Resonator and method of manufacturing the same
Patent Information
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- SPECTRON (SHENZHEN) TECH CO LTD
- Filing Date
- 2026-07-13
- Publication Date
- 2026-08-07
Smart Images
Figure CN122533548A_ABST
Abstract
Description
Technical Field
[0001] This application relates to the field of resonator technology, and in particular to a resonator and a method for manufacturing the resonator. Background Technology
[0002] A thick Lamb Acoustic Wave Resonator comprises a thick dielectric layer disposed above the top electrode. This dielectric layer enables the extended acoustic cavity formed by the metal-piezoelectric-metal stack and the upper dielectric layer to operate in harmonic modes.
[0003] Q value (quality factor) is an important indicator of a resonator's capability. In many applications, a sufficiently high Q value is required for the resonator. Summary of the Invention
[0004] Therefore, it is necessary to provide a high-Q resonator and its manufacturing method.
[0005] A resonator includes: an acoustic mirror; a bottom electrode located on the acoustic mirror; a piezoelectric layer located on the bottom electrode; a top electrode located on the piezoelectric layer; the upper surface of the bottom electrode includes an inner region where the orthographic projection of the top electrode onto the upper surface of the bottom electrode is located, and an outer region located outside the inner region; a dielectric layer covering the piezoelectric layer and the top electrode, the upper surface of the dielectric layer directly above the top electrode and the upper surface of the dielectric layer directly above the outer region are in the same plane, the distance between the upper surface of the top electrode and the upper surface of the dielectric layer directly above the top electrode is H, H is close to an integer multiple of the half wavelength of the acoustic wave corresponding to the acoustic mode of the resonator's resonant cavity thickness, the thickness of the dielectric layer directly above the outer region is H+T1, T1 is the thickness of the top electrode; the harmonic order of the acoustic mode is greater than 1.
[0006] The aforementioned resonator reduces transverse acoustic leakage by keeping the upper surface of the dielectric layer flat, thereby achieving a higher Q value and reducing the difference in cutoff frequencies between the internal and external regions of the resonator.
[0007] In one embodiment, λ is the acoustic wavelength corresponding to the acoustic mode of the resonant cavity thickness, and n is the harmonic order of the acoustic mode.
[0008] In one embodiment, the distance H' between the upper surface of the top electrode and the lower surface of the bottom electrode is approximately an integer multiple of the half wavelength of the acoustic wave.
[0009] In one embodiment, λ is the acoustic wavelength corresponding to the acoustic mode of the resonant cavity thickness, and n is the harmonic order of the acoustic mode.
[0010] In one embodiment, the resonator further includes a frame located on the top electrode and at the edge of the top electrode, the frame being covered by the dielectric layer, and the thickness of the dielectric layer directly above the frame being H-T2, where T2 is the thickness of the frame.
[0011] In one embodiment, the resonator further includes a passivation layer located on the dielectric layer.
[0012] In one embodiment, the acoustic reflector is a Bragg reflector.
[0013] In one embodiment, the resonator is a sandwich-structured transducer acoustic resonator.
[0014] In one embodiment, the resonator is a thickness Lamb wave resonator.
[0015] In one embodiment, the upper surface of the dielectric layer is planarized.
[0016] In one embodiment, the planarization process includes chemical mechanical polishing.
[0017] A method for manufacturing a resonator includes: obtaining a wafer having an acoustic mirror, a bottom electrode, a piezoelectric layer, and a top electrode stacked sequentially; the upper surface of the bottom electrode includes an inner region where the orthographic projection of the top electrode onto the upper surface of the bottom electrode is located, and an outer region located outside the inner region; forming a dielectric layer covering the piezoelectric layer and the top electrode; planarizing the dielectric layer; after the planarization is completed, the upper surface of the dielectric layer directly above the top electrode and the upper surface of the dielectric layer directly above the outer region are on the same plane, the distance between the upper surface of the top electrode and the upper surface of the dielectric layer directly above the top electrode is H, H is close to an integer multiple of the half wavelength of the acoustic wave corresponding to the acoustic mode of the resonant cavity thickness of the resonator, and the thickness of the dielectric layer directly above the outer region is H+T1, where T1 is the thickness of the top electrode.
[0018] The above-mentioned method for manufacturing resonators reduces transverse acoustic leakage by planarizing the upper surface of the dielectric layer, thereby achieving a higher Q value and reducing the difference between the cutoff frequencies of the internal and external regions of the resonator.
[0019] In one embodiment, prior to the step of forming a dielectric layer covering the piezoelectric layer and the top electrode, a step of forming a border located at the edge of the top electrode is further included; after the planarization process is completed, the thickness of the dielectric layer directly above the border is H-T2, where T2 is the thickness of the border.
[0020] In one embodiment, after the step of planarizing the dielectric layer, a step of forming a passivation layer on the dielectric layer is further included.
[0021] In one embodiment, the distance between the upper surface of the top electrode and the lower surface of the bottom electrode is approximately an integer multiple of the half-wavelength of the acoustic wave.
[0022] In one embodiment, the acoustic reflector is a Bragg reflector.
[0023] In one embodiment, the resonator is a sandwich-structured transducer acoustic resonator.
[0024] In one embodiment, the resonator is a thickness Lamb wave resonator.
[0025] In one embodiment, the planarization process includes chemical mechanical polishing. Attached Figure Description
[0026] To more clearly illustrate the technical solutions in the embodiments of this application or the conventional technology, the drawings used in the description of the embodiments or the conventional technology will be briefly introduced below. Obviously, the drawings described below are only some embodiments of this application. For those skilled in the art, other drawings can be obtained based on these drawings without creative effort.
[0027] Figure 1 This is a schematic cross-sectional view of an exemplary TE1LAW SMR formed by a metal-piezoelectric-metal stack.
[0028] Figure 2 This is a cross-sectional view of an exemplary ECTE2LAW SMR with a thick dielectric layer that has not been planarized.
[0029] Figure 3 This is a schematic diagram of the deteriorated morphology that may form at the step when a thick deposited medium layer is not planarized.
[0030] Figure 4 This is a schematic cross-sectional view of the resonator in one embodiment of this application.
[0031] Figure 5 This is a cross-sectional structural diagram of the resonator in another embodiment of this application.
[0032] Figure 6 This is a cross-sectional structural schematic diagram of the resonator in another embodiment of this application.
[0033] Figure 7a The simulation results show the acoustic dispersion curves of a comparative ECTE2LAW SMR without planarization of the dielectric layer.
[0034] Figure 7b The simulation results show the acoustic dispersion curve of an ECTE2LAW SMR according to an embodiment of this application.
[0035] Figure 8 These are the simulation results and the curves showing the Q value and conductance as a function of frequency in the embodiments of this application.
[0036] Figure 9 This is a flowchart of a method for manufacturing a resonator in one embodiment of this application.
[0037] Figure 10a This is a cross-sectional structural diagram of the device after step S213 is completed.
[0038] Figure 10b This is a cross-sectional structural diagram of the device after step S215 is completed.
[0039] Figure 10c This is a cross-sectional structural diagram of the device after step S217 is completed.
[0040] Figure 10d This is a cross-sectional structural diagram of the device after step S219 is completed.
[0041] Figure 10e This is a schematic diagram of the cross-sectional structure of the device after the frame is formed.
[0042] Figure 10f This is a cross-sectional structural diagram of the device after step S220 is completed.
[0043] Figure 10g This is a cross-sectional structural diagram of the device after step S220 is completed.
[0044] Figure 11 This is a flowchart of a sub-step of step S210 in one embodiment of this application. Detailed Implementation
[0045] To facilitate understanding of this application, a more complete description will be provided below with reference to the accompanying drawings, which illustrate embodiments of the present application. However, the present application can be implemented in many different forms and is not limited to the embodiments described herein. Rather, these embodiments are provided so that the disclosure of this application will be thorough and complete.
[0046] Unless otherwise defined, all technical and scientific terms used herein have the same meaning as commonly understood by one of ordinary skill in the art to which this application belongs. The terminology used herein in the specification of this application is for the purpose of describing particular embodiments only and is not intended to be limiting of this application.
[0047] It should be understood that when an element or layer is referred to as "on," "adjacent to," "connected to," or "coupled to" other elements or layers, it may be directly on, adjacent to, connected to, or coupled to other elements or layers, or there may be intervening elements or layers. Conversely, when an element is referred to as "directly on," "directly adjacent to," "directly connected to," or "directly coupled to" other elements or layers, there are no intervening elements or layers. It should be understood that although the terms first, second, third, etc., may be used to describe various elements, parts, regions, layers, doping types, and / or portions, these elements, parts, regions, layers, doping types, and / or portions should not be limited by these terms. These terms are only used to distinguish one element, part, region, layer, doping type, or portion from another element, part, region, layer, doping type, or portion. Therefore, without departing from the teachings of this invention, the first element, component, region, layer, doping type, or portion discussed below may be represented as a second element, component, region, layer, or portion; for example, the first doping type may be referred to as the second doping type, and similarly, the second doping type may be referred to as the first doping type; the first doping type and the second doping type are different doping types, for example, the first doping type may be P-type and the second doping type may be N-type, or the first doping type may be N-type and the second doping type may be P-type.
[0048] Spatial relation terms such as “below,” “under,” “below,” “under,” “above,” “above,” etc., are used herein to describe the relationship between one element or feature shown in the figure and other elements or features. It should be understood that, in addition to the orientation shown in the figure, spatial relation terms also include different orientations of the device in use and operation. For example, if the device in the figure is flipped, the element or feature described as “below,” “under,” or “below” will be oriented “above” the other element or feature. Therefore, the exemplary terms “below” and “under” can include both above and below orientations. Furthermore, the device may also include other orientations (e.g., rotated 90 degrees or other orientations), and the spatial descriptive terms used herein will be interpreted accordingly.
[0049] When used herein, the singular forms of “a,” “an,” and “the” may also include the plural forms unless the context clearly indicates otherwise. It should also be understood that the terms “comprising / including” or “having,” etc., specify the presence of the stated features, wholes, steps, operations, components, parts, or combinations thereof, but do not preclude the possibility of the presence or addition of one or more other features, wholes, steps, operations, components, parts, or combinations thereof. Meanwhile, in this specification, the term “and / or” includes any and all combinations of the associated listed items.
[0050] Embodiments of the invention are described herein with reference to cross-sectional views illustrating ideal embodiments (and intermediate structures) of the invention, thus allowing for variations in the illustrated shape due to, for example, manufacturing techniques and / or tolerances. Therefore, embodiments of the invention should not be limited to the specific shapes of the regions shown herein, but rather include shape deviations due to, for example, manufacturing techniques. For instance, implantation regions shown as rectangular typically have rounded or curved features at their edges and / or implantation concentration gradients, rather than a binary change from implantation regions to non-implantation regions. Similarly, the buried regions formed by implantation can result in some implantation in the region between the buried region and the surface traversed during implantation. Therefore, the regions shown in the figures are substantially schematic, and their shapes do not represent the actual shapes of regions of the device and do not limit the scope of the invention.
[0051] Sandwich-structure-based acoustic resonators and filters are key components in radio frequency (RF) front-end modules. Traditional sandwich-structure-based resonators include thin film bulk acoustic resonators (FBARs) and solid-mounted resonators (SMRs).
[0052] Exemplary thickness Lamb acoustic wave (TLAW) resonators typically operate in the fundamental thickness-stretching mode (TE1), and are therefore also called TE1LAW resonators. The same resonator structure can also operate at higher harmonics (TE3, TE5, etc.), in which case the acoustic modes are primarily confined within the piezoelectric layer by metallic electrodes. In this configuration, only odd harmonics are electromechanically coupled to the resonator cavity.
[0053] A recent development in TLAW resonators is the introduction of ECTLAW resonator technology, which employs a thick dielectric layer deposited on one side (typically the top of the resonator) of a metal-piezoelectric-metal stack. Because the resonant cavity extends beyond the traditional metal-piezoelectric-metal stack of a typical TLAW resonator, it is referred to herein as ECTLAW (Extended Cavity Thickness Lamb Wave). This technology can also be called ECTnLAW, where n represents the harmonic order of the acoustic mode. In distinguishing mode polarization, ECTEnLAW and ECTSnLAW can be used to represent thickness stretching (TE) or thickness shearing (TS) operating modes, respectively. The thick dielectric layer expands the acoustic cavity, allowing higher-order modes (TE2, TE3, TS2, TS3, etc.) of the metal-piezoelectric-metal-dielectric structure to be excited, not just those of the metal-piezoelectric-metal structure. By adjusting the thickness of this thick dielectric layer, the operating frequency of the device can be adjusted, allowing the electromechanical coupling coefficient (k...) to be controlled.2 It provides more uniformity across the frequency adjustment range (although typically lower than the traditional TE1 mode) and significantly improves temperature compensation (TCF).
[0054] For the exemplary TE1LAW resonator, its structure is essentially composed of a metal-piezoelectric-metal stack, with no dielectric layer above the top electrode, or only a single passivation layer, i.e., a thin dielectric layer typically used for passivation purposes (see [link to SMR implementation]). Figure 1 In the FBAR implementation, thin dielectric layers can also be placed on both the bottom and top electrodes.
[0055] For resonators based on aluminum nitride (AlN) and scandium-doped aluminum nitride (Sc-doped AlN) – the most common sandwich resonators – the dispersion type of TE1 mode depends on the specific implementation; typically, SMR devices are type I and FBAR devices are type II.
[0056] The exemplary TE1LAW resonator comprises two main lateral regions: an inner region where the projection of the top electrode lies, and an outer region where the projection of the top electrode lies outside the projection of the bottom electrode. Lateral acoustic leakage depends on the acoustic boundary conditions between the two main lateral regions. In the exemplary ECTnLAW structure, the resonator operates within a multilayered acoustic cavity formed by a metal-piezoelectric-metal stack and an upper thick dielectric layer (see [link to documentation]). Figure 2 ). Figure 2 This is a cross-sectional view of an exemplary ECTE2LAW SMR with an unplanarized, thick dielectric layer, taken from an electrically isolated region, away from wiring and adjacent resonators. Depending on the material stack and whether the resonator is a suspended structure or an SMR-based structure, its dispersion type may be Type I or Type II. The conditions required to minimize lateral leakage vary depending on the dispersion type, as detailed below:
[0057] For Type I dispersion (typically SMR), the inner region is heavily mass-loaded by the electrodes. The outer region needs to have a reduced mass load relative to the inner region—usually achieved by removing at least one metallic mass load in the region to avoid electrode overlap, so that the cutoff frequency is higher than that of the inner region.
[0058] For type II dispersion (typically FBAR), the inner region is heavily mass-loaded by the electrodes. The outer region requires an increased mass load relative to the inner region—usually achieved by extending the overlapping electrodes and increasing the metal thickness in that region, so that the cutoff frequency is lower than that of the inner region.
[0059] However, it is not only important to consider the relative magnitude of the corresponding cutoff frequencies, but also to carefully control the difference (interval) between the cutoff frequencies of the inner and outer regions during the resonator design process in order to regulate the propagation of transverse sound waves.
[0060] The thick dielectric layer exerts a load on both the internal and external regions. This load, along with the metallic mass load, establishes a dispersion relationship between the internal and external regions, which may or may not be suitable depending on the specific stack configuration. Therefore, as with conventional TELAW resonators, boundary conditions must be carefully evaluated to suppress lateral acoustic leakage, whether maintaining the existing configuration or modifying the conditions of the external region.
[0061] The thick dielectric layer is deposited on top of patterned electrodes. Due to the presence of electrode steps, shadowing and cusping effects occur, deviating from the ideal situation of clear boundaries between regions. See [link to relevant documentation]. Figure 3 Among these, the shadowing effect refers to the phenomenon where, during deposition, material arrives along a specific direction, and the electrode edge blocks part of the flux, causing the dielectric layer profile to thin or tilt instead of forming a vertical boundary. The spike effect refers to the phenomenon where growth fronts from both sides of a step converge above the step, forming a ridge or peak shape instead of a flat surface.
[0062] These non-ideal geometries generate irregular boundary conditions, leading to acoustic mode scattering. They also increase the complexity of frequency fine-tuning and often result in poor wafer-level repeatability because these geometric features cannot be consistently reproduced. Therefore, these effects limit the practical application of high-order ECTnLAW devices.
[0063] This embodiment of the application planarizes the thick dielectric layer of the aforementioned ECTnLAW resonator to form a flat free surface above the resonator. Similar to the non-planarized case, the dispersion type may be Type I or Type II, depending on the material stack and the resonator implementation (suspended or SMR). The planarization of the thick dielectric layer alters the acoustic boundary conditions by clearly defining the boundaries, in which case the boundaries are determined by the sharp metallic edges of the electrodes, rather than by the irregular dielectric morphology present in the non-planarized case.
[0064] This application provides a TnLAW resonator (where n represents the harmonic order of the acoustic mode) operating in harmonic mode, which includes a thick dielectric layer disposed on the top electrode, the dielectric layer enabling the extended acoustic cavity formed by the metal-piezoelectric-metal stack and the upper dielectric layer to operate in harmonic mode. Figure 4 This is a schematic cross-sectional view of a resonator in one embodiment of this application. The cross-section is taken from the electrically isolated region, away from the wiring and adjacent resonators. (Refer to...) Figure 4The resonator comprises an acoustic mirror 120, a bottom electrode 130, a piezoelectric layer 140, a top electrode 150, and a dielectric layer 160, stacked sequentially. Specifically, the bottom electrode 130 is located on the acoustic mirror 120, the piezoelectric layer 140 is located on the bottom electrode 130, and the top electrode 150 is located on the piezoelectric layer 140. The upper surface of the bottom electrode 130 is divided into an inner region and an outer region. The orthographic projection of the top electrode 150 onto the upper surface of the bottom electrode 130 is the inner region, and the outer region is the area outside the inner region. (Refer to...) Figure 4 The area containing the inner region is divided into the inner region, and the area containing the outer region is divided into the outer region. Dielectric layer 160 covers piezoelectric layer 140 and top electrode 150. The upper surfaces of dielectric layer 160 in the inner and outer regions are on the same plane; that is, the upper surface of dielectric layer 160 directly above top electrode 150 is on the same plane as the upper surface of dielectric layer 160 directly above the outer region. The distance between the upper surface of top electrode 150 and the upper surface of dielectric layer 160 directly above top electrode 150 (in...) Figure 4 In the embodiment shown, the thickness of the dielectric layer 160 in the internal region is H, where H is approximately an integer multiple of the half-wavelength of the acoustic wave corresponding to the acoustic mode of the resonant cavity thickness, i.e.:
[0065] (1)
[0066] Where λ is the acoustic wavelength corresponding to the acoustic mode of the resonant cavity thickness, and n is the harmonic order of the acoustic mode, and n is an integer. In this type of ECTnLAW device, the dielectric layer above the top electrode 150 extends the acoustic cavity laterally to the outside of the conventional metal-piezoelectric-metal stack structure. The thickness of the dielectric layer is selected to provide the additional acoustic cavity length required for operation in the nth harmonic mode. Therefore, the thickness of the dielectric layer is designed to approximately satisfy the aforementioned formula (1). H approaches (n-1)λ / 2, meaning that H=(n-1)λ / 2 is theoretically a preferred embodiment, but in actual products, due to process errors, material and structural differences, H may deviate slightly from the theoretical value. In one embodiment of this application, H=(n-1)λ / 2±(15%λ / 2).
[0067] The thickness of the dielectric layer 160 directly above the outer region is H+T1, where T1 is the thickness of the top electrode 150.
[0068] The resonator structure of this application embodiment is based on ECTnLAW technology. The dielectric layer 160 with a thickness of H on the top electrode 150 defines the operating frequency of the resonator, which can excite higher-order thickness modes (including TE2, TE3, TS2, TS3 and other modes) of the cavity formed between the bottom electrode and the free surface, and provide temperature compensation (TCF) for the resonator.
[0069] The aforementioned resonator, by keeping the upper surface of the dielectric layer 160 flat, reduces lateral acoustic leakage, thereby achieving a higher Q value. Furthermore, it reduces the difference between the cutoff frequency fi in the internal region and the cutoff frequency fe in the external region of the resonator.
[0070] In one embodiment of this application, the distance H' between the upper surface of the top electrode 150 and the lower surface of the bottom electrode 130 approaches (n-1)λ / 2. While H' approaching (n-1)λ / 2 is theoretically a preferred embodiment, in actual products, due to process errors, material and structural differences, H' may deviate slightly from the theoretical value. In one embodiment of this application, H' = (n-1)λ / 2 ± (15%λ / 2).
[0071] In one embodiment of this application, a border 152 may also be provided on the top electrode 150. The border 152 is used to mitigate lateral parasitic modes. When a border region is introduced to mitigate lateral parasitic modes, the acoustic characteristics and cutoff frequencies of the inner and outer regions must be considered to select their acoustic characteristics and cutoff frequencies in order to suppress lateral sound leakage and maintain energy confinement within the inner region. Therefore, the characteristics of the inner and outer regions must be synergistically optimized. In the embodiment where the border 152 is provided, the inner region is located inside the border 152, and the outer region is located outside the top electrode 150. In one embodiment of this application, the border 152 adopts a raised structure, see [reference needed]. Figure 5 The material of the border 152 can be at least one of the following: aluminum (Al), aluminum-copper alloy (AlCu), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), ruthenium (Ru), aluminum nitride (AlN), titanium dioxide (TiO2), tantalum pentoxide (Ta2O5), etc. The border 152 is located at the edge of the top electrode 150 and is covered by a dielectric layer 160. The thickness of the dielectric layer 160 directly above the border 152 is H-T2, where T2 is the thickness of the border 152. In one embodiment of this application, the border can also adopt a recessed structure, defined by forming a recess at the edge of the top electrode 150 by patterning the top electrode layer.
[0072] In one embodiment of this application, a passivation layer 162 may also be provided on the dielectric layer 160, see [link to relevant documentation]. Figure 6 The passivation layer 162 is used to isolate the resonator from the external environment, thereby protecting the resonator. The thickness T3 of the passivation layer 162 can be very thin; in one embodiment of this application, H+T3 approaches (n-1)λ / 2. The material of the passivation layer 162 can be at least one of silicon nitride (SiNx), aluminum nitride (AlN), and aluminum oxide (Al2O3). In one embodiment of this application, the dielectric layer 160 is made of silicon dioxide (SiO2) and / or silicon nitride (SiNx).
[0073] In one embodiment of this application, the resonator further includes a substrate 110, on which an acoustic mirror 120 is located. The substrate 110 may be made of silicon (Si), silicon carbide (SiC), quartz, sapphire, glass, or other suitable materials. The silicon substrate may be made of a silicon material with high resistivity.
[0074] In one embodiment of this application, the acoustic reflector 120 is a Bragg reflector, comprising a low acoustic impedance layer 122 and a high acoustic impedance layer 124. The low acoustic impedance material of the low acoustic impedance layer 122 may be silicon dioxide, and the high acoustic impedance material of the high acoustic impedance layer 124 may be at least one selected from molybdenum, tungsten, aluminum nitride, and aluminum oxide. It is understood that in other embodiments, the low acoustic impedance material and the high acoustic impedance material may also be combinations of other materials with a large impedance ratio. In some embodiments, the high acoustic impedance layer 124 may be patterned to reduce parasitic electromagnetic effects. In one embodiment of this application, the acoustic reflector 120 may also be a suspended acoustic reflector (air cavity).
[0075] In one embodiment of this application, the material of the bottom electrode 130 includes at least one of aluminum (Al), aluminum-copper alloy (AlCu), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), ruthenium (Ru), platinum (Pt), and iridium (Ir).
[0076] In one embodiment of this application, the material of the piezoelectric layer 140 includes: aluminum nitride (AlN), scandium-doped aluminum nitride (AlN), etc. 1-x Sc x At least one of N, lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and zinc oxide (ZnO).
[0077] In one embodiment of this application, the material of the top electrode 150 includes at least one of aluminum (Al), aluminum-copper alloy (AlCu), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), ruthenium (Ru), platinum (Pt), and iridium (Ir).
[0078] In one embodiment of this application, the resonator is a sandwich-transduced bulk acoustic wave resonator. Further, it is a thick Lamb wave resonator.
[0079] In one embodiment of this application, the upper surface of the dielectric layer 160 is planarized. In one embodiment, chemical mechanical polishing (CMP) is used to planarize the upper surface of the dielectric layer 160; in other embodiments, etch-back or other planarization techniques may also be used.
[0080] For Type I ECTnLAW, planarization reduces the effective dispersive contrast between the inner and outer regions because the outer region actually contains a thicker dielectric layer than the inner region. Therefore, the acoustic load becomes more similar, reducing the difference (spacing) between the cutoff frequency fe of the outer region and the cutoff frequency fi of the inner region.
[0081] For type II ECTnLAW, the opposite is true: the spacing between the dispersion curves increases. Depending on the dispersion characteristics of a particular stack, this altered spacing can reduce transverse acoustic propagation, improve energy confinement, and increase the Q value.
[0082] Planarization eliminates the shadowing and spike effects caused by depositing thick dielectric layers on electrode steps and, as mentioned above, creates a clearer transition between the inner and outer regions. This leads to improved manufacturing yields, more defined acoustic boundaries for more predictable energy limits and overall device performance, greater repeatability of trimming behavior, and improved wafer-level performance uniformity. This is because planarization reduces the difference between the cutoff frequency fe of the outer region and the cutoff frequency fi of the inner region, where the outer region effectively bears a greater dielectric load than in the non-planarized case. Depending on the stack configuration and dispersion characteristics, lateral acoustic wave propagation can be reduced, thereby improving the quality factor (Q value).
[0083] The following provides a specific embodiment of a resonator of this application, which is an ECTE2LAW SMR with a planarized thick top dielectric layer for operating frequencies above 5 GHz. This resonator exhibits the aforementioned type I dispersion; therefore, for effective lateral confinement, the cutoff frequency of the outer region is kept higher than that of the inner region. The structure of this resonator can be referred to... Figure 6 It is an ECTE2LAW SMR, which includes, from bottom to top:
[0084] Substrate 110, made of a high resistivity material <111> The crystal orientation is monocrystalline silicon with a thickness of 200 μm.
[0085] The acoustic reflector 120, specifically the Bragg reflector, includes an alternating low acoustic resistance layer 122 and a high acoustic resistance layer 124. The low acoustic resistance layer 122 is made of silicon dioxide (SiO2) with a thickness of 215-325 nm; the high acoustic resistance layer 124 is made of aluminum nitride (AlN) with a thickness of 400-600 nm.
[0086] Seed layer ( Figure 6 (Not shown in the image), the material is aluminum nitride (AlN), with a thickness of 20-40 nm. The seed layer is used to promote the growth of the film layer above it.
[0087] The bottom electrode is 130, made of molybdenum (Mo), with a thickness of 80-120 nm.
[0088] The piezoelectric layer 140 is made of scandium-doped aluminum nitride (Al 70% Sc 30% N) and has a thickness of 280-420 nm.
[0089] The top electrode 150 comprises molybdenum (20-40nm), titanium (5-15nm), aluminum-copper alloy (80-120nm), and titanium (5-15nm) stacked sequentially.
[0090] The border 152 is made of titanium (Ti) with a thickness of 60-100nm. It is patterned to define a 1.5μm wide ring at the edge of the top electrode 150 as the border 152.
[0091] The dielectric layer 160 serves as temperature coefficient (TCF) compensation and frequency definition, and is made of silicon dioxide (SiO2). After planarization, the dielectric layer 160, located directly above the inside of the frame 152, has a thickness of 320-480 nm.
[0092] The passivation layer 162 is made of silicon nitride (SiNx) and has a thickness of 40-60 nm.
[0093] We performed numerical simulations on the resonator of the aforementioned embodiment to evaluate the effect of the planarization of the dielectric layer 160 on the dispersion characteristics and quality factor (Q). Figure 7a This is a comparative example of an ECTE2LAW SMR without planarization of dielectric layer 160 (its structure can be found in [reference]). Figure 2 Simulation results of the acoustic dispersion curve of ) Figure 7b The simulation results show the acoustic dispersion curve of an ECTE2LAW SMR according to an embodiment of this application. The external dispersion curve is extracted from a cross-section of the electrically isolated region, away from the wiring and adjacent resonators. Figure 7a and Figure 7b The wave number on the horizontal axis represents the in-plane (transverse) wave number used in the dispersion analysis. It represents the propagation constant k = 2π / λ parallel to the resonator surface, where λ is the transverse wave wavelength. Therefore, the dispersion curve describes the relationship between the resonant frequency and the transverse wave propagation. The results show that, for the resonator with the considered type I dispersion, planarization reduces the spacing between the cutoff frequencies of the interior and exterior regions compared to the non-planarization case.
[0094] Figure 8These are the Q-value and conductance curves as a function of frequency for a comparative example (dielectric layer unplanarized) and the embodiment of this application (dielectric layer planarized). The simulation includes isotropic mechanical damping, and the uniform Q-value for all materials is 2000. The simulation is extracted from a profile of the electrically isolated region, away from wiring and adjacent resonators. The embodiment of this application reduces lateral acoustic leakage by planarizing the dielectric layer 160, thereby achieving a higher Q-value.
[0095] The simulations above confirm that planarizing the dielectric layer 160 can improve acoustic confinement without sacrificing electrical performance. Alternatively, similar confinement could be achieved by reducing the thickness of the metal electrodes in the internal regions; however, this would increase resistive losses. Therefore, planarization can simultaneously achieve low acoustic losses and low resistive losses.
[0096] This application provides a method for manufacturing a resonator, which can be used to manufacture the resonator described in any of the above embodiments. Figure 9 This is a flowchart of a method for manufacturing a resonator according to an embodiment of this application, including the following steps:
[0097] S210, obtaining a wafer having an acoustic mirror, a bottom electrode, a piezoelectric layer and a top electrode stacked sequentially.
[0098] The device structure obtained after step S210 can be referred to Figure 10d See also Figure 11 In one embodiment of this application, step S210 specifically includes:
[0099] S211, Obtain the substrate wafer.
[0100] The substrate 110 can be made of silicon (Si), silicon carbide (SiC), quartz, sapphire, glass, or other suitable materials. The silicon substrate can be made of silicon material with high resistivity.
[0101] S213 forms an acoustic mirror on a substrate wafer.
[0102] In one embodiment of this application, the acoustic reflector 120 is a Bragg reflector formed by alternately depositing a low acoustic resistance layer 122 and a high acoustic resistance layer 124 on a substrate 110, with reference to... Figure 10a .
[0103] S215 forms the bottom electrode on the acoustic mirror.
[0104] In one embodiment of this application, the bottom electrode 130 is obtained by depositing a bottom electrode material and then patterning it (e.g., photolithography followed by etching), as shown below. Figure 10bIn one embodiment of this application, the material of the bottom electrode 130 includes at least one of aluminum (Al), aluminum-copper alloy (AlCu), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), ruthenium (Ru), platinum (Pt), and iridium (Ir).
[0105] In one embodiment of this application, prior to step S215, a step of forming a seed layer on the acoustic reflector 120 is included, with the bottom electrode 130 formed on the seed layer. In one embodiment of this application, the material of the seed layer is aluminum nitride.
[0106] In one embodiment of this application, the bottom electrode 130 is embedded in the structure of its underlying layer, and the bottom electrode 130 needs to be planarized before step S217.
[0107] S217 forms a piezoelectric layer on the bottom electrode.
[0108] In one embodiment of this application, a piezoelectric layer material is deposited on the bottom electrode 130 and the acoustic reflector 120 to form a piezoelectric layer 140, as shown in the reference. Figure 10c In one embodiment of this application, the material of the piezoelectric layer 140 includes: aluminum nitride (AlN), scandium-doped aluminum nitride (AlN), etc. 1-x Sc x At least one of N), lithium niobate (LiNbO3), lithium tantalate (LiTaO3), and zinc oxide (ZnO). In one embodiment of this application, the piezoelectric layer 140 may also be patterned.
[0109] S219 forms the top electrode on the piezoelectric layer.
[0110] In one embodiment of this application, a top electrode 150 is obtained by depositing a top electrode material and then patterning it (e.g., photolithography followed by etching), thereby defining the transducer region, as shown below. Figure 10d The top electrode 150 is located directly above the bottom electrode 130 and has a smaller area than the bottom electrode 130. The upper surface of the bottom electrode 130 includes an inner region containing the orthographic projection of the top electrode 150 onto the upper surface of the bottom electrode 130, and an outer region located outside the inner region. In one embodiment of this application, the material of the top electrode 150 includes at least one of aluminum (Al), aluminum-copper alloy (AlCu), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), ruthenium (Ru), platinum (Pt), and iridium (Ir).
[0111] At this point, step S210 is complete, and we proceed to step S220.
[0112] S220 forms a dielectric layer covering the piezoelectric layer and the top electrode.
[0113] A dielectric material is deposited on the front side of the wafer to form a dielectric layer 160. In one embodiment of this application, the material of the dielectric layer 160 is silicon dioxide (SiO2) and / or silicon nitride (SiNx).
[0114] In one embodiment of this application, after step S219 and before step S220, a step of forming a border 152 located at the edge of the top electrode 150 is further included. In one embodiment of this application, the border 152 is obtained by depositing border material on the top electrode 150 and then patterning it (e.g., photolithography followed by etching), as shown below. Figure 10e The dielectric layer 160 formed in step S220 also covers the border 152, as shown in the figure. Figure 10f In one embodiment of this application, the material of the frame 152 may be at least one of the following: aluminum (Al), aluminum-copper alloy (AlCu), titanium (Ti), copper (Cu), molybdenum (Mo), tungsten (W), ruthenium (Ru), aluminum nitride (AlN), titanium dioxide (TiO2), tantalum pentoxide (Ta2O5), etc.
[0115] S230, planarization of the dielectric layer.
[0116] Reference Figure 10g After planarization, the upper surface of the dielectric layer 160 directly above the top electrode 150 and the upper surface of the dielectric layer 160 directly above the outer region are on the same plane. The distance between the upper surface of the top electrode 150 and the upper surface of the dielectric layer 160 directly above the top electrode 150 is H, where H is approximately an integer multiple of the half-wavelength of the acoustic wave corresponding to the acoustic mode of the resonant cavity thickness, and the harmonic order of the acoustic mode is greater than 1. The thickness of the dielectric layer 160 directly above the outer region is H + T1, where T1 is the thickness of the top electrode 150.
[0117] The aforementioned resonator manufacturing method reduces transverse acoustic leakage by planarizing the upper surface of the dielectric layer 160, thereby achieving a higher Q value. Furthermore, it reduces the difference between the cutoff frequency fi in the internal region and the cutoff frequency fe in the external region of the resonator.
[0118] In one embodiment of this application, the dielectric layer 160 is made of silicon dioxide (SiO2) and / or silicon nitride (SiNx).
[0119] In one embodiment of this application, after step S230 is completed, the thickness of the dielectric layer 160 directly above the border 152 is H-T2, where T2 is the thickness of the border 152.
[0120] In one embodiment of this application, the planarization process may employ a chemical mechanical polishing process.
[0121] In one embodiment of this application, after step S230, a step of forming a passivation layer 162 on the dielectric layer 160 is further included. The resonator structure after forming the passivation layer 162 can be referred to... Figure 6 In one embodiment of this application, the material of the passivation layer 162 may be at least one of silicon nitride (SiNx), aluminum nitride (AlN), aluminum oxide (Al2O3), etc.
[0122] In one embodiment of this application, single-layer or multi-layer trimming based on frequency or thickness can also be performed.
[0123] The manufacturing method of the resonator in this application is based on the same inventive concept as the resonator. For details not specifically described in the manufacturing method of the resonator, please refer to the previous introduction of the resonator.
[0124] It should be understood that although the steps in the flowchart of this application are shown sequentially as indicated by the arrows, these steps are not necessarily executed in the order indicated by the arrows. Unless explicitly stated herein, there is no strict order restriction on the execution of these steps, and they can be executed in other orders. Moreover, at least some steps in the flowchart of this application may include multiple steps or multiple stages, which are not necessarily completed at the same time, but may be executed at different times, and the execution order of these steps or stages is not necessarily sequential, but may be performed alternately or in turn with other steps or at least some of the steps or stages of other steps.
[0125] In the description of this specification, references to terms such as "some embodiments," "other embodiments," and "ideal embodiments" indicate that a specific feature, structure, material, or characteristic described in connection with that embodiment or example is included in at least one embodiment or example of the invention. In this specification, the illustrative descriptions of the above terms do not necessarily refer to the same embodiments or examples.
[0126] The technical features of the above embodiments can be combined in any way. For the sake of brevity, not all possible combinations of the technical features of the above embodiments are described. However, as long as there is no contradiction in the combination of these technical features, they should be considered to be within the scope of this specification.
[0127] The embodiments described above are merely illustrative of several implementation methods of this application, and while the descriptions are relatively specific and detailed, they should not be construed as limiting the scope of the patent application. It should be noted that those skilled in the art can make various modifications and improvements without departing from the concept of this application, and these all fall within the protection scope of this application. Therefore, the protection scope of this patent application should be determined by the appended claims.
Claims
1. A resonator, characterized in that, include: Acoustic reflector; The bottom electrode is located on the acoustic mirror; A piezoelectric layer is located on the bottom electrode; The top electrode is located on the piezoelectric layer; The upper surface of the bottom electrode includes an inner region where the orthographic projection of the top electrode onto the upper surface of the bottom electrode is located, and an outer region located outside the inner region. A dielectric layer covers the piezoelectric layer and the top electrode. The upper surface of the dielectric layer directly above the top electrode and the upper surface of the dielectric layer directly above the outer region are on the same plane. The distance between the upper surface of the top electrode and the upper surface of the dielectric layer directly above the top electrode is H. H is close to an integer multiple of the half wavelength of the acoustic wave corresponding to the acoustic mode of the resonant cavity thickness. The thickness of the dielectric layer directly above the outer region is H+T1, where T1 is the thickness of the top electrode. The harmonic order of the acoustic mode is greater than 1.
2. The resonator according to claim 1, characterized in that, The distance between the upper surface of the top electrode and the lower surface of the bottom electrode is approximately an integer multiple of the half wavelength of the sound wave.
3. The resonator according to claim 1, characterized in that, It also includes a frame located on the top electrode and at the edge of the top electrode, the frame being covered by the dielectric layer, and the thickness of the dielectric layer directly above the frame being H-T2, where T2 is the thickness of the frame.
4. The resonator according to claim 1, characterized in that, It also includes a passivation layer located on the dielectric layer.
5. The resonator according to claim 1, characterized in that, The acoustic reflector is a Bragg reflector.
6. The resonator according to claim 1, characterized in that, The resonator is a sandwich-structured transducer acoustic resonator.
7. The resonator according to claim 6, characterized in that, The resonator is a thickness Lamb wave resonator.
8. The resonator according to claim 1, characterized in that, λ is the acoustic wavelength corresponding to the acoustic mode of the resonant cavity thickness, and n is the harmonic order of the acoustic mode.
9. The resonator according to any one of claims 1-8, characterized in that, The upper surface of the dielectric layer has been planarized.
10. A method for manufacturing a resonator, characterized in that, include: Obtain a wafer having an acoustic mirror, a bottom electrode, a piezoelectric layer and a top electrode stacked sequentially; the upper surface of the bottom electrode includes an inner region where the orthographic projection of the top electrode onto the upper surface of the bottom electrode is located, and an outer region located outside the inner region; A dielectric layer is formed covering the piezoelectric layer and the top electrode; The dielectric layer is planarized. After the planarization is completed, the upper surface of the dielectric layer directly above the top electrode and the upper surface of the dielectric layer directly above the outer region are on the same plane. The distance between the upper surface of the top electrode and the upper surface of the dielectric layer directly above the top electrode is H. H is close to an integer multiple of the half wavelength of the acoustic wave corresponding to the acoustic mode of the resonant cavity thickness of the resonator. The thickness of the dielectric layer directly above the outer region is H+T1, where T1 is the thickness of the top electrode.