Loaded series resonator for tuning the frequency response of an acoustic wave resonator

Abstract

An acoustic wave filter device (710) is disclosed. The device includes an acoustic wave filter element (100) and a first resonator (702) and a second resonator (712) coupled to the acoustic wave filter element. The acoustic wave filter element includes an interdigitated input electrode (150) and an output electrode (170) located on the top surface of a piezoelectric layer (110). Each of the first resonator and the second resonator includes a top electrode (732, 734) on the top surface of the piezoelectric layer and a bottom electrode (736, 738) on the bottom surface of the piezoelectric layer. At least one of the electrodes of each of the first resonator and the second resonator is electrically connected to the acoustic wave filter element. The first resonator has a first notch in the resonator impedance at a first frequency. The second resonator includes a first mass loading layer (750) on the second resonator electrode so that the second resonator has a second notch in the resonator impedance at a second frequency different from the first frequency.

Description

Technical Field

[0001] The present invention relates to thin film radio frequency acoustic wave filters. Background Art

[0002] Radio frequency ("RF") components such as resonators and filters based on microacoustic and thin film technologies are widely used in radio applications such as mobile phones, wireless networks, satellite positioning, etc. Their advantages over lumped element, ceramic, and electromagnetic counterparts include smaller size and mass production capability. Summary of the invention

[0003] This specification describes techniques for bandpass lateral 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.

[0004] LBAW can be used as a bandpass filter. The bandpass filter may include one or more undesired (or parasitic) sidebands. Embodiments of the present disclosure provide techniques for suppressing undesired sidebands by adding one or more acoustic resonators in series with the LBAW.

[0005] The LBAW filter is formed by a piezoelectric layer sandwiched between two pairs of electrodes. One electrode in each pair of electrodes is located on the top surface of the piezoelectric layer and forms the input or output of the LBAW. The input electrode and the output electrode are separated by a certain gap. Each pair of electrodes also has a counter electrode located on the bottom surface of the piezoelectric layer. By applying an AC voltage to the piezoelectric layer of the input resonator, a mechanical resonance is formed in the piezoelectric layer below the input electrode. The thickness of the piezoelectric layer and the gap between the electrodes can be designed so that the mechanical resonance is coupled to the output resonator across the gap. The frequency range in which this coupling occurs determines the achievable bandwidth (or passband width) for the LBAW filter.

[0006] The foregoing and other embodiments may each optionally include one or more of the following features, alone or in combination.

[0007] In general, an innovative aspect of the subject matter described in this specification can be embodied in an acoustic wave filter device, which includes an acoustic wave filter element, a first resonator, and a second resonator. The acoustic wave filter includes an input electrode and an output electrode located on the top surface of a piezoelectric layer. The first resonator includes a first resonator top electrode on the top surface of the piezoelectric layer and a first resonator bottom electrode on the bottom surface of the piezoelectric layer. The first resonator has a first notch in the resonator impedance at a first frequency, wherein one of the top electrode and the bottom electrode of the first resonator is electrically connected to the acoustic wave filter element. The second resonator is coupled to the acoustic wave filter element and includes a second resonator top electrode on the top surface of the piezoelectric layer, a second resonator bottom electrode on the bottom surface of the piezoelectric layer, and a first mass load layer on the second resonator top electrode, so that the second resonator has a second notch in the resonator impedance at a second frequency different from the first frequency. One of the top electrode and the bottom electrode of the second resonator is electrically connected to the acoustic wave filter element.

[0008] The first frequency and the second frequency may be within a sideband of a resonator impedance of the acoustic wave filter element.The first frequency and the second frequency may differ by at least 1%.

[0009] In some implementations, the first resonator bottom electrode is electrically coupled to the input electrode, and the second resonator bottom electrode is electrically coupled to the output electrode.

[0010] The first resonator top electrode may be the uppermost layer of the first resonator.

[0011] In some embodiments, the first mass loading layer does not cover the second resonator top electrode.

[0012] The acoustic wave filter device may include a second mass loading layer on the first resonator top electrode. The first mass loading layer and the second mass loading layer may be the same material, but have different thicknesses. The first mass loading layer and the second mass loading layer may be different materials with different densities and / or different hardnesses. In some embodiments, the first mass loading layer does not cover the second resonator top electrode. In some embodiments, the first mass loading layer covers the first resonator top electrode, and the second mass loading layer does not cover the second resonator top electrode.

[0013] The first mass loading layer may be a different material than the second resonator top electrode.

[0014] The first mass loading layer may be the same material as the second resonator top electrode.The first resonator top electrode and the second resonator top electrode may have different thicknesses.

[0015] In some embodiments, the first resonator bottom electrode is electrically connected to the acoustic wave filter element through a first conductive via extending through the piezoelectric layer. The second resonator bottom electrode can be electrically connected to the acoustic wave filter element through a second conductive via extending through the piezoelectric layer.

[0016] The input electrode, the output electrode, the first resonator electrode and / or the second resonator electrode may be provided by separate portions of the same electrode layer on the top surface of the piezoelectric layer.

[0017] The thickness of the piezoelectric layer and the gap width between the input electrode and the output electrode may be such that application of a radio frequency voltage between the input electrode and the counter electrode will create symmetric and antisymmetric acoustic thickness extensional resonant modes in the piezoelectric layer.

[0018] The acoustic wave filter device may include a counter electrode on a bottom surface of the piezoelectric layer below the interdigitated input and output electrodes.The acoustic wave filter element may be a Laterally Acoustically Coupled Bulk Acoustic Wave (LBAW) filter.

[0019] One innovative aspect of the subject matter described herein can be embodied in an acoustic wave filter device comprising: an acoustic wave filter element comprising an interdigitated input electrode and an output electrode located on a top surface of a piezoelectric layer; and a resonator comprising a resonator top electrode on the top surface of the piezoelectric layer and a resonator bottom electrode on the bottom surface of the piezoelectric layer. The resonator is electrically connected in series to the acoustic wave filter element. The resonator has a notch in the resonator impedance at a first frequency that is outside a passband of the acoustic wave filter element.

[0020] The resonator may include a mass loading layer on a top electrode of the resonator, wherein a thickness of the mass loading layer affects the change in the first frequency. The resonator may be electrically connected to the acoustic wave filter element via an electrical connection between the top surface of the resonator and one of the input electrode and the output electrode of the acoustic wave filter element.

[0021] The subject matter described in this specification can be implemented in specific embodiments to achieve one or more of the following advantages. The embodiments described herein improve the overall / broadband / stopband response of a vocal bandpass filter (e.g., an LBAW filter) by suppressing parasitic sidebands. Suppression can be performed in a specific frequency or within a frequency range. In addition, the manufacture of the LBAW filter described herein can be simpler because the LBAW filter uses only a single piezoelectric layer compared to the two piezoelectric layers in a vertically stacked bulk acoustic wave (BAW) coupled resonator filter. They can also operate at higher frequencies as surface acoustic wave (SAW) filters because their operation is more determined by the thickness of the piezoelectric layer rather than the size of the interdigital transducer (IDT) electrode. In some embodiments, LBAW filters can also achieve a wider bandwidth than BAW filters. Compared with the case of nearly 10 lithographic patterning steps in BAW, the LBAW filter can be performed as a filter with a single lithographic patterning step and can operate in a smaller size without the need for a reflector in SAW.

[0022] The details of one or more embodiments of the subject matter of this specification 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

[0023] Figure 1A is a schematic perspective view of a securely mounted LBAW filter.

[0024] Figure 1B is a schematic perspective view of a self-supporting LBAW filter.

[0025] Figure 1C is a schematic plan view of an interdigital transducer ("IDT") electrode structure.

[0026] Figure 2A -B is a schematic diagram of two types of propagating plate wave modes in the LBAW piezoelectric layer.

[0027] Figure 3 is the dispersion curve of an exemplary LBAW.

[0028] Figure 4A Schematic diagram of the two resonance modes in LBAW.

[0029] Figure 4B is an illustrative transmission response of the LBAW as a function of frequency.

[0030] Figure 5 is the experimental transmission curve of LBAW as a function of frequency.

[0031] Fig. 6A -B are schematic cross-sectional and plan views, respectively, of a circuit including a LBAW connected to an acoustic resonator structure.

[0032] Figure 6C yes Fig. 6A -B is a circuit diagram of the circuit.

[0033] Fig. 7A and Figure 7B A top view and a side view, respectively, of a first example bandpass filter including an acoustic resonator in series with a LBAW filter are illustrated.

[0034] Figure 7C Picture shows FIG. 7A to FIG. 7B Connections between components of a bandpass filter.

[0035] Fig.7D and Fig. 7E A top view and a side view, respectively, of a second example bandpass filter including an acoustic resonator in series with a LBAW filter are illustrated.

[0036] Figure 7F Picture shows FIG. 7D to FIG. 7E Connections between components of a bandpass filter.

[0037] Figure 7G and Figure 7H A top view and a side view, respectively, of a third example bandpass filter including an acoustic resonator in series with a LBAW filter are illustrated.

[0038] Fig.7I Picture shows Figures 7G to 7H Connections between components of a bandpass filter.

[0039] Fig. 8A and Figure 8B Illustrated are top and side views, respectively, of an example bandpass filter including an acoustic resonator with different mass loadings in series with a LBAW filter.

[0040] Fig. 9A and Fig. 9B Illustrated are top and side views, respectively, of another example bandpass filter including an acoustic resonator with different mass loadings in series with a LBAW filter.

[0041] Fig. 9C Picture shows FIG. 9A to FIG. 9B Connections between some components of a bandpass filter.

[0042] Fig. 10A and Fig. 10B Illustrated are example effects of the size of a resonator on the impedance and resistance of the resonator at resonant and anti-resonant frequencies.

[0043] Like reference numbers and designations in the various drawings indicate like elements. DETAILED DESCRIPTION

[0044] Figure 1A , Figure 1C An example of an LBAW filter (or resonator) 100 is shown having input 150 and output 170 electrodes having an interdigitated geometry (also referred to as an "interdigitated transducer" or "IDT" LBAW). The LBAW filter 100 includes a piezoelectric ("piezo") layer 110 having a thickness d, an IDT electrode structure 102 located on the top surface of the piezoelectric layer, and a bottom counter electrode 120 located on the bottom surface of the piezoelectric layer. The IDT electrode structure ("IDT") 102 includes two comb-shaped 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, which provide the "teeth" or "teeth" or "fingers" of a "comb". The electrode 150 and the counter electrode 120 form an input resonator with the piezoelectric layer 110. The electrode 170 and the counter electrode 120 form an output resonator with the piezoelectric layer 110.

[0045] Acoustic vibrations are created in the piezoelectric layer 110 by applying an oscillating (or alternating) input voltage across the IDT electrode 150 and the bottom counter electrode 120 at the input port 160. The applied voltage is converted into mechanical (e.g., acoustic) vibrations via the piezoelectric effect. Under resonant conditions (e.g., with certain acoustic resonance modes, as further described below), such vibrations can create standing waves under the input electrode 150 and produce evanescent waves (with exponentially decaying amplitudes) in the gap region 190. With the vibration frequency and gap width G appropriately selected, the standing wave can mechanically couple from the piezoelectric region under the electrode 150 to the piezoelectric region under the electrode 170 across the gap 190, and create a similar standing wave in the piezoelectric layer 110 under the electrode 170. The standing wave under the electrode 170 produces an output signal voltage having the same frequency at the output port 180 via the inverse piezoelectric effect. The frequency range in which such coupling occurs in 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 100 as well as the spacing can be tuned to alter the RF response and passband of the filter.

[0046] The reflective structure 130 can be used to isolate vibrations in the piezoelectric layer 110 from the underlying substrate 140 and prevent acoustic leakage. The thin layer structure can be, for example, composed of alternating high and low acoustic impedance ("Z ac”) material layers. In some embodiments, the thickness of these layers can be designed so that frequencies at and close to the passband of the LBAW filter are reflected back to the piezoelectric layer 110 and all other frequencies pass through the mirror.

[0047] In some embodiments, the LBAW 100 does not directly cover the substrate 140 (eg, Figure 1A ), but is self-supporting, such as Figure 1B In this arrangement, the substrate 140 and the mirror 130 are replaced by an air gap, wherein the piezoelectric portion extending laterally beyond the region where the LBAW 100 is fabricated is supported by the substrate 140 .

[0048] In some embodiments, Figure 1C As shown in FIG. 1 , extensions 150a and 170a are rectangular and have a width W, a length L, and are spaced apart 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 K.

[0049] although Figure 1C A rectangular interdigitated electrode 150 / 170 with parallel extensions 150a / 170a of the same geometry and spacing G is shown, but other electrode geometries are also contemplated. Design considerations include the gap between the electrodes, the length of the electrodes, and the number (if any) and shape of the electrode extensions. The gap can be used to control the coupling between the input electrode and the output electrode. Longer electrodes can also increase coupling. The number of extensions K can be used to control bandwidth and / or increase coupling and provide impedance matching. In some embodiments, the electrode is composed of a rectangular strip with two or more extensions (e.g., K≥2). For example, each extension can be a rectangular strip. In some embodiments, the electrodes are concentric circles or spirals with a common axis.

[0050] The piezoelectric layer 110 may be formed of a variety of piezoelectric materials. Exemplary materials include ZnO, AlN, CdS, PZT, LiNbO3, LiTaO3, quartz, KNN, BST, GaN, Sc alloyed AlN, or the foregoing materials doped or alloyed with additional elements. Doping may be used to improve or adjust the electromechanical properties of the piezoelectric layer 110. As further described below, the piezoelectric layer thickness d is selected so that a thickness extension mode of a frequency close to the desired bandwidth of the LBAW filter is generated in the piezoelectric layer. In some embodiments, the piezoelectric layer thickness d is λ z 20% to 50% or λ z 30% to 45%, of which λ z is the wavelength of the piezoelectric vibration in the thickness direction. In some embodiments, d is 1500nm to 2500nm or 1800nm ​​to 2200nm.

[0051] The thin film IDT 102 can be made of various materials. In some embodiments, the IDT electrodes 150 and 170 are metals. For example, the electrode material includes Al, Mo, Pt, Cu, Au, Ag, Ti, W, Ir, Ru or a multilayer metal and / or a metal doped with additional materials (e.g., AlSi, AlSiCu, polysilicon, etc.). Doping can be used to improve or adjust the electrical or mechanical properties of the IDT.

[0052] although Figure 1A A single common counter electrode 120 is shown, but the filter 100 may include separate electrodes for the input and output resonators. Various materials are suitable for (multiple) counter electrodes (e.g., electrode 120). For example, the electrode may include a metal such as Al, Mo, Pt, Cu, Au, Ag, Ti, W, Ir, Ru, or multiple layers of metal and / or metal doped with additional materials (e.g., AlSi, AlSiCu, etc.) Doping may be used to improve or adjust the IDT electrical or mechanical properties. For example, the electrode may be Ti+Mo, Ti+W, AlN+Mo, or Al+W. The electrode may be multilayered. The electrode may have a special thin seed layer deposited beneath the electrode.

[0053] The reflective structure 130 may be composed of alternating layers of different materials. For example, the reflective structure 130 may include alternating layers of two of the following: tungsten (W), SiO2, silicon (Si), carbon (C). For example, the high acoustic impedance layer includes W, Mo, Ir, Al2O3, diamond, Pt, AlN, Si3N4. The low acoustic impedance layer may include SiO2, glass, Al, Ti, C, a polymer, or a porous material. The Si layer provides an intermediate acoustic impedance. Various materials are suitable for the substrate 140, such as Si or SiO2 or glass, sapphire, quartz. The substrate 140 material may have a high resistivity. 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 Si wafer with a thickness of 675 μm may be purchased and thinned to achieve a desired device thickness, for example, for a mobile platform.

[0054] Modeling the acoustic response of the LBAW 100 can provide guidance on how to tune the design parameters of the individual elements of the structure to achieve a desired bandpass characteristic. For example, the LBAW 100 can be designed to have a resonant mode at a specific frequency. In general, the geometries of various LBAW 100 components can be selected to achieve various acoustic characteristics. The LBAW 100 characteristics may depend on a combination of these geometries, which may not be independent of each other.

[0055] In the piezoelectric layer 110, different bulk acoustic vibration modes may occur at different excitation frequencies f of the input voltage (e.g., at port 160). Acoustic vibrations in the piezoelectric layer 110 may propagate laterally as Lamb waves (or plate waves), where the particle motion is in a plane containing the wave propagation direction and the plate normal (e.g., Figure 1A The z-axis in the FIG. 2A to FIG. 2B Two such modes are shown in FIG. Figure 2A , the thickness extensional (TE or longitudinal) bulk mode 200 has particle displacements 210 that are primarily perpendicular to the direction of propagation (in the z-direction). Figure 2B , the second-order thickness shear (TS2) bulk mode 220 has a particle displacement 230 that is 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 piezoelectric layer 110 is equal to half the wavelength λ z (ignoring the thickness of the electrode 150 / 170); in other words, when When N=1 and higher harmonics, the lowest resonance occurs after N=1 and higher harmonics, where N is an integer greater than one. N indicates the order of resonance. For TE1 mode, As discussed further below, the width W of the electrodes and the gap G between the electrodes can be designed to form a lattice having a specific lateral wavelength λ || The TE1 mode standing wave can couple across the gap G through its evanescent tail to create two mechanical resonant modes.

[0056] The acoustic characteristics of the LBAW resonator 100 can be described by a dispersion curve. Figure 3 , an example dispersion curve of the LBAW 100 shows the transverse wave number k of vibration as a function of the voltage input frequency f || ,in In the figure, a first-order longitudinal (thickness extension TE1) vibration mode and a second-order thickness shear (TS2) mode are shown. In the first-order longitudinal vibration mode, the combined thickness d of the piezoelectric layer and the thickness of the (multiple) electrodes 150 or 170 include approximately half the wavelength λ of the body vibration. z / 2; In the second-order thickness shear mode, the body vibration is mainly perpendicular to the thickness direction ( Figure 2B z axis in the middle) and a sound wavelength λ z The TE1 mode is the darker portion of each dispersion curve, and the TS2 mode is the lighter region of each dispersion curve. The top curve (“No Electrode”) represents the dispersion characteristics of the piezoelectric layer below gap 190. The bottom curve (“Electrode”) represents the dispersion characteristics of the piezoelectric layer below electrodes 150 / 170 (also referred to as the active region). More specifically, the “Electrode” curve is plotted against k ||= 0, the TE1 mode has a thickness of about λ contained in the combined thickness of the electrode 150 or 170 and the piezoelectric layer. z / 2. This is approximate because the wave can extend into the Bragg reflector. || = 0 line shows the intersection of the "electrode-free" curve at about λ z / 2 contains modes in the combined thickness of only the bottom electrode and the piezoelectric layer. This type of dispersion (where the TE1 mode has increasing k with increasing frequency f) || ) is called type 1. The intersection k between the electrode area and the non-electrode area || = 0 frequency determines a hard limit on the achievable bandwidth of the filter.The gap width G, the electrode width W and the number of extensions K can be used to vary the coupling strength within the limits set by the dispersion differences.

[0057] In some embodiments, the LBAW 100 can be designed to produce type 1 dispersion. For example, a piezoelectric layer 100 material can be selected in which type 1 dispersion can occur. For example, ZnO can be used. In another example, appropriate design of the acoustic Bragg reflector 130 can help achieve type 1 dispersion. For example, using aluminum nitride ("AIN") for the piezoelectric layer 110 can generally produce type 2 dispersion, where the TE1 mode appears as having an initially decreasing k with increasing frequency f rather than monotonically. || , then with increasing k as the frequency f increases || (and Figure 3 1, but TE1 and TS2 are interchanged). However, in some embodiments, with an appropriately designed reflective structure 130 (e.g., an acoustic Bragg reflector), the LBAW 100 can use AlN in the piezoelectric 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," Proceedings of the IEEE International Symposium on Ultrasonics, 2005, pp. 1175-1178.

[0058] exist Figure 3 In, k || Positive values ​​of k represent real wave numbers (propagating waves) and negative k ||The value corresponds to the imaginary wave number (evanescent wave). In order to produce resonance, the acoustic energy must be captured inside the LBAW resonator structure. In the thickness (z-axis) direction, isolation from the substrate (using the reflective structure 130) can be used for energy capture. In the lateral direction, energy capture can occur when an evanescent wave is formed outside the electrode area (for example, on the "electrode-free" curve). In order to obtain resonant coupling between the two resonators of the LBAW (for example, electrodes 150 / 170 and 120), a standing wave of the TE1 mode is formed in the active area of ​​the piezoelectric layer (under the electrode), while an evanescent wave is formed in the "electrode-free" area. In other words, k || The curve for TE1 "electrode" is positive, while the curve for TE1 "no electrode" is negative. Figure 3 , which occurs in the frequency range labeled "trapping range". Energy trapping can be more easily achieved in Type I dispersion. Without wishing to be bound by theory, as the monotonically increasing dispersion curve (e.g. Figure 3 The thick TE1 line in the figure, for an "electrode", there is a single imaginary wave number available at a single frequency within the capture range, or a single real wave number above the capture range. The former means that TE1 does not propagate outside the electrode, while the latter means that TE1 can couple to a propagating wave outside the electrode and thus "leak". Type 2 dispersion can be described by a similar curve, but with the TE1 and TS2 curves interchanged. The fact that the curve in Type 2 is non-monotonic means that at a given frequency, there can be several real wave numbers. Having several wave numbers for a frequency means that a propagating wave is available outside the electrode, which can lead to "leakage".

[0059] FIG. 4A to FIG. 4B The relationship between the standing wave resonance mode and the LBAW band gap is shown in the figure. Figure 4A , a portion of the LBAW 100 includes two adjacent electrodes 401 and 402 of width W (e.g. Figure 1A The bandpass frequency response of the LBAW 100 is formed by two (or more) transverse standing resonant modes 410 and 420 that occur in the structure. When plate waves are reflected from the edges of the electrodes 401 and 402, transverse standing wave resonances may occur. In the even mode resonance 410, the piezoelectric layers under the two electrodes 150 and 170 vibrate in phase, while in the odd mode resonance 420, the phases are opposite. When the total width of the structure is approximately equal to the transverse wavelength λ of the mode || Half: When , even transverse standing wave resonance may occur.

[0060] In the limit of infinitesimal gap width G, λ even Approach the total width from below. Figure 4A As shown in evenIt becomes smaller when G becomes larger, and becomes larger when G becomes larger. In the case of small gap (such as zero gap), λ even close to 4W, while in the case of large gaps, λ even Close to 2W. When the width of the electrode is roughly equal to the lateral wavelength λ of the mode || Half: When , odd transverse standing wave resonance may occur.

[0061] See also Figure 4B , the even 410 mode and the odd 420 mode are shown as transmission peaks as a function of input frequency f for a LBAW with type 1 dispersion. For type 1 dispersion, the even mode 410 has a longer wavelength and is lower in frequency than the shorter wavelength odd mode 420. 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 size of the IDT resonator 102. The acoustic coupling strength can be defined in terms of the (resonant) frequency difference between the even (symmetric) resonance and the odd (antisymmetric) resonance: where f symm and f asymm are the symmetric characteristic frequency and the antisymmetric characteristic frequency respectively, and f0=(f symm +f asymm ) / 2 is the center frequency between the two modes.

[0062] In some embodiments, increasing the number of extensions (e.g., 150a and 170a) in each electrode (e.g., 150 and 170) can increase the frequency difference between the even mode and the odd mode in the LBAW, and thus increase the bandwidth. This effect can be caused by the fact that the lateral wavelength of the odd mode can depend on the periodicity of the electrode structure (e.g., the width W), while the even mode can depend on the entire width of the structure (e.g., adding up all the widths W and the 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 lateral acoustic wave at the even mode resonant frequency is || Close to or slightly shorter than:

[0063]

[0064] However, the odd transverse standing wave resonance in this structure is close to or slightly larger than:

[0065]

[0066] Additionally or alternatively, in some embodiments, the total width of the structure, K·W+K·G, may be such that the highest order mode captured in the structure is the desired odd mode resonance. For example, K may be 31, W may be 3 μm, and G may be 2 μm.

[0067] 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 the electrode extensions may be between 50 μm and 2000 μm or between 70 μm and 500 μm.

[0068] In some embodiments, the gap G is selected to allow coupling of the evanescent tail of the standing wave formed under the electrodes 150 and 170. For example, the gap G between the electrode extensions may be between 0.1 μm and 10 μm or between 2 μm and 5 μm.

[0069] In some embodiments, the electrodes 150 and 170 topology can be designed so that the gap width G provides good enough coupling between the electrode extensions to create a single even mode 410 across the entire width of the structure. For example, the gap width G can be the decay length of the evanescent acoustic wave (i.e., the original amplitude A in the gap at the desired even resonant mode). o The amplitude is A = A0•e -1 The gap to G can be optimized. Reducing the gap to too small a width (1) can eventually pull the even and odd modes too far from each other, creating a dip in the passband, (2) can result in a reduced coupling coefficient for the odd mode, or (3) can increase capacitive feedthrough between fingers, resulting in poor out-of-band attenuation.

[0070] In some embodiments, the gap width G can be defined relative to the piezoelectric layer thickness d. For example, G can be designed to be 10% to 300% of d or 25% to 150% of d.

[0071] In some embodiments, the width W of the electrode extension may be between 0.1 μm and 30 μm or between 2 μm and 5 μm. In some embodiments, W may be designed to obtain a desired odd-mode resonant frequency λ. odd The wavelength of the transverse sound wave is λ || .

[0072] In some embodiments, the electrode width W is designed so that multiple half wavelengths cannot fit into the electrode width. For example, W can be designed to be smaller than the wavelength λ of the transverse acoustic wave in the desired odd resonant mode. || , for example, where λ || =λ odd .

[0073] In some embodiments, the thicknesses of the various LBAW 100 components may be selected to achieve various acoustic properties, and these thicknesses may be interdependent. For example, the piezoelectric layer 110 thickness d (minimum and maximum values) may first be determined relative to the acoustic wavelength in the piezoelectric material (λ) at the operating frequency f. In some embodiments, the thicknesses (minimum and maximum values) of the other LBAW 100 layers may be selected based on the selection of the piezoelectric thickness d. For example, the combined thickness of the electrodes (including the counter electrode 120) and the piezoelectric layer may be selected to be approximately half the wavelength of the mode being used, such as longitudinal bulk waves for thickness extensional modes. The fundamental mode (first mode, i.e., first harmonic) with N=1 may allow for greater coupling, but N>1 modes are also possible. For example, the thicknesses of the electrodes 150 and 170, the bottom electrode 120, and the reflective structure 130 may be defined as a percentage of the piezoelectric layer thickness d. In some embodiments, once all thicknesses are selected, the geometry of the electrode extensions 150a and 170a, such as the number K, width W, gap G, and length L, may be tuned to match the LBAW 100 electrical impedance to the system impedance. Without wishing to be bound by theory, impedance matching can help avoid losses and reflections in a system.

[0074] In some embodiments, the thickness of electrodes 150 and 170 is between 1% and 30% of d, or 2% and 25% of d, or 3% and 15% of d.

[0075] In some embodiments, the thickness of the bottom electrode 120 is between 5% and 50% of d, or 10% and 30% of d, or 10% and 20% of d.

[0076] In some embodiments, when the reflective structure 130 is a Bragg reflector, the alternative layers of the reflector can be designed to obtain the desired reflectivity of the passband wavelength. For example, the thickness of each layer can be equal to, less than, or greater than the acoustic wavelength λ in the thickness direction. z In some embodiments, a single layer in a Bragg reflector may be 15% to 80% of d or 20% to 70% of d.

[0077] The mass load of the IDT 102 determined by the thickness and material of the electrodes 150 and 170 may be designed so that the k of the TE1 mode of the electrode region and the TS2 mode of the outer electrode region is || = 0 frequency is smaller. Without wishing to be bound by any particular theory, when the frequency difference between the TS2 mode of the outer region and the TE1 mode of the electrode region is smaller, the capture range is larger. More specifically, the k of the TS2 mode of the outer region is ||=0 frequency can be 95% to 99% of the TE1 cutoff frequency of the electrode region. || =0 frequency is designed to be relatively large, for example, 5% to 15% of the TE1 mode cutoff frequency of the electrode region, for example, 6.5% to 7.5%.

[0078] According to some embodiments of the present invention, k of the TS2 mode in the outer zone || = 0 frequency is greater than or equal to 98%, or between 98% and 99.5%, or 98.9% of the cutoff frequency of the electrode region TE1. Similarly, the frequency of the electrode region TE1 and the external region TS2 k is expressed as || =The frequency distance of the frequency difference between the 0 frequency: It should be small, for example about 1%. As an 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%.

[0079] Figure 5 A plot of insertion loss IL (in decibels) versus frequency f for an exemplary LBAW 100 is shown. The plot shows two passbands, with peak 510 corresponding to TE1 waves and peak 520 corresponding to TS2 waves. As discussed above, the width of each passband is determined by the frequency difference between the even mode and the odd mode for the corresponding type of wave. Here, the TS2 mode corresponds to sideband 520a (also referred to herein as "TS2 passband"), and the TE1 mode corresponds to passband 510a (also referred to herein as "TE1 passband"). In some embodiments, the LBAW 100 is designed to suppress the peak 520 corresponding to the TS2 mode while maintaining the characteristics of the peak 510 corresponding to the TE1 mode. Without wishing to be bound by any particular theory, TE1 mode operation can be selected because the piezoelectric thin film material has a stronger electromechanical coupling in the thickness direction. In other words, the TE1 longitudinal mode vibration is more efficiently coupled to the electrical excitation across the thickness of the piezoelectric layer 110.

[0080] In some embodiments, the LBAW 100 can be designed to have a passband of the TE1 mode between 0.5 GHz and 10 GHz or between 1 GHz and 4 GHz. In some examples, the TE1 passband is between 1.8 GHz and 3.7 GHz. The limitation of the passband can include design considerations. For example, the size of the device can grow very large or very small. Too large a size may take up too much space or lead to low efficiency. Since thin and narrow electrodes cause resistance and loss, too small a size may degrade performance. In some embodiments, the LBAW 100 can be designed to have a TE1 passband width 510a of 0.5 to 15% relative to the center frequency (e.g., 10% or 5% or 2% or 1% relative to the center frequency). In some embodiments, the insertion loss at the passband is better than -7 dB, such as -7 dB to -0.5 dB or -5 dB to -0.5 dB.

[0081] LBAW can be used as a bandpass filter. The IDT electrode of LBAW can be designed to couple the driving electrical signal to the desired fundamental TE1 mode. The effective coupling leads to Figure 5 170a. However, the coupling also results in one or more sidebands similar to the TE1 passband of 510a. Sideband 520a can be at a lower frequency than passband 510a and can be 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). The extensions produce an asymmetric electric field in the thickness direction of the piezoelectric, and the asymmetric electric field couples to the TE1 mode and the TS2 mode.

[0082] Embodiments of the present disclosure provide techniques for suppressing LBAW sidebands created by TS2 modes. Embodiments suppress the sidebands by connecting acoustic resonators to the LBAW. At least one of the acoustic resonators has an impedance notch at a resonant frequency within the sideband bandwidth. As described in further detail below, the impedance notch results in an increase in the insertion loss of the LBAW at the resonant frequency and results in an overall increase in the insertion loss in the sideband.

[0083] Acoustic resonators can be added in series or in parallel with the LBAW 100. For example, see Fig. 6A -B, cross-sectional and plan views of structure 600 including LBAW 100 connected to resonators 612 , 613 , 615 , and 616 . Figure 6C The corresponding circuit diagram of the structure 600 is shown. In the structure 600, the piezoelectric layer 110 is common to the LBAW 100 and all connected filters. Figure 6B100, parallel resonator 612 and series resonator 613 are located before the input port 160 of LBAW 100. Series resonator 615 and parallel resonator 616 are located after the output port 180 of LBAW 100. In parallel resonators 612, 616, the lower electrode is grounded. In series resonators 613, 615, the signal crosses the piezoelectric layer 110 to enter the lower non-grounded electrode.

[0084] Embodiments with one or more series resonators can be designed so that the resonant frequency of the series resonator falls within the passband frequency of the sideband and suppresses the sideband. An acoustic resonator (e.g., a BAW / FBAR resonator) has a very high impedance at its anti-resonant frequency. This high impedance prevents the drive electrical signal from passing through and reduces signal transmission through the filter. Therefore, resonators 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 signal transmission and suppress the sideband of the LBAW.

[0085] Embodiments with one or more parallel resonators can be designed so that the resonant frequency of the parallel resonator falls within the passband frequency of the sideband and suppresses the sideband. Acoustic resonators (e.g., BAW / FBAR resonators) have very low impedance at their resonant frequencies. This low impedance shunts the drive electrical signal to the ground and reduces signal transmission through the filter. Therefore, resonators with one or more resonant frequencies within the sideband of the LBAW filter can be added in parallel to the LBAW filter to reduce signal transmission at one or more resonant frequencies and suppress the sideband of the LBAW. 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 and / or by (ii) connecting one or more parallel resonators to the LBAW filter.

[0086] The resonant and anti-resonant frequencies of a resonator can be tuned by adjusting the mass loading of the resonator. Mass loading can be achieved by applying one or more mass loading layers on one or both electrodes of the resonator. The mass loading layer can be made of a different material or the same material as the underlying electrode. In the latter case, the two resonators can be considered as electrodes with different thicknesses.

[0087] Different mass loading between two resonators can be achieved by i) applying a mass loading layer on the electrodes of one resonator but not on the electrodes of the other resonator, ii) applying different thicknesses of the same (or different) material(s) on the two corresponding electrodes of the two resonators and / or iii) by applying different material layers on the two corresponding electrodes of the two resonators. In addition, different mass loading between two resonators can be achieved by making the electrodes of the two resonators have different thicknesses.

[0088] Between two resonators with mass loading layers made of the same material, the resonator with the thicker mass loading layer has more mass and therefore has a lower anti-resonance frequency than the resonator with the thinner electrodes. Therefore, the anti-resonance frequency can be adjusted by adding or removing loads on top of the electrodes of the resonator.

[0089] A series resonator (i.e., a resonator in series with the LBAW) can be designed to have an anti-resonance frequency within the frequency range of one or more sidebands to be suppressed (e.g., the frequency range of sideband 520a). Also, multiple series resonators with different anti-resonance frequencies can be designed to suppress sidebands over a wider frequency range (compared to series resonators with the same resonant frequency) or to suppress multiple sidebands.

[0090] 7A to 9B An example bandpass filter including an acoustic resonator in series with a LBAW 100 is illustrated. FIG. 7A to FIG. 7B , FIG. 8A to FIG. 8B as well as FIG. 9A to FIG. 9B A top view and a cross-sectional view of bandpass filters 700, 710, and 720 are illustrated, respectively. The filters 700, 710, and 720 may be generally identical, except that the filters 700, 710, and 720 may differ in one or more mass loading layers in one or more of their series resonators (also referred to herein as "resonators"). The filters 700, 710, and 720 may be generally identical to the filter assembly 600, except as described. For example, the filters 700, 710, and 720 may optionally omit the parallel resonators 612, 616, but may still include such parallel resonators between the LBAW filters.

[0091] The filter 700 includes series resonators 702, 704 connected in series with the LBAW filter 100, the filter 710 includes series resonators 702, 712 connected in series with the LBAW filter 100, and the filter 720 includes series resonators 722, 724 connected in series with the LBAW filter 100. Each of the resonators 702, 704, 712, 722, 724 has a top electrode and a bottom electrode sandwiching the piezoelectric layer 110. The top electrode can serve as an output electrode of the filters 700, 710, 720. The resonators 702, 704, 712, 722, 724 and the LBAW 100 can share a common piezoelectric layer 110.

[0092] The LBAW filter 100 includes an IDT 102 having an input electrode 150 having an extension 152 from a common input electrode 154 and an output electrode 170 having an extension 172 from a common output electrode 174. The counter electrode 120 can be positioned on the underside of the piezoelectric layer in the same area as the extensions 152 and / or 172. Thus, in the LBAW 100, the piezoelectric layer 110 is sandwiched between the extension 150 and the counter electrode 120. The counter electrode 120 can be grounded. Although the outer edge of the counter electrode 120 is illustrated as being aligned with the inner edge of the common electrodes 154, 174, this is not required. For example, the counter electrode 120 can extend partially under the common electrodes 154, 174, in which case they form a parallel resonator, or stop the short circuit of the common electrodes 154, 174.

[0093] See also Fig. 7A , Figure 7B as well as Figure 7C , the filter 700 includes two series resonators 702, 704 respectively coupled to the input electrode 150 and the output electrode 170 of the LBAW 100. Specifically, each series resonator 702, 704 includes a corresponding conductive layer 732, 734 as a top electrode, and includes a corresponding conductive layer 736, 738 as a bottom electrode. In the series resonator 702, the piezoelectric layer 110 is sandwiched between the conductive layers 732, 736, and in the series resonator 704, the piezoelectric layer 110 is sandwiched between the conductive layers 734, 738.

[0094] Each bottom electrode is electrically coupled to a corresponding input electrode 150 and an output electrode 170. The conductive layers 736, 738 may be electrically connected to the common electrodes 154, 174, respectively. Specifically, conductive vias may be formed through the piezoelectric layer 110 to connect the input and output electrodes of the LBAW 100 to the bottom electrodes. For example, a conductive via 740a formed through the piezoelectric layer 110 may connect the common electrode 154 to the conductive layer 736. Similarly, a conductive via 742 formed through the piezoelectric layer 110 may connect the common electrode 174 to the conductive layer 738.

[0095] In addition to the LBAW 100 being connected to the series resonator 702 via the conductive connector 740b and the counter electrode 120 extending below the extension 154, FIG. 7D to FIG. 7F and FIG. 7A to FIG. 7C Connector 740B electrically connects the common electrode 154 of the LBAW 100 to the conductive layer 732 of the series resonator 702 .

[0096] In addition to the LBAW 100 being electrically connected to the series resonator 706 (which is electrically connected to the series resonator 702), FIG. 7G to FIG. 7I and FIG. 7A to FIG. 7C The series resonator is formed by the piezoelectric layer 110 sandwiched between at least a portion of the extension 154 and at least a portion of the bottom conductive layer 736. The series resonator 706 is electrically connected to the series resonator 702, for example, through the conductive layer 736.

[0097] As previously explained, the series resonators 702 and 704 (in 7A to 7I ) or both of the resonators 702, 704. To reduce the anti-resonance frequency of the resonators 702, 704, a layer providing mass loading may be deposited on top of the conductive layers 732, 734 of the respective resonators. To increase the anti-resonance frequency of the resonators 702, 704, the conductive layers 732, 734 of the respective resonators may be partially removed, i.e., thinned by etching or by manufacturing these conductive layers to have a smaller thickness.

[0098] Fig. 8A and Figure 8B A bandpass filter 710 is shown having a series resonator 702 and a series resonator 712. Specifically, the mass loading of the two resonators 702, 712 is different so that the two resonators 702, 704 have different anti-resonance frequencies. Both anti-resonance frequencies may be within the frequency range of the sideband 520 of the LBAW 100.

[0099] The series resonator 712 is formed by adding a mass load layer 750 on top of the conductive layer 734 (or top electrode) of the resonator 704. In some embodiments, the conductive layer 734 is composed of aluminum (Al), copper (Cu), or polysilicon (Poly-Si), and the layer 750 is composed of silicon oxide (SiO2) and / or silicon nitride (SiN). Due to the addition of the mass load layer 750, the resonator 712 can have a lower anti-resonance frequency than the resonator 704.

[0100] The thickness of mass loading layer 750 may be selected to provide a desired anti-resonant frequency for resonator 712. For example, if the anti-resonant frequency of resonator 704 would otherwise be above or below the frequency range of sideband 520a, then the thickness of layer 750 may be selected to shift the resonant frequency to provide the anti-resonant frequency within sideband 520a of resonator 712. The thickness may also be adjusted by further thickening (e.g., by depositing more material) or thinning (e.g., by etching) layer 750.

[0101] Resonator 702 may have a different thickness than resonator 712. The thickness difference may be caused by different thicknesses of the two conductive layers 732, 734, or by a mass loading layer 750 that is present in resonator 712 but not in resonator 702, or by different thicknesses of the mass loading layers on the two conductive layers 732, 734. Other options that may lead to different thicknesses of the two resonators 702 and 712 are different thicknesses in the piezoelectric layer, different thicknesses in any other layer of the two resonators, or different thicknesses of multiple layers of the two resonators.

[0102] Resonator 712 may be composed of one or more materials not included in resonator 702. For example, mass load layer 750 in the top electrode of resonator 702 may be composed of a different material (e.g., silicon oxide, silicon nitride, etc.) than the material (e.g., aluminum, copper, etc.) of conductive layers 732, 734.

[0103] Mass load layer 750 can be composed of the same material or a different material than conductive layer 734. For example, conductor layer 734 can be composed of aluminum (Al), and mass load layer 750 can be composed of Al, silicon oxide, and / or silicon nitride. In the case where mass load layer 750 is a conductor (e.g., the same conductive material as conductive layer 734), resonator 712 can be considered to have a thicker electrode than resonator 702.

[0104] although Fig. 8A and Figure 8B Different mass loading is illustrated by including a mass loading layer 708 in resonator 712 and not including a mass loading layer in resonator 702, but other techniques are possible. For example, the two 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 composed of the same material but different thicknesses.

[0105] As another example, the mass loading layers of the two resonators 702, 704 can be composed of different materials, optionally with the same thickness. Alternatively or in addition, the thickness of the resonator electrodes (i.e., conductor layer 732) of resonator 702 can be different from the thickness of the electrodes (i.e., conductive layer 734) of resonator 712. Alternatively or in addition, the material of conductor layer 732 can be different from the material of conductive layer 734 to provide different densities of resonators 704 and 702, and therefore provide different mass loading.

[0106] As previously mentioned, multiple resonators having different anti-resonant frequencies within the sidebands can be connected in series to the LBAW to suppress a wider frequency range of the sidebands of the LBAW (compared to a configuration with a single series resonator or a single anti-resonant frequency). Multiple series resonators having different anti-resonant frequencies provide a high impedance that prevents the driving electrical signal from passing and reduces signal transmission through the filter at each of the anti-resonant frequencies. For example, when the two resonators 702 and 712 of the filter 710 have different anti-resonant frequencies that fall within the sideband frequencies of the LBAW 100 (e.g., sideband 520a), the sidebands are suppressed over a wider frequency range than when the two resonators have the same anti-resonant frequency.

[0107] 9A to 9C An example bandpass filter 720 is depicted having two series resonators 722, 724, each of which includes multiple regions with different mass loadings. For example, the series resonator 722 may include regions 760 and 762 with different first and second mass loadings, and the series resonator 724 may include regions 764 and 776 with different third and fourth mass loadings.

[0108] Specifically, resonator 722 may include mass load layer 750 on top of first portion 760 of conductive layer 732, but not on second portion 762 of conductive layer 732. Resonator 724 may include multiple mass load layers 752 and 754 on top of conductive layer 734. For example, resonator 724 may include a single mass load layer 752 on top of first portion 764 of conductive layer 734, multiple mass load layers 752 and 774 on second portion 766 of conductive layer 734.

[0109] Layers 750, 752, 754 can be made of the same or different materials. For example, conductive layers 732, 734 can be made of aluminum (Al), copper (Cu), or polysilicon, and mass load layers 750, 752, 754 can be made of silicon oxide (SiO2), silicon nitride (SiN), and / or one or more metals. Layers 732, 734, 750, 754, 756 can have different thicknesses. In some examples, conductive layer 732 can have a different thickness in resonator 722 than in resonator 724.

[0110] Depending on the characteristics (e.g., thickness, material) of the four regions of the two series resonators 722, 724, the bandpass filter 720 may function as a LBAW in series with the two resonators 722 and 724 (each including two parallel resonators). Fig. 9CAs shown, two parallel resonators in the resonator 722 are formed by the first portion 762 and the second portion 762. Two parallel resonators in the series resonator 724 are formed by the third portion 764 and the fourth portion 766.

[0111] 7A to 9B Each of the layers 732, 734, 750, 752, 754 of the LBAW extension (e.g., extension 150a or 170a) can be made of the same or different material as the LBAW extension. In some embodiments, the electrodes 732, 734 and / or the extension are made of aluminum (Al), and the layers 750, 752, 754 are made of silicon oxide (SiO2) and / or silicon nitride (SiN). For example, layer 750 can be made of SiO2 and layer 752 can be made of SiN. In some examples, the layer made of SiO2 is less than 500nm thick and the layer made of SiN is less than 100nm thick. In some examples, the layer made of SiO2 is less than 50nm to 250nm thick, and the layer made of SiN is 5nm to 50nm thick.

[0112] In some embodiments, one or more resonator electrodes are the uppermost layer of the corresponding resonator. For example, layer 750 can be used as an electrode of resonator 712.

[0113] The anti-resonance 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 larger electrode surface) has a lower resistance at its anti-resonance frequency and blocks a smaller portion of the drive electrical signal. Therefore, in order to have a strong blocking, a small resonator can be a desirable resonator for suppressing the LBAW sideband.

[0114] If the width of the resonator (e.g., the width of the resonator electrodes) is narrower than the threshold width, then its anti-resonance frequency begins to depend on the width of the resonator. For such narrow resonators, the anti-resonance frequency depends on the width of the resonator, and the narrower the resonator, the higher its anti-resonance frequency (assuming type 1 dispersion, i.e., the frequency increases as the lateral wavelength decreases). The resonator can have any shape, such as circular, rectangular, annular, etc. The size and shape of the resonator can be adjusted to produce a spectrum of closely spaced resonances in a way that achieves broadband suppression. For example, the electrodes of the resonator can be in annular form, and a parallel resonator in an annular form can be formed. The impedance of a narrow annular resonator can peak at more than one resonant frequency, resulting in suppression of insertion loss over a wider frequency range than a single resonant frequency resonator (e.g., a rectangular resonator). It should be noted that when deciding the form of the resonator, the resonant frequency and resistance of the resonator at the anti-resonance frequency should be considered. For example, compared to a rectangular resonator, a ring resonator can have multiple resonant frequencies, but has a lower resistance at each anti-resonance frequency, resulting in a milder blocking effect at the anti-resonance frequency.

[0115] FIG. 10A to FIG. 10B Illustrated are example effects of the size of a resonator on the impedance and resistance of the resonator at resonant and anti-resonant frequencies. Fig. 10A The resonator impedance as a function of size is plotted for three different sizes, and Fig. 10B The resonator resistance as a function of size is depicted for the three sizes. Graphs 1002 and 1012 carefully depict the impedance and resistance of the smallest resonator in the three sizes. Graphs 1004 and 1014 carefully depict the resistance of the largest resonator in the three sizes. As shown, the smallest resonator (1002) has the largest impedance at the anti-resonant frequency 1006 and the resonant frequency 1008. The largest resonator (1004) has the lowest impedance at the anti-resonant frequency 1006 and the resonant frequency 1008. The smallest resonator also has the largest resistance (1012) at the anti-resonant frequency (e.g., compared to the resistance of the largest resonator 1014).

[0116] Several implementations have been described. However, it will be appreciated that 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.

[0117] Claims of protection are sought.

Claims

1. An acoustic wave filter device, comprising: an acoustic wave filter element comprising interdigitated input and output electrodes on a top surface of a piezoelectric layer; as well as a resonator comprising a resonator top electrode on the top surface of the piezoelectric layer and a resonator bottom electrode on the bottom surface of the piezoelectric layer, wherein the resonator is electrically connected in series to the acoustic wave filter element, wherein the resonator has a notch in the resonator impedance at a first frequency, the first frequency being within a sideband of the acoustic wave filter element, and wherein the first frequency is an inverse frequency of the resonator.

2. The device according to claim 1, wherein: The resonator is electrically connected to the acoustic wave filter element through an electrical connection between one of the input electrode and the output electrode of the acoustic wave filter element and the top surface of the resonator.

3. An acoustic wave filter device, comprising: an acoustic wave filter element comprising an input electrode and an output electrode located on a top surface of the piezoelectric layer; a first resonator comprising a first resonator top electrode on the top surface of the piezoelectric layer and a first resonator bottom electrode on the bottom surface of the piezoelectric layer, the first resonator having a first notch in resonator impedance at a first frequency, wherein one of the top electrode and the bottom electrode of the first resonator is electrically connected to the acoustic wave filter element; and a second resonator coupled to the acoustic wave filter element and comprising a second resonator top electrode on the top surface of the piezoelectric layer, a second resonator bottom electrode on the bottom surface of the piezoelectric layer, and a first mass loading layer on the second resonator top electrode, such that the second resonator has a second notch in resonator impedance at a second frequency different from the first frequency, and wherein one of the top electrode and the bottom electrode of the second resonator is electrically connected to the acoustic wave filter element, wherein the first frequency is the anti-resonance frequency of the first resonator, and the second frequency is the anti-resonance frequency of the second resonator, and Therein, both the first frequency and the second frequency are within a sideband of a resonator impedance of the acoustic wave filter element.

4. The device according to claim 3, wherein: The first resonator bottom electrode is electrically coupled to the input electrode, and the second resonator bottom electrode is electrically coupled to the output electrode.

5. The device according to claim 3, wherein: The first resonator top electrode is the uppermost layer of the first resonator.

6. The device according to claim 3, wherein: The first mass loading layer covers only a portion of the second resonator top electrode.

7. The device of claim 3, comprising a second mass loading layer on the first resonator top electrode.

8. The device according to claim 7, wherein: The first mass loading layer and the second mass loading layer are of the same material but have different thicknesses.

9. The device according to claim 7, wherein: The first mass carrying layer and the second mass carrying layer are different materials having different densities and / or different hardnesses.

10. The device according to claim 7, wherein: The first mass loading layer does not cover the second resonator top electrode.

11. The device according to claim 7, wherein: The first mass loading layer covers the first resonator top electrode, and the second mass loading layer does not cover the second resonator top electrode.

12. The device according to claim 3, wherein: The first mass loading layer is a different material than the second resonator top electrode.

13. The device according to claim 3, wherein: The first mass loading layer is the same material as the second resonator top electrode, and the first resonator top electrode and the second resonator top electrode have different thicknesses.

14. The device according to claim 3, wherein: The first resonator bottom electrode is electrically connected to the acoustic wave filter element through a first conductive via extending through the piezoelectric layer, and the second resonator bottom electrode is electrically connected to the acoustic wave filter element through a second conductive via extending through the piezoelectric layer.

15. The device according to claim 3, wherein: The input electrode, the output electrode, the first resonator electrode and the second resonator electrode are provided by separate portions of the same electrode layer on the top surface of the piezoelectric layer.

16. The device according to claim 3, wherein: The first frequency and the second frequency differ by at least 1%.

17. The device of claim 3, comprising a counter electrode on a bottom surface of the piezoelectric layer below the input electrode and the output electrode.

18. The device according to claim 17, wherein: The acoustic wave filter element is a laterally acoustically coupled bulk acoustic wave (LBAW) filter.

19. The device according to claim 17, wherein: The thickness of the piezoelectric layer and the gap width between the input electrode and the output electrode are such that application of a radio frequency voltage between the input electrode and the counter electrode will create symmetric and antisymmetric acoustic thickness extensional resonant modes in the piezoelectric layer.

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