CN117639715A

CN117639715A - BAW resonator with dual-step oxide boundary ring structure

Info

Publication number: CN117639715A
Application number: CN202311047316.1A
Authority: CN
Inventors: A·塔切克; T·贝尔; I·韦雷斯
Original assignee: Qorvo US Inc
Current assignee: Qorvo US Inc
Priority date: 2022-08-30
Filing date: 2023-08-18
Publication date: 2024-03-01

Abstract

The present disclosure relates to BAW resonators having dual-step oxide boundary ring structures. A Bulk Acoustic Wave (BAW) resonator is disclosed that includes a bottom electrode, a piezoelectric layer over the bottom electrode, and a top electrode structure having a top electrode and a dual-step BO ring structure. Herein, the dual-step BO structure is formed over the piezoelectric layer and around the perimeter of the top electrode structure such that a central portion of the piezoelectric layer is not covered by the dual-step BO structure. The dual-step BO structure is formed of an oxide material and includes an inner BO ring having a first height and an outer BO ring having a second height greater than the first height such that the height of the dual-step BO structure decreases toward the central portion of the piezoelectric layer. The top electrode is formed over the central portion of the piezoelectric layer and extends over the dual-step BO structure.

Description

BAW resonator with dual-step oxide boundary ring structure

RELATED APPLICATIONS

The present application claims the benefit of provisional patent application Ser. No. 63/402,245 filed 8/30, 2022, the disclosure of which is incorporated herein by reference in its entirety.

Technical Field

The present disclosure relates to a Bulk Acoustic Wave (BAW) resonator, and in particular to a BAW resonator having a dual-step oxide boundary ring structure.

Background

Acoustic resonators, particularly Bulk Acoustic Wave (BAW) resonators, are used in many high frequency communication applications. In particular, BAW resonators are commonly used in filter networks operating at frequencies above 1.5 gigahertz (GHz) and requiring a flat passband, with exceptionally steep filter skirts (filter skirts) and shoulders at the upper and lower ends of the passband, and providing excellent rejection outside the passband. BAW-based filters also have relatively low insertion losses, tend to decrease in size as the operating frequency increases, and are relatively stable over a wide temperature range. Thus, BAW-based filters are the filters of choice for many 3 rd generation (3G) and 4 th generation (4G) wireless devices, and are intended to dominate the filter applications of 5 th generation (5G) wireless devices. Most of these wireless devices support cellular, wireless fidelity (Wi-Fi), bluetooth, and/or near field communications on the same wireless device, and thus present a very challenging filtering requirement. While these demands continue to increase the complexity of wireless devices, there is a constant need to improve the performance of BAW resonators and BAW-based filters, as well as reduce the cost and size associated therewith.

Disclosure of Invention

The present disclosure relates to a Bulk Acoustic Wave (BAW) resonator having a double-step oxide Boundary (BO) ring structure. The disclosed BAW resonator includes a bottom electrode, a piezoelectric layer over the bottom electrode, and a top electrode structure having a top electrode and the dual-step BO ring structure. Herein, the dual-step BO structure is formed over the piezoelectric layer and around the perimeter of the top electrode structure such that a central portion of the piezoelectric layer is not covered by the dual-step BO structure. The dual-step BO structure includes an inner BO loop having a first height and an outer BO loop having a second height that is greater than the first height such that the height of the dual-step BO structure decreases toward the central portion of the piezoelectric layer. The top electrode is formed over the central portion of the piezoelectric layer and extends over the dual-step BO structure.

In one embodiment of the BAW resonator, the dual-step BO structure is formed of a dielectric material.

In one embodiment of the BAW resonator, the dual-step BO structure is formed of silicon oxide.

In one embodiment of the BAW resonator, the first height of the inner BO ring is 40% -60% of the second height of the outer BO ring.

In one embodiment of the BAW resonator, the first height of the inner BO ring is between 100nm and 500nm and the second height of the outer BO ring is between 200nm and 1000 nm.

In one embodiment of the BAW resonator, the inner BO ring has a first width between 500nm and 1.25 μm and the outer BO ring has a second width between 1 μm and 2.25 μm.

In one embodiment of the BAW resonator, the dual stepped BO structure further comprises a first transition section laterally between the inner BO ring and the outer BO ring. Herein, the height of the first transition section varies from a first height of the inner BO ring to a second height of the outer BO ring to form a tapered wall.

In an embodiment of the BAW resonator, the first angle formed between the conical wall of the first transition section and a horizontal plane parallel to the top surface of the piezoelectric layer is between 30 and 60 degrees.

In one embodiment of the BAW resonator, the dual-step BO structure further includes a second transition section formed around an inner perimeter of the dual-step BO structure. Herein, the height of the second transition section varies from zero to the first height of the inner BO ring to form a tapered wall.

In an embodiment of the BAW resonator, the second angle formed between the conical wall of the second transition section and the horizontal plane is between 30 and 60 degrees.

In an embodiment of the BAW resonator, the first angle and the second angle have different angle values.

In an embodiment of the BAW resonator, the first angle and the second angle have the same angle value.

In one embodiment of the BAW resonator, the top electrode structure further comprises a BO extension and a top electrode lead. Herein, the BO extension is in contact with and extends outwardly from an outer BO ring of the dual-step BO structure. The top electrode lead is in contact with the top electrode and extends over the BO extension.

In one embodiment of the BAW resonator, the BO extension is formed of the same material as the dual step BO structure.

In one embodiment of the BAW resonator, the top electrode comprises: a first top electrode layer formed over a central region of the piezoelectric layer and extending over the dual-step BO structure; an electrode seed layer formed over the first top electrode layer; and a second top electrode layer formed over the electrode seed layer.

In one embodiment of the BAW resonator, the first top electrode layer is formed of tungsten (W), molybdenum (Mo) or platinum (Pt), the electrode seed layer is formed of titanium Tungsten (TiW) or titanium (Ti), and the second top electrode layer is formed of aluminum copper.

According to one embodiment, the BAW resonator further comprises a passivation layer covering the top electrode structure and the portion of the piezoelectric layer exposed by the top electrode structure. Herein, the passivation layer is formed of silicon nitride (SiN), siO2, or silicon oxynitride (SiON), havingTo->And a thickness therebetween.

In an embodiment of the BAW resonator, a portion of at least one of the first top electrode layer, the electrode seed layer, the second top electrode layer and the passivation layer has a thickness variation. Herein, certain portions are above and confined within the internal BO loop.

In an embodiment of the BAW resonator, a portion of at least one of the first top electrode layer, the electrode seed layer, the second top electrode layer and the passivation layer has a thickness variation. Herein, certain portions are above and confined within the outer BO loop.

In another aspect, any of the foregoing aspects, and/or the various individual aspects and features as described herein, may be combined singly or together to obtain additional advantages. Any of the various features and elements disclosed herein may be combined with one or more other disclosed features and elements unless indicated to the contrary herein.

Those skilled in the art will recognize the scope of the present disclosure and appreciate additional aspects thereof upon reading the following detailed description of the preferred embodiments and the associated drawings.

Drawings

The accompanying drawings, which are incorporated in and form a part of this specification, illustrate several aspects of the present disclosure and, together with the description, serve to explain the principles of the disclosure.

Fig. 1 is a diagram showing a conventional Bulk Acoustic Wave (BAW) resonator.

Fig. 2 is a graph graphically showing the magnitude and phase of electrical impedance as a function of frequency for a relatively ideal BAW resonator.

Fig. 3A to 3C are diagrams graphically illustrating phase curves of various conventional BAW resonators.

Fig. 4 is a diagram showing a conventional BAW resonator with a top electrode that includes a Boundary (BO) ring.

FIG. 5 graphically illustrates BO ring width versus frequency at anti-resonance (Q _p ) Correlation of quality factor and relative intensity of BO mode formedIs a drawing.

Fig. 6 is a graph graphically showing the phase curves of BAW resonators with and without BO rings.

Fig. 7 is a cross-sectional view showing a BAW resonator in which BO regions are arranged in a configuration similar to the BAW resonator of fig. 4.

Fig. 8 is a cross-sectional view showing a typical BAW resonator in which the BO region forms a dual step configuration.

Fig. 9 is a cross-sectional view illustrating an exemplary BAW resonator having a dual stepped boundary ring structure in accordance with an embodiment of the present disclosure.

Fig. 10 is a cross-sectional view illustrating a portion of a BAW resonator having an extended dual step boundary ring structure in accordance with an embodiment of the present disclosure.

FIGS. 11A-11C are diagrams illustrating simulated 1- |S for various configurations of BAW resonators ₁₁ Graph of response.

Fig. 12A-12C are graphs graphically illustrating quality factor simulation results for various configurations of BAW resonators.

It should be appreciated that for clarity of illustration, FIGS. 1-12C may not be drawn to scale.

Detailed Description

The embodiments set forth below represent the information necessary to enable those skilled in the art to practice the embodiments and illustrate the best mode of practicing the embodiments. Upon reading the following description in light of the accompanying drawing figures, those skilled in the art will understand the concepts of the disclosure and will recognize applications of these concepts not particularly addressed herein. It should be understood that these concepts and applications fall within the scope of the disclosure and the accompanying claims.

It will be understood that, although the terms first, second, etc. may be used herein to describe various elements, these elements should not be limited by these terms. These terms are only used to distinguish one element from another element. For example, a first element could be termed a second element, and, similarly, a second element could be termed a 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.

It will be understood that when an element such as a layer, region or substrate is referred to as being "on" or "extending" another element, it can be directly on or extend directly onto the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or "directly extending onto" another element, there are no intervening elements present. Also, it will be understood that when an element such as a layer, region or substrate is referred to as being "over" or "extending over" another element, it can extend directly over the other element or intervening elements may also be present. In contrast, when an element is referred to as being "directly on" or extending "directly over" another element, there are no intervening elements present. It will also be understood that when an element is referred to as being "connected" or "coupled" to another element, it can be directly connected or coupled to the other element or intervening elements may be present. In contrast, when an element is referred to as being "directly connected" or "directly coupled" to another element, there are no intervening elements present.

Relative terms, such as "below" or "above" or "upper" or "lower" or "horizontal" or "vertical" may be used herein to describe one element, layer or region's relationship to another element, layer or region as illustrated. It will be understood that these terms and those discussed above are intended to encompass different orientations of the device in addition to the orientation depicted in the figures.

The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of 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 indicates otherwise. It will be further understood that the terms "comprises" and/or "comprising," when used herein, specify the presence of stated features, integers, steps, operations, elements, and/or components, but do not preclude the presence or addition of one or more other features, integers, steps, operations, elements, components, and/or groups thereof.

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. It will be further understood that terms used herein should be interpreted as having a meaning that is consistent with their meaning in the context of this specification and the relevant art and will not be interpreted in an idealized or overly formal sense unless expressly so defined herein.

Embodiments are described herein with reference to schematic illustrations of embodiments of the disclosure. As such, the actual dimensions of the layers and elements may vary, and are expected to vary from the illustrated shapes due to, for example, manufacturing techniques and/or tolerances. For example, a region illustrated or described as square or rectangular may have rounded or curved features, and a region shown as a straight line may have some irregularities. Thus, the regions illustrated in the figures are schematic and their shapes are not intended to illustrate the precise shape of a region of a device and are not intended to limit the scope of the present disclosure. In addition, the size of structures or regions may be exaggerated relative to other structures or regions for illustrative purposes and, thus, structures or regions are provided to illustrate the general structures of the present invention and may or may not be drawn to scale. Common elements between the drawings may be shown with common element numbers herein and will not be described later.

The present disclosure relates to a Bulk Acoustic Wave (BAW) resonator, and in particular to a BAW resonator having a double ladder Boundary (BO) ring structure. The disclosed BAW resonator has a high quality factor, suppression of parasitic modes, and suppression of BO modes.

Before delving into the details of these concepts, an overview of BAW resonators and filters employing BAW resonators is provided. BAW resonators are used in many high frequency filter applications. An exemplary BAM resonator 10 is shown in fig. 1. BAW resonator 10 is a firmly mounted resonator (solidly mounted resonator, SMR) BAW resonator and generally includes a substrate 12, a reflector 14 mounted over substrate 12, and a transducer 16 mounted over 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 may be formed of tungsten (W), molybdenum (Mo), platinum (Pt), or the like, and the piezoelectric layer 18 may be formed of aluminum nitride (AlN), zinc oxide (ZnO), or other suitable piezoelectric material. Although shown as comprising a single layer in fig. 1, the piezoelectric layer 18, the top electrode 20, and/or the bottom electrode 22 may comprise multiple layers of the same material, multiple layers wherein at least two layers are different materials, or multiple layers wherein each layer is a different material.

The BAW resonator 10 is divided into an active region 24 and an outer region 26. The active region 24 generally corresponds to a section of the BAW resonator 10 where the top electrode 20 overlaps the bottom electrode 22, and also includes layers below the overlapping top electrode 20 and bottom electrode 22. The outer region 26 corresponds to a section of the BAW resonator 10 surrounding the active region 24.

For BAW resonator 10, application of an electrical signal across top electrode 20 and bottom electrode 22 excites acoustic waves in piezoelectric layer 18. These sound waves propagate mainly vertically. The primary goal in BAW resonator design is to confine these vertically propagating acoustic waves within the transducer 16. The upwardly traveling acoustic wave is reflected back into the transducer 16 through the air-metal boundary at the top surface of the top electrode 20. The sound waves traveling downward are reflected back into the transducer 16 by the reflector 14 or by an air cavity that is disposed just below the transducer 16 in a Film Bulk Acoustic Resonator (FBAR).

Reflector 14 is typically formed from a stack of Reflector Layers (RL) 28A-28E (commonly referred to as reflector layers 28) alternating in material composition to create a significant reflectance at the junction adjacent reflector layers 28. Typically, reflector layers 28 alternate between materials having high acoustic impedance and low acoustic impedance, such as tungsten (W) and silicon dioxide (SiO) ₂ ). Although only five reflector layers 28 are shown in fig. 1, the number of reflector layers 28 and the structure of the reflector 14 will vary from design to design.

The magnitude (Z) and phase (phi) of the electrical impedance provided in fig. 2 varies with the frequency (GHz) of the relatively ideal BAW resonator 10. The magnitude (Z) of the impedance is shown by the solid line, while the phase (phi) of the impedance is shown by the dashed line. The unique feature of BAW resonator 10 is that it hasBoth resonant and antiresonant frequencies. The resonant frequency is commonly referred to as the series resonant frequency (f _s ) And the antiresonant frequency is commonly referred to as the parallel resonant frequency (f _p ). When the magnitude of the impedance or reactance of the BAW resonator 10 approaches zero, a series resonant frequency (f _s ). When the magnitude of the impedance or reactance of the BAW resonator 10 peaks at a significantly higher level, a parallel resonant frequency (f _p ). Typically, the series resonant frequency (f _s ) Depending on the thickness or height of the piezoelectric layer 18 and the mass of the top electrode 20 and the bottom electrode 22.

For phase, BAW resonator 10 functions similarly to a series resonant frequency (f _s ) With parallel resonance frequency (f _p ) Providing an inductance of 90 deg. phase shift. In contrast, BAW resonator 10 functions similarly to a series resonant frequency (f _s ) Below and at the parallel resonance frequency (f _p ) The above provides a capacitance of-90 ° phase shift. The BAW resonator 10 has a series resonance frequency (f _s ) Exhibits very low, near zero resistance at the parallel resonant frequency (f _p ) The lower exhibits extremely high resistance. The electrical properties of BAW resonator 10 are suitable for achieving extremely high quality factor (Q) inductance over a relatively short frequency range, which has proven to be very beneficial in high frequency filter networks, particularly those operating at frequencies of about 1.8GHz and above.

Unfortunately, the phase (φ) curve of FIG. 2 represents an ideal phase curve. In practice, approaching this ideal is challenging. A typical phase curve of the BAW resonator 10 of fig. 1 is shown in fig. 3A. Instead of being a smooth curve, the phase curve of FIG. 3A is included in the series resonant frequency (f _s ) Hereinafter, at the series resonance frequency (f _s ) With parallel resonance frequency (f _p ) Between and at the parallel resonant frequency (f _p ) The above corrugations. The ripple is the result of a spurious mode (spurious mode) that is caused by spurious resonances that occur at the corresponding frequencies. Although the vast majority of sound waves in BAW resonator 10 propagate vertically, various boundary conditions around transducer 16 result in the propagation of transverse (horizontal) sound waves, known as transverse standing waves. This is The presence of these lateral standing waves reduces the potential quality factor (Q) associated with BAW resonator 10.

As shown in fig. 4, a BO loop 30 is formed on or in the top electrode 20 (not shown) to suppress certain parasitic modes. The parasitic mode suppressed by the BO loop 30 is at the series resonant frequency (f _s ) Those parasitic modes above are highlighted as circles a and B in the phase curve of fig. 3B. Circle a shows the frequency of the series resonance residing in the passband of the phase curve (f _s ) With parallel resonance frequency (f _p ) The ripple between them and thus the suppression of parasitic modes. Circle B shows the frequency at parallel resonance (f _p ) The above ripple and thus suppression of parasitic modes. Notably, spurious modes in the upper shoulder of the passband (at exactly the parallel resonant frequency (f _p ) Below) and spurious modes above the passband are suppressed, such as at the series resonant frequency (f _s ) With parallel resonance frequency (f _p ) Between and at the parallel resonant frequency (f _p ) The above smooth or substantially ripple-free phase profile demonstrates.

The BO ring 30 corresponds to the mass loading of the portion of the top electrode 20 extending around the perimeter of the active region 24. In this regard, the BO ring 30 with mass loading forms a raised frame disposed about the perimeter of the top electrode 20. The BO ring 30 can correspond to the application of a thickened portion of the top electrode 20 or an additional layer of suitable material over the top electrode 20. The portion of the BAW resonator 10 that contains and resides below the BO ring 30 is referred to as the BO zone 32. Thus, the BO region 32 corresponds to the outer peripheral portion of the active region 24 and resides inside the active region 24.

Although the BO ring 30 effectively suppresses the resonance frequency (f _s ) The parasitic mode above, but the BO ring 30 pair is at the series resonant frequency (f _s ) The effect of those parasitic modes below is little or no, as shown in fig. 3B. A technique called apodization is typically used to suppress the drop to a frequency at the series resonance frequency (f _s ) The following parasitic modes.

Apodization is used to avoid or at least significantly reduce any lateral symmetry in the BAW resonator 10 or at least in the transducer 16 thereof. Lateral symmetry corresponds to a transducer16 and avoiding lateral symmetry corresponds to avoiding symmetry associated with sides of the coverage area. For example, coverage areas corresponding to pentagons rather than squares or rectangles may be chosen. Avoiding symmetry helps reduce the presence of lateral standing waves in transducer 16. Circle C of fig. 3C shows the effect of apodization, where the frequency at the series resonance frequency (f _s ) The following parasitic modes are suppressed. Assuming that the BO loop 30 is not provided, it can be readily seen in fig. 3C that apodization cannot be suppressed at the series resonant frequency (f _s ) Those parasitic modes above. Thus, a typical BAW resonator 10 employs both apodization and BO rings 30.

The thickness or height of the BO ring 30 can be measured in a direction perpendicular to or away from the top surface of the piezoelectric layer 18, and the width of the BO ring 30 can be measured in a direction parallel to or laterally across the piezoelectric layer 18. The thickness and width of the BO loop 30 can be tuned simultaneously to suppress spurious modes and improve the quality factor (Q) at anti-resonant frequencies _p ). The additional mass associated with the BO ring 30 generally causes the BO region 32 to resonate at a slightly lower frequency than the rest of the active region 24. Thus, the BO ring can exist at a frequency lower than the series resonant frequency (f _s ) To introduce undesirable modes or BO modes.

FIG. 5 graphically illustrates BO ring width versus frequency at anti-resonance (Q _p ) A plot of the quality factor versus the relative intensity of the formed BO modes. In FIG. 5, the x-axis represents BO ring width in micrometers (μm), while the primary y-axis represents Q _p And the secondary y-axis represents the relative intensity or magnitude of the formed BO modes. The graph of fig. 5 plots data for three wafers, each containing BAW resonators with different BO ring widths. As shown, Q _p The value generally increases with increasing BO ring width, and the highest Q _p The values correspond to BO ring widths just above 3 μm. As also shown, BO mode intensity generally also increases with BO ring width. For higher BO ring widths, Q _p The value decreases while the BO mode intensity value remains higher. In this way, tuned to provide high Q _p It is also possible that the BO loop of (c) introduces undesirable BO modes to the corresponding BAW device.

Fig. 6 is a graph graphically showing the phase curves of BAW resonators with and without BO rings. As shown, spurious modes present within the passband of BAW resonators without BO rings are suppressed by the addition of BO rings; however, the presence of the BO loop introduces undesirable BO modes below the passband. The BO modes may be introduced outside or even inside the passband of the resonator and may limit the design or use of BAW resonators for wide bandwidth filtering applications. If the BO mode is within the passband, insertion loss can be affected. For BAW multiplexing applications, BO modes that exist outside the passband may be problematic, where BAW filters of different frequency bands operate simultaneously. In such multiplexing applications, the BO mode of one BAW filter may fall into the passband of the other BAW filter and introduce interference during multiplexing.

Fig. 7 is a cross-sectional view showing a BAW resonator 34 in which the BO region 32 is arranged in a similar configuration to the BAW resonator 10 of fig. 4. For illustrative purposes, fig. 7 is a simplified view of the BAW resonator 34 and is not necessarily drawn to scale; however, it should be appreciated that BAW resonator 34 may include many of the same components as BAW resonator 10 of fig. 4. As shown in fig. 7, the BO zone 32 is disposed about the perimeter of the top electrode 20 and laterally defines a central region 36 of the top electrode 20 inside the BO zone 32. The BO ring 30 is formed on or within the top electrode 20 to suppress certain parasitic modes as described above with respect to fig. 4. In fig. 7, the active region 24 is indicated as a section in which the top electrode 20 and the bottom electrode 22 overlap on opposite sides of the piezoelectric layer 18. In this way, the active region 24 generally corresponds to a portion of the piezoelectric layer 18 that is electrically driven such that an electric field is provided between the overlapping portions of the top electrode 20 and the bottom electrode 22. The outer region 26 generally corresponds to a portion of the piezoelectric layer 18 that is external to the active region 24, and in this regard, the outer region 26 is not typically electrically driven. In the configuration of fig. 7, the BO zones 32 and corresponding BO rings 30 are disposed within the active zone 24.

Fig. 8 is a cross-sectional view showing a BAW resonator 38 having a typical dual step BO configuration around the perimeter of the top electrode 20. For illustrative purposes, fig. 8 is a simplified view of the BAW resonator 38 and is not necessarily drawn to scale; however, it should be appreciated that BAW resonator 38 may include many of the same components as BAW resonator 10 of fig. 4. The BO zone 32 includes an inner step 40 and an outer step 42 that collectively form a stepped configuration having a raised height that decreases from the perimeter of the BO zone 32 toward the central region 36 of the top electrode 20. The inner step 40 is a first mass-loaded portion of the top electrode 20 and the outer step 42 is a second mass-loaded portion of the top electrode 20. As indicated in fig. 8, the central region 36 of the top electrode 20 has a first height H1 measured from the piezoelectric layer 18, the inner step 40 of the top electrode 20 has a second height H2 measured from the piezoelectric layer 18, and the outer step 42 of the top electrode 20 has a third height H3 measured from the piezoelectric layer 18. The third height H3 is greater than the second height H2 and the second height H2 is greater than the first height H1, thereby forming a dual-step configuration of BO zones 32 that decrease in height toward the central zone 36.

The top electrode 20 may include a number of conductive electrode layers (not shown). The inner step 40 is formed as a result of the incremental thickness (i.e., the incremental thickness of about H2-H1) of one or more conductive electrode layers in the BO region 32 as compared to the central region 36. The outer step 42 is formed due to the increasing thickness of the dielectric collar 44 and one or more of the conductive electrode layers in the BO region 32. Herein, the dielectric ring layer 44 is vertically positioned between the top electrode 20 and the piezoelectric layer 18, and the peripheral edge of the dielectric ring layer 44 is aligned with the peripheral edge of the top electrode 20. Typically, the second height H2 is 40 nanometers (nm) to 80nm greater than the first height H1, and the third height H3 is 80nm to 180nm greater than the second height H2.

By having a dual step configuration in which the inner step 40 and the outer step 42 are arranged at different heights, the BO zone 32 is thereby configured to provide two different acoustic impedances. This provides an acoustic impedance mismatch for propagating lamb waves laterally within the BAW resonator 38, which would otherwise result in energy loss or leakage and a reduction in the Q factor of the BAW resonator 38. In this way, the dual-step configuration in BAW resonator 38 significantly reduces cross-directional energy leakage, thereby providing a high Q value for BAW resonator 38. Furthermore, the dielectric properties of the dielectric ring layer 44 serve to reduce some of the electric field in the piezoelectric layer 18, and will reduce coupling in that domain, thereby suppressing the magnitude of the BO mode formed. However, for some applications, such as multiplexing applications, the BO mode suppression in the BAW resonator 38 may not be sufficient (more details are shown in FIGS. 11A-11C). A large BO mode suppression that does not sacrifice the Q of the BAW resonator is highly desirable.

Fig. 9 is a cross-sectional view illustrating an exemplary BAW resonator 50 having a dual stepped BO structure 52 in accordance with an embodiment of the present disclosure. For purposes of this illustration, BAW resonator 50 is a BAW Securely Mounted Resonator (SMR) and includes reflector 54, bottom electrode structure 56 over reflector 54, piezoelectric layer 58 over bottom electrode structure 56, and top electrode structure 60 over piezoelectric layer 58. In different applications, BAW resonator 50 may be a Film Bulk Acoustic Resonator (FBAR), with reflector 54 omitted.

In detail, the reflector 54 includes a low acoustic impedance region 62, and a plurality of high acoustic impedance layers 64 are embedded within the low acoustic impedance region 62. For purposes of this illustration, there are two high acoustic impedance layers 64: an upper high acoustic impedance layer 64-U, and a lower high acoustic impedance section 64-L. In different applications, there may be fewer or more high acoustic impedance layers 64 embedded in the low acoustic impedance region 62. Herein, the lower high acoustic impedance layer 64-L resides above the bottom portion 62-B of the low acoustic impedance region 62. The upper high acoustic impedance layer 64-U is located vertically above the lower high acoustic impedance layer 64-L and is separated from the lower high acoustic impedance layer 64-L by the middle portion 62-M of the low acoustic impedance region 62. The top portion 62-T of the low acoustic impedance region 62 is above the upper high acoustic impedance layer 64-U. The low acoustic impedance region 62 has a lower acoustic impedance, lower density, and lower hardness than the high acoustic impedance layer 64, and may be formed of SiO ₂ And (5) forming. Each high acoustic impedance layer 64 is formed of a high acoustic impedance material such as W, mo or Pt. Each of the bottom portion 62-B of the low acoustic impedance region 62, the lower high acoustic impedance layer 64-L, the middle portion 62-M of the low acoustic impedance region 62, the upper high acoustic impedance layer 64-U, and the top portion 62-T of the low acoustic impedance region 62 is one RL of the reflector 54.

The bottom electrode structure 56 is formed over the top portion 62-T of the low acoustic impedance region 62 and includes a bottom electrode 66 and a planar oxide 68. The bottom electrode 66 is located vertically above the high acoustic impedance layer 64. The planarizing oxide 68 surrounds the bottom electrode 66 and can be electrically caused toThe bottom electrode 66 is separated from an external bottom electrode (not shown). Bottom electrode 66 may include two bottom electrode layers 70 and 72. The second bottom electrode layer 72 is located above the top portion 62-T of the low acoustic impedance region 62 and may be formed of aluminum copper (AlCu), while the first bottom electrode layer 70 is located above the second bottom electrode layer 72 and may be formed of W, mo or Pt. The planarizing oxide 68 may be formed of SiO ₂ And (5) forming.

The piezoelectric layer 58 is formed over the bottom electrode structure 56 and at least completely covers the bottom electrode 66. The piezoelectric layer 58 may be formed of AlN, znO, or other suitable piezoelectric material, and may have a thickness between 0.3 μm and 1.4 μm.

A top electrode structure 60 is formed above the piezoelectric layer 58 and vertically above the bottom electrode 66. The top electrode structure 60 includes a dual-step BO structure 52 formed over the piezoelectric layer 58 and surrounding the perimeter of the top electrode structure 60, and a top electrode 76 formed over the piezoelectric layer 58 and extending over the dual-step BO structure 52. The peripheral edge of the dual-step BO structure 52 may be aligned with the peripheral edge of the top electrode 76.

BAW resonator 50 is divided into an active region 78 and an outer region 80. The active region 78 corresponds to the section of the BAW resonator 50 where the top and bottom electrodes 76, 66 overlap, and also includes layers between and below the overlapping top and bottom electrodes 76, 66. The outer region 80 corresponds to a section of the BAW resonator 50 surrounding the active region 78. Active region 78 is divided into a central region 82 and a BO region 84. The BO region 84 corresponds to a section of the BAW resonator 50 that includes the dual-step BO structure 52, resides above the dual-step BO structure, and resides below the dual-step BO structure. The central region 82 is laterally defined inside the BO region 84 and is not covered by the double stepped BO structure 52.

Notably, the bottom electrode 66 may extend beyond the peripheral edge of the top electrode 76. As previously described, an active region 78 is formed in which the top and bottom electrodes 76, 66 overlap. In this way, misalignment of the top electrode 76 with the bottom electrode 66 during fabrication may compromise the performance of the BAW resonator 50. By arranging the bottom electrode 66 with a larger lateral dimension than the top electrode 76, the alignment tolerance for placement of the top electrode 76 may be increased, thereby improving manufacturing tolerances.

The dual step BO structure 52 includes a structural body having an inner loop height H _IN And has an outer ring height H, and an inner BO ring 86 of _OUT An outer BO ring 88 of (c). Herein, outer ring height H _OUT Is greater than the height H of the inner ring _IN Such that the height of the dual-step BO structure 52 decreases toward the central region 82. In one embodiment, the top electrode 76 has a uniform thickness and the mass loaded portion of the top electrode structure 60 has a dual step configuration and is from the dual step BO structure 52.

By having a dual step configuration, the mass loading portion of the top electrode structure 60 within the BO zone 84 is thereby configured to provide two different acoustic impedances. This provides an acoustic impedance mismatch for propagating lamb waves laterally within BAW resonator 50, which would otherwise result in energy loss or leakage and a reduction in the Q factor of BAW resonator 50. In order to achieve the desired large acoustic mismatch and corresponding large reflection coefficient, a material with a large mass density is required for the inner BO ring 86 and the outer ring 88. Furthermore, to excellently suppress BO modes, materials that can reduce some of the electric field in one portion of piezoelectric layer 58 within BO zone 84 (as compared to the electric field of another portion of piezoelectric layer 58 within central zone 82) and thereby reduce coupling in that domain are highly desirable. Thus, the entire dual-step BO structure 52 is formed of, for example, siO ₂ And dielectric materials.

In addition, the inner ring height H of the inner BO ring 86 _IN And outer ring height H of outer BO ring 88 _OUT Will significantly affect the inhibition of BO modes and must be carefully chosen. In one embodiment, the inner ring height H of the inner BO ring 86 _IN Outer ring height H of the outer BO ring 88 _OUT 40% -60% of (C). Inner ring height H of the inner BO ring 86 _IN Between 100nm and 500nm, while the outer ring height H of the outer BO ring 88 _OUT Between 200nm and 1000 nm. Except for the height H of the inner ring and the outer ring _IN And H _OUT In addition, the widths of the inner BO loop 86 and the outer BO loop 88 may also be tuned simultaneously to improve the cross-directional energy limits and quality factors. In one embodiment, the width of the inner BO ring 86 is between 500nm and 1.25 μm, while the width of the outer BO ring 88 is between 1 μm and 2.25 μm.

To effect the height change between the inner BO ring 86 and the outer BO ring 88, the dual-step BO structure 52 further includes a first transition section 90 laterally between the inner BO ring 86 and the outer BO ring 88. The height of the first transition section 90 is from the inner ring height H _IN Height H of outward ring _OUT Varying to form a tapered wall. The first angle α1 formed between the tapered wall of the first transition section 90 and a horizontal plane (e.g., parallel to the top surface of the piezoelectric layer 58) is between 30 and 60 degrees. In addition, the dual-step BO structure 52 also includes a second transition section 92 formed around the inner periphery of the BO zone 84 and laterally between the central zone 82 and the inner BO ring 86. The height of the second transition section 92 varies from zero to the inner ring height to form a tapered wall. The second angle α2 formed between the tapered wall of the second transition section 92 and a horizontal plane (e.g., parallel to the top surface of the piezoelectric layer 58) is between 30 and 60 degrees. The first angle α1 and the second angle α2 may be different or the same.

The top electrode 76 includes a first top electrode layer 94 formed over the piezoelectric layer 58 and extending over the dual-step BO structure 52 within the central region 82, an electrode seed layer 96 formed over the first top electrode layer 94, and a second top electrode layer 98 formed over the electrode seed layer 96. Herein, the first top electrode layer 94 may be formed of W, mo, pt, or other conductive material having high acoustic impedance properties. The electrode seed layer 96 may be formed of titanium Tungsten (TiW) or titanium (Ti). The second top electrode layer 98 may be formed of AlCu or other highly conductive material.

Furthermore, the BAW resonator 50 may also include a passivation layer 100 to protect the exemplary BAW resonator 50 from the external environment. The passivation layer 100 covers the top electrode structure 60 and the portion of the piezoelectric layer 58 exposed by the top electrode structure 60. The passivation layer 100 may be made of silicon nitride (SiN), siO ₂ Or silicon oxynitride (SiON) formation withTo->And a thickness therebetween.

In one embodiment, each of the first top electrode layer 94, the electrode seed layer 96, the second top electrode layer 98, and the passivation layer 100 has a uniform thickness, and the mass loading portion of the top electrode structure 60 is from the dual-step BO structure 52. In one embodiment, a portion of at least one layer above and confined within the inner BO ring 86 (e.g., a portion of the first top electrode layer 94, a portion of the electrode seed layer 96, a portion of the second top electrode layer 98, and/or a portion of the passivation layer 100) has a thickness variation (either an incremental thickness or a decremental thickness). In one embodiment, a portion of at least one layer above and confined within the outer BO ring 88 (e.g., a portion of the first top electrode layer 94, a portion of the electrode seed layer 96, a portion of the second top electrode layer 98, and/or a portion of the passivation layer 100) has a thickness variation (either an incremental thickness or a decremental thickness). As such, the mass loading portion of the top electrode structure 60 may result from the dual step BO structure 52, with the thickness variation of the top electrode 76/passivation layer 100 being limited in the inner BO ring 86 and/or the outer BO ring 88 (not shown).

It should be noted that BAW resonator 50 always includes bottom electrode structure 56, piezoelectric layer 58 over bottom electrode structure 56, and top electrode structure 60 with oxide dual-step BO structure 52 over piezoelectric layer 58, regardless of the presence of reflector 54 (i.e., regardless of SMR and FBAR applications). The oxide material of the dual-step BO structure 52 and the dual-step configuration improve the Q-factor of the BAW resonator 50 and significantly suppress the BO mode of the BAW resonator 50 (see fig. 11A-12C for more details).

In various applications, the top electrode structure 60 may further include a BO extension 102 connected to the dual-step BO structure 52, and a top electrode lead 104 connected to the top electrode 76, as shown in fig. 10. Herein, the BO extension 102 is in contact with and extends outwardly from the outer BO ring 88 of the dual step BO structure 52. The BO extension 102 may be made of the same oxide material (e.g., siO ₂ ) And (5) forming. The combination of the dual step BO structure 52 and the BO extension 102 forms an extended BO structure 52E. The BO extension 102 has the same height as the outer BO ring 88 of the dual step BO structure 52 such that the extension BO structure 52E also hasA double step configuration.

The top electrode lead 104 extends outward from the top electrode 76 and extends over the BO extension 102. The top electrode 76 and top electrode lead 102 are formed from a common first top electrode layer 94, a common electrode seed layer 96, and a common second top electrode layer 98. The BO extension 102 and top electrode lead 104 reside within the outer zone 80.

FIGS. 11A-11C illustrate 1-S for various configurations of BAW resonators as shown in FIGS. 8-10 ₁₁ Simulation result of response (1- |S ₁₁ I is equal to the power ratio lost in the resonator). Fig. 11A shows 1-S of two simulated BAW resonators having the same configuration shown in fig. 8 ₁₁ Response. Each of the two simulated BAW resonators has a dual step configuration comprising a tungsten inner BO ring with a 75nm height and SiO with a 100nm height ₂ An external BO ring and does not contain a BO extension. For one of the two simulated BAW resonators, the tungsten inner BO ring had a width of 0.625 μm and SiO ₂ The outer BO ring has a width of 1.125 μm, while for the other of the two simulated BAW resonators, the tungsten inner BO ring has a width of 1 μm and SiO ₂ The outer BO ring has a width of 2.875 μm.

Fig. 11B shows 1-S of two simulated BAW resonators having the same configuration shown in fig. 9 ₁₁ Response. Each of the two simulated BAW resonators has a dual step configuration comprising SiO with a height of 300nm ₂ Internal BO ring and SiO with 750nm height ₂ An external BO ring and does not contain a BO extension. For one of the two simulated BAW resonators, siO ₂ The internal BO ring has a width of 0.1875 μm and SiO ₂ The outer BO ring has a width of 2 μm, whereas for the other of the two simulated BAW resonators, siO ₂ The internal BO ring has a width of 1 μm and SiO ₂ The outer BO ring has a width of 2.125 μm.

Fig. 11C shows 1-S of two simulated BAW resonators having the same configuration shown in fig. 10 ₁₁ Response. Each of the two simulated BAW resonators has a dual step configuration comprising SiO with a height of 300nm ₂ Internal BO ring and SiO with 750nm height ₂ An external BO ring, and further comprising a BO extension. For one of the two simulated BAW resonators, siO ₂ The internal BO ring has a width of 0.25 μm and SiO ₂ The outer BO ring has a width of 0.875 μm, whereas for the other of the two simulated BAW resonators, siO ₂ The internal BO ring has a width of 0.1875 μm and SiO ₂ The outer BO ring has a width of 1 μm.

Obviously, regardless of the presence or absence of the BO extension, both the inner BO ring and the outer BO ring are made of SiO ₂ Formed and having a large height (e.g., 300nm and 750nm, respectively), the BO mode is significantly suppressed (fig. 11B and 11C). On the other hand, when the inner BO ring is formed of W and the inner BO ring and the outer BO ring have relatively small heights (e.g., 75nm and 100nm, respectively), the BO mode is comparable to the main resonance (fig. 11A).

Fig. 12A-12C show quality factor simulation results for various configurations of BAW resonators. Fig. 12A shows the quality factor simulation results of the two simulated BAW resonators utilized in fig. 11A, fig. 12B shows the quality factor simulation results of the two simulated BAW resonators utilized in fig. 11B, and fig. 12C shows the quality factor simulation results of the two simulated BAW resonators utilized in fig. 11C.

With thick SiO in the absence of BO extensions ₂ BAW resonator with inner and outer BO rings and having relatively thin W inner BO ring and relatively thin SiO ₂ BAW resonators with external BO rings can achieve similar high-value quality factors. On the other hand, has a thick SiO ₂ The quality factor of the BAW resonators of the inner and outer BO rings and BO extensions has been reduced but still acceptable.

It is contemplated that any of the foregoing aspects may be combined and/or various individual aspects and features described herein to achieve additional advantages. Any of the various embodiments disclosed herein can be combined with one or more other disclosed embodiments, unless indicated to the contrary herein.

Those skilled in the art will recognize improvements and modifications to the preferred embodiments of the present disclosure. 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) resonator, comprising:

a bottom electrode;

a piezoelectric layer over the bottom electrode; and

a top electrode structure comprising a top electrode and a double step Boundary (BO) ring structure, wherein:

the dual-step BO structure is formed over the piezoelectric layer and around the perimeter of the top electrode structure such that a central portion of the piezoelectric layer is not covered by the dual-step BO structure;

the dual-step BO structure includes an inner BO ring having a first height and an outer BO ring having a second height greater than the first height such that the height of the dual-step BO structure decreases toward the central portion of the piezoelectric layer; and is also provided with

The top electrode is formed over the central portion of the piezoelectric layer and extends over the dual-step BO structure.

2. The BAW resonator of claim 1, wherein the dual-step BO structure is formed of a dielectric material.

3. The BAW resonator of claim 2, wherein the dual-step BO structure is formed of silicon oxide.

4. The BAW resonator of claim 1, wherein the first height of the inner BO ring is 40% -60% of the second height of the outer BO ring.

5. The BAW resonator of claim 1, wherein the first height of the inner BO ring is between 100nm and 500nm and the second height of the outer BO ring is between 200nm and 1000 nm.

6. The BAW resonator of claim 1, wherein the inner BO ring has a first width between 500nm and 1.25 μιη and the outer BO ring has a second width between 1 μιη and 2.25 μιη.

7. The BAW resonator of claim 1, wherein the dual stepped BO structure further includes a first transition section laterally between the inner BO ring and the outer BO ring, wherein a height of the first transition section varies from the first height of the inner BO ring to the second height of the outer BO ring to form a tapered wall.

8. The BAW resonator of claim 7, wherein a first angle formed between a tapered wall of the first transition section and a horizontal plane parallel to a top surface of the piezoelectric layer is between 30 and 60 degrees.

9. The BAW resonator of claim 7, wherein the dual-step BO structure further includes a second transition section formed around an inner perimeter of the dual-step BO structure, wherein a height of the second transition section varies from zero to the first height of the inner BO ring to form a tapered wall.

10. The BAW resonator of claim 9, wherein:

a first angle formed between a tapered wall of the first transition section and a horizontal plane parallel to a top surface of the piezoelectric layer is between 30 and 60 degrees; and is also provided with

A second angle formed between the tapered wall of the second transition section and the horizontal plane is between 30 and 60 degrees.

11. The BAW resonator of claim 10, wherein the first angle and the second angle have different angle values.

12. The BAW resonator of claim 10, wherein the first angle and the second angle have the same angle value.

13. The BAW resonator of claim 1, wherein the top electrode structure further includes a BO extension and a top electrode lead, wherein:

the BO extension is in contact with and extends outwardly from the outer BO ring of the dual-step BO structure; and is also provided with

The top electrode lead is in contact with the top electrode and extends over the BO extension.

14. The BAW resonator of claim 13, wherein the BO extension is formed of the same material as the dual-step BO structure.

15. The BAW resonator of claim 14, wherein the dual stepped BO structure and the BO extension are formed of silicon oxide.

16. The BAW resonator of claim 1, wherein:

the top electrode includes a first top electrode layer formed over the central region of the piezoelectric layer and extending over the dual-step BO structure, an electrode seed layer formed over the first top electrode layer, and a second top electrode layer formed over the electrode seed layer.

17. The BAW resonator of claim 16, wherein:

the first top electrode layer is formed of tungsten (W), molybdenum (Mo), or platinum (Pt);

the electrode seed layer is formed of titanium Tungsten (TiW) or titanium (Ti); and is also provided with

The second top electrode layer is formed of aluminum copper.

18. The BAW resonator of claim 17, further comprising a passivation layer covering the top electrode structure and a portion of the piezoelectric layer exposed by the top electrode structure, wherein the passivation layerThe chemical layer is formed of silicon nitride (SiN), siO2 or silicon oxynitride (SiON) and hasTo->And a thickness therebetween.

19. The BAW resonator of claim 18, wherein a portion of at least one of the first top electrode layer, the electrode seed layer, the second top electrode layer, and the passivation layer has a thickness variation, wherein the portion is above and confined within the inner BO ring.

20. The BAW resonator of claim 1, wherein a portion of at least one of the first top electrode layer, the electrode seed layer, the second top electrode layer, and the passivation layer has a thickness variation, wherein the portion is above and confined within the outer BO ring.