Acoustic wave resonator

Abstract

The application relates to an acoustic resonator, comprising: a piezoelectric layer; a first electrode structure on a first main surface of the piezoelectric layer, comprising a first electrode; a second electrode structure on a second main surface of the piezoelectric layer, comprising a second electrode; the first main surface and the second main surface are opposite surfaces; the first electrode structure and / or the second electrode structure has a composite structure, the composite structure comprising: a first dielectric layer; a first conductive layer between the first dielectric layer and the piezoelectric layer; the sum of the acoustic thicknesses of the first conductive layer and the first dielectric layer approaches one quarter of the wavelength of the acoustic wave at the resonant frequency of the resonator. The application can reduce the thermal-elastic dissipation of the resonator.

Description

Technical Field

[0001] This application relates to the field of resonator technology, and in particular to an acoustic resonator. Background Technology

[0002] Acoustic resonators, such as thin-film bulk acoustic resonators (FBARs) and solid-state assembled resonators (SMRs), are fundamental components of modern RF front-end modules. The growing market demand for higher operating frequencies, wider relative bandwidths, lower insertion loss, higher rejection ratios, higher power handling capabilities, better thermal stability, and stronger long-term reliability has driven the development of resonator architectures that can achieve a high quality factor (Q value) while minimizing electrical and mechanical energy dissipation, while also possessing a high electromechanical coupling coefficient (kt). 2 ) and the temperature coefficient of frequency (TCF) which is close to zero.

[0003] One limitation of traditional electrode structures (especially at high frequencies) is thermoelastic dissipation (TED). During resonator operation, significant acoustic strain occurs within the electrode stack. Since metals such as aluminum (Al) exhibit relatively high thermoelastic losses when subjected to cyclic acoustic strain, placing high mechanical strain regions within metal electrodes leads to increased energy loss, which in turn reduces the resonator's Q value. Summary of the Invention

[0004] Therefore, it is necessary to provide an acoustic resonator that can improve thermoelastic dissipation.

[0005] An acoustic resonator includes: a piezoelectric layer; a first electrode structure located on a first main surface of the piezoelectric layer, including a first electrode; and a second electrode structure located on a second main surface of the piezoelectric layer, including a second electrode; the first and second main surfaces are opposite to each other; the first electrode structure and / or the second electrode structure have a composite structure, the composite structure including: a first dielectric layer; and a first conductive layer located between the first dielectric layer and the piezoelectric layer; the sum of the acoustic thicknesses of the first conductive layer and the first dielectric layer is approximately one-quarter wavelength of the acoustic wave at the resonant frequency of the resonator.

[0006] The aforementioned acoustic resonator has a composite quarter-wavelength layer (including a first dielectric layer and a first conductive layer) on one or both sides of the piezoelectric layer, which can reduce the thermoelastic dissipation of the resonator.

[0007] In one embodiment, if the first electrode structure has the composite structure, then the first electrode includes the first conductive layer.

[0008] In one embodiment, if the second electrode structure has the composite structure, then the second electrode includes the first conductive layer.

[0009] In one embodiment, the composite structure further includes a second conductive layer located between the first conductive layer and the piezoelectric layer, wherein the acoustic impedance of the second conductive layer is greater than that of the first conductive layer.

[0010] In one embodiment, the first electrode includes the second conductive layer.

[0011] In one embodiment, the second electrode includes the second conductive layer.

[0012] In one embodiment, the first conductive layer and the first dielectric layer have similar acoustic impedances.

[0013] In one embodiment, the composite structure further includes a passivation layer with an acoustic thickness approaching a quarter wavelength of the sound wave, and the first dielectric layer is located between the passivation layer and the first conductive layer.

[0014] In one embodiment, the acoustic impedance of the passivation layer is greater than that of the first conductive layer.

[0015] In one embodiment, the first dielectric layer is located in a region where the acoustic strain is greater than that of the first conductive layer when the acoustic resonator is operating.

[0016] In one embodiment, the material of the first conductive layer includes metals and / or alloys.

[0017] In one embodiment, the material of the first conductive layer includes aluminum or an aluminum alloy.

[0018] In one embodiment, the material of the passivation layer includes one or more of silicon nitride, aluminum nitride, and aluminum oxide.

[0019] In one embodiment, the material of the first dielectric layer includes silicon dioxide.

[0020] In one embodiment, the composite structure further includes one or more adhesive layers located between adjacent layers.

[0021] In one embodiment, the acoustic resonator further includes a border region configured to suppress parasitic acoustic modes.

[0022] In one embodiment, the acoustic resonator is a bulk acoustic resonator.

[0023] In one embodiment, the acoustic resonator further includes an acoustic mirror, and the second electrode structure is located between the acoustic mirror and the piezoelectric layer.

[0024] In one embodiment, the acoustic reflector employs an air cavity structure.

[0025] In one embodiment, the acoustic reflector employs a distributed Bragg reflector structure.

[0026] In one embodiment, the acoustic resonator is a thin-film bulk acoustic resonator.

[0027] In one embodiment, the acoustic resonator is a solid-state assembled resonator. Attached Figure Description

[0028] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.

[0029] Figure 1 This is a schematic diagram of an exemplary thin-film bulk acoustic resonator.

[0030] Figure 2 This is a simulated acoustic stress distribution diagram corresponding to an exemplary thin-film bulk acoustic resonator.

[0031] Figure 3 This is a schematic diagram of the structure of an acoustic resonator in one embodiment of this application.

[0032] Figure 4 This is a schematic diagram of the acoustic resonator in another embodiment of this application.

[0033] Figure 5 This is a schematic diagram of the acoustic resonator in another embodiment of this application.

[0034] Figure 6 This is a schematic diagram of the acoustic resonator in another embodiment of this application.

[0035] Figure 7 This is a simulated acoustic stress distribution diagram of an acoustic resonator in one embodiment of the present invention.

[0036] Figure 8 These are simulation curves of the electrical admittance and conductance frequency response of the embodiments and comparative examples of this application.

[0037] Figure 9 The effective electromechanical coupling coefficient (kt) of the embodiments and comparative examples of this application. 2 The curve of how the resonant frequency (fs) changes.

[0038] Figure 10The piezoelectric film thickness (h) of the embodiments and comparative examples of this application is... piezo The curve of how the resonant frequency (fs) changes. Detailed Implementation

[0039] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.

[0040] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein is for the purpose of describing particular embodiments only and is not intended to be limiting of the application.

[0041] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, parts, regions, layers, doping types, and / or portions, these elements, parts, regions, layers, doping types, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, part, region, layer, doping type, or portion from another element, part, region, layer, doping type, or portion. Therefore, without departing from the teachings of this invention, the first element, component, region, layer, doping type, or portion discussed below may be represented as a second element, component, region, layer, or portion; for example, the first doping type may be referred to as the second doping type, and similarly, the second doping type may be referred to as the first doping type; the first doping type and the second doping type are different doping types, for example, the first doping type may be P-type and the second doping type may be N-type, or the first doping type may be N-type and the second doping type may be P-type.

[0042] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, an element or feature described as “below,” “under,” or “below” other elements or features will be oriented “above” other elements or features. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein will be interpreted accordingly.

[0043] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, in this specification, the term “and / or” includes any and all combinations of the associated listed items.

[0044] Embodiments of the invention are described herein with reference to cross-sectional views illustrating ideal embodiments (and intermediate structures) of the invention, thus allowing for variations in the illustrated shape due to, for example, manufacturing techniques and / or tolerances. Therefore, embodiments of the invention should not be limited to the specific shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing techniques. For instance, implantation regions shown as rectangular typically have rounded or curved features at their edges and / or implantation concentration gradients, rather than a binary change from implantation regions to non-implantation regions. Similarly, the buried regions formed by implantation can result in some implantation in the region between the buried region and the surface traversed during implantation. Therefore, the regions shown in the figures are substantially schematic, and their shapes do not represent the actual shapes of regions of the device and do not limit the scope of the invention.

[0045] The background art mentions that exemplary resonators face the TED problem. In another exemplary resonator structure, a thin conductive layer with a relatively high acoustic impedance (Z) is disposed immediately adjacent to the piezoelectric layer, so that kt 2 To maximize this, a thicker conductive layer (typically Al or AlCu) with low resistivity is then deposited to reduce the sheet resistance of the electrodes while maintaining acceptable acoustic performance. Commercial resonators also require one or more dielectric layers to provide environmental passivation protection, and in many cases, these dielectric layers are also used for TCF compensation. Figure 1An exemplary thin-film bulk acoustic resonator (FBAR) including a dielectric layer for environmental passivation protection is shown, comprising, from bottom to top, a first substrate 102, a first air cavity structure 110, a dielectric layer 122, a low acoustic impedance metal layer 124, a high acoustic impedance metal layer 126, a first piezoelectric layer 130, a high acoustic impedance metal layer 146, a low acoustic impedance metal layer 144, and a dielectric layer 142. However, dielectric layers 122 and 142 introduce additional acoustic mass loading, thereby altering the resonant characteristics of the device, which is typically accompanied by kt. 2 The reduction in efficiency. As the operating frequency increases, this adverse effect becomes more pronounced because high-frequency resonators require thinner piezoelectric and electrode layers, and are therefore increasingly sensitive to the mass loading introduced by the overlying dielectric layer.

[0046] The acoustic strain distribution within the electrode stack is determined by the acoustic impedance (Z) and acoustic thickness of each constituent layer. In conventional electrode architectures, this distribution results in a large portion of the acoustic strain occurring within the conductive metal layer, where thermoelastic losses are greatest. Figure 2 An exemplary FBAR structure is shown, illustrating the acoustic stress distribution. The figure displays a cross-sectional schematic of the electrode stack structure and its corresponding one-dimensional acoustic stress (σ). zz Distribution curve, Figure 2 The vertical dashed line in the middle is σ zz The coordinate axis is 0, and its left side is σ. zz <0, its right side σ zz >0. It should be noted that, Figure 2 The diagram shows acoustic stress rather than strain because stress remains continuous at material interfaces, while strain is typically discontinuous; since stress is proportional to strain within each material, the stress distribution map accurately indicates the spatial distribution of TED (Electrical Tense Dissipation). Therefore, the electrode material itself becomes a major source of energy dissipation, especially when device size is reduced to accommodate high-frequency operation. It should be noted that... Figure 2 The thicknesses of dielectric layer 122, low acoustic impedance metal layer 124, low acoustic impedance metal layer 144 and dielectric layer 142 are all much smaller than λ / 4, where λ represents the wavelength of the sound wave at the resonant frequency of the resonator.

[0047] To address the aforementioned challenges, the following methods can be employed, for example:

[0048] Introducing silicon dioxide (SiO2) into the electrode stack structure improves the temperature coefficient of frequency (TCF). However, the additional dielectric layer introduces acoustic mass loading, which typically reduces kt. 2 Furthermore, the adverse effects become more severe as the frequency of operation increases.

[0049] A stacked piezoelectric layer structure is employed to achieve high-frequency operation while maintaining a relatively thick piezoelectric film. Although this method alleviates the need for extremely thin piezoelectric layers, it significantly increases manufacturing complexity and requires periodically polarizing the piezoelectric film, thereby reducing manufacturing yield.

[0050] A quarter-wavelength electrode architecture is employed, combining a low-impedance metal layer with an acoustic thickness of approximately λ / 4 with a high-impedance metal layer with an acoustic thickness of approximately λ / 4, to acoustically isolate the upper diaphragm layer from the underlying resonator stack structure. While these architectures improve acoustic confinement and allow for the use of thicker piezoelectric layers at high frequencies, the low-impedance quarter-wavelength layer is entirely metallic, resulting in a significant portion of the acoustic strain being concentrated within the metal layer, leading to severe TED losses and a decrease in the resonator Q value.

[0051] This application provides an innovative resonator architecture that delivers high kt without sacrificing high-frequency performance and manufacturability. 2 Low sheet resistance, reduced TED, TCF compensation, effective acoustic isolation, and reliable environmental passivation protection.

[0052] Figure 3 This is a schematic diagram of the structure of an acoustic resonator in one embodiment of this application, including a piezoelectric layer 230, a first electrode structure 24, and a second electrode structure 22. The first electrode structure 24 is located on the first main surface of the piezoelectric layer 230 and includes a first electrode. The second electrode structure 22 is located on the second main surface of the piezoelectric layer 230 and includes a second electrode. The first and second main surfaces are opposite to each other. The first electrode structure and / or the second electrode structure adopt a unique composite structure, that is, the composite structure can be provided on one side of the piezoelectric layer 230, or the composite structure can be provided on both sides of the piezoelectric layer 230 to form a symmetrical structure. For embodiments where the composite structure is provided only on one side of the piezoelectric layer 230, the other side can use an electrode structure known in the art. The composite structure includes a first conductive layer and a first dielectric layer, with the first conductive layer located between the first dielectric layer and the piezoelectric layer 230. The sum of the acoustic thicknesses of the first conductive layer and the first dielectric layer approaches one-quarter wavelength (λ / 4) of the acoustic wave at the resonant frequency of the resonator, that is, the first conductive layer and the first dielectric layer form a composite quarter-wavelength layer. In one embodiment of this application, an acoustic thickness approaching λ / 4 means that the acoustic thickness = (1 ± 25%)λ / 4. In embodiments where the first electrode structure employs the composite structure, the first electrode includes a first conductive layer. In embodiments where the second electrode structure employs the composite structure, the second electrode includes a first conductive layer.

[0053] The aforementioned acoustic resonator, by providing a composite quarter-wavelength layer composed of a first conductive layer and a first dielectric layer on one or both sides of the piezoelectric layer 230, can transfer the local maxima of acoustic strain from the conductive layer to the dielectric layer, thereby reducing the thermoelastic dissipation (TED) of the resonator.

[0054] In one embodiment of this application, the composite quarter-wavelength layer is a composite low acoustic impedance layer. The material of the first conductive layer includes metals and / or alloys, such as aluminum (Al), aluminum-copper alloy (AlCu), or other conductive materials with relatively low acoustic impedance and low resistivity. The first dielectric layer is made of silicon dioxide (SiO2) or other dielectric materials with relatively low acoustic impedance. In embodiments where the first dielectric layer is made of silicon dioxide, the first dielectric layer also serves as TCF compensation.

[0055] Figure 4 This is a schematic diagram of the acoustic resonator structure in another embodiment of this application. In this embodiment, the composite structure is provided on both sides of the piezoelectric layer 230. On the front side of the piezoelectric layer 230, the first conductive layer 246 of the first electrode structure and the first dielectric layer 244 of the first electrode structure form a composite quarter-wavelength layer. On the back side of the piezoelectric layer 230, the first conductive layer 226 of the second electrode structure and the first dielectric layer 224 of the second electrode structure form a composite quarter-wavelength layer. The acoustic thickness is close to λ / 4. Figure 4 The double arrow in the middle indicates this.

[0056] In one embodiment of this application, the acoustic resonator further includes an acoustic mirror, and a second electrode structure is located between the acoustic mirror and the piezoelectric layer 230. Figure 4 In the illustrated embodiment, the acoustic mirror is an air cavity structure 210 located on substrate 202. In other embodiments, the acoustic mirror may also be other types of acoustic mirrors known in the art, such as a distributed Bragg reflector (DBR).

[0057] In one embodiment of this application, the composite structure further includes a passivation layer with an acoustic thickness approaching λ / 4. In one embodiment, an acoustic thickness approaching λ / 4 means an acoustic thickness of (1 ± 25%)λ / 4. In the composite structure, a first dielectric layer is located between the passivation layer and the first conductive layer. The composite quarter-wavelength layer and the passivation layer together constitute an acoustic Bragg reflector, thereby confining acoustic energy within the resonator (within the main resonator region). By setting the acoustic thickness of the passivation layer to approximately λ / 4, sound waves can be efficiently reflected back to the piezoelectric layer 230 while minimizing sound wave leakage in the vertical direction.

[0058] Therefore, while the passivation layer provides mechanical protection and environmental passivation, it achieves substantial acoustic isolation from the main resonant mode. In other words, the passivation layer is acoustically "masked," allowing for the use of relatively thick dielectric materials without introducing the acoustic mass loading typically associated with conventional resonator structures. This acoustic isolation advantage becomes more pronounced as the operating frequency increases. In conventional resonators, increasingly thin piezoelectric layers are typically required to compensate for the mass loading introduced by thick electrodes and the passivation layer. This radical reduction in size can compromise device manufacturability, mechanical strength, and power reliability. In contrast, the Bragg-engineered architecture of this embodiment largely decouples the chemical function of the passivation layer from its acoustic effects. Therefore, the resonator maintains a high electromechanical coupling coefficient (kt). 2 While achieving high-efficiency acoustic constraints, thicker passivation layers and thicker piezoelectric films can be used.

[0059] In one embodiment of this application, the acoustic impedance of the passivation layer is greater than that of the first conductive layer.

[0060] In one embodiment of this application, the material of the passivation layer includes one or more of silicon nitride (Si3N4), aluminum nitride (AlN), and aluminum oxide (Al2O3).

[0061] Figure 5 This is a schematic diagram of the acoustic resonator in another embodiment of this application. In this embodiment, the composite structure on the front side of the piezoelectric layer 230 includes a first conductive layer 246 of the first electrode structure, a first dielectric layer 244 of the first electrode structure, and a passivation layer 242 of the first electrode structure. The composite structure on the back side of the piezoelectric layer 230 includes a first conductive layer 226 of the second electrode structure, a first dielectric layer 224 of the second electrode structure, and a passivation layer 222 of the second electrode structure.

[0062] In one embodiment of this application, the composite structure further includes a second conductive layer located between the first conductive layer and the piezoelectric layer, wherein the acoustic impedance of the second conductive layer is greater than that of the first conductive layer. The second conductive layer is made of a conductive material with high acoustic impedance; by incorporating the second conductive layer, the kt of the resonator can be improved. 2 In one embodiment of this application, the first electrode includes a second conductive layer; in another embodiment of this application, the second electrode includes a second conductive layer. For embodiments where the first electrode structure employs the composite structure, the first electrode includes a first conductive layer and a second conductive layer. For embodiments where the second electrode structure employs the composite structure, the second electrode includes a first conductive layer and a second conductive layer. This reduces mass loading or simplifies manufacturing processes compared to maximizing the electromechanical coupling coefficient (kt). 2In more demanding applications, a second conductive layer may be omitted, although such embodiments typically exhibit lower kt. 2 However, they allow for the use of thicker piezoelectric layers, simplified manufacturing processes, and improved manufacturability, which is particularly advantageous for resonators operating at extremely high frequencies.

[0063] In one embodiment of this application, the second conductive layer comprises molybdenum (Mo), tungsten (W), ruthenium (Ru), or other conductive materials with relatively high acoustic impedance.

[0064] Figure 6 This is a schematic diagram of the acoustic resonator in another embodiment of this application. In this embodiment, the composite structure on the front side of the piezoelectric layer 230 includes a second conductive layer 248 of the first electrode structure, a first conductive layer 246 of the first electrode structure, a first dielectric layer 244 of the first electrode structure, and a passivation layer 242 of the first electrode structure. The composite structure on the back side of the piezoelectric layer 230 includes a second conductive layer 228 of the second electrode structure, a first conductive layer 226 of the second electrode structure, a first dielectric layer 224 of the second electrode structure, and a passivation layer 222 of the second electrode structure.

[0065] In one embodiment of this application, the acoustic resonator is specifically a bulk acoustic wave (BAW) resonator. In another embodiment, the acoustic resonator is specifically a thickness lambda acoustic wave (TLAW) resonator for radio frequency (RF) applications. In yet another embodiment, the acoustic resonator is specifically a thin-film bulk acoustic resonator (FBAR). In yet another embodiment, the acoustic resonator is specifically a solid-state assembled resonator (SMR).

[0066] Figure 6 The resonator architecture of the embodiment shown is engineered to control the acoustic strain distribution within the composite quarter-wavelength layer by means of the spatial arrangement of the conductive and dielectric materials, based on their respective electrical, thermal, and mechanical properties.

[0067] To achieve this objective, the materials of the first conductive layer and the first dielectric layer are rationally selected to have sufficiently similar acoustic impedances, resulting in acoustic reflections at their interface being significantly less than those at the interface with surrounding high-impedance layers. Therefore, the first conductive layer and the first dielectric layer acoustically behave as a single, continuous low-impedance quarter-wavelength layer, while retaining their respective unique physical properties; that is, the composite quarter-wavelength layer acoustically behaves as a substantially continuous low-impedance quarter-wavelength layer. In one embodiment of this application, the acoustic impedance ratio Z1 / Z2 of the first conductive layer and the first dielectric layer satisfies the following relationship: 2 / 3 ≤ Z1 / Z2 ≤ 3 / 2.

[0068] Figure 7 This is a simulated acoustic stress distribution diagram of an acoustic resonator in one embodiment of the present invention, showing the distribution of acoustic strain throughout the resonator stack structure. The diagram displays a schematic cross-sectional view of the active region stack structure (including the piezoelectric layer, second conductive layer, first conductive layer, first dielectric layer, and passivation layer), and the corresponding 1D σ. zz (One-dimensional normal stress) distribution curve. Figure 7 The acoustic thicknesses of the passivation layer 222 of the second electrode structure and the passivation layer 242 of the first electrode structure are both close to λ / 4. The sum of the acoustic thicknesses of the first conductive layer 226 and the first dielectric layer 224 of the second electrode structure is close to λ / 4, and the sum of the acoustic thicknesses of the first conductive layer 246 and the first dielectric layer 244 of the first electrode structure is close to λ / 4. Figure 7 As shown, the interface between the second conductive layer and the first conductive layer coincides with the stress node, where the acoustic stress is approximately zero. Conversely, the interface between the first dielectric layer and the passivation layer corresponds to a local maximum of the acoustic stress amplitude.

[0069] In some embodiments of the invention, for the composite quarter-wavelength layer, the first dielectric layer is placed in a higher strain region, while the first conductive layer is confined to a lower strain region. Since the thermoelastic dissipation (TED) of the dielectric material is much lower than that of the conductive material, this arrangement significantly reduces the overall TED without compromising conductivity. In contrast, in the exemplary quarter-wavelength electrode architecture, the high-strain region is entirely occupied by metal (see...). Figure 2 ), thus leading to a larger TED.

[0070] In one embodiment of this application, the acoustic resonator may be fabricated on a supporting substrate, the substrate 202 being made of materials including but not limited to: high-resistivity silicon, quartz, sapphire, glass, or any other substrate material with suitable mechanical properties.

[0071] Acoustic isolation can be achieved by suspending a resonator stack above an air cavity (common in FBARs) or by supporting a resonator stack on a distributed Bragg reflector (common in SMRs).

[0072] In one embodiment of this application, the resonator stack structure comprises the following film layers from bottom to top:

[0073] A λ / 4 bottom passivation layer. The material can be AlN and / or Si3N4. It serves as an environmental passivation protection layer and, together with the bottom composite quarter-wavelength layer, forms a Bragg reflector.

[0074] Bottom dielectric layer. The material can be SiO2. It serves to suppress TED and compensate for TCF.

[0075] Bottom conductive layer. The material can be Al and / or AlCu. The bottom conductive layer, together with the bottom dielectric layer, forms the bottom composite quarter-wavelength layer. The bottom conductive layer serves to reduce sheet resistance.

[0076] High acoustic impedance bottom electrode. The material can be at least one of Mo, W, and Ru. This improves the electromechanical coupling coefficient (kt). 2 The role of ).

[0077] Piezoelectric layer. Materials can be AlN and / or Al. 1-x% Sc x% N. It serves as an acoustic transducer.

[0078] High acoustic impedance top electrode. The material can be at least one of Mo, W, and Ru. This improves the electromechanical coupling coefficient (kt). 2 The role of ).

[0079] Top conductive layer. The material can be Al and / or AlCu. The top conductive layer, together with the top dielectric layer, forms the top composite quarter-wavelength layer. The top conductive layer contributes to low sheet resistance.

[0080] Top dielectric layer. The material can be SiO2. It serves to suppress TED and compensate for TCF.

[0081] A λ / 4 top passivation layer. The material can be AlN and / or Si3N4. It serves to provide environmental passivation protection and, together with the top composite quarter-wavelength layer, constitutes the Bragg reflector.

[0082] In the foregoing embodiments, aluminum (Al) or an aluminum-copper alloy (AlCu) and silicon dioxide (SiO2) constitute the conductive and dielectric portions of the composite quarter-wavelength layer, respectively. In other embodiments, these alternative materials may also be used for the composite quarter-wavelength layer, provided that the acoustic impedance (Zs) of other materials is sufficiently similar to maintain acoustic continuity while providing the required electrical, thermal, and mechanical properties.

[0083] In one embodiment of this application, the composite structure further includes one or more adhesive layers located between adjacent layers.

[0084] In one embodiment of this application, the acoustic resonator further includes a frame region configured to suppress parasitic acoustic modes.

[0085] The impact of the composite quarter-wavelength layer on TED in this application embodiment was evaluated by simulating a symmetrical (i.e., composite structures are placed above and below the piezoelectric layer) floating FBAR embodiment. The resonator stack structure (located on the air cavity) used in the simulation is shown in Table 1:

[0086] Table 1

[0087]

[0088] The simulated admittance and conductance frequency response of the embodiments shown in Table 1 are compared with those of the comparative examples, with reference to... Figure 8 The comparative example differs from the embodiment shown in Table 1 in that both the 75nm thick top and bottom dielectric layers are replaced with approximately 95nm thick Al layers, so that the resonators in the embodiment and the comparative example exhibit essentially the same resonant frequency and overall λ / 4 acoustic thickness. In the simulation, TED is assumed to be the only loss mechanism. Figure 8 The solid line represents the admittance magnitude |Y| (unit: dBS), and the dashed line represents the conductance (real part of admittance) G (unit: dBS). From... Figure 8 As can be seen, the resonator in this embodiment of the invention achieves a corresponding improvement in Q-value compared to the comparative equivalent resonator using an all-metal, low-impedance quarter-wavelength layer. Simulation results show that the comparative all-metal quarter-wavelength layer exhibits significantly greater energy dissipation, resulting in a wider resonance characteristic and a lower Q-value. In contrast, the composite quarter-wavelength layer in this embodiment of the invention generates a sharper resonance peak and a significantly higher Q-value by transferring the region of maximum acoustic strain to a low-loss dielectric material while retaining the electrical advantages of the metallic portion.

[0089] To evaluate the scalability of the architecture of this application embodiment at increasingly higher operating frequencies, the resonator structure was optimized in a representative frequency range of approximately 6 GHz to 14 GHz, and high-frequency scaling verification was performed. The optimized resonator stack structure (located on the air cavity) is shown in Table 2 from bottom to top.

[0090] Table 2

[0091]

[0092] For the resonator architectures in the embodiments and comparative examples of this application, the thickness of the aluminum (Al) electrode layer is fixed at 50 nm to provide the required sheet resistance. In the comparative FBAR, the Si3N4 passivation layer is disposed adjacent to the Al electrode, and its thickness is limited to at least 50 nm to ensure adequate environmental passivation protection. Although a thin SiO2 layer may be selectively introduced in conventional resonators for TCF compensation, the thickness of this layer is typically much less than a quarter wavelength, and its thickness is entirely determined by the required TCF. Therefore, this SiO2 layer is omitted in the comparative example. In the embodiments shown in Table 2, the Si3N4 passivation layer is optimized to have an acoustic thickness of approximately λ / 4. Simultaneously, the thickness of the SiO2 dielectric portion is optimized so that the composite layer consisting of the fixed 50 nm Al electrode layer exhibits an overall acoustic thickness of approximately a quarter wavelength. While satisfying these respective constraints, the thicknesses of the remaining layers in both architectures are optimized to maximize the effective electromechanical coupling coefficient (kt) at each target resonant frequency. 2 ).

[0093] Figure 9 It is the effective electromechanical coupling coefficient (kt) 2 The curve showing how the frequency (fs) changes with the resonant frequency. Figure 10 It is the thickness of the piezoelectric thin film (h) piezo The curve showing the change of frequency (fs) with resonant frequency. (Refer to...) Figure 9 and Figure 10 The high-frequency scaling simulation comparison diagram shows that, because the passivation layer directly contributes to the acoustic quality loading, the performance of the scaled model gradually degrades more severely as the operating frequency increases. In contrast, the composite structure architecture engineered by Bragg in this application acoustically masks the passivation layer, thereby allowing for the maintenance of excellent kt... 2 At the same time, a significantly thicker piezoelectric film is maintained. The exact frequencies at which these advantages become significant depend on the chosen materials, resonator topology, and boundary conditions; however, compared to comparative conventional resonator architectures, the designs of this application consistently demonstrate improved capabilities to extend to higher frequencies. Figure 9 and Figure 10 As shown, at higher frequencies—which depend on the specific materials and configuration of the resonator—for Figure 9 and Figure 10 It is approximately 10 GHz—the architecture of this application maintains a thicker piezoelectric layer and a higher coupling coefficient than the comparative FBAR, while maintaining sufficient electrode thickness to ensure low sheet resistance and sufficient passivation layer thickness to ensure long-term environmental reliability. This application's embodiments generally offer advantages in high-frequency extension, although the exact frequency at which they surpass the performance of conventional FBARs may vary.

[0094] Based on all the above embodiments, this application provides a bulk acoustic wave (BAW) resonator, which includes a multifunctional multilayer stacked structure disposed on at least one side of a piezoelectric layer. The multilayer stacked structure includes conductive and dielectric materials, and its arrangement can simultaneously provide conductivity, temperature coefficient of frequency (TCF) compensation, acoustic reflection, and environmental passivation functions, while controlling the acoustic strain distribution within the stacked structure. This multilayer stacked structure integrates conductivity, acoustic reflection, thermoelastic dissipation (TED) suppression, environmental passivation, and optional temperature coefficient of frequency (TCF) compensation functions within a unified architecture. By combining acoustic strain engineering with acoustic Bragg reflection, the embodiments of this application can simultaneously achieve reduced TED and high electromechanical coupling coefficient (kt). 2 It features low sheet resistance, efficient acoustic confinement, reliable environmental passivation protection, improved manufacturability, and the ability to extend to higher operating frequencies, while allowing the use of relatively thick piezoelectric films.

[0095] In the description of this specification, references to terms such as "some embodiments," "other embodiments," and "ideal embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.

[0096] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features of the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.

[0097] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.

Claims

1. An acoustic resonator, comprising: piezoelectric layer; The first electrode structure, located on the first main surface of the piezoelectric layer, includes a first electrode; The second electrode structure is located on the second main surface of the piezoelectric layer and includes a second electrode; the first main surface and the second main surface are two opposing surfaces. An acoustic reflector, wherein the second electrode structure is located between the acoustic reflector and the piezoelectric layer; The first electrode structure and / or the second electrode structure are characterized by having a composite structure, the composite structure comprising: First dielectric layer; A first conductive layer is located between the first dielectric layer and the piezoelectric layer; The sum of the acoustic thicknesses of the first conductive layer and the first dielectric layer is close to one-quarter of the wavelength of the sound wave at the resonant frequency of the resonator.

2. The acoustic resonator according to claim 1, characterized in that, The composite structure further includes a second conductive layer located between the first conductive layer and the piezoelectric layer, wherein the acoustic impedance of the second conductive layer is greater than that of the first conductive layer.

3. The acoustic resonator according to claim 1, characterized in that, The first conductive layer and the first dielectric layer have similar acoustic impedances.

4. The acoustic resonator according to claim 1, characterized in that, The composite structure further includes a passivation layer with an acoustic thickness approximately equal to one-quarter wavelength of the sound wave, and the first dielectric layer is located between the passivation layer and the first conductive layer.

5. The acoustic resonator according to claim 1, characterized in that, The first dielectric layer is located in a region where the acoustic strain is greater than that of the first conductive layer when the acoustic resonator is operating.

6. The acoustic resonator according to claim 1, characterized in that, The material of the first conductive layer includes metals and / or alloys.

7. The acoustic resonator according to claim 6, characterized in that, The material of the first conductive layer includes aluminum or an aluminum alloy.

8. The acoustic resonator according to claim 1, characterized in that, The material of the first dielectric layer includes silicon dioxide.

9. The acoustic resonator according to claim 1, characterized in that, The acoustic reflector adopts an air cavity structure or a distributed Bragg reflector structure.

10. The acoustic resonator according to claim 9, characterized in that, The acoustic resonator is a thin-film bulk acoustic resonator or a solid-state assembled resonator.

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