Etch stop and protective layer for capacitor processing in electroacoustic devices

Abstract

Electroacoustic devices having capacitive elements and methods of manufacturing such electroacoustic devices. An exemplary method includes forming an acoustic device over a first region of a substrate and forming a capacitive element over a second region of the substrate adjacent to the acoustic device. Forming the capacitive element includes forming a protective layer over the substrate, a first portion of the protective layer over the second region of the substrate and a second portion of the protective layer over the first region of the substrate, forming a dielectric region over the protective layer, and forming an electrode over the dielectric region. The dielectric region can include a different material than the protective layer.

Description

[Technical Field]

[0001]

[0001] Some aspects of the present disclosure relate generally to electro-acoustic devices, and more particularly to electro-acoustic devices implemented with capacitive elements. [Background technology]

[0002] Electronic devices include traditional computing devices such as desktop computers, notebook computers, tablet computers, smartphones, wearable devices such as smartwatches, and Internet servers. These various electronic devices provide information, entertainment, social interaction, security, safety, productivity, transportation, manufacturing, and other services to human users. These various electronic devices rely on wireless communications for many of their functions. Wireless communication systems and devices are widely deployed to provide various types of communication content, such as voice, video, packet data, messaging, broadcasts, and the like. These systems may be able to support communication with multiple users by sharing available system resources (e.g., time, frequency, and power). Examples of such access systems include code division multiple access (CDMA) systems, time division multiple access (TDMA) systems, frequency division multiple access (FDMA) systems, and orthogonal frequency division multiple access (OFDMA) systems (e.g., Long Term Evolution (LTE) systems, or New Radio (NR) systems).

[0003]

[0003] Wireless communication transceivers used in these electronic devices typically include multiple radio frequency (RF) filters for filtering signals for specific frequencies or ranges of frequencies. Electroacoustic devices (e.g., "acoustic filters") are used in many applications to filter high-frequency (e.g., generally greater than 100 MHz) signals. Using a piezoelectric material as a vibration medium, acoustic resonators operate by converting an electric signal wave propagating along a conductor into an acoustic wave propagating through the piezoelectric material. Acoustic waves propagate at a velocity significantly smaller than the propagation velocity of electromagnetic waves. Generally, the magnitude of the wave propagation velocity is proportional to the wavelength of the wave. As a result, after the conversion of an electric signal to an acoustic signal, the wavelength of the acoustic signal is significantly smaller than the wavelength of the electric signal wave. The resulting smaller wavelength of the acoustic signal allows filtering to be performed using a smaller filter device. This allows acoustic resonators to be used in electronic devices with size constraints, such as the electronic devices listed above (e.g., including portable electronic devices such as cellular phones).

[0004]

[0004] Today, surface acoustic wave (SAW) or bulk acoustic wave (BAW) components may be used in wireless communication devices, such as to implement RF filters. In SAW technology, acoustic waves propagate laterally on the surface of a piezoelectric substrate, and piezoelectric motion is generated by metallic interdigital transducers (IDTs) on the surface. The wavelength of the acoustic wave can be defined by the pitch of the IDTs (e.g., the width of the metal fingers and gaps). In BAW technology, acoustic waves propagate vertically through a three-dimensional structure with an electric field applied through electrodes above and below the piezoelectric material. The wavelength, in this case, is defined by the thickness of the piezoelectric material.

[0005]

[0005] As the number of frequency bands used in wireless communications increases and the desired frequency bands of filters become wider, the performance of acoustic filters becomes increasingly important in order to reduce losses and increase the overall performance of electronic devices. Therefore, there is a need for acoustic filters with improved performance, especially filters with reduced intermodulation distortion. Summary of the Invention

[0006] The systems, methods, and devices of the present disclosure each have several aspects, none of which is solely responsible for its desirable attributes. Without limiting the scope of the present disclosure as expressed by the claims that follow, some features will now be briefly discussed. After considering this discussion, and particularly after reading the section entitled "Detailed Description," one will understand how the features of the present disclosure provide advantages, including the implementation of capacitive elements in conjunction with acoustic devices in electro-acoustic devices.

[0007] Certain aspects of the present disclosure provide a method for fabricating an electro-acoustic device. The method generally includes forming an acoustic device over a first region of a substrate and forming a capacitive element over a second region of the substrate and adjacent to the acoustic device. Forming the capacitive element includes forming a protective layer over the substrate, a first portion of the protective layer over the second region of the substrate and a second portion of the protective layer over the first region of the substrate; forming a dielectric region over the protective layer, the dielectric region comprising a different material from the protective layer; and forming an electrode over the dielectric region.

[0008] Some aspects of the present disclosure provide an apparatus for signal processing. The apparatus generally includes an acoustic device disposed above a first region of a substrate and a capacitive element disposed adjacent to the acoustic device above a second region of the substrate. The capacitive element generally includes a first electrode, a protective layer above the substrate, where a first portion of the protective layer is disposed above the second region of the substrate, a dielectric region disposed above the protective layer and the first electrode, the dielectric region including a different material from the protective layer, and a second electrode disposed above the dielectric region.

[0009] To the accomplishment of the foregoing and related ends, the one or more aspects comprise the features hereinafter fully described and particularly pointed out in the claims. The following description and the annexed drawings set forth in detail certain illustrative features of the one or more aspects. These features are indicative, however, of but a few of the various ways in which the principles of the various aspects may be employed.

[0010]

[0010] So that the above-described features of the present disclosure can be understood in detail, a more particular description may be had by reference to embodiments briefly summarized above, some of which are illustrated in the accompanying drawings. It should be noted, however, that the accompanying drawings illustrate only certain exemplary embodiments of this disclosure and therefore should not be considered as limiting its scope, as other equally effective embodiments may also be recognized for purposes of illustration. [Brief explanation of the drawings]

[0011] [Figure 1A] FIG. 1A is a diagram of a perspective view of an exemplary electro-acoustic device according to certain aspects of the present disclosure. [Figure 1B]

[0012] FIG. 1B is a diagram of a side view of the example electro-acoustic device of FIG. 1A, according to an embodiment of the present disclosure. [Figure 2A]

[0013] FIG. 2A is a top view of an exemplary electrode structure of an electro-acoustic device according to an embodiment of the present disclosure. [Figure 2B]

[0014] FIG. 2B is a top view of another exemplary electrode structure of an electro-acoustic device according to an embodiment of the present disclosure. [Figure 3]

[0015] FIG. 3 is a diagram of a perspective view of an exemplary electro-acoustic device according to an embodiment of the present disclosure. [Figure 4]

[0016] FIG. 4 is a diagram of a side view of an exemplary electro-acoustic device according to an embodiment of the present disclosure. [Figure 5A]

[0017] FIG. 5A illustrates an exemplary electro-acoustic device having a temperature-compensating layer according to an embodiment of the present disclosure. [Figure 5B]

[0018] FIG. 5B illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 5A, according to certain embodiments of the present disclosure. [Figure 5C] FIG. 5C illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 5A, according to certain embodiments of the present disclosure. [Figure 5D] FIG. 5D illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 5A, according to certain embodiments of the present disclosure. [Figure 5E] FIG. 5E illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 5A, according to certain embodiments of the present disclosure. [Figure 5F] FIG. 5F illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 5A, according to certain embodiments of the present disclosure. [Figure 5G] FIG. 5G illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 5A, according to certain embodiments of the present disclosure. [Figure 5H]FIG. 5H illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 5A, according to certain embodiments of the present disclosure. [Figure 5I] FIG. 5I illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 5A, according to certain embodiments of the present disclosure. [Figure 5J] FIG. 5J illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 5A, according to certain embodiments of the present disclosure. [Figure 6A]

[0019] FIG. 6A illustrates an exemplary electro-acoustic device having a surface acoustic wave (SAW) element, according to certain aspects of the present disclosure. [Figure 6B]

[0020] FIG. 6B illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 6A, according to certain embodiments of the present disclosure. [Figure 6C] FIG. 6C illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 6A, according to certain embodiments of the present disclosure. [Figure 6D] FIG. 6D illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 6A, according to certain embodiments of the present disclosure. [Figure 6E] FIG. 6E illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 6A, according to certain embodiments of the present disclosure. [Figure 6F] FIG. 6F illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 6A, according to certain embodiments of the present disclosure. [Figure 6G] FIG. 6G illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 6A, according to certain embodiments of the present disclosure. [Figure 6H] FIG. 6H illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 6A, according to certain embodiments of the present disclosure. [Figure 6I]FIG. 6I illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 6A, according to certain embodiments of the present disclosure. [Figure 6J] FIG. 6J illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 6A, according to certain embodiments of the present disclosure. [Figure 6K] FIG. 6K illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 6A, according to certain embodiments of the present disclosure. [Figure 6L] FIG. 6L illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 6A, according to certain embodiments of the present disclosure. [Figure 7A]

[0021] FIG. 7A illustrates an exemplary electro-acoustic device including a metal-insulator-metal capacitor (MIMCAP) according to an embodiment of the present disclosure. [Figure 7B]

[0022] FIG. 7B illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 7A, according to certain aspects of the present disclosure. [Figure 7C] FIG. 7C illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 7A, according to certain embodiments of the present disclosure. [Figure 7D-7E] 7D-7E illustrate a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 7A, according to certain embodiments of the present disclosure. [Figure 7F] FIG. 7F illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 7A, according to certain embodiments of the present disclosure. [Figure 7G] FIG. 7G illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 7A, according to certain embodiments of the present disclosure. [Figure 7H] FIG. 7H illustrates a manufacturing process for an exemplary electro-acoustic device, such as the electro-acoustic device of FIG. 7A, according to certain embodiments of the present disclosure. [Figure 8]

[0023] FIG. 8 is a flow diagram illustrating exemplary operations for forming an electro-acoustic device according to certain embodiments of the present disclosure. [Figure 9]

[0024] FIG. 9 is a functional block diagram of at least a portion of an exemplary simplified wireless transceiver circuit in which an electroacoustic filter circuit may be used, according to some aspects of the present disclosure. [Figure 10]

[0025] FIG. 10 is a diagram of an environment including an electronic device having a wireless transceiver, according to an embodiment of the present disclosure. DETAILED DESCRIPTION OF THE INVENTION

[0012]

[0026] To facilitate understanding, wherever possible, like reference numerals have been used to designate like elements common to the figures. It is contemplated that elements disclosed in one embodiment may be beneficially utilized in other embodiments without specific recitation.

[0013] Detailed Description

[0027] Some aspects of the present disclosure generally relate to techniques for fabricating an electro-acoustic device together with a capacitive element on a substrate using a passivation layer. The electro-acoustic device may be formed adjacent to the capacitive element. The electro-acoustic device may be implemented as a surface acoustic wave (SAW) device or a bulk acoustic wave (BAW) device.

[0014]

[0028] In some aspects, a protective layer may be deposited after forming the electrodes of the capacitive element and before forming the dielectric region of the capacitive element. The protective layer can act as an etch stop layer on the substrate, electro-acoustic device, or other underlying structure associated with the electro-acoustic device during the etching process of the dielectric region. At least a portion of the protective layer may be removed (e.g., using a wet chemical etching process) after etching of the dielectric region is completed. The wet chemical etching may have a negligible effect on the integrity of the electro-acoustic device or other underlying structure due to the implementation of the protective layer.

[0015]

[0029] In some implementations, the acoustic layer may be deposited after the dielectric region etching process is complete, in which case the protective layer can prevent (or at least reduce the likelihood of) damage to the substrate (e.g., since, without the protective layer, the substrate could be damaged by the formation of a capacitive layer, which could affect acoustic performance).

[0016]

[0030] The detailed description set forth below in connection with the accompanying drawings is intended as a description of example implementations and is not intended to represent the only implementations in which the present disclosure may be practiced. The term "exemplary" as used throughout this specification means "serving as an example, instance, or illustration," and should not necessarily be construed as preferred or advantageous over other example implementations. The detailed description includes specific details for the purpose of providing a thorough understanding of example implementations. In some instances, some devices are shown in block diagram form. Drawing elements common between the following figures may be identified using the same reference numerals.

[0017] Exemplary Electroacoustic Devices

[0031] 1A is a diagram of a perspective view of an exemplary electroacoustic device 100. Electroacoustic device 100 may be configured as, or may be part of, a surface acoustic wave (SAW) resonator. In certain descriptions herein, electroacoustic device 100 may be referred to as a SAW resonator. However, there may be other electroacoustic device types that may be constructed based on the principles described herein.

[0018]

[0032] The electroacoustic device 100 includes an electrode structure 104, sometimes referred to as an interdigital transducer (IDT), on a surface of a piezoelectric material 102. The electrode structure 104 generally includes first and second interdigitated electrode structures (conductive and typically metallic) extending from two bus bars and having interlocking (e.g., interdigitated) electrode fingers disposed between the two bus bars. An electrical signal excited in the electrode structure 104 (e.g., by applying an AC voltage) is converted into an acoustic wave 106 that propagates in a specific direction through the piezoelectric material 102. The acoustic wave 106 is converted back to an electrical signal and provided as an output. In many applications, the piezoelectric material 102 has a specific crystal orientation such that, when the electrode structure 104 is positioned relative to the crystal orientation of the piezoelectric material 102, the acoustic wave propagates primarily in a direction perpendicular to the direction of the fingers (e.g., parallel to the bus bars).

[0019]

[0033] Figure 1B is a diagram of a side view of the electro-acoustic device 100 of Figure 1A along the cross section 108 shown in Figure 1A. The electro-acoustic device 100 is illustrated with a simplified layer stack including a piezoelectric material 102 having an electrode structure 104 disposed thereon.

[0020]

[0034] The electrode structure 104 is electrically conductive and is typically formed from a metallic material. Alternatively, the electrode structure 104 may be formed from an electrically conductive but non-metallic material (e.g., graphene).

[0021]

[0035] Piezoelectric material 102 may be formed from a variety of materials, such as quartz, lithium tantalate (LiTaO), lithium niobate (LiNbO), doped variations thereof, other piezoelectric materials, or other crystals. It should be understood that more complex layer stacks including layers of various materials may be possible within the stack. For example, a temperature compensating layer 110, indicated by dashed lines, may optionally be disposed over electrode structure 104. Piezoelectric material 102 may be stretched with multiple interconnected electrode structures disposed thereon to form a multi-resonator filter or to provide multiple filters.

[0022]

[0036] Although not shown, when provided as an integrated circuit component, a cap layer may be provided over the electrode structure 104. The cap layer is applied such that a cavity is formed between the electrode structure 104 and the underside of the cap layer. Electrical vias or bumps may also be included to allow the component to be electrically connected (e.g., via flip-chip or other techniques) to connections on a substrate.

[0023]

[0037] 2A is a top view of an exemplary electrode structure 204a of an electro-acoustic device. The electrode structure 204a has an IDT 205 including a first bus bar 222 (e.g., a first conductive segment or rail) electrically connected to a first terminal 220 and a second bus bar 224 (e.g., a second conductive segment or rail) spaced apart from the first bus bar 222 and connected to a second terminal 230. A plurality of conductive fingers 226 are interdigitally connected to either the first bus bar 222 or the second bus bar 224. The fingers 226 connected to the first bus bar 222 extend toward but do not connect to the second bus bar 224 such that a small gap exists between the ends of the fingers 226 and the second bus bar 224. Similarly, the fingers 226 connected to the second busbar 224 extend toward but do not connect to the first busbar 222 such that a small gap exists between the ends of the fingers 226 and the first busbar 222. Similarly, a small gap may also be formed between the fingers 226 and any structure (e.g., stub fingers) that extends from the first busbar 222 or the second busbar 224.

[0024]

[0038] Between the busbars are overlap regions, including a central region where a portion of one finger overlaps a portion of an adjacent finger, as illustrated by central region 225. This central region 225, including the overlap, may be referred to as an aperture, track, or active region, where an electric field is generated between the fingers 226 to propagate acoustic waves within this region of the piezoelectric material 102. The periodicity of the fingers 226 is referred to as the pitch of the IDT. The pitch may be indicated in various ways. For example, in some embodiments, the pitch may correspond to the magnitude of the distance between the fingers within central region 225. This distance may be defined, for example, as the distance between the respective center points of the fingers (measured generally between the right (or left) edge of one finger and the right (or left) edge of the adjacent finger when the fingers have a uniform width). In some embodiments, the average of the distances between adjacent fingers may be used for the pitch. The frequency at which the piezoelectric material vibrates is the primary resonant frequency of electrode structure 204a. This frequency is determined at least in part by the pitch of the IDT 205 and other characteristics of the electroacoustic device 100 .

[0025]

[0039] The IDT 205 is positioned between two reflectors 228, which in the configuration shown reflect acoustic waves back toward the IDT 205 to convert the acoustic waves into an electrical signal through the IDT 205 and to prevent losses (e.g., to confine the acoustic waves). Each reflector 228 has two bus bars and a lattice structure of conductive fingers, each of which connects to both bus bars. The pitch of the reflectors may be similar to or the same as the pitch of the IDT 205 to reflect acoustic waves within the resonant frequency range. However, many configurations are possible.

[0026]

[0040] When converted back to an electrical signal, the converted electrical signal may be provided as an output, such as to one of the first terminal 220 or the second terminal 230, with the other terminal acting as an input.

[0027]

[0041] Various electrode configurations are possible. FIG. 2A may generally illustrate a one-port configuration. Other configurations (e.g., two-port configurations) are also possible. For example, electrode structure 204a may have an input IDT 205 with each terminal 220 and 230 functioning as an input. In this case, an adjacent output IDT (not shown) may be provided adjacent to input IDT 205 and positioned between reflectors 228 to convert acoustic waves propagating within piezoelectric material 102 into electrical signals that are output to output terminals of the output IDT.

[0028]

[0042] 2B is a top view of another exemplary electrode structure 204b of an electroacoustic device. In this case, a dual-mode SAW (DMS) electrode structure 204b is illustrated, which is a structure capable of inducing multiple resonances. The electrode structure 204b includes multiple IDTs disposed between reflectors 228 and connected as shown. The electrode structure 204b is provided to illustrate various electrode structures to which the principles described herein may be applied, including the electrode structures 204a and 204b of FIGS. 2A and 2B.

[0029]

[0043] While a particular number of fingers 226 are illustrated, it should be understood that the actual number of fingers, as well as the length and width of the fingers 226 and busbars, may vary in an actual implementation. Such parameters depend on the particular application and desired filter characteristics. Furthermore, a SAW filter may include multiple interconnected electrode structures (e.g., multiple interconnected resonators or IDTs to form a desired filter transfer function), each including multiple IDTs to achieve a desired passband.

[0030]

[0044] Electroacoustic devices such as SAW resonators are being designed to cover more frequency ranges (e.g., 500 MHz to 6 GHz), have higher bandwidths (e.g., up to 20%), and have improved efficiency and performance. Generally, SAW resonators suffer from nonlinearities that result in intermodulation distortion (IMD). For example, slight conductivity through air or dielectric between IDT electrodes can cause arcing, which can worsen the device's nonlinearity, power handling, and compression. Cascading acoustic tracks can reduce some intermodulation distortion, but this technique occupies increased space for implementation and results in larger SAW devices.

[0031]

[0045] In particular, the dielectric constant (εr) of the piezoelectric substrate affects the intermodulation (nonlinear) characteristics of a SAW filter. The nonlinear Mason equivalent circuit model has been used to simulate the effect of the substrate's dielectric constant on the nonlinearity of a SAW filter. Furthermore, the dielectric constant of the material separating the electrodes that form the IDT on a SAW device also affects the nonlinear behavior of the device. By adjusting the dielectric constant of specific dielectric structures within a SAW device, the intermodulation distortion of the device can be reduced.

[0032]

[0046] FIG. 3 is a perspective diagram of another example of an electrode structure 300. The electroacoustic device 300 (e.g., may be configured as or be part of a SAW resonator) is similar to the electroacoustic device 100 of FIG. 1A but has a different layer stack. In particular, the electroacoustic device 300 includes a thin piezoelectric material 302 disposed on a substrate 310 (e.g., silicon). The electroacoustic device 300 may, in some cases, be referred to as a thin-film SAW resonator. Depending on the type of piezoelectric material 302 used (e.g., typically has a higher coupling coefficient relative to the electroacoustic device 100 of FIG. 1) and the controlled thickness of the piezoelectric material 302, the specific acoustic wave modes excited may be slightly different from those in the electroacoustic device 100 of FIG. 1A. Based on the design (e.g., layer thicknesses and material selection), the electroacoustic device 300 may have a higher quality factor (Q) compared to the electroacoustic device 100 of FIG. 1A. In general, substrate 310 can be substantially thicker than piezoelectric material 302 (e.g., potentially on the order of 50 to 100 times thicker, or more, as an example). Substrate 310 may include other layers (or other layers may be included between substrate 310 and piezoelectric material 302).

[0033]

[0047] FIG. 4 is a diagram of a side view of the electro-acoustic device 300 of FIG. 3 (along cross section 307) showing an exemplary layer stack. In the example shown in FIG. 4, the substrate 310 may include sublayers such as substrate sublayer 310-1 (e.g., of silicon) that may have a higher resistance (e.g., relative to other layers—high-resistivity layers). The substrate 310 may further include a trap-rich layer 310-2 (e.g., polysilicon). The substrate 310 may further include a compensation layer 310-3 (e.g., silicon dioxide (SiO2) or another dielectric material) that may provide temperature compensation and other properties. These sublayers can be considered part of the substrate 310 or separate layers in their own right. A relatively thin piezoelectric material 302 is provided on a substrate 310 at a particular thickness to provide a particular acoustic mode (e.g., compared to the electroacoustic device 100 of FIG. 1A, the thickness of the piezoelectric material 102 may not be a critical design parameter above a certain thickness, and may generally be thicker compared to the piezoelectric material 302 of the electroacoustic device 300 of FIGS. 3 and 4). An electrode structure 304 is positioned above the piezoelectric layer 302. Additionally, in some embodiments, there may be one or more layers (not shown) above the electrode structure 304 (e.g., a thin passivation layer, etc.).

[0034]

[0048] Depending on the type, thickness, and overall layer stack of the piezoelectric material, the coupling to the electrode structure 304 and the speed of sound within the piezoelectric material in different regions of the electrode structure 304 may differ between different types of electro-acoustic devices, such as between the electro-acoustic device 100 of FIG. 1A and the electro-acoustic device 300 of FIGS. 3 and 4.

[0035] Exemplary SAW Device with Capacitor

[0049] As described above, electro-acoustic devices may be implemented using a network of multiple interconnected acoustic elements and other passive elements, such as capacitive elements. Electro-acoustic devices may use on-die capacitive elements to meet specific specifications for filter performance. For example, capacitive elements may be used in electro-acoustic devices for bandwidth adjustment (e.g., bandwidth widening), frequency response modeling or tailoring, or matching.

[0036]

[0050] In some implementations, the capacitive element may be realized using an acoustic element. For example, an acoustic element (e.g., a SAW resonator) may be configured such that the phase associated with the response of the acoustic element is rotated 90 degrees or such that the resonant frequency of the acoustic element is shifted from the operating frequency of the filter. In this manner, the acoustic element can operate as a capacitive element due to the electrical isolation between the interdigital transducer (IDT) fingers of the acoustic element.

[0037]

[0051] The use of acoustic elements to create capacitive elements may have some drawbacks. For example, a significant portion of the signal power applied to the capacitive element may result in excitation of acoustic waves on or within the piezoelectric substrate, resulting in power loss. In some embodiments, a plate capacitor may be used to overcome such drawbacks. However, the plate capacitor may include silicon dioxide (SiO2) as the dielectric region. SiO2 may have a low dielectric constant, resulting in significant area consumption by the plate capacitor. Also, SiO2 may be subject to sputtering, resulting in defects and particles in the dielectric region.

[0038]

[0052] A process flow for fabricating a plate capacitor may involve deposition of a dielectric region adjacent to an acoustic element (also referred to herein as an “acoustic device”) and subsequent etching of the area where the dielectric region may have been deposited. The etching process for removing the area of ​​the dielectric region may be detrimental to the integrity and functionality of the acoustic element or other underlying structures associated with the filter. Some aspects of the present disclosure are directed to techniques for protecting the acoustic element or other underlying structures associated with the filter to facilitate forming capacitive elements on the same die as the acoustic element.

[0039]

[0053] There are different types of etching processes that may be used during the manufacture of the filter. One type of etching process can alter the stoichiometry of the wafer surface used to implement the filter. Another type of etching process can alter the roughness of the wafer surface. Thus, depending on the type of etching process used, the area where the electro-acoustic element is located may be protected prior to etching, as described in more detail herein.

[0040]

[0054] In some implementations, photoresist may be used to protect the acoustic device wafer surface. However, because deposition of dielectric regions may typically be performed at high temperatures, photoresist tends to outgas during the dielectric region deposition process. Therefore, the photoresist may be annealed at temperatures higher than those used in the dielectric region deposition process. Due to cross-linking in the photoresist at these high temperatures, photoresist removal processes (e.g., using solvents such as dimethyl sulfoxide (DMSO) or N-methyl-2-pyrrolidone (NMP)) may not be effective. In some cases, plasma-based processes can be performed to remove the photoresist. However, plasma-based processes may be ineffective and inefficient.

[0041] Exemplary Etch Stop and Protective Layers for Capacitor Processing

[0055] Some aspects of the present disclosure are directed to techniques for protecting acoustic devices by depositing a protective layer prior to deposition of a dielectric region for a capacitive element formed within the acoustic device. The protective layer can function as an etch stop and safety layer that can prevent damage to the substrate, the acoustic device, and / or other underlying structures of the electroacoustic device during the selective removal (e.g., dry etching) process of the dielectric region. As one example, the protective layer may be an aluminum oxide (Al2O3) layer. In another example, the protective layer may be an aluminum nitride (AlN) layer.

[0042]

[0056] In some embodiments, a protective layer may be disposed either between the electrode of the capacitive element and the dielectric region, or between the substrate of the capacitive element and the bottom electrode. The protective layer may be removed in some areas where the dielectric region has been etched. A wet chemical etching process may be implemented to remove the protective layer. For example, a tetramethylammonium hydroxide (TMAH) or ammonia (NH3) solution may be used to remove the protective layer. The application of wet chemical etching to remove the protective layer may have negligible impact on the integrity of the metal layer stack or other underlying structure of the electroacoustic element, as described herein.

[0043]

[0057] FIG. 5A illustrates an electro-acoustic device 500 in accordance with certain embodiments of the present disclosure. It will be understood that the term "layer" includes a film and should not be construed as indicating vertical or horizontal thickness unless otherwise specified. As used herein, the term "substrate" may refer to the substrate of a diced wafer or the substrate of an undiced wafer.

[0044]

[0058] The electro-acoustic device 500 includes an acoustic device 502 (e.g., a SAW element) and a capacitive element 504. The capacitive element 504 and the acoustic device 502 are formed on different regions of a substrate 505. For example, the acoustic device 502 may be formed above a first region 506a of the substrate 505, and the capacitive element 504 may be formed above a second region 506b of the substrate 505. The capacitive element 504 is disposed adjacent to the acoustic device 502, as shown. A third region 506c of the substrate 505 may be between the first region 506a and the second region 506b.

[0045]

[0059] The capacitive element 504 includes a first electrode 508 (e.g., a bottom electrode of the capacitive element 504), a protective layer 510, a dielectric region 512, and a second electrode 514 (e.g., a top electrode of the capacitive element 504). The first electrode 508 may overlie a portion of the second region 506b of the substrate 505. The protective layer 510 may be formed above the first electrode 508 and a portion of the substrate 505 and adjacent to a side of the first electrode 508, as shown. The dielectric region 512 may be formed above the protective layer 510, and the second electrode 514 may be formed above at least a portion of the dielectric region 512, as shown.

[0046]

[0060] Acoustic device 502 includes an interdigital transducer (IDT) 516, a temperature-compensating layer 518, and a third electrode 520. IDT 516 can be formed over a portion of first region 506a of substrate 505. Temperature-compensating layer 518 may be formed over a portion of IDT 516 and a portion of first region 505a of substrate 506. Third electrode 520 is electrically coupled to a bus bar of IDT 516 and is formed over the bus bar. A portion of third electrode 520 may be formed on temperature-compensating layer 518.

[0047]

[0061] 5B through 5J illustrate techniques for fabricating electro-acoustic devices, such as electro-acoustic device 500 of FIG. 5A, according to some embodiments of the present disclosure.

[0048]

[0062] 5B, one or more components of acoustic device 502 can be formed. The one or more components of acoustic device 502 include an IDT 516 and a temperature compensating layer 518 formed on a first region 506a of substrate 505.

[0049]

[0063] One or more components of acoustic device 502 may be formed in multiple processes. In a first process, substrate 505 may be deposited. Substrate 505 may include a piezoelectric layer including a piezoelectric material. Piezoelectric materials may include lithium niobate (LiNbO), such as LiNbO single crystal, lithium tantalate (LiTaO), such as LiTaO single crystal, gallium arsenide (GaAs), etc. In some cases, the piezoelectric material may include gallium nitride (GaN), zinc sulfide (ZnS), cadmium sulfide (CdS), quartz, or any combination thereof.

[0050]

[0064] The IDT 516 may be formed over a portion of the first region 505a of the substrate 506. In one embodiment, the IDT 516 may contact a portion of the first region 506a of the substrate 505. In another embodiment, one or more other layers (e.g., adhesive layers) may be disposed between the IDT 516 and the portion of the first region 506a of the substrate 505. Although some layers or regions are generally shown as adjacent regions or layers, one or more layers (e.g., adhesive layers) may be implemented between those regions or layers in some implementations.

[0051]

[0065] In a second process, temperature-compensating layer 518 may then be formed over first region 506a of substrate 505 and portions of IDT 516. In one embodiment, temperature-compensating layer 518 may include silicon oxide.

[0052]

[0066] 5C illustrates the formation of an insulating layer 522 over substrate 505, IDT 516, and temperature compensating layer 518. For example, insulating layer 522 may be Al2O3. In some embodiments, insulating layer 522 may be about 0.7 nm thick (e.g., an Al2O3 layer about 0.7 nm thick). Insulating layer 522 may be used to improve the reproducibility of photoresist footing.

[0053]

[0067] 5D illustrates the formation of the first electrode 508. To form the first electrode 508, a portion of the insulating layer 522 can be removed to form an opening. The first electrode 508 can then be formed in the opening. The first electrode 508 can be formed adjacent to the acoustic device 502. The first electrode 508 can include, for example, Cr and / or Cu.

[0054]

[0068] 5E illustrates the formation of a protective layer 510 over the first electrode 508 and the insulating layer 522. The protective layer 510 can be formed using an atomic layer deposition (ALD) process or other suitable process. In some embodiments, the protective layer 510 can be composed of Al2O3, and in other embodiments, the protective layer 510 can be an AlN layer. The thickness of the protective layer 510 can be 15 nm in some implementations.

[0055]

[0069] FIG. 5F illustrates the formation of a dielectric region 512 above the protective layer 510. As shown, the dielectric region 512 may be formed above both the first region 506a, the second region 506b, and the third region 506c. The dielectric region 512 comprises a different material than the protective layer 510. For example, the dielectric region 512 comprises SiO2. In some implementations, the dielectric region 512 is formed from a silicon nitride (SiN) layer approximately 385 nm thick (e.g., approximately 385 nm thick). x N y ) layer).

[0056]

[0070] FIG. 5G illustrates an etching process performed to remove a portion of dielectric region 512. In one embodiment, a dry etch resist material 524 may be deposited over a portion of dielectric region 512. As illustrated in FIG. 5H, a dry etch process or other suitable process can be used to remove the portion of dielectric region 512 that is outside the shadow of dry etch resist material 524. During the etching of dielectric region 512, protective layer 510 effectively acts as an etch stop layer by protecting and preventing dry etching of material below protective layer 510. As shown in FIG. 5I, dry etch resist material 524 can be removed after etching of dielectric region 512.

[0057]

[0071] Once the dry etching of the dielectric regions 512 is complete, a wet chemical etching process or another suitable process may be used to remove the portions of the protective layer 510 that are not covered by the dielectric regions 512, as shown in Figure 5J. The wet chemical etching process may use a TMAH or NH3 solution to remove the portions of the protective layer 510.

[0058]

[0072] 5A, a second electrode 514 can be formed over the dielectric region 512, and a third electrode 520 can be formed over the bus bars of the IDT 516. The second electrode 514 and the third electrode 520 can include, for example, titanium (Ti), Cu, and / or Al layers having a thickness of about 2.5 μm.

[0059]

[0073] FIG. 6A illustrates an electro-acoustic device 600 in accordance with certain aspects of the present disclosure. The electro-acoustic device 600 includes an acoustic device 602 (e.g., a SAW element) and a capacitive element 604. In some embodiments, the capacitive element 604 and the acoustic device 602 may be formed on different regions of a substrate 605. As shown, the acoustic device 602 may be formed above a first region 606a of the substrate 605, and the capacitive element 604 may be formed above a second region 605b of the substrate 605. As shown, the capacitive element 604 may be disposed adjacent to the acoustic device 602. A third region 606c of the substrate 605 may be between the first region 606a and the second region 606b.

[0060]

[0074] As shown, the capacitive element 604 includes a first electrode 608 (e.g., a bottom electrode of the capacitive element 604), a protective layer 610, a dielectric region 612, an insulating layer 614, and a second electrode 616 (e.g., a top electrode of the capacitive element 604). The first electrode 608 can be located above the second region 606b of the substrate 605. Additionally, the protective layer 610 may be above the first electrode 608 and a portion of the second region 605b of the substrate 605. The dielectric region 612 may be above the protective layer 610. The insulating layer 614 may be formed above the dielectric region 612, a portion of the second region 606b of the substrate 605, a third region 605c of the substrate 605, and the first region 605a of the substrate 605. In some embodiments, as shown, a portion of the insulating layer 614 may be removed to form an opening in which the second electrode 616 may be formed.

[0061]

[0075] In some embodiments, the acoustic device 602 may include an IDT 618 and a third electrode 620. As described in more detail herein, one or more openings may be formed in the insulating layer 614 to form an opening in which the IDT 618 may be formed. The third electrode 620 may be electrically coupled to and formed above a bus bar of the IDT 618. A portion of the third electrode 620 may be formed above a portion of the first region 606a of the substrate 605, as shown.

[0062]

[0076] 6B through 6L illustrate techniques for fabricating electro-acoustic devices, such as electro-acoustic device 600 of FIG. 6A, according to some embodiments of the present disclosure.

[0063]

[0077] As shown in FIG. 6B, a substrate 605 may be formed or provided. The substrate 605 may include a piezoelectric layer including a piezoelectric material. In some implementations, the piezoelectric material may include LiNbO, such as a LiNbO single crystal, or LiTaO, such as a LiTaO single crystal, GaAs, or the like. In some cases, the piezoelectric material may include GaN, ZnS, CdS, quartz, or any combination thereof.

[0064]

[0078] 6C illustrates the formation of an insulating layer 622 over the substrate 605. The insulating layer 622 may be, for example, Al2O3. The insulating layer 622 may be about 0.7 nm thick (e.g., an Al2O3 layer that is about 0.7 nm thick).

[0065]

[0079] 6D illustrates the formation of the first electrode 608. To form the first electrode 608, a portion of the insulating layer 622 can be removed to form an opening. The first electrode 608 can be formed in the opening. The first electrode 608 can include, for example, Cr—Cu—Cr.

[0066]

[0080] 6E illustrates the formation of a protective layer 610 over the first electrode 608 and the insulating layer 622. The protective layer 610 can be formed using an ALD process or other suitable process. In some embodiments, the protective layer 610 may include Al2O3. In some embodiments, the protective layer 610 may include an AlN layer. The thickness of the protective layer 610 may be 15 nm in some implementations.

[0067]

[0081] 6F illustrates the formation of a dielectric region 612. The dielectric region 612 may be formed above the protective layer 610. The dielectric region 612 may comprise a different material than the protective layer 610. For example, the dielectric region 612 may comprise SiO2 or Si x N y In some implementations, the dielectric region 512 may include a thickness of about 385 nm (e.g., a Si x N y layer).

[0068]

[0082] FIG. 6G illustrates an etching process performed to remove a portion of dielectric region 612. For example, dry etch resist material 624 may be deposited over a portion of dielectric region 612 (e.g., over second region 606b) as shown. As illustrated in FIG. 6H, a dry etch process or other suitable process can be used to remove the portion of dielectric region 612 outside the shadow of dry etch resist material 624. As illustrated in FIG. 61, dry etch resist material 624 can be removed after etching of dielectric region 612. During the etching of dielectric region 612, protective layer 610 effectively acts as an etch stop layer by protecting and preventing dry etching of material below protective layer 610.

[0069]

[0083] Once the dry etching of the dielectric regions 612 is complete, a wet chemical etching process may be used to remove the portions of the protective layer 610 that are not covered by the dielectric regions 612, as shown in Figure 6J. The wet chemical etching process may use a TMAH or NH3 solution to remove the portions of the protective layer 610.

[0070]

[0084] 6K illustrates the formation of an insulating layer 614 over the dielectric region 612 and the substrate 605. For example, the insulating layer 614 may be formed over the dielectric region 612, the first region 606a, and the third region 606c of the substrate 605. The insulating layer 614 may be composed of, for example, Al2O3. The thickness of the insulating layer 614 may be 0.7 nm in some implementations.

[0071]

[0085] 6L illustrates the formation of the IDT 618. To form the IDT 618, one or more portions of the insulating layer 614 can be etched to form openings in the insulating layer 614. The IDT 618 is then formed within these openings in the insulating layer 614. The IDT 618 can include, for example, Ti—Cu—Al.

[0072]

[0086] 6A, a second electrode 616 and a third electrode 620 may be formed. As described herein, to form the second electrode 616, a portion of the insulating layer 614 is etched to form an opening in the insulating layer 614. The second electrode 616 is then formed in the opening. In some embodiments, the second electrode 616 may include a Ti, Cu, and / or Al layer having a thickness of about 2.5 μm. The third electrode 620 may be formed above the bus bar of the IDT 618.

[0073] Exemplary Etch-Stop Protective Layer for Bulk Acoustic Wave (BAW) On-Die Capacitive Device Applications

[0087] An electro-acoustic device may be implemented using a network of multiple interconnected bulk acoustic wave (BAW) resonators and other passive elements, such as capacitive and / or inductive elements. In some implementations, the capacitive elements may be realized as plate capacitors. The top electrode of the BAW resonator may function as the bottom electrode of the capacitive element. The bottom electrode may be covered by a dielectric region. An electrical pad (ePAD), as described in more detail herein, can serve as the top electrode of the capacitive element. Other regions of the electro-acoustic device may also be covered by the same dielectric region, which may be used for local frequency correction (e.g., acoustic trimming) and / or passivation.

[0074]

[0088] Some process flows may limit the use of dielectric materials to those suited to the specific acoustic properties of the BAW resonator. Furthermore, since the same dielectric region can be used for both the capacitive and acoustic elements, compromises can be made regarding the thickness of the dielectric region. For example, the thickness of the dielectric region may be selected to provide sufficient breakdown characteristics for the capacitive element while also meeting the target characteristics of the acoustic device.

[0075]

[0089] The flexibility of using different dielectric layers (e.g., for the capacitive element and the acoustic element), each tailored for a particular purpose, allows for improved filter performance. When different dielectric regions are used, certain portions of each dielectric region may be removed. The etching process for removing portions of the dielectric region may be detrimental to the integrity and functionality of the acoustic element or other underlying structure associated with the filter. Some aspects of the present disclosure are directed to techniques for protecting the acoustic element or other underlying structure associated with an electro-acoustic device to facilitate the formation of the capacitive element.

[0076]

[0090] FIG. 7A illustrates an electro-acoustic device 700 in accordance with certain aspects of the present disclosure. The electro-acoustic device 700 may include an array of acoustic devices. For example, the electro-acoustic device 700 may include a first acoustic device 702 and a second acoustic device 790. The electro-acoustic device 700 includes a first acoustic device 702 (e.g., a BAW element) and a capacitive element 704, where the capacitive element 704 is formed adjacent to and above the second acoustic device 790, as described in more detail herein. The capacitive element 704 and the first acoustic device 702 may be formed above different regions of a piezoelectric layer 705. The first acoustic device 702 may be formed above a first region 706a of the piezoelectric layer 705, and the capacitive element 704 may be formed above a second region 706b of the piezoelectric layer 705. The capacitive element 704 may be disposed adjacent to the first acoustic device 702, as shown. A third region 706c of the piezoelectric layer 705 may be located between the first region 706a and the second region 706b.

[0077]

[0091] The first acoustic device 702 includes one or more lateral features 707 (e.g., constructed of silicon dioxide (SiO2)) and an electrode 709. As used herein, lateral features generally refer to localized features at the edges of the resonator (e.g., mass loading to reduce lateral energy leakage from the resonator). The capacitive element 704 may be reinforced / formed by one or more layers that may be used to form the one or more lateral features 707 of the first acoustic device 702, thereby enhancing the electrode thickness and / or dielectric thickness.

[0078]

[0092] As described herein, the electro-acoustic device 700 includes a second acoustic device 790. The second acoustic device 790 may include a number of lateral features 708 (e.g., constructed from SiO2) and an electrode 710. The electrode 710 of the second acoustic device 790 may be configured as an electrode (e.g., a bottom electrode) of the capacitive element 704.

[0079]

[0093] As shown, the capacitive element 704 includes an electrode 710, a dielectric region 714, and an electrode 716 (e.g., an ePAD). A first protective layer 712 may be disposed over the electrode 709, the piezoelectric layer 705, and the electrode 710. The dielectric region 714 may be formed over the first protective layer 712. The electrode 716 may be formed over a portion of the dielectric region 714. A portion of the electrode 716 may be adjacent to a side of the electrode 710, as shown. A second protective layer 718 may be formed over the electrode 716, a portion of the dielectric region 714, and a portion of the first protective layer 712. The second protective layer 718 may provide corrosion protection for the electrode 716.

[0080]

[0094] 7B through 7H illustrate techniques for fabricating electro-acoustic devices, such as electro-acoustic device 700 of FIG. 7A, according to some embodiments of the present disclosure.

[0081]

[0095] 7B, acoustic devices 702, 790 are formed on a piezoelectric layer 705. Piezoelectric layer 705 can include AlN or an AlN-based layer enriched with dopants to enhance the piezoelectric effect, LiNbO (such as LiNbO single crystal), LiTaO (such as LiTaO single crystal), GaAs, etc. In some embodiments, the piezoelectric material can include GaN, ZnS, CdS, quartz, or any combination thereof.

[0082]

[0096] A first acoustic device 702 includes a side feature 707 and an electrode 709. The electrode 709 of the first acoustic device 702 may be formed over the side feature 707, as shown. A second acoustic device 790 includes a side feature 708 and an electrode 710. The electrode 710 of the second acoustic device may be formed over the side feature 708 of the second acoustic device, as shown.

[0083]

[0097] 7C illustrates the formation of a first protective layer 712 over the electrodes 709, 710 and piezoelectric layer 705 of the acoustic devices 702, 790. The first protective layer 712 may be formed using an atomic layer deposition (ALD) process or another suitable process. The first protective layer 712 may include, for example, Al2O3. In other embodiments, the first protective layer 712 may be an AlN layer.

[0084]

[0098] 7D illustrates the formation of a dielectric region 714. As shown, the dielectric region 714 may be formed above the first protective layer 712. The dielectric region 714 may comprise a different material than the first protective layer 712. For example, the dielectric region 714 may comprise SiO2 or Si x N y may include:

[0085]

[0099] 7E illustrates an etching process performed to remove a portion of dielectric region 714. For example, resist may be deposited over a portion of dielectric region 714 (e.g., over second region 706b). The portion of dielectric region 714 not covered by the resist material may be removed using an etching process. During the etching process, first protective layer 712 effectively acts as an etch stop layer by protecting and preventing dry etching of material below first protective layer 712.

[0086]

[0100] Once the dry etching of the dielectric regions 714 is complete, a selective etching process (e.g., a wet etching process) can be used to optionally remove portions of the first protective layer 712 that are not covered by the dielectric regions 714, as illustrated in FIG. 7F. In some embodiments, any wet chemical etching process can be used to remove portions of the first protective layer 712. The wet chemical etching process may, in some implementations, use a TMAH or NH3 solution. In some implementations, portions of the first protective layer 712 may not be removed, as shown in FIG. 7G.

[0087]

[0101] 7G illustrates the formation of electrode 716. Electrode 716 may be formed over a portion of dielectric region 714, as shown. A portion of electrode 716 may be formed adjacent to a side of electrode 710.

[0088]

[0102] 7H illustrates the formation of a second protective layer 718. As shown, the second protective layer 718 can be formed over the electrode 716, the dielectric region 714, and the first protective layer 712. In some embodiments, the second protective layer 718 can be a dielectric layer.

[0089]

[0103] The second protective layer 718 may be formed using a plasma enhanced chemical vapor deposition (PECVD) process. After forming the second protective layer 718, a portion of the second protective layer 718 may be trimmed to meet the target characteristics (e.g., frequency) of the first acoustic device 702, as shown in FIG.

[0090]

[0104] 8 is a flow diagram depicting example operations 800 for manufacturing an electro-acoustic device according to certain embodiments of the present disclosure. Operations 800 may be performed, for example, by a manufacturing facility.

[0091]

[0105] The operation 800 may begin in block 802 with a manufacturing facility forming an acoustic device (e.g., acoustic device 502, 602, or 702 in Figures 5A, 6A, and 7A) above a first region (e.g., first region 506a, 606a, or 706a in Figures 5A, 6A, and 7A) of a substrate (e.g., substrate 505 or 605 in Figures 5A, 6A, and 7A, or piezoelectric layer 705).

[0092]

[0106] In block 804, a capacitive element (e.g., capacitive element 504, 604, or 704 in Figures 5A, 6A, and 7A) is formed above a second region of the substrate (e.g., second region 506b, 606b, or 706b in Figures 5A, 6A, and 7A) adjacent to the acoustic device.

[0093]

[0107] In some embodiments, forming the capacitive element includes forming a protective layer over the substrate. A first portion of the protective layer (e.g., protective layer 510, 610, or 712 in FIGS. 5A, 6A, and 7A) may be formed over a second region of the substrate, and a second portion of the protective layer may be formed over a first region of the substrate. Forming the capacitive element may further include forming a dielectric region (e.g., dielectric region 512, 612, or 714 in FIGS. 5A, 6A, and 7A) over the protective layer. The dielectric region may, in some embodiments, comprise a different material from the protective layer. Forming the capacitive element may further include forming a first electrode (e.g., second electrode 514, 616, or 716 in FIGS. 5A, 6A, and 7A) over the dielectric region.

[0094]

[0108] In some embodiments, a first portion of the protective layer may be formed over a second electrode of the capacitive element (e.g., first electrode 508, 608, or 710 in FIG. 5A, 6A, or 7A). In some embodiments, a manufacturing facility may form an insulating layer (e.g., insulating layer 522 or 622 in FIG. 5A or 6A) and then remove a portion of the insulating layer. The second electrode may then be formed in the opening where the portion of the insulating layer was removed. In some embodiments, the protective layer may be formed over the second electrode. In certain embodiments, the insulating layer and the protective layer comprise the same material. In some embodiments, the thickness of the protective layer may be greater than the thickness of the insulating layer.

[0095]

[0109] In certain embodiments, forming the dielectric region includes forming a dielectric region over the first region and the second region of the substrate and etching a portion of the dielectric region above the first region of the substrate. In certain embodiments, a second portion of the protective layer is formed over the acoustic device. After etching the portion of the dielectric region above the first region of the substrate, the second portion of the protective layer is removed above the acoustic device. In certain embodiments, a third portion of the protective layer may be above a third region of the substrate (e.g., third region 506c, 606c, or 706c in Figures 5A, 6A, and 7A). The third region of the substrate may be between the first and second regions of the substrate. In certain embodiments, after etching the portion of the dielectric region above the third region of the substrate, the third portion of the protective layer may be removed.

[0096]

[0110] In certain embodiments, a second electrode may be formed over a second region of the substrate, and a first portion of the protective layer may be formed over the second electrode of the capacitive element.

[0097]

[0111] In some embodiments, the manufacturing facility can remove a second portion of the protective layer above the first region of the substrate and form an insulating layer (e.g., insulating layer 614 of FIG. 6A ) above the dielectric region and the first region of the substrate after removing the second portion of the protective layer. In certain embodiments, the insulating layer may be formed before forming the acoustic device. In some embodiments, forming the acoustic device includes etching one or more portions of the insulating layer to form one or more openings in the insulating layer and forming an IDT (e.g., IDT 516 or 618 of FIG. 5A or 6A ) in the one or more openings.

[0098]

[0112] In some embodiments, the semiconductor fabrication facility forms a third electrode (e.g., third electrode 520 or 620 of FIG. 5A or FIG. 6A ) above the bus bar of the IDT. In some embodiments, the fabrication facility can form another acoustic device (e.g., second acoustic device 790 of FIG. 7A ) having a top electrode above a second region (e.g., piezoelectric layer) of the substrate. A first portion of the protective layer may be formed above the second electrode of the capacitive element, which is the top electrode of the other acoustic device. In certain embodiments, the first portion of the protective layer may be formed above the other acoustic device. In certain embodiments, a portion of the first electrode may be formed adjacent to a side of the top electrode.

[0099]

[0113] In some embodiments, the manufacturing facility forms another protective layer (e.g., second protective layer 718 in FIG. 7A) over the acoustic device and the first electrode and trims a portion of the other protective layer over the acoustic device. The other protective layer can be formed using a PECVD process.

[0100]

[0114] In certain embodiments, the substrate can include a piezoelectric substrate formed from a piezoelectric material. The protective layer can include an Al2O3 layer or an AlN layer. In certain embodiments, the protective layer can be formed using an ALD process. In some embodiments, the protective layer can include an etch stop layer configured to prevent dry etching below the etch stop layer.

[0101]

[0115] 9 is a functional block diagram of at least a portion of an example of a simplified wireless transceiver circuit 900 in which the electro-acoustic device 500, 600, or 700 of FIG. 5A, 6A, or 7A may be used. The transceiver circuit 900 is configured to receive signals / information (shown as in-phase (I) and quadrature (Q) values) for transmission, which are provided to one or more baseband (BB) filters 912. The filtered output is provided to one or more mixers 914 for upconversion to a radio frequency (RF) signal. The output from the one or more mixers 914 may be provided to a driver amplifier (DA) 916, the output of which may be provided to a power amplifier (PA) 918 to generate an amplified signal for transmission. The amplified signal is output through one or more filters 920 (e.g., a duplexer if used as a frequency division duplex transceiver or other filter) to an antenna 922. The one or more filters 920 may include the electroacoustic devices 500, 600, or 700 of Figures 5A, 6A, or 7A.

[0102]

[0116] The antenna 922 may be used for both transmitting and receiving data wirelessly. The transceiver circuit 900 includes a receive path in which the received RF signal is provided to a low noise amplifier (LNA) 924 and further filters 920, and then through one or more filters 926 for downconversion from a receive frequency to a baseband frequency through one or more mixer circuits 928 before the signal is further processed (e.g., provided to an analog-to-digital converter (ADC) and then demodulated or otherwise processed in the digital domain). There may be separate filters for the receive circuitry (e.g., may have a separate antenna or may have separate receive filters), which may be implemented using the electro-acoustic devices 500, 600, or 700 of FIG. 5A, 6A, or 7A.

[0103]

[0117] 10 is a diagram of an environment 1000 including an electronic device 1002 in which aspects of the present disclosure may be implemented. In the environment 1000, the electronic device 1002 communicates with a base station 1004 over a wireless link 1006. As shown, the electronic device 1002 is depicted as a smartphone. However, the electronic device 1002 may be implemented as any suitable computing device or other electronic device, such as a cellular base station, a broadband router, an access point, a cellular or mobile phone, a gaming device, a navigation device, a media device, a laptop computer, a desktop computer, a tablet computer, a server computer, a network-attached storage (NAS) device, a smart appliance, a vehicle-based communication system, an Internet of Things (IoT) device, a sensor or security device, an asset tracker, and the like.

[0104]

[0118] The base station 1004 communicates with the electronic device 1002 via a wireless link 1006, which may be implemented as any suitable type of wireless link. While depicted as a base station tower of a cellular wireless network, the base station 1004 may represent or be implemented as another device, such as a satellite, a terrestrial broadcast tower, an access point, a peer-to-peer device, a mesh network node, a fiber optic line, another electronic device as generally described above, etc. Thus, the electronic device 1002 may communicate with the base station 1004 or another device via a wired connection, a wireless connection, or a combination thereof. The wireless link 1006 may include a downlink of data or control information communicated from the base station 1004 to the electronic device 1002 and an uplink of other data or control information communicated from the electronic device 1002 to the base station 1004. The wireless link 1006 may be implemented using any suitable communication protocol or standard, such as 3rd Generation Partnership Project Long-Term Evolution (3GPP® LTE), 3GPP NR 5G, IEEE 802.11, IEEE 802.16, Bluetooth®, and the like.

[0105]

[0119] The electronic device 1002 includes a processor 1080 and a memory 1082. The memory 1082 may be part of or form a part of a computer-readable storage medium. The processor 1080 may include any type of processor, such as an application processor or a multi-core processor, configured to execute processor-executable instructions (e.g., code) stored by the memory 1082. The memory 1082 may include any suitable type of data storage medium, such as volatile memory (e.g., random access memory (RAM)), non-volatile memory (e.g., flash memory), optical media, and magnetic media (e.g., disks or tapes). In the context of the present disclosure, the memory 1082 is implemented to store instructions 1084, data 1086, and other information for the electronic device 1002, and therefore, when configured as or as part of a computer-readable storage medium, the memory 1082 does not include a transitory, propagating signal or carrier wave.

[0106]

[0120] The electronic device 1002 may also include input / output ports 1090. The I / O ports 1090 allow for data exchange or interaction with other devices, networks, or users, or between components of the device.

[0107]

[0121] The electronic device 1002 may further include a signal processor (SP) 1092 (e.g., a digital signal processor (DSP) or the like), which may function similarly to a processor and may be capable of executing instructions and / or processing information in conjunction with the memory 1082.

[0108]

[0122] For communication purposes, the electronic device 1002 also includes a modem 1094, a wireless transceiver 1096, and an antenna (not shown). The wireless transceiver 1096 provides connectivity to respective networks and other electronic devices connected thereto using radio frequency (RF) wireless signals and may include the transceiver 900 of FIG. 9. The wireless transceiver 1096 may facilitate communication over any suitable type of wireless network, such as a wireless local area network (WLAN), a peer-to-peer (P2P) network, a mesh network, a cellular network, a wireless wide area network (WWAN), a navigation network (e.g., a North American Global Positioning System (GPS) or another Global Navigation Satellite System (GNSS)), and / or a wireless personal area network (WPAN).

[0109] Exemplary Embodiments

[0123] Examples are described in the following numbered aspects:

[0110]

[0124] In a first aspect, a method for manufacturing an electro-acoustic device comprises forming an acoustic device over a first region of a substrate; and forming a capacitive element over a second region of the substrate and adjacent to the acoustic device, wherein forming the capacitive element comprises forming a protective layer over the substrate, wherein a first portion of the protective layer is over the second region of the substrate and wherein the second portion of the protective layer is over the first region of the substrate; forming a dielectric region on the protective layer, wherein the dielectric region comprises a different material than the protective layer; and forming a first electrode over the dielectric region.

[0111]

[0125] In a second aspect in combination with the first aspect, the first portion of the protective layer is formed above the second electrode of the capacitive element.

[0112]

[0126] In a third aspect in combination with one or more of the first and second aspects, the method further comprises forming an insulating layer and removing a portion of the insulating layer, wherein the second electrode is formed in the opening where the portion of the insulating layer was removed, and wherein the protective layer is formed above the second electrode.

[0113]

[0127] In a fourth aspect in combination with the third aspect, the insulating layer and the protective layer comprise the same material, wherein the thickness of the protective layer is greater than the thickness of the insulating layer.

[0114]

[0128] In a fifth aspect in combination with one or more of the first to fourth aspects, forming the dielectric region comprises forming the dielectric region above the first region and the second region of the substrate, and etching a portion of the dielectric region above the first region of the substrate.

[0115]

[0129] In a sixth aspect in combination with the fifth aspect, a second portion of the protective layer is formed above the acoustic device, and the method further comprises removing the second portion of the protective layer above the acoustic device after etching the portion of the dielectric region above the first region of the substrate.

[0116]

[0130] In a seventh aspect in combination with one or more of the fifth to sixth aspects, the third portion of the protective layer is above a third region of the substrate, and the third region of the substrate is between the first and second regions of the substrate.

[0117]

[0131] In an eighth aspect in combination with the seventh aspect, the method further comprises removing the third portion of the protective layer after etching the portion of the dielectric region above the third region of the substrate.

[0118]

[0132] In a ninth aspect in combination with one or more of the first to eighth aspects, further comprising forming a second electrode of the capacitive element above a second region of the substrate, wherein the first portion of the protective layer is formed above the second electrode of the capacitive element.

[0119]

[0133] In a tenth aspect in combination with one or more of the first to ninth aspects, the method further comprises removing a second portion of the protective layer above the first region of the substrate, and forming an insulating layer above the first region of the substrate after removing the second portion of the protective layer.

[0120]

[0134] In an eleventh aspect in combination with the tenth aspect, the insulating layer is formed before forming the acoustic device.

[0121]

[0135] In a twelfth aspect in combination with the eleventh aspect, forming the acoustic device comprises etching one or more portions of another protective layer to form one or more openings in the protective layer, and forming an interdigital transducer (IDT) in the one or more openings.

[0122]

[0136] In a thirteenth aspect in combination with the twelfth aspect, the method further comprises forming a third electrode above the bus bar of the IDT.

[0123]

[0137] A fourteenth aspect in combination with one or more of the first to thirteenth aspects further comprises forming another acoustic device having an upper electrode above a second region of the substrate, wherein the first portion of the protective layer is formed above a second electrode of the capacitive element, and wherein the second electrode of the capacitive element is the upper electrode of the another acoustic device.

[0124]

[0138] In a fifteenth aspect in combination with the fourteenth aspect, the first portion of the protective layer is formed above the other acoustic device.

[0125]

[0139] In a sixteenth aspect in combination with one or more of the fourteenth to fifteenth aspects, a portion of the first electrode is formed adjacent to a side surface of the upper electrode.

[0126]

[0140] In a seventeenth aspect in combination with one or more of the fourteenth to sixteenth aspects, the method further comprises forming another protective layer above the acoustic device and the first electrode, and trimming a portion of the another protective layer above the acoustic device.

[0127]

[0141] In an eighteenth aspect in combination with the seventeenth aspect, the further protective layer is formed using a plasma enhanced chemical vapor deposition (PECVD) process.

[0128]

[0142] In a nineteenth aspect in combination with one or more of the first to eighteenth aspects, the substrate comprises a piezoelectric substrate.

[0129]

[0143] In a twentieth aspect, alone or in combination with one or more of the first to nineteenth aspects, the protective layer comprises an aluminum oxide (Al2O3) layer or an aluminum nitride (AlN) layer.

[0130]

[0144] In a 21st aspect in combination with one or more of the first to 20th aspects, the protective layer is formed using an atomic layer deposition (ALD) process.

[0131]

[0145] In a 22nd aspect in combination with one or more of the 1st to 21st aspects, the protective layer comprises an etch stop layer configured to prevent dry etching below the etch stop layer.

[0132]

[0146] In a 23rd aspect, an apparatus for signal processing comprises an acoustic device arranged above a first region of a substrate and a capacitive element arranged on a second region of the substrate and adjacent to the acoustic device, wherein the capacitive element comprises a first electrode, a protective layer on the substrate, wherein a first portion of the protective layer is arranged above the second region of the substrate, a dielectric region arranged above the protective layer and the first electrode and comprising a material different from the protective layer, and a second electrode arranged above the dielectric region.

[0133]

[0147] In a twenty-fourth aspect in combination with the twenty-third aspect, the first portion of the protective layer is disposed above the first electrode.

[0134]

[0148] In a twenty-fifth aspect in combination with one or more of the twenty-third to twenty-fourth aspects, the acoustic device comprises an interdigital transducer (IDT).

[0135]

[0149] In a twenty-sixth aspect in combination with the twenty-fifth aspect, the third electrode is disposed above a bus bar of the IDT.

[0136]

[0150] In a 27th aspect in combination with one or more of the 23rd to 26th aspects, the substrate comprises a piezoelectric substrate.

[0137]

[0151] In a 28th aspect in combination with one or more of the 23rd to 27th aspects, the protective layer comprises an aluminum oxide (Al2O3) layer.

[0138]

[0152] In a 29th aspect in combination with one or more of the 23rd to 27th aspects, the protective layer comprises an aluminum nitride (AlN) layer.

[0139]

[0153] In a thirty-third aspect in combination with one or more of the twenty-third to twenty-ninth aspects, the protective layer comprises an etch stop layer configured to prevent dry etching beneath the etch stop layer.

[0140] Additional Considerations

[0154] The various operations of the methods described above may be performed by any suitable means capable of performing the corresponding functions, which may include various hardware and / or software components and / or modules, including, but not limited to, circuits, application specific integrated circuits (ASICs), or processors.

[0141]

[0155] As an example, the elements, or any portion of the elements, or any combination of the elements, may be implemented as a "processing system" including one or more processors. Examples of processors include microprocessors, microcontrollers, graphics processing units (GPUs), central processing units (CPUs), application processors, digital signal processors (DSPs), reduced instruction set computing (RISC) processors, systems-on-chips (SoCs), baseband processors, field programmable gate arrays (FPGAs), programmable logic devices (PLDs), state machines, gate logic, discrete hardware circuits, and other suitable hardware configured to perform various functionality described throughout this disclosure. One or more processors in a processing system may execute software. Software should be construed broadly to mean instructions, instruction sets, code, code segments, program code, programs, subprograms, software components, applications, software applications, software packages, routines, subroutines, objects, executable files, threads of execution, procedures, functions, etc., whether referred to as software, firmware, middleware, microcode, hardware description language, or otherwise.

[0142]

[0156] Generally, where operations are illustrated in figures, those operations may have corresponding counterpart means-plus-function components that are similarly numbered.

[0143]

[0157] As used herein, the term "determining" includes a wide variety of actions. For example, "determining" may include calculating, computing, processing, deriving, investigating, looking up (e.g., looking up in a table, database, or another data structure), ascertaining, etc. "Determining" may also include receiving (e.g., receiving information), accessing (e.g., accessing data in a memory), etc. "Determining" may also include resolving, selecting, choosing, establishing, etc.

[0144]

[0158] Within this disclosure, the term "exemplary" is used to mean "serving as an example, instance, or illustration." Any implementation or aspect described herein as "exemplary" should not necessarily be construed as preferred or advantageous over other aspects of the disclosure. Likewise, the term "aspect" does not require that all aspects of the disclosure include the described feature, advantage, or mode of operation. The term "coupled" is used herein to refer to a direct or indirect coupling between two objects. For example, if object A physically contacts object B, and object B contacts object C, objects A and C may be considered coupled to each other—even though they are not in direct physical contact with each other. For example, a first object may be coupled to a second object even though the first object was never in direct physical contact with the second object. The terms "circuit" and "circuitry" are used broadly and are intended to include hardware implementations of both electrical devices and conductors that, when connected and configured, enable the performance of the functions described in this disclosure, without limitation as to the type of electrical circuit.

[0145]

[0159] The apparatus and methods described in the following detailed description are illustrated in the accompanying drawings by various blocks, modules, components, circuits, steps, processes, algorithms, etc. (collectively referred to as "elements"), which may be implemented using hardware, for example.

[0146]

[0160] One or more of the components, steps, features, and / or functions illustrated above may be rearranged and / or combined into a single component, step, feature, or function, or embodied in several components, steps, or functions. Additional elements, components, steps, and / or functions may also be added without departing from the novel features disclosed herein. The apparatus, devices, and / or components described above may be configured to perform one or more of the methods, features, or steps described herein.

[0147]

[0161] It should be understood that the specific order or hierarchy of steps in the disclosed methods is an illustration of a sample process. Based on design preferences, it is understood that the specific order or hierarchy of steps in the methods may be rearranged. The accompanying method claims present elements of the various steps in a sample order, and are not intended to be limited to the specific order or hierarchy presented, unless expressly stated herein.

[0148]

[0162] The foregoing description is provided to enable any person skilled in the art to implement the various aspects described herein. Various modifications to these aspects will be readily apparent to those skilled in the art, and the generic principles defined herein may be applied to other aspects. Accordingly, the claims are not intended to be limited to the aspects set forth herein, but rather should be accorded the full scope consistent with the language of the claims, wherein reference to a singular element is not intended to mean "one and only one" unless expressly so stated, but rather "one or more." Unless expressly stated otherwise, the term "any" means one or more. A phrase referring to "at least one" of a list of items refers to any combination of those items, including single members. By way of example, "at least one of a, b, or c" is intended to cover a, b, c, ab, ac, bc, and abc, as well as any combination of the same elements (e.g., aa, aaa, aab, aac, abb, acc, bb, bbb, bbc, cc, and ccc, or any other permutation of a, b, and c). All structural and functional equivalents to the elements of the various aspects described throughout this disclosure that are known or later become known to those of ordinary skill in the art are expressly incorporated herein by reference and are intended to be encompassed by the claims. Furthermore, nothing disclosed herein is intended to be dedicated to the public, whether or not expressly recited in the claims. No claim element shall be construed under the provisions of 35 U.S.C. § 112(f) unless the element is expressly recited using the phrase "means for," or, in the case of a method claim, unless the element is recited using the phrase "step for."

[0149]

[0163] It is to be understood that the scope of the present claims is not limited to the precise configuration and components described above. Various modifications, changes, and variations may be made in the arrangement, operation, and details of the methods and apparatus described above without departing from the scope of the claims. The inventions described in the claims of the present application as originally filed are set forth below. [C1] A method for manufacturing an electroacoustic device, comprising: forming an acoustic device over a first region of a substrate; forming a capacitive element above a second region of the substrate and adjacent to the acoustic device, wherein forming the capacitive element includes: forming a protective layer over the substrate, wherein a first portion of the protective layer is over the second region of the substrate and a second portion of the protective layer is over the first region of the substrate; forming a dielectric region above the protective layer, the dielectric region comprising a different material than the protective layer; forming a first electrode over the dielectric region. [C2] The method of C1, wherein the first portion of the protection layer is formed above a second electrode of the capacitive element. [C3] forming an insulating layer; removing a portion of the insulating layer, a second electrode is formed in an opening formed by removing a portion of the insulating layer, and the protective layer is formed above the second electrode; The method described in C1. [C4] The method of C3, wherein the insulating layer and the protective layer comprise the same material, and the thickness of the protective layer is greater than the thickness of the insulating layer. [C5] Forming the dielectric region forming the dielectric region above the first region and the second region of the substrate; Etching a portion of the dielectric region above the first region of the substrate; The method of claim C1, comprising: [C6] The second portion of the protective layer is formed above the acoustic device; The method of C5, wherein the method further comprises removing the second portion of the protective layer above the acoustic device after the etching of the portion of the dielectric region above the first region of the substrate. [C7] The method of C5, wherein the third portion of the protective layer is above a third region of the substrate, and the third region of the substrate is between the first region and the second region of the substrate. [C8] The method of C7, further comprising removing the third portion of the protective layer after etching the portion of the dielectric region above the third region of the substrate. [C9] further comprising forming a second electrode of the capacitive element above the second region of the substrate; The method of C1, wherein the first portion of the protection layer is formed over the second electrode of the capacitive element. [C10] removing the second portion of the protective layer above the first region of the substrate; forming an insulating layer over the first region of the substrate after removing the second portion of the protective layer; The method of C1, further comprising: [C11] The method of C10, wherein the insulating layer is formed before forming the acoustic device. [C12] Forming the acoustic device includes: etching one or more portions of the insulating layer to form one or more openings in the insulating layer; forming an interdigital transducer (IDT) within the one or more apertures; The method of claim 11, comprising: [C13] The method of C12, further comprising forming a third electrode above a bus bar of the IDT. [C14] further comprising forming another acoustic device having an upper electrode above the second region of the substrate; the first portion of the protection layer is formed above a second electrode of the capacitive element, the second electrode of the capacitive element being the top electrode of another acoustic device; The method described in C1. [C15] The method of C14, wherein the first portion of the protective layer is formed above the other acoustic device. [C16] The method according to C14, wherein a portion of the first electrode is formed adjacent to a side surface of the upper electrode. [C17] forming another protective layer over the acoustic device and the first electrode; trimming a portion of the other protective layer overlying the acoustic device; The method of C14, further comprising: [C18] The method of C17, wherein the other protective layer is formed using a plasma enhanced chemical vapor deposition (PECVD) process. [C19] The method of C1, wherein the substrate comprises a piezoelectric substrate. [C20] The protective layer is made of aluminum oxide (Al 2 O 3 ) layer or an aluminum nitride (AlN) layer. [C21] The method of C1, wherein the protective layer is formed using an atomic layer deposition (ALD) process. [C22] The method of C1, wherein the protective layer comprises an etch stop layer configured to prevent dry etching beneath the etch stop layer. [C23] An apparatus for signal processing, comprising: an acoustic device disposed above the first region of the substrate; a capacitive element disposed above the second region of the substrate and adjacent to the acoustic device, wherein the capacitive element comprises: a first electrode; a protective layer disposed over the substrate, wherein a first portion of the protective layer is disposed over the second region of the substrate; a dielectric region disposed above the protective layer and the first electrode, the dielectric region comprising a material different from that of the protective layer; a second electrode disposed above the dielectric region. [C24] The device of C23, wherein the first portion of the protective layer is disposed above the first electrode. [C25] The apparatus of C23, wherein the acoustic device comprises an interdigital transducer (IDT). [C26] The apparatus of C25, wherein a third electrode is disposed above a bus bar of the IDT. [C27] The apparatus of C23, wherein the substrate comprises a piezoelectric substrate. [C28] The protective layer is made of aluminum oxide (Al 2 O 3 ) layer. [C29] The apparatus of C23, wherein the protective layer comprises an aluminum nitride (AlN) layer. [C30] The apparatus of C23, wherein the protective layer comprises an etch stop layer, the etch stop layer configured to prevent dry etching beneath the etch stop layer.

Claims

1. 1. A method for manufacturing an electroacoustic device, comprising: forming an acoustic device over a first region of a substrate; forming a capacitive element over a second region of the substrate and adjacent to the acoustic device, wherein forming the capacitive element includes: forming a protective layer over the substrate, wherein a first portion of the protective layer is over the second region of the substrate and a second portion of the protective layer is over the first region of the substrate, the protective layer comprising an etch stop layer configured to prevent dry etching beneath the etch stop layer; forming a dielectric region above the protective layer, the dielectric region comprising a different material than the protective layer; forming a top electrode above the dielectric region.

2. The method of claim 1 , wherein the first portion of the protection layer is formed above a bottom electrode of the capacitive element.

3. forming an insulating layer; removing a portion of the insulating layer, the lower electrode is formed in an opening formed by removing a portion of the insulating layer, the protective layer is formed above the lower electrode, the insulating layer and the protective layer are made of the same material, and the thickness of the protective layer is greater than the thickness of the insulating layer; The method of claim 2.

4. forming the dielectric region forming the dielectric region above the first region and the second region of the substrate; Etching a portion of the dielectric region above the first region of the substrate; 2. The method of claim 1, wherein the method further comprises removing the second portion of the protective layer above the acoustic device after the etching of the portion of the dielectric region above the first region of the substrate.

5. forming a bottom electrode of the capacitive element above the second region of the substrate; the first portion of the protection layer is formed on the bottom electrode of the capacitive element. The method of claim 1.

6. forming another acoustic device having a top electrode above the second region of the substrate; the first portion of the protective layer is formed above a bottom electrode of the capacitive element, the bottom electrode of the capacitive element being the top electrode of another acoustic device; The method of claim 1.

7. The method of claim 6 , wherein the first portion of the protective layer is formed over the other acoustic device.

8. The method of claim 6 , wherein a portion of the top electrode is formed adjacent a side of the bottom electrode.

9. The method of claim 1 , wherein the substrate comprises a piezoelectric substrate.

10. The protective layer is made of aluminum oxide (Al ２ O ３ 10. The method of claim 1, wherein the protective layer comprises a silicon nitride (SiN) layer or an aluminum nitride (AlN) layer, the protective layer being formed using an atomic layer deposition (ALD) process.

11. 1. An apparatus for signal processing, comprising: an acoustic device disposed above a first region of the substrate; a capacitive element disposed above the second region of the substrate and adjacent to the acoustic device, wherein the capacitive element comprises: a protective layer disposed above the substrate, wherein a first portion of the protective layer is disposed above the second region of the substrate, the protective layer comprising an etch stop layer configured to prevent dry etching beneath the etch stop layer; a dielectric region disposed above the protective layer, the dielectric region comprising a material different from that of the protective layer; an upper electrode disposed above the dielectric region.

12. The device of claim 11 , wherein the first portion of the protective layer is disposed above a bottom electrode.

13. The apparatus of claim 11 , wherein the acoustic device comprises an interdigital transducer (IDT), and the third electrode is disposed above a bus bar of the IDT.

14. The apparatus of claim 11 , wherein the substrate comprises a piezoelectric substrate.

15. The protective layer is made of aluminum oxide (Al ２ O ３ 12. The device of claim 11, further comprising a silicon dioxide (SiO2) layer, or an aluminum nitride (AlN) layer.

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