A lateral excitation bulk acoustic wave resonator and a method of fabrication
Patent Information
- Application Number
- CN202611529345.5
- Authority / Receiving Office
- CN · China
- Patent Type
- Applications(China)
- Current Assignee / Owner
- Filing Date
- 2026-09-30
- Publication Date
- 2026-11-03
AI Technical Summary
Existing transverse exciter acoustic resonators suffer from problems such as over-etching damaging the piezoelectric film or under-etching leading to insufficient cavity release during cavity formation. Furthermore, the etching process is sensitive to time, temperature, and release agent, resulting in unstable cavity boundaries.
An embedded lateral cutoff layer is set in the sacrificial layer. An embedded lateral cutoff groove is formed by etching and filled with cutoff material to limit the lateral etching during the release process of the sacrificial layer, avoid damage to the piezoelectric layer, and control the cavity size by preset boundary.
It improves cavity size consistency and wafer-level manufacturing stability, reduces the risk of edge cracks and stress concentration in piezoelectric films, achieves a higher process window and manufacturing stability, and improves product consistency and reliability.
Smart Images
Figure CN123034804A_ABST
Abstract
Description
Technical Field
[0001] This invention belongs to the field of resonator-related technology, and particularly relates to a transverse exciter acoustic resonator and its fabrication method. Background Technology
[0002] The statements in this section are merely background information related to the present invention and do not necessarily constitute prior art.
[0003] With the development of 5G, Sub-6G, and subsequent high-frequency communication systems, RF front-end filters face higher requirements in terms of operating frequency, bandwidth, insertion loss, power handling capability, and manufacturing consistency. Traditional surface acoustic wave (SAW) filters are limited in the high-frequency band by photolithographic linewidth and material sound velocity, while the operating frequency of thin-film bulk acoustic resonators (FCAS) mainly depends on the thickness of the piezoelectric film, making further improvements in frequency and bandwidth challenging due to technological limitations. Lateral excitation bulk acoustic resonators utilize the lateral electric field in the piezoelectric film to excite bulk acoustic modes, possessing potential for higher frequency, wider bandwidth, and miniaturization, representing an important development direction for RF filters.
[0004] Existing methods for forming cavities in transverse exciter acoustic resonators mainly include back-side deep etching release and front-side sacrificial layer release. With back-side deep etching, over-etching near the piezoelectric or dielectric layer interface can damage the piezoelectric film, while under-etching can lead to insufficient cavity release. With front-side sacrificial layer release, the sacrificial layer release typically exhibits transverse etching characteristics, and the etched area continuously expands with increasing release time, making the cavity boundary highly sensitive to time, temperature, release agent concentration, and local pattern density. Summary of the Invention
[0005] To overcome the shortcomings of the prior art, the present invention provides a transverse excitation acoustic resonator and its fabrication method. An embedded lateral cutoff layer is set in the sacrificial layer, so that the transverse etching during the release process of the sacrificial layer automatically stops at a preset boundary position, and the thin film damage to the piezoelectric layer is reduced, thus avoiding structural problems caused by excessive transverse etching.
[0006] To achieve the above objectives, the present invention adopts the following technical solution: In a first aspect, the present invention provides a transverse exciter acoustic resonator, comprising: Substrate; A sacrificial layer located above the substrate; An embedded lateral stop layer located at the predetermined target cavity boundary position within the sacrificial layer; A piezoelectric layer located above the sacrificial layer and the embedded lateral stop layer; Metal electrodes disposed on the surface of the piezoelectric layer; And a passivation layer covering the metal electrode and the piezoelectric layer.
[0007] In a second aspect, the present invention provides a method for fabricating a transverse exciter acoustic resonator, comprising: Provide substrate; A sacrificial layer is formed above the substrate; An embedded stop groove is etched at the predetermined target cavity boundary position in the sacrificial layer, and a stop material is filled in the embedded stop groove to form an embedded lateral stop layer. A piezoelectric layer is formed above the embedded lateral stop layer and the sacrificial layer; A metal electrode is formed above the piezoelectric layer; A passivation layer is formed above the piezoelectric layer and the metal electrode; Release the sacrificial layer corresponding to the preset target cavity location. The above one or more technical solutions have the following beneficial effects: In this invention, a buried lateral cut-off layer is set at the preset target cavity boundary position in the sacrificial layer, so that the lateral etching during the sacrificial layer release process automatically stops at the preset boundary position. The target cavity boundary control is changed from subsequent release time control to front-end patterned structure control, which is beneficial to improve cavity size consistency and wafer-level manufacturing stability. In addition, the buried lateral cut-off layer does not penetrate the piezoelectric layer, thereby reducing the risk of edge cracks, defects and stress concentration of the piezoelectric film.
[0008] Advantages of additional aspects of the invention will be set forth in part in the description which follows, and in part will be obvious from the description, or may be learned by practice of the invention. Attached Figure Description
[0009] The accompanying drawings, which form part of this invention, are used to provide a further understanding of the invention. The illustrative embodiments of the invention and their descriptions are used to explain the invention and do not constitute an improper limitation of the invention.
[0010] Figure 1 This is a schematic diagram of a sacrificial layer structure formed on a substrate in an embodiment of the present invention; Figure 2 This is a schematic diagram of an embedded stop-off groove structure formed in the sacrificial layer in an embodiment of the present invention; Figure 3 This is a schematic diagram of the embedded lateral stop layer structure in an embodiment of the present invention; Figure 4 This is a schematic diagram of the piezoelectric layer structure formed in an embodiment of the present invention; Figure 5 This is a schematic diagram of the metal electrode and passivation layer structure formed in an embodiment of the present invention; Figure 6 This is a schematic diagram of the target cavity structure formed in an embodiment of the present invention; Figure 7This is a schematic diagram showing the locations of the effective acoustic aperture region and the non-acoustic aperture region in an embodiment of the present invention; Figure 8 This is a scanning electron microscope image of the sacrificial layer structure after release in an embodiment of the present invention; Figure 9 This is a schematic diagram of the three-dimensional structural model of the resonator unit in an embodiment of the present invention; In the figure, 1 is the substrate, 2 is the sacrificial layer, 3 is the buried cutoff trench, 4 is the buried lateral cutoff layer, 5 is the piezoelectric layer, 6 is the metal electrode, 7 is the passivation layer, 8 is the release window, 9 is the target cavity, 10 is the effective acoustic aperture region, and 11 is the non-acoustic aperture region. Detailed Implementation
[0011] It should be noted that the following detailed descriptions are exemplary and intended to provide further illustration of the invention. Unless otherwise specified, 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 invention pertains.
[0012] It should be noted that the terminology used herein is for the purpose of describing particular implementations only and is not intended to limit the exemplary implementations of the present invention.
[0013] Where there is no conflict, the embodiments and features in the embodiments of the present invention can be combined with each other.
[0014] Terminology Explanation: XBAR: Transverse exciter acoustic resonator, typically includes a piezoelectric thin film, interdigitated electrodes disposed on the surface of the piezoelectric thin film, and a cavity structure located below the piezoelectric thin film; it utilizes a transverse electric field to excite the acoustic modes and can be used in high-frequency, broadband radio frequency filters.
[0015] Example 1 like Figures 1-9 As shown, this embodiment discloses a transverse exciter acoustic resonator, including: a substrate 1; a sacrificial layer 2 located above the substrate 1; a buried lateral cut-off layer 4 located at a predetermined target cavity boundary position in the sacrificial layer 2; a piezoelectric layer 5 located above the sacrificial layer 2 and the buried lateral cut-off layer 4; a metal electrode 6 disposed on the surface of the piezoelectric layer 5; and a passivation layer 7 covering the metal electrode 6 and the piezoelectric layer 5.
[0016] In this embodiment, substrate 1 provides structural support; sacrificial layer 2 is formed above substrate 1 to form a target cavity after subsequent release; embedded lateral stop layer 4 is disposed at a predetermined target cavity boundary position in sacrificial layer 2 to limit the lateral expansion of sacrificial layer 2 during release; as Figure 4 As shown, the piezoelectric layer 5 is disposed above the sacrificial layer 2 and the embedded lateral stop layer 4, as... Figure 5As shown, the metal electrode 6 is disposed on the surface of the piezoelectric layer 5, and the passivation layer 7 covers the surface of the metal electrode and the piezoelectric layer, serving to protect the electrode and the piezoelectric layer. The target cavity is formed by the release and removal of the sacrificial layer 2, and its lateral boundary is defined by the embedded lateral stop layer 4.
[0017] This embodiment no longer uses the closed release groove inside the piezoelectric layer as the main boundary control structure, but forms an embedded lateral cutoff layer in the sacrificial layer, changing the control of the preset target cavity boundary from subsequent release time control to front-end patterned structure control, which is beneficial to improve cavity size consistency and wafer-level manufacturing stability.
[0018] like Figures 2-3 As shown, in one specific implementation, the embedded lateral stop layer 4 does not penetrate the piezoelectric layer and does not need to form a closed isolation groove in the piezoelectric layer; the embedded lateral stop layer 4 is located corresponding to the boundary of the target cavity and can be located inside the sacrificial layer 2 or in the boundary region of the sacrificial layer 2. The embedded lateral stop layer 4 is used to block the lateral etching during the release process of the sacrificial layer 2.
[0019] The embedded lateral stop layer 4 can extend from the upper surface of the sacrificial layer 2 to the upper surface of the substrate 1, or it can extend only to a portion of the thickness of the sacrificial layer 2.
[0020] Preferably, the height of the embedded lateral stop layer 4 is 70%–100% of the thickness of the sacrificial layer 2. When the embedded lateral stop layer 4 penetrates the thickness direction of the sacrificial layer 2, full-thickness etching stop can be achieved, reducing bottom etch around the edge.
[0021] When the embedded lateral stop layer 4 does not completely penetrate the thickness of the sacrificial layer 2, a partial stop structure can be formed according to the release rate and structural stress requirements. If the designed thickness of the sacrificial layer 2 is more than twice the distance between the embedded lateral stop layer 4 and the release hole, the release rate is affected by the depth of the release hole; the deeper the hole, the slower the rate. Therefore, the embedded lateral stop layer 4 does not need to be embedded too deeply into the sacrificial layer, reducing the process difficulty.
[0022] The cross-section of the embedded lateral stop layer 4 can be rectangular, trapezoidal, inverted trapezoidal, or other structures that can restrict the lateral release of the sacrificial layer 2.
[0023] Preferably, the embedded lateral cutoff layer 4 adopts an inverted trapezoidal or rectangular cutoff layer to simultaneously restrict the lateral etching of the upper and lower parts of the sacrificial layer 2, thereby reducing the problem of cavity boundary displacement caused by excessive etching of the sacrificial layer.
[0024] The material of the embedded lateral stop layer 4 has an etching selectivity ratio with the material of the sacrificial layer 2. The etching selectivity ratio of the material of the sacrificial layer 2 to the material of the embedded lateral stop layer 4 is greater than 300:1, which ensures that the embedded lateral stop layer can achieve a good stop effect with minimal loss.
[0025] As one specific implementation, the embedded lateral stop layer 4 is specifically segmented, and the embedded lateral stop layer 4 includes at least one stop layer unit. Gaps, release communication channels or stress buffer areas are reserved between the stop layer units.
[0026] The segmented structure can avoid the continuous accumulation of residual stress in the sacrificial layer deposition process, reducing the risk of suspension membrane warping or rupture.
[0027] A segmented cutoff layer layout can take the following form: Double-sided cutoff layout: A set of cutoff layer units is set on the left and right sides of the effective acoustic aperture region 10 to restrict the main lateral release direction. For example, the cutoff layer unit on the left side of the effective acoustic aperture region 10 needs to be located on the left side of the release window and at a short distance. Since the released gas is released at the same rate on both sides of the release window, the design of the cutoff layer unit can ensure that the released gas is blocked from being released laterally to the left side of the release window during the release process of the cavity in the effective acoustic region on the right side of the release window, thus ensuring that the cavity size accuracy is consistent with the design value.
[0028] When using a double-sided cutoff layout, the target cavity is typically a rectangular structure, with the longer side being 2 to 3 times longer than the shorter side. The release groove is designed parallel to the longer side of the rectangular structure, as is the cutoff layer. The thin film above the target cavity requires support, which is located at the shorter side of the rectangular structure, making it impossible to design a release groove there. During the release process, gas enters along the release groove. Due to isotropic etching, the etching rate is consistent on both sides of the release groove. Therefore, a cutoff layer is needed to limit the etching on one side, allowing it to etch along the other side to reach the target cavity. The shorter side of the rectangular structure, being farther from the release hole, will experience some etching, but the etching length is limited.
[0029] Four-sided segmented cutoff layout: Multiple spaced cutoff layer units are set around the target cavity to restrict the release boundaries in multiple directions. For example, if the release window is located around the effective acoustic area, cutoff layer units need to be designed around the perimeter to block lateral etching in the opposite direction of the effective acoustic area. Segmenting the embedded lateral cutoff layer into four sections can effectively reduce process problems such as film voids, cracks, and wafer warpage caused by excessive stress in the embedded film layer.
[0030] When adopting a four-sided segmented cutoff layout, similar to the double-sided cutoff layout, the corner block with a longer side length of the target cavity is designed, and the position of the support structure is reserved. The cutoff layer cannot be a completely closed pattern to ensure that the restricted release hole does not need to release the drilling corrosion on one side.
[0031] Comb-shaped cutoff layout: Multiple short strip-shaped cutoff layer units are arranged along the boundary of the target cavity, forming an etched boundary constraint structure similar to comb teeth. If the sacrificial layer is thick, the thickness of the embedded lateral cutoff layer 4 also increases accordingly. When the embedded lateral cutoff layer 4 is thick, the comb-shaped segmented arrangement can effectively reduce the embedding difficulty and avoid process problems such as detachment, breakage, and voids caused by excessive internal stress of the film layer. The narrow spacing between the short strip-shaped cutoff layer units results in a small contact area with the released gas and a limited lateral release distance, thus having a smaller impact on the cavity structure.
[0032] The width of the cut-off layer differs between the four-sided segmented cut-off layout and the comb-tooth cut-off layout. The comb-tooth layout is more densely arranged, and the cross-sectional width of the cut-off layer is usually more than 5 micrometers and the length is more than 50 micrometers, which facilitates process implementation.
[0033] The segmented cutoff layout reduces film defects caused by the buried cutoff layer process. Simultaneously, when the etching front reaches the segmented cutoff layer unit, the release boundary is restricted, preventing over-release. Compared to a continuous closed structure, the segmented layout provides a more flexible stress adjustment space for the film edge, helping to reduce stress concentration at the piezoelectric film edge, lowering the risk of film warping and cracking during large-area release, and improving the manufacturing consistency of large-area or arrayed XBAR devices.
[0034] like Figure 6 As shown, in one specific implementation, the release window is generally located in the non-acoustic aperture region 11 of the XBAR resonator. The so-called non-acoustic aperture region 11 refers to the region located outside the effective interdigitated electrode region, or the region that contributes little to the main resonant mode. Generally, the cutoff layer is designed to coincide with the cavity boundary of the XBAR structure, and the release window on the same side is designed to be laterally adjacent to the cutoff layer, which serves to prevent the release gas from being laterally etched from the opposite direction of the cavity structure.
[0035] The release window can be a rectangular hole, a strip groove, a polygonal hole, an array of holes, or a combination thereof. The release window penetrates the passivation layer and the piezoelectric layer and reaches the sacrificial layer 2.
[0036] Preferably, the release window 8 is kept at a certain distance from the effective acoustic aperture region 10 so that the release window will not damage the effective excitation region of the interdigital electrode.
[0037] The release window and the embedded lateral stop layer are staggered in the planar direction, so that the released gas first enters the sacrificial layer, then propagates laterally to the target cavity area, and finally stops at the stop layer.
[0038] The horizontal distance between the release window and the stop layer can be determined based on the sacrificial layer release rate, release time, target cavity size, and release process window. This horizontal distance can be used to define a release margin, making the release process more tolerant.
[0039] like Figure 7 As shown, during the release process, the etching gas enters the sacrificial layer 2 through the release window 8 of the non-acoustic aperture region 11. Since the material of the sacrificial layer 2 can be etched by the release agent, the etching front propagates laterally along the sacrificial layer, gradually removing the sacrificial layer below the working area and forming a cavity. When the etching front propagates to the embedded lateral stop layer, because the material of the embedded lateral stop layer has a higher etching selectivity than the sacrificial layer material, the etching rate of the etching gas on the embedded lateral stop layer is significantly lower than the etching rate on the sacrificial layer, thus blocking the lateral etching propagation.
[0040] Therefore, the cavity boundary is primarily determined by the pre-fabrication position of the cutoff layer, rather than entirely by the etching time. Even with some deviation in the release time, the cutoff layer can still limit the cavity from further expansion, thereby improving the consistency of the target cavity size and the process window.
[0041] As a specific implementation method, a SiO2 sacrificial layer system is adopted, specifically: the sacrificial layer 2 is made of SiO2, the embedded lateral stop layer 4 and the segmented stop layer are made of one or more of polycrystalline silicon, amorphous silicon, Si3N4, Al2O3, SiC, and W, and the release agent is one or more of gaseous HF, wet HF, and BOE.
[0042] As a specific implementation method, a silicon-based sacrificial layer system is used, which can be applied to piezoelectric layers or electrode systems that are not suitable for HF release. Specifically, the sacrificial layer 2 is made of one or more combinations of polycrystalline silicon, amorphous silicon, and epitaxial silicon; the embedded lateral stop layer 4 and the segmented stop layer are made of one or more combinations of SiO2, Si3N4, Al2O3, and SiC; and the release agent used is XeF2, fluorine-containing plasma, TMAH, or KOH system.
[0043] As a specific implementation method, a polymer sacrificial layer system is adopted, which has a lower release temperature and stress, making it suitable for some low-temperature processes. Specifically, the sacrificial layer 2 is made of polyimide, photoresist, BCB or other organic sacrificial materials, the embedded lateral stop layer 4 and the segmented stop layer are made of one or more combinations of SiO2, Si3N4, Al2O3 and metal layers, and the release agent is oxygen plasma, organic solvent or thermal decomposition process.
[0044] As a specific implementation method, a composite sacrificial layer system is adopted to achieve multi-stage release and complex cavity height control. Specifically, the sacrificial layer 2 is made of SiO2 / polycrystalline silicon composite layer or SiO2 / polymer composite layer, the embedded lateral stop layer 4 and the segmented stop layer are made of media or metal materials that are selective to the target release layer, and the release agent is a combination of step-release agents.
[0045] This embodiment uses a pre-patterned embedded lateral stop layer to define the target cavity release boundary, which reduces the impact of release time fluctuations on cavity size compared to the sacrificial layer release method that relies solely on release time control. The height of the embedded lateral stop layer is 70%–100% of the sacrificial layer thickness, avoiding the formation of closed isolation grooves in the piezoelectric layer and intermediate dielectric layer, thus reducing the risk of piezoelectric film damage and edge stress concentration.
[0046] Example 2 The purpose of this embodiment is to provide a method for fabricating a transverse exciter acoustic resonator, including: Provides sinking; A sacrificial layer is formed above the substrate; An embedded stop groove 3 is etched at the predetermined target cavity boundary position in the sacrificial layer, and a stop material is filled in the embedded stop groove 3 to form an embedded lateral stop layer. A piezoelectric layer is formed above the embedded lateral stop layer and the sacrificial layer; A metal electrode is formed above the piezoelectric layer; A passivation layer is formed above the piezoelectric layer and the metal electrode; Release the sacrificial layer corresponding to the preset target cavity position.
[0047] As a specific implementation method, a method for fabricating a transverse exciter acoustic resonator includes: Step 1: Provide a substrate.
[0048] The substrate can be a silicon substrate, silicon-on-insulator substrate, sapphire substrate, quartz substrate, silicon carbide substrate, glass substrate, diamond substrate, or other substrates suitable for manufacturing XBAR devices.
[0049] Silicon substrates are preferred to facilitate compatibility with MEMS and semiconductor processes.
[0050] The substrate is cleaned to remove surface particles, organic contaminants, and metal ion contaminants.
[0051] If necessary, a buffer layer, insulating layer, or bonding aid layer can be formed on the substrate surface.
[0052] Step 2: Form a sacrificial layer on the substrate.
[0053] The sacrificial layer can be formed by thermal oxidation, chemical vapor deposition, plasma-enhanced chemical vapor deposition, low-pressure chemical vapor deposition, sputtering, or spin coating.
[0054] The sacrificial layer material is preferably SiO2, and the thickness of the sacrificial layer can be 0.2 μm to 10 μm, more preferably 0.5 μm to 5 μm.
[0055] The sacrificial layer thickness determines the subsequent target cavity height. For XBAR resonators, the target cavity height needs to balance acoustic energy isolation, mechanical support stability, and release efficiency. Insufficient sacrificial layer thickness may lead to acoustic leakage or inadequate release, while excessive thickness may increase film stress and release time.
[0056] Step 3: Etch embedded stop grooves in the sacrificial layer.
[0057] Based on the target cavity boundary location, an embedded stop groove 3 is etched in the sacrificial layer. The embedded stop groove 3 can be formed using photolithography and etching processes.
[0058] The embedded cut-off groove 3 is preferably located outside the effective acoustic aperture area of the XBAR and at a preset distance from the effective area of the interdigital electrode.
[0059] The embedded stop groove 3 can be a strip groove, a rectangular groove, a circular arc groove, a polygonal groove, or a combination thereof.
[0060] The depth of the buried stop trench 3 can be equal to the thickness of the sacrificial layer, or it can be 70%–100% of the thickness of the sacrificial layer. When the buried stop trench 3 penetrates the sacrificial layer to the substrate surface, a stronger lateral stop effect can be obtained. When the buried stop trench 3 does not completely penetrate the sacrificial layer, etching damage and stress concentration can be reduced.
[0061] In this embodiment, the position of the embedded cutoff groove 3 is defined by photolithography, and the embedded structure is formed by deposition and planarization. The process flow is compatible with MEMS and semiconductor manufacturing and is suitable for mass production of XBAR resonators and filters.
[0062] In this embodiment, the target cavity boundary is mainly determined by the position of the embedded cut-off groove defined by photolithography, rather than simply by the release time, which is beneficial to improving the cavity size consistency between different devices within the same wafer.
[0063] The embedded stop groove 3 can be installed continuously or in segments. In this embodiment, a segmented structure is preferred to form the subsequent segmented stop layer.
[0064] In this embodiment, the segmented cutoff layout can limit over-release while retaining the necessary support area and release connection area, which helps to reduce the risk of film collapse, warping and insufficient edge support.
[0065] Step 4: Fill with cut-off material and flatten.
[0066] The embedded stop groove 3 is filled with stop material to form an embedded lateral stop layer.
[0067] Optionally, segmented embedded lateral stop layers can be fabricated through segmented design of the photolithographic pattern.
[0068] The cutoff material and the sacrificial layer material should have an etching selectivity ratio. When SiO2 is used as the sacrificial layer, the cutoff material can be polycrystalline silicon, amorphous silicon, Si3N4, Al2O3, SiC, tungsten metal, or other materials whose etching rate in the HF system is significantly lower than that of SiO2.
[0069] Preferably, polycrystalline silicon is used as the stop layer material. The polycrystalline silicon can be filled into the stop trench by low-pressure chemical vapor deposition or other deposition processes. After filling, the excess stop material on the surface of the sacrificial layer is removed by chemical mechanical polishing or etch-back process so that the upper surface of the stop layer is basically flush with the upper surface of the sacrificial layer.
[0070] After this step is completed, an embedded lateral stop layer is formed within the sacrificial layer. The embedded lateral stop layer is located inside the sacrificial layer and does not need to penetrate the subsequent piezoelectric layer, thus avoiding the formation of closed isolation grooves in the piezoelectric film and reducing edge cracks, defects, and stress concentrations in the piezoelectric film.
[0071] Step 5: Form a piezoelectric layer on the sacrificial layer and the embedded lateral stop layer.
[0072] The piezoelectric layer material can be lithium niobate, lithium tantalate, aluminum nitride, zinc oxide, lead zirconate titanate, or other piezoelectric materials.
[0073] For high-performance XBAR devices, monocrystalline lithium niobate or monocrystalline lithium tantalate thin films are preferred.
[0074] Piezoelectric layers can be formed by methods such as thin film transfer, bonding thinning, ion slicing, sputtering deposition, chemical vapor deposition, or epitaxial growth.
[0075] The thickness of the piezoelectric layer can be 100 nm to 3000 nm, preferably 300 nm to 1500 nm.
[0076] When forming the piezoelectric layer, since the embedded lateral stop layer is embedded in the sacrificial layer and the surface is planarized, the problems of surface discontinuity and stress concentration of the piezoelectric layer can be reduced.
[0077] Step 6: Form a metal electrode on the piezoelectric layer.
[0078] The metal electrode 6 can be an interdigitated electrode, or it can include lead-out electrodes, connecting pads, and matching structures.
[0079] The metal electrode material can be Al, Mo, Au, Pt, Cu, Ti, Cr, W or a multilayer combination thereof.
[0080] The thickness of the metal electrode can be 50 nm to 2000 nm, preferably 100 nm to 1000 nm.
[0081] The period, finger width, spacing, and aperture of the interdigitated electrodes are determined based on the target operating frequency, the sound velocity of the piezoelectric material, the electromechanical coupling coefficient, and the filter design requirements.
[0082] Step 7: Form a passivation layer on the metal electrode and the piezoelectric layer.
[0083] The passivation layer material can be SiO2, Si3N4, Al2O3, polyimide, benzocyclobutene, or other dielectric materials.
[0084] The passivation layer thickness can be 50 nm to 3000 nm, preferably 100 nm to 1500 nm.
[0085] Passivation layers are used to protect electrodes, regulate frequency, improve environmental stability, or enhance compatibility with subsequent release processes.
[0086] Step 8: Form a non-acoustic aperture release window.
[0087] The release window can be formed through photolithography and etching processes, and extends through the passivation layer and piezoelectric layer to the sacrificial layer.
[0088] The release window is preferably located outside the effective interdigitated electrode region, such as on the outer side of the electrode, in the lead gap, near the device edge, or near the support region. The release window does not directly pass through the main acoustic excitation region to reduce the impact on the dominant modal vibration and Q value.
[0089] The release window can be an array of multiple apertures or a strip groove. Multiple release windows can be distributed along the device edge or cavity boundary to improve release uniformity.
[0090] Step 9: Release the sacrificial layer.
[0091] The sacrificial layer is released by introducing a release etching medium through a release window. Taking a SiO2 sacrificial layer as an example, the release agent can be gaseous HF, wet HF, buffered oxide etchant, or other etching media capable of selectively etching SiO2.
[0092] The released etching medium propagates laterally along the sacrificial layer, removing the sacrificial layer below and around the effective acoustic aperture region to form the target cavity. When the etching front reaches the embedded lateral stop layer, the release process is restricted at this location due to the higher etching selectivity of the stop layer relative to the sacrificial layer, thus achieving self-stop at the cavity boundary.
[0093] Step 10: After release, clean, dry and encapsulate the device.
[0094] Supercritical drying, vapor-phase release drying, or low-surface-tension solvent replacement are preferred to reduce the risk of film adhesion; then wafer dicing, packaging, electrical connection and testing are performed to obtain XBAR resonators or XBAR filters.
[0095] In this embodiment, since the embedded lateral stop layer is formed before the piezoelectric layer is prepared, and can be flush with the surface of the sacrificial layer through a planarization process, it will not directly destroy the continuity of the piezoelectric film like the closed groove in the piezoelectric layer. This structure is beneficial to reduce edge defects and stress concentration of the piezoelectric film.
[0096] In this embodiment, by prefabricating an embedded lateral stop layer within the sacrificial layer, the release etching stops after reaching a preset boundary, reducing the sensitivity of cavity size to release time, etching rate, and local pattern density.
[0097] In this embodiment, the filter array composed of multiple XBAR resonators prepared can reduce crosstalk between adjacent resonators, improve the frequency consistency of the array devices and the overall filter performance.
[0098] While the specific embodiments of the present invention have been described above in conjunction with the accompanying drawings, this is not intended to limit the scope of protection of the present invention. Those skilled in the art should understand that various modifications or variations that can be made by those skilled in the art without creative effort based on the technical solutions of the present invention are still within the scope of protection of the present invention.
Claims
1. A transverse exciter acoustic resonator, characterized in that, include: Substrate; A sacrificial layer located above the substrate; An embedded lateral stop layer located at the predetermined target cavity boundary position within the sacrificial layer; A piezoelectric layer located above the sacrificial layer and the embedded lateral stop layer; Metal electrodes disposed on the surface of the piezoelectric layer; And a passivation layer covering the metal electrode and the piezoelectric layer.
2. The transverse exciter acoustic resonator as described in claim 1, characterized in that, The embedded lateral stop layer is segmented, and the embedded lateral stop layer includes at least one stop layer unit, with gaps provided between the stop layer units.
3. The transverse exciter acoustic resonator as described in claim 2, characterized in that, The embedded lateral cutoff layer includes cutoff layer units disposed on opposite sides of the effective acoustic aperture region.
4. The transverse exciter acoustic resonator as described in claim 2, characterized in that, The embedded lateral cutoff layer includes multiple cutoff layer units arranged at intervals around the preset target cavity.
5. The transverse exciter acoustic resonator as described in claim 1, characterized in that, It also includes a release window, which is one or more of the following: a circular hole, a rectangular hole, a strip groove, a polygonal hole, and an array of holes.
6. The transverse exciter acoustic resonator as described in claim 1, characterized in that, The height of the embedded lateral stop layer is 70%–100% of the thickness of the sacrificial layer; the cross-section of the embedded lateral stop layer is one of the following: rectangular, trapezoidal, T-shaped, inverted T-shaped, L-shaped, or stepped.
7. The transverse exciter acoustic resonator as described in claim 1, characterized in that, The etching selectivity ratio of the material of the embedded lateral stop layer to the material of the sacrificial layer is greater than 300:
1.
8. The transverse exciter acoustic resonator as described in claim 1, characterized in that, The embedded lateral barrier layer is formed by one of the following methods: thermal oxidation, chemical vapor deposition, plasma-enhanced chemical vapor deposition, low-pressure chemical vapor deposition, sputtering, or spin coating.
9. A method for fabricating a transverse exciter acoustic resonator, characterized in that, include: Provides sinking; A sacrificial layer is formed above the substrate; An embedded stop groove is etched at the predetermined target cavity boundary position in the sacrificial layer, and a stop material is filled in the embedded stop groove to form an embedded lateral stop layer. A piezoelectric layer is formed above the embedded lateral stop layer and the sacrificial layer; A metal electrode is formed above the piezoelectric layer; A passivation layer is formed above the piezoelectric layer and the metal electrode; Release the sacrificial layer corresponding to the preset target cavity position.
10. The method for fabricating a transverse exciter acoustic resonator as described in claim 9, characterized in that, Also includes: Segmented cutoff grooves are etched in the pre-defined target cavity of the sacrificial layer, and cutoff material is filled into the segmented cutoff grooves to form a segmented cutoff layer.