Bulk acoustic wave resonators stacked on an integrated passive device
The BAW-assisted filter structure, with a BAW resonator stacked on an IPD, addresses the challenge of high-frequency filtering by reducing losses and enhancing performance, suitable for 3G, 4G, and 5G wireless devices.
Patent Information
- Authority / Receiving Office
- JP · JP
- Patent Type
- Applications
- Current Assignee / Owner
- QORVO US INC
- Filing Date
- 2026-03-17
- Publication Date
- 2026-06-09
AI Technical Summary
BAW-based filters struggle to filter signals above approximately 6 GHz due to increasing losses with frequency, posing a challenge in high-frequency communication applications.
A bulk acoustic wave (BAW) assisted filter structure is developed by stacking a BAW resonator on an integrated passive device (IPD), which includes a transducer with electrodes and a piezoelectric layer, electrically coupled to the IPD, reducing parasitic losses and enabling high-frequency operation.
The BAW-assisted filter structure achieves low insertion loss and improved filter performance, allowing for high-frequency filtering with greater flexibility in design and reduced size, particularly effective in 3G, 4G, and 5G wireless devices.
Smart Images
Figure 2026094466000001_ABST
Abstract
Description
[Technical Field]
[0001] The present invention relates to a bulk acoustic wave (BAW) assist filter structure having at least one BAW resonator stacked on an integrated passive device for high-frequency processing. [Background technology]
[0002] Acoustic resonators, and especially bulk acoustic wave (BAW) resonators, are used in many high-frequency communication applications. In particular, BAW resonators are often employed in filter networks, which operate at frequencies above 1.5 GHz, require a flat passband, have very steep filter tails and rectangular shoulders at the upper and lower ends of the passband, and provide excellent stopband outside the passband. BAW-based filters also have relatively low insertion loss, tend to decrease in size as the operating frequency increases, and are relatively stable over a wide temperature range. Therefore, BAW-based filters are the filter of choice for many third-generation (3G), fourth-generation (4G), and fifth-generation (5G) wireless devices. Most of these wireless devices support cellular, wireless fidelity (Wi-Fi), Bluetooth, and / or short-range communications on the same wireless device, thus presenting very challenging filtering requirements. These demands mean that while the complexity of wireless devices continues to increase, there is always a need to improve the performance of BAW resonators and BAW base filters, and to reduce their associated costs and sizes.
[0003] Currently, BAW-based filters struggle to filter signals above approximately 6 GHz. In particular, losses typically increase proportionally with increasing frequency. Therefore, filtering at high frequencies using BAW-based filters remains a challenge. [Overview of the project]
[0004] Embodiments of this disclosure relate to bulk acoustic wave (BAW) assisted filter structures having a BAW resonator stacked on an integrated passive device (IPD). In exemplary embodiments disclosed herein, the BAW filter structure includes a transducer having electrodes and a piezoelectric layer between those electrodes. The IPD is electrically coupled to the BAW resonator and provides high-frequency operation. In such a configuration, the BAW assisted filter structure has low insertion loss and reduced parasitic losses due to its electrical proximity to the BAW resonator stacked on the IPD. Furthermore, the BAW assisted filter structure can filter high frequencies, improving filter performance and providing greater flexibility in the design of the filter transfer function.
[0005] One embodiment of the present disclosure relates to a bulk acoustic wave (BAW) assist filter structure including a laminate. The BAW assist filter structure further includes at least one integrated passive device (IPD) on the laminate. The at least one IPD includes an electrical circuit. The BAW assist filter structure further includes at least one BAW resonator on the IPD, which includes a substrate. The at least one BAW resonator further includes at least one transducer on the substrate. The at least one transducer includes a first electrode, a second electrode, and a piezoelectric layer between the first electrode and the second electrode. The electrical circuit of the at least one IPD is electrically coupled to the BAW resonator.
[0006] Another embodiment of the present disclosure relates to a method for manufacturing a bulk acoustic wave (BAW) assisted filter structure, which includes positioning at least one integrated passive device (IPD) on a laminate. The method involves positioning at least one BAW resonator on at least one IPD. Further including stacking, the BAW resonator includes a substrate and at least one transducer on the substrate. The at least one transducer includes a first electrode, a second electrode, and a piezoelectric layer between the first electrode and the second electrode. The method further includes electrically coupling at least one BAW resonator to an electrical circuit of at least one IPD.
[0007] Those skilled in the art will understand the scope of the present disclosure and recognize its additional aspects after reading the following detailed description of the preferred embodiments in connection with the figures of the accompanying drawings.
[0008] The figures of the accompanying drawings incorporated in and forming a part of this specification illustrate some aspects of the present disclosure and, together with the description, serve to explain the principles of the present disclosure.
Brief Description of the Drawings
[0009] [Figure 1] Illustrating a conventional bulk acoustic wave (BAW) resonator. [Figure 2] A graph of the magnitude and phase of impedance over the frequency response as a function of the frequency of an ideal BAW resonator. [Figure 3A] A graph of the phase response of various BAW resonator configurations. [Figure 3B] A graph of the phase response of various BAW resonator configurations. [Figure 3C] A graph of the phase response of various BAW resonator configurations. [Figure 4] Illustrating a conventional BAW resonator having a boundary ring. [Figure 5A] A schematic diagram of a conventional ladder-shaped circuit network. [Figure 5BC] A graph of the frequency response of a BAW resonator in the conventional ladder-shaped circuit network of FIG. 5A and the frequency response of the conventional ladder-shaped circuit network of FIG. 5A. [Figure 6ABCDE] An equivalent circuit of the ladder-shaped circuit network of FIG. 5A at the frequency points 1, 2, 3, 4, and 5 specified in FIG. 5C. [Figure 7] This is a cross-sectional side view of a BAW-assisted filter structure having BAW resonators stacked on an integrated passive device (IPD). [Figure 8] Figure 7 is a perspective view of an exemplary embodiment of the BAW assist filter structure. [Figure 9] Figures 7 and 8 illustrate the branching of the electrical filter circuit between the BAW resonator and the IPD in the BAW assist filter structure. [Figure 10] Figures 7-9 illustrate the performance improvement of the BAW-assisted filter structure compared to a BAW filter structure without an IPD. [Figure 11] Figures 7-10 are flowcharts showing the steps for manufacturing the BAW-assisted filter structure. [Modes for carrying out the invention]
[0010] The embodiments described below represent the information necessary to enable those skilled in the art to practice the embodiments and illustrate the best mode of practice. By reading the following description in reference to the drawings, those skilled in the art will understand the concepts of this disclosure and recognize the uses of these concepts that are not specifically addressed herein. It should be understood that these concepts and uses are included within the scope of this disclosure and the appended claims.
[0011] Terms such as "First," "Second," etc., may be used herein to describe various elements, but it should be understood that these elements should not be limited by these terms. These terms are used solely to distinguish one element from another. For example, the first element may be referred to as the second element, and similarly, the second element may be referred to as the first element without departing from the scope of this disclosure. Where used herein, the term "and / or" includes any and all combinations of one or more of the related enumerated items.
[0012] Furthermore, when an element is described as being "connected" or "joined" to another element, it should be understood that the element may be directly connected or joined to the other element, or there may be an intermediary element. In contrast, when an element is described as being "directly connected" or "directly joined" to another element, there is no intermediary element.
[0013] To describe various elements, this specification may use terms such as “top,” “bottom,” “bottom,” “middle,” “center,” and “top,” but it should be understood that these elements should not be limited by these terms. These terms are used solely to distinguish one element from another. For example, a first element may be referred to as a “top” element without departing from the scope of this disclosure, and similarly, a second element may be referred to as a “top” element depending on the relative orientation of these elements.
[0014] The technical terms used herein are solely for the purpose of describing specific embodiments and are not intended to limit this disclosure. Where used herein, the singular forms “a,” “an,” and “the” are intended to also include the plural forms unless the context specifically indicates otherwise. Where used herein, the terms “equip,” “equip,” “include,” and / or “include” specify the presence of a described feature, integer, step, action, element, and / or component, but do not exclude the presence or addition of one or more other features, integers, steps, actions, elements, components, and / or groups thereof.
[0015] Unless otherwise defined, all terms used herein (including technical and scientific terms) have the same meanings as commonly understood by those skilled in the art to which this disclosure belongs. Terms used herein should be construed in a way that is consistent with their meanings in the context of this specification and the related art, and it will be further understood that they should not be construed in an idealized or overly formalized sense unless expressly defined herein.
[0016] Embodiments of this disclosure relate to bulk acoustic wave (BAW) assisted filter structures having a BAW resonator stacked on an integrated passive device (IPD). In exemplary embodiments disclosed herein, the BAW filter structure includes a transducer having electrodes and a piezoelectric layer between those electrodes. The IPD is electrically coupled to the BAW resonator to provide high-frequency operation. In such a configuration, the BAW assisted filter structure has low insertion loss and reduced parasitic losses due to its electrical proximity to the BAW resonator stacked on the IPD. Furthermore, the BAW assisted filter structure can filter high frequencies, improving filter performance and providing greater flexibility in the design of the filter transfer function.
[0017] Before delving into the details of these concepts, an overview of BAW resonators and filters that use BAW resonators is provided. BAW resonators are used in many high-frequency filter applications. An exemplary BAW resonator 10 is shown in Figure 1. This BAW resonator 10 is a fixed-mount resonator (SMR) type BAW resonator 10 and generally includes a substrate 12, a reflector 14 mounted on the substrate 12, and a transducer 16 mounted on the reflector 14. The transducer 16 rests on the reflector 14 and includes a piezoelectric layer 18 sandwiched between a top electrode 20 and a bottom electrode 22. The top electrode 20 and bottom electrode 22 can be formed from tungsten (W), molybdenum (Mo), platinum (Pt), or similar materials, and the piezoelectric layer 18 can be formed from aluminum nitride (AlN), zinc oxide (ZnO), or other suitable piezoelectric material. Although shown in Figure 1 as including a single layer, the piezoelectric layer 18, top electrode 20, and / or bottom electrode 22 are multiple layers of the same material. It may include several layers, multiple layers in which at least two layers are different, or multiple layers in which each layer is made of a different material.
[0018] The BAW resonator 10 is divided into an active region 24 and an outer region 26. The active region 24 typically corresponds to the section of the BAW resonator 10 where the top electrode 20 and bottom electrode 22 overlap, and also includes a layer below the overlapping top electrode 20 and bottom electrode 22. The outer region 26 corresponds to the section of the BAW resonator 10 surrounding the active region 24.
[0019] In the BAW resonator 10, acoustic waves are excited within the piezoelectric layer 18 by applying electrical signals to both ends of the top electrode 20 and bottom electrode 22. These acoustic waves propagate mainly vertically. The main goal in BAW resonator design is to restrict these vertically propagating acoustic waves within the transducer 16. Acoustic waves traveling upward are reflected back into the transducer 16 by the air-metal boundary on the upper surface of the top electrode 20. Acoustic waves traveling downward are reflected back into the transducer 16 by the reflector 14 or by an air cavity located directly beneath the transducer in the thin-film BAW resonator (FBAR).
[0020] The reflector 14 is typically formed by a stack of reflector layers (RL) 28A-28E (commonly referred to as reflector layers 28) that alternate in material composition to generate a significant reflection coefficient at the junctions of adjacent reflector layers 28. Typically, reflector layers 28A-28E alternate between materials with high acoustic impedance, such as tungsten (W) and silicon dioxide (SiO2), and materials with low acoustic impedance. Although only five reflector layers 28A-28E are shown in Figure 1, the number of reflector layers 28 and the structure of the reflector 14 will vary depending on the design.
[0021] For a relatively ideal BAW resonator 10, the magnitude (Z) and phase (φ) of the electrical impedance as a function of frequency (GHz) are provided in Figure 2. The magnitude (Z) of the electrical impedance is shown by a solid line, while the phase (φ) of the electrical impedance is shown by a dashed line. An inherent feature of the BAW resonator 10 is that it has both a resonant frequency and an anti-resonant frequency. The resonant frequency is typically referred to as the series resonant frequency (fs), and the anti-resonant frequency is typically referred to as the parallel resonant frequency (fp). This series resonant frequency (fs) occurs when the magnitude of the impedance or reactance of the BAW resonator 10 approaches zero. This parallel resonant frequency (fp) occurs when the magnitude of the impedance or reactance of the BAW resonator 10 peaks at a significantly high level. Generally, the series resonant frequency (fs) is a function of the thickness of the piezoelectric layer 18, as well as the masses of the bottom electrode 22 and the top electrode 20.
[0022] Regarding phase, the BAW resonator 10 behaves like an inductance that gives a 90° phase shift between the series resonant frequency (fs) and the parallel resonant frequency (fp). In contrast, the BAW resonator 10 behaves like a capacitance that gives a -90° phase shift below the series resonant frequency (fs) and above the parallel resonant frequency (fp). The BAW resonator 10 exhibits very low, almost zero resistance at the series resonant frequency (fs) and very high resistance at the parallel resonant frequency (fp). The electrical properties of the BAW resonator 10 are themselves well-suited to realizing very high quality factor (Q) inductance over a relatively short frequency range, which has proven to be very beneficial in high-frequency filter networks, particularly in their operation at frequencies around and above 1.8 GHz.
[0023] Unfortunately, the phase (φ) curve in Figure 2 represents an ideal phase curve. In reality, approaching this ideal is difficult. A typical phase curve for the BAW resonator 10 in Figure 1 is illustrated in Figure 3A. The phase curve in Figure 3A is not a smooth curve, but rather a series resonant curve. Ripples are present below the wavenumber (fs), between the series resonant frequency (fs) and the parallel resonant frequency (fp), and above the parallel resonant frequency (fp). These ripples are a result of spurious modes caused by spurious resonances occurring at the corresponding frequencies. While most acoustic waves within the BAW resonator 10 propagate vertically, various boundary conditions around the transducer 16 lead to the propagation of acoustic waves in the transverse (horizontal) direction, which are referred to as transverse standing waves. The presence of these transverse standing waves reduces the potential quality factor (Q) associated with the BAW resonator 10.
[0024] As illustrated in Figure 4, a boundary (BO) ring 30 is formed above or inside the top electrode 20 to suppress certain spurious modes. The spurious modes suppressed by the BO ring 30 are those above the series resonant frequency (fs), as highlighted by circles A and B in the phase curve in Figure 3B. Circle A shows the suppression of spurious modes within the passband of the phase curve, i.e., ripple, that exists between the series resonant frequency (fs) and the parallel resonant frequency (fp). Circle B shows the suppression of spurious modes above the parallel resonant frequency (fp), i.e., ripple. In particular, spurious modes on the upper shoulder of the passband, just below the parallel resonant frequency (fp), and spurious modes above the passband are suppressed, as evidenced by the smooth or substantially ripple-free phase curve between the series resonant frequency (fs) and the parallel resonant frequency (fp), and above the parallel resonant frequency (fp).
[0025] The BO ring 30 corresponds to the mass loading of the portion of the top electrode 20 that extends around the periphery of the active region 24. The BO ring 30 may correspond to a thickened portion of the top electrode 20, or to the application of an additional layer of appropriate material on the top electrode 20. The portion of the BAW resonator 10 that includes the BO ring 30 and lies beneath it is referred to as the BO region 32. Thus, the BO region 32 corresponds to the outer peripheral portion of the active region 24 and lies inside the active region 24.
[0026] The BO ring 30 is effective in suppressing spurious modes above the series resonant frequency (fs), but as shown in Figure 3B, the BO ring 30 has little to no effect on those spurious modes below the series resonant frequency (fs). Often, a technique called apodization is used to suppress spurious modes below the series resonant frequency (fs).
[0027] Apodization works to avoid, or at least significantly reduce, any lateral symmetry within the BAW resonator 10, or at least within the transducer 16 of that BAW resonator. This lateral symmetry corresponds to the location of the transducer 16, and avoiding lateral symmetry corresponds to avoiding symmetry associated with the sides of the location. For example, a location corresponding to a pentagon rather than a square or rectangle may be chosen. Avoiding symmetry helps reduce the presence of lateral standing waves within the transducer 16. Circle C in Figure 3C shows the effect of apodization where spurious modes below the series resonant frequency (fs) are suppressed. It is easily seen in Figure 3C that, assuming the BO ring 30 is not provided, apodization would fail to suppress those spurious modes above the series resonant frequency (fs). Therefore, a typical BAW resonator 10 employs both apodization and the BO ring 30.
[0028] As described above, the BAW resonator 10 is often used in filter networks that operate at high frequencies and require a high Q factor. A basic ladder network 40 is illustrated in Figure 5A. This ladder network 40 consists of two series resonators B SER and two parallel resonators B SH These include, and they are aligned in a conventional ladder configuration. Typically, as shown in Figure 5B, a series resonator B SER , has the same or similar first frequency response, Parallel resonator B SHhas the same or a similar second frequency response, which is different from the first frequency response. In many applications, parallel resonator B SH is a detuned version of series resonator B SER . As a result, the frequency responses of series resonator B SER and parallel resonator B SH are generally very similar but still offset from each other. For this reason, the parallel resonance frequency (f P,SH ) of the parallel resonator is approximated to the series resonance frequency (f SER ) of series resonator B S,SER . It should be noted that the series resonance frequency (f S,SH ) of parallel resonator B SH is smaller than the series resonance frequency (f S,SER ) of series resonator B SER . The parallel resonance frequency (f P,SH ) of parallel resonator B SH is smaller than the parallel resonance frequency (f P,SER ) of series resonator B SER .
[0029] Figure 5C is related to Figure 5B and illustrates the response of ladder network 40. The series resonance frequency (f SH ) of parallel resonator B S,SH corresponds to the lower side of the skirt of the passband (phase 2), and the parallel resonance frequency (f P,SER ) of series resonator B SER corresponds to the higher side of the skirt of the passband (phase 4). The substantially matched series resonance frequency (f S,SER ) of series resonator B SER , and the parallel resonance frequency (f P,SH ) of parallel resonator B SH are within the passband.
[0030] Figures 6A - 6E provide equivalent circuits for five phases of the response of ladder network 40. During the first phase (phase 1, Figures 5C, 6A), ladder network 40 functions to attenuate the input signal. As it approaches the series resonance frequency (f S,SH ) of parallel resonator B SH , as it approaches the series resonance frequency of parallel resonator B SHThe impedance drops sharply, and as a result, parallel resonator B SH This is the series resonant frequency (f) of the parallel resonator (phase 2, Figures 5C and 6B). S,SH ) provides an effective short circuit to ground. Parallel resonator B SH The series resonant frequency (f S,SH In (phase 2), the input signal is effectively blocked from the output of the ladder-type network 40.
[0031] Parallel resonator B SH The series resonant frequency (f S,SH ) and series resonator B SER The parallel resonant frequency (f P,SER The space between ) corresponds to the passband, where the input signal passes to the output with relatively little or no attenuation (phase 3, Figures 5C, 6C). Within the passband, the series resonator B SER This exhibits a relatively low impedance, and in contrast to this, parallel resonator B SH The series resonator B exhibited a relatively high impedance, and the combination of two leads to a flat passband resulted in a steep low-end and a high-end. SER The parallel resonant frequency (f P,SER As we approach the series resonator B, SER The impedance becomes very high, and as a result, the series resonator B SER This itself is the parallel resonant frequency (f) of a series resonator. P,SER The opening in ) is substantially presented (phase 4, Figures 5C, 6D). Series resonator B SER The parallel resonant frequency (f P,SER During phase 4, the input signal is again substantially blocked from the output of the ladder network 40. During the final phase (phase 5, Figures 5C, 6E), the ladder network 40 functions to attenuate the input signal in a similar manner to that provided in phase 1. Series resonator B SER The parallel resonant frequency (f P,SER ) After passing through, series resonator B SER The impedance of parallel resonator B decreases, SH The impedance normalizes. Therefore, the ladder-type network 40 is a parallel resonator BSH The series resonant frequency (f S,SH ) and series resonator B SER The parallel resonant frequency (f P,SER ) functions to provide a high-Q passband between them. The ladder-type network 40 has parallel resonators B SH The series resonant frequency (f S,SH ), and the parallel resonant frequency (f) of the series resonator. P,SER It provides extremely high damping in both of the following ways. The ladder-type network 40 is a parallel resonator B SH The series resonant frequency (f S,SH Below ) and in series resonator B SER The parallel resonant frequency (f P,SER It provides good damping above ).
[0032] Having provided an overview of BAW resonators and filters that use BAW resonators, Figures 7A–711 discuss the details of BAW-assisted filter structures.
[0033] Figure 7 is a cross-sectional side view of a BAW-assisted filter structure 50 having a BAW filter structure 52 (which may also be referred to as a BAW die) stacked on an integrated passive device (IPD) 54. The BAW filter structure 52 includes one or more BAW resonators 10 (see Figure 1). In particular, the BAW-assisted filter structure 50 includes a base 56, an IPD 54 on the base layer 56, and a BAW resonator 52 on the IPD 54. In certain embodiments, the base 56 includes a laminate (e.g., a high-frequency (RF) laminate) or a printed circuit board (PCB). Furthermore, in certain embodiments, the BAW-assisted filter structure includes a cover 58 (e.g., a plastic cover) that covers at least a portion of the BAW filter structure 52, the IPD 54, and / or the base 56.
[0034] As described above, each BAW resonator 10 of the BAW filter structure 52 includes a substrate 12 and a transducer 16 on the substrate 12. The transducer 16 includes a top electrode 20, a bottom electrode 22, and a piezoelectric layer 18 between the top electrode 20 and the bottom electrode 22. The BAW resonators 10 of the BAW filter structure 52 may share a common substrate 12, top electrode 20, bottom electrode 22, and / or piezoelectric layer 18. Furthermore, the BAW filter structure 52 includes conductive pillars 60 for electrical coupling to the IPD 54. In certain embodiments, the BAW filter structure 52 includes a BAW fixed-mount resonator (SMR). In certain embodiments, the BAW filter structure 52 is fabricated on a die including a silicon carrier wafer having a plurality of BAW resonators 10 (e.g., BAW-SMR resonators), in which case the die further includes conductive pillars 60 (e.g., copper pillars).
[0035] The IPD54 includes an electrical circuit electrically coupled to the BAW filter structure 52. In certain embodiments, the IPD54 includes a conductive landing pad 62 (which may also be called a conductive via) configured to electrically couple to the BAW filter structure 52. In particular, this conductive landing pad 62 of the IPD54 (e.g., a copper landing pad) is matched to and in contact with (e.g., soldered to) a conductive pillar 60 of the BAW filter structure 52. In certain embodiments, the IPD54 includes a glass IPD, but other high-Q materials may be used. In certain embodiments, the IPD54 includes LC elements (inductors and capacitor elements) fabricated on a photo-defined and etchable glass die.
[0036] In a particular embodiment, the BAW filter structure 52 is inverted onto the IPD 54 to form a stacked die 64. The internal electrical nodes of the BAW filter structure 52 (e.g., its BAW resonator 10) and / or the IPD 54 are easily accessible, allowing for flexibility in the filter topology. The stacked die 64 can then be soldered (also referred to as solder joint) to a base layer 56 such as a laminate (e.g., a high-frequency (RF) laminate) or a printed circuit board (PCB).
[0037] The stacked die 64 of the BAW filter structure 52 and IPD 54 can handle frequencies higher than those that the BAW resonator 10 itself can handle (e.g., above 6 GHz). In particular, stacking the BAW filter structure 52 on top of the IPD 54 reduces the transmission path from the BAW filter structure 52 to the IPD 54, which increases Q. Thus, the BAW-assisted filter structure 50 can filter high frequencies with high Q. In certain embodiments, the stacked die 64 (e.g., the BAW filter structure 52 and / or IPD 54) includes an elliptic filter. An elliptic filter is a signal processing filter that has equalized ripple behavior in both the passband and stopband. The amount of ripple in each band is independently adjustable. In certain embodiments, the IPD 54 is a passband filter that includes a high-pass filter or a low-pass filter (e.g., a high-pass elliptic filter, a low-pass elliptic filter, etc.).
[0038] Figure 8 is a perspective view of an exemplary embodiment of the BAW assist filter structure of Figure 7. In particular, as discussed above, the BAW filter structure 52 is stacked on the IPD 54 to form a stacked die 64. As described above, the BAW filter structure 52 includes a conductive pillar 60 (see Figure 7) that is matched with and electrically coupled to the conductive landing pad 62 (see Figure 7) of the IPD 54. The IPD 54 is configured to receive an RF signal input 66 (e.g., via an input planar waveguide) and transmit an RF signal output 68 (e.g., via an output planar waveguide). The BAW filter structure 52 is electrically coupled to the IPD 54 at two or more junctions 70(1) to 70(3) downstream from the RF signal input 66 (between the RF signal input 66 and the RF signal output 68). In particular, the BAW filter structure 52 includes BAW resonators 10(1) to 10(3) that are electrically coupled at each of the junctions 70(1) to 70(3).
[0039] In a particular embodiment, the BAW resonators 10(1) to 10(3) of the BAW filter structure 52 are parallel BAW resonators 10(1) to 10(3) that communicate with parallel LC tank circuits 72(1), 72(2) (including inductors and capacitors). Each of the BAW resonators 10(1) to 10(3) forms a BAW resonator branch 74(1) to 74(3), respectively. The parallel BAW resonators 10(1) to 10(3) and / or parallel LC tank circuits 72(1), 72(2) are configured to create a low-resistance path for current.
[0040] The IPD includes series capacitors 76(1) to 76(4) (e.g., high-Q capacitors) between each of the BAW resonator branches 74(1) to 74(3). The series capacitors 76(1) to 76(4) couple the energy between the RF input 66 and the RF output 68.
[0041] In a particular embodiment, the IPD54 includes vias (e.g., via glass vias) that allow RF signals to propagate from the top to the bottom of the IPD54. Furthermore, these vias conduct heat and / or provide a high Q for the inductor.
[0042] Figure 9 is a circuit diagram illustrating the branching of the electrical filter circuit between the BAW filter structure 52 and the IPD 54 of the BAW assist filter structure 50 shown in Figures 7 and 8.
[0043] As described above, the BAW filter structure 52 is stacked on the IPD 54 to form a stacked die 64. The IPD 54 is configured to receive an RF signal input 66, and the BAW filter structure 52 is electrically coupled to the IPD 54 at three junctions 70(1) to 70(3) downstream from the RF signal input 66. In other words, the coupling of the conductive landing pad 62 (see Figure 7) to the pillar 60 (see Figure 7) is present at each of the junctions 70(1) to 70(3). Furthermore, the BAW resonator 10 of the BAW filter structure 52 is a parallel BAW resonator that electrically communicates with parallel LC tank circuits 72(1), 72(2) (including inductors and capacitors) provided on the IPD 54. The IPD 54 includes series capacitors 76(1) to 76(4) between each of the BAW resonator branches 74(1) to 74(3).
[0044] The resulting signal path includes an input RF signal 66 propagating to the first junction 70(1), where the first signal portion propagates to ground through the first BAW resonator branch 74(1), and the remaining main signal portion propagates through the first series capacitor 76(1). Next, the second signal portion propagates through the first parallel LC tank circuit 72(1), and the remaining main signal portion propagates through the second series capacitor 76(2). Next, the third signal portion propagates to ground through the second BAW resonator branch 74(2), and the remaining main signal portion propagates through the third series capacitor 76(3). Next, the fourth signal portion propagates through the second parallel LC tank circuit 72(2), and the remaining main signal portion propagates through the fourth series capacitor 76(4). Next, the fifth signal portion propagates to ground through the third BAW resonator branch 74(3), and the remaining The main signal portion of the signal propagates as the output RF signal 68.
[0045] As a result, the BAW-assisted filter structure has low insertion loss. In particular, the high-Q inductor and capacitor structure of the glass IPD54 can be utilized in the design and, through stacking, can be efficiently distributed to the internal nodes of the filter network and electrically close to the high-Q BAW resonator 10. The BAW-assisted filter structure has high-frequency operation. In particular, the high self-resonance (SRF) characteristics of the glass IPD54 and three-dimensional inductor structure can be utilized in design topologies that lead to higher frequency filters (e.g., above 6 GHz).
[0046] The BAW-assisted filter structure 50 has the advantage of a useful transfer function. In particular, the reduction of parasitic electrical length is achieved through die stacking and the effectiveness of short interconnect lengths. RF grounding and RF grounding coupling become dominant in the high-frequency region where the electrical length of the interconnect significantly affects the filter RF transfer function.
[0047] The BAW-assisted filter structure 52 provides a flexible filter topology because the stacking of dies allows for greater flexibility in the design of the filter transfer function. The BAW filter structure enables pseudo-elliptic filter topologies for high-pass and low-pass filters, and a wider achievable bandwidth. This is an advantage of the BAW resonator over the bandwidth limitations of other band-pass ladder structures, in which case the fixed impedance characteristics are inherent to an acoustic resonator where parallel and series resonances are tuned by the acoustic coupling coefficient (k²eff).
[0048] Figure 10 is a graph illustrating the performance improvement of the BAW-assisted filter structures shown in Figures 7-9 compared to BAW filter structures without IPD. In particular, this graph shows the transfer function of the BAW filter structure 78 exhibiting wider bandwidth and high-frequency operation compared to the LC high-pass filter 80 in a similar order. As shown in the figure, the BAW-assisted filter structure provides a steeper tail with a wider bandwidth. In certain embodiments, the BAW-assisted filter structure has a partial bandwidth of 15-25%. In certain embodiments, the partial bandwidth is 18-22%. In certain embodiments, the partial bandwidth is approximately 21%. The BAW-assisted filter structure provides low loss and a steep transition.
[0049] Figure 11 is a flowchart of the steps for manufacturing the BAW-assisted filter structures shown in Figures 7-10. Step 1100 includes stacking at least one BAW resonator on an IPD. The BAW resonator includes a substrate and at least one transducer, the at least one transducer comprising a first electrode, a second electrode, and a piezoelectric layer between the first electrode and the second electrode. Step 1102 includes electrically coupling the at least one BAW resonator to the IPD.
[0050] In certain embodiments, at least one IPD includes a glass IPD. In certain embodiments, the IPD includes a series capacitor. In certain embodiments, the IPD includes a parallel LC tank circuit. In certain embodiments, the IPD includes a series capacitor and a parallel LC tank circuit. In certain embodiments, the IPD includes a conductive landing pad for electrically coupling to at least one BAW resonator. In certain embodiments, at least one BAW resonator includes a pillar for electrically coupling to the IPD. In certain embodiments, the IPD includes a conductive landing pad, and at least one BAW resonator includes a pillar that is matched to and electrically coupled to the conductive landing pad of the IPD. In certain embodiments, the IPD is configured to receive an RF signal input, and at least one BAW resonator is electrically coupled to the IPD at two or more junctions downstream from the RF signal input.
[0051] Those skilled in the art will recognize improvements and modifications to preferred embodiments of this disclosure. All such improvements and modifications are considered within the scope of the concepts disclosed herein and the subsequent claims.
Claims
1. A bulk acoustic wave (BAW) assist filter structure, An integrated passive device (IPD) including an electrical circuit, The IPD comprises at least one BAW resonator, circuit board and The substrate has at least one transducer, and the at least one transducer is The first electrode and The second electrode and A bulk acoustic wave (BAW) assist filter structure comprising: at least one transducer, each having a piezoelectric layer between the first electrode and the second electrode, wherein the electrical circuit of the at least one IPD is electrically coupled to the BAW resonator.
2. The BAW assist filter structure according to claim 1, wherein the at least one IPD comprises a glass IPD.
3. The BAW assist filter structure according to claim 1, wherein the at least one IPD comprises an elliptic filter.
4. The BAW assist filter structure according to claim 1, wherein the at least one IPD comprises at least one of a high-pass filter or a low-pass filter.
5. The BAW assist filter structure according to claim 1, wherein the IPD comprises a series capacitor.
6. The BAW assist filter structure according to claim 1, wherein the IPD comprises a parallel LC tank circuit.
7. The BAW assist filter structure according to claim 1, wherein the IPD comprises a series capacitor and a parallel LC tank circuit.
8. The BAW assist filter structure according to claim 1, wherein the IPD comprises a conductive landing pad for electrically coupling to the at least one BAW resonator.
9. The BAW assist filter structure according to claim 1, wherein the at least one BAW resonator comprises a pillar for electrically coupling to the IPD.
10. The IPD is equipped with a conductive landing pad, The at least one BAW resonator comprises a pillar that is matched to and electrically coupled with the conductive landing pad of the IPD. The BAW assist filter structure according to claim 1.
11. The BAW assist filter structure according to claim 1, wherein the IPD is configured to receive an RF signal input, and the at least one BAW resonator is electrically coupled to the IPD at two or more junctions downstream of the RF signal input.
12. A method for manufacturing a bulk acoustic wave (BAW) assist filter structure, Stacking at least one BAW resonator on at least one integrated passive device (IPD), wherein the BAW resonator comprises a substrate and at least one on the substrate A transducer comprising, wherein at least one transducer comprises a first electrode, a second electrode, and a piezoelectric layer between the first electrode and the second electrode, and is stackable. The at least one BAW resonator is electrically coupled to the electrical circuit of the at least one IPD, Methods that include...
13. The method according to claim 12, wherein the at least one IPD comprises a glass IPD.
14. The method according to claim 12, wherein the IPD comprises a series capacitor.
15. The method according to claim 12, wherein the IPD comprises a parallel LC tank circuit.
16. The method according to claim 12, wherein the IPD comprises a series capacitor and a parallel LC tank circuit.
17. The method according to claim 12, wherein the IPD comprises a conductive landing pad for electrically coupling to the at least one BAW resonator.
18. The method according to claim 12, wherein the at least one BAW resonator comprises a pillar for electrically coupling to the IPD.
19. The IPD is equipped with a conductive landing pad, The at least one BAW resonator comprises a pillar that is matched to and electrically coupled with the conductive landing pad of the IPD. The method according to claim 12.
20. The method according to claim 12, wherein the IPD is configured to receive an RF signal input, and the at least one BAW resonator is electrically coupled to the IPD at two or more junctions downstream of the RF signal input.