Film bulk acoustic wave FBAR resonator with parasitic mode suppression mechanism

Abstract

A mechanism for suppressing parasitic signals or modes in FBAR resonators and filters incorporates the effects of an electromagnetic (EM) cavity resonant physics field model. The suppression of parasitic signals is realized by modifying the characteristics of the EM cavity resonance of the FBAR resonator. This is achieved by keeping the fundamental piezoelectric resonant frequency of the resonator constant and shifting the EM cavity resonance to a lower frequency. This offset in the EM cavity resonant frequency ensures that the sub-parasitic signal resulting from the interaction between the piezoelectric resonant frequency and the EM cavity resonant frequency is offset to a lower frequency, which is advantageously located in the suppression band region outside the passband of the piezoelectric resonance. The FBAR resonator is shaped to include a "zipper" edge upper electrode that includes a series of localized ridges or peaks and valleys typically between adjacent ridges or peaks.

Description

Background Technology

[0001] With the rapid development of cellular phones, satellite communications, and other types of wireless communication systems, filters have become an important part of these devices to prevent interference between different types of communication systems. However, traditional radio frequency (RF) filters cannot meet the miniaturization and high-frequency operation requirements of modern communication systems due to their relatively large size and power consumption.

[0002] Thin-film bulk acoustic resonators (FBARs) are typically acoustic isolation devices that consist of a piezoelectric thin film material sandwiched between two electrodes, formed on a semiconductor substrate such as silicon (Si) or gallium arsenide (GaAs). Resonance is induced due to the piezoelectric properties of the thin film. Commonly used FBAR resonators utilize piezoelectric films with thicknesses ranging from a few micrometers to a tenth of a micrometer and resonate in a frequency range of approximately 100 MHz to 10 GHz. Materials commonly used for the piezoelectric film include aluminum nitride and zinc oxide. Aluminum nitride offers advantages such as low acoustic attenuation and stable chemical properties, while also providing high-speed manufacturing processes compatible with existing complementary metal-oxide-semiconductor (CMOS) fabrication processes.

[0003] FBAR resonator devices can be miniaturized to have a size less than 1% of the size of a corresponding dielectric or LC filter, and can have less than half the insertion loss of a surface acoustic wave (SAW) device.

[0004] One application or use of FBAR resonators is in RF filters used in cellular phones and other wireless devices. These filters are typically constructed using multiple resonators and are designed to remove unwanted frequencies while allowing transmission and reception of frequencies of interest. FBAR resonators can also be used in sensor applications where the device is subjected to some type of mechanical force that shifts its resonant frequency.

[0005] FBAR filters possess excellent frequency selectivity and filtering performance, enabling high-quality signal filtering and benefiting high-speed data transmission and spectral efficiency in next-generation RF networks. FBAR filters can be miniaturized and integrated, improving the integration and performance density of next-generation communication systems and opening up new application scenarios and possibilities. They are increasingly used in various fields, such as advanced smartphones, Internet of Things (IoT) devices, satellite communications, connected vehicles, and industrial automation.

[0006] The diaphragm resonator is the foundation of the FBAR filter. When a standard FBAR filter resonates, at the series resonant frequency F... sParasitic signals or modes often exist in or near the low-frequency range of an FBAR resonator, which significantly affects the performance of filters incorporating such resonators. In an FBAR resonator, the resonant frequency F0 is the frequency at which the resonator impedance is minimum. At F0, the inductive and capacitive reactances cancel each other out, resulting in maximum admittance (minimum impedance). This is also known as the fundamental resonant frequency. s It is the series resonant frequency, and is usually the same as F0.

[0007] The distortion caused by parasitic modes leads to passband loss and may even cause the FBAR filter to fail. Therefore, effectively suppressing resonant parasitic signals is an important goal for the normal operation of FBAR filters.

[0008] Piston modes, often referred to as the fundamental thickness extension mode, are the desired vibrational modes in FBAR devices. In this mode, the entire thickness of the resonator oscillates uniformly. The vibration occurs primarily in a direction perpendicular to the resonator plane, resulting in efficient energy conversion and minimal energy loss. Parasitic modes, or signals, are unwanted vibrational modes that can occur at frequencies outside the fundamental mode. These modes, including transverse modes, arise from various factors, such as non-uniformities in the resonator structure. Parasitic modes can degrade FBAR performance by introducing additional resonances, leading to increased insertion loss, reduced filter selectivity, and potential interference in the frequency response.

[0009] Traditionally, the mechanism inducing parasitic signals in FBAR resonators is considered to be the effect of transverse resonance. Resonator resonance refers to the various resonant modes that can occur in an FBAR resonator. More specifically, transverse resonance refers to the occurrence of vibrations parallel to the plane of the resonator. Furthermore, piston resonance in FBAR refers to the uniform vibration of the entire cross-section of the thin piezoelectric film along its thickness direction. This uniform vibration is analogous to the motion of a piston in an engine, where the entire surface moves in phase without any significant deformation. Piston resonance leads to a high quality factor (Q factor) and reduces the occurrence of parasitic modes and mode separation, resulting in a more stable and predictable frequency response. Mode separation refers to the phenomenon where the fundamental thickness-extended mode (piston mode) is not a single frequency, but rather separates into multiple closely spaced frequencies of piston mode and parasitic modes.

[0010] Besides the main piston resonance excited by the FBAR electrodes, resonator resonance can also occur due to the discontinuity of acoustic impedance at the edges of the resonator electrodes and the air-crystal resonance region. An air-crystal resonance region emerges when the sound waves generated in the piezoelectric film interact with the air or vacuum in the cavity beneath the diaphragm. The air-crystal resonance region is the frequency band where the sound waves generated by the piezoelectric layer couple with the surrounding air, resulting in different resonance characteristics. This region is characterized by the interaction between the acoustic impedance of the piezoelectric material and the acoustic impedance of the air, thus affecting energy transfer and reflection at the resonator surface.

[0011] The presence of air can cause a shift in the resonant frequency and, due to additional boundary conditions, potentially split the main piston mode into multiple modes. In fact, defects can cause the main piston mode to split into multiple closely spaced resonances, resulting in undesirable resonances that, due to the lateral mode, appear at frequencies outside the main piston mode. This interaction can alter the resonant characteristics of the FBAR, affecting its frequency response and overall performance.

[0012] In the air-crystal resonant region, the acoustic impedance mismatch between the piezoelectric material and the air or vacuum cavity can cause sound waves to reflect at the interface between the piezoelectric film and the air / vacuum cavity, thereby generating standing wave patterns and affecting the resonance conditions. Interaction with air or vacuum can lead to a shift in the resonant frequency of the FBAR, potentially affecting the Q factor of the resonance, and may cause coupling between different resonant modes, potentially generating complex resonant patterns and parasitic modes.

[0013] Lateral resonance is generally considered the primary cause of parasitic signals in FBAR resonators. Therefore, efforts are underway to suppress or eliminate lateral resonance by introducing raised structural frames, air rings, or air bridges at the electrode edges of the resonator. Besides potentially increasing the parallel impedance of the resonator, these structures can also partially suppress lateral resonance, thereby suppressing parasitic signals to some extent.

[0014] However, introducing raised frames, air rings, or air bridges can lead to multimode resonances in FBAR resonators, and the interactions between the multimode resonant reactances are extremely complex. Multimode resonance refers to the presence of multiple vibrational modes within the device, each resonating at a different frequency. These modes include the main piston mode and various parasitic modes. Transverse modes are one type of parasitic mode, where vibrations occur parallel to the plane of the resonator. Raised frames, air rings, and air bridges alter the mechanical boundary conditions of the resonator. These structures introduce additional mechanical constraints and discontinuities, which can cause the resonator to support multiple vibrational modes. The resonator can exhibit complex vibrational modes with different resonant frequencies rather than uniform vibration.

[0015] The presence of these structures causes reflection and scattering of sound waves within the resonator. Interference between the incident and reflected waves generates standing wave patterns corresponding to different resonant modes. Each mode will have its own characteristic frequency, resulting in multiple resonant peaks. The raised frame, air rings, and air bridges can couple different vibrational modes, such as longitudinal, shear, and transverse modes. This coupling can lead to energy transfer between modes, further enhancing the multimode response. As a result, the resonator can resonate at frequencies corresponding to each of these coupled modes.

[0016] These structures can also introduce local resonances, where certain parts of the resonator vibrate at frequencies different from the rest of the resonator. For example, air rings and air bridges can create local regions with different resonant behaviors. These local resonances contribute to the total multimode resonant spectrum of the FBAR. The introduction of raised frames, air rings, or air bridges alters the geometry and material distribution within the resonator. These discontinuities can support additional resonant modes that are not present in uniform resonators. Each geometric feature can function as a separate resonator with its own set of resonant frequencies.

[0017] Furthermore, introducing raised frames, air rings, or air bridges will cause an acoustic impedance mismatch between the piezoelectric material and the air or vacuum cavity. This can cause sound waves to reflect at the interface between the piezoelectric film and the air / vacuum cavity, thereby generating standing wave patterns and affecting the resonance conditions. Interaction with air or vacuum can lead to coupling between different resonance modes, potentially producing complex resonance patterns and parasitic modes, known as "multimode resonance."

[0018] Currently, there is no reliable multiphysics model to accurately describe this interaction, and it can only be characterized through experimental and empirical data accumulated during the production process. In practical applications, achieving effective suppression of parasitic signals in FBAR resonators and corresponding filters requires higher precision microfabrication equipment and process control, as well as multiple iterations of production preparation for each frequency band and FBAR filter design. However, for UHF (ultra-high frequency) FBAR products above 5 GHz, the high cost, difficulty, and low yield have become bottlenecks in optimizing and producing FBAR filters, limiting their rapid development and time-to-market goals.

[0019] Furthermore, the raised frame introduces additional parasitic signals in the low-frequency range of FBAR resonator resonance, which partially affects the overall performance of the FBAR filter and limits its widespread use in advanced communication systems. Therefore, the FBAR filter industry needs a better solution to effectively suppress parasitic signals in FBAR resonators and filters. Summary of the Invention

[0020] In one embodiment, the present invention relates to a mechanism for suppressing parasitic signals or modes in FBAR resonators and filters, particularly for UHF products above 5 GHz, which incorporates the effects of an electromagnetic (EM) cavity resonance physical field model. EM cavity resonance refers to the resonant modes of the electromagnetic field in the cavity surrounding the FBAR, which can couple with the acoustic resonance of the device. When an RF signal is applied to the FBAR, it generates not only acoustic waves but also electromagnetic (EM) fields. These EM fields can resonate within the cavity or surrounding structure and interact with the acoustic resonance, resulting in complex coupling effects that affect the overall performance of the FBAR.

[0021] The physical structure of a FBAR, including a substrate, piezoelectric layer, and electrodes, can form a cavity that supports standing-wave electromagnetic waves. If the lateral dimensions or interlayer spacing of the FBAR are on the order of the EM wavelength (or a considerable portion thereof), they can support EM resonant modes. Driving the resonator by applying an AC voltage across the piezoelectric layer generates an alternating electromagnetic field. This field can interact with the structure of the resonator and its surrounding environment, leading to EM cavity resonance. The patterning and arrangement of the electrodes can create regions where the electromagnetic field can resonate. These fields can be reflected between the electrodes and the device boundaries, forming standing waves.

[0022] Parasitic signals are typically generated by the interaction between the fundamental piezoelectric resonant frequency of an FBAR resonator and the resonant frequency of the EM cavity within the resonator. This leads to complex physical field coupling and mixing near the filter's resonant frequency, resulting in subparasitic modes. Unlike parasitic modes caused by transverse resonances, subparasitic modes refer to those generated by the interaction between transverse resonances and the resonator's EM resonances, resulting in a mixture of subparasitic modes. Subparasitic modes typically occur at frequencies below or above the principal resonant frequency and its harmonics, but are not harmonic-dependent. Because the interaction between the resonator's parasitic transverse modes and the resonator's EM resonances results in a mixture of subparasitic modes, EM resonances interacting with acoustic resonances are considered to have a mixture of subparasitic modes.

[0023] Therefore, parasitic signal suppression can be achieved by modifying the characteristics of the EM cavity resonance of the FBAR resonator. This can be achieved by keeping the fundamental piezoelectric resonant frequency of the resonator constant and shifting the EM cavity resonance to a lower frequency. According to an embodiment of the invention, the conventional FBAR resonator is modified to include a "zipper" edge upper electrode, which has a series of local ridges / peaks and valleys typically between adjacent ridges or peaks. The ridges and valleys of the zipper edge upper electrode are used to increase the effective resonant length of the upper electrode, thereby changing the frequency response characteristics of the EM cavity resonance of the FBAR resonator.

[0024] This shift in the EM cavity resonant frequency ensures that the subparasitic signal generated by the interaction between the piezoelectric resonant frequency and the EM cavity resonant frequency is shifted to a lower frequency, which is advantageously located in the suppression band region outside the passband of the piezoelectric resonance. This effectively suppresses parasitic signals that might appear in the passband.

[0025] The novel method described above in this invention represents a significant advancement over traditional theories regarding the generation of parasitic signals by transverse resonance. Instead, according to embodiments of the invention, it should be understood that the coupling and mixing of multiple physical fields between piezoelectric resonance and EM cavity resonance generates parasitic signals, which better aligns with the actual operating principles and phenomena of FBAR resonators. This novel method provides a more effective framework for suppressing parasitic signals in FBAR resonators, particularly for UHF products.

[0026] An effective solution for suppressing parasitic signals in FBAR resonators according to embodiments of the present invention is based on a mechanism that addresses parasitic signal generation through multiphysics coupling and mixing of piezoelectric resonance and EM cavity resonance. By modifying the characteristics of the EM cavity resonance—specifically—shifting the cavity resonance to a lower frequency—the subparasitic signal products of multiphysics coupling and mixing outside the filter passband of the piezoelectric resonance are shifted to the frequency corresponding to the series resonant frequency F. s The lower frequencies in the suppression band region above effectively suppress parasitic signals. Attached Figure Description

[0027] This disclosure will be understood and better understood from the following detailed description taken in conjunction with the accompanying drawings. Identical structures, elements, or parts appearing in more than one figure are generally labeled with the same or similar numerals in all the figures in which they appear, wherein:

[0028] Figure 1 This is a perspective view of an FBAR resonator;

[0029] Figure 2 This is a perspective view of an FBAR resonator, showing the active region;

[0030] Figure 3 This is a cross-sectional view of an FBAR resonator;

[0031] Figure 4 This is a cross-sectional view of an FBAR resonator;

[0032] Figure 5 This is a diagram of an existing FBAR resonator;

[0033] Figure 6 This is a graph showing the impedance of an existing FBAR resonator as a function of frequency.

[0034] Figure 7It is a graph of the phase response of an existing FBAR resonator as a function of frequency;

[0035] Figure 8 This is a diagram of an FBAR resonator according to an embodiment of the present invention;

[0036] Figure 9 This is a graph showing the impedance of an FBAR resonator as a function of frequency according to an embodiment of the present invention.

[0037] Figure 10 This is a graph showing the phase response of an FBAR resonator as a function of frequency according to an embodiment of the present invention;

[0038] Figure 11 This is a block diagram of an FBAR filter according to an embodiment of the present invention. Detailed Implementation

[0039] In the following detailed description, numerous specific details are set forth in order to provide a thorough understanding of the invention. However, those skilled in the art will understand that the invention can be practiced without some of these specific details. In other instances, well-known methods, processes, and components have not been described in detail so as not to obscure the invention.

[0040] Now for reference Figure 1 The diagram illustrates an FBAR resonator 100. The FBAR 100 may include an upper electrode 102, typically parallel to and positioned above a lower electrode 104. Between the electrodes is a piezoelectric layer 106. The electrodes may typically have the same dimensions, or one electrode may be larger than the other. Furthermore, in one embodiment, the first electrode may be larger than the second electrode. Similarly, the piezoelectric layer may have the same dimensions as one or both of the electrodes, or alternatively, the piezoelectric layer may be larger than one or both of the electrodes. The electrodes may be made of molybdenum (Mo), ruthenium (Ru), tungsten (W), or titanium-tungsten (TiW).

[0041] Now for reference Figure 2 The diagram shows a perspective view of an FBAR resonator 200. The FBAR includes an upper electrode 202, a lower electrode 204, and a piezoelectric film 206. The overlapping region between the upper electrode 202 and the lower electrode 204 forms an active region 208 where signal resonance primarily occurs.

[0042] Now for reference Figure 3The diagram shows a cross-sectional view of an FBAR resonator 300. The FBAR 300 includes an upper electrode 302, a lower electrode 304, and a piezoelectric layer 306 between the two electrodes 302 and 304. The electrodes 302 and 304 and the piezoelectric layer 306 are formed on a semiconductor substrate (such as silicon 308). An air cavity 310 is formed in the silicon 308 and below the lower electrode. The air cavity 310 below the resonator acts as an acoustic reflector, thereby minimizing the transmission of acoustic energy into the substrate. This reduces acoustic loss and improves the quality factor (Q factor) of the resonator. Without the air cavity 310, acoustic waves could couple into the substrate, leading to energy dissipation and unwanted resonance. The air cavity 310 prevents this coupling, ensuring that acoustic energy remains confined within the resonant structure.

[0043] The air cavity 310 allows standing wave acoustic waves to be formed within the resonator. This is necessary for achieving clear and distinct resonances at specific frequencies. By providing effective acoustic isolation, the air cavity 310 helps achieve a higher Q factor, which is crucial for the performance of the resonator in filtering and frequency control applications.

[0044] The air cavity 310 also affects the effective thickness of the resonant structure. Variations in the size of the air cavity 310 can be used to fine-tune the resonant frequency of the FBAR. The presence of the air cavity 310 ensures that the resonant frequency is less sensitive to external mechanical or thermal disturbances, thus contributing to frequency stability.

[0045] The air cavity 310 also provides mechanical isolation from the substrate 308, thereby reducing the impact of substrate vibration and mechanical stress on resonator performance. By minimizing mechanical coupling, the air cavity 310 helps improve the long-term reliability and durability of the resonator, especially under harsh operating conditions.

[0046] The air cavity 310 acts as a thermal barrier, thereby reducing the thermal conductivity between the resonator and the substrate 308. This helps manage the thermal stability of the resonator and mitigates thermally induced frequency shifts. By providing thermal isolation, the air cavity 310 allows the FBAR to maintain consistent performance even in high-temperature environments.

[0047] Now for reference Figure 4 The figure shows another cross-sectional view of the FBAR resonator 400. As shown, the FBAR 400 includes an upper electrode 404 and a lower electrode 408, which can be formed of Mo (molybdenum). Between the electrodes 404 and 408 is a piezoelectric film 406, which can be formed of aluminum nitride (AlN), Sc(x)Al(1-x)N, Ba(x)Sr(1-x)TiO3, LiNbO3, or LiTaO3. The piezoelectric layer can be formed using a single-crystal material. Additionally, a passivation layer 402 can be formed above the upper electrode 404 and can be formed of aluminum nitride (AlN).

[0048] FWHM usually refers to Full Width at Half Maximum (FWHM). It is a measure used to describe the peak width in a distribution. Specifically, FWHM is the peak width at half its maximum intensity. Lower FWHM values ​​indicate sharper peaks, which correspond to higher crystallinity and fewer defects in the crystal structure. In piezoelectric layers, an FWHM value of less than 1 degree indicates that the layer has very high crystal quality and minimal structural defects.

[0049] Figure 5 The layout of a conventional FBAR resonator 500 is shown. (As shown...) Figure 5 As shown, the FBAR resonator 500 includes an upper electrode 506, a lower electrode 502, and a piezoelectric film 504 located between the upper and lower electrodes. The FBAR resonator 500 also includes a through hole 508 for contacting the piezoelectric film 504, and an upper electrode 510 and a contact pad 512 for contacting the upper electrode 506.

[0050] according to Figure 8 The embodiments of the present invention shown are as follows: Figure 5 The conventional FBAR resonator 500 is modified to include an "upper electrode" 802 on the "zipper" edge as part of the resonator 800. The upper electrode 802 on the zipper edge includes a series of local ridges or peaks 812 and valleys 822, wherein the valleys 822 are typically located between adjacent ridges or peaks 812. The ridges and valleys of the upper electrode 802 are used to increase the effective resonant length of the upper electrode 802, thereby altering the frequency response characteristics of the EM cavity resonance of the FBAR resonator 800. The ridges or peaks 812 and valleys 822 may be uniform in height and / or spacing, or they may be non-uniform, with some ridges 812 being higher or wider than others. Additionally, some valleys 822 may be lower or wider than others. The resonator 800 also includes a through-hole 804 for the piezoelectric film. The resonator 800 also includes an edge 806 between the island and the through-hole 804 for the piezoelectric film. Additionally, the resonator 800 includes a pad (e.g., Au) 808 for contacting the upper electrode 802. In embodiments of the invention, the purpose of the ridges and valleys is to increase the effective resonant length of the electrode. This can be achieved by creating a non-smooth or non-uniform edge profile of the electrode.

[0051] In various embodiments of the invention, the "zipper" edge may be provided only on a portion of the upper electrode, or it may be provided on the entire upper electrode. In another alternative, the "zipper" edge may be provided in a selected region of the upper electrode, wherein the region between the "zipper" edges has a conventionally smooth edge. Additionally, in different embodiments, the various versions of the "zipper" edge described herein may be provided as a portion of the lower electrode. In other embodiments, the various versions of the "zipper" edge described herein may be provided on both the upper and lower electrodes.

[0052] The frequency response of the EM cavity resonance of an FBAR resonator is typically determined by the following relationship:

[0053]

[0054] Where c is the speed of light, a, b, and d are the dimensions of the cavity in the x, y, and z directions, and m, n, and p are the mode numbers in the x, y, and z directions, respectively. The mode numbers usually refer to different EM resonances.

[0055] Due to the longer length introduced by the electrode 802 on the zipper edge, the cavity resonant frequency is shifted to a lower frequency. However, for the piezoelectric resonant characteristics of the FBAR resonator, the electrode 802 on the zipper edge is essentially equivalent to a conventional smooth edge electrode and has almost the same resonator area. The piezoelectric resonant frequency of the FBAR resonator is typically determined by the following relationship:

[0056]

[0057] The resonant frequency f0 is a function of the total mass m of the FBAR resonator and the stiffness k of the piezoelectric film material. The area of ​​the electrodes affects their mass, thus contributing to the total effective mass of the FBAR resonator. From the above relationship, it can be seen that increasing the mass m of the FBAR resonator will decrease the resonant frequency f0. Conversely, increasing the total stiffness k of the piezoelectric film will increase the resonant frequency f0.

[0058] Therefore, with the introduction of electrode 802 on the zipper edge, the fundamental piezoelectric resonant frequency remains unchanged. This is because the introduction of the zipper edge does not change the area of ​​the upper electrode, nor does the corresponding mass and stiffness. Thus, the fundamental piezoelectric resonant frequency remains essentially unchanged.

[0059] However, due to the lower shift in the cavity resonant frequency, the subparasitic signals or modes (a mixture resulting from the interaction of EM resonance and acoustic resonance) generated by multi-physics coupling and mixing within the resonator are shifted outside the passband of the piezoelectric resonance, reaching the low-frequency stopband region below the series resonant frequency F0, thus effectively suppressing parasitic signals. The fundamental piezoelectric resonance of the resonator remains unchanged, while the EM resonance of the resonator shifts to a lower frequency due to the zipper edge effect. Therefore, the mixing products are shifted to lower frequencies outside the passband but within the filter's suppression band.

[0060] Now for reference Figure 6 The example shown is for, for, such as Figure 5 The diagram shows the resonant impedance as a function of frequency for a traditional FBAR resonator. Conversely, Figure 9 It shows that for such as Figure 8 The electrode on the "zipper edge" shown in the embodiment of the present invention is represented by a similar impedance curve as a function of frequency. Figure 6 and Figure 9 As shown, it can be seen that Figure 6 The impedance curve shows two distinct peaks: a sharp peak and a less pronounced peak near 5 GHz. The sharp peak suggests a strong resonance, indicating a high Q factor for this mode. The other smaller peaks or perturbations indicate parasitic resonances.

[0061] In comparison, Figure 9 The impedance plot shows a single spike near 5 GHz, similar to Figure 6 However, it has a cleaner profile, without any additional, less noticeable peaks. A single sharp peak still indicates a strong resonance with a high Q factor. However, the presence of fewer other, less noticeable peaks or perturbations suggests fewer parasitic resonances.

[0062] The effective solution derived from the zipper edge and its suppression of parasitic resonances is based on addressing the mechanism of parasitic signals generated by the mixing of multi-physics coupling and piezoelectric resonance with EM cavity resonance. Modifying the characteristics of the EM cavity resonance by the zipper edge, specifically shifting the cavity resonance to a lower frequency, causes the sub-parasitic signal products of multi-physics coupling and mixing, which occur outside the filter passband of the piezoelectric resonance, to shift to a lower frequency corresponding to frequencies above the series resonant frequency F. s The stopband region effectively suppresses parasitic signals.

[0063] Now for reference Figure 7 The example shown is for, for, such as Figure 5 The diagram shows the resonant phase response of a conventional FBAR resonator as a function of frequency. Conversely, Figure 10 It shows that for such as Figure 8 The electrode on the "zipper edge" according to an embodiment of the present invention is shown as a similar curve to the phase response as a function of frequency. Figure 7 and Figure 10 As shown, it can be seen that Figure 7 The phase response curve exhibits two distinct spikes: a sharp spike and a less noticeable spike near 4.75 GHz. The sharp spike suggests a strong phase discontinuity, indicating parasitic resonances within the passband. The additional, smaller spike indicates lower-frequency parasitic resonances. In contrast, Figure 10 The cleaner phase response curves show that there are far fewer parasitic resonances.

[0064] Compared to conventional "smooth" raised frame electrodes that introduce additional parasitic signals in the low-frequency range (e.g., in the 4.75 GHz range), the resonant response curve of an FBAR resonator with a zipper edge upper electrode is substantially smooth, effectively suppressing parasitic signals and improving the overall performance of the FBAR filter. The zipper edge can be implemented as part of either the upper or lower electrode of the FBAR resonator. Alternatively, the zipper edge can be implemented as part of both the upper and lower electrodes. Furthermore, the zipper edge can be implemented along the entire edge portion of one of the electrodes, or it can be implemented along a portion of the edge portion of one of the electrodes, i.e., not extending along the entire periphery of the electrode. In yet another alternative, the zipper edge can be implemented along multiple portions of the electrode, with smooth edge portions between the zipper edge portions.

[0065] Furthermore, the electrodes on the zipper edge do not require an elevated frame, which reduces the requirements for handling equipment and process control, resulting in lower production costs and higher yields. In one embodiment, this invention provides an innovative and effective solution for parasitic suppression in FBAR resonators, possessing significant practical value and application prospects.

[0066] Now for reference Figure 11 The diagram illustrates a block diagram of a trapezoidal filter 1100 constructed using FBAR resonators according to an embodiment of the present invention. The illustrated trapezoidal filter 1100 includes an input IN and an output OUT. Multiple FBAR resonators connected in series are arranged between the input and output, as shown in 1, 3, 5, 7, and 9. The specific number of resonators connected in series can be more or less than shown, and can be selected based on the desired filter and the filter characteristics to be obtained. Between each pair of series-connected resonators are resonators connected in parallel, shown in 2, 4, 6, and 8. The specific number of resonators connected in parallel can be more or less than shown, and can be selected based on the desired filter and the filter characteristics to be obtained. Each parallel-connected resonator has a first node connected between the two series-connected resonators and a second node grounded. In a single-stage filter that may have a single series-connected resonator, the parallel-connected resonator will connect its first node to the OUT output of the filter. In a trapezoidal filter for electronic signals, the series resonators provide a passband that allows the desired frequency to pass. Parallel resonators generate notch filters at specific frequencies to block unwanted signals, thereby enhancing filter performance in terms of selectivity and insertion loss. This combination of series and parallel resonators forms the "steps" and "staircases" of a ladder filter, giving it its characteristic name and function.

[0067] It should be understood that the above-described methods and apparatus can be varied in many ways, including omitting or adding elements or steps, changing the order of steps, and the type of equipment used. It should also be understood that different features can be combined in different ways. In particular, not all of the above-described features in a particular embodiment are necessary in every embodiment of the invention. Further combinations of the above-described features are also considered to be within the scope of some embodiments of this disclosure.

[0068] Those skilled in the art will understand that the present invention is not limited to what has been specifically shown and described above. Rather, the scope of the invention is defined only by the appended claims.

Claims

1. A bulk acoustic resonator, comprising: The first electrode has a first planar portion; The second electrode has a second planar portion, which is disposed substantially parallel to the first planar portion; as well as A piezoelectric layer is disposed between the first planar portion and the second planar portion and is in contact with the first planar portion and the second planar portion; In this embodiment, at least a portion of the edge of one of the electrodes is formed with multiple peaks and valleys, which are operable to increase the effective resonant length of the electrode, thereby changing the frequency response characteristics of the electromagnetic resonance of the resonator.

2. The bulk acoustic resonator of claim 1, wherein the plurality of peaks and valleys are formed substantially along the entire length of an electrode.

3. The bulk acoustic resonator of claim 1, wherein the plurality of peaks and valleys are formed along a portion of the first electrode and the second electrode.

4. The bulk acoustic resonator according to claim 1 further includes an air cavity located below the first electrode and above the second electrode, thereby generating a diaphragm bulk acoustic resonator (FBAR).

5. The bulk acoustic resonator of claim 4, wherein the electromagnetic resonance generated by the air cavity below the first electrode is shifted to a lower resonant frequency.

6. The bulk acoustic resonator according to claim 1, wherein the piezoelectric layer is selected from the group consisting of AlN, Sc(x)Al(1-x)N, Ba(x)Sr(1-x)TiO3, LiNbO3 and LiTaO3.

7. The bulk acoustic resonator according to claim 5, wherein the piezoelectric layer has an FWHM value of less than 1 degree.

8. The bulk acoustic resonator of claim 5, wherein the piezoelectric layer is formed using a single-crystal material.

9. The bulk acoustic resonator according to claim 1, wherein the first electrode is larger than the second electrode.

10. The bulk acoustic resonator according to claim 1, wherein the piezoelectric layer is larger than the first electrode.

11. The bulk acoustic resonator of claim 1, wherein the first electrode layer and the second electrode layer are made of a material selected from the group consisting of Mo, Ru, W and TiW.

12. The bulk acoustic resonator of claim 1, wherein the first electrode is an upper electrode, and the peaks and valleys are formed as part of the upper electrode.

13. The bulk acoustic resonator according to claim 1, wherein the height of the peak is substantially uniform.

14. The bulk acoustic resonator according to claim 1, wherein the width of the peak is substantially uniform.

15. The bulk acoustic resonator of claim 1, wherein the height of the valley is substantially uniform.

16. The bulk acoustic resonator of claim 1, wherein the width of the valley is substantially uniform.

17. An electronic signal filter having an input and an output, the filter comprising: At least one resonator connected in series has a first node connected to the filter input and a second node connected to the filter output; At least one resonator connected in parallel has a first node connected to the second node of the resonator connected in series and a second node grounded; Each of the series-connected resonators and the parallel-connected resonators further includes a first electrode having a first planar portion and a second electrode having a second planar portion disposed substantially parallel to the first planar portion; as well as A piezoelectric layer is disposed between and in contact with the first planar portion and the second planar portion, wherein at least a portion of the edge of one of the electrodes is formed with a plurality of peaks and valleys, the plurality of peaks and valleys being operable to increase the effective resonant length of the electrode, thereby altering the frequency response characteristics of the electromagnetic resonance of the resonator.

18. An electronic signal filter having an input and an output, the filter comprising: A plurality of resonators connected in series, wherein the first resonator of the plurality of resonators has a first node connected to the input of the filter, and the last resonator of the series-connected resonators has a second node connected to the output of the filter; Multiple resonators connected in parallel, each resonator having a first node connected between two resonators connected in series, and each resonator having a second node grounded; Each of the series-connected resonators and the parallel-connected resonators further includes a first electrode having a first planar portion and a second electrode having a second planar portion, the second planar portion being disposed substantially parallel to the first planar portion; as well as A piezoelectric layer is disposed between and in contact with the first planar portion and the second planar portion, wherein at least a portion of the edge of one of the electrodes is formed with a plurality of peaks and valleys, the plurality of peaks and valleys being operable to increase the effective resonant length of the electrode, thereby altering the frequency response characteristics of the electromagnetic resonance of the resonator.

19. The filter of claim 18, wherein the plurality of peaks and valleys are formed substantially along the entire length of an electrode.

20. The filter of claim 18, wherein the plurality of peaks and valleys are formed along a portion of both the first electrode and the second electrode.

21. The filter of claim 18, wherein the height of the peaks is substantially uniform.

22. The filter of claim 18, wherein the width of the peak is substantially uniform.

23. The filter of claim 18, wherein the height of the valleys is substantially uniform.

24. The filter of claim 18, wherein the width of the valley is substantially uniform.

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