the acoustic impedance of the first material to the acoustic impedance of the second material.

20. A radio frequency module, comprising: A filter device having a plurality of BAW resonators, one or more of the plurality of BAW resonators comprising an acoustic Bragg reflector between a substrate and a piezoelectric layer, on which an interdigital transducer (IDT) is configured to excite BAW in the piezoelectric layer; as well as A radio frequency circuit is coupled to the filter device, the filter device and the radio frequency circuit are packaged in a common package, wherein the acoustic Bragg reflector comprises alternating layers of a first material and a second material, the second material having a higher acoustic impedance than the first material, The thicknesses of the first material and the second material of the acoustic Bragg reflector are configured to produce a reflection frequency band centered at a shift frequency f0′, wherein the shift frequency f0′ is based on the resonant frequency f0 of the one or more BAW resonators. r The harmonic spurs are relative to the resonant frequency f r shift occurs, and The thickness of the first material and the second material are measured along a direction substantially perpendicular to the substrate.

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