Loaded resonators for tuning the frequency response of acoustic wave resonators - Patents.com

Abstract

An acoustic wave filter device is disclosed. The device includes an acoustic wave filter element and first and second resonators coupled to the acoustic wave filter element. The acoustic wave filter element includes interdigital input and output electrodes located on an upper surface of a piezoelectric layer and a counter electrode in contact with a lower surface of the piezoelectric layer. Each of the first and second resonators includes a resonator electrode in contact with the upper surface of the piezoelectric layer and a resonator counter electrode in contact with the lower surface of the piezoelectric layer. The first resonator has a first valley in its resonator impedance at a first frequency. The second resonator includes a first mass load layer in contact with the second resonator electrode such that the second resonator has a second valley in its resonator impedance at a second frequency different from the first frequency.

Description

[Technical field]

[0001] This specification relates to thin film high frequency acoustic wave filters. [Background technology]

[0002] Radio frequency ("RF") components based on microacoustic and thin-film technologies, such as resonators and filters, are widely used in wireless applications such as mobile phones, wireless networks, satellite positioning, etc. Their advantages over lumped element, ceramic, and electromagnetic counterparts include their small size and ability to be mass-produced. [Prior art documents] [Patent documents]

[0003] [Patent Document 1] U.S. Patent No. 9,893,712 [Patent Document 2] International Patent Application No. PCT / FI00 / 00591 [Non-patent literature]

[0004] [Non-Patent Document 1] Fattinger et al., "Optimization of acoustic dispersion for high performance thin film BAW resonators", Proc. IEEE International Ultrasonics Symposium, 2005, pp.1175-1178 Summary of the Invention [Problem to be solved by the invention]

[0005] This specification describes techniques for bandpass shear bulk acoustic wave ("LBAW") filters. More specifically, the present disclosure provides techniques for suppressing sidebands in LBAW filters and improving the bandpass filter characteristics of LBAW filters. [Means for solving the problem]

[0006] LBAW can be used as a bandpass filter. The bandpass filter may include one or more unwanted (or parasitic) sidebands. Implementations of the present disclosure provide techniques for suppressing the unwanted sidebands by adding one or more acoustic resonators in parallel with the LBAW.

[0007] An LBAW filter is formed from a piezoelectric layer sandwiched between two pairs of electrodes. One electrode from each pair is located on the top surface of the piezoelectric layer and forms the input or output electrode of the LBAW. The input and output electrodes are separated by a gap. Each pair also has a counter electrode located on the bottom surface of the piezoelectric layer. By applying an AC voltage to the piezoelectric layer at the input resonator, a mechanical resonance is created in the piezoelectric layer below the input electrode. The thickness of the piezoelectric layer and the gap between the electrodes can be designed such that this mechanical resonance is coupled to the output resonator through the gap. The frequency range over which such coupling occurs determines the achievable bandwidth (or width of the passband) of the LBAW filter.

[0008] Optionally, each of the above and other embodiments may include one or more of the following features, alone or in combination.

[0009] In general, one innovative aspect of the subject matter described herein may be embodied in an acoustic wave filter device including an acoustic wave filter element, a first resonator, and a second resonator. The first resonator and the second resonator are coupled to the acoustic wave filter element. The acoustic wave filter element includes interdigital input and output electrodes located on an upper surface of the piezoelectric layer and a counter electrode in contact with a lower surface of the piezoelectric layer. The first resonator includes a first resonator electrode in contact with the upper surface of the piezoelectric layer. The first resonator also includes a first resonator counter electrode in contact with a lower surface of the piezoelectric layer. The first resonator has a first valley of a resonator impedance at a first frequency. The second resonator includes a second resonator electrode in contact with an upper surface of the piezoelectric layer and a second resonator counter electrode in contact with a lower surface of the piezoelectric layer. The second resonator also includes a first mass load layer in contact with the second resonator electrode such that the second resonator has a second valley in the resonator impedance at a second frequency different from the first frequency.

[0010] The first frequency and the second frequency can be within a sideband of a resonator impedance of the acoustic wave filter element. In some examples, the first frequency and the second frequency can differ by at least 3%.

[0011] The resonator electrode may be electrically coupled to an input electrode, and the second resonator electrode is electrically coupled to an output electrode.

[0012] The first resonator electrode may be electrically coupled to the input electrode or the output electrode, and the second resonator electrode is electrically coupled to the first resonator electrode. In some embodiments, the first resonator electrode has a first end facing the acoustic wave filter element, the first resonator electrode has a second end on a side of the first resonator electrode further away from the acoustic wave filter element, and a third end connects the first end and the second end. In some examples, the second resonator electrode is disposed adjacent to the second end of the first resonator electrode. In some examples, the second resonator electrode is disposed adjacent to the third end of the first resonator electrode. In some embodiments, the first resonator electrode and the second resonator electrode are electrically coupled by sharing a common end. In some embodiments, the first resonator electrode and the second resonator electrode are electrically coupled by a conductive line spanning a gap between the first resonator electrode and the second resonator electrode.

[0013] The acoustic wave filter device may include a third resonator coupled to the acoustic wave filter element, the third resonator may include a third resonator electrode in contact with a top surface of the piezoelectric layer, a third resonator counter electrode in contact with a bottom surface of the piezoelectric layer, a first mass load layer in contact with the third resonator electrode, and a second mass load layer in contact with the third resonator electrode, such that the third resonator has a third valley in a resonator impedance at a third frequency different from the first and second frequencies.

[0014] The second mass load layer may be disposed on the first mass load layer. The first mass load layer may include a silicon oxide layer. The second mass load layer may include a silicon nitride layer.

[0015] The acoustic wave filter device may include a fourth resonator coupled to the acoustic wave filter element. The fourth resonator may include a fourth resonator electrode in contact with the top surface of the piezoelectric layer and a fourth resonator counter electrode in contact with the bottom surface of the piezoelectric layer. The fourth resonator may have a fourth valley of a resonator impedance at the first frequency.

[0016] In some embodiments, the first resonator electrode is the top layer of the first resonator. In some embodiments, the first mass load layer does not cover the second resonator electrode.

[0017] A first portion of the first mass load layer may be disposed in contact with the first resonator electrode and a second portion of the first mass load layer may be disposed in contact with the second resonator electrode, and the first and second portions may have different thicknesses.

[0018] The counter electrode of the acoustic wave filter element, the first resonator counter electrode, and the second resonator counter electrode may be provided by a common counter electrode that continuously spans the acoustic wave filter element, the first resonator, and the second resonator.

[0019] The input electrode, the output electrode, the first resonator electrode, and the second resonator electrode may be provided by separate portions of the same electrode layer in contact with the top surface of the piezoelectric layer.

[0020] In some embodiments, the thickness of the piezoelectric layer and the gap width between the input and output electrodes are such that application of a high frequency voltage between the input and counter electrodes produces symmetric and asymmetric thickness-extensional acoustic resonance modes in the piezoelectric layer.

[0021] The acoustic wave filter element may be a laterally acoustically coupled bulk acoustic wave (LBAW) filter.

[0022] Another innovative aspect of the subject matter described herein may be embodied in an acoustic wave filter device including an acoustic wave filter element, a first resonator, and a second resonator. The first resonator and the second resonator are coupled to the acoustic wave filter element. The acoustic wave filter element includes interdigital input and output electrodes located on a top surface of a piezoelectric layer. The first resonator includes a first resonator electrode in contact with the top surface of the piezoelectric layer. The first resonator has a first valley of a resonator impedance at a first frequency. The second resonator includes a second resonator electrode in contact with the top surface of the piezoelectric layer. The second resonator also includes a first mass load layer in contact with the second resonator electrode such that the second resonator has a second valley of a resonator impedance at a second frequency different from the first frequency.

[0023] Another innovative aspect of the subject matter described herein may be embodied in an acoustic wave filter device including an acoustic wave filter element, a first resonator, and a second resonator. The first resonator and the second resonator are coupled to the acoustic wave filter element. The acoustic wave filter element includes an electrode located on a top surface of a piezoelectric layer and a counter electrode located on a bottom surface of the piezoelectric layer. The first resonator includes a first resonator electrode in contact with the top surface of the piezoelectric layer and a first resonator counter electrode in contact with the bottom surface of the piezoelectric layer. The first resonator has a first valley of a resonator impedance at a first frequency. The second resonator includes a second resonator electrode in contact with the top surface of the piezoelectric layer and a second resonator counter electrode in contact with the bottom surface of the piezoelectric layer. The second resonator also includes a first mass load layer in contact with the second resonator electrode such that the second resonator has a second valley of a resonator impedance at a second frequency different from the first frequency.

[0024] The subject matter described herein may be implemented in certain embodiments to achieve one or more of the following advantages: The bandpass filters described herein improve the bandpass response of an acoustic filter, e.g., an LBAW filter, by suppressing parasitic sidebands. This suppression may occur at a specific frequency or over a range of frequencies. In addition, the LBAW filters described herein may be easier to manufacture because they use only a single piezoelectric layer, compared to two piezoelectric layers in vertically stacked bulk acoustic wave (BAW) coupled resonator filters. They may also operate at higher frequencies than surface acoustic wave (SAW) filters, since their operation is determined by the thickness of the piezoelectric layer, rather than the dimensions of the interdigital transducer (IDT) electrodes. In some embodiments, LBAW filters may also achieve a wider bandwidth than BAW filters. LBAW filters are smaller in size, since they can act as a filter with a single lithographic patterning step, compared to nearly ten lithographic patterning steps in BAW, and can operate without the reflectors required in SAW.

[0025] The details of one or more embodiments of the subject matter herein are set forth in the accompanying drawings and the description below. Other features, aspects, and advantages of the subject matter will become apparent from the description, drawings, and claims. [Brief description of the drawings]

[0026] [Figure 1A] FIG. 1 is a schematic perspective view of a solidly-mounted LBAW filter. [Figure 1B] 1 is a schematic perspective view of a self-supporting LBAW filter. [Figure 1C] FIG. 2 is a schematic plan view of an interdigital transducer ("IDT") electrode structure. [Figure 2A] 1 is a schematic diagram of one of two types of plate wave propagation modes in an LBAW piezoelectric layer. [Figure 2B]FIG. 2 is a schematic diagram of the other of the two types of plate wave propagation modes in an LBAW piezoelectric layer. [Diagram 3] FIG. 1 is a diagram of an exemplary LBAW dispersion curve. [Figure 4A] FIG. 1 is a schematic diagram of two resonant modes in LBAW. [Figure 4B] 1 is a diagram of an example transmission response of LBAW as a function of frequency. [Diagram 5] FIG. 1 shows experimental transmission curves of LBAW as a function of frequency. [Figure 6A] FIG. 1 is a schematic cross-sectional view of a circuit including an LBAW connected to an elastic filter structure. [Figure 6B] FIG. 1 is a schematic plan view of a circuit including an LBAW connected to an elastic filter structure. [Figure 6C] FIG. 5 is a circuit diagram of the circuit in FIGS. 6A and 6B. [Figure 7A] FIG. 2 is a diagram of an example bandpass filter including one or more acoustic resonators in parallel with an LBAW filter. [Figure 7B] FIG. 2 is a diagram of an example bandpass filter including one or more acoustic resonators in parallel with an LBAW filter. [Figure 7C] FIG. 2 is a diagram of an example bandpass filter including one or more acoustic resonators in parallel with an LBAW filter. [Figure 8] FIG. 1 shows an experimental plot of insertion loss of an LBAW filter with multiple parallel resonators and an experimental plot of impedance of the parallel resonators. [Figure 9A] FIG. 2 is a diagram of an exemplary resonator integrated into an LBAW filter through one or more connections. [Figure 9B] FIG. 2 is a diagram of an exemplary resonator integrated into an LBAW filter through one or more connections. [Figure 10] FIG. 1 is a diagram of an example of a filter including an LBAW in parallel with multiple resonators. DETAILED DESCRIPTION OF THE PREFERRED EMBODIMENTS

[0027] Like reference numbers and designations in the various drawings indicate like elements.

[0028] 1A, 1C show an example of an LBAW filter (or resonator) 100 (also called an "interdigital transducer" or "IDT" LBAW) with an input electrode 150 and an output electrode 170 having a comb-shaped geometry. The LBAW filter 100 includes a piezoelectric ("piezo") layer 110 having a thickness d, an IDT electrode structure 102 located on the upper surface of the piezo layer, and a lower counter electrode 120 located on the lower surface of the piezo layer. The IDT electrode structure ("IDT") 102 includes two comb-like electrodes 150 and 170 of a conductive material, e.g., metal or polysilicon. The IDT electrodes 150 and 170 have parallel extensions 150a and 170a, respectively, that are the "claws" or "teeth" or "fingers" of the "comb". The electrodes 150 and the counter electrode 120 form an input resonator with the piezo layer 110. The electrode 170 and the counter electrode 120 form an output resonator with the piezoelectric layer 110 .

[0029] Acoustic vibrations are generated in the piezo layer 110 by applying an oscillating (or alternating) input voltage between the IDT electrode 150 and the lower counter electrode 120 at the input port 160. The applied voltage is converted to mechanical (e.g., acoustic) vibrations via the piezoelectric effect. Under resonant conditions (e.g., involving certain acoustic resonance modes, as further detailed below), the vibrations can generate standing waves below the input electrode 150 and evanescent waves (with exponentially decaying amplitudes) in the gap region 190. By appropriately selecting the vibration frequency and gap width G, the standing waves can mechanically couple across the gap region 190 from the piezo region under the electrode 150 to the piezo region under the electrode 170 to generate a similar standing wave in the piezo layer 110 below the electrode 170. The standing wave under the electrode 170 results in an output signal voltage of the same frequency at the output port 180 via the inverse piezoelectric effect. The frequency range over which this coupling occurs at mechanical resonance with strong piezoelectric coupling forms the passband (or bandwidth) of the LBAW filter 100. In some examples, the frequency range is between 1.8 GHz and 1.95 GHz. As discussed further below, the thickness and geometry of the various layers of the LBAW filter 100, as well as the separation, can be adjusted to change the RF response and passband of the filter.

[0030] The reflective structure 130 can serve to isolate the vibrations in the piezo layer 110 from the backing substrate 140, preventing acoustic leakage. ac ") material layer and a layer of low acoustic impedance material. In some embodiments, the thicknesses of these layers can be designed such that frequencies at and near the passband of the LBAW filter are reflected into the piezo layer 110 and all other frequencies pass through the mirror.

[0031] In some embodiments, the LBAW 100 is not stacked directly on the substrate 140 (as shown in FIG. 1A), but is self-supported as shown in FIG. 1B. In such a configuration, the substrate 140 and mirror 130 are replaced by an air gap, and a piezo portion that extends laterally through the area in which the LBAW 100 is fabricated is supported by the substrate 140.

[0032] 1C, the extensions 150a and 170a are rectangular, have a width W, a length L, and are separated by a gap width G. Each electrode 150 and 170 has one or more extensions 150a and 170a, respectively. The total number of electrode extensions is designated as K.

[0033] FIG. 1C shows rectangular interdigitated electrodes 150 / 170 with parallel extensions 150a / 170a with the same geometry and separation G, but other electrode geometries are contemplated. Design considerations include the gap between the electrodes, the length of the electrodes, and the number and shape of electrode extensions, if any. The gap can be used to control the coupling between the input and output electrodes. Longer electrodes can also increase coupling. The number of extensions K can be used to control bandwidth and / or increase coupling while conserving the area occupied by the electrodes. In some embodiments, the electrodes consist of rectangular plates with two or more extensions (e.g., K≧2). For example, each extension can be a rectangular plate. In some embodiments, the electrodes are concentric circles or vortices with a common axis.

[0034] The piezo layer 110 may be formed from a variety of piezoelectric materials. Exemplary materials include ZnO, AlN, CdS, PZT, LiNbO3, LiTaO3, quartz, KNN, BST, GaN, Sc-doped AlN, or the aforementioned materials doped or alloyed with additional elements. Doping may be used to improve or tailor the electromechanical properties of the piezo layer 110. As described in more detail below, the thickness d of the piezo layer is selected such that a thickness extensional mode near the frequency of the desired bandwidth of the LBAW filter is produced in the piezo layer. In some embodiments, the thickness d of the piezo layer is greater than or equal to λ. z 20% to 50% of λ z 30% to 45% of λ z is the wavelength of the piezoelectric vibration in the thickness direction. In some embodiments, d is between 1500 nm and 2500 nm, or between 1800 nm and 2200 nm.

[0035] The thin film IDT 102 can be made of a variety of materials. In some embodiments, the IDT electrodes 150 and 170 are metals. For example, electrode materials include multiple layers of Al, Mo, Pt, Cu, Au, Ag, Ti, W, Ir, Ru, or metals doped with metals and / or additional materials, e.g., AlSi, AlSiCu, polysilicon, etc. Doping can be used to improve or tailor the electrical or mechanical properties of the IDT.

[0036] Although FIG. 1A shows a single common counter electrode 120, the LBAW filter 100 may include separate electrodes for the input and output resonators. Various materials are suitable for the counter electrode (e.g., electrode 120). For example, the electrode may include multiple layers of Al, Mo, Pt, Cu, Au, Ag, Ti, W, Ir, Ru, or metals doped with metals and / or additional materials, e.g., AlSi, AlSiCu, etc. Doping may be used to improve or adapt the electrical or mechanical properties of the IDT. For example, the electrode may be Ti+Mo, Ti+W, AlN+Mo, or Al+W. The electrode may be multi-layered. The electrode may have an extra thin seed layer disposed under the electrode.

[0037] The reflecting structure 130 may consist of alternating layers of different materials. For example, the reflecting structure 130 may include two alternating layers of tungsten (W), SiO2, silicon (Si), and carbon (C). For example, the high acoustic impedance layers include W, Mo, Ir, Al2O3, diamond, Pt, AlN, Si3N4. The low acoustic impedance layers may include SiO2, glass, Al, Ti, C, polymers, or porous materials. A layer of Si provides an intermediate acoustic impedance. Various materials are suitable for the substrate 140, such as Si or SiO2 or glass, sapphire, quartz, etc. The material of the substrate 140 may have a high electrical resistance. The substrate may have a thickness suitable for RF applications, such as integration into a mobile phone platform. For example, the substrate may have a thickness of less than 500 microns, or less than 200 microns. For example, a 675 μm thick Si wafer may be purchased and thinned to achieve a desired device thickness, for example, for a mobile platform.

[0038] Modeling the acoustic response of the LBAW 100 can provide guidance on how to adjust the design parameters of the individual elements of the structure to achieve the desired bandpass characteristics. For example, the LBAW 100 can be designed to have resonant modes at specific frequencies. In general, the geometries of the various LBAW 100 components can be selected to achieve different acoustic characteristics. The characteristics of the LBAW 100 can depend on a combination of these geometries, which may not be independent of each other.

[0039] Different bulk acoustic vibration modes can occur in the piezoelectric layer 110 at different excitation frequencies f of the input voltage (e.g., at port 160). Acoustic vibrations in the piezo layer 110 can propagate laterally as Lamb waves (or plate waves), with particle motion in a plane containing the direction of wave propagation and in a perpendicular plane (e.g., the z-axis in FIG. 1A). Two such modes are shown in FIGS. 2A-2B. With reference to FIG. 2A, a thickness extensional (TE or longitudinal) bulk mode 200 has particle displacements 210 primarily perpendicular to the propagation direction (in the z-direction). With reference to FIG. 2B, a second order thickness shear (TS2) bulk mode 220 has particle displacements 230 primarily parallel to the propagation direction (in the y-direction). For both modes, the lowest frequency at which resonance in the thickness direction can occur is when the thickness d of the piezo layer 110 is equal to a wavelength λ z (ignoring the thickness of the electrodes 150 / 170). In other words,

[0040]

number

[0041] where N is an integer indicating the order of resonance. For the TE1 mode,

[0042]

number

[0043] As discussed further below, the width W of the electrodes and the gap G between the electrodes define a certain lateral wavelength λ that can couple across the gap G through the evanescent tail to produce two mechanical resonant modes. || The design can be such that a standing wave of TE1 mode with

[0044] The acoustic characteristics of the LBAW resonator 100 can be expressed as a dispersion curve. Referring to FIG. 3, an example dispersion curve for the LBAW resonator 100 is shown as a function of the voltage input frequency f, with respect to the shear wave number k of vibration. || where

[0045]

number

[0046] The sum of the thickness d of the piezoelectric layer and the thickness of the electrode 150 or 170 is approximately half the wavelength of the bulk vibration, λ z / 2, and the bulk vibration is primarily perpendicular to the thickness direction (z-axis in FIG. 2B) and is spaced apart by one acoustic wavelength λ over the sum of the thickness d of the piezoelectric layer and the thickness of electrodes 150 and 170. z The second order thickness shear (TS2) modes, which include TE1 and TS2 modes, are shown in the figure. The TE1 modes are the darker portions of each dispersion curve, and the TS2 modes are the lighter areas of each dispersion curve. The top curve ("No Electrodes") represents the dispersion characteristics of the piezoelectric layer below the gap region 190. The bottom curve ("Electrodes") represents the dispersion characteristics of the piezoelectric layer below the electrodes 150 / 170, also known as the active region. More specifically, where the "Electrodes" curve crosses k=0, the TE1 mode has a dispersion of approximately λ z / 2 is included in the combined thickness of the electrode 150 or 170 and the piezoelectric layer. This is an approximation since the wave can extend into the Bragg reflector. The intersection of the "no electrode" curve with the k=0 line is approximately λ z / 2 is included in the total thickness of the lower electrode only and the piezoelectric layer. In the TE1 mode, k ||This type of dispersion, where increases, is called Type 1. The difference in frequency of the intersection point k||=0 between the electroded and non-electrode areas determined a hard limit on the achievable bandwidth of the filter. The gap width G, electrode width W, and number of extensions K can be used to vary the coupling strength within the limits set by the difference in dispersion.

[0047] In some embodiments, the LBAW 100 may be designed to produce Type 1 dispersion. For example, a material may be selected for the piezo layer 100 in which Type 1 dispersion may occur. For example, ZnO may be used. In another example, appropriate design of the acoustic Bragg reflector 130 may help achieve Type 1 dispersion. For example, the use of aluminum nitride ("AlN") for the piezo layer 110 may typically produce Type 2 dispersion, where the TE1 mode initially decreases with increasing frequency f, k || decreases, and k increases with increasing frequency f. || (generally similar to that described in the dispersion curve of FIG. 3, but with TE1 and TS2 swapped). However, in some embodiments, with proper design of the reflecting structure 130 (e.g., acoustic Bragg reflector), the LBAW 100 can use AlN in the piezo layer 100 and still achieve Type 1 dispersion. See, e.g., Fattinger et al., "Optimization of acoustic dispersion for high performance thin film BAW resonators," Proc. IEEE International Ultrasonics Symposium, 2005, pp. 1175-1178.

[0048] In Figure 3, k || Positive values ​​of k indicate real wave numbers (propagating waves), and negative values ​​of k ||The value of corresponds to the imaginary wave number (evanescent wave). For resonance to occur, the acoustic energy must be confined inside the LBAW resonator structure. In the thickness (z-axis) direction, isolation from the substrate (using the reflecting structure 130) can be used for energy confinement. In the lateral direction, energy confinement can occur when evanescent waves form outside the electrode area (e.g., on the "no electrode" curve). To obtain a resonant coupling between two LBAW resonators (e.g., electrodes 150 / 170 and 120), a standing wave of the TE1 mode forms in the active area of ​​the piezo layer (below the electrodes) and an evanescent wave forms in the "no electrode" area. In other words, k || is positive for the TE1 "electrode" curve and negative for the TE1 "no electrode" curve. According to Fig. 3, this occurs in the frequency range labeled "confined range". Energy confinement may be easier to achieve in Type I dispersion. Without wishing to be bound by theory, when the dispersion curve increases monotonically, such as the thick TE1 line in Fig. 3, for the "electrode", there is either a single imaginary wave number available at a single frequency inside the confinement range, or a single real wave number above the confinement range. The former means that TE1 does not propagate outside the electrode, the latter means that TE1 can couple with propagating waves outside the electrode and thus "leak". Type 2 dispersion may be described by a similar curve, but with the TE1 and TS2 curves swapped. The fact that the curves in Type 2 are non-monotonic means that there can be several real wave numbers at a given frequency. Having several wave numbers for a frequency means that propagating waves are available outside the electrode, which may cause "leakage".

[0049] 4A-4B show the relationship between standing wave resonance modes and LBAW band gaps. Referring to FIG. 4A, a portion of the LBAW 100 includes two adjacent electrodes 401 and 402 (e.g., corresponding to the extensions 150a and 170a of the electrodes 150 and 170, respectively, in FIG. 1A) with a width W. The bandpass frequency response of the LBAW 100 is formed by two (or more) lateral standing wave resonance modes 410 and 420 arising in the structure. The lateral standing wave resonances can occur when the Lamb waves are reflected from the ends of the electrodes 401 and 402. In the even mode resonance 410, the piezoelectric layers under both electrodes 150 and 170 vibrate in phase, while in the odd mode resonance 420, the phases are opposite. The total width of the structure is equal to the lateral wavelength λ of the modes. || When the even mode transverse standing wave resonance can occur, the even mode transverse standing wave resonance can occur when the even mode is approximately equal to half the even mode.

[0050]

number

[0051] In the limit of infinitesimal gap width G, λ even As shown in Figure 4A, λ approaches the total width from below. even becomes smaller as G increases and becomes larger as G increases. For small gaps (e.g., zero gap), λ even approaches 4W, and for larger gaps, λ even approaches 2 W. The width of the electrode is the transverse wavelength λ of the mode. || When the θ is approximately equal to half of the θ, odd-mode lateral standing wave resonance can occur.

[0052]

number

[0053] 4B, the even and odd modes 410 and 420 are shown as transmission peaks as a function of input frequency f for an LBAW with Type-1 dispersion. With Type-1 dispersion, the even mode 410 has a longer wavelength and lower frequency than the odd mode 420, which has a shorter wavelength. The frequency difference 430 between the modes determines the achievable bandwidth of the LBAW filter 100 and depends on the acoustic properties of the structure and the dimensions of the IDT resonator 102. The strength of the acoustic coupling is related to the difference in (resonant) frequency between the even (symmetric) and odd (asymmetric) resonances:

[0054]

number

[0055] where f symm and f asymm are the symmetric and asymmetric natural frequencies, respectively, and f0=(f symm +f asymm ) / 2 is the center frequency between the two modes.

[0056] In some embodiments, increasing the number of extensions (e.g., 150a and 170a) of each electrode (e.g., 150 and 170) can increase the frequency difference between the even and odd modes in the LBAW, and therefore the bandwidth. This effect can be attributed to the fact that the transverse wavelength of the odd mode can depend on the periodicity (e.g., width W) of the electrode structure, while the even mode can depend on the overall width of the structure (e.g., the sum of all widths W and gap G). For example, if the total number of electrode extensions is K, the electrode width is W, and the gap width is G, then the wavelength λ of the transverse elastic wave at the even mode resonant frequency is || teeth,

[0057]

number

[0058] Approaching or slightly shorter than

[0059] However, the odd-mode transverse standing wave resonance in this structure is

[0060]

number

[0061] Approaching or slightly larger than

[0062] Additionally or alternatively, in some embodiments, the overall width K·W+K·G of the structure may be such that the higher order modes confined to the structure are the desired odd mode resonances. For example, K may be 31, W may be 3 μm, and G may be 2 μm.

[0063] In some embodiments, the number K of electrode extensions is between 2 and 200, or between 10 and 60. In some embodiments, the length L of an electrode extension can be between 50 μm and 2000 μm, or between 70 μm and 500 μm.

[0064] In some embodiments, the gap G is selected to allow coupling of the evanescent tails of standing waves formed under electrodes 150 and 170. For example, the gap G between the electrode extensions can be between 0.1 μm and 10 μm, or between 2 μm and 5 μm.

[0065] In some embodiments, the topology of electrodes 150 and 170 can be designed such that the gap width G provides good enough coupling between the electrode extensions to produce a single even mode 410 across the entire width of the structure. For example, for a gap in the desired even resonant mode, the gap width G is the decay length of the evanescent acoustic wave, i.e., the amplitude A=A0·e, where A is the original amplitude. -1The gap width G can be 2%-300%, or 10%-100% of the length where G = 1. The gap width G can be optimized. Making the gap width too narrow can (1) end up causing valleys in the passband because the even and odd modes are too far apart from each other, (2) lead to a poor coupling coefficient for the odd mode, or (3) increase the finger-to-finger capacitive feedthrough, resulting in poor out-of-band attenuation.

[0066] In some embodiments, the gap width G can be defined in terms of the thickness d of the piezo layer. For example, G can be designed to be between 10% and 300% of d, or between 25% and 150% of d.

[0067] In some embodiments, the width W of the electrode extension can be between 0.1 μm and 30 μm, or between 2 μm and 5 μm. In some embodiments, W is equal to the wavelength λ of the shear acoustic wave at the desired odd-mode resonant frequency. || λ odd can be designed to obtain

[0068] In some embodiments, the electrode width W is designed such that no multiple of a half wavelength falls within the electrode width. For example, W is less than the wavelength λ of the shear acoustic wave in the desired odd resonant mode. || It may be designed to be smaller, for example λ || = λ odd It is.

[0069] In some embodiments, the thicknesses of the various LBAW 100 components may be selected to achieve various acoustic properties and may be interdependent. For example, the thickness d (minimum and maximum) of the piezo layer 110 may first be determined in terms of the acoustic wavelength (λ) in the piezo material at the operating frequency f. In some embodiments, the thicknesses (minimum and maximum) of the other LBAW 100 layers may be chosen based on the selection of the piezo thickness d. For example, the sum of the thicknesses of the electrodes (including the counter electrode 120) and the piezoelectric layer may be selected to be about half the wavelength of the bulk longitudinal wave for the mode being used, e.g., the thickness extensional mode. The fundamental mode (first mode, i.e., first harmonic) with N=1 may allow for greater coupling, but modes with N>1 are also possible. For example, the thicknesses of the electrodes 150 and 170, the lower counter electrode 120, and the reflecting structure 130 may be defined as percentages of the piezo layer thickness d. In some embodiments, once all thicknesses are selected, the geometry of extensions 150a and 170a, such as number K, width W, gap G, and length L, can be adjusted to match the electrical impedance of LBAW 100 with the system impedance. Without being limited to a particular theory, impedance matching can help prevent losses and reflections in the system.

[0070] In some embodiments, the thickness of electrodes 150 and 170 is between 1% and 30% of d, or between 2% and 25% of d, or between 3% and 15% of d.

[0071] In some embodiments, the thickness of the lower counter electrode 120 is between 5% and 50% of d, or between 10% and 30% of d, or between 10% and 20% of d.

[0072] In some embodiments where the reflecting structure 130 is a Bragg reflector, the alternate layers of the reflector can be designed to obtain the required reflectivity of the passband wavelengths. For example, the thickness of each layer is set to 1 / 2 the acoustic wavelength λ in the thickness direction to reflect the odd and even TE1 resonant modes. zIn some embodiments, a single layer in the Bragg reflector may be between 15% and 80% of d, or between 20% and 70% of d.

[0073] The mass loading of the IDT 102, determined by the thickness and material of the electrodes 150 and 170, reduces the k || k = 0 frequency and TS2 mode in the outer region of the electrode || = 0 frequency. Without wishing to be bound by theory, when the difference in frequency between the TS2 mode in the outer region and the TE1 mode in the electrode region is small, the confinement range is large. More specifically, the k || The k = 0 frequency can be 95% to 99% of the TE1 cutoff frequency in the electrode region. || = 0 frequency and k of the TE1 mode in the outer region || The difference in frequency from the =0 frequency is designed to be large, for example, 5% to 15%, for example 6.5% to 7.5%, of the TE1 mode cutoff frequency of the electrode region.

[0074] According to some embodiments of the present invention, the k of the TS2 mode in the outer region || The k = 0 frequency is greater than or equal to 98%, between 98% and 99.5%, or 98.9% of the TE1 cutoff frequency of the electrode region. Similarly, the k || = 0 frequency and k of the TS2 mode in the outer region || = 0 frequency

[0075]

number

[0076] should be small, for example of the order of 1%. By way of example, the frequency distance may be between 0.2% and 2.1%, or between 0.5% and 1.8%, or between 0.8% and 1.5%, or for example 1.1%.

[0077] FIG. 5 shows a curve of insertion loss IL (in decibels) versus frequency f for an exemplary LBAW 100. The curve shows two passbands with a peak 510 corresponding to a TE1 wave and a peak 520 corresponding to a TS2 wave. As discussed above, the width of each passband is determined by the difference in frequency between the even and odd modes for each type of wave. Here, the TS2 mode corresponds to a sideband 520a (also referred to herein as the "TS2 passband"), and the TE1 mode corresponds to a passband 510a (also referred to herein as the "TE1 passband"). In some embodiments, the LBAW 100 is designed to maintain the characteristics of the peak 510 corresponding to the TE1 mode while suppressing the peak 520 corresponding to the TS2 mode. Without being limited to a particular theory, the TE1 mode of operation may be selected because the piezo thin film material has stronger electromechanical coupling in the thickness direction. In other words, the TE1 longitudinal mode vibration couples more efficiently to the electrical excitation across the thickness of the piezo layer 110.

[0078] In some embodiments, the LBAW 100 may be designed to have a passband between 0.5 GHz and 10 GHz or between 1 GHz and 4 GHz for the TE1 mode. In some examples, the TE1 passband is between 1.8 GHz and 3.7 GHz. The limits of the passband may factor into design considerations. For example, the dimensions of the device may be very large or very small. Dimensions that are too large may take up too much space resulting in inefficiency. Dimensions that are too small may lead to resistance and losses, degrading performance due to thin and narrow electrodes. In some embodiments, the LBAW 100 may be designed to have a TE1 passband 510a that is between 0.5% and 15% of the center frequency, for example, 10%, or 5%, or 2%, or 1% of the center frequency. In some embodiments, the insertion loss in the passband is better than -7 dB, for example, between -7 dB and -0.5 dB, or between -5 dB and -0.5 dB.

[0079] The LBAW can be used as a bandpass filter. The IDT electrodes of the LBAW can be designed to couple the driving electrical signal to the desired fundamental TE1 mode. The effective coupling results in a passband similar to the TE1 passband of 510a in FIG. 5. However, this coupling also results in one or more sidebands similar to sideband 520a. Sideband 520a may be lower in frequency and narrower than passband 510a. Sideband 520a is generated due to the electric field between the parallel extensions of the LBAW (e.g., extensions 150a and 170a). These extensions result in an asymmetric electric field in the thickness direction of the piezo, which couples to both the TE1 and TE2 modes.

[0080] Implementations of the present disclosure provide techniques for suppressing LBAW sidebands produced by the TS2 mode. The implementations suppress the sidebands by connecting acoustic resonators to the LBAW. At least one of the acoustic resonators has an impedance valley at a resonant frequency within the bandwidth of the sideband. As described in more detail below, the impedance valley causes an increase in the insertion loss of the LBAW at the resonant frequency, resulting in an overall increase in the insertion loss in the sideband.

[0081] Acoustic resonators can be added in series or parallel with the LBAW 100. For example, referring to FIG. 6A-6B, cross-sectional and plan views of a structure 600 include the LBAW 100 connected to resonators 612, 613, 615, and 616. FIG. 6C shows the corresponding circuit diagram of the structure 600. In the structure 600, the piezo layer 110 is common to the LBAW 100 and all connected filters. Moving from left to right in FIG. 6B, the parallel resonator 612 and the series resonator 613 are located before the input port 160 of the LBAW 100. The series resonator 615 and the parallel resonator 616 are located after the output port 180 of the LBAW 100. In the parallel resonators 612, 616, the lower electrodes are grounded. In the series resonators 613, 615, the signal goes to the lower, ungrounded electrodes beyond the piezo layer 110.

[0082] An embodiment with one or more series resonators can be designed such that the resonant frequency of the series resonator is within the passband frequency of the sideband and suppresses the sideband. Acoustic resonators (e.g., BAW / FBAR resonators) have very high impedance at the anti-resonant frequency. Such high impedance prevents the driving electrical signal from passing and reduces the signal transmission through the filter. Therefore, a resonator with one or more anti-resonant frequencies within the sideband of the LBAW filter can be added in series to the LBAW filter to reduce the signal transmission at one or more resonant frequencies (which are parallel frequencies with the LBAW) to suppress the LBAW sideband.

[0083] The embodiment with one or more parallel resonators can be designed such that the resonant frequency of the parallel resonator is within the passband frequency of the sideband and suppresses the sideband. The acoustic resonator (e.g., BAW / FBAR resonator) has very low impedance at the resonant frequency. Such low impedance causes the driving electrical signal to flow to ground, reducing the signal transmission through the filter. Therefore, a resonator with one or more resonant frequencies within the sideband of the LBAW filter can be added in parallel to the LBAW filter to reduce the signal transmission at one or more resonant frequencies (which are in series with the LBAW) and suppress the LBAW sideband. In general, one or more parallel resonators can be integrated into the LBAW filter by (i) using the input or output electrode of the LBAW as a parallel resonator (e.g., similar to Figs. 7A-7C) and / or (ii) connecting one or more parallel resonators to the LBAW filter (e.g., Figs. 9A-9B).

[0084] The frequency of the resonators can be adjusted by choosing their mass loading. Mass loading can be achieved by applying one or more mass loading layers to one or both electrodes of the resonators. The mass loading layers can be made of a different material than the electrode behind it or of the same material. In the latter case, it can be considered that the two resonators have electrodes of different thicknesses.

[0085] Differential mass loading between the two resonators can be achieved by i) applying a mass loading layer to the electrodes of one resonator but not to the electrodes of the other resonator, ii) applying different thicknesses of the same material to the two respective electrodes of the two resonators, and / or iii) applying layers of different materials to the two respective electrodes of the two resonators. Additionally, different mass loading between the two resonators can be achieved by having different thicknesses of the electrodes of the two resonators.

[0086] Of two resonators with mass load layers made of the same material, the resonator with the thicker mass load layer has a lower resonant frequency than the resonator with the thinner electrodes because it has more mass. Therefore, the resonant frequency can be adjusted by adding or removing loads on the electrodes of the resonator.

[0087] A parallel resonator (i.e., a resonator in parallel with the LBAW) may be designed to have a resonant frequency within the frequency range of one or more sidebands to be suppressed (e.g., the frequency range of sideband 520a). Moreover, multiple parallel resonators with different resonant frequencies may be designed to suppress a sideband over a wider range of frequencies (compared to a parallel resonator with the same resonant frequency) or to suppress multiple sidebands.

[0088] 7A-7C show an exemplary bandpass filter including an acoustic resonator in parallel with the LBAW 100. FIGS. 7A-7C show top and cross-sectional views of bandpass filters 700, 710, and 720, respectively. Filters 700, 710, and 720 may be generally the same, except that one or more mass load layers in one or more of their parallel resonators (also referred to herein as "resonators") may differ. Filters 700, 710, 720 may be generally the same as filter assembly 600, except as described. For example, filters 700, 710, 720 may optionally omit series resonators 613, 615, although such series resonators may still be included between the LBAW filters.

[0089] Filter 700 includes parallel resonators 702, 704, filter 710 includes parallel resonators 702, 712, and filter 720 includes parallel resonators 722, 724, 726, and 728. Each of resonators 702, 704, 712, 722, 724, 726, and 728 has a resonator electrode (also referred to herein as an "electrode") and a resonator counter electrode. The resonator electrode and the counter electrode may be used to apply a driving electrical signal. One or more resonators may have a common electrode (e.g., electrode 150 or 170) with the LBAW 100, such that an extension of the LBAW 100 protrudes from the common electrode. One or more of the resonators may have a common counter electrode (e.g., counter electrode 120) with the LBAW 100. In some embodiments, the common counter electrode continuously spans the LBAW and each resonator that shares a common counter electrode with the LBAW. In some examples, the common counter electrode is grounded. Each of the parallel resonators 702, 704, 712, 722, 724, 726, and 728 may be made of the same or different material as the LBAW 100. The parallel resonators may be made of polysilicon, metal, silicon dioxide, or silicon nitride.

[0090] Referring to FIG. 7A, the filter 700 includes two parallel resonators 702, 704 respectively coupled to the input and output electrodes of the LBAW 100. Specifically, each parallel resonator 702, 704 includes a respective conductive layer 732, 734 as a resonator electrode and a counter electrode, which sandwich the piezo layer 110 together. Each conductive layer 732, 734 is electrically coupled to the extension 716 of the respective input and output electrodes. Specifically, each of the conductive layers 732, 734 can provide a common electrode (e.g., electrode 150, 170 in FIG. 1A) from which the respective extension 716 (e.g., extension 150a, 170a) protrudes relative to the respective input and output electrodes. The common electrode is common between the LBAW 100 and the respective parallel resonators. For example, one or both of the conductive layers 732, 734 and the LBAW extension can be provided by separate portions of the same electrode layer contacting the top surface of the piezoelectric layer. The parallel resonators 702 and / or 704 may be electrically coupled to an input electrode or port and / or an output electrode or port (e.g., ports 160, 180) of the LBAW 100. The resonators 702, 704 and the LBAW 100 share a common counter electrode 120, e.g., the counter electrode for each resonator 702, 704 may be provided by a respective portion of the counter electrode 120. The resonators 702, 704 and the LBAW 100 also share a common piezo layer 110. The counter electrode 120 may be grounded.

[0091] As previously described, the resonant frequency of either or both of the parallel resonators 702, 704 may be adjusted by adding or removing mass loading from the respective conductive layers 732, 734. To lower the resonant frequency of the resonators 702, 704, a layer that provides a mass loading may be deposited on the conductive layers 732, 734 of the respective resonators. To raise the resonant frequency of the resonators 702, 704, the conductive layers 732, 734 of the respective resonators may be partially removed, for example through etching.

[0092] 7B shows a bandpass filter 710 with a parallel resonator 702 and a parallel resonator 712. Specifically, the mass loadings of the two resonators 702, 712 are different such that the two resonators 702, 704 have different resonant frequencies. Both resonant frequencies may be within the frequency range of the sidebands 520 of the LBAW 100.

[0093] The parallel resonator 712 is formed by adding a mass load layer 708 on top of the conductive layer 734 (or electrode) of the resonator 704. In some embodiments, the conductive layer 734 is made of aluminum (Al) or copper (Cu) and the mass load layer 708 is made of silicon oxide (SiO2) and / or silicon nitride (SiN). With the addition of the mass load layer 708, the resonator 712 may have a lower frequency than the resonator 704.

[0094] The thickness of the mass load layer 708 may be selected to provide a desired resonant frequency for the resonator 712. For example, if the resonant frequency of the resonator 704 were otherwise higher than the frequency range of the sideband 520a, the thickness of the mass load layer 708 may be selected to shift the resonant frequency to provide a resonant frequency within the sideband 520a for the resonator 712. The thickness may also be adjusted by making the mass load layer 708 thicker (e.g., by depositing additional material) or thinner (e.g., by etching).

[0095] The resonator 702 may have a different thickness than the resonator 712. This difference in thickness may be due to different thicknesses of the two conductive layers 732, 734, or the presence of a mass load layer in the resonator 712 but not in the resonator 702, or different thicknesses of a mass load layer in contact with the two conductive layers 732, 734.

[0096] The resonator 712 may be made of one or more materials not included in the resonator 702. For example, the electrodes of the mass load layer 708 of the resonator 702 may be made of a different material (e.g., silicon oxide, silicon nitride, etc.) than the material (e.g., aluminum, copper, etc.) of the conductive layers 732, 734.

[0097] The mass load layer 708 may be made of the same material as the conductive layer 734 or a different material. For example, the conductive layer 734 may be made of aluminum (Al) and the mass load layer 708 may be made of Al, silicon oxide, and / or silicon nitride. If the mass load layer 708 is a conductor, e.g., the same conductive material as the conductive layer 734, the resonator 712 may be considered to have thicker electrodes than the resonator 702.

[0098] 7B illustrates achieving the different mass loading by including a mass loading layer 708 in the resonator 712 and not including a mass loading layer in the resonator 702, other configurations are possible. For example, both resonators may include mass loading layers of different thicknesses and / or materials. For example, the mass loading layers of the two resonators 702, 704 may be made of the same material but have different thicknesses. As another example, the mass loading layers of the two resonators 702, 704 may be made of different materials, optionally with the same thickness. Alternatively or additionally, the thickness of the resonator electrode (i.e., the conductive layer 732) of the resonator 702 may be different from the thickness of the electrode (i.e., the conductive layer 734) of the resonator 712.

[0099] As mentioned before, in order to suppress a wider range of frequencies of the sideband of the LBAW (compared to a configuration with a single parallel resonator or a single resonant frequency), multiple resonators with different resonant frequencies within the sideband can be connected in parallel to the LBAW. Multiple parallel resonators with different resonant frequencies run the driving electrical signal to ground at each of the resonant frequencies. For example, when the two resonators 702 and 712 of the filter 710 have different resonant frequencies that are within the sideband frequency of the LBAW 100 (e.g., sideband 520a), the sideband is suppressed over a wider range of frequencies compared to when the two resonators have the same resonant frequency.

[0100] FIG. 8 shows an experimental plot 800 of insertion loss for an LBAW filter with two parallel resonators and a simulated plot 810 of impedance for the two parallel resonators. For example, the two resonators can be resonators 722, 728 of FIG. 7C. As shown in plot 810, the two resonators have two different resonant frequencies 804 and 808. The solid line in plot 800 corresponds to the insertion loss of the LBAW. The dashed line in plot 800 shows the insertion loss of the same LBAW connected in parallel with two resonators, whose impedances are shown in plot 810. For example, the solid line in plot 800 can represent the insertion loss of the LBAW 100, and the dashed line can represent the LBAW 100 in parallel with resonators 702 and 712, as shown in FIG. 7B.

[0101] As shown in plot 800, the low impedance of the two parallel resonators at the resonant frequencies reduces the transmission through the filter, resulting in two valleys 802 in the sideband 520a at the resonant frequencies 804 and 808 of the parallel resonators. The two valleys reduce the overall insertion loss in the sideband and also suppress the peak of the sideband. The two resonant frequencies may have a frequency difference of about 0.1% to 3% with respect to their center frequencies. Either of these two resonant frequencies may have a frequency difference of at least 3%, for example at least 10%, with respect to the frequency of the skirt end 806.

[0102] In addition to suppressing sidebands, one or more parallel resonators may be added to the LBAW to mitigate the steepness of the edge of the LBAW passband. A parallel resonator with a resonant frequency at the edge of the passband results in a sharp valley at the edge, causing a steeper skirt for the TE1 passband. Further details on specific filter configurations and their effect on the edge of the passband are disclosed in U.S. Pat. No. 9,893,712, which is incorporated by reference in its entirety. For example, a third parallel resonator may be added to the filter corresponding to FIG. 8 to increase the steepness of the skirt edge 806. As another example, the resonant frequency of the parallel resonator 702 may be tuned to the frequency of the skirt edge 806 to increase the steepness of the skirt edge 806.

[0103] Configurations with more than two parallel resonators may be implemented according to configurations described herein. FIG. 7C shows an example bandpass filter 720 including four parallel resonators 722, 724, 726, and 728. The four resonators of the filter 720 are in parallel with the LBAW 100. Similar to the resonators 702, 704, and 712, each of the resonators 722-728 includes a piezo layer sandwiched between a resonator electrode and a resonator counter electrode. The piezo layer (e.g., piezo 110), the counter electrode (e.g., counter electrode 120), and / or the electrodes of the resonators may be common between the resonators and the LBAW 100.

[0104] Resonators 724, 726 include conductive layers 732, 734 that may be coupled to input or output electrodes of the LBAW 100. Resonators 722 and 728 include one or more layers of mass loads on the respective conductive layers 732, 734. Resonator 728 includes a mass load layer 708 on the conductive layer 734. Resonator 722 includes multiple mass load layers 732 and 738 on the conductive layer 732.

[0105] The layers 732, 734, 708, 736, and 738 may be made of the same or different materials. For example, the layers 732, 734 may be made of Al or copper, and the layers 708, 736, and 738 may be made of silicon oxide (SiO2), silicon nitride (SiN), and / or one or more metals. The layers 732, 734, 708, 736, and 738 may have different thicknesses. In some examples, the conductive layer 732 may have a different thickness in the resonator 722 than in the resonator 724. In some examples, the conductive layer 734 may have a different thickness in the resonator 726 than in the resonator 728.

[0106] Depending on the characteristics (e.g., thickness, material) of the four parallel resonators 722-728, the bandpass filter 720 may act against insertion loss as an LBAW in parallel with four or fewer resonators. When the four resonators have four different resonant frequencies, the insertion loss of the filter 720 is suppressed at four different resonant frequencies. When two of the resonators have the same resonant frequency, the insertion loss of the filter 720 is suppressed at three different frequencies, because the resonators only provide three different resonant frequencies. Similarly, when three or four of the resonators have the same resonant frequency, the suppression of insertion loss only occurs at two or one frequency, respectively.

[0107] For example, if the resonators 724 and 726 have the same resonant frequency, the bandpass filter 720 acts for insertion loss as an LBAW with three parallel resonators (a), (b), and (c). The parallel resonator (a) is formed by the resonators 724 and 726, the parallel resonator (b) is formed by the resonator 728, and the parallel resonator (c) is formed by the resonator 722. Since the two parallel resonators 724 and 726 share the same resonant frequency, they act as one resonator (i.e., the parallel resonator (a)) for the purpose of suppressing sidebands. For example, if the resonators 724 and 726 have the same size (e.g., the same thickness) and are made of the same material, they may have the same resonant frequency.

[0108] Each of layers 732, 734, 708, 736, 738 of FIGS. 7A-7C may be made of the same or different material as the LBAW extension (e.g., extension 150a or 170a). In some embodiments, electrodes 732, 734 and / or LBAW extension are made of aluminum (Al) and layers 708 and 736 are made of silicon oxide (SiO2) and / or silicon nitride (SiN). For example, layer 708 may be made of SiO2 and layer 736 may be made of SiN. In some examples, the layer of SiO2 is less than 500 nm thick and the layer of SiN is less than 100 nm thick. In some examples, the layer of SiO2 is 50 nm to 250 nm thick and the layer of SiN is 5 nm to 50 nm thick.

[0109] In some embodiments, the resonator electrode or electrodes are the top layer of the respective resonator. For example, layer 708 may be used as an electrode for resonator 712.

[0110] 9A-9B show exemplary resonators integrated into an LBAW filter through one or more connections. The filter 900 shown in FIG. 9A can generally be any of the filters 700, 710, or 720, except that it has additional resonators 914, 916 in parallel with the LBAW 100. The resonators 914 and 916 each include electrodes 904 and 906, which are connected to an electrode 908 through common ends 910 and 912, respectively. The electrode 908 may be an electrode of the LBAW 100 or may be an electrode of one or more resonators (e.g., resonators 702, 704, 712, 722, 724, 726, 728) in parallel with the LBAW 100. The resonators 914 and 916 may be electrically coupled to the input or output electrodes of the LBAW 100 or to the electrodes of one or more resonators in parallel with the LBAW 100. For example, electrode 908 may be the conductive layer 734 and may be electrically coupled to resonator electrode 906 by sharing a common end 912. Resonators 914 and 916 share a common counter electrode 120 (see FIG. 1A) with LBAW 100. Resonators 914 and 916 may also share a common piezo layer 110 with LBAW 100. Counter electrode 120 may be grounded. Ground via (or contact) 902 is also shown in FIG. 9A.

[0111] One or more parallel resonators may also be connected to the LBAW filter or to one or more other parallel resonators through one or more conductive lines. FIG. 9B shows a conductive line 936 connecting a first parallel resonator 932 to a second parallel resonator 934. The first parallel resonator 932 has a first electrode 942 and the second parallel resonator has a second electrode 944. The first electrode 942 has a first end 922 facing the LBAW filter 100, a second end 924 further away from the LBAW filter, and a third end connecting the first and second ends. The second electrode 944 may be connected to any side, end, or corner of the first electrode 942. In the illustrated example, the second electrode 944 is disposed adjacent to the third end 926 of the first electrode 942. In some examples (not shown), the second electrode 944 may be disposed adjacent to the second end 924 of the first electrode 942. In the illustrated example, there is a gap between the first electrode 942 and the second electrode 944, which is spanned by a conductive line 936. In some embodiments, the first electrode and the second electrode share a common end (similar to the common end 910 between electrodes 908 and 904 in FIG. 9A). The first parallel resonator 932 and the second parallel resonator 934 are electrically coupled through the first electrode 942 and the second electrode 944, for example, by sharing a common end or a conductive line.

[0112] The electrodes of the first parallel resonator 932 and / or the second parallel resonator 934 may be loaded by one or more mass loading layers (e.g., layers 708, 736, 738). The one or more mass loading layers may be selected such that the resonant frequency of each parallel resonator is within the sidebands of the LBAW 100. The size (e.g., thickness) of the first electrode 942, the second electrode 944, and / or the conductive line 936 may be adjusted to tune the resonant frequency of each resonator within the sidebands of the LBAW 100.

[0113] 10 shows another example of a filter 1000 including a LBAW 100 in parallel with multiple resonators. Ground vias 1002 are also shown in FIG.

[0114] The resonators 1004, 1006, 1008, and 1010 are in parallel with the LBAW 100. The resonators share a counter electrode 120 (see FIG. 1A) with the LBAW 100. The counter electrode 120 may be grounded. The resonators 1004 and 1006 share a conductive electrode layer 1018, and the resonators 1008 and 1010 share a conductive electrode layer 1026. Either or both of the layers 1018 and 1026 may be electrically coupled to the input and / or output electrodes of the LBAW 100. In some examples, one or both layers 1018 and 1026 may provide a common electrode between the LBAW and one or more resonators. An extension of the LBAW 100 protrudes from the common electrode. Each of the layers 1018 and 1026 may be made of a metal, for example, Al.

[0115] The resonator 1004 includes a mass load layer 1016 on top of a conductive electrode layer 1018. The layer 1016 covers a portion of the layer 1018. The layer 1016 may cover substantially all of the electrode layer 1018 in the resonator 1004.

[0116] The resonator 1006 includes a mass load layer 1014 on an electrode layer 1018. The layer 1014 may be in the form of a frame, e.g., relatively thin-walled compared to the area enclosed by it. The frame may form a hollow polygon. The frame may extend along the periphery of the resonator 1006. For example, in FIG. 9B, a frame 938 may be formed (e.g., by deposition or etching) on ​​the electrode 932 to provide a frame-like resonator. Further details on frame-like resonators may be found in International Patent Application No. PCT / FI00 / 00591, entitled "Resonator Structure and a Filter Comprising Such a Resonator Structure," which is incorporated herein in its entirety.

[0117] The resonator 1008 includes a mass load layer 1020 on top of an electrode layer 1026. Like layer 1014, layer 1020 may be in the form of a frame.

[0118] The resonator 1010 includes two mass load layers 1022 and 1024 on top of an electrode layer 1026. Each of the mass load layers 1022 and 1024 may cover substantially all of the electrode layer 1026 in the resonator 1010. The layer 1022 may cover all or a portion of the surface of the layer 1024.

[0119] Each of the mass load layers 1014, 1016, 1020, 1022, and 1024 (each of which may be referred to as a "load") may be made of a metallic or semiconductor material. In the exemplary filter 1000, layers 1014, 1016, 1020, and 1024 are made of SiO2, and layer 1022 is made of SiN. In some embodiments, the SiO2 layers are less than 500 nm thick, and the SiN layers are less than 100 nm thick. For example, the SiO2 layers may be 50 nm to 250 nm thick, and the SiN layers may be 5 nm to 50 nm thick.

[0120] In embodiments involving multiple parallel resonators, two or more of the resonators may have electrodes of the same shape or may have electrodes of different shapes (or sizes). For example, conductive layer 732 in FIG. 7A may be circular and conductive layer 734 may be rectangular. The resonators (e.g., one or both electrodes of the resonators) may also have a graded thickness to spread the shunting effect over a range of frequencies.

[0121] The resonant frequency of the resonator can also be tuned by adjusting the lateral shape of the resonator. A larger resonator (e.g., a resonator with a large electrode surface) has a lower resistance at the resonant frequency, resulting in a stronger shunting effect. Therefore, to obtain a strong shunting effect, a large resonator with a high Q (sharp response peak and low resistance) may be the desired resonator for suppressing the LBAW sidebands.

[0122] If the width of the resonator (e.g. the width of the resonator electrodes) is narrower than a threshold width, then the resonant frequency becomes dependent on the resonator width: for such narrow resonators, the resonant frequency depends on the resonator width, and the narrower the resonator, the higher its resonant frequency (assuming type II dispersion, i.e. frequency increases with lateral wavelength shortening).

[0123] The resonator may be any shape, such as circular, rectangular, donut, etc. For example, the electrodes of the LBAW may be in the shape of a donut, forming a donut-shaped parallel resonator. The impedance of a narrow donut resonator may be peaked at more than one resonant frequency, resulting in reduced insertion loss over a wider range of frequencies compared to a single resonant frequency resonator (e.g., a rectangular resonator). It should be noted that both the resonant frequency and the resistance of the resonator at the resonant frequency should be considered when determining the shape of the resonator. For example, compared to a rectangular resonator, a donut resonator may have multiple resonant frequencies, but may have a larger resonance at each resonant frequency, resulting in a weaker shunting effect at the resonant frequency.

[0124] Although several implementations have been described, various modifications may be made without departing from the spirit and scope of the present disclosure. Accordingly, other implementations are within the scope of the following claims. [Explanation of symbols]

[0125] 100 LBAW filter 102 IDT electrode structure 110 Piezo Layer 120 Lower counter electrode 130 Reflective structure, mirror 140 Substrate 150 Input electrode, IDT electrode 150a extension 160 input ports 170 Output electrode, IDT electrode 170a extension 180 output ports 190 Interstitial area 200 Bulk Mode 210 Displacement 230 Displacement 401 Electrode 402 Electrode 410 Even Mode 420 Strange Mode 430 Frequency Difference 510 Peak 510a passband 520 Peak 520a sideband 600 Structure, Filters, Assembly 612 parallel resonator 613 Series resonator 615 Series resonator 616 parallel resonator 700 Filters 702 parallel resonator 704 parallel resonator 708 Mass load layer 710 Filter 712 parallel resonator 716 Extension 720 Filter 722 parallel resonator 724 parallel resonator 726 parallel resonator 728 parallel resonator 732 Conductive layer, mass loading layer 734 Conductive layer 736 layers 738 Mass load layer 802 Valley 804 resonant frequency 806 Skirt end 808 resonant frequency 902 Ground Via 904 Electrode 906 Electrode 908 Electrode 910 Common End 912 Common End 914 resonator 916 resonator 922 First End 924 Second End 926 Third End 932 First parallel resonator 934 Second parallel resonator 936 Conductive Wire 938 frames 942 First electrode 944 Second electrode 1002 Ground via 1004 resonator 1006 resonator 1008 resonator 1010 resonator 1014 Mass load layer 1016 Mass load layer 1018 Conductive electrode layer 1020 Mass load layer 1022 Mass load layer 1024 Mass load layer 1026 Conductive electrode layer

Claims

1. an elastic wave filter element including: comb-shaped input and output electrodes located on an upper surface of a piezoelectric layer; and a counter electrode facing the input and output electrodes and in contact with a lower surface of the piezoelectric layer; a first resonator coupled to the acoustic wave filter element, the first resonator having a first resonator electrode in contact with the top surface of the piezoelectric layer and a first resonator counter electrode in contact with the bottom surface of the piezoelectric layer, the first resonator having a first valley of a resonator impedance at a first frequency; a second resonator coupled to the acoustic wave filter element, the second resonator comprising: a second resonator electrode in contact with the top surface of the piezoelectric layer; a second resonator counter electrode in contact with the bottom surface of the piezoelectric layer; and a first mass load layer in contact with the second resonator electrode, such that the second resonator has a second valley of a resonator impedance at a second frequency different from the first frequency; Equipped with the first resonator counter electrode and the second resonator counter electrode are grounded; An acoustic wave filter device, wherein the first frequency and the second frequency are within a sideband of the acoustic wave filter element, which is a parasitic passband of the acoustic wave filter element.

2. The device of claim 1 , wherein the first and second frequencies differ by at least 3%.

3. The device of claim 1 , wherein the first resonator electrode is electrically coupled to the input electrode and the second resonator electrode is electrically coupled to the output electrode.

4. The device of claim 1 , wherein the first resonator electrode is electrically coupled to the input electrode or the output electrode, and the second resonator electrode is electrically coupled to the first resonator electrode.

5. 5. The device of claim 4, wherein the first resonator electrode has a first end facing the acoustic wave filter element, a second end contacting a side of the first resonator electrode away from the acoustic wave filter element, and a third end connecting the first end and the second end.

6. The device of claim 5 , wherein the second resonator electrode is disposed adjacent the second end of the first resonator electrode.

7. The device of claim 5 , wherein the second resonator electrode is disposed adjacent the third end of the first resonator electrode.

8. The device of claim 4 , wherein the first and second resonator electrodes are electrically coupled by sharing a common end.

9. The device of claim 4 , wherein the first and second resonator electrodes are electrically coupled by a conductive line spanning a gap between the first and second resonator electrodes.

10. 2. The device of claim 1, further comprising: a third resonator coupled to the acoustic wave filter element, the third resonator comprising: a third resonator electrode in contact with the top surface of the piezoelectric layer; a third resonator counter electrode in contact with the bottom surface of the piezoelectric layer; the first mass load layer in contact with the third resonator electrode; and a second mass load layer in contact with the first mass load layer, such that the third resonator has a third valley in a resonator impedance at a third frequency different from the first and second frequencies.

11. The device of claim 10 , wherein the second mass load layer is disposed adjacent to the first mass load layer.

12. The device of claim 11 , wherein the first mass load layer comprises a silicon oxide layer.

13. The device of claim 12 , wherein the second mass load layer comprises a silicon nitride layer.

14. 11. The device of claim 10, further comprising a fourth resonator coupled to the acoustic wave filter element, the fourth resonator comprising a fourth resonator electrode in contact with the top surface of the piezoelectric layer and a fourth resonator counter electrode in contact with the bottom surface of the piezoelectric layer.

15. The device of claim 14 , wherein the fourth resonator has a fourth valley in a resonator impedance at the first frequency.

16. The device of claim 1 , wherein the first resonator electrode is a top layer of the first resonator.

17. The device of claim 1 , wherein the first mass load layer does not cover the first resonator electrode.

18. 2. The device of claim 1 , wherein a first portion of the first mass load layer is disposed in contact with the first resonator electrode and a second portion of the first mass load layer is disposed in contact with the second resonator electrode, the first portion and the second portion having different thicknesses.

19. 2. The device of claim 1 , wherein the counter electrode, the first resonator counter electrode, and the second resonator counter electrode of the acoustic wave filter element are provided by a common counter electrode that continuously spans a first resonator and a second resonator of the acoustic wave filter element.

20. The device of claim 1 , wherein the input electrode, output electrode, first resonator electrode, and second resonator electrode are provided by separate portions of a same electrode layer in contact with the top surface of the piezoelectric layer.

21. 2. The device of claim 1, wherein the thickness of the piezoelectric layer and the gap width between the input and output electrodes are such that application of a high frequency voltage between the input and counter electrodes produces symmetric and asymmetric thickness-extensional acoustic resonance modes in the piezoelectric layer.

22. The device of claim 1 , wherein the acoustic wave filter element is a laterally acoustically coupled bulk acoustic wave (LBAW) filter.

23. an acoustic wave filter element including an electrode located on an upper surface of a piezoelectric layer and a counter electrode located on a lower surface of the piezoelectric layer and facing the electrode; a first resonator coupled to the acoustic wave filter element, the first resonator having a first resonator electrode in contact with the top surface of the piezoelectric layer and a first resonator counter electrode in contact with the bottom surface of the piezoelectric layer, the first resonator having a first valley of a resonator impedance at a first frequency; a second resonator coupled to the acoustic wave filter element, the second resonator comprising: a second resonator electrode in contact with the top surface of the piezoelectric layer; a second resonator counter electrode in contact with the bottom surface of the piezoelectric layer; and a first mass load layer in contact with the second resonator electrode, such that the second resonator has a second valley of a resonator impedance at a second frequency different from the first frequency; Equipped with the first resonator counter electrode and the second resonator counter electrode are grounded; An acoustic wave filter device, wherein the first frequency and the second frequency are within a sideband of the acoustic wave filter element, which is a parasitic passband of the acoustic wave filter element.

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