Solidly mounted bulk acoustic resonator with mass load tuned frequency in acoustic reflector and method of manufacture

Abstract

A bulk acoustic wave (BAW) resonator (100) on a substrate (102) is provided, including a piezoelectric element (104), a bottom electrode (106) on a first face (104A) of the piezoelectric element, and a top electrode (108) on a second face (104B) of the piezoelectric element opposite the first face. The BAW resonator further includes a reflective element (112) between the bottom electrode and the substrate. The reflective element includes at least a first layer (114A) of a first material having a first acoustic impedance and a second layer (114B) of a second material having a second acoustic impedance different from the first acoustic impedance. The first layer or the second layer includes one or more structures (116A, 116B, 116C) of a third material having a third acoustic impedance different from the first and second acoustic impedances. The structures form an acoustic impedance modulation layer embedded in the first and / or second layer, which can be used for frequency tuning of the resonator by mass loading. By patterning resonators with different third structures on the same die, different frequencies can be precisely tuned for ladder or lattice structure filters without relying on thickness control of specific layers. By symmetrically arranging the frequency tuning structures (116A, 116B, 116C), additional transverse modes can be suppressed.

Description

Technical Field

[0001] This invention generally relates to the field of semiconductor technology; more specifically, to resonators, such as bulk acoustic wave (BAW) resonators. Furthermore, this invention relates to an integrated circuit package comprising multiple BAW resonators. Additionally, this invention relates to a method of manufacturing a BAW resonator. Background Technology

[0002] Acoustic devices, such as micro-mechanical (MEMS) resonators, are key components used as building blocks for front-end modules (FEMs) in modern electronic circuits due to their excellent mechanical and acoustic qualities and significantly lower energy loss compared to their purely electrical counterparts, such as capacitors and inductors. For example, acoustic devices are used as filters to improve signal reception and transmission in mobile phones and Wi-Fi receivers. Currently, the industry primarily uses two types of acoustic devices for manufacturing MEMS resonators (filters). The first type is based on surface traveling wave (SAW) resonators. These devices are traditionally fabricated on low-loss piezoelectric materials and operate by coupling an external electric field into the acoustic field, thereby generating an electroacoustic mode that propagates into the piezoelectric material. The second type includes bulk acoustic wave (BAW) resonators, which use an external electric field to trigger a bulk wave in the piezoelectric material. SAW resonators tend to localize acoustic energy to the surface of the piezoelectric material, while BAW resonators tend to generate waves throughout most of the piezoelectric material.

[0003] BAW resonators are widely used in high-frequency, communications applications because they are generally highly compatible with state-of-the-art microfabrication techniques, enabling their use in high-volume, high-integration solutions for wireless chipset products. BAW resonators include film bulk acoustic resonators (FBARs), which consist of a stack of resonators formed on a substrate cavity, and solid-mounted resonators (SMRs), which consist of a stack of resonators formed on an acoustic reflector (e.g., a Bragg mirror). Traditionally, BAW resonators include a piezoelectric layer, the thickness of which typically determines the operating frequency of the BAW resonator. For example, in the case of an SMR-BAW resonator operating in longitudinal mode, the operating frequency is primarily defined by the thickness of the piezoelectric core resonator. If more frequencies are required on the same die, it is necessary to use different mass-loaded elements, which are localized variations in electrode thickness and / or additional deposited material (e.g., dielectric) for a given resonator. Typically, mass-loaded elements are deposited above or below the top electrode in the Bragg layer structure.

[0004] It should be noted that when multiple frequencies are required on the same die, the actual thickness variation of different layers due to imperfect manufacturing processes can, in some cases, be significantly greater than the fine thickness difference required to tune the operating frequencies of different microresonators. In other words, it is challenging to realize a large number of frequency-sensitive elements on the same die, replicated across the entire wafer; therefore, in practical terms, achieving many different operating frequencies becomes more difficult. To mitigate this, additional highly controlled deposition steps are mandatory (i.e., extremely high precision is required in thickness deposition), but this also increases manufacturing complexity, requiring a trade-off between performance gain and process cost. Furthermore, it should be considered that when mass-loaded elements are deposited below the bottom electrode in the Bragg layer structure, proper planarization of the subsequent film deposition is necessary.

[0005] Therefore, based on the above discussion, it is necessary to overcome the aforementioned drawbacks associated with traditional acoustic wave devices, especially BAW resonators, in order to facilitate the use of multiple frequencies on the same die. Summary of the Invention

[0006] This invention seeks to provide a bulk acoustic wave (BAW) resonator, an integrated circuit package including multiple BAW resonators, and a method for manufacturing a BAW resonator. The object of this invention is to provide a technical solution that at least partially overcomes the problems encountered in the prior art, and to provide an improved device and method capable of efficiently and reliably generating resonant frequencies. This invention seeks to provide a technical solution to the existing problem of defining multiple operating frequencies for the BAW resonator. This invention provides a novel method for planarly defining the operating frequencies of a surface-mounted resonator / bulk acoustic wave resonator (SMR-BAW).

[0007] The objective of this invention is achieved through the technical solutions provided in the appended independent claims. Advantageous embodiments of the invention are further defined in the dependent claims.

[0008] On one hand, the present invention provides a bulk acoustic wave (BAW) resonator on a substrate. A BAW resonator on a substrate includes a piezoelectric element, a bottom electrode on a first surface of the piezoelectric element, and a top electrode on a second surface of the piezoelectric element opposite to the first surface. The BAW resonator further includes a reflective element between the bottom electrode and the substrate. The reflective element includes at least a first layer of a first material having a first acoustic impedance and a second layer of a second material having a second acoustic impedance, wherein the second acoustic impedance is different from the first acoustic impedance. The first layer or the second layer includes one or more structures of a third material having a third acoustic impedance, the third acoustic impedance being different from both the first and second acoustic impedances, the structures forming an acoustic impedance modulation layer embedded in the first and / or second layers.

[0009] The BAW resonator of this invention provides frequency shift without requiring precise deposition of different layer thicknesses. Here, the acoustic impedance modulation layer (AIML) modulates the effective impedance of a specific layer, thereby tuning the operating frequency of the BAW resonator. Furthermore, the AIML improves the acoustic confinement efficiency in the piezoelectric element of the BAW resonator. The AIML also serves to electrically shield any radiated and induced currents entering the BAW resonator substrate.

[0010] In one implementation, the reflective element is a Bragg layer comprising multiple interwoven first and second layers.

[0011] Here, a reflective element composed of alternating low-impedance and high-impedance acoustic materials generates an acoustic reflector at the operating frequency of the BAW resonator, which enables the reflection of almost all incident energy through constructive interference phenomena. Furthermore, the alternation of the first and second layers, with one layer having low mechanical impedance and the other having relatively high mechanical impedance, limits energy leakage to the substrate.

[0012] In one implementation, the reflective element is composed of alternating layers of the first material and the second material, such that the reflective element is arranged to operate at the operating frequency of the BAW resonator.

[0013] By allowing corresponding alternations of the first and second materials in the first and second layers of the reflective element, wherein one of the first and second materials has low mechanical impedance and the other has relatively high mechanical impedance, the operating frequency of the BAW resonator can be tuned.

[0014] In one implementation, the acoustic impedance modulation layer is embedded in a layer adjacent to the bottom electrode of the reflective element.

[0015] AIML embedded near the bottom electrode (i.e., the upper core portion of the reflective element) allows for the reduction of noise in the signal (i.e., unwanted signal), thereby reducing interference and degradation of the signal, and reducing regional operation as a spurious mode.

[0016] In one implementation, the thickness of the one or more structures is on the order of the acoustic wavelength or a fraction of the acoustic wavelength at the fundamental operating frequency of the BAW resonator.

[0017] Here, the thickness of one or more structures can modify the effective density of the reflective element, which affects the acoustic propagation constant and, consequently, the phase velocity of the volume wave propagating in that particular region, to define the operating frequency of the BAW resonator. Therefore, the thickness of the one or more structures at the fundamental operating frequency of the BAW resonator is determined on the order of magnitude of the acoustic wavelength or a fraction of the acoustic wavelength.

[0018] In one implementation, the one or more structures comprise a semiconductor material having a sufficiently high dopant concentration to alter the mass density and / or acoustic phase velocity.

[0019] Since the acoustic impedance modulation layer is made of semiconductor material, changing the dopant concentration therein alters the mass density of the acoustic impedance modulation layer, thereby changing the acoustic phase velocity of the signal. Changes in mass density and / or acoustic phase velocity change the associated acoustic impedance, thus allowing tuning of the operating frequency of the BAW resonator.

[0020] In one implementation, the acoustic impedance modulation layer is arranged such that it extends into both layers of the reflective element.

[0021] The AIML extends into the first and second layers of the reflective element to provide the structural geometry of the reflective element to provide the desired frequency offset.

[0022] In one implementation, the structure is asymmetrically distributed to form the acoustic impedance modulation layer.

[0023] Here, the asymmetric distribution of the structure facilitates the creation of asymmetric boundary conditions in the event of lateral stray modes. Furthermore, the asymmetry in the AIML can alter the acoustic impedance and mass density, which can be used to tune the BAW resonator to the desired operating frequency.

[0024] In one implementation, the BAW resonator also includes at least one mass load layer on the top electrode.

[0025] The mass load layer allows multiple frequencies to be generated on the same BAW resonator. These multiple frequencies are generated by varying the thickness of the mass load layer.

[0026] In one implementation, the mass load layer is embedded or partially embedded in the top electrode.

[0027] The mass load layer is embedded or at least partially embedded in the top electrode, which makes it easier to manufacture.

[0028] On one hand, an integrated circuit package is provided. The integrated circuit package includes at least a first BAW resonator and a second BAW resonator. The first BAW resonator and the second BAW resonator have different acoustic impedance modulation layers.

[0029] The integrated circuit package of the present invention, having the BAW resonator, provides different frequencies on the same die without typically or substantially increasing its overall size. The integrated circuit package of the present invention does not require precise thicknesses of the different layers of the first and second BAW resonators to achieve this, thereby reducing manufacturing complexity and overall cost. Furthermore, the integrated circuit package provides the smallest achievable frequency spacing resolution for adjacent first and second BAW resonators.

[0030] In one implementation, the integrated circuit package includes a plurality of BAW resonators configured in a ladder structure or lattice structure.

[0031] The trapezoidal structure and the lattice structure can fully optimize the transmission characteristics of the filter made from the plurality of BAW resonators. Here, the trapezoidal structure exhibits high rejection close to the filter passband, but poor out-of-band rejection. On the other hand, the lattice structure exhibits high out-of-band rejection, but poor rejection close to the filter passband. The integrated circuit package can combine these two structural configurations to obtain a hybrid trapezoidal-lattice filter to achieve the desired characteristics.

[0032] On one hand, a method for manufacturing a BAW resonator is provided. The method includes the step of depositing a reflective element on a substrate, the reflective element comprising at least a first layer and a second layer made of a first material and a second material, respectively having a first acoustic impedance and a second acoustic impedance. The method further includes placing one or more structures of a third material having a third acoustic impedance different from the first and second acoustic impedances within the reflective element, the structures forming an acoustic impedance modulation layer.

[0033] This method enables the fabrication of BAW resonators that provide a frequency shift without requiring precise thickness deposition of different layers in the bulk acoustic wave resonator. The AIML (Alternating Current Imaging) allows modulation of the effective acoustic impedance of the reflective element, which tunes the operating frequency of the resonator. Furthermore, the AIML improves the acoustic confinement efficiency in the piezoelectric element.

[0034] In one implementation, placing the one or more structures includes depositing a third layer of the third material on the first or second layer, and etching the third layer to form the structure. The method further includes covering the third layer with a capping layer of the first or second material and planarizing the capping layer.

[0035] The deposition of the third material alters the density of the third layer to modulate the effective impedance of the reflective element, thereby tuning the operating frequency of the BAW resonator. The third layer is etched to form a pattern for removing material. Planarization of the capping layer provides a smooth surface, ensuring proper deposition of the subsequent thin film in the BAW resonator.

[0036] In one implementation, the step of placing the one or more structures includes etching a first or second layer to create space for the structure, depositing a third layer of the third material, and planarizing the third layer.

[0037] The etching process removes material from the first or second layer in a pattern, causing the third material to fill the spaces created in the first or second layer to form the structure. These structures collectively form the third layer (i.e., the acoustic impedance modulation layer). The third layer is planarized to ensure proper deposition of the subsequent thin film in the BAW resonator.

[0038] In one implementation, the acoustic modulation layer is photolithographically defined and formed using a photolithographic mask for the entire substrate.

[0039] In this method, the acoustic modulation layer is formed in one step throughout the entire wafer of different BAW resonator units in the integrated circuit package, and no separate process steps are required to form different resonator units, thereby reducing manufacturing complexity, time and cost.

[0040] It should be noted that all devices, elements, circuits, units, and modules described in this application can be implemented in software elements or hardware elements, or any combination thereof. The steps performed by the various entities described in this application, and the functions to be performed by the various entities, are intended to refer to the various entities performing the respective steps and functions. Even in the description of the following specific embodiments, if a particular function or step to be performed by an external entity is not reflected in the description of the specific detailed elements of the entity performing that particular step or function, it will be clear to those skilled in the art that these methods and functions can be implemented in the corresponding software or hardware elements, or in any combination of such elements. It is understood that the features of the present invention are readily combined in various combinations without departing from the scope of the invention as defined by the appended claims.

[0041] Other aspects, advantages, features, and objects of the invention will be clearly described by the accompanying drawings and the detailed description of illustrative embodiments interpreted in conjunction with the appended claims. Attached Figure Description

[0042] The foregoing summary of the invention and the following detailed description of illustrative embodiments can be better understood when read in conjunction with the accompanying drawings. Exemplary structures of the invention are shown in the drawings to illustrate the invention. However, the invention is not limited to the specific methods and means disclosed herein. Furthermore, those skilled in the art will understand that these drawings are not drawn to scale. Where possible, the same elements are represented by the same numbers.

[0043] The embodiments of the present invention will now be described by way of example only, in conjunction with the accompanying drawings.

[0044] Figure 1 This is an exemplary cross-sectional view of a bulk acoustic wave (BAW) resonator provided in an embodiment of the present invention;

[0045] Figure 2 This is an exemplary cross-sectional view of a unit cell of a BAW resonator provided in an embodiment of the present invention;

[0046] Figures 3A to 3C This is an exemplary cross-sectional view of a bulk acoustic wave (BAW) resonator provided in an embodiment of the present invention;

[0047] Figure 4A This is an exemplary top view of an integrated circuit package provided in an embodiment of the present invention, the package having two different acoustic impedance modulation layers;

[0048] Figure 4B This is provided by an embodiment of the present invention. Figure 4A An exemplary cross-sectional view of an integrated circuit package along its axis AA';

[0049] Figure 5 This is a list of steps in a flowchart of a method for manufacturing a BAW resonator provided in an embodiment of the present invention;

[0050] Figure 6A and Figure 6B An exemplary graphical representation of the frequency shift of a BAW resonator provided in an embodiment of the present invention.

[0051] In the accompanying diagrams, underlined numbers indicate the item to which the underlined number is located or the item adjacent to the underlined number. Ununderlined numbers are associated with the item identified by the line linking the ununderlined number to that item. When a number is ununderlined but has an associated arrow, the ununderlined number identifies the general item that the arrow points to. Detailed Implementation

[0052] The following detailed description illustrates embodiments of the present invention and their implementation. While some embodiments of the present invention have been disclosed, those skilled in the art will recognize that other embodiments for carrying out or practicing the present invention can also be implemented.

[0053] In this specification, reference to "an embodiment" or "an embodiment" means that a particular feature, structure, or characteristic described in connection with an embodiment is included in at least one embodiment of the invention. The appearance of the phrase "in one embodiment" in different places in the specification does not necessarily refer to the same embodiment, nor does it necessarily mean that a single or alternative embodiment is mutually exclusive with other embodiments. Furthermore, the term "a (and an)" herein does not indicate a limitation of quantity, but rather the presence of at least one of the referenced items. In addition, various features that may be demonstrated by some embodiments but not by others are described. Similarly, various requirements are described that may be requirements of some embodiments but not of others.

[0054] It should be understood that when a component such as a layer, region, or substrate is referred to as "on" or "extended" to another component, it can be directly on or directly extended to the other component, or intermediate components may exist. Conversely, when a component is referred to as "directly on" or "directly coupled to" another component, no intermediate components exist. Similarly, it should be understood that when a component such as a layer, region, or substrate is referred to as "on" or "extended" to another component, it can be directly on or directly extended to the other component, or intermediate components may exist. Conversely, when a component is referred to as "directly on" or "directly extended" to another component, no intermediate components exist. It should also be understood that when a component is referred to as "connected" or "coupled" to another component, it can be directly connected or coupled to the other component, or intermediate components may exist. Conversely, when a component is referred to as "directly connected" or "directly coupled" to another component, no intermediate components exist.

[0055] The relative terms “below” or “above” or “horizontal” or “vertical” or “under” or “horizontal” or “vertical” may be used here to describe the relationship between one element, layer, or region and another element, layer, or region, as shown in the figures. It should be understood that these terms, and those discussed above, are intended to include different orientations of the device in addition to those described in the figures.

[0056] This invention generally relates to acoustic wave devices, which are key components used in modern electronic circuits. Acoustic wave devices are commonly used in filter networks that require flat passbands. In acoustic wave devices, because such devices require high-frequency selectivity while maintaining low electron insertion loss, a high-quality factor mechanical resonator needs to be coupled into the filter topology. A bulk acoustic wave (BAW) device is a mechanical resonator that couples an electrically time-varying signal to a mechanical wave propagating within a piezoelectric material. The fundamental vibrational mode electromechanically coupled to a BAW device is the thickness-extensional (TE) mode, which is a longitudinal wave propagating within the thickness of a thin piezoelectric film. In some cases, other types of piezoelectric materials can be used, in which case the fundamental vibrational mode can also be the thickness-shear (TS) mode. That is, the roles of TE and TS are interchangeable depending on the core vibrational mode of the selected piezoelectric material.

[0057] To achieve high-quality electrical signals, the mechanical resonance generated within the resonator needs to be as efficient as possible while minimizing mechanical losses. Mechanical losses in BAW devices are primarily caused by acoustic radiation of mechanical energy entering the substrate through reflective elements. Other pathways of mechanical loss include radiation and energy scattering at the resonator edges, where the Bragg layer / reflective element is not located. Furthermore, with the increasing number of filters and devices in electronic devices, stringent requirements are placed on the overall implementation size of the filters, necessitating a reduction in the planar area of ​​the resonators and the distance between them. Additionally, it is necessary to maintain the performance of these highly integrated filter technologies while improving yield and reducing process costs.

[0058] Therefore, to improve the termination performance of the filter, multiple frequency elements are needed within an integrated circuit package. Traditional BAW devices are fabricated using a thin piezoelectric layer disposed on a reflective element. In the case of a thin-film bulk acoustic resonator (FBAR), the reflective element is a cavity; while in the case of a solid-mounted resonator (SMR), the reflective element is an acoustic mirror or Bragg reflector comprising alternating layers of high and low acoustic impedance materials. In the case of SMR-BAW, frequency tuning is achieved by using mass-loaded elements with different deposition thicknesses. However, as the frequency count increases, changing the deposition thickness (requiring very fine control) increases fabrication complexity.

[0059] Figure 1 This is an exemplary description of a bulk acoustic wave (BAW) resonator 100 provided in an embodiment of the present invention. The BAW resonator 100 is a microresonator that generates high-precision and ultra-low jitter signals at specific frequencies. The BAW resonator 100 is also capable of generating signals with variable frequencies in wired and wireless circuits. For example, the BAW resonator 100 can generate variable frequencies in the range of 100 MHz to 20 MHz. The BAW resonator 100 can be used in Global Positioning Systems (GPS), data transmission (e.g., WLAN and Bluetooth), cellular mobile systems (e.g., CDMA, UMTS, GSM), satellite communications, and military applications.

[0060] The BAW resonator 100 is constructed on a substrate 102 (sometimes also referred to as the body). Specifically, the BAW resonator 100 is deposited on the substrate 102. The substrate 102 serves as the base supporting various elements or layers of the BAW resonator 100. The substrate 102 can be formed from various types of materials, including semiconductor materials compatible with semiconductor processes, which are used for integrating interconnects and electronics, thereby reducing size and cost. The substrate 102 can be fabricated using silicon, glass, ceramics, and combinations thereof. In one example, the substrate 102 may include, but is not limited to, silicon, silicon-on-insulator (SOI) technology substrates, gallium arsenide, gallium phosphide, gallium nitride, and indium phosphide. In another example, the substrate 102 may include alloy semiconductors such as GaAsP, AlInAs, GaInAs, GaInP, GaInAsP, or combinations thereof. In some examples, the BAW resonator 100 may include an electromagnetic shield disposed on a substrate 102 that blocks radio frequency (RF) and electromagnetic radiation from adjacent resonators to reduce coupling losses, such as eddy current losses in the substrate 102.

[0061] BAW resonator 100 includes a piezoelectric element 104. The piezoelectric element 104 is a layer of piezoelectric material that generates a signal at a desired resonant frequency when an electric field (e.g., voltage) is applied to it. In the BAW resonator 100, an electrically time-varying signal is coupled to a mechanical wave traveling within the body of the piezoelectric element 104. Typically, the thickness of the piezoelectric element 104 determines the frequency of the signal generated by the BAW resonator 100, and therefore the frequency of the generated signal can be changed by altering the thickness of the piezoelectric element 104. Typically, the piezoelectric element 104 is a planar structure; however, the piezoelectric element 104 can be formed to have other shapes, including but not limited to cylindrical, conical, etc., without any limitation.

[0062] The piezoelectric element 104 is typically a combination of undoped and doped piezoelectric materials, wherein the doped piezoelectric material may be doped with at least one rare earth element. Combining undoped and doped piezoelectric materials improves the piezoelectric properties of the piezoelectric element 104, for example, increasing the coupling coefficient beyond that of completely undoped piezoelectric materials (e.g., Sc, Er). Simultaneously, the undoped and doped piezoelectric materials reduce and more uniformly distribute stress within the piezoelectric element 104, thereby reducing the total compressive stress and distributing it more evenly across the substrate 102. In this embodiment, the materials used to manufacture the piezoelectric element 104 may include, but are not limited to, lithium niobate, lithium tantalate, aluminum nitride, zinc oxide, etc.

[0063] The BAW resonator 100 also includes a bottom electrode 106 on a first surface 104A of the piezoelectric element 104 and a top electrode 108 on a second surface 104B of the piezoelectric element 104 opposite to the first surface 104A. The top electrode 108 is placed on the second surface 104B and is in direct contact with the piezoelectric element 104. In other words, the piezoelectric element 104 is sandwiched between the bottom electrode 106 on the first surface 104A and the top electrode 108 on the second surface 104B. Typically, the bottom electrode 106 is a planar structure; however, the bottom electrode 106 can be formed to have other shapes, including but not limited to cylindrical, conical, etc., without any limitation. The thickness of the bottom electrode 106 is selected to give the BAW resonator 100 optimal acoustic characteristics. For example, the thickness of the bottom electrode 106 is selected to obtain maximum effective coupling and minimum temperature coefficient of frequency (TCF).

[0064] The BAW resonator 100 is divided into an active region and an external region. The active region typically corresponds to the overlapping portion of the bottom electrode 106 and the top electrode 108 of the BAW resonator 100, and also includes the layer beneath the overlapping top electrode 106 and bottom electrode 108. The external region corresponds to the portion of the BAW resonator 100 that surrounds the active region, and it is not electrically driven. Although in Figure 1 The diagram shows that each electrode comprises a single layer, but the bottom electrode 106 and / or the top electrode 108 may comprise multiple layers of the same material, multiple layers of at least two different materials, or multiple layers of different materials. In this embodiment, the materials used to manufacture the bottom electrode 106 may include, but are not limited to, tungsten, titanium, tantalum, molybdenum, platinum, iridium, ruthenium, or combinations thereof, and the materials used to manufacture the top electrode 108 may include, but are not limited to, molybdenum, platinum, tungsten, and iridium.

[0065] According to one embodiment, the BAW resonator 100 further includes at least one mass load layer 110 on the top electrode 108. The mass load layer 110 can vary the thickness of the top electrode 108 of the BAW resonator 100. By changing the thickness of the mass load layer 110 in the BAW resonator 100, multiple resonant frequencies can be generated in the BAW resonator 100. In one example, increasing the thickness of the mass load layer 110 increases the acoustic path length of the BAW resonator 100, which results in a decrease in its resonant frequency. In another example, decreasing the thickness of the mass load layer 110 decreases the acoustic path length of the BAW resonator 100, which results in an increase in its resonant frequency. In another example, the BAW resonator 100 may include a mass load layer 110 on the bottom electrode 106 without departing from the scope of the invention. In some examples, the BAW resonator 100 may include multiple mass load layers 110 on the top electrode 108 to further change its resonant frequency.

[0066] The mass loading layer 110 may correspond to a thickened portion of the top electrode 108 or an additional layer on the top electrode 108 to which a suitable material is applied. The mass loading layer 110 extends around the periphery of the active region in the top electrode 108. Therefore, the portion of the BAW resonator 100 that includes and resides beneath the mass loading layer 110 is referred to as the active region. In one example, the mass loading layer 110 may be made of a conductive substrate, such as, but not limited to, tungsten, tungsten alloys, molybdenum, aluminum, iridium, and platinum. In another example, the mass loading layer 110 may be made of a dielectric material, such as, but not limited to, silicon dioxide, silicon nitride, diamond, and amorphous aluminum nitride. Typically, the mass loading layer 110 may be a single metal layer, such as tungsten, or an alloy, such as AlCu, or a multilayer of metals, such as tungsten and AlCu.

[0067] According to one embodiment, a mass load layer 110 is embedded or partially embedded in the top electrode 108. The mass load layer 110 is embedded in the top electrode 108 by depositing mass load material substantially along the edge of the top electrode 108 to define a boundary region. The defined boundary region may have areas, particularly at the corners where the metal is depleted, that allow the bottom electrode 106 to extend to the lead connection without experiencing a direct electric field. By various examples, the mass load layer 110 can be provided as a frame-like structure formed of a metal heavier than the metal of the top electrode 108 and various formations of a frame-like structure adjacent to the top electrode 108, including outside, above, below, and between the layered electrodes. It is understood that this is in contrast to conventional BAW resonators, in which the mass load layer is placed on the top electrode to typically generate a downward offset of the mechanical load and operating frequency.

[0068] The BAW resonator 100 also includes a reflective element 112 between the bottom electrode 106 and the substrate 102. The reflective element 112 is also referred to as an acoustic mirror or Bragg reflector. The reflective element 112 comprises alternating layers of high acoustic impedance material and low acoustic impedance material to generate a resonant signal at the desired frequency. The reflective element 112 can be fabricated using a dielectric material, which may include, but is not limited to, SiCOH, phosphosilicate glass, aluminum, silicon, germanium, gallium, indium, tin, antimony, tellurium, bismuth, titanium, vanadium, chromium, manganese, cobalt, nickel, copper, zinc, zirconium, niobium, molybdenum, palladium, cadmium, helium, tantalum, tungsten, or combinations thereof. Alternatively, the reflective element 112 can be fabricated using a fiber optic grating or a semiconductor material, such as silicon oxide.

[0069] The reflective element 110 includes at least a first layer 114A of a first material having a first acoustic impedance and a second layer 114B of a second material having a second acoustic impedance, wherein the second acoustic impedance is different from the first acoustic impedance. That is, the first layer 114A and the second layer 114B have different acoustic impedances. Acoustic impedance is the product of the medium density for signal propagation and the signal wave velocity. Here, the first layer 114A and the second layer 114B are made of different materials and have different acoustic impedances. Materials with low acoustic impedance are typically low-density materials. In this embodiment, the materials used for the low acoustic impedance layer (e.g., the first layer 114A) may include, but are not limited to, silicon dioxide, aluminum, and SiOC. Furthermore, materials with high acoustic impedance are typically high-density materials. In this embodiment, the materials used for the high acoustic impedance layer (e.g., the second layer 114B) may include, but are not limited to, iridium, molybdenum, and tungsten.

[0070] According to one embodiment, the reflective element 112 comprises alternating layers of a first material and a second material, such that the reflective element 112 is arranged to operate at the operating frequency of the BAW resonator. That is, the reflective element 112 includes alternating layers of low acoustic impedance material and high acoustic impedance material. For example, the reflective element 112 includes a first layer 114A, followed by a second layer 114B, then another first layer 114A and another second layer 114B, and so on, to form alternating layers of first layer 114A and second layer 114B. This is done to generate a significant reflection coefficient at the junction of adjacent layers in the reflective element 112. The thickness and distance between the first layer 114A and the second layer 114B are determined according to the expected resonant frequency of the BAW resonator 100 to generate constructive interference at that frequency. In one example, the thickness of the first layer 114A and the second layer 114B corresponds to one-quarter of the design frequency wavelength, and the distance between the first layer 114A and the second layer 114B is half of the design frequency wavelength.

[0071] According to one embodiment, the reflective element 112 is a Bragg layer comprising multiple interlaced first layers 114A and second layers 114B. Here, the Bragg layer is a series of planar surfaces with different acoustic impedances. This makes it possible to reflect almost the entire incident signal through constructive interference phenomena. This is possible as long as the incident signal wave is close to normal incidence. As discussed, the reflective element 112 comprises multiple layers, including spaced-apart first layers 114A and second layers 114B. Multiple layers, including first layers 114A and second layers 114B, are arranged alternately in the Bragg layer configuration of the reflective element 112. Each layer boundary causes partial reflection of the signal wave. For waves with vacuum wavelengths approaching four times the layer thickness, numerous reflections combine with constructive interference, thus the Bragg layer generally acts as a high-quality filter.

[0072] The first layer 114A or the second layer 114B includes one or more structures of a third material having a third acoustic impedance different from the first and second acoustic impedances, the structures forming an acoustic impedance modulation layer 116 embedded in the first layer 114A and / or the second layer 114B. In one example, the acoustic impedance modulation layer 116 may be embedded in either the first layer 114A or the second layer 114B. In another example, the acoustic impedance modulation layer 116 may be embedded in both the first layer 114A and the second layer 114B. Figure 1 In the exemplary illustration, the first layer 114A is shown to include four structures 116A, 116B, 116C, and 116D that collectively form the acoustic impedance modulation layer 116. Structures 116A, 116B, 116C, and 116D are different patches on the first layer 114A used for tuning the operating frequency of the BAW resonator 100. In one example, the acoustic impedance modulation layer 116 is formed of a dielectric material, which may include, but is not limited to, SiN, SiO2, AlN, or combinations thereof. In another example, the acoustic impedance modulation layer 116 is formed of a conductive material, which may include, but is not limited to, aluminum, tungsten, platinum, or combinations thereof. Specifically, structures 116A, 116B, 116C, and 116D are made of a third material, different from the first material of the first layer 114A and the second material of the second layer 114B, having a third acoustic impedance that differs from the first acoustic impedance of the first layer 114A and the second acoustic impedance of the second layer 114B.

[0073] The different acoustic impedances (and densities due to the different corresponding materials) of the first layer 114A, the second layer 114B, and the acoustic impedance modulation layer 116 can modify the effective impedance (and effective density) of the reflective element 112. Modulation in the effective impedance directly affects the sound propagation constant, which in turn changes the signal velocity in that particular region, thus affecting the overall operating frequency of the BAW resonator 100. In this way, the acoustic impedance modulation layer 116 tunes the operating frequency of the BAW resonator 100. Furthermore, the acoustic impedance modulation layer 116 improves the acoustic confinement efficiency in the piezoelectric element 104. In some examples, the acoustic impedance modulation layer 116 can also be patterned to change the density of one or more structures 116A, 116B, 116C, and 116D to enhance the modulation of the effective impedance of the reflective element 112 and thus tune the operating frequency of the BAW resonator 100.

[0074] Figure 2 This is the BAW resonator provided in the embodiments of the present invention (e.g., Figure 1 An exemplary description of the unit cell 200 of the BAW resonator 100. Already combined with Figure 1 The components are described Figure 2 . Reference Figure 2 The figure illustrates the relative positions and deposition thicknesses of different components or layers of the BAW resonator 100. As shown, the BAW resonator 100 includes a substrate 102 as a bottom layer and a piezoelectric element 104 as a top layer. A reflective element 112 is disposed between the substrate 102 and the piezoelectric element 104. A bottom electrode 106 is disposed on a first surface 104A of the piezoelectric element 104 between the piezoelectric element 104 and the reflective element 112. The reflective element 112 includes an acoustic impedance modulation layer 116 on which a first layer 114A or a second layer 114B is disposed. As shown, the acoustic impedance modulation layer 116 is embedded near the bottom electrode 106 at a distance L1 from the bottom electrode 106. Furthermore, the deposition thickness of the acoustic impedance modulation layer 116 is L2.

[0075] According to one embodiment, one or more structures 116A, 116B, 116C, and 116D comprise a semiconductor material having a sufficiently large dopant concentration to change its mass density and / or acoustic phase velocity. Here, the acoustic impedance modulation layer 116 comprises a semiconductor material having a dopant concentration that changes its mass density and acoustic phase velocity of the resonant signal generated by the BAW resonator 100. It is contemplated that such a change in mass density and / or acoustic phase velocity generally alters the third acoustic impedance in the reflective element 112. Therefore, the semiconductor material in the acoustic impedance modulation layer 116 can tune the operating frequency of the bulk acoustic wave resonator 100. In this embodiment, the semiconductor material can be an n-type or p-type material. In one example, the semiconductor material used for one or more structures can include, but is not limited to, silicon, germanium, silicon carbide, silicon-germanium, boron, arsenic, phosphorus, and combinations thereof.

[0076] According to one embodiment, the thickness of one or more structures 116A, 116B, 116C, and 116D is on the order of the acoustic wavelength or a fraction of the acoustic wavelength at the fundamental operating frequency of the BAW resonator 100. As previously described, it can be understood that the thickness of structures 116A, 116B, 116C, and 116D is determined based on the expected resonant frequency of the BAW resonator 100. In the BAW resonator 100 of this disclosure, the thickness of one or more structures 116A, 116B, 116C, and 116D corresponds to one-quarter of the wavelength of the expected frequency. Furthermore, the fundamental operating frequency of the BAW resonator 100 generally decreases with increasing thickness of one or more structures 116A, 116B, 116C, and 116D.

[0077] According to one embodiment, structures 116A, 116B, 116C, and 116D are asymmetrically distributed to form an acoustic impedance modulation layer 116. Here, the acoustic impedance and density of the acoustic impedance modulation layer 116 vary with the implementation of structures 116A, 116B, 116C, and 116D. Thus, the asymmetry in the acoustic impedance modulation layer 116 allows for changes in the acoustic impedance and its mass density, which can be used to tune the BAW resonator 100 to the desired operating frequency. Specifically, the asymmetry in the distribution of structures 116A, 116B, 116C, and 116D contributes to the formation of asymmetric boundary conditions in the event of lateral spurious mode accumulation. Here, the positions of structures 116A, 116B, 116C, and 116D in the reflecting element 112 are determined according to the frequency offset required for tuning the BAW resonator 100, in order to form the acoustic impedance modulation layer 116. Furthermore, in order to form the acoustic impedance modulation layer 116, the structural geometry of structures 116A, 116B, 116C, and 116D is also determined according to the frequency offset required for tuning the BAW resonator 100.

[0078] Figure 3A This is an illustration of a BAW resonator 300A provided in another embodiment of the present invention. Figure 3 is in conjunction with... Figure 1 The components of the BAW resonator 100 are described below, and these components are generally similar in construction. The BAW resonator 300A includes a substrate 102 and a piezoelectric element 104. The BAW resonator 300A also includes a reflective element 112 between the substrate 102 and the piezoelectric element 104. The BAW resonator 300A also includes a bottom electrode 106 between the first surface 104A of the piezoelectric element 104 and the reflective element 112. The reflective element 112 includes an acoustic impedance modulation layer 302 formed in a first layer 114A or a second layer 114B.

[0079] The acoustic impedance modulation layer 302 includes multiple structures 302A, 302B, 302C, 302D, 302E, and 302F. Structures 302A, 302B, 302C, 302D, 302E, and 302F are asymmetrically distributed to form the acoustic impedance modulation layer 302. This asymmetrical arrangement of structures 302A, 302B, 302C, 302D, 302E, and 302F provides variations in the signal mass density and acoustic phase velocity of the acoustic impedance modulation layer 302, making the acoustic impedance within the acoustic impedance modulation layer 302 variable. Therefore, the asymmetrical arrangement of structures 302A, 302B, 302C, 302D, 302E, and 302F allows the tuning of the BAW resonator 300A to define its operating frequency. Furthermore, the asymmetric arrangement of structures 302A, 302B, 302C, 302D, 302E, and 302F eliminates unwanted signals and noise in the signal, thereby reducing signal interference and degradation. Therefore, asymmetry helps establish lateral spurious modes by creating asymmetric boundary conditions. In this embodiment, the positions of structures 302A, 302B, 302C, 302D, 302E, and 302F are determined based on the frequency offset required for tuning the BAW resonator 300A in order to form the acoustic impedance modulation layer 302. Furthermore, the structural geometry and thickness of structures 302A, 302B, 302C, 302D, 302E, and 302F are also determined based on the frequency offset required for tuning the BAW resonator 300A in order to form the acoustic impedance modulation layer 302.

[0080] In one embodiment, the acoustic impedance modulation layer 116 is embedded in a layer adjacent to the bottom electrode 106 of the reflective element 112. Embedding the acoustic impedance modulation layer 116 near the bottom electrode 106 (i.e., the upper core portion of the reflective element 112) helps reduce noise in the signal (i.e., unwanted signals), thereby reducing interference and degradation of the signal. Thus, the acoustic impedance modulation layer 116 operates as a spurious mode reduction region due to the accumulation of lateral propagating modes. Based on the dispersion characteristics of these lateral propagating modes, the acoustic impedance modulation layer can provide the necessary boundary conditions at the edges of the core resonator region to reduce the accumulation of spurious modes. This has a strong impact on the performance of the BAW resonator 100. Alternatively, the acoustic impedance modulation layer 116 can be embedded in the reflective element 112 adjacent to the substrate 102 without departing from the scope and spirit of the invention.

[0081] Figure 3B This is a diagram of a BAW resonator 300B provided in another embodiment of the present invention. Figure 3B Combination Figure 1 and Figure 3AThe following describes the components of a BAW resonator, which are generally similar in construction. BAW resonator 300B includes a substrate 102 and a piezoelectric element 104. BAW resonator 300B also includes a reflective element 112 between the substrate 102 and the piezoelectric element 104. BAW resonator 300B also includes a bottom electrode 106 between a first surface 104A of the piezoelectric element 104 and the reflective element 112. The reflective element 112 includes an acoustic impedance modulation layer 302 formed in a first layer 114A or a second layer 114B. The acoustic impedance modulation layer 302 includes multiple structures 302A, 302B, 302C, 302D, 302E, and 302F. Structures 302A, 302B, 302C, 302D, 302E, and 302F are embedded in the first layer 114A of the reflective element 112, adjacent to the bottom electrode 106.

[0082] Here, the acoustic impedance modulation layer 302 is embedded in the first layer 114A. In one implementation, a third material is first deposited on the first layer 114A, and then the acoustic impedance modulation layer 302 is etched by forming structures 302A, 302B, 302C, 302D, 302E, and 302F. The acoustic impedance modulation layer 302 is then covered with a capping layer (not shown) of the first material of the first layer 114A. In another implementation, the first layer 114A is first etched to create space to form structures 302A, 302B, 302C, 302D, 302E, and 302F. Then, a third material is deposited in the formed structures 302A, 302B, 302C, 302D, 302E, and 302F to form the acoustic impedance modulation layer 302. The acoustic impedance modulation layer 302 is then covered by a capping layer (not shown) of the first material of the first layer 114A. In some examples, the acoustic impedance modulation layer 302 is planarized before being embedded (i.e., before the application of the overlay layer) into the first 114A, which significantly improves the smoothness of the surface of the acoustic impedance modulation layer 302. The planarization of the surface of the acoustic impedance modulation layer 302 can be performed using chemical mechanical polishing (CMP) techniques.

[0083] In one embodiment, the acoustic impedance modulation layer 116 is arranged such that it extends into both layers of the reflective element 112. Here, the acoustic impedance modulation layer 116 may be embedded within the first layer 114A and the second layer 114B. As discussed, in another example, the acoustic impedance modulation layer 116 may be embedded simultaneously within both the first layer 114A and the second layer 114B. According to one embodiment, a third layer of a third material is deposited on either the first layer 114A or the second layer 114B, and then the third layer is etched to form structures 116A, 116B, 116C, and 116D, after which the third layer is covered by a capping layer (not shown) of either the first or second material. According to another embodiment, the first layer 114A or the second layer 114B is etched to create spaces to form structures 116A, 116B, 116C, and 116D, and then a third layer of the third material is deposited thereon. In some examples, the acoustic impedance modulation layer 116 is planarized before embedding the first layer 114A and / or the second layer 114B, which significantly improves the smoothness of the surface of the acoustic impedance modulation layer 116. The planarization of the surface of the acoustic impedance modulation layer 116 can be performed using chemical mechanical polishing (CMP) techniques.

[0084] Figure 3C This is a diagram of a BAW resonator 300C provided in another embodiment of the present invention. Figure 3C Combination Figure 1 , Figure 3A and Figure 3B The following describes the components of a BAW resonator, which are generally similar in construction. BAW resonator 300C includes a substrate 102 and a piezoelectric element 104. BAW resonator 300C also includes a reflective element 112 between the substrate 102 and the piezoelectric element 104. BAW resonator 300C also includes a bottom electrode 106 between a first surface 104A of the piezoelectric element 104 and the reflective element 112. The reflective element 112 includes an acoustic impedance modulation layer 302 formed in a first layer 114A or a second layer 114B. The acoustic impedance modulation layer 302 includes multiple structures 302A, 302B, 302C, 302D, 302E, and 302F. Structures 302A, 302B, 302C, 302D, 302E, and 302F are embedded in the first layer 114A and the second layer 114B of the reflective element 112.

[0085] Here, the acoustic impedance modulation layer 302 extends into and is embedded within the first layer 114A and the second layer 114B. In one implementation, a third material is deposited between the first layer 114A and the second layer 114B, and then structures 302A, 302B, 302C, 302D, 302E, and 302F are etched therein to form the acoustic impedance modulation layer 302. In another implementation, the gap between the first layer 114A and the second layer 114B is etched to create space, and then structures 302A, 302B, 302C, 302D, 302E, and 302F are formed by depositing (i.e., filing) the third material, in which the acoustic impedance modulation layer 302 is present.

[0086] Figures 4A to 4B This is an illustration of an integrated circuit package 400 provided according to one embodiment. Examples of integrated circuit package 400 include, but are not limited to, digital logic circuits, analog circuits, processor cores, digital signal processor (DSP) cores, etc. Integrated circuit package 400 can be made of any suitable material and can have any suitable shape, size, etc., without any limitation. Integrated circuit package 400 can be a wafer-level package or a die-level package. For example, integrated circuit package 400 can include multiple identical, integrally connected wafer portions, each wafer portion including the same structure and circuitry. If desired, these identical portions can later be separated in a die forming process. The integrated circuit package 400 of the present invention can include microelectromechanical (MEMS) structures, such as bulk acoustic wave (BAW) structures, formed on top of the wafer. Multiple MEMS structures, such as BAW structures or other structures, can be disposed on each wafer portion, or such multiple MEMS structures can be included in one or more cavities of the wafer portion.

[0087] The integrated circuit package 400 includes at least a first BAW resonator 402A and a second BAW resonator 402B. In this embodiment, the integrated circuit package 400 is a semiconductor-based device (or chip) having a first BAW resonator 402A and a second BAW resonator 402B connected to each other. Although, in Figures 4A to 4B In the illustration, the integrated circuit package 400 is shown to include two BAW resonators, namely the first BAW resonator 402A and the second BAW resonator 402B; however, it is understood that the integrated circuit package 400 may include more than two BAW resonators without any limitation.

[0088] the following, Figures 4A to 4B Already combined Figure 1The components are described in Figure 3. In some examples, the first BAW resonator 402A and the second BAW resonator 402B may be similar to each other. However, in a preferred example, the first BAW resonator 402A and the second BAW resonator 402B are constructed differently to produce different resonant frequencies in the integrated circuit package 400. In one embodiment, the first BAW resonator 402A and the second BAW resonator 402B may be similar to BAW resonator 300A, as discussed in the preceding paragraphs. Here, the first BAW resonator 402A and the second BAW resonator 402B have different acoustic impedance modulation layers. That is, the first BAW resonator 402A has an acoustic impedance modulation layer 404A similar to acoustic impedance modulation layer 116, and the second BAW resonator 402B has an acoustic impedance modulation layer 404B similar to acoustic impedance modulation layer 302. Different acoustic impedance modulation layers 404A and 404B allow for multiple frequencies on the same integrated circuit package 400 without requiring precise thickness deposition of different layers of the first BAW resonator 402A and the second BAW resonator 402A (as is conventionally required).

[0089] As discussed, the first BAW resonator 402A and the second BAW resonator 402B may each include corresponding acoustic impedance modulation layers 404A and 404B. Figures 4A to 4B As shown, the acoustic impedance modulation layer 404A of the first BAW resonator 402A includes one or more structures 406A, and the acoustic impedance modulation layer 404B of the second BAW resonator 402B includes one or more structures 406B. It can be understood that different acoustic impedance modulation layers 404A and 404B can be formed by using different patterns, geometries, relative positions, doping concentrations, etc., of one or more of the structures 406A and 406B.

[0090] As shown in the figure, the integrated circuit package 400 has a generally flat top surface and a generally flat bottom surface. The integrated circuit package 400 includes a substrate 408 (similar to substrate 102) shared with a first BAW resonator 402A and a second BAW resonator 402B, on which the first BAW resonator 402A and the second BAW resonator 402B are deposited. The integrated circuit package 400 also includes a piezoelectric layer 410 (similar to piezoelectric layer 104) and a reflective element 412 (similar to reflective element 112). The first BAW resonator 402A includes a bottom electrode 414A, and the second BAW resonator 402B includes a bottom electrode 414B (both similar to bottom electrode 106).

[0091] Furthermore, the reflective element 412 comprises alternating layers of high acoustic impedance material and low acoustic impedance material to generate a signal at the desired frequency. Specifically, the reflective element 412 includes a first layer 416A and a second layer 418A for the first BAW resonator 402A, and a first layer 416B and a second layer 418B for the second BAW resonator 402B. The first layers 416A, 416B and the corresponding second layers 418A, 418B are layers with different acoustic impedances. The first layers 416A, 416B have a first acoustic impedance, and the second layers 418A, 418B have a second acoustic impedance; for example, the first acoustic impedance is lower than the second acoustic impedance.

[0092] In this embodiment, structures 406A and 406B reduce RF and eddy current losses to substrate 408 by forming open current loops. Structures 406A and 406B include varying spacing and patch sizes throughout the process to form corresponding acoustic impedance modulation layers 404A and 404B. The varying spacing and patch sizes create asymmetry in the acoustic impedance modulation layers 404A and 404B, which helps establish lateral spurious modes by creating asymmetric boundary conditions.

[0093] According to one embodiment, the integrated circuit package 400 includes a plurality of BAW resonators 402A and 402B configured in a trapezoidal or lattice structure. Since the integrated circuit package 400 is used to construct a micromechanical filter with potentially finely optimized in-band ripple, this micromechanical filter is obtained through the electrical interconnection of a plurality of individual BAW resonators 402A and 402B similar to those configured in a trapezoidal or lattice structure. In the trapezoidal structure, the plurality of BAW resonators 402A and 402B are arranged in a series-parallel configuration. For example, a first BAW resonator 402A is arranged in series, followed by a second BAW resonator 402B arranged in parallel, and again immediately following the first BAW resonator 402A arranged in series, and so on. In the lattice structure, the plurality of BAW resonators 402A and 402B are arranged as a lattice. Both the trapezoidal and lattice structures enable full optimization of the transmission characteristics of the filter provided by the integrated circuit package 400 made of the plurality of BAW resonators 402A and 402B. Here, the trapezoidal structure exhibits high suppression close to the filter passband, but poor out-of-band suppression. On the other hand, the lattice structure exhibits high out-of-band suppression, but poor suppression close to the filter passband. The integrated circuit package 400 can combine these two structural configurations to obtain a hybrid trapezoidal-lattice filter to achieve the desired characteristics.

[0094] Figure 5This is a flowchart of a method 500 for manufacturing a BAW resonator according to an embodiment of the present invention. The various embodiments and variations disclosed above are applicable to the method for manufacturing a BAW resonator by comparison. It should be understood that the method may vary depending on the specific steps and order without departing from the scope and spirit of this disclosure.

[0095] In step 502, a substrate is provided (e.g., Figure 1 The substrate 102). The substrate serves as the base for various elements or layers supporting the BAW resonator. In step 504, the reflective element (e.g., Figure 1 The reflective element 112 is deposited on the substrate (e.g., the reflective element 112) Figure 1 The reflective element (102) is used. The reflective element is also called an acoustic mirror or Bragg reflector. The reflective element comprises alternating layers of high acoustic impedance material and low acoustic impedance material to generate a resonant signal at the desired frequency. Additionally, a piezoelectric element (e.g., Figure 1 The piezoelectric element 104 is deposited on the reflective element.

[0096] In step 506, the first layer and the second layer (e.g., Figure 1 A first layer 114A and a second layer 114B are deposited on the reflective element. The first and second layers are made of a first material and a second material, respectively, having a first acoustic impedance and a second acoustic impedance. That is, the first and second layers are layers with different acoustic impedances. The first layer has a first acoustic impedance, and the second layer has a second acoustic impedance. The material used for the low acoustic impedance layer (e.g., the first layer) may include, but is not limited to, silicon dioxide, aluminum, and SiOC. The material used for the high acoustic impedance layer (e.g., the second layer) may include, but is not limited to, iridium, molybdenum, and tungsten. The reflective element consists of alternating layers of the first and second layers, such that the reflective element is arranged to operate at the operating frequency of the BAW resonator. For example, the reflective element includes a first layer, followed by a second layer, followed by another first layer, and so on, to form alternating layers of the first and second layers.

[0097] In step 508, one or more structures of a third material having a third acoustic impedance are placed in the first and / or second layers, wherein the third acoustic impedance differs from the first acoustic impedance. The structures form an acoustic impedance modulation layer (similar to...) within the reflective element. Figure 1The acoustic impedance modulation layer 116 is embedded in the first and / or second layer. The different acoustic impedances of the first, second, and acoustic impedance modulation layers can modify the effective impedance (and effective density) of the reflecting element. Modulation in the effective impedance directly affects the acoustic propagation constant, which in turn changes the signal velocity in that particular region, thus affecting the overall operating frequency of the resonator. Therefore, the acoustic impedance modulation layer tunes the operating frequency of the BAW resonator. Furthermore, the acoustic impedance modulation layer generates multiple resonant frequencies from the same BAW resonator without requiring precise control of the thickness of different layers of the resonator. Additionally, the acoustic impedance modulation layer improves the acoustic confinement efficiency in the piezoelectric elements of the BAW resonator.

[0098] According to one embodiment, the step of placing one or more structures includes depositing a third layer of a third material on a first or second layer, and etching the third layer to form the structure. The method further includes covering the third layer with a capping layer of the first or second material and planarizing the capping layer. An etching process is used to remove material from the acoustic impedance modulation layer (i.e., the third layer) in a pattern to form the structure. The acoustic impedance modulation layer can be removed by coating it with photoresist or a hard mask (typically an oxide or nitride) and exposing the acoustic impedance modulation layer to the pattern during photolithography. These structures alter the density of the third layer to modulate the effective impedance of the reflective element, thereby tuning the operating frequency of the BAW resonator. Furthermore, these structures are capable of generating multiple resonant frequencies from the same BAW resonator. Therefore, the structure of the acoustic impedance modulation layer determines the frequency offset and allows for fine control of the frequency spacing in the BAW resonator. Additionally, a capping layer composed of a first or second material is deposited (depending on which of the first or second layers is etched). The capping layer is planarized to ensure proper deposition of the subsequent thin film in the BAW resonator. The overlay can be planarized using chemical mechanical polishing (CMP) technology, which uses a combination of chemical and mechanical methods, including abrasives and corrosive chemical slurries (usually colloids), to achieve ultra-precision polishing of the overlay surface, thus creating a third layer in the reflective element.

[0099] According to one embodiment, the step of placing one or more structures includes etching a first or second layer to create space for the structure, depositing a third layer of a third material, and planarizing the third layer. The etching process can be used to remove material from the first or second layer in a pattern such that the third material fills the spaces created in the first or second layer to form the structure. These structures collectively form an acoustic impedance modulation layer for a BAW resonator. In this document, the third layer is planarized to ensure proper deposition of the subsequent thin film in the BAW resonator. The third layer can be planarized using chemical mechanical polishing (CMP), a technique that uses a combination of chemical and mechanical methods, including abrasives and corrosive chemical slurries (typically colloids), to achieve ultra-precision polishing of the surface of the third layer.

[0100] According to one embodiment, the acoustic modulation layer is photolithographically defined and formed using a single photomask for the entire substrate. The photolithographically defined acoustic impedance modulation layer allows for the design of multiple frequencies on a single substrate. Therefore, if we need N individual frequencies, we do not need N different process steps to form each of the N different resonators. It should be understood that the photolithographically defined acoustic impedance modulation layer provides the minimum frequency spacing resolution between adjacent resonators. Using a single photomask for the entire substrate, the acoustic modulation layer is formed in a single step across the entire wafer of the different BAW resonator units in the integrated circuit package, and separate process steps are not required to form the different resonator units, thereby reducing manufacturing complexity, time, and cost.

[0101] Figure 6A and Figure 6B An exemplary graphical representation of the frequency shift of a BAW resonator 100 provided in an embodiment of the present invention. (See reference...) Figure 6A The graphic representation 600A shows the frequency shift of a BAW resonator 100 with an a / p ratio of 2. Here, the a / p ratio is the ratio between the surface area and the perimeter of the BAW resonator 100. The a / p ratio depends on the shape of the resonator. For a given value of "a", the a / p of a square is greater than that of a triangle, and the a / p of a circle is the largest. Regardless of shape, the a / p ratio always increases with the value of "a". Therefore, large resonators have large a / p ratios, and small resonators have relatively small a / p ratios. In the graphic representation 600A, line 602 represents the frequency shift of the BAW resonator 100. The frequency shift is achieved through the acoustic impedance modulation layer of the BAW resonator 100. (Reference) Figure 6BA graphical representation 600B is also shown, illustrating the frequency shift of the BAW resonator 100 when its a / p ratio is 4. In graphical representation 600B, line 604 represents the frequency shift of the BAW resonator 100. The frequency shift is achieved through the same acoustic impedance modulation layer of the BAW resonator 100. Therefore, it can be understood that modulation within the frequency shift range is obtained according to the design of a single BAW resonator 100 by using an acoustic impedance modulation layer configuration. It should be noted that the quality factor (Q) and electromechanical coupling coefficient (kt2) factor are preserved in this paper. This configuration provides fine frequency tuning wit = h ripple enhancement (similar to SAW resonators). Furthermore, it can be understood that the dispersion type of the BAW resonator can be shifted (via photolithography) to provide spurious mode suppression options.

[0102] The BAW resonator 100 of the present invention relies on the deposition and patterning of an acoustic impedance modulation layer 116 in the upper core portion of the reflective element 112. Including different material patches in this upper core portion of the reflective element 112 can alter the effective density of the first layer 114A (or the second layer 114B), directly affecting the acoustic propagation constant, which in turn changes the phase velocity of the volume wave propagating in that particular region. This modification of the acoustic parameters affects the overall operating frequency of the BAW resonator 100. It should be noted that this tuning of the effective impedance and effective density is accomplished solely by varying the implementation of the patterned shape of the acoustic impedance modulation layer 116. The acoustic impedance modulation layer 116 is patterned once across the entire wafer surface and can be modulated with photolithographically defined effective density of the first layer 114A (or the second layer 114B). Therefore, adjacent BAW resonators can have different frequencies, even if they are located on the same die.

[0103] The BAW resonator 100 achieves frequency shift settings via photolithography of the acoustic impedance modulation layer 116, eliminating the need for precise thickness deposition (as is conventionally required). This design allows for the realization of numerous frequencies on the same wafer and enables fine optimization of in-band ripple. Here, the acoustic impedance modulation layer 116 can be positioned near the bottom electrode 106 (i.e., near the edge of the BAW resonator 100), thus functioning as a spurious mode reduction / frame region. The acoustic impedance modulation layer 116 also serves to electrically shield any radiation and induced current entering the substrate 102. Furthermore, the acoustic impedance modulation layer 116 adds additional optimization parameters to improve the acoustic confinement efficiency in the piezoelectric element 104. Moreover, the acoustic impedance modulation layer 116 with added dummy elements significantly improves the planarization of the surface before the deposition of the core piezoelectric element 104.

[0104] The bulk acoustic wave (BAW) resonator of this invention can be used in many high-frequency communication applications. Specifically, current BAW resonators are used in filter networks operating at frequencies above 1.5 GHz that require a flat passband; they have exceptionally steep filter skirts and square shoulders at the upper and lower ends of the passband; and they provide significant suppression outside the passband. The BAW resonator of this invention has relatively low insertion loss, tends to decrease in size as the operating frequency increases, and is relatively stable over a wide temperature range. Therefore, this BAW resonator can be used in many third-generation (3G) and fourth-generation (4G) wireless devices, and further in filter applications for fifth-generation (5G) wireless devices. It is understood that these wireless devices support cellular, Wi-Fi, Bluetooth, and / or near-field communication on the same wireless device, thus presenting extremely challenging filtering requirements that can be handled by the BAW resonator of this invention.

[0105] Modifications to the embodiments of the invention described above may be made without departing from the scope of the invention as defined by the appended claims. Expressions such as “comprising,” “including,” “combined,” “having,” and “are” used to describe and claim the invention should be interpreted in a non-unique manner, allowing for the appearance of items, parts, or elements not explicitly described. Singular references should also be interpreted in relation to the plural. The term “exemplary” as used herein means “as an example, instance, or illustration.” Any “exemplary” embodiment is not necessarily to be construed as preferential or superior to other embodiments, and / or does not exclude combinations of features from other embodiments. The term “optionally” as used herein means “provided in some embodiments and not in others.” It should be understood that certain features of the invention described in the context of a single embodiment for clarity may also be provided in combination in a single embodiment. Conversely, for the sake of brevity, various features of the invention described in the context of a single embodiment may also be provided individually or in any suitable combination or as any other suitable embodiment of the invention.

Claims

1. A bulk acoustic wave (BAW) resonator on a substrate, characterized in that, The BAW resonator includes a piezoelectric element, a bottom electrode on a first surface of the piezoelectric element, and a top electrode on a second surface of the piezoelectric element opposite to the first surface. The resonator also includes a reflective element between the bottom electrode and the substrate. The reflective element comprises at least a first layer of a first material having a first acoustic impedance and a second layer of a second material having a second acoustic impedance, the second acoustic impedance being different from the first acoustic impedance. The first layer or the second layer includes one or more structures of a third material having a third acoustic impedance, the third acoustic impedance being different from both the first and second acoustic impedances. These structures form an acoustic impedance modulation layer embedded in the first layer and / or the second layer. The structure is asymmetrically distributed to form the acoustic impedance modulation layer.

2. The BAW resonator according to claim 1, characterized in that, The reflective element is a Bragg layer comprising multiple interwoven first and second layers.

3. The BAW resonator according to claim 1, characterized in that, The reflective element is composed of alternating layers of the first material and the second material, such that the reflective element is arranged to operate at the operating frequency of the BAW resonator.

4. The BAW resonator according to claim 1, characterized in that, The acoustic impedance modulation layer is embedded in the layer adjacent to the bottom electrode of the reflective element.

5. The BAW resonator according to claim 1, characterized in that, The thickness of the one or more structures is on the order of the acoustic wavelength or a fraction of the acoustic wavelength at the fundamental operating frequency of the BAW resonator.

6. The BAW resonator according to claim 1, characterized in that, The one or more structures comprise semiconductor materials having a sufficiently high dopant concentration to alter mass density and / or acoustic phase velocity.

7. The BAW resonator according to claim 1, characterized in that, The acoustic impedance modulation layer is arranged such that it extends into both layers of the reflective element.

8. The BAW resonator according to any one of claims 1-7, characterized in that, It also includes at least one mass load layer on the top electrode.

9. The BAW resonator according to claim 8, characterized in that, The mass load layer is embedded or partially embedded in the top electrode.

10. An integrated circuit package, characterized in that, It includes at least a first BAW resonator and a second BAW resonator, the first BAW resonator and the second BAW resonator being the BAW resonator according to any one of claims 1-9, the first BAW resonator and the second BAW resonator having different acoustic impedance modulation layers.

11. The integrated circuit package according to claim 10, characterized in that, It includes a plurality of BAW resonators according to any one of claims 1 to 9, wherein the plurality of BAW resonators are configured in a trapezoidal structure or a lattice structure.

12. A method for manufacturing a BAW resonator according to any one of claims 1 to 9, characterized in that, The step includes depositing a reflective element on a substrate, the reflective element comprising at least a first layer and a second layer made of a first material and a second material having a first acoustic impedance and a second acoustic impedance, respectively, placing one or more structures of a third material having a third acoustic impedance different from the first acoustic impedance and the second acoustic impedance, the structures forming an acoustic impedance modulation layer within the reflective element; The structure is asymmetrically distributed to form the acoustic impedance modulation layer.

13. The method according to claim 12, characterized in that, The step of placing the one or more structures includes depositing a third layer of the third material on a first or second layer and etching the third layer to form the structure. The method further includes covering the third layer with a cover layer of the first or second material and planarizing the cover layer.

14. The method according to claim 12, characterized in that, The steps of placing the one or more structures include etching a first or second layer to create space for the structure, depositing a third layer of the third material, and planarizing the third layer.

15. The method according to any one of claims 12 to 14, characterized in that, The acoustic impedance modulation layer is defined and formed using a photolithographic mask for the entire substrate.

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