Bulk acoustic wave resonator stacked on integrated passive device

Abstract

To provide a bulk acoustic wave (BAW) assist filter structure and a manufacturing method thereof that improve a performance of an integrated BAW resonator and a BAW base filter, and reduces cost and size associated with them.SOLUTION: A BAW assist filter structure 50 includes a BAW filter structure 52, an integrated passive device (IPD) 54, and a base 56. The IPD 54 is electrically coupled to a BAW resonator having an electrode and a piezoelectric layer to provide a high frequency operation. The BAW assist filter structure is in electrical proximity to the BAW resonator stacked on the IPD, has low insertion loss, and reduces parasitic losses along an electrical length. The BAW assist filter structure improves a high frequency filtering performance.SELECTED DRAWING: Figure 7

Description

[Technical Field]

[0001] The present invention relates to a bulk acoustic wave (BAW) assisted filter structure having at least one BAW resonator stacked on an integrated passive device for high frequency processing. [Background technology]

[0002] Acoustic resonators, and particularly bulk acoustic wave (BAW) resonators, are used in many high-frequency communications applications. In particular, BAW resonators are often employed in filter networks that operate at frequencies above 1.5 GHz, require a flat passband, have very steep filter skirts and rectangular shoulders at the upper and lower ends of the passband, and provide excellent rejection bands outside the passband. BAW-based filters also have relatively low insertion loss, tend to decrease in size as operating frequency increases, and are relatively stable over a wide temperature range. Therefore, BAW-based filters are the filters 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 posing very challenging filtering requirements. These demands continue to increase the complexity of wireless devices, while there is a constant need to improve the performance of BAW resonators and BAW-based filters and reduce their associated cost and size.

[0003] Currently, BAW-based filters have difficulty filtering signals above approximately 6 GHz. In particular, as frequency increases, losses typically increase as well. Filtering at higher frequencies with BAW-based filters remains challenging. Summary of the Invention

[0004] Embodiments of the present disclosure are directed to a bulk acoustic wave (BAW)-assisted filter structure having a BAW resonator stacked on an integrated passive device (IPD). In the exemplary embodiment disclosed herein, the BAW filter structure includes a transducer having electrodes and a piezoelectric layer between the 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 mitigates parasitic electrical length 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 designing the filter transfer function.

[0005] One embodiment of the present disclosure relates to a bulk acoustic wave (BAW)-assisted filter structure including a laminate. The BAW-assisted 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-assisted 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 and second electrodes. 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 fabricating a bulk acoustic wave (BAW)-assisted filter structure, including positioning at least one integrated passive device (IPD) on a stack. The method further includes stacking at least one BAW resonator on the at least one IPD, the BAW resonator comprising 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 and second electrodes. The method further includes electrically coupling the at least one BAW resonator to an electrical circuit of the at least one IPD.

[0007] Those skilled in the art will appreciate the scope of the present disclosure and realize additional aspects thereof after reading the following detailed description of the preferred embodiments in conjunction with the accompanying drawing figures.

[0008] The accompanying drawing figures, which are incorporated in and form a part of this specification, illustrate several aspects of the disclosure and, together with the description, serve to explain the principles of the disclosure. [Brief explanation of the drawings]

[0009] [Figure 1] 1 illustrates a conventional bulk acoustic wave (BAW) resonator. [Figure 2] 1 is a graph of the impedance magnitude and phase over frequency response as a function of frequency for an ideal BAW resonator. [Figure 3A] 1 is a graph of the phase response of various BAW resonator configurations. [Figure 3B] 1 is a graph of the phase response of various BAW resonator configurations. [Figure 3C] 1 is a graph of the phase response of various BAW resonator configurations. [Figure 4] 1 illustrates a conventional BAW resonator with boundary rings. [Figure 5A] FIG. 1 is a schematic diagram of a conventional ladder network. [Figure 5BC]5B is a graph of the frequency response of a BAW resonator in the conventional ladder network of FIG. 5A and the frequency response for the conventional ladder network of FIG. 5A. [Figure 6ABCDE] 5C is an equivalent circuit of the ladder network of FIG. 5A at frequency points 1, 2, 3, 4, and 5 identified in FIG. 5C. [Figure 7] FIG. 1 is a cross-sectional side view of a BAW-assisted filter structure having a BAW resonator stacked on an integrated passive device (IPD). [Figure 8] 8 is a perspective view of an exemplary embodiment of the BAW-assisted filter structure of FIG. 7. [Figure 9] FIG. 9 is a circuit diagram illustrating a branch of an electrical filter circuit between a BAW resonator and an IPD in the BAW-assisted filter structure of FIGS. 7 and 8. [Figure 10] 10 is a graph illustrating the performance improvement of the BAW-assisted filter structure of FIGS. 7-9 compared to a BAW filter structure without an IPD. [Figure 11] 11 is a flowchart of steps for manufacturing the BAW-assisted filter structure of FIGS. DETAILED DESCRIPTION OF THE INVENTION

[0010] The embodiments described below represent the necessary information to enable one skilled in the art to practice the embodiments and illustrate the best modes of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, one skilled in the art will understand the concepts of the present disclosure and recognize applications of these concepts not specifically addressed herein. It is understood that these concepts and applications are included within the scope of the present 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 only to distinguish one element from another. For example, a first element may be referred to as a second element, and similarly, a second element may be referred to as the first element without departing from the scope of the present disclosure. As used herein, the term "and / or" includes any and all combinations of one or more of the associated listed items.

[0012] It should also be understood that when an element is referred to as being "connected" or "coupled" to another element, the element may be directly connected or coupled to the other element, or there may be intervening elements. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements.

[0013] Terms such as "top," "lower," "bottom," "middle," "center," and "top" may be used herein to describe various elements, but it should be understood that these elements are not limited by these terms. These terms are used only to distinguish one element from another. For example, a first element may be referred to as the "top" element without departing from the scope of the present disclosure, and similarly, a second element may be referred to as the "top" element, depending on the relative orientation of these elements.

[0014] The terminology used herein is for the purpose of describing particular embodiments only and is not intended to limit the disclosure. As used herein, the singular forms "a," "an," and "the" are intended to include the plural forms as well, unless the context clearly dictates otherwise. It will be further understood that as used herein, the terms "comprises," "comprises," "includes," and / or "comprising" specify the presence of stated features, integers, steps, operations, elements, and / or components, but do not exclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and / or groups thereof.

[0015] Unless otherwise defined, all terms (including technical and scientific terms) used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this disclosure belongs. Terms used herein should be interpreted as having a meaning consistent with their meaning in the context of this specification and related art, and will be further understood not to be interpreted in an idealized or overly formalized sense unless expressly defined as such herein.

[0016] Embodiments of the present disclosure are directed to a bulk acoustic wave (BAW)-assisted filter structure having a BAW resonator stacked on an integrated passive device (IPD). In the exemplary embodiment disclosed herein, the BAW filter structure includes a transducer having electrodes and a piezoelectric layer between the 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 mitigates parasitic electrical length 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 designing the filter transfer function.

[0017] Before delving into the details of these concepts, an overview of BAW resonators and filters that use BAW resonators will be provided. BAW resonators are used in many high-frequency filter applications. An exemplary BAW resonator 10 is shown in FIG. 1. The 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 the bottom electrode 22 can be formed of tungsten (W), molybdenum (Mo), platinum (Pt), or a similar material, and the piezoelectric layer 18 can be formed of aluminum nitride (AlN), zinc oxide (ZnO), or other suitable piezoelectric materials. Although shown in FIG. 1 as including a single layer, piezoelectric layer 18, top electrode 20, and / or bottom electrode 22 may include multiple layers of the same material, multiple layers where at least two layers are different layers, or multiple layers where each layer is a different material.

[0018] BAW resonator 10 is divided into an active region 24 and an outer region 26. The active region 24 generally corresponds to the section of BAW resonator 10 where top and bottom electrodes 20, 22 overlap, and also includes layers below the overlapping top and bottom electrodes 20, 22. The outer region 26 corresponds to the section of BAW resonator 10 that surrounds active region 24.

[0019] For BAW resonator 10, acoustic waves are excited in piezoelectric layer 18 by applying an electrical signal across top electrode 20 and bottom electrode 22. These acoustic waves propagate primarily vertically. A primary goal in BAW resonator design is to confine these vertically propagating acoustic waves within transducer 16. Upward-propagating acoustic waves are reflected back into transducer 16 by the air-metal boundary on the upper surface of top electrode 20. Downward-propagating acoustic waves are reflected back into transducer 16 by reflector 14 or by an air cavity located directly below the transducer in a 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 produce a significant reflection coefficient at the junction of adjacent reflector layers 28. Typically, the reflector layers 28A-28E alternate between materials having high acoustic impedances, such as tungsten (W) and silicon dioxide (SiO2), and materials having low acoustic impedances. Although only five reflector layers 28A-28E are shown in FIG. 1, the number of reflector layers 28 and the structure of the reflector 14 will vary by design.

[0021] The magnitude (Z) and phase (φ) of the electrical impedance as a function of frequency (GHz) for a relatively ideal BAW resonator 10 are provided in FIG. 2. The magnitude (Z) of the electrical impedance is shown as a solid line, while the phase (φ) of the electrical impedance is shown as a dashed line. A unique 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 higher level. In general, the series resonant frequency (fs) is a function of the thickness of the piezoelectric layer 18 and the masses of the bottom electrode 22 and top electrode 20.

[0022] In terms of phase, the BAW resonator 10 behaves like an inductance, imparting 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, imparting a -90° phase shift below the series resonant frequency (fs) and above the parallel resonant frequency (fp). The BAW resonator 10 presents very low, nearly 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 lend themselves to achieving very high quality factor (Q) inductance over a relatively short range of frequencies, which has proven very beneficial in high-frequency filter networks, particularly those operating at frequencies near and above 1.8 GHz.

[0023] Unfortunately, the phase (φ) curve in FIG. 2 represents an ideal phase curve. In reality, it is difficult to approach this ideal. A typical phase curve for the BAW resonator 10 of FIG. 1 is illustrated in FIG. 3A. The phase curve in FIG. 3A is not smooth but contains ripples below the series resonance frequency (fs), between the series resonance frequency (fs) and the parallel resonance frequency (fp), and above the parallel resonance frequency (fp). The ripples are the result of spurious modes caused by spurious resonances occurring at the corresponding frequencies. While the majority of acoustic waves within the BAW resonator 10 propagate vertically, various boundary conditions around the transducer 16 result in the propagation of transverse (horizontal) acoustic waves, 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 FIG. 4, a boundary (BO) ring 30 is formed on or within the top electrode 20 to suppress certain spurious modes. The spurious modes suppressed by the BO ring 30 are those above the series resonance frequency (fs), as highlighted by circles A and B in the phase curve of FIG. 3B. Circle A indicates the suppression of ripples, i.e., spurious modes within the passband of the phase curve that exist between the series resonance frequency (fs) and the parallel resonance frequency (fp). Circle B indicates the suppression of ripples, i.e., spurious modes above the parallel resonance frequency (fp). In particular, spurious modes in the upper shoulder of the passband just below the parallel resonance frequency (fp) and spurious modes above the passband are suppressed, as evidenced by the smooth or substantially ripple-free phase curves between the series resonance frequency (fs) and the parallel resonance frequency (fp) and above the parallel resonance 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 an appropriate material on the top electrode 20. The portion of the BAW resonator 10 that includes and resides below the BO ring 30 is referred to as the BO region 32. The BO region 32 thus corresponds to the outer periphery of the active region 24 and resides within the active region 24.

[0026] While the B-O ring 30 is effective in suppressing spurious modes above the series resonant frequency (fs), as shown in Figure 3B, the B-O ring 30 has little or no effect on those spurious modes below the series resonant frequency (fs). A technique called apodization is often used to suppress spurious modes below the series resonant frequency (fs).

[0027] Apodization serves 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 may be selected rather than a square or rectangle. Avoiding symmetry helps reduce the presence of lateral standing waves within the transducer 16. Circle C in Figure 3C illustrates the effect of apodization in suppressing spurious modes below the series resonant frequency (fs). It is easy to see in Figure 3C that apodization fails to suppress those spurious modes above the series resonant frequency (fs) if the B-O ring 30 were not provided. Therefore, a typical BAW resonator 10 employs both apodization and a B-O ring 30.

[0028] As mentioned above, BAW resonators 10 are often used in filter networks that operate at high frequencies and require high Q values. 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 , which are arranged in a conventional ladder configuration. Typically, as shown in FIG. 5B, a series resonator B SER have the same or similar first frequency response, and parallel resonator B SH has the same or similar second frequency response, which is different from the first frequency response. In many applications, the parallel resonator B SH is the series resonator B SER As a result, the series resonator B SER and parallel resonator B SH The frequency responses of the parallel resonators are generally very similar, but still offset from each other, so that the parallel resonant frequency (f P,SH ) is the series resonator B SER The series resonance frequency (f S,SER ) Parallel resonator B SH The series resonance frequency (f S,SH ) is the series resonator B SER The series resonance frequency (f S,SER ) is smaller than the parallel resonator B. SH The parallel resonance frequency (f P,SH ) is the series resonator B SER The parallel resonance frequency (f P,SER ) is smaller than

[0029] Figure 5C is related to Figure 5B and illustrates the response of ladder network 40. Parallel resonator B SH The series resonance frequency (f S,SH ) corresponds to the lower side of the passband skirt (phase 2), and the series resonator B SER The parallel resonance frequency (f P,SER ) corresponds to the higher side of the passband skirt (phase 4). SER The substantially matched series resonant frequency (f S,SER ), and parallel resonator B SHThe parallel resonance frequency (f P,SH ) is within the passband.

[0030] 6A-6E provide equivalent circuits for the five phases of the response of ladder network 40. During the first phase (phase 1, FIGS. 5C and 6A), ladder network 40 functions to attenuate the input signal. SH The series resonance frequency (f S,SH ), the parallel resonator B SH The impedance of the parallel resonator B drops sharply. SH is the series resonant frequency (f S,SH ) provides a short circuit to ground. SH The series resonance frequency (f S,SH ) (Phase 2), the input signal is substantially blocked from the output of ladder network 40.

[0031] Parallel resonator B SH The series resonance frequency (f S,SH ) and series resonator B SER The parallel resonance frequency (f P,SER ) corresponds to the passband, where the input signal passes to the output with relatively little or no attenuation (Phase 3, Figures 5C and 6C). Within the passband, the series resonator B SER presents a relatively low impedance, whereas the parallel resonator B SH presents a relatively high impedance, and the combination of the two leads to a flat passband results in a steep lower and upper skirt. SER The parallel resonance frequency (f P,SER ), the series resonator B SER The impedance of the series resonator B becomes very high. SER is itself the parallel resonant frequency of the series resonator (f P,SER ) is presented as an opening in the series resonator B (phase 4, Figs. 5C and 6D). SER The parallel resonance frequency (f P,SER) (Phase 4), the input signal is again substantially blocked from the output of ladder network 40. During the final phase (Phase 5, FIGS. 5C, 6E), ladder network 40 functions to attenuate the input signal in a manner similar to that provided in Phase 1. SER The parallel resonance frequency (f P,SER ) passes through the series resonator B SER The impedance of the parallel resonator B decreases. SH Therefore, the ladder network 40 is connected to the parallel resonator B SH The series resonance frequency (f S,SH ) and series resonator B SER The parallel resonance frequency (f P,SER ) and the ladder network 40 functions to provide a high-Q passband between the parallel resonator B SH The series resonance frequency (f S,SH ), and the parallel resonant frequency of the series resonator (f P,SER ) provides extremely high attenuation. The ladder network 40 includes a parallel resonator B SH The series resonance frequency (f S,SH ) and series resonator B SER The parallel resonance frequency (f P,SER ) provides good attenuation above

[0032] Having provided an overview of BAW resonators and filters that use BAW resonators, FIGS. 7A-11 consider the details of BAW-assisted filter structures.

[0033] 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 FIG. 1 ). In particular, the BAW-assisted filter structure 50 includes a base 56, an IPD 54 on the base layer 56, and the BAW resonator 52 on the IPD 54. In certain embodiments, the base 56 includes a laminate (e.g., a radio 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 and bottom electrodes 20 and 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. Additionally, the BAW filter structure 52 includes conductive pillars 60 for electrically coupling to the IPD 54. In a specific embodiment, the BAW filter structure 52 includes a BAW fixed-mount resonator (SMR). In a specific embodiment, 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), where the die further includes conductive pillars 60 (e.g., copper pillars).

[0035] The IPD 54 includes electrical circuitry electrically coupled to the BAW filter structure 52. In a particular embodiment, the IPD 54 includes conductive landing pads 62 (which may also be referred to as conductive vias) configured to electrically couple to the BAW filter structure 52. In particular, the conductive landing pads 62 (e.g., copper landing pads) of the IPD 54 are aligned with and contact (e.g., solder-bonded to) the conductive pillars 60 of the BAW filter structure 52. In a particular embodiment, the IPD 54 includes a glass IPD, although other high-Q materials may be used. In a particular embodiment, the IPD 54 includes LC elements (inductor and capacitor elements) fabricated on a photodefined die and etchable glass.

[0036] In one 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 resonators 10) and / or the IPD 54 are easily accessible, allowing for flexibility in filter topology. The stacked die 64 can then be soldered (which may also be referred to as solder bonding) to a base layer 56, such as a laminate (e.g., a radio frequency (RF) laminate) or a printed circuit board (PCB).

[0037] The stacked die 64 of the BAW filter structure 52 and the IPD 54 can handle higher frequencies (e.g., above 6 GHz) than the BAW resonator 10 itself can handle. In particular, stacking the BAW filter structure 52 on the IPD 54 reduces the transmission path from the BAW filter structure 52 to the IPD 54, which increases the Q. Therefore, the BAW-assisted filter structure 50 can filter high frequencies with a high Q. In a specific embodiment, the stacked die 64 (e.g., the BAW filter structure 52 and / or the IPD 54) includes an elliptic filter. An elliptic filter is a signal processing filter that has equalized ripple behavior in both the passband and the stopband. The amount of ripple in each band is independently adjustable. In a specific embodiment, 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] FIG. 8 is a perspective view of an exemplary embodiment of the BAW-assisted filter structure of FIG. 7. In particular, as discussed above, the BAW filter structure 52 is stacked on the IPD 54 to form a stacked die 64. As noted above, the BAW filter structure 52 includes conductive pillars 60 (see FIG. 7) aligned with and electrically coupled to conductive landing pads 62 (see FIG. 7) of the IPD 54. The IPD 54 is configured to receive an RF signal input 66 (e.g., at an input planar waveguide) and transmit an RF signal output 68 (e.g., at an output planar waveguide). The BAW filter structure 52 is electrically coupled to the IPD 54 at two or more junctions 70(1)-70(3) downstream from the RF signal input 66 (between the RF signal input 66 and the RF signal output 68). In particular, BAW filter structure 52 includes BAW resonators 10(1)-10(3) electrically coupled at each of junctions 70(1)-70(3), respectively.

[0039] In one particular embodiment, BAW resonators 10(1)-10(3) of BAW filter structure 52 are parallel BAW resonators 10(1)-10(3) in electrical communication with parallel LC tank circuits 72(1), 72(2) (including inductors and capacitors). BAW resonators 10(1)-10(3) each form a BAW resonator branch 74(1)-74(3), respectively. Parallel BAW resonators 10(1)-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)-76(4) (e.g., high-Q capacitors) between each of the BAW resonator branches 74(1)-74(3). The series capacitors 76(1)-76(4) couple energy between the RF input 66 and the RF output 68.

[0041] In one particular embodiment, the IPD 54 includes vias (e.g., through glass vias) that allow RF signals to propagate from the top of the IPD 54 to the bottom of the IPD 54. Additionally, the vias conduct heat and / or provide a high Q for the inductors.

[0042] FIG. 9 is a circuit diagram illustrating the branch of the electrical filter circuit between the BAW filter structure 52 and the IPD 54 of the BAW-assisted filter structure 50 of FIGS.

[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)-70(3) downstream from the RF signal input 66. In other words, coupling of the conductive landing pad 62 (see FIG. 7) to the pillar 60 (see FIG. 7) occurs at each of the junctions 70(1)-70(3). Furthermore, the BAW resonator 10 of the BAW filter structure 52 is a parallel BAW resonator in electrical communication with parallel LC tank circuits 72(1), 72(2) (including an inductor and a capacitor) provided on the IPD 54. The IPD 54 includes series capacitors 76(1)-76(4) between each of the BAW resonator branches 74(1)-74(3).

[0044] The resulting signal path involves the input RF signal 66 propagating to the first junction 70(1), where a first signal portion propagates through the first BAW resonator branch 74(1) to ground and the remaining main signal portion propagates through the first series capacitor 76(1). Then, a 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). Then, a third signal portion propagates through the second BAW resonator branch 74(2) to ground and the remaining main signal portion propagates through the third series capacitor 76(3). Then, a 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). The fifth signal portion then propagates through the third BAW resonator branch 74(3) to ground, and the remaining main signal portion 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 structures of the glass IPD 54 can be exploited in the design and distributed efficiently to the internal nodes of the filter network through stacking and in electrical proximity to the high-Q BAW resonators 10. The BAW-assisted filter structure has high-frequency operation. In particular, the high self-resonance (SRF) characteristics of the glass IPD 54 and three-dimensional inductor structures can be exploited in design topologies leading to higher frequency filters (e.g., above 6 GHz).

[0046] The BAW-assisted filter structure 50 has transfer function advantages. In particular, electrical length parasitic mitigation is achieved by virtue of die stacking and short interconnect lengths. RF ground and RF ground coupling become dominant at high frequencies where the electrical length of interconnects significantly impacts the filter RF transfer function.

[0047] The BAW-assisted filter structure 52 offers flexible filter topologies because die stacking allows for greater flexibility in the design of the filter transfer function. The BAW filter structure allows for high-pass and low-pass quasi-elliptic filter topologies and wider achievable bandwidths. This is an advantage of BAW resonators over the bandwidth limitations of other bandpass ladder structures, where the fixed impedance characteristics are inherent to acoustic resonators where the parallel and series resonances are tuned by the acoustic coupling coefficient (k2eff).

[0048] FIG. 10 is a graph illustrating the performance improvement of the BAW-assisted filter structure of FIGS. 7-9 compared to a BAW filter structure without an IPD. In particular, the graph shows a transfer function illustrating the wide bandwidth and high-frequency operation of the BAW filter structure 78 relative to a similarly ordered LC high-pass filter 80. As shown, the BAW-assisted filter structure provides a steeper tail with a wider bandwidth. In one specific embodiment, the BAW-assisted filter structure has a fractional bandwidth of 15-25%. In one specific embodiment, the fractional bandwidth is 18-22%. In one specific embodiment, the fractional bandwidth is approximately 21%. The BAW-assisted filter structure provides low loss and a sharp transition.

[0049] FIG. 11 is a flowchart of steps for fabricating the BAW-assisted filter structure of FIGS. 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 including 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, the 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 the at least one BAW resonator. In certain embodiments, the 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 the at least one BAW resonator includes a pillar aligned with 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 the 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 the preferred embodiments of the present disclosure, and all such improvements and modifications are considered within the scope of the concepts disclosed herein and the claims that follow.

Claims

1. A bulk acoustic wave (BAW) assist filter structure, the bulk acoustic wave (BAW) assist filter structure comprising: At least one integrated passive device (IPD) including an electrical circuit including an inductor and a capacitor element; Located on the at least one IPD and A substrate; At least one BAW resonator provided with at least one transducer on the substrate And at least one BAW resonator, the at least one transducer comprising: A first electrode; A second electrode; A piezoelectric layer between the first electrode and the second electrode And the electrical circuit of the at least one IPD is electrically coupled to the at least one BAW resonator, The at least one IPD includes a conductive landing pad and a photo-patterned and etchable glass die, and the inductor and capacitor elements are on the die, The at least one BAW resonator includes pillars aligned and electrically coupled with the conductive landing pads of the at least one IPD, A bulk acoustic wave (BAW) assist filter structure.

2. The BAW assist filter structure according to claim 1, wherein the at least one IPD includes an elliptical filter.

3. The BAW assist filter structure according to claim 1, wherein the at least one IPD includes at least one of a high-pass filter or a low-pass filter.

4. The BAW assist filter structure according to claim 1, wherein the at least one IPD includes a series capacitor.

5. The BAW assist filter structure according to claim 1, wherein the at least one IPD includes a parallel LC tank circuit.

6. The BAW assist filter structure according to claim 1, wherein the at least one IPD includes a series capacitor and a parallel LC tank circuit.

7. The BAW assist filter structure according to claim 1, wherein the at least one IPD includes a conductive landing pad for electrically coupling to the at least one BAW resonator.

8. ​ The BAW assist filter structure according to claim 1, wherein the at least one BAW resonator comprises the pillar for electrically coupling to the at least one IPD.

9. The BAW assist filter structure according to claim 1, wherein the at least one IPD is configured to receive an RF signal input, and the at least one BAW resonator is electrically coupled to the at least one IPD at two or more joints downstream from the RF signal input.

10. A method of manufacturing a bulk acoustic wave (BAW) assist filter structure, a step of stacking at least one BAW resonator on at least one integrated passive device (IPD), wherein the at least one BAW resonator comprises a substrate and at least one transducer on the substrate, and the at least one transducer comprises a first electrode, a second electrode, and a piezoelectric layer between the first electrode and the second electrode, the IPD comprising an electronic circuit having inductor and capacitor elements, and a die of photo-patterned and etchable glass, on which the inductor and capacitor elements are located, a step; a step of electrically coupling the at least one BAW resonator to an electrical circuit of the at least one IPD, wherein the at least one IPD comprises a conductive landing pad, and the at least one BAW resonator comprises a pillar aligned with and electrically coupled to the conductive landing pad of the at least one IPD and including.

11. The method according to claim 10, wherein the at least one IPD comprises a series capacitor.

12. The method according to claim 10, wherein the at least one IPD comprises a parallel LC tank circuit.

13. The method according to claim 10, wherein the at least one IPD comprises a series capacitor and a parallel LC tank circuit.

14. The method according to claim 10, wherein the at least one IPD comprises the conductive landing pad for electrically coupling to the at least one BAW resonator.

15. The method according to claim 10, wherein the at least one BAW resonator comprises the pillar for electrically coupling to the at least one IPD.

16. The method according to claim 10, wherein the at least one 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 from the RF signal input.

Images